Stock material or miscellaneous articles – Composite – Of silicon containing
Reexamination Certificate
2000-06-30
2002-08-06
Dawson, Robert (Department: 1712)
Stock material or miscellaneous articles
Composite
Of silicon containing
C528S012000, C528S017000, C528S021000, C528S023000, C528S026000, C528S029000, C528S040000, C556S463000, C556S465000, C427S387000, C106S287120, C106S287130
Reexamination Certificate
active
06428898
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to low VOC (volatile organic component) curable coating compositions and more particularly relates to high solids coating compositions having low application viscosity, which are particularly suited for automotive finishes.
As the amount of the VOC from solvent based coating compositions permitted to be released in the atmosphere continues to drop, there is a continuing need for reducing the VOC content of solvent based coating compositions without attenuating their performance characteristics or the ease with which the coatings from these compositions can be applied over substrates. A number of approaches have been tried, one being to increase the solids content of the coating compositions without affecting the performance characteristics of the resultant coating, particularly the mar-resistance and environmental etch resistance.
One such approach, described in PCT Publication No. WO97/44402, is directed to a low VOC coating composition having a linear or branched cycloaliphatic moiety-containing oligomers which, upon cure, form a three-dimensional network having chains of substantially uniform, and controllable molecular weight between the crosslinks. The functionalized oligomers have weight average molecular weights not exceeding 3,000 and a polydispersity not exceeding 1.5. However, a need still exists for low VOC, high performance coating compositions that not only cure under ambient conditions or at elevated temperatures but are still easy to apply using conventional application processes, such as spray coating. The present invention solves the problem by reducing the application viscosity at high solids level without adversely affecting the performance characteristics of the resultant coating.
SUMMARY OF THE INVENTION
The present invention is directed to a curable coating composition comprising a binder, which comprises:
a silicon/hydroxyl component and a crosslinking component, said silicon/hydroxyl component comprising:
(I). A silicon/hydroxyl reactive oligomer having a linear or branched cycloaliphatic moiety and at least two functional groups with at least one of said groups being a silane or a silicate, the remaining groups being hydroxyl groups;
(II). A silicon reactive oligomer having a linear or branched cycloaliphatic moiety and at least two functional groups being a silane, silicate or a combination thereof, and a hydroxy acrylic polymer, a hydroxy polyester, a silicon free reactive oligomer having a linear or branched cycloaliphatic moiety and at least two hydroxyl groups, or a combination thereof; or
(III). A combination of said (I) and (II),
wherein said silicon/hydroxyl reactive oligomer, said silicon reactive oligomer and said silicon free reactive oligomer all having a GPC weight average molecular weight not exceeding 4,000 and a polydispersity not exceeding about 1.7; and
said crosslinking component comprising a blocked crosslinker or an unblocked crosslinker wherein said blocked or unblocked crosslinkers being provided with at least two isocyanate groups and wherein the ratio of equivalents of isocyanate per equivalent of hydroxyl groups is in the range of from 0.3/1 to 2.0/1.
One of the advantages of the coating composition of the present invention is its significantly low VOC content even at significantly high solids level.
The coating composition of the present invention advantageously provides for a highly crosslinked system at significantly low application viscosities.
Another advantage of the coating composition of the present invention is that it produces coatings having high performance characteristics, such as mar and etch resistance even at high gloss.
DETAILS OF THE INVENTION
As defined herein:
“Two-pack coating composition” means a thermoset coating composition comprising two components stored in separate containers. These containers are typically sealed to increase the shelf life of the components of the coating composition. The components are mixed prior to use to form a pot mix. The pot mix has a limited potlife typically of minutes (15 minutes to 45 minutes) to a few hours (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 is cured under ambient conditions or cure-baked at elevated temperatures to form a coating on the substrate surface having desired coating properties, such as high gloss, mar-resistance and resistance to environmental etching.
“One-pack coating composition” means a thermoset coating composition comprising two components that are stored in the same container. However, the crosslinker component is blocked to prevent premature crosslinking. After the application of the one-pack coating composition on a substrate, the layer is exposed to elevated temperatures to unmask the blocked crosslinker. Thereafter, the layer is bake-cured at elevated temperatures 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 then 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 87 percent and more preferably in the range of from 55 to 80 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 (GPC). 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. The sizer 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.
“Silanes” means the silicon compounds having the Si—C bond.
“Silicates” means the silicon compounds having the Si—O—C bond.
The present invention is directed to a low VOC curable coating composition that is particularly suited for use in automotive refinishing and OEM (original equipment manufacturer) process. The composition includes a binder in an organic solvent. The amount of organic solvent used results in the composition having a VOC of less than 0.6 kilogram (5 pounds per gallon), preferably in the range of 0.1 kilogram to 0.53 kilogram (1 pound to 4.4 pounds per gallon) and more preferably in the range of 0.1 kilogram to 0.4 kilogram (1 pound to 3 pounds per gallon) of an organic solvent per liter of the composition.
The binder includes a silicon/hydroxyl component and a crosslinking component. The silicon/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 the following:
I. A silicon/hydroxyl reactive oligomer having a linear or branched cycloaliphatic moiety and at least two functional groups. At least
Barsotti Robert J.
Hazan Isidor
Nordstrom John David
Dawson Robert
E. I. du Pont de Nemours & Company
Robertson Jeffrey B.
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