972
I N D UXTRIAL A N D ENGINEERING CHEMISTRY Pigments
The next step was to vary the pigment combinations. Into 850 grams of plasticizers and gum solutions the folloming pigments were ground: A- 850 grams Titanox, 850 Keystone filler, and 170 talc B-1190 grams white lead, 1190 Keystone filler, and 170 talc C-1075 grams zinc oxide, 1075 Keystone filler, and 170 talc D-1190 grams Titanox, 1190 white lead, and 170 talc E-1075 grams Titanox, 1075 zinc oxide, and 170 talc F-1190 grams lithopone, 1190 Keystone filler, and 170 talc G-1190 grams silica, 1190 Keystone filler, and 170 talc
These bases were then thinned with l/n-second cotton solution, some additional gum solution, and reducer. Two panels, previously primed with oil primer and baked, were sprayed with two coats of each surfacer. The films were force-dried in an electric oven at 66" C. (150' F.) for 45 minutes. Both panels were sanded to a good surface. One stood in water overnight, while the other was sprayed with two double coats of lacquer and baked 48 hours in an oven a t 121" C. (250" F.). The next morning the panels which were stood in water u-ere cut with a knife, both above and below the water line, to ascertain their relative elasticity and adherence to the primer. All the surfacers were found t o stand a good water and knife test. The combination of Titanox and white lead and the combination of lithopone with Keystone filler all sanded well, while the silica with Keystone filler sanded very hard, and the zinc oxide with Keystone and Titanox with white lead sanded hard. The surfacer containing zinc oxide and Keystone cut the best, both above and below water, but it stood the bending
Vol. 19, No, 9
test poorly. On cutting after baking, the films gave a ribbon in the following order: A, F,B, C, E, D, and G. The bending test after baking gave the following order of results: D, A, F, B, E, C, and G. Panels coated with those surfacers made with the seven pigment combinations were sprayed over half the surface with two coats of blue finishing lacquer and exposed on the roof for about, 6 months. At the end of this time the surfacer made with white lead and Keystone showed the best, both with and without finishing lacquer over it. The combination of lithopone and Keystone was a close second. The combination of Titanox and white lead was the poorest, while the other combinations varied between these two extremes. Conclusions
1-A good lacquer surfacer can be manufactured on a burr stone mill. 2--A combination of oil, chemical plasticizer, and gum solution makes a good grinding medium. 3-A satisfactory lacquer for production work must stand a good water test. 4-Gum is essential for waterproofness, adhesion, and satisfactory rubbing properties. 5-Gums are satisfactory in the following order: shellac, dammar, ester gum, and kauri. However, a combination of dammar and ester gum may be used with satisfactory results. 6-Half-second cotton gives better results than cotton of higher viscosity reduced to '/rsecond viscosity. 7-Of all pigment combinations used, white lead and Keystone filler showed the best results after 6 months' outdoor exposure, both with and without finishing lacquer sprayed over the surfacer.
Uniform Varnish Films for Exposure Tests' By H. A. Gardner and G . G. Sward IKSTITUTE OF P A I N T A N D \ T A R X I S H R E S E A R C H , W A S H I N G T O N ,
w
HEN panels of any type are brush-coated with var-
nish, it is considered necessary to apply a t least two and preferably three coats in order to get a continuous film and one of sufficient thickness to give fairly good durability over a period of three months' exposure in the summer. It has been found, however, that various operators working with the same varnish may apply films of marked variation in thickness. Naturally, when exposed the durability of such panels would vary. It was thought that much more uniform results could be obtained if the various operators would use some uniform method of preparing films. The writers, for their own work, have standardized upon one-coat films which are spun upon revolving disks. The apparatus consists of a 12-inch (30-cm.) circular spinning table, set within a drain pan 18 inches (46 cm.) in diameter and 8 inches (20 cm.) high to catch the varnish thrown off by centrifugal force. The power is furnished by a 0.1 horsepower motor. The speed of the apparatus is controlled by varying the size of the pulleys. Walker and Thompson2 have prepared films of paint and varnish by spinning on glass disks. They found that plastic 1 Received April 6, 1927. Presented under t h e title "Methods of Producing Uniform Films for Exposure Tests" a s a p a r t of t h e Symposium on Lacquers, Surfacers, and Thinners before t h e Section of Paint and Varnish Chemistry a t t h e 73rd Meeting of t h e American Chemical Society, Richmond, Va.,April 11 t o 16, 1927. 2 Proc. A m . SOC.Testing Materials, 22, Pt. 11, 464 (1922).
D.
c
materials, such as paint, gave films that were much thicker at the center than at the edge of a 25-em. disk. On the other hand, viscous materials, such as varnish, gave films varying but a few microns over the entire disk. For a study of many properties of the paint they decided that a speed of 300 r. p. m. maintained for 3 minutes produced the best results. No extensive study of varnish films was made. Pulsifer3 found that the thickness of a normal brush coat of a varnish could be expressed as F = (IOV N ) , where F equals the thickness in microns, V equals the absolute viscosity in poises at 25" C., and N equals the percentage of non-volatile matter in the varnish. For example, a varnish possessing a viscosity of 1.4 poises and a non-volatile percentage of 50 should give a film 32 microns thick. None of the above investigators attempted to control the thickness of the film by altering the conditions of preparation to suit the material under consideration.
+
Preparation of Films
I n view of the influence of the film thickness upon the results of most tests on varnish films, it was thought desirable to study the spinning method to learn if films of predetermined thickness could be prepared. The method was essentially the same as that of Walker and Thompson,2 but using, in8
Drugs, Ozls, Painls, 39, 354 (1924)
INDUSTRIAL A-VD ENGI NEERING CHEMISTRY
September, 1927
stead of glass disks, metal panels 6 by 12 inches (15 by 30 cm.) Two reasons exist for the change. The metal panels are cheaper and varnish films prepared by this method may be used for exposure tests. The varnishes were first flowed oveI the entire panel, which was then placed on the spinning device and spun for the desired time and a t the desired speed. If any uncoated portions were shown after flowing, they were immediately coated by the varnish as soon as the panel was spun. Five varnishes ranging in viscosity from 0.95 to 2.2 poises and from 40 to i o per cent non-volatile content were prepared. (Table I) Numbers 1, 3, and 5 comprise a series in which the viscosity is constant, and the per cent non-volatile is variable. Kumbers 2, 3, and 4 comprise a series in which the viscosity is variable and the per cent non-volatile is constant.
VARNISH
Table I-Properties of Varnishes PER CENT VISCOSITY hTON-VOLATILE Gardner-Holdt Scale 40 F 50 C-D
F
50
I
50 70
F
Poises 1.4 0.95 1.4 2.2 1.4
973
Table IV-Variation in Film Thickness with Viscosity (hlon-volatile of each, 50 per cent) THICKNESS AT INDICATED DISTANCEFROM CENTGR VARNISH VISCOSITY SPEED . 3 cm. 8 cm. 13 cm. Mean Poises R. 0. m. p P P B 31 31 33 32 2 0.95 215 38 35 38 37 3 1.4 215 4 2.2 215 61 60 59 60 2 3 4
0.95 1.4 2.2
290 290 290
25 29 44
26 29 43
26 29 43
26 29 43
2 3 4
0.95 1.4 2.2
375 375 375
22 26 40
23 25 39
21 25 38
22 25 39
of Film Thickness with Non-Volatile Percentage (Viscosity of each, 1.4 poises) THICKNESS AT INDICATED DISTANCE KONPROM CENTER VARNISH VOLATILE SPEED 3 cm. 8 cm. 13cm. Mean Per cent R.9 . m. P P Ir B 26 26 215 26 25 1 40 37 35 35 37 3 50 215 44 44 45 44 5 70 215
Table V-Variation
3 5
1
40 50 70
290 290 290
22 29 34
21 29 36
21 29 36
21 29 35
1 3 5
40 50 70
375 375 375
18 26 31
19 25 30
20 24 29
19 25 30
With these varnishes the following variables were studiedspeed of spinning, duration of spinning, viscosity of the varnish, and per cent non-volatile of the varnish. Three speeds were available-215, 290, and 3i.5 r. p. m. Three time intervals were selected-30, 60, and 120 seconds. All panels were prepared a t 25" C.
cn 60
z
2
-
0
Measurement of Film Thickness
2-40 m
m
After preparation and thorough drying of the films, the thicknesses were measured with an Xmes dial. The instrument may be read with a precision of *l micron. Measurements were made at distances of 3, 8, and 13 em. from the center of the panel, a t least two measurements being made at each distance. The variation in thickness at any specific distance from the center seldom exceeded 1 micron, and the variation over the entire panel was usually not more than 3 microns.
3 30
of Film Thickness with Speed of Spinning (Spun for 60 seconds) FILMTHICKNESSA T INDICATED DISTANCES FROM CENTER SPZED 3 cm. 8 cm. 13 cm. Mean
Table 11-Variation
VARNISH
R. p . m.
P
P
P
P
215 290 375
26 22
1s
25 21 19
26 21 20
26 21 19
2
215 290 375
31 25 22
31 26 23
33 26 21
32 26 22
3
215 290 375
37 29 26
35 29 25
38 29 24
37 29 25
4
215 290 375
61 44 40
60 43 39
59 43 3s
60 44 39
1
0 8 50
60 50
=-40 v,
2 30
W
0
0
E 2o
30
60 90 120
g 20 VISCOSITY, POISES
TIME, SECONDS
60
m z
8 50 0
0 2-40 co 30 x 020
5 40
vi
cn
9 30
Y
0 20 I
P.M.
.PM .P M
c
I-
200 _. .
300 ~.
SPEED, R.P.M.
400 ..
C l40I 50i t 60m 70z 80u PER CENT, NON VOLATILE
The data obtained are presented in Tables 11, 111, I V , and V and graphically in the accompanying curves. An examination of the curves reveals that none of the functions, not even the viscosity or the percentage non-volatile, is a straight line. Calculation of Film Thickness
i n Film Thickness with Time of Spinning (Speed, 290 r. p. m.) THICKNESS OF FILM AT INDICATED DISTANCES FROM CENTER TIME 3 cm. 8cm. 13cm. Mean Seconds U LL u U 30 27 29 31 29 60 25 26 26 26 120 23 23 22 23
Table 111-Variation
VARNISH 2
3
30 60 120
33 29 25
33 29 27
33 29 25
33 29 26
4
30 60 120
54 44 35
53 43 36
53 43 36
53 43 36
If the thickness is calculated according to Pulsifer's formula
(F
=
--),2
which is probably satisfactory for brushed
films, the results do not correspond in any regular manner with the writers' observed values for spun films. I n other words, there is no speed or time of spinning which yields a film comparable with a brush coat for varnishes varying widely in their properties. After some calculation, the best formula developed for calculating the thickness of spun films was F = 0.4N v4 3
+
+
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 120seconds0.9 Factors:For215r.p.m.1.3,375r.p.m.0.8;for30secondsl.l, VISPL-ON-VOLAFILMTHICKNESS
+
VARNISH
+
COSITY
Poises 1
1.4
TILE
SPEED
Per c e n t R.p . m. 40 215 290
0.95
50
50
Diff. P
30 23
+4
60
26 21 19
215
60
31
-1
290
30
32 29
26
-3
375 1.4
Calcd. P
290 290
3
Sec. 60
P
375
2
TIME Obsd.
60
60
26
60
22
120
23
290 375
30 60 120 60
37 33 29 26 25
215 290
60 60
44
373
60
215 290 290
60
18
24 22 19
35 30 27 24
+2 -1
-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.
5
1.4
70
35 30
35 28
Maximum deviation Mean deviation
U . S , Tech. Czrc. 306.
-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.
