Chemistry: electrical and wave energy – Processes and products – Electrophoresis or electro-osmosis processes and electrolyte...
Reexamination Certificate
1999-04-22
2001-02-20
Mayekar, Kishor (Department: 1744)
Chemistry: electrical and wave energy
Processes and products
Electrophoresis or electro-osmosis processes and electrolyte...
C204S493000, C204S500000, C204S506000, C524S901000
Reexamination Certificate
active
06190525
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to improved coating compositions and, in particular, to electrodeposition baths containing a resinous phase dispersed in an aqueous medium, the resinous phase comprised of an ionic electrodepositable resin, a curing agent therefor, a source of yttrium; and to their use in the method of electrodeposition.
BACKGROUND OF THE INVENTION
Electrodeposition as a coating application method involves deposition of a film-forming composition onto a conductive substrate under the influence of an applied electrical potential. Electrodeposition has become increasingly important in the coatings industry because, by comparison with non-electrophoretic coating means, electrodeposition offers increased paint utilization, improved corrosion protection and low environmental contamination.
Initially, electrodeposition was conducted with the workpiece being coated serving as the anode. This was familiarly referred to as anionic electrodeposition. However, in 1972, cationic electrodeposition was introduced commercially. Since that time, cationic electrodeposition has steadily gained in popularity and today is by far the most prevalent method of electrodeposition. Throughout the world, more than 80 percent of all motor vehicles produced are given a primer coating by cationic electrodeposition.
Typically, electrodepositable coatings comprise an electrodepositable film-forming polymer and a curing agent, in combination with, inter alia, pigments. Lead-containing pigments such as lead silica chromate, basic lead silicate, lead chromate, and lead sulfate are often used in electrodepositable coatings because they impart excellent corrosion resistance to the electrocoated article. However, the acid used in cationic electrodeposition baths often solubilizes a portion of the lead pigment forming lead salts which are soluble in the aqueous phase of the electrodeposition bath. These lead salts often find their way into the ultrafiltrate of the bath, thus necessitating the removal and subsequent disposal of metallic lead and/or ionic or organic lead-containing materials.
In recent years, due to environmental concerns, particularly in Europe and Japan, the use of lead-free coatings has been mandated. Although surface coatings of excellent quality can be achieved by means of cationic electrodeposition of lead-free coatings, the removal of corrosion inhibitive lead pigments can result in reduced corrosion resistance of these coatings, particularly when applied to untreated or poorly pretreated steel substrates.
U.S. Pat. No. 4,789,441 discloses a metallic coating on a substrate applied by composite electrodeposition of a metallic matrix of nickel, cobalt or iron which contains particles of CrAlM
2
where M
2
is yttrium, silicon, or titanium. The composite electrodeposition metallic coating imparts corrosion resistance to substrates which are used in aggressive media and is particularly useful for coating gas turbine blades. This “coating” is completely metallic in nature and must be fused with the substrate at temperatures of greater than 700° C., preferably over 1100° C. in order to achieve diffusion of the deposited metals into the substrate. Such coatings are unsuitable for general use in common industrial painting applications.
The use of yttrium to improve corrosion resistance of conventional organic coatings is not known in the art. Nor is the effectiveness of yttrium as a corrosion inhibitor in conventional, cationic electrodepositable coatings known. It, therefore, would be advantageous to provide a lead-free electrodeposition bath containing a yttrium source which provides improved corrosion resistance of the electrocoated metal substrates, especially untreated steel.
SUMMARY OF THE INVENTION
In accordance with the present invention, a coating composition comprising (a) an active hydrogen group-containing resin and (b) a curing agent having functional groups reactive with the active hydrogen groups of (a). The composition contains yttrium or a compound of yttrium in an amount of about 0.005 to 5 percent, preferably not more than 2.5 percent, and more preferably not more than 1.0 percent by weight of yttrium (measured as elemental yttrium) based on weight of total resin solids.
In a particular embodiment, the invention resides in an electrodeposition bath, having improved corrosion resistance, comprising a resinous phase dispersed in an aqueous medium. The resinous phase comprises the following components:
(a) an active hydrogen-group containing ionic electrodepositable resin, and
(b) a curing agent having functional groups reactive with the active hydrogen groups of (a). Yttrium or a compound of yttrium is present in the electrodeposition bath in an amount from about 10 to about 10,000 parts per million of total yttrium (measured as elemental yttrium) based on electrodeposition bath weight.
Also provided is a method of electrocoating a conductive substrate serving as a charged electrode in an electrical circuit comprising the electrode and an oppositely charged counter electrode which are immersed in an aqueous electrodeposition bath described above, and metallic substrates coated by the method.
DETAILED DESCRIPTION OF THE INVENTION
Generally, the electrodeposition bath of the present invention comprises a resinous phase dispersed in an aqueous medium wherein the resinous phase comprises the following components:
(a) an active hydrogen group-containing ionic electrodepositable resin, and
(b) a curing agent having functional groups reactive with the active hydrogen groups of (a), wherein the improvement comprises an electrodeposition bath containing yttrium present in an amount from about 10 to about 10,000 parts per million, preferably not more than about 5,000 parts per million, and more preferably not more than about 1,000 parts per million, of total yttrium (measured as elemental yttrium).
At levels lower than 10 parts per million total yttrium, based on electrodeposition bath weight, no appreciable improvement in corrosion resistance of the electrocoated substrate is observed. At levels of yttrium greater than 10,000 ppm stability and application characteristics of the electrocoating bath compositions can be negatively effected.
Both soluble and insoluble yttrium compounds may serve as the source of yttrium in the electrodeposition baths of the invention. Examples of yttrium sources suitable for use in the lead-free electrodeposition bath of the present invention are soluble organic and inorganic yttrium salts such as yttrium acetate, yttrium chloride, yttrium formate, yttrium carbonate, yttrium sulfamate, yttrium lactate and yttrium nitrate. When the yttrium is to be added to an electrocoat bath as an aqueous solution, yttrium nitrate, a readily available yttrium compound, is a preferred yttrium source. Other yttrium compounds suitable for use in the electrodeposition baths of the present invention are organic and inorganic yttrium compounds such as yttrium oxide, yttrium bromide, yttrium hydroxide, yttrium molybdate, yttrium sulfate, yttrium silicate, and yttrium oxalate. Organoyttrium complexes and yttrium metal can also be used. When the yttrium is to be incorporated into an electrocoat bath as a component in the pigment paste, yttrium oxide is the preferred source of yttrium.
Besides the aforementioned yttrium compounds, the electrodeposition baths of the present invention also contain, as a main film-forming polymer, an active hydrogen-containing ionic, preferably cationic, electrodepositable resin. A wide variety of electrodepositable film-forming polymers are known and can be used in the electrodeposition baths of the invention so long as the polymers are “water dispersible,” i.e., adapted to be solubilized, dispersed or emulsified in water. The water dispersible polymer is ionic in nature, that is, the polymer will contain anionic functional groups to impart a negative charge or, as is preferred, cationic functional groups to impart a positive charge.
Examples of film-forming resins suitable for use in anionic electrodeposition bath compos
Karabin Richard F.
Kaylo Alan J.
Altman Deborah M.
Mayekar Kishor
PPG Industries Ohio Inc.
Uhl William J.
LandOfFree
Electrodeposition baths containing yttrium does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Electrodeposition baths containing yttrium, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Electrodeposition baths containing yttrium will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2561283