JPH051072B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field] The present invention is used for powder classification in which a high-speed swirling vortex is generated in powder supplied to a classification chamber to centrifugally separate it into a fine powder group and a coarse powder group. Regarding air flow classifier.

[Background technology]

When the powder raw material flowing into the classification chamber flows in a swirling manner in the classification chamber, centrifugal force and inward air resistance force act on each particle of the powder raw material, and this centrifugal force and air resistance force act on each particle of the powder raw material. The classification point is determined by the balance of.

Large particles swirl on the outside of the classification chamber, and small particles swirl on the inside. Separate collection (classification) of fine powder and coarse powder by forming powder discharge ports at the center and outer periphery of the bottom of the classification chamber.
can do.

In such an air classifier, it is important for the powder raw material to be sufficiently dispersed in the classification chamber to become primary particles in order to improve the classification accuracy.

As this type of classifier, the Iiya classifier and the Clacyclone have been proposed. However, this type of classifier has problems in that it is extremely difficult to control the classification point, poor dispersion, and poor classification accuracy at high dust concentrations. Various proposals have been made to improve this problem. For example, JP-A-54-48378 or JP-A-54-
There is a proposal described in Publication No. 79870. An example of a classifier that has been put into practical use is the classifier sold under the name DS separator. In this type of classifier, it has become possible to control the classification point, but since the powder is supplied to the classification chamber via the cyclone section, the powder is concentrated before entering the classification chamber. There was a tendency for the powder to be insufficiently dispersed. This caused a decrease in classification efficiency. The conventional device will be further explained with reference to FIGS. 5 and 6 of the accompanying drawings.

FIG. 5 is a schematic view of the outer surface of the conventional device, and FIG. 6 is a schematic cross-sectional view of the conventional device.

5 and 6, 1 is a main body casing, 2 is a lower casing connected to the lower part of the casing 1, and a hopper 3 is attached to the lower part of the lower casing.
Inside the main casing 1,
A classification chamber 4 is formed. A guide tube 10 stands up on the upper part of the main body casing 1, and a supply tube 9 is connected to the upper outer peripheral surface of the guide tube 10. Guide tube 1
A discharge guide plate 15 having a conical (umbrella-shaped) center is attached to the lower part of the interior of the discharge guide plate 15.
An annular supply groove 11 is formed around the outer periphery of the lower edge. The bottom of the classification chamber 4 is equipped with a conical (umbrella-shaped) classification plate 5 with a high central portion, and an annular coarse powder discharge groove 6 is formed around the lower edge of this classification plate 5. Further, a fine powder discharge port 7 is formed in the center of the classification plate 5. A gas inlet 8 for inflowing air is provided around the outer circumference of the lower peripheral wall of the classification chamber 4, and this gas inlet 8 is usually arranged between a plurality of blade-shaped classification louvers 14. It is made up of. The direction of the air introduced from the gas inlet 8 is adjusted by the classification louver 14 so that it is ejected in the swirling direction of the powder material descending while swirling in the classification chamber 4, thereby dispersing the powder material and increasing the swirling speed. is accelerating.

FIG. 4b shows a cross-sectional view taken from FIGS. 5 and 6. The gas inlet 8 shown in FIG. 4 is one specific example, and it is also possible to change the shape of the classification louver. The interval between the classification louvers 14 can be adjusted, and by changing this interval, the rotation speed of the powder in the classification chamber 4 can be changed, and the classification point can be changed. Further, the height of the classification chamber 4 can also be adjusted. In such a conventional air classifier, the powder raw material is pressure-fed from the supply tube 9 to the guide tube 10 by the airflow, descends while swirling around the inside and outside of the guide tube 10, and enters the classification chamber through the annular supply groove 11. 4
It is swirled inward. In the classification chamber 4, each particle is centrifugally separated into a coarse powder group and a fine powder group by centrifugal force acting on each particle. However, in conventional devices, the raw material powder is supplied into the classification chamber 4 while being concentrated on the inner wall of the guide cylinder due to centrifugal force, so the dispersion of the powder particles is insufficient, and the powder is similar to the cyclone. Since the material descends in a helical strip inside the guide cylinder, the concentration supplied to the classification chamber is also uneven depending on the location, making it impossible to obtain sufficient classification accuracy. That is, when fine powder forms aggregates or when fine powder is attached to coarse powder, if dispersion is insufficient, the tendency of fine powder to mix into the coarse powder group increases. Furthermore, if the dispersion is insufficient, the dust concentration within the classification chamber 4 will become non-uniform, the classification accuracy itself will deteriorate, and the resulting classified product will have a wide particle size distribution. This tendency becomes more pronounced as the particle size of the powder raw material becomes finer, especially when powder
When the diameter becomes 10 μm or less, the tendency for the classification accuracy to decrease becomes more pronounced.

[Purpose of the invention]

The present invention solves the various problems mentioned above.

An object of the present invention is to provide an air classifier with good classification efficiency.

An object of the present invention is to provide an air classifier capable of producing classified powder with a sharp particle size distribution.

An object of the present invention is to provide an air classifier whose classification point can be easily adjusted.

An object of the present invention is to provide an air classifier that is less likely to generate fine powder aggregates.

Specifically, an object of the present invention is to provide an airflow classifier for classifying powder by airflow, in which a supply port for supplying powder is formed in the upper part of a classification chamber, and a supply port for supplying powder is formed in the lower part of the classification chamber. is equipped with a conical classification plate with a high central part, and a coarse powder discharge port is provided around the lower edge of the classification plate for discharging the coarse powder group classified by air. In the center of Bunkuri-zaka,
A fine powder discharge port is provided to discharge the fine powder group classified by wind, and air is supplied from the outside air to the upper part of the classification chamber to disperse the supplied powder by air circulation around the upper part of the classification chamber. A first gas inflow means having a plurality of inflow passages each having a first air inlet for suctioning and introducing the powder is provided, and around the lower part of the classification chamber there is provided air for wind classification of the dispersed powder. A second air inflow passage having a plurality of inflow passages each having a second air inlet for sucking and introducing air from the outside air into the lower part of the classification chamber to generate a swirling flow.
A gas inflow means is provided, and the total opening area of the first air inlet of the first gas inflow means is A (cm ² ), and the total opening area of the second air inlet of the second gas inflow means is A (cm 2 ). An object of the present invention is to provide an air classifier characterized in that A and B satisfy the following formula: 1≦A/B≦20, where the total area is B (cm ² ).

[Specific description of the invention]

In view of the problems of the conventional device described above, the air flow classifier of the present invention is equipped with a gas inflow means for dispersing powder by swirling flow around the upper part of the classification chamber, thereby improving the dispersion of powder inside the classification chamber. This improves the classification accuracy. A detailed description will be given below based on the drawings.

As an example of the air classifier according to the present invention, one of the type shown in FIG. 1 (showing the outer surface of the device) and FIG. 2 (showing a longitudinal sectional front view of the device) can be exemplified.

1 and 2, 1 indicates a main casing, 2 a lower casing connected to the lower part of the casing 1, and a hopper 3 at the lower part.
A classification chamber 4 is formed inside the main casing 1. A guide tube 10 stands up on the upper part of the main body casing 1, and a supply tube 9 is connected to the upper outer periphery of the guide tube 10. A conical (umbrella-shaped) discharge guide plate 15 with a high central portion is attached to the lower part of the guide cylinder 10, and an annular supply groove 11 is formed around the lower edge of the discharge guide plate 15.
A conical (umbrella-shaped) classification plate 5 with a high central part is provided at the bottom of the classification chamber 4.
An annular coarse powder discharge groove 6 for discharging the coarse powder group is formed around the lower edge of the classification plate 5, and a fine powder discharge port 7 for discharging the fine powder group is formed in the center of the classification plate 5. . On the outer periphery of the upper peripheral wall of the classification chamber 4, a first
An inflow path having a first air inlet 12 is provided as an airflow inflow means. A preferable example is one constructed by a space between a plurality of vane-shaped dispersion louvers 13. Third
The figure shows a cross-sectional view taken from the side in FIGS. 1 and 2.
As shown in FIG. 3, the direction of the air 16 sucked and introduced from the first air inlet 12 is downward while swirling around the inside and outside of the guide cylinder 10, and the air 16 is directed downward through the annular supply groove 1.
It is adjusted by the dispersion louver 13 so that the powder material swirlingly flows into the classification chamber 4 from 1 and ejects in the swirling direction. The airflow inlet means formed by the dispersion louver 13 plays the role of actively dispersing the powder immediately after it has entered the classification chamber 4, reducing the amount of powder aggregates, and further accelerating the powder. This significantly improves the classification accuracy of powder. Classification room 4
A second air inlet 8 for introducing air is provided around the outer circumference of the lower peripheral wall of. The inflow path having the second air inlet 8 is formed between a plurality of blade-shaped classification louvers 14, as shown in FIG. 4a. The direction of the air 17 sucked and introduced from the second air inlet 8 is adjusted by the classification louver 14 so that it is ejected in the swirling direction of the powder material descending while swirling in the classification chamber 4, and the powder material is dispersed again. It is designed to perform wind classification by increasing the rotation speed and accelerating the rotation speed.

Spacing between classification louvers 14 and distribution louvers 1
The interval between 3 is adjustable, and the classification louver 14
The height of the dispersion louver 13 can also be set appropriately.

According to the configuration of the present invention, the powder material that is concentrated on the inner wall of the guide cylinder 10 by centrifugal force and swirls and flows into the classification chamber 4 from the annular supply groove 11 is moved by the air 16 flowing from the first air inlet 12. The particles are dispersed and the swirling speed is accelerated to swirl and fall to the lower part of the classification chamber, where the swirling speed is further accelerated by the air 17 flowing in from the gas inlet 8 and separated into a coarse powder group and a fine powder group. Classified efficiently. The state of dispersion of the powder raw material in the classification chamber 4 has a great influence on the classification performance. In conventional air classifiers, this dispersion is insufficient for highly accurate classification, and the present invention solves this problem by providing the first air inlet 12 at the top of the classification chamber. It is. The first air inlet 12 provided in the upper part of the classification chamber is preferably provided above the center of the overall height of the classification chamber 4, and is preferably provided below the annular supply groove 11. The wind speed of the air 16 flowing in from the first air inlet 12 is preferably adjusted to be equal to or slower than the wind speed of the air 17 flowing in from the gas inlet 8 at the bottom of the classification chamber. The main purpose of the air 16 flowing in from the first air inlet 12 is to disperse particles constituting the powder, while the air 17 flowing in from the second air inlet 8 has a strong swirling force on the particles. It is based on the technical idea that the powder is classified into coarse powder and fine powder based on the difference in centrifugal force.

The total opening area of the first air inlet 12 is A
(cm ² ), the total opening area of the second air inlet 8 is B
(cm ² ), it is preferable to adjust the opening area so that A and B satisfy the following formula 1≦A/B≦20 in order to improve the classification performance. One of the features of the present invention is that an air inlet is provided in the upper part of the classification chamber to suck and introduce air from the outside air in order to disperse the supplied powder. The present invention is not limited to the configuration illustrated in .

In the apparatus of the present invention, each particle has a very high tendency to be sufficiently dispersed down to the primary particle in the classification chamber.
The classification efficiency is high, and the particles classified by the device of the present invention exhibit a precise particle size distribution, and the classification yield is also better than that of conventional devices. Furthermore, in the apparatus of the present invention, it is also possible to make the separation particle size for comparison smaller than that in the conventional apparatus.

The air classifier of the present invention can be effectively used in conjunction with a crusher, as shown in the flowchart of FIG. In this case, the pulverized raw material is supplied to the air classifier of the present invention, and the coarse powder having a certain specified particle size or more is introduced into the pulverizer, and after being pulverized, it is circulated to the air classifier again. Particles pulverized to a specified particle size or less are removed from the air classifier by an appropriate removal means. In such a grinding system, conventional air classifiers do not sufficiently disperse the powder in the classification chamber.
It is difficult to completely loosen aggregates made up of ultrafine particles or fine particles attached to coarse powder, and such aggregates get mixed into the coarse powder group during classification and are recycled to the pulverizer. This tends to cause over-grinding and reduce the grinding efficiency. In order to solve this problem, the air classifier of the present invention sufficiently disperses the particles in the classification chamber, so it is possible to loosen such aggregates, prevent them from being mixed into the coarse particles, and turn the fine particles into fine particles. The pulverization efficiency can be further improved.

In the classification device of the present invention, the smaller the particle size of the powder, the more
Also, the higher the dust concentration in the classification chamber, the more pronounced the effect is, and it is particularly effective in the area of 10 μm or less, and is even more effective when used in combination with a crusher.

The apparatus of the present invention can be used for electrostatic image developing toners, powder coatings, etc. whose final products are required to be fine particles.
Suitable for manufacturing magnetic materials, polymer materials, etc. It is particularly suitable as an air classifier used for producing toner for developing electrostatic images, which is susceptible to electrostatic force and tends to agglomerate.

The final product of the electrostatic image developing toner is required to have fine particles and to have a precise particle size distribution in which particles having a specified particle size or less are removed. In order to remove particle groups below a certain specified particle size, conventional air classifiers of the type shown in Figures 5 or 6 still have unsatisfactory classification accuracy, and the particle size distribution of the resulting product is There was a tendency for them to become wide-ranging.

Further, even if a fine particle size distribution can be obtained using the conventional method, the classification yield decreases and the cost becomes high. On the other hand, according to the classification device of the present invention, the powder in the classification chamber is sufficiently dispersed and coarse powder and fine powder can be efficiently separated. ) can be produced without reducing the yield.

Hereinafter, the present invention will be explained in detail based on examples.

Example 1 Styrene-acrylic ester resin (weight average molecular weight approximately 300,000) 100 parts by weight Magnetic ferrite (particle size 0.2 μm) 60 parts by weight low molecular weight polyethylene 2 parts by weight Negative charge control agent 2 parts by weight Mixture of the above formulation Approximately 180 toner raw materials
After melting and kneading for about 1.0 hours at ℃, it was cooled to solidify, coarsely ground into particles of 100 to 1000 μm using a hammer mill, and then crushed to particles with a weight average particle size of 10.5 μm (particle size
A pulverized product containing 9.3% by weight of particles of 5.04 μm or less was obtained. The obtained pulverized product was introduced into an air classifier shown in FIGS. 1 and 2 and classified. In the air classifier, air is sucked in at a flow rate of 5 m ³ /min from a fine powder discharge pipe having a fine powder discharge port 7 to suck the crushed products, and air 16 is supplied from outside air to disperse the crushed products in the upper part of the classification chamber. The first air inlet 12 for sucking and introducing the air has 20 openings of 2 cm in length and 0.6 cm in width (total opening area 2 x 0.6 x 20 = 24 cm ² ) using dispersion louvers 13. A second air inlet 8 for sucking in air 17 from the outside air is provided with a vertical 2
cm, 20 openings with a width of 0.2 cm (total opening area 2 x
0.2×20=8cm ² ), and the height of the classification chamber was 14cm. As a result of classifying the pulverized product, a classified product from which fine powder has been removed is a classified product that is preferable as a toner with a weight average particle size of 11.5 μm (contains 0.3% by weight of particles with a particle size of 5.04 μm or less). Obtained at 81%. The classification yield here refers to the ratio of the amount of the finally obtained classified product (product) to the total amount of the supplied raw material for the pulverized product. All particle size data are from Coulter Electronics. These are the measurement results using a Coulter Counter made by Manufacturer.

Example 2 Styrene-acrylic ester resin (weight average molecular weight approximately 300,000) 100 parts by weight Magnetic ferrite (particle size 0.2 μm) 60 parts by weight low molecular weight polyethylene 2 parts by weight Negative charge control agent 2 parts by weight Mixture of the above formulation Approximately 180 toner raw materials
After melt-kneading for about 1.0 hours at ℃, it is cooled to solidify, coarsely ground into particles of 100 to 1000 μm with a hammer mill, and then crushed with a weight average particle size of 7.0 μm (particle size
A pulverized product containing 8.0% by weight of particles of 4.0 μm or less was obtained. The obtained pulverized product was introduced into the air classifier shown in FIGS. 1 and 2 and classified. In the air classifier, air is sucked at an air volume of 5 m ³ /min, and the first air inlet 12 at the top of the classification chamber has 20 openings (total opening area 2 x 0.2 x 20=8cm ² ), and the second air inlet 8 at the bottom of the classification chamber is set vertically by the classification louver 14.
cm, 20 openings with a width of 0.1 cm (total opening area 2 x
0.1×20=4cm ² ), and the height of the classification chamber was 16cm. As a result of classifying the pulverized product, a product with a weight average particle size of 7.5 μm (containing 2.0% by weight of particles with a particle size of 4.0 μm or less) from which fine powder had been removed was obtained with a classification yield of 78%. It was done.

Example 3 Styrene-acrylic acid ester resin (weight average molecular weight approximately 300,000) 100 parts by weight Magnetic ferrite (particle size 0.2 μm) 60 parts by weight low molecular weight polyethylene 2 parts by weight Negative charge control agent 2 parts by weight Mixture of the above formulation Approximately 180 toner raw materials
After melt-kneading for about 1.0 hour at ℃, the mixture was cooled to solidify, coarsely ground into particles of 100 to 1000 μm using a hammer mill, and then ground to a pulverized product with a weight average particle size of 30 μm using an ACM pulverizer manufactured by Hosokawa Micron.
The obtained pulverized material was introduced into the air classifier shown in FIGS. 1 and 2, and finely pulverized based on the flowchart shown in FIG. 7. The crusher used was a supersonic jet mill type 5 manufactured by Nihon Neumatic Kogyo Co., Ltd., and the air classifier sucked at an air volume of 5 m ³ /min.
2 has 20 holes (total opening area 2 x 0.2 x 20 = 8 cm ² ) with holes of 2 cm in length and 0.2 cm in width. There were 20 locations (total opening area 2 x 0.2 x 20 = 8 cm ² ), and the height of the classification room was 12 cm. per hour
Raw materials were supplied at a rate of 40 kg, and those crushed to below the specified particle size were taken out as fine powder.

The particle size of the obtained fine powder was a weight average diameter of 11.2 μm.
(Contains 5.0% by weight of particles with a particle size of 5.04 μm or less,
The coarse powder containing 0.5% by weight of particles larger than 20.2 μm was finely classified.

Comparative Example 1 A pulverized product obtained in the same manner as in Example 1 was introduced into an air classifier of the type shown in FIGS. 5 and 6 and classified. The air classifier sucks at an air volume of 5 m ² /min, and the gas inlet at the bottom of the classification chamber is 2 cm long and 0.2 cm wide.
The classification room was set at 20 locations, and the height of the classification room was 10 cm. As a result of classifying the pulverized product, the weight average particle size of the classified product from which fine powder was removed was 11.2μm (particle size
A product containing 0.9% by weight of particles of 5.04 μm or less was obtained with a classification yield of 72%. Classification yield is Example 1
When the obtained product was further examined, it was found that it was dotted with aggregates of 5 μm or more, which were ultrafine particles aggregated.

Comparative Example 2 A pulverized product obtained in the same manner as in Example 2 was introduced into the air classifier shown in FIGS. 5 and 6 and classified. The air classifier sucked in air at an air volume of 5 m ² /min, and 20 gas inlets were set at the bottom of the classification chamber with a length of 2 cm and a width of 0.1 cm, and the height of the classification chamber was 12 cm. As a result of classification, a product with a weight average particle size of 7.3 μm (containing 4.1% by weight of particles with a particle size of 4.0 μm or less) from which fine powder has been removed has a classification yield of 70%.
Obtained with. The classification yield was inferior to that of Example 2, and when the obtained classified product was observed, it was found that aggregates of 3 μm or more, which were ultrafine particles aggregated, were scattered.

Comparative Example 3 A pulverized product obtained in the same manner as in Example 3 was introduced into the air classifier shown in FIGS. 5 and 6, and finely pulverized based on the flowchart shown in FIG. 7. The crusher used was an ultrasonic jet mill type 5 manufactured by Nippon Neumatics Co., Ltd. The air classifier sucked at an air volume of 5 m ² /min, and the gas inlet at the bottom of the classification chamber was 2 cm long.
There were 20 classification rooms with a width of 0.2 cm, and the height of the classification room was 8 cm.

The raw material was supplied at a rate of 30 kg per hour, and the raw material was crushed to a specified particle size or less and taken out as a fine powder. The particle size of the obtained fine powder has a weight average particle size of 11.5 μm (contains 9.1% by weight of particles with a particle size of 5.04 μm or less, and 5.1% by weight of particles with a particle size of 20.2 μm or more), with a wide range on the coarse powder side. It had a similar distribution.

[Brief explanation of the drawing]

FIG. 1 shows a schematic view of the outer surface of an air classifier implementing the device according to the present invention, FIG. 2 shows a schematic longitudinal sectional front view, and FIG. 3 shows a - sectional view,
Fig. 4a shows a - view sectional view, Fig. 4b shows a - view sectional view, Fig. 5 shows an external surface view of a conventional air classifier, and Fig. 6 shows a longitudinal sectional front view. be. FIG. 7 is a flowchart in which the apparatus according to the present invention is applied to a crushing system. 1... Main body casing, 2... Lower casing, 3... Hopper, 4... Classifying chamber, 5... Classifying plate, 6... Coarse powder discharge groove, 7... Fine powder discharge chute, 8... Second air Inflow port, 9... Supply cylinder, 10
... Guide tube, 11 ... Supply groove, 12 ... First air inlet, 13 ... Dispersion louver, 14 ... Classification louver, 15 ... Discharge guide plate.

Claims (1)

[Claims] 1. In an airflow classifier for classifying powder by airflow, a supply port for supplying powder is formed in the upper part of the classification chamber, and a conical cone is provided in the lower part of the classification chamber. A classification plate with a high center part is provided, and a coarse powder discharge port is provided around the lower edge of the classification plate for discharging the coarse powder group that has been air-classified. The part is equipped with a fine powder outlet for discharging the air-classified fine powder group, and the upper part of the classification chamber is equipped with a fine powder discharge port for discharging the fine powder group that has been classified by wind. A first gas inflow means having a plurality of inflow passages each having a first air inlet for sucking and introducing air from the outside air is provided in the classification chamber, and the area around the lower part of the classification chamber is provided with a first gas inflow means for wind-classifying the dispersed powder. a second air inlet having a plurality of inflow passages having a second air inlet for sucking and introducing air from the outside air into the lower part of the classification chamber to generate a swirling flow of air;
A gas inflow means is provided, and the total opening area of the first air inlet of the first gas inflow means is A (cm ² ), and the total opening area of the second air inlet of the second gas inflow means is A (cm 2 ). An air classifier characterized in that A and B satisfy the following formula: 1≦A/B≦20, where the total area is B (cm ² ). 2. The inflow path is adjusted so that the wind speed of the air suctioned in from the outside air via the first gas inflow means is equal to or slower than the wind speed of the air suctioned in from the outside air via the second gas inflow means. An air classifier according to claim 1. 3 The inflow path having the first air inflow port is formed between the louvers installed in an annular shape, and the inflow path has the first air inflow port.
3. The air classifier according to claim 1, wherein the inlet passage having the air inlet is formed between louvers arranged annularly.