JPH10182840A - Production of fine particles and apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a process and apparatus for producing fine particles,. having a high sphericity and a narrow particle size distribution by solidifying fine liquid drops, formed by a centrifugal force, without deforming them. SOLUTION: In an apparatus A for producing fine particles, a liquid material (a) for forming particles is fed into a rotator 2 through a pump 1, and liquid drops are formed and scattered by the centrifugal force generated by rotating a rotating shaft 3. The rotator 2 is surrounded by a cylindrical wall 4, and a cyclic reservoir 5 for storing a solidifying liquid (b) is installed at the top of the outside of the wall 4. The top of the reservoir 5 is open to form an outlet 6, and the solidifying liquid (b) fed by circulation with a pump 7 is allowed to overflow and thereby to naturally fall inside the wall 4 by the gravity. The bottom of the wall 4 is made in a funnel shape, and a reticular filter 9 for recovering the fine particles 8 by separating them from the solidifying liquid (b) disposed below the bottom of the wall 4 and in a lower part of a recovering tank 10.

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 particles by coagulating droplets scattered from a rotating body by centrifugal force, and an apparatus for producing fine particles.

[0002]

2. Description of the Related Art In general, it is known to use a rotating disk to atomize a liquid, and this method is applied to the case of atomizing a metal or a polymer material.

[0003] For example, as a method for producing fine particles made of a thermoplastic resin or the like, a molten resin material is supplied to the upper wall surface of a rotating body, and dispersed as droplets from the edge of the rotating body. JP-A-59-172522 describes a method of contacting with a cold gas to cool and solidify.

[0004] As a method for producing metal powder, a cooling liquid is supplied to the inner peripheral surface of a rotating drum to form a liquid layer having a required layer thickness which is swirled by a constant centrifugal force, and is jetted into the drum. Japanese Patent Application Laid-Open No. 4-337015 describes a method in which a droplet (molten metal) captured by the liquid layer is cooled and solidified.

In addition, as a method for producing metal powder, a cooling liquid layer is formed by spraying and supplying a cooling liquid from a tangential direction along an inner peripheral surface of a cylindrical body to form a swirling cooling liquid layer. A method of cooling and solidifying molten metal) in the liquid layer is disclosed in
No. 329806.

[0006] By the way, the fine particles produced in this manner are required to be formed into a desired shape, specifically a true spherical fine particle, and to increase the yield of the fine particles in a required particle size range depending on the use. ing.

[0007]

However, among the above-mentioned conventional methods for producing fine particles, in the method of cooling and solidifying in a cold airflow such as air, the formed droplets are secondarily split in a high-speed cold airflow. At that time, there is a problem in that air is mixed into the particles and the strength is reduced or the particle size distribution is increased.

On the other hand, a method for producing fine particles for forming a coagulation liquid layer on the inner peripheral surface of a rotating drum by centrifugal force, capturing droplets jetted into the drum in the coagulation liquid layer and coagulating the same, and a cylindrical body The method of producing fine particles, in which a coagulating liquid is ejected from the tangential direction along the inner surface of the liquid and forms a cooling liquid layer that swirls along the inner surface, and the liquid droplets are captured and coagulated by the cooling liquid layer, are all high-speed. This is a method for producing fine particles by finely dividing liquid droplets in a liquid layer swirling in the above, so the technology is different from the purpose of the invention of the present application. Will have large variations.

In such a conventional method for producing fine particles,
It is not possible to easily respond to the requirements of particle sphericity and particle size distribution, and usually it is necessary to classify using a sieve in order to obtain a particle having a small particle size distribution. Problems such as an increase and a decrease in the yield occur, which increases the manufacturing cost. In addition, it is considered that it is almost impossible industrially to collect only spherical particles.

[0010] The inventors of the present application have considered a method of naturally falling droplets scattered in the horizontal direction and capturing the droplets in a coagulation tank having an upper surface opening as an ideal method for improving the sphericity and particle size distribution of the fine particles. However, the surface area of the liquid surface of the coagulation tank is extremely large, and it is difficult to collect the fine particles. In such a manufacturing method and apparatus, it is also difficult to circulate the coagulating liquid for stabilizing the liquid quality of the coagulating liquid.

Accordingly, an object of the present invention is to solve the above-mentioned problems and to coagulate fine droplets formed by centrifugal force without impairing the shape thereof, and to provide fine particles having a high sphericity and a small particle size distribution. And to reduce the size of the apparatus used in the above-mentioned manufacturing method with a structure as simple as possible.

Another object of the invention relating to an apparatus for producing fine particles is to continuously and efficiently produce fine particles having a high sphericity and a small particle size distribution.

[0013]

In order to solve the above-mentioned problems, in the present invention, a liquid particle forming material is supplied to a rotating body, and droplets scattered from the rotating body by centrifugal force are solidified to form fine particles. In the method of manufacturing, a liquid storage tank for storing the coagulation liquid of the droplet is provided on an upper part of a cylinder arranged so as to surround the rotating body, and the coagulation liquid is supplied from the liquid storage tank along the inner surface of the cylinder. This is a method of producing fine particles which are caused to flow out at a substantially uniform flow rate in the direction, and to capture and coagulate the droplets in a coagulating liquid flow which naturally falls along the inner surface.

Further, a cylinder is provided so as to surround a rotating body which scatters droplets by centrifugal force, and the coagulation liquid of the droplets is stored in the upper part of the cylinder, and the coagulation liquid flows out to the inside of the cylinder. A liquid storage tank is provided, and an outlet of the liquid storage tank is arranged and formed such that the coagulation liquid naturally falls at a substantially uniform flow rate in the circumferential direction along the inner surface of the cylindrical body. The apparatus for producing fine particles was provided with a coagulating liquid circulating means for returning to the storage tank.

In the invention relating to the method for producing fine particles, the coagulating liquid flow is a gentle flow flowing down along the inside of the wall surface,
Each of the horizontal cross sections has a uniform thickness. For example, when expressed by a Reynolds number which is a parameter indicating the flow property, 100
A flow close to laminar flow of 00 or less is preferred.

The coagulation liquid flows out of the liquid reservoir at an initial velocity of 0 or at an extremely low initial velocity depending on the depth according to the arrangement of the openings. The flow velocity increases in accordance with the distance flowing down along the inner surface, but reaches a steady state in accordance with the resistance to the inner surface of the cylinder and the inherent viscosity of the fluid, so that it can flow down at a substantially constant speed. To further reduce the speed, the installation angle of the inner surface of the cylinder can be arbitrarily changed. In the solidified liquid flow thus obtained, droplets can be captured at any height, and the captured droplets solidify in a state where the spherical shape formed by the surface tension at the time of scattering hardly changes, Fine particles having a high sphericity and a small particle size distribution can be produced.

In the invention according to the apparatus for producing fine particles,
The outlet of the liquid storage tank provided at the upper part of the cylinder surrounding the rotating body is arranged and formed such that the coagulation liquid naturally falls along the inner surface of the cylinder at a substantially uniform flow rate in the circumferential direction. As a specific form of such an outlet, a groove-shaped liquid storage tank surrounding the cylindrical body, an upper surface opening of which allows the coagulation liquid to overflow to the inside of the wall surface, or a ring-shaped liquid surrounding the cylindrical body is used. A peripheral groove-shaped slit that opens to the inner surface of the cylinder may be formed in the lower part of the liquid reservoir.

[0018] Such an apparatus for producing fine particles,
As in the invention relating to the method for producing fine particles described above, the coagulating liquid flow becomes a steady state after flowing out, and thereafter flows down at a constant speed, so that the liquid droplets can be captured at any height of the coagulating liquid flow, and are captured. The droplets solidify in a state where the spherical shape formed by the surface tension at the time of scattering hardly changes, and since the coagulating liquid can be repeatedly used by the circulating means, fine particles having a high sphericity and a small particle size distribution are used. It can be manufactured continuously and efficiently.

[0019]

DETAILED DESCRIPTION OF THE INVENTION The material of the droplet used in the present invention is as follows.
Well-known molding materials including cellulose, natural polysaccharides such as chitosan, synthetic resins and other high-molecular materials, or metals, are appropriately adopted, in the form of solutions or melts by heating, or slurries, emulsions, etc. And the constituents of the liquid are not limited.

Further, the rotating body used in the present invention is not limited to the one having a specific structure, as long as it has a function of turning the liquid particle forming material into spherical liquid droplets and scattering by centrifugal force.
For example, a well-known rotating disk, a rotating discharge hole, or the like can be employed. In the above-mentioned rotating disk, a liquid particle forming material as a raw material of fine particles is supplied to the center of the rotating disk, and the liquid spreads in a film shape with a uniform thickness along the surface of the rotating disk, from the periphery of the disk. It breaks down into droplets by centrifugal force and scatters small droplets.

The rotary discharge hole is formed by forming a large number of through holes in the peripheral wall of a hollow disk-shaped rotary container, or by attaching a nozzle through the peripheral wall to form a liquid particle of a fine particle material in the rotary container. The material is supplied and the rotating container is rotated. At this time, the coagulating liquid is discharged from the through hole or the nozzle by centrifugal force to form droplets.

According to these droplet forming means, the formed fine droplet scatters in the air and becomes spherical due to surface tension before coming into contact with the coagulating liquid. In this case, by ensuring a sufficient distance between the rotating body and the coagulating liquid flow, the scattered droplets are formed into a spherical shape by surface tension.

The coagulation liquid is appropriately changed according to the raw material of the liquid droplets, and the components are not particularly limited. For example, as a coagulating liquid for viscose which is a material for forming cellulose particles, an acidic solution such as hydrochloric acid can be used, and as a coagulating liquid for a chitosan solution, an alkaline solution such as an aqueous sodium hydroxide solution is used. Can be. To cool and solidify the thermoplastic resin or metal particles, methanol or the like can be used.

The coagulating means is capable of coagulating the particles without deformation by causing the coagulating liquid to fall naturally by gravity along the inner surface of the cylindrical body arranged so as to surround the rotating body. It forms a gentle laminar flow with a thickness that does not penetrate when it comes into contact with the liquid. Even when using a coagulating liquid that solidifies very quickly,
If the coagulating liquid is convective at high speed around the rotating body or is turbulent, the liquid droplets are undesirably deformed or broken before solidifying.

As described above, the flow rate of the coagulating liquid that does not cause deformation or division until the liquid drops solidifies depends on the type, viscosity, density (specific gravity), solid content concentration, composition, etc. of the particle forming material to be used and solidification. Depends on the combination with the liquid. Under any conditions, if a gradual liquid film of the coagulation liquid having a sufficient thickness is formed by utilizing gravity, the microdroplets can be coagulated without impairing the shape.

In the apparatus for producing fine particles according to the first embodiment shown in FIG. 1, a liquid particle forming material a is supplied to a rotating body 2 via a pump 1 and a centrifugal force is applied by rotation inputted to a rotating shaft 3. The wall surface 4 of the cylindrical body is provided so as to surround the periphery of the rotating body 2 with the coagulating liquid b
An annular liquid reservoir 5 for storing the liquid is provided, and the upper surface of the liquid reservoir 5 is opened to form an outlet 6, so that the coagulating liquid b supplied by the pump 7 overflows and falls naturally along the inside of the wall surface 4. The lower part of the wall surface 4 is formed in a funnel shape, and below it is a fine particle manufacturing apparatus A provided with a mesh filter member 9 provided below the collecting tank 10 for separating and collecting the fine particles 8 from the coagulating liquid b. .

In this apparatus, the lower part of the recovery tank 10 and the liquid storage tank 5 are connected by a flow path 11 via a pump 7, so that the coagulation liquid b is circulated and used. Also, the filtering member 9
The fine particles 8 separated on the substrate can be recovered from the recovery tank 10 after the separation. As a material for forming the filtering member 9, polyvinylidene chloride and the like are preferable.

The apparatus B for producing fine particles according to the second embodiment shown in FIG. 2 has a circumferential groove-like shape which opens downward at the inner peripheral portion instead of the liquid reservoir 5 having the upper surface open in the apparatus according to the first embodiment. An annular liquid reservoir 13 having a slit 12 formed therein,
The configuration is exactly the same as that of the first embodiment except that the coagulation liquid b naturally falls along the inside of the wall surface 4 from the slit 12.

Using the apparatus for producing fine particles of the above-described embodiment, spherical fine droplets formed by centrifugal force are coagulated without impairing the shape, and fine particles having a high sphericity and a small particle size distribution are obtained. Can be manufactured continuously.

[0030]

【Example】

Example 1 Fine particles were produced using the apparatus of the first embodiment described with reference to FIG. As shown in FIG. 3, the rotating body is a cylindrical stainless steel rotating container 14 (diameter 100 mm, height 200 mm) attached to the rotating shaft 3, and the liquid is supplied to the upper surface thereof. A hole having a hole 15 having a diameter of 50 mm and 1620 holes 16 having a diameter of 0.3 mm formed at equal intervals on a peripheral side surface was used.

Then, viscose (cellulose concentration: 8.5% by weight, alkali concentration: 5.3% by weight) is added to the rotary container.
And rotated at 800 rpm. The recovery tank 10 contains 2N hydrochloric acid and is supplied to the liquid storage tank 5 at a flow rate of 270 liters / minute by the pump 7 and circulated. That is, the same flow rate overflows from the upper edge of the wall surface 4 of the cylindrical body. The scattered liquid droplets were applied to the surface of the flowing liquid to be captured in the coagulating liquid, solidified in the flowing liquid, and collected on the filtering member 9.

[0032] The recovered cellulose fine particles were subjected to desulfurization, bleaching, and washing with water. As a result of measuring the particle size distribution of the obtained cellulose fine particles with a laser light scattering type particle size distribution analyzer, the average particle size was 793 μm, and the particle size distribution was determined by the Rosin-Rammler distribution function formula R _(DP) = 100 · ex
The value of n in p (−bD _P ⁿ ) was 4.76 (rounded to the first decimal place). Note that R in the distribution function equation
_(DP) is the weight% on the integrated sieve, D _P is the particle diameter, b and n are constants, log {log (100 / R _(DP) )} is plotted against log D _P and n The value was determined.

When the obtained cellulose fine particles were classified by a sieve, all the particles were found to have a mesh of 710 μm and a size of 85 μm.
Settled between 0 μm wet sieve.

As shown in FIG. 5, when the shape of the particles was observed with an optical microscope, all the particles were spherical and no pores were observed inside the particles.

Example 2 Fine particles were produced using the apparatus of the first embodiment. The rotating body is a cylindrical acrylic resin rotating container 19 (diameter 100 mm, height 40 mm) attached to the rotating shaft 3 as shown in FIG. 4, and the liquid is supplied to the upper surface thereof. Hole 17 with a diameter of 50 mm
A nozzle having 0.4 nozzles with an inner diameter of 0.4 mm attached to the peripheral side surface at equal intervals was used.

Then, the viscose used in Example 1 was supplied to the rotating container 19 and rotated at 1,000 rpm. Thereafter, cellulose fine particles were produced in exactly the same manner as in Example 1. As a result of measuring the particle size distribution of the obtained cellulose fine particles using a laser light scattering type particle size distribution analyzer, the average particle size was 504 μm, and the particle size distribution was 4.69 in the Rosin-Rammler distribution function equation.
(Rounded to two decimal places).

Example 3 Fine particles were produced using the apparatus of the first embodiment. Note that the rotating body used had the same shape as that used in Example 2 shown in FIG.

Then, a chitosan solution (chitosan concentration 7.5% by weight, acetic acid concentration 10% by weight in aq,
5250 cp viscosity at 20 ° C. measured with a B-type viscometer
s) was supplied and rotated at a rotation speed of 1000 rpm. The recovery tank 10 contains 2% sodium hydroxide and 270
The liquid is supplied to and circulated from the liquid reservoir 5 by the pump 7 at a flow rate of 1 liter / min. After having been (solidified), it was recovered from above the filtering member 9.

The particle size distribution of the obtained chitosan fine particles was measured by a laser light scattering type particle size distribution measuring device. As a result, the average particle size was 484 μm, and the particle size distribution was determined by the value of n in the Rosin-Rammler distribution function equation. It turned out to be 4.88 (rounded to the nearest third decimal place).

Example 4 Fine particles were produced using the apparatus of the first embodiment described with reference to FIG. The rotating body is a disk-shaped rotating disk (diameter 100 m) attached to a rotating shaft.
m), whose liquid was supplied to the upper surface thereof.

Then, viscose having a cellulose concentration of 8.0% by weight and an alkali concentration of 5.3% by weight was supplied to the above rotating disk at a rate of 4.5 ml / min by a tube pump, and the rotation speed was 1,000 rpm. After rotation, the cellulose was coagulated in the same manner as in Example 1 under the other conditions, and then collected from the filtration member 9 to obtain cellulose fine particles.

The obtained cellulose fine particles had an average particle size of 719 μm, and the particle size distribution was found to be 3.75 (rounded to the third decimal place) in the equation of the Rosin-Rammler distribution function. .

Further, as shown in FIG. 6, when the particle shape was observed with an optical microscope, all the particles were truly spherical, and no pores were observed inside the particles.

[Comparative Example 1] The viscose used in Example 1 was supplied to the rotating container used in Example 2, and the rotation speed was 100.
Rotated at 0 rpm.

Then, instead of the liquid storage tank of the first embodiment,
As shown in FIG. 7, eight hoses 20 are arranged at equal intervals on the upper edge of the wall surface 4 of the cylindrical body, with the opening ends facing obliquely downward, and 2N hydrochloric acid is supplied at a flow rate of 135 liters / min per tube. The liquid was discharged to form a liquid layer, and the viscose droplets scattered from the rotating container were captured in the liquid and solidified to form cellulose fine particles.

The obtained cellulose fine particles had an average particle size of 479 μm, and the particle size distribution was such that the value of n in the expression of the Rosin-Rammler distribution function was 2.96 (rounded to the third decimal place).

Further, as shown in FIG. 8, when the particle shape was observed with an optical microscope, the particle shape was not uniform and the particle size was not uniform.

[0048]

As described above, the method and apparatus for producing fine particles of the present invention achieve the object with a simple and small apparatus, and have an inner surface of a cylindrical body arranged so as to surround a rotating body on which droplets scatter. A coagulating liquid flow with a substantially uniform thickness is formed in the circumferential direction along with the liquid droplets, and the liquid droplets are captured and coagulated by the coagulating liquid flow. There is an advantage that solidification can be performed without impairing the shape, and fine particles having a high sphericity and a small particle size distribution can be produced.

The invention relating to the apparatus for producing fine particles has an advantage that fine particles having a high sphericity and a small particle size distribution can be continuously and efficiently produced.

[Brief description of the drawings]

FIG. 1 is an explanatory view of a first embodiment of an apparatus for producing fine particles.

FIG. 2 is an explanatory view of a second embodiment of the apparatus for producing fine particles.

FIG. 3 is a perspective view of a rotating body used in the first embodiment.

FIG. 4 is a perspective view of a rotating body used in a second embodiment.

FIG. 5 is an optical micrograph of the fine particles of Example 1.

FIG. 6 is an optical micrograph of the fine particles of Example 3.

FIG. 7 is an explanatory diagram of an apparatus for producing fine particles of Comparative Example 1.

FIG. 8 is an optical micrograph of the fine particles of Comparative Example 1.

[Explanation of symbols]

 1, 7 Pump 2 Rotating body 3 Rotating shaft 4 Wall of cylindrical body 5, 13 Liquid reservoir 6 Outlet 8 Fine particles 9 Filtration member 10 Recovery tank 11 Flow channel 12 Slit 14, 19 Rotating container 15, 17 Hole 16 Hole 18 Nozzle 20 Hose a Particle forming material b Coagulating liquid A, B Fine particle manufacturing equipment

Claims (2)

[Claims] 1. A liquid particle forming material is supplied to a rotating body,
In the method of producing fine particles by coagulating droplets scattered by centrifugal force from the rotating body, a liquid storage tank for storing the coagulating liquid of the droplet is provided on an upper part of a cylindrical body arranged so as to surround the rotating body, The coagulating liquid is allowed to flow out from the liquid reservoir along the inner surface of the cylindrical body at a substantially uniform flow rate in the circumferential direction, and the liquid droplets are captured and coagulated in the coagulating liquid flow that naturally falls along the inner surface. A method for producing fine particles. 2. A cylindrical body is provided so as to surround a rotating body that scatters droplets by centrifugal force, and a coagulating liquid of the droplets is stored in an upper portion of the cylindrical body, and the coagulating liquid flows out inside the cylindrical body. A liquid storage tank is provided, and an outlet of the liquid storage tank is arranged and formed such that the coagulation liquid naturally falls at a substantially uniform flow rate in the circumferential direction along the inner surface of the cylindrical body. An apparatus for producing fine particles, comprising a coagulating liquid circulating means for returning to a storage tank.