9 -4 Coatings Technology Handbook, Third Edition Colborn, Robert, Modern Science and Technology . Princeton, NJ: Van Nostrand, 1965. Foreman, Jon, “Dynamic mechanical analysis of polymers,” American Laboratory, January 1997, p. 21. Hassel, Robert L., “Evaluation of polymer flammability by thermal analysis,” American Laboratory, January 1997 . Hassel, Robert L., Using Temperature to Control Quality, Second Quarter 1991 P1 Quality. Hitchcock, 1991 . Hassel, Robert L., “Thermomechanical analysis instrumentation for characterization of materials,” Amer- ican Laboratory, January 1991. Kelsey, Mark, et al., “Complete thermogravimetric analysis,” American Laboratory, January 1997, p. 17. Neag, C. Michael, Coatings Characterizations by Thermal Analyses . ASTM Manual 17. West Consho- hocken, PA: American Society for Testing and Materials, 1995. Park, Chang-Hwan, et al., “Syntheses and characterizations of two component polyurethane flame retar- dant coatings using 2,4dichlor modified polyester,” J. Coat. Technol., December 1997, p. 21. Reading, Micheal, et al., “Thermal analysis for the 21 st century,” American Laboratory, January 1998, p. 13. Riesen, Rudolf, “Maximum resolution in TGA by rate adjustment,” American Laboratory, January 1998, p. 18. TA Instruments Company, Thermal Analysis Application briefs available from TA Instruments Company, New Castle, Delaware: TA-8A, Thermal Solutions — Long Term Stability Testing of Printing Inks by DSC; TA-73, A Review of DSC Kinetics Methods; TA-75, Decomposition Kinetics Using TGA; TA-121, Oxidation Stability of Polyethylene Terephthalate; TA-123, Determination of Polymer Crystallinity by DSC; TA-125, Estimation of Polymer Lifetime by TGA Decomposition Kinetics; TA-134, Kinetics of Drying by TGA; and TA-135, Use of TGA to Distinguish Flame-Retardant Polymers from Standard Polymers. DK4036_book.fm Page 4 Monday, April 25, 2005 12:18 PM © 2006 by Taylor & Francis Group, LLC 10 -1 10 Color Measurement for the Coatings Industry Color is the most important appearance of coatings for their formulation, application, or inspection. Color is also the most subjective parameter to characterize visually, and characterization is often attempted under uncontrolled conditions that result in poor color judgement. Proper viewing conditions require controlled lighting in a viewing booth where the different types of light, such as simulated daylight, tungsten, and fluorescent light sources, can be used for evaluation. Visual evaluation always requires a physical standard for comparison because the “color memory” of the brain is quite poor without one, but very good when two samples are compared beside each other. Even when proper viewing conditions are used, it is often difficult to determine the direction and intensity of color difference between two samples. This process requires a trained colorist to make the evaluation. A more accurate and consistent approach to evaluate color difference is the use of a color measurement instrument. The two types of instruments that can be used for this purpose are colorimeters and spectrophotometers. A colorimeter uses optical filters to simulate the color response of the eye, and a spectrophotometer breaks the visible spectrum into intervals that mathematically simulate the color response of the eye. The advantage of using spectrophotometers to determine color difference is in their accuracy, stability, and ability to simulate various light sources. Spectrophotometer cost and complexity of operation are greatly reduced on new versions of the instruments. There are three different technologies that are used in modern industrial spectrophotometers: inter- ference filters, gratings, and light-emitting diodes (LEDs). Interference filters require a filter for each wavelength measured and usually have 16 or 31 filters depending on the resolution required. Grating- based instruments have diode arrays of 20 to 256 elements to provide higher resolution for applications that require it. The advantage of interference filters is in their simplicity of operation and mechanical ruggedness. However, they are difficult to make consistent and deteriorate over time. High-performance instruments usually have gratings that give more resolution and better consistency, but they are usually more expensive and complex to build and calibrate. A new market entrant for spectrophotometers is based on LEDs of different illumination colors. Up to nine separate color LEDs are now available to cover most of the visible spectrum. The instruments operate by illuminating one LED at a time while measuring the reflected light. The advantage is that they can be made very small and cost less to manufacture. The disadvantages are reduced accuracy and stability, but the technology is improving with the advent of newer LEDs with better methods for compensation. There are several different measurement geometries: sphere, 45/0, and multiangle. A sphere instrument illuminates a sample from all directions and views the sample at near normal or perpendicular. The 45/ 0 illuminates the sample at 45 degrees from all directions and views the sample normal. It is also possible to illuminate at 0 and view at 45. The multiangle approach illuminates at multiple angles and views at a fixed angle. It is also possible to illuminate at a fixed angle and view at multiple angles. Harold Van Aken GretagMacbeth DK4036_book.fm Page 1 Monday, April 25, 2005 12:18 PM © 2006 by Taylor & Francis Group, LLC Bibliography 10-2 11 -1 11 The Use of X-ray Fluorescence for Coat Weight Determinations 11.1 Introduction 11- 1 11.2 Technique 11- 1 11.3 Method 11- 2 11.4 Accuracy 11- 3 11.5 Repeatability and Reproducibility 11- 3 11.6 Conclusion 11- 5 11.1 Introduction The technique of elemental analysis by x-ray fluorescence (XRF) has been applied to the quality control of coating weights at the plant level. Measurements by nonlaboratory personnel provide precise and rapid analytical data on the amount and uniformity of the applied coating. XRF has proved to be an effective means of determining silicone coating weights on paper and film, titanium dioxide loading in paper, and silver on film. 11.2 Technique XRF is a rapid, nondestructive, and comparative technique for the quantitative determination of elements in a variety of matrices. XRF units come in a variety of packages; however, the type of unit most prevalent in the coating industry is described in this chapter. The XRF benchtop analyzer makes use of a low level radioisotope placed in close proximity to the sample. The primary x-rays emitted from the excitation source strike the sample, and fluorescence of secondary x-rays occurs. These secondary x-rays have specific energies that are characteristic of the elements in the sample and are independent of chemical or physical state. These x-rays are detected in a gas-filled counter that outputs a series of pulses, the amplitudes of which are proportional to the energy of the incident radiation. The number of pulses from silicon x-rays, for example is proportional to the silicone coat weight of the sample. Because the technique is nondestructive, the sample is reusable for further analysis at any time. To ensure optimum excitation, alternate radioisotopes may be necessary for different applications. For silicone coatings and titanium dioxide in paper, an iron-55 (Fe-55) source is used. Fe-55 x-rays are soft (low energy) and do not penetrate far into a sample. For silver on film, a more energetic americanum- 241 source has been used. Wayne E. Mozer Oxford Analytical, Inc. DK4036_book.fm Page 1 Monday, April 25, 2005 12:18 PM © 2006 by Taylor & Francis Group, LLC 11 -4 Coatings Technology Handbook, Third Edition FIGURE 11.2 Differences in sensitivities in products from different suppliers of silicone. FIGURE 11.3 Differences in paper backings. X-Ray CPS 200 150 100 50 .25 .50 .75 1.00 Concentration g/m 2 Vendor A Vendor B Vendor C X-Ray CPS 200 150 100 50 .25 .50 .75 1.00 Concentration g/m 2 DK4036_book.fm Page 4 Monday, April 25, 2005 12:18 PM © 2006 by Taylor & Francis Group, LLC 12 -1 12 Sunlight, Ultraviolet, and Accelerated Weathering 12.1 Introduction 12- 1 12.2 Sunlight 12- 1 Va riability of Sunlight 12.3 Accelerated Light Sources Compared to Sunlight 12- 2 The Importance of Short-Wavelength Cutoff 12.4 Arc-Type Light Sources 12- 4 12.5 Fluorescent UV Lamps 12- 7 12.6 Conclusions 12- 9 Acknowledgments 12- 9 References 12- 10 12.1 Introduction Sunlight is an important cause of damage to coatings. Short-wavelength ultraviolet (UV) light has long been recognized as being responsible for most of this damage. 1 Accelerated weathering testers use a wide variety of light sources to simulate sunlight and the damage that it causes. Comparative spectroradiometric measurements of sunlight and laboratory testers of various types show a wide variety of UV spectra. These measurements highlight the advantages and disadvantages of the commonly used accelerated light sources: enclosed carbon arc, sunshine carbon arc, xenon arc, and fluorescent UV. The measurements suggest recommendations for the use of different light sources for different applications. 12.2 Sunlight The electromagnetic energy from sunlight is normally divided into ultraviolet light, visible light, and Infrared energy (not shown) consists of wavelengths longer than the visible red wavelengths and starts above 760 nanometers (nm). Visible light is defined as radiation between 400 and 760 nm. Ultraviolet light consists of radiation below 400 nm. The International Commission of illumination (CIE) further Patrick Brennan Q-Panel Lab Products Carol Fedor Q-Panel Lab Products DK4036_book.fm Page 1 Monday, April 25, 2005 12:18 PM © 2006 by Taylor & Francis Group, LLC Enclosed Carbon Arc (ASTM G 153) • Sunshine Carbon Arc (Open Flame Carbon Arc: ASTM G 152) • Xenon Arc (ASTM FS-40 Lamps (F40-UVB) (ASTM G 154) • UVB-313 Lamp G 155) (ASTM G 154) • UVA-340 Lamp (ASTM G 154) infrared energy. Figure 12.1 shows the spectral energy distribution (SED) of noon midsummer sunlight. 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 -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 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 [...]...DK4036_book.fm Page 1 Monday, April 25, 2005 12 :18 PM 14 Test Panels 14 .1 Cold Rolled Steel Panels 14 -1 Surface Profile • Surface Carbon • Surface Preparation • Applications 14 .2 Aluminum Panels 14 -4 Douglas Grossman Q-Panel Lab Products Patrick Patton Q-Panel Lab Products Surface Finish • Pretreatment • Applications 14 .3 Zinc-Coated Steel Panels 14 -6 Surface Preparation 14 .4 Handling... 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... 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 10 08 and 10 10 are examples of suitable grades of steel for test panel... panels have been described in both national and international standards These include ISO 15 14: Paints and Varnishes — 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 22 01: Standard Practice for Preparation of Zinc Coated and Zinc Alloy Coated Steel Panels for... 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 14 -1 © 2006 by Taylor & Francis Group, LLC ... 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 . Determinations 11 .1 Introduction 11 - 1 11. 2 Technique 11 - 1 11. 3 Method 11 - 2 11 .4 Accuracy 11 - 3 11 .5 Repeatability and Reproducibility 11 - 3 11 .6 Conclusion 11 - 5 11 .1 Introduction . 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. feedback. 11 .3 6.2 Log Resistivity 0 0 40 80 12 0 16 0 200 50 10 0 15 0 200 250 300 Glass Transition (C) Time (min) Log Ion Viscosity 13 12 11 10 9 8 7 6 5 Temperature (°F) 300 250 200 15 0 10 0 50 350 40 0 45 0 05 010 0