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
2000-05-22
2002-12-03
Reddick, Judy M. (Department: 1713)
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...
C156S332000, C524S459000
Reexamination Certificate
active
06489391
ABSTRACT:
BACKGROUND OF THE INVENTION
1) Field of the Invention
The invention relates to a process for preparing aqueous, protective colloid stabilized vinyl ester homopolymer and copolymer dispersions of defined solids content.
2) Background Art
Aqueous, polyvinyl alcohol stabilized dispersions of vinyl ester homopolymers or vinyl ester copolymers are used in particular as adhesives.
Dispersions having particular defined solids contents are required depending on the application in which these dispersions are to be used. Since the solids content of a polymer dispersion cannot be controlled precisely during the polymerization, and can only be increased even after the end of the polymerization by means of technically complex measures, the removal of water in vacuo being one example, which increases the production costs by prolonging the preparation times, the procedure adopted in practice is to prepare polyvinyl ester dispersions with a solids content higher than that required and then dilute the dispersion to the required solids content by adding water.
A problem with this “water dilution process” is that in the range of solids contents which is relevant in practice, of between 40% and 60%, the viscosity of polyvinyl alcohol stabilized polyvinyl ester dispersions does not rise linearly with the solids content; in this range, rather, the viscosity of the dispersions increases exponentially. A consequence of this is that, in the polymerization of dispersions having a solids content higher than that to be established subsequently by water dilution, polymerization is carried out with polymerization batches which are of relatively high viscosity. The relatively high viscosity hinders the dissipation of heat by way of the reactor walls, so necessitating the installation of additional cooling equipment such as reflux condensers, leading to the formation of wall deposits, and, furthermore, markedly increasing the polymerization times. A further disadvantage is that the removal of residual monomers from dispersions of relatively high viscosity is made more difficult.
DE-A 3724331 discloses a process in which the viscosity of aqueous polyvinyl ester dispersions is increased by adding pulverulent copolymers of vinyl alcohol-1-methylvinyl alcohol copolymers. With these rheological additives it is, indeed, possible to increase markedly the viscosity of the dispersions with a virtually unchanged solids content; however, this rheological additive does alter the performance properties of the dispersions. For example, even low-level additions of these additives, which are readily soluble in cold water, impair the water resistance.
In order to increase the solids content it is proposed in a number of patent applications, for example, EP-A 614922 (US-A 5430092), EP-A 567812 (US-A 5340858), EP-A 708122, and WO-A 96/11234, to prepare the polymer dispersions in the presence of seed latices which are included in whole or in part in the initial charge or are metered in their entirety, giving polymer dispersions having a biomodal particle size distribution. A disadvantage of this procedure is the predominantly highly complex process regime. Furthermore, although dispersions of high solids content are obtainable by means of this procedure, this solids content also can no longer be increased subsequently.
SUMMARY OF THE INVENTION
The object was therefore to provide a process for preparing aqueous, protective colloid stabilized polyvinyl ester dispersions by means of which polymer dispersions of defined solids content are obtainable without the occurrence of the abovementioned disadvantages of the water dilution process, without the need for complex process steps, and without adversely affecting the performance properties of the polymer dispersions.
The invention provides a process for preparing aqueous, protective colloid stabilized vinyl ester homopolymer and copolymer dispersions of defined solids content by emulsion polymerization in the presence of protective colloid, characterized in that it comprises preparing a dispersion with a solids content lower than the defined solids content and, after the end of the polymerization, thickening the dispersion to the defined solids content by adding water-redispersible polymer powder of the same polymer composition, and prepared by the same process with subsequent drying, as the emulsion polymer.
The procedure of the invention is suitable for polymerizing one or more monomers from the group of the vinyl esters of unbranched or branched alkylcarboxylic acids having 1 to 15 carbon atoms, or mixtures of said vinyl ester monomers with one or more comonomers from the group of the methacrylic esters and acrylic esters of unbranched or branched alcohols having 1 to 12 carbon atoms, the fumaric and maleic monoesters or diesters of unbranched or branched alcohols having 1 to 12 carbon atoms, the dienes such as butadiene or isoprene, the olefins such as ethene or propene, the vinyl halides such as vinyl chloride.
Preferred vinyl esters are vinyl acetate, vinyl propionate, vinyl butyrate, vinyl 2-ethylhexanoate, vinyl laurate, 1-methylvinyl acetate, vinyl pivalate and vinyl esters of alpha-branched monocarboxylic acids having 5 to 11 carbon atoms, for example, VeoVa9® or VeoVa10® (trade names of Shell). Vinyl acetate is particularly preferred.
Preferred methacrylic esters or acrylic esters are methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate, n-butyl acrylate, t-butyl acrylate, n-butyl methacrylate, t-butyl methacrylate, and 2-ethylhexyl acrylate.
Preferred ester groups of the fumaric and maleic acid are methyl, ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl, t-butyl, hexyl, ethylhexyl, and dodecyl groups.
If desired it is also possible to copolymerize from 0.05 to 10.0% by weight of auxiliary monomers, based on the overall weight of the monomer mixture. Examples of auxiliary monomers are ethylenically unsaturated carboxylic acids, preferably acrylic acid or methacrylic acid; ethylenically unsaturated carboxamides, preferably acrylamides; ethylenically unsaturated sulfonic acids and/or their salts, preferably vinylsulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid. Further examples are precrosslinking comonomers such as polyethylenically unsaturated comonomers, for example, divinyl adipate, diallyl maleate, allyl methacrylate or triallyl cyanurate, or postcrosslinking comonomers, for example, acrylamidoglycolic acid (AGA), methacrylamidoglycolic acid methyl ester (MAGME), N-methylolacrylamide (NMA), N-methylolmethacrylamide, N-methylolallylcarbamate, alkyl ethers, such as the isobutoxy ether, or esters of N-methylolacrylamide, of N-methylolmethacrylamide or of N-methylolallylcarbamate.
Examples of preferred vinyl ester polymers which comprise if desired said auxiliary monomer units in the stated amounts are:
vinyl acetate and vinylpropionate polymers;
vinyl ester-ethylene copolymers such as vinyl acetate-ethylene copolymers having an ethylene content of from 1 to 60% by weight;
vinyl ester-ethylene-vinyl chloride copolymers having an ethylene content of from 1 to 40% by weight and a vinyl chloride content of from 20 to 90% by weight, vinyl esters present being preferably vinyl acetate and/or vinylpropionate and/or one or more copolymerizable vinyl esters such as vinyl laurate, vinyl pivalate, vinyl 2-ethylhexanoic acid ester, vinyl esters of an alpha-branched carboxylic acid, especially Versatic acid vinyl esters;
vinyl acetate copolymers with from 1 to 50% by weight of one or more copolymerizable vinyl esters such as vinyl laurate, vinyl pivalate, vinyl 2-ethylhexanoic acid ester, vinyl esters of an alpha-branched carboxylic acid, especially Versatic acid vinyl esters (VeoVa9®, VeoVa10®), which if desired also contain from 1 to 40% by weight of ethylene;
vinyl ester-acrylic ester copolymers with from 30 to 90% by weight of vinyl ester, especially vinyl acetate, and from 1 to 60% by weight of acrylic ester, especially n-butyl acrylate or 2-ethylhexyl acrylate, which if desired also contain from 1 to 40% by weigh
Riepl Georg
Schilling Bernd
Brooks & Kushman P.C.
Reddick Judy M.
Wacker-Chemie GmbH
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