1304 INDUSTRIAL AND ENGINEERING CHEMISTRY VOL. 32, NO. 10

weight polystyrene, usually plasticized with one of the chemi- cal plasticizers such as tricresyl phosphate, dibutyl phthalate, or the like. High-molecular-weight polystyrene is, however, incompatible with most of the ingredients commonly used in paints and varnishes, particularly the drying oils-a fact which until recently has prevented them from being utilized widely for coating purposes. Recent work upon the control of the styrene reaction has now made practical the production of styrene polymers of relatively low molecular weight which are readily soluble in the drying oils to produce oleoresinous varnishes,

Perhaps the most outstanding feature these new styrene resins impart to oleoresinous varnish films is the combination of excellent flexibility and film strength with high resistance to moisture absorption and moisture permeability. These two properties are seldom found together in resin-oil varnishes, but are necessary for many important applications, including the fabric and paper coating fields, waterproof sandpaper, varnished cambric and tapes for electrical insulation, and coatings for metal food containers and for improving the moisture resistance of transparent cellulose derivatives used in packaging foods, tobacco, and other products.

These new oil-soluble styrene products also retain the de- sirable properties of good color, heat stability, and high re- sistance to alkalies and acids. The extent to which these properties are preserved in the varnish film depends largely upon the ratio of resin and drying oil used in preparing the varnish. A varnish containing as much as 50 per cent resin and 50 per cent tung oil, for instance, yields a tough, flexible film of outstanding moisture and alkali resistance and of unusually good gloss and leveling properties. Varnishes containing two to four parts oil to one part styrene resin are still more flexible, though of somewhat lower moisture and chemical resistance, and are well suited for electrical insulating purposes since they have a high dielectric breakdown of around 2200 volts per mil.

Sources for Monomeric Styrene The increasing commercial importance of polystyrene as a

plastic and in coating materials is directing attention more and more towards the various possible sources for monomeric styrene. The synthetic production through the stage of ethylbenzene has long been known, but styrene has become commercially available in large quantity in this country only within the last few years. The issuance of several recent

patents (4, 7) on the pyrolysis of ethylbenzene indicates that this process is still of interest.

I n addition to the synthetic sources, a large amount of sty- rene is also formed as a by-product in various hydrocarbon cracking processes. Cambron and Bayley (3) studied the pyrolysis of propane and found that an appreciable yield of styrene was obtained a t 800’ C. Birch and Hague (1) car- ried out somewhat similar studies on gas mixtures rich in pro- pane, and estimated, on the basis of their results, that a plant capable of dealing with a throughput of 5,000,000 cubic feet of propane-rich gas per day could produce 59,000 liters of motor benzene containing 3400 liters of styrene. The pres- ence of styrene in considerable amounts in the drip oil from carbureted water gas was demonstrated by Ward, Jordan, and Fulweiler ( I d ) . It is not unreasonable to suppose that in the near future there will be a large supply of material available from such sources as these a t a cost relatively low in com- parison with other thermoplastic materials. Under such conditions we may expect to see a considerable expansion in the use of polystyrene.

Literature Cited Birch, S. F., and Hague, E. N., IND. ENO. CHEM., 26, 1008 (1934).

Burk, R. E., Thompson, H. E., Weith, A. J., and Williams, I., “Polymerization”, New York, Reinhold Publishing Corp., 1935.

Cambron, A., and Bayley, C. H., Can. J. Research, 10, 145 (1934).

Dreisbach, R. R. (to Dow Chemical Co.), U. S. Patent 2,110,829 (March 8, 1938).

Ellis, C., “Chemistry of Synthetic Resins”, New York, Rein- hold Publishing Corp., 1935.

Humphrey, L. E., Modern Plastics, 17, No. 2. 100 (1939). Mark, H., and Wulff, C. (to I. G . Farbenindustrie), U. S.

Marvel, C. S., and Moon, N. S., J. Am. Chem. Soc., 62, 45

Schulz, G . V., 2. physik. Chem., B32, 27-45 (1936). Schulz, G. V., and Husemann, E., Ibid., B34, 187-213 (1936);

Staudinger, H., and Steinhofer, A., Ann., 517, 35 (1935). Ward, A. L., Jordan, C. W., and Fulweiler, W. H., IND. ENG.

Whitby, G. S., J. Phys. Chem., 36, 198 (1932).

Patent 2,110,833 (March 8, 1938).

(1940).

B36, 184-94 (1937).

CHEM., 24,969, 1238 (1932).

PRESENTED as part of the joint symposium on Plastics and Resins from Hydrocarbons before the Divisions of Petroleum Chemistry, of Paint and Varnish Chemistry, and of Rubber Chemistry, at the 98th Meeting of the American Chemical Society, Boston, MRSS. Other papers in this symposium appeared in March, 1940. pages 293-323.

Vat Dyes as Pigments CRAYTON K. BLACK

E. I. du Pont de Nemours & Company, Inc., Wilmington, Del.

0 0

C C II AT dyes are well known for the excellent properties I!

they impart to textiles. These include not only resist- ance to light and washing, but also excellent fastness to

ing, and other color-destroying agencies encountered in textile use.

The term “vat” dye is derived from the method of applica-

Structurally, several chemical groups are included. The tion of these colors rather than from any chemical family.

indigoids are characterized by the presence of the structure,

s r y l e n e / b = d‘arylene chlorine bleach, dry cleaning, rubbing, perspiration, hot press- \d b/

where X = 0, S, NH, CHI, etc.

On reduction with such agents as alkaline sodium hydro- sulfite, the leuco or soluble form is produced, the carbonyl group becoming

OCTOBER, 1940 INDUSTRIAL AND ENGINEERING CHEMISTRY 1305

The so-called anthraquinone vats are derivatives of anthra- quinone, benzanthrone, dibenzanthrone, pyranthrone, di- benzopyrenequinone and other insoluble, colored, poly- nuclear ketonic bodies. They all contain a conjugated system involving carbonyl groups which can be reduced to alkali- soluble, phenolic, leuco forms.

This leuco form, which is soluble, is absorbed (because of its substantivity) by the textile fiber in the dyeing or print- ing operation. On oxidation, the insoluble pigment form of the dye is regenerated in and on the cellular structure of the fiber. Thus, the dye is fixed and becomes a more or less permanent part of the fabric to which it has been applied.

Some of the properties of these dyes on textiles are of value in pigment work. In many pigment problems extreme fast- ness to light, particularly in pale tints, resistance to acid and alkali, and fastness to bleed in oils, alcohol, and water are required. Vat dyes in general fulfill these requirements. When used as pigments, certain requirements not encountered in textile work must be met. These include texture, resist- ance to bronzing, either on severe buffing or outdoor exposure, resistance to lithographic breakdown, etc.

The Colour Index1 reports the shades and structural formulas of most of the commercial vat dyes now available. These dyes as sold to the textile trade, either as pastes or water-dispersible powders, are in proper physical condition for conversion to leuco bodies. This form is not necessarily the correct one for pigment use where a reduction and re- oxidation process is not used and where the size and shape of the insoluble dye particle are the important factors.

It would appear that an inert base might be treated x i th a vat dye leuco and the pigment regenerated by oxidation to form an excellent lake. Unfortunately, promising results have not been obtained to date by the procedure, no advantage being found over a simple slurry mixing of the base and the vat dye pigment.

Field for Vat Dyes

In spite of their excellent pigment properties, the present cost of vat dyes is such that they cannot generally displace in large volume the common types of cheaper pigments now in use. However, there are certain pigment requirements which seem to be met best by this class of dyes. This applies par- ticularly to light tints in which extreme light-fastness is re- quired. I n these pale shades high cost of the color is not so objectionable as i t is in heavy shades. A few pigment prob- lems for which vat dyes may present a solution are listed here.

WALL PAPER. The light-fastness requirements of pig- ments for this use have been increased steadily. It is dif- ficult to meet these requirements with certain colors, particu- larly in tints. In addition, fastness to alkali is required in many of the new washable types of paper.

COLD-WATER PAISTS. Again fastness to light and alkali is required.

PLASTICS. Vat dyes, particularly oil-soluble anthraquinone bases, have been found valuable in this field. The bases are soluble in many plastics and are resistant to the heat of molding.

I n tinting high-grade whites, small amounts of extremely light-fast red-shade blues are re- quired. They must be so finely divided that no specking occurs.

Pale tints for outdoor poster work always have presented problems to the pigment and ink chemist. Many pigments which are durable in full shades fade rapidly when used as tints such as a flesh shade. Toluidine toner is an outstanding example of this type. Pigments fast to alkali

PAPER BEATER DYEING.

PRINTING INK.

1 Soc. of Dyers and Colourists. ed. by F 11 Rowe, 1924

for use in soap wrappers also have been difficult to find over a complete shade range.

Fastness to light as well as to vulcanizing and curing is required. It is also important that the color show no solubility or migration in the rubber.

RUBBER.

The excellent properties of these dyes when used on textiles carry over into pigment work. While they have been neglected be- cause of high cost, there are many places where vat dyes can be used to advantage in solving pigment problems. The extreme light-fastness, even in pale tints, is of' value in wall paper, cold-water paint, printing ink for outdoor posters, paper beater dye- ing, and lacquers, particularly of the auto- mobile finishing type. The importance of proper physical form for pigment work is dis- cussed, as well as possible applications of vat dyes to the automobile finishing industry.

PAINTS AND LACQUERS. Durability problems always have confronted the automobile trade. The need for colors of greater light-fastness has been intensified by the advent of the so-called metallic finishes. In this type, aluminum pow- der replaces a portion of the pigment so that a tinting effect is obtained. Many colors having adequate light-fastness in full shades are poor under these conditions. Maroons, which have been mostly azo colors until recently, have been notori- ously poor not only in light-fastness but in film durability. Even now that certain excellent formulations containing maroon pigment are available, no single azo maroon is good in all formulas. Iron blues possess certain recognized limita- tions in fastness as tints, while phthalocyanines, which are fast, are available in green-shade blues and green shades only.

Automobile stylists have been handicapped by the in- ability of the pigment industry to furnish light-fast shades in all the desired hues. Practically the same problem of light- fastness of tint is encountered in the sign enamel trade.

Experimental Work Attempts have been made to demonstrate the possibility

of using vat dyes to solve some of the problems mentioned above.

An indanthrene blue has been ground into an alkyd resin- nitrocellulose lacquer and tinted with a chalk-resistant type of titanium dioxide. Comparisons with ultramarine, iron blue, and copper phthalocyanine, similarly tinted to the same strength on automobile-body steel panels, were made after 10 months of exposure in Florida a t 45" south. After polish- ing, the vat blue and the phthalocyanine showed practically no change. The iron blue had faded to a weak green, and ultramarine had faded completely. In this same series copper phthalocyanine was shaded with (a) a vat Triolet and (b) an alizarin lake to produce a red-shade blue. The alizarin lake had faded out on exposure, leaving t,he green-shade copper phthalocyanine, while the panel shaded with the vat dye showed practically no change. Only the use of vat blues and violets permits the practical formulation with phthalocya- nines of red-shade blues without loss of light-fastness.

1306 INDUSTRIAL AND ENGINEERING CHEMISTRY VOL. 32, NO. 10

A series of maroon pigments was formulated in an alkyd resin-nitrocellulose lacquer with a small amount of aluminum powder as the extender and exposed on steel panels as in the previous series. This set included an azo pigment dyestuff (toluidine type), a precipitated azo dye (litho1 type), and a thioindigo red (vat dye). After 12-month exposure in Florida both azo maroons had faded badly, while the vat dye was in practically perfect condition. The vat dye exhibited no bronzing under severe buffing, which is an important prop- erty of a maroon.

Certain Prussian blues have been found to drift in shade when used as a tint in lacquer. Milori blue, which is greener in shade, does not show this tendency. Since vat violets do not drift, it was possible to shade Milori blue with a vat violet to match the shade of Prussian blue and have a nondrifting combination.

Printing inks containing (a) rhodamine phosphotungstate and (b) a thioindigo pink were made up on the following for- mula: 1 part color, 5 titanium dioxide, 4 zinc oxide, and 15 lithographic varnish. Prints on paper were exposed to the rays of a carbon arc for 50 hours. The rhodamine phospho- tungstate faded badly, while the vat dye faded only slightly. Although this method of determining fade is not necessarily a true measure of the relative out-of-door fastness properties of the two colors, the obvious advantage of the vat dye does carry over into practical trial.

Vat dyes are fast to alkali and, when formulated with a fast vehicle, can be used for soap wrappers and linoleum where there is a definite need (particularly for reds) to meet this requirement.

Bronzing is, of course, undesirable.

In the case of beater dyeing of high-grade white papers, vat blues and violets in highly dispersed form can be used to advantage. They are extremely light-fast even in the small amounts used and can be produced sufficiently fine to prevent specking.

I n order to demonstrate the point that vat dyes stand- ardized for textiles do not always produce maximum pigment results, wall paper brush-outs using a clay-glue size were made with (a) a thioindigo pink standardized for the textile trade and (b) the same color reduced in particle size by wet grinding. These brush-outs containing the same amounts of vat dye show that b has approximately twice the tinctorial strength of a. This effect is apparently due to a decrease in the aggre- gate size by grinding. Pigment a settles out of a water slurry rapidly, while 6 stays suspended more or less indefinitely,

The foregoing survey shows that, in spite of a relatively high pigment cost, vat dyes may fit into certain gaps in the present line of pigments and assist in the solution of problems which cannot be easily solved without them. Particularly in the case of pale tints in which only a small quantity of vat color is required, this may be an economical solution to ai problem.

Acknowledgment The writer wishes to acknowledge assistance given by

D. H. Parker and other members of the staff of Krebs Pig- ment and Color Corporation.

PRESENTED before the Division of Paint and Varnish Chemistry a t the 99th Meeting of the American Chemical Society, Cincinnati, Ohio.

Cashew Nut Shell Liquid M. T. HARVEY AND S . CAPLAN, Harvel Research Corporation, Irvington, N. J.

IQUID from the shells of the cashew nut, once an un- desirable by-product of the cashew kernel industry of southern India, has become a valuable raw material in

the manufacture of numerous industrial products. Poly- merization products of this oil, alone and in combination with other materials, have found their way into such diverse uses as insulating varnishes, typewriter rolls, oil- and acid-proof cold- setting cements, industrial floor tile, and automobile brake linings. Industrial uses of shell liquid have kept pace with the gradual growth of the Indian kernel trade which, in imports to the United States alone, grew from 100,000 pounds in 1923 to 27,000,000 pounds in 1937. Up to the present time recovery of shell oil is incidental to the kernel extraction, and much of the oil is wasted. The oil cells of the cashew nut shell are honeycombed and prevent ready removal of a kernel, and the natives have resorted to a crude charring process to destroy the cell wall which permits the oil from the ruptured cell to es- cape. Newer methods of treatment, employing extraction with hot oils, have been developed which remove 50 per cent of the available shell oil. As the ratio of kernel to oil, on a weight basis, is approximately 1 to 1, the oil in the shells of the cashew kernels imported into the United States during 1937 alone amounted to 27,000,000 pounds. Added to this is the potential supply of oil from the large portion of cashew nuts consumed by the natives of India. An estimated quantity (8) of shelled kernels available for shipment during 1938 was put a t 58,000,000 pounds, and with efficient extrac-

L tion methods, 29,000,000 pounds of oil should be available for commercial purposes yearly.

Manufacturing Operations

The raw commercial cashew shell liquid, almost solely im- ported from southwest India, is received in 55-gallon drums and then stored in 25,000-gallon tanks a t the processing plant of the Irvington Varnish and Insulator Company, a t Irvington, N. J. As usual the samples for test purposes are taken prior to any chemical processing. Testing consists of determination of moisture, iodine number, and polymeriza- tion. There are two main specifications for cashew liquid: The iodine number (Wijs) must be over 250, and the material must polymerize to a rubbery mass when heated with a small amount of acid.

The first step in the processing of the oil consists of a light chemical treatment with materials such as hydrocarbon sul- fates and sulfuric acid. This performs two important func- tions; mineral salts are precipitated and there is a reduction in the content of skin vesicant present in cashew shell oil. While still hot, the charge is passed through a plate-and- frame filter press, using wool felt as the filter cloth, and the filtrate is pumped to an intermediate storage tank. The precipitate thus separated has been analyzed and found to consist mainly of the salts of ammonium, calcium, and po- tassium.