June, 1928
I-VDUSTRIAL AIVD E S G I N E E RIiYG CHEMISTRY
already been reported.6 When incorporated in lacquers it appears that a satisfactory black, pliable coating composition can be prepared without the use of extraneous pigments. Certain modifications of these resins may find use in the 8
Groggins, Ckem. Met. Eng., 34, 291 (1927).
599
electrical industry. A sample submitted to the Bureau of Standards was found by H. C. Curtiss to possess the following factors: dielectric constant, 2.5; power factor, 3.0 per cent; resistivity, l O I 4 ohm centimeters; dielectric strength, 20 kilovolts per millimeter.
Acetone Condensation Resins’ H. A. Gardner and C. A. Knauss THEINSTITUTE OF PAINT
AND V A R N I S H
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N T H E preparation of cellulose lacquers resins are used to a considerable extent, Some of the resins which manufacturers have desired to apply in this direction, because of alkali resistance or other favorable properties, do not always work well with the type of solvents used for the cellulose compounds. Precipitation and “blushing” have been the main defects. When this investigation was started, it was believed that resins produced from acetone might be found entirely soluble in most lacquer solvents. It has been known for some time that acetone forms solid condensation products with certain types of compounds, and, as acetone is a good solvent for nitrocellulose and miscible with practically all other solvents, it seemed to be a lead in the proper direction. Werner2 in 1904 mentioned acetone resins produced by the condensation of acetone with formaldehyde solution in the presence of alkali; he obtained an orange-colored powder which was soluble in alcohol and acetone. Muller3 and Ellis4 and others have studied similar products, using various alkalies as condensing agents. The work of these investigators seemed to indicate the possibilities of producing materials that could be applied in the direction mentioned above. Their work was not repeated, however, as it seemed more desirable to condense the acetone with some of the higher aldehydes that are becoming available in large quantities. Some of those tried were acetaldehyde, paraldehyde, aldol, and furfural. Preliminary Experiments
The procedure in the preliminary experiments consisted of refluxing a mixture of 58 grams (1 mol) of acetone with 88 grams (1mol) of aldol in the presence of a 10 per cent caustic potash solution for several hours, or until a viscous liquid layer separated from the aqueous layer. The resinous liquid thus produced was then treated with dilute acetic acid to neutrality. The product was then heated to about 150” C. for 30 minutes to drive off occluded water. I n this work paraldehyde did not condense with the acetone. This was to be expected, since paraldehyde does not give the common aldehyde reactions. The products obtained with the other aldehydes, however, were soluble in acetone and toluene, and possessed peculiar aldehydic odors. An equal quantity by weight of these products was then fused with rosin and dissolved in acetone to form 50 per cent solutions. Metal panels were coated with these solutions, and exposed on the testing racks along with panels coated with ester gum and dammar. The color of the products thus obtained from the synthetic resinous materials was considerably darker than dammar, being of deep amber tints. The durability, however, 1 Received March 28. 1928. Presented before the Division of Paint and Varnish Chemistry a t the 75th Meeting of the American Chemical Society, S t . Louis. Mo., April 16 to 19, 1928. J . Ckem. SOC.( L o n d o n ) , 196, 20 (1904). B n . , 64, 1192 (1921). 4 “Synthetic Resins and Their Plastics,” p. 226.
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compared favorably in many cases with dammar, although in some instances early checking was observed. Hardened Resin Form
To prevent the formation of gummy products, it was decided to add rosin directly to the reaction mixtures. In order to have the rosin combine with the condensation products, it was necessary to use a weak acid condensing agent in place of the caustic potash solution previously employed. To 1 part of acetone there were added 2 parts by weight of rosin. This mixture was refluxed until the rosin had completely dissolved. The aldehydes were then added in quantity equivalent to 1 mol of aldehyde to 1 mol (58 grams) of acetone present in the acetone-rosin mixture. Hydrochloric acid (0.25 N ) was then added and the mixture refluxed for about 6 hours. The resinous mass produced was washed and neutralized with sodium carbonate, and then heated to drive off the water. The finished products were hard, of dark color, and rather brittle. Furfural and aldol were the aldehydes used in these experiments, as they gave greater promise of success than the others. The one produced from the furfural aldehyde was darker than that produced from aldol. These were dissolved t o a 50 per cent concentration in solvents, coated out upon metal panels, and exposed upon the testing racks on the roof. The type of failure seemed to be early checking, but the durability was fair. Solubility in acetone, toluene, and butyl acetate in practically any ratio was observed. The resin solutions were then combined with nitrocellulose, using as a formula 100 parts of 32-ounce (907 grams) solution of l/Z-second nitrocellulose in butyl acetate as the base. To this were added 60 grams of a 50 per cent solution of the aldehyde resin dissolved in toluene. Five grams of tricresyl phosphate and 40 grams of acetone were also employed. These lacquers were coated out upon panels and exposed. The durability was fairly comparable to that of the resins produced from ester gum and dammar, but the color was considerably darker. Cellulose Resins
An attempt was next made to produce a solid resin containing cellulose compounds. Since aldol and nitrocellulose or cellulose acetate are soluble in acetone, it was believed that a solution of these products could be condensed to obtain a compound which might be of general interest in lacquer work. To 464 grams (8 mols) of acetone, and 254 grams (3 mols) of aldol were added 40 grams of dry nitrocellulose. When the nitrocellulose dissolved, the mixture was slowly refluxed while dry hydrochloric acid gas was passed into the mixture. After refluxing for an hour and a half, 15 grams of rosin were added and heating was continued for about 2 hours. A viscous, reddish yellow, clear solution was formed, which became hard when the excess acetone was evaporated. A lacquer was made with this resin, and exposed for 28
ISDUSTRIAL A S D ENGIA'EERISG CHEMISTRY
600
days during the most trying period of the summer months. The lacquer was of fairly light color and very clear, but possessed a somewhat distinctive aldehyde odor. The durability was good. Similar resins were made from cellulose acetate and other cellulose esters and ethers produced a t this laboratory. The main difficulty in the work was the production of resins of very light color to compare with such resins as dammar and extra pale ester gum* The seemed most interesting, however, and point to the possibilities of producing materials of this character. Chemistry of Process I n the condensation of acetone with aldehydes the first step is a simple additive product as follows: CHI. CO.CHa CH3.CH(0H).CH2.CHO+ CH3.CO.CHz. (0H)CH.CHz. CH(0H)CHs
+
Vol. 20, No. 6
Kater is then lost by heating, and an unsaturated compound, which is in the form of a viscous liquid, is produced: CH3.C0. CH : CH.CH : CH.CH,. Upon further heating there seems to be a polymerization of this unsaturated compound, with the formation of a solid resin of the probable formula CH3 CO.CH.CH:CH.CH.CHs
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CHI. CO.CH.CH:CH.CH.CHa This final product does not add bromine, so it is apparently saturated, but no definite tests could be made to determine its constitution, owing to traces of free acetone and aldehyde in all the final products. This paper cannot be considered as a report of a finished investigation on acetone condensation products, but it is presented as a summary which may be of general interest to investigators in this field.
Adhesion of Films' Further Results on the Adherence of Films to Various Surfaces H. A. Gardner and A. W. Van Heuckeroth IXSTITUTE O F PAINT
A N D V A R N I S H R E S E A R C H , m'ASHINICTON,
OME preliminary results on adhesion were outlined in a recent publication of the American Paint and Varnish Manufacturers' Association.2 In this work the Gardner-Parks tensile strength meter was used for the quantitative determination of adherence. Recently an opportunity has been afforded to determine the adherence by this method of a number of lacquer materiak, when applied to surfaces of black iron, galvanized iron, wood, glass, tin, and aluminum. There has been much discussion as to whether the addition of certain resinous materials to a lacquer would add to or lessen the adhesive properties of the lacquer when applied and dried to a film condition. A number of qualitative tests have been heretofore used to determine this result, but none of them have been entirely satisfactory.
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Experimental
In the tests made at this laboratory panels 3 by 5 inches (7.6 by 12.7 em.) in size were selected. I n the case of the metal panels it was found necessary to have the surfaces absolutely clean and free from grease. Otherwise comparable results could not be obtained. It was found after considerable experimental work, that the best method of cleansing was to scrub the surface of the panel thoroughly with benzene and later with acetone. Surfaces free from grease are thus secured. In operating the t'est, the lacquer is brushed upon the panel and a piece of silk of the same width as the panel and twice as long is immediately embedded in the coating. There is then applied a second coat of lacquer, which is brushed over the silk before the first coat has a chance to harden. By this means the silk is thoroughly sandwiched in the coating and pressed down with the brush so that no air bubbles are allowed to remain. After drying for 2 or 3 hours, the silk cloth embedded in the film is cut 1 Presented before the Division of Paint and Varnish Chemistry a t the 75th Meetina of the American Chemical Society, Si. Louis, Mo., April 16 to 19, 1928. 2 A m . Point V a r n i s h Mfrs. Assocn. U . S., Tech. Circ. 343 (February, 192R). 8 W. C. Norris, of the Palmerton Laboratory of the New Jersey Zinc Co., has been conducting similar work on the adhesion of films and has devised the use of silk for imbedding in films as outlined also in this paper.
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with a sharp razor blade into test strips about 1 em. wide. The test panel is then fastened into the tensile strength apparatus as shown in the illustration, and the end of one of the strips is loosened from the panel t o form a grip for the machine. After the panel is inserted in the machine, the load is applied and the strip slowly and gradually removed from the coated panel. The load usually shows a constant pull all the way down the panel, indicating that the adhesion is the same over the entire surface where normal conditions obtain. ( The results on a number of lacquers upon various types of surfaces are given in Table I. It should be pointed out that the tensile strength machine on which these tests were run is only correct to * 20 grams. It will be noted that on the galvanized iron, tin, black iron, and aluminum panels the adhesion of lacquers 1 to 8 was very low, while that of lacquers 9 t o 14 was comparatively high. This would seem to indicate that the presence of resin in a lacquer gives greater adhesion t o metals of the type mentioned above. Generallyspeaking, the adhesion of the films to the metals increases with the amount of resin, u p to a c e r t a i n percentage. On wood panels comparatively high adFigure e hesion results were shown. This T e n si l e s t r e n g t h Meter would be expected because of the ~~~~~&~~ ~ $ ~ ~ great porosity of wood, which Films Upper portion of picture shows allows-of the-penetration of the steel plate to which lacquer has film material which anchors it- been applied and in which there is embedded a sheet of silk. This self in the pores. The results on has been cut into seven strips, of which have been orlare glass panels were surprisingly three being pulled off, disclosing the high. black metal beneath.
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