DK147697B - MICROCapsule comprising a core and a shell comprising a film-forming polycarbodiimide as well as a process for its preparation - Google Patents

Description

147697 o

The invention relates to a microcapsule comprising a core and a shell, the shell comprising a film-forming polycarbodiimide, and a method of making such a microcapsule.

Various types of microcapsules and their production are known. A variety of polymers can be used for the shell material, the choice in question being determined by the chemical nature of the core material to be encapsulated. For example, if the core material. is hydrophilic, the shell-forming polymers should be as hydrophobic as possible. On the other hand, if the core material is hydrophobic, the shell-forming polymers should be as hydrophilic as possible. In addition to these requirements, the release property or permeability of the shell with respect to the material to be encapsulated is another critical factor in the choice of the shell materials. In this connection, the general rule is that the core material and the shell-forming polymer must have opposite solubility parameters (for example, hydrophobic shell polymers are less permeable to hydrophilic than to hydrophobic encapsulated materials). However, there are several boundary cases where a suitable shell-forming polymer is not available for a given core material. In such cases, it is sometimes possible to make two polymer shells of different polymers one above the other. However, even in this way it is not possible to achieve any required combination of properties.

Polymers, polycondensates and polyaddition products can be used as polymers with shell-forming properties. Suitable polymers are e.g. common homopolymers and copolymers of ethylene, propylene, vinyl chloride, vinylidene chloride, vinyl acetate, acrylonitrile, styrene, acrylic acid alkyl esters and methacrylic acid alkyl esters. Suitable polycondensates are e.g. polyamides, polysulfonamides, polyesters and polycarbonates, while suitable polyaddition products e.g. are polyurethanes and polyurix substances.

It has now been found that film-forming polycarbodiimides can also be used in the preparation of shells for microcapsules. Conventional encapsulation technique can be used for the preparation of microcapsules with polycarbodiimides. Conventional encapsulation techniques are mainly physical and chemical processes. The physical processes include coating the core materials in the form of droplets or particles with polymers that cannot be mixed with core materials, the encapsulation technique being physically induced at an early stage. In the chemical process, it is standard practice to prepare dispersions of the core material or solutions of the core material in an immiscible dispersion medium and then to deposit or prepare the shell forming polymer at the interface in such a way that it surrounds the core material in the form of a film. The polymer can be formed either directly from the inner phase or from the outer phase depending on the particular method of preparation chosen.

Chemical encapsulation methods can be roughly divided into phase separation processes and interface polymerization processes.

The following are examples of typical chemical encapsulation methods: 1) Coacervation or complex coacervation process. By setting the correct temperature and pH, a polymer coacervate is deposited at the interface and can then be cured.

A typical example is the gelatin / gum arabic system which can be cured with formaldehyde.

3 147697 2) The reactive process. In this process, two components dissolved separately in the outer phase and in the inner phase of the dispersion react with each other at the interface to form the polymer, e.g. a polycondensate or polyaddition product.

3) The evaporation process. The core material is encapsulated by depositing the polymer by evaporation of a solvent for the polymer from the dispersion.

4) The precipitation process. The polymer is deposited by precipitation from a polymer solution with a non-solvent. The individual microencapsulation techniques are described in further detail by J.E. Hiking in "Microencapsulation, Processes and Applications", Plenum Press, New York 1974.

Thus, the present invention relates to a microcapsule comprising a core and a shell, said microcapsule being characterized in that the shell comprises a film-forming polycarbodiimide containing repeating units of the formula -RN = C = N- R- wherein R is optionally substituted alkylene, cycloalkylene or the aryl, and wherein the end groups are NCO groups and / or reaction products of these NCO groups with NCO reactive compounds.

The invention further relates to a process for preparing the present microcapsules, characterized in that a) the polycarbodiimide is dissolved in an inert solvent, a compatible core material is dispersed in the formed solution and the resulting dispersion is introduced in a cutting gradient - miscible liquid phase in which is or to which isocyanate-reactive polyamine is added or b) dissolves the polycarbodiimide in a solvent having a boiling point below 100 ° C or forming an azeotropic boiling at a temperature below 100 ° C, a compatible core material is dispersed or dissolved in the resulting solution, the mixture is dispersed in a liquid immiscible with the polymer solvent and the dispersion is then heated to evaporate the solvent, or c) dissolve the polycarbodiimide in a solvent, a core material the resulting solution, and that a polycarbo precipitate the diimide is added with stirring.

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The use of the present polycarbodiimides for microencapsulation provides a number of surprising advantages.

Thus, film-forming carbodiimides can be used in the dissolved form in the evaporation process and in the precipitation process. The reactive process can be used with polycarbodiimides containing free isocyanate groups.

The microencapsulation can be performed in several ways using one and the same polymer.

Due to the reactivity of the carbodiimide groups, it is possible to chemically modify the polycarbodiimide prior to the actual encapsulation so as to obtain a greater variation in solubility, molecular weight, film formation, etc. than with pure polyisocyanates. Something similar applies to the enclosure itself while the shell is being formed and, of course, to the finished capsule shell after the encapsulation is completed. This ability to adapt the polycarbodiimides also allows them to be used for encapsulation by very different methods.

On the other hand, one can also set the most different capsule properties, e.g. high density or high permeability, hydrophilia or hydrophobia, high or low softening and opening temperature, flavor or leakage density and so-called "controlled release" properties.

Carboxyl groups or amino groups can e.g. added. Thus, it is possible to further cross-link the linear polycarbodiimide chains by e.g. reaction with dicarboxylic acids, e.g. adipic acid, or adding a second shell, chemically linked to the first by reaction with the amino and carboxyl groups of gelatin (or analogous hydrophilic polymers) by the coacervation methods or by the complex coacervation.

Thus, the properties of the polycarbodiimide shells can be widely adapted to any core material. Accordingly, in principle, any organophilic, liquid or solid can be encapsulated in film-forming polycarbodiimides.

Suitable polymeric carbodiimides are aromatic, aliphatic, cycloaliphatic and aliphatic-aromatic polycarbodiurides and mixtures thereof.

The polycarbodiimides can be prepared from the corresponding isocyanates, e.g. from 2,4- and 2,6-diisocyanatotoluene and their isomeric mixtures, in particular an isomeric mixture consisting of 80% 2,4- and 20% 2,6-diisocyanatotoluene, from 4,4'-diisocyanatodiphenylmethane, from phosgenation products of acid-catalyzed aniline-formaldehyde condensates, from 1,3-diisocyanatobenzene, 1,3,5-trimethyl- and 1,3,5-triisopropylbenzene-2,4-diisocyanate, from 1,6-diisocyanato hexane and from 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethyl-cyclohexane. However, polycarbodiimides suitable for use in the described process are obtained not only from the pure isocyanates, because it is also possible to use their non-distilled precursors and also reaction products of these polyisocyanates at monoalcohols or polyalcohols having an NCO: OH ratio of greater than 1 and modification products of these polyisocyanates, e.g. polyisocyanates which further contain biuret; allophanate, isocyanurate and carbodiimide groups.

For microencapsulation in the evaporation process, the precipitation process and the reactive process, it is important that the polycarbodiimides used be soluble in water-immiscible solvents.

In the reactive process, these solvents must also be inert to the isocyanate groups.

In the evaporation process, their boiling points must be less than water or, alternatively, the solvents must be capable of being removed from the dispersion in the form of an azeotrope with water and / or another solvent.

Polycarbodiimides suitable for use according to the invention preferably contain free terminal isocyanate groups, i.e. has the idealized structure ·

OCN- [R-N = C = NX3-R-NCO

in which R is alkylene, cycloalkylene or aryl and x is an integer from 2 to 40, R is an alkylene group of 2-6 carbon atoms, a cycloalkylene group of 5-7 carbon atoms, or an arylene group of 6-12 carbon atoms.

Some of the carbodiimide groups can also be converted with isocyanate to urethone imine groups, thus yielding polymers containing the repeating unit: -R-N = C-lj [-R-— N - C = 0 6 147697

The evaporation process and the precipitation process can preferably be carried out with carbodiimides containing phosphonio or rp - n - structural units, e.g. with the idealized structure OCN [-R-N = C = N-R] -N = P ^ * T ^ R 'X | "R" in which x and R are as defined above, while R 'is alkyl or cycloalkyl groups. R' is preferably alkyl of 1-6 carbon atoms and cycloalkyl of 5-7 carbon atoms and R "is alkyl or aryl, preferably methyl, ethyl and phenyl.

Some of the carbodiimide groups may also be converted with phospholine oxides or phospholane oxides to structural units of the type -R-N = C - N-R- 1 l ^ r R.

in which R, R 'and R "have the meaning given above.

The preparation of polycarbodiimides of this kind is known and described in e.g. "Encyclopedia of Polymer Science and Technology", Vol. 7, pages 751-754. In the simplest case, the polycarbo-diimides are obtained by the addition of phospholine oxides or phospholan oxides to the isocyanates, and size reduction of the foam-like material is obtained.

According to the invention, it is possible to encapsulate solids or liquids. The liquid substances must be compatible with the polymer solution. Examples of suitable core materials are mineral oils, fatty oils, trichloroethyl phosphate, thiophosphoric esters, ethoxylated alkyl phenols, perfumes, aromatic and aliphatic hydrocarbons and chlorinated hydrocarbons and mixtures thereof, color solutions, titanium dioxide, methylene blue, crystal violet and carbons.

The individual microencapsulation techniques are performed e.g. as follows: 1) In the reactive process, the polycarbodiimide is first dissolved in an inert solvent and a compatible core material is mixed with the resulting solution.

This mixture is introduced into a cutting gradient, preferably produced by intensive mixing with small mixers or mixing machines, in a non-immiscible liquid phase, e.g. water containing an isocyanate-reactive polyamine. The amine can also be added later.

Suitable polyamines are e.g. 1,2-Ethylenediamine, 1,4-diamino-butane, bis- (3-aminopropyl) -amine, hydrazino-2-ethanol, bis- (2-methylaminoethyl) -methylamine, 1,4-diamino-benzene , 4,4'-diaminio-diphenyl-methane, 1,4-diaminocyclohexane, 3-amino-1-methylamino-propane, N-hydroxyethylethylenediamine, N-methyl-bis- (3-aminopropyl) -amine, hydrazine and 1, 2-ethylene-diamine-N-ethanesulfonic acid (Na salt).

2) In the evaporation process, the polycarbodiimide is first dissolved in a solvent having a boiling point below 100 ° C or forming an azeotrope boiling at a temperature below 100 ° C. A compatible core material is then mixed with the resulting solution. This mixture is dispersed by preferably vigorous stirring in a liquid which is immiscible with the polymer solvent, e.g. water, followed by stepwise heating to temperatures above the boiling point of the polymer solvent or azeotrope. The solvent is evaporated and the polycarbodiimide encapsulates the core material to form the inner phase at the interface. Emulsifying aids or emulsifiers are preferably added to the aqueous phase for better emulsification and to stabilize the dispersion. Examples of such products which act as protective colloids are carboxymethyl cellulose, gelatin and polyvinyl alcohol. Examples of emulsifiers are ethoxylated 3-benzyl-4-hydroxybiphenyl and reaction products of nonylphenol with various amounts of ethylene oxide.

3) In the precipitation process, the polycarbodiimide is first dissolved, and the core material is then added to the solution formed and, with stirring, a precipitant for the polymer which is miscible with the polymer solvent is added. Effective solvents for the polycarbodiimide are e.g. chlorinated aliphatic and aromatic hydrocarbons, e.g. methylene chloride and chloroform, aromatic hydrocarbons, e.g. toluene and benzene, esters such as ethyl acetate and cyclic ethers, e.g. tetrahydrofuran or dioxane. Effective solvents for the film-forming polycarbodiimides are also aprotic solvents, e.g. Ν, Ν-dimethylformamide, dimethylsulfoxide, Ν, Ν-dimethylacetamide, N, N-di-n-butylformamide, N-methylpyrrolidone, and N, N-di-n-butylacetamide.

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Whichever method is used, the polycarbodiimide shell can be further modified. P.eks. For example, compounds that react with the carbodiimide groups can be added to the microcapsule dispersion. Examples of such compounds are polyfunctional carboxylic acids, e.g. adipic acid, polyacrylic acid or their copolymers, and also polyfunctional amines, e.g. 2,5-diaminobenzene sulfonic acid, 4,4'-diaminobenzene and amino compounds mentioned during the reactive process. The polycarbodiimide shell can be cured in this way.

The curing agents can be added either before or during the preparation of the dispersion to the outer phase. However, the curing agents may also be added after the formation of the microcapsules in the form of a solution or solvent compatible with the outer phase.

Continuous and batch operation is possible. The degree of turbulence during mixing determines the diameter of the microcapsules obtained. The diameter of the microcapsules can be between approx. 5 and 5000, u, depending on the mixing conditions.

The weight ratio of the core material to the shell material in the finished microcapsules is usually 50 to 90:50 to 10.

The microcapsules obtained can e.g. contain pesticides, flame retardants, color solutions, plasticizers, catalysts, oils, perfumes, pigments and dyes already commercially used in encapsulated form.

Example 1 a) Preparation of the polymeric 139 g of a mixture of 80% by weight 2,4-diisocyanatotuene and 20% by weight 2,6-diisocyanatotoluene is mixed with stirring at room temperature with 2g of 1-methylphospholine-1-oxide.

The mixture is foamed slowly and gives after approx. 12 hours a lightly powdered polycarbodiimide foam soluble in solvents such as methylene chloride, chloroform, chlorobenzene, o-dichlorobenzene, toluene, tetrahydrofuran, N-methylpyrrolidone and dimethylformamide. The softening range of the reaction product is above 200 ° C.

It is advisable to store the polycarbodiimide at temperatures below 5 ° C in order to avoid further reaction as far as possible.

B) Encapsulate 1 g of the polycarbodiimide prepared according to al is dissolved in 3 g of chloroform and the resulting solution is added to 22 g of polychlorinated diphenyl (Clophen A 30).

The homogeneous mixture is then stirred into 300 ml of water containing 1.5 g of polyvinyl alcohol (Moviol 70/98} as an emulsifier, which results in foaming of the dispersion.

It turns out to be sufficient to use a simple Lenart-Rapid-type laboratory stirrer that rotates at 500 rpm. minute. A 1 liter glass beaker is used as a reaction vessel. A solution of 14 g of ethylenediamine in 56 ml of water is then added to the resulting dispersion.

The mixture is rapidly heated to 60 ° C with continuous stirring and allowed to stand at this temperature for approx. 1 hour, forming microcapsules.

The capsules are filtered out and have a diameter of up to approx. 2 mm.

By changing the dispersion conditions, it is possible to make capsules of the order of microcapsules, ie. with a diameter of approx. 5 to 100 µ.

Example 2

The encapsulation of 25 g of chlorobenzene as a core material is carried out as described in lb) with the following changes: 2 g of the polycarbodimide prepared according to la) is dissolved in the chlorobenzene without the addition of chloroform. Under analogous conditions, 30 g of bis- (3-amino-propyl) methylamine is added as a reactant in the outer aqueous phase.

Example 3 a) Preparation of the polymer 228 g of 1,3,5-triisopropylbenzene-2,4-diisocyanate are mixed with 2 g of 1-methylphospholine-1-oxide and the resulting mixture is maintained at ca. 110 ° C for 5 to 6 hours. A solid is formed by the stepwise evolution of carbon dioxide. The solid formed has a softening range of 90 to 110 ° C and is found to be soluble in solvents such as methylene chloride, chloroform, chlorobenzene, N-methylpyrrolidone, toluene, a mixture of aromatic hydrocarbons (Solvesso 100),

Clophen A 30, xylene, ethylene chloride, 1,3-dichloropropane, light gasoline, benzene, tetrahydrofuran, acetone, methyl ethyl ketone and diethyl ether. The polycarbodimide can be easily reduced in size and thus can be stored at temperatures below 5 ° C.

b) Encapsulate 2 g of the polycarbodiimide based on 1,3,5-triisopropylbenzene-2,4-diisocyanate prepared according to Example 3a), dissolved in 6 g of methylene chloride and the resulting solution is added to 20 g of tri-n -butylphosphat. The homogeneous mixture is dispersed by a simple laboratory stirrer in the same manner as described in lb) followed by the addition of 14 g of ethylenediamine in 56 ml of water. The work-up is carried out in the same way as in Example 1b).

Example 4 a) Preparation of the polymer 134 g of hexamethylene-1,6-diisocyanate are mixed with 2 g of 1-methylphospholine-1-oxide and the resulting mixture is heated to 50 ° C for 15 hours. A very viscous product is formed during the stepwise development of carbon dioxide. The product is soluble in the following solvents: Methylene chloride, chloroform, chlorobenzene, toluene, solvent naphtha (mixture of aromatic hydrocarbons, BV Aral), Chlophen A 30, tri-n-butyl phosphate, tris-chloroethyl phosphate, ethylene chloride, 1.3 -dichloropropane, cyclohexane, light petrol, methyl ethyl ketone, acetone, ethyl acetate, pyrrolidone, N-methyl-pyrrolidone, dimethylformamide, benzene, dioxane and tetrahydrofuran. The polycarbodiimide should be stored at temperatures below 5 ° C.

b) Encapsulation

Example I; 2 to 5 g of the polycarbodiimide prepared according to 4a) are dissolved in 25 g of chlorobenzene and dispersed in 300 ml of water by means of a Lenart-Rapid-type laboratory stirrer, rotating at 500 rpm. minute. 14 g of ethylenediamine dissolved in 56 ml of water are added to the resulting mixture.

Example II: To encapsulate 25 g of tri-n-butyl phosphate, 2 g of the polycarbodiimide of hexamethylene-1,6-diisocyanate is dissolved in the phosphate and further processed as described in Example I:

Example III: 2.5 g of the polycarbodiimide prepared according to 4a) are dissolved in 25 g of solvent naphtha and further processed as described in Example I. In this case, 2 g of the polycarbodimide represents the lower limit.

Mixtures I and III are worked up as described in lb). Another notable feature common to all of these three mixtures is that there is no need for an increase in temperature during work-up, which is why the capsules are not adversely affected. It is even possible to make microcapsules without any need for extended post-stirring. However, in this regard, experiments with only 2 g of the polycarbodiimide are problematic because the capsule membranes obtained are less stable. By providing suitable dispersion conditions, it appears to be possible in all experiments to produce microcapsules having a diameter of from 5 to 100 µ.

Example 5 10 g of the polycarbodiimide based on tolylene diisocyanate prepared according to Ia) are dissolved in 90 g of chloroform. 40 g of a mixture of aromatic hydrocarbons (cumene, xylene, toluene, naphthenic oils = solvent naphtha produced by BV Aral) are then added and the homogeneous mixture is dispersed in a solution of 2.5 g of polyvinyl alcohol (Moviol 70/98) and 2 , 5 g of hydrazino-ethanol in 500 g of water. 2.5 g of gelatin or 2.5 g of carboxymethyl cellulose (sodium salt) can also be used as an emulsifier. A 1 liter beaker is used as the reaction vessel. The dispersion is heated to 60 ° C and the polymeric solvent is slowly distilled off over 4 hours. It turns out to be sufficient to use a simple Lenart-Rapid laboratory stirrer for the dispersion. The capsules have an average diameter of approx. 85 yes. at a stirring speed of 1750 rpm. and a mean diameter of approx. 150 µl at a stirring rate of 700 rpm. minute. It turns out that the hydrazino-ethanol used to cure the polycarbodiimide shells can also be added with a similar effect after the dispersion or after most of the polymeric solvent has been distilled off. The resulting capsules are filtered off and dried.

Example 6 10 g of the tolylene diisocyanate based polylcarbodiimide prepared according to Ia) are dissolved in 90 g of methylene chloride and processed as described in Example 5 with the following changes: 40 g of a diphenyl heating bath oil (Marlotherm, a Huls / Marl product) is added to the polymer solution as a core material. 2.5 g of carboxylic methylcellulose (sodium salt) and 2.5 g of a nonylphenol and ethylene oxide emulsifier (emulsifier NP 7, a product of Bayer AG) are used as emulsifying aid for the homogeneous disperse phase. The dispersion is heated to only 40-45 ° C. 5 g of adipic acid are added to the aqueous phase as a hardening agent for the capsule shell. The resulting capsules are filtered off and dried. As described in Example 5, it appears to be possible to use gelatin or polyvinyl alcohol (Moviol 70/98) in place of carboxymethyl cellulose as an emulsifier.

Example 7 a) Preparation of the polymer

To prepare a polycarbodiimide from 1-isocyanate-3,5,5-trimethyl-5-isocyanate methylcyclohexane, 177 g of the diisocyanate is thoroughly stirred with 2 g of 1-methylphospholine-1-oxide followed by storage for ca. 12 hours at a temperature of 100-110 ° C.

This provides a very viscous product. The product is soluble in solvents such as methylene chloride, chloroform, chlorobenzene, toluene, Solvesso 100, tri-n-butyl phosphate, ethylene chloride, 1,3-dichloropropane, trichlorethylene, methyl ethyl ketone, acetone, tetrahydrofuran, dioxane and benzene.

b) Encapsulation

Example I: 2.5 g of the polycarbodiimide prepared according to Example 7a) is dissolved in 25 g of chlorobenzene or Solvesso 100, dispersed in 300 ml of water at 500 rpm. minute followed by the addition of 14 g of ethylenediamine dissolved in 56 ml of water. A simple laboratory stirrer of the Lenart-Rapid type is used as a stirrer. In contrast to enclosures with other polycarbodiimides, the best results in this case are obtained by stirring for 1 hour at room temperature, ie. without heating. The obtained capsules are then filtered off and dried in air.

Example II: 5 g of the polycarbodiimide of Example 7a) are dissolved in .... 10 g of chlorobenzene., And the resulting solution are added to 20 g of Chlophen A 30.

This solution is dispersed in 300 ml of water and further processed as described in Example I.

Example 8 4 g of the polycarbodiimide of 1,3,5-triisopropylbenzene-2,4-diisocyanate prepared according to 3a) are dissolved in 196 g of methylene chloride and the resulting solution is mixed with 20 g of finely powdered medical carbon using a Lenart Rapid laboratory stirrer with 200 rpm. minute.

The resulting dispersion is maintained at ca. 25 ° C followed by an addition over 1 hour with continuous stirring of 250 ml of acetone, the polycarbodiimide precipitates quantitatively in fine form with the activated carbon enclosed.

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The effect of the contained activated carbon on the aqueous methylene blue solution (analogous to the standardization according to DAB 6) was clearly diminished, the change to a core to shell ratio to 50:50 further decreases the activity of the contained activated carbon.