Water dispersible low-reflectance chemical resistance coating compostion

A water dispersible low-reflectance coating composition which is a CARC cosition and results in a coating that is flexible at ambient and sub-zero temperatures. The composition is a three component system, where the first component includes: hydroxyl-functional polyurethane, pigments, polymeric beads, emulsion of hydrophobic solids, micro-milled calcium carbonate, anti-settling agent, dispersing agent, water solvent, and non-ionic emulsion. The second component includes polyisocyanate and a solvent, while the third component is water solvent.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention generally relates to coating compositions and more 
specifically, to water dispersible low-reflectance chemical agent 
resistance coating compositions. 
2. Description of Prior Art 
Low observable coatings are materials developed to provide electro-optical 
signature reduction. There are four bands in the electromagnetic spectrum 
which enemy sensors can use to seek and detect targets. The current 
camouflage chemical Agent Resistant Coatings (CARC) addresses two of these 
bands: the visual and near infrared (IR). The three color woodland pattern 
and the desert tan match the visual effects of the background and, in the 
near IR, the green color matches the sharp reflectance rise of chlorophyll 
present in all green foliage. The first camouflage coating to combine the 
very low gloss in the visual with the chlorophyll tunnel requirements in 
the near IR appeared in the mid 1970s as MIL-E-52798, based on an oil 
modified polyester polymer. In 1985, CARC became the standard camouflage 
coating for the Army as: MIL-C-46168 (incorporated herein by reference in 
its entirety), based on a two component urethane consisting of a aliphatic 
diisocyanate and a saturated polyester. 
The basic camouflage topcoat required on all Army combat, combat support, 
and essential ground support equipment, plus tactical wheeled vehicles and 
aircraft is military specification MIL-C-46168. Among the many benefits of 
this coating is resistance to penetration of the paint film by chemical 
warfare agents. This results in an easier decontamination procedure or, in 
the absence thereof, a much more rapid return of equipment to service due 
to the natural environmental breakdown of agents. Additional benefits of 
the coating are a much longer service life before refinishing is required 
and improved resistance to corrosion. The Department of the Army (DA) 
required implementation in fiscal year 1985. Since then, in response to a 
variety of environmental regulations and worker safety issues, the 
original material has been found to not be environmentally acceptable. The 
prior art CARC coatings could not be applied in localities where the 
current compositions exceeds Volatile Organic Compound (VOC) limits. 
Flexibility of the applied coating had not been a major or critical 
element with respect to tactical type equipment. This resulted in 
subsequent CARC formulations that are satisfactory at ambient temperatures 
but have difficulty at zero and sub-zero temperatures. 
While the prior art has reported using low-reflectance coatings and CARC 
compositions, none have established a basis for a specific apparatus that 
is dedicated to the task of resolving the particular problem at hand. What 
is needed in this instance is a water dispersible low-reflectance coating 
composition which is a CARC composition and also results in a coating that 
is flexible at ambient and sub-zero temperatures. 
SUMMARY OF THE INVENTION 
It is therefore the object of the invention to provide a water dispersible 
low-reflectance coating composition which is a CARC composition and also 
results in a coating that is flexible at ambient and sub-zero 
temperatures. 
According to the invention, there is disclosed a water dispersible 
low-reflectance coating composition which is a CARC composition and 
results in a coating that is flexible at ambient and sub-zero 
temperatures. Polymeric beads provides for a composition that achieves a 
highly diffuse, low observable coating which eliminates the poor scratch 
and burnishing characteristics that is associated with prior art CARC. 
Since the polymeric beads are non-siliceous in composition, the three 
component formula will tend to provide a greater resistance to chalking 
and overall improvement to outdoor weathering than current coating 
systems. When active methanal condensate and polyurethane beads comprise 
the polymeric beads, there is imparted tremendous matting and reduction in 
gloss to the coating, yet less material by weight is required compared to 
formulas using siliceous type extenders of similar gloss values. This 
reduction in pigment solids reduces the overall pigment volume 
concentration (PVC) to binder ratio which improves the integrity and 
chemical resistance of the coating. 
The prime pigments are chosen for specific chroma, hue and saturation 
properties for the camouflage color desired. Certain pigments can simulate 
a desired reflectance curve detected in the near-IR region. The hydroxyl 
functional polyurethane dispersion and water dispersible polyisocyanate 
provide the necessary OH and NCO groups to provide a high performance 
polyurethane film. The polymeric beads are active flattening agents to 
impart low gloss and sheen. The remaining additives and modifiers are 
antisettling, leveling and antifoaming materials. The water is used for 
viscosity correction and application purposes.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION 
Referring now to the drawings, and more particularly to FIG. 1, there is 
shown a table depicting the three component generic formulation of the 
coating composition of the present invention. Polymeric beads provides for 
a composition that achieves a highly diffuse, low observable coating which 
eliminates the poor mar and burnishing characteristics that is associated 
with prior art CARC. Since the polymeric beads are non-siliceous in 
composition, the three component generic formula will tend to provide a 
greater resistance to chalking and overall improvement to outdoor 
weathering than current coating systems. This reduction in pigment solids 
reduces the overall pigment volume concentration (PVC) to binder ratio 
which improves the integrity and chemical resistance of the coating. 
The prime pigments are chosen for specific chroma, hue and saturation 
properties for the camouflage color desired. Certain pigments can simulate 
a desired reflectance curve detected in the near-IR region. The hydroxyl 
functional polyurethane dispersion (considered a polyester resin for the 
purposes of this invention) and water dispersible polyisocyanate provided 
the necessary OH and NCO groups to provide a high performance polyurethane 
film. The polymeric beads are active flattening agents to impart low gloss 
and sheen. A non-ionic high density polyethylene emulsion is also used. 
The remaining additives and modifiers are antisettling (sepiolite 
mineral), leveling and antifoaming materials. The water is used for 
viscosity correction and application purposes. 
The invention is illustrated in the following preferred embodiment in which 
all parts are by weight. It is understood that the invention is not 
limited to the specific embodiment disclosed. The low observable diffuse 
coating, which is comprised of 943 parts, is dispersed using a high speed 
mill and a grinding media such as sand and/or glass beads to aide in the 
dispersion process. Fifty percent parts by weight of the hydroxyl 
functional polyurethane dispersion is dispersed with 92.75 parts by weight 
of prime pigments to produce the required chroma, hue and saturation along 
with various flow and antisettling agents which comprise of less than one 
percent parts by weight of the total mixture. The remaining fifty percent 
parts by weight of the hydroxyl functional polyurethane is quickly 
dispersed into the prime paste with 4.1 percent parts by weight of an 
additional emulsion. Removal of the dispersion media with any suitable 
mesh and/or screening device permits the final components to be 
incorporated into the material. Active methanal condensate and 
polyurethane beads comprise the polymeric beads, which imparts tremendous 
matting and reduction in gloss to the coating, yet less material by weight 
is required compared to formulas using siliceous type extenders of similar 
gloss values. A combination of polyurethane urea material condensate with 
reactive methyl groups of 6.18 percent parts be weight, with the addition 
of 11.55 parts of water completes the first component of the three 
component mixture. 
The prime pigments Chrome Oxide, Colhalt Spinel, Magnesium Ferrite, and Red 
Iron Oxide are primarily for chroma, hue and saturation for a camouflage 
green. The cobalt and chrome oxide are specifically used to simulate the 
chlorophyll reflectance curve detected in the near-IR region. 
The second component is a blend of a solvent free water dispersible 
aliphatic polyisocyanate resin based on hexamethylene diisocyanate (HDI) 
where the NCO content ranges from 18.95 to 19.45 percent and which has an 
equivalent weight average of 220. The second components constitute 25.63 
percent parts by weight of the mixture where 75 parts of the HDI is mixed 
thoroughly with 25 parts of an appropriate solvent which when combined 
represent the second component. Finally, when component one and two are 
properly combined and dispersed, the final solvent, water, is slowly 
introduced and represents 141.53 parts by weight. Table 1 is a compilation 
of the formula of the example shown in parts by weight. 
TABLE 1 
______________________________________ 
TS BY WEIGHT 
______________________________________ 
COMPONENT I 
Raw Materials 
CHROME OXIDE GREEN 44.21 
COBALT SPINNEL 30.92 
RED IRON OXIDE 0.77 
CARBAZOLE VIOLET (DISPERSION) 
2.25 
MAGNESIUM FERRITE 9.68 
ACTIVE FLATTENING AGENT 
58.28 
(POLYMERIC BEADS) 
SOLVENT - DISTILLED WATER 
108.97 
VEHICLE - HYDROXYL FUNCTIONAL 
189.88 
POLYURETHANE 
DEFOAMER - EMULSION OF 1.18 
HYDROPHOBIC SOLIDS 
ANTI-FLOATING-MICRO- 1.49 
MILLED CALCIUM CARBONATE 
ANTI-SETTLING AGENT (6.0% solids) 
74.121 
DISPERSING AGENT 2.24 
EMULSION - NONIONIC EMULSION 
38.73 
35% SOLIDS 
ADHESION PROMOTER - 3.67 
MERCAPTOPROPYLTRIMETHOXYSILANE 
COMPONENT II 
POLYISOCYANATE 104.31-191.25 
SOLVENT - ALKYL ACETATE 
34.77-63.75 
COMPONENT III 
SOLVENT - DISTILLED WATER 
141.53 
TOTAL WEIGHT 943.11 
______________________________________ 
The function of the components and subcomponents of the invention behave in 
such a manner to provide chemical agent resistance and camouflage 
properties. The prime pigments Chrome Oxide, Colbalt Spinel, Magnesium 
Ferrite, Red Iron Oxide and Carbozle Violet are primarily for chroma, hue 
and saturation for a camouflage green. The cobalt spinel and chrome oxide 
are used specifically to simulate the chlorophyll reflectance curve 
detected in the near-infrared region. Polymeric beads may be of a urea 
methanal condensate type or any variety of polymeric or synthetic type 
which may be solid, pigmented, coated and/or vesiculated and range from 
.ltoreq.1 um to 100 um with respect to particle size distribution. 
The pigmentation of this invention may be changed or altered to account for 
specific camouflage applications and/or scenarios that may present 
themselves, therefore alternative formulations which are in accordance to 
this invention may be processed in a similar fashion. Exact chroma, hue 
and saturation of the respective colors may be found in the military 
specification entitled: "Coating Aliphatic Polyurethanes, Chemical Agent 
Resistant MIL-C-46168D(ME)", 21 May 1987, listed in Section 1.2.1 Colors, 
and more definitely in Table V titled Pigmentation. 
FIG. 2 is a table of color reflectance performance data and tristmulus 
values obtained for a coating of the composition of the preferred 
embodiment with various pigments. The tristimulus values and data provide 
an exact color space for each specified camouflage color and the allowable 
minimum/maximum of infrared reflectance for those colors. 
The wavelengths disclosed in the table of FIG. 2, under listed "Infrared 
Min." and "Infrared Max." are defined by selected ordinates for 
determining infrared and red reflectance values from spectrophotometric 
ordinates as follows in Table 2: 
TABLE 2 
______________________________________ 
Magenta 
Red Region Infrared Region 
Nanometers Nanometers 
______________________________________ 
620 .times. 1 720 800 
630 .times. 1 740 810 
640 .times. 2 760 830 
650 .times. 3 770 840 
660 .times. 3 780 860 
______________________________________ 
The ratio disclosed in the table of FIG. 2 under "Allowable ratio min." was 
calculated by dividing the value of the infrared by the value of the red 
spectral range. 
FIG. 3 is a table of spectra reflectance limit data obtained for a coating 
utilizing the composition of the preferred embodiment with pigments DARK 
GREEN 34082 and GREEN 383, 34094. The spectra reflectance curve from 
600-900 simulates the chlorophyll tunnel which background foliage such as 
grass, leaves, etc. generate. To remain undetected from near IR sensors, 
dark green and 383 green must conform to these reflectance minimum/maximum 
requirements. 
Specular gloss requirements for various pigmentation's would be as shown in 
Table 3: 
TABLE 3 
______________________________________ 
Dark Sandstone 33510, Sand 33303, 
Earth Yellow 33245 and Tan 33446: 
60.degree. 1.5 
85.degree. 3.5 
Other Camouflage Colors: 
60.degree. 1.0 
85.degree. 3.5 
Aircraft Green 34031 and 
Interior Aircraft Black 32031: 
60.degree. .5 
85.degree. 1.0 
Other Colors: 
60.degree. 3.0 
85.degree. 8.0 
______________________________________ 
Low reflectance type coatings, as defined for the purpose of the invention, 
must impart low gloss to remain undetected visually. This table defines 
maximum gloss limits for the particular colors listed. It should be noted 
that reflectance properties, gloss and tristimulus values given in 
preceding examples do not limit the invention in any way, and the coating 
in accordance to the invention may be formulated to exact specific 
end-user demands. 
Weathering performance of a resultant coating utilizing the composition of 
the preferred embodiment was conducted, where the source was a xenon 
light. Randomly selected commercial batch samples of two-component 
polyurethanes were provided as a comparative baseline. Samples were tested 
until they exceeded the 2.5 NBS color change limit currently used for 
two-component polyurethanes in MIL-C-46168. The resultant coating 
weathered for 2,400 hr and the standard weathered only 600 hr before 
failure in the Xenon Weather meter. The data suggests that the preferred 
embodiment is significantly more colorfast and weather resistant than 
standard control in an accelerated weathering test. The Xenon exposure is 
a current requirement for the current CARC material. 
Other properties include: outstanding flexibility in sub-zero conditions 
and excellent mar/abrasion resistance, hydrocarbon fluid, water and impact 
resistance. Therefore, the present coating would provide a more flexible 
environmentally compliant chemical resistant coating that can provide a 
basis for extended longevity of a coating system due to it's chemical 
resistance, ease in washability and it's exceptional durability with 
respect to mar and abrasion resistance. The composition may be applied to 
primed ferrous and nonferrous surfaces or composite type materials. The 
composition may also be applied to composite ferrous and non-ferrous 
substrates as a topcoat for camouflage purposes. It is understood that the 
invention is not limited to a specific substrate or level of coat. The 
properties of flexibility and mar resistance are unparalleled with respect 
to a coating that is chemical agent resistant. 
This resultant composition of the invention allows for an environmentally 
compliant water dispersible coating which can be applied in localities 
which the current CARC exceeds Volatile Organic Compound (VOC) limits. 
Current CARC is available at 3.5 lbs/gal. Most areas which have 
restriction are at 2.5-1.8 lbs/gal requirements. The current invention is 
from 4.0-1.5 lbs/gal. The composition of the present invention provides a 
material which can exceed all federal and local regulations resulting from 
the clean air act and it's amendments restricting the amount of VOCs may 
be applied with minimal restriction due to it's inherent formulation. 
The resultant coating using the composition of the invention provides a 
coating that endures a lower limit of -60.degree. F. (-51.degree. 
C.).+-.5.degree. F. on a 1/8" mandrel flexibility test according to ASTM 
D522 Method B--Cylindrical Mandrel Test without failure. The resultant 
coating provides a coating with gloss values of .ltoreq.1 unit at 
60.degree. gloss and .ltoreq.3.5 units at 85.degree. sheen and resist mar 
and burnishing while providing exceptional weathering resistance. The 
current water dispersible coatings formulations impart mar and burnishing 
resistance that far exceeds our present Mil Spec material. The current 
invention when tested according to MIL-C-46168D paragraph 4.3.22 is able 
to exceed the pass/fail criteria by a minimum of 400 cycles to a maximum 
of 800 cycles. 
While this invention has been described in terms of preferred embodiment 
consisting of a water dispersible low-reflectance coating composition, 
those skilled in the art will recognize that the invention can be 
practiced with modification within the spirit and scope of the appended 
claims.