Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Patent
1982-08-09
1987-12-15
Bleutge, John C.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
525514, C08G 1232, C08G 1212, C08L 6124, C08L 6128
Patent
active
047134275
DESCRIPTION:
BRIEF SUMMARY
Reference is made to commonly assigned and concurrently filed U.S. applications Ser. Nos. 425,191 entitled "Glycidyl-Hydroxy-Acrylic High Solids Coating Compositions" and 432,897, now abandoned, "Acrylic-Hydroxy-Epoxy High Solids Coating Compositions", both to Chattha et al.
TECHNICAL FIELD
This invention relates to high solids thermosetting coating compositions which, when cured, provide an automotive topcoat demonstrating hardness, high gloss, outstanding durability and excellent resistance to solvents and water. More particularly, this invention relates to low viscosity, high solids compositions having superior weathering properties and comprising a mixture of a low molecular weight polyol, dicarboxylic acid anhydride including at least about 50 weight percent of alkyl hexahydrophthalic anhydride, epoxy, and amine-aldehyde crosslinking resins. The composition mixture reacts in situ during curing at elevated temperatures to form the coating.
BACKGROUND OF THE INVENTION
Because of increasingly strict solvent emissions regulations in recent years, low solvent emission paints have become very desirable. A number of high solids paint compositions have been proposed to meet these low solvent emission requirements. However, many of these compositions are deficient because of difficulty in application, slow curing rates, complex and/or consuming composition formulation, poor durability and low solvent and water resistance of the coating.
Compositions which have been proposed to overcome these deficiencies are taught in U.S. applications Ser. Nos. 334,698, 334,800 and 334,801, filed Dec. 12, 1981 in the name of Chattha. In these compositions, branched diols react with anhydrides of dicarboxylic acids to produce hydroxy acids and polyacids. The composition of such a mixture is largely dictated by the stoichiometry of the reactants employed. These acid products can then be reacted with epoxies to produce hydroxy resins. Subsequently, a composition comprising a mixture of these hydroxy resins and amine-aldehyde crosslinking agent can be applied to a substrate and cured at elevated temperatures to obtain crosslinked structures. Unexpectedly, we have now found that all the materials use to prepare these prior compositions can be singly combined and all of the aforementioned reactions carried out in situ during curing on the substrate to obtain high solids coatings with excellent physical properties. While not wishing to be bound by theory, it is believed that in this reaction sequence the polyol reacts with the anhydride to produce acid functionality which further reacts with the epoxy to produce hydroxy moiety; then at higher temperatures, the amine-aldehyde reacts with hydroxy functionality to produce a crosslinked network. This crosslinking reaction is facilitated by the unconsumed acid present in the composition.
DISCLOSURE OF THE INVENTION
The low viscosity thermosetting coating composition of this invention preferably contains greater than about 60% by weight, more preferably greater than 70% by weight, of nonvolatile solids. The composition is characterized in that it comprises a mixture of:
(A) polyol having a number average molecular weight (M.sub.n) of between about 130-5000, preferably between about 150 and about 3500;
(B) dicarboxylic acid anhydride comprising at least about 50 weight percent of alkyl, preferably methyl, hexahydrophthalic anhydride;
(C) epoxy having one or more, preferably two, epoxide groups per molecule and having a number average molecular weight (M.sub.n) between about 130 and about 1500; and
(D) amine-aldehyde crosslinking agent. The composition reacts in situ during curing at elevated temperatures to form the coating.
The dicarboxylic acid anhydride is included in an amount so as to provide between about 0.25 and about 1.5, preferably between about 0.3 and 1.2, anhydride groups per hydroxyl group on the polyol. The epoxy is included in an amount so as to provide at least about 1.0, preferably between about 1.1 and 1.2 epoxide groups per anhydride group. The amine aldehyde i
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Chattha Mohinder S.
Theodore Ares N.
Bleutge John C.
E. I. Du Pont de Nemours and Company
Fricke Hilmar L.
Sellers II Robert E. L.
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