Coated granular fertilizer and method for producing coated granular fertilizer

Abstract

This coated granular fertilizer comprises a granular fertilizer and a coating film that coats the granular fertilizer, wherein the coating film contains hydrogenated vegetable oil and talc, and the talc forms two or more talc layers overlapping in the thickness direction of the coating film.

Description

Coated granular fertilizer and method for producing the coated granular fertilizer CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority from Japanese Patent Application No. 2024-012500, the entire disclosure of which is incorporated herein by reference.

[0002] The present invention relates to a coated granular fertilizer and a method for producing the coated granular fertilizer.

[0003] Coated granular fertilizers have the advantage of controlling the elution of fertilizer components and maintaining their effectiveness after a single application, thereby reducing the number of times they are applied. For example, the coated granular fertilizer described in Patent Document 1 has a resin coating on the surface of a granular fertilizer containing fertilizer components.

[0004] Furthermore, the coated granular fertilizer described in Patent Document 2 is provided with a coating made of petroleum wax that is degradable in the fertilization environment, such as soil, with the aim of reducing the burden on the environment.

[0005] As a method for producing coated granular fertilizer, for example, as described in Patent Document 3, a method is known in which a coating is formed on the granular fertilizer using a resin dissolved in a solvent such as thinner in order to prevent the coated granular fertilizer from sticking together and forming blocks, and then mineral short fibers are powder-coated before the coating dries and sticks.

[0006] Japanese Patent Publication No. 2003-104787 Japanese Patent Publication No. 2002-293684 Japanese Patent Publication No. 47-041813

[0007] The inventors have discovered that coated granular fertilizers having a coating made of petroleum-based wax have problems in that they are insufficiently degradable in the fertilization environment and also have insufficient impact resistance when used with a spreader such as a side stripe fertilizer applicator, which may result in the leaching of fertilizer components early.

[0008] An object of the present invention is to provide a coated granular fertilizer that is degradable and can suppress the early leaching of fertilizer components after application using a spreader such as a side stripe fertilizer applicator, and a method for producing the same.

[0009] The present inventors discovered that a coated granular fertilizer having a coating with a multilayer structure formed from a hardened vegetable oil layer and a talc layer is degradable and can suppress the early leaching of fertilizer components even when applied using a spreader such as a side-stripe fertilizer applicator, and thus arrived at the present invention. Specifically, the coated granular fertilizer according to the present invention is as follows: (1) A coated granular fertilizer comprising a granular fertilizer and a coating coating the granular fertilizer, wherein the coating contains hardened vegetable oil and talc, and the talc forms two or more talc layers overlapping in the thickness direction of the coating. (2) The coated granular fertilizer according to (1) above, wherein the hardened vegetable oil forms two or more hardened vegetable oil layers overlapping in the thickness direction of the coating. (3) The coated granular fertilizer according to (2) above, wherein the hardened vegetable oil layer forms the outermost layer of the coating. (4) The coated granular fertilizer according to any one of (1) to (3) above, wherein the mass ratio of the granular fertilizer to the coating is 1:0.1 or more and 1:0.5 or less. (5) The coated granular fertilizer according to any one of (1) to (4) above, wherein the content of the talc in the coating is 5% by mass or more and 60% by mass or less. (6) The coated granular fertilizer according to any one of (1) to (5) above, wherein the melting point of the hydrogenated vegetable oil is 60°C or more and 100°C or less. (7) The coated granular fertilizer according to any one of (1) to (6) above, wherein the particle size of the talc is 1 μm or more and 35 μm or less.

[0010] The present invention also provides a method for producing a coated granular fertilizer as follows: (8) A method for producing a coated granular fertilizer, comprising: a first step of adding heat-melted hardened vegetable oil to a granular fertilizer in a rolling state; and a second step of adding talc to the granular fertilizer in a rolling state, wherein each of the first step and the second step is repeated two or more times. (9) A method for producing a coated granular fertilizer as set forth in (8) above, wherein the first step and the second step are alternately repeated two or more times. (10) A method for producing a coated granular fertilizer as set forth in (8) or (9) above, wherein the mass ratio between the granular fertilizer and the total amount of the hardened vegetable oil added in the first step is from 1000:100 to 1000:280. (11) A method for producing a coated granular fertilizer as set forth in any of (8) to (10) above, wherein the mass ratio between the granular fertilizer and the total amount of the talc added in the second step is from 1000:20 to 1000:180. (12) The method for producing a coated granular fertilizer according to any one of (8) to (11) above, wherein a mass ratio of the granular fertilizer to the amount of talc added per one cycle of the second step is from 1000:0.1 to 1000:50. (13) The method for producing a coated granular fertilizer according to any one of (8) to (12) above, wherein a hardened plant oil layer and a talc layer that coat the granular fertilizer are formed by the first step and the second step, respectively.

[0011] According to the present invention, it is possible to provide a coated granular fertilizer that is degradable and can suppress the early leaching of fertilizer components after application using a spreader such as a side-stripe fertilizer applicator, and a method for producing the same.

[0012] A coated granular fertilizer according to an embodiment of the present invention will be described.

[0013] The coated granular fertilizer according to this embodiment includes a granular fertilizer and a coating that coats the granular fertilizer.

[0014] The granular fertilizer contains fertilizer components. The granular fertilizer may contain any additives. The granular fertilizer can be produced by a known method. For example, the granular fertilizer can be obtained by granulating the fertilizer components themselves alone using a conventional granulation method for granulation of granules, or by mixing the fertilizer components and the additives and granulating the mixture. Examples of such granulation methods include prilling granulation, stirring granulation, extrusion granulation, fluidized bed granulation, rolling granulation, compression granulation, drum granulation, pan granulation, coating granulation, and adsorption granulation. The granular fertilizer is preferably spherical, but may also be rectangular or cylindrical.

[0015] The particle size of the granular fertilizer is usually 0.1 to 15.0 mm. The particle size of the granular fertilizer is preferably 1 to 5 mm. The particle size of the granular fertilizer is measured by the sieving method specified in JIS Z8801.

[0016] Examples of fertilizer components include nitrogenous fertilizer components, phosphate fertilizer components, potassium fertilizer components, silicate fertilizer components, magnesium fertilizer components, calcium fertilizer components, manganese fertilizer components, boron fertilizer components, and iron-containing fertilizer components. Examples of nitrogenous fertilizer components include urea, ammonium nitrate, magnesium ammonium nitrate, ammonium chloride, ammonium sulfate, ammonium phosphate, sodium nitrate, potassium nitrate, calcium nitrate, lime nitrogen, formaldehyde-modified urea (UF), acetaldehyde-modified urea (CDU), isobutyraldehyde condensed urea (IBDU), guanylurea (GU), and soybean flour. Examples of phosphate fertilizer components include superphosphate, triple superphosphate, fused phosphate fertilizer, humic acid phosphate fertilizer, calcined phosphate fertilizer, double-burned phosphate, magnesium superphosphate, sodium polyphosphate, ammonium polyphosphate, potassium metaphosphate, calcium metaphosphate, magnesium ammonium phosphate, ammonium sulfate, potassium ammonium phosphate, and ammonium phosphate salt. Examples of the potassium fertilizer component include potassium chloride, potassium sulfate, potassium soda sulfate, potassium magnesium sulfate, potassium bicarbonate, and potassium phosphate. Examples of the silicate fertilizer component include calcium silicate. Examples of the magnesium fertilizer component include magnesium sulfate and magnesium chloride. Examples of the calcium fertilizer component include quicklime and slaked lime. Examples of the manganese fertilizer component include manganese sulfate, manganese magnesium sulfate, and manganese slag. Examples of the boron fertilizer component include boric acid and borates. Examples of the iron-containing fertilizer component include steel slag. The granular fertilizer may contain only one of these fertilizer components, or may contain two or more of them.

[0017] Optional additives that may be contained in the granular fertilizer include, for example, anti-floating agents, composition uniformity promoters, effect development promoters, colorants, and granulation promoters. Examples of the anti-floating agents include andesite powder, peridotite powder, shale powder, sandstone powder, and silica powder. Examples of the composition uniformity promoters include gypsum, andesite powder, shale powder, sandstone powder, humic acid, zeolite, lignite, and peat. Examples of the effect development promoters include ferric oxide, lime nitrate, ferrous sulfate, zinc sulfate, ethylenediaminetetraacetic acid iron, copper sulfate, diethylenetriaminepentaacetic acid iron, ethylenediaminetetraacetic acid zinc, ferric sulfate, ethylenediaminetetraacetic acid calcium, and ethylenediaminetetraacetic acid molybdenum. Examples of the colorants include humic acid and carbon black. Examples of the granulation accelerator include peridotite powder, silica powder, diatomaceous earth, zeolite, gypsum, starch, molasses, lignin sulfonic acid, konjac flying powder, sepiolite, concentrated yeast fermentation waste liquid, ammonia liquid, kaolin, sandstone powder, sulfuric acid, phosphoric acid liquid, attapulgite, pulp waste liquid, andesite powder, carboxymethyl cellulose, corn starch, rice bran, light-burned magnesia, and slaked lime.

[0018] The coating contains hydrogenated vegetable oil and talc. In the coating, the talc forms two or more talc layers overlapping in the thickness direction. In the coating, the hydrogenated vegetable oil forms two or more layers overlapping in the thickness direction. That is, the coating has a multilayer structure formed from the hydrogenated vegetable oil layer and the talc layer. This improves the impact resistance of the coating and suppresses early leaching of the fertilizer components. More specifically, the two or more talc layers prevent the progression of cracks that may occur in the thickness direction of the coating, thereby suppressing the impairment of the coating's ability to control the leaching of the fertilizer components. Furthermore, even if cracks do occur, they tend to progress along the surface direction of the talc layer, i.e., they are less likely to progress inward in the thickness direction toward the granular fertilizer. In the coating, the hydrogenated vegetable oil layer mainly functions to control the leaching of the fertilizer components.

[0019] The coating may have a structure in which high-density and low-density regions of the talc are repeated in the thickness direction in a cross section passing through the center of the coated granular fertilizer, with the high-density regions forming the talc layer. In this case, the coating may contain the vegetable hydrogenated oil throughout the thickness direction by containing the vegetable hydrogenated oil in each talc layer. This allows each talc layer to contribute auxiliary to release control. The coating may have a structure in which high-density and low-density regions of the vegetable hydrogenated oil are repeated in the thickness direction in the cross section, with the high-density regions forming the vegetable hydrogenated oil layer. In the coating, the talc and the vegetable hydrogenated oil may alternate to form the talc layer and the vegetable hydrogenated oil layer.

[0020] It is preferable that the hydrogenated vegetable oil forms the innermost layer of the coating. Such a coating is less likely to peel off from the granular fertilizer than when the talc forms the innermost layer. It is also preferable that the hydrogenated vegetable oil forms the outermost layer of the coating. A coated granular fertilizer having such a coating is less likely to lose the talc. It is also preferable that the talc forms both the innermost and outermost layers of the coating. It is also preferable that the talc forms the innermost layer and the hydrogenated vegetable oil forms the outermost layer of the coating. It is also preferable that the hydrogenated vegetable oil forms the innermost layer and the talc forms the outermost layer of the coating.

[0021] The number of each of the talc layers and the hydrogenated vegetable oil layers in the coating may be, for example, 3 or more, 5 or more, 10 or more, or 15 or more. The upper limit of the number of each of the talc layers and the hydrogenated vegetable oil layers is not particularly limited, and may be 100 or less, 50 or less, 25 or less, or 20 or less. The number of the hydrogenated vegetable oil layers in the coating may be less than the number of the talc layers, may be equal to the number of the talc layers, or may be greater than or equal to the number of the talc layers. The number of the talc layers and the hydrogenated vegetable oil layers can be identified by observing a cross section passing through the center of the coated granular fertilizer using a scanning electron microscope (SU-3800, manufactured by Hitachi High-Technologies Corporation) in BSE mode.

[0022] The mass ratio of the granular fertilizer to the coating is preferably 1:0.1 or more and 1:0.5 or less.

[0023] The talc content in the coating is preferably 5% by mass or more and 60% by mass or less, and more preferably 10% by mass or more and 30% by mass or less. Meanwhile, the hydrogenated vegetable oil content in the coating is preferably 30% by mass or more, and more preferably 40% by mass or more. The hydrogenated vegetable oil content in the coating may be 95% by mass or less, or may be 90% by mass or less. In the coating, the talc content is preferably less than the hydrogenated vegetable oil content.

[0024] The mass ratio of the coating to the talc in one talc layer (each talc layer) is preferably 100:0.3 or more and 100:15 or less, more preferably 100:0.3 or more and 100:5 or less. The mass of talc in one talc layer is the average mass calculated by dividing the mass of the talc in the coating by the number of the talc layers.

[0025] The mass ratio of the coating to the hydrogenated vegetable oil in one hydrogenated vegetable oil layer (each hydrogenated vegetable oil layer) is preferably 100: 2 or more and 100: 40 or less. The mass of the hydrogenated vegetable oil in one hydrogenated vegetable oil layer is an average mass calculated by dividing the mass of the hydrogenated vegetable oil in the coating by the number of the hydrogenated vegetable oil layers.

[0026] The mass ratio of the mass of talc in the talc layer 1 to the mass of the hydrogenated vegetable oil in the hydrogenated vegetable oil layer 1 is preferably 1:0.4 or more and 1:10 or less. It is believed that the multilayer structure in which each talc layer is separated by a hydrogenated vegetable oil layer of an appropriate thickness prevents the progression of cracks that may occur in the thickness direction of the coating, thereby preventing the coating from impairing its ability to control the elution of the fertilizer components.

[0027] From the viewpoint of environmental impact, it is preferable that the coating does not include a non-degradable resin layer. Examples of resins constituting the non-degradable resin layer include thermoplastic resins and thermosetting resins. Examples of thermoplastic resins include olefin-based resins, diene-based resins, and polyvinyl chloride. Examples of olefin-based resins include polyethylene, polypropylene, polybutene, polystyrene, ethylene-propylene copolymer, butene-ethylene copolymer, butene-propylene copolymer, ethylene-vinyl acetate copolymer, ethylene-acrylic acid copolymer, ethylene-acrylic acid ester copolymer, ethylene-methacrylic acid copolymer, ethylene-methacrylic acid ester copolymer, and ethylene-carbon monoxide copolymer. Examples of diene-based resins include butadiene copolymer, isoprene polymer, chloroprene polymer, butadiene-styrene copolymer, and styrene-isoprene copolymer. Examples of thermosetting resins include epoxy resin, alkyd resin, phenolic resin, urea resin, melamine resin, and silicone resin.

[0028] From the viewpoint of maintaining controlled release, the coating preferably does not include a biodegradable resin layer, such as polylactic acid, polyhydroxyalkanoate, polybutylene adipate terephthalate, polycaprolactone, polybutylene succinate, polyethylene succinate, polyvinyl alcohol, polyglycolic acid, polyaspartic acid, cellulose fatty acid ester, and polybutylene succinate adipate.

[0029] Preferably, the coating is substantially free of the resin. The content of the resin in the coating is, for example, 0.5% by mass or less, preferably 0.1% by mass or less. The biodegradable resin has high water vapor permeability, making it unsuitable as a coating component from the viewpoint of improving the control of fertilizer component elution. When melted by heating, the biodegradable resin has low fluidity and is prone to caking during the production of the coated granular fertilizer, making it unsuitable as a coating component from the viewpoint of manufacturability. Furthermore, among the biodegradable resins, thermoplastic resins are difficult to coat on the granular fertilizer unless they are soluble in solvents, making them unsuitable as a coating component from the viewpoint of manufacturability. Furthermore, among the biodegradable resins, those with low solubility in solvents require the use of highly toxic halogen-based solvents, which is undesirable from the viewpoint of environmental impact. Some types of biodegradable resins decompose only under specific environments, and decomposition rarely occurs in natural environments such as soil or the ocean. On the other hand, hydrogenated vegetable oils have a structure similar to that of animal and plant fats and can be decomposed by lipolytic bacteria that are widespread in natural environments.

[0030] The thickness of the coating is, for example, 30 to 250 μm. The thickness of the coating can be measured by observing a cross section passing through the center of the coated granular fertilizer using a scanning electron microscope (SU-3800, manufactured by Hitachi High-Technologies Corporation) in BSE mode. The thickness of the coating can be determined by drawing 10 line segments perpendicular to the coating for the coated granular fertilizer and averaging their lengths.

[0031] The talc is a type of mineral, also known as talc or stearite, and is a compound containing Mg ３ Si ４ O １０(OH) ２ The talc includes hydrated magnesium silicate represented by the formula: The talc may be, for example, powdered talc containing spherical, scaly, or plate-like particles. Powdered talc containing plate-like particles is preferred because it easily uniformly covers the surface of the granular fertilizer. Specific examples of the talc include the Micro Ace series, such as Micro Ace L-1 (manufactured by Nippon Talc Co., Ltd.), the Nano Ace series, such as Nano Ace D-600 (manufactured by Nippon Talc Co., Ltd.), the Crown Talc series, such as the SG series (manufactured by Nippon Talc Co., Ltd.), LU-R (manufactured by Nippon Talc Co., Ltd.), and Crown Talc ID (manufactured by Matsumura Sangyo Co., Ltd.), the Talcan Powder series (manufactured by Hayashi Kasei Co., Ltd.), the Micron White series (manufactured by Hayashi Kasei Co., Ltd.), the KHP series (manufactured by Hayashi Kasei Co., Ltd.), the Hi Filler series (manufactured by Matsumura Sangyo Co., Ltd.), the HTP series (manufactured by IMI Fabi Co., Ltd.), the HM series (manufactured by IMI Fabi Co., Ltd.), and the Mistron Vapor series (manufactured by IMI Fabi Co., Ltd.). The coating may contain only one of these, or may contain two or more of them.

[0032] The talc preferably has a particle size of 1 μm or more and 35 μm or less, and more preferably 5 μm or more and 35 μm or less. The talc layer formed by such talc is suitable for imparting the above-mentioned impact resistance to the coating. Specifically, in a talc layer formed by talc with a relatively large particle size of 1 μm or more, linear portions in which multiple talc particles are connected in the circumferential direction are formed, which makes it easier to prevent cracks from progressing in the thickness direction of the coating. In other words, it is thought that cracks will progress more easily along the surface direction of the talc layer. The particle size of the talc refers to the volume-based median diameter (D50) and can be measured by a dry method using a laser diffraction particle size analyzer (Malvern Analytical, Mastersizer 3000).

[0033] The talc preferably has a circularity coefficient of 0.4 to 1.0, more preferably 0.5 to 0.9, and even more preferably 0.6 to 0.8. The talc layer formed by such talc is suitable for imparting the above-mentioned impact resistance to the coating. Specifically, a talc layer formed by talc with a circularity coefficient of 0.4 or more is likely to cover the fertilizer surface without gaps, making it easier to prevent cracks from progressing in the thickness direction of the coating; in other words, it is thought that cracks will progress more easily along the surface direction of the talc layer. The circularity coefficient of the talc can be measured based on images of the talc in the micrometer range using a scanning electron microscope (SU-3800, manufactured by Hitachi High-Tech Corporation). Specifically, a talc sample was adhered to a test table using conductive tape, and platinum sputtering was performed for 120 seconds at 20 mA using an ion sputtering device (Hitachi, Ltd., E-1030) to prepare a photographed object. Next, the sample was photographed at a magnification of approximately 50 to 3000 times depending on the size, with approximately 10 to 100 particles per field of view, to obtain a photographed image. Then, the circularity coefficient (4π × area × perimeter) of 100 or more particles captured in the photographed image was measured using image analysis particle size distribution software (Mountec Co., Ltd., Mac-View), and the average value of these values ​​was calculated.

[0034] The talc preferably has an aspect ratio constant of 1.0 to 15.0, more preferably 1.3 to 7.0, and even more preferably 2.0 to 5.0. The talc layer formed by such talc is suitable for imparting the above-mentioned impact resistance to the coating. Specifically, in a talc layer formed by talc with an aspect ratio constant of 1.0 or more, the shape-anisotropic talc is likely to be oriented in the circumferential direction, making it easier to prevent cracks from progressing in the thickness direction of the coating. In other words, it is thought that cracks are more likely to progress along the surface direction of the talc layer. The aspect ratio constant of the talc was defined as {D50-Dmean} / Dmean, where D50 is the median diameter and Dmean is the median diameter measured by centrifugal sedimentation according to JIS R1619.

[0035] The hydrogenated vegetable oil is obtained by adding hydrogen to a vegetable oil containing unsaturated fatty acid triglycerides to saturate the unsaturated bonds of the unsaturated fatty acid triglycerides. The hydrogenated vegetable oil also includes chemically synthesized products with the same chemical structure as the hydrogenated vegetable oil. Examples of such hydrogenated vegetable oils include castor oil, rapeseed oil, soybean oil, palm oil, peanut oil, jojoba oil, cottonseed oil, and coconut oil. The coating may contain only one or two or more of the hydrogenated vegetable oils.

[0036] The hydrogenated vegetable oil has moderate decomposition properties in a fertilization environment such as soil. Specifically, the hydrogenated vegetable oil can exert elution control properties in the coating without immediately decomposing in the fertilization environment, and can decompose at a moderate rate so that its remaining in the fertilization environment is not a problem. In other words, a coated granular fertilizer having a coating containing the hydrogenated vegetable oil has excellent decomposition properties and elution control properties.

[0037] The hydrogenated vegetable oil is solid at 25°C. The hydrogenated vegetable oil preferably has a melting point of 60°C or higher and 100°C or lower, and more preferably a melting point of 80°C or higher and 90°C or lower. Hydrogenated vegetable oils with such melting points can be melted by heating. Therefore, they can be handled in a liquid state without using a solvent. Furthermore, by using hydrogenated vegetable oils with such melting points, it is possible to prevent the fertilizer components from being decomposed by heat during the production of the coated granular fertilizer. Furthermore, by including hydrogenated vegetable oils with such melting points in the outermost layer of the coated granular fertilizer, caking of the fertilizers during production and storage is suppressed.

[0038] Examples of optional additives that may be contained in the coating include the anti-floating agent, the colorant, and the antibacterial agent. The content of the optional additives in the coating is, for example, 0.1 to 10% by mass.

[0039] The coated granular fertilizer can have a fertilizer component elution rate E1 that satisfies E1 < 30% when left standing in water for 7 days at a concentration of 2.5 g / 100 mL. Furthermore, when the coated granular fertilizer is applied using a side stripe fertilizer applicator (Yanmar Co., Ltd., YK6D) and then promptly recovered, and left standing in water for 7 days in the same manner as above, and the elution rate E2 is defined as E2 - E1 < 15%. The coated granular fertilizer can have a fertilizer component elution rate E3 that satisfies E3 < 30% when left standing in water for 42 days at a concentration of 2.5 g / 100 mL. Furthermore, when the coated granular fertilizer is applied using the side stripe fertilizer applicator and then promptly recovered, and left standing in water for 42 days in the same manner as above, and the elution rate E4 is defined as E4 - E3 < 15%. The elution rate can be calculated by measuring the concentration of the fertilizer components in water collected after a predetermined time has elapsed using an ultraviolet-visible spectrophotometer (UV-1900i, manufactured by Shimadzu Corporation).

[0040] A coated granular fertilizer having such release controllability and impact resistance can be suitably used for cultivating agricultural crops in paddy fields, such as the cultivation of grass crops. The coated granular fertilizer may be sprayed alone onto the paddy field (soil). Alternatively, the coated granular fertilizer may be sprayed onto the paddy field (soil) as a compound fertilizer. That is, the compound fertilizer may contain the granular fertilizer without the coating together with the coated granular fertilizer. Alternatively, the coated granular fertilizer may be sprayed onto the paddy field (soil) together with other coated granular fertilizers that are not included therein. With such a compound fertilizer, the granular fertilizer with exposed fertilizer components can supply sufficient amounts of the fertilizer components to grass crops immediately after spraying, and the coated granular fertilizer can sustain the supply of the fertilizer components for a predetermined period of time.

[0041] The coated granular fertilizer can be used for spreading on soil using a spreader such as a side-stripe fertilizer applicator. These spreaders typically include a fertilizer hopper, a dispensing device, and a fertilizer hose with an opening at its tip, configured to supply fertilizer and air toward the opening into the fertilizer hose. This configuration allows the spreader to transport the fertilizer toward the opening by free fall and air flow within the fertilizer hose, thereby spreading the fertilizer on the soil or other fertilization environments. In this process, the fertilizer is subjected to impacts not only when passing through the dispensing device, but also when the fertilizer collides with other fertilizer particles and with the inner wall of the fertilizer hose. The coating of the coated granular fertilizer, including two or more talc layers, suppresses damage caused by such impacts and prevents early leaching of the fertilizer components.

[0042] Next, a method for producing the coated granular fertilizer will be described.

[0043] The method for producing the coated granular fertilizer comprises a coating process including a first step of adding the hardened vegetable oil to the granular fertilizer in a rolling state and a second step of adding the talc to the granular fertilizer in a rolling state. In the first step, the hardened vegetable oil can be dissolved in a solvent or heated and melted before being added to the granular fertilizer. The method of adding the heated and melted hardened vegetable oil to the granular fertilizer is preferable from the perspective of environmental impact because it does not use a solvent. In the second step, the talc can be dispersed in a solvent or added in powder form to the granular fertilizer. The method of adding the talc in powder form to the granular fertilizer is preferable from the perspective of environmental impact because it does not use a solvent. When the steps of adding the talc and the hardened vegetable oil to the granular fertilizer separately are employed, a defect-free coating is more easily formed, thereby enabling the production of a coated granular fertilizer with excellent release controllability. In the coating process, the first and second steps are each repeated two or more times. As a result, in the coating step, the hardened vegetable oil layer and two or more talc layers that coat the granular fertilizer are formed.

[0044] The first step may be performed as the initial step of the coating process. That is, the first step may involve adding the hardened vegetable oil to the granular fertilizer, which is the starting material for the coating process. Forming the hardened vegetable oil layer in the innermost layer of the coating in this manner is preferable from the viewpoint of improving the release controllability of the coated granular fertilizer. The amount of hardened vegetable oil added in the first step as the initial step is preferably greater than the amount of hardened vegetable oil added per first step from the second step onwards. The amount of hardened vegetable oil added in the first step as the initial step is preferably greater than the average amount added in the first step from the second step onwards. This allows the density of the talc layer to increase with increasing distance from the center of the coated granular fertilizer, which is considered preferable from the viewpoint of impact resistance. The second step may be performed as the initial step of the coating process. That is, the second step may involve adding the talc to the granular fertilizer, which is the starting material for the coating process. This is considered to prevent the granular fertilizer from caking during production while it is rolling.

[0045] The amount of hydrogenated vegetable oil added in the first step as the initial step is preferably greater than the amount of talc added per one time in the second step. The amount of hydrogenated vegetable oil added in the first step as the initial step is preferably greater than the average amount added in the second step.

[0046] Furthermore, the mass ratio of the amount of hydrogenated vegetable oil added in the first step per time from the second time onward to the amount of talc added in the second step per time is preferably 1:0.4 or more and 1:3 or less, thereby further improving the elution controllability and impact resistance of the coating.

[0047] The first step may be carried out as the final step of the coating step, thereby forming the hydrogenated vegetable oil layer as the outermost layer of the coating.

[0048] It is preferable that any m+1th first step is not carried out consecutively with the mth first step. For example, the step following the mth first step is preferably a step using a component other than the hydrogenated vegetable oil, more specifically, the second step of adding the talc to the intermediate obtained in the mth first step is preferred. Similarly, it is preferable that any n+1th second step is not carried out consecutively with the nth second step. For example, the step following the nth second step is preferably a step using a component other than the talc, more specifically, the first step of adding the hydrogenated vegetable oil to the intermediate obtained in the nth second step is preferred.

[0049] In the coating formation process, the first step and the second step may be alternately repeated. In the coating formation process, the first step and the second step are preferably each performed at least twice, more preferably five or more times, and may be performed ten or more times, or may be performed fifteen or more times. The upper limit of the number of times each of the first step and the second step is performed may be 100 or less, 50 or less, 25 or less, or 20 or less. In the coating formation process, the number of times the first step is performed and the number of times the second step is performed may be the same or different. In the first step following the second step, the vegetable hydrogenated oil may be partially impregnated into the talc layer formed in the second step. This may form adjacent talc layers and vegetable hydrogenated oil layers connected by the vegetable hydrogenated oil.

[0050] The first step of adding the heated and melted hardened vegetable oil to the granular fertilizer in a rolling state can be carried out as the first step of the coating process. The second step of adding the talc can be carried out following the first step. Furthermore, the first step and the second step can be carried out alternately from the second time onwards, and the first step or the second step can be carried out as the final step of the coating process.

[0051] The second step of adding the talc to the granular fertilizer in a rolling state can be carried out as the first step of the coating process. The first step of adding the hydrogenated vegetable oil can be carried out following the first step. Furthermore, the second step and the first step can be carried out alternately from the second time onwards, and the first step or the second step can be carried out as the final step of the coating process.

[0052] In the coating process, the mass ratio of the granular fertilizer to the total amount of hydrogenated vegetable oil added (the amount of hydrogenated vegetable oil added in all of the first processes) is typically 1000:50 or more and 1000:500 or less, and preferably 1000:100 or more and 1000:280 or less. Also, in the coating process, the mass ratio of the granular fertilizer to the total amount of talc added (the amount of talc added in all of the second processes) is typically 1000:1 or more and 1000:500 or less, and preferably 1000:20 or more and 1000:180 or less.

[0053] In the coating process, the mass ratio of the granular fertilizer to the amount of hydrogenated vegetable oil added per one cycle of the first process is typically from 1000:1 to 1000:500, and preferably from 1000:2 to 1000:240. In addition, in the coating process, the mass ratio of the granular fertilizer to the amount of talc added per one cycle of the second process is preferably from 1000:0.1 to 1000:150, and more preferably from 1000:1 to 1000:50.

[0054] The number of times each of the first step and the second step may be, for example, 3 or more, 5 or more, 10 or more, or 15 or more. The upper limit of the number of times each of the first step and the second step is not particularly limited, but may be 100 or less, 50 or less, 25 or less, or 20 or less.

[0055] The method for producing coated granular fertilizer may further include a pre-treatment step, prior to the coating formation step, of contacting the granular fertilizer, which has been rolled using a rolling device, with paraffin while heating it with hot air. This step has the advantage of improving the rolling properties of the granular fertilizer within the rolling device, making it easier for the hydrogenated vegetable oil to adhere to the granular fertilizer. Furthermore, the method for producing coated granular fertilizer may further include a post-treatment step, following the coating formation step, of adding any additive, such as a surfactant or an anti-caking agent, to the surface of the coating. The pre-treatment step and the post-treatment step are not the coating formation step.

[0056] The coated granular fertilizer and the method for producing the coated granular fertilizer according to the present invention are as described above, but the coated granular fertilizer and the method for producing the coated granular fertilizer according to the present invention are not limited to the configurations of the above-described embodiments. The coated granular fertilizer and the method for producing the coated granular fertilizer according to the present invention can be modified in various ways without departing from the gist thereof.

[0057] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0058] [Granular fertilizer] Urea (manufactured by China Blue Chemical Limited, particle size (D50) approximately 3 mm) (hereinafter referred to as large granular urea) [Hydrogenated vegetable oil] "Hydrogenated castor oil" manufactured by Ito Oil Mills, melting point 80-90°C (hereinafter referred to as castor hydrogenated oil 1) "Extremely hydrogenated soybean oil" manufactured by Yokozeki Oil Industries, melting point 67°C (hereinafter referred to as soybean hydrogenated oil 1) "Extremely hydrogenated rapeseed oil" manufactured by Yokozeki Oil Industries, melting point 67°C (hereinafter referred to as rapeseed hydrogenated oil 1) [Talc] "Micro Ace L-1" manufactured by Nippon Talc Co., Ltd. (hereinafter referred to as talc 1) "LU-R" manufactured by Nippon Talc Co., Ltd. (hereinafter referred to as talc 2) "Nano Ace D-600" manufactured by Nippon Talc Co., Ltd. (hereinafter referred to as talc 3) "Crown Talc ID" manufactured by Matsumura Sangyo Co., Ltd. (hereinafter referred to as Talc 4) [Mineral inorganic fibers] "EFDE50-01" manufactured by Central Glass Fiber Co., Ltd. (hereinafter referred to as Glass Fiber 1) "EFH150-01" manufactured by Central Glass Fiber Co., Ltd. (hereinafter referred to as Glass Fiber 2) [Petroleum-based waxes] "HNP-51" manufactured by Nippon Seiro Co., Ltd. (hereinafter referred to as Paraffin wax) Hydrocarbon ("Sasol C80" manufactured by Kato Yoko Co., Ltd.) (hereinafter referred to as FT wax) [Vegetable-based waxes] "Refined Carnauba Wax No. 2" manufactured by Kato Yoko Co., Ltd. (hereinafter referred to as Carnauba wax) "Refined Candelilla Wax" manufactured by Kato Yoko Co., Ltd. (hereinafter referred to as Candelilla wax) [Others] "Lunac S-98" manufactured by Kao Chemical Corporation (hereinafter referred to as Stearic acid) "Nissan Electol WEP-5" manufactured by NOF Corporation (hereinafter referred to as Fatty acid ester) "Kalcol 220-80" (hereinafter referred to as behenyl alcohol) manufactured by Kao Chemical Corporation

[0059] Example 1 Large granular urea (1,000 parts by mass) was placed in a rotating tank and heated to about 70°C with hot air. Liquid paraffin (Moresco White P-350P, manufactured by MORESCO Corporation) (10 parts by mass) was then added, and the rolling state was continued for 5 minutes. The paraffin-coated large granular urea was then heated and added with castor oil 1 (170 parts by mass) that had been heated and melted at 105°C. The rolling state was maintained under heated conditions for 3 minutes or more, thereby carrying out the first step, and a first hydrogenated vegetable oil layer was formed. Next, talc 1 (45 parts by mass) was added, and the rolling state was maintained under heated conditions for 3 minutes or more, thereby carrying out the first step, and a first talc layer was formed outside the first hydrogenated vegetable oil layer. Next, the second step was carried out in the same manner as the first step, except that the amount of hydrogenated castor oil 1 used was changed to 20 parts by mass, and a second hydrogenated vegetable oil layer was formed outside the first talc layer. Next, the second step was carried out in the same manner as the first step, forming a second talc layer on the outside of the second hardened vegetable oil layer. Next, the third step was carried out in the same manner as the second step, forming a third hardened vegetable oil layer on the outside of the second talc layer. Thereafter, the fertilizer was cooled to about room temperature, yielding a coated granular fertilizer equipped with a coating having a multilayer structure formed of three hardened vegetable oil layers and two talc layers.

[0060] [Example 2] The first step was repeated four times and the second step was repeated three times alternately, and a coated granular fertilizer having a coating film with a multilayer structure formed of four layers of hydrogenated vegetable oil and three layers of talc was obtained in the same manner as in Example 1, except that the amount of castor hydrogenated oil 1 used in the first first step was 150 parts by mass and the amount of talc used in each second step was 30 parts by mass.

[0061] [Example 3] The first step was repeated seven times and the second step was repeated six times alternately, and a coated granular fertilizer having a coating with a multilayer structure formed of seven layers of hydrogenated vegetable oil and six layers of talc was obtained in the same manner as in Example 1, except that the amount of castor hydrogenated oil 1 used in the first first step was 90 parts by mass and the amount of talc used in each second step was 15 parts by mass.

[0062] [Example 4] The first step was repeated ten times and the second step was repeated nine times, and a coated granular fertilizer having a coating with a multilayer structure formed of ten layers of hydrogenated vegetable oil and nine layers of talc was obtained in the same manner as in Example 1, except that the amount of castor hydrogenated oil 1 used in the first first step was 30 parts by mass and the amount of talc used in each second step was 10 parts by mass.

[0063] Example 5 A coated granular fertilizer having a coating with a multilayer structure formed of 19 layers of hydrogenated vegetable oil and 18 layers of talc was obtained in the same manner as in Example 1, except that the first step was repeated 19 times and the second step was repeated 18 times, and the amount of castor hydrogenated oil 1 in the first step was 30 parts by mass, the amount of castor hydrogenated oil 1 in the second and subsequent first steps was 10 parts by mass, and the amount of talc in each second step was 5 parts by mass.

[0064] [Example 6] The first step was repeated 91 times and the second step was repeated 90 times alternately, and the amount of castor hydrogenated oil 1 used in the first step was 30 parts by mass, the amount of castor hydrogenated oil 1 used in the first step from the second step onwards was 2 parts by mass, and the amount of talc used in each second step was 1 part by mass. In the same manner as in Example 1, a coated granular fertilizer was obtained, which had a coating film with a multilayer structure formed of 91 layers of hydrogenated vegetable oil and 90 layers of talc.

[0065] Comparative Example 1 Castor hydrogenated oil 1 (210 parts by mass) was heated and melted at 105°C, and mixed with talc 1 (90 parts by mass) heated to 105°C to obtain a coating composition in which talc 1 was dispersed in castor hydrogenated oil 1. Large urea granules (1,000 parts by mass) were charged into a rotating drum and tumbling. The large urea granules were heated to about 70°C with hot air, and then liquid paraffin (Moresco White P-350P, manufactured by MORESCO Corporation) (10 parts by mass) was added, and the tumbling state was continued for 5 minutes. Next, the coating composition heated to 105°C was added to the paraffin-coated large urea granules in the tumbling state, and the tumbling state was maintained under heating conditions for 3 minutes or more, and then the mixture was cooled to near room temperature to obtain a coated granular fertilizer.

[0066] [Comparative Example 2] The paraffin-coated large urea particles obtained in the same manner as in Comparative Example 1 were rolled, and 190 parts by mass of hydrogenated castor oil 1 heated to 105°C was added. The rolling state was maintained under heated conditions for at least 3 minutes to form a first hydrogenated vegetable oil layer. Next, 90 parts by mass of talc 1 was added, and the rolling state was maintained under heated conditions for at least 3 minutes to form a first talc layer outside the first hydrogenated vegetable oil layer. Next, a second hydrogenated vegetable oil layer was formed outside the first talc layer in the same manner as in the first step, except that the amount of hydrogenated castor oil 1 used was 20 parts by mass, and then the resultant mixture was cooled to near room temperature to obtain a coated granular fertilizer having a multilayer coating formed of two hydrogenated vegetable oil layers and one talc layer.

[0067] [Example 7] A coated granular fertilizer having a coating with a multilayer structure formed of three layers of hydrogenated vegetable oil and two layers of talc was obtained in the same manner as in Example 1, except that the first step was repeated three times and the second step was repeated twice, and the amount of hydrogenated castor oil 1 used in the first step was 240 parts by mass, and the amount of talc used in each second step was 10 parts by mass.

[0068] [Example 8] A coated granular fertilizer having a coating with a multilayer structure formed of four layers of hydrogenated vegetable oil and three layers of talc was obtained in the same manner as in Example 1, except that the first step was repeated four times and the second step was repeated three times, and the amount of castor hydrogenated oil 1 used in the first first step was 210 parts by mass, and the amount of talc used in each second step was 10 parts by mass.

[0069] [Example 9] A coated granular fertilizer having a coating with a multilayer structure formed of five layers of hydrogenated vegetable oil and four layers of talc was obtained in the same manner as in Example 1, except that the first step was repeated five times and the second step was repeated four times, and the amount of castor hydrogenated oil 1 used in the first first step was 180 parts by mass, and the amount of talc used in each second step was 10 parts by mass.

[0070] [Example 10] The first step was repeated six times and the second step was repeated five times alternately, and a coated granular fertilizer having a coating film with a multilayer structure formed of six layers of hydrogenated vegetable oil and five layers of talc was obtained in the same manner as in Example 1, except that the amount of castor hydrogenated oil 1 used in the first first step was 150 parts by mass and the amount of talc used in each second step was 10 parts by mass.

[0071] [Example 11] The first step was repeated seven times and the second step was repeated six times alternately, and a coated granular fertilizer having a coating film with a multilayer structure formed of seven layers of hydrogenated vegetable oil and six layers of talc was obtained in the same manner as in Example 1, except that the amount of castor hydrogenated oil 1 used in the first first step was 120 parts by mass and the amount of talc used in each second step was 10 parts by mass.

[0072] [Example 12] The first step was repeated eight times and the second step was repeated seven times alternately, and a coated granular fertilizer having a coating with a multilayer structure formed of eight layers of hydrogenated vegetable oil and seven layers of talc was obtained in the same manner as in Example 1, except that the amount of castor hydrogenated oil 1 used in the first first step was 90 parts by mass and the amount of talc used in each second step was 10 parts by mass.

[0073] Example 13 A coated granular fertilizer having a coating with a multilayer structure formed of 15 layers of hydrogenated vegetable oil and 14 layers of talc was obtained in the same manner as in Example 1, except that the first step was repeated 15 times and the second step was repeated 14 times, and the amount of castor hydrogenated oil 1 in the first step was 20 parts by mass, the amount of castor hydrogenated oil 1 in the second and subsequent first steps was 10 parts by mass, and the amount of talc in each second step was 10 parts by mass.

[0074] Example 14 A coated granular fertilizer having a coating with a multilayer structure formed of 19 layers of hydrogenated vegetable oil and 18 layers of talc was obtained in the same manner as in Example 1, except that the first step was repeated 19 times and the second step was repeated 18 times, and the amount of castor hydrogenated oil 1 used in the first step was 12 parts by mass, the amount of castor hydrogenated oil 1 used in the second and subsequent first steps was 6 parts by mass, and the amount of talc used in each second step was 10 parts by mass.

[0075] Comparative Example 3 A coated granular fertilizer was obtained in the same manner as in Comparative Example 1, except that 300 parts by mass of hardened castor oil 1 was used and no talc was used.

[0076] Comparative Example 4 A coated granular fertilizer provided with a coating having a multilayer structure formed of two layers of hydrogenated vegetable oil and one layer of talc was obtained in the same manner as in Comparative Example 2, except that the amount of castor hydrogenated oil 1 used in the first step of the first run was 270 parts by mass and the amount of talc used in the second step of the first run was 10 parts by mass.

[0077] Example 15 A coated granular fertilizer having a coating film with a multilayer structure formed of four layers of hydrogenated vegetable oil and three layers of talc was obtained in the same manner as in Example 8, except that the amount of hydrogenated castor oil 1 used in the first step was 180 parts by mass and the amount of talc used in each of the second steps was 20 parts by mass.

[0078] Example 16 A coated granular fertilizer having a coating film with a multilayer structure formed of four layers of hydrogenated vegetable oil and three layers of talc was obtained in the same manner as in Example 8, except that the amount of hydrogenated castor oil 1 used in the first step was 120 parts by mass, and the amount of talc used in each of the second steps was 40 parts by mass.

[0079] [Example 17] A coated granular fertilizer provided with a coating having a multilayer structure formed of four layers of hydrogenated vegetable oil and three layers of talc was obtained in the same manner as in Example 8, except that the amount of hydrogenated castor oil 1 used in the first step was 90 parts by mass, and the amount of talc used in each of the second steps was 50 parts by mass.

[0080] [Examples 18 to 20] Coated granular fertilizers provided with a coating having a multilayer structure formed of four layers of hardened vegetable oil and three layers of talc were obtained in the same manner as in Example 8, except that Talcs 2 to 4 were used instead of Talc 1.

[0081] [Example 21] A coated granular fertilizer having a coating film with a multilayer structure formed of 10 layers of hardened vegetable oil and 9 layers of talc was obtained in the same manner as in Example 4, except that Talc 2 was used instead of Talc 1.

[0082] [Example 22] A coated granular fertilizer having a coating film with a multilayer structure formed of four layers of hydrogenated vegetable oil and three layers of talc was obtained in the same manner as in Example 8, except that hydrogenated soybean oil 1 was used instead of hydrogenated castor oil 1 and the heating temperature of the large urea particles was set to 55°C.

[0083] Example 23 A coated granular fertilizer having a coating film with a multilayer structure formed of four layers of hydrogenated vegetable oil and three layers of talc was obtained in the same manner as in Example 8, except that hydrogenated rapeseed oil 1 was used instead of hydrogenated castor oil 1 and the heating temperature of the large urea particles was set to 55°C.

[0084] Example 24 Large granular urea (1,000 parts by mass) was placed in a rotating tank and tumbling. The large granular urea was heated to about 70°C with hot air, after which liquid paraffin (Moresco White P-350P, manufactured by MORESCO Corporation) (10 parts by mass) was added and the tumbling state was continued for 5 minutes. The paraffin-coated large granular urea was tumbling, and talc 1 (10 parts by mass) was added. The tumbling state was maintained under heated conditions for 3 minutes or more, and the first second step was carried out to form a first talc layer. Next, castor hydrogenated oil 1 (20 parts by mass) was added, and the tumbling state was maintained under heated conditions for 3 minutes or more, and the first step was carried out to form a first hydrogenated vegetable oil layer on the outside of the first talc layer. Thereafter, the second step was repeated eight times and the first step was repeated seven times alternately. Next, the ninth first step was carried out in the same manner as the first first step, except that the amount of castor hydrogenated oil 1 used was 50 parts by mass, and a ninth hydrogenated vegetable oil layer was formed on the outside of the ninth talc layer. The fertilizer was cooled to near room temperature, and a coated granular fertilizer with a coating having a multilayer structure formed from nine talc layers and nine hydrogenated vegetable oil layers was obtained.

[0085] Example 25 Large granular urea (1,000 parts by mass) was placed in a rotating tank and heated to about 70°C with hot air. Liquid paraffin (Moresco White P-350P, manufactured by MORESCO Corporation) (10 parts by mass) was then added, and the rolling state was continued for 5 minutes. The paraffin-coated large granular urea was then heated and added with castor oil 1 (50 parts by mass) melted at 105°C. The rolling state was maintained under heated conditions for 3 minutes or more, thereby carrying out the first step, and a first hydrogenated vegetable oil layer was formed. Next, talc 1 (10 parts by mass) was added, and the rolling state was maintained under heated conditions for 3 minutes or more, thereby carrying out the first step, and a first talc layer was formed outside the first hydrogenated vegetable oil layer. Next, the second step was carried out in the same manner as the first step, except that the amount of castor oil 1 used was changed to 20 parts by mass, and a second hydrogenated vegetable oil layer was formed outside the first talc layer. Thereafter, the first step was repeated alternately seven times in the same manner as the second step eight times and the first step two times, and the mixture was cooled to near room temperature to obtain a coated granular fertilizer provided with a coating having a multilayer structure formed of nine talc layers and nine hardened vegetable oil layers.

[0086] Comparative Example 5 A coated granular fertilizer was obtained in the same manner as in Comparative Example 1, except that 240 parts by mass of hardened castor oil 1 and 60 parts by mass of talc 1 were used.

[0087] Comparative Example 6 A coated granular fertilizer was obtained in the same manner as in Comparative Example 1, except that 150 parts by mass of hardened castor oil 1 and 150 parts by mass of talc 1 were used.

[0088] [Comparative Example 7] A coated granular fertilizer was obtained in the same manner as in Comparative Example 2, except that the amount of castor hardened oil 1 used in the first step of the first run was 260 parts by mass, and the amount of talc used in the second step was 20 parts by mass.

[0089] [Comparative Example 8] A coated granular fertilizer was obtained in the same manner as in Comparative Example 2, except that the amount of castor hardened oil 1 used in the first step was 230 parts by mass, and the amount of talc used in the second step was 50 parts by mass.

[0090] Comparative Examples 9 and 10 Coated granular fertilizers were obtained in the same manner as in Example 8, except that glass fibers 1 and 2 were used instead of talc 1.

[0091] Comparative Examples 11 and 12 Coated granular fertilizers were obtained in the same manner as in Example 4, except that glass fibers 1 and 2 were used instead of talc 1.

[0092] Comparative Examples 13 and 16 Coated granular fertilizers were obtained in the same manner as in Example 4, except that paraffin wax or stearic acid was used instead of hardened castor oil 1 and the heating temperature of the large urea particles was set to 55°C.

[0093] Comparative Examples 14 and 15 Coated granular fertilizers were obtained in the same manner as in Example 4, except that FT wax or carnauba wax was used instead of hardened castor oil 1.

[0094] [Evaluation of soil degradability of vegetable hydrogenated oils, petroleum-based waxes, etc.] (Method of preparing evaluation samples) 10 g of evaluation samples, such as vegetable hydrogenated oils and petroleum-based waxes shown in Table 1, were placed in a thermostatic chamber set at 105°C and melted. The molten evaluation samples were cast onto a glass plate using a film applicator (manufactured by Allgood Co., Ltd., gap 600 μm), cooled and solidified at room temperature, and a film with a thickness of approximately 300 μm was created. (Evaluation method) 20 g of soil (collected from Kasai City, Hyogo Prefecture) was placed in a plastic cup (50 mL). The prepared film was cut into a 2 cm square, approximately 100 mg test piece and weighed (M1). The test piece was placed on the soil, and 20 g of soil was added from above. The sample was then lightly tapped on the ground approximately 10 times and packed. The sample and a cup of water for moisture retention were arranged on a tray, placed in a plastic bag, and loosely tied at the top. The test pieces were placed in an incubator set at 28°C, and the weight of the cup was measured every two weeks from the start of the test. If any changes were observed, water was added using a spray bottle. After one month, the test pieces were recovered from the soil, lightly washed, and thoroughly dried at room temperature overnight or more. The mass of the test pieces was measured again (M2), and the mass loss rate (W = M2 / M1 x 100 (%)) was calculated. (Evaluation criteria) A: Mass loss rate W is 20% or more but less than 40% B: Mass loss rate W is 10% or more but less than 20% or 40% or more but less than 60% C: Mass loss rate W is less than 10% or 60% or more A rating of A indicates that the soil decomposition of the coated granular fertilizer as a coating is good. The results are shown in Table 1.

[0095]

[0096] [Evaluation of manufacturability of coated granular fertilizers] (Evaluation method) The degree of sticking between the coated granular fertilizers or between the coated granular fertilizers and the rotating tub that occurred during the production of the coated granular fertilizers of Comparative Examples 13 to 16 and Example 4 was evaluated visually. The results are shown in Table 2. (Evaluation criteria) ◯: Almost no sticking occurred between the coated granular fertilizers or between the coated granular fertilizers and the rotating tub. ×: Significant sticking occurred between the coated granular fertilizers or between the coated granular fertilizers and the rotating tub.

[0097]

[0098] [Measurement of Particle Size of Talc or Inorganic Fiber] The particle size of talc or inorganic fiber was defined as the median diameter (D50) obtained in particle size distribution measurement using the measuring instrument shown below. The measurement was performed in a dry state using a dry laser diffraction particle size measuring instrument (Mastersizer 3000, manufactured by Malvern Analytical). [Measurement of Circularity Coefficient of Talc or Inorganic Fiber] Images of talc or inorganic fiber in the micrometer range were taken using a scanning electron microscope (SU-3800, manufactured by Hitachi High-Tech Corporation). Talc or inorganic fiber was adhered to a sample stage using conductive tape and subjected to platinum sputtering at 20 mA for 120 seconds using an ion sputtering instrument (E-1030, manufactured by Hitachi, Ltd.). Images were then taken at a magnification of approximately 50 to 30,000 times, depending on the size of the talc or inorganic fiber, so that there were approximately 10 to 100 particles per field of view. The photographed images of the talc or inorganic fibers were analyzed using image analysis particle size distribution measurement software (Mac-View, manufactured by Mountec Co., Ltd.) to measure the circularity coefficient (= 4π × area × perimeter). More than 100 particles were analyzed to obtain an average value. [Measurement of aspect ratio constant of talc or inorganic fibers] The aspect ratio constant of talc or inorganic fibers was defined as {D50 - Dmean} / Dmean, using the median diameter (D50) and the median diameter (Dmean) measured by centrifugal sedimentation according to JIS R1619.

[0099] [Evaluation 1: Initial Dissolution Controllability] 2.5 g (60 to 80 granules) of the prepared coated granular fertilizer was placed in a sample bottle, 100 mL of water was added, and the fertilizer was allowed to stand at 25°C. After 7 days, 0.6 mL of water was collected from the sample bottle, and the urea concentration was measured using an ultraviolet-visible spectrophotometer (UV-1900i, manufactured by Shimadzu Corporation). Based on the measured urea concentration, the urea dissolution rate E1 (%) from the coated granular fertilizer was calculated. The results are shown in Tables 3 to 10. (Evaluation Criteria) A: Dissolution rate E1 is less than 10% B: Dissolution rate E1 is 10% or more but less than 30% C: Dissolution rate E1 is 30% or more A rating of A or B indicates that the dissolution controllability is good.

[0100] [Evaluation 2: Impact resistance (initial)] The urea elution rate E2 (%) after 7 days of coated granular fertilizers that had been spread using a side stripe fertilizer applicator (manufactured by Yanmar Co., Ltd.) was measured in the same manner as above, and evaluation was performed based on the value of E2 - E1. The results are shown in Tables 3 to 7, 9, and 10. (Evaluation criteria) A: E2 - E1 is less than 5% B: E2 - E1 is 5% or more but less than 15% C: E2 - E1 is 15% or more A rating of A or B can be considered to indicate good impact resistance.

[0101] [Evaluation 3: Medium-Term Release Controllability] After 42 days, 0.6 ml of water was collected from the sample bottle in the same manner as in Evaluation 1, and the release rate E3 (%) of urea from the coated granular fertilizer was calculated. The results are shown in Tables 3 to 7, 9, and 10. (Evaluation Criteria) A: Release rate E3 is less than 20% B: Release rate E3 is 20% or more but less than 40% C: Release rate E3 is 40% or more When the rating is A or B, the release controllability can be evaluated as good. [Evaluation 4: Impact Resistance (Medium Term)] The release rate E4 (%) of urea after 42 days of the coated granular fertilizer, which had been applied using a side stripe fertilizer applicator (manufactured by Yanmar Co., Ltd.), was measured in the same manner as above, and evaluation was performed based on the value of E4 - E3. The results are shown in Tables 3 to 7, 9, and 10. (Evaluation Criteria) A: E4-E3 is less than 5% B: E4-E3 is 5% or more and less than 15% C: E4-E3 is 15% or more When the evaluation is A or B, the impact resistance can be evaluated as good.

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Claims

1. A coated granular fertilizer comprising a granular fertilizer and a coating that coats the granular fertilizer, the coating containing hydrogenated vegetable oil and talc, the talc forming two or more talc layers that overlap in the thickness direction of the coating.

2. The coated granular fertilizer according to claim 1, wherein the hardened vegetable oil forms two or more layers of hardened vegetable oil that overlap in the thickness direction of the coating.

3. The coated granular fertilizer according to claim 2, wherein the hardened vegetable oil layer forms the outermost layer of the coating.

4. The coated granular fertilizer according to claim 1, wherein the mass ratio of the granular fertilizer to the coating is 1:0.1 or more and 1:0.5 or less.

5. The coated granular fertilizer according to claim 1, wherein the talc content in the coating is 5% by mass or more and 60% by mass or less.

6. The coated granular fertilizer according to any one of claims 1 to 5, wherein the melting point of the hydrogenated vegetable oil is 60°C or higher and 100°C or lower.

7. The coated granular fertilizer according to any one of claims 1 to 5, wherein the particle size of the talc is 1 μm or more and 35 μm or less.

8. A method for producing a coated granular fertilizer, comprising: a first step of adding heated and melted hardened vegetable oil to the granular fertilizer in a rolling state; and a second step of adding talc to the granular fertilizer in a rolling state, wherein the first step and the second step are each repeated two or more times.

9. The method for producing a coated granular fertilizer according to claim 8, wherein the first step and the second step are each repeated alternately two or more times.

10. A method for producing a coated granular fertilizer as described in claim 8 or 9, wherein the mass ratio of the granular fertilizer to the total amount of the hydrogenated vegetable oil added in the first step is 1000:100 or more and 1000:280 or less.

11. A method for producing a coated granular fertilizer according to claim 8 or 9, wherein the mass ratio of the granular fertilizer to the total amount of the talc added in the second step is 1000:20 or more and 1000:180 or less.

12. A method for producing a coated granular fertilizer according to claim 8 or 9, wherein the mass ratio of the granular fertilizer to the amount of talc added per second step is 1000:0.1 or more and 1000:50 or less.

13. A method for producing a coated granular fertilizer according to claim 8 or 9, wherein a hardened vegetable oil layer and a talc layer that coat the granular fertilizer are formed by the first step and the second step, respectively.

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