FR2692754A1 - Double coated granules for agricultural use - allow rapid release of active cpds. e.g. insecticide or fungicide, starting several weeks after spreading, timed by appropriate choice of coating polymers. - Google Patents

Abstract

Compsn. (A) comprises a nucleus contg. an agricultural chemical, a primary coating of a hydrophilic polymer which swells by water absorption and a second coating of an olefinic polymer, polyamide, polyester, polyether or polyimide. Also claimed is a compsn. (B) comprising a nucleus contg. an agricultural chemical with a primary coating of an alkaline material and a second coating of a mixt. of a polymer soluble in aq. alkali and an olefinic polymer, polyamide, polyester, polyether, or polyimide. USE/ADVANTAGE - Water absorption by the coated granules causes rupture and release of the agricultural chemical. Choice of coatings determines how long after application this takes place. It is possible to make one application of a coated granule mixt. which will release the agricultural chemicals at several stages during crop growth, hence reducing labour. The active chemical may have a neutral support or be combined with a fertilizer. The active chemical may be an insecticide, fungicide, etc.

Description

CHEMICAL COMPOSITIONS FOR AGRICULTURE, IN GRANULES A
DOUBLE COATING
The present invention relates to chemical compositions for agriculture, in double-coated granules, which are controlled with regard to the time when their chemical components for agriculture are released into water or aqueous media.

 We wanted to reduce the labor force in agricultural work and the exploitation of farms. In order to reduce the workforce, mechanical spraying of agricultural chemicals has been proposed and used. Also, improvements and modifications to agricultural chemicals as such have been studied. For example, agricultural chemicals based on potassium chloride coated with a water-soluble polymer film have been proposed. These agricultural chemicals with a coating are advantageous because the spreading of these agricultural chemicals with a coating can be done easily over a shortened period of time without the use of '' specific spreading instruments.

 In fields and farms, various insects and microorganisms have harmful effects on cultivated plants or farm products throughout their growing seasons in different ways. So far, large numbers of studies have been done to collect data on harmful insects and microorganisms, such as their growth time, ovulation, hatching time, spore formation, pathways transmission of contagious diseases, etc. On the basis of the data thus collected, it was suggested to apply various agricultural chemicals to different harmful insects and microorganisms at the most appropriate times. However, these applications of various agricultural chemicals at many different times cannot be easily achieved.

 For example, rice wilt diseases, that is, very harmful rice rusts, are observed throughout the rice growing seasons. A particularly harmful rice wilt disease is rice wilt disease, which occurs a month after the rice is planted. Rice wilt disease, which occurs a month before harvest time, is also very troublesome. In order to prevent streak wilt from spreading, it is suggested that appropriate agricultural chemicals be applied when wilt disease is expected to appear. In addition, if rice wilt disease develops and then spreads widely in the field, the application of agricultural chemicals should be repeated every 7-10 days.

In order to prevent the wilting disease of rice ears from occurring, it is suggested to repeatedly apply suitable agricultural chemicals during the period of swelling and production of the rice ears.

Such multiple application procedures are naturally inconvenient.

 Consequently, it is an objective of the present invention to propose a chemical composition for agriculture, in coated granules, which can be controlled in order to keep its active chemical ingredient for the culture action within it for a determined period and , when the predetermined period has passed, release the active ingredient quickly.

 In accordance with the present invention, a chemical composition for agriculture is proposed, in double-coated granules, comprising a core containing a chemical compound for agriculture, a first coating layer of hydrophilic polymer which swells by absorption of water, and a second coating layer of olefinic polymer, polyamide, polyester or polyether.

 In accordance with the invention, a chemical composition for agriculture is also proposed, in granules with double coating, comprising a core containing a chemical compound for agriculture, a first coating layer of an alkaline compound, and a second coating layer of a mixture of polymer soluble in aqueous alkalis and of olefinic polymer, polyamide, polyester, polyether or polyimide.

BRIEF DESCRIPTION OF THE DRAWINGS
- Figure 1 represents curves which show the
release of an agricultural chemical
(Pyroquilon) from the chemical composition for
agriculture, in coated granules, of Examples 1 and 2,
once in the water
- Figure 2 represents curves which show the
release of an agricultural chemical
(Pyroquilon) from the chemical composition for
agriculture, coated granules, Examples
Comparatives 1 and 2, once submerged in the water;
- Figure 3 represents a curve which shows the
release of an agricultural chemical
(Pyroquilon) from the chemical composition for
agriculture, in coated granules, of Example 3, a
times immersed in water
- Figure 4 represents a curve which shows the
release of an agricultural chemical
(Pyroquilon) from the chemical composition for
agriculture, in coated granules, from Example
Comparison 3, once submerged in water
- Figure 5 represents curves which show the
release of an agricultural chemical
(Pyroquilon) from the chemical composition for
agriculture, in coated granules, of Examples 4 to 8,
once in the water
- Figure 6 represents curves which show the
release of an agricultural chemical
(Pyroquilon) from the chemical composition for
agriculture, coated granules, Examples
Comparatives 4 to 6, once immersed in the water;
- Figure 7 represents curves which show the
release of an agricultural chemical
(Pyroquilon) from the chemical composition for
agriculture, in coated granules, of Examples 9 to 12,
once in the water;
- Figure 8 represents curves which show the
release of an agricultural chemical
(Pyroquilon) from the chemical composition for
agriculture, coated granules, Examples
Comparisons 7 and 8, once immersed in the water.

 The chemical composition for agriculture, in double-coated granules, of the invention comprises the hearts, the first coating layer arranged around the hearts, and the second coating layer arranged around the first coating layer. .

 The core of the composition preferably comprises a support and a chemical compound for agriculture. The support, preferably, takes a spherical shape and is chemically neutral. The support is preferably inert with respect to the agricultural chemical ingredient contained with it and moreover with respect to the material of the first coating layer. Examples of the supports include silica, diatomaceous earth, clay, bentonite, talc, kaolin, and other known inactive granular supports.

 The support is preferably a granular fertilizer. If the combination of fertilizer and agricultural chemical is chosen so that the time for application of the first coincides with the time for application of the second, both the fertilizer and the chemical for agriculture can be released at the same appropriate time by spreading the coated granules, all at once, in the fields. The fertilizer can be of any type. However, it is preferable to use a granular fertilizer which does not contain or contains a smaller quantity of nitrogen in the form of ammonia. For example, granular fertilizers of nitrogenous fertilizers, such as oxamide, urea, sodium nitrate, condensation product of urea and an acetaldehyde and condensation product of urea and isobutyl aldehyde; phosphate fertilizers, such as molten phosphate, calcined phosphate, treated phosphate, mixed phosphate and fumic acid phosphate fertilizers; potassium fertilizers, such as potassium sulphate, potassium chloride, potassium sulphate magnesia, potassium hydrogen carbonate and potassium silicate; compound fertilizers, such as potassium phosphate and potassium nitrate; organic fertilizers; and mixtures of these fertilizers. These fertilizer materials can be processed by known methods to give granular fertilizers. There are no specific limitations on the diameter of the granules. However, the granules preferably have an average diameter in the range of 1 to 4 mm.

There are no specific limitations on agricultural chemicals to be used in the composition of the invention. Examples of combinations of agricultural chemicals that can be used and insects and diseases to be treated with chemicals are described below - 1,2,5,6-Tetrahydropyrrolo [3,3,1-ij] quinolin-4-one
(Pyroquilon, Diseases: wilting of rice, rot
grain bacteria, etc.) - O-6-ethoxy-2-ethylpyrimidin-4-yl O, O-dimethylphosphoro-
thioate (Etorimfos, Insects: common cabbage worm,
cruciferous moth, leucania caterpillar, agrotis
harvests, beetles, etc.) - (2-Isopropyl-4-methylpyrimidyl- 6) -diethyl thiophosphate
(Diazinon, Insects: rice boring insect, flea
leaves, plant lice, onion maggot, agrotis
harvests, beetle larvae, etc.) - O-ethyl O-2-isopropoxycarbonylphenyl isopropylphospho
ramidothioate (Isofenphos, Insects: beetle, larvae
wireworm, etc.) - 2-Methoxy-4H-l, 3,2-benzoxaphospholine-2-sulfide
(Salithion, Insects: plant louse, caterpillar of the
leucania, apple moth, cochineal, tortricidae,
cabbage worm, maggots, etc.) - (RS) -a-cyano-3-phenoxybenzyl- (RS) -2,2-dichloro-l
(4-ethoxyphenyl) cyclopropane carboxylate (Cycloprothrin,
Insects: rice water weevil, etc.) 2-Dimethylamino-5,6-dimethylpyrimidin-4-yl dimethyl
carbamate (Pirimicarb, Insects: aphids, etc.) 2- (4-Ethoxyphenyl) -2-methylpropyl-3-phenoxybenzyl ether
(Ethofenprox, Insects: rice water weevil,
bedbugs of the pentatomidae family, flea
leaves, European moth, aphids, tortricidae,
corn boring insect, bean moth, etc.) - Trans-S- (4-chlorophenyl) -N-cyclohexyl-4-methyl-2-oxy-
thiazolidine-3-carboxamide (Hexythiazox, Insects: mite
citrus red, European red mite, etc.) - 2-Tert-butylimino-3-isopropyl-5-phenyl-3, 4,5, 6-tetra-
hydro-2H-l, 3, 5-thiadin-4-one (Buprofezin, Insects
leaf flea, penta family bedbugs
tomids, rice boring insect, etc.) - Zinc dimethyldithiocarbamate (Ziram, Diseases
rust, scabies, black spots, leaf curl,
leaf spots, etc.) - Tetrachloroisophthalonitrile (Daconil, Diseases: spots
black, downy mildew, leaf curl,
mildew, gray mold, anthracnose, stains,
brown rot, drying of stems, spots of
leaves, etc.) - 4,5,6,7-Tetrachlorophthalide (Phthalide, Diseases
rice wilt disease, etc.) - (RS) -N- (l-butoxy-2, 2, 2-trichloroethyl) salicylamide
(Trichlamid, Diseases: hernia of cabbage, rot
strawberry roots, etc.) - 5-Methyl-1,2,4-triazolo- [3,4-b] benzothiazole
(Tricyclazole, Diseases: wilting disease of
rice, etc.) - 3-Hydroxy-5-methylisoxazole (Hydroxyisoxazole, Diseases:
rust of young plants, etc.) - 2-Chloro-2'-ethyl-N- (2-methoxy-1-methylethyl) -6'-methyl-
acetanilide (Metolachlor, Weeds: weeds
herbs belonging to the higher herb family,
weeds belonging to the nutcracker family
small flowers, etc.); and - DL-homoalanin-4-yl- (methyl) ammonium phosphinate
(Glufosinate, annual and perennial weeds
belonging to higher grasses, weeds
with broad leaves, etc.).

 The agricultural chemicals which can be used in the invention are not limited to chemicals which are stable under alkaline conditions. Agricultural chemicals which are unstable under alkaline conditions can also be used by imparting alkali resistance to the chemicals, for example by coating the chemicals with a resin film.

As described above, there are two modes of coating in the invention
- a mode (Mode I) includes the combination of a first
coating layer of a hydrophilic polymer which swells
by absorption of water and a second coating layer
an olefinic polymer, polyamide, polyester or
polyether; and
- another mode (Mode II) includes the combination of a
first coating layer of an alkaline compound and a
second coating layer of a mixture of a polymer
soluble in aqueous alkalis and a polymer
olefinic, polyamide, polyester or polyether.

 First of all, Mode I of the composition for agriculture, in granules with double coating, of the invention is explained in detail.

The hydrophilic polymer constituting the first coating layer preferably swells by absorption of water to increase its volume by not less than five times or more. Particularly preferred polymers are those which transform into a gel by slight dissolution and show a high swelling pressure. Examples of preferred hydrophilic polymers include isobutylene polymers (e.g. KI Gel-201K, KI Gel-201K-F2,
KI Gel Solution System, KI Gel ME-10 and KI Gel Compound, all available from Kuraray Co. Ltd., acrylic acid - vinyl alcohol copolymers, polyoxyethylene modified resins (e.g. Sumika Gels type S, type L, and type R, all available from
Sumitomo Chemical Industries, Co., Ltd, Japan), sodium acrylate polymers (e.g. Sumika Gel type S, available from Sumitomo Chemical Co., Ltd), grafted starches, carboxymethyl cellulose (CMC) , metal salts of carboxymethyl cellulose, and bentonite.

 The amount of the first coating layer depends on the degree of swelling and the swelling pressure, etc.

hydrophilic polymer. In general, the first coating layer is present in the amount of 0.5 to 20 by weight (preferably 1 to 10 t by weight), based on the amount of the core portion, which comprises a support and a agricultural chemical. If the amount of the first coating layer is less than the lower limit of the above range, the first coating layer is likely to swell poorly and, therefore, fail to break the second layer coating such that the release of the contained agricultural chemical is delayed or a sufficient release rate is not achieved. When the amount of the first coating layer is greater than the upper limit, the breaking of the second coating layer is easily effected. However, because of the increase in the amount of the first coating layer, it is generally necessary to reduce the amount of the core portion.

 The second coating layer is composed of an olefinic polymer, polyamide, polyester, polyether, or polyimide. These polymers can be used individually or in combination.

 The olefinic polymer can be a homopolymer of an olefinic monomer or a copolymer of an olefinic monomer and another monomer having an olefinic double bond. Preferred examples of olefin polymers include ethylene-acrylate copolymers (e.g., ethylene-methyl acrylate, and ethylene-ethyl acrylate), ethylene-methacrylate copolymers (e.g., ethylene-methyl methacrylate, and ethylene methacrylate). 'ethyl), low density polyethylenes, ethylene - propylene copolymers and ethylene - vinyl acetate copolymers.

Examples of the polyamides include polylactams, such as Nylon 6, Nylon II and
Nylon 12; polyamides prepared from a dicarboxylic acid and a diamine, such as Nylon 66,
Nylon 610 and Nylon 612; copolymerized polyamides, such as Nylon 6/66, Nylon 6/610, Nylon 6/12,
Nylon 6/612, Nylon 6/66/610, and Nylon 6/66/12; semi-aromatic polyamides prepared from an aromatic dicarboxylic acid (for example, isophthalic acid) and metaxylene diamine or an alicyclic diamine, such as Nylon 6 / 6T (T: terephthalic component); polyesteramides; and polyetheramides and polyesteretheramides. These polyamides may contain unreacted monomers or oligomers.

 Examples of the polyesters include thermoplastic saturated polyesters, prepared from a dicarboxylic acid and a glycol, and thermoplastic polyesters prepared by condensation polymerization of an oxyacid or by ring-opening polymerization of lactone nuclei. Saturated thermoplastic polyester should have ester linkages in the main chain of its molecular structure.

 Examples of polyethers include polyoxymethylene (i.e., polyacetal), poly (phenylene oxide), phenoxy resin, chlorinated polyether, glycol condensation polymerization products, such as polyethylene glycol and polypropylene glycol, and polyethersulfones prepared from bisphenol A and diphenylsulfone.

 In general, the second coating layer is present in an amount of 2 to 50% by weight (preferably 4 to 20% by weight), based on the amount of the core portion, which comprises a support and a agricultural chemical. If the amount of the second coating layer is less than the lower limit of the above range, it becomes not easy to uniformly arrange the second coating layer on the first coating layer.

In addition, the second coating layer of a lesser amount (which means a very thin second coating layer) has a low mechanical strength, so that it is liable to break easily during handling and of his training. If the amount of the second coating layer is greater than the upper limit, it is generally necessary to reduce the amount of the core portion. In addition, the second coating layer that remains in the soil can cause disturbances if its quantity increases.

It is assumed that the chemical composition for agriculture, in double-coated granules, conforms to the
Mode I mentioned above, acts in water or in an aqueous medium as follows
Water (surrounding water) gradually penetrates into the second coating layer. The first coating layer absorbs water passing through the second coating layer and swells to exert pressure on the second coating layer. When it receives this pressure, the second coating layer breaks or cracks. As a result, surrounding water comes into the core portion containing the agricultural chemical (and optionally a fertilizer). The agricultural chemical is then released from the granular composition.

 Therefore, if the nature and amount (thickness of the layer) of the olefinic polymer or other specified polymers of the second coating layer are appropriately selected, the rate of penetration of water through the second layer d coating can be controlled. In addition, if the nature and quantity (layer thickness) of the swellable material of the first coating layer is appropriately selected, the speed and degree of rupture of the second coating layer or of its cracking can to be controlled. Consequently, by choosing the natures and the quantities of the constituent materials of the first and second layers, the moment when the agricultural chemical contained must be released (i.e. the induction period or the time d wait) as well as the release rate can be adjusted. Thus, the chemical composition for agriculture, in double coated granules, of Mode I of the invention, can be prepared in response to various requirements of the release time.

The composition of granules with double coating of
Mode I can be prepared by a first coating of the core composition (support and chemical for agriculture) with the hydrophilic polymer, in order to form the first coating layer, then by coating the first coating layer with the olefinic polymer or another specified polymer, to form the second coating layer.

 The first coating layer can be formed as follows.

 The granular composition of an agricultural chemical and a fertilizer is placed on a tilted pan granulator, and an aqueous solution or a solution in an organic solvent of the hydrophilic polymer with high water absorption capacity ( that is to say the coating solution) is added, in fractions, to the granular composition with blowing of air heated to 30-70 "C. The first coating layer is thus formed, and the solvent or the water is evaporated.

 The hydrophilic polymer to be used for the formation of the first coating polymer is preferably crosslinked. Therefore, a crosslinking agent can be incorporated into the coating solution. By giving the first coating layer the crosslinked structure, the first coating layer is made resistant in its dissolution in water passing through the second coating layer.

 A suitable adhesive such as an ethylene-vinyl acetate, neoprene-phenyl, polyethylene glycol or polymethacrylate ester copolymer is preferably incorporated into the coating solution for the formation of the first coating layer. This adhesive is effective in firmly bonding the first coating layer to the granular core composition.

 The adhesive can be directly mixed with the agricultural composition, in granules, on the tray granulator, so that the granular composition can have a tacky character on its surface. The hydrophilic polymer in the pulverulent state is then mixed with the granular, sticky composition on the tank granulator, to obtain the granular composition, coated with the layer of hydrophilic polymer (first coating layer).

 For the formation of the first coating layer, other coating machines, such as a Nauta mixer, an air ventilation type coating machine, a rotary coating machine and a drum granulator, can also be employed.

 The second coating layer can be formed on the first coating layer in known machines for coating the granules. The granular composition, provided with the first coating layer, is first placed in the coating machines, and a solution of the olefin polymer, or of another specified polymer, in an organic solvent, is added to the composition. granular with blowing air heated to 30-100 C. In the machine, the solvent is evaporated in order to form the second coating layer on the granular composition, coated with the first coating layer.

 Solvents can be recovered from the coating machines and used repeatedly.

 Secondly, Mode II of the chemical composition for agriculture, in double-coated granules, of the invention, is explained below.

 The alkaline compound constituting the first coating layer may be an inorganic compound or an organic compound. Preferably, the alkaline compound is solid at ordinary temperatures and reacts with water in a moderate manner (i.e., not violently). Examples of the alkali compounds include carbonates, hydroxides and oxides of alkaline earth metals, carbonates, phosphates and silicates of alkali metals, and alkali metal salts of organic acids, and alkylamides. Preferred alkaline compounds are calcium carbonate, calcium oxide, calcium hydroxide, magnesium carbonate, magnesium oxide, magnesium hydroxide, sodium carbonate, potassium carbonate, potassium triphosphate, sodium silicate, sodium acetate, acetamide, propionamide and butylamide.

 The alkaline compound of the first coating layer is generally present in an amount of 0.1 to 10 parts by weight per 100 parts by weight of the core part, which comprises a carrier and an agricultural chemical. In addition, the amount of the alkaline compound of the first coating layer preferably represents from 0.2 to 10 times the amount of the polymer soluble in aqueous alkalis to be contained in the second coating layer.

If the amount of the alkaline compound of the first coating layer, relative to the amount of the polymer soluble in aqueous alkalis is less than the lower limit of the above range, the first coating layer does not dissolve the polymer soluble in the aqueous alkalis of the second coating layer on contact with water, and, therefore, fails to break the second coating layer, so that the release of the agricultural chemical content is delayed or a sufficient release speed is not reached. If the amount of the alkaline compound of the first coating layer, relative to the amount of the polymer soluble in aqueous alkalis is greater than the upper limit, the breaking of the second coating layer is easily effected. 'increase in the amount of the first coating layer, it is generally necessary to reduce the amount of the core part.

 The second coating layer of Mode II is composed of a mixture of a polymer soluble in aqueous alkalis and an olefinic polymer, polyamide, polyester, polyether or polyimide.

 These polymers can be used individually or in combination.

 The polymer soluble in aqueous alkalis is soluble in an aqueous alkaline solution, but is insoluble or is hardly soluble in neutral or acidic water. Preferred examples of the polymers soluble in aqueous alkalis include isobutylene maleic anhydride copolymers, their maleimide derivatives, their alcohol modified derivatives, acrylic acid acrylic ester copolymers, and carboxymethyl cellulose (CMC). The most preferred are the isobutylene maleic anhydride copolymers, their maleimide derivatives, their alcohol-modified derivatives. The isobutylene-maleic anhydride copolymer can be hydrolyzed to give a corresponding copolymer having carboxylic acid units and carboxylate units. This hydrolyzed copolymer is somewhat soluble in water and is not used individually.

 The isobutylene-maleic anhydride copolymer is hardly soluble in water (only 10% by weight or below are dissolved in water at 25 "C after two weeks), but it is very soluble in a solution alkaline aqueous (80% by weight or more are dissolved in an aqueous solution of potassium carbonate at 25 "C after two weeks). This copolymer is also soluble in organic solvents, such as dimethylformamide and dimethylsulfoxide.

 The isobutylene-maleic anhydride maleimide copolymer is insoluble in water (not soluble in water at 25 "C even after two weeks), but it is very soluble in an aqueous alkaline solution (80% by weight or more are dissolved in an aqueous solution of potassium carbonate at 25 "C after two weeks). This copolymer is also soluble in organic solvents.

 The second coating layer also comprises an olefinic polymer, polyamide, polyester, polyether or polyimide. With regard to these polymers, reference is made to the descriptions mentioned above, given for Mode I of the invention.

 In the second coating layer, the quantity of the polymer soluble in aqueous alkalis can be varied as desired depending on the desired rate of release of the chemical for agriculture. In general, the aqueous alkali-soluble polymer is incorporated in an amount of 2 to 80% by weight, preferably 4 to 50% by weight, based on the total amount of the aqueous alkali-soluble polymer and the olefin polymer. (or polyamide, polyester, polyether or polyimide). If the amount of the aqueous alkali-soluble polymer exceeds the upper limit of the above range, the physical strength decreases, and it is likely to break or crack during handling or dispensing of the granules. In these cases, the agricultural chemical contained in the granules is released before the predetermined release time. If the amount of the aqueous alkali-soluble polymer is less than the lower limit, the chemical may not be released at the predetermined release time.

 In general, the second coating layer is present in the amount of 2 to 50% by weight (preferably 4 to 20% by weight), based on the amount of the core portion, which comprises a support and a agricultural chemical. If the amount of the second coating layer is less than the lower limit of the above range, it becomes not easy to uniformly coat the first coating layer with the second coating layer.

In addition, the second coating layer if it is formed in a smaller quantity (which means a very thin second coating layer) has a low mechanical strength, so that it is liable to break easily during handling. and his training. If the amount of the second coating layer is greater than the upper limit, it is generally necessary to reduce the amount of the core portion. In addition, the second coating layer that remains in the soil can cause disturbances if its quantity increases.

It is assumed that the chemical composition for agriculture, in double-coated granules, conforms to the
Mode II mentioned above, acts in water or in an aqueous medium in the following manner
Water (surrounding water) gradually penetrates into the second coating layer. The alkaline compound of the first coating layer is dissolved in water passing through the second coating layer. Thus, the alkaline solution produced dissolves the polymer soluble in the aqueous alkalis of the second coating layer. Thereby, the aqueous alkali-soluble polymer is removed from the second coating layer, and the second coating layer becomes porous. The surrounding water then enters the core part through the pores, and the agricultural chemical is dissolved in the water and is released from the granules.

 Consequently, if the natures and amounts of the polymer soluble in aqueous alkalis and of the olefin polymer (or of the other specified polymers) of the second coating layer and the thickness of the second coating layer are chosen appropriately, the speed of penetration of water through the second coating layer can be controlled. In addition, if the nature and amount (layer thickness) of the alkaline compound of the first coating layer is appropriately selected, the speed and degree of pore formation of the second coating layer can be controlled. Consequently, by choosing the natures and quantities of the constituent materials of the first and second coating layers, the moment when the agricultural chemical contained must be released (i.e. induction period or time d 'wait) as well as the release speed can be adjusted.

Thus, the chemical composition for agriculture, in double coated granules, of Mode II of the invention can be prepared in response to the various requirements of the release time.

The composition of granules with double coating of
Mode II can be prepared by a first coating of the core composition (support and chemical for agriculture) with the alkaline compound, in order to form the first coating layer, then by coating the first coating layer with a blend of the aqueous alkali-soluble polymer and the olefin polymer (or other specified polymer) to form the second coating layer.

The first coating layer can be formed as follows
The granular composition of an agricultural chemical and a fertilizer is placed in an inclined pan granulator, and an aqueous solution or solution in an organic solvent of the alkaline compound (i.e. solution of coating) is added, in fractions, to the granular composition with blowing of air heated to 30 70 "C. The first coating layer is thus formed, and the solvent or water is evaporated. A suitable adhesive, such as an ethylene-vinyl acetate, phenyl neoprene, polyethylene glycol or polymethacrylate ester copolymer is preferably incorporated into the coating solution to form the first coating layer. This adhesive is effective in firmly bonding the first coating layer on the granular composition of the core.

 The adhesive can be directly mixed with the chemical composition for agriculture, in granules, on the tray granulator, so that the granular composition can have a tacky character on its surface. The alkaline compound in the pulverulent state is then mixed with the sticky granular composition, on the tank granulator, in order to obtain the granular composition coated with the layer of alkaline compound (first coating layer).

 For the formation of the first coating layer, other coating machines, such as a Nauta mixer, an air ventilation type coating machine, a rotary coating machine, and a drum granulator, can also be used.

 The second coating layer can be formed on the first coating layer in known machines for coating the granules. The granular composition provided with the first coating layer is first placed in the coating machines, and a solution of a mixture of the polymer soluble in aqueous alkalis and of the olefin polymer (or of another specified polymer) in an organic solvent is added to the granular composition with the blowing of air heated to 30-100 C. In the machine, the solvent is evaporated in order to form the second coating layer on the granular composition, coated with the first layer d 'coating.

 Solvents can be recovered from the coating machines and used repeatedly.

 Consequently, in accordance with the present invention, there is provided a chemical composition for agriculture, in coated granules, which is controlled to conserve its active agricultural chemical ingredient within it at a predetermined period and, when the period predetermined time has elapsed, then release the active ingredient quickly.

 In more detail, the chemical composition for agriculture, in double coated granules, of the invention, can easily be prepared so as to keep the agricultural chemical contained therein for a certain predetermined period of time. , and subsequently release the agricultural chemical quickly, by appropriate adjustment of the composition, thickness, etc. coating layers.

 Consequently, if different agricultural chemical compositions, in double-coated granules, in accordance with the present invention are formulated to exhibit different release times, a single application (application) operation is sufficient to supply the fields with compositions granular chemicals for agriculture, exhibiting different release times. For example, if a double-coated pellet composition containing an agricultural chemical to prevent rice wilt disease from wilting, as well as a double-coated pellet composition containing an agricultural chemical to prevent wilting disease of rice cobs, are produced in accordance with the present invention so as to exhibit different release times and are spread in the field one month before planting the rice, the first pellets will release the chemical with a short waiting time to prevent strand wilt disease, and the latter will release the chemical after a relatively long period of time has passed to prevent rice wilt disease.

 Examples and comparative examples are given below.

EXAMPLE 1
In 600 g of toluene, 18 g of powdered crosslinked isobutylene polymer (KI Gel 201K-F2, manufactured by Kuraray Co., Ltd) and 5.4 g of polyethylene glycol (Polyethylene Glycol 20,000, manufactured by Nihon) were dissolved. Oil & BR <
Fats Co., Ltd.), to give a first coating solution.

In 380 g of toluene, 20 g of ethylene-ethyl acrylate copolymer were dissolved (content of ethyl acrylate units: 8 mol%, melt index 13 g / 10 min., DPD J-8026 manufactured by Nippon Unicar Co.,
Ltd.) at 90-100 C, to give a second coating solution.

500 g of Coratop 5 Granules (obtained from Kumiai) were placed in a stainless steel granulator with an inclined tank, equipped with a rotation control device (diameter: 500 mm, depth: 100 mm)
Chemical Industries, Co., Ltd) containing 5% Pyroquilon (agricultural chemical, obtained from Ciba
Geigy Japan Ltd.). The granulator was started at a rotational speed of 15 rpm; and the first coating solution was introduced, in portions, into the granulator over a period of 10 minutes, with blowing, into the granulator, hot air, heated to approximately 30 "C, to form a first coating layer on Coratop Granules containing Pyroquilon.

In a ventilation type vacuum coating machine (Hicoater Mini, obtained from Froint
Industries, Co., Ltd., volume of the coating pan 0.65 liter), were placed 415 g of Coratop Granules containing Pyroquilon, provided with the first coating layer (containing 400 g of Coratop Granules). The coating pan was rotated at a rotational speed of 30 rpm The second coating solution was sprayed into the coating pan at an introduction speed of 10 ml / min., With introduction and extraction heated air (approximately 30 "C), to form a second coating layer around the first coating layer of Coratop Granules containing Pyroquilon.

 The double coating granules thus obtained comprised 3.8 parts by weight of the first coating layer and 4.6 parts by weight of the second coating layer, per 100 parts by weight of the Coratop Granules containing Pyroquilon.

EXAMPLE 2
The procedures of Example 1 were repeated except that the amounts of the powdered crosslinked isobutylene polymer, polyethylene glycol and toluene were changed to, respectively, 9 g, 2.7 g and 30 g, to give a first coating solution.

 In 760 g of toluene, 40 g of ethylene-ethyl acrylate copolymer were dissolved (content of ethyl acrylate units: 18 mol%, melt index 6 g / 10 min., NUC-6170 manufactured by Nippon Unicar Co., Ltd.) at 80-90 "C, to give a second coating solution.

 The procedures of Example 1 were again repeated, except that the above first and second coating solutions were used to give double coated granules.

 The double coated granules thus obtained comprised 2.0 parts by weight of the first coating layer and 9.3 parts by weight of the second coating layer, per 100 parts of the Coratop Granules containing Pyroquilon.

COMPARATIVE EXAMPLE 1
In the coating machine (Hicoater Mini), 400 g of Coratop Granules containing Pyroquilon were placed without having a coating layer. The coating pan was rotated at a rotational speed of 30 rpm

The second coating solution of Example 1 was sprayed into the coating pan at an introduction speed of 10 ml / min., With introduction and extraction of heated air (at approximately 30 "C), to form a single coating layer around the Coratop Granules containing Pyroquilon.

The single coating granules thus obtained comprised 4.8 parts by weight of the coating layer, per 100 parts by weight of the Coratop Granules containing
Pyroquilon.

COMPARATIVE EXAMPLE 2
The coating procedure of the Example
Comparative 1 was repeated using the second coating solution of Example 2, in order to form a single coating layer around the Coratop Granules containing
Pyroquilon.

The single coating granules thus obtained comprised 9.5 parts by weight of the coating layer, per 100 parts by weight of the Coratop Granules containing
Pyroquilon.

EVALUATION OF COATED GRANULES
The coated granules of Examples 1 and 2 and
Comparative Examples 1 and 2 were respectively immersed in water and stored in a thermostatic enclosure at 25 "C + 1" C, for 30 weeks. Part of the stored granules was removed each week and was subjected to the measurement of the quantity of Pyroquilon released. The quantitative analysis of Pyroquilon was carried out according to the process described in "Registered Agricultural Chemical Residue
Standard Handbook "(edited by" Study Group for Environmental
Security Against Agricultural Chemicals ", pages 435-437, The
Chemical Daily Co., Ltd., 1990).

 The release curve thus obtained (abscissae weeks of release, ordinates: cumulative percentage of release%) is shown in Figures 1 and 2.

The Figures clearly show that the single-coated granules of the Comparative Examples started to release the Pyroquilon after a certain period of time had passed or immediately after their immersion, and then gradually released the Pyroquilon. On the contrary, the double-coated granules of the Examples kept the Pyroquilon within them without release for a certain period, then began to release the
Pyroquilon very quickly in the same way as that observed just after conventional uncoated granules were immersed in water.

EXAMPLE 3
In 600 g of toluene, 18 g of powdered crosslinked isobutylene polymer (KI Gel 201K-F2, manufactured by Kuraray Co., Ltd) and 5.4 g of polyethylene glycol (Polyethylene Glycol 20,000, manufactured by Nihon) were dissolved. Oil & BR <
Fats Co., Ltd.), to give a first coating solution.

In 380 g of methanol, 20 g of Nylon 6 / Nylon 66 / Nylon 12 terpolymer were dissolved (pf 90-95 "C, UBE
NYLON 6021X18, manufactured by Ube Industries Ltd.), to provide a second coating solution.

In a granulator with a tilted tank, made of stainless steel, equipped with a rotation control device, 500 g of Coratop 5 Granules, containing 5% of
Pyroquilon, have been placed. The granulator was started at a rotational speed of 15 rpm, and the first coating solution was introduced, in fractions, into the granulator, over a period of time of 10 minutes, with insufflation, into the granulator, with hot air, heated to approximately 30 "C, in order to form a first coating layer on the Coratop Granules containing
Pyroquilon.

In the coating machine (Hicoater Mini), 415 g of Coratop Granules containing Pyroquilon were placed, fitted with the first coating layer (containing 400 g of
Coratop granules). The coating pan was rotated at a rotational speed of 30 rpm The second coating solution was sprayed into the coating pan at an introduction speed of 10 ml / min., With introduction and extraction hot air (at approximately 30 "C), in order to form a second coating layer around the first coating layer of Coratop Granules containing
Pyroquilon.

 The double coating granules thus obtained comprised 3.8 parts by weight of the first coating layer and 4.6 parts by weight of the second coating layer, per 100 parts by weight of the Coratop Granules containing Pyroquilon.

COMPARATIVE EXAMPLE 3
In the coating machine (Hicoater Mini), 400 g of Coratop Granules containing Pyroquilon were placed without having a coating layer. The coating pan was rotated at a rotational speed of 30 rpm

The second coating solution of Example 3 was sprayed into the coating pan at an introduction speed of 10 ml / min., With introduction and extraction of heated air (at approximately 30 "C), to form a single coating layer around the Coratop Granules containing Pyroquilon.

The single coating granules thus obtained comprised 4.8 parts by weight of the coating layer, per 100 parts by weight of the Coratop Granules containing
Pyroquilon.

EVALUATION OF COATED GRANULES
The coated granules of Example 3 and of Example
Comparative 3 were evaluated for their release behavior in the manner mentioned above.

 The release curve thus obtained (abscissae weeks of release, ordinates: cumulative percentage of release t) is illustrated in Figures 3 and 4.

The Figures clearly show that the single-coated granules of Comparative Example 3 started to release the Pyroquilon after a certain period of time had passed or immediately after their immersion, and then gradually released the Pyroquilon. On the contrary, the double-coated granules of Example 3 kept the Pyroquilon within them without release for a certain period of time, then started to release the
Pyroquilon very quickly in the same way as that observed just after conventional uncoated granules were immersed in water.

EXAMPLE 4
To 40 g of toluene were added 12 g of calcium hydroxide, 3.6 g of polyethylene glycol (adhesive,
Polyethylene Glycol 20,000, manufactured by Nihon Oil & Fats
Co., Ltd.), to give a first coating solution.

In 380 g of toluene, 29.2 g of ethylene-ethyl acrylate copolymer were dissolved (content of ethyl acrylate units: 8 mol%, melt index 13 g / 10 min., DPD J- 8026 manufactured by Nippon Unicar Co.,
Ltd., hereinafter referred to as the resin EEA-1), at 90,100 "C. Separately, in 360 g of methyl ethyl ketone, were dissolved 10.8 g of isobutylene-maleic anhydride (BM-30) copolymer , manufactured by Kuraray Co., Ltd., hereinafter referred to as BM-30 resin, at 60-70 "C.

The solutions thus produced were mixed to give a second coating solution, which was then stored at a temperature of 80 + 5 "C.

In a granulator with an inclined tank, made of stainless steel, equipped with a rotation control device, 500 g of Coratop 5 Granules containing 5% of
Pyroquilon were placed. The granulator was started at a rotational speed of 15 rpm, and the first coating solution was introduced, in fractions, into the granulator over a period of 10 minutes, with blowing, into the granulator, d hot air, heated to approximately 30 "C, to form a first coating layer on Coratop Granules containing Pyroquilon.

In the coating machine (Hicoater Mini), 410 g of Coratop Granules containing Pyroquilon having the first coating layer were placed (containing 400 g of
Coratop granules). The coating pan was rotated at a rotational speed of 30 rpm The second coating solution was sprayed into the coating pan at an introduction speed of 10 ml / min., With introduction and extraction with hot air (at approximately 30 "C), in order to form a second coating layer around the first coating layer of Coratop Granules containing
Pyroquilon.

 The double coated granules thus obtained comprised 2.6 parts by weight of the first coating layer and 9.5 parts by weight of the second coating layer, per 100 parts by weight of the Coratop Granules containing Pyroquilon. The ratio of alkaline compound to polymer soluble in aqueous alkalis was 78/100.

EXAMPLE 5
The procedures of Example 4 were repeated, except that the amounts of EEA-1 resin, BM-30 resin and toluene were changed to, respectively, 35 g, 13 g and 456 g, to give a second coating solution.

 The procedures of Example 4 were repeated, except that the above second coating solution was used to give double coated granules.

 The double coated granules thus obtained comprised 2.6 parts by weight of the first coating layer and 11.1 parts by weight of the second coating layer, per 100 parts by weight of the Coratop Granules containing Pyroquilon. The ratio of alkaline compound to polymer soluble in aqueous alkalis was 67/100.

EXAMPLE 6
The procedures of Example 4 were repeated, except that 12 g of calcium hydroxide were replaced by 12 g of potassium carbonate, to give a first coating solution.

 The procedures of Example 4 were then repeated, except that the first coating solution above was used to give double coated granules.

 The double coated granules thus obtained comprised 2.5 parts by weight of the first coating layer and 11.0 parts by weight of the second coating layer, per 100 parts by weight of the Coratop Granules containing Pyroquilon. The ratio of alkali compound to polymer soluble in aqueous alkalis was 65/100.

EXAMPLE 7
The procedures of Example 4 were repeated, except that the amounts of EEA-1 resin and BM-30 resin were changed to, respectively, 20 g and 20 g, to give a second coating solution .

 The procedures of Example 4 were repeated, except that the above second coating solution was used to give double coated granules.

 The double coated granules thus obtained comprised 2.6 parts by weight of the first coating layer and 9.2 parts by weight of the second coating layer, per 100 parts by weight of the Coratop Granules containing Pyroquilon. The ratio of alkaline compound to polymer soluble in aqueous alkalis was 43/100.

EXAMPLE 8
In 456 g of toluene, 43.7 g of ethylene-ethyl acrylate copolymer were dissolved (content of ethyl acrylate units: 7 mol%, melt index 4 g / 10 min., NUC-6220 manufactured by Nippon Unicar Co., Ltd., hereinafter referred to as EEA-2) resin at 90-100 C.

Separately, in 456 g of methyl ethyl ketone, 4.3 g of isobutylene-maleimid anhydride copolymer (resin BM-30) were dissolved at 60-70 "C. The solutions thus produced were mixed at a temperature of 80 + 5 "C to give a second coating solution.

 The procedures of Example 4 were repeated, except that the above second coating solution was used to give double coated granules.

 The double coated granules thus obtained comprised 2.6 parts by weight of the first coating layer and 11.0 parts by weight of the second coating layer, per 100 parts by weight of the Coratop Granules containing Pyroquilon. The ratio of alkaline compound to polymer soluble in aqueous alkalis was 202/100.

COMPARATIVE EXAMPLE 4
In 380 g of toluene, 20 g of the EEA-1 resin were dissolved to give a coating solution. Then this coating solution was maintained at 90-100 C after the completion of the preparation.

 In the coating machine (Hicoater Mini), 400 g of Coratop Granules containing Pyroquilon containing no coating layer were placed. The coating pan was rotated at a rotational speed of 30 rpm.

The above coating solution was sprayed into the coating pan at an introduction rate of 10 ml / min., With introduction and extraction of heated air (at approximately 30 "C), in order to form a single coating layer around the Coratop Granules containing Pyroquilon.

The single coating granules thus obtained comprised 4.7 parts by weight of the coating layer, per 100 parts by weight of the Coratop Granules containing
Pyroquilon.

COMPARATIVE EXAMPLE 5
The procedures of Comparative Example 4 were repeated, except that the amounts of EEA-1 resin and toluene were changed to, respectively, 35 g and 665 g, to give a coating solution.

 The procedures of Comparative Example 4 were repeated, except that the above coating solution was used to give granules with a single coating.

The single coating granules thus obtained comprised 8.2 parts by weight of the coating layer, per 100 parts by weight of the Coratop Granules containing
Pyroquilon.

COMPARATIVE EXAMPLE 6
The procedures of Comparative Example 4 were repeated, except that 20 g of the EEA-1 resin were replaced by 43.7 g of the EEA-2 resin and that the amount of toluene was changed to 830 g, to give a coating solution.

 The procedures of Comparative Example 4 were repeated, except that the above coating solution was used to give granules with a single coating.

The single coating granules thus obtained comprised 10.4 parts by weight of the coating layer, per 100 parts by weight of the Coratop Granules containing
Pyroquilon.

EVALUATION OF COATED GRANULES
The coated granules of Examples 4-8 and
Comparative Examples 4-6 were evaluated for their release behavior as mentioned above.

 The release curve thus obtained (abscissae weeks of release, ordinates: cumulative percentage of release%) is shown in Figures 5 and 6.

The Figures clearly show that the single-coated granules of Comparative Examples 4 and 6 started to release Pyroquilon after a certain period of time had elapsed or immediately after their immersion, and then gradually released the
Pyroquilon Single Coated Granules of Example
Comparative 5 almost did not release Pyroquilon, because their coating layers were very thick.

On the contrary, the double-coated granules of the
Examples 4-8 kept the Pyroquilon in their midst without release for a certain period of time, then started to release the Pyroquilon very quickly in the same manner as that observed just after conventional uncoated granules were immersed in water.

EXAMPLE 9
To 40 g of toluene were added 12 g of calcium hydroxide, 3.6 g of polyethylene glycol (adhesive,
Polyethylene Glycol 20,000), to give a first coating solution.

29.2 g of Nylon 6 / Nylon 66 / Nylon 12 terpolymer were dissolved in 380 g of methanol (pf: 90-95 "C, UBE
NYLON 6021X18, manufactured by Ube Industries Ltd.), at room temperature. Separately, in 360 g of methyl ethyl ketone, were dissolved 10.8 g of isobutylene maleic anhydride (BM-30) copolymer, at 60-70 "C. The solutions thus produced were mixed to give a second solution of coating, which was then stored at a temperature of 50-60 "C.

In a granulator with an inclined tank, made of stainless steel, equipped with a rotation control device, 500 g of Coratop 5 Granules containing 5
Pyroquilon were placed. The granulator was started at a rotational speed of 15 rpm, and the first coating solution was introduced, in fractions, into the granulator over a period of 10 minutes, with blowing, into the granulator, d 'hot air, heated to approximately 30 "C, to form a first coating layer on Coratop Granules containing
Pyroquilon.

In the coating machine (Hicoater Mini), 410 g of Coratop Granules containing Pyroquilon were placed, provided with the first coating layer (containing 400 g of
Coratop granules). The coating pan was rotated at a rotational speed of 30 rpm The second coating solution was sprayed into the coating pan at an introduction speed of 10 ml / min., With introduction and extraction hot air (at approximately 30 "C), in order to form a second coating layer around the first coating layer of Coratop Granules containing
Pyroquilon.

 The double coated granules thus obtained comprised 2.6 parts by weight of the first coating layer and 9.5 parts by weight of the second coating layer, per 100 parts by weight of the Coratop Granules containing Pyroquilon. The ratio of alkaline compound to polymer soluble in aqueous alkalis was 78/100.

EXAMPLE 10
The procedures of Example 9 were repeated, except that the amounts of Nylon UBE 6021X18, BM-30 resin, methanol and methyl ethyl ketone were changed to, respectively, 35 g, 13 g, 456 g and 456 g, to give a second coating solution.

 The procedures of Example 9 were repeated except that the above second coating solution was used to give double coated granules.

 The double coated granules thus obtained comprised 2.6 parts by weight of the first coating layer and 11.1 parts by weight of the second coating layer, per 100 parts by weight of the Coratop Granules containing Pyroquilon. The ratio of alkaline compound to polymer soluble in aqueous alkalis was 67/100.

EXAMPLE 11
The procedures of Example 9 were repeated, except that 12 g of calcium hydroxide was replaced by 12 g of potassium carbonate, to give a first coating solution.

 The procedures of Example 9 were then repeated, except that the first coating solution above was used to give double coated granules.

 The double coated granules thus obtained comprised 2.5 parts by weight of the first coating layer and 11.0 parts by weight of the second coating layer, per 100 parts by weight of the Coratop Granules containing Pyroquilon. The ratio of alkali compound to polymer soluble in aqueous alkalis was 65/100.

EXAMPLE 12
The procedures of Example 9 were repeated except that the amounts of UBE 6021X18 Nylon and BM-30 resin changed to 20 g and 20 g, respectively, to give a second coating solution.

 The procedures of Example 9 were repeated except that the above second coating solution was used to give double coated granules.

 The double coated granules thus obtained comprised 2.6 parts by weight of the first coating layer and 9.2 parts by weight of the second coating layer, per 100 parts by weight of the Coratop Granules containing Pyroquilon. The ratio of alkaline compound to polymer soluble in aqueous alkalis was 43/100.

COMPARATIVE EXAMPLE 7
In 380 g of methanol, 20 g of the
Nylon UBE 6021X18 to give a coating solution. Then this coating solution was kept at 50-60 "C after the completion of the preparation.

 In the coating machine (Hicoater Mini), 400 g of Coratop Granules containing Pyroquilon containing no coating layer were placed. The coating pan was rotated at a rotational speed of 30 rpm.

The above coating solution was sprayed into the coating pan at an introduction rate of 10 ml / min., With introduction and extraction of heated air (at approximately 30 "C), in order to form a single coating layer around the Coratop Granules containing Pyroquilon.

The single coating granules thus obtained comprised 4.7 parts by weight of the coating layer, per 100 parts by weight of the Coratop Granules containing
Pyroquilon.

COMPARATIVE EXAMPLE 8
The procedures of Comparative Example 7 were repeated, except that the amounts of UBE Nylon 6021X18 and methanol were changed to, respectively, 35 g and 665 g, to give a coating solution.

 The procedures of Comparative Example 7 were repeated, except that the above coating solution was used to give granules in a single coating.

The single coating granules thus obtained comprised 8.2 parts by weight of the coating layer, per 100 parts by weight of the Coratop Granules containing
Pyroquilon.

EVALUATION OF COATED GRANULES
The coated granules of Examples 9-12 and
Comparative Examples 7 and 8 were evaluated for their release behavior as mentioned above.

 The release curve thus obtained (abscissa weeks of release, ordinates: cumulative percentage of release) is shown in Figures 7 and 8.

 The Figures clearly show that the single-coated granules of Comparative Example 7 started to release the Pyroquilon after a certain period of time had passed or immediately after their immersion, and then gradually released the Pyroquilon . The single-coated granules of Comparative Example 8 hardly released Pyroquilon because their coating layers were very thick.

On the contrary, the double-coated granules of the
Examples 9-12 kept the Pyroquilon in their midst without release for a certain period of time, then started to release the Pyroquilon very quickly in the same way as that observed just after conventional uncoated granules were immersed in water.

Claims (10)

 1 - Chemical composition for agriculture, in granules with double coating, characterized in that it comprises a core containing a chemical compound for agriculture, a first coating layer of hydrophilic polymer which swells by absorption of water , and a second coating layer of olefinic polymer, polyamide, polyester, polyether or polyimide.  2 - Chemical composition for agriculture, in granules with double coating, according to claim 1, characterized in that the hydrophilic polymer of the first coating layer swells by absorption of water to increase its volume by not less than five times or more.  3 - Chemical composition for agriculture, in granules with double coating, according to claim 1, characterized in that the hydrophilic polymer of the first coating layer is chosen from the group consisting of isobutylene polymers, copolymers acrylic acid - vinyl alcohol, resins modified by polyoxyethylene, polymers of sodium acrylate, grafted starch, carboxymethyl cellulose, metal salts of carboxymethyl cellulose and bentonite.  4 - Chemical composition for agriculture, in granules with double coating, according to claim 1, characterized in that the olefinic polymer is chosen from the group consisting of ethylene - acrylate copolymers, ethylene - methacrylate copolymers, low polyethylenes density, ethylene propylene copolymers and ethylene-vinyl acetate copolymers.  5 - Chemical composition for agriculture, in granules with double coating, according to claim 1, characterized in that the first coating layer and the second coating layer are present in amounts, respectively, of 0.2 at 20% by weight and from 2 to 50% by weight, based on the total amount of the chemical composition for agriculture.  6 - Chemical composition for agriculture, in granules with double coating, characterized in that it comprises a core containing a chemical compound for agriculture, a first coating layer of an alkaline compound, and a second layer for coating a mixture of polymer soluble in aqueous alkalis and of olefinic polymer, polyamide, polyester, polyether or polyimide.  7 - Chemical composition for agriculture, in granules with double coating, according to claim 6, characterized in that the alkaline compound is chosen from the group consisting of carbonates, hydroxides and oxides of alkaline earth metals, carbonates, alkali metal phosphates and silicates, alkali metal salts of organic acids, and alkylamides.  8 - Chemical composition for agriculture, in granules with double coating, according to claim 6, characterized in that the polymer soluble in aqueous alkalis is chosen from the group consisting of isobutylene-maleic anhydride copolymers, their maleimide derivatives and their alcohol-modified derivatives.  9 - Chemical composition for agriculture, in granules with double coating, according to claim 6, characterized in that the olefinic polymer is chosen from the group consisting of ethylene - acrylate copolymers, ethylene - methacrylate copolymers, low polyethylenes density, ethylene propylene copolymers and ethylene-vinyl acetate copolymers.  10 - Chemical composition for agriculture, in granules with double coating, according to claim 6, characterized in that the first coating layer and the second coating layer are present in amounts, respectively, of 0.2 at 20% by weight and from 2 to 50% by weight, based on the total amount of the chemical composition for agriculture.