Chemistry: fertilizers – Processes and products – Forms or conditioning
Reexamination Certificate
1999-03-25
2002-07-02
Griffin, Steven P. (Department: 1754)
Chemistry: fertilizers
Processes and products
Forms or conditioning
C071S064110, C071S064060, C427S212000, C427S213000, C427S213300, C427S213310
Reexamination Certificate
active
06413292
ABSTRACT:
The present invention relates to the use of a polyester dispersion comprising water and a biodegradable copolyester which contains structural units derived from both aliphatic and aromatic carboxylic acids or their derivatives, and to the coated fertilizer granules prepared using this polyester dispersion, and to a process for their preparation. The present invention furthermore relates to a fertilization method in which the coated fertilizer granules according to the invention are used.
It is generally known to employ, as fertilizers, fertilizer granules which are coated with a polymer layer. The coating increases the efficacy of these fertilizers because the coated fertilizer releases the substances which act as plant nutrients in a delayed manner and it can thus display its action over a prolonged period. Such slow-release fertilizers are described, for example, in Ullmann's Encyclopedia of Industrial Chemistry, 5th Edition 1987, Vol. A10, pp. 363-369, and the advantages are compiled in Fert. Res. 1993, Vol. 35, pp. 1-12.
A large number of fertilizer granules coated with biodegradable polymers have been described in the past.
Thus, WO 95/03260 relates to a fertilizer provided with a coating composed of two layers. This coated fertilizer, which can be used both in arable farming and in hydroponics, comprises an inner layer which is biodegradable and constructed of an aliphatic polyester and/or polyurethane and an outer layer which is insoluble in water and comprises polymers which are slowly biodegradable, for example biodegradable cellulose derivatives, low-coating, are especially high.
In general, it should be possible for the polymers used as coatings to be applied to the fertilizer starting granules without resorting to the use of organic solvents. The amount of polymer required for coating the granules in order to achieve a sufficiently pronounced slow-release effect should furthermore be as small as possible.
In addition, the coated fertilizer granules should have no tendency to stick, in particular at temperatures as they are normally found during storage or transport, without special precautions being necessary. However, this means that the coated fertilizer granules must also show virtually no tackiness at temperatures which are considerably above room temperature (25° C.).
On the other hand, the polymers used for the coating must not show undue hardness and brittleness, since the coating would otherwise be damaged, or could even chip off, when the coated fertilizer granules are exposed to mechanical stress as is the case, for example, during repackaging or, in particular, during mechanical spreading.
The above-described fertilizer granules of the prior art have as yet not been able to meet all these requirements. Problems occur in particular in relation to tackiness (in particular in the case of polyurethanes) and insufficient mechanical properties (in particular in the case of aliphatic polyesters).
The copolyesters used in accordance with the invention furthermore have good film-forming properties, which means that only small amounts of the copolyester are required for producing a stable layer, which is advantageous from an economical point of view.
Organic solvents for dispersing the copolyesters can largely or totally be dispensed with, so that it is possible (largely) to avoid the problems associated with the use of organic solvents, such as toxicity, disposal and explosion hazard, when preparing the dispersions according to the invention.
It is accordingly an object of the present invention to provide coated fertilizer granules which meet the above profile of requirements.
We have found that this object is achieved by the use of a polyester dispersion for coating fertilizer granules, which polyester dispersion comprises
(A) 20 to 90% by weight of water and
(B) 10 to 80% by weight of a biodegradable copolyester (B) with structural units derived from both aliphatic and aromatic carboxylic acids or their derivatives, obtainable by reacting a mixture which comprises:
(a1) a mixture comprising
(a11) 10 to 95 mol % of an aliphatic dicarboxylic acid or of a cycloaliphatic dicarboxylic acid or of an ester-forming derivative thereof or of a mixture of two or more thereof,
(a12) 5 to 90 mol % of an aromatic dicarboxylic acid or of an ester-forming derivative thereof or of a mixture of two or more thereof,
(a13) 0 to 10 mol % of a sulfonate-containing compound or of a mixture of two or more thereof,
the total of the individual mol percentages being 100,
(a2) a dihydroxy compound or an amino alcohol or a mixture of two or more thereof,
the molar ratio of (a1) to (a2) being selected within a range of from 0.4:1 to 2.5:1,
(a3) 0 to 10% by weight, based on the mixture (a1), of a chain extender or of a mixture of two or more thereof, and
(a4) 0 to 20% by weight, based on the mixture (a1), of a compound having at least three groups capable of ester formation or of a mixture of two or more thereof,
the recurring units derived from the (cyclo)aliphatic and aromatic carboxylic acid being randomly or alternately distributed, the copolyester having a viscosity number in the range of from 5 to 450 ml/g (measured in o-dichloro-benzene/phenol (weight ratio 50/50) at a concentration of 0.5% by weight of copolyester at 25° C.) and the amount of components (a13) and (a4) not simultaneously being in each case zero.
The biodegradable copolyesters which comprise recurring units, which are derived from both aromatic carboxylic acids or their derivatives and from aliphatic carboxylic acids or their derivatives and which are employed in the aqueous polyester dispersion used in accordance with the invention, are known per se and have been described in U.S. Pat. No. 5,446,079 and in the parallel international application WO 92/09654, in the DE-A-44 32 161 and in a series of applications of the Applicant Company itself (P 44 40 858.7, P 44 40 850.1, P 44 40 837.4, P 44 40 836.6, 195 00 757.0, 195 00 756.5, 195 00 755.7, 195 00 754.9, 195 05 185.8, 195 05 186.6).
Nevertheless, the aqueous dispersions of a biodegradable copolyester preferably used for the purposes of the present invention will be described hereinbelow.
The term “biodegradable” as used for the purposes of the present invention refers to the fact that the copolyesters, exposed to environmental factors, disintegrate after use according to the invention within an appropriate and measurable period. As a rule, degradation is hydrolytic and/or oxidative, but mostly due to the action of microorganisms such as bacteria, yeasts, fungi and algae. However, degradation may also be enzymatic, for example as described by Y. Tokiwa and T. Suzuki in “Nature”, Vol. 270, pp. 76-78, 1977. For the purposes of the present invention it is possible, by selecting a suitable ratio between recurring units derived from aliphatic carboxylic acids and those derived from aromatic carboxylic acids, to vary the biodegradation rate, ie. the point in time by which the polyesters used in accordance with the invention are essentially fully degraded. A rule of thumb says that the higher the proportion of recurring units derived from aliphatic carboxylic acids, the higher the biodegradation rate of the copolyesters. Furthermore, the higher the proportion of sections with alternating sequence of recurring units derived from aliphatic and aromatic carboxylic acids or their derivatives, the higher the biodegradation rate of the copolyester.
Nutrient release can furthermore also be controlled by the number of layers and their thickness.
The polyester dispersion used in accordance with the invention comprises approximately 10 to approximately 90, preferably approximately 10 to approximately 65 and more preferably approximately 15 to approximately 40% by weight of solids, ie. of the copolyester used in accordance with the invention.
In general, aliphatic dicarboxylic acids which can be used for the purposes of the present invention have 2 to 10 carbon atoms, preferably 4 to 6 carbon atoms. The cycloaliphatic dicarboxylic acids which can be used for th
Erhardt Klaus
Kim Son Nguyen
v. Locquengh Klaus Horchler
Warzelhan Volker
Yamamoto Motonori
BASF - Aktiengesellschaft
Griffin Steven P.
Keil & Weinkauf
Nave Eileen E.
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