Lightweight plasterboard and plaster slurry composition used for its manufacture

Abstract

A plaster slurry composition includes plaster, water and starch, the starch having a Brookfield viscosity of less than 60 cps at a temperature below 600 C and a Brookfield viscosity greater than 10,000 cps at a temperature of 700 C.

1 . Plaster slurry composition comprising plaster, water and starch, said starch having a Brookfield viscosity of less than 60 cps at a temperature below 60° C. and a Brookfield viscosity greater than 10,000 cps at a temperature of 70° C. 
   
   
       2 . Composition according to  claim 1 , in which the starch has a Brookfield viscosity of less than 20 cps at a temperature of 60° C. 
   
   
       3 . Composition according to  claim 1 , in which the starch has a Brookfield viscosity of greater than 20,000 cps, preferably greater than 30,000 cps, at a temperature of 70° C. 
   
   
       4 . Composition according to  claim 1 , in which the starch has a Brookfield viscosity of greater than 60,000 cps at a temperature of 80° C. 
   
   
       5 . Composition according to  claim 1 , in which the starch is of the non-retrograding type. 
   
   
       6 . Composition according to  claim 1 , in which the starch has a viscosity at 25° C., after cooling following heating of the starch solution up to 90° C., which is greater than the maximum viscosity obtained during heating of said starch solution. 
   
   
       7 . Composition according to  claim 1 , in which the starch has a viscosity at 25° C., after cooling following heating of the starch solution up to 90° C., of at least 100,000 cps, advantageously of at least 300,000 cps. 
   
   
       8 . Composition according to  claim 1 , comprising, relative to the weight of plaster, between 0.05 and 1%, preferably between 0.1 and 0.5% by weight of starch. 
   
   
       9 . Composition according to  claim 1 , having a pH between 5.5 and 8.5, preferably between 6 and 7.5. 
   
   
       10 . Composition according to  claim 1 , in which the W/P ratio varies from 0.55 to 0.95, preferably from 0.65 to 0.80. 
   
   
       11 . Composition according to  claim 1 , comprising, in addition, a thin-boiling starch. 
   
   
       12 . Plasterboard comprising a core obtainable by setting of a plaster slurry according to  claim 1 . 
   
   
       13 . Plasterboard according to  claim 12 , having a core density varying from 540 kg/m 3  to 1100 kg/m 3 , preferably from 750 kg/m 3  to 950 kg/m 3 . 
   
   
       14 . Plasterboard according to  claim 12 , having one, preferably two, facing(s). 
   
   
       15 . Plasterboard according to  claim 14 , in which the facing is paper, or a mat or nonwoven, preferably a mat of glass fibres and/or of synthetic and/or cellulose fibres, said facing being optionally filled with a fine filler and/or a filler that has optionally received a surface treatment. 
   
   
       16 . Method for preparing a plasterboard consisting of a core based on plaster and at least one, advantageously two, facing(s), said method comprising the following steps:
 preparation of a slurry of the plaster composition according to  claim 1  by mixing the various constituents of the composition with water in a mixer;   deposition of the slurry thus prepared on at least one facing, followed by shaping, into a ribbon, with optional covering of the upper face of the slurry using a second facing;   where appropriate, shaping the edges of the ribbon of the board obtained previously by moulding of the ribbon on profiled bands;   hydraulic setting of the plaster on a manufacturing line while the ribbon of board runs along a conveyor belt; —cutting the ribbon at the end of the line into predetermined lengths; and   drying the boards obtained.   
   
   
       17 . A method for manufacturing a plasterboard, the method comprising using starch having a Brookfield viscosity of less than 60 cps at a temperature below 60° C. and a Brookfield viscosity greater than 10,000 cps at a temperature of 70° C. 
   
   
       18 . A method for increasing the compressive strength of a plasterboard, by at least 0.5 MPa, the method comprising using starch having a Brookfield viscosity of less than 60 cps at a temperature below 60° C. and a Brookfield viscosity greater than 10,000 cps at a temperature of 70° C. 
   
   
       19 . The method of manufacturing a plasterboard, of starch having a Brookfield viscosity of less than 60 cps at a temperature below 60° C. and a Brookfield viscosity greater than 10,000 cps at a temperature of 70° C., in which the starch is according to  claim 2 .