Coated granular fertilizer and production method for coated granular fertilizer

Abstract

A coated granular fertilizer according to the present invention comprises a granular fertilizer and a coating film that coats the granular fertilizer. The coating film includes a hardened vegetable oil and inorganic fibers. The inorganic fibers are at least one type of inorganic fibers selected from the group that consists of wollastonite fibers, titanium oxide fibers, carbon fibers, and halloysite fibers.

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 Nos. 2023-186146 and 2024-154193, the disclosures of which are 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 being able to control the leaching of fertilizer components, maintain their effectiveness for a long period of time, and reduce the number of times they are applied. Conventionally, coated granular fertilizers have been known in which the surface of granular fertilizers containing fertilizer components is coated with a resin film (Patent Document 1).

[0004] In order to prevent the resin used in the coating from remaining in soil, etc. after the fertilizer components of the coated granular fertilizer have been leached out, a coated granular fertilizer has been developed that is provided with a coating made of wax that is decomposable in natural environments such as soil (Patent Document 2).

[0005] Regarding coated granular fertilizers having a coating made of wax, coated granular fertilizers containing mineral fibers have been developed to prevent the coated granular fertilizers from sticking together and forming blocks during production (Patent Document 3).

[0006] Japanese Patent Publication No. 54-003104 Japanese Patent Publication No. 2002-293684 Japanese Patent Publication No. 47-041813

[0007] The present inventors have found that coated granular fertilizers having a coating containing degradable wax have a problem in that, when the fertilizer is spread using a spreader such as a side stripe fertilizer applicator, the coating is damaged and the fertilizer components are leached out earlier than intended, because the strength of the coating is insufficient.

[0008] An object of the present invention is to provide a coated granular fertilizer that has a coating containing degradable wax and that can suppress the early leaching of fertilizer components even when applied 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 containing specific inorganic fibers 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 inorganic fibers, and the inorganic fibers are at least one fiber selected from the group consisting of wollastonite fibers, titanium oxide fibers, carbon fibers, and halloysite fibers. (2) The coated granular fertilizer according to (1) above, in which the inorganic fibers are dispersed in the hardened vegetable oil in the coating. (3) The coated granular fertilizer according to (1) or (2) above, in which the mass ratio of the granular fertilizer to the coating is 1:0.1 or more and 1:0.3 or less. (4) The coated granular fertilizer according to any one of (1) to (3) above, wherein the content of the inorganic fibers in the coating is 0.1% by mass or more and 30% by mass or less. (5) The coated granular fertilizer according to any one of (1) to (4) above, wherein the coating has a first layer containing the hardened vegetable oil and a second layer containing the hardened vegetable oil and the inorganic fibers. (6) The coated granular fertilizer according to (5) above, wherein the mass of the hardened vegetable oil in the second layer is equal to or less than the mass of the hardened vegetable oil in the first layer. (7) The coated granular fertilizer according to (5) or (6) above, wherein the content of the hardened vegetable oil in the second layer is 70% by mass or more and 99% by mass or less, and the content of the inorganic fibers is 1% by mass or more and 30% by mass or less. (8) The coated granular fertilizer according to any one of (5) to (7) above, wherein the second layer is disposed outside the first layer. (9) The coated granular fertilizer according to any one of (5) to (8) above, wherein the second layer is the outermost layer of the coating. (10) The coated granular fertilizer according to any one of (1) to (9) above, wherein the inorganic fibers have an aspect ratio of 5 or more and 12 or less. (11) The coated granular fertilizer according to any one of (1) to (10) above, wherein the inorganic fibers are the carbon fibers, the titanium oxide fibers, or the halloysite fibers. (12) The coated granular fertilizer according to any one of (1) to (10) above, wherein the inorganic fibers are the wollastonite fibers.(13) The coated granular fertilizer according to (12) above, wherein the fiber length of the wollastonite fibers is 15 μm or more and 200 μm or less. (14) The coated granular fertilizer according to (12) (or (13)) above, wherein the particle size of the wollastonite fibers is 5 μm or more and 60 μm or less. (15) The coated granular fertilizer according to any one of (1) to (14) above, wherein the hydrogenated vegetable oil is at least one selected from the group consisting of hydrogenated castor oil, hydrogenated rapeseed oil, and hydrogenated soybean oil. (16) The coated granular fertilizer according to any one of (1) to (15) above, wherein the melting point of the hydrogenated vegetable oil is 60°C or more and 100°C or less.

[0010] The present invention also provides a method for producing a coated granular fertilizer as follows: (17) A method for producing a coated granular fertilizer, comprising the steps of adding heat-melted hardened vegetable oil to a granular fertilizer, and adding a coating composition containing hardened vegetable oil and inorganic fibers to the granular fertilizer, wherein the inorganic fibers are at least one selected from the group consisting of wollastonite fibers, titanium oxide fibers, carbon fibers, and halloysite fibers. (18) The method for producing a coated granular fertilizer according to (17), wherein the inorganic fibers are dispersed in the hardened vegetable oil in the coating composition.

[0011] According to the present invention, it is possible to provide a coated granular fertilizer that has a coating containing degradable wax and that can suppress the early leaching of fertilizer components even when applied 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, and the coating contains hardened vegetable oil and inorganic fibers.

[0014] The granular fertilizer contains fertilizer components and may contain optional 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, or by mixing and granulating the fertilizer components and the additives. 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 cuboidal, cylindrical, or the like.

[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 a sieving method using a sieve 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, bentonite, clay, humic acid, zeolite, sepiolite, 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, clay, silica powder, diatomaceous earth, zeolite, gypsum, starch, molasses, bentonite, lignin sulfonic acid, konjac flying powder, sepiolite, concentrated yeast fermentation waste liquid, ammonia liquid, kaolin, sandstone powder, sulfuric acid, phosphoric acid liquid, talc powder, attapulgite, pulp waste liquid, andesite powder, carboxymethyl cellulose, corn starch, rice bran, light-burned magnesia, and slaked lime.

[0018] The coating may have a first layer containing the hardened vegetable oil and a second layer containing the hardened vegetable oil and the inorganic fibers. The second layer may contain a higher content of the inorganic fibers than the first layer. When the second layer is located outside the first layer, the mass of the hardened vegetable oil in the second layer is preferably equal to or less than the mass of the hardened vegetable oil in the first layer. This allows the outer second layer containing a high content of the inorganic fibers to be relatively thinner than the inner first layer, resulting in a denser overall inorganic fiber structure. The first layer may be layered on the granular fertilizer, and the second layer may be layered on the first layer from the outside, or the second layer may be layered on the granular fertilizer, and the first layer may be layered on the second layer from the outside. That is, the first layer containing a lower content of inorganic fibers may be located inside the second layer or outside the second layer.

[0019] When the second layer is formed outside the first layer, the mass of the hardened vegetable oil in the first layer located on the inside of the coating may be equal to or greater than the mass of the hardened vegetable oil in the second layer located on the outside.

[0020] The coating may have two or more of the first layers, or may have two or more of the second layers. In this case, it is preferable that the coating has the first layer and the second layer adjacent to each other in the thickness direction. Furthermore, the coating may have a layer structure consisting of one first layer, the second layer contacting the first layer from the inside, and the second layer contacting the first layer from the outside, or may have a layer structure consisting of one second layer, the first layer contacting the second layer from the inside, and the first layer contacting the second layer from the outside.

[0021] The primary function of the first layer is to control the leaching of the fertilizer components. Meanwhile, the primary function of the second layer is to protect the portions disposed further inward, particularly the first layer, from mechanical impact. Furthermore, by containing the hydrogenated vegetable oil, the second layer also functions to control the leaching of the fertilizer components. With this layer structure, the coated granular fertilizer can be prevented from being damaged during transportation, storage, and application by the spreader, thanks to the second layer functioning primarily as a reinforcing layer, thereby preventing premature leaching of the fertilizer components. Furthermore, the coated granular fertilizer can be provided to the soil over a predetermined period of time, thanks to the first layer functioning primarily as a leaching control layer. Furthermore, the coated granular fertilizer inhibits premature leaching of the fertilizer components compared to a coating consisting of a single layer containing the hydrogenated vegetable oil and the inorganic fibers, thereby facilitating the long-term supply of the fertilizer components to the soil.

[0022] The coating may be formed from a coating composition containing the hardened vegetable oil, the inorganic fibers, and optional additives. When the first layer and the second layer each contain the hardened vegetable oil and the inorganic fibers, each layer may be formed from a coating composition containing the hardened vegetable oil and the inorganic fibers. That is, in each of the first layer and the second layer, the inorganic fibers may be dispersed in the hardened vegetable oil. More specifically, each of the first layer and the second layer may be formed from a coating composition containing the hardened vegetable oil, the inorganic fibers, and optional additives. In each of the first layer and the second layer formed from such a coating composition, at least half of the inorganic fibers are dispersed so that their length direction is aligned with the circumferential direction of the coated granular fertilizer. Therefore, when the second layer is disposed outside the first layer, it is believed to function to divert the propagation path of cracks generated on the surface of the coating from a path toward the center of the coated granular fertilizer, thereby suppressing the propagation of the cracks toward the first layer.

[0023] The first layer may be the innermost layer of the coating or the outermost layer of the coating. The second layer may be the innermost layer of the coating or the outermost layer of the coating. When the second layer is the outermost layer of the coating, the coated granular fertilizer has excellent abrasion resistance.

[0024] The content of the vegetable hardened oil in the first layer is preferably 80% by mass or more, more preferably 85% by mass or more, even more preferably 90% by mass or more, and even more preferably 95% by mass or more. The content of the vegetable hardened oil in the first layer may be 100% by mass. Meanwhile, the content of the inorganic fibers in the first layer is preferably 5% by mass or less, more preferably 1% by mass or less, and even more preferably 0.1% by mass or less. The first layer may be substantially free of inorganic fibers. A first layer containing a predetermined amount or more of vegetable hardened oil can fully function as an elution control layer.

[0025] The content of the inorganic fibers in the second layer is preferably 0.5% by mass or more, more preferably 1% by mass or more, and even more preferably 2% by mass or more. The content of the inorganic fibers in the second layer is preferably 35% by mass or less, more preferably 30% by mass or less, and even more preferably 20% by mass or less. Meanwhile, the content of the vegetable hardened oil in the second layer is preferably 65% ​​by mass or more, more preferably 70% by mass or more, and even more preferably 80% by mass or more. The content of the vegetable hardened oil in the second layer may be 95% by mass or less, 90% by mass or less, 85% by mass or less, or 80% by mass or less. A second layer containing a predetermined amount or more of inorganic fibers can fully function as a reinforcing layer. Furthermore, by keeping the content of inorganic fibers below a predetermined amount, thickening of the coating composition during production is suppressed. This has the advantages of making it easier to form a second layer with excellent inorganic fiber dispersibility and reducing the risk of coating defects.

[0026] The mass ratio of the first layer to the second layer may be, for example, 1:9 to 9:1. The mass of the first layer is preferably equal to or greater than the mass of the second layer. The mass ratio of the first layer to the second layer is preferably 5:5 to 8:2, and more preferably 6:4 to 8:2.

[0027] The mass ratio of the hydrogenated vegetable oil in the second layer to the hydrogenated vegetable oil in the first layer is preferably 1:0.5 or more, more preferably 1:1 or more, and even more preferably 1:2 or more. The mass ratio is preferably 1:5 or less.

[0028] The mass ratio of the granular fertilizer to the coating is preferably 1:0.1 or more and 1:0.5 or less, more preferably 1:0.3 or more and 1:0.4 or less, and even more preferably 1:0.3.

[0029] The content of the inorganic fibers in the coating is preferably 0.1% by mass or more and 30% by mass or less, and more preferably 0.5% by mass or more and 20% by mass or less.

[0030] 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.

[0031] 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.

[0032] Preferably, the coating is substantially free of the biodegradable resin. The content of the biodegradable 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 animal and plant fats and can be decomposed by lipolytic bacteria that are widespread in natural environments.

[0033] The thickness of the coating is, for example, 50 to 250 μm. The thickness of the coating can be measured by observing the cross section 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.

[0034] The inorganic fibers are at least one selected from the group consisting of wollastonite fibers, titanium oxide fibers, carbon fibers, and halloysite fibers.

[0035] Wollastonite is a type of mineral, also known as wollastonite, wollastonite, or wollastonite, and is a silicate, CaSiO ３ The wollastonite fiber contains calcium silicate represented by the formula: The wollastonite fiber is a type of wollastonite having needle-like or columnar crystals and has physical properties commonly used in the fiber field. That is, the wollastonite fiber has an aspect ratio of at least 3, preferably 24 or less, and more preferably 5 or more and 12 or less. The wollastonite fiber also preferably has a circularity coefficient of less than 0.6. Furthermore, the fiber length of the wollastonite fiber is preferably 10 μm or more and 400 μm or less, more preferably 15 μm or more and 200 μm or less, and even more preferably 15 μm or more and 100 μm or less. A fiber length of 10 μm or more allows the first layer to function sufficiently as a reinforcing layer. Furthermore, a fiber length of 400 μm or less is thought to prevent the wollastonite fiber from protruding from the first layer, thereby suppressing the early leaching of fertilizer components caused by this protrusion. These physical properties can be measured based on images of wollastonite fibers in the micrometer range captured using a scanning electron microscope (SU-3800, manufactured by Hitachi High-Tech Corporation). Specifically, a sample of wollastonite fiber is attached to a test table using conductive tape, and platinum sputtering is performed for 120 seconds at 20 mA using an ion sputtering device (E-1030, manufactured by Hitachi, Ltd.) to prepare a photographic subject. Next, the sample is photographed at a magnification of approximately 50 to 3000 times, depending on the size, so that approximately 10 to 100 fibers per field of view are captured, and images are obtained. Then, using image analysis particle size distribution software (Mac-View, manufactured by Mountec Co., Ltd.), the fiber length (i.e., the major axis), minor axis, aspect ratio (major axis / minor axis), and circularity coefficient (4π × area × perimeter) of 100 or more fibers captured in the photographic image are measured, and the average values ​​of these are calculated. Here, the major axis is defined as the maximum distance between two points on the fiber surface captured in the fiber image. The minor axis is defined as the maximum value of the length of the line segment perpendicular to the major axis. If there are multiple such maximum values, the average value of these is taken as the minor axis.

[0036] Specific examples of the wollastonite fiber include the KGP series such as KGP-H45 (manufactured by Kansai Matec Co., Ltd.), the KAP series such as KAP-150 (manufactured by Kansai Matec Co., Ltd.), the KTP series such as KTP-H02, the KSP series such as KSP-N01, the WP series such as WP200 (manufactured by Nippon Talc Co., Ltd.), the WFA series such as WFA80 (manufactured by Nippon Talc Co., Ltd.), the WFB series such as WFB15 (manufactured by Nippon Talc Co., Ltd.), the WFC series such as WFC5 (manufactured by Nippon Talc Co., Ltd.), the NYAD series such as NYAD 1250 (manufactured by IMERYS), and the NYGLOS series such as NYGLOS 12 (manufactured by IMERYS). The coating may contain only one of these, or may contain two or more of them.

[0037] The titanium oxide fibers are titanium oxide fibers having needle-shaped crystals and an aspect ratio of 3 or more. The aspect ratio of the titanium oxide fibers is preferably 21 or less, more preferably 10 or less. The circularity coefficient of the titanium oxide fibers is preferably less than 0.6. The fiber length of the titanium oxide fibers is preferably 1 μm or more and 10 μm or less, but may be 10 μm or more and 400 μm or less, or may be 15 μm or more and 200 μm or less. These physical properties of the titanium oxide fibers can be measured in the same manner as for the wollastonite fibers.

[0038] The aspect ratio of the carbon fiber is preferably 3 or more and 20 or less, more preferably 5 or more and 15 or less. The circularity coefficient of the carbon fiber is preferably less than 0.6. The fiber length of the carbon fiber is preferably 10 μm or more and 400 μm or less, more preferably 15 μm or more and 200 μm or less. These physical property values ​​of the carbon fiber can be measured in the same manner as the wollastonite fiber.

[0039] The particle size of the inorganic fibers is preferably 5 μm or more and 70 μm or less. More specifically, the particle size of the wollastonite fibers is preferably 5 μm or more and 60 μm or less. The particle size of the titanium oxide fibers is preferably 15 μm or more and 25 μm or less. The particle size of the carbon fibers is preferably 60 μm or more and 70 μm or less. These particle sizes refer to volume-based median diameters (D50), and can be measured by a dry method using a laser diffraction particle size analyzer (Mastersizer 3000, manufactured by Malvern Analytical).

[0040] The halloysite fiber is a type of mineral, and Al ２ Si ２ O ５ (OH) ４ ・2H ２ The halloysite fiber contains an alumino-silica mineral represented by O. The halloysite fiber is a type of halloysite having needle-shaped crystals, and preferably has an aspect ratio of 3 or more. The aspect ratio of the halloysite fiber is preferably 20 or less, more preferably 15 or less. The circularity coefficient of the halloysite fiber is preferably less than 0.6. The fiber length of the halloysite fiber is preferably 0.1 μm or more and 5 μm or less, but may be 0.1 μm or more and 400 μm or less, or may be 0.1 μm or more and 200 μm or less. These physical property values ​​of the halloysite fiber can be measured in the same manner as the wollastonite fiber.

[0041] The inorganic fiber is preferably the wollastonite fiber. Specifically, while the titanium oxide fiber and the carbon fiber are artificially produced synthetically, the wollastonite fiber is a natural product. Therefore, using the wollastonite fiber reduces the energy consumption required to produce the coated granular fertilizer, which is advantageous from the perspective of environmental impact. Furthermore, the titanium oxide fiber tends to form irregularities on the surface of the coated granular fertilizer, while the carbon fiber tends to turn the coated granular fertilizer black. In other words, the titanium oxide fiber and the carbon fiber impair the appearance of the coated granular fertilizer. On the other hand, the wollastonite fiber does not exhibit this problem. Furthermore, calcium silicate, which constitutes the wollastonite fiber, can contribute to the promotion of agricultural crop growth, similar to fertilizer components. Therefore, even if the coating is left in soil, such as a paddy field, after its intended purpose, it is unlikely to adversely affect the cultivation of agricultural crops.

[0042] 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 hydrogenated castor oil, hydrogenated rapeseed oil, hydrogenated soybean oil, hydrogenated palm oil, hydrogenated peanut oil, hydrogenated jojoba oil, hydrogenated cottonseed oil, and hydrogenated coconut oil. The coating may contain only one or two or more of the hydrogenated vegetable oils. Among these, at least one hydrogenated vegetable oil selected from the group consisting of hydrogenated castor oil, hydrogenated rapeseed oil, and hydrogenated soybean oil is preferred.

[0043] 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.

[0044] 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 a low-viscosity hydrogenated vegetable oil in the outermost layer of the coating, caking of the fertilizer particles during production and storage is suppressed.

[0045] Examples of optional additives that may be contained in the coating include the anti-floating agent, the colorant, the antibacterial agent, etc. The content of the optional additives in the coating is, for example, 0.1 to 10% by mass.

[0046] The coated granular fertilizer can have a fertilizer component elution rate E1 of 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 of the fertilizer components is defined as E2, the fertilizer component elution rate can be E2 - E1 < 15%. The elution rate can be calculated by measuring the concentrations of the fertilizer components in water collected after a predetermined time has elapsed using an ultraviolet-visible spectrophotometer (Shimadzu Corporation, UV-1900i).

[0047] 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 and other coated granular fertilizers not included therein may be sprayed onto the paddy field (soil). With such a compound fertilizer, the granular fertilizer with exposed fertilizer components can supply sufficient amounts of fertilizer components to grass crops immediately after spraying, while the coated granular fertilizer can sustain the supply of fertilizer components for a predetermined period of time.

[0048] 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 soil and other external environments. In this case, 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. With the coated granular fertilizer, the coating, which functions as a reinforcing layer, suppresses damage caused by such impacts and prevents early leaching of the fertilizer components.

[0049] Next, a method for producing the coated granular fertilizer will be described.

[0050] The method for producing the coated granular fertilizer includes a coating forming step of forming the coating on the surface of the granular fertilizer.

[0051] The coating process involves contacting the granular fertilizer in a rolling state with the hardened vegetable oil heated to above its melting point to form the first layer on the granular fertilizer. Separately, the inorganic fibers are dispersed in the hardened vegetable oil heated to above its melting point to prepare a heated coating composition. The granular fertilizer having the first layer in a rolling state is then contacted with the heated coating composition, the second layer is layered on the surface of the first layer, and the mixture is cooled to obtain the coated granular fertilizer. The coated granular fertilizer thus produced by first preparing a coating composition and then contacting the granular fertilizer having the first layer has the advantage that the inorganic fibers are uniformly dispersed in the second layer, thereby preventing aggregation of the inorganic fibers and resulting in excellent coating smoothness and strength. The coated granular fertilizer can also be obtained by forming the second layer on the surface of the granular fertilizer and then forming the first layer on the surface of the second layer. Alternatively, the coated granular fertilizer can be obtained by forming only the second layer on the surface of the granular fertilizer.

[0052] The method may further include, prior to the coating formation step, a pre-treatment step in which the granular fertilizer, which has been brought into a rolling state using a rolling device, is brought into contact with paraffin while being heated with hot air. Such treatment has the advantage of improving the rolling properties of the granular fertilizer in the rolling device, making it easier for the coating composition to adhere to the granular fertilizer. Furthermore, the method may further include, after the coating formation step, a post-treatment step in which an optional additive, such as a surfactant or an anti-caking agent, is added to the surface of the coating. The pre-treatment step and the post-treatment step are not the coating formation step.

[0053] 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.

[0054] For example, in another embodiment of the coated granular fertilizer according to the present invention, the coating covering the granular fertilizer may have only a single layer containing both hardened vegetable oil and inorganic fibers. In this case, in order for the single layer to function both as a reinforcing layer and as an elution control layer, the content of the single layer relative to the granular fertilizer may be 20% by mass or more, the content of the inorganic fibers in the single layer may be 10% by mass to 30% by mass, and the content of the hardened vegetable oil in the single layer may be 70% by mass to 90% by mass.

[0055] In this case, the inorganic fibers are dispersed in the hardened vegetable oil heated above its melting point to prepare a heated coating composition, and the granular fertilizer in a rolling state is brought into contact with this coating composition, followed by cooling to obtain a coated granular fertilizer having a single-layer coating.

[0056] 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. In the examples, "%" means "% by mass" unless otherwise specified.

[0057] [Granular fertilizer] Large-grain urea: urea (manufactured by China Blue Chemical Limited, particle size (D50) approximately 3 mm) [Hydrogenated vegetable oil] Hydrogenated castor oil: fatty acid triglyceride ("Hydrogenated castor oil" manufactured by Ito Oil Mills, Ltd., melting point 80 to 90°C) Hydrogenated rapeseed oil: fatty acid triglyceride ("Extremely hydrogenated rapeseed oil" manufactured by Yokoseki Oil Industries Co., Ltd., melting point 67°C) Hydrogenated soybean oil: fatty acid triglyceride ("Extremely hydrogenated soybean oil" manufactured by Yokoseki Oil Industries Co., Ltd., melting point 67°C) [Inorganic fibers] Wollastonite fiber 1 ("KGP-H45" manufactured by Kansai Matec Co., Ltd.) Wollastonite fiber 2 ("KGP-H40" manufactured by Kansai Matec Co., Ltd.) Wollastonite fiber 3 ("KTP-H02" manufactured by Kansai Matec Co., Ltd.) Wollastonite fiber 4 ("WFB15" manufactured by Nippon Talc Co., Ltd.) Wollastonite fiber 5 (Kansai Matec Co., Ltd. "KGP-H85") Wollastonite fiber 6 (Nippon Talc Co., Ltd. "WFA80") Wollastonite fiber 7 (Kansai Matec Co., Ltd. "KSP-N01") Carbon fiber 1 (Mitsubishi Chemical Corporation "Dialead K223HM (200μ)") Carbon fiber 2 (Teijin Limited "HT M100 40MU") Titanium oxide fiber 1 (Ishihara Sangyo Kaisha, Ltd. "FTL-100") Titanium oxide fiber 2 (Ishihara Sangyo Kaisha, Ltd. "FTL-400") Halloysite fiber 1 (Fimatec Co., Ltd. "HP-M") Halloysite fiber 2 (Fimatec Co., Ltd. "HP-A") [Filler] Glass fiber 1 (Central Glass Fiber Co., Ltd. "EFDE-50-01") Glass fiber 2 (Central Glass Fiber Co., Ltd. "EFH150-01") Talc ("Micro Ace P-2" manufactured by Nippon Talc Co., Ltd.) Calcium carbonate ("Vigot-15" manufactured by Shiraishi Calcium Co., Ltd.) [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) [Plant-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" manufactured by Kao Chemical Corporation (hereinafter referred to as behenyl alcohol).

[0058] [Example 1] Castor oil (72 parts by mass) was heated and melted at 105°C, and mixed with wollastonite fiber 1 (18 parts by mass) heated to 105°C, to obtain a coating composition in which wollastonite fiber 1 was dispersed in castor oil. Granular fertilizer (large granular urea, particle size (D50) approximately 3 mm, 1,000 parts by mass) was placed in a rotating tank and tumbling. The large granular urea was heated to approximately 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, hardened castor oil (210 parts by mass) heated to 105°C was added to the paraffin-coated large granular urea in the tumbling state, and the tumbling state was maintained under heated conditions for 3 minutes or more, thereby forming a first layer. The granular fertilizer having the first layer was tumbling under heated conditions, and the coating composition heated to 105°C was added, and the tumbling state was maintained under heated conditions until the total amount of the added hardened castor oil and coating composition reached 300 parts by mass, thereby forming a second layer. The fertilizer was cooled to near room temperature, and a coated granular fertilizer was obtained.

[0059] Example 2 A coated granular fertilizer was obtained in the same manner as in Example 1, except that Wollastonite Fiber 2 was used instead of Wollastonite Fiber 1.

[0060] Example 3 A coated granular fertilizer was obtained in the same manner as in Example 1, except that Wollastonite Fiber 4 was used instead of Wollastonite Fiber 1.

[0061] Example 4 A coated granular fertilizer was obtained in the same manner as in Example 1, except that Wollastonite Fiber 5 was used instead of Wollastonite Fiber 1.

[0062] Example 5 A coated granular fertilizer was obtained in the same manner as in Example 1, except that Wollastonite Fiber 6 was used instead of Wollastonite Fiber 1.

[0063] Example 6 A coated granular fertilizer was obtained in the same manner as in Example 1, except that Wollastonite Fiber 7 was used instead of Wollastonite Fiber 1.

[0064] [Example 7] A coated granular fertilizer was obtained in the same manner as in Example 1, except that the amount of hardened castor oil added to form the second layer was 63 parts by mass and the amount of wollastonite fiber 1 added was 27 parts by mass.

[0065] [Example 8] A coated granular fertilizer was obtained in the same manner as in Example 1, except that the amount of hardened castor oil added to form the second layer was 63 parts by mass, wollastonite fiber 3 was used instead of wollastonite fiber 1, and the amount of wollastonite fiber added was 27 parts by mass.

[0066] [Example 9] A coated granular fertilizer was obtained in the same manner as in Example 1, except that the amount of hardened castor oil added to form the second layer was 63 parts by mass, wollastonite fiber 5 was used instead of wollastonite fiber 1, and the amount of wollastonite fiber added was 27 parts by mass.

[0067] [Example 10] A coated granular fertilizer was obtained in the same manner as in Example 1, except that the amount of hardened castor oil added to form the second layer was 81 parts by mass and the amount of wollastonite fiber 1 added was 9 parts by mass.

[0068] [Example 11] A coated granular fertilizer was obtained in the same manner as in Example 1, except that the amount of hardened castor oil added to form the second layer was 81 parts by mass, wollastonite fiber 5 was used instead of wollastonite fiber 1, and the amount of wollastonite fiber added was 9 parts by mass.

[0069] [Example 12] A coated granular fertilizer was obtained in the same manner as in Example 1, except that the amount of hardened castor oil added to form the second layer was 87.7 parts by mass, wollastonite fiber 5 was used instead of wollastonite fiber 1, and the amount of wollastonite fiber added was 2.3 parts by mass.

[0070] [Example 13] A coated granular fertilizer was obtained in the same manner as in Example 1, except that the amount of hardened castor oil added to form the second layer was 89.1 parts by mass, wollastonite fiber 5 was used instead of wollastonite fiber 1, and the amount of wollastonite fiber added was 0.9 parts by mass.

[0071] [Example 14] A coated granular fertilizer was obtained in the same manner as in Example 1, except that the amount of hardened castor oil added to form the first layer was 150 parts by mass, the amount of hardened castor oil added to form the second layer was 120 parts by mass, and the amount of wollastonite fiber 1 added was 30 parts by mass.

[0072] [Example 15] A coated granular fertilizer was obtained in the same manner as in Example 1, except that the amount of hardened castor oil added to form the first layer was 90 parts by mass, the amount of hardened castor oil added to form the second layer was 168 parts by mass, and the amount of wollastonite fiber 1 added was 42 parts by mass.

[0073] [Example 18] A coated granular fertilizer was obtained in the same manner as in Example 1, except that the amount of hardened castor oil added to form the first layer was 280 parts by mass, the amount of hardened castor oil added to form the second layer was 96 parts by mass, and the amount of wollastonite fiber 1 added was 24 parts by mass.

[0074] [Example 16] Castor oil (240 parts by mass) was heated and melted at 105°C, and mixed with wollastonite fiber 1 (60 parts by mass) heated to 105°C, to obtain a coating composition in which wollastonite fiber 1 was dispersed in castor oil. Granular fertilizer (large granular urea, particle size (D50) approximately 3 mm, 1000 parts by mass) was placed in a rotating tank and tumbling. The large granular urea was heated to approximately 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 granular urea in the tumbling state, and the tumbling state was maintained under heated conditions until the total amount of coating composition added reached 300 parts by mass, thereby forming a layer. The tumbling state was continued until the total amount of coating composition added reached approximately 300 parts by mass, and the tumbling state was obtained by cooling to near room temperature.

[0075] [Example 17] A coated granular fertilizer having a coating consisting of only a single layer containing hardened castor oil and wollastonite fiber 1 was obtained in the same manner as in Example 16, except that the amount of hardened castor oil added to form the second layer was 168 parts by mass and the amount of wollastonite fiber 1 added was 42 parts by mass.

[0076] [Example 19] Hardened rapeseed oil (72 parts by mass) was heated and melted at 105°C, and mixed with wollastonite fiber 1 (18 parts by mass) that had been heated to 105°C, to obtain a coating composition in which wollastonite fiber 1 was dispersed in hardened rapeseed oil. Granular fertilizer (large granular urea, particle size (D50) approximately 3 mm, 1,000 parts by mass) was placed in a rotating tank and tumbling. The large granular urea was then heated to approximately 55°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. Next, hardened rapeseed oil (210 parts by mass) heated to 105°C was added to the paraffin-coated large granular urea in the tumbling state, and the tumbling state was maintained under heated conditions for 3 minutes or more, thereby forming a first layer. The granular fertilizer having the first layer was tumbling under heated conditions, and the coating composition heated to 105°C was added, and the tumbling state was maintained under heated conditions until the total amount of the added hardened rapeseed oil and coating composition reached 300 parts by mass, thereby forming a second layer. The fertilizer was then cooled to near room temperature, yielding a coated granular fertilizer.

[0077] Example 20 A coated granular fertilizer was obtained in the same manner as in Example 19, except that hydrogenated soybean oil was used instead of hydrogenated rapeseed oil.

[0078] Example 21 A coated granular fertilizer was obtained in the same manner as in Example 1, except that carbon fiber 1 was used instead of wollastonite fiber 1.

[0079] [Example 22] A coated granular fertilizer was obtained in the same manner as in Example 21, except that the amount of hardened castor oil added to form the second layer was 63 parts by mass and the amount of carbon fiber 1 added was 27 parts by mass.

[0080] Example 23 A coated granular fertilizer was obtained in the same manner as in Example 1, except that the wollastonite fiber 1 was replaced with the carbon fiber 2.

[0081] Example 24 A coated granular fertilizer was obtained in the same manner as in Example 1, except that titanium oxide fiber 1 was used instead of wollastonite fiber 1.

[0082] Example 25 A coated granular fertilizer was obtained in the same manner as in Example 1, except that titanium oxide fiber 2 was used instead of wollastonite fiber 1.

[0083] [Example 26] A coated granular fertilizer was obtained in the same manner as in Example 25, except that the amount of hardened castor oil added to form the second layer was 63 parts by mass and the amount of titanium oxide fiber 2 added was 27 parts by mass.

[0084] Example 27 A coated granular fertilizer was obtained in the same manner as in Example 1, except that halloysite fiber 1 was used instead of wollastonite fiber 1.

[0085] Example 28 A coated granular fertilizer was obtained in the same manner as in Example 1, except that halloysite fiber 2 was used instead of wollastonite fiber 1.

[0086] [Example 29] Castor oil (120 parts by mass) was heated and melted at 105°C, and mixed with wollastonite fiber 1 (30 parts by mass) heated to 105°C to obtain a coating composition in which wollastonite fiber 1 was dispersed in castor oil. Granular fertilizer (large granular urea, particle size (D50) approximately 3 mm, 1,000 parts by mass) was placed in a rotating tank and tumbling. The large granular urea was heated to approximately 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 granular urea in the tumbling state, and the tumbling state was maintained under heated conditions for 3 minutes or more, thereby forming a second layer as the innermost layer. The granular fertilizer having the innermost layer was tumbling under heated conditions, and hydrogenated castor oil heated to 105°C was added, and the tumbling state was maintained under heated conditions until the total amount of the added hydrogenated castor oil and coating composition reached 300 parts by mass, thereby forming an outermost layer. The granular fertilizer was cooled to near room temperature, and a coated granular fertilizer was obtained.

[0087] Example 30 Castor oil (199.5 parts by mass) was heated and melted at 105°C, and mixed with wollastonite fiber 1 (10.5 parts by mass) heated to 105°C to obtain coating composition 1 in which wollastonite fiber 1 was dispersed in castor oil. Separately, castor oil (72 parts by mass) was heated and melted at 105°C, and mixed with wollastonite fiber 1 (18 parts by mass) heated to 105°C to obtain coating composition 2 in which wollastonite fiber 1 was dispersed in castor oil. Granular fertilizer (large granular urea, particle size (D50) approximately 3 mm, 1000 parts by mass) was placed in a rotating tank and tumbling. The large granular urea was heated to approximately 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 1 heated to 105°C was added to the paraffin-coated large granular urea in the tumbling state, and the tumbling state was maintained under heating conditions for 3 minutes or more, thereby forming an innermost layer. The granular fertilizer with the innermost layer was tumbling under heating conditions, and the coating composition 2 heated to 105°C was added, thereby forming an outermost layer. The fertilizer was cooled to around room temperature, and a coated granular fertilizer was obtained.

[0088] Example 31 Castor oil (40 parts by mass) was heated and melted at 105°C, and mixed with wollastonite fiber 1 (10 parts by mass) that had been heated to 105°C to obtain coating composition 1 in which wollastonite fiber 1 was dispersed in castor oil. Separately, castor oil (32 parts by mass) was heated and melted at 105°C, and mixed with wollastonite fiber 1 (8 parts by mass) that had been heated to 105°C to obtain coating composition 2 in which wollastonite fiber 1 was dispersed in castor oil. Granular fertilizer (large granular urea, particle size (D50) about 3 mm, 1000 parts by mass) was charged into a rotating tank and kept in a rolling state. The large granular urea was 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 rolling state was continued for 5 minutes. Next, the coating composition 1 heated to 105°C was added to the paraffin-coated large granular urea in the rolling state, and the rolling state was maintained under heating conditions for 3 minutes or more, and finally A second layer that would become the inner layer was formed. The granular fertilizer having the second layer that would become the innermost layer was rolled under heated conditions, and hardened castor oil (210 parts by mass) heated to 105°C was added. The rolling state was maintained under heated conditions for 3 minutes or more, thereby forming a first layer that would become the intermediate layer. The granular fertilizer having the first layer that would become the intermediate layer was rolled under heated conditions, and the coating composition 2 heated to 105°C was added, thereby forming a second layer that would become the outermost layer. The mixture was cooled to near room temperature, thereby obtaining a coated granular fertilizer.

[0089] [Comparative Example 1] A coated granular fertilizer was obtained in the same manner as in Example 16, except that glass fiber 1 was used to form the second layer, the amount of glass fiber 1 added was 10.5 parts by mass, and the amount of hardened castor oil added was 199.5 parts by mass.

[0090] Comparative Example 2 A coated granular fertilizer was obtained in the same manner as in Example 1, except that glass fiber 1 was used instead of wollastonite fiber 1.

[0091] Comparative Example 3 A coated granular fertilizer was obtained in the same manner as in Example 14, except that glass fiber 1 was used instead of wollastonite fiber 1.

[0092] Comparative Example 4 A coated granular fertilizer was obtained in the same manner as in Example 1, except that the glass fiber 2 was used instead of the wollastonite fiber 1.

[0093] Comparative Example 5 A coated granular fertilizer was obtained in the same manner as in Comparative Example 1, except that talc was used to form the second layer.

[0094] Comparative Example 6 A coated granular fertilizer was obtained in the same manner as in Comparative Example 2, except that talc was used instead of the glass fiber 1.

[0095] Comparative Example 7 A coated granular fertilizer was obtained in the same manner as in Comparative Example 5, except that the amount of hardened castor oil added was 210 parts by mass and the amount of talc added was 90 parts by mass.

[0096] Comparative Example 8 A coated granular fertilizer was obtained in the same manner as in Example 1, except that calcium carbonate was used instead of the wollastonite fiber 1.

[0097] Comparative Example 9 A coated granular fertilizer was obtained in the same manner as in Example 30, except that glass fiber 1 was used instead of wollastonite fiber 1, the amount of hardened castor oil added to the innermost layer was 142.5 parts by mass, the amount of glass fiber 1 added was 7.5 parts by mass, and the amount of hardened castor oil added to the outermost layer was 120 parts by mass, and the amount of glass fiber 1 added was 30 parts by mass.

[0098] Comparative Example 10 Granular fertilizer (large granular urea, particle size (D50) approximately 3 mm, 1,000 parts by mass) was placed in a rotating tank and tumbling. The large granular urea was heated to approximately 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, hardened castor oil (80 parts by mass) heated to 105°C was added to the paraffin-coated large granular urea in the tumbling state, and the tumbling state was continued under heated conditions until the total mass of the added hardened castor oil reached 80 parts by mass, thereby forming a layer. The tumbling state was continued until the total mass of the hardened castor oil added reached approximately 80 parts by mass, and the tumbling state was continued until the tumbling state reached approximately room temperature, thereby obtaining a coated granular fertilizer having a coating consisting of a layer containing only hardened castor oil.

[0099] Comparative Example 11 A coated granular fertilizer was obtained in the same manner as in Comparative Example 10, except that the amount of hydrogenated castor oil added was 100 parts by mass.

[0100] Comparative Example 12 A coated granular fertilizer was obtained in the same manner as in Comparative Example 10, except that the amount of hardened castor oil added was 210 parts by mass.

[0101] Comparative Example 13 A coated granular fertilizer was obtained in the same manner as in Comparative Example 10, except that the amount of hydrogenated castor oil added was 300 parts by mass.

[0102] Comparative Example 14 Granular fertilizer (large urea granules, particle size (D50) approximately 3 mm, 1,000 parts by mass) was placed in a rotating tank and tumbling. The large urea granules were heated to approximately 55°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, hydrogenated rapeseed oil (30 parts by mass) heated to 105°C was added to the paraffin-coated large urea granules in the tumbling state, and the tumbling state was maintained under heated conditions until the total mass of the hydrogenated rapeseed oil added reached 300 parts by mass, thereby forming a layer. The tumbling state was continued until the total mass of the hydrogenated rapeseed oil added reached approximately 300 parts by mass, and the tumbling state was continued until the tumbling state reached approximately room temperature, thereby forming a coated granular fertilizer with a coating consisting of a layer containing only each hydrogenated vegetable oil.

[0103] Comparative Example 15 A coated granular fertilizer having a coating consisting of a layer containing only hydrogenated soybean oil was obtained in the same manner as in Comparative Example 14, except that hydrogenated soybean oil was used instead of hydrogenated rapeseed oil.

[0104] [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 (collection location: 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 test piece was then lightly tapped on the ground approximately 10 times and packed. The sample and a cup of water for moistening 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.

[0105]

[0106] [Evaluation] <Evaluation of inorganic particle particle size> The particle size of wollastonite fiber 1 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). The particle sizes of wollastonite fibers 2 to 7, carbon fiber 1, carbon fiber 2, titanium oxide fiber 1, titanium oxide fiber 2, glass fiber 1, glass fiber 2, talc, and calcium carbonate were also defined and measured in the same manner. <Evaluation of fiber length, aspect ratio, and circularity coefficient of inorganic particles> Images of wollastonite fiber 1 in the micrometer range were taken using a scanning electron microscope (SU-3800, manufactured by Hitachi High-Tech Corporation). Wollastonite fiber 1 was adhered to a sample stage using conductive tape and subjected to platinum sputtering at 20 mA for 120 seconds using an ion sputtering device (E-1030, manufactured by Hitachi, Ltd.). The resulting sample was then photographed at a magnification of approximately 50 to 30,000 times, depending on the size of the wollastonite fiber 1, so that there were approximately 10 to 100 particles per field of view. The photographed image of wollastonite fiber 1 was analyzed using image analysis particle size distribution measurement software (Mac-View, manufactured by Mountec Co., Ltd.), and the fiber length (major axis), aspect ratio (= major axis / minor axis), and circularity coefficient (= 4π × area × perimeter) were measured. More than 100 particles were analyzed, and an average value was obtained. This average value was defined as the fiber length. The fiber length, aspect ratio, and circularity coefficient were defined and measured in the same manner for wollastonite fibers 2 to 7, carbon fiber 1, carbon fiber 2, titanium oxide fiber 1, titanium oxide fiber 2, halloysite fiber 1, halloysite fiber 2, glass fiber 1, glass fiber 2, talc, and calcium carbonate. Here, the major axis is defined as the maximum distance between two points on the fiber surface shown in the fiber image. The minor axis is defined as the maximum value of the length of a line segment perpendicular to the major axis. When multiple maximum values ​​exist, the average value of these values ​​is taken as the minor axis.

[0107] [Evaluation method: elution 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 bottle was left to stand at 25°C. Every 7 days, 0.6 mL of water was sampled 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 elution rate E1 (%) of urea from the coated granular fertilizer was calculated. The results are shown in Tables 2 to 8. (Evaluation criteria) A: elution rate E1 is less than 10% B: elution rate E1 is 10% or more but less than 30% C: elution rate E1 is 30% or more A rating of A or B indicates that elution controllability is good.

[0108] [Evaluation method: impact resistance] A 2 kg sample, which was a 4:1 mixture of chemical fertilizer (Tama Kasei S) and the prepared coated granular fertilizer, was spread using a side stripe fertilizer applicator (YK6D, manufactured by Yanmar Co., Ltd.). The urea elution rate E2 (%) of the coated granular fertilizer after spreading was measured using the same method as above, and evaluation was performed based on the value of E2 - E1. The results are shown in Tables 2 to 8. (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.

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[0115]

Claims

1. A coated granular fertilizer comprising a granular fertilizer and a coating that coats the granular fertilizer, the coating containing hardened vegetable oil and inorganic fibers, and the inorganic fibers being at least one type selected from the group consisting of wollastonite fibers, titanium oxide fibers, carbon fibers, and halloysite fibers.

2. The coated granular fertilizer according to claim 1, wherein the inorganic fibers are dispersed in the hardened vegetable oil in the coating.

3. A coated granular fertilizer according to claim 1 or 2, wherein the mass ratio of the granular fertilizer to the coating is 1:0.1 or more and 1:0.3 or less.

4. A coated granular fertilizer according to claim 1 or 2, wherein the content of the inorganic fibers in the coating is 0.1% by mass or more and 30% by mass or less.

5. The coated granular fertilizer according to claim 1 or 2, wherein the coating has a first layer containing the hardened vegetable oil and a second layer containing the hardened vegetable oil and the inorganic fibers.

6. The coated granular fertilizer according to claim 5, wherein the mass of the hardened vegetable oil in the second layer is equal to or less than the mass of the hardened vegetable oil in the first layer.

7. A coated granular fertilizer as described in claim 5, wherein in the second layer, the content of the hardened vegetable oil is 70% by mass or more and 99% by mass or less, and the content of the inorganic fibers is 1% by mass or more and 30% by mass or less.

8. The coated granular fertilizer according to claim 7, wherein the second layer is disposed outside the first layer.

9. The coated granular fertilizer of claim 8, wherein said second layer is the outermost layer of said coating.

10. The coated granular fertilizer according to claim 1 or 2, wherein the inorganic fibers have an aspect ratio of 5 or more and 12 or less.

11. The coated granular fertilizer according to claim 1 or 2, wherein the inorganic fibers are the carbon fibers, the titanium oxide fibers, or the halloysite fibers.

12. The coated granular fertilizer of claim 1, wherein said inorganic fibers are said wollastonite fibers.

13. The coated granular fertilizer according to claim 12, wherein the fiber length of the wollastonite fibers is 15 μm or more and 200 μm or less.

14. The coated granular fertilizer according to claim 12 or 13, wherein the particle size of the wollastonite fibers is 5 μm or more and 60 μm or less.

15. The coated granular fertilizer according to claim 12, wherein the hydrogenated vegetable oil is at least one selected from the group consisting of hydrogenated castor oil, hydrogenated rapeseed oil, and hydrogenated soybean oil.

16. The coated granular fertilizer according to claim 15, wherein the melting point of the hardened vegetable oil is 60°C or higher and 100°C or lower.

17. A method for producing a coated granular fertilizer, comprising: a step of adding heated and melted hardened vegetable oil to a granular fertilizer; and a step of adding a coating composition containing hardened vegetable oil and inorganic fibers to the granular fertilizer, wherein the inorganic fibers are at least one type selected from the group consisting of wollastonite fibers, titanium oxide fibers, carbon fibers, and halloysite fibers.

18. The method for producing a coated granular fertilizer according to claim 17, wherein in the coating composition, the inorganic fibers are dispersed in the hardened vegetable oil.

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