Coatings Technology Handbook 2010 Part 3 docx

Sunlight, Ultraviolet, and Accelerated Weathering 12 -3 of cycles, or the reproducibility of results. For simulations of direct sunlight, artificial light sources should be compared to what we call the “solar maximum” condition: global, noon sunlight, on the summer solstice, at normal incidence. The solar maximum is the most severe condition met in outdoor service, and, as such, it controls which materials will fail. It is misleading to compare light sources against “average optimum sunlight,” which is simply an average of the much less damaging March 21 and September 21 equinox readings. In this chapter, graphs labeled “sunlight” refer to the solar maximum: noon, global, midsummer sunlight. Despite the inherent variability of solar UV, our measurements show surprisingly little variation in the solar maximum at different locations. Figure 12.3 shows measurements of the solar maximum at three widely varied locations. FIGURE 12.2 Seasonal variation of sunlight UV. FIGURE 12.3 Solar maximum at three locations. 400380360340320300280260 1.2 1.0 0.8 0.6 0.4 0.2 0.0 Wavelength (nm) Irradiance (W/m 2 /nm) December June March Equinox 400380360340320300280260 1.2 1.0 0.8 0.6 0.4 0.2 0.0 Wavelength (nm) Irradiance (W/m 2 /nm) Kitt Peak 6/86 Cleveland 6/86 Miami 6/87 DK4036_book.fm Page 3 Monday, April 25, 2005 12:18 PM © 2006 by Taylor & Francis Group, LLC 12 -4 Coatings Technology Handbook, Third Edition 12.3.1 The Importance of Short-Wavelength Cutoff Photochemical degradation is caused by photons of light breaking chemical bonds. For each type of chemical bond, there is a critical threshold wavelength of light with enough energy to cause a reaction. Light of any wavelength shorter than the threshold can break the bond, but longer wavelengths of light cannot break it, regardless of their intensity (brightness). Therefore, the short-wavelength cutoff of a light source is of critical importance. For example, if a particular polymer is sensitive only to UV light below 295 nm (the solar cutoff point), it will never experience photochemical deterioration outdoors. If the same polymer is exposed to a laboratory light source that has a special cutoff of 280 nm, it will deteriorate. Although light sources with spectra that include the shorter wavelengths produce faster tests, there is a possibility of anomalous results if a tester has a wavelength cutoff too far below that of the material’s end-use environment. 12.4 Arc-Type Light Sources 12.4.1 Enclosed Carbon Arc (ASTM G 153) The enclosed carbon arc has been used as a solar simulator in accelerated weathering and lightfastness testers since 1918. Many test methods still specify its use. When the light output of this apparatus is compared to sunlight, some deficiencies become obvious. Figure 12.4 compares the UV spectral energy distribution of summer sunlight (solar maximum) to that of the enclosed carbon arc. The UV output of the enclosed carbon arc primarily consists of two very large spikes of energy, with very little output below 350 nm. Because the shortest UV wavelengths are the most damaging, the enclosed carbon arc gives very slow tests on most materials and poor correlation on materials sensitive to short-wavelength UV. 12.4.2 Sunshine Carbon Arc (Open Flame Carbon Arc: ASTM G 152) The introduction of the sunshine carbon arc in 1933 was an advantage over the enclosed carbon arc. D filters). While the match with sunlight is superior to the enclosed carbon arc, there is still a very large spike of energy, much greater than sunlight, at about 390 nm. A more serious problem with the spectrum of the sunshine carbon arc is found in the short wave- shows solar maximum versus sunshine carbon arc between 260 and 320 nm. The carbon arc emits a FIGURE 12.4 Enclosed carbon arc and sunlight. 400380360340320300280260 12 10 8 6 4 2 0 Wavelength (nm) Irradiance (W/m 2 /nm) Enclosed Carbon Arc Sunlight DK4036_book.fm Page 4 Monday, April 25, 2005 12:18 PM © 2006 by Taylor & Francis Group, LLC Figure 12.5 plots the UV SED of summer sunlight against the SED of a sunshine carbon arc (with Corex lengths. To illustrate this, a charge of scale is necessary to expand the low end of the graph. Figure 12.6 12 -6 Coatings Technology Handbook, Third Edition Another type of xenon arc filter that is intended to simulate sunlight through window glass is the Window Glass Filter. It is typically used to test products with a primary service life that will be indoors. Figure 12.8 shows the SPD of noon summer sunlight behind glass compared to a xenon arc with a Window Glass Filter. 12.4.3.2 Xenon Arc Moisture The xenon arc uses a system of intermittent water spray to simulate the effects of rain and dew. The water-spray cycle is especially useful for introducing thermal shock and mechanical erosion. 12.4.3.3 Effect of Irradiance Setting Modern xenon arc models, including the Q-Sun, have a light monitoring system to compensate for the inevitable light output decay due to lamp aging. The operator presets a desired level of irradiance or brightness. As the light output drops off, the system compensates by increasing the wattage to the xenon 2 how these two irradiance settings compare to noon summer sunlight. Several different sensors to measure and control irradiance are available (depending on the manufac- turer): 340 nm, 420 nm, TUV (total ultraviolet), or total irradiance. The difference between these sensors is the wavelength or wavelength band at which they control the irradiance, and the wavelength or wavelength band to which they are calibrated (through a NIST-traceable calibration radiometer). FIGURE 12.7 Xenon arc with Daylight Filter versus sunlight. FIGURE 12.8 Xenon arc with Window Glass Filter versus sunlight through window glass. 400380360340320300280260 1.2 1.0 0.8 0.6 0.4 0.2 0.0 Wavelength (nm) Irradiance (W/m 2 /nm) Sunlight Xenon with Daylight Filter 400380360340320300280260 1.2 1.0 0.8 0.6 0.4 0.2 0.0 Wavelength (nm) Irradiance (W/m 2 /nm) Sunlight through Glass Xenon with Window Glass Filter DK4036_book.fm Page 6 Monday, April 25, 2005 12:18 PM © 2006 by Taylor & Francis Group, LLC burner. The most common irradiance settings are 0.35 or 0.55 W/m /nm at 340 nm. Figure 12.9 shows 12 -8 Coatings Technology Handbook, Third Edition 40 is in the UV-B portion of the UV spectrum, along with some UV-A. This lamp has demonstrated good correlation to outdoor exposure for the gloss retention on coatings 5 and for the material integrity of plastics. However, the short-wavelength output below the solar cutoff can occasionally cause anomalous results, especially for color retention of plastics and textile materials. 6 12.5.2 UVB-313 Lamp (ASTM G 154) Introduced in 1984, the UVB-313 is essentially a second-generation FS-40. It has the same SED as the FS-40, but its output is higher and more stable. Figure 12.11 plots the solar maximum against the UVB- 313 and the FS-40. Because of its higher output, the UVB-313 gives significantly greater acceleration over the FS-40 for most materials. With the exception of the automotive industry, the UVB-313 is the most widely used light source for the ASTM G 154 devices. FIGURE 12.10 Xenon spectrum change due to aging. FIGURE 12.11 UVB-313 and FS-40. 610 660560510460410360310260 1.2 1.4 1.6 1 0.8 0.6 0.4 0.2 0 Wavelength (nm) Irradiance 636 Hours 400 Hours 20 Hours 0 Hours Xenon Spectrum Change due to Burner/Filter Aging 400380360340320300280260 1.2 1.0 0.8 0.6 0.4 0.2 0.0 Wavelength (nm) Irradiance (W/m 2 /nm) Sunlight UVB-313 FS-40 DK4036_book.fm Page 8 Monday, April 25, 2005 12:18 PM © 2006 by Taylor & Francis Group, LLC Sunlight, Ultraviolet, and Accelerated Weathering 12 -9 12.5.3 UVA-340 Lamp (ASTM G 154) The UVA-340 was introduced in 1987 to enhance correlation in the G 154 devices. Figure 12.12 shows the UVA-340 compared to the solar maximum. This lamp is an excellent simulation of sunlight in the critical short-wavelength UV region, from about 365 nm, down to the solar cutoff of 295 nm. Because the UVA-340 eliminates the short-wavelength output (i.e., five output lower than sunlight), which can cause unnatural test results, it allows more realistic testing than many of the other commonly used light sources. The UVA-340 has been testing on both plastics and coatings and greatly improves the correlation possible with the fluorescent UV and condensation devices. 12.6 Conclusions The correlation between laboratory and natural exposure probably will always be controversial. As Fischer had indicated, 7 test speed and test accuracy tend toward opposition. Accelerated light sources with short-wavelength UV give fast test results but may not always be accurate. But, there they are wrong, however, as they usually err on the safe side if they are too severe. Light sources that eliminate wavelengths below the solar cutoff of 295 nm will give better, more accurate results, but the price for increased correlation is reduced acceleration. Users must educate themselves to make this choice. In addition, we should point out that despite many chemists’ fascination with light energy, the spectrum of a test device is only one part of the picture. With any accelerated tester, there are a number of parameters that must be programmed: UV spectrum, moisture, humidity, temperature, and test cycle. Furthermore, the parameters that one chooses are, to a certain extent, arbitrary. No single test cycle or device can reproduce all the variables found outdoors in different climates, altitudes, and latitudes. Consequently, even the most elaborate tester is really just a screening device. Accelerated weathering data are comparative data. The real usefulness of accelerated testers is that they can give a reliable, relative indication of which material performs best under a specific set of conditions. Acknowledgments Most of the data in this paper were originally presented at the Society of Plastics Engineers Automotive RETEC, November 1987. The authors are grateful for the cooperation of Kitt Peak National Observatory, Kitt Peak, Arizona, and Ohio Spectrographic Service, Parma, Ohio. FIGURE 12.12 UVA-340 and sunlight. 400380360340320300280260 1.2 1.0 0.8 0.6 0.4 0.2 0.0 Wavelength (nm) Irradiance (W/m 2 /nm) Sunlight UVA-340 DK4036_book.fm Page 9 Monday, April 25, 2005 12:18 PM © 2006 by Taylor & Francis Group, LLC 12 -10 Coatings Technology Handbook, Third Edition References 1. N. Searle and R. Hirt, “UV SED of sunlight,” J. Opt. Soc. Am., 55 , 11 (1965). 2. CIE Standard No. 20, 19. 3. D. Grossman, “Know your enemy: The weather,” J. Vinyl Technol., 3 , 1 (1981). 4. G. Zerlaut, “Accelerated weathering & UV measurements,” ASTM STP 781. Philadelphia: American Society for Testing and Materials, 1982. 5. G. Grossman, “Correlation of weathering,” J. Coat. Technol., 49 , 633 (1977). 6. J. Dick, et al., “Weathering of pigmented plastics,” SAE Technical Paper No. 850350, 1985. 7. R. Fischer, “Accelerated test with fluorescent UV-condensation,” SAE Technical Paper No. 841022, 1984. DK4036_book.fm Page 10 Monday, April 25, 2005 12:18 PM © 2006 by Taylor & Francis Group, LLC 13 -1 13 Cure Monitoring: Microdielectric Techniques 13.1 The Dielectric Response 13- 1 13.2 Changes In Resistivity During Cure 13- 2 13.3 Summary 13- 5 Developments in the area of microelectronics now enable the fabrication of microdielectric sensors that can analyze drying, curing, and diffusion phenomena in coatings. 1 Several types of microdielectric sensors have evolved in the past few years, the most sensitive being based on interdigitated electrodes and field effect transistors fabricated on a 3 × 5 mm silicon chip. 2 The chip sensor is housed in a polyamide package 13.1 The Dielectric Response The dielectric response arises from mobile dipoles and ions within the material under test. As a coating cures, the mobilities of dipoles and ions are drastically reduced, sometimes by as much as seven orders of magnitude. Microdielectric sensors are sensitive enough to follow those changes and are therefore useful for cure monitoring, cure analysis, and process control. 3 The dielectric response is typically expressed by the quantities of permittivity or dielectric constant (E ′ ) and loss factor (E ″ ): (13.1) (13.2) where ( E 4 – E u )/(1 + wt 2 ) is the dipole term, se 0 ω is the conductivity term, and E ′ = dielectric constant E ″ = loss factors s = bulk ionic conductivity e 0 = permittivity of free space (a constant) ′ =+ − + EE EE u ru 1 2 ωτ ′′ =+ − + E s e EE ru 0 2 1 ω ωτ ωτ David R. Day Micromet Instruments, Inc. DK4036_book.fm Page 1 Monday, April 25, 2005 12:18 PM © 2006 by Taylor & Francis Group, LLC Process Control through Dielectric Feedback • Process Control References 13-5 through Dielectric–Thermal Feedback and configured for ease of placement in various processing environments (Figure 13.1). 13 -4 Coatings Technology Handbook, Third Edition 1. Heat and hold at 250 ° F until a log resistivity of 7.0 is reached (allows for degassing while preventing premature cure). 2. Hold log resistivity (viscosity) at 7.0 until 350 ° F is reached (allows for controlled curing and prevents second viscosity minimum). 3. Hold at 350 ° F until the dielectric reaction rate is near zero (allows reaction to go to completion). 4. Cool and notify operator that cycle has been completed. FIGURE 13.4 Ionic resistivity data and T g during isothermal epoxy–amine cure. FIGURE 13.5 Process control of epoxy graphite cure utilizing microdielectric feedback. 11.3 6.2 Log Resistivity 0 0 40 80 120 160 200 50 100 150 200 250 300 Glass Transition (C) Time (min) Log Ion Viscosity 13 12 11 10 9 8 7 6 5 Temperature (°F) 300 250 200 150 100 50 350 400 450 050100 150 200 Time (min) Hold at 250°F until Ionvisc. = 7.0 Hold Ionvisc. at 7.0 until Temp. = 350°F Hold at 350°F until Slope = 0 Cool Down 1 & 10 Hz 1 K & 10 K Hz Pressure Signal Issued 100 Hz Temperature (°F) Fiberite F-934 DK4036_book.fm Page 4 Monday, April 25, 2005 12:18 PM © 2006 by Taylor & Francis Group, LLC 14 -1 14 Test Panels 14.1 Cold Rolled Steel Panels 14- 1 14.2 Aluminum Panels 14- 4 14.3 Zinc-Coated Steel Panels 14- 6 Surface Preparation 14.4 Handling and Storage of Test Panels 14- 7 Bibliography 14- 7 When performing coatings tests, it is important to make sure that problems with the metal substrate do not skew the test results. Test standards exist for all sorts of coatings characteristics, including adhesion, flexibility, corrosion resistance, and appearance. These standards establish test conditions designed to control variables, which can influence test results. These variables include the method of application, the film thickness, the cure method, and the test substrate. In a controlled laboratory environment, the application method, film thickness, and cure method can be controlled with some degree of precision. In many cases, it is not possible to exercise the same degree of control over the test substrate. For this reason, coatings technicians use standardized test panels when conducting critical tests. A standardized panel is produced from carefully specified material and is prepared in a tightly controlled process designed to yield a consistent test surface that can be relied upon to provide reproducible results from test to test and from batch to batch. There are many different types of standardized test panels available. The requirements for these panels have been described in both national and international standards. These include ISO 1514: Paints and Var nishes — Standard Panels for Testing , ASTM D 609: Standard Practice for Preparation of Cold-Rolled Steel Panels for Testing Paint, Varnish, Conversion Coatings and Related Coating Products , and ASTM D 2201: Standard Practice for Preparation of Zinc Coated and Zinc Alloy Coated Steel Panels for Testing Paint and Related Coating Products . The following is a general description of the different types of test panels included in these standards, along with a discussion of the primary applications and sources of variability for each panel type. 14.1 Cold Rolled Steel Panels There are a number of points to consider when preparing a specification for standardized cold rolled steel test panels. The type of steel selected should be of a standard grade and quality. It is important that the steel be widely available. SAE 1008 and 1010 are examples of suitable grades of steel for test panel production. The steel used should also be free from rusting and staining. Standardizing on a particular grade of steel helps to eliminate variability in the chemical composition that can influence the results of some types of testing. Douglas Grossman Q-Panel Lab Products Patrick Patton Q-Panel Lab Products DK4036_book.fm Page 1 Monday, April 25, 2005 12:18 PM © 2006 by Taylor & Francis Group, LLC Surface Profile • Surface Carbon • Surface Preparation • Applications Surface Finish • Pretreatment • Applications [...]... DK4 036 _book.fm Page 1 Monday, April 25, 2005 12:18 PM 17 Under What Regulation? Arthur A Tracton Consultant 17.1 17.2 17 .3 17.4 17.5 17.6 17.7 17.8 17.9 Introduction 17-1 Code of Federal Regulations 17-1 Title 29 (Labor) 17-1 Protection 17-2 Biocides 17 -3 Testing 17 -3 Volatile Organic Substances (VOCs) .17 -3 Food and Drug Administration (FDA) 17 -3. .. 50 titles, each subdivided into a number of books 17 .3 Title 29 (Labor) In Title 29 (Labor) is section XVII (Occupational Safety and Health Administration, Department of Labor) Under this section is part 1910.1200, Material Safety Data Sheet (MSDS) The MSDS started by proposing safety considerations for asbestos during the process of cutting ships apart It has progressed to cover almost all chemicals... 17-1 © 2006 by Taylor & Francis Group, LLC DK4 036 _book.fm Page 1 Monday, April 25, 2005 12:18 PM II Coating and Processing Techniques II-1 © 2006 by Taylor & Francis Group, LLC DK4 036 _book.fm Page 1 Monday, April 25, 2005 12:18 PM 18 Wire-Wound Rod Coating 18.1 18.2 18 .3 18.4 18.5 Introduction 18-1 History .18-2 Theory and Principle 18 -3 Film Thickness 18-4 The Rod Coating... is mounted between the side frames of the coating machine, and the metering rods are placed in the grooves The “V” groove © 2006 by Taylor & Francis Group, LLC DK4 036 _book.fm Page 6 Monday, April 25, 2005 12:18 PM 18-6 Coatings Technology Handbook, Third Edition FIGURE 18.6 Rod holder FIGURE 18.7 Wrap angle should be ground and polished to minimize wear on the rod and should be mounted accurately, at...DK4 036 _book.fm Page 1 Monday, April 25, 2005 12:18 PM 15 Design of Experiments for Coatings 15.1 Introduction 15-1 15.2 Standard Two-Level Factorial Designs 15-2 Mark J Anderson Stat-Ease, Inc Patrick J Whitcomb Stat-Ease, Inc Case study — Screening Factors thought to Affect a Spin Coater 15 .3 Optimization via Response Surface Methods (RSMs)... volumetrically reducing cross section (Figure 19.1), and T-shaped, with a constant cross section (Figure 19.2) 19-1 © 2006 by Taylor & Francis Group, LLC DK4 036 _book.fm Page 3 Monday, April 25, 2005 12:18 PM Slot Die Coating for Low Viscosity Fluids 19 -3 In either style, flow through the manifold is analogous to flow through a pipe in that there is an increasing resistance to material flow as the length increases... adequately design a coat-hanger die, the following information is required: 1 Rheology curve (see Figure 19 .3) — a rheology curve, a fingerprint of a particular resin, predicts its viscosity level at a given shear rate; this is required for all non-Newtonian or shear thinning fluids 2 Flow rate or range of rates 3 Material density at processing temperatures 4 General material characteristics, such as heat degradability... processes or formulated products 15-1 © 2006 by Taylor & Francis Group, LLC DK4 036 _C016.fm Page 1 Thursday, May 12, 2005 9:40 AM 16 Top 10 Reasons Not to Base Service Life Predictions upon Accelerated Lab Light Stability Tests 16.1 Light Spectra 16-1 Fluorescent Lamps • Xenon Arc Lamps 16.2 Light Intensity 16-4 16 .3 Temperature Sensitivity of Materials .16-4 Standard Temperature • Humidity... involve lowering the metering rod and its holder when the coater is turned off FIGURE 18.8 Automatic throw-off © 2006 by Taylor & Francis Group, LLC DK4 036 _book.fm Page 1 Monday, April 25, 2005 12:18 PM 19 Slot Die Coating for Low Viscosity Fluids 19.1 19.2 19 .3 19.4 Introduction 19-1 Manifold Theory and Design 19-1 Air Entrapment 19-4 Lip Design 19-4 Lip Adjustment Design •... Introduction Civilization is based on laws and regulations for the common good Way back, the law was as simple as, “don’t kill each other.” As time passed and technology grew, the laws and regulations became more complex to keep up with the technology Regulations were and are issued by the federal government, the state government, the county government, and the local government With everyone enacting . through window glass. 40 038 036 034 032 030 0280260 1.2 1.0 0.8 0.6 0.4 0.2 0.0 Wavelength (nm) Irradiance (W/m 2 /nm) Sunlight Xenon with Daylight Filter 40 038 036 034 032 030 0280260 1.2 1.0 0.8 0.6 0.4 0.2 0.0 Wavelength. Parma, Ohio. FIGURE 12.12 UVA -34 0 and sunlight. 40 038 036 034 032 030 0280260 1.2 1.0 0.8 0.6 0.4 0.2 0.0 Wavelength (nm) Irradiance (W/m 2 /nm) Sunlight UVA -34 0 DK4 036 _book.fm Page 9 Monday, April. maximum at three locations. 40 038 036 034 032 030 0280260 1.2 1.0 0.8 0.6 0.4 0.2 0.0 Wavelength (nm) Irradiance (W/m 2 /nm) December June March Equinox 40 038 036 034 032 030 0280260 1.2 1.0 0.8 0.6 0.4 0.2 0.0 Wavelength