MXPA99006609A - Encapsulation of fertilizers in poliurea-uretano simetr - Google Patents

Abstract

This invention relates to processes for the production of symmetric polyurea-urethane-coated granular fertilizer products and to the symmetric poly-urea-urethane granular fertilizer products produced by these processes. These processes consist of coating fertilizer granules with compounds that react to form urethane coatings containing terminal isocyanate groups, followed by polymerization of these urethanes to form symmetrical polyurea urethanes. Suitable compounds consist of a) an organic polyisocyanate component and b) an alkanolamine component containing at least one tertiary amine group and at least one hydroxyl group. These compounds are present in amounts sufficient for the molar ratio of isocyanate groups to isocyanate-reactive groups to be about 1.6: 1.0 to about 10.0: 1.0 in each encapsulating layer. It is necessary to apply sufficient amounts of these compounds to the fertilizer granules, in such a way that the granular fertilizer particles coated with symmetrical polyurea-urethane contain from about 0.5 to about 15% by weight of polyurea-urethane, based on the Total weight of encapsulated fertilizer particles

Description

ENCAPSULATION OF ILLUSTRATING FER IN POLYUREA-SYRETHRICAL URETHANE BACKGROUND OF THE INVENTION This invention relates to a process for the production of granular fertilizer particles coated with symmetrical polyurea-urethane and with granular fertilizer particles produced by this process. The polyurea-urethane coatings consist of a) a polyisocyanate, preferably an aromatic polyisocyanate and, more preferably, a polymethylene poly (phenyl isocyanate) and b) an alkanolamine containing at least one tertiary amine group and at least one hydroxyl group, presence of moisture. Commercial particulate fertilizers are produced and marketed in different particle types, ie, granular fertilizers, pellets, powders, pills and pips. In addition, they can be formed with inorganic substances, organic substances or combinations of these. The improvements of the present invention can be applied to any of these types of particulate fertilizers. To be effective in promoting the growth of plants, fertilizers must contain some amount of nutrients for water-soluble plants. These are typically in the form of water-soluble compounds of nitrogen, phosphorus and potassium, alone or in combination, and frequently together with other elements, such as, for example, calcium, boron, magnesium, zinc, chlorine, etc. Said particulate fertilizers can be manufactured with a single component, for example urea, ammonium nitrate, potassium chloride, etc., or with multiple components, often mixed with water-soluble inert materials or insoluble in water, as in fertilizers. common denominated 6-6-6, 4-6-4, 10-10-10, 20-20-5, 14,16-0, 5-20-20 and the like. In addition, specialized fertilizers may contain potential additives, such as herbicides, insecticides, trace elements, iron salts, sulfur, etc. Perfections of the present invention can be applied to any of these fertilizers. Historically, particulate fertilizers possessed a number of known defects, the most notable being the too rapid release of food for soluble plants, which produces phytotoxicity, and the rapid depletion of plant nutrients by leaching. Other problems included tendencies to clump together and form dust. These problems are well documented in previous patents that offered solutions to one or more of the known defects, including US Pat. 3,475,154, 3,259,482, 3,264,088, 3,264,089, 4,711,659, and 4,772,490 and Japanese Patent 52-38361. The present invention provides additional improvements in the construction of particulate fertilizers, which make them highly resistant to attrition, and longer release properties. A series of slow release coatings for particular fertilizers has been previously proposed. The process of coating sulfur with urea particles is described in US Pat. 3,342,577 and was developed in the late 1960s by the Tennessee Valley Au-thority (TVA) as an economic system to reduce the rate of dissolution when urea particles are applied to the soil as fertilizer. This procedure requires high levels of sulfur, which reduces the nutrient analysis of the fertilizer particles, and even then, there are still imperfections in the coating, making it necessary to apply a sealant coating, which is composed of a mixture of 30% polyethylene resin in 70% refined heavy mineral oil. Attempts to seal the sulfur coating have been described in US Pat. 5,219,465. Upper layers are formed on the sulfur layer using various polymers, which include a polyurethane based on polymethylene po-li (phenyl isocyanate) and polyester polyols. In this procedure, the addition of a catalyst is necessary to promote the curing of the polyurethane on the surface. U.S. Pat. No. 5,599,374 relates to a process for producing slow release fertilizers coated with sulfur that have improved impact and abrasion resistance properties. This process applies liquid monomers sequentially on the surface of hot sulfur-coated urea granules and copolymerizes these to form a firm, adhesion-free and water-insoluble polymeric sealant coating sealant. Suitable liquid monomers are diisocyanates such as diphenylmethane diisocyanate and a mixture of diethylene glycol polyols (DEG) and triethanolamine (TEOA). The TEOA serves both as a reactive polyol and as a catalyst. This patent attempts to overcome the deficiencies of the use of sulfur only to achieve slow release properties. The polyurethane serves to coat and cover the areas of the fertilizer particle not covered by the sulfur and, therefore, provide better release properties over time. Coatings in which preformed polymer resins are applied from solvents have been described, for example, in US Pat. 3,475,154 and 3,264,089. The use of solvents creates a risk of vapors when drying the products and the evaporation stage of the solvent can lead to pore-type imperfections in the coatings when applied. U.S. Pat. No. 4,369,055 attempted to facilitate the degradation of coating materials while maintaining the function to control the rate of dissolution by dispersing inorganic powders, such as sulfur and talc, in low molecular weight olefin polymer. However, the described coating materials are difficult to apply in uniform layers, because the polymers must be kept in the molten state. Polyurethane coatings such as those described in U.S. Pat. 4,711,659 and 4,969,947 require that the substrate contain a minimum amount of reactive -NH2 groups. Thus, these are not applicable to all fertilizer compositions for which the slow release properties may be desirable. The coating of fertilizer compositions with a biodegradable polymer was described in U.S. Pat. 5,176,734 and 5,206,341 and in Japanese Patent Application No. 146492/1991. These references describe the coating of the fertilizer composition with a biodegradable coating material in a single layer. The single-layer coating has difficulties in controlling the rate of dissolution of fertilizer nutrients while maintaining biodegradability. Japanese Patent Application No. 97561/1993 describes a three-layer coating, which was prepared using a type of biodegradable film and a water-soluble resin. This coating also has difficulty in controlling both the rate of dissolution and the biodegradability at the same time. The thickness of the dressing material is described as 500 to 2,000 μm. Said coating material requires a higher cost, thus making it questionable for commercial use. Canadian Patent Application No. 2,135,788 relates to the coating of fertilizer compositions with at least two types of coating materials, where the two coating materials have different dissolution rates and moisture permeability in a multilayer structure. U.S. Pat. 5,538,531 describes also controlled release fertilizers and a method for their production. These controlled release fertilizers have a central mass of particulate fertilizer containing at least one water soluble plant nutrient surrounded by a plurality of coatings. The inter-no coating consists of the reaction product of (A) an aromatic polyisocyanate or derivatives thereof, which contain about 1.5 to 3 NCO groups per molecule and an NCO group content of 10 to 50% by weight, and (B) a polyol having from 2 to 6 hydroxyl moieties and at least one alkyl moiety which It contains approximately 10 to 22 carbon atoms. An external coating is also necessary. The external coating essentially consists of an organic wax having a melting point of pouring between 50 and 120 ° C. U.S. Pat. 5,704,962 describes compositions for the treatment of granular fertilizers, to reduce dust and reduce the caking of fertilizers during storage. These compositions consist of fatty onoamines, specifically fatty secondary dialkylamines or their mixtures as primary fatty amines. The advantages of the present invention include the fact that better overall properties of fertilizer release are produced at a given percentage of organic encapsulant. Moreover, the present invention does not require a central isocyanate-reactive base, so that any isocyanate and isocyanate-reactive component application sequence can be used. The present invention also makes it possible to mix the isocyanate and the isocyanate-reactive components before applying them to the surface of the fertilizer. Finally, by incorporating a moisture curing catalyst into the curing mass, the odors that can be attributed to the amine catalysts are significantly reduced. COMPENDIUM OF THE INVENTION This invention relates to a process for producing granular fertilizer particles coated with symmetrical polyurea-urethane and with the coated granular fertilizer particles produced by this process. The polyurea-urethane-urea coatings consist of a) at least one polyisocyanate, preferably a polyisocyanate aromatic liisocyanate, more preferably a polymethylene poly (phenyl isocyanate), and b) at least one alkanolamine corresponding to the general formula: wherein: Ri represents a hydrogen atom or a Cx to C4 alkyl group; R2 and R3 may be the same or different and each represents a Ci to C4 alkyl group or a -CH2-CH-OH group Ri where: Ri is defined as before; or R2 and R3 are joined together in a ring, thus forming a cyclic ring of 3 to 8 members; And x represents a number from 1 to 4. The process of producing granular fertilizer particles coated with symmetrical polyurea-urethane of the present invention consists in the steps of 1) coating fertilizer particles with a first compound, followed by coating with a second compound, the first and the second compound being capable of reacting to form a urethane containing terminal isocyanate groups, and 2) polymerizing the urethane adduct of 1) with moisture on the surface of the fertilizer particles to form a sealant coating. symmetrical polyurea-urethane that imparts slow release properties to the fertilizer. Suitable compounds consist of a) at least one organic polyisocyanate, preferably an aromatic polyisocyanate, more preferably a polymethylene poly (phenyl isocyanate), and b) at least one alkanolamine corresponding to the formula (I). The amounts of components a) and b) used to form the polyurea-urethane layer should be such that the NCO: H ratio is from about 1.6: 1 to about 10: 1, preferably 2.0: 1 to 10: 1, more preferably 2: 1 to 8: 1 and, more preferably, 4: 1 to 8: 1: These compounds are applied in amounts sufficient for the granular fertilizer particles coated with polyurea-urethane symmetrically contain from about 0.5 to about 15%, preferably from 1 to 10%, more preferably from 3 to 7% by weight of polyurea-urethane, based on the total weight of the particles of fertilizer encapsulated. In the present invention, the NCO: H ratios here disclosed are defined as the relative molar amounts of isocyanate groups to isocyanate-reactive groups necessary to form an asymmetric polyurea-urethane layer, or poly-lurea, polyurethane, etc. The percentage by weight of encapsulating material is based on the weight of the fertilizer particles, as well as the combined weight of all the layers of encapsulating materials. In one embodiment of the present invention, the method consists in: 1) applying a) at least one organic polyisocyanate, preferably an aromatic polyisocyanate, more preferably polymethylene poly (phenyl isocyanate), to fertilizer particles containing at least one nutrient for water-soluble plants, to form isocyanate coated fertilizer particles; 2) apply b) at least one alkanolamine compound, corresponding to formula (I) above, on the isocyanate-coated fertilizer particles of step 1) to obtain fertilizer particles encapsulated in urethane, where the urethane contains isocyanate end groups; 3) polymerize the urethane adduct of 2) with moisture to form a symmetrical polyurea-urethane sealant coating, and, optionally, 4) repeat steps 1) to 3) as many times as necessary, replacing the encapsulated fertilizer particles in polyurea-urethane from stage 3) to the fertilizer particles from stage 1) above. In this embodiment, the total amounts of components a) and b) are such that the NCO: H ratio in each encapsulation layer is from about 1.6: 1 to about 10: 1, preferably 2.0: 1. to 10: 1, more preferably from 2: 1 to 8: 1 and, more preferably, from 4: 1 to 8: 1. These compounds are applied in sufficient amounts so that the granular fertilizer particles coated with symmetrical polyurea-urethane contain approximately 05 to about 15% by weight, preferably from 1 to 10%, more preferably from 3 to 7% by weight of polyurea-urethane, based on the total weight of the encapsulated fertilizer particles. In another embodiment of the present invention, the method consists of: 1) applying b) at least one alkanol-amine compound corresponding to formula (I) above to fertilizer particles containing at least one water-soluble plant nutrient, to form alkaline-amine coated fertilizer particles; 2) apply a) at least one organic polyisocyanate, preferably an aromatic polyisocyanate, more preferably polymethylene poly (phenyl isocyanate), onto the alkanolamine coated fertilizer particles of step 1) to obtain fertilizer particles encapsulated in urethane, where the urethane contains isocyanate end groups; 3) polymerizing the urethane adduct of 2) with moisture to form a symmetrical polyurea-urethane sealant coating, and, optionally, 4) repeating steps 1) to 3) as many times as necessary to form the desired thickness of the coating. symmetric polyurea-urethane that encapsulates the fertilizer particles, replacing the fertilizer particles encapsulated in symmetrical polyurea-urethane from stage 3) to the fertilizer particles from stage 1) above. In this embodiment, the total amounts of components a) and b) are such that the NCO: H ratio present in each encapsulation layer is from about 1.6: 1 to about 10: 1, preferably from 2.0: 1 to 10: 1, more preferably from 2: 1 to 8: 1 and, more preferably, from 4: 1 to 8: 1. These compounds are applied in sufficient amounts, so that the granular fertilizer particles coated with symmetrical polyurea-urethane contain from about 0.5 to about 15% by weight, preferably from 1 to 10%, more preferably from 3 to 7% by weight of polyurea-urethane, based on the total weight of the encapsulated fertilizer particles. DETAILED DESCRIPTION OF THE INVENTION In the present invention, the term symmetric with respect to polyurea-urethanes refers to the fact that the residual groups attached to the urea group are equal to each other, while, in asymmetric polyurea-urethanes, these groups residuals are different. This is due to the fact that the urea portion arises from the reaction of the isocyanate with the amines generated by the reaction of a portion of the isocyanate with water. As used herein, the term "molecular weight" refers to the number-average molecular weight (Mn) and is determined by analysis of final groups. Examples of suitable polyisocyanates that can be used as the polyisocyanate component according to the present invention include monomeric diisocyanates, preferably NCO prepolymers and, more preferably, polyisocyanate adducts. Suitable monomeric diisocyanates can be represented by the formula: R (NCO) 2 where R represents an organic group obtained by separating the isocyanate groups from an organic diisocyanate having a molecular weight of from about 56 to 1,000, preferably from about 140 to 400. Preferred diisocyanates for the process according to the invention are those represented by the above formula, wherein R represents a divalent aliphatic hydrocarbon group having from 4 to 18 carbon atoms, a divalent cycloaliphatic hydrocarbon group having from 5 to 15 carbon atoms. carbon, a divalent araliphatic hydrocarbon group having from 7 to 15 carbon atoms or a diva-lens aromatic hydrocarbon group having from 6 to 15 carbon atoms. Examples of suitable organic diisocyanates include 1,4-tetramethylene diisocyanate, 1,6-hexamethylene diisocyanate, 2,2,4-trimethyl-1,6-hexamethylene diisocyanate, 1, 12-dode-cametylene diisocyanate, cyclohexane-1,3- and -1,4-diisocyanate, l-isocyanate-2-isocyanatomethylcyclopentane, 1-isocyanato-3-isocyanatomethyl-3,5,5-trimethylcyclohexane (isophorone diisocyanate or DIIF), bis (4-isocyanatocyclohexyl) methane, 2,4'-dicyclohexylmethane diisocyanate, 1,3- and 1,4-bis- (isocyanatomethyl) cyclohexane, bis (4-isocyanato-3-methylcyclohexyl) methane, diisocyanate of a, a, a ', a' -tetramethyl-1, 3-y / o -1, 4-xylylene, l-isocyanato-l-methyl-4 (3) -isocyanatomethylcyclohexane, 2,4- and / or diisocyanate 2,6-hexahydrotoluene, diisocyanate of 1, 3- and / or 1,4-phenylene, 2,4- and / or 2,6-toluene diisocyanate, 2,4- and / or 4,4'-diphenylmethane diisocyanate, 1,5-diisocyanatophthalene and mixtures do these It is also possible to use aromatic polyisocyanates containing 3 or more isocyanate groups, such as 4,4 ', 4"-triphenylmethane diisocyanate and polymethylene poly (phenyl isocyanates) obtained by phosgenation of añiline / formaldehyde condensates. present invention, at least a portion of the polyisocyanate component can be present in the form of an NCO prepolymer or a polyisocyanate adduct, more preferably a polyisocyanate adduct.They are suitable polyisocyanate adducts containing isocyanurate, uretdione, biuret, urethane, allophanate, carbodiimide and / or oxadiazinetrione The polyisocyanate adducts have an average functionality of 2 to 4 and an NCO content of 5 to 30% by weight.The following types of components are included as suitable adducts / prepolymers: 1) Polyisocyanates containing isocyanurate groups, which can be prepared as described in DE-PS 2,616,416, EP-OS 3,765, EP-OS 10,589, EP-OS 47,452, US-PS 4,288,586 and US-PS 4,324,879. The isocyanato isocyanurates generally have an average NCO functionality of from 3 to 4.0, preferably from 3.2 to 3.6, and an NCO content of from 5 to 30%, preferably from 10 to 25% and, more preferably, from 15 to 25% by weight. 2) uretdione diisocyanates, which can be prepared by oligomerization of a portion of the isocyanate groups of a diisocyanate in the presence of a trialkyl phosphine catalyst and which can be used in admixture with other aromatic, aliphatic and / or cycloaliphatic polyisocyanates, particularly those polyisocyanates containing isocyanurate groups indicated above in (1). 3) Polyisocyanates containing biuret groups, which can be prepared according to the procedures described in US Pat. Nos. 3,124,605, 3,358,010, 3,655,490, 3,862,973, 3,906,126, 3,903,127, 4,051,165, 4,147,714 or 4,220,749, using co-reactants such as water, tertiary alcohols, primary monoamines and secondary and primary and / or secondary diamines. These polyisocyanates preferably have an NCO content of 18 to 22% by weight and an average NCO functionality of 3 to 3.5. 4) Polyisocyanates containing urethane groups, which can be prepared according to the process described in US Pat. No. 3,183,112, by reacting excess amounts of polyisocyanates, preferably diisocyanates, with glycols and low molecular weight polyols, having molecular weights of less than 400, such as tripropylene glycol, trimethylolpropane, glycerin, 1-2. dihydroxypropane and its mixtures. The polyisocyanates containing urethane groups have a more preferred NCO content of 12 to 20% by weight and (average) NCO functionality of 2.5 to 3. 5) Polyisocyanates containing allophanate groups, which can be prepared according to procedures described in US Pat. No. 3,769,318, 4,160,080 and 4,177,342. The polyisocyanates containing allophanate groups have a more preferred NCO content of 12 to 21% by weight and (average) NCO functionality of 2 to 4. 6) Polyisocyanates containing isocyanurate and allophanate groups, which can be prepared according to procedures described in US Pat. 5,124,427, 5,208,334 and 5,235,018, the descriptions of which are hereby incorporated by reference. 7) Polyisocyanates containing carbodiimide groups, which can be prepared by oligomerization of di- or po-Liisocyanates in the presence of known carbodiimidation catalysts, as described in DE-PS 1,092,007, US-PS 3,152,162 and DE- OS 2,504,400, 2,537,685 and 2,552,350. 8) Polyisocyanates containing oxadiazinetrione groups and containing the reaction product of two moles of a diisocyanate and one mole of carbon dioxide. Preferred polyisocyanate adducts are polyisocyanates containing urethane groups, isocyanurate groups, biuret groups or mixtures of isocyanurate and allophanate groups.

The NCO prepolymers, which may also be used as the polyisocyanate component according to the present invention, are prepared from the above-described monomeric polyisocyanates or polyisocyanate adducts, preferably monomeric diisocyanates, and organic compounds containing at least two isocyanate-reactive groups, preferably at least two hydroxy groups. These organic compounds include high molecular weight compounds having molecular weights of 500 to about 5,000, preferably 800 to about 3,000 and, optionally, low molecular weight compounds with molecular weights less than 400. Molecular weights are number average molecular weights (Mn) and are determined by final group analysis (OH number). The products obtained by reaction of polyisocyanates exclusively with low molecular compounds are polyisocyanate adducts containing urethane groups and are not considered to be NCO prepolymers. It is preferred that the polyisocyanates for the present invention are aromatic polyisocyanates. Examples of suitable aromatic polyisocyanates are 1,3- and / or 1,4-phenylene diisocyanate, 2,4- and / or 2,6-toluene diisocyanate, 2,4'- and / or 4,4-diisocyanate. '-diphenylmethane, 1,5-diisocyanatophthalene and their mixtures. Aromatic polyisocyanates containing 3 or more isocyanate groups, such as 4,4 ', 4"-triphenylmethane diisocyanate and polymethylene poly (phenyl isocyanates), obtained by phosphonic condensation of aniline / formaldehyde can also be used. It is preferred that the polyisocyanates for the presently claimed invention be polymethylene poly (phenyl isocyanate) compositions with a functionality of from about 2.1 to about 3.5, preferably 2.2 to 3.2 and, more preferably, 2.3 to 2.8, and an NCO group content of about 26% to 33.6%, preferably from about 30.5% to about 33%, and a monomer content of about 30% to about 90 % by weight, preferably from about 40% to about 70%, where the monomer content consists of up to about 5% by weight of the 2,2'-isomer, from about 1 to about 20% by weight of the is 2,4 'oxide and from about 25 to about 65% by weight of the 4,4' isomer, based on the total weight of the composition. The polymeric DIM content of these isocyanates ranges from about 10 to about 70% by weight, preferably from about 20% to about 60% by weight.

Polymeric DIM, as used herein, refers to products containing three rings and / or more rings derived by phosgenation of condensation products of aniline-iormaldehyde. More preferred polyisocyanates include, for example, polymethylene poly (phenyl isocyanate) compositions having an average functionality of from about 2.2 to about 3.2, preferably from about 2.3 to about 2.8, a content in NCO groups of about 26 to 33% by weight and a monomer content of about 40 to about 80% by weight, wherein the monomer content consists of no more than about 3% by weight of isomer 2, 2 ', from about 2 to about 25% by weight of the 2, 4' isomer and from about 35 to about 60% by weight of the 4,4 'isomer, based on the total weight of the mixture. This isocyanate composition consists of about 20 to about 60% by weight of polymeric DIM. Also suitable are mixtures of polyisocyanate compositions as described above with DIM adducts, including, for example, DIM allophanates, as described, for example, in US Pat. 5,319,053, 5,319,054 and 5,440,003, the descriptions of which are hereby incorporated by reference; DIM urethanes as described, for example, in US Pat. 5,462,766 and 5,558,917, the descriptions of which are hereby incorporated by reference, and DIM carbodiimides, as described, for example, in US Pat. 2,853,473, 2,941,966, 3,152,162, 4,088,665, 4,294,719 and 4,244,855, the descriptions of which are hereby incorporated by reference. Suitable alkanolamines for the present invention include the alkanolamines corresponding to the general formula: wherein: Ri represents a hydrogen atom or an alkyl group Ci to C; R2 and R3 may be the same or different and each represents a Ci to C4 alkyl group or a -CH2-CH-OH group where : Ri is defined as before; or R2 and R3 are joined together in a ring, thus forming a cyclic ring of 3 to 8 members, and x represents a number of 1 to 4. In general, these alkanolamines have molecular weights of from about 89 to about 360, more preferably from About 89 to about 160. It is also preferred that these alkanolamines contain from 1 to 4 tertiary amine groups and from 1 to 6 hydroxyl groups, more preferably from 1 to 2 tertiary amine groups and from 1 to 4 hydroxyl groups and, more preferably, 1 tertiary amine group and from 1 to 3 hydroxyl groups. According to the present invention, it is possible to be able to use a mixture of two or more alkanolamines corresponding to the formula (I) above. To reduce the processing time, a mixture of an alkanolamine corresponding to formula (I) above can be used with at least one polyamine capable of reacting with isocyanate groups. This combination would result in a mixture of symmetric and asymmetric polyurea urethanes. Virtually any mixture containing at least one alkanolamine corresponding to formula (I) above in the present invention can be used, under the following conditions: (i) that alkanolamines containing primary and / or secondary amine groups are preferably not and (ii) that diethylene glycol is preferably not present. In fact, it is preferred that the alkanolamines corresponding to the formula (I) of the present invention are not mixed or used together with any other isocyanate-reactive component containing hydroxyl groups. Examples of suitable alkanolamines for use in the present invention include, but are not limited to, compounds such as N-methyldiethanolamine, N, N-dimethylethanolamine, triethanolamine, N, N-diethylethanolamine, N, N, N ', N' -tetraethanolethylenediamine, N, N'-dimethyl-N, N-diethanolethylenediamine, N-ethanolpiperidine, N-ethanol-pyrrolidine, N-ethanolmorpholine, etc. Preferred alkanolamines include N, N-dimethylethanolamine, N-methyldiethanolamine and triethanolamine. It is also possible to include other additives in the isocyanate reactive component or in the polyisocyanate component before applying the component to the fertilizer particles. Possible additives include, for example, catalysts, preferably ones that are non-toxic and do not contain heavy metals; flow aids; surfactants; defoamers, and other additives known to those skilled in the art. Any additive that aids in the formation of the symmetrical polyurea-urethane coating that encapsulates the fertilizer particles in one or both of these components can be included. It is preferred, however, not to include additional catalysts in either of the two components. It is more preferred not to use heavy metal catalysts in the process of the present invention. Suitable fertilizer particles for the present encapsulation process include any of the known chemical fertilizers. Some examples are ammonium sulfate, ammonium nitrate, urea, guanidine, inelamin, sodium nitrate, ammonium phosphate, potassium phosphate and combinations of these. These fertilizer particles are obviously soluble in water. In the present application, it is not necessary, although it is, however, acceptable, that the fertilizer particles contain some reactive functional groups, such as, for example, NH2 groups. As used herein, the phrase "fertilizer particles" refers to any of the commercial particulate fertilizers, which are produced and marketed in various types of particle. Some examples include granular fertilizers, pellets, powders, pills and pips. A controlled release particulate fertilizer resistant to attrition can be prepared by applying the isocyanate reactive component and the polyisocyanate to fertilizer particles, which are heated to a temperature between about 60 and 105 C. The fertilizer particles are maintained in a continuous movement of low cut and low impact in relation to each other by means of a mixing apparatus. Examples of suitable mixing apparatuses include fluidized bed, rotary drum, bucket granulator and any other that can provide a continuous low-cut movement of the fertilizer particles. More specifically, controlled release fertilizers resistant to attrition can be produced (i) by disposing of a quantity of fertilizer particles and heating them to a temperature not higher than approximately 120 ° C; (Li) stirring the fertilizer particles in such a way that a gentle mixture of them is maintained; (iii) adding to the agitated fertilizer particles an isocyanate-reactive component consisting of at least one alkanolamine compound corresponding to the formula (I); (iv) adding, after uniformly spreading the isocyanate-reactive component, to the agitated fertilizer particles a polyisocyanate component in an amount such that the ratio of NCO groups to isocyanate-reactive groups is about 1.6: 1 , 0 to about 10.0: 1.0, preferably 2.0: 1 to 10.0: 1.0, more preferably 2: 1.0 to 8: 1.0 and, more preferably, 4: 1. to 8: 1; (v) allowing the polyisocyanate and the isocyanate-reactive materials to react, thereby forming a solidified symmetric polyurea-urethane coating on the fertilizer particles, and (vi) cooling the coated fertilizer particles to about room temperature or slightly above of it, with continuous agitation. The dosage of the streams of the poly-socyanate component and of the isocyanate-reactive component on the fertilizer particles can be continuous. It can, however, be advantageously discontinuous, when only a portion of the total amount of each of the two reagents is added and allowed to react before applying additional portions. The success in the application of the coatings of the present invention to particulate fertilizers depends on factors such as i) a fairly accurate temperature control, ii) a continuous movement of non-cutting of the fertilizer particles during the application of the coatings of urethane eventually successive and iii) followed by cooling. It is very important to maintain the movement of the particles to ensure continuous coatings and to prevent the agglomeration of the fertilizer particles.

It is not necessary for the fertilizer particles to contain reactive groups for the adhesion of the coating material and only a very small portion of the reactive groups in the fertilizer particles that contain them are actually exposed on the surface and these reactive groups are in a solid phase, which does not react easily with the liquid isocyanate component. It is possible to be able to use many different types of techniques and compositions in the encapsulation of fertilizer particles. In the spirit of this invention, it is necessary that at least one layer consist of the symmetric polyurea-urethane of the present invention. Other compositions suitable for forming layers of encapsulating materials include, for example, those compositions as described in US Pat. copending serial numbers 08 / 777,426, filed December 30, 1996, and 08 / 777,427, filed December 30, 1996, both commonly assigned, and in the US Application Ser. Applicants (File Number of Agent Mo-4818), filed with the United States Patent and Trademark Office on the same day as the present invention. This embodiment can also result in other similar encapsulated fertilizer particles, where the composition of the encapsulating compounds used to form layers on the fertilizer particles varies. Suitable encapsulating compounds consist of symmetrical polyurea urethanes of the present invention, other layers being selected from symmetric polyureas, polyurethanes, polyurea urethanes, etc. In the present invention, it is preferred not to use polymer coatings formed by copolymerization of diethylene glycol triethanolamine polyol and a diisocyanate and, in fact, they are preferably absent in the process of forming encapsulating layer compositions of the present invention. However, to improve the resistance to attrition of the encapsulated fertilizer particles, it is possible to increase the flexibility of the polymer coatings by incorporation of higher molecular weight polyols, preferably polyether polyols, known to those skilled in the art. The following examples still illustrate details for the methods and products of this invention. The invention, set forth in the foregoing description, is not limited in spirit or scope by these examples. Those skilled in the art will readily understand that known variations of the conditions of the following procedures can be used. Unless otherwise indicated, all temperatures are degrees Celsius and all parts and percentages are parts by weight and percentages by weight, respectively. EXAMPLES The following components were used in the examples. L-succinate A: A polymethylene poly (phenyl isocyanate) containing 64% of diphenylmethane diisocyanate monomers and 36% of higher functional homologs and having an overall isocyanate group content of approximately 32.3% and a functionality of 2.3. Isocyanate B: A mixture of polymethylene poly (phenyl isocyanate) modified with urethane having an average functionality of about 2.4 and an average content in NCO groups of about 27%. This mixture was prepared by mixing equal amounts of (i) a polymethylene poly (phenyl isocyanate) containing 43% diphenylmethane diisocyanate monomers and 57% homologs of higher functionality and having an overall isocyanate group content. of about 32.0% and a functionality of 2.7 to 2.8 and (ii) a prepolymer of 182 equivalent weight prepared by the reaction of 4,4 '-diphenylmethane diisocyanate with a technical grade of tripropylene glycol to a content in NCO of 23%. Example 1: (Comparative Example) N-Methyldiethanolamine (0.73 g) was added to 100 g of Agway 5-10-10 fertilizer pellets in an 8-ounce bottle. The bottle was stirred until the N-methyldiethanolamine was deposited on the pellets (approximately 2 to 3 minutes). Isocyanate A (1) was added, 6 g) were added to the alkanolamine coated pellets and the bottle was stirred until the isocyanate coated the alkanolamine coated fertilizer pellets (approximately 5 minutes). This mixture was poured into an aluminum bucket and placed in a 110 C oven (the pellets were mixed 2 to 3 times while in the oven to prevent the pellets from adhering to each other) until they were dry and no longer adhered to each other (approximately 10 minutes). This process of coating and heating the pellets was repeated twice more using the same amounts of alkanolamine and isocyanate. Theoretically, this procedure would result in approximately 6.53% polyurea-urethane encapsulation of the pellets, based on the total weight of the encapsulated fertilizer particles. However, the actual amount of encapsulation in polyurea-urethane was about 5.9%, due to the loss of coating on the walls of the bottle. Example 2: (Comparative Example) Triethanolamine (0.63 g) was added to 100 g of Agway 5-10-10 fertilizer pellets in an 8-ounce bottle. The bottle was shaken until the triethanolamine was deposited on the pellets (approximately 2 to 3 minutes). Isocyanate a (1.65 g) was added to the alkanolamine coated pellets and the bottle was stirred until the isocyanate coated the alkanol amine-coated fertilizer pellets (approximately 5 minutes). This mixture was poured into an aluminum tray and put in an oven at 110 ° C (the pellets were mixed 2 to 3 times while in the oven to prevent the pellets from adhering to each other) until they were dry and no longer they adhered to each other (approximately 10 minutes). This method of coating and heating the pellets was repeated two more times using the same amounts of alkanolamine and isocyanate. After the third coating, the pellets were left in the oven for 2 hours at 110 C. Theoretically, this would result in approximately 6.4% encapsulation in polyurethane, based on the total weight of the encapsulated fertilizer particles. However, the actual amount of polyurea-urethane encapsulation was about 5.8%, due to the loss of coating on the walls of the bottle. Example 3: Isocyanate A (2.29 g) was added to 100 g of Agway 5-10-10 Fertilizer pellets in an 8-ounce bottle. This bottle was stirred until the isocyanate was deposited on the pellets (approximately 2 to 3 minutes). N-methyldiethanolamine (0.26 g) was added to the isocyanate-coated pellets and the bottle was stirred until the alkanolamine coated the isocyanate-coated fertilizer pellets (approximately 2 to 3 minutes). The mixture was poured into an aluminum tray and allowed to cure at room temperature (the pellets were mixed while they were in the tray to prevent the pellets from adhering to each other) until they were dry and no longer adhered to one another (approximately 30 to 60 minutes). This process of coating and heating the pellets was repeated two more times using the same amounts of alkanolamine and isocyanate. After the last coating, the pellets were left in the bucket overnight to cure. Theoretically, this would result in approximately 7.11% encapsulation in polyurea-urethane, based on the total weight of the encapsulated fertilizer particles. However, the actual amount of encapsulation in polyurea-urethane was about 6.5%, due to the loss of coating on the walls of the bottle. Example 4: Dimethylethanolamine (0.60 g) was added to 100 g of Agway 5-10-10 fertilizer pellets in an 8-ounce bottle. The bottle was stirred until the dimethylethanolamine was deposited on the pellets (approximately 2 to 3 minutes). Isocyanate A (1.76) was added to the alkanolamine-coated pellets and the bottle was stirred at room temperature until the isocyanate coated the alkanolamine-coated fertilizer pellets and the pellets were dry and no longer adhered to each other (approximately 5%). minutes). This procedure was repeated twice more using the same amounts of alkanolamine and isocyanate. After 5 minutes, the third coating was not dry, so the pellets were poured into an aluminum tray at room temperature until the pellets were dry (approximately 1 minute). Theoretically, this would result in approximately 6.61% encapsulation in polyurea-urethane, based on the total weight of the encapsulated fertilizer particles. However, the actual amount of encapsulation in polyurea-urethane was about 6.0%, due to the loss of coating on the walls of the bottle.

Example 5: Isocyanate A (2.0 g) was added to 100 g of Agway 5-10-10 fertilizer pellets in an 8-ounce bottle. The bottle was stirred until the isocyanate was deposited on the pellets (approximately 2 to 3 minutes). Dimethylethanolamine (0.34 g) was added to the isocyanate-coated pellets and the bottle was shaken until the alkanolamine coated the pellets. Isocyanate coated fertilizer (approximately 2 to 3 minutes). This mixture was poured into an aluminum tray and allowed to cure at room temperature (the pellets were mixed periodically in the bucket to prevent the pellets from adhering to each other) until they were dry and no longer adhered to each other (approximately 3 minutes) This coating procedure was repeated and cured twice more using the same amounts of alkanolamine and isocyanate After the last layer, the pellets were left Theoretically, this would result in approximately 6.56% encapsulation in polyurea-urethane, based on the total weight of the product. The encapsulated fertilizer particles. However, the actual amount of en-capsulation in polyurea-urethane was about 5.9%, due to the loss of coating on the walls of the bottle.

Example 6: Isocyanate A (2.0 g) was added to Harvest King 5-10-10 fertilizer pellets in an 8 oz bottle. The bottle was stirred until the isocyanate was deposited on the pellets (approximately 2 minutes). Dimethylethanolamine (0.17 g) was added to the isocyanate coated pellets and the bottle was stirred until the isocyanate coated the isocyanate-coated fertilizer pellets (approximately 2 minutes). This mixture was poured into an aluminum bucket and allowed to cure at room temperature (the pellets were mixed periodically in the bucket to prevent the pellets from adhering to each other) until they were dry and no longer adhered to each other (approximately 3 minutes). This process of coating and mixing / curing at room temperature was repeated two more times using the same amounts of alkanolamine and isocyanate. The last layer was left in the bucket overnight for curing. Theoretically, this would result in approximately 6.11% encapsulation in polyurea-urethane, based on the total weight of the encapsulated fertilizer particles. However, the actual amount of encapsulation in polyurea-urethane was about 5.5%, due to the loss of coating on the walls of the bottle. Example 7: Isocyanate B (2.0 g) was added to 100 g of Harvest King 5-10-10 fertilizer pellets in an 8-ounce bottle. The bottle was stirred until the isocyanate was deposited on the pellets (approximately 2 minutes). Di-methylethanolamine (0.17 g) was added to the isocyanate-coated pellets and the bottle was stirred until the alkanolamine coated the isocyanate-coated fertilizer pellets (approximately 2 minutes). This mixture was poured into an aluminum tray and allowed to cure at room temperature (the pellets were mixed periodically in the bucket to prevent the pellets from adhering to each other) until they were dry and no longer adhered to one another (approximately 3 minutes). This coating and mixing / curing process was repeated at room temperature two more times using the same amounts of alkanolamine and isocyanate. The last layer was left in the bucket overnight for curing. Theoretically, this would result in approximately 6.05% encapsulation in polyurea-urethane, based on the total weight of the encapsulated feryl tillers. However, the actual amount of polyurea-urethane encapsulation was about 5.4%, due to the loss of coating on the walls of the bottle. Test procedure for the slow release properties After one week, the encapsulated fertilizer granules were compared with unmodified fertilizer using the following test procedure: 20 g of the fertilizer were combined with 80 g of water and stored at room temperature. environment in a glass jar closed for 8 h and 20 h. After this time, the solids were filtered and the amount of dissolved solids in the aqueous phase was determined after evaporation of the water for 4 h in a furnace at ioo'c.

TABLE 1: PROPERTIES OF SLOW RELEASE 1 Average of two (2) operations. 2 Average of three (3) operations, 3 Comparative example TABLE 2: Although the invention has been described in detail in the foregoing for illustrative purposes, it is to be understood that said detail has only that purpose and that those skilled in the art can make variations therein without departing from the spirit and scope of the invention, except in what may be limited by the claims.

Claims (21)

Claims

1. A process for the preparation of granular fertilizer particles coated with symmetrical polyurea-urethane, consisting of the following steps: 1) coating fertilizer particles with a first compound, followed by coating with a second compound, said first and second compounds being capable of react to form a urethane containing terminal isocyanate groups; 2) polymerizing the urethane adduct of l) with moisture on the surface of said fertilizer particles to form a symmetrical polyurea-urethane sealant coating imparting slow release properties to the fertilizer, wherein said compounds consist of a) at least one polyiso - '"Organic Lanate and b) at least one corresponding alkanolamine tooth to the formula: where: Ri represents a hydrogen atom or a Ci to C4 alkyl group; R2 and R3 may be the same or different and each represents a C1 to C4 alkyl group, a group -CH2-CH-OH Ri where: Ri is defined as before; or R2 and R3 are joined together in a ring, thus forming a cyclic ring of 3 to 8 members, and x represents a number from 1 to 4, with the amounts of a) and b) being the NCO: H ratio in each encapsulating layer is from about 1.6: 1 to about 10: 1, and where the resulting symmetrical polyurea-urethane coated granular fertilizer particles contain from about 0.5 to about 15% by weight of polyurethane-urethane, in based on the total weight of the encapsulated fertilizer particles.

2. The process of Claim 1, wherein a) said organic polyisocyanate consists of an aromatic polyisocyanate.

3. The process of Claim 2, wherein a) said organic polyisocyanate consists of polymethylene po-li (phenyl isocyanate).

4. The method of Claim 3, wherein the polymethylene poly (phenyl isocyanate) has a functionality of about 2.1 to 3.5, a content of NFCO groups of about 26% to about 33.6%, a content of Polymeric DIM of about 10 to 70% by weight and a monomer content of about 30 to 90% by weight.

5. The method of Claim 3, wherein the polymethylene poly (phenyl isocyanate) has a functionality of from 2.3 to 2.8, a NCO group content of from about 26% to about 33%, a polymeric DIM content of about 20% to about 60% by weight and a monomer content of about 40 to 80% by weight.

6. The process of Claim 1, wherein said alkanolamines have molecular weights of from about 90 to about 260 and contain from 1 to 2 tertiary amine groups and from 1 to 4 hydroxyl groups.

7. The process of Claim 1, wherein said alkanolamine is selected from the group consisting of dimethylethanolamine, N-methyldiethanolamine, triethanolamine and mixtures thereof.

8. A process for the preparation of granular fertilizer particles coated with symmetrical polyurea-urethane consisting of: 1) applying a) an organic polyisocyanate component to fertilizer particles containing at least one water-soluble plant nutrient, to form coated fertilizer particles of isocyanate; 2) apply b) at least one alkanolamine compound corresponding to the formula: wherein: Ri represents a hydrogen atom or a Ci to C4 alkyl group; R2 and R3 may be the same or different and each represents a Ci to C4 alkyl group or a group -CH2-CH-OH I Ri where Ri is defined as above; or R2 and R3 are joined together in a ring, thus forming a cyclic ring of 3 to 8 members, and x represents a number from 1 to 4; on the isocyanate-coated fertilizer particles of step 1), to obtain a urethane containing terminal isocyanate groups; polymerize the urethane adduct of 2) with moisture to obtain fertilizer particles encapsulated in symmetrical polyurea-urethane, the amounts of components a) and b) being such that the NCO: H ratio in each encapsulating layer is from about 1.6: 1 to about 10: 1, and, eventually, 4) repeating steps 1) to 3) as many times as necessary, where the fertilizer particles encapsulated in symmetrical polyurea-urethane of step 3) replace the fertilizer particles of step 1) above, where the resulting encapsulated fertilizer particles contain about 0, 5 to about 15% by weight of polyurea-urethane, based on the total weight of the encapsulated fertilizer particles.

9. The process of Claim 8, k wherein a) said organic polyisocyanate consists of an aromatic polyisocyanate.

10. The process of Claim 9, wherein a) said organic polyisocyanate consists of polymethylene poly (phenyl isocyanate).

11. The method of Claim 10, wherein the polymethylene poly (phenyl isocyanate) has a functionality of about 2.1 to 3.5, a NCO group content of about 26% to about 33.6%, a content of Polymeric DIM of about 10 to 70% by weight and a monomer content of about 30 to 90% by weight.

12. The method of Claim 10, wherein the polymethylene poly (phenyl isocyanate) has a functionality of from 2.3 to 2.8, an NCO group content of from about 26% to about 33%, a polymeric DIM content of about 20% to about 60% by weight and a monomer content of about 40 to 80% by weight.

13. The process of Claim 8, wherein said alkanolamines have molecular weights of from about 90 to about 260 and contain from 1 to 2 tertiary amine groups and from 1 to 4 hydroxyl groups.

14. The process of Claim 8, wherein said alkanolamine is selected from the group consisting of dimethylethanolamine, N-methyldiethanolamine, triethanolamine and mixtures thereof.

15. A process for the preparation of symmetrical polyurea-urethane coated fertilizer particles consisting of: applying b) at least one alkanolamine compound corresponding to the formula: where: R x represents a hydrogen atom or a C x to C 4 alkyl group; R2 and R3 may be the same or different and each represents a Cx to C4 alkyl group or a group -CH2-CH-OH I Ri where Rx is as defined above; or R2 and R3 are joined together in a ring, thus forming a cyclic ring of 3 to 8 members, Y x represents a number of 1 to 4; on fertilizer particles containing at least one plant nutrient soluble in water, to form alkanolamine coated fertilizer particles; 2) applying a) an organic polyisocyanate component onto the alkanolamine coated fertilizer particles of step 1) to obtain a urethane containing terminal isocyanate groups; 3) polymerizing the urethane adduct of 2) with moisture to obtain fertilizer particles encapsulated in symmetrical polyurea-urethane, the amounts of components a) and b) being such that the NCO: H ratio in each encapsulating layer is about 1.6: 1 to about 10: 1, and, eventually, 4) repeating steps 1) to 3) as many times as necessary, where the fertilizer particles encapsulated in symmetrical polyurea-urethane from step 3) replace the fertilizer particles from step 1) above, wherein the resulting encapsulated fertilizer particles contain from about 0.5 to about 15% by weight of polyurea-urethane, based on the total weight of the encapsulated fertilizer particles.

16. The process of Claim 15, wherein a) said organic polyisocyanate consists of an aromatic polyisocyanate.

17. The method of Claim 16, wherein a) said organic polyisocyanate consists of polymethylene poly (phenyl isocyanate).

18. The method of Claim 17, wherein the polymethylene poly (phenyl isocyanate) has a functionality of about 2.1 to 3.5, a NCO group content of about 26% to about 33.6%, a content of Polymeric DIM of about 10 to 70% by weight and a monomer content of about 30 to 90% by weight.

19. The method of Claim 17, wherein the polymethylene poly (phenyl isocyanate) has a functionality of 2.3 to 2.8, a NCO group content of about 26% to about 33%, a DIM content. polymer from about 20% to about 60% by weight and a monomer content of from about 40 to 80% by weight.

20. The process of Claim 15, wherein said alkanolamines have molecular weights of about 90 to about 260 and contain from 1 to 2 tertiary amine groups and from 1 to 4 hydroxyl groups.

21. The process of Claim 15, wherein said alkanolamine is selected from the group consisting of dimethylethanolamine, N-methyldiethanolamine, triethanolamine and mixtures thereof.