Coated fertilizer, fertilizer coating material, and manufacturing method of coated fertilizer

Abstract

To provide a coated fertilizer superior in seawater-decomposability.SOLUTION: A coated fertilizer includes a granular fertilizer and a coating layer that coats a surface of the granular fertilizer, where the coating layer contains an ion cross-linked water-absorptive polymer.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a coated fertilizer, a material for coating a fertilizer, and a method for producing the coated fertilizer. [Background technology]

[0002] Various developments have been made so far regarding fertilizer coating technologies. For example, the technology described in Patent Document 1 is known as this type of technology. Patent Document 1 describes coated granular urea having granular urea and a talc coating that coats the surface of the granular urea (Claim 1, Examples, etc. of Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2020-007167 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, as a result of studies by the present inventors, it was found that the coated fertilizer described in Patent Document 1 above has room for improvement in terms of seawater decomposition. [Means for solving the problem]

[0005] In the above Patent Document 1, talc, an inorganic compound, is used as the fertilizer coating material, while commercially available products use polyolefin resins such as polyethylene. These fertilizer coating materials are non-degradable materials and may remain in the soil. Furthermore, the residues remaining in the soil may be discharged as microplastics into rivers or the sea through the water cycle.

[0006] As a result of further investigation, the present inventors found that the seawater decomposition property of the fertilizer can be improved by using an ion-crosslinked material as a coating material for the fertilizer, and thus completed the present invention.

[0007] According to one aspect of the present invention, there are provided the following coated fertilizer, fertilizer coating material, and method for producing the coated fertilizer. 1. Granular fertilizer and A coating layer that coats the surface of the granular fertilizer. A coated fertilizer, wherein the coating layer comprises an ionically crosslinked water-absorbing polymer. 2. The coated fertilizer according to 1., A coated fertilizer, wherein the ionically cross-linked water-absorbing polymer contains at least two or more of the following (A) to (D) as a polymer salt, and the polymer salt contains at least one or more of the following (i) to (vi): (i) (A) and (C), (ii) (A), (C) and (D) (iii) (A), (B), and (C) (iv) (A) and (B) (v)(B) and (D) (vi) (A), (B), (C) and (D) (A) A polyanion having a monovalent or divalent or higher anionic group (B) A polycation having a monovalent or divalent or higher cationic group (C) Polyvalent inorganic cations having divalent or higher cations (D) Anionic monomer having a monovalent or divalent or higher anionic group 3. The coated fertilizer according to 1. or 2. the ionically cross-linked water-absorbent polymer is a polymer salt containing at least one of (A) a polyanion having a monovalent or divalent or higher anionic group and (D) an anionic monomer having a monovalent or divalent or higher anion; The polyanion (A) having a monovalent or divalent or higher anionic group includes one or more polyanions A1 selected from the group consisting of polysaccharides containing at least one of carboxylic acid, sulfonic acid, and phosphoric acid in the molecule, and complex carbohydrates containing the polysaccharides, (D) The anionic monomer having a monovalent or divalent or higher anionic group includes an anionic monomer having one or more carboxyl groups. Coated fertilizer. 4. The coated fertilizer according to 3., The coated fertilizer, wherein the polysaccharide and the complex carbohydrate contain one or more selected from the group consisting of alginic acid, carboxymethylcellulose, carrageenan, homogalacturonan, glycosaminoglycan, hyaluronic acid, and chondroitin sulfate. 5. A coated fertilizer according to 3. or 4., A coated fertilizer, wherein the (A) polyanion having a monovalent or divalent or higher anionic group contains one or more polyanions A2 selected from the group consisting of lignosulfonic acid and polyglutamic acid. 6. A coated fertilizer according to any one of 2. to 5., A coated fertilizer, wherein the (C) polyvalent inorganic cation having a cation valence of divalent or higher contains one or more ions selected from the group consisting of calcium ions, magnesium ions, and aluminum ions. 7. A coated fertilizer according to any one of 1. to 6., A coated fertilizer, wherein the coating layer contains a filler. 8. A fertilizer coating material used to form a coating layer containing an ion-crosslinked water-absorbent polymer on the surface of a granular fertilizer, comprising: A fertilizer coating material comprising at least an ionically crosslinkable polymer capable of forming ionically crosslinks with an ionically crosslinking agent. 9. The fertilizer coating material according to 8., A first container containing the ionically crosslinkable polymer; a second container containing the ionic crosslinker; the ionically crosslinkable polymer contains at least one of (A) a polyanion having a monovalent or divalent or higher anionic group and (B) a polycation having a monovalent or divalent or higher cationic group; The fertilizer coating material, wherein the ionic crosslinking agent contains at least one of (C) a polyvalent inorganic cation having a cation that is divalent or higher and (D) an anionic monomer having a monovalent or divalent or higher anionic group (provided that one of the ionically crosslinkable polymer and the ionic crosslinking agent contains at least an anion and the other contains a cation). 10. A method for producing a coated fertilizer, comprising a coating step of reacting an ionically cross-linkable polymer with an ionically cross-linking agent to form a coating layer containing an ionically cross-linked water-absorbent polymer on the surface of a granular fertilizer. Effect of the Invention

[0008] According to the present invention, there are provided a coated fertilizer having excellent seawater decomposability, a fertilizer coating material used therefor, and a method for producing the coated fertilizer. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] The coated fertilizer of this embodiment will be described.

[0010] The coated fertilizer of the present embodiment includes a granular fertilizer and a coating layer that coats the surface of the granular fertilizer, and the coating layer contains an ionically cross-linked water-absorbent polymer.

[0011] According to the findings of the present inventors, it has been found that it is possible to impart seawater decomposability to an ionically cross-linked material by combining it with an appropriate material. In other words, the use of an ionically cross-linked material makes it possible to enhance seawater decomposability compared to conventional coating materials such as polyolefin resins.

[0012] The term "seawater decomposability" refers to a change in the properties of an ion-crosslinked material to one that makes it more soluble in aqueous solvents as a result of an ion exchange reaction between ions present in seawater and ions in the ion-crosslinked material.

[0013] According to this embodiment, by using an ion-crosslinked material having seawater decomposability as a coating material for a fertilizer, it is expected that the coated fertilizer remaining in the soil will be decomposed in rivers or seawater. In other words, even if at least a part of the coated fertilizer flows out into the ocean, it is expected that the generation of microplastics will be reduced. Therefore, the coated fertilizer of this embodiment can reduce the environmental load. In addition, by using a polymer derived from a natural substance as the ionically cross-linked water-absorbent polymer, the environmental load can be further reduced.

[0014] (granular fertilizer) The form of the granular fertilizer is not particularly limited as long as it is solid in the atmosphere at 25°C. The shape of the granular fertilizer may be, for example, a powder, granule, pellet, briquette, or any other predetermined shape, among which, from the viewpoint of dispersibility, the shape of the granular fertilizer is preferably spherical.

[0015] The granular fertilizer can be produced by using a known granulation method such as a fluidized bed granulation method, a rolling granulation method, a coating granulation method, an adsorption granulation method, an agglomeration granulation method, etc. However, the production method of the granular fertilizer is not limited to these.

[0016] The fertilizer used in the granular fertilizer can be any known fertilizer, and for example, one or more of a nitrogenous fertilizer, a phosphorous fertilizer, and a potassium fertilizer can be used. As nitrogenous fertilizers, for example, ammonium salts and nitrates are used, and specific examples thereof include ammonium sulfate, ammonium chloride, urea, lime nitrogen, sodium nitrate, and ammonium nitrate. Examples of phosphorus fertilizers include superphosphate, triple superphosphate, molten phosphorus fertilizer, and calcined phosphorus fertilizer. Examples of potassium fertilizers include potassium chloride and potassium sulfate. In addition to the above three fertilizers, the fertilizer may contain other fertilizers (calcareous fertilizers, silicic acid fertilizers, manganese fertilizers, boron fertilizers, etc.) and one or more known inorganic compounds containing inorganic nutrients.

[0017] The granular fertilizer may contain other ingredients as long as the effects of the present invention are not impaired. Other components may include, for example, carriers such as clay, kaolin, talc, bentonite, calcium carbonate, etc.; binders such as polyvinyl alcohol, sodium carboxymethylcellulose, starches, etc.; and, if necessary, surfactants such as polyoxyethylene nonylphenyl ether, blackstrap molasses, animal oil, vegetable oil, hydrogenated oil, fatty acid, fatty acid metal salt, paraffin, wax, glycerin, etc. These may be used alone or in combination of two or more.

[0018] (covering layer) The coating layer may cover at least a part of the surface of the granular fertilizer, or may cover the entire surface.

[0019] The coating layer contains an ionically cross-linked water-absorbing polymer. The coating layer in the coated fertilizer is preferably in a dry state (not in a gel state having fluidity) from the viewpoint of storage in a package, etc. However, the use of the coated fertilizer is not limited to this.

[0020] The dryness of the coating layer can be defined by the moisture absorption rate (wt%) measured according to the following procedure. The rate of change in the above moisture content is as follows: The sample is dried in a vacuum oven at 35° C. for 6 hours, and the weight (Wa) of the sample when dry is measured. Subsequently, the dried sample is left to stand in a thermo-hygrostat set at 30° C. and 80% RH for 72 hours, and the weight (Wb) of the sample after moisture absorption is measured. Using the measured Wa and Wb, the weight change of the sample is calculated based on [(Wb-Wa) / Wbx100], and this is regarded as the water absorption rate (wt%). Although a part of the coating layer can be used as the sample, the granular fertilizer itself may also be used as the sample. In this embodiment, the lower limit of the moisture absorption rate of the coating layer is, for example, 5% by weight or more, preferably 7.5% by weight or more, and more preferably 10% by weight or more. This means that the coating layer is in a moderately dry state. In addition, it is possible to maintain an appropriate shape and strength. On the other hand, the upper limit of the moisture absorption rate of the coating layer is, for example, 50% by weight or less, preferably 45% by weight or less, more preferably 40% by weight or less. This makes it possible to control the amount of liquid such as water that permeates. In addition, the coating layer may swell slightly when absorbing water and become in a gel state.

[0021] The ionically cross-linked water-absorbent polymer is more capable of absorbing water and swelling than conventional coating materials such as polyolefin resins. Although the detailed mechanism is unclear, it is believed that because the salt concentration of the fertilizer inside is high, water penetrates into the interior through the coating layer due to osmotic pressure, and when the coating layer cracks due to an increase in internal pressure caused by volume expansion, the fertilizer is released from the cracks in the coating layer, resulting in a sustained release of fertilizer. Also, even if the ion-crosslinked water-absorbent polymer that has absorbed water gels, it is believed that the fertilizer inside dissolves in the water in the gel and is released to the outside. The ionically cross-linked water-absorbent polymer is only required to be capable of absorbing water, and may or may not absorb oil other than water.

[0022] The ionically cross-linked water-absorbent polymer can be made to have seawater decomposability by using polymer salts constituted by an appropriate combination. In this embodiment, it is preferable to use an ionically cross-linked water-absorbent polymer that contains at least two of the following (A) to (D) as a polymer salt containing at least one of the following (i) to (vi). (i) (A) and (C), (ii) (A), (C) and (D) (iii) (A), (B), and (C) (iv) (A) and (B) (v)(B) and (D) (vi) (A), (B), (C) and (D) (A) A polyanion having a monovalent or divalent or higher anionic group. (B) a polycation having a monovalent or divalent or higher cationic group; (C) Polyvalent inorganic cations having divalent or higher cations (D) Anionic monomer having a monovalent or divalent or higher anionic group

[0023] In this specification, the valence in (A), (B), and (D) refers to the valence per ionic functional group (ionic dissociation group) contained in a monomer or polymer. As an example of an ionic functional group in a side chain of a polymer (polymer), a carboxylic acid is monovalent, and a dicarboxylic acid (oxalic acid, fumaric acid, etc.) is divalent. On the other hand, in the case of the valence in (C), a sodium ion is monovalent, and a calcium ion is divalent. To give a specific example, polyacrylic acid polymers are classified as "polyanions having monovalent anionic groups," and alkylphosphonic acid polymers are classified as "polyanions having divalent anionic groups." In addition, in polyacrylic acid or polymers containing acrylic acid as a component, if the acrylic acid forms a calcium salt, it is classified as "a polyanion in which a monovalent anionic group forms a salt with a divalent cation." In addition, in polymers containing phosphonic acid as a component, if the phosphonic acid forms a sodium salt, it is classified as "a polyanion in which a divalent anionic group forms a salt with a monovalent cation."

[0024] The presumed mechanism of seawater decomposition will be explained using an example in which the ion-crosslinked water-absorbent polymer contains the polymer salts (A) and (C) as the combination (i) above. However, the ion-crosslinked water-absorbent polymer is not limited to this. An ionic cross-linked polymer of an alginate polymer (a polyanion having a monovalent anionic group) and calcium ions (a polyvalent inorganic cation) forms an ionic cross-linked structure in water, but in salt water (seawater), the calcium ions are exchanged for sodium ions, dissociating the cross-links, making the polymer soluble in salt water.

[0025] (B) Polycations having a monovalent or divalent or higher cationic group include, for example, polylysine and chitosan.

[0026] (C) The polyvalent inorganic cation having a cation valency of divalent or higher may include, for example, one or more ions selected from the group consisting of calcium ions, magnesium ions, and aluminum ions.

[0027] In another embodiment, it is preferable that the ion-crosslinked water-absorbent polymer is a polymer salt containing at least one of (A) a polyanion having a monovalent or divalent or more anionic group and (D) an anionic monomer having a monovalent or divalent or more anion. More specifically, it is more preferable to use a polymer salt containing at least one of the above (i) and (ii).

[0028] (A) The polyanion having a monovalent or divalent or higher anionic group preferably includes one or more polyanions A1 selected from the group consisting of polysaccharides containing at least one of carboxylic acid, sulfonic acid, and phosphoric acid in the molecule, and complex carbohydrates containing polysaccharides. From the viewpoint of preventing eutrophication in the ocean and the like, it is preferable that the polyanion A1 contains at least one of carboxylic acid and sulfonic acid.

[0029] As used herein, a monosaccharide is a sugar composed of one type of sugar. Examples of sugars include glucose, mannose, galactose, glucosamine, galactosamine, xylose, sialic acid, glucuronic acid, iduronic acid, fucose, maltose, trehalose, and lactose.

[0030] In this specification, a polysaccharide is a saccharide formed by glycosidic bonds between two or more monosaccharides. A polysaccharide may be a homopolysaccharide having a single type of monosaccharide, or a heteropolysaccharide having two or more types of monosaccharides (sometimes called a complex polysaccharide). Furthermore, the polysaccharide may be any polysaccharide as long as it has a sugar chain (main chain) consisting of a repeating structure of structural units derived from monosaccharides, and the side chain in the sugar chain may or may not have a functional group. Examples of the functional group formed on the side chain include polar functional groups such as a carboxyl group, a sulfonic acid group, an amide group, an acetyl group, an acetylamide group, and an amino group.

[0031] As used herein, a glycoconjugate is a complex in which a polysaccharide is covalently bound to other biological compounds other than sugars, such as proteins, lipids, peptides, etc. Examples of glycoconjugates include biopolymers such as glycoproteins, proteoglycans, and glycolipids.

[0032] The polysaccharide in polyanion A1 may include, for example, one or more selected from the group consisting of alginic acid, carboxymethylcellulose, carrageenan, homogalacturonan, and glycosaminoglycan. Furthermore, the complex carbohydrate in the polyanion A1 may contain, for example, one or more members selected from the group consisting of hyaluronic acid and chondroitin sulfate.

[0033] (D) The anionic monomer having a monovalent, divalent or higher anion may include an anionic monomer having one or more carboxyl groups. Examples of anionic monomers having one or more carboxyl groups include oxalic acid, fumaric acid, ethylenediaminetetraacetic acid (EDTA), citric acid, adipic acid, etc. These may be used alone or in combination of two or more.

[0034] In another embodiment, the polyanion having a monovalent or divalent or higher anionic group (A) may contain one or more polyanions A2 selected from the group consisting of lignin sulfonic acid and polyglutamic acid. That is, when the ionically cross-linked water-absorbent polymer contains (A), (A) may contain polyanion A1 alone, polyanion A2 alone, or both polyanion A1 and polyanion A2. When the ionically cross-linked water-absorbent polymer contains polyanion A1, the film-forming property of the coating layer can be improved, and when the ionically cross-linked water-absorbent polymer contains polyanion A2, the flexibility of the coating layer can be improved.

[0035] The weight average molecular weight of each of the ionically cross-linked water-absorbent polymer, the polyanion (A), and the polycation (B) may be, for example, not less than 1,000 and not more than 10,000,000. The weight average molecular weight is a value calculated in terms of polystyrene. The molecular weight of the ionically crosslinked water-absorbent polymer, the raw material monomers of the (A) polyanion and (B) polycation, and the (D) anionic monomer may be, for example, 1 to less than 1,000.

[0036] The coating layer may contain a functional additive, if necessary, in addition to the ionically cross-linked water-absorbing polymer. The functional additive is not particularly limited as long as it is used in the coating material of the fertilizer, and examples thereof include fillers, thickeners, adhesion promoters, surface modifiers, pH adjusters, crosslinking retarders (chelating agents), reinforcing materials, gas barrier agents, magnetic materials, decomposition inhibitors, etc. These may be used alone or in combination of two or more kinds.

[0037] As the filler, for example, at least one of an inorganic filler and an organic filler can be used. The inorganic filler can be selected from the viewpoints of strength, cost, or disintegrability, and examples thereof include silica, talc, magnesium oxide, calcium oxide, alumina, titanium oxide, calcium carbonate, clay, potassium titanate, mica, glass flakes, whiskers, wood powder, ferrite, iron oxide, and zeolite. The organic filler may be a biodegradable organic filler, and examples thereof include alginic acid, starch, cellulose, polylactic acid, PHA, PHBH, PBAT, PBS, and PGA. Furthermore, natural products such as coconut shells may be used as fillers.

[0038] The method for producing the coated fertilizer of the present embodiment will be described below.

[0039] An example of a method for producing a coated fertilizer of the present embodiment includes a coating step of reacting an ionically cross-linkable polymer with an ionically cross-linking agent to form a coating layer containing an ionically cross-linked water-absorbent polymer on the surface of the granular fertilizer.

[0040] As a method for coating the surface of the granular fertilizer, a known method for coating the surface of a solid particle can be used, for example, a chemical method such as a non-aqueous wet method, an aqueous wet method, a gas phase reaction method, or a mechachemical method, or a physical method such as a mechanical surface treatment method, a laser ablation method, an aerial suspension coating method, or a spray drying method.

[0041] In the method for producing a coated fertilizer, it is possible to use a fertilizer coating material used for forming a coating layer containing an ionically cross-linked water-absorbent polymer on the surface of the granular fertilizer. The fertilizer coating material may be any material that contains at least an ionically crosslinkable polymer capable of forming ion crosslinks with an ionically crosslinking agent. The form of the fertilizer coating material may be a two-component liquid containing an ion crosslinking agent and an ion crosslinkable polymer separately, or a one-component liquid containing both of them.

[0042] The ionically crosslinkable polymer may, for example, be at least one of the above-mentioned (A) polyanion and (B) polycation. In addition, the ionic crosslinking agent is selected from those corresponding to the ionic crosslinkable polymer. When the ionic crosslinkable polymer contains (A) a polyanion, the ionic crosslinking agent may contain, for example, one or more selected from the group consisting of the above-mentioned (B) polycation, (C) polyvalent inorganic cation, and (D) anionic monomer. When the ionic crosslinkable polymer contains (B) a polycation, the ionic crosslinking agent may contain, for example, one or more selected from the group consisting of the above-mentioned (A) polyanion, (C) polyvalent inorganic cation, and (D) anionic monomer. however,

[0043] In another embodiment, the fertilizer coating material may include a first container containing an ionically crosslinkable polymer and a second container containing an ionically crosslinking agent, in which the ionically crosslinkable polymer contains at least one of (A) a polyanion having a monovalent or divalent or higher anionic group and (B) a polycation having a monovalent or divalent or higher cationic group, and the ionically crosslinking agent contains at least one of (C) a polyvalent inorganic cation having a divalent or higher cation and (D) an anionic monomer having a monovalent or divalent or higher anionic group (with the proviso that at least an anion is contained in one of the ionically crosslinkable polymer and the ionically crosslinking agent, and a cation is contained in the other). The combinations of (A) to (D) that can be adopted are as described above. As examples of the above (A) to (D), those mentioned above can be used.

[0044] Although the embodiments of the present invention have been described above, these are merely examples of the present invention, and various configurations other than those described above can be adopted. Furthermore, the present invention is not limited to the above-described embodiments, and modifications and improvements within the scope of the present invention are included in the present invention. EXAMPLES

[0045] The present invention will be described in detail below with reference to examples, but the present invention is not limited to the descriptions of these examples.

[0046] (Examples 1 and 2) A varnish shown in Table 1 below was applied onto a PET film placed on a SUS plate, and the varnish was dried in an oven at 35° C. for 24 hours to form a film. The film was immersed in a 2% by mass aqueous solution of calcium chloride (ionic crosslinking agent) to cause an ionic crosslinking reaction in the film. After ionically crosslinking, the film was dried in an oven at 35° C. for 24 hours to obtain a test film having a thickness of about 20 μm.

[0047] (Comparative Examples 1 and 2) A test film having a thickness of approximately 50 μm was obtained in the same manner as in Example 1, except that a varnish containing a thermoplastic polymer and tetrachloroethylene shown in Table 1 was used instead of the ionically crosslinkable polymer and water, and the film was dried without undergoing an ionically crosslinking reaction.

[0048] The varnish was obtained by mixing the components shown in Table 1 in the mixing ratios shown in Table 1 with a solvent. The viscosity of the varnish was measured using a viscosity meter (manufactured by Anton-Paar) at room temperature and 10 rpm. The sodium alginate used was manufactured by Kimica Co., Ltd., and the sodium and magnesium lignosulfonates used were manufactured by Nippon Paper Industries Co., Ltd. PE was polyethylene manufactured by Sumitomo Chemical Co., Ltd., and EVA was ethylene vinyl acetate copolymer manufactured by Mitsui Dow Polychemicals Co., Ltd.

[0049] (Moisture absorption rate) The test film was dried in a vacuum oven at 35° C. for 6 hours, and the dry weight (Wa) was measured. Subsequently, the dried test film is left to stand in a thermo-hygrostat set at 30° C. and 80% RH for 72 hours, and the weight (Wb) after moisture absorption is measured. Using the measured Wa and Wb, the weight change of the test film was calculated based on [(Wb-Wa) / Wbx100], and this was taken as the water absorption rate (wt%). The moisture absorption rate was 22.7% by weight in Example 1, 24.2% by weight in Example 2, 0.4% by weight in Comparative Example 1, and 0.2% by weight in Comparative Example 2. From these results, it was found that in Examples 1 and 2, an ionically cross-linked water-absorbent polymer was formed by curing the ionically cross-linked polymer with an ionically cross-linking agent.

[0050] [Table 1]

[0051] The obtained test films were subjected to the following evaluations.

[0052] (Evaluation of seawater degradability) A small piece cut from the obtained test film was immersed in a 3.4% aqueous sodium chloride solution at 23° C., and the change over time was observed. In Examples 1 and 2, the pieces were broken into pieces in about 7 to 12 days, and decomposition was confirmed to have progressed, so the seawater decomposition was evaluated as good. On the other hand, in Comparative Examples 1 and 2, the shape of the pieces did not change from the initial state even after about 14 days had passed, so the seawater decomposition was evaluated as poor.

[0053] (Evaluation of Water Swellability) A small piece cut out from the obtained test film was immersed in ion-exchanged water at a liquid temperature of 23° C. for 24 hours. In this case, the weight of the small piece before immersion was Wa', and the weight of the small piece after immersion for 24 hours was Wb', and the swelling ratio (%) was calculated based on [(Wb'-Wa') / Wa']×100. The swelling ratios were 40% for Example 1, 70% for Example 2, 0% for Comparative Example 1, and 0% for Comparative Example 2. From these results, Examples 1 to 3 were evaluated as having good water swelling properties, and Comparative Examples 1 and 2 were determined to have poor water swelling properties.

[0054] (Mechanical strength measurement) The storage modulus (E') of the obtained test film was measured at 30° C. by dynamic mechanical analysis (DMA). As a result, Example 1 showed a lower storage modulus and improved flexibility compared to Example 2.

[0055] The results showed that the ionically cross-linked polymers of Examples 1 and 2 had higher seawater decomposition properties than the thermoplastic polymers of Comparative Examples 1 and 2, which are commonly used as fertilizer coating materials. The ionically cross-linked polymers of Examples 1 and 2 also showed excellent water swelling properties. The ionically cross-linked water-absorbent polymer obtained by using the ionically cross-linked polymer of such an embodiment can be suitably used as a material for covering fertilizer.

Claims

1. Granular fertilizer and a coating layer that coats the surface of the granular fertilizer; A coated fertilizer, wherein the coating layer contains an ionically cross-linked water-absorbing polymer.

2. The coated fertilizer according to claim 1, The ion-crosslinked water-absorbing polymer contains a polymer salt containing at least two or more of the following (A) to (D): The coated fertilizer, wherein the polymer salt contains at least one of the following (i) to (vi): (i) (A) and (C), (ii) (A), (C) and (D) (iii) (A), (B), and (C) (iv) (A) and (B) (v) (B) and (D) (vi) (A), (B), (C) and (D) (A) Polyanion having monovalent or divalent or higher anionic groups (B) Polycations having monovalent or divalent or higher cationic groups (C) Polyvalent inorganic cations having divalent or higher cations (D) Anionic monomer having a monovalent or divalent or higher anionic group

3. The coated fertilizer according to claim 2, the ionically cross-linked water-absorbing polymer is a polymer salt containing at least one of (A) and (D), (A) comprises one or more selected from the group consisting of polysaccharides containing at least one of carboxylic acid, sulfonic acid, and phosphoric acid in the molecule, and complex carbohydrates containing the polysaccharides; (D) comprises an anionic monomer having one or more carboxyl groups; Coated fertilizer.

4. The coated fertilizer according to claim 3, The coated fertilizer, wherein the polysaccharide and the complex carbohydrate comprise one or more selected from the group consisting of alginic acid, carboxymethylcellulose, carrageenan, homogalacturonan, glycosaminoglycan, hyaluronic acid, and chondroitin sulfate.

5. The coated fertilizer according to claim 3, A coated fertilizer, wherein (A) contains one or more selected from the group consisting of lignosulfonic acid and polyglutamic acid.

6. The coated fertilizer according to claim 2, (C) is a coated fertilizer containing one or more ions selected from the group consisting of calcium ions, magnesium ions, and aluminum ions.

7. The coated fertilizer according to claim 1 or 2, A coated fertilizer, wherein the coating layer contains a filler.

8. A fertilizer coating material comprising an ionic cross-linking agent and an ionically cross-linkable polymer, ionic crosslinking occurs between the ionic crosslinking agent and the ionically crosslinkable polymer in water, A fertilizer coating material, wherein the ionic crosslinks dissociate in salt water.

9. The fertilizer coating material according to claim 8, A fertilizer coating material used to form a coating layer containing an ionically cross-linked water-absorbing polymer on the surface of granular fertilizer.

10. A fertilizer coating material according to claim 8 or 9, The ionically crosslinkable polymer is (A) a polyanion having a monovalent or divalent or higher anionic group and (B) a polycation having a monovalent or divalent or higher cationic group, The ionic crosslinking agent is When the ionically crosslinkable polymer contains the (A) polyanion, it contains one or more selected from the group consisting of the (B) polycation, (C) polyvalent inorganic cation having a cation with a valence of two or more, and (D) anionic monomer having a monovalent or divalent or more anionic group, or When the ionically crosslinkable polymer contains the (B) polycation, the fertilizer coating material contains one or more selected from the group consisting of the (A) polyanion, the (C) polyvalent inorganic cation, and the (D) anionic monomer.

11. The fertilizer coating material according to claim 8 or 9, The fertilizer coating material is in the form of a first container containing the ionically cross-linkable polymer; a second container containing the ionic cross-linking agent; the ionically crosslinkable polymer contains at least one of (A) a polyanion having a monovalent or divalent or higher anionic group and (B) a polycation having a monovalent or divalent or higher cationic group, A fertilizer coating material, wherein the ionic crosslinking agent contains at least one of (C) a polyvalent inorganic cation having a cation with a valence of two or more and (D) an anionic monomer having a monovalent or divalent or more anionic group (provided that one of the ionically crosslinkable polymer and the ionic crosslinking agent contains at least an anion and the other contains a cation).

12. A method for producing a coated fertilizer, comprising a coating step of forming a coating layer that covers at least a portion of the surface of a granular fertilizer by subjecting an ionically crosslinkable polymer and an ionically crosslinking agent to an ionically crosslinking reaction.

13. A method for producing the coated fertilizer according to claim 12, comprising: In the coating step, the coating layer is formed containing an ionically cross-linked water-absorbing polymer formed by an ionically cross-linking reaction between the ionically cross-linkable polymer and the ion cross-linking agent.