Applications for Alkyds a m Polyesters E. M. Beavers The Rohm & Haas Compuny, Philadelphia, P a .
Ester resins are used in large quantities for a multitude of applications. Properties and performance can be adjusted over broad ranges, depending on the choice of raw materials used i n the manufacture of the products. The majority of the present applications are in the general field of protective and decorative coatings. Linear polyesters, particularly, show potentialities also as elastomers, fibers, lubricants, and molding powders.
U
8ES for alkyd resins and linear polyesters in recent years have become widespread and varied. There are sound, basic reasons for a reputation of broad usefulness. First, some of the ram materials required for alkyds occur naturally in large quantities, with a variety of properties, and a t low cost. Others are manufactured synthetically in large volume, a t costs xhich are permissible for many applications. Secondly, sincr most alkyds are made from t,hree or more components, each of which mag be varied in nature, many coinbinat,ioiis and permutations are possible, to realize different effects. Thirdly, the chemist has acquired a n appreciat,ion of cause and effect in manipulat,ingthese raw materials, and is adept a t fulfilling the particular rcquirementa of many different applications. Fourthly, the inanufact,ureof these products is readily adaptable to large scale operation.
TABLEI. PRODUCTIOK AND SALESOF ESTER RESINSIN 1947" Production, Lb. Benzenoid Types Phthallo alkyd resins (oil a n d solid types), 224,120,000
total
Unmodified Modified (with rosin ester, phenolformaldehyde, etc.)
170,601,000 53,519,000
Nonbenzenoid Types Alkyd resins (oil a n d solid types), t o t a l 58,944,000 12,227,000 Unmodified 46,717,000 Modified 5 267 000 Rosin adducts
Rosin esters
78:280:000
Sales. Lb. 171,419,000 127,313,000 44,106,000
tion of polyester content. While all constituents of the alkyd are coreactants, t)he oil and any excess of either plyfunctional paw material are considered the solvent for the p m o s e of calculating alkyd rat'io. I n an alkyd made from a vegetable ail, glycerol, and phthalic anhydride, for example, the alkyd ratio is the \%-eight percentage of glyceryl pht'halate in the compmition. These alkyds are used as hardeners for alkyds of highw oil content, and have the advantage over urea-formaldehyde hardeners, for example, of detracting less from adhesion arid flexibility of the final film. Glyptal 2.160 and Itezyl 1102 w e typical commcrcia1 products of this type. With 38 .to 42% phthalic anhydride, corresponding t o alkyd ratios of 49 t o 64, the so-called short-oil alkyds are produced. These usually require strong aromahic solvents and have high viscosity. They are used primarily for baked coatings, arid may be combined with such hardening agents as urea 01' mc!:irriirie resina, or with nit,rocellulose. Because of the relatively small amount' of fatty acid i n this type of resin, air drying wit.hout baking is usually quite poor, particnularly in development of through-hardness. When baked, Iiowever, they are charact'erized by excellent speed of cure, good ndhesion, fair to good flexibility-, and good durability, color, and color retention. The short-oil alkyds are used in applications such as finishw lor Venetian blinds, fast dr ing finishes for metal cabinets, call and cap coatings (where fabi cation and processing of the coated sheet metal are requirements), and in nitrocellulose lacquers and wood sealers. The recent trend in automotive enamels is t o baked finishes based on short-oil alkyds, usually with sniall amounts of urea or melamine resins as hardeners. Among the alkyds of t8hisclass on t'he market today are Aroplaz 1130 and 1295, Beckasol 1307, Duraples A-27 and A4-29,Glyptal 2462 and Rezyl 330-5.
52,371,000 11,045,000 41,326,000 4 031 000
70:005:000
Reported by United States Tariff Cornmiasion.
Limiting our consideration for the moment to alkyds based on phthalic anhydride and drying oils, a correlation of chemical composition with properties and present uses of the products may be made. The esterification products of phthalic anhydride and simple polyhydric alcohols alone have fourid little use. The niaxinium amounts of phthalic anyhdride ordinarily found practical in drying &l alkyds are about 50% and slightly higher; this corresponds t o alkyd ratios of about 65 or somewhat higher. Alk d ratio is a term of convenience which is more generally applicabre than glyceryl phthalate content. For an alkyd based on oil, polybasic acid, and polyhydric alcohol, the alkyd ratio is the weight concentration of the esterification product of the polyhydric alcohol and polybasic acid. If a n excess of either polyfunctional reactant is used, the excess is not included in the calcula-
COURTESY FOSTORIA PRESSED STEEL C O R P O R A T I O N
Baking Alkyd Finishes in Infrared Tunnels
April 1949
INDUSTRIAL A N D ENGINEERING CHEMISTRY
,4third, general elass of phthalic resin is the medium-oil alkyd, based on 30 to 35% phthalic anhydride, which corresponds t o alkyd ratios of 39 to 45. This type represents probably the most versatile of the alkyds today. At this alkyd ratio, solubility in aliphatic solvents is realized, and viscosities generally are lower than those of the preceding class. The alkyd ratio is high enough to givr satisfactory performance in some baking applications, and some of the alkyds in this class will tolerate up t o 20% of melamine resin. The medium-oil alkyds are well adapted either to spraying or to roller coating. I n baking, the rate of cure is good, although not as fast as t h a t of the short-oil alkyds. The films develop excellent durability and flexibility. Their color and color retention are good, but generally not as good as those of the short-oil alkyds when used in baking enamels. On the other hand, the medium-oil alkyds contain enough drying oil or drying fatty acid component t o provide excellent air drying properties. They set fairly rapidly and develop excellent hardness in relatively short time. Their brushing properties vary from fair to good depending on the oils used and the viscosity of the resin. Because of these general properties, the medium-oil alkyd most closely approaches the universal vehicle and finds wide application for such uses as air drying or baking white and colored enamels, maintenance paints, metal decorating work where flexibility is important, auto and truck refinishing enamels, metal sign paints and many other applications where adaptability t o spraying, roller coating, or brushing is necessary. Duraplex C-45-HV, based on linseed oil, and Duraplex C-49, based on soybean oil, are typical of the medium-oil alkyds. Aroplaz 1086, Beckosol 1331, Glyptal 2527 and 2509, and Rezyl 823-1 and 807-1 are a few of the many resins in this class. The long-oil alkyds constitute a third general category, utilizing about 24y0 phthalic anhydride, which corresponds to a n alkyd ratio of about 31. These are not particularly adapted to baking, but find wide application in architectural brushing enamels and unpigmented films. They are characterized by good brushing properties and may be formulated t o give fast drying, flexible films of outstanding durability, color retention, and gloss retention. Some of the alkyds of this class have a degree of outdoor durability which makes them especially suitable for marine finishes; this type of alkyd found much use during the war for this purpose. lllthough the field of architectural enamels accounts for a large part of the usage of medium- to l o n g 4 1 alkyds, they have many other applications, such as metal decorating where extreme flexibility is required (coatings for toothpaste tubes, for example), trim and trellis paints, mill whites, and wall coatings. Among the medium- t o long-oil alkyds on the market today are -4roplaz 1240 and 1241, Beckosol P-296, Duraplex D,-65-AJ Glyptal 2466, and Rezyl 873-1. Jn the foregoing, attention has been focused on alkyds made with drying oils. Nondrying alkyds find important uses. These resins are usually based on raw castor oil or coconut oil, with 39 to 50% phthalic anhydride, resulting in alkyd ratios ot 50 to 65. They are essentially nonoxidizing and nonpolymerizing, and must be hardened with some material such as urea or melamine resin, or with nitrocellulose. Despite the fact t h a t these resins are permanently thermoplastic, some of the more recent ones yield finishes of excellent resistance t o alkali and acid. The development of color in films from drying oil alkyds is closely related to the degree of unsaturation of the oil. Inasmuch a s the nondrying alkyds utilize oils having iodine numbers usually well below 120, their color and color retention are outstanding. One of the chief applications for nondrying alkyds is the high quality finishing of refrigerators, stoves, and washing machines, where the ultimate in color is essential. Automotive and wood lacquers comprising nondrying alkyds and nitrocellulose enjoy a large demand. I n this use, the alkyd contributes flexibility
739
Polyester-Styrene Copolymers Vary in Rigidity a s Chemical Composition i s Varied
without severe softening of the film and is permancnt. Such lacquers have a high degree of durability as required for automotive finishes. Aroplaz 905 and 906, Beckosol 1323, Duraplex ND-77-B and ND-78, Glyptal 2477 and 2570, and Rezyl 92-5 and 99-4 are a few of the nondrying alkyds available. Alkyds employing dibasic acids other than phthalic anhydride have commercial importance. Natural gums and resins have been largely displaced or complemented by synthetics in recent years. The latter are usually polyhydric alcohol esters of abietic acid or of the Diels-Alder adduct of abietic acid with maleic or fumaric acid, and are usually called the maleic resins. One of these may serve as the sole vehicle in some fcir applications, such as the sealer for plaster t o protect the final top coat from the alkalinity of damp lime. -More often, the maleics are cooked into drying oils to form varnishes, in which the resin is a hardener for the oil, or are used t o give film body and hardness to nitrocellulose lacquers. They are often blended into drying oil-alkyd vehicles t o speed drying and improve hardness. At least one such resin, Amberol 750, is soluble in alcohol or aqueous ammonia and has found use in some applications formerly employing shellac. The synthetic resin has the advantage of greater uniformity than the natural product. I n ink vehicles, i t produces better adhesion to cellophane and gives brighter colors. I n self-polishing waxes, it represents a better balance between slip and gloss. Maleic resins available commercially include Amberol 801 and 926, Arochem 600, Beckacite 1120, Cellolyn 102 and 103, Pentalyn G, and Teglac 2152. Softer unmodified alkyds can be achieved with aliphatic polyacids of lower polarity, such as sebacic, azelaic, and adipic. Some of these found vital use during the war in caulking compounds, particularly for aircraft. These products also have valuable features as plasticizers for film formers such as the cellulose derivatives and are used to some extent where permanence and stability are critical. Also, oil may be used with the softer acids. Such resins give unusually flexible coated fabrics, and are frequently used in lacquers for rubber articles which will be flexed and stretched, for cable coatings, for high quality furniture finishes, and for automotive finishes. Some of the oil-modified or unmodified soft alkyds on the market are Paraplex G-20, RG-2, and RG-8, and Ultraflex 28. Perhaps the most outstanding achievement in the industry during the past 5 t o 8 years has been the successful utilization of
140
INDUSTRIAL AND ENGINEERING CHEMISTRY
COURTESY BOEINO AIRCRAFT COMPANY
Caulking Compounds from Soft Alkyds Found Vital W-artime Usage
pentaerythritol in alkyd resins. Some of the products already mentioned are based on pentaerythritol as part or all of the polyhydric alcohol, and some of the virtues cited in applications may be attributed at least in part to the contribution of the pentaerythritol. Generally, the most striking results with pentaerythritol have been achieved with soybean oil in long- and medium-oil alkyds. By comparison to the glycerol iesins, the pentaerythritol analogues have better hardness, better initial gloss, and are much more resistant to water and alkali. The pentaerythritol alkyds, in some cases, have about the same solvency and compatibility as their glycerol counterparts, yet have some of the virtues of shorteroil glycerol alkyds. The reniarkable durability of medium-oil pentaerythritol alkyds in marine paints is a discovery of about the last 2 years. Because of manufacturing difficulties, short-oil pentaerythritol alkyds have not become popular in the industry. Aroplaz 1241, Beckacite P-470, Duraplex A-29, D-65-A, and ND-78, Parapen 4511 and 4513, and Rezyl 873-1 are pentaerythritol alkyds. Linear polyester plasticizers, from bifunctional reactants, have shown an unexpectedly wide range of compatibility with other polymeric materials, and have proved especially valuable with polyvinyl chloride and chloride-acetate copolymers. As plasticizers, the polyesters show the advantages of extremely low volatility and migratibility, high resistance to water and solvents, excellent stability under ultraviolet light and at elevated temperatures, and improvements in some processing characteristics. The first large scale exploitation of these properties was made during the war in a n improved jacket for radar cables. The use of Paraplex 6-25, a sebacic acid polyester, as the plasticizer for this jacket resulted in an effective life severalfold longer than when the conventional monomeric plasticizer was used. I n peacetime electrical installations, the polyesters are valuable for their stability and permanence and the resistance of their polyvinyl chloride stocks to deformation at elevated temperatures. The feature of low- volatility is of particular importance in free films with polyvinyl chloride, and there are myriad uses for such film. The surface quality of calendered film is improved by the incorporation of polyester plasticizers. Lacquers based on the vinyl resins and polyester plasticizers
Vol. 41, No. 4
are a new and promising development. Such a coating, for cxample, has been found impervious t o marine borers, when used as a ship-bot,tom finish, even though t,hese animals have shown t,hr capacity for boring through plynood, stone, and poorly mixed concrete. Polyester plasticizers available conimerciaily are Paraplex C;25, 6-40, and G-50. A new type of laminating resin appeared during the war; it consisted primarily of solutions of unsaturated linear polyesters in vinyl monomers. These have become knoTvn as contact resins because only contact pressure with the mold is necessary in curing the resin. The polyester component contains iinsaturation introduced by maleic or fumaric acid, for example, and during thc cure is capable of copolynierization with the vinyl monomer. The latter is styrenc in most cases. The curing operation is accelerated by peroxide catalysts, and even fnster auxiliary catalysts have appeared recently. . The bulk of the ,contact resins used during the v a r went into the preparation of glass-cloth laminates for radar domes and armor for personnel. Some glass-cloth laminate for aircraft is being produced in peacetime, but the most promising applications seem to be flat paper lamiriates for drainboards and table and cabinet t,ops; colorful, washable n d coverings; potting of elcctrical equipment, such as condensers; and casting of articles. For potting and casting applications, an advantage over urea-formaldehyde and phenol-formaldehyde resins is that the contact. resins contain no inert solvent, and no by-products of the curing process are produced. The toughness and flexibility of contact) resin laminates adapts them particularly for bus and train installations. Contact resins available at' present' include Laniinac 4125, Paraplex P-13 and P-43, Selectron 5003 and 5026, and Vibrin 103. Physical properties of the linear polyesters are highly sensitive to changes in chemical composition, and the products can be varied from liquids to elastomers, to plastics, and t'o fibers. The properties are such that new and unusual plasticizers, lubricant's, molding powders, rubbers, fabrics, and coat'ings of the polyester type are future possibilities. Some of the problems n-hich st.ill confront. the chemist' in this field are as follows:
A fundamental correlation of brushing and sagging characteristics of alkyd composit,ions with the physical and chemical properties of the alkyds themselves. -4better understanding of baslc causes should help to eliminate t,his main disadvantage of alkyd vehicles. A second goal is the achievement of a stable, wster- or nmmonia-soluble alkyd which will be air drying. The difficulty with attempts to date has been either a high sensitivity of the products to hydrolysis or lack of convertibility after application in film form. Such products should be useful as plasticizers for other water-soluble materia.ls-for example, the brittle urea-formaldehyde adhegves-or as vehicles for true water paints. A third objective is the long-sought solventless varnish. The contact resins are the closest approach io this aim to date, but ordinarily they have thc disadvantage for coatings use of having to be cured in the absence of air. An ideal solventless varnish would have the obvious advantages of economy, of simplicity (eliminating solvent recovery systems), of reduct,ion of the dangers of toxicity and fire hazard, arid of yielding films with less shrinkage and better fullness. There is, of course, the fourth omnibus project of constant improvement in one property or another; this is generally characteristic of the American cheniical industry and is particularly a feature of the alkyd resin business.
Acknomledgment The author is indebted to C. L. Levesque, V. N. Sheet.s, and E. B. Slaght, of the Rohm & Haas laboratories. RECEIVED March 2 6 , 1948.
[End of Symposium on Alkyd Resins]
