JPH04210254A - Crushing method by jet mill - Google Patents

Abstract

PURPOSE:To stably obtain a crushed product having a desired volume average grain diameter and a sharp grain size distribution by detecting a load current value, adjusting the supply of a material to be crushed or the turning rate of a rotary classifier or both to fix the solid concn. in a jet mill. CONSTITUTION:The material to be crushed from a feeder 1 is introduced into a jet mill main body 9 from a material inlet 18, dispersed by a dispersing blade provided at the upper part of a rotary classifier 14 and introduced into a crushing chamber 13. Meanwhile, compressed air from a compressed air chamber 11 is supplied to an injection nozzle 10 and injected into the chamber 13, and the material is crushed. The crushed powder is classified by the classifier 14 in a spacer 17, the coarse powder is returned to the chamber 13, and the fine powder is passed through an exhaust pipe 12 and a crushed product outlet 19 and recovered in a cyclone 4 as the crushed product. The air discharged from the cyclone is passed through a bag filter 5, in which fine powder is collected, and exhausted by a blower 6. Consequently, the solid concn. in the jet mill is kept constant, the material is stably crushed, and a crushed product having stabilized grain diameter and grain size distribution is obtained.

Description

[Detailed description of the invention]

[00011

[Industrial Field of Application] The present invention relates to a method of pulverizing a solid material using a jet mill, and more particularly to a pulverizing method for producing a developer for developing electrostatic images. [0002] BACKGROUND OF THE INVENTION [0002] In order to produce a fine powder of a developer for developing an electrostatic image, it has been conventionally practiced to pulverize a pulverized raw material using a jet mill. [0003] In a jet mill, the concentration of solids in the grinding chamber is one of the factors that affects the grinding efficiency, and the solids change. Therefore, if the internal solids concentration is kept constant, operation with stable pulverized product particle size can be performed, and for this purpose, it is important to keep the supply amount of pulverized raw materials constant. However, if this alone changes the grindability due to a lot change of the grinding raw material, etc., the solids concentration in the grinder will shift or fluctuate, and the particle size of the ground product will deviate from the intended particle size. Therefore, JP-A-50-119
As described in Japanese Patent No. 352, a method has been proposed in which the amount of pulverized raw material supplied to a jet mill is controlled based on the sound pressure of a specific frequency of the pulverization sound in the jet mill. However, this method has the drawback that the supply amount of the pulverized raw material may be controlled by sensing sounds other than the pulverizing sound, and the control cannot be carried out reliably. [0004] Also, among jet mills, fluidized bed mills use a level meter or a weighing scale as described in Japanese Utility Model Application No. 164942/1982 and No. 164943/1983. It is known to control the solids concentration in a crusher to be constant. However, when using a level meter, it is difficult to clearly detect the boundaries of the powder surface. Further, in order to increase reliability, level meters may be installed at several locations, but this is not preferable because it may change the shape of the inside of the grinding chamber and further increases the cost. On the other hand, when using a weight scale, it is difficult to detect weight changes because the weight of the solids is too small compared to the dynamic load of the mill. Furthermore, if a weighing scale with a wide measurement range is attached, detection becomes possible, but the measurement accuracy is low and the cost is extremely high. [0005]

[Problems to be Solved by the Invention] Due to the above-mentioned circumstances, in the conventional technology, it is not possible to sufficiently detect the concentration of solids in the jet mill, and as a result, changes in the pulverization state of the pulverized raw material cannot be detected. The problem was that it was impossible to respond. That is, there is a problem that the volume average particle diameter D50 (hereinafter simply referred to as D50) of the obtained pulverized product changes. Specifically, (1) when the solids concentration in the jet mill increases, D50 increases and the amount of coarse powder increases; (2) when it decreases, over-grinding progresses,
There is a problem in that the D50 decreases and the amount of fine powder increases, making it impossible to obtain a pulverized product having the desired D50 and particle size distribution. [0006] The present invention has been made in view of the above-mentioned problems in the conventional technology. [0007] Therefore, the object of the present invention is to provide a jet mill having a rotary classifier therein.
It is an object of the present invention to provide a pulverization method that can stably obtain pulverized products having a particle size distribution of 50 mm and a sharp particle size distribution. [0008]

[Means for Solving the Problems] The present invention provides a method for pulverizing solid matter as a pulverizing raw material using a jet mill having a rotary classifier inside, in which the load current value of the rotary classifier is detected and the pulverizing raw material is supplied. It is characterized by adjusting and controlling one or both of the amount and the rotation speed of the rotary classifier to maintain a constant concentration of solids in the jet mill. [00091] Hereinafter, the present invention will be explained with reference to the drawings. [00101 FIG. 1 is a process diagram of the solid material pulverizing method of the present invention, in which 1 is a pulverized raw material feeder, 2 is a jet mill, and 3
is a rotary classifier, 4 is a cyclone, 5 is a bag filter 6
is a blower, 7 is a converter, and 8 is a computer. [0011] The jet mill 2 used has, for example, the cross-sectional structure shown in FIG. In Figure 2, 9
is a jet mill main body, and has a crushing chamber 13 inside. An exhaust pipe 12 having a pulverized product outlet 19 is disposed at the lower center of the pulverization chamber, and a rotary classifier 14 is attached to overhang the exhaust pipe. In addition, a pulverized raw material supply port 18 is provided at the upper center, and a plurality of pulverized nozzles 10 are provided at the periphery.
It is configured to blow out compressed air from the compressed air chamber 11. In addition, 15 is a classifier drive device, 16 is a coarse powder intrusion prevention ring, and 17 is a spacer. [0012] In FIGS. 1 and 2, the pulverized raw material supplied from the pulverized raw material feeder 1 enters the jet mill main body 9 from the pulverized raw material supply port 18, and passes through the dispersion blades provided at the top of the rotary classifier 14. is dispersed and guided to the crushing chamber 13. On the other hand, compressed air is supplied from the compressed air chamber 11 to the injection nozzle 10 and ejected into the crushing chamber, whereby the supplied crushed Kyoshi is crushed. The crushed powder is
The coarse powder is classified by the rotary classifier 14 located in the spacer 17, and the coarse powder is returned to the crushing chamber 13, while the fine powder is passed through the exhaust pipe 12 and the crushed product outlet 19, and then sent to the cyclone 4 as a crushed product. It will be collected. Note that the air discharged through the cyclone collects fine powder through a bag filter 5 and is exhausted through a blower 6. The load current value of the rotary classifier 3 is processed by the computer 8 via the converter 7, and converted into a signal that controls one or both of the supply amount of the pulverized raw material feeder 1 and the rotation speed of the rotary classifier 3. be done. That is, after filtering the load current value of the rotary classifier 3, it is automatically sampled, and the result of trend analysis by a computer is fed back to the pulverized raw material feeder 1 and the rotary classifier 3 as a control amount,
The supply amount of the pulverized raw material feeder 1 and the rotation speed of the rotary classifier 3 are adjusted so that the load current value corresponding to the solids concentration is maintained at each rotation speed of the rotary classifier 3 as shown in FIG. control by increasing or decreasing one or both. As for the priority order of control, it is preferable to perform the control in the order of the supply amount of the pulverized raw material and the number of revolutions of the classifier. [0013] In the above case, the detected load current value is subjected to signal processing, averaged, and the fluctuation trend of the average value during the pulverization operation is monitored, and one of the pulverized raw material supply amount and the rotation speed of the rotary classifier is Alternatively, both may be adjusted and controlled. [0014]

[Example] Next, the present invention will be explained by referring to an example. [0015] Example 1 Using the jet mill shown in FIG. 2, pulverization was carried out according to the pulverization process shown in FIG. [0016] As a jet mill, the internal diameter of the grinding chamber is 1045
mmφ, with an inner diameter of 204.7 mmφ at the center bottom of the grinding chamber.
, an exhaust pipe with a height of 350 mm, and a spacer with an inner diameter of 470 mmφ and a height of 180 M was provided at the top of the grinding chamber, and inside the spacer was installed an exhaust pipe with an inner diameter of 220 mmφ and a height of 170111ffl,
A rotary classifier with a width of 25 mm and 120 blades was used. The crushing nozzle has an inner diameter of 7. 7mm
Ten Laval nozzles with a diameter of φ were installed at an angle shifted by 35° from the center direction. (0017) Also, the load current value of the motor for driving the rotary classifier of the jet mill is changed to -order slow converter MS4016 (
After working for MTT Co., Ltd., he developed FA Computer 980.
Connected to 1F (manufactured by NEC), 1 minute after the start of crushing,
The filtered load current value data is sampled in a second cycle, and while monitoring the fluctuation trend of the average value within the cycle, the load current value range corresponding to the solids concentration during stable grinding is set in advance for 3 cycles. We created a system so that feedback control can be applied to the pulverized raw material feeder (Accurate Feeder Model 604+610, manufactured by Kuma Engineering Co., Ltd.) and rotary classifier if the limit is exceeded continuously. [0018] The above jet mill, pulverized raw material feeder, control system, cyclone, bag filter, blower
The pulverized raw material was supplied to the jet mill main body from the pulverized raw material supply port provided on the upper part of the spacer, and pulverized. [0019] As the pulverized raw material, a developer composition for developing an electrostatic image shown below was melt-kneaded and then pulverized in a hammer mill to D50 = 300 to 500 (μm). [00203 Styrenic copolymer 70 parts by weight Styrenic crosslinked polymer 20 parts by weight Colorant
The conditions for crushing 10 parts by weight were as follows. [0021] Grinding pressure: 8.0 (kg/cm2G)
Blower exhaust air volume: 52-54 (m3/min). [0022] Using hammer mill crushed products A and B of different polymer lots as raw materials, continuous crushing operation was performed in the order of A→B. As a preliminary experiment, the raw material of lot A was used at D50=
As a result of pulverization to obtain a particle size of 11.0±0.5 (μm), the amount of pulverized raw material supplied was 110 (kg/hr), the number of revolutions of the rotary classifier was 4200 (rpm), and the load current value of the rotary classifier was 12. .0±0. 5 (A). The results of this preliminary experiment were used as initial settings. [0023] FIG. 4 shows the pulverized product D50 (μm), 2
0. Coarse powder amount (wt%) of 2 μm or more, ND value (Ros
Determined from the in-Raumler diagram. The larger the value, the sharper the particle size distribution. ), solid weight in the mill (kg), pulverized raw material supply amount (kg/hr),
It shows changes over time in the rotational speed (rpm) of the rotary classifier and the load current value (A) of the rotary classifier. In addition, Coulter Counter TA-11 type (manufactured by Coulter Electronics Co., Ltd.) was used to measure D50 and the amount of coarse powder. [0024] As can be seen from FIG. 4, by controlling the supply amount of the pulverized raw material so as to keep the load current value of the rotary classifier within the set range, even in the case of pulverized raw materials of different lots,
A ground product with a stable D50 was obtained. [0025] Example 2 Grinding was performed under the same initial setting conditions as in Example 1. The results are shown in FIG. In this example, control was performed based on the rotation speed of the rotary classifier. In this case, the load current value corresponding to the solids concentration is maintained for each rotation speed of the rotary classifier by taking into account the difference in the load current value due to the difference in rotation speed, and as a result, as can be seen from FIG. 4, By controlling the rotational speed, it was also possible to obtain a pulverized product with a stable D50. [0026] Comparative Example 1 Pulverization was carried out under the same setting conditions as in Example 1, except that the rotary classifier was not controlled by detecting the load current value. The results are shown in FIG. As shown by the decrease in the load current value, the decrease in solids concentration in the jet mill makes over-grinding more likely to occur, and D50 is lower than the target of 1.
It became less than 1.0±0.5 (μm). Furthermore, there was a large variation over time, and the amount of coarse powder was also large, resulting in a broad particle size distribution. The weight of the solids after pulverization was also less than half of the weight at the start of pulverization, and both of these results indicate that the solids concentration decreased and the powder could not be pulverized in a stable state. [0027]

[Effects of the Invention] As is clear from the comparison between Examples and Comparative Examples, in a jet mill that has a rotary classifier inside, the load current value of the rotary classifier is detected, and the amount of pulverized raw material supplied and the rotary classifier are determined. By adjusting and controlling one or both of the machine rotational speeds, it is possible to maintain a constant concentration of solids within the jet mill, resulting in stable pulverization operation, and the particle size and particle size distribution of the pulverized product. [0028] When control based on load current value detection is not performed, the amount of coarse powder in the pulverized product increases compared to when control is performed, but this is due to a decrease in the concentration of solids in the jet mill. This is because the balance between centrifugal force and centripetal force in the rotary classifier was disrupted, and unpulverized materials flew into the exhaust pipe. On the other hand, in the present invention,
By keeping the solids concentration in the jet mill constant, the balance in the rotary classifier will not be lost and the amount of coarse powder can be reduced. Therefore, the present invention is particularly suitable for producing a developer for developing electrostatic images.

[Brief explanation of the drawing]

FIG. 1 is a process diagram for carrying out the pulverization method of the present invention.

FIG. 2 is a sectional view of an example of a jet mill for implementing the present invention.

FIG. 3 is a graph showing the relationship between the weight of solids in the jet mill and the load current value of the rotary classifier.

FIG. 4 shows the load current value of the rotary classifier, the rotation speed of the rotary classifier, the weight of solid matter in Geno 1-mill, the supply amount of pulverized raw materials, and the D50 of the pulverized product in Examples 1 and 2 and Comparative Example.
It is a graph showing changes over time in the amount of coarse powder of 20.0 μm or more and the ND value.

[Explanation of symbols]

1. Pulverized raw material feeder, 2. ,,jet mill,
3. , , Rotary classifier, 4. ,,,cyclone,5.
, , Bag filter 6 , , Blower 17 , , Converter 8. ,,,Computer 9. , , jet mill body, 10. , , Grinding nozzle, 11, , Compressed air chamber, 12. ,,exhaust pipe,13. ,,,Crushing chamber, 1
4. , , Rotary classifier, 15. , , Classifier drive device 16 , , Coarse powder intrusion prevention ring 17. −、、
Spacer 18, . . . Grinding raw material supply port, 19. ,,,Crushed product outlet.

[Figure 3]

Claims (3)

[Claims] Claim 1: In a method of pulverizing solid matter as a pulverizing raw material by a jet mill having a rotary classifier inside, the load current value of the rotary classifier is detected, and the supply amount of the pulverizing raw material and the rotation speed of the rotary classifier are determined. control one or both of the
A method for pulverizing solids characterized by maintaining a constant concentration of solids in a jet mill. [Claim 2] The load current value is subjected to signal processing and averaged, and then the fluctuation trend of the average value is monitored to control one or both of the supply amount of the pulverized raw material and the rotation speed of the rotary classifier. The solids concentration in the jet mill is maintained constant by adjusting and controlling and maintaining the load current value corresponding to the solids concentration at each rotation speed of the classifier. Grinding method. 3. The pulverizing method according to claim 1, wherein the pulverizing raw material is a composition for producing a developer for developing electrostatic images.