JPH08290001A - Spray drying method using two-fluid nozzle - Google Patents

Abstract

PURPOSE: To prevent the generation of coarse particles caused by the collision and unification of atomized particles by cutting a circulating current in a drier by operating drying so that a specified relationship is formed among total flow rate of atomizing gas, flow rate of drying gas, flow rate of liquid to be atomized, and cross section of the straight barrel part of the drier. CONSTITUTION: In spray drying of a solution or dispersion liquid of solid using a two-fluid nozzle concurrent type spray drier having conical parts above and below a cylindrical straight barrel part, the drying is operated so that the following formulas (1)-(4) can be expressed among total flow rate of atomizing gas (FS (kg/hr)), flow rate of drying gas (FD (kg/hr)), flow rate of liquid to be atomized (F1 (kg/hr)), and cross section of the straight barrel part of a drier (A (m<2> )): (1) 1<=FD/FS<=500 (kg/kg), (2) 0.5<=FS/FL<=10 (kg/kg), (3) 0.1<=FS/A 200 (kg/m<2> .hr), (4) 100<=FD/A<=3000 (kg/m<2> .hr).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spray drying method using a two-fluid nozzle capable of stably obtaining fine spray dried particles.

[0002]

2. Description of the Related Art As atomizers (sprayers) in a spray drying method for obtaining fine dry particles from a solid solution or dispersion liquid, there are a rotary disk type atomizer, a pressure nozzle, a two-fluid nozzle and the like. It is used properly according to its characteristics. Of these, the two-fluid nozzle is easy to maintain and control, and the particle size can be controlled relatively easily by changing the pressure of the atomizing gas or the feed weight ratio of the gas and the liquid to be atomized. It is suitable when a fine and uniform spray is required.

However, according to these conventional methods, it was difficult to industrially stably produce particles having a fine particle diameter of 50 μm or less, particularly 30 μm or less. For example, even in spray drying using a two-fluid nozzle that is suitable for obtaining fine spray droplets, the gas flow rate for spraying and the flow rate of the liquid to be sprayed are simply combined for the purpose of atomizing the spray droplets. Even if the ratio is increased, a circulating flow is generated in the dryer, especially in the vicinity of the two-fluid nozzle, which is thought to be caused by the interaction between the atomizing gas and the dry air flow, and the atomized particles remain insufficiently dried and other There were many cases in which the particles collided and coalesced with dried spray particles and dried particles, resulting in the formation of particles much larger than the intended particle size.

As a method for preventing the formation of coarse particles in spray drying, for example, JP-A-54-4195 is known.
As disclosed in Japanese Patent Laid-Open No. 1, a method is disclosed in which the spray direction of a nozzle is adjusted to cause a rotating motion of a dry air flow in a drying tower to give an appropriate heat history to the obtained dry particles. However, even with this method, it may be impossible to obtain sufficiently fine particles, possibly because a circulating flow is generated depending on the spray drying conditions.

As a method for preventing the occurrence of such a circulating flow, Japanese Patent Publication No. 51-46299 discloses that:
A method of introducing an upward swirl flow along the cylinder wall from the cylinder wall has been proposed. However, in order to carry out this method, equipment for introducing the gas for swirling flow is required, which makes maintenance complicated and increases equipment cost.

[0006]

It is an object of the present invention to perform spray drying of a solid solution or dispersion by using a circulating flow inside the dryer so that the liquid droplets to be sprayed remain insufficiently dried. Collide with undried spray particles and dried particles
Combined, it is possible to stably form fine dry particles that prevent the formation of particles much larger than the intended particle size and do not require or simplify the crushing or sieving process. It is to provide a spray-drying method using a possible two-fluid nozzle.

Another object of the present invention is to obtain fine dry particles of vinyl chloride polymer from vinyl chloride polymer latex based on the above method.
It is to provide a spray drying method using a two-fluid nozzle.

[0008]

The inventor of the present invention has found that the total flow rate of gas for atomization (hereinafter referred to as "F
Shown as _S ", the unit kg / hour), drying air showing a flow (hereinafter" F _D "units kg / hr), and shows the the spray liquid flow rate (hereinafter" F _L ", the unit kg / h) and yield As a result of examining the relation with the particle size of the dried particles, the above-mentioned items include the cross-sectional area of the straight section of the dryer (hereinafter referred to as “A”, unit m ² ) between each item. It was found that by selecting the drying conditions so that a specific relationship is established, the circulation flow in the dryer can be reduced, and the generation of coarse particles due to collision / coalescence of spray particles can be greatly reduced. Completed the invention.

That is, the gist of the present invention is to spray-dry a solid solution or dispersion using a two-fluid nozzle parallel-flow spray dryer having cones above and below a straight cylindrical body. atomizing gas total flow rate (F _S (kg / hr)), dried airflow (F _D (kg / h)), the spray liquid flow rate (F
_L (kg / hour)) and the cross-sectional area (A
(M ² )), the drying operation is performed so that the following relationships (1) to (4) are established.

[0010]

(6) (1) 1 ≦ F _D / F _S ≦ 500
(Kg / kg)

[0011]

(2) 0.5 ≦ F _S / F _L ≦ 10
(Kg / kg)

[0012]

(3) 0.1 ≦ F _S / A ≦ 200
(Kg / m ² · hour)

[0013]

(4) 100 ≦ F _D / A ≦ 3000
(Kg / m ² · hour)

The present invention will be described in more detail below. (1) Dryer A two-fluid nozzle parallel-flow spray dryer having a cylindrical body and cones above and below is used. As for the size, the diameter of the straight body is usually 1 to 15 m and the height is 0.5.
It is preferable to use one having a range of up to 50 m. If the diameter of the straight body is too large, the space at the center of the body cannot be used effectively for drying, or the support arm for inserting the nozzle becomes long, causing problems such as powder adhesion to this arm. There is a risk of The shape of the cone portion is preferably a truncated cone shape.

The flow direction of the airflow is preferably a vertical downflow type in which the direction of the dry airflow is a downflow. The dryer is a vertical type, the dry airflow is introduced from the top of the dryer, and the dried powder and the outlet of the dry airflow are discharged from the side wall of the lower cone even in the model discharged from the bottom of the dryer. The model may be used.

At the inlet of the dry air flow, a dispersion plate (disperser) for rectifying this air flow into a uniform downward flow.
Is preferably provided. As this dispersion plate,
A metal plate having a large number of holes, a so-called punched metal (perforated plate) having several layers is preferable, but it is not particularly limited as long as it can rectify an air flow.

(2) Two-fluid nozzle Nozzle type: There are two types of two-fluid nozzle, such as an external mixing type and an internal mixing type, both of which can be used, but the external mixing type is preferred because clogging is less likely to occur. preferable.

Nozzle shape: The shape is not particularly limited as long as fine spraying is possible. However, for the spray angle (θ) representing the spread of spray from the nozzle tip, 5 ° or more,
It is preferably 10 ° or more and 90 ° or less, preferably 50 ° or less. When θ is less than 5 °, the shape of the spray becomes rod-shaped or linear and is not suitable for atomization. Conversely, when θ exceeds 90 °,
Interference with the spray from the adjacent nozzles occurs, and the possibility of formation of coarse particles due to collision of spray droplets increases, which is not preferable.

Nozzle mounting position: The nozzle is preferably installed at a position below the upper cone of the dryer or above the straight body. If the nozzles are installed too close to the inlet of the dry air flow, the effective tower cross-sectional area will be small when many nozzles are arranged, making it difficult to secure sufficient distance to prevent interference between nozzles. become. On the contrary, when the nozzle is installed below the straight body, the ratio of the portion used for drying in the total volume of the dryer is reduced, and the equipment efficiency is deteriorated.

Nozzle arrangement: The number of nozzles used is determined according to the required drying capacity. The number of normal nozzles is 4
~ 200 lines. The arrangement is preferably such that the sprayed droplets do not collide or coalesce. The arrangement density is usually 0.05 to 100 pieces / m ² ,
It is preferably 0.5 to 5 lines / m ^2, and 0.0
If it is less than 5 lines / m ² , the diameter of the dryer becomes extremely large and the equipment cost increases. On the other hand, if it exceeds 100 lines / m ² , the possibility of collision and coalescence of spray droplets is high. Become. The distance between the nozzles is preferably 10 to 500 cm, particularly 25 to 150 cm.

As a specific arrangement of the nozzles, the nozzles are usually arranged on a single circumference centered on the axis of the dryer or on a plurality of concentric circles. When arranged on a plurality of concentric circles, the individual circles need not be on the same plane. Spraying direction: The spraying direction of the nozzles means the direction in which the center line of the installed nozzles faces, but in the method of the present invention, the spraying directions of all nozzles may be the same direction. However, they may form an angle of 0 to 180 ° with each other.

The angle between the spray direction of the nozzle and the dry air flow is not particularly limited, but is 0 ° to 90 ° with respect to the air flow direction.
Is preferable, and it is particularly preferable that the angle is in the range of 0 ° to 15 °. If this angle exceeds 90 °, it becomes a so-called “countercurrent” type, and the turbulence of the drying air flow due to spraying becomes severe, making uniform drying difficult, and interference within the spray from the same nozzle. Tends to occur, and problems such as generation of coarse particles tend to occur.

(3) Spray drying conditions Liquid to be sprayed: A liquid to be sprayed suitable for applying the spray drying method of the present invention is formed into fine droplets by a nozzle to volatilize a solvent or a dispersion medium, and is dried or powdered. If it can be granulated, it can be targeted without particular limitation,
For example, thermosetting resin such as dispersion liquid or melt liquid of thermoplastic resin such as polyester, polystyrene, polyamide, polyurethane, polyolefin, polyvinyl chloride, polyphenol, urea resin, melamine resin, silicone resin, epoxy resin, unsaturated polyester resin, etc. Dispersion, detergent
Soaps, dyes and pigments, insecticides, herbicides, fungicides and other agricultural chemicals, skim milk, instant coffee, cocoa, malt extract, starch, other foods, natural and synthetic flavors, antibiotics, serum, plasma , Various vitamins, penicillin, glucose, pharmaceuticals such as various amino acids, and the like. Among these, it is preferable to spray a dispersion or solution of the polymer to collect fine and uniform powdery particles, and particularly to spray-dry a latex of a vinyl chloride-based polymer. Is suitable.

The flow rate of the liquid to be sprayed per nozzle is usually 1 to 200 kg / hour, preferably 10 to 100 k.
It is good that it is g / hour. If it is less than 1 kg / hour, the treatment efficiency of the dryer tends to be low, whereas if it exceeds 200 kg / hour, fine spraying tends to be difficult. When using a plurality of nozzles, it is preferable for control that the flow rate of the sprayed liquid in each nozzle is uniform.

Gas for atomization: selected depending on the property of the substance to be atomized, but usually air, an inert gas (nitrogen, helium, neon, argon, etc.) or water vapor is used. You may use the mixture of 2 or more types of these. The temperature of the atomizing gas is preferably in the range of 0 to 300 ° C, and more preferably in the range of 5 to 40 ° C. If the temperature is lower than 0 ° C, the amount of heat radiated to the gas for spraying increases, and the drying efficiency decreases, while if the temperature exceeds 300 ° C, the material to be dried in the liquid to be sprayed is thermally decomposed and thermally deteriorated. I'm going to get tired.

The flow rate of the atomizing gas depends on the optimum load amount of the nozzle to be used, but in general,
0.1 to 2000 kg / piece / hour, preferably 1 to 100
0 kg / piece ・ hour, more preferably 1-500 kg / piece ・
Time is good. If the flow rate is less than 0.1 kg / line / hour, it is difficult to make the liquid droplets fine, while 2000 kg /
At a flow rate that exceeds this time, the wear in the gas flow path of the nozzle becomes severe.

Drying gas: As with the atomizing gas, it is selected according to the properties of the material to be atomized. Usually, air is often used because it is easily available. Further, the flow rate is determined from the heat balance in the dryer in consideration of the drying temperature, but as will be described later in the present invention, the value of the ratio to the total flow rate of the gas for spraying and the cross-sectional area of the straight body part of the dryer is also determined. It is necessary to select it within a certain range.

Drying temperature: The processing temperature needs to be adjusted according to the properties of the material to be dried. Usually, the conditions are set according to the target drying efficiency, the heat resistance of the material to be dried and the temperature of the supply heat source. Generally, the hot air temperature for drying is often 50 to 450 ° C. at the dryer inlet and 25 to 200 ° C. at the outlet. If the outlet temperature is 25 ° C or lower, it tends to be difficult to keep the temperature stable in relation to the outside temperature,
Also, water-based spraying may result in insufficient drying.

(4) Operating Conditions In order to stably obtain fine spray-dried particles without generating a circulating flow inside the dryer, it is necessary to select operating conditions that satisfy all the following relationships. is there. F _D / F _S (kg / kg) (ratio of dry gas flow rate and total gas flow rate for atomization) The value of F _D / F _S is 1 or more, preferably 3 or more, and 500 or less, preferably 300 or less. It is necessary to be. If this value is less than 1, a circulating flow tends to occur, and it becomes difficult to obtain fine dry particles. On the other hand, this value is 5
Under the condition of exceeding 00, it is necessary to supply a remarkably large amount of drying gas, which is disadvantageous in terms of equipment and thermal energy.

F _S / F _L (kg / kg) (ratio between the total flow rate of the gas for spraying and the flow rate of the liquid to be sprayed) The value of F _S / F _L is called the "mass ratio", and the two-fluid nozzle This is the main operating condition in the spray used. This value is 0.5 or more, preferably 1 or more and 10 or less, preferably 5 or less. If this value is smaller than 0.5, the spray droplets themselves become large, and it becomes difficult to obtain fine dry particles. Further, if this value exceeds 10 and is large, it is effective for atomizing the spray droplets, but the consumption amount of the spray gas increases, and the cost for the compressed gas manufacturing facility and the facility operating cost increase. In addition, a circulating flow is also likely to occur, and particles are likely to collide and coalesce.

F _S / A (kg / m ² · hour) (ratio of total flow rate of atomizing gas to cross-sectional area of straight body of dryer) The value of F _S / A is 0.1 or more, preferably 0.1. 5 or more, more preferably 5 or more, 200 or less, preferably 150
Hereafter, it is more preferably 100 or less. If this value is 0.
When it is less than 1, the yield of dried products is smaller than the size of the dryer, and the productivity is low. On the other hand, if this value exceeds 200, a circulating flow is likely to occur, causing collision or coalescence between spray droplets or between spray droplets and dried particles,
It becomes impossible to stably obtain fine particles.

F _D / A (kg / m ² · hour) (ratio of dry air flow rate and cross-sectional area of straight body of dryer) The value of F _D / A is 100 or more, preferably 200 or more, more preferably It is 300 or more and 3000 or less, preferably 2000 or less, more preferably 1000 or less. If this value is less than 100, a circulating flow is likely to occur, while on the other hand, if the operating conditions exceed 3000, not only is the gas consumption for drying increased, which is economically disadvantageous, but also in the lower cone portion. Airflow turbulence occurs and the airflow inside the dryer tends to become unstable.

(5) Spray drying of vinyl chloride polymer latex The latex in which vinyl chloride polymer particles are emulsified and dispersed is dried by the method of the present invention by a spray dryer equipped with a two-fluid nozzle to obtain excellent quality. It is possible to produce a vinyl chloride resin for paste. This will be described below, but the above description may be followed except for special notes.

Composition: As a latex in which vinyl chloride polymer particles are emulsified and dispersed (hereinafter referred to as "latex"), vinyl chloride or a mixture of vinyl chloride and a comonomer copolymerizable therewith is used in an aqueous medium as an emulsifier. And a method of emulsion polymerization in the presence of a water-soluble polymerization initiator,
Alternatively, a particle size of 0.01 to 2 produced by a method of fine suspension polymerization in the presence of an emulsifier and an oil-soluble polymerization initiator.
Those containing 0 μm of vinyl chloride polymer particles are suitable.

Comonomers copolymerizable with vinyl chloride include vinyl esters such as vinyl acetate, vinyl propionate, vinyl stearate, acrylic acid, methacrylic acid,
Mono-unsaturated acids such as itaconic acid, alkyl esters of these mono-unsaturated acids, vinyl ethers such as methyl vinyl ether, ethyl vinyl ether, octyl vinyl ether, lauryl vinyl ether, di-unsaturated acids such as maleic acid, fumaric acid, etc. Alkyl ester of diunsaturated acid, vinylidene halide such as vinylidene chloride,
Examples thereof include one kind or a mixture of two or more kinds such as unsaturated nitrile.

Polymerization prescription: In the case of emulsion polymerization, the polymerization initiator used in the production of the vinyl chloride polymer latex is, for example, a persulfate (sodium salt, potassium salt, ammonium salt, etc.), water-soluble hydrogen peroxide, etc. -Soluble peroxides, or water-soluble redox initiators comprising these water-soluble peroxides and a water-soluble reducing agent (for example, sodium sulfite, sodium pyrosulfite, sodium bisulfite, ascorbic acid, sodium formaldehyde sulfoxylate, etc.), In the case of fine suspension polymerization, monomer-soluble (oil-soluble) initiators such as azobisisobutyronitrile, azobis-2,4-dimethylvaleronitrile, lauroyl peroxide and t-butylperoxypivalate, or these. Redox initiation consisting of a combination of the oil-soluble initiator of And the like.

Examples of emulsifiers used in the production of latex include higher alcohol sulfate ester salts (alkali metal salts, ammonium salts), alkylbenzene sulfonates (alkali metal salts, ammonium salts), higher fatty acid salts (alkali metal salts). , Ammonium salts), other anionic surfactants, nonionic surfactants, and cationic surfactants. These surfactants may be used alone or in combination of two or more. Particularly preferred are anionic surfactants. Further, the anionic surfactant and / or nonionic surfactant may be added separately from the emulsifier for polymerization during or after preparation of the latex.

Further, in the production of latex, a polymerization degree adjusting agent and other auxiliaries may be used. As the polymerization degree adjusting agent, for example, trichloroethylene, carbon tetrachloride,
Examples thereof include chain transfer agents such as 2-methylcaptoethanol and octyl mercaptan, and crosslinking agents such as diallyl phthalate, triallyl isocyanurate, ethylene glycol diacrylate and trimethylolpropane trimethacrylate.

In addition to the above, other auxiliary agents include, for example, water-soluble transition metal salts such as cupric chloride, ferrous sulfate and nickel (II) nitrate which act as activators of redox initiators, or phosphorus. Examples thereof include pH adjusting agents such as acid mono- or dihydrogen alkali metal salts, potassium hydrogen phthalate, and sodium hydrogen carbonate.

Latex concentration: The solid content in the vinyl chloride polymer latex is not particularly limited and is usually 20 to 80% by weight, preferably 40 to 65% by weight. It may be used as it is, or may be concentrated by a method such as ultrafiltration. The viscosity of latex is usually 0.1 Pa · sec or less.

Drying conditions: As the two-fluid nozzle, an external mixing type is preferable. The temperature conditions are hot air temperature of 50 to 300 ° C. at the dryer inlet and 2 at the dryer outlet.
It is preferable to use 5 to 90 ° C. When the outlet temperature is 25 ° C. or lower, it becomes difficult to keep the temperature stable and the drying tends to be insufficient. If the temperature is 90 ° C or higher, the treatment amount decreases and the drying efficiency decreases. Also, F _S / F
_L (mass ratio) is 0.5-5, preferably 1-2.
It is better to use the range of 5.

Atomizing gas: Air is usually used. However, when fine atomizing is desired, it is efficient to use water vapor or a mixed gas of water vapor and an inert gas.

[0043]

EXAMPLES Hereinafter, specific embodiments of the present invention will be described in more detail with reference to Examples, but the present invention is not limited to the following Examples unless the gist thereof is exceeded. "Parts" and "%" in the examples mean "parts by weight" and "% by weight", respectively, unless otherwise specified.

(1) Two-fluid nozzle The material is stainless steel, the cross-sectional area of the opening is 95 mm ² in the liquid channel (inner tube), and the gas channel (outer tube-inner tube gap) is about 48.
Six mm ² external mixing nozzles were used in Examples 1 to 16 and Comparative Examples 3 to 8, and 8 nozzles were used in Comparative Examples 1 and 2.

(2) Drying device A spray dryer having a straight body portion diameter of 4 m (straight body portion cross-sectional area of 12.6 m ² ), an upper cone portion length of 4 m, a straight body portion length of 4 m, and a lower cone portion length of 3.1 m was used. used. The above-mentioned two-fluid nozzle was installed on the same circumference through the arm inside the dryer of this upper cone portion (about 1 m above the connecting portion with the straight body portion). The spray angles of the nozzles were all directed vertically downward. Also,
The dry air flow was rectified by an air disperser mounted on the upper cone of the dryer and supplied as a downflow.

(3) Production of Vinyl Chloride Polymer Latex A vinyl chloride polymer latex was produced by polymerizing vinyl chloride monomers by a seeded emulsion polymerization method. The polymerization initiator used was a redox initiator of potassium persulfate-sodium pyrosulfite, and the main emulsifier was sodium lauryl sulfate. The reaction temperature was 55 ° C., the solid content of the obtained latex was 46% by weight, and the average particle size of the polymer particles in the latex was 1.1 μm. The average degree of polymerization of the produced polyvinyl chloride was 1200. Further, water was separated from this latex by using an ultrafiltration membrane to obtain a vinyl chloride polymer latex having a solid content of 50%, 60% and 65% in sequence.

(4) Spray Drying The latex obtained in (3) was spray dried under the conditions shown in the table using the drying apparatus in (2) above.

(5) Measurement of Particle Size Distribution of Dry Vinyl Chloride Resin The particle size distribution of the vinyl chloride resin obtained by spray drying was measured by the following method to measure the volume median diameter.

A flow cell holder was set in a laser diffraction particle size distribution measuring device (LA-500 manufactured by Horiba, Ltd.), and about 200 ml of 0.1% polyoxyethylene sorbitan monolaurate aqueous solution was placed in a bath as a dispersion medium. , Stir and circulate. A blank of the diffraction pattern is measured, a small amount of the vinyl chloride resin obtained in (4) above is added to the bath and dispersed for 30 seconds, and then the particle size distribution of the sample is measured. The average particle size (median size) is calculated from the obtained particle size distribution.

(6) Evaluation of results The results are summarized in the table. As can be seen from this table, when the conditions for spray drying are within the scope of the present invention, the particle size of the dry vinyl chloride resin is 50 μm or less.

[0051]

EFFECTS OF THE INVENTION By carrying out spray drying by selecting conditions according to the method of the present invention, it is possible to reduce the circulating flow in the dryer, particularly in the vicinity of the spray nozzle, and to generate coarse particles due to collision or coalescence of spray particles. It is possible to prevent it, and it is possible to stably obtain fine dry particles.

Further, by applying the present method to the spray drying of vinyl chloride polymer latex, the production of coarse particles can be reduced, so that the steps such as crushing and sieving can be omitted or simplified.

[0053]

[Table 1]

[0054]

[Table 2]

[0055]

[Table 3]

[0056]

[Table 4]

[0057]

[Table 5] *: Nozzle blockage

Claims (6)

[Claims] 1. When the solid solution or dispersion liquid is spray-dried using a two-fluid nozzle parallel flow spray dryer having a cylindrical straight body and cones above and below, the total gas flow rate for spraying ( hereinafter referred to as "F _S", the unit kg / hour), drying shows a gas flow rate (hereinafter "F _D" units kg / hr), shown as the spray liquid flow rate (hereinafter "F _L", the unit kg / h) , And a straight body section area (hereinafter, referred to as “A”, unit m ² ) of the dryer, a drying operation is performed so that the following relationships (1) to (4) are established. Spray drying method using a two-fluid nozzle. ## EQU1 ## (1) 1 ≦ F _D / F _S ≦ 500
(Kg / kg) [Equation 2] (2) 0.5 ≦ F _S / F _L ≦ 10
(Kg / kg) [Formula 3] (3) 0.1 ≦ F _S / A ≦ 200
(Kg / m ² · hour) [Equation 4] (4) 100 ≦ F _D / A ≦ 3000
(Kg / m ² · hour) 2. The spray drying method according to claim 1, wherein an angle formed by the spray direction of the two-fluid nozzle and the flowing direction of the dry air flow is 0 ° or more and 90 ° or less. 3. The spray drying method according to claim 1, wherein the following relation (5) is satisfied in the relational expression (2) according to claim 1. (5) (5) 0.5 ≦ F _S / F _L ≦ 5
(Kg / kg) 4. The spray drying method according to claim 1, wherein the liquid to be sprayed is a latex in which vinyl chloride polymer particles are emulsified and dispersed. 5. The spray drying method according to claim 4, wherein the vinyl chloride polymer particles are produced by an emulsion polymerization method or a fine suspension polymerization method. 6. The vinyl chloride polymer particles have a particle size of 0.01.
The spray-drying method according to claim 4 or 5, wherein the spray-drying method is about 20 μm.