WO2011146027A2

WO2011146027A2 - Granular fertilizer with controlled release of nutrients

Info

Publication number: WO2011146027A2
Application number: PCT/SK2011/050007
Authority: WO
Inventors: Jan Kovacik; Gabriela Herencsarova; Zdenko Tokar; Milan Kralik; Michal Ferenci; Pavol Kerdo
Original assignee: Duslo, A.S.
Priority date: 2010-05-18
Filing date: 2011-05-16
Publication date: 2011-11-24
Also published as: UA107228C2; RU2579460C2; SK288066B6; SK500232010A3; WO2011146027A4; RU2012154636A; WO2011146027A3; EP2571831A2

Abstract

Granular fertilizer with controlled release of nutrients can be prepared by coating the fertilizer granules with a mixture of epoxide resin with low molecular weight between 100 and 400 in the amount of 50 to 85 % w/w, imidazole derivative in the amount of 1 to 20 % w/w and modified vegetable oil in the amount of 10 to 30 % w/w. The epoxide resin with low molecular weight between 100 and 400 is preferably bisphenol A diglycidyl ether with epoxide equivalent of 182-192 g/mol, imidazole derivative is preferably 2-ethyl-4-methylimidazole and modified vegetable oil is preferably methylester of rape oil. The coating mixture contains preferably 77.3 % w/w of epoxide resin, 3.4 % w/w of imidazole derivative and 19.3 % w/w of methylester of rape oil, and the fertilizer is coated by gradual spraying of 3 to 20 doses of the coating mixture, wherein the coating is performed in the rotary cylindrical container or fluid apparatus at the temperature of 60 to 120 °C, preferably 105 to 115 °C. The layer of coating mixture makes 6 to 25 % w/w of the overall weight of the coated granule.

Description

GRANULAR FERTILIZER WITH CONTROLLED RELEASE OF NUTRIENTS

Field of the Invention

The invention relates to a fertilizer with controlled release of nutrients, which can be prepared by coating the granules of fertilizer with a mixture of epoxide resin, imidazole derivative as a hardener and modified vegetable oil. The release rate is regulated by the amount of epoxide resin.

Background of the Invention

Nutrition of plants depends on the accessibility of mineral nitrogen, phosphor and potassium in soil. A wide range of mineral fertilizers is produced throughout the world, differring only in mutual ratio of these three components, or also by the presence of other elements (Mg, S, Ca) or trace elements. All these mineral fertilizers have a high solubility in water, which is their common

disadvantage. This problem can be solved essentially by developing new types of fertilizers, which provide for a slower release of nutrients into soil, so that they are utilised gradually. Fertilizers with slower release of nutrients can be divided into two classes:

1 . Slow-Release Fertilizers (SRF)

2. Controlled (Regulated) Release Fertilizer (CRF).

CRF can comprise traditional soluble fertilizers, with quickly available nutrients, wherein following the process of granulation, prilling or crystallization, a protective coating with a layer for controlled (regulated) release into soil influencing the solubility and release rate of nutrients is employed. A typical core component includes urea or N-P-K in various combinations, with or without addition of microelements.

Depending on type of the coating polymer and a method of preparation, there are three classes of fertilizers coated with polymer (Polymer Coated

Fertilizer - PCF):

- a thermosetting copolymer is coated on the surface of the fertilizer;

- a thermoplastic polymer or copolymer is coated on the surface of the fertilizer; - two monomers are coated on the surface of the ferilizer, which polymerize together on this surface.

According to US 6,187,074 (2001 ), granules of the fertilizer can be coated with carboxyl-ethylene copolymer [75 to 95 % of ethylene and 10 % to 25 % of unsatured carboxylic acids (acrylic, metacrylic, maleic, crotonic, fumaric)]. Tg value of the polymer ranges from -20 °C to + 20 °C. Acrylamide, metacrylamide, N-metylolacrylamide, N-butoxymetacrylamide, glycidyl metacrylate and

hydroxyethyl acrylate are also recommended as a comonomer to ethylene. The preferred melting point of the polymer is above 1 10 °C. The coating (layer) of the copolymer makes between 2 % and 10 % w/w of the granule. Lignin, starch or cellulose are added in order to control discharging of nutrients. Coating with copolymer occurs at the temperature between 30 °C and 70 °C. SiO2 or T1O2 is added after coating the layer of the polymer in order to prevent sticking the granules together.

A hygroscopic polymer (sodium polyacrylate, acrylic acid-vinylalcohol copolymer, polymers inoculated with starch, carboxymethylcellulose) can be coated on the fertilizer granules as a first step, and than polyurethane resin (US 6,358,295; 2002). Polyurethane resin will result from the reaction of isocyanate (e.g. toluene diisocyanate (TDI), diphenylmethane diisocyanate (MDI),

hexamethylene diisocyanate) and polyol (propylene glycol, trimethylolpropane, polytetramethylene ether glycol). The ratio of groups -NCO/-OH in the employed isocyanate and polyol is typically 0.9:1 .2. NaOH, urea or triethylenediamine can be added to harden the polyurethane resin. The amount of hygroscopic polymer ranges between 1 and 20 WU (weight units) per 100 WU of urethane resin. The urea is heated to 70 °C, hygroscopic polymer is added, followed by dispersion and adding of isocyanate, polyol and hardener.

A polymer component of the coating can also comprise a polysaccharide dispersed in resin: cellulose, starch or sugars: glucose, fructose, xylose, arabinose (US 102,829; 1993). Oxidized starch, alkyl or hydroxyalkyi ether starch, starch modified by phosphoric acid, nitric acid, succinic acid, carboxymethylated starch, hydroxyalkylated starch, cationic starch and cellulose derivatives:

carboxymethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose,

methylcellulose and carboxymethylethylcellulose are also applicable. Carboxymethylcellulose is recommended. A vinylidene-chloride polymer, copolymer of vinylidene chlorid with ethylene, propylene, butene,

ethylenevinyl ketone, vinylchloride or vinylideneacrylated copolymer can be used as a resin. Adding of powder polysaccharide or sugar makes 0,5 % to 20 % w/w of the resin. Water-unsoluble and sparingly soluble filler, e.g. talc, CaCO3, S1O2, sulphur, zeolite, is added to the polymer mixture. Adding of the filler makes 20 % to 70 % w/w of the resin. The polymer component of the coating is dissolved on the organic solvent and sprayed at the granular fertilizer. After coating of the particles the solvent is evaporated due to hot air and the coating hardens.

Duration of the controlled dissolving of the fertilizer is 26 to 315 days.

Slowly soluble nitrogen fertilizer can also be prepared by copolymerization of acrylic acid and maleic anhydride (dihydro-2,5-dioxofurane) using N,N- methylenebisacrylamide as a cross-linking agent in water environment in the presence of urea, ammonium peroxydisulphate and sodium sulfite as an initiator (Liu M., Liang R., Zhan F., Liu Z., Niu A., 2006: Synthesis of a slow-release and superabsorbent nitrogen fertilizer and its properties, Research Article, Department of Chemistry, Lanzhou University, China). The product was cross-linked on its surface with trihydroxymethylpropane glycidol ether for improving the slow dissolution and an ability to retain water. The content of nitrogen in the synthetized fertilizer was 28.5 % and absorption of water cca 900 g/g in distilled water and 180 g/g in tap water. On the basis of the results of testing the rate of dissolution of nitrogen and absorption of water, it was found out that the surface cross-linked product provides not only for slow dissolution of nitrogen fertilizer, but also for a high capacity of retaining the soil humidity. The fertilizer could be utilized in dry regions.

The granules of fertilizer can first of all be coated with a layer of wax, than the material based on alkyd resin and a substance capable of swelling (JP

08151286; 1994). The urea (diameter 3.3 mm) is heated to 70 °C and the paraffin wax is sprayed at this temperature (60 °C). The wax layer makes 6.2 % w/w of the coated granule. Than the second layer, consisting of the mixture of alkyd resin on the basis of soya oil, tung oil and absorbing resin on the basis of sodium

polyacrylate (Aqua Keep 10 SH) at the ratio of 95:5, is sprayed. This layer makes 8.1 % w/w of the coated granule. Such a surface-treated urea releases 8 % of nitrogen after 30 days in water and 75 % after 120 days.

The fertilizer granules can also be coated with thermoplastic resin and than by a substance selected from the group comprising other thermoplastic resins, heat-hardening resins or inorganic substances (JP 07315975; 1994). Granules of urea having diameter of 3.3 mm were coated with wax and than by a mixture of alkyd resin, tung resin, pentaerythritol linolane and metallic soap.

The patent JP 07033575 (1993), presents granules coated with mixture based on oil modified resin (based on soya oil), unsaturated oil with conjugated double bonds (palm oil, tung oil, tall oil), pentaerythritols (anhydrid of maleic or phthalic acid), metallic soap and amino resin (melamine resin, benzoguanamine resin, glycoluryl resin). No organic solvents were used in surface treating. The rate of releasing the nutrients from the coated granules was regulated by a type and amount of the employed amino resin. The amino resin was tested either as an upper layer of the coating in case of a two-layer coating, or in the mixture with alkyd resin in case of a one-layer coating.

In JP patent 06056567 (1992) the coating mixture contains an oil modified alkyd resin, unsaturated oil with conjugated double bonds and wax as the main component. The granules of urea having diameter of 3.3 mm were coated with mixture of soya oil modified alkyd resin (30 % w/w), tung oil (50 % w/w), pentaerythritol ester of linoleic acid (15 % w/w), metallic soap (3 % w/w) and conditioner (2 % w/w).

The fertilizer granules in EP 520456 B1 (1991 ) are also coated with mixture containing an oil modified alkyd resin and unsaturated oil with conjugated double bonds. The metallic soap can be present as well. The coating mixture contains soya oil based alkyd resin (30 % w/w), tung oil (49 % w/w), pentaerythritol ester of linoleic acid (15 % w/w), zirconium octylate (1 .2 % w/w), cobaltous octylate (1 .2 % w/w), manganous naphthenate (0.6 % w/w) and an anti-crusting agent (2 % w/w). After its heating the mixture was sprayed on the fluidized urea.

In JP patent 021 1 1686 (1988) the coating mixture contains the heat- hardening resin with terminal carboxyl group and a filler, e.g. talc. The

concentration of filler in the mixture is between 5 and 25 % w/w. The fertilizer granules, comprising 20 % N and 10 % K₂O, were coated with mixture of alkyd resin based on soya oil and talc (5.9 and 1 .5 % w/w). Duration of releasing 80 % of the nutrients was 96 days.

The fertilizer with gradual release of nutrients was prepared by coating the fertilizer granules with mixture of resin based on oil modified phthalic acid and miscible oil resin (JP 63095189; 1986). Resinoid varnish modified by soya oil based on phthalic acid (250 WU) was mixed with aromatic oil resin (25 WU) in order to obtain the coating mixture. The fertilizer granules (1 kg) containing N 18 % and K₂O 16 % were poured into the rotary drum and the coating mixture was sprayed on the granules through jets at the temperature of 60 to 100 °C. The percentage of the released ammonia nitrogen from the fertilizer in water on Day 10, 30, 50, 80 and 100 was 13 %, 34 %, 52 %, 71 % and 79 %. In case of fertilizer granules coated only with oil resin, 100 % N was released after 10 days.

The polymer for coating the surface of the fertilizer granules can also be obtained by reaction of polyisokyanate and alkyd resin modified by sorbitol fatty acid ester (JP 2008222536; 2007). The mixture of alkyd resin, containing 22 % of castor oil, 8 % of oleic acid, 16 % of adipic acid, 24 % of trimethylolpropane and 30 % of tristearate sorbitol, was blended with catalyst and heated. The urea granules (1 kg) in the centrifugal rotary granulating machine were heated to 70 °C, and than the alkyd resin (4 g) and Sumidur 44V10 (2 g) as a polyisocyanate component were sprayed on them separately through two nozzles. When the resin hardened, the process of spraying the alkyd and polyisocyanate was repeated until the coating layer made 10 % w/w of the coated urea. The polymer coating showed biological degradability of 12.5 % and 88.3 % of nitrogen was released after 130 days. Similar granules coated with mixture based on alkyd resins without tristearate sorbitol showed biological degradability of only 2.5 % and 93.6 % of nitrogen was released after 40 days.

According to patent CN101289349 (2008) CRF consists of the core

(fertilizer) and the coating containing sulphur on the surface of the granule, and on the surface of the sulphur there is a polymer film based on water-soluble alkyd resin. The amount of sulphur and polymer film is between 5 and 30 %, or between 0.5 and 10 % w/w of the coated fertilizer. The water-soluble alkyd resin contains an alkyd polymer having the acid value of 10 - 150 mg KOH/g of the resin. The alkyd pre-polymer is obtained by polycondensation of unsaturated conjugated vegetable oil or fatty acid of vegetable origin with synthetic fatty acid or its anhydride. The coating can also contain inorganic layer (montmorillonite, chalk, kaoline, talc).

In production of the polymer coated fertilizer according to US 569 8002 (1997), the basic coating is made of the reaction product of epoxide with at least two epoxide groups/mol and at least one amino hardener with at least two N-H groups. The structure of biphenol A diglycidyl ether (DER 330 and 331 from Dow CHC) is preferred from among the commercially available epoxide resins. As regards the hardeners based on polyalkylpolyamides, triethylenetetramine is preferred. 2-aminoethylpiperazine is added in order to speed up hardening. The most suitable ratio of epoxide equivalents of epoxide resins to hydrogen atoms bound on amino nitrogen of the amino hardener is 1 . The amount of the basic coating is ranging between 1 and 20 % w/w of granules. Another at least one polymer layer is coated on the basic coating, which layer consists either of further epoxide polymers, in-situ reaction polymers (urethans as a reaction product of polyols with isokyanates), thermoplastic polymers (polyalkylacrylates, styrene- butadienes) or wax (paraffins, hydrogenated vegetable oils). Adding of wax makes between 1 and 6 % w/w of granules. The samples of urea coated with polymer were prepared, using DER 330, long-chain amine (C14 to C18) and C30 alpha olefine. During 7 days of testing in water at the temperature of 25 °C, 7 to 100 % of nitrogen was released in individual samples.

In CN patent 101037368 (2007) the coated fertilizer is prepared by evenly distributed spray of water soluble polymer. The ratio of fertilizer granules to polymer is (0.3-0.4) : (9.6-9.7). The water soluble polymer is prepared from cellulose (22-35 % w/w), oxidized starch (1 -2 % w/w), polyvinylalcohol (4-8 % w/w), polyurethane pre-polymer (5 - 8 % w/w), epoxide resin E 44 (6-18 % w/w), hardener of the epoxide resin T593 (2-3 % w/w), N-hydroxy-metylacrylamide as a cross-linker (1 -2 % w/w), potassium peroxodisulphate as an initiator (0.001 - 0.002 % w/w) and deionized water (35-51 % w/w). The fertilizer prepared in this way has good characteristics from the point of view of controlling the rate of releasing nutrients, high utilization of nitrogen by plants, low consumption and low pollution.

According to US 3264088 (1996) the resin is prepared by reaction of epoxy compounds, such as epichlorhydrin with dihydric phenols (bisphenol A), resulting in glycidyl ethers. Aliphatic or aromatic amines, dihydric acid anhydrides, can be used as a hardener. The coating mixture consists of a mixture of epoxide resin and its hardener in the presence of acetone. The coating mixture layer makes between 3 and 15 % w/w of granules, depending on smoothness of the surface. The granules are preferably heated to 56 - 160 °C. Each layer of the coated mixture is dried until the gelatinization starts. Stirring of granules in the drum during drying improves the extent of coating, evenness of the film and reduces formation of agglomerates. The coating was carried out in a 76.2 cm long drum having diameter of 40.6 cm, in vertical position, using the apparatus for air flowing, heated to the temperature of 78 - 139 °C, in direction of the drum axis. There were dividing walls in the drum and peripheral rotation rate was 330 - 360 cm/min. The prilled urea was coated with 12.5 % w/w of the resin containing 80 units of Epon 815 (liquid bisphenol-epichlorhydrin resin, having terminal epoxide groups and epoxide equivalents <500) and 20 units of reaction product of epoxidation of oleonitrile and triethylenetetramine. The urea was pre-heated to 89 °C and the coating mixture was gradually applied in 9 doses. The first applied dose made 2 % w/w of granules, the following four doses 1 ,5 % w/w each, and the last four 1 % w/w each. When 20 g of the product was mixed with 100 ml of water, 19 % of nutrients was dissolved after 72 hours of rest.

The fertilizer granules (prilled urea, ammonium nitrate) according to US 3259482 (1966) were coated with several layers of epoxide resins. The fertilizer was poured into rotary drum and heated to 139 °C. The resin was gradually sprayed on the heated granules. At the same time, the air heated to 145 °C was flowing through the drum. The resin A (dichloro pentadiene copolymer with modified vegetable oil, dissolved in organic solvent) was added in 5 doses. The first one made 3 % w/w of granules, the remaining four doses made 1 .5 % w/w each. Then resin B was added in three doses, each making 1 .5 % w/w of granules. The resin B was a mixture of epoxidated soya and linseed oil with oxirane (over 7 %) in organic solvent, hardener with acid value of 160-70, prepared in advance from phthalic acid anhydride, chlorendic acid and

pentaerythritol, wherein the initial ratio of CO₂H groups to OH groups before esterification was 1 .8:1 . A mixture of dimethylphenol and cellosolve acetate was used a solvent. After the last spraying, the drying continued until the granules became unsticky. After 72 hours, the rate of releasing nutrients was only 0.7 %.

Regulation of releasing the nutrients also depends on the employed coating. In case of alkyd resins the releasing is obtained by different composition of the coating or its thickness. In case of polyurethane resins, but also many other types of resins and thermoplastic polymers, the releasing is controlled mainly by temperature, wherein the soil humidity, pH, weather or microbiological activity have only a weak influence on releasing. In case of polyethylene coatings a part of low permeable polyethylene is replaced by highly permeable polymer, e.g. ethylene-vinylacetate.

The principal disadvantage of using the resins for coating results from their strong stickeness in the original state. Therefore, individual granules of the fertilizer get stuck together during coating. When the resin hardens, it is possible to separate individual granules, but the coating gets damaged. In order to avoid sticking the granules together during the coating process, it is recommended to add a native vegetable oil (palm, rape, castor, linseed oil).

However, if the oil is not a part of the polymer chain, it can be degraded under certain conditions and thus the quality of the coating deteriorates. A high viscosity of resins for coating is another problem of their direct use. In patents it is mostly recommended to dilute them in organic solvent, but this method is harmful to the environment due to volatility of the solvent.

The aim of solution according to the present invention is to provide a granular fertilizer with substantially minimizing the above-cited disadvantages.

Summary of the Invention

The above-cited deficiencies are to a large extent removed by a granular fertilizer with regulated (controlled) releasing of nutrients, with surface film, according to the present invention. The granular fertilizer with surface film according to the invention can be prepared from the basic granular fertilizer and polymer coating, wherein the polymer coating (film, layer) is based on epoxide resin with low molecular weight between 100 and 400. Epoxide resins are made by alkaline condensation of 2,2-bis(4-hydroxyphenyl)-propane (diane) with epichlorhydrin, resulting in formation of resinoid products, containing reactive epoxide groups. Epoxide resins are hardened by using hardeners under high or low temperatures. The volume changes during reaction of hardening the epoxide resins are very small and no volatile products are formed therein, the hardener is chemically bound to the resin.

The epoxide resin free of organic solvent and softener is used for coating the granular fertilizer. The amount of epoxide resin in the coating mixture was ranging from 50 to 85 % w/w. Bisphenol A diglycidyl ether with epoxide equivalent of 182-192 g/mol can preferably be used as an epoxide resin.

In their structure the epoxide resins contain reactive epoxide groups able to react with hydrogens of primary and secondary aminogroups. Therefore, amine derivatives with at least two N-H groups (ethylenediamine, polypropylene glycol diamine, glycol triamines, triethylene glycol triamine, triethylene tetraamine), piperazine and imidazole derivatives can be applied as suitable hardeners of epoxide resins.

Imidazole derivative was used as a suitable hardener of epoxide resin. The concentration of hardener in the mixture with epoxide resin was ranging from 1 to 20 % w/w.

Due to high viscosity of epoxide resin it is necessary to use a suitable substance for diluting it. The effort of inventors to find a substance, which would dilute the resin, prevent the granules from sticking together during the process of forming a surface film, and which would also be unvolatile under given conditions, resulted in adding a liquid prepared by re-esterification of crude vegetable oil with methanol. Its amount was ranging from 10 to 30 % w/w. The use of modified vegetable oil for avoiding the sticking of granules is preferable in comparison to natural oil in the mixture with epoxide resin, because the nutrients are released much slowly through the coating formed on the surface of granules (see examples).

The coating mixture can be prepared in the container with mixer at the room temperature. After weighing the epoxide resin, the hardener is added gradually. The mixture is thoroughly stirred and then vegetable oil is poured. After homogenization the mixture is prepared for coating. Coating under laboratory conditions was performed in Aeromatic AG jet drier and the coating mixture was sprayed by means pressured air. The granules were carried away and dried by the flow of warm air from the lower, narrower part of the collumn. Dosing of the coating mixture into the air flow was provided by syringe. The coating mixture was sprayed in 3 to 20 even doses. Drying was carried out at the temperature of 70 to 120 °C. Each folowing dose of the mixture was sprayed after complete hardening of the previous dose on the surface of granules, namely at the intervals of 5 to 15 minutes. The resulting film has a character of cross-linked polymer, like in case of thermosets, which reduces the thermal sensitivity of penetrability of water through the film.

Examples

The rate of releasing the nutrients from the coated fertilizer was tested in duplicator container with fertilizer granules integrated in the layer of sand. After closing the container the duplicator was poured with distilled water, which was flowing through the sand layer with granules and was soaking it. Water for analysing the concentration of released nutrients was retained in glass flask after flowing through the sand layer with samples of granular fertilizer. The water soaking cycle was repeated in relevant time intervals.

Granules of urea produced by SKW Piesteritz (Germany), namely Piagran 46 (N content 46 %) were used for coating. The diameter of granules was between 2 and 5 mm. The granules were coated with mixtures based on epoxide resin according to Examples 1 to 9.

Methods of Evaluating the Fertilizers with Controlled Releasing of Nutrients by Water Testing

Prepared samples of granular fertilizer with controlled releasing of nutrients (40 g) were tested in duplicator container, incorporated in the layer of sand.

A fine, washed and dried sand was used, i.e. inert material without any organic substances. The container was closed, water pump of thermostat for circulation circuit of warming the jacket was switched on. Temperature of circulation water was set on a constant value of 23 °C. The same was done for the temperature of water in thermostat and of distilled water for extraction of nutrients from the coated samples.

The period of dosing the water (500 ml) through the filling with a sample of fertilizer was optimalized to cca 120 minutes. The rate of dosing the water during the first approximately 5 minutes was set to max. 14 ml/min. After creating the surface on the sand in the container, this surface was maintained at the dosing rate range of 3.5-4 ml/min.

Water intended for analysing the concentration of releasing the nutrients was retained in glass flask after having gone through the sand layer with a sample of fertilizer.

E x a m p l e s 1 - 7

The granules of urea Piagran 46 (1 kg) were used for preparing the granular fertilizer according to the present invention. The coating mixtures of the following compositions were prepared for coating the granules:

1 . 63.3 % epoxide resin (CHS Epoxy 520), 1 1 .4 % imidazole derivative

(IMICURE EMI-24), 25.3 % modified rape oil (MERO)

2. 67.4 % epoxide resin (CHS Epoxy 520), 10.1 % imidazole derivative

(IMICURE EMI-24), 22.5 % modified rape oil (MERO)

3. 73.3 % epoxide resin (CHS Epoxy 520), 8.3 % imidazole derivative

(IMICURE EMI-24), 18.4 % modified rape oil (MERO)

4. 77.5 % epoxide resin (CHS Epoxy 520), 7.0 % imidazole derivative

(IMICURE EMI-24), 15.5 % modified rape oil (MERO)

5. 80.5 % epoxide resin (CHS Epoxy 520), 6.0 % imidazole derivative

(IMICURE EMI-24), 13.5 % modified rape oil (MERO)

6. 82.8 % epoxide resin (CHS Epoxy 520), 5.3 % imidazole derivative

(IMICURE EMI-24), 1 1 .9 % modified rape oil (MERO)

7. 77.3 % epoxide resin (CHS Epoxy 520), 3.4 % imidazole derivative

(IMICURE EMI-24), 19.3 % modified rape oil (MERO) 8. 70.7 % epoxide resin (CHS Epoxy 520), 7.6 % imidazole derivative (IMICURE EMI-24), 10.9 % linseed oil , 10,8 % castor oil

9. 70.7 % epoxide resin (CHS Epoxy 520), 7.6 % imidazole derivative

(IMICURE EMI-24), 21 .7 % linseed oil.

Granules of urea were heated to 1 10 °C by the flow of hot air. The coating mixture was dosed gradually. After coating the fertilizer granules the samples underwent water testing as described above. The course of releasing the nitrogen from individual samples of granular fertilizer is shown in Tables 1 and 2.

Table 1 : Water testing of samples of granular fertilizer (GF) according to

Examples 1 - 7

Concentration of released N [%]

GF GF GF GF GF GF GF

Measurement Day with with with with with with with mixture mixture mixture mixture mixture mixture mixture

No. 1 No. 2 No. 3 No. 4 No. 5 No. 6 No. 7

1 1. 1.7 1.8 2.2 0.8 0.9 0.5 0

2 2. 13.5 5.2 3.5 2.0 1.7 1.2 0

3 4. 1 1.4 4.3 2. 2.6 1.8 0.9 2.9

4 7. 10.7 6.4 2.1 3.3 2.6 1.0 6.6

5 17. 21.8 8.8 3.2 12.5 1 1.2 4.4 20.1

6 28. 8.4 18.4 12.5 6.3 5.8 4.5 10.3

7 56. 2.4 4.9 6.2 2.7 2.7 3.2 8.2

8 84. 1.5 1.6 1.7 1.9 3.0 3.1 2.1

TOTAL 71.4 51.5 33.4 32.1 29.7 18.8 50.2

% w/w of the coating 5.8 6.0 8.2 9.5 10.4 14.0 9.8 Table 2: Water testing of samples of granular fertilizer (GF) according to Examples 8 - 9

Following the comparison of results in Table 2, 99.5 % of nitrogen was released after 28 days of testing when using natural oils, whereas in Table 1 it was less than 71 .5 % even after 84 days.

Industrial applicability

The present invention can be used in production of granular fertilizers with controlled releasing of nutrients (PCF).

Claims

1 . Granular fertilizer with controlled releasing of nutrients, which fertilizer can be prepared by coating the fertilizer granules with a mixture of epoxide resin with low molecular weight between 100 and 400 in the amount of 50 to 85 % w/w, imidazole derivative in the amount of 1 to 20 % w/w and modified vegetable oil in the amount of 10 to 30 % w/w.

2. Granular fertilizer according to claim 1 , characterized in that the epoxide resin with low molecular weight between 100 and 400 is bisphenol A diglycidyl ether with epoxide equivalent between 182 and 192 g/ mol.

3. Granular fertilizer according to claims 1 and 2, characterized in that the imidazole derivative is 2-ethyl-4-methylimidazole.

4. Granular fertilizer according to any of claims 1 to 3, characterized in that the modified vegetable oil is methylester of rape oil.

5. Granular fertilizer according to any of claims 1 to 4, characterized in that the coating mixture preferably contains 77.3 % w/w of epoxide resin, 3.4 % w/w of imidazole derivative and 19.3 % w/w of methylester of rape oil.

6. Granular fertilizer according to any of claims 1 to 5, characterized in that the fertilizer is coated by gradual applying of 3 to 20 doses of coating mixture, wherein the coating is performed in rotary cylindrical container or fluid apparatus at the temperature of 60 to 120 °C, preferably 105 to

1 15 °C.

7. Granular fertilizer according to claim 6, characterized in that the layer of the coating mixture makes 6 to 25 % w/w of the overall weight of the coated granule, preferably 8 to 12 % w/w.