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:
"USE OF WOLLASTONITE IN FIBER CEMENT ROOFING SHEETS PRODUCTION TO IMPROVE FILTRATION"
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 cost effective reinforced fiber cement roofing sheet to improve filtration thereby improving productivity and raw material yield. In particular, the present invention relates to both asbestos and non-asbestos fiber cement roofing sheets comprising the use of wollastonite, in the composite material, which helps in carrying fine materials and thereby helps in keeping water system clean during production. The invention further relates to in the production of reinforced Fiber cement roofing sheets on Hatschek machine to improve the filtration and the product properties.
BACKGROUND & PRIOR ART:
Fiber Cement roofing sheets are known for their strength and durability. They are mainly of two types: Asbestos Fibre Cement Roofing sheets and Non-Asbestos Fibre Cement Roofing sheets.
Asbestos Fiber Cement roofing sheet is a composite material made up of Pozzolonic materials, Cement, Asbestos fibers, and Cellulose fibers. In case of non asbestos fiber cement roofing sheets, synthetic fibers like Polypropylene and Polyvinyl alcohol fibers are used as reinforcing elements. Both asbestos and non asbestos roofing sheets are used for roofing and cladding application. These sheets are usually manufactured by Hatcheck process. In the manufacturing of these sheets, solid material is reinforced with asbestos and other fibers. Retention of the solids on sieve is improved by fibrous material.
Wollastonite is used as one of the fiber in making asbestos roofing sheet as a partial replacement to asbestos fiber. Wollastonite is a white coloured calcium inosilicate mineral (CaSiO3) that may contain small amounts of iron, magnesium, and manganese substituting for calcium. It is formed when impure limestone or dolostone is subjected to high temperature and pressure, sometimes in the presence of silica-bearing fluids as in skarns or contact metamorphic rocks. It is named after the English chemist and mineralogist William Hyde Wollaston (1766-1828). Wollastonite is an industrially important mineral due to its high brightness and whiteness, fluorescence, low moisture

and oil absorption and low volatile content. One of the important properties that make wollastonite so useful is its shape. It has high aspect ratio.
In an article appearing in Indian Concrete Journal, Vol. 60, May 1986 titled "Use of wollastonite in asbestos-cement products" by Kalyan Dass et. al., authors have proposed wollastonite as an alternate to chrysotile asbestos in asbestos-cement sheet products. Studies in this article reveal that the substitution upto 10 percent of chrysotile fiber by wollastonite in asbestos-cement sheet products is possible without significantly affecting their properties.
A US Patent No. 4377415 titled "Reinforce cement sheet product containing wollastonite for reducing shrinkage" relates to a cement-wollastonite product comprising Portland cement binder in an amount of between about 40% and 90% by weight, a wollastonite in an amount between about 10% and 60% by weight to provide low wet-to-dry dimensional changes. The cement-wollastonite product further includes silica in an amount of between about 5% and 30% by weight, fibers such as acetalized polyvinyl alcohol in an amount of between about 1% and 15%.
A US Patent No. 4428775 titled "Reinforced cement sheet product containing no asbestos for fabricating Hatschek machine" relates to reinforced cement sheet product which does not contain asbestos. It discloses a fiber-cement product comprising Portland cement in an amount between 40% and 80% by weight, fibers in an amount of between 1% and 15% by weight, clay in an amount of between about 2% and 15% by weight and polyethylene oxide in a sufficient amount to co-act with said in an aqueous slurry containing said Portland cement, fibers and clay to retain fines in a mat formed from said slurry.
The present inventors have attempted to make cost effective fiber cement roofing sheets including the use of wollastonite which improves filtration thereby improving the product properties like density, strength and stiffness of the products and also improves productivity and yield of raw material.

SUMMARY OF INVENTION:
In an aspect, the present invention discloses a reinforced fiber cement roofing sheet composition including wollastonite to improve filtration thereby improving productivity and raw material yield. The fiber cement roofing sheet of the instant invention consists both asbestos and non-asbestos roofing sheets including wollastonite along with pulp, synthetic fiber, flyash and cement.
In another aspect, the present invention discloses the manufacture of reinforced fiber cement roofing sheet on Hatschek machine.
The composition comprises pulp, synthetic fiber, flyash, cement and wollastonite.
DETAILED DESCRIPTION:
The present invention relates to cost effective Fiber cement roofing sheets composite material including the use of wollastonite in said composite material to improve the filtration thereby improving the productivity and raw material yield. The present invention also relates to the production of same on Hatschek machine. Further, the fiber cement roofing sheet is asbestos as well as non-asbestos type.
The Fiber Cement roofing sheets which are composite materials are made up of Pozzolonic materials, cement, Asbestos fibers, cellulose fibers. In case of non asbestos fiber cement roofing sheets synthetic fiber like Polypropylene and Polyvinyl alcohol fiber are used as reinforcing elements. Both asbestos and non asbestos roofing sheets are mainly used either for roofing or for cladding applications.
In an embodiment, the present invention discloses a reinforced fiber cement roofing sheet to improve filtration; characterized in that the composition of asbestos fiber cement roofing sheets comprises; asbestos in 10-15%, pulp 1-5%, synthetic fibers 1-5%, flyash 25-40%, cement 50-60%, wollastonite 5-15%; and characterized in that the composition of non-asbestos fiber cement roofing sheets comprises; pulp 1-5%, synthetic fibers 1-5%, flyash 10-20%), cement 70-80%, wollastonite 5-15%, additives 5-10%; wherein process

characteristics of asbestos fiber cement roofing sheets have 100-150ml/lit sieve filtrate without wollastonite, and 40-60 ml/lit sieve filtrate with wollastonite; and wherein process characteristics of non-asbestos fiber cement roofing sheets have 200-250 ml/lit sieve filtrate without wollastonite and 50-80 ml/lit with wollastonite; further wherein product density in range of 1300-1350 without wollastonite, 1400-1450 with wollastonite.
In another embodiment, the present invention discloses the manufacture of reinforced fiber cement roofing sheet on Hatschek machine. The entire process of manufacturing is carried out by using slurry system. Raw materials are prepared with the predetermined consistency in water separately and finally mixed in a main mixing tank with the use of propeller to mix and agitate the slurry to get uniform mix of composite material. Thus prepared slurry is fed into Hatschek machine to manufacture sheets. In the manufacturing of these sheets, solid material is reinforced with asbestos or synthetic and other fibers. Retention of the solids on sieve is improved by using fibrous material.
The filtration is improved by using wollastonite. Since wollastonite is a fibrous mineral, fines are carried along with wollastonite when forms a layer on the sieve cylinder. Since wollastonite carries fine particles of raw materials, the product density is improved and porosity is reduced. Thus, handleability of non-asbestos fiber cement roofing sheets is improved.
The retention of the solid is increased with the use of wollastonite in the Hatscheck process. Wollastonite also acts as a very good filtration aid. The pick up of fine particles is enhanced with the use of wollastonite, which otherwise would have been lost. These fines contribute to better packing density in the product and helps in increasing the strength and performance properties of the product. It is observed that improved filtration also results in fast pick up of the solids hence improves production and bonding between layers. Since ultra fine particles are picked up, system water is very clear and same is effectively helpful in felt cleaning. Wollastonite is a mineral fibrous material with high aspect ratio, it has proven to be a very good process aid which controls process parameters effectively and hence other fibers like cellulose and asbestos are replaced by wollastonite.

The following are advantages of wollastonite:-
1. Better filtration - Wollastonite helps in better filtration process and clear water is drained resulting in maintaining improved process conditions.
2. Better pick up of the fine matrix helps stable and effective process running, increase the productivity & improves packing density of the final product.
3. Dimensional stability of the product is achieved by the use of wollastonite. Also formation of any cracks due to moisture variation is avoided.
4. It has better affinity with fine powders; hence the strength of the product and layer bonding is increased.
5. It is locally available in ample quantity.
6. Wollastonite is environmentally safe material compare to asbestos.
7. Being a fibrous material, other fibrous material like asbestos and cellulose are partially replaced by wollastonite.
8. Effective cost of the formulation is reduced and hence it is one of the good cost reduction options.
During the process, it is added in the shear edge runner mill along with asbestos fibers. Abrasion and hardness property of the Wollastonite helps proper opening of asbestos fibers and ease the milling process. Time of the milling is shortened because of wollastonite. In the present process, wollastonite is treated with asbestos fiber and hence a uniform and homogeneous mixture is formed. This entanglement of wollastonite with asbestos gives effective utilization and is beneficial to the process.

Example 1:

Asbestos fiber cement roofing sheets (%) Non-asbestos fiber cement roofing sheets (%)
Asbestos 10-15 Nil
Pulp 1-5 1-5
Synthetic fibers 1-5 1-5
Flyash 25-40 10-20
Cement 50-60 70-80
Wollastonite 5-15 5-15
Other additives Nil 5-10
The process characteristics are as follows:

Asbestos Fiber Cement Non-asbestos Fiber
Roofing sheets Cement Roofing sheets
Sieve filtrate without 100-150 200-250
Wollastonite (ml/lit)
Sieve filtrate with 40 -60 50-80
Wollastonite (ml/lit)
The product densities are as follows:

Asbestos Fiber Cement Non-asbestos Fiber Cement
Roofing sheets Roofing sheets
Density (kg/m3) Density (kg/m3)
Without wollastonite 1300-1350 1300-1350
With Wollastonite 1400-1450 1400-1450

WE CLAIM,
1. A reinforced fiber cement roofing sheet produced by Hatschek process to improve filtration, characterized in that the composition of asbestos fiber cement roofing sheets comprises; (i) asbestos in 10-15%, (ii) pulp 1-5%, (iii) synthetic fibers 1-5%., (iv) flyash 25-40%, (v) cement 50-60%, (vi) wollastonite 5-15%;
and characterized in that the composition of non-asbestos fiber cement roofing sheets comprises; (i) pulp 1-5%, (ii) synthetic fibers 1-5%, (iii) flyash 10-20%, (iv) cement 70-80%, (v) wollastonite 5-15%, (vi) additives 5-10%;
wherein process characteristics of asbestos fiber cement roofing sheets have 100-150 ml/lit sieve filtrate without wollastonite, and 40-60 ml/lit sieve filtrate with wollastonite; and wherein process characteristics of non-asbestos fiber cement roofing sheets have 200-250 ml/lit sieve filtrate without wollastonite and 50-80 ml/lit with wollastonite; further wherein product density in range of 1300-1350 without wollastonite, 1400-1450 with wollastonite.