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I N D U S T R I A L A N D ENGINEERING CHEMISTRY
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Vel. 21, No. 7
Ethyl Abietate' Alan C. Johnston HERCCLES POWDER COMPANY, WILMINGTON, DEL.
UNDAMENTALLY, a modern nitrocellulose lacquer is a properly plasticized nitrocellulose film. Such a film has certain faults, such as lack of luster and adhesion, which have been overcome by adding resins. The resins ordinarily used in varnishes and oil enamels have quite naturally been used in lacquers, since they were readily available and their properties well known. Unfortunately, the materials which are the best solvents for nitrocellulose are the poorest solvents for these resins, and vice versa. With some resins it is very difficult to get a homogeneous solution containing both nitrocellulose and resin, and practically impossible t o get a homogeneous film. With any natural resin the lacquer formulator must balance his resin and lacquer solvents very skilfully, and he is constantly confronted with the difficulty that he has, as an ingredient, a material which in many respects is incompatible with nitrocellulose.
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Preparation I n preparing alkyl esters of abietic acid it has been the practice t o prepare pure abietic acid, which is then esterified. The abietic acid has been made by refining gum rosin by crystallization, a troublesome and expensive process. Laboratory methods of preparing the esters have included the reaction (1) of the silver salt of abietic acid with ethyl iodide, (2) of dimethyl sulfate upon sodium abietate, (3) of the acid chloride with alcohol, or (4) of refluxing alcoholic rosin solution with sulfuric acid. Initial preparation of abietic acid has now been found unnecessary ( I ) , * and a brownish red, commercial mood rosin, as distinguished from gum rosin, may be used. In esterification, instead of an acid or a neuhral solution, an excess of caustic alkali can be used. For example, in the preparation of ethyl abietate 20 parts of sodium hydroxide are dissolved in 25 parts of water and then diluted with 150 parts of ethanol; 150 parts of a brownish red rosin are added, and the mixture is refluxed until a clear solution is obtained; 40 parts of diethyl sulfate (115 per cent of theory) are added gradually, and the ethanol is distilled off. The residue is then heated to 145" C. for 1 or 2 hours, with stirring, and the ethyl ester of abietic acid distilled off in vacuo. The color substances contained in commercial wood rosin do not pass over during distillation, so that a clear ester is obtained . The important feature of the process is the use of a relatively dark wood rosin, a comparatively cheap product, which renders the cost of the alkyl abietate sufficiently low to find commercial application. Properties The alkyl esters of abietic acid are very thick, T~lSCOUS ' liquids, which are very difficult to saponify. They may be said to colloid nitrocellulose, although this requires some explanation. If the definition of a plasticizer means a solvent for nitrocellulose, ethyl abietate is not a plasticizer, but if ethanol and ethyl abietate are mixed with nitrocellulose the nitrocellulose dissolves and gives a plastic film. They are miscible in all proportions with other organic esters, benzene, acetone, and butanol. They are very soluble in 95 per cent ethanol, and dissolve ester gum and dammar gum readily but manila copal less readily. 1
Received March 20, 1929.
* Refers to literature cited at end of articla.
Ethyl abietate is now available in quantity. It distils a t 195-200" C. a t 4 mm., but tends to decompose a t higher temperatures. This decomposition starts a t about 280" C., and is quite rapid a t 345" C. Its flash point by the Cleveland open cup method is 178" C.; its ignition point by the same method is 216" C. I t s freezing point is about -45" C., a t which temperature it becomes a semi-crystalline mass. At -40" C. it is plastic, and a t -30" C. exceedingly viscous. From -30" to -10" C. its viscosity decreases slowly, and above -10" C. its viscosity decreases rapidly with rise of temperature. Ethyl abietate has a refractive index of 1.520. No watersoluble acid is present, but determination of the acid number by the standard method for resins gives 1.5 or less, representing about 0.8 per cent abietic acid. Its viscosity is 6.5 poises a t 25" C., its specific gravity 1.0200 a t 20"/20" C., giving a weight per gallon of 8.52 pounds. Boiling with water gives no water-soluble acid, as shown by titration. The saponification number by the standard method is about 5.7i. e., it is practically unsaponifiable, making it one of the best alkali-proof materials available in the paint and varnish industries. Its Wijs iodine number is 182. Use in Lacquers
Commercial ethyl abietate has a very slight but agreeable odor. I n lacquers the odor is not apparent. The Lovibond color is near 15 amber, which is lighter than that of X gum rosin. Sunlight does not discolor the material itself. When used in a lacquer containing zinc oxide and nitrocellulose, the film does not discolor any more than does a lacquer containing zinc oxide, nitrocellulose, dibutyl phthalate, and dammar gum, both films discoloring to a considerably less extent than films containing zinc oxide, nitrocellulose, dibutyl phthalate, and ester gum. Commercial ethyl abietate dissolves completely dammar, elemi, mastic, ester gum, and rosin. It dissolves partly copal, sandarac, and pontianac, while kauri is very slightly soluble. It swells both vulcanized and unvulcanized rubber in the cold, the action being increased greatly by heat. It is completely miscible with coal-tar and petroleum hydrocarbons. No specific solvents or solvent mixtures are necessary to hold it in solution, as is the case with fossil and synthetic resins. Ethyl abietate retains about the same quantities of solvents in nitrocellulose films that blown castor oil does, an amount which is somewhat more than that held by either Lindol or dibutyl phthalate, but not so large as that retained by the fossil and ester gums. Films containing (1) 10 parts of RS half-second nitrocellulose and 26 parts of ethyl abietate, or (2) 10 parts of RS halfsecond nitrocellulose, 10 parts of ester gum, and either 16 parts of blonn castor oil, 13 parts of Lindol, or 10 parts of dibutyl phthalate, were not tacky, whereas films composed of 10 parts of RS half-second nitrocellulose, 10 parts of ester gum, and either 16 parts of Lindol or 13 parts of dibutyl phthalate were tacky. The effect of ethyl abietate on the hardness of nitrocellulose films is such that a film composed of 10 parts of nitrocellulose and 13 parts of ethyl abietate has about the same hardness as one containing 10 parts of nitrocellulose, 8 parts of ester gum, and 5 parts of Lindol. Ethyl abietate imparts very good adhesive properties to
INDC;STRIAL ALIrDEXGINEERING CHEMISTRY
July, 1929
nitrocellulose films which retain their original adhesion, whereas nitrocellulose-resin films lose part of their adhesiveness after air-drying for a month. I n using ethyl abietate in nitrocellulose lacquers it has been found best to substitute it for both the plasticizers and the gum (or resin) now used, rather than for either alone. By so doing, lacquers are obtained which have a better heat resistance but not a better light resistance. Ethyl abietate is of value in interior, furniture, and wood lacquers, as well as lacquer undercoats. I n ethyl abietate a natural resin has been changed in chemical composition in such a way that, while it still retains its primary resin characteristics and imparts to the film gloss, depth, body, and adhesion, as a resin should, it has ceased to
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be incompatible with nitrocellulose and has come to have actually a latent solvent action on nitrocellulose. Conclusion
Every chemist mho has formulated lacquers will recognize in some of his own formulas the steps taken t o insure a homogeneous film using nitrocellulose with a resin not entirely compatible therewith, and will appreciate, the simplification of formulas made possible by using a resin which not only is soluble in nitrocellulose solvents but is in itself a latent nitrocellulose solvent. Literature Cited ( 1 ) Johnston, U S P a t e n t 1,682,280 (1925)
Some Aspects of Chemical Patent Searches’ Frederick H. Untiedtz XAIIONAL PRESSBUILDING, WASHINGTON, D. C
OOK before you leap” has its chemical counterpart in “Search before you research.” Patent searches are now well recognized as essential to any research program having in view the development of new processes or new materials. The value of patent protection in the creation of a non-competitive industry is now so fully understood and appreciated that the strength and ability of a corporation to stay in business is sometimes best estimated by the patents it o m s . It is believed that a short description of the functions of the various types of patent searches commonly made will be of interest to the chemist whose contact with patents and patent lawyers may be only to tell the attorney what his invention is, how it differsfrom some prior invention, and t o sign papers. The Patent Ofice has arranged all the United States patents into classes and subclasses. The classification represents years of study and makes it possible for one familiar with the system to locate patents pertinent to an invention with a minimum of time and effort. For example, class 260 covers carbon compounds and in its various subclasses all of the art of making definite organic compounds, such as dyes, resins, alcohols, organic acids, etc., is to be found. Class 23 embraces inorganic compounds and processes of making them. Here one finds, in the appropriate subclasses, processes of making ammonia, sulfuric acid, salts of sulfur, inorganic nitrates, carbonates, aluminates, and the whole field of inorganic chemistry as applied t o the making of inorganic compounds. Class 252 covers “substance preparation” and includes classified patents on refrigerating compounds, flotation agents, and a host of other compositions. Other classes contain patents on liquid coating compositions such as paints, lacquers, and enamels; still others, paten1 s relating to the refining of petroleum, distillation processes, and so on. Generally speaking, patent searches are of four kindsnovelty, validity, infringement, and state-of-the-art-although there is much overlapping. ((
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Novelty Searches
A novelty search is normally concerned only with developing patents and publications which anticipate some specific invention already made. It is not so exhaustive as a validity search and its chief purpose is to determine approximately the patentability of, for instance, a process which has passed I 2
Received M a r c h 2 3 , 1929 P a t e n t lawyer
the experimental stages and is ready t o be embraced in a formal patent application. As a matter of fact, however, it is better t o have a novelty search made just as soon as the laboratory results show something of promise in order to determine as soon as possible whether or not the invention is patentable. If it is not, then it may be advisable t o discontinue the experimental work and, in any event, the patents developed in the novelty search are of material assistance in the further progress of the research. Indeed, instituting a novelty search immediately following the conception of an invention is feasible if there is something more or less definite to look for-that is, if the invention has been conceived in a concrete embodiment. Making a novelty search as soon as possible will often save many dollars otherwise uselessly spent in working out a process thought to be new but which is in fact old. But a novelty search is commonly restricted to some precise invention and is not extended far enough to corer all of a particular field. That is the province of a stateof-the-art search, as will be more fully explained. When making a novelty search, the attorney confines himself to the subclass or classes wherein the invention will most likely be found and to such additional subclasses as would be expected to yield pertinent art. Immediately available foreign patents and literature references, such as Chemical Abstracts, should also be consulted if the nature of the invention indicates that an anticipation is likely to be found therein. Validity Searches
Validity searches, as the name suggests, are for the purpose of developing patents and publications which antedate, and hence invalidate, some existing patent. They are ordinarily made when it appears that a competitor is about to bring suit upon a patent he owns, although validity searches are frequently initiated long before there is any suggestion of a suit in the courts. As an illustration, let us suppose that the XYZ company would like to make and sell a particular type of lacquer, but as a result of an infringement search, wisely made before funds have been expended in a manufacturing and marketing program, it appears that there is an adversely owned patent which will be infringed if the company goes ahead with its plans. Obviously it would not be good business to spend money in developing manufacturing processes and a sales organization to place the lacquer upon the market in the face of a patent that would be infringed if such steps were taken. But if the patent is invalid, then there is no
