Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From aldehyde or derivative thereof as reactant
Reexamination Certificate
2000-08-09
2001-03-27
Truong, Duc (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From aldehyde or derivative thereof as reactant
C528S248000, C528S482000, C528S492000, C528S494000, C528S495000, C525S509000, C525S511000, C427S372200, C427S385500, C427S388300
Reexamination Certificate
active
06207791
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to low free formaldehyde and low N-methylol group containing melamine derived crosslinker compositions and to low formaldehyde emitting thermosetting coating compositions based on these crosslinkers compositions, which coating compositions can provide durable, substantially defect-free films upon curing. The low formaldehyde emitting thermosetting coating compositions in accordance with the present invention contain, in their broadest concept, a low free formaldehyde and low N-methylol group containing partially alkoxymethylated high NH (high imino) melamine crosslinking agent and a polyfunctional material containing functional groups capable of reacting therewith.
2. Description of Related Art
Currently, the majority of important industrial coatings include melamine-formaldehyde crosslinked liquid systems. Such liquid coatings which employ partially or fully alkoxymethylated amino resin crosslinkers are in general well-known to those of ordinary skill in the art, as exemplified by numerous references including, for example, U.S. Pat. No. 4,081,426, U.S. Pat. No. 4,101,520, U.S. Pat. No. 4,129,681, U.S. Pat. No. 4,243,705, U.S. Pat. No. 4,276,212, U.S. Pat. No. 4,330,458, U.S. Pat. No. 4,374,164, U.S. Pat. No. 4,433,143, U.S. Pat. No. 4,425,466, U.S. Pat. No. 4,873,298, U.S. Pat. No. 5,155,201, JP-A-51125102 and GB-A-2254328, all of which are incorporated herein by reference for all purposes as if fully set forth. These and other references disclose a wide variety of backbone resins, catalysts, additives and amino resin crosslinkers therefor including, for example, tris- and tetra-substituted melamines for coatings applications. The present invention is concerned with liquid amino resin crosslinkers and, in particular, with the alkoxymethyl substituted melamine derived crosslinkers.
A problem with melamine formaldehyde resins is that they emit formaldehyde during the curing process, creating potential health and safety hazards and environmental pollution problems. Because of the health, safety and environmental concerns associated with large scale use of compositions containing melamine-formaldehyde crosslinking agents, demand for lower formaldehyde emitting coatings has steadily increased in recent years providing an incentive to find a practical solution to the problem.
One common approach to solving this problem has been the use of low free formaldehyde containing melamine derived crosslinking agents. While employing low free formaldehyde crosslinkers has been generally helpful to some extent, the improvement has been modest because preparation of low free formaldehyde containing crosslinkers has been difficult and emission problems have persisted even when low free formaldehyde containing crosslinkers are employed. Surprisingly, formaldehyde emissions during cure are greater than the actual free formaldehyde levels present in the starting coatings compositions. The origin of the excess formaldehyde released during cure has not been completely elucidated to date and, as a result, the problem of formaldehyde discharge into the environment continues to concern the coatings industry.
It has now been surprisingly discovered, in accordance with the present invention, that formaldehyde emission levels of well-known melamine-formaldehyde crosslinked systems can be reduced by replacing the previous melamine formaldehyde crosslinkers with a certain class of low free formaldehyde, low N-methylol and relatively high NH group containing liquid alkoxymethylated melamine resins. Curable compositions containing these crosslinkers of the present invention cure rapidly under normal cure conditions to produce durable films without emitting unacceptably high levels of formaldehyde.
SUMMARY OF THE INVENTION
As indicated above, the present invention is a liquid, partially alkoxymethylated melamine crosslinker composition having from about 2.6 to about 4.6 moles of combined formaldehyde per mole of melamine, from about 1.4 to about 4.4 moles of alkyl per mole of melamine, from about 1.3 to about 3.4 moles of NH per mole of melamine, a free formaldehyde level of less than about 0.5 weight percent based on 100 percent solids, and an N-methylol level of less than about 6.0 weight percent, preferably less than about 5.0 weight percent, and more preferably less than about 4.0 weight percent, based on 100 percent solids.
The present invention is further a low formaldehyde emitting curable composition which, when cured, produces a formaldehyde emission of less than about 7.5 weight percent based on the weight of the crosslinker, comprising the above-described crosslinker of the present invention and a polyfunctional material reactive therewith. These compositions are rapid curing but do not emit unacceptably high levels of formaldehyde.
The present invention is still further a process for preparing the crosslinkers of the invention said process comprising the step of contacting a liquid partially alkoxymethylated melamine crosslinker and a reagent selected from the group consisting of an amino group containing compound and an etherification agent, as described in further detail below.
The present invention is still further a method of coating a substrate by applying onto a substrate the low formaldehyde emitting curable compositions of the invention and then heat curing the so applied coating.
Finally, the present invention is crosslinked film or coated article prepared by the above method of coating. Such crosslinked films possess good hardness, impact resistance and solvent resistance, and are substantially surface defect-free with desirable appearance characteristics such as gloss and lack of pinholes or blisters.
These and other features and advantages of the present invention will be more readily understood by those of ordinary skill in the art from a reading of the following detailed description.
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Bright John H.
Lawless Barry A.
Lees Robert G.
Lin Lon-Tang Wilson
Szita Jeno G.
Cytec Technologies Corp.
Pennie & Edmonds LLP
Truong Duc
LandOfFree
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