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
2001-11-09
2004-05-11
Sanders, Kriellion A. (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...
C524S803000, C524S832000, C526S291000, C526S315000, C526S319000
Reexamination Certificate
active
06734246
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to polyvinylacetal-grafted polymers in the form of their aqueous dispersions or water-redispersible powders, to processes for their preparation and to their use.
2. Description of the Related Art
Polymers stabilized with protective colloids are used in a wide range of applications, in particular, in the form of their aqueous dispersions or water-redispersible polymer powders. Examples include their use as coating materials or as adhesives for a variety of substrates, for instance as cement-containing tile adhesives. The protective colloids used as stabilizers are, as a rule, polyvinyl alcohols. The use of polyvinyl alcohol is desirable, since in contrast to systems stabilized by low molecular weight compounds (emulsifiers), the polyvinyl alcohol also contributes to the overall strength, for example, to adhesive strength values in tile cements. However, difficulties may arise during the preparation and use of polymers stabilized with protective colloids. In particular, when polymers in the form of their redispersion powders are employed to improve mortar properties, a main field of use of redispersion powders, the formulations must remain stable over a certain time and may not substantially change their processing consistency as reflected by, for example, viscosity stability or cement stability. Polyvinyl alcohol-stabilized polymer powders are mentioned, for example, in EP-A 149098, in EP-A 477900 and in WO-A 99/16794. Although such polyvinyl alcohol-stabilized polymer powders exhibit good viscosity and processing behavior in applications which involve use of cement, it is desirable in many cases to further improve this behavior.
Polyvinylacetals having sulfonate functional groups are known as protective colloids useful in the preparation of aqueous polymer dispersions. DE-A 3316948 describes polyvinylacetals which have sulfonate functional groups in which up to 10 mol % of OH groups have been acetalated with an aldehyde bearing sulfonate functional groups. EP-A 655464 relates to a process for the preparation of polymer dispersions employing polyvinylacetals having a high degree of acetalation and up to 20 mol % of sulfonate groups as protective colloids.
EP-A 1020493 describes a process for the preparation of dispersion powders stabilized with protective colloids, the parent polymer dispersions having been stabilized with polyvinyl alcohol as a protective colloid, and partially acetalated polyvinyl alcohols then used as a protective colloid for spray drying the dispersions. The use of the partially acetalated polyvinyl alcohols as protective colloids during polymerization is ruled out, since the latter are said to decompose at low pH and to be precipitated from aqueous solution at high temperatures. The use of partially acetalated polyvinyl alcohols as protective colloids for the preparation of frost-stable, aqueous dispersions is disclosed in DE-B 1202982, where partially hydrolyzed polyvinyl alcohols or polyvinylacetals having a high vinyl acetal content are used. DD-A 222880 describes the preparation of polyvinyl acetates having improved water resistance by polymerizing vinyl acetate in the presence of polyvinyl alcohol acetalated with acetaldehyde.
SUMMARY OF THE INVENTION
It is an object of the invention to provide polymers which, when employed in cement-based applications, have improved viscosity stability and cement stability and do not retard setting of the cement, as compared with polyvinyl alcohol-stabilized polymers. These and other objectives are attained by means of polyvinylacetal-grafted polymers or redispersible powders obtained therefrom, wherein the aldehydes employed in acetalation of the polyvinylacetal polymers comprise 3 to 7 C atom-containing aldehydes.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The invention relates to polyvinylacetal-grafted polymers in the form of their aqueous dispersions or water-redispersible powders prepared by emulsion or suspension polymerization of one or more monomers from the group of vinyl esters, (meth)acrylates, vinylaromatics, olefins, 1,3-dienes, and vinyl halides, and, if desired, further monomers copolymerizable therewith, the resulting polymers being grafted with polyvinylacetals having from 0 to 5.0 mol % of vinyl acetate units, from 75 to 95 mol % of vinyl alcohol units and from 0.1 to 20 mol % of acetal units derived from aldehydes having 3 to 7 C atoms.
The invention furthermore relates to a process for the preparation of polyvinylacetal-grafted polymers in the form of their aqueous dispersions or water-redispersible powders by means of free radical emulsion or suspension polymerization, in an aqueous medium, of one or more monomers from the group of vinyl esters, (meth)acrylates, vinylaromatics, olefins, 1,3-dienes and vinyl halides and, if required, further monomers copolymerizable therewith, in the presence of one or more protective colloids a) and, if required, drying of the polymer dispersions obtained thereby in the presence of one or more protective colloids b), the polymerization being carried out at a pH of from 5 to 8, wherein protective colloids a) comprise partially acetalated polyvinyl alcohols having from 0 to 5.0 mol % of vinyl acetate units, from 75 to 99 mol % of vinyl alcohol units and from 0.1 to 20 mol % of acetal units derived from aldehyde(s) having 3 to 7 C atoms, the parent polyvinyl alcohol having a viscosity of from 2 to 30 mPa·s, and wherein protective colloids b) comprise one or more protective colloids differing from a) for drying, preferably spray drying.
Suitable vinyl esters are those of carboxylic acids having 1 to 12 C atoms. Vinyl acetate, vinyl propionate, vinyl butyrate, vinyl 2-ethylhexanoate, vinyl laurate, 1-methylvinyl acetate, vinyl pivalate and vinyl esters of &agr;-branched monocarboxylic acids having 9 to 11 C atoms, for example VeoVa9
R
or VeoVa10
R
(trade names of Shell), are preferred. Vinyl acetate is particularly preferred.
Suitable monomers from the group consisting of acrylates or methacrylates are esters of straight-chain or branched alcohols having 1 to 15 C atoms. Preferred methacrylates or acrylates are methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate, n-butyl acrylate, n-butyl methacrylate, tert-butyl acrylate, tert-butyl methacrylate and 2-ethylhexyl acrylate. Methyl acrylate, methyl methacrylate, n-butyl acrylate, tert-butyl acrylate and 2-ethylhexyl acrylate are particularly preferred.
Preferred vinylaromatics are styrene, methylstyrene and vinyltoluene. A preferred vinyl halide is vinyl chloride. The preferred olefins are ethylene and propylene, and the preferred dienes are 1,3-butadiene and isoprene.
Optionally, from 0.1 to 5% by weight, based on the total weight of the monomer mixture, of auxiliary monomers may also be copolymerized. From 0.5 to 2.5% by weight of auxiliary monomers are preferably used. Examples of auxiliary monomers are ethylenically unsaturated mono- and dicarboxylic acids, preferably acrylic acid, methacrylic acid, fumaric acid and maleic acid; ethylenically unsaturated carboxamides and carbonitriles, preferably acrylamide and acrylonitrile; mono- and diesters of fumaric acid and maleic acid such as their diethyl and diisopropyl esters, maleic anhydride, and ethylenically unsaturated sulfonic acids and salts thereof, preferably vinylsulfonic acid and 2-acrylamido-2-methylpropanesulfonic acid. Further examples of auxiliary monomers are precrosslinking comonomers such as polyethylenically unsaturated comonomers, for example divinyl adipate, diallyl maleate, allyl methacrylate, and triallyl cyanurate, or postcrosslinking comonomers, for example acrylamidoglycolic acid (AGA), methylacrylamidoglycolic acid methyl ester (MAGME), N-methylolacrylamide (NMA), N-methylolmethacrylamide and N-methylolallylcarbamate, alkyl ethers such as isobutoxy ether, and esters of N-methylolacrylamide, of N-methylolmethacrylamide and of N-methylolallylcarbamate. Comonomers having epoxide functional groups, such as
Ball Peter
Tschirner Peter
Weitzel Hans-Peter
Brooks & Kushman P.C.
Sanders Kriellion A.
Wacker Polymer Systems GmbH & Co. KG
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