1、ULTRAVIOLET REFLECTANCE OF PAINT AMERICAN WELDING SOCIETY I ULTRAVIOLET REFLECTANCE OF PAINTS O. A. Ullrich and R. M. Evans August 6, 1976 BATTELLE Columbus Laboratories 505 King Avenue Columbus, Ohio 43201 ULTRAVIOLET REFLECTANCE OF PAINTS APPENDIX to MONTHLY LETTER REPORT to AMERICAN WELDING SOCIE
2、TY by O. A. Ullrich and R. M. Evans from BATTELLE Columbus Laboratories August 6, 1976 INTRODUCTION Of importance in assuring safety in the welding environment regarding ultraviolet radiations is the ultraviolet reflectance of walls and objects in the welding area. Preliminary to making recommendati
3、ons concerning reflectivity or embarking on a program of measurement is the collection of data already available. made for data on the ultraviolet reflectance of paints, resulting in the compilation constituting this report. generalizations have been made, this report is not intended to be a thoroug
4、h analysis of the subject. Toward this end, a search has been Although some observations and The search for data dealing specifically with paint reflectance has yielded relatively little concerning commercial paints for interior use. Hence, data also were collected on the UV reflectance of outdoor p
5、aints and W optical properties of materials used as ingredients in paints, i.e., pigments, binders, drying agents and other constitutents. Some laboratory work was done to supplement the meager findings for indoor paints. 2 BACKGROUND When radiation strikes a surface, a very small portion of it refl
6、ects without entering the surface at all, the amount being dependent on the index of refraction of the surface. Unless pigment particles protrude, the surface is made up of the binder constituent of the paint. The refractive index of these materials in the wavelength region from 200 to 800 nm genera
7、lly falls in the range from 1.4 to 1.7. These indices can give rise to a single- surface reflectance of from 4 to 8 percent. Surface reflections will be “white“; that is, they are not wavelength selective, because they have not entered the paint layer and thus have not been subjected to the absorpti
8、ons that give rise to the characteristic color of the pigment. The greatest contribution to reflection for a paint, whether in the visible or the W, arises from multiple reflections involving pigment particles within the paint layer, even though the binder may be relatively absorptive. Usually the b
9、inder layer between the paint surface and the pigment particl-es is so thin that the absorptivity has relatively little effect. If the pigment is not too strongly absorbing, much of the radiation which enters the pigment particles may be scattered back out of the paint layer. Colors arise because of
10、 the spectrally selective nature of the optical absorptance of the pigment particles. A diffusely reflecting, or matte, surface will avoid shiny, specular reflections and thereby be advantageous in some cases, but does not reduce the overall reflectance of a paint which contains pigments that strong
11、ly scatter and reflect UV radiation. SOURCES AND ORGANIZATION OF DATA Data for this review have been collected from journal articles, books, special reports, and private communications. Seven journals specific to the paint industry were reviewed, primarily through the National Paint, 3 Varnish, and
12、Lacquer Association Abstract Review back through 1945; also, an abstract service of the International Institute of Welding was searched. A total of 28 references were found to contain information of at least some relevance. Further, phone calls were made to several paint and pigment manufacturers, b
13、ut these resulted in no specific information on W reflectance of paint. One of these calls led, however, to an offer to measure a limited number of paint samples. The W data collected have been organized in four categories: (1) Reflectance of paints (Plates 1 through 49) (2) Reflectance of pigments
14、(Plates 50 through 59) (3) Reflectance or absorbance of resins and other vehicle constituents (Plates 60 through 69) Reflectance characteristics of other materials that might be present in the welding area. This material was not sought specifically, but was found in the course of following leads on
15、paint reflectances. (Plates 70 through 91) (4) Much of the data presented here derived from work done 30 to 50 years ago; some derive from work done on satellite temperature control as part of the space program within the past 15 years. Indexes of I - Paints, II - Pigments, III - Binders, and IV - M
16、iscel- laneous Materials are provided at the end of the report. References References for data included in this compilation are listed after Plate 91 and are designated throughout by the underlined letter at the right of the figures and tables. Many of the references contain much information about v
17、arious aspects of paints, pigments and vehicles but relatively little specific to W reflectance of paint or paint constituents. For conciseness, only the most 4 relevant data were extracted, generally in the form of a figure or a table. When possible, the figure numbers or table numbers and captions
18、 given in the original reference have been copied to facilitate locating the information more easily. (Some of the references have hundreds of figures and tables.) The inclusion of original-source figure numbers has necessitated identifying the figures in this compilation in some other way, hence th
19、e use of plate-number designations. Use of Data This compilation of W-reflectance data for paints and paint constituents is not intended to be an exhaustive study, but it should provide a broad base of data to aid the AWS Radiation Committee in deciding what further information is needed. However, i
20、t also could provide specific infor- mation for immediate use. For example, if a complaint is received about a certain painted wall reflecting erythemal radiation to a dangerous degree, and the paint is known to consist primarily o zinc oxide in a Silicone binder, rcfc!r(w.c to Pl;itc 5 woiiltl show
21、 that such il paint would bc expected to reflect less than 10 percent of the incident radiatioq in the erythemal range. Such quantitative information might quickly guide one to look for a more likely cause for the complaint. DEFINITIONS OF TERMS The erythemal spectral region, in which radiation caus
22、es a quickly noticeable reaction on the skin and cornea ofeye (ultraviolet erythemal and ultraviolet keratoconjunctivitis, respectively), is considered to cover the range from 200 to 315 nanometers. Because the original forms of the data have been preserved as they are presented in the original refe
23、rences, a great diversity occurs in the units included in this report. Following is a tabulation of units, with definitinc, equivalents, and conversion factors: 5 1. Wavelength, X : Nanometers (nm) or millimicrons (mp) Angsirom (A, or A.U.) Micrometer (um), or micron (u) Wave number: the reciprocal
24、of the wavelength expressed in 1 nm = 1 mp = 10-9 meter (m) i A = 10-10 m = 10-8 cm = 0.1 nm O cm, giving optical vibrational cycles per cm. 2. Reflectance: the fraction of incident radiation that is reflected from a surface; e.g., if 1/2 of the radiation is reflected, the reflectance is 0.5. 3. Spe
25、ctral Reflectance is a more specific term indicating that reflectance has been measured point by point through the radiation spectrum (rather than averaging it over a relatively wide spectral band, such as the entire visible range or the band from 280 to 320 nm e.g., Plate 511). 4. Reflectivity (loo
26、sely also called reflectance, reflection, reflection factor, or coefficient of reflection): reflected radiation in terms of per cent; e.g., if 1/2 of the radiation is reflected, the reflectivity is 50 percent. 5. Transmittance, T: the fraction of radiation transmitted through a material. 6 Transmiss
27、ion: transmittance expressed in percent. 7. Absorbance: the fraction of incident radiation that is absorbed. However, in Reference U, Plate 63, absorbance is defined as A = loglo , which is the present-day definition of optical density. 1 8. Absorptivity: absorbance expressed in percent. 9. Absorpti
28、on Coefficient, a: a property of a substance denoting the degree to which radiation is absorbed; it is usually designated a, and is related to transmittance as follows: -ut -e I T=- 9 6 where T is the transmittance, I is the intensity of radiation transmitted, I is the intensity of radiation enterin
29、g (equivalent to incident radiation minus reflectance), e is the base of natural logarithm system, t is the thickness (usually in cm), and a is the absorption coefficient (usually in -). In present-day terminology, ci should not be confused with other similar optical quantities such as K (kappa) - a
30、bsorption index, and k - extinction coefficient. However, Stutz (1927) called absorption coefficient K, and used 10 as the logarithm base; the form of his equation thus is I = I where t is in cm. 10. Extinction Coefficient, k: a means of expressing the ability of a body to absorb radiation, related
31、to absorption coefficient by the expression: O 1 cm O 4n k a=- O A where a is the absorption coefficient and X is the wavelength at which the absorption measurements are made. In another form: O -4 k/ Ao I=Ie O In reference Q (Plate 62), extinction coefficient is denoted K, and is defined as I = I ,
32、 where c is the concentration of the absorbing constituent of a transparent solvent, grams/liter, 2 is the cell length in cm, and the logarithm base is 10. O-K R O SUMMARY OF MOST-PERTINENT DATA COLLECTED Generalizations It appears that almost any present-day paint, white or colored, is safe to use
33、in the welding environment from the standpoint of low reflec- tance of the UV. The principal reason for this is that most present-day paints contain up to 50 percent or more Ti02 as a pigmenting agent, and Ti02 has very 7 low reflectance at wavelengths shorter than 360 nm. Furthermore, with the exce
34、ption of turquoise blue , all colored pigments for which data were found also have very low reflectance at wavelengths shorter than about 310 nm. This generalization covers more than 30 pigments and dyes. * Singular exceptions to this generalization about the UV safety of paints are paints containin
35、g a significant proportion of metallic particles, particularly aluminum flakes. In such cases, reflectance can be as high as 50 or even 75 percent at wavelengths through the visible and ultraviolet to 220 nm, and thus should be avoided in the welding environment. Nonmetallic pigments identified as h
36、aving reflectances greater than 50 percent in the W, ranging from the visible to Wavelengths shorter than 290 nrn are listed below. Chemical Symbol Common Names MgO CaCO 3 Ca (OH) 2 Sb203 Bas04 (See below) A1203 2Si02 2H20 Ca/Mg Silicates s i02 PbC03 and Pb(OH)2 Bas04 - 70 percent ZnS - 30 percent m
37、agnesium oxide; magnesia calcium carbonate; whiting; precipi- kalsomine; calcimine; slaked lime antimony trioxide barium sulfate; barytes terra alba (any of several white tated chalk mineral substances: gypsum, kaolin, magnesia) china clay asbes t ine Silex; quartz sublimed white lead, apparently al
38、so termed basic carbonate white lead when in “pur er“ form lithopone * Turquoise Blue - a hydrated aluminum phosphate, A(OH)POI,HO. 8 Chemical Symbol Common Names The following, chief constituents in the material having the common name “terra alba“, also have high UV reflectance: MgCo3 magnesia alba
39、 A12Si205 (OH) 4 kaolinite gypsum; alabastine; hydrated calcium sulfate; plaster of paris This list includes materials often used as walls or wall finishes, such as plaster and calcimine, which should be avoided from the standpoint of high W reflectance. Various references indicate that relatively s
40、mall percentages f an absorbing pigment have, because of the multiple light-scattering nature of pigment layers, a strong effect on the reflectance of the composite layer. For example, only 5 percent of zinc oxide in white lead can reduce the reflec- tance at about 315 nm from 70 percent to 20 perce
41、nt, and a 30-percent content reduces the reflectance to about 5 percent (Plate 53). Zinc oxide is non- reflective at wavelengths shorter than about 360 nm. In addition to UV absorption provided by the pigment component in paints, absorptive binder resins also can contribute, to some degree, to low r
42、eflectivity; among these are alkyds, urethanes, and epoxies. On the other hand, resins and binders such as acrylics, vinyls, silicones, casein and nitrocellulose, because they are not greatly absorbing in the erythemal UV, would not contribute significantly to low UV reflectivity In fact, Bas04 in a
43、 polyvinyl alcohol binder may have a reflectance as high as 80 percent at 230 m, 95 percent at 290 to 340 nm (Plate 14), and even higher reflectance in the near W and visible. I Ultraviolet radiation often has the effect of causing transparent organic materials to become yellow with exterided exposu
44、re. Yellowing is the result of increased absorption in the blue and blue-green portion of the visible spectrum, and is usually (if not always) accompanied by increased UV 9 absorption. Thus, the generalization could be made that if paint degradation takes place as a result of welding-arc exposure, i
45、t will be accompanied by a safer UV-reflectance condition rather than a more dangerous one. of oil-based paints also is induced by classes of materials such as (i) ammonia, ozone, and sulfur dioxide, (2) amides, amines, acid salts, peroxides in paints that contain drying oils, and (3) various driers
46、 that contain cobalt, lead or manganese, or pigments such as titanium dioxide. Yellowing A more thorough review of the data given in this report and of the references cited no doubt would reveal further inferences and generalizations pertinent to UV reflectance of paints. Data on Paints The principl
47、e sources of data on the W reflectance of paints using modern binder resins were reports concerning the space program, where interest was centered on degradation of the reflecting properties of high-reflectivity paints when exposed to charged-particle bombardment. Data of value for AWS, for example,
48、 are the preirradiation curves of Plates 1 through 5. Plates 1 through 27 present data from the literature and include the following formulations; those showing reflectances greater than 10 percent in the 240 to 320 nm spectral range are marked with an asterisk: Pigment Binder ZnO Silicone; K2Si03 Z
49、n S Silicone; Acrylic; K2Si03 Ti02 Silicone; Alkyd *CaCO 3 Silicone *MgO Silicone; Acrylic; Alkyd/Melamine *PbCOj/Pb (OH) 2 Silicone; Butylacrylate; Butylated Urea formaldehyde; Nitrocellulose *Bas04 10 Pigment Bind er *Al203 *Sb2O3 *Al flake *Various K2Si04 K2SiOQ Silicone Various (Plate 23, Luckiesh and Holladay, 1931) Also included are numerous paints identified by color but not by either specific pigment or binder, some of which show erythemal-band reflectance greater than 10 percent (Plates 17 through 20, and 25 and 26). Plates 28 through 49 are spectral reflectance curves,
