S. E. BECK, Holabird Ordnance Depot, Baltimore, RId. Two series of lusterless olive drab enamels were prepared; the extender or extender combination was varied in one series, and the pigment volume percentage of total solids in the other. Steel panels coated with the paints were exposed out of doors for one
year. Results indicate that all extenders studied are satisfactory and that pigment volumes exceeding 60 per cent of the total solids volume cause failure by fading and chalking. All work was done on an alkyd resin vehicle. the relation between pigment volume and durability. Thc. investigation was confined to alkyd resin base enamels. Spray-outs of the enamels were made on 4 X 12 inch, 20gage primed steel panels. The same primer was used througliout. Dry film thickness of the lusterless enamel coats ranged from 1.2 t o 1.8 mils. Duplicate panels were exposed in Baltimore at 45" t o the south for one year. The panel5 were returned to the racks following inspection, and further observations will be reported a t the end of the second year.
L
USTERLESS olive drab enamels used by the Army for painting equipment have much higher pigment contents than ordinary paints intended for outdoor use. The pigmentation consists largely of extenders. A typical material contains 43 per cent pigment by weight, corresponding to 47 per cent pigment by volume on total solids.bases. The pigment contains 80 per cent extenders by volume. I n enamels where the extender content is so high, extender performance assumes unusual importance. The total pigment content is also an important factor. I n general, the highest possible pigment volumes are used in lusterless enamels t o obtain freedom from gloss and to achieve the economy necessary in a highly competitive market. A project was undertaken t o determine, for lusterless olive drab finishes, the durability of various extenders and
EFFECTOFEXTENDER
A master lusterless drab enamel formula was used; and extenders of various types were incorporated on an equal pigment volume basis. Total solids was fixed a t 60 per cent by weight. The formula is shown in Table I. Fixed resin and color pigments were used in all materials t o
Photo by courtesy of U. S. Army Signal Corps.
594
INDUSTRIAL AND ENGINEERING CHEMISTRY
May, 1943
TABLB I. FORMULA FOR EXTENDER STUDY 7 -
Pigmentation-
% by vol. of total pigment
Hydrated yellow oxide Lamp black Chrome dium, c. yellow P. meExtender
13.6 3.3 3.5
79.6 100.0
TABLE
I
Formulation wt. 7%by of total paint
Solids Alkyd resin anhydride) (35% phthalic Total pigment Volatile (mineral spirits)
.GO. . . .,
vol. % by of solids total 53:3
46.7 100.0
40
100
11. EFFECTOF EXTENDER ON
595
no change on exposure; 35 to 48 per cent showed slight fading, and 50 to 70 per cent gave moderate to extensive fading, increasing directly with pigment volume. However, only panels from 60 to 70 per cent, inclusive, showed bad enough fading or chalking to be considered failures. Adhesion was satisfactory up to 60 per cent pigment volume; other factors, such as abrasion resistance, might affect the suitability of such a high pigment volume. Above 60 per cent, films were powdery, dry, and easily removed with the thumbnail. Howevei, even the 70 per cent pigment volume material adhered to the primer and showed no noticeable erosion or wearing through.
COLOR
RETENTION AND
CHALKINQ
RESISTANCE PANEL
EXTENDER Asbestine Asbestine 50%, CaCOa 50% Asbestine 50%, barytes 50% Asbestine 50410, diatomaceous silica 50% Asbestine 50%, silica 50% Asbestine 50%, slate flour 50%
Asbestine 50%, waterground mica 50% Asbestine 50%, china clay 50% CaCOs Barytes Diatomaceous silica Diatomaceous silica 50%, CaC03 50% Diatomaceous silica 50%, barytes 50% Diatomaceous silica 50%
silica 50%,
Diatomaceous silica 50%, slate flour 50%
EXTENDER
No.
Diatomaceous silica 50%, water-ground mica 60% Diatomaceous silica 50%, china clay 50% Silica
172
Slight chalking
1,2
Moderate chalking
1 2 1 2
Marked chalking and fading Moderate chalking Slight chalking No change Very slight chalking Slight chalking Moderate chalking Very slight chalking No change
EXPOSURE OBSERVATION Slight chalking No change Very slight darkening Very slight chalking Moderate chalking Slight chalking Moderate chalking Very slight chalking Slight chalking
No change Slight darkening and chalking Slight chalking No change Slight chalking Slight darkening, very slight chalking Moderate fading and chalking Slight darkening and chalking Moderate chalking Slight chalking, darkening
Slate flour Water-ground mica China clay Asbestine 331/a%, diatomaceous silica 33l/s%, CaCOa
1 2 1 1 2
331/a%
Asbestine 331/s%, diatomaceous silica 3 3 1 / ~ % , China clay 33I/a% Asbestine 40%, diatomaceous silica 40%, barytes 20% Slate flour 50%, china clay 50% Slate flour 50%, CaC03 50% Asbestine SO%, diatomaceous silica 30%, CaCOa
Moderate chalking and fading Very slight chalking Very slight chalking No change
1 2 1
2 1
2 L 2
1 2
EXPOSURE OBSERVATION
Moderate chalking Slight chalking No change Moderate fading Very slight chalking
10%
Diatomaceous silica SO%, asbestine 30%, CaCOs 10%
1 2
Slight chalking Slight darkening, ahalking
TABLB 111. FORMULA FOR PIGMENT VOLUME
obtain uniformity. Enamels were ground on a ball mill. Drier content (in per cent of resin solids) follows: 0.03 cobalt, 0.01 manganese, and 0.20 lead. Evaluations of duplicate panels are reported in Table I1 for each extender. Appraisals were made by the same operator and were based on visual appearance only. The results indicate that none of the extenders studied is so poor that it is necessary to omit it from formulations for lusterless olive drab enamel. Calcium carbonate appears to be the most desirable from the point of view of color retention and chalking resistance.
-Pigmentation-
--Formulation
% by wt. of total pigment Hydrated yellow oxide Lamp black Chrome yellow medium, c. P.
18
Asbestine Diatomaceous silica
38 26
Barytes
2 7
14 100
%by wt. of total paint
%by vol. of total solids
Solids Total pigment Alkyl resin (35’3’ hthalic anhGd2de)
60 .... ..
100--0
Volatile (mineral spirits)
40 -
... -0
100
100
EFFECT OF VOLUME OF PIGMENT
Materials used, conditions of grind, driers, etc., were the same as in the extender study. Pigment volumes are expressed on a total solids basis. A range from 20 to 70 per cent pigment volume was used, increasing in steps of 5 per cent between 20 and 40 and between 60 and 70, and of 2 per cent between 42 and 60. The general formula is shown in Table 111. Inspections were based both on visual appearance and mechanical film properties. No panel-by-panel description is necessary because of the uniform manner in which fading and chalking increased directly with pigment volume. With a pigment volume of 20 to 30 per cent there was practically
ACKNOWLEDGMENT
The author wishes to express his indebtedness to the Cook Paint and Varnish Company, the Ditzler Color Company, E. I. du Pont de Nemours & Company, Inc., the Enterprise Paint Manufacturing Company, the Pittsburgh Plate Glass Company, and C. K. Williams & Company for their cooperation in preparing the paints. TEIS report is based on laboratory findings and is presented only for ita technical interest. It is not to be considered in the light of an o5cial Government pronouncement, nor is adoption of any of these recommendations or formulas required of manufacturers dealing with the Government, directly or indirectly.
