Chemistry: electrical and wave energy – Processes and products – Electrophoresis or electro-osmosis processes and electrolyte...
Reexamination Certificate
1999-07-20
2001-02-20
Mayekar, Kishor (Department: 1741)
Chemistry: electrical and wave energy
Processes and products
Electrophoresis or electro-osmosis processes and electrolyte...
C204S493000, C204S498000, C523S409000, C523S412000
Reexamination Certificate
active
06190523
ABSTRACT:
FIELD OF THE INVENTION
The invention concerns anodic electrocoat coating compositions and processes for electrocoating substrates.
BACKGROUND OF THE INVENTION
Electrodeposition coating compositions and methods are widely used in industry today. One of the advantages of electrocoat compositions and processes is that the applied coating composition forms a uniform and contiguous layer over a variety of conductive substrates regardless of shape or configuration. This is especially advantageous when the coating is applied as an anticorrosive coating onto a substrate having an irregular surface, such as a motor vehicle body. The even, continuous coating layer on all portions of the metallic substrate provides maximum anticorrosion effectiveness.
Electrocoat baths usually include an aqueous dispersion of a principal film-forming resin, such as an acrylic or epoxy resin, having ionic stabilization. For automotive or industrial applications for which hard electrocoat films are desired, the electrocoat compositions are formulated to be curable compositions. This is usually accomplished by including in the bath a crosslinking agent that can react with functional groups on the principal resin under appropriate conditions (such as with the application of heat) and thus cure the coating. During electrodeposition, coating material containing an ionically-charged resin is deposited onto a conductive substrate by submerging the substrate in an electrocoat bath having dispersed therein the charged resin, and then applying an electrical potential between the substrate and an electrode of opposite charge. The charged coating material migrates to and deposits on the conductive substrate. The coated substrate is then heated to cure the coating.
Typically, the crosslinker resin does not carry a charge. In order to have the crosslinker resin disperse in the aqueous electrocoat coating bath and migrate to the substrate when the electrical potential is applied, the crosslinker resin is blended with the ionically-charged principal resin to form an organic phase which is then dispersed in the aqueous phase. The charged principal resin then carries the crosslinker that it disperses to the substrate, where the crosslinker is deposited along with the resin. For this to happen, it is important that the crosslinker remain associated with the charged resin. Thus, a crosslinker that is water soluble will dissolve in the aqueous phase will not electrodeposit during the electrocoating process and will not be suitable for preparing curable electrocoat coating films.
SUMMARY OF THE INVENTION
I have now invented an electrocoat coating composition including, in an aqueous medium, an anionic, emulsion-polymerized addition polymer, a water-insoluble crosslinking resin, and an anionic dispersing resin for dispersing the crosslinking resin.
The present invention further provides a method of coating a conductive substrate. In the method of the invention, a conductive substrate is immersed in an electrodeposition coating composition. The electrodeposition coating composition includes, in an aqueous medium, an emulsion-polymerized anionic addition polymer and a water-insoluble curing agent dispersed along with an anionic dispersing resin. Then, a potential of electric current is applied between a cathode and the conductive substrate (which is then the anode) to deposit a coating layer onto the conductive substrate. The deposited coating layer is cured by reaction between the anionic latex polymer and the curing agent.
In another aspect of the invention, a conductive substrate is electrocoated with a first layer of a first electrocoat coating composition containing a conductive pigment. The electrodeposited first layer is then cured to provide a conductive coating layer. Then, a second layer of a second electrocoat coating composition is applied to the substrate and cured. the electrocoat coating composition of the invention is applied in a second electrocoat coating layer and cured. At least one of the first electrocoat coating composition and the second electrocoat coating composition is an electrocoat coating composition according to the present invention that includes, in an aqueous medium, an anionic, emulsion-polymerized addition polymer, a water-insoluble crosslinking resin, and an anionic dispersing resin for dispersing the crosslinking resin.
DETAILED DESCRIPTION OF THE INVENTION
The electrocoat composition of the invention is an aqueous dispersion that includes at least an anionic addition polymer latex as a principal film-forming resin, a curing agent that is substantially water insoluble, and an anionic dispersing resin that disperses the curing agent. The anionic addition polymer latex is preferably polymerized with at least one acrylic monomer. When used herein, “acrylic” is used to encompass not only acrylic monomers but also methacrylic monomers and the like.
Anionic addition polymers, including, without limitation, acrylic polymers, contain acid groups that may be incorporated by polymerization of acid-containing monomers, especially carboxylic acid-containing monomers such as, without limitation, acrylic acid, methacrylic acid, crotonic acid, maleic anhydride and the acid, maleic acid, to which it hydrolyzes; itaconic anhydride and itaconic acid; monoalkyl maleates, isocrotonic acid, vinylacetic acid, or other polymerizable acid monomers or anhydride monomers.
The monomers used to prepare the emulsion copolymer also include at least one group suitable for crosslinking. While the acid group that is used to electrodeposit the resin may also be used as a functional site for crosslinking, if the acid functionality is too high it may cause problems such as in deposition and/or increased viscosity of the emulsion. Preferably, another monomer having a crosslinkable functionality is copolymerized in forming the emulsion copolymer. Alternatively, a crosslinkable functionality can be reacted onto the addition polymer. Suitable crosslinkable functionalities include, without limitation, hydroxyl, carboxylic acid, carbamate, and urea functionalities.
Useful hydroxyl-functional ethylenically unsaturated monomers include, without limitation, hydroxyethyl methacrylate, hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, hydroxybutyl acrylate, hydroxybutyl methacrylate, vinyl acetate (which hydrolyzes to the alcohol), the reaction product of methacrylic acid with styrene oxide, and so on. Preferred hydroxyl monomers are methacrylic or acrylic acid esters in which the hydroxyl-bearing alcohol portion of the compound is a linear or branched hydroxy alkyl moiety having from 1 to about 8 carbon atoms.
The monomer bearing the crosslinkable functional group such as a hydroxyl group and the monomer bearing the acid group for salting may be polymerized with one or more other ethylenically unsaturated monomers. Such monomers for copolymerization are known in the art. Illustrative examples include, without limitation, alkyl esters of acrylic or methacrylic acid, e.g., methyl methacrylate, ethyl acrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate, isopropyl acrylate, isopropyl methacrylate, butyl acrylate, butyl methacrylate, isobutyl acrylate, isobutyl methacrylate, t-butyl acrylate, t-butyl methacrylate, amyl acrylate, amyl methacrylate, isoamyl acrylate, isoamyl methacrylate, hexyl acrylate, hexyl methacrylate, 2-ethylhexyl acrylate, decyl acrylate, decyl methacrylate, isodecyl acrylate, isodecyl methacrylate, dodecyl acrylate, dodecyl methacrylate, cyclohexyl acrylate, cyclohexyl methacrylate, substituted cyclohexyl acrylates and methacrylates, 3,5,5-trimethylhexyl acrylate, 3,5,5-trimethylhexyl methacrylate, the corresponding esters of maleic, fumaric, crotonic, isocrotonic, vinylacetic, and itaconic acids, and the like; and vinyl monomers such as styrene, t-butyl styrene, alpha-methyl styrene, vinyl toluene and the like. Other useful polymerizable co-monomers include, for example, alkoxyethyl acrylates and methacrylates, acryloxy acrylates and methacrylates, and compounds such as acrylonit
BASF Corporation
Budde Anna M.
Mayekar Kishor
LandOfFree
Electrocoat coating composition and process for... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Electrocoat coating composition and process for..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Electrocoat coating composition and process for... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2581301