HK1135130B - Polymer film for surface-coating composite fiber-plastic materials - Google Patents

Description

Surface-coated polymer film for fiber-plastic composites

Technical Field

The invention relates to the use of a resin matrix for producing a substrate-supporting polymer film for the surface coating of fibre-plastic composites, and to a method for coating fibre-plastic composites produced using prepregs.

Background

Fiber-plastic composites are used in a wide range of aeronautical fields because of their advantageous properties, such as their low weight and their high tensile strength. As such, they are used, for example, in the interior space structure of passenger aircraft. Such so-called interior components, such as side walls or hatracks, must have a particular surface quality, since they are directly within the field of vision of the passengers.

In order to achieve mechanical properties which are as good as possible with as little weight as possible, the components are usually produced as a Sandwich (Sandwich-) structure. Of these, a honeycomb body made of paper impregnated with a phenolic resin (known, for example, under the trade name Nomex-Waben) is used as the core and a thin layer of prepreg is used.

A prepreg is a semi-finished product consisting of continuous fibres and an uncured thermoset matrix. The continuous fibers may be present as unidirectional layers, as a woven fabric, or as a laid-up web (Gelege). Conventional fiber types are, for example, glass fibers, carbon fibers or aramid fibers. Glass fibers are popular.

The plastic matrix contains a mixture of resin and curing agent and optionally an accelerator. The curing agent and optional accelerator determine the curing temperature, i.e. the temperature at which the curing process starts. Matrix systems are distinguished by their curing temperature and type of resin.

To prepare the sandwich member, a number of different methods are used. In these methods, a member is obtained by fitting the above-described structure into a mold and curing in the mold.

In the vacuum bag process (Vakuumsackverfahren), the prepreg is first placed in a mold, the honeycomb is placed thereon and then the prepreg is placed again. The mold is then transferred to a vacuum forming bag and vacuum is applied. If the structure has been fitted to the mould, the mould is heated, thereby initiating curing. In this process, the starting temperature depends on the matrix system used.

Another variant of the vacuum forming bag process is the so-called autoclave process. The evacuated vacuum-formed bag containing the structure is cured in an autoclave under elevated pressure and elevated temperature.

In the hot-pressing method, the structural prepreg, honeycomb prepreg, is placed in a heated mold and pressed under pressure. In this case, unlike the vacuum bag method, the mold has already reached the temperature required for curing, so that the sandwich structure must be produced before being inserted into the mold.

For aerospace components, and in particular for interior components, fire resistance is important. Fire resistance is the ability of a material, product or component to withstand the effects of a fire or fire source, or to inhibit the spread of a fire energetically, kinetically, chemically or mechanically. This concept is not standardized and the performance itself is not measurable (see-Lexikon rockeund Druckfarben; U.S. Zorll, Thieme Verlag Stuttgart New York, 1998; Kunststoff-Kompendium, A.Franck, Vogel Buchverlag, Warzburg, 1996). The test method for the fire resistance is to simulate the actual combustion under conditions of reproducibility. In which different physicochemical data, such as flash point and ignition point or the composition of the pyrolysis vapors, are obtained depending on the test method, respectively.

Prepregs based on phenol-formaldehyde resins (phenolic resins for short) are generally used as materials for interior components in order to meet the requirements for FST performance (flammability, smoke, toxicity) in the cabin region of civil aircrafts. The phenolic resin itself has a fire behaviour suitable for this application: they emit less toxic gases when burned than other thermosets and extinguish when the flame is removed.

Phenolic resins are among the traditional condensation resins, i.e. they are polymerized or crosslinked under the dissociation of water. Since the prepregs placed in the mould are usually cured at temperatures in excess of 100 ℃, for example at temperatures of 130 to 200 ℃, the formation of a dense and closed surface is suppressed due to the water escaping in the gaseous state. As a result, the raw component generally has poor surface quality.

In order to achieve the desired coloration and the desired surface structure of the component for the cabin area, the component must subsequently be painted or laminated with a film. However, a high surface quality is required for this purpose. This is usually achieved by scraping and subsequently grinding the component, and these method steps must be repeated as appropriate. This requires high time and operating costs and is accompanied by high costs.

In order to eliminate these process steps, it is desirable to use an in-mold Coating (Inmould-Coating). An in-mold coating is a surface coating that is applied to a mold prior to placing the prepreg structure in the mold (Einformen) and curing, or that is formed during the molding process. The in-mold coating should improve the surface quality of the rough-formed component in such a way that it can be painted or laminated without complicated pretreatment. Furthermore, the FST requirements must also be met.

Solvent-based in-mold coating systems that are applied to the mold surface prior to placement of the prepreg are known. However, the use of this system in a vacuum formed bag process does not show the desired results. Depending on the geometry of the mould, the solvent in certain regions of the mould can only be removed insufficiently by vacuum. This leads to the formation of bubbles and pits on the surface of the component at elevated temperatures in the subsequent curing.

In the hot press method, a solvent-based in-mold coating system cannot be used because the temperature of the mold is much higher than the boiling point of the conventionally used solvent. By the high temperature, the solvent is immediately evaporated from the system, and thus a uniform film cannot be obtained.

Another possibility is a solvent-free system as an in-mold coating. One example of this is a gel coat for the tempering of epoxy laminates.

Description of the invention

The aim of the invention is to improve the surface quality of a cured component made of a fiber-plastic composite material. In particular, the invention is intended to improve the surface quality of components made of prepregs.

This object is achieved by the use of a substrate-supported polymer film according to claim 1 and by a method according to claim 14. Particular embodiments are described in the dependent claims and in the description.

According to the invention, a resin matrix is used for the production of the substrate-supported polymer film, said resin matrix containing at least one difunctional or more-functional aromatic organic cyanate and at least one difunctional or more-functional aromatic alcohol in such a proportion that the molar ratio of OCN groups to OH groups in the starting material of the resin matrix is 95: 5 to 70: 30, and at least one filler.

Wherein the cyanate ester component and the alcohol component are used in a preferred quantity ratio which ensures a molar ratio of OCN groups to OH groups in the starting materials of the resin matrix of 93: 7 to 75: 25 and particularly preferably of 91: 9 to 80: 20.

The resin matrix in the polymer film of the present invention has a degree of crosslinking below its gel point. This enables processing or curing in the range of about 100 ℃ to 200 ℃. By using the resin matrix described in patent application DE102006041037.8, the polymer film also has good storage stability and little brittleness. The materials obtained by curing the polymer films according to the invention exhibit high flame resistance, because of the low heat release rate in the case of combustion, the low smoke density and the low toxicity of the combustion gases formed.

Finding a suitable cyanate resin matrix for the present invention is difficult because particularly fire-resistant phenolic novolac (Phenol-Novolaken) based cyanate resins, such as PT-resins from Lonza corporation, have a very high glass transition temperature after complete curing. In order to achieve complete conversion of the cyanate ester groups, it is therefore necessary to use very high curing temperatures. Although curable at low temperatures, since the reaction can be promoted, for example, by using conventional catalysts such as metal-acetylacetonate complexes; however, by using such a catalyst, the maximum glass transition temperature is not lowered. At curing temperatures well below those necessary for maximum conversion of the OCN groups, the reaction freezes at a particular OCN conversion. This conversion is dependent on the curing temperature or its distance from the maximum glass transition temperature, i.e. the glass transition temperature at maximum OCN conversion. However, below this conversion, the cyanate ester network is brittle.

It has therefore been possible to find other catalysts which are also network modifiers. They will expand (aufweiten) networks and at the same time will also catalyze the crosslinking reaction (trimerization) of the cyanate ester resin. By network expansion, the glass transition temperature will drop, making it possible to select a curing temperature that is lower than that required for pure cyanate ester resins. It is therefore likewise possible to avoid the abovementioned embrittlement as a result of too small a conversion of the OCN groups.

But this search has proven to be quite problematic. The addition of monofunctional phenols described in the literature does not appear to be very reliable, for example. Monofunctional phenols as used in the prior art intercalate into the polymer during the reaction. The basic mechanism is very complex. It has been found that the number of OH groups remains constant despite the insertion of phenol. The reason is as follows: for each OH group entered into the reaction, one OH group is released at the other position. The monofunctional phenol thus has the effect that difunctional linkages are formed from trifunctional crosslinking sites, since the OH groups constitute network chain ends. Thus, the network density is excessively strongly reduced due to the monofunctional phenol. They therefore lower the glass transition temperature to a significant extent beyond any desired extent and are therefore unsuitable for the purposes of the present invention.

In addition, undesirably high sol contents have been found in resin matrices. Another disadvantage is that components with relatively high volatility remain in the resin matrix, which can cause gas release at a later stage. This is also to be avoided because, as mentioned above, the result may be an insufficient surface quality of the coating according to the invention, for example due to the formation of bubbles on or in close proximity to the surface. Furthermore, the initial components are volatile, which can cause problems in processing and handling.

Due to the presence of hydroxyl groups in the resin matrix, it is additionally to be taken into account that the crosslinking reaction to form the polymer film does not end as desired at least over a longer period of time (as may occur during storage) before the gel point is reached, but rather proceeds to a degree of crosslinking well above the gel point. In this case, the polymer film is no longer homogeneously meltable and can therefore no longer be processed within the meaning of the invention. However, good storage stability is necessary anyway, since the polymer films produced according to the invention using the resin matrix must generally be stored for a relatively long period of time and then transferred to the final curing step.

The choice of the polyfunctional cyanate used as the initial component of the resin matrix is not critical. In principle, it is possible to use each of the at least difunctional aromatic cyanate esters: (). Preferably, the resin matrix is prepared using one or more difunctional or more functional aromatic organic cyanate esters selected from aromatic cyanate esters having the following formula I

Wherein R is¹To R⁴Independently of one another, hydrogen, straight-chain or branched C₁-C₁₀Alkyl radical, C₃-C₈-cycloalkyl, C₁-C₁₀-alkoxy, halogen, phenyl or phenoxy, wherein said alkyl or aryl group may be fluorinated or partially fluorinated,

an aromatic cyanate selected from formula II below

Wherein R is⁵To R⁶Such as R¹To R⁴And z is a chemical bond, SO₂、CF₂、CH₂、CHF、CH(CH₃) Isopropylidene, hexafluoroisopropylidene, C₁-C₁₀Alkylene radical O, NR⁹N-CH N, CH, COO, CH N, CH, N-CH, having C₁-C₈Alkyleneoxyalkylene of alkylene, S, Si (CH)₃)₂Or a residue of formula IIa, IIb or IIc

Or an aromatic cyanate selected from the following formula III

Wherein R is⁹Is hydrogen or C₁-C₁₀-alkyl radicalAnd n is a value of 0 to 20. The cyanate esters can be used alone or in mixtures with one another or with other monofunctional or polyfunctional cyanate esters as monomers or as precrosslinked polymers.

It is particularly preferred to use one or more difunctional or more functional aromatic organic cyanates selected from the group consisting of novolak-type cyanates, bisphenol A-dicyanate derivatives, 4' -ethylenediphenyldicyanates or compounds of the formula III

Wherein n is equal to 1, 2 or 3, R⁹Is hydrogen and the methylene groups are all in the ortho position to the cyanate ester group.

The difunctional or more functional (polyvalent) aromatic alcohols to be used are preferably compounds of the formula IV

Wherein R is¹To R⁴Independently of one another, hydrogen, straight-chain or branched C₁-C₁₀-alkyl radical, C₃-C₈-cycloalkyl radical, C₁-C₁₀-alkoxy, halogen, phenyl or phenoxy, wherein the alkyl or aryl group may be fluorinated or partially fluorinated,

a compound of the formula V

Wherein R is⁵To R⁶Such as R¹To R⁴Is defined by (a) and zIs a chemical bond, SO₂、CF₂、CH₂、CHF、CH(CH₃) Isopropylidene, hexafluoroisopropylidene, C₁-C₁₀Alkylene radical O, NR⁹N-CH N, CH, COO, CH N, CH, N-CH, having C₁-C₈Alkyleneoxyalkylene of alkylene, S, Si (CH)₃)₂Or a residue of formula IIa, IIb or IIc

Or a compound of formula VI

Wherein R is⁹Is hydrogen or C₁-C₁₀-alkyl and n is a value from 0 to 20. The alcohols mentioned can be used alone or in mixtures with one another or in mixtures with other monofunctional, difunctional or more functional alcohols, as monomers or as precrosslinked polymers.

Preferably, the polyvalent aromatic alcohol is a di-or higher-functional phenol. However, it is also possible, for example, to use fused aromatic compounds, such as naphthol derivatives. Particular preference is given to using aromatic difunctional alcohols in which the hydroxyl groups are each bonded directly to an aromatic ring. Preferred are bisphenols, such as bisphenol a, 4' -ethylenediphenol and bis (hydroxyphenyl) sulfide (bishydorxyphenylsulfonate).

Although the use of compounds whose catalytic action can be expected to give further reaction of the resin matrix together with aromatic alcohols as defined above, latency (Latenz) is surprisingly achieved.

Latency means herein that after heat treatment, the crosslinking reaction of the resin matrix to form a polymer film terminates over a longer period of time (as may occur on storage) before reaching the gel point. In this case, the polymer film can still be melted homogeneously and is therefore processable in the sense of the present invention.

This latency makes it possible to produce, transport and store the polymer films according to the invention produced using a resin matrix.

By using a resin matrix according to the invention in which the cyanate ester component defined above is modified with the polyvalent phenol defined above, the polymer film of the invention can be cured at moderate temperatures, for example in the range of 100 ℃ to 200 ℃.

Unlike the known cyanate ester modification with epoxy, the inherent fire resistance is retained. The resin matrix used according to the invention and the polymer film according to the invention should therefore preferably be free of epoxy resin components.

The reactivity of the resin matrix used according to the invention can be increased, where appropriate, by adding known catalysts, such as metal acetylacetonates.

The resin matrix used according to the invention has been inherently flame resistant due to its network structure (structure due to heteroaromatic and high nitrogen content). Which combines a low heat release rate in the case of combustion with a small smoke density and a small proportion of toxic gases. In order to meet specific requirements, in particular for FST-performance (flammability, smoke, toxicity) in the region of the cabin of civil aircrafts, the substrate-supported polymer films of the invention may be provided with one or more additional flame retardants. Preferred are inorganic flame retardants, halogen-containing, nitrogen-containing or boron-containing flame retardants, intumescent (intumeszierende) flame retardants or mixtures thereof.

Suitable inorganic flame retardants are, for example, nonflammable inorganic fillers, such as oxides, hydroxides, oxide-hydrates, mixed oxides, sulfides, sulfates, carbonates, phosphates, fluorides, aluminum oxides (hydroxides), magnesium oxide, aluminum trihydroxide, magnesium dihydroxide, metal phosphates, ammonium polyphosphates, borates, zinc borates, sodium tetraborate decahydrate, boric acid, antimony trioxide, antimony pentoxide, red phosphorus, natural or synthetic silicon oxides such as diatomaceous earth, silica, quartz, cristobalite, silicates, talc, kaolin, mica, asbestos, pumice (Bimsmehl), perlite, feldspar, mullite, wollastonite, magnesium oxide, magnesium hydroxide, magnesium dihydroxide, magnesium hydroxide, metal phosphates, magnesium polyphosphate, aluminum oxide (hydroxide), magnesium oxide, magnesium hydroxide, magnesium dihydroxide, metal phosphates, aluminum polyphosphate, zinc borate, sodium tetraborate decahydrate, antimony trioxide, antimony pentoxide, red phosphorus, natural or synthetic silicon oxides such as diatomaceous earth, silica, quartz, silicate, kaolin, mica, asbestos, pumice (Bimsmehl), vermiculite, basalt, shale flour (Schiefermehl), glass powder, lava or aluminosilicates intergrown with quartz, synthetic silicon oxides such as pyrogenic silica, precipitated silica, silica gel, translucent quartz glass (Quarzgut), sheet silicates, bentonites, sulfates of metals of the second main group, such as calcium sulfate, magnesium sulfate, barium sulfate, synthetic and natural carbonates such as calcium carbonate, chalk, calcite or dolomite, silicon carbide, rock wool, graphite, glass spheres, hollow glass spheres, glass fibers, fibrous fillers such as asbestos, inorganic pigments or dyes.

Suitable halogen-containing flame retardants are, for example, decabromodiphenyl ether, ethane-1, 2-bis (pentabromophenol), ethylene-bis-tetrabromophthalimide, bromopolystyrene, tribromodiphenyl ether, tetrabromodiphenyl ether, pentabromodiphenyl ether, hexabromodiphenyl ether, heptabromodiphenyl ether, octabromodiphenyl ether, nonabromodiphenyl ether, decabromodiphenyl ether, tetrabromobisphenol A and derivatives thereof, polybrominated biphenyls such as decabromobiphenyl, hexabromocyclododecane, tetrabromophthalic anhydride (TBPA), TBPA-diester/ether, ethylene bis (tetrabromophthalimide) (EBTBP), salts of tetrabromophthalate, dibromoethyldibromocyclohexane, ethylene-bis (dibromonorbornane dicarboximide (-dicarboximide)), dibromoneopentyl glycol (DBNPG), tribromoneopentanol (TBNPA), vinyl bromide (VBr), 2, 4, 6-Tribromophenol (TBP); bis (tribromophenoxy) ethane (HBPE); tribromophenyl allyl ether (TBP-AE), poly (dibromophenyl ether) (PDBPO), pentabromoethylbenzene (5BEB), tetradecylboro-diphenoxybenzene (TDBDPB), poly (pentabromobenzyl acrylate) (PBB-PA) and Polydibromostyrene (PDBS).

Suitable nitrogen-containing flame retardants are, for example, melamine or melamine salts of boric acid, phosphoric acid or other inorganic acids.

Suitable phosphorus-containing flame retardants are, for example, phosphoric esters, ammonium polyphosphate, triphenyl phosphate, tricresyl phosphate, resorcinol-bis (diphenyl phosphate), dimethyl 2- ((hydroxymethyl) carbamoyl) ethyl) phosphonate, tetraphenylresorcinol bis (diphenyl phosphate) or organic phosphinic esters.

Suitable boron-containing flame retardants are, for example, boric acid, borax, borates, zinc borate, barium metaborate, calcium metaborate, sodium tetrafluoroborate or potassium tetrafluoroborate.

Suitable intumescent flame retardants are, for example, pure melamine, melamine monophosphate, melamine polyphosphate, melamine cyanurate, melamine pyrophosphate, Melam (Melam) (1, 3, 5-triazine-2, 4, 6-triamine-n- (4, 6-diamino-1, 3, 5-triazine-2-yl), melem (-2, 5, 8-triamino-1, 3, 4, 6, 7, 9, 9 b-heptaazaphenalene (heptazaphenalene)) [ CAS-No. 1502-47-2], Melon (Melon) (poly [ 8-amino-1, 3, 4, 6, 7, 9, 9 b-heptaazaphenalene-2, 5-diyl ] imino) or expandable graphite.

Particularly preferred flame retardants are, for example, oxides, hydroxides, oxide-hydrates and borates of Al, Mg, Ti, Si, Sb, Fe and Zn, glass spheres or hollow glass spheres, tetrabromobisphenol a, tetradecambroxylbiphenoxybenzene, bromopolystyrene, Polydibromostyrene (PDBS), decabromodiphenyl ether and derivatives thereof, polybromobiphenyl and 2, 4, 6-tribromophenol and mixtures formed from two or more of the foregoing flame retardants.

In a preferred embodiment of the invention, one or more other substances are added to the resin matrix to adjust the viscosity and rheology. The resin matrix used according to the invention alone may have a viscosity which is too low for further processing into a substrate-supported polymer film. Thus, suitable substances for adjusting the viscosity of the resin matrix or for adjusting the viscosity of the mixture for producing the polymer film according to the invention can be used. Suitable substances are, for example, silica, ceramic materials, organically modified silicates. The substances mentioned can be used individually or as mixtures.

In a further preferred embodiment of the invention, further additives are used which influence the properties of the invention. The skilled worker is aware of the additives which are customarily used for preparing paint and coating materials (cf. Lackadditive; Bieleman, Johan; Wiley-VCH-VerlagGmbH, Weinheim, 1998). Suitable additives are, for example, surface-modifying agents, in particular agents which reduce the surface tension, such as fluorocarbon-modified polymers.

In order to obtain a uniform and closed surface on the component coated according to the invention, it is particularly preferred that the polymer film produced according to the invention is free of plastic, glass or carbon fibers, in particular free of woven and laid webs.

In a particularly preferred embodiment of the invention, the additional substances are used in a proportion of from 0% to 85%, preferably from 5% to 75%, particularly preferably from 10% to 70%, based on the weight of the heat-treated polymer film.

In a preferred embodiment of the present invention, for the preparation of the resin matrix, suitable amounts of the cyanate ester component and the alcohol component are generally dissolved separately or jointly in a suitable solvent. Suitable amounts in the sense of the present invention are those of the cyanate ester component and the alcohol component which ensure that the abovementioned molar ratio of OCN groups to OH groups is achieved. Solvents suitable for the cyanate ester component and the alcohol component are known to the skilled person; solvents which are generally used are, for example, methyl ethyl ketone or acetone. The separately prepared solutions were then mixed.

In yet another embodiment of the present invention, the cyanate ester component may also be melted without solvent at mild temperatures (e.g., in the range of 40 ℃ to 80 ℃). The alcohol component is added in an amount suitable to obtain the desired molar ratio.

Where appropriate, catalysts, for example metal acetylacetonate complexes, may be added to promote crosslinking.

To prepare a polymer film according to the present invention, one or more additional substances are added to the resin matrix. They may be added at any time to any of several solutions of the cyanate ester component and the alcohol component or to the only or combined solution. If the operation is carried out in the absence of solvent, these further substances are added to the solvent-free mixture or to one of the starting components for this purpose. When fillers are added, dispersion is usually carried out using customary auxiliaries.

It is preferable, in particular, to add the filler to the cyanate ester component before the cyanate ester component is combined with the alcohol component, since, by stirring in the highly viscous mixture, heat is formed which strongly increases the reactivity and, in the worst case, can lead to complete thorough curing of the entire mixture. The alcohol component is then added.

The mixture is then applied in the form of a layer to a suitable substrate, for example by uniformly distributing the mixture over the substrate. Those conventional methods for applying layers are known to the skilled worker, for example knife coating, roller coating, spraying, pouring, dipping, drawing (Ziehen), brush coating, painting or centrifugal coating (Schleudern).

The mixture is applied to a substrate which serves as a support material and protection for the polymer film. The substrate is removed from the polymer film again after the polymer film has been applied to the prepreg, and preferably before the prepreg has been cured.

Suitable as carrier materials are, in particular, paper or plastic films which can be peeled off from the polymer films according to the invention. For this purpose, it is advantageous to use films or papers which are composed of materials which exhibit a low surface tension with respect to water, i.e. are hydrophobic, or which are coated with such materials. The base material of the plastic film is preferably a thermoplastic, particularly preferably polypropylene. Suitable as coating are in particular single-sided or double-sided silicone coatings.

Preferably, the mixture according to the invention is applied to a substrate in a layer thickness which ensures that the polymer film produced according to the invention has a thickness of from 1 μm to 500 μm, preferably from 1 μm to 200 μm. It is particularly preferred that the mixture is applied in a layer thickness which ensures that the polymer film has a thickness of 1 μm to 150 μm, more preferably 1 μm to 100 μm, most preferably 1 μm to 70 μm.

Subsequently, the mixture applied as a layer is subjected to a heat treatment at a temperature of 40 ℃ to 160 ℃. By this heat treatment, the resin matrix is prepolymerized, i.e., crosslinked. Wherein the temperature is selected such that possible solvents are removed but the gel point of the resin matrix is not reached. If a thermoplastic film is used as the carrier substrate, care should additionally be taken that the film does not soften.

The conditions of the heat treatment, such as temperature and duration, determine the degree of prepolymerization or crosslinking. The degree of preliminary polymerization or crosslinking is selected according to the respective requirements, but care is taken, as already mentioned, to be positioned before the gel point is reached, so that renewed melting and thus later shaping is possible. The heat treatment is preferably carried out at a temperature of between 40 ℃ and 160 ℃, preferably between 50 ℃ and 130 ℃, particularly preferably between 60 ℃ and 100 ℃.

The mixture used for the preparation of the polymer films according to the invention can, where appropriate, be stored in the form of a stack without predrying before it is formed into the layer form. Regardless of the form, it is preferably stored refrigerated during storage, where the temperature is generally between-40 ℃ and 0 ℃, preferably at-26 ℃.

Furthermore, the polymer film produced according to the invention can have a slight tackiness so that it remains adherent when placed on the inside of a prepreg, a green part or a mold. This tack must be sufficient to inhibit slippage on the one hand, and small enough to allow easy removal of the polymer film of the invention from the surface of the prepreg, component or mold without damaging or destroying it. The viscosity can be adjusted without further difficulty with tools known to the skilled person, where appropriate.

The substrate-supported polymer films produced according to the invention are used in the inventive method for the surface coating of fiber-plastic composites produced using prepregs, wherein the polymer film is applied to the prepreg surface on the resin side before the composite structure is placed in a mold and cured, the carrier substrate is removed and the (umden) comprising the polymer film is allowed to stand) The composite structure is then subjected to elevated temperatures to effect curing.

The polymer film of the invention is cured (corresponding to the curing temperature) at a temperature of from 100 to 200 ℃, preferably from 130 ℃ to 190 ℃, particularly preferably from 150 ℃ to 170 ℃.

Components, in particular interior components, made of fiber-plastic composite materials are usually produced from prepregs in a Core-crush (crusted-Core) process, i.e. in an autoclave or hot-pressing process, under pressure, wherein the pressure is adjusted such that the honeycomb Core is also easily deformed. The substrate-supported polymer film of the present invention is used as an in-mold coating in this process. In this process, the polymer film can be applied to the prepreg structure, for example, immediately before curing, or else it can be applied to the prepreg itself, and if appropriate bonded thereto, during the production of the prepreg.

The polymer film of the invention may for example be used in a one-step process in which a substrate-supported polymer film of the invention is applied to the surface of a prepreg structure, the structure is pressed into a mould after peeling off the substrate and removed from the mould after curing.

The polymer film of the invention can also be used, for example, in a two-step process in which the prepreg structure is first cured in a mold, after curing it is removed from the mold and then a polymer film is applied to the component, the component covered with the polymer film is cured again in the mold after peeling off the substrate and after curing the coated component is removed from the mold.

Since the substrate-supported polymer film of the invention inhibits the release of volatile components from the prepreg structure as gases by constituting a very dense and closed film, it can preferably be used as a coating for a phenolic resin-containing prepreg in a one-step process.

In a particular embodiment of the invention, a polymer film is applied to the surface of the prepreg structure, the prepreg structure is placed in a preheated mould after peeling off the substrate, the mould is pressed with pressure and the prepreg structure is cured. Preference is given to sandwich structures having a honeycomb core between prepreg layers containing phenolic resins and a curing time of from 2 to 20 minutes, particularly preferably from 5 to 15 minutes, and at a temperature of from 100 ℃ to 200 ℃, particularly preferably from 140 ℃ to 170 ℃, very particularly preferably at 160 ℃, and at a pressure of from 1.5 to 8bar, particularly preferably at 4 bar.

The FST properties of the fiber-plastic composite components coated according to the invention can be tested, for example, using standard test methods for fire resistance in connection with aeronautics, for example international standard ISO TC92/SC1 or Airbus directive (Airbus directive) ABD 0031.

The invention is illustrated in more detail below with reference to examples.

Examples

Example 1: preparation of Polymer films

The cyanate ester component is degassed, melted at a suitable, mild temperature and dissolved in acetone as needed. The alcohol component was separately dissolved in acetone. The fillers and flame retardants (see table 1) were added to the cyanate ester component. These components are then combined and mixed under stirring. The viscosity of the mixture is adjusted, where appropriate, by adding further fillers or additives. The resulting mixture was drawn down on one side of each of the siliconized films. The film thus coated is subsequently subjected to a heat treatment in a heating cabinet at a temperature of 60 ℃ to 100 ℃ over a period of 1 minute to 40 minutes. Here, the conditions of the heat treatment are selected according to the resin matrix used, so that the degree of pre-polymerization or pre-crosslinking of the polymer film is below its gel point.

Table 1:

composition of mixture for preparing polymer film

An optional (n.B.)

Example 2: preparation of coated interior Components for aviation

The Nomex honeycomb core was covered on both sides with prepreg layers impregnated with phenolic resin. The polymer film from example 1 was placed with the resin side on the surface of the structure. The carrier film is subsequently removed, the structure is placed in a mold heated to 160 ℃ and the mold is closed. A pressure of about 4bar was applied and the member was pressed at 160 ℃ for about 15 minutes. During the pressing time, the structure is shaped in a mold and cured in the mold. The finished component is then removed from the mold.

Claims (19)

1. Use of a substrate-supported polymer film, said polymer film comprising a film composed of a resin matrix, and said resin matrix being prepared with the following ingredients:

(a) at least one difunctional or more aromatic organic cyanate and

(b) at least one di-or higher functional aromatic alcohol,

the ratio of the two amounts being such as to ensure a molar ratio of OCN groups to OH groups in the starting materials used for preparing the prepolymer of between 95: 5 and 70: 30, and

(c) at least one filler, wherein the filler is selected from the group consisting of,

wherein the resin matrix has a degree of crosslinking below its gel point;

the use is as a surface coating for a fibre-plastic composite component which is produced from a composite structure comprising a core and at least one prepreg coating according to the core-breaking method,

it is characterized in that the preparation method is characterized in that,

the polymer film is applied with the resin side to the prepreg surface before the composite structure is cured and optionally before it is placed in a mould, wherein the curing is carried out under the action of pressure and at elevated temperature.

2. The use as claimed in claim 1, wherein the difunctional or more functional aromatic organic cyanate or one of these cyanates is selected from aromatic cyanates of the formula I,

wherein R is¹To R⁴Independently of one another, hydrogen, straight-chain or branched C₁-C₁₀-alkyl radical, C₃-C₈-cycloalkyl radical, C₁-C₁₀-alkoxy, halogen, phenyl or phenoxy, wherein said alkyl or aryl group may be fluorinated or partially fluorinated,

an aromatic cyanate selected from formula II below

Wherein R is⁵To R⁸Such as R¹To R⁴And z is a chemical bond, SO₂、CF₂、CH₂、CHF、CH(CH₃) Isopropylidene, hexafluoroisopropylidene, C₁-C₁₀Alkylene radical O, NR⁹、N＝N、CH＝CH、COO、CH N, CH-N-CH with C₁-C₈Alkyleneoxyalkylene of alkylene, S, Si (CH)₃)₂Or

And an aromatic cyanate selected from formula III below

Wherein R is⁹Is hydrogen or C₁-C₁₀-alkyl and n is a value from 0 to 20,

and prepolymers selected from the aforementioned cyanate esters.

3. Use according to claim 1 or 2, wherein the di-or more functional aromatic alcohol or one of these alcohols is selected from compounds having the structures I to III as described for cyanate esters in claim 2, and wherein the cyanate ester group is replaced by a hydroxyl group.

4. Use according to claim 1 or 2, wherein the difunctional or more functional aromatic organic cyanate or one of these cyanates is selected from the group consisting of novolak-type cyanate esters, bisphenol a-dicyanate derivatives, 4' -ethylenediphenyldicyanate and compounds having the formula III according to claim 2, and wherein n is 1, 2 or 3, R is⁹Is hydrogen and the methylene groups are all ortho to the cyanate ester groups, and/or the di-or higher functional aromatic alcohol or one of these alcohols is selected from bisphenol a and bis (hydroxyphenyl) sulfide.

5. Use according to claim 1 or 2, wherein the filler or at least one of the fillers is selected from organic salts of phosphorus.

6. Use according to claim 1 or 2, wherein the filler or at least one of the fillers is selected from silica, ceramic materials, organically modified silicones or siloxanes or mixtures thereof.

7. Use according to claim 1 or 2, wherein the filler content of the resin matrix is not more than 50% by weight.

8. Use according to claim 1, wherein the polymer film has one or more flame retardants selected from inorganic flame retardants.

9. Use according to claim 1, wherein the polymeric film has one or more flame retardants selected from halogen-, nitrogen-or boron-containing flame retardants.

10. Use according to claim 1, wherein the polymer film has one or more flame retardants selected from intumescent flame retardants.

11. Use according to one of claims 8 to 10, wherein the at least one flame retardant is selected from the group consisting of oxides, hydroxides, oxide-hydrates, borates, glass spheres, tetrabromobisphenol a, tetradecbromobisphenoxy benzene, bromopolystyrene, Polydibromostyrene (PDBS), decabromodiphenyl ether or derivatives thereof, polybromobiphenyl or 2, 4, 6-tribromophenol of Al, Mg, Ti, Si, Sb, Fe or Zn.

12. The use of claim 11, wherein the glass spheres are hollow glass spheres.

13. Use according to claim 1 or 2, wherein the resin matrix has at least one further additive.

14. Use according to claim 13, wherein the additive is selected from surface-modifying agents.

15. Use according to claim 1 or 2, wherein the polymer film has as a substrate a carrier film consisting of a thermoplastic material.

16. Use according to claim 1 or 2, wherein the polymer film has a thickness of 1 to 500 μm.

17. A method for surface coating a fiber-plastic composite structure, characterized in that,

a) applying a polymer film according to one of claims 1 to 16 with a resin side onto a prepreg surface of a fiber-plastic composite structure,

b) removing the substrate from the polymer film prior to curing and

c) the composite structure comprising the polymer film is shaped and cured at a temperature of 130 to 200 ℃ and at a pressure of 1.5 to 8bar for a time of 5 to 30 minutes.

18. The method of claim 17, wherein the polymer film is placed onto the composite structure prior to being placed into the mold.

19. The method of claim 17, wherein the polymer film is first placed into a mold and the composite structure is then placed on the polymer film within the mold.