Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2000-12-22
2003-07-29
Sanders, Kriellion A. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C524S439000
Reexamination Certificate
active
06599965
ABSTRACT:
BACKGROUND OF THE INVENTION
As used herein, “automotive refinish” refers to compositions and processes used in the repair of a damaged automotive finish, usually an OEM provided finish. Refinish operations may involve the repair of one or more outer coating layers, the repair or replacement of entire automotive body components, or a combination of both. The terms “refinish coating” or “repair coating” may be used interchangeably.
Automotive refinishers must be prepared to paint a wide variety of materials. Examples of commonly encountered materials are one or more previously applied coatings, plastic substrates such as RIM, SMC and the like, and metal substrates such as aluminum, galvanized steel, and cold rolled steel. Bare metal and plastic substrates are often exposed as a result of the removal of the previously applied coating layers containing and/or surrounding the defect area. However, it is often difficult to obtain adequate adhesion of refinish coatings applied directly to exposed bare substrates.
Among the many factors influencing the degree of refinish coating/substrate adhesion are the type of exposed substrate, the presence or absence of adhesion promoting pretreatments and/or primers, the size of the exposed area to be repaired, and whether previously applied “anchoring” coating layers surround the exposed repair area.
For example, refinish adhesion is particularly challenging when the exposed substrate is a bare metal such as galvanized iron or steel, aluminum or cold rolled steel. It is especially hard to obtain adequate refinish adhesion to galvanized iron. “Galvanized iron or steel” as used herein refers to iron or steel coated with zinc. “Steel” as used herein refers to alloys of iron with carbon or metals such as manganese, nickel, copper, chromium, molybdenum, vanadium, tungsten and cobalt.
Refinish operations have traditionally used adhesion pretreatments to overcome the adhesion problems associated with the coating of bare metal substrates. Pretreatment as used herein may refer to either mechanical or chemical alterations of the bare metal substrate. Mechanical alterations used to obtain improved adhesion include sanding, scuffing, and the like. Chemical alterations include treatment of the substrate with compositions such as chromic acid conversion coatings, acid etch primers and the like.
Although such pretreatments have obtained improved refinish adhesion, they are undesirable for a number of reasons. Most importantly, pretreatments are inefficient and expensive to apply in terms of material, time, and/or labor costs. Some chemical pretreatments also present industrial hygiene and disposal issues. Finally, the use of some pretreatments such as acid etch primers may contribute to water sensitivity and/or coating failure under test conditions of extreme humidity.
Accordingly, it is highly desirable to eliminate the need for substrate pretreatment as regards the refinish coating of bare metal substrates.
In addition, adhesion to bare metal substrates is improved when the defect area to be repaired is relatively small and is surrounded by previously applied coating layers. Such previously applied coating layers act as an ‘adhesion anchor’ to the refinish coating. However, many refinish repairs are of a size such that they lack any surrounding adhesion anchors. Moreover, such anchoring adhesion may be completely absent when replacement body parts are painted with a refinish coating.
Finally, improvements in refinish adhesion to bare exposed metal substrates must not be obtained at the expense of traditional refinish coating properties. Such properties include sandability, recoatability, corrosion resistance, durability, ambient or low temperature cure, application parameters such as pot life, sprayability, and clean up, and appearance. Performance properties such as sandability, recoatability and corrosion resistance are particularly important for coating compositions intended for use as primers over steel substrates.
However, it has been difficult for the prior art to obtain the proper balance with regard to sandability, recoatability, corrosion resistance, and metal adhesion requirements.
Failure to provide adequate corrosion resistance or salt spray resistance typically manifests as “scribe creep”. “Scribe creep” refers to the degree of corrosion and/or loss of adhesion which occurs along and underneath film adjacent to a scribe made in a cured film after the scribed film has been placed in a salt spray test apparatus. The scribe generally extends down through the film to the underlying metal substrate. As used herein, both ‘corrosion resistance’ and ‘salt spray resistance’ refer to the ability of a cured film to stop the progression of corrosion and/or loss of adhesion along a scribe line placed in a salt spray test apparatus for a specified time. Cured films that fail to provide adequate salt spray resistance are vulnerable to large scale film damage and/or loss of adhesion as a result of small or initially minor chips, cuts and scratches to the film and subsequent exposure to outdoor weathering elements.
Although urethane coatings have been known to be useful as refinish primers, they have not achieved the desired balance of properties.
In particular, for polyurethane films to provide desirable salt spray resistance, they have typically relied upon the use of corrosion protection components containing heavy metal pigments such as strontium chromate, lead silica chromate, and the like. Unfortunately, sanding such a film produces dust that is environmentally disfavored due to the presence of the heavy metal containing pigments. Since sanding is a necessity for automotive refinish primers, this disadvantage can render the coating unusable in most commercial refinish application facilities. Accordingly, it would be advantageous to provide a coating which can provide adequate salt spray resistance but which is substantially free of any heavy metal containing pigments.
Aluminum pigments have traditionally been used to provide a desirable metallic or lustrous appearance. For example, the 1977 Federation Series on Coatings Technology teaches that aluminum pigment containing paints have no specific anti-corrosive effect, such as is afforded by rust-inhibitive pigments traditionally used in commercially acceptable metal primers. Indeed, it is further taught that strontium chromate should be used in combination with aluminum pigments to provide aluminum containing paints having an anti-corrosive effect.
Aluminum pigments, especially leafing aluminums, are known to produce an apparently continuous film of aluminum metal.
Barrier pigments, especially platy or platelet pigments have been known to provide anticorrosive effects.
However, leafing aluminums and barrier pigments have traditionally been somewhat disfavored due to recoatability and/or sanding performance issues. Moreover, the anticorrosive effect of the coating post sanding can be impaired due to the removal of the barrier or leafing layer. As a result, the use of aluminum pigments in primers is to some extent disfavored.
The prior art has thus failed to provide a coating composition intended for use as a direct to metal primer which has commercially acceptable performance properties with regard to salt spray resistance, sandability, recoatability and adhesion to metal substrates, especially iron and/or steel.
Accordingly, it is an object of the invention to provide a curable coating composition that can be applied directly to a metal substrate and provides a commercially acceptable level of salt spray resistance.
It is a further object of the invention to provide a curable coating composition which has commercially acceptable performance properties with regard to direct to metal adhesion and salt spray resistance and further can be sanded without the production of environmentally disfavored dust.
It is a further object of the invention to provide a curable coating composition which has commercially acceptable performance properties with regard to direct to metal adhesion, salt spray resistance, sandabi
Lane Matthew T.
Newton David L.
BASF Corporation
Golota Mary E.
Sanders Kriellion A.
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