I,VDUSTRIAL AND ENGINEERING CHEMISTRY
974
where
F = film thickness, microns iV = per cent non-volatile V = viscosity, poises
This formula gives values which d o not deviate much from those observed at 290 r. p. m. for 60 seconds. For speeds of 215 and 375 r. p. m., multiply the values for 290 r. p. m. by the factors 1.3 and 0.8, respectively. For times of spinning of 30 and 120 seconds, respectively, multiply the values obtained a t 60 seconds by the factors 1.1 and 0.9, respectively. The observed and calculated values are shown in Table VI. Films for Tensile Strength and Elongation Tests
I n preparing f i l m for the determination of tensile strength and elongation, tin-plate panels amalgamated with mercury are used. Upon such panels the coating- are poured, allowed to dry, and then stripped previous to cutting up into test pieces. The writers have now adopted the spinning device for the preparation of films of fairly uniform thickness upon such panels. After spinning to the desired thickness, the coating is allowed to dry and then is stripped. Very smooth films of the desired thickness are obtained.
Vol. 19, No. 0
are readily obtained. Similarly] linseed oil extension tests upon varnishes can be made by coating panels by this same process. It is believed that differences in results obtained by different operators with the kauri gum reduction test on varnishes are often due to differences in film thickness. Some may be thick and some may be thin. The use of the spinning method should greatly reduce such variations. Table VI-Observed a n d Calculated Film Thicknesses F = 0.4.V 1-4 3 at 290 r . p. m. and 60 seconds Factors:For215r.p.m.1.3,375r.p.m.0.8;for30secondsl.l, 120seconds0.9 VISPL-ON-VOLAFILMTHICKNESS V A R N I S H COSITY TILE SPEED TIME Obsd. Calcd. Diff. Poises Per c e n t R.p . m. Sec. P P P 1 1.4 40 215 60 26 30 +4 290 60 21 23 +2 375 60 19 18 -1
+
2
+
0.95
50
215
60
290 290
30
1.4
50
31
-1
-3
23 22
60
37 33 29 26 25
35 30 27 24
375
30 60 120 60
215 290
60 60
44
373
60
375 215 290 290 290
60
26
26
120
290
3
32 29
24 22 19
60
-2
-1 -3 -2
-3 -2 -2
22
-3
46
+2 0
Other Tests by This Method
Hickson4 refers to the preparation of panels coated with flat wall paints by the spinning process, and he has used these panels for the kauri gum reduction test to determine the elasticity of the applied product. Such a method can be highly recommended, as films of fairly uniform thickness 4 Paint Mfm ’ Assocn. U . S , Tech. Czrc. 306.
5
1.4
70
35 30
35 28
Maximum deviation Mean deviation
-2
+5 -2
Application and Formation of Lacquer Surfacers’ By F. W. Hopkins ~ I C R P HVARNISH Y Co., NEWARK, N J.
SATURE OF PIGamw-In the manufacture of surfacers with an oleoresinous vehicle, iron oxides, together with a certain percentage of fillers or extenders, have been found to be the best pigments. Practically the same pigments are used in the manufacture of lacquer surfacers. Red oxides of iron are best eliminated, for a t times they give a reddish speckled effect to the finishing lacquer enamel, especially noticeable if the lighter tints are used. This may be due to the use of a so-called bleeding pigment, or even a pigment of the non-bleeding type after fine sanding if precautions have not been taken to clean carefully. Some of the dust is stirred up by the air from the spray gun and settles in the undried lacquer enamel. Pigments high in magnesium silicate content should not be used, as they impart to the lacquer surfacer a very smooth, greasy character. A lacquer enamel applied over such a surface is liable to peel off, especially when a masking tape has been used over a freshly lacquered enameled surface. PERCEKTAGE OF PIGMENT-In the manufacture of a lacquer surfacer it is necessary to maintain a definite percentage of pigment, so that when the surfacer is reduced it will have good filling and building qualities. The customary reduction is approximately equal parts thinner and surfacer, or 100 per cent. REDUCTION IN THINNING-If the surfacer is overly pigmented, and reduced as usual, it may crack after application, 1 Presented under the title “Lacquer Surfacers” as a part of the Symposium on Lacquers, Surfacers, and Thinners before the Section of Paint and Varnish Chemistry at the 73rd Meeting ol the American Chemical Society. Richmond, Va., April 11 to 16, 1927.
producing a so-called crackled-finish effect over the primer, A lacquer surfacer reduced to excess will not fill sufficiently, and thus thinner will be sprayed and wasted, instead of pigment and binder. In this case, on rubbing the surfacer, it would be very easy to rub through into the primer. Unless the pigments are stirred thoroughly into the vehicle, a condition exists which may be identical either t o excess pigmentation or excess reduction, depending upon whether the surfacer is from the bottom or top of the can. Most of the complaints on lacquer surfacer would never have occurred had the operator mixed the material thoroughly. SPRAYNOZZLE ASD GUNMAsIPuLaTIos-The spray nozzle used in the application of the surfacer should be of medium size so that too much material will not be sprayed in one coat. I n manipulating the spray gun the operator should be careful to hold the gun about 8 to 10 inches from the surface which is being finished. If held any nearer the surface too much pigment may be deposited within a given area, and a crackled effect will probably result. Too great a distance will produce little more than spray dust. If a lacquer surfacer is not properly reduced or is overpigmented, or applied improperly, it may appear to produce a satisfactory surface, but after rubbing and the application of a lacquer enamel the surface will crack open. IDEAL SuRFacER-An ideal surfacer is, therefore, one which builds quickly, dries rapidly without indications of orange peel, and sands easily to a hard, non-porous surface of such character that lacquer enamels may be applied with perfect adhesion. Such a surfacer must be free from any pigments which bleed or discolor the lacquer enamel.
September, 1927
INDUSTRIAL A N D ENGINEERING CHEMISTRY
975
Protecting Wood with Aluminum Paint' By Junius D. Edwards and Robert I. Wray ALUMINUM C!OMPANY
OF AMERICA.N E W 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 t w o d i f f e r e n t times and tive measure of wood proso long as they maintain a reasonable degree of tested. In general, where tection. They state? 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 Aluminum paints or coatings made u p of a priming 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, a n d Thinners before the Section of Paint a n d Varnish Chemistry a t the 73rd Meeting of the American Chemical Society, Richmond, Va., April 11 t o 16, 1927. 2 Unpublished paper read before t h e Section of Pain!: a n d Varnish Chemistry of t h e 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 a n d 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 a n d 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. White paint No. 3--lithopone, zinc' oxide, inert-"40-40-20" formula. 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
