Stock material or miscellaneous articles – Composite – Of polyamidoester
Reexamination Certificate
1999-03-18
2001-04-24
Short, Patricia A. (Department: 1712)
Stock material or miscellaneous articles
Composite
Of polyamidoester
C427S385500, C525S131000, C525S440030, C524S147000, C524S153000, C528S053000, C528S058000, C528S080000
Reexamination Certificate
active
06221494
ABSTRACT:
This invention generally relates to low VOC (volatile organic component) curable coating compositions used in automotive refinish applications and it more particularly relates two-pack reactive oligomer containing isocyanate coating compositions that cure under ambient conditions.
BACKGROUND OF THE INVENTION
A number of clear and pigmented coating compositions are utilized in various coatings, such as, for example, basecoats and clearcoats used in automotive refinish coatings, which are generally solvent based.
In repairing damage, such as dents to autobodies, the original coating in and around the damaged area is typically sanded or ground out by mechanical means. Some times the original coating is stripped off from a portion or off the entire autobody to expose the bare metal underneath. After repairing the damage, the repaired surface is coated, preferably with low VOC coating compositions, typically in portable or permanent low cost painting enclosures vented to atmosphere to remove the organic solvents from the freshly applied paint coatings in environmentally safe manner. Typically, the drying and curing of the freshly applied paint takes place within these enclosures. Furthermore, the foregoing drying and curing steps take place within the enclosure to also prevent the wet paint from collecting dirt in the air or other contaminants.
As these paint enclosures take up significant floor space of typical small autobody paint repair shops, these shops prefer to dry and cure these paints as fast as possible. More expensive enclosures are frequently provided with heat sources, such as conventional heat lamps located inside the enclosure to cure the freshly applied paint at accelerated rates. Therefore, to provide more cost effective utilization of shop floor space and to minimize fire hazards resulting from wet coatings from solvent based coating compositions, there exists a continuing need for low VOC fast curing coating formulations which cure under ambient conditions while still providing outstanding performance characteristics particularly mar-resistance and resistance to environmental etching.
One of the approaches used in addressing the foregoing involves utilizing a binder containing a linear or branched cycloaliphatic moiety-containing oligomer. However, these coating compositions disclosed in PCT Application U.S. 97/08179, cure at significantly high cure temperatures, in the range of from 120° C. to 150° C. Thus, a continuing need still exists for a low VOC coating composition that cures under ambient conditions.
STATEMENT OF THE INVENTION
This invention concerns an ambient curable coating composition comprising a binder, which comprises:
a hydroxyl component comprising a linear or branched cycloaliphatic moiety-containing reactive oligomer having a GPC weight average molecular weight not exceeding 3,000 and a polydispersity not exceeding about 1.7, said reactive oligomer having at least two hydroxyl groups, at least one of said hydroxyl groups on average being a primary hydroxyl group; and
a crosslinking component comprising an oligomeric crosslinker provided with at least two isocyanate groups wherein the ratio of equivalents of isocyanate per equivalent of hydroxyl groups is in the range of from 0.5/1 to 3.0/1.
This invention further concerns a process for producing a coating on the surface of a substrate, said process comprising:
mixing hydroxyl and crosslinking components of a binder of an ambient coating composition to form a potmix, wherein said hydroxyl component comprises a linear or branched cycloaliphatic moiety-containing reactive oligomer having a GPC weight average molecular weight not exceeding 3,000 and a polydispersity not exceeding about 1.7, said reactive oligomer having at least two hydroxyl groups, at least one of which on average being a primary hydroxyl group, and wherein said crosslinking component comprising an oligomeric crosslinker provided with at least two isocyanate groups wherein the ratio of equivalents of isocyanate per equivalent of hydroxyl groups is in the range of from 0.5/1 to 3.0/1;
applying a layer of said pot mix on said surface; and curing said layer under ambient conditions to form said coating on said surface of said substrate.
DETAILED DESCRIPTION OF THE INVENTION
As used herein:
“Two-pack coating composition” means a thermoset coating composition comprising two components that are stored in separate containers, which are typically sealed for increasing the shelf life of the components of the coating composition. The components are mixed just prior to use to form a pot mix, which has a limited pot life, typically few minutes, such as 15 minutes to 45 minutes to few hours, such as 4 hours to 6 hours. The pot mix is applied as a layer of desired thickness on a substrate surface, such as an autobody. After application, the layer dries and cures to form a coating on the substrate surface having desired coating properties, such as, high gloss, mar-resistance and resistance to environmental etching.
“Low VOC coating composition” means a coating composition that includes less than 0.6 kilograms of organic solvent per liter (5 pounds per gallon) of the composition, as determined under the procedure provided in ASTM D3960.
“High solids composition” means a coating composition having solid component of above 40 percent, preferably in the range of from 45 to 85 percent and more preferably in the range of from 50 to 65 percent, all in weight percentages based on the total weight of the composition.
“GPC weight average molecular weight” means a weight average molecular weight measured by utilizing gel permeation chromatography. A high performance liquid chromatograph (HPLC) supplied by Hewlett-Packard, Palo Alto, Calif. was used. Unless stated otherwise, the liquid phase used was tetrahydrofuran and the standard was polymethyl methacrylate.
“Polydispersity” means GPC weight average molecular weight divided by GPC number average molecular weight.
“(Meth)acrylate” means acrylate and methacrylate.
“Polymer particle size” means the diameter of the polymer particles measured by using a Brookhaven Model BI-90 Particle Sizer supplied by Brookhaven Instruments Corporation, Holtsville, N.Y., which employs a quasi-elastic light scattering technique to measure the size of the polymer particles. The intensity of the scattering is a function of particle size. The diameter based on an intensity weighted average is used. This technique is described in Chapter 3, pages 48-61, entitled Uses and Abuses of Photon Correlation Spectroscopy in Particle Sizing by Weiner et al. in 1987 edition of American Chemical Society Symposium series.
“Polymer solids” or “Binder solids” means a polymer or binder in its dry state.
The present invention is directed to a two-pack low VOC ambient curable coating composition that is particularly suited for use in automotive refinishing process. The composition includes a binder in an organic solvent. The amount organic solvent used results in the composition having VOC of less than 0.6 kilograms (5 pounds per gallon) and preferably in the range of 0.25 kilograms to 0.53 kilograms (2.1 pounds to 4.4 pounds per gallon) of organic solvent per liter of the composition.
The binder includes a hydroxyl and a crosslinking component. The hydroxyl component includes in the range of from 2 weight percent to 100 weight percent, preferably in the range of from 10 weight percent to 90 weight percent, more preferably in the range of from 20 weight percent to 80 weight percent and most preferably in the range of from 30 weight percent to 50 weight percent of a linear or branched cycloaliphatic moiety-containing reactive oligomer or a blend of such oligomers. The reactive oligomer is provided with a GPC weight average molecular weight not exceeding about 3000, preferably in the range of from 300 to 2000, more preferably in the range of from 500 to 1200. Applicants have discovered that if the molecular weight of the reactive oligomer exceeds 3000, the reactive oligomer becomes too viscous. As a result, larger amount of solvent is needed to pro
Barsotti Robert J.
Corcoran Patrick Henry
Jaycox Gary Delmar
Lewin Laura Ann
Deshmukh Sudhir G.
E.I. Du Pont de Nemours and Company
Short Patricia A.
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