PEELABLE SHIM HAVING INCREASED STRENGTH

Abstract

A method for producing a peelable sheet, includes the steps of adhesively bonding woven fibres with a preparation of base components for a thermosetting resin so as to form adhesively bonded sheets; stacking the adhesively bonded sheets in a stack; and converting the base components into thermoset resin. The stack of sheets is kept under pressure and, prior to being adhesively bonded, the woven fibres are coated with a deposit of a fluoropolymer.

Claims

1. A method for producing a peelable plate, the method including the following steps: adhesively bonding woven fibers with a preparation of base components for a thermosetting resin to form adhesively bonded sheets, stacking the adhesively bonded sheets in a stack, and converting the base components into thermoset resin, the stack of sheets being kept under pressure and, prior to being adhesively bonded, wherein the woven fibers are coated with a deposit of a fluoropolymer.

2. The method for producing a peelable plate according to claim 1, wherein the fluoropolymer is polytetrafluoroethylene and that before adhesively bonding the fiber sheets coated with said deposit are stripped.

3. The method for producing a peelable plate according to claim 1, wherein the woven fibers form a satin-type mesh.

4. The method for producing a peelable plate according to claim 1, wherein the fibers are coated with said deposit by micro-spraying, before being adhesively bonded.

5. The method for producing a peelable plate according to claim 1, wherein the resin is a cyanate ester resin.

6. The method for producing a peelable plate according to claim 1, wherein the conversion into a thermoset resin comprises heating to 180° C.

7. The method for producing a peelable plate according to claim 1, wherein the fibers are glass, carbon, ceramic, or aramid fibers.

8. A peelable plate comprising: a stack of woven fiber sheets coated with a fluoropolymer, held together by a thermoset resin.

9. Use as a shim of a peelable plate according to claim 8, or obtained by a producing method comprising adhesively bonding woven fibers with a preparation of base components for a thermosetting resin so as to form adhesively bonded sheets, stacking the adhesively bonded sheets in a stack, and converting the base components into thermoset resin, the stack of sheets being kept under pressure and, prior to being adhesively bonded, wherein the woven fibers are coated with a deposit of a fluoropolymer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Other features and advantages of the disclosure will emerge clearly from the description given below, which is indicative and in no way limiting, with reference to the appended drawings, in which:

[0024] FIG. 1 is a perspective view of the fabric used in the disclosure before impregnation;

[0025] FIG. 2 is a perspective view of a fabric from FIG. 1 impregnated for the purpose of the disclosure; and

[0026] FIG. 3 is a perspective view of the product being assembled.

DETAILED DESCRIPTION OF THE DRAWINGS

[0027] The disclosure relates to a laminated product comprising a stack of sheets of woven fibers such as sheet 14 shown in FIG. 1 comprising a satin type weave of fibers 12 that may in particular be glass fibers.

[0028] These fibers 12 are interwoven, and may be fibers of glass, carbon, ceramic or aramid, or of any other material having comparable mechanical properties. Several types of fibers can be mixed in the same fabric.

[0029] Pieces of the above-mentioned fibrous fabric 12 are first cut and bonded to the desired dimensions. Each of them will form a sheet of the rolled product after processing.

[0030] These sheets are subject to impregnation by spraying or micro-spraying of a fluorinated polymer, in the mode of production presented, PTFE or polytetrafluoroethylene. A minimum amount of PTFE is applied so that the sheets are coated without being unnecessarily weighed down or thickened, as shown in FIG. 2, where a coated sheet 3 is visible, comprising sheet 14 with a PTFE impregnation 8. The fibers 12 are embedded in a fine PTFE environment 8.

[0031] Another fluoropolymer can be used, such as polyvinyl fluoride (PVF), polyvinylidene fluoride (PVDF), polychlorotrifluoroethylene (PCTFE), perfluoroalkoxy (PFA), fluorinated ethylene propylene (FEP), ethylene tetrafluoroethylene (ETFE), polyethylene chlorotrifluoroethylene (ECTFE), perfluoropolyether (PFPE), perfluorosulfonic acid (PFSA), perfluoropolyoxetane, or fluoroelastomers.

[0032] The coated sheets 3 are then treated with a stripping agent to allow them to bond to each other. The stripping agent (or corrosive agent) can be the commercially available Tetra-Etch agent (which concerns an organic solution). Other chemical or physical stripping methods can be used such as an alkaline solution (soda, potash), another organic stripping solution, or exposure to fire or plasma.

[0033] Once the stripping effect is achieved, the stripping agent is removed or withdrawn and the sheets are bonded, on one or both sides, with a thermosetting resin preparation comprising a solvent, the monomer or precursor, and optionally the chemical activating agent. In a preferred method, a cyanate ester resin is used, which allows the final product to withstand high temperatures.

[0034] The bonding operation is carried out by any type of bonding machine, spraying by means of a nozzle or a gun, by application with a manual roller, by printing on an offset type machine, or by dipping the fabric in a bath of adhesive material.

[0035] The thermosetting resin, after its process of cross-linking of monomer to polymer an adhesive material, its quantity and treatment being selected and adapted so that the bond strength between the two sheets is lower than the tear resistance of the sheets, so that each sheet can be detached from the stack without tearing.

[0036] The resin is polymerized either by heat treatment or at room temperature. In addition to a cyanate-ester resin, this can be an epoxy, phenolic, vinyl-ester or polyvinyl resin. It is preferably mono-constituent, but it can be a mixture of resins of different chemical natures.

[0037] Additives are added to the resin in some cases. These additives may include hardeners to impart specific mechanical characteristics, hardness, stiffness, or tensile and compressive strength to the rolled product.

[0038] Finally, the adhesively bonded fabric sheets 4 undergo a final polymerization process under pressure. This operation comprises arranging the sheets in stack 2, as shown in FIG. 3, between two parallel-plane supports, these supports being pressed against each other at room temperature or hot in a heating press for a predetermined time. The resin polymerizes.

[0039] This operation gives the rolled product the desired mechanical qualities of parallelism, flatness, cohesion and peelability.

[0040] The flat supports are made up of two calibrated steel plates of a high thickness, such as 50 mm. The plates are traversed at the periphery by threaded rods or screws, to which a clamp is applied.

[0041] The polymerization is carried out with temperature cycles at 120° C. and 180° C.

[0042] Finally, the rolled product is machined or cut to the correct dimensions, if necessary, so that it has the right shape and dimensions in the sheet plane.

[0043] Rolled products of this type are well suited for use as shims for the aircraft industry, for airplanes or helicopters for example, including in very hot areas such as engines, for example in an a 400° C. environment.

[0044] These laminated products can also be used as peelable shims in other fields, generally wherever light weight and mechanical and thermal resistance characteristics are required, and can be used in chemically aggressive or humid environments.

[0045] They are resistant to occasional shocks, even violent ones, created by a point hitting their surface.