Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2002-04-19
2004-07-13
Sastri, Satya B. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S559000, C524S555000, C524S556000, C524S562000, C524S577000
Reexamination Certificate
active
06762240
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to dispersions of crosslinked polymeric microparticles and thermosetting compositions containing such dispersions. More particularly, the present invention is directed to coating compositions containing crosslinked polymeric microparticles used in multi-component composite coating compositions such as primers, pigmented or colored basecoats, and/or transparent topcoats which provide good smoothness and appearance.
2. Background of the Invention
Over the past decade, there has been a concerted effort to reduce atmospheric pollution caused by volatile solvents which are emitted during painting processes. However, it is often difficult to achieve high quality, smooth coating finishes, such as are required in the automotive industry, without the inclusion of organic solvents which contribute greatly to flow and leveling of a coating.
Due to environmental concerns, volatile organic compounds (“VOCs”) and/or Hazardous Air Pollutants (“HAPs”) have come under strict regulation by the government. Therefore, one of the major goals of the coatings industry is to minimize the use of organic solvents by formulating waterborne coating compositions which provide a smooth, high gloss appearance, as well as good physical properties including resistance to acid rain. Unfortunately, many waterborne coating compositions, particularly those containing metallic flake pigments, do not provide acceptable appearance properties because, inter alia, they can deposit as a rough film under conditions of low humidity. Although smooth films can be obtained if the humidity is controlled within narrow limits, this often is not possible in industrial applications without incurring considerable expense.
The paint application process in an automotive industrial paint shop consists of four steps: storage in a tank; circulation in pipelines; spraying via a bell and/or a spray gun nozzle; and film formation on the surface of the substrate. The shear rates active on the paint in each of the steps are quite different and require varying paint rheological properties for each step. To design proper paint viscosity in waterborne automotive coatings, a distinct rheology profile is needed to provide good sprayability, sag resistance and levelling properties simultaneously. In basecoat compositions, shear thinning flow behavior is usually preferred. In many cases, special rheology control agents are used in coating formulations to provide the desired flow behavior.
Microgels or crosslinked microparticles have been used in the paint industry to improve the Theological properties properties of coating compositions as well as the physical properties of the coating, such as tensile strength, solvent resistance, and gas permeability. A particular goal has been to provide good sprayability, sag resistance and leveling properties simultaneously. In basecoat paints, proper shear thinning flow behavior is required to achieve this goal.
Basecoat coating compositions containing “effect” or reflective pigments, such as metallic flake pigments e.g., aluminum flake and micaceous pigments have increased in popularity in recent years because of the “glamorous” and distinctive chromic effects they provide. In such coatings, orientation of the aluminum flakes parallel to the surface of the substrate produces a unique metallic effect often referred to as “flip-flop” or “flop”. A higher flop effect provides a more desired, brighter metallic appearance having a high level of color transition or “travel” with changes in viewing angle. The rheological properties of the coating composition, especially as affected by microgels, can greatly impact the flop property by promoting proper metallic flake orientation.
U.S. Pat. No. 6,291,564 to Faler, et al. discloses an aqueous coating composition that includes a crosslinkable film-forming resin and polymeric microparticles. However, under certain application conditions, the coating compositions can provide less than optimal appearance properties when metallic flake pigments are included in the coating composition. For example, the coatings can be prone to mottling (that is, an uneven distribution of metal flakes in the cured film) and sometimes do not have a smooth appearance. Furthermore, the resulting aqueous coating may include an unacceptable level of HAPs in the form of organic solvents.
Hong et al., “Core/Shell Acrylic Microgel as the Main Binder of Waterborne Metalic Basecoats”,
Korea Polymer Journal
, Vol. 7, No. 4, pp 213-222 (1999) discloses an alkali swellable core/shell acrylic microgel emulsions having a hydrophobic core and a shell that included low levels of 2-hydroxyethyl acrylate and/or methacrylic acid as well as up to 8% crosslinking monomer content. The microgels provide pseudoplastic or shear thinning behavior in aqueous metallic basecoats. Addition of an alkali is required to promote swelling of the microgel, which can be problematic in achieving reproducible rheological properties.
Polymeric microparticles may be prepared by latex emulsion polymerization, where a suitable crosslinking monomer is included in the dispersed, water insoluble monomer phase. The macroscopic interactions and kinetics of latex emulsion polymerizations are generally described by the Smith-Ewart model. In the latex emulsion polymerization technique, water-insoluble or slightly water-soluble monomers are added to an aqueous continuous phase and form dispersed monomer droplets. A very small fraction of the monomers go into solution and form monomer micelles. A free radical source is added to the emulsion and polymerization is initiated within the micelles, to which additional monomer is fed from the monomer droplets. The end result is polymer particles dispersed in an aqueous continuous phase. See
Principles of Polymerization
, Second Edition, Odian, Wiley-Interscience, pp. 319-331 (1983).
When water soluble monomers are incorporated into the monomer mix in a latex emulsion polymerization process, initiation of polymerization in the aqueous continuous phase can result. When water-soluble monomers are polymerized in the aqueous continuous phase of a latex emulsion polymerization, the resulting polymer typically ranges from grit or coagulum to a thick solution or gel, rather than a dispersed polymer particle. The risk of such adverse results has limited the use of water-soluble monomers in latex emulsion polymerization processes.
U.S. Pat. No. 5,102,925 to Suzuki, et al. discloses an air-drying paint composition that includes internally cross-linked polymer microparticles, a film-forming resin and a volatile organic solvent. The use of thermosetting resins in the paint composition is not disclosed. The microparticles are produced by emulsion polymerization of ethylenically unsaturated monomers and at least one cross-linking monomer in the presence of an emulsifier.
U.S. Pat. No. 4,705,821 to Ito, et al. discloses an anticorrosive metal surface pretreating composition that includes an aqueous emulsion of hard polymer microparticles and a water soluble chromium compound. The polymer microparticles are prepared by emulsion polymerization of mono-unsaturated monomers and polyfunctional monomers.
European Patent Application No. 0 358 221 to Grutter et al. discloses electrodeposition coatings that include an aqueous dispersion of a cathodic or anodic deposition resin and polymer microparticles. The polymer microparticles include 0.1 to 5%, less than 2% by example, of monomers containing hydrophilic groups.
Generally, the known microgel thickeners used in aqueous basecoat coating compositions are deficient in that the resultant basecoatings can be susceptible to penetration by a solvent-based clear topcoat into the cured basecoat (commonly referred to as “soak in” or “strike in”) and typically are only effective with certain limited clearcoats. Further, additional rheology modifiers or thickeners are often required to ensure a desired rheological profile for the cured coating composition, which also typically include HAPs solvents.
Endlich Brian
Haley M. Frank
Kania Charles M.
Olson Kurt G.
Pagac Edward S.
Altman Deborah M.
PPG Industries Ohio Inc.
Sastri Satya B.
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