EP0254618A1 - Preformed inhibitor based on rubber gum for a composite propellant with a polyurethane binder - Google Patents

Abstract

The preformed inhibitor comprises a matrix based on rubber gum and fillers. The rubber gum is either an ethylene-propylene-diene monomer copolymer or an isoprene-isobutylene copolymer, with peroxide compounds and a sulphur system respectively as a vulcanising system. The propellants containing a polyurethane binder adhere directly to these inhibitors. The invention is useful especially in the field of self-propelled craft.

Description

The invention relates to a preformed inhibitor for composite propellant.

The invention relates more particularly to a preformed inhibitor having as matrix a rubber rubber to which a composite propellant with a polyurethane binder is directly adhered.

By inhibitor is meant any part which is placed on at least part of a propellant block to limit the combustion surface thereof. The inhibitors of the present invention also play a role in protecting the structure of the craft.

In the context of the present invention, the term inhibitor also designates parts of the inhibition of a block, such as for example the bottoms or the end faces, the other parts of the inhibition being able to be carried out with other inhibitory compositions.

• - un premier groupe dans lequel la composition inhibitrice est déposée sur la surface du bloc de propergol déjà réticulé.
• - un second groupe de procédés dans lesquels la composition inhibitrice est coulée dans un moule et au moins partiellement réticulée pour former une enveloppe dans laquelle sera coulée le propergol. Les procédés du second groupe permettent de fabriquer des blocs libres ou des blocs moulés collés. Dans ce dernier cas, l'inhibiteur est préformé directement dans la structure de l'engin autopropulsé, le propergol étant ensuite coulé dans cette structure.

The propellant block inhibition methods can be classified into two groups:

• - A first group in which the inhibitor composition is deposited on the surface of the propellant block already crosslinked.
• - A second group of processes in which the inhibiting composition is poured into a mold and at least partially crosslinked to form an envelope in which the propellant will be poured. The methods of the second group make it possible to manufacture free blocks or glued molded blocks. In the latter case, the inhibitor is preformed directly in the structure of the self-propelled vehicle, the propellant then being poured into this structure.

The inhibitors of the present invention are used for carrying out the methods of the second group.

Inhibitors are already known having as matrix rubber rubbers. However, these inhibitors are used with a composite propellant based on polybutadiene with terminal carboxyl functions (PBCT), and do not adhere to the composite propellant based on polybutadiene with terminal hydroxyl functions (PBHT). Furthermore, an inhibitor based on a gum rubber is known, the ethylene-propylene-diene-monomer elastomer, more commonly called EPDM for a composite propellant based on PBHT. However, the adhesion of the inhibitor to the propellant is obtained by the presence of an adhesion layer also called "primary" deposited between the inhibitor and the propellant. The need to provide this adhesion layer is a major drawback. In fact, the application of this adhesion layer to the inhibitor increases the duration and the manufacturing costs. In addition, it can generate defects in the load obtained, for example, by trapping air bubbles. To avoid any defect and to obtain a uniform adhesion on all the block, this application requires a lot of precaution.

The object of the present invention is in particular to remedy these drawbacks by proposing a preformed inhibitor based on gum rubber to which a propellant with a polyurethane binder is directly adhered. To this end, the invention provides a preformed inhibitor for a composite propellant block based on a polyurethane binder obtained from a polyol and a polyisocyanate. This inhibitor includes a rubber-based matrix, fillers, a rubber vulcanization system, and is characterized in that the rubber is chosen from the group comprising ethylene-propylene-diene-monomer copolymers (called EPDM rubbers). and isoprene-isobutylene copolymers (called Butyl rubbers), the vulcanization system of EPDM rubber being a system based on peroxide compounds, that of Butyl rubber being a system based on sulfur.

Thus, the composite propellants adhere directly to the inhibitors according to the invention, without the use of an adhesion or "primary" layer.

According to another characteristic of the invention, the inhibitor contains a bonding dopant.

When the matrix is based on EPDM rubber, the bonding dopant is oxamide, preferably present at a concentration of between 50 and 200 parts by weight per 100 parts of gum rubber.

In the case of a Butyl rubber matrix, the doping agent is diethylene glycol (D.E.G.), preferably present at a concentration of between 1 and 5 parts by weight per 100 parts of gum rubber.

As butyl rubbers suitable for the invention, mention may be made of the various known butyl rubbers, the percentage of unsaturation being indifferent, as well as halogenated butyl rubbers, such as chlorobutyl.

The sulfur vulcanization systems suitable for the invention are those containing sulfur, and vulcanization accelerators. Sulfur can be supplied by vulcanization accelerators.

By way of example, as a vulcanization accelerator suitable for the invention, mention may be made of zinc salts and dithiocarbamic acid such as zinc dibutyldithiocarbamate, zinc diethyl dithiocarbamate or zinc ethylphenyl dithiocarbamate , or thiurams such as, mercaptobenzothiazole (MTB), benzothiazyl disulfide (MBTS), or guanidines or amines, or the like.

The sulfur vulcanization systems suitable for the invention do not contain a vulcanization activator such as, for example, stearic acid, zinc oxide. These products have a detrimental effect on the propellant adhesion properties.

Vulcanization systems suitable for EPDM rubbers include one or more peroxide compounds such as, for example, dicumyl peroxide; 2.5 methyl 2.5 Bis peroxide; 2,5 dimethyl 2,5 dimethyl hexane peroxide; 2,5 dimethyl 2,5 bis (t-butyl) hexyne 3 peroxide; 1,3 bis (t-butylisopropyl) benzene peroxide; 1-1 bis (t-butyl) 3,3,5 trimethyicyciohexane peroxide and t-butylcumyl peroxide or the like.

The concentration of peroxide or sulfur vulcanization system is that indicated and recommended by the rubber manufacturers for their use.

Other fillers can be added to the rubber such as fillers which reinforce the mechanical properties.

Advantageously, at least part of these charges is an electrically conductive charge, such as, for example, carbon black. Preferably the concentration by weight of this conductive filler is between 5 and 50 parts per 100 parts of gum rubber.

The addition of such an electrically conductive charge makes it possible to obtain an inhibitor having an improved electrical conductivity which is very advantageous for ensuring the evacuation of the electrostatic current generated in the charges or machines, in particular during the storage of these charges.

Without departing from the scope of the invention, it is possible to add various additives known to those skilled in the art, such as, for example, antioxidants, etc.

Polyurethane binder propellants are composite propellants comprising an inert binder, an oxidant, a fuel, ballistic additives, catalysts. In addition, these compositions can contain an explosive such as tetramethylenetetranitramine, trimethylenetrinitramine, for example. As is known to those skilled in the art, other compounds not mentioned above can be added to these propellant compositions.

Propellants suitable for the invention have as an inert binder, a polyurethane obtained by reaction of a polyol with a polyisocyanate.

As preferred polyols of the invention, mention may be made of polybutadienes containing terminal hydroxyl functions (PBHT), in particular those marketed by the company ARCO under the trade names R45M and R45HT, polyalkylene ether glycols such as polypropylene glycols or polyethylene glycols, polyalkylene ester glycols, or the like.

As polyisocyanates suitable for the invention, aromatic, aliphatic, arylaliphatic or alkylaromatic polyisocyanates can be used.

Difunctional isocyanates are preferred, such as, for example, 2,4-tolylene diisocyanate; 2,6-tolylene diisocyanate; isophorone diisocyanate, hexamethylene diisocyanate, d.imeryl dllsocyanate or the like.

Other objects, details and characteristics of the invention will appear more clearly in the light of the detailed description which follows, given with reference to the examples given solely by way of illustration and indication.

The inhibitors of the invention are prepared according to conventional methods of using rubbers.

Thus, by way of example, the compositions are prepared in a mixer by first plasticizing the rubber compound at ambient temperature, then by introducing fillers such as carbon black, oxamide. After homogenization of the assembly, the various additives such as adhesion doping agents and antioxidant agents are always introduced at ambient temperature. Finally, the vulcanizing agents are mixed with the composition.

The composition is calendered in the form of a sheet with an average thickness of 5 millimeters.

These sheets are then cut to the desired dimensions and placed in a mold where they are shaped and vulcanized under pressure, at a temperature of the order of 160 ° C. and a duration of 30 to 60 minutes. The number of sheets deposited depends on the thickness of the part to be produced.

Of course, the vulcanization temperature and duration are given for information only and are determined, in a manner well known to those skilled in the art, by measuring a mechanical property to determine the optimum degree of vulcanization suitable for rubber application. For example, shear strength can be monitored using a cone rheometer.

The part thus formed is placed either in a mold when it is desired to make free blocks, or in the structure of a machine when the propellant charge is of the "molded-glued" type.

The propellant is then poured into the mold or structure, and crosslinked by heat treatment according to a process well known to those skilled in the art.

Advantageously, the surface of the rubber part is sanded, dusted and dried before the propellant is poured.

The propellant used in Examples 1 to 6 has the following composition:

• Sm : contrainte maximale en MPa
• E : allongement élastique en %
• E : module d'Young en MPa
• er : allongement relatif à la rupture en % ainsi que les caractéristiques de l'adhésion au propergol :
• C : résistance au cisaillement en Mpa
• T : résistance à la traction au MPa
• P : résistance au pelage en daN/cm

For each inhibitor, its mechanical properties are determined:

• Sm: maximum stress in MPa
• E: elastic elongation in%
• E: Young's modulus in MPa
• er: elongation relative to rupture in% as well as the characteristics of adhesion to the propellant:
• C: shear strength in Mpa
• T: tensile strength at MPa
• P: peel strength in daN / cm

Example 1

• - Copolymère isoprène-isobutylène (commercialisé par la Société ESSO sous la dénomination Butyl 065 contenant 0,65 moles d'isoprène pour 100 moles d'isobutylène)
• - Noir de carbone (commercialisé par AKZO sous la dénomination noir de Ketjenblack) 25 phr
• - Disulfure de tétraméthylènethiurame (DTMT) 1 phr
• - Disulfure de benzothiazyle (MBTS) 1 phr
• - Soufre 1,5 phr

The inhibitor is based on butyl gum rubber and has the following composition expressed in parts by weight per 100 parts of gum rubber (phr).

• - Isoprene-isobutylene copolymer (marketed by the company ESSO under the name Butyl 065 containing 0.65 moles of isoprene per 100 moles of isobutylene)
• - Carbon black (marketed by AKZO under the black name of Ketjenblack) 25 phr
• - Tetramethylenethiuram disulfide (DTMT) 1 phr
• - Benzothiazyl disulfide (MBTS) 1 phr
• - Sulfur 1.5 phr

• Sm = 8,7 MPa
• E = ₁₆₃ %
• E = 5,3 MPa
• er = _{960 %}

The mechanical properties measured at 20 ° C after vulcanization at 160 ° C for 30 minutes are:

• Sm = 8.7 MPa
• E = ₁₆₃ %
• E = 5.3 MPa
• er = _960%

• C = 0,47 MPa
• T = 0,80 MPa
• P = 1,3 daN/cm

The characteristics of the bonding are:

• C = 0.47 MPa
• T = 0.80 MPa
• P = 1.3 daN / cm

Example 2

• E = 219 %
• E = 6,2 MPa
• er = 990 %

A composition identical to that of Example 1 is produced, but by replacing the isoprene-isobutylene copolymer (Butyl 065) with an isoprene-isobutylene copolymer also marketed by ESSO under the name Butyl 365 containing 2.25 moles of isoprene per 100 moles of isobutylene. This inhibitor, after vulcanization at 160 ° C for 30 minutes has the following mechanical properties: Sm = 13.5 MPa

• E = 219%
• E = 6.2 MPa
• er = 990%

• C = ₀,₅₃ MPa
• T = 0,87 MPa
• P = ₁,₂ daN/cm

The characteristics of the bonding are:

• C = _{0, 53} MPa
• T = 0.87 MPa
• P = _{1, 2} daN / cm

Example 3

The inhibitor has the composition of that of Example 2 in which a bonding dopant, diethylene glycol, has been added in a proportion of 2 phr.

• Sm = 7 MPa
• E = 122 %
• E = ₅,₈ MPa
• er = 10200/0 et les caractéristiques de l'adhésion ont les valeurs suivantes :
• C = 0,56 MPa
• T = 0,90 MPa
• P = 1,3 daN/cm

The mechanical properties are:

• Sm = 7 MPa
• E = 122%
• E = _{5, 8} MPa
• er = 10200/0 and the characteristics of the adhesion have the following values:
• C = 0.56 MPa
• T = 0.90 MPa
• P = 1.3 daN / cm

Example 4

• - copolymère éthylène propylène diène-monomère (commercialisé par la Société ESSO sous la dénomination Vistalon 2504, le diène étant un éthylène norbodène)
• - noir de carbone (noir de Ketjenblack) 25 phr
• - système de vulcanisation : peroxyde de 2,5-diméthyl 2,5 Bis 5 phr

The composition of the inhibitor is as follows:

• - ethylene propylene diene-monomer copolymer (sold by the company ESSO under the name Vistalon 2504, the diene being an ethylene norbodene)
• - carbon black (Ketjenblack black) 25 phr
• - vulcanization system: 2,5-dimethyl 2,5 Bis 5 phr peroxide

• Sm = 18 MPa C = 0,76 MPa
• E = ₁₃₀,₃ % T = ₀,₉₂ MPa
• E = 1₄ MPa P = 0,8 daN/cm
• er = 400 %

The mechanical and characteristic properties of the adhesion are:

• Sm = 18 MPa C = 0.76 MPa
• E = _{130, 3%} T = _{0, 92} MPa
• E = 1 ₄ MPa P = 0.8 daN / cm
• er = 400%

Example 5

• - copolymère éthylène propylène diène-monomère (Vistalon 2504)
• - noir de carbone (noir de Ketjenblack) 20 phr
• - oxamide 100 phr
• - DBPC (ditertiobutyle paracrésol) 1 phr
• - peroxyde de dicumyle 6 phr

The composition of the inhibitor is as follows:

• - ethylene propylene diene-monomer copolymer (Vistalon 2504)
• - carbon black (Ketjenblack black) 20 phr
• - oxamide 100 phr
• - DBPC (ditertiobutyle paracrésol) 1 phr
• - dicumyl peroxide 6 phr

• Sm = 5 MPa C = 0,97 MPa = 32,5 % T : 1,25 MPa
• E = 16 MPa P = ₂,₂ daN/cm
• er = 400 %

The mechanical properties and characteristics of the bonding are:

• Sm = 5 MPa C = 0.97 MPa = 32.5% T: 1.25 MPa
• E = 16 MPa P = _{2, 2} daN / cm
• er = 400%

Example 6

• Sm = 9 MPa C = 0,69 MPa
• E = 260 T = 1,06 MPa
• E = ₃,₅ MPa P = 1,3 daN/cm
• er = ₅₀₀

A test is carried out with the same composition as for Example 5 but without adding oxamide, and replacing the dicumyl peroxide with 2,5-dimethyl 2,5 Bis peroxide. The mechanical properties and characteristics of the bonding are:

• Sm = 9 MPa C = 0.69 MPa
• E = 260 T = 1.06 MPa
• E = _3, P = 1.3 MPa ₅ daN / cm
• er = ₅₀₀

Examples 5 and 6 show the effect of oxamide on the characteristics of the bonding.

Example 7 was carried out with a propellant of the following composition:

• Sm = 6 MPa C = 0,61 MPa
• E = 100 % T = 1,02 MPa
• E = 6 MPa P = 1,9 daN/cm
• er = 675 %

The composition of the inhibitor tested, its mechanical properties and its bonding characteristics are as follows:

• Sm = 6 MPa C = 0.61 MPa
• E = 100% T = 1.02 MPa
• E = 6 MPa P = 1.9 daN / cm
• er = 675%

Examples 8 and 9 are comparative examples not falling within the scope of the present invention.

Example 8

The composition of the inhibitor, which is based on butyl rubber, differs from that of Example 1 in that a vulcanization activator is added in the following weight proportions: Zinc oxide 3 phr
Stearic acid 1 phr

The bonding properties on a propellant identical to that used in Example 1 are as follows: C = 0.48 _MP a
T = 0.51 MPa P = 0.7 daN / cm

These results clearly show the harmful effect of the presence of a vulcanization activator on the bonding, in particular on the tensile and peel strength.

Example 9

• ZnO 5 phr
• Acide stéarique 1 phr
• DTMT 2 phr
• MBTS 2 phr
• S 1 phr

The bonding properties of an inhibitor based on an EPDM gum rubber identical to that of Example 4 were also evaluated, but using a sulfur vulcanization system in the following proportions:

• ZnO 5 phr
• Stearic acid 1 phr
• DTMT 2 phr
• MBTS 2 phr
• S 1 phr

• C = 0,44 MPa
• T = 0,48 MPa
• P = 0,3 daN/cm

The bonding properties obtained are:

• C = 0.44 MPa
• T = 0.48 MPa
• P = 0.3 daN / cm

These results compared to those of Example 4 clearly show the technical effect (direct bonding between the propellant and the inhibitor) obtained with a vulcanization system with peroxide compounds.

Claims (8)

1. Preformed inhibitor for composite propellant with polyurethane binder, comprising a rubber-based matrix, fillers, characterized in that the rubber-rubber is chosen from the group comprising ethylene-propylene-diene monomer copolymers (EPDM) and copolymers isoprene-isobutylene (Butyl), the vulcanization system of EPDM rubber being a system based on peroxide compounds, that of Butyl rubber being a sulfur system. 2. Inhibitor according to claim 1 characterized in that it comprises an adhesion doping agent. 3. Inhibitor according to claim 2, characterized in that the adhesion doping agent is diethylene glycol for a rubber matrix Butyl rubber, the concentration of adhesion doping agent is between 1 and 5 parts by weight per 100 rubber eraser parts. 4. Inhibitor according to claim 2, characterized in that the adhesion doping agent is oxamide for a rubber matrix of EPDM gum, the concentration of adhesion doping agent being between 50 and 200 parts by weight per 100 rubber eraser parts. 5. Inhibitor according to one of the preceding claims, characterized in that at least part of the charges is an electrically conductive charge. 6. Inhibitor according to claim 5, characterized in that the concentration of the electrically conductive charge is between 5 and 50 parts by weight per 100 parts of gum rubber. 7. Inhibitor according to one of claims 1 to 3 and 5, 6 characterized in that the vulcanization system of butyl gum rubber contains sulfur and a vulcanization accelerator. 8. Inhibitor according to one of claims 1, 2, 4, 5 or 6 characterized in that the vulcanization system of the EPDM rubber contains at least one peroxide compound chosen from the group containing dicumyl peroxide; 2,5-dimethyl 2,5 Bis peroxide; 2.5 dimethyl peroxide 2.5 dimethyl hexane; 2,5 dimethyl 2,5 bis (t, butyl) hexyne peroxide 3; 1.3 bis (t, butylisopropyl) benzene peroxide, t-butylcumyte peroxide, and 1-1 bis (t-butyl) 3.3.5 trimethylcyclohexane peroxide.