Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
1998-10-27
2001-08-28
Michl, Paul R. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C528S489000
Reexamination Certificate
active
06281282
ABSTRACT:
DESCRIPTION
The present invention relates to a process for preparing polymer powders redispersible in aqueous solution comprising copolymers carrying free acid or base groups and, if appropriate, auxiliaries, which comprises adjusting the pH of the dispersion by the addition of a buffer system to a pH of from 2.0 to 6.5 in the case of copolymers carrying acid groups or a pH of from 7.5 to 12 in the case of copolymers carrying base groups.
The invention further relates to polymer powders redispersible in aqueous solution and their use in cosmetic and pharmaceutical formulations and compositions for crop protection.
Patent DE 2 512 238 discloses film-forming polymer powders prepared from aqueous plastic dispersions. These film-forming powders are used, after dissolution in an organic solvent, for coating solid drug formulations.
The use of organic solvents when coating solid drug formulations presents considerable technical problems. All the equipment used has to be explosion-proof to prevent ignition of the solvent. For environmental and cost reasons, the evaporated solvent has to be recovered from the waste air. In addition, the solvent has to be removed completely from the pharmaceutical formulations. Alternatives to using organic solvents were therefore sought.
Consequently, a number of processes employing water as solvent were developed. However, these processes have a number of disadvantages.
In U.S. Pat. No. 5,252,704, Bright et al. disclose redispersible polymer powders which can be prepared from copolymers by adding large amounts of polyvinylpyrrolidone prior to spray-drying. The high percentage of polyvinylpyrrolidone added, however, detrimentally affects the solubility of the polymer film obtained after film-forming.
EP-B 88 951 and EP-B 161 326 disclose the redispersion of emulsion polymer powder having free carboxyl or amino groups by converting these groups into their salts. Free carboxyl groups are thus converted into their salts by adding bases, and free amino groups are converted into their salts by adding acids. This is carried out after drying the polymer dispersion, by stirring an alkaline solution into the carboxyl-containing polymer powder which is finely dispersed in water.
If the polymer carries free amino groups, an acid solution is stirred in for dispersion.
For carboxyl-containing polymers, the possibility of partial neutralization of the free carboxyl groups by adding alkali prior to spray-drying has been described.
In this case, however, the dispersion viscosity and the degree of coagulum formation prior to spray-drying are critical parameters. In addition, if the alkali is added prior to drying, undesirable coagulum is easily formed during the subsequent redispersion. The neutralization of the polymer powders, ie. the salt formation, is therefore preferably carried out after drying the powders, just before the solid drug formulations are prepared. For the user, this poses the problem of having to provide additional facilities for the neutralization and storage of the bases or acids.
It is an object of the present invention to develop redispersible polymers which can be dispersed directly without the disadvantages described to give an aqueous solution, and to make them available for applications in the cosmetic and pharmaceutical sectors and in crop protection.
We have found that this object is achieved by adjusting the pH of the dispersion prior to 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 from 7.5 to 12 in the case of copolymers carrying base groups, so as to provide a polymer powder which is readily redispersible.
The polymer powder according to the invention, which has a very long shelf life, redisperses quickly in aqueous solution without forming coagulum, for example.
They are [sic] therefore ideally suitable as a film former in cosmetic, pharmaceutical or crop protection formulations.
Suitable buffers for the process according to the invention are, in principle, all known buffers such as described for example in Handbook of Biochemistry (H. A. Sober, R. A. Horte (Eds.). The Chemical Rubber Co., J 195-J 199, 1968).
The pH of the dispersion containing copolymers carrying free acid or base groups is advantageously adjusted prior to 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 from 7.5 to 12 in the case of copolymers carrying base groups. Preferably, the pH is adjusted prior to drying to a pH of from 3.0 to 6.0 in the case of copolymers carrying acid groups and to a pH of from 7.5 to 11 in the case of copolymers carrying base groups. By adjusting the pH, some of the free acid or base groups of the copolymers are converted to their salts.
Buffer systems are conventional buffers and/or polymeric buffers.
Suitable buffers are, for example, all salts formed from weak acids and strong bases or strong acids and weak bases, the salts being from identical acids or bases or mixtures of salts from different acids or bases.
The buffers 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. The buffer region of the buffer system is preferably from pH 1 to 7. Suitable buffers or buffer solutions having a buffer region in the acidic range from pH 1 to 7 are for example buffers such as the 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 3.5-5.8), Sørensen citrate buffer (disodium citrate/HCl, pH 2.2-4.8), Sørensen glycine buffer I (glycine, NaCl/HCl, pH 1.2-3.6), Clark and Lub phthalate buffer I (potassium biphthalate/HCl, pH 2.2-3.8), Clark and Lub phthalate buffer II (potassium biphthalate/NaOH, pH 4.0-6.2), Smith and Smith piperazine buffer (piperacine [sic], 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). Likewise, suitable buffers are MES, ADA, PIPES or ACES, which are common buffers in biochemistry, or amino acid buffers. Preference is given to buffers which are advantageously prepared from weak acids and their salts, such as sodium acetate/acetic acid, sodium borate/boric acid, sodium phosphate/phosphoric acid, hydrogen carbonate/sodium carbonate, sodium hydroxide/citric acid, sodium hydroxide/tartaric acid. Suitable buffers are also buffers prepared from weak bases and their salts. Individual buffers or mixtures can be used for adjusting the pH of the dispersions. The buffers used in the case of copolymers carrying free base groups, for example copolymers having free N-alkyl, amino or imino groups, comprise at least one buffer system. The buffer region of the buffer system is preferably from pH 7 to 13. Suitable buffers or buffer solutions having a buffer region in the basic range from 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 Sørensen glycine buffer II (glycine, NaCl/HCl, pH 8.4-13). Likewise, suitable buffers are cholamine chloride, BES, TES, HEPES, acetamidoglycine, glycinamide, Tris, Bicine, Tricine or glycylglycine, which are common buffers in biochemistry, or amino acid buffers.
Preferred are buffers which can advantageously be prepared from weak acids and their salts. Suitable buffers are also buffers prepared from weak bases and their salts. Single buffers or mixtures can be used for adjusting the pH of the dispersions.
If polymeric buffers or buffer solutions are used for neutralizing the free acid groups or the free base groups of the copolymer, these polymeric buffers can be prepared advantageously by adding a neutralizing agent to a polymer carrying free acid groups or free base groups. Suitable polymers are copolymers carrying free acid groups or
Breitenbach Jorg
Kolter Karl
Schmitt Angelika
BASF - Aktiengesellschaft
Keil & Weinkauf
Michl Paul R.
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