Use of pre-coated mat for preparing gypsum board

Abstract

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 method of making a fiber mat faced gypsum wall board comprising:
 depositing the gypsum slurry for forming a set gypsum core onto a non-coated side of a pre-coated fiber mat, the fiber mat having a coating on a side opposite the non-coated side,
 the coating weighing about 30 to 100 pounds per 1000 square feet of mat and comprising a combination of
 (i) a mineral pigment, 
 (ii) an organic binder and optionally 
 (iii) an inorganic binder, the coating extending from a surface of 
 
 the side opposite into the fiber mat, and 
 having a microporosity, as measured by a modified Gurley method, of between 2 and 45 seconds, which allows air to flow through as gypsum penetrates the mat and water to evaporate through the pre-coated mat from the gypsum core during preparation of the board, 
 the deposited gypsum slurry penetrating into the non-coated side and through interstices of the fiber mat to fill the interstices with gypsum and form a bond between the gypsum and the coating; and 
   drying the gypsum slurry to form a set gypsum core, the set gypsum core having in a region near the bond has at least 17 percent combined water.   
   
   
       2 . The method of  claim 1  wherein the organic binder is a hydrophobic, UV resistant polymer latex. 
   
   
       3 . The method of  claim 1  wherein the mat contains glass fibers nominally about 10 to 16 microns in diameter. 
   
   
       4 . The method of  claim 1  in which the mat, in the absence of the coating, has a basis weight of 1 to 3 pounds per 100 square feet. 
   
   
       5 . The method of  claim 1  having a gypsum core density of 40 to 55 pounds per cubic foot. 
   
   
       6 . The method of  claim 1  wherein, on a dry weight basis, the mineral pigment comprises from about 75 to 99 weight percent of the coating, the inorganic binder comprises from about 0 to 20 weight percent of the coating and the organic binder comprises from about 1 to 17 weight percent of the coating and the microporosity of the coating as measured by the modified Gurley method is between 5 and 20 seconds. 
   
   
       7 . The method of  claim 6  wherein, on a dry weight basis, the mineral pigment comprises from about 83 to 95 weight percent of the coating, the inorganic binder comprises from about 0 to 10 weight percent of the coating and the organic binder is a hydrophobic, UV resistant polymer latex binder and comprises from about 1 to 12 weight percent of the coating. 
   
   
       8 . The method of  claim 7  wherein the coating was applied to a surface of the fiber mat as an aqueous coating composition and dried to form the pre-coated mat. 
   
   
       9 . The method of  claim 8  wherein the aqueous coating composition includes about 0.1 to about 5 wt. % of one or more additives selected from the group consisting of a thickener, dispersant, colorant, defoaming agent and preservator. 
   
   
       10 . The method of  claim 8  wherein the set gypsum core contains a water-resistant additive in an amount of at least about 0.2 wt. %. 
   
   
       11 . The method of  claim 10  wherein the water resistant additive is selected from the group consisting of a wax emulsion, a wax-asphalt emulsion, poly(vinyl alcohol), a polysiloxane, a siliconate and mixtures thereof. 
   
   
       12 . The method of  claim 1  wherein the organic binder is a hydrophobic, UV resistant polymer latex adhesive binder and consists essentially of a (meth)acrylic or (meth)acrylate polymer or a (meth)acrylic or (meth)acrylate copolymer. 
   
   
       13 . The method of  claim 12  wherein the pre-coated fiber mat consists essentially of glass fibers and wherein the set gypsum core of the fiber mat faced gypsum board is faced on an opposite side with another fibrous mat which consists essentially of a blend of glass fibers and synthetic fibers. 
   
   
       14 . The method of  claim 1 , wherein depositing comprises discharging a first stream of gypsum slurry onto the pre-coated mat to form a first gypsum layer, then discharging a second, lower-density stream of a gypsum slurry onto the first layer. 
   
   
       15 . The method of  claim 1 , wherein the first stream is 18 percent to 20 percent more dense than the second stream. 
   
   
       16 . The method of  claim 1 , wherein depositing comprises discharging a first stream of gypsum slurry onto the pre-coated mat to form a first gypsum layer, then discharging a second, lower-density stream of a gypsum slurry onto the first layer. 
   
   
       17 . The method of  claim 16 , wherein the first stream is 18 percent to 20 percent more dense than the second stream. 
   
   
       18 . The method of  claim 1 , wherein the mineral pigment is limestone and the organic binder is an acrylic copolymer having a three-minute Cobb value of 1.5 grams or below. 
   
   
       19 . The method of  claim 1 , wherein the coating penetration is within about 30 percent to about 50 percent of the thickness of the glass fiber mat over at least 50 percent of the surface area across the entire mat. 
   
   
       20 . The method of  claim 1 , wherein the coating penetration is within about 35 percent to about 50 percent of the thickness of the glass fiber mat over at least 75 percent of the surface area across the entire mat. 
   
   
       21 . The method of  claim 1 , wherein the microporosity of the coating is about 2 to about 45 seconds over at least 50 percent of the surface area across the entire mat, wherein the microporosity as measured by a modified Gurley method. 
   
   
       22 . The fiber mat faced gypsum board of  claim 21 , wherein the microporosity of the coating is about 5 to about 20 seconds over at least 75 percent of the surface area of the entire mat, as measured by a modified Gurley method. 
   
   
       23 . The method of  claim 21 , wherein the density of the core of the pre-coated fiber mat is within about 40 to about 55 pounds per cubic foot over at least 50 percent of the surface area of the entire mat. 
   
   
       24 . The method of  claim 21 , wherein the pre-coated fiber mat is essentially liquid impermeable. 
   
   
       25 . The method of  claim 21 , wherein a bond between the gypsum core and the mat facer of the fiber mat faced gypsum board has a tensile strength of about 16 pounds per square inch.