Bonding Butyl Rubber to Brass R. W. Kaereher' and George W. Blum C a s e Institute of Technologg, Cleueland, Ohio
volving the tearing of a strip of rubber from a bonded surface. The former method is described by the American Society of Testing Materials and has been used with modification by Yerzley (66), Buchan ( l a ) ,and Gurney ($0). The strip test described by Werkenthin yields no basis for design, and loads often vary during the test. I t is a rapidly determined testing method, excellent for exploratory research. The procedure employed for testing in this work is a modification of the A.S.T.M. method, and the test pieces can be re-used many times by a refaciny of the surface.
T h e results of an investigation of some factors important in the adhesion of Butyl type synthetic rubber to a series of brass compositions are presented. A testing method for the evaluation of comparative bonding strength is shown, based on the pounds per square inch of tensile pull, normal to the plane of bonding, required to rupture the bond. Brass sheets of nominally 95, 90, 85, and 70Yo copper, with the balance essentially zinc, were employed. Brass disks used for bonding had 1 square inch of bonding surface and were bonded by sandwiching a sheet of uncured Butyl rubber between two disks. Following each experimental determination, the disks were resurfaced and re-used. A standardized testing procedure was employed throughout the work reported. The influence of methods of surface preparation, pickling conditions, and surface contamination on the various brass compositions is shown graphically. The essential need for uniform surface preparation is shown; accompanying photomicrographs illustrate the yarious degrees of surface uniformity, as well as the nonuniform attack of the acid on the machined surface when preliminary polishing is eliminated. Optimum conditions found in this investigation are reported for the time, temperature, and pressure of cure, effect of brass composition, and the relative strength obtained from different methods of surface preparation.
The brass test pieces, shown in Figures 1 and 2 , are prepared by cutting circular disks from the brass sheets : these are subsequently machined to the proper dimensions to provide exactly 1 square inch of surface area. These brass flange disks are drilled and tapped and attached by four screw bolts to steel supporting disks, as shown in Figure 2 . Thus a simple, solid, and true assembly is provided for attachment to the testing machine, as well as to a lathe in machining for re-use. Some of the test pieces were used as many as sixteen times merely by machining alvay the bonded surface with a cut of only a few thousandths of a n inch.
5/32 DRILL
A
CLEAR understanding of the effect of numerous conditions and variables which are encountered in industrial operations of rubber to metal bonding is necessary to obtain operations favorable to maximum and reproducible bond strength. Bonded rubber-metal articles are useful in many industrial applications, and the recognition and avoidance of factors deletarious to good bonding should result in a reduced number of rejected production units, The many investigators working in this field have observed, with varying degrees of emphasis, the complexity of chemical and physical forces which may potentially contribute toward a strong bond. Increased use of Butyl-type synthetic rubber for industrial adhesion of rubber to metal, especially in the manufacture of inner tubes, indicates a need for experimental data specific to this low unsaturation polymer. Industrial methods of testing bond strength of molded rubber articles frequently involve the destructive testing of a representative sampling of a given production quantity. Such a procedure is purely empirical and qualitative in nature; it destroys units t h a t have adequate adhesion to the metal core without providing any basis for estimating whether the rejected percentage of the number tested is representative of the over-all production quantity. Furthermore, no means is afforded for eliminating from the production shipment the poor quality production not included in the test sample group, and no means is provided for explaining why some samples from the group strongly adhere whereas others, presumably manufactured by identical techniques, are not satisfactory in adhesion. -4n improved method of determination of bond strength, under clearly defined and controlled conditions suitable for investigation of the processing variables encountered, appeared therefore to be desirable. I n general two methods of testing adhesion were employedone involving a direct pull in tension or shear and the other in1
p-
1-7/8
4-
Figure 1. Brass Test Pieces for Bonding Rubber
The bonded samples were tested on a 5000-pound Tate-Emery Universal testing machine, which is extremely seneitive and accurate. The four ranges of 5000, 1000, 200, and 50 pounds are controlled by a General Electric Thymotrol control system. The specimen is assembled with the grips as shown in Figure 2 . All determinations were made in an atmosphere of 70" * 2" F. and 40 f 27, relative humidity. A constant rate of pull of 0.028 inch per minute was maintained, and the time normally required to effect a rupture of the adhesion bond was about 1 to 2 minutes.
Experimental Procedure Brass Preparation. The brass sheets, as well as the composition data shown in Table I, were furnished by the Chase Brass Co. The sheets were 3 / ~ inch in thickness and were supplied with a ho t-rolled finish.
Present address, American Can Co., hlaywood, Ill.
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.k
The brass tsst pieces were cut from the sheets by a band saw and finished on a lathe to a fine surface smoothness. They were theh degreased in two baths of carbon tetrachloride, the second bath being fresh solvent. The samples were agitated in the solvent by ' means of stainless steel tongs. A 9inch wheel covered with canvas was used for polishing with a water dispersion of flour of emery. Following the polishing the specimens were stored in cold water prior to pickling. For this operation a 1000-ml. beaker half filled with pickling acid was used; the beaker rested in a warm water bath. The washing operation included immersion in each of the two enameled pans containing distilled water: the first wash was a t room temperature; the second was heated to 90" C., for a hot wash, by placing it on a hot plate controlled by a Variac. A thermometer was used t o check the temperatures of both the pickle and the hot wash before and during the pic: ling. The time of pickling was carefully checked with a stop watch. A desiccator was used to store the pickled pieces after their edges had been dried, following the hot wash. Temperatures of 50°, 20", and 90" C. were employed for the pickling, first wash, and final washing operation, respectively. Each pan of wash water contained at least a liter of distilled water, and this was changed after each group of eight or less pieces had been washed. Pickling was accomplished by grasping the pieces by the flange on opposite sides of the circumference and leveling the piece so t h a t the side to be bonded was horizontal and facing downward. This surface was then quickly immersed in the pickle as the stop watch was started; thus prolonged contact with the fumes issuing from the pickle was avoided. The piece was then agitated slowly in a lateral direction to assist in the removal of air and entrained gas bubbles from the surface, When the stopwatch indicated the correct interval, the piece was lifted hastily from the pickle and plunged into the cold water bath, agitated vigorously for a few seconds, and then plunged into the 90' C. water bath. After the hot wash, the piece was rapped on the aide against a towel to remove excess drops of water; the heat of the metal quickly evaporated the remaining water.
Table I. Brass Comaosition Code A B
C D E
Copper
84.55
Lead 0.015 0.015 0.015 0.015
69.15
0.015
69.60
90.00 94.58
Per Cent Nickel 0.01 0.01 0.01 0.01 0.01
Tin 0.01 0.01 0.01
0.01 0.01
Zinc Balance Balance Balance Balance Balance
Rubber Preparation. The following rubber formulation was employed in all the work reported here: Grams Butyl rubber 212 Furnex beads 112 18 Micronex VC-'6 Pine Tar 6 Paraflux 6 Kadox 15 ZnO 16 4 Captax 4 Thiuram M Sulfur 6 384 The sheeted rubber was conditioned for several days a t 70" F. and 4001, relative humidity prior to bonding. The thickness of
Figure 2.
489
Brass Test Pieces
the two brass plates was measured and a small piece of rubber stock (0.050 inch thick) was laid between them. The test pieces were machined in sets of four to the same thickness t o enable the curing of two sandwiches containing the same rubber thickness, simultaneously. The faces of the brass disks were aligned prior to curing so that the holes in each section of the disk laminate were parallel. The 8-inch square platens on the 20-ton electrically heated press were carefully checked for alignment to provide a uniform molding pressure of the sandwich laminates. The platens were heated to the desired temperature for about an hour prior to molding the laminates in order to provide good control of the temperature by the thermostat. After the completion of the desired curing period, the laminates were conditioned a t the constant temperature and humidity for 18 to 24 hours prior to testing. Uniformity in the cooling of both sides of the laininate was considerably aided by standing the laminates on end during the cooling period. Testing. Before the laminates were mounted in the grips of the testing machine, they were measured for thickness, and by difference with the sum of the thicknesses of the two brass disks, the thickness of the cured rubber was determined. This thickness was found t o be virtually a direct function of the pressure applied, since the excess rubber present was forced out t o the edges of the brass disks, and later trimmed off. Rubber thickness at the 1750 pounds per square inch applied throughout most of this work was in the range of 0.0005 t o 0.0015 inch. T h e strength of adhesion of the rubber bond was determined at a constant crosshead speed of 0.025 inch per minute which had been carefully calibrated. I n testing the bonded samples, the d a t a recorded included the ultimate strength of the bond, the time required for failure at the fixed rate of pull, and a description of the stress-strain irregularities. A brief description of the appearance of the faces of t h e fractured samples was made prior to refacing the disks in the lathe; this included the estimate of the percentage of the total area covered by bond failure and by rubber failure and the color of the background metal where the bond had failed. After curing slabs of the compounded Butyl rubber stock, tensile strength, modulus, and elongation data were obtained by t h e regular A.S.T.M. procedures.
Results and Discussion Surface Preparation.
The first experiments were conducted on brass surfaces which were not polished but merely machined, degreased, and pickled. This method did not give entirely satisfactory results, and bond strengths never exceeded 825 pounds per square inch with this type surface. Bright, uniform pickling was difficult t o obtain, probably because of entrapped air in the ridges, left by the machining (Figures 3 and 5). These ridges and the tiny center knob may cause entrapped air, unequal pressures, and nonuniform thicknesses of the rubber film during the curing
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INDUSTRIAL AND ENGINEERING CHEMISTRY
Figure 3 specimen maohined and desreased s h o w ridges and (.enter knoh
Figure 4 Specinien polished roughly with flour of emery on canvas shows uniform surface appearance
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Vol. 43, No. 2
Figure 5 hlachined specimen after 10-second pickle shows black knobs aligned in ridges, crystals (dullness) begin to appea;
Test Specimens (100 X)
Figure 6
Figure 7
Figure 8
Specimen polished and pickled until dull shows black knobs, amorplioiis dullness (lower right) and crystalline dullnesi
Specimen polished and pickled bright in old pickle s h o m poorly defined background etch and whiteness around knobs
Specimen poliahed and pickled bright in fresh new pickle shows background etch well defined
Hrass Test Specimens (1OOX)
operation, They may also serve as focuses for the development of stresses during the testing. Since mechanical adhesion or thr keying of the adhesive int’o surface irregularities has been shown to have little part in rubber bonding, the roughness of the machined surfaces did not, a.id in bonding. Despite these difficulties the results obtained by this method were considered t o give n valid representation of the effect of the varia.bles tested, as long as all samples compared were prepared by this same method. Comparable run8 for polishpd and pickled surfaces showed t>hat t h e strength of the bond averagrd 200 to 300 pounds per square inch greater, b u t the effect, of other variable8 tested was about the same witch polished, pickled surfaces as with the machined, pickled samples (Figures 3 to 12). T i t h the except,ion of Figure 15, results reported in Figurps 13 to 19, inclusive, apply to machined, pickled brass surfaces. Dissatisfaction with machined surfaces initiated a short investigation of the polished, nonpickled surfaces, as suggested by Yerzley (66). Reproducible results were not obtained wit’h these surfaces, but one sample gave a bond strength of 930 pounds per square inch, which was sufficient to illustrate t h a t good bonds could be produced on a highly polished surface having little mechanical adhesion. Polished surfaces appeared to be especially prone to cont,amination, but pickling after polishing provided a uniform surface for good, consistent bonds. It was found t h a t high polish prior to pickling was not necessary to achieve uniform, bright pickling. The recipe for the pickle composition waR taken from Hogaboom (33); i t consisted of equal parts by volume of sulfuric acid, nitric acid, and water, with
O.Zyoof concentratcd hydrochloric acid addcci. This pickle is a coinmercial “bright dip,” and it gave much better results than plain sulfuric or dichromate dips whicah were also tested. Optimum bond strengths were obtained on surfaces pickled for the maximum time possible to retain a uniform brightness, on brasses of 70j30 composition. At 50” C. the optimum pickling time W L S from 10 to 15 seconds (Figure 13). Bright pickling was inore difficult with the high copper brasses, hut in the 90/10 brass, dull pickling ga.ve better bonding than hright, in contrast to t,he behavior of 70/30 brass. The effect oi‘ pickling temperature on bond strength is shown in Figure 14. Bright pickling was most readily accomplishcd a t approximately 50” C., and hrst bond strengths were obtained a t this temperaturr. In the course of experimental work, it, was o h s ~ ~ r ~ thiit, w l whenever a new pickling solution was used, t,hrre apprared an “induction effect” which gave poor bond strengths on the first few piecee pickled. Data showing this effect arc given in Figure 15, and photomicrographs of t’he surfaces produced by old and new pickle solutions are shon-n in Figures 7 and 8. The et’ch produced by the new pickle was coarse and well defined as compared to t h a t of the old, used pickle solution. I n attempting to ~liminatethe induction effect, which has been observed in commercial pickling and pla.t,ing operations, mixtures of old and fresh pickle baths n-ere used. A 50: 50 mixture was not successful, but a mixture of 10% of old pickle with 90% of fresh acid solution was successful jn improving the bond strengths of t’he first pieces pickled. As experiments progressed, the importance of the role which contamination plays in successful honding was rralinrd. That
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INDUSTRIAL AND ENGINEERING CHEMISTRY
When machined pickled surfaces were being t)onded, i t was found that the hard surface layer produced in the of the brass sheets would not bond as well as would the main body of the brass. Since polishing before pickling eliminated this difficulty, the dependency of good
491
Figure 9
Figure 10
Brass D (85/15) polished a n d piqkled bright shows numerous knobs; orystalllne dullness a t top
Brass B (90/10)polished and pickled bright shows large crystalline dullness spot at lower left
Brass Test Specimens (100 X)
F i g u r e 11 F i g u r e 12 whose color is caused by the presence of beta Speciniaii polished pickled bonded and Specimen polished a n d bonded without pickor gamma crystalline forms. Gurney found that rubber dissolved %Gayshow heavy attack of ling, a n d rubber dissolved away shows slight the transition from good to Bero bonding was attack of bonding reartion on surfare hondine, reaction a t top. at bottom right bond was not Ao stiong sharp. Figure 17 shows how the Butyl bond strength Brass Test Specimens (100 X ) varied with brass composition under a number of pickling conditions. Brass with 85% copper contact with the metal for bonding. The efiects of various rubwill give a good bond under the conditions of a 20-second pickle a t ber ingredients on Butyl bonding were not investigated How50' C. Bonds produced with brasses containing 90 and 95% copper were inferior, never exceeding 250 pounds per square ever, good bonds were obtained using an ultra-accelerator, a hich inch, but this might be improved by alteration of the rubber is necessary to cure the slow curing Butyl type rubber, whereas it formulation or the more complete elimination of contamination. is generally accepted that the use of ultra-accelerators prevents good bonding with most rubbers. This indicates that it is not Rubber Properties. The rubber was found t o have good the nature of the accelerator itself but rather the extent to which bonding properties and tensile strength even after 4 months of it speeds up the vulcanisation of thr particular rubber used, that aging. The rubber was masticated each time before using for is important in bonding. bonding, and i t waa necessary to sheet i t smoothly in order to prevent the formation of air pockets when the sheet was placed in
I EFFECT OF RCKUNG TIME BRASSA
60.0.
PICKLING T I M E -
Figure 13
sec.
I
I
EFFECT OF PICKLE TEMPERATURE
Po r r o n d
PICKLE
pickle
TEMPERATURE
Figure 14
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I
INDUCTION
EFFECT
B R A S S E -POLISHED
0
-
~ R D E ROFSAMPLES AS PIGLED
40
20
EFFECT
OF BRASS COMPOSITION
85
90 BRASS
80
- 9. COPPER
COMPOSITION
70
75
Figure 1'7
BRASS
IO
15
20
A.
25
x)
35
40
45
CURING TIME - rninules
Figure 18
EFFECT OF CURING PRESSURE
-7 5 0 1
I
120
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EFFECT OF CURING T I M E I
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AIR
Figure 16
,
100
Do
80
60
T I M E OF EXPOSURE TO
Figure 15
900,
Vol. 43, No. 2
BRASS
A.
1 6
I
I
0
1003
I a00
I 3x0
CURING
I 4ooo
PRESSURE
-
5x0
6ooo
PSI.
Figure 19 Curing. The principal function of the curing operation in bonding is to bring the rubber into intimate contact with the metal, raise it to temperature as quickly as possible, and cause it to flow quickly into its final position before vulcanization begins. Pressure is the usual means of accomplishing this, Throughout these experiments the curing temperature was fixed a t 325' F., and curing time and pressure were varied to fmd the optimum ranges; the results are shown in Figures 18 and 19. The shapes of the curves are more important than the numerical values assigned to them, since the latter are dependent on the formulation and other conditions such as temperature. The optimum curing pressure appeared to be in the range of most plastic materials, 1500 to 2000 pounds per square inch; lower pressures do not provide intimate contact quickly enough, and excessive pressures may cause continued flow during vulcanization, thus
weakening the bond. The greater tendency of Butyl rubber to flow may make curing pressure especially critical, Although a minimum curing time of 20 minutes is evidenced, the actual curing time is not especially critical with Butyl rubber. Undercure is more deleterious to bond strength, but overcure may cause incipient deterioration of the rubber. Testing Characteristics. Since elongation of the test specimens was so slight, it was impossible to obtain a stress-strain curve by the usual methods. Observation of the load pointer during testing indicated t h a t good specimens showed a regular, incremental increase in load u p to about 400 pounds per square inch, whereupon the loading rate slowed down, stopped, or even retraced 20 to 30 pounds per square inch before continuing the slow and steady rise in load to the point where fracture suddenly occurred. Even the strongest samples had as high as 30% failure occurring in the bond rather than in the rubber interlayer, indicating that even better bond strengths were possible. Figures 11 and 12 show the surface structure of the brass after it has been bonded, and after the rubber has been dissolved off. When contamination and other difficulties are minimized, the values of the calculated bond strength are reproducible within .t5% of the mean. Choice of Curing Method. I n the exploratory stages of study on the problem, the various methods of measuring bond strength employed by other investigators were (S, 6,ZZ) examined. In most instances the specimens to be tested were compression molded in a cavity-type die, with the rubber retained within the cavity walls. This method would require a constant and uniform thickness of brass disks used, virtually eliminating the practice of continued resurfacing and re-use. Many of the apparent discrepancies in the literature are believed to be due to the use of overly thick rubber layers and consequent nonreproducible condition of the cured rubber. Under a constant compression load, such a3
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INDUSTRIAL AND ENGINEERING CHEMISTRY
would be obtained with the use of a cavity die, slight differences in the thickness of the disks could potentially account for wide variation in the state of cure of the rubber, the thickness of the laminate, and the adhesion resulting. The primary objective here was to investigate the nature of the rubber to metal interface, with the hope of learning something of the chemical nature of the bond obtained. Primary concern was the bond failure rather than the rubber failure; thus i t was deemed desirable to maintain a minimum of rubber in the laminate by providing means of squeezing out the excess to the outer walls and trimming off this excess flash. With the exception of the data shown in Figure 19, a constant pressure of 1750 pounds per square inch was used for molding; data obtained on each cured sample showed conclusively t h a t the thickness of the rubber a t this pressure was 0.001 * 0.0005 inch and t h a t slight variations encountered did not materially affect the bond strength. The correlation between the bond strength and the area of bond failure indicates t h a t this method of molding produces a rubber film of essentially constant tensile strength and thickness. The rate of tensile pull was arbitrarily chosen as 0.025 inch per minute, since at this speed, the time required for bond failure shown by previous investigators (1 to 2 minutes), was obtained. The significance of the optimum rate of pull in relation to the cured thickness was not determined in this work, nor is i t cited in previous literature. Optimum Conditions. On the basis of these experiments the optimum conditions for bonding Butyl rubber to brass are suggested as follows: 1. Brass composition: 70% co per, 30% zinc 2. Surface preparation: rougi polishing followed by degreasing and pickling 3. Pickling composition: equal volumes of sulfuric acid, nitric acid, and water plus 0.2%hydrochloric acid 4. Pickling time: 10 seconds 5. Pickling temperature: 50” C. 6. Exposure t o air: less than 45 minutes for 70/30 brass 7. Curing time: 28 t o 30 minutes 8. Curing pressure: 1750 pounds per square inch
Optimum conditions were followed in all the work presented in the graphs, except as noted. Machined pickled surfaces were employed in all data shown except in Figure 15.
Summary
-F
.E
Despite the unique chemical nature of Butyl rubber and its high degree of saturation, i t was found possible to produce strong bonds of over 1000 pounds per square inch between Butyl rubber and brass by conforming to the optimum conditions found and reported here. The method of testing bond strength developed in these experiments provided accurate data under controlled conditions in a useful form. The study presented was primarily directed toward the examination of surface preparation. Further data for polished brass surfaces of a similiar nature to those presented for machined and pickled brass surfaces, are now being obtained and should be useful for comparison. Following the completion of many additional phases of the problem i t is hoped t h a t sufficient evidence will be available to establish more clearly the nature of the chemical bond of adhesion.
Bibliography Adler, 0. E., U. 8. Patent 2,435,191 (1948). Alfrey, T., I n d i a Rubber W o r l d , 112, 577 (1946); 113, 653 (1946). American Society for Testing Materials, Committee D-14 on Adhesives, A.S.T.M. D 897-461, A.S.T.M. Standards, Part 111-B, 1217 (1946). Ibid., A.S.T.M. Supplement 111-B, 205 (1947). Ibid., Symposium on Adhesives, Philadelphia, Pa. (1945).
493
(6) Anon., N a t l . B u r . Standards Tech. N e w s Bull., 33, No. 6, 67 (1949). (7) Anon., Rubber Age, 58, 74 (1945). ApRoberts, J. P., Monthly Rev. Am. Electroplaters’ SOC.,28, 271 (1941). Rikerman, J. J., J . Colloid Sei., 2, 163 (1947). Brams, S. L., U. S. Patent 2,424,736 (1947). Browne, F. L., and Brouse, D., IND. ENQ.CHEM.,21, 80 (1929). Buchan, S., “Rubber to Metal Bonding,” London, Crosby, Lockwood and Son Ltd., 1948. Buchan, S.,T r a n s . I n s t . Rubber I n d . , 19, 25 (1943). Buchan, S., and Rae, W. D., Ibid., 20, 205 (1945). lbid,, 21, 323 (1946). Buchan, S.,and Shanks, J. R., Ibid., 21, 266 (1945). Chase Brass and Copper Co., .Waterbury, Conn. “Commercially Important Wrought Copper Alloys,” 6th ed., 1948. Chrysler Corp., Modern Plastics, 21, No. 1, 65 (1943). Crowther, H. A. H., Sheet Metal Ind., 16, 1711, 1903; 17, 97, 291. 303. 493 11943). Delmonte, J., “Technology of Adhesives,” New York, Reinhold Publishing Co., 1947. DeLollis, N. J., Product Eng., 18, No. 12, 137 (1947). DeLollis, N. J., Rucker, Nancy, and Wier, J. E., Aratl. Advisoru Comm. Aeronautics, Tech. A‘oter, 1863 (1949). Domm, E. C., U. S. Patent 2,002,261 (1935). Ibid., 2,002,262-3 (1935). Fajans, K., “Chemicai Forces and Optical Properties of Substances,” New York, McGraw-Hill Book Co., 1931. Griffith, T. R., U. S. Patent 2,386,212 (1945). Grinter, H. W., Ibid., 2,188,434 (1940). Grinter, H. W., and Gross, M. E., Ibid., 2,399,019 (1946). Gross, M. E., Ibid., 2,354,011 (1944). Gurney, W. A,, Trans. I n s t . Rubber I n d . , 18, 207 (1943). Gurney, W. A., Ibid., 21, 31 (1945) [reprinted, Rubber Chem. and Technol., 19, 199 (1946)l. Hayward, C. R., Chem. & M e t . Eng., 18, 650 (1918). Hogaboom, G. B., Metal Finishing, 44, 198 (1946). Hood, G. H., I n d i a Rubber W o r l d , 44, 374 (1911). Hosking, 0. W., U. S. Patent 2,337,555 (1943). McBain, J. W., et al., Repts. 1, 2, and 3, Adhesives Research Committee, London, H. M. Stationery Office (1922, 1926, and 1932). McBain, J. W., and Hopkins, D. G., J . P h y s . Chem., 29, 188 (1925). McBain, J. W., and Lee, W. B., IND.ENG. CHEM.,19, 1006 (1927). McBain, J. W., and Lee, W. B., J . P h y s . Chem., 31, 1675 (1927). Ibid., 32, 1178 (1928). McLaren, A. D., Paper Trade J . , 125, No. 19, 96 (1948). Meissner, H. P., and Merrill, E. W., A . S . T . M . Bull., 151, 80 (TP88) (1948). Merrill, J. A., Rubber Age, 59, 313 (1946). Messenger. T. H.. India-Rubber J.. 102. 439 (1941). . , Metal industries Publishing Co., New York, “Plating and Finishing Guidebook,” 1940. (46) Meyer, J., Pro?. Am. Electroplaters’ Soc.. 1939, 84. (47) Morron, J. D., I n d i a Rubber W o r l d , 98, No. 4, 35 (1938). (48) Nordlander, H., J. Phus. Chem., 34, 1873 (1930). (49) Pierce, R. E., U. S. Patent 2,307,801 (1943). (50) Proske, G. E., Kautschuk u. G u m m i , I, 209 (1948). (51) Remick, A. E., “Electronic Interpretations of Organic Chemistry,’’ 2nd ed., New York, John Wiley & Sons, 1949. (52) Rice, H. L , Org. Finishing, 9, No. 6, 24 (1948). (53) Rinker, R. C., and Kline, G. M., N a t l . Advisory C o m m . Aeronautics, Tech. Notes, 989 (1945). (54) Rose, K., Materials and Methods, 27, No. 2, 94 (1948). (55) Sanderson, C., Brit. Patent 3288 (1862). (56) Satake, S., Rubber Chem. and Technol., 9, 281 (1936). (57) Schade, J. W., U. S. Fatent 2,240,862 (1941). ENG.CHEM.,in press. (58) Schmidt, E., IND. (59) Scholl, E. L., U. S. Patent 2,165,818 (1939). (60) Ibid., 2,220,460 (1940). (61) Steams, R. S., and Johnson, B. L., IND.EXG.CHEM.,43, 146 (1951). (62) Turner, P. S., M o d e r n Plastics, 24, No. 4, 153 (1946). (63) Van Roy, L., Paper I n d . and Paper W o r l d , 25, 1102 (1944). (64) Werkenthin, T. A , , Rubber Age, 59, 173 (1946). (65) Weyl, W. A., Am. Soc. Testing Materials Proc., 46, 1506 (1946). (66) Yerzley, F. L., IND.ENQ.CHEM.,31, 950 (1939). 1
RECEIVED October 16, 1950.
(End o f Symposium)
