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
2001-03-23
2003-05-20
Niland, Patrick D. (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...
C427S393600, C524S423000
Reexamination Certificate
active
06566434
ABSTRACT:
BACKGROUND OF THE INVENTION
1) Field of the Invention
The invention relates to the use of protective colloid-stabilized vinylaromatic-1,3-diene copolymers in the form of their aqueous polymer dispersions or polymer powders which are redispersible in water for the modification of gypsum-based materials or of materials based on calcium carbonate.
2) Background Art
Gypsum is a building material which is available in large quantities at low cost. Apart from naturally occurring forms of gypsum, considerable amounts of gypsum are obtained from flue gas desulfurization plants and there is worldwide interest in utilizing these. Apart from the use of gypsum in jointing compositions, gypsum mortars are used, in particular, for interior plasters and coatings. Since gypsum cures with an increase in volume, it is the ideal binder for coatings and moldings in order to avoid possible crack formation. However, owing to their water-sensitivity which is reflected, inter alia, in an unsatisfactory freezing/thawing behavior, renders comprising plaster of Paris as binder, with or without proportions of builder's lime, may, according to DIN standard 18550, be used only for interior plasters subject to stresses customary for these, but not for damp rooms or for external renders. In order to be able to use gypsum-based building materials for external applications and wet applications, too, they have to be sufficiently hydrophobicized.
In DE-A 3704439 (U.S. Pat. No. 4,851,047), the use of silicones and siloxanes, steareates and paraffin waxes is proposed for hydrophobicizing gypsum mortars. EP-A 320982 describes the use of redispersion powders based on vinyl acetate-Versatic acid-vinyl ester copolymers for hydrophobicizing gypsum-based materials. EP-A 477900 discloses the use of dispersible powder compositions based on vinyl ester polymers or styrene-acrylate polymers as additives for improving mechanical properties such as adhesion, abrasion resistance and flexural strength in gypsum, building adhesives and mortars. EP-A 728715 recommends the use of compositions of dispersible powders and thixotropic additives for hydrophobicizing gypsum, with the dispersible powders recommended being ones based on vinyl acetate copolymers and on styrene-acrylate copolymers.
JP-A 5/836 (Derwent Abstract AN 93-49422) describes the hydrophobicization of cement and gypsum by means of a pulverulent mixture of polysiloxane and a copolymer of vinylaromatics, dienes and/or acrylates. JP-A 57/205352 (Derwent Abstract AN 83-10505K) describes the production of water-resistant gypsum moldings by addition of polymer latices of acrylate, styrene, vinyl ester and epoxy resins to the gypsum mortar and subsequent heat treatment to cure the moldings.
A disadvantage of the previously mentioned hydrophobicizing agents is their not negligible hydrophilicity, for example in the case of vinyl ester or acrylic ester polymers, which leads to a low water resistance. In the abovementioned Japanese publications, the emulsifier content of the latices employed leads to increased water absorption. This can be improved by the addition of additives such as siloxanes, but only within certain limits. In many cases, the mechanical strength obtained in the hydrophobicization is also unsatisfactory.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide a composition for the hydrophobicization of gypsum-based materials and of materials based on calcium carbonate, which leads to hydrophobicized materials having a high water resistance and high mechanical strength without further additives.
The invention provides for the use of protective colloid-stabilized vinylaromatic-1,3-diene copolymers in the form of their aqueous polymer dispersions or polymer powders which are redispersible in water for the modification of gypsum-based materials or of materials based on calcium carbonate, wherein the polymer dispersions or polymer powders are obtained by emulsion polymerization of a mixture comprising at least one vinylaromatic and at least one 1,3-diene, in the presence of one or more protective colloids and in the absence of emulsifiers, and, if desired, drying of the aqueous polymer dispersions obtained in this way.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Suitable vinylaromatics are styrene and methylstyrene; preference is given to copolymerizing styrene. Examples of 1,3-dienes are 1,3-butadiene and isoprene; preference is given to 1,3-butadiene. In general, the copolymers comprise from 20 to 80% by weight, preferably from 30 to 70% by weight, of vinylaromatic and from 20 to 80% by weight, preferably from 30 to 70% by weight, of 1,3-diene. Further monomers may also be present if desired, and the percentages quoted in each case add up to 100% by weight.
If desired, up to 30% by weight, based on the total weight of the monomer phase, of further monomers which can be copolymerized with vinylaromatics and 1,3-dienes, e.g. ethylene, vinyl chloride, (meth)acrylic esters of alcohols having from 1 to 15 carbon atoms or vinyl esters of unbranched or branched carboxylic acids having from 1 to 15 carbon atoms, may be additionally present in copolymerized form.
If desired, from 0.05 to 10% by weight, based on the total weight of the monomer mixture, of auxiliary monomers may be additionally present in copolymerized form. Examples of auxiliary monomers are ethylenically unsaturated monocarboxylic and dicarboxylic acids, preferably acrylic acid, methacrylic acid, fumaric acid and maleic acid; ethylenically unsaturated carboxamides and nitriles, preferably acrylamide and acrylonitrile; monoesters and diesters of fumaric acid and maleic acid, e.g. the diethyl and diisopropyl esters, and also maleic anhydride, ethylenically unsaturated sulfonic acids or their salts, preferably vinylsulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid. Further examples are precrosslinking comonomers such as multiply ethylenically unsaturated comonomers, for example divinyl adipate, diallyl maleate, allyl methacrylate or triallyl cyanurate, or after-crosslinking comonomers, for example acrylamidoglycolic acid (AGA), methyl methylacrylamidoglycolate (MAGME), N-methylolacrylamide (NMA), N-methylolmethacrylamide, N-methylol(allyl carbamate), alkyl ethers such as the isobutoxy ethers or esters of N-methylolacrylamide, of N-methylolmethacrylamide and of N-methylol(allyl carbamate). Also suitable are epoxy-functional comonomers such as glycidyl methacrylate and glycidyl acrylate. Further examples are silicon-functional comonomers such as acryloxypropyltri(alkoxy)silanes and methacryloxypropyltri(alkoxy)silanes, vinyltrialkoxysilanes and vinylmethyldialkoxysilanes, where alkoxy groups present can be, for example, ethoxy and ethoxypropylene glycol ether radicals. Mention may also be made of monomers containing hydroxy or CO groups, for example hydroxyalkyl methacrylates and hydroxyalkyl acrylates, e.g. hydroxyethyl, hydroxypropyl or hydroxybutyl acrylate or methacrylate, and also compounds such as diacetoneacrylamide and acetylacetoxyethyl acrylate or methacrylate.
The choice of monomers or the choice of the proportions by weight of the comonomers is made so that, in general, a glass transition temperature T
g
of from −70° C. to +100° C., preferably from −50° C. to +50° C., particularly preferably from −20° C. to +40° C., results. Preference is given to copolymerizing styrene and 1,3-butadiene in the ratios mentioned without further comonomers. The glass transition temperature T
g
of the polymers can be determined in a known manner by means of differential scanning calorimetry (DSC). The T
g
can also be calculated approximately beforehand by means of the Fox equation. According to Fox T. G., Bull. Am. Physics Soc. 1, 3, page 123 (1956): 1/T
g
=x
1
/T
g1
+x
2
/T
g2
+ . . . +x
n
/T
gn
, where x
n
is the mass fraction (% by weight/100) of the monomer n, and T
gn
is the glass transition temperature in degrees Kelvin of the homopolymer of the monomer n. T
g
values for homopolymers are listed in Polymer Handbook 2nd
Fritze Peter
Härzschel Reinold
Mayer Theo
Weitzel Hans-Peter
Brooks & Kushman P.C.
Niland Patrick D.
Wacker-Chemie GmbH
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