Stock material or miscellaneous articles – Composite – Of silicon containing
Reexamination Certificate
2001-07-31
2003-11-04
Dawson, Robert (Department: 1712)
Stock material or miscellaneous articles
Composite
Of silicon containing
C428S413000, C428S416000, C528S005000, C528S008000, C528S013000, C525S100000, C525S101000, C525S113000, C525S124000
Reexamination Certificate
active
06641923
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to curable, weldable coating systems having improved adhesion, and more particularly, to curable, weldable, corrosion-inhibitive coating systems for metal substrates.
BACKGROUND OF THE INVENTION
The production of light gauge steel for end uses such as architectural construction materials to automobiles is well known. Such steel substrate typically is produced on a rolling mill as continuous sheets of various thicknesses and widths. The steel sheets may be coated with a thin layer of zinc metal via a galvanizing process. Eventually, a mill oil is applied to the uncoated or galvanized steel sheets, and the steel is either stored or shipped in a coil to a customer for further processing.
As previously mentioned, such customers can include automobile manufacturers. At automotive assembly plants, the coiled metal sheet is first passed through a lubricating station and then to a forming operation where the substrate is cut and formed into automobile body parts, for example, fenders, doors, and deck lids. The various parts are then welded together to form an automobile body. Thereafter, the automobile body is cleaned, treated with a zinc phosphating solution to enhance corrosion protection, and rinsed with deionized water. The thus treated automobile body typically is then passed through an electrodeposition bath where a corrosion resistant primer is applied.
In the interest of cost savings, many automobile manufacturers have elected to streamline their operations, for example, by having some of the pretreatment and coating operations described above done outside the automobile assembly plant, i.e., at the steel mill or a custom coater location. One major problem with moving certain operations to a steel mill or a custom coater is that any coating applied at such locations must be weldable Consequently, there is a strong demand in the automotive industry for weldable, corrosion resistant coating compositions that can be applied outside the automobile assembly plants, for example, at a steel mill or at a custom coating facility.
Such a weldable, corrosion resistant coatings could be applied at a custom coater, known as a coil coater, and the coated coil substrate shipped to the automobile assembly plant where the coated substrate would be formed into parts and welded together to form the autobody. This approach would have the advantage of eliminating the necessity for the metal pretreatment operation and, perhaps, the electrodeposition process, since the metal received by the automobile manufacturer would already be coated with a corrosion resistant coating.
Similarly, a weldable, corrosion resistant coating composition could be mill-applied. Steel mill-application of the weldable, corrosion resistant coating enables the automobile manufacturer to receive corrosion resistant metal directly without the expense associated with shipment to a custom coil coater.
After the various autobody parts are welded to form an automobile body, the automobile body undergoes further cleaning and coating treatments. The subsequent treatments and coating layers may include phosphate treatment, electrodeposited primer, and automotive topcoats, for example a color-plus-clear coating system.
Some known weldable primer compositions have exhibited poor adhesion to a hot dipped galvanized steel substrate when subsequently coated with electrodeposited primer. This poor adhesion to the substrate can result on poor scratch resistance and poor crosshatch tape adhesion.
A number of patents disclose the use of boric acid in polymeric compositions. For example, U.S. Pat. Nos. 5,951,747 and 6,059,867 discloses the use of boric acid and borates in conjunction with a succinate in non-chromate, corrosion-inhibiting coating compositions for improved adhesion to metallic surfaces. Such compositions further include inhibitors such as phosphates, phosphosilicates, silicates, titanates, and zinc salts. U.S. Pat. No. 4,832,990 discloses a process for improving adhesion of polyolefins to metal substrates comprising mechanical cleaning of the metal surface, treating the metal surface with a water-alcohol solution containing an alkoxysilane and boric acid, thermally treating the acid treated substrate, and subsequently treating the substrate with a polyolefin-based composition comprising zeolites and carbon black pigment. U.S. Pat. No. 5,073,455 discloses a thermoplastic laminated film which has improved adhesion to hydrophilic polymers, hydrophobic polymers and inorganic substances. The film comprises a base film of thermoplastic resin and a layer formed on the base film comprising a composition of one or more of water-soluble resins, water emulsified resins and water-dispersible resins, and an organic boron polymer or a mixture composed of an organic boron polymer and vinyl alcohol. These references do not describe, however, the addition of boric acid or a borate to a thermosetting composition to improve intercoat adhesion between the boron-containing coating and a subsequently applied coating.
In view of the foregoing, there remains a need in the automotive industry for a weldable, corrosion-inhibitive primer composition having excellent adhesion to a substrate as well as excellent intercoat or interlayer adhesion with subsequently applied coating layers.
SUMMARY OF THE INVENTION
In one embodiment, the present invention provides a thermosetting coating composition comprising (A) a resinous binder comprising (1) at least one functional group containing polymer, and (2) at least one curing agent having functional groups reactive with the functional groups of the functional group containing polymer (1); at least one electroconductive pigment dispersed in the resinous binder (A); and (C) at least one boron-containing compound selected from boric acid, boric acid equivalents, and mixtures thereof, wherein each component is different. The thermosetting composition is characterized in that when deposited and cured on a metal substrate, the cured coating is weldable.
In another embodiment, the present invention provides a thermosetting coating composition comprising (A) a resinous binder comprising (1) at least one functional group containing polymer, and (2) at least one curing agent having functional groups reactive with the functional groups of the polymer (1); at least one electroconductive pigment dispersed in the resinous binder (A); and (C) at least one compound formed from components comprising: (a) at least one polysiloxane comprising at least one reactive functional group, the polysiloxane comprising at least one of the following structural units (I):
R
1
n
R
2
m
SiO
(4−n−m)/2
(I)
wherein each R
1
, which may be identical or different, represents H, OH, a monovalent hydrocarbon group or a monovalent siloxane group; each R
2
, which may be identical or different, represents a group comprising at least one reactive functional group, wherein m and n fulfill the requirements of 0<n<4, 0<m<4 and 2≦(m+n)<4; (b) at least one reactant comprising at least one functional group that is reactive with the reactive functional group of the polysiloxane (a); and (c) at least one compound selected from borates, aluminates, titanates, zirconates, silicates, siloxanes, silanes, and mixtures thereof, wherein each component is different. The thermosetting composition is characterized in that when deposited and cured on a metal substrate, the cured coating is weldable.
The present invention also provides a multilayer composite coating comprising a weldable primer coat formed over at least a portion of a substrate from the thermosetting composition described above, and a topcoat over at least a portion of the primer coating formed from a topcoat film-forming composition.
The present invention also provides substrates coated with the above-described thermosetting weldable compositions and multilayer composite coatings.
DETAILED DESCRIPTION OF THE INVENTION
Other than in the operating examples, or where otherwise indicated, all numbers expressin
Anderson Lawrence G.
Gaggini Sherry M.
Jones Dennis W.
Sadvary Richard J.
Altman Deborah M.
Dawson Robert
Keehan Christopher M
PPG Industries Ohio Inc.
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