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
1998-10-23
2001-05-29
Niland, Patrick D. (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...
C524S588000, C524S590000, C524S838000, C525S101000, C525S487000, C528S028000
Reexamination Certificate
active
06239212
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to curable coating compositions, comprising a carbmate material, crosslinking agent reactive therewith and a hydroxyl functional polysiloxane component, for use in multilayer coatings.
BACKGROUND OF THE INVENTION
Coating compositions are often divided into thermoplastic and thermoset compositions. Thermoplastic coating compositions utilize high molecular weight polymers dispersed in an organic or aqueous solvent. After the coating composition is applied to a substrate, the solvent is removed and the polymers is set up to form a film. Thermoset or curable coating compositions utilize two components that are reactive with one another under certain cure conditions. The reactive groups on these components are referred to as ‘functional groups’. After the composition containing these components is applied, the coated substrate is subjected to cure conditions, causing the functional groups to react and form a cured film of a crosslinked matrix.
Thermoset or curable coating compositions that cure via the formation of urethane bridges in the crosslinked coating are widely used in the art. Urethane bonds are often desirable for their durability, resistance to attack by various agents in the environment, impact resistance, and other physical properties such as stress release. Urethane bridges can be formed by various combinations of functional groups, such as OH functional groups and isocyanate functional groups, carbamate groups and aminoplast resins, or cyclic carbonate groups and amino groups.
In many coating applications, it is often necessary to apply an additional coating on top of an already-cured coating. This may be done to achieve certain visual or physical properties, or it may be necessary to repair areas where the cured coating has been damaged or where coating defects exist. In such cases, it is important that the coating applied on top of the cured coating have adequate adhesion to the cured coating. Sanding the surface generally improves adhesion, but it may not be desirable to sand a surface because of resulting change in the appearance of the sanded surface. Even when the cured coating is sanded prior to application of the additional coating, the adhesion factor is still a concern with regard to overspray areas onto unsanded coating surfaces.
Intercoat adhesion can be of particular concern with regard to coatings that form urethane linkages upon cure, due to the physical and chemical properties of the coating. Intercoat adhesion may be poor due the highly crosslinked nature of the cured film. It has unexpectedly been found that the addition of a polysiloxane compound to a coating composition based on a carbamate-melamine cure system improves intercoat adhesion when compared to a coating of an identical composition without the polysiloxane compound. Additionally, the present invention is directed toward providing curable coating compositions having good intercoat adhesion properties when a cured coated surface is subjected to repair conditions. Repair conditions generally involve application of at least one additional coating followed by application of heat. This result is unexpected, since polysiloxanes which are usually used to improve flow and leveling and to improve mar resistance, generally adhere poorly to subsequent coatings, as described in U.S. Pat. No. 4,812,518.
It is also desirable to promote and/or improve adhesion of basecoat and/or the clearcoat coating compositions to sealant materials, such as where windshield or other sealants are applied to a cured coating. Accordingly, the present invention is also directed toward a cured coating composition having good adhesion to sealant materials.
SUMMARY OF THE INVENTION
The present invention provides a curable coating composition comprising at least:
(A) At least one polymer comprising a plurality of carbamate groups,
(B) a component comprising a plurality of groups that are reactive with the carbamate groups on component (A), and
(C) a hydroxy functional polysiloxane component having a hydroxyl value of between about 50 and about 170.
Optionally, the coating composition may additionally include hydroxyl functional oligomers or polymers, and carbamate functional oligomers and mixtures thereof. The polysiloxane component may also include a polymeric component such as polester or polyether.
Coatings prepared according to the present invention can be cured and coated with additional coating(s), and have good intercoat adhesion to the additional coating and good adhesion to surface sealants.
The invention also includes a method for improved intercoat adhesion comprising applying to a substrate at least a basecoat layer and a clearcoat layer, followed by application of at least one additional coating layer, wherein at least one layer of the coating composition comprises components (A)-(C). The invention also includes a method for improved adhesion of a cured coating composition to sealant materials.
REFERENCES:
patent: 4613641 (1986-09-01), Haubennestel et al.
patent: 4636552 (1987-01-01), Gay et al.
patent: 4812518 (1989-03-01), Hanbennestel et al.
patent: 5430083 (1995-07-01), Klier et al.
patent: 5872195 (1999-02-01), Green et al.
BASF Corporation.
Niland Patrick D.
Sabourin Anne Gerry
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