JPH0930883A - Coated granular fertilizer and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a coated fertilizer free from coating film defect even in a relatively thin film and having reduced initial dissolution by applying at least two coating layers consisting of a 1st layer containing a wax and a 2nd layer containing a thermoplastic resin to the surface of a granular fertilizer particle. SOLUTION: A nearly spherical granular fertilizer having particle diameter of 1-4mm is charged into a coating apparatus having a structure and function to mix and stir a granular substance and sufficiently contact the substance with a gaseous flow. A solvent solution of a wax is sprayed at a rate of 0.05-0.2wt.% based on the granular fertilizer through a spray nozzle into the coating apparatus while keeping the temperature of the fertilizer to 50-100 deg.C with hot air to form the 1st coating layer on the fertilizer particle. A solvent solution of a coating mixture is sprayed at a rate of 5-15wt.% based on the granular fertilizer with the coating apparatus under the condition same as the spraying condition of the 1st layer to form the 2nd coating layer on the coated fertilizer particle.

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. On the other hand, a method of increasing the coverage (ratio of coating weight to raw material fertilizer weight) is usually taken to reduce coating defects, but this reduces the concentration of the active ingredient of the fertilizer and the commercial value is lowered. There's a problem.

One of the causes of such a film defect is the rupture of bubbles generated in the film. When a thermoplastic resin, especially a polyolefin resin, is used as the coating material, there is a problem in that the adhesion to the surface of the fertilizer particles, which is an inorganic substance, is poor, and voids are formed between the film and the particles, resulting in bubbles.

[0006]

In view of the above facts, the present inventors have proposed a coated fertilizer having a relatively thin film when a thermoplastic resin is used as a coating material and having few particles having film defects. The manufacturing method was examined. As a result, they have found that the amount of film defects generated can be reduced by precoating the surface of the granular fertilizer with wax (first layer) and then coating with a thermoplastic resin (second layer). It is considered that the effect of the precoating by the wax is to improve the adhesion between the second layer and the fertilizer particles and to fill the recesses on the particle surface.

That is, the gist of the present invention is that the first layer containing wax and the second layer containing thermoplastic resin are provided on the surface of the granular fertilizer particles.
A coated granular fertilizer having at least two coating layers, or a coating material comprising at least two layers of a first layer containing a wax and a second layer containing a thermoplastic resin on the surface of the granular fertilizer particles. A method for producing a coated granular fertilizer characterized by coating. Hereinafter, the present invention will be described in detail.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION (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 morphology is preferably closer to a sphere than an angular one.

(2) Coating Material (a) First Layer Wax The type of wax used in the present invention is not particularly limited. Examples include natural waxes such as animal / vegetable waxes, mineral waxes and petroleum waxes, or synthetic waxes such as polyethylene wax and Fischer-Tropsch wax, and compounded waxes obtained by processing these waxes,
Examples thereof include oxide wax and hydrogenated wax. Among them, oxidized paraffin wax and oxidized petrolatum wax obtained by oxidizing petroleum wax are suitable. These waxes can be used alone or as a mixture of two or more kinds.

(B) Resin of the Second Layer Although a thermoplastic resin is used as the coating material for the resin of the second layer, its type is not particularly limited. Examples include polyolefin, polyvinylidene chloride resin, polyvinyl chloride resin, polystyrene resin, polycarbonate, polyamide, polymethylmethacrylate, polyurethane, ethylene-vinyl acetate, etc. Polyolefin resins such as polyethylene and polypropylene, which are highly effective, 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, in the case of coating with a resin having high water permeability as described above, talc, calcium carbonate, clay, diatomaceous earth, siliae, metal oxides, sulfur, etc., for the purpose of adjusting the elution property and increasing the amount of resin, etc. In addition to inorganic
An organic substance such as a surfactant may be added.

(3) Solvent Both the wax of the first layer and the thermoplastic resin of the second layer are dissolved in a solvent to perform a coating operation such as spray coating. At this time, 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 easiness of recovery, the toxicity, the safety, the price, etc. of the compound as the film material. For example,
When a polyolefin resin, particularly low-density polyethylene, is used as the coating material for the second layer, a hydrocarbon solvent such as hexane, octane, toluene, xylene, tetralin or the like, or a chlorinated hydrocarbon solvent such as trichloroethylene or tetrachloroethylene is preferred. . The same solvent as the polyolefin resin can be used for the wax of the first layer.
It is industrially preferable to use the same solvent for both the first layer and the second layer. Regarding the wax, the kind of wax that liquefies at a relatively low temperature of about 100 ° C. can be directly spray-coated on the fertilizer particles without using a solvent.

The concentration of the solution is 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.
Usually used at 0.1 to 30% by weight. 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 for the second layer and tetrachloroethylene is used as the solvent, the concentration of the solution is 1-12% by weight, preferably 3-10.
% By weight. Further, when using oxidized paraffin wax as the first layer wax and tetrachloroethylene as the solvent, the concentration of the solution is 0.01-1% by weight, preferably 0.05-0.5%. In general, many polymer compounds are insoluble in a solvent when they are cold, so heating and stirring are usually required to dissolve them.

(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 the movement of the apparatus itself. Coater (JP-A-7-8869, JP-A-7-31914)
And the like. 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. As a type that vigorously stirs, a Wurster type or a spouted bed type coater in which particles are blown off and circulated and mixed, and a fluidized bed type coater (Japanese Patent Publication No.
Publication). 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 (a) Coating of the first layer The granular fertilizer as a raw material was charged into the coating device of (4), and a spray nozzle was used while keeping the temperature of the product at 50 to 100 ° C. with hot air. Coating is carried out by spraying a wax solution on it. The amount of wax impregnated has an optimum value depending on the particle size and morphology of the granular fertilizer used and the type of resin in the second layer. If it is too small, the fertilizer surface cannot be sufficiently covered, while if it is too large, it elutes in the second layer resin. However, since the second layer resin is softened, it becomes easier to form a film defect. Therefore, the amount of wax impregnated is usually 0.01-0.5 for granular fertilizer.
% By weight, preferably 0.05-0.2% by weight.

(A) Coating of the second layer Coating is performed by spraying the coating material solution under the same conditions as the first layer. At this time, the fertilizer coated with the first layer may be once taken out of the coating apparatus and then again subjected to the second layer coating in the coating apparatus, but industrially, the first layer coating is not performed. After that, it is advantageous to directly perform the second layer coating. The amount of the second layer impregnated depends on the target performance such as the length of the dissolution prevention period, but usually 3 to 20% by weight, preferably 5 to 1% by weight of the granular fertilizer.
5% by weight.

The coated granular fertilizer of the present invention may be provided with a known layer in addition to these two layers. Next, the present invention will be described specifically with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist.

[0017]

【Example】

(Examples 1, 2, 3 and Comparative Example 1) Granular urea was selected as a granular fertilizer used as a raw material, and coated with this by the method described in <Coating method> below to prepare coated urea. Regarding the obtained coated urea, based on the method shown in <Quality evaluation method>, 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 and FIG. Summarized.

<Coating method> (1) Coating device Rotating ventilation coating device (SRTA2 manufactured by Okawara Seisakusho)
-Type) was used. A schematic diagram is shown in FIG.

(2) Preparation of coating solution (a) First layer solution Oxidized paraffin wax (NPS-807 manufactured by Nippon Seiro Co., Ltd.)
0) 10 g to 8 kg of solvent tetrachloroethylene 8
It was dissolved at 0 ° C. to prepare a 0.1% first layer solution. (A) Second layer solution 1.5 kg of low-density polyethylene (“M420” manufactured by Mitsubishi Kasei) with a melting point of 106 ° C. as a coating material, polyoxyethylene nonylphenol ether as an elution regulator (“Emulgen 909” manufactured by Kao)
Weigh 40.5g and use the solvent tetrachloroethylene 2
In addition to 8.5 kg, both materials were dissolved at 80 ° C. to prepare a second layer solution.

(3) Coating Granular urea 8.0 sieved to a particle size of 2.0 to 3.4 mm
kg was charged into the coating apparatus, and 110 ° C. air was blown into the apparatus at a flow rate of 540 Nm 3 / h while rotating the rotary drum at 19 rpm. When the urea product temperature reached 70 ° C., the first layer solution was sprayed at 400 g / min for 20 minutes using a two-fluid nozzle (in the case of 0.1% coating). During this time, the temperature of the blown air was adjusted so that the product temperature was maintained at 70 ° C. Then, the second layer solution was subsequently sprayed for 40 minutes under the same conditions (when the coverage was 10%). When the first layer coating is omitted in the comparative example,
Only the second layer solution was sprayed under the condition that the product temperature was 70 ° C to prepare a coated fertilizer.

<Quality Evaluation> (a) Measurement of Coverage 10 g of the 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.

[0022]

[Equation 1]

(B) Measurement of the number of defective particles 10 g of coated fertilizer was weighed 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 the coated fertilizer is weighed, 200 g of water is added, and the container is hermetically sealed and placed in a 25 ° C. constant temperature bath. 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.

[0025]

[Equation 2]

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

[0027]

[Table 1]

[0028]

According to the coated granular fertilizer of the present invention,
Even with a relatively thin film, there is no film defect, and a good fertilizer with reduced initial elution can be obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing a urea elution pattern in a comparative example of an example of the present invention.

FIG. 2 is a diagram showing an example of a coating device used in the present invention.

Claims (7)

[Claims] 1. A first method comprising wax on the surface of granular fertilizer particles.
A coated granular fertilizer having at least two coating layers, a layer and a second layer containing a thermoplastic resin. 2. The coated granular fertilizer according to claim 1, wherein the wax is an oxidized paraffin wax or an oxidized petrolatum wax. 3. The coated granular fertilizer according to claim 1, wherein the weight% of the coating material of the first layer with respect to the raw material granular fertilizer is 0.05 to 0.2%. 4. The coated granular fertilizer according to claim 1, wherein the thermoplastic resin is a polyolefin resin. 5. The coated granular fertilizer according to claim 1, wherein the weight% of the coating material of the second layer with respect to the raw material granular fertilizer is 5 to 15%. 6. A first surface containing wax on the surface of granular fertilizer particles
A method for producing a coated granular fertilizer, which comprises coating with a coating material comprising at least two layers, a layer and a second layer containing a thermoplastic resin. 7. The method for producing a coated granular fertilizer according to claim 6, wherein the coating method is a spray coating method.