Aromatic Coefficient of Paint Thinners R. J. DEGRAY AND A. E. ESSER, JR. Socony-Vacuum Oil Company, Inc., New York, N. Y. A new test for the evaluation of paint thinners is described, called the "aromatic coefficient" (A. C.).
calculated. From the minimum A. C. of the resin, the stability of the reduced resin may be predicted also. The A. C. of the thinner is independent of the body at which it is determined from body T to body A. The A. C. of a mixture of thinners is exactly proportional to the composition of the mixture and the A. C. of each component. The A. C. depends upon the resin to be thinned, the chemical composition of the thinner, and the viscosity of the thinner. The A. C. of thinners of the same type are straight-line functions of their viscosities.
This compares the amount of xylene needed to reduce a given resin to a given body w i t h the amount of thinner necessary for the same reduction. Being based on commercial resins, a widely utilized standard, and the viscosity scale used in paints and varnishes, the A. C. is of practical application. Resins may be characterized by two constants. With these and the A. C. of the thinner for the resin, the amount of thinner needed to reduce a given resin to any desired body may be
H E thinning power of paint and varnish thinners has received considerable attention, and many tests for the evaluation of this property have been proposed. A bibliography of the subject and a discussion of the physicochemical factors involved in the dispersion of resins in thinners were given by Kurtz, Harvey, and Lipkin (9). A review of the literature indicates that the problem has been approached from the standpoint of the chemical composition of the thinner, and methods for the proximate analysis of thinners have received attention (2,4, 6, 7, 8). Also, conventional tests such as the Kauri butanol value and aniline cloud point are empirical evaluations of chemical composition. The present work has shown that this chemical and physicochemical approach must be augmented by a consideration of the purely physical concept of dilution, as follows.
Thus, for even more reasons than those cited by Kurtz (3) or Toby ( l o ) ,the thinning power of any thinner depends upon the resin being thinned. It follows that the thinning power of a naphtha cannot be predicted fully by the Kauri butanol value, or by any other test for chemical composition alone. A true measure of thinning power, therefore, can be obtained only by actually thinning the given resin with various amounts of the given naphtha. The results of such tests would appear to be wholly specific. A method of expression of these results was sought, however, which would permit a correlation of results and a prediction of thinning powers from thinner t o thinner.
Experimental The viscosities of the resins thinned with the various solvents were determined a t 77" * 0.1" F. (25' * 0.05" C.) by the Gardner bubble viscometer (A. S. T. M. designation D 154-28). The bubble tubes were standardiaed by comparison with blends of mineral oils whose viscosities were measured in centistokes in accordance with A. S. T. M. method D 445-39-T, B (modified Ostwald viscometer). The specific gravities of these blends were determined at 77" F. by hydrometers. Typical data from this standardization are shown in Table I. The bubble tubes appear t o be calibrated in stokes rather than poises. This may be expected, since the specific gravity of the liquid is a factor in the speed of bubble rise. Hence this instrument measures kinematic not absolute viscosity. However, in deference to established custom, our results are shown as poises, though they are actually stokes.
Mechanism of Thinning If a light (low-viscosity) oil is added to a heavy (highviscosity oil), the viscosity of the heavy oil is reduced. The higher the viscosity of the heavy oil, the more light oil needed to give a blend of a given viscosity. Similarly, the lower the viscosity of the light oil, the less light oil is needed. This assumes that the light and heavy oils are truly soluble in each other. Usually, in the case of varnishes and paints, some part of the resin will be truly soluble even in a paraffinic thinner. For this part of the resin, the relative thinning powers of two naphthas will depend solely on their viscosities and not a t all on their chemical natures. That part of the resin which is not truly soluble in the thinner, however, is reduced in viscosity by dispersion of the resin particles throughout the thinner, as described by Kurtz et al. (3). For this part of the resin the relative thinning powers of two naphthas will depend more upon their chemical natures and less, if at all, upon their viscosities. I n general, aromatics are better dispersing agents than are p a r a f i s . The thinning power of a naphtha or other thinner thus depends upon: the viscosity of the naphtha, the chemical nature of the naphtha, the percentage of the resin truly soluble in the naphtha, the viscosity of the soluble portion of the resin, and the relative ease of dispersion of the dispersible portion of the resin by aromatics, naphthenes, paraffins, etc.
TABLEI. STANDARDIZATION OF GARDNER TUBES Oil Blend No. 1 3 5 12 17
SD. Gr. 0.872 0.873 0.874 0.877 0.879
Stokes 0.619 0.999 1.479 3.383 5.002
Poises
0.54 0.87 1.29 2.97 4.45
Matches Tube Letter "Poises"
B D F N S
0.65 1.00 1.40 3.40 5.00
The thermoviscosity of each thinner was determined at 77" F. by the Saybolt thermoviscometer (9). This test has been used in the petroleum industry for burning oils and naphthas. The thermoviscosity is directly related to the kinematic viscosity (1). The thinners used are shown in Table 11. The toluene was the c. P. grade. Various samples of xylene of the 10' grade, both c. P. and industrial, were used with identical results. The other 525
Val. 33, No. 4
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526
TABLE 11. PROPERTIES OF THINNERS Dis t 11, Thinner Range, F. Xylene 275-288 High-flash naphtha 209-400 ..... Toluene 311-360 Turpentine 240-243 Butanol Methyl ethyl ketone 174-176 274-354 Saphtha A Saphtha B 357-413 138-225 Saphtha C Naphtha D 200-270 Naphtha E 242-320 Saphtha F 311-390 Naphtha G 345-460 345-460 Xaphtha H Naphtha I 296-391 a Visoosity, 20 centipoises.
Thermoviscosity a t
770 F.
Class
120 150 109 272 527 187 131 213 100 117 139 189 263 239 161
A
A A A
Kauri Butanol Value 98.6 96.2 106 m
..
A A B B B B B
....
Kauri gum 100 93 103 63 70 160 97 77 110 104 96 79 53
m m
75.0 78.5 35.1 38.5 39.2 38.2 35.8 30.5 76.0
solvents were all of commercial grade. Naphthas A to Z were commercial petroleum solvents, manufactured by various companies. Naphthas A and B were Edeleanu extracts of an aromatic crude. Naphthas C, D,E , F , and G represented various straight-run cuts from a mid-continent crude. Naphtha H was of the same distillation range as naphtha G, but it was taken from a Pennsylvania crude. Naphtha I was made by hydrocarbon rearrangement over a catalyst. The resins used are also shown in Table 11. The Glyptals, Resyl, Beckosol, and chlorinated rubber were of commercial manufacture. All of these except the rubber were resin “solutions” containing 50 per cent solids. The Kauri gum also contained 50 per cent solids, and was a solution in butanol. Thus this solution is similar to the other resins in solids content and to the solution used for Kauri butanol values in composit,ion. From 5 to 10 grams of resin were weighed to PROCEDURE. 1 mg. in a 125-ml. Erlenmeyer flask. An appropriate amount of thinner was then weighed into the flask, which was tightly stoppered and swirled until the contents were homogeneous. With 50 per cent resin solutions, this required approximately 15 minutes. Solid resins required standing overnight. Gentle warminz facilitated the dispersion and was found not to affect the res&. When dispersion was uniform, the viscosity was determined. The amount of thinner was chosen to give bodies from T to A (from 5.50 to 0.50 poise). The viscosities of duplicate mixtures agreed to within 0.05 poise. With xylene a t least ten mixtures were made with each resin, giving bodies from T to A. With all other thinners a t least five mixtures, covering the same viscosity range, were used. Various combinations of thinners also were prepared and tested similarly. Approximately seven hundred solutions were tested.
lb. of xylene/100 Ib. of resin t o give desired viscosity lb. of thinner/100 lb. of resin t o give same viscosity
(’)
Xylene was chosen as the standard for comparison because i t is a pure aromatic, yet is commonly used in the paint and varnish industry. Its thinning power is one of the highest for the hydrocarbons; yet it is not too strong to render comparison difficult with the poorest thinners, nor too weak t o permit comparison with the more powerful alcohols, ketones. esters, etc. The comparison of the amounts of thinners needed to give equal viscosities follows the work of Ware and Teeters on nitrocellulose (11). One advantage of this method over the comparison of the viscosities given by equal amounts of thinners (3, 6) is that the results can be used in practical formulation. Thus, if the A. C. of one thinner and the amount of i t needed for a given viscosity are known, the amount of any other thinner necessary for the same reduction may be found directly from the A. C. of that thinner. The aromatic coefficients of all the thinners on all the
... ...
Aromatic Coefficient Glyptal Rezyl 2464 775 -1 100 IC0 94 91 102 104 72 53 ... 290
.98 .
98 83 68 65 61 52 39 40
... ...
83 74 72 70 64 55 50 84
...
Beckosol 1303 100 90 104 51 3 15
...
..
97 72 63 60 55 43 27
96 70 37 33 28 16 0 3 73
46
77
Chlorinatpd rubbero 1 0 92 103 60 47 11.5 97 76 64 64 64 64 64
77
resins were calculated from the data by Equation 1. If necessary, interpolation was used to find the amount of xylene needed to match the viscosity given by some thinner. The method of interpolation is described later under “Xylene Reduction Curve”. The A. C. values obtained are shown in Table 11. The class is explained under “Correlation of A. C.”. The lack of correlation between the actual ability of a solvent to reduce the viscosity of Kauri gum (A. C.) and its tendency to precipitate that gum (K. B. value) is illustrated by Table 11, especially for xylene, turpentine, and naphtha C. Table I1 also indicates that the A. C. scale can extend from 0 to a t least 315. Properties of Aromatic Coefficient IKDEPENDENCE OF VISCOSITY. The definition of A. C. (Equation 1) does not specify the viscosity a t which it is to
be determined. Such specification is unnecessary (Table 111) for two solvents. T is the pounds of solvent used per 100 pounds of resin. B is the viscosity of the mixture in poises. The naphtha used was a mixture of 32 per cent xylene with 68 per cent naphtha F , since naphtha F alone will precipitate the Beckosol resin. TABLE 111. INDEPENDENCE OF A. C. 1303)
Aromatic Coefficient These seven hundred viscosities represent a practical but cumbersome test for thinning power. A method of expression of these results was found which could have given the same information, and more, from only eighty-five of these viscosities. This method of expression is the aromatic coefficient (A. C.), which is defined by:
c, = loo
Glyptal 2462 100 94 102 72
OF
VISCOSITY(BECKOSOL
High-Flash Kaphtha
T
pouAds 15 20 25 30 40 50
B. poises 4.18 2.75 2.0.5 1.50 0.85 0.50 Average
Naphtha
A. C. 90 92 89 90 90 90 90
T,
pounds 25 30 40 50 60
io
B,
poises 5.60 4.40 2.90 2.20 1.65 1.25
A. C. 43 43 44 43 42 43 43
INDEPEKDENCE OF THE PRESENCE OF OTHER SOLVENTS. Since many commercial resins are marketed as solutions, i t is important that a thinning power test should not be affected by the solvent already present, whose nature may be unknown. The independence of the A. C. is illustrated by Table IV. T again is the pounds of solvent per 100 pounds of resin, whether the resin is 100 or 50 per cent solids. OF A. C. TABLE IV. IKDEPEKDENCE
Resina a a b b C C
Resins used: solids in methyl a
OF
OTHERSOLVENTS
A. C . of Naphtha B on 20-Centipoise B, Chlorinated Rubber Poises 3.70 1.65 3.60 1.90 2.50 1.40 b = 50% solids
Since the A. C. is independent of the presence of other thinners, the reduction of a resin may be considered in steps, as the 20-centipoise chlorinated rubber of Table IV. On the other hand, the additivity of A. C. values permits the entire process to be considered as the action of the final mixture. This has been verified by reducing the rubber with methyl ethyl ketone and then with naphtha B, or with naphtha B and then with methyl ethyl ketone, or with a mixture of the two. If the final composition is the same, the final viscosities agree with one another within the limit of error. Obviously, all of the above properties of the A. C. will not obtain if the resin precipitates, even incipiently. Tables 111, IV, and V also illustrate the reproducibility of the A. C. determination. For thinners whose A. C. is less than about 125, two determinations will agree to within 3 A. C. units, and generally to within 2 or less. For higher A. C. values the discrepancies may increase, as Table V shows. More precise viscosity measurements might result in smaller limits of error.
The dispersion of a solid resin requires far more agitation and time than does the reduction of a resin solution. Many commercial resins may contain small amounts of extraneous material which will not dissolve. Small samples thus may not be representative of the lot. Both convenience and accuracy may be enhanced, therefore, by preparing a large stock solution of a solid resin in any appropriate solvent, with any desired solids content, and determining the A. C. of all other thinners on this stock solution. ADDITIVITY OF A. C. If the A. C. of a mixture of thinners is directly proportional to the A. C. of the components and the amounts of the components, (A. C.)IWI (A. C.)zW, 4- .. . . A . C. of mixture = (2)
+
w1 + wz + ....
where W1, TV2, etc. = amounts of components 1, 2, etc.
Table V illustrates the validity of this assumption, as applied to mixtures of the two most disparate thinners. As shown in Table 11, the A. C. of butanol on Beckosol 1303 is 315, while that of naphtha G is 0. The theoretical A. C. shown in Table V is that calculated from Equation 2. TABLEV.
527
INDUSTRIAL AND ENGINEERING CHEMISTRY
April, 1941
Viscosity of Thinner
ADDITIVITYOF A. C. AS APPLIEDTO BUTANOLNAPHTHA G ON BECKOSOL 1303
Wt. 7 of Naphtxs G
T PouAds
Poises
?,
Found
20 20 50 50 70 70
10 15 15 20 20 40
2.10 0.90 2.25 1.40 3.35 0.95
250 255 160 156 95 93
A. C. Theoretical 252.0 252.0 157.5 157.5 94.5 94.5
The A. C. values of mixtures of three thinners are also found t o be expressed accurately by Equation 2. This property of the A. C. permits the determination of t h e thinning power of a solvent which would cause precipitation of the resin, for a strong solvent can be mixed with the weak one, the A. C. of the mixture determined, and the A. C. .of the weak solvent calculated. The A. C. of naphtha G on Beckosol 1303 was found in this way by mixing with xylene. .Since the naphtha shown in Table I has an A. C. of 43 while that of xylene is 100, it can be calculated that the A. C. of naphtha F is 16. This is the value given in Table 11.
I n addition to the resins shown in Table 11, a high-viscosity cylinder stock was used to study the behavior of a resin which is perfectly soluble even in paraffinic thinners. The A. C. values of all the hydrocarbon thinners were determined on this resin. If these A. C. values are plotted against the thermoviscosities of the thinners, a straight line is obtained (Figure 1). If the A. C. values of the same thinners on Beckosol 1303 are plotted similarly, one straight line is not obtained (Figure 2). However, many of the points may be connected by two straight lines, as shown. Similar plots for every other resin show that straight lines will always connect the points corresponding to these two groups of thinners, though these lines for various resins have various slopes (Figure 3). Though not shown on Figure 2, benzene also lies on the same line as toluene, xylene, etc. Xylene here is a mixture of ortho, meta, and para isomers, each of which may have its own thinning power and its own thermoviscosity. That this mixture lies on the same lines as do benzene and toluene, which are chemical individuals, indicates either that all of the isomers possess the same A. C. and the same thermoviscosity, or that the varying A. C. values are compensated for by varying viscosities. I n either case, a xylene of 120 thermo-
I 3 l O p l E N 775-1 ~ 7-
3101
='"I
I
270
230
I70
P
A E NAPHTHA A XYLENE
I30
\
NAPHTHA D
I10
NAPHTHA C
90 JO
50
60
70
80
100 AROMATIC COEFFICIENT
90
110
I20
90 0
10
20
30
NAPHTHA C
50 60 70 80 AROMATIC COEFFICIENT
40
90
100
110
40
50
60 70 80 90 100 AROMATIC COEFFICIENT
FIQURE1 (Left). THERMOVISCOSITY us. AROMATIC COEFFKCIENT ON CYLINDER STOCK FIQURE 2 (Center). THERMOVISCOSITY us. AROMATIC COEFFICIENT ON BECEOSOL 1303 FIQURE3 (Right). THERMOVISCOSITY v8. AROMATIC COEFFICIENT OF VARIOUS RESINSIN CLASSA THINNERS
528
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 33, No. 4
viscosity is a definite, reproducible material and may be used cosities. Hence five A. C. values are found from two actual as a standard. measurements. Another line on Figure 2 connects naphthas C, D,E , F , For the group of thinners including toluene-xylene-turpenand G. These products represent fractions of the same or tine, similar relations are true. Since the A. C. of xylene is similar crude source and the same method of manufacture. defined as 100 for all resins, the evaluation of a new resin reHence they may be expected t o be of similar composition. quires the determination of the A. C. of only one other memFor these two groups of thinners, the A. C. values of all ber of the group, such as naphtha B. This, and the 100 for thinners of similar chemical composition are linear functions xylene, are plotted against the thermoviscosities, a straight of their viscosities. This substantiates the mechanism of line is drawn, and six A. C. values are found from one actual thinning which was postulated: The chemical composition measurement. If a new thinner is submitted, its A. C. on two dissimilar determines the dispersion of the resin, while the viscosity effect augments the reduction of body by true dilution. The resins, such as Beckosol 1303 and Glyptal 2464, is obtained. different slopes of the lines (such as those of Figure 3) for If these A. C. values fit on the straight lines which include different resins are due to the various effects of dispersion and naphthas C to G, we know that the new thinner is related to dilution on different resins. these other naphthas. From the thermoviscosity of the new The interplay of chemical dispersion and physical dilution thinner, its A. C. on all other resins evaluated can be found. is illustrated by a comparison of the A. C. values of naphthas Hence, from two determinations any number of A. C. values G and H (Table 11). Naphtha H is more paraffinic, so would can be obtained. The same is true if the new thinner is found t o belong to the toluene-xylene-turpentine group. be a poorer dispersing agent. However, by virtue of its As an illustration of the work saved by this correlation, conparaffinicity, its viscosity is lower than that of the more sider Table 11. These eighty-one A. C. values were detercyclic naphtha G, for the same boiling range. Consequently, naphtha H is a better diluting agent. On Glyptal 2462 and mined experimentally. Sixty-six of them, however, could Beckosol 1303, what naphtha H lacks in dispersing power have been found with equal accuracy (3 A. C. units or better) , happens to be compensated for almost exactly by its better from only eighteen actual determinations. The other fortyeight values, or 73 per cent of these A. C. values, could have diluting power. The dependence of thinning power on boiling range (and been read from graphs such as Figure 2. hence on viscosity) has been observed before but has been The correlation described is only empirical. This does not detract from its usefulness, but we do not expect that a diexplained by the concept of "moles of solvent per gram of vision into classes of thinners has any basic theoretical meanresin" ( 3 ) . The molecular weight of the thinner is independent of the resin being thinned. Hence the rate of change of ing. Attempts to correlate the A. C. values of a class of thinners with the composition of the thinners have failed. thinning power with boiling range (or with viscosity) should The thinners falling on the toluene-xylene line are desigbe independent of the resin. However, in Figure 1 the slope nated "class A" (Table 11). It might be expected that this of the line for the aromatics is identical with the slope of the class would be of definite chemical composition (100 per cent line for the more paraffinic naphthas C to G, in Figure 2 the aromatic), but the fact that turpentine happens to fall in slope of the line for naphthas C to G is greater than that for this group indicates otherwise. Similarly, class B embraces the aromatics. This shows that some additional factor is opthose thinners which happen to behave like naphthas C to G. erating to modify the effect of molecular weight. Of the fifteen thinners shown in Table 11, four do not fit This additional factor is believed to be the precipitating into either of the two classes. For these, the A. C. values on action of the paraffinic components of naphthas C to G. As each resin must be determined experimentally. As more molecular weight and viscosity of the thinner increase, the thinners are evaluated, it is expected that some of them will be precipitating power decreases, and the A. C. does not fall off found to fall into new classes, permitting additional correlation, so rapidly as would be predicted by molecular weight alone. Since the aromatics do not contain these precipitating components, this action is not in operation. The slope of the line for naphthas C t o G OB A. C. VALUES TABLB VI. CORRELATION more nearly approaches that of the aromatic A . C. o n Class A, A. C. on Class B, line for those resins which are least likely to >1in. Viscosity Viscosity % R A . C . 120 230 120 250 precipitate with these naphthas. Resin Solids Q For a given chemical type, there is a relation Cylinder stock 100 44 +I . . 100 61 100 61 50 71 +6 .. 100 68 100 58 36 100 58 32 between boiling point, specific gravity, molecular ~ ~ ~ $ ~ ~50 ~ 3 650 3 -4 weight, refractive index, and viscosity. The 20;~?;~do~;b;~~222 -1143 8j loo 66 64 64 65 42 mechanism of thinning indicates that the visGiyptai 2462 50 41 -8 40 100 76 50 33 +3 .. 100 76 72 57 cosity of the thinner is the most fundamental 50 57 4-3 35 100 60 59 30 of these colligative properties. An application of the other properties (as in the graphic resin solvency, 4) might produce analogous, if indirect, results. Table V I sliows the A. C. values of thinners of 120 and 250 thermoviscosity in each of the two present classes. These Correlation of A. C. Values points determine straight lines (as in Figure 2), from which may be found the A. of all other thinners in those classes. As Figure 2 shows, naphthas C, D,E, F , and G happen to A complete family of lines for all resins evaluated for class be so related that their A. C. values on Beckosol 1303 are A is shown in Figure 3. If preferred, the A. C. of a thinner linear functions of their thermoviscosities. The same linear may be calculated from the A. C. of the 120- and 250-thermorelation has been found with all other resins examined to date. viscosity thinners, instead of plotting the line. The minimum If a new resin is submitted, it suffices to determine the A. c.,0, and R (Table VI) are explained below. A. C. of only two of these naphthas, such as C and G, on the The A. C. values of the 120- and 250-thermoviscosity thinnew resin. These two A. C . values are plotted against the ners for classes A and B also give information concerning the thermoviscosities of naphthas C and G, a straight line is relative effects of viscosity and chemical composition of the drawn between the two points, and the A. C. of naphthas D,E, thinner on the resin. and F is read from this line a t the appropriate thermovis-
2~~~7"5"-";"
c.
INDUSTRIAL AND ENGINEERING CHEMISTRY
April, 1941
Xylene Reduction Curve One great disadvantage in comparing thinners on the basis of constant viscosity is the difficulty of obtaining equal viscosities with different thinners. This can be overcome by the use of an accurate interpolation formula. The form most commonly used is logarithmic, but this leads to appreciable errors. The development of an improved form not only permitted accurate interpolation but also furnished interesting mathematical explanations for the properties of the A. C. discussed above. At least ten points on the xylene reduction curve were obtained for all the resins, including the cylinder stock. Figure 4 shows the curves obtained with this stock and with Beckosol 1303. The two curves are similar in shape although the materials are dissimilar. Since these curves appear to be hyperbolic, an equation of the following general form was applied: B+S=-
Q
529
viscosities above 5.50 poises have not been measured, the upper limit for Equation 4 cannot be given. The determination of Q and R for any resin should involve the measurement of a t least five viscosities, a t approximately bodies S, P, K, G, and B. When these constants are known for a resin, the determination of the A. C. of any thinner on that resin requires the preparation of only two mixtures of thinner and resin. The amounts of xylene needed for the same viscosities as were obtained with the thinner are calculated from Equation 4,and the A. C. of the thinner is found from Equation 1.
(3)
T+R
where B = viscosity, poises T = Ib. thinner/100 lb. resin Q,R, S = constants For all of the resins a solution of Equation 3 gave an S value of 1.00. Hence the reduction curve may be expressed by: B + l = - - - - - -Q -
(4)
T+R
Table VI1 gives the data from which the curves of Figure 4 were plotted, as well as the viscosities calculated by Equation 4 and by the conventional logarithmic form. The values of Q and R used for these resins are shown in Table VI.
0.01 IO
20
40
30
0.65460
TABLEVII. XYLENEREDUCTION CURVE Cylinder Stock B , Poises T Calcd. Pouids Measured a
b
5.25 5.25 5.27 4.50 4.50 4.62 3.55 3.58 4.10 3.40 3.64 ’ 3.40 2.95 3.00 3.22 2.35 2.38 2.56 1.75 1.75 1.84 1.10 1.09 1.09 0.69 0.69 0.70 0.55 0.54 0.55 a B 1 = 44/(T 1). 5 yo solids = -16.25 log E 17.36. C B 1 = 65/(T 4). d yo solids = -15.80 log B 26.15. 6 7 8 9 10 12 15 20 25 27.5
+ +
+
-
0.55
Beckosol 1303 B , Poises T Calcd. PouAds Measured c 14 15 17 20 22.5 25 30 35 40 45
5.45 4.85 3.95 3.05 2.50 2.10 1.50 1.10 0.80 0.55
5.50 4.90 4.00 3.06 2.51 2.09 1.50 1.10 0.80 0.58
0.50 4
5.45 5.00 4.16 3.19 2.60 2.12 1.46 1.03 0.75 0.55
+
+
0.45 0.40 0.35 a30
025 0.20 0.15
0
The use of Q and R of Table VI’in Equation 4 will permit the calculation of the viscosity of any mixture of xylene with one of the resins, from body T to body A (5.50 to 0.50 poise). The calculated values will agree with the measured values within 0.05 poise a t all points. This is the limit of error of the viscosity measurement. The errors associated with the logarithmic form may be as large as 0.25 poise, as indicated in Table VII. From the body obtained with any amount of xylene, the A. C. of any thinner, and Equation 1, the body obtained with any amount of thinner also may be calculated. Hence, for the “classified” thinners, Table V I alone, with Equations 1 and 4, permits the calculation of the body obtained with any amount of any of the thinners on any of the resins, from body T to body A. For 20-centipoise chlorinated rubber, R is - 143. Equation 4 would predict an infinite viscosity if T were 143 pounds and a negative viscosity if T were less than 143. It is obvious that Equation 4 cannot be used a t high viscosities. Since
20 30 40 T’LBS. XYLENE PER 100 LBS RESIN
IO
FIQURE4 (Above). XYLENE-REDUCTION CURVEFOR B FIGURE5 (Below). XYLFJNE-REDUCTION CURVEFOR 1)
+
Equation 4 predicts a linear relation between T and 1/(B 1). Figure 5 illustrates this, again for cylinder stock and Beckosol 1303. The errors indicated in Table VI1 do not show a t the scale used for either Figures 4 or 5.
+
Significance of Q and R Suppose we need TIpounds of xylene per 100 pounds of resin to reduce the resin to body S (5.00 poises), and TI pounds of xylene to give body D (1.00poise). By Equation 4,
T‘ - TI
=
6,
Q is thus a measure of the ease of reduction of a resin.
Q appears to be a fundamental characteristic of a resin.
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
530
Two separate samples of Glyptal 2462, Glyptal 2464, and 20centipoise chlorinated rubber have shown constant Q values. Three separate samples of Beckosol 1303 have given the same Q. One of these was stored for a year, and Q was unchanged. The value of R has varied several units from batch to batch of resin. Equation 4 shows that the xylene reduction curve is a pure rectangular hyperbola if the coordinate axes are translated by 1 unit of viscosity and R units of xylene. The significance of R is no more understood than is that of 1 .
Vol. 33. No. 4
The total reduction to viscosity B’ is accomplished by the mixture of thinners 2 and 3, so
Combining ,
iManipulation of Equation 4
The sample of Beckosol 1303 used in the reductions of Table I11 showed a Q of 65 and an R of - 1. (Table V I gives 65 and -4. This illustrates the constancy of Q but variation in R for various samples of the same resin.) The application of Equation 4 to the reduction with high-flash naphtha gives a Q of 72 and an R of - 1, while the data for the naphtha require a Q of 151 and an R of - 2 . , This illustrates that Equation 4 is not limited to the reduction Tvith xylene alone. Consider a resin whose xylene reduction curve involves the constants Q1 and R1, while the reduction with some second thinner involves Q z and Rz. To reduce the resin to some viscosity B requires T I pounds of xylene or T z pounds of the second thinner per 100 pounds of resin, and a lower viscosity B t requires TI pounds of xylene or Ti pounds of thinner. Then by Equation 4,
This additivity of A. C. values was illustrated by Table V. Hence the properties of the A. C. might have been predicted from Equation 4, though they cannot be derived from a logarithmic form of reduction equation. Consider a solid resin whose xylene reduction equation involves Q’ and R’. Now reduce this resin with some thinner to a solution whose fraction of solids is S. The xylene reduction curve of this solution will involve Q and R. From Equation 4 it can be shown that Q R
=
=
Q’S
(100) (1 - S)
(12)
A. C. (m) + R’S
where the A. C. is that of the thinner used. The experiments from which the data of Table I V were taken may be used t o check Equations 12 and 13. For resin a Table V I shows that Q’ = 222 and R’ = - 143. For resin b from the data, whence Q1T6
- QITZ= QzT: - QPTI A. - -C . - -Ti = - Ti 100 T2 Ti
S
The Q and R values given above, derived from the data of Table 111, may be used to check Equation 9. For the highflash naphtha, QI 65 R -1 A. C = 0.90;
I-
R2
=
= -1
1.00; -:100 = 0.90
For the naphtha,
Since R is rounded off to the nearest 0.5, the above agreement of Rl/R2is considered to be satisfactory. Similar experiments have verified Equation 9 for the cylinder stock and the rubber. Equation 9 expresses the first property of the A. C. discussed above. That is, since Q and R are independent of viscosity, the A. C. must be similarly independent. Combining Equations 7 and 9,
-
TI= -
Ti
Tg - T P
= 0.50;
Q
= 111; R = -22;
From Equations 12 and 13, Q resin c from the data,
By definition (Equation l),
q2= 72
S
A. C . 100
(7‘: - T I ) is the amount of xylene needed for a reduction from viscosity B t o viscosity B’, while (TI - T2) is the amount of thinner needed for the same reduction. Hence the A. C. can be determined on a partially reduced resin, regardless of the thinner used originally t o give viscosity B. This property of the A. C. was illustrated by Table IV. Suppose thinner 2 is used t o reduce the resin to viscosity B as before, and that thinner 3 is then added to obtain viscosity B’:
=
0.50; Q
111; K
=
A.
c. =
100
111 and R = -22.5.
For
-14; A. C. = 113
From Equations 12 and 13 Q = 111 and R = -14. Knowing Q and R for a resin solution, and the solids content, &’ and R’ for the solid resin may be found by Equation 12 and 13. Since Q is a measure of the difficulty of thinning a resin, it is of interest to compare the Q values of solid resins. Thus the application of Equation 12 to the Q values given in Table V I shows that Glyptal2464 is harder to reduce than is the cylinder stock. Equation 12 does not involve the A. C. of the thinner, which may be unknown. The increased convenience and accuracy of preparing stock solutions of solid resins, instead of using the solid for all reductions, has been mentioned. Equations 12 and 13 render unnecessary the determination of even the xylene reduction curve on the solid resin, if that of the stock solution is known. Equation 4 also may be used to point out some difficulties associated with an alternate method for thinning powers-the comparison of viscosities at a given solids content (3, 6 ) . If an amount of xylene T gives viscosity B1, while the same amount of a second thinner gives viscosity Bz, Equation 4 predicts that
Bi B2
+ 1 - (A. C./100)T + R
+1
T+R
(14)
where A. C. is that of the second thinner. Since A. C. and R are independent of T , it is obvious that Bl/B2 cannot be independent of T . Hence the constant solids content method of evaluating thinning power cannot be independent of the solids content. Equation 14 shows that if the resin is modified by the addition of thinner so that R is zero, BJB2 will be a constant indepmdent of T. Hence the slight departure from con-
INDUSTRIAL A N D ENGINEERING CHEMISTRY
April, 1941
stancy of the resin solvency noted by Kurtz (3)is due to the R factor of the resins used. Equation 13 may be used to reduce the resin to make R equal zero. Thus 20-centipoise chlorinated rubber would have to be cut to 43 per cent solids with xylene, or to 44.5 per cent solids with methyl ethyl ketone, to give an R of zero. Even if this were done, however, the resin solvency or a similar test would not be additive, unless it were defined as (& 1)/(Bt 1).
+
+
Storage Stability Naphtha D has an A. C. of 33 on Beckosol 1303 (Table 11). From the Q and R values for this resin (Table VI), it oan be calculated that 60 pounds of naphtha D per 100 pounds of resin will give body K-, while 70 pounds will give body H. Actual determination gave body K-, as predicted; but instead of body H, body M was obtained. The first solution was stable in storage, but the second, though apparently free from turbidity, separated after one week. Similar experiments have indicated that whenever a higher viscosity is obtained than that predicted by the A. C. and Equation 4, the solution giving that viscosity is not stable. This is a more sensitive test than is turbidity. A naphtha of low A. C. was mixed with xylene to give a series of graduated A. C. values. It was found that a 25-A. C. thinner could reduce Beckosol 1303 satisfactorily to body S but not lower. A 33-A. C. thinner could be used to body K, but a 36-A. C. thinner was needed for body A. For safety, therefore, a thinner of at least 36 A. C. should be used to reduce Beckosol 1303. This is the minimum A. C. shown in Table VI. Our poorest classified thinner, naphtha G, could be used with Glyptal 2464 without difficulty. Hence, no minimum A. C. is shown for this resin. Possibly an A. C. of 30 would cause separation, but we have found no commercial thinner which has such a low A. C. on this resin. The concept of minimum A. C. indicates the fallacy of comparing thinning powers on a resin, when one thinner may be below the minimum. The reduction given by a thinner which causes incipient precipitation bears no relation to the contribution which that same thinner can make if combined with a stronger solvent to prevent precipitation. If 10 per cent of xylene is added to the thinner and the A. C. of the mixture is determined, precipitation can be detected; for the A. C. of the thinqer, calculated from that of the mixture, will be higher than that of the thinner alone. If this occurs, 20 per cent of xylene should be used, etc., until two mixtures give the same calculated A. C. for the thinner itself. Instead of xylene, of course, any other strong solvent of known A. C. can be used. With 20-centipoise chlorinated rubber a thinner of class B must be strengthened with enough xylene to give a mixture of 85 A. C., while naphtha B alone, with 76 A. C., is satisfactory. Apparently the precipitating action of the paraf3n.s in class B must be offset by the addition of more xylene than would be indicated by the A. C. alone. However, turpentine, a member of class A, also must be strengthened for use of this rubber. Obviously, minimum A. C. is not understood completely, and work is in progress on this problem.
Mixtures of Resins The thinning powers of mixtures of thinners on a resin can be calculated from the A. C. values of the components. An analogous relation for the thinning power of a thinner on a mixture of resins has not been found. For instance, Beckosol 1303was reduced to body B with xylene; 20-centipoise chlorinated rubber also was reduced to body B with xylene. When
531
equal amounts of these solutions were mixed, body D resulted. Similar experiments with Aroclor 1254 and the rubber, however, gave lower bodies than would be expected. Apparently, a mixture of resins must be regarded as a new resin, and the A. C. values determined on this new resin may have no relation to the A. C. values on the components. Consequently, our work on mixtures of resins, similar to that of the Los Angeles club (6),has not been fruitful. When the Aroclor was mixed with the rubber, the minimum A. C. requirements for the rubber were lowered. From this and a few other experiments, it may be suggested that a material which will plasticize a resin is one which will raise the apparent A. C. of a thinner on that resin.
Summary
1. The A. C. of a thinner is a practical measurement of the thinning power and is different for different resins. 2. The A. C. values of thinners of similar chemical composition are directly related to the viscosities of the thinners. 3. The A. C. is independent of the viscosity at which it is determined and is independent of the presence of other thinners. It may be measured on a resin as such, or on a solution of that resin in any appropriate solvent, with the same results. 4. The A. C. values of thinners are additive. The A. C. of a mixture of thinners can be calculated accurately. 6 . Mixtures of resins must be considered as new resins and studied as such. 6. The reduction of the viscosity of a resin by a thinner is a combination of physical dilution and chemical dispersion. 7. The reduction of a resin by a thinner is accurately expressed by a hyperbolic €unction, over the range of body T to body A (5.50 to 0.50 poise a t 77" F.). Literature Cited (1) Brown, L. R.,A . S. T.M . Bull., p. 23,Dec., 1940. (2) Huff et al., Am. Paint J., 24, Convention Daily 12 (Nov. 1. 1939). (3) Kurts, Harvey, and Lipkin, IND.ENG. CHEM.,Anal. Ed., 11, 476 (1939). (4) Zbid., 11, 484 (1939). ( 5 ) Loa Angeles Paint and Varnish Production Club, Am. Paint J., 24, Convention Daily 12 (Nov. 1, 1939). (6) McArdle, Moore, Terrell, Haines et al.. IND. ENG. CHEM.. Anal. Ed., 11, 248 (1939). (7) Philadelphia Paint and Varnish Production Club, Am. Paint J.. 23, 52 (Nov. 14, 1938). (8) Ibid., 24, Convention Daily 23 (Nov. 3, 1939). (9) Tag Manual for Inspectors of Petroleum, 25th ed., p. 67 (1939). (IO) Toby, E. M., Oficial Digest Federation Paint & Varnish Production Clubs, 1938, 261. (11) Ware and Teeters, IND. ENG.CHEM.,31, 738 (1939). P R I W ~ N before T ~ D the Division of Paint and Varnish Chemistry a t the 99th Meeting of t h e Amerioan Chemical Society, Cincinnati, Ohio.
