MXPA98008778A - Polys of polymers redispersable in solution acu - Google Patents

Abstract

The present invention consists of polymer powders redispersible in aqueous solution, their use in cosmetic formulations, pharmaceutical or for the protection of crops, and in a process for preparing polymer powders redispersible in aqueous solution containing copolymers bearing free acid or base groups and , if appropriate, auxiliary, consisting of adjusting the pH of the dispersion, before drying, by adding at least one buffer system to a pH of 2.0 to 6.5, in the case of copolymer-carrying acid groups, or at a pH from 7.5 to 12 in the case of copolymers bearing base groups

Description

REDISPERSIBLE POLYMER POWDERS IN AQUEOUS SOLUTION Description The present invention relates to a process for preparing polymeric powders redispersible in aqueous solution containing copolymers carrying free acid or base groups and, if appropriate, auxiliaries, the process consists of adjusting the pH of the dispersion by adding a damper system from a system from 2.0 to 6.5 in the case of copolymers carrying acidic groups or a pH from 7.5 to 12 in the case of copolymers bearing base groups. The invention also relates to polymer powders redispersible in aqueous solution and their use in cosmetic and pharmaceutical formulations, and to compositions for the protection of crops. Patent DE 2 512 238 discloses film-forming polymer powders which are prepared from aqueous dispersions of the plastic, these film-forming powders are used, after dissolution in an organic solvent, to coat solid drug formulations. The use of organic medicines when coating solid formulations of drugs presents considerable technical problems. All equipment that is used must be explosion proof to avoid ignition of the solvent. By. For environmental and cost reasons, the evaporated solvent has to be recovered from the residual air. In addition, the solvent has to be completely removed from the pharmaceutical formulations. Therefore, alternatives to the use of organic solvents have been sought. As a result, several processes have been developed that use water as a solvent. However, these processes have various disadvantages. In US Patent No. 5,252,704 to Bright et al, redispersible polymer powders are described which can be prepared from copolymers by the addition of large amounts of polyvinylpyrrolidone before spray drying. In a high percentage of added polyvinylpyrrolidone, however, it detrimentally affects the solubility of the polymeric film obtained after the formation of the film. Patents EP-B 88 951 and EP-B 161 326 describe the redispersion of the emulsion polymer powder bearing free carboxyl or amino groups by converting these groups into their salts. The free carboxyl groups in this way are converted into their salts by adding bases, and the free amino groups are converted into their salts by adding acid. This is carried out after drying the polymer dispersion by stirring an alkaline solution in the carboxyl-containing polymer powder which is finely dispersed in water. If the polymer carries free amino groups, an acid solution is stirred for the dispersion. For carboxyl-containing polymers the possibility of partial neutralization of free carboxyl groups by adding alkali before spray drying has been described. However, in this case, the viscosity of the dispersion and the degree of clot formation before spray drying are crucial parameters. Furthermore, if the alkali is added before drying, during the subsequent redispersion, undesirable clots are easily formed. The neutralization of the polymer powders, that is, the formation of the salt, is therefore preferably carried out after the drying of the powders, before the solid formulations of the medicament are prepared. For the user this presents the problem of having to provide additional facilities for the neutralization and storage of bases and acids. An objective of the present invention is to develop redispersible polymers that can be dispersed directly without the described disadvantages to produce an aqueous solution, and make them available for applications in the cosmetics and pharmaceutical sectors and in crop protection. We have found that this objective is achieved by adjusting the pH of the dispersion before drying by the addition of at least one buffer system to a pH of from 2.0 to 6.5 in the case of copolymers carrying acid groups or a pH of 7.5 to 12 in the case of copolymers carrying base groups, to provide a polymeric powder that is easily redispersible. The polymer powder according to the invention, which has a very long storage life, is rapidly redispersed in aqueous solution without the formation of clots, for example. Therefore, these are [sic] ideally suitable as film formers in cosmetic, pharmaceutical or crop protection formulations. Suitable buffer solutions for the process according to the invention are, in principle, all known buffer solutions as described, for example in Handbook of Biochemistry (HA: Sober, RA Horte (eds.), The Chemical Rubber Co. J 195 -J 199, 1968). The pH of the dispersion containing polymers of the free acid or base groups is advantageously adjusted before drying by the addition of at least one buffer system to a pH of 2.0 to 6.5 in the case of copolymers carrying acid groups or a pH from 7.5 to 12 in the case of copolymers carrying base groups. Preferably, the pH is adjusted before drying to pH from 3.0 to 6.0 in the case of copolymers carrying acid groups and at a pH of 7.5 to 11 in the case of copolymers bearing the base group. By adjusting the pH, some of the acid or free base groups of the copolymers are converted into their salts. The shock absorbing systems are conventional shock absorbers and / or polymeric shock absorbers. Suitable buffers are, for example, all salts that are formed of weak acids and strong bases or of strong acids and weak bases, the salts of the acids or bases being identical or mixtures of the salts of different acids or bases. Buffer solutions which are used in the case of copolymers carrying free acid groups, for example copolymers having free phosphono, sulfo or carboxyl groups, comprise at least one buffer system. In the buffer region of the buffer system it is preferably from pH 1 to 7. Suitable buffer solutions or buffer solutions having a buffer region in the acid range of pH 1 to 7 are, for example, buffer solutions such as Walpole buffer (acetic acid / Na acetate, pH 3.6-5.6), Gomori aconite buffer (aconitic acid / NaOH, pH 2.5-5.7), Kolthoff buffer (borax / succinate, pH 3.5-5.8), S0rensen citrate buffer (disodium citrate / HCl , pH 2.2-4.8), glycine buffer S0rensen I (glycine, NaCl / HCl, pH 1.2-3.6,), buffer. of phthalate Clark and Lub I (potassium biftalate / HCl, pH 2.2-3.8), phthalate buffer Clark and Lub II (potassium biftalate / NaOH, pH 4.0-6.2), piperazine buffer Smith and Smith (piperazine [sic] , HCl / NaOH, pH 4.8-7.0), potassium chloride buffer / Clark and Lub HCl (KC1 / HC1, pH 1.0-2.2), Tris maleate Gomori buffer (trismaleate / NaOH, pH 5.2- '8.6), or succinate buffer Gomori (succinate / NaOH, ph 3.8-6.0). In the same way, the MES, ADA, PIPES or ACES buffer solutions are suitable, which are common buffer solutions in biochemistry or amino acid buffer solutions. Preference is given to buffer solutions which are advantageously prepared from weak acids and their salts, such as sodium acetate / acetic acid, sodium borate / boric acid, sodium phosphate / phosphoric acid, sodium bicarbonate / carbonate, Sodium hydroxide / citric acid, sodium hydroxide / tartaric acid. Suitable buffer solutions are also buffer solutions that are prepared from weak bases and their salts. Individual buffer solutions or mixtures can be used to adjust the pH of the dispersions. The buffers which are used in the case of the components of the copolymers bearing free base groups, for example copolymers having free N-alkyl, amino or imino groups, comprise at least one damping system. The buffer region of the buffer system is preferably from pH 7 to 13. Buffers or suitable buffer solutions that have a buffer region in the basic range of pH 7 to 13 are, for example, buffer solutions such as Borate Clark and Lub buffer (boric acid, KCl / NaOH, pH 7.8-10.0), Deloryn and King buffer (carbonate / bicarbonate, pH 9.2-10.7), or S0rensen II glycine buffer (glycine NaCl / HCl, pH 8.4-13). In the same way, suitable buffer solutions are colamine chloride, BES, TES, HEPES, acetamidoglycine, glycinamide, Tris, Bicine, Tricine or glycylglycine, which are buffer solutions common in biochemistry or amino acid buffers. Preferred buffers are those which can be advantageously prepared from weak acids and their salts. Suitable buffer solutions are also buffer solutions prepared from weak bases and their salts. Individual buffer solutions or mixtures can be used to adjust the pH of the dispersions. If polymeric buffer solutions or buffer solutions are used to neutralize the free acid groups or free base groups in the copolymer, these polymer buffer solutions can be advantageously prepared by adding a neutralizing agent to a polymer carrying free acid groups or free base groups . Suitable polymers are copolymers bearing free acid groups or free base groups which are prepared by free radical polymerization of (meth) acrylic acid, its derivatives, maleic acid, fumaric acid, itaconic acid, crotonic acid, vinyl sulfonic acid, vinyl acid phosphonic, polyethyleneimine and / or its salts, esters and, if appropriate, its anhydrides. Suitable anhydrides are, for example, acrylic anhydride, methacrylic anhydride or maleic anhydride. Polymers suitable for preparing polymeric buffer solutions are also natural polymers having free acid or base groups, such as alginic acid or hyaluronic acid. The composition of the monomers of the dispersion in the buffer solution or added polymer buffer can be identical or different.The polymeric buffer solution, or the polymer buffer, is preferably prepared from a portion of the dispersion that is going to drying by adding a neutralizing agent When the polymer solution is prepared, the neutralization of the monomer units can be carried out partially or completely In an advantageous form, from 50 to 100% by weight of the monomers of the buffering polymer which can form salts they are in the form of the salt, preferably from 70 to 95% by weight of the monomers are in the form of the salt.Full neutralization is particularly preferred.Depending on the kind of free groups that the polymer carries, Bases or acids are used for neutralization.The suitable neutralizing agents are all bases or physiologically acceptable acids, such as it can be sodium hydroxide, sodium acetate, sodium phosphate, sodium carbonate, citric acid, tartaric acid, phosphoric acid, acetic acid and / or formic acid. However, the buffer solutions or buffers mentioned above are also suitable. Acids, bases or individual buffer solutions for neutralization or combinations thereof can be used to prepare the polymeric buffer solution. The initial dispersion can thus be converted into a dispersion which produces a redispersible powder after drying by simply adjusting a basic acid pH by the addition of at least one buffer system. Suitable damping systems are individual buffer systems and / or polymeric dampers or mixtures of buffer solutions and / or polymeric buffers. Regardless of the nature of the salt forming group, in all cases it is possible to use the same solution.buffer and / or polymer buffer. The addition of an additional acid or base is not necessary, although it is perfectly possible. It is also possible to redisperse the dispersion powders obtained by free radical polymerization and dried without the addition of the buffer solution by stirring in at least one buffer solution and / or at least one polymer buffer. For economic reasons, the solids content of the dispersion to be dried is usually greater than 25% by weight. However, when preparing the polymeric buffer solution from this dispersion, it is convenient to initially adjust to a solids content of less than 15% by weight and then mix a neutralizing agent. The diluted solution of the polymeric buffer prepared in this way is subsequently combined with the dispersion to be dried. The solids content of the combination of dispersion and buffer and / or polymer buffer is from 1 to 50% by weight. Preferred is 5 to 40% by weight, particularly preferably 20 to 35% by weight.

. It is an advantage that the dispersions prepared using the addition of buffer solution and / or polymer buffer according to the invention can withstand pH fluctuations during processing without the formation of clots. By adding the solution _. Buffering the opening pH, that is, the pH at which the polymer begins to swell and then dissolve, can vary within precise ranges. This is particularly advantageous if a controlled release of an active compound is desired to obtain optimum bioavailability by this means. In principle, all copolymers obtainable by free radical polymerization are suitable for preparing the redispersible polymer powders according to the invention. Suitable monomers forming the building blocks of these copolymers include mono- and dicarboxylic C3-C8 monoethylenically unsaturated acids, their anhydrides, esters, amides or salts, or mixtures of the carboxylic acids, anhydrides, esters, amides and salts mentioned. Suitable carboxylic acids are, for example, acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid or crotonic acid. Suitable anhydrides are, for example, acrylic anhydride, methacrylic anhydride or maleic anhydride. The . suitable esters are, for example, C1-C10 alkyl esters or C1-C10 hydroxyalkyl esters of the aforementioned carboxylic acids. Preferred alkyl esters are methyl, ethyl, propyl, butyl, i- > butyl, tert-butyl, pentyl, i-pentyl-2,2-dimethylpropyl [sic], hexyl, i-hexyl, heptyl, i-heptyl, octyl, i-octyl, 2-ethylhexyl, nonyl, i-nonyl, decyl or i-decyl esters of acrylic or methacrylic acid, Methyl, ethyl, propyl, butyl-butyl or tert-butyl esters are particularly preferred, if the monomers are used in the form of their salts for the polymerization, the alkaline earth metal, alkali metal or ammonium salts, or salts of organic amines, alkali metal and ammonium salts are particularly preferred.The suitable basic monomers forming the building blocks of the copolymers are vinyl imidasol, vinylimidazoline, vinylimidazolidine, vinylpyrrolidone, the monoalkyl or dialkyl aminoalkyl esters or monoalkyl or dialkylaminoalkylamides of the aforementioned unsaturated carboxylic esters The individual monomers or mixtures can be used as initial monomers for preparing the copolymers. two for the redispersible dispersion powders according to the invention are advantageously copolymers containing from 80 to 15% by weight, preferably from 70 to 30% by weight, and a free radical polymerizable monomer capable of forming salts. The dispersion powders preferably contain from 20 to 85% by weight of units [sic], preferably from 30 to 70% by weight of another monomer component consisting of at least one of the alkyl esters of acrylic and / or methacrylic acid aforementioned. Suitable polymers are advantageously copolymers of methacrylic acid and ethyl acrylate, methacrylic acid and methacrylic esters, terpolymers of dimethylaminomethyl methacrylate, methyl and butyl methacrylate and 'copolymers of vinyl acetate and crotonic acid. Preferred copolymers are copolymers of methacrylic acid and ethyl acrylate. In addition, the polymer solution or dispersion may contain other auxiliaries. The auxiliaries include polysaccharides such as cellulose, for example hydroxyalkyl cellulose [sic] such as methyl cellulose or ethyl cellulose, or hydroxy (alkyl) alkyl celluloses such as hydroxypropyl cellulose or hydroxypropyl methyl cellulose phthalate, starch, degraded starch, pectin, chitin, chitosan, arabinogalactan, xylan, xanthan gum, galactomannans such as ghatti gum [sic] locust bean gum or gum tragacanth. Proteins such as casein or gelatin or shellac can also be used as auxiliaries. Sugars are also suitable, such as mono-, di- and trisaccharides, for example, glucose, sugar or sucrose, sugar derivatives or sugar alcohols or urea. The auxiliaries also include substances such as pentaerythritol, pentaerythritol tetraacetate, polymers such as polyethylene oxides or polypropylene oxides and their block copolymers, phosphatides such as lecithin and lysolecithin, homo- and copolymers of vinylpyrrolidone, surfactants, citric acid, succinic acid, bile acids , sterols and other materials, as described in JL Ford (Pharm. Acta Helv. 61, 69-88, 1986). The surfactants are, for example, the various types of Brij®, ie, cetyl, lauryl, oleyl or stearyl ethers having from 2 to 100 polyoxyethylene units (= POE), the different types of Span® such as - Span 20 (monolaurates of sorbitan), Span 40 (sorbitan monopalmi), Span 60 (sorbitan monostearate) or Span 80 (sorbitan monooleates), the different types of Tween ® such as Tween 20 (POE (20) sorbitan monolaurate), Tween 40 (POE (20) sorbitan monopalmitates), Tween 60 (POE (20) sorbitan monostearates) or Tween 80 (POE (20) sorbitan monooleates), the various types of Triton® (octyl phenol ethoxylates) as may be Triton X-15, X-35, X-100 C, X-305 (70%), X-405 (70%), X-705 (70%), ethoxylated castor oil such as glycerol polyoxyethylene triricinoleate 35 (Cremophor ® EL) or polyoxyethylene 40 glycerol trihydroxystearate (Cremophor ® RH 40), ethoxylated 12-hydroxystearic acid such as polyoxyethylene-6 60-12'-hydroxystearate (Solutol ® HS15) or sodium lauryl sulfate. Auxiliaries further include, for example, fillers, glidants, waxes, wetting agents, lubricants, mold release agents, plasticizers, blowing agents, stabilizers, emulsifiers, colorants, flavors, connecting agents [sic], fluidifying agents and mixtures thereof. . Examples of plasticizers are low molecular weight poly (alkylene oxides), such as poly (ethylene glycols), 'poly (propylene glycols), poly (ethylene propylene glycols), low molecular weight organic plasticizers such as glycerol, pentaerythritol. glycerol monoaetate, diacetate or triacetate, propylene glycol or sodium diethylsulfosuccinate, phthalates, citrates, sebacates or glycerides of acetylated fatty acids. Examples of dyes are known as azo dyes, organic or inorganic pigments or dyes of natural origin. Preference is given to inorganic pigments. In addition, other additives may be added as fats of animal or vegetable origin, preferably in their hydrogenated form, in particular those which are solid at room temperature (20 ° C). These fats preferably have a melting temperature of 50 ° or higher. Preference is given to triglycerides of C12- fatty acids. Cl Ci6- and Ci8. The same function can also be carried out using waxes such as carnauba wax, candelilla wax, oricury wax, sugarcane wax, retama wax, animal waxes, such as beeswax, shellac waxes, waxes Chinese insect, or lanolin, petroleum, lignite, peat waxes or other mountain waxes, polyolefin waxes, paraffin waxes, acid waxes, ester waxes, alcohol or amide waxes. These waxes can be modified, partially or completely synthetic. Of course, individual waxy components such as waxy acids, waxy alcohols, waxy ketones, waxy hydroxy acids, paraffins, resin acids, polyterpenes, resin alcohols, sterols, petrolatums or fatty acids or mixtures may also be added. These fats, waxes, fat derivatives or waxes can be advantageously mixed together or together with ono-and / or diglycerides or phosphatides, especially lecithin. The mono- and diglycerides are preferably derived from the aforementioned types of fats, that is, C12 fatty acids. C? , Cie, and Cis. Other suitable auxiliaries are different emulsifiers. Commercially available emulsifiers are mentioned, for example in M.I. Ash, Handbook of Industrial Surfactants, Gower Publishing Co., Hants, (1993). These may be polymeric or low molecular weight compounds. The low molecular weight compounds generally contain a straight or branched chain alkyl radical, saturated or unsaturated or unsaturated [sic], cyclic or acyclic, aromatic or aliphatic, having from 8 to 40, preferably from 10 to 30, in particular of 12 to 22 carbon atoms in the molecule. In addition, stabilizers such as oxidants, photostabilizers, hydroperoxide decomposers, radical scavengers and stabilizers to prevent microbial attacks can be added. The auxiliaries are also bases and acids added to control the solubility of an active compound (see, for example K. Thoma et al., Pharm.Ind 51, 98-101 (1989)). The auxiliaries can be added to the dispersion before or after drying. If appropriate, the auxiliaries are added to the dispersion in an amount from 0.5 to 50% by weight, preferably from 1 to 30% by weight, based on the total solids content of the dispersion. Polymers containing free acids or bases are prepared in a conventional manner by free radical polymerization by any of the known processes. The copolymers which are used to prepare the redispersible polymer powders can be prepared by various processes, for example by precipitation polymerization, reverse-emulsion polymerization, reverse suspension polymerization, emulsion polymerization, suspension polymerization or solution polymerization. The polymerization can be carried out batchwise or continuously, with or without the use of seed polymers, initially by charging all or part of the components of the reaction mixture, or first by partially charging and then forming all or some of the components of the reaction mixture or dosing the components without an initial charge. In DE-A-4 325 158, for example, a process for precipitation polymerization is described. To dry the dispersion already prepared, any of the usual techniques can be used, such as thin film drying, fluidized bed spray drying, spray drying or lyophilization, in addition, the dispersions to be sprayed can contain spraying auxiliaries , such as polyvinyl alcohols, cellulose derivatives, starch derivatives, lignin sulfonates, polyacrylic acid and polyacrylamides. Suitable antiblocking agents which may be added are alimunium silicates such as bentonite, kieselguhr, colloidal silica gel, diatomaceous earth, calcium carbonate, magnesium silicates such as talc or tricalcium phosphate. The preferred atomization is carried out as hydrodynamic atomization by liquid pressure or air pressure by means of nozzles such as single component nozzles, multi component nozzles or disk nozzles using the conventional spray equipment. The basic principle is the atomization of the solution in very small droplets. These drops have a very large surface area that allows rapid evaporation. The small diameter of the drops, necessary, is obtained by the speed of the atomizer wheel or the atomizing gas pressure. The degree of evaporation that is obtained is sufficient to completely eliminate moisture from the drops. Due to the loss of heat of evaporation and the short time that the particles remain suspended, thermal damage to the product is avoided.

The drops of liquid can be dried in a conventional spray tower using air or an inert gas such as nitrogen, argon or helium as drying gas in a flow with the current or countercurrent with the drops of the liquid. Preferably, the gas for drying is used in a flow with the current, the temperature of the gas entering the tower being from 60 to 160, preferably from 90 to 140 ° C, and the temperature when it leaves the tower. 40 to 100, preferably 60 to 80 ° C. The evaporation of the solvent can be carried out at an atmospheric pressure or from 0.6 to 1.2 bar. The resulting powder can be separated from the gas stream in a customary manner using a cyclone. The residual solvent content of the powder thus formed, in general, is not more than 7.5% by weight. The particle size of the resulting powder particles in general is from 10 to 150 microns. By using spray granulation, the particle size can be obtained up to 450 microns. The polymer powders, according to the invention, redispersible in aqueous solution, can be redispersed more easily than those of the prior art. In all the experiments the redispersion was > 90% An advantage of the films prepared from the dispersions according to the invention is that they dissolve more quickly than the films prepared from the initial dispersions. Thus, in the small intestine, the active compound is released more rapidly from the coated administration forms. The dispersible, redispersible powders according to the invention or the dispersions prepared from these or other by-products are suitable for all solid or semi-solid cosmetic or pharmaceutical formulations or for compositions used in the protection of crops or animals. . Solid or semi-solid cosmetic or pharmaceutical formulations include, in a non-limiting sense, tablets, crystals containing an active compound, icrotablets, sugar coated tablets, granules, pills, capsules, microcapsules and granules. A particular method of application of the redispersible dispersion powders is the preparation of transdermal therapeutic systems. Applications in crop protection include teromone traps for harmful insects that require a sustained, sustained release of the theroman. EXAMPLES Example 1 Buffer solutions that were used in Examples 1, 2, 5 and 6.

- Merck pH 5.0 buffer solution contains in 1 1 20.256 g of citric acid 7.84 of NaOH - Merck buffer solution pH 6.0 contains 1 1 2 .526 g of citric acid 6. 32 g of NaOH - "Merck buffer solution 4.66 contains in 1 1 6.005 g of acetic acid 8.204 g of Na acetate 600 g of a dispersion at 30% concentration of Eudragit® L30D are mixed with 100 g of a buffer solution of citric acid at 0.9% concentration, with stirring.The resulting pH is then 4.0.The whole solution is then spray dried by the known methods (drying gas: nitrogen with the stream, inlet temperature: 125 ° C, temperature output: 50 ° C.) A redispersible polymer powder is obtained which can be redispersed by stirring in water.The percentage of the clot of <50 microns is 0% (for the determination see Example 7). is 5.5.

Example 2 180 g of methacrylic acid / ethyl acrylate copolymer (ratio - 1: 1) are stirred in an aqueous solution containing a citrate buffer at 0.8% concentration. This produces a dispersion of the methacrylic acid copolymer that was not previously redispersible.

Example 3 Preparation of a redispersible powder prepared from Eudragit® L30D (Róh GmbH, dispersion of acrylate prepared from ethyl acrylate and methacrylic acid). a) Preparation of an aqueous polyacrylate buffer 93.4 g of a 10% concentration dispersion (Eudragit® L30D) are converted to 114.1 g of an aqueous acrylate solution having a pH of 7.0 by the addition of 20.7 g of a aqueous solution of NaOH at 10% concentration. b) Preparation of the mixture 1000 g of a dispersion at 30% concentration (Eudragit® L30D, approximate pH 2-3) are mixed with 114 g of a solution prepared in part a). This gives a polyacrylate dispersion having a pH of 5.2. The dispersion is then spray dried. This produces a redispersible powder.

Example 4 a) Preparation of an aqueous polyacrylate buffer 93.4 g of a dispersion at 10% concentration (Kollicoat® MAE 30D, BASF AG, acrylate dispersion made from ethyl acrylate and methacrylic acid, approximate solids content 30%) are converted to 1 ^ 4.1 g of an aqueous acrylate solution having a pH of 7.0 by addition of 20.7 g of an aqueous solution of NaOH at 10% concentration. b) Preparation of the mixture 1000 g of a dispersion at 30% concentration (Kollicoat ® MAE 30D, BASF AG, acrylate dispersion "made of ethyl acrylate and methacrylic acid, solids content approximately 30%, pH approx. 2-3 ) are mixed with 114 g of a solution prepared in part a) This gives a polyacrylate dispersion having a pH of 5.2 The dispersion is then spray dried, this produces a redispersible powder.

Example 5 Coating for tablets In a horizontal drum (Accela Cota type, Manesty), 5000 g of propranolol tablets with an active compound content of 40 mg and a tablet weight of 250 mg were coated with a resistant film coating to gastric juices based on a copolymer of methacrylic acid / redispersible ethyl acrylate with a content of 2% buffer of acetates pH 4. 66, based on the film former, applying 6 mg / cm2 of the former of the gastric juice-resistant film former of this amine or 8 mg / cm2 of solids. The spraying of the dispersion was of the following composition: Pigment Suspension: titanium dioxide 0.5% Talcum 2.0% Sicovit Red 30 0.5% Kollidon 30 0.5% Water 10.0% Coating Suspension: methacrylic acid / ethyl acrylate copolymer with a content 2% acetates buffer pH 4.66 15.0% Triethyl citrate 1.5% Water 70.0% Total weight 100.0% The pigment suspension was homogenized in a corundum disc mill. The methacrylic acid / ethyl acrylate copolymer with a content of 2% acetates buffer was redispersed by slowly stirring the solids in water using a paddle stirrer, thus immediately forming a very fine dispersion. 1680.8 g of the spray suspension was sprayed at an incoming air temperature of 46 ° C, a leaving air temperature of 33 ° C and a spray speed of 40 g / min. The coating was a smooth red color, regular and uniform. The release in artificial gastric juice (pH: 1.2) showed _ > the coating resistant to gastric juice during 2 h, and the subsequent passage to a buffer solution pH 6.8 showed the rapid opening of the coating in the neutral region (99% release within 60 min). Release rate: 60 min pH 1.2 0.5% active compound released 120 min pH 1.2 0.8% active compound released In another buffer solution at pH 6.8 using phosphate buffer 150 min 99.0% active compound released Example 6 Redispersibility 20 g of redispersible ethyl methacrylic acid / acrylate-copolymer copolymer with a content of 2% acetates buffer or 5% citrate buffer, based on each * case in the film former, were suspended in 80 g of demineralized water using a magnetic stirrer. The total agitation time was 60 min. The suspension was then passed through two sieves stacked one on top of the other with 125 μ and 50 μ mesh sites, and the residue - if present - was washed with little water. After drying, the residue was determined gravimetrically.

Claims (1)

1. CLAIMS A process for preparing polymeric powders redispersible in aqueous solution with a content of c polymers carrying free acid or base groups and, if appropriate, auxiliaries, the process consists of adjusting the pH of the dispersion by adding at least one buffer system to a pH from 2.0 to 6.5 in the case of copolymers carrying acid groups or at a pH of 7.5 to 12 in the case of copolymers carrying base groups, before drying. process, as mentioned in claim 1, wherein the pH of the dispersion is adjusted by the addition of at least one buffer system to a pH from 3.0 to 6.0 in the case of copolymers carrying acid groups or from 7.5 to 11 in the case of copolymers carrying base groups, before drying. process, as mentioned in claim 1 or 2, wherein the buffer system used contains salts of weak acids and strong bases or salts of strong acids and weak bases. process, as mentioned in claim 1 or 2, wherein the buffer system used contains polymeric buffers obtainable by the addition of a neutralizing agent to a polymer carrying free acid or base groups. 5. The process, as mentioned in any of claims 1 to 4, wherein the polymeric powder that is used consists of copolymers carrying groups c_a > rboxyl or amino-free. The process, as mentioned in any of claims 1 to 5, wherein the polymer powder used consists of copolymers having from 20 to 85% by weight of an alkyl ester of acrylic and / or methacrylic acid and from 80 to 15% by weight of a monomer polymerizable by free radicals capable of forming salts. 7. The polymeric powders redispersible in aqueous solution obtainable by any of the processes as recited in claims 1 to 6. 8. The use of the redispersible polymer powders in aqueous solution, as mentioned in claim 7, in cosmetic formulations or pharmaceutical products or compositions for the protection of crops. 9. The use of a buffer system, as mentioned in claims 3 or 4 for redispersible polymer powders containing copolymers bearing free carboxyl or amino groups, dried without the addition of the buffer. 10. Cosmetic, pharmaceutical or crop protection formulations containing the polymeric powders redispersible in aqueous solution as mentioned in claim 7, and customary additives.