Plasma-treated film and its use for the manufacture of composite material parts, method of manufacturing such a part

Abstract

The present invention relates to a thermoplastic release film for molding composite material parts, particularly in the aeronautical industry. The film of the invention is very easy to use, environmentally friendly and can be recycled.

Description

Title of the invention: Plasma-treated film and its use for the manufacture of composite material parts, method for manufacturing such a part Field of the invention

[0001] The present invention relates to a thermoplastic release film for molding composite material parts.

[0002] The fields of use of the present invention include in particular the aeronautical industry, the manufacture of wind turbine blades, boat hulls, or automobile parts. Prior art

[0003] In the context of the present invention, a composite material comprises at least one fibrous material and a crosslinkable polymer resin or a thermoplastic material, the combination of which makes it possible to obtain a complex whose properties surpass those of the starting materials. Thus, the parts made of composite material have numerous advantages linked in particular to their properties of strength, lightness and ease of shaping. These parts can be produced by vacuum molding or vacuum infusion, or any other technique known to those skilled in the art.

[0004] A covering and protective film, called a separator film, is placed on the part during its production, if necessary on a tear-off fabric which covers the part. It can in turn be covered with a draining net or a draining fabric or a draining felt or a draining grid. The separator film must have demolding properties. It is based on a polymer, which is a homopolymer or a copolymer, preferably a homopolymer. This polymer is most often polyester or polyolefin (polymethylpentene or PMP; or polyethylene, or polypropylene), or fluoropolymer (or fluoropolymer) (such as: fluorinated ethylene-propylene resin or FEP; poly(ethylene-co-tetrafluoroethylene) or ETFE; polytetrafluoroethylene or PTFE), or even polyamide or polyimide. Preferably, it is polyethylene or PTFE.

[0005] By “based on”, we mean according to the invention consisting mainly, or even principally, of.

[0006] The separator film may be inherently mold-releasable (typically in the case of a fluoropolymer or a polyolefin, such as polyethylene or polypropylene), or it may be made mold-releasable by coating (typically in the case of polyester).

[0007] Coated polymers have the problem that their coating coating can be transferred at least partially by release into the composite material, which is not desirable. In addition, coating polymers often have recycling issues. For example, silicone-coated thermoplastic polyolefins contain too much silicone to be recycled.

[0008] Polyolefins also have the disadvantage of low temperature resistance, typically below 150°C, although they naturally have mold release properties.

[0009] On the other hand, PET is known to have good temperature resistance, often high (i.e. generally above 150°C), but does not have any release properties. This lack of release properties is also the case for polyesters but also, although to a lesser extent, for polyamides and polyimides.

[0010] On the other hand, fluoropolymers such as PTFE also exhibit good resistance to high temperatures. However, they are not environmentally compatible materials. Their use could even be prohibited by applicable regulations within a few years.

[0011] There is therefore a need to have a thermoplastic release film that is compatible with the environment and can be recycled. Statement of the invention

[0012] The Applicant has developed a thermoplastic release film for molding, typically under vacuum, parts made of composite material, which is very easy to use, compatible with the environment and can be recycled.

[0013] More specifically, the present invention relates to a thermoplastic release film, having been treated on at least one surface by plasma treatment with at least one compound chosen from the group formed by silicone compounds, fluorinated compounds and carbon compounds, said thermoplastic release film being intended to be used for molding a composite part based on a polymer resin or a thermoplastic material, preferably a polymer resin, and a fibrous reinforcement. Fluorinated compounds are considered for the treatment, but do not constitute a preferred case, for the reasons set out above.

[0014] The compound selected from the group consisting of silicone compounds, fluorinated compounds and carbon compounds is preferably selected from the group consisting of silicone compounds and carbon compounds, more preferably selected from silicone compounds. Even more preferably, said compound is a polysiloxane.

[0015] The molding is carried out by using a polymer resin, thermosetting and therefore which will crosslink, or a thermoplastic material, which will melt under the effect of heat then harden, and a fibrous reinforcement. This reinforcement is advantageously made of fibers of at least one material chosen from carbon, glass, linen and aramid, as is known to those skilled in the art.

[0016] The molding is preferably carried out under vacuum and if necessary at elevated temperature, preferably by vacuum molding or vacuum infusion, but an RTM type process (or resin transfer molding), filament winding, stamping, contact molding, pultrusion, balloon inflation molding, or any other technique known to the person skilled in the art may also be used. All these molding techniques are well known to the person skilled in the art.

[0017] According to a first embodiment, a composite part is prepared by using a fibrous reinforcement and a thermosetting polymer resin. It may in particular be a reinforcement pre-impregnated with polymer resin or a dry reinforcement which is then infused.

[0018] The polymer resin is generally chosen from the group formed by polyesters, vinyl ester polymers, epoxy polymers, phenolic polymers, acrylic polymers, polyurethanes, and mixtures thereof. The resin is advantageously a thermosetting polymer resin whose crosslinking generally takes place at high temperature, in the case of a pre-impregnated reinforcement, and at room temperature, in the case of a dry reinforcement.

[0019] In the particular case of a pre-impregnated reinforcement, for information purposes, crosslinking is generally obtained between 120 and 250°C.

[0020] In the case of a dry reinforcement, the infusion is generally carried out at a temperature between 10°C and 40°C, for example at room temperature (approximately 20°C), and may undergo post-cooking at higher temperatures (120°C).

[0021] By interval “from X to Y” or “between X and Y”, it is understood according to the invention that the limits (X and Y) are included, unless otherwise specified.

[0022] According to a second embodiment, a composite part is prepared by using a fibrous reinforcement and a thermoplastic material. It may in particular be a reinforcement pre-impregnated with thermoplastic material.

[0023] The thermoplastic material is generally chosen from the group formed by polycarbonates (PC), polyamides (PA), polyetherimides (PEI), polyether-etherketones (PEEK), polyetherketones (PEK) and their mixtures. The thermoplastic material is advantageously melted so that it can deform and thus take the shape of the final part.

[0024] In the context of the invention, the thermoplastic release film is advantageously based on a polymer chosen from the group formed by polyesters, polyamides, polyolefins, polyimides and their copolymers, preferably chosen from the group formed by polyesters, polyamides, polypropylenes, polyethylenes, polyimides and their copolymers, and even more preferably polyesters. The polyester is preferably poly(ethylene terephthalate) (PET).

[0025] According to the invention, the term "thermoplastic film" means a film mainly made of thermoplastic polymer (homopolymer or copolymer). According to the invention, the term "release film" means a film that has been functionalized by plasma treatment on at least one of its faces, so as to have release film properties, i.e. allowing release. The functionalization leads to the creation of groups, typically silicones (which are polysiloxanes) in the case of the use of a silicone compound, on at least one surface of the film. This functionalization is either carried out on a polymer with little or no release properties which is thus made releaseable, or on a polymer with release properties which is thus made more releaseable.

[0026] The thermoplastic demolding film can be used directly, for example at the end of extrusion (in the case of inflation or “cast” type molding), after plasma treatment. But it can also undergo at least one other operation before use, for example chosen from: embossing, printing, perforation, coloring (including transparency), opacification, aluminization, carried out before or after the plasma treatment.

[0027] The treatment of the thermoplastic demolding film is advantageously carried out by plasma treatment in a controlled atmosphere, usually in an enclosure, in the presence of the compound or under vacuum, preferably in a controlled atmosphere. By "controlled atmosphere" is meant here an atmosphere consisting of neutral gas such as argon or nitrogen.

[0028] This plasma treatment makes it possible to graft a sufficient quantity of compound (generally chemically transformed) onto the surface, leading to a functionalization of said surface of the film. This surface functionalization is not to be considered as a coating in the strict sense. In addition, unlike fluorinated films or films coated with silicone, the plasma-treated films according to the invention can be recycled.

[0029] Thus, in the preferred case where the compound is a silicone compound, the plasma treatment makes it possible to create silicone functions on the surface of the film.

[0030] Silicones are, according to the definition of the IUP AC, the family of chemical compounds consisting of a silicon and oxygen skeleton, of general empirical formula [-OSiR2-], where R is not H. They are oligomeric or polymeric, and generally considered to have an unbranched structure. The silicone compound used for plasma treatment is preferably a polysiloxane.

[0031] In a molding process, the thermoplastic release film can advantageously be used, generally in a single layer, then removed without difficulty.

[0032] According to a particularly preferred embodiment, the thermoplastic release film according to the invention is free of fluorine.

[0033] Furthermore, in the preferred case where the compound is a silicone compound, the relatively small amount of silicone obtained on the surface by this treatment very advantageously allows the subsequent recycling of the thermoplastic release film, which is not possible in the case of a silicone coating on the film. Furthermore, in this case, the plasma-treated polymer is less harmful to produce and to process, compared to the fluoropolymers used as such.

[0034] Plasma treatment can be carried out under vacuum or in a controlled atmosphere. It is generally carried out in a controlled atmosphere, in the absence of oxygen and generally of humidity.

[0035] Plasma treatment is a conventional treatment method as is known to those skilled in the art. The temperature and duration conditions are usual. By duration, we mean the time the film spends in a plasma treatment chamber.

[0036] According to a particularly preferred embodiment, the thermoplastic release film is based on thermoplastic polyester (PET).

[0037] According to one embodiment, the thermoplastic release film is perforated and has holes with an average diameter of approximately 0.1 to 1.5 mm, preferably approximately 0.5 to 0.8 mm.

[0038] According to one embodiment, the thermoplastic release film is perforated and has a thickness of approximately 1 to approximately 500 μm, preferably approximately 5 to approximately 100 μm, even more preferably approximately 5 to approximately 50 μm.

[0039] When placed under vacuum and possibly under high temperature, the polymer resin or thermoplastic material is distributed homogeneously and is generally almost entirely retained by the thermoplastic release film unless said film is perforated, in which case the polymer resin or thermoplastic material can pass through the thermoplastic release film.

[0040] According to the invention, and as is known to the person skilled in the art, the thermoplastic release film may be combined with a draining net or a draining fabric or a draining felt or a draining grid, and / or with a tear-off fabric. The following combinations are particularly preferred: thermoplastic release film alone; thermoplastic release film combined with a net; thermoplastic release film combined with a draining fabric; thermoplastic release film combined with a draining grid; thermoplastic release film combined with a draining felt; thermoplastic release film combined with a net and a tear-off fabric; thermoplastic release film combined with a draining felt and a tear-off fabric. These combinations are easy to implement for the person skilled in the art.

[0041] Different means of association can be envisaged, to the extent that the overall permeability of the thermoplastic release film is not substantially modified. Thus, the association can be achieved by gluing with glue dots.

[0042] By A “and / or” B, we mean either A, or B, or A and B.

[0043] As is known, the tear-off fabric makes it possible in particular to structure the surface of the composite part after tearing, in particular to facilitate the adhesion of layers deposited subsequently such as glue, paint, etc.

[0044] As is known, the drainage net or grid helps drainage by combining thermoplastic release film and drainage elements. This drainage generally involves air in the case of felt or fabric, and polymer resin or thermoplastic material in the case of a drainage grid or net.

[0045] According to a particular embodiment, the thermoplastic release film may be associated with a reinforcing film, advantageously a non-woven textile, a knitted textile or a polyester-based laminated film. This reinforcing film is on the upper face of the thermoplastic release film, that is to say on the face opposite the facing face of the composite material part. The reinforcing film is therefore in contact with the draining felt or with the vacuum film. The reinforcing film makes it possible to improve the tear resistance of the thermoplastic release film.

[0046] The present invention also relates to a method of manufacturing by molding a part from a composite material, comprising the following steps: - forming in a mold the blank of the part made of composite material, said blank comprising a fibrous reinforcement and possibly a polymer resin or a thermoplastic material; - installation of a thermoplastic release film, so as to completely cover said blank; - installation of a vacuum film, so as to cover the thermoplastic release film; - sealing the entire mold and vacuum film, for example by placing a sealing mastic between the mold and the vacuum film; - vacuuming and evacuation of gases between the vacuum film and the mold, and where the blank does not include polymer resin or thermoplastic material, infusion of polymer resin or thermoplastic material; - crosslinking of the polymer resin or hardening of the thermoplastic material; - removal of the vacuum film; - removal of the thermoplastic release film.

[0047] This method can therefore comprise a step of placing a draining net or felt or a draining fabric or a draining grid, and / or a tear-off fabric, under or on the thermoplastic release film thus associated, and a step of removing the draining net or felt or draining fabric or draining grid and / or the release fabric. Typically the release fabric is placed between the reinforcement and the thermoplastic release film, and the drainage net or felt or drainage fabric or drainage grid is (are) placed above the thermoplastic release film and below the vacuum film if applicable.

[0048] In the particularly preferred case of a vacuum molding process, the resin or thermoplastic material is present in the blank from the start (case of pre-impregnated fiber reinforcement), then the resin is crosslinked or the thermoplastic material is melted and then uniformly distributed during the vacuum treatment, generally at high temperature. This step is generally followed by cooling.

[0049] In this case, the steps of vacuum molding are generally as follows: - forming in a mold the blank of the composite material part; the blank comprising polymer resin or thermoplastic material, and a fiber reinforcement; - covering the fiber reinforcement with a thermoplastic release film; - placing a vacuum film over the thermoplastic release film; - sealing of the entire mold and vacuum film; - vacuuming and evacuation of gases between the vacuum film and the mold; - crosslinking of the polymer resin, or melting and uniform distribution of the thermoplastic material; - removal of the vacuum film; - removal of the thermoplastic release film.

[0050] In the case of a vacuum infusion process, the resin to be crosslinked or the thermoplastic material is infused, drawn by the vacuum into the fibrous reinforcement once the vacuum is created, then the resin is crosslinked or the molten material is cured once in place.

[0051] The invention and the advantages resulting therefrom will emerge more clearly from the following figures and examples given to illustrate the invention and in a non-limiting manner. Brief description of the figures

[0052] [Fig-1] [Fig.l] is a sectional view of the thermoplastic release film according to the invention, used in association with a tear-off fabric and a draining felt, prior to the process of manufacturing a part in a composite material.

[0053] [Fig.2] [Fig.2] is a sectional view of the thermoplastic release film according to the invention, used alone, prior to the process for manufacturing a part from a composite material. Detailed description of the invention

[0054] The method of manufacturing a part from a composite material impregnated with a polymer resin comprises several steps, in the particular and preferred case of vacuum molding described herein.

[0055] In Figures 1 and 2, the fiber reinforcement is a fabric of glass fibers pre-impregnated with a resin. It is placed in a mold (5) so as to form a blank (1) of the part made of composite material impregnated with the polymer resin.

[0056] A tear-off fabric (2) and a draining felt (4) can advantageously be put in place, framing the thermoplastic release film (3). This creates a combination of the tear-off fabric, the thermoplastic release film and the draining felt (2, 3, 4) ([Fig.l]).

[0057] A vacuum film (6) is then placed on the sealing mastic (7), so as to cover the draining felt (4). The gases are evacuated by vacuum (8). The evacuation of the gases is therefore carried out through the thermoplastic demolding film (3). The gases are drained if necessary by the draining felt (4). In addition, the vacuum allows the resin to be distributed uniformly within the fibrous reinforcement. It also penetrates the tear-off fabric (2).

[0058] The resin is then crosslinked at room temperature, or at elevated temperature (typically in the case of a pre-impregnated reinforcement).

[0059] After crosslinking, the vacuum film and the drainage felt are removed. The thermoplastic release film and the tear-off fabric can be kept on the composite material part as protective films, then removed in a second step for secondary operations.

[0060] When there is neither draining felt nor tear-off fabric, all of layers 2, 3 and 4 are replaced by a single layer of thermoplastic film (3), and the steps are simplified ([Fig.2]). Examples of achievements

[0061] The example is carried out according to the diagram in [Fig.l].

[0062] A composite material part is made from a fibrous reinforcement and a polymer resin (ratio 66 / 34).

[0063] The fiber reinforcement is a carbon fiber fabric pre-impregnated with epoxy resin.

[0064] The thermoplastic release film is a PET film, one surface of which has been plasma-treated, from a HMDSO (Hexamethyldisiloxane) type precursor. It has a thickness of 12 μm. The diameter of the holes is 0.5 mm. The plasma treatment led to the creation of a hydrophobic “nanometric” coating.

[0065] A polyester tear-off fabric (marketed by the company DIATEX under the reference PES90) is present and has a weight of 90 g / m2.

[0066] The combination of the tear-off fabric and the thermoplastic release film is advantageously covered with a 340 g / m2 polyester draining felt.

[0067] After installation of the polyamide vacuum film, the blank is placed under vacuum, at - 1 bar (- 105 Pa). The assembly is then placed in an autoclave, at a pressure of 7 bar (7.105 Pa). The vacuum is reduced to - 0.2 bar (- 0.2.105 Pa), when the autoclave pressure reaches the value of 1 bar (105 Pa).

[0068] The resin is then crosslinked at 180°C for 120 min. After cooling to 60°C, the assembly is removed from the autoclave for demolding.

[0069] After removing the vacuum film, the drainage felt is removed from the part, effortlessly, thanks to the "release" action of the release film. The assembly is demolded in one piece, without waste on the part, or in this case, on the tear-off fabric.

Claims

Claims

1. Thermoplastic release film (3), having been treated on a surface by plasma treatment with at least one compound chosen from the group formed by silicone compounds, fluorinated compounds and carbon compounds, said thermoplastic release film (3) being intended to be used for molding a composite part based on a polymer resin or a thermoplastic material, and a fibrous reinforcement.

2. Thermoplastic release film (3) according to claim 1, characterized in that the thermoplastic release film is based on a polymer chosen from the group formed by polyesters, polyamides, polyolefins, polyimides and their copolymers, preferably chosen from the group formed by polyesters, polyamides, polypropylenes, polyethylenes, polyimides and their copolymers, and even more preferably polyesters, preferably poly(ethylene terephthalate) (PET).

3. Thermoplastic release film (3) according to claim 1 or 2, characterized in that the thermoplastic release film has a thickness of between 1 and 500 μm, preferably 5 to 100 μm, even more preferably 5 to 50 μm.

4. Thermoplastic release film (3) according to one of claims 1 to 3, characterized in that the film is perforated and has holes with an average diameter of 0.1 to 1.5 mm, preferably 0.5 to 0.8 mm.

5. Thermoplastic release film (3) according to one of claims 1 to 4, characterized in that the thermoplastic release film is associated with a draining net or a draining felt or a draining fabric or a draining grid (4), and / or with a tear-off fabric (2).

6. Thermoplastic release film (3) according to one of claims 1 to 5, characterized in that the silicone compound is a polysiloxane.

7. Thermoplastic demolding film (3) according to one of claims 1 to 6, characterized in that the plasma treatment is a treatment under vacuum or under controlled atmosphere.

8. Manufacturing method by molding a part in a composite material, comprising the following steps: - formation in a mold (5) of the blank (1) of the part in composite material, said blank comprising a fibrous reinforcement and optionally a polymer resin or a thermoplastic material;

9. - placing a thermoplastic release film (3) in place, so as to completely cover said blank; - placing a vacuum film (6), so as to cover the thermoplastic demolding film (3); - sealing of the entire mold (5) and the vacuum film (6); - vacuuming and evacuation of the gases between the vacuuming film (6) and the mold (5), and when the blank does not include polymer resin or thermoplastic material, infusion of polymer resin or thermoplastic material; - crosslinking of the polymer resin, or melting and uniform distribution of the thermoplastic material; - removal of the vacuum film (6); - removal of the thermoplastic release film (3). Method according to claim 8, characterized in that it comprises a step of placing a draining net or a draining felt or a draining fabric or a draining grid (4), and / or a tear-off fabric (2), on the thermoplastic demolding film (3) thus associated, and a step of removing the draining net or draining felt or draining fabric or draining grid (4) and / or the tear-off fabric (2).

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