Coated granular fertilizer

Abstract

To provide a coated granular fertilizer superior in biodegradability and controllability with respect to elution of a fertilizing component.SOLUTION: A coated granular fertilizer includes a granular fertilizer and a coating that covers a surface of the granular fertilizer, where the coating contains polybutylene succinate (A) that satisfies the following condition (i): (i) a melt flow rate (MFR) measured with 2.16 kg load at 190°C in accordance with ISO 1133 falls in a range of 0.1-20 g / 10 minutes.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This invention relates to coated granular fertilizer. [Background technology]

[0002] Coated granular fertilizers, in which the surface of granular fertilizer is covered with a coating material such as synthetic resin, are known. Coated granular fertilizers offer excellent control over the leaching of fertilizer components, and have been shown to have effects such as reducing labor in agricultural work and lowering the environmental burden caused by fertilizer components. Cultivation techniques using such coated granular fertilizers have been spreading in recent years. However, many conventional coated fertilizers are coated with persistent resins, and the persistence of these resins in the coating after the fertilizer components have leached out into the environment is a problem. To solve this problem, for example, Patent Document 1 discloses a coated fertilizer coated with a polyolefin-based coating to which organometallic complexes have been added, and which exhibits excellent coating degradation properties. Patent Document 2 discloses a fertilizer coating composition using biodegradable raw materials obtained by reacting a polyester polyol component with a polyisocyanate component. Patent Document 3 discloses a fully biodegradable coated granular fertilizer in which the surface of the granular fertilizer coated with biodegradable resin is covered with a biodegradable coating having at least ammonia nitrogen on its surface or inside. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 10-231190 [Patent Document 2] Japanese Patent Publication No. 2009-1467 [Patent Document 3] Japanese Patent Application Publication No. 10-291882 [Overview of the project] [Problems that the invention aims to solve]

[0004] However, it has been pointed out that the technology described in Patent Document 1 may remain in the ocean for a long period of time in fragmented form during the decomposition process of the coating. Furthermore, the biodegradability of the coating in the technology described in Patent Document 2 was not satisfactory. The technology described in Patent Document 3 had the problem that the biodegradable resin had high moisture permeability, making it difficult to suppress the leaching of fertilizer components from the coated granular fertilizer. Therefore, the object of the present invention is to provide a coated granular fertilizer that is excellent in biodegradability and control of the leaching of fertilizer components. [Means for solving the problem]

[0005] The inventors diligently studied to solve the above problems. As a result, they found that the above problems can be solved by having the following configuration, and thus completed the present invention. The present invention relates, for example, to the following [1] to [4]. [1] A coated granular fertilizer having granular fertilizer and a coating film covering the surface of the granular fertilizer, A coated granular fertilizer wherein the coating contains polybutylene succinate (A) that satisfies the following requirement (i). (i) The melt flow rate (MFR), measured at 190°C and a 2.16 kg load in accordance with ISO 1133, is in the range of 0.1 to 20 g / 10 min. [2] The coated granular fertilizer according to [1], wherein the melt flow rate (MFR) of the polybutylene succinate (A) is in the range of 4 to 6 g / 10 min. [3] The coated granular fertilizer according to [1] or [2], wherein the material forming the coating contains 30 to 100% by mass of the polybutylene succinate (A). [4] The coated granular fertilizer according to any one of [1] to [3], wherein the ratio of the coating to 100% by mass of the coated granular fertilizer is 3 to 20% by mass. [Effects of the Invention]

[0006] According to the present invention, it is possible to provide a coated granular fertilizer that is excellent in biodegradability and control of the elution of fertilizer components. [Brief explanation of the drawing]

[0007] [Figure 1] Figure 1 shows an example of an apparatus for producing the coated granular fertilizer of the present invention. [Modes for carrying out the invention]

[0008] Next, the present invention will be described in detail. <Coated granular fertilizer> The coated granular fertilizer of the present invention is a coated granular fertilizer having a granular fertilizer (hereinafter also referred to as "core material") and a coating that covers the surface of the granular fertilizer, wherein the coating contains polybutylene succinate (A) (hereinafter also simply referred to as "polybutylene succinate (A)") that satisfies the following requirement (i). (i) The melt flow rate (MFR), measured at 190°C and a 2.16 kg load in accordance with ISO 1133, is in the range of 0.1 to 20 g / 10 min.

[0009] <Polybutylene succinate (A)> Polybutylene succinate (A) is a polybutylene succinate that is a copolymer of 1,4-butanediol and succinic acid, and satisfies the following requirement (i). (i) The melt flow rate (MFR), measured at 190°C and a 2.16 kg load in accordance with ISO 1133, is in the range of 0.1 to 20 g / 10 min.

[0010] Polybutylene succinate (A) has a melt flow rate (MFR) measured at 190°C and a 2.16 kg load in accordance with ISO 1133, preferably 0.1 to 20 g / 10 min, more preferably 0.1 to 10 g / 10 min, even more preferably 2 to 10 g / 10 min, and particularly preferably 4 to 6 g / 10 min. When the MFR of polybutylene succinate (A) is within the above range, film formation is good, so coating granular fertilizers with few defects in the film and a small initial elution amount of fertilizer components can be produced. More specifically, if the MFR is too low, the viscosity of the coating liquid containing the coating material becomes high, and as a result, the coating liquid droplets do not spread sufficiently on the granular fertilizer, increasing film defects and making it difficult to sufficiently suppress elution. Also, if the MFR is too high, the viscosity of the coating liquid becomes too low, so after the coating liquid droplets adhere to the granular fertilizer, they are likely to scatter without staying on the granular fertilizer, increasing film defects and coating unevenness, and easily causing problems with the strength of the film against elution and impact. In the production method of dissolving or dispersing the coating material in a solvent and spraying it, this tendency is remarkable.

[0011] The density of polybutylene succinate (A) measured in accordance with ISO 1183 is preferably 1.1 to 1.4 g / cm 3 and more preferably 1.2 to 1.3 g / cm 3 When the density of polybutylene succinate (A) is within the above range, the moisture permeability is low and there is a tendency to easily suppress elution.

[0012] The melting point of polybutylene succinate (A) measured in accordance with ISO 3146 is preferably 100 to 130 °C, more preferably 110 to 120 °C. When the melting point of polybutylene succinate (A) is within the above range, it is easy to control the precipitation of the resin during coating, so there is a tendency for good film formation.

[0013] The production method of polybutylene succinate (A) is not particularly limited, and known methods can be used. For example, polybutylene succinate (A) can be synthesized by polycondensation reaction of 1,4-butanediol and succinic acid. Also, polybutylene succinate (A) may be added with a small amount of binder to the polycondensation reaction product and controlled to a desired high molecular weight by a bonding reaction.

[0014] Commercially available products can also be used as polybutylene succinate (A). Specifically, BioPBS manufactured by Mitsubishi Chemical Corporation TMExamples include FZ91. Furthermore, any polybutylene succinate from other manufacturers that meets requirement (i) can be preferably used. These commercially available products may be used individually or in combination of two or more types.

[0015] Polybutylene succinate (A) is a type of biodegradable resin that biodegrades in natural environments where microorganisms are present (in soil, freshwater, seawater, and compost), ultimately breaking down into carbon dioxide and water, thus minimizing environmental impact. It also exhibits mechanical properties (strength and elongation) similar to polyolefins, making it tough. Furthermore, its low glass transition temperature in the amorphous region gives it excellent cold resistance. In addition, the extremely low number of carboxyl groups at the ends of its molecular chains results in excellent thermal stability. Because polybutylene succinate (A) possesses these excellent properties, coatings containing polybutylene succinate (A) are tough, cold-resistant, thermally stable, and highly biodegradable. The coated granular fertilizer of the present invention, having the aforementioned coating, exhibits excellent biodegradability and superior control over the leaching of fertilizer components. More specifically, the coated granular fertilizer of the present invention has a low leaching rate of fertilizer components in the initial stages after application, thus minimizing adverse effects on plant growth.

[0016] <Granular fertilizer> The granular fertilizer used in this invention may contain one or more fertilizer components such as nitrogen, phosphorus, and potassium. Specifically, in addition to nitrogenous fertilizers, phosphate fertilizers, and potassium fertilizers, fertilizers containing trace elements such as calcium, magnesium, sulfur, iron, manganese, and boron, as well as silicon, which are essential plant elements, can be used as needed. Fertilizers containing nitrification inhibitors or pesticide components are also acceptable. Among these, nitrogenous fertilizers containing ammonium sulfate, urea, ammonium nitrate, etc., which have high water solubility and are easily released into the environment, potassium fertilizers containing potassium sulfate, potassium chloride, etc., and compound fertilizers containing urea, ammoniacal nitrogen, and nitrate nitrogen are preferred, with urea being more preferred due to its low unit cost per fertilizer component. Fertilizer components may be used individually or in combination of two or more types.

[0017] The granular fertilizer may contain other components as long as they do not impair the effects of the present invention. Examples of other components contained in the granular fertilizer include carriers, binders, surfactants, molasses, animal oils, vegetable oils, hydrogenated oils, fatty acids, fatty acid metal salts, paraffin, waxes, and glycerin, which may be used individually or in combination of two or more.

[0018] The method for producing the granular fertilizer used in the present invention is not particularly limited and can be produced using known granulation methods. For example, the granular fertilizer can be produced using a fluidized bed granulation method, a rolling granulation method, a coated granulation method, an adsorption granulation method, and the like.

[0019] The shape of the granular fertilizer used in the present invention is not particularly limited, but a spherical shape is preferred from the viewpoint of easily uniformly coating the surface with the coating material. Specifically, the shape of the granular fertilizer is preferably such that the circularity coefficient, calculated by the following formula (I), is between 0.7 and 1, more preferably between 0.75 and 1, and most preferably between 0.8 and 1. The maximum value of the circularity coefficient is 1, and the closer it is to 1, the closer the granular fertilizer particles are to a perfect circle, and the smaller the circularity coefficient becomes as the particle shape deviates from a perfect circle. Circularity coefficient = {(4π × projected area of ​​the particle) / (length of the outline of the particle projection)} 2} ...Formula (I)

[0020] In the present invention, the granular fertilizer preferably has an average particle size of 1 to 10 mm, more preferably 2 to 5 mm. Having the granular fertilizer within this range is preferable because it facilitates the creation of coated granular fertilizer by coating its surface. As granular fertilizer, commercially available granular fertilizer or manufactured granular fertilizer can be used, and the average particle size can be adjusted to the desired value by using a sieve or the like as appropriate. In this invention, the average particle size refers to the average particle size calculated by a particle size distribution analyzer such as dynamic image analysis.

[0021] In the present invention, commercially available granular fertilizers that can be used include, for example, urea (manufactured by PETRONAS Fertilizer (Kedah) Sdn. Bhd) as granular urea, ammonium phosphate (manufactured by Central Green Co., Ltd.) as granular ammonium phosphate, and potassium sulfate (manufactured by Asahi Agria Co., Ltd.) as granular potassium.

[0022] <Coating> The coated granular fertilizer of the present invention comprises granular fertilizer and a coating that covers the surface of the granular fertilizer. The coating contains polybutylene succinate (A) as the material that forms the coating (hereinafter also referred to as the "coating material"). The coated granular fertilizer of the present invention preferably contains 30 to 100% by mass of polybutylene succinate (A) in 100% by mass of the material forming the coating, and more preferably 60 to 100% by mass. If the content of polybutylene succinate (A) in 100% by mass of the material forming the coating is less than 30% by mass, the initial elution amount of fertilizer components may increase.

[0023] Other biodegradable resins (B) besides polybutylene succinate (A) may be added to the material that forms the coating, as long as it does not impair the effects of the present invention. The melting point of the other biodegradable resin (B) is 70°C or higher. Other biodegradable resins (B) include starch polyester, cellulose acetate, polylactic acid, polyhydroxybutyrate, poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), (poly(3-hydroxybutyrate-co-3-hydroxyvalerate)), starch, cellulose, lignin, chitin, chitosan, polyglycolic acid, polylactic acid / polyether copolymer, butanediol / long-chain dicarboxylic acid copolymer, aliphatic aromatic polyester, polytetramethylene adipate-co-terephthalate, polyethylene terephthalate succinate, polyethylene terephthalate copolymer, polybutylene succinate adipate, polydioxane, polyvinyl alcohol, polybutylene adipate terephthalate, and polybutylene succinates other than polybutylene succinate (A).

[0024] Among the other biodegradable resins (B), since a manufacturing method from biomass raw materials has been established, if environmental considerations are taken into account, polybutylene succinate (A), polybutylene succinate adipate, polyhydroxybutyrate, poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) are preferred. From the viewpoint of being able to utilize natural materials, starch, cellulose acetate, lignin, chitin, and chitosan are preferred. From the viewpoint of being resistant to breakage when force is applied, polylactic acid and polyglycolic acid, which have excellent physical properties, are preferred. From the viewpoint of resistance to impact, polybutylene adipate terephthalate, which has excellent film flexibility, is preferred.

[0025] Other biodegradable resins (B) may be used alone or in combination of two or more. Other biodegradable resins (B) may be mixed with polybutylene succinate (A) to form a coating, or a multilayer coating may be formed by layering a polybutylene succinate (A) layer with a coating of the other biodegradable resin layer.

[0026] When adding another biodegradable resin (B) to the material forming the coating, the other biodegradable resin (B) is preferably present in an amount of 0.1 to 70% by mass, and more preferably 5 to 30% by mass, of 100% by mass of the material forming the coating. Within the above range, the effects of the present invention are unlikely to be impaired.

[0027] The material forming the coating may contain a biodegradable resin with a melting point lower than 70°C, but its content is preferably 70% or less, more preferably 50%, and even more preferably less than 10% of 100% by mass of the material forming the coating. It is even more preferable that the material forming the coating does not contain polycaprolactone, which is a biodegradable resin with a melting point lower than 70°C. When biodegradable resins with a melting point lower than 70°C, particularly those with a melting point around 60°C and a molecular weight of 10,000 or more, are included in the material forming the coating, blocking occurs during the coating process, where the coated granular fertilizers fuse together. Examples of biodegradable resins with a melting point around 60°C and a molecular weight of 10,000 or more include polycaprolactone.

[0028] Fillers may be added to the film-forming material, to the extent that they do not impair the effects of the present invention. Examples of fillers include plate-shaped fillers such as talc, mica, and hydrotalcite, inorganic substances such as calcium carbonate, silica, clay, various crushed ores, and sulfur, as well as organic substances such as surfactants. Fillers may be used individually or in combination of two or more types. Because they are relatively inexpensive, inorganic fillers are preferred, plate-shaped fillers are more preferred because they improve the strength of the coating and cause less deterioration in elution control when added, and talc is even more preferred.

[0029] The median diameter of the filler is preferably 100 μm or less, and more preferably 1 to 50 μm. When the median diameter is within the above range, problems such as the coating peeling off during film formation or the coating resin composition clogging spray nozzles are less likely to occur if the median diameter is too large. Even if the median diameter of the filler is larger than the thickness of the coating and a portion of it protrudes from the surface of the coating, the intended purpose is achieved as long as a portion of it is incorporated into the coating and adheres to it. The median diameter can be measured using, for example, the laser diffraction particle size distribution analyzer or other known methods.

[0030] When incorporating fillers, depending on the type of filler, it is preferable that the filler be present in 20 to 80% by mass, and more preferably 40 to 70% by mass, of 100% by mass of the film-forming material. If the filler content in 100% by mass of the film-forming material is less than 20% by mass, the effect of improving film strength by the addition tends to be small. If the filler content in 100% by mass of the film-forming material exceeds 80% by mass, the elution control tends to be significantly worse.

[0031] In the present invention, the ratio of the material forming the coating to 100% by mass of the coated granular fertilizer is defined as the coating rate, and the coating rate can be expressed by the following formula (II). Coverage rate (%) = (Mass of material forming the coating) / (Mass of coated granular fertilizer) × 100 ...Formula (II) The mass of the material forming the coating was calculated by subtracting the mass of the uncoated granular fertilizer from the mass of the coated granular fertilizer. Furthermore, the average mass of 350 units of either the coated or uncoated granular fertilizer was used for each calculation. The coverage rate varies depending on the shape and size of the granular fertilizer, but is preferably 3-20%, more preferably 5-12%. A coverage rate within this range is preferable because it provides excellent control over the leaching of fertilizer components.

[0032] <Controllability of fertilizer component leaching> The controllability of fertilizer component leaching in coated granular fertilizers can be evaluated, for example, by the leaching rate (%) of fertilizer components when the coated granular fertilizer is immersed in water. The leaching rate (%) of fertilizer components can be expressed by the following formula (III). Dissolution rate (%) = (Mass of dissolved fertilizer components) / (Mass of fertilizer components contained in coated granular fertilizer) × 100 ...Formula (III)

[0033] The leaching rate of fertilizer components can be measured, for example, by placing coated granular fertilizer in water at 25°C and quantitatively analyzing the fertilizer components that leach into the water over time. An example of a quantitative analysis method for fertilizer components is the method proposed by the Environmental Technology Research Institute of the Ministry of Agriculture, Forestry and Fisheries ("Detailed Explanation of Fertilizer Analysis Methods," edited by Masayoshi Koshino, 1988, published by Yokendo).

[0034] Fertilizer components are generally water-soluble, and if there are defects in the coating, many fertilizer components will dissolve simultaneously with fertilization, resulting in insufficient dissolution control. The dissolution control properties of the coated granular fertilizer of the present invention preferably include a dissolution rate of 30% by mass or less after 2 hours in water at 25°C, and more preferably 20% by mass or less.

[0035] <Method for producing coated granular fertilizer> The method for producing the coated granular fertilizer of the present invention is not particularly limited. The coated granular fertilizer can be produced by coating the surface of a core material with the above-mentioned coating material. For example, known techniques such as spraying a molten and dispersed coating material onto the surface of a core material, spraying a coating material obtained by dissolving or dispersing the coating material in a solvent onto the surface of a core material (solvent spray method), spraying a monomer onto the surface of a core material and allowing it to react on the surface to form a resin (coating), and a dipping method in which the core material is immersed in the coating material can be used. Among these, the solvent spray method is preferred. When dissolving or dispersing a coating material in a solvent, the solvent is not particularly limited as long as it can dissolve or disperse the coating material, but a solvent with a boiling point of 30°C or higher and 150°C or lower is preferred. If the boiling point is below 30°C, condensation and recovery are difficult, and if it is above 150°C, drying is difficult. From the viewpoint of non-flammability or flame retardancy, halogen-based solvents or water are preferred, and examples of halogen-based solvents include dichloromethane, chloroform, dichloroethane, trichloroethane, trichloroethylene, and perchloroethylene. Solvents can also be used in mixtures. From the viewpoint of environmental impact, solvents other than halogen-based solvents are preferred, and examples include toluene, xylene, acetone, methyl ethyl ketone, methyl isobutyl ketone, ethyl acetate, isopropyl acetate, butyl acetate, tetrahydrofuran, dimethoxyethane, and diethoxyethane.

[0036] The apparatus used for coating is not particularly limited, and examples of coating methods include apparatus employing pan coating, jet coating, fluidized bed coating, rolling coating, dry coating, or combinations thereof. In the present invention, it is preferable to use jet coating or fluidized bed coating.

[0037] One aspect of the present invention is a coated granular fertilizer having granular fertilizer and a coating film covering the surface of the granular fertilizer, wherein the coating film contains polybutylene succinate (A) that satisfies the following requirement (i), and the coated granular fertilizer is manufactured by spraying a coating solution obtained by dissolving or dispersing the coating material in a solvent onto the surface of the granular fertilizer. (i) The melt flow rate (MFR), measured at 190°C and a 2.16 kg load in accordance with ISO 1133, is in the range of 0.1 to 20 g / 10 min. This type of coated granular fertilizer is produced by spraying a coating solution, in which polybutylene succinate (A) is dissolved or dispersed in a solvent, onto the surface of the granular fertilizer. This results in a coating with few defects, thus providing excellent control over the leaching of fertilizer components.

[0038] One aspect of the present invention is a method for producing coated granular fertilizer, comprising the following steps (α) to (δ): removing dust from a fluid gas containing a solvent discharged from a coating device using a dust remover, recovering the solvent using a condenser, heating the gas separated in the condenser using a heater, and circulating and reusing the recovered solvent and the heated gas. Coating solution preparation step (α): A step of preparing a coating solution by dissolving or dispersing a coating material containing polybutylene succinate (A) in a solvent; Coating step (β): A step in which the coating liquid is sprayed onto the core material under a flowing gas stream within the coating apparatus, and the solvent in the coating liquid is instantly evaporated and dried to form a coating on the surface of the core material; Degassing step (γ): A step of removing the solvent contained in the core material on which the coating has been formed by the coating step (β) by degassing with air, thereby reducing its concentration to 500 ppm or less relative to the core material on which the coating has been formed; and Recovery process (δ): A process of recovering the solvent from the gas used for degassing by air in the degassing process (γ) using a condenser and / or activated carbon.

[0039] As a preferred embodiment of the method for manufacturing coated granular fertilizer, the fluidized bed coating method will be described with reference to the coating apparatus shown in Figure 1. The fluidized gas flows from the bottom to the top of the fluidized bed 1, passes through the dust collector 6, is cooled in the condenser 7, and the solvent is condensed and recovered. The gas that has passed through the condenser 7 is heated by passing through the heater 12 and circulated back to the fluidized bed 1 as hot air. By employing such a closed system, the solvent is not discharged to the outside. The gas flow is carried out by the blower 8, but its installation position is not particularly limited. The core material is introduced through an inlet located on the side of the fluidized bed 1, and the fluidized gas introduced from the bottom of the fluidized bed 1 and the agitators located at the bottom of the fluidized bed 1 create a fluidized state. At this time, the core material temperature can be adjusted by the gas flow rate and the temperature of the fluidized gas. The fluidized gas flow rate is adjusted while being measured with a flow meter, and the temperature of the fluidized gas is adjusted while measuring the core material temperature and the exhaust temperature (temperature at the top of the fluidized bed 1).

[0040] In the coating solution preparation step (α), the coating solution is prepared by adding other materials as needed to polybutylene succinate (A), weighing out the coating material, and dissolving or dispersing this coating material in a solvent. When using materials such as fillers that are insoluble in the solvent, it is preferable to stir vigorously in order to uniformly disperse them in the coating solution. The coating solution is preferably adjusted so that the proportion of the coating material is typically 0.1 to 20% by mass, particularly preferably 1 to 15% by mass, and even more preferably 2 to 10% by mass.

[0041] In the coating process (β), the coating apparatus transports the coating material to the core material 3, which is in a fluid state, via piping 5, and sprays it using a spray nozzle 2. Simultaneously, it sprays the coating material onto the surface of the core material 3, and at the same time, it uses a high-temperature fluidized gas from the bottom of the fluidized bed 1 to instantly evaporate and dry the solvent in the coating liquid adhering to the surface of the core material. The spraying time varies depending on the concentration of the resin in the coating liquid, the spraying speed of the coating liquid, the coating rate, etc., and these should be appropriately selected according to the purpose.

[0042] For ventilation in the degassing process (γ), a gas that does not contain a solvent, such as heated nitrogen, air, or water vapor, is preferred. Degassing may be performed using the coating device described above, but it may also be performed using a separate degassing device.

[0043] The refrigerant used in the condenser used in the recovery process (δ) is not particularly limited, and known refrigerants can be used. Activated carbon is preferred in granular form because it is easier to handle. When treating degassed gas containing a large amount of solvent in the recovery process, it is preferable to reduce the solvent concentration in the condenser and then use activated carbon in combination.

[0044] Other coating devices that can be used in the present invention besides the coating device shown in Figure 1 include, as a fluidized bed type or jet bed type coating device, a device disclosed in Japanese Patent Publication No. 42-24281 and Japanese Patent Publication No. 42-24282 that uses a gas to form a fountain-type fluidized bed of granular fertilizer and sprays a coating agent onto the granular fertilizer dispersion layer formed in the center, and as a rotary type coating device, a device disclosed in Japanese Patent Application Publication No. 7-31914 and Japanese Patent Application Publication No. 7-195007 that uses the rotation of a drum to transport granular material upward by a lifter attached to the inner circumference of the drum, then drops it, and applies a coating agent to the surface of the falling granular material to form a coating film. [Examples]

[0045] The present invention will now be described in more detail with reference to examples, but the present invention is not limited thereto. Unless otherwise specified, "%" in the following examples refers to mass percent.

[0046] <Measuring Melt Flow Rate (MFR)> The melt flow rate (MFR) of polybutylene succinate and polylactic acid used in the examples and comparative examples was measured in accordance with the ISO 1133 method. The melting temperature was 190°C, the piston load of the measuring device was 2.16 kg, and the extrusion time was 10 minutes. The measurement results are shown in Table 1.

[0047] (Example 1) [Manufacturing of coated granular fertilizer] Using the manufacturing apparatus shown in Figure 1, the surface of the granular fertilizer (granular urea) was coated by the following method. In the manufacturing apparatus shown in Figure 1, hot air flowed from the bottom to the top of the fluidized bed 1, passed through the dust collector 6, cooled the gas in the condenser 7, and condensed and recovered the solvent. The gas that passed through the condenser 7 was heated by passing through the blower 8 and heater 12, and circulated back to the fluidized bed 1 as hot air.

[0048] As particle 3, granular urea ("urea" manufactured by PETRONAS Fertilizer (Kedah) Sdn. Bhd, sieved to a particle size of 3.0-4.0 mm, with an average particle size of 3.3 mm and a circularity coefficient of 0.9) was used. The particle size and average particle size were measured using dynamic image analysis (Millitrac JPA: manufactured by Nikkiso Co., Ltd.). 400g of granular urea was added through an inlet located on the side of fluidized bed 1, and the mixture was brought into a fluid state by hot air introduced from the bottom of fluidized bed 1 and a stirring blade installed at the bottom of fluidized bed 1. At this time, the hot air flow rate and hot air temperature were adjusted so that the particle temperature was 60±2℃. The hot air flow rate was adjusted while measuring it with a flow meter installed between blower 8 and fluidized bed 1, and the hot air temperature was adjusted while measuring the particle temperature and exhaust temperature (temperature at the top of fluidized bed 1).

[0049] In the dissolution tank 9 shown in Figure 1, polybutylene succinate (BioPBS manufactured by Mitsubishi Chemical Corporation) is used as the coating material. TM FZ91, density 1.26g / cm 3 100 parts by mass of (ISO1183, melting point 115°C (ISO3146), also known as PBS-1) and 1900 parts by mass of trichloroethylene as the solvent for the coating solution were added and mixed and stirred at 79±2°C for 90 minutes to uniformly dissolve and prepare a uniform spray solution 5 with a concentration of 5% by mass. The dissolution tank 9 was also stirred continuously until the coating was completed.

[0050] The spray liquid 5 was transported at a flow rate of approximately 35.5 ml / min to a spray nozzle 2 installed at the top of the fluidized bed 1 and sprayed onto the granular urea in the fluid. The trichloroethylene contained in the sprayed spray liquid was condensed and recovered by a condenser 7 and stored in a tank 11 before being led to a dissolution tank 9.

[0051] The aforementioned coating operation began when the temperature of the granular urea in the fluidized bed reached 60°C and continued until the coating rate reached 8.4% by mass. Afterward, drying was carried out by blowing only hot air for 10 minutes, while carefully maintaining the particle temperature at 60±2°C and adjusting the temperature of the hot air. Once drying was complete, the coated granular urea was discharged from the outlet 13 at the bottom of the fluidized bed 1, and then degassed by aeration for 0.5 to 1 hour to remove trichloroethylene and obtain coated granular fertilizer. The amount of trichloroethylene contained in 100% by mass of the coated granular fertilizer after degassing was 2.2 ppm. The trichloroethylene-containing gas used for degassing by aeration was recovered by separating and adsorbing the trichloroethylene using activated carbon.

[0052] The manufacturing conditions for coated granular fertilizer can be summarized as follows: Granular urea: 400g Particle temperature during coating: 60℃ Melting temperature: 79±2℃ Spray liquid temperature: 79±2℃ Hot air temperature: 70~80℃ Spray flow rate: 35.5 ml / min

[0053] (Example 2) Polybutylene succinate (BioPBS manufactured by Mitsubishi Chemical Corporation) is added to the dissolution tank 9 as a coating material. TM Polybutylene succinate-coated granular fertilizer for Example 2 was obtained in the same manner as in Example 1, except that 40 parts by mass of FZ91, PBS-1, 60 parts by mass of talc (manufactured by Fuji Talc Industry, MS412, median diameter 12 μm), and 1900 parts by mass of trichloroethylene were added as the solvent for the coating solution.

[0054] (Examples 3-6) Coated granular fertilizers for Examples 3 to 6 were obtained in the same manner as in Example 1, except that the coverage rate was changed by varying the time of the coating operation. The coverage rates are shown in Table 1.

[0055] (Example 7) Polybutylene succinate (BioPBS manufactured by Mitsubishi Chemical Corporation) is added to the dissolution tank 9 as a coating material. TM33 parts by mass of polybutylene succinate (PBS - 1) and 67 parts by mass of polybutylene adipate terephthalate (PBAT) (manufactured by BASF, ECOFLEX) were used. Except that 3200 parts by mass of trichloroethylene was added as the solvent of the coating solution, the coated granular fertilizer of Example 7 was obtained in the same manner as in Example 1. The mass ratio of polybutylene succinate to PBAT was 2:1.

[0056] (Comparative Example 1) 100 parts by mass of polybutylene succinate (BioPBS manufactured by Mitsubishi Chemical Corporation, also known as PBS - 2, density 1.26 g / cm³ (ISO1183), melting point 115 °C (ISO3146)) was put into the dissolution tank 9. Except that 3200 parts by mass of trichloroethylene was added as the solvent of the coating solution, the polybutylene succinate coated granular fertilizer of Comparative Example 1 was obtained in the same manner as in Example 1. TM FZ71, density 1.26 g / cm 3 (ISO1183), melting point 115 °C (ISO3146), also referred to as PBS - 2) and 3200 parts by mass of trichloroethylene as the solvent of the coating solution were added. Except for this, the same procedure as in Example 1 was followed to obtain the polybutylene succinate coated granular fertilizer of Comparative Example 1.

[0057] (Comparative Example 2)​​​​​​​​​​​​​​​​​​​The coating operation was carried out in the same manner as in Example 1, except that 33 parts by mass of FZ91, PBS-1) and 67 parts by mass of polycaprolactone (Ingevity, Capa6500, melting point 60°C) were added, with 3200 parts by mass of trichloroethylene as the solvent for the coating solution. However, blocking occurred and the mixture did not become granular, and coated granular fertilizer could not be obtained.

[0060] [Measurement of coverage rate] The coverage rate was calculated using the following formula (IV). Coverage rate (%) = (Mass of material forming the coating) / (Mass of coated granular fertilizer) × 100 ...Formula (IV) The mass of the material forming the coating was calculated by subtracting the mass of the uncoated granular fertilizer from the mass of the coated granular fertilizer. Furthermore, the average mass of 350 units of either the coated or uncoated granular fertilizer was used for each calculation. The results are shown in Table 1.

[0061] [Measurement of dissolution rate] The leaching rate of fertilizer components into water was measured for the coated granular fertilizers obtained in the examples and comparative examples. 10 g of the coated granular fertilizer from the examples and comparative examples, along with 200 ml of distilled water pre-adjusted to 25°C, were added to a 250 ml lidded plastic container and left to stand in an incubator set to 25°C. After 2 hours, all the water was removed from the container, and the amount of urea contained in the removed water (urea leaching amount) was determined by quantitative analysis (dimethylaminobenzaldehyde method, "Detailed Explanation of Fertilizer Analysis Methods, Second Revised Edition," edited by Masayoshi Koshino, 1988, Yokendo), and this was recorded as the amount of urea leached. Separately, the urea content in coated granular fertilizer from the same lot was also measured using the dimethylbenzaldehyde method. The leaching rate was calculated using the following formula (V). Dissolution rate (%) = (Amount of urea dissolved) / (Amount of urea contained in coated granular fertilizer) × 100 ...Formula (V) The results are shown in Table 1.

[0062] [Table 1]

[0063] Table 1 shows that Examples 1 and 2 have lower dissolution rates compared to Comparative Examples 1, 2, and 3. The dissolution rate of coated granular fertilizer using polybutylene succinate with an MFR of 5 g / 10 min was 30% by mass or less after 2 hours, demonstrating high dissolution controllability. Furthermore, Examples 5 and 6 also showed low dissolution rates despite having lower coating rates than Comparative Examples 1 and 2, indicating their effectiveness in suppressing dissolution. The dissolution suppression effect can be further enhanced by increasing the coating rate. [Explanation of Symbols]

[0064] 1. Fluidized bed 2. Spray nozzle 3. Particles 4. Hot air 5. Spray liquid 6. Dust collector 7. Capacitor 8. Blower 9.Dissolution tank 10. Pump 11. Tank 12. Heater 13. Dispensing opening

Claims

1. A coated granular fertilizer having granular fertilizer and a coating film covering the surface of the granular fertilizer, A coated granular fertilizer wherein the coating contains polybutylene succinate (A) that satisfies the following requirement (i). (i) The melt flow rate (MFR), measured at 190°C and a 2.16 kg load in accordance with ISO 1133, is in the range of 4 to 6 g / 10 min.

2. The coated granular fertilizer according to claim 1, wherein the material forming the coating contains 30 to 100% by mass of the polybutylene succinate (A).

3. The coated granular fertilizer according to claim 1 or 2, wherein the ratio of the coating to 100% by mass of the coated granular fertilizer is 3 to 20% by mass.

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