FIBER-REINFORCEMENT OF FOAM MATERIALS, CONSISTING OF INTERCONNECTED SEGMENTS

Abstract

The present invention relates to a molding made from foam, wherein at least one fiber (F) is partly within the molding, i.e. is surrounded by the foam. The two ends of the respective fibers (F) that are not surrounded by the foam thus each project from one side of the corresponding molding. The foam comprises at least two mutually bonded foam segments.

Claims

1.-15. (canceled)

16. A molding made of foam, said foam comprising at least two mutually bonded foam segments, wherein at least one fiber (F) is present with a fiber region (FB2) within the molding and is surrounded by the 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, where the fiber (F) has been partly introduced by a process comprising the following steps a) to f): a) optionally applying at least one layer (S2) to at least one side of the foam, b) producing one hole per fiber (F) in the foam and in any layer (S2), the hole extending from a first side to a second side of the foam and through any layer (S2), c) providing at least one fiber (F) on the second side of the foam, d) passing a needle from the first side of the foam through the hole to the second side of the 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 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 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.

17. The molding according to claim 16, wherein i) at least two of the mutually bonded foam segments have been bonded to one another by adhesive bonding or welding, or ii) the individual foam segments have a length (x direction) of at least 2 mm, a width (y direction) of at least 2 mm and a thickness (z direction) of at least 2 mm, or iii) the individual foam segments have a slab shape, or iv) the individual foam segments have a ratio of length (x direction) to thickness (z direction) of at least 5, or v) the individual foam segments have a ratio of width (y direction) to thickness (z direction) of at least 3, or vi) at least one fiber (F) passes through at least one bonding surface between two mutually bonded foam segments of the foam, or vii) the at least one fiber (F) passes partly or completely through at least one bonding surface between two mutually bonded foam segments at an angle δ of ≧20°, or viii) at least one bonding surface between at least two of the mutually bonded foam segments has/have a thickness of at least 2 μm, or ix) the thickness of at least one bonding surface between at least two of the mutually bonded foam segments is greater than the sum total of the mean cell wall thicknesses of the mutually bonded foam segments.

18. The molding according to claim 16, wherein the foam segments of the foam are made from a molded foam, an extruded foam, a reactive foam or a masterbatch foam, that has been produced in a 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, IV) calibrating the expanded foam from step III) by conducting the expanded foam through a shaping tool to obtain the extruded foam, V) optional material-removing processing of the extruded foam obtained in step IV), where i) the polymer melt provided in step I) optionally comprises at least one additive, or ii) at least one additive is optionally 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 optionally applied during step III) to the expanded foam or during step IV) to the expanded foam, or iv) at least one layer (S2) is optionally applied to the extruded foam during or directly after step IV).

19. The molding according to claim 16, wherein the foam segments comprise cells, where i) at least 50% of the cells of at least two foam segments, or ii) the ratio of the largest dimension (a direction) to the smallest dimension (c direction) of at least 50% of the cells of at least two foam segments is ≧1.05, or iii) at least 50% of the cells of at least two foam segments, based on their largest dimension (a direction), are aligned at an angle γ of ≦45° relative to the thickness direction (d) of the molding.

20. The molding according to claim 16, wherein the foam segments of the foam are 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.

21. The molding according claim 16, wherein all foam segments of the foam are based on the same polymers.

22. The molding according to claim 16, 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 at least 10, in the case of glass fibers and 1000 to 50 000 in the case of carbon fibers, or 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 foam at an angle α of 0° to 60°, or of 10° to 70° 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 fibers (F) projects is opposite the second side of the molding from which the fiber region (FB3) of the fibers (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.

23. A panel comprising at least one molding according to claim 16 and at least one layer (S1).

24. The panel according to claim 23, wherein the layer (S1) comprises at least one resin.

25. The panel according to claim 24, wherein the resin being based on epoxides, acrylates, polyurethanes, polyamides, polyesters, unsaturated polyesters, vinyl esters or mixtures thereof.

26. The panel according to claim 23, 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.

27. The panel according to claim 23, 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.

28. The panel according to claim 23, wherein i) the fiber region (FB1) of the fibers (F) is in partial or complete contact with the first layer (S1), or ii) the fiber region (FB3) of the fibers (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).

29. The panel according to claim 28, wherein the layer (S2) preferably being composed of two-dimensional fiber materials or polymeric films.

30. A process for producing a molding according to claim 16, which comprises partly introducing at least one fiber (F) into the foam by means of steps a) to f): a) optionally applying at least one layer (S2) to at least one side of the foam, b) producing one hole per fiber (F) in the foam and in any layer (S2), the hole extending from a first side to a second side of the foam and through any layer (S2), c) providing at least one fiber (F) on the second side of the foam, d) passing a needle from the first side of the foam through the hole to the second side of the 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 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 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, optionally with simultaneous performance of steps b) and d).

31. A process for producing a panel according to claim 23, 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 16.

32. The use of a molding according to claim 16 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 I1, C2, I3, C4, C8 and C9

[0209] First of all, foam segments in slab form are produced with different compositions. The foam segments are produced as extruded foams comprising polyphenyl ether (PPE) and polystyrene (PS) in a tandem extrusion system. A melting extruder (ZSK 120) is supplied continuously with a polyphenylene ether masterbatch (PPE/PS masterbatch, Noryl C6850, Sabic) and polystyrene (PS 148H, BASF), in order to produce an overall blend comprising 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 (carbon dioxide, ethanol and isobutane) are injected into the injection port under pressure with various compositions. The total throughput including the blowing agents and additives is 750 kg/h. The foamable polymer melt is cooled down in a downstream cooling extruder (ZE 400) and extruded through a slot die. The expanded foam 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 width about 800 mm and thickness 60 mm. The mean density of the extruded foam is 50 kg/m.sup.3.

[0210] In example I1, bonding surfaces are produced by welding two foam slabs. In this case, the surface is first removed by means of a mill and leveled off. These foam slabs are subsequently heated contactlessly with a heating element welding machine and joined. The mean welding temperature is 350° C., the heating time is 2.5-4.0 s, and the distance between the heating element and foam slab is 0.7 mm. The resulting loss of thickness in welding is between 3-5 mm. The foam thus obtained is subsequently planed to thickness 20 mm.

[0211] A comparison used is an unwelded slab (comparative example C2), which is planed to thickness 20 mm.

[0212] A further comparison used is a slab according to comparative example C2 into which fibers have additionally been introduced by a tufting method (comparative example C8).

[0213] Likewise used as a comparison was a welded slab according to example I1, with fibers having been introduced by a tufting method (comparative example C9).

[0214] In the tufting method, a tufting needle from Schmitz with needle system designation 0647LH0545D300WE240RBNSPGELF was used with the CANU 83:54S 2 NM 250. This is the smallest tufting needle from Schmitz which is not specially manufactured.

[0215] In a tufting method, the fiber bundle is passed directly with the tufting needle from the first side of the foam through the foam to the second side of the foam and then the tufting needle is pulled back to the first side. A loop of the fiber bundle is formed on the second side of the foam. Since, in the tufting method, the hole in the foam is produced during the passage of the tufting needle along with the fiber bundle, the frictional forces that act on the tufting needle and the fiber bundle are high; at the same time, the bending radius of the fiber bundle in the eye of the needle is very tight. This combination leads to severing and splicing of the fiber bundles, such that they do not always form a loop and, moreover, not all fibers of the fiber bundle are introduced into the foam.

[0216] In order to very substantially eliminate these disadvantages and assure comparability with the process of the invention for introduction of the fiber, the tufting method in comparative example C8 and C9 was conducted as follows:

[0217] First of all, the hole was made in advance with the above-described tufting needle, then the fiber bundle, as described above, was introduced into the foam together with the tufting needle.

[0218] The same fiber bundles (rovings) as in example I1 and 13 and in comparative example C2 and C4 were used.

[0219] Polyester foams are subjected to foam extrusion through a multihole die in an extrusion system; the individual strands are bonded directly in the process. The mixture of polymer (mixture of 80 parts PET (bottle grade, viscosity index 0.74, M&G, P76) and 20 parts material recycled in the process), nucleating agent (talc, 0.4 part, masterbatch in PET), chain extender (PMDA, 0.4 part, masterbatch in PET) and polyolefin elastomer (Proflex CR0165-02, 10 parts, masterbatch in PET) is melted and mixed in a co-rotating twin screw extruder (screw diameter 132 mm). After the melting, cyclopentane is added as blowing agent (cyclopentane, 4.5 parts). Directly after addition of the blowing agent, the homogeneous melt is cooled by means of the downstream housing and the static mixer. The temperature of the extruder housing is 300° C. to 220° C. Before it reaches the multihole die, the melt has to pass through a melt filter. The multihole die has 8 rows each having a multitude of individual holes. The total throughput is about 150 kg/h. The die pressure is kept at at least 50 bar. The foamable polymer 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 with a slab thickness of 35 mm and joined by thermal welding parallel to the extrusion direction. The mean density of the foam is 50 kg/m.sup.3.

[0220] In example I3, internal support sites are produced by joining the foam slabs by means of thermal welding parallel to the extrusion direction. Contact welding after heating of the foam slab by means of a Teflon-coated hotplate is the method chosen. The foam thus obtained is subsequently planed to thickness 20 mm.

[0221] A comparative example used is an unwelded foam slab (comparative example C4), which is planed to thickness 20 mm.

[0222] The mean cell wall thickness of the foam segments and the thickness of the bonding surfaces are determined by statistical evaluation of scanning electron micrographs. The mean wall thickness of the support sites is determined in an analogous manner. The typical dimensions are shown in table 1.

[0223] An important factor for the handling of the moldings is that the fibers remain fixed within the foam slab in the course of handling. A quantitative measure determined is the pullout resistance or the force required to pull out the fibers by a pullout test.

[0224] The fibers in the form of rovings (E glass, 400 tex) are at first manually introduced into the foam perpendicularly to the surface and perpendicularly to the bonding surface in example I1 and I3 and comparative example C2 and C4. For this purpose, the fiber roving is introduced by a combined sewing/hooking 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 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 foam. Finally, the roving is cut off on the second side and the roving loop formed is hung up on the needle.

[0225] After the roving has been introduced, in all examples and comparative examples, the roving loop is secured to the load cell by means of a small bolt and, after the load cell has been balanced to zero, the foam is moved at a speed of 50 mm/min. A 1 kN load cell with an effective resolution of 1 mN is used. The foam is fixed manually during the movement of the machine. For the assessment of the pullout force, the force maximum is evaluated (mean from three measurements). In the tests, the maximum force always occurs at the start of the test, since the initial bond friction is greater than the subsequent sliding friction.

[0226] The maximum pullout force in the case of integration of the fiber rovings into the support sites, by the process according to the invention, is distinctly higher than in the case of fixing into the straight foam (I1 and I3 versus C2 and C4).

[0227] By contrast, there is no apparent effect of the support sites on the pullout force of fiber rovings that have been introduced by means of a tufting method (comparative example C9). This is a pointer that support sites are severely damaged in the tufting method and/or the clamp force is reduced by the size of the hole.

TABLE-US-00001 TABLE 1 Ratio of the bonding surface thickness to sum total of the mean Maximum cell wall thickness pullout Exam- Bonding of the two mutually force ple Foam segment surface bonded foam segments (N) I1 Extruded foam Weld ~100 1.17 (PPE/PS) seam C2 Extruded foam — — 0.74 (PPE/PS) I3 Extruded foam Weld ~500 0.62 (PET-based) seam C4 Extruded foam — — 0.46 (PET-based) C8 Extruded foam — — 0.47 (PPE/PS) C9 Extruded foam Weld ~100 0.19 (PPE/PS) seam

Example I5

[0228] Moldings comprising mutually bonded foam segments and enveloped fibers are produced from the above-described PPE/PS foams (example I1), In the case of the extruded foam, the joined foam slabs are used in their present form with a thickness of 20 mm. The bonding surface runs exactly through the middle of the joined slabs. The slab has dimensions of 800 mm×600 mm; the mean thickness of the two joined slab elements was originally 60 mm; after the material-removing reduction in thickness, foam segments for final bonding of thickness 10 mm are obtained.

[0229] The compressive strength of the two foam segments in thickness direction (d) is 0.8 MPa and hence about 3.9 times higher than in the longitudinal or transverse direction (according to DIN EN ISO 844). In addition, the largest dimension (a direction) of the cells that have been analyzed by microscope images is oriented in thickness direction (d). The fibers are introduced at an angle α relative to thickness direction (d) of 45° and hence likewise at an angle of 45° to the bonding surface. The fibers used are glass rovings (S2 glass, 406 tex, AGY). The glass fibers are introduced in a regular rectangular pattern with equal distances a=12 mm. This gives rise to an area density of 27 778 rovings/m.sup.2, all of which are fixed by the bonding surface. On both sides, about 5.5 mm of the glass fibers are additionally 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 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 foam. Finally, the roving is cut off on the second side and the roving loop formed is cut open at the needle.

[0230] The utilization of the support sites in the foam enables distinctly better fixing of the fibers and hence better handling of the moldings. In addition, it is possible to reduce pullout of fibers in material-removing processing of the moldings.

Example I6

[0231] Moldings comprising bonded foam segments and enveloped fibers are produced from the above-described PET foams (example I3). In the case of the extruded foam, first of all, several foam slabs having a length of 1500 mm, a width of 700 mm and a thickness of 35 mm are bonded by thermal welding. The foam obtained having a total thickness of 700 mm is subsequently cut by a bandsaw perpendicularly to the bonding surfaces and to the longitudinal direction of the original, unjoined slab into slabs having width/length dimensions of 700 mm×700 mm and a thickness of 20 mm. The foam slab thus consists of about 22 joined foam segments oriented perpendicularly to the slab thickness. The compressive strength of the foam elements in thickness direction (d) of the joined slab is 0.6 MPa and hence about 4.1 times higher than in the longitudinal or transverse direction (according to DIN EN ISO 844).

[0232] In addition, the largest dimension (a direction) of the cells that are analyzed by microscope images is oriented in thickness direction (d). The largest dimension (a direction) has a length of about 0.5 mm; the smallest dimension (c direction) is about 0.2 mm. The fibers are introduced at an angle α relative to thickness direction (d) of 45° and hence likewise at an angle δ of 45° to the bonding surface. The fibers are introduced analogously to example I5. Of the 27 778 rovings/m.sup.2, about 30% have been fixed by the bonding surface.

[0233] The utilization of the support sites in the foam enable distinctly better fixing of the fibers and hence better handling of the moldings. In addition, it is possible to reduce pullout of fibers in material-removing processing of the moldings.

Example I7

[0234] Panels are produced from the moldings for example I5. Fiber-reinforced outer plies are produced by means of vacuum infusion. 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 (fiber-reinforced) foams. 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.

[0235] 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+/−2° C., infusion is effected onto the preheated structure (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. The panels can be manufactured without difficulty. Moreover, the support sites can prevent pullout of the fibers in the preparation for vacuum infusion. For later mechanical stress in use, moreover, better fiber alignment and hence better durability are assured.