Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
2000-07-08
2004-06-08
Aftergut, Jeff H. (Department: 1733)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C524S833000, C524S823000
Reexamination Certificate
active
06746555
ABSTRACT:
BACKGROUND OF THE INVENTION
1) Field of the Invention
The invention relates to low-emission adhesives based on an aqueous, protective-colloid-free polymer dispersion or to water-redispersible dispersion powders, obtainable therefrom, and also to vinyl acetate-ethylene copolymers.
2) Background Art
It is known to use dispersions based on acrylate polymers as pressure-sensitive adhesives and flooring adhesives. These dispersions are suitable for applications as pressure-sensitive and flooring adhesives since owing to the low glass transition temperature of the acrylate polymers, usually based on butyl acrylate and/or 2-ethylhexyl acrylate, the required surface tack is achieved.
EP-A 17896 (U.S. Pat. No. 4,322,516) discloses vinyl acetate-ethylene copolymers which contain a high proportion of acrylate and which exhibit good surface tack even without the addition of tackifier resins. EP-A 185356 (U.S. Pat. No. 4,831,077) and EP-A 216210 (U.S. Pat. No. 4,997,879) relate to vinyl acetate-ethylene copolymers which have an acrylate fraction and which owing to the copolymerization of hydroxy-functional comonomers still exhibit excellent adhesion even at elevated temperatures.
On an alkaline substrate at a pH >9.0, however, as a result of hydrolysis of the ester group, acrylate-containing dispersions give off the corresponding alcohols. For instance, butyl acrylate gives off butanol and 2-ethylhexyl acrylate gives off 2-ethylhexanol, which may be emitted to the ambient air. Since this hydrolysis cannot be stopped, these alcohols will be emitted to the environment from the applied dispersion over a period of weeks, months and years.
The object of the invention is therefore to develop an adhesive dispersion with which this emissions problem does not arise but which in terms of surface tack, adhesion, and tackiness, is characterized by properties comparable with that of acrylate-containing dispersions.
This object has been achieved by replacing the acrylate fraction in the copolymer with branched vinyl ester units.
From EP-A 699692 (U.S. Pat. No. 5,665,816) it was known, for the purpose of improving the adhesion on untreated polyolefin substrates, to use adhesive dispersions containing cellulose ethers grafted onto vinyl acetate-ethylene copolymers which also have acrylate fractions and fractions of branched vinyl esters. In EP-A 841351, it is recommended that the acrylates be copolymerized with vinyl esters of neo acids in order to improve the adhesion of polyacrylate-based pressure-sensitive adhesives on nonpolar surfaces. U.S. Pat. No. 5,371,137 describes the use of vinyl acetate-ethylene copolymers modified with long-chain vinyl esters for improving the adhesion on nonpolar surfaces.
SUMMARY OF THE INVENTION
The invention provides low-emission adhesives based on an aqueous, protective-colloid-free polymer dispersion or water-redispersible dispersion powders, obtainable therefrom, of vinyl acetate-ethylene copolymers, obtainable by free-radically initiated emulsion polymerization, in an aqueous medium and in the presence of one or more emulsifiers, of a comonomer mixture comprising
a) from 5 to 50% by weight of ethylene,
b) from 20 to 80% by weight of one or more vinyl esters from the group of vinyl esters of unbranched or branched carboxylic acids having 1 to 9 carbon atoms whose homopolymers have a glass transition temperature Tg >0° C.,
c) from 5 to 70% by weight of one or more vinyl esters from the group of vinyl esters of branched carboxylic acids having 8 to 13 carbon atoms whose homopolymers have a glass transition temperature Tg <0° C.,
d) from 0.5 to 10% by weight of one or more ethylenically unsaturated monocarboxylic or dicarboxylic acids having 3 or 4 carbon atoms,
e) from 0 to 10% by weight of one or more ethylenically unsaturated, hydroxyalkyl-functional comonomers,
f) from 0 to 10% by weight of further, mono- or polyethylenically unsaturated comonomers,
the % by weight being based in each case on the overall weight of the comonomers and adding up to 100% by weight, and the dispersion obtained therewith being dried if desired.
It is preferred to copolymerize from 10 to 40% by weight of ethylene.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Suitable vinyl esters b) from the group of vinyl esters of unbranched or branched carboxylic acids having 1 to 9 carbon atoms whose homopolymers have a glass transition temperature Tg >0° C. are vinyl acetate, vinyl propionate, vinyl butyrate, 1-methylvinyl acetate, vinyl pivalate, and vinyl esters of &agr;-branched monocarboxylic acids having 9 carbon atoms (VeoVa9®, a trade name of the Shell company). Preference is given to vinyl acetate, vinyl propionate, and VeoVa9®. Particular preference is given to vinyl acetate. Most preferably, from 45 to 70% by weight of vinyl esters b) are copolymerized.
Suitable vinyl esters c) from the group of vinyl esters of branched carboxylic acids having 8 to 12 carbon atoms whose homopolymers have a glass transition temperature Tg >0° C. are vinyl 2-ethylhexanoate, vinyl esters of &agr;-branched monocarboxylic acids having 10 or 11 carbon atoms (VeoVa10®, VeoVa11® trade names of Shell), and vinyl esters of branched monocarboxylic acids having 10 to 13 carbon atoms (Exxar Neo12). Preference is given to the vinyl esters of &agr;-branched monocarboxylic acids having 10 or 11 carbon atoms (VeoVa10®, VeoVa11®). Most preferably, from 10 to 45% by weight of vinyl esters c) are copolymerized.
Suitable ethylenically unsaturated monocarboxylic and dicarboxylic acids d) are acrylic acid, methacrylic acid, itaconic acid, fumaric acid, and maleic acid, preference being given to acrylic acid, methacrylic acid, and itaconic acid. Acrylic acid and methacrylic acid are particularly preferred. Most preferably, from 2 to 6% by weight of comonomers d) are copolymerized.
Suitable ethylenically unsaturated, hydroxyalkyl-functional comonomers e) are methacrylic and acrylic hydroxyalkyl esters having a C
1
to C
5
alkyl radical such as hydroxyethyl, hydroxypropyl or hydroxybutyl acrylate or methacrylate; preferably, hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate. Most preferably, from 0 to 5% by weight of comonomers e) are copolymerized.
Examples of mono- or polyethylenically unsaturated comonomers f) are functional comonomers such as ethylenically unsaturated carboxamides and carbonitriles, preferably acrylamide and acrylonitrile; monoesters and diesters of fumaric acid and maleic acid such as the diethyl and diisopropyl esters and also maleic anhydride, ethylenically unsaturated sulfonic acids and their salts, preferably vinylsulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid. Further examples are pre-crosslinking comonomers such as polyethylenically unsaturated comonomers, examples being divinyl adipate, diallyl maleate, allyl methacrylate and triallyl cyanurate or postcrosslinking comonomers, examples being N-methylolacrylamide (NMA), N-methylolmethacrylamide, alkyl esters such as the isobutyoxy ether or esters of N-methylolacrylamide. Also suitable are epoxy-functional comonomers such as glycidyl methacrylate and glycidyl acrylate. Further examples are silicon-functional comonomers, such as acryloxypropyltri(alkoxy)- and methacryloxypropyltri(alkoxy)-silanes, vinyltrialkoxysilanes, and vinylmethyldialkoxysilanes.
The preferred auxiliary monomers f) are ethylenically unsaturated carboxamides such as acrylamide and methacrylamide, ethylenically unsaturated sulfonic acids and their salts such as vinylsulfonic acid and vinylpyrrolidone. Acrylamide is particularly preferred. Most preferably, from 0 to 2% by weight of comonomers f) are copolymerized.
In the copolymers, the amounts in percent by weight add up in each case to 100% by weight. In general, the monomers and/or the weight fractions of the comonomers, are selected so as to give a glass transition temperature Tg of less than 0° C., preferably, from −60° C. to −10° C.
The glass transition temperature Tg of the polymers can be determined in a known manner by means of differential scanning calorimetry (DSC). The Tg c
Künstle Holger
Weissgerber Rudolf
Aftergut Jeff H.
Brooks & Kushman P.C.
Wacker-Chemie GmbH
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