Coating processes – With post-treatment of coating or coating material – Heating or drying
Reexamination Certificate
2002-05-31
2003-10-07
Cameron, Erma (Department: 1762)
Coating processes
With post-treatment of coating or coating material
Heating or drying
Reexamination Certificate
active
06630205
ABSTRACT:
The invention relates to a self-crosslinking coating system based on fluorine containing polycondensates, to a method for coating substrates with this coating composition, and to coated substrates thereby obtainable.
Thin, in many cases almost monomolecular, layers and impregnations of silanes and siloxanes containing perfluorinated side groups are used in order to give the surface of substrates water and oil repellency. However, the impregnations or layers, a few nanometers thick, do not provide the substrate surface with durable protection in the face of mechanical or chemical attack.
EP 0 587 667 (corresponding to DE 41 18 184) describes durable coating compositions based on polycondensates of one or more hydrolysable compounds M from main groups III to V and transition groups II to IV of the periodic table of the elements, at least some of these compounds being hydrolysable compounds containing perfluorinated side groups, especially hydrolysable silanes containing perfluorinated groups. These coating compositions can be cured but it is necessary to carry out crosslinking on the substrate by means of photochemical polymerization or of thermal polymerization at a temperature of at least 50° C. As a result, their use is technically complex, since appropriate curing equipment is required. For large-surface-area applications in particular, such as on the facades of buildings, for example, this represents a considerable restriction.
It is an object of the present invention to provide a method for coating substrates which provides coatings having antistick properties without a special curing step and without specific curing equipment. These coatings should nevertheless be scratch resistant and durable with respect, for example, to chemical or mechanical attack. It is further intended that the coating material should be provided in an easy-to-handle and storage-stable form. This object is achieved in accordance with the invention by a method for coating a substrate by preparing a self-crosslinking coating composition based on
a) at least one hydrolysable silane containing at least one nonhydrolysable substituent, the silane containing one or more electrophilic groups X on at least one nonhydrolysable substituent,
b) at least one hydrolysable silane containing at least one nonhydrolysable substituent, the silane containing one or more nucleophilic groups Y on at least one nonhydrolysable substituent, and
c) at least one hydrolysable silane containing at least one nonhydrolysable carbonic group having on average from 2 to 30 fluorine atoms attached to one or more aliphatic carbon atoms separated by at least two atoms from the silicon atom,
the silanes (a), (b) and/or (c) having undergone prior condensation if desired and it being possible either for the silanes (a) to be replaced in whole or in part by organic compounds containing at least two groups X or for the silanes (b) to be replaced in whole or in part by organic compounds containing at least two groups Y,
applying it to a substrate and curing it at ambient temperature (below 40° C.) to form a coating.
The coating composition used in the method of the invention may be obtained, for example, in the form of an easy-to-handle, storage-stable two-component coating system. This two-component coating system is characterized by
a component (A) comprising at least one—optionally precondensed—hydrolysable silane (a) containing at least one nonhydrolysable substituent, the silane (a) having one or more electrophilic groups X on at least one nonhydrolysable substituent, and
a component (B) comprising at least one—optionally precondensed—hydrolysable silane (b) containing at least one nonhydrolysable substituent, the silane (b) containing one or more nucleophilic groups Y on at least one nonhydrolysable substituent,
it being possible either for the silanes (a) to be replaced in whole or in part by organic compounds containing at least two groups X or for the silanes (b) to be replaced in whole or in part by organic
compounds containing at least two groups Y, and component (A) and/or (B) further comprising a hydrolysable silane (c) containing at least one nonhydrolysable carbonic group having on average 2 to 30 fluorine atoms attached to one or more aliphatic carbon atoms separated by at least two atoms from the silicon atom.
In one specific embodiment the coating composition of the invention further comprises nanoscale inorganic particulate solids which may have been surface modified.
Specific examples of the electrophilic group X are the epoxide, anhydride, acid halide and isocyanate groups.
Specific examples of the nucleophilic group Y are the amino group and the hydroxyl group.
Pairings which have proven to be particularly suitable for ambient temperature self-crosslinking include epoxy/amino and isocyanate/hydroxyl.
In accordance with the invention, self-curing, highly scratch-resistant coatings of low surface energy are obtained which adhere particularly well to the coated substrate without the need for a special curing step. The resulting coatings possess excellent antistick and easy-to-clean properties.
To prepare the coating composition the method of the invention uses as component a) at least one hydrolysable silane containing at least one nonhydrolysable substituent, the silane containing one or more electrophilic groups X on at least one nonhydrolysable substituent.
This component a) comprises a silicon compound possessing 1 to 3, preferably 2 or 3, with particular preference 3, hydrolysable radicals and 1, 2 or 3, preferably 1 or 2, especially one, nonhydrolysable radical(s). At least one of the nonhydrolysable radicals possesses at least one electrophilic group X.
Examples of hydrolysable groups, which may be identical to or different from one another, are hydrogen, halogen (F, Cl, Br or I, especially Cl and Br), alkoxy (e.g. C
1-6
alkoxy, especially C
1-4
alkoxy, such as methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, isobutoxy, sec-butoxy, tert-butoxy), aryloxy (preferably C
6-10
aryloxy, such as phenoxy), acyloxy (e.g. C
1-6
acyloxy, especially C
1-4
acyloxy, such as acetoxy or propionyloxy) and alkylcarbonyl (preferably C
2-7
alkylcarbonyl, such as acetyl). Preferred hydrolysable radicals are halogen, alkoxy groups and acyloxy groups. Particularly preferred hydrolysable radicals are alkoxy groups, especially methoxy and ethoxy.
Examples of nonhydrolysable radicals containing no group X are alkyl (preferably C
1-8
alkyl, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, s-butyl and tert-butyl, pentyl, hexyl, octyl or cyclohexyl), alkenyl (preferably C
2-6
alkenyl, such as vinyl, 1-propenyl, 2-propenyl and butenyl), alkynyl (preferably C
2-6
alkynyl, such as acetylenyl and propargyl) and aryl (preferably C
6-10
aryl, such as phenyl and naphthyl). The radicals may if desired contain one or more customary substituents, such as halogen or alkoxy, or functional groups not included among electrophilic groups X, examples being (meth)acryloyl groups and (meth)acryloyloxy groups.
Suitable electrophilic groups X are known to the person skilled in the art. Preferred examples include epoxy, anhydride, acid halide and isocyanate groups. Where two or more electrophilic groups X are present in the silane or where different silanes containing electrophilic groups X are used, X may have the same meaning or a different meaning.
Examples of nonhydrolysable radicals containing an epoxy group are in particular those which possess a glycidyl or glycidyloxy group. Specific examples of silanes of component a) which contain an epoxy group and can be used in accordance with the invention can be found, for example, in EP 0 195 493, whose entire disclosure is incorporated into the present specification by reference.
The nonhydrolysable radicals containing acid halide groups or acid anhydride groups X may, for example, be radicals deriving from carboxylic anhydrides or carbonyl halides. The halides in question may be the acid chloride, bromide or iodide, the acid chlorides being preferred. They may be anhydrides or halides of straight
Brueck Stefan
Lesniak Christoph
Schirra Hermann
Schmidt Helmut
Cameron Erma
Heller Ehrman White & McAuliffe LLP
Institut für Neue Materialien gem. GmbH
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