Gloss and degradation of hydroxyl polyacrylic resin/hexamethylene‐1,6‐diisocyanate coatings under ultraviolet and natural‐exposure aging

Abstract

Reactive coatings of hydroxyl polyacrylic resin (HPAR) with hexamethylene-1,6-diisocyanate were carried out under accelerated 313-nm ultraviolet (UV) aging for 2000 h and under natural exposure in Lhasa, Tibet, for 24 months. With UV irradiation and exposure time, the gloss changes in coatings with HPAR containing 3.0% or less hydroxyl groups decreased exponentially, whereas the gloss decay of coatings with HPAR containing over 4.5% hydroxyl groups decreased linearly. During 254-nm UV aging, the gloss changes in coatings with HPAR containing 1.4% or less hydroxyl groups decreased as a Gaussian function. The weather resistance of a coating was correlated to the HPAR, UV irradiation, temperature, and humidity. Scanning electron microscopy indicated that there were degradation reactions and that some substance was lost in the matrix polymer during accelerated UV aging; then, uneven surfaces appeared and caused decreased gloss. Accelerated UV aging was faster than naturalexposure aging, and the aging velocity of 254-nm UV was 3-5 times faster than that of 313-nm UV. Through the changes in the gloss, the aging tolerance of a coating could be monitored, and its aging resistance could also be predicted. The dynamic mechanical thermal analysis results showed that the coatings had good properties.

Preparation, property characterization and UV‐converting application of poly(conjugated azomethine‐urethane)/hydroxyl polyacrylate resin

“…T g and E ′ of HPAR/HDI coating films7, 20 were below 55.9°C and 10 9 Pa, respectively. Compared with HPAR/HDI coatings, the HPAR/CAUP coating films had higher glass transition temperature, which were over 97.0°C.…”

“…In this peak vicinity of tanδ T curve versus temperature, the modulus of HPAR/CAUP coating film declined more than 10 3 M Pa with increasing temperature. According to DMTA analysis, here the glass transition temperature ( T g ) of the HPAR/CAUP coating film was reported as the temperature at which tanδ T was the maximum 7, 19. From Figure 4, T g s of the three HPAR/CAUP film samples were all over 97.0°C, among which the T g of the HPAR/CAUP‐B film was the highest.…”

“…During our previous application tests of HPAR/HDI coatings in the Qing‐Zang plateau in China, under the natural exposure to ageing in Lhasa and accelerated 254 and 313 nm UV ageing in the years from 2004 to 2007, we found that UV severely affected the film to age and that its gloss of HPAR/HDI film exponentially decayed under UV irradiation 7. HPAR/HDI films had excellent anti‐photodegradation and anti‐photo abilities and it could be used in severe UV irradiation areas in the Qing‐Zang plateau.…”

“…Unless otherwise indicated, the others were used without further purification treatments. HPAR was prepared based on our former method7 by copolymerizing methacrylic acid, methyl methacrylate, butyl acrylate, 2‐hydroxylethyl acrylate and 2‐hydroxylpropyl acrylate. HPAR was dissolved in DMF for use.…”

“…By changing a hard segmental component that contained NCO functional group, or by changing a soft segmental component that contained OH functional group, the hard‐soft‐two‐component polyurethane coatings with various kinds of properties had been produced. Hydroxyl polyacrylate resin (HPAR) is a transparent functional polymer that has resistance to ultraviolet (UV) rays and does not absorb in the visible light range 7. Because HPAR has excellent hardness, gloss, flexibility and adhesive to substrate materials, various kinds of HPARs are manufactured and applied in the coating industry.…”