Coating compositions containing alkoxysilanes

Details Coating compositions containing alkoxysilanes Coating compositions containing alkoxysilanes

1999-12-01

2001-08-28

Dawson, Robert (Department: 1712)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

From silicon reactant having at least one...

C528S025000, C528S038000, C528S039000, C528S044000, C428S423100, C428S447000, C106S287110

Reexamination Certificate

active

06281322

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to coating compositions, which preferably dry at room temperature, contain alkoxysilane groups and are based on polyisocyanates prepared from 4,4′-diisocyanatodicyclohexyl-methane, and to their use as a protective coating.
2. Description of the Prior Art
Damage to coatings due to the penetration of dyes, caused by graffiti, for example, constitutes an increasing problem. Conventional organic coatings swell due to the solvent contained in the lacquer spray and, thus, can readily be penetrated by dyes. It is then no longer possible to clean the surface without destroying the coating.
Therefore, there is a need for coatings which form an effective barrier to solvents and dyes and which thus protect the underlying substrate from contamination.
Coatings that can be removed with the dye or with the contaminant (e.g. FR-A 2,747,325, WO 97/24407), do provide satisfactory protection, but involve considerable cost, since they have to be freshly applied again and again.
Permanent coatings can be treated with silicone polymers or fluoropolymers in order to decrease their surface energy (e.g. EP-A 695 772, FR-A 2,681,072), so that wetting of the surface is made more difficult. A disadvantage of this treatment is that the fluoro- or silicone polymers, which are not chemically bonded, are washed out over time due to weathering effects and lose their effectiveness. In contrast, chemically bound polymers result in incompatibility effects, haze effects and poor adhesion to the substrate, so that decorative clear coatings, which exhibit a high level of transparency, cannot be treated in this manner.
In contrast, ultra-hard sol-gel coatings (e.g. EP-A 576 166) provide good protection from graffiti. However, these systems have to be stoved at elevated temperatures, so that they are unsuitable for use for coating large vehicles, for example. Also, these coating compositions exhibit poor adhesion, particularly to other coatings, and often exhibit unsatisfactory resistance to the impact of stones.
Reaction products of aminosilanes with polyisocyanates (silane-functional ureas) are known and can be used, for example, for the production of flexible coatings (U.S. Pat. Nos. 5,700,868, 4,625,012, 4,474,933, 3,979,344, DE-A 4,234,325, DE-A 2,155,259). Since these products for the most part are based on high molecular weight polymers and their density of crosslinking is low, these coatings are less suitable as protective coatings against color-imparting liquids. In principle, however, silicone-functional ureas can be used for the production of sol-gel coatings with a high density of crosslinking. Their disadvantages are their tendency to crystallize, which is often pronounced, and/or their rate of hardening at room temperature, which is often so low that an efficient protective coat has not formed even several days after application.
An object of the present invention is to provide a protective coating which preferably does not have to be stoved and 24 hours after application at room temperature has hardened to such an extent that the penetration of dyes (e.g. graffiti) is effectively prevented. An additional object is to provide a coating that has good visual quality and exhibits good scratch resistance such that it is suitable for use an automotive coating.
These objects may be achieved in accordance with the siloxane-curing coatings of the present invention, which are based on highly functional 4,4′-diisocyanato-dicyclohexylmethane polyisocyanates and form an efficient barrier layer against dyes from graffiti within 24 hours after application. These coatings can be applied to any substrate, exhibit good scratch resistance, and provide effective protection from contaminants.
SUMMARY OF THE INVENTION
The present invention relates to coating compositions containing 40 to 100% by weight, based on resin solids, of an alkoxysilyl-functional polyisocyanate polyurea which is reaction product of
A) a polyisocyanate component having an average functionality of 2.5 to 5.5, an NCO content of 11.0 to 20.0% by weight and a monomeric diisocyanate content of less than 10% by weight, and containing at least 50% by weight of a polyisocyanate prepared from 4,4′-diisocyanatodicyclohexyl-methane with
B) at least 0.7 equivalents, based on the equivalents of isocyanate groups, of an aminosilane corresponding to formula (I)
(RO)
n
Y
(3−n)
Si—CH
2
CH
2
CH
2
—NHZ  (I),
 wherein
R represents methyl or ethyl,
Y represents methyl,
Z represents H, a C
1
-C
12
alkyl or CH
2
CH
2
CH
2
—Si(OR)
n
Y
3−n
, and
n is 1, 2 or 3, and
C) optionally other isocyanate-reactive compounds.
The present invention also relates the hydrolyzates/condensates that are prepared by adding water or an aqueous solution of a catalyst to the coating compositions according to the invention.
DETAILED DESCRIPTION OF THE INVENTION
Component A) has an average NCO functionality of 2.5 to 5.5, preferably 2.8 to 5.0 and more preferably 3.0 to 4.5; an NCO content, based on solids, of 11.0 to 20.0% by weight, preferably 11.5 to 17.0% by weight and more preferably 12.0 to 16.0% by weight; and a monomeric diisocyanate content of less than 10% by weight, preferably less than 2.0% by weight and more preferably less than 0.5% by weight. More than 50% by weight, preferably more than 70% by weight and more preferably more than 80% by weight of the isocyanates used to prepare the compounds present in component A) are prepared from 4,4′-diisocyanatodicyclohexylmethane.
Any polyisocyanates prepared from 4,4′-diisocyanatodicyclohexylmethane can be used for the production of component A), such as biurets, isocyanurates (trimers), iminooxadiazine diones, uretdiones, allophanates and addition products with low molecular weight polyfunctional alcohols such as trimethylolpropane, 1,6-hexanediol, 1,5-pentanediol, diethylene glycol, triethylene glycol, 2,2,4-trimethyl-1,3-propanediol, neopentyl glycol and mixtures thereof.
Isocyanurate (trimers) prepared from 4,4′-diisocyanatodicyclohexyl-methane are preferred, especially those having an NCO content of 12 to 16% by weight, an NCO functionality of 3.0 to 4.5 and a monomer content of <2% by weight. The trimers can be produced by a trimerization process as described, e.g., in EP-A 330 996.
Component A) may also contain other di- or polyisocyanates, for example, monomeric diisocyanates such as 1,4-butane diisocyanate, 1,6-hexane diisocyanate (HDI), 3-isocyanatomethyl-3,3,5-trimethylcyclohexyl isocyanate (isophorone diisocyanate or IPDI), 2-methyl-1,5-pentane diisocyanate, 2,2,4-trimethyl-hexamethylene diisocyanate (TMDI), 1,12-dodecane diisocyanate and bis(isocyanatomethyl)norbornane; triisocyanates such as 4-isocyanatomethyl-1,8-octane diisocyanate; and polyisocyanates which can be prepared from these isocyanate starting materials, such as those which are described in J. prakt. Chem. 1994, 336, 185-200 and Lackharze, Chemie, Eigenschaften and Anwendungen, edited by D. Stoye and W. Freitag, Hanser Verlag, Munich, Vienna 1996. The mixtures should satisfy the preceding requirements regarding NCO content, NCO functionality and monomer content.
In order to make them easier to handle, polyisocyanate mixtures A) can be thinned with up to 50% by weight of known coating solvents. Suitable solvents include those which are not reactive with NCO groups, such as butyl acetate, ethyl acetate, 1-methoxy-2-propyl acetate, toluene, 2-butanone, xylene, 1,4-dioxane, N-methylpyrrolidone, dimethylacetamide, dimethylformamide and dimethyl sulphoxide.
Polyisocyanates A) are reacted with at least 0.7 equivalents, preferably with at least 0.8 equivalents and more preferably with at least 0.9 equivalents, based on the equivalents of isocyanate groups, of an aminosilane corresponding to formula (I)
(RO)
n
Y
(3−n)
Si—CH
2
CH
2
CH
2
—NHZ  (I),
wherein
R represents methyl or ethyl,
Y represents methyl,
Z represents H, a C
1
-C
12
alkyl or CH
2
CH
2
CH
2
—Si(OR)
n
Y
3−n
, and
n is 1, 2 or 3.
Examples

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