FORM 2
THE PATENTS ACT, 1970
(39 OF 1970)
As amended by the Patents (Amendment) Act, 2005
&
The Patents Rules, 2003
As amended by the Patents (Amendment) Rules, 2006
PROVISIONAL SPECIFICATION
(See section 10 and rule 13)
TITLE OF THE INVENTION
Casting composition having improved thermal conductivity
APPLICANTS
Crompton Greaves Limited, CG House, Dr Annie Besant Road, Worli, Mumbai 400 030, Maharashtra, India, an Indian Company
INVENTORS
Dr Jaiswal Rajendra, Patil Vijay, Ghosh Susmita and Dr Singal Vivek, Crompton Greaves Ltd, Advanced Material & Process Technology Centre, CG Global R&D Centre, Kanjur Marg (East), Mumbai 400042, Maharashtra, India, all Indian nationals
PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the nature of this invention:

FIELD OF THE INVENTION
This invention relates to casting composition having improved thermal conductivity. This invention also relates to a method for manufacturing the above mentioned casting composition having improved thermal conductivity.
This invention also relates to use of the above mentioned casting composition for electrical encapsulation.
BACKGROUND
Electrical devices and equipments generate heat and in many applications this heat needs to be effectively dissipated to improve the efficiency of the equipment. Thus thermal management in the electrical equipments forms an important aspect in its development and improvement. Casting compositions based on polymer resins are widely used for encapsulating electrical equipments such as dry transformers. Besides giving weather protection and mechanical strength, encapsulation also imparts electrical insulation properties and thermal conductivity (heat dissipation). Conventionally, epoxy resin based and unsaturated polyester based resin compositions are used for encapsulation.
Unsaturated polyester resin based compositions are also used for encapsulation of electrical apparatuses. Unsaturated polyester based resin compositions are cheaper and


processable at room temperature. They are however, characterized by a lower thermal conductivity of the order of 0.5 W/mK.
Generally, the fillers such as fumed silica, finely divided quartz powder, amorphous silica, carbon black, graphite, diamond, metals, silicon carbide aluminum hydrates, metal nitrides, metal oxides either alone or in combinations are used to prepare thermally conducting compositions. The fillers are blended with pre-accelarted unsaturated polyester system to prepare the composition and finally cured by using curing agent. However, physical blending of the fillers with unsaturated polyester system may result into non-uniform distribution of fillers in the polymer system thus reducing thermal conductivity which results in reduced heat transfer between the equipment and the surroundings, resulting in local heating that is detrimental to the performance of the equipment.
In order to improve the cooling efficiency and performance of electrical apparatus it is important to encapsulate them with the casting compositions having good thermal conductivity besides the other desirable properties.
OBJECTS OF INVENTION
An object of the invention is to provide an unsaturated polyester based casting composition having improved thermal conductivity besides the other desirable properties. Another object of the invention is to provide the unsaturated based polyester composition having improved thermal conductivity which is curable at room temperature.


Another object of the invention is to provide a method for producing the above mentioned unsaturated polyester based casting composition having improved thermal conductivity wherein the method comprises mixing of unsaturated polyester system including styrene with a filler such as alumina by sonication thereby resulting in uniform distribution of alumina in the polyester system which increases heat dissipation and thus improving thermal conductivity.
Another object of the invention is to provide casting composition having improved thermal conductivity which is used for encapsulation of electrical apparatuses.
DETAILED DESCRIPTION
According to the invention there is provided a casting composition having improved thermal conductivity; the casting composition comprising
15 to 25 % by weight of preaccelerated unsaturated polyester system including 0.5 to 2 % of styrene and 75-85% by weight of the filler system including 4 to 15 % alumina, 0.1 to 0.4 % silane, 40 to 80% silica, 0.8 to 2.4 % titanium dioxide, 7 to 15 % aluminum trihydrate and coloring agent and curing system including 0.05 to 0.6 % methyl ethyl ketone peroxide and 0.05 to 0.3% cobalt naphthhenate.
According to the invention there is also provides a method of manufacturing the casting composition having improved thermal conductivity; the method comprises :
a) mixing a 15 to 25 % by weight of preaccelerated unsaturated polymer system; 0.5 to 2 % by weight of styrene, 0.1 to 0.4 % by weight of silane, 4 to 15 % by


weight of alumina and 0.05 to 0.3% by weight of cobalt naphthanate by ultrasonication to obtain homogenous mixture;
b) blending the mixture obtained from step (a) with 0.05 to 0.6 % by weight of methyl ethyl ketone peroxide, 40 to 80% by weight of silica powder, 0.8 to 2.4 % by weight of titanium dioxide and 7 to 15 % by weight of aluminium trihydrate to obtain viscous mixture; and
c) pouring the composition into mould and curing the composition.
Examples of polyester resins that can be used for preparing the composition include maleic anhydride, isophthalic acid, phthalic anhydride, o-phthalic anhydride, polyethylene terephthalate, and copolyesters thereof.
The alumina powders used in the composition is y-alumina modified with organic modifiers.
The ultrasonication mixing of the preaccelerated unsaturated polyester resin including styrene, silane and alumina and cobalt naphthanate naphthenate is carried out at 250 to 400 rpm for 3 to 5 hours.
The method further comprises demoulding the cast specimens and subjected the specimens at 80 to 90° C.
The thermal conductivity of the compositions were compared and studied by using Lee's Disk Method. In this technique thin polymer sample is placed between two plates in


conjugation with heat source. The heat loss can be determined by measuring the cooling rate at the equilibrium temperature with lower plate covered with a pad of insulation
If the disk cools at the rate of dT/dt then rate of heat loss is given by
Q= m Cp dT/dt (1)
Where m = mass of the plate. Cp = heat capacity of plate material
The sample used to measure the thermal conductivity using this method is in the form of a disk whose thickness x, is small relative to its diameter D. This aspect ratio removes the need to lag the edges of the disk to reduce heat loss since the cross sectional area of disk A= IID /4 is large compared to the exposed area of the edge, a = IIDx.
The thermal conductivity of the composition without alumina powder was found to be 0.49 W/m.K. Thermal conductivity of the composition according to the invention with alumina and manufactured by using ultrasonication showed the thermal conductivity of 1.2 W/mK. The thermal conductivity of the composition with alumina manufactured by using physical blending and without ultrasonication was found to be 0.7 W/mK.
Thus ultrasonication method gives uniform distribution of alumina in the polymer system which improves the thermal conductivity of the present invention. Because of the better thermal conductivity of the composition of the invention it is ideal for use in the encapsulation of electrical apparatuses so as to improve cooling efficiency and performances of the apparatuses. It is to be, however, clearly understood that the scope of the application of the composition of the invention is not confined to electrical


apparatuses. It can be effectively used in any application where the properties of the composition, especially heat dissipation are desirable. It can be used to encapsulate/impregnate electrical equipments. The electrical equipments that can be encapsulated/impregnated with the casting composition of the invention include dry type transformers, current transformers, electrical equipments, and the like. The thermal conductivity of the composition of the invention ensures that heat generated in the electrical equipment during operation will be dissipated. Further, reduction in the heat load of the composition of the invention also ensures that no crack, breakdown of the casting composition takes place. Therefore, the casting composition of the invention provides enhanced protection to the equipments from weathering, mechanical damage, heat, electrical leakage and short circuits.
The invention is further illustrated by way of the following nonlimiting examples
Examples Example 1 by using Ultrasonication
17.5% part by weight of unsaturated polyester resin, 1.2% parts by weight of styrene, 0.24% parts by weight of silane, 10% parts by weight of alumina and 0.1% parts by weight of cobalt naphthanate were taken in a beaker, the mixture was kept for sonication at speed of 300 for 3 hrs and followed by high speed mixing for half an hour to obtain homogeneous mixture. The mixture was blended with 0.21% parts by weight of MEKP, 58.35% parts by weight of silica powder, 1.6% parts by weight of titanium dioxide and 10.4% parts by weight of Aluminium trihydrate. This viscous mixture was stirred for 5-10 minutes uniformly. The mixture was ultimately poured in a mold for casting. It was


kept for 3-4 hour for curing. De-molding was done after 4 hours. The composite was placed for 24 hrs at room temperature. The post curing is done at 80-90°C for 3 hrs. Thermal conductivity of the composition was 1.2 W/mK.
Examples Example 2: by using physical blending
17.5% part by weight of unsaturated polyester resin, 1.2% parts by weight of styrene, 0.24% parts by weight of silane, 10% parts by weight of alumina and 0.1% parts by weight of cobalt naphthanate were taken in a beaker, the mixture was physically blended for 3 hrs to obtain the mixture. The mixture was blended with 0.21% parts by weight of MEKP, 58.35% parts by weight of silica powder, 1.6% parts by weight of titanium dioxide and 10.4% parts by weight of Aluminium trihydrate. This viscous mixture was stirred for 30 minutes uniformly. The mixture was ultimately poured in a mold for casting. It was kept for 3-4 hour for curing. De-molding was done after 4 hours. The composite was placed for 24 hrs at room temperature. The post curing is done at 80-90°C for 3 hrs. The thermal conductivity of the composition was found to be 0.7 W/mK.
The compositions are suitable for various applications, especially for those applications where the heat load during the curing of the cast and the casted electrical component during operation leads to several undesirable effects, including damage to the casted material/equipment as well as to the occurrence of safety hazards. Thus, the casting


compositions of the invention provide enhanced safety and stability apart from providing heat dissipation and compactness to the encased materials/equipments.