September, 1927
I N D U S T R I A L A N D ENGINEERING CHEMISTRY
975
Protecting Wood with Aluminum Paint' By Junius D. Edwards and Robert I. Wray ALUMINUM C!OMPANY
OF AMERICA.NEW KENSINGTON, PA.
panels when exposed to a 95 t o 100 per cent saturated atmosaluminum pigment, as a protective medium for metals. phere for 14 days. Its use for protecting wood also has much merit. Two Moisture-Proofing Tests of the outstanding characteristics of an aluminum paint Table I gives comparative data o n the moisture-proofing film are its durability and high moisture-proofing power. The checking and cracking of wood as the result of rapid efficiency of three coats of aluminum paint and three coats changes in its moisture content are minimized by a moisture- of different types of white paints, as well as combinations of proof coating, such as aluminum paint, and the durable the white paints as top coats with aluminum paint, zinc character of the paint assures maintenance of the protection. dust paint, and red lead as primers. The moisture-proofing Dunlap and Browne, of the Forest Products Laboratory, efficiency obviously depends to an important extent upon have been so impressed with the importance of moisture- the thickness of the coating. I n painting small test panels it was difficult to regulate proofing efficiency as a facthe amount of paint applied tor in determining the effective value of a paint coatwith the desired precision. Data are presented in confirmation of the conclusions In the present case two pets ing on wood that they have of Dunlap and Browne t h a t paint coatings continue of panels were painted a t proposed it as a quantitato protect wood adequately against weathering only tive measure of wood prot w o d i f f e r e n t times and so long as they maintain a reasonable degree of tection. They state? tested. In general, where moisture-excluding efficiency, as measured by the the moisture-proofing effiDunlap method. The data indicate further t h a t The method to be discussed ciency of the duplicates was coatings having a moisture-excluding efficiency still is based upon the understandnot in close agreement, the ing that paint is used to prohigher than the traditional house paints afford m a one with the thicker paint tect wood against weathering. terially greater protection against wood weathering. The process of weathering, as coating showed the highest or coatings made u p of a priming Aluminum paints considered here, has nothing efficiency, although occacoat of aluminum paint covered by ordinary house to do with the action of fungi sionally there were discrepor other living organisms upon paints are highly impermeable to moisture, especially ancies not to be explained wood, but is attributed princieffective in preventing wood weathering, and very pally to the disintegrating i n t h i s 1%-ay. Although durable. effect of internal stresses set agreement between duphup in the wood a s a result of cates is not alwavs so close the fluctuating moisture cona s d e s i r e d , it [s believed tent of those portions exposed directly to the weather. Other factors, such as mechanical abrathat the averages are significant.
I
T IS natural to think of aluminum paint, wit11 its metallic
sion and photochemical conversion of cellulose to oxycellulose, doubtless play parts in the weathering process, but swelling and shrinking in response to changing atmospheric conditions are believed to take the leading part. Paint coatings protect wood against weathering by damping out extreme fluctuations in moisture content through their retarding action on the passage of moisture into or out of the wood. I t is not necessary for the coating to prevent the transfusion of moisture completely; it need only retard the movement. I t is impossible as yet to say precisely what degree of moistureretarding efficiency is required for the coating to furnish adequate protection from weathering; this will probably depend upon various extrinsic factors such as the species of wood and the climatic conditions. But, as will be seen, it is not necessary to fix the point exactly in order to apply the technic suggested herein to the comparison of the protective values of different paints when applied to wood.
The present writers have obtained additional data that support these views. Certain of these data, showing the effect of aluminum bronze powder in increasing the moistureproofing efficiency of oils and varnishes, have already been p r e ~ e n t e d . ~I n making these measurements, t,he method described by IIunlap4 has been employed and his paper should be consulbed for details. It is sufficient to say that the efficiency of a coating is determined by the relative aniounts of moisture absorbed by bare and coated birch Presented as a part of the Symposium on 1 Received April 1, 1927. Lacquers, Surfacers, and Thinners before the Section of Paint and Varnish Chemistry a t the 73rd Meeting of the American Chemical Society, Richmond, Va., April 11 to 16, 1927. 2 Unpublished paper read before the Section of Pain!: and Varnish Chemistry of the American Chemical Society a t Madison, Wis., May, 1926. 3 THISJ O U R N A L , 17, 639 (1925). ' I b i d . , 18, 1230 (1926).
T a b l e I-Moisture-Proofing PANEL No. COATING
1
2
3 4 5
6
7 8 9 10 11 12
3 coats aluminum paint 1 coat aluminum paint, paint No. 1 1 coat aluminum paint, paint No. 2 1 coat aluminum paint, paint h'o. 3 1 coat zinc dust Daint. paint h-0. 1 1 coat zinc dust paint, .
naint = ----
No. .? -
I
2 2 2
2 2
Efflciency of Various P a i n t s 1Sl 2ND SERISS SERIESAVERAGE P e v cent Per cepit Per cent 89 90 90 coats white 79 '30 85 coats white 89 81 85 coats white 90 82 86 coats white 80 79 80 coats white 7..Q
R:, _-
en
vu
1 coat red lead, 2 coats white paint KO.1 69 76 72 1 coat red lead, 2 coats white paint No. 3 76: 75 76 3 coats white paint No. 1 79 72 76 3 coats white paint No. 3 79 83 81 Birch panel without coating 0 0 0 Birch panel without coating 0 0 0 Formulas of Paints U s e d (Percentages by weight) Aluminum paint: Standard varnish aluminum powder.. . . . . . . . . . . . . . . . . . . . . . . . . 21 Kettle-bodied linseed oil . . . . . . . . . . . . . . . . . . . . Mineral spirits and drier . . . . . . . . . . . . . . . . . . . . . . . . . . . 79 Zinc dust paint: z - inc oxide.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 I 7Y Zinc d u s t . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80 j Boiled linseed o i l . . . . . . . . . . . . . . . . . . . . . . . . . 82 21 Mineral spirits and drier . . . . . . . . . . . . . . . . . . . 1 8 1 . . Red lead paint: 79 D r y red lead (95 per cent PbaOn) . . . . . . . . . . . . . . . . . . . . . . . . . . . Raw and boiled linseed o i l , . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 Turpentine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . White paint No. 1-white lead, zinc oxide inert pnint--"55-35-10" formula. White paint No. 2-titanium oxide zinc oxide paint. formula. White paint No. 3--lithopone, zinc' oxide, inert-"40-40-20" The white paints were commercial paints purchased on the open market. ~~
No data are yet available on the effect of exposure on the moisture-proofing power of the coatings on the test panels
INDUSTRIAL A N D ENGINEERING CHEMISTRY
976
of Table I. However, a few measurements on aluminum painted and varnished panels of the same character, which had been exposed for one year, are given in Table 11. T a b l e 11-Moisture-Proofing Efficiency of Various C o a t i n g s f o r Wood a f t e r O n e Y e a r O u t d o o r s a t New K e n s i n g t o n , Pa. (Southern exposure, vertical suspension) AFTER I YEAR’S BEFORE EXPOSURE EXPOSURE COATING APPLIED(3 COATS) Pinea Birch Pinea Birch Per cent Per cent Per cent Per cent Aluminum paint made with spar varnish No. 1: AoDlied bv diooine 87 9 .1 91 RQ ._ __Applied b$ b;u’shiGg 85 92 77 90 Spar varnish No. 1 (dipped) 43 63 46 42 Spar varnish hTo.2 (dipped) 62 76 59 75 a Western yellow pine.
For comparison with the data of Table I, the moistureproofing efficiency of paint coatings on western yellow pine was measured after 18 months’ exposure. Samples were cut from large exposure panels and the back and cut ends coated with aluminum foil, in order to measure the moistureproofing efficiency of the coating on the exposed face only. A similar technic has been suggested by Dunlap and Browne. (Table 111) T a b l e 111-Moisture-ProoRng Efficiency of A l u m i n u m and W h i t e Paints a f t e r 18 M o n t h s O u t d o o r s a t New K e n s i n g t o n , Pa. (Southern exposure, 45-degree position) PANEL No. COATING’
Per cent
1 2 3
Aluminum paint made with kettle-bodied linseed oil Same a s on No. 1 Same a s on No. 1 4 Same a s o n No 1 Aluminum paint made with long oil varnish 5 6 Same a s on No. 5 White lead-zinc oxide paint (“55-35-10” formula) 7 Same a s on No. 7 8 Same a s on No. 7 9 Same a s on No. 7 10 11 Bare 12 Entirely coated with aluminum foil a Two coats on western yellow pine.
70 71
7i 57
83 81 11 8 24 16 0 100
Tables I1 and I11 show that the observed moisture-proofing power of any particular paint is lower on western yellow pine than on birch. The paint film itself doubtless has the same permeability on each wood, but the absorptive characteristics of the two woods differ. I n the case of the first tests given in Table 11, the bare (blank) western yellow pine panel absorbed 4.24 grams of water and the birch panel, 9.18 grams. The aluminum-painted panels absorbed about the same amounts of water-namely, 0.54 and 0.63 gram, respectively. However, the calculated efficiencies are appreciably different. 4.24
-
0’54 = 87 per cent and 9.18 - 0.63 = 93 per cent 9.18 4.24
Exposure Tests
For comparison with these moisture-proofing tests, exposure tests are given covering periods up to 3 years. H. A. Gardners has described a series of seventy test panels arranged to test the efficiency of aluminum paint as a protection for wood, and also its value as a primer under white paints. These tests were made on five different kinds of wood and with a variety of paints Mr. Gardner sent a duplicate set of panels to the writers, who exposed them in the “industrial atmosphere” of New Kensington. after 2 years’ exposure only a few of the panels were in good enough condition to be continued longer in the test. Table IV describes the condition of part of these panels after 2 and 3 years’ exposure. I n summarizing the results of these tests one point stood out above everything else. The five panels (51 to 55) which received three coats of aluminum paint made with heavybodied linseed oil showed no signs of wood weathering after 2 years’ exposure, and the paint films themselves were in 6
Paint Mfrs.‘ Assocn. U.S . . Tech. Circ. 231 ( A ~ r i l .1925).
Vol. 19, N o . 9
T a b l e IV-Paint T e s t s on Various T y p e s of Wooden P a n e l s (Exposed January 11, 1924, a t New Kensington, Pa.; southern exposure, 45-degree position) PANEL WOODA N D NO. P A I N T Nos.” CONDITION AFTER 2 YEARS 1 Moderate fine wood checking on upper half of panel; W-6-6-6 paint flaking above wood checks 2 W-1-6- 6 Wood sound; moderate paint checking 3 F-6-6-6 Slight checking of wood on upper half; moderate paint checking; rosin exudations 4 F-1-6-6 Wood sound; moderate paint checking; rosin exudation-
5
(2-6-6-6
6 7
C-1-6-6 Y-6-6-6
8 9 10
Y-1-6-6 R-6-6-6 R-1-6-6
11 12
W-3-3-3 W-1-3-3
13
F-3-3-3
14
F-1-3-3
15
c-3-3-3
16
C-1-3-3
17 18
Y-3-3-3 Y-1-3-3
19
R-3-3-3
20
R-1-3-3
21 22
W-2-2-2 w-1-2-2
23 24 25 26 27 28
F-2-2-2 F-1-2-2 c-2-2-2 c-1-2-2 Y-2-2-2 Y-1-2-2
29
R-2-2-2
30
R-1-2-2
51 52 53 54 55
W-4-4-4 F-4-4-4 c-4-4-4 Y-4-4-4 R-4-4-4
9 10 26
R-6-6-6 R-1-6-6 c-1-2-2
30
R-1-2-2
51 52 53
nr-4-4-4 F-4-4-4 c-4-4-4
Man fine wood checks over entire panel; paint flazing above wood checks Wood sound. moderate paint checking Wood check& very badly; paint scaling badly over entire Dane1 Mediumchecking of wood; moderate paint checking Wood sound; moderate paint checking Wood sound; moderate paint checking Wood checked badly. paint nearly all chalked off Many fine wood checks; top coats completely chalked off Considerable checking of wood; paint badly chalked; rosin exudations Slight checking of wood; top coats practically Fine chalked surface offchecking of wood; paint nearly all chalked off A few fine surface checks in wood; top coats of paint chalked off Wood badly checked. paint scaling and badly chalked Wood badly check6d; top coats all chalked off; orimer flakins Sli’ght checkingoof wood (edge grained) ; considerable chalking of paint Medium checking of wood (flat grained); paint flaking and chalking Wood badly checked; paint flaking badly Moderate number of fine wood checks; slight flaking of paint Wood badly checked; paint flaking badly Slight wood checking. moderate paint checking Moderate wood checking. paint flaking badly Slight wood checking. doderate paint checking Wood very badly checked, paint nearly all scaled off Wood badly checked; pa& flaking badly on summer wnoa
Wo’o-iiflat grain) very badly checked; paint flaking Wood and (edge checking grain) sound; moderate checking of paint Wood Wood Wood Wood Wood
sound; paint sound; paint sound; paint sound; paint sound; paint
sound sound; rosin exudation sound sound sound
CONDITION AFTER 3 YEARS Wood sound; considerable paint checking Wood sound; considerable paint checking Considerable wood checking; slight flaking of paint, considerable chalking Wood sound; paint shows moderate checking; top coats entirely chalked off
Wood sound; paint sound Wood sound; paint sound; some rosin exudation Wood checking in one small area over summer wood; paint cracked a t this point, otherwise sound condition 54 Y-4-4-4 One fine wood check about an inch long near top of panel, otherwise sound; paint coating sound condition 55 Wood sound; paint sound R-4-4-4 “ K e y to Numbers and Letters W-white pine; F-douglas fir; C-cypress; Y-yellow pine; Rredwood. Paint 30.I--Aluminum paint with spar varnish (diluted 2:l). lead-zinc oxide paint (50:50). Paint KO.2-White Paint No. 3-Titanox-zinc oxide paint (32). Paint No. 4-Aluminum paint with heavy-bodied linseed oil (diluted 3 %-turpentine). carbonate white lead paint. Paint No. 6-Basic Example: Panel W-1-6-6 is a white pine panel with a priming coat of aluminum paint No. 1 and two top coats of white lead paint No. 6.
sound condition without any sign of checking or chalking. Even after 3 years’ exposure their condition was excellent. The performance of the aluminum paint on the yellow pine was particularly noteworthy. No other paint combination gave adequate protection to the yellow pine. After 3 years’ exposure the protection of the yellow pine was almost perfect, there being but one very fine wood check on the panel, with the paint still in good condition. The panels having an aluminum primer with two top coats of white were, in general, better protected than similar panels having three coats of white. There were fifteen pairs of panels with and without the aluminum primer, and in twelve cases the aluminum primer
September, 1927
II1’DUSTRIAL AA’D ENGINEERING C H E M I S T R Y
was distinctly helpful in protecting the wood. In two cases there was no choice, and in one (19 and 20) the panel with the aluminum primer was distinctly worse, although the difference in the grain of wood could readily explain this. I n these exposure tests the paint coatings having the highest initial moisture-proofing efficiency proved the most durable and gave the best protection; these were the aluminum paint coatings. The next in order of moisture-proofing efficiency, as well as durability, were the combinations of a prime coat of aluminum paint with top coats of white. That aluminum paint may have high moisture-proofing efficiency after 18 months’ severe exposure is shown by other tests (Table 111), where there were observed values of 70 to 80 per cent. The white paint exposed a t the same time was badly deteriorated and the checking of the wood indicated failure in its moisture-proofing power, which according to the writers’ measurements was only about 10 to 20 per cent.
977
Heat-bodied (kettle-bodied) linseed oil, diluted with about 40 per cent mineral spirits or turpentine and with added drier, makes the most generally satisfactory vehicle for aluminum paint for protecting wood. Varnishes should only be used when they are exceptionally long in oil-say, an 80-gallon varnish, or better. Conclusion These tests show that moisture-proofing efficiency and wood protection go hand in hand. It is important also that relatively high impermeability be maintained if the protection is to continue. Checking and cracking of the wood resulting from failure of the moisture-proofing power of the paint film must accelerate the mechanical disintegration of the overlying paint film. Disintegration of the paint film further accelerates wood weathering, and so a vicious cycle is established. In a very practical sense, therefore, protected wood helps preserve the paint.
Dilution Ratios of Nitrocellulose Solvents‘ By J. G. Davidson and E. W. Reid CARBIDEA N D CARBONCHEMICALS CORPORATIOS, NEWYORK,N. Y.
A conti?zuatiovt
of previous work2 discussing, i i z addition to the usud aromztic hydrocarbon diluetits, a aumber of
experiments carried out xith uarious types of gasoliue.
T
HE dilution ratio of a nitrocellulose solvent is a measure of its solvent power and is obtained by dividing the
volume of diluent that must be added to cause incipient precipitation of the nitrocellulose by the volume of solvent in which the nitrocellulose is dissolved, or -‘Vd_ - D. R T 7n where Vd = volume of diluent Vn = volume of solvent
It therefore corresponds to the solvent-power numbers of Mardles,3 who defines them as “the volume of the liquid (diluent) in cc. required to begin precipitation from 1 cc. of a 5/100 concentration sol.’’ Determination of Dilution Ratios The dilution ratio (D. R.) will vary with the following factors: (1) solvent, (2) diluent, (3) temperature, (4) type of nitrocellulose, and (5) concentration of nitrocellulose. For the purpose of this paper variables (3) and (4) hare been eliminated by using the same type of nitrocellulose and by working with all solutions a t a temperature of approximately 20” C. The influence of variable (5) is described briefly a t the end of the paper. but with this exception all solutions from which data were derked contained the same concentration of nitrocellulose. The procedure was approximately the same as reported before,* although the concentration of nitrocellulose mas somewhat greater for these experiments. It consisted siniply in dissolving 2.5 grams of dry l/e-second nitrocellulose in 7.5 grams of solvent. After solution was complete the diluent was carefully added with vigorous stirring until precipitation of nitrocellulose was just evident. Some investigators maintain that results determined in this manner are subject t o error because the solutions become 1 Presented by J. G . Davidson under the title “Diluents and Dilution Ratios” as a part of the Symposium on Lacquers, Surfacers and Thinners before the Section of Paint and Varnish Chemistry a t the 73rd Meeting of the American Chemical Society, Richmond, Va., Aprll 11 to 16, 1927. 2 THISJOURNAL, 18, 669 (1926). 8 J . SOC.Chem I n d , 42, 129T (1923).
supersaturated and there is considerable lag in the appearance of the precipitate even though the true dilution ratio has been exceeded. In order to obtain a true measure of the solvent power it is proposed to start with nitrocellulose and a diluent to which mixture solvent is gradually added with stirring until the nitrocellulose just dissolves. Another advocated method involves the production of various mixtures of solvent and diluent. The solvent power of each mixture is determined and the composition of the mixture which is just able to dissolve the nitrocellulose is noted. The ratio of the diluent to true solvent in this mixture may also be called the dilution ratio. The authors have experimented with all three methods and find no great difference in the results. Certainly the relative rating of the various solvents by each method is the same. Results Table I shows that the ethers of the glycols have in general better dilution ratios than the butyl esters with respect to benzene, toluene, and xylene. Figure 1 expresses the same information in a graphic manner. The numbers in the tables and a t the bottom of the charts correspond with the numbers shown opposite the list of compounds below: KUMBER TABIX I 1 2 3 4 5 6 7 8 9
FOR
10
11
12 13 14 15 16 17
NUMBER CHARTS 1 1 2 2 3 3 4 5 5 6
FOR
Methyl ether of ethylene glycol Methyl ether of propylene glycol Ethyl ether of ethylene glycol Ethyl ether of propylene glycol Propyl ether of ethylene glycol Propyl ether of propylene glycol Isopropyl ether of ethylene glycol Butyl ether of ethylene glycol Butyl ether of propylene glycol Isobutyl ether of ethylene glycol Isobutyl ether of propylene glycol Isoamyl ether of ethylene glycol Isoamyl ether of propylene glycot Ethylene glycol monoethyl ether acetate Butyl acetate Secondary butyl acetate Butyl propionate, commercial
6
7 7 8 9 10
11
On the charts, the dotted lines represent the ethers of propylene glycol and the numbers refer to the same alkyl
