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
1999-02-10
2002-03-05
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...
C523S415000, C524S555000, C525S528000
Reexamination Certificate
active
06353057
ABSTRACT:
INTRODUCTION
The present invention is directed to a method of catalyzing the process for de-blocking blocked isocyanates to form crosslinked coatings. More particularly, the present invention relates to the use of certain bismuth carboxylates that are effective in catalyzing both a solvent borne and a waterborne process to form such crosslinked coatings.
The bismuth carboxylates of the present invention are useful at a very low concentration of 0.05-0.5 wt % of metal based on the total resin weight and are highly effective. This is very desirable in that the emission into the environment of bismuth, a low toxicity metal, is reduced to very low levels.
BACKGROUND OF THE INVENTION
Blocked isocyanates have been used in many coating applications, such as powder coatings, electrocoatings, coil coatings, wire coatings, automotive clear topcoatings, stone chip resistant primers, and textile finishes. Traditionally, these coating processes employ organic solvents, which may be toxic and/or obnoxious and cause air pollution. In recent years, the legal requirements for low or no pollution of the environment have led to an increase in the interest in waterborne and high solids coatings.
In processes wherein blocked isocyanates are used, heating to an elevated temperature is necessary to remove the blocking group from the blocked isocyanate to form free isocyanates. The free isocyanates then react with polyols (polymers containing hydroxy functional groups) to form a crosslinked network as a thin film coating. An obstacle to the use of this process is the high temperature required to remove the blocking group. The process is extremely slow without a catalyst. It is known that metal compounds such dialkyltin and certain bismuth and zinc salts are excellent catalysts in these solvent borne coating processes. “Crosslinking with Polyurethanes.” W. J. Blank,
ACS Proceedings of Polymeric Materials Science and Engineering
(1990) 63:931-935.
Bismuth organo-compounds have been used in a variety of processes wherein polyisocyanates or blocked isocyanates is an ingredient. For example, EP 95-109602 describes an epoxide amine adduct with a bismuth compound as being useful in a conventional cationic coating process. U.S. Pat. No. 5,702,581 describes the use of organic bismuth complexes in phosphate dip coating compositions to provide corrosion resistance. The bismuth organic complexes include bismuth carboxylates, such as bismuth lactate. WO 95/29007 disclosed the use of bismuth compounds/mercapto complexes for curing polyisocyanate organic solvent compositions. The bismuth compounds disclosed include bismuth carboxylates, nitrates and halides. WO 96/20967 also described bismuth/zinc mixture with a mercapto complex as a catalyst for producing polyurethane. See also Frisch et al., “Novel Delayed-Action Catalyst/Co-catalyst system for C.A.S.E. Applications”, 60
Years Polyurethanes
, Kresta et al. ed., Technomic: Lancaster, Pa. 1998, pp. 287-303. Further, WO 95/08579 described bismuth/mercapto complexes as latent catalysts in a polyol-polyisocyanate adhesive system. The catalyst is described as useful in promoting the rapid cure of the system. The bismuth carboxylates described in these references are those wherein the carboxylate has ten carbons or less in the hydrocarbon structure. These conventional bismuth carboxylates do not provide improved resin performance nor are they effective in water-borne formulations.
WO 95/07377 described the use of bismuth lactate in cationic lacquer compositions, which employ urethane reactions. A mixture of bismuth and an amino acid or amino acid precursor was disclosed for catalyzing a cationic electrodeposition of a resin film on a metal substrate. The bismuth may be present in the form of nitrates, oxides, trioxides, or hydroxide. DE 19,532,294A1 also disclosed bismuth carboxylates as catalysts for single component polyurethane lacquer coatings in a solvent borne formulation.
Unfortunately, when the known bismuth catalysts are employed in waterborne coatings formulations, it was found that they were not effective. It is suspected that the loss of activity is related to the hydrolysis of the bismuth salt in water. Moreover, even if these compounds function as catalysts in waterborne processes, it has been our experience that a very high level is necessary, usually 10 to 100 times higher than in solvent borne processes. This is undesirable because bismuth has a low degree of toxicity and would cause environmental pollution if a large amount is released into the environment.
Bismuth carboxylates have been used as catalysts in processes that do not involve de-blocking of blocked isocyanates. Bismuth dimethylol propionate has been disclosed in DE 93-43,300,002 as being useful in an electrocoating process for coating phosphate dipped metals to provide anti-corrosion and weather resistance. Bismuth carboxylates are also described in DE 96-19,618,825 for use in an adhesive gel formulation that is safe for contact with human skin. The formulation contains polyether polyols with hydroxy groups, antioxidants, Bismuth(III) C
2
-C
18
carboxylates soluble in the polyether polyols and OCN(CH
2
)
6
NCO. JP 95-351,412 describes the use of bismuth neodecanoate as a catalyst for two part adhesive formulations containing polyisocyanates, polyols with an ethylenediamine. These formulations do not involve the de-blocking of blocked isocyanates.
For waterborne processes, the catalysts known to be useful are organo-tin and lead compounds. See WO 95/04093, which describes the use of organo-tin alone or in a mixture with other compounds including bismuth oxide in a low temperature curing process employing blocked isocyanates. There is no disclosure of bismuth carboxylates alone as a catalyst for de-blocking isocyanates. Organo-tin compounds have also been used in coatings, e.g. in paints for anti-fouling applications. Organo-tin compounds in mixtures with bismuth hydroxy carboxylic acid salt was described in DE19,613,685. The use of bismuth lower carboxylates was described as being useful in a phosphate dip process to provide corrosion resistance to lacquer coatings. The bismuth carboxylates described therein as being useful are lower carboxylate of bismuth wherein the carboxylic acid has up to ten carbons. The substrate is then coated with an epoxy resin in the presence of a blocked isocyanate as the crosslinking agent using a zinc organo compound and/or lead compound as the catalyst. EP0,509,437 disclosed a mixture of a dibutyltin aromatic carboxylate with a bismuth and a zirconium compound as the dissociation catalyst for electrocoating wherein a blocked isocyanate is used. Polystannoxane catalysts are also described in EPO,810,245 A1 as an low temperature catalyst for curing compositions comprising a blocked isocyanate. Bismuth compounds, including carboxylates were described as being useful as a co-catalyst. However, the process is one in which the reaction temperature was in the range of 100° C., quite a bit below the normal temperature of 120° C. to 150° C. for de-blocking blocked polyisocyanates. JP 94-194950 described a formulation for coating materials which are rapidly curable in contact with an amine catalyst vapor or mist. The coating formulation included polyols, polyisocyanates, antimony or bismuth catalysts with mercaptans in an organic solvent. The toxicity of both lead and tin compounds present serious environmental hazards The use of solvents in solvent borne processes further result in the undesirable release of toxic and obnoxious chemicals into the environment. For these reasons, the use of organo tin and lead compounds and solvents has been banned in many applications and is highly restricted in electrocoating.
It is, therefore, important to develop other catalysts or catalysts systems for waterborne processes.
SUMMARY OF THE INVENTION
Certain bismuth carboxylates have now been developed as effective catalysts for coatings processes wherein a temperature of at least 130° C. is used to de-block blocked isocyanate employed as the crosslinking agent. The bismuth carbox
Blank Werner J.
He Zhiqiang
Picci Marie E.
KIng Industries, Inc.
Morgan & Finnegan , LLP
Sellers Robert E. L.
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