May, 1928
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Cellosolve and Its Derivatives in Nitrocellulose Lacquers' E. W. Reid and H. E. Hofmann hlELLON INSTITUTE O F INDUSTRIAL RESEARCH, UNIVERSITY OF PITTSBURGH, PITTSBURGH, PA.
this property that Cellosolve Acetate finds its greatest use in high-grade automobile lacquers and in other products YNTHETIC chemistry has seen in the last few years intended to be used in humid climates. Butyl Cellosolve has the highest boiling point and the the development of an entirely new line of aliphatic chemical compounds. Among the most important of lowest rate of evaporation of the Cellosolve derivatives. the products are ethylene glycol and its derivatives. The I t is therefore chiefly of interest in the manufacture of lacethers of glycol, notably the monoethyl ether, have found quers intended to be applied with a brush or by dipping. wide use in the lacquer industry on account of their high It has a very mild odor, good tolerance of hydrocarbon dilsolvent action. The monoethyl ether of ethylene glycol is uents, and is an excellent resin solvent. While possessing being marketed under the name "Cellosolve." Because of good solvent power for nitrocellulose, its solvent action is its hiah solvent action on nitrocellulose, high dilution ratio rather slow, which is distinctly desirable in a brushing lacquer intended for use over wit h-h y d r o c a r b o n s , and old paint or varnish. Conpresent low price, it has sequently Butyl Cellosolve made possible the formulaThe ether derivatives of ethylene glycol are excellent is especially recommended tion of good lacquers a t a solvents for nitrocellulose. Ethylene glycol monoas an ingredient of houselow cost. ethyl ether, ethylene glycol monoethyl ether acetate, hold lacquers. I n addition to Cellosolve and ethylene glycol monobutyl ether are available in It will be apparent that itself, the other derivatives commercial quantities and are finding wide application each of these solvents has its offered to the lacquer indusand use in the lacquer industry. special and particular place try at this time are CelloThe properties of each solvent are discussed and in lacquer formulation, and solve Acetate (the acetate of comment is made on the use of various resins in conthat none of them is a direct the monoethyl ether of nection with them. The manufacture of lacquers substitute for any solvent ethylene glycol), and Butyl involving the use of the glycol ethers is discussed and nom in use. In other words, Cellosolve (the monobutyl type formulas are given for lacquers suitable for use the formulas to be given for ether of ethylene glycol). in the automobile, furniture, and brush lacquer fields. the use of Cellosolve and its All t h r e e compounds are derivatives in nitrocellulose good solvents for nitrocellulose and resins and are in the lacquers are intended for high-boiling class-i. e., they have slow rates of evaporation. specific types of lacquers, and have not been obtained by This latter property is a distinct advantage, as the last por- substituting one of the Cellosolve compounds for another tion of the solvent mixture t o evaporate will be a good solvent ingredient in any existing lacquer formula. It is of vital for the non-volatile ingredients, and thus give a clear homo- importance that this fact be borne in mind by the prospective user. geneous film. The ordinary physical and chemical constants of these The Cellosolve derivatives have very mild odors, and Cellosolve itself is practically odorless. This is an important con- compounds are given in Table I. sideration in the manufacture of brushing lacquers or lacTable I-Properties of Cellosolve and Its Derive tives quers for the commercial finishing of refrigerators, kitchen CELLOSOLVE BUTYL CELLOSOLVE ACETATE CELLOSOLVE. cabinets, and the like, where a disagreeable residual odor is Specific gravity (2O0/2Oo C.) 0.930 0.976 0.902 decidedly a disadvantage. The odors of all three solvents Refractive index (25' C.) 1.4050 1.4051 1.4169 Roiling point, C. 13 1 153 170 are much more agreeable than that of ordinary denatured Acidity ( a s acetic acid), per cent ... 0.02 ... alcohol. Ester content, per cent ... 95.0 ..* Dilution ratios: Kext to its pleasant odor, the principal feature of Cellosolve Toluene 5 2 3.0 2.6 Turpentine 1.9 2.8 is its extraordinarily high tolerance of coal-tar hydrocarPetrol (80-130' C.) 0.8 1.5 1.2 bons. This property is no doubt attributable to its dual Flash point (open-cup), C. 40 53 60 ether-alcohol nature, and it is indeed an advantage in the The variation of specific gravity with temperature is shown preparation of industrial lacquers containing large amounts of the cheaper diluent, toluene. Butyl acetate will tolerate graphically for each solvent in Figure 1, and the mutual solu2.5 times its own volume of toluene before it ceases to be a bility curves of water with Cellosolve Acetate and Butyl solvent for nitrocellulose, but Cellosolve will take about 5.2 Cellosolve are presented in Figure 2. The boiling-point data (obtained by the A. S. T. M. distillation method) are times its volume of toluene. The chief advantage of Cellosolve Acetate, in addition plotted in Figure 3, and evaporation curves of a wide varito its very mild, ester-like odor, is its ability to prevent blush- ety of solvents are shown in Figure 4. From these data ing under extremely humid conditions. It evaporates more the lacquer technologist may deduce some of the properties slowly than Cellosolve, is only partly soluble in water, and that the Cellosolve compounds will exhibit when incorporated is a good solvent for nitrocellulose and the usual resins. Tests with other solvents in a lacquer formula. made by spraying a large number of commercial automobile Other Solvents That May Be Used with Cellosolve lacquers, after thinning with mixtures containing Cellosolve Practically any solvent or diluent now used in the industry Acetate, showed that the latter will prevent blushing eren a t 90 per cent relative humidity at 90" F. It is becauce of may be used in conjunction with Cellosolve and its related compounds; but for best results, as well as for the lowest 1 Received March 26, 1928. Properties of Cellosolve and Its Derivatives
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costs consistent with quality, the following solvents are recommended: toluene, xylene, denatured alcohol, ethyl acetate, certain petroleum distillates, and, to a limited extent, butyl alcohol and butyl acetate. By means of these cheaper solvents, with the proper admixture of Cellosolve, Cellosolve Acetate, or Butyl Cellosolve, high-grade lacquers meeting the strictest requirements as to performance may be formulated. Use of Resins with Cellosolve Derivatives
Certain resins that are essentially soluble in hydrocarbons or esters are not very soluble in Cellosolve. Sometimes a resin may be soluble in Cellosolve but not compatible withnitrocellulose in the presence of Cellosolve, especially when the propor-
tion of resin present is high. The most common resins of this class are the Albertol (formaldehyde-phenol) resins, coumarone resin, and rosin ester (ester gum). It is inadvisable to use a considerable quantity of coumarone resin or an Albertol resin with Cellosolve. Within certain limitations rosin ester may be used with satisfactory results, and higher proportions are compatible when Butyl Cellosolve is employed as an additional solvent. Since these resins possess certain inherent disadvantages-for example, coumarone resin turns yellow upon exposure to light, and rosin ester gum has inferior outdoor durability-it is advisable to use other resins that are not only more durable but also more compatible with Cellosolve. The resins and combinations of resins which have been found satisfactory for use in Cellosolve lacquers are as follows: dammar (de-waxed), rosin, elemi, elemi rosin ester, bleached shellac, shellac rosin, dammar rosin ester, kauri, and pontianac. There are certain other patented preparations-e. g., the glycerol-phthalic anhydride resin-which give excellent results in lacquers containing Cellosolve; but with the above resins almost any type of lacquer may be manufactured at a reasonable cost, and a t 8 saving (when Cellosolve solvents are used) over the cost of a similar lacquer made with butyl and amyl acetates. The solubilities of the various resins in the Cellosolve derivatives are listed in Table 11.
+
+
of Resins CELLOSOLVE BUTYL CELLOSOLVB ACETATE CELLOSOLVE S S S
-
RosrN-The properties of rosin are well known, and it is the most readily soluble resin available. It is also compatible with nitrocellulose in any amount in the presence of any solvent (for nitrocellulose). Its use in lacquers is therefore limited only by its acidity and it,s softness. These last factors render it suitable for use only with inert pi-ments, and in the cheaper lacquers, where low cost, coupled with as high a solid content as possible, are the chief requisites. ROSINEsmR-This substance, manufactured from rosin and glycerol, has greater hardness and less stickiness and acidity than rosin. It also is of fairly pale color and moderate cost, which factors have brought about its widespread use. It has the objectionable feature, however, of becoming brittle (in a lacquer film)with age, a property which most of the natural resins and some other artificial resina do not possess. On account of the poor compatibility of rosin ester with nitrocellulose and Cellosolve, the use of the former is limited to quantities approximately equal to the amount of plasticizer (dibutyl phthalate) present. The proportions of rosin ester that may be used under different circumstances will be discussed later under lacquer formulation. With Butyl Cellosolve much larger quantities of rosin ester may be used than with Cellosolve itself. DAMMAR-This is a semi-fossil resin containing about 18 per cent of a waxy material, insoluble in alcohol, which must be removed in order to render the resin useful in nitrocellulose lacquers. This de-waxing is done in the preparation of the solution. The whole resin is dissolved in a suitable hydrocarbon and then alcohol is added to precipitate the wax. The following formula has been found most satisfactory for this purpose, and is recommended for general use: Dissolve 80 pounds of Batavia dammar in a mixture composed of 20 pounds of ethyl acetate and 40 pounds of a petroleum distillate having a boiling range of 80-130° C. When completely dissolved (in a mixer equipped with a mechanical agitator), add 100 pounds of denatured alcohol, agitate for a time, and then allow to settle overnight. The waxy precipitate forms a cake in the bottom of the vesse1,and when the clear supernatant solution has been drawn off the wax cake is removed. This wax has not yet found any special use, and is generally burned.
1* 140
S
PS
-
S
S S
S
PS
S
PS S
S
S
S partly soluble, the in-
$
1
u IZ0
+
Table 11-Solubility
RESIN Rosin Rosin ester ss Dammar PS S Elemi S Kauri Pontianac S Shellac (bleached) S S = soluble. SS somewhat soluble. soluble part consisting chiefly of wax.
Vol. 20, No. 5
3 3
100 n
Y BO
.: 5
60= 40
IO
20
30
40
M
PERCENT %LVE>T
60
70
BO
90
IO!
BY WEIGHT
The solution as prepared above contains about 30 per cent of resin by weight, and is used as described under “Lacquer Formulation.” EmMI-This is really an oleoresin, as it contains essential oil in addition to the resin. This oil gives the elemi a pleasant, camphor-like odor, and causes it to be soft and sticky. It is readily soluble in a wide variety of solvents, but the following solvent mixture has been found the most practical for general use: toluene 60, butyl alcohol 10, ethyl acetate 15, and Cellosolve 15 per cent by volume.
May, 1928
I X D U S T R I A L AND ENGINEERING CHEMISTRY
The solution should usually contain 50 per cent of the oleoresin, by weight, since the necessary quantity may then be obtained by taking a double weight of solution. Elemi is very pale and of moderate price but gives a residual odor to the film, and becomes somewhat brittle upon aging, owing to the loss of the essential oil. I(AuRI-Thk is the most widely used fossil resin, because it is the most easily soluble. The higher grades, which include the palest and hardest pieces, are as a rule high in price, but the lower grades, which are usually darker and crumble easily, are cheaper and also more readily and completely soluble in the usual lacquer solvents and in alcohol. Kauri is generally entirely insoluble in hydrocarbons; hence the solvent mixtures in which it is used usually contain a considerable proportion of alcohol. The solubility of kauri resin, as well as of any natural resin (except shellac), may be improved by subjecting the finely powdered resin to atmospheric oxidation, by keeping it in a heated current of air exposed in thin layers on cloth or wire trays. Kauri solutions for lacquer work are usually made in denatured alcohol or in a mixture of about 85 per cent denatured alcohol and 15 per cent ethyl acetate, and contain either 33l/3 or 40 per cent of resin by weight. PONTImACThiS resin is finding considerable use in certain types of lacquers because of its solubility in alcohol and its pale color. Like kauri, its solubility is improved by oxidation, and solutions of pontianac resin are prepared in the same way as those of kauri. BLEACHEDSHELLACT~~S material is sometimes called white shellac or wax-free shellac. It is entirely insoluble in hydrocarbons and practically insoluble in the usual esters (except ethyl acetate). It has a definite use in certain kinds of lacquers, and its solutions usually contain 40 or 50 per cent of shellac dissolved in alcohol. Bleached shellac should be dissolved as soon as possible after it is received, for it becomes insoluble in alcohol with age and exposure to the air. Manufacture of Lacquers with Cellosolve, Etc.
Cellosolve, Cellosolve Acetate, and Butyl Cellosolve are meeting with success as solvents for nitrocellulose lacquers on account of their peculiar properties, as noted above. But in order to be successful a formula must be worked out especially for these materials. PREPARATION OF NITROCELLULOSE SOLUTIONS-In general, the best practice is to work out a satisfactory complete formula for a particular lacquer in the laboratory, and then make the nitrocellulose solution, resin solution, etc., with the same solvent. This method gives much better results than dissolving the nitrocellulose in one ingredient, the resin in another, etc., and then mixing them, with the further addition, perhaps, of toluene or another non-solvent for nitrocellulose. Although Cellosolve and its derivatives have extraordinarily high solvent power, their solvent action is rather slow. Therefore, the use of a moderate amount of a very active solvent, such as ethyl acetate, is recommended with Cellosolve. It will further be found that Cellosolve Acetate is a more rapid solvent than Cellosolve itself. The usual stock solution of nitrocellulose contains 20 per cent of l/n-second nitrocellulose and correspondingly smaller quantities of higher viscosity types. The old method of designating a solution as containing so many ounces of nitrocotton per gallon is ambiguous and unsatisfactory, especially since most manufacturers now mix their formulas by weight. If a 20 per cent solution is used, 100 pounds of cotton solution give 20 pounds of dry nitrocellulose; and if it is dissolved in a solvent whose composition is the same as that of the finished lacquer, no errors will be made in obtaining the correct final solvent composition.
499
RESINSoLuTIoNS-with the exception of rosin and rosin ester, each resin requires a particular solvent or solvent mixture, some of which have already been discussed. If possible, the solvent used in the resin solution should also be a solvent for nitrocellulose, in order that it will not precipitate nitrocellulose when added to the rest of the batch. GRINDINGPIGmNTS-The ball or pebble mill is widely used in the manufacture of lacquers, because it is economical to operate, and may be closed, thus preventing loss of solvent. The chief objections to such miUs are the long time necessary for the proper grinding of certain pigments, with the consequent lower production per unit, and the fact that it is difficult to obtain with the pebble mill a product which gives a gloss. The roller mill is not very generally accepted as a practical means of grinding pigments for lacquers, so the buhrstone mill is recommended as the best all-around machine. Itrequires more power than a pebble mill, but has greater paste capacity and gives a better dispersion of the pigments.
Since the incorporation of a pigment is really not a grinding operation, but a dispersion, some liquids and mixtures are better grinding media than others, owing to their superior wetting power. Tests on the wetting power of a large number of liquids showed, in general, that the alcohols (and compounds of alcoholic nature, such as Cellosolve) have the best wetting power, the esters next, and the hydrocarbons the, poorest. As a rule, resin solutions are good grinding media, but the paste is liable to settle and form a hard cake after grinding. This is not true for all resins, however, as a dammar solution gives very satisfactory results. Chemical plasticizers, such as dibutyl phthalate, are poor grinding liquids, but oils, especially castor oils, are excellent grinding media. Just as the nitrocellulose solution should contain a solvent whose composition is the same as that in the finished lacquer, the grinding liquid should have the non-volatile ingredients (except nitrocellulose) in the same ratio as they appear in the finished lacquer. For example, if a certain lacquer is to contain 12 per cent nitrocellulose, 10 per cent resin, 5 per cent castor oil, and 5 per cent phthalate, the grinding liquid in which pigments for this lacquer are to be ground should consist of 10 parts resin, 5 parts castor oil, and 5 parts dibutyl phthalate, with enough mixed solvent to give the desired consistency. A very useful solvent mixture for this purpose is composed of xylene 70, butyl alcohol 10, and Cellosolve 20 per cent by volume. This mixture has good wetting power, and a low rate of evaporation, thus minimizing the solvent loss during grinding, but should not be used unless it is a solvent for the resin under consideration. MIXINGTHE LACQUER-fiOm the foregoing it will readily be seen that the finished lacquer will consist of only three,
I N D U S T R I A L A N D ENGINEERING CHEMISTRY
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or possibly four, things-the pigment paste, the nitrocellulose solution, the extra solvent, and, in some cases, additional grinding liquid. With these four items any lacquer with the resin, castor oil, and dibutyl phthalate in the ratio of 10:5:5 may be formulated. The usual practice is first to mix the color pastes in the proper proportions in the agitator, adding then the additional mixed grinding liquid (if any), the nitrocellulose solution, and the mixed solvents necessary to obtain the desired viscosity. This practice of mixing solvents and grinding liquids in certain definite proportions is now becoming widespread as it eliminates a
TIWE 1~ M o m 5
large amount of tedious calculation and reduces the possibility of error when the mixing of the batch is in unskilled hands. Lacquer Formulation
THINNERS-under this heading are included the usual thinners or reducers employed to thin the average industrial lacquer to spraying consistency. It may also include solvent mixtures used to thin brushing lacquers. The usual ’ thinners are of rather poorer solvent power than the solvent with which the lacquer is made; in fact, their compositions sometimes lie on the boundary between a solvent and a nonsolvent for nitrocellulose. It seems that the prime consideration in formulating a thinner is the obtaining, a t the lowest possible cost, of a mixture which, when added to a lacquer, will not precipitate the nitrocellulose. The business in lacquer thinners is very competitive, and a large number of industrial organizations using considerable quantities of thinners are now preparing their own. According to the views of many specialists in the industry, a satisfactory thinner for use with lacquers to be sprayed should have the following characteristics: (1) good solvent power; (2) good thinning power; (3) good blush resistance; (4)proper speed of evaporation; and ( 5 ) low cost. By good thinning power is meant that property of a thinner whereby the viscosity of the lacquer is reduced as much as possible with a minimum addition of thinner. Some thinners do not reduce the viscosity of a lacquer as much as others, and produce an effect generally known as “false body.” This may be a wetting or surface tension phenomenon, but usually runs parallel to the solvent power of the thinner. I n other words, a mixture with a good margin of solvent power will also possess the requisite thinning properties.
Vol. 20, No. 5
I n Figures 5 t o 8 are shown, on triangular coordinate charts, the limit of solubility of 1/2-second nitrocellulose in mixtures of three components: Cellosolve, alcohol, and toluene; Cellosolve Acetate, alcohol, and toluene; Cellosolve, ethyl acetate, and toluene; and Cellosolve Acetate, butyl alcohol, and toluene. These charts may also include a series of straight lines passing through all points which have a constant cost (raw material cost only). It is therefore an easy matter to find a point on each chart which represents that mixture of the three ingredients in question which is cheapest, but is still a solvent for nitrocellulose. It must be borne in mind, however, that points lying on the solubility curve represent compositions which will just fail to dissolve nitrocellulose (since the data were obtained by a precipitation method). The composition chosen should be at such a distance from this “danger line” as to possess sufficient solvent and thinning power. Another fact of interest in the formulation of thinnersand, in fact, all solvent mixtures-is that a small amount of an alcohol, which is a non-solvent for nitrocellulose, will greatly increase the solvent power of a mixture containing no alcohol. This is shown graphically on Figure 6, where point A represents a mixture of 75 per cent toluene and 25 per cent Cellosolve Acetate. This mixture is not a solvent for nitrocellulose; but if alcohol is added so as to change the composition to 60 per cent toluene, 20 per cent alcohol, and 20 per cent Cellosolve Acetate, it becomes a solvent for nitrocellulose and a good thinner, as shown at point B. An important feature of the new solvents, Cellosolve and its derivatives, is their remarkably high tolerance of coaltar hydrocarbons as compared with the usual aliphatic esters. For this reason a satisfactory thinner may be formulated with a smaller amount of Cellosolve, with properties equal to or superior to those of the usual thinner, and at a lower cost. The next requisite of a good lacquer solvent or thinner is resistance to humidity, or blush resistance. Blushing under moist conditions is not so much a function of evaporation rate as of solubility of water in the solvent. Thus, a benzene solution of a resin, for example, will not blush a t a given humidity, whereas an alcoholic solution of the same substance will blush badly, even though the alcohol evaporates more slowly than the benzene. On this account Cellosolve, which is miscible with water in all proportipns, has a lower resistance to blushing than the related compound, Cellosolve Acetate, which has been found superior to all other solvents of similar evaporation rate in the prevention of blushing under conditions of high humidity. Cellosolve Acetate dissolves only a slight amount of water and is an excellent solvent with a relatively slow evaporation. Hence it remains until the last and causes a smooth, homogeneous film to form. Figure 6 shows that a good thinner may be made with only 10 per cent Cellosolve Acetate. Since it is difficult to study graphically a four-component system where all four components are variable, it is usually necessary to do a little experimenting, as follows: Assume that a mixture of 15 per cent Cellosolve Acetate, 20 per cent ethyl acetate, and 65 per cent toluene is chosen as being a good thinner. Perhaps it may be improved, or perhaps the cost may be lowered, other properties being the same, by a change or two. As noted above, the introduction of a small amount of alcohol will increase the solvent power, and if this alcohol is substituted for a material of higher cost, the total cost of the thinner will be lowered. Table I11 gives three extremely satisfactory thinner formulas containing one or more of the Cellosolve derivatives. These formulas have been worked out with good blush resistance, sufficient solvent power, and low cost as the principal
May, 1928
I N D U S T R I A L A N D ENGINEERING CHEMISTRY
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in the soh-ent used. The mere fact that nilrocellulose and a given resin are each soluble in a solvent is no assurance that they are compatible when both are present in the solvent together. This peculiar phenomenon causes considerable trouble in the formulation of lacquers by the “guesswork” or “hitand-miss” methods. Furthermore, the fact that a solution of a resin and nitrocellulose is perfectly clear and homogeneous is no as. . * . . . surance that the film deposited therefrom -==-- - . will likewise be clear and homogeneous. The reverse is also sometimes true; that is, a nonTOLUCNL 95iA homogeneous lacquer may deposit a Figure 6-Solubility of %-Second R. S. Figure 5-Solubility of %-Second R.S. Nitrocellulose in Mixtures of Cellosolve clear film. These results are caused by the Nitrocellulose in Mixtures of Cellosolve, Acetate, 95 Per Cent Alcohol, a n d Toluene 95 Per C e n t Alcohol, a n d Toluene changing composition of the solvent ture upon evaporation, whereby a lacquer considerations, and all have proved trustworthy in a long may pass through or into a stage of heterogeneity during period of practical usage. The blush resistance decreases evaporation, in which the non-volatile ingredients are not slightly from the left to right, formula No. 1 having withstood miscible with each other in the solvent composition which repeatedly a relative humidity of 90 per cent a t 90” F. For- exists at that time. It is therefore essential, in the formulation of a lacquer of mula KO.3 has better solvent power than the others, but slightly less blush resistance, and is recommended for use in any type, to test out the clear solution to see if it also gives a clear film; for if it does not, it will be weak and give unthe winter or in only moderately humid atmospheres. satisfactory service. This test must be made with the clear Table 111-Lacquer Thinner Formulas lacquer, just as it is to be used, but without the pigment, Avo 1 so 2 No. 3 which would obscure the effect of any incompatibility or (Per cent by volume) 70 blush that might exist. Toluene 70 Petrol Alcohol(8C-130° C.) 5 65 5 Once a definite combination of ingredients has been selected Ethyl acetate 15 20 ‘5 as the basis for a lacquer, the next step is to investigate the Cellosolve compatibility of this mixture in all possible combinations of Cellosolve Acetate 10 io 5 the solvents to be used. This is done with the help of the These formulas are recommended for use as thinners, but it triangular chart, on which a line is found that separates is not thought that Nos. 1 and 2 would be quite satisfactory satisfactory solvent formulas from those that are unsatisfactory. as the entire lacquer solvent. AUTONOBILE LACQUERS-In the manufacture of lacquers As an example, assume that it is desired to prepare a lacit is good practice to use a more powerful solvent than the quer containing 4 parts of l/rsecon8 nitrocellulose, 1 part usual thinner. I n other words, the point on the triangular of wax-free, bleached shellac, and 1 part of dibutyl phthalate. chart representing the solvent composition should be further The solvent is to be some combination of toluene, methylated from the limit of solubility; it should contain less hydro- spirit, and Cellosolve. The procedure is to prepare a numcarbon and more nitrocellulose solvent. This * c b.irrrr procedure facilitates the preparation of nitrocellulose solutions of high concentration in a minimum time. - The following properties are required in a _ * . - . good automobile lacquer: (1) good durability, (2) moderate flexibility, and (3) the ability to polish to a high gloss. The first requires that the lacquer contain a considerable proportion of nitrocellulose, which is the ingredient im- - --parting toughness and durability to the prod._ uct. The second requires a moderate amount - -----.._.. of plasticizer, and the third demands that the . . - . - -- - *. plasticizer and resin content be not too high, Of since they detract from the Figure 7-Solubility of %-Second R.S. Figure &Solubility of %-Second R.S. After considerable experimenting and prac- Nitrocellulose in Mixtures of Cellosolve, Nitrocellulose in Mixtures of Cellosolve Acetate, Butanol, a n d Toluene and tical tests under actual conditions of service, most manufacturers have found that, in order to obtain a lacquer with the above characteristics, the ratio of ber of lacquers of this type in different proportions of the nitrocellulose l o resin to plasticizer in the lacquer should be three solvent ingredients, and then to test each one to find approximately 4:1:2. The composition of any given lacquer whether it produces a clear film. The points representing may vary slightly from this, depending upon the nature of the compositions which give clear films, as well as those which give unsatisfactory films, are marked on the chart and a line resin or plasticizer used. Once this ratio has been determined, it is a comparatively is drawn separating the zone of good solvents from the zone simple matter to prepare an automobile lacquer. Besides of incompatibility. The triangular chart may then be dithe purely incidental matter of obtaining the proper color and vided into three parts: in zone 1 are mixtures which do not adjusting the proportion of pigment, which is in no way an even dissolve nitrocellulose; in zone 2 are mixtures which inherent property of the lacquer, the most important con- form a clear lacquer solution but a turbid or milky film; and sideration is the compatibility of the non-volatile ingredients in zone 3 are those which give both a clear solution and a LOICL
Cr
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A.
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