TITLE:
A nano-additive modified epoxy resin composition for high voltage insulation
applications.
FIELD OF INVENTION
This invention relates to an additive-modified epoxy resin composition and a
method for fabrication into composites bodies thereof. The invention specifically
relates to an additive-modified epoxy formulation, which are free from solvents
or halogens for impregnating, casting and moulding of high voltage transformer
product/s targeting improvement in FRLS (Fire Retardant Low Smoke) properties
as compare to that of blank epoxy bodies.
BACKGROUND OF THE INVENTION
Composites based on epoxy resins and inorganic or organic reinforcing materials
have become very important in many industrial fields and in everyday life. The
processing of epoxy resins are relatively simple. The good mechanical electrical
and thermal properties of cured epoxy resin moulded materials are
advantageously used for different applications including that of high voltage
insulation application.
Epoxy resins are processed into composites and moulded objects through
different techniques. For this purpose inorganic or organic reinforcing materials
or embedding components in the form of fibres, non-woven and woven fabrics,
round or of flat-shaped articles are impregnated with the resin. In the case of
moulded high voltage insulated objects this is accomplished with a solvent free,
low viscosity resin at elevated temperatures. When they are processed into

composites and moulded objects, the resin should be able to freely penetrate
through the porous reinforcing materials and bond with the reinforcing materials
or embedding components as well as with the materials provided for the
composite as firmly and permanently as possible under pressure, i.e. the cross-
linked epoxy resin matrix must have a high interfacial adhesion to the reinforcing
materials, or embedding components, as well as to the materials to be bonded
such as metals, ceramics, minerals, and organic materials.
In the cured state, composites and moulded objects are normally expected to
have high mechanical strength and thermal stability, as well as chemical
resistance, and heat distortion or resistance to ageing. For electrotechnical and
electronic applications, the requirements also include adequate high electrical
insulation capability and, for special applications, a plurality of other
requirements. For use as moulded high voltage insulating objects, high
dimensional stability over a broad temperature range, good adhesion to glass
and copper, high surface resistivity, low dielectric loss factor and low water
absorption are required.
Flame resistance is an important requirement in many areas due to possible
hazards in the use of high voltage 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 required
combustibility test, i.e., UL 94 V combustibility test via V-0 classification or
equivalent classification for validating their flammability. The epoxy resin
industrially used worldwide for flame-retardant applications 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 certain properties which are not acceptable

while dealing other compliances. For example, antimony trioxide is listed as a
carcinogenic chemical and hence incorporation of such material puts different
threats. On the other hand, during the course of thermal decomposition,
aromatic bromine compounds, readily split into bromine radicals and hydrogen
bromide, which are highly corrosive. Besides, brominated aromatic compounds
also form highly toxic substances like, polybromine benzofurans and polybromine
benzodioxins, upon decomposition in the presence of oxygen or air. The disposal
of bromine-containing waste materials and toxic waste represents another
problem and hence utilization of such compounds should carefully be decided,
despite improving FRLS characteristics in polymer bodies.
Extensive research has been reported in literature to replace bromine-containing
fireproofing agents with less toxic substances. Thus, for example, fillers with
extinguishing gas effects such as aluminium oxide hydrates (Refer to 1 Fire and
Flammability, Vol. 3 (1972), pp. 51 ff), basic aluminium carbonates (Refer to
Plast. Engng., Vol. 32 (1976), pp. 41 ff) and magnesium hydroxides (European
application No. 0,243,201A), as well as vitrifying fillers such as borates (Refer to
Modern Plastics, Vol. 47(1970), No. 6, pp. 140 ff) and phosphates (Refer to
Materials 2010, 3, 4300-4327; doi:10.3390/ma3084300 & U.S. Pat Nos.
2,766,139 and 3,398,019) 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 connected arrangement.
Since conventional east 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. US patent
US5955542 refers to a polymer composition, restricted for use in products such
as housings for computers, business equipments, galzing and various structures.
US patent US6284824 and US6509421 refers to Polycarbonate Resin Composition
containing organopolysiloxanes primarily meant for optical transparency
applications. US Patent US6916539 and US20100004370 refers to a halogen free
flame retardant insulating epoxy resin composition, with high level or filler /
additive loading. US patent US7678852 refers to a melamine polyphosphate
containing halogen free flame retardant insulating epoxy resin composition for
coating composition for printed circuit boards. US patent US7723407,
US7829188, US7829188 & WO2010078689A1 refers to the use of organic solvent
for disbursing the ingredients in the formulation.
The prior art search indicates that addition of fillers and / or additives like
Aluminium Hydroxide (ATH), Magnesium Hydroxide, Red Phosphorus and / or
Halogen containing flame retardants are used in the formulation of epoxy-
anhydride resin system to achieve the FRLS properties. ATH and Magnesium
Hydroxide require high loading levels in order to obtain equivalent flame

retardant properties and hence are not found suitable for cast epoxy
transformers as uniform distribution of the filler without any intra-molecular
voids throughout the insulation layer is difficult to achieve. US patent US6767941
refers to a halogen free flame retardant composition containing organic
phosphorus compound used in polyester and polyimide resin systems. US patent
US5994429 refers to a Halogen Free Epoxy Resin composition containing so-
called red phosphorous. Red Phosphorus imparts the red colour that could lead
to discoloration of polymers and the formation of toxic phosphine gas during
combustion and long term storage. The Patents EP1626065B1 and US7723407
pertain to cured films with enhanced transparency.
The need exists for developing additive formulations, which are halogen free for
the manufacture of high voltage insulating products such as cast epoxy
transformers / dry type transformer and other high voltage insulating products
with improved FRLS properties to that of the blank resin system.
OBJECT OF THE INVENTION:
It is an object of the invention to provide a additive modified epoxy-resin
composition for high voltage application and a method for preparation thereof.
It is further an object of the invention to propose a nano structured alumina
filled epoxy resin formulation for impregnation or casting or moulding high
voltage transformers products
Another object of the invention is to propose a nano structured alumina filled
epoxy resin formulation with improved electrical mechanical and thermal
stability.

Yet another object of the invention is to propose a solvent free halogen free
flame retardant epoxy resin composition with improved FRLS (Flame Retardant
Low Smoke) properties
Yet another object of the invention is to propose a nano structured alumina filled
epoxy resin formulation with improved partial discharge extinction voltage level
and breakdown voltage level.
Still another object of the invention is to propose a solvent free nanostructured
alumina filled epoxy formulation for overcoming the drawbacks of solvent
entrapment & intermolecular void, thereby reducing the weight of the
transformer.
BRIEF DESCRIPTION OF THE INVENTION
According to the invention there is provided An additive-modified epoxy-resin
formulation for high voltage application, comprising an inorganic additive system
in a polymer matrix of Bisphenol-A epoxy resin in the proportion of 90-100 parts
by weight and a hardener ranging between 90-100 parts by weight, followed by
a two-stage curing within a temperature range of 60°C - 145°C, wherein nano
structured alumina powder of 2-5 part by volume, inorganic phosphate of 0.5-2.0
part by weight, inorganic carbonate of 0.5-2.0 part by weight, hollow glass micro
spheres of 0.5-2.0 part by volume.
In accordance to this invention, there is also provided a method for the
fabricating the said epoxy resin composition comprising the following step of:
formulating an additive-mixed polymer composite dough, moulding the additive-
mixed polymer composite dough in the required geometry and dimension of the

product with the formation of a green body, curing the green body in the first
stage, curing the first-cured composite body in the second stage.
Nanostructured alumina in very low amount in the volume range of 2 - 5% along
with other additives in the formulation are to be mixed using a homogenizer in
order to get a mixed additive powder. The mixed additive powder as per the
proportion is then to be mixed with the epoxy resin, which can easily get
dispersed into the resin matrix forming a dough, which is to be poured in a
mould depending on the dimension and geometry of the product and to be cured
yielding the additive-modified composite product with improved FRLS properties
to that of the blank resin material. Due to the availability of more surface area
for these identified fillers, an optimized filler composition can improve the FRLS
properties of the cast epoxy transformer product. The hollow glass microspheres,
on the other hand, due to the inherent availability of more surface area in the
hollow morphology associated with low tap density and good thermal
conductivity, offers a number of important benefits, including higher filler
loading, lower viscosity/improved flow and reduced shrinkage and warpage. The
casted epoxy transformer product hence consists of commercially available
Bisphenol W epoxy resin, carboxylic acid anhydride, nanostructured alumina,
inorganic phosphates such as aluminum phosphate, inorganic carbonates such as
calcium carbonate and hollow glass microspheres as a part of the additive
formulation in various proportions so as to derive the best composite body with
the best FRLS characteristics to that of the blank body.
DETAILED DESCRIPTION OF THE INVENTION
The additive-modified epoxy composite for the targeted high voltage transformer
product in the present invention consists of commercially available Bisphenol 'A'
epoxy resin, carboxylic acid anhydride, nanostructured alumina, inorganic

phosphates such as aluminium phosphate, inorganic carbonates such as calcium
carbonate, hollow glass microspheres respectively.
The Bisphenol 'A' epoxy resin is a reaction product of Bisphenol 'A' with
epichlorohydrin or the like, as is well known. The Bisphenol 'A' epoxy resin used
in the present invention usually has an epoxy equivalent of 170 or more. Such
Bisphenol 'A' epoxy resin/s are commercially available as EPIKOTE series from
Yuka Shell, Japan, ARALDITE series from Huntsman, Germany, Lapox series from
Atul Limited, India and such similar sources. Suitable heat curing hardeners of
carboxylic acid anhydride type, compatible with the identified epoxy resin, so
selected, are also available commercially.
THE ADDITIVE SYSTEM
As mentioned, the constituents of the additive system are nanostructured
alumina powder, aluminum phosphate and calcium carbonate along with hollow
glass microspheres. Table 1 describes the additive system along with their
counter proportions in the weight range in which additives are to be used in
specific proportions for fabricating a given composite body.
Table 1: Chemical Composition of the inorganic additive system for
fabricating the composite body


The above constituents are to be taken in dry condition in exact ratios in the
given range and to be mixed using a mixer/homogenizer in order to get a
homogeneous mix of the additives.
Other than the nanostructured alumina powders, all the other materials in the
additive formulation were sourced commercially in which physical and chemical
properties of the materials could vary from source to source to certain extent.
The nanostructured alumina powder is a patented product of BHEL vide Patent
No. 217626 Dt. 28/03/2008 and the technical specification of the material is
furnished as given below.
Table 1.1 The technical specification of the nanostructured alumina
powder (patented product of BHEL vide Patent No. 217626 Dt.
28/03/2008):

In case of aluminum phosphate, it is important that iron (Fe) content in the
material need to be less than 0.01 parts and could be sourced commercially.

The purity of calcium carbonate need to be more than 98% purity and is
available commercially.
In case of hollow glass microspheres, these are chemically hollow spherical soda
lime borosilicate glass or hollow spherical alumino silicate glass with particle
diameter broadly in the range of 30-60 microns with a counter wall-thickness of
1-2 microns. Hollow glass microsphere has a specific gravity of about 0.15 - 0.60
g/cc and Thermal conductivity of 0.03 - 0.12 w/m.k. and are available
commercially.
THE POLYMERIC SYSTEM
The identified polymers are of Bisphenol 'A' epoxy resin, which is a reaction
product of Bisphenol XA' with epichlorohydrin or the like that normally has an
epoxy equivalent of 170 or more. However, the additive system along with the
process mentioned in the invention is also applicable to similar group of
polymers.
Besides, the polymer Bisphenol 'A', a hardener, carboxylic acid anhydride is also
to be used along with the polymer for accelerating the setting and hardening
process of the polymer. The hardener need to be selected on the basis of
compatibility of mixing and hardening process to that of its base polymer.
However, different other hardener could find compatibility with base polymer
described here and could be available from a number of commercial sources.
FABRICATION OF THE COMPOSITES
For the fabrication of the composite body, the inorganic additive system
comprising i) Nanostructured alumina (2-5 part by volume), ii) Aluminum

Phosphate (0.5 - 2.0 part by weight), iii) calcium carbonate (0.5 - 2.0 part by
weight) and iv) hollow glass microsphere (0.5 - 2.0 part by volume) in the
desired proportion are to be mixed homogeneously with the epoxy resin
Bisphenol 'A' (90 - 100 parts) along with the carboxylic acid anhydride hardener
(90 - 100 parts) in a mixing chamber for a period of 6 - 10 hours using a
homogenizer by maintaining a temperature of the mixing chamber in the range
of 60-65°C with counter vacuum level in the range of 4-5 Torr in order to get a
additive-mixed polymer dough. The range of formulations comprising inorganic
additive and the polymer along with its counter hardener is furnished in the
Table 2.

The so-derived additive-mixed polymer mix is now to be poured into an alloy
steel mould with required geometry and dimension depending on the dimension
and geometry/profile of the composite body to be fabricated and the polymer-
filled mould is then kept in an air-circulating oven for a period of 3-5 hours by
maintaining the mould temperature in the range of 140-145 deg.C at normal
atmosphere in order to cure the composite body in required shapes and
dimension. This step explains the first stage of curing. In the second stage of

curing process, the first-cured composite body upon cooling to room temperature
is to be placed on a tray/container and further cured in an air-circulating oven for
a period of 8-12 hours by maintain a body temperature in the range of 130-
140°C which explains the 2nd stage of curing. The second-stage cured composite
body is to be removed from the oven after cooling to room temperature and the
fabricated body is called additive-modified composite body (polymer body with
incorporating the disclosed additive formulation with defined ratios) that has
improved FRLS characteristics as compare to that of the blank polymer without
incorporation of any such additives.
The derived composite bodies are then subjected to FRLS tests following UL 94 V
combustibility test via V-0 classification or equivalent classification that showed
an improvement in the range of 30- 50% in all composite bodies fabricated by
the permutation and combination of the inorganic-additive system and the
polymer towards the flammability characteristics of the fabricated composites as
compare to that of the blank body without incorporation of any such additives.
The merit of the invention could be realized better by taking un-limited number
of examples fabricating the composite body with various shapes and dimensions
following the given fabrication procedure and by using the disclosed additive
system.
Example 1:
In this example, the additive-modified epoxy composite dough is prepared as per
the formulation in the following table that comprises both the compositions of
the additive part and the polymeric part respectively and their specific
formulation:

Table 3: Formulation for fabricating the additive-modified Epoxy
Composite Body

As described previously, separately additive composition and polymeric
composition were prepared and mixed in order to get dough of the additive-
modified epoxy formulation. The additives and the resins were mixed in a
vacuum chamber for 6 hours at a pressure of 4 torr with a counter temperature
of 60 DegC.
The dough was then poured in an alloy steel mould having inner dimensions of
300mm OD x 200mm ID having the cavity filled with wound wound fiber glass
mat, fiber glass cloth and fiber glass tape that resulted the green body of the
additive-modified epoxy composite product.
The green body is then cured at 140 deg.C for a period of 3 hours in Stage 1
curing and then at 135 deg.C for a period of 12 hours in stage 2 curing, which
resulted additive-modified epoxy body that has improved FRLS properties to that
of the blank composites with any additive to the extent of around 30% and
Flame retardance of V-0.

Example 2:
In this example, the additive-modified epoxy composite dough is prepared as per
the formulation in the following table that comprises both the compositions of
the additive part and the polymeric part respectively and their specific
formulation:
Table 3: Formulation for fabricating the additive-modified Epoxy
Composite Body

As described previously, separately additive composition and polymeric
composition were prepared and mixed in order to get dough of the additive-
modified epoxy formulation. The additives and the resins were mixed in a
vacuum chamber for 6.5 hurs at a pressure of 4 torr with a counter temperature
of 60 DegC.
The dough was then poured in an alloy steel mould having inner dimensions of
300mm OD x 200mm ID having the cavity filled with wound fiber glass mat, fiber
glass cloth and fiber glass tape that resulted the green body of the additive-
modified epoxy composite product.

The green body is then cured at 140 deg.C for a period of 3 hours in Stage 1
curing and then at 135 deg.C for a period of 12 hours in stage 2 curing, which
resulted additive-modified epoxy body that has improved FRLS properties to that
of the blank composites with any additive to the extent of around 38% and
Flame retardance of V-0.
Example 3:
In this example, the additive-modified epoxy composite dough is prepared as per
the formulation in the following table that comprises both the compositions of
the additive part and the polymeric part respectively and their specific
formulation:
Table 3: Formulation for fabricating the additive-modified Epoxy
Composite Body


As described previously, separately additive composition and polymeric
composition were prepared and mixed in order to get dough of the additive-
modified epoxy formulation. The additives and the resins were mixed in a
vacuum chamber for 7 hours at a pressure of 4 torr with a counter temperature
of 60 DegC.
The dough was then poured in an alloy steel mould having inner dimensions of
300mm OD x 200mm ID having the cavity filled with wound wound fiber glass
mat, fiber glass cloth and fiber glass tape that resulted the green body of the
additive-modified epoxy composite product.
The green body is then cured at 140 deg.C for a period of 3 hours in Stage 1
curing and then at 135 deg.C for a period of 12 hours in stage 2 curing, which
resulted additive-modified epoxy body that has improved FRLS properties to that
of the blank composites with any additive to the extent of around 49% and
Flame retardance of V-0.

WE CLAIM:
1) An additive-modified epoxy-resin formulation for high voltage application,
comprising an inorganic additive system in a polymer matrix of Bisphenol-
A epoxy resin in the proportion of 90-100 parts by weight and a hardener
ranging between 90-100 parts by weight, followed by a two-stage curing
within a temperature range of 60°C - 145°C, wherein
i) nano structured alumina powder of 2-5 part by volume,
ii) inorganic phosphate of 0.5-2.0 part by weight,
iii) inorganic carbonate of 0.5-2.0 part by weight,
iv) hollow glass micro spheres of 0.5-2.0 part by volume.
2) The composition as claimed in claim 1, wherein the inorganic phosphate
used is aluminum phosphate powder.
3) The composition as claimed in claim 1 where in the inorganic carbonate
used is calcium carbonate powder.
4) The composition as claimed in claim 1, wherein the said hollow glass
micro sphere are chemically hollow spherical soda lime borosilicate glass
on hollow spherical alumina silicate glass with a particle diameter broadly
in the range of 30-60 micron, a counter wall thickness of 1-2 micron.
5) The composition as claimed in claim 1, wherein the said Bisphenol epoxy
resin is a reaction product of Bisphenol 'A' with epichlorohydrin.
6) The composition as claimed in claim 1, wherein the same hardener is a
carboxylic acid anhydride.

7) A method for the fabricating the said epoxy resin composition comprising
the following step of:
- formulating an additive-mixed polymer composite dough,
- moulding the additive-mixed polymer composite dough in the
required geometry and dimension of the product with the formation
of a green body,
- curing the green body in the first stage,
- curing the first-cured composite body in the second stage.

8) The method as claimed in claim 7, wherein the additive-mixed polymer
composite dough is fabricated by mixing the additive formulation, the
polymer along with the hardener using a homogenizer.
9) The method as claimed in claim 8, wherein the temperature range of the
mixing chamber is maintained between 60-65°C
10) The method as claimed in claim 7, wherein the additive-mixed polymer
composite dough is moulded by pouring the viscous dough into an alloy
steel or steel or similar mould, as per the required geometry and
dimension of the composite body to be fabricated thereby generating
green body.
ll)The method as claimed in claim 7, wherein green body is cured in the first
stage in a temperature range of 140°C -145°C for a period of 3-5 hours.

12) The method as claimed in claim 7, wherein the first-cured composite
body is cured in the second stage in a temperature range of 130°C -
140°C. for a period of 8-12 hours.