EVACUABLE MOLD FOR FIBER COMPOSITE PLASTIC COMPONENTS

Abstract

Evacuable, stable mold having a design obtained by thermal deformation at temperatures 240 C. and corresponding to a fiber composite plastic component to be produced, consisting of an at least two-layered thermoplastic, vacuum-tight plastic film from a surface layer which is made of at least one thermoplastic polyamide or copolyimide, which has optionally functional groups, and a separating layer which form the inner side and is made of at least one thermoplastic fluorinated copolymer which has functional groups.

Claims

1. A stable evacuable mold with a shape obtained by thermoforming at temperatures 240 C. and corresponding to the respective fiber-composite plastics component to be produced therewith, and made of an at least two-layer vacuum-tight thermoplastic film comprising a) a surface layer made of at least one thermoplastic polyamide or copolyamide which optionally has functional groups, and b) a release layer forming the internal side of the mold and made of at least one thermoplastic tetrafluoroethylene copolymer, which has functional groups, composed of b1) ) copolymerized units of tetrafluoroethylene and ) copolymerized units of monounsaturated aliphatic dicarboxylic acids or cyclic anhydrides thereof, and also ) copolymerized units of at least one fluorinated monomer differing from tetrafluoroethylene, selected from the group consisting of CF.sub.2CFOR.sup.1, where R.sup.1 is a C.sub.1-10 perfluoroalkyl moiety which can comprise an oxygen atom, CF.sub.2CF(CF.sub.2).sub.pOCFCF.sub.2, where p is 1 or 2, perfluoro (2-methylene-4-methyl-1,3 dioxolane) and CH.sub.2CX.sup.3(CF.sub.2).sub.QX.sup.4, where X.sup.3 is a hydrogen atom or a fluorine atom, Q is an integer from 2 to 10 and X.sup.4 is a hydrogen atom or a fluorine atom, and/or ) copolymerized units of C.sub.2-C.sub.4 olefins, or b2) an olefin/tetrafluoroethylene copolymer which has been modified by free-radical grafting of from 0.01 to 5 mol % of carboxy groups, hydroxy groups, ester groups, isocyanate groups, epoxy groups, amide groups or cyclic anhydride groups, where the plastics film has no tie layer between the layers a) and b).

2. The mold as claimed in claim 1, wherein the layer a) is based on at least one thermoplastic aliphatic, semiaromatic or aromatic polyamide or copolyamide or of a mixture of at least two of the polyamides mentioned, a copolyamide of hexamethylenediamine, adipic acid and -caprolactam, or a mixture of PA-6 or PA-6,6 and from 5 to 20% by weight of a semiaromatic polyamide with softening point 240 C., whereby the polyamide or copolyamide units are composed of an at least trifunctional polyamine or of an at least trifunctional polycarboxylic acid in a quantity of from 0.01 to 5 mol %, based on 100 mol % of the copolyamide.

3. The mold as claimed in claim 1 wherein the layer b) is composed of a tetrafluoroethylene copolymer made of polymerized units of ) tetrafluoroethylene, ) C2-C4-olefins, and ) monounsaturated polycarboxylic acids or cyclic anhydrides thereof, whereby the tetrafluorocopolymer is composed of from 50 to 90 mol % of )-units, of from 10 to 50 mol % of ()-units, and of from 0.01 to 5 mol % of )-units, where the sum of the units )+)+) must always be 100 mol %.

4. The mold as claimed in claim 1 wherein the layer b) is composed of an ethylene/tetrafluoroethylene copolymer which has been modified by free-radical grafting of at least from 0.01 to 5 mol % of carboxy groups, hydroxy groups, ester groups, isocyanate groups, epoxy groups, amide groups or maleic anhydride groups.

5. The mold as claimed in claim 1 wherein the layer b) is composed of a thermoplastic tetrafluoroethylene copolymer made of ) copolymerized units of tetrafluoroethylene, ) copolymerized units of at least one fluorinated monomer differing from tetrafluoroethylene, selected from the group consisting of CF.sub.2CFOR.sup.1, where R.sup.1 is a C.sub.1-10 perfluoroalkyl moiety which can comprise an oxygen atom, CF.sub.2CF(CF.sub.2).sub.pOCFCF.sub.2, where p is 1 or 2, perfluoro(2-methylene-4-methyl-1,3 dioxolane) and CH.sub.2CX.sup.3(CF.sub.2).sub.QX.sup.4, where X.sup.3 is a hydrogen atom or a fluorine atom, Q is an integer from 2 to 10 and X.sup.4 is a hydrogen atom or a fluorine atom, ) copolymerized units of C.sub.2-C.sub.4 olefins and ) copolymerized units of monounsaturated aliphatic dicarboxylic acid or cyclic anhydrides thereof.

6. The mold as claimed in claim 5, wherein the layer b) is composed of a tetrafluoroethylene copolymer made of polymerized units ), ) and ), where the copolymer has from 50 to 99.8 mol % of )-units, from 0.01 to 5 mol % of )-units and from 0.1 to 49.99 mol % of )-units, based in each case on ), ) and ).

7. The mold as claimed in claim 5, wherein the copolymer is composed of from 50 to 90 mol % of )-units, from 5 to 35 mol % of )-units, from 0.1 to 20 mol % of )-units and from 0.01 to 5 mol % of )-units, based in each case on )-).

8. The mold as claimed in claim 1, wherein the mold has at least one closable evacuation system.

9. A method for the production of a fiber-composite plastics component with the mold of claim 1.

10. The method of claim 9, wherein the mold produced from the thermoplastic film has a softening point that is higher by at least 10 C. than the curing temperature of the fiber-composite plastics component hardened in the mold.

11. The method of claim 10, wherein the fiber-composite plastics component is a carbon-fiber-composite plastics component for aircraft, spacecraft, trains or motor vehicles, or a component for wind turbines.

Description

DETAILED DESCRIPTION

[0017] Said adhesion without any tie layer is achieved between the layer a) and the layer b) of the plastics film used according to the invention, because the preferably used thermoplastic tetrafluoroethylene copolymer for the production of the layer b) and optionally the polyamide or copolyamide of the layer a) have functional groups, whereby preferably such functional groups of the two layers can, and are intended to, react with one another.

[0018] Accordingly, the layer a) can be based on at least one thermoplastic, aliphatic, semiaromatic or aromatic polyamide or copolyamide, or on a mixture of at least two of the polymers mentioned, where the polyamide or the copolyamide can optionally be composed of at least one at least trifunctional polyamine or an at least trifunctional polycarboxylic acid in a quantity of from 0.01 to 5 mol %.

[0019] It is preferable that the layer a) is composed of at least one thermoplastic aliphatic polyamide or copolyamide, preferably made of an alkylenediamine having from 4 to 8 C atoms and an aliphatically carboxylic acid having from 6 to 14 C atoms, and/or made of a lactam, preferably having from 4 to 6 C atoms, particularly preferably of an -caprolactam (PA-6), or of a polyamide made of hexamethylenediamine and adipic acid (PA-6,6), of a hexamethylenediamine and sebacic acid, or of a hexamethylenediamine and dodecanedioic acid, or of a copolyamide made of hexamethylenediamine, adipic acid and -caprolactam, preferably having from 5 to 50% by weight of -caprolactam units (PA-6,6/6), of a semiaromatic polyamide made of an alkylenediamine having from 4 to 6 C atoms and terephthalic acid or isophthalic acid, preferably a polyamide made of hexamethylenediamine and terephthalic acid (PA-6T) or of hexamethylenediamine and isophthalic acid (PA-6I), or of a thermoplastic, aromatic polyamide composed of aromatic diamines and aromatic dicarboxylics, preferably of isophthalic acid or terephthalic acid and phenylenediamine, where the softening point of the respective polyamide or copolyamide must be 240 C.

[0020] Mixtures made of PA-6 or PA-6,6 and respectively preferably from 5 to 20% by weight, based on the entire mixture, of a semiaromatic polyamide, preferably of a PA-6I, cause in particular an improved thermoformability.

[0021] Each of the polyamides or copolyamides or mixtures thereof can optionally comprise the abovementioned functional groups, if at least trifunctional compounds are also used for the polycondensation process.

[0022] As mentioned before, the layer b) is based on a thermoplastic fluorocopolymer, preferably tetrafluoro-ethylene copolymer.

[0023] Suitable fluorocopolymers are in particular tetrafluoro-ethylene copolymers which have

[0024] ) copolymerized units of tetrafluoroethylene,

[0025] ) copolymerized units of at least one fluorinated monomer differing from tetrafluoroethylene, selected from the group consisting of [0026] CF.sub.2CFOR.sup.1, wherein R.sup.1 is a C.sub.1-10 perfluoroalkyl moiety which can comprise an oxygen atom,

[0027] of CF.sub.2CF(CF.sub.2).sub.pOCFCF.sub.2, wherein p is 1 or 2,

[0028] of perfluoro (2-methylene-4-methyl-1,3 dioxolane) and [0029] CH.sub.2CX.sup.3 (CF.sub.2).sub.QX.sup.4, wherein X.sup.3 is a hydrogen atom or a fluorine atom, Q is an integer from 2 to 10 and X.sup.4 is a hydrogen atom or a fluorine atom,

[0030] ) copolymerized units of nonfluorinated monomers, preferably C.sub.2-C.sub.4 olefins, preferably of ethylene or propylene or of vinyl ester or vinyl ether, preferably vinyl acetate and

[0031] ) copolymerized units of monounsaturated aliphatic dicarboxylic acid or cyclic anhydrides thereof,

[0032] wherein a fluorocopolymer used according to the invention, preferably tetrafluoroethylene copolymer, must not necessarily be composed of all of the copolymerized units )- ) mentioned.

[0033] Preferably that the functional groups of the fluorocopolymer, preferably tetrafluoroethylene copolymer, are derived from polymerized units of ) monounsaturated, aliphatic dicarboxylic acids, for example itaconic acid, citraconic acid, or maleic acid, or cyclic anhydrides thereof, for example maleic anhydride, itaconic anhydride or citraconic anhydride. The proportion of these polymerized units is preferably from 0.01 to 5 mol %, whereby the sum of all polymerized units must always be 100 mol %.

[0034] The layer b) is thus composed of a fluorocopolymer, preferably of a tetrafluoroethylene copolymer, composed of polymerized units of ) tetrafluoroethylene, ) C.sub.1-C.sub.4- olefins, preferably ethylene, and ) monounsaturated polycarboxylic acids or cyclic anhydrides thereof, preferably itaconic acid, itaconic anhydride, citraconic acid, citraconic anhydride, maleic acid or maleic anhydride, and the tetrafluorocopolymer is composed of from 50 to 90 mol % of )-units, of from 10 to 50 mol % of )-units, preferably ethylene units, and of from 0.01 to 5 mol % of )-units, whereby the sum of the units )+)+) must always be 100 mol %.

[0035] For the composition of the layer b), preference is also given to a tetrafluoroethylene copolymer of polymerized units ), ) and ), which copolymer is composed of from 50 to 99.8 mol % of )-units, from 0.01 to 5 mol % of )-units and from 0.1 to 49.99 mol % of )-units, in each case based on the sum of ), ) and ).

[0036] Another preferred tetrafluoroethylene copolymer for the composition of the layer b) is a tetrafluoroethylene copolymer made of polymerized units ), ), ) and ), where the copolymer is composed of from 50 to 90 mol % of )-units, from 5 to 35 mol % of )-units, from 0.1 to 20 mol % of )-units and from 0.01 to 5 mol % of )-units, in each case based on the sum of )-).

[0037] It is also possible to provide the tetrafluoroethylene copolymer with functional groups by a chemical treatment, corona discharge treatment or plasma discharge treatment to provide free radicals to the surface of the layer b) and by using a conventional method for grafting unsaturated dicarboxylic acids, cyclic anhydrides thereof and/or epoxides or hydroxy groups thereto in an amount that the functional groups are in a proportion of from 0.01 to 5 mol %, based on 100 mol % of the tetrafluoroethylene copolymer, before bonding layer b) to the layer a).

[0038] As mentioned above, the plastics film used according to the invention preferably has two layers, and has no tie layer in between. In case both the layer a) and the layer b) have functional groups, it is therefore advisable that functional groups present are of the type that they can react with each another. Examples of these are carboxy groups, hydroxy groups, cyclic anhydride groups and amino groups.

[0039] The thermoformability and stability of the plastics film used according to the invention are influenced by the overall thickness and the thickness ratio of the layer a) to the layer b). The total thickness of the plastics film not yet thermoformed is preferably at least 250 m, particularly preferably at least from 400 to 700 m, whereby the thickness ratio of the layer a) to the layer b) is in the range of from 95:5 to 70:30.

[0040] The plastics film used according to the invention can be produced by extrusion, preferably by coextrusion. It is particularly preferable that the plastics film used according to the invention is produced in the form of cast film by extrusion, preferably coextrusion, through a flat-film die, whereupon an excellent adhesion is obtained.

[0041] The plastics film used according to the invention is hydroscopic because of the polyamide layer a), and is preferably stored in a packaging impermeable to moisture, after its drying, and preferably again dried before thermoforming. Immediately after the inventive mold has been produced and cooled, this is also stored under conditions that exclude moisture, and optionally again dried before being used for the production of a fiber-composite plastics component.

[0042] Because of the unfluorinated units of the tetrafluoroethylene copolymer the softening point of the plastics film used according to the invention is 240 C.

[0043] It is thus possible to thermoform the plastics film in conventional forming equipment, preferably by deep-draw thermoforming under heating to the forming temperature, to produce the inventive mold which thermoformed mold has the shape corresponding to the fiber-composite plastics component to be produced in the inventive mold. The temperature for thermoforming of the plastics film is preferably 240 C., particularly preferably in the range of from 210 to 240 C.

[0044] The thermoforming procedure can be carried out under vacuum and optionally under mechanical assistance, for example, of a ram.

[0045] The plastics film used according to the invention is preferably transparent, and it is therefore also possible to provide transparent molds for the production of fiber-composite plastics components. This allows inspection during curing of the impregnated fiber-plastics laminates, to ensure a defect-free production.

[0046] In order to avoid embrittlement of the mold during thermoforming, it is advantageous to add to the polyamide antioxidants, e.g. sterically hindered phenols, phosphites or sterically hindered amines. This provides long-term antioxidative thermal stabilization, i.e. a prevention of a thermal polymer degradation which can lead to embrittlement of the mold during curing of the fiber-composite plastics component. Thermal stabilization can also be achieved by adding Cu(II) compounds, such as Cu(II)KI complexes. Addition of as little as from 1 to 10% by weight, preferably from 1 to 5% by weight, of the additives mentioned can achieve adequate stabilization against embrittlement and any undesired discoloration of the mold. The thermoformability of the film used according to the invention can also be further improved by the use of one of the before mentioned mixtures of polyamides comprising a high-viscosity amorphous polyamide such as PA-6I for the production of the polyamide layer a).

[0047] It is thus possible to prevent any undesired softening or disruption of the film web that might occur during thermoforming.

[0048] It is moreover possible to add conventional quantities of conventional processing aids such as lubricants or antistatic agents into the film used according to the invention.

[0049] It is particularly preferable that the total thickness of the thermoplastic film that has not yet been thermoformed is at least 250 m, preferably up to 700 m, where the thickness ratio of the layer a) to the layer b) is in the range from 95:5 to 70:30.

[0050] A possibility for the production of large-surface-area fiber-composite plastics components which may have a repeating shape is to juxtapose identically shaped mold segments which can be bonded to one another in the overlapping region of two segments, preferably by heat-sealing in order to prepare a respective mold.

[0051] The inventive mold has at least one evacuation equipment, which after being filled with the plastics-resin-impregnated fiber laminate, is closed with a further, vacuum-tight moldthe sealing moldto provide an entire vacuum-tight mold.

[0052] The design of this second (closing) mold for the vacuum-tight sealing of the inventive mold can preferably differ from the inventive mold.

[0053] This closing mold preferably has the shape of a panel or of a shaping mold on which the plastics-impregnated fiber laminate is first placed before the vacuum-tight closing with the inventive mold. To this end, the said closing mold must have a surface provided with release agents, and must maintain its original flexural strength during the entire production process, particularly in the evacuated condition of the entire mold, in order to avoid impairment of the inventive mold and thus of the composite component to be produced. If the flexural stiffness of the closing mold is not sufficient, there is specifically the risk that the fiber-composite plastics molding will not have the desired shape.

[0054] Another possibility, however, is in case the fiber-composite plastics component should have a different shape on its two surfaces, to use a closing mold likewise made of a plastics film used according to the invention with a shape appropriate to the shape of such second surface. It is likewise possible to introduce the plastics film according to the invention between the shaping mold and the laminate, for example in order to omit use of conventional release agents (solvent-containing or water-based release agents). It is of course also possible, if necessary, that the entire closing mold has a concave or convex shape, if this is necessary for the shaping of the fiber-composite plastics component. Shaping can be achieved by folding, or folding-together, of appropriate mold halves.

[0055] As stated before, the production of the fiber-composite plastics component is carried out as follows: the fiber laminate impregnated with the curable plastics resin, preferably a curable epoxy resin, is provided on the closing mold, and then the inventive mold is combined with the closing mold, to give the entire mold, and the system is sealed so that it is vacuum-tight. A vacuum is applied in order to compress the inventive mold, with compaction of the fiber material. While the vacuum is maintained, the entire mold with the molded laminate is placed in an autoclave and heated to the curing temperature of the curable plastics resin, and retained for the entire curing time, mostly a number of hours.

[0056] Alternatively to the use of an autoclave it is possible to operate with pressure in a press or to operate under atmospheric pressure (i.e. oven curing).

[0057] Curing can also be achieved by the action of microwave radiation.

[0058] After the curing time, and after cooling, the fiber-composite plastics component is removed from the entire mold and, as far as possible under exclusion of moisture, packed for final use.

[0059] Fibers used for the production of the composite components are preferably carbon fibers or glass fibers.

[0060] The inventive mold can be used to produce fiber-composite plastics components, preferably carbon-fiber composite plastics components, which in particular can be used as components for means of transport of any type, preferably for aircraft, spacecraft, trains or motor vehicles, or as components for wind turbines, preferably as rotor blades.

[0061] Determination of Adhesion

[0062] Adhesion between the layer a) and the layer b) is determined by testing test strips of a multilayer film used according to the invention, each with width 15 mm and length about 150 mm. Each test strip is fixed in a tensile tester in such way that the angle formed by the strips to be separated from one another (layer a) and layer b)) is about 180 C., and the strips are then separated from one another. The maximal and average separation force is determined across the measurement distance. The measurement equipment used for the test is a computer-controlled tensile tester. Adhesion is determined here by plotting force against displacement. The force measured in N corresponds to the force required to achieve full separation of the layers (layer a) and layer b)) of the test strip.

EXAMPLE

[0063] A two-layer cast film is produced by coextrusion of PA-6 comprising 5% by weight of PA-6I as layer (a) and of an ethylene/tetrafluoroethylene copolymer with 0.5 mol % of - and -units incorporated into the polymer. The thickness of the polyamide layer a) is 400 m and the thickness of the release layer b) is 100 m. The coextruded film could be thermoformed very successfully at 229 C., and exhibits excellent adhesion: it could not be separated into two layers according to the Determination of adhesion test described before, either mechanically or with the aid of test adhesive tapes. Delamination was not possible.