Chemistry: electrical and wave energy – Processes and products – Electrophoresis or electro-osmosis processes and electrolyte...
Reexamination Certificate
1998-12-21
2001-04-10
Gorgos, Kathryn (Department: 1741)
Chemistry: electrical and wave energy
Processes and products
Electrophoresis or electro-osmosis processes and electrolyte...
C204S492000, C204S476000, C204S493000, C204S495000, C204S498000, C105S287000, C105S287000
Reexamination Certificate
active
06214188
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to coating compositions for use in anodic electrodeposition coating processes and methods of anodic electrodeposition. More particularly, the invention provides anodic electrocoat compositions having a carbamate functional resin. The invention also provides methods of anodically electrodepositing a coating on a substrate using the coating compositions of the invention.
BACKGROUND OF THE INVENTION
Coating compositions are widely in use today which utilize a variety of cure mechanisms. Among these are anodic and cathodic electrodeposition coating compositions and methods.
During electrodeposition, an ionically-charged polymer having a relatively low molecular weight is deposited onto a conductive substrate by submerging the substrate in an electrocoat bath having dispersed therein the charged resin, and applying an electrical potential between the substrate and a pole of opposite charge, usually a stainless steel electrode. This produces a relatively soft coating of low molecular weight on the substrate. This coating is usually converted to a hard high molecular weight coating by curing or crosslinking of the resin.
One curing mechanism utilizes a melamine formaldehyde polymer curing agent in the electrodepositable coating composition to react with hydroxyl functional groups on the electrodeposited resin. This curing method provides good cure at relatively low temperatures (e.g., 132° C.), but the crosslinked bonds contain undesirable ether linkages and the resulting coatings provide poor overall corrosion resistance as well as poor chip and cyclic chip-corrosion resistance.
In order to address some of the problems with melamine-crosslinked electrocoats, many users employ polyisocyanate crosslinkers to react with hydroxyl functional groups on the electrodeposited resin. This curing method provides desirable urethane crosslink bonds, but it also entails several disadvantages. In order to prevent premature gelation of the electrodepositable coating composition, the highly reactive isocyanate groups on the curing agent must be blocked (e.g., with an oxime, lactam, or alcohol).
Blocked polyisocyanates, however, require high temperatures (e.g., 176° C. or more) to unblock and begin the curing reaction. The resulting electrocoats can also be susceptible to yellowing. Moreover, the volatile blocking agents released during cure can cause other deleterious effects on various coating properties, as well as increasing VOC. In addition, use of some the volatile blocking agents may give rise to environmental concerns. Finally, the volatile blocking agents account for significant and disadvantageous weight loss upon crosslinking.
There is thus a need in the art for electrodepositable coating compositions that can provide desirable urethane crosslink linkages, but avoid the problems that accompany the use of blocked polyisocyanate curing agents. In particular, it is desireable to provide a anodic electrodeposition coating composition capable of providing urethane linkages at low bake temperatures of 121° C. or less with decreased weight loss upon crosslinking, while being free of isocyanates and the volatile blocking agents used with isocyanates.
SUMMARY OF THE INVENTION
The foregoing objects are achieved with a polymer having a polymer backbone having appended thereto at least one carbamate functional group, the polymer represented by randomly repeating units according to the formula:
R
1
represents H or CH
3
, R
2
represents H, alkyl, or cycloalkyl, L represents a divalent linking group, A represents repeat units comprising at least one repeat unit having a pendant carboxylic acid group, x represents 10 to 90 weight %, and y represents 90 to 10 weight %.
The invention further provides an anodic electrocoat coating composition comprising an aqueous dispersion of a polymer (a) comprising a polymer backbone having appended thereto at least one carbamate functional group, said polymer (a) represented by randomly repeating units according to the formula:
R
1
represents H or CH
3
, R
2
represents H, alkyl, or cycloalkyl, L represents a divalent linking group, A represents repeat units comprising at least one repeat unit having a pendant carboxylic acid group, x represents 10 to 90 weight %, y represents 90 to 10 weight %, and (b) a compound having a plurality of functional groups that are reactive with said carbamate groups, wherein the repeat units A having a pendant carboxylic acid group are base-salted.
Finally, the invention provides an anodic electrodeposition method requiring 1) immersing a conductive substrate in a coating composition comprising, in an aqueous medium: (a) a polymer backbone having appended thereto at least one carbamate functional group, said first component represented by randomly repeating units according to the formula:
R
1
represents H or CH
3
, R
2
represents H, alkyl, or cycloalkyl, L represents a divalent linking group, A comprises at least one repeat unit having a pendant carboxylic acid group which is base-salted, x represents 10 to 90 weight %, and y represents 90 to 10 weight %, and (b) a compound having a plurality of functional groups that are reactive with said carbamate groups, 2) applying a voltage between a cathode and the conductive substrate, and 3) removing the substrate from the coating composition.
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Chemical Process and Technology Encyclopedia, ISBN 0-07-012423-X, p. 217, 1974, No Month Available.
BASF Corporation
Golota Mary E.
Gorgos Kathryn
Maisano J.
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