Coating processes – Restoring or repairing – Metal article
Reexamination Certificate
2000-06-22
2003-03-18
Beck, Shrive P. (Department: 1762)
Coating processes
Restoring or repairing
Metal article
C427S289000, C427S327000, C427S355000
Reexamination Certificate
active
06534121
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to methods of coating metal substrates, especially bare metal substrates which have not been chemically and/or mechanically altered with a pretreatment process.
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 provide a method of coating bare, untreated metal substrates which eliminates the step of applying one or more substrate pretreatments, especially a method useful in refinish operations.
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.
Accordingly, it would be desirable to provide a method of refinishing a previously coated substrate wherein a coating could be applied to a bare, untreated metal substrate lacking any such ‘adhesion anchors’ and desireable adhesion obtained.
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, durability, ambient or low temperature cure, application parameters such as pot life, sprayability, and clean up, and appearance. Illustrative refinish coatings having such properties include urethane coatings, especially two component urethane coating.
Accordingly, it would be desirable to provide a method of refinishing a previously coated substrate, wherein a urethane based refinish coating having improved adhesion could be applied to a bare, untreated metal substrates and desireable preformance properties and refinish adhesion obtained.
SUMMARY OF THE INVENTION
These and other objects have been achieved with the method of the invention. The invention provides a method of coating a bare untreated metal substrate. The method requires the steps of (i) providing a bare, untreated metal substrate, the substrate being substantially free of mechanical and/or chemical alterations, (ii) applying a two-component urethane coating composition directly to the bare, untreated metal substrate so as to make a coated metal substrate, and (iii) sanding at least a portion of the coated metal substrate within one hour from the time the two-component urethane coating composition was applied to the bare, untreated metal substrate. The resulting coated metal substrate has an initial adhesion loss of less than 20% as measured by a cross hatch adhesion test per ASTM D-3359.
The invention further provides a method of refinishing a previously coated substrate. This method requires (i) providing a substrate having thereon a previously applied and cured coating film, (ii) removing substantially all of the previously applied and cured coating film from at least a portion of the substrate so as to make a bare metal subtrate substantially free of mechanical and/or chemical alterations, (iii) applying a two-component urethane coating composition directly to the bare, untreated metal substrate so as to make a coated metal substrate, and (iv) sanding at least a portion of the coated metal substrate within one hour from the time the two-component urethane coating composition was applied to the bare, untreated metal substrate, wherein the coated metal substrate has an initial adhesion loss of less than 20% as measured by a cross hatch adhesion test per ASTM D-3359.
In the most preferred embodiments of the methods of the invention, one or more components of the two-component urethane coating composition used in the method will comprise a material selected from the group consisting of a mixture of compound (I) and compound (II), a silane oligomer (B), and mixtures thereof. The mixture of compound (I) and compound (II) comprise a compound (I) having an acid number of from 70 to 120 mg KOH/g, a hydroxyl number of from 200 to 400 mg KOH/g, a number average molecular weight of from 150 to 3000, and which is the reaction product of (a) at least one difunctional carboxylic acid, (b) at least one trifunctional polyol, (c) at least one chain stopper, and (d) phosphoric acid, and a compound (II) comprising one or more carboxy phosphate esters having the formula:
wherein M is hydrogen, metal, or ammonium, x is a number from 0 to 3, R is an C
5
-C
40
aliphatic group having one or more —COOR
1
groups, wherein R
1
is H, metal, ammonium, C
1
-C
6
alkyl, or C
6
-C
10
aryl. The silane oligomer (B) comprises the reaction product of an isocyanate functional compound (A) and a coupling agent (X) comprising (i) at least one alkoxysilane functional group, and (ii) at least one group reactive with isocyanate selected from the group consisting of thiol groups, secondary amine groups, primary amine groups and mixtures thereof, wherein the silane oligomer (B) comprises an average of at least two free isocyanate groups.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The methods of the invention allow for the coating of bare untreated metal substrates. Suitable metal substrates include but are not limited to galvanized
Newton David L.
Plassmann William H.
BASF Corporation
Beck Shrive P.
Crockford Kirsten A.
Golota Mary E.
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