FIELD OF THE INVENTION:
The present invention is in the field of fabrication of epoxy resin cast body having superior „Flame Retardant and Low Smoke (FRLS)‟ properties by incorporating suitable additive material/s into conventional epoxy resin-hardener system in the process of fabrication/casting/moulding. More particularly, the present invention relates to a process of fabricating/casting/moulding additive – modified epoxy resin cast body with targeted level of flame retardant and low smoke properties for high-voltage insulation application.
BACKGROUND OF THE INVENTION
The use of fillers in both thermoplastic and thermosetting polymers is know in the art. The primary motivation for filling various fillers in polymers is to obtain enhanced physical properties of the composite body besides achieving the aspects of cost reduction. Conventionally, fillers are commercial grade material with particle diameter of several microns. In recent years, fillers with nanostructures in the particulates have been reported to be introduced in order to achieve composite materials (both in thermoplastic and thermosetting polymers) with enhanced electrical, mechanical, thermal and environmental properties.
Fillers could be active or inert. When the fillers are inert, they are primarily extenders. However, with the addition of an active filler material or in the form of active coating, fillers can be utilized as reinforcements in the composites.
The most widely used extender type of filler for plastics is calcium carbonate. Calcium carbonate is also been coated with stearic acid and calcium stearate to improve theological properties. Other organic materials, like, salts of alkylolamines and long chain polyaminoamides (high molecular weight acids) have also been used as coating materials.
Flame resistance is an important requirement in many areas due to possible hazards in the use of high voltage fabricated/moulded/cast epoxy transformers / dry type transformers

and other insulating products due to the risk of fire caused by a short circuit. Therefore these products and materials must pass the UL 94 V combustibility test via V-0 classification or equivalent classification for evaluating their flammability. The epoxy resin industrially used worldwide for flame-retardant application contains comparably high concentrations of halogen compounds of ring-brominated aromatic epoxy components, often also combined with antimony trioxide as a synergist. The problem with these compounds is that, while they are highly effective as fireproofing agents, they also have very objectionable properties. Thus, antimony trioxide is listed as a carcinogenic chemical, and aromatic bromine compounds, during thermal decomposition, not only split off bromine radicals and hydrogen bromide, which are highly corrosive, but, especially the highly brominated aromatic compounds may also form highly toxic polybromine benzofurans and polybromine benzodioxins upon decomposition in the presence of oxygen. The disposal of bromine-containing waste materials and toxic waste represents another problem.
Extensive research has been reported in literature to replace bromine-containing fireproofing agents with less problematical substances. Thus, for example, fillers with extinguishing gas effects such as aluminium oxide hydrates, basic aluminium carbonates and magnesium hydroxides, as well as vitrifying fillers such as borates and phosphates have been proposed. Most of these fillers have, however, the disadvantage of worsening, in some cases considerably, the mechanical, chemical, and electrical properties of the composites. In addition, they can leak out of the resin matrix during further processing and cause non-homogeneous castings. As said filler containing resin compositions tend to sedimentation and increase the viscosity of the filled resin system, they require more complicated processing methods.
Conventional high voltage insulating products such as cast epoxy transformers / dry type transformer uses epoxy-anhydride resin system to impregnate or mould or cast the products. The transformer coils are wound with glass fabric tape, glass wool, glass surface mat and such other insulating materials and are impregnated with suitable epoxy resin system. The thickness of the epoxy layer of the transformer coil is commensurate with the desired electrical property of the transformer. The impregnated transformer coils are housed in a metallic housing with suitable fixing and connecting arrangement.

Polymers/Epoxy resins are quantitatively the most important products of the chemical industry used worldwide in everyday life. Epoxy resins have found use in various industrial applications in the last 60 years since they have been commercially available, due to their excellent characteristics as toughness, chemical, mechanical and electrical resistance, low shrinkage on cure and high adhesion to many substrates. They are widely used for surface coatings, castings, laminates, adhesives, composites, potting and painting materials, especially in application areas where their technical advantages balance their higher costs compared to other thermosetting polymers, e.g. electronic and electrical industry, transportation industry. The main disadvantage of epoxy resins, as generally of other organic polymers, is their flammability. In order to meet application requirements their flame retardant properties have to be improved by maintaining other important characteristics as thermal and mechanical properties, and also considering environmental issues as risks for human life and environment, waste treatment and recycling. In the last decade, it was already possible to decrease the total number of fire deaths due to concentrated use of fire retarded materials. it is necessary to further improve the fire retardancy of polymeric materials to minimise the occurrence of a fire and/or to avoid fast propagation of fire in the goal to further decrease the number of fire deaths. At the same time, it is essential to reduce smoke release in case of fire. Indeed, about fifty percent of the fire casualties are due to suffocation with smoke and gases produced in a fire.
Since conventional cast epoxy transformers are moulded with epoxy-anhydride resin system having no filler or additives in the system, it is difficult to achieve the FRLS (Fire Retardant Low Smoke) properties for the transformer.
A comparatively expensive resin system is obtained if aromatic and/or heterocyclic polyepoxy resins, i.e. polyglycidyl compounds, are combined with aromatic polyamines acting as hardening agents. Such polyamines known, for example, from German Patent 2,743,680, result in network polymers that exhibit a particularly high heat distortion and resistance to ageing. European Patent No. 0274646B discloses that, using 1,3,5-tris(3-amino-4-alkylphenyl)-2,4,6-trioxohexahydrotriazines as hardening agents, laminates with a glass transition temperature of up to 245.degree. C. and good processing and machining characteristics can be obtained.

Although the above-mentioned resin systems have a widely different flammability, they all share the disadvantage of being insufficiently flame-retardant. Therefore, in order to meet the requirement of passing the UL 94 V combustibility test via V-0 classification, which is essential for many applications, the use of highly effective bromine-containing fireproofing agents cannot be avoided. As a result, both the potential hazard associated with bromine compounds and the impaired thermal-mechanical characteristics caused by the bromine compounds must be taken into account.
The flame-retardant properties of red phosphorus has also been described (UK Patent No. 1112139), optionally in combination with finely dispersed silicon dioxide or aluminium oxide hydrate (U.S. Pat. No. 3373135). According to these documents, materials are obtained whose use in electro technical and electronic applications is limited due to the phosphoric acid produced in the presence of moisture and the associated corrosion. Moreover the formation of phosphines is expected when red phosphorus is contacted with moisture at higher temperatures. Organic phosphorus compounds, such as phosphoric acid esters, phosphonic acid esters and phosphines, have also been proposed as flame-retardant additives. Since these compounds are known for their "softening" characteristics and are therefore extensively used worldwide as plasticizers for polymers (UK Patent No. 19794), this alternative is therefore also not very promising.
JP-B 60421/1987 discloses a flame retardant resin composition comprising an organic resin and a silicone resin containing at least 80% by weight of trifunctional siloxane units. In consideration of the melt processing with the organic resin, a silicone resin consisting essentially of trifunctional siloxane units is used. Since such a silicone resin imparts less flame retardance, more than 10% by weight of the silicone resin must be added in order to achieve a satisfactory flame retardant effect.
JP-B 31513/1988 discloses a thermal oxidation resistant resin composition in which an alkoxy-terminated silicone resin is added. A liquid low molecular weight silicone having a high alkoxy group content is used. The silicone of this type, even when added in a minor amount, can have substantial influence on the outer appearance and strength of moulded resin parts and tends to bleed out of moulded resin parts. The silicone of this type is

susceptible to hydrolysis to form as by-products flammable low-melting compounds such as alcohols. Then, no satisfactory flame retardant effect is expected.
JP-B 48947/1991, 78171/1996, and 33971/1996 disclose flame retardant resin compositions in which silicone resins consisting of monofunctional and tetrafunctional siloxane units are added. JP-A 128434/1995 discloses a flame retardant resin composition in which a silicone resin containing vinyl-bearing siloxane units is added. However, in order for these compositions to exert satisfactory flame retardant effects, the amount of silicone resin must be increased, and inorganic fillers such as aluminium hydroxide must be used in admixture with halogen or phosphorus compounds.
Thus the prior art fail to disclose a less expensive resin systems for the manufacture of high voltage insulating products such as cast epoxy transformers / dry type transformer and other high voltage insulating products, which are halogen free and which meet the depicted high voltage insulation requirements.
OBJECTS OF THE INVENTION
It is therefore an object of the invention is to propose a process of fabricating/casting/moulding additive – modified epoxy resin cast body with targeted level of flame retardant and low smoke properties for high-voltage insulation application.
Another object is to propose a process of fabricating/casting/moulding additive – modified epoxy resin cast body with targeted level of flame retardant and low smoke properties for high-voltage insulation application in which additive material/s such as nanostructured alumina, calcium carbonate, aluminium phosphate and zinc borate is used.
A further object of the invention is to propose a process of
fabricating/casting/moulding additive – modified epoxy resin cast body with targeted level of flame retardant and low smoke properties for high-voltage insulation application, in which the level/s of loading/incorporation of additive

materials into the conventional epoxy resin-hardener system is predetermined so as to achieve superior Flame Retardant and Low Smoke (FRLS) properties in the additive-modified epoxy a still further object of the invention is to propose a process of fabricating/casting/moulding additive - modified epoxy resin cast body with targeted level of flame retardant and low smoke properties for high-voltage insulation application, in which the processing conditions and process parameters are pre-defined.
SUMMARY OF THE INVENTION
According to this invention there is provided a process of fabricating/casting/moulding additive - modified epoxy resin cast body with targeted level of flame retardant and low smoke properties for high-voltage insulation application. As per the disclosed process, an epoxy resin-hardener composite body is modified by incorporating various additives materials, i.e. nanostructured alumina, calcium carbonate, aluminium phosphate, zinc borate materials respectively into conventional epoxy resin-hardener system. Nanostructured alumina material having a tap density in the range of 0.2 - 0.3 g/cc is synthesized.
The incorporation and fabrication of the nano-structured amorphous alumina, calcium carbonate, aluminium phosphate, zinc borate filler material, comprise the following steps:
. synthesizing nanostructured alumina additive material, having a tap density in the range of 0.2 - 0.3 g/cc by synthesis process with defined properties and characteristics of the material (Table 1);
• preparing an “emulsion of additive material comprising nanostructured alumina along with other additive materials such as calcium carbonate,

aluminium phosphate, zinc borate material” by mixing and treating the additive
materials, with a functionalization agent for example liquid silane and a hardener
for example, carboxylic acid based anhydride in a commercial Epoxy Resin
system, wherein a 3D mixer is adapted, and wherein a
predetermined weight ratio in each of the additive material including the silane and hardener is applied;
• preparing a “mixed liquid” containing conventional Epoxy Resin for example
bisphenol-a Epoxy Resin, flexibility for example polyglycol liquid, and
accelerator for example tertiary amine liquid in a pre-defined ratio to obtain
the “mixed liquid” using a high shear mixer;
. mixing the “emulsion of alumina, calcium carbonate, aluminium phosphate, zinc borate additive material: and the “mixed liquid” together under a vacuum with pre-determined ratio of the two components to produce a “filler-modified Epoxy Resin emulsion”;
• casting thus-obtained “additive-modified Epoxy Resin emulsion” into moulds as per the dimension/shape of the components/specimens including removal of the air bubble in the composite body through de-gassing during casting;
• heat treatment of the cast body in an air circulated oven in a temperature range of 80-90oC preferably at 80oC for a period of 6-8 hours, and produce a pre-cured additive-modified resin body; and
• heat treatment of the pre-cured additive-modified resin body with air in an over at a temperature range of 140o - 150o C preferably at 140oC for a period of 6 - 8 hours, which produces a fully-cured additive-modified Epoxy Resin composite body”.

According to the invention, a validation of the process was made by testing of thus-derived “additive-modified Epoxy Resin composite body: for Flame Retardant and Low Smoke properties (FRLS) as per IEC standard IEC 60076-11.
The derived „epoxy composites‟ according to the invention, can be used as a superior electrical insulation material in the field of high voltage insulation system for producing numerous insulation components for indoor and outdoor use, various bushings in GlS, potential transformers, current transformers, and also for base insulators in the medium-voltage sector, in the production of insulators associated with outdoor power switches, measuring transducers, lead-through, and overvoltage protectors, in switchgear construction, in power switches, dry-type transformers etc.
DETAILED DESCRIPTION OF THE INVENTION:
The present invention teaches modification of conventional Epoxy Resin cast body by identifying and incorporating a new dielectric material (as a filler), i.e., nanostructured amorphous alumina, calcium carbonate, aluminium phosphate, zinc borate filler material and thereby fabricating/casting/moulding an epoxy composite body following pre-defined procedure and process parameters, composite body of which has enhanced Flame Retardant and Low Smoke (FRLS), which would serve as a superior electrical insulating material in high voltage applications.
According to the present invention, there is provided a process for incorporating nano-structured amorphous alumina, calcium carbonate, aluminium phosphate, zinc borate filler material for fabricating filler-modified epoxy composites using variable loading of filler in the Epoxy Resin system so as to enhance the FRLS, which is disclosed in this invention.
In a more particular embodiment of the present invention, the synthesis of nano-structured amorphous alumina, calcium carbonate, aluminium phosphate, zinc borate dielectric material as a filler along with its properties is defined in Table 1.0 (below) and the same is synthesized by adopting appropriately synthesis procedure

in-house. As described, the new filler dielectric material, i.e., nanostructured alumina, calcium carbonate, aluminium phosphate, zinc borate has unique properties, which is amorphous in the XRD and having a tap density in the range of
0.2 - 0.3 g/cc and preferably the material with a tap density of about 0.22-0.28 g/cc were chosen in this invention.
Table 1.0: Properties of Nano Structured Amorphous Barium Aluminate Filler

As per the invention, said nanostructured alumina, calcium carbonate, aluminium phosphate, zinc borate filler material having a loading in the range of 1 - 5 weight% are first to be mixed with silane (Υ-glycidoxypropyltrimethoxysilane) in a weight

range of 0.5 – 2 % along with the hardener liquid (which is chemically carboxylic acid anhydride based liquid) in the conventional Epoxy Resin system using a 3D mixer or a planetary mixer after which an emulsion results.
The resultant emulsion is then mixed with Epoxy Resin (bisphenol-A Epoxy Resin) along with flexibilizer (polyglycol based liquid) and accelerator (tertiary amine based liquid) in pre-determined proportions using a vacuum mixer (with de-gassing attachment) for a period of 30 – 60 minutes, maintaining the vacuum level (0.5 – 3 mbar; lower is better) in which an emulsion-based filler-modified Epoxy Resin system results.
The resultant emulsion-based filler-modified Epoxy Resin system is then casted as per the shape/size of component and then de-gassed followed by heat treatment in air circulated oven by maintaining a set temperature range of 80 - 90oC preferably at 80oC for a period of 6 – 8 hours, which results in pre-cured filler-modified Epoxy Resin body.
The thus-derived pre-cured filler-modified epoxy body is to be heat treated in air circulated oven at a set temperature range of 140 – 150oC preferably at 140oC for a period of 6 - 8 hours and then to be cooled down to ambient temperature by which the fully cured filler-modified epoxy composite body results.
The cured filler-modified epoxy composite bodies/articles are then removed from the moulds in which a standard mould releasing agent was applied prior to casting the filler-modified epoxy composite body.
The filler-modified epoxy composites are then tested for Flame Retardant and Low Smoke (FRLS) performance using standard dimensions of the test samples as per IEC 60076-11 norms.

The Table 2.0 and 3.0 represents FRLS test profile of the filler-modified epoxy composites as compared to blank conventional epoxy system, both of which have been casted under identical conditions.


The invention would be more understood in terms of taking various examples, which are explained in the following:
EXAMPLE 1:
As per this example, Nnano-structured amorphous alumina, calcium carbonate, aluminium phosphate, zinc borate filler dielectric material which is used as a filler was synthesized in-house by adopting appropriately a synthesis process using LPG-fired Spray Pyrolysis System (LPG=liquid petroleum gas).
As described this filler material has its typical properties which is amorphous in the XRD and has a tap density in the range of 0.2 – 0.3 g/cc and the material with a tap density of 0.249g/cc was used in this example. The filler material was oven dried in air at a set temperature of 300oC for a period of 2 hours before using it; this procedure is to let out the filler material from the entrapped moisture.
90-100 parts by weight of liquid hardener (carboxylic acid anhydride based liquid) is first mixed with liquid silane (Gamma-glycidoxypropyltrimethoxysilane) (1-5% wt). To this solution, nanostructured alumina, calcium carbonate, aluminium phosphate, zinc borate filler material 1 wt% equivalent to 1-5%wt is then mixed using a high speed mechanical stirrer for a period of 30 minutes and then ultrasonicated for a period of 15 minutes so that the filler powders are dispersed into the solution and an emulsion is resulted, which is termed as “Emulsion A”.
In another container (glass/plastic or stainless steel), Epoxy Resin (bisphenol A) (90-100%wt), flexibiliser (polyglycol based liquid) (5-10%wt) and accelerator (tertiary amine based liquid) (1-5%wt) were taken and mixed using a mechanical stirrer for a period of 20 minutes to get a uniformly mixed liquid resulted, which is termed as “Liquid B”.

“Liquid B” is then mixed with the “Emulsion A” for a period of 45 minutes using a high shear mechanical mixer. After this mixing, the whole mix is transferred to a vacuum casting system wherein it is degassed.
Stainless steel moulds with pre -determined dimensions are first smeared with standard mould releasing agent and the degassed mix is then vacuum casted to these moulds by maintaining a cavity.
These liquid filled moulds are then transferred to an oven and heat treated in air at 80-90oC for a period of 6 hours which resulted the pre-cured “nanostructured alumina, calcium carbonate, aluminium phosphate, zinc borate filler modified epoxy composites”.
The said pre-cured composites is then heat treated at 140-150oC for a period of another 6 hours and then cooled down at ambient temperature by which the fully cured “nanostructured alumina, calcium carbonate, aluminium phosphate, zinc borate filler modified epoxy composites” with pre- determined dimensions resulted which were released from the moulds and tested for FRLS characteristics following IEC norms.
For comparison, conventional Epoxy Resin body with pre- determined dimensions was also casted without using any filler in the epoxy system and subjected to FRLS characteristics tests following the same IEC norms.
The derived composite showed a weight loss after the Fire Test which is about 3.0% compared to the blank conventional epoxy body of 17.0%.
Example 2 :
In this example, the procedure and all the experimental conditions were followed exactly the same that is described in the example 1, except that the filler load, i.e., the load of nanostructured alumina, calcium carbonate, aluminium phosphate, zinc borate filler material was 2 wt% instead of 1 wt% in the example 1.

The derived composite showed a weight loss after the Fire Test which is about 3.0% compared to the blank conventional epoxy body of 17.15%.
Example 3 :
In this example, the procedure and all the experimental conditions were followed exactly that is described in the example 1, except that the filler load, i.e., load of nanostructured alumina, calcium carbonate, aluminium phosphate, zinc borate filler material was 3 wt% instead of 1 wt% in the example 1.
The derived composite showed a weight loss after the Fire Test which is about 3.5% compared to the blank conventional epoxy body of 17.5%.
Example 4 :
In this example, the procedure and all the experimental conditions were followed exactly that is described in the example 1, except that the filler load, i.e., the load of nanostructured alumina, calcium carbonate, aluminium phosphate, zinc borate filler material was 4 wt% instead of 1 wt% in the example 1.
The derived composite showed a weight loss after the Fire Test which is about 3.2% compared to the blank conventional epoxy body of 17.5%.

WE CLAIM :
1. A process of fabricating/casting/moulding additive-modified epoxy
resin cast body with targeted level of flame retardant and low smoke properties for high voltage insulation application comprising the steps of :
. synthesizing nanostructured alumina additive material, having a tap density in the range of 0.2 - 0.3 g/cc by synthesis process with defined properties and characteristics of the material (Table 1);
• preparing an “emulsion of additive material comprising nanostructured alumina along with other additive materials such as calcium carbonate, aluminium phosphate, zinc borate material” by mixing and treating the additive materials, with a functionalization agent for example liquid silane and a hardener for example, carboxylic acid based anhydride in a commercial Epoxy Resin system, wherein a 3D mixer is adapted, and wherein a
• predetermined weight ratio in each of the additive material including the silane and hardener is applied;
• preparing a “mixed liquid” containing conventional Epoxy Resin for example bisphenol-a Epoxy Resin, flexibility for example polyglycol liquid, and accelerator for example tertiary amine liquid in a pre-defined ratio to obtain the “mixed liquid” using a high shear mixer;
. mixing the “emulsion of alumina, calcium carbonate, aluminium phosphate, zinc borate additive material: and the “mixed liquid” together under a vacuum with pre-determined ratio of the two components to produce a “filler-modified Epoxy Resin emulsion”

• casting/fabricating/moulding thus-obtained “additive-modified Epoxy Resin emulsion” into moulds as per the dimension/shape of the components/specimens including removal of the air bubble in the composite body through de-gassing during casting;
• heat treatment of the cast body in an air circulated oven in a temperature range of 80-90oC preferably at 80oC for a period of 6-8 hours, and produce a pre-cured additive-modified resin body; and
• heat treatment of the pre-cured additive-modified resin body with air in an over at a temperature range of 140o - 150o C preferably at 140oC for a period of 6 - 8 hours, which produces a fully-cured additive-modified Epoxy Resin composite body”.

2. The process as claimed in claim 1, wherein the nanostructured alumina is amorphous in the x-ray diffraction (XRD) pattern with a tap density in the range of 0.2 - 0..3 g/cc, preferably using the filler material with a tap density of 0.25 g/cc and other additive materials are calcium carbonate, aluminium phosphate, zinc borate powers.
3. The process as claimed in claim 1, wherein the „emulsion of nanostructured alumina, calcium carbonate, aluminium phosphate, zinc borate additive material‟ is prepared by mixing and milling, maintaining a weight ratio of “1-5%: 1-5%: 90-100%” for “alumina, calcium cabonate, aluminium phosphate, zinc borate (filler material): silane: hardener” depending on the load of barium aluminate filler to be used in the epoxy composites.

4. The process as claimed in claim 1, wherein the „mixed liquid‟ is prepared by maintaining a weight ratio of “90-100%: 5-10%: 1-5%” for “epoxy: flexibiliszer accelerator”.
5. The process as claimed in any of the preceding claims, wherein the “mixed liquid” is mixed with the “emulsion of nanostructured alumina, calcium carbonate, aluminium phosphate, zinc borate (filler material)” by maintaining a weight ratio of “1:1” in order to obtain “filler-modified epoxy emulsion”.
6. The process as claimed in claim 5, wherein the “filler-modified epoxy emulsion” is cast under vacuum (0.5 – 3 mbar) in a stainless steel mould depending on the dimension of the component for obtaining “green epoxy composite body” which is then pre-cured in an oven with air in the temperature range of 80-90oC preferably at 80oC for a period of 6-8 hours in order to obtain “pre-cured epoxy composite body”.
7. The process as claimed in claim 6, wherein the “pre-cured epoxy composite body” is fully cured by heat treating in the temperature range of 140o-150oC preferably at 140oC for a period of 6 – 8 hours to obtain a ”fully-cured epoxy composite body”.
8. The process as claimed in claim 1, wherein the fully-cured epoxy composite shows FRLS characteristics with weight loss in the range of 3.0-3.5% depending on the load of nanostructured alumina, calcium carbonate, aluminium phosphate, zinc borate filler material filler material in the

composite body as compared to a blank conventional epoxy body with similar dimension 17.0-17.5%, which is hence an enhancement of FRLS properties to that of its counter 'blank conventional epoxy body'.
9. The process as claimed in claim 1, wherein the fully-cured epoxy composite shows FRLS characteristics with less smoke which is clearly visible during testing as compared the dense smoke with toxic gases liberated during burning of 'conventional cast epoxy body'