JPH0930884A - Production of coated granular fertilizer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the leakage of a fertilizer component during a dissolution- preventing period by using a granular fertilizer having a specific particle form as a starting material in the production of a coated granular fertilizer surface- coated with a polymeric compound. SOLUTION: This coated granular fertilizer is produced by coating the surface of a granular fertilizer with a coating material containing a polymeric compound. The granular fertilizer has a minor axis/major axis ratio of 0.80-0.95. The coating is carried out by a spray-coating method and the coating material is preferably a polyolefin resin. The weight of the coating material is preferably 5-15% based on the granular fertilizer used as a raw material.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing a coated granular fertilizer used as a slow-release fertilizer.

[0002]

2. Description of the Related Art In recent years, the sustainability of continuously supplying fertilizer components over the entire growing period of a crop with only one application of fertilizer, as environmental problems have become more serious due to a decrease in agricultural population and runoff of fertilizer. Fertilizer development is desired. Various types of such persistent fertilizers have been developed in the past, and among them, a coated fertilizer in which the surface of the fertilizer is coated with a thin film of a polymer substance has recently attracted attention.
Furthermore, looking at the fertilizer component elution pattern, particularly for paddy rice, the so-called time capsule type or sigmoid type (hereinafter abbreviated as S type) type in which the fertilizer component begins to elute after a certain period of about 30-70 days. The demand for is increasing. As such an S-type coating material,
Conventionally, thermoplastic resins have been used, and among them, polyolefin resins and polyvinylidene chloride resins having low water permeability are known.

[0003]

Now, one of the requirements for such S-type coated fertilizer is that the fertilizer component is not eluted during the 30-70 days (hereinafter referred to as "elution prevention period"). One example is to make the elution rate as low as possible. "Leakage" of fertilizer components during such elution prevention period
Too much (hereinafter, referred to as “initial elution”) is not preferable because, of course, the fertilizer component will be insufficient when elution is started later. Of course, some initial dissolution can be corrected by increasing the amount of coated fertilizer applied, but this is against the original purpose of coated fertilizer, and it is desirable to make coated fertilizer with as low initial dissolution as possible. It is rare. Although such a problem is serious for S-type coated fertilizers, other types, for example, so-called linear elution-type coated fertilizers in which the fertilizer component is eluted in proportion to the time from the time of fertilization without the elution prevention period. In this case, the occurrence of the film defect becomes a problem because the initial dissolution pattern is disturbed.

The cause of the initial dissolution is that water mainly intrudes from the film defects such as pinholes.
In order to reduce the initial dissolution, it is necessary to form a film with few defects. On the other hand, looking at the manufacturing method of coated fertilizer, in the case of a synthetic resin film, a method in which a resin dissolved in an appropriate solvent is sprayed on granular fertilizer under hot air flow and the solvent is dried and removed to form a film ( So-called spray coating) is conventionally used. Although this method is simple and suitable for industrial production, it involves various factors that cause film defects. Generally, a method of increasing the coverage (ratio of the coating weight to the weight of fertilizer as a raw material) is used to reduce coating defects, but in the case of spray coating, the coating rate is 10%.
The initial dissolution rate decreases in proportion to the coverage, but
There is a problem in that the initial elution of 10 to 20% does not decrease even if the coverage is increased to 10% or more.

[0005]

In view of the above facts, the present inventors have examined a method for producing a coated fertilizer having a relatively thin film and a small number of particles having a film defect particularly in the spray coating method. As a result, it was found that many of the film-defect particles are particles with horns or dents, and that the defect parts are unevenly distributed at the tips of the corners and dents. Furthermore, when the degree of "distortion" of such particle shape is expressed by the short axis / long axis ratio of the particles, it was found that the number of defective particles is significantly reduced in the fertilizer particles selected to be 0.80 or more. Invented.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. (1) Granular fertilizer to be coated The fertilizer used in the present invention is not particularly limited. urea,
In addition to granular simple fertilizers such as ammonium sulfate, ammonium chloride, potassium chloride, sulfuric acid and ammonium phosphate, granular fertilizers containing multiple components such as N1, K2O and P2O5 are used as the raw fertilizer of the present invention. The particle size of the fertilizer is not particularly limited, but generally 1-4 mm is suitable. The short axis and long axis of the granular fertilizer, which is the main point of the present invention, are measured as follows. Use a magnifying device such as a stereoscopic microscope to magnify the granular fertilizer so that it looks like a grain of about 10 mm, and take the shortest part of the parallel lines as the short axis and the long part as the long axis. Measure the distance. In this way, the minor axis / major axis ratio of one grain is calculated, 100 grains are measured, and the average value is taken as the overall minor axis / major axis ratio. The short axis in a true sphere /
The major axis ratio is 1, and becomes smaller as the shape becomes distorted. In the present invention, the minor axis / major axis ratio is 0.80 to 0.9.
5, preferably 0.85 to 0.95. 0.80
If it is lower, large protrusions are present, and the surface energy of this portion is high, so that the coating is difficult to attach, and even if the coverage is increased, it is difficult to close the defect in that portion. on the other hand,
Theoretically, defects should be reduced as the minor axis / major axis ratio approaches 1, but it is extremely difficult to produce granular fertilizers that normally exceed 0.95, and industrial products cannot be obtained. Therefore, the present inventors produced a granular fertilizer having a corner of more than 0.95 by mixing granular fertilizer of about 0.9 with a ball mill, and tried spray coating, but found no defects. ．
It was increased rather than 95 or less. Although the reason is not clear, it is considered that fine irregularities are generated on the surface. Further, in this method, since the surface of the particles is worn, fine powder is generated, particle hardness is lowered, and the yield is low. Therefore, the short axis / long axis ratio is 0.
It is not preferable to exceed 95.

(2) Coating material A polymer compound is used as the coating material.
There is no particular limitation. For example, polyolefin, polyvinylidene chloride resin, polyvinyl chloride resin, polystyrene resin, polycarbonate, polyamide, polymethyl methacrylate, polyurethane, thermoplastic resin such as ethylene-vinyl acetate, alkyd resin, phenol resin, urea resin, Thermosetting resin such as melamine resin, ABS resin, epoxy resin, silicone resin, other natural rubber and SB
Synthetic rubbers such as R and NBR, furthermore, polycaptolactone, polybutyric acid, aliphatic polyester, polyglycot,
Examples thereof include degradable polymers such as polyvinyl alcohol and polyethylene oxide. Among them, polyolefin resins such as polyethylene and polypropylene, which have a high elution-preventing effect even with a small amount due to low water permeability, are suitable. These resins can be used alone or as a mixture of two or more kinds. Further, as long as the purpose of coating is not impaired, the coating may be carried out in the presence of other inorganic or organic substances in addition to the polymer compound. For example, when coated with a resin having high water permeability as described above, for the purpose of adjusting the dissolution property or increasing the amount of the resin, talc, calcium carbonate, clay, diatomaceous earth, syria, metal oxide, sulfur, etc. Organic substances such as surfactants and waxes may be added in addition to inorganic substances.

(3) Solvent The solvent species is not particularly limited, but is appropriately selected in consideration of various conditions. Examples of the judgment material include the dissolving power, the melting temperature, the handling property, the ease of recovery, the toxicity, the safety, and the price of the polymer compound as the film material. For example, when using a polyolefin resin as a coating material, especially low-density polyethylene, hexane, octane,
Hydrocarbon solvents such as toluene, xylene, tetralin,
Chlorinated hydrocarbon solvents such as trichlorethylene and perchlorethylene are preferred. Water is used as a solvent when coating with a water-soluble polymer, emulsion resin, latex or the like.

The concentration of the solution is also not particularly limited.
For example, a higher concentration is preferable because the amount of solvent used is reduced and the processing time is shortened. Further, when the concentration is lowered, the viscosity of the solution is lowered and the handleability is improved.
However, in the case of spray coating, it is necessary to adjust the concentration according to the spray nozzle and the spray pressure to be used so that the viscosity can obtain an appropriate spray state. As a specific example, when low-density polyethylene is used as the coating material and perchlorethylene is used as the solvent, the concentration of the solution is 1 to 12% by weight, preferably 3 to 10%.
% By weight. In general, when the polymer compound is cold,
Since many solvents are insoluble, heating usually requires stirring for dissolution.

(4) Coating Device The coating device applicable to the present invention is not particularly limited as long as it is a device having a structure and a function of mixing and agitating the particulate matter and sufficiently bringing it into contact with the air flow. When classified by the mixing and agitation method, examples of a device of a mixing and agitation type using a stirring blade include a Henschel mixer and a Nauta mixer. A rotary drum type coater (Japanese Unexamined Patent Publication No. 52-61216), a rotary pan type coater (Japanese Unexamined Patent Publication No. 5-85873), and a rotary falling type are used as a device for agitating particulate matter in association with movement of the apparatus itself. Examples thereof include coaters (JP-A-7-8869, JP-A-7-31914). Further, a vibrating and fluidizing device (Japanese Patent Laid-Open No. 1-245847) that is agitated by an oscillating force is preferable because it can violently agitate a large amount of particulate matter. Examples of the type that vigorously stirs include a Wurster type or spouted bed type coater in which particles are blown and circulated and mixed, and a fluidized bed type coater (Japanese Patent Publication No. 4-61840) is used as a method of floating particles. The application of the coating solution to the particulate material is usually carried out by using a one-fluid or two-fluid spray nozzle and spraying at the appropriate location in the agitated particles. The solvent is removed by a hot air stream as described above. As the gas, in addition to air, an inert gas such as nitrogen or carbon dioxide can be used from the viewpoint of safety.

(5) Manufacturing method The raw material granular fertilizer is charged into the coating apparatus of (4), and the coating material is sprayed using a spray nozzle while maintaining the product temperature at 50 to 100 ° C. with hot air. Ting. The coating amount of the coating material depends on the target performance such as the elution prevention period, but is usually 3 to 20% by weight, preferably 5 to 15% by weight based on the granular fertilizer. Next, the present invention will be specifically described with reference to Examples.
The present invention is not limited to the following examples unless it exceeds the gist.

[0012]

【Example】

(Examples 1-4 and Comparative Examples 1-5) Short axis / as fertilizer
Seven types of granular urea having different major axis ratios were selected and coated with the method described in <Coating method> below to prepare coated urea. Regarding the obtained coated urea, <Quality evaluation method>
Based on the method shown in Table 1, the coverage, the number of film defect particles, and the elution pattern of urea in water were examined, and the results are shown in Table-1.
FIG. 1 (Example 1-4) and FIG. 2 (Comparative example 1-)
It is summarized in 5).

<Coating method> (1) Coating device Rotating ventilation coating device (SRTA2 manufactured by Okawara Seisakusho)
-Type) was used. A schematic diagram is shown in Figure 3. (2) Preparation of coating solution 1.5 kg of low density polyethylene (“M420” manufactured by Mitsubishi Kasei) having a melting point of 106 ° C. as a coating material, and 40.5 g of polyoxyethylene nonylphenol ether (“Emulgen 909” manufactured by Kao) as an elution regulator. Weighed out, added to 28.5 kg of solvent perchlorethylene, dissolved both materials at 80 ° C. to prepare a coating solution.

(3) Coating: 8.0 kg of granular urea, which was sieved to a particle size of 2.0 to 3.4 mm (after sieving, measurement of minor axis / major axis ratio), was charged into the above coating apparatus, and a rotary drum was rotated at 19 rpm. Meanwhile, 110 ° C. air was blown into the apparatus at a flow rate of 540 Nm ³ / h. When the urea product temperature reached 70 ° C, the coating solution was sprayed at 400 g / min (using a two-fluid nozzle). During spraying, the gas temperature was adjusted so that the product temperature was kept at 70 ° C, and the coating liquid was sprayed for 40 minutes (covering rate 10%
in the case of).

<Quality evaluation> (a) Measurement of coating rate 10 g of coated fertilizer is weighed, pulverized with a small pulverizer, water is added to dissolve urea, and only the film is collected by filtration. The coating was dried and weighed to calculate the coverage from the following equation.

[0016]

[Equation 1]

(B) Measurement of the number of defective particles 10 g of coated fertilizer was placed in a test tube, and 10 cc of ink was added.
, And left for 1 hour in constant temperature water at 40 ° C, and then the coated fertilizer is collected by filtration. When the adhered ink is washed with water, the color of the ink remains at the defective portion of the film, so that defective particles can be distinguished. Count the three types of particles that are partially colored in this way, the particles that are entirely colored due to the large defect area, and the shell particles that have already eluted urea and become a film only. I do. The total number of particles of 10 g of the coated urea in the example was about 700.

(C) Elution pattern 7 g of coated fertilizer is weighed, 200 g of water is added, and the container is sealed and placed in a constant temperature bath at 25 ° C. It is taken out every week and replaced with water. At that time, urea eluted in water is measured by a total nitrogen analyzer, and the elution rate is calculated by the following equation.

[0019]

[Equation 2]

When the cumulative value of the dissolution rate is plotted against the number of days, the dissolution pattern can be drawn.

[0021]

[Table 1] * Elution rate at 25 ° C for 2 weeks

[0022]

According to the coated granular fertilizer of the present invention,
A good coated fertilizer with reduced leakage of fertilizer components during the dissolution prevention period can be obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing patterns of elution rates of Examples 1 to 4.

FIG. 2 is a diagram showing patterns of elution rates of Comparative Examples 1 to 5.

FIG. 3 is a diagram showing an example of a rotary ventilation coating device used in Examples.

Claims (4)

[Claims] 1. When producing a coated granular fertilizer by coating the surface of the granular fertilizer with a coating material containing a polymer compound,
A method for producing a coated granular fertilizer, which comprises using a granular fertilizer having a short axis / long axis ratio of 0.80 to 0.95. 2. The method for producing a coated granular fertilizer according to claim 1, wherein the coating method is a spray coating method. 3. The method for producing a coated granular fertilizer according to claim 1, wherein the coating material is a polyolefin resin. 4. The method for producing a coated granular fertilizer according to claim 1, wherein the weight% of the coating material with respect to the raw material granular fertilizer is 5 to 15%.