R.osin Derivatives in Paint Products JOHN &E. SANDERSOB American Cyanamid & Chemical Corporation, New York. IC’. Y.
During the past twenty-fiae years the status of rosin in the paint industry has gradually progressed from a surreptitious use in the cheapest products to a position of unquestioned importance in surface coatings of the highest quality. This remarkable change has been brought about by utilizing rosin, not in its raw state, but in the f o r m of chemical compounds prepared from it. Since the major constituent of rosin is abietic acid, the most obvious chemical use is the preparation from it of metallic soaps. Rosin partly neutralized by heating with lime is harder and less sticky than raw rosin and effecis corresponding improvements in the varnishes made from it. Lead, manganese, and cobalt resinates are used as driers. Zinc, magnesium, and other metallic resinates .find some limited use in tarnish products. The most important use of rosin for the paint industry at the present time is in the preparation of a variety of synthetic resins. These include ester gum, as well as modified phenol and alkyd types. Liquid esters of rosin are finding some use in lacquers for semi-plasticizing effects. M a n y other new and interesting rosin derivatives are in course of development.
C o u r t e s y , C . S. Departmcnt of A v i c u l t u r e
FIGURE 1.
TURPESTINE S T I L L
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ECEXTLY published statistics indicate that over 20 per cent of the total domestic consumption of rosin goes into Tarnish and allied products, and that only two other industries-namely, paper and soap-use larger quantities of this material. The position of unquestioned importance which rosin novi occupies in surface coatings of the highest quality represents a definite contribution of chemistry to the paint industry, since it has been attained by using rosin in the form of a wide variety of chemical compounds. A description of the uses of rosin by the paint industry must therefore, of necessity, be a study of these various rosin derivatives and the way in which paint and allied products are formulated from them.
ROSINAS
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VARNISHRESIN
For hundreds of years past and up until very recently all good varnishes were made from fossil resins. In order to render them soluble in drying oils and turpentine, it was necessary to “run” them, which was in reality a process of destructive distillation. Some varnish maker found that the addition of a little rosin to “grease the kettle bottom” kept the fossil resin from charring and that the addition of a little more served as a flux to make it melt more readily to an oil-soluble stage. Since fossil resins mere costly and rosin was relatively cheap, the obvious result was the use of greater proportions of rosin and less fossil resin until the consumer awoke to the fact that such varnishes, while imparting beautiful initial fullness and gloss, were soft, sticky, and decidedly lacking in water-resistance and durability. This attached to rosin the stigma of poor quality which is only now being removed. The major constituent of rosin is abietic acid, an unsaturated monobasic acid. It reacts readily with many metals to form soaps and with alcohols t o form esters. Various compounds may be formed by direct addition to the unsaturated bonds, and combination soaps, esters, and addition compounds are possible. Abietic acid is a strong solvent or dispersing agent for polymerized oils, metallic soaps, asphalts, and synthetic resins, and some of its regular uses in paints and varnishes are based on this property.
Rosin is readily soluble in alcohol and assists in the complete solution of Manila, Pontianak, and other natural resins. It therefore has a definite value when used in small proportions with these resins in spirit varnishes, although by itself it is entirely too soft and sticky.
LIMEDROSIN l’arnish makers long ago discovered that rosin partly neutralized by heating with lime was harder and less sticky than in its raw state, and produced correspondingly more satisfactory varnishes. Hence, up to the introduction of synthetic resins the greater part of the rosin used in paint products n-as given a lime treatment. The proportion of lime ranges from 6 to 8 per cent of the rosin, as a more completely neutral linie soap is only partially soluble in the ordinary varnish oils and solvents. A pure, finely pulverized;
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hydrated lime is needed for good results. Detailed require- based on its improved hardness compared to rosin. Still ments are well covered by A. S. T. hI. Standard Specification C better hardness is obtained with a combined resinate made 47-27. Magnesium and iron are the impurities which cause from 3 per cent each of zinc oxide and calcium oxide. Zinc the most trouble, the former imparting poor solubility and the resinate is used to harden the film of dammar and other latter dark color. Chemical analysis alone is not sufficient; varnishes and to retard surface wrinkling where cobalt drier hence a test is provided in the specifications to show how the is employed. It may also be used, because of lo^ solubility, lime will react, to increase the viscosity of some oils and varnishes. The customary varnish maker's procedure for liming rosin Magnesium resinate is much less soluble in oils and naphtha is to heat it to 575" F. (to offset any crystallizing tendencies of than the calcium soap. It finds little use alone, but, when the rosin), then cool to 400" F., and stir in the lime gradually. gloss oil of high viscosity is desired, a lime containing more It is ordinarily sifted in dry, although somewhat better re- than the usual proportion of magnesium may be used. sults may be obtained by mixing with a little linseed oil and Certain metals, notably lead, manganese, and cobalt, water, and adding about 0.1 per cent calcium or lead acetate when incorporated in soluble form in paints and varnishes, as a catalyst. The rosin is then heated to 500" F. with stir- have an accelerating effect on the drying and hardening of the ring to keep the lime from settling out. When it is completely film. For such use the rosin soaps of these metals are ecotaken up and all the water is driven off, it is poured out into nomical, effective, readily soluble, and easy to use. As with cooling pans. Best control of color, clarity, and acidity are other oil-soluble soaps, their drying effect depends largely on obtained by cooking large batches in closed kettles under the amount of metal present. careful supervision. Reaction with 6 per cent lime reduces Precipitated lead resinate, for use as a drier, contains about the acid number from 165 to about 70. 24 per cent lead. The fused resinate, generally containing Limed rosin is sometimes made by melting the rosin, thin- less than 10 per cent lead, is also used as a drier but finds ning with about 40 pounds mineral spirits per 100 pounds more extensive use because of its strong solvent or dispersive rosin, cooling to 190" F., stirring in the lime gradually, and action on polymerized wood oil and is therefore employed to heating slowly. The lime will practically all take up below prevent gelling in the cooking of many varnishes. -4com230" F. but the solution must be heated to about 300" F. to bined lead and calcium resinate is sometimes used for this drive off all the water. Forty t o sixty pounds more mineral purpose. Since better drying is secured with manganese or spirits are then added, depending on the viscosity desired. cobalt in conjunction with lead than with any one of these This process produces a paler color than is secured by the usual metals alone, combined resinates of these metals find some fusion method but is more expensive and not well adapted to use. More leeway in formulation is, however, secured with the individual resinates. the usual varnish-making equipment. Precipitated resinate containing about 7 per cent manAnother method is to saponify the rosin with caustic soda in water, precipitate with a water solution of calcium chloride, ganese is extensively used as a drier. It takes up very easily and wash carefully to remove impurities. Precipitated cal- in hot varnish and yields a pale colored product. It darkens cium resinate is generally paler and more readily soluble than on exposure to light, but in this respect it is the same as other oil-soluble manganese soaps. Fused manganese resinate is a fused resinate of equal calcium content. Limed rosin dissolved in petroleum naphtha is commonly generally quite low in metal content, dark in color, and comknown in the paint industry as "gloss oil." The higher its paratively little used. Fused resinate containing 1 to 2 per cent cobalt is used to lime content, the greater the viscosity of the solution a t a given concentration. Some free abietic acid is required to some extent as a drier. The use of the precipitated resinate of prevent precipitation of calcium resinate from the solution higher cobalt content is limited by the readiness with which it on storage, 10 per cent lime being about the top limit for ignites spontaneously. Copper resinate, usually the precipitated type containing stability a t room temperature. As indicated by its name, gloss oil imparts gloss to paints and varnishes to which it is about 9 per cent metal, is used in some ship bottom paintq for added but detracts appreciably from both flexibility and dura- the prevention of marine growths. It is also used in impregnating compounds for lumber, as well as for awnings and bility. Limed rosin cooked with wood oil yields varnishes which tents, to prevent mildew and fungus growth. Water-soluble sodium or ammonium resinates are used in dry quicker and harder but which are a little less flexible and water-resistant than those made from raw rosin. Its lower the manufacture of the precipitated resinates just described. acidity reduces to some extent the tendency of the varnish t o They are also employed as emulsifying agents in paints, either liver with basic pigments. It catalyzes the condensation of just a small quantity to keep the pigments in suspension or in some resins and retards the gelation of r o o d oil more than larger amount in emulsified paints and asphalt coatings. ester gum of the same acid number. It therefore finds some Rosin emulsified with a mixture of ammonia and triethanoluse in varnishes in conjunction with the so-called "100 per amine has recently been advocated for this purpose. cent phenol" resins. SYNTHETIC RESINS OTHER~ ~ E T A L L I RESINaTES C The most important use of rosin today for the paint While none of them is used in volume comparable to limed industry is as an essential constituent of a variety of synrosin, there are several rosin soaps of other metals which find thetic resins. This use has placed rosin in paint products definite and extensive use in the paint industry. They may of the highest quality and is accounting for an increasingly be made either by precipitating from a water solution of large proportion of the total rosin consumption of this indussaponified rosin or by fusion of the rosin with an oxide or salt try. The history of synthetic resins goes back many years, but of the metal. The precipitated types have, in general, a higher and more uniform metallic content, they possess a it is only recently that they have attained large-volume use in pale color, and they go into solution more readily. The fused surface coatings. With the consumer continually demanding types are cheaper to make and are free from any mater-soluble new qualities, and with chemists striving to investigate every impurities which may retard drying or impart turbidity t o possibility of resin manufacture, the synthetic resin family has almost overnight attained amazing proportions. A clear varnish in which they are used. As already indicated, the main uses of calcium resinate are understanding of the characteristics of each group of resins
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is necessary in order t o select the most limited number of types from which can be formulated a wide variety of paint products. Many of the m o d commonly used synthetic resins contain rosin as an essential component. It may be present as a n ester of abietic acid or as a mixed ester in which abietic and other acids are linked t o the same polyhydric alcohol. It may be used as a dispersing agent. Or it may be reacted by addition to the unsaturated bonds, with or without change in its carboxyl group. Resins formed by these various processes look much alike; in fact, they do not differ materially in general appearance from rosin itself. It requires careful investigation by both chemical and physical tests to distinguish them from one another since it is possible to make resins of entirely different types which are identical not only in appearance but also in such characteristics as specific gravity, acid number, and hardness. In the final analysis each resin must be evaluated individually by its behavior in the finished paint product. ESTERGUM This is the first of the synthetic resins made from rosin to attain commercial importance in paint products. It is made by combining rosin with about 10 per cent of glycerol and consists of abietic triglyceride with some mono- and diglycerides, together with some decomposition products and the unsaponifiable portion of the original rosin. The apparatus and manufacturing technic required to obtain an ester gum of satisfactory quality are much more complicated than the apparent simplicity of the reaction would indicate. Ordinary requirements both for lacquer and varnish are met with a n ester gum having an acid number of 4 to 6, softening point 82" t o 88" C. (ball and ring method), and a color of K or paler. Ester gum of W W color can now be produced and is desirable for use in whites and clear finishes. Very dark ester gum is in little demand and its application limited. It can, however, be made harder and more ret;istant to gasoline and oils than the pale grades. Ester gum is used in varnishes as a n improvement over raw or limed rosin for water resistance, outdoor durability, and freedom from livering with basic pigments. Ordinary lowacid types have little solvent effect on polymerized wood oil and rather poor wetting properties for pigments. Hence, there is some demand for ester gum having an acid number of about 15, and a few varnish makers require even higher acid numbers. Ester gum is extensively used in lacquers as it is quite
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freely compatible not only with nitrocellulose but also with most of the ordinary lacquer plasticizers and solvent mixtures. I n lacquers for automobiles and other surfaces subjected to outdoor exposure, its use is limited to small proportions. I t is used to a much greater extent in lacquers for furniture and other indoor surfaces. When ester gum was first introduced, it was prepared by pouring into cooling pans and then breaking down to small lumps. From force of habit the trade has continued to demand it in this form, packaged in wood barrels. There is, however, a growing realization that ester gum poured direct from the still into light steel drums is paler and cleaner, and that shipment and storage in this form avoid much of the surface oxidation which causes darkening when the ester gum is cooked into varnish.
OTHERABIETICESTERS Ordinary ester gum can be modified by replacing part or all of the glycerol with other polyhydric alcohols such as ethylene glycol, propylene glycol, or polyglycerol. The resin produced by the use of an unusually high proportion of glycerol, to yield mostly monoglyceride, is said to be compatible with cellulose acetate. Such resins are not, however, as yet of commercial importance. The methyl and ethyl esters of abietic acid are liquid resins which find some use in nitrocellulose lacquers. They are good solvents for many other resins but dissolve nitrocellulose only in the presence of alcohol. They impart a semi-plasticizing action and good adhesion. They gradually darken, harden, and become brittle through oxidation as the film ages. As will be noted later, hydrogenation is utilized to reduce these difficulties. They are much more resistant than ester gum to water, acids, and alkalies. MODIFIEDPHENOL RESINS The tremendous expansion in the use of nitrocellulose lacquers which followed shortly after the war stimulated a demand for varnishes which would dry rapidly and yet be reasonably durable. At that time the best outdoor durability was attained with linseed-oil, fossil-resin varnishes, which required a n inordinately long time to dry thoroughly, while quick-drying was secured only by cutting the oil-resin proportion t o a point where outdoor durability was almost entirely sacrificed. T o meet this need there was introduced just about ten years ago the first of a considerable number of resins which
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for convenience we group under the loosely descriptive term can be dissolved in mineral spirits without difficulty and "modified phenol" resins. These are sold commercially under diluted considerably m-ithout precipitation. They are also such trade names as Amberol, Beckacite, and Phenac. They quite freely compatible with oil. The extrahard grades can consist essentially of compounds of phenol (or cresol, xylenol, be dissolved in an equal weight of mineral spirits but require etc.) with formaldehyde (or furfuraldehyde, etc.) dispersed in the addition of coal-tar naphtha if the solution is to be more or less completely esterified rosin. The hardness and diluted to a very low solids content without precipitation. other good qualities of phenol-formaldehyde resins had been They are generally compatible mith oils only after cooking known for many years, but it required dispersion in rosin to together a t temperatures around 5C'O" F. The high-acid make them oil-soluble and open the way for their use in type is only partially soluble in mineral spirits but can be ordinary oleoresinous dissolved in coal-tar varnishes. In view naphtha arid diluted of t h e n u m b e r of with the same s o l p h e n o l s a n d aldevent to around 15 per hydes which a r e cent s o l i d s b e f o r e available and t h e precipitation occurs. possibilities of conIt has a limited densing and disperscompatibility w h e n ing t h e m b y differcooked with oils ent methods and in a n d is therefore different proportions, a d a p t e d only for i t is readily seen use in short varnishes that a great variety -that is, \-here the of these r e s i n s c a n p r o p o r t i o n of oil is be m a d e . Most of less than 18 gallons the varnish maker's p e r 100 p o u n d s of needs are, however, resin. m e t with t h r e e or A t y p i c a l 4-hour varnish for g e n e r a l four grades differing from e a c h o t h e r in h o u s e h o l d use contains 20 to 24 gallons such characteristics as color, h a r d n e s s , of wood oil a n d 4 Courtesg, C . S Department o/ Agriculture to 6 gallons of heatsolubility, and FIGVRE 2. PARTOF THE STILLSHOWN I N FIGURE 1 b o d i e d l i n s e e d oil acidity. A m o n g t h e synp e r 100 p o u n d s of thetic resins made from rosin, this "modified phenol'' group the hard or extrahard resin. The usual procedure is to is now a close second t o ester gum in volume used in paint cook the resin v-ith the wood oil to a top heat of about products. While these resins are utilized for a variety of 550" F. and check by the addition of the linseed and somefinishes, their most generally familiar application is in the times also a few pounds of fused lead resinate. Another so-called "4-hour" enamels which replaced brushing lacquer method is to chill below the danger point of gelling by pouring a gallon or two of water directly into the hot varnish. for household use. I n this group, resins of K or paler color are in most demand This is an operation requiring some skill. Another method, aJthough, where a darker color is not objectionable, some which is adapted only for use with the more soluble resins of saving in cost can be effected. Varnish makers' preference is this group, is to heat-body the oils first n-ith a little of the about evenly divided between the hard grade and the extra- resin, add the balance, and cook just enough t o have it melted hard. The former has a softening point of 125" to 130" C. before thinning. Spar varnish intended for outdoor use is generally formu(by the ball and ring method), and is, generally speaking, readily soluble, easy t o manipulate with wood oil without lated with 35 to 40 gallons of oil per 100 pounds of resin, and gelling, and has little tendency to discolor. The latter, with a is more durable and water-resistant than a similar varnish softening point of 140" to 145" C., yields varnishes which dry made from ester gum. Varnish for floors and general inquicker, harder, more resistant to water and alkali, and which terior use may be shortened to about 20 gallons oil length. The high-acid type of modified phenol resin, which is the have a little better outdoor durability than is secured with the hardest of this group, is used in short-oil varnishes which must hard grade. The acid number of both grades is usually below 18. How- harden quickly and thoroughly by air-drying or baking. This ever, thickening with basic pigments as well as resistance to includes furniture-rubbing varnishes, baking enamels for water and alkali are influenced not only by the acidity of the industrial use, pigmented primers and surfacers, etc. A resin but also by the kind and proportion of oil and the way it higher proportion of linseed t o wood oil is frequently used with this resin than with the ordinary extrahard grade. is cooked into varnish. Because the resins in this group contain substantial proporThere is another generally accepted but newer grade of these resins, in addition to the hard and extrahard types, tions of abietic acid as a dispersing agent, there has been Some which for lack of a better term we will designate as the "high- attempt to classify them on the basis of relative proportions of acid" type. It has a softening point around 145" to 155' C. phenol and rosin and, in some instances, to replace them with Because this extra hardness involves lower solubility, i t is mixtures of the so-called "100 per cent phenol" resins and made with an acid number of about 100 to insure complete ester gum. Analytical data of this sort have, however, proved misleading since there are so many other factors which deterdispersion when cooked into varnish. The solubility of these modified phenol resins can be de- mine the usefulness of these resins. I n comparison with the scribed only in rather general terms, since the products of mixtures referred to above, these modified phenol resins imdifferent resin manufacturers vary considerably in this re- part better hardening of the varnish film and adhesion t o the spect. However, increasing hardness in these resins is usually surface, improved outdoor durability, and less tendency t o accompanied by poorer solubility. Most of the hard grades darken with age.
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ROSIS-MODIFIEDALKYDRESINS Another use of rosin in paint products, which has been developed during the past six years to a position of rapidly increasing importance, is as a constituent of certain of the alkyd resins. These resins are made from polybasic acids (such as phthalic, maleic, or succinic) and polyhydric alcohols (such as glycerol, glycol, etc.) combined under different conditions and modified in various proportions with fatty or resin acids to produce resins of specific characteristics for use in widely different paint, varnish, and lacquer products. The alkyd resins sold comniercially under the trade names Glyptal and Rezyl are essentially fatty acid modified types. In a fenof them rosin is used as a part of the modifying agent to improve specific properties, such as gloss and hardening of the film, with some sacrifice in distensibility. The alkyd resins modified principally with rosin or other natural resin acids differ essentially from the fatty acid types and are used accordingly. This group includes the resins sold under the trade name Teglac as well as some grades of Amberol and Beckacite. These resins are generally pale although dark grades can be made. They range in hardness from a little above ester gum to grades fully comparable to the hardest of the modified phenol types. They are characterized by high refractire index n-hich imparts exceptional gloss and depth to clear finishes formulated from them. The resins in this group first attained widespread use in nitrocellulose lacquers. They can readily be dissolved hot or cold in toluene or ester solvents and will stand considerable dilution with petroleum naphtha. They require no demaxing or other special treatment, as do many of the natural resins previously employed. They are freely compatible not only with nitrocellulose but also with most of the usual plasticizers and other lacquer ingredients. One of the largest uses of these resins is in lacquer sealers to which they impart remarkably easy sanding properties because of their hardness and low solvent retention. This hardness combined with a toughness superior t o dammar or ester gum accounts for their general use in both clear and pigmented lacquers for furniture and other indoor applications. These same qualities permit an increase in the usual ratio of resin which is particularly desirable for high solid content in lacquers formulated with nitrocellulose of 5-second or greater viscosity. The resistance of the resins in this group t o rubbing oils and alcohol is a further reason for their use. While originally developed for lacquers, some of these rosinmodified alkyd resins, particularly the very hard grades, have been found to be excellently adapted for certain varnishes. They impart not only pale original color but very excellent resistance to afteryellowing, either on baking or aging, which are distinct advantages over other resins of comparable hardness. Short-oil rubbing varnish made from the hardest of these alkyd resins will harden as quickly and thoroughly, and rub better than one made from the best of the phenol resins-namely, the high-acid type previously described. The varnish made from the alkyd resin will stand considerable dilution 71-ith petroleum naphtha, while the other will not, Compared to ester gum, these rosin-modified alkyd resins offer some advantages not only in color retention but also in hardness, speed of drying, resistance to water and alkali, and outdoor durability.
OTHER ROSINCOMPOUXDS The materials already described may be modified in important characteristics and other new ones produced by reacting the unsaturated linkages of abietic acid. In the manufacture of resins and metallic soaps, oxidation
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is generally avoided as carefully as possible since it is accompanied by darkening and lower solubility in naphtha. On the other hand, ester gum, oxidized by aging in a pulverized condition, becomes harder and more soluble in alcohol, which is advantageous in some special lacquers. The oxidation of rosin products is accelerated by exposure t o ozone. Complete saturation of rosin by hydrogenation appears to be a difficult problem which is now on the verge of commercial accomplishment. This has interesting possibilities in modifying many rosin products. There is already available a hydrogenated methyl abietate which shows much improved retention of color and flexibility compared to the ordinary unsaturated ester already described. It is finding use as a plasticizer for chlorinated rubber as well as in lacquers. Certain unsaturated anhydrides, such as maleic, can be added to the abietic acid molecule, and lime or other soaps made from the combined acid. Such soaps have not as yet found commercial use although they appear to have interesting possibilities. Chlorinated rosin is said to be compatible with cellulose acetate and may find some use with it in surface coatings. Rosin-soap lake pigments are formed by precipitating an acid azo dye and a soluble resinate with a metallic salt so that the final product contains 5 to 50 per cent of resinate. Such pigments hare found more extensive use in printing inks than in paint products. Rosin oil finds some application in surface coatings as a semi-drying oil.
TYPEOF ROSINFOR PAINTPRODUCTS Only a very few years ago wood rosin was practically rejected for paint products because of its dark color and relative softness. Today, with the pale shades available and a better knowledge of how to utilize it, wood rosin is used as freely as the gum grade with the choice based on the specific properties imparted by each type. In varnishes made on identical formulas, a pale wood rosin should impart a lighter color than an equal gum grade. The varnish film will be a little softer but this can frequently be offset by cooking longer with the oil or by the addition of a little extra lime or other hardener. When made into fused limed rosin, pale wood rosin requires a little more lime to obtain hardness and viscosity equal to that made from gum rosin. It may also require the use of a little calcium acetate as a catalyst to react with satisfactory speed. There is more difference between gum and wood rosins in the B grade, qince the latter contains not only a high proportion of oxidized rosin but also the accumulated condensate from the process used to produce the pale grades. Its use in paint products is limited not only by its dark color but also by poor solubility although it does appear to have some possibilities for its extrahardnecs and resistance to oil and gasoline. TT’ithout attempting to draJy up exact specifications or impose undue restrictions on rosin producers, the ideal rosin for paint products should be free from moisture, dirt, metals, volatile oils, crystallized rosin, or oxidized materials, all of xhich cause trouble or loss in its use. RECEIVED March 30, 1934. Presented as part of the joint Symposium
on Naval Stores before the Divisions of Agricultural and Food Chemistry and of Industrial and Engineering Chemistry a t the 87th Meeting of t h e American Chemical Society, St. Petersburg, Fla., March 25 t o 30, 1934.
WHOLESALE PRICES O F CHEMICALS IN GERMAXY AXD BELGIUM DECREASE.Index numbers of wholesale prices for chemicals during the first quarter of 1934 were downward in Germany and Belgium and upward in Italy, according to data published in the Board of Trade Journal, London. The index number of chemicals and drugs for the United States was up 2 points, to the highest of the past two years.
