Primer or solvent resistant protective coating

A novel coating composition is disclosed that is useful for primary resin based composition. The composition comprises an aqueous aliphatic polyurethane, an anionic surfactant and a carbon containing pigment.

BACKGROUND OF THE INVENTION 
When certain resin based compositions are exposed to solvents the resins 
may be adversely affected by the degradative effects of the solvent. In 
addition, there is a need for coating compositions that are capable of 
functioning as a so called primer for resin based, non-metallic alloy 
compositions. For example, automotive assemblies are made from various 
resin systems known as non-metallic alloys that require individually 
specialized painting systems. This procedure does not permit prior 
assembly of parts followed by a one-step painting operation. 
Examples of this problem are the use of a polyurethane reaction injected 
molding composition for an automotive fender and the use of sheet molding 
compound for the front hoods. These body parts cannot be painted at one 
time because of overspray. 
Other resin compositions such as the polycarbonates have exceptional 
properties that permit them to be used for applications, such as 
automobile bumpers, where they are likely to be exposed to aggressive 
hydrocarbon solvents. It is well known that aggressive solvents such as 
premium unleaded gasoline can adversely affect or completely destroy these 
resins. 
The applicant has discovered a composition which comprises an aqueous 
colloidal dispersion of an aliphatic urethane, an anionic surfactant and a 
carbon containing pigment that is thermally curable to a coating which 
adheres tenaciously to a wide variety of substrates. This coating can 
function as a primer for a subsequent painting step or will function as a 
solvent resistant protective coating. 
The use of this type of a composition which relies on surface adhesion is 
vastly different from currently used produces that rely on solvent 
"etching" to slightly degrade the surface of resinous materials to form 
bonding sites for the any coating that is subsequently applied. 
DETAILED DESCRIPTION OF THE INVENTION 
The composition of the invention comprises: 
(a) an aqueous colloidal dispersion of an aliphatic urethane prepolymer; 
(b) an anionic surfactant; and 
(c) a carbon containing pigment. 
The compositions include a carbon containing pigment volume content of 5-20 
and preferably 10-15 volume percent to impart electrostatic properties for 
use in connection with an electrically charged object. Suitable elemental 
carbon containing pigments include graphite or lampblack. Other film 
hardeners, pigments, dispersants, defoamers and the like may also be 
employed. The composition should have a pH of about 8.0 to 8.2 although 
this pH is not critical. 
The aqueous aliphatic urethane may be prepared using procedures that are 
described in the Encyclopedia of Polymer Science and Technology, Vol. II, 
pp. 555-558. Briefly these materials are prepared by reaction of a 
diisocyanate with a polyol or water. Suitable diisocyanates are of the 
formula OCN--R--NCO when R is an organic radical. Suitable R groups 
include (CH.sub.2)n, wherein n is an integer of from 1 to 8. Specific 
examples of the diisocyanates include hexamethylene diisocyanate; 
methylcyclohexene diisocyanate; lysine diisocyanate; 
bis(2-isocyanatoethyl) fumarate and bis(2-isocyanatoethyl) carbonate. 
A preferred aliphatic urethane is Neorez R-960 which is available from 
Polyvinyl Chemical Industries, 730 Main St., Wilmington, Mass. 01887. 
The particular anionic surfactant is not critical to the invention and 
various materials such as sodium lauryl sulfate, sodium alkyl sulfonates, 
alkyl aryl sulfonates, sodium 2,2-dinaphthyl-methane-6,6'-disulfonate and 
the like may be used. Other anionic surfactants are listed in McCutcheon's 
Detergents and Emulsifiers; 1979 Edition which is incorporated by 
reference. 
To impart resistance to polar solvents such as methanol, an additive to the 
base composition may be utilized which is a trifunctional aziridine 
compound, which is a derivative of ethyleneimine, having the formula: 
##STR1## 
This is available from Cordova Chemical Co., Sacramento, California under 
the tradename XAMA-7. 
The compositions of the invention preferably include from about 50 to 80 
parts by weight of a 20-40% by weight aqueous dispersion of an aliphatic 
polyurethane; froom about 0.5 to 5 parts by weight of the anionic 
surfactant and from 1 to 15 parts by weight of a pigment. The 
trifunctional aziridine may be added at from 0.5 to 5 parts by weight of 
composition, if desired. 
The compositions may be prepared by first combining the pigments in a ball 
mill with a portion of the aqueous aliphatic polyurethane to wet the 
pigments. After 1-24 hours of milling the balance of the aqueous aliphatic 
polyurethane is added so that the urethane is left significantly free of 
pigment wetting and is available to wet the substrate that is to be 
coated. Once the substrate is wetted, hydrogen bonding and Van der Waal 
forces from the urethane group can provide adhesion to the substrate as 
distinguished from solvent based compositions that degrade the resin 
surface and are substrate specific. These solvent based coatings 
inevitably weaken the resin substrate. 
The coating compositions of this invention will cure on a substrate at 
temperatures of from 25.degree. C. to about 93.degree. C. The aziridine 
containing compositions should be utilized within about 12 hours and the 
other compositions within two months. 
The coating compositions of the present invention can be applied to a 
variety of solid substrates by conventional methods, such as flowing, 
spraying or dipping, to form a continuous surface film. Substrates which 
are especially contemplated herein are metals and solid or foamed, 
transparent, as well as non-transparent, plastics, wood, and the like. 
More particularly, the plastics can be synthetic organic polymeric 
substrates such as acrylic polymers like poly(methylmethacrylate), 
polyesters, such as poly(ethylene terephthalate), poly(butylene 
terephthalate), etc., polyamides, polyimides, 
acrylonitrile-styreneacrylonitrile-butadiene copolymers, polyvinyl 
chloride, butyrates, polyethylene and the like. As noted above, the 
coating compositions of this invention are especially useful as coatings 
for polycarbonates, such as those polycarbonates known as LEXAN, sold by 
General Electric Company, and for polyphenylene ethers and compositions 
thereof such as NORYL, sold by General Electric Company. The metal 
substrates on which the present protective coatings are utilized include 
bright and dull metals like aluminum and bright metallized surfaces like 
sputtered chromium alloy, and treated metals, such as Bonderites. Other 
solid substrates contemplated herein include painted wood surfaces, 
leather, glass, ceramics and the like. 
A hard coating having all of the aforementioned characteristics and 
advantages is obtained by the removal of the solvent and volatile 
materials. The coating composition will air-dry to a tack-free condition, 
but heating in the range of 66.degree. C. to 93.degree. C., for 10 to 20 
minutes may be used to obtain final cure.

In order that those skilled in the art may better understand how to 
practice the present invention,the following examples are given by way of 
illustration and not by way of limitation. 
DESCRIPTION OF THE PREFERRED EMBODIMENTS 
EXAMPLE 1 
A composition is prepared by ball milling 1.16 parts of an anionic 
surfactant.sup.1, 14.05 parts by weight of 35% solids of an aqueous 
aliphatic polyurethane.sup.2 ; 0.37 parts by weight of lampblack 
(LB-1011.sup.3); 3.88 parts by weight of graphite in a steel ball and mill 
for 24 hours. The material is drained out, and combined with 4.62 parts by 
weight of water, 3.23 of amorphous silicon dioxide.sup.4 combined with an 
additional 67.02 parts by weight of the aqueous aliphatic polyurethane. 
FNT 1. Tamol 165, Rohm & Haas 
FNT 2. NeoRez R-960 is an aqueous colloidal dispersion of an aliphatic urethane 
having 34.+-.1 solids, a pH of 7.5-8.5 , a viscosity of 400-800 cps and a 
density of 8.8 lbs/gal. 
FNT 3. Pfizer 
FNT 4. Syloid 244 
The composition has the following components: 
Solids by weight 38.8% 
Solids by volume 32.5% 
Pigment volume content 13% 
pH 8.0-8.2 
Viscosity 90-95 KU's 
Shelf life 2 months 
This composition has the following properties set forth in Table 1 when 
coated and air dried on a Lexan brand polycarbonate composition. 
TABLE 1 
______________________________________ 
w/Lt. 
w/White Met Blue 
Primer 
PPG PPG 
Only "300" "300" 
______________________________________ 
Tape Adhesion (cross hatch 
then Scotch 710 tape pull) 
100% 100% 100% 
Heat Age (7 days at 70.degree. C. in 
air circulated oven) & 
Tape Adhesion 100% 100% 100% 
Water Immersion (24 hrs - 
Per ASTM D-870-54) 
Pass Pass Pass 
Heat Age & Water Immersion 
Pass Pass Pass 
Humidity (240 hrs-100% 
relative humidity at 39.degree. C.) 
Pass Pass Pass 
Heat Age & Humidity 
Pass Pass Pass 
Chip Resistance (Per SAE-J400, 
rated per GM standards) 
(1X) 9 8 7.+-. 
(10X) 8 7 7 
Heat Age & Chip Resistance 
9 7 7.+-. 
Humidity & Chip Resistance 
9 8 8- 
Detergent Resistance 
(Per GM Spec CMR-AA009) 
Pass Pass Pass 
Acrylic Cold Crack Cycle 
(24 hrs at 100% relative 
humidity at 38.degree. C., 20 hrs at 
-18.degree. C., 4 hrs at 23.degree. C., cycle 
repeated 15 times) 
Pass Pass Pass 
Stress Crack Resistance (psi) 
(Panel coated and baked on 
stress bar at given psi) 
&gt;3400* &gt;3400* &gt;3400* 
Gasoline Exposure.sup.1 
Stress During Coating (psi).sup.2 
2500 2500 2500 
Stress After Coating (psi).sup.3 
2500 2500 2500 
Impact Resistance (in lbs- 
Per Ford MD-BO 17-2 or GM 
CMR AA009) 
As is 431.3 361.2 356.7 
After Gasoline Exposure 
316.1 322.1 323.5 
______________________________________ 
.sup.1 Exposure to Amoco premium unleaded for 30 seconds, 15 minute 
recovery period while on stress bar at given psi, cycle repeated 10 times 
.sup.2 Panel coated and baked on bar of Lexan brand polycarbonate 
.sup.3 Panel coated and baked then placed on bar of Lexan brand 
polycarbonate 
This composition has excellent impact retention at -20.degree. F. following 
exposure to gasoline under stress on the surface of a polycarbonate 
composition using the following data impact procedure. It also has 
increased dry film conductivity for electrostatic application of the 
topcoat. 
EXAMPLE 2 
A modified composition was prepared by adding 3.0 parts by weight of a 
polyfunctional aziridine.sup.1 to the composition of Example 1. This 
composition is resistant to attack by polar solvents such as methanol. 
FNT 1. Xama-7 a polyfunctional aziridine derived from a 3:1 mol ratio of 
1,3-propane diol and aziridine. 
Obviously, other modifications and variations of the present invention are 
possible in light of the above teachings. It is, therefore, to be 
understood that changes may be made in the particular embodiments of the 
invention described which are within the full intended scope of the 
invention as defined by the appended claims.