FORM 2
THE PATENTS ACT 1970
(39 of 1970)
AND
The Patents Rules, 2003
COMPLETE SPECIFICATION
(See section 10 and rulel3)
1. TITLE OF THE INVENTION:
"MANUFACTURING OF HIGHER THICKNESS BOARDS BY FUSIONING
PROCESS"
2. APPLICANT:
(a) NAME: EVEREST INDUSTRIES LIMITED
(b)NATIONALITY: Indian Company incorporated under the Companies Act, 1956
(c) ADDRESS: Gat 152, Lakhmapur Village, Dindori Taluka,
Post Bag No.5, District Nashik -422202, Maharashtra, India.
3. PREAMBLE TO THE DESCRIPTION:
The following specification particularly describes the invention and the manner in which it is to be formed.

FIELD OF INVENTION:
The present invention relates to the manufacturing of higher thickness fiber cement board (FCB). More particularly, present invention relates to the process for production of higher thickness fiber cement board.
BACKGROUND & PRIOR ART:
Fiber Cement is a composite material made up of silica, cement and cellulose fibers. It is mainly used for construction. FCBs are usually manufactured by Hatcheck process. In this manufacturing process, the cement board is prepared by building layer by layer.
Even with the most conventional manufacturing process, making FCB of higher thickness i.e. above 20 -25mm is not possible. Several constraints in the Hatscheck process make it difficult to produce higher thickness boards.
While producing higher thickness sheets after the cut-off of sheet from the bole, the bole bumps on press roller, which will damage the press roller. Handling of higher thickness boards by conveyor and also further by pad is also an issue. Cutting of higher thickness boards from sheet cutting mechanism provided on bole (wire rope) and also further cutting by mechanical cutting system and also water jet cutting system are also major issues of production. As the thickness of sheet increases the bonding between layers also becomes weak and results in delamination of layers during handling and application. Controlling of moisture in green sheet is also one of the issue. Higher the moisture will result in low density, low strength and also high porosity. Consequently there will be an increase in moisture absorption of sheets.
The inventors have made an attempt to solve this problem of conventional Hatschek process of manufacturing FCB by providing a simple and cost-effective process, which is commercially established. Accordingly, in the instant process, two or more fiber cement boards produced by Hatcheck process are fused together by the use of polymer film, eventually producing a single high thickness FCB.

SUMMARY OF INVENTION:
The present invention discloses a novel process for production of high thickness fiber cement board (FCB) comprising bonding or Fusioning of at least two fiber cement board (FCB) by sandwiching at least one polymer film.
Further, the process comprises heating a composite of at least two pre-cured fibre cement board (FCB) sandwiching at least one polymer film. Fusioning takes place when pre-cured FCB goes for final curing at temperature in the range of 175-190° C by introducing steam at 7-12 bar for 8-10 hrs and followed by cooling to room temperature.
FCB produced by the disclosed process has a thickness higher than that of produced by conventional methods, i.e. more than 20mm.
The methodology according to the present invention to produce high thickness board with fusion to have desired characteristic product which overcomes manufacturing limitation of Hatcheck process and explore high thickness product for various applications.
BRIEF DESCRIPTION OF DRAWINGS:
Fig. 1 illustrates the fusion process or process of bonding
DETAILED DESCRIPTION OF INVENTION:
The present invention herein discloses a process for production of high thickness fiber cement board (FCB) comprising bonding or fusioning of at least two fiber cement board sheets by sandwiching at least one polymer film.
Preferably, the process comprises at least two pre-cured fibre cement boards(2) made out of Hatscheck process are sandwiched with at least one polymer film(l). FCB sheets have to be cured for high temperature to gain the final strength, at a temperature in the range of 175-190° C by introducing steam at 7-12 bar for 8-10 hours and followed by cooling to room temperature. Fig. 1 illustrates the process of fusion / bonding of two pre-cured fiber cement board sheets(2). According to Fig. 1, the polymer film(l) is laid flat on the surface

of one of the pre-cured fiber cement board sheet(2). Then the second pre-cured sheet is placed carefully on the polymer film. This arrangement is termed as composite in the present disclosure for better understanding. In order to gain final strength to the composites it is heated from room temperature to 190° C by introducing steam in the chamber at 7-12 bar and hold for 8-10 hours. During heating, the polymer film melts and forms liquid layer. Liquid penetrates into the porous surface of the board sheets and on cooling bonds two board sheets. The contents are allowed to cool for 3-4 hours and are brought to room temperature, thereby forming a single high thickness FCB.
The polymer film(l) consists of co-polymers of ethylene vinyl acetate film, ethylene vinyl alcohol film, ethylene chloride vinyl acetate film, ethylene carbon monoxide film and/or ethylene acrylic film. The thickness of the polymer film(l) is in the range of 15 micron to'150 micron and is corona treated on both sides for better adhesion. Multilayer film can also be used for sandwiching between two fiber cement board sheets. The layers of the film(l) can vary from 2 to 22. Preferably, the surface of the film(l) in contact with fiber cement board sheet(2) is reactive with cementitious surface. The surface tension of the film must be increased on both the side to 40-50 dyne/cm.
The high thickness FCB produced by the process described above is more than 20 mm in thickness. In one embodiment, it is 60 mm in thickness. In another embodiment, it is 100 mm in thickness.
The high thickness FCB produced by the process described above has performance related parameters satisfactorily same or better than the low thickness boards produced by the Hatschek process. By this process we can make Fusioning of any density board. Typical example of one fused board is compared with boards made with conventional board. Table -1 indicates comparison of the performance properties.
Table 1

Sr.
No Properties Normal board Fused board
1. Density 1220-1230 kg/m3 1220-1230 kg/m3

2. Modulus of Rupture 12-15 Mpa 13-15 Mpa
3. Water absorption by weight 30-35% 30-35%
3. Water dampness No droplet at the bottom No droplet at the bottom
4 Inter-lamina bond strength 0.8-1.3 Mpa 0.8 to 1.5 Mpa
5. Performance - Type test (Heat, Rain / warm water / freeze thaw / soak dry) Passes Passes
6. Moisture movement 0.2-0.25% 0.2-0.25%
7. Application workability Standard Similar to standard
The present invention enables to use the high thickness FCB for application like Access floors and mezzanine floors or applications where high Uniform distribution load is required. By this method, a designer board of higher thickness by fusioning (bonding) top layer with designer board and bottom with normal board can be made which is not possible by conventional Hatscheck process. Thus, the present invention successfully overcomes the limitations imposed by the Hatschek process of manufacturing fiber cement boards of higher thicknesses.
Further details of the present invention will be apparent from the examples presented below which are purely illustrative and are not limited to the particular embodiments illustrated herein.
Example 1:
The polymer film is laid flat on the surface of one of the pre-cured fiber cement board sheet. Then the second pre cured sheet is placed carefully on the polymer film. As a part of final curing, the composite is heated from room temperature to 190° C by introducing steam in the chamber at 7-12 bar and hold for 8-10 hours. During heating, the polymer film melts and forms liquid layer. Liquid penetrates into the porous surface of the board sheets and on cooling bonds two board sheets. The contents are allowed to cool for 3-4 hours and then brought to room temperature. A single FCB with thickness of 60mm is formed.

We claim,
1. A process for production of high thickness fiber cement board(FCB) comprising bonding or fusioning of at least two fiber cement board sheets(2) by sandwiching at least one polymer film(l).
2. The process for production of high thickness FCB according to claim 1, wherein said process comprises heating a composite of at least two pre-cured fiber cement board sheets(2) sandwiching at least one polymer film(l) at a temperature in the range of 175-190° C by introducing steam at 7-12 bar for 8-10 hours and followed by cooling to room temperature.
3. The process for production of high thickness FCB as claimed in claim 1, wherein the FCB has a thickness greater than 20mm.
4. The process for production of high thickness FCB as claimed in claim 1, wherein said polymer film(l) comprises co-polymers of ethylene vinyl acetate film, ethylene vinyl alcohol film, ethylene chloride vinyl acetate film, ethylene carbon monoxide film and/or ethylene acrylic film.
5. The process for production of high thickness FCB as claimed in claim 3; wherein thickness of said polymer film(l) is in the range of 15 micron to 150 micron.
6. The process for production of high thickness FCB as claimed in claim 1; wherein said polymer film(l) is corona treated on both sides for better adhesion.
7. The high thickness fiber cement board composition produced by a process claimed in claim 1.
8. The high thickness FCB as claimed in claim7; wherein the FCB has thickness of more than 20mm.