Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Adhesive outermost layer
Reexamination Certificate
2000-04-20
2004-02-10
Szekely, Peter (Department: 1714)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Adhesive outermost layer
C523S414000, C523S415000, C523S417000, C523S456000, C523S459000, C523S334000, C106S015050, C556S002000, C556S006000, C556S088000, C556S090000
Reexamination Certificate
active
06689459
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention is directed to a cathodic electrocoating composition and in particular to a clear non-pigmented cathodic electrocoating composition.
The coating of electrically conductive substrates by an electrodeposition process, also called an electrocoating process, is a well known and important industrial process. Electrodeposition of primers to automotive substrates is widely used in the automotive industry. In this process, a conductive article, such as an autobody or an auto part, is immersed in a bath of a coating composition of an aqueous emulsion of film forming polymer and acts as an electrode in the electrodeposition process. An electric current is passed between the article and a counter-electrode in electrical contact with the aqueous emulsion, until a desired coating is deposited on the article. In a cathodic electrocoating process, the article to be coated is the cathode and the counter-electrode is the anode.
Resin compositions used in the bath of a typical cathodic electrodeposition process also are well known in the art. These resins typically are made from polyepoxide resins which have been chain extended and then an adduct is formed to include amine groups in the resin. Amine groups typically are introduced through reaction of the resin with an amine compound. These resins are blended with a crosslinking agent usually a blocked polyisocyanate and then neutralized with an acid to form a water emulsion which is usually referred to as a principal emulsion.
The principal emulsion is combined with pigment, coalescent solvents, water, and other additives to form the electrocoating bath. The electrocoating bath is placed in an insulated tank containing the anode. The article to be coated is the cathode and is passed through the tank containing the electrodeposition bath. The thickness of the coating that is deposited on the article being electrocoated is a function of the bath characteristics, the electrical operating characteristics, the immersion time, and the like.
The resulting coated article is removed from the bath after a set period of time and is rinsed with deionized water. The coating on the article is cured typically in an oven at sufficient temperature to produce a crosslinked finish on the article.
Cathodic electrocoating compositions, resin compositions, coating baths and cathodic electrodeposition processes are disclosed in Jarabek et al U.S. Pat. No. 3,922,253 issued Nov. 25, 1975; Wismer et al U.S. Pat. No. 4,419,467 issued Dec. 6, 1983; Belanger U.S. Pat. No. 4,137,140 issued Jan. 30, 1979 and Wismer et al U.S. Pat. No. 4,468,307 issued Aug. 25, 1984.
There currently is a demand for electrocoating compositions that are clear and non pigmented. Such compositions have greater stability in the electrocoating bath since there are no pigments that can settle out. Improved bath stability allows the bath to be operated under higher temperatures and cooling is either not needed or significantly less cooling is needed which reduces energy cost for cooling the bath. Electrocoating composition that do not contain pigments are much easier to manufacture since pigment dispersions are not required to be separately formed as is done with conventional pigment. Pigment dispersions are relatively difficult to manufacture and are expensive. By eliminating the use of pigment dispersion, results in substantial savings in time and materials. Also, coverage per unit of coating composition is increased due to the removal of high density pigments.
There is a problem with formulating such a clear coating composition. Alkyl tin oxide catalysts such as dibutyl tin oxide are used in the composition to catalyze the reaction between the polyepoxide resin and the blocked isocyanate crosslinking agent. This catalyst is a solid that is not water soluble and conventionally is dispersed in water often with pigments and then added to the electrocoating composition. Having the catalyst dispersed in the electrocoating composition would not provide a clear composition when it is electrodeposited and the catalyst can settle out of the electrocoating bath. Both are undesirable. It would be desirable to formulate a clear coating composition having a water soluble catalyst.
SUMMARY OF THE INVENTION
An improved aqueous cathodic electrocoating composition having a binder of an epoxy-amine adduct which is an epoxy resin that has been reacted with an amine, a blocked polyisocyanate crosslinking agent and an organic or inorganic acid as the neutralizing agent for the epoxy amine adduct; where the improvement is a catalyst of an alkyl tin oxide that has been dissolved with an organic or inorganic acid to provide a clear cathodic electrocoating composition.
DETAILED DESCRIPTION OF THE INVENTION
The clear electrocoating composition of this invention is an aqueous composition having a solids content of 5-50% by weight of a principal emulsion of a cathodic film forming resin and a blocked polyisocyanate crosslinking agent, additives, and the like and the composition usually contains organic coalescing solvents and has a pH of 5.5-8.0. The composition contains 0.01-5% by weight, based on the weight of the composition, of an alkyl tin oxide dissolved by an acid in aqueous composition as the catalyst for the reaction of the film forming resin with the isocyanate.
Typical alkyl tin oxides that are used are dibutyl tin oxide, dipropyl tin oxide, diethyl tin oxide and the like with dibutyl tin oxide being the preferred because of its catalytic activity. The alkyl tin oxide is dissolved in the aqueous electrocoating composition with an organic or inorganic acid to form a water soluble salt. Typically useful acids are lactic acid, acetic acid, formic acid, sulfamic acid, alkane sulfonic acids such as methane sulfonic acid, ethane sulfonic acid and propane sulfonic acid.
The novel composition is a clear non pigment containing electrocoating composition that has all the advantages associated with clear coating composition. Storage stability and stability in the electrocoating tank are substantially increased since there is no pigment present that will settle out. The composition is less costly since pigment dispersion are not used which are relatively expensive and time consuming to manufacture and the composition has higher coverage since the density is lower in comparison to pigmented compositions.
The cathodic film forming binder of the principal emulsion used to form the cathodic electrocoating composition is an epoxy amine adduct and a blocked polyisocyanate crosslinking agent and is dispersed in an aqueous medium. The epoxy amine adduct is formed of an epoxy resin which preferably is chain extended and then reacted with an amine. Typical aqueous cationic electrocoating compositions are shown in DebRoy et al U.S. Pat. No. 5,070,149 issued Dec. 3, 1991 and the aforementioned U.S. Pat. Nos. 3,922,253; 4,419,467; 4,137,140 and 4,468,307.
The epoxy resin used in the epoxy amine adduct is a poly epoxy hydroxy ether resin having an epoxy equivalent weight of 100-2000.
Epoxy equivalent weight is the weight of resin in grams which contains one gram equivalent of epoxy.
These epoxy resins can be any epoxy hydroxy containing polymer having a 1,2 epoxy equivalency of two or more epoxy groups per molecule. The preferred are polyglycidyl ethers of cyclic polyols. Particularly preferred are polyglycidyl ethers of polyhydric phenols such as bisphenol A. These polyepoxides can be produced by etherification of polyhydric phenols with epihalohydrin or dihalohydrin such as epichlorohydrin or dichlorohydrin in the presence of alkali. Examples of polyhydric phenols are 2,2-bis-(4-hydroxyphenyl)ethane, 2-methyl-1,1-bis-(4-hydroxyphenyl)propane, 2,2-bis-(4-hydroxy-3-tertiarybutylphenyl)propane, 1,1-bis-(4-hydroxyphenol)ethane, bis-(2-hydroxynaphthyl)methane and 1,5-dihydroxy-3-naphthalene.
Besides polyhydric phenols, other cyclic polyols can be used in preparing the polyglycidyl ethers of cyclic polyol derivatives. Examples of other cyclic polyols are alicyclic polyols, particularly cycloaliphatic
Chung Ding-Yu
Liu Yuehua
Benjamin Steven C.
E.I. du Pont de Nemours and Company
Szekely Peter
LandOfFree
Clear cathodic electrocoating compositions does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Clear cathodic electrocoating compositions, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Clear cathodic electrocoating compositions will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3291539