Fibrous batts, mats or boards are used to thermally insulate various surfaces, such as the inside or outside of pipes and ducts, as well as refrigerators, air conditioners, furnaces, automobile hoods and the like. Heating, cooling or ventilating systems usually use air ducts, through which flows air as the heating and cooling medium. These ducts are constructed in various shapes, for example as round tubes or having a rectangular shape. They are usually made of sheet metals, such as galvanized steel, or plastics, or fiberglass reinforced plastics, or cellulosic materials such as wood or fiberboard, and the like. The construction and method of making these ducts and conduits is described in U.S. Pat. Nos. 3,092,529; 3,212,529; and 3,394,737. The inside of these ducts is usually black so as not to see the duct through the vents. The innner surface of these ducts should be smooth, to allow the air to flow with as little friction as possible, to save energy in transporting the air. This is usually achieved by first coating the fiberglass insulation which is then installed in the air ducts. The coating of the fiberglass insulation normally does not interfere with the excellent noise dampening qualities of the fiberglass insulation. The duct noise is often generated by the fan and by the flowing air, or, in the case of refrigerators, automobiles, furnaces and the like, by the engines and motors. Generally, the fiberglass mats, or batts are coated with an aqueous coating composition, often after the surface of the fiberglass mat has first been covered with a woven or nonwoven fabric.
Conventionally, the coatings are applied by spraying the coating composition onto the surface of the fiberglass batting. The coating is then dried in heated ovens, or by radiant heat. These procedures are generally carried out continuously. The finished fiberglass batting is then pulled up and often compressed by applying vacuum before shipping in order to save on shipping costs.
One such coating composition is disclosed in U.S. Pat. No. 3,926,894. The coating composition of U.S. Pat. No. 3,926,894 consists of a halogenated organophosphorous plasticizer, a latex binder and a mineral filler. However, a serious disadvantage of such a coating composition is the relative volatility of the plasticizer, especially in air ducts where large volumes of heated air pass over the coating, which makes the coating environmentally undesirable because the vapors emanating from the plasticizers are quite toxic.
Accordingly, it is an object of this invention to provide a coating having good mechanical properties, low volatility of the ingredients, fire retardation, as well as low black smoke generation. Furthermore, it is an object of this invention to apply the coating more efficiently to the fiberglass insulation by whipping air into the coating composition and applying the coating as a heat collapsible foam by roller or knife coating.