RELATION OF THINNERS IN
Overlapping Varnish
I
N THE first paper on this subject the authors2 discussed the effect of various thinners on the wet-edge time limit of a straight China wood oil-phenolic re s i n v a r n i s h . With the various thinners tried in this varnish the percentage of thinner remaining a t the wetedge time limit lay between 70 and 80 per cent. The viscosity of the varnish a t the wetedge time limit seemed to be J. K. STEWART AND H. L. BEWICK' practically the same for the Anderson-Prichard Oil Corporation, Chicago, 111. several thinners tried. A critical point was noticed after the wet-edge time limit was reached, after which the viscosity Mineral S irits -A. 8. T. M. increased rapidly. Considerable difference was found in the KO. Initial b. p. wet-edge time limits by the use of various mixtures of mineral F. C. spirits and different types of kerosene. 1 324 162.2
Coatings
2
307
152.8
p a r t s , a n d e a c h p a r t was thinned separately. In one case the naphtha portion of the thinner was mineral spirits 1,* and the resulting varnish was designated as varnish 8. I n the other case mineral spirits 2 was used, and the varnish designated as varnish 9. Varnishes 8 and 9 differed, then, only in the type of mineral spirits used. Figure 1 and the following table show the physical characteristics of mineral spirits 1 and 2: DistillationDry point OF.
392 390
OC. 200 198.9
Comparative Spot Dry Time Min. 9 8
Solvenoy in 20 Grams Kauri Butanol Soh. (2%. 33.6 34.0
I n the previous work on this subject, data were obtained regarding the percentage of thinner remaining in the film a t various points, including the wet-edge time limit, the viscosity of the film a t various points including the wet-edge time limit, and homogeneity of the varnish film. The procedure for obtaining these data was described in the previous paper.2 Figure 2 shows the percentage of thinner remaining in the film a t the wet-edge time limit.
FIGURE 1. EVAPORATION CURVES OF MINERAL
SPIRITS
The present paper gives similar data on a different varnish, comparing two naphthas in the mineral spirits range. I n this work the varnish used was a clear 25-gallon-length varnish of a type suitable for architectural purposes. The resin was of the 100 per cent phenolic type. China wood oil was used with a small amount of bodied oil as a check after cooking. The varnish was reduced with a mixture of 71.4 per cent naphtha, 23.8 per cent turpentine, and 4.8 per cent xylene. The mineral spirits and turpentine were added to the hot varnish. The xylene was added after the varnish had been cooled. The reduced varnish contained about 48.5 per cent volatile material. One batch of varnish was cooked and then divided in two 1
FIQURE 2. EVAPORATION CURVES OF VARNISHES
The viscosity curves of the varnish films (Figure 3) are similar to those given in the previous paper. The critical point of varnish 8, with the longer wet-edge time limit, occurs before that of varnish 9; this behavior falls in line with the previous work (see table which follows).
Present address, Sherwin Williams Company, Chicago, Ill. 940-3 (1936).
* IND.ENQ. CHEM.,28,
8
167
Used as the mineral spirits portion of the thinners in t h e previous paper.
Varniah NO.
R&+
WeYet-Edge Time Limlt at 80' F. Min.
Thinner Remaining s t W. E. T. L. from Evaporation Curves s t 80' F. %
Viscasitiea a t W. E. T. L. at SO' F. SS.
7 6
80 70.4
11
S Q
12
The value found for the viscosity of varnishes a t the webedge time limit is approximately the same as that found for the varnishes previously studied.* T h e viscosity pointsat the wet-edge time limits given in the previous paper Iav closer to the bend FronaE 3. VISCOSITYCURYESOB i i the curve than is VARNISH FIlrM8 found to be the case for varnishes 8 and 9. This mav be cxnlained on the followine hasis: The thinners used in Garnishes 8 and 9 evaporated m&h more rapidly than those in the previous work. Any cooling effect due to the more rapid evaporation of the thinners would tend to incrfase the setting up of the junction. Again, the wetedge time Innit occurred when 70 to 80 per cent of the thinner remained. As regards the condition of homogeneity, the tests used in the previous paper were applied with similar results. Figure 4 shows wrinkling on E film of varnish 9 but no wrinkhg on varnish 8. Again it was found that varnish fitms, when dried to the wet-edge time limit, scraped off, thoroughly mixed, and reapplied, gave no junction with a fresh varnish a m brushed onto it a t right angles. In the previous paper a study of the viscosity and evaporation c w c s led to the idea that the varnish showing the longer wet-edge time limit would also show a lesser rate of change in the viscosity as it dried to the wet-edge time limit. With more experimental data a t hand, this hypothesis was confirmed as shown in the following table:
Min.
S
Scc. bubblc lime
7 3'
Q
1.0 1.35
1.1 1.5
TABLE I.
Slower Faster
SUMMARY OF
Isolvent More soivant
~ I Q U R E4.
Summary The data from the two papers indicate that two phenolic resin varnishes, which differ considerably, have some definite physical characteristics a t the wet-edge time limit point in common: 1. The percentage of solvent in the varnish at this point lies between 70 and 80 per cent. 2. The critics1 point in the viscosity of the varnish in the film lies in roximity to this fPi"t. , , 3. ' h e viscosity of t e varnlsh m the 6Im at the wet-edge time limit mint lies within narrow limits. 4. The*wet-edge time limit is inversely proportional to the rate of change of the viscosity of the varnish in the film, a8 it dries to the time limit point. The varnishes used d8ered as follows: Length, gal. E5 Oil Straight China
DATAON VAKNISEES
woad
---
Thin+: Varnish Cornpaition*
%
Relative 10FQ0% 90-S0% Euapn. Rate of solven$ Wet-Edge thinner thinn:r Time Linrit iernsining iemniriing from Varnlsh Mi". 9%. bubble time
Thinner Mixture
KI 15'M.S 85 KI 16: M.S. 86 K< 15, M.S. 85
6
28.26.27 20 22 24 20:23:22 19, 18.22
0.23
0.27 0.27
0.50
0.20 0.20 0.20
Sloweat Third Seaond Most rapid
Least solvent Mast advent Second Third
0.25
Mostrwid siowest Second
Least solvent Seaond Most solvent
Slowest Seaond Mostranid
h a s t advent Second
0.44
l3rouo 2
K 1 2 5 M.S.75
2
~ ~ 2 M.S. 5 ' rs
7 4
I 4 2 5 : M.S.75
25 23 25 23'22'24 19:20:22
0.36 0.41 0.53
0.32
0.38
Group 3 3A
3B *K
Ks 15. M.S. 85 Same 2B Same 3B
+ +
=
kerosene: M.S.
20 22.24
-
0.27
0.20 0.27 0.29 mineralspirits: B = butanol.
19:20.21
IS.. IQ.20 .
0.30 0.33
Mineral &ita Kerosene
Relative Sol"@noY of Thinner
Group 1
Ki 1.5 M.S. 85
1
3 6
COMPARISON OF WBINKLING OF VARNISH FIMS
Tho value 1.5 seconds per minute was obtained by dividing the daerence in the viscosity of fresh varnish 9 and varnish 9 evaporated to 90 per cent solvent remaining, by the time interval (2.5 minutes). Table I, which gives similar data from the previous work, apparently supports the hypothesis.
Rate of Viaoosity Change WBIMm. EXPosUW
3
VOL. 29, NO. 2
INDUSTRIAL AND ENGINEERING CHEMISTRY
168
Mast *&rant
25
China wood and a ems11 Bmomt of bodied linaeed Mineiai spirits Turpentine and xylene
Acknowledgment The writers are indebted to C. Hopper for assistance in the production of panels demonstrating the wrinkling of the varnish film. They are also indebted to D. Fay and A. Luetz for laboratory assistance and drawing of charts. Rzomvao SeDtambez 14, 1938. Pi-ented before the =id. lion d Paint and Varnish Chemistry at the 22od Meeting of the Amexis.%nChemiaal Sooistu. Pittsburgh, Pa., September 7 to 11. 1936.
