DE2951697C1 - Inhibiting coating for homogeneous powder blocks - Google Patents

Description

The invention relates to an inhibiting coating for homogeneous powder blocks based on sili konelastomeren, which adheres directly to the powder block.

The use of silicone elastomer coatings, between the steel wall of the drive device and the powder block are turned on to its It is already in place to inhibit and regulate combustion known.  

Silicone resins possess with regard to their application as inhibitors interesting properties, when they burn only little smoke produce.

In their current commercial form the silicones, however, compared to homogeneous powder blocks only a relatively low adhesion on. It is also necessary to use one as a primer designated liability mediator, the the adhesion of the silicone elastomer to the homogeneous powder block guaranteed.

This method is particularly in the FR-PS 2 161 435 and DE-OS 22 57 742, which describes a method for inhibiting of propellants by an inhibiting coating composition which consist of a silicone elastomer exists, with the block previously for warranty a secure adhesion coated with a primer layer becomes.

The use of a primer is, however, in In terms of technical implementation with numerous Disadvantages. The primer is on the one hand Product that is environment sensitive. The coating the block with the primer is also a delicate process step, which conveniently avoided becomes. After completion of the coating with the primer is also the implementation of various controls steps to ensure that the Primer layer has appropriate thickness and uniformity. Although this can also only by visual Control, but this will be little obtained reliable results.  

For the above reasons it is therefore desirable to avoid a primer application.

In US-PS 3,054,253 is also a homo to Progolblöcken adhesive composition indicated, the

• a) a silicone copolymer with R₃-Si-O and SiO₂- Groups,
• b) a benzene-soluble diorganosiloxane of the general formula and
• c) a hydrocarbon solvent

contains. This composition is before evaporation of the hydrocarbon solvent on the propellant applied block.

However, this method is not free from Disadvantages. The bond between the Propergolblock namely, the silicone inhibitor is adhesive and not Cohesive, which means that the fracture at the interface the two materials occurs while in the Case of a cohesive bond a break in the interior one of the two materials occurs. It is therefore desirable to achieve a cohesive bond, in which case the tensile strength of the maximum strength corresponds with the corresponding Materials is available.  

In addition, those according to the above US-PS obtained mechanical properties unsatisfactory. In addition to the adhesion properties, however, must Such coatings also have mechanical properties which have good strength over the during acceleration during launching loads occurring to lead.

A particular difficulty is also in the Bonding of inhibiting coatings with homogeneous blocks of powder in the circumstance that nitro contained in the block glycerin has a tendency to adhere to the block surface diffuse, which leads to a detachment of the coating. This appearance is more important the higher the Nitroglycerine content is. Because of this fact Sticking the bond with time getting worse.

The invention is based on the object, a indicate inhibiting coating for homogeneous powder blocks, the no previous primer coating of the powder requires more blocks. The coating should also have a temporally stable cohesive connection between the Silicone elastomer and the homogeneous powder block too allow for blocks with increased nitroglycerin content. The mechanical properties obtained should further with those of other known inhibiting coatings be comparable and at the same time explained above Disadvantages of conventional coatings do not possess.

The task is solved according to the claim.

The inhibiting coating according to the invention for homogeneous powder blocks is based on a silicone  elastomeric, which adheres directly to the powder block and consists of a one- or two-component system, by hydrolysis and then by silanol condensation is networked, and is characterized in that he by addition of 0.5 to 12 wt .-%, based on the silicone system, an aminosiloxane of the general formula

With
R₁ = C₁ to C₈ alkyl,
R₂ = C₁- to C₈-alkylene and
R₃ = H, C₁- to C₈-alkyl or aminoalkyl

is available before crosslinking.

Under the term silicon system here is the Understood system comprising all reactants, the achievement of a silicone elastomer by crosslinking enable.

The term siloxane base material designates Oligomers with silanol end groups. The term elastomer relates to the resulting after networking Final product.

It should be noted that all silicone systems by hydrolysis and subsequent silanol crosslinking condensation, for the invention Zu composition are usable.

The silicone systems can depending on their Vernetzungsweise be divided into the following three groups:

• A. By hydrolysis and subsequent silanol condensation Crosslinking silicone systems (conventional systems).
• These silicone systems can be subdivided into the following subgroups:
  • 1. One-component systems.
    However, these systems have the disadvantage of high sensitivity to moisture in terms of their technical application, which is why certain precautions are required during storage.
  • 2. two-component systems.
    These systems are easier to handle and are therefore used over one-component systems.
• B. By addition of Si-H to an ethylenic double bond crosslinking silicone systems.
• C. Crosslinking by chemical reaction of Si-H with SiOH Silicone systems (for the formation of silicone foams leading systems).

The invention relates only to silicone systems Type A. These silicone systems are in detail from the following reactants:

• a) a polysiloxane-based resin blocked at the chain ends with reactive groups such as hydroxyl groups, alkoxy groups or acetoxy groups.
  This polysiloxane-based resin can be represented by the general formula be defined in the
  R₁ at the same time or independently hydrolyzable atoms or groups such as hydrogen, alkyl groups, acetyl groups udgl. and
  R is at the same time or independently usually methyl, ethyl, phenyl or 3,3,3-trifluoropropyl;
• b) a crosslinking agent which is also hydrolyzable Has groups, for example alkoxysilanes, Acetoxysilanes and the like;
• c) a crosslinking catalyst which is among the organo tin compounds and the lead salts is selected.

The above-mentioned silicone systems crosslink at Room temperature in the presence of moisture. you are known as so-called cold vulcanizing elastomers. Although all of the above explained Silicone systems are suitable according to the invention, is immediate it can be seen that the use of two-component systems Safeguards to protect such systems Moisture avoids why these products according to the invention  are preferred. These silicone systems are liquid or impasto and go at room temperature or a little higher temperature in elastic, soft masses over. They are also available in large numbers on the market.

In the commercial silicone systems are generally for reinforcing fillers before. in this connection these are in particular silicic acid or diatomaceous earths as well as quartz powder, calcium carbonate or Iron oxides.

Although according to the invention all of the above general formula II encompassed aminosiloxanes, it was found that the composition was even better Adhesive properties, if used Aminosiloxane has the following general formula:

With
R₁ = C₁ to C₄ alkyl,
R₂ = C₃- to C₈-alkylene and
R₃ = H or a lower aminoalkyl group.

Included in the above general formula Aminosiloxanes are preferred as two compounds in terms of improvement of self-adhesion properties the silicone elastomers as well as the good mechanical behavior of the coatings accessible therewith gave particularly interesting properties; these preferred Connections are:

γ-Aminopropyltriäthylsiloxan

H₂N-CH₂-CH₂-CH₂-Si (OC₂H₅) ₃ IIa

and

N- (β-aminoethyl) -γ-aminopropyltrimethylsiloxan

H₂N-C₂H₄-NH-C₃H₆-Si (OCH₃) ₃ IIb

Although these aminosiloxanes are within a wide range Range of mixing ratios of 0.5 to 12.5% by weight, based on the silicone system, within the scope of the invention Concept can be mixed, is an area from 0.5 to 8% by weight preferred to deteriorate avoid the mechanical properties and at the same time to facilitate the application.

After a particularly advantageous invention Embodiment in which ensures optimal bonding becomes and has excellent mechanical properties result in 1 to 6 wt .-% aminosiloxane (e), based on the siloxane base material used.

To improve the mechanical properties as well the thermal stability of the coatings is further advantageous, the silicone system before the introduction of the Aminosiloxane with fibers to reinforce. This will a considerable improvement in the modulus of elasticity achieved the resulting elastomers. Because the connection between the coating according to the invention and the homogeneous Powder block is also cohesive, thereby occurs at the same time a considerable improvement in tensile strength as in Example 3 below is apparent.  

Fibers added to the silicone system advantageous are aluminum fibers, silica fibers in particular and all fibers made of heat-resistant materials.

According to the invention it has been found that it is particularly is advantageous, a fiber content of 3 to 30 wt .-%, based on the filled silicone system, apply.

Another, particularly favorable invention Further education is based on the finding that still uncrosslinked silicone systems can be used on the silanol end groups of the siloxane base materials the above-explained Aminosiloxanverbindungen were previously grafted. This improvement is simplified also the processing to achieve self-adhesive Coatings, since the silicone systems after this training according to the invention directly usable, ie are ready to use, with the step of introduction the aminosiloxane corresponding deleted.

According to the invention, the following compositions are preferred used:

Composition I parts Commercially available two part silicone-vulcanizing system (RTV 3120), DOW CORNING 100 Catalyst (10% dibutyltin dilaurate) 5 Aminosiloxane IIa 3

Composition II parts Silicone system RTV 3120 100 Aminosiloxane IIa 3 Catalyst (10% by weight of tin dibutyl dilaurate) 1

Composition III parts Silicone system RTV 3120 (filled with 8% fibers) 100 Aminosiloxane II 3 Catalyst (10% by weight of tin dibutyl dilaurate) 1

Composition IV parts Commercially available cold vulcanizing silicone system (RTV 589) 100 Aminosiloxane IIa 2 Catalyst (10% by weight of tin dibutyl dilaurate) 4

Composition V parts Silicone system RTV 3120 100 Aminosiloxane IIb 10 Catalyst (10% by weight of tin dibutyl dilaurate) 10 methylene chloride 300 methyl ethyl ketone 100

In this composition, the presence of a Solvent desired because the viscosity increases rapidly.

Composition VI parts Silicone system RTV 3120 100 Aminosiloxane IIa 7 Catalyst (about 10% by weight of tin dibutyl dilaurate) 2

Further, 4 parts of silica are added, whereby the composition has thixotropic properties receives.

The composition is particularly suitable for sealing the grooves on reinforcement tubes.

The composition is also self-adhesive.

The invention accordingly also relates to the process for the preparation the above-mentioned self-adhesive silicone coatings and the powder blocks available in this way.

Generally, the procedure is that a specific Amount of silicone resin is weighed and then 0.5 Up to 12 wt .-% aminosiloxane are introduced. To Homogenization, the mixture is degassed for a few minutes. After that, in the case of a two-component system the crosslinking catalyst added and homogenized again. After degassing, the solution will vary depending on the obtained viscosity to a homogeneous powder block or Propergolblock poured around or -gespritzt.

The material thus obtained is homogeneous for all Powder blocks applicable such. B. according to the so-called SD method (Process without solvent) prepared homogeneous Powder or for so-called cast-glued blocks. The Material is also suitable for inhibiting gunpowder, for example for guns. The material can have a sufficiently low viscosity to the To allow production of very thin layer thicknesses of the coating.  

The bond obtained by this procedure with the homogeneous powder block is always cohesive. The tensile strength of the bond of the coating with the homogeneous powder block is under shear stress measured as follows: The above general Method produced silicone elastomers are homogenized with trichlorethylene previously degreased Poured around powder rods. Of these, slices of 10 mm cut, the shear strength at different Pulling speeds in the temperature range from -40 to + 60 ° C is measured. The variation of Temperature on the one hand allows the detection of the temperature independent good properties of the inhibitor and on the other hand, the confirmation that the bonding in the observed temperatures is always cohesive. elastomers are harder at low temperatures, with the value of Shear strength more of the hardness of the elastomer than depends on the strength of the compound at the interface. If the fracture is cohesive, the numerical values obtained are at -40 ° C higher, without this from a better Adhesive effect could be closed.

The invention will be described below with reference to Ausfüh examples, which are not restrictive are.

example 1

A homogeneous powder rod was used which was prepared by the SD method (without solvent) and having the following composition:

Wt .-% Nitrocellulose with 11.7% nitrogen 55.5 nitroglycerin 37 stabilizer 2 combustion catalysts 5.5

The rod was so carried out with the composition I. Pour coating that the coating has a radial thickness of 3 mm.

The transverse shear strength was at a Zugge speed of 10 mm / min after several long Measured aging.

The following results were obtained:

The results show that the break at the three temperatures is cohesive, and further that with the aging achieved a time-dependent improvement which is due to the in the introduction to the description difficulties discussed is completely surprising.

The Young's modulus (elicitation modulus) of the inhibitor Material is 36 bar at 20 ° C.  

Example 2

In the same manner as in Example 1, the (crosslinked) Composition II to a same homogeneous Cast powder block.

The following results were obtained:

The break is always cohesive.

The modulus of elasticity of the coating is 24 bar at 20 ° C.

Example 3

The silicone system used was, as in Zusammen tion III previously filled with fibers.

The silicone system was then at a same Powder block as poured in the previous cases.

The following results were obtained:

The fracture is cohesive in all cases.

The Young's modulus of the coating is 150 bar at 20 ° C.

From the results it can be seen that the mechanical properties of the coatings as well as the train strength can be significantly improved, the Break is always cohesive.

Example 4

Using Composition IV proceed as above.

The following results were obtained:

The modulus of elasticity of the coating is 20 bar at 20 ° C.

Example 5 (comparative experiments)

To illustrate the invention achieved Property improvement were adhesive tests at 20 ° C. carried out on blocks of powder with those of the above Examples were identical, the following compositions were used:

• A coating of a silicone composition II composition, but without aminosiloxane, but with previous coating of the homogeneous powder block with a commercially available primer (Composition: 3% silicone oil, 10% (aminosilane + Vinylsilane) and 87% toluene, hexanol);
• B coating of composition II;
• C coating of composition V.

The following results were obtained:

From the results, the invention is in terms of the adhesive effect achieved improvement clearly it should be emphasized that these results are without previous coating of the block with a primer were.

Example 6

Composition III was prepared according to the same Ver By way of procedure, cast as above on a homogeneous powder rod, the SD method (without solvent) had been prepared and had the following composition:

Wt .-% Nitrocellulose with 11.7% nitrogen 33.3 Nitrocellulose with 12.5% nitrogen 22.5 nitroglycerin 35.2 softener 3 combustion catalysts 3.2 stabilizer 2.8

The following results were obtained:

The fracture is cohesive in all cases.

The modulus of elasticity of the coating is 150 bar at 20 ° C.

Example 7

Composition III was prepared by the same procedure as above on a homogeneous powder block cast (glued), the following Composition:

Wt .-% Nitrocellulose with 12.6% nitrogen 59 nitroglycerin 27.3 stabilizer 2.2 combustion catalysts 2 softener 9.5

The following results were obtained:

Example 8 (comparative experiments)

To illustrate the present invention obtained Ver Improvements were carried out comparative experiments, the refer to the adhesive strength at 20 ° C; the experiments were also with a cast-glued block as in Example 7 using the following compositions carried out:

• A Composition III without aminosiloxane, however with prior coating of the cast-glued Block with a commercially available primer as in example 5, composition A.
• B Composition III.

The following results were obtained:

Example 9

The experiment refers to direct grafting an aminosiloxane on the siloxane base material, the  according to a method described in US Pat. No. 774,830 had been made.

The siloxane base material contained 7% aminoethyl aminopropyl methoxysiloxan groups.

The silicone system was placed on a homogenous powder rod of the same composition as in Example 1 poured.

The following result was obtained:

Example 10

To determine the thermal and mechanical Behavior of the inhibitor also became a practical one Shooting test of the composition III performed.

The experiment was carried out with a Propergolblock, the had been produced by the so-called Epictète process, made under frontal combustion. The shooting curves showed excellent behavior of the inhibitor (stable pressure curve). Furthermore, no replacement occurred of the inhibitor.

Claims (8)

1. Inhibiting coating for homogeneous powder blocks, which adheres directly to the powder block and consists of a crosslinked by hydrolysis and subsequent silanol condensation one- or two-component silicone system, obtainable by addition of 0.5 to 12 wt .-%, based on the silicone system, one Aminosiloxane of the general formula With
R₁ = C₁ to C₈ alkyl,
R₂ = C₁- to C₈-alkylene and
R₃ = H, C₁- to C₈-alkyl or aminoalkyl
before networking. 2. Inhibiting coating according to claim 1, obtainable by direct grafting of the aminosiloxane onto the siloxane Base material before crosslinking. 3. inhibiting coating according to claim 1 or 2, characterized characterized in that the amount of amino used siloxane 0.5 to 8 wt .-%, based on the silicone system, is.   4. An inhibiting coating according to any one of claims 1 to 3, obtainable with an aminosiloxane of the general formula With
R₁ = C₁ to C₄ alkyl,
R₂ = C₃- to C₈-alkylene and
R₃ = H or a lower aminoalkyl group. 5. inhibiting coating according to any one of claims 1 to 4, characterized in that the amount of used Aminosiloxane 1 to 6 wt .-%, based on the silicone system, is. 6. An inhibiting coating according to any one of claims 1 to 5, obtainable with γ-aminopropyltriethylsiloxane of the formula H₂N-CH₂-CH₂-CH₂-Si (OC₂H₅) ₃ as aminosiloxane. 7. Inhibiting coating according to one of claims 1 to 5, available with N- (β-aminoethyl) -γ-aminopropyltrimethyl siloxane of the formula H₂N-C₂H₄-NH-C₃H₆-Si (OCH₃) ₃. 8. inhibiting coating according to any one of claims 1 to 7, obtainable by the silicone system prior to introduction of the aminosiloxane is filled with fibers.