Painting and Coating of Acoustic Materials

Acoustic materials are used to treat indoor and outdoor spaces to make speech intelligible, and places less noisy and more pleasant to be in. Whilst most treatments are old and well established, in recent years there has been a growth in innovative products, which overcome difficulties with the old technologies, especially when making the treatments more visually acceptable to architects. Modern construction depends a great deal on acoustic materials to act as sound containment or sound control, either in residential or commercial applications. Sound-absorbing materials are highly porous to increase their sound absorption qualities. The amount of absorption depends on the thickness of the porous material, the size and number of pores, and the frequency of the noise. When painting acoustic materials, the painter should be very careful that the paint does not close up the acoustic surfaces; perforations or fissures. It is through these openings in the surface that sound waves enter the body of the acoustic material and are absorbed. It is the control of the paint droplet size upon the surface that affects the acoustic properties and the aesthetic appearance of the coated surface. An investigation into the coating performance with regard to acoustic absorption and aesthetic appearance was performed in a true-scale automotive spray booth using five different types of paint: three aerosol paints, domestic emulsion and acoustic paint. The sprays produced by the aerosols, emulsion and acoustic paints, applied using an air assist spray-gun, were characterised using a Mastersizer-X laser instrument. The flow rate of the paint through the spray gun was varied during the experiments between 50 ml/min and 500 ml/min. The work has highlighted the operating parameters for the air-assist spray gun in order to produce the smallest drop sizes. The measuring of the acoustic coefficient of the coated materials has shown that the aerosol and air-assist gun produced too large a droplet to produce a good acoustic coating. The use of the acoustic paint did create a good absorption coefficient but the work has highlighted the requirement for the atomizing process to be optimised for this highly viscous acoustic paint.