Environment-friendly biological coating agent as well as preparation method and application thereof

Abstract

The invention relates to an environment-friendly biological coating agent as well as a preparation method and application thereof. The invention relates to an environment-friendly biological coating agent which comprises the following main components: gellan gum and chitin or chitosan, and a cross-linked structure is formed through ion exchange of the gellan gum and the chitin or chitosan. The coating agent has biodegradability, has small influence on the environment, and can replace plastics and solve the problem of wastes. When the slow-release fertilizer is used, nutrient release can be regulated and controlled, the fertilizer efficiency is improved, and the coating layer has high mechanical strength and water resistance. In addition, the coating agent is harmless to human bodies and can be widely applied to the fields of food packaging, medical coatings, biodegradable materials and the like.

Description

Technical Field

[0001] This invention relates to an environmentally friendly bio-coating agent, specifically, to an environmentally friendly and biodegradable bio-coating agent, its preparation method and its uses, and more specifically, to the use of an environmentally friendly bio-coating agent as a coating agent for slow-release fertilizers. Background Technology

[0002] Slow-release fertilizers, also known as controlled-release fertilizers, are fertilizers that contain plant nutrients in a form that delays plant absorption and utilization after application. They enhance their function by coating the surface of fast-acting fertilizers (such as ammonium nitrate, urea, ammonium phosphate, and calcium chloride), allowing plants to utilize these fertilizers for a longer period. Because these slow-release fertilizers should supply the required nutrient content according to the crop's growth stage, the coating layer should be resistant to damage, and the nutrient supply should be continuously provided by regulating water movement within the coating layer.

[0003] Currently, due to restrictions imposed by developed countries on chemical resin coatings, research is being conducted on novel environmentally friendly coating methods with high slow-release or controlled-release properties. Furthermore, research on core technologies such as the composition of coating agents, the water permeability, stability, and environmental friendliness of fertilizers is becoming a promising area of ​​development.

[0004] On the other hand, according to data from Statistics Korea and the Korea Credit Information Service, the market size of compound fertilizers in South Korea decreased from 1.058 trillion won in 2015 to 920.2 billion won in 2017. This was due to poor harvests caused by factors such as cold damage, extreme heat, and farmland subsidence caused by the rainy season, and a decrease in the shipment volume of compound fertilizers since 2015. However, due to the increasing preference for environmentally friendly agricultural products and food, as well as increased government subsidies, the market size of environmentally friendly fertilizers in South Korea is growing at an average annual rate of 1.1%, and is expected to reach 1.0407 trillion won in 2023.

[0005] Currently, even though the overall agricultural environment is aging, with a decrease in the number of farmers and a shrinking arable land area, the increasing number of farmers cultivating fruit trees and high-quality crops is expected to drive up the demand for specialized fertilizers, such as slow-release fertilizers that offer labor-saving benefits. Furthermore, the aging population, changing food and consumer values, and the integration of agriculture with information and communication technologies (ICT) are becoming macro trends in the compound fertilizer market. Simultaneously, compound fertilizer manufacturers are developing products that can improve crop yield and quality with less labor, energy, and nutrients.

[0006] The prior art related to this invention is as follows.

[0007] Korean Patent No. 10-2205869 (granted on January 15, 2021) relates to a granular slow-release fertilizer and a method for preparing the same, and more specifically, to a granular slow-release fertilizer and a method for preparing the same, which improves slow-release properties by coating the outer surface of the fertilizer. The technology relates to a slow-release fertilizer comprising: 40% by weight feldspar, 20% by weight kaolin, 25% by weight bentonite, 1% by weight microorganisms, 10% by weight rice bran, 2% by weight plant extracts, 1% by weight molasses, and 1% by weight seaweed extract. The slow-release fertilizer comprises: a core composed of natural minerals including feldspar, kaolin, and bentonite; and a coating layer composed of microorganisms including chitin-degrading microorganisms, gelatin-degrading microorganisms, and collagen-degrading microorganisms, plant extracts consisting of organic matter including rice bran, bamboo shoot extract, cedar extract, and ginkgo extract, and seaweed extract obtained from molasses and kelp. Through the composition of the slow-release fertilizer, it is safe and has regulated slow-release properties, providing nutrients suitable for the crop's growth stage. This technology is partially similar to the present invention in that it uses chitin-degrading microorganisms to form the coating layer, but differs significantly in that it does not contain natural polysaccharides such as gellan gum.

[0008] Furthermore, Japanese Patent Application No. 2022-161098 (filed on October 5, 2022) relates to a coated granular fertilizer and a method for preparing the same. This coated granular fertilizer is coated with a membrane composed of a coating material, and a pre-coating layer containing a biodegradable resin is provided between the fertilizer and the membrane. This technology provides a method for preparing a coated granular fertilizer, in which a pre-coating layer is provided between the fertilizer and the membrane. The biodegradable resin is composed of polyvinyl alcohol resin, starch, cellulose, lignin, chitin, chitosan, PBS, PBSA, PBAT, PCL, starch, cellulose acetate, PHB, PHBH, PHBV, PLA, PDO, and copolymers thereof. The biodegradable resin inhibits flocculation and dissolution, and decomposes after exerting its effect, thereby reducing the environmental impact. While this technology is partially similar to the present invention in that it uses chitin as a biodegradable substance, it uses plant-based substances (such as corn starch) as polysaccharides, and is therefore considered different from the present invention.

[0009] Additionally, Japanese Patent Application No. 2022-061365 (filed March 31, 2022) relates to a coating material for fertilizers, a coated granular fertilizer, and a method for preparing the same. This invention provides a slow-release coated granular fertilizer, in which the granular fertilizer is coated with a fertilizer coating material, and after dissolution, it does not cause environmental impact due to coating residue. The technology constitutes a pre-coating layer, and the biodegradable resin used in this pre-coating layer includes polyglycolic acid (PGA). The difference between this technology and the present invention is that, although a slow-release coated granular fertilizer is provided, the polysaccharides used to strengthen the polymer binding do not contain carrageenan.

[0010] Existing technical documents

[0011] Patent documents

[0012] Patent Document 0001: Korean Patent No. 10-2205869 (granted on January 15, 2021)

[0013] Patent Document 0002: Japanese Patent Application No. 2022-161098 (filed on October 5, 2022)

[0014] Patent Document 0003: Japanese Patent Application No. 2022-061365 (filed on March 31, 2022) Summary of the Invention

[0015] The technical problem to be solved by the present invention

[0016] The purpose of this invention is to provide an environmentally friendly and biodegradable biocoating agent using naturally derived materials. In particular, this invention provides an environmentally friendly biocoating agent that reduces environmental pollution and improves durability and water resistance by developing a coating that can replace non-environmentally friendly materials (such as plastics).

[0017] Another objective of this invention is to provide a slow-release coated fertilizer. By applying an environmentally friendly bio-coating agent to the slow-release coated fertilizer, the effective components of the fertilizer can be released at a constant rate, thereby maximizing the efficiency of the fertilizer and reducing environmental pollution caused by overuse of fertilizers.

[0018] Technical solution

[0019] To address the aforementioned problems, one aspect of the present invention provides an environmentally friendly bio-coating agent comprising gellan gum as a natural substance and chitin or chitosan.

[0020] A preferred embodiment of one aspect of the invention is characterized by comprising gellan gum and chitin or chitosan, wherein the gellan gum forms a three-dimensional gel structure and is cross-linked by an ion exchange reaction between the carboxyl groups (-COOH) of the gellan gum and the amino groups (-NH2) of the chitosan.

[0021] A preferred embodiment of one aspect of the invention is characterized in that, by weight, gellan gum and chitin or chitosan are contained in a ratio of 1:1 to 1:3 (gellan gum: chitin / chitosan).

[0022] A preferred embodiment of one aspect of the invention is characterized in that it further comprises Ca 2+ Supply source and / or carrageenan, the Ca 2+ The supply source can form additional crosslinks by combining with gellan gum, and the carrageenan can undergo an ion exchange reaction with chitosan, wherein the Ca... 2+ The supply sources are selected from calcium nitrate (Ca(NO3)2), calcium chloride (CaCl2), calcium sulfide (CaS), calcium sulfate (CaSO4), calcium carbonate (CaCO3), calcium phosphate (Ca3(PO4)2), calcium hypophosphite (Ca2P2O4), calcium hypophosphite (Ca(H2PO2)2), calcium hydroxide (hydrated lime) (Ca(OH)2), calcium oxide (quicklime) (CaO) and calcium acetate (Ca(C2H3O2)2).

[0023] A preferred embodiment of one aspect of the invention is characterized in that it further comprises a plasticizer or an additive for improving the flexibility of the film.

[0024] In addition, another aspect of the present invention provides a method for preparing the environmentally friendly bio-coating agent of the present invention.

[0025] Specifically, another aspect of the present invention provides a method for preparing the environmentally friendly bio-coating agent of the present invention, comprising: a first step of dissolving gellan gum in water while heating and mixing to obtain a gellan gum aqueous solution with a concentration of 0.5% to 2% by weight; a second step of additionally adding chitosan and a weak acid to water and mixing in a weakly acidic environment to obtain a chitosan aqueous solution with a concentration of 0.5% to 2% by weight; and a third step of mixing and stirring the gellan gum aqueous solution of the first step and the chitosan aqueous solution of the second step, such that the ratio of gellan gum to chitosan reaches 1:1 to 1:3 by weight to obtain a homogeneous aqueous solution mixture.

[0026] A preferred embodiment of another aspect of the invention is characterized in that, in the first step, 0.1% to 1% by weight of Ca is further added to the gellan gum aqueous solution. 2+In the third step, carrageenan is added to the aqueous mixture at a concentration of 0.1% to 1% by weight.

[0027] A preferred embodiment of another aspect of the invention is characterized in that, in the third step, a plasticizer or an additive for improving the flexibility of the film is further added to the aqueous mixture.

[0028] In another aspect, the present invention provides a slow-release fertilizer having a coating layer, which is formed by uniformly coating the surface of the fertilizer particles to be coated with the environmentally friendly biological coating agent of the present invention and then drying and gelling them.

[0029] A preferred embodiment of another aspect of the invention is characterized in that the fertilizer is selected from fertilizers containing nitrogen, phosphate and potassium, compost, manure and feed.

[0030] In another aspect, the present invention provides a food packaging material, a medical film, or a biodegradable packaging material, wherein the food packaging material, medical film, or biodegradable packaging material has a coating layer, which is formed by uniformly coating the surface of the packaging material or substrate to be coated with the environmentally friendly bio-coating agent of the present invention and then drying and gelling it.

[0031] Beneficial effects

[0032] This invention utilizes gellan gum and chitin / chitosan, which are natural materials, and are therefore biodegradable with very little environmental impact. They can also be used as plastic alternatives, thus solving the waste problem.

[0033] In addition, the coating agent of the present invention, when used in slow-release coated fertilizers, can regulate the slow release of fertilizer components, thereby providing nutrients suitable for the needs of crops at the appropriate time and ensuring the sustained effect of the fertilizer.

[0034] In addition, the coating layer formed by the coating agent of the present invention has excellent mechanical strength and can be firmly maintained even in the external environment due to its high water resistance.

[0035] In addition, the coating agent of the present invention is harmless to the human body, and therefore can be used in a variety of application fields such as food packaging materials, medical coatings and biodegradable packaging materials. Attached Figure Description

[0036] Figure 1 This is a flowchart illustrating the preparation method and coating method of the present invention step by step. Detailed Implementation

[0037] Unless otherwise defined, all technical and scientific terms used in this specification have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Generally, the nomenclature used in this specification is well-known and commonly used in the art.

[0038] Throughout the specification of this application, when a part “includes” a constituent element, unless otherwise stated, this means that other constituent elements may also be included, and does not mean that other constituent elements are excluded.

[0039] The present invention will now be described in detail.

[0040] One aspect of the present invention provides an environmentally friendly bio-coating agent.

[0041] Specifically, the present invention provides an environmentally friendly bio-coating agent, characterized in that it comprises: gellan gum, and chitin or chitosan; the gellan gum forms a three-dimensional gel structure, and cross-linking is formed through an ion exchange reaction between the carboxyl groups (-COOH) of the gellan gum and the amine groups (-NH2) of the chitosan.

[0042] Gellan gum is used as the first component of the environmentally friendly bio-coating agent of this invention.

[0043] Gellan gum is a natural polysaccharide produced through microbial fermentation. Specifically, it is obtained by purifying, drying, and pulverizing a high-molecular-weight polysaccharide gum substance obtained by pure culture and fermentation of carbohydrates using Pseudomonas elodea, using isopropanol. It is a heteropolysaccharide composed of rhamnose, glucuronic acid, and glucose in a 1:1:2 ratio. In addition, it may contain esters linked to O-glycosides, namely acyl groups (glycerol and acetyl groups).

[0044] When this gellan gum dissolves in water, in its aqueous solution state, it reacts with specific ions, especially with Ca. 2+ In this process, gellan gum molecules combine and form a gel, during which they bond together to form a stable three-dimensional gel structure, and bind with specific ions, especially Ca2+. 2+ Together they form a strong cross-linked bond, making the gel structure more rigid and stable. Therefore, it plays a role in improving the strength and stability of the coating layer. It also provides high viscosity while expanding by absorbing water molecules. Thus, even after the water evaporates, the coating layer can form a stable layer to maintain the physical properties of the coating layer and has the durability to resist the physical influence of the external environment.

[0045] Chitin or chitosan is used as the second component of the environmentally friendly bio-coating agent of the present invention.

[0046] Chitin or chitosan are natural polymers extracted from the shells of crustaceans. Deacetylation of chitin converts it into chitosan, resulting in higher water solubility and biodegradability. Chitin or chitosan possesses excellent mechanical strength and durability. In particular, chitosan can undergo ion exchange reactions with other substances (especially carrageenan) through its amino groups (-NH2) to form strong bonds, thereby improving the strength and durability of the coating layer. Furthermore, chitin or chitosan is readily soluble in acidic environments and provides excellent water resistance through chemical bonds on the coating surface. Additionally, the coating layer is not easily damaged when exposed to external moisture or water and maintains its waterproof function.

[0047] Both gellan gum and chitin / chitosan are natural substances with excellent biodegradability. Gellan gum is decomposed by natural microorganisms, and chitin / chitosan is broken down into monosaccharides by microbial enzymes, ultimately converting into CO2 and water. Due to these properties, the environmentally friendly biocoating agent of this invention can be easily decomposed in nature and has minimal impact on the environment.

[0048] Furthermore, the gellan gum and chitin / chitosan form cross-links and hydrogen bonds through their mixing, thereby improving structural stability. Specifically, the carboxyl groups (-COOH) of gellan gum and the amino groups (-NH2) of chitosan form a strong cross-link through an ion exchange reaction. This bond provides the coating layer with structural strength to withstand external impacts or abrasion. Therefore, the coating layer is not easily broken and has strong durability against external physical environments. In addition to this cross-linking, hydrogen bonds are also formed between gellan gum and chitosan, thereby improving the uniformity and durability of the coating layer. These hydrogen bonds can also facilitate the interaction between the coating layer surface and water, allowing the coating layer to adhere well to the surface and remain firmly in place.

[0049] The coating layer formed by combining gellan gum and chitosan not only has mechanical strength but also excellent water resistance.

[0050] In the environmentally friendly bio-coating agent of the present invention, gellan gum and chitin or chitosan are contained in a ratio of 1:1 to 1:3 (gellan gum: chitin / chitosan) on a weight basis. When the ratio is exceeded, the following problems may occur: due to insufficient cross-linking and hydrogen bonding, the structural stability, mechanical strength and water resistance are reduced.

[0051] In the conformation-preserving biological coating agent of the present invention, Ca is used as an additional ingredient. 2+ Supply source and / or carrageenan.

[0052] Ca 2+ The supply source is Ca, which is added during the gelation process of gellan gum to form additional cross-linking bonds with gellan gum. 2+The source of ions. Ca can be used in this invention. 2+ The supply source is selected from calcium nitrate (Ca(NO3)2), calcium chloride (CaCl2), calcium sulfide (CaS), calcium sulfate (CaSO4), calcium carbonate (CaCO3), calcium phosphate (Ca3(PO4)2), calcium hypophosphite (Ca2P2O4), calcium hypophosphite (Ca(H2PO2)2), calcium hydroxide (hydrated lime) (Ca(OH)2), calcium oxide (quicklime) (CaO), and calcium acetate (Ca(C2H3O2)2). Preferably, it is selected from calcium phosphate (Ca3(PO4)2), calcium hypophosphite (Ca2P2O4), calcium hypophosphite (Ca(H2PO2)2), calcium hydroxide (hydrated lime) (Ca(OH)2), calcium oxide (quicklime) (CaO), and calcium acetate (Ca(C2H3O2)2). Based on 100 parts by weight of gellan gum, its content is preferably 20 to 50 parts by weight. When the range is below the specified range, the following problems may occur: the additional cross-linking bonds formed are weak, resulting in reduced durability; when the range is exceeded, the following problems may occur: cross-linking bonds no longer form, resulting in the effects of the added ingredients not being apparent.

[0053] Additionally, carrageenan, as an optional additive, is added to improve the strength and durability of the coating layer, and exerts its effect of enhancing physical properties through an ion exchange reaction with chitosan. Based on 100 parts by weight of chitosan, its content is preferably 20 to 50 parts by weight. When the content is below this range, the following problems may occur: the additional ion exchange reaction is weak, resulting in a reduced effect on enhancing physical properties; when the content exceeds this range, the following problems may occur: the additional ion exchange reaction no longer forms, resulting in the additive's effect not being apparent.

[0054] In addition to the described additional components, the environmentally friendly bio-coating agent of the present invention may selectively include additives. The additives may also include plasticizers or additives for improving the flexibility of the film. Plasticizers or additives for improving flexibility include all plasticizers used in the art that can improve the flexibility of the coating layer formed by the environmentally friendly bio-coating agent of the present invention, and additives for improving flexibility. Based on 100% by weight of the coating agent, its content is preferably 0.1% by weight to 5% by weight. When below this range, the effect of increasing flexibility is weak; when above this range, the additional effect may not increase due to the additional addition, and the strength may decrease due to excessive increase in flexibility.

[0055] In addition, another aspect of the present invention provides a method for preparing the environmentally friendly bio-coating agent of the present invention.

[0056] Specifically, the present invention provides a method for an environmentally friendly biological coating agent (see reference). Figure 1 The method comprises: a first step of dissolving gellan gum in water while heating and mixing to obtain a gellan gum aqueous solution with a concentration of 0.5% to 2% by weight; a second step of additionally adding chitosan and a weak acid to water and mixing in a weakly acidic environment to obtain a chitosan aqueous solution with a concentration of 0.5% to 2% by weight; and a third step of mixing and stirring the gellan gum aqueous solution from the first step and the chitosan aqueous solution from the second step, to achieve a gellan gum:chitosan ratio of 1:1 to 1:3 by weight to obtain a homogeneous aqueous solution mixture.

[0057] First, as step 0, provide materials such as gellan gum, chitin / chitosan, and Ca. 2+ The ingredients of the supply source, carrageenan, and additives. Descriptions of each ingredient are as described above and will be omitted here.

[0058] In the first step, gellan gum is dissolved in water to obtain a gellan gum aqueous solution. Specifically, gellan gum is mixed in water to prepare an aqueous solution with a concentration of 0.5% to 2% by weight. The aqueous solution is heated to a high temperature (e.g., 80°C to 90°C) and mixed to ensure complete dissolution. At concentrations below this level, the following problems may occur: a fragile coating forms due to the low concentration, resulting in reduced water resistance. At concentrations above this level, the following problems may occur: low economic efficiency due to the time and cost required for preparation, and insufficient strength even at high concentrations.

[0059] A small amount of Ca can be added to the dissolved gellan gum aqueous solution. 2+ Ions. Ca 2+ Ions from Ca 2+ Supply source added, and usable Ca 2+ The supply source is selected from calcium nitrate (Ca(NO3)2), calcium chloride (CaCl2), calcium sulfide (CaS), calcium sulfate (CaSO4), calcium carbonate (CaCO3), calcium phosphate (Ca3(PO4)2), calcium hypophosphite (Ca2P2O4), calcium hypophosphite (Ca(H2PO2)2), calcium hydroxide (hydrated lime) (Ca(OH)2), calcium oxide (quicklime) (CaO), and calcium acetate (Ca(C2H3O2)2), preferably selected from calcium phosphate (Ca3(PO4)2), calcium hypophosphite (Ca2P2O4), calcium hypophosphite (Ca(H2PO2)2), calcium hydroxide (hydrated lime) (Ca(OH)2), calcium oxide (quicklime) (CaO), and calcium acetate (Ca(C2H3O2)2). The concentration is adjusted to a range of 0.1% by weight to 1% by weight to form a cross-linked bond. When the concentration is outside this range, problems may occur with reduced strength and durability of the coating layer.

[0060] In the second step, a chitosan aqueous solution is prepared separately. Specifically, chitosan is mixed in water to prepare an aqueous solution with a concentration of 0.5% to 2% by weight, and then completely dissolved in a weakly acidic environment at pH 4 to 6. A weak acid, such as acetic acid, can be added to achieve this weakly acidic environment. At concentrations below this level, the following problems occur: a fragile coating forms due to the low concentration, and water resistance is reduced; at concentrations above this level, the following problems occur: low economic efficiency due to the time and cost of preparation, and insufficient strength even at high concentrations.

[0061] In the third step, the gellan gum aqueous solution from the first step and the chitosan aqueous solution from the second step are mixed. Specifically, the gellan gum aqueous solution from the first step and the chitosan aqueous solution from the second step are mixed to a gellan gum:chitosan ratio of 1:1 to 1:3 by weight, and stirred at room temperature for a specified period, such as about 0.5 to 1 hour, to obtain a homogeneous aqueous solution mixture. When this range is exceeded, the following problems may occur: insufficient cross-linking and hydrogen bonding leads to reduced structural stability, mechanical strength, and water resistance.

[0062] In this mixture, 0.1% to 1% by weight of carrageenan is added to the aqueous solution. This is to further improve the strength and durability of the coating layer, which can be strengthened and made more durable through ion exchange reaction with chitosan.

[0063] In these steps, the carboxyl and amine groups of gellan gum form cross-links through ion exchange reactions and hydrogen bonds, ultimately increasing the strength of the coating layer.

[0064] Additionally, plasticizers and other additives may be added to the homogeneous aqueous solution. Adding a small amount of plasticizer increases the flexibility of the coating layer, thereby allowing it to better withstand external impacts. Other additives may be added to impart additional functionalities, and these can be readily selected by those skilled in the art.

[0065] The homogeneous mixed aqueous solution obtained in this way can be uniformly coated on the surface to be coated and then dried and gelled, making it ready for use.

[0066] In addition, another aspect of the present invention provides the use of the environmentally friendly bio-coating agent of the present invention.

[0067] Specifically, the present invention provides a slow-release fertilizer having a coating layer, which is formed by uniformly coating the surface of the fertilizer particles to be coated with the environmentally friendly biological coating agent of the present invention and then drying and gelling it.

[0068] Fertilizer granules are typically available in granular form with a particle diameter of 2 mm to 4 mm, and these can be readily selected by those skilled in the art. The fertilizers that can be used in this invention are fertilizers containing nitrogen, phosphate, and potassium, compost, manure, and animal feed, provided they have a particle shape and are used as slow-release fertilizers; no particular limitation is made in this invention.

[0069] As an example, fertilizer coating can be carried out in the following manner (refer to...) Figure 1 ).

[0070] First, prepare the fertilizer particles to be coated and dry them in advance in preparation for coating.

[0071] The homogeneous aqueous solution containing gellan gum and chitosan, prepared by the aforementioned method, is uniformly coated onto the surface of the fertilizer particles. This coating can be achieved using spraying, brushing, or roller coating methods to achieve a uniform thickness.

[0072] Next, the coated fertilizer can be left at room temperature for a few minutes to allow it to evaporate naturally, or it can be dried using a low-temperature dryer (e.g., 30°C to 50°C). During this process, gelation of the gellan gum and cross-linking of the chitosan form a strong yet flexible coating film over the fertilizer.

[0073] Finally, after the coated fertilizer particles are completely dried, the fertilizer's strength, durability, and water resistance can be evaluated and adjusted according to the required characteristics. After checking the coating quality, the fertilizer can be packaged and shipped.

[0074] In another aspect, the present invention provides a food packaging material, a medical film, or a biodegradable packaging material, wherein the food packaging material, medical film, or biodegradable packaging material has a coating layer, which is formed by uniformly coating the surface of the packaging material or substrate to be coated with the environmentally friendly bio-coating agent of the present invention and then drying and gelling it.

[0075] Because the environmentally friendly bio-coating agent of the present invention contains natural substances and is easily decomposed in nature, it has little impact on the environment and can be used as a plastic substitute. It has excellent mechanical strength and high water resistance, so it can be firmly maintained even in the external environment. In addition, since it is harmless to the human body, it can be used in a variety of applications, such as food packaging materials, medical coatings or biodegradable packaging materials.

[0076] The following examples and experimental cases will illustrate the details of the present invention. These are typical examples related to the present invention, and are not intended to limit the scope of the invention.

[0077] <Examples 1 to 3> Preparation of the Environmentally Friendly Biofilming Agent of the Present Invention

[0078] Step 1: Preparation of gellan gum aqueous solution

[0079] Add and mix gellan gum to water, heat to 80°C to 90°C and stir until the gellan gum is completely dissolved. The concentration of gellan gum at this point is shown in Table 1 below.

[0080] Add and mix as Ca in the aqueous solution 2+ A source of calcium chloride (CaCl2) was supplied to a concentration ranging from 0.1% to 1% by weight to prepare an aqueous solution of gellan gum. At this point, Ca... 2+ The concentrations of the supply sources are shown in Table 1 below.

[0081] Step 2: Preparation of chitosan aqueous solution

[0082] In an additional container, chitosan was added to and mixed with water, along with a small amount of acetic acid to provide a weakly acidic environment (pH 4 to 6) to allow the chitosan to dissolve completely. The chitosan concentration at this point is shown in Table 1 below.

[0083] When using chitin, it is deacetylated and converted into chitosan before use.

[0084] Third step: Preparation of aqueous solution mixture

[0085] The gellan gum aqueous solution from the first step and the chitosan aqueous solution from the second step were mixed to achieve a gellan gum:chitosan ratio of 1:1 to 1:3 by weight, and stirred at room temperature for 30 minutes to prepare a homogeneous aqueous solution mixture.

[0086] A small amount of carrageenan and plasticizer were additionally added and mixed into the aqueous solution mixture.

[0087] Table 1

[0088]

[0089] <Example 4> Preparation of slow-release fertilizer

[0090] 10 kg of granular urea fertilizer with a particle size of 2 mm to 4 mm is placed in a fluidized bed coating machine and preheated at 60°C for 10 minutes to prevent moisture in the fertilizer, thereby fluidizing the fertilizer particles.

[0091] Slow-release fertilizers were prepared by coating the surface of fertilizers with the coating agents prepared according to Examples 1 to 3 and Comparative Examples 1 to 3. When adding water for single-layer coating, the concentration of the final coating layer was adjusted to reach 25% by weight. When performing secondary coating, the concentration of the first coating layer was adjusted to reach 25% by weight and the concentration of the second coating layer was adjusted to reach 20% by weight. The coating layer temperature was 45°C and the nozzle air pressure was 2 kg / cm². 2 Under the condition of a spray volume of 100g / min, the first and second coating processes were carried out.

[0092] The coated fertilizer can be left at room temperature for a few minutes to allow it to evaporate naturally, or it can be dried in a dryer at 30°C to 50°C. At this time, gelation of gellan gum and cross-linking of chitosan will form, thereby forming a strong yet flexible coating layer covering the fertilizer.

[0093] The fertilizer coated according to Example 1 provides adequate strength and water resistance. The fertilizer coated according to Example 2 can increase the coating by strengthening the cross-linking bond and has excellent water resistance and durability. The fertilizer coated according to Example 3, as a high-concentration combination, has very high strength and improved durability and water resistance.

[0094] Conversely, no Ca was added. 2+ In Comparative Example 1, the cross-linking was weak and the durability was insufficient. In Comparative Example 2, due to the very low concentrations of gellan gum and chitosan, a fragile coating was formed and it had low water resistance. In Comparative Example 3, due to the absence of added Ca... 2+ The ions do not form cross-links, and even with high concentrations, the strength is still insufficient.

[0095] <Experimental Example 1> Fertilizer Dissolution Rate Test

[0096] Experiment 1 aims to determine the slowness of fertilizer component release in soil by evaluating the dissolution rate of coated fertilizer.

[0097] A sample of the fertilizer prepared in Example 4 was taken, with 2.5g of pure fertilizer (excluding the coating agent) placed in a 250ml flask containing distilled water. The flask was then placed in a 30°C incubator. The amount of urea dissolved in the water was measured weekly using a high-performance liquid chromatograph (HPLC) equipped with an RI detector. The flask was sealed to prevent evaporation of moisture and nutrients.

[0098] The results of the dissolution characteristics in water are shown in Table 2 below. In Table 2, a lower dissolution rate not only indicates better coating strength and water resistance of the coating layer, but also better dissolution regulation ability of the coating layer. Furthermore, by analyzing this dissolution rate, the sustained effect of the coating layer can be evaluated.

[0099] Table 2

[0100]

[0101] As shown in Table 2, it can be seen that the dissolution rate of fertilizers coated with the coating agents of Examples 1 to 3 of the present invention gradually increases over time, dissolution is slow, and the components remain after 6 weeks, thus allowing for long-term supply. In particular, the fertilizer coated with the coating agent of Example 3 exhibits the lowest dissolution rate (75% dissolution rate after 6 weeks), which indicates the best coating strength and water resistance.

[0102] Conversely, the fastest dissolution rate was confirmed in fertilizers coated with the coating agents of Comparative Examples 1 to 3, especially when no Ca was added. 2+ When the supply source (Comparative Example 1 and Comparative Example 3) is used, it can be seen that the release regulation capacity is significantly reduced.

Claims

1. An environmentally friendly bio-coating agent, characterized in that, it comprises: a gellan gum, and chitin or chitosan; the gellan gum forms a three-dimensional gel structure; in the environmentally friendly bio-coating agent, a cross-linking bond is formed by an ion exchange reaction between the carboxyl group of the gellan gum and the amine group of the chitosan.

2. The environmentally friendly bio-coating agent according to claim 1, characterized in that, in the environmentally friendly bio-coating agent, the gellan gum and the chitin or chitosan are contained in a ratio of 1:1 to 1:3 on a weight basis.

3. The environmentally friendly bio-coating agent according to claim 1, characterized in that, The environment-friendly biological coating agent further comprises Ca 2+ gelling agent, The Ca 2+ The supply source can form additional cross-linking bonds by binding with the gellan gum, which is ion-exchanged with the chitosan. The Ca 2+ The supply source is selected from calcium nitrate, calcium chloride, calcium sulfide, calcium sulfate, calcium carbonate, calcium phosphate, calcium hypophosphite, calcium hypophosphite, calcium hydroxide, calcium oxide, and calcium acetate.

4. The environmentally friendly bio-coating agent according to claim 1 or 2, characterized in that, the environmentally friendly bio-coating agent further comprises a plasticizer or an additive for improving the flexibility of a film.

5. A method for preparing an environmentally friendly bio-coating agent, the environmentally friendly bio-coating agent being the environmentally friendly bio-coating agent according to claim 1, characterized in that, it comprises: a first step of dissolving a gellan gum in water while heating and mixing to obtain a gellan gum aqueous solution having a concentration of 0.5 to 2% by weight, a second step of additionally adding chitosan to water and adding a weak acid and mixing in a weakly acidic environment to obtain a chitosan aqueous solution having a concentration of 0.5 to 2% by weight, and a third step of mixing and stirring the gellan gum aqueous solution of the first step and the chitosan aqueous solution of the second step so that the ratio of gellan gum:chitosan becomes 1:1 to 1:3 on a weight basis to obtain a uniform aqueous solution mixture.

6. The method for preparing an environmentally friendly bio-coating agent according to claim 5, characterized in that, In the first step, also a CaCl2solution with a concentration of 0.1 to 1 wt.-% is added to the aqueous solution of the Knoell gel 2+ supply source, in the third step, carrageenan having a concentration of 0.1 to 1% by weight is further added to the aqueous solution mixture.

7. The method for preparing an environmentally friendly bio-coating agent according to claim 5, characterized in that, in the third step, a plasticizer or an additive for improving the flexibility of a film is further added to the aqueous solution mixture.

8. A slow-release fertilizer, characterized in that, the slow-release fertilizer has a coating layer, the coating layer is formed by uniformly coating the environmentally friendly bio-coating agent according to claim 1 or the environmentally friendly bio-coating agent prepared by the method according to claim 5 on the surface of a fertilizer particle to be coated and drying and gelling.

9. The slow-release fertilizer according to claim 8, characterized in that, the fertilizer is selected from the group consisting of a fertilizer containing nitrogen, phosphorus, and potassium, compost, manure, and feed.

10. A food packaging material, a medical coating, or a biodegradable packaging material, characterized in that, the food packaging material, the medical coating, or the biodegradable packaging material has a coating layer, the coating layer is formed by uniformly coating the environmentally friendly bio-coating agent according to claim 1 or the environmentally friendly bio-coating agent prepared by the method according to claim 5 on the surface of a packaging material or a substrate to be coated and drying and gelling.

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