Coating processes – Solid particles or fibers applied
Reexamination Certificate
2001-02-09
2004-02-03
Cameron, Erma (Department: 1762)
Coating processes
Solid particles or fibers applied
C427S385500
Reexamination Certificate
active
06685985
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to curable coating compositions containing rheology modifiers and methods of using the same. More particularly, the invention relates to methods of coating articles, including a preferred method for coating articles having both vertically and horizontally orientated surfaces using coating compositions containing a particular rheology control agent.
BACKGROUND OF THE INVENTION
Composite color-plus-clear coatings are widely utilized in the coatings art. They are particularly desirable where exceptional gloss, depth of color, distinctness of image, and/or special metallic effects are required.
As used herein, the term “composite color-plus-clear” relates to composite coating systems requiring the application of a first coating, typically a colored basecoat coating, followed by the application of a second coating, generally a clearcoat, over the noncured or “wet” first coating. The applied first and second coatings are then cured. Thus, such systems are often described as “wet on wet” or “two-coat/one bake”. Drying processes that fall short of complete cure may be used between the application of the coatings.
Color-plus-clear systems are often selected when an exterior coating must possess an optimum visual appearance as well as superior durability and weatherability. As a result, the automotive industry has made extensive use of color-plus-clear composite coatings, especially for automotive body panels. Minimum performance requirements for clearcoat coating compositions intended for use on automotive body panels include high levels of adhesion, scratch and mar resistance, chip resistance, humidity resistance, and weatherability as measured by QUV and the like. The clearcoat composition must also be capable of providing a visual appearance characterized by a high degree of gloss, distinctness of image (DOI), and smoothness. Finally, such coatings must also be easy to apply in a manufacturing environment and be resistant to application defects.
Clearcoats used in color-plus-clear systems are normally applied at film builds significantly higher than the film builds at which the colored basecoat is applied. Such higher clearcoat film builds are an aspect of the system that contributes toward the desired appearance and/or durability of the overall color-plus-clear system. For example, automotive original equipment manufacturing (OEM) facilities typically apply clearcoat compositions at wet film builds of from 0.8 to 6.0 mils to provide cured clearcoat film builds of from 0.5 to 3.5 mils. In contrast, the colored basecoat compositions are usually applied at wet film builds of from 0.2 to 4.0 mils to provide cured basecoat film builds of from 0.1 to 2.0 mils.
Unfortunately, the higher film build requirement for clearcoats can exacerbate the tendency of a clearcoat composition to sag. Occurring primarily on vertically orientated surfaces, sag may be described as the undesirable downward flow of an applied coating. Often manifesting as drips or runs, sag is sometimes attributed to the “too heavy” or “too wet” application of a coating. Ideally, a commercially successful clearcoat composition will have an inherent tendency to resist sagging regardless of application and/or facility parameters. The more resistant a clearcoat is to sagging on vertically orientated surfaces, the easier it will be to apply in an automotive OEM facility.
However, a clearcoat resistant to vertically orientated sagging has traditionally shown increased resistance to flow on horizontally orientated surfaces. “Vertically orientated” as used herein refers to surfaces which are substantially parallel to the direction of gravity, i.e., at an angle of 90°±45° relative to the surface of the earth, more preferably at an angle of 90°±30° relative to the surface of the earth. “Horizontally orientated” refers to surfaces which are substantially perpendicular to the direction of gravity, i.e., at an angle of 180°±45° relative to the surface of the earth, more preferably at an angle of 180°±30° relative to the surface of the earth.
A coating composition's resistance to flow on horizontally orientated surfaces often results in “orange peel” and/or an overall unacceptable appearance in terms of the smoothness, gloss and DOI of the resulting cured film. Orange peel may be described as a reoccurring irregularity in the surface of a cured film resulting from the inability of an applied wet film to “level out” after application. Although an orange peeled cured film may feel smooth to the touch, it appears as a continuous series of small bumps or dimples. The greater the inability of an applied wet film to “level out” or flow, the more pronounced or defined the small bumps or dimples will appear to the observer. The presence of such surface irregularities make it particularly difficult to obtain a smooth, glossy coated clearcoated surface having a high DOI rating.
The prior art has attempted to provide coating compositions having improved rheology.
U.S. Pat. No. 4,522,958 to Das et al., discloses an essentially solvent-based, organic, high-solids coating composition containing (A) a film-forming binder system containing a crosslinkable resin having a weight average molecular weight of from about 500 to about 10,000; (B) substantially colorless, substantially inorganic microparticles stabley dispersed in the coating composition; and (C) a solvent system for the crosslinkable resin. The inorganic microparticles prior to incorporation in the coating composition range in size from about 1 to about 150 nanometers and are in the form of a sol of the microparticles in which carbon-containing molecules are chemically bonded to the inorganic microparticles at the surface of the microparticles.
U.S. Pat. No. 5,468,461 discloses an anticorrosive primer composition comprising (1) 100 parts by weight of an epoxy resin having a number-average molecular weight of from 500 to 10,000, (2) from 10 to 60 parts by weight of an aromatic polyamine containing from 2% to 30% by weight, based on the aromatic polyamine, of a promoter selected from the group consisting of phenol compounds and cresol compounds, (3) from 10 to 60 parts by weight of a polyisocyanate, (4) from 10 to 40 phr, based on the sum of components (1), (2), and (3), of silica particles of colloidal silica or fumed silica or a mixture of these, (5) from 0.5 to 5 phr of a lubricant, and (6) an organic solvent. The composition is particularly suitable for use to apply onto the chromate coating of a chromated, zinc-plated steel sheet.
U.S. Pat. Nos. 4,311,622, 4,677,028 and 4,851,294 disclose sag control agents that are the reaction products of an amine and a diisocyanate optionally reacted in the presence of a resinous binder. These sag control agents are typically crystalline in nature and their effectiveness is dependent on the size and shape of the crystals as well as their concentration.
U.S. Pat. No. 6,111,001 discloses compositions comprised of (a) a polymer containing pendant and/or functional groups selected from the group consisting of carbamate, urethane and/or amide functional groups, and (b) a rheology modifier comprising the reaction product of an amine and an isocyanate; and, optionally, a polymer which is different from the polymer (a) which contains carbamate, urethane and/or amide functional groups. Also disclosed are curable compositions comprised of the compositions described above which further comprise (c) a curing agent having functional groups reactive with the functional groups of the polymer (a). The curable compositions are taught to be useful for a variety of applications such as adhesives, sealants and surface coatings where the presence of a carbamate, urethane and/or amide functional polymer in conjunction with the rheology modifier provides improved thixotropy and superior sag resistance.
However, all of the foregoing have been unable to provide coating compositions having a desirable balance between vertically orientated sag resistance and horizontal orientated rheology and flow.
As a
Boisseau John E.
Clinard Dustin
Hoffman Kurt D.
Kowalewski Mark
BASF Corporation
Cameron Erma
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