Claims:1. An inorganic additive composition, said inorganic additive comprising:
i. 10-50 wt% of kaolin clay; and
ii. 50-90 wt% of silica sand;
wherein, said kaolin clay comprises 43-45% SiO2, 35-39% Al2O3, 0.5-1% Fe2O3 and 0.3-0.6 % TiO2 ; and
wherein, said silica sand comprises <0.02% Fe2O3 and <0.01% TiO2.
2. The inorganic additive as claimed in claim 1, wherein said inorganic additive, optionally, further comprises 0% to 25% attapulgite clay.

3. The inorganic additive as claimed in claim 1, wherein said kaolin clay has loss on ignition (LOI) in the range of 12-15%.

4. The inorganic additive as claimed in claim 1, wherein said silica sand is obtained from clay washing.

5. A process for preparing the inorganic additive as claimed in claim 1, said process comprising following steps;
a) milling silica sand to obtain silica sand powder, having a particle size less than 25 micron;
b) milling kaolin clay to obtain kaolin clay powder, having a particle size in the range of 25-35 micron;
c) admixing said silica sand powder and said kaolin clay powder to obtain a mixture; and
d) blending said mixture to obtain the inorganic additive,
wherein, said inorganic additive has a particle size less than 45 microns.
6. The process as claimed in claim 5, wherein the step of mixing said kaolin in step b) comprises at least one pre-step of washing, purifying and drying.

7. The process as claimed in claim 5, wherein the mixture obtained in step c) is optionally mixed with ground attapulgite clay having a particle size less than 45 microns.

8. A gasket composition comprising:
a. 45-70 % of at least one polymer;
b. 20-30% of said inorganic additive as claimed in claim 1;
c. 1-5 % of at least one vulcanizing agent;
d. 0.2-2% of at least one curing catalyst; and
e. 10-20 % of at least one filler material.

9. The gasket composition as claimed in claim 8, wherein said gasket composition, optionally, further comprises 5% to 30% of aramid fibers.

10. The gasket composition as claimed in claim 8, wherein said filler material is at least one selected from the group consisting of calcium carbonate, white carbon black, kaolin clay, and soapstone.

11. The gasket composition as claimed in claim 8, wherein said polymer is at least one selected from the group consisting of natural rubber, epoxy resin, PET, polyurethane, teflon, and polyester.

12. The gasket composition as claimed in claim 8, wherein said vulcanizing agent is at least one selected from the group consisting of sulfur, peroxide, and bispheonol.

13. The gasket composition as claimed in claim 8, wherein said curing catalyst is at least one selected from the group consisting of of zinc oxide and stearic acid. , Description:FIELD
The present disclosure relates to an inorganic additive, particularly for use in a non-asbestos gasket composition.
DEFINITIONS
As used in the present disclosure, the following words and phrases are generally intended to have the meaning as set forth below, except to the extent that the context in which they are used indicate otherwise.
The expression ‘gasket’ for the purpose of the present disclosure refers to a material which fills the space between two or more mating surfaces, generally to prevent leakage from or into the joined objects while under compression.
The expression ‘calendaring’ for the purpose of the present disclosure refers to a finishing process under rollers at high temperatures and pressures.
The expression ‘aramid fibers’ for the purpose of the present disclosure refers to a class of heat-resistant and strong synthetic fibers and used as an asbestos substitute.
The expression ‘kaolin clay’ also known as ‘china clay’ for the purpose of the present disclosure refers to a clay mineral with the chemical composition Al2Si2O5(OH)4.
The expression ‘silica sand’ for the purpose of the present disclosure refers to a naturally occurring granular material composed of finely divided rock and mineral particles.
The expression ‘attapulgite clay’ also known as ‘palygorskite’ for the purpose of the present disclosure refers to magnesium aluminium phyllosilicate of formula (Mg,Al)2Si4O10(OH)•4(H2O).
The expression ‘aging’ for the purpose of the present disclosure refers to a process of keeping a mixture/composition under predetermined conditions so as to complete the reactions between a polymer and other material. In rubber processing, the term curing is used, where cross linking of the rubber is enhanced by providing some reaction time in solvents, i.e, aging.
BACKGROUND
Gaskets are widely used as sealing elements in various fields. Gaskets have the ability to prevent leakage of fluids from through joints. Compressed asbestos fiber (CAF) material has been used for preparing non-metallic gaskets. Asbestos is a natural fibrous material and is microscopic in nature. Asbestos is extremely durable, resistant to fire, most chemical reactions and breakdowns. Due to these properties, asbestos has been used in a number of different commercial and industrial applications, such as fire retardant coatings, concrete, bricks, pipes and fireplace cement; heat, fire, and acid resistant gaskets, pipe insulation, ceiling insulation, fireproof drywall, flooring, roofing, lawn furniture, and drywall joint compound. The strength of asbestos, combined with its resistance to heat, allows it to be the material of choice in a variety of products including, but not limited to, roofing shingles, floor tiles, ceiling materials, cement compounds, textile products, automotive parts, and the like.

Recently, the use of asbestos has been strictly regulated because of its toxicity. Exposure to asbestos has been linked to a number of lung and respiratory health conditions, mesothelioma and pleural changes.

Thus, nowadays, asbestos is required to be replaced by alternative fibers, fillers, or additives. These substitutes to asbestos were developed using reinforcing fibers to achieve high strength, and additives like inorganic materials such as clays and precipitated silica were used. Such material needs to have mechanical properties such as resilience, stress relaxation, and compressibility, particularly for replacing the use of asbestos in gaskets.

Therefore, there is a need for a non-asbestos material/composition that has the desired mechanical properties as that of asbestos.

OBJECTS
Some of the objects of the present disclosure, which at least one embodiment herein satisfies, are as follows.
It is an object of the present disclosure to ameliorate one or more problems of the prior art or to at least provide a useful alternative.
An object of the present disclosure is to provide an inorganic additive for non-asbestos gasket composition.
Another object of the present disclosure is to provide an inorganic additive which when added to a gasket material gives the desired mechanical properties.
Yet another object of the present disclosure is to provide an inorganic additive for improving transverse tensile strength and resilience rate of gasket composition.
Still another object of the present disclosure is to provide an inorganic additive that has fine particle size distribution.
Yet another object of the present disclosure is to provide a leak proof gasket.
Other objects and advantages of the present disclosure will be more apparent from the following description, which is not intended to limit the scope of the present disclosure.

SUMMARY
In one aspect, the present disclosure relates to an inorganic additive for non-asbestos gasket composition. The inorganic additive composition comprises 10 wt% to 50 wt% of kaolin clay, 50 wt% to 90 wt% of silica sand. The kaolin clay used in the additive composition comprises 43-45% SiO2, 35-39% Al2O3, 0.5-1% Fe2O3, and 0.3-0.6 % TiO2; and has 12-15% of LOI (Loss on Ignition). The inorganic additive may optionally further comprise attapulgite clay in the range of 0 wt% to 25 wt%.
In another aspect, the present disclosure comprises a process for preparing the inorganic additive.
Initially, silica sand is milled to obtain a powder of silica sand having a particle size less than 25 micron. In the second step, kaolin clay undergoes milling to obtain ground kaolin having a particle size in the range of 25 micron to 35 micron. In the third step, the silica sand powder and the kaolin clay powder obtained in the above steps are mixed to obtain a mixture and the mixture is blended to obtain the inorganic additive, having a particle size less than 45 micron.
The present disclosure further relates to a gasket composition comprising the inorganic additive, for preparing gasket sheets.
DETAILED DESCRIPTION
In accordance with the first aspect of the present disclosure, an inorganic additive composition is provided for improving transverse tensile strength and resilience rate of a gasket composition, particularly in non-asbestos gasket sheets. The inorganic additive composition comprises: 10-50 wt% of kaolin clay; 50-90 wt% of silica sand.
The kaolin clay used in the additive composition comprises 43-45% SiO2, 35-39% Al2O3, 0.5-1% Fe2O3, 0.3-0.6 % TiO2 and has 12-15% of LOI (Loss on Ignition). The silica sand used in the additive composition comprises 0.02 to 0.2% Fe2O3 and 0.01 to 0.5% TiO2. In an embodiment of the present disclosure, the silica sand is obtained from clay washing.
The inorganic additive may optionally further comprises attapulgite clay in an amount ranging from 0 wt% to 25 wt%.
The inorganic additive can be used in non-asbestos gasket composition. It may also be used in fillers, which are used in paint, refractory, and ceramic composition.
The second aspect of the present disclosure provides a process of preparing the inorganic additive material. The process involves, fine grinding of natural mineral materials such as the silica sand and kaolin clay. Silica sand is milled to obtain silica powder, having a particle size less than 25 micron. Kaolin clay is milled to obtain kaolin clay having a particle size in the range of 25 micron to 30 micron.

In one embodiment of the present disclosure, silica sand used is generated as a by-product from clay washing. The silica sand content in the inorganic additive composition varies from 50-90 %.
The amount of kaolin clay in the inorganic additive composition is in the range of 10-50%. Crude kaolin clay can be first subjected to washing to remove coarse grits and impurities, to purify the kaolinite content. Further, the iron impurities of kaolin clay can be reduced by bleaching process and dewatering process using a pressure filter press, followed by drying process to remove the moisture content.
The process of the present disclosure, optionally further comprises attapulgite clay in the range of 0 wt% to 25 wt%. Attapulgite clay is ground to obtain ground attapulgite clay having a particle size in the range of 400 mesh to 1000 mesh. In the inorganic additive composition of the present disclosure, the proportion of both, kaolin clay and attapulgite clay (palygorskite) mineral varies from 10-50%. Attapulgite clay (palygorskite) can be separately milled when used in the inorganic additive composition.
In one embodiment, the silica sand is milled by using wet ball mill to obtain a powder, having a particle size in the range of 15 microns to 25 microns. The grinding media used to grind the silica sand are quartz lumps of size in the range of 200 mm to 500 mm. Water is used as a liquid media to facilitate the grinding process to obtain the required mesh sizes. Kaolin clay is milled by using dry milling system separately, to obtain particles having a particle size in the range of 25 microns to 35 microns. Attapulgite clay is ground to a particle size in the range of 400 - 1000 mesh, which can optionally be mixed with silica sand and kaolin clay in the process of preparing the inorganic additive composition. All powdered materials are mixed thoroughly in a dry process, followed by blending in a high shear mixer, such as ribbon blender or sigma blender, to obtain the inorganic additive. The particle size of the so obtained inorganic additive is less than 45 micron.
The third aspect of the present disclosure provides a gasket composition based on the inorganic additive. The gasket composition comprises 20-50% of at least one polymer/rubber; 5-25% of the inorganic additive of the present disclosure; 1-4% of at least one vulcanizing agent; 0.2-2% of at least one curing catalyst; and 5-10 % of at least one filler material.
In the gasket composition of the present disclosure, the polymer can be at least one selected from the group consisting of natural butyl rubber natural rubber contains mostly poly-isoprene group, ethylene propylene rubber (EPM), Silicone rubber, and the like. The natural butyl rubber can have varying purity along with other elastomers. The other elastomer can be selected from the group consisting of synthetic isoprene, butyl rubber, styrene butadiene rubber (SBR), Nitrile rubber, ethylene vinyl acetate (EVA), polyacrylic rubber, and the like.
The filler material can be at least one selected from the group consisting of calcium carbonate, white carbon black, Kaolin clay, and soapstone.
The vulcanizing agent can be at least one selected from the group consisting of sulfur, peroxide, bispheonol, and the like.
The curing catalyst can be at least one selected from the group consisting of zinc oxide, stearic acid and the like
The process of manufacturing of non-asbestos gasket composition in the form of gasket sheet involves the processes of mixing-molding, calendaring and drying. In one embodiment, the inorganic additive of the present disclosure is used in fillers, which are used in paint, refractory, and ceramic compositions.

The incorporation of the inorganic additive material of the present disclosure in rubber/polymers can be carried out by using a mill mixer to improve the plasticity of rubber or polymer. The thoroughly mixed mixture is allowed to age for 14 -20 hours using organic solvents and further subjected to a calendaring process. The required shape of the gasket sheet can be obtained by pressing the major components, i.e., rubber and/or polymer in a roller mill at a temperature in the range of 60 oC to 120 oC. The rubber or polymer can be mixed using a roller mill where the distance between the rollers is in the range of 5 mm to 20 mm. The other additives such as fibers, precipitated silica, clays, and other rheological additives can also be added during the mixing process at a temperature in the range of 60 oC to 90 oC, to mix the components with rubber/polymer.

Different layers of polymer mixes can be added one by one to produce a single sheet of non-asbestos gasket sheet. Further, rollers rotating in opposite directions in the calendaring process can be adjusted in terms of speed, clearance between the rollers and optimized temperatures to produce the gasket sheets. In an exemplary embodiment, the gasket sheet contains two layered or three layered sheet, wherein during calendaring the first layer is calendered and then the second layer is spread to form a two layer sheet. So visually the top layer can be of a different color such as yellow, off-white, orange and the bottom layer can be green, red or any other color.

Improved smoothness and surface finish are obtained in gaskets which are prepared by the use of the inorganic additive composition of the present disclosure. The inorganic additive composition can be added in the range of 5 % to 25 % during the initial mixing of the polymer/rubber, and further aging can be carried out followed by the calendaring process. Addition of the inorganic additive of the present disclosure results in improved mechanical properties, i.e., tensile strength, resilience rate and elongation properties are enhanced by 30 % to 40 % based on the ratio of mixing and dose of the inorganic additive material.
The present disclosure is further illustrated herein below with the help of the following experiments. The experiments used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of embodiments herein. The present disclosure is further described in light of the following experiments which are set forth for illustration purpose only and not to be construed for limiting the scope of the disclosure. These laboratory scale experiments can be scaled up to industrial/commercial scale.
EXPERIMENTAL DETAILS:
Experiment 1: Preparation of the inorganic additive in accordance with the present disclosure-
800 g waste silica sand generated from the kaolin/clay industry was ground and ball milled to obtain a powder having particle size 22 microns. 150 g of china clay/kaolin was mixed with the silica sand powder having particle size 32 microns. The mixing was done in a ribbon blender for 2 hours. 50 g of attapulgite with fineness 41 microns was mixed thoroughly for 50 minutes. Thus prepared inorganic silicate additive was used in the gasket formulation.
Experiment 2: Preparation of the inorganic additive in accordance with the present disclosure-
200 g of kaolin (previously washed, dried and fine milled) with a particle size of 29 microns was mixed with finely grinded 750 g waste silica sand having a particle size 25 microns in ribbon blender for 2 hours. Thus prepared inorganic silicate additive was used in the gasket formulation
Experiment 3: Gasket composition based on the inorganic additive of Expt 1 and 2:
The conventional gasket composition and the gasket composition comprising the inorganic additive of experiment 1 and 2 are given in the following Table 1 and the corresponding properties are illustrated below-

Table 1:
Components Gasket composition as per Conventional method (without Inorganic additive) Gasket composition using Inorganic additive of Expt 1 in accordance with the present disclosure Gasket composition using Inorganic additive of Expt 2 in accordance with the present disclosure

Composition
Natural rubber 48 wt% 48 wt% 32 wt%
Epoxy resin 20 wt% 20 wt% 26 wt%
Aramid fibers 9 wt% 0 0
Peroxide based vulcanizing agent 2.3 wt% 2.3 wt% 2.3 wt%
Curing catalyst- Stearic acid 0.7 wt% 0.7 wt% 0.7 wt%
Kaolin Clay 8 wt% 0 0
Calcium carbonate 12 wt% 12 wt% 12 wt%
Inorganic additive of the present disclosure 0 17 wt% 27 wt%
Properties
Transverse tensile strength (mPa) 7.81 9.69 (24%) 8.91(14%)
Elongation, % 7.5 10.8 (44%) 9.74 (30%)
Resilence rate 43.71 53.5 (22%) 51.2 (17%)
Smoothness Slightly rough Smooth Smooth
From Table 1 it is observed that the properties of gasket composition using inorganic additive is improved, such as there is 24% improvement in tensile strength, 22% increase in resilience rate and 44% improvement in elongation percentage of gasket composition/sheet. Further, in experiment no 2, the formulatin is varied by increasing the epoxy resin content. The results shows that 14% improvement in tensile strength, 17% increase in resilience rate and 30% in improvement in elongation percentage.
TECHNICAL ADVANCES AND ECONOMICAL SIGNIFICANCE
The present disclosure described herein above has several technical advantages including, but not limited to, the realization of:
? improvement in mechanical properties of the gasket composition in the form of gasket sheet, such as tensile strength and resilence rate;
? the inorganic additive of the present disclosure provides a smooth surface of the gasket sheet; and
? a simple process for preparing the inorganic additive.

Throughout this specification the word “comprise”, or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.
The use of the expression “at least” or “at least one” suggests the use of one or more elements or ingredients or quantities, as the use may be in the embodiment of the disclosure to achieve one or more of the desired objects or results.
Any discussion of documents, acts, materials, devices, articles or the like that has been included in this specification is solely for the purpose of providing a context for the disclosure. It is not to be taken as an admission that any or all of these matters form a part of the prior art base or were common general knowledge in the field relevant to the disclosure as it existed anywhere before the priority date of this application.
The numerical values mentioned for the various physical parameters, dimensions or quantities are only approximations and it is envisaged that the values higher/lower than the numerical values assigned to the parameters, dimensions or quantities fall within the scope of the disclosure, unless there is a statement in the specification specific to the contrary.
While considerable emphasis has been placed herein on the components and component parts of the preferred embodiments, it will be appreciated that many embodiments can be made and that many changes can be made in the preferred embodiments without departing from the principles of the disclosure. These and other changes in the preferred embodiment as well as other embodiments of the disclosure will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the disclosure and not as a limitations.