Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2000-10-26
2003-01-28
Nutter, Nathan M. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S123000, C525S142000, C525S157000, C525S328200, C525S528000, C204S500000, C204S506000
Reexamination Certificate
active
06512048
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to coating compositions for use in cathodic electrodeposition coating processes and methods of cathodic electrodeposition. More particularly, the invention provides cathodic electrocoat compositions having a carbamate functional resin. The invention also provides methods of cathodically 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.
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 cathodic 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 cationic salting group, x represents 10 to 90 weight %, and y represents 90 to 10 weight %.
The invention further provides a cathodic 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 cationic salting 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 cationic salting group are reacted with an acid.
Finally, the invention provides a cathodic 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 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 comprises repeat units comprising at least one repeat unit having a pendant cationic salting group which is reacted with an acid, 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 an anode and the conductive substrate, and 3) removing the substrate from the coating composition.
DETAILED DESCRIPTION OF THE INVENTION
The polymer (a) of the invention will have at least one carbamate functional group appended to a polymer backbone, preferably a plurality of pendant carbamate functional groups. It is preferred, but not necessary, that the polymer backbone to which the carbamate functional group is appended be an acrylic polymer.
Polymer (a) of the invention can be prepared in a variety of ways.
One way to prepare such polymers is to prepare an acrylic monomer having carbamate functionality in the ester portion of the monomer. Such monomers are well known in the art and are described, for example in U.S. Pat. Nos. 3,479,328, 3,674,838, 4,126,747, 4,279,833, and 4,340,497, the disclosures of which are incorporated herein by reference. One method of synthesis involves reaction of a hydroxy ester with urea to form the carbamyloxy carboxylate (i.e., carbamate-modified acrylic). Another method of synthesis reacts an &agr;,&bgr;-unsaturated acid ester with a hydroxy carbamate ester to form the carbamyloxy carboxylate. Yet another technique involves formation of a hydroxyalkyl carbamate by reacting a primary or secondary amine or diamine with a cyclic carbonate such as ethylene carbonate. The hydroxyl group on the hydroxyalkyl carbamate is then esterified by reaction with acrylic or methacrylic acid to form the monomer. Other methods of preparing carbamate-modified acrylic monomers are described in the art, and can be utilized as well. The acrylic monomer can then be polymerized along with other ethylenically-unsaturated monomers, if desired, by techniques well-known in the art. In a preferred embodiment, at least one of the ethylenically unsaturated monomers will have a pendant cationic salting group.
As used herein, the term “cationic salting site” refers to a functional group which is sufficiently basic to undergo reaction with an acid to produce a salt, which, while in an aqueous dispersion in the presence of a voltage, will undergo decomposition and facilitate the formation of a insoluble polymer which deposits on a substrate immersed in the aqueous dispersion. Preferred cationic salting groups are amine functional groups and quaternary ammonium salts. The amine functional groups of the polymer (a) may be primary, secondary, tertiary amino groups or quaternary ammonium salts. Quaternary ammonium salts and tertiary amines are most preferred, with tertiary amine groups especially preferred. Such groups may also be part of polyamines and/or alkanol amines.
The cationic salting site can be incorporated into or grafted to the polymer backbone in a variety of ways.
For example, a carbamate functional acrylic monomer can be copolymerized with an ethylenically unsaturated monomer having at leas
December Timothy S.
Menovcik Gregory G.
Ohrbom Walter H
BASF Corporation
Golota Mary E.
Nutter Nathan M.
Tran Thao
LandOfFree
Cathodic electrocoat having a carbamate functional resin does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Cathodic electrocoat having a carbamate functional resin, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Cathodic electrocoat having a carbamate functional resin will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3042627