GB1585713A - Adhesive liner composition for case bonded solid propellant - Google Patents

Description

(54) ADHESIVE LINER COMPOSITION FOR CASE BONDED SOLID PROPELLANT (71) We, THIOKOL CORPORATION, a corporation of the State of Virginia, United States of America, of P.O. Box 1000, Newtown, Pennsylvania 18940, United States of America, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed to be particularly described in and by the following statement:- This invention relates to adhesive liner compositions for case bonded solid propellants and to a process for bonding certain propellant grains to a rocket motor casing.

In general, case bonded solid propellant grains possess greater strength because of the additional support given by their adherence to the rocket motor casing in which they are contained. To ensure the maximum strength and to prevent separation of the propellant grain from the motor walls which would create voids and therefore a potential for uneven burning, it is desirable that the propellant grain be bonded to the motor casing uniformly and firmly.

This is usually accomplished by very careful cleaning and descaling of the inside surface of the metal motor casing, followed by coating the inside surface with a liner, normally the bonder used for the propellant grain, then casting the propellant grain in place and curing. The liner serves as a bonding agent between the casing and the propellant grain, as an inhibitor preventing burning down the outer surface of the grain and as an insulator, protecting the casing from the heat and gases of combustion when burning has progressed to the point at which the casing would otherwise be exposed.

The present invention relates to case liners containing an aziridine compound, methods for their formulation and use. The liners are formulated from hydroxy terminated polybutadiene based polyurethane binders.

U.S. Patent No. 3,974,131 and British Patent No. 1,513,706 relate to the use of various acylated aziridinyl monomers and polymers and their use as adhesive promoters in vinyl formulations. The compounds contemplated for use in this invention are intended for use in enhancing the adhesiveness of polyurethanes.

The present invention provides a curable liner composition for a case bonded solid propellant based upon a liquid hydroxyl-terminated polybutadiene and a polyisocyanate and containing, as a promoter of bonding to the propellant and the motor casing, an aziridine.

The invention also provides a process for case bonding a liquid hydroxyterminated polybutadiene based polyurethane bound solid propellant grain to a rocket motor casing which comprises: (a) lining a rocket motor casing with a cured liner composition comprising a mixture of an aziridine and a liquid hydroxy-terminated polybutadiene which has been cured with a polyisocyanate curing agent; (b) casting said liquid hydroxy-terminated polybutadiene based propellant grain, in an uncured form and comprising a polyisocyanate curing agent, into the desired configuration within said rocket motor casing; and (c) curing said propellant grain.

Particularly preferred embodiment of the curable liner composition of the invention are those in which the aziridine is: Trimesoyl - I - (2 ethyl - aziridine), Tris - 2,4,6 (1 - aziridinyl) - 1,3,5 - triazine, Bis - isophthaloyl - 1 - (2 - methyl) - aziridine, Bis - isosebacoyl - 1 - (2 - ethyl) - aziridine, Bis - isosebacoyl - 1 - aziridine, Tri - [1 - (2 - methyl) - aziridinyl] - phosphine oxide, Bis[l - (2 - methyl) - aziridinyl] - ethyl sulfone, or the polyfunctional aziridines PFAZ300 and PFAZ301--supplied by Ionac Chemical Company, Birmingham, New Jersey.

The invention also provides an improved case bonded solid propellant rocket motor comprising propellant grains coated with a liquid hydroxy-terminated polybutadiene cured with a polyisocyanate curing agent and in which the motor casing has been lined with a liquid hydroxyl-terminated polybutadiene and an aziridine acid at least partially cured by reaction with a polyisocyanate.

The invention will now be more particularly described with reference to a specific embodiment thereof, namely a rocket motor casing liner comprising the liquid hydroxy-terminated-polybutadiene cured with a polyisocyanate as a binder and having the trade designation R-45M and the specific aziridine, trimesoyl - I (2 - ethyl) - aziridine.

The hydroxy-terminated polybutadiene polymer R-45M is sold by Arco Chemical Company and its structure may be represented as:

The R-45M is blended with the trimesoyl - 1 - (2 - ethyl) - aziridine, a conventional diisocyanate curing agent, which may be DDI, a C36 liquid aliphatic diisocyanate sold by General Mills, and, if desired, one or more fillers such as carbon black. The blended composition is vacuum degassed and cast as a liner into a previously descaled and degreased steel rocket motor casing and cured at elevated temperature from about 145F to about 200"F. After curing or partial curing is complete a hydroxy-terminated polybutadiene based propellant grain, such as, for example, a propellant consisting of R-45M as a binder in an amount ranging from 8.5 to about 24 /n by weight of the total weight of the propellant grain and including such conventional compounding ingredients as dioctyl adipate as a plasticizer, a polyisocyanate curing agent such as isophorone diisocyanate or the above mentioned DDI up to about 2% of the total weight, an oxidizing agent such as ammonium perchlorate up to 75 to 90 /n of the total weight, if desired, a portion of metallic fuel such as aluminium metal, and other conventional combustion stabilizers and flame coolants may be cast and cured in place in the lined motor in conventional fashion.

In addition to the R-45M binder specifically illustrated herein, it will be understood that any liquid hydroxy terminated polybutadiene polymer known to be useful as a propellant grain binder will be applicable in the invention. Illustrative of these polymers are, for example, those sold under the trade designations R-45HT, R-15M and CS-15, by Arco Chemical Company, and Butarez HTS by Phillips Petroleum Company. It will similarly be evident that in addition to the DDI illustrated herein any polyisocyanate may be used to effect cure of the binder.

Illustrative of other suitable polyisocyanates are, for example, isophorone diisocyanate, hexamethylene diisocyanate, PAPI (Registered Trade Mark) polymeric diisocyanates sold by the Upjohn Company and Desmodure N-100 (Registered Trade Mark) a polyisocyanate sold by I. G. Farben Industries, and also such isocyanates as: 1 - methoxyphenyl - 2,4 - diisocyanate, I - methyl - 4 methoxyphenyl - 2,5 - diisocyanate, I - ethoxyphenyl - 2,4 - diisocyanate, 1,3 dimethoxyphenyl - 4,6 - diisocyanate, 1,4 - dimethoxyphenyl - 2,5 diisocyanate, I - propoxyphenyl - 2,4 - diisocyanate, I - isobutoxy - 2,4 diisocyanate, 1,4 - diethoxyphenyl - 2,5 - diisocyanate, toluene - 2,4 diisocyanate, toluene - 2,6 - diisocyanate, diphenylether - 2,4 - diisocyanate, naphthalene - 1,4 - diisocyanate, 1,1''- dinaphthalene - 2,2' - diisocyanate, biphenyl - 2,4 - diisocyanate, 3,3' - dimethylbiphenyl - 4,4' - diisocyanate, 3,3' dimethoxybiphenyl - 4,4' - diisocyanate, diphenylmethane - 4,4' - diisocyanate, diphenylmethane - 2,4' - diisocyanate, diphenylmethane - 2,2' - diisocyanate, 3,3' - dimethoxy diphenylmethane - 4,4' - diisocyanate, benzophenone - 3,3' diisocyanate, ethylene diisocyanate, propylene diisocyanate, butylene diisocyanate, pentylene diisocyanate, methylbutylene diisocyanate, tetramethylene diisocyanate, pentamethylene diisocyanate, dipropyl diisocyanate ether, heptamethylene diisocyanate, 2,2 - dimethylpentylene diisocyanate, 3 - methoxy hexamethylene diisocyanate, octamethylene diisocyanate, 2,2,4 trimethylpentylene diisocyanate, 3 - butoxyhexamethylene diisocyanate, 1,3 dimethylbenzene diisocyanate, 1,4 - dimethylbenzene diisocyanate, 1,2 dimethylcyclohexane diisocyanate, 1,4 - dimethylcyclohexane diisocyanate, 1,4 dimethylnaphthalene diisocyanate, 1,5 - dimethylnaphthalene diisocyanate, cyclohexane - 1,3 - diisocyanate, cyclohexane - 1,4 - diisocyanate, I methylcyclohexane - 2,4 - diisocyanate, 1 - methylcyclohexdne, -2,2 diisocyanate, 1 - ethylcyclohexane - 2,4 - diisocyanate, dicyclohexylmethane 4,4' - diisocyanate, dicyclohexylmethylmethane - 4,4 - diisocyanate, dicyclohexyldimethylmethane - 4,4' - diisocyanate, 2,2 dimethyldicyclohexylmethane - 4,4' - diisocyanate, 3,3',5,5' tetramethyldicyclohexylmethane - 4,4' - diisocyanate, 4,4' methylenebis(cyclohexylisocyanate), ethylidene diisocyanate, 4,4' diphenyldiisocyanate, dianisidine diisocyanate, 1,5 - naphthalene diisocyanate, m - phenylene diisocyanate, isopropylidene bis(phenyl or cyclohexyl isocyanate), 1,3 - cyclopentylene diisocyanate, 1,2- cyclohexylene diisocyanate, 1,4cyclohexylene diisocyanate, 4,4',4"- triphenylmethane triisocyanate, 1,3,5 triisocyanate benzene and phenylethylene diisocyanate.

It will also be apparent that in addition to trimesoyl - 1 - (2 - ethyl)aziridine illustrated herein other aziridines are the full equivalents for the purposes of this invention. Illustrative of these are, for example, tris - 2,4,6 - (1 - aziridinyl) 1,3,5 - triazine, bis - isophthaloyl - 1 - (2 - ethyl)aziridine, bis isosebacoyl - 1 aziridine, tri - [1 - (2 - methyl)aziridine]phosphine oxide, bis - [I - (2 - methyl) aziridinyl]ethyl sulfone and the polyfunctional aziridines sold under the trade designations PFAZ300, PFAZ301 by Ionac Chemical Company. It will also be apparent that in addition to the carbon black illustrated herein as being optionally employed as a filler other materials will be suitable for use as fillers and may also optionally be employed singly or in admixture with each other or with carbon black. Illustrative of these are: titanium dioxide, silicon dioxide, silica, aluminium oxide, milled glass, and alumino silicate clays.

The aziridines used in the invention may be incorporated in amounts of from about 1 to 10% by weight of the total weight of the liner mixture. Preferably they may be incorporated in amounts of from about 4 to 8%, conveniently about 6% by weight of the total mixture.

The following example illustrates the best mode known to us for the practice of the invention.

EXAMPLE The following Example illustrates the preparation of a typical liner composition using an adhesion enhancer of the invention.

To R-45M (41.85 weight %) is added DDI (12.15 weight %), trimesoyl - I (2 - ethyl)aziridine (6.0 weight %) and carbon black (40.0 weight %), the aziridine being melted prior to addition and the entire mixture blended for about 45 minutes and then degassed by conventional techniques such as vacuum mixing or slit deaeration. The mixture is then cast by standard procedures and cured at 1700F for 96 to 168 hours. The normal thickness obtained in one application to a motor casing is from 1/32 to 1/16 inch.

Typical physical properties obtained from cured samples of the mixture are as follows: Tensile Strength (ASTM D 412) Test Temp. ("F) 0 77 150 200 Stress, ultimate (psi) 1043 543 331 258 Strain, ultimate (%) 464 431 324 282 Stress100% strain (psi) - 118 - Stress-300% strain (psi) - 379 - Stress500% strain (psi) - 509 - Tear strength, pli 111 Hardness (Shore A at ambient temperature) 52.

Ageing Properties (Test at 770 F) Ageing Temperature 1300F Ageing Temperature 170"F Ageing Time (Weeks) Ult. Stress Ult. Strain Ult. Stress Ult. Strain 0 501 389 501 389 2 513 325 781 146 4 548 339 847 121 8 630 267 878 136 12 589 194 861 136 Typical Bond Properties Samples of the above mixture were cured on steel surfaces, grit blasted and vapor degreased, or were cured and typical propellant and insulation material formulations cured on the liner surface. Tensile adhesion and peel strengths were then determined with the results shown which may be compared to 6-9 pli peel strength, with thin coat of propellant failure, for the bond at ambient temperature (77"F) between similar propellant and liner formulations without aziridine where the liner is not fully cured prior to cure of propellants, and 3-6 pli where the liner is fully cured prior to propellant addition.

Adjacent Test Temp. Tensile Adhesion (pli) Peel (pli) Matertial ( F) Load Type of Failure Initial Average type of Failure Steel -65 1333 2-Liner 7197.3 - 3-Tab broke 1-Plate beat Steel 77 249.3 3-Liner 43.0 35.7 3-Thin coat liner Steel 165 184.7 3-Thin coat 13.8 16.0 3-Thin coat liner liner Steel 200 170.7 3-Thin coat 27.3 15.7 3-Thin coat liner liner Steel 250 160.0 3-Liner 25.5 14.5 2-Liner pulled from shim 1-Thin coat liner Steel 300 117.7 3-Liner 17.6 10.6 3-Liner pulled from shim Asbestosfilled -65 1586 2-Thin coat of 75.5 105.0 2-Insulation polyisoprene liner 1-Thin coat of liner rubber based 1-insulation insulation Asbestosfilled 77 163.0 3-Thin coat 14.0 16.1 5-Bond polyisoprene of liner rubber based insulation Asbestos filled 165 103.0 3-Thin coat 4.0 9.1 3-Thin coat of liner polyisoprene of liner rubber based insulation Asbestos filled 200 107.5 2-Thin coat 4.4 7.4 3-Thin coat of liner polyisoprene of liner rubber based insulation Asbestos filled 250 126.3 3-Thin coat 12.4 12.4 2-Thin coats of polyisoprene of liner liner-1-Thin coat rubber based of liner, and liner insulation pulled from shim Asbestos filled 300 129.0 2-Thin coat of 12.7 11.1 2-Thin coat of liner polyisoprene liner-1-liner 1-Liner pulled rubber based from shim insulation Adjacent Test Temp. Tensile Adhesion (pli) Peel (pli) Material ( F) Load Type of Failure Initial Average Type of Failure R-45M based -65 808 2-Thin coat 75.0 49.7 3-Thin coat ammonium propellant propellant perchlorate 1-Thin coat oxidizer propellant & isophorone liner diisocyanate cured propellant** R-45M based 77 176 3-Propellant 24.5 46.1 3-Liner ammonium perchlorate oxidizer isophorone diisocyanate cured propellant** R-45M based 165 114 3-Propellant 25.4 27.7 2-Liner+ ammonium propellant perchlorate 1-Liner oxidizer isophorone diisocyanate cured propellant** **Liner precured for 24 hours at 145 F.

Typical bond properties on ageing were also determined-Tests were run at 77 F.

Storage Tensile Adhesion (pli) Peel (pli) Time Temp.

Adjacent Material (Weeks) ( F) Load Failure Initial Average Failure R-45M based propellant containing 0 111 174.7 5-Propellant 29.6 32.5 5-Propellant and liner ammonium perchlorate oxidizing agent cured with DDI, liner precured 32 hours at 145 F R-45M based propellant containing 2 130 215.7 5-Propellant 24.7 31.1 5-Propellant ammonium perchlorate oxidizing agent cured with DDI, liner precured 32 hours at 145 F R-45M based propellant containing 2 170 184.5 5-Propellant 20.8 - 3-Liner pulled from ammonium perchlorate oxidizing agent shim-2-Liner+ cured with DDI, liner precured 32 Propellant hours at 145 F R-45M based propellant containing 4 130 217.7 5-Propellant 28.9 30.9 5-Propellant and liner ammonium perchlorate oxidizing agent cured with DDI, liner precured 32 hours at 145 F R-45M based propellant containing 4 170 178.9 5-Propellant 21.0 - 3-Liner pulled from ammonium perchlorate oxidizing agent shim-2-Liner+ cured with DDI, liner precured 32 Propellant hours at 145 F R-45M based propellant containing 8 130 225.9 5-Propellant 24.4 27.2 4-Propellant+their ammonium perchlorate oxidizing agent coat liner cured with DDI, liner precured 32 1-Liner pulled from shim hours at 145 F R-45M based propellant containing 8 170 153.5 5-Propellant 16.0 9.2 4-Propellant ammonium perchlorate oxidizing agent 1-Liner pulled from shim cured with DDI, liner precured 32 hours at 145 F R-45M based propellant containing 12 130 228.8 5-Propellant 24.9 - 5-Liner pulled from shim ammonium perchlorate oxidizing agent cured with DDI, liner precured 32 hours at 145 F R-45M based propellant containing 12 170 155.8 5-Propellant 14.5 - 4-Liner pulled from shim ammonium perchlorate oxidizing agent 1-Propellant cured with DDI, liner precured 32 hours at 145 F

Claims (6)

WHAT WE CLAIM IS:

1. A curable liner composition for a case bonded solid propellant based upon a liquid hydroxyl-terminated polybutadiene and a polyisocyanate and containing, as a promoter of bonding to the propellant and the motor casing, an aziridine.

2. A liner composition as claimed in Claim 1, in which the aziridine is trimesoyl - 1 - (2 - ethyl)aziridine, tris - 2,4,6 - (I - aziridinyl) - 1,3,5 - triazine, bis - isophthaloyl - 1 - (2 - ethyl)aziridine, bis - isosebacoyl - 1 - aziridine, tri [1 - (2 - methyl)aziridine] - phosphine oxide, or bis - [1 - (2 - methyl)aziridinyl] ethyl sulfone.

3. A process for case bonding a liquid hydroxy-terminated polybutadiene based polyurethane bound solid propellant grain to a rocket motor casing which comprises: (a) lining a rocket motor casing with a cured liner composition comprising a mixture of an aziridine and a liquid hydroxyl-terminated polybutadiene which has been cured with a polyiso-cyanate curing agent; (b) casting said liquid hydroxy terminated polybutadiene based propellant grain, in an uncured form and comprising a polyisocyanate curing agent, into the desired configuration within said rocket motor casing; and (c) curing said propellant grain.

4. An improved case bonded solid propellant rocket motor comprising propellant grains based upon a liquid hydroxyl-terminated polybutadiene cured with a polyisocyanate curing agent and in which the motor casing which has been lined with liquid hydroxy-terminated polybutadiene and an aziridine and at least partially cured by reaction with a polyisocyanate.

5. A curable liner composition according to Claim 1 and substantially as hereinbefore described with reference to the Example.

6. A process for case'bonding a solid propellant grain to a rocket motor casing according to Claim 3 and substantially as hereinbefore described.