FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
As amended by the Patents (Amendment) Act, 2005
&
The Patents Rules, 2OO3
As amended by the Patents (Amendment) Rules, 2005
COMPLETESPECIFICATlON
(See section 10 and rule 13)
CURABLE COMPOSITION WITH IMPROVED THERMAL STABILITY AND ITS USE AS CASTING RESIN
APPLICANTS
Crompton Greaves Limited, CG House, Dr Annie Besant Road, Prabhadevi, Mumbai 400 030, Maharashtra, India, an Indian Company
INVENTORS
Jaiswal Rajendra, D'melo Dawid, Chaudhari Lokesh Kisan; all of Crompton Greaves Ltd, AMPTC, CG Global R&D Centre, Ranjur (E), 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.

Technical field:
The present invention relates to curable composition comprising modified unsaturated polyester with bismaleimide having improved thermal stability and its use as casting resin in the manufacture of transformer and other electric components. The cross-linked products obtained by curing the said compositions, which simultaneously exhibit the features of improved thermal stability besides other characteristic properties.
The present invention also relates to cast resin transformer which is made from curable composition of the invention.
Background of the invention:
Casting resin for transformer should not only provide insulation but also at the same time should contribute to good mechanical and electrical properties. The casting resin having high thermal conductivity and excellent dimensional stability, strength and surface properties are useful for casting transformer or any electrical components.
Generally casting resin used in the Transformer field is epoxy resin in combination with anhydride hardener along with the fillers. The general process used for casting transformer by using curable composition comprising epoxy resin in combination with anhydride hardener along with filler consisting of following steps :
a) The fillers are dried at 120° C for 12 hours;
b) The epoxy resin and filler are mixed at 65° C for 1 hour under 10 mbar pressure to get first mixture;
c) The anhydride hardener and filler are mixed at 65° C for 1 hour under 10 mbar pressure to get Second mixture;
d) The first mixture is mixed with second mixture at 65° C for 2 hours under 4 mbar pressure to get final mixture which is further mixed at 65° C for 0.5 hour under 10 mbar pressure;

e) The final mixture is subjected to coil drying at 100° C for 4 hours under 4 mbar pressure;
f) Pouring the final mixture in mould at 85° C for 3-5 hours under 10 mbar pressure;
g) Casted mould is subjected to curing at 110° C for 10 hours followed by post curing at 140° C for 6 hours; and
h) The casted article is de-moulded.
Thus the overall process time required is at least 39.5 to 41.5 hours for casting the article, particularly transformer.
The curing temperature and post curing temperature of 110° and 140° is high as well as time required for curing and post curing is 10 hours and 6 hours. This fact leads to high energy consumption. Further epoxy resin is costly in combination with high energy consumption that increases the cost of the casting and hence, the article, particularly, transformer.
Further epoxy resin is costly as compared to polyester, but polyester does not have good thermal stability. There is need for modifying the polyester which can cure at low temperature and also having good thermal stability.
Therefore there is a need for casting resin formulations that cures at low temperature and is cost-effective without scarifying thermal stability.
Objects of the invention:
An object of the invention is to provide a curable composition comprising modified unsaturated polyester resin and bismaleimide in which curing is carried out at 30° C and having improved thermal stability.
It is another object of the invention to provide the curable composition comprising modified unsaturated polyester resin and bismaleimide, which is easily curable at 30° C, thereby reducing energy consumption.

It is another object of the invention to provide the curable composition comprising modified unsaturated polyester resin and bismaleimide, which is easily curable at 30° C in short period, thereby making the composition cost-effective.
It is another object of the invention to provide a method of making the described curable composition which is curable at 30° C.
It is another object of the invention to provide a crosslinked product obtained by curing composition of the invention with improved thermal stability.
ft is another object of the invention to provide method of casting transformer which is cost-effective without sacrificing mechanical and electrical and thermal properties.
It is still another object of the invention to provide cast resin transformer casted by using the curable composition of the invention having good thermal stability.
Other objects and advantages will become apparent from the following description and the appended claims.
Detailed Description of the invention:
According to the invention there is provided a curable composition comprising
a. 100 parts by weight of unsaturated polyester resins having solid content
50 to 70%;
b. 0.5 to 20 parts by weight of Maleimide;
c. 0 to 60 parts by weight thermally pretreated filler and coloring agent;
d. 0 to 2 parts by weight coupling agent;
e. 0.1 to 0.7 parts by weight accelerator; and
f. 0.5 to 2 parts by weight initiator;
the composition is cured at 30° C and having improved thermal stability.
The curable composition of the invention has improved thermal stability without sacrificing other characteristic properties required for casting.
According to the invention, there is also provided a method of making a curable resin composition which comprises

a) Preparing a mixture comprising 100 parts by weight of base resin, unsaturated polyester resins having solid content 50 to 70% with 0.5 to 20 parts by weight of Maleimide; 0 to 60 parts by weight thermally pretreated filler and coloring agent 0 to 2 parts by weight coupling agent; 0.1 to 0.7 parts by weight accelerator and 0.5 to 2 parts by weight initiator at 20 to 40° C for 0.5 hour which is further mixed at 20 to 40° C for 0.5 hour under 279 mbar pressure; and
b) Subjecting the mixture to coil drying at 100° C for 4 hours under 4 mbar pressure;
the said composition is cured at 30° C and having improved thermal stability.
The curable epoxy composition is used immediately for casting any electrical insulating products such as transformer bushings, winding, etc.
"Thermally pretreated" in this context means that, by means of heat treatment, water is removed from the fillers advantageously in an amount of from 2-5 to about 0.01-0.1% by weight based on the original weight before removal of water.
In the present invention the filler are subjected to heating at 100 to 140°C for 6 to 20 hours followed by cooling down and maintaining the fillers to 60°C to obtained thermally pretreated fillers.
The unsaturated polyester resins having solid content 50 to 70% in the present invention are diluted with reactive diluents intend to cover styrene, acrylic acid, butyl acrylate, methacrylic acid, methyl methacrylate, acrylonitrile, etc. Particularly, the unsaturated polyester resin are selected from those based on but not limited to diacids such as adipic acid, terephthalic acid, isophthalic acid, suberic acid, sebacic acid, etc, and anhydrides such maleic anhydride, succinic anhydride, phthalic anhydride, chlorendic anhydride, etc; and glyols such as 1,2 propane diol, 1,3 propane diol, ethane diol, neopentyl glycol, etc.
The maleimide used in the present invention is bis-maleimide, derived from the condensation product of maleic anhydride and various diamines such as 4,4'-diamino diphenyl methane, para-phenylene diamine, meta-phenylene diamine, 4,4'-diaminodiphenyl sulphone, etc.

The fillers used in the curable composition of the invention is selected from but not limited to silica, alumina, talc, clays, titanium dioxide, barium sulphate, zinc oxide, zinc sulphide, lithopone, calcium carbonate, aluminium trihydroxide, magnesium silicate, calcium silicate, mica, etc.
The colouring agents including coloured pigments used in the curable composition of the invention are selected from but not limited to chrome yellow, phthalocyanines, molybdate oranges, zinc yellows, magnesium oxide, red lead based pigments, nickel titanates, calcium based pigments, chrome greens, etc.
The Initiator used in the curable composition of the invention is selected from but not limited to peroxide initiators such as peroxide, dicumyl peroxide, diacetyl peroxide, dibenzoyl peroxide, di-p-chlorobenzoyl peroxide, dilauroyl peroxide, t-butyl hydroperoxide, cyclohexanone hydroperoxide, methylethyl ketone hydroperoxide; , ketone peroxides such as cyclohexanone peroxide, acetyl acetone peroxide or azobisisobutyrnitrile, etc. The initiator helps to initiate the curing reaction. Any substance which will cause initiation of curing of curable polyester composition of the invention can be used as initiator.
Accelerators is catalyst which catalyze the curing and is selected from but not limited to Cobalt naphthenate, cobalt octoate, substituted anilines, triphenyl phosphine, tricyclohexyl phosphine, tri-n-butyl phosphine, triphenyl phosphite etc. Any substance which will catalyze of curing of curable polyester composition of the invention can be used as accelerator.
Coupling agents are those chemicals which increase the interaction between the polymer and filler particles through chemical reaction and is selected from but not limited to gamma-methacryloxypropyltrimethoxy silane, vinyltriethoxy silane, vinyltrimethoxy silane, vinylmethyldimethoxy silane etc. Any substance which will increase the interaction between the polymer and filler covered by the invention can be used as coupling agent.
Any suitable additive can be used in the present composition to obtain desired characteristics.

According to the invention, there is also provided crosslinked product obtained by curing composition according to the invention.
According to the invention, there is also provided cast resin transformer wherein transformer is casted with curable composition of the invention.
According to the invention, there is also provided method for production of cast resin transformer, the method comprises
a) Preparing a mixture comprising 100 parts by weight of base resin, unsaturated polyester resins having solid content 50 to 70% with 0.5 to 20 parts by weight of Maleimide; 0 to 60 parts by weight thermally pretreated filler and coloring agent; 0 to 2 parts by weight coupling agent; 0.1 to 0.7 parts by weight accelerator and 0.5 to 2 parts by weight initiator at 20 to 40° C for 0.5 hour which is further mixed at 20 to 40° C for 0.5 hour under 279 mbar pressure;
b) Subjecting the mixture to coil drying at 100° C for 4 hours under 4 mbar
pressure;
c) Pouring the mixture in mould of the transformer at 30° C for 0.25 hours under 146 mbar pressure;
d) Subjecting the casted mould to curing at 30° C for 4 hours followed by post curing at 80-100° C for 4 hours; and
e) The casted article is de-moulded.
According to the invention there is also provided an improved method for the production of an electrical components utilizing the curable composition of the invention wherein the improvement comprises the use of curable composition of the invention as the casting resin.
The electrical components are selected from the group consisting of electrical components of transformer including winding, bushings, insulators, switches, sensors, converters, etc.
The present invention provides curable composition comprising modified unsaturated polyester resin and bismaleimide where maleimide is easily soluble in unsaturated polyester and its cures at low temperature ie 30° C. The curing time is substantially reduced in curing as well as post curing cycle. The post curing

temperature is reduced to 80-100° C. Thus the energy consumption is less. The costly epoxy resin is effectively replaced by cheap unsaturated polyester resin. Thus, both the advantages make the product as well as process cost-effective. The composition also has good thermal stability without affecting other characteristic properties of the cast resin as well as curable products including transformer. The method of casting any electrical component including transformer is easy.
The following experimental examples are illustrative of the invention but not limitative of the scope thereof:
Example 1:
(UPR 1 STANDARD COMPOSITION)
100 parts by weight of base resin, unsaturated polyester resins having solid content 60% (UPR-M, M/s Suketu Organics Pvt. Ltd. India) is mixed 30 parts by weight thermally pretreated silica; 0.4 parts by weight Co-naphthenate and 1.2 parts by weight methyl ethyl ketone peroxide at 20 to 40° C for 0.5 hour which is further mixed at 20 to 40° C for 0.5 hour under 279 mbar pressure. The mixture is subjected to coil drying at 100° C for 4 hours under 4 mbar pressures. The mixture is poured in mould of the transformer at 30° C for 0.25 hours under 146 mbar pressure. The casted mould is subjected to curing at 30° C for 4 hours followed by post curing at 80-100° C for 4 hours; and the transformer is de-moulded.
Example 2:
(UPR 1 COMPOSITION WITH 2.5 % MALEIMIDE)
100 parts by weight of base resin, unsaturated polyester resins having solid content 60% (UPR-M, M/s Suketu Organics Pvt. Ltd. India) is mixed with 5 parts by weight of Maleimide (ABRON-BMI, ABR Organics Pvt. Ltd, Hyderabad, India); 30 parts by weight thermally pretreated silica; 0.4 parts by weight Co-naphthenate and 1.2 parts by weight methyl ethyl ketone peroxide at 20 to 40° C for 0.5 hour which is further mixed at 20 to 40° C for 0.5 hour under 279 mbar pressure. The mixture is subjected to coil drying at 100° C for 4 hours under 4 mbar pressures. The mixture is poured in mould of the transformer at 30° C for 0.25 hours under 146 mbar pressure. The casted mould is subjected to curing at 30° C for 4 hours followed by post curing at 80-100° C for 4 hours; and the transformer is de-moulded.

Example 2:
(UPR 2 STANDARD COMPOSITION)
100 parts by weight of base resin, unsaturated polyester resins having solid content 60% (prepared in house by using phthalic anhydride, propylene glycol and maleic anhydride) is mixed 30 parts by weight thermally pretreated silica; 0.4 parts by weight Co-naphthenate and 1.2 parts by weight methyl ethyl ketone peroxide at 20 to 40° C for 0.5 hour which is further mixed at 20 to 40° C for 0.5 hour under 279 mbar pressure. The mixture is subjected to coil drying at 100° C for 4 hours under 4 mbar pressures. The mixture is poured in mould of the transformer at 30° C for 0.25 hours under 146 mbar pressure. The casted mould is subjected to curing at 30° C for 4 hours followed by post curing at 80-100° C for 4 hours; and the transformer is de-moulded.
Example 2:
(UPR 2 COMPOSITION WITH 2.5 % MALEIMIDE)
100 parts by weight of base resin, unsaturated polyester resins having solid content 60% (prepared in house by using phthalic anhydride, propylene glycol and maleic anhydride) is mixed with 5 parts by weight of Maleimide (ABRON-BMI, ABR Organics Pvt. Ltd, Hyderabad, India); 30 parts by weight thermally pretreated silica; 0.4 parts by weight Co-naphthenate and 1.2 parts by weight methyl ethyl ketone peroxide at 20 to 40° C for 0.5 hour which is further mixed at 20 to 40° C for 0.5 hour under 279 mbar pressure. The mixture is subjected to coil drying at 100° C for 4 hours under 4 mbar pressures. The mixture is poured in mould of the transformer at 30° C for 0.25 hours under 146 mbar pressure. The casted mould is subjected to curing at 30° C for 4 hours followed by post curing at 80-100° C for 4 hours; and the transformer is de-moulded.
The compositions prepared according to examples 1 to 4 were tested for Thermograms which are illustrated in Figure l to 4. The activation energy and the thermal index of the compositions were calculated from the interpretation of the thermogram using the ERDA-DiCerbo method. The results of Table 1 show that

the thermal index of the compositions is increased by addition of maleimide in the composition.
Table 1 : The thermal index of the compositions of examples 1 to 4

Sr. No. ■
Composition Activation
energy
(kcal/mol) Thermal index Tg (0C)
1 Standard UPR 1 23.35 90 75.69
2 UPR 1 composition with 2.5% maleimide 24.95 101 67.47
3 Standard UPR 2 20.62 113 114
4 UPR 2 composition with 2.5% maleimide 36.91 137 106.5
Figures 1, 2, 3 and 4 illustrate "Thermogram" of Standard UPR 1, UPR 1 composition with 2.5% maleimide, Standard UPR 2 and UPR 2 composition with 2.5% maleimide respectively. Thermogram illustrates weight loss in % against temperature.

We claim :
1. A curable composition comprising
a. 100 parts by weight of unsaturated polyester resins having solid content 50
to 70%;
b. 0.5 to 20 parts by weight of Maleimide;
c. 0 to 60 parts by weight thermally pretreated filler and coloring agent;
d. 0 to 2 parts by weight coupling agent;
e. 0.1 to 0.7 parts by weight accelerator; and
f. 0.5 to 2 parts by weight initiator
the composition is cured at 30° C and having improved thermal stability.
2. The curable composition as claimed in claim 1, wherein the unsaturated polyester resins having solid content 50 to 70 % are diluted with reactive diluents like styrene, acrylic acid, butyl acrylate, methacrylic acid, methyl methacrylate or acrylonitrile.
3. The curable composition as claimed in claim 2 wherein the unsaturated polyester resins are selected from those based on diacids such as adipic acid, terephthalic acid, isophthalic acid, suberic acid, sebacic acid, etc and anhydrides such as maleic anhydride, succinic anhydride, phthalic anhydride, chlorendic anhydride, etc; and glyols like 1,2 propane diol, 1,3 propane diol, ethane diol, neopentyl glycol, etc.
4. The curable composition as claimed in claim 1, wherein the maleimide used is bis-maleimide, derived from the condensation product of maleic anhydride and diamines like 4,4'-diamino diphenyl methane, para-phenylene diamine, meta-phenylene diamine, 4,4'-diaminodiphenyl sulphone, etc.
5. The curable composition as claimed in claims 1, wherein the fillers used in the curable composition of the invention is selected from silica, alumina, talc, clays, titanium dioxide, barium sulphate, zinc oxide, zinc sulphide, lithopone, calcium carbonate, aluminium trihydroxide, magnesium silicate, calcium silicate or mica.
6. The curable composition as claimed in claim 1, wherein the colouring agents used are selected from chrome yellow, phthalocyanines, molybdate oranges, zinc yellows, magnesium oxide, red lead based pigments, nickel titanates, calcium based pigments or chrome greens.
7. The curable composition as claimed in claim 1, wherein the coupling agent used are selected from gamma-methacryloxypropyltrimethoxy silane, vinyltriethoxy silane, vinyltrimethoxy silane or vinylmethyldimethoxy silane.

8. The curable composition as claimed in claim 1, wherein the Initiator used in the curable composition of the invention is selected from but not limited to peroxide initiators such as peroxide, dicumyl peroxide, diacetyl peroxide, dibenzoyl peroxide, di-p-chlorobenzoyl peroxide, dilauroyl peroxide, t-butyl hydroperoxide, cyclohexanone hydroperoxide, methylethyl ketone hydroperoxide; , ketone peroxides such as cyclohexanone peroxide, acetyl acetone peroxide or azobisisobutyrnitrile.
9. The curable composition as claimed in claim 1, wherein the accelerators are selected from Cobalt naphthenate, cobalt octoate, substituted anilines, triphenyl phosphine, tricyclohexyl phosphine, tri-n-butyl phosphine or triphenyl phosphite.
10. A method of making a curable resin composition which comprises

a) Preparing a mixture comprising 100 parts by weight of base resin, unsaturated polyester resins having solid content 50 to 70% with 0.5 to 20 parts by weight of Maleimide; 0 to 60 parts by weight thermally pretreated filler and coloring agent; 0 to 2 parts by weight coupling agent; 0.1 to 0.7 parts by weight accelerator; and 0.5 to 2 parts by weight initiator at 20 to 40° C for 0.5 hour which is further mixed at 20 to 40° C for 0.5 hour under 279 mbar pressure; and
b) Subjecting the mixture to coil drying at 100° C for 4 hours under 4 mbar
pressure; the said composition is cured at 30° C and having improved thermal stability.
11.The method as claimed in claim 10, wherein the unsaturated polyester resins having solid content 50 to 70 % are diluted with reactive diluents like styrene, acrylic acid, butyl acrylate, methacrylic acid, methyl methacrylate or acrylonitrile.
12.The method as claimed in claims 10 and 11, wherein the unsaturated polyester resins are selected from those based on diacids such as adipic acid, terephthalic acid, isophthalic acid, suberic acid, sebacic acid, etc and anhydrides such as maleic anhydride, succinic anhydride, phthalic anhydride, chlorendic anhydride, etc; and glyols such as 1,2 propane diol, 1,3 propane diol, ethane diol, neopentyl glycol, etc.
13.The method as claimed in claim 10, wherein the maleimide used is bis-maleimide, derived from the condensation product of maleic anhydride and diamines like 4,4'-diamino diphenyl methane, para-phenylene diamine, meta-phenylene diamine, 4,4'-diaminodiphenyl sulphone, etc.

14.The method as claimed in claim 10, wherein the fillers used in the curable composition of the invention is selected from but not limited to silica, alumina, talc, clays, titanium dioxide, barium sulphate, zinc oxide, zinc sulphide, lithopone, calcium carbonate, aluminium trihydroxide, magnesium silicate, calcium silicate or mica.
15.The method as claimed in claim 10, wherein the colouring agents selected from chrome yellow, phthalocyanines, molybdate oranges, zinc yellows, magnesium oxide, red lead based pigments, nickel titanates, calcium based pigments or chrome greens.
16.The method as claimed in claim 10, wherein the coupling agent used are selected from gamma-methacryloxypropyltrimethoxy silane, vinyltriethoxy silane, vinyltrimethoxy silane or vinylmethyldimethoxy silane.
17.The method as claimed in claim 10, wherein the Initiator used in the curable composition of the invention is selected from but not limited to peroxide initiators such as peroxide, dicumyl peroxide, diacetyl peroxide, dibenzoyl peroxide, di-p-chlorobenzoyl peroxide, dilauroyl peroxide, t-butyl hydroperoxide, cyclohexanone hydroperoxide, methylethyl ketone hydroperoxide; , ketone peroxides such as cyclohexanone peroxide, acetyl acetone peroxide or azobisisobutyrnitrile.
18.The method as claimed in claim 10, wherein the accelerators are selected from Cobalt naphthenate, cobalt octoate, substituted anilines, triphenyl phosphine, tricyclohexyl phosphine, tri-n-butyl phosphine or triphenyl phosphite.
19.A crosslinked product obtained by curing the composition according to the
claims 1 to 9. 20.The use of the composition according to the claims 1 to 9 in casting electrical
components and resin transformer. 21 .A method for production of cast resin transformer, the method comprises
a) Preparing a mixture comprising 100 parts by weight of base resin, unsaturated polyester resins having solid content 50 to 70% with 0.5 to 20 parts by weight of Maleimide; 0 to 60 parts by weight thermally pretreated filler and coloring agent; 0 to 2 parts by weight coupling agent; 0.1 to 0.7 parts by weight accelerator; and 0.5 to 2 parts by weight initiator at 20 to 40° C for 0.5 hour which is further mixed at 20 to 40° C for 0.5 hour under 279 mbar pressure;
b) Subjecting the mixture to coil drying at 100° C for 4 hours under 4 mbar
pressure;

c) Pouring the mixture in mould of the transformer at 30° C for 0.25 hours under 146 mbar pressure;
d) Subjecting the casted mould to curing at 30° C for 4 hours followed by post curing at 80-100° C for 4 hours; and
e) The casted article is de-moulded.
22. The method as claimed in claim 21, wherein the unsaturated polyester resins having solid content 50 to 70 % are diluted with reactive diluents like styrene, acrylic acid, butyl acrylate, methacrylic acid, methyl methacrylate or acrylonitrile.
23.The method as claimed in claims 21 and 22, wherein the unsaturated polyester resins are selected from those based on diacids such as adipic acid, terephthalic acid, isophthalic acid, suberic acid, sebacic acid, etc and anhydrides such as maleic anhydride, succinic anhydride, phthalic anhydride, chlorendic anhydride, etc; and glyols like 1,2 propane diol, 1,3 propane diol, ethane diol, neopentyl glycol, etc.
24.The method as claimed in claim 21, wherein the maleimide used is bis-maleimide, derived from the condensation product of maleic anhydride and diamines like 4,4'-diamino diphenyl methane, para-phenylene diamine, meta-phenylene diamine, 4,4'-diaminodiphenyl sulphone, etc.
25.The method as claimed in claim 21, wherein the fillers used in the curable composition of the invention is selected from but not limited to silica, alumina, talc, clays, titanium dioxide, barium sulphate, zinc oxide, zinc sulphide, lithopone, calcium carbonate, aluminium trihydroxide, magnesium silicate, calcium silicate or mica.
26.The method as claimed in claim 21, wherein the colouring agents selected from chrome yellow, phthalocyanines, molybdate oranges, zinc yellows, magnesium oxide, red lead based pigments, nickel titanates, calcium based pigments or chrome greens.
27. The method as claimed in claim 21, wherein the coupling agent used are selected from gamma-methacryloxypropyltrimethoxy silane, vinyltriethoxy silane, vinyl trimethoxy silane or vinylmethyldimethoxy silane.
28.The method as claimed in claim 21, wherein the Initiator used in the curable composition of the invention is selected from but not limited to peroxide initiators such as peroxide, dicumyl peroxide, diacetyl peroxide, dibenzoyl peroxide, di-p-chlorobenzoyl peroxide, dilauroyl peroxide, t-butyl hydroperoxide, cyclohexanone hydroperoxide, methylethyl ketone

hydroperoxide; , ketone peroxides such as cyclohexanone peroxide, acetyl acetone peroxide or azobisisobutyrnitrile. 29.The method as claimed in claim 21, wherein the accelerators are selected from Cobalt naphthenate, cobalt octoate, substituted anilines, triphenyl phosphine, tricyclohexyl phosphine, tri-n-butyl phosphine or triphenyl phosphite.