Chemistry: fertilizers – Processes and products – Forms or conditioning
Reexamination Certificate
1996-12-30
2003-01-07
Langel, Wayne (Department: 1754)
Chemistry: fertilizers
Processes and products
Forms or conditioning
C071S064110
Reexamination Certificate
active
06503288
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a process for producing encapsulated fertilizers which are biodegradable. This process comprises applying at least one coat of an isocyanate-reactive component comprising at least one polyester polyol or at least one polyether polyol to fertilizer particles, and applying at least one coat of an organic polyisocyanate to fertilizer particles, thus forming polyurethane encapsulated fertilizer particles. The present invention also relates to the encapsulated fertilizers produced by this process.
Commercial particulate fertilizers are produced and marketed in several different particle types, i.e., granular, pelletized, dusts, pilled, and prilled fertilizers. Also, they may be formed of inorganic substances, organic substances, or combinations thereof. The improvements of the present invention can be applied to any of these types of particulate fertilizers.
In order to be effective in promoting plant growth, fertilizers must contain some amount of water soluble plant nutrients. These are typically in the form of water soluble compounds of nitrogen, phosphorus and potassium, alone or in combination, and often in conjunction with other elements such as, for example, calcium, boron, magnesium, zinc, chlorine, etc. Such particular fertilizers can be made of a single component, e.g., urea, ammonium nitrate, potassium chloride, etc., or of multiple components often mixed with inert water soluble or water insoluble materials as in common fertilizers designated as 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 optional additives such as herbicides, insecticides, trace elements, iron salts, sulfur, etc. The improvements 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 soluble plant food, causing phytotoxicity and the rapid depletion of the plant nutrients by leaching. Other problems included tendencies to cake and form dust. These problems are well documented in previous patents that professed solutions to one or more of the known defects, including U.S. Pat. Nos. 3,475,154, 3,259,482, 3,264,088, 3,264,089, 4,711,659, 4,772,490 and Japanese Patent 52-38361. The present invention provides additional improvements in the construction of particulate fertilizers which render them highly attrition resistant, biodegradable, and further extended release properties.
A number of slow release coatings for particular fertilizers have previously been proposed. The process of sulfur coating urea particles is described in U.S. Pat. No. 3,342,577 and was developed in the late 1960's by the Tennessee Valley Authority (TVA) as an economical system for reducing the rate of dissolution when urea particles are applied to the soil as fertilizer. This process requires high levels of sulfur, which reduces the nutrient analysis of the fertilizer particles, and even then, imperfections remain in the coating making it necessary to apply a sealant coating, which is composed of a mixture of 30% polyethylene resin in a 70% bright stock mineral oil.
Coatings in which preformed polymer resins are applied from solvents have been described in, for example, U.S. Pat. Nos. 3,475,154 and 3,264,089. The use of solvents creates a vapor hazard as the products are dried and the solvent evaporation step can result in pinhole imperfections in the coatings when applied.
U.S. Pat. No. 4,369,055 tried to facilitate degradation of coating materials while maintaining the function for controlling the dissolving-out rate by dispersing inorganic powders such as sulfur and talc in a low molecular weight olefin polymer. However, the disclosed coating materials are not completely degraded and thus remain intact in the soil.
Polyurethane coatings as disclosed in U.S. Pat. No. 4,711,659 and 4,969,947 require that the substrate contains a minimum quantity of reactive —NH
2
groups. Thus, these are not applicable to all fertilizer compositions for which slow release properties may be desirable.
Coating of fertilizer compositions with a biodegradable polymer was described in U.S. Pat. No. 5,176,734 and 5,206,341 and Japanese Patent Application No. 146492/1991. These references disclose coating the fertilizer composition with a biodegradable coating material in a single layer. The single layer coating has difficulties controlling the dissolving out rate of fertilizer nutrients while maintaining biodegradability simultaneously.
Japanese Patent Application No. 97561/1993 discloses a three layer coating which was prepared by using one type of biodegradable film and a water soluble resin. This coating also has difficulty in controlling both the dissolving-out rate and the biodegradability at the same time. The thickness of the coating material is disclosed as being from 500 to 2,000 &mgr;m. Such a coating material requires increased cost, thus making it unsuitable for commercial use.
Canadian Patent Application No. 2,135,788 relates to coating fertilizer compositions with at least two types of coating materials wherein the two coating materials have different dissolving-out rates and moisture permeability in a multi-layer structure.
U.S. Pat. No. 5,538,531 also describes controlled release fertilizers and a method for their production. These controlled release fertilizers have a central mass of particulate fertilizer which contains at least one water soluble plant nutrient surrounded by a plurality of coatings. The inner coating comprises 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 containing from about 10 to 22 carbon atoms. An outer coating is also necessary. The outer coating consists essentially of an organic wax having a drop melting point of between 50 and 120° C. These encapsulated fertilizers are not, however, biodegradable.
As used herein, the term biodegradable means a nearly quantitative biological degradation and conversion process (i.e., composting) of the coatings produced according to the present invention. Biodegradation is brought about mainly by bacteria such as, for example, actinomycetes and fungi such as, for example, members of the genera Aspergillus, Penicillium and Mucor and yeast. This requires an aerobic medium with sufficient moisture. Thus, the synthetic coating composition to be composted according to the present invention must satisfy several fundamental requirements. It must be completely mineralized without leaving a residue and converted into CO
2
and water or into a biomass (i.e., a living cell). Both the material (i.e., coating composition) and all metabolites and degradation products must be toxicologically and ecotoxicologically harmless.
Advantages of the present invention include the fact that this process provides a more uniform coating on the fertilizer particles with good time release properties while the fertilizer is being absorbed into the soil. Additionally, the coating degrades, leaving no harmful residue in the soil.
SUMMARY OF THE INVENTION
This invention relates to a process for the production of biodegradable polyurethane encapsulated fertilizer particles. This process comprises 1) applying a) an isocyanate-reactive component comprising one or more polyester polyols or one or more polyether polyols to fertilizer particles coated with an isocyanate-reactive component, wherein said polyester polyols and polyether polyols have functionalities of from 1.5 to 4, preferably from 2 to 3, and a molecular weight of from 500 to 5,000, preferably from 1,000 to 3,000; and 2) applying b) a (cyclo)aliphatic polyisocyanate to the fertilizer particles from step 1) to form polyurethane encapsulated fertilizer particles. These two steps are optionally repeated (successively) as many times as necessary to form the desired thickness of the
Bayer Corporation
Brown N. Denise
Gil Joseph C.
Langel Wayne
LandOfFree
Process for the production of biodegradable encapsulated... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Process for the production of biodegradable encapsulated..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Process for the production of biodegradable encapsulated... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3058099