RELATION OF THINNERS IN
OVERLAPPING VARNISH COATINGS The purpose of this paper is to discuss the possible effect the type of petroleum thinner may have on the wet-edge time limit of one type of varnish. Similar performance may be expected of a pigmented varnish. Further work will center around other types of varnish and the corresponding pigmented varnishes. For the particular varnish tested here, the percentage of thinner remaining at the wet-edge time limit lay between 70 and 80 per cent. The viscosity of the varnish in the film at the wet-edge time limit was between rather narrow limits. A critical point was reached in the rate of change of viscosity shortly after the wet-edge time limit was reached. Beginning a t this point the viscosity increased rapidly. The type and amount of kerosene must be considered in connection with the wet-edge time limit. The addition of a small amount of butanol to this varnish decreased the wet-edge time limit. Indications are that the type of kerosene used may affect the homogeneity of this particular varnish in a film at the wet-edge time limit.
S
EVEKAL tests were mentioned by Gardner in 1935 for evaluating the brushing and leveling properties of paint (1). In actual practice an additional property is looked for-the maintenance of a wet edge. After the first strip of varnish is applied to a large surface such as a wall or ceiling, often several minutes elapse before the second strip of varnish is applied. To obtain a smooth union a t the joining line of the two strips, the edge of the first strip must be n e t enough. The desirability of a long wet-edge time limit is apparent. The wet-edge time limit is defined as the shortest time that elapses from the application of a varnish film to the time of the application of the second varnish film applied a t right angles and overlapping, which maintains a permanently visible junction \\-ith the original varnish film.
The Problem To determine the possible effect of the petroleum thinner, it was proposed to study the condition of the varnish film as it passed through the zone of the wet-edge time limit by obtaining data on ( a ) percentage of solvent in the varnish film, ( b ) viscoqity of varnish in the film, and (c) homogeneity of the film. In this preliminary work the problem was reduced to simple terms : A clear, 50-gallon-length varnish was used in order to avoid the effects of pigments. The resin was of the 100 per cent phenolic type, and straight China wood oil was employed. The varnish was heated for approximately 30 minutes to 550" F. After being held a t this temperature for 2 minutes, it a a s allowed to cool to 475" F. and thinned. The varnish was reduced with a small amount of petroleum thinner in the mineral spirits range. The reduced material is referred to as the "base varnish." The base varnish contained 331,3 per cent volatile matter. Samples of the base varnirh were further reduced with mixtures of the thinner already descriked and of thinners in the kerosene range. Eventually the varnish samples contained 50 per cent volatile matter. Determination of Wet-Edge Time Limit At present, certain laboratories use a practical method for evaluating the wet-edge time limit: 1. Brush a varnish lengthwise on half of a metal panel and note the time. 2. After specified time intervals, brush at right angles into the varnish films. 3. The wet-edge time limit is taken when the film brushed on at right angles maintains a definite junction which may be seen. The same brush is used throughout the test without cleaning.
The following modifications of this method were used: 1. .4t approximately 77" F., 1.5 cc. of the varnish were dropped on half of a 4 X 10 inch steel panel, placed horizontally. A clean, dry 0.5-inch camel's hair brush was used to spread the varnish film lengthwise over half of the steel panel within a period of one minute. The same camel's hair brush was cleaned with benzene or acetone and dried between tests. When 1.5 cc. of the varnish were brushed out on half of a 4 X 10 inch panel by this method, the resulting dried varnish film averaged 0.0013 inch. Tests with a few of these varnishes gave roughip the same value-. g., panel 1A = 0.00123 inch, panel 3B = 0.00132 inch. 2. In this test one-minute intervals were used for brushing in at right angles. 3. Special precautions were found necessary to obtain consistent data: A special room was used and kept closed during the tests to avoid drafts. A constant-temperature room was not availahle, so room temperature was held between 74" and 79" F. by making adjustments bet ween tests.
J. K.STEWART A N D H. L. BEWICK Anderson-Prichard Oil Corporation, Chicago, Ill.
By repeated trials it was found possible to check the wetedge time limit within one r e a d i n g 4 e., one minute. 9-10
AUGUST, 1936
INDUSTRIAL AND ENGINEERING CHEMISTRY
DETERMINATION O F SOLVEST REMAINIKG I N VArtXIsH FILM. The Rubek and Dah1 method, developed in 1934 ( 2 ) , was adapted for these experiments as follows:
-4 friction-top can lid ( 2 ) was fitted with a watch glass cover to stop evaporation during weighing. The amount of varnish sufficient t o give a film of approximately the same thickness as t,he film used in the wet-edge test was introduced into the can lid with a calibrated eye dropper. The varnish was weighed, and a stop watch started; the watch glass was removed and the varnish spread evenly with the small weighed copper strip, which was allowed to remain in the varnish for the remainder of the test. The percentage of thinner remaining at each 5-minute interval was calculated and plotted against time. The graph thuy obtained !vas designated an “evaporation curve.’’
This niethod was tested by spreading varnish and allowing the watch glass to remain in place during the entire run. At the end of a n hour, only about 2 per cent of the thinner had evaporated.
Determination of Viscosity of Wet Varnish Film REGULAR METHOD. One test for determining viscosity n-as as follows:
Six and seven-tenths cubic centimeters of the varnish sample were measured out on an 8 X 20 inch steel panel with a Luer syringe. An average film thickness of approximately 0.0013 inch i b obtained for this type of varnish. A clean dry brush was used t o spread t,he varnish film over the entire panel. The time allowed for brushing was one minute, and the time Tvas noted as the brush entered the varnish. The panels were allowed to lie F.) and free horizontally in a room at a uniform temperature ( i i o from drafts for the required length of time. The time interval was taken from the beginning of the brushing period. At the end of the time interval the varnish was scraped into a small aluminum trough a t the end of the panel. The varnish in the trough was transferred to a Gardner-Holdt body tube. Thirty seconds were allowed for this entire operation. The viscosity of the sample !vas determined by counting the number of seconds required by the bubble to rise a specified dist.ance in the Gardner-Holdt tube. In comparing two varnish samples, therefore, the varnish which allowed the bubble to rise more rapidly had the lower viscosity. I t was of utmost iniportance that the temperature of the varnishes should be constant (e. g., i?”F.) before readings were taken. Slight changes in the temperature of the varnish affected the viscosity reading coniderably. The aluminum trough was made to fit the end of a mall spatula so that the varnish could be removed quickly. Comments regarding film thickness, condition of brush, and room conditions, as given under “Determination of Wet-Edge Time Limit” apply here also. Consecutive readings on various samples checked within 6 per cent. RIETHOD. The second inethod for estimating ALTERNATE viscosity was as follows : Forty cubic centimeters of the varnish sample were measured into a Petri dish (3.5 inches in diameter). The varnish was allowed to evaporate at room temperature until a definite weight of the solvent remained in the varnish. A body tube was filled with the evaporated varnish and the viscosity determined. The layer of varnish in the Petri dish was not of the same order of thickness as that ordinarily found in a varnish film. Slower drying took place (approximately 36 hours). For this reason it was not practicable to hold conditions constant. During drying, skinning sometimes occurred. The precision of this method is indicated by the maximum variation from t h e average as shown in Table 111. The value of this method lies in the fact that the results obtained for a figure corresponding to the wet-edge time limit approach the figure obtained by the regular method; t h e method therefore acts tis aii independent check.
94 1
Methods for Studying the Film Homogeneity The s a m p l e s u s e d were fresh varnish and varnish dried to the point of the wet-edge limit. Some of the varnish scraped from the panel a t its wet-edge t i m e limit was brushed on a section of a steel panel. An overlapping section of t h e p a n e l w a s brushed with fresh varnish. T h e p o i n t of junction was observed. T h i s p r o c e d u r e was tried on varnishes 1A a n d 3 B . I n neither case was a junction line discernible. V a r n i s h 1A had the longest wete d g e t i m e limit, and v a r n i s h 3B had the shortest. Varnishes were poured, a t the same time, on an 8 X 20 inch steel panel. The dripping panels were held vertically a t right angles to the draft from an electric fan for an hour. The panels were then removed from the d r a f t and allowed to finish drying a t room temperature. The film of varnish 3B showed wrinkling over a n area of a b o u t 10 s q u a r e inches. The adjacent 1 - TIME IN MINUTES J area of v a r n i s h 1.4 FIGURE 1. EVAPORATION CURVES s h o w e d n o signs of OF VARXISHES wrinkling. The space ( T o p ) Varnishes 1 , 3, 5 , 6 : 7.5 per cent between the two areas kerosene and 42.5 per cent mineral spirits by weight (thinner mixture kerosene 1 5 averaged about 1 inch. and mineral spirits 85 per c$nt) This behavior is inter(Center) Varnishes 2, 4, 7: 12.5 per cent kerosene and 37.5 per cent mineral spirits esting in view of the by wei,ght (thinner mixture, kerosene 2.5 and mineral spirits 75 per cent) fact that thinner mix(Rottom) Varnish 3 and modifications: ture 3B had g r e a t e r 3.4 contains 1 per cent and 3 H contains 1.5 per cent butanol by weight solvency than thinner mixture 1-4. Several panels were poured and the same relative results were obtained in each case. WET-EDGETIMELIMIT. Fresh samples were made from the second base varnish, as shown under “Check on batch 2,” Table I. The first and the second base varnishes differed in two respects: The phenolic resin used for the second base Tarnish was made by a new process, and the second base varnish was cooked some weeks after the first base varnish. To obtain a n ample supply of the second base varnish, several half-gallon laboratory batches were cooked, thinned, and blended. The data on batch 2 give a comparison of two serieq of reduced-varnish wmples inade from the qame base
varnish. The reading for varnish 6, batch 2, is 18. Apparently this value is out of line. The explanation m a y lie in the fact that this was the only sample that skinned, indicating some abnormal factor. The values shown for batch 1 a r e of t h e same order as those for batch 2. Furthermore, the values shown for t h e check on batch 2 are slightly greater t h a n t h e corres p o n d i n g values shown for batch 2. This d i f f e r e n c e may have been due t o the f a c t t h a t t h e s e c o n d base varnish ha d skinned, thus making it necessary to strain it before the check samples were made.
THINXER PER-
FIGCRE 2.
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INDUSTRIAL AND ENGINEERISG CHEMISTRY
942
VISCOSITY CURVES OF V.4RNISH
FILMS
(Top) Varnishes 1 , 3 , 5 , 6 : 7.5per cent kerosene and 42.5 per cent mineral splrlts by welght (thinner mixture. kerosene 15 and mineral spirits 85 per cent) (Center) Varnishes 2 , 4 , 7 : 12.5 per cqnt kerosene and 37.5 per cent mineral splrlts by weight (thinner mixture, kerosene 25 and mineral spirits 75 er cent) (Bottom) Varnis: 3 and modifications: 3.4 contains 1 per cent and 3B contains 1.5 per cent butanol by weight
CEKTSGE. The p e r c e n t a g e of thinner remaining in the film a t the wet-edge time limit is shown in Table I1 and Figure 1. VISCOSITY. The v i s c o s i t y of the varnish in the film a t the w e t - e d g e time limit is shown in Table 111. The
r
TABLE I. WET-EDGETIMELIMIT,IN MINUTES -Second BaseFirst Base Varnish Varnish Batch Check on 2 batch 2 Sample Description" Batch i 1 K1 1 5 7 , M.S. 85 28 26 27 1.4 K1 15%, M.S. 85%, 1/z% X 27 25 27 2 K 1 2 5 7 M S 75 25 23 25 2-4 K1 2 5 d : M:S: 75%. 1./ a %._X 26 23 25 20 22 24 19 20 21 18 19 20 4 K2 25 M.S. 75 19 20 22 5 K3 1.58; M.S. 8 5 8 20 23 22 6 K415 M S 85 19 18 22 7 K4 25& M:S: 75% 23 22 24 .a K = kerosene: M. 9. mineral spirits: X xylene: B = butanol
+ +
-
-
TABLE 11. THINKER PERCENTAGE
FROM EV.4PORATION CURVES Sample Descriptiona Batch 1 Batch 2 1 K115 M S 85 69% 1A K1 15%; M:S: 85%, '/n% X 75 ;$% 2 K125 M S 75 77.5 75 2A K1 25%: M:S: 7 5 2 . 1/1% X 73.5 75 3 X 2 1 5 . - M.S. 85 73 74 3 8 K2 1 5 9 ' M.S. 85 , 4-2 7 B 77.3 73 3B K2 15%: M.S. 8 5 $ , 3% B 78 72 4 K 2 2 5 7 , M.S. 75 80 79 5 K 3 15%, M.S. 8 5 8 73 75 6 K 4 1 5 7 M S 85 76.5 80 7 K4 25%: M:S: 75% 78 77 a X kerosene; M. S . = mineral spirits; X xylene: B butanol.
+ + +
-
-
T.4BLE
111. REL.4TIVE
Designation 1 1A 2
2h
3 3A 3B 4 5 6 7 AV:
VIsCOSITIES AT 13SECOSDS
Alternate Method, Batch 1 33 12 11.5 13.5 13.0 9
KET-EDGE TIMELIMIT,
--Regular Ratch 2
MethodCheck on batch 2
15 15 13 11 14 13 15 10.5
7
8 12 8 11 12.5
-
12
+- 250 .. 55
8 11 12.5
+- 24 .. 55
11.0 11.0 10.0 11.0 10.0 11.0 11.0 9.5 10.0 11.0 11.0 10.5 f 0 . 5 1.0
-
slightly lower average of 10.5 seconds for the check is lower than the average of 12.5 seconds for batch 2. This difference may be due to the greater aging of the second base varnish used for the checking samples. The straining of the second base varnish may also have been a factor. Figure 2 shows viscosity curves for the samples discussed. The critical points in the curves appear in the proximity of the points indicating the wet-edge time limits. KEROSENETYPE. The effect of the type of kerosene is indicated by a comparison of samples 1, 3, 5, and 6 (Table I). In each case the thinner mixture was made up of 15 per cent kerosene and 85 per cent mineral spirits. The same mineral spirits was used throughout, so that the only change was in the type of kerosene. The effect of kerosene type is also indicated by comparison of samples 2 , 4 , and 7. I n each case the thinner mixture was made up of 25 per cent kerosene and 75 per cent mineral spirits. Samples 2, 7, and 4 in Table I are arranged in the order of decreasing wet-edge time limits; i. e., sample 2 had the longest wet-edge time limit, and 4 the shortest. The comparative spot-dry time was obtained by flooding one-quarter sectors of filter paper and noting the time necessary for drying. The varnish breakdoarn figures (shown in the last column of Table IV) were obtained as follows: Five grams of the varnish were weighed into a cone graduate. The thinner
AUGUST, 1936
INDUSTRIAL AND ENGINEERING CHEMISTRY
943
of decreasing wet-edge time limits. Therefore, in this case the addition of butanol to thevarBoiling Range, Varnish Kauri nish decreased the wet-edge time limit. The viss. T. M. ComparaBreak-Cc. Butanol Co. cosity of the varnish a t the wet-edge time limit, Distn., F. tive down Solvency Initial D ~ Y Spot-Dry Naphtha/5 G. Saphtha/iO G. SP. Gr. as well as the percentage of thinner in the varSample b. p. point Time, Hr. Base Varnish K. B. Soln. a t 60’ F. nish a t this point, lay between rather narrow 73.6 325 396 0.25 Mineral spirits 33.4 0.7839 limits. 2 1 . 5 2 8 . 6 0.8100 415 472 2.5y Kerosene 1 b Kerosene 2 371 456 43 02 .. 15 00 .. 88 31 4482 FILM HOMOGEXEITY. The tests regarding the 96.1 360 500 22“. 2 5 a Kerosene 3 Kerosene 4 379 502 2.75“ 29.5 29.6 0.8123 homogeneity of the film were qualitative. When varnish in the film a t the wet-edge time limit was a * 15 minutes. b No breakdown a t 200 cc. throughly mixed so as t o become homogeneous, it could be brushed into a fresh varnish film without forming a noticeable junction. If the wrinto be tested was added from a buret until a permanent kling of a film was due to a lack of homogeneity between the cloud was formed. More of a high-solvency thinner could be surface and the rest of the varnish film, it might be inferred added before the cloud point was reached than a low-solvency that the varnish with the larger wet-edge time limit, other thinner. factors being equal, had a greater degree of homogeneity. Kerosenes 2 , 3, and 4 have, roughly, the same distillation Acknowledgment range, but different solvencies; i. e., kerosene 2 has a higher solvency than kerosene 3, which in turn has higher solvency The writers are indebted to C. Hopper for assistance in than kerosene 4. obtaining preliminary data on the wet-edge time limit as PERCEKTAGE OF KEROSENE. The effect of the percentage well as the production of the panels demonstrating the of kerosene used is indicated by a comparison of the following wrinkling of the varnish film. They are indebted to D. Fay pairs: samples 1 and 2, 3 and 4, and 6 and 7 . Each pair and L4.Luetz for laboratory assistance, and wish to acknowlcontained the same type of kerosene. I n the case of the first edge also the helpful suggestions of D. D. Rubek and G. W. two pairs (1and 2 , 3 and 4) the wet-edge time limit decreased Dahl. with an increase of the kerosene percentage. The third pair Literature Cited (6 and 7) indicated that the reverse was true. (1) Gardner, H. rl., “Physical and Chemical Examination of Paints, BUTASOL.The effect of small amounts of butyl alcohol is Varnishes, Lacquers, Colors,’’7th ed., pp. 601-7,611,Washingindicated by a comparison of samples 3, 3A, and 3B. These ton, Inst. of Paint & Varnish Research, 1935. samples contained the same thinner mixture of 15 per cent (2) Rubek, D. D., and Dahl, G. W., IXD.ENG.CHEM.,Anal. Ed., 6, kerosene 2 and 85 per cent mineral spirits. However, in 421 (1934). sample 3A, 2 per cent of the thinner mixture was replaced RECEIVED April 21, 1935. Presented before the Division of Paint and Varwith butanol, and in 3B, 3 per cent was replaced with butanol. nish Chemistry a t the 91st Meeting of the American Chemical Society, In Table I samples 3, 3d, and 3B are arranged in the order Kansas City, M o . , April 13 t o 17, 1936. I
TABLEIV. DESCRIPTION OF KEROSESES
*.
Glue Tanning with Formaldehyde Application to the Manufacture of Hectograph Masses ERIK R. NIELSEN The Miner Laboratories, Chicago, Ill.
T
HIS investigation was carried out during the development of a new process (2) for the manufacture of hectograph masses. A hectograph mass is essentially a glue-glycerol-water composition to which small quantities of other compounds are usually added for hardening, preserving, and pigmenting the composition. The old-fashioned pan hectograph has largely been replaced by the hectograph roll-that is, a hectograph copying surface in roll form, adapted for use in special machines which permit speed in copy-taking. The roll is unwound in the machine, section by section, over a copying platen, a fresh section being used for each different master. The rolls are long (about 16 feet) to permit the copying of several masters without change of roll. As the roll leaves the platen, it is rewound; on the following day the roll should have absorbed the excess ink so that it may be used over again.
Analyses of a number of rolls of different manufacture showed that they were hardened or tanned (at least in part) with formaldehyde. Figure 1 gives the melting point curves for a number of these rolls. Some were fresh or “green” when purchased-that is, only slightly hardened, as indicated by the low melting points. Such rolls were At, Aa, Ag, B, Cz,and D. Other rolls were already considerably tanned at the time of purchase, such as AI, A d , and C1. Curve A , represents the untanned composition obtained from one manufacturer.
Experimental evidence is offered which indicates the advantages of adjusting the pH between 7 and 9 in the preparation of glue-glycerol-formaldehyde compositions of predetermined melting point. The effects of certain other factors involved in this reaction are also reported.
