Experimental Investigation On The Aging Behavior Of The Painting Films For The Outdoor Wooden Furniture

The aging of the surface painting film is a common phenomenon during the usage of outdoor wooden furniture, which shortens their work lives. Many environmental factors could affect the behavior of aging, e.g. sunlight radiation, heat radiation, mechanical stresses, humidity, biological effects. Among numerous factors, sunlight, temperature and humidity are dominant. In this paper, experiments on the aging behavior of the surface paint films of permanent outdoor wooden furniture were performed. Beech wood was selected as representative substrate, and the sunlight, temperature and humidity were taken into consideration. The experimental weather simulated the climate of Nanjing.In the experiments, four categories of painting films were selected, and they are pure polyurethane resin painting film, pure alkyd resin painting film,"polyurethane resin+ alkyd resin"compounded painting film, and"polyurethane resin + phenolic resin"compounded painting film. After the specified aging conditions, a variety of performance indices of these painting films were measured and then analyzed.The results showed that: (1) After the aging processes; all sample paint films would reach a second stable condition in terms of mass, size, glossiness and hardness, but these variations are not significant; (2) On the former aging stage, the water content in the substrates generally present a"one-way"motion, that is, the quantity of water penetrated into the substrates from painting films is more than the water leaked out. Thus, the painting films are like one-way tap; (3) The color variations of compounded painting films are obviously less than the pure material painting films; (4) The permeability of alkyd resin paint films are greater than those of the polyurethane resin paint films; (5) The phenolic resin paint films lose their glossiness rapidly during aging processes, hence would affect the appearance if used on the outdoor wooden furniture; (6) Polyurethane resin paint films have smaller permeability and higher adhesion than the alkyd resin paint films; (7) After comprehensive comparisons, the"polyurethane resin+ alkyd resin"compounded painting films have best performances. Compared to the pure polyurethane resin painting film, this compounded painting film could also reduce the painting costs.