Degradable material coated slow-release fertilizer and manufacturing method thereof

Abstract

The invention provides a slow-release fertilizer coated with a degradable material and a manufacturing method of the slow-release fertilizer. The slow-release fertilizer comprises fertilizer particles and a degradable material, the first wrapping layer comprises a first hydrophobic material and wraps the outer sides of the fertilizer particles; the second wrapping layer comprises a second hydrophilic material and wraps the outer side of the first wrapping layer; the first coating layer comprises a first hydrophobic material, the second coating layer comprises a second hydrophilic material, the third coating layer comprises a third hydrophobic material, the outer side of the second coating layer is coated with the third hydrophobic material, the first hydrophobic material, the second hydrophilic material and the third hydrophobic material are all biodegradable materials, and the first hydrophobic material and the third hydrophobic material are the same or different materials. According to the present invention, through the at least three-layer coating design, the completeness of the fertilizer can be maintained, the slow release even controlled release effect can be achieved, the material used by the coating layer is the degradable polymer, such that the pollution to the natural environment can be reduced, and in addition, the safe and volatile solvent is matched with the simple coating processing process so as to achieve the environmental protection effect; and the convenience and the applicability can be greatly improved.

Description

Technical Field

[0001] The invention relates to a slow-release fertilizer and a method for making the same, and in particular to a slow-release fertilizer coated with more than two hydrophilic / hydrophobic biodegradable polymers in multiple layers and a method for making the same. Background Art

[0002] Traditional chemical fertilizers are usually hydrophilic and have an efficiency of only about 30%. The main reason is that the fertilizers dissolve too quickly, and the nutrients, such as soluble nitrogen and potassium in nitrogen fertilizers and potash fertilizers, are lost with rain or irrigation water, and cannot be absorbed by plants in time. Alternatively, due to the excessive amount of fertilizer dissolved instantly, there is an oversupply of nutrients, and the hydrophilic phosphorus is converted into insoluble phosphorus and loses its fertilizer effect, resulting in a mismatch between the nutrient supply and the plant growth cycle requirements. In addition, excessive use of traditional chemical fertilizers not only increases agricultural production costs, but also causes soil quality deterioration and environmental pollution. For example, excessive nitrogen and phosphorus flow into nearby pools, ditches, and even groundwater, causing water pollution.

[0003] Therefore, in order to solve the above problems, a technology has been developed to use slow / controlled release fertilizers to reduce the extent of fertilizer loss during application and improve fertilizer utilization. After the fertilizer enters the soil, the slow-release fertilizer can significantly reduce the release rate of effective nutrients in it compared to general instant chemical fertilizers, so as to control the time and amount of nutrients released into the soil to make it consistent with the nutrient demand pattern of the crop growth cycle.

[0004] There are two main methods for manufacturing slow / controlled release fertilizers: in the chemical method, the main nutrients in the fertilizer are directly or indirectly bonded to the polymer by covalent bonds or ionization; in the physical method, the fertilizer is coated with a film. Both methods achieve the purpose of slow / controlled release fertilizers by making the polymer or film insoluble. However, the technology for manufacturing slow / controlled release fertilizers by chemical methods is more complicated and the production cost is higher. Therefore, developing slow / controlled release fertilizers by film coating is a more economical direction.

[0005] Based on the above requirements, slow / controlled release fertilizers formed by the physical method of coating fertilizers with films can be roughly divided into the following categories: the first type is inorganic coated fertilizers, such as sulfur-coated urea, that is, urea coated with sulfur. This type of slow / controlled release fertilizer must use a larger amount of coating material, which relatively reduces the proportion of fertilizer components, so its applicability is lower; the second type is organic material coated fertilizers. The coating materials used in this type of slow / controlled release fertilizer are mainly polymer materials from the petrochemical industry. Although the slow / controlled release effect is better, these coating materials cannot be decomposed, and the coating film remaining in the soil will cause irreversible pollution.

[0006] As a more ideal solution, the third type is a slow / controlled release fertilizer that uses a degradable polymer material (such as a biodegradable material) as a coating film. In addition to achieving the slow release function as the film gradually degrades, the time and degree of degradation can also be changed by adjusting factors such as the film thickness of the coating film, thereby achieving the purpose of controlled release.

[0007] However, in practice, in the method of coating fertilizers with degradable polymer materials, the material must first be dissolved in a solvent or heated to a temperature above the melting point to become a liquid state. However, since most polymer materials must be dissolved in solvents with higher boiling points, it is difficult to remove the solvent after coating and forming a film. In addition, heated and molten liquid polymers usually have poor fluidity and are not easy to process into a film. At the same time, the high-temperature heating process will cause the nutrient components such as nitrogen fertilizers and phosphoric anhydride to crack and lose. Summary of the invention

[0008] In view of this, the main purpose of the present invention is to provide a slow-release fertilizer coated with a degradable material and a method for manufacturing the same, wherein the fertilizer is coated with multiple layers of degradable materials, which can achieve the slow-release function as the film gradually degrades, and the time and degree of degradation can be changed by adjusting factors such as film thickness to achieve the purpose of controlled release.

[0009] Furthermore, another object of the present invention is to provide a slow-release fertilizer coated with a biodegradable material and a method for manufacturing the same, wherein the coating film formed by the hydrophilic material has barrier properties to moisture and gas, thereby effectively preventing the fertilizer from rapidly losing nutrients such as nitrogen and phosphorus due to contact with moisture.

[0010] In addition, another object of the present invention is to provide a slow-release fertilizer coated with a degradable material and a method for manufacturing the same, wherein the coating film formed by the hydrophobic material can respectively protect the fertilizer particles and the hydrophilic material from being quickly dissolved by rainwater or irrigation water, and can maintain the integrity of the fertilizer particles during the coating process.

[0011] In addition, another object of the present invention is to provide a slow-release fertilizer coated with a degradable material and a method for manufacturing the same, wherein a volatile solvent is used as a solvent for the hydrophobic material, so that the fertilizer can be easily processed at a relatively low temperature.

[0012] In addition, another object of the present invention is to provide a slow-release fertilizer coated with a degradable material and a method for manufacturing the same, which can solve the problems of low applicability of inorganic coated fertilizers in the prior art and residual coating films using polymer materials from the petrochemical industry.

[0013] In order to achieve the above-mentioned object, the present invention provides a slow-release fertilizer coated with a degradable material, comprising:

[0014] Fertilizer granules;

[0015] A first coating layer, comprising a first hydrophobic material, coating the outside of the fertilizer particles;

[0016] A second coating layer, comprising a second hydrophilic material, coated on the outside of the first coating layer; and

[0017] The third coating layer comprises a third hydrophobic material and is coated on the outside of the second coating layer, wherein:

[0018] The first hydrophobic material, the second hydrophilic material and the third hydrophobic material are all biodegradable materials, and the first hydrophobic material and the third hydrophobic material are the same or different materials.

[0019] According to the present invention, there is also provided a method for manufacturing a slow-release fertilizer coated with a degradable material, comprising:

[0020] A solution preparation step, dissolving the first hydrophobic material, the second hydrophilic material and the third hydrophobic material with a first solvent, a second solvent and a third solvent respectively to form a first coating solution, a second coating solution and a third coating solution respectively;

[0021] A first coating step, coating the fertilizer particles with a first coating solution and drying the solution to form a film, so as to form a first hydrophobic coating layer on the surface of the fertilizer particles;

[0022] a second coating step of coating the fertilizer particles having the first hydrophobic coating layer formed thereon with a second coating solution and drying the coating to form a second hydrophilic coating layer on the outer surface of the first hydrophobic coating layer; and

[0023] The third coating step is to coat the fertilizer particles having the first hydrophobic coating layer and the second hydrophilic coating layer thereon with a third coating solution and dry the coating to form a third coating layer on the outer surface of the second hydrophilic coating layer, thereby preparing a slow-release fertilizer coated with a degradable material.

[0024] In summary, compared with the uncoated or single-layer coated fertilizers in the prior art, the slow-release fertilizer coated with degradable materials of the present invention can maintain the integrity of the fertilizer and achieve a slow-release or even controlled-release effect through a three-layer coating design of hydrophobicity-hydrophilicity-hydrophobicity. Moreover, the material used in the coating layer is a degradable polymer, thereby reducing pollution to the natural environment. In addition, the use of safe and volatile solvents combined with a simple coating process can greatly increase convenience and applicability. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a structural diagram of the slow-release fertilizer coated with degradable materials of the present invention;

[0026] Figure 2 It is a flow chart of the method for manufacturing the slow-release fertilizer coated with degradable materials of the present invention;

[0027] Figure 3 shows the degradation rate of cellulose acetate in an environment of 25±5°C; and

[0028] Figure 4 The figure shows the disintegration of uncoated fertilizer and slow-release fertilizer coated with three layers of degradable materials after standing in water for 24 hours.

[0029] Description of Figure Numbers:

[0030] 10: Fertilizer Granules

[0031] 20: First coating layer

[0032] 30: Second coating layer

[0033] 40: The third coating layer

[0034] S10: Solution preparation step

[0035] S20: First coating step

[0036] S30: Second coating step

[0037] S40: Third coating step DETAILED DESCRIPTION

[0038] Hereinafter, the slow-release fertilizer coated with a degradable material and the method for producing the same will be described in detail with reference to the accompanying drawings.

[0039] In the absence of any contradiction, the technical features in any embodiment described in this specification may be applicable to other embodiments of the present invention.

[0040] To achieve the above objectives, the present invention uses hydrophobic and hydrophilic biodegradable polymers to coat fertilizers in multiple layers, thereby preparing a slow-release fertilizer coated with at least three layers of hydrophobic-hydrophilic-hydrophobic films.

[0041] After the slow-release fertilizer of the present invention is applied, the hydrophilicity of the middle layer can prevent the nutrients in the fertilizer from being lost quickly. As the hydrophobic film of the outermost layer degrades, the polyvinyl alcohol film of the middle layer gradually dissolves due to contact with water, thereby destroying the moisture and gas barrier properties of the middle layer. Finally, as the hydrophobic film of the innermost layer degrades, the fertilizer components are gradually released, thereby achieving a slow-release effect.

[0042] According to this, if Figure 1As shown, the present invention provides a slow-release fertilizer coated with a degradable material, comprising: a fertilizer granule 10, a first coating layer 20 coated on the outside of the fertilizer granule 10, a second coating layer 30 coated on the outside of the first coating layer 20, and a third coating layer 40 coated on the outside of the second coating layer 30.

[0043] The fertilizer granules 10 used in the present invention may be solid chemical fertilizers available on the market, for example, may contain at least one of the three main inorganic nutrient components (i.e. nitrogen, phosphorus and potassium) and organic components in common chemical fertilizers.

[0044] According to the types of nutrients contained, the fertilizer particles 10 can be simple fertilizers or compound fertilizers. As simple fertilizers, nitrogen fertilizers can be urea or ammonium sulfate, phosphorus fertilizers can be phosphoric anhydride or ammonium phosphate, potassium fertilizers can be potassium oxide, potassium chloride or potassium nitrate, etc.; compound fertilizers can be a combination of the above simple fertilizers.

[0045] Specifically, the first coating layer 20 and the third coating layer 40 are hydrophobic coating layers, respectively comprising a first hydrophobic material and a third hydrophobic material, and the second coating layer 30 is a hydrophilic coating layer, comprising a second hydrophilic material.

[0046] It should be noted that since the nutrient components of general chemical fertilizers are hydrophilic, and hydrophilic biodegradable polymers use water as a solvent, if a hydrophilic polymer aqueous solution is used to form the first coating layer 20, when the fertilizer particles 10 contact the aqueous solution, the nutrients therein will dissolve and mix with the hydrophilic film, so that the coating cannot be formed in the end. Therefore, it is necessary to form a hydrophobic first coating layer 20 on the surface of the fertilizer particles 10 to ensure that the hydrophilic fertilizer particles 10 can maintain their integrity during the coating step and can prevent the external water vapor from eroding the fertilizer particles 10.

[0047] Furthermore, since the hydrophobic film pre-coated with the first coating layer 20 serves as the bottom layer, the second coating layer 30 can form a hydrophilic film with a relatively uniform thickness.

[0048] Thereafter, a third coating layer 40 is formed on the outside of the second coating layer 30 with a hydrophobic material to protect the hydrophilic film of the second coating layer 30 from losing its moisture and gas barrier effect due to rapid dissolution by rainwater or irrigation water.

[0049] The first hydrophobic material, the second hydrophilic material and the third hydrophobic material are all biodegradable materials, which will be decomposed into carbon dioxide and water in the soil, and thus will not remain in the soil to cause irreversible environmental pollution.

[0050] The first hydrophobic material, the second hydrophilic material and the third hydrophobic material can be in the form of unplasticized flakes or powders, or in the form of thermoplastic granules after hot melt extrusion. Considering the processing convenience, the above materials are preferably in the form of granules.

[0051] More specifically, in the present invention, both the first hydrophobic material and the third hydrophobic material can be cellulose acetate (CA). Cellulose acetate is hydrophobic, so it can protect the fertilizer from being eroded by water, and generally speaking, cellulose acetate film can be degraded by more than 90% in 6 to 12 months, so it has excellent biodegradability.

[0052] In other embodiments, the first hydrophobic material and the third hydrophobic material may also be composed of different degradable polymers, but are not limited thereto.

[0053] Generally speaking, as a hydrophobic coating material, the physical properties of cellulose acetate depend on its degree of acetylation. The present invention uses diacetate cellulose, and its degree of acetyl substitution is between 2.0 and 2.6.

[0054] Furthermore, the bound acid content of cellulose acetate may be between 50% and 58%, preferably between 52% and 55%. The bound acid content of cellulose acetate should be at least 50%, otherwise the solubility in organic solvents will be poor.

[0055] In addition, the number average molecular weight of cellulose acetate is generally between 12,000 and 90,000 g / mol.

[0056] The second hydrophilic material may be polyvinyl alcohol (PVOH). The polyvinyl alcohol film has excellent barrier properties to both moisture and gas, thus preventing the nutrients in the fertilizer from being deliquesced and lost quickly due to moisture in the environment during storage and / or use of the fertilizer.

[0057] Generally speaking, as a hydrophilic coating material, the alkalinity of polyvinyl alcohol is between 70% and 99%, and the number average molecular weight is between 20,000 and 120,000 g / mol.

[0058] Generally speaking, the particle size of the fertilizer granules 10 may be between 2 mm and 4 mm, the thickness of the first coating layer 20 and the third coating layer 40 may be between 0.008 mm and 0.06 mm, and the thickness of the second coating layer 30 may be between 0.004 mm and 0.06 mm. The thickness of the first coating layer 20 and the third coating layer 40 may be the same, but is not limited thereto.

[0059] Although the above description is for three-layer coating materials, the slow-release fertilizer of the present invention is not limited to three-layer coated fertilizers, but can also be fertilizers coated with five, seven or more layers of hydrophobic and hydrophilic materials alternately, as long as the innermost and outermost coating layers are both hydrophobic films.

[0060] To prepare the above-mentioned slow-release fertilizer coated with degradable materials, Figure 2 As shown, the present invention provides a method for manufacturing a slow-release fertilizer coated with a degradable material, comprising a solution preparation step S10 and first to third coating steps S20 to S40.

[0061] In the solution preparation step S10 , the first hydrophobic material, the second hydrophilic material and the third hydrophobic material are dissolved in the first solvent, the second solvent and the third solvent respectively to form a first coating solution, a second coating solution and a third coating solution respectively.

[0062] In the first or third coating solution formed in the solution preparation step S10 , the concentration of the first or third hydrophobic material may be between 5 and 15 wt %.

[0063] Specifically, the first solvent or the third solvent may include at least one of ethyl acetate, acetone, tetrahydrofuran, dichloromethane, chloroform, dimethyl sulfoxide, and ethyl acetate / ethanol mixed solution.

[0064] Considering factors such as safety, low toxicity, low boiling point and volatility, the solvent of the hydrophobic material is preferably acetone or ethyl acetate, so that the coating process can be performed in a safer manner with a lower operating temperature, thereby increasing industrial applicability.

[0065] In the second coating solution formed in step S10, the concentration of the second hydrophilic material may be between 5 and 20 wt%, and the second solvent may be water. Since polyvinyl alcohol as a hydrophilic material is a high-polarity polymer, water is generally the most ideal solvent.

[0066] Furthermore, the first or third coating solution may further contain 1 to 5 wt% of an auxiliary agent, and the second coating solution may further contain 1 to 10 wt% of an auxiliary agent. The auxiliary agent may be a commonly used small molecule polyol (such as glycerol), polyethylene glycol, glycerides, etc., or citrates.

[0067] The main function of the above-mentioned additives is to destroy the hydrogen bonds within the polymer molecules to reduce the glass transition temperature (Tg) during hot melt granulation, thereby further dissolving the polymer material into the solvent at a lower operating temperature while avoiding the disadvantages caused by the aforementioned high temperature heating process.

[0068] The auxiliary agent used in the present invention can be directly added to the coating solution, or first prepared into colloid particles with a hydrophobic or hydrophilic material, and then mixed with a solvent to form a coating solution.

[0069] In summary, in the manufacturing method of the present invention, the first or third coating solution may contain 5 to 15% of a hydrophobic material, 1 to 5% of an auxiliary agent, and 80 to 96% of a solvent; and the second coating solution may contain 5 to 20% of a hydrophilic material, 1 to 10% of an auxiliary agent, and 70 to 94% of a solvent.

[0070] Next, in the first to third coating steps S20 to S40, the fertilizer particles are coated with three layers, from inside to outside, in the order of hydrophobic film-hydrophilic film-hydrophobic film, for example, cellulose acetate film-polyvinyl alcohol film-cellulose acetate film.

[0071] Specifically, in the first coating step S20 , the fertilizer granules 10 are coated with a first coating solution and dried to form a film, so as to form a hydrophobic first coating layer 20 on the surface of the fertilizer granules 10 .

[0072] Thereafter, in the second coating step S30 , the fertilizer granules on which the first coating layer 20 is formed are coated with a second coating solution and dried to form a hydrophilic second hydrophilic coating layer 30 on the outer surface of the first coating layer 20 .

[0073] Finally, in the third coating step S40, the fertilizer particles 10 having the first coating layer 20 and the second hydrophilic coating layer 30 formed thereon are coated with a third coating solution and dried to form a film to form a hydrophobic third coating layer 40 on the outer surface of the second hydrophilic coating layer 30, thereby preparing the slow-release fertilizer of the coated degradable material of the present invention.

[0074] Specifically, in the first to third coating steps S20 to S40, the coating method may be a commonly used coating processing method, such as spraying, fluidized bed, rolling, casting, etc., or a combination of the above methods, but not limited thereto.

[0075] In the spray method or fluidized bed method, the coating solution is uniformly sprayed onto the fertilizer particles using a spray device and allowed to dry to form a coating film.

[0076] In the rolling method, the fertilizer granules are placed in a rotating drum, and a coating solution is added, and then the coating solution is attached to the surface of the fertilizer granules through a rolling motion and dried to form a coating film.

[0077] In the casting method, the coating solution is evenly spread or poured on the surface of the fertilizer particles, followed by a flowing and drying process to form a coating film.

[0078] The degradation rate and / or dissolution rate of the hydrophobic film and the hydrophilic film depends on the soil environment, the degree of polymerization (number average molecular weight) of the coating material, the concentration of the coating solution and the thickness of the coating layer. Therefore, in summary, in the present invention, the degradation rate and / or dissolution rate of the hydrophobic material and / or the hydrophilic material can be changed by adjusting the degree of polymerization, the solution concentration or the thickness of the coating layer, thereby controlling the slow release effect of the fertilizer. In addition, according to the growth requirements of the crop, the solution concentration of the inner and outer layers of the hydrophobic coating material and / or the thickness of the coating layer can also be the same or different.

[0079] In particular, in embodiments where the hydrophobic material is cellulose acetate and / or the hydrophilic material is polyvinyl alcohol, the degradation rate and / or dissolution rate of each layer can also be adjusted by changing the acid binding content of cellulose acetate and / or the alkalinity of polyvinyl alcohol.

[0080] Therefore, the slow-release fertilizer of the present invention can be more widely regulated and designed for the growth time and fertilizer utilization efficiency of various crops, and in addition to achieving the slow-release effect, it can further achieve the efficacy of controlled-release fertilizer.

[0081] Experimental methods

[0082] In order to verify the efficacy of the present invention, various experiments were conducted to test the degradability of the hydrophobic material, the integrity of the slow-release fertilizer after contact with water, and the slow-release effect after application.

[0083] raw material

[0084] Fertilizer granules: compound fertilizer purchased from the market, which contains 12 parts by weight of nitrogen fertilizer, 18 parts by weight of phosphorus fertilizer, 12 parts by weight of potassium fertilizer and 10 parts by weight of organic matter, and the particle diameter is 2 mm to 4 mm. This fertilizer granule is also the fertilizer used in the following comparative example 1.

[0085] Hydrophobic material: cellulose acetate particles, purchased from the market, comprising 65 to 85 parts by weight of cellulose acetate and 15 to 35 parts by weight of an auxiliary agent, triacetin.

[0086] Hydrophilic material: polyvinyl alcohol particles, purchased from the market, containing 75 to 90 parts by weight of polyvinyl alcohol and 10 to 25 parts by weight of triacetin, an auxiliary agent.

[0087] Degradability test of hydrophobic materials

[0088] In order to verify the biodegradability of the cellulose acetate granules used in the present invention, a hydrophobic film with a thickness of 0.06 mm was prepared on the outer surface of the fertilizer granules by hot melt extrusion casting using the cellulose acetate granules as a raw material.

[0089] According to the international standard NF T51-800, the biodegradability of the cellulose acetate film was tested at an ambient temperature of 25±5°C. Figure 3 As shown, the degradation rate of the cellulose acetate film used in the present invention is about 75% after 150 days at normal ambient temperature, and the results prove that the film has excellent biodegradability.

[0090] Preparation of coating solution

[0091] At room temperature, thermoplastic cellulose acetate particles and acetone are fully stirred and mixed in a sealed container at a ratio of 12 parts by weight: 88 parts by weight until the cellulose acetate particles are completely dissolved. The obtained solution is used for coating the hydrophobic layer.

[0092] At room temperature, polyvinyl alcohol (basicity of 88%, number average molecular weight of about 80,000) particles and water are thoroughly stirred and mixed in a closed container at a ratio of 10 parts by weight: 90 parts by weight until the polyvinyl alcohol particles are completely dissolved. The obtained solution is used for coating the hydrophilic layer.

[0093] Preparation of the slow-release fertilizer of the present invention

[0094] First layer of hydrophobic film coating: After the above-prepared cellulose acetate acetone solution and fertilizer particles are fully mixed in a ratio of 10 parts by weight: 90 parts by weight, the mixture is placed on a rolling cylinder and continuously rolled for coating until the acetone is completely volatilized and it is confirmed that there is no obvious adhesion between the fertilizer particles, thereby obtaining a first fertilizer semi-finished product coated with a first hydrophobic layer. This semi-finished product is also the fertilizer used in the following Comparative Example 2.

[0095] The second layer of hydrophilic film coating: After the above-prepared polyvinyl alcohol aqueous solution and the first fertilizer semi-finished product are fully mixed in a ratio of 10 parts by weight: 90 parts by weight, the mixture is placed on a rolling cylinder and continuously rolled for coating until the water is completely evaporated and it is confirmed that there is no obvious adhesion between the fertilizer particles, thereby obtaining a second fertilizer semi-finished product coated with a first hydrophobic layer and a second hydrophilic layer.

[0096] The third layer of hydrophobic film coating: After the above-configured cellulose acetate acetone solution and the second fertilizer semi-finished product are fully mixed in a ratio of 10 parts by weight: 90 parts by weight, they are placed on a rolling cylinder and continuously rolled for coating until the acetone is completely volatilized and it is confirmed that there is no obvious adhesion between the fertilizer particles, thereby obtaining the slow-release fertilizer coated with three layers of degradable polymers of the present invention (Example 1).

[0097] Collapse test

[0098] 10 to 15 grams of uncoated fertilizer granules (Comparative Example 1) and the slow-release fertilizer coated with three layers of biodegradable materials of the present invention (Example 1) were placed in test tubes, and 10 times the weight of water was added to make sure that all granules were submerged in the water. After standing for 24 hours, the test tubes were shaken manually to observe the disintegration of the fertilizer granules in each test tube.

[0099] The results are as follows Figure 2 As shown, the uncoated fertilizer granules on the left (Comparative Example 1) completely collapsed, while the three-layer coated slow-release fertilizer on the right (Example 1) still maintained a good appearance. The results confirm that compared with the uncoated fertilizer, the slow-release fertilizer of the present invention can avoid erosion by water and maintain its integrity.

[0100] Dissolution test

[0101] According to the various fertilizer categories and specifications in Appendix 1 of the second point of the announcement of the Ministry of Agriculture "Fertilizer Types and Specifications" (revised on April 24, 2020, Announcement No. 1091068958A of the Ministry of Agriculture), the initial nitrogen dissolution rate test value of coated urea fertilizers (item number 1-02) and coated compound fertilizers (item number 6-02) must be lower than 50%.

[0102] According to the second point of the same announcement document, the nitrogen initial dissolution rate test method (method number AFS1402-1) is based on the standard CNS13028 fertilizer test method (determination of the dissolution rate of coated fertilizers).

[0103] The dissolution test of the present invention is carried out according to the standard CNS13028. The results are shown in Table 1 below. For the initial dissolution rate of nitrogen of various fertilizers, the slow-release fertilizer coated with three layers of degradable materials of the present invention (Example 1) is 32.7%, the fertilizer coated with only one layer of cellulose acetate film (Comparative Example 2) is 68.2%, and the uncoated fertilizer (Comparative Example 1) is 99.3%.

[0104] Therefore, it can be confirmed that the slow-release efficiency of the three-layer coated slow-release fertilizer of the present invention is far superior to that of the single-layer coated and uncoated fertilizers. At the same time, it is proved that the three-layer coated slow-release fertilizer of the present invention also meets the national standards for coated fertilizers, that is, the initial nitrogen dissolution rate detection value is less than 50%.

[0105] Table 1

[0106]

[0107] In summary, the slow-release fertilizer coated with degradable materials of the present invention has the following advantages:

[0108] (1) Using biodegradable polymers as the material for coating fertilizers solves the problem of irreversible pollution caused by film residues in the soil;

[0109] (ii) Using safe and volatile solvents as solvents for dissolving biodegradable polymers greatly increases the applicability of the industry;

[0110] (iii) The coating process can be carried out by common methods such as spraying, fluidized bed, rolling or casting, without the need for setting up special devices or equipment;

[0111] (iv) Through the design of hydrophobic-hydrophilic-hydrophobic three-layer coating, the integrity of the fertilizer particles and the barrier properties to water vapor and gas are taken into account;

[0112] (V) The release time and amount of fertilizer nutrients can be controlled according to the needs of the plant growth cycle by adjusting the thickness of each coating layer, the concentration of the coating solution or the degree of polymerization of the degradable polymer to achieve the effect of controlled release; and

[0113] (VI) The slow-release fertilizer coated with three layers of degradable materials of the present invention has a slow-release performance superior to that of the coated fertilizer coated with a single layer of degradable polymer cellulose acetate, while meeting the national standard for CNS coated fertilizers.

[0114] The exemplary embodiments of the present invention are for illustrative purposes only and are not intended to limit the technical spirit of the present invention. The technical scope of the present invention is not limited thereto. Therefore, it should be understood that the above exemplary embodiments are illustrative in all embodiments and do not limit the present invention.

[0115] Although the preferred embodiments of the present invention are disclosed for illustrative purposes, those skilled in the art will clearly understand that without departing from the spirit or scope of the present invention disclosed in the appended claims, they should still be included in the scope of protection intended by the present invention.

Claims

1. A slow-release fertilizer coated with a degradable material, comprising: Fertilizer granules; A first coating layer, comprising a first hydrophobic material, coated on the outside of the fertilizer particles; A second coating layer, comprising a second hydrophilic material, coated on the outside of the first coating layer; and The third coating layer, comprising a third hydrophobic material, is coated on the outside of the second coating layer, wherein The first hydrophobic material, the second hydrophilic material and the third hydrophobic material are all biodegradable materials, and wherein: The first hydrophobic material and the third hydrophobic material are the same or different materials.

2. The slow-release fertilizer according to claim 1, wherein At least one of the first hydrophobic material and the third hydrophobic material is cellulose acetate, and The second hydrophilic material is polyvinyl alcohol.

3. The slow-release fertilizer according to claim 2, wherein The cellulose acetate has a bound acid content of 50% to 58% and a number average molecular weight of 12,000 to 90,000 g / mol.

4. The slow-release fertilizer according to claim 2, wherein The polyvinyl alcohol has a basicity between 70% and 99%, and a number average molecular weight between 20,000 and 120,000 g / mol.

5. The slow-release fertilizer according to claim 1, wherein The particle size of the fertilizer particles is between 2 mm and 4 mm. The thickness of at least one of the first coating layer and the third coating layer is between 0.008 mm and 0.06 mm, and The thickness of the second coating layer is between 0.004 mm and 0.06 mm.

6. A method for producing a slow-release fertilizer coated with a degradable material, comprising: A solution preparation step, dissolving the first hydrophobic material, the second hydrophilic material and the third hydrophobic material according to any one of claims 1 to 5 with a first solvent, a second solvent and a third solvent, respectively, to form a first coating solution, a second coating solution and a third coating solution, respectively; A first coating step, coating the fertilizer particles with the first coating solution and drying the coating solution to form a first coating layer on the surface of the fertilizer particles; a second coating step of coating the fertilizer particles on which the first coating layer is formed with the second coating solution and drying the coating solution to form a second hydrophilic coating layer on the outer surface of the first coating layer; as well as The third coating step is to coat the fertilizer particles having the first coating layer and the second hydrophilic coating layer thereon with the third coating solution and dry the coating solution to form a third coating layer on the outer surface of the second hydrophilic coating layer, thereby preparing a slow-release fertilizer coated with a degradable material.

7. The manufacturing method according to claim 6, wherein: At least one of the first solvent and the third solvent includes at least one of ethyl acetate, acetone, tetrahydrofuran, dichloromethane, chloroform, dimethyl sulfoxide, and an ethyl acetate / ethanol mixed solution, and The second solvent is water.

8. The manufacturing method according to claim 6, wherein: At least one of the concentration of the first hydrophobic material in the first coating solution and the concentration of the third hydrophobic material in the third coating solution is between 5 and 15 wt %, and The concentration of the second hydrophilic material in the second coating solution is between 5 and 20 wt %.

9. The manufacturing method according to claim 6, wherein: At least one of the first coating solution and the third coating solution further comprises 1 to 5 wt % of an auxiliary agent, and, The second coating solution further comprises 1 to 10 wt % of an auxiliary agent, and wherein The auxiliary agent contained in at least one of the first coating solution, the second coating solution and the third coating solution includes at least one of small molecule polyols, polyethylene glycol, glycerides and citrates.

10. The manufacturing method according to claim 6, wherein: In at least one of the first coating step, the second coating step and the third coating step, the coating method includes spraying, fluidized bed, rolling, casting and a combination of the above methods.

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