UV Aging Test Introduction

Weather and solar irradiation are the primary causes of damage to coatings, plastics, inks, and other polymer materials. This damage includes loss of gloss, fading, yellowing, cracking, peeling, brittleness, strength reduction, and delamination. Since solar radiation has dual effects of thermal radiation and photochemical reactions, high-temperature tests cannot substitute for light exposure aging tests. Similarly, pure ultraviolet (UV) or infrared (IR) radiation alone cannot replace comprehensive solar radiation testing.

Overview of UV Aging Test

UV aging falls under the category of solar irradiation aging, where UV stands for Ultraviolet. It is commonly used to assess the rate at which products degrade under UV exposure. Solar irradiation aging is the primary form of degradation for materials used outdoors. Even for indoor materials, they can still experience some degree of solar irradiation aging or aging caused by UV radiation from artificial light sources (such as UV lamps and the UV spectrum in fluorescent lights). UV radiation encompasses the visible light and ultraviolet portions of the solar spectrum. Ultraviolet light is categorized into UVA, UVB, and UVC rays, with wavelength ranges of 400-315nm, 315-280nm, and 280-190nm, respectively. According to relevant UV aging standards, UV (ultraviolet) radiation cannot fully simulate the entire spectrum of sunlight. Its principle lies in the fact that for durable materials exposed outdoors, the short-wave UV spectrum (300-400nm) is the primary cause of aging damage. In the short-wave UV region, spanning from 365nm to the lowest wavelength of sunlight, UV fluorescent lamps can effectively simulate sunlight.

Modes of UV Aging Test

The UV aging test can be configured with three aging modes: light exposure, condensation, and spray.

1. Light Exposure Phase:
   This phase simulates the daylight duration (typically between 0.35W/m² and 1.35W/m², with the solar irradiance at noon in summer being approximately 0.55W/m²) and test temperature (50℃ to 85℃) in natural environments. This allows for the simulation of various usage conditions of products to meet the testing requirements of different regions and industries.

2. Condensation Phase:
   This phase simulates the phenomenon of moisture condensation on the sample surface at night. During the condensation phase, the fluorescent UV lamps are turned off (dark condition), and only the test temperature (40-60℃) is controlled, with the sample surface humidity maintained at 95-100% RH.

3. Spray Phase:
   This phase simulates the process of rainfall by continuously spraying water onto the sample surface. Due to the harsher conditions of accelerated UV aging tests compared to natural environments, aging damage that would take several years to occur outdoors can be simulated within just a few days or weeks. Based on differences in spectral distribution, fluorescent UV lamps can be classified into UVA and UVB types. UVA lamps emit less than 2% of their total light energy below 300nm, while UVB lamps emit more than 10% of their total light energy in this range.

Introduction to UV Aging Lamps

• UVA-340: Primarily used to simulate the medium to short wavelength range of solar UV radiation, typically for outdoor product light aging tests.
• UVA-351: Mainly used to simulate the medium to short wavelength range of solar UV radiation filtered through window glass, generally for indoor products.
• UVB-313: These lamps emit a significant amount of radiation below 300nm, which is the nominal cutoff wavelength for solar radiation. This can induce aging phenomena that would not occur outdoors. The use of such lamps is not recommended for simulating sunlight. Instead, they are widely used for accelerated durability testing of materials and for qualitative comparisons between two or more materials.

Reference Irradiance Levels for UVA-340 Lamps (for reference):

• 0.69W/m² @ 340nm: Equivalent to sunlight at noon in summer, yielding rapid results.
• 1.38W/m² @ 340nm: Equivalent to the maximum solar irradiance, yielding rapid results.
• 0.35W/m² @ 340nm: Equivalent to sunlight in March/September, suitable for general tests or tests requiring low UV intensity.

Common Reference Standards for UV Aging

• GB/T 16422.3: Plastics - Methods of Exposure to Laboratory Light Sources - Part 3: Fluorescent UV Lamps.
• ISO 4892-3: Plastics - Methods of Exposure to Laboratory Light Sources - Part 3: Fluorescent UV Lamps.
• ASTM G154: Standard Practice for Operating Fluorescent Light Apparatus for UV Exposure of Nonmetallic Materials.