Chemistry: electrical and wave energy – Processes and products – Electrophoresis or electro-osmosis processes and electrolyte...
Reexamination Certificate
1999-03-26
2001-02-20
Mayekar, Kishor (Department: 1741)
Chemistry: electrical and wave energy
Processes and products
Electrophoresis or electro-osmosis processes and electrolyte...
C204S500000, C204S505000, C524S415000
Reexamination Certificate
active
06190524
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to novel organosulfur bismuth compounds, cationic electrodepositable compositions containing organosulfur bismuth compounds as catalysts, and to the use of such cationic electrodepositable compositions in an electrodeposition process.
BACKGROUND OF THE INVENTION
The application of a coating by electrodeposition involves depositing a film-forming composition to an electrically conductive substrate under the influence of an applied electrical potential. Electrodeposition has gained prominence in the coatings industry because in comparison with non-electrophoretic coating methods, electrodeposition provides higher paint utilization, outstanding corrosion resistance, and low environmental contamination. Early attempts at commercial electrodeposition processes used anionic electrodeposition, where the workpiece being coated served as the anode. However, in 1972, cationic electrodeposition was introduced commercially. Since that time, cationic electrodeposition has become increasingly popular and today is the most prevalent method of electrodeposition. Throughout the world, more than 80 percent of all motor vehicles manufactured are given a primer coating by cationic electrodeposition.
Many cationic electrodeposition compositions used today are based on active hydrogen-containing resins derived from a polyepoxide and a capped polyisocyanate curing agent. These cationic electrodeposition compositions conventionally contain organotin catalysts such as dibutyl tin oxide and lead catalysts to activate cure of the electrodeposition composition. Because of cost and environmental considerations, the levels of these catalysts are kept low. However, low catalyst levels may lessen the cure response of a coating composition, providing weaker properties in the cured film than desired. Appearance of the cured film may also be adversely affected.
Schipfer et al. in South Africa Patent Application No. 93/2977 discloses the use of cationic electrodepositable coating compositions which contain catalysts that are salts of bismuth and carboxylic acids, in particular hydroxycarboxylic acids. The reference does not disclose the use of organosulfur bismuth compounds as catalysts in cationic electrodepositable compositions.
Karol et al. in U.S. Pat. No. 5,631,214 disclose the preparation of bismuth dialkyldithiocarbamates for use in lubricant compositions. The reference does not disclose organosulfur bismuth compounds of the type presently claimed, nor the use of such compounds as catalysts in cationic electrodepositable compositions.
Bismuth compounds such as bismuth hydroxy acids have been proposed as catalysts in aqueous electrodepositable compositions. See for example U.S. Pat. No. 5,670,441. However, such compounds are prone to hydrolysis, drastically lowering the pH of the electrodepositable composition making it more corrosive to iron pipes and pumps and yielding bismuth oxide which is insoluble and relatively ineffective as a catalyst.
Bossert et al. in U.S. Pat. No. 5,859,165 disclose the use of a metal catalyst in cationic electrocoating compositions. The metal catalyst is based on the reaction product of a metal, such as manganese, cobalt, zinc or bismuth, with a mercaptan or hydroxy mercaptan or an organic acid. Such catalysts are typically used in cationic electrocoating compositions in conjunction with organotin compounds, for example triorganotin compounds. Use of such metal catalysts is often avoided, however, due to the objectionable odor generated thereby.
It would be desirable to provide an electrodepositable composition which demonstrates acceptable cure response without loss of cured film properties or appearance and which contains catalysts that do not have the shortcomings of those of the prior art.
SUMMARY OF THE INVENTION
In accordance with the present invention, a composition is provided comprising a reaction product of (1) a bismuth compound; and (2) a heterocyclic compound having mercapto functionality. Also provided are an electrodepositable composition comprising the bismuth reaction products mentioned above in conjunction with (a) an active hydrogen-containing, cationic salt group-containing resin electrodepositable on a cathode and (b) a capped polyisocyanate curing agent; and to the use of these compounds in a method of electrodeposition using the electrodepositable composition. Pigment pastes containing the bismuth reaction products and a method of preparing these pastes are also provided.
It has been found that the above-described bismuth reaction products which comprise heterocyclic compounds containing mercapto functionality provide efficient catalytic activity (i.e., fast cure response at lower cure temperatures) when used in electrodepositable compositions with little or no objectionable odor.
Other than in the operating examples, or where otherwise indicated, all numbers expressing quantities of ingredients or reaction conditions used in the specification and claims are to be understood as modified in all instances by the term “about”. As used herein, in the specification and the claims, the term “polymer” is meant to include oligomers.
DETAILED DESCRIPTION
The compositions of the present invention comprise a reaction product of (1) a bismuth compound; and (2) a heterocyclic compound having mercapto functionality. Preferably, a molar excess of mercapto groups in the heterocyclic compound of (2) to bismuth in the bismuth compound of (1) is used. Most preferably, the molar ratio of mercapto groups in the heterocyclic compound of (2) to bismuth in the bismuth compound of (1) 2:1 to 3:1.
Suitable bismuth compounds include bismuth oxide, bismuth metal and bismuth salts of organic or inorganic acids, such as bismuth nitrate pentahydrate, and the like.
The heterocyclic compounds that may be used to prepare the composition of the present invention may be aliphatic or aromatic, mono- or polycyclic. The heterocyclic compounds contain mercapto, i. e., thiol (—SH) functionality. The heterocyclic compounds also preferably contain azole, including diazole, functionality. Suitable heterocyclic compounds include, inter alia, 5-amino-1,3,4-thiadiazole-2-thiol, 5-methyl-1,3,4-thiadiazole-2-thiol, 2,5-dimercapto-1,3,4-thiadiazole. Other heterocyclic mercapto compounds can be used such as 2-mercaptobenzimidazole, 2-mercaptobenzothiazole, and dimercaptodiphenylsulfide.
The compositions of the present invention may be prepared by combining the reactants in an aqueous or organic medium (or mixed media such as water and alcohol) and stirring for thirty to 210 minutes. Reaction temperatures may range from ambient to about 65° C. The reaction product precipitates from the reaction medium and is then isolated and washed. Optionally, a catalytic amount of an acid can be used to facilitate solution of the bismuth compound. The preferred acid is sulfamic acid. The amount of the acid can range from 0.01 to 1.0, preferably 0.05 to 0.5 equivalents based on bismuth metal content.
The compositions of the present invention are useful as catalysts in cationic electrodepositable compositions, minimizing or even eliminating the need for lead- and tin-based catalysts conventionally used in such systems. Such electrodepositable compositions comprise (a) an active hydrogen-containing, cationic salt group-containing resin electrodepositable on a cathode; (b) a capped polyisocyanate curing agent; and (c) the bismuth compositions described above.
The cationic resin of component (a) may be any suitable cationic resin known to those skilled in the art. It is preferably derived from a polyepoxide, which may be chain extended by reacting together a polyepoxide and a polyhydroxyl group-containing material selected from alcoholic hydroxyl group-containing materials and phenolic hydroxyl group-containing materials to chain extend or build the molecular weight of the polyepoxide. Such chain extension reactions may be conducted under typical conditions as known to those skilled in the art. The resin contains cationic salt groups and active hydrogen groups selected f
Anderson Lawrence G.
Kollah Raphael O.
Scott Matthew S.
Woodworth Brian E.
Altman Deborah M.
Mayekar Kishor
PPG Industries Ohio Inc.
Uhl William J.
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