FIELD OF THE INVENTION
This invention relates to a hybrid fabric-epoxy resin composite with better
thermal conductivity and enhanced capacitance value.
This invention further relates to a process for the preparation of hybrid
(Carbon-Basalt Fabric) fabric laminates with commercial epoxy resin system
so as to improve the electrical insulation system with a specific emphasis on
better thermal conductivity and enhancing capacitance of the derived hybrid
(Carbon-Basalt Fabric) fabric - epoxy resin composite materials with
reference to that of the conventional glass fabric – epoxy laminate.
BACKGROUND OF THE INVENTION
The use of glass fabric-epoxy resin laminates as electrical insulating
material is an established prior art for years together and is very common.
Conventionally, glass fabrics are commercial grade material with fabrics of
various thickness as well as densities. In recent years, different fabrics
such as carbon fabrics, S-glass fabrics have been reported to be introduced
in order to achieve composite laminates with enhanced mechanical, thermal
and environmental properties. While targeting the enhancement of electrical
properties and thermal properties, particularly for high voltage electrical
insulation applications, the thermal conductivity value and the capacitance
value of these laminates are of significant interest.
European Patent Number EP137715 B1 relates to a flexible product
comprising a Hybrid (Carbon-Basalt Fabric) fabric provided with a coating
layer.The flexible product of the invention, as per the claim, consist of at
least a polyester polyurethane coating layer coating at least partly a face of
the fabric.
The Patent publication Number WO 2009/109216 A1 describes an electrical
article like an electrical hollow core insulator wherein the wall of said
electrical insulator is made from a fibre reinforced organic polymer
composite system comprising a hardened or cured electrically insulating
matrix resin composition and a reinforcing fibre comprising an outer layer

and an inner layer, wherein the outer layer of the wall is reinforced with a
corrosion sensitive fibre having the inner layer of the wall reinforced with a
corrosion resistant fibre selected fiber preferably being poly-
ethyleneterephthalate (PET) or alumina.
The patent publication Number WO2004/101872 A1 describes a thin
polyester polyurethane coating on at least one face of a Hybrid (Carbon-
Basalt Fabric) fabric and a metallic reinforcing element for a fire resistant
product having specified abrasion resistance.
The patent US7740925B2 describes a laminate consisting of a substrate
layer, a knitted porous layer disposed in a thermoplastic material and an
epoxy resin to form a bagging hopper or vibratory panel.
The patent Number US4913955 describes an epoxy resin laminate of glass
fibre woven cloth with the outer layers made of organic fibre.
The patent publication number WO2012/078058 A1 describes flame
retardant epoxy resins and epoxy glass reinforced laminates.
The patent number EP0040848 A1 describes the electrical laminate
comprising a plurality of fibrous cellulosic substrate layers and alternately
interposed layers of cured epoxy or unsaturated polyester resin between the
adjacent substrate layers, wherein each of the substrate layers is embedded
in a matrix of said cured resin which is substantially integral with said
layers of cured resin.
OBJECTS OF THE INVENTION:
It is therefore the primary object of this invention to propose a hybrid fabric-
epoxy resin composite with better thermal conductivity and enhanced
capacitance value.
It is a further object of this invention to propose a hybrid fabric- epoxy resin
composite suitable for application as an electrically insulating material.

A still further object of this invention is to propose a hybrid fabric- epoxy
resin composite which can be prepared using commercially available epoxy
resin system consisting of a bisphenol-A epoxy, a suitable carboxylic acid
anhydride based liquid hardener and the tertiary amine accelerator to
obtain composite laminate suitable for application as an electrically
insulating material.
Another object of this invention is to propose a hybrid fabric- epoxy resin
composite which is prepared using an impregnating process under vacuum
and heating to obtain composite laminate suitable for application as an
electrically insulating material.
Yet another object of this invention is to propose a hybrid fabric- epoxy resin
composite with better thermal conductivity and dielectric properties of
enhanced capacitance value.
These and other objects and advantages of the invention will be apparent
from the ensuing description.
SUMMARY OF THE INVENTION
The invention describes the processing and fabrication of Hybrid (Carbon-
Basalt Fabric) fabric-epoxy resin composite laminate with better thermal
conductivity for application as electrical insulation and dielectric properties
of enhanced capacitance. It is therefore the primary object of the invention
to prepare a Hybrid (Carbon-Basalt Fabric) fabric - epoxy resin composite
laminate suitable for application as an electrically insulating material.
The hybrid fabric-epoxy resin composite laminate is prepared using
commercially available epoxy resin system consisting of a bisphenol-A epoxy
resin system, a suitable carboxylic acid anhydride based liquid hardener
and the tertiary amine accelerator to obtain composite laminate suitable for
application as an electrically insulating material.

The Hybrid (Carbon-Basalt Fabric) fabric - epoxy resin composite laminate is
prepared using an impregnating process under vacuum and heating to
obtain composite laminate.
The Hybrid (Carbon-Basalt Fabric) fabric-epoxy resin composite laminate
has better thermal conductivity for application as electrical insulation and
dielectric properties of enhanced capacitance.
Fabric, which is manufactured from the naturally occurring igneous Basalt
Fabric rock along with carbon fabric arranged in the cavity of a suitable die,
is then treated together with commercially available epoxy resin system of
bisphenol-A epoxy resin, carboxylic acid anhydride based liquid hardener
and the tertiary amine accelerator in a pre-defined reacting ratio followed by
heat treatments both for pre and post curing in order to fabricate the Hybrid
(Carbon-Basalt Fabric) fabric - epoxy resin composite laminate. The derived
Hybrid (Carbon-Basalt Fabric) fabric - epoxy resin composite laminate show
better thermal conductivity and enhancement of capacitance value of 100,
which is three times more than that of the glass fabric – epoxy resin
composite laminate. The Hybrid (Carbon-Basalt Fabric) fabric - epoxy resin
composite laminate has great potential for fabricating as various
components or sub-components in the area of high voltage electrical
insulation applications.
DETAILED DESCRIPTION OF THE INVENTION:
According to this invention is provided a hybrid fabric-epoxy resin
composite. According to this invention is further provided a process along
with its parameters for the preparation of Hybrid (Carbon-Basalt Fabric)
fabric-epoxy resin composite laminate using an impregnating process under
vacuum and heating the obtained composite laminate for achieving
enhanced dielectric properties of higher capacitance value.
The present invention differs from the practices disclosed in the prior art.
This invention does not use any conventional fabrics like glass fabric.

Instead, this invention utilizes the Hybrid (Carbon-Basalt Fabric) fabric for
the preparation of the laminate. This material is arranged one layer over the
other in a suitable die and vacuum moulded under heat with an epoxy resin
system consisting of a bisphenol- A epoxy, a suitable carboxylic acid
anhydride based liquid hardener and the tertiary amine accelerator to
obtain a laminate. This approach produces Hybrid (Carbon-Basalt Fabric)
fabric – epoxy resin composite laminate with better thermal conductivity and
higher capacitance value for application as electrical insulation.
In accordance with this invention, the process of preparation of the Hybrid
(Carbon-Basalt Fabric) fabric - epoxy resin composite laminate comprises
the following steps:
a) Cutting the Hybrid (Carbon-Basalt Fabric) fabric to a suitable size
b) Preparing the commercially available epoxy resin system
consisting of a bisphenol-A epoxy, carboxylic acid anhydride based
liquid hardener and the tertiary amine accelerator and degassing
the mixture under vacuum to remove the entrapped gases inside
the resin mixture
c) Arranging the required number of suitably cut Hybrid (Carbon-
Basalt Fabric) fabric in a cavity of a suitable die and closing the die
with suitable nuts and bolts to obtain a leak proof cavity
containing the Hybrid (Carbon-Basalt Fabric) fabric
d) Casting the resin mixture into moulds as per the dimension/shape
of the components/specimens and ensuring thereby de-gassing as
well during casting in order to remove the air bubble in the
composite body
e) Heat treatment of the casted body in air circulated oven in the
temperature range of 80-90oC preferably at 80oC for a period of 1 –

2 hours, which results in pre-cured Hybrid (Carbon-Basalt Fabric)
fabric - resin body
f) Heat treatment of the pre-cured Hybrid (Carbon-Basalt Fabric)
fabric - resin body in air circulated oven in the temperature range
of 140o-150oC preferably at 140oC for a period of 4 – 6 hours,
which results in fully-cured Hybrid (Carbon-Basalt Fabric) fabric -
epoxy resin composite laminate
g) Opening the nuts and bolts of the die to obtain the fully cured
Hybrid (Carbon-Basalt Fabric) fabric–epoxy resin composite
laminate
h) Testing of the Hybrid (Carbon-Basalt Fabric) fabric–epoxy resin
composite laminate for thermal conductivity and the dielectric
property of capacitance.
In accordance with a particular embodiment of the present invention, the
Hybrid (Carbon-Basalt Fabric) fabric of 200-250 grams per square meter
(GSM) density and a thickness of 0.15 to 0.20 millimetres is chosen in this
invention. The material is to be dried at a temperature in the range of 90 –
100 degree Celsius for a period of 20-60 minutes to make it dry and free of
moisture before using.
As per the invention, 15 to 18 pieces of Hybrid (Carbon-Basalt Fabric) fabric
of 200 grams per square meter density and a thickness of 0.15 to 0.20
millimetre are dried in the temperature range of 90 – 100 degree Celsius, for
a period of 20-60 minutes to make it dry and free of moisture. The dried
Hybrid (Carbon-Basalt Fabric) fabric pieces are stacked one over the other
inside the cavity of the pre-fabricated die and then the cavity is closed with
the cover securely using the required nuts and bolts.
As per the invention, a commercially available liquid epoxy resin system of
bisphenol-A epoxy resin is mixed with the carboxylic acid anhydride based

liquid hardener and the tertiary amine accelerator in pre-determined
proportions using an anchor shaped laboratory mixer with de-gassing
attachment for a period of 30 – 60 minutes, maintaining a vacuum level of 3
– 5 mbar.
The mixed epoxy resin system is admitted into the cavity of the die
containing the Hybrid (Carbon-Basalt Fabric) fabrics and de-gassed under
heat of set temperature of 80 – 90 degree Celsius preferably at 80 Celsius for
a period of 1 – 2 hours. The temperature is then increased 140 – 150 Celsius
preferably at 140 Celsius for a period of 4 - 6 hours and then is cooled down
to ambient temperature.
The die is then opened to obtain the Hybrid (Carbon-Basalt Fabric) fabric –
epoxy resin composite laminate.
The Hybrid (Carbon-Basalt Fabric) fabric – epoxy composite laminates are
then tested for the thermal conductivity and the dielectric property of
capacitance.
The invention will now be explained in greater details with the help of the
following non limiting examples. The examples are however not to be
construed as limiting the scope of the invention.
EXAMPLE 1:
15 pieces of Hybrid (Carbon-Basalt Fabric) fabric of 200-250 grams
per square meter (GSM) density and a thickness of 0.20 millimetres
are dried at the temperature of 90 degree Celsius for a period of 40
minutes to make it dry and free of moisture. The dried Hybrid
(Carbon-Basalt Fabric) fabric pieces are stacked one over the other
inside the cavity of the pre-fabricated die having an inside cavity of
150 millimetre x 150 millimetre x 3 millimetre and then the cavity is
closed with the cover securely using the required nuts and bolts. A
commercially available liquid epoxy resin system of bisphenol-A epoxy
resin (30 grams) is mixed with the carboxylic acid anhydride based

liquid hardener (30 grams) and the tertiary amine accelerator (6
grams) using an anchor shaped laboratory mixer with de-gassing
attachment for a period of 20-40 minutes, maintaining a vacuum level
of 3 – 5 mbar.
The mixed epoxy resin system is admitted into the cavity of the die
containing the Hybrid (Carbon-Basalt Fabric) fabrics and de-gassed
under heat of set temperature of 80 degree Celsius for a period of 1
hour. The temperature is then increased 140 for a period of 4 - 6
hours and then is cooled down to ambient temperature.
The die is then opened to obtain the Hybrid (Carbon-Basalt Fabric)
fabric–epoxy resin composite laminate.
The Hybrid (Carbon-Basalt Fabric) fabric – epoxy composite laminates
are then tested for the thermal conductivity and the dielectric property
of capacitance.
For comparison, glass fabric–epoxy resin composite laminate
specimens with conventional cast samples of commercially available
liquid epoxy resin system of bisphenol-A epoxy resin mixed with the
carboxylic acid anhydride based liquid hardener and the tertiary
amine accelerator as well as conventional glass fabric and
commercially available liquid epoxy resin system of bisphenol-A epoxy
resin mixed with the carboxylic acid anhydride based liquid hardener
and the tertiary amine accelerator in the same proportions and the
process were also prepared and the dielectric property of capacitance
value compared under identical conditions.
The derived Hybrid (Carbon-Basalt Fabric) fabric–epoxy composite
laminate showed better thermal conductivity for application as
electrical insulation and a capacitance value of 100, which is three
times more than that of the glass fabric–epoxy resin composite
laminate (Table 1).

Example 2:
In this example, the procedure and all the experimental parameters
and conditions thereof remained the same as that of as described in
the Example 1, except that the pieces of Hybrid (Carbon-Basalt
Fabric) fabric was 16 pieces instead of 15 pieces in the example 1.
The derived Hybrid (Carbon-Basalt Fabric) fabric – epoxy composite
laminate showed better thermal conductivity for application as
electrical insulation and a capacitance value of 100, which is three
times more than that of the glass fabric – epoxy resin composite
laminate (Table 1).
Example 3:
In this example, the procedure and all the experimental parameters
and conditions thereof remained the same as that of as described in
the Example 1, except that the pieces of Hybrid (Carbon-Basalt
Fabric) fabric was 18 pieces instead of 15 pieces in the example 1.
The derived Hybrid (Carbon-Basalt Fabric) fabric – epoxy composite
laminate showed better thermal conductivity for application as
electrical insulation and a capacitance value of 100, which is three
times more than that of the glass fabric – epoxy resin composite
laminate (Table 1).
The Table 1 and Table 2 represents the thermal conductivity and the
Capacitance values of the Hybrid (Carbon-Basalt Fabric) fabric –
epoxy composite laminate in comparison with pure epoxy casting and
glass fabric – epoxy composite laminate.

We Claim :
1. A hybrid fabric–epoxy composite laminate for use as an electrically
insulating material, said composite comprising a hybrid Carbon-Basalt
Fabric and an epoxy resin and having better thermal conductivity and
enhanced capacitance value.
2. The hybrid fabric - epoxy resin composite laminate as claimed in
Claim 1 prepared using hybrid Carbon-Basalt Fabric and commercially
available epoxy resin system consisting of a bisphenol-A epoxy resin, an
acid anhydride hardener and a tertiary amine accelerator to obtain
composite laminate suitable for application as an electrically insulating
material.
3. A process for the preparation of a hybrid fabric - epoxy resin
composite laminate, comprising the steps of drying a hybrid (Carbon-Basalt
Fabric) fabric to make it dry and free of moisture,
preparing a resin system by mixing a bisphenol-A epoxy resin, an acid
anhydride hardener and a tertiary amine accelerator in pre-determined
proportions followed by degassing the mixture,
arranging the required number of suitably cut hybrid fabric pieces in the
cavity of a die and closing the die to obtain a leak proof cavity containing the
hybrid fabric,
admitting the mixed epoxy resin system into the cavity of the die containing
the hybrid fabric with de-gassing during casting in order to remove the air
bubble in the composite body,
subjecting the cast body to a first heat treatment with degassing in air
circulated oven at a temperature in the range of 80-90ºC to obtain a pre-
cured hybrid fabric - resin body,
followed by a second heat treatment with degassing of the pre-cured hybrid
fabric - resin body in air circulated oven at a temperature in the range of

140º-150ºC and cooling to ambient temperature to obtain the fully-cured
hybrid (Carbon-Basalt Fabric) fabric - epoxy resin composite laminate.
4. The process as claimed in Claim 3, wherein the hybrid fabric is dried
at a temperature in the range of 90 – 100 degree Celsius for a period of 20-
60 minutes.
5. The process as claimed in Claim 3, wherein the epoxy resin system is
mixed using an anchor shaped laboratory mixer with de-gassing attachment
for a period of 30 – 60 minutes, maintaining a vacuum level of 3 – 5 mbar.
6. The process as claimed in Claim 3, wherein said first heat treatment is
effected preferably at a temperature of 80º C.
7. The process as claimed in Claim 3, wherein said first heat treatment is
effected for a period of 1 – 2 hours.
8. The process as claimed in Claim 3, wherein said second heat
treatment is effected preferably at a temperature of 140º C.
9. The process as claimed in Claim 3, wherein said second heat
treatment is effected for a period of 4 - 6 hours.
10. The hybrid (Carbon-Basalt Fabric) fabric – epoxy resin composite
laminate, prepared by the process of Claims 3 to 9, suitable for application
as an electrically insulating material with better thermal conductivity for
application as electrical insulation and dielectric properties of enhanced
capacitance value.