JPH08225387A - Production of coated granular fertilizer - Google Patents

Abstract

PURPOSE: To obtain a coated granular fertilizer having a low initial elution rate during the period of preventing its elution and a relatively thin membrane, and capable of reducing membrane defects. CONSTITUTION: This method for producing a coated granular fertilizer using a thermoplastic resin as a coating material, comprises forming a membrane on the surface of the fertilizer at <=(Tm-10) deg.C material temperature and then heat-treating the membrane at >=(Tm-30) deg.C for 0.05-10hr by taking Tm as the melting point of the resin.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing coated granular fertilizer in which granular fertilizer is coated with a thermoplastic resin film to control the dissolution rate.

[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 sustainable fertilizers have been developed in the past, and recently, coated fertilizers in which the surface of the fertilizer is coated with a thin film of a polymeric substance have attracted attention.
Furthermore, looking at the fertilizer component elution pattern, especially for paddy rice, the so-called time capsule type or sigmoid type (hereinafter abbreviated as S type) in which the fertilizer component begins to elute after a certain period of about 30 to 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]

[Problems to be Solved by the Invention] As one of the requirements for such S-type coated fertilizers, during the period during which the fertilizer components are not eluted during the aforementioned 30 to 70 days (hereinafter referred to as "elution prevention period"). The elution rate can be 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.

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 thermoplastic resin film, a method in which a resin dissolved in an appropriate solvent is sprayed on granular fertilizer under a hot air stream, and the film is laminated by removing the solvent by drying. (So-called spray coating) is conventionally used. But with this method,
Particles adhere to each other during spraying, and they peel off during drying.Breakage of the surrounding gas during spraying and bursting of bubbles in the film due to residual solvent vapor, etc. There is a problem that a film defect is likely to occur due to particles colliding with the vessel wall of the apparatus and cracking of the film. As a countermeasure to this, a method of increasing the film thickness has been conventionally taken, but this would increase the cost of the film material and reduce the amount of fertilizer active ingredient of the coated fertilizer by the film thickness, thus reducing the commercial value. . Further, since the dissolution prevention period is proportional to the film thickness to some extent, making the film thicker than necessary is not preferable from the viewpoint of elution control of fertilizer components. 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.

[0005]

In view of the above facts, the present inventors have studied a method for producing a coated fertilizer having a relatively thin film and having few particles having film defects, as a result,
It has been found that, when the coating film of the thermoplastic resin is formed by spray coating, the coating defects which can be recognized from the appearance as described above are reduced as the product temperature of the granular fertilizer is lowered from the melting point of the resin. However, the lower the product temperature, the insufficient fusion between the film layers stacked by spray drying, and the formation of a uniform resin layer becomes difficult. As a result, water gradually penetrates through the gaps between the resin layers, resulting in a problem that the elution prevention period becomes shorter than intended, and reproducibility is lost. Therefore, once the film was formed at a low temperature and then heat-treated at a temperature close to the melting point, the fine gaps between the resin layers were fused, and as a result, a coated fertilizer having a uniform resin layer with no holes in the film could be obtained. The present invention was found out and the present invention was reached. That is, the gist of the present invention is that when a coated fertilizer is produced by using a thermoplastic resin as a coating material, a film is formed on the fertilizer surface at a product temperature of (Tm −10) ° C. or lower, where the melting point of the resin is Tm. Then, at a temperature of (Tm -30) ° C or higher,
It exists in the manufacturing method of the coated granular fertilizer characterized by performing heat processing for 05 to 10 hours.

The present invention will be described in detail below. (1) Coated granular fertilizer 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, potassium sulfate, and ammonium phosphate, granular fertilizers containing multiple components such as N ₂ , K ₂ O and P ₂ O ₅ are the original fertilizers of the present invention. Used for. The particle size and shape of fertilizer are not particularly limited, but generally 1 to 4 mm
Then, particles having a spherical shape or a shape close to a spherical shape are preferable to those having an angular shape or a very irregular shape.

(2) Coating material A thermoplastic resin is used as the coating material.
There is no particular limitation. Examples include polyolefin, polyvinylidene chloride resin, polyvinyl chloride resin, polystyrene resin, polycarbonate, nylon, polymethylmethacrylate, polyurethane, and the like. Polyolefin resins such as polypropylene and polypropylene are suitable. These resins can be used alone or as a mixture of two or more kinds. In addition to the thermoplastic resin, other inorganic substances or organic substances may coexist and be coated as long as the purpose of coating is not impaired. 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 substances, surfactants and organic substances such as wax may be added.

(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 thermoplastic resin that is 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. 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 used and the spray pressure so that the viscosity is such that an appropriate spray state is obtained. 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. Further, in general, many polymer compounds are insoluble in a solvent when they are cold, so that 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 stirring the particulate matter and sufficiently bringing it into contact with the air flow. When classified according to the mixing and stirring method, examples of the type of apparatus for mixing and stirring using a stirring blade include a Henschel mixer and a Nauter mixer. A rotary drum type coater (Japanese Patent Application Laid-Open No. 52-61216) and a rotary pan type coater (Japanese Patent Application Laid-Open No. Hei.
85873), rotary drop coater (Japanese Patent Application No. 5-139)
376, 5-185612, 5-342527) and the like. Further, a vibrating flow device (Japanese Patent Laid-Open No. 1-245847) which stirs by vibrating force is preferable because a large amount of granular substance can be vigorously stirred. Examples of the type that is vigorously stirred include a Wurster type or jet-bed type coater in which particles are blown off 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 a two-fluid spray nozzle and spraying at appropriate locations 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 manufacturing method of the present invention is divided into two steps. The first stage is
This is a step in which the product temperature of the granular fertilizer is maintained at a temperature lower than the melting point of the thermoplastic resin as the coating material, and a resin film is formed on the fertilizer surface by spray coating in the coating device.
Here, the product temperature refers to the surface temperature of the granular fertilizer, and is the temperature measured when the fertilizer and the temperature measuring terminal are brought into contact with each other in a state where there is substantially no influence of the surrounding hot air flow. From the viewpoint of reducing film defects, the product temperature is preferably lower than the melting point of the resin, but if it is lowered too much, the removal rate of the solvent decreases,
The film may not be formed. On the other hand, if the melting point is too close to the melting point, the resin softens and the film defects due to the above-mentioned (1) to (3) occur. Therefore, the product temperature is (Tm-
The temperature is kept at 10) C or lower, preferably below (Tm-30) C. On the other hand, the lower limit value is 20 ° C, preferably 30 ° C. The spray coating time is determined depending on the coating solution concentration, the solvent removal rate, the coating rate, etc.
It is 1 to 10 hours, preferably 0.2 to 3 hours. For example, to granular urea, low density polyethylene having a melting point of 106 ° C. as shown in the following examples is used as a coating material, perchlorethylene is used as a solvent, and a 5% concentration coating solution is sprayed at a temperature of 80 to 100 ° C. If you do, the product temperature is 30 to 7
0 ° C., preferably 45-65 ° C., spraying time 0.5-
1.5 hours. The temperature of the product is adjusted and maintained with a hot air stream that removes the solvent. As a matter of course, the temperature of the hot airflow needs to be equal to or higher than the product temperature, and the flow rate is determined from the solvent removal rate.
The amount of the resin film attached is usually 3 to 20% by weight, and preferably 5 to 15% by weight, based on the granular fertilizer, although it depends on the target performance such as the elution prevention period. The melting point of the thermoplastic resin can be measured by various methods, and for example, a method using DSC can be mentioned.

The second step is a step of heat-treating the coated fertilizer produced in the first step. Here, the fine gaps generated in the coating layer are fused, but the heating temperature is too low, the heat treatment effect becomes insufficient, and if it is too high, the coated fertilizers are fused to form a lump, Problems such as fusion with the wall of the heating device occur. Therefore, the heating temperature is (Tm -3
0) ° C to (Tm +100) ° C, preferably (Tm-
20) ° C to (Tm +50) ° C. The heating time mainly depends on the temperature, but is usually 0.05 to 10 hours, preferably 0.5 to 2 hours. As the heating device, a device such as a general dryer or electric furnace can be used. Also,
You may heat with a hot air stream as it is in the coating device used at the 1st step. However, stirring the coated fertilizer during heating for the purpose of improving heat transfer rather increases the number of film defects, so heating in a stationary state is preferable. Although the coated fertilizer production method of the present invention has been described by dividing it into two stages, it is not particularly necessary to clearly divide it into two stages. For example, during film formation (during spray coating), the product temperature is initially kept low, A method of gradually raising the temperature and finally reaching the heating temperature in the second stage may be adopted. Next, the present invention will be specifically described by way of examples, but the present invention is not limited to the following examples unless it exceeds the gist.

[0012]

【Example】

[Example 1] Granular urea was selected as a fertilizer, which was coated by the method described in <Coating method> below to prepare coated urea, and then heat treated by the method described in <Heat treatment>. With respect to the coated urea thus obtained, the coverage, the number of film defect particles, and the elution pattern of urea in water were examined based on the method shown in <Quality evaluation method>, and the results are shown in Table 1.
And summarized in FIG. As a coating device, a falling cylinder (4) (cross section 0) installed in the drum while circulating granular fertilizer (3) by a bucket (2) provided inside a rotating drum (1) (inner diameter 3.8 m) .15 x 0.25
A rotary dropping coater was used in which the fertilizer was continuously dropped into the dropping cylinder and the coating solution was sprayed into the dropping cylinder (see FIG. 2).

<Coating method> (1) 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 polyoxyethylene nonylphenol ether (Emulgen 909 manufactured by Kao) 40 as an elution regulator 0.5 g was weighed and added to 28.5 kg of solvent perchlorethylene, and both materials were dissolved at 80 ° C. to prepare a coating solution.

(2) From the lower part (5) of the drop cylinder of the coating coater, a temperature of 10
After introducing air at 0 ° C. and an empty cylinder speed of 4.4 m / s, the rotation speed of the rotary drum was adjusted to 8 rpm so that the air was discharged from the upper part (6) of the falling cylinder, and then granular urea (particle diameter: 2.
(0-3.4 mm) 10 kg was charged into a coater to make a state in which the fertilizer continuously dropped in the dropping cylinder. Next, the coating solution of (1) was sprayed from the side surface (7) of the upper part of the dropping cylinder for 50 minutes using a one-fluid nozzle under the conditions of a spraying speed of 400 g / min and a spraying pressure of 3 kg / cm ² G. At this time, the temperature of the air introduced into the dropping cylinder was adjusted so that the temperature sensor inserted in the dropping fertilizer at the spraying position maintained 55 ° C. The temperature at this spray position was 55 ° C. when part of the fertilizer dropped was taken out and the product temperature was measured, which was found to be equal to the product temperature during spraying.

<Heat Treatment> 500 g of the coated urea prepared as described above was placed in a beaker and placed in a ventilation drier for 10
It was left at 5 ° C. for 1 hour. <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 rate was calculated from the following equation by drying and weighing this film.

[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.
Is added and left in constant temperature water at 40 ° C. for 1 hour, and then the coated fertilizer is collected by filtration. When the deposited ink is washed with water, the color of the ink remains in the defective portion of the film, so that defective particles can be distinguished. Count three types of particles, partially colored particles, particles that are entirely colored due to the large defect portion, and shell particles that have already eluted only urea to form a film. To do. The total number of particles of coated urea (10 g) 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 dissolved in water is measured by a total nitrogen analyzer, and the dissolution rate is calculated by the following formula.

[0019]

[Equation 2]

When the cumulative value of the dissolution rate is plotted against the number of days, the dissolution pattern can be drawn. [Example 2] After coating under the same conditions as in Example 1, heat treatment was performed at 90 ° C for 2 hours. The quality of the obtained coated urea was evaluated by the method described in Example 1. The results are shown in Table 1 and FIG. [Example 3] In the coating process of Example 1, the product temperature was set to 65 ° C,
Others were coated under the same conditions. After that, 105 ℃,
After heat treatment for 1 hour, the quality of the obtained coated urea was evaluated by the method described in Example 1. The results are shown in Table 1 and FIG.

Example 4 In the coating step of Example 1, coating was carried out under the same conditions except that the product temperature was 70 ° C. Then, heat treatment was carried out at 105 ° C. for 1 hour, and the quality of the obtained coated urea was evaluated by the method shown in Example 1. The results are shown in Table 1 and FIG. [Comparative Example 1] Coating was performed under the same conditions as in Example 1. Thereafter, heat treatment was not performed, and the quality of the obtained coated urea was evaluated by the method described in Example 1. The results are shown in Table 1 and FIG.

[Comparative Example 2] Coating was performed under the same conditions as in Example 3. Thereafter, heat treatment was not performed, and the quality of the obtained coated urea was evaluated by the method described in Example 1. The results are shown in Table 1 and FIG. [Comparative Example 3] In the coating process of Example 1, the product temperature was set to 80 ° C,
Others were coated under the same conditions. Thereafter, heat treatment was not performed, and the quality of the obtained coated urea was evaluated by the method described in Example 1. The results are shown in Table 1 and FIG. [Comparative Example 4] In the coating process of Example 1, the product temperature was set to 85 ° C,
Others were coated under the same conditions. Thereafter, heat treatment was not performed, and the quality of the obtained coated urea was evaluated by the method described in Example 1. The results are shown in Table 1 and FIG.

[0023]

[Table 1]

As can be seen from Table 1 and FIG.
4 and Comparative Examples 3 and 4 each have an elution prevention period of 40 to 50 days, but the urea coated at the high product temperature of Comparative Examples 3 and 4 has many particles with film defects, and therefore has a large amount of initial elution. .
On the other hand, the coated fertilizer coated and heat-treated at a product temperature of Tm-10 ° C or lower has a low initial dissolution rate and a clear dissolution prevention period. On the other hand, even if the samples were coated at 55 and 65 ° C. product temperature and were not heat-treated as in Comparative Examples 1 and 2, the number of defective particles was small, but there was no clear elution prevention period. Thus, the effect of the present invention is particularly remarkable as a method for producing an S-type coated fertilizer.

[0025]

Industrial Applicability The coated granular fertilizer obtained by the production method of the present invention has a low initial elution rate, a clear elution prevention period, and a small number of defective particles. It has a great advantage as a manufacturing method.

[Brief description of drawings]

FIG. 1 is a diagram showing an elution pattern of urea obtained in Examples and Comparative Examples of the present invention.

FIG. 2 is a schematic view of a rotary drop coater used in an example of the present invention.

[Explanation of symbols]

 1 rotating drum 2 bucket 3 granular fertilizer 4 falling cylinder 5 hot air inlet 6 exhaust port 7 spray port 8 motor

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yuka Ota 1-1 Kurosaki Shiroishi, Hachimannishi-ku, Kitakyushu City Mitsubishi Chemical Corporation Kurosaki Development Laboratory

Claims (1)

[Claims] 1. When producing a coated fertilizer using a thermoplastic resin as a coating material, when the melting point of the resin is Tm, (T
A method for producing a coated granular fertilizer, comprising forming a film on the fertilizer surface at a product temperature of m-10) ° C or lower, and then performing heat treatment at a temperature of (Tm-30) ° C or higher for 0.05 to 10 hours. .