INDUSTRIAL AND E N G I N E E R I N G CHEMISTRY
are unity. Considerable data on this subject have been presented by Sage and Lacey (7), and they found .that K varies with the molecular weight and chemical nature of the other components present. Brown and Souders (8) also observed an appreciable deviation of K values at low concentrations of the particular component in the liquid. The limitations of the calculated K values are fully discussed by Dodge (3). For temperatures below 300’ F. and for pressures between 10 and 300 pounds per square inch absolute, Figure 1 gives results which agree exceptionally well with the calculated K values. Outside this r d g e , the K values obtained from the nomograph should be checked against actual experimental data in line with the limitations discussed in the preceding paragraph. Thus Figure 1 can be used over the range of conditions usually encountered in engineering design to give results as reliable aa the equilibrium constant data upon which it is bmed.
Vd. 37, No. 1
The authors wish to thank Hydrocarbon Research, Inc., for permiaeion to publish this work. LITERATURE CITED
Brown, G. G., Vaporisation Equilibrium Constant Charts ( a h reproduced in following reference). Brown, G. G., and Souders, M.,, in “Science of Petroleum”, New York, Oxford Univ. Press,1938. Dodge, B. F., “Chemical Engineering Thermodynamics”, New York, McGraw-Hill Book Co., 194.4. Miller, C. O., and Barley, R. C., IND.ENQ.CHIM., 36, io18 (1944). Othmer, D. F., Zbid., 36,669 (1944). Robinson, C. S., and Qilliland, E. R., “Elements of Fractional Distillation”, 3rd ed., New York, McGraw-Hill Book Co., 1939. Sage,B. H., and Lacey, W. H., IND.ENQ.Cnm., 1934-44. Sherwood, T. K., “Absorption and Extraction”, New York. McGraw-Hill Book Co., 1937. Shiah, C. D., Refiner Natural Gasoline Mfr., 21, 132 (1942).
NITROCELLULOSE LACQUERS Factors Affecting Amount of Nonvolatiles at Sprayable Viscosity’ William Koch, N. C. Phillips, and Rufus Wint HERCULES POWDER COMPANY, WILMXNGTON, DEL.
ITROCELLULOSE lacquers of increased nonvolatile content at spraying viscosity have an economic appeal because they offer real promise as a means of reducing finishing costs, through a saving in solvent, and a reduction in the number of finishing coats required. Several factors have been recognized as having an influence on the nonvolatile content of nitrocellulose lacquers: ( a ) Since the n i t r o c e l l u l o s e , because of i t s highly polymeric nature, is the principal viscosity-contributing ingredient in a lacquer, the use of lower-viscosity types makes possible higher solids at a n y selected viscosity level without otherwise altering the composition. (b) It is well known that the lower-molecularweight esters and ketones, such as ethyl acetate, acetone, and methyl ethyl ketone, have a greater capacity to disperse nitrocellulose than highermolecular-weight esters and ketones, such as butyl acetate and methyl isobutyl ketone. This is reflected in lacquers of higher nonvolatile content a t the same viscosity level (.$, 6). It is also well known that 1 The first article in this series appeared in August, 1944 (6).
Viscpsity-concentration dat? were obtained on nitrocellulose lacquers to determine how nitrocellulose viscosity, richness or activity of solvent, high-temperature application, and ratio of nitrocellulose to resin affect the percentage of nonvolatiles. Plotted data illustrate the influence of each of these factors and the relation between them. The nonvolatile content of lacquers at maximum spraying viscosity (80 centipoises) was taken from the plotted graphs. These data show that the gain in nonvolatile content contributed by each factor is cumulative when two or more methods of increasing nonvolatiIe content are utilized at the same time. In this way high solids, compared to past practice, are possible. Recognized limitations of these methods for increasing nonvolatile content are discussed to show how each of the factors can contribute to higher nonvolatile content, without sacrificing the inherent high-quality performance of nitrocellulose lacquers. Thus it is considered safe to use nitrocellulose as low in viscosity as 30 to 35 centipoises, in a ratio of 1 :2 nitrocellulose to nonoxidizing alkyd resin with a high-solvency type solvent toobtain appro~imately29.5~~ non’volatile, or at elevated temperaturesashigh as70’Ctoobtain approximately 36.570nonvolatile in clear compositions. Pigmentation will increase these gains somewhat, depending upon the pigment employed.
the addition of a diluent, Buch 88 toluene or an aliphatic petroleum distillate, will’ increase the viscosity of a lacquer considerably as the limit of dilution is approached @, 7‘). Thus, by making me of greater proportions of the more active lowmolecular-weight nitrocellulose solvents and less diluent, and p r o p erly balancing the solvent mixture for good spraying performance, i t is possible to effect greater nonvolatile concentration at spraying viscosity. This principle will be referred to as the high-solvency type of formulation. (c) It is possible to increase the nonvolatile content of a lacquer and yet maintain a desired viscosity by raising its temperature of application (3). This technique has been termed “hot-spray” application. ( d ) Finally, i t is possible to increase nonvolatile content by increasing the proportion of resin to nitrocellulose in the lacquer composition. The purpose of this article is to illustrate how each of these factors affect nonvolatile content, and to point out how the benefits of each can be realized without eacrificing in any way the recognized high-quality performance of nitrocellulose lacquers.
INDUSTRIAL A N D ENGINEERING CHEMISTRY
FORMULATION AND TESTlNG
S E ~ C ~OFO M NA ~ R J K L SClear . compositions for ~ c o s i t y measurements were prepared by formulating one typical nonoxidizing alkyd resin (Aroplaz 905) with RS nitrocellulose (I/P second, l/rsecond, 30-35 centipoises, and 1'8-25 centipoises) in ratios, respectively, of 1:1, 1:2, 1:3, and 1:4 nitrocelluloseto resin. The nitrocelluloses selected are standard types. Their viscosity relations are illustrated in Figure 1. The substitution of other commercial alkyd resins for the one 400 chosen results in 300 I 2 5 4 small Merencea in solids concentration, in some c a a e s slightly more and in others slightly less, a t any given viscos,ity. The composition of the solvents used in this work is given in Table I and, for I5 25 PERCWT SOLIDS convenience, will be referred to as Figure 1. Viscosity-Concentration the standard, Curves for Low-Viscosity-Type Nitrocelluloeee in 75% Butyl Acetate-25% high-solvency, Denatured Ethan61 Solvent 'and hot-spray 1 RS 1/~-.80. 125 cantipoh) types. The atand2: RS ~*-.ec. 15o osntipoim) ard solvent se3. RS 9 0 9 5 wntipoimea lected is a mix4. RS 18-26 antipoft u r e which has been used in the laboratory for years because it has good dissolving capacity for dl lacquer ingredients; it can be sprayed in fairly humid atmospheric conditions without developing blush and develops very little orange peel effect. Many commercial solvent combinations in use are considerably lower in active solvent ingredient and higher in diluent than this standard mixture and, consequently, have less dissolving capacity, which is reflected in lower solids at a given viscosity level. The high-solvency formula was selected from a preliminary study of solvent mixtures to have an optimum combination of good spraying properties with a capacity to dissolve high nonvolatile content at spraying viscosity. The hot-spray formula was selected from a preliminary study of solvent mixtures to have good spraying properties a t an elevated temperature of 70' C. A large stock solution of each solvent mixture was prepared, so that all lacquers made with each solvent had exactly the same solvent composition. PROCEDUBII. Each lacquer waa prepared at a nonvolatile content such that its viscosity preferably would lie between about 100 and 200 centipoises. The empty bottle was weighed to the nearest 0.1 gram before introduction of the lacquer ingredients, each of which was weighed into the bottle with the same accuracy. (The authors are aware that commercial lacquer formulators are primarily interested in the weight of nonvolatiles
BLENDSFOR VISCOSITY-CONCENTRATION STUDIES
Compn % by weight Butyracetate
Stsndsrd 3b 16
HighSolvency 20 10 10
HotSpray 37.6 12.5
.... .... .... 60
Sp. gr. of composite solvent (20/ 200 C . )
Eth lacetate &;~&lf-;~;~
per unit volume of lacquer. However, the specific gravity values given in Table I show that the three solvents are very close tog&ther, so that it makes practically no difference whether comparisons are made on a weight percentage basis, as done here, or on a weight per unit volume basis.) Since several solvent aombinations were employed, the nitrocellulose was dried before use. (The experimental results with dried nitrocellulose will not correspond exactly with the results to be expected in commercial practice where alcohol-wet nitrocellulose is used. This is beaause alcohol-wet nitrocellulose contains a small percentage of water which has some effect on the viscosity of a lacquer a t a given solids content.) Care was exercised at all times to avoid loss of solvent by evaporation. After determination of the viscosity, the lacquer remaining in the bottle was reweighed; a calculated amount of the proper solvent mixture to reduce nonvolatile content by a predetermined amount was weighed into the lacquer and thoroughly mixed, and a second viscosity was determined. This procedure was repeated to obtain a third viscosity at a still'lower nonvolatile concentration. In most instances the nonvolatile content was lowered by 2.5% steps, although in a few cases larger steps were necessary to obtain the desired viscosity range because the initial nonvolatile level chosen gave viscosities higher than anticipated. The matter of knowing what the initial solids content should be was based largely on experience gained in preliminary work. Viscosities were measured with the Ubbelohde viscometer (1) a t 25' 0.1' C. for lacquers made with the standard and highsolvency type solvents. Viscosity w&smeasured a t 70' * 0.1' C. for lacquers made with the hot-spray type solvent. All viscosity determinations were corrected for specific gravity. The viscosity-concentration data are plotted in Figure 2. A significant feature is that these curves are essentially straight lines within the viscosity range examined. This is important because it justifies 8 small extrapolation of a few of the curves into the range of sprayable viscosities where the data failed to extend. PHYSICAL Tame. Data on hardness and resistance to water spotting, presented to illustrate the effect of resin to nitrocellulose ratios, were obtained on lacquer films sprayed on clean, sanded, steel panels to a thickness of 2 m i l s using the high+olvency type solvent. Sward hardness (4) was measured after 2 4 hour drying a t room temperature; the water-spot test was made after the lacquers had remained exposed in the laboratory for 1-2 weeks. This test wtw carried out by confining water on the film under a watch glass for 24 hours at room temperature; the water f-
TABLE 11. NONVOLATILE CONTENT OF NITROCIDLLULOSII LACQU~RSQ AT MAXIMUM SPRAYING VISCOSITY (80 CENTIPOISES) Type of Nitrooellulose R8 Vs-sec. RS V w m . RS 30-36 cp. RS 18-26 cp. 0
A 17.0% 20.6 21.6 23.0
1:l Rstiob B C 19.8% 23.4% 24.0 28.6 24.8 29.9 26.6 31.6
A 21.2% 26.1 26.6 27.0
1:2 Ratios B 26.3% 28.8 29.b 31.4
Formulated with Aroplac 906,a t pica1 nonoxidising alk d resin Ratio of nitrooellulose to renin: I atandard solvent C.): B
C 31.3% 34.8 36.6 37.3
A 24.1% 27.8 28.6 30.0
high-solvency @So CJ: C
E 28.2% 33.0 33.6 34.8
C 33.3% 38.5 39.0 40.4
hotspray (70° C.).
A 26.9% 30.2 31.4 32.8
B 30.2% 36.6 36.0 37.5
C 37.0% 40.8 42.0 43.6
INDUSTRIAL AND ENGINEERING CHEMISTRY
27.5 30 32.5 PERCENT SOLIDS NITROCELLULOSE : RESIN-1:I
8 6M):RATIO Y 400
t In >
27.5 30 3Z.5 35 PERCENT SOLIDS RATIO NITROCELLULOSE :RESIN=I:2
30 32 5 35 37.5 PERCENT SOLIDS
8oo -RATIO NITROCELLULOSE:
30 3s PERCENT SOLIDS
37.5 40 42.5 PERCENT SOLIDS
4 0 42.5 4 5 47.5 PERCENT SOLIDS
Viscosity-Concentration Data f o r Nitrocellulose Lacquers
A , ntandard nolvent; B , high-solvency nolrent) C. hot-npray solvent. Curve 1, RS */Isecond nitrocellulose; 2, RS 1/psecond; 3, 30-35 cantipoimen; 4, 18-25 centipohea.
Vol. 37, No. 1
was then removed, and observation was made immediately for blush and softening effect. These panels were allowed to dry for 24 hours and then observed for permanence of blush. Blush was rated. as slight, medium, or heavy, with added notation that the blush was either temporary or permanent. Softening effect was noted immediately after removal of the water from the film by a fingernail test and recorded as slight, medium, or bad softening. DISCUSSION OF DATA
The curves in Figure 2 are grouped to illustrate the relation between the four different viscosity types of nitrocellulose. In every solvent and in all ratios of nitrocellulose to resin the greatest single gain in nonvolatile a t any viscosity was obtained by using RS '/*-second nitrocellulose in place of RS '/a-second. This gain averaged about 3.5% for the standard solvent and about 4.5% for the high-solvency and hotspray formulas. An additional small gain averaging about 1% in each of the solvent types was possible by using 30-35 centipoise material, and another slightly larger gain averaging about 1.5% in each of the solvent types was possible by using 18-25 centipoise nitrocellulose. The ultimate average gain by using 18-25 centipoise nitrocellulose instead of 'lrsecon d t y p e a m o u n t e d t o a b o u t '6-7y0 i n nonvolatile content, regardless of the solvent type or ratio of nitrocellulose to resin. Figure 3 illustrates more clearly the relation between the three different solvents. These curves were obtained by regrouping the Rs '/*-second nitrocellulose data from Figure 2. At any viscosity level and a t all ratios of nitrocellulose to resin there was a marked gain in nonvolatile content by using the high-solvency instead of the standard solvent. This increase ranged between about 3 and 4.570 solids for the data illustrated in Figure 3. The use of hot-spray application instead of the highsolvency formula resulted in another marked gain in nonvolatile content ranging between about 3.5 and 6.5aJ, solids for the data illustrated. The ultimate gain in nonvolatile content by using hot-spray in place of standard solvent amounted t o 6.5-1170. Data for the lower-viscosity nitrocelldoses did not differ from the trend illustrated with Rs l/z-second data. Figure 4 similarly illustrates the relztion between the different ratios of nitrocellulose to resin by regrouping the R s l,ln-second nitrocellulose data from Figure 2. The increase in nonvolatile content made possible by 1:2 in place of 1 :1 ratio was about 4.0% in standard solvent, 5.5% in high-solvency solvent, and 7.0% in hot-spray. An additional increase by using a 1:3 in place of the 1:2 ratio
INDUSTRIAL AND ENGINEERING CHEMISTRY
TABLE 111. HARDNESS AND Ratio, RS '/Nitroz*eClose: Resin 1:l 1:2
With Aroplas 905 swardwater Resistance ' hardSo!tenneaa Blush mg 82 VSTa Slight ST Slight 24 Medium 4 HT HP Medium 6
RESISTANCE OF NITROCELLULOSE LACQUER8 FORMULATED WITH NONOXIDIZING ALKYDRESINS
With Glyptal 2477 With Reayl B9-6 iward Water reaistance sward Water resistanoe hardSoften- hardSoftenness Blush ing ness Blush ing 28 VST Slight 26 VST Slight 14 ST Slight 24 ST Slight 8 HP Bad 16 HP Medium 2 HP Bad 8 HP Bad
With Reayl 12-6 sward Water resistanoe ' ' Sqftenhardness Blush ing 80 VST Slight 21 ST Slight 18 MT Medium 6 HP Medium
With Syntex 18 sward Water resistanoe hardSoftenneaa Blush ing 20 ST Slight
VBT, very slight temporary; ST, slight temporary; HT, heavy temporary; HP, heavy permanent; MT, medium temporary.
RATIO NITROCELLULOSE:RESIN, I : I ar/
RATIO NITROCELWLOSE:RESIN,I .Z
25 30 35 PERCENT SOLIDS
30 35 40 PERCENT SOLIDS
Viscosity-Concentration Data for RS I/pSecond Nitrocellulose Lacquers in Various Solvents
Curve 1 with standard, 2 with high-solvenoy, and 3 with hot-spray solvent.
amounted to about 3.0% for all three solvents; the additional increase for the 1:4 ratio was about 3.0% for standard and high-solvency solvents, and about 4.Oy0 for hot-spray. The ultimate gain in nonvolatile content amounted to about 10% in standard solvent, 11.5% in high-solvency, and 13.5% in hot-spray. Again data for the three lower-viscosity nitrocelluloses followed the same general trend illustrated with the RS '/*-second data. From Figure 2 it is possible to read off directly the concentration of nonvolatile at spraying viscosity. A level of 80 centipoises was chosen as representing about the maximum viscosity which can be sprayed without instahtion of special equipment. Table I1 shows the comparative nonvolatile content at this chosen viscosity level for the four viscosity type nitrocelluloses, for the four ratios of nitrocellulose to resin, and for standard, high-solvency, and hotspray solvents. The data show that the individual gains in nonvolatile content accomplished by using lowerviscosity nitrocelluloses, higher resin ratios, and high-solvency. or hot-spray solvents are cumulative. The ultimate cumulative gain shown in Table I1 is from 1i'yOnonvolatile for a 1:l ratio of RS '/$-second type in standard solvent to 43.6% nonvolatile for a 1:4 ratio of 18-25 centipoise type in hotspray.
There is real danger, however, that the inherent high-quality performance of nitrocellulose lacquers may be sacrificed in an enthusiastic quest to accomplish an ultimate gain in nonvolatile content. Each of the factors discussed can contribute toward increased nonvolatile content without impairing the quality of the resulting lacquers, if certain limiting factors are taken into consideration. A previous article on the use of low-viscosity nitrocelluloses with nonoxidizing alkyd resins (6) demonstrated that high-quality lacquers could be formulated with nitrocelluloses of viscosities as low rn 27 centipoises. Such lacquers showed no mcrifice of hardness, cold check resistance, or weathering resistance. It seems clear, therefore, that RS 30-35 centipoise type can be used without fear of loss in quality. Still lower-viscosity types have been utilized successfully in finishes based on oxidizing-type alkyd resins where the resin is relied upon t o impart strength to the film. Table 111 gives Sward hardness and water resistance data for lacquer compositions based on ratios of 1: 1, 1:2, 1:3, and 1:4 nitrocellulose to resin, using several typical commercial nonoxidiz-
PERCENT SOLIDS SOLVENT
z *too5; 0
Figure 4. Viscosity-Concentration Data for R S c/pSecond Nitrocellulose Lacquers at Various Ratios of Ni$mcellulose to Re-iin curre 1 for 111.2 for 112.8 for 113, .nd 4 for 114 ratio.
INDUSTRIAL A N D ENGINEERING CHEMISTRY
ing alkyd resins. These data show that there was a marked reduction in hardness at‘ratios of 1 :3 and 1: 4 nitrocellulose to resin. Experience has shown that lacquer films with hardness values of about 10 or less have poor scuff resistance and are prone to collect dirt badly. Also the high resin ratios had poor water resistance. This is illustrated by both blush and softening effect. Ratios of 1: 1 and 1: 2 show very slight or slight temporary blush; the 1:3 ratio ranges from a medium temporary to a heavy permanent blush, depending upon the resin; the 1:4 ratio in every case showed a hedvy permanent blush. The lower 1: 1 and 1:2 ratios showed good resistance to softening, whereas the 1:3 and 1:4 ratios exhibited either medium or poor resistance to softening, depending on the reain. These data indicate that high-quality performance was maintained a t ratios up to 1:2 nitrocellulose to resin, but there was some sacrifice a t a 1:3 ratio and considerable sacrifice in performance when higher proportions of resin were used. Experience has shown that hot-spray application of nitrocollulose lacquers is possible a t temperatures as high as 70” C. without deteriorating the nitrocellulose in any way. At higher temperatures of 80-90: C., however, a definite degradation of the nitrocellulose has been found which is reflected in brittle films with poor durability. CONCLUSIONS
The data have demonstrated that nonvolatile content can be increased in nitrocellulose lacquers by using lower-viscosity nitrocelluloses and larger proportions of nonoxidizing alkyd resins with a more active solvent, or by applying the lacquers at an
Vol. 3’2,No. 1
elevated temperature up to 70” C. The gain in nonvolatile content contributed by each factor is cumulative, so that quite high solids are possible. To maintain high-quality performance, the nitrocellulose used should be the 30-35 centipoise type or higher, and the proportion of nonoxidizing alkyd resin should not exceed a 1:2 ratio of nitrocellulose to resin. Table I1 indicates that it should be possible t o increase nonvolatile content from 17% in the 1:l ratio, using RS ‘/Z-second type with the standard solvent, to 29.5% in the 1:2 ratio, using 30-35 centipoise type with the high-solvency formula. This is an increase of 73.5% in nonvolatile content. Similarly, there was an increase from 17 to 38.5% when hot-spray application was employed. This amounted to an increase of 114% in nonvolatile content at spraying viscosity. Pigmentation would increase these gains somewhat, depending upon the pigment employed. LITERATURE CITED
Am. SOC.for Testing Materials, D445-37T, Tenhtive Methods of Test for Kinematic Viscosity. Doolittle, A. K., IND.ENQ.CHEM.,30, 189-203 (1938). Ericsson, R. L., Am. Paint J . , 27, No.32, 40-52 (May 10, 1943). Gardner, H.A., “Physical and Chemical Examination of Paints. Varnishes, Lacquers and Colors”, 9th ed., p. 117, Washington. Inst. of Paint and Varnish Research, 1939. Koch, William, IND.ENG.CEEM.,36, 756-8 (1944). Lowell, J. H.(to D u Pont Co.), U.S. Patent 2,291,284 (July 28. 1942). (7) Ware, V. W., and Teeters, W. O., IND.ENG.CX~EY., 31, 1118-21 (1939). PRESENTED before the Division of Paint, Varnish, and Plsstics Chemistry a t the 108th Meeting of the AYERICAN CHEXICAL SOCIETY, New York, N. Y.
Polypengaerythritol Drying Oils Harry Burrell HEYDEN CHEMICAL CORPORATION, GARFIELD, N. J.
HEN the tung oil shortage developed as a result of the ?in+ Japanese war, the American paint and varnish industry converted available drying oils by a t least three processes to products which more closely resembled ‘‘wood oil”: (1) dehydration of castor oil; (2) increasing the effective unsaturation of the fatty acids by (a) fractionating by distillation or solvent extraction or (a) conjugating the double bonds by treatment with alkali; and (3).esterification of the unsaturated fatty acids by alcohols more polyhydric than glycerol. The present production of dehydrated castor oil is considerable, but the product requires careful preparation and formulation to avoid slow-drying soft films and aftertack. Increasing the unsaturation in the fatty acid components has been of limited helpfulness, and in many cases has been commercially successful only because such improved acids were esterified by higher polyhydric alcohols as described by Stingley (19) and Bradley and Richard-
son (6). The method of re-esterification has been a natural and logical development based on Carothers’ theory (IO) of functionality, especially as it was expanded and interpreted by Bradley (6). In practice, pentaerythritol has proved to be a useful polyalcohol. The ready acceptance by the trade of coating compositions containing pentaerythritol, augmented by other wartime demands, led to the production of this alcohol in tonnage quantities. The preparation of pentaerythritol (tetramethylolmethane) was reported inr1891 by Tollens and Wigand (60). It is a tetrahydric primary alcobol with a quaternary carbon atom. “Pentaerythritol” is an unfortunate misnomer since it is not accurately descriptive and is difficult to wonounce; nevertheless, the usage is firmly established and it seems best to retain it. The ether
polymers of pentaerythritol have been termed “polypentserythritols”. Drying-oil fatty acid esters of pentaerythritol were prepared over fourteen years ago by Krzikalla and Wolf (16) and later by I,.& Bruson (7) and Arvin (1). Drinberg and Blagonravova (?11, 19, 13) reported many data of theoretical value, including comparisons with esters of other alcohols, both more and less polyhydric; they also evaluated practical aspects. As tung oil replacements, the pentaerythritol esters of linseed and soybean acids are useful in many instances because drying time, water resistance, and weather resistance are satisfactory (8). A major difference between tung oil and the pentaerythritol drying oils lies in the slower bodying rates; on the other hand, one of the outstanding characteristics of the polypentaerythritol drying oils is the ability to approximate tung oil more closely in this respect (9). Pentaerythritol does not occur in nature but is manufactured by the alkaliie condensation of formaldehyde h l d acetaldehyde. The reaction occurs more or less stepwise with the preliminary aldol condensation to form pentaerythrose, followed by a Cannizarro-type reduction to the alcohol:
LH*OH CHzOH HOH2C--LC-H20H