1. Field of the Invention
The present invention relates to a permeable glass mat and a method of preparation therefor. More specifically, the porosity of the glass mat from fully sealed to highly open can be controlled by employing the method of the present invention.
2. Description of the Related Art
Fibrous non-woven mats are often formed into a wet mat from an aqueous dispersion of fibers such as glass and/or synthetic organic fibers. The dispersion can include other fibers such as cellulose fibers, ceramic fibers, etc. and can also include particles of inorganic material and/or plastics. Usually a solution of urea formaldehyde resin, usually modified with a thermoplastic polymer, or one of many other known resin binders is applied to the wet non-woven web of fibers and then, after removing excess binder and water, the binded web is dried and heated further to cure the urea formaldehyde resin or other resin binder to form a non-woven mat product. Typical processes are disclosed in U.S. Pat. No. 7,138,346, the disclosure of which is hereby incorporated herein by reference.
In prior coating methods, often a raw glass mat enters a coating station at a level lower than the top of an application roll. The direction of travel of the glass mat is parallel to a machine direction. The application roll is driven to rotate about its axis and dip into a coating pan. The coating pan is filled with a coating mix up to a level that is sufficient for the application roll to pull an adequate amount of coating to the top of the application roll. The speed of rotation of the application roll is adjusted to get adequate amounts of coating mix up into the glass mat as the glass mat is conveyed. The glass mat can extend around the application roll to the degree desired. A scraper blade is used to scrape off excess coating, which falls preferably back into the coating pan. The coated mat then proceeds into a dryer section.
The history of gypsum board development has passed many milestones, many of these milestones being related to the surfaces, or facers, covering the broad surface of a gypsum board. In almost all cases, the subject of a facer stability was an issue. Also the facers have had to resist weathering as well as retaining constant dimensions. Mildew and mold have been a problem with the original multi-ply paper facers used on gypsum board. Unfortunately, the paper facers also might not allow water vapor to escape. Yet the escape of water vapor is essential in curing the gypsum. While these paper facers have been modified with chemicals to improve their properties, most of the gypsum board progress and success has come by changing from paper facers to fiberglass mat facers.
The entire scope of manufacturing different facer materials for building products is extensive, encompassing both fields of gypsum board fiberglass facers and thermosetting polyiso foam insulation board facers. In recent years, many facer-related methods and products thereof have been taught in various publications, including numerous United States patents.
Coating processes often fail to permit close control of the porosity of a glass mat. This can be important, particularly with a heavy solid coating mix, and for gypsum facers. As mentioned above, the escape of water vapor is essential in curing/drying gypsum. The key is to control the porosity of the coated facer mat so that the coating is protective, yet porous enough to allow the water vapor to escape during heating.
It is an objective of the present invention to provide such a process for coating glass mats, with coatings having a wide range of solid content, in order to control the porosity of the mat.