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
2001-04-10
2004-08-24
Seidleck, James J. (Department: 1711)
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...
C524S356000, C524S361000
Reexamination Certificate
active
06780909
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to high solids coating compositions, particularly automotive topcoat coating compositions.
BACKGROUND OF THE INVENTION
Curable, or thermosettable, coating compositions are widely used in the coatings art, particularly for topcoats in the automotive and industrial coatings industry. Basecoat-clearcoat composite coatings are particularly useful as topcoats for which exceptional gloss, depth of color, distinctness of image, or special metallic effects are desired. The automotive industry has made extensive use of these coatings for automotive body panels.
Aqueous coating compositions and powder coating compositions have been increasingly used to meet legal restrictions on organic solvent emissions. Each of these technologies, however, has its drawbacks. Waterborne coatings include either resins with a high concentration of saltable or polyether groups or include surfactants, either of which make the coating water-sensitive. Waterborne coatings tend to have viscosity instability, with accompanying degradation of metallic appearance. Further, waterborne coatings require expensive, special application equipment, all stainless steel, and humidity controlled conditions. Powder coatings also require special applications and handling equipment. Powder coatings are also relatively expensive to manufacture and must be made with high glass transition temperature resins to avoid sintering on storage. Due to these special considerations, powder coatings technologies require high temperature curing, which again adds to their expense. Moreover, there is a concern of regulated emissions of particulates below a certain particle size.
The content of volatile organic compounds has also been reduced by using resins of lower viscosity, for example very low molecular weight polymeric or oligomeric materials or reactive diluent compounds. The physical requirements of the cured film, such as hardness and durability, remain the same, however, and it becomes more difficult to achieve those properties as the molecular weight is reduced further and further. Consequently, there is a practical limit to how low the molecular weight of the vehicle components can be. On the other hand, the high solids can be achieved by formulating the coating composition at a higher viscosity. High viscosity coating compositions, however, require special equipment to handle and apply them, such as bigger diameter pipes and bigger pumps in the recirculation system or heated pipes to lower the viscosity. These modifications are expensive and require down time of the plant paint shop.
Thus, there remains a need for coating compositions that have low volatile organic content and can be applied using existing equipment in plants that are configured to handle more traditional coatings technology. Such a coating composition still must provide a cured coating having the desired physical properties.
SUMMARY OF THE INVENTION
The coating composition of the invention includes an organic phase including a polymer, especially an acrylic polymer, having hydroxyl and/or primary carbamate functionality; a water-miscible organic solvent; a low hydrogen bonding oxygenated solvent; and water that is emulsified in the organic phase. The polymer is not dissolved or dispersed in water, but rather remains in a continuous, organic phase. Because the acrylic resin does not contain a high concentration of salted groups, it avoids the problems of emissions of a salting base and water sensitivity from a high concentration of acid groups.
The term “primary carbamate group” as used in connection with the present invention refers to a group having a structure:
The term “water-miscible organic solvent” as used in connection with the present invention refers to an organic compound that is liquid at room temperature and that is completely soluble in water.
The “low hydrogen bonding oxygenated solvent” of the invention is an organic compound that is liquid at room temperature and that contains at least one oxygen atom and has as a Hanson solubility parameter a hydrogen bonding value up to about 6.0.
In a particularly advantageous embodiment, the coating composition of the invention is a clearcoat coating composition, preferably an automotive clearcoat coating composition. The invention further provides an article, such as an automotive vehicle, having a surface coated with a coating derived from the coating composition of the invention, particularly a composite coating having a basecoat layer and a clearcoat layer, and a method of producing such a coating on a substrate, particularly as a basecoat/clearcoat composite coating, with the coating composition of the invention preferably being at least the clearcoat of the composite coating.
The coating composition of the invention provides especially low volatile organic content, with significant reductions of 25% or more from comparable previous coating compositions. The lower VOC of the present water-containing composition is further enhanced by the water being preferentially evaporated during spraying and in the flash tunnel, while the coating tends to retain the organic solvent until the curing oven bake. This behavior is especially significant for minimizing regulated emissions of the paint shop, as the emissions from the oven can be thermally oxidized. In particular, the present coating composition unexpectedly also provides excellent leveling, which can be quantified by wave scan or Autospec™ of the coating. Finally, the emulsified water helps to reduce the odor and increase the flashpoint of the coating composition.
DETAILED DESCRIPTION OF THE INVENTION
The coating composition includes, in an organic phase, a polymer, preferably an acrylic polymer, having functionality selected from hydroxyl groups, primary carbamate groups, and combinations of these; a water-miscible organic solvent; an oxygenated solvent that is not strongly hydrogen bonding; and water. The water is emulsified in the coating. The coating thus has a solventborne continuous phase.
The polymer includes hydroxyl groups, primary carbamate groups, or both hydroxyl groups and primary carbamate groups. Suitable polymers for the coating composition include, without limitation, acrylic polymers, polyurethane polymers, and polyester polymers. Preferred among these are acrylic polymers.
Synthesis of such polymers for coatings are well-known in the art. A typical synthesis of the preferred acrylic polymer will be described, but the person skilled in the art should understand that the principles apply likewise to other suitable coatings resins.
With particular reference to the preferred acrylic polymer, then, the hydroxyl and/or carbamate functionality may be conveniently introduced by polymerizing a monomer having an hydroxyl group and/or polymerizing a monomer having a primary carbamate group, although it is also possible to polymerize with a monomer having functionality that may be reacted to supply an hydroxyl and/or carbamate group after polymerization. Examples of addition polymerizable monomers having hydroxyl or primary carbamate functionality include, without limitation, hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, hydroxybutyl acrylate, and hydroxybutyl methacrylate; polyalkylene glycol acrylates and methacrylates; and the reaction product of a glycidyl-group containing monomer, such as glycidyl acrylate, glycidyl methacrylate, and allyl glycidyl ether, with a carboxylic acid. Hydroxyl and/or primary carbamate functionality can be introduced to an acrylic polymer by a number of reactions, including, without limitation, reacting glycidyl functionality with a carboxylic acid; reacting a carboxylic acid group with a glycidyl compound; and by other methods, such as those set out in Ohrbom et al, U.S. Pat. No. 6,160,058 and McGee et al., U.S. Pat. No. 5,726,244, both of which are incorporated herein by reference.
The acrylic polymer of the organic phase includes a sufficient amount of the hydroxyl and/or carbamate functionality so that the
Balatan Sergio E.
Laugal James A.
Menovcik Gregory G.
Stauffer Michele L.
West Mark
BASF Corporation
Rajguru U. K.
Seidleck James J.
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