HK1118043B - Coated fertiliser with a controlled release of active ingredients, and method for the production thereof - Google Patents

Description

Coated fertilizer with controlled release of active ingredient and method for preparing same

Technical Field

The invention relates to fertilizers having a coating with a biologically or hydrolytically degradable oligomer or polymer which allows a controlled release of the active ingredient which proceeds significantly delayed in time compared to the uncoated fertilizer.

Background

So-called "slow-release" or "delayed-release" fertilizers are known from the prior art, which make it possible to achieve a slow and controlled release of active ingredients throughout the crop growth period, wherein this is attempted in particular by coating the fertilizer granules with a film.

It is suggested in US 4,019,890a1 to use polymers such as polyethylene, polypropylene or polystyrene as the coating material. These coating materials are biologically very inert, however, since the materials do not completely decay during one plant growth phase, they are undesirably concentrated in areas where agriculture is heavily used.

It is likewise proposed in US 4,801,498a1 to use water-insoluble, neutralized and carboxylated polymers as coating materials, which are dissolved with the aid of organic solvents before coating. Tetrahydrofuran, acetic acid, xylene or toluene are suggested as organic solvents. In addition to the problem of similar enrichment, the necessary solvents are also considered disadvantageous for agricultural use here. Similar coating materials are also suggested in US 4,829,124a 1.

In WO97/48664 a biodegradable mixture of biuret, urethane and tung oil is disclosed as coating material. Here, the reaction leading to the formation of a dense and mechanically strong polymer layer on the particle surface is brought about by wetting the urea with the polyisocyanate and reacting said polyisocyanate with the alcohol. The reaction described is disadvantageous in that urea is consumed and biurets with phytotoxic action are formed. A similar coating is proposed in WO03/082003A2, in which urea is polymerized with formaldehyde.

Another coating known in the prior art is by means of elemental sulphur. From a phytological point of view, low concentrations of sulphur are a desirable nutrient, which is only slightly soluble in water and is therefore suitable in principle as a coating material. Such Fertilizer coatings are known from Ullmann (Ullmann) (6 th edition "Fertilizer", section 4.4.5.1) or WO92/17424A 1. Known coating materials are listed very comprehensively, in particular in WO92/17424A 1. Sulfur coatings present the problem that an optimum between nutrient release and the amount of sulfur applied must be found so as not to cause phytotoxic sulfur enrichment in the soil.

DE 69419125T2 describes a fertilizer with two coatings. The first inner layer is biodegradable and consists of an aliphatic polyester, such as for example poly-L-lactic acid with a preferred weight average molecular weight of 150,000 to 250,000, or polyurethane, and the water-insoluble outer layer consists of a polymer which is slowly biodegradable or which is degradable by light, such as for example a cellulose derivative.

It is of particular economic interest that the fertilizer can be produced industrially simply. In this case, it is considered disadvantageous that the fertilizer granules must be coated with two different materials.

Disclosure of Invention

It is therefore an object of the present invention to provide economically advantageous coated fertilizer granules which can delay the release of active ingredients over time and inhibit the release of active ingredients without phytological disadvantages. In addition, the invention aims to disclose a method for preparing the coated fertilizer.

The invention achieves the stated object by proposing a coated fertilizer granule, the coating of which consists of one or more biologically or hydrolytically degradable polymers, oligomers or mixtures of polylactide or copolyesters comprising L (+) lactic acid, more than 40 mol% of the molecular basic building blocks of polylactide consisting of L (+) -lactic acid units, according to claim 1.

Here, biodegradability of a polymer or oligomer is to be understood as defined for aerobic degradation of plastics as in a.2.2 and a.3.1 in EN 13434, wherein this can be determined by means of tests like ISO14855 or ASTM D5338. Here, the degradation caused by organisms and hydrolysis of the fertilizer according to the invention and here in particular of the coating on the agricultural sector, of course, lasts for a significantly longer time than the industrial composting under extreme conditions.

Hydrolysis is understood to mean the dissociation of a molecule by the addition of water molecules. Where the hydrogen atoms are attached to one molecular fragment and the remaining hydroxyl groups are attached to another fragment. The new molecules thus produced can thus be used, after one or optionally more hydrolysis, for carrying out a subsequent biological enzymatic hydrolysis process.

The nutrient fraction with the largest percentage content in the fertilizer granules according to the invention consists here of nitrogen, phosphorus or potassium compounds or mixtures thereof. In this connection, particular mention may be made of the following nutrients, such as urea, ammonium nitrate, calcium ammonium nitrate, monoammonium or diammonium phosphate, sulfates, such as ammonium sulfate, and mixtures thereof.

The fertilizer granules described herein above may contain low proportions of micronutrients. The micronutrients are in particular alkali or alkaline earth metals, sulphur, copper, zinc, boron, cobalt, manganese, molybdenum or selenium and compounds or mixtures comprising these substances.

In an advantageous embodiment of the fertilizer granule according to the invention, the polymer or oligomer is a polylactide or copolyester of L (+) -lactic acid, wherein ideally more than 40 mol% of the molecular building blocks of the polylactide consist of L (+) -lactic acid units. The number average molar mass of the low polylactide or polylactide here can be between 500 and 300,000 g/mol.

It has proven advantageous here when the number-average molar mass of the polymers or oligomers is greater than or equal to 500 g/mol. Oligomers with a molar mass below 500 have too high a viscosity. The coating with such a low molar mass of polylactide has good biodegradability and can furthermore be produced industrially simply. Polylactide having a molar mass of less than 5,000g/mol can be prepared by direct polycondensation of lactic acid, wherein it is generally not necessary to use a catalyst for the reaction, so that no catalyst remains as an impurity in the product either. The biodegradability can be controlled in a wide range by the polymer grade, the residual amounts of monomers and dimers, and the comonomer content.

A further advantageous development of fertilizer granules coated with polylactide consists in the remaining basic building blocks of the non-L (+) -lactic acid unit consisting of a D (-) -lactic acid unit, of a unit of at least one hydroxycarboxylic acid or a mixture thereof. Examples of suitable hydroxycarboxylic acids are glycolic acid, hydroxybutyric acid, hydroxyvaleric acid.

Furthermore, the fertilizer granule may be optimized in such a way that the polylactide polymer or oligomer contains dilactide, lactoyl lactic acid or a mixture thereof in an amount of less than or equal to 5 wt-%. Higher concentrations accelerate degradation, while lower concentrations retard degradation. The degradation rate of polylactide by hydrolysis and biodegradation can furthermore be influenced by the modification of the end groups. Here, fatty acids and fatty alcohols reduce the degradation rate. Polyethylene glycol increases the rate of degradation. These additives may be added to the reaction mixture at the beginning, during or at the end of the polymerization reaction.

Another embodiment of the fertilizer of the invention is the application of two or more polymer or oligomer layers. These may be of the same material or consist of different materials or mixtures of materials. In a further embodiment, an additional layer of fertilizer active ingredient is provided between the two polymer or oligomer layers.

In addition, the invention also encompasses that at least one of the biodegradable polymer or oligomer layers contains micronutrients, wherein the micronutrients are ideally completely contained in one of the biodegradable polymer and oligomer layers. The main advantage is that it does not have to be adapted in connection with the mass production of the main nutrient components to the locally given soil and crop requirements in each case, but can be carried out separately therefrom.

If micronutrients are applied separately to the growing area, there has hitherto been the problem that these relatively small quantities have to be distributed evenly and uniformly over a large area. In the usual spraying of aqueous solutions, it is a known problem that in the tanks the unmixed, fine droplets drift and propagate with the wind, or penetrate too quickly and into the ground water. Furthermore, the problem is that separate spraying means an additional operating step for the farmer.

Another advantage is that the biodegradable coating materials used in the present invention are inert and do not undergo side or subsequent reactions relative to the primary and micronutrients described above.

The micronutrients used in the present invention are derived from alkali or alkaline earth metals, sulphur, copper, zinc, boron, cobalt, molybdenum, manganese, selenium and compounds or mixtures comprising these substances.

In this case, it is particularly advantageous in comparison with the coating materials known from the prior art that, irrespective of the incorrect dosage of micronutrients, the vegetation circle or the hydrolysis system of the cultivated area may not be subjected to toxic contamination at any time, even if the amount or quality of the polymeric or oligomeric coating material is incorrectly adjusted.

The invention also includes a method of making the coated fertilizer granule described above. Characterized in that-uncoated solid or partially solidified fertilizer granules are wetted at least once with liquefied polymers, oligomers or mixtures of such polymers or oligomers according to the above composition and-subsequently solidified by drying, cooling or both, wherein-wetting and solidification can be repeated a plurality of times and, furthermore, -polymers, oligomers or mixtures thereof are used which are the same or different from the previous wetting process. The polymer or oligomer is liquefied by dissolving in a suitable solvent or melting without solvent.

In a variant of a further embodiment of the process according to the invention for producing coated fertilizer granules, after first wetting and subsequent curing, a layer of the fertilizer active ingredient is applied to the surface of the coating, the layer of the fertilizer active ingredient is subsequently cured by drying, cooling or both, and finally a further layer of a polymer or oligomer is applied in a similar manner, wherein these steps can be carried out alternately a plurality of times.

When polymers or oligomers having a very low molar mass are used, there is a certain stickiness which can cause problems in subsequent processing. The results show that the described disadvantages can be very easily overcome when the outermost layer is prepared from the basic nutrients of the fertilizer or other non-polymeric nutrients. However, essential nutrients are preferred here, since they are always present in the process as a melt or solution and only have to be applied finally in a further coating stage.

A modified variant of the process described envisages that the polymer or oligomer is mixed with a micronutrient, for example selected from the group consisting of alkali or alkaline earth metals, sulphur, copper, zinc, boron, cobalt, selenium, manganese, molybdenum and compounds or mixtures comprising these, before the uncoated or partially coated fertilizer granules are wetted. In the case of using a primary nutrient as the final coating, a micronutrient may also be added to the melt or solution provided for the final coating.

Any coating apparatus may be provided for coating the fertilizer granules, wherein in an advantageous embodiment of the process of the invention a fluidised bed granulator or a coating drum is used. In this case, the liquefied polymers, oligomers or mixtures thereof are applied to the granules to be coated by means of a nozzle which can be heated ideally.

Ideally, the liquefied polymer, oligomer or mixture is provided as a substantially solvent-free melt, as this simplifies exhaust gas purification, which is economically advantageous.

Claims (24)

1. Coated fertilizer granule, characterized in that the coating consists of one or more biodegradable polymers, oligomers or mixtures thereof, comprising polylactide or copolyester of L (+) -lactic acid, characterized in that more than 40 mol% of the molecular building blocks of polylactide consist of L (+) -lactic acid units and that the polymer or oligomer has a content of dilactide, lactyllactic acid or mixtures thereof of less than or equal to 5 wt.%.

2. Fertilizer granule according to claim 1, characterized in that the remaining basic building blocks other than the L (+) -lactic acid unit consist of D (-) -lactic acid units and/or units consisting of at least one hydroxycarboxylic acid or a mixture thereof.

3. Fertilizer granule according to claim 1 or 2, characterized in that the number average molar mass of the polymer or oligomer is between 500 and 5,000 g/mol.

4. Fertilizer granule according to any one of claims 1 to 3, characterized in that the nutrient fraction with the largest percentage content in the fertilizer is a nitrogen-, phosphorus-or potassium-compound or a mixture thereof.

5. Fertilizer granule according to claim 4, characterized in that the nutrient fraction with the largest percentage content in the fertilizer is urea, ammonium nitrate, calcium ammonium nitrate, mono-or di-ammonium phosphate, potassium nitrogen phosphate, sulphate or a mixture thereof.

6. The fertilizer granule according to claim 5, characterized in that said sulfate is ammonium sulfate.

7. Fertilizer granule according to any one of claims 1 to 6, characterized in that said fertilizer granule comprises a low proportion of the following micronutrients:

-an alkali metal or an alkaline earth metal,

-boron, cobalt, copper, manganese, molybdenum, sulfur, selenium, zinc,

and compounds or mixtures comprising these.

8. Fertilizer granule according to claim 7, characterized in that said compound is calcium carbonate, potassium bicarbonate or sodium bicarbonate.

9. Fertilizer according to any one of claims 1 to 8, characterized in that it has two or more polymer or oligomer layers consisting of the same or different substances.

10. Fertilizer according to claim 9, characterized in that a further layer of fertilizer active ingredient is present between the two polymer or oligomer layers.

11. Fertilizer according to any one of claims 1 to 10, characterized in that the outermost layer consists of one or more nutrients as defined in any one of claims 4 to 8.

12. The fertilizer material of claim 11, wherein the outermost layer is composed of nutrients which are the major components of the fertilizer by weight.

13. Fertilizer according to any one of claims 1 to 12, characterized in that at least one layer of biodegradable polymers, oligomers or mixtures thereof comprises micronutrients.

14. Fertilizer according to any one of claims 1 to 13, characterized in that said micronutrients are completely contained in one of the biodegradable polymer or oligomer layers.

15. A method of making the coated fertilizer granule of any one of the preceding claims,

-wetting uncoated solid or partially solidified fertilizer granules at least once with a liquefied polymer, oligomer or mixture of such polymers or oligomers as defined in any of the preceding claims, and,

-subsequently solidifying by drying, cooling or both, wherein,

the wetting and curing can be repeated a number of times and, furthermore,

-using the same or different polymers, oligomers or mixtures thereof as the previous wetting process.

16. The process for the preparation of coated fertilizer granules according to claim 15, characterized in that in a first step polylactide or copolyester of L (+) -lactic acid is prepared by direct condensation and subsequently, after first wetting and subsequent curing,

-applying a layer of fertilizer active ingredient to the surface of the coating,

in a second step, the fertilizer active ingredient layer is likewise solidified, and

finally, another layer of polymer, oligomer or mixtures thereof is applied in a similar manner, wherein these steps can be carried out alternately in a plurality of steps.

17. The method of making a coated fertilizer granule of claim 15,

after the first wetting and subsequent curing,

-applying a layer of fertilizer active ingredient to the surface of the coating,

in a second step, the fertilizer active ingredient layer is likewise solidified, and

finally, another layer of polymer, oligomer or mixtures thereof is applied in a similar manner, wherein these steps can be carried out alternately in a plurality of steps.

18. The method according to any one of claims 15 to 17, characterized in that the polymer, oligomer or mixture thereof is mixed with micronutrients before or after liquefaction and before wetting of the uncoated or partially coated fertilizer granules.

19. The method according to claim 18, characterized in that the micronutrient is selected from the group consisting of alkali or alkaline earth metals, sulphur, copper, zinc, boron, cobalt, manganese, molybdenum or selenium and compounds or mixtures comprising these.

20. The process for producing coated fertilizer granules according to any one of claims 15 to 19, characterized in that for coating any coating equipment is used.

21. The process for preparing coated fertilizer granules according to claim 20, characterized in that for coating, a fluidized bed granulator or a coating drum is used.

22. The method of making coated fertilizer granules of any one of claims 15 to 21, wherein the liquefied polymer or oligomer is applied to the granules to be coated using a spray nozzle.

23. The method of making a coated fertilizer granule according to claim 22, characterized in that the nozzle is heatable.

24. The method of producing a coated fertilizer granule according to any one of claims 15 to 23, characterized in that an outermost layer consisting of one or more nutrients selected from the group defined in any one of claims 4 to 8 is applied.