FIELD OF THE INVENTION
The present invention is in the field of design and incorporation of nanostructured
amorphous alumina additive materia! into commercial epoxy resin
system so as to improve the electrical insulation characteristics with a speeifre
specia! emphasis on enhancing AC breakdown strength of the derived epoxy
resin composite materials with reference to that of the parent epoxy resin. More
pafticularly the present invention relates to a nano-structured amorphous
alumina modified composite materia! with enhanced AC breakdown strength for
high voltage electrical insulation applications.
BACKGROUND OF THE INVENTION
The use of fillers in both thermoplastic and thermosetting polymers has been
common. The primary motivation for using various fillers into polymers is to
obtain enhanced physical properties of the composite body besides achieving
the cost reduction. Conventionally, fillers are commercial grade material with
pafticle diameter of several microns. In recent years, usage of nano fillers for
achieving composite materials (both in thermoplastic and thermosetting
polymers) with enhanced electrical, mechanica!, thermal and environmental
propefties. While considering the electrical properties, particularly for high
voltage electrical insulation applications, AC breakdown voltage of the insulation
materia! is of significant interest.
3
Fillers coutd be chemically active or inert in the composite matrix. When the
fillers are chemically inert, they are primarily extenders in the composites.
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.
Calcium carbonate is the most widely used extender type of filler for plastics.
Calcium carbonate is also been coated with stearic acid to improve rheological
properties. Other organic materials, like, salts of alkylolamines and long chain
polyaminoamides (high molecular weight acids) have also been used as
extender type coating materials.
Alumino-silicate materials !ike, kaolin clay is another common materia! that is
used as extender in plastics, which is often treated with silane, polyester, and
metal hydroxide for surface modifications is also well known in this area.
Other aiuminosilicate materials !ike, glass, asbestos group of materials, and
wollastonite etc have been reported as reinforcements with and without
combinations of various surface modiffing agents and have been used in
various industria! applications.
European Patent Number EP2195813 A1 dated June 16, 2010 by Martin Carlen
et al (ABB Research Ltd) describes the electrical insulation system with improved
electrical breakdown strength, in which the said electrica! insulation system
consists a polymeric hardener a conventional filler material and another pretreated
filler material. The hardener is selected from epoxy resin systems,
polyesters, polyamides, polybutylene terephthalate, polyurethanes and
polydicyclopentadiene, the conventional filler material is a known filler material
having an average grain size distribution within the range of 1 - 500 pm, being
present in a quantity within the range of 40 - 65 o/o by weight and the selected
pre- treated filler material is silica, quarE, or a silicate,
4
or is a mixture of these compounds, having an average grain size distribution
within the range of 1-500 pm.
European Patent Number Ep2532010 A1 dated Dec !2, zolz by Xavier
Kornmann et a! (ABB Research Ltd) describes the etectrical insulation system
with improved electrical breakdown strength, said electrical insulation system
comprising a polymeric hardener having incorporated therein a conventional
filler materia! and a selected nano-scale filler materiat, wherein (a) said
polymeric hardener is selected from epoxy resin compositions, potyesters,
polyamides, polybutylene terephtharate, polyurethanes and
polydicyclopentadiene, and preferably is a hardened epoxy resin system; (b) said
conventional filler material is a known filler material having an average grain size
distribution within the range of 1-500 pm, being present in a quantity within the
range of 40-650/o by weight, and (c) said selected nano-scale sized sitica powder
is a pre-treated nano-scale sized filler materiat, having been produced by a solgel
process; wherein said selected nano- scale sized silica powder is present
within the electrical insulation system in an amount of about L-2Oo/o by weight.
EP0500587 A1 dated Sep 2, L992 by Bradley Keith Coltrain et al (Eastman
Kodak Company) describes modified epoxy resins and composites which have
silicon- containing functiona! groups along the polymer backbone are prepared
by reacting a polyether having non-terminal hydroxy groups with a modiffing
agent which (i) reacts with hydroxy groups and (ii) which atso contains
trialkoxysilane groups. The modified resins can be reacted with a silicon oxide
precursor to form an organic/inorganic composite. The composites are shown to
have improved propefties at elevated temperatures.
European Patent Number EP1858969 A2 dated Nov 28, 2007 by Robert John
Keefe et al (Rensselaer Polytechnic Institute) describes nanostructured dielectric
composite materials suitable for electrical insulation includes a polymer
compounded with a substantially homogeneously distributed functionalized
nanoparticle filler. The nanocomposite material is produced by compounding the
polymer with the functionalized nanoparticle filler by impafting a shear force to
a mixture of the polymer and filler capable of preventing agglomeration of the
filler whereby the filler is substantially homogeneously distributed in the
nanocomposite material. The electrical insulation may be adapted for AC or DC
high voltage, and may also be adapted for low or medium voltage to prevent
formation of water tree structures.
EP2007830 A1 dated Dec 31, 2008 (also published in US20090289234 &
WO2007119231A1) by J. Werner Blau et al (The Provost, Fellows And Scholars
Of The College Of The Holy And Undivided Trinity Of Queen Elizabeth Near
Dublin) describes a process for the preparation of modified nanoclay in one case
comprises the steps of providing an organoclay, dispersing the organoclay in a
solvent or mixture of solvents andlor sufactant, providing nariotubes or
nanowires, dispersing the nanotubes or nanowires in a solvent or mixture of
solvents and/or sufactant, and mixing the organoclay suspension with the
nanotube and/or nanowire suspension. The organoclays modified with
nanowires or nanotubes provide nanoadditives, which have enhanced therma!
stability and electrical conductivity properties. The nanoadditive may include an
inherently conducting polymer such as polyaniline. Also provided are polmyer
composites including the nanoadditive.
5
6
EP24L7L7L A1 dated Feb 15, 2OL2 by Linda Schadler et al (Rensselaer
Polytechnic Institute) describes to an electric insulation materiat including
modified nanoparticles, a porous substrate and polymer matrix, wherein the
modified nanoparticles include a nanoparticle and a diblock copotymer
covalently attached to the nanopafticte, the diblock copolymer inctuding a first
block polymer of molecular weight greater than 1000 and a glass transition
temperature below room temperature attached to the nanopafticle and a
second block polymer of molecular weight greater than 1000 covalently linked
to the firct block polymer, wherein the second btock polymer and the matrix
both possess the same chemical functionality. Other electrical insulation
materials and methods of making such electrical insulation materials are atso
disclosed.
United States Patent Number Us8389603 dated March 5, 2013 by Tapas yadav
et al describes the use of nanoscale powders as a component of novel
composites and devices. By incorporating powders having dimensions less than
a characteristic domain size into polymeric and other matrices, nanocomposites
with unique propefties can be produced and methods for preparing
nanocomposites with thermal properties modified by powder size below 100
nanometers. Both low loaded and highly loaded nanocomposite were reported.
Nanoscale coated, uncoated, whisker type fillers are taught. Thermal
nanocomposite layers may also be prepared on substrates.
The present invention differs from the practices disclosed in the prior art. This
invention does not use any conventional filler materiats, like catcium carbonate,
clay or glass. Instead, this invention utilize one tailor-made, nano-structured
alumina material which is amorphous and porous with retatively low tap density
in the range of 0.01-0.3 glcc, preferably at 0.07 glcc.
7
This material is functionalized with Iiquid silane alone with the polymeric
hardener in the epoxy resin system, which is then incorporated into the
commercial grade epoxy resin system to derive the composite material with an
objective to enhance the AC breakdown voltage of the derived epoxy
composites.
OBIECTS OF THE INVENTION
It is therefore an object of the invention to propose a nano-structured
amorphous alumina modified epoxy composite material with enhanced AC
breakdown strength for high voltage electrical insulation applications.
Another object of the invention is to propose a nano-structured amorphous
atumina modified epoxy composite materia! with enhanced AC breakdown
strength for high voltage electrical insulation applications, in which the
nanostructured alumina has amorphous structure in an X-ray powder diffraction
pattern (XRD) with porosity in the particle agglomerates with typica! propefties
and synthesized according to a known process.
A still another object of the invention is to propose a nano-structured amorphous
alumina modified epoxy composite material enhancing AC breakdown strength
for high voltage electricat insulation applications, in which the additive
concentration of the nanostructured amorphous alumina into commercial epoxy
system is selected so as to maximize the ac breakdown strength in the modified
composite body.
8
A further object of the invention is to propose a nano-structured amorphous
alumina modified epoxy composite material enhancing AC breakdown strength
for high voltage electrica! insulation applications, which teaches the processing
conditions and process parameters for incorporation of the additives to allow
fabrication of the inventive epoxy composites with targeted levels of AC
breakdown strength.
A sti!! fufther object of the invention is to propose a process for fabrication of
nano-structured amorphous alumina modified epoxy composite to enhance AC
breakdown strength of the composites.
SUMMARY OF THE INYENTION
According to this invention, there is provided a nano-structured amorphous
alumina modified composite material enhancing. AC breakdown strength for high
voltage electricat insulation applications, comprising a combination of a
commercial grade epoxy resin system and a tailor-made additive material,
wherein the nanostructured amorphous alumina additive material is synthesized
following in-house patented process maintaining pre-defined properties and
characteristics, wherein the synthesized material is dried in a temperature range
of 200-3000C for a period of 30-120 minutes resulting in a dried additive
material, and wherein the additive material is nanostructured alumina powder
which is amorphous in the x-ray diffraction (XRD) pattern with porous structure
in inter/intra-particle agglomerates with a tap density in the range of 0.01-0.3
9lcc.
9
The invention further provided a process along with its parameters for
incorporation and fabrication of nanostructured amorphous alumina modified
epoxy composites for achieving enhanced AC breakdown strength of the
composites as compared to plain (virgin) epoxy resin body.
The incorporation and fabrication process of the nano-structured modified
epoxy composites comprise the following steps:
a) synthesis of nanostructured amorphous alumina additive material
following in-house patented process with pre-defined propefties and
material characteristics and drying off the powder in order to eliminate
the entrapped moisture from the powder;
b) preparing an "emulsion of nanostructured amorphous alumina
additives" by mixing and treating the dried nanostructured alumina
additive materia! with a liquid silane (functionalization agent) and a
carboxylic acid based anhydride (polymeric hardener) in a mixer using
predetermined weight ratio in each of the components;
c) preparing another "mixed liquid" containing epoxy resin (bisphenol A
Epoxy resin), flexibilizer (ployglycol liquid) and accelerator (teftiary amine
liquid) in pre-defined weight/volume ratio to obtain the "mixed liquid"
using a high shear mixer;
d) mixing the "emulsion of nanostructured amorphous alumina additive"
and the "mixed liquid" together under vacuum with pre-determined ratio
of the two components to obtain a "additive modified epoxy resin
emulsion"
10
e) casting the thus obtained "additive modified epoxy resin emulsion"
into moulds as per the dimension/shape of the components/specimens
including degassing during casting in order to remove the air bubble in
the composite body ;
f) heat treating the casted body in air in an oven in a temperature range
of 80-90oC preferably at 80oC for a period of 6 - 8 hours, which
preduces a pre-cured additive modified resin body;
g) heat treating the pre-cured additive modified resin body in air in an
oven in the temperature range of 140o-150oC preferably at 140oC for a
period of 6- 8 hours, which results a fully-cured "nanostructured
amorphous alumina modified epoxy resin composite body"; and
h) testing of thus-derived "nanostructured amorphous alumina modified
epoxy resin composite body" for AC breakdown voltage and dielectric
constant as per specific IEC standards as applicable.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
Figure 1 shows a breakdown voltage profile of nanostructured amorphous
alumina-modified epoxy composites as compared to plain epoxy resin body.
11
DETAILED DESCRIPTION OF THE INVENTION:
The present invention describes modification of commercial epoxy system by
incorporating nanostructured porous amorphous alumina (additive material)
thereby fabricating the additive-modified epoxy composite body following predefined
procedure and process parameters, composite body of which has
enhanced Ac breakdown strength, which would serue as an electrical
insulation in high voltage applications.
According to the present invention and in order to accomplish the above
objects, there is provided a process for incorporating nano-structured
amorphous alumina additive material for fabricating additive-modified epoxy
composites using variable levels of additives in the epoxy resin system so as to
enhance the ac breakdown voltage, which is disclosed in this invention.
In a more particular embodiment of the present invention, the
synthesis of nano-structured amorphous alumina additive material along
with its properties are already defined and the same is synthesized
following the pre-defined procedure and used as the additive material.
The additive materia!, i.e ., nanostructured amorphous alumina has
unique properties, which is amorphous in the XRD and also has
significant porosity in the agglomerate structure of the particles thus
having a low tap density in the range of 0.01-0.3 glcc or preferably the
material with a tap density of 0.07 glcc were chosen in this invention.
The material is to be dried in the temperature range of 200-300oC for a
period of 30-120 minutes before using.
L2
As per the invention, the said nanostructured amorphous alumina
additive material having the concentration in the range of 1 - 4
weighto/o are first to be mixed with silane yglycidoxypropyltrimethoxysilane
in the weight range of 1 - 2 o/o along
with the polymeric hardener liquid (which is chemically carboxylic acid
anhydride in the epoxy resin system using a suitable mixer which
results in an emulsion.
The resultant emulsion is then to be mixed with epoxy resin (bisphenol
A epoxy resin) along with a polymeric flexibilizer (polyglycol based
liquid) and an accelerator material (tertiary amine based liquid) in predetermined
proportions using a suitable mixer (with de-gassing
attachment) for a period of 30 - 60 minutes, maintaining the vacuum
level (0.5 - 5 mbar) in which an 'emulsion-based additive-modified
epoxy resin system' results.
The resultant 'emulsion-based additive-modified resin system' is now to
be casted as per the shape/dimension of the targeted insulation
component and then to be de-gassed and further to be heat treated in
air by maintaining the set temperature range of 80 - 90oC preferably at
80"C for a period of 6 - 8 hours, which results in 'pre-cured additivemodified
epoxy composite' body.
The derived 'pre-cured additive-modified epoxy composite' body is to be
heat treated in air at a set temperature in the range of 140 - 150oC
preferabty at t40oC for a period of 6 - 8 hours and then to be cooled
down to ambient temperature by which the fully-cured 'additive-modified
epoxy composite' body results.
13
The cured 'additive modified epoxy composite' body/article (whatever the
case may be) is then removed from the moulds in which a standard mould
releasing agent was applied prior to casting the'additive-modified epoxy
composite body'.
The 'additive-modified epoxy composites' are then to be tested for AC
breakdown strength and other related electrical tests as per IEC
standard as applicable.
The figure 1 represents AC breakdown voltage profile of the 'additivemodified
epoxy composites as compared to plain/virgin epoxy body'.
The invention would be more understood in terms of taking various examples,
which are explained in the following:
HGMPLE 1:
As per this example, nano-structured amorphous alumina additive powder was
synthesized by following the same procedure as described in the Indian Patent
Number 252217 dated May 02, 2012 (PG Journal No. 18/2012). As described this
additive material has its typical characteristic propefties which is amorphous in
the XRD and also has significant porosity in the agglomerate structure of the
particles thus having a low tap density in the range of 0.01 - 0.3 g/cc and the
material with a tap density of 0.07 g/cc was used in this example. The additive
material was heat treated in air at a set temperature of 300oC for a period of 2
hours before using; this procedure is to dry out the additive powder from the
entrapped moisture.
L4
Liquid polymeric hardener (carboxylic acid anhydride) is first mixed with liquid
silane (7-glycidoxypropyltrimethoxysilane) wherein a mixed liquid resulted. To
this mixed liquid, nanostructured amorphous alumina powder is then mixed
using a high speed mechanical mixer/stirrer for a period of 30 minutes by
maintaining a weight ratio of 200 : 4.22 : 4.22 (hardener: silane :
nanostructured amorphous alumina) and then milled for a period of about 120
minutes using a planetary mill so that the additive powders are dispersed into
the mixed liquid uniformly by which an emulsion is resulted, which is termed
as "Emulsion A".
In another container (glass/plastic or stainless steel), epoxy resin (bispheno!
A), polymeric flexibilizer (polyglyco! based liquid) and accelerator (tertiary
amine based liquid) were taken by maintaining a weight ratio of 200 : 20 :2
(epoxy : flexibilizer: accelerator) and mixed using a mechanica! stirrer/mixer
for a period of about 20 minutes to get a uniformly-mixed liquid, which is
termed as "Liquid B".
"Liquid B" is then mixed with the "Emulsion A" for a period of about 60
minutes using a high shear mechanical mixer by maintaining a weight
ratio of 1: 1 (Emulsion A : Liquid B). After this mixing, the whole mix is
transferred to a vacuum casting system wherein it is degassed resulting
'degassed mix'.
Stainless steel moulds with dimensions of (150 x 150 x 1.5 mm) are first
smeared with standard mould releasing agent and the 'degassed mix' is
then vacuum casted to those moulds.
Those resin filled moulds are then kept in an oven and heat treated in air at
80oC for a period of about 6 hours which resulted the 'pre-cured
nanostructured amorphous al umina modifi ed epoxy composites'.
15
The said 'pre-cured nanostructured amorphous alumina modified epoxy
composites' is then heat treated at 140oC for a period of another 6 hours
and then cooled down at ambient temperature by which the 'fully-cured
nanostructured amorphous alumina modified epoxy composites' with
dimensions of 150 x 150 x 1.5 mm resulted which were released from the
moulds and tested for AC breakdown voltage.
For comparison, epoxy specimens using the same system without any
additive were also fabricated and AC breakdown voltage of the plain/virgin
body is compared under identical conditions.
The derived composite showed a breakdown voltage of 60 kV, which is about
15olo higher than that of the virgin epoxy body (Figure 1).
Examole 2 :
In this e>