Title of Invention	"A PROCESS FOR THE PREPARATION OF HYDROXY TERMINATED POLYBUTABIENE (HTPB) BASED LINER".
Abstract	A process for the preparation of hydroxy terminated poly butadiene (HTPB) based liner which comprises by the steps of deaerating 58 to 70% basic binder as herein described, mixing of 0.015 to 3% cross-linking cum anti-oxidant as herein described and 0.5 to 1.1% tackifier as herein described, three phased addition of fillers as herein described followed by addition of a curative as herein described.

Title of Invention

"A PROCESS FOR THE PREPARATION OF HYDROXY TERMINATED POLYBUTABIENE (HTPB) BASED LINER".

Abstract

A process for the preparation of hydroxy terminated poly butadiene (HTPB) based liner which comprises by the steps of deaerating 58 to 70% basic binder as herein described, mixing of 0.015 to 3% cross-linking cum anti-oxidant as herein described and 0.5 to 1.1% tackifier as herein described, three phased addition of fillers as herein described followed by addition of a curative as herein described.

Full Text	FIELD OF INVENTION The present invention relates to a process of preparation of hydroxy terminated poly-butadiene (HTPB) based liner being used for case bonded composite propellant motors. PRIOR ART Solid propellant motors contain two distinctive systems, namely propellants and the subsystems that are not combustible and are elastomeric in nature. Three main basic subsystems are insulation, liner and inhibition. Of the three, the requirement for liner is very stringent and varies from motor to motor. These motors include a motor case which surrounds a solid propellant having a star or other shaped hollow core, which defines a combustion chamber, an ignitor assembly, which is usually mounted on top of the propellant and a bottom mounted nozzle assembly. An insulator, which usually comprises one or more layers of a rubber material bonded to the case wall, prevents excessive heating and possible burn through of the casing. Generally, a liquefied formulation is applied to the insulator surface and partially cured, forming a thin liner which enhances bonding of the propellant to the insulator. The propellant slurry is then prepared and poured into the motor case, contacting the semi-cured liner. The slurry cast motor is then kept for curing. During the process of curing, the propellant and liner undergo chemical rross-linking thereby resulting in a firm bond between the propellant and the insulator by means of the liner coat. Carboxy terminated poly-butadiene (CTPB) based liner material with trifunctional epoxy resin and tris— (-2-methy1 aziridinyl) phosphine oxide (MAPO) as a curative with carbon-black as filler have been used for various cartridge devices. A liner formulation based on epoxy/PBAN (polybutadiene acrylic acid acrylonitrile) has also been used for Aerojet applications. HTPB based composite propel1ants are widely used in present day propellant motors. One of the liner formulations uses HTPB (RM—45) , di-octyl sebacate (DOS), carbon black filler with dimeryl diisocyanate (DDI) as a curative. The main disadvantage of the known liner formulation is that it contains di-octyIs-sebacate (DOS) as plasticiser while the propel lant. contains di-octyl adipate (DOA) as plasticiser, which leads to plasticiser migration. A MIL-standard describes liner formulation based on HTPB—C— talack-DDI and imine curing bonding agent. One of the disadvantage of such a known liner formulations is that it uses MAPO as one of the ingredients which is highly toxic and carcinogenic. Yet another disadvantage of such known liner liner formulations is that MAPO has poor thermal stability Further disadvantage of such known liner formulations is that MAPO has got side reactions due to which repeatable properties are not achieved. OBJECTS OF THE PRESENT INVENTION The primary object of the present invention is to provide HTPB based liner for case bonded composite propellants and a process for preparation thereof where-in the liner composition forms covalent bond between the propellant and the liner. Another object of the present invention is to develop HTPB based liner for case bonded composite propellants having interfacial bond which is completely reliable. Yet another object of the present invention is to develop HTPB based liner for case bonded composite propellants having superior bond strengths. Further object of the present invention is to develop HTPB based liner for case bonded composite propellants having burn rates of 5-20 mm/sec at 70 kgf/cm2. Yet further object of the present invention is to develop HTPB based liner for case bonded composite propellants whose pot life is such that the liner is cured to a tacky state till casting of the propellant is completed. Still further object of the present invention is to develop HTPB based liner for case bonded composite propellants so that curing can be performed preferably at room temperature. Even further object of the present invention is to develop HTPB based liner for case bonded composite propellants overcoming the problem of aging. Still further object of the present invention is to develop HTPB based liner for case bonded composite propellants overcoming the migration of plastisizers and other reactive components from the propellant to the liner, during curing of the propellant. DESCRIPTION OF INVENTION According to the present invention, there is provided a process for the preparation of hydroxy terminated poly butadiene (HTPB) based liner which comprises by the steps of deaerating 58 to 70% basic binder as herein described, mixing of 0.015 to 3% cross-linking cum anti-oxidant as herein described and 0.5 to 1.1% tackifier as herein described, three phased addition of fillers as herein described followed by addition of a curative as herein described. In accordance with this invention, the steps are carried out under controlled humidity of 55+5%. The process consists in the steps described subsequently herein. Preparation of Liner HTPB, 58 to 70% by weight more preferably 62 to 66% by weight (deaerated under vacuum weight metre preferably 22 to 24% by weight is added in three equal instalments with 5 minutes intermittent mixing. After complete addition, the mixing is continued without vacuum and thereafter o o with vacuum ( cooling this mixture to a temperature of (2,4- and 2,6- toluene diisocyanate) . is added according to — NCO:OH ratio required to obtain curative index of 0.0 to 1.3 more preferably to obtain a curative index of 1.0 to 1.05 (Liner composition contains excess NCO group, whereas propel 1 ant composition contains excess OH groups, so NCO of liner and OH of propellant react to form a bond). The insulator is abraded, cleaned by trichloroethy lene to o remove oily or greasy matter and kept in oven at 70 C for 2 to 3 hours for evaporation of solvent. The liner composition is diluted with dry dichloromethane (CH Cl ) in 1:1 proportion and 2 mixed well with mechanical stirrer for five minutes. Thin layer is applied on insulation layer manually by brush or by spray gun depending upon the size of the rocket motor. The liner coated motor is preserved under vacuum till the propellant is cast. The liner coat remains tacky from 22 hours to 72 hours of application. The propellant has to be cast during tacky condition. After casting of propellant the motor is cured, NDT tested and statically evaluated. This invention will now be illustrated with a working example which is intended to be typical example to explain the technique of the present invention and is not intended to be taken restrictively to imply any limitation in the scope of the present invention. EXAMPLE 650 g of HTPB was deaerated under vacuum ( TDI (2,4- and 2,6-toluene diisocyanate was added. After addition of TDI the mix was stirred for 15 minutes and evacuated for 10 minutes and poured in tray to obtain 2.5 -3.0 mm thick sheets. The sheets were cured at ambient for three days and tested for mechanical properties according to ASTM D-638 M, Type M-II. The interface properties were studied by Wheel-peel measurements with composite propellants. Bond strength was determined by placing the propellant pieces (50 x 20 x 20mm) in Al mould, 10 mm apart and the liner formulation was filled in the gap and cured. The samples were tested on Instron Universal Testing Machine. The results of characterization of the liner formulation are summerised in Table 1. 1 Tensile strength (kgf/cm2) 18-20 2 % Elongation 40-50 3 Density (g/cc) 1.18-1.20 4 Shore Hardness A 58-60 5 Tensile bond strength with composite propellant (kgf/cm2) 5 to 8 6 Peel strength (cohesive failure in propellant) (kgf/cm2) 1.2 - 2.222 7 Pot life (tacky condition 72 hours The efficacy of interface properties was studied at extremes of temperatures from -30°C to + 55°C also. In all the cases the failure observed is cohesive in propellant than at the interface. This is further confirmed by NDT testing and proved by static testing the rocket motors in endwise-burning as well as in radial mode. The tacky behaviour of the final product for the desired extended duration is produced by the synergistic effect on each other by the different constituent of the present formulation. This tacky behaviour is absent in any of the individual constituents. WE CLAIM; 1. A process for the preparation of hydroxy terminated poly butadiene (HTPB) based liner which comprises by the steps of deaerating 58 to 70% basic binder as herein described, mixing of 0.015 to 3% cross-linking cum anti-oxidant as herein described and 0.5 to 1.1% tackifier as herein described, three phased addition of fillers as herein described followed by addition of a curative as herein described. 2. A process as claimed in claim 1 wherein the said deaeration of basic binder is carried out under vacuum less than 10 mm for 30 minutes. 3. A process as claimed in claim 1 wherein the said mixing of fillers is done firstly without vacuum and later under vaccum less than 10 mm of Hg. 4. A process as claimed in claim 1 wherein the said basic binder is hydroxy terminated poly-butadiene (HTPB) preferably in quantity of 62 to 66% by weight. 5. A process as claimed in claim 1 wherein said cross-linking cum anti-oxidant is pyrogallol in quantity preferably of 0.018 to 0.22% by weight. 6. A process as claimed in claim 1 wherein said tackifier is capolyte in quantity preferably of 0.8 to 0.82% by weight. 7. A process as claimed in claim 1 wherein first filler is carbon black in quantity of preferably 8 to 12% by weight. 8. A process as claimed in claim 1 wherein second filler used is antimony trioxide preferably in quantity of 22 to 24% by weight. 9. A process as claimed in claim 1 wherein the said curative is 2,4- and 2,6-toluene diisocyanate (TDI). 10. A process as claimed in claim 1 wherein said curative is added according to D-NCO:OH ratio required preferably to obtain curative index of 1.0 to 1.05. 11.A process for the preparation of hydroxy terminated poly- butadiene (HTPB) based liner as substantially described and illustrated herein.

Full Text

FIELD OF INVENTION
The present invention relates to a process of preparation of hydroxy terminated poly-butadiene (HTPB) based liner being used for case bonded composite propellant motors.
PRIOR ART
Solid propellant motors contain two distinctive systems, namely propellants and the subsystems that are not combustible and are elastomeric in nature. Three main basic subsystems are insulation, liner and inhibition. Of the three, the requirement for liner is very stringent and varies from motor to motor. These motors include a motor case which surrounds a solid propellant having a star or other shaped hollow core, which defines a combustion chamber, an ignitor assembly, which is usually mounted on top of the propellant and a bottom mounted nozzle assembly. An insulator, which usually comprises one or more layers of a rubber material bonded to the case wall, prevents excessive heating and possible burn through of the casing. Generally, a liquefied formulation is applied to the insulator surface and partially cured, forming a thin liner which enhances bonding of the propellant to the insulator. The propellant slurry is then prepared and poured into the motor case, contacting the semi-cured
liner. The slurry cast motor is then kept for curing. During the
process of curing, the propellant and liner undergo chemical rross-linking thereby resulting in a firm bond between the
propellant and the insulator by means of the liner coat. Carboxy terminated poly-butadiene (CTPB) based liner material with
trifunctional epoxy resin and tris— (-2-methy1 aziridinyl) phosphine oxide (MAPO) as a curative with carbon-black as filler
have been used for various cartridge devices. A liner formulation based on epoxy/PBAN (polybutadiene acrylic acid acrylonitrile) has
also been used for Aerojet applications. HTPB based composite propel1ants are widely used in present day propellant motors. One of the liner formulations uses HTPB (RM—45) , di-octyl sebacate (DOS), carbon black filler with dimeryl diisocyanate
(DDI) as a curative.
The main disadvantage of the known liner formulation is that
it contains di-octyIs-sebacate (DOS) as plasticiser while the propel lant. contains di-octyl adipate (DOA) as plasticiser, which
leads to plasticiser migration.
A MIL-standard describes liner formulation based on HTPB—C—
talack-DDI and imine curing bonding agent. One of the disadvantage of such a known liner formulations is that it uses MAPO as one of
the ingredients which is highly toxic and carcinogenic.
Yet another disadvantage of such known liner liner formulations is that MAPO has poor thermal stability
Further disadvantage of such known liner formulations is that MAPO has got side reactions due to which repeatable properties are not achieved.
OBJECTS OF THE PRESENT INVENTION
The primary object of the present invention is to provide HTPB based liner for case bonded composite propellants and a process for preparation thereof where-in the liner composition forms covalent bond between the propellant and the liner.
Another object of the present invention is to develop HTPB based liner for case bonded composite propellants having interfacial bond which is completely reliable.
Yet another object of the present invention is to develop HTPB based liner for case bonded composite propellants having superior bond strengths.
Further object of the present invention is to develop HTPB based liner for case bonded composite propellants having burn rates of 5-20 mm/sec at 70 kgf/cm2.
Yet further object of the present invention is to develop HTPB based liner for case bonded composite propellants whose pot life is such that the liner is cured to a tacky state till casting of the propellant is completed.
Still further object of the present invention is to develop HTPB based liner for case bonded composite propellants so that curing can be performed preferably at room temperature.
Even further object of the present invention is to develop HTPB based liner for case bonded composite propellants overcoming the problem of aging.
Still further object of the present invention is to develop HTPB based liner for case bonded composite propellants overcoming the migration of plastisizers and other reactive components from the propellant to the liner, during curing of the propellant.
DESCRIPTION OF INVENTION
According to the present invention, there is provided a process for the preparation of hydroxy terminated poly butadiene (HTPB) based liner which comprises by the steps of deaerating 58 to 70% basic binder as herein described, mixing of 0.015 to 3% cross-linking cum anti-oxidant as herein described and 0.5 to 1.1% tackifier as herein described, three phased addition of fillers as herein described followed by addition of a curative as herein described.
In accordance with this invention, the steps are carried out under controlled humidity of 55+5%. The process consists in the steps described subsequently herein.
Preparation of Liner
HTPB, 58 to 70% by weight more preferably 62 to 66% by weight (deaerated under vacuum weight metre preferably 22 to 24% by weight is added in three equal instalments with 5 minutes intermittent mixing. After complete
addition, the mixing is continued without vacuum and thereafter
o o with vacuum ( cooling this mixture to a temperature of (2,4- and 2,6- toluene diisocyanate) . is added according to — NCO:OH ratio required to obtain curative index of 0.0 to 1.3 more
preferably to obtain a curative index of 1.0 to 1.05 (Liner composition contains excess NCO group, whereas propel 1 ant
composition contains excess OH groups, so NCO of liner and OH of propellant react to form a bond).
The insulator is abraded, cleaned by trichloroethy lene to
o remove oily or greasy matter and kept in oven at 70 C for 2 to 3
hours for evaporation of solvent. The liner composition is
diluted with dry dichloromethane (CH Cl ) in 1:1 proportion and 2 mixed well with mechanical stirrer for five minutes. Thin layer
is applied on insulation layer manually by brush or by spray gun depending upon the size of the rocket motor. The liner coated
motor is preserved under vacuum till the propellant is cast.
The liner coat remains tacky from 22 hours to 72 hours of
application. The propellant has to be cast during tacky condition. After casting of propellant the motor is cured, NDT
tested and statically evaluated.
This invention will now be illustrated with a working example which is intended to be typical example to explain the technique of the present invention and is not intended to be taken restrictively to imply any limitation in the scope of the present invention.
EXAMPLE
650 g of HTPB was deaerated under vacuum ( TDI (2,4- and 2,6-toluene diisocyanate was added. After addition of TDI the mix was stirred for 15 minutes and evacuated for 10 minutes and poured in tray to obtain 2.5 -3.0 mm thick sheets. The sheets were cured at ambient for three days and tested for mechanical properties according to ASTM D-638 M, Type M-II. The interface properties were studied by Wheel-peel measurements with composite propellants. Bond strength was determined by placing the propellant pieces (50 x 20 x 20mm) in Al mould, 10 mm apart and the liner formulation was filled in the gap and cured. The samples were tested on Instron Universal Testing Machine.
The results of characterization of the liner formulation are summerised in Table 1.
1 Tensile strength (kgf/cm2) 18-20
2 % Elongation 40-50
3 Density (g/cc) 1.18-1.20
4 Shore Hardness A 58-60
5 Tensile bond strength with composite propellant (kgf/cm2) 5 to 8
6 Peel strength (cohesive failure in propellant) (kgf/cm2) 1.2 - 2.222
7 Pot life (tacky condition 72 hours
The efficacy of interface properties was studied at extremes of temperatures from -30°C to + 55°C also. In all the cases the failure observed is cohesive in propellant than at the interface. This is further confirmed by NDT testing and proved by static testing the rocket motors in endwise-burning as well as in radial mode.
The tacky behaviour of the final product for the desired extended duration is produced by the synergistic effect on each other by the different constituent of the present formulation. This tacky behaviour is absent in any of the individual constituents.

WE CLAIM;
1. A process for the preparation of hydroxy terminated poly
butadiene (HTPB) based liner which comprises by the steps of
deaerating 58 to 70% basic binder as herein described, mixing of
0.015 to 3% cross-linking cum anti-oxidant as herein described
and 0.5 to 1.1% tackifier as herein described, three phased
addition of fillers as herein described followed by addition of a
curative as herein described.
2. A process as claimed in claim 1 wherein the said deaeration of
basic binder is carried out under vacuum less than 10 mm for
30 minutes.
3. A process as claimed in claim 1 wherein the said mixing of
fillers is done firstly without vacuum and later under vaccum
less than 10 mm of Hg.
4. A process as claimed in claim 1 wherein the said basic binder is
hydroxy terminated poly-butadiene (HTPB) preferably in
quantity of 62 to 66% by weight.
5. A process as claimed in claim 1 wherein said cross-linking cum
anti-oxidant is pyrogallol in quantity preferably of 0.018 to
0.22% by weight.
6. A process as claimed in claim 1 wherein said tackifier is capolyte in quantity preferably of 0.8 to 0.82% by weight.
7. A process as claimed in claim 1 wherein first filler is carbon black in quantity of preferably 8 to 12% by weight.
8. A process as claimed in claim 1 wherein second filler used is antimony trioxide preferably in quantity of 22 to 24% by weight.
9. A process as claimed in claim 1 wherein the said curative is
2,4- and 2,6-toluene diisocyanate (TDI).
10. A process as claimed in claim 1 wherein said curative is
added according to D-NCO:OH ratio required preferably to
obtain curative index of 1.0 to 1.05.
11.A process for the preparation of hydroxy terminated poly- butadiene (HTPB) based liner as substantially described and illustrated herein.

Documents:

511-del-2000-abstract.pdf

511-del-2000-claims.pdf

511-del-2000-correspondence-others.pdf

511-del-2000-correspondence-po.pdf

511-del-2000-description (complete).pdf

511-del-2000-form-1.pdf

511-del-2000-form-19.pdf

511-del-2000-form-2.pdf

511-del-2000-form-3.pdf

511-del-2000-gpa.pdf

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Patent Number

208733

Indian Patent Application Number

511/DEL/2000

PG Journal Number

40/2007

Publication Date

05-Oct-2007

Grant Date

08-Aug-2007

Date of Filing

15-May-2000

Name of Patentee

MINISTRY OF DEFENCE, GOVT OF INDIA

Applicant Address

B-341, SENA BHAWAN, DHQ P.O. NEW DELHI-110011 INDIA.

Inventors:

#	Inventor's Name	Inventor's Address
1	MANOJ GUPTA	HEMRL, PUNE-411 021 INDIA.
2	VIVEK DATTATRAYA DEUSKAR	HEMRL, PUNE-411 021 INDIA.
3	SEEMA DILIP KAKADE	HEMRL, PUNE-411 021 INDIA.
4	PRABHAKAR GOPAL SHROTRI	HEMRL, PUNE-411 021 INDIA.

PCT International Classification Number

C06B 25/00

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA