DD240843A1 - METHOD OF MICROPELLING PESTICIDES - Google Patents

Abstract

The invention relates to a process which makes it possible to encapsulate solidicides in such a way that adequate stability, reduced general toxicity and a long period of action are achieved. The task was to enable capsule formation using water-soluble amino resins in aqueous dispersion. The object could be achieved by adding to the aqueous dispersion partially methanol-esterified, water-soluble, cationically modified melamine-formaldehyde condensation products without further additives having a content of free methylol groups of from 0.75 to 3.0 mol / mol of melamine.

Description

Field of application of the invention

The invention relates to a process for the microencapsulation of pesticides. The microencapsulated pesticides are particularly suitable as pesticides in agrochemistry.

Characteristic of the known technical solutions

Pesticides, eg. As phosphoric acid esters, are normally used as pesticides in aqueous-organic solution or emulsion. A disadvantage of this application form is its short duration of action after application, the majority of the insecticidal activity of insecticidal phosphoric acid esters has largely subsided already one to two days after application.

Another disadvantage is the often high warm-blooded toxicity of these pesticides. Thus, the LD ₅₀ for parathion-methyl-concentrate with 50% active substance thiophosphoric OO-dimethyl-Op-nitrophenyl ester (Wofatox of VEB Chemiekombinat Bitterfeld, GDR) is only 39 mg per kg rat, it therefore belongs to the Poison Department I.Wegen of high toxicity, it is desirable to find forms of administration in which the acute toxicity of the phosphoric esters is reduced. For the solution of the listed problems, there are already pesticides containing phosphoric acid ester in microencapsulated form. The microcapsules are obtained by interfacial polycondensation of dicarboxylic acid chlorides with diamines and marketed as the commercial product Pencap M (Penwalt Corporation, USA). The encapsulation reduced toxicity to approximately 10% of the toxicity of the unencapsulated drug, prolonging its duration of action to over 8 days (CB DeSarigny and EE Iry in JEVandegaer "Microencapsulation" Plenum Press, New York and London, 1974).

However, this microencapsulation process for insecticidal phosphoric acid esters has some serious disadvantages. Thus, the applied interfacial polycondensation is bound to not easily accessible, expensive and inconveniently manageable starting products (dicarboxylic acid chlorides and diamines). To make matters worse, due to the irreversibility of the polymer formation reaction on the pellets of the emulsified insecticides, phosphoric acid esters must maintain accurate stoichiometric ratios of the components, requiring very precise dosing of the components. The microencapsulation of agrochemicals with water-soluble urea-formaldehyde resins has already been mentioned in ÜSP 3516941 among many other examples. For example, a herbicide is encapsulated with a triethanolamine-modified urea resin. The herbicide has maintained its effectiveness through microencapsulation for two weeks.

British Patent 2113170 describes the microencapsulation of pesticides with mixtures of water-soluble cationic urea resins η and amino resin precondensates. For capsule formation, a special cationic urea resin, one to two amino resin precondensates and an anionic surfactant intended to stabilize the dispersion and thus provide favorable capsule wall formation were used. The process is carried out by dispersing the core substance in an aqueous phase containing the water-soluble cationic urea resin and anionic surfactant, and feeding the prepolymer before, during or after the dispersing phase. However, the procedure used has, like all previously described methods for microencapsulation with water-soluble amino resins, a number of significant disadvantages. These include, for example:

The sensitivity to low property fluctuations of the water-soluble copolymers used as emulsifiers (eg molecular weight, molecular weight distribution, copolymerization ratios)

- the complexity of the process

The need for particularly high shear in dispersing and during capsule formation to prevent agglomeration

- strong influences of the emulsifier quality on the capsule properties

The fact that the systems tend to have high viscosity and therefore only dilute dispersions can be obtained

The low deposition tendency of the solute wall-forming materials on the core material, which often leads to poor quality capsules

The dependence of the capsule wall properties on the properties of the resins used

- Prevention of the formation of thick walls with better retention of the encapsulated substances with the addition of increased amounts of wall formers.

The solution to the many problems of using aqueous amino resin solutions is seen in EP-PS 120504 is that non-water-soluble amino resins are used.

Object of the invention

The aim of the invention is a method that makes it possible. Encapsulate pesticides so that the resulting microcapsules have sufficient stability, reduced general toxicity and a prolonged period of action and simple starting materials can be used for encapsulation.

Explanation of the essence of the invention

- Task

The invention has for its object to provide the capsule formation using water-soluble amino resins in aqueous dispersion containing non-core or non-water-soluble pesticides as core substance.

Features of the invention

The object could be achieved by adding partially methanol-etherified, water-soluble cationically modified melamine-formaldehyde condensation products without further additions of the aqueous dispersion for the formation of the capsule wall.

For encapsulation are pesticides consisting of individual substances, eg. As phosphoric acid esters or polychlorocamphenes, and mixtures thereof or individual substances in admixture with other active ingredients or non- or poorly soluble in water solvents and diluents.

In addition to melamine, the resins may contain other additives customary in amino resin chemistry, such as urea, dicyandiamide, benzoguanamine, acetoguanamine or similar compounds.

As cationic modifiers, alkylamines such as ethylenediamine, hexamethylenediamine and the like, alkanolamines such as mono-, di-triethylamine or the like are used.

In addition to methanol-etherified methylol groups, the partially methanol-etherified water-soluble cationically modified amino resins used according to the invention contain free methylol groups in concentrations between 0.75 and 3 moles per mole of melamine and are prepared by reacting formalin with melamine, then partial etherification with methanol and addition of cationic modifier.

The capsule formation takes place according to the invention at pH values between 1.0 and 7.0, preferably between 2.0 and 5.0, temperatures up to 100 ° C. and reaction times between 30 minutes and 20 hours. The encapsulation is carried out in such a way that the water-insoluble insecticides or phosphors to be encapsulated are emulsified under high shear in water adjusted to the reaction pH without further additions. The emulsion can already be heated to the reaction temperature, but it is also possible to add the water-soluble partially methanol-etherified cationically modified melamine resin already at room temperature and only then to heat.

After addition of the resin, the emulsion is held for a further 5 to 240 minutes with thorough mixing at the reaction temperature, then the capsule formation can be completed with slow stirring. After completion of the capsule formation, the aqueous acidic capsule dispersion can be neutralized.

As insecticidal phosphoric acid esters to be encapsulated in the context of the present invention, all non- or only slightly water-soluble insecticides are phosphoric acid esters, such as e.g. B.

- Dichlorovos (phosphoric acid O.O-dimethyl-O ^^ - dichlorovinyl-ester),

Naled (phosphoric acid O, -dimethyl-O-II-dibromo, di-dichloro-ethyl-J-ester),

- butonate (i-butyryloxy) - trichloroethylphosphoric O-O-dimethyl ester),

ChlorfenvinphostPhosphorsäure O.O-diethyl-O-I ^ -chlor-i ^^ - dichlorophenyl-l-vinyl ester), thiophosphoric acid esters, such as. B.

Parthion methyl (thiophosphoric acid O.O-dimethyl-O-p-nitrophenyl ester),

- Bromophos (thiophosphoric acid 0,0-dimethyl-0- [4-bromo-2,5-dichlorophenyl] ester), dithiophosphoric acid esters, such as. B.

Dimethoate (dithiophosphoric acid-OjO-dimethyl-S-IN-methylcarbonoyü-ester),

Malathion (dithiophosphoric acid O.O-dimethyl-S-F 1 -dicarbethoxyethyl ester),

- Phosmet (dithiophosphoric O-dimethyl-S-phthalimidomethyl ester) and other insecticidal phosphoric acid esters understood.

The average size of the capsules is adjustable by choosing the mixing conditions within the first 240 minutes after the addition of the amino resin between about 3 and 50 microns, so that it is relatively easy to produce optimal capsule sizes for certain applications.

The adjustment of the pH value is carried out by inorganic or organic acids, it can also be successfully used buffer systems.

The high mechanical stability of the capsules is advantageous in the case of the microcapsules prepared according to the invention, so that even after several days a high active substance concentration is retained and their reduced toxicity, which is particularly important for use as insecticide, and the use of simple starting materials for the formation of the capsule wall.

embodiments example 1 A. Preparation of Resin Solutions General procedure

A certain amount of formalin is adjusted to pH 9 and heated to 8O ⁰ C, added the appropriate amount of melamine and heated to about 95 ° C. Thereafter, the solution is cooled to 60 ° C, with half konz. HCI acidified and the 3-fold molar amount of methanol (based on the amount of formaldehyde used) was added. The initially turbid solution clears after stirring for 10 to 60 minutes at 60 ⁰ C. Then, the cationic modifier is added and stirred at 60 ° C for a further 10-30 min. Subsequently, the azeotrope water / methanol is distilled off in vacuo. Following this general procedure, the following resin solutions were prepared (Table 1).

Preparation and characterization of the resin solutions: Table 1 A1 A2 A3

A4

A6

Mass melamine (g) 126.2 126.2 63.1 63.1 63.1 63.1 80.0 Mass of formalin 300 400 250 300 350 400 354.3 30proz. (G) Mass of methanol (g) 288.4 384.5 240.3 288.4 336.4 384.5 342.9 Mass Trietha 8th 8th 8th 8th 8th 8th 8th nolamin (g) melamine content 36.5 36.5 32.8 19.4 16.5 19.3 23.7 MoI (CH ₂ OH) 0.46 0.75 0.77 1.23 1.98 1.22 1.58 per mole of melamine

B. Preparation of the microcapsules

The microencapsulation of the parathion-methyl (thiophosphoric acid-OjO-dimethyl-O-p-nitrophenyl ester) used as an example compound was carried out according to the following general procedure:

100 ml of distilled water is added to a certain amount of acid to adjust the reaction pH.

Instead of distilled water and acid and buffer solutions can be used with a certain pH. In the water heated to the reaction temperature, phosphoric acid ester is emulsified under high shear or the water-insoluble or sparingly soluble insecticides and then the water-soluble, partially etherified cationically modified melamine resin is added dropwise. After a stirring time of 10 to 240 minutes under high shear at the reaction temperature, the microcapsule dispersion formed is slowly stirred for a period of 30 minutes to 20 hours to cure the capsule wall 'further. Thereafter, the capsule dispersion can be formulated and used in terms of application technology. Typical examples of microencapsulation are shown in Table 2. It is understood by "poor" capsule properties that the capsules are not dry, but melt when drying on a substrate and release the drug.

"Good" capsules are dry-proof.

The resins Al and A2 are not suitable for capsule formation because of their incomplete water solubility and low content of unetherified methylol groups, although the resin A3 gives microcapsules under well-defined reaction conditions, but they are not completely dry and partly disintegrate slightly.

Capsules according to Example 1, B8 resulted in the laying of potato beetle larvae L _4a on freshly sprayed potato plants

a mortality of over 80% within six days;

with capsules according to Example 1, B10 the mortality was 100% under the same conditions

Table 2: Microencapsulation of pesticides on the example of insecticidal phosphoric acid ester (based on 100 ml of aqueous solution), active ingredient: parathion-methyl, 79% active ingredient content

Example- resin phosphoric acid acid PH value reaction Stirring time Nachhär capsule own No. ester temp. u. higher processing time companies shear B1 4,0gA1 30.8 g ants 3.5 60 ⁰ C 15 minutes 60 min no capsule acid education B2 3.72 gA2 30.8 g ascorbic 3.2 60 ° C 30 min 360 min bad acid B3 ' 4,12gA3 30.8 g sebacic 3.5 6O ⁰ C 30 min 360 min bad acid B4 6.97 g A4 30.8 g ants 3.3 60 ⁰ C 30 min 300 min Well acid B5 8,2gA5 30.8 g phosphorus 3.6 65 ⁰ C 40 min 320 min Well acid B6 8.1 gA6 30.8 g ants 3.0 55 ° C 45 min 240 min Well acid B7 7,0gA7 30.8 g Lemons 3.2 60 ° C 25min 240 min Well acid

Example resin no.

Phosphoric acid, acid ester

pH Reaction Stirring Time Posthardening capsule temp. u. HIGH TIME SHOPS

shear

B8 5.8gA6 B9 7.0gA7 B10 5.8gA6

15.4 g + 15.4 g of xylene 7.7 g + 23.1 g of xylene 15.4 g + 15.4 g of dioctyl phthalate

Formic acid citrate buffer ascorbic acid

3.1 60 ⁰ C 2,7 60 ⁰ C

3.2 60 ⁰ C

Good 60 minutes 240 minutes

Good 60 minutes 240 minutes

50 min 300 min good

Table 3: Result of a long-term test on L ₃ potato beetle larvae compared with unencapsulated active substance (same active substance concentration)

Bonitur Experimental approach after plant treatment 1. Second 4th 7th day variant Day (Mortality of the larvae in%) 0 0 0 0 0th 5 0 0 0 Parathion- 1. 70 5 0 0 0 methylkonzen- Second 76.6 10 10 0 0 tratK50 4th 76.6 15 10 0 0 6th 76.6 25 0 15 0 10th 76.6 55 5 15 0 Kapselnnach 1. 63.3 75 25 30 0 Example B 6 Second 86.6 75 45 30 0 4th 93.3 80 50 40 10 6th 93.3 10th 93.3

Table 4: Results of biological tests with caterpillars of the cabbage larvae or larvae of the Mexican bean beetle microcapsules

according to example 2.2 (mortality in%) a) caterpillars of the coal ow

Efficiency after days

13

concentration

concentration

0.01 0.1 0.01 0.1 Parathion Methyl K 50 0 36 0 2 Capsules according to Example B7 28 90 30 70 b) Larvae of the Mexican bean beetle

Efficiency after days

13

concentration

concentration

0.01

0.01

0.1

Parathion Methyl K 50

15

Capsules according to Example B 8

10

85

Dry strength microcapsules are formed when the methylol content of the partially etherified cationically modified melamine resins is above 0.75 to 3.0 moles of methylol groups per mole of melamine. The test results given in Tables 3 and 4 demonstrate the long-term effect of the microcapsules prepared according to the invention over the unencapsulated product on the example of parathion-methyl.

Example 2

A mixture of 7.7 g parathion-methyl, 7.7 g Naled and 15.4 g xylene is microencapsulated with 5.8 g of resin A6 according to Example 1. The mortality of L rtoffelkäferlarven ₃ -Ka that are placed on potato leaves one day after spraying, after 6 days of 95%.

Example 3

100 g of a 10% solution of camphechlor (polychlorophene) in xylene are homogeneously mixed with 15 g of parathion-methyl.

35 g of this mixture are microencapsulated with 7.0 g of resin A7 according to Example 1.

The mortality of L ₃ -Kartoffelkäferlarven that are placed immediately after the spraying, is after 5 days

Claims (2)

Invention claim: 1. A process for the microencapsulation of pesticides, in aqueous dispersion using water-soluble amino resins, characterized in that partially encapsulated methanol-etherified, water-soluble cationic-modified melamine-formaldehyde condensation products without further additives having a content of free methylol groups from 0.75 to 3 Be added mol / mol of melamine. 2. Method according to item!, Characterized in that the pH is between 1.0 and 7.0.