Use of pre-coated mat for preparing gypsum board
A gypsum board which comprises a set gypsum core sandwiched between and faced with fibrous mats, wherein a free surface of one of said mats is pre-coated with a combination of a mineral pigment, optionally an inorganic adhesive binder and an organic binder, preferably a hydrophobic, UV resistant polymer latex adhesive binder applied to said surface as an aqueous coating composition, said aqueous coating composition upon drying and setting providing a pre-coated mat satisfying certain morphology requirements.
1. A gypsum board comprising:
a gypsum core;
a fiber mat comprising a first side and second side opposite the first side, the second side is bonded to the gypsum core such that a tensile strength of the bond is at least 16 pounds per square inch, wherein the gypsum core in the region of the bond has at least 17 percent combined water; and
a coating penetrating the mat from the first side into the fiber mat to a depth of about 30 percent to about 50 percent of the thickness of the fiber mat, the coating comprises a mineral pigment and an organic binder, wherein the organic binder comprises at least about 1 percent and no more than 17 percent by weight and the mineral pigment has a particle size such that at least 95 percent by weight of the mineral pigment particles pass through a 100 mesh wire screen, with at least 75 percent of the particles by number being greater than 5 microns.
2. The gypsum board of claim 1 , wherein the fiber mat comprises glass fibers nominally about 10 to 16 microns in diameter and about one-quarter (¼) to about one (1) inch in length, the fiber mat in the absence of the coating has a basis weight of 1 to 3 pounds per 100 square feet, and the fiber mat has a thickness from about 0.02 inch to about 0.045 inch.
3. The gypsum board of claim 1 , wherein the coating penetrates the mat about 35 percent to about 50%.
4. The gypsum board of claim 1 , wherein the coating weighs on a dry weight basis about 30 to 100 pounds per 1000 square feet of mat.
5. The gypsum board of claim 4 , where the coating has a microporosity, as measured by a modified Gurley method, of less than about 45 seconds.
6. The gypsum board of claim 5 , wherein the microporosity is less than about 20 seconds.
7. The gypsum board of claim 6 , wherein the microporosity is between 5 and 20 seconds.
8. The gypsum board of claim 1 , wherein the mineral pigment has a number average particle size of about 40 microns.