JPH0644995B2 - Method for producing hydrous microcapsules - Google Patents

Description

TECHNICAL FIELD The present invention relates to hydrous microcapsules useful as a medium for regenerative heat storage.

(Prior Art and Problems Thereof) Conventionally, hydrous microcapsules containing an aqueous substance such as water as a core substance have been used as heat storage medium for heat storage by utilizing latent heat of the core substance ( For example, Japanese Patent Publication Sho 60
-23279).

That is, when water is transformed from solid phase to liquid phase or from liquid phase to solid phase, heat of about 80 Kcal / cm ³ is transferred.

However, since the microcapsules used in the prior art as described above follow the volume increase of water as a core substance, the microcapsules used in the prior art as described above, for example, undergo volume expansion when transforming from a liquid phase to a solid phase. However, there is a problem in that the capsule is broken as a result.

(Means for Solving the Problems) Therefore, an object of the present invention is to provide a method for producing hydrous microcapsules which does not break even when the phase of the core substance changes.

That is, according to the present invention, the monomer for the encapsulating polymer and the radical polymerization initiator are dispersed in an aqueous solution containing a foaming agent to form W.
/ O emulsion is prepared, and then the W / O emulsion is dispersed in an aqueous medium to prepare a [W / O] / W emulsion, and polymerization is carried out under the foaming conditions of a foaming agent in this emulsion system. A method for producing hydrous microcapsules is provided.

(Operation) That is, in the present invention, the volume of the aqueous core substance in the normal state is in the range of 70 to 90% with respect to the volume of the shell, so that the aqueous substance undergoes a phase change from the liquid phase to the solid phase. Also in this case, an increase in the volume of the aqueous substance due to the phase change is allowed, and it becomes possible to effectively prevent the breakage of the capsule during the phase change of the core substance.

(Preferred Embodiment of the Invention) Production of Microcapsule The production method of the hydrous microcapsule of the present invention is as follows.

First, a foaming agent is dissolved in water to prepare a foaming agent aqueous solution.

As the foaming agent, water-soluble inorganic foaming agents such as sodium hydrogencarbonate, ammonium carbonate, ammonium hydrogencarbonate are used, and sodium hydrogencarbonate is particularly preferable.

The concentration of this aqueous foaming agent solution varies depending on the type of the foaming agent, but is usually 100 to 300% by weight, and particularly preferably 150 to 200% by weight.

Next, the monomer for the encapsulated polymer, the radical polymerization initiator and the surfactant are stirred and mixed into the aqueous foaming agent solution, and W
/ O form an emulsion.

As the encapsulating polymer monomer, all known per se can be used as long as it is water-insoluble per se and can form a water-insoluble polymer, for example, styrene,
Vinyl acetate, acrylic acid or methacrylic acid ester, vinylidene chloride and the like are generally used, and these may be a combination of two or more kinds.

The monomer for the encapsulated polymer is the same as the aqueous foaming agent solution 1
It is suitable to use 100 to 300 parts by weight, especially 150 to 200 parts by weight, per 100 parts by weight.

As the radical polymerization initiator, for example, organic peroxides such as benzoyl peroxide and azobisisobutyronitrile are preferably used.

This radical polymerization initiator may be used in a so-called catalytic amount, and it is usually suitable to use it in a ratio of 0.1 to 10 parts by weight per 100 parts by weight of the monomer.

As the surfactant, various anionic, cationic and nonionic surfactants can be used as long as they do not adversely affect the radical polymerization reaction, but from the viewpoint of forming a W / O emulsion, particularly alkaline earth Metal soaps such as metals, aluminum and zinc, and nonionic surfactants having a low HLB value are suitable.

These surfactants are used in an amount ratio such that a W / O emulsion can be formed.

According to the invention, the W / O emulsion is then agitated and mixed in an aqueous medium such as water to form a [W / O] / W emulsion.

In this case, in order to keep the emulsion stable, it is preferable to add and mix an organic or inorganic dispersion stabilizer in the aqueous medium.

Examples of the organic dispersant include gelatin, starch, water-soluble starch derivatives, water-soluble cellulose derivatives such as carboxymethyl cellulose and Ethocel, polyvinyl alcohol, water-soluble acrylic resins, water-soluble polymers such as vinyl ether / maleic acid copolymers, and anions. Examples thereof include nonionic, nonionic, cationic and amphoteric surfactants.

As the inorganic dispersant, hardly soluble inorganic fine particles, for example, calcium carbonate, calcium phosphate, magnesium carbonate,
Various clays such as magnesium phosphate, barium sulfate, silica, marmina, talc, bentonite, diatomaceous earth and the like can be mentioned.

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

These dispersants are generally 0.1 to 3.0 parts by weight, based on 100 parts by weight of the aqueous medium, although they vary depending on the type.
Particularly, it is preferable to use it in an amount ratio of 0.5 to 1.0 part by weight.

In the present invention, the W / O emulsion is used in an amount of 10 to 100 parts by weight, particularly 2 parts by weight, per 100 parts by weight of the aqueous medium.
It is preferable to add and mix it at a ratio of 0 to 50 parts by weight.

According to the present invention, [W / O] / W formed as described above
With respect to the emulsion system, polymerization is usually carried out in a temperature range of 80 to 95 ° C. under the condition that the foaming agent foams.

As a result, the polymerization proceeds at the interface between the monomer and water, and W /
Water-containing microcapsules corresponding to the particle diameter of the O emulsion (several tens of microns to several mm) can be obtained.

In this case, since the foaming is being performed at the same time as the polymerization, the volume of the polymer film which becomes the shell is larger than the volume of water which is the core substance to be encapsulated, and the volume of water which is in a normal state (as a liquid state) is large. Is in the range of 70 to 90% of the shell volume, especially 80 to 85%.

The obtained microcapsules are washed with water and dried to obtain the final product.

Hydrous Microcapsules The microcapsules thus obtained by the method of the present invention are characterized in that the capsule volume is larger than the volume of water as the core substance.

The microcapsules are effectively used as a cold storage heat medium such as a heat exchanger by utilizing the latent heat of water as a core substance.

(Effect) According to the present invention, it is possible to effectively prevent capsule breakage due to volume increase due to phase change of water, which is a core substance, and it is possible to effectively use hydrous microcapsules as a heat storage medium for cold storage.

The invention is illustrated by the following example.

(Example) 2 g of sodium hydrogen carbonate as a foaming agent was dissolved in 30 ml of water, and subsequently 0.45 g of SPAN80 (trade name, manufactured by ICI Co., Ltd.) as a surfactant, 36 g of styrene monomer, 12 g of vinylidene chloride, and a peroxide. 1.4 g of benzoyl oxide was put into the above water and stirred with a homogenizer to prepare a W / O emulsion. The whole system of the [W / O] / W emulsion obtained by adding the obtained emulsion to 400 ml of a 1.0 wt% calcium phosphate aqueous solution and stirring the mixture was heated to 95 ° C. and the polymerization reaction was continued for 5 hours. Then, microcapsules were obtained.

Then, microcapsules were obtained in the same manner as above except that sodium hydrogencarbonate as a foaming agent was not used.

Then, the microcapsules obtained by carrying out the reaction in the presence of the above-mentioned foaming agent and the microcapsules obtained by carrying out the reaction without using the above-mentioned foaming agent are the same in number of microcapsules having substantially the same particle diameter. As a result of measuring the total weight, the weight of the microcapsules obtained in the presence of the foaming agent was 80% as compared with that without addition, and it was confirmed that the capsules had pores.

Claims (1)

[Claims] 1. A W / O emulsion is prepared by dispersing an encapsulating polymer monomer and a radical polymerization initiator in an aqueous solution containing a foaming agent, and then the W / O emulsion is dispersed in an aqueous medium. A method for producing hydrous microcapsules, which comprises preparing a [W / O] / W emulsion, and polymerizing the emulsion system under foaming conditions of a foaming agent.