INDUSTRIAL A N D ENGINEBRING CIiEMISTRY
558
Yo1 17, s o . 6
Airplsne View, Alcohol Plant. U. S. Industrial Alcohol C ~ m p n n y
Solvents and Automobile Lacquers' By D. B. Keyes U b I N D U ~ ~ XAI LACLO ~ I OCu ~ ,NRWYon=
T
HE production of lacquers both for wood and metal has iiicreased enormously in the United States within the last two years. This has probably been dne largely to the production and the placing on the market of a lowviscosity nitrocellulose, thus enabling the lacquer manufacturer to make a product containing a large percentage of solids. It has also been due to the production and the placing on the market of several new and powerful solvents for nitrocellulose. The old-time metal lacquer usually consisted of a relatively high-viscosity nitrocellulose dissolved in an organic liquid and resembled very little the oil varnish. The modern lacquer, on the other hand, consists of low-viscosity nitrocelIuloRe and a resin dissolved in an organic liquid with the addition of various modifying constituents. This product resembles an oil varnish. It has t,henecessary solid content, so that only a few coats are required to produce a relatively t.hick film. The common constituents of the modern lacquers can be classified as follows: nitrocellulose (low viscosity), resin, pigment (optional),solvents, diluents, plasticiser, and softener. The difficulties that have developed in the preparation of a satisfactory product have been due chiefly to uncertainty in picking the proper solvents and plasticizer. Practically one t
l'resatcd before the Section of Paint and Varnish Chemistry at t h e
69th Meeting of the American Chemical Society, BdUmore. Md.. April 6 t o 10, 1925.
N Y
kind of nitrocellulose and only a few of the soft resins havr: been used. The effect on the finished filmof the other harder and more desirable resins has been known, but the proper solvent composition has been determined only recently. An attempt will he made in this arbicle to classify the solvents according bo their function, to show the advantages and disadvantages of individual solvents, and the relative proportions of the various types of solvents necessary for the compounding of a satisfactory automobile lacquer. It will first be necessary to give the requirements of a lacquer, and something regarding t,he characteristics of the various kinds of nitrocellulose and resins. Requirements of a Lacquer The trade is chiefly familiar wit,h W < J O ~lacquers, so a survey was made covering many of the lacquer manufacturers in the East and Middle West in order to ascertain what were considered to he the requirements for a satisfactory wood lacquer. As a result of this survey the following lkt. of requirements has heen drawn up, the first part being more essential than the second.
June, 1925
INDUSTRIAL A N D ENGINEERING CHEMISTRY
3-The lacquer must have a good flow, and the film must have a smooth surface free from bubbles, wrinkles, “Orange Peel,” etC. 4-The lacquer must go on without a permanent “blush” in conditions of high humidity and preferably with no “blush” at all. +The lacquer must have a good “body” (about 300 grams of solids Per liter Or 32 Ounces Per gallon) in order to reduce the number of coats necessary to about three. 6-A clear lacquer should be as nearly colorless as possible. 7-The lacquer should set in 20 minutes SO that it can be handled, and dry in 8 to 12 hours so that it can be rubbed. 8-The film must not be affected by boiling water, ice, weak acid, or 50 per cent alcohol. Part II
559
moisture. Resins by increasing the hardness of the film often give it the property that allows the possibility of rubbing; this in turn permits the production of a greater gloss and brilliancy. Resins often increase the body of the lacquer without increasing the viscosity, a most desirable property. hfany resins are cheaper per pound than nitrocellulose and therefore tend to reduce the cost Of the lacquer. Resins may be classified according to their hardness, but for lacquer purposes classification by solubility is preferred. The harder the resin the less is the solubility in the common organic solvents. The soft resins-rosin, for example-seem to contain natural blending agents that increase materially 1-The film should have no residual odor and the lacquer the solubility. These so-called blending agents have low should have no objectionable odor. 2-The lacquer should be uniform; that is, lacquer made in melting points and are probably the constituents that make two batches a t different times should be the same. the rosin soft. If these products are removed the rosin 3-The film must not change after polishing-shrink, or sink. becomes hard and less soluble. 4-The film must not soften a t 49” C. (120” F,). The accompanying table (page 560, f i s t Column) classifiesthe 5-The film must not check upon outside e x p o s u r e 4 5 degree angle and southern exposure. resins accordingtotheirsolubility. The 6-The lacquer must work with all line of demarcation between one type of types of spray guns and over a range of resin and another is not sharp; there1300 to 5000 mm. (25 to 100 pounds T h e aim of t h e m o d e r n lacquer fore, classification is relative rather pressure). m a n u f a c t u r e r is t o produce a prod;-The lacquer must not bleed the than absolute. u c t t h a t goes on a n d s t a n d s u p stain. This classification was made with like a lacquer, b u t looks like an anhydrous solvents. A very small oil varnish film. It can thus be seen that the aim and amount of mater will decrease the ambition of the lacquer manufacturer The m o d e r n automobile lacsolubility. This is nicely illustrated is to produce a product that goes on q u e r s a r e composed of t h e followby noting the difference between the and stands up like a lacquer, but looks ing c o n s t i t u e n t s : nitrocellulose solubility of resins-for example, kauri like an oil varnish film. (low viscosity), a resin, a pigment, -in 95 per cent by volume ethyl solvents, diluents, a n d a plastialcohol and in 100 per cent anhydrous Nitrocellulose cizer. Success depends u p o n the ethyl alcohol. careful selection of solvents a n d Resins that are soluble in alcohols The nitrocellulose is an important resin. The solvents are the m o s t are most soluble in ethyl alcohol and constituent in the lacquer because it is i m p o r t a n t constituent. They m a y less soluble in higher alcohols. The the film-forming c o n s t i t u e n t . I t be classified i n t o t h r e e m a i n solvent combination that approaches renders the lacquer films inert towards groups-the low boilers, the medimost nearly a universal resin solvent the various reagents mentioned above; um boilers, a n d the h i g h boilers. is anhydrous alcohol with a small perin other words, it makes the finish Proper proportions of e a c h g r o u p centage of anhydrous ester, and the durable. It also allows the use of must be present. Each solvent preferred mixture is composed of fast-evaporating inert solvents in place w i t h i n a g r o u p has its particular anhydrous ethyl alcohol and anhyof the oxidizing solvents used in advantages, a n d disadvantages. varnishes. drous ethyl acetate. This mixture T h e application of the lacquer has is also a good solvent for nitrocelluSeveral types of nitrocelluloses are been m o r e o r less standardized. now on the market, the most comlose. If this were the sole function of a lacquer solvent this mixture would mon being as follows: be ideal. 1-Alcohol-soluble nitrocellulose has a nitrogen content of The resins not only must be dissolved in a solvent but the 11.5 to 11.7 per cent by weight and a viscosity of a half second solution must blend with the nitrocellulose solution; other(common steel ball method). It is soluble in alcohols (anhydrous) as well as in esters and ketones. This nitrocellulose is used for wise one constituent is thrown out of solution and the film modern lacquers whenever the resin present requires a low formed is imperfect. If the nitrocellulose is dissolved in a ester and high alcohol content in the active solvent. mixture of anhydrous ethyl alcohol and anhydrous ethyl ace2-Regular soluble (R.S.) nitrocellulose has a nitrogen content tate and the resin dissolved in anhydrous ethyl alcohol, the of 12.0 to 12.2 per cent by weight and a viscosity of a half second. two solutions will blend in all proportions provided the resin I t is soluble in esters, ketones, and in alcohols with esters or ketones. This is the common low-viscosity nitrocellulose used in is rosin, thus, elemi, or shellac. If mastic, dammar, sandarac, or kauri is used, it is necessary to add a hydrocarbon modern lacquers, both wood and metal. 3-Dope nitrocellulose has a nitrogen content of 11.8 to 12.4 in order to blend the solutions. Pontianac, soft manila, per cent by weight and a viscosity of 15 to 30 seconds. It is congo, and Zanzibar are even more difficult and sometimes soluble in esters and ketones but not to such great extent as R. S. require not only a hydrocarbon but also a soft resin as a nitrocellulose. This product is used especially in the manufacblending agent. Some solvents also permit the addition of ture of artificial leather. 4-Lacquer nitrocellulose has a nitrogen content of 11.8 to large quantities of hydrocarbons (a nonsolvent for nitrocellu12.4 per cent by weight and a viscosity of 60 t o 80 seconds. lose). An example of this type of nitrocellulose solvent is This product has been used for many years in the well-known ethyl lactate. brass and metal lacquers. The relative adhesion of the films formed with these various resins is an interesting property. The following resins Resins seem to give the lacquer film good adhesive properties: The resin supplies the properties to the lacquer which tend shellac, rosin, thus, elemi, kauri, pontianac, congo, and zanto make the finished film resemble an oil varnish. I n gen- zibar. The following resins, on the other hand, seem to give eral, resins are added to give the film gloss, brilliance, hard- the lacquer film poor adhesive properties: mastic and ness, adhesion, body, and render it more impervious to sandarac.
INDUSTRIAL AND ENGINEERING CHEiMISTRY
560
Vol. 17, No. 6
solvent, or the raw materials from which it is made, should be abundant. Dammar Ester gum
i
Esters
soluble in
Classification
+
hydrocarbons or esters Alcohols partly soluble in Alcohols Ketones
{
‘
I”___
-
Hydrocarbons Alcohols (more soluble than in alcohol
Pontianac
Hard manilas Congo Benauela Angola Madagascar Zanzibar
Alcohols
IJ
partly soluble in
insoluble in
+ hydrocarbons
A1cohols (Alcohols
+ esters
(esters must be in small amount)
Esters Ketones
The word “soluble” in this classification means that 95 per cent by weight or more of the resin was soluble in the solvent, but it is no indication of how much solvent was required to dissolve one unit weight of the resin. The maximum concentration of resin in the solution is much greater with the soft resins (rosin, dammar, ester gum, etc.) than it is with bard resins (kauri, congo, etc.). If solutions are made using the two types of resins in the same concentration and the same solvent, the soft resin solution will be much less viscous. Some resins-for example, shellac-have a waxy residue if not “refined.” This residue is not considered as part of the resin in this solubility classification.
It is more difficult to discover the effect of the various resins on the density and strength of the lacquer film. A few generalities have been noticed, however. Rosin and soft resins appear to form a hard but brittle lacquer film. The medium soft resins-for example, dammar-form a soft and tough film, whereas the hard resins, such as kauri and congo, form a hard and tough film, the kind that is most desired. These properties are only apparent when the resin is present in appreciable amounts; otherwise the lacquer film resembles the straight nitrocellulose film.
Solvents As previously stated, the difference between success and failure in the compounding of a lacquer depends largely upon the proper selection of solvents. The selection of the proper nitrocellulose and resin can be made much more easily. No one solvent will do, but several are necessary and they must be present in correct proportions. Requirements of an Ideal Solvent
First of all, it should be a good solvent for both the nitrocellulose and the resin. Any water that is absorbed by the solvent should not materially affect this solubility. The solvent should ‘preferably be nonhygroscopic. It should act as a blending agent for the two solutions, nitrocellulose and resin. It should evaporate fast a t first and slowly a t the end. This slow evaporation a t the end is important because the lacquer must have time to flow out and produce a smooth and glossy surface free from gas bubbles. The solvent must be able t o produce a solution of low viscosity even though the solution has become concentrated by evaporation. An oil varnish has a relatively long setting time and therefore the final film is smooth and glossy. This property of good flow is one of the most difficult to produce in a lacquer, because one depends entirely upon solvent evaporation (there is no oxidation of the solvent), and this evaporation for the most part must be rapid. The solvent should preferably have no objectionable odor such as the choking odor of butyl alcohol and fusel oil. It should be stable and should not decompose on standing, with the formation of corrosive products. It should be relatively cheap to make and stand dilution with hydrocarbons which are added to improve the flow and further cheapen the cost of the lacquer. The
It can thus be seen that no one solvent will be satisfactory. It is necessary, therefore, to classify the various common solvents and show the function of each class. After several methods of classification were tried out the following classification by boiling points seemed to be the most satisfactory. The solvents within a class are arranged according to chemical type-esters, alcohols, ketones, and hydrocarbons. Hydrocarbons have been included in this list because they are solvents for certain resins. They will be considered further under Diluents. LOWBOILERS(boiling below 100’ C.):
Boiling point 0
c.
77 Ethyl acetate (anhydrous) Methyl acetate 56 to Ethyl propionate 98 to Ethyl alcohol (anhydrous) 78 Ethyl alcohd ether >35 Isopropyl alcohol 82 Acetone 57 80 Benzene .. MEDIUM BOILERS (boiling near 125’ C.): 125 Diethyl carbonate 125 Butyl acetate 138 to Amyl acetate 121 Ethyl butyrate 117 Butyl alcohol 120 to Amvl alcohol Tolbene 111 HIGHBOILERS(boiling between 150’ and 200’ C.): Ethyl lactate 155 Ethyl acetoacetate 181 Diethyl oxalate 180 Ethyl benzoate 212 Benzyl alcohol 205 Diacetone alcohol (ketone properties are predominant) 104 Xvlene 143 --< - ~ PLASTICIZERS AND SOFTENERS (boiling near 300’ C . or above): Tricresyl phosphate >350 Triphenyl phosphate >325 Diethyl phthalate 290 Dibutyl phthalate 340 Diamyl phthalate 340 Diethyl tartrate 280 Dibutyl tartrate >300 Triacetin 207 Camphor (solid) 209
57 102
+
142 132
~~
>
Each of the three solvent groups does its particular and necessary function; consideration of the plasticizers will be left until later. Briefly, the functions are as follows: The LLlow boilers” are the solvents that reduce the viscosity of the lacquers so the lacquers can be sprayed. Their evaporation rate is high and they give the lacquer the property of quick drying. The “medium boilers” give the lacquers the property of flow. The “high boilers” act as residual solvents, thus preventing “blushing” or precipitation of either the nitrocellulose or the resin. They are the last solvents to leave the film and therefore produce the final flow in the lacquer, causing the film to be smooth and glossy. This group should not be confused with the plasticizers and softeners that are expected to be a part of the permanent film. These solvents in these groups have still other properties. The low boilers have for the most part rather pleasant odors, more so than any other group. They are the most inexpensive, and absolute ethyl alcohol, one of this group, is the solvent that can be most easily made and in the largest quantity, and most nearly approaches the universal resin solvent. Most of the solvents in this group produce constant boiling mixtures with water, which tend to eliminate the latter. The medium boilers, besides providing flow to the lacquer, are often used in large quantities in order to perform the functions allotted to the high boilers. This is done because the efficiency of the high boilers is little appreciated a t the present time and because their cost is relatively high. The high boilers acting as residual solvents should be the strongest solvents for nitrocellulose and resins that are present in lacquers. This requirement is partly fulfilled.
June, 1925
INDUSTRIAL AND ENGINEERING CHEMISTRY
Ethyl lactate, one of this group, is the strongest of the common solvents for nitrocellulose. The low evaporation rate and strong solvent properties (tending to give solutions of low viscosity) of this group are the cause of the final flow of the lacquer which produces a smooth and glossy film. The low evaporation rate prevents cooling of the surrounding air and subsequent condensation of water on the lacquer surface. In order to use the various types of resins, it is necessary to choose both an alcohol and an ester from this group so that there may be residual solvents present both for the nitrocellulose and the resin. If a satisfactory alcohol is not present in this group, one must be taken from the medium boilers. It can thus be seen that no one group would be satisfactory alone. If the high boilers chosen are strong enough solvents for both the nitrocellulose and the particular resin used, it is then possible to get the required low viscosity and flow without any of the medium boilers. This is approaching the ideal solvent combination. ANHYDROUSSoLvEms-Most solvents on the market are anhydrous, but several of the low boilers are not. The difference between anhydrous and 95 per cent by volume ethyl alcohol, for example, is quite marked and worthy of note. The anhydrous product is a much stronger solvent for both nitrocellulose and resins. Furthermore, anhydrous ethyl alcohol ndl dissolve more kinds of resins, and will blend these resin solutions with nitrocellulose solutions-a property the 95 per cent by volume ethyl alcohol does not possess. Anhydrous ethyl alcohol solutions have lower viscosity and these solutions will stand greater dilution with hydrocarbons than solutions with the 95 per cent product. What has been said holds true with wet and dry ethyl acetate, another low boiler. There is no question of the distinct advantages of the anhydrous product over the wet product. ‘LBLUsHING’’--‘LB1ushing,”or the precipitation of the nitrocellulose or the resin from the solution, causing the film to become white and opaque, is a phenomenon that depends upon the characteristics of the solvents present in the lacquer. Some technical men still believe that “blushing” occurs only when the solvents present have boiling points below that of water. They believe that the solvents tend to evaporate off before the water, and when the water, a nonsolvent, reaches a certain concentration the nitrocellulose precipitates and the lacquer blushes. This conception is not sound, because the relative vapor pressures of the solvents and the water a t room temperatures, and not the boiling points, are the important factors in this theory. It has been found that butyl acetate, boiling a t 120’ C., and amyl acetate, boiling a t 135’ C., have higher vapor pressures than water a t room temperatures. Another theory, which appears to be more nearly correct, is that of water condensation from the atmosphere. If the rate of solvent evaporation is high and the latent heat of the solvent is great, a cooling effect is produced as the rapid evaporation takes place. If the surrounding atmosphere is near the dew point, the temperature of the atmosphere may be lowered until the dew point is passed and water condenses in the lacquer surface, causing “blushing.” This does not preclude the use of solvents with a high vapor pressure, because the solid content of most lacquers is large and dissolved solids lower the partial vapor pressure of the solvent; for example, shellac and rosin lower appreciably the partial vapor pressure of ethyl alcohol. Moreover many of these low-boiling, fast-evaporating solvents form constant-boiling mixtures with water and thus boil off, carrying with them large quantities of water. It is natural to suppose that there are constant evaporating mixtures of solvent and water which will act in the same manner.
561
There is still another theory that is simpler than the other two and less open to criticism. “Blushing” usually occurs just before the lacquer sets, One of the requirements of an ideal solvent is that it must hold the nitrocellulose and the resin in solution until the lacquer sets. If this requirement is not fulfilled, one of the solid constituents will be precipitated and “blushing” will occur. I n practice, as stated previously, it has been found advantageous to use an alcohol and an ester belonging to the high-boiler group, in order to hold both the nitrocellulose and the resin in solution after the low boilers and medium boilers have evaporated, and thus prevent “blushing.” If a blending agent is necessary because of the imcompatability of the two solutions, this blending agentfor example, xylene-must belong to this same group, the high boilers; otherwise it may evaporate first and thus cause precipitation or “blushing.” Evaporation Time of Solvents Gardner and Parks2 have done some excellent work on the evaporation time of many well-known nitrocellulose solvents both alone and with nitrocellulose. Some of the very interesting results may be briefly summarized as follows: PURE SOLVENTS Ethyl acetate Anhydrous ethyl alcohol (C. D. No. 6) Butyl acetate Diethyl carbonate
Time for complete evaporation of sample Minutes 30 57 155 160 Per cent evaporation in 180 minutes 80 59
Amyl acetate Water Butyl alcohol Fusel oil
48
34 Time for 87 per cent evaporation Minutes 30 63
COTTON SOLUTIONS~ Ethyl acetate Anhydrous ethyl alcohol (C D No 6) 115 Dlethyl carbonate Butyl acetate 125 Amyl acetate 170 a 120 grams of nitrocellulose in 1 liter (16 ounces in 1 gallon) of solvent.
These data show the importance of vapor pressure determinations rather than boiling points, and the lowering of the vapor pressure due to dissolved solids. There is given below a short statement for each one of the common solvents. This statement includes a brief description of the process of manufacture, a summary of the particular advantages and disadvantages of the solvent, together with any other interesting data that may have been determined. Low Boilers
ANHYDROUS ETHYLALcoHoL-Anhydrous ethyl alcohol has been made in commercial quantities for solvent purposes in this country since 1919, by the use of the principle first described in detail by Young.3 Ethyl alcohol, water, and a hydrocarbon such as benzene form a constant-boiling ternary mixture in which the water content is approximately 7.4 per cent by weight, which is greater than the per cent of water in the well-known constant-boiling binary mixture considing of ethyl alcohol and water. This ternary mixture has a lower boilink point than the binary mixture just mentioned; therefore, in the rectification of a mixture of the three subtances the ternary constant-boiling mixture will distil over first. The distillate will separate into two layers and the hydrocarbons may be used over again. As there is more water removed than added, an anhydrous ethyl alcohol will be left in the still. 2
3
Parnt Mfrs d s s o c , Czvc 218 J . Chsm. SOC.(London),81T (19021, several articles.
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INDUSTRIAL A N D ENGINEERING CHEMISTRY
Anhydrous ethyl alcohol as a lacquer solvent has many advantages. It is a good solvent for certain types of nitrocellulose and it is probably more nearly the universal resin solvent than any other single compound. Its odor is unquestionably pleasant. Its evaporation rate is high, but not too high for its class. Resins dissolved in anhydrous ethyl alcohol give a solution with a lower viscosity than in other solvents. The ethyl alcohol acts as a blending agent for solutions of nitrocellulose and resins. It is stable and has little effect on the ordinary priming coat which prevents the lacquer from sinking or peeling. It is relatively cheap and abundant. It will stand dilution with hydrocarbons, which fact will make its use in lacquers still more economical. Anhydrous ethyl alcohol requires a special type of nitrocellulose when used alone because it is an alcohol, if a high nitrocellulose type of lacquer is desired. Solubility tests on the various resins show the following results: Anhydrous ethyl alcohol will completely dissolve rosin, thus, kauri, pontianac, and manila. It will dissolve elemi, mastic, shellac, and dammar, but will leave a waxy residue. It was necessary to add to the alcohol between 20 and 30 per cent of a hydrocarbon or an ester in order to obtain complete solution of ester gum or cumar. The hard copals, such as congo and Zanzibar, were soluble after heat treatment. ANHYDROUS ETHYLACETATE-The ordinary commercial 85 per cent ethyl acetate is not anhydrous. It is made by the esterification of acetic acid with alcohol, using sulfuric acid as a catalyst. The manufacture of anhydrous ethyl acetate is more complicated. Advantage is taken of the constant-boiling ternary mixture of ethyl acetate, ethyl alcohol, and water, not only to dehydrate the ethyl acetate, but also to increase the rate of esterification and the yield. Anhydrous ethyl acetate has many good properties as a low-boiling lacquer solvent, many of them being the same as for anhydrous ethyl alcohol. Anhydrous ethyl acetate is an ester and is therefore a better solvent for nitrocellulose than anhydrous ethyl alcohol; in fact, it is one of the best nitrocellulose solvents. Probably because of its high solvent power nitrocellulose solutions made with it will stand about 50 per cent more dilution than the corresponding solution made with anhydrous ethyl alcohol. Anhydrous ethyl acetate, however, is not such a good solvent for resins as anhydrous ethyl alcohol, showing again its ester characteristics. A combination of the two solvents is better than either alone in this particular respect. This combination also makes a better nitrocellulose solvent. Ethyl acetate has little tendency to blend nitrocellulose and resin solutions. This solvent will dissolve almost completely rosin, thus, mastic, ester gum, and cumar. From 5 to 30 per cent by volume anhydrous ethyl alcohol must be added to dissolve elemi, dammar, shellac; and sandarac, kauri, pontianac, and manila are partly soluble. The hard copals such as congo and Zanzibar are insoluble. METHYLACETATE-MethYl acetate is manufactured by the esterification of acetic acid with a methanol, using sulfuric acid as a catalyst; no departure from the standard method of esterification is necessary. This solvent has no particular advantages over anhydrous ethyl acetate as a constituent of lacquers; but it has several disadvantages. Its evaporation rate is too high and the commercial product has an unpleasant odor. As it usually contains free methanol it must be treated as a toxic substance, and is somewhat dangerous t o handle. It is a solvent for most types of cellulose acetate and whenever thelatter becomes an important constituent of lacquers, methyl acetate will become ode of the essential solvents. Methanol, from which it is made, is produced entirely from wood distillation
Vol. 17, No. 6
in this country at the present time. Furthermore, methanol is only a by-product in wood distillation; the chief product, charcoal, has llttle sale at this time. These facts tend to keep the cost of methyl acetate above that of ethyl acetate. Many attempts have been made to make methanol synthetically and at a cost that will permit competition with ethyl alcohol. It is probable that such a synthetic process will eventually be successful; already considerable quantities of methanol, said to be a synthetic product, have entered the United States from Germany. ETHYLPROPIONATE-This ester is made from propionic acid and ethyl alcohol in the usual manner. No particular advantages for it have been found as yet. It is costly to make because there is no good source for propionic acid. During the war seaweed was collected and fermented to produce various acids, one of these being propionic acid. Large, stocks from this source were on hand after the war, and it was the utilization of these stocks that brought ethyl propionate on the market. ACETONE-For many years acetone has been recovered as a by-product; in wood distillation; it has also been manufactured by the destructive distillation of calcium acetate. During the war there was an enormous demand for this product to be used in the manufacture of cordite, the British standard propellant. I n order to meet this demand many processes were resorted to; the most interesting was the fermentation of corn to butyl alcohol and acetone. Since the war butyl alcohol has found a ready market in the lacquer industry, and today the demand for butyl alcohol has increased the stocks of acetone beyond the requirements of the market. Acetone is a powerful solvent for nitrocellulose, even more so than ethyl acetate, and, as can be inferred from above, it is probably the most economical powerful solvent for nitrocellulose on the market today. On the other hand, acetone is a poor solvent for most resins; this is evidently a characteristic of ketones. It has a very high rate of evaporation, almost twice that of ethyl acetate (85 per cent). If a solution of nitrocellulose is made in acetone alone and then poured on glass,nofilmis formed. This is not true of other low boilers. It is thought that the a c e tone leaves the nitrocellulose so rapidly that the latter does not have the proper conditions for film formation. If the rate of evaporation is decreased by artificial means a film is produced. Acetone has a rather nauseating odor. Several investigators4 have determined the solvent power of acetone for various resins. Work along these lines in this laboratory has shown that acetone will completely dissolve rosin and resins in that group, but no others. Shellac, kauri, and pontianac are about 66 per cent soluble in acetone a t room temperature and the other resins are even less soluble. The particular grade of resinused influences the results appreciably. ISOPROPYL ALcoRoL-Isopropyl alcohol is made from propylene, one of the gases produced in the cracking of petroleum distillates. This gas is absorbed in sulfuric acid, forming propyl sulfate, and the latter is hydrolyzed to form isopropyl alcohol and to recover the sulfuric acid. Another method is the hydrogenation of acetone directly to isopropyl alcohol, This method has been recently put into successful operation in this country. The total production is not large a t the present time. Isopropyl alcohol may be used as a substitute for ethyl alcohol in lacquers, but no particular advantages have been discovered. It is not such a good solvent for the various resins. It has a stronger and less attractive odor than ethyl alcohol. On account of its high cost of manufacture and limited production it has not been used in any quantity in b c quers. 4
See booklet on “Acetone” by R. F. Remler, of the Mellon Institute, for of work done on the solvent powers of acetone.
e, review
June, 1925
INDUSTRI.4 L A N D ENGINEERING GHEMISII'I1Y
563
*L
Medium Boilers
DIETHYI. C ~ U B ~ N A T E of - Obhe ~ ~most interestiiig 8olvents in this class is diethyl carbonate, which until recently has been a i:hemical curiosity but is now made synthetically nil a large scale. It is an excellent solvcnt for nitrocellulose; t.&s have shown t.hat it has a solvent power equal to that of eornmercial
contain unusually large amouuts of hydrocarhous it has been found necessary to use ethyl lactate with thc diethyl carbonate in order to keep the mixt.ure blended. .4 series of test lacyiiers was made up using diethyl carbonate as the medium boiler in o m case and commercial butyl acetate (equal, amounts) in the other. Ester gum and dammar vere the resins employed; an attempt was made to approach the average composition of the present-day lacquers.
U. S . Industrial Chemical Company
butyl acetate (85 per cent ester). It is a solvcirt for the estcrsoluble resins and has the property of blending certain resin solutions (kauri, shellac, elemi, thus, and rosin) with nitrocellulose solutions, thus eliminating the use of medium-boiling alcohols which arc found necessary if butyl acetate or amyl acctate is the solvent. It has approximately the same evaporation rate as buty1acetat.e about one-fifth that of ethyl acetate), and imparts Aow to the lacquer. It is a stable compound, and its corresponding acid, carbonic acid, is an extremely weak acid. Nitroccllulose solutions made with this solvent will not tarnish brass. Most of the medium boilers have very disagreeable odors; diethyl carbonate has a pleasant odor. This is a very important feature because it is not always possible to spray lacquers in specially ventilated hoods. Amyl acetate and butyl acetate arc made from the corresponding alcohols, which in turn are produced by fermentation processes. Diethyl carbonate is a syuttietic product and 110 living organism is involved in its manufacture. It could be made in almost unlimited quantities. Diethyl carbonate has certain defects. Corresponding solutions of uitrocellulose made with diethyl carbonate and commercial butyl acetate show that the diethyl carbonate solution is much more viscous. This can be explained, not by the individual charact.eristics of the diethyl carbonate but by the fact that commercial butyl acetate contains approxinrately 15 per cent of its weight of butyl alcohol. If we add a corresponding amount of alcohol to the diethyl carbonate inuclr of t.his difference disappears. This same difference has been uoted between solutions made with pure arid with commercial amyl acetate. Diethyl carbonate has a characteristic which is distinctive of the compound itself-its solutions of nitrocellulose will not stand so much dilution with hydrocarbons as the other medium boilers. In lacquers which
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I Y D C-STRTAL AXD EA\-GINEERIA’G CHEMISTRY
manufacture of ethyl alcohol. Less than 0.5 per cent by volume of the crude ethyl alcohol is fusel oil. It can be easily seen that the production of amyl acetate is limited. It is a stronger solvent for nitrocellulose than butyl acetate, but it has practically the same solvent power for the various resins. Its evaporation rate is lower than that of diethyl carbonate or butyl acetate. This tends to give better flow to the lacquer. Amyl acetate will stand greater dilution with hydrocarbons than butyl acetate. It has, howeyer, a very choking odor, and this fact coupled with the relatively small source of supply prevents this excellent solvent from becoming very popular. ETHYL BUTYRATE-Butyric acid, from which ethyl butyrate is made, is another acid produced in the fermentation of seaweed during the war. Tests on ethyl butyrate as a medium boiling splvent have not disclosed any particular advantages. Ethyl butyrate has a horrible odor that lingers almost indefinitely. This fact is enough to condemn it as a lacquer solvent. BUTYLALCOHOL-AS previously stated, butyl alcohol is made by the fermentation of corn using a special organism. It has been produced from butylene by absorption in sulfuric acid and a subsequent hydrolysis. It also has been synthesized from acetylene through acetaldehyde, aldol, etc. I n general, alcohols may be considered resin solvents and esters nitrocellulose solvents. Comparing butyl alcohol with diethyl carbonate this idea is borne out. Butyl alcohol will completely dissolve all the various resins except the estersoluble resins such as ester gum and the hard copals such as congo. It is not, however, such a good solvent for resins as anhydrous ethyl alcohol, a low boiler. The higher boiling alcohols are as a rule not such good solvents as ethyl alcohol. Butyl alcohol fulfils the requirements for an alcohol in this POUP. AMYLA L C O H O L - ~ Y alcohol ~ is a constituent of fusel oil which, as previously stated, is obtained as a by-product in ethyl alcohol fermentation. It has also been made, although not to any great extent, from amylene found in the gases given off in cracking processes, by absorption in sulfuric acid and subsequent hydrolysis. Compared with butyl alcohol there is very little difference in properties. The two have practically the same solvent power for the various resins. Amyl alcohol has a lower vapor pressure and evaporation rate than butyl alcohol. This difference is noticeable in clear lacquers and careful work. The lacquers containing amyl alcohol will have better flow and a smoother lacquer film. Amyl alcohol has a more irritating odor than butyl alcohol. On the whole, amyl alcohol is an excellent solvent and is chiefly hampered by a lack of supply. If a satisfactory synthesis could be discovered the excess production could be easily used. High Boilers
ETHYLLACTATE-Though made by the esterification of lactic acid with ethyl alcohol, this solvent requires a special process of manufacture. It is commonly considered an ester, but as a solvent for resins it is an alcohol as well as an ester. The structure of the molecule indicates the possibility of alcohol properties and tests indicate that ethyl lactate is more of an alcohol than an ester. This combination structure is probably the reason ethyl lactate has greater solvent power for nitrocellulose than any other common solvent. The addition of 25 per cent of water has little effect on its solvent power. Its solutions of nitrocellulose will stand more dilution with hydrocarbons than solutions made with any other solvent; for example, ethyl lactate will stand twice as much dilution as anhydrous ethyl acetate and three times as much as butyl acetate. Ethyl lactate dissolves practically completely
T’ol. 17, No. 6
rosin, ester gum, shellac, kauri, and pontianac. Dammar and congo are insoluble or very slightly soluble. Owing to its alcohol properties it will dissolve more resins than any other common ester solvent. It acts as a blending agent for resin and nitrocellulose solution. Any substance that is a solvent for both resin and nitrocellulose should exhibit this property. Where a hydrocarbon is the blending agent required, ethyl lactate will permit more hydrocarbon to be added and thus aid in the blending. Ethyl lactate, like all solvents of this class, has a low vapor pressure. It is also an excellent gloss producer. Two properties are responsible for this, its great solvent power for both resins and nitrocellulose and its low vapor pressure. It has a pleasant odor and films made with it have no residual odor. In brief, it is as near the ideal solvent in this group as we have at the present time. DIACETONE A ~ c o ~ o ~ - D i a c e t o nalcohol e is made by condensing two mols of acetone using an alkaline material as the catalyst. It has a combination structure, part alcohol and part ketone. The alcohol in this case is tertiary. The ketone group is more active than the alcohol group. These two facts seem to cut down its solvent powers compared with ethyl lactate. It is, however, a very good solvent for nitrocellulose and many resins. Such a combination, an alcohol and a ketone, would be expected to be an excellent solvent for nitrocellulose. Solubility tests on resins indicate that it is not quite so good as ethyl lactate, but i t seemed to dissolve more of congo. It has a pleasanter odor than acetone. Its raw material (acetone) is both cheap and abundant and its process of manufacture relatively simple. Nothing is known a t present regarding its stability. Like ethyl lactate it is an excellent gloss producer, because it meets the requirements of this solvent class as to solvent power and vapor pressure. BENZYL ALCOHOL-Benzyl alcohol is made by hydrolyzing benzyl chloride, which is made from toluene by chlorination using direct sunlight as the catalyst. Benzyl alcohol resembles the aliphatic alcohols in solvent power. It dissolves alcohol-soluble nitrocellulose and the alcohol-soluble resins. It is not as good a solvent as anhydrous ethyl alcohol but it compares very favorably with the medium-boiling alcohols, and it is a better resin solvent than ethyl lactate. It has a pleasant odor and is a good gloss producer. Its raw material, toluene, is abundant and cheap. If the demand was sufficient this high boiler could be made economically. ETHYLACETOACETATE-Ethyl acetoacetate is made by condensing two mols of anhydrous ethyl acetate using metallic sodium. The substance is a combination of ketone and ester and, as would be expected, is a good solvent for nitrocellulose. It is, however, a very poor solvent for resins, only esters in the class with rosin and ester gum being soluble in this solvent. It has a low vapor pressure, but owing to its poor solvent power for resins it is not a good gloss producer. It is also more costly to make than the other solvents in this group. DIETHYLOXALATE-Diethyl oxalate is made by the esterification of oxalic acid with ethyl alcohol. It is an excellent solvent for nitrocellulose, second only to ethyl lactate. Its nitrocellulose solutions will stand twice as much dilution with hydrocarbons as will solutions made with butyl acetate. It will not, however, stand as much dilution as ethyl lactate. It is a poor resin solvent, similar to ethyl acetoacetate, dissolving only rosin and ester gum. It has a mild odor. It is stable. The raw materials for its manufacture are abundant and cheap. It has a lower vapor pressure than ethyl lactate, but owing to its poor solvent power for resins it is not a good gloss producer.
June, 1925
IA-DCSTRIAL AiYD E S G I S E E R I S G CHE.IfIISTRY
ETHYL BENzoAnE-Ethyl benzoate is made by the esterification of benzoic acid with ethyl alcohol in the usual manner. It is an excellent solvent for nitrocellulose and the ester soluble resins. It has a tendency to improve the flow and thereby cause the film to become smooth and glossy. It has a pleasant odor. It can be made in large quantities, but the benzoic acid from which it is made is costly to produce by present methods.
565
tricresyl phosphate blushed and the film was still gummy after 24 hours.
Diluents
The diluents are the hydrocarbons-benzene, toluene, xylene. They are not only diluents but also solvents for certain resins and blending agents, for nitrocellulose, and certain resin solutions. From an economic standpoint they are considered as diluPlasticizers and Softeners ents because of their comparatively low cost. They are Plasticizers and softeners may be considered as the very solvents for rosin, thus, elemi, mastic, dammar, ester gum, high boiling solvents that are expected to stay permanently and cumar, as previously shown. For this reason they may in the lacquer film. The function of the plasticizer is to im- be used as thinners to reduce the viscosity of a concentrated prove the flow of the lacquer just before it sets, to prevent lacquer containing these resins in order that it may be sprayed. blushing, and to make the film smooth and glossy. This Clear solutions of kauri and congo in anhydrous ethyl alcohol means that the plasticizer should be a good solvent for both when added to a clear solutionof nitrocellulose (alcohol-soluble) nitrocellulose and resin and also a blending agent if necessary. in the same solvent give cloudy mixtures. This mixture may The solutions should have low viscosity. The plasticizer be converted to a clear solution by the addition of these hydrocarbons. More benzene can be added than toluene and more should have a low vapor pressure (or a high boiling point300" C., or above). These qualifications are nearly the same toluene than xylene. However, the resin was first dissolved as those of the high boilers. There is this difference, however: in anhydrous ethyl alcohol and any waxy residue discarded. the high boilers are expected to leave the film before the job The hydrocarbons are not strong enough blending agents to is completed, whereas the plasticizers are expected to remain keep this waxy residue in solution in alcohol. They also often form constant-evaporating mixtures with other solvents and in the film permanently. The functions of the softener are to make the film tough, water and thus help to eliminate the latter. Care should be taken not to add too much of these hydroelastic, flexible, adhesive, and permanent. In order to perform these functions the softener, like the plasticizer, should carbons because they are not nitrocellulose solvents and be a good solvent for both resin and nitrocellulose. It has therefore tend to gel nitrocellulose solutions if used in too not been determined as yet just what property of the softener great a quantity. Furthermore, if the nitrocellulose solmakes the film elastic, adhesive, and flexible beyond the fact vents evaporate off first these hydrocarbons will cause the nitrocellulose to precipitate. This means that the hydrothat it should be a liquid a t ordinary temperature. Many of the plasticizers and softeners given under the carbon selected should depend upon the solvent group used. classification of solvents act both as plasticizers and softeners. Benzene boiling a t 80" C. is a low boiler, toluene boiling a t They are all esters. Two oils, castor oil and rapeseed oil, are 111" C. is a medium boiler, and xylene boiling a t 143" C. is commonly used, but mainly as softeners and not as plasti- a high boiler. A n investigation was made to find out the amount of toluene cizers. They are not solvents for resins and cotton and are of nitrocellulose in some of the common solvents solutions therefore seriously handicapped. The present popular method of testing plasticizers is to would stand before becoming cloudy. The solution contained make a standard strip of film using a definite amount of plas- 240 grams per liter of R. S. nitrocellulose (32 ounces per ticizer and test this film for elongation under various 10ads.~ gallon). The following result3 show the maximum number of cubic centimeters of toluene that could be added to 100 CC. The phthalates seem to be better than the phosphates. Tests were made on several plasticizers to determine the of thiq solution: per cent evaporation per day. Diamyl phthalate and dibutyl \iOL1 FXT Cc. of toluene phthalate showed no evaporation within the accuracy of the Diethyl carbonate 1.50 240 Butyl acetate (85 per cent, work. Tricresyl phosphate seemed to absorb water and then "Ansol" (anhydrous ethyl alcohol and ethyl acetate! 260 give it up; the average weight did not change, however. Amyl acetate-(85 per cent) Diacetone alcohol Diethyl phthalate and dibutyl tartrate evaporated to the Ethvl acetate (anhvdrous' phosphate extent of about 0.01 per cent per day. Triacetin evaporated Tricresyl Diethyl phthalate oxalate approximately 0.3 per cent per day, and diamyl tartrate lost Diethyl Ethyl lactate 700 over 0.9 per cent per day. The following practical test was devised for plasticizers and Automobile Lacquers softeners: One gram of the plasticizer was added to 10 cc. of a solution of 480 grams of a resin in 1 liter of anhydrous The present commercial product has several distinct ethyl alcohol (a "4-pound cut" of a resin in anhydrous ethyl advantages over the old-time varnish. It can be applied in a alcohol). This solution was poured on glass and air-dried much shorter time. The cost of materials and labor is less; for 24 hours. Another sample was dried for 24 hours a t 77" there is no chemical action on drying; the film once formed is C. (170' F.). Both films were then immersed in water. permanent. There is no change in shade on drying. The lacThe film was examined for toughness, hardness, blush, and quer film is more durable and tests have shown that a lacadhesion. Tricresyl phosphate and diamyl phthalate were quer film properly made will withstand the following: sun's tried with the following resins-ester gum, dammar, kauri, rays, heat, cold, water, ice, sand, soap, weak acid, weak and congo. Diamyl phthalate appeared to be the better alcohol, oil, and tar. plasticizer. Ester gum and dammar gave no blush, whereas It has, on the other hand, several disadvantages. The tricresyl phosphate blushed badly. It also proved to be finish has not the high gloss that is common to a varnish more adhesive. With kauri it showed the same results as job, primarily because it is almost impossible to put a coat of tricresyl phosphate except that the film was more adhesive. clear lacquer over a pigmented coat and have the clear coat With congo it showed no blush and gave a tough film, whereas stand up under summer sunlight. It is commonly supposed that the ultra-violet rays present to a marked degree in 1 H A. Nelson, of the New Jersey Zinc Co , will publish very soon his summer sunlight tend to decompose the nitrocellulose, results using this method of testing
whereupon the film cracks giving separations in the neighborFormulas for Automobile Lacquers inrh) in width. This docs iiot happen hood of 0.8 mm. I t is not difficult to compound an automobile lacquer that to the pigmented coat because the pigment adsorbs the rays axid protects tlre nitrocellulose beneath. It has been will form a film of satisfactory appearance, provided cost of shown that a dear nitrocellulose has a marked tendency to materials and labor are not essential factors, especially if the shrink as the liigh-boiling solvcnts are elimiiiated either by finish produced by tire use of the softer resins is all that is evaporation or by adsorption in the under coat. The pig- desired. If low cost of lacquer and application is essential ment.ed film docs not show this tendency bo a marked extent,. and the hard copal resins must be used to obtain t,hc desired It has also been noticed that this crackiug takes place sooner results, then t,he problem becomes complicated and a more if tlie laiqoer film is put on nietal tliari if it. is put on wood. careful study of new solvents becomes necessary.
U. S. Industrial Alcohol Company
Clear lacquers eontuinirig rrlativeiy large amounts of soft,ener will stand up longer than thocc containing small amounts. Spcoialiy prrpnred nitrocellulose of cxtrcmelg low viscosity exhibits much greater resistance to summer sunlight xvheii used in t,hc clear lacqucr bhaii. t,lie ordinary coumiercial 1Tlriety. The laak of a sabisfactiiry clear coat has forced the i w r to resort to rubbing the pigmented coat. The nitrocellirlose film is t.ough and soft and cannot be rubbed to a high glnss. Tlie lacquer film containing nitrocellulose, resin, and plasticizer is mucli better in this respect, but still not SO good as a varnish film. The harder tlie resin the higher the polish that can be obtained. In order to cut the rubbing to a rensonable amount it is essential that the surface as formed be as smooth as possible; in other words, the lacquer should contain satisfactory high-boiling solvents in order to obtain flow just before set.ting. Several rubbing machines are on themarket,but theyarenotyetahle toduplicate handrubbing. The modern automobile lacquer has another disadvantage. It looks like a baked enamel finish rather than a good varnish finish. It has no depth or appearanre of depth. This also is due to the lack of clear tup coats. Clear varnish has been tried over pigmented lacquer, but without success. At the present time only the softer resins are used in yuantity in automobile lacquers, and in addition the pigment contciit is made very high in order to get covering in two coats. This means that the lacquer film is thin and soft and will wear through in spots. This, however, applies only to the lacquer jobs done on a large production scale at a minimum cost for materials and labor. If cost is not. the important item the manufacturer can afford to use more coats containing less pigment and a harder resin, which usually results in a more durable finish.
There is given below a general foruiuln for ail automobile 1at:quer in Idrich any of tlie softer rosins may be used:
Soiids 15 to 26 per cent hy weight of total
Nitrocellulose 40 to 60 per ccnl of solids ( 0 . 5 second R . S. 1 i i i i o c e i i i i l 0 ~ 4 Resin 20 to BO per cent of solids (ester sum) Plasticizer and softener 50 to 80 per cent of the nitrocellulose (limy1 phthalate) Pigment 6 to 26 per cent of solids
The solid eoritent depeiids largely upon how much can he added to the lacquer before tlie viscosity of the lacquer becomes too high for satisfactory spraying. The higher the solid content the fewer the number of coats. Viscosity of the 1iicrper.is largely dependent upon the viscosity of the nitrocellulose used. There is a limit to which the nitrocellulose viscosity can bo reduced before the film properties are lost. It is conceivable, however, that the film-forming properties may be brought back in some other film-forming agent. In the formula given above a 0.5 second R. S. nitrocellulose is recommended. This type of nitrocellulose has been found practical whenever the resin used is ester-soluble. Twice as much nitrocellulose as resin is used; if the relative amount of resin is much greater the film becomes more like a varnish aud less like a lacquer. For special purposes this may he desirableas, for example, in wood lacquers-hut for automobile purposes the ratio of two to one has been found more satisfactory. The resin may be not only ester gum hut also dammar, or a resin from the rosin group. If dammar is used
June, 1925
INDUSTRIAL AND ENGINEERING CHEMISTRY
the resin should first be dissolved in an alcohol and the insoluble waxy residue discarded in order to avoid blending difficulties. The same is true of shellac, but in using this resin further care must be taken to see that the ester content of the lacquer is low. Tests have shown that the plasticizer should be present to the extent of 50 to 60 per cent of the nitrocellulose in order to prevent the film from becoming brittle and also to make certain that the film adheres well to the under coat. As previously stated, diamyl phthalate has shown itself to be a satisfactory plasticizer and softener. The pigment content should be sufficient to prevent any effect on the film of summer sunlight and rapid changes in temperature. The greater the amount of pigment used the fewer the coats, but the less the natural gloss obtained. The liquid content is the difference between the total and the solid content, and, as shown above, averages 75 to 85 per cent of the total. It is recommended, but not essential, that all three types of solvents be present. I n case it is desired to use only low boilers and high boilers, certain requirements must be met which will be explained later. The low boilers suggested in the above formula are anhydrous ethyl alcohol and anhydrous ethyl acetate because, as shown in the section on solvents, they fulfil better than the others the functions of this type of solvent. It is preferable to use both the alcohol and ester and to add as much as possible for economic reasons. Diethyl carbonate, rather than butyl and amyl acetate, is chosen as the medium boiler because of superior odor. If the resin is ester-soluble it is not necessary to add an alcohol of this group. In case of shellac, if the low boiler is chiefly anhydrous ethyl alcohol, and ethyl lactate is used as the high boiler, no medium boiling alcohol will be necessary. The amount of diethyl carbonate recommended, 20 to 40 per cent of the liquids, is high in order to insure a good flow for the lacquer and a resulting smooth surface. It is possible to use less and increase the amount of low boiler, provided there is a very high percentage of pigment, and still obtain a satisfactory surface. The high boiler recommended, ethyl lactate, is satisfactory because of its combined ester and alcohol properties. It would be more advantageous, however, if a primary alcohol boiling near the boiling point of ethyl lactate could be added along with this ester. At present there is no such product on the market. Fortunately, it is not essential when the softer resins are used. This high-boiling type of solvent cannot be added to a much greater extent than 10 per cent of the liquids without causing the film to dry slowly, provided the medium boilers are present. The remaining portion of the liquid is the diluent, toluene, though benzene may replace part of the toluene if faster evaporation is desired, and xylene if slower evaporation is desired. The fossil resins such as kauri and congo, when used in lacquers, make a harder and tougher film and one that presents a more pleasing appearance. These resins are not so soluble as the softer resins in lacquer solvents and their solutions are more viscous; therefore, the formula given above must be modified. The total solids will be nearer 15 per cent than 25 per cent; the resin will be one-fourth of the weight of the nitrocellulose, instead of one-half; the amount of plasticizer will be increased; the low-boiling solvent, anhydrous ethyl alcohol and anhydrous ethyl acetate, will be increased to 3 0 4 0 per cent of the liquids; the medium-boiling solvent will be decreased to 15-20 per cent of the liquids and mill contain amyl alcohol as well as diethyl carbonate; and the high-boiling solvent, ethyl lactate, can be used if kauri is the resin employed, but must be changed to some other member in this group with better resin solvent power if congo is employed. Experiment has shown that lacquers can be made without the medium-boiling solvents, and the films produced from such
567
lacquers appear to be the equal of the other type. The liquid composition of this new type is approximately as follows: Solvents: Low boilers High boilers Diluents
Per cent of liquids 45 to 50 10 to 15 35 to 45
If the softer resins are used the solvents mentioned in the first formula given may be used in this case; that is, anhydrous ethyl alcohol and anhydrous ethyl acetate for the low boilers, ethyl lactate for the high boilers, and toluene for the diluent. With kauri or congo it is necessary to use nearly all alcohol for the low boilers and only those solvents boiling between 150" and 170" C. for the high boilers, in order to obtain the proper flow and viscosity in' the absence of the medium boilers. Lacquers have been manufactured and sold that contained only low-boiling solvents, and others that contained the low-boiling and medium-boiling solvents but no highboiling solvents. These two combinations are not recommended, for reasons that are obvious after reading the functions of each solvent group. The formulas given in detail above are based on the results of many tests in which lacquers were made and applied to automobiles, but these same formulas could have been developed from the known properties of resins and solvents without actually making or applying a single lacquer. Tests were made to prove the soundness of this method of development, and in no case when the properties of all the constituents were known did the finished lacquer fail to meet the predictions. Application of the Lacquer
E. M. Flaherty,6 of the du Pont Company has written an excellent article on the application of an automobile lacquer giving all of the necessary detail of the procedure. He also gives figures showing the saving of time, labor, materials, and floor space due to the use of a lacquer in place of a varnish. It seems quite evident that the lacquer finish for automobiles is an important development and an innovation that has come to stay. If the saving in time, labor, materials, and floor space were ignored, it would still be a step forward to use a finish that would last 12 to 24 months over one that was only good for 4 to 6 months. The big field for lacquer, the finishing of furniture and interiors, has only been touched, and it is here that lacquer will mean so much to humanity. Acknowledgment
The author is indebted to the following men for all the experimental results in this article: H. F. Willkie, R. L. Moylan, R. Wysocki, W. E. Brophy, C. Wilczewski, and W. F. Weber. The work was carried out in the Research Department of the E. S. Industrial Alcohol Co., and covers a period of about four years. 0
P a i n t , 021 Chem. Rev., 78 (August 16, 1924)
Filing Foreign Patent Applications in Canada-A decision rendered Arovember 11, 1924, pertaining to the Canadian patent act is of utmost importance t o American patentees. It affects the construction of Section 8, which provides that an inventor electing to patent his invention in a foreign country before obtaining a patent for the same invention in Canada must apply for the patent in Canada within one year from the earliest date of filing his application in the foreign country. The decision holds that applications may be filed in Canada without regard to corresponding foreign applications, provided that a t the time of filing in Canada no patent has been issued thereon for more than two years. The date of filing foreign patent applications is extended one year and, in addition, the two-year period commences on the date of granting the patent rather than on the date of filing.
