Stock material or miscellaneous articles – Composite – Of silicon containing
Reexamination Certificate
2000-11-07
2002-04-30
Feely, Michael J (Department: 1712)
Stock material or miscellaneous articles
Composite
Of silicon containing
C428S423100, C524S837000, C524S853000, C524S858000, C525S123000, C525S124000, C525S127000, C528S027000, C528S028000
Reexamination Certificate
active
06379807
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention is directed to coating compositions, in particular, to a high solids clear coating composition used as a clear coating applied over a base coating on a motor vehicle. The cured clear coating of the present invention has improved acid etch resistance in comparison to conventional clear coatings currently in use.
2. Description of the Prior Art
The finish of choice presently being used on the exterior of automobiles and trucks includes a clear coating applied over pigmented base coating. The clear coating provides protection to the pigmented base coating and improves the appearance of the overall finish, such as gloss and distinctness of image. Conventional clear coatings tend to have low acid etch resistance. Acid etching occurs when the clear coating is exposed to acid rain and other air pollutants.
Typically, the binder of a conventional clear coating composition contains crosslinking agents such as, a melamine component, as shown in EP 0 708 159 A2, EP 0 135 741 and DE 195 29 124 C 1. By increasing the amount of the melamine component, it generally reduces the acid etch resistance but does improve the mar resistance that also is an important property of a clear coating. Clear coatings compositions containing acrylosilane polymers have been used to improve mar and acid etch resistance are shown in Hazan et al U.S. Pat. No. 5,066,698 issued Nov. 19, 1991, Nordstrom et al U.S. Pat. No. 5,532,027 issued Jul. 2, 1996 and Lewin et al U.S. Pat. No. 5,684,084 issued Nov. 4, 1997. However, acrylosilane polymers significantly increase the cost of the clear coating compositions. To date, none of the clear coating compositions currently in use have the necessary balance of physical properties, in particular acid etch resistance, along with low cost desired for an automotive OEM (original equipment manufacturing) clear coating composition.
Thus, there is a need for an OEM clear coating composition for automobiles and trucks that will form finishes that are resistant to acid etching and water spotting caused by acid rain and has the desired costs.
SUMMARY OF THE INVENTION
A coating composition comprising 40% to 75% by weight of a film forming binder and 25% to 60% by weight of a volatile liquid carrier for the binder; all weight percentages are based on the total weight of the composition; wherein the binder comprises
a. 20% to 70 % by weight, based on the weight of the binder solids, of an acrylosilane polymer of polymerized monomers from a monomer mixture comprising: an alkyl methacrylate, an alkyl acrylate, each having 1 to 12 carbon atoms in the alkyl group, cycloaliphatic alkyl methacrylate, cycloaliphatic alkyl acrylate, styrene or any mixture of these monomers; hydroxy containing monomers from the following group: hydroxy alkyl methacrylate, hydroxy alkyl acrylate each having 1 to 4 carbon atoms in the alkyl group, or any mixtures of these monomers; and a mono-ethylenically unsaturated silane monomer; wherein the polymer has a weight average molecular weight of 1,000 to 15,000 determined by gel permeation chromatography;
b. 10% to 60% by weight, based on the weight of the binder solids, of an organic polyisocyanate; and
c. 5% to 40% by weight, based on the weight of the binder solids, of a melamine component.
DETAILED DESCRIPTION OF THE INVENTION
A typical auto or truck body is produced from a steel sheet or a plastic or a composite substrate. If steel is used, it is first treated with an inorganic rust-proofing compound, such as zinc or iron phosphate and then a primer coating is applied by electrodeposition. Typically, these electrodeposition primers are epoxy modified resins crosslinked with a polyisocyanate. Such electrodeposition primers are applied by a cathodic electrodeposition process. Optionally, a primer can be applied over the electrodeposited primer, usually by spraying, to provide better appearance and/or improved adhesion of the base coating to the primer. A pigmented base coating is then applied.
A typical pigmented base coating composition includes pigment, a film forming binder which can be a polyurethane, an acrylourethane, an acrylic polymer or a silane polymer, and a crosslinking agent such as, an aminoplast, an alkylated melamine formaldehyde crosslinking agent or a polyisocyanate crosslinking agent. The base coating composition can be solvent or water borne and can be in the form of a dispersion or a solution. Generally, pigments used in the base coating composition include metallic flake pigments, such as aluminum flake or pearl flake pigments.
Typically, a clear coating is then applied over the base coating before the base coating is fully cured, a so called wet on wet process, and the base coating and clear coating are then fully cured usually by baking at 100° C. to 150° C. for 45 to 15 minutes. The base coating and clear coating preferably have a dry coating thickness ranging from 2.5 to 75 microns and 25 to 100 microns, respectively.
The clear coat composition of this invention contains 40% to 75% by weight of a film forming binder and 25% to 60% by weight, based on the total weight of the composition, of a volatile organic liquid carrier, that usually is a solvent for the binder and volatilizes at 35° C. and above. The clear coating also can be in dispersion form. The film forming binder of the clear coating composition contains 20% to 70% by weight, preferably, 30% to 60% by weight and most preferably, 35% to50% by weight, of an acrylosilane polymer having reactive silane and hydroxyl groups; 10% to 60% by weight, preferably, 15% to 40% by weight and most preferably, 25% to 35% by weight, of an organic polyisocyanate crosslinking agent and 5% to 40% by weight, preferably, 10% to 35% by weight and most preferably, 15% to 30% by weight, of a melamine component. All the foregoing percentages are based on the total weight of the binder solids. Preferably, the ratio of isocyanate groups of the organic polyisocyanate to hydroxyl groups of the acrylosilane polymer ranges from 0.4:1 to 1.3:1.
The acrylosilane polymer comprises polymerized non-silane containing monomers of alkyl methacrylates, alkyl acrylate, each having 1 to 12 carbon atoms in the alkyl groups, cycloaliphatic alkyl methacrylate, cycloaliphatic alkyl acrylate, styrene or mixtures of any of the above monomers. The acrylosilane polymer also comprises polymerized hydroxy containing monomers such as hydroxy alkyl methacrylate, hydroxy alkyl acrylate, each having 1 to 4 carbon atoms in the alkyl group or a mixture of these monomers and one or more polymerized mono ethylenically unsaturated silane monomers. The acrylosilane polymer has a weight average molecular weight of 1,000 to 15,000 and preferably, 3,000 to 12,000.
All molecular weights disclosed herein are determined by gel permeation chromatography (GPC).
One preferred acrylosilane polymer is the polymerization product of 35% to 75% by weight of non silane containing monomers of an alkyl methacrylate, an alkyl acrylate each having 1 to 8 carbon atoms in the alkyl group, styrene or mixtures of these monomers; 20% to 40% by weight of hydroxy alkyl methacrylate having 1 to 4 carbon atoms in the alkyl group; and 5% to 25% by weight of a mono-ethylenically unsaturated silane containing monomer.
Typically useful ethylenically unsaturated non-silane containing monomers are alkyl acrylates, alkyl methacrylates where the alkyl groups have 1 to 12 carbon atoms such as methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, isobutyl methacrylate, pentyl methacrylate, hexyl methacrylate, octyl methacrylate, nonyl methacrylate, lauryl methacrylate; methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, isobutyl acrylate, pentyl acrylate, hexyl acrylate, octyl acrylate, nonyl acrylate, and lauryl acrylate. Cycloaliphatic alkyl methacrylates and acrylates can also be used, for example, such as cyclohexyl methacrylate, cyclohexyl acrylate, trimethylcyclohexyl methacrylate, trimethylcyclohexyl acrylate, iso-butyl cyclohexyl methacrylate, t-butyl cyclohex
Lin Jun
Nordstrom John D
Deshmukh Sudhir G.
E. I. du Pont de Nemours and Company
Feely Michael J
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