Sprayable liner for supporting the rock surface of a mine

Abstract

The invention provides a liner which is the product of reaction of a (a) hydrophilic prepolymer bearing isocyanate groups; and (b) a water-borne polyurethane dispersion, the polyurethane bearing groups that are reactive to isocyanate groups.

We claim:  
     
         1 . A liner comprising the product of reaction of: 
 (a) a hydrophilic prepolymer bearing isocyanate groups; and    (b) a water-borne polyurethane dispersion, the polyurethane bearing groups that are reactive to isocyanate groups.    
     
     
         2 . A liner according to  claim 1 , wherein the polyurethane used in component (b) has a molecular weight in the range of from about 100,000 to about 700,000.  
     
     
         3 . A liner according to  claim 1 , wherein the polyurethane of component (b) is in the form of particles of a size from about 30 to about 1000 nm.  
     
     
         4 . A liner according to  claim 1 , wherein a film prepared from the polyurethane used in component (b) has a modulus of at least about 14 MPa at 100% elongation.  
     
     
         5 . A liner according to  claim 1 , wherein a film prepared from the polyurethane used in component (b) has a value of T g  greater than about 40° C.  
     
     
         6 . A liner according to  claim 1 , wherein the dispersion of the polyurethane contains no co-solvent.  
     
     
         7 . A liner according to  claim 1  which develops a strength of at least about 1 MPa within about 4 hours.  
     
     
         8 . A liner according to  claim 1 , wherein said prepolymer is formed by reacting a polymer bearing hydroxyl groups with a polyisocyanate to form a urethane-containing polymer bearing isocyanate groups, which is purified by removing unreacted polyisocyanate or by quenching unreacted polyisocyanate with a compound that is reactive to isocyanate groups.  
     
     
         9 . A liner according to  claim 1 , wherein the polyurethane dispersion is in admixture with a dispersion of an acrylate polymer, an acrylate polymer, an acrylic-styrene copolymer, a styrene-butadiene copolymer, or a vinyl acetate polymer.  
     
     
         10 . A liner according to  claim 1 , wherein the weight ratio of component (a) to component (b) is in the range of from about 1:3 to about 1:10.  
     
     
         11 . A liner according to  claim 1 , further comprising at least one additive selected from the group consisting of rheological additives, fillers, fire retardants, defoamers and coloring matters.  
     
     
         12 . A liner comprising 
 (a) the product of reaction of: 
 (1) a hydrophilic prepolymer derived from a polyether polyol and bearing isocyanate groups derived from an aromatic polyisocyanate; and  
 (2) a water-borne polyester-acrylate based polyurethane dispersion, the polyurethane bearing groups that are reactive to isocyanate groups; and  
   (b) expandable graphite.    
     
     
         13 . A method for providing a surface with a liner, the method comprising 
 (a) applying to the surface 
 (1) a hydrophilic prepolymer bearing isocyanate groups, and  
 (2) a water-borne polyurethane dispersion, the polyurethane bearing groups that are reactive to isocyanate groups; and  
   (b) allowing the applied components (a) and (b) to react to form the liner.    
     
     
         14 . A method according to  claim 13 , wherein the polyurethane used in component (b) has a molecular weight in the range of from about 100,000 to about 700,000.  
     
     
         15 . A method according to  claim 13 , wherein the polyurethane of component (b) is in the form of particles of a size from about 30 to about 1000 nm.  
     
     
         16 . A method according to  claim 13 , wherein a film prepared from the polyurethane of component (b) has a modulus of at least about 14 Mpa at 100% elongation.  
     
     
         17 . A method according to  claim 13 , wherein a film prepared from the polyurethane of component (b) has a value of T g  greater than about 40° C.  
     
     
         18 . A method according to  claim 13 , wherein the dispersion of the polyurethane contains no co-solvent.  
     
     
         19 . A method according to  claim 13 , wherein the liner develops a strength of at least about 1 Mpa within about 4 hours.  
     
     
         20 . A method according to  claim 13 , wherein said prepolymer (a) is formed by reacting a polymer bearing hydroxyl groups with a polyisocyanate to form a urethane-containing polymer bearing isocyanate groups, which is purified by removing unreacted polyisocyanate or by quenching unreacted polyisocyanate with a compound that is reactive to isocyanate groups.  
     
     
         21 . A method according to  claim 13 , wherein the polyurethane dispersion (b) is in admixture with a dispersion of an acrylate polymer, an acrylate polymer, an acrylic-styrene copolymer, a styrene-butadiene copolymer, or a vinyl acetate polymer.  
     
     
         22 . A method according to  claim 13 , wherein the weight ratio of component (a) to component (b) is in the range of from about 1:3 to about 1:10.  
     
     
         23 . A method according to  claim 13 , further comprising at least one additive selected from the group consisting of rheological additives, fillers, fire retardants, defoamers and coloring matters.  
     
     
         24 . A method according to  claim 13 , wherein the thickness of the liner is in the range of from about 0.5 mm to about 6 mm.  
     
     
         25 . A method according to  claim 13 , wherein said surface is in a mine opening.  
     
     
         26 . A method for providing a surface with a liner, the method comprising 
 (a) applying to the surface 
 (1) a hydrophilic prepolymer derived from a polyether polyol and bearing isocyanate groups derived from an aromatic polyisocyanate;  
 (2) a water-borne polyester-acrylate based polyurethane dispersion, the polyurethane bearing groups that are reactive to isocyanate groups; and  
 (3) expandable graphite; and  
   (b) allowing the applied components (a) and (b) to react to form the liner.    
     
     
         27 . A mine opening lined with a liner formed by the method of  claim 13 .  
     
     
         28 . A mine opening lined with a liner formed by the method of  claim 26.