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
2000-02-10
2001-03-06
Michl, Paul R. (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...
C524S502000
Reexamination Certificate
active
06197863
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 which liberate acid in the presence of water 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.
EP-A 721004 discloses crosslinkable, redispersible powder mixtures comprising film-forming polymer particles having at least one functional, crosslinkable group. The crosslinker component can be a water-soluble or emulsifiable monomer or polymer, or else a pulverulent mixture of the crosslinker and an inorganic carrier such as CaCO
3
, clay or silicon dioxide. The crosslinker component is bound to these carrier substances by physical adsorption. This has the disadvantage that these mixtures have the same odor, if somewhat attenuated, as the pure crosslinker component. In addition, owing to the weak physical bonding, the crosslinker component can become detached and penetrate into the polymer to be crosslinked, which, particularly in the case of very reactive substances, can lead to a reduced shelf life or premature crosslinking.
It is therefore an object of the invention to provide a crosslinkable powder composition which is redispersible in water and has a high storage stability and blocking stability and is free-flowing.
SUMMARY OF THE INVENTION
The invention provides a crosslinkable powder composition which is redispersible in water and comprises
a) from 30 to 95 parts by weight of one or more water-insoluble, film-forming polymers of one or more free-radically polymerizable, ethylenically unsaturated monomers,
b) from 5 to 70 parts by weight of one or more water-soluble polymers,
where at least one of the polymer components a) and b) comprises one or more comonomer units containing crosslinkable groups, and the parts by weight of a) and b) add up to 100 parts by weight, and
c) from 0.5 to 30% by weight, based on the total weight of a) and b), of inorganic or organic solids which are insoluble in water and in organic solvents and have a mean particle size of from 5 nm to 100 &mgr;m, which solids have, chemically bound to their surface, functional groups capable of forming covalent bonds with the crosslinkable groups of the polymers a) and b).
DESCRIPTION OF THE PREFERRED EMBODIMENT
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 VeoVa09® of 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 in the esters of fumaric and maleic acids are methyl, ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl, t-butyl, hexyl, ethylhexyl and dodecyl groups.
Suitable comonomers having crosslinkable groups are generally those containing functional groups which crosslink via nucleophilic substitution reactions, condensation reactions or addition reactions. 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 ethoxypropylene glycol ether radicals. Preference is given to vinyltriethoxysilane and gammamethacryloxypropyltriethoxysilane.
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, caprolactam, dialkyl malonates, alkyl acetoacetates, 2,2-dimethyl-1,3-dioxane-4,6-dione.
Further examples of crosslinkable comonomers are hydroxyl-containing comonomers such as hydroxyalkyl acrylates and methacrylates which may, if desired, be acetoacetylated, e.g. hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate and hydroxybutyl (meth)acrylate. Also suitable are carboxyl- or sulfo-functional comonomers such as vinylsulfonic acid, acrylic, methacrylic, maleic, fumaric, crotonic and itaconic acids, the monoesters of maleic and fumaric acids, monovinyl succinate and methylenemalonic acid. Examples of crosslinkable comonomers containing anhydride g
Barthel Herbert
Eck Herbert
Figge Reiner
Burgess, Ryan & Wayne
Michl Paul R.
Moran William R.
Wacker-Chemie GmbH
Wayne Milton J.
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