Color Stability of Olive Drab InfraredReflecting Camouflage Finishes E. E. JUKKOLI AND ROT COHEN 4ir ,\lateriel
Coni mand. Wright FirlrI, D a y t o n , Ohio pigrncn t 5 ere used to replace the carbon iii the pigmeiitation required to match t h e oliie drab color standards. Unsuitable pigments and pigment combinations contributed to poor color stability. Excessive chalking and poor durability of the finish appear to be caused by improper choice of pigment and high ratio of pigment to .rehicle. Infrared reflectanre a i not appreciably changed when measured twforr and after r\pmiire.
Infrared reflectance requirements for aircraft finishes necessitated changes i n pigmentation i n olive drab colors from t h a t previously used and resulted in materials with poor color stability on weather exposure. New formulations were evaluated for color stability by subjecting test panels to accelerated weathering tests in t h e laboratory a n d to six months of weather exposure a t JIianii, Fla. Extreme color changes were noted when organic darkening
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medium p t ~ 1 ;,:I, ; i I:md C U I C I ~ ~An . investigation was untlert :tken OR camouflage purposes, Army aircraft were finidicd in to determine tht. probable causes of these changes in order t o various colors t o blend with the background rvhen v i e w d cstnhlish ii means of determining the color stability properties of from enemy aircraft. T h e most common colors chosen for e:irtii camniiflnpc, m a t i ~ i ~ iini lx~d hy t h r d r m y Air Forces. background were olive drab, medium green, and sand. It KI? essential t h a t no great contrasts in color existed when observed visually or photographed by various means ( 2 ) . Figure 1 illu3I'Rk,t'\RiTIOY OF TEST PANELS trates differences achieved photographically on a model a i r p b n r 'l'esr Y:LIIII,I~- ui olive drab camouflage paint materials formufinished with a n olive drab color on t h e upper surfare- ovt-r :I l n t t d t o iiirlurl(~iiit'r:ivt.il r3~tIt~c.t3nrc~ requirements were requested mass background. T h e finish on the ltxft wing i y :in iiii'v.~rwifiom a number of manureflecting type of olive facturers. Twenty-one drab which corresponds dopes, tnenty-five lacto the grass in color in quers, and twenty-one infrared photography, enamels were submitted whereas, the remaining tor test and waluaolive drsb finish shows t ion. up dark. It v a s apStandard 5 X 16 inch parent t h a t an infraredmposure panels of alumireflecting material was num-surfaced aluminum desirable to conceal airalloy, Federal Specificacraft m o s t , effectively. tion QQ-A-362, were Accordingly, the specirleaned with alcoholic fications for aircraft phoqphoric acid aceordcamouflage finishes were ing t o U. S.Army Specirevised t o include a n infication 98-20007. One frared-refledng requirecoat of zinc chromate ment. pIimer, AAF specificaT h e adoption of intion 14080, was applied frared-reflecting type of over approximately half finishes eliminated the the width of the panel use of carbon black and and allowed t o air-dry other commonly used for 16 hours. The panels darkening pigments, and were then finished either the substitution of other with two coats of olive pigments resulted in condrab camouflage lacquer, siderable changes in color AA%F Specification 14105, stability, especially of or n-ith one coat of olive the olive drab. Esdrab camouflage enamel, ressive color changes and .%.lFSpecification 1.1109. chalking tendencies were Fabric-covered exponoted on weather exsure panels were preposure test panels which pared on wooden frames, had not previously been 16 X 16 inches, accordobserved with t h e noning t o Army-Savy heroFigure 1. (Above) 3Iodel Airplane with Olive Drab Camouflage infrared-reflecting olive Finish on Lpper Surfaces Photographed over Green Grass nautical Specification drab finishes. No such Background with Panchromatic Film; Finish on L e f t Wing AS-TT-C-516, General difficulty was experiand l a i l Surface Is Infrared Reflecting RIaterial. (Below) Same Specification (Methods enced with t h e revised Airplane Photographed with Infrared Film. Y
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I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
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for Sampling and Testing), by covering both sides with mercerized cotton airplane cloth conforming t o Specification AX-CCC-C-399. These panels wercb finished with two brush plus two spray coats of clear cellulose nitrate dope, .4XA Specification AS-7'1'D-514, plus two spray coats of the infrared-reflevtine olive drab camouflage dope, AAF Specification 14106. All the panels, bo'th fabric and metal, w jected t o six-month weather exposure a t Fla. The results of the durability test are listcd in Table3 I, 11, and I11 in which the more unstablc colors arc listed first for each type of material. The colors before and after exposure are described by Munsell color designations. Pigmentation, rhalking properties, and pigment-vehicle ratios nrtt , given for each sample. Similrtr panels were prepared of a number of the paint,s and subjected to a carbon-arc-accelerated test unit operating a t 50 volts * 2% and 60 arnpereb * 297, a t the arc. The temperature within the apparatus was controlled by the circ,ulation ai suffirient air to produce a black panel temperature of 145" * 5 " F. and with clean water striking the test panel a t a temperature of 60" * 10" F. in a fine spray under a pressure of 25-30 pounds per square inch for 15 minutes out of every hour. The panel& were examined periodically for color changes, anti the tests were continued for a total of 168 hours of cxposure. Evaluation of the resulting color changes is also included in Tables I, 11, and 111; in most cases the changes were similar to those obtained after 6-month Florida exposure (3). It had been noticed that a fen of the materials containinr organic pigments changed color on heating; there.fore, following the 168 hours of accelerated exposure test, all of the finishes were subjccted to 24hour baking a t 100" C. These color changes arc. also indicated in the tables. EFFECT O F VARIOUS CONSTITUENTS
The infrared reflectance values of these paint Inateriala were measured both before and after exposure and are listed in Table IV. It is evident that the change in infrared reflectance was very small for camouflage lacquer and enamel and I K I ~ determinable for camouflage dopes (6). Excessive color change of the finishee appeurs to be due in many cases to selection of unsuitable pigment combinations, but differences in types of vehicles used are indicated t o have affected the results also. The chalking tendencies, especially of dopes anti lacquers, can apparently be predicted from a knowledge of the type and proportions of pigments used and the pigment-vehicle ratio. T h e vehicle composition, especially of enamels, appears t,ci have a considerable effect on the chalking in some of the specification 14109 enamels of similar pigmentw tion and pigment-vehicle ratios. The vehicle of the Specification 14106 camouHage dopes given in Table I consisted of cellulose nitrate, plus chemical and oil plasticizers, excepr D-9, D-lo, D-12, and D-16 in which no oil plasticiari was used. Although an at,tempt has been made to arrange the pan& with the greater and more undesirable color changes fist as based on t,he color of washed areas of the panels, this order might be somewhat different. if the nolor oi
INDUSTRIAL AND ENGINEERING CHEMISTRY
September, 1946
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