Building board having high fastener sealability

1. A building board, comprising:

a cementitious layer sandwiched between a first fiber mat and a second fiber mat, the first fiber mat and the second fiber mat being directly embedded in the cementitious layer;

a bi-axially stretched extruded polymer film overlying the first fiber mat and/or the second fiber mat, the extruded polymer film having a thickness in a range of at least 5 microns and not greater than 130 microns and consisting essentially of polyethylene terephthalate;

a thermoplastic coating layer directly overlying the extruded polymer film, the thermoplastic coating layer having a thickness in a range of at least 30 microns and not greater than 260 microns, and the thermoplastic coating layer has a Shore D hardness of at least 30; and

an adhesive layer between the polymer film and the first fiber mat and/or the second fiber mat, the adhesive layer directly attaching the polymer film to the first fiber mat and/or second fiber mat,

wherein the extruded biaxially stretched polymer film consisting essentially of polyethylene terephthalate has a thickness Tp and the thermoplastic coating layer has a thickness Tc, and a ratio of Tp to Tc is between 1:10 and 1:20, and

the building board is adapted for using fasteners for installation and passes fastener sealability testing according to a modified ASTM D1970 by having a water uptake of not greater than 0.35 wt % of the board, the fastener sealability testing employing a fastener being 635 microns overdriven in the building board for a period of three days, the fastener being a drywall screw #6 having a Phillips Head.

2. The building board according to claim 1 , wherein the polymer film has a Young's modulus of at least 1500 MPa and not greater than 3500 MPa.

3. The building board according to claim 1 , wherein the extruded polymer film has a tensile strength of at least 30 MPa and not greater than 110 MPa.

4. The building board according to claim 1 , wherein the thermoplastic coating layer has a Shore D hardness of at least 30 and not greater than 60.

5. The building board according to claim 1 , wherein the first fiber mat and/or the second fiber mat comprise glass fibers.

6. The building board according to claim 1 , wherein the cementitious layer includes at least one cementitious material selected from gypsum, Portland cement, magnesium oxide, magnesium phosphate, or any combination thereof.

7. The building board according to claim 1 , wherein the thickness of the extruded polymer film is at least 10 microns and not greater than 100 microns.

8. The building board according to claim 1 , wherein the polymer film comprises perforations having openings of a size of at least 10 μm and not greater than 1 mm.

9. The building board according to claim 1 , wherein the thermoplastic coating layer comprises a thermoplastic polymer selected from the group consisting essentially of an ethylene vinyl acetate copolymer, a polyolefin, an ethylene methacrylate (EMA) copolymer, an ethylene acrylic acid copolymer (EAA), a styrene block copolymer, a polyurethane, a polyamide, or any combination thereof.

10. The building board according to claim 9 , wherein an amount of the thermoplastic polymer is at least 10 wt % and not greater than 70 wt %.

11. The building board according to claim 1 , wherein the thermoplastic coating layer further comprises a wax in an amount of at least 5 wt % and a tackifying resin in an amount of at least 15 wt %.

12. The building board according to claim 1 , wherein the thermoplastic coating is a hot-melt coating.

13. The building board according to claim 1 , wherein the thermoplastic polymeric coating layer solidifies in less than 45 seconds.

14. The building board of claim 1 , wherein the thermoplastic coating layer has a water vapor permeability of not greater than 1 perm measured according to ASTM E96-13 at 21° C.

15. A method for manufacturing a building board, comprising:

providing an extruded bi-axially stretched polyethylene terephthalate film having a thickness in a range of at least 5 microns and not greater than 130 microns and attaching the extruded bi-axially stretched polyethylene terephthalate film with an adhesive layer onto a first surface of a first fiber mat, the adhesive layer directly attaching the extruded bi-axially stretched polyethylene terephthalate film to the first fiber mat;

applying a cementitious layer on top of a second surface of the first fiber mat, the second surface being opposite to the first surface of the first fiber mat, the first fiber mat being directly embedded in the cementitious layer;

applying a second fiber mat on top of the cementitious layer to obtain a fiber mat sandwiched cementitious layer composite, the second fiber mat being directly embedded in the cementitious layer;

drying the fiber mat sandwiched cementitious layer composite; and

applying a thermoplastic coating layer onto an outer surface of the extruded bi-axially stretched polyethylene terephthalate film, the thermoplastic coating layer having a thickness in a range of at least 30 microns and not greater than 260 microns,

wherein the extruded bi-axially stretched polyethylene terephthalate film has a thickness Tp and the thermoplastic coating layer has a thickness Tc, wherein a ratio of Tp to Tc is between 1:10 and 1:20, and

the building board is adapted for using fasteners for installation and passes fastener sealability testing according to a modified ASTM D1970-15 by having a water uptake of not greater than 0.35 wt % of the board, the modified testing comprising employing a fastener being 635 microns overdriven in the building board for a period of 3 days at 22° C., the fastener being a drywall screw #6 having a Phillips Head, and the thermoplastic coating layer has a Shore D hardness of at least 30.