FIBER-REIMFORCED MOLDED BODIES MADE OF EXPANDED PARTICLE FOAM MATERIAL

Abstract

The present invention relates to a molding made of expanded bead foam, wherein at least one fiber (F) is partly within the molding, i.e. is surrounded by the expanded bead foam. The two ends of the respective fibers (F) that are not surrounded by the expanded bead foam thus each project from one side of the corresponding molding. The present invention further provides a panel comprising at least one such molding and at least one further layer (S1). The present invention further provides processes for producing the moldings of the invention from expanded bead foam or the panels of the invention and for the use thereof, for example as rotor blade in wind turbines.

Claims

1.-16. (canceled)

17. A molding made of expanded bead foam, wherein at least one fiber (F) is present with a fiber region (FB2) within the molding and is surrounded by the expanded bead 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 projects from a second side of the molding, where the fiber (F) has been introduced into the expanded bead foam at an angle α of 10° to 70° relative to the thickness direction (d) of the molding.

18. The molding according to claim 17, wherein the expanded bead foam is based on at least one polymer selected from polystyrene, polyphenylene oxide, a copolymer prepared from phenylene oxide, a copolymer prepared from styrene, polysulfone, polyether sulfone, polypropylene, polyethylene, polyamide, polycarbonate, polyacrylate, polylactic acid, polyimide, polyvinylidene difluoride or a mixture thereof.

19. 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 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 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).

20. The molding according to claim 17, wherein i) the fiber (F) has been introduced into the expanded bead foam at an angle α of 30° to 60°, relative to the thickness direction (d) of the molding, or ii) 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 iii) the molding comprises a multitude of fibers (F), or comprises more than 10 fibers (F) or fiber bundles per m.sup.2.

21. The molding according to claim 17, wherein the expanded bead foam of the molding is produced by a process comprising the following steps I) to VI): I) producing expandable polymer beads from the corresponding polymer in the presence of a blowing agent at elevated temperature, II) optionally cooling or expanding the blowing agent-laden expandable polymer beads, optionally with expansion of the polymer beads to partly expanded polymer beads, III) optionally performing a pelletization of the expandable polymer beads, IV) optionally prefoaming the expandable polymer beads and or optionally the partly expanded polymer beads at elevated temperature in the range from 95 to 150° C., or at low pressures in the range from 1 to 5 bar, in the presence of steam or of a steam/air mixture, to obtain expanded beads, V) introducing the partly expanded polymer beads from step II) or the pelletized beads from step III) or the expanded beads from step IV) into a shaping mold, VI) contacting the partly expanded polymer beads from step II) or the pelletized beads from step III) or the expanded beads from step IV) with steam at elevated pressure in the range from 1 to 25 bar, or elevated temperature in the range from 100 to 220° C., in the shaping mold to obtain the moldings made of expanded bead foam.

22. The molding according to claim 21, characterized in that the beads for production of the expanded bead foam of the molding have been produced by a suspension process, a melt impregnation process, a melt expansion process or a tank expansion process.

23. The molding according to claim 17, wherein i) the surface of at least one side of the molding has at least one recess, or ii) the total surface area of the molding is closed to an extent of more than 30%.

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

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

26. The panel according to claim 26, wherein the resin being based on epoxides, acrylates, polyurethanes, polyamides, polyesters, unsaturated polyesters, vinyl esters or mixtures thereof.

27. The panel according to claim 24, 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 wovens, or ii) the fibrous material comprises organic, inorganic, metallic or ceramic fibers.

28. The panel according to claim 24, 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 layer in the molding.

29. The panel according to claim 24, 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).

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

31. A process for producing a molding according to claim 17, which comprises partly introducing at least one fiber (F) into the expanded bead foam, as a result of which the fiber (F) is present with the fiber region (FB2) within the molding and is surrounded by the expanded bead 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 expanded bead foam at an angle α of 10° to 70° relative to the thickness direction (d) of the molding.

32. The process according to claim 31, wherein the at least one fiber (F) is partially introduced into the expanded bead foam by sewing it in using a needle.

33. The process according to claim 32, 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 expanded bead foam, b) producing one hole per fiber (F) in the expanded bead foam and in any layer (S2), the hole extending from a first side to a second side of the expanded bead foam and through any layer (S2), c) providing at least one fiber (F) on the second side of the expanded bead foam, d) passing a needle from the first side of the expanded bead foam through the hole to the second side of the expanded bead 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 expanded bead 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 expanded bead 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.

34. The process according to claim 33 with simultaneous performance of steps b) and d).

Description

EXAMPLE 1 (COMPARATIVE EXAMPLE, MOLDING MADE FROM EXPANDED BEAD FOAM WITHOUT FIBER REINFORCEMENT)

[0149] For all experiments according to example 1, bead foams based on blends of PPE and PS are used (mixture of PPE/PS masterbatch, Noryl C6850, Sabic and PS 158K, BASF). The expandable polymer beads were manufactured by a melt impregnation process with subsequent pressurized underwater pelletization.

a) Production of the Expandable Polymer Beads

[0150] A twin-screw extruder with a screw diameter of 43 mm and a ratio of length to diameter of 44 is charged with 59.5 parts by weight of a PPE/PS blend (composition: 50% PPE, 50% PS) from Sabic (Noryl C6850), 40 parts by weight of a PS from BASF SE (PS 158 K Q4) and 0.5 parts by weight of talc from Mondo Minerals (Microtalc IT Extra) by metered addition. The aforementioned thermoplastic polymers are melted in the melting zone of the twin-screw extruder and mixed with the talc. After the thermoplastic polymers have melted and the talc has been mixed in, 4 parts by weight based on the amount of solids (polymer and talc) of a mixture of n-pentane and isopentane (80% by weight of n-pentane and 20% by weight of isopentane based on the total amount of pentane) and 0.3 part by weight, based on the amount of solids (polymer and talc), of nitrogen as blowing agent are added. In the course of passage through the rest of the extruder length, the blowing agent and the polymer melt are mixed with one another, so as to form a homogeneous mixture. The total throughput of the extruder comprising the polymers, talc and the blowing agent is 70 kg/h.

[0151] In the examples, the following process parameters are set: The extruder speed is set at 140 rpm. The extruder temperature in the melting zone and during the mixing of the talc into the polymers is between 230° C. and 240° C. The temperature at the extruder housing of the injection site is lowered down to 230° C. to 220° C., and of all subsequent housings as far as the end of the extruder down to 220° C. to 210° C. The melt pump and the start-up valve are kept at 210° C., and a downstream housing at 215° C. By means of the melt pump, a pressure at the end of the extruder of 85 bar is established. The temperature of the oil-heated perforated plate heated to a target temperature of 290° C.

[0152] For all examples, the mixture of polymer, talc and blowing agent is forced through the perforated plate having 50 holes having a diameter of 0.85 mm and chopped by 10 rotating blades secured to a blade ring in the downstream pelletizing chamber through which there was a flow of water. This produces beads having an average size of about 1.25 mm and a weight of about 1.1 mg. The pressure in the pelletizing chamber is 12 bar. The temperature-controlled medium is kept constant at 50° C. The process medium and the pellets/beads produced are subsequently separated in a rotary drier.

b) Production of the Moldings from Expanded Bead Foam

[0153] Subsequently, the expandable polymer beads are processed further to give moldings made from expanded bead foam. At a pressure of 1.2 bar over the course of 200 seconds, the particles are prefoamed at a stirrer speed of 60 rpm. This gives a bulk density of 49 kg/m.sup.3. Subsequently, the beads are stabilized at room temperature for 24 hours. The foam slabs are produced with a foam molding machine as rectangular slabs for experiments C1, C2 and C4. In addition, rectangular slabs with slots are produced (C3), which result from the molding tool (slot separation: 30 mm, orientation: longitudinal and transverse on one side of the slab, slot width: 2 mm, slot depth: 19 mm). Production is effected by cross-steaming at 1.5 bar for 10 seconds and autoclave steaming at 2.2 bar for 15 seconds. Thereafter, the foam block is cooled down and removed from the mold. The density of the blocks after 24 hours at room temperature is 50 g/L.

c) Resin Absorption by the Moldings to Form a Panel

[0154] For the resin absorption, slabs were compared directly after production with a closed surface (C1) and after removal of the surface material by planing (C2). Slotted slabs are produced either by material removal by means of corresponding molds in the bead foaming process (C3) or by material-removing processing by means of circular saws from slabs (C4). In each case, the slot separation in longitudinal and transverse direction 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).

[0155] To determine the resin absorption, 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, also referred to hereinafter as sandwich materials, 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. For the determination of the resin absorption, a separation film is inserted between the molding, also referred to hereinafter as core material, and the glass rovings, in contrast with the standard production of the panels. In this way, the resin absorption of the pure molding 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.

[0156] 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.

[0157] At the start, the moldings 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 moldings present are analyzed again by ISO 845. The difference in the densities gives the absolute resin absorption. Multiplication by the thickness of the molding then gives the corresponding resin absorption in kg/m.sup.2.

[0158] The results shown (see table 1) demonstrate that it is possible to distinctly reduce resin absorption in the case of moldings made from molded foams. The result is consequently a reduced density of the panel.

TABLE-US-00001 TABLE 1 Closed Resin Example Material surface absorption C1 Slab directly after processing (closed >90% <0.2 kg/m.sup.2  surface) C2 Slab after removal of surface material  <5% 0.4 kg/m.sup.2 C3 Slotted slab directly after processing >90% 3.3 kg/m.sup.2 C4 Slotted slab by material-removing  <5% 3.8 kg/m.sup.2 processing

EXAMPLE 2 (MOLDING MADE FROM EXPANDED BEAD FOAM WITH FIBER REINFORCEMENT)

[0159] In order to improve peel resistance with simultaneously low resin absorption at the surface, the experiments from example 1 are repeated, except that the molding (expanded bead foam) is first partly reinforced with glass fibers (rovings, S2 glass, 400 tex, AGY).

[0160] 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 to one another (0°, 90°, 180°, 270°). An identical number of glass fibers is introduced in all spatial directions. The glass fibers are introduced in a regular rectangular pattern with equal distances (a). In the experiments, the distance is varied from a=10 mm up to a=20 mm. On both sides, about 10 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 molded 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 molded 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. A total of 40 000 reinforcing glass fiber elements (rovings)/m.sup.2 at a distance of 10 mm and 10 000 glass fiber elements/m.sup.2 in a pattern of a.sub.x=a.sub.y=20 mm were introduced.

[0161] Subsequently, panels were produced from the moldings by application of fiber-reinforced outer plies by means of vacuum infusion as described above for example 1. In contrast to example 1, no separation film is introduced between the molding and the glass rovings.

[0162] 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 peel resistance determined as

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

with B as the sample width.

TABLE-US-00002 TABLE 2 Material, angle α, Resin absorption Example distances a.sub.x × a.sub.y Peel resistance through surface C1 unplaned foam 0.7 kJ/m.sup.2 <0.2 kg/m.sup.2 C2 planed foam 0.8 kJ/m.sup.2  0.4 kg/m.sup.2 I5 C1, fiber reinforced at 1.3 kJ/m.sup.2 <0.2 kg/m.sup.2 45°/20 mm × 20 mm I6 C1, fiber reinforced at 3.5 kJ/m.sup.2 <0.2 kg/m.sup.2 45°/12 mm × 12 mm I7 C1, fiber reinforced at 6.9 kJ/m.sup.2 <0.2 kg/m.sup.2 45°/10 mm × 10 mm I8 C2, fiber reinforced at 1.4 kJ/m.sup.2  0.4 kg/m.sup.2 45°/20 mm × 20 mm

[0163] As is clearly apparent from table 2, it is possible by means of the moldings of the invention with integrated fibers which comprise an expanded bead foam to distinctly increase peel resistance in a panel (15 to 18). The improvement in peel resistance by planing of the surface, by contrast, enables only moderate increases in peel resistance and is simultaneously associated with elevated resin absorption (C2). The fiber reinforcement of the molded foam thus permits a distinct increase in peel resistance with virtually identical resin absorption of the surface. Specifically, the strength depends only slightly on the surface roughness or pre-treatment and hence enables decoupling of the two optimization aims of peel strength and resin absorption.

EXAMPLE 3 (DESIGN OF A PANEL FOR ILLUSTRATION OF THE PREFERRED FIBER ANGLES, THEORETICAL DETERMINATION)

[0164] The mechanical properties of a molding comprising an expanded bead foam according to example C1 were determined theoretically. The fibers (F) used were glass fibers (rovings, S2 glass, 406 tex, AGY). 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 were assumed to be in four different spatial directions at the angle β (0°, 90°, 180°, 270°) to one another. Regular patterns with equal distances a=12 mm and, at an angle α of 0°, 27 778 glass fiber elements/m.sup.2 were assumed.

[0165] 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 expanded bead foam had a thickness of 25 mm, a shear stiffness G=19 MPa, and a compression stiffness E=35 MPa. The resin absorption at the surface of the foam was assumed to be 0.2 kg/m.sup.2 (conservative estimate, since <0.2 kg/m.sup.2 in experiments).

[0166] The fiber bundles consist of S glass fibers. As a result of the manufacturing process, the reinforcing elements had a thickness of 2×406 tex (=812 tex); the fiber volume content was assumed to be 40% by volume and the diameter to be 1.0 mm. This gives rise to the figures reported in table 3 for shear moduli, densities of the molding in the processed panel and specific shear moduli.

TABLE-US-00003 TABLE 3 Density of the Specific shear Angle α Shear modulus molding moduli Example (°) (MPa) (kg/m.sup.3) (MPa/(kg/m.sup.3) C9 0 14 127 0.11 I10 10 25 128 0.20 I11 20 53 131 0.41 I12 30 91 135 0.67 I13 40 127 144 0.88 I14 45 140 150 0.94 I15 50 148 157 0.94 I16 60 147 182 0.81 I17 70 121 232 0.52 C18 80 74 388 0.19

[0167] It is clearly apparent that shear stiffness increases rapidly with rising fiber angle before dropping again over and above about 60°.

[0168] 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:

[00002]$F\ge \frac{{\pi }^2.Math.D}{\left(t^2+\frac{{\pi }^2.Math.\mathrm{Dt}}{{\mathrm{Gd}}^2}\right)}.Math.b$

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.

[0169] The flexural stiffness of the panel is calculated from:

[00003]$D=\frac{E_D.Math.t_D^3}{6}+\frac{E_D.Math.t_D.Math.d^2}{2}+\frac{E_K.Math.t_K^2}{12}$

[0170] 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.

[0171] 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.

[0172] The moldings used were the moldings according to examples C9 to C18.

[0173] The results are reported in table 4.

TABLE-US-00004 TABLE 4 Density of the Blister Specific blister Angle α molding stability stability Example (°) (kg/m.sup.3) (kN) (kN/(kg/m.sup.3) C19 0 127 30 0.24 I20 10 128 47 0.36 I21 20 131 77 0.59 I22 30 135 101 0.74 I23 40 144 114 0.80 I24 45 150 118 0.79 I25 50 157 120 0.76 I26 60 182 120 0.66 I27 70 232 112 0.48 C28 80 388 90 0.23

[0174] It is clearly apparent that blister stability increases rapidly with rising angle α before dropping again over and above about 60°.