Weathering performance testing cans of paint with

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Weathering Performance Testing Cans of paint with "polyurethane" on the label do not all have the same weathering performance. Formulation variables, such as the type of polyurethane resin, the type of pigment, the ratio of resin and pigment and the amount of UV-absorbing additives, all determine the weathering properties. Weathering performance information, like corrosion performance information, is best determined by field testing of laboratory-applied coatings, but the test methods are different. Test fences most often are situated in hot, sometimes humid, regions such as Florida, Arizona or Australia, but it is not unusual to see test fences on paint manufacturing sites in all parts of the country.
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SYSTEMS PAGE 54 Usually field tests are run for a minimum of two years. By this time, a good understanding of weathering life can be estimated. Because developing new paint is a continuous activity, two-year paint data may not be available for newly introduced coatings. If this is the case, one-year data coupled with accelerated laboratory methods may be used. Two accelerated lab methods are relied on—Weather-O-Meter™ or Q-UV™ weathering apparatus. Both meth- ods use cycles of light and dark, dry and wet. The Weather-O-Meter typically uses a Xinon arc that generates an intense light to accelerate coating deterioration. Six months' exposure in the Weather-O-Meter is similar to two years in Florida. The Q-UV uses a special fluorescent type of light bulb. Three months in an instrument using a Q-UV-A bulb is about the same as two years in Florida. Accelerated lab methods should only be used in combination with outdoor exposure information—for example, if only one year of Florida data is available. The correlation between accelerated weathering and Florida weath- ering does not allow for an accurate comparison of different types of paint. It is most suitable for examining minor formulation variations and as a screening tool. This information is a routine part of topcoat performance analy- sis. Ask for it! Other Types of Performance Environments The above sections describe in detail different environments and test methods for evaluating resistance to corro- sion and weathering. Other types of environments could be identified. These include, for example, chemical and solvent environments, abrasive environments or immersion—water or soil—environments. To make things more complicated, one environment often influences paint performance for another environment. For example, if a coating does not resist the effects of the weather, erosion of the coating could lead to prema- ture failure due to corrosion. Similarly, if a coating does not resist chemicals, the coating could dissolve and lead to premature failure of the desired gloss retention.
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