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
1999-06-23
2001-06-26
Sellers, Robert E. L. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C502S170000, C525S176000, C525S438000, C525S533000
Reexamination Certificate
active
06251999
ABSTRACT:
CROSS REFERENCE TO OTHER PATENT APPLICATIONS
This patent application is filed on the same day as the patent application entitled “Color-Plus-Clear Composite Coating Composition Containing Tin Catalysts” (Anderson, et. al.)
The present invention relates to catalyst compositions. More specifically, to catalyst compositions that are useful in epoxy-based film-forming coating compositions containing polyacid curing agents.
Epoxy-acid coating compositions may be powder coating compositions or liquid coating compositions and are well known in the art. Typical examples of epoxy-acid coating compositions are described in U.S. Pat. Nos. 4,650,718; 5,196,485 and 5,407,707: Epoxy-acid coating compositions are useful as clear topcoats or colored basecoats in color-plus-clear coating systems and have become increasingly popular as original finishes on motor vehicles such as automobiles, trucks and motorcycles. Epoxy-acid coating compositions may be cured at elevated temperatures after being applied to a ware such as an automobile. Catalysts may be present in the epoxy-acid coating compositions to accelerate the cure of the coating. Typically, tertiary amines are used as catalysts; however, some organotin compounds may also be used as catalysts in these epoxy-acid coating compositions.
One particularly useful organotin catalyst is triphenyltin hydroxide, hereinafter referred to as “TPTOH”. A major problem associated with the use of TPTOH is the evolution of benzene during the curing process. Benzene is known to be environmentally undesirable and, as such, there are stringent regulations on the allowed amount of benzene released into the atmosphere from any given source. Because of the high volumes of air exiting typical automobile paint curing ovens and the relatively low levels of benzene evolved during the paint curing process, it is considered technologically and economically unfeasible to treat the exiting oven air for the removal of benzene.
The use of some organotin compounds as catalysts are known in the art. For example, U.S. Pat. No. 3,773,694 to Nakata, et al. discloses a polymerization catalyst for use in the polymerization of vicinal alkylene oxides, which is a reaction product of an organotin compound and an ester of an oxyacid of phosphorous or an acetyl derivative of (HO)
3
PO. It is known that automotive coating compositions containing phosphites may have poor exterior durability. Additionally, it is known in the art that compounds with P-O-C linkages, such as those disclosed in Nakata, are prone to hydrolysis which may lower the humidity resistance of coatings containing these compounds.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an organotin catalyst that is suitable for use in epoxy-acid coating compositions and that is effective at reduced concentrations, such that the coating compositions have good appearance, stability and durability, and evolve no, or extremely low levels of benzene during the curing process of the applied coating. By “extremely low levels of benzene”, it is meant less than 20 parts per million (hereinafter referred to as “ppm”).
It is another object of the invention to provide epoxy-acid coating compositions which have good appearance, durability and stability, and that evolve no, or extremely low levels of benzene during the curing process of the applied epoxy-acid coating composition.
These and other objects of the invention are achieved by the development of a tin carboxylate adduct which is useful as a catalyst in epoxy-acid coating compositions and which will generate no, or extremely low levels of benzene during the curing process of the coating in which it is used. The tin carboxylate adduct is comprised of the reaction product of (A) a compound with mono-, di-, or poly-carboxylic acid functionality and (B) an organotin compound containing one to three aryl groups and at least one halogen or hydroxyl group attached to the tin atom.
There is also provided an epoxy-acid coating composition, which incorporates the catalytic tin carboxylate adduct described above, having good appearance, durability and stability and which generates no, or extremely low levels of benzene during the curing process of the applied coating composition.
DETAILED DESCRIPTION OF THE INVENTION
The catalytic tin carboxylate adduct of the present invention is formed by the reaction of (A) a carboxylic acid functional compound having at least one carboxyl group and (B) an organotin compound having the general formula:
R
n
—Sn—Y
(4-n
)
where R is an aryl group, Y is a halogen or hydroxyl group, and n is an integer from I to 3. Suitable aryl groups include tolyl, napthyl, phenyl, and substituted phenyl such as 4-ethylphenyl, 3,5-dimethylphenyl, and 4-methoxyphenyl. Preferably, R is a phenyl group and Y is a hydroxyl group.
Preferably, the carboxylic acid functional compound used has the general formula:
R′(COOH)
m
where R′ is a mono, di or polyvalent alkyl or aryl radical and m is an integer from 1 to 4.
In the practice of this invention, the carboxylic acid functional compound may be a mono-, di-, or poly-carboxylic acid; however, dicarboxylic acids are preferred. Some nonlimiting examples of suitable carboxylic acids include isostearic acid, lauric acid, tridecanoic acid, myristic acid, palmitic acid, adipic acid, succinic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, dodecanedioic acid, terephthalic acid, isophthalic acid, phthalic acid, tetrahydrophthalic acid and hexahydrophthalic acid. A preferred dicarboxylic acid used in the practice of this invention is dodecanedioic acid. Additionally, the carboxylic acid functional compound may be an acid functional polymer such as an acrylic, polyester or polyurethane polymer containing at least one carboxylic group per molecule. Carboxylic acid functional polyesters and half-acid esters can be used which are based on the condensation of aliphatic polyols with aliphatic and/or aromatic polycarboxylic acids or anhydrides, or the reaction of aliphatic polyols and aliphatic and/or aromatic anhydrides, respectively. Examples of suitable aliphatic polyols include ethylene glycol, propylene glycol, butylene glycol, 1,6-hexanediol, trimethylol propane, di-trimethylol propane, neopentyl glycol, 1,4-cyclohexanedimethanol, pentaerythritol and the like. The polycarboxylic acids and anhydrides may include, terephthalic acid, isophthalic acid, phthalic acid, phthalic anhydride, tetrahydrophthalic acid, tetrahydrophthalic anhydride, hexahydrophthalic acid, alkylhexahydrophthalic anhydride, chlorendic anhydride and the like.
The organotin compound used in the practice of this invention may contain one to three aryl groups attached to the tin atom. Preferably, the organotin compound contains three aryl groups. Suitable, but nonlimiting examples of organotin compounds include triphenyltin hydroxide, tritolyltin hydroxide, triphenylchlorotin, triphenylbromotin, tritolylchlorotin, tritolylbromotin, tris-4-ethylphenyltin hydroxide, tris-3,5-dimethylphenyltin hydroxide, tris-4-methoxyphenyltin hydroxide and phenyltin trichloride. Preferably, the organotin compound is triphenyltin hydroxide.
The catalytic tin carboxylate adduct of the present invention is formed by reacting a carboxylic acid and an organotin compound, usually in an inert atmosphere. Typically, the mole ratio of carboxylic acid to organotin compound ranges from about 2:1 to 10:1, preferably from about 3:1 to 7:1. The reaction is normally carried out at elevated temperatures, preferably from about 120° C. to 160° C., more preferably from about 120° C. to 140° C. Preferably, the reaction is carried out in a nitrogen atmosphere at atmospheric pressure. When the organotin compound contains phenyl groups, a normal by-product of the reaction is benzene, which can be distilled off and removed from the reaction vessel. The reaction should be kept at elevated temperatures for a sufficient time to remove most of the benzene from the reaction product, typically from about 1 to 4 hours; however, longer or shorter times may be used.
It i
Barkac Karen A.
Humbert Kurt A.
Kamarchik, Jr. Peter
Rardon Daniel E.
Wozniak Mark E.
Altman Deborah M.
Miles Jacques B.
PPG Industries Ohio Inc.
Sellers Robert E. L.
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