Biodegradable resin-coated granular fertilizer

Abstract

This invention provides a biodegradable resin-coated fertilizer that solves the problem of reduced spreadability due to fertilizer solidification and powdering during mechanical application of granular fertilizer, and does not impose an environmental burden due to the coating. [Solution] A coated granular fertilizer in which a film of poly(3-hydroxybutyrate) resin is formed on the surface of granular fertilizer, wherein the poly(3-hydroxybutyrate) resin is a copolymer of 3-hydroxybutyrate units and other hydroxyalkanoate units, and the copolymerization ratio of other hydroxyalkanoate units is 1 mol% or more and 6 mol% or less, and the coated granular fertilizer has a elution rate of 50% or more of water-soluble fertilizer components after 24 hours in water at 30°C.

Description

Technical Field

[0001] The present invention relates to a biodegradable resin-coated granular fertilizer that solves the problem of reduced spraying performance due to caking and pulverization of fertilizers in the mechanical spraying of granular fertilizers and does not impose an environmental burden due to the coating shell.

Background Art

[0002] In recent years, due to the need for labor saving associated with the aging of agricultural workers, the mechanical spraying of fertilizers has advanced, and in some cases, the spraying of fertilizers using drones has been put into practical use. However, especially in the case of spraying in paddy fields, the work is often carried out in a hot and humid environment, so often the fertilizer grains absorb moisture, causing the fertilizer grains to adhere to each other, resulting in caking to form lumps, or the shape of the fertilizer to collapse and pulverize, causing problems such as clogging of the spraying machine.

[0003] Conventionally, in order to avoid problems caused by the moisture absorption of fertilizers, it has been common practice to coat the surface of granular fertilizers with inorganic powders such as diatomaceous earth, talc, silica fine powder, silica fume, lime silicate, zeolite, perlite, silica powder, clay, silica gel, and bentonite as anti-caking materials. However, simply coating the fertilizer surface with inorganic powders easily peels off, reducing the anti-caking effect. Therefore, in order to further enhance the anti-caking effect, as shown in Patent Documents 1 to 3, studies have been made to reduce the peelability by combining mineral powders and liquid anti-caking materials.

[0004] Also, as shown in Patent Document 4, studies have been made to enhance the anti-caking effect only with anti-caking materials. It is said that the anti-caking effect is enhanced by coating the surface of granular fertilizers with talc having a particle size of 10 μm or less and a purity of 90% or more. However, all of these studies are aimed at preventing caking when storing fertilizers packaged in plastic films, and are not satisfactory for preventing caking that occurs in fertilizers opened at the fertilization site under extremely hot and humid conditions.

[0005] Patent document 5 proposes granular fertilizers coated with wax, mineral oil, and a miscible resin as a measure against moisture absorption in high-temperature and high-humidity environments. However, these use non-biodegradable resins, and after the applied fertilizer dissolves, plastic residue remains in the environment for a long period, increasing the environmental burden. Until now, no fertilizer has been invented that prevents the problem of moisture absorption and solidification in high-temperature and high-humidity environments while also being environmentally friendly. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Special Publication No. 5-4954 [Patent Document 2] Special Publication No. 8-009515 [Patent Document 3] Japanese Patent Publication No. 2006-265061 [Patent Document 4] Patent No. 6429825 [Patent Document 5] Special Publication No. 2018-502033 [Overview of the project] [Problems that the invention aims to solve]

[0007] Conventional methods for preventing caking and moisture absorption of granular fertilizers are insufficient in high-temperature, high-humidity environments during fertilization, resulting in problems such as caking and powdering of fertilizer granules during application, and consequently, reduced spreadability. Furthermore, the coating residue left behind after application can remain in the soil and flow into the ocean, causing environmental pollution. [Means for solving the problem]

[0008] The inventors of the present invention have discovered that by coating granular fertilizer with a poly(3-hydroxybutyrate) resin having certain specific properties, it is possible to obtain a fertilizer that does not harm the environment while preventing caking due to moisture absorption and caking due to the adhesion of the resin coating, and have thus completed the present invention.

[0009] In other words, the gist of this invention is as follows: (1) A coated granular fertilizer in which a film of poly(3-hydroxybutyrate) resin is formed on the surface of the granular fertilizer, wherein the poly(3-hydroxybutyrate) resin is a copolymer of 3-hydroxybutyrate units and other hydroxyalkanoate units, and the copolymerization ratio of the other hydroxyalkanoate units is 1 mol% or more and 6 mol% or less, and the coated granular fertilizer has a elution rate of 50% or more of water-soluble fertilizer components after 24 hours in water at 30°C. (2) The coated granular fertilizer according to (1), wherein the copolymerization ratio is 1 mol% to 3 mol%. (3) The coated granular fertilizer according to (1) or (2) above, wherein the weight of the coating of the coated granular fertilizer is 0.4% to 5% by weight relative to the weight of the granular fertilizer. (4) The coated granular fertilizer according to (1) or (2) above, wherein the weight of the coating of the coated granular fertilizer is 0.8% to 1.5% by weight relative to the weight of the granular fertilizer. (5) The coated granular fertilizer according to (1), wherein the other hydroxyalkanoate units in the poly(3-hydroxybutyrate) resin are 3-hydroxyhexanoate (hereinafter, sometimes referred to as "3HH") units. (6) The coated granular fertilizer according to (2), wherein the other hydroxyalkanoate units in the poly(3-hydroxybutyrate) resin are 3-hydroxyhexanoate units. (7) The coated granular fertilizer according to (3), wherein the other hydroxyalkanoate units in the poly(3-hydroxybutyrate) resin are 3-hydroxyhexanoate units. (8) The coated granular fertilizer according to (4), wherein the other hydroxyalkanoate units in the poly(3-hydroxybutyrate) resin are 3-hydroxyhexanoate units. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a fertilizer that does not impair the ability to be sprayed by drones even in harsh high-temperature and high-humidity environments, exhibits a rapid fertilizer effect after spraying, and, because the coating after the fertilizer has dissolved is made of biodegradable resin, is completely biodegradable without burdening the environment. [Brief explanation of the drawing]

[0011] [Figure 1] Figure 1 is a graph showing the water dissolution characteristics of coated granular fertilizer. [Modes for carrying out the invention]

[0012] The coated granular fertilizer in the present invention is manufactured by coating the surface of the granular fertilizer with a composition containing a poly(3-hydroxybutyrate) resin having specific properties using a known method.

[0013] <Granular fertilizer> As granular fertilizers, granular nitrogen fertilizers such as urea, ammonium sulfate, sodium nitrate, oxamide, acetaldehyde condensed urea, formaldehyde condensed urea, and isobutyraldehyde condensed urea are used; granular phosphorus fertilizers such as fused phosphorus fertilizer, calcined phosphorus fertilizer, processed phosphorus fertilizer, mixed phosphorus fertilizer, and humic acid phosphorus fertilizer are used; granular potassium fertilizers such as potassium sulfate, potassium chloride, magnesium sulfate, potassium bicarbonate, and potassium silicate fertilizer are used; granular compound fertilizers such as potassium phosphate fertilizer and potassium nitrate fertilizer are used; granular organic fertilizers; ammonium salts such as ammonium nitrate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, ammonium sulfate, and ammonium chloride are used; calcium salts such as calcium nitrate, calcium phosphate, calcium sulfate, and calcium chloride are used; magnesium salts such as magnesium nitrate, magnesium phosphate, magnesium sulfate, and magnesium chloride are used; and granular fertilizers obtained by granulating mixtures thereof using methods that are known in themselves are used. Among these, granular fertilizer particularly preferred for use in the coated granular fertilizer of the present invention is granular urea, which is economically advantageous due to its low unit cost per nitrogen component, but which tends to have problems with hygroscopicity.

[0014] Regarding the particle size, particle size distribution, and shape of the granular fertilizer, there are no particular restrictions as long as there are no problems in the spraying process during production or the fertilization operation. However, the particle size is preferably 0.5 mm or more and 10 mm or less, particularly preferably 2 mm or more and 4 mm or less. If the particle size is less than 0.5 mm, the coating surface area per unit weight of the granular fertilizer increases, and when spraying is performed with a film thickness capable of exerting an anti-caking effect, it becomes difficult to ensure the amount of active ingredient of the fertilizer. If the particle size is more than 10 mm, the fertilization operation becomes difficult.

[0015] <Poly(3-hydroxybutyrate) resin> The poly(3-hydroxybutyrate) resin may be poly(3-hydroxybutyrate) having only 3-hydroxybutyrate as a repeating unit, or may be a copolymer of 3-hydroxybutyrate and other hydroxyalkanoates.

[0016] In one embodiment of the invention, the poly(3-hydroxybutyrate) resin may be a mixture of a homopolymer and one or more copolymers, or may be a mixture of two or more copolymers. The form of copolymerization is not particularly limited and may be random copolymerization, alternating copolymerization, block copolymerization, graft copolymerization, etc.

[0017] In one embodiment of the present invention, examples of the poly(3-hydroxybutyrate) - based resin include poly(3-hydroxybutyrate) (P3HB), poly(3-hydroxybutyrate - co - 3-hydroxyhexanoate) (P3HB3HH), poly(3-hydroxybutyrate - co - 3-hydroxyvalerate) (P3HB3HV), poly(3-hydroxybutyrate - co - 4-hydroxybutyrate) (P3HB4HB), poly(3-hydroxybutyrate - co - 3-hydroxyoctanoate) (P3HB3HO), poly(3-hydroxybutyrate - co - 3-hydroxyoctadecanoate) (P3HB3HOD), poly(3-hydroxybutyrate - co - 3-hydroxydecanoate) (P3HB3HD), poly(3-hydroxybutyrate - co - 3-hydroxyvalerate - co - 3-hydroxyhexanoate) (P3HB3HV3HH), and the like. Among them, P3HB, P3HB3HH, P3HB3HV, and P3HB4HB are preferred because they are easy to produce industrially.

[0018] Also, by changing the composition ratio of the repeating units, the melting point and crystallinity can be changed, and as a result, physical properties such as Young's modulus and heat resistance can be changed, and it is possible to impart physical properties between those of polypropylene and polyethylene. From the perspective that it is easy to produce industrially and is a physically useful resin as described above, P3HB3HH, which is a copolymer of 3-hydroxybutyric acid and 3-hydroxyhexanoic acid, is more preferred.

[0019] In one embodiment of the present invention, from the perspective of the balance between flexibility and strength, the copolymerization ratio of the repeating units is such that the copolymerization ratio of other hydroxyalkanoate units is 1 mol% or more and 6 mol% or less (the ratio of 3-hydroxybutyrate units is 94 mol% or more and 99 mol% or less), preferably 1 mol% or more and 3 mol% or less (the ratio of 3-hydroxybutyrate units is 97 mol% or more and 99 mol% or less). When the copolymerization ratio is high, the adhesiveness of the film increases, blocking occurs during coating, and the product is likely to solidify, which is not preferable.

[0020] The method for producing P3HB3HH in the present invention may be either a method of production from microorganisms or a chemical synthesis method, and is not particularly limited. Among these, the method of production from microorganisms is preferred because P3HB3HH can be obtained by culturing microorganisms using oils and fats as raw materials, and the process is simpler and less expensive compared to the chemical synthesis method. Therefore, P3HB3HH produced from microorganisms is preferred.

[0021] In this invention, commercially available P3HB3HH can be used, specifically Green Planet® X331N manufactured by Kaneka Corporation. Other manufacturers' products can also be suitably used as long as they have a 3-hydroxyhexanoate ratio of 1 mol% or more and 6 mol% or less, preferably 1 mol% or more and 3 mol% or less.

[0022] <Coating> The coverage rate (percentage of fertilizer weight) of the poly(3-hydroxybutyrate) resin-derived coating material on granular fertilizer is 0.4% by weight or more and 5% by weight or less, preferably 0.5% by weight or more and 2% by weight or less, more preferably 0.7% by weight or more and 1.6% by weight or less, and particularly preferably 0.8% by weight or more and 1.5% by weight or less. Note that "0.4% by weight or more and 5% by weight or less" is expressed as "0.4% by weight to 5% by weight". If the coverage rate is less than 0.4% by weight, it is difficult to form a uniform coating, and the anti-caking effect tends to be insufficient. If the coverage rate exceeds 5% by weight, it takes time for the fertilizer effect to be exerted after application, making it unsuitable for drone application aimed at application at the appropriate timing, and the increased cost impairs economic efficiency.

[0023] When spraying fertilizer in paddy fields using a drone, a surfactant may be added as appropriate to prevent the fertilizer from floating on the water surface and drifting after being dropped. Furthermore, mineral powder may be applied to the surface of the fertilizer granules to enhance the effect of preventing caking due to moisture absorption. In this case, a coating oil may be used to improve the adhesion of the mineral powder. Commonly used anti-caking materials such as diatomaceous earth, talc, silica powder, silica fume, calcium silicate, zeolite, perlite, silica powder, clay, silica gel, and bentonite can be used as mineral powders, and mineral oil or rapeseed oil can be used as coating oils. When these compounds are added, they act as anti-floating and anti-caking agents for the coated granular fertilizer. Additionally, by adding compounds to prevent caking due to moisture absorption, the coated granular fertilizer of the present invention exhibits the effect of preventing caking due to moisture absorption.

[0024] Since the above coating is made of biodegradable resin, the coating husk after application of the coated granular fertilizer of the present invention is completely biodegraded.

[0025] <Method for producing coated granular fertilizer> The coated granular fertilizer of the present invention can be manufactured by a known method in which an organic solvent solution of the coating material is sprayed onto the granular fertilizer while it is flowing, thereby coating the granular fertilizer. Methods for flowing the granular fertilizer include rolling it on a rotating pan or drum, and using hot air to flow it. Both methods are feasible, but the method using hot air is more suitable as it is less likely to cause blocking between the fertilizer granules. When selecting the organic solvent, it is necessary to consider the boiling point, the solubility of the coating material, etc. Representative examples of usable organic solvents include methyl ethyl ketone, methyl isobutyl ketone, N,N-dimethylacetamide, N,N-dimethylformamide, and chlorinated hydrocarbon solvents such as chloroform, methylene chloride, and 1,2-dichloroethane; aromatic solvents such as benzene, toluene, xylene, and orthodichlorobenzene; or mixed solvents containing two or more of these.

[0026] As the aforementioned organic solvent, for example, an organic solvent containing 100% toluene can be suitably used, but a mixed solvent of toluene / methyl ethyl ketone can also be suitably used. The ratio of toluene to methyl ethyl ketone in the mixed solvent can be any ratio, but it is preferably 5:5 to 9:1 (w / w).

[0027] For spraying, either a single-fluid spray nozzle or a two-fluid spray nozzle can be used, but a two-fluid spray nozzle is preferred because it produces finer spray particles and allows for more uniform film formation.

[0028] The coating material solution concentration should be 1% by weight or more, preferably around 15% by weight or less. If the concentration is higher than 15% by weight, the solution viscosity will increase, the spray particle size will increase, impairing the uniformity of the coating, and clogging of pipes, pumps, and nozzles due to the precipitation of solid components will be more likely to occur.

[0029] In the coating process, first, an appropriate amount of urea particles is placed in the coating device, and gas is blown up from the bottom of the device to make the urea flow. Once the device reaches a predetermined temperature, the resin liquid is sprayed onto the flowing urea using a spray nozzle at the bottom of the device to perform the coating. The inside of the device is heated to 40-70°C to accelerate the drying of the resin liquid sprayed onto the urea surface. The resin liquid is delivered using a liquid delivery pump. If the delivery speed is too fast, the resin liquid will be delivered before the coating can dry, causing the urea particles to stick together and blockage to occur. If the speed is too slow, the resin liquid will dry before it can form a coating on the urea surface, making it impossible to form a uniform coating. Examples of gases used for blowing up the fertilizer particles and spraying the resin liquid include air, nitrogen, and helium, but when using flammable organic solvents, it is preferable to use inert gases such as nitrogen and helium that do not pose a risk of ignition.

[0030] There are no particular restrictions on the drying method of the resin liquid sprayed onto the urea granules, as long as it removes the solvent from the coating and hardens the film. The drying temperature can be either natural drying or heat drying. [Examples]

[0031] The present invention will be described in detail below with reference to examples, but the scope of the present invention is not limited to these examples.

[0032] [Method for testing moisture absorption and caking] 50 g of the sample was placed in a glass petri dish with a diameter of 75 mm and left in a constant temperature and humidity chamber at 30°C and 80% relative humidity until the sample absorbed 1% by weight of moisture relative to its weight. The resulting sample with a moisture absorption rate of 1% by weight was placed in a cylindrical plastic container with an inner diameter of 40 mm and a height of 50 mm, and a cylindrical plastic container with an outer diameter of 40 mm and a height of 50 mm was placed on top as a lid. The container was left to stand in a constant temperature chamber at 40°C for 90 minutes, after which it was removed from the chamber. Subsequently, a load of 20 kg was applied from above the cylindrical plastic container that was acting as a lid, and the container was left to stand for 150 minutes. The weight of the solidified material in the sample was measured, and the solidification rate was calculated from the ratio of the solidified material to the total weight of the sample.

[0033] [Powdering Test Method] For the sieving of the sample, 110g of the sample was placed in a sieve with a mesh size of 1.00mm and shaken for 2 minutes using a rotap shaker. After shaking, the sample on the sieve was collected, and 100g of the sample and 3 alumina balls (2 x 55g, 1 x 13.5g) were placed in a magnetic pot (outer diameter: 130mm, height: 180mm) and the lid was closed. The magnetic pot was placed on the rollers of a pot stand and rotated for 15 minutes (rotation speed of the magnetic pot: 75 rpm). After rotation, the entire sample was placed in a sieve with a mesh size of 1.00mm and shaken for 2 minutes using a rotap shaker. After shaking, the weight of the sample below the sieve was measured, and the pulverization rate was calculated from the weight of the sample below the sieve relative to the weight of the sample placed in the magnetic pot.

[0034] [Method for testing elution in water] 50 g of the sample and 1000 mL of deionized water were placed in a 1000 mL glass beaker, sealed with a poly film, and left to stand in a constant temperature bath at 30°C. After the prescribed time had elapsed, the amount of urea eluted was quantified by measuring the urea concentration in the water using p-dimethylaminobenzaldehyde spectrophotometric analysis, and the elution rate was calculated from the ratio of the amount of eluted urea to the total amount of urea in the sample.

[0035] (Example 1) In a 500 mL flat-bottom separable flask equipped with a condenser, 252 g of toluene and 10.5 g of P3HB3HH (manufactured by Kaneka Corporation, Green Planet® X331N), with a copolymerization ratio of 6 mol% of 3HH, were added and stirred under heating to dissolve. The concentration of the coating material solution was 4% by weight. 1300 g of granular urea with a particle size of 2-4 mm was placed in an acrylic resin spray fluidized bed with a height of 1500 mm and a diameter of 230 mm, and the fluidized bed was made to flow from the bottom of the bed by hot air from a blower. The organic solvent solution of the coating material was pumped and sprayed from the bottom of the fluidized bed. The temperature of the hot air was controlled so that the temperature inside the fluidized bed was between 52°C and 53°C. The spraying process took approximately 4 minutes. After the spraying was completed, the fluidized bed was kept flowing with hot air from a blower for 25 minutes to dry and cool, producing coated granular urea with a coating rate of 0.8% by weight. The granular urea exhibited excellent fluidity during the spraying process, and no blocking occurred. Furthermore, 0.65g of surfactant (Marpomarce PT, manufactured by Matsumoto Oil & Fat Pharmaceutical Co., Ltd.) was applied to the finished coated granular fertilizer, and then 6g of silica fume was applied as a powder coating to prevent flotation.

[0036] (Example 2) Coated granular urea with a coating rate of 0.8% by weight was produced under the same conditions as in Example 1, except that P3HB3HH (manufactured by Kaneka Corporation, Green Planet®), with a copolymerization ratio of 3 mol% of 3HH, was used as the resin raw material. The spraying process time at this time was approximately 4 minutes. The fluidity of the granular urea during the spraying process was very good, and no blocking occurred. The finished coated granular fertilizer was subjected to a flotation prevention treatment in the same manner as in Example 1.

[0037] (Example 3) Coated granular urea with a coating rate of 1.5% by weight was produced under the same conditions as in Example 2, except that toluene was changed to 475g and P3HB3HH (manufactured by Kaneka Corporation, Green Planet®) with a copolymerization ratio of 3 mol% of 3HH was changed to 19.8g. The spraying process time at this time was approximately 7 minutes. The fluidity of the granular urea during the spraying process was very good, and no blocking occurred. The finished coated granular fertilizer was subjected to a flotation prevention treatment in the same manner as in Example 2.

[0038] (Comparative Example 1) 200g of granular urea with a particle size of 2-4mm was coated with 0.10g of surfactant (Marpomarce PT, manufactured by Matsumoto Oil & Fat Pharmaceutical Co., Ltd.), and then coated with 0.92g of silica fume powder.

[0039] (Comparative Example 2) Coated granular urea with a coating rate of 0.8% by weight was produced under the same conditions as in Example 1, except that P3HB3HH (manufactured by Kaneka Corporation, Green Planet®), with a copolymerization ratio of 3HH of 11 mol%, was used as the resin raw material. The spraying process time at this time was approximately 4 minutes. A decrease in the fluidity of the granular urea was observed during the spraying process, but it was not enough to cause blocking. The finished coated granular fertilizer was subjected to a flotation prevention treatment in the same manner as in Example 1.

[0040] Table 1 shows the copolymerization ratio of 3HH constituting P3HB3HH in the resin raw materials of the examples and comparative examples, the coating rate, the addition rate of the anti-flotation agent, and the results of the moisture absorption and solidification test and the powdering test.

[0041] [Table 1]

[0042] When the 3HH copolymerization ratio exceeded 6 mol%, the caking rate tended to worsen compared to uncoated urea, and it was confirmed that an improvement in the caking rate was only observed when the copolymerization ratio was between 1 mol% and 6 mol%. Furthermore, the powdering rate improved in all prototypes coated with P3HB3HH, including Comparative Example 2.

[0043] For Examples 2 and 3, an underwater elution test was conducted to confirm that the fertilizer components leached out quickly after application and that the fertilizer effect was exerted. The results are shown in Figure 1.

[0044] Under conditions of 30°C water, it was confirmed that more than 50% of Example 2 (coverage rate 0.8% by weight) dissolved after 2 hours, and more than 50% of Example 3 (coverage rate 1.5% by weight) dissolved after 24 hours. Therefore, it was expected that the fertilizer effect would be rapidly exerted when applied to an actual field.

Claims

1. A coated granular fertilizer having a film of poly(3-hydroxybutyrate) resin formed on the surface of the granular fertilizer, wherein the poly(3-hydroxybutyrate) resin is a copolymer of 3-hydroxybutyrate units and other hydroxyalkanoate units, and the copolymerization ratio of the other hydroxyalkanoate units is 1 mol% or more and 6 mol% or less, and the coated granular fertilizer has a elution rate of 50% or more of water-soluble fertilizer components after 24 hours in water at 30°C.

2. The coated granular fertilizer according to claim 1, wherein the copolymerization ratio is 1 mol% to 3 mol%.

3. The coated granular fertilizer according to claim 1 or claim 2, wherein the weight of the coating of the coated granular fertilizer is 0.4% to 5% by weight relative to the weight of the granular fertilizer.

4. The coated granular fertilizer according to claim 1 or claim 2, wherein the weight of the coating of the coated granular fertilizer is 0.8% to 1.5% by weight relative to the weight of the granular fertilizer.

5. The coated granular fertilizer according to claim 1, wherein the other hydroxyalkanoate units in the poly(3-hydroxybutyrate) resin are 3-hydroxyhexanoate units.

6. The coated granular fertilizer according to claim 2, wherein the other hydroxyalkanoate units in the poly(3-hydroxybutyrate) resin are 3-hydroxyhexanoate units.

7. The coated granular fertilizer according to claim 3, wherein the other hydroxyalkanoate units in the poly(3-hydroxybutyrate) resin are 3-hydroxyhexanoate units.

8. The coated granular fertilizer according to claim 4, wherein the other hydroxyalkanoate units in the poly(3-hydroxybutyrate) resin are 3-hydroxyhexanoate units.

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