Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2002-04-17
2004-10-05
Egwim, Kelechi C. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C524S048000, C524S052000, C524S053000, C524S800000, C524S804000
Reexamination Certificate
active
06800675
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an emulsion (co)polymerization method in which starch in a preferably modified and/or derivatized form, optionally along with other emulsifiers or auxiliary agents known per se, is used to stabilize the emulsion, and an aqueous polymer dispersion containing such starches and optionally emulsifiers or auxiliary agents known per se.
By emulsion (co)polymerization method (which, for reasons of simplicity, will be referred to as an emulsion polymerization method below), a (co)polymerization method in which liquid monomers are present in an aqueous emulsion and subjected to polymerization in this state is generally understood. Such methods yield aqueous polymer dispersions which are either fed directly to a purpose of use or are subsequently dried to recover the polymers. The monomers, as a rule, are ethylene-unsaturated compounds which are processed to homopolymers or copolymers. Starch primarily functions as a protective colloid, sometimes also as an emulsifier, for the monomers, thus serving as a stabilizer for the monomer emulsions as well as for the polymer dispersions forming.
The basic advantage of the use of starch, modified starch and starch derivatives in industrial processes, in general, and in emulsion polymerization methods, in particular, resides in that starch is a natural raw material renewing every year and available in excess quantities at low cost. Consequently, starch is actually frequently used in technology for various applications.
Other protective colloids usually used in emulsion polymerization methods are partially or completely hydrolyzed polyvinyl alcohols, natural and synthetic rubbers as well as cellulose ethers such as methyl cellulose, hydroxyethyl cellulose, ethylhydroxyethyl cellulose, etc. The fact that these substances tend to precipitate under specific circumstances and, as a result, are no longer able to function as protective colloids speaks against the use of polyvinyl alcohols and cellulose ethers. Moreover, cellulose ethers, polyvinyl alcohols and various rubbers constitute relatively expensive substances, what makes their use again unfavorable.
2. Prior Art
There are various documents that deal with the preparation of polymer dispersions in the presence of starch or starch derivatives as protective colloids:
U.S. Pat. No. 3,632,535 (R. E. Gramera, 1972) describes the use of oxidized starches as protective colloids in the preparation of vinylester polymers proposed for use in paper finishing, textile impregnation, as adhesives or as protective covers.
U.S. Pat. No. 3,769,248 (L. P. Kovats, 1973) describes the use of carboxymethylated starches and hydroxyalkyl starches and, in particular, hydroxypropyl starches alone, and mixtures of hydroxypropyl and hydroxyethyl starches, as stabilizers in the radical polymerization of vinyl acetate.
EP-A1 0 021 542 (P. F. T. Lambrechts, 1981) likewise describes the preparation of aqueous vinyl acetate (co)polymer dispersions in the presence of hydroxypropyl and/or hydroxy-ethyl starches as protective colloids, proposing the use of such dispersions as adhesives and covers or in the color and dye industry.
EP-A2 0 133 899 (H. Brabetz et al., 1985) describes the use of cyanoalkylated, hydroxyalkylated and/or carboxymethylated starches as protective colloids in the polymerization of vinyl esters.
U.S. Pat. No. 4,940,741 (D. R. De Wacker, 1990) describes the production of chip boards by using a polyvinyl acetate emulsion polymerized in the presence of a starch derivative. As vegetable origins, maize, tapioca and waxy maize are mentioned, the starches optionally being octenylsuccinylated, hydroxyproplyated, acidically, enzymatically or oxidatively degraded.
The two applications EP-A0 223 145 (C. P. Iovine et al., 1987) and EP-A2 0 245 718 (J. G. Palmer, 1987) filed by National Starch and Chemical Corporation, respectively, refer to the use of hydrophobed and, in particular, alkenylsuccinylated starches, imidazol-containing starches, cationic starches and acidically or enzymatically degraded starches as protective colloids in the polymerization of emulsions for the preparation of vinyl ester polymers, characterized in that waxy maize and tapioca are cited as preferred vegetable origins.
Another field of application of emulsion polymerization methods in the presence of starches, modified starches or starch derivatives consists in the preparation of polyacryl polymers and copolymers with dextrins and degraded starches being preferred. Chemically not further modified starch degradation products are mentioned in a number of applications by BASF AG (EP-A1 0 536 597; WO 94/08085; WO 97/17387; WO 98/24821), in some cases enzymatic degradation also takes place only immediately prior to polymerization in the same reaction vessel (EP-A2 0 276 770; WO 95/13194; WO 98/24821).
The copolymerization of (meth)acrylonitrile, one or more acrylic acid esters and optionally other ethylene-unsaturated copolymerizable monomers in the presence of oxidatively degraded or cationized, degraded potato starches, as well as the use of hydroxyethyl starches in general, are described in EP-A1 0 257 412 (H. Degen et al., 1988) and EP-A2 0 276 770 (H. Degen et al., 1988). The applications EP-A2 0 134 449 (H. Brabetz et al., 1985), EP-A2 0 134 451 (J. Schulze et al., 1985), DE-A1 39 22 784 (G. Rinck et al., 1991), EP-A1 0 334 515 (R. Kniewske et al., 1989) and EP-A1 0 536 597 (K. Wendel et al., 1993), in which the preparation of aqueous polymer dispersions by the radical aqueous emulsion polymerization of ethylene-unsaturated monomers in the presence of starches, modified starches or starch degradation products are described, should also be mentioned. Every starch form has its own characteristic features differing from those of other forms. To jump to conclusions from one form to another is neither possible nor permissible.
Also EP-A0 257 412 and 0 276 770 describe the emulsion polymerization of monomer mixtures carried out in the presence of degraded starches having viscosities of 0.12 to 0.50 dl/g and from 0.04 to less than 0.12 dl/g, respectively. In doing so, fine-particle aqueous polymer dispersions are obtained, which serve as paper sizing agents. It is pointed out that any native starch may be used, yet without having observed any advantages or disadvantages of specific starches.
SUMMARY OF THE INVENTION
The present invention is based on the surprising finding that amylopectin potato starch both in the native and in the modified or derivatized forms in emulsion polymerization methods is particularly effective as a protective colloid for the stabilization of the emulsion not only in special cases, but in a very general aspect. In this context, it is essential both from a chemical and from an economical point of view that the amylopectin potato starch is one obtained from potatoes inhibited in terms of amylose formation either by cultivation or by recombinant or other molecular-biological methods. These socalled amylopectin potatoes produce starches that constitute pure amylopectin.
Native starches obtained from ordinary potatoes or cereals, as a rule, consist of two different glucose polymers, i.e., about 65 to 85% amylopectin and about 15 to 35% amylose. Amylose and amylopectin are no uniform substances, but mixtures of polymers having different molecular weights. Amylose consists of unbranched or hardly branched alpha-1,4-linked glucose polymer chains, amylopectin constitutes a high-molecular and highly branched polyglucose structure which comprises 1,6-links in addition to the alpha-1,4-links at the branching sites. The commercially most important types of starch like maize starch, potato starch, wheat starch, tapioca starch, rice starch, etc. contain approximately 15 to 30% amylose. Waxy cereals like the waxy mutants of rice, sorghum, rye and, in particular, maize produce starches that consist merely of amylopectin. Waxy maize is by far the most important waxy cereal, yet would not grow particularly well in countries with rougher or cooler climates such as
Grüll Dietmar
Marnik Michel Wastyn
Pfalz Monika
Egwim Kelechi C.
Greenberg Laurence A.
Locher Ralph E.
Stemer Werner H.
Südzucker Aktiengesellschaft Mannheim/Ochsenfurt
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