Composite material comprising a mica-based flooring layer

Abstract

The invention relates to a multilayer prepreg comprising a first fibrous prepreg (1) and a second fibrous prepreg (2), one or two mica prepregs (3, 6) and a B-staged thermosetting resin (12, 22, 32), which can be different or identical for each layer. The mica prepreg is located on the upper (outer) part of the fibrous prepreg. The multilayer prepreg can present several additional fibrous prepregs (4, 5). The mica prepreg preferably comprises mica flakes in the form of a mica paper. The use of such a prepreg as a top or near-top surfacing layer of a composite material enables to determine an improvement of the burn-through and flame retardant properties of the composite material. The invention also discloses a cured composite panel, such as an aircraft part, obtainable by curing the multilayer prepreg to the C-stage.

Description

Background Technology

[0001] Large-scale public transportation industries, including air, rail, and sea transport, have been committed to reducing the weight of structural components in order to save fuel. This issue, for example, has led to the use of lightweight materials, particularly in the aircraft industry, a trend that has become even more pronounced due to climate discussions. A primary method for reducing component weight is to replace heavier metal (especially aluminum) components with corresponding composite parts made of fiber-reinforced thermosetting resins. Composite parts made of fiber-reinforced thermosetting resins are used in structural applications and for cabin interiors. These parts typically begin with so-called prepregs, which are sheets or reinforcing fibers impregnated with a stage B thermosetting resin. The prepreg is molded into the final shape of the part in a hot press or autoclave, with temperature applied while simultaneously applying vacuum and / or pressure, thereby curing the thermosetting resin to its final rigid stage C. Single-glass or carbon fiber reinforced prepregs containing thermosetting resins are commercially available and are commonly used in several large transportation applications.

[0002] However, since the introduction of such composite material parts into aircraft cabin interiors (especially commercial aircraft), fire has become a major safety hazard requiring attention from all certification bodies. In particular, commonly used thermosetting resins such as phenolic or epoxy resins are highly flammable. The heat, smoke, and gases released by burning such resins, as well as the degradation of the structural integrity of composite parts, can rapidly jeopardize aircraft safety. Specifically, the Federal Aviation Administration (FAA) has issued several regulations to certify the use of composite materials listed in FAR 25.853. Those regulations applicable to cabin interior materials will only permit the use of materials with very high fire resistance or flame retardancy.

[0003] Some materials, if simply used as coverings for aircraft structures (conventional metals or composites), may offer protection in fire situations. For example, major aircraft companies have added thermal insulation blankets to the walls of their fuselage structures, demonstrating that such solutions can withstand burn-through and provide passengers with at least five minutes of fire protection even without insulation. Thermal insulation layers can delay temperature rise and reduce heat transfer through the structure; however, layers suitable for this purpose are associated with a significant increase in weight. This, in turn, increases the aircraft's weight and can negatively impact fuel economy and maintainability.

[0004] EP 0373137 A2 discloses a fire-resistant structural element comprising mica paper impregnated with a thermosetting resin. This disclosure does not specify a preferred amount of mica used per square meter. Some exemplary embodiments involve a composition of 34 g / m². 2A laminate of a fine glass fabric supporting and impregnated with a layer of mica paper of a resin. The resin content is claimed to be in the range of 5% to 40%, preferably a silicone resin in the range of 10% to 15% is used.

[0005] US 2002 / 0017590 Al discloses an insulation system for an aircraft fuselage for increasing the burn-through resistance of the aircraft fuselage, which insulation system comprises a first insulation layer, a second insulation layer and a first interlayer. The insulation layers can be glass fiber containing layers. The insulation layers can preferably comprise reflective sheet minerals, such as vermiculite. The first interlayer is an "intermediate layer" (= sandwiched by the first and second insulation layers) of the first insulation layer and the second insulation layer (see drawings and related description). As no B-stage thermosetting resin is contained, the insulation system is not a prepreg.

[0006] WO 01 / 98434 Al also discloses an insulation system essentially in the form of a "mat" consisting of one or more layers of fibers surrounded by a sheath comprising at least a first support of organic material having sealing properties and an anti-condensation system, and of an impregnated mica paper. The mica paper preferably has a weight per unit area of less than 50 g / m 2 , and the mica flakes preferably have a shape factor (ratio of diameter to thickness) of more than 1000. The impregnant is an organic resin such as a silicone resin. This barrier product is also not a prepreg, as no B-stage thermosetting resin is mentioned.

[0007] US 5595817 A discloses a flame penetration barrier for fuselages, which flame penetration barrier comprises a composite of 100 g / m 2 to 600 g / m 2 of a phlogopite or white mica mica paper, laminated on at least one side of the phlogopite or white mica mica paper with a 30 to 300 g / m 2 of a needle felt layer consisting of flame resistant fibers, the mica paper being bonded to the needle felt layer by an adhesive which is a partially cross-linked latent adhesive as a component of the mica paper itself. The "needle felt layer" is obviously non-woven.

[0008] WO 2011 / 051090 Al discloses a fireproof plastic construction part for an aircraft. The plastic construction part comprises a substrate with a hard plastic or thermosetting resin and at least one mica-containing layer coated on the substrate. The substrate is preferably a composite material comprising reinforcing fibers. One exemplary embodiment comprises two prepregs of glass fabric impregnated with an epoxy resin (with a Nomex core sandwiched in between), and a pure mica paper laminated directly thereon. The amount of mica is preferably less than 50 g / m 2 of the substrate surface.

[0009] Mica insulation products have been used in lithium ion batteries to prevent thermal runaway. GB 2568688 A discloses for example a fireproof composite for protecting a lithium ion battery from thermal runaway, the fireproof composite comprising a single fiber core laminated between at least two layers of “phyllosilicate insulator”, each layer of “phyllosilicate insulator” comprising a phyllosilicate mineral (which can be a mica paper), optionally in an amount greater than 50% by weight of the insulating material, an optional layer of coarse cloth, and optionally further comprising a filler and / or a binder and / or fibers. Other publications disclosing mica insulation products for lithium ion batteries comprising a single layer of uncompressed, compressible fibers are WO 2017 / 042308 A1 and WO 2018 / 011384 A1.

[0010] In the field of rotating electrical machines, so-called “resin-rich” mica insulation tapes are well known. These mica insulation tapes typically consist of a backing glass cloth, a mica paper adhered to the backing glass cloth, and a B-stage resin (in particular an epoxy resin) embedded in the glass cloth and the mica paper. Such resin-rich tapes are typically provided wound on a spool, often used together with a separator tape to prevent individual fabric / mica turns from sticking together. Such resin-rich tapes are optionally B-staged around the winding of an electrical machine, in case of overlap, and subsequently the winding comprising the resin-rich insulation tapes is heated under pressure to form a thermoset mica-containing electrical insulation.

[0011] Another problem arises when a part is made from a multi-layer prepreg. In case of only one layer of prepreg, the thickness that can be achieved in the finished part can be insufficient. It is well known in the composite manufacturing industry to stack multiple prepreg layers in an up-down stack, thereby obtaining an increased thickness in the finished part. Such stacking brings the problem that air can be trapped at the boundaries between adjacent prepreg layers after stacking on top of each other. Boundaries with such air inclusions are sites of reduced mechanical strength in the cured finished part. The degree of air entrapment at the boundaries becomes more pronounced if the individual prepreg layers exhibit some degree of tackiness at their surfaces, which is desirable in view of the adhesion between each other to form a multi-layer prepreg stack. An easier method to cure such multi-layer prepreg with removal of most of the trapped air is to cure under vacuum, for example in a vacuum bag, however, this can become insufficient at higher amounts of air entrapment. In these cases, it can become necessary to cure under a more demanding pressure in terms of technology. An overview of problems related to multi-layer prepreg curing is found in the “Problems to be solved by the invention” section of US 10647828 B2.

[0012] The most advanced solutions and materials based on impregnated mica are based on silicon-based prepregs or other prepregs traditionally non-tacky. Then, although they provide some fire barrier properties, such prepregs cannot be used in the industry for co-curing with other traditional prepreg layups to avoid creating cured composite panels with high air inclusion, low interlaminar shear strength properties and low impact resistance. Composites with low interlaminar shear strength at the interface between a prepreg layup containing mica and the nearby prepreg layup, in case of application of impacts due to passenger abuse or loads generated due to additional weight and aircraft maneuvering, can lead to part cracking and failure. Examples of composite parts requiring high structural properties, high interlaminar shear strength values, low weight and good fire resistance are aircraft floors or seat components such as seat backrests and seat cushions.

[0013] Therefore, there is still a particular need in the aerospace industry for fire and flame resistant multilayer composites that can also be molded into aircraft parts, such as cabin or seat structures, while providing structural properties, limited weight addition and low cost manufacturing processes. SUMMARY

[0014] The present invention provides a prepreg material comprising at least:

[0015] • a mica-based layer comprising at least a thermosetting resin and mica

[0016] • a fibrous layer comprising at least a thermosetting resin and reinforcing fibers.

[0017] The present invention also provides a method for manufacturing said multilayer prepreg.

[0018] The present invention also further relates to a cured composite panel obtainable by curing the multilayer prepreg.

[0019] The present invention also relates to a method for manufacturing said cured composite panel.

[0020] Preferred embodiments of the above objects are as described in the respective dependent claims. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 is a schematic cross-sectional view of a multilayer prepreg of the present invention or of a composite panel of the present invention having essential features of the present invention.

[0022] Figure 2 is a schematic cross-sectional view of a multilayer prepreg of the present invention or of a composite panel of the present invention having essential features and some optional or preferred additional features. DETAILED DESCRIPTION

[0023] REFERENCE Figure 1The multilayer prepreg of the present invention having the essential features comprises: a prepreg 1 comprising a first fiber layer, said prepreg 1 comprising first reinforcing fibers 11 and a B-staged first thermosetting resin 12; a prepreg 2 comprising a second fiber layer, said prepreg 2 comprising second reinforcing fibers 21 and a B-staged second thermosetting resin 22; and a first mica prepreg 3 comprising a first mica layer 31 and a B-staged second thermosetting resin 32 and optionally a second mica prepreg. The thermosetting resins 12, 22 and 32 can have the same or different resin composition.

[0024] Optionally, as shown in the dashed box, the multilayer prepreg of the present invention can comprise one or more prepreg layers 4, 5 comprising additional fiber layers, which are similar or identical in structure to the prepregs 1, 2 comprising the first and second fiber layers. The multilayer prepreg of the present invention can also optionally comprise, instead of or in addition to the above-mentioned additional fiber- containing prepregs, a second mica prepreg 6 having a similar or identical structure to the first mica prepreg 3. The optional second mica prepreg 6 and the first mica prepreg 3 sandwich all fiber- containing prepregs therebetween. Figure 2 The following sections describe the individual components.

[0025] Fiber prepregs 1, 2 and optionally 4, 5

[0026] Each fiber prepreg comprises reinforcing fibers. Reinforcing fibers include glass, carbon or graphite fibers having a high tensile strength. The tensile strength of all reinforcing fibers is preferably at least 3000 MPa, more preferably their tensile strength is in the range of 3500 to 10000 MPa, more preferably 3500 to 6000 MPa. Reinforcing fibers can be in the form of continuous tows composed of multiple filaments, as continuous unidirectional or multidirectional tapes, or as woven fabrics. Furthermore, the fibers can be sized or not sized. Preferably, for all fiber- containing prepreg layers, the reinforcing fibers are in the form of fiber layers, such as woven fabric layers. The fiber layers preferably have an areal weight in the range of 100 g / m 2 to 400 g / m 2 and / or a thickness in the range of 0.1 mm to 0.4 mm (as measured with a thickness gauge such as a caliper at 0.2 bar overpressure). More preferably, the woven fabric layers are in the form of a satin weave, most preferably fulfilling all of the aforementioned features. A preferred fiber material for any of the aforementioned fiber embodiments is glass, i.e. E-glass, S-glass or basalt. The most preferred example of a fiber layer is a Tuffnel® 7781 E-glass fabric and a Tuffnel® 6580 S-glass fabric.

[0027]

[0028] ​Based on the fiber prepreg, the content of reinforcing fibers in any fiber prepreg is preferably in the range of 30 to 70 volume %, more preferably in the range of 50 to 65 volume %.

[0029] The first and second fiber prepreg are arranged adjacent to each other, wherein no mica layer is arranged between any of them. The multilayer prepreg of the present invention can optionally comprise one or more additional fiber prepregs, provided also that these fiber prepregs are arranged adjacent to each other and to the prepreg comprising the first fiber layer, wherein no mica layer is arranged between any of them. If additional prepregs are present, their number is preferably 1-10, more preferably 1-5. Due to the inclusion of the mandatory first and second fiber prepregs, this gives 3 to 12 and 3 to 7 fiber prepregs, respectively, as preferred embodiments.

[0030] In addition to the reinforcing fibers, the first, second and optional one or more further fiber prepregs comprise an impregnated, partially cured B-stage thermoset resin. These thermoset resins can be cured at a temperature, as exemplified below. Preferably, each fiber prepreg comprises in total at least 98 wt.%, more preferably 100 wt.% of reinforcing fibers and impregnated B-stage thermoset resin.

[0031] The first mica prepreg 3 and the optional second mica prepreg 6

[0032] The mica prepreg 3, 6 comprises a mica layer 31 of mica in the form of a particulate sheet silicate (phyllosilicate). The sheet silicate is more preferably a flake, for example in the form of mica flakes. Examples of sheet silicates of the mica group are phlogopite, muscovite, fluorophlogopite, biotite, lepidolite, xanthophyllite, ecladonite or a combination of two or more thereof.

[0033] The first mica layer 31 is provided with sheet silicate (e.g. mica) in an amount of at least 50 grams per square meter (g / m 2 , preferably 50 to 200 grams per square meter, more preferably 55 to 100 grams per square meter, it being understood that “per square meter” refers to the square meter of the second surface 14 adjacent to the first mica prepreg. Preferably, especially in case of limited weight addition is required, for example in aircraft applications, the weight per area of the mica paper is 55 g / m 2 to 100 g / m 2 .

[0034] The first mica layer can also optionally comprise a first support glass screen, preferably a lightweight glass screen. More preferably, the first support glass screen exhibits a geometric surface of its own of 20 to 50 grams per square meter.

[0035] The second mica layer preferably provides the sheet silicate (e.g. mica) in an amount of at least 50 grams per square meter (g / m 2 , more preferably 50 to 200 grams per square meter, even more preferably 55 to 100 grams per square meter, it being understood that “per square meter” refers to the square meter of the first surface 13 that the second mica pre-preg is facing. Preferably, especially in case of limited weight addition is required, for example in aircraft applications, the weight per unit area of the mica paper is 55 g / m 2 to 100 g / m 2 .

[0036] The second mica layer can also optionally comprise a second support glass screen, preferably a lightweight glass screen. More preferably, the second support glass screen itself exhibits a geometric surface of 20 to 50 grams per square meter.

[0037] Sheet silicates such as mica flakes can not expand or can expand if subjected to high temperatures or fire. Expanding refers hereinafter to a mechanism in which a material increases its volume as a result of the application of heat. Expanding can contribute to reduce the thermal conductivity of the surface layer, thereby improving the heat and fire resistance properties of the composite substrate. An example of thermally expanding mica flakes are uncalcined mica flakes. Uncalcined mica flakes are typically produced from mica by a hydraulic mechanical process. Particularly preferred for the purposes of the present invention are expandable mica flakes such as uncalcined phlogopite mica flakes.

[0038] Most preferably, the mica layer comprises mica, such as expandable mica flakes of uncalcined phlogopite mica in the form of a mica paper. In the context of the present invention, by the term “mica paper” it is understood that, based on the sheet, the sheet comprises at least 95% by weight, preferably close to or equal to 100% by weight of mica in the form of oriented flakes.

[0039] Such mica papers are typically produced by reducing mica extracted from mines in the form of flakes into granules, which can be achieved by mechanical disintegration under water and processing the slurry thus obtained on machines similar to paper machines (Fourdrinier machines). An example of such mica paper production is described in CH274605A.

[0040] In these known manufacturing processes, to manufacture such mica papers, it is necessary to use a slurry in which 90% by volume of mica flakes of less than 800 pm are present. Furthermore, these flakes need to have a specific thickness range to produce a mica layer that acts as a fire barrier. Therefore, in one embodiment of the present application, the mica flakes have a diameter and a thickness in a range such that the shape factor, i.e. the diameter divided by the thickness, is lower than 1000, preferably lower than 500. On the other hand, the shape factor is typically at least 100. Typical average diameter of uncalcined mica flakes is 500 pm and typical average thickness is 1.5 pm, resulting in a shape factor of about 330. For the purpose of the present application, any diameter, thickness and shape factor of the flakes are determined as described in Example 1.

[0041] The inventors believe that the use of mica flakes having a shape factor in the range as indicated above allows to manufacture a prepreg material and then a cured composite panel having a low resin content (in the mica layer) and a high adhesion. It is believed that the use of calcined flakes having a shape factor higher than 1000 would result in a mica based prepreg having a low adhesion and thus not suitable for curing. On the other hand, a prepreg having a very high resin content would be more adhesive but then this would result in an excess of thermoset resin in the final cured composite panel. Said excess of resin results in low fire properties, in particular high vertical burn self-extinction time and high heat release values. Said higher resin content would also affect the burn-through behavior and increase the possibility of flame penetration through the composite panel.

[0042] The mica paper thus obtained does not have any support layer, such as a support glass fabric, and can be used for the purpose of the present application in this form. However, a commercial type of mica paper which can comprise such a support layer can also be used in the present application.

[0043] Optionally, the mica prepreg further comprises a layer of light weight support fibers to facilitate the impregnation process and handling of the mica prepreg. When present, the layer of light weight support fibers is preferably a glass fabric. When present, the layer of light weight support fibers is more preferably a glass fabric in an amount of 20 to 35 g / m2.

[0044] In addition to the sheet silicate, the mica prepreg further comprises a B-stage thermoset resin as exemplified below and impregnating the sheet silicate. In particular, it was found that the B-stage thermoset resin is present in an amount of 40 to 60 wt%, more preferably 45 to 55 wt% based on the total weight of the respective mica prepreg. It is believed that a lower resin content would result in a prepreg having a low adhesion and thus not suitable for Figure 1 or 2, while an excess of resin content would result in a prepreg having a low fire resistance. The mica prepreg preferably comprises at least 98 wt%, more preferably 100 wt% of the sheet silicate and the impregnated B-stage thermoset resin in total.

[0045] In particular, it was found that based on the first mica layer, at least 40% of resin is needed in the first mica prepreg to obtain a good interlaminar shear strength at the interface between the first mica prepreg and the first fiber prepreg.

[0046] The interlaminar shear strength property describes the shear strength between a layer comprising a fiber prepreg and a layer comprising a mica prepreg when the multilayer prepreg of the present invention is cured to the C-stage. The interlaminar shear strength of laminates with thermoset matrices, such as those made from epoxy resins, is typically determined using the short beam shear test (SBS). ASTM D2344 is a standard test method for determining the apparent interlaminar shear strength of parallel fiber-reinforced composite materials cured to the C-stage.

[0047] The thickness of each fiber prepreg comprising a B-stage thermoset resin is preferably in the range of 0.2 to 0.6 mm, more preferably in the range of 0.3 to 0.5 mm.

[0048] The thickness of each mica prepreg (comprising a B-stage thermoset resin) is preferably in the range of 0.2 to 0.6 mm, more preferably in the range of 0.3 to 0.5 mm.

[0049] The optional second mica prepreg can have a different composition than the first mica prepreg, or can have the same composition. The latter is preferred.

[0050] Thermoset resin

[0051] The following explanations apply to the thermoset resin present in each fiber prepreg as well as in the first mica prepreg and the optional second mica prepreg. In general, as used herein, “thermoset resin” refers to the resin as originally synthesized, in the A-stage, where no significant curing has yet occurred. As present in any prepreg layer, the thermoset resin is prefixed with “B-stage” or “B-stage” at the partial curing stage. As present in the composite sheet of the present invention, the fully cured resin is referred to herein as “C-stage thermoset resin” or “thermoset resin”.

[0052] The thermoset resin is a thermally curable system with high viscosity at ambient temperature.

[0053] The thermoset resin can be the same for all prepregs, or can be different for the mica-containing layers and the other fiber prepregs. Preferably, it is the same for all prepregs of the multilayer prepreg of the present invention.

[0054] The thermosetting resin is typically a resin containing functional groups in the amount and type that enable covalent crosslinking upon heating. Depending on the type of crosslinkable functional groups, it may be used with a hardener or a free radical initiator while remaining substantially unreactive at room temperature.

[0055] The thermosetting resin (or resin composition) used for impregnating / soaking reinforcing fibers is preferably a curable or heat-curable resin containing one or more uncured thermosetting resins, including but not limited to epoxy resins, imides (e.g., polyimide or bismaleimide), vinyl ester resins, cyanate ester resins, isocyanate-modified epoxy resins, phenolic resins, furan resins, benzoxazine, formaldehyde condensation resins (e.g., resins condensed from formaldehyde with urea, melamine or phenol), polyesters, acrylics, mixtures thereon, blends and combinations thereof.

[0056] Commercially available epoxy resins suitable for the main resin matrix include those with a viscosity of 8-20 Pa, preferably at 25°C. Linear phenolic resins (Novolac resin); glycidyl ethers of linear phenolic resins (e.g., DEN431 or DEN438 from Dow); dicyclopentadiene-based linear phenolic resins (e.g., Tactix 556 from Huntsman); diglycidyl esters of 1,2-phthalic acid (e.g., GLY CEL A-100); diglycidyl derivatives of dihydroxydiphenylmethane (bisphenol F) (e.g., PY 306 from Huntsman). Other epoxy resins include alicyclic compounds, such as 3',4'-epoxycyclohexyl-3,4-epoxycyclohexane carboxylate (e.g., CY 179 from Huntsman).

[0057] Adding a curing agent and / or catalyst to a curable matrix resin is optional, but if desired, the use of such a curing agent and / or catalyst may increase the curing rate and / or decrease the curing temperature.

[0058] Thermosetting resins may contain toughening elements that can be added to the resin composition during the mixing process, such as polymers based on amorphous thermoplastics, such as polyetherimide, polyimide, or polyethersulfone, to form a toughened thermosetting resin system with increased viscosity and resin toughness, thereby improving the impact resistance of the final cured composite laminate.

[0059] A preferred heat-curing resin is an epoxy resin. Suitable epoxy resins include polyglycidyl derivatives of aromatic diamines, aromatic monoprimarines, aminophenols, polyphenols, polyols, polycarboxylic acids. The epoxy resin is preferably a composition comprising 50 to 70 wt% of an epoxy resin component, the epoxy resin component comprising one or more epoxy resins. Di-, tri- and tetra-functional epoxy resins can be used.

[0060] A more preferred group of heat-curing epoxy resins are linear phenolic glycidyl ethers comprising or consisting of moieties of formula (I):

[0061] (I)

[0062] wherein

[0063] - R a is always hydrogen or always methyl;

[0064] - B is always *-CH2-** or always ;

[0065] - 0.8 to 0.99 of the Y moieties are -O-glycidyl groups, the remainder of the Y moieties being essentially OH, a monovalent residue of structure *-O-CH2-CH(OH)-CH2-OH or a divalent bridging spacer of structure *-OCH2-CH(OH)-CH2-O-** connecting two moieties according to the above formula (I).

[0066] and wherein the linear phenolic glycidyl ether has an epoxy equivalent weight EEW in the range of 160 to 270 g / eq. Commercial examples of the above are DEN431 and DEN438 from Dow Chemical and Tactix 556 from Huntsman.

[0067] Other more preferred heat-curing epoxy resins are 1,2-phthalic acid diglycidyl ester (e.g. GLYCEL A-100); reaction products of dihydroxydiphenylmethane (bisphenol F) with epichlorohydrin (e.g. PY 306 from Huntsman); and epoxy-containing cycloaliphatic compounds such as 3',4'-epoxycyclohexyl-3,4-epoxycyclohexane carboxylate (e.g. CY179 from Huntsman).

[0068] The heat-curing resin preferably has a viscosity of 8-20 Pa s at 25°C measured with a Brookfield viscosimeter (paddle method, 200 rpm) before any curing to B-stage.

[0069] The heat-curing resin can further comprise a curing agent, a hardener and / or an accelerator.

[0070] In the case of epoxy resins, the curing agent is usually a dicyandiamine.

[0071] If a latent curing accelerator is used in the thermally curable epoxy resin, the latent curing accelerator is preferably a urea derivative of formula (II):

[0072] (II)

[0073] wherein

[0074] R 1a and R 1b may be the same or different and are each selected from the group consisting of hydrogen, Ci-C6-alkyl and C3-C6-cycloalkyl; or R 1a and R 1b together with the nitrogen atom to which they are attached form a heterocyclic ring substituent selected from the group consisting of aziridinyl, azetidinyl, pyrrolidinyl and piperidinyl;

[0075] R 2a and R 2b are the same or different and are each selected from the group consisting of hydrogen and Ci-C6-alkyl; and

[0076] R 3a , R 3b and R 4 are the same or different and are each selected from the group consisting of hydrogen, halogen, Ci-C6-alkyl, Ci-C6-alkoxy, -C(O)R 5 , -N(H)-C(O)-NR 1a R 1b , -CN, NO2, trifluoromethyl, -SOR 6 and SO2R 6 ; wherein R 5 is selected from the group consisting of hydrogen, Ci-C6-alkyl, Ci-C6-alkoxy, C3-C6-cycloalkyl and NR 1a R 1b , and R 6 is selected from the group consisting of Ci-C6-alkyl, Ci-C6-alkoxy and C3-C6-cycloalkyl.

[0077] Preferably, in formula (II), R 1a and R 1b are the same or different and are both Ci-C6-alkyl; more preferably, they are both the same Ci-C6-alkyl; most preferably, they are both methyl. Preferably, in formula (II), R 2a and R 2b are different, one being hydrogen and the other being Ci-C6-alkyl; more preferably, one of R 2a and R 2b is hydrogen and the other is methyl. Preferably, in formula (II), R 3aand R 3b one of R 5 and the other is selected from -C(O)R 1a R 1b , -CN, -SOR 6 and SO2R 6 , more preferably R 3a and R 3b one of R 1a and the other is hydrogen. Preferably, in formula (II), R 1a is hydrogen or Ci-C6alkyl. 4

[0078] These accelerators are conventional per se, some of them being commercially available. For such accelerators, reference can be made to, for example, formula (II) of US4283520A, formula (I) of GB1192790A and GB2300187A; these publications are incorporated herein by reference.

[0079] A more preferred sub-group of compounds of formula (II) has the following combinations:

[0080] - both R 1a and R 1b are methyl;

[0081] - one of R 2a and R 2b is hydrogen and the other is methyl;

[0082] - one of R 3a and R 3b is -N(H)-C(O)-NR 1a R 1b and the other is hydrogen; and

[0083] - R 4 is hydrogen.

[0084] If dicyandiamide is used in the preferred heat-curable epoxy resin which does not contain urea derivatives of formula (II) above, the molar amount m e of dicyandiamide relative to the total amount of epoxy units is preferably in the range of 10 to 20 mole %, more preferably 15 to 20 mole % of dicyandiamide, wherein said m e can be calculated by the following formula

[0085]

[0086] wherein

[0087] MW 双氰胺 is the molecular weight of dicyandiamide (in g / mol).​

[0088] EEW g is the epoxy equivalent weight (in g / eq) of the linear phenol formaldehyde glycidyl ether (I); and

[0089] m 双氰胺 and m g are the amounts (in g) of dicyandiamide and linear phenol formaldehyde glycidyl ether (I), respectively.

[0090] In a more preferred embodiment of the present application, the thermosetting resin comprises a linear phenol formaldehyde resin glycidyl ether as described above, dicyandiamide as indicated above and a urea derivative of formula (II). In this case, the above-mentioned m e Preferably, dicyandiamide is in the range of 2.0 to 5.0 mol%, more preferably in the range of 3.0 to 4.0 mol%. Furthermore, here the amount of dicyandiamide is preferably in the range of 0.3 to 2.0 wt.%, more preferably in the range of 0.5 to 1.5 wt.%, and the urea derivative of formula (II) is preferably in the amount of 3 to 7 wt.%, more preferably 4 to 6 wt.%, based on the total composition.

[0091] Preferably, the thermosetting resin 12, 22 further comprises one or more flame- retardant liquid or solid additives. These flame-retardant liquid or solid additives are more preferably selected from the group consisting of:

[0092] a) a compound of the following formula (III):

[0093] (III)

[0094] wherein R 7 is selected from the group consisting of hydrogen, alkyl and -(CH2) p COO(CH2) q CH3, wherein p and q are integers from 2 to 4;

[0095] b) aluminum or magnesium hydroxide;

[0096] c) ammonium polyphosphate; and

[0097] d) a phosphate ester of the general formula (IV):

[0098] (IV)

[0099] wherein R 8 , R 9 and R 10 may be the same or different and are each selected from the group consisting of C 1-8 alkyl and phenyl.

[0100] Flame retardant a) is commercially available and known, for example, from DE 2646218 A1 which is incorporated herein by reference. Preferably, in compound (III) R 7 is hydrogen or -(CH2)2COO(CH2)3CH3. The total amount of flame retardant a) (if present) is preferably in the range of 3 to 10 wt.-%, based on the heat-curing resin. More preferably, 4 to 8 wt.-% of compound (III) (wherein R 7 = only -(CH2)2COO(CH2)3CH3), or a combination of 2 to 5 wt.-% of compound (III) (wherein R 7 = (CH2)2COO(CH2)3CH3) and 4 to 6 wt.-% of compound (III) (wherein R 7 = H) are present.

[0101] Flame retardant b) is actually a hydrated oxide, namely MgO*H2O and AI2O3*3H2O. When subjected to high temperatures, they respectively dehydrate to the inert (non-flammable) MgO and AI2O3. This dehydration reaction is endothermic and consumes the heat of the fire; the released water acts as a heat sink to stop the fire from spreading. Flame retardant b) is preferably a powder that is milled or micronized to have a particle size distribution such that D 90 is 20 microns, i.e. 90% of the particles have a particle size of at most 20 microns. Flame retardant b) (if present) is preferably used in an amount of 10 to 25 wt.-%, based on the heat-curing resin.

[0102] Flame retardant c) is commercially available and can be made according to the art by reacting phosphoric acid (54% P2O5 or higher, e.g. orthophosphoric acid) with gaseous ammonia, thereby neutralizing the heat-vaporized water and dehydrating the ammonium polyphosphate, followed by granulation in a pug mill or a rotary granulator. Flame retardant c) (if present) is preferably used in an amount of 2 to 15 wt.-%, based on the heat-curing resin.

[0103] Flame retardant d) is commercially available. Preferably, in formula (IV) R 8 , R 9 and R 10 are identical. More preferably, they are all butyl groups. Flame retardant d) (if present) is preferably used in an amount of 2 to 4 wt.-%, based on the heat-curing resin.

[0104] Preferably, the heat-curing resin comprises at least one of flame retardants a) and b), and optionally also c) and / or d).

[0105] More preferably, the heat-curing resin comprises a combination of:

[0106] As for flame retardant a), 4 to 8 wt.-% of compound (III) (wherein R 7= only -(CH2)2COO(CH2)3CH3), or 2 to 5 wt.-% of compound (III) (wherein R 7 = (CH2)2COO(CH2)3CH3) in combination with 4 to 8 wt.-% of compound (III) (wherein R 7 = H);

[0107] as flame retardant b), 10 to 25 wt.-% of aluminum hydroxide, based on the thermally curable resin;

[0108] optionally as flame retardant c), 2 to 6 wt.-% of ammonium polyphosphate, based on the thermally curable resin; and

[0109] optionally as flame retardant d), 2 to 5 wt.-% of tributyl phosphate, based on the thermally curable resin.

[0110] Further examples of flame retardants and smoke suppressants that impart specific flame retardant properties are metal oxides, zinc borate and phosphorus-modified epoxy resins.

[0111] The thermally curable resin can further comprise additional ingredients, such as ceramic microspheres and / or performance enhancers or modifiers. As an example, the performance enhancers or modifiers can be selected from the group consisting of softeners, tougheners / particles, additional accelerators, core-shell rubbers, UV stabilizers / additives, viscosity modifiers / flow control agents and wetting agents.

[0112] The thermally curable resin can further comprise a reaction product of a diglycidyl ether of bisphenyl A and / or bisphenyl F with a carboxyl-terminated butyl nitrile rubber as a tackifier. The term "carboxyl-terminated butyl nitrile rubber" (abbreviated as CTNB) is conventional in the art and refers to a butadiene-acrylonitrile rubber that is terminated by, for example, using an organometallic reagent (in particular a dilithium organometallic reagent, such as butyllithium), followed by quenching with carbon dioxide. More preferably, the carboxyl-terminated butyl nitrile rubber herein is liquid at room temperature. The reaction product is preferably used in an amount of 10 to 25 wt.-%, more preferably 3 to 6 wt.-%, based on the thermally curable resin. Such reaction products of CTNB with the diglycidyl ether of bisphenyl A or F are also known and can typically be carried out in a weight ratio of 1 to 10 parts by weight of CTNB per 100 parts by weight of the diglycidyl ether of bisphenyl A or B.

[0113] The thermally curable resin can further comprise, as an air release additive, a polyether-modified methylalkyl polysiloxane copolymer having the structure of formula (VI):

[0114] (VI)

[0115] wherein

[0116] R 1 is a linear or branched monovalent C 1-10alkyl, in particular methyl;

[0117] G is a monovalent polyoxyalkylene group having formula (VII):

[0118] (VII)

[0119] wherein R is a divalent C 2-20 alkylene group; X is selected from the group consisting of hydrogen and linear or branched C 1-6 alkyl; m is an integer in the range of 2 to 50; n is an integer in the range of 0 to 50; and the sequence of oxyethylene and 2-oxypropylene units can be block or random;

[0120] Q is R 1 or G, preferably R 1 , most preferably methyl;

[0121] j is an integer in the range of 1 to 20; and

[0122] k is an integer in the range of 0 to 200.

[0123] The air release polyether-modified methylalkyl polysiloxane copolymer is preferably used in an amount of 0.1 to 1 wt.-% based on the thermosetting resin. Examples thereof are known, e.g., from EP 0 341 952 A1, further examples thereof are marketed, e.g., by Byk as defoaming agents.

[0124] It is in particular found that in any one of the above thermosetting resins, in particular in the above epoxy resins, a combination comprising:

[0125] i) the adhesion-enhancing reaction product of the above diglycidyl ether of bisphenol A and / or bisphenol F and

[0126] ii) the above air release polyether-modified methylalkyl polysiloxane copolymer

[0127] allows the production of fabric-containing prepreg layers having tacky surfaces, which can be stacked into multilayer prepregs exhibiting sufficiently low air content at the borders of the prepregs to allow curing under simpler vacuum technology. The resulting cured composite layers exhibit high interlaminar shear strength values and impact resistance.

[0128] When used in combination, the amounts of the above i) and ii) are preferably in the range of 5 to 25 wt.-% and 0.1 to 1 wt.-%, respectively, or more preferably 10 to 20 wt.-% and 0.2 to 0.7 wt.-%, respectively, and even more preferably 10 to 15 wt.-% and 0.2 to 0.5 wt.-%, respectively, based on the total thermosetting resin.

[0129] The present invention also relates to a process for manufacturing the multilayer prepreg of the present invention.

[0130] The first method initially produces each prepreg from a mica layer and two or more reinforcing fiber layers, that is, each of the mica layer and the reinforcing fiber layers is separately impregnated with a thermosetting resin and each impregnated layer is separately cured to the B-stage. Depending on the type of thermosetting resin impregnated into the reinforcing fabric and the mica layer, the curing conditions, in particular the curing temperature and time, can be easily determined by the skilled person based on the desired degree of tackiness of the multilayer prepreg. This method is suitable for different thermosetting resins for each layer or the same thermosetting resin for all layers. The individual B-stage prepregs are then stacked on top of each other in the order according to the application. The residual tackiness allows sufficient adhesion between the individual prepregs. Preferably here, for the production of each impregnated layer, the thermosetting resin in pure form is first applied in a controlled grammage on a planar support, for example a PET foil or paper, and the resin film is then used to impregnate the mica layer and / or the reinforcing fiber layer. Then, depending on the thermosetting resin, the impregnation is preferably carried out at slightly elevated temperature (e.g. 100 to 150 °C) to sufficiently reduce the viscosity of the resin so as to impregnate the mica layer and the reinforcing fiber layer. Alternatively, the resin is first dissolved or suspended in a solvent to reduce the viscosity, preferably with a known volume or weight dilution factor, and then the respective mica layer and / or reinforcing fiber layer is directly impregnated with the resin solution or dispersion at room temperature or at a temperature generally below 100 °C. The solvent is then dried off and the individual B-stage prepregs, which usually contain a lower amount (typically less than 5 wt% of the final prepreg) of residual volatiles, are heated.

[0131] The second method is suitable for the case where the thermosetting resin is the same in all layers of the multilayer prepreg. This method employs resin transfer. In this method, a number of reinforcing fiber layers corresponding to the number of reinforcing fiber-containing prepregs in the multilayer prepreg of the application and the required number of mica layers (e.g. mica paper) are stacked on top of each other in the appropriate order, so that if there are two mica layers, they sandwich all the reinforcing fiber layers. The layered composite thus obtained is then transferred to a vacuum bag and impregnated with a thermosetting resin in a single step by means of vacuum by injection or infusion of the thermosetting resin. Suitable thermosetting resins for injection or infusion are available on the market. However, the inventors prefer to provide a formulated resin system with low viscosity, long pot life and good self-extinguishing properties.

[0132] The impregnated layered composite thus obtained can be cured again under vacuum or pressure to the B-stage multilayer prepreg of the application.

[0133] However, there is no need to cure the multilayer prepreg immediately into a C-stage product. The latent hardener and / or accelerator of the thermosetting resin can be chosen as is customary in the art, with a sufficient degree of delay to allow the multilayer prepreg of the application to be stored under refrigerated conditions or even possibly at room temperature for a reasonable shelf life.

[0134] The application also relates to a composite panel obtainable from the multilayer prepreg of the application.

[0135] Herein, a "composite panel" is understood to be the multilayer prepreg of the application cured to C-stage, thus comprising at least the thermosetting resin. In addition to the C-stage multilayer prepreg of the application, the composite panel of the application can optionally comprise a core of another material (e.g. polyurethane or rubber foam or honeycomb). Said core can give the composite panel more bulk, helping to further reduce weight and / or helping to mold the composite panel into a desired shape (see below). The C-stage multilayer prepreg will generally be completely embedded in the optional core. Alternatively, if the multilayer prepreg of the application comprises a sufficient number of other fiber prepregs, it can be cured and molded directly without the need for such a core to be used in conjunction with the intended parts exemplified above. If the multilayer prepreg comprises only one mica layer, this mica layer will preferably end up facing the outside of the core-containing composite panel, i.e. towards the environment. The composite panel of the application can be applied to a variety of mass transportation applications, including but not limited to aircraft and railway applications. The composite panel can be in the form of a top or near-top deck layer of a composite material (e.g. an aircraft). Examples of the composite panel are, on the one hand, the primary and secondary structures of the exterior of an aircraft, including but not limited to the fuselage, the wings, the nacelles or the engine fire containment shroud. Other preferred embodiments of the composite panel of the application are parts of the interior structure of an aircraft, such as the fuselage interior fire barrier, the floor panels, the cargo compartment liner, the cabin walls and the composite sandwich, which would benefit from the use of the application in view of the improved fire, smoke and toxicity (FST) performance and reduced heat release (HR) values. By way of example, other applications include some parts of an aircraft seat. The C-stage composite panel of the application does not exhibit flame penetration during a burn-through test at a temperature of 1100°C for 5 minutes. The composite panel of the application is able to simultaneously determine an improved burn-through performance and an improved fire retardancy of the cured composite material.

[0136] The composite panel of the application is also by Figure 1 or Figure 2and the related explanations, no optional core embedded therein is shown in the figures, except for any B-stage thermoset resin 12, 22, 32 which is converted into the corresponding C-stage thermoset resin. The first mica prepreg 3 and the optional second mica prepreg 6, after curing to the C-stage, act as a fire barrier when exposed to fire. They provide a tolerance of more than 5 minutes to the composite panel if exposed to a temperature of about 1100°C. They also reduce the temperature transferred to the composite panel, thus delaying the combustion process. They furthermore provide an improvement in FST, which means a reduction in fire time, smoke and toxic gas emissions, and a reduction in the HR (Heat Release) value of the composite panel in case of fire event. Depending on the grammage of the mica layer contained therein, they even further provide a delay of 30 seconds or more in the peak heat release in case of fire.

[0137] The present invention also relates to a method of producing such a composite panel.

[0138] The conversion of the multilayer prepreg of the present invention into such a composite panel can be carried out similarly to prior art prepregs. In one variant, the B-stage multilayer prepreg of the present invention can be inserted into a plate or a forming mold of a hot press, optionally in common use with a compressible core to facilitate the covering of the mold by the multilayer prepreg, and cured under heat and pressure into a C-stage composite panel.

[0139] The term "forming mold" is understood here as a set of at least two rigid heat-resistant parts, for example made of ceramic or steel, each having a molding surface and at least one mating surface, intended to mate tightly with one of the mating surfaces of one or more other parts of the set, so that, when all the parts of the set are joined together without the multilayer prepreg and mate tightly on their mating surfaces, their molding surfaces together form a cavity corresponding to the shape of the part to be molded, and, with the multilayer prepreg of the present invention placed on or inserted into one or more of the molding surfaces, when all the parts of the set are joined together on their mating surfaces, they mate tightly on application of pressure and sufficient heat to cause the initial softening of the B-stage resin of the encapsulated multilayer prepreg.

[0140] In another variant, the method for producing the multilayer prepreg of the present invention using vacuum and said single impregnation resin can be carried out, but the direct curing of the C-stage composite panel of the present invention is then obtained by using more stringent curing conditions.

[0141] The curing to the C-stage is preferably carried out at elevated temperatures up to 180°C, preferably in the range of 120°C to 160°C, and wherein a high pressure is used, suitably a pressure of at most 10 bar (1 MPa), preferably in the range of 3 bar (0.3 MPa) to 7 bar (0.7 MPa), to suppress the distortion effect of the evolving gases, or to suppress void formation. Preferably, the curing temperature is obtained by heating the two dies of the press at the specific temperature. Post-curing can be carried out at temperatures of 160°C to 200°C and atmospheric pressure, with a suitable heating rate to increase the glass transition temperature of the C-stage resin matrix.

[0142] The application will now be further illustrated by the following non-limiting examples.

[0143] Example 1 : Measurement of the shape of mica flakes

[0144] As understood in the present application, the process starts from a mica paper. A sample of mica paper is diluted in demineralized water and sonicated with ultrasound at room temperature for 30 minutes. A drop of the solution is deposited on a silicon support. After drying, the mica flakes are observed in SEM and digitally photographed in 8-bit grayscale. 10 pictures are taken at 1000x magnification at different sites at the place where the drop was dried. On each image, the Feret diameter of all mica particles along all possible directions is determined by pixel color intensity using the image processing software ImageJ (step 5°), and an average value is formed therefrom to give the "diameter of the mica particles" as understood in the present application. The "thickness of the mica flakes" as understood in the present application can also be determined from SEM pictures at a magnification of 1000x with the dried mica sample placed vertically. The "shape factor of the mica flakes" as understood in the present application is then formed by dividing the diameter by the thickness.

[0145] Example 2: Thermosetting resin for impregnation of mica layers and / or fabric layers

[0146] Table 1 : Thermosetting resin compositions for impregnation of mica layers and / or fabric layers.

[0147]

[0148] The components numbered 1, 2 and 3 are mixed at 40-50°C under stirring for 20 minutes. Then to them are mixed under stirring at the same temperature the components numbered 6 and 7 for 15-20 minutes. Then the component numbered 4 is added under stirring at the same temperature for a further 20-30 minutes. Finally, to them is mixed under stirring at the same temperature the component numbered 5 for a further 15-20 minutes. The obtained resin formulation can be used directly for prepreg manufacturing (see example 3 below). Alternatively, the formulation can be cooled to room temperature or stored refrigerated.

[0149] Example 3: Preparation of a fiber-containing prepreg

[0150] The thermosetting resin 2 of Table 1 in Example 2 was used. The prepreg was prepared on a Menzel type impregnator. At a temperature of 55°C, the resin was applied in a neat (solvent-free) form in a fine thickness film on a PET carrier foil using a doctor blade. Fresh resin was fed from a bath to the doctor blade, the resin flowing from the bath to the doctor blade by its own gravity. The resin level in the bath was kept constant by a sensor, the bath being replenished from a reservoir by a pump if necessary. The thickness of the applied film was given by the gap between the doctor blade and the carrier foil. The resin content of the final prepreg was directly related to the thickness of the resin film on the PET carrier foil. The thickness of the resin film was chosen so that the weight per unit area of the PET carrier foil was about two thirds of the weight per unit area of the fabric contained in the prepreg, in this case a 296 g / m 2 E-glass fabric (type US 7781). The fabric was stacked on the resin film on the PET carrier foil at 100°C, whereby the glass fabric was impregnated with the semi-solid formulation film and impregnated due to the capillary action of the resin, which was improved due to the presence of the polyether-modified methylalkyl polysiloxane copolymer in the resin. The thus obtained impregnated fiber-containing layer contained about 200 g / m 2 and thus about 40% by weight of the thermosetting resin. It was passed through a drying oven kept at 140°C, with a residence time usually in the range of 4 to 6 min, whereby the degree of B-stage curing and the tackiness of the resin could be controlled by choosing the appropriate residence time. The final B-stage could be controlled manually or by DSC measurement. The thus obtained fiber-containing prepreg had a weight per unit area of about 495 g / m 2 after peeling off the PET carrier foil. The fiber-containing prepreg could be wound on a roll, with the PET film still on it as a release foil to prevent the wound prepreg layers from sticking together.

[0151] Example 4: Preparation of a mica prepreg

[0152] The same procedure as in Example 3 was followed, except that instead of the glass fabric of type US 7781, a mica paper containing uncalcined, expandable white mica flakes was applied on it, at 120 g / m 2 The thus prepared mica prepreg contained about 45% by weight of the B-stage resin. The resulting prepreg was tacky enough to be further used as a layer in a stacking sequence suitable for the final curing.

[0153] Example 5: Preparation of a multilayer prepreg and curing it into a composite product in the form of a fireproof sheet

[0154] Three multilayer prepregs were built as follows (the table rows represent the order in which the prepreg layers are stacked on top of each other):

[0155] Table 2 Build from multilayer prepregs.

[0156]

[0157] All three B-stage multilayer prepregs were cured in a vacuum bag at 160°C for 20 minutes to give C-stage composite panels 2 and 3 of the invention (from multilayer prepregs 2 and 3, respectively) or C-stage comparative composite panel 1 (from multilayer prepreg 1), respectively. All composite panels were tested as follows.

[0158] Table 3

[0159]

[0160] The result is surprising because the use of mica in thermoset composite laminates is not expected to provide fire retardant properties. The prior art uses silicone in combination with mica to achieve good self-extinguishing properties. The present result is surprising because it uses an epoxy-based thermosetting system which traditionally has a high tendency to burn and a high heat release compared to the silicone of the prior art. The test shows that the composite panels of the invention, whether containing only one mica cured layer 3 or two mica cured layers 3, 6, have the required fire resistance because in neither case did flame penetration occur within the 15 minutes of fire exposure during the test. The comparative composite panel 1 showed flame penetration only 150 seconds after the start of the test.

[0161] Example 6: Manufacturing of composite panels by vacuum resin infusion

[0162] A commercial one-component epoxy isocyanate resin (BLENDURIK01 sold by Covestro), basalt-based fabric or glass fabric of type US 7781, and mica paper with a weight of 160 g / m2were used. Six layers of basalt (or glass) fabric were stacked on top of each other, optionally with a layer of mica paper arranged on one side of the stack of basalt (or glass) fiber layers. Then all the layered resin-free composite material was closed under a vacuum bag and the epoxy isocyanate resin was infused under vacuum, thereby simultaneously impregnating the entire layered composite material. The impregnated layered composite material was then cured at 160°C for 20 min, directly to the C-stage. The total resin content of the resulting composite panels was about 40 wt% in all cases. Those layered composite materials containing mica paper provided a transition intermediate of the invention during curing of the B-stage multilayer prepreg of the invention, and then provided a C-stage composite panel. Thus, the composite panels obtained were built as follows (the table rows represent the order in which the layers are stacked on top of each other before impregnation): 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2

[0163] Table 4

[0164]

[0165] Flame penetration tests similar to those described in Table 4 above were performed on all four composite panels. It was shown that the inventive composite panels 6.2 and 6.4 exhibited small burn lengths and no flame penetration after 5 minutes, while the control composite panels 6.1 and 6.3 exhibited visible burning and flame penetration after a short time.

Claims

1. A multilayer prepreg, comprising: a) First fiber prepreg (1) comprising a first surface (13), a second surface (14) and a first reinforcing fiber (11) impregnated with a first stage B thermosetting resin (12). b) A second fiber prepreg (2), adjacent to the first surface (13) of the first fiber prepreg (1), comprises a second reinforcing fiber (21) impregnated with a second stage B thermosetting resin (22); and c) A first mica prepreg (3), adjacent to the second surface (14) of the first fiber prepreg (1), comprising a content of at least 50 g / m². 2 The first mica layer (31) is impregnated with a third stage B thermosetting resin (32) in an amount of at least 40% by weight based on the first mica prepreg (3).

2. The multilayer prepreg according to claim 1, comprising one or more additional fiber prepregs (4, 5) adjacent to the second fiber prepreg (2), each of the one or more additional fiber prepregs (4, 5) comprising additional reinforcing fibers impregnated with additional thermosetting resin.

3. The multilayer prepreg according to claim 1 or 2, comprising a second mica prepreg (6), the second mica prepreg (6) comprising a second mica layer and impregnated with another additional B-stage thermosetting resin, such that the first mica prepreg (3) and the second mica prepreg (6) sandwich all fiber prepregs (1, 2, 4, 5) therebetween.

4. The multilayer prepreg according to claim 1, wherein the first mica layer (31) comprises mica in an amount of 50 to 200 g / m².

5. The multilayer prepreg according to claim 1, wherein the first mica prepreg (3) comprises mica in the form of mica flakes.

6. The multilayer prepreg according to claim 5, wherein the mica flakes are uncalcined mica flakes.

7. The multilayer prepreg according to claim 1, wherein the first mica prepreg (3) comprises a first supporting glass screen.

8. The multilayer prepreg according to claim 1, wherein all B-stage thermosetting resins (12, 22, 32) comprise flame retardant additives selected from: a) Compounds of formula (III): (III) Where R 7 Choose from hydrogen, alkyl groups, and -(CH2). p COO(CH2) q A group consisting of CH3, where p and q are integers from 2 to 4; b) Aluminum hydroxide or magnesium hydroxide; c) Ammonium polyphosphate; and d) Phosphates of general formula (IV): (IV) Where R 8 R 9 and R 10 Selected independently from C 1-8 Alkyl and phenyl.

9. The multilayer prepreg of claim 1, wherein all B-stage thermosetting resins (12, 22, 32) comprise a combination of the following substances: i) The reaction products of diglycidyl ethers of bisphenol A and / or bisphenol F with carboxyl-terminated nitrile rubber, and ii) Polyether-modified methylalkyl polysiloxane copolymers having the structure of formula (VI): (WE) in R 1 Is the unit price C of a straight chain or a branch chain? 1-10 alkyl; G is a monovalent polyoxyethylene group having formula (VII): (VII) Where R is divalent C 2-20 alkylene group; X is selected from hydrogen and straight-chain or branched C. 1-6 The group consisting of alkyl groups; m is an integer in the range of 2 to 50; n is an integer in the range of 0 to 50, where n is not 0; and the sequence of the oxyvinyl unit and the 2-oxypropenyl unit is block or random; Q is R 1 Or G; j is an integer in the range 1 to 20; and k is an integer in the range of 0 to 200; Furthermore, in each stage B thermosetting resin (12, 22, 32), based on the amount of the stage B thermosetting resin, the amounts of i) and ii) are in the range of 10 to 20% by weight and 0.1 to 1.0% by weight, respectively.

10. The multilayer prepreg according to claim 1, wherein all B-stage thermosetting resins (12, 22, 32) are selected from the group consisting of imides, formaldehyde condensation resins, epoxy resins, free radical crosslinkable resins, cyanate ester resins, furan resins, benzoxazine, and combinations thereof.

11. The multilayer prepreg according to claim 1, wherein all B-stage thermosetting resins are B-stage epoxy resins.

12. The multilayer prepreg of claim 1, wherein all B-stage thermosetting resins (12, 22, 32) are identical.

13. The multilayer prepreg of claim 3, wherein the second mica layer comprises mica in an amount of 50 to 200 g / m².

14. The multilayer prepreg according to claim 3, wherein the second mica prepreg (6) comprises mica in the form of mica flakes.

15. The multilayer prepreg according to claim 3, wherein the second mica prepreg (6) comprises a second supporting glass screen.

16. A method for preparing the multilayer prepreg of claim 1, comprising the following steps: a) Provide a first reinforcing fiber (11), impregnate the first reinforcing fiber with a first B-stage thermosetting resin (12), and cure the resin-impregnated reinforcing fiber to the B-stage to obtain a first fiber prepreg (1) having a first surface (13) and a second surface (14). b) Provide a second reinforcing fiber (21), impregnate the second reinforcing fiber (21) with a second B-stage thermosetting resin (22), and cure the resin-impregnated reinforcing fiber to the B-stage to obtain a second fiber prepreg (2); c) Optionally, additional reinforcing fibers and one or more additional thermosetting resins are provided, the additional reinforcing fibers are impregnated with the one or more additional thermosetting resins, and the additional reinforcing fibers impregnated with the additional resins are cured to stage B to obtain one or more additional fiber prepregs (4, 5), each of the one or more additional fiber prepregs (4, 5) comprising additional reinforcing fibers impregnated with an additional stage B thermosetting resin. d) Provide a first mica layer (31), the first mica layer comprising a content of at least 50 g / m². 2 The first mica layer (31) is impregnated with a third B-stage thermosetting resin (32) and the resin-impregnated first mica layer (31) is cured to the B-stage to obtain the first mica prepreg (3). e) Optionally, it may be provided to include a concentration of at least 50 g / m². 2 The second mica layer of mica in an amount of ) is impregnated with another additional thermosetting resin, and the second mica layer impregnated with the other additional thermosetting resin is cured to stage B to obtain the second mica prepreg (6). The order of a), b), optional c), d), and optional e) is arbitrary; and f) Arrange the second fiber prepreg (2) adjacent to the first surface (13); g) Arrange the first mica prepreg (3) adjacent to the second surface (14); h) Optionally, if step c) is performed, the one or more additional fiber prepregs (4, 5) are arranged adjacent to and adjacent to each other with the second fiber prepreg (2); i) Optionally, if step e) is performed, then the second mica prepreg (6) is made... - If step c) is not performed, then it is adjacent to the second fiber prepreg (2), or - If step c) is performed, then the first mica prepreg (3) and the second mica prepreg (6) are adjacent to the one or more additional fiber prepregs (4, 5) such that the first mica prepreg (3) and the second mica prepreg (6) sandwich all the fiber prepregs (1, 2, 4, 5) therebetween.

17. The method of claim 16, wherein the preparation comprises having a concentration of at least 50 g / m². 2 The steps of the first mica prepreg (3) or the second mica prepreg (6) also include providing an additional lightweight support fiber layer and impregnating the mica and the fiber layer with the same thermosetting resin.

18. A method for preparing the multilayer prepreg of claim 1, comprising the following steps: i) Provide a first reinforcing fiber (11) having a first surface (13) and a second surface (14) in the form of a layer; ii) Provide a second reinforcing fiber (21); iii) Optionally, additional reinforcing fibers may be provided; iv) Provides a product containing at least 50 grams per square meter (g / m²) 2 The first mica layer of mica (31); v) Optionally, it may be provided to include a concentration of at least 50 g / m². 2 The second mica layer contains a significant amount of mica. The order of i), ii), optional iii), iv), and optional v) is arbitrary; and vi) Arrange the second reinforcing fiber (21) adjacent to the first surface (13); vii) Arrange the first mica layer (31) adjacent to the second surface (14); viii) Optionally, if step iii) is performed, the additional reinforcing fiber is arranged adjacent to the second reinforcing fiber (21); ix) Optionally, if step v) is performed, the second mica layer is arranged as follows: - If step iii) is not performed, then it is adjacent to the second reinforcing fiber (21), or - If step iii) is performed, then the additional reinforcing fibers are adjacent to each other, such that the first mica layer (31) and the second mica layer sandwich all the reinforcing fibers between them; x) Place the layered composite material containing all reinforcing fibers and all mica layers in a vacuum; xi) Impregnating the layered composite material with a thermosetting resin under vacuum; and xii) The impregnated layered composite material is cured to stage B to obtain the multilayer prepreg.

19. A composite board that can be obtained through the following steps: 1) Provide a multilayer prepreg according to any one of claims 1 to 15; 2) Optionally, a core is provided and the core is encapsulated in the multilayer prepreg; and 3) Use heat and pressure to cure the multilayer prepreg, optionally including a core, in a molding die to stage C.

20. The composite panel according to claim 19, wherein the composite panel is in the form of an aircraft component.

21. A method for producing a composite board according to claim 19 or 20, comprising the following steps: 1) Provide a multilayer prepreg according to any one of claims 1 to 15; 2) Optionally, a core is provided and the core is encapsulated in the multilayer prepreg; and 3) Use heat and pressure to cure the multilayer prepreg, optionally including a core, in a molding die to stage C.

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