Process for preparing a powder of water-insoluble polymer which

Details Process for preparing a powder of water-insoluble polymer which Process for preparing a powder of water-insoluble polymer which

1988-12-09

1990-11-06

Dixon, Jr., William R.

Compositions: coating or plastic

Coating or plastic compositions

Carbohydrate or derivative containing

106198, 523334, C08K 300, C08L 108

Patent

active

049683500

DESCRIPTION:

BRIEF SUMMARY
The invention pertains to the area of latexes, dispersions in a liquid phase of water-insoluble polymers, also called pseudo-latexes, and powders of such polymers which can be redispersed in a liquid phase. Specifically, the objective of the invention is a process for preparing a powder of water-insoluble polymer, which can be redispersed in a liquid phase, as well as utilization of such a powder to produce a pseudo-latex.
At present, pseudo-latexes in the liquid dispersion state are manufactured according to the process described in U.S. Pat. No. 4,177,177 and U.S. Pat. No.4,330,338 or according to minor variations thereof. This process consists of dissolving a water-insoluble polymer in an organic solvent which is not miscible with water, emulsifying the resulting solution in an aqueous phase containing cationic, anionic or nonionic surfactants, passing the crude emulsion through a high-pressure homogenizer and finally removing the solvent by evaporation at reduced pressure. In principle, according to the above patents, practically any polymer which is simultaneously insoluble in pure water and soluble in an organic solvent which is not miscible with water can be converted into an aqueous dispersion.
Pseudo-latexes are currently offered particularly as aqueous coating means or as medication vectors. During prolonged storage periods, however, a progressive loss of stability is noted, due, among other things, to the phenomenon of irreversible hydrolysis or flocculation. These pseudo-latexes sometimes contain high proportions of surfactants, which can render them unsuitable for certain purposes, especially pharmaceutical ones. In addition, for a given proportion of particles in liquid dispersion, it is necessary to transport large volumes of liquids, which is very costly on an industrial scale.
At present, desiccation of such pseudo-latexes for the purpose of obtaining therefrom a powder which can subsequently, at a desired time, be redispersed in an aqueous medium, implies prior addition to the liquid dispersion (pseudo-latex) of large proportions of surfactants or protective agents which remain behind in the resulting powder.
On the other hand, several processes for obtaining dried redispersible latex powders are known, but these are only applicable to a small number of water-insoluble polymers. U.S. Pat. No.4,462,839 describes a process for preparing powdered pseudo-latexes of cellulose acetophthalate, hydroxypropylmethylcellulose phthalates and polyvinyl acetophthalate. This technique is based on the addition of tribasic phosphates to the latex, followed by drying by atomization. The same authors (EP 0,111,103) describe a technique for obtaining a redispersible powdered pseudo-latex of cellulose acetophthalate, designed for coating purposes, involving the addition to the preformed pseudo-latex of an acetylated monoglyceride and then drying by atomization. In addition, U.S. Pat. No. 2,800,463 describes the conversion of a polyvinyl acetate latex into a powder which can be redispersed by adding a protective hydrocolloid (polyvinyl alcohol, gum arabic, gum, tragacanth, etc.), again followed by drying by atomization.
Thanks to the present invention, it is now possible to obtain, easily and with practically no limitation, microparticles of water-insoluble polymers in the form of easily redispersible powders, as well as pseudolatexes in the liquid dispersion state, without being faced with the disadvantages enumerated above. The invention is defined in particular in claims 1 and 9. The invention is based on the discovery that certain organic solvents, although miscible in all proportions with pure water, lead to the formation of a two-phase liquid-liquid system when they are added to concentrated aqueous solutions of a salt or even of a substance not subject to electrolytic dissociation.
Selection of the solute is just as critical as that of the solvent, and all combinations resulting in precipitation of the solute in solid form are, of course, unsuitable. The condition of complete miscibility between the sol

REFERENCES:
patent: 2809120 (1957-10-01), Sloan et al.
patent: 2809192 (1957-10-01), Sloan et al.
patent: 3485651 (1969-12-01), Ganz
patent: 4462839 (1984-07-01), McGinley

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