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requirements. Paint makers consider that nothing is gained by extending the pigment. It is preferable merely to use a sufficient amount of pure green to give satisfactory optical covering. Purchasing System
The total cost of the paints purchased by a large railroad makes the purchasing system well worth study. Ordinary dry pigments, paste paints, and oil paints may readily be purchased on a specification basis. The larger roads have specifications for a number of varieties. The Mechanical
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Section of the American Railway Association has standardized several, and the American Society for Testing Materials offers specifications for numerous individual pigments, dry, in oil, and in japan, as well as for oils, thinners, and solvent's. Although a few specifications have been written for varnish, it may be said in general that it is not yet possible to frame specifications which will fully determine all properties, incIuding durability, of varnishes, enamels, and lacquers. If this is ultimately done, it will doubtless be on the basis of physical and accelerated aging tests, with chemical analysis playing only a minor part.
The Evaluation of Industrial Finishes' A. E. Schuh BELLTELEPHONE LABORATORIES, NEWYORI, N. Y.
HE consumer of indus-
The thousands of different parts employed in the these finishes may be classitrial organic finishing telephone industry require a great variety of finishes ficd according to the followmaterials is interested designed for protective, decorative, or insulating puring types: (1) clear and pigprimarily in the performance poses. The inadequacy of previously employed methmerited l a c q u e r s , (2) clear of the finishes obtained with ods of evaluation made necessary the development of and pigmented varnishes, and a comprehensive program for determining or predicting (3) japans. In a d d i t i o n , these materials. Theoretically at least, he has no conthe performance of the various types of organic finishlimited use is found for oil ing materials. Instead of relying mainly upon service cern as to c o m p o s i t i o n or p a i n t s , b i t u m i n o u s subformulation if he is able to performance and accelerated exposure tests, the prostances, resin solutions, and gram of testing methods being developed consists of measure adequately the ata few novelty surface crintributes of satisfactory persubjecting coatings of uniform thicknesses to conkling and recrystallizing formance. In his attempt to trolled environments and periodically measuring finishes. judge quality he must rely changes in physical properties which take place. Apart from the desirable upon the physical behavior of These changes are measured by instruments in the performance of finish coatthe coatings, since up to the main recently devised for determining abrasion reings themselves, it occasionpresent time no definite relasistance, impact resistance, flexibility, and adhesion. ally arises that their local a p tionship between composition While the method is being used primarily as a means plication or their behavior in and performance has been esof selecting materials for finishes, it should prove to service i n t e r f e r e s with the tablished and information as be of value to the manufacturer and research chemist proper functioning of assoto formulation is not now supin the paint industry. ciated a p p a r a t u s . As an plied him. As a large coni l l u s t r a t i o n , in the telesumer of diverse organic finishing products, the telephone in- phone central office where continuity of service is the dustry has found it necessary to make a critical study of watchword, three serious hazards could be introduced by organic finishes. One is the danger of fire, and consequently methods for the evaluation of quality. The development of a system of testing adequate for a no coatings of low ignition temperature are used on base complete evaluation is influenced by several conditions materials of low thermal conductivity. A further precaution peculiar to a large public utility company. The most im- requires that solvents used in various touch-up materials have portant requirement of a satisfactory telephone communica- flash points above 100" F. For similar reasons spraying is tion system is continuity of service. This involves the proper avoided in refinishing practices within central offices. Anfunctioning of thousands of delicately attuned pieces of a p other hazard which may be introduced by solvent vapors is paratus, nearly all of which a t various points in their as- that of tarnish or corrosion of electrical contacts. For insembly require organic finishes so selected as to insure uninter- stance, turpentine, although not a serious fire hazard in the rupted performance. Moreover, since the telephone system above sense, is known to promote tarnish and corrosion. In is the principal consumer of its own equipment, durability of fact, because of these special conditions, only a limited number finish is of prime importance. These considerations have of organic solvents are suitable. A third hazard is found to be tended to focus attention upon the development of methods dust particles derived from the degradation of finishes, which for evaluating the quality of finishes, which permits critical interfere with contacts, causing noise in the electrical cirinitial selection of materials and the determination of their cuits. Thus pigmented finishes showing chalking tendencies aging cannot be used. - - characteristics. All special requirements are not confined, however, to Special Problems of Telephone Service telephone central offices. For instance, in a telephone transI n order to meet the protective, decorative, and insulating mitter, traces of the volatile constituents of organic finishes finish requirements of telephone apparatus, about 350 organic used for insulation and for protection against corrosion may be finishes have been standardized. In the case of each finish, adsorbed by the granular carbon, resulting in impairment of the method of surface preparation of the base material, the the microphonic properties. method of application of the finish, and the particular brands The paint requirements of the telephone industry for outr of various paints to be used-.are specified. The majority of door finishes are not so large, diversified, or unique as those for indoor telephone apparatus. Considerable use is found for 1 R d v e d September 10, 1931.
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December, 1931
INDUSTRIAL AND ENGINgERING CHEMISTRY
bituminous coatings in the protection of metallic underground structures. Experience has shown that the ordinary thin paint coatings are not effective for long periods under the various soil conditions encountered, and thus the practice of applying heavy coats of bituminous materials, reinforced in many different fashions, has been resorted to. Developments in this field should be towards thinner coatings of sufficient toughness to give protection against corrosion and soil stresses equal to that obtained by the present costly heavy coatings. Much use is also found for outdoor paints of high durability. For instance, aerial loading coil cases are painted with a neutral gray paint which must have good corrosion protective properties and a t the same time retain its color. In some localities the telephone poles are painted for sake of appearance with a well-blending green paint. A conspicuous white coating on the lower part of telephone poles paralleling certain highways is often demanded by the authorities as an aid to motorists. Difficultyhas been encountered in applying this light-reflecting coating to poles previousiy impregnated with creosote. Improvements Sought and Practiced
of the Bell System, and in many &stances the annual p&uction of a particular part receiving a given finish runs into millions. It becomes at once evident why the quicker drying types of materials are used for the majority of finishes on telephone apparatus. The predominant method of application is by spraying. Wheuever the size of the annual production warrants, continuous mechanical methods for application are devised, thereby both speeding up production and improving the uniformity of the finish. The possibilities along these lines have by no means been cxhausted and engineers are continually introducing new and ingenious devices of mechanization.
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advantage of the greater drying speed and quality of performance. Furthemore, these modem finishing materials frequently show a decided improvement in quality when subjected to a mild heat treatment. This favorable response to heat is in some cases so outstanding that a comprehensive study has been undertaken which may result in 8 drastic change of many present finishing practices. Thus, it seems highly probable that the present japan vehicles which require temperatures of 350' to 450" F. and time schedules of one to three hours are replaceable by synthetic varnish enamels which set up more rapidly at lonw temperatures and which a t the same time give coatings of superior quality. As a second example, aluminum bronze powder finishes, used chiefly because of neat appearance and high light reflectivity, are markedly improved when various synthetic resin short-oil varnishes, baked a t 175' F. for a half hour, are substituted for the usual type of air-drying vehicles requiring ahout twelve hours for complete drying. A further example of the benefit obtained by mild heatinglies in the field of hardwood G h i n g . Laboratory-scale experiments have shown that, instead of the customary period of several days normally required between the amlication of the filler and the final rubbing of the last is far superior to thatbbtainedby the ordinary procedure. This brief survey exemplifies the diverse character of the organic finishing problems encountered in the telephone industry. The exacting nature of the behavior requirements for most of the finishes and the economy to he redized by the telephone system in minimizing the refinishing of its equipment have made necessary the development of a comprehensive system of quality evaluation of organic finishes. Tests Generally Used to Examine Finishes
The many tests generally employed in the examination of finishes and finishing materials may be divided into three
Figure l--Inatrumenf Used In Abrasion Test
New finishing Inateials are constautly sought which are either more rapiddryiug or more durable, or both. For example, the improvement of finish quality attributable to the use of recently developed synthetic resins in quickdrying varnishes, lacquers, and their enamels is bringing ahout a general revision of most of thestandard finishes in order to take
categories: control tests, initia1;suitability tests, and performance-quality tests. Control tests are employed to make certain, in so far as practical, that successive lots of the same brand of finishing material are identical. They do not ordinarily measure properties directly related to finish performance, but consist of determinations of such chemical and
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INDUSTRIAL A N D ENGINEERING CHEMISTRY
physical properties as specific gravity, refractive index, solids content, consistency, iodine value, acid number, chemical. composition, etc. Nearly all of the control tests pertain to properties of the liquid sample. In any individual case, the properties that identify a material and serve as a means of control may be few in number. Initial-suitability tests comprise the methods for determining whether a finishing material can be employed for the production of a desired finish. Certain of these tests are conducted on the liquid material, such as tests for type and rate of settling, rate of evaporation, consistency, etc. The majority of suitability tests, however, are made on freshly formed finish coatings, where they may serve either as elimination tests prior to studying the quality of continued performance, or as supplementary control tests. In these preliminary tests are included drying-time tests, hidingpower determinations, color and gloss comparisons, leveling and homogeneity characteristics, etc. Finishing materials which fail to satisfy these requirements are frequently made acceptable by minor modifications having little or no bearing on durability. Performance-quality tests are concerned wholly with the long-time behavior of finish coatings, beginning in their operation where the initial-suitability tests leave off. Since the consumer is interested primarily in finishes rather than finishing materials, he needs a t his command means whereby he can measure the quality of finish coatings throughout their entire life. It is a known fact that a series of finishes exhibiting a certain relative order of quality soon after application may lose that order with age and eventually display an entirely different relative order of merit. While paint technology haa made noteworthy strides in recent years in the field of control and suitability tests, it has not made corresponding progress in the accurate measurement of quality of performance. Finishes usually serve primarily one of several functions. They may be used for their corrosion protective value, in which case the deterioration is essentially dependent on exposure to the immediate environment, or they may be used for their mechanical serviceability, in which case their value may be determined by their resistance to mechanical stresses inherent in the service requirements. I n another instance, the finish may have to perform a specialized function, such as electrical or thermal insulation, resistance to specific chemical fumes or liquids, etc. Although any one finish may occasionally have to perform several functions simultaneously, most finishes are evaluated on the basis of their ability to withstand the deteriorating forces found either in the environment or in mechanical service. The durability of a finish on exposure to most environments is usually sufficiently high that recourse is taken to acceleration of the failure processes in order to permit desired rapid evaluation. This acceleration at once imposes certain limitations, such as the difficulty of choosing suitable relative intensities of deteriorating factors and the danger of intensifying one of the factors to the point where reactions to environment may be introduced which normally would either not occur at all, or else a t very slow rates. The method is limited to a technic of comparison, and even then only pronounced trends of behavior, rather than fine distinctions of differences, can be relied upon, Whether acceleration is induced artificially by means of suitably adapted cycles or by the severe outdoor exposure in hot moist climates, the estimation of durability is based upon the appearance of visible changes occurring late in the life of the coatings. Whereas the method has found wide application on the comparison of exterior finishes, it is much less reliable for the examination of finishes used indoors, since in this case the environmental factors of deterioration are much milder. In fact, no trustworthy
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method of artificially shortening the test period for interior finishes has as vet been devised. When the phmary function of a finish lies in resistance to mechanical stress, such as wear, impact, or bending, the customary procedure is to perform service trials, preferably under surroundings where the mechanical stresses are more severe or more frequent than normally encountered. At times, when such surroundings are not readily available, ingenious devices are set up which simulate service conditions and permit some control of the intensity and frequency of the particular mechanical stresses the coating is designed to withstand. In either case, the method of evaluation by service trials is costly, and hence means of reducing the number of samples to be tested are needed. A more serious limitation, which applies to all of these methods, lies in the fact that the concurrent action of many independent variables is associated. Qualitative terminology in the expression of test results is often necessary, resulting frequently in confusion owing to the unavoidable ambiguity of the terms used. For these reasons, this laboratory was confronted particularly with the problem of developing better methods of evaluation of the quality of indoor performance. The methods that have been devised in response to this need are capable of following quantitatively the degradation of the coatings. Owing to the complexity of the chemical changes which occur during the life of a coating, these methods have sought to measure the accompanying physical changes. For this reason the first step consisted in developing new instruments capable of measuring the physical characteristics of coatings and the change in such properties with time. Since this method of approach implies the attempt of segregation and control of the many significant variables which influence the behavior of all coatings, it may be of interest to the worker in the paint field. Instruments Recently Developed
The major factors which determine the quality of a finish throughout its service are the composition and physical state of the finishing material before application, nature and preparation of base material, thickness and age of the film, and character of exposure during aging. The consumer has no control over the composition and physical state of the finishing material, but he is in a position, by controlling the other factors enumerated, to relate a given material to its behavior as a finish. Since the instruments used in this method of testing are capable of measuring with precision small changes in the physical characteristics of coatings, the exposure conditions during aging need not be so severe as they are in accelerated weathering tests. Although fundamentally these tests are concerned with adhesion tensions at film-base interface and the cohesion and flow characteristics of the coatings, it has not been possible in all cases to devise instruments by which these characteristics can be directly measured. Nevertheless, the tests now in use at this laboratory and about to be described have made progress towards the investigation of coatings along fundamental lines. These tests are concerned with the measurement of essential properties in terms of which the quality of coatings may be defined-namely, adherence, flexibility, and toughness. Since coatings react to environment at different rates, the one which stands highest in these physical properties for the longest time is automatically defined as the best coating. In outlining the experimental procedure employed in the quality rating of finishes, it becomes necessary first to describe the method of preparing coated panels for test. Since variation in film thickness is one of the factors affecting the behavior of a finish for the comparison of materials of a ghen type, it is necessary to obtain coatings of uniform and con-
stant thicknesses. For example, a series of clear lacquer coatinga might be compared at a thickness ranging from 7.6 x 10-4 cm. (3.0 X lo-* inches) to 12.7 X em. (5.0 x IO-' inches), whereas varnishes might be compared a t 10.0 x lo-' em. (4.0 X 10-4 inches) to 15.2 X em. (6.0 X 10-4 inches). On the other hand, duplicate panels (if the same materials are held to within less than *2.5 X 10 em. (* 1.0 X 10-4 inches). The thickness level to Le eliosim in a comparative study of the products of several suppliers is determined by the average thickrrcss olitained in the cornmcrcial application of thesc materials. The instruments employed in the preparation of these coatings of controlled thickness and desired uniformity are the Walker-Thompson (4)spinning disk and a modificationof
The factors which determine the abrasion value of a given coating are the nature of the abrasive-i. e., the size, shape, hardness, and mass of the individual abrasive particles-and the velocity and angle a t which these particles strike the test specimen. By the selection of Carborundnm of a fixed average size, the variables pertaining to the nature of the abrasive are fixed. Constancy of velocity of abrasive particles depends on air pressure and design of abrasion tube, in which air a t controlled speeds imparts velocity to the abrasive particles. With a given d e s i p of nozzle, a constant distribution of part.iole velocities is obtained, although it has been found that nuzzles of similar design may show different distribiition patterns with varying rates of introduction of abrasive into the air stream. There would be a definite ad-
Flgmre 2 - A p p e r a ~ sUsed In RepeQfed Impact Test
i t described by A. H. Pfund. The Walker-Thompson instrument consists of rotating a wetted panel and thus utilizing centrifugal force as the leveling agent. Pfund has effected an improvement whereby the wet panel is rotated on its own axis while revolving as a whole about a main center. With either instrument, the desired 6lm thickness may be obtained by varying either the speed or the time of rotation. Immediately after spinning, the panels are placed on level trays in a dust-proof cabinet, and when dry are conditioned for a week to ten days before testing. ABRASION TEST-A method termcd the "abrasion test (3')" is used to determine the resistance of a material to mild and controlled abrasiouaf forces. The instrument used for this purpose is shown in Figure 1. A definite velocity is imparted to Carborundum particles o f a given average size (mean diameter 0.0081 em.) by means of an air stream flowing through a nozzle in which the air and Carborundum particles are thoroughly mixed. These particles are allowed to impinge upon the material under test, and the total number of them (their total weight) required to wear throngh the film is taken as a measure of the abrasion resistance of the material. From this weight the weight required to wear through unit thickness of the 6lm is computed, and this is referred to as "abrasion value" of that material. This value is related to the cohesive forces of the coating, and when the conditions are so chosen as to produce uniform rate of wear, the adhesion of the coating to the base plays a negligible part.
vantage if the abrasion tube design were 80 modified as to impart uniform velocity and distribution to all abrasive particles. Such a tube might make possible the use of this instrument in the fundamental investigation of cohesive forces of materials. I n the routine application of the test, it is essential that the test variables be held eonshut or that a correction be applied for any change in them. The test apparatus provides automatic means for maintaining a constant value for some of these variables, whereas the constancy of others nust be checked and maintained by the operator. In order to calibrate the instrument, a stable material of high abrasion value, such as a baked japan coating 12.7 X 10.' em. (0.0005 inch) to 25.4 X 1 0 - 4 cm. (0.001 inch) thick, has been found adquate for the purpose. REPEATED IMPACT TESI-A second method for examining the characteristics of a coating is termed the "repeated impact test." The apparatus used for this purpose and developed at thie laboratory is shown in Figure 2. In this test, the coated panel, fastened securely to a horizontal hase, is subjected to repeated blows by a case-hardened steel ball on a short arm which pivots on the end of a longer rotating arm. In the present test, this long arm is geared to a synchronous motor which imparts a speed of either 150or 360r. p. m. The impact value is defined as the number of impacts of the ball required to expose the bare panel. Placing the coated panel nearer
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INDUSTRIAL ANL) ENGINEERING CHEMISTRY
the rotating arm usually increases the impact value; increasing the speed of rotation lowers it. In the operation of this instrument it is the practice to place the coating a t a fixed distance beneath the driving shaft. The coated panel is clamped in position and must be flat, for otherwise a spring action may be introduced which will modify the impact value The action of the film on being struck and the subsequent end point are observed by means of a low-powered telescope. If in the comparison of a series of materials, the values obtained at a speed of 360r. p. m. donot
Piaura 3-Modlfied
Vol. 23, No. 12
being turned about a cylinder of a definite radius. An instrument constructed in this laboratory permits metal panels of thicknesses up to 0.159 em. (‘/Minch) to be bent about any one of six mandrels varying in diameter from 0.318 cm. inch) to 2.54 em. (1 inch). The design of the a p paratus insures that the panels will follow closely the contour of the mandrels. The instrument which is shown in Figure 4 is operated by hand, and the motion of the crank handle is translated, by means of a system of gears, to a master bar which bends the panels uver any or d l mandrels simulta-
Apparafma Weed in Repeated Impact Teat
reveal inherent differences, the speed is reduced to 150 r. p. m. An improved form of this instrument, more recently designed in these laboratories and illustrated in Figure 3 provides for rotation of the coated panel under impact. This modification extends considerably the area subjected to impact, and in this manner minimizes the effect of localized differences in the film and its adhesion. In this test, then, the coating is given a blow by a masS moving’at controlled velocity. The angle to the coating a t which the mass strikes determines the magnitude of the vertical and horizontal force components of impact. Variation in the angle of impingement affects the relative magnitudes of these components, and consequently the impact value for a material. The values obtained in this test are a function of the ductility of the coating, which in turn is influenced by the adhesion of tlie film to the base. Impact values for a coating, consequently, are influenced by the composition of the base panel. The behavior of coatings as judged by this test may conveniently be characterized as brittle or plastic. Brittle materials are either worn away or shattered, depending upon whether the limit of elastic flow of the coating has been exceeded by the force of the impact. Plastic materials, on the other hand, all flow, but a t rates which depend upon the force of impact and the flow characteristics of the material. MANnnm TEs-The commonly used “mandrel” test has proved to be of value when relined and placed upon a quantitative basis. In this test, a metal panel coated with an organic film is clamped a t one end in a fixed position so that the free end may be bent from a straight line into the arc of a circle by
neonsly. Experience to date with this instrument bas shown that test results are relatively insensitive to the rate of bending. As a coated panel is bent about a mandrel, the organic tilm undergoes a definite amount of stretching. The per cent elongation depends upon the panel thickness and the mandrel diameter. Elongations varying from 1 to 26 per cent may be obtained with the apparatus described above. During stretching, the film may crack or flake off the panel. The distensibility of a coating material when applied to a particular base is expressed by stating the maximum elongation, in terms of per cent, which it. will stand without cracking. Evidence of cracking is sought by means of a low-powered microscope, inasmuch as the cracks are sometimes not otherwise discernible. The analysis of data obtained in this test indicates that the distensibility of the film on a given base is a function not only of the distensibility which this film would have by itself, but also of the adhesion characteristics a t the film-base interface. Thus a film, when applied over various base materials, will exhibit decreasing distensibility wit.h decreasing interfacial tension, until, when applied over an amalgamated surface, when adhesion tension is almost zero, the distensibility of the coating approaches that of the film itself. h E C l S I O N OF TESTS-In addition to describing the operation of the foregoing three test.8, it is necessary to mention their precision and the range of values normally obtained with them. The precision attainable in the determination of abrasion value is limited by the precision with which the thickness of the coating at point of abrasion c m be measured.
INDUSTRIAL A N D ENL
December, I931
For instance, wiLh an instrument capable of measuring thicknesses of an order of 10.63 X lo-* em. (10.025 mil), coatings ranging in thickness from 6.3 X cm. (0.25 mil) to 25.4 X em. (1.0 mil) would have a limiting precision in abrasion value from i.10 to 1 2 . 5 per cent, respectively. When a series of similar commercial materials is tested, the abrasion values frequently TWY over a range from 20 to 200 grams per mil, thus showing that the above precision is adequate for the differentiation of materials. The precision of the repeated impact test is somewhat lower. With the first form of the apparatus, five impact observations are averaged and called the "impact value." An analysis of test data on forty different sets of impact readings obtnined on a variety of materials representing a wide range in impact test levels has shown that the probable error of the mean of any one set of observations is within .t20 per cent. Ilowever, the numerical range in impact values of different materials is wide, showing a range of values from five to five thousand. The mandrel test permits the determination of elongation with a precision within *2 per cent when one panel thickness is used. This precision is sufficient for practical purposes, inasmuch as a series of commercial materials may show elongations varying over a range of 1 to 20 per cent. Not only are such wide ranges of values found for each of these tests at any one period of their aging, but wide divergencies in rates of degadatbn are also revealed. OTHERTESTS UsEn---In addition to these tests, which find application in the examination of almost every telephone apparatus finish,frequent use is found for other tests, such as the Pfund hardness test (3)and the apparatus designed liy the New Jersey Zinc Company for measuring tensile strength ( 1 ) . Both of these instruments are familiar to the paint technologist and their value has been repeatedly demonstrated. IIo\s~ever, in the system uf quality evaluation under discussion, these tests have not been generally employed for the following reasons: The measurement of film hardness by the Pfund instrument is markedly influenced by the hardness of the base material. This is particularly true for filmthicknesses within the usual range of organic coatings-i. e., 0.0025 em. (0.001 inch) or less-and this difficulty is accentuated with increasing hardness of the films. The New Jersey Zinc Company tensile-strength apparatus permits the study of only a limited ...
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number of materials, since many are too brittle to be tested in films of normal thickness. Furthermore, it is well known that the behavior of finishing materials as stripped films is not necessarily equivalent to the behavior of the same materials in form of coatings. At times, tests of a highly specific nature need to be developed. As an example, the lacquer finish on telephone apparatus, such as the telephone handset, is rapidly attacked by perspiration. I n the search for a synthetic composition
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tensitnlity as shown by the mandrel test had dropped from over 17 to about 6 per cent in three months. The agreement between physical tests and accelerated exposures indicates that it may become possible to make reliable selections of finishing materials at a period appreciably before the appearance of the various gross visible signs of failure. However, it has not as yet obviated the need of continuing a certain amount of exposure testing in order to discover what types of visible failures eventually occur
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INDlJSTRTAL AND ENGINEERING CHEMISTRY Acknowledgment
tory.
Vol. 23, No. 12
Literature Cited
(4) Wnlker and Thompson, Proc. Am. SOC. Testing. Materials, 22, Pt. 1 1 , 465 (1Q22)i
Automobile Coatings' H. C. Mougey and R. J. Wirshing RESEARCH LABORATORY, GENRRAL MOTORS CORPORATION, DETROIT, MICHIGAN
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The materials used and typical finishing systems for ,HERE are only two restill leads the field, although bodies, fenders, wheels, and chassis are described. quirements for autosome lacquers as well as synDisadvantages of the present materials and systems mobile finishes-good thetic-resin materials are beare discussed. The following improvements, given in appearance that is retained in ing used in small quantities. the order of their importance, are desired: rustservice, and low cost. For wood and wire wheels, resistant fender enamel; lacquer with better chalkBy good a p p e a r a n c e is old-fashioned v a r n i s h maresisting properties; increased resistance to chipping meant not only the initial apterials are still in use, but it from stones thrown up by tires, etc.; a surfacer or pearance on the showroom a p p e a r s that the syntheticsurfacing system that will give a surface ready for floor, but the appearance durresin materials will soon relacquer or the color coats at lower cost, counting both ing the life of the car. Replace them, except in the case material and labor; a lacquer or color material or sistance to cracking and reof black wire wheels where painting system that will give the desired final appeartention of luster are recogblack baking enamel may be ance at lower cost, counting both material and labor; nized as necessary qualities, desirable under certain cona material or system for producing colored fenders at a but resistance to mechanical ditions. cost comparable to that of the present black enamel injury is just as important. For chassis, baking enamels fenders; a material or system for finishing chassis at a A finish might show satisfacof the oil-asphalt type appear cost comparable to that obtained at present but with tory properties when tested to be best suited for the primer much greater resistance to rust and chipping from on an exposure-test panel, and coats with oil-asphalt, synstones, etc. yet it might be entirely unthetic resins, or lacquer for the suited for automobile use. If top coats. Typical schedules the finish mars by being scratched with dust when the car is for finishing with these various materials are given below, cleaned, its other desirable properties will not be appreciated On account of commercial conditions these schedules must be considered as typical only, with variations in the number of by the owner. By low cost is meant a total low cost for time, labor, and coats, drying schedules, etc., in different plants. material. A certain finishing material might have a low cost Schedule for Finishes per gallon, and yet, because of time required for application, high cost of labor, etc., the resulting finish might be very BODY-(^) Metal is cleaned with Sunoco spirits or phosexpensive. The effect of high-labor cost appears a t once in phoric acid, and dried. the cost records, but the time factor is much more intangible. (2) Primer (usually oil type) is sprayed and baked 1 hour Cost of floor space, interest on work in process, etc., are a t 180" to 200" F. (82.2"to 93.3" (3.). regular items in the books of the cost accountant, but these (3) Surfacer (usually oil type) is sprayed on and baked 1 items are not the important ones from the standpoint of time. hour a t 180" to 200" F. (82.2' to 93.3' C.). The real reason why a short finishing time is important is that In some cases the primer is not baked but allowed to air-dry it gives the car manufacturer the ability to produce cars when for a few minutes, after which the surfacer is applied and then the public is willing to buy them. Cars are very bulky and baked an hour at 180' to 200" F. (82.2" to 93.3" C.) cannot be stored in large numbers, and even if they could be The PX type primers and surfacers are not in wide use at stored, the rapid improvements made in cars might make the the present time. The PX primer does not adhere to the ones in storage obsolete. The rapidly changing ideas of the metal as well as the oil-type primer under production condipublic in regard to color, etc., are even more important in tions here. The PX type surfacer does not offer advantages their effect on the possibility of storing cars before sale. to offset its increase in cost. Many times in the history of the automobile industry it has (4) The surfacer is websanded and then dried. been necessary to withdraw cars from storage and repaint (5) Formerly japan ground coat was applied before the them in different colors in order to sell them. Some times finishing lacquer. However, trouble due to lack of adhesion this change was from somber colors, such as a black or gray, of the lacquer to the ground coat and "pinholing" of the to red or other bright colors, and at other times the reverse lacquer caused the use of japan ground coats to be diswas true. continued. At present, when a ground coat is used, a coat of These requirements for automobile hishes appear to be the finishing lacquer is applied as a ground coat and forcevery simple, but, on account of production conditions, entirely dried for 30 to 60 minutes a t 125" F. (51.7" C.). different types of materials must be used for bodies, fenders, The finishing lacquer, properly thinned, is sprayed, usually wheels, and chassis. For the top coats on bodies, nothing has in 3 or 4 double coats. Force-drying between coats from 5 to appeared on the market to dispute the supremacy of lacquer, 15 minutes a t 100" to 125" F. (37.8' to 51.7" C.) is helpful in although the primer and surfacer coats are usually oil type, producing a smoother finish. with or without synthetic resins. For fenders, black enamel The application of a certain number of coats of lacquer with a high percentage of thinner is preferable to a fewer number of 1 Received September 10, 1931.
