Method of bonding layer of elastomeric material to aluminum substrate

Abstract

The invention relates to a method for bonding a layer of elastomeric material (CE) to an aluminum substrate (SM), characterised in that it comprises the following steps: a) treating the surface (S) of the aluminum substrate (SM) in order to roughen it; b) treating the surface (S) by means of argon plasma; c) exposing said surface (S) to a plasma in the presence of a gaseous chemical precursor selected from the group consisting of epoxides, acrylics, olefins, alkynes and imides, until a deposit of chemical substances having a thickness of 5 nm to 110 nm is obtained; d) bringing the layer of elastomeric material (CE) into contact with the surface (S) of the aluminum substrate (SM); e) vulcanizing the layer of elastomeric material, said step c) being carried out at a low pressure, i.e. At a pressure of 10-2 mbar to 10-5 mbar.

Description

Technical Field

[0001] The present invention relates to a method of bonding a layer of elastomeric material to an aluminum substrate.

[0002] It is particularly suitable for use in the aviation sector, for example in the manufacture of fuel tanks or defrost devices. Background Art

[0003] In many industrial sectors, manufactured products are made from assemblies of materials including elastomers. In order to ensure their mechanical strength, the substrates on which the elastomers are deposited are covered with an adhesive.

[0004] The need for high mechanical properties increases the complexity of the methods for depositing these agents. In fact, the deposition process is usually manual, involving the repeated application of one or more adhesive layers and depending on the complex geometry of the parts to be assembled.

[0005] Thus, in the aeronautical field, it is known to manufacture fuel tanks and defrost devices from elastomeric products, requiring the gluing of thermoplastics and vulcanized rubber substrates to metal.

[0006] In the case of fuel tanks, they integrate accessories of different chemical nature, which are assembled by gluing to the rest of the product wall. These gluing processes must therefore provide a perfect seal and significant mechanical resistance. Thus, for example, in order to meet crash tests, these fuel tanks must remain sealed during a fall from a standard height of 15 meters.

[0007] Therefore, the adhesion between the attachment and the tank wall is a critical parameter for these assemblies.

[0008] With regard to defrost devices, attempts are being made to achieve fewer mechanical constraints. On the other hand, these components must be able to withstand large temperature variations during operation (defrost cycle), ranging from -55°C at altitude (without icing) to approximately 100°C for metal RTDs assembled by bonding.

[0009] These limitations are caused by the different expansion of the components (metal / rubber). These products are subjected to adverse environmental conditions (temperature changes, humidity, presence of ozone, abrasion, etc.) due to their use in the environment outside the aircraft.

[0010] Until now, such components have been assembled by surface preparation of the metal substrate (eg sandblasting, grinding, sanding), cleaning, deposition of an adhesive primer, deposition of a glue layer and finally gluing with an elastomer layer.

[0011] These components are integrated into the manufacture of the product (fuel tank or defrost unit) and are then placed under vacuum and vulcanized in an autoclave.

[0012] Adhesive primers and glue layers are usually in liquid phase (water-based or organic). Therefore, operators are exposed to chemicals that are potentially harmful to health. In addition, regulations on chemical risks are becoming increasingly stringent, and some adhesive products are facing elimination.

[0013] Therefore, some bonding primers use ethanol and ethyl acetate, both of which are very flammable, and ethyl acetate is also an irritant.

[0014] The relevant prior art consists of document US2017 / 154866 and the article “Characterization of functionalized coatings prepared from pulsed plasma polymerization” (JI Marisol et al. / 2021).

[0015] The object of the present invention is to overcome the above mentioned problems and for this purpose proposes a metal / elastomer assembly technique, in this case aluminium / elastomer, which is achieved by dry preparation of the substrates, that is to say without the use of bonding primers or glues at the metal / rubber interface. Summary of the invention

[0016] Therefore, the present invention relates to a method for bonding a layer of elastic material to an aluminum substrate, characterized in that the method comprises carrying out the following steps:

[0017] a) treating the surface of the aluminum substrate to roughen it;

[0018] b) treating the surface by argon plasma;

[0019] c) exposing the surface to a plasma in the presence of a gaseous chemical precursor selected from the group consisting of epoxides, acrylics, olefins, alkynes and imides until a chemical deposit having a thickness of 5 nm to 110 nm is obtained;

[0020] d) bringing the elastic material layer (CE) into contact with the surface (S) of the aluminum substrate;

[0021] e) vulcanizing the elastic material layer, wherein step c) is performed under low pressure, i.e. at 10 -2 mbar to 10 -5 mbar pressure.

[0022] Thanks to the invention, the use of liquid bonding chemicals used hitherto is eliminated.

[0023] Furthermore, unlike the prior art, where, due to manual methods, inhomogeneities were observed during the preparation of the metal surface prior to bonding, the method according to the invention is easier to implement, in particular due to the reduction in the number of steps and labor savings during the preparation of the metal surface.

[0024] Furthermore, the deposition of the chemical is uniform in composition and thickness, regardless of the part geometry.

[0025] Furthermore, a thinner deposit thickness (5 nm - 100 nm) is achieved compared to 100 μm for prior art primers.

[0026] It should also be noted that steps b) and c) can be performed during masked time since they do not require labor during the plasma treatment process.

[0027] Finally, the approach helps reduce the environmental footprint of the technology, particularly by reducing the use of chemical products that violate existing or future environmental standards and regulations.

[0028] Other advantageous but non-limiting features according to the invention are as follows:

[0029] In step a), the surface is treated until a roughness Ra of 2 to 20 microns is obtained;

[0030] In step a), the surface treatment is performed by laser ablation or by mechanical treatment such as shot peening, sanding or scraping;

[0031] Step c) is carried out using argon plasma;

[0032] Step c) is carried out under the following operating conditions:

[0033] - Pulsed plasma mode;

[0034] - Power: 5W to 600W, preferably 5W to 100W;

[0035] - Frequency: 5KHz to 50KHz, preferably 5KHz to 30KHz;

[0036] - Argon flow rate: 5 cm 3 / min to 50cm 3 / minute, preferably 10cm 3 / min to 40cm 3 / minute;

[0037] - Total duration: 11 minutes to 60 minutes;

[0038] - Duty cycle: 4% to 30%, preferably 8% to 11% for pulse mode. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Other characteristics and advantages of the invention will emerge from the description given hereinafter, with reference to the accompanying drawings which show, in an indicative and non-limiting way, possible embodiments of the invention.

[0040] In these drawings:

[0041] Figure 1 is a very simplified schematic diagram of an assembly obtained according to the method of the invention. DETAILED DESCRIPTION

[0042] As mentioned above, the method according to the present invention comprises performing the following steps:

[0043] a) treating the surface of the aluminum substrate to roughen it;

[0044] b) treating the substrate surface by argon plasma;

[0045] c) exposing the substrate surface to a plasma, in particular an argon plasma, in the presence of a chemical precursor selected from the group consisting of epoxides, acrylics, olefins, alkynes and imides, until a chemical substance deposit having a thickness of 5 nm to 110 nm is obtained;

[0046] d) contacting the elastic material layer with the surface of an aluminum substrate;

[0047] e) Vulcanizing the elastomeric material layer.

[0048] Each of these steps and their variations and / or preferred embodiments are described below.

[0049] Treating the surface of the aluminum substrate to make it rough

[0050] The purpose of this treatment is to prepare the free surface S of the metal substrate SM (see Figure 1 ) to facilitate the subsequent anchoring of the chemical species layer produced in the subsequent plasma treatment step.

[0051] It is also intended to remove common anti-corrosion protective layers, such as sulfuric acid anodizing (abbreviated "SAO"), from the surface of metal substrates.

[0052] Preferably, the surface is treated until a roughness Ra of 2 to 20 microns is obtained.

[0053] To do this, laser ablation may be used or mechanical processing may be used to create a roughened surface, such as shot peening, sanding or scratching.

[0054] Argon plasma treatment of the substrate surface

[0055] The main purpose of this treatment is to remove from the surface S of the substrate SM any oxides that may have formed thereon and any organic contaminants. In fact, between the previous step and this one, a "reoxidation" may have occurred.

[0056] Advantageously, the treatment may be carried out under the following parameters:

[0057] - Plasma in continuous mode;

[0058] -Power: 200W;

[0059] - Argon flow rate: 20cm 3 / minute;

[0060] - Duration: 20 minutes.

[0061] The surface is exposed to a plasma, such as an argon plasma, in the presence of a chemical precursor.

[0062] This precursor allows the creation, by plasma deposition, of a polymer layer that will render the metal surface chemically compatible with the elastomer.

[0063] The thickness of the layer must be sufficient to allow interdiffusion of the polymers.

[0064] According to the invention, the precursor is selected from epoxy compounds, acrylic compounds, olefins, alkynes and imides until a chemical substance deposit having a thickness of 5 nm to 110 nm is obtained (at Figure 1 DP in the figure).

[0065] For example, acetylene gas.

[0066] It should be noted that thicknesses below the above mentioned thicknesses result in a mechanical resistance lower than that required. This can also result in poor metal coverage.

[0067] Above 110 nm, no significant improvement in adhesion was detected and too thick a layer would lead to internal stress embrittlement.

[0068] Advantageously, this step is carried out under the following operating conditions:

[0069] - Pulsed plasma mode;

[0070] - Power: 5W to 600W, preferably 5W to 100W;

[0071] - Frequency: 5KHz to 50KHz, preferably 5KHz to 30KHz;

[0072] - Argon flow rate: 5 cm 3 / min to 50cm 3 / minute, preferably 10cm 3 / min to 40cm3 / minute;

[0073] - Total duration: 11 minutes to 60 minutes;

[0074] - Duty cycle: 4% to 30%, preferably 8% to 11% for pulse mode.

[0075] These operating conditions promote the growth of the deposit DP, which in a subsequent step undergoes interdiffusion between the deposit and the elastomer layer.

[0076] The elastic material layer is brought into contact with the surface of the aluminum substrate

[0077] The substrate SM is then used to bond with an elastomeric layer such as PVC-NBR (a mixture of polyvinyl chloride and butadiene-acrylonitrile) (in Figure 1 The samples were assembled as shown in Figure 5 (marked as CE).

[0078] If necessary, the contact surface of the elastomer has been previously and advantageously brightened with a solvent in order to provide "stickiness" to the surface before assembly. In other words, this operation not only cleans the surface, but also swells the elastomer to facilitate diffusion / migration towards the deposit.

[0079] Elastomers such as polyurethane elastomers and EVA (ethylene vinyl acetate) may also be used.

[0080] Vulcanized elastomeric material layer

[0081] The assembly thus obtained is, for example, placed under vacuum and vulcanized. In this step, chemical anchoring occurs due to the reactivity between the plasma deposit DP and the elastomer to be vulcanized.

[0082] Another method is to perform the vulcanization under pressure.

[0083] A thickness of material, such as an impact resistant AC material, may then be bonded to the surface opposite the elastomeric layer CE.

[0084] The anti-collision material is usually a polyamide-based fabric with an elastomeric coating. The coated side of the fabric is manually brought into contact with the brightness-enhancing layer of elastomer CE. After this contact, the assembly is compacted using a notched roller.

[0085] Alternatively, one or more thicknesses of material reinforced with textiles or other components / substrates may be used, depending on the intended application.

[0086] In the attached Figure 1 The thickness shown does not reflect the actual situation.

[0087] For purely indicative purposes these thicknesses are as follows:

[0088] SM: less than 4 mm;

[0089] DP: 5nm to 110nm;

[0090] CE: 0.2 mm to 2 mm;

[0091] AC: 0.1 mm to 10 mm.

[0092] According to this method, adhesion test specimens are assembled and cured in an autoclave.

[0093] The adhesion values ​​thus obtained are higher than the value required by the standard TSO-C80 (2 N / mm).

[0094] Regarding the stability of the metal / elastomer interface in contact with the fuel, adhesion values ​​greater than 1.08 N / mm were observed after immersion in an isooctane / toluene mixture.

Claims

1. A method for bonding a layer of elastic material (CE) to an aluminum substrate (SM), characterized in that The method comprises performing the following steps: a) treating the surface (S) of the aluminum substrate (SM) to roughen it; b) treating the surface (S) by argon plasma; c) exposing the surface (S) to a plasma in the presence of a gaseous chemical precursor selected from the group consisting of epoxides, acrylics, olefins, alkynes and imides until a chemical deposit having a thickness of 5 nm to 110 nm is obtained; d) bringing the layer of elastic material (CE) into contact with the surface (S) of the aluminum substrate (SM); e) vulcanizing the elastic material layer, wherein step c) is performed under low pressure, i.e. at 10 -2 mbar to 10 -5 mbar pressure.

2. The method according to claim 1, characterized in that In step a), the surface (S) is treated until a roughness Ra of 2 to 20 microns is obtained.

3. The method according to claim 1 or 2, characterized in that: In step a), the surface treatment (S) is performed by laser ablation or by mechanical treatment such as shot peening, sanding or scraping.

4. The method according to any one of claims 1 to 3, characterized in that Step c) is carried out using argon plasma.

5. The method according to one of the preceding claims, characterized in that The step c) is carried out under the following operating conditions: - Pulsed plasma mode; - Power: 5W to 600W, preferably 5W to 100W; - Frequency: 5KHz to 50KHz, preferably 5KHz to 30KHz; - Argon flow rate: 5 cm 3 / min to 50cm 3 / minute, preferably 10cm 3 / min to 40cm 3 / minute; - Total duration: 11 minutes to 60 minutes; - Duty cycle: 4% to 30%, preferably 8% to 11% for pulse mode.

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