CS197280B2 - Method of making ammeliorated polyurea microcapsules - Google Patents

Abstract

Polyurea microcapsules having individual capsule walls are produced. The capsule walls are obtained by interfacial polymerisation. Firstly, an organic phase is formed, which contains water-immiscible material to be encapsulated, a solvent which is capable of excluding water from the organic material and/or of controlling the porosity of the polyurea wall in accordance with the solubility parameter for the polyurea microcapsule wall, and a polyisocyanate. This organic phase is dispersed in an aqueous phase which, in addition to water, contains a surfactant and a protective colloid. The individual polymer walls of the capsules are then formed. This process allows the quality, in particular the porosity and thus the permeability of the capsule walls to be controlled.

Description

The invention relates to encapsulation and more particularly to a process for the production of small or microcapsules consisting of a shell or a thin wall of an organic polymer containing a water-immiscible material as an organic liquid. In particular, the invention relates to the production of improved discrete polyurea microcapsules containing various core materials by adding a solvent to the organic phase.

The improvement is a result of the selective control of the porosity of the polyurea walls leading to the formation of bounded polyurea walls.

The process according to the invention relates to such capsules, where a solvent or non-solvent of the polymeric wall is added before the microencapsulation to the organic phase.

Belgian Patent No. 796,746 describes a method of encapsulating various water-immiscible materials using an organic isocyanate as an intermediate to form a polyurea capsule containing a water-immiscible material dispersed in an aqueous continuous phase.

Capsules of this nature and description have different uses, such as for coloring, ink, chemical reagents, pharmaceuticals, - fertilizers, fungicides, bactericides, pesticides such as herbicides, insecticides and the like, which can be dissolved, suspended or otherwise disperse or as core material may be contained in the capsule. The material to be encapsulated may be used in the initial dispersion at a temperature above its melting point or dissolved - or dispersed in a suitable water-immiscible organic solvent. The nature of the water-immiscible material to be encapsulated may be of organic or inorganic origin. On encapsulation, the - liquid or other form is protected, - until it - is - released in some way or by - a tool that breaks, - crushes, melts, dissolves or otherwise removes the capsule shell, or - until diffusion release occurs - under appropriate conditions. An important specific feature of the invention is - among other advantages - a novel method for selectively controlling the porosity of the walls and forming bounded polyurea walls by removing water from the original organic phase during the polymerization involving the reaction between the polyisocyanate monomers.

The effective encapsulation of the interphase by polymerizing the organic - isocyanate of the lever - - - intermediate can be achieved by using two substantially immiscible liquids, one aqueous phase and the other organic phase, characterized in that a physical dispersion of the organic phase is formed in the aqueous phase. The organic phase comprises an isocyanate intermediate for the shell of a polyurea capsule. Interfacial polymerization involves hydrolyzing the isocyanate monomer to form an amine that reacts with another isocyanate monomer to form a polyurea shell. . The capsules formed in this way have a size in the range of 0.5 to 100 μη.

Certain organic materials and materials labeled "immiscible with water" are capable of dissolving a significant amount of water. When this occurs · when. formation of the polyurea wall of the microcapsule on the surface of the droplet, the proportion of the forming polymer in the core material increases. While water is important in a system using organic polyisocyanates to prepare polyurea walls, the water content of the water-immiscible material in the capsule core is not desirable. The presence and amount of water in the organic or water-immiscible material to be encapsulated depends on the nature of the material. According to the invention, it is possible to exclude water from the core material or organic phase, thereby providing improved separation of the polyurea microcapsule with bounded well formed walls.

There was a need to provide improved microcapsules that can control the loss of effective core material. Previous methods required the permeability of the microcapsule walls, which were to be controlled by varying their thickness and crosslink density. It is also desirable and still difficult to remove water from the organic phase during the formation of polyurea microcapsules containing certain organic materials that dissolve undesirable amounts of water.

It is therefore an object of the present invention to provide a novel microencapsulation process and novel products thus produced which are characterized by an optimum release rate in the formation of polyurea walls and by selective control of the porosity of the wall.

Another object of the present invention is to provide a novel microencapsulation system using a preferred solvent which, with good polymer dissolution capability, reduces the pore size of the microcapsule wall. Conversely, if a poor polymer solvent is used, the permeability of the capsule wall can be increased by increasing the pore size of the microcapsule wall.

It is another object of the present invention to provide microcapsules having improved release rate control capability. This release rate is due to the diffuse permeability of the resulting microcapsule wall.

Another object of the invention is to provide an improved method of obtaining separate thin-walled, relatively impermeable microcapsules with respect to the core material, up to the desired time and release conditions. The process is multifunctional and products of different wall thickness, permeability, polymer composition and release characteristics can be obtained.

The above objects are achieved by forming polyurea capsules using a good polymer solvent in the core together with the active ingredient. Conversely, an increase in permeability is achieved using a poor solvent for the polymer. The permeability of the microcapsule wall to control the porosity of the wall is achieved by including solvents or non-solvents. polymeric. microcapsule walls into the organic phase prior to microencapsulation. The encapsulation process is basically described in Belgian Patent No. 796,746; however, it has been found that by selecting the organic solvent included in the capsule core, the desired effect of reducing or enlarging the pore size and eliminating water from the core material, i.e. the active material, can be affected.

The choice of solvent is generally large, depending on the particular monomer system to be used. Use microcapsules in the production of the porous polymer wall.

The solvent should not be as good a solvent for a polymer that is miscible in all proportions, nor would it be. should not be a non-solvent substance. for the monomer. In general, materials that are completely soluble lead to a polymer that has no apparent pore size and swells by solvent, while microcapsules having polymer walls made using a non-solvent have a pore size too large for practical use. Suitable solvents of the invention may be undiluted or unmixed solvents, although suitable solvents are readily prepared by mixing solvents and non-solvents or by selecting a suitable solvent having the desired properties.

Suitable solvents and solvent mixtures are readily determined for the preparation of a specific polymeric system using the ratio: § = o 0 ± 0.8, where je is the solubility parameter of the polymer. Low porosity of the polymer is achieved when the solubility parameter falls within this range. The solubility of the parameter is discussed in "Some Factors Affecting the Solubility of Polymers," PA Smali, Journal of Applied Chemistry 3.71 (1953), and also by Harry Burnell in "Interchemical Review", 14, 3-16, 31-46 ( 1955). For mixed solvents the value is. § easily calculated from averages on a mass basis.

A method of forming improved discrete polyurea microcapsules having improved release rate control capability by selectively controlling the porosity of the polyurea walls resulting in the formation of bounded urea walls formed by the interphase polymerization of the polyisocyanate-containing organic phase and the aqueous phase, characterized in that the water-immiscible material to be encapsulated adds a solvent capable of eliminating water from the organic material and the polyisocyanate having a solubility parameter of · · = o ± 0.8, where _{0 0} is the solubility parameter of the polymer, forming an organic phase dispersion in the aqueous a water-containing phase, a surfactant, and a protective colloid to form bounded polyurea polymer walls.

It is particularly advantageous and advantageous to use xylene as a solvent in the process of the invention. It has been found that xylene is extremely advantageous as a solvent in the core of polyurea microcapsules. The loss of core material can be reduced by forming a confined and airtight, i.e., denser, more compact wall structure to reduce permeability.

In a preferred embodiment of the invention, the core material can be effectively microencapsulated by interfacial polymerization of an organic isocyanate intermediate by using two substantially immiscible liquids, one designated as an aqueous phase and the other as an organic phase and establishing physical dispersion. the organic phase in the aqueous phase. The organic phase comprises an organic isocyanate intermediate for the shell of the polyurea capsule, the active ingredient, and the polymer solvent. The interfacial polymerization to form the capsule wall involves hydrolyzing the isocyanate monomer to form an amine that reacts with another isocyanate monomer to form a polyurea coating.

There is no need to add another reactant at a time, dispersion of the organic phase droplets in a continuous liquid phase such as an aqueous phase is achieved. The polyurea shell of the capsule is then formed, preferably with gentle stirring of the dispersion, around the dispersed organic droplets by heating the continuous liquid phase or introducing a catalytic amount of a basic amine or other agent capable of accelerating the hydrolysis of isocyanate such as tri-n-butyl tin acetate. in addition to controlling the pH dispersion, thereby carrying out the desired condensation reactions at the interface between the organic droplets and the continuous phase.

In this way, a separate microcapsule having a shell or an outer wall of urea produced by the reaction and containing an encapsulated core material and a polymeric solvent is fully satisfactorily formed. In the process according to the invention, the reaction generally takes place to form the shell of the capsule completely so that substantially no unreacted polyisocyanate remains. If a good polymeric solvent is used in the core, the pore size of the microcapsule wall is reduced and the wall permeability is reduced. When a poor polymer solvent is used, the wall becomes more porous and permeability increases. There is no need to divide the capsules for the desired use, ie the encapsulated material may be directly usable, depending on the intended use. However, this separation prior to use may be carried out by any normal separation method, such as sedimentation, filtration or centrifugation of the collected capsules, washing and optionally drying. The product obtained by the process of the invention is particularly suitable for direct agricultural pesticidal applications, other agents such as Thickeners, biocides, surfactants and dispersants to improve storage stability and application. The initial dispersion of the organic phase in the aqueous phase can be improved by a suitable emulsifying or dispersing agent and the size and uniformity of the finished capsules is readily accomplished by any conventional single liquid dispersion method. in the second.

The improved microcapsules having polyurea walls are prepared by the process of the invention. The invention is further illustrated by the following examples without limitation.

Example 1

The use of the polymer solvent technique of the invention has been applied to encapsulate the herbicide Eptam (EPTC), S-ethyl-dipropylthiocarbaminane to reduce the loss of the active ingredient by creating a less permeable wall and to eliminate increased water penetration into the core material. xylene was chosen for the aromatic polyurea wall.

Microcapsules were prepared as follows:

Water (300 mL) containing 2.0% neutralized poly (methyl vinyl ether) maleic anhydride) of the protective colloid. and 0.3% linear alkool ethoxylate as emulsifier was placed in an open reaction vessel. 270 g of S-ethyldipropylthiocarbaminane (herbicide), 68 g of xylene, 18.2 g of polymethylene polyphenylisocyanate (PAPI) and 9.1 g of tolylenediisocyanate (TDI 80% 2.4 and 20% w / w 2.6) were mixed in a separate vessel. mixture was then added to the reaction vessel and emuligovala vysokooběžného using a stirrer. the resulting · particle range was about 5 to 30 μΐη. · the reaction is completed under moderate agitation. the temperature of the reactants was increased within 20 and 50 minutn ^q C. the temperature was maintained 2 hours 40 minutes at 50 ° C.

3.5 g of Attagel 40 (Attapulgt clay), 14.0 g of sodium tripolyphosphate and 0.35 g of Dowcid G (sodium pentachlorophenate) were dispersed with vigorous stirring into the microcapsule dispersion. The pH was adjusted to 11.0 with 3.5 mL · 50% sodium hydroxide.

This composition disperses very well in water and separate microcapsules are observed under a microscope. These capsules have a wall content of about 7.5%.

The prepared materials were tested biologically by determining the percentage of grass control 24 hours after application. Within 24 hours, the EPTC normally evaporates, providing substantially reduced herbicidal activity. A comparison is made between the samples and the emulsifiable concentrate as a control. All materials are applied at an effective dose of 1.1 kg / ha. The results of these experiments are shown in Table I.

TABLE I

Ingredients % wall Ratio Ratio Biological test of wet soil 0.453 kg in a microcapsule PAPI EPTC % regulation of grass EPTC / 3,785 1 TDI Xylene 1.1 kg / ha

h 24 'h

EPTC 6 * 99 42 EPTC 6 ** 25 2,0 EPTC only 98 80 EPTC 3 ** 17 2,0 EPTC only 99 35 EPTC ^and 6 * » 7.5 2,0 4,0 ' 99 96 EPTC '3 ** 7.5 2,0 9.0 99 96 EPTC 3 ** 7.5 2,0 19.0 99 97 EPTC ** · 15 Dec 2,0 4.0 99 98 * = emulsifiable concentrate (not microcapsules)

** = microcapsule dispersion a = prepared as illustrative examples

The results show that the loss of volatility of the EPTC from the microcapsule increases considerably as the percentage of wall decreases from 25% to 17% in the absence of xylene. However, in the presence of xylene, an excellent mixing efficiency in wet soil is achieved with a 7.5% wall system. Xylene. reduces the pore size in the polyurea wall and therefore. reduces its permeability to EPTC.

Since the xylene content is reduced in the thin wall (7.5% of the wall) of the microcapsule, a less confined wall is achieved, and with the thin microcapsule wall where the xylene content is reduced to zero, it is not possible to form separate microcapsules with bounded wall.

Example 2

In the same way as in Example 1, the microencapsulated herbicide RO-NEET cycloate S-ethylcyclohexylethylthiocarbaminan. The purpose of the process of the invention was to reduce the loss of volatility. The following Table II summarizes the products and gives the test results.

TABLE II

Sample Composition% Wall PAPI RO- Biological test of wet soil no. 0,453 kg / / 3,785 1 RO- TDI -NEET _W % Control grass · (1.1 kg / ha) and ^p hkace -NEET ® Xylene 0 hrs 24 hrs

** 4 7.5 2,0 - 51 39 ** 3 7.5 2,0 4.0 17 28 3 * 3 15.0 2,0 4.0 5 3 ** 4 15.0 2,0 51 49 5 ** 6E -  - - 42 1

* - 1—4 - microcapsule dispersion · - emulsifiable concentrate (not microcapsule)

Formulations 1 and 4 are compared the herbicidal ^account? Ge ^Ron TEM ® ^{6E. In} zor ^k y 2 and 3, the xylene in the organic phase. This makes the wall less porous and therefore less permeable to the herbicide. A small percentage of grass control in samples 2 and 3, when applied immediately, demonstrates the effect of xylene in the organic phase during microencapsulation to produce less porous and therefore less permeable walls.

Example 3

Experimental procedure g of sample R-20458 (4-ethylphenylgeranyl / etherepoxide) microcapsule (containing approximately 10% R-204453) was diluted to 100 ml with deionized water and then 2 ml of this suspension was diluted to 2 l with deionized water to give 4 ppm R -20458 solution if all the poison was released from the capsule (at μπ), or was filtered with a fresh Celite 454 filter cake using a vacuum pump. Both operations were performed under a slight vacuum; 250 ml filtration lasted only one to two minutes for each method.

0, 15, 6Ό. A 250 ml sample was taken from the stirred suspension for 120 minutes, the microcapsules were filtered off and the filtrate analyzed on R-20458. Two filtration methods were used in two separate tests. The suspension was filtered through a fresh Millipore 0.68 filter each time

TABLE III

Contents R-20458 aqueous suspension of R-20458 microcapsule

Sample no. 1 2 3 4 5 % wall 7.5 25 7.5 7.5 7.5 PAPI / TDI 2,0 2 2,0 2,0 2,0 solvent - - xylene 1,1,1-trichloro- ethylene- ethane dichloride (solvent R-20458th (2) (2) (2) Sample ppm R-20458 t = 0 0.2 (, 6) ^a Год 0.1 (0,1) 0.1 t = 15min. 1.1 (1.2) од 0.1 0.1 0.1 t = 60min. 1.5 (1.8) 0.1 0.1 0.1 0.1 (0.1) t = 120min. 1.8 (2.2) 0.1 0.1 0.1 0.17 (0.2)

ⁿ = the first value from Millipore filtration and the second value in brackets from Celite filtration. Only one value when the values in both procedures are the same.

The juvenile insect hormone readily passed through the microcapsule with a 7.5% wall, but was stopped with a 25% wall microcapsule and solvent containing walls formed during the microencapsulation in the presence of a solvent in the organic phase.

Example 4

In the same manner as in Example 1, a microcapsule of thiocarbaminan herbicide and antidote, EPTC and N, N-diallyldiacetacetamide was prepared and bioassayed in wet soil. The bioassay found the percentage of grass suppression and the percentage of crop damage to be compared to immediate application and application after 24 hours. As mentioned above, the solvent present, such as xylene, in the microcapsules during the wall formation during encapsulation reduces the size of the micropores in the polyurea wall, thereby reducing the permeability of the organic molecules through the microcapsule wall.

Microcapsules containing EPTC *, N, N-dialkyldichloroacetamide

Sample No. 0.453 kg / 0.453 kg Weight% PAPI wall% Grass control *% crop damage / Eptam / antidote / ratio in micro-TDI crop application PAG / 3,785 1 / 3,785 1 in micro-capsule application

Ί3 O Д

Ф CM

O

Ф CM

Oj

O

OQOinOOOO rH CO CO

OOOQOOOO

QO Q) OQ Ф CD

O) O) CM)

CD CD <D cm "cm" cm "

ΙΌ 1П 1П t *

CD (D CD, CT) o in ID ID

CM, CM, CM ~ o 'o' o '

Co- 4. Q what “co” μ “rH cm μ o o rH

CD

CD cm 'in

• rH with σ + - »(D ω cd f-l o Ξ

CJ чЗ έ of β д

4— '

O fn

1L o 'o (D

WHAT co

cn o

what ”*

* * * ♦

This assay demonstrates that reducing the xylene or solvent content of the microcapsule results in an increased loss of volatility of the antidote compound.

As is apparent from the foregoing, the method is OBJECT

Claims (5)

SUBJECT CLAIMS 1. A method of forming improved discrete polyurea microcapsules having improved release rate control capability by selectively controlling the porosity of polyurea walls to form bounded polyurea walls formed by interfacial polymerization of a polyisocyanate-containing organic phase and aqueous phases, characterized in that water-immiscible organic phase containing material to be encapsulated, adds a solvent capable of eliminating water from the organic material and polyisocyanate having a solubility parameter of §0 = ₀ ± 0.8, where §0 is the solubility parameter of the polymer, a dispersion of the organic phase in the aqueous phase containing water is formed; active agent and protective colloid to form bounded polyurea polymer walls. ' 2. The process of claim 1 wherein the solvent is xylene. 3. A method according to claim 1, characterized in that the organic phase-containing material not according to the invention can be used with various alternatives and modifications which may differ from those described above. For this reason, it is clear that they serve for illustrative purposes only, without limiting the scope of the invention. ynAllisable water-miscible to be encapsulated adds a good solvent of the polyurea polymer wall of the microcapsule and polyisocyanate having a solubility parameter of § = §0 + 0.8, where §0 is the polymer solubility parameter, forming a dispersion of the organic phase in the aqueous phase containing water , a surfactant, and a protective colloid to form bounded polyurea polymer walls. 4. The process of claim 3 wherein the solvent is xylene. 5. The method of claim 1, wherein a non-solvent of the polyurea polymer wall of the microcapsule and the polyisocyanate is added to the organic phase containing the water-immiscible material to be encapsulated, forming a dispersion of the organic phase in the aqueous phase containing water, surfactant and protective colloid to form bounded polyurea polymer walls. Severography, n. P., Plant 7, Most