Gypsum fiber board and method for producing gypsum fiber boards

Abstract

A gypsum fiber board produced in a Siempelkamp dry-process, comprising 75 wt % to 90 wt % (relative to the total dry mix) of calcium sulfate hemi-hydrate and 10 wt % to 25 wt % (relative to the total dry mix) paper fibers, wherein the calcium sulfate hemi-hydrate is a mixture of α-calcium sulfate hemi-hydrate and β-calcium sulfate hemi-hydrate, wherein the content of α-calcium sulfate hemi-hydrate in the mixture is at least 5 wt % (relative to the total calcium sulfate hemi-hydrate) is disclosed. Also disclosed is a method for producing a gypsum fiber board of a thickness of 23 mm in a Siempelkamp dry-process.

What is claimed is: 
     
         1 . Gypsum fiber board produced in a Siempelkamp process, comprising 75 wt % to 90 wt %, relative to the total dry mix, of calcium sulfate hemi-hydrate and 10 wt % to 25 wt %, relative to the total dry mix, paper fibers, wherein the calcium sulfate hemi-hydrate is a mixture of α-calcium sulfate hemi-hydrate and β-calcium sulfate hemi-hydrate, wherein the content of α-calcium sulfate hemi-hydrate is at least 5 wt %, relative to the total calcium sulfate hemi-hydrate. 
     
     
         2 . Gypsum fiber board according to  claim 1 , wherein the content of α-calcium sulfate hemi-hydrate is at least 20 wt %, relative to the total calcium sulfate hemi-hydrate, in particular, about 30 wt %, relative to the total calcium sulfate hemi-hydrate. 
     
     
         3 . Gypsum fiber board according to  claim 1 , wherein the content of β-calcium sulfate hemi-hydrate is at least 50 wt %, relative to the total calcium sulfate hemi-hydrate, in particular, about 60 wt %, relative to the total calcium sulfate hemi-hydrate. 
     
     
         4 . Gypsum fiber board according to  claim 1 , further comprising retardant, in particular, citric acid. 
     
     
         5 . Gypsum fiber board according to  claim 1 , further comprising an accelerator, in particular, dihydrate. 
     
     
         6 . Gypsum fiber board according to  claim 1 , wherein the board has a thickness greater than 19 mm, in particular, of about 23 mm. 
     
     
         7 . Gypsum fiber board according to  claim 1 , wherein a portion of less than 90% in particular less than 70% of the gypsum fiber composition has a granulation above 1 μm. 
     
     
         8 . Gypsum fiber board according to according to  claim 1 , wherein the fibers have a minimum length of 1 μm, and wherein the content of fibers having a length greater than 90 μm is less than 45 wt %, relative to the total amount of paper fibers. 
     
     
         9 . Gypsum fiber board according to  claim 1 , further comprising wetting agents. 
     
     
         10 . Gypsum fiber board according to  claim 1 , wherein the finished board has a bulk density within the range of 1000 to 1500 kg/m 3 , in particular 1220 to 1390 kg/m 3 , and a weight per unit area in the range of 25 to 35 kg/m 2 , in particular 28 to 32 kg/m 2 . 
     
     
         11 . A method for producing gypsum fiber boards, comprising the steps of:
 preparing a compressible mat of gypsum-containing material from a mixture comprising 75 wt % to 90 wt %, relative to the total dry mix, of calcium sulfate hemi-hydrate and 10 wt % to 25 wt %, relative to the total dry mix, of paper fibers, wherein the calcium sulfate hemi-hydrate is a mixture of α-calcium sulfate hemi-hydrate and β-calcium sulfate hemi-hydrate, wherein the content of α-calcium sulfate hemi-hydrate in the mixture is at least 10 wt %, relative to the total calcium sulfate hemi-hydrate;   moving the dry compressible mat of gypsum-containing material on a conveyor belt to a hydration water tank, and   hydrating the gypsum-containing material with hydration water added from above to the top surface of the mat in excess prior to passing the gypsum-containing material through a continuous press to form an endless gypsum fiber board having a thickness greater than 19 mm.   
     
     
         12 . The method according to  claim 11 , wherein the step of preparing the compressible mat comprises mixing at least 20 wt %, relative to the total calcium sulfate hemi-hydrate, of α-calcium sulfate hemi-hydrate, with a least 50 wt %, relative to the total calcium sulfate hemi-hydrate, of β-calcium sulfate hemi-hydrate. 
     
     
         13 . The method according to  claim 11 , wherein the step of preparing the compressible mat comprises mixing about 30 wt %, relative to the total calcium sulfate hemi-hydrate, of α-calcium sulfate hemi-hydrate with about 60 wt %, relative to the total calcium sulfate hemi-hydrate, of β-calcium sulfate hemi-hydrate. 
     
     
         14 . The method according to  claim 11 , further comprising a step of adding a retardant and/or a step of adding an accelerator. 
     
     
         15 . The method according to  claim 11 , further comprising a step of adding a citric acid retardant and/or a step of adding an a coated dihydrate accelerator. 
     
     
         16 . The method according to  claim 11 , wherein the granulation of less than 90% of the gypsum fiber composition is above 1 μm. 
     
     
         17 . The method according to  claim 11 , wherein the granulation of less than 70% of the gypsum fiber composition is above 1 μm. 
     
     
         18 . The method according to  claim 11 , wherein the thickness of the dry compressible mat of gypsum-containing material prior to adding water is within the range of 80 mm to 100 mm, in particular 85 mm to 95 mm. 
     
     
         19 . The method according to  claim 11 , wherein the thickness of the dry compressible mat of gypsum-containing material prior to adding water is within the range of 85 mm to 95 mm.