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
COMPLETE SPECIFICATION
(See section 10 and rule 13)
TITLE OF THE INVENTION
Shrinkage resistant casting composition
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 and the manner in which it is to be performed:

Field of Invention
The invention relates to shrinkage resistant casting composition comprising a nanocomposite of an unsaturated polyester resin and modified clay.
Background
Casting compositions based on polymer resins are widely used for encapsulating electrical equipments such as dry transformers. Conventionally, epoxy resin based and unsaturated polyester based resin compositions are used for encapsulation. US 20070190332 discloses a resin composition comprising cyanate resin and a mineral filler for encapsulating electrical equipments such as dry type transformers. The compositions disclosed here, are however, prone to shrinkage on curing leaving air gaps between the equipment and the encapsulant. Presence of such air gaps results in reduced heat transfer between the equipment and the surroundings, resulting in local heating that is detrimental to the performance of the equipment
Accordingly the invention provides a shrinkage resistant casting composition comprising a nanocomposite of an unsaturated polyester resin and modified clay.
In one embodiment, the invention provides a shrinkage resistant casting composition, the composition comprising 15-25% of an unsaturated polyester resin and 1.8 to around 2.2 % of modified clay


In another embodiment, the invention provides a shrinkage resistant casting composition for electrical equipments, the composition comprising 15 to 25 % of an unsaturated polyester resin and 1.8 to around 2.2 % of modified clay
In a further embodiment, the invention provides an electrical equipment encapsulated or impregnated with a composition comprising a nanocomposite of an unsaturated polyester resin and a modified clay
The casting composition of the invention comprises a nanocomposite of an unsaturated polyester and modified clay. 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 clays that can be used for the preparation of the nanocomposite composition include siliceous and non-siliceous clays expandable by intercalation with organic modifiers. Apart from the modified clay and the unsaturated resin, the nanocomposite composition of the invention comprises 0.5 to 2.0% of styrene, 0.1 to 0.4% silane, 40-80% silica, 0.8 to 2.4 % titanium dioxide and 7 to 15 % aluminium trihydride (ATH), 0.1 to 0.8% of colorant, 0.05 to 0.6% of Methyl-ethyl ketone peroxide (MEKP) and 0.05 to 0.3% cobalt naphthenate.
The casting composition of the invention is a shrinkage resistant resin-clay nanocomposite composition. 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 shrinkage resistance of the composition of the invention ensures that no air gap is formed on curing of the cast around the equipment. Further, absence of shrinkage of the composition of the invention also ensures that no crack is formed in the cast. Therefore, the casting composition of the invention provides enhanced protection to the equipments from weathering, mechanical damage, electrical leakage and short circuits.
The invention is further illustrated by way of the following nonlimiting examples
Examples
Example 1: Preparation of modified clay
50 g of montmorillonite clay was dispersed in 2 liters of distilled water at 80°C with stirring for 1 hr. 0.05 moles of the intercalating agent, stearyl amine modified quaternary ammonium chloride was added to the solution. The resultant mixture was stirred for 4 hours. The solution was then filtered and the modified clay was washed with hot water for about 3-4 times to remove residual modifiers. The complete removal of the modifier was confirmed by testing for halogen in the washings. The modified clay obtained was then dried in an air circulating oven at 100+ 10 °C for 8-10 hrs and ground into a fine powder which was then passed through 200 mesh sieve.
Example 2: Preparation of resin-clay nanocomposite composition
36 part by weight of unsaturated polyester resin, 4 parts by weight of styrene, 1 parts by weight of silane, 4 parts by weight of modified MMT clay and 0.6 parts by weight of


cobalt naphthanate were taken in a beaker, the mixture was kept for sonication for 3 hrs and followed by high speed mixing for half an hour. After uniform mixing it was blended with 0.6 parts by weight of MEKP and 119 parts by weight of silica powder, 4.4 parts by weight of titania and 27 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 at room temperature. 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.
Example 3: Shrinkage studies on resin-clay nanocomposite
The volumetric shrinkage was determined by measuring the change in volume of the casting before and after curing in graduated vials. The known volume of the compounded resin was placed in the vial and allowed to cure. Once the curing had been completed the volume deficit resulting from polymerization shrinkage was compensated for by the addition of water from a graduated burette.
The variation of percentage shrinkage of polyester resin compositions with clay loading is given in figure 1. The shrinkage of resin composition without clay was found to be 5.66%. No shrinkage was observed for a composition having a loading of modified clay of around 2.2 %. Beyond around 2.2% loading of the clay, the composition exhibited swelling till a clay loading of 5 % beyond which the percentage shrinkage remained unchanged with the clay loading.
The casting composition of the invention comprises 15-25%) of unsaturated polyester resin and 1.8% to around 2.2% of clay. The compositions are suitable for various applications, especially for those applications where the shrinkage on curing of the cast 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 provides enhanced safety and stability apart from providing mechanical protection and compactness to the encased materials/equipments.
The above description is illustrative only and is not limiting. The present invention is defined by the claims which follow and their full range of equivalents


We Claim
1. A shrinkage resistant casting composition, the composition comprising 15 to 25 % of an unsaturated polyester resin and 1.8 % to around 2.2 % of modified clay.
2. A shrinkage resistant casting composition for electrical equipments, the composition comprising 15 to 25 % of an unsaturated polyester resin and 1.8 to around 2.2 % of modified clay.
3. An electrical equipment encapsulated with the composition as claimed in claim 2.
Dated this 18th day of March 2008


ABSTRACT
The invention relates to a shrinkage resistant casting composition, the composition comprising 15 to 25 % of an unsaturated polyester resin and 1.8 % to around 2.2 % of modified clay.