NL9020411A - PROCESS FOR MAKING AN ECOLOGICAL CAPSULE OF NATURAL ORIGIN FOR PRODUCTS WITH CONTROLLED DELIVERY OF THE ACTIVE SUBSTANCE. - Google Patents

Description

Process for making an ecological capsule of natural origin for controlled release products of the active ingredient.

This invention relates to a method of making ecological capsules of natural origin which decompose in the environment, which is preferably used for selective plant protection agents, with release of the protective component over time.

In recent decades, intensive efforts have been made all over the world to make such capsules in order to give plant protection preparations with maximum effect, even in minimal doses, at the same time leaking the plant protection agent from the utilization zone or from unwanted, premature decomposition products thereof (e.g. after irradiation with UV).

In the event that the root zone is understood as the utilization zone, it is of the utmost importance that the plant protection agent can properly treat all harmful organisms, such as fungi and pathogenic bacteria, weeds and other soil-dwelling parasites.

The application of plant protection agents does not always coincide with the occurrence of pathogenic and parasitic creatures. Another problem lies in the lifespan of the active ingredients, and their warranty time.

The application of natural polymers or derivatives thereof, which complex with a given plant protection agent, is one of the successful solutions to this problem. For example, the use of starch or starch derivatives for encapsulating EPTC was also known and has attempted to bind urea-formaldehyde resins, which has the additional advantage that the carrier can also serve as a fertilizer.

Another method has also been developed in which, starting from an emulsion, a hard crust is made by condensation at the interface. This crust ensures that the active ingredient gets onto the intended surface when decomposed or as a semi-permeable film.

Experts also work with the combination of various natural polymers, such as starch, latex and synthetic resins. For example, the lifespan on the plant could be successfully extended and the release of the active ingredient could be controlled, even though ensuring the correct particle size was a problem.

In Japanese patent applications 0072-806, 2033-103, 2003-795, 0072-804, 1129-138, 8021-602 and 0104-095, various cyciodextrin derivatives have been proposed for formulating active ingredients of plant protective agents.

According to Japanese patent application 8021-605, porous supports (e.g., a sponge, paper, a cloth, etc.) are impregnated with volatile plant protection compositions.

According to WIPO patent 8300-796, hollow cellulose-based rods are used for encapsulating plant protection agents, the outer surface of which is optionally treated with paraffin.

As will be apparent from WlPO patent 8303-61, a double capsule system is formed, the larger capsule of which comprises multiple microcapsules. Cellulose acetate is used to make such capsules.

According to Japanese Patent Application No. 8121-212, for the controlled release of the active ingredient, a product of the gel type, i.e. a plant protection agent, is made from polyacrylate and epoxy resin.

According to European patent application 205,978, polyvinyl alcohol and starch-containing carriers are used as capsules for various pesticides (parathion and trifluralin), for pheromones and regulators.

According to European Patent 121,712, biocides and drugs are encapsulated with organophilic cellulose ethers.

German Patent 1,567,066 suggests encapsulating plant growth regulators and herbicides with supports made of thermoplastic resin and a solvent-soluble resin.

According to Japanese Patent No. 9,142,264, polysulfone, polycarbonate, cellulose and vinyl acetate copolymers are used as carriers for insecticides.

U.S. Pat. No. 4,451,635 describes a support for which water-soluble polymeric quaternary ammonium salts and ion exchangers are used.

Japanese Patent 7185-344 describes making a carrier for sustained release of the active ingredient from attractions, disinfectants and plant protection agents. Polycaprolactam is used as the carrier, which can be combined with other synthetic materials, e.g. nitrocellulose, butyl calcium, etc., using silica gel, calcium carbonate or aluminum oxide as filler.

According to Japanese Patent 8010-503, a polymer with a high water absorbing capacity, e.g. the grafted copolymer of starch with polyacrylonitrile, which is also cross-linked, is used for the preparation of agricultural chemicals.

According to European Patent 214,396A, water-soluble polymers (e.g. polyvinyl alcohol and hydroxyethyl, hydroxypropyl and methyl cellulose) are used. Condensation with a urea resin can also occur.

European Patent 158,449 specifies a method of making capsules for water-immiscible liquids, in which a porous crust is formed from the prepolymer of urea with formaldehyde in an organic solvent to encapsulate plant protection substances and fertilizers.

According to Japanese Patent 2201-156, a slow-release barrier of the active ingredient is made by using binders and film-forming materials, such as polyvinyl alcohol, polyvinyl acetate, polyethylene, and silicone resin.

US patent 4,615,883 describes the preparation of a macrocapsule with a grain size of 0.4-5.0 mm from hydrogel, which itself can be made again from sodium alginate, gelatin and gum arabic.

According to Australian Patent A8 767,199, a polymer which is prone to biological decomposition is used in such a way that micro-organisms are encapsulated, the number of germs can be 106-1010 germ per gram, and the size of the beads is between 0.5 and 40 mm. As material, gelatin, alginate, polyacrylamide and cellulose ether can be used.

According to Japanese Patent 9050-086, a granulate is made from some hydrophobic materials such as paraffin, resins and waxes. A paraffin shell serves to coat fertilizer granules.

Japanese patent 9048-402 provides a solution for making capsules with volatile insecticides. Evaporation of the active ingredient is achieved by a controllable calorific method. Calorification is initiated or controlled by the diffusion of oxygen.

U.S. Patent 4,400,391 suggests a solution for capturing volatile insecticides: alginate beads. Cu, Zn, Al and Pb salts can be used as gelling agents.

According to research activities in the United States, the results of which were published in 1975 and 1976, starch xanthogenate is very suitable for encapsulating plant protection substances, as a matrix that allows the slow release of the active ingredient. When using xanthogenate, cross-linking can be achieved with epichlorohydrin and with hydrogen peroxide. In this case, water-soluble and insoluble plant protection substances are encapsulated.

Plant protection substances encapsulated with starch xanthogenate are stable; they can be stored without any problems. The active ingredients are released on contact with water.

EPTC (S-ethyl-dipropyl-thiocarbamate) and DBPC (1,2-dibromo-3-chloropropane) give a stable capsule, from which the active ingredients evaporate satisfactorily simultaneously; at the same time, the preparation is well resistant to sunlight.

These investigators tested the suitability of latex in connection with the above active ingredients, with small amounts of latex being added to the starch for xanthogenation and cross-linking with sodium nitrite. Zinc sulfate was also used for cross-linking in some tests.

In laboratory tests, N- (phosphomethyl) glycine and ammonium sulfate could be encapsulated with good results.

The effect of SBR 1502 (a styrene-butadiene latex) on the encapsulation of DBCP has been tested; with a certain mixing ratio, an excellent service life could be achieved. (Northern Regional Research Laboratory Agricultural Research Service, U.S. Department of Agriculture at Peoria, Illinois 61604) received March 12, 1976).

The purpose of this invention:

The capsules as developed by us are ecological, they consist of rapidly decomposing and cheap material, the decomposition of which leaves no harmful residues in the soil. The novelty of the method according to the invention lies in that the aggregate of microcapsules - optionally in colloidal distribution - is made rigid in a solid matrix; both in terms of bond strength and release, they act as separate particles.

We have also found another method by which the microcapsule enters the center of the solid matrix and where communication with the outside world is realized with channels and cavities in the matrix.

Another construction relies on recognizing, insofar as the spherical matrix is permeated with active support polymer supports and channels, that the microscopic size occurs in only one dimension, while the other dimension falls in the mezzo region.

The matrix according to the invention is characterized in that it is insoluble in water but decomposes in the soil without harmful residues; neither does the active filler dissolve in water and is ecological.

A new aspect of the method according to the invention lies in the fact that the plant-protecting substance to be encapsulated is readily prepared for fixing to the carrier, in the capsule. For example, a stable suspension in carbon sulfur is made from the well-known active ingredient benomyl, or the solution thereof is used in heptane. Like benomyl, the fungicide carbendazim can be encapsulated with systemic action. In formulating the fungicide captan, we started from solutions in ethanol or acetone.

In the method according to the invention for making capsules or microcapsules, we start from natural polymers. For example, from an aqueous solution of cellulose, from an aqueous suspension or solution of starch, from a latex, or from a solution of urea-formaldehyde resin with a low condensation degree, condensation continuing in the course of encapsulation in the presence of a coagulation catalyst .

In the initial phase of capsule production, activated carbon with a very specific grain size is optionally added to the polymer present. In the course of capsule formation, which takes place in the mixture of inorganic and organic acids, surfactants such as the BEROL products and copper complexes are used as crosslinkers. In some cases powdered polyacrylonitrile with a particle size between 1 and 10 µm is used.

The formulation of the capsules can be carried out by any method known per se, and drying can also be carried out in various ways.

The active ingredient (the solution, suspension or emulsion) is absorbed by the finished capsule by methods known per se. In certain cases, condensation may also occur at the phase front in the method according to the invention.

The details of the invention are illustrated in the examples below.

Example 1

A carrier (capsule) for encapsulating selective herbicides can be made as follows: 100 dm3 cellulose solution was measured in a 0.25 m3 kettle equipped with a stirrer (related to a 5% cellulose solution) and 50 dm3 starch suspension was added thereto (the suspension can be made from corn starch and 5% NaOH solution to give a 10% suspension). To this was also added 1 dm3 ammonia latex, containing 60% active substance.

After vigorous stirring, 10 dm3 urea-formaldehyde precondensate was mixed with it, adding the required catalyst with the acidic solution before precipitation.

As crosslinker, 1 dm3 of 1% tetramine copper hydroxide was added. The polymer mixture thus made was placed in an acid bath known per se in a molding equipment, which was preferably a mixture of 10% sulfuric acid and 5% acetic acid in water. The bath also contained 1-2 g / dm3 surfactant (BEROL SPINN 62).

The capsules thus obtained were washed and dried. Thus, we obtained a granular support with a diameter of 1-2 mm, after which the prepared plant protection agent was adsorbed thereon.

The application of the product to the soil was carried out in soil known for sowing cultivated plants in a manner known per se. Under the influence of moisture from the soil (as a result of rainwater), the active substance will gradually be leached.

Example 2

A 4.8-5.3% cellulose solution was introduced into a 0.25m3 enameled kettle equipped with a stirrer. Of the cellulose, 80% was cellulose xanthogenate, 15% carboxymethyl cellulose and 5% starch xanthogenate.

To this solution was added 6 kg of activated carbon with a specific surface area of 1000 m2 / g, and also 20 kg of finely divided bran. Finally, 2 kg of urea-formaldehyde precondensate was added, after which the mixture was stirred with an anchor stirrer for 2 hours. The solution thus obtained was passed through a 100 µm screen cloth.

The filtered polymer concentrate was divided into drops. When the drops were contacted with acidic vapor, they coagulated and the coagulated substance was washed and dried. Thus, we obtained a support with 0.5-1.0 mm granules encapsulating a selective effect herbicide (e.g. EPTC) in a manner known per se.

The polymer components used bind the plant protection substances with varying strength and thus the combined carrier ensures a time-spread release of the active ingredients. This release of the active ingredients is completed when the carrier falls apart in the ground.

Example 3

Using the equipment described in Example 2, we mixed 10 kg of powdered acrylonitrile-styrene sulfonate copolymer with 200 dm3 of cellulose solution (grain size between 1 and 10 µm). The ion exchange groups of this supplement allowed binding of the plant protection agents and controlled release of the active substances.

Claims (4)

Method for making cellulose and / or starch-containing capsules or microcapsules, characterized in that 0-50% by weight of polymer is added to the capsule material at a temperature of 10 to 50 ° C, the suspension is stirred vigorously, and then 0-50 wt.% urea-formaldehyde prepolymer is mixed with it, the colloidal solution thus obtained is applied to the acidic solution mixture - preferably 10% sulfuric acid - containing 0.1 to 5 wt.% crosslinking catalyst - at preferably ammonium sulfate - and further containing 0.01 to 5% by weight surfactant ethoxylated amine, washing the capsules thus obtained and drying at 40-100 ° C, after which various active ingredients or solutions thereof are contacted with the capsules and the loaded capsules are pulverized. 2. Process according to claim 1, characterized in that ammonium sulfate, ammonium carbonate, tetramine zinc hydroxide or tetramine copper hydroxide are added as gel-forming additives to make capsules. Method according to claim 1, characterized in that in addition to the microcapsule structure fixed in the matrix, a loosely bound crust is made on the grain surface by using the so-called pulverization method, which leads to a double shell structure, whereby adhesion with a solution of a natural polymer or with its powder is achieved, preferably with a powder or solution of potassium humate or of carboxymethyl cellulose. A method according to claim 1 or claim 3, characterized in that when the active ingredient is prepared, in particular from a plant-protecting substance to be encapsulated, a stable suspension or solution is produced in a solvent which is both ecologically effective as harmless, and which also contains additives (preferably carbon sulfur) that promote adsorption in the capsule and chemical compound, while desorption into the soil is assured with the effect of moisture.