JPH0345734B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing spherical and finely powdered cellulose acetate.

In recent years, fine powders of various polymer resins have been increasingly used as cosmetic additives, colorants, lubricants, antiblocking agents, etc. in place of inorganic fine powders.

Spherical fine powder of cellulose acetate, for example, has appropriate oil absorption, hygroscopicity, and water retention properties as a cosmetic additive, and not only has a high affinity for the skin and provides a favorable feeling of use, but also has good dispersibility regarding the uniformity of cosmetics. It is thought that it has good mixability, and can also be excellent in moldability, fillability, and safety.

However, no product has yet been obtained that satisfies the conditions suitable for use as a cosmetic additive, such as being spherical and having an average particle size of 2 to 37 microns.

As a method for producing spherical fine particles of cellulose acetate that has been known so far, for example,
According to Publication No. 7759, a solution of cellulose triacetate in methylene chloride, chloroform, or a mixed solvent mainly composed of these is dropped into an aqueous medium with stirring, and the aqueous medium containing the generated suspended particles is heated. There is a method of obtaining spherical particles of cellulose triacetate by evaporating the organic solvent. In this method, in which a cellulose triacetate solution is dropped into an aqueous medium, it is necessary to lower the viscosity of the cellulose triacetate solution in order to obtain relatively small spherical particles with an average particle size of 2 to 37μ. Therefore, solutions with relatively low concentrations or cellulose triacetate with a low degree of polymerization must be used. However, lowering the concentration is economically disadvantageous as more organic solvent must be evaporated, and lowering the degree of polymerization of cellulose triacetate reduces the physical strength of the resulting cellulose triacetate spherical microparticles. There are problems such as the impact on

Furthermore, if the aqueous medium is a liquid in which only gelatin or a dispersing agent such as polyvinyl alcohol is dissolved,
When heating an aqueous medium containing suspended particles of cellulose triacetate to evaporate the organic solvent, in order to avoid violent foaming, the aqueous medium containing suspended particles of cellulose triacetate must be kept at a temperature 2 to 6 degrees Celsius below the boiling point of the organic solvent for a certain period of time, and a considerable amount of There are time and energy disadvantages in that the organic solvent must be evaporated.

Furthermore, JP-A No. 55-28763 discloses a method for obtaining spherical microparticles by spray drying a solution in which cellulose fatty acid ester is dissolved in a mixed solvent consisting of a combination of three or more solvents having boiling point differences of 30°C or more. There is. In order to obtain relatively small spherical fine particles with an average particle size of 2 to 37μ using this method, it is necessary to reduce the size of droplets after spraying with an atomizer, and the
Similar to the method described in No. 53-7759, this method has economic disadvantages such as the need to lower the viscosity of the solution of cellulose fatty acid ester.

The present invention relates to a method for efficiently producing spherical microparticles of cellulose acetate having an average particle size of 2 to 37 microns.

That is, in the present invention, a solution of cellulose acetate in an organic solvent is mixed with an aqueous medium containing a dispersant such as gelatin and carboxymethylcellulose, a surfactant, and an antifoaming agent using a homogenizer or the like to increase the circumferential speed of a rotor.
Mix and stir at a stirring speed of 450 m/min or more and 2000 rpm or more to form an aqueous medium containing suspended particles mainly composed of cellulose acetate solution, and then heat this as it is to evaporate the organic solvent to obtain an aqueous medium with an average particle size of 2 to 200 rpm. This is a method for efficiently producing spherical micropowder of cellulose acetate with a size of 37μ.

The cellulose acetate used in the present invention is obtained by acetylating pulp, linter, etc. with acetic acid, acetic anhydride, or sulfuric acid in a conventional manner. ) can be used.

What is the appropriate degree of substitution for cellulose acetate?
It is between 1.2 and 3.0, preferably between 1.4 and 2.9.
If it is less than 1.2, the longer the saponification time, the more economically disadvantageous it becomes. The degree of polymerization is suitably 80-360, preferably 120-320.

It is also possible to mix and use two or more types of cellulose acetates having different degrees of substitution and degrees of polymerization in any ratio. Furthermore, cellulose acetate butyrate, cellulose acetate propionate, etc. may be mixed.

The solvent for dissolving cellulose acetate must be appropriately selected depending on the degree of substitution, and methylene chloride, chloroform, ethane tetrachloride, methyl ethyl ketone, etc. may be used alone, or a mixture of two or more of these may be used. It is also possible to mix methanol, ethanol, acetone, nitromethane, water, etc. with these solvents as main components.

In order to obtain fine powder with an average particle size of 2 to 37μ in good yield, the concentration of the cellulose acetate solution should be 1 to 37μ.
15% by weight is suitable, preferably 3-12% by weight. If it is lower than 1% by weight, manufacturing efficiency will be poor;
Economically disadvantageous. Further, if the amount is 15% by weight or more, it is difficult to suppress the average particle size of the obtained spherical particles to 37μ or less.

However, the average particle size is related not only to the concentration of the cellulose acetate solution, but also to the degree of polymerization of cellulose acetate, the type of solvent system used, etc., so the average particle size should be an appropriate value within the range of 2 to 37μ. It is necessary to make a comprehensive decision.

Depending on the purpose, plasticizers, dyes, pigments, antistatic agents, ultraviolet absorbers, aromatics, etc. may be added to the cellulose acetate solution.

The aqueous medium used in the present invention contains gelatin, carboxymethyl cellulose, polyvinyl alcohol, hydroxyethyl cellulose, hydroxypropyl cellulose, albumin, gum arabic, etc. as a dispersant in an amount of 0.05 to 4.5% by weight, preferably 0.3 to 1.5% by weight, and a surfactant. 0.02 to 1.5% by weight, preferably 0.1 to 1.0% by weight of an anionic or nonionic surfactant or a mixture thereof as an agent, silicone resin, modified silicone resin, nonionic polyether type, polyalkylene glycol type as an antifoaming agent. Water containing 0.02 to 10% by weight, preferably 0.1 to 0.5% by weight of an antifoaming agent or the like is used.

Examples of anionic surfactants include higher alcohol sulfate ester sodium salts, alkyl phosphate salts, dialkyl sulfosuccinates, polyoxyethylene sulfate salts, and nonionic surfactants such as polyoxyethylene alkyl ether and sorbitan fatty acid esters. , polyoxyethylene sorbitan fatty acid ester, polyoxyethylene acyl ester, and the like.

The above-mentioned dispersants and surfactants are necessary to create a stable suspension by mixing and stirring, and generally, if the dispersant is 0.05% by weight or less and the surfactant is 0.02% by weight or less, the solvent in the suspension solution will evaporate. During this process, the particles fuse together and form lumps, making it difficult to stably produce microspherical powder. on the other hand,
Although it is possible to exceed the above-mentioned amounts, it is economically disadvantageous. Further, antifoaming agents are extremely effective in suppressing foaming when mixing and stirring a cellulose acetate solution and an aqueous medium and when evaporating the solvent in a suspended solution. When foaming is significant during mixing and stirring, when the foam collapses, particle fusion occurs and becomes dust-like, so suppressing foaming is advantageous in terms of yield.

Furthermore, when the solvent in the suspension solution is evaporated, if bubbles are generated violently, the suspension solution will also be distilled off at the same time as the solvent starts to evaporate, making it difficult to separate the solvent.

Generally, if the amount of antifoaming agent added is less than 0.02% by weight, the foam suppressing effect will be small, and if it is more than 10% by weight, it is economically disadvantageous.

The mixing ratio of the organic solvent solution and the aqueous medium obtained as described above is not particularly limited, but it can generally be carried out in a weight ratio of 100 for the former and 50 to 5,000 for the latter.

Stirring methods used in the present invention include methods using a homogenizer, homomixer, colloid mill, and the like.

The peripheral speed of the tip of the rotor blade during stirring is 450 to 3500
m/min, preferably 900 to 1800 m/min,
Also, the rotation speed of the rotor blade is 2000 to 15000 rpm,
Preferably it is 4000-8000 rpm. Stirring time is 10
The time period is from seconds to 30 minutes, preferably from 30 seconds to 10 minutes.

If the tip circumferential speed of the rotary blade during stirring is set to 450 m/min or less, the particle size of the obtained fine particles increases,
The yield of particles with an average particle size of 2-37μ is reduced. Moreover, when the speed is 3500 m/min or more, the spherical shape of the particles is lost.

In addition, when the rotation speed of the rotor is lower than 2000 rpm, the particle size of the obtained fine particles increases, and the yield of particles with an average particle size of 2 to 37μ decreases, and when the rotation speed is higher than 15000 rpm, the spherical shape of the particles is lost. .

The stirring time must be at least 10 seconds; if the stirring time is less than 10 seconds, it will be difficult to stably obtain spherical particles, and at the same time, the yield of particles with an average particle size of 2 to 37μ will decrease. .

Methods for evaporating the organic solvent in the suspension solution by heating include conventional methods, such as heating the solution in an oil bath, water bath, etc., blowing hot air into the suspension solution, blowing steam, and the like. After the organic solvent in the suspension solution has been evaporated, the aqueous dispersion containing spherical particles of cellulose acetate is subjected to solid-liquid separation by centrifugation, filtration, etc., and then dried to obtain the desired powder particles. It will be done.

The shape of the spherical microparticles of cellulose acetate in the present invention was confirmed by observation using a microscope or the like. The average sphere diameter was measured using a Coulter Counter manufactured by Coulter Electronics.

The spherical microparticles of cellulose acetate obtained by the present invention have a uniform spherical shape with an average particle size of 2 to 37μ, and can be used as cosmetic additives, lubricants, antiblocking agents, etc.
It is extremely useful as a colored product and as a material for producing sintered bodies.

Examples are shown below to explain the present invention in more detail. However, the present invention is not limited to these examples. Parts indicate parts by weight.

Example 1 Cellulose acetate (degree of substitution 2.9, average degree of polymerization 280,
Solution (A) in which 100 parts of raw material cellulose (pulp) was dissolved in 1900 parts of a mixed solvent of methylene chloride and methanol (mixing ratio: methylene chloride/methanol = 91/9 weight ratio), 6.6 parts of gelatin, and higher alcohol sulfate ester soda Aqueous medium solution (B) 2000 in which 2.2 parts salt and 8.0 parts modified silicone resin antifoaming agent are dissolved in 2000 parts water.
of the cellulose acetate solution was placed in a homogenizer container, and stirred for 5 minutes at a liquid temperature of 20°C, a circumferential speed of the tip of the rotor blade of 1390 m/min, and a rotational speed of the rotor blade of 6000 rpm to obtain a suspension containing microparticles of cellulose acetate solution. And so. This suspension solution was transferred into a flask, and while stirring at a rotation speed of 100 rpm, the liquid temperature was raised by external heating with a water bath, and methylene chloride and methanol were evaporated and removed from the system. The time required to evaporate a total of 1670 g of methylene chloride and methanol (including some water) from the start of heating the suspension solution was approximately 100 g.
It was hot in minutes.

The obtained aqueous dispersion in which cellulose acetate microparticles were dispersed was separated into solid and liquid using a centrifuge (7000 rpm), and the microparticles were dried to obtain a fine cellulose acetate powder.

When the obtained fine powder was observed under a microscope, it was found to be almost perfectly spherical. The average sphere diameter measured with a Coulter Counter (Coulter Electronics) was 4.2μ.

Comparative Example 1 The solution (A) used in Example 1 and 6.6 parts of gelatin were mixed with water.
The aqueous medium solution (C) dissolved in 2000 parts was stirred in the same manner as in Example 1 to form a suspension solution, but the suspension solution clearly had bubbles collapsed and particles fused to form a dust-like substance. There were things floating on the surface. Furthermore, this suspension solution was transferred to a flask and the temperature of the solution was raised in the same manner as in Example 1, but the suspended microparticles of the cellulose acetate solution fused and formed into large lumps, and no fine powder was obtained. Ta.

Comparative Example 2 Solution (A) used in Example 1, 6.6 parts of gelatin, 2.2 parts of higher alcohol sulfate ester soda salt, 2000 parts of water
The suspension solution obtained by stirring the aqueous medium solution (D) dissolved in the solvent in the same manner as in Example 1 was transferred to a flask, and the liquid temperature was raised in the same manner as in Example 1. The suspended solution was also distilled out at the same time as the distillation, and the solvent alone could not be evaporated or removed from the system.

Example 2 Cellulose acetate (degree of substitution 2.1, average degree of polymerization 120,
A solution (E) in which 100 parts of raw material cellulose (pulp) was dissolved in 1900 parts of a mixed solvent of methylene chloride and methanol (mixing ratio: methylene chloride/methanol = 91/9 weight ratio) and a solution (B) used in Example 1. was treated in the same manner as in Example 1 to obtain a fine powder of cellulose acetate.

The obtained fine powder is spherical and the average particle size is 5.4μ
It was hot.

Example 3 Liquid (F) and liquid (B) prepared by dissolving 100 parts of cellulose acetate used in Example 2 in 1900 parts of methyl ethyl ketone were treated in the same manner as in Example 1 to obtain fine powder of cellulose acetate.

The obtained fine powder is spherical and the average particle size is
It was 16.8μ.

Example 4 Solution (G) and solution (B) in which 150 parts of the cellulose acetate used in Example 1 were dissolved in 1850 parts of a mixed solvent of methylene chloride and methanol (mixing ratio: methylene chloride/methanol = 91/9 weight ratio) was treated in the same manner as in Example 1 to obtain a fine powder of cellulose acetate.

The obtained fine powder is spherical, and the average spherical diameter is
It was 10.6μ.

Comparative Example 3 The solution (A) used in Example 1 was dropped into the solution (B) being stirred at 300 rpm through a nozzle with a nozzle diameter of 1 mm to form a suspension solution, and then the solution was added in the same manner as in Example 1. Solvent evaporation, solid-liquid separation, and drying yielded a fine powder of cellulose acetate.

The obtained fine powder was spherical, but the average particle size was
It was 46μ.

Comparative Example 4 The cellulose acetate solution (G) used in Example 4 was dropped through the nozzle used in Comparative Example 3 into the liquid (B) which was being stirred at 300 rpm.

However, the particles did not become spherical, but instead became thread-like.

Example 5 Diethyl phthalate 30 was added to the solution (A) used in Example 1.
After stirring 2000 parts of liquid (I) and aqueous medium liquid (B) in the same manner as in Example 1, the organic solvent was evaporated, solid-liquid separation was performed, and dried to obtain a fine powder of cellulose acetate containing diethyl phthalate. I got it.

The obtained fine powder is spherical, with an average spherical diameter of 4.5μ
It was hot.

Example 6 Cellulose acetate (degree of substitution 2.9, average degree of polymerization 280,
A solution (J) and a solution (B) obtained by dissolving 100 parts of raw material cellulose (linter) in a mixed solvent of methylene chloride and methanol (methylene chloride/methanol = 91/9 weight ratio) were treated in the same manner as in Example 1. A fine powder of cellulose acetate was obtained.

The fine powder was spherical, and the average spherical diameter was 4.0μ.

Claims (1)

[Claims] 1. A solution of cellulose acetate in an organic solvent and an aqueous medium containing a dispersant, a surfactant, and an antifoaming agent are mixed at a speed at which the tip circumferential speed of the rotor blade is at least 450 m/min or more, and
A method for producing a spherical micropowder of cellulose acetate, which comprises stirring and mixing at a stirring speed of 2000 rpm or more for at least 10 seconds, and heating an aqueous medium containing the generated suspended particles to evaporate the organic solvent.