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Aqueous polymer dispersionRelated Patent Categories: Drug, Bio-affecting And Body Treating Compositions, Topical Sun Or Radiation Screening, Or Tanning PreparationsAqueous polymer dispersion description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20060193798, Aqueous polymer dispersion. Brief Patent Description - Full Patent Description - Patent Application Claims
[0001] The invention relates to an aqueous polymer dispersion prepared by free-radical polymerization of vinyl acetate, to a process for preparing an aqueous polymer dispersion of this type, and to the use thereof. [0002] U.S. Pat. No. 5,252,704 discloses polymer powders which can be redispersed in water and which are prepared using polyvinylpyrrolidone (PVP) as dispersant. The polymer powders are prepared with use inter alia of vinyl esters in a conventional emulsion polymerization. PVP is added to the emulsion before the spray drying. The polymer powders are intended in particular as additives for cement mixtures. [0003] DE 43 41 156 C1 discloses the use of plastic dispersion powders which are redispersible in water as pharmaceutical carriers in drug forms with controlled delivery of active ingredient, the powders having a core/shell structure with particular values of Tg for the core polymers and shell polymers. [0004] DE 197 09 532 A describes the use of redispersible polymer powders or polymer granules for coating pharmaceutical or agrochemical dosage forms, the powders or granules consisting of 10 to 95% by weight of polyvinyl acetate and 5 to 90% by weight of an N-vinylpyrrolidone-containing polymer and, where appropriate, other additives. [0005] For producing pharmaceutical dosage forms there are frequently used, as in DE 197 09 532, polymer powders which must be redispersed in water to produce these dosage forms. The reasons for this preparation of redispersible powders is that it is frequently impossible to stabilize the aqueous preparations appropriately for them to comply with the great demands made on starting materials for pharmaceuticals. Thus, for example, there must be no microbiological attack nor any increase in particle size, to say nothing of coagulation or sedimentation, because reliable production of the pharmaceutical is endangered thereby. The aqueous preparations are often stable only for some weeks. To prolong the stability, the aqueous preparations are converted into powders from which it is necessary in turn to prepare an aqueous preparation by stirring into water before use. This procedure consumes a large amount of energy and time and the thermal and mechanical stresses on the product during spray drying and stirring change the original properties. In addition, the reproducibility of important properties of the dosage forms, such as, for example, the release of active ingredient, is often poor because redispersible powders frequently result in coatings which adhere poorly, do not form complete films and are inhomogeneous. One reason for this is certainly that it is never possible to obtain a 100% redispersion of the powders, and such redispersions therefore always contain proportions of coarse particles or particle agglomerates (larger than 1 .mu.m in diameter). A shift in the average particle diameter to values greater than 300 nm is enough to result in poor use properties. [0006] Solid pharmaceutical dosage forms such as tablets, capsules, pellets, granules, crystals etc. are coated, i.e. provided with a film coating, for a wide variety of reasons. Thus, for example, it is possible to mask an unpleasant odor or taste and improve the swallowability. The stability of the active ingredient may be increased by the coating since less water vapor and oxygen reaches the interior of the tablets. The dosage forms have a better appearance and can be distinguished better by incorporating dyes. In addition, it is possible in particular to adjust the rate of release of active ingredient by the film coating. These criteria also apply in a similar way to agrochemical dosage forms. [0007] In general, a distinction is made between instant release forms and sustained or slow release forms. [0008] The intention with instant release forms is to release the active ingredient in the shortest possible time. In these cases the coating must impede release of the active ingredient from the core only slightly or not at all. In pharmaceutical technology, instant release forms are preparations from which more than 80% of the active ingredient are released within one hour. [0009] By contrast, release from sustained release forms is delayed in order, for example, to avoid plasma level peaks and thus possible side effects, or to reduce the frequency of intake. In the so-called coated sustained release forms, a film coating slows down the release of the drug substance. Frequently employed for this purpose are water-insoluble cellulose derivatives such as ethylcellulose or (meth)acrylate copolymers, in particular Eudragit.RTM. NE, RS and RL (Rohm Pharma). For Eudragit.RTM. RS and RL it is recommended to add from 10 to 20% by weight, based on the film former, of plasticizer. An even higher plasticizer content (about 30% by weight) is indispensable for ethyl cellulose. Only Eudragit.RTM. NE requires no plasticizer because it has a very low glass transition temperature and minimum film-forming temperature. However, this causes it to be tacky and difficult to process. [0010] It is an object of the present invention to provide starting materials for producing in particular pharmaceutical dosage forms, which are very stable on storage, which can be processed very easily, which in particular easily result in good, homogeneous film coatings with very reproducible release and which, where appropriate, need not be prepared from powders which are initially dried and then redispersed in H.sub.2O. [0011] We have found that this object is achieved by an aqueous polymer dispersion prepared by free-radical polymerization of vinyl acetate in the presence of at least one ionic emulsifier, at least one free-radical initiator and at least one protective colloid, wherein the polymerization is carried out in the presence of a polymerization regulator and wherein the ratio by weight of protective colloid to ionic emulsifier is at least 4:1, preferably at least 8:1, particularly preferably in the range between 8:1 and 12:1, and wherein the ratio by weight of vinyl acetate monomer to protective colloid is between 19:1 and 4:1, preferably between 15:1 and 6:1. [0012] A preferred embodiment of the abovementioned aqueous polymer dispersion is prepared by free-radical polymerization at a pH in the range from 1 to 7, particularly preferably in the range from 3 to 6. [0013] It has proved advantageous in this connection for the pH to be kept constant in the range from pH 1 to pH 7 during the polymerization by addition of a reagent with a basic action. A pH kept constant means, both during and after the polymerization, a pH with variations in the region of +/-1.5, preferably +/-1, particularly preferably +/-0.5 units. [0014] The reagents with a basic action used for the purposes of the invention are preferably alkali metal or alkaline earth metal hydroxides, particularly preferably aqueous solutions of an alkali metal or alkaline earth metal hydroxide--especially sodium hydroxide or potassium hydroxide solution--and aqueous ammonia solutions. [0015] It has proved to be particularly advantageous for the pH to be kept constant during the polymerization by addition of a buffer system. [0016] Buffer systems mean conventional buffer and/or polymeric buffers. [0017] Examples of suitable buffers are all salts of weak acids and strong bases or strong acids and weak bases, it being possible for the salts to be of the same acids or bases or mixtures of different acids or bases. [0018] It is preferred in this connection for the buffering range of the buffer system to be chosen between pH 1 to 7. Suitable buffers or buffer solutions with a buffering range in acidic medium between pH 1 to 7 are, for example, buffers such as Walpole buffer (acetic acid/Na acetate, pH 3.6-5.6), Gomori aconitate buffer (aconitic acid/NaOH, pH 2.5-5.7), Kolthoff buffer (borax/succinate, pH 3.0-5.8), Sorensen citrate buffer (disodium citrate/HCl, pH 2.2-4.8), Sorensen glycine I buffer (glycine, NaCl/HCl, pH 1.2-3.6), Clark and Lub phthalate I buffer (potassium biphthalate/HCl, pH 2.2-3.8), Clark and Lub phthalate II buffer (potassium-biphthalate/NaOH, pH 4.0-6.2), Smith and Smith piperazine buffer (piperazine, HCl/NaOH, pH 4.8-7.0), Clark and Lub potassium chloride/HCl buffer (KCl/HCl, pH 1.0-2.2), Gomori tris maleate buffer (tris maleate/NaOH, pH 5.2-8.6) or Gomori succinate buffer (succinate/NaOH, pH 3.8-6.0). Buffers such as MES, ADA, PIPES or ACES, which are buffers customary in biochemistry, or amino acid buffers are also suitable buffers. [0019] Preferred buffers are those which can advantageously be prepared from weak acids and their salts, such as, for example, sodium acetate/acetic acid, sodium borate/boric acid, sodium phosphate/phosphoric acid, bicarbonate/sodium carbonate, sodium hydroxide/citric acid, sodium hydroxide/tartaric acid. Buffers of weak bases and their salts are also suitable. It is possible to use individual buffers or mixtures for adjusting the pH in the dispersions. [0020] It is also possible to use buffer systems with a buffer range between pH 7 to 13. Suitable buffers and buffer solutions with a buffering range in basic medium between pH 7 to 13 are, for example, buffers such as Clark and Lub borate buffer (boric acid, KCl/NaOH, pH 7.8-10.0), Delory and King buffer (carbonate/bicarbonate, pH 9.2-10.7) or Sorensen glycine II buffer (glycine, NaCl/HCl, pH 8.4-13). Buffers such as cholamine chloride, BES, TES, HEPES, acetamidoglycine, glycinamide, tris, bicine, tricine or glycylglycine, which are buffers customary in biochemistry, or amino acid buffers are also suitable buffers. [0021] Buffer systems which can also be used are salts, for example sodium salts of succinic acid, pyruvic acid, maleic acid, malonic acid, malic acid, lactic acid and other amino acids. It is also possible to consider as buffer salts of polyacrylic acid, polymethacrylic acid, acrylic acid/methacrylic acid copolymers, carboxymethylcellulose, carboxymethyl starch, hemiesters of cellulose, hydroxypropylmethylcellulose or polyvinyl alcohol with polybasic acids such as phthalic acid, succinic acid or trimellitic acid. [0022] It is possible with this aqueous polymer dispersion, without the need for redispersion with the disadvantages associated therewith, to apply homogeneous film coatings with great reproducibility in a simple process step, in particular to pharmaceutical, agrochemical or nutritional dosage forms, which adhere extremely well, are resistant to external influences and ensure reproducible release of active ingredient. Compared with powders which are redispersible in H.sub.2O, the amount which must be applied to achieve a particular release rate is less, thereby saving further costs. [0023] "Nutritional dosage forms" mean tablets, capsules, granules or similar solid forms which do not contain active pharmaceutical ingredients but contain food supplements such as vitamins, carotenoids, minerals, plant extracts or nutraceuticals. [0024] The preparations of the invention are unexpectedly insensitive to other auxiliaries normally employed in spray preparations, such as pigments, fillers, thickeners, suspension stabilizers, emulsifiers, gloss improvers, release accelerators etc. and to shear stress and variations in the coating process. Because the (polymer) films are very elastic, no fissuring occurs on storage because the coatings comply with the changes in shape of the core, for example caused by a change in ambient humidity. Coatings of this type are therefore also stable in regions with extremes of climate such as cold or high humidity. Continue reading about Aqueous polymer dispersion... Full patent description for Aqueous polymer dispersion Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Aqueous polymer dispersion patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. 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