After low-temperature refrigeration operation, a large amount of condensed water will be enriched on the surface of hydrophilic aluminum foil of the exchanger. When the indoor temperature reaches the temperature set by the air conditioner, the outdoor unit stops working, the indoor unit switches to the "air supply" mode, and the condensed water continuously volatilizes and diffuses into the air. If hydrophilic aluminum foil has "odor", at this time, water vapor will bring "odor" into the air during volatilization.
Reason: Hydrophilic aluminum foil is composed of a layer of organic paint attached to the surface of aluminum products. Hydrophilic aluminum foil for air conditioning usually has the characteristics of high corrosion resistance and high hydrophilicity. Coatings coated on the surface of hydrophilic aluminum foil can be divided into anticorrosive coatings and hydrophilic coatings, also known as primer (HD) and topcoat (HW). Most industrial organic coatings are provided by Guangzhou Huigu Chemical Co., Ltd. and Almonte Company. The coating belongs to water-soluble thermosetting organic resin, and its main component is acrylic resin. Acrylic resin is synthesized from different acrylic monomers, which are substances with strong smell. Mixing acrylic resin emulsion with curing agent, auxiliary agent and water to prepare coating; After painting, the coating is baked at high temperature to produce cross-linking and curing reaction, resulting in small molecular volatiles, decomposition products and water. After curing, a coating is formed. Acrylic monomer is a odorous substance, but it contains carbon-carbon double bonds, which have reacted in the synthesis stage of resin emulsion, and the monomer is polymerized to form polymer resin. Coating manufacturers will monitor the monomer content when synthesizing the resin to ensure that there is almost no acrylic monomer residue in the resin. Even if there is a small amount of unreacted monomer, if the coating process is set reasonably, it will react or volatilize during baking and curing. After the surface of aluminum foil is coated with primer and topcoat, it will be baked at high temperature for a period of time and cross-linked and cured to form a coating with certain functions. In this process, some small molecular volatiles and coating decomposition products will be produced, which have a certain smell. If these substances remain or adsorb on the surface of aluminum foil, it will produce a special smell, which is greatly influenced by coating process (such as coating thickness, drying temperature, drying time, production line speed, ventilation, etc.). The process setting is reasonable, the coating is completely dry, and the hydrophilic aluminum foil coating will not produce odor; If the coating process is not set properly, the coating film cannot be completely cured, and the hydrophilic aluminum foil coating absorbs moisture in the air, which will release sour taste. The optimum curing temperature of the coating is 150 ~ 200℃. Too low temperature will lead to incomplete curing, and too high temperature will lead to the decomposition of molecules that have been crosslinked into networks, both of which will produce odor.
References: Study on Causes and Prevention Methods of Odor in Air-conditioning Heat Exchanger Xie Wei, Zhao Bingqing, Li Wentao, Zhang Zhonghu.