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
2002-05-22
2004-03-16
Mulcahy, Peter (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...
C524S005000, C524S004000, C524S560000, C524S503000, C524S557000, C524S803000, C526S087000, C106S724000, C106S802000
Reexamination Certificate
active
06706805
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to the use of copolymers which are derived from vinyl ester, (meth)acrylic ester and optionally ethylene comonomers and are stabilized with a protective colloid, in the form of their aqueous dispersions or redispersible polymer powders, and their use in building materials, i.e. in mortar compositions.
2. Background Art
Polymers which are stabilized with protective colloids are often used in building materials in the form of their aqueous dispersions or as polymer powders which are redispersible in water. As protective colloids, use is generally made of polyvinyl alcohols. The use of polyvinyl alcohol is desirable because, in contrast to systems which are stabilized by low molecular weight compounds (emulsifiers), the polyvinyl alcohol itself also contributes to the strength of the cured (set) compositions, for example, to the tensile bond strength in tile adhesives. Preference has hitherto been given to using vinyl esters and ethylene as monomers for preparing redispersible powders, since the stabilization of acrylate copolymers or styrene-acrylate copolymers by polyvinyl alcohol is difficult to achieve. In particular, stabilizing an acrylate dispersion with polyvinyl alcohol alone in such a way that the resulting powders are blocking resistant and storage-stable is not a trivial exercise. The combination of vinyl ester and ethylene comonomers together with (meth)acrylate comonomers is also frequently unsatisfactory for the same reason. Aqueous dispersions prepared from such comonomers, for example, vinyl acetate-butyl acrylate copolymers or vinyl acetate-acrylate-ethylene copolymers, have been widely described. However, these dispersions are emulsifier-stabilized and cannot be spray dried to give redispersible powders.
When using the combination of vinyl esters with ethylene, the T
g
range which can be obtained is restricted to from about +30° C. (vinyl acetate homopolymer) to about −25° C. Higher glass transition temperatures cannot be obtained, since there is no monomer appropriate to the system which leads to glass transition temperatures higher than those obtained using vinyl acetate. Vinyl chloride is no longer acceptable for ecological reasons and its use as a comonomer has virtually ceased. On the other hand, glass transition temperatures below −25° C. can be obtained only with difficulty, since they require a proportion of ethylene significantly above 50 mol % of the monomer mixture. Although these high-ethylene polymers can be prepared, they tend to crystallize, so that a distinct glass transition is no longer found. Furthermore, these polymers do not display the highly elastic properties expected for such T
g
values. The combination of vinyl esters and ethylene with (meth)acrylates would easily enable the T
g
range to be extended to higher and lower T
g
values. The problems discussed heretofore relative to the preparation of such copolymer systems with purely polyvinyl alcohol stabilization which are suitable for producing redispersible powders stand in the way of such an extension.
Moreover, problems occur not only in the preparation but also in the use of the polymers. Particularly when using polymers in the form of their redispersion powders for improving mortar properties, a main application area for redispersion powders, the formulations have to remain stable for some time and their processing consistency must not change significantly, as indicated, for example, by viscosity stability or cement stability. Furthermore, the mechanical properties such as compressive strength, porosity and thus the air pore content, play an important role in the concrete and mortar industry. In addition, hydraulically setting systems which have been modified with the dispersion powder should give better adhesion compared to the unmodified or conventionally modified systems.
DE-A 19962566 discloses redispersible powders based on copolymers of vinyl esters and (meth)acrylates. In the method of preparation described there, all or some of the vinyl ester component is introduced into the polymerization vessel initially, and the (meth)acrylate component is metered in after commencement of polymerization. The polymerization is carried out at a relatively high temperature. This procedure has the disadvantage that the polymers obtainable in this way have relatively low molecular weights; the K value is less than 100. As a result, the mechanical properties are not fully satisfactory when these polymers are used in the building materials sector.
U.S. Pat. Nos. 5,391,608 and 5,439,960 describe polymer dispersions which are used for preparing wood adhesives having improved water resistance. The polymer dispersions are prepared by means of a process in which vinyl acetate is copolymerized with a post-crosslinking comonomer such as N-methylolacrylamide (NMA) in a first step and, after cooling the polymer dispersion, a methyl methacrylate polymer is polymerized by means of addition of methyl methacrylate.
EP-A 381122 describes the preparation of binders for the production of nonwovens. Here, copolymers of vinyl esters with comonomers such as methyl methacrylate or styrene which are incompatible therewith are prepared. Vinyl acetate and optionally ethylene is/are polymerized to a residual vinyl acetate content of <5% in a first step, and the incompatible monomer is subsequently metered in and polymerized.
SUMMARY OF THE INVENTION
The invention provides stable, low-viscosity dispersions stabilized by a protective colloid, and the corresponding dispersion powders which are redispersible in water, the polymers being prepared from vinyl ester monomers, ethylene monomers and (meth)acrylic ester monomers, and which exhibit fully satisfactory viscosity stability and cement stability when used in cement applications, which do not hinder the setting of the cement, and which display improved mechanical properties, in particular tensile bond strengths, and their use in adhesive mortars such as tile adhesives and mortars for composite thermal insulation systems.
It has surprisingly been found that two-phase polymerization of vinyl esters and optionally ethylene as one component, and (meth)acrylates as the other component, provides dispersions which, despite the presence of the (meth)acrylate homopolymer formed, can be spray dried to give redispersion powders which are blocking resistant and cement-stable. It has also surprisingly been found that good tensile bond strengths are obtained in adhesive mortars, in particular after wet storage and freeze thaw cycles.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)
The invention provides copolymers which are derived from vinyl ester, (meth)acrylic ester and optionally ethylene comonomers and are stabilized with a protective colloid, in the form of their aqueous dispersions or polymer powders redispersible in water, and their use in building materials, where the copolymers are obtained by means of free-radically initiated emulsion or suspension polymerization of one or more esters of acrylic acid or methacrylic acid with vinyl esters, optionally also with ethylene and further monomers copolymerizable therewith, in the presence of one or more polyvinyl alcohol protective colloids wherein:
a) the vinyl ester component is polymerized, if desired in the presence of ethylene and further copolymerizable comonomers, to a conversion of from 90 to 100% by weight in a first step, and
b) the ester(s) of acrylic acid or methacrylic acid is/are subsequently added and polymerized in a second step, and optionally drying the aqueous dispersion thus obtained.
Suitable acrylic acid and methacrylic acid ester monomers include esters of unbranched or branched alcohols having from 1 to 15 carbon atoms. Preferred methacrylic esters or acrylic esters are methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate, n-butyl acrylate, n-butyl methacrylate, 2-ethylhexyl acrylate and norbornyl acrylate. Particular preference is given to methy
Brooks & Kushman P.C.
Mulcahy Peter
Sastri Satya
Wacker Polymer Systems GmbH & Co. KG
LandOfFree
Use of copolymers of vinyl ester, (meth)acrylic ester and... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Use of copolymers of vinyl ester, (meth)acrylic ester and..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Use of copolymers of vinyl ester, (meth)acrylic ester and... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3204737