JP2002249512A - Production process for fine powder, and fine powder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently produce a fine powder having an average primary particle size of 10 μm or lower from a fine particle dispersion by a spray drying method almost without causing agglomeration. SOLUTION: This fine powder is obtained by spray drying a fine particle dispersion with a spray dryer equipped with a four-stream nozzle. The fine particle dispersion is preferably a dispersion of fine polymer particles obtained by polymerizing a monomer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing fine particle powder and a fine particle powder obtained by the method.

[0002]

2. Description of the Related Art A method for producing fine particle powder by spray-drying a dispersion liquid of fine particles by a spray dryer is known. This type of spray drying method has an advantage that steps such as filtration, drying, pulverization, and classification can be omitted.

As an atomizer (sprayer), a spray dryer having a pressurizing nozzle (one-fluid nozzle), a two-fluid nozzle, and a rotating disk type (disk type) is used. Among such spray dryers, a spray dryer equipped with a two-fluid nozzle is suitable for obtaining fine-particle powder having a fine particle diameter.

However, even if a spray dryer equipped with a two-fluid nozzle is used and the ratio of the gas flow rate for spraying to the spraying liquid is increased for the purpose of making the spray droplets fine, the drying gas in the dryer is not affected. In many cases, the backflow of water occurs, and the spray droplets and the collision between the spray droplets and the dried particles occur and coalesce to produce coarse particles (agglomerated particles) much larger than the target particle diameter. Can be seen.

In order to prevent the formation of coarse particles (agglomerated particles), Japanese Patent Application Laid-Open No. 9-71608 discloses a spray dryer equipped with a two-fluid nozzle, in which the opening angle of the upper cone of the dryer and the opening angle of the upper cone are reduced. A method is disclosed in which the ratio between the entrance diameter and the diameter of the straight body of the dryer is adjusted to prevent collision and coalescence of spray droplets and dried particles.

However, even with this method, it is difficult to efficiently produce a fine particle powder having an average primary particle diameter of 10 μm or less with little agglomeration.

[0007]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems. It is an object of the present invention to obtain fine particles having an average primary particle diameter of 10 μm or less from a dispersion of fine particles by a spray drying method. It is an object of the present invention to provide a method for producing a fine particle powder which can be efficiently produced with almost no agglomeration of the powder, and a fine particle powder obtained by the production method, particularly a fine particle powder having an average primary particle diameter of 10 μm or less.

[0008]

The above object can be achieved by spray-drying a dispersion of fine particles with a spray dryer equipped with a four-fluid nozzle. In particular, a dispersion of fine polymer particles obtained by polymerizing a monomer is suitable as a dispersion of fine particles.

[0009] Here, a spray dryer having a four-fluid nozzle is defined as two gas passages as described in "Chemical Equipment", June 2000, pages 60 to 65, issued by the Industrial Research Council. A spray dryer having two liquid passages and a nozzle configured to form a collision focal point where fluid ejected from the outlets of these gas passages and liquid passages converge at one point.

The four-fluid nozzle of the spray dryer will be described with reference to the drawings. FIG. 1 is a cross-sectional view showing an example of a four-fluid nozzle of a spray dryer. The four-fluid nozzle 10 has a nozzle edge formed in a straight line (a straight line in a direction perpendicular to the drawing). ing. 11a and 11b denote two gas paths, 12a and 12b denote two liquid paths, and a collision in which the fluid 20 spouted from the outlet of the gas paths 11a and 11b and the liquid paths 12a and 12b collects at one point. Focus 2
1 are formed.

FIG. 1 shows an external mixing system in which the collision focal point 21 is formed outside the nozzle. However, an internal mixing system in which the collision focal point 21 is formed inside the nozzle may be used.
However, the external mixing method is preferable because clogging hardly occurs. FIG. 1 shows a straight-edge four-fluid nozzle 10 in which the nozzle edge is formed in a straight line, but a circle-edge four-fluid nozzle in which the nozzle edge is formed in a cylindrical shape can also be used. .

In the case of the straight-edge type four-fluid nozzle 10, the nozzle edge is formed in a straight line having an appropriate length (for example, 2 to 30 mm) depending on the spray amount.
a, 11b and the liquid paths 12a, 12b are spaced at a certain interval (for example, 0.1 to 0.3 m) in accordance with the edge length.
m) is a slit-shaped outlet that maintains accuracy.

In the case of the two-fluid nozzle, the spray outlet cannot be changed significantly from the hole-shaped structure. However, the four-fluid nozzle shown in FIG. 1 has a nozzle edge formed in a straight line, and has two gas paths and two liquid paths, thereby simultaneously solving the purpose of atomizing the spray liquid and mass spraying. be able to.

In FIG. 1, spraying gas is injected into gas passages 11a and 11b on both sides toward a collision focal point 21 at the tip of a nozzle edge, and a liquid passage 12 on both sides is pressed.
A dispersion liquid of fine particles is injected into a and 12b. Then, the high-speed gas flow coming out of the slits of the gas passages 11a and 11b thinly stretches the dispersion liquid of the fine particles that comes out of the slits of the liquid passages 12a and 12b while mixing on the fluid flow surface. The dispersion liquid of the elongated fine particles is further miniaturized by a shock wave generated at the collision focal point 21 at the tip of the edge to form a fine droplet 20.

The dispersion liquid of fine particles to be injected into the liquid passages 12a and 12b is formed into fine liquid droplets by the four-fluid nozzle 10 so that the solvent and the dispersion medium can be volatilized, dried, and granulated. Without limitation, for example, a dispersion liquid of fine particles composed of a thermoplastic resin such as poly (meth) acrylate, polyester, polystyrene, polyamide, polyurethane, polyolefin, or polyvinyl chloride; polyphenol, urea resin, melamine resin, silicone resin, epoxy resin, A dispersion liquid of fine particles made of a thermosetting resin such as an unsaturated polyester resin may be used.

Also, clay, silica, calcium carbonate,
Dispersion of fine particles comprising inorganic filler such as titanium oxide; dispersion of fine particles such as organic foaming agent, detergent, pigment, insecticide, herbicide, fungicide, instant coffee, cocoa, malt extract, starch, and other Dispersions of fine particles of pharmaceuticals such as foods, natural and synthetic flavors, cosmetics, antibiotics, serum, plasma, various vitamins, penicillin, glucose, various amino acids and the like can be mentioned.

Among them, a dispersion of polymer fine particles obtained by polymerizing a monomer is sprayed, and it is suitably used for recovering fine and uniform fine particle powder. As the polymerization method of the monomer, a polymerization method requiring a liquid medium, for example, an emulsion polymerization method, a suspension polymerization method, a microsuspension polymerization method, a soap-free polymerization method, a dispersion polymerization method, a seed polymerization method, a solution polymerization method And the like. Polymer fine particle powder is used for medical drug carriers, liquid crystal display spacers,
It is suitably used for toners, powder coatings and the like.

The type of the spray gas to be injected into the gas passages 11a and 11b is selected according to the properties of the dispersion liquid of the fine particles to be applied. Usually, air is used because it is easily available. In spray drying, it is preferable to use an inert gas such as nitrogen for safety. The flow rate and flow rate of the gas for spraying are appropriately determined from the heat balance in the spray dryer in consideration of the drying temperature.

The fine droplets 20, which are finely divided at the collision focal point 21 at the edge of the edge, efficiently contact dry hot air in a drying chamber (not shown) of the spray drier and are instantaneously dried to become fine particle powder, which is cyclone. -Collected by bag filters. The drying chamber and the cyclone bag filter of the spray dryer are configured in the same manner as the conventional one.

The drying temperature needs to be adjusted according to the properties of the fine particles in the dispersion. Usually, conditions are set based on the target drying efficiency, heat resistance of the fine particles, and the temperature of the supply heat source. Generally, the hot air temperature for drying is often 50 to 450 ° C. at the inlet of the spray dryer and 40 to 200 ° C. at the drying room temperature.

When the temperature in the drying chamber is 25 ° C. or lower, it becomes difficult to maintain the temperature stably in relation to the outside air temperature, and the water-based spray sometimes results in insufficient drying. Further, when drying polymer fine particles obtained by polymerizing the monomer, it is necessary to control the temperature of the dried particles to be equal to or lower than the glass transition temperature of the polymer in order to prevent secondary aggregation of the particles, Is preferably set to 40 to 90 ° C.

The particle size of the obtained fine particle powder can be controlled by controlling the concentration of the dispersion liquid of the fine particles to be applied and the ratio of the total flow rate of the spray gas to the flow rate of the liquid to be sprayed. Etc., as appropriate.

The higher the concentration of the dispersion of fine particles, the larger the particle size. In addition, the ratio between the total flow rate of the spray gas and the flow rate of the liquid to be sprayed becomes small, so that the spray droplets themselves become large, so that it is difficult to obtain fine dry particles. However, the consumption of the atomizing gas increases, and the cost for the facility for producing the compressed gas and the facility operation cost increase, which is economically disadvantageous.

In this way, from a dispersion of fine particles, particularly a dispersion of polymer fine particles obtained by polymerizing a monomer, a fine particle powder having an average primary particle diameter of 10 μm or less can be efficiently obtained with almost no agglomeration.

[0025]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Examples and comparative examples of the present invention are shown below. (Example 1) <Preparation of dispersion liquid of polymer fine particles> 200 g of methyl methacrylate, trimethylolpropane triacrylate 2
g and lauroyl peroxide 1 g were mixed with stirring. 400 g of ion-exchanged water and 2 g of sodium dodecylbenzenesulfonate were added thereto, and the mixture was stirred with a homogenizer to prepare an emulsion monomer liquid.

On the other hand, 400 g of ion-exchanged water was put into a polymerization vessel equipped with a stirrer and a jacket, and stirring was started. After reducing the pressure inside the polymerization vessel and deoxidizing the inside of the vessel, the pressure was returned to atmospheric pressure with nitrogen, and the inside was set to a nitrogen atmosphere.
The emulsified monomer liquid was added to this at once.

Thereafter, the temperature inside the polymerization vessel was raised to 70 ° C. to start emulsion polymerization. The polymerization reaction was completed in 1 hour, and after an aging period of 1 hour, the mixture was cooled to room temperature. As a result of the polymerization reaction, a dispersion liquid containing polymer fine particles having a solid content (polymer) concentration of about 20% by weight and an average particle diameter (primary particles) of 4.3 μm was obtained. The average particle size of the polymer fine particles in the dispersion,
Laser diffraction particle size distribution analyzer LA-910 manufactured by HORIBA, Ltd.
It measured using.

<Spray drying of dispersion liquid of polymer fine particles> FIG.
As a spray dryer with a four-fluid nozzle as shown in
Fujisaki Electric Micro Mist Dryer MDL-05
0 (nozzle edge length 3mm, gas path slit 0.2m
m, the liquid path slit was 0.25 mm), and the dispersion containing the polymer fine particles was spray-dried to produce polymer fine powder. The drying conditions were a hot air inlet temperature of 120 ° C., a drying room temperature of 65.2 ° C., and a dispersion feed rate of 20 ml / min.

Observation of the morphology of the obtained polymer fine particle powder using a scanning electron microscope Model S-4200 manufactured by Hitachi, Ltd. revealed that the polymer fine particles exhibited complete primary particles.

(Example 2) <Preparation of polymer fine particle dispersion> 190 g of styrene and 10 g of divinylbenzene were stirred and mixed. 400 g of ion-exchanged water and 2 g of sodium dodecylbenzenesulfonate were added thereto, and the mixture was stirred with a homogenizer to prepare an emulsion monomer liquid.

On the other hand, 400 g of ion-exchanged water was put into a polymerization vessel equipped with a stirrer and a jacket, and stirring was started. After depressurizing the inside of the polymerization vessel and deoxidizing the inside of the vessel, the pressure was returned to the atmospheric pressure with nitrogen, and the inside was set to a nitrogen atmosphere. Then, the inside of the polymerization vessel was heated to 70 ° C.

Thereafter, 0.2 g of ammonium persulfate was added into the polymerization vessel, and the mixture was stirred for 15 minutes. Then, 10% by weight of the emulsified monomer liquid was added at a time to start emulsion polymerization. Twenty minutes after the start of the polymerization, dropping of the remaining emulsified monomer liquid into the polymerization system was started. Dropping was completed in 2 hours, and after an aging period of 1 hour, the mixture was cooled to room temperature.
As a result of the polymerization reaction, the solid content (polymer) concentration is about 20% by weight,
A dispersion liquid containing polymer particles having an average particle diameter (primary particle) of 0.21 μm was obtained. The average particle size of the polymer fine particles in the dispersion was measured using a laser diffraction particle size distribution analyzer LA-9 manufactured by Horiba, Ltd.
10 was used.

<Spray drying of dispersion liquid of polymer fine particles> FIG.
As a spray dryer equipped with a four-fluid nozzle as shown in
Fujisaki Electric Micro Mist Dryer MDL-05
Using 0, the dispersion containing the polymer fine particles was spray-dried to produce powder of the polymer fine particles. Drying conditions were as follows: hot air inlet temperature 120 ° C., drying room temperature 59.5.
° C and the dispersion feed rate was 20 ml / min.

Observation of the morphology of the obtained polymer fine particle powder using a scanning electron microscope Model S-4200 manufactured by Hitachi, Ltd. revealed that the polymer fine particles showed agglomerated particles of only 1 μm or less. However, the majority showed complete primary particles.

(Comparative Example 1) As a spray dryer provided with a two-fluid nozzle, AGM-35SD manufactured by Hosokawa Micron Corporation was used, and the dispersion containing the polymer fine particles obtained in Example 1 was spray-dried. Drying conditions are hot air inlet temperature 8
The temperature was 0 ° C., the drying room temperature was 58.4 ° C., and the feed rate of the dispersion was 100 ml / min.

Observation of the morphology of the obtained polymer fine particle powder using a scanning electron microscope Model S-4200 manufactured by Hitachi, Ltd. revealed that the particles were aggregated.
Many aggregated particles of 10 μm or more were observed.

(Comparative Example 2) As a spray drier equipped with a two-fluid nozzle, AGM-35SD manufactured by Hosokawa Micron Corporation was used, and the dispersion containing the polymer fine particles obtained in Example 2 was spray-dried. Drying conditions are hot air inlet temperature 8
The temperature was 0 ° C., the drying room temperature was 62.9 ° C., and the feed rate of the dispersion was 120 ml / min.

When the morphology of the obtained fine polymer particles was observed using a scanning electron microscope Model S-4200 manufactured by Hitachi, Ltd., a large number of aggregated particles of 10 μm or more were observed.

[0039]

As described above, a dispersion of fine particles, particularly a dispersion of polymer fine particles obtained by polymerizing a monomer, is spray-dried by a spray drier equipped with a four-fluid nozzle, whereby a dispersion of fine particles is obtained. Average particle size of primary particles from 10μ
m or less can be efficiently produced with little agglomeration, and the steps of pulverization and classification can be omitted or simplified.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an example of a four-fluid nozzle of a spray dryer.

[Explanation of symbols]

 Reference Signs List 10 Four-fluid nozzle 11a, 11b Gas path 12a, 12b Liquid path 20 Fluid 21 Fluid collision focus

Claims (5)

[Claims] 1. A method for producing fine particle powder, wherein a dispersion liquid of fine particles is spray-dried by a spray dryer equipped with a four-fluid nozzle. 2. The method for producing fine particle powder according to claim 1, wherein a dispersion liquid of polymer fine particles obtained by polymerizing a monomer is used. 3. The temperature in the drying chamber of the spray dryer is 40 to 9
The method for producing fine particle powder according to claim 1, wherein the temperature is 0 ° C. 4. 4. A fine particle powder obtained by the production method according to claim 1. 5. The fine particle powder has an average particle size of 0.1 to 10 μm.
The fine particle powder according to claim 4, comprising primary particles of the following.