JP7299931B2 - Method for producing controlled fertilizer - Google Patents

Description

The present invention relates to a method for producing a coated granular magnesium sulfate fertilizer with highly controlled leaching.

Conventionally, in order to meet the labor-saving needs associated with the aging of agricultural workers, elution-controlled fertilizers capable of reducing the labor for additional fertilization have been proposed, and various forms of commercial products have been put to practical use. Among them, coated granular fertilizers, in which the elution of internal components is controlled by coating the surface of granular fertilizers with an organic resin, have become the most widely used and mainstream. Thermoplastic resins or thermosetting resins are widely used as organic resins used as coating materials.

As an example of using a thermoplastic resin, there is a fertilizer coated with a coating material mainly composed of a mixture of an olefin resin and an ethylene-vinyl acetate copolymer, as shown in Patent Document 1, and the coating method is a spouted bed. A method is used in which a granular fertilizer is preheated in a fluidized state using a device, and a resin dissolved in an organic solvent is sprayed onto the fertilizer and instantly dried with hot air to form a film.

On the other hand, as an example of using a thermosetting resin, there is a fertilizer coated with a coating material mainly composed of urethane resin as shown in Patent Document 2. A method is used in which the granular fertilizer is preheated, uncured urethane resin is added, and heat curing is repeated while maintaining heat to form a coating.

Regarding fertilizers coated with a coating material containing urethane resin as a main component, various studies have been made on efficient production methods thereof. For example, as shown in Patent Document 3, uncured thermosetting resin It is known that the combined use of a raw material and a hydrophobic substance such as wax increases the hydrophobicity of the polyurethane film and reduces the water permeability, making it possible to control elution with a smaller amount of resin. there is

Granular urea is most commonly used as a fertilizer to be coated with coated granular fertilizer. The reason for this is that it is relatively inexpensive for its high nitrogen content, and it is easy to manufacture a high-component fertilizer as a bulk blend fertilizer with general chemical fertilizers containing nitrogen, phosphoric acid, and potassium. Since the adverse effect on growth and yield is the greatest when it is not supplied to crops at the appropriate time without additional fertilization, the use of controlled-release fertilizers is highly valued.

On the other hand, there is magnesium sulfate fertilizer as a fertilizer with high utility value as top dressing. Magnesium sulfate fertilizer contains water-soluble magnesium as the main component, so it can be quickly effective as a fertilizer, but it is more likely to be washed away than materials such as molten fertilizing, which have citric acid-soluble magnesium as the main component. Because of its properties, it is important to apply it at the right time to maximize its fertilizing effect on crops. For example, in paddy rice cultivation, applying additional fertilizer before the young panicle formation stage promotes the assimilation of rice plants, strengthens root growth, improves the ripening rate, and reduces lodging, leading to improved yields. It has been known.

Magnesium sulfate fertilizers that are generally commercially available are roughly divided into two types according to the manufacturing method: one with a magnesium content of about 25% obtained from magnesium sulfate, which is a by-product when salt is made from seawater, and one with a magnesium content of about 25%. Magnesium content of about 14 to 17% is obtained by reacting crushed magnesium-containing minerals such as rocks with sulfuric acid. Each magnesium sulfate fertilizer differs in the composition and subcomponents of the hydrated salt of magnesium sulfate contained. On the other hand, the latter contains magnesium sulfate monohydrate as the main ingredient, magnesium sulfate hexahydrate, magnesium sulfate heptahydrate, and additional ingredients such as silicon, iron, calcium, boron, etc. Contains useful elements.

Regarding the method for producing the granular product of magnesium sulfate fertilizer obtained by the reaction of the pulverized product of the magnesium-containing mineral and sulfuric acid, as shown in Patent Document 4, the product temperature of the reaction product of the mineral powder and sulfuric acid is 60 ° C. The method of adding water and granulating at the above time is an industrially very advantageous production method from the viewpoint of less energy required for production and high hardness of the produced granular product. Among the products obtained by this manufacturing method, compared with the granular product obtained by granulating the reaction product after cooling, polyhydrate sulfuric acid consisting of magnesium sulfate hexahydrate and magnesium sulfate heptahydrate It is known to contain a large amount of magnesium (the content ratio is 0.2 mol or more of magnesium sulfate hexahydrate per 1 mol of magnesium sulfate monohydrate).

As for the resin-coated magnesium sulfate fertilizer, a product with a magnesium content of 21 to 23%, which is obtained by coating granular magnesium sulfate fertilizer with a magnesium content of 25% derived from seawater, has been commercialized. However, its distribution volume is extremely small, and it is not popular in general. The reason for this is that currently available coated granular magnesium sulfate fertilizers are very expensive compared to uncoated ones, so even if the yield increases due to the effect of application, it does not necessarily lead to an improvement in profits. be done.

The reason why the coated granular magnesium sulfate fertilizer cannot be provided at a low cost is the low productivity in the coating process peculiar to the magnesium sulfate fertilizer. As shown in Non-Patent Document 1, polyhydrate magnesium sulfate such as magnesium sulfate heptahydrate or magnesium sulfate hexahydrate, which is the main component of magnesium sulfate fertilizer, is heated to 50 ° C. or higher in an open system. It is known that the water of crystallization then dissociates and evaporates, transforming it into an anhydrous salt in sequence. As shown in the above Patent Documents 1 to 3, since preheating of the granular fertilizer to be coated is required in a general coating manufacturing process, magnesium sulfate fertilizer absorbs heat by dissociation and evaporation of water of crystallization at that time. , more heat energy was required to raise the temperature to the target product temperature. Furthermore, as the water of crystallization changes, the shape of the particles collapses, and some of them become pulverized and stick to the device. and organic solvents that dissolve it, polyisocyanates as raw materials for thermosetting resins, animal and vegetable oils, waxes, paraffins, etc. as lubricants and elution modifiers) are taken into the inside from the particle surface. However, there is a problem that the resin raw material is not evenly coated, resulting in defects in the formed coating. In order to compensate for defects in the coating, it is necessary to repeat the coating process to thicken the coating.

As a prior art related to these problems, Patent Document 5 discloses a technique of forming a coating film using a polyurethane curing reaction at room temperature, considering volatilization and deterioration of fertilizer components due to heat treatment during the coating process. . However, since the curing reaction speed at room temperature is very slow, one coating process requires two hours, which is not practical.

Japanese Patent Publication No. 60-21952 JP-A-9-202683 JP-A-2003-104787 Japanese Patent Publication No. 4-70273 Japanese Patent Publication No. 54-39298

Kimio Isa, Masahiro Nogawa, "Thermal Decomposition of Magnesium Sulfate Hydrate in Autogenous Atmosphere", Thermal Measurement, Japan Thermal Measurement Society, January 1983, Vol. 10, No. 1, p. 2-7

The currently commercially available method for producing coated fertilizers with high productivity requires heating of the fertilizer particles to be coated. , an increase in the energy required to raise the temperature of the product and a loss of coating uniformity are obstacles to improving productivity. Therefore, the present invention solves this problem by suppressing the change in water of crystallization due to heating in the coating process of granular magnesium sulfate fertilizer, provides a highly productive production method, and provides a coating with high economic utility value. The object is to provide a granular magnesium sulfate fertilizer.

The present inventors added an uncured thermosetting resin at a temperature lower than 50°C where the water of crystallization in the magnesium sulfate fertilizer component begins to change, and formed a coating film, and after that, a high temperature region of 50°C or higher. The present inventors have found that the dissociation and evaporation of water of crystallization are suppressed when heated to 200 rpm, and have completed the present invention by further studies based on this finding.

That is, the present invention includes the following contents.
(1) A method for producing a coated granular magnesium sulfate fertilizer in which a coating film is formed on the surface of the granular magnesium sulfate fertilizer, comprising: After adding the raw material at less than 50 ° C., the surface temperature of the fertilizer is in the range of room temperature to 70 ° C. After applying a primary coating with the above-mentioned hydrophobic substance and thermosetting resin having a melting point of less than 50 ° C., further hydrophobic from above. A process for producing a coated granular magnesium sulfate fertilizer with a secondary coating of a curable material and a thermosetting resin.
(2) The production method according to (1) above, wherein the granular magnesium sulfate fertilizer is obtained by granulating a product obtained by reacting a pulverized magnesium-containing mineral with sulfuric acid.
(3) The ratio of magnesium sulfate hydrate in the granular magnesium sulfate fertilizer is 0.2 mol or more of magnesium sulfate hexahydrate per 1 mol of magnesium sulfate monohydrate. manufacturing method.
(4) The production method according to any one of (1) to (3) above, wherein the thermosetting resin is a urethane resin obtained by reacting a polyisocyanate compound and a polyol compound on the surface of the granular fertilizer.
(5) The production method according to any one of (1) to (4) above, wherein the hydrophobic substance having a melting point of less than 50°C in the primary coating step is one or more substances selected from vegetable oils and fats.
(6) The production method according to any one of (1) to (5) above, wherein the hydrophobic substance in the secondary coating step is one or more substances selected from waxes.
(7) In the primary and secondary coating steps, after adding a hydrophobic substance to the granular magnesium sulfate fertilizer in a rolling state, (i) a step of adding a thermosetting resin raw material, and (ii) in a rolling state. The production method according to any one of the above (1) to (6), which includes the step of forming a film by a thermosetting reaction, and repeating the steps of (i) and (ii) two or more times in total.

By the primary coating step of the present invention, by suppressing the problem caused by heating the crystal water in the polyhydrate magnesium sulfate contained in the magnesium sulfate fertilizer, the secondary coating step for the purpose of elution control can be carried out in a conventional manner. Therefore, it can be carried out in a temperature zone with high productivity. In the secondary coating step, a hydrophobic substance capable of imparting high elution control performance can be added, and the uniformity of the coating is higher than when the primary coating is not applied, making it possible to make the coating thinner. As a result, it is possible to provide a coated granular magnesium sulfate fertilizer that is economically highly useful.

In the production method of the present invention, it is important to efficiently perform the primary coating for the purpose of preventing the change (dissociation and evaporation) of the water of crystallization in the magnesium sulfate fertilizer component due to heating. The primary coating can be effective even if the thermosetting resin raw material is added only once and the coating is thermally cured. Higher effect can be obtained. The amount of resin to be added at one time is appropriately adjusted depending on the shape and particle size distribution of the fertilizer to be coated. Yes, preferably in the range of 0.3 to 0.7% by weight. If it is less than 0.1% by weight, the coating will be uneven due to the lack of the resin amount, and if it is more than 1% by weight, the adhesion between the particles will become strong during thermosetting, which may cause defects in the coating. The greater the number of times the coating is laminated, the higher the hermeticity, but this leads to an increase in the amount of resin used and the production time. Therefore, the range of 2 to 10 times is preferable from the purpose of the present invention, which aims to improve productivity.

A preferable procedure of the primary coating step in the present invention is to first add a hydrophobic substance to a tumbling granular fertilizer, disperse it uniformly on the particle surface, and then add a thermosetting resin raw material. This step can be carried out at any temperature below 50° C. at which the water of crystallization does not change, and can also be carried out at room temperature. Then, while maintaining the tumbling state, heating is started, the rate of temperature increase is appropriately adjusted, and it is confirmed that a thermosetting reaction has occurred at a temperature of less than 50°C. Confirmation of the thermosetting reaction is confirmed by visual observation that the fluidity of the rolling particles temporarily drops due to the gelation of the thermosetting resin, and then the fluidity recovers as the curing reaction progresses. can do. In this state, the primary coating step can be finished and the secondary coating step can be performed. It can be implemented by repeating the step of thermosetting. The product temperature at that time does not necessarily need to be maintained at a temperature of less than 50°C, and it is possible to carry out while raising the temperature in the range of over 50°C and within 70°C.

The subsequent secondary coating step is a coating step for the purpose of controlling the elution by forming a coating having a high elution-suppressing effect on the primary-coated fertilizer particles. The secondary coating process includes a process of preheating the fertilizer particles to the coating temperature, a process of adding a hydrophobic substance and uniformly dispersing it on the particle surface, and a process of adding a thermosetting resin raw material, maintaining the temperature, and heat curing. By repeating the process of adding the thermosetting resin raw material and thermosetting, the thickness of the film of the final product can be adjusted, and a product with an arbitrary dissolution rate can be obtained. The surface temperature of the fertilizer particles during the secondary coating process can usually be in the range of 60° C. to 90° C., and a range of 70° C. to 80° C. is preferable from the viewpoint of the thermosetting reaction speed and production stability. The amount of resin added at one time in the secondary coating process is the same as in the primary coating process, with respect to the fertilizer to be coated, the thermosetting resin raw material is usually in the range of 0.1 to 1% by weight, preferably 0.3 to 0. .7% by weight. The coating can be laminated any number of times until the desired elution thickness is obtained, but generally it is in the range of 2 to 40 times.

The hydrophobic substance used in the primary coating process and the secondary coating process plays a role as a lubricant that prevents adhesion between fertilizer particles during rolling and adhesion between the fertilizer particles and the wall surface of the rolling device, and also between the structure of the resin film. It plays a role in controlling elution by entering and changing the hydrophobicity of the membrane. That is, in the primary coating process, it has the effect of preventing coating defects caused by the adhesion and improving the sealing property of the coating, and in the secondary coating process, it improves the uniformity of the coating and increases the hydrophobicity of the membrane, so that a small amount of There is an effect of controlling elution efficiently by the amount of resin. The amount of the hydrophobic substance added in the primary coating process and the secondary coating process is usually in the range of 0.1 to 2% by weight, preferably in the range of 0.2 to 1% by weight, based on the fertilizer to be coated. Also, the hydrophobic substance can be added all at once before the first addition of the thermosetting resin raw material in each coating step, or can be divided and added in multiple batches.

Hydrophobic substances used in the primary coating process need to spread evenly over the entire surface of rolling particles as a lubricant at a temperature of less than 50°C. Substances with a melting point of less than 50°C fall under this category. Specific examples include beef tallow, lard, chicken fat, horse fat, fish oil, and butter as animal oils; palm oil, soybean oil, rapeseed oil, sunflower oil, palm kernel oil, cottonseed oil, peanut oil, and olive oil as vegetable oils. , coconut oil, corn oil, sesame oil, linseed oil, safflower oil, rice oil, perilla oil; capric acid, lauric acid, oleic acid, linoleic acid, linolenic acid, erucic acid as fatty acids; some low-melting paraffins as waxes Wax; hydrocarbons such as liquid paraffin; silicones such as silicone oils such as dimethylpolysiloxane; Among these hydrophobic substances, vegetable oils such as rapeseed oil are particularly preferred.

Hydrophobic substances used in the secondary coating step may be hydrophobic substances having a melting point of 50° C. or higher in addition to the hydrophobic substances used in the primary coating step. Specific examples include natural waxes such as carnauba wax, beeswax and rice wax; petroleum waxes such as paraffin wax and microcrystalline wax; synthetic waxes such as Fischer-Tropsch wax and polyethylene wax; Mixtures of two or more can be used. Among these hydrophobic substances, paraffin wax is particularly preferred. Since the hydrophobic substance used in the secondary coating process must be uniformly dispersed throughout the tumbling fertilizer particles, it can be heated to a temperature above the melting point of the hydrophobic substance used and added in a liquid state. Preferably, the surface temperature of the fertilizer particles is preferably maintained at a temperature equal to or higher than the melting point of the hydrophobic substance in order to prevent solidification during rolling.

A known thermosetting resin can be used in the present invention. Examples thereof include urethane resins, epoxy resins, phenol resins, alkyd resins, melamine resins, unsaturated polyester resins, and the like, and one or a mixture of two or more selected from these can be used. Among these thermosetting resins, urethane resins are easy to handle and are preferable from the standpoint of product quality. A urethane resin is a resin obtained by reacting a polyisocyanate compound and a polyol compound, and by adding these raw materials to tumbling fertilizer particles, it is possible to form a film on the particle surface. The polyisocyanate compound and the polyol compound can be added simultaneously or separately, or can be added after premixing to form a coating. The polyisocyanate compound is not particularly limited, and examples thereof include toluene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), polymethylene polyphenyl polyisocyanate (polymeric MDI), naphthalene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate and the like. Mixtures of these can also be used as appropriate. Among these, MDI, polymeric MDI and the like are particularly preferably used. The polyol compound is also not particularly limited, and examples thereof include polyether polyol, polyester polyol, castor oil, modified castor oil, and the like. In addition, a catalyst can be added during the reaction between the polyisocyanate compound and the polyol compound to accelerate the curing reaction, which is a useful technique in terms of production efficiency. A known catalyst can be used, such as triethylenediamine, N-methylmorpholine, N,N-dimethylmorpholine, diazabicycloundecene, 2,4,6-tris(dimethylaminomethyl)phenol. An amine catalyst such as is preferably used. As for the method of adding the catalyst, the catalyst may be added separately from other resin raw materials, or may be added after previously being dispersed in a polyol compound.

There is no particular limitation on the device for rolling the granular fertilizer, and known devices such as rotating pans, rotating drums, sugar-coating machines, concrete mixers, and the like can be used. Further, it is preferable to attach a heating device attached to the rolling device from the viewpoint of controlling the temperature of the granular fertilizer and stabilizing the quality of the product. The heating equipment is not particularly limited, and known equipment such as a heavy oil boiler or a kerosene heater for hot air ventilation, an infrared heater, a far infrared heater, or the like can be used.

The granular magnesium sulfate fertilizer to be coated in the present invention is not particularly limited as long as it is a granular fertilizer containing magnesium sulfate fertilizer registered as a fertilizer, and can be used regardless of the manufacturing method and the amount of magnesium component. can be done. Examples include magnesium sulfate fertilizer, which is made from magnesium sulfate, which is a by-product of the seawater salt production process, and magnesium sulfate fertilizer, which is obtained by reacting crushed magnesium-containing minerals such as peridotite and serpentinite with sulfuric acid. , Magnesium sulfate fertilizer obtained by reacting sulfuric acid with pulverized chemical products such as magnesium hydroxide and light burnt magnesia, and granular composite fertilizers containing one or more selected from them. be done. The method of granulation is not particularly limited, and it is a granular product granulated by a known granulator, and the type of granulation binder and the presence or absence of addition are not limited. Among these, for the purpose of suppressing an increase in manufacturing costs, products are manufactured by a manufacturing method in which only water is added and granulated when the product temperature of the pulverized magnesium-containing mineral and the reaction product of sulfuric acid is 60°C or higher. It is particularly preferable from the viewpoint of cost and grain hardness.

The grain size of the granular magnesium sulfate fertilizer to be coated is not particularly limited, but a grain size in the range of 1 to 5 mm is preferable for production, and a grain size in the range of 1.7 to 4 mm is suitable for mechanical spraying. It is particularly preferred from the standpoint of practical applicability.

EXAMPLES 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.

(Example 1)
10 kg of granular magnesium sulfate fertilizer (manufactured by MC Ferticom, trade name: Sunmate) was charged into a concrete mixer (inner diameter: 480 mm) and rotated at 27 rpm to make the fertilizer tumbling. 100 g of rapeseed oil (canola oil) as a hydrophobic substance, 47.2 g of polymeric MDI (manufactured by Sumika Covestro Urethane, trade name: Sumidule 44V20L) as a resin raw material, polyether polyol (manufactured by Sumika Covestro Urethane, trade name) 52.8 g of Sumifene TM) and 1.2 g of 2,4,6-tris(dimethylaminomethyl)phenol as an amine catalyst were added, and a heat gun (Ishizaki Electric Seisakusho, trade name: Plaget PJ-216A) was supplied with hot air, and heating was started. Eight minutes after the start of heating, when the surface temperature of the fertilizer reached about 47° C., the fluidity of the tumbling fertilizer particles temporarily decreased, confirming the thermosetting reaction of the urethane resin. Three minutes later, after confirming that the fluidity had recovered, 23.6 g of polymeric MDI, 26.4 g of polyether polyol, and 0.6 g of amine catalyst were added again, and heating was continued while rolling to heat cure. let me The same amount of urethane resin raw material was added and heat-cured again until the surface temperature of the fertilizer reached 70°C. . At this time, it took 35 minutes from the start of heating until the fertilizer surface temperature reached 70°C. In the subsequent secondary coating step, first, 60 g of paraffin wax (manufactured by Nippon Seiro, trade name: Paraffin Wax-155, melting point: 69 ° C.) was added and uniformly dispersed, then 23.6 g of polymeric MDI, polyether 26.4 g of polyol and 0.6 g of amine catalyst were added, and heat curing was performed while maintaining the fertilizer temperature at 70-75°C. Under these temperature conditions, the thermosetting reaction was almost completed 3 minutes after the addition of the resin raw material, and the next resin raw material could be added. was repeated a total of 12 times, and a total of 6% by weight of the urethane resin raw material was added to the fertilizer to be coated to complete the resin addition in the secondary coating step. After the last resin addition, the fertilizer temperature was maintained at 70-75°C for 10 minutes to fully cure the resin to form a coated granular magnesium sulfate fertilizer.

(Comparative example 1)
10 kg of granular magnesium sulfate fertilizer (manufactured by MC Ferticom, trade name: Sunmate) was charged into a concrete mixer (inner diameter: 480 mm) and rotated at 27 rpm to make the fertilizer tumbling. Then, hot air from a heat gun (Ishizaki Denki Seisakusho, trade name: PLAJET PJ-216A) was passed through, and the fertilizer was heated until the surface temperature reached 70°C. At this time, it took 100 minutes from the start of heating until the fertilizer surface temperature reached 70°C. Next, 60 g of paraffin wax (manufactured by Nippon Seiro, trade name: Paraffin Wax-155, melting point: 69 ° C.) was added and uniformly dispersed, followed by polymeric MDI (manufactured by Sumika Covestro Urethane, trade name: Sumidule 44V20L). ), 26.4 g of polyether polyol (manufactured by Sumika Covestro Urethane, trade name: Sumifen TM), and 0.6 g of amine catalyst (2,4,6-tris(dimethylaminomethyl)phenol). Then, heat curing was performed while maintaining the fertilizer temperature at 70 to 75°C. The process of adding the same amount of resin material every 3 minutes while maintaining the fertilizer temperature was repeated a total of 16 times, and a total of 8% by weight of urethane resin material was added to the fertilizer to be coated to complete resin addition. From the last resin addition, the fertilizer temperature was maintained at 70-75°C for 10 minutes to fully cure the resin to make coated granular magnesium sulfate fertilizer.

(Comparative example 2)
A sample was prepared in the same manner as in Example 1, except that no hydrophobic substance was added in the primary coating step. At this time, it took 32 minutes from the start of heating until the fertilizer surface temperature reached 70°C.

(Example 2)
100 kg of granular magnesium sulfate fertilizer (manufactured by MC Ferticom, trade name: Sunmate) was charged into a concrete mixer (inner diameter: 1000 mm) and rotated at 18 rpm to make the fertilizer tumbling. 1000 g of rapeseed oil (canola oil) as a hydrophobic substance, 472 g of polymeric MDI (manufactured by Sumika Covestro Urethane, trade name: Sumidur 44V20L) as a resin raw material, polyether polyol (manufactured by Sumika Covestro Urethane, trade name: Sumifen) TM) and 12 g of 2,4,6-tris(dimethylaminomethyl)phenol as an amine catalyst were added, and heating was started by applying hot air from a jet heater to the outer wall of the device while maintaining the tumbling state. Twenty-nine minutes after the start of heating, when the surface temperature of the fertilizer reached about 46° C., the fluidity of the tumbling fertilizer particles decreased temporarily, confirming the thermosetting reaction of the urethane resin. Five minutes later, after confirming that the fluidity had recovered, 236 g of polymeric MDI, 264 g of polyether polyol, and 6 g of amine catalyst were added again, and the mixture was heated while rolling to heat cure. The same amount of urethane resin raw material is added and heat-cured twice until the fertilizer product temperature reaches 70 ° C. A total of 2.5% by weight of urethane resin raw material is added to the fertilizer to be coated, and the primary coating process is performed. completed. In the subsequent secondary coating step, first, 600 g of paraffin wax (manufactured by Nippon Seiro, trade name: Paraffin Wax-155, melting point: 69 ° C.) was added and uniformly dispersed, and then 236 g of polymeric MDI and polyether polyol were added. 264 g and 6 g of an amine catalyst were added, and heat curing was performed while maintaining the fertilizer temperature at 70-75°C. Under these temperature conditions, the thermosetting reaction was almost completed 3 minutes after the addition of the resin raw material, and the next resin raw material could be added. was repeated a total of 11 times, and a total of 5.5% by weight of urethane resin raw material was added to the fertilizer to be coated, completing the resin addition in the secondary coating process. The fertilizer temperature was maintained at 70-75° C. for 10 minutes from the last resin addition to fully cure the resin to form a coated granular magnesium sulfate fertilizer.

(Comparative Example 3)
A sample was prepared in the same manner as in Example 2 except that no hydrophobic substance was added in the primary coating step, the total amount of primary coating resin added was 3.5% by weight, and the total amount of secondary coating resin added was 4.5%. bottom.

The coated fertilizers prepared in Examples and Comparative Examples were immersed in water and kept at 25° C., sampled over time, the amount of eluted magnesium was measured, and the elution rate was calculated. In addition, the moisture content of the granular magnesium sulfate fertilizer before coating and the samples prepared in each example and comparative example was measured from the change in weight after drying at 100° C. for 5 hours.

Table 1 summarizes the implementation in Examples 1 and 2 and Comparative Examples 1 and 3, Table 2 summarizes the results of moisture measurement before and after coating, and Table 3 summarizes the transition of the magnesium elution rate.

As a result of the comparison of the moisture content shown in Table 2, it is shown that Example 1 and Comparative Example 2 in which the primary coating was applied suppressed a decrease in the moisture content in comparison with Comparative Example 1 in which the primary coating was not applied. was done. This result corresponds to the fact that the heating time until reaching the coating temperature was 35 minutes in Example 1 and 32 minutes in Comparative Example 2, whereas it was 100 minutes in Comparative Example 1. This indicates that the coating suppresses the evaporation of the water of crystallization and significantly improves the productivity. Moreover, from the transition of the magnesium elution rate shown in Table 3, it was found that in Examples 1 and 2, the magnesium was stably eluted over a long period of time. In Comparative Example 2, in which no hydrophobic substance was added in the primary coating step, the final elution rate was the same as in Example 1, but the elution was rapid in the first half, and from the purpose of slowing the fertilization effect. I don't like it. This result indicates that the use of a hydrophobic substance in the primary coating step improves the uniformity of the coating and has the effect of stabilizing the elution.

Claims (7)

A method for producing a coated granular magnesium sulfate fertilizer in which a coating film is formed on the surface of the granular magnesium sulfate fertilizer, comprising adding 50 hydrophobic substances having a melting point of less than 50°C and a thermosetting resin raw material to the granular magnesium sulfate fertilizer. After addition at less than ° C., the fertilizer surface temperature is in the range from room temperature to 70 ° C., after applying a primary coating with the above-mentioned hydrophobic substance and thermosetting resin having a melting point of less than 50 ° C., then further hydrophobic substance and A method for producing a coated granular magnesium sulfate fertilizer in which a secondary coating is applied with a thermosetting resin. 2. The production method according to claim 1, wherein the granular magnesium sulfate fertilizer is a granular magnesium sulfate fertilizer obtained by granulating a product obtained by reacting a pulverized magnesium-containing mineral with sulfuric acid. 3. The production method according to claim 2, wherein the ratio of the magnesium sulfate hydrate in the granular magnesium sulfate fertilizer is 0.2 mol or more of magnesium sulfate hexahydrate per 1 mol of magnesium sulfate monohydrate. The production method according to any one of claims 1 to 3, wherein the thermosetting resin is a urethane resin obtained by reacting a polyisocyanate compound and a polyol compound on the surface of the granular fertilizer. The production method according to any one of claims 1 to 4, wherein the hydrophobic substance having a melting point of less than 50°C in the primary coating step is one or more substances selected from vegetable oils and fats. The production method according to any one of claims 1 to 5, wherein the hydrophobic substance in the secondary coating step is one or more substances selected from waxes. In the primary and secondary coating steps, after adding a hydrophobic substance to the granular magnesium sulfate fertilizer in a rolling state, (i) a step of adding a thermosetting resin raw material, and (ii) maintaining the rolling state. 7. The production method according to any one of claims 1 to 6, which includes a step of forming a film by a thermosetting reaction, and the steps (i) and (ii) are repeated two or more times in total.