JPH0367737B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention particularly relates to a method for microencapsulating a substance or a soft substance that is liquid or sticky at room temperature.

Microcapsules are widely used in pressure-sensitive copying paper, medicine, agricultural chemicals, fragrances, and other applications.

Typical conventional methods for producing microcapsules include: 1. Coacervation method, 2. Interfacial polymerization method, 3. In situ polymerization method, 4. In-liquid drying method, 5.
Examples include the melting and dispersion cooling method, 6. the orifice method, 7. the spray drying method, 8. the air suspension coating method, and 9. the inorganic wall microencapsulation method. However, when using this production method to microcapsule substances that are liquid or sticky at room temperature, such as water, organic solvents, starch syrup, adhesives, adhesives, or soft substances, there are the following drawbacks: There is.
That is, in methods 1 to 5, when a core material made of the above-mentioned material is dispersed in a dispersion medium, if the core material has adhesive properties, the core material particles adhere to each other and form agglomerates. In addition, it is necessary to adjust the wetting of the core material and the polymer solution and the specific gravity, which makes the work laborious and the properties of the finished capsules are also poor. Furthermore, method 6 is difficult to produce micron-order capsules and has low production efficiency. Furthermore, although methods 5, 7, and 8 are used to encapsulate toner, it is difficult to produce capsules with a uniform film thickness and complete coverage, and they also lead to agglomeration if the substance is more adhesive than the toner. . In addition, since methods 1 to 8 use water or organic solvents, it is not possible to encapsulate the core substance that is immersed or reacts in water or organic solvents, and post-treatment of the organic solvent is troublesome. Drying is required to extract it as a powder, which poses the risk of fire and explosion. Furthermore, in method 9, when the core material is a soft material, a large amount of wall material is mixed into the core material, which tends to result in a mixture rather than a capsule.

As described above, in any of the conventional microencapsulation methods 1 to 9, microcapsules cannot be manufactured in a satisfactory state from substances that become liquid or agglomerate at room temperature when powdered. Nakatsuta.

This invention was made in view of the above circumstances, and it is possible to easily and efficiently prepare substances that are liquid or sticky at room temperature, or soft substances, or substances that are immersed in or react with water or organic solvents, in a high yield. Another object of the present invention is to provide a method for producing microcapsules that can be safely microencapsulated without causing any alteration or denaturation of the above-mentioned substances.

This invention will be explained in detail below.

Core substances used in the production method of this invention include aqueous solutions, aqueous dispersions, pressure-sensitive adhesives, adhesives, paints,
Organic solvents, etc., when made into powder, are kept at room temperature (0
The material used is a substance that becomes liquid or agglomerates at temperatures between 50°C and 50°C, and cannot maintain its powder form.

In addition, the fine powder that coats this core substance includes fine silica powder, various bentonites, aluminum oxide, carbon black, calcium carbonate, talc, kaolin, magnesium carbonate, titanium oxide,
Zinc oxide, aluminum powder, ceramic fine powder,
Examples include plastic fine powders such as polyethylene, nylon, and methacrylate, phytic acid and its metal salts, starch, and surface-modified fine powders of these fine powders, but those having no affinity with the core substance are selected. Particularly when the core substance is a liquid with a viscosity of about 100 centipoise, fine powders that have an affinity for it must be avoided. That is, if the core substance is hydrophilic, it is necessary to select a hydrophobic fine powder, and if the core substance is hydrophobic, it is necessary to select a hydrophilic fine powder. Further, a fine powder having a particle size smaller than the particle size of the powder obtained by freeze-pulverizing the core material, preferably 1/10 or less is used.

Next, microencapsulation will be explained.
First, the core material is frozen using cold heat such as liquid nitrogen, and in this state is turned into powder. The temperature at this time is
The temperature varies depending on the type of core material; for aqueous solutions and dispersions, the temperature is around -20°C, and for sticky or easily agglomerated materials such as adhesives and adhesives, the temperature is -50°C or more.
The temperature is around -80℃. Then, by adjusting the rotation speed (grinding speed) and grinding temperature of the grinder as appropriate, the average particle size is 1 to 1.
Make a powder of 100μm.

Next, while maintaining this powder at a low temperature to prevent agglomeration or melting, the fine powder is added and mixed and stirred to form microcapsules.
For this mixing and stirring, it is preferable to use a high-speed stirrer with a cutter equipped with a liquefied nitrogen cooling jacket, and the stirring conditions are a stirring speed of 5000 to 2000 rpm and a stirring time of 5 to 60 seconds. In particular, when this type of stirrer is used, the above-mentioned freeze-pulverization can also be performed within this device.
It is advantageous in terms of process. In addition, a ball mill, a stirrer with a cutter, an attritor, etc. can also be used for mixing and stirring. The temperature during stirring is about the same as the temperature during the above-mentioned freezing and pulverization, and in order to prevent temperature rise due to frictional heat, it is necessary to continue cooling the stirrer by passing a coolant such as liquefied nitrogen. Also,
The mixing ratio of core material powder and fine powder also depends on the shape of the core material powder.If the powder is spherical, a small amount of fine powder is required, but usually it is mixed per 100 parts by weight of core material powder. The fine powder is 0.5 to 20 parts by weight. Furthermore, the particle size of the resulting microcapsules is determined by the particle size of the core material powder and the film thickness of the fine powder, so it also depends on the freeze-grinding conditions, the mixing ratio of the core material and the fine powder, and the mixing and stirring conditions. The particle size can be adjusted as desired, and microcapsules with an average particle size of 1 to 1,500 μm can be obtained satisfactorily.

The microcapsules obtained in this way are
The core material powder is completely covered with fine powder, resulting in a smooth and fluid powder even at room temperature.

Furthermore, if it is desired to enhance the sealing effect of the core material of the microcapsules obtained and the strength of the capsules, the microcapsules thus obtained may be further coated with a polymer film. That is, the core material powder is coated with a relatively small amount of fine powder, and then a polymer film is coated by a conventional microencapsulation method. In this case, it is necessary to take into account the compatibility of the capsule with the polymer film and the polymer film solution. For microcapsules coated with hydrophilic fine powder, microencapsulation using a water-soluble polymer is suitable, and specifically, a coacervation method using gelatin can be used. Furthermore, for microcapsules coated with hydrophobic fine powder, a microencapsulation method using a hydrophobic polymer such as a coacervation method using an organic solvent solution is suitable.

In addition, the higher the viscosity of the core substance, the better the ability to maintain the shape of the microcapsules and the better the stability.
In the case of a low-viscosity core material, it is preferable to add a filler, thickener, gelling agent, etc. to the core material to thicken or gel it.

According to this method of manufacturing microcapsules, the core material is freeze-pulverized and powdered, and fine powder is added to this and mixed and stirred at low temperature, so that there is less fine powder mixed into the core material. Therefore, the core material can be efficiently coated with a very small amount of fine powder, and the deterioration of the performance of the microcapsule core material due to the fine powder can be kept to a minimum. In addition, there is no loss of core material or fine powder during production, and microcapsules can be produced with a 100% yield.The process is simple and can be produced in a short time, and the production equipment requires only a stirrer, so the production cost is significant. It becomes very low. Furthermore, since all steps are carried out at low temperatures, there is no denaturation or alteration of the core material or fine powder, and even unstable core materials can be microencapsulated. Furthermore, compared to conventional methods that use water or organic solvents, there is no need for a drying process or wastewater treatment, and the process is highly stable. Since the particle size of the microcapsules can be arbitrarily and easily adjusted, microcapsules with a particle size suitable for the purpose can be easily prepared.

Hereinafter, a specific explanation will be given by showing examples.

Example 1 After cooling and solidifying water colored with methylene blue, it was pulverized with a stirrer equipped with a cutter, and the average particle size was
50μm frozen powder, 100 parts by weight of this powder,
The mixture was mixed and stirred with 5 parts by weight of hydrophobic silica fine powder (trade name Aerosil R972, average particle size 16 mm, manufactured by Nippon Aerosil Co., Ltd.) in a high-speed stirrer equipped with a cutter while maintaining the temperature at -20°C, which is a low temperature at which it will not dissolve. . When stirred for 10 seconds at a stirring speed of 20,000 rpm,
Microcapsules were obtained in which the surface of colored water powder was coated with hydrophobic silica fine powder. The temperature after the mixing and stirring was -10°C. This microcapsule had excellent fluidity and remained smooth even at room temperature. When the microcapsules were spread on paper and pressurized, blue water was released from the microcapsules, staining the paper blue.

Example 2 Microcapsules were produced in exactly the same manner as in Example 1 using commercially available starch paste (trade name Yamato paste) as the core material, and a smooth powder with excellent fluidity even at room temperature was obtained. After scattering this microcapsule powder onto a piece of paper, another piece of paper was applied to it and dried under pressure, and the two pieces of paper adhered well.

Example 3 Butter was cooled and frozen at −60° C. with liquid nitrogen, and ground into frozen powder with an average particle size of 50 μm using a stirrer equipped with a cutter. Fine silica powder (trade name Aerosil 200, average particle size 16 mμ) was added to 100 parts by weight of this powder while maintaining it at -50°C, a temperature that does not cause agglomeration.
Stir with 5 parts by weight using a stirrer with a cutter at a stirring speed.
When mixed and stirred at 20,000 rpm for 10 seconds, butter silica fine powder capsules were obtained with a yield of 100%. This powder was smooth and had good fluidity even at room temperature.

Example 4 Acrylate adhesive (manufactured by Soken Kagaku Co., Ltd., trade name
SK Dyne 1504) until it has sufficient adhesive strength.
Crosslinked and solvent removed. After freezing this material with liquefied nitrogen, it was frozen to an average size of 50 μm using a stirrer with a cutter.
powder. While maintaining 100 parts by weight of this powder at -60°C, which is a temperature that does not cause agglomeration, it was stirred with 10 parts by weight of silica fine powder (trade name Aerosil 200) using a stirrer with a cutter at a speed of 20,000 rpm.
After mixing and stirring for 30 seconds, fine silica powder capsules of the adhesive were obtained.

Example 5 10g of microcapsule powder obtained in Example 4
After dispersing in 30g of 10% gelatin warm water solution, 10
% aqueous gum arabic solution, 140 ml of water at 40° C. was added with stirring, and 10% acetic acid was added dropwise to adjust the pH to 4.2, and the above powder was encapsulated with coacervate droplets. After further cooling this dispersion to 5°C, 1 ml of 30% formalin was added and an additional 10%
Add NaOH aqueous solution to adjust the pH to 9, then 1℃/
When the mixture was heated to 50° C. at a temperature increase rate of 10 minutes, double microcapsules were formed in which the surfaces of the microcapsules were coated with gelatin. When this double microcapsule was spray-dried, a microcapsule powder with good shape retention and fluidity was obtained.

As explained above, the method for producing microcapsules of the present invention is to remove the core material, which is made of a material that becomes liquid or agglomerates at room temperature when it is made into powder and cannot maintain its powder state, into powder. The material is freeze-pulverized at a low temperature that will not cause melting or agglomeration, and then mixed and stirred with fine powder at this temperature. Substances that are eroded by solvents or react with them can be used as core substances, and these core substances can be made into microcapsules in a short period of time with 100% yield through extremely simple process operations, and can be used as adhesives. It can be used in a wide range of applications, including adhesives, paints, electrophotographic materials such as toner, medicines, and foods. Furthermore, compared to conventional methods, since no water or organic solvents are used during production, there is no need for a drying process or drainage treatment, and the process is highly stable. Further, it has the advantage that microcapsules of any particle size can be easily produced, and microcapsules with a wide variety of purposes can be produced.

Claims (1)

[Claims] 1. A core material made of a material that is liquid at around room temperature or that cannot maintain its powder form due to agglomeration when made into a powder is heated to a low temperature below its melting point or glass transition temperature. freeze-mill, and then maintain this low temperature to infuse the freeze-milled core material with a substance having a water affinity that is opposite to that of the core material, with a particle size smaller than that of the milled core material. A method for producing microcapsules, characterized in that a core substance is coated with fine powder by adding it as a powder and mixing and stirring. 2 The core material, which is a liquid at room temperature or is made of a material that cannot maintain its powder form due to agglomeration when made into a powder, is freeze-pulverized at a low temperature below its melting point or glass transition temperature, and then this material is A substance having a water affinity that is contrary to the water affinity of the core material is added to the freeze-pulverized core material while maintaining a low temperature as a fine powder having a particle size smaller than the particle size of the crushed core material, and the mixture is stirred. A method for producing microcapsules, which comprises coating a core substance with a fine powder, and then coating the core substance with a polymer film.