Crosslinkable powder composition which is redispersible in...

Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...

Reexamination Certificate

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C524S503000

Reexamination Certificate

active

06228937

ABSTRACT:

BACKGROUND OF THE INVENTION
1) Field of the Invention
The invention relates to a crosslinkable powder composition which is redispersible in water and also to its use.
2) Background Art
EP-A 601518 describes crosslinkable dispersion powders which are redispersible in water and based on carboxyl-containing acrylate copolymers which are dried in the presence of polyvinyl alcohol and can contain polyvalent metal ions for crosslinking. Similar crosslinkable dispersion powders are also known from U.S. Pat. No. 3,409,578 in which powder compositions comprising carboxyl-containing polymers and/or carboxyl-containing protective colloids are crosslinked in the presence of polyvalent metal ions A disadvantage is that such compositions comprising polyvalent metal salts often liberate acid in the presence of water and tend to crosslink prematurely, especially in contact with moisture.
To avoid premature crosslinking, EP-A 702059 (U.S. Pat. No. 5,608,011) proposes using crosslinkable dispersion powders comprising N-methylol-containing copolymers and a catalyst combination of water-soluble or water-dispersible peroxo acid salts or reducing agents. EP-B 687317 describes crosslinkable powders which are redispersible in water and are based on N-methylol-functional copolymers which crosslink on heating. A disadvantage of the latter powder is the fact that exclusively heat-crosslinkable powders cannot be used in many applications.
EP-A 723975 discloses crosslinkable dispersion powders based on copolymers containing epoxide groups. For crosslinking, external crosslinkers such as polyamines, polycarboxylic acids, hydroxy-functionalized polymers and polyvalent metal salts are added. A problem with the use of polyamines or polyvalent metal salts is the low storage stability. The use of polycarboxylic acid or hydroxy-functionalized polymers does not impair the storage stability; however, elevated temperatures have to be employed for the reaction with the epoxy groups since otherwise the stabilization, as indicated in the application, of the dispersion powders by customary protective colloids would not be possible.
EP-A 721004 discloses crosslinkable, redispersible powder mixtures which comprise film-forming polymer particles having at least one functional, crosslinkable group. The crosslinkable group can also be introduced via the protective colloids. For crosslinking, this document, too, recommends the addition of an external crosslinker comprising at least one reactive component which forms nonionic bonds with the functional groups after the mixture is redispersed in water.
It is an object of the invention to provide a crosslinkable polymer powder composition which is redispersible in water and has good storage stability and offers the opportunity of matching the crosslinking rate to the respective field of application. A further object of the invention 1s to make available crosslinkable dispersion powders which can be crosslinked without addition of external crosslinkers.
SUMMARY OF THE INVENTION
This is surprisingly achieved by the use of phase transfer catalysts in admixture with crosslinkable polymers, where the functlonalities of the protective colloids present in redispersible powders can also be exploited for crosslinking.
The invention provides a crosslinkable powder composition which is redispersible in water and comprises
a) from 30 to 95 parts by weight of a water-insoluble, film-forming polymer of one or more free-radically polymerizable, ethylenically unsaturated monomers,
b) from 5 to 70 parts by weight of a water-soluble polymer, where at least one of the polymer components a) and b) comprises one or more comonomer units containing reactive groups which can form a chemical, nonionic bond with one another or with crosslinkers, and the parts by weight of a) and b) add up to 100 parts by weight, and
c) from 0.01 to 5% by weight, based on the total weight of a) and b), of at least one phase transfer catalyst.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Suitable water-insoluble, film-forming polymers comprise one or more monomer units selected from the group consisting of vinyl esters of unbranched or branched alkylcarboxylic acids having from 1 to 15 carbon atoms, methacrylic and acrylic esters of unbranched or branched alcohols having from 1 to 12 carbon atoms, fumaric and maleic monoesters or diesters of unbranched or branched alcohols having from 1 to 12 carbon atoms, dienes such as butadiene or isoprene, olefins such as ethene or propene, vinylaromatics such as styrene, methylstyrene or vinyltoluene, and vinyl halides such as vinyl chloride. For the purposes of the present invention, water-insoluble means that the solubility of the polymers under normal conditions is less than 1 g per liter of water. For film formation, the polymer composition is generally selected such that film formation occurs at the processing temperature, preferably such that a glass transition temperature Tg of from −30° C. to +80° C. results.
Preferred vinyl esters are vinyl acetate, vinyl propionate, vinyl butyrate, vinyl 2-ethylhexanoate, vinyl laurate, 1-methylvinyl acetate, vinylpivalate and vinyl esters of alpha-branched monocarboxylic acids having from 5 to 11 carbon atoms, for example VeoVa9
R
or VeoVa10 (trade names of Shell). Particular preference is given to vinyl acetate.
Preferred methacrylic 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, 2-ethylhexyl acrylate. Particular preference is given to methyl acrylate, methyl methacrylate, n-butyl acrylate and 2-ethylhexyl acrylate.
Preferred ester groups of fumaric and maleic acids are methyl, ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl, t-butyl, hexyl, ethylhexyl and dodecyl groups.
Monomer units in the polymer a) and/or b) which are suitable for crosslinking reactions are those which contain crosslinkable groups which undergo accelerated crosslinking in the presence of phase transfer catalysts. These are generally functional groups which crosslink with one another or with other functional groups by means of nucleophilic substitution reactions, condensation reactions or addition reactions. From this, it is possible to deduce the reactive groups which are suitable for the crosslinking reactions and may be present in the water-insoluble polymer a) and/or in the water-soluble protective colloid b).
In the water-insoluble polymer a), the crosslinkable groups are preferably incorporated by copolymerization of monomers containing the desired functional groups. However, appropriately substituted comonomer units can also be functionalized subsequently.
Monomers suitable for crosslinking via condensation reactions are alkoxysilane-functional monomer units such as acryloxypropyltri(alkoxy)silanes and methacryloxypropyltri(alkoxy)silanes, vinyltrialkoxysilanes and vinylmethyldialkoxysilanes; alkoxy groups which may be present are, for example, methoxy, ethoxy, methoxyethylene, ethoxyethylene, methoxypropylene glycol ether and eLhoxypropylene glycol ether radicals. Preference is given to vinyltriethoxysilane and gamma-methacryloxypropyltriethoxysilane.
Further examples of comonomers which can be crosslinked by a condensation reaction are acrylamidoglycolic acid (AGA), methyl methacrylamidoglycolate (MMAG), N-methylolacrylamide (NMAA), N-methylolmethacrylamide, N-methylolallyl carbamate, alkyl ethers of N-methylolacrylamide or N-methylolmethacrylamide, e.g. their isobutoxy ethers or n-butoxy ethers.
Comonomers which can be crosslinked by means of addition reactions are comonomers containing epoxide groups, for example glycidyl acrylate, glycidyl methacrylate, glycidyl vinyl ether and glycidyl allyl ether, and isocyanate monomers such as meta- and para-isopropenyl-alpha, alpha-dimethylbenzyl isocyanate (TMI), 2-methyl-2-isocyanatopropyl methacrylate; the isocyanate groups of the monomers mentioned may also, if desired, be blocked, for example by means of phenol, salicylic esters, ketoxime, c

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