Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Patent
1997-10-29
1999-11-02
Short, Patricia A.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
525124, 525159, 525160, 525162, 524507, 524512, 524513, C09D13306, C09D16128, C09D16708, C09D17504
Patent
active
059772565
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention concerns a metal-coating composition containing acrylic polyol(s), polyester polyol(s) and a crosslinking agent.
2. State of the Art
The coating composition of this invention is useful primarily on metallic-substrates, particularly on vehicles such as automobiles and trucks. Such coating will protect the substrate and provide an attractive aesthetic finish. A typical vehicle has several coating layers. The substrate is typically first coated with an inorganic rust-proofing zinc or iron phosphate layer over which is applied an electrocoated primer or repair primer. Optionally, a primer surfacer can be employed for better appearance and improved adhesion. A pigmented basecoat or colorcoat is next applied over the primer. A typical basecoat or colorcoat may contain metallic flakes to provide a metallic finish. To protect and preserve the aesthetic qualities of the color finish, a clear (unpigmented) topcoat is often applied over the pigmented basecoat to protect the basecoat even on prolonged weathering. Clearcoats are predominantly based on a technology where the binders are hydroxy functional acrylics crosslinked with alkoxylated melamine formaldehyde adducts. The coatings are typically baked at .+-.130.degree. C. after application wet-on-wet on a basecoat. Because of severe field complaints, the automobile coating industry is asking for improved scratch resistance of the clearcoats.
The composition of this invention has been found to provide particularly desirable scratch-resistance to the metallic substrate coating art. This improvement is in addition to attributes of good weatherability, chemical-resistance, water-resistance, etch-resistance and mechanical characteristics. This improved package of properties derives from the interrelationship of the selected acrylic and polyester polyols and the crosslinker selected for use therewith. Most particularly, the improved properties are derived from the dimer acid/alcohol component of the polyester polyol as will be described in more detail hereafter.
SUMMARY OF THE INVENTION
The coating composition of this invention is a crosslinkable binder in an organic solvent, the binder comprising the following components based on total weight of binder: molecular weight of about 2,500 to 40,000; a hydroxyl value of about 50 to 180 mg KOH/g; and a glass transition temperature of between -30 to 70.degree. C.; having a weight average molecular weight of about 2,000 to 80,000; and a hydroxyl value of about 50 to 220 mg KOH/g; hydrogenated reaction product of at least one of: two groups selected from acid and alcohol functionalities; and one of an alkoxylated melamine formaldehyde adduct and a polyisocyanate (which may be blocked).
Preferred compositions are those in which the acrylic polyol has a molecular weight of 3,000 to 10,000; a hydroxyl value of 80 to 150; and a glass transition temperature of -10 to 50.degree. C. Also preferred are compositions in which the acrylic polyol contains at least one trialkoxysilyl or urethane group; in which the polyester polyol has a molecular weight of 2,500 to 15,000; a hydroxyl value of 100 to 170; and about 30 to 60 percent, by weight of polyester polyol, of hydrogenated reaction product selected from a), b) and c); in which the polyester polyol contains substituents selected from at least one member of the group trialkoxysilyl and urethane; in which the binder comprises about 20 to 85 percent by weight of the solvent plus binder; and in which the polyester polyol comprises at least 10 percent of hydrogenated reaction product.
Most preferred are compositions comprising acrylic and polyester polyols and alkoxylated melamine formaldehyde adducts in a one-package system. Such a system may contain a blocked polyisocyanate. Other compositions are two-package systems comprising the acrylic and polyester polyols in one package and an unblocked polyisocyanate in the second package. The coatings of this invention are useful in topcoats for metallic substrates that includ
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Betz, P., Bartelt, A., Scratch-resistant Clear Coats: Development of new testing methods for improved coatings, Prog. Org. Coat., 22, 27-37, 1993.
Huybrechts Jozef
Kernaghan Stuart Alexander
Vervoort Robert
Costello James A.
Deshmukh Sudhir G.
E.I. Du Pont de Nemours and Company
Short Patricia A.
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