EP4041786A1

EP4041786A1 - Method for covering the inner surface of a tank

Info

Publication number: EP4041786A1
Application number: EP20797821.4A
Authority: EP
Inventors: Antoine Lavaud; Yann Guelou
Original assignee: Cmp Composites; Centre National dEtudes Spatiales CNES
Current assignee: Cmp Composites; Centre National dEtudes Spatiales CNES
Priority date: 2019-10-11
Filing date: 2020-10-09
Publication date: 2022-08-17
Also published as: WO2021069848A1; FR3101807A1; FR3101807B1

Abstract

Method for covering the inner surface (2) of a tank (100), the method comprising the following steps: - a) providing a tank (100) made of a composite material, such as a thermoplastic material or a thermosetting material, the tank being configured to receive a pressurised fluid, - b) spraying a liquid composition (6) comprising a fluoropolymer, a prepolymer and a crosslinking agent of the prepolymer onto the inner surface (2) of the tank (100) so as to form a cover layer (7) covering the inner surface (2), and - c) polymerising the cover layer (7) so as to generate a polymeric binder encapsulating the fluoropolymer and form a fluorinated coating (8) covering at least part of the inner surface (2).

Description

DESCRIPTION

TITLE: PROCESS FOR COVERING THE INTERNAL SURFACE OF A

TANK

The present invention relates to a method for covering the internal surface of a tank, intended to receive cryogenic propellants or other flammable fuels (fuel / oxidizer), for applications in particular in the space field, aeronautics or for land vehicles. . According to another aspect, the present invention relates to a reservoir comprising a fluorinated coating generated according to said coating method.

The tanks receiving fluids under pressure in the space field must be light, resistant, tight and their price must be attractive. Until now, in order to withstand very low temperatures while retaining satisfactory sealing properties, these tanks were designed in metal and more generally in aluminum. However, the cost of forming the metal is high and the designed tank is heavy. Engineers then turned to the use of lighter materials, such as composite materials, formed from thermoplastic or thermosetting polymers which have good mechanical resistance.

However, a new problem has arisen with the use of these composite materials. Indeed, their tightness is severely tested due to the pressure of the fluid received, cryogenic operating temperatures and thermal shocks. The majority of these composite materials tire and microcracks appear which can lead to leaks. Tanks formed from these materials give rise to leaks incompatible with use in launchers.

One recommended solution requires the use of a very thin internal metal casing placed in the composite material reservoir. However, the cost of manufacturing such an envelope remains prohibitive.

An alternative solution recommended consists in inserting, during the manufacture of the reservoir, a sealed envelope of a polymeric material. The nature of the polymer is chosen for its compatibility with the storage of liquid oxygen (LOX according to English terminology). This envelope is formed by rotational molding on a steel mold to shape a skin of polymeric material, which is then placed in the shell with a view to being bonded there to the internal surface. The skin thus positioned in the shell must have a sufficiently large thickness to be able to be handled without deterioration. Therefore, the cycle time is long, the amount of material for forming thick skin is large and expensive. In addition, the use of materials with heterogeneous thermomechanical characteristics induces a risk of decohesion between the various constituent elements of the tank. The handling of the skin after manufacture remains delicate even when it is thick.

One of the aims of the present invention is to overcome these drawbacks. To this end, the present invention provides a method of covering the internal surface of a tank, the method comprising the following steps:

-a) supply of a reservoir made of a composite material such as a thermoplastic material or a thermosetting material, configured to receive a pressurized fluid,

-b) spraying a liquid composition comprising a fluoropolymer, a prepolymer and a crosslinking agent of said prepolymer, on the internal surface of the reservoir, so as to form a covering layer covering the internal surface, and

-c) polymerization of the covering layer so as to generate a polymer binder encapsulating the fluoropolymer and to form a fluoropolymer covering at least partially the internal surface.

Thus, the present invention provides a method of covering a reservoir with an envelope of fluorinated material formed in situ, directly in the reservoir. This avoids a two-step process consisting in forming a tight skin and then applying it against the internal surface of the reservoir. According to the present invention, the fact of spraying the composition directly on the internal surface of the reservoir avoids having to use any other additional material and fades the risks of microcracks appearing with repeated thermal shocks and the pressure applied. In addition, the method according to the invention allows quality adhesion of the fluorinated coating on a surface made of thermoplastic material, which remains delicate with conventional application methods.

Also, the cycle time of the recovery process is reduced. The reservoir can be prepared in series and the fluorinated coating is rapidly obtained by simple spraying in situ on the internal surface of a liquid composition comprising a fluoropolymer, a prepolymer with its crosslinking agent, followed by its polymerization.

In addition, in this embodiment consisting in forming the fluorinated coating by direct deposition, the method avoids the constraints of handling a rotomolded skin such as provided in the prior art since the fluorinated coating is formed by depositing the precursor materials. in situ. The method according to the present The invention is also exempt from a step consisting in positioning and making said skin adhere to the reservoir in a leaktight manner.

According to the invention, it is no longer necessary to manufacture a skin in the form of a self-supporting layer, necessarily thick in order to be able to be handled and having to at least reach a thickness of the order of 10-15 mm.

The coating of the present invention having the aim of limiting the permeability of the tank to the gaseous sky of the liquid which it contains when used in a tank for liquid propellant, or the permeability to the gas itself for use in a tank gas only, which is critical for the small molecules of H2, He and a little less critical for the molecules of Ü2, CH ₄ , it is not necessary to achieve such large thicknesses. Thus, the method according to the invention makes it possible to limit the thickness necessarily obtained in the prior art.

The fluorinated coating of the invention being formed in situ on the walls of the reservoir, it is not necessary to move it after formation, and it is thus limited to a fluorinated coating of approximately 1 mm at most. Of course, the cycle time to reach this thickness is shorter and also less expensive in terms of the quantity of raw materials required, but also makes it possible to reduce the overall mass of a tank.

In addition, the fact of using a fluoropolymer and therefore not oxidizable by oxygen makes it possible to obtain a coating compatible with LOX and GOX (from the English terminology “Gaseous Oxygen” meaning gaseous oxygen), which is important. for tanks receiving and storing gaseous or liquid oxidants.

In addition, the fluoropolymer family of materials retains non-zero ductility even around cryogenic temperatures. Thus the risks of microcracks observed in other polymers are very limited in the case of using these fluoropolymers at low temperature. These fluoropolymers thus retain very good sealing at the operating temperatures considered.

By “polymerization of the covering layer”, it is understood in the present document, the crosslinking of the prepolymer using the associated crosslinking agent by encapsulating the fluoropolymer present in the liquid composition.

By the term “composite material” is meant in the present document, in accordance with the knowledge of a person skilled in the art, an assembly of at least two immiscible components, but having a high penetration capacity, and whose properties complement each other, to form a material with improved overall performance. Preferably, the spraying step b) is carried out so as to cover the entire internal surface of the reservoir so as to obtain a fluorinated coating covering the entire internal surface.

Advantageously, the spraying step b) is carried out so as to obtain a covering layer having a substantially constant thickness of between 10 micrometers and 50 micrometers.

To do this, step b) is carried out with a rotational movement of the reservoir or a rotation of a spray rod for the liquid composition around an axis of extension E along which the reservoir extends and a displacement in translation of the spray rod along the axis of extension E of the reservoir concomitantly with the rotation. The speeds of these movements are optimized according to the viscosity of the liquid composition, the area of the internal surface to be covered and the diameter of the reservoir, the spray rate of the liquid composition and the adhesion properties of said composition.

This method facilitates the spraying of the liquid composition on the internal surface so that its coverage by the liquid composition can be complete. The covering layer obtained is thus deposited uniformly over the entire internal surface of the reservoir, in a circumferential as well as a longitudinal direction (along the extension axis E).

The spray rod is advantageously an endoscopic rod.

The interfacial tension between the surface of the reservoir and the liquid composition coupled with the rotation of the reservoir or of the spray rod make it possible to avoid drips.

The covering layer is thus deposited and is smooth, that is to say that it exhibits little or no irregularities so as to obtain a very low roughness and a very limited risk of the appearance of bubbles.

This method thus makes it possible to optimize the quantity of sprayed liquid composition. This results in very limited risks of sagging and the formation of a qualitative layer. Any sags obtained according to a conventional process are liable to generate differences in homogeneity in the thickness of the layer and may make the subsequent polymerization more complex to configure. By avoiding runs and high roughness, the process is more easily reproducible, with the same amount of liquid composition, the formed cover layer always covers the same internal surface area of the tank.

Thanks to this process, the liquid composition is then polymerized homogeneously (uniform layer) over the entire internal surface of the tank. This precision spraying enables optimum and regular polymerization to be carried out for also optimum cycle time.

In addition, the fluorinated coating thus formed has substantially identical properties regardless of the location considered on the internal surface of the reservoir.

According to one possibility, the spraying is carried out from at least one nozzle adapted to the fluidity of the sprayed liquid composition. In the case of the use of a fixed injection head, the reservoir and the device allowing the implementation of the method are configured to ensure the mobility of the reservoir, including a displacement capacity along the extension axis E to a determined speed.

According to one arrangement, step b) and step c) are repeated n times, so as to obtain a fluorinated coating formed of a stack of n covering layers, n being an integer between 1 and 20. Thus, the thickness of the fluorinated coating obtained can be parameterized by repeating the operations of steps b) and c) according to a chosen value of n. The value of the thickness of the fluorinated coating is not dictated by manufacturing constraints. It is freely chosen, to meet the needs and according to the targeted applications.

The fine adjustment of the thickness of each of the deposited layers makes it possible to obtain a precise and optimal fluoride coating thickness. The additional costs are thus avoided.

The thickness of the final fluorinated coating is in particular between approximately 10 micrometers to 1 mm for conventional use of the reservoir at around 80 K (ie approximately -193 ° C.).

This very thin final thickness promotes the resistance of the fluorinated coating to the internal surface. Also, the excess weight associated with the presence of the fluorinated coating is minimal compared to the weight of the tank alone.

According to an alternative embodiment, the method further comprises, between step b) and step c): a step d) of partial polymerization of the prepolymer, and a step e) of additional spraying of the liquid composition.

This exemplary embodiment is particularly relevant in the case where a single spraying of step b) does not lead to a sufficiently thick fluorinated coating. Taking into account the constraint linked to the fact that the spraying must make it possible to obtain a homogeneous layer of uniform thickness, it is not possible to increase the amount of the sprayed liquid composition, it is necessary to carry out the spraying / polymerization steps several times. However, we encounter a new problem if the sprayed material contains Teflon ^® (brand of PTFE, acronym of the term PolyTetraFluoroEthylène). Indeed, the adhesion of an additional layer of Teflon ^® which is deposited on a first layer of Teflon ^® could not be good if the polymerization of the composition were complete. On the other hand, partial polymerization of the first layer of Teflon ^® makes it possible to obtain good adhesion of the additional layer of Teflon ^® . The experiments and analyzes of a section of the fluorinated coating obtained at the end of the process showed no sign of the presence of a stack of different covering layers which would suggest a probable delamination in the long term. In contrast, the final fluorinated coating exhibits the appearance and behavior of a monolayer. This ensures great cohesion to the fluorinated coating, which contributes to its longevity, its mechanical resistance and its resistance to the internal surface of the tank. It is moreover resistant to significant thermal shocks (between 70 K and 273 K) and to cryogenic temperatures in the same way as a fluorinated coating obtained from the spraying of a single layer.

For example, a sample of composite material covered with a fluorinated coating does not degrade after soaking for 30 seconds in liquid nitrogen. This quenching is repeated ten times and after each quenching, the coating is brought back to room temperature. Also, after each quenching, observation with a binocular magnifying glass and then with a scanning electron microscope of the interface of the fluorinated coating and of the composite material made it possible to observe that no detachment had taken place.

According to one possibility, steps d) and e) are repeated between 1 and 3 times. Thus, the fluorinated coating obtained at the end of the process has a thickness equivalent to that of two to five times the thickness of a sprayed layer.

According to one possibility, step c) is carried out in a heating device configured to heat the covering layer deposited in step b) until the fluoropolymer is obtained.

Of course, the heating of the deposited covering layer is carried out according to instructions determined according to the nature of the liquid composition (humidity, temperature and controlled duration, etc.). The heating device is an oven for example.

Advantageously, step b) and step c) are carried out in the same heating device. In this case, it is not necessary to handle and move the reservoir, as in the prior art. This limits the risk of damaging the tank during movement from the location where the projection is carried out to the heating device. This contributes to saving time during the implementation of the method. According to one arrangement, step a) comprises providing a tank comprising a shell delimiting said internal surface of the tank, the shell and the internal surface being made of a composite material, and in particular a composite material chosen from a thermoplastic material or a material. thermosetting, the shell being configured to receive a pressurized fluid, in particular a cryogenic propellant. The pressure undergone by the hull can vary according to the targeted applications between 3 and 60 bars. As part of the transport of liquid hydrogen, the tank must remain impermeable to pressures of the order of 3-4 bars. When using a small-sized space engine without a turbopump, the required fluid pressure will be all the higher, up to 40-60 bars.

Preferably, the fluorinated coating obtained mainly comprises a fluorinated polymer such as a type of PTFE Teflon ^®, Viton ^®, a FEP (Fluorinated Ethylene Propylene), PVF (Poly Vinyl Fluoride), and a polymeric binder such as an epoxide, a polyamide, a polyethersulfone, a polyimide, a polyaryletherketone, a polyurethane, a bio-based polymer. The fluoropolymer can also comprise at least one additive such as a pigment, an adhesion agent, an antistatic agent, an electrically conductive agent, etc. For example, the fluoropolymer is present in a proportion ranging from 70 to 80% by weight, the polymer binder is present in a proportion ranging from 10 to 16% by weight and the additive is present in a proportion ranging from 4 to 15% by weight, all of these components of the fluorinated coating forming 100% by weight.

The liquid composition making it possible to obtain the coating can also comprise a solvent such as acetone, an alcohol, a methyl ethyl ketone, xylene, water, in a proportion making it possible to obtain a viscosity suitable for spraying. desired.

The polymer binder makes it possible to hold the sprayed covering layer on the internal surface of the tank, while the fluoropolymer will be at the origin of the characteristics including the mechanical properties of the fluorinated coating. Of course, the polymer binder is not a fluorinated material. The additives are mainly adhesion agents and / or agents improving the electrical conductivity. The presence of a solvent makes it possible to facilitate the dissolution of the polymer binder and to adapt the viscosity of the liquid composition to optimize the spraying.

According to one arrangement, polymerization step c) is carried out in an oven in which the reservoir supplied in step a) is placed. During this step, the precursor of the polymer binder is heated to a polymerization temperature Tp.

Of course, the nature of the polymer binder is chosen so that its temperature Tp is lower than the degradation temperature of the materials constituting said. reservoir, in particular when the reservoir provided in step a) comprises a shell made of composite material, composed of thermosetting or thermoplastic materials.

According to an alternative embodiment, the precursor of the polymer binder of the liquid composition is a polymer which polymerizes under the action of UV radiation.

Step c) then consists in applying a treatment by UV radiation in the direction of the covering layer of the liquid composition. It is then possible to polymerize the deposited layer as its deposition progresses in situ in the spraying device. The cycle time for the manufacture of the fluorinated coating is thus very short. Step b) and step c) are carried out with a slight time lag. For example, the UV radiation is produced in parallel with the rotation of the reservoir and the movement of the spray rod spraying the liquid composition of step b). This variant also makes it possible not to heat the surrounding materials because when using a UV diode, the illuminated surface does not heat up. In addition, the sprayed layer is hardened rapidly as it is deposited, so that its thickness is very regular and homogeneous. This also saves time on the manufacturing cycle.

Advantageously, the reservoir provided in step a) extends along an axis of extension E arranged substantially vertically,

the spraying of step b) is carried out by a spray rod configured to move in translation along the extension axis E and to move in rotation around said extension axis E concomitantly, and

- step c) comprises the application of UV radiation in the direction of the cover layer.

In this variant embodiment, the application of UV radiation is advantageously carried out by a source of UV radiation provided on said spray rod. It is not necessary for the reservoir to be rotated in steps b and c).

According to yet another variant embodiment, the precursor of the polymer binder is capable of crosslinking by application of a heat treatment. The recovery process is then carried out so that

- the reservoir supplied in step a) extends along an axis of extension E arranged substantially vertically,

the spraying of step b) is carried out by a spray rod configured to move in translation along the extension axis E and to move in rotation around said extension axis E concomitantly, and - step c) comprises the application of IR irradiation in the direction of the cover layer.

Advantageously, the application of IR irradiation is carried out by an IR source provided on said spray rod. Steps b) and c) are thus carried out with a slight time lag in order to obtain the fluorinated coating very quickly. In addition, it is not necessary for the reservoir to be rotated in steps b and c).

In the case where step c) does not include UV or IR radiation, but for example when step c) is carried out by a heat treatment in an oven, the process is carried out so that during step b): the reservoir is driven in rotation around the extension axis E placed substantially horizontally, the spraying is carried out using a spray rod configured to move in translation along of the axis of extension E concomitantly with the rotation of the reservoir, and that during step c) the reservoir is driven in rotation around the axis of extension E until the end of the polymerization.

Preferably, the method comprises between step a) of supplying the reservoir and step b) of spraying the liquid composition, a step k) of activating the internal surface condition of the reservoir so as to optimize the resistance of the fluoride coating and coating. Consequently, the adhesion of the fluorinated coating is optimal.

Step k) comprises a step i) of surface preparation consisting of cleaning the internal surface of the tank with a chemical solvent and / or steam degreasing, which makes it possible to remove contaminating residues from the surface which may alter the surface. holding of the deposit of the liquid composition.

Step k) also comprises or as an alternative to step i), a step ii) of micro-sandblasting or micro-blasting of the internal surface of the reservoir making it possible to increase its specific surface. This mechanical surface treatment increasing the roughness makes it possible to artificially increase the adhesion surface of the reservoir and allows better adhesion of the fluorinated coating. For example, the internal surface of the reservoir has a roughness Ra of 1 to 2 nm rms after step k).

The increase in the roughness of the internal surface generates better grip of the sprayed liquid composition. The deposition and obtaining of a uniform covering layer, of a substantially constant thickness, is facilitated, in particular on composite materials made of thermoplastic or thermosetting materials. According to one possibility, step k) comprises as an alternative or in addition to steps i) and ii) a plasma or corona treatment applied to the internal surface of the reservoir.

According to another aspect, the invention provides a reservoir intended to receive and store a fluid under pressure, in particular at cryogenic temperatures, the reservoir is made of a composite material and comprises an internal surface covered at least partially by a fluorinated coating comprising a fluoropolymer. and a polymeric binder. This coating is obtained by spraying a liquid composition comprising a fluoropolymer, a prepolymer and a crosslinking agent of said prepolymer, on the internal surface of the reservoir, and polymerization so as to generate a polymer binder encapsulating the fluoropolymer for forming a fluorinated coating covering at least part of the internal surface.

Said reservoir is thus prepared to receive a fluid under a pressure of 3 bars to 60 bars.

Preferably, the internal surface is completely covered by the fluorinated coating. In other words, the coverage offered by the fluorinated coating is such that it covers the entire internal surface of the reservoir intended to be in contact, even indirectly, with the fluid received in the reservoir.

It is understood in the present application that the fluorinated coating is in direct contact with the internal surface of the reservoir. By the expression “direct contact” is meant in the present document that the association between the reservoir and the fluorinated coating is devoid of any element other than the material constituting the internal surface of the reservoir and the fluorinated coating. The present invention thus avoids the use of any adhesive or element having an adhesion or bonding role between the reservoir and the fluorinated coating.

According to one arrangement, the reservoir comprises a shell delimiting said internal surface of the reservoir covered by the fluorinated coating, the shell and the internal surface being made of composite material, and in particular a composite material chosen from a thermoplastic material such as polyvinyl chloride or a polyaryl ether ketone, or a thermosetting material, such as a polyester or an epoxy, configured to receive a pressurized fluid, in particular cryogenic propellants.

Advantageously, the fluorinated coating has a thickness of between 10 micrometers and 1 mm. This thin covering layer is resistant to large-amplitude thermal variations (293K -70K), remains attached to the tank in use even under drastic conditions and makes it possible to increase the permeability limits of the tank to gas, even in the case of molecules of small sizes (H2, He, etc ...). In other words, the present invention relates to a method of covering the internal surface of a shell of a tank intended to receive a cryogenic propellant, the method comprising the following steps:

-a) providing a shell of a tank, the shell being made of a composite material, such as a thermoplastic material or a thermosetting material, and configured to receive a pressurized fluid,

-b) spraying a liquid composition comprising a fluoropolymer, a prepolymer and a crosslinking agent of said prepolymer, on the internal surface of the shell of the tank, so as to form a covering layer covering the internal surface, and

-c) polymerization of the covering layer so as to generate a polymer binder encapsulating the fluoropolymer and to form a fluoropolymer covering at least partially the internal surface of the shell and to obtain the tank for cryogenic propellant.

According to other characteristics, the method of the invention comprises one or more of the following optional characteristics considered alone or in combination. said covering layer formed in step b) has a substantially constant thickness and preferably between 10 micrometers and 50 micrometers.

Step b) and step c) are repeated n times so as to obtain a fluorinated coating formed by a stack of n covering layers, n being an integer between 1 and 20.

Between step b) and step c) there is provided a step d) of partial polymerization of said prepolymer, and a step e) of additional spraying of the liquid composition.

Step c) is carried out in a heating device configured to heat the covering layer deposited in step b) until the fluorinated coating according to step c) is obtained.

The tank shell extends along an extension axis E and during step b), the tank shell is rotated around the extension axis E, and spraying is performed using a spray rod configured to move in translation along the extension axis E concomitantly with the rotation of the shell of the tank. Step a) comprises the provision of the shell delimiting said internal surface of the tank, the shell and the internal surface being made of composite material, and in particular a composite material, composed of materials thermoplastics, such as polyvinyl chloride or a polyaryl ether ketone, or thermosetting materials, such as a polyester or an epoxy, the shell being configured to receive a pressurized fluid, in particular a cryogenic propellant.

The fluorinated coating comprises predominantly a fluorine-containing polymer such as a type of PTFE Teflon ^®, Viton ^®, a FEP (Fluorinated Ethylene Propylene), PVF (Poly Vinyl Fluoride) and a polymeric binder, such as epoxy, polyamide, polyethersulfone, a polyimide, a polyaryletherketone, a polyurethane, a bio-based polymer.

The prepolymer of the liquid composition is capable of polymerizing under the action of UV radiation.

The shell of the tank provided in step (a) extends along an extension axis E disposed substantially vertically, the spraying of step b) is carried out by a spray rod configured to move in translation on the along the extension axis E and to move in rotation around said extension axis E concomitantly, and step c) comprises applying UV radiation towards the cover layer.

The shell of the tank provided in step (a) extends along an extension axis E arranged substantially vertically, the spraying of step b) is carried out by a spray rod configured to move in translation on the along the extension axis E and to move in rotation around said extension axis E concomitantly, and step c) comprises applying IR irradiation towards the cover layer.

Between step a) of supplying the shell of the reservoir and step b) of spraying the liquid composition, the method comprises a step k) of activating the internal surface condition of the shell of the reservoir so to optimize the resistance of the covering layer and of the fluorinated coating. According to another aspect, the present invention relates to a tank intended to receive a cryogenic propellant, the tank comprising a shell which is made of composite material and which delimits an internal surface of the tank, said internal surface being covered at least partially by a fluorinated coating comprising a fluoropolymer and a polymeric binder. According to other characteristics, the reservoir of the invention comprises one or more of the following optional characteristics considered alone or in combination.

The composite material is composed of thermoplastic materials or thermosetting materials, the shell being configured to receive a pressurized fluid, in particular a cryogenic propellant.

The fluorinated coating has a substantially constant thickness of between 10 micrometers and 1 mm.

The composite material includes fibers selected from T300, T700, T800, and IM7.

The composite material comprises resins selected from hexcel 8552, Hexcel M18, Hexcel 914, Hexcel 3501, and Arkema Elium.

The composite material is made up of fiber / resin pairs chosen from Toray T300 / Hexcel 5208, Toray T300 / Hexcel 914, Hexcel IM6 / 914, Hexcel M55J / M18, Hexcel AS4 / 3501-6, Hexcel IM7 / 8552, and the Toray T700 / Arkema Elium couple.

Other characteristics and advantages of the present invention will emerge clearly from the detailed description below of an embodiment, given by way of non-limiting example, with reference to the accompanying drawings.

In the remainder of the description, for the sake of simplification, the elements common to the various embodiments bear the same numerical references in which:

[fig. 1] illustrates a sectional view of a reservoir during a spraying step according to a first embodiment of the method of the invention,

[fig. 2] illustrates a sectional view of a reservoir during a polymerization step according to a second embodiment of the process of the invention,

[fig. 3] illustrates a sectional view of a reservoir during a polymerization step according to a third embodiment of the process of the invention.

FIG. 1 illustrates steps a) and b) of the method according to the invention. It shows a reservoir 100 configured to receive a pressurized fluid supplied according to step a) of the process and a step b) of spraying a liquid composition 6 comprising a fluoropolymer, using a rod 4 provided a spray head including standard nozzles. To do this, the reservoir 100 is mounted on a device (not illustrated) allowing its rotation around its axis of extension E arranged horizontally. The reservoir 100 is also provided with a base 5 through which the spray rod 4 is introduced. The latter is mounted to move in translation in the direction of the axis. extension E so that the rotation of the reservoir 100 and the movement of the spray rod 4 make it possible to spray the liquid composition 6 at any point of the internal surface 2 of the reservoir 100 in the form of a covering layer 7. Thus, step b) is facilitated by the rotation of the reservoir 100 around its axis of extension E at the same time as the rod 4 is moved in translation along said axis of extension E. The rotational speed of the reservoir, which is adapted as a function of the viscosity of the liquid composition 6, the flow rate of the spraying, the wettability and the surface tension of the polymer, is of the order of 10 revolutions per minute for a reservoir with a diameter of between 250 mm and 600 mm. For a smaller diameter, such as 10 to 15 cm, the rotational speed can reach 90 rpm while for a larger diameter, for example 1 m, the rotational speed will be between 2 and 5 rpm.

The liquid composition 6 used comprises at least one fluoropolymer, a prepolymer and its crosslinking agent which will be polymerized by heat treatment to form a fluorinated coating 8 waterproofing the internal surface 2 of the tank 100. According to this embodiment, not visible in FIG. 1 the liquid composition 6 comprises a polymer based on Teflon ^® or Viton ^®, in a proportion of 70% by weight, a precursor of the polymeric binder of epoxy in an amount of 10% by weight, an additive in a proportion of 4% by weight and a toluene-based solvent in a proportion of 7% by weight, the whole of the composition forming 100% by weight. This makes it possible to achieve the appropriate properties, in particular in terms of viscosity which must be adapted for a homogeneous spraying, and a reduced propensity to sag once the composition 6 is sprayed on a tank 100 comprising a shell 1 formed of a thermoplastic material. . The covering layer 7 thus formed on the internal surface 2 has a uniform thickness exhibiting a small variation in thickness, which optimizes the subsequent polymerization. The expected fluorinated coating 8 will ultimately limit the permeability of the reservoir 100 to the fluid received and the risks of ignition in the presence of LOX or GOX. Certain ready-to-use liquid compositions 6 suitable for spraying to form a fluorinated coating 8 are commercially available.

The polymerization according to step c) is carried out by heat treatment in a heating device at a temperature Tp of 200 ° C. for 3 h. Advantageously, the heating device used is configured so as to allow prior spraying in situ. A step of moving the reservoir 100 between step a), b) and c) is thus avoided. At the end of the heat treatment, a fluorinated coating 8 with a thickness of 10-20 micrometers is then obtained, which ensures good impermeability to methane or to oxygen 02. Teflon ^® being LOX and GOX, it cannot be 'oxidize with oxygen, it leads to a fluorinated coating 8 of choice in terms of safety for the storage of 02 (fluorine being a more powerful oxidant than oxygen)

However, for small molecules such as H2 or He, it is necessary for the fluorinated coating 8 to have a greater thickness. According to an alternative embodiment not visible in FIG. 1, steps b) and c) are repeated 4 times so that the final thickness of the coating reaches approximately 60 micrometers.

In order to allow good adhesion of an ^{additional Teflon ®} covering layer 7 ^{on a previously formed Teflon ®} covering layer 7, the process according to which steps b) and c) are repeated is slightly adapted (not illustrated) . The modified method according to the invention provides for carrying out, between step b) and step c), a step d) of partial polymerization of the pre-polymer binder and of its crosslinking agent (non-fluorinated) of the covering layer 7 deposited. in step b), and a step e) of additional spraying of the liquid composition 6 on the partially polymerized covering layer 7. These steps d) and e) are repeated until the coating reaches the desired thickness, here four times to reach a thickness of about 60 micrometers. Total polymerization of the stack of cover layers 7 is obtained during the performance of step c) at the end of the process.

According to an arrangement not visible in FIG. 1, the method further comprises a step k) carried out before step b) consisting in preparing the surface condition of the reservoir 100 in order to optimize the grip of the covering layer 7 formed by spraying as well as that of the fluorinated coating 8 after polymerization. According to one possibility, this step k) consists of a succession of steps comprising a step i) of cleaning the internal surface 2 of the reservoir 100, and a step ii) of sandblasting at grain 600 to increase the internal specific surface of the reservoir 2 until a roughness Ra of 1 to 2 nm rms is reached. According to a variant not shown, the preparation of step k) comprises only one of these steps or else an alternative step such as a microbeading of the internal surface 2 of the reservoir 100 or a plasma or corona treatment step applied. on the inner surface 2.

FIG. 2 illustrates a process different from that described above, in particular in that the liquid composition 6 comprises a polymeric binder which can be polymerized under ultraviolet (UV) illumination. Thus a liquid composition 6 comprising a binder of photopolymerizable polyacrylic type (Urethane type Acrylate) is sprayed using an endoscopic cane 4 so as to cover the entire internal surface 2 of the reservoir 100. As illustrated in FIG. 2, a UV illumination source 11 of the diode type such as a LED emitting UV radiation (between 200 and 470 nm) is used to apply UV in the direction of the internal surface 2 covered by the liquid composition 6. The frequency of the UV LED is judiciously chosen according to the maximum absorption frequency for the crosslinking of the photopolymer. Thus, this embodiment makes it possible to harden the covering layer 7 as it is deposited, in situ, which optimizes the regularity of the thickness of the final fluorinated coating 8 and reduces the cycle time of the process.

The UV illumination source 11 is placed directly on the spray rod 4 so that the device allowing the implementation of the method is very simple to manufacture and inexpensive and does not heat the surface of the tank.

According to a third embodiment of the invention illustrated in FIG. 3, the precursor of the binder polymerizes under the effect of temperature. Step b) of the method of this embodiment is similar to that illustrated in FIG. 1. An endoscopic rod 4 introduced through a base 5 of the reservoir 100 allows the spraying of the liquid composition 6, preferably over the entire internal surface. 2 of tank 100.

The polymerization is carried out by local heating according to step c) obtained this time by infrared radiation (IR) thanks to an IR source placed on the endoscopic rod 4, the source being configured to emit in the direction of the surface. internal 2 covered by the covering layer 7. Since there is only a slight time lag between the spraying of the liquid composition 6 and the application of the IR radiation to the covering layer 7, it is not necessary to 'drive the reservoir 100 in rotation to obtain a smooth covering layer 7 of constant thickness. It suffices to place the axis of extension E of the reservoir 100 vertically and to animate the endoscopic rod 4 with a rotational movement around the axis of extension E and with a translational movement along the extension axis E to spray the liquid composition 6 uniformly on the internal surface 2. The polymerization taking place very quickly after spraying, the covering layer 7 remains smooth and of constant thickness until the end of the spraying process. polymerization. The process of the invention and the fluorinated coating 8 are then reproducible. In this variant embodiment of the method, the time saving over a recovery cycle is considerable.

This variant embodiment can also be produced when the precursor of the polymer binder is photopolymerizable. The reservoir 100 is advantageously placed vertically and the endoscopic rod 4 for spraying and UV treatment is driven in rotation around the vertical axis of extension E of the reservoir 100. The rod 4 is also driven in translation along the axis of extension E so as to spray the liquid composition homogeneously over the entire internal surface 2. Since the spraying and the UV treatment are carried out in a very rapid succession of steps, the rotation of the reservoir 100 is not necessary. Due to the fact that it is not necessary to carry out a rotational drive of the reservoir 100, the risks of damage are reduced. The device for implementing the method according to this variant embodiment is less complex and also less expensive.

Thus, besides the fact that the materials used in the design of the tank 100 are inexpensive, another advantage of the present invention is that the material of the fluorinated coating 8 does not oxidize in the presence of oxygen. The risks of ignition are reduced and it is conceivable to use such tanks 100 for the storage of combustible fluids under high pressure also in the automotive field.

In addition, the method of manufacturing this tank 100 is simple to implement since it involves forming a shell 1 in a light composite material (thermosetting or thermoplastic) of the desired shape and volume, then spraying a mixture. of fluorinated polymers of the PTFE ^® type and a thermosetting resin before applying a heat treatment finalizing the fluorinated coating 8.

The method according to the present invention thus does away with the preparation of a thick skin and its bonding to the internal surface 2 as described in the prior art. Thanks to the process according to the invention, the fluorinated coating 8 is generated in situ, in direct contact with the internal surface 2 of the tank 100. The manufacturing cycle time is improved, the process is inexpensive and the fluorinated coating 8 is resistant to damage. thermal shocks and at low temperatures while remaining very efficient.

It goes without saying that the invention is not limited to the embodiment described above by way of example but that it includes all the technical equivalents and the variants of the means described as well as their combinations.

Claims

1. A method of covering the internal surface (2) of a tank (100), the method comprising the following steps:

-a) providing a reservoir (100) made of a composite material, such as a thermoplastic material or a thermosetting material, configured to receive a pressurized fluid,

-b) spraying a liquid composition (6) comprising a fluoropolymer, a prepolymer and a crosslinking agent of said prepolymer, on the internal surface (2) of the reservoir (100), so as to form a covering layer (7) covering the inner surface (2), and

-c) polymerization of the covering layer (7) so as to generate a polymer binder encapsulating the fluoropolymer and to form a fluoropolymer coating (8) at least partially covering the internal surface (2).

2. A method of covering the internal surface (2) of a tank (100) according to claim 1, wherein said covering layer (7) formed in step b) has a substantially constant thickness and preferably between 10 micrometers and 50 micrometers.

3. A method of covering the internal surface (2) of a reservoir (100) according to one of claims 1 to 2, wherein step b) and step c) are repeated n times so as to obtain a fluorinated coating (8) formed from a stack of n covering layers (7), n being an integer between 1 and 20.

4. A method of covering the internal surface (2) of a reservoir (100) according to one of claims 1 to 3, in which between step b) and step c) the method further comprises:

- a step d) of partial polymerization of said prepolymer, and

- a step e) of additional spraying of the liquid composition (6).

5. A method of covering the internal surface (2) of a tank (100) according to one of claims 1 to 4, wherein step c) is carried out in a heating device configured to heat the covering layer. (7) deposited in step b) until the fluorinated coating (8) according to step c) is obtained.

6. A method of covering the internal surface (2) of a reservoir (100) according to one of claims 1 to 5, wherein the reservoir (100) extends along an axis of extension (E ) and during step b): the reservoir (100) is driven in rotation around the extension axis (E), and the spraying is carried out using a spray rod (4) configured to move in translation along the axis of extension (E) concomitantly with the rotation of the reservoir (100).

7. A method of covering the internal surface (2) of a tank (100) according to one of claims 1 to 6, wherein step a) comprises providing a tank (100) comprising a shell delimiting said internal surface (2) of the reservoir (100), the shell and the internal surface (2) being made of a composite material, and in particular a composite material chosen from a thermoplastic material such as polyvinyl chloride or a polyaryl ether ketone, or a thermosetting material, such as a polyester or an epoxy, the shell being configured to receive a pressurized fluid, in particular a cryogenic propellant.

8. A method of covering the internal surface (2) of a reservoir (100) according to one of claims 1 to 7, in which the fluorinated coating (8) predominantly comprises a fluoropolymer such as a PFTE of the Teflon type. ^® , Viton ^® , an FEP (Fluorinated Ethylene Propylene), PVF (Fluorinated Poly Vinyl) and a polymer binder, such as an epoxy, a polyamide, a polyethersulfone, a polyimide, a polyaryletherketone, a polyurethane, a biobased polymer.

9. A method of covering the internal surface (2) of a reservoir (100) according to one of claims 1 to 8, wherein the prepolymer of the liquid composition (6) is capable of polymerizing under the action. UV radiation.

10. A method of covering the internal surface (2) of a reservoir (100) according to claim 9, in which:

- the reservoir (100) supplied in step (a) extends along an axis of extension (E) arranged substantially vertically,

- The spraying of step b) is carried out by a spray rod (4) configured to move in translation along the extension axis (E) and to move in rotation around said extension axis ( E) concomitantly, and - step c) comprises the application of UV radiation in the direction of the cover layer (7).

11. A method of covering the internal surface (2) of a reservoir (100) according to claim 1 to 5 and 7 to 9, in which

- The spraying of step b) is carried out by a spray rod (4) configured to move in translation along the extension axis (E) and to move in rotation around said extension axis ( E) concomitantly, and

- step c) comprises the application of IR irradiation in the direction of the cover layer (7).

12. A method of covering the internal surface (2) of a reservoir (100) according to one of claims 1 to 11, in which between step a) of supplying the reservoir (100) and step b) for spraying the liquid composition (6), the method comprises a step k) of activating the internal surface condition (2) of the reservoir (100) so as to optimize the resistance of the covering layer (7) and fluoride coating (8).

13. Reservoir (100) intended to receive a pressurized fluid, the reservoir (100) is made of a composite material and comprises an internal surface (2) covered at least partially by a fluorinated coating (8) comprising a fluoropolymer and a polymer binder. .

14. Tank (100) according to claim 13, wherein the tank (100) comprises a shell delimiting said internal surface (2) of the tank (100) covered by the fluorinated coating (8), the shell and the internal surface (2). ) being made of a composite material, in particular chosen from a thermoplastic material or a thermosetting material, the shell being configured to receive a pressurized fluid, in particular a cryogenic propellant.

15. Reservoir (100) according to one of claims 13 to 14, wherein the fluorinated coating (8) has a substantially constant thickness between 10 micrometers and 1 mm.