Title of Invention

"AN INSULATION COMPOSITION BASED ON HTPB PROPELLANTS AND A PROCESS THEREOF"

Abstract

This invention relates to a process for preparation of an insulation composition based on HTPB propellants comprising in the steps of preparing a binder matrix comprising of liquid ingredients 38-42% Hydroxyl Terminated-Polybutadiene (HTPB), 8-10% Di-octyl-Adipate as plasticiser, 0.2 to 0.4% poly ethylene glycol Mono stearate as processing aid, 0.15-0.25% Hexanetriol as crosslinker and 4-6% capolyte as tackifier, Mixing Antimony Trioxide as fire retardent with 2 micron particle size silica and 40-48 microns particle size carbon black as fillers, Adding 1.0-1.1 Hexamethylene Di-isocynate as curative, Preparation of dough as herein described, Calendaring of insulation sheets, Curing of insulation sheets as herein described.

Full Text

FIELD OF INVENTION This invention relates to a process for preparation of an insulation composition based on HTPB propellants and more particularly to an insulation composition for case bonded rocket motors utilising Hydroxyl terminated polybutadiene based composite propellants and a process for the preparation thereof. PRIOR ART Rocket motors utilising solid composite propellants basically utilise either carboxyl-terminated polybutadiene (CTPB) or Hydroxyl-terminated polybutadiene (HTPB) based solid propellants. An important requirement of such rocket motors is that the wall insulation should adequately adhere to the combustion chamber and similarly composite propellant should adequately adhere to the insulation system and the one major requirement for achieving this adherence is that the insulation system should be compatible with the solid propellant used in the rocket motor. The combustion of a propellant in the rocket motor creates a hostile environment inside the rocket motor chamber characterised by extremely high temperature, pressure Another disadvantage of EPDM insulation system is that it utilises asbestos as "filler material which is highly toxic in nature and is banned in many countries. Still another disadvantage of EDPM insulation system is that in case of hydroxyl terminated butadiene propellant, there is a mismatch between young's modulus of propellant and the insulation system resulting in a weaker bond between them. Nitrile rubber is yet another type of insulation system, known in the art, utilised for rocket motors based on hydroxyl terminated polybutadiene propel1ants. However, this insulation system also suffers from following disadvantages. The main disadvantage of nitrile rubber insulation system is that its compatibility with the HTPB based propellant is not as good as the compatibility between the insulator and propellant having the same binder matric, thereby affecting the shelf life of rocket motors and behavior of insulator-propellant bond at lower temperatures. Another disadvantage of the above insulation system is that its glass transition temperature is o around (-50 C) which does not match with that of the o propellant (-70 C) and as such the insulation may break even before the propellant at lower temperatures. Still another disadvantage of Nitrile rubber insulation is that its thermal conductivity is higher thereby lowering its ability in protecting exposed rocket motor parts from high temperatures generated inside the motor chamber during the combustion. OBJECTS OF THE INVENTION Primary object of the present invention is to provide an insulation formulation for rocket motors based on HTPB propellants which is compatible with the HTPB propellant thereby resulting in stronger bond between the insulation formulation and the propellant and a process for the preparation thereof. Yet another object of the present invention is to provide an insulation formulation for rocket motors based on HTPB props11ants wherein there is a complete match between the binder matrix of insulation formulation and the propel1ant. Still another object of the present invention is to provide an insulation formulation for rocket motors based on HTPB propellants which does not get affected with ageinq thus improving the shelf life of the rocket motors. Yet another object of the present invention is to provide an insulation formulation for rocket motors based on HTPB propellants wherein the bonding between insulation system and propellant is not affected even at o very low temperatures around -30 C at which the rocket motors are normally tested for evaluation of their low temperature performance. Further object of the present invention is to provide an insulation formulation for rocket motors based on HTPB propellants which does not utilise any toxic materials. Yet another object of the present invention is to provide an insulation formulation for rocket motors based on HTPB propellents which has sufficiently long pot life (3—4 hours) thus facilitating the calendering and rolling of the insulation system. Still further another object of the present invention is to provide an insulation formulation for rocket motors based on HTPB propellants which has lower density thereby reducing the inert weight of the rocket motor. Even further object of the present invention is to provide an insulation formulation for rocket motor* o which has a glass transition temperature (-77 C) nearly o matching with that of the propellant (—70 C) . Still further object of the present invention is to provide an insulation for rocket motors which has a o lower thermal conductivity of 0.108 w/m/ K thereby improving its ability to protect exposed rocket motor parts from high temperatures generated inside the rocket chamber during combustion. Yet further object of the present invention is to provide an insulation formulation for rocket motors based on HTPB propellants which has comparable rate of ablation (0.21 mm/sec) resulting in lower erosion rate of insulation layer during combustion. Still another object of the invention is to provide an insulation formulation for rocket motors based on HTPB propellants which can be prepared utilising simpler processing techniques. DESCRIPTION OF THE INVENTION According to this invention there is provided a process for preparation of an insulation composition based on HTPB propellants comprising in the steps of:- a) preparing a binder matrix comprising of liquid ingredients 38-42% Hydroxyl Terminated-Polybutadiene (HTPB), 8-10% Di-octyl-Adipate as plasticiser, 0.2 to 0.4% poly ethylene glycol Mono stearate as processing aid, 0.15-0.25% Hexanetriol as crosslinker and 4-6% capolyte as tackifier. b) Mixing Antimony Trioxide as fire retardent with 2 micron particle size silica and 40-48 microns particle size carbon black as fillers, c) Adding 1.0-1.1 Hexamethylene Di-isocynate as curative, d) Preparation of dough as herein described, e) Calendaring of insulation sheets, f) Curing of insulation sheets as herein described. The insulation system has a very long shelf life and the insulation propellant bond is not affected even at very low temperature around -30°C, the temperature at which the low temperature performance of racket motor is normally evaluated. It has a higher pot li.f« thus facilitating the calendering and rolling of the insulation sheets and it does not utilise any banned material. Further, it has lower density thereby reducing the inert weight of the rocket motor. It has lower thermal conductivity thus improving its ability to protect exposed rocket motor parts from high temperatures generated inside rocket motor chamber during combustion of the propellant. The process of preparation of the insulation formulation comprises of the steps of preparation of binder matrix by mixing all the liquid ingredients in • mixer bowl, addition of solid additives, addition of curatives, final mixing of all the ingredients, calendering of insulation sheets and curing of insulation sheets. DESCRIPTION OF THE PROCESS The composition of all the constituents of the sheet insulation system providing percentage range of all the constituents (weight wise), required for the insulation formulation, are given below. Liquid Ingredients (Binder matrix) 1. HTPB 38 - 42 % 2. DOA (Plasticizer) 8-12 (Di-Octyl-Adipate) 3. PEGMS (Processing Aid) 0.2 - 0.4 (Poly Ethylene Glycol Mono Stearate) 4. HT (Crosslinker) 0.15-0.25 (Hexanetriol) 5. Capolyte (Tackifier) 4-6 Solid Ingredients (Additives) 1. Sb203 (fire retardant) 3 - 5 (Antimony Trioxide) 2. Silica 3 - 5 (Average particle size approx.2.0 microns) 3. C-Black (N-550) 34-38 (Average particle size approx.40-48 microns) Curative HDI Curative Index 1.0-1.1 (Hexamethylene Di-isocynate) The process of preparing insulation formulation of the present invention, comprises of following steps. (a) Preparation of Binder matrix All the liquid ingredients constituting binder system mentioned above, are individually weighed and poured into the mixer bowl with sigma blades FIELD OF INVENTION This invention relates to a process for preparation of an insulation composition based on HTPB propellants and more particularly to an insulation composition for case bonded rocket motors utilising Hydroxyl terminated polybutadiene based composite propellants and a process for the preparation thereof. PRIOR ART Rocket motors utilising solid composite propellants basically utilise either carboxyl-terminated polybutadiene (CTPB) or Hydroxyl-terminated polybutadiene (HTPB) based solid propellants. An important requirement of such rocket motors is that the wall insulation should adequately adhere to the combustion chamber and similarly composite propellant should adequately adhere to the insulation system and the one major requirement for achieving this adherence is that the insulation system should be compatible with the solid propellant used in the rocket motor. The combustion of a propellant in the rocket motor creates a hostile environment inside the rocket motor chamber characterised by extremely high temperature, pressure FIELD OF INVENTION This invention relates to a process for preparation of an insulation composition based on HTPB propellants and more particularly to an insulation composition for case bonded rocket motors utilising Hydroxyl terminated polybutadiene based composite propellants and a process for the preparation thereof. PRIOR ART Rocket motors utilising solid composite propellants basically utilise either carboxyl-terminated polybutadiene (CTPB) or Hydroxyl-terminated polybutadiene (HTPB) based solid propellants. An important requirement of such rocket motors is that the wall insulation should adequately adhere to the combustion chamber and similarly composite propellant should adequately adhere to the insulation system and the one major requirement for achieving this adherence is that the insulation system should be compatible with the solid propellant used in the rocket motor. The combustion of a propellant in the rocket motor creates a hostile environment inside the rocket motor chamber characterised by extremely high temperature, pressure WORKING EXAMPLE Composition of the individual constituents needed for 1 Kg of insulation system is given below. Liquid Ingredients (Binder matrix) 1. HTPB 390 gm 2. DOA (Plasticizer) 85 gm (Di-Octyl-Adipate) 3. PEGMS (Processing Aid) 03 gm (Poly Ethylene Glycol Mono Stearate) 4. HT (Crosslinker) 02 gm (Hexanetriol) 5. Capolyte (Tackifier) 40 gm Solid Ingredients (Additives) 1. Sb203 (fire retardant) 50 gm (Antimony Trioxide) (Particle size approx. 1.8mm) 2. Silica 50 gm (particle size approx.2.0um) 3. C-Black (N-550) 380 gm (Average particle size apx.40-48um) Curative 1. HDI 25 gm (Hexa Methylene Di-isocynate) All the liquid ingredients constituting binder matrix (HTPB) are individually weighed and poured into the mixer bowl. The solution is mixed and deaerated under vacuum (pressure instalments and after every instalment mixing process is repeated for 10 minutes by rotating the mixer blades. After addidon of final installment of carbon black, mixing is done for 30 minutes under vacuum (pressure It is to be understood that the process of present invention is susceptible to adaptations, changes, modifications by those skilled in the art. Such adaptations, changes, modifications are intended to be within the scope of the present invention, which is further set forth by the following claims. WE CLAIM; 1. A process for preparation of an insulation composition based on HTPB propellants comprising in the steps of:- a) preparing a binder matrix comprising of liquid ingredients 38-42% Hydroxyl Terminated-Polybutadiene (HTPB), 8-10% Di-octyl-Adipate as plasticiser, 0.2 to 0.4% poly ethylene glycol Mono stearate as processing aid, 0.15-0.25% Hexanetriol as crosslinker and 4-6% capolyte as tackifier. b) Mixing Antimony Trioxide as fire retardent with 2 micron particle size silica and 40-48 microns particle size carbon black as fillers, c) Adding 1.0-1.1 Hexamethylene Di-isocynate as curative, d) Preparation of dough as herein described, e) Calendaring of insulation sheets, f) Curing of insulation sheets as herein described. 2. A process as claimed in claim 1 wherein said calendaring of dough into insulation sheets is carried out under controlled relative humidity of 55%. 3. A process as claimed in claim 1 wherein said curing of insulator sheets is carried out for 120-170 hours in a sealed polyethylene bag. 4. An insulation composition for rocket motors based on HTPB propellants prepared by the process as claimed in claim 1 comprising a binder matrix of liquid ingredients hydroxyl terminated polybutadiene (HTPB), a Di-octyl-Adipate as plasticiser, Hexaneteriol as crosslinker, Mono stearate as processing aid and copolyte as tackifier, Antimony Trioxide as fire retardants, silica and carbon block as fillers, Di-iso cynate as curatives. 5. A process for preparation of an insulation composition based on HTPB propellants substantially as described and illustrated herein.

Documents:

498-del-2000-abstract.pdf

498-del-2000-claims.pdf

498-del-2000-correspondence-others.pdf

498-del-2000-correspondence-po.pdf

498-Del-2000-Description (Complete).pdf

498-del-2000-form-1.pdf

498-del-2000-form-19.pdf

498-del-2000-form-2.pdf

498-del-2000-form-26.pdf

498-del-2000-form-3.pdf