Document MM8qQYOQKrMknxQQBnzq89p49

e CC: TO liSilL LABOBATOBT Li J. ..XIiff, Lab. R. Morgan Lab. P. B. Evans, Lab, p.Robinson, Lab* S. C. Horning, Lab. J, H* ioisfill, Lab . E. B, Eita%brald, Lab. H. L. Wagner, Lab, (3) * Pile: : $658 Marshall Laboratory July* if, 1952 :*Su23'52 MEMORANDUM REPORT HO. M-480 siifefe -4 V Lf LITERATURE SURVEY ON ACCELERATED WEATHERING Introduction: This report consists of two partsj the first Is a critical summary of the literature on accelerated weatherring published Since about 1922, with special emphasis on the more recent papers; the second consists of a brief summary of each of the more .interesting papers, A complete list of references follows the report. At present a paint product is evaluated by exposure to the elements in one or more localities for an extended period of time, usually at least six months. The importance of shortening' this time between formulation and evaluation need hardly be emphasised in this discussion. Summary* Beginning in 1922, B, A. lelson, at times in collaboration with F. C, Sehmutz and D. L. Gamble, published the results of some of the first systematic work on the subject' of accelerated weathering. Since then many papers on the. subject have appeared, but the problem has not yet been solved, completely. It is difficult to arrive at any basic conclusions from the extant literature* The procedures have to a great extent been necessarily empirical, particularly with respect to the measurement and evaluation of film deterioration. There are hardly any ways of measuring appearance variables quantitatively, except for gloss. Consequently the attempt to correlate the results of outside exposure with accelerated exposure has been handicapped not only by the intrinsic difficulties of CCfrCPN weather* duplication but also by the lack of the proper tools for evaluation. This fundamental difficulty probably accounts In large part for the disagreement among authors presumably working in the same way. Another fundamental difficulty is the lack of reliable information on the results of outside weathering, This information Is difficult to obtain for a number of reasons, the most important being the fact that the results vary with season and year, it appears necessary to settle on some average weather, or perhaps an extremely deleterious weather as a standard, and the weathering apparatus should be designed to duplicate the effects of such weather. This might be done for several localities. Films fall in several ways, the principal ones being loss of gloss, checking or cracking and blistering. Loss of gloss is perhaps best considered as an erosion, whereas checking and blistering are associated with physical or mechanical failure. The film may crack because the accumulated stresses in the film have exceeded its cohesive forcesi it may blister or flake away because of the failure of the adhesive forces between film and substrate. The stresses to which a film is subject are due to such things as volume changes caused by physical and chemical reactions involved in drying and weathering, swelling of th@- film and differential swelling between film and substrate, and the differential expansion of film and substrate due to temperature changes. Since fresh paint films are quite distensible the weathering process must modify, chemically or physically by agents such as water, light and heat, the elastic properties of the film. When the film is thus modified further stresses are applied which cause breakdown, To devise a satisfactory laboratory accelerated procedure it is first necessary to identify the variables of the natural weathering process and so increase their intensity so that breakdowns will occur in the same way as in natural weathering. Some authors have attempted to do this by a careful determination of the intensity of the natural factors and then intensifying all the artificial one proportionately. This is very difficult and has probably never been accomplished! the fact that there is no artificial light source at present which has exactly the same spectral distribution as sunlight is one reason why exact duplication is difficult. But evep i^* escact duplication were possible it still might not be satisfactory. The consecutive stages of the overall reaction of weathering will probably not respond linearly to variation In intensity of the weathering factors, or perhaps one stage may be so much slower than the rest that It becomes rate controlling, thereby distorting the entire breakdown process. Consequently it will probably be necessary to arrive at the correct combination of weathering agents principally by trial and error. The main discernible variables in the process of natural DUP030003404 -3~ weathering are; (a) Radiation of the sun of which the ultraviolet portion (down to about 2900 A) is most significant. (b) water (c) Temperature and temperature changes There are other probably less important factors involved such as acidic gases- (in industrial atmospheres), dust and dirt, mildew, etc* Gay (57) has summarised some conclusions deduced from a survey of previous work on accelerated weathering, it is evident that although numerous cycles have been devised, there is no systematic data available regarding the behavior In the various cycles of a common range of paints of defined outside behavior. Thus there is no firm basis of judgement as to the usefulness of the different cycles. The general conclusions follow? 1. The dominant wavelengths for film breakdown lie in the ultraviolet region between 2900 A and 3100 A. In industrial atmospheres, since wavelengths below 3400 A do not penetrate* an important part of the breakdown must occur by wavelengths greater than 3400 A. 2. Ultraviolet radiation at zero or low humidity produces less deterioration than at higher humidities or in the presence of spray. Spray is more effective than high humidity. 3. Failure by checking or cracking is rarely observed at zero or low humidity, but there is evidence that water treatment after irradiation may increase fine checking. 4. Low pressure oxygen treatment in combination with exposure in the weathering apparatus gave promising indication of correlation in mode of-breakdown by chalking,checking and cracking. io systematic work has been reported on this variable. 5- The application of water Is most effective when it is applied so as to penetrate the film and cause swelling for a long enough time. The purity of the water used in many tests is usually unknown; this may account for many of the variations in the results. 6, There is some evidence that high humidity with dew deposition is more effective than direct spraying of panels, but fine water spray seems to be the best compromise in practical apparatus. 7. The rate of film deterioration attained in combined ultraviolet radiation, water spray cycles Increases with increasing panel temperature over a certain range. The temperature must be controlled to avoid heat polymerization, which with some media DUP030003405 -3r Light is a 30 inch mercury arc 3. V. G* Jolly journal society Chemical Industry 4l, 329 (4933) in the weathering machine used here, the light source consisted of a $0 ampere carbon arc at 75 volts, The cycle consisted of eighteen minutes of light, then 2 minutes of light and cold water-, for 14 hours per day and 10 hours of rest. For a wide variety of clean and pigmented oleoreslnous products, it is claimed that the test gave failure of the same kind and order as with outside exposure. However, no quantitative relationships existed for nitrocellulose formulations, and no correlation of the results was possible, 4. sward and Hart Scientific Section, American paint and Varnish Manufacturing association--^^rriTF^WTTOI"----------------------- ----------- ------*~ fhe results of this work have been mentioned previously in Part l. The low wavelength arcs (therapeutic carbon and uviares) did not cause checking with checking formulations as did the "Weatherometer,, 13 ampere carbon arc and the "sunshine" carbon arc, (and outside exposure) but the paint seemed to erode with chalking. This could be caused by continual washing away of the chalk as it is formed. For materials which fall by chalking the therapeutic and uviares cause more rapid failure than the other light sources. 5- Cincinattl-payton Indianapolis Club Scientific Section, American paint and Varnish Manufacturing The authors found that there is a certain correlation between various sets of outside exposures (same groups of materiala exposed in different sections of the country) and attribute the discrepancies mainly to individual differences and localized climatic conditions, it was also found that some materials tested under various types of accelerated weathering showed a certain corrleation. However, there was very little or no correlation in breakdown between the outside exposure and the accelerated exposure. Five different tests were used, none of which were very similar. The usual cycle consisted of various combinations of light, water temperature and humidity. cm cycle included immersion* in podium chloride solution. ( 5. Cinc-|patt:L"Dayton Indianapolis Club i? Scientific section, paint and varnish Manufacturing Ttmmrxnm--"--~-----t- Humorous cycles cf water spray, light, temperature and humidity were tried. Very many contradictions and Expected results were found, but a few general results were observed. ! DUP030003409 ! 4- may greatly Improve durability or cause decomposition. 55* C. has teen suggested as a maximum working temperature. 8. Hapid temperature changes of wide amplitude result in stresses which cause breakdown after elasticity has been reduced by weathering, sometimes this induces failure toy checking and cracking. 9.; Refrigeration alone has relatively little effect on film deterioration. The main problem in the design of a satisfactory accelerated weathering' cycle is to obtain the correct balance of intensity among the various weathering agents so that overall breakdown is accelerated without distorting the form of/breakdown. It is hoped that with increased knowledge and experience this balance will eventually be reached. MARSHALL LABORATORY HLWscms DUP030003406 ! Abstracts of important papers 1, g. A. Kelson# F, C* Sehmatz, 0. I*. Gamble A. S T. K. proceedings - Vol. 26, p. 563 (1926) Accelerated feathering: Summary: Further Development of Apparatus and Exposure Cycles Conclusions from the study of accelerated weathering have indicated that a flexible exposure system is desirable for obtaining the most satisfactory results. The equipment describee in this paper is "designed to obtain the maximum of flexibility and still be practical for routine testing". The different types of exposure cycles thus made possible are limited only by the number of practical combinations that can be made of the following: 1. bight (Mercury or carbon Arc) (a) At controlled, slightly elevated temperatures (14o f .) (b) With 100 percent relative humidity (c) With less than % relative humidity (d) In an atmosphere charged with active gases as, for example, oxygen. 2. Water Spray 3. Eefrigeration (Temperature Changes) The introduction of siliea gel as a dehydrator, which provides for humidity control without necessitating air conditioning by refrigeration, is interesting. The use ofadditional oxygen in the light exposure chamber has facilitated the reproduction of the checking type of failure. The average weather of a given locality is used to determine the weathering machine cycle. The decrease in the intensity of the quartz mercury arc with use varies the effectiveness of the accelerated test. No actual results are presented in this paper. 2. H. A. Nelson and F. C. Schauta Ind. gag. Chen. 18, 1222 ,(25) The authors discuss their apparatus (See proe, A, S* T. M* 26, 563 (26)) and then go into a consideration of some fundamentals governing its applications. t DUP030003407 -2- (1) Heat; aa an auxiliary to light Too high a temperature reduces distensibility too greatly for correlation With normal weathering. Low temperatures reduce rate too greatly, (2) Humidity '* Light acting upon water soaked film Is the most destructive weathering combination. nevertheless, most failure is accelerated by high humidity followed by low humidity exposures. weakening In film caused by high humidity shows up when it has less dlstensibillty In less humid situation. (3) Special Atmospheres with Light Exposures increasing oxygen content from 21 to 30 percent increased checking markedly, in addition generalised acceleration was found. In pure oxygen the acceleration was extremely marked. (4) water spray washing Hot much actual acceleration of the deterioration process can be obtained in the water spray washing exposures representing rain. The author distinguished this from effect of humidity. (5) Temperature changes Materials of low original dlstensibillty are very severely affected by stresses and strains resulting from temperature change. Any system involving an excessive number of temperature changes Is especially severe on finishes of low distensibility, small temperature changes may be effective if a critical distensibility is reached. Weathering Cycle Used Monday Tuesday Wednesday Thursday Friday Saturday Sunday to Monday Refrigeration 0F. Water 90q f . Light l40F, (30$ 02) water Ref. Light (30# oxygen atmos.) Ref. Light (30# oxygen atmos.) water Ref* Water , Light (30# 0g atmos.) Ref, Water Light (30# 0g atmos.) Ref. Water Light (30# Cg atmos.) Light (30# Og) 2 hrs . 3 hrs. 18 (16 wet, 2 dry) 3 2 18 (X6 wet, 2 dry) 3 (wet) *Lq 2 230 2, ll (wet) 2 3 15 27 (24 dry, 3 wet) DUP030003408 -5- A brief historical review of accelerated weathering development is given and the limitations and valuable uses of the accepted methods of testing are described. An apparatus has been built with which some of the more important features of ''weather*1 can be varies .g., intensity and time of ultraviolet irradiation, amount of mater treatment and period of revolution of the test drum. Attempts to increase the rate of polymer degradation by treatment of paint films with oxygen at elected pressures to accelerate its diffusion into the films have given promising results, Films subjected to the oxygen pressure treatment described have broken down in a manner comparable with that obtained outdoors. There are indications that a study of the oxygen concentration variable will provide one of the most hopeful developments in durability testing procedure.for paints, a Company Literature 10* Denningt?>n, r . f . Imperial Chemical industries, xmt. l^^rcn~ang^^viIop^ivr^p^7^eport The ffiachin consists essentially or a board moving vertically to which the panels under test are fined and which faces In turn a cold box, moist, hot box and an ultraviolet lamp, .As set up at the time, the panels were subjected to the same period xr:#a@h eouoitioa* The results' indicate that long periods in each condition (50 minutes at each station la th; order cold-hot and moist-ultraviolet) emphasised chalking while short periods (7 minutes, same order of stations) in each condition emphasizes cracking. When the order of the conditions were changed {order'ultraviolet* hot and moist-cold) the type of cracking changed# 11. o. b . weeeott ffLggg*jCgi-l|^g.sBlvlgtog. ghlla...Mb.31/22/39 II Research Report #680 Work with carbon-arc instruments has been so limited that no definite conclusions cun bo drawn. The earlier work showed that they -offer possibilities for obtaining relative checking resistance. The present'study has shown that differences' In the chalking characteristics can be detected and appear in the same general order as produced by -normal exposure, but are not of the same magnitude. possible uses for the carbon arc Instruments are (1) indication of color retention or chalking characteristics where time is a factor, (2) breakdown of short oil enamels where sales needs require urgent action (3) evaluation of material from new sources of supply versus an .established standard (4) check on customers' or competitors' claims based on information obtained with accelerated units. DUP030003411 1. Mercury arc caused faster breakdown than carhcn arc, particularly chalking. $ 2. The mercury arc alone causes chalking and dulling, but no checking, 3* Salt spray alone is not a very useful indication of overall durability. The same may be said foriafrared exposure. 4. The combination of salt spray, light and water does result In checking, 7* Cleveland paint and varnish production Club Official Digest, Federation of paint and Varnish production CTuEa^gTS;' -- ------ --------- :----------- ~* This report may best be summarized by the conclusions the authors arrived at concerning the operation of weathering machines to obtain check results between exposures for a known time in Miami and the machines. Four basic recommendations are made. The water supply must be treated for purity, comparatively long water exposure is necessary, and a maximum temperature of l45F* must be maintained for at least one-half of the total radiation houts to duplicate results of Florida exposure. The machines used in the test were generally of the commercial Variety. At the time this report was written, a good correlation had not yet been found among the machines or between any of the machines and Florida. 8, Fancutt, F. Paint Technol, 14, 159, 106-11 (19%) The author claims that better correlation between actual and accelerated weathering of paints and varnishes has been achieved by means of a new test cycle. Earlier discrepancies were reduced or eliminated by the use of sraasoa spray, and this was later replaced by a procedure involving SO2 in the humidified test chamber. The machine ultimately evolved exposed the paint to ultraviolet light, water, and a warm saturated atmosphere into which SO2 is passed. Different cycles are used to correspond with rural, industrial, and highly corrosive conditions, 9, flay, P. J, Journal of oil and Colour Chemists Ass8n. 34-43 (51) "Tgceljggggr^ Films" The breakdown of paint film during weathering is due to degradation of their polymer structure so that they can no longer, accomodate the physical stresses resulting from temperature changes and water absorption. Accelerated weathering seeks .to hasten the polymer degradation and impose physical stresses of a high order. DUP030003410 6- - Uhe disadvantages are (1) limited space (2) unable to produce low temperatures which are likely to cause flaking end peeling as on galvanized metal finishes. They do not yield information on mildew sad dirt collection, stain resistance, jHHidh is especially necessary xor douse paints. 12. R. E. Pike Results of Exposure Study series Ho. 91kk August'Triw----rTM1------------ No report issued. 13. Baltimore ^ pigments Dept, Work ,,/ The Pigments Department finds that the commercial type of Instrument gives good correlation with Florida results except in a small percentage of the cases, without further work it is impossible to say what these discrepancies are due to -- iron contamination m the water is a possibility. The data are now on rlie with us * DUP030003412 Appendix. Period 1922-1929 X* Nelson, H. A., Proc. A. S. 3?. M., 1922, 22, Pt. 2, 485-98. Accelerated Wea^erlnl^of^aints on Woocflhd Metal surfaces. 2. Nelson, H. A., N, P. VJL., Sci, sect. Giro., 1923, No. 184 Recent progress'~6nnvestlga,slonB on Accelerated Weathering of paints and varnishes 3. Nelson, H. A., and Scbmutz, y. c, Proc. A.*S. T. M., 1924, 24, Pt. 2, 920-42. Further Study oriccelerateot Weatherings Effect of Variations in Exposure Cycle Combinations on Common types of varnishes 4. Gardner, h . A., N. P. V. L, sci. sect. cire. 1925, No, 226 Accelerated testi^WXiiets --... ........... 5. Nelson, H. A., Schmutz, P. C., and Gaulle, D. L. proc. A. S. T. M., 1926, 26/ Pt. 2, 563-75 ----- ~~ Accelerated weatherings Further Development of Apparatus and Exposure cycles 6. Nelson, H. A., and schrautz, F. C. Ind. Eng. chem.* 1926, 18 1, 222-7. Accelerated weathering 7. Schmutz, F. C., and Gamble, D. L. ind. Eng, chem., Anal. Ed. 1928, 1, 83, Studies of DestructivFT^HF^oSrces^or^sr^ in Accelerated Weathering systems. 8. Gardner, B. A., N. P. V. L. Sci. sect, Circ., 1928, No. 323 New Accelerated o|MWlSar----- ~----- 9. Ritter, E., Korrosion and Mefcalischutz, 1929, 5, 64. , Testing of paints k 10. Nettmann, p,, Farben 2tg., 1929, 34, 1, 554-5 A New Accelerated test for paints 11. Wolff, H., Farben ztg,, 1929, 35, 192-5. Length of Life paints - tests and Theis* interpretation period 1930-1934 12. Came, c. L. Bureau of standards. J. of Research, 1930, 4, 247-59. Durability tests of 50 Spar Varnishes 13. Schmufcz, F. C., and palmer, Ind. Eng. Chem, 1930, 22, 84-7 Drying of Exterior paints Conditions and over Different Woods 14. N, P. V, L,, Sci. -Sect7 Oirc. 1931, No. 4ofy, p. 473-8 DUP030003413 32. Each, W, Runstoffe, 32, 9 02) 33 Elgnsbergen> J. p. H. van, Verfkronlek, 1942, 15, Mo. 83 138-42; No. 9,148-52. AccelerS^TSM Other Weathering Tests for Modern paints and Lacquers 34. Arth, H. G., A, S. T. M. Bull, 1942, NO* 116, 9-17 Results of QueBtioni&ire^ on " Accelerated Weathering 35. Kittelberger, H. W., Xnd. Eng, cheat., 1942, |4, n o . 8, 943-8 Water immersion Testing of Metal protective paints 40. Pittsburgh production Club, paint. Oil Chem. Rev., 1943, 106, No*. 10, 78-9. Correlation bf 'th,e,,,l!fiilrercts "of Varying 5TTmat:Lc Conditions in Typical House paints and Exterior Enamels. * 41. prinkley, P. G., and Harp, D. P*, J. Oil Col. Chem. Assoc,, 1944, 27 No. 291, 167-187j The LiSKttatSons 'oTUofial' 'ahcT~ Accelerated weathering panel Tests 42. sward, 0, G. N. P. V* L, Circ., 1944, No. 671. Accelerated Weathering TeftFUnO. B. Government paint Specifications 43* Matlork, R. w., A. S. T, . Bull, 1944, Nc*. 131, 34-6 44. Darsey, V. M*, A, S, T. M. Bull, 1944, No, 128, 31-4 45, Parker, D. H., and Scofield, P., off. Dig., 1944, No, 236-220-26 Correlation of Accelerated weathering with Exterior Exposure of oil Type camouflage paint 46. Butcher, j, p. and Raekham, E. H., Paint Nanuf,, 1944, 14, No; 12, 344-7, photo Micrographic Method of Forecasting^ Behavior of paint Films 47, A. S. T* M. Specification (1946), Designation;, D822-46T, 1946, r2i"T76X47^eHtaWv^SecdraB^nded Practice of operating Light and water Exposure Apparatus (carbon-Are Type) for Testing paint, varnish. Lacquer and Related products 48, Burns; R, M.> md^ Eng. Chem., Anal. Ed., 1945, 17, No. 5, 299-302 ------ ""----------^ 49. Kettering, C. F., A* S. T. M, Bulletin, 1945, No. 137, 15-18 50. Cleveland Paint and varnish production Club, Off. Dig., TSTthe Cleveland club Area, Pt. 1. 51. Cleveland paint and varnish Production Club; Off, Big. 1945 No. 262, 518-34. Weathering Machine correlation 'mT"the Cleveland Club Area, part 2. DUP030003415 -a- 15. A, S,T. n,a Prop. 1931, 31, Pt. 1, 511-14. report of Ian Accelerated Weathering Wests 16. A. S. T. M. Proc. 1932, 32, Pt. 1, 452-5. Report of Sub committee on AcceleratecTWeatherlng Wests 17. Clnclnattl, Dayton, Indianapolis Paint and Varnish production Club. N, P, V, I>, Sol. Sect. Circ. 1932 18. Gardner, H. A. Ind, Eng. Chem., Anal. Ed., 1932, 4, 94-7 Rapid Exposure WsfsPoa Plnlhhd '' ' *" 19. A. S, T. M.i Proc., 1933, 33, Pt* 1, 379-35. Report of Sub-C;oimlttee non Accelerate Weathering wests 20. Jolly, V. G., J. oil Col. Chem. Assoc*, 1933, 16, 366-83 Accelerated weathering of faints" and Varnishes 21. schuk, A. E., and Theurer, H. C., Ind, Eng. Chem., Anal. Ed. 1934, 6, No. 2, 91-7. Physic^i^al^ation ofHHIsEei Period 1935-1939 22. A. S, T, M., Pros. 1935, 35, Pt. 1, $97-9. Report of Sub-Cctamitiee on AccoTeraWd Weathering Tests 23 A. S, T, M., Proc. 1936, 36, Pt. 1, p. 366-82, Report of SublC61amittee^`bn`AcceleraWd Weathering Tests for protective Coatings 24. A. S. T, M,, Proc. 1937, 37 Pt. 1, 350-2. Report of Sub-Cbiaarttee on"Accelerated Weathering of House Paints period 1940 to present 25* A, S. T. M., Proc., 1940, 40, 282, Report of Sub-Committee on Acceleratemeatherlng Wsts 26. A. S. T. M., Proc., 1940, 40, 289-94, Report of Sub-Committee oh 'AcceleratebTWa thering of Enamels 27. Jolly, V. Q. J, Oil Col. Chem, Assoc. 1$)40, 23, Wo. 246, 356-63 , RellaM'ritF^f^c^erior Exposure Tests on Paints and Varnishes * 28. Ashrnar, G. W,, Ind. Eng, chem. 28, 934 (1936) panel Test Evaluation of Exterior House paints 29. Wirshing, R. J., 2nd. Eng, Chem., Ind* Ed., 1941, 33, No. 2 234-7. Some causes ' * 'i 30. Qllenger, 0. G., Paint, oil Chem, Rev., 1941, 103, No. 6, 9-12. AccelerateoTfestlH|" 31. Blom, A. V* Verfteonlelc 1931, 14, No. 12, 246-8. Accelerated W^fHering~bf palntTpilms DUP030Q03414 52. Wheeler, a, n ., J. oil Col. Chen. Assoc,, 1946* 29, Ho. 314, 171-181. Short~ferm Vjeat;fiering l'es^ as a Criterion of performance 53. Cooke, T. p. and yickiund, a. e . ind. Eng. Chera., Anal. Ed., 1946, X-Ho. 1, 59-6. Tropical Testing XimmFer " T"T 54. Thomas, B, E., Am. Dyestuff Reptr., 1946, 35, 280-2. Soma Pitfulls in Accelera'tecrWa^ng'' 55. Gardner, H. A, physical and chemical Examination of paints. Varnishes, Lacquers^ancf Colotigs; Wnt'h BflVrPff'' .... ' 56. Fancutt, F. paint Technol, 14, 159, 106-11 (1949) 57. Qay, P. J. j. oil and Colour Chemists Assn. 34j 43(51). Accelerated Wel^HeFihg' of paint"ah3,n^Wi^ir*'pilnis 58. Armstrong W. if. B., and sohierholta 0. J. Can, chemical process rad. 34, 735-41 (mo .) 59. Hill, Roy W., Cook, George.S., Moyer, w E. A, S. T. M, Bulletin, 164, 32-4$ (50) 60. Wlrshlng, R. j., and McBfaster. W, D. paint and Varnish production 41, Mo. $. DUP030003416