JP2719923B2 - Method for producing liquid or molten fine particles - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing liquid or molten fine particles.

BACKGROUND OF THE INVENTION Originally, methods for producing liquid or melt particulates were obtained by air spray or two liquid spray.
However, the size of these fine particles varies in size, ranging from a few microns to a few hundred microns, and these cannot be said to be fine particles. In the airless spray, the particle size distribution is relatively stable, but their particle size is in the range of 20 to 60 microns,
If a cross-cut nozzle developed by Nordson Corporation is used, the particle size will be even smaller, around 12 microns. However, the operation conditions at this time are those where the ejection amount is relatively small, that is, 4.73 cc / min, the distance between the nozzle and the surface to be coated is 300 mm, and the width of the bottom of the spray pattern is 250 mm. Where
In particular, when the viscosity is relatively high, a tail phenomenon always occurs in both ends of the spray pattern, and a large droplet of several hundred microns is generated in the same part. That is, it was difficult to obtain uniformly fine particles as a whole. Therefore, the spray was hit against a hard plate in the past (see FIG. 12), and the collision crushed large particles to obtain smaller particles.

[Problems to be Solved] As described above, according to the hard plate collision method, it is effective to obtain fine particles, and particles having a size of about 1 micron can be obtained. However, on the other hand, some of them were several tens of microns, and so-called grain alignment was poor and unstable.

However, in recent years, with the demand for advanced technology, there has been an increasing demand from the industry for always requiring uniform and stable fine particles.

The motivation of the present invention was to meet the above needs.

[Means for Solving the Problems] Before that, in the case of the above-mentioned conventional hard plate collision method, I would like to investigate the cause of generation of irregular fine particles.
See FIG. When the liquid or the molten material is sprayed from the spray nozzle (72) in the chamber (71) and hits the hard plate (75), the particles in the spray collide with the hard plate and are crushed and airborne. And scatter into smaller particles. However, it is good at first, but over time, liquid or melt adheres to the hard plate (75) surface,
Gradually, it becomes thicker as seen in FIG. Also, their surfaces gradually dry, that is, the viscosity of the liquid or melt increases, and may eventually solidify. When the hardness of the plate surface changes over time,
The size of the particles crushed by colliding with those surfaces also changes with time. It is considered that this is a major reason why the particle size of the fine particles in the hard plate collision method becomes unstable with time.

However, the above phenomenon is an unavoidable problem as long as a hard plate is used. Therefore, the present inventor paid attention to applying the spray flow to the surface of the liquid or the molten material which is staying downward without using a hard plate. The surface of the liquid or melt does not change over time as in the case of the hard plate. Accordingly, the force for crushing the particles is not changed, and fine particles having a uniform size can always be stably obtained.

Since the surface of the liquid is much softer than the surface of the hard plate, the effect of crushing is small, and it is likely that it is difficult to obtain finer fine particles. However, the force at the time of collision is proportional to the square of the speed at that time, and when it reaches a certain speed or more, the kinetic energy becomes larger,
Demonstrates sufficient crushing power even on soft liquid surfaces,
It was confirmed experimentally that the required fine particles could be obtained.

The gist of the present invention is to strike a spray of a liquid or a melt on the surface of the same liquid or a melt, thereby breaking up atomized particles in the spray and making the liquid or the melt finer. This is a method in which particles are scattered in gas on the surface to obtain smaller fine particles.

First, the method of the present invention will be described. The liquids targeted by the present invention include solvents and emulsions, suspensions and the like. The behavior in which these particles are made finer differs slightly depending on these types, and these will be described separately.

(1) In the case of a solvent This is the case of a solvent such as water or oil. This case is the basis of the method of the present invention. Please refer first to FIG. The liquid (L) is sprayed inside the chamber (1) with the spray nozzle (2) facing downward (S
P) It is assumed that a liquid (L) of the same type as described above accumulates at the bottom of the chamber (1), and the liquid level (Ls) is maintained to be always constant. The spray (SP) flow is hit on the liquid level (Ls) (see FIG. 2). The particles (P) in the spray collide with the liquid surface (Ls), are crushed, become fine, and scatter above the liquid surface (see FIG. 3).
Among these finely divided fine particles, for example, those having a particle size of 10 μm or less are defined as p, and those having a size larger than that are defined as P ₁ . The gas in the chamber (1) becomes a rising airflow (CG) by the spray following the nozzle (see FIG. 4),
The particles (p) having a relatively large surface area / weight, for example, the above-mentioned fine particles (p) having a size of 10 μm or less rise in a rising velocity (CG) at a certain speed because of their relatively large gas resistance or buoyancy. On the other hand, fine particles (P ₁ ) having a surface area / weight smaller than those described above, for example, fine particles (P ₁ ) having a size of 10 μm or more have relatively small air resistance, that is, a levitation force, and therefore, the upward air flow (C
Descent against G). That is, the size of the fine particles rising or falling according to the speed of the rising air flow is determined,
The speed is determined by the amount of gas sprayed by the two fluids or the amount of gas introduced into the chamber (1).

The gas containing the fine particles (p) separated and raised in this way, that is, the aerosol is led out of the chamber (1),
It is used for various purposes.

On the other hand, the fine particles (P ₁ ) that have fallen in the chamber (1) reach the same liquid level (Ls), are absorbed by the same liquid (L), and are temporarily stored. Then, it is returned into the tank on the spray circuit and sprayed repeatedly.

By keeping the liquid level (Ls), that is, the level, constant, the distance to the nozzle (2) is constant, the speed at the time of collision and the crushing force are constant, and fine particles having a uniform particle size can be obtained. It is.

(2) In the case of a solution A solution is a liquid in which a resin or the like is dissolved, for example.
This is one in which the dispersoids are dispersed in a liquid solvent in the form of molecules. The state of miniaturization due to the crushing of the solution particles at the time of these collisions is almost the same as the case of the above liquid (item (1)), but since the behavior from micronization to micronization is slightly different, Will be described.

Originally, in a solution that is a liquid in a solution, molecules such as other resins are dispersed in a molecular state,
Generally, the solvent often has a lower boiling point than the dispersoid.

The liquid surface collision of the spray particles of these solutions and the miniaturization by crushing are almost the same as those of the liquid of the above item (1). The solvent quality in the particles (P ₁ ) thus refined is vaporized or reduced (P ₁ → P ₁ ′ → pc) as shown in FIG. 5 due to the relatively low boiling point. The high boiling point dispersoids remain and their mixing ratios are reversed. That is, the solvent quality is vaporized by the heating operation, and fine particles of a solution having a required mixing ratio can be obtained depending on the degree of the evaporation.

Further, when the solvent is completely vaporized, fine particles consisting of only the dispersoid can be obtained.

(3) In the case of an emulsion An emulsion is a liquid in which another kind of liquid is dispersed in a particulate state. In other words, it can be considered that the molecular dispersion in the above item (2) is replaced by the particle dispersion. Therefore, in the behavior in collision crushing, the particles become fine particles through almost the same process as in the case of the solution. You can think that it will be. Therefore, the composition ratio of the emulsion of finely divided fine particles can be changed within a certain range, and fine particles consisting of only dispersoids can be obtained.

(4) In the case of a suspension A suspension is a liquid in which solid particles are dispersed in a liquid, and examples thereof include a dispersion type coating agent and a powder slurry. This liquid is slightly different from the above-mentioned liquids, and the state of collision and crushing will be described. See FIG. Among the particles sprayed (SP ₁ ) from the nozzle (2) of the suspension (DS), particles of a solid alone (p), a plurality of aggregated particles of a solid (pp), and particles of a liquid only (Pl) ), Mixed particles of liquid and solid particles (Pp) and the like. When the latter particle (Pp) collides with the liquid surface (DSs), fine particles (ρ) consisting of only solids or a plurality of fine particles (p) as shown in FIG. Individually agglomerated particles (pp), liquid-only particles (P
l), liquid-only fine particles (pl), and mixed particles of liquid and solid fine particles (Pp ₁ ). Among these, the fine particles (p) of a solid simple substance and the fine particles (pl) of a liquid alone are shown in FIG. 8 because their surface area / weight is relatively large as described in the above item (1). Thus, ascending in the updraft, those smaller ones descend against the updraft and are separated by particle size. Further, by heating them, a necessary amount of the vaporizable liquid can be removed, or only solid fine particles can be obtained.

In addition, although the description will be before and after, in the case of suspensions, solid particles tend to settle while moving in the piping of the spray circuit, so care must be taken not to stop their flow. Is essential.

The above description has been given of the case of various forms of liquid. Next, the case of melt is described. A melt is a material that is melted by heating to become a liquid. Although its area is wide, such as metals and ores, thermoplastics, silicic acids, etc. are targeted for the time being. When these are sprayed, the behavior of forming fine particles is almost the same as in the case of the above-mentioned liquid (1), and in the case of a melt in which fine particles having a higher melting point are dispersed in the melt. Can obtain those fine particles as in the case of the suspension in the above item (4). When handling the melt, it is necessary to heat the liquid storage chamber (5) to a temperature higher than the melting point of the melt by a known heating means. Further, the melt supplied to the spray nozzle (2) is also supplied by being melted by a known heating and melting means.

There are two methods for spraying the liquid or the melt described above, two-fluid spray and airless spray. However, both of them have special features, and these will be described.

Originally, a two-fluid spray sprays a considerable amount (a few hundred times the weight of a liquid) of gas upon the spray.
After the ejection, the gas becomes a carrier airflow for separating fine particles as described above. And the flow velocity necessarily depends on the amount of jet. However, the flow rate is not always optimal for separation. Rather, it is rare to satisfy both conditions simultaneously.

On the other hand, in airless spraying, no gas is used for spraying. Therefore, it is necessary to create a flow of gas for separation. For example, if a gas is introduced from the outside, it can be separated from the spray and alone can satisfy the conditions of the airflow for separation. In the case of airless spraying, since no air is used, the liquid surface does not dry, that is, without increasing the concentration (viscosity) of the liquid surface to be sprayed, so that a constant state can always be maintained. is there. These are the advantages of airless spraying.

In addition, as a result of performing various experiments on the basic type of the present invention, various data and additional items for obtaining better results were obtained.

1) The spray is airless spray or airless spray with auxiliary air or their hot type.

2) The spray is a two-fluid spray or its hot spray.

3) The initial velocity of the jet from the nozzle hole is 25m / sec or more. This is, of course, to increase the kinetic energy and further increase the crushing force at the time of collision.

4) The distance from the nozzle (2) tip to the liquid level (Ls) is 75
mm or less. This is an important factor, especially when the flow rate from the nozzle is small.

5) Spray pattern opening angle (angle α in Fig. 1)
Is 70 degrees or more. The purpose of this is to reduce the size of the particles during the airless spray, that is, the size of the particles before the impact crushing, particularly in the case of the airless spray.

6) In order to prevent aggregation of a large number of fine particles generated by the liquid surface collision of the spray, the fine particles are charged with static electricity and thereby repulsively separated from each other. That is, corona discharge is performed in the chamber.

7) In the case of an airless spray, a gas is introduced into the chamber (1) to generate an updraft (CG).

8) in the spraying of the emulsion or suspension, heating the aerosol consisting of the liquid and solid particles produced by the collision and evaporating the liquid particles to reduce the liquid particles, or To produce an atomization consisting solely of solid particulates.

9) Cooling the aerosols produced by spray impingement of liquids or melts and rapidly solidifying the fine particles therein.

10) Spray a suspension containing fine particles with a particle size of 1 micron or less as a dispersoid, and obtain an aerosol from the fine particles.

Next, the basic structure of the device based on the above method will be described. See FIG. Airless spray device (26) almost at the middle of the outer wall of the vertical chamber (11)
The gun (13) is provided, and the gun penetrates the side wall.
An arm (14) protrudes into the vertical chamber (11), a spray nozzle (12) is provided downward at the tip thereof, and the spray nozzle and the gun (13) are connected by piping. Alternatively, it is connected to the pulse controller by wiring. The lower part of the vertical chamber (11) is a liquid storage chamber (15) for temporarily storing liquid, and the lower end of the liquid storage chamber is a return pipe (1).
The pipe is connected to 6), and is led to the tank (19) of the airless spray device via the opening / closing valve (45). In addition,
When handling molten material, liquid reservoir (15) and tank (19)
Is maintained at a temperature equal to or higher than the melting point of the melt by a known heating means. The tank is connected to the gun (13) by a conventional airless spray pipe (27) via a pump (28), a filter (29), a regulator (47) and the like. In the case of a two-fluid spray, as shown by the phantom line in the figure, the pipe (21) of the liquid supply device (20) is supplied from the tank (19) via a regulator (22), etc. A pipe (24) of the gas supply device (23) is connected to the gun (13) from the gas generator (CA) via a regulator (25) and the like. In addition, heaters (48, 49, 54) are provided on these pipes (21, 24, 27) as necessary to control the temperature of each fluid. The tank (19) can be removed, and the liquid reservoir (15) can be used together with the tank. In this case, the return pipe (16) from the liquid storage chamber to the tank (19) is connected to the pump (2) through the check valve (59).
8) Connected to the entrance.

Since the liquid level in the liquid reservoir (15) is desirably kept at a certain distance from the tip of the spray nozzle (12), for example, 75 mm, the level (Ls) of the liquid level is automatically kept constant. A level controller (36) is provided for keeping the level. The figure shows a capacitance type.

In the case of airless spray, the above level (L
Slightly above s), on the side wall of the vertical chamber (11), it is desirable to provide a gas inlet (18) and a gas supply device (30) connected thereto.

The upper end of the inside of the above chamber (11)
7), but if necessary, an eliminator (53) for removing liquid fine particles is provided in front of the port. A gas discharge pipe (50) is connected to the aerosol discharge port (17), and a heater (55) is mounted on the pipe if necessary.

It is desirable that the chamber (11) main body is vertically elastic. In this case, the main body is divided into upper and lower parts and connected by a cylindrical slide type (11A, 11B). This is for adjusting the height (H) from the spray nozzle (12) to the upper part in the chamber (11) in the chamber (11), and when the eliminator (53) is attached as described above, the adjustment is performed. The height (H ₁ ) to the lower part of the eliminator will be adjusted. The reason for the adjustment is required for the separation of the fine particles by the carrier airflow.

The terminal of the gas discharge pipe (50) may be left open, but various devices are attached according to their uses. In this figure, a storage tank (56) for aerosols is shown. A uniform flow of gas is blown from the bottom of the tank to prevent sedimentation of fine particles.

[Operation] The operation of the device of the present invention will be described. First, the case of a typical liquid solvent will be described. The liquid (L) is sprayed downward (SP) from the spray nozzle (12) of the conventional airless spray device (26) or the air spray device (20, 23), and the flow thereof flows into the liquid storage chamber (15). It hits on the surface of the liquid (L) which has accumulated. It is desirable that the distance (S) between the spray nozzle (12) and the liquid surface, that is, the level (Ls) is 75 mm or less, which is easily performed by adjusting the position of the level (Ls). Adjustment of the level (Ls) and holding of a fixed position are performed by a level controller (36).

The spray (SP) atomized liquid particles impinge on the liquid surface and are crushed and subdivided, reflected and scattered into the gas above the liquid surface. Since the process of atomization has been described in detail in the section of the method of the present invention, the description is omitted here.

Among the fine particles thus formed, those having a relatively small diameter, for example, those having a diameter of 10 μm or less, ride on the upward convection airflow accompanying the spray flow in the airless spray in the vertical chamber (11). If it rises above 10 microns, it will not fall against its airflow.
As described above in the section of the method of the present invention. In this case, it is assumed to be 10 microns, but the size selection is determined by the speed of the updraft. The updraft in the convection described above is continually generated by the spray in the airless spray, and its speed cannot be selected. Therefore, when an appropriate flow velocity is required, a gas must be separately introduced from the outside by an independent operation to generate an ascending air flow having a required velocity.
That is, the amount of gas required by adjusting the regulator (33) is introduced into the chamber (11) by the gas supply device (30) (G). In this way, the fine particles of a certain particle size generated in the chamber (11) are subjected to ascending current (CG).
Is separated by ascending or descending, but the ascending distance (H) is also limited. Although it varies depending on the substance and particle size of the fine particles, experimental data of about 200 mm or more have been obtained.

In this way, the aerosol containing fine particles having a required small particle diameter is taken out of the chamber (11) through the aerosol exhaust pipe (50) from the gas outlet (17). And it is directly used for various applications.

The case of a liquid solvent has been described above. Next, a case of a plurality of liquids having different boiling points, that is, a case of a solution or an emulsion will be described.

The process of forming the liquid particles into fine particles on the liquid surface and the process of selecting the same are the same as in the case of the above-described liquid solvent, and only the particles having a relatively small diameter rise. However, among them, a single kind or plural kinds of fine particles are mixed. When it is desired to remove a certain kind of fine particles from among these plural kinds of fine particles, and when it is lower in boiling point than other kinds of fine particles, the fine particles may be heated to the boiling point or higher. The heating method is based on various spray devices (2) before the spray nozzle (12).
0,23,26) or gas supply device (30), chamber (1
1) The inside of the liquid storage chamber (15), the aerosol discharge pipe (50), etc. may be heated. In this way, an aerosol composed only of fine particles having a high boiling point can be taken out from the gas discharge pipe (50).

In the case of a suspension, fine particles of the liquid and the solid are generated after the liquid level collision, so that it is sufficient to heat the liquid to a temperature higher than the boiling point of the liquid. An aerosol with only fine particles is obtained.

Heating has been mentioned as a method for removing a low-boiling liquid in the case of the above-mentioned solution, emulsion and suspension, but an eliminator (53) can also be used as shown in FIG. However, this is desirably used in combination with the various heaters described above.

Finally, as for the melt, if it is a single-substance melt, a fine particle aerosol composed of the same melt is obtained through substantially the same process as in the case of the liquid solvent described above. In addition, if physically mixed with a plurality of types of substances, as in the case of the above-mentioned solution or emulsion or suspension, by heating to a temperature higher than the boiling point in them, it was removed. Solid fine particles can be obtained.

[Embodiment] 1. In the above description, the chamber in the present apparatus is of a vertical type, but it may be of a horizontal type. See FIG. In the horizontal type, the carrier gas is caused to flow in the horizontal direction (CG ₁ ), and relatively large particles are settled during the horizontal movement (Lw). In the case of the vertical type, the horizontal type is settled by the combination (F) of the wind force (CG ₁ ) and gravity (W) as shown in FIG. Between (1) and (2), fine particles of various sizes are mixed, so that there is a disadvantage that clear separation is difficult. However, for reasons of space or equipment before and after the process, a horizontal type may be suitable.

2. As described in the method section of the present invention, it is desirable that the interval (S) between the spray nozzle (12) and the liquid level (Ls) is constant. Therefore, as described above, the level controller (36) is required to keep the level constant. Although there are various types of the level controller, it is desirable to use a capacitance type in the device of the present invention. The reason is that there are no moving parts. In the atmosphere where the liquid splatters,
The placement of the mechanically movable part is because the liquid adheres to the movable part and its operation is hindered. In contrast, the capacitance type has no moving parts at all, and can operate normally even when exposed to liquid.

The configuration of the capacitance type level controller (36) will be briefly described. Please refer to FIG. 9 again. The capacitance sensor (37) consists of two electrodes. One is an amplifier (38)
To the high-frequency oscillator (39), the other one is the amplifier (4
The comparator (42) in parallel with the indicator (41) via the 0)
Then, it is electrically connected to a valve drive motor (44) or an air-operated valve (46) using an electromagnet via a relay (43). Next, the operation will be described. First, the high frequency is oscillated by the high frequency oscillator (39), amplified (38), and reaches one electrode in the capacitance type sensor (37). The amount of electricity generated around the electrode in accordance with the distance between the electrode and the liquid surface (Ls) is sensed by another electrode and amplified (4).
0), and input to the comparator (42) in parallel with the signal from the indicator (41), compare the above two signals in the comparator, transmit a plus or minus signal, and relay it to the relay (43). The control signal is transmitted to the valve drive motor or the electromagnet via the liquid storage chamber (15) to operate the open / close valve (46) or the liquid amount adjustment valve on the return pipe (16) from the liquid storage chamber (15) to the tank (19). Thus, the level (L
keep s) constant. The height of the above level is arbitrarily adjusted by adjusting the indicator (41).

3. When airless spraying is performed in this apparatus, it is necessary to introduce gas into the chamber (11). The reason for this is that, as described above, large and small particles generated in the chamber (11) are separated by wind power. The configuration will be described. See also FIG. Slightly above the liquid level (Ls) in the sump (15) and below the spray nozzle (12) and in the chamber (1
A gas introduction port (18) is provided on the side wall of 1), and the port is directed to the air blower (32). The air flow indicator (35), the filter (34), and the air flow regulator (33) are connected in this order. (31) Connect, and if necessary, provide a heater (52) on the piping. The gas inlet (18) is better provided below the capacitance type sensor (37). The above gas supply device (3
The operation of (0) is the same as the conventional one, and the description is omitted. However, it is important that the flow of the gas introduced into the chamber (11) be raised as a parallel flow without causing turbulence. It is.

4. When removing liquid fine particles from the generated fine particles using a suspension or the like in this device, the eliminator (53) is moved to the fumes above the chamber (11) to help remove the liquid fine particles by heating. It can be provided in front of the body outlet (17).

[Effect] According to the method of the present invention, fine particles generated by spraying a liquid or a melt have no large variation and can be obtained stably from beginning to end.

[Brief description of the drawings]

FIG. 1 is an explanatory view of a method of the present invention (hereinafter, the present invention will be omitted unless otherwise specified). FIG. 2 is an explanatory view of a state in which a spray of a liquid or a melt collides with a liquid surface. FIG. Is an enlarged view of "A" part in the above figure.
Fig. 5 is an enlarged view of part "B" in Fig. 2. Fig. 5 is an explanatory view of a state in which vaporized components in particles such as a solution or an emulsion or a suspension evaporate and decrease. FIG. 7 is an enlarged view of a part “C” in the above figure. FIG. 8 is an enlarged view of a part “D” in the same figure. FIG. 9 is a vertical apparatus. FIG. 10 is a side sectional view of the structure of the horizontal type device in the first embodiment. FIG. 11 is an enlarged view of the “E” part in the above figure. FIG. 12 is a conventional spray collision. FIG. 13 is an explanatory view of a state in which liquid is laminated on the surface of the collision plate. FIG. 13 is an explanatory view of main symbols. 1,11,61... Chamber, 2,12,62... Spray nozzle, 3,
13,63 …… Gun, 5,15,65 …… Reservoir, 16 …… Return piping,
17: aerosol discharge port, 18: gas inlet, 19: tank 20: two-fluid spray device, 23: gas supply device for spraying, 26 ... airless spray device 30: gas supply device, 36 …… Capacitive controller,
50: aerosol discharge pipe, 75: collision plate CG: carrier gas, DS: suspension, DSs: suspension liquid surface, G: introduction gas, p: single solid fine particles, pp ……
Aggregated particles of multiple solid fine particles Pp …… Agglomerated particles of liquid and solid fine particles pl …… Liquid fine particles

Claims (1)

(57) [Claims] A liquid (L) or a molten material is sprayed (SP) from a nozzle (2), and collides with a liquid surface (Ls) of a liquid or a molten material of the same kind as the liquid (L) or the molten material. A fine particle suspended in a gas to obtain fine particles of a liquid or a melt.