INDUSTRIAL A N D ENGINEERING CHEMISTRY
732
Table IV-Accelerated
DEPTHO F SUPERNATANT PENETRATION TEST LIQUID Plunger Weight Time Cm. Grams Seconds 20 hours, 20 min.: 1.9 1 142 31 Oven, 18 hours 2 242 11 Centrifuge, 20 minutes 3 542 10 Room, 2 hours
RE-INCOR-
STANDARD CYcLEa
24 hours, 40 min.: Oven, 22 hours Centrifuge, 40 min. Room, 2 hours
3.6
43 hours: Oven, 40 hours Centrifuge, 60 min. Room, 2 hours
3.7
67 hours, 40 min.: Oven 64 hours Centhuge, 100 min. Room, 2 hours
4.0
1
342 542 1042
4 31
2 3
1
542 542 1042
1 2 3
1042 1042
68
2 3
Vol. 20, No. 7
T e s t Using Centrifugal Force a n d Heat (Flat Wall Paint C) PORATION
hfICROSCOPIC EXAMINATION OF SETTLED PIGMENT
TEST
Minufes 2
Top, flocculated; bottom, flocculated
Top, flocculated; bottom, small amount of dispersed material
2'/1
11 16 Incomplete penetration
Top, flocculated; bottom, flocculated with some apparently dry pigment
2'/a
6
Top, flocculated and lumpy; bottom, hard aggregates and dispersed pigment that appears dry
9
...
*.
a See footnote to Table 11.
accelerated cycle. Still, on comparison of the results of the penetration tests (ignoring the results on the sample of paint B which was tested after 8 months' storage and apparently falls somewhat out of line), one finds that each 24 hours of the cycle represents approximately 5 months' shelf storage. Several outside paints and enamels, which from previous observations were known not to develop settling even after several years of storage, were tested. No settling was ob-
5'12
(Formed lump, which dispersed very slowly)
tained in any case, after 7 days, when the tests were discontinued. Conclusion
The writers do not feel that either a perfected test or an ideal cycle has been submitted, but they do believe that the results obtained definitely demonstrate that a test applying heat and centrifugal force is an excellent tool with which the settling tendencies of a paint can be determined.
Settling of Pigments in House Paints
.
H. L. Beakes PEASLEE-GAULBERT Co., LOUISVILLE, KY.
0 STUDY the settling of pigments in house paints, single pigment paints were made up, using as the liquid 90 per cent taw linseed oil, 3 per cent drier, and 7 per cent mineral spirits. The pigments used were: zinc oxide (5 per cent leaded), sulfate white lead, Titanox, red lead (96 to 97 per cent), asbestine, silica, barytes, and china clay. Each of these pigments was ground separately. Two twopigment paints were also made up from the above pigments: (1) 50 per cent lead with 50 per cent zinc, and (2) 60 per cent red lead with 40 per cent asbestine. These paints were adjusted to the same consistency using the Gardner-Parks mobilometer,' the consistency being that of the customary white house paint. (Table I) All paints were filled into 10-gallon filler drums 31.11 by 53.34 cm. (12l/4 by 21 inches) and the container was filled full. Each drum was equipped with five openings from which samples could be drawn through 7-mm. (outside diameter) glass tubing. The tubing projected 89 cm. (3.5 inches) into the container. The five openings for sampling were arranged vertically, 10.16 cm. (4inches) from center to center. The working height of the drum inside was 50.80 cm.
T
1
Paint Mfrs. Assocn. U. S., Tech. Circ. 866. Table I-Mobilometer
WEIGKT ZINC SULFATE OXIDE WHITE RED ADDEDTO TITANOX LEAD PLUNQER(5% LEADED) LEAD
(20 inrhes). The lowest opening for sampling was 3.81 cm. (1.5 inches) from the bottom. Each top opening is accordingly 44.45 cm. (17.5 inches) from the bottom of the can (inside measurement). All paints were made up one week before the final adjustment to standard consistency. The paints were then filled into the containers, a sample being retained of each paint. The following day samples were drawn from each opening and as often thereafter as seemed necessary. Determinations of the pigment content are given in Table 11. It is noticeable that Titanox, which had been considered as a pigment that settled out rapidly, does not show this tendency when used alone. Zinc alone and lead alone settled very slowly, whereas the half-and-half mixture of these was very rapid by comparison. To determine whether the lead was dropping out, leaving the zinc in suspension, analyses were made of the pigment for zinc oxide content. (Table 111) No change in zinc oxide content was found from that of the original paint, indicating that the pigment is settling as a whole, instead of one constituent more than another. The specific gravity of the different constituents apparently is not a factor.
Data for Paints Containing Various P i g m e n t s
ASBESTINE SILICA BARYTES
CHINA CLAY
Crams (Temperature, 23.35' C. (74'
F.); weight of plunger, 79 grams)
50% LEAD 50% ZINC
60% REDLEAD 40% ASBESTINB
OUTSIDE WHITE HOUSE PAINT
INDUSTRIAL A N D ENGINEERING CHEMISTRY
July, 1928
Table 11- P i g m e n t C o n t e n t of House P a i n t s after Settling (Containers filled February 13, 1928)
SECOND THIRD
TOP
OPESING OPENING OPENING
DATE
ZINC OXIDE (6 PER CENT LEADED)-PIGMEIT
2-14-28 2-18-28 2-20-28 2-21-28 2-2 5-2 8 3- 2-28 3-13-28
63.2 63.7 64.3 63.7 65.0 61.0 3.0
SULFATE WHITE
2-14-28 2-18-28 2-20-28 2-21-28 2-25-28 3- 2-28 3-13-28
63.3 63.5 64.0 63.8 64.4 63.9 64.3
LEAD-PIGMENT
74.3 75.0 75.6 75.3 75.3 77.5 10.0 63.9 65.4 66.5 66.7 67.1 1.3
...
... ...
65.8
80.9 81.3 81.7 83.1 82.9 83.1 83.2 80.1 83.9 83.4 83.5 83.7 84.0 84.1
80.9 81.5 82.5 82.8 82.9 83.2 83.4 83.9 84.1 83.9 84.3 84.0 84.6 84.4
74.2 74.2 75.1 74.9 75.8 76.4 77.1 64.2 64.4 64.3 65.1 65.2 66.0 80.8 81.4 81.5 82.0 82.9 82.8 83.1 85.8 83.9 83.5 83.6 83.8 84.4 84.7
47.3 46.7 47.2 45.9
46.8 46.4 46.7 45.9
CHINA
2-14-28 2-18-28 2-21-28 2-25-28 3- 2-28
68.6 1.8 0.9
... ... ... ... ... ... ...
... ... ... ...
59.4 59.4 60.0 61.2 62.0 62.5 62.8 65.3 69.7 76.6 80.8 81.7 82.0 82.9 83.0 83.5 83.7 48.3 20.0 4.8 0.8
... ...
CLAY- -PIGMENT
51.2 50.5 50.3 50.8 51.4
ma
6Q
71.2 70.6 51.8 0.8
... ... ... ... ... ... ... ... ... ...
PER CENT RED LEAD WITH 2-14-28 2-21-28 2-25-28 3- 2-28 3-14-28
64.4 64.1 64.5 64.6 64.0
Table 111-Zinc Oxide DATE FROM ZINC SAMPLEDOPENINGAT OXIDE Per cent 2-14-28 Top 49.0 2-14-28 Bottom 50.0 2-16-28 Top 49.0 2-16-28 Bottom 50.0 2-18-28 2-18-28 2-20-28 2-20-28 2-21-28
59.4 61.3 60.5 62.6 64.0 63.7 64.4 66.7 67.6
51.2 50.9 50.6 50.8 50.3
76.6 81.8 82.5 83.6 84.2 84.8 84.7 84.8 85.2 85.2 85.4 86.4 85.4 84.8
71.0 71.0 73.6 74.2 74.6 74.6 75.2 75.9 75.3 75.6 75.5 75.8 75.5 72.2
78.1 81.8 82.4 82.7 83.0 83.5 83.5 83.4 83.9 84.6 84.6 85.1 85.5 85.7
CONTENT 61. 26 PER
50.5 51.0 50.8 50.5 50.5 70.6 70.7 75.4 76.1 76.5 76.8 77.4 75.2 77.3 77.4 77.3 77.4 78.3 78.0
lost
75.7 75.8 76.0 75.9 76.1 76.9 77.0
40 PER CENT ASBESTINE-PIG?dXNT M.I) PER CENT
64.6 64.3 64.4 64.2 64.6
64.5 64.1 64.3 64.4 64.4
87.2 88.6 88.6 88.8 50.5 50.9 50.9 50.7 50.8
CONTENT 70.6 PER CENT
70.6 71.8 75.0 75.6 74.5 75.0
64.6 64.3 64.6 65.1 65.7
2-21-28 2-23-28 2-23-28 2-25-28 2-25-28 3- 1-28 3- 1-28 3- 1-28 3- 1-28
ZINC OXIDE Per cent
Bottom Bottom Second
49.5 49.5 49.5
Second Bottom Second Third Fourth Bottom
49.4 49.4 49.4 49.4 49.4 49.3
50 75 100 125 150
91 66 56 45 40
92 64 57 44 38
85 61 50 42 36
Red Lead and Asbestine Paints Pigment Content: Red lead Asbestine 607, red lead paint paint 40% asbestine
SuZfote While Lead and X X Zinc Oxide Paints Sulfate X X Zinc -PIGMENTCONTENT MIXTURESwhite lead oxide 2q% Lead 50% Lead 75% Lead paint paint 73% Zinc 50% . _ Zinc 25% . _ Zinc
Weight added to plunger 50 75 100 125 150
80 61 52 42 37
81 62 53 43 38
79 58 49 41 35
78 58 49 40 34
76 57 48 41 37
Paints Conlaining Tilanox with Carbonate White Lead and with Zinc Oxide
lost
CENT
51.3 50.8 50.8 50.8 50.4
Determinations DATE FROM SAMPLED OPENINGAT
Table IV-Mobilometer Data on Mixed P a i n t s (Temperature, 23.35' C. (74' F.), weight of plunger, 79 grams) Sulfate While Lead and Zinc Oxide Paints Weight added to Sulfate white Zinc oxide Pigment Content: plunger lead paint (5% lead) paint 507, lead, 50% zinc Grams
59.3 59.3 60.5 62.0 63.5 64.8 66.4 69.2 69.7 77.9 80.8 81.7 83.2 83.5 85.7 85.5 86.3 86.1
49.4 49.4 49.5 49.4 49.5
%om Second Bottom Second
PER CENT
59.3 60.9 60.4 61.1 63.4 64.0 65.2 66.3 67.4
60 PER CBNT LEAD WITH 60 PER CENT ZINC-PIGMENT
2-14-28 2-16-28 2-18-28 2-20-28 2-21-28 2-23-28 2-25-28 2-27-28 2-28-28 2-29-28 3- 1-28 3- 2-28 3- 7-28 3-12-28
Examination of the percentage of pigment in the leadzinc paint shows that it is 70.6 per cent, whereas only 68.75 per cent is called for theoretically by calculation in combining the single-pigment lead paint and the single-pigment zinc paint. The mobilometer data do not show the lead-zinc paint to be any thicker than the lead paint or the zinc paint. This indicates that mixing a lead paint and a zinc paint of identical consistency results in a thinner paint. Carefully adjusted lead and zinc single-pigment paints were made up and mixed. The resulting mixture was found to be thinner. The mobilometer data for this and other mixed paints are given in Table IV.
46.9 46.8 47.2 46.2
BPIRYTES--PIGMENT CONTENT 7 5 . 6 PER CENT
2-14-28 2-16-28 2-17-28 2-20-28 2-21-28 2-23-28 2-24-28 2-25-28 2-28-28 3- 1-28 3- 2-28 3- 5-28 3- 9-28 3-12-28
Pigment Settling in Mixed Paints
CONTENT 4 7 . 0 PER CENT
CONTENT
SILICA-PIGMENT
59.3 60.6 59.3 51.6 49.0 0.6
64.3 64.4 64.7 65.3 65.5 65.4
lost
46.9 46.7 46.7 48.4
47.0 46.7 46.8 46.5
CENT
CONTENT 80.95 PER CENT
ASBESTINE-PIGMENT
2-14-28 2-17-28 2-18-28 2-21-28 2-23-28 2-25-28 2-28-28 3- 2-28 3- 7-28
64.3 64.7 65.3 65.6
81.4 81.6 82.5 82.8 83.5 83.7 84.2 84.9 84.8 85.0 84.5 84.5 84.7 85.1
...
PER
74.4 75.3 75.0 75.1 75.5 75.9 76.4
63.2 63.3 63.3 63.5 64.2 64.4 65.0
CONTENT 64.2 PER CENT
65.4 64.9
... ...
2-14-28 2-21-28 2-25-28 3- 2-28
74.4 74.9 75.1 75.1 75.5 76.1 76.4
lost
81.9 81.3 82.4 79.9 77.8 34.5 1.0
63.4 63.5 63.5 63.5 65.0 64.8 64.6
CONTENT 74.8
64.2 64.5 65.1
RED LEAD-PIGMENT
2-14-28 2-16-28 2-17-28 2- 18-28 2-20-28 3-21-28 2-23-28 2-25-28 2-28-28 2-29-28 3- 1-28 3- 2-28 3- 9-28 3- 12-28
CONTENT 63.2 PER CENT
63.2 63.5 63.3 63.4 64.0 64.6 64.3
74.3 75.2 75.1 75.8 75.8 76.0 76.0
TITANOX-PIGMENT
2-14-28 2-18-28 2-21-28 2-25-28 3- 2-28 3-13-28
FOURTH BOTTOM OPENING OPENING
733
70.7 71.8 76.2 75.3 75.4 75.8 75.5 76.4 76.7 76.6 76.7 76.6 76.9 77.7 CONTENT
64.5
64.6 64.3 64.4 65.4
plunger paint Grams 50 75 100 125 150
79 60 48 40 34
paint
paint
50%Zini
80 63 53 42 37
75 60 50 42 37
78 57 45 37 32
75 53 47 40 35
75 55 46 40 35
P a i n l s Containing Titanor with Sulfate White Lead and with X X Zinc Oxide -PIGMENT CONTENT MIXTURES-Sulfate XX 50% 50% 50y0 Titanox Weight white Zinc Titanox 50% Lead 25%Lead added to lead Titanox oxide 507, Titanox 50YP X X 25% plunger paint paint paint X X Zinc 50% Lead Zinc X X Zinc 50 75 100 125 150
-80 62 50 43 36
77 59 47 38 33
-83 59 48 41 35
81 59 47 40 35
71 55 45 37 33
74 57 46 40 32
76 55 45 38 32
Mixture of Carbonate and Sulfate White Lead Paints Pigment Content: Carbonate Sulfate 50% Carbonate white white lead white lead lead paint paint 50% Sulfate white lead
Weight added to plunger Grams 50 75 100 125 150
76 60 48 41
36
77 59 48 42 a6
75 60 48 43 35
INDUSTRIAL A N D ENGINEERING CHEMISTRY
734
Table IV- Concluded Two-Lead Paint wilh X X Zinc Oxide Paint 10% 50% Carbonate XX ZINCOXIDECONTENT Titanox Weight lead, XX Zinc OB COMBINATION 45% Caradded to 50% sulfate oxide TWO-LEAD PAINT bonate lead plunger lead paint 3% Zinc 10% Zinc 45% Sulfate lead . -
50 75 100 125 150
75 60
48 43 35
Weight added to plunger Grams
50 75 100 125 150 Weight added to plunger
50 75 100
125 150
83 59 48 41 36 X X Zinc Oxide and Barytes paint
76 70 59 54 48 46 41 40 36 35 Bar5’tes Paints
XX Zinc oxde paint
Pigment Content:
55% XX Zinc oxide 45% Barytes
73 75 57 59 48 47 42 40 37 35 Sulfate White Lead and Barytes Paints Sulfate white lead paint
Barytes paint
71 57 48 41 37
73 57 4s 42 37
72 56 47 40 35
74 58 47 39 35
Pigment Content:
50% Sulfate white lead 50% Barytes 65 53 44 38 34
A similar condition was found with respect to the red leadasbestine paint. Theoretically, 62.8 per cent pigment is required when combining the single-pigment red-lead paint and the single-pigment asbestine paint. Actually, 64.3 per cent pigment concentration was required. Single-pigment paints of red lead and asbestine adjusted t o the same consistency of mixing resulted in a thinner paint. Similar thinning was found with the sulfate white-lead single-pigment paint when mixed with varying quantities of a single-pigment paint made with XX zinc oxide. Titanox with carbonate white lead (Anaconda process) and with zinc oxide (5 per cent leaded) resulted in thinning, as did also a mixture of these three pigments. Titanox with XX zinc oxide did not result in thinning,
Vol. 20, No. 7
although Titanox and sulfate white lead, and also XX zinc oxide with sulfate white lead thinned. A combination of these three pigments likewise thinned. As the two varieties of white lead had been found to thin with zinc, and as a mixture of lead and Titanox had been found to thin out, it seemed reasonable to forecast that a mixture of the two leads would not thin out. Mobilometer results showed that they did not. There should be some point, then, a t which a thinning of this mixture of the two leads would occur if some singlepigment XX zinc oxide paint were added. It is indicated that this point lies between a zinc oxide content of the pigment of 3 per cent and 10 per cent. Ten per cent of Titanox in the pigment content likewise produced thinning. A mixture of single-pigment paint was made to give a pigment content of 55 per cent XX zinc and 45 per cent barytes, which is a combination that has been found to give good satisfaction as a house paint. KOthinning was found. As barytes and XX zinc oxide are similar in action as regards thinning, it seemed reasonable that barytes and lead should thin out, then, similar to the way zinc and lead thinned out. Examination of the settling data, particularly of the paints which have settled to some extent, such as the barytes paint and the combination lead and zinc paint exhibit a peculiar and persistent lag in the next to the bottom opening, yet the data, read vertically, seem to give the gradual increased pigment concentration to be expected. As no evidence could be found that this was due to experimental error, further study (as yet not completed) was undertaken using a 10-gallon container with eighteen openings. As the above is only a preliminary report of the nature of the work undertaken and now under way, no deduction or no generalizations will be made at this time. Certain unexpected results have been encountered which are being further studied.
Some Theories of Pigment Settling Paul R. Croll PITTSBURGH PLATEGLASSCOMPANY, MILWAUKEE, Wis.
HE annoying defect of pigment settling so commonly found in paints and enamels is one of the most interesting phenomena among the many and varied moods of paint behs,.:or. The practical-minded paint mixer is so anxious to overcome settling difficulties that he will try almost any suggested remedy and may even give some attention to a recital of theories as to the causes of his trouble. Since all pigments have considerably greater densities than the paint liquids or vehicles, the settling problem cannot be avoided. One might imagine equally troublesome the effects of pigments lighter than paint vehicles, and then could expect hard cakes of floated pigment in cans labeled “stir well from the top down.” We could hardly hope for a choice of various colored pigments exactly matching the vehicles in density.
T
Effect of Particle Size of Pigment
The “settling force” may be defined as the weight of a unit volume of pigment minus the weight of an equal volume of vehicle. When a finely divided solid, such as a paint pigment, is immersed in a liquid, certain forces are exerted between the solid and liquid and between various particles
of the solid, the magnitude of which is proportional to the area of surface or solid-liquid interface. However, since decreasing the particle size rapidly increases surface area, these internal forces also increase. Since the practical result of increasing the interfacial forces is to overcome or decrease settling, we are led to choose finer pigments as one aid toward overcoming settling. The particle size of a pigment refers to the individual crystal and not to an aggregate of particle pressed into place. The first precaution toward overcoming settling by use of finer pigments, therefore, is to disperse the pigment mechanically in the vehicle so that each discrete particle is completely surrounded by liquid. Otherwise, the full value of the increased surface is not obtained. ~VECHANCAL DISPERSIOXIN LIquID-considering the case of an individual pigment particle of fine size immersed in a paint or enamel vehicle, the settling force of gravity will tend toward sending the particle to the bottom of the can. In falling, the particle creates a viscous sheer in the vehicle. On the assumption that the vehicle is a true liquid and not a colloidal suspension of oil or gum aggregates, the rate of fall of the particle will be affected by the viscosity of the liquid. A very viscous vehicle may slow up the rate of
