JPH11347477A - Coating method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a uniform coating film of small film thickness having a very similar shape to that of the surface of particles to be coated, by using a spray nozzle having such a property that the frequency distribution of liquid drops having diameters of a specified multiple or more of the Sauter average particle size is a specified value or low to the all liquid drops. SOLUTION: When particulate substances are to be coated by using a spray nozzle, such a spray nozzle is used that the frequency distribution of liquid drops having diameters twice or larger as the Sauter average diameter is <=15 wt.% to the all liquid drops. If the frequency distribution exceeds this value, the purpose to uniformly coat particles with a thin film is not realized. Moreover, deposition amount of a resin on a device increases. The proportion is preferably <=5 wt.%, and more preferably <=1 wt.%. The kinds of the spray nozzle are not limited, and a flat spray nozzle, solid spray nozzle or the like can be used. The particulate material is not limited, and preferably it contains a fertilizer as the main component.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The coating of various substances on the surface of a granular substance has been applied in various fields. In the field of fertilizers, coated fertilizers in which the surface of granular fertilizers are coated with a high molecular substance such as sulfur, alkyd resin, polyurethane, or polyethylene are widely used for the purpose of slowing effect.
In the field of pharmaceuticals, sugar, cellulose,
BACKGROUND ART Pharmaceuticals having solubility or the like in place by coating with various substances such as starch have been put to practical use. Also, in the field of foods, such a coating technique is applied from the viewpoint of moisture proof and taste.

[0002] The present invention relates to a method for coating such a granular material, and particularly to a method for coating the granular material with a high ability to follow the surface of the granular material to form a uniform film. The present invention relates to a coating method capable of exhibiting the effect of (1) and having less contamination of the apparatus.

[0003]

2. Description of the Related Art There are several methods for coating the surface of particulate matter. The first is a method in which a granular substance is immersed in a dissolved or melted coating substance, and then dried if necessary. Although this method is characterized in that it can be coated with a simple apparatus, it has a drawback that it is difficult to control the amount of coating and the surface morphology after coating. The second is a method in which a powdery substance is adhered to the surface and then melted for coating. Although this method has a feature that no solvent or the like is used, it has been difficult to form a uniform film. On the other hand, the method of coating the surface of the granular material using a spray nozzle has a feature that a relatively thin film can be easily achieved. However, the particulate material to be coated does not necessarily have a smooth surface and a shape without irregularities. Even small amounts for such substances,
That is, there has not always been a technique capable of achieving the desired performance with a thin film thickness. In addition, when using a spray, droplets adhere to equipment other than the target object,
Periodic removal work was required.

[0004]

The problem to be solved by the present invention is that, as described above, it has a high followability to the surface of the granular material to be coated, and can be uniformly coated in a small amount, that is, in a thin film thickness. It is an object of the present invention to provide a coating technique which can achieve a desired performance and has low contamination to a device.

[0005]

SUMMARY OF THE INVENTION In a method of coating a particulate material using a spray nozzle, the present inventor pays attention to the particle size distribution of sprayed droplets, and the spray nozzle has a constant distribution. Have been found to be able to solve the above problem, and have completed the present invention. That is, in the present invention, in the method of coating the surface of a granular substance using a spray nozzle, the frequency distribution of droplets having a diameter of twice or more the average diameter of the Sauter (hereinafter sometimes referred to as α)
Using a spray nozzle having a particle size of 15% by weight or less with respect to all the droplets.

[0006] The type of spray nozzle in the present invention is not particularly limited, and known sprays such as a flat spray nozzle, a solid spray nozzle, a full cone spray nozzle, a hollow cone spray nozzle, a two-fluid spray nozzle, and a multi spray nozzle. Nozzles can be applied. The Sauter mean diameter in the present invention is a value measured under the following conditions. That is, the spray liquid uses water at 20 ° C.
Water pressure 2.0 kg / cm ² in the case when the fluid spray nozzle of 3.0 kg / cm ^2, 2-fluid spray nozzle, the water pressure 2.0
Spray vertically downward at kg / cm ² . The particle diameter is measured by a laser light scattering method under the conditions of 20 ± 2 ° C., 50 ± 5% humidity, and no wind, and is measured on a horizontal plane 300 mm vertically away from the tip of the spray nozzle. For those indicating a circular or ring-shaped spray area, a spray nozzle indicating a shape other than a circle or ring at a point 3 r / 4 (r is the radius of the outer circumferential circle of the spray area) in the radial direction from the center. Is measured with light passing through the center of gravity of the spray area. Commercially available so-called full cone nozzles and hollow cone nozzles exhibit circular or ring-shaped spray areas.

From the measured droplet distribution, the Sauter mean diameter can be calculated using the known equation: D _s = Σnd ³ / Σnd ² where D _s: Sauter mean diameter, n: number of droplet particles, d: droplet diameter. The coating method according to the invention is thus characterized by α
It is necessary to use a spray nozzle having a maximum of 15% by weight. If α exceeds this value, it is not possible to achieve the effect of being able to achieve uniform performance with a thin film thickness, which is the object of the present invention, and to achieve initial performance. In addition, adhesion of resin to the device and the like increase. It is preferably at most 5% by weight, more preferably at most 1% by weight.

Further, according to the present invention, the average diameter of the Sauter is 1/2.
It is preferable to use a spray nozzle in which the frequency distribution (hereinafter, sometimes referred to as β) of all droplets having the above diameter is 90% by weight or more. If β is less than this amount, it is difficult to obtain a uniform film, the yield decreases,
Furthermore, it is not preferable because the resin adheres to the apparatus. In particular, when the vapor partial pressure of the liquid ejected from the spray nozzle under the atmosphere to be coated is 500 mmHg or less, or when coating is performed under the condition of the boiling point of the liquid or more, it is preferable to satisfy this condition. It is preferably at least 95% by weight.

In the present invention, it is preferable that the ratio of the Sauter mean diameter of the droplet to the volume mean diameter of the particulate matter (hereinafter, sometimes referred to as γ) is 0.04 to 0.2.
If γ is below this range, the productivity will be poor, and if γ exceeds this range, the uniformity may be impaired. The volume average diameter of the granular substance can be measured by a conventionally known method such as image analysis.

There is no particular limitation on the granular material in the present invention, and any known granular material can be used. The particle size is preferably between 0.1 mm and 100 mm. Specific examples of the particulate material include urea, aldehyde condensed urea, isobutyraldehyde condensed urea, formaldehyde condensed urea, nitrogen-containing organic compounds such as guanylurea oxamide, lime nitrogen, ammonium nitrate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, ammonium sulfate, Ammonium compounds such as ammonium chloride, potassium nitrate, potassium phosphate Potassium salts such as potassium sulfate, potassium chloride, calcium salts such as calcium phosphate, calcium sulfate, calcium nitrate, calcium chloride, magnesium nitrate, magnesium chloride, magnesium phosphate, magnesium sulfate, etc. Magnesium salts, iron salts such as ferrous nitrate, ferric nitrate, ferrous phosphate, ferric phosphate, ferrous sulfate, ferric sulfate, ferrous chloride, ferric chloride, and the like Main component is double salt Fertilizers, various granular pharmaceuticals, foods and the like. Among them, it is preferable that the particulate matter contains a fertilizer as a main component.The feature of the present invention is that the ability to follow the surface of the particulate matter to be coated is high, and a small amount, that is, a uniform film thickness is small. Although it is possible to coat and achieve the intended performance, it is more preferable that the surface of the granular material is smooth and nearly spherical.

Next, the liquid to be sprayed will be described. The liquid to be sprayed must be liquefied by itself or the film material covering the particulate material must be contained in the solvent in a dissolved or dispersed state. As the film material, conventionally known materials can be used, such as polyolefins such as polyethylene and polypropylene, copolymers of ethylene and other vinyl monomers such as ethylene-vinyl acetate copolymer, urethane resin prepolymers, alkyd resins and the like. Synthetic polymer substances, saccharides, natural polymer substances such as celluloses and their modified products, pigments, sulfur, talc, clay,
An inorganic substance such as calcium carbonate, an emulsifier, a colorant, and additives such as various crosslinking agents can be included. It is a preferable example that a polymer substance is contained in the film agent substance.

There is no limitation on the solvent used. It may be appropriately selected in consideration of the solubility, boiling point, and the like of the film agent to be used. Specific examples include water, aromatic solvents such as benzene, toluene, xylene and mesitylene, aliphatic solvents such as hexane, heptane, n-octane, 2-ethylhexane and 2-ethylcyclohexane, and alcohols such as methanol and ethanol. And ethers such as methyl ether and ethyl ether, and chlorinated hydrocarbons such as dichloromethane, trichloromethane, tetrachloromethane, trichloroethylene and tetrachloroethylene.

When a solvent is used, the content is preferably 1-2.
0% by weight is preferable, and 3 to 15% by weight is more preferable.
It is. Deviating from the lower limit results in poor productivity, and deviating from the upper limit results in poor uniformity of the coating. The present invention is a method of coating using a spray nozzle, and examples of devices that can be used in this method include a conventionally known jet device or rolling device. That is, in the jet tower and the rolling tank body,
It is a device equipped with a blower for sending hot air, a solution pump for sending the coating liquid, a spray nozzle, a thermometer, and the like. A granular substance to be coated is introduced into the apparatus, and a gas at a predetermined temperature is blown from a blower or the like. In the case of a spout tower, adjustment is made so that a jet of particulate matter occurs stably in the apparatus. When the temperature inside the apparatus reaches a desired temperature, a film can be formed on the surface of the granular material by supplying a predetermined liquid from a spray nozzle.

In forming the film, there is no particular limitation on the spray temperature at the time of film formation, and it may be determined in consideration of the boiling point of the liquid used, the melting point of the coating substance, and the like. Usually, a temperature of 30 ° C. or more and a temperature at which adhesion of particles does not occur is set. Specifically, a range of about 30 to 150 ° C, more preferably a range of 30 to 100 ° C is selected. Hot air stably rolls or jets the granular particles,
In addition, it should be set to a temperature and an air flow required to maintain the above temperature. For these techniques, conventionally known techniques can be applied.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Examples of the present invention and comparative examples will be specifically described below. In addition, the test in an Example and a comparative example was based on the following method. <Dissolution test> 5 parts by weight of the coated granular fertilizer was immersed in 200 parts by weight of pure water and stored in a 25 ° C constant temperature bath. Ten days later, the nitrogen component in the fertilizer eluted into the water was measured by a total agricultural soil analyzer ZA-II. The dissolution rate is expressed as a percentage of the dissolved component relative to the nitrogen component contained in the original coated fertilizer. This value is referred to as A value.

[0016]

EXAMPLES 1-3 AND COMPARATIVE EXAMPLE 1 A coated fertilizer was produced using a jet apparatus using several spray nozzles shown in Table 1. The droplet diameter was measured using a laser particle size distribution analyzer (Mastersizer, manufactured by Malvern).
Water at a temperature of 3.0 ° C. and a water pressure of 3.0 kg / cm ² , and a spray radial direction of 3 r /
At point 4, the measurement was performed under the conditions of a temperature of 20 ° C., a humidity of 50%, and no wind.

An ethylene / vinyl acetate copolymer (trade name)
Evaflex 360, Mitsui Dupont Polychemical
2.5 parts by weight, polyethylene (trade name Sante)
2.5M parts by weight M2270, manufactured by Asahi Kasei Corporation
300 parts by weight of tetrachloroethylene are added and the solvent
These were dissolved by heating and refluxing to the boiling point. Sa
Further, 5.0 parts by weight of talc was added to this solution, and the mixture was thoroughly stirred.
To prepare a dispersion. Volume average grain sieved at 2-4mm
Granular phosphoric acid potassium nitrate having a diameter of 3.0 mm (N, P_TwoO_Five, K _TwoO
(Each component is 15%) 100 parts by weight are charged into a jet device,
Hot air is blown and the temperature inside the device is stable at 60 ° C.
Awakened. Next, the dispersion prepared above
Takes 10 minutes from the spray nozzle to the jet device
Supplied. During this time, the temperature inside the jet device should be 55 ± 2 ° C.
The temperature of the hot air was adjusted. Then switch hot air to cold air
When the temperature drops below 35 ° C, the contents are removed from the jet device.
Started.

The coated fertilizer produced was 110 parts by weight in all of Examples 1 to 3, and it was found that almost all of the supplied solid content was coated. On the other hand, in Comparative Example 1, the amount was 109.6 parts by weight, and deposits such as resin were observed below the jetting device. Table 1 shows the A value relating to nitrogen elution of the obtained coated granular fertilizer. These results show that the effect of coating greatly differs when the α value is 15%, indicating that the method of the present invention is excellent in coatability.

[0019]

[Table 1]

[0020]

According to the present invention, the ability to follow the surface of the granular material to be coated is high, the coating can be uniformly performed with a small amount, that is, a thin film, and the desired performance can be achieved. It is possible to provide a coating technique with less.

Claims (5)

[Claims] 1. A method for coating the surface of a granular material using a spray nozzle, wherein the frequency distribution of droplets having a diameter of twice or more the Sauter mean diameter is 15% by weight or less based on all the droplets. A method for coating particulate matter, comprising using a spray nozzle. 2. The coating method according to claim 1, wherein the frequency distribution of the droplets having a diameter equal to or more than 1/2 of the Sauter's average diameter is 90% by weight or more based on all the droplets. 3. The coating method according to claim 1, wherein the Sauter mean diameter of the droplet is 0.04 to 0.2 of the volume mean diameter of the granular substance. 4. The coating method according to claim 1, wherein the granular substance is a substance containing a fertilizer as a main component. 5. The coating method according to claim 1, wherein the substance to be coated contains a polymer substance.