Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
1999-04-27
2001-03-13
Dawson, Robert (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C523S414000, C523S418000
Reexamination Certificate
active
06201043
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to aqueous dispersions which are obtainable by polymerizing an ethylenically unsaturated monomer or a mixture of ethylenically unsaturated monomers in an aqueous solution of an at least partially protonated epoxide-amine adduct, and to their use for preparing electrophoretically depositable coating materials. -Electrophoretically depositable coating materials are coating compositions with which it is possible by means of (usually cationic) electrodeposition coating to prepare coat films on an electrically conducting substrate. In the course of electrodeposition coating, the article to be coated is dipped in a bath containing the deposition coating material, the article being connected as anode or cathode and thus producing an electrical field in the bath. The process is usually operated with voltages of 50-500V. Under the action of the field, the deposition coating material is deposited on the article. It is self-evident that for this purpose the deposition coating material must have a certain conductivity, i.e. that the substances which form the coat film must migrate in the field. In this procedure, the amount of coating material deposited is directly proportional, in first approximation, to the amount of current supplied. Current is usually supplied until a predetermined thickness of the coat film is reached. Electrodeposition coating is used in particular for priming motor vehicle bodywork parts, and is generally operated cathodically. In the course of this description the term solution is used in its most general sense, in other words such that it refers not only to solutions in the customary sense but also to dispersions.
In a dispersion of the type mentioned at the outset, the ethylenically unsaturated monomer or the mixture of ethylenically unsaturated monomers forms polymers which ultimately contribute to the solids content of the electrodeposition coating material. The polymers are formed, for example, by emulsion polymerization. The term emulsion polymerization refers to a specific technique of polymerization, in which monomers which per se are insoluble in water are emulsified in water with the aid of emulsifiers and are polymerized using initiators. Emulsion polymerization per se is well known.
Since the dispersion concerned is an aqueous dispersion, its use is directed toward the technology of aqueous coating materials. In aqueous coating materials, the coating material contains water as “solvent”.
A dispersion of the type mentioned at the outset is known from the literature reference WO 93/18099 (PCT/US93/01512). According to this prior art, ethylenically unsaturated monomers, namely dienes, for example butadiene, are polymerized in aqueous phase and in the presence of a cationic, surface-active polymer and also in the presence of regulators for the chain length. As cationic, surface-active polymers it is also possible in principle to employ protonized epoxide-amine adducts. Cationic compounds are employed as initiators. Resulting from the ethylenically unsaturated monomers, polymers are obtained whose mass-average molecular weight is 50,000 or less. The technical problem on which this prior art is based is to reduce the so-called cratering in the course of coating. The effects used to reduce cratering, however, bring with them disadvantages in other respects, namely a considerably impaired adhesion of subsequently applied coating films, especially when the coating films have a polar basis, such as fillers, for example. This is disruptive for obvious reasons. Limitation to a maximum of 40% solids content avoids excessive agglomeration and/or an excessive viscosity of the dispersion; however, this dispersion viscosity is not connected with the viscosity of the subsequent coat film during the stoving process.
For the viscosity of the coat film during the stoving process, the conditions are as follows: The coat film is in general composed of three components: the resin component, which comes from the binder dispersion; the grinding resin component, from the pigment paste; and the pigments. Of these, the resin components constitute the components of relatively low viscosity and the pigments constitute the high-viscosity (solid) components. When binders are used exclusively, therefore, a low-viscosity coat film is produced which shows marked retreat from the edges. Only by using pigment paste is the viscosity adjusted to the desired level. In this case the pigments act simply as “lumps” in a melt. This has nothing to do with the viscosity of the initial aqueous pigment paste, but depends exclusively on the volume concentration and on the specific properties of the pigment particles.
Because of the pigment particles, accordingly, the density of the finished coating is raised in a disruptive manner. A high density is disruptive since the deposition of the coating material is controlled in accordance with the film thickness to be obtained, and for the same film thickness a high-density film leads to greater consumption of deposition coating material and to an increase in the weight of the coated article.
DE 4412187 A1 [lacuna] fillers of polyacrylonitrile which are prepared by emulsion polymerization and are employed directly as a paste substitute. In the case of these fillers, styrene is added, albeit in a minor amount. The necessary use for acrylonitrile, however, is undesirable on toxicological grounds and is also expensive.
Against this background, the technical problem underlying the invention is to provide an aqueous dispersion which can be prepared using as large as possible an amount of styrene and which, consequently, avoids the disadvantages of the use of polyacrylonitrile.
To solve this problem the invention provides aqueous dispersions which are obtainable by polymerizing an ethylenically unsaturated monomer or a mixture of ethylenically unsaturated monomers in an aqueous solution of an at least partially protonated epoxide-amine adduct, the epoxide-amine adduct being obtainable by reacting (A) a glydicyl ether of a polyphenol that contains on statistical average at least one epoxide group in the molecule, or a mixture of such glycidyl ethers, (B) a polygycidyl ether of a polyol that contains on statistical average more than 1.0 epoxide groups in the molecule, or a mixture of such polyglycidyl ethers and (C) a compound that contains a primary amino group in the molecule, or a mixture of such compounds, to give the epoxide-amine adduct, components (A) and (B) being employed in a ratio of equivalents of from 1.0:0.5 to 1.0:8.0 and from 0.3 to 0.7 mol of component (C) being employed per equivalent of epoxide groups of (A) and (B). An epoxide-amine adduct of the abovementioned type is known per se from the literature reference EP 0505445 B1. -Examples of ethylenically unsaturated monomers are substances from the group “aliphatic or aromatic ethylene derivatives, alkyl acrylates, alkyl methacrylates, hydroxyalkyl acrylates, hydroxyalkyl methacrylates, halogenated forms of the monomers mentioned” or mixtures thereof, preferably diene-free compounds, especially styrene. Styrene is on the one hand available inexpensively and on the other hand can be used to prepare dispersions having outstanding properties. Examples of suitable acrylates of the general formula H
2
C═CH—COOR are: methyl, ethyl, n-butyl and isobutyl acrylates. Examples of hydroxyalkyl acrylates are hydroxyethyl acrylate and hydroxypropyl acrylate. The preferred methacrylates of the general formula
are: methyl, butyl, hexyl and octyl methacrylate. Examples of hydroxyalkyl methacrylates are hydroxyethyl and hydroxypropyl methacrylates.
Surprisingly, owing to the polymerization of the monomers in the presence of the specific epoxide-amine adduct indicated, the following advantages are achieved. First of all, it is not only the dispersion itself which is very stable but also the deposition coating material which is prepared using the novel dispersion. This also applies when comparatively large amounts of a novel dispersion are adde
Bremser Wolfgang
Grosse-Brinkhaus Karl-Heinz
Ott Gunther
Strickmann Frank
Aylward D.
BASF Coatings AG
Dawson Robert
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