JPH04210253A - Crushing method by jet mill - Google Patents

Abstract

PURPOSE:To obtain a crushed product having a desired average grain diameter and a sharp grain size distribution by detecting the pressure fluctuation in a rotary crushing chamber by a pressure sensor set in a jet mill, and adjusting the supply of the material to be crushed to fix the solid concn. in the chamber. CONSTITUTION:The material to be crushed supplied from a fixed delivery feeder 1 is introduced into a rotary crushing chamber 16 from a material inlet 17 of a jet mill 2 along with air. Meanwhile, compressed air is supplied to a crushing nozzle 13 from a compressed air chamber 14 and injected into the chamber, and the material is crushed. The crushed powder is classified in a discharge pipe 15 by a centrifugal force-centripetal force balance, the coarse powder is returned to the chamber 16, and the fine powder is passed through the discharge pipe and recovered as a crushed product in a cyclone 3. The air discharged from the cyclone is passed through a bag filter 4, in which fine powder is collected, and exhausted by a blower 5. Consequently, 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 for pulverizing solid materials using a jet mill, and particularly to a method for producing a developer for developing electrostatic images. [Prior Art] In order to produce fine powder such as a developer for developing an electrostatic image, it has been conventionally practiced to finely pulverize a pulverized raw material using a jet mill. [0003] In a jet mill, the solids concentration within the grinding chamber is one of the factors that affects the grinding efficiency, and as the solids concentration changes, the throughput and the particle size of the ground product change. Therefore, if the internal solid concentration is kept constant, operation with stable pulverized product diameter can be achieved, and for this purpose, it is important to keep the supply amount of pulverized raw materials constant. however,
If this alone changes the pulverizability due to a change in the lot of pulverized raw materials, etc., the solid concentration within the pulverizer will shift or fluctuate, causing the pulverized product particle size to deviate from the intended particle size. Therefore, as described in JP-A-50-119352, a method has been proposed in which the amount of pulverized raw material supplied to the 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 is sometimes controlled by sensing sounds other than the pulverizing sound, and the control cannot be carried out reliably. [00041 Among jet mills, fluidized bed type mills are used for grinding using a level meter or a gravimeter, as described in Japanese Utility Model Application No. 62-164942 and No. 62164943. It is known to control the solids concentration inside the jet mill to be constant, and according to this method, it is possible to keep the solids concentration inside the jet mill constant. Further, Japanese Patent Application Laid-Open No. 63-209763 discloses that the amount of pulverized raw material supplied is adjusted by detecting the pressure difference between the fluidized bed of a jet mill and the air flow. However, these conventionally known technologies related to fluidized bed jet mills cannot be applied to other types of jet mills (e.g. micronizer type, jet oomizer type, etc.), and as a result,
There is a problem in that it is not possible to respond to changes in the pulverization state of the pulverized raw material. That is, the volume average particle size of the resulting pulverized product is
There is a problem in that the value (simply referred to as D50) changes. Specifically, (1) when the solid concentration in the jet mill increases, D50 increases and the amount of coarse powder increases; (2) when it decreases, over-grinding progresses and D50 decreases. As a result, the amount of fine powder increases, making it impossible to obtain a pulverized product having the desired D50 and particle size distribution. [0005] The present invention has been made in view of the above-mentioned problems in the prior art. [0006] Therefore, an object of the present invention is to provide a pulverization method that can stably obtain a pulverized product having the desired D50 and sharp particle size distribution using a jet mill of a type other than the fluidized bed type. be. [0007]

[Means for Solving the Problems] The pulverizing method of the present invention includes jets for injecting compressed air into a rotating pulverizing chamber from a plurality of nozzles to form a swirling airflow, supplying pulverized raw materials into the circling pulverizing chamber, and pulverizing the raw material. When pulverizing raw materials using a mill, a pressure sensor installed in the jet mill detects pressure fluctuations in the rotating crushing chamber, and adjusts the supply amount of the pulverizing raw materials so that the solids concentration in the rotating crushing chamber is maintained constant. It is characterized by adjusting. [0008] The jet mill used in the present invention is
It is not a fluidized bed type, but a type in which pulverization is performed by supplying the pulverized raw material into a swirling jet stream generated in a rotating pulverization chamber, and for example, a micronizer or a jet-omizer can be used. [0009] Hereinafter, the present invention will be explained with reference to the drawings. FIG. 1 is a process diagram of the method for pulverizing solids according to the present invention, in which 1 is a pulverized raw material quantitative feeder, 2 is a jet mill, 3 is a cyclone, 4 is a bag filter, 15 is a blower, 16 is an interface, and 7 is a It's a computer. jet mill 2
For example, one having a cross-sectional structure shown in FIG. 2 is used. In FIG. 2, 11 is a jet mill main body, which has a rotating crushing chamber 16 inside. An exhaust pipe 15 is provided at the lower center of the rotating grinding chamber, a pulverized raw material supply port 17 is provided at the upper center, and a plurality of grinding nozzles 13 are provided at the periphery of the rotating grinding chamber. It is configured to blow out compressed air. Moreover, a pressure sensor 12 for detecting the pressure inside the rotating crushing chamber is attached to the rotating crushing chamber. [00101 In FIGS. 1 and 2 above, the pulverized raw material supplied from the pulverized raw material quantitative feeder 1 is sent from the pulverized raw material supply port 17 of the jet mill 2 to the rotating crushing chamber 1 together with supply air.
6 will be introduced. On the other hand, compressed air is supplied from the compressed air chamber 14 to the crushing nozzle 13 and ejected into the rotating crushing chamber, whereby the supplied crushed raw material is crushed. The pulverized powder is classified in the discharge pipe 15 by the balance of centrifugal force and centripetal force, and the coarse powder is returned to the rotating grinding chamber, passes through the fine powder discharge pipe, and is recovered as a pulverized product in the cyclone 3. Note that the air discharged through the cyclone collects fine powder through a bag filter 4 and is exhausted through a blower 5. [0011] The pressure inside the rotating crushing chamber is measured by a pressure sensor 12.
is detected, and pressure fluctuations during grinding are monitored. The detected pressure data is processed through the interface 6 and the computer 7 and converted into a signal that controls the feed rate of the pulverized raw material metering feeder 1. That is, the internal pressure in the rotating crushing chamber 16 is measured at equal time intervals, and a computer-processed signal is sent to the crushing raw material quantitative feeder 1, so that the crushing raw material is kept at a preset stable crushing pressure. Control by increasing/decreasing the supply amount of the quantitative feeder. [0012] FIG. 3 is a sectional view of another example of a jet mill used in the present invention. This jet mill is
Basically, it has the same structure as the jet mill shown in FIG. 2, but a rotary classifier 18 is attached to overhang the discharge pipe 15. In addition, 19
20 is a coarse powder intrusion prevention ring, 20 is a classifier drive unit, 21 is a spacer, and other symbols have the same meanings as in FIG. 1. The pulverized raw material enters the jet mill main body 11 from the pulverized raw material supply port 17, is dispersed by dispersing blades provided at the top of the rotary classifier 18, and is guided to the rotating crushing chamber 16. On the other hand, compressed air is supplied from the compressed air chamber 14 to the crushing nozzle 13 and ejected into the rotating crushing chamber, whereby the supplied crushed raw material is crushed. The crushed powder is classified by the rotary classifier 18 located in the spacer 21, and the coarse powder is returned to the rotating crushing chamber, while the fine powder passes through the discharge pipe 15 and is sent to the cyclone 3 as a crushed product. It will be collected. [0013] The pressure inside the rotating crushing chamber is measured by a pressure sensor 12.
The pressure fluctuations during grinding are monitored. Based on the detected pressure data, the supply amount of the pulverized raw material quantitative feeder is controlled in the same manner as described above, and the pressure in the rotating pulverization chamber is maintained constant. [0014]

[Example] Next, the present invention will be explained by referring to an example. [0015] Example 1 Using the jet mill shown in FIG. 1, pulverization was performed according to the pulverization process shown in FIG. 2. The jet mill has a rotating crushing chamber diameter of 420 mmφ, a circumferential height of the rotating crushing chamber of 50 mm, and a center height of 100 mm, and has an exhaust pipe with an inner diameter of 138 rmφ and a height of 74 mm at the center bottom of the crushing rotating chamber. I used what I had. The crushing nozzle has an inner diameter of 5.2 nusφ
Four Laval nozzles of
(manufactured by Krone Co., Ltd.), installed in the rotating crushing chamber,
It was connected to an interface and a computer so that it could control a belt feeder BFE14 type (manufactured by Tohishikoki Kogyo Co., Ltd.). [0016] A fine grinding device consisting of the jet mill described above is combined with a belt feeder, a cyclone, a bag filter, a blower 1 and a control system, and the grinding raw material is supplied from the grinding raw material supply port to the jet mill body by air injection. Then, the powder was crushed. The pulverized raw material used was one for producing a developer for developing electrostatic images having the following composition. [0017] Styrene-〇-butyl methacrylate 93
Parts by weight Carbon black 7 parts by weight The grinding conditions were as follows. [0018] Grinding pressure: 7.8 (kg/cm2)
Exhaust air volume: 11.8-12.0 (m2/min). [0019] Different lots of hammer mill crushed products A and B
, C (D50=300 to 500 (μm)′) was used as a raw material, and continuous pulverization operation was performed in the order of ABC. According to a preliminary experiment, the raw material of lot A was D50=10.8 (
As a result of pulverization so that the amount of pulverized raw material was 20 kg/hr and the internal pressure was 1201 mAq. Based on the results of this preliminary experiment, the set value of the internal pressure was set to 1201nInAq.
, the initial setting value of the supply amount of the pulverized raw material was 20 kg/hr. [00201 Figure 4 shows the changes over time in the pulverized product D50 (μm), the amount of pulverized raw material supplied (kg/hr), and the pressure in the rotating pulverization chamber (mmAq). In addition, Coulter counter TA-II type (manufactured by Coulter Electronics) was used to measure D50. [00211 As can be seen from FIG. 4, by controlling the supply amount of the pulverized raw material so as to keep the internal pressure constant, a stable pulverized product of D50 was obtained even when the pulverized raw material was used in different lots. [0022] Comparative Example 1 Grinding was carried out under the same initial setting conditions as in Example 1 (=pulverization raw material supply rate fixed at 20 kg/hr), except that the supply rate of the crushed raw material was not controlled by detecting the pressure in the rotating crushing chamber. went. The results are shown in FIG. [0023] The grindability varied due to differences in the lots of raw materials to be ground, but since no control was carried out, the grinding products obtained from each lot had different particle sizes. [0024] Example 2 A jet mill having a rotary classifier inside as shown in FIG. 3 was used to carry out pulverization according to the pulverization process shown in FIG. The jet mill has a rotating grinding chamber with a diameter of 420 mm, an exhaust pipe with an inner diameter of 110 inches and a height of 164 mm at the center bottom of the rotating grinding chamber, and a spacer with an inner diameter of 280 mm and a height of 100 inches at the top of the rotating grinding chamber. Internal diameter 118M
A rotary classifier with φ, height 65n+door, width 15mm, and 72 blades was used. As for the crushing nozzles, four Laval nozzles each having an inner diameter of 5.2 mmφ were installed at an angle shifted by 35° from the center direction. A pulverized raw material having the same composition as in Example 1 was supplied to the jet mill main body from a pulverized raw material supply port provided at the top of the spacer, and pulverized. [0025] The following conditions were adopted as the pulverization conditions. [0026] Grinding pressure: 7.6 (kg/cm2
) Exhaust air volume: 11.5~12.5 (m2/min
) Classifier rotation speed: 5000 rpm Hammer mill crushed material (D50=300
~500 (μm)), D50=11 (μm
). A preliminary experiment similar to that in Example 1 was conducted, and pulverization was performed with the internal pressure set value = 70 mmAQ and the pulverized raw material supply rate set initially to 20 kg/hr. D50 (μm) of the pulverized product, amount of coarse powder of 20.2 μm or more (wt%), ND value (determined from the Rosin-Rammler diagram. The larger the value, the sharper the particle size distribution.)
, the hold-up amount in the jet mill (kg), and the pressure in the rotating crushing chamber (mmAq) over time are shown in FIG. [00271 As can be seen from FIG. 6, D50
．． The amount of coarse particles of 20.2 μm or more and the ND value are all stable. The amount of hold-up in the rotating crushing chamber also remained almost unchanged before and after crushing, which also indicates that stable crushing was performed. [0028] Comparative Example 2 Grinding was carried out under the same setting conditions as in Example 2, except that the supply amount of the grinding raw material was not controlled by detecting the internal pressure of the rotating grinding chamber. The results are shown in FIG. [0029] D50 was determined because over-grinding became more likely to occur due to a decrease in solids concentration in the whirl-pulverizing chamber of the jet mill.
The particle size was lower than the target particle size of 11 μm, and the variation from time to time was large. Also, the amount of coarse powder was large, and as a result, the particle size distribution was wide. Further, the hold-up amount was half the amount at the start when the grinding was completed, which also indicates that the solid concentration had decreased and the grinding could not be carried out in the original stable state. [00301] [Effect of the invention] As is clear from the comparison of the above examples and comparative examples, by installing a pressure sensor in the jet mill, detecting the internal pressure fluctuation, and controlling the supply amount of the pulverized raw material from the value. , the solid concentration in the jet mill can be kept constant, and stable grinding operation, grinding product particle size, and particle size distribution can be obtained. [00311 In addition, when using a jet mill that has a rotary classifier inside, if control is not performed by pressure fluctuation detection, the amount of coarse powder in the pulverized product will increase due to upward vibration when control is performed. This is thought to be due to large fluctuations in pressure, which disrupted the balance between centrifugal force and centripetal force in the rotary classifier, causing unpulverized materials to jump into the discharge pipe. In contrast, in the present invention, the amount of coarse powder can be reduced and the particle size distribution can be made sharper. [0032] Therefore, the present invention is extremely suitable for producing a developer for developing an electrostatic image.

[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 a jet mill for implementing the present invention.

[Fig. 3] Cross-sectional view of a jet mill for carrying out the present invention

[Figure 4] Raw material supply amount in Example 1 and Comparative Example 1, D
50 is a graph showing the change in pressure in the rotating crushing chamber over time.

FIG. 5 is a graph showing changes over time in raw material supply amount, D50, and pressure in the rotating crushing chamber in Comparative Example 1.

FIG. 6: D50 in Example 2, amount of coarse powder of 20.2 μm or more, ND value, amount of hold up in the jet mill,
It is a graph showing the change in the pressure in the rotating crushing chamber over time.

[Figure 7] D50 in Comparative Example 2. Amount of coarse powder of 20.2 μm or more, ND value, hold up amount in jet mill)
, is a graph showing the change in pressure in the rotating crushing chamber over time.

[Explanation of symbols]

1. pulverized raw material quantitative feeder, 2. , , ,
Jet mill, 3, Cyclone, 4. , ,Bag filter-15, ,Blower-16, ,Interface,7. ,,, Computer, 11. ,,,
Jet mill body, 12. ,,,pressure sensor, 13,
, , Grinding nozzle, 14. , , ,compressed air chamber, 1
5. , , Exhaust pipe 16 , , Rotating crushing chamber 17 .
, , , pulverized raw material supply port, 18. , , Rotary classifier, 19. , , Coarse powder intrusion prevention ring, 20. ,
,, classifier drive unit, 21. ,,, spacer

[Figure 1]

Claims (2)

[Claims] [Claim 1] In pulverizing the pulverized raw material using a jet mill that injects compressed air from a plurality of nozzles into a rotating pulverization chamber to form a swirling airflow, and supplies the pulverized raw material into the gyrating crushing chamber and pulverizes the pulverized raw material, A solid product characterized in that a pressure sensor installed in the jet mill detects pressure fluctuations in the rotating crushing chamber and adjusts the supply amount of the crushed raw material so that the concentration of solids in the rotating crushing chamber is maintained constant. Grinding method. 2. The pulverizing method according to claim 1, wherein the pulverizing raw material is a composition for producing a developer for developing electrostatic images.