JP7752002B2 - Method for producing fatty acid microparticles - Google Patents

Description

The present invention relates to a method for producing fatty acid microparticles.

Synthesized from raw materials such as methyl methacrylate, styrene, nylon, and urethane, these organic microparticles with nano- and micro-sized particles are now being used in skin care applications such as cosmetic additives and scrubbing agents in facial cleansers and body soaps, taking advantage of their extensibility and light-diffusing properties.

It has been pointed out that when used in skin care products such as cosmetics, facial cleansers, and body soaps, and then washed away after use and released into the environment as wastewater, they can have an impact on the ecosystem as so-called microbeads.

Furthermore, because organic microparticles are made from petroleum-derived ingredients, concerns have been raised about the burden they place on the environment.

On the other hand, while naturally derived ingredients can be obtained without putting a burden on the environment, many of them are in the form of wax, gum, or chips, making it difficult to convert them into fine particles and use them as a substitute for organic fine particles.

Patent Document 1 discloses a hydrophobic treatment of polyvalent metal alginate particles. The treatment aims to overcome the limited use of polyvalent metal alginate in cosmetics due to its high hygroscopicity, but there is still room for improvement compared to conventional organic fine particles.
Patent Publication No. 2020-125256

The objective of the present invention is to provide a method for producing fatty acid microparticles that are highly biodegradable and suitable for skin care applications such as cosmetics, facial cleansers, and body soaps.

A method for producing fatty acid microparticles, characterized by the step of adding a solution containing a phosphate compound to a solution containing a fatty acid microparticle dispersion and calcium ions under basic conditions.

The manufacturing method of the present invention makes it possible to easily obtain fatty acid microparticles suitable for skin care applications such as cosmetics, facial cleansers, and body soaps. In particular, it is advantageous in that it does not require special equipment, produces only a small amount of by-products, and is easy to handle.

The manufacturing method of the present invention includes the steps of preparing a dispersion in which fatty acids are dispersed in the form of fine particles, and then adding a solution containing a phosphate compound to a solution containing calcium ions.

Fatty acids suitable for use in the present invention include those with long-chain alkyl groups. Specific examples include lauric acid, myristic acid, pentadecylic acid, palmitic acid, margaric acid, stearic acid, nonadecylic acid, and alkylic acid.

The method for preparing the fatty acid microparticle dispersion is not particularly limited, but examples include a method in which fatty acids are dispersed in water in the presence of a dispersant such as a polymer dispersant or a surfactant.

Examples of polymeric dispersants include gelatin, methylcellulose, hydroxyethyl cellulose, hydroxypropyl methylcellulose, carboxymethyl cellulose, polyethylene glycol, polyoxyethylene-polyoxypropylene block copolymer, polyacrylamide, polyacrylates, sodium alginate, polyvinyl alcohol, and polyvinylpyrrolidone, and these may be used alone or in combination of two or more. When using a polymeric dispersant, it is preferable to use 5 to 20 parts by weight per 100 parts by weight of fatty acid.

When using a cellulose-based polymer dispersant, adding cellulase after preparing the fatty acid microparticle dispersion can promote decomposition, making it less likely to remain in the fatty acid microparticles.

Surfactants include anionic surfactants, cationic surfactants, nonionic surfactants, amphoteric surfactants, polymer surfactants, etc., and may be used alone or in combination of two or more. When using a surfactant, it is preferable to use 0.1 to 3 parts by weight per 100 parts by weight of fatty acid.

In addition, by using a combination of a polymer dispersant and a surfactant, it becomes easier to obtain spherical particles with particle sizes of several tens of micrometers, which are required for applications such as cosmetics.

These dispersants are dissolved in water and mixed with fatty acids. After heating above the melting point of the fatty acids and stirring while applying shear force, the mixture becomes cloudy and fatty acid droplets form. By cooling this to room temperature, a fatty acid microparticle dispersion can be prepared.

Next, by adding a phosphate compound to the fatty acid microparticle dispersion and a solution containing calcium ions, the fatty acid microparticles are converted into hydroxyapatite, which prevents aggregation when extracted as a powder and makes the microparticles easier to handle.

The calcium ion source compound can be any known water-soluble calcium compound, such as calcium nitrate, calcium nitrate tetrahydrate, calcium chloride, calcium chloride mono- to hexahydrate, calcium lactate, calcium chlorate dihydrate, calcium perchlorate, calcium bromide, calcium acetate, or calcium glutamate. These can be used alone or in combination of two or more. It is preferable to use 0.005 to 0.5 moles of the calcium ion source compound per mole of fatty acid, and 0.05 to 0.2 moles is more preferable.

The phosphate compound can be any known water-soluble phosphate compound, such as diammonium hydrogen phosphate, ammonium dihydrogen phosphate, disodium hydrogen phosphate, sodium dihydrogen phosphate monohydrate, sodium dihydrogen phosphate dihydrate, potassium phosphate, dipotassium hydrogen phosphate, or potassium dihydrogen phosphate. These compounds can be used alone or in combination of two or more. It is preferable to use 0.005 to 0.5 moles of the phosphate compound per mole of fatty acid, and more preferably 0.03 to 0.1 moles.

When adding a phosphate compound, it is preferable to make the solution basic, specifically, to maintain a pH of 7.8 or higher, preferably a pH of 8 or higher, and more preferably a pH of 9 or higher. By maintaining a pH of 9 or higher, the precipitation rate of hydroxyapatite becomes optimal, and it becomes easier to form a hydroxyapatite coating layer.
Examples of additives for making the solution basic include ammonia, sodium hydroxide, potassium hydroxide, etc. Among these, ammonia is preferred because it is easy to remove during drying. The amount of ammonia to be added is not particularly limited as long as it is within the range that satisfies the above basic condition.

During this hydroxyapatite treatment, the temperature may be constant or may be changed midway or at each stage, for example, between 0 and 95°C. The method for adding the phosphate compound is not particularly limited, and known methods can be used, such as charging the entire amount all at once at the beginning, charging a portion at the beginning and adding the remainder as a continuous feed, or adding intermittently. The time for adding the solution containing the phosphate compound is also not particularly limited and can be set as appropriate, for example, between 0.5 and 120 minutes from start to finish. The reaction time after adding the phosphate compound is also not particularly limited, and can be set as appropriate depending on the progress of the reaction, for example, between 5 and 180 minutes.

Fatty acid microparticles are obtained by removing water from an aqueous dispersion of hydroxyapatite-converted fatty acid microparticles. Water can be removed by known methods such as filtration, centrifugal dehydration, and vacuum drying. The fatty acid microparticles obtained in this manner have reduced secondary agglomerates and coarse particles, but if necessary, they can be further refined by pulverization using a hammer mill or by sieving or air classification.

Because fatty acid microparticles are roughly spherical with particle diameters of around several tens of micrometers, they can be used in a variety of applications where organic microparticles are used. In particular, they can be used in the same way as conventional organic microparticles in skin care applications such as cosmetics, facial cleansers, and body soaps, and because they are biodegradable, they pose a small environmental burden even when washed and released into the environment as wastewater after use.

The present invention will be explained in more detail below with examples and comparative examples, but these are intended to be specific examples and are not intended to be limiting. Unless otherwise specified, experiments were carried out at a room temperature of 25°C and a relative humidity of 65%.

Preparation of fatty acid microparticle dispersion: 240 parts by weight of an aqueous solution of hydroxypropyl methylcellulose (Metolose 90SH-100, product name, manufactured by Shin-Etsu Chemical Co., Ltd.) adjusted to 5% by weight with water and 0.4 parts by weight of sodium polyoxyethylene alkyl sulfosuccinate (Neohitenor S-70, product name, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) were added to a separable flask equipped with a stirrer and stirred to obtain a mixed aqueous dispersion.

90 parts by weight of melted stearic acid was mixed into the mixed aqueous dispersion, and the mixture was stirred at 72°C using a stirring blade to apply shear force. The mixture became cloudy and droplets were confirmed to have formed.

The resulting droplets were cooled to room temperature to obtain an aqueous dispersion of stearic acid fine particles.
Example 1
The stearic acid microparticle aqueous dispersion was diluted with 200 parts by weight of ion-exchanged water. Next, 0.09 parts by weight of cellulase (Yakult Pharmaceutical Co., Ltd., Cellulase Y-NC, product name) and 0.09 parts by weight of cellulase (Yakult Pharmaceutical Co., Ltd., Cellulase Onozuka 3S, product name) were added and stirred. Next, 47 parts by weight of a 28.6% by weight calcium chloride monohydrate aqueous solution was added, followed by 20 parts by weight of 28% by weight ammonia water, to adjust the pH of the dispersion to 10.3. To this dispersion, 188 parts by weight of 4.0% by weight ammonium dihydrogen phosphate was added 45 parts by weight of 28% by weight ammonia water to a pH of 11.2. 3.2% by weight ammonium dihydrogen phosphate was added dropwise over 30 minutes, and the mixture was allowed to react at room temperature for 1 hour to obtain a dispersion of hydroxyapatite-converted stearic acid microparticles. The resulting dispersion was then centrifuged and vacuum dried to remove water, yielding the stearic acid microparticles of Example 1. The volume average particle diameter of the obtained particles was measured using an electrical resistance particle size distribution analyzer (Multisizer 3, manufactured by Beckman Coulter, Inc.) and found to be 6.9 μm. The shape of the obtained particles was observed using a scanning electron microscope (JEOL, JSM-6510LV) and found to be spherical.
Comparative Example 1
The aqueous dispersion of stearic acid microparticles was directly subjected to a centrifugal dehydrator and a vacuum dryer to remove water, thereby obtaining stearic acid microparticles of Comparative Example 1. The volume average particle diameter of the particles was similarly measured and found to be 6.1 μm. The shape of the obtained particles was also non-spherical.
Sieving evaluation
The obtained stearic acid microparticles were passed through a vibrating sieve or ultrasonic vibrating sieve with a mesh size of 35 μm, and the numerical value was calculated from the mass of the microparticles that passed through the sieve. Evaluation was performed as follows: 70% or more passed through; 20% or more but less than 70% passed through; and x passed through less than 20%. Comparative Example 1, which was evaluated as x, was not further evaluated.
Tactile evaluation
The tactile sensation was evaluated by 10 panelists. Industrially produced and used polymethyl methacrylate particles (Ganzpearl GMX-0610, product name, manufactured by Aica Kogyo Co., Ltd.) were used as a reference sample (Reference Example 1). The evaluation method involved taking 0.1 g of the powder, spreading it on the back of the hand, and rubbing it with the fingers. Sensory evaluations were compared for "goodness of smoothness,""whether or not a squeaky feeling was felt," and "goodness of touch." A score of 0 was given if 7 or more panelists rated it as good, a score of △ if 4 to 6 panelists rated it as good, and an × if 3 or fewer panelists rated it as good.

The stearin microparticles of Example 1 had a texture equivalent to that of organic microparticles and also had good sieving properties. On the other hand, the stearic acid microparticles of Comparative Example 1 had poor sieving properties and were not practical.

Claims (3)

A method for producing fatty acid microparticles, comprising the step of adding a phosphate compound to a solution containing a fatty acid microparticle dispersion and calcium ions under basic conditions ,
the fatty acid is one or more compounds selected from the group consisting of lauric acid, myristic acid, pentadecylic acid, palmitic acid, margaric acid, stearic acid, nonadecylic acid, and alkynyl acid;
The fatty acid microparticle dispersion is obtained by dispersing a fatty acid in water in the presence of a dispersant ,
A method for producing fatty acid microparticles, characterized in that a polymer dispersant and a surfactant are used as the dispersant. 2. The method for producing fatty acid microparticles according to claim 1 , wherein 5 to 20 parts by weight of the polymer dispersant and 0.1 to 3 parts by weight of the surfactant are used relative to 100 parts by weight of the fatty acid. 3. The method for producing fatty acid microparticles according to claim 1, wherein the solution containing calcium ions is an aqueous calcium chloride solution, and the phosphate compound is ammonium dihydrogen phosphate.