Coated seeds and process for their obtention

The present invention relates to coated seeds and a method for obtaining coated seeds.

Seed coating has become a common practice. It aims in particular to improve the germination characteristics, to provide various additives likely to intervene at any time in the establishment and growth of plants, to protect the seeds or even to give the seed a shape or dimension which suitable for automatic seeding. It has thus been proposed to coat seeds with nutrients, fillers, fungicides, herbicides, insecticides, etc.

It has also been proposed to improve the germinative power of beet seeds (Belgian Patent 859,566 filed October 11, 1977 in the name of the Applicant) to incorporate calcium peroxide into the coating.

The known coating methods, however, have many drawbacks.

It is common that the coating agent does not adhere properly to the seed so that it does not resist the various handling operations to which the seeds are subjected. This phenomenon is particularly sensitive for seeds with rapid water uptake. Indeed, during the coating, there is frequently a significant swelling of certain seeds due to the absorption of water. After drying, the seed contracts to return to its initial dimension while the coating does not generally contract in the same proportions; as a result, it no longer adheres properly to the seed and it becomes fragile, disintegrates or disintegrates.

Some coatings, on the other hand, are so hard and resistant that they do not dissolve or disintegrate easily under the action of moisture and water once the seed is in place, which is also harmful.

During the coating, use is made of small amounts of water, in particular for moistening the seeds before the coating itself to dissolve or disperse at least one of the constitutive agents of the coating or also to dissolve or disperse the tackifying agents used to ensure the adhesion of the other constituent agents of the coating. The presence of water has drawbacks which are particularly important when the seeds are poorly protected and absorb water quickly. Indeed, some seeds can absorb water during the coating which can lead to premature initiation of germination so that the seeds can no longer be stored. Furthermore, it is often not possible to properly dry the seed under the coating layer, which leads to risks of degradation during storage. These effects are particularly sensitive when the seeds used are seeds of legumes, corn and crucifers.

In addition, certain constituent agents of the coating agent, which on the whole have advantageous properties, may have side effects of phytotoxicity for certain seeds.

Finally, in some cases, it is difficult to coat the seeds uniformly because their surfaces are not regular and do not allow a uniform attachment of the coating. The tackifying agents which are usually used to adhere the other constituent agents of the coating agent to the seed do not make it possible to overcome all of these drawbacks simultaneously.

EP-A-0 017 193 discloses a process for obtaining coated seeds in which the seeds are treated with an aqueous phase, they are coated with a coating containing a peroxidized compound and a hydrophilic polymer and the seeds obtained are dried after manufacture.

The present invention aims to provide coated seeds and a method for obtaining them which do not have the respective disadvantages of seeds and known methods.

In the coated seeds according to the invention, the coating is very resistant in particular to embrittlement and to dry disintegration and it adheres well to the seeds so that the resistance of the coated seeds to storage is excellent. The coating agent disintegrates, disintegrates or dissolves under the action of humidity or water when the seeds are placed in their growing medium. In addition, it has no phytotoxic effect and it prevents premature seed germination.

The seeds coated according to the invention have an excellent germination rate and there is a significant reduction in the time necessary for the emergence of the germs. When the coating contains active additives, these are released slowly, which allows them to maintain their activity for a fairly long period. In addition, the invention provides seeds which may contain phytosanitary products, which makes it possible to avoid, at the time of sowing, handling of products which, often, have a certain toxicity for the users.

The method according to the invention has the advantage of not requiring the use of water during the coating of the seeds and thus of avoiding all the drawbacks associated with its use.

The present invention relates for this purpose to seeds coated with an anhydrous coating containing a peroxidized compound in which the coating also contains a polyester selected from the polymers of ε-caprolactone.

By polyesters whose melting temperature is low is meant to denote those whose melting temperature does not exceed 80 ° C and preferably not 60 ° C. In general, the polyesters are chosen from those whose melting temperature is lower than 60 ° C.

Various types of polyesters are suitable. Polyesters with a low melting point are generally well suited, in particular those whose melting temperature does not exceed 80 ° C, and preferably 60 ° C. The polyesters can be homopolymers or copolymers. The polyesters are chosen from homo- and copolymers of the_E-caprolactone.

Lactone copolymers can contain various types of comonomeric units. In general, they are copolymers of a lactone with an olefin oxide such as ethylene oxide or propylene oxide, with a lactam such as caprolactam, with another lactone, or also with a mixture of a glycol such as ethylene glycol and a preferably acyclic dicarboxylic acid such as adipic acid. Lactone copolymers can contain varying amounts of monomeric units derived from lactone. In general, they contain at least 10% and most often at least 20% of their weight of monomeric units derived from lactone. This proportion usually does not exceed 95% and preferably not 90% of the weight of the polymer.

Polyesters of the homopolymer type are very suitable. Homopolymers of_E- caprolactone have given excellent results.

The polyesters according to the invention can have variable average molar masses. In general their average molar mass is at least 300 and most often at least 500. In general their average molar mass does not exceed 60,000 and most often not 50,000. Excellent results have been obtained with polyesters with an average molecular weight of about 800 to about 10,000.

All types of organic or inorganic peroxide compounds can be used in the coating of seeds according to the invention. Mixtures of peroxide compounds are also suitable. Among the organic peroxide compounds which can be used, there are compounds such as benzoyl peroxide and its halogenated derivatives, alkyl perbenzoates such as tert-butyl perbenzoate, p-menthane hydroperoxide as well as additi products there is hydrogen peroxide such as urea peroxide. The inorganic peroxide compounds are generally chosen from persalts such as perborates, percarbonates, persulfates, perphosphates of alkali or alkaline earth metals and metallic peroxides. Most often, it is preferred to use inorganic peroxide compounds such as metal peroxides, more particularly peroxides of alkaline earth metals. Very good results have been obtained using calcium or magnesium peroxides. The best results have been obtained with calcium peroxide. When it comes to calcium peroxide, a commercial product is generally used containing from 30 to 90% by weight of calcium peroxide, the balance consisting in particular of calcium hydroxide and optionally a calcium salt and d 'water. Other qualities of calcium peroxide may also be suitable.

The coating can also contain various additives. It can thus contain fillers of organic or mineral type. Mixtures of fillers can also be incorporated therein. The fillers are fine powders generally having a particle size such that they pass through a sieve of 170 and preferably 325 mesh (US Standard). As organic fillers, natural products based on cellulose are generally used, such as wood-derived powder or peat flour. As fillers of inorganic or mineral type, products based on silica, silicates, carbonates, calcium salts are used. In general, fillers chosen from ground or precipitated silica, ground sand, bentonite, talc, kaolin, diatomaceous earth, fuller's earth, vermiculite, clay, limestone, chalk, are used. calcium carbonate, calcium oxide, calcium hydroxide, plaster and their mixtures. In general, non-phytotoxic fillers are used.

The coating can also contain one or more other additives such as phytosanitary products, more particularly insecticides, nematicides, fungicides, disinfectants, repellents, herbicides and growth regulators, agents for preserving seeds against the harmful effects of selective herbicides such as activated carbon, nutrients (fertilizers), agents capable of improving germination and the quality of products, bacteria capable of favorably influencing the germination, establishment or growth of plants, etc.

Good results are obtained when the coating agent contains a nutritive agent.

Good results are obtained when the coating agent contains phytosanitary products and more particularly fungicides. Examples of suitable fungicides are given in the List of Phytopharmaceuticals published by the Ministry of Agriculture, Plant Protection Service, Brussels, 1968 and 1981 and in the Phytosanitary Index published by ACTA, Paris, 1981, pages 195 to 268. Methoxyethylmercury acetate, benomyl, captan, copper oxyquinoleate, thiram, thiabendazole, ethyrimol maneb and captafol are well suited. Good results have been obtained with benomyl, captan and methoxyethylmercury acetate.

The total dose of coating agent can vary within very wide limits depending on the type of seed, its shapes and dimensions. The total dose of coating agent is generally at least 0.0001 times the weight of the seeds. Most often, this dose does not exceed 100 times the weight of the seeds without this limit being critical. When it is not necessary to give the coated seeds a predetermined shape or dimensions, the dose of coating agent is most often at least 0.01 and preferably at least 0.1% of the weight of the seeds. seeds and it does not generally exceed 300% and preferably not 200% of their weight. When it is desired to give the seeds a predetermined shape and dimensions, the dose of coating agent is generally at least 0.5 and most often at least 1 times the weight of the seeds and it generally does not exceed 100 and most often 50 times their weight.

The doses of polyesters in the coating agent according to the invention can be very variable. They can be from 0.01 to 90% of the total weight of the coating agent. In general, the polyester content represents from 1 to 60% of the weight of the coating agent if the fillers are excluded.

The amount of peroxide compound present in the coating agent can vary within wide limits. It is generally between 0.1 and 99% of the total weight of the coating. Most often the coating contains from 1 to 90% by weight of peroxidized compound. Good results have been obtained when the content of peroxidized compound represents from 10 to 80% of the weight of the coating agent if the charges are excluded.

The filler content can vary within very wide limits. It is generally between 0 and 99% of the total weight of the coating agent and preferably between 0.1 and 99% of the total weight of the coating agent. Contents between 1 and 98% are suitable.

The other additives can be present in variable proportions which can range up to 95% of the weight of the coating. The content of these other additives is generally from 0.00001 to 95% of the weight of the coating agent. In general, the content of these other additives represents from 0.1 to 95%, and most often from 5 to 90%, of the weight of the coating agent if the fillers are excluded.

Particularly advantageous coatings can thus contain from 5 to 60% by weight of polyesters according to the invention, and from 40 to 95% by weight of peroxidized compounds, the coating being present in amounts of 0.01 to 200% of the weight of uncoated seeds. These coatings can also contain up to 20% and more often from 0.1 to 20% of their weight of various additives.

Other coating agents which are also advantageous may contain from 0.1 to 50% by weight of polyesters according to the invention, from 30 to 75% by weight of peroxide compounds and from 20 to 60% by weight of various additives, the coating agent being present in amounts of 0.01 to 300% of the weight of the uncoated seeds.

Other particularly advantageous coatings can contain from 0.1 to 20% by weight of polyesters according to the invention, from 0.1 to 30% by weight of peroxidized compounds, from 30 to 99.7% by weight of fillers and 0.01 to 30% by weight of other additives, the coating being present in amounts of 0.5 to 100 times the weight of the uncoated seeds. The latter are suitable when it is desired to give the seeds a predetermined shape or size.

The invention can be applied to various types of seeds, such as seeds of legumes, grasses or dicots. In general, it is used for the seeds of legumes such as various kinds of peas, beans and lentils, alfalfa, clover, vetch, soybean, peanut, faba bean and lupine, seeds grasses such as ryegrass and cereals (corn, oats, rye, wheat, millet, sorghum, barley, rice, etc.), dicot seeds such as chicory, lettuce, tobacco, tomato, carrot, cabbage and rapeseed and cruciferous seeds such as radish. Good results are obtained with legume seeds such as pea and soybean seeds and with grass seeds such as barley, oats and barley.

The present invention also relates to a method for coating seeds. According to the invention, the seeds are kneaded in the absence of water with the peroxidized compound, a layer of polyester is applied in the liquid or molten state in the absence of water and the polyester is solidified on the seeds . The application of the polyester layer can be carried out by various techniques such as immersing the seeds in a bath containing the polyester or even spraying the polyester on the seeds. The spray application technique is preferred.

According to a particular embodiment of the invention, the seeds are rotated, kneaded with the peroxidized compound and coated with polyester.

To print the rotary movement with seeds, any process and more particularly any device for coating making it possible to carry out such a movement such as ribbons, containers of various shapes, apparatuses with open sphere or cylinder, apparatuses used for the mixture of liquids or solids, granulators, rotary drums, rotating floors, are suitable for carrying out the process according to the invention.

In general, we use devices with rounded or spherical edges which can be inclined on their axis.

Preferably, a container with rounded edges animated with a planetary movement and whose axis of rotation can be inclined from 0 to 90 is used.^- with respect to the vertical.

In general, the polyesters contained in the coating agent are chosen from those whose melting point is less than 80 ° C., preferably 60 ° C.

The coating can be done using various techniques. The polyester can be used as it is in the liquid or molten state or in the form of a solution in an organic solvent.

A particular technique consists in treating the seeds by means of the peroxidized compound and by means of polyester in the liquid or molten state. According to this particular technique, the polyester is selected from those whose melting temperature is less than 80 ° C., preferably 60 ° C. It is thus possible to apply the seeds to the polyester and, simultaneously, consecutively or alternately, add the peroxidized compound. It is also possible, if necessary, to add fillers or other possible additives at any time during the coating. In general, the polyester is applied to the seeds in the liquid or molten state and then the peroxide compound and the fillers or other optional additives are added. The introduction of polyester in the liquid or molten state may continue during the introduction of the peroxidized compound and fillers or other optional additives. The introduction of the peroxidized compound and of the fillers or other optional additives can be interrupted one or more times and in the meantime a new application of polyesters in the liquid or molten state and this until the seeds are completely coated. .

According to this particular technique, the seed coating apparatus must be preheated to a temperature between 45 and 80 ° C so as to maintain the polyester at its softening point. The polyester is sprayed on the rotating seeds in the coating apparatus by means of any device capable of dividing it into fine droplets, for example by means of a pneumatic gun.

In the process according to the invention, the polyester is brought into the tank of the spraying device at a temperature sufficient to keep it in the molten state. The temperature of the coating apparatus and that of the spraying device are not critical and depend on the nature of the polyester. They are however to be determined carefully in each case for the particular polyester used and are directly related to the softening and melting temperatures of said polyester. In general, the temperature of the spray device is set within a range of 10 to 40 ° C higher than the softening temperature of the particular polyester used and preferably 20 to 30 ° C higher than this temperature. The temperature of the coating apparatus is most often selected in the range of 0.5 to 10 ° C higher than the softening temperature of the particular polyester used and preferably 1 to 5 ° C higher than this temperature.

Another technique consists in using the polyester in the form of a solution in an organic solvent. The following operations are similar to those used for coating with the intervention of polyesters in the liquid or molten state.

Various organic solvents can be used for this purpose. They are generally chosen from organic solvents containing aromatic groups or organic solvents substituted by halogens such as chlorine and bromine, nitro groups, carbonyl groups, carboxyl groups, ester groups and alkoxy groups. Mixtures of solvents can also be used. It is thus possible to use mixtures of the abovementioned solvents with one another or with alcohols. The solvents are most often chosen from organic compounds containing from 1 to 12 carbon atoms; when it comes to aromatic compounds their number of carbon atoms is from 4 to 12. Alcohols generally contain from 1 to 8 carbon atoms.

Good results have been obtained with halogenated solvents or more particularly chlorinated solvents alone or in admixture with alcohols.

The best results have been obtained with a chloromethane such as methylene chloride alone or as a mixture with an alcohol such as methanol.

Polyester solutions can contain varying amounts of polyesters. In general, for economic reasons, solutions are used whose concentration is equal to or close to saturation. Good results are obtained with solutions containing from 10 to 60% of their weight of polyesters.

After coating, the seeds are spread in a thin layer on a flat surface.

When the polyester is used in the form of a solution, the seeds are further dried after coating to remove the solvent still present in the coating. The drying can be done according to any technique known in itself such as by passing a stream of forced air possibly heated over the seeds which can be arranged for this purpose in devices such as sieves, or by drying by natural ventilation.

In order to illustrate the invention without limiting its scope, practical examples of implementation are given below.

Examples 1 R to 2

Coating and germination of soybean seeds

200 g of Corsoy variety soybeans are introduced into a circular drum 40 cm in diameter, with rounded edges, driven by a rotary movement of 50 rpm. The inclination of the axis of rotation of the drum was then adjusted so as to give it an angle of 60 ° with the vertical.

Using a pneumatic sprayer of the paint gun type equipped with a spray head with a needle of 3 mm in diameter, a total of 0.28 g of a solution containing 50% by weight was sprayed in three successive admissions. poly-c-caprolactone and 50% methylene chloride (CH_ZTHIS_Z).

When the seeds were lightly and regularly covered with polycaprolactone, we began to introduce by means of a vibrating dosing device whose spout was located inside the circular drum 20 g of commercial powder of calcium peroxide at 60% by weight of Ca0₂ with an average particle size of 8 m. When the flow rate of the powder was continuous and regular, an additional 2.52 g of the polycaprolactone solution in CH was sprayed at regular intervals.₂THIS₂. We managed to do this to regulate the flow of Ca0 powder₂ at 3 g / min.

After incorporating all of the Ca0 powder₂, the remainder of the polycaprolactone solution was sprayed after which the drum was left to rotate for 2 min. The whole operation lasted a total of 15 min.

The seeds thus coated were then extracted from the drum and spread in a 2 cm thick layer at room temperature on a porcelain plate and under good ventilation to ensure rapid and total evaporation of the CH₂THIS₂ still present in the coating. After 30 min under these conditions, any solvent odor had dissipated and the seeds were ready for use.

The coated seeds were then put to germinate on wet filter paper (example 2). The germination tests were carried out at 20 - 22 ° C.

A germination test of uncoated seeds was carried out for comparison (example 1 R).

The characteristics of the coating agent and the results obtained are collated in Table 1.<tables id="tabl0001" num="0001"><img file="EP0148522B1_D0001.tif" /></tables>

Examples 3R and 4

Pea seed coating and germination

200 g of Oberon pea seeds were coated (Example 4) with a 50% by weight solution of polycaprolactone in methylene chloride in the same apparatus and according to the same technique as in Example 2.

The coated seeds were then germinated on wet filter paper. The germination tests were carried out at 20 - 22 ° C.

A germination test of uncoated seeds was carried out for comparison (example 3R).

The characteristics of the coating agent and the results obtained are collated in Table 2.<tables id="tabl0002" num="0002"><img file="EP0148522B1_D0002.tif" /></tables>

Example 5

Pea seed coating

In a circular drum similar to that used in the previous examples, 200 g of Obéron variety pea seeds were introduced. The drum was then set to rotation set at 50 rpm and the seeds and the sole were heated to about 40 ° C. by means of a current of hot air delivered by a fan provided with an electrical resistance of 1500 watts.

The quantity (3 g) of poly-c-caprolactone was melted at 50 ° C. and poured into a pneumatic spraying device similar to that of the preceding examples and the reservoir of which was kept at 70 ° C. by means of a strip. electric heater wound on its outer surface.

The senences were impregnated with a first regular layer of 0.3 g of polycaprolactone after which the addition of a commercial powder of calcium peroxide containing 60% Ca0 was started.₂ using the same vibrating doser as in the previous examples. The powder addition was carried out with a flow rate of 2 g / min in conjunction with the spraying at regular intervals of polycaprolactone so as to ensure a regular coating of the seeds.

The coating lasted in total 20 min and required the application of 3 g of molten polycaprolactone.

Once the operation was finished, the coated seeds were extracted from the drum and spread out in a layer 5 cm thick at room temperature on a porcelain plate. After cooling, the seeds were ready for use.