Title of Invention	A CURABLE COATING COMPOSITION CONTAINING HYDROXY POLY SILOXANE AND A PROCESS FOR PREPARING THE SAME
Abstract	This invention relates to a curable coating composition comprising a blend of a premix dispersion and a curing component. The premix consists of a mixture of hydroxy terminated poly dimethyl siloxane, silica, ferric oxide and zinc oxide dispersed in an organic solvent and the curing component consists of a mixture of alkoxy tris alkyl alkoxy silane, amino alkyl trialkoxy silane and an organo tin compound.

Title of Invention

A CURABLE COATING COMPOSITION CONTAINING HYDROXY POLY SILOXANE AND A PROCESS FOR PREPARING THE SAME

Abstract

This invention relates to a curable coating composition comprising a blend of a premix dispersion and a curing component. The premix consists of a mixture of hydroxy terminated poly dimethyl siloxane, silica, ferric oxide and zinc oxide dispersed in an organic solvent and the curing component consists of a mixture of alkoxy tris alkyl alkoxy silane, amino alkyl trialkoxy silane and an organo tin compound.

Full Text	This invention relates to a curable coating composition containing hydroxy poly siloxane and a process for preparing the same. The composition when coated on substrates and cured exhibits low thermal diffusivity and is therefore found ideally suitable for thermally protecting installations such as aerospace vehicles. High velocity of aerospace vehicles generate very high temperature while in motion. This results in critical material failure, deterioration due to chemical attack, thermal shock, erosion and differences in thermal expansion coefficients. Heat generated from the propulsion system or the heat transferred from the hot skin of the vehicles may cause strenuous temperature conditions to develop affecting the vehicles' performance. The skin of the structure of the launch vehicles are therefore to be isolated from the hypercondition of the environment which is conventionally effected with the help of thermal protection system. Conventional thermal protection systems are based on polyurethanes, polyesters and epoxies. The systems based on polyurethanes have low temperature stability and their properties deteriorate at high temperatures- The systems based on polyesters and epoxies have processing problems and exhibit unsatisfactory performance at high temperatures. Further, they show poor ageing properties. Thermal protection systems based on polysiloxane exhibit the required thermophysical characteristics and good ageing properties. However a composition having lower density than polysiloxane is preferred in thermal protecting system as it helps in reducing the total mass thereby improving the payload mass. The main objective of this invention is to develop a process for the preparing a curable composition useful in aerospace thermal protection system having low density and low thermal diffusivity to protect aerospace vehicle structures from thermal shock and chemical attack during its ascend. The skin of the aerospace vehicle is known to experience a temperature upto 450^C during this period. Since the heat shield of the launch vehicle is made of aluminium alloy which starts deteriorating from a temperature of 120oC onwards it is necessary to maintain the skin temperature below 120oC. Low density thermal protective system having low thermal diffusivity achieves this object. A premix is prepared from a linear hydroxy terminated poly-dimethyl siloxane having molecular weight between 10000 to 50000 by adding silica fillers like precipitated silica, fumed silica, and optionally finely powdered oxides of iron and zinc. Mechanical properties of the hydroxy terminated poly dimethyl siloxane are improved by the additions of fillers. Linear hydroxy terminated polydimethyl siloxane is produced by anionic equilibration of the hydrolysate obtained by the hydrolysis of dimethyl chlorosilane. The premix is dispersed in an organic solvent before admixing the curing component thereto. The curing component is prepared by mixing alkyl tris aikyloximinosilane, aminoalkyl trialkylsilane and an organotin compound such as dibutyltin dilaurate. Curing takes place at ambient temperature when the premix dispersion is mixed with the curing component. Crosslinking of the hydroxy terminated poly dimethyl siloxane takes place by the reaction of Si-OH with oximinosilane in the presence of atmospheric moisture. Oximinosilane of the curing component has B', and R" may be alkyl groups having 1-10 carbon atoms. Easily hydrolysable Si-O-N linkage of these compounds break up to form Si-OH in the presence of atmospheric oxygen which then condenses with Si-O-Si linkage to effect cross linking. incorporated in the curing component improve the adhesive characteristics of the final product R, R', R", and R"" are alkyl groups having 1-4 carbon atoms. The highly polar NH2 group improves the bond strength of the composition with the substrate on which it is applied to through polar and hydrogen bondings. The alkoxy group-OR' cross links with hydroxy terminated polysiloxane. Organotin compounds act as a catalyst to enhance the rate of cross linking reaction. In general the premix is prepared from 1000 parts of hydroxy terminated poly dimethyl siloxane of molecular weight 50000 to 100000. Pretreated fumed silica ferric oxide and sine oxide may be added in the range of 60-80 parts, 10 to 20 parts and 5 to 15 parts by weight respectively. This premix is dispersed in a solvent such as toluene, xylene, n-hexane or petroleum ether till a sprayable viscosity is obtained by controlling the quantity of solvent used. The curing component consisting of alkyl tris alkyl ketoxime silane, 3 amino alkyl trialkoxysilane and dibutyltin dilaurate in the weight ratio of 100 : 10 ; 1 to 100 : 40 : 3 is prepared separately. The range may be controlled according to the required tack free and cure time of the final product 8-12 parts by weight of the curing component is added to the solution of the premix to obtain the curable composition of the invention and may be sprayed on the substrate to be protected. Curing takes place at ambient conditions within a minimum period of one hour when the solvent is evaporated and in the presence of atmospheric moisture and is completed within 24 hours of application. This invention relates to a curable coating composition which comprises a blend of a premix dispersion and a curing component, wherein said premix consists of a mixture of hydroxy terminated polydimethyl siloxane, silica, ferric oxide and zinc oxide dispersed in an organic solvent, and said curing component consists of a mixture of alkyl tris alkyl alkoxy silane, amino alkyl trialkoxy silane and an organotin compound. This invention also relates to a process for preparing a curable coating composition which comprises the step of (a) preparing a premix by blending hydroxy terminated poly dimethyl siloxane, silica, ferric oxide and zinc oxide and subsequently dispersing said premix in an organic solvant (b) preparing a curing component by mixing alkyl tris alkyl trialkoxy silane, amino alkyl trialkoxy silane and an organotin compound and (c> admixing said premix dispersion with said curing component to produce the curable coating composition. The following example particularly describes a specific embodiment of the process according to this invention. 1000 parts of hydroxy terminated poly dimethyl siloxane of molecular weight 50000 is blended with 75 parts of fumed silica filler, 15 parts of ferric oxide and 7.5 parts of ainc oxide in a triple roll mill, and then kneaded in a kneader to obtain the premix. 200 parts of this premix is dispersed in 250 parts of toluene. The curing component is prepared by mixing methyl tris methyl ethyl ketoxime silane, 3-aminto propyl tri ethoxy silane and dibutyl tri dilaurate in the ratio of 100 : 20 : 2. 10 parts of the curing component is added to the premix dispersion and mixed thoroughly. This composition is sprayed on a substrate using a pressure gun. After one hour, the solvent toluene gets evaporated and the composition gets cured and is found tack free. Subsequent coatings may be effected after a minimum interval of one hour. Substrates thus coated show low density. liOw thermal conductivity and high specific heat which in toto imparts a thermal diffusivity of 8.0 cm /sec. Addition of ferric oxide enhances the thermal stability and improving adhesive strength. They are used as hollow fillers for controlling the density of the composition. Though the invention has been described hereinabove with reference to a specific embodiment, equivalents and modifications known to persons skilled in the art are not excluded from the scope of the appended claims. WE CLAIM : 1. A curable coating composition comprising a blend of a premix dispersion and a curing component wherein said premix consists of a mixture of hydroxy terminated poly dimethyl siloxane, silica, ferric oxide and zinc oxide dispersed in an organic solvent and said curing component consists of a mixture of alkoxy tris alkyl alkoxy silane, amino alkyl trialkoxy silane and an organo tin compound. 2. The curable coating composition as claimed in Claim 1, wherein said hydroxy terminated poly dimethyl siloxane has a molecular weight in the range of 50000 to 100000. 3. The curable coating composition as claimed in Claim 1 and 2 wherein said premix consists of 1000 parts by weight of said poly dimethyl silane, 60 to 80 parts by weight of silica 10-20 parts by weight of ferric oxide and 5 to 15 parts by weight of sine oxide. 4. The curable coating composition as claimed in Claim 3, wherein the organic solvent is selected from toluene, xylene, n-hexane, or petroleum ether. 5. The curable coating composition as claimed in Claim 1, wherein said curing component consists of alkyl tris alkyl ketoxime silane, 3 amino alkyl trialkyl silane and dibutyl tin laurate in the weight ratio of 100 : 10 : 1 to 100 : 40 : 3 respectively. 6, The curable coating composition as claimed in Claims 1 to 5, wherein 200 parts by weight of said premix is dispersed in 250 parts by weight of toluene. 7. The curable coating composition as claimed in Claims 1 to 6, wherein said curing component consists of methyl tris methyl ethyl ketoxime silane, 3-amino propyl triethoxy silane and dibutyl tin laurate in the ratio of 100 : 20 : 2. 8. The curable coating composition as claimed in Claims 6 and 7, wherein said 200 parts by weight of the premix dispersed in 250 parts by weight of toluene is mixed with 10 parts by weight of said curing component. 9. A process for 'preparing a curable composition comprising the step of : (a) preparing a premix by blending hydroxy terminated poly dimethyl siloxane, silica, ferric oxide and zinc oxide, dispersing said premix in an organic solvent, and (b) preparing a curing component by mixing alkyl tris alkyl trialkoxy silane, amino alkyl trialkoxy silane, and an organo tin compound ; and (c) admixing said premix dispersion with said curing component to produce the curable coating composition. 10. The process for preparing a curable composition as claimed in Claim 9, wherein said hydroxy terminated poly dimethyl siloxane has a molecular weight range of 50000 to 10000, said silica is fumed silica. 11. The process for preparing a curable composition as claimed in claim 9, wherein said premix components are blended in a triple roll mill. 12. The process for preparing a curable composition as claimed in claims 9 to 11 wherein 1000 parts by weight said poly dimethyl silane, 60-80 parts by weight of silica, 10-20 parts by weight of ferric oxide and 5 to 15 parts by weight of sine oxide are blended together. 13. The process for preparing a curable composition as claimed in claim 9, wherein said curing component is prepared by mixing alkyl tris alkyl, ketoxime, silane, 3 amino alkyl trialkoxy silane and dibutyl tin laurate in weight ratio of 100 : 10 -■ 1 to 100 : 40 : 3 respectively. 14. A process for preparing a curable composition as claimed in Claims 9 to 13, wherein the premix is dispersed in an organic solvent selected from toluene, xylene, n-hexane, or petroleum ether. 15, A curable coating composition containing hydroxy poly siloxane substantially as described hereinabove. 16. A process for preparing a curable coating composition siloxane substantially as described hereinabove and exemplified.

Full Text

This invention relates to a curable coating composition containing hydroxy poly siloxane and a process for preparing the same. The composition when coated on substrates and cured exhibits low thermal diffusivity and is therefore found ideally suitable for thermally protecting installations such as aerospace vehicles.
High velocity of aerospace vehicles generate very high temperature while in motion. This results in critical material failure, deterioration due to chemical attack, thermal shock, erosion and differences in thermal expansion coefficients. Heat generated from the propulsion system or the heat transferred from the hot skin of the vehicles may cause strenuous temperature conditions to develop affecting the vehicles' performance. The skin of the structure of the launch vehicles are therefore to be isolated from the hypercondition of the environment which is conventionally effected with the help of thermal protection system.
Conventional thermal protection systems are based on polyurethanes, polyesters and epoxies. The systems based on polyurethanes have low temperature stability and their properties deteriorate at high temperatures- The systems based on polyesters and epoxies have processing problems and exhibit unsatisfactory performance at high temperatures. Further, they show poor ageing properties. Thermal protection systems based on

polysiloxane exhibit the required thermophysical characteristics and good ageing properties. However a composition having lower density than polysiloxane is preferred in thermal protecting system as it helps in reducing the total mass thereby improving the payload mass.
The main objective of this invention is to develop a process for the preparing a curable composition useful in aerospace thermal protection system having low density and low thermal diffusivity to protect aerospace vehicle structures from thermal shock and chemical attack during its ascend. The skin of the aerospace vehicle is known to experience a temperature upto 450^C during this period. Since the heat shield of the launch vehicle is made of aluminium alloy which starts deteriorating from a temperature of 120oC onwards it is necessary to maintain the skin temperature below 120oC. Low density thermal protective system having low thermal diffusivity achieves this object.
A premix is prepared from a linear hydroxy terminated poly-dimethyl siloxane having molecular weight between 10000 to 50000 by adding silica fillers like precipitated silica, fumed silica, and optionally finely powdered oxides of iron and zinc. Mechanical properties of the hydroxy terminated poly dimethyl siloxane are improved by the additions of fillers. Linear hydroxy terminated polydimethyl siloxane is produced by anionic equilibration of the hydrolysate obtained by the hydrolysis of

dimethyl chlorosilane. The premix is dispersed in an organic solvent before admixing the curing component thereto.
The curing component is prepared by mixing alkyl tris aikyloximinosilane, aminoalkyl trialkylsilane and an organotin compound such as dibutyltin dilaurate.
Curing takes place at ambient temperature when the premix dispersion is mixed with the curing component. Crosslinking of the hydroxy terminated poly dimethyl siloxane takes place by the reaction of Si-OH with oximinosilane in the presence of atmospheric moisture. Oximinosilane of the curing component has

B', and R" may be alkyl groups having 1-10 carbon atoms. Easily hydrolysable Si-O-N linkage of these compounds break up to form Si-OH in the presence of atmospheric oxygen which then condenses with Si-O-Si linkage to effect cross linking.

incorporated in the curing component improve the adhesive characteristics of the final product R, R', R", and R"" are alkyl groups having 1-4 carbon atoms. The highly polar NH2 group

improves the bond strength of the composition with the substrate on which it is applied to through polar and hydrogen bondings. The alkoxy group-OR' cross links with hydroxy terminated polysiloxane. Organotin compounds act as a catalyst to enhance the rate of cross linking reaction.
In general the premix is prepared from 1000 parts of hydroxy terminated poly dimethyl siloxane of molecular weight 50000 to 100000. Pretreated fumed silica ferric oxide and sine oxide may be added in the range of 60-80 parts, 10 to 20 parts and 5 to 15 parts by weight respectively. This premix is dispersed in a solvent such as toluene, xylene, n-hexane or petroleum ether till a sprayable viscosity is obtained by controlling the quantity of solvent used.
The curing component consisting of alkyl tris alkyl ketoxime silane, 3 amino alkyl trialkoxysilane and dibutyltin dilaurate in the weight ratio of 100 : 10 ; 1 to 100 : 40 : 3 is prepared separately. The range may be controlled according to the required tack free and cure time of the final product 8-12 parts by weight of the curing component is added to the solution of the premix to obtain the curable composition of the invention and may be sprayed on the substrate to be protected. Curing takes place at ambient conditions within a minimum period of one hour when the solvent is evaporated and in the presence of atmospheric moisture and is completed within 24 hours of application.

This invention relates to a curable coating composition which comprises a blend of a premix dispersion and a curing component, wherein said premix consists of a mixture of hydroxy terminated polydimethyl siloxane, silica, ferric oxide and zinc oxide dispersed in an organic solvent, and said curing component consists of a mixture of alkyl tris alkyl alkoxy silane, amino alkyl trialkoxy silane and an organotin compound.
This invention also relates to a process for preparing a curable coating composition which comprises the step of (a) preparing a premix by blending hydroxy terminated poly dimethyl siloxane, silica, ferric oxide and zinc oxide and subsequently dispersing said premix in an organic solvant (b) preparing a curing component by mixing alkyl tris alkyl trialkoxy silane, amino alkyl trialkoxy silane and an organotin compound and (c> admixing said premix dispersion with said curing component to produce the curable coating composition.
The following example particularly describes a specific embodiment of the process according to this invention.
1000 parts of hydroxy terminated poly dimethyl siloxane of molecular weight 50000 is blended with 75 parts of fumed silica filler, 15 parts of ferric oxide and 7.5 parts of ainc oxide in a triple roll mill, and then kneaded in a kneader to obtain the premix. 200 parts of this premix is dispersed in 250 parts of toluene.

The curing component is prepared by mixing methyl tris methyl ethyl ketoxime silane, 3-aminto propyl tri ethoxy silane and dibutyl tri dilaurate in the ratio of 100 : 20 : 2.
10 parts of the curing component is added to the premix dispersion and mixed thoroughly.
This composition is sprayed on a substrate using a pressure gun. After one hour, the solvent toluene gets evaporated and the composition gets cured and is found tack free. Subsequent coatings may be effected after a minimum interval of one hour.
Substrates thus coated show low density. liOw thermal conductivity and high specific heat which in toto imparts a thermal diffusivity of 8.0 cm /sec.
Addition of ferric oxide enhances the thermal stability and improving adhesive strength. They are used as hollow fillers for controlling the density of the composition.
Though the invention has been described hereinabove with reference to a specific embodiment, equivalents and modifications known to persons skilled in the art are not excluded from the scope of the appended claims.

WE CLAIM :
1. A curable coating composition comprising a blend of a premix dispersion and a curing component wherein said premix consists of a mixture of hydroxy terminated poly dimethyl siloxane, silica, ferric oxide and zinc oxide dispersed in an organic solvent and said curing component consists of a mixture of alkoxy tris alkyl alkoxy silane, amino alkyl trialkoxy silane and an organo tin compound.
2. The curable coating composition as claimed in Claim 1, wherein said hydroxy terminated poly dimethyl siloxane has a molecular weight in the range of 50000 to 100000.
3. The curable coating composition as claimed in Claim 1
and 2 wherein said premix consists of 1000 parts by weight of said poly dimethyl silane, 60 to 80 parts by weight of silica 10-20 parts by weight of ferric oxide and 5 to 15 parts by weight of sine oxide.
4. The curable coating composition as claimed in Claim 3, wherein the organic solvent is selected from toluene, xylene, n-hexane, or petroleum ether.
5. The curable coating composition as claimed in Claim 1, wherein said curing component consists of alkyl tris alkyl

ketoxime silane, 3 amino alkyl trialkyl silane and dibutyl tin laurate in the weight ratio of 100 : 10 : 1 to 100 : 40 : 3 respectively.
6, The curable coating composition as claimed in Claims 1 to 5, wherein 200 parts by weight of said premix is dispersed in 250 parts by weight of toluene.
7. The curable coating composition as claimed in Claims 1 to 6, wherein said curing component consists of methyl tris methyl ethyl ketoxime silane, 3-amino propyl triethoxy silane and dibutyl tin laurate in the ratio of 100 : 20 : 2.
8. The curable coating composition as claimed in Claims 6 and 7, wherein said 200 parts by weight of the premix dispersed in 250 parts by weight of toluene is mixed with 10 parts by weight of said curing component.
9. A process for 'preparing a curable composition
comprising the step of :
(a) preparing a premix by blending hydroxy terminated poly dimethyl siloxane, silica, ferric oxide and zinc oxide, dispersing said premix in an organic solvent, and
(b) preparing a curing component by mixing alkyl tris alkyl trialkoxy silane, amino alkyl trialkoxy silane, and an organo tin compound ; and

(c) admixing said premix dispersion with said curing component to produce the curable coating composition.
10. The process for preparing a curable composition as claimed in Claim 9, wherein said hydroxy terminated poly dimethyl siloxane has a molecular weight range of 50000 to 10000, said silica is fumed silica.
11. The process for preparing a curable composition as claimed in claim 9, wherein said premix components are blended in a triple roll mill.
12. The process for preparing a curable composition as
claimed in claims 9 to 11 wherein 1000 parts by weight said poly
dimethyl silane, 60-80 parts by weight of silica, 10-20 parts by
weight of ferric oxide and 5 to 15 parts by weight of sine oxide
are blended together.
13. The process for preparing a curable composition as
claimed in claim 9, wherein said curing component is prepared by
mixing alkyl tris alkyl, ketoxime, silane, 3 amino alkyl
trialkoxy silane and dibutyl tin laurate in weight ratio of 100 :
10 -■ 1 to 100 : 40 : 3 respectively.
14. A process for preparing a curable composition as
claimed in Claims 9 to 13, wherein the premix is dispersed in an
organic solvent selected from toluene, xylene, n-hexane, or
petroleum ether.

15, A curable coating composition containing hydroxy poly
siloxane substantially as described hereinabove.
16. A process for preparing a curable coating composition
siloxane substantially as described hereinabove and exemplified.

Documents:

979-mas-1999-abstract.pdf

979-mas-1999-claims duplicate.pdf

979-mas-1999-claims original.pdf

979-mas-1999-correspondance others.pdf

979-mas-1999-correspondance po.pdf

979-mas-1999-description complete duplicate.pdf

979-mas-1999-description complete original.pdf

979-mas-1999-form 1.pdf

979-mas-1999-form 19.pdf

979-mas-1999-form 26.pdf

979-mas-1999-form 3.pdf

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Patent Number

206804

Indian Patent Application Number

979/MAS/1999

PG Journal Number

26/2007

Publication Date

29-Jun-2007

Grant Date

11-May-2007

Date of Filing

07-Oct-1999

Name of Patentee

INDIAN SPACE RESEARCH ORGANISATION

Applicant Address

ANTARIKSH BHAVAN NEW BEL ROAD , BANGALORE-560 094

Inventors:

#	Inventor's Name	Inventor's Address
1	GANGADHARAN PRABHAKARAN	VIKRAM SARABHAI SPACE CENTRE TRIVANDRUM-695022
2	SURJAN SINGH DROVER	VIKRAM SAEABHAI SPACES CENTRE TRIVANDRUM-695022

PCT International Classification Number

C07F7/10

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA