FIBER REINFORCEMENT FOR ANISOTROPIC FOAMS

Abstract

The invention relates to a molding composed of extruded foam, wherein at least one fiber (F) is present with a fiber region (FB2) within the molding and is surrounded by the extruded foam, while a fiber region (FB1) of the fiber (F) projects from a first side of the molding and a fiber region (FB3) of the fiber (F) projects from a second side of the molding, and the extruded foam is produced by an extrusion process comprising the following steps: I) providing a polymer melt in an extruder, II) introducing at least one blowing agent into the polymer melt provided in step I) to obtain a foamable polymer melt, III) extruding the foamable polymer melt obtained in step II) from the extruder through at least one die aperture into an area at lower pressure, with expansion of the foamable polymer melt to obtain an expanded foam, and IV) calibrating the expanded foam from step III) by conducting the expanded foam through a shaping tool to obtain the extruded foam.

Claims

1.-16. (canceled)

17. A molding made of extruded foam, wherein at least one fiber (F) is present with a fiber region (FB2) within the molding and is surrounded by the extruded foam, while a fiber region (FB1) of the fiber (F) projects from a first side of the molding and a fiber region (FB3) of the fiber (F) projects from a second side of the molding, and the extruded foam is produced by an extrusion process comprising the following steps: I) providing a polymer melt in an extruder, II) introducing at least one blowing agent into the polymer melt provided in step I) to obtain a foamable polymer melt, III) extruding the foamable polymer melt obtained in step II) from the extruder through at least one die aperture into an area at lower pressure, with expansion of the foamable polymer melt to obtain an expanded foam, and IV) calibrating the expanded foam from step III) by conducting the expanded foam through a shaping tool to obtain the extruded foam, wherein the fiber (F) has been introduced into the extruded foam at an angle α of 10° to 70° relative to the thickness direction (d) of the molding and wherein two or more fibers (F) are at an angle β to one another in the molding, where the angle β is in the range of β=360°/n where n is an integer.

18. The molding according to claim 17, wherein i) the polymer melt provided in step I) comprises at least one additive, or at least one additive is added during step II) to the polymer melt or between step II) and step III) to the foamable polymer melt, or iii) at least one additive is applied during step III) to the expanded foam or during step IV) to the expanded foam, or iv) at least one layer (S2) is applied to the extruded foam during or directly after step IV), or v) the following process step is conducted after step IV): V) material-removing processing of the extruded foam obtained in step IV).

19. The molding according to claim 17, wherein the extruded foam is based on at least one polymer selected from polystyrene, polyester, polyphenylene oxide, a copolymer prepared from phenylene oxide, a copolymer prepared from styrene, polyaryl ether sulfone, polyphenylene sulfide, polyaryl ether ketone, polypropylene, polyethylene, polyamide, polyamide imide, polyether imide, polycarbonate, polyacrylate, polylactic acid, polyvinyl chloride, or a mixture thereof.

20. The molding according to claim 19, wherein the polymer being styrene, a mixture of polystyrene and poly(2,6-dimethylphenylene oxide), a mixture of a styrene-maleic anhydride polymer and a styrene-acrylonitrile polymer (SMA/SAN), or a styrene-maleic anhydride polymer (SMA).

21. The molding according to claim 20, wherein a copolymer prepared from styrene having, as comonomer for styrene, a monomer selected from α-methylstyrene, ring-halogenated styrenes, ring-alkylated styrenes, acrylonitrile, acrylic esters, methacrylic esters, N-vinyl compounds, maleic anhydride, butadiene, divinylbenzene and butanediol diacrylate.

22. The molding according to claim 17, wherein the extruded foam comprises cells, where i) at least 50% of the cells are anisotropic, or the ratio of the largest dimension (a direction) to the smallest dimension (c direction) of at least 50% of the cells is ≧1.05, or iii) the mean size of the smallest dimension (c direction) of at least 50% of the cells is in the range from 0.01 to 1 mm, or iv) at least 50% of the cells are orthotropic or transversely isotropic, or at least 50% of the cells, based on their largest dimension (a direction), are aligned at an angle γ of ≦45° relative to the thickness direction (d) of the molding, or vi) the extruded foam has a closed cell content of at least 80%, or vii) the fibers (F) are at an angle ε of ≦60° relative to the largest dimension (a direction) of at least 50% of the cells of the extruded foam.

23. The molding according to claim 17, wherein i) at least one of the mechanical properties of the extruded foam is/are anisotropic, or ii) at least one of the elastic moduli of the extruded foam behave(s) in the manner of an anisotropic material, or iii) the ratio of the compressive strength of the extruded foam in thickness (z direction) to the compressive strength of the extruded foam in length (x direction) or the ratio of the compressive strength of the extruded foam in thickness (z direction) to the compressive strength of the extruded foam in width (y direction) is ≧1.1.

24. The molding according to claim 15, wherein i) the extruded foam has a thickness (z direction) in the range from 4 to 200 mm, a length (x direction) of at least 200 mm and a width (y direction) of at least 200 mm, or ii) the surface of at least one side of the molding has at least one recess and at least one recess being produced on the surface of at least one side of the molding after the performance of step IV), or iii) the surface of at least one side of the molding has at least one recess and at least one recess being produced on the surface of at least one side of the molding after the performance of step V).

25. The molding according to claim 17, wherein i) the fiber (F) is a single fiber or a fiber bundle, or ii) the fiber (F) is an organic, inorganic, metallic or ceramic fiber or a combination thereof, or iii) the fiber (F) is used in the form of a fiber bundle having a number of single fibers per bundle of 300 to 10 000 in the case of glass fibers and 1000 to 50 000 in the case of carbon fibers, or iv) the fiber region (FB1) and the fiber region (FB3) each independently account for 1% to 45% and the fiber region (FB2) for 10% to 98% of the total length of a fiber (F), or v) the fiber (F) has been introduced into the extruded foam at an angle α of 30° to 60° relative to the thickness direction (d) of the molding, or vi) in the molding, the first side of the molding from which the fiber region (FB1) of the fiber (F) projects is opposite the second side of the molding from which the fiber region (FB3) of the fiber (F) projects, or vii) the molding comprises a multitude of fibers (F), or comprises more than 10 fibers (F) or fiber bundles per m.sup.2.

26. A panel comprising at least one molding according to claim 17 and at least one layer (S1).

27. The panel according to claim 26, wherein the layer (S1) comprises at least one resin.

28. The panel according to claim 27, wherein the resin being based on epoxides, acrylates, polyurethanes, polyamides, polyesters, unsaturated polyesters, vinyl esters or mixtures thereof.

29. The panel according to claim 26, wherein the layer (S1) additionally comprises at least one fibrous material, where i) the fibrous material comprises fibers in the form of one or more laminas of chopped fibers, webs, scrims, knits or weaves, or ii) the fibrous material comprises organic, inorganic, metallic or ceramic fibers.

30. The panel according to claim 26, wherein the panel has two layers (S1) and the two layers (S1) are each mounted on a side of the molding opposite the respective other side in the molding.

31. The panel according to claim 26, wherein i) the fiber region (FB1) of the fiber (F) is in partial or complete contact with the first layer (S1), or ii) the fiber region (FB3) of the fiber (F) is in partial or complete contact with the second layer (S1), or iii) the panel has at least one layer (S2) between at least one side of the molding and at least one layer (S1), or iv) the at least one layer (S1) comprises a resin and the extruded foam of the molding of the panel has a surface resin absorption of ≦2000 g/m.sup.2, or v) the at least one layer (S1) comprises a resin and the panel has a peel resistance of ≧200 J/m.sup.2.

32. A process for producing a molding according to claim 17, which comprises partly introducing at least one fiber (F) into the extruded foam, as a result of which the fiber (F) is present with the fiber region (FB2) within the molding and is surrounded by the extruded foam, while the fiber region (FB1) of the fiber (F) projects out of a first side of the molding and the fiber region (FB3) of the fiber (F) projects out of a second side of the molding, as a result of which the fiber (F) has been introduced into the extruded foam at an angle α of 10° to 70° relative to the thickness direction (d) of the molding.

33. The process according to claim 32, wherein at least one fiber (F) is partially introduced into the extruded foam by sewing it in using a needle.

34. The process according to claim 33, wherein the partial introduction being effected by means of steps a) to f): a) optionally applying at least one layer (S2) to at least one side of the extruded foam, b) producing one hole per fiber (F) in the extruded foam and in any layer (S2), the hole extending from a first side to a second side of the extruded foam and through any layer (S2), c) providing at least one fiber (F) on the second side of the extruded foam, d) passing a needle from the first side of the extruded foam through the hole to the second side of the extruded foam, and passing the needle through any layer (S2), e) securing at least one fiber (F) on the needle on the second side of the extruded foam, and f) returning the needle along with the fiber (F) through the hole, such that the fiber (F) is present with the fiber region (FB2) within the molding and is surrounded by the extruded foam, while the fiber region (FB1) of the fiber (F) projects from a first side of the molding or from any layer (S2) and the fiber region (FB3) of the fiber (F) projects from a second side of the molding.

35. The process according to claim 34, wherein the process is carried out with simultaneous performance of steps b) and d).

36. A process of producing a panel according to claim 26, which comprises producing, applying and curing the at least one layer (S1) in the form of a reactive viscous resin on a molding according to claim 17.

37. The process according to claim 36, which is carried out by liquid impregnation methods.

38. The use of a molding according to claim 17 or of a panel according to claim 34 for rotor blades in wind turbines, in the transport sector, in the construction sector, in automobile construction, in shipbuilding, in rail vehicle construction, for container construction, for sanitary installations or in aerospace.

Description

EXAMPLES

Example 1

[0198] a) Production of the Foams

[0199] For all the inventive experiments, various extruded foams (examples IF1 to IF6) are used. For comparison, polymer foams were produced by the particle foaming process (comparative examples CF7 and CF8). Table 1 gives an overview of the foams used and the characteristic properties thereof. The individual foams are produced as follows and then trimmed to 20 mm for the reinforcement:

[0200] IF1, IF2 and IF3:

[0201] The foam slabs of the invention are produced in a tandem extrusion system. 100 parts polystyrene (PS 148H, BASF) are supplied continuously to a melting extruder together with flame retardant and additives (0.2 part talc). The flame retardants and additives are in the form of masterbatches in polystyrene (PS 148H, BASF). Through an injection port incorporated in the melting extruder (ZSK 120), blowing agents (CO.sub.2, ethanol, i-butane) are fed in continuously. The total throughput including the blowing agents is 750 kg/h. The blowing agent-containing melt is cooled down in a downstream cooling extruder (KE 400) and extruded through a slot die. The foaming melt is taken off by a heated calibrator, the surfaces of which have been coated with Teflon, via a conveyor belt at different takeoff speeds and formed to slabs. Typical slab dimensions prior to mechanical processing are about width 700 mm (y direction) and thickness 50 mm (z direction).

[0202] IF4:

[0203] Analogously to IF1, the foam slab is produced in a tandem extrusion system. The melting extruder (ZSK 120) is supplied continuously with polyphenylene ether masterbatch (PPE/PS masterbatch, Noryl C6850, Sabic) and polystyrene (PS 148H, BASF), in order to produce an overall blend consisting of 25 parts PPE and 75 parts PS. In addition, additives such as talc (0.2 part) are metered in via the intake as a PS masterbatch (PS 148H, BASF). Blowing agents (CO.sub.2, ethanol and i-butane) are injected into the injection port under pressure. The total throughput including the blowing agents and additives is 750 kg/h. The blowing agent-containing melt is cooled down in a downstream cooling extruder (ZE 400) and extruded through a slot die. The foaming melt is taken off by a heated calibrator, the surfaces of which have been coated with Teflon, via a conveyor belt and formed to slabs. Typical slab dimensions prior to mechanical processing are about width 800 mm (y direction) and thickness 60 mm (z direction).

[0204] IF5:

[0205] Analogously to IF1, the same tandem extrusion system is used with the same throughputs. The polymer used is a blend of 50 parts styrene-maleic anhydride polymer (SMA) (Xiran SZ26080, Polyscope) and 50 parts styrene-acrylonitrile polymer (SAN) (VLL25080, BASF). In addition, nucleating agents (0.2 part talc) and stabilizers (0.2 part Tinuvin 234) are added. The blowing agents used are CO.sub.2, acetone and i-butane.

[0206] IF6:

[0207] Polyester foams are foam-extruded through a multihole die in an extrusion system. The thermoplastic polymers (dried PET beads) are melted in the melting zone of the twin screw extruder (screw diameter=132 mm, ratio of length to diameter=24) and mixed with nucleating agent. After the melting, cyclopentane is added as blowing agent. The total throughput is about 150 kg/h. Directly after addition of the blowing agent, the homogeneous melt is cooled by means of the downstream housings and the static mixer. Before it reaches the multihole die, the melt has to pass through a melt filter. The expandable melt is foamed by means of the multihole die and the individual strands are combined to a block by means of a calibrator unit. The extruded slabs are subsequently subjected to finishing by material removal to a constant outer geometry and joined by thermal welding parallel to the extrusion direction. The mean density of the foam is 60 kg/m.sup.3.

[0208] CF7:

[0209] The foam used is a polyester-based molded foam. The expandable beads and the foam slabs are produced analogously to WO 2012/020112, example 7.

[0210] CF8:

[0211] The foam used is a polystyrene-based molded foam which is produced as a foam slab in a particle foaming machine and then sawn into slabs (raw material basis: Styropor P326, BASF).

[0212] b) Characterization of the Foams

[0213] The properties of the foams are determined as follows: [0214] Glass transition temperature (T.sub.G): Glass transition temperature is determined according to ISO 11357-2 (July 2014 version) at a heating rate of 20 K/min under a nitrogen atmosphere from the second heating run. [0215] Anisotropy: For the determination of anisotropy, microscope images of the cells of the middle region of the foams are evaluated statistically. The largest dimension of the cells is referred to as “a direction”, and the two other, orthogonally oriented dimensions (b direction and c direction) result therefrom. Anisotropy is calculated as the quotient between the a direction and c direction. [0216] Orientation of the a direction of the cell relative to the thickness direction (d); angle γ: The orientation of the a direction of the cell is likewise evaluated by means of microscope images. The angle formed between the a direction and the thickness direction (d) gives the orientation. [0217] Smallest dimension of the cell (c direction): Analogously to anisotropy, the smallest dimension of the cells is determined by statistical analysis of the microscope images. [0218] Compressive strength in z direction: Compressive strength is determined in accordance with DIN EN ISO 844 (as per German version October 2009). [0219] Ratio of compressive strength of the foam in z direction to the compressive strength of the foam in x direction (compressive strength z/x): The ratio of compressive strength in z direction to the compressive strength in x direction is determined by the quotient of the two individual values. [0220] closed-cell content: closed-cell content is determined according to DIN EN ISO 4590 (as per German version August 2003). [0221] Density: The density of the pure foams is determined according to ISO 845 (October 2009 version). [0222] Resin absorption: For resin absorption, foams are compared after material has been removed from the surface by planing. As well as the resin systems used, the foam slabs and glass rovings, the following auxiliary materials are used: nylon vacuum film, vacuum sealing tape, nylon flow aid, polyolefin separation film, polyester tearoff fabric and PTFE membrane film and polyester absorption fleece. Panels are produced from the moldings by applying fiber-reinforced outer plies by means of vacuum infusion. Two plies of Quadrax glass rovings (E glass SE1500, OCV; textile: Saertex, isotropic laminate [0°/−45°/90°45°] with 1200 g/m.sup.2 in each case) each are applied to the upper and lower sides of the foams. For the determination of the resin absorption, a separation film is inserted between the foam and the glass rovings, in contrast with the standard production of the panels. In this way, the resin absorption of the pure foam is determinable. The tearoff fabric and the flow aids are mounted on either side of the glass rovings. The construction is subsequently equipped with gates for the resin system and gates for the evacuation. Finally, a vacuum film is applied over the entire construction and sealed with sealing tape, and the entire construction is evacuated. The construction is prepared with a glass surface on an electrically heatable stage. [0223] The resin system used is an amine-curing epoxide (resin: BASF Baxxores 5400, curing agent: BASF Baxxodur 5440, mixing ratio and further processing according to data sheet). After the two components have been mixed, the resin is evacuated at down to 20 mbar for 10 minutes. At a resin temperature of 23.sup.+/.sub.−2° C., infusion is effected onto the preheated construction (stage temperature: 35° C.). By means of a subsequent temperature ramp of 0.3 K/min from 35° C. to 75° C. and isothermal curing at 75° C. for 6 h, it is possible to produce panels consisting of the moldings and glass fiber-reinforced outer plies. [0224] At the start, the foams are analyzed according to ISO 845 (October 2009 version), in order to obtain the apparent density of the foam. After the resin system has cured, the processed panels are trimmed in order to eliminate excess resin accumulations in the edge regions as a result of imperfectly fitting vacuum film. Subsequently, the outer plies are removed and the foams present are analyzed again by ISO 845. The difference in the densities gives the absolute resin absorption. Multiplication by the thickness of the foam then gives the corresponding resin absorption in kg/m.sup.2. [0225] Vacuum stability: Vacuum stability is assessed qualitatively. The foams are applied to an aluminum plate, covered with polyester fleece and, after application of a vacuum film, subjected to a reduced pressure in the range of 10-20 mbar. Changes in dimensions are observed qualitatively. [0226] Thermoformability: Thermoformability is assessed qualitatively. For this purpose, a heated aluminum body is applied to the foam under gentle pressure and formability is assessed while simultaneously avoiding thermal degradation.

TABLE-US-00001 TABLE 1 Foams and essential properties Foam IF1 IF2 IF3 IF4 IF5 IF6 CF7 CF8 Production process (—) extrusion extrusion extrusion extrusion extrusion extrusion beads beads Polymer (—) PS PS PS PPE/PS SMA/ polyester polyester PS SAN Glass transition (° C.) n.a. n.a. n.a. n.a. n.a. n.a. 118 n.a. temperature Anisotropy of the (—) 1.3 1.3 1.4 1.2 1.1 1.2 no no main cell axes γ (°) 0 90 0 0 0 0 — — c direction (mm) 0.09 0.09 0.14 0.07 0.08 0.25 n.a. n.a. Compressive strength in (MPa) 0.82 0.81 0.4 0.77 0.35 0.70 0.35 0.48 z direction Compressive strength z/x (—) 3.6 3.4 1.5 3.9 4.0 4.1 — — closed-cell content (%) >95 >95 >95 >95 >95 >95 n.a. n.a. Thickness (z direction) (mm) 20 20 20 20 20 20 20 20 Resin absorption (kg/m.sup.2) 0.2 0.2 0.2 0.2 0.1 1.8 2.0 n.a. Density (kg/m.sup.3) 47 47 32 48 31 60 51 47 Compressive strength to (kPa/(kg/m.sup.3)) 17 5 12 16 11 12 7 10 density Vacuum stability (—) very good good good very good very good very good very good very good Thermoformability (—) good good good good good very good good good

[0227] The extruded foams of the invention are notable for high anisotropy, a high closed-cell content and good vacuum stability. Moreover, all extruded foams are formable by thermal processes. In addition, high compressive strengths in thickness direction can be achieved at low densities, and resin absorption, particularly in the case of IF1 to IF5, can be kept very low.

[0228] c) Production of the Moldings (Reinforcement of the Foams)

[0229] All foams are reinforced with glass fibers. The moldings are produced as follows; the properties of the moldings are shown in table 2. Depending on the experiment, hand specimens ranging up to larger samples are produced.

[0230] CM1:

[0231] The foam IF1 is reinforced with glass fibers (rovings, S2 glass, 406 tex, AGY). The glass fibers are introduced in the form of rovings at an angle α of 0°. The glass fibers have been introduced in a regular rectangular pattern with equal distances a.sub.1=a.sub.2 12 mm. On both sides, about 5.5 mm of the glass fibers have additionally been left as excess at the outer ply, in order to improve the binding to the glass fiber mats that will be introduced later as outer plies. The fibers or fiber rovings are introduced in an automated manner by a combined needle/hook process. First of all, a hook needle (diameter of about 0.80 mm) is used to penetrate completely from the first side to the second side of the extruded foam. On the second side, a roving is hooked into the hook of the hook needle and then pulled from the second side by the needle back to the first side of the extruded foam. Finally, the roving is cut off on the second side and the roving loop formed is cut open at the needle. The hook needle is thus ready for the next operation.

[0232] IM2:

[0233] The foam IF1 is reinforced in analogy to CM1 with glass fibers (rovings, S2 glass, 406 tex, AGY). The glass fibers are introduced in the form of rovings at an angle α of 45° in four different spatial directions at an angle β of 90°.

[0234] CM3:

[0235] The foam IF2 is reinforced analogously to CM1; only the angle ε is different.

[0236] CM4:

[0237] The foam IF3 is reinforced analogously to CM1.

[0238] IM5:

[0239] The foam IF4 is reinforced analogously to IM2.

[0240] IM6:

[0241] The foam IF4 is reinforced analogously to IM2. Prior to the reinforcement, slotted slabs are produced by material-removing processing by means of circular saws. The slot separation in the longitudinal and transverse directions is 30 mm. The slots are introduced only on one side of the slab with a slot width of 2 mm and a slot depth of 19 mm (slab thickness of 20 mm).

[0242] IM7:

[0243] The production is analogous to IM6. In addition to the introduction of the slots, a textile backing textile (canvas fabric, 50 g/m.sup.2, E glass with thermoplastic binder) is applied by thermal means on the unslotted side.

[0244] IM8:

[0245] The foam IF4 is reinforced analogously to IM5. The difference is that a different hook needle (diameter about 1.12 mm) and a thicker roving (E glass, SE1500, 900 tex, 3B) are used.

[0246] IM9:

[0247] The foam IF4 is reinforced with a barbed hook needle. For this purpose, chopped glass fibers composed of rovings (E glass) having a length of 30 mm are applied over the full area of the foam and then pressed into and through the foam by needle bonding with a needle bar having several barbed hook needles. After the needles have been withdrawn, a large portion of the fibers remains in the foam; excess fibers at the surface are removed by suction. The step is repeated for all desired directions. The proportion of fibers in the different directions is virtually identical.

[0248] IM10:

[0249] The foam IF5 is reinforced analogously to IM2.

[0250] IM11:

[0251] The foam IF6 is reinforced analogously to IM2.

[0252] CM12:

[0253] The foam CF7 is reinforced analogously to IM2.

[0254] CM13:

[0255] The foam CF8 is reinforced analogously to IM2.

[0256] d) Characterization of the Moldings [0257] Drapability: The drapability of the moldings is determined qualitatively. For this purpose, the moldings are placed onto a curved mold having a radius of curvature of 2 m. The fitting to the curvature of the mold and the avoidance of loss of material or defects in the molding are assessed. [0258] Sewing resistance: For the assessment of manufacturing-related advantages in reinforcement by rovings, comparative penetration tests are conducted. The needle is mechanically secured to a dynamic testing machine. Subsequently, the needle is used to penetrate the foam at 5 different points and the force-distance profile is recorded. The sinusoidal half-wave has an amplitude of 25 mm, and so the needle penetrates 25 mm into the foam. On needle impact, the needle has a velocity of 2 m/s. According to the sample thickness, the sample is penetrated. The sample surface forms the zero point of the measurement. The force is measured by a piezoelectric force transducer. The values reported are mean values from the measurements and reflect the force at penetration depth 10 mm in newtons (N).

TABLE-US-00002 TABLE 2 Moldings and essential properties Molding (—) CM1 IM2 CM3 CM4 IM5 IM6 IM7 IM8 IM9 IM10 IM11 CM12 CM13 Foam (—) IF1 IF1 IF2 IF3 IF4 IF4 IF4 IF4 IF4 IF5 IF6 CF7 CF8 Fiber (—) hook hook hook hook hook hook hook hook barbed hook hook hook hook introduction needle needle needle needle needle needle needle needle hook needle needle needle needle method Fiber material (—) S glass S glass S glass S glass S glass S glass S glass E glass E glass S glass S glass S glass S glass Fiber thickness (tex) 406 406 406 406 406 406 406 900 900 406 406 406 406 α (°) 0 45 0 0 45 45 45 45 45 45 45 45 45 β (°) — 90 — — 90 90 90 90 90 90 90 90 90 ε (°) 0 45 90 0 45 45 45 45 45 45 45 — — Number (—) 1 4 1 1 4 4 4 4 4 4 4 4 4 of fiber orientations Fiber (mm × 12 × 12 12 × 12 12 × 12 12 × 12 12 × 12 12 × 12 12 × 12 12 × 12 20 × 20 12 × 12 12 × 12 12 × 12 12 × 12 separations mm) (a.sub.1 × a.sub.2) Fiber region (%) 63 71 63 63 71 71 71 71 51-56 71 71 71 71 (FB2)/overall fiber (F) Number (1/m.sup.2) 6944 27778 6944 6944 27778 27778 27778 27778 10000 27778 27778 27778 27778 of fibers Sewing (N) 7.4 7.9 9.1 6.1 — — — — — — — — resistance Introduction (—) no no no no no yes yes no no no no no no of slots Application of (—) no no no no no no yes no no no no no no further layers (S2) Drapability (—) no no no no no good very no no no no no no good

[0259] The extruded foams of the invention can be processed in a simple and reproducible manner by means of fibers to give moldings of the invention. It is advantageous to introduce fibers at angles ε of less than 60° to the largest dimension (a direction) of the cells, since it is thus possible to reduce the penetration resistance in the reinforcement process (see rise in angle and in sewing resistance from CM1 to CM3). In addition, it is possible to further reduce penetration resistance by means of extruded foams of reduced density (CM4). Drapability of the moldings can be achieved by means of slots, which are advantageously introduced prior to the introduction of the fibers into the moldings (IM6 versus IM5). A further improvement can be achieved by means of a textile carrier on the reverse side, which stops the cut foam elements from breaking free and improves the overall integrity (IM7). Finally, it is possible to utilize different fiber types (IM8), introduction processes (IM9) and extruded foams (IM10, IM11).

[0260] e) Production of the Panels

[0261] The moldings are subsequently used to produce panels by application of fiber-reinforced outer plies by means of vacuum infusion (VI), as described above in section a) (determination of resin absorption). Rather than the foam, however, the molding is used; by contrast with the determination of resin absorption, in addition, no separation film is introduced between the moldings and the glass rovings.

[0262] f) Characterization of the Panels [0263] Shear stiffness and stability: Shear properties are determined according to DIN 53294 at 23° C. and 50% relative humidity (February 1982 version). [0264] Peel resistance: The peel resistance of the panels is determined with single cantilever beam (SCB) samples. The molding height of the samples is 20 mm; the outer layers each consist of quasi-isotropic glass fiber-reinforced epoxy resin layers of thickness about 2 mm. The samples are tested in a Zwick Z050 tensile tester at a speed of 5 mm/min, with application of the load to each specimen and removal thereof in a repeated manner (3 to 4 times). The growth in cracking or the increase is assessed visually in each load cycle (Δa). The force-distance plot is used to ascertain the crack growth energy (ΔU). This is used to ascertain the tear strength or peeling resistance as

[00001]$G_{\mathrm{IC}}=\frac{\Delta .Math..Math.U}{B.Math..Math.\Delta .Math..Math.a}$

with B as sample width. [0265] Crease resistance: Resistance to creasing of the outer plies (microwrinkling) is calculated on the basis of the measured base properties of the material. Blister resistance to creasing of the outer plies can be determined as

[00002]${\sigma }_c=0.85.Math.\sqrt[3]{E_{C.Math..Math.3}.Math.E_f.Math.G_C}$

with E.sub.C3: core stiffness in thickness direction, E.sub.f: stiffness of the outer layer, G.sub.C: shear stiffness of the core material

TABLE-US-00003 TABLE 3 Panels of the invention and essential properties Panel (—) CP1 IP2 CP3 CP4 IP5 IP6 IP7 IP8 IP9 IP10 IP11 CP12 CP13 Molding (—) CM1 IM2 CM3 CM4 IM5 IM6 IM7 IM8 IM9 IM10 IM11 CM12 CM13 Layer (—) VI VI VI VI VI VI VI VI VI VI VI VI VI application Layer (—) epoxy/ epoxy/ epoxy/ epoxy/ epoxy/ epoxy/ epoxy/ epoxy/ epoxy/ epoxy/ epoxy/ epoxy/ epoxy/ construction E glass E glass E glass E glass E glass E glass E glass E glass E glass E glass E glass E glass E glass fibers fibers fibers fibers fibers fibers fibers fibers fibers fibers fibers fibers fibers Shear stiffness (MPa)  14* — — — 147 — — 201 115 114 — 105* 101* Shear (MPa) — — — — 2.1 — — — — — — — — resistance Peel resistance (kJ/m.sup.2) — — — — 3.5 — — — — — — — — Crease (MPa) 230 230 178 195 233 233 233 233  82 152 238 108  164  resistance* *calculated values

[0266] All panels of the invention are notable for high crease resistance coupled with low density (IP2 and IP5 to IP11), specifically in the case of orientation of the main cell axes parallel to the slab orthogonal (IP2 versus CP3). It is thus possible to avoid potential failure in use. It is additionally found to be particularly advantageous to use foams that are produced by extrusion through a slot die (IP2 and IP5 to IP10). Peel resistance and shear stiffness/resistance are high in the case of low densities. By contrast, the crease resistance of the comparative foams is low, or the densities required to achieve higher characteristics are high.

Example 2 (Design of a Panel for Illustration of the Preferred Fiber Angles, Theoretical Determination)

[0267] The mechanical properties of a molding comprising the extruded foam IF4 were determined theoretically. The fibers (F) used were glass fibers (rovings, E-Glass, 900 tex, 3B). The angle α at which the fibers (F) were assumed to have been introduced was in the range from 0° to 80°. At angles α>0°, the fibers (F) were assumed to be in four different spatial directions at an angle β (0°, 90°, 180°, 270°) to one another. Regular rectangular patterns with equal distances a=16 mm and, at an angle α of 0°, 625 glass fiber elements/m.sup.2 were assumed.

[0268] The shear moduli were calculated for different angles α. For this purpose, a strut and tie model with flexible struts was used for connection of the upper and lower outer layers. The outer layers were assumed to be infinitely stiff. The extruded foam had a thickness of 25 mm, a shear stiffness G=14 MPa, and a compression stiffness E=MPa. The resin absorption at the surface of the foam was assumed to be 0.2 kg/m.sup.2.

[0269] The fiber bundles consist of E glass fibers. As a result of the manufacturing process, the reinforcing elements had a thickness of 2×900 tex (=1800 tex); the fiber volume content was assumed to be 40% by volume and the diameter to be 1.5 mm. This gives rise to the figures reported in table 4 for shear moduli, densities of the molding in the processed panel and specific shear moduli as a function of the angle α.

TABLE-US-00004 TABLE 4 Density of the Specific shear Angle α Shear modulus molding moduli Example (°) (MPa) (kg/m.sup.3) (MPa/(kg/m.sup.3) CM14 0 15 129 0.12 IM15 10 27 129 0.21 IM16 20 60 132 0.45 IM17 30 104 137 0.76 IM18 40 145 145 1.00 IM19 45 160 151 1.06 IM20 50 169 159 1.06 IM21 60 168 183 0.92 IM22 70 138 234 0.59 CM23 80 83 388 0.21

[0270] It is clearly apparent that shear stiffness increases rapidly with rising fiber angle before dropping again over and above about 60°.

[0271] For the use of the panels, flexural stiffness or blister resistance is generally very important. The blister stiffness of a panel with parallel symmetric outer layers can be determined as follows with standard force introduced at the end:

[00003]$P\ge \frac{{\pi }^2.Math.D}{\left(l^2+\frac{{\pi }^2.Math.\mathrm{Dt}}{{\mathrm{Gd}}^2}\right)}.Math.b$

where F is the force before occurrence of global blistering (=blister resistance), D is the flexural stiffness of the panel, G is the shear modulus of the molding (=core material), t is the thickness of the molding of the panel, b is the width of the panel and d is the thickness of the molding (=core material) plus one outer layer thickness.

[0272] The flexural stiffness of the panel is calculated from:

[00004]$D=\frac{E_D.Math.t_D^3}{6}+\frac{E_D.Math.t_D.Math.d^2}{2}+\frac{E_K.Math.t_K^3}{12}$

[0273] E.sub.D is the modulus of elasticity of the outer layer, E.sub.K is the modulus of elasticity of the molding (=core material), t.sub.D is the thickness of the outer layer per side, t.sub.k is the thickness of the molding (=core material), d is the thickness of the core material plus the thickness of one outer layer.

[0274] The width of the panel was assumed to be 0.1 m; the length was 0.4 m. The thickness of the molding was 25 mm, the thickness of the outer layer 2 mm, and the modulus of elasticity of the outer layer 39 GPa.

[0275] The moldings used were the moldings according to examples CM14 to CM23.

[0276] Table 5 states the results.

TABLE-US-00005 TABLE 5 Density of the Blister Angle α molding stability Specific blister stability Example (°) (kg/m.sup.3) (kN) (kN/(kg/m.sup.3) CP14 0 129 35 0.28 IP15 10 129 55 0.43 IP16 20 132 89 0.67 IP17 30 137 113 0.82 IP18 40 145 126 0.87 IP19 45 151 129 0.85 IP20 50 159 131 0.82 IP21 60 183 130 0.71 IP22 70 234 123 0.52 CP23 80 388 102 0.26

[0277] It is clearly apparent that blister stability increases rapidly with rising angle α before dropping again over and above about 60°.