Multi-layered fibre composite material

Abstract

The present invention relates to a multilayer composite, comprising at least three superimposed plies of fibre composite which are defined relative to one another as two outer plies of fibre composite and at least one inner ply of fibre composite, wherein each of these at least three plies of fibre composite comprises endless fibres, the endless fibres being unidirectionally aligned within the respective ply and embedded in a polycarbonate-based plastic, wherein the polycarbonate is selected from homopolycarbonate or copolycarbonate, the inner plies of fibre composite essentially have the same orientation and their orientation relative to the outer plies of fibre composite is rotated by 30° to 90° , wherein the orientation of a ply of fibre composite is determined by the orientation of the unidirectionally aligned fibres present therein.

Claims

1. A multilayer composite comprising at least three superimposed plies of fibre composite which are defined relative to one another as two outer plies of fibre composite and at least one inner ply of fibre composite, wherein (a) each of these at least three plies of fibre composite comprises endless fibres, wherein the endless fibres within the respective ply are unidirectionally aligned and are embedded in a polycarbonate-based plastic, wherein the polycarbonate is selected from homopolycarbonate or copolycarbonate, (b) the inner plies of fibre composite have substantially the same orientation and their orientation relative to the outer plies of fibre composite is rotated by 30° to 90° , wherein the orientation of a ply of fibre composite is determined by the orientation of the unidirectionally aligned fibres present therein, and wherein the thickness ratio of the sum of the two outer plies to the sum of all inner plies of fibre composite is 0.3 to 0.65, and wherein the outer plies have a fiber content of not more than 42% by volume.

2. The multilayer composite according to claim 1, wherein the fibre composite plies are obtainable by applying a molten polycarbonate-based plastic onto a dry fibre band preheated to above the glass transition temperature of the plastic, wherein the applying is effected under application of pressure-shear vibration and wherein the polycarbonate is selected from homopolycarbonate or copolycarbonate.

3. The multilayer composite according to claim 1, wherein the at least three plies of fibre composite are arranged in substantially symmetrical fashion, wherein the two outer plies of fibre composite have a substantially identical construction in terms of at least one feature from the group comprising chemical composition, fibre volume content and layer thickness.

4. The multilayer composite according to claim 1, wherein the multilayer composite has a total thickness in the range from 0.5 mm to 2 mm.

5. The multilayer composite according to claim 1, wherein the thickness ratio of the sum of the two outer plies to the sum of all inner plies of fibre composite is 0.35 to 0.58.

6. The multilayer composite according to claim 1, wherein the multilayer composite comprises three to six inner fibre composite plies.

7. The multilayer composite according to claim 1, wherein the inner plies of fibre composite have the same orientation and their orientation relative to the outer plies of fibre composite is rotated by 90°±5°.

8. The multilayer composite according to claim 1, wherein the at least three plies of fibre composite comprise essentially no voids.

9. The multilayer composite according to claim 1, wherein the endless fibres are selected from the group comprising glass fibres, carbon fibres, basalt fibres, aramid fibres, liquid crystal polymer fibres, polyphenylene sulphide fibres, polyether ketone fibres, polyether ether ketone fibres, polyether imide fibres and mixtures thereof.

10. A process for producing a multilayer composite according to claim 1, comprising the steps of providing at least one inner ply of fibre composite and two outer plies of fibre composite, wherein the production of the individual fibre composite plies is effected by applying a molten polycarbonate-based plastic onto a dry fibre band preheated to above the glass transition temperature of the plastic, wherein the applying is effected under application of pressure-shear vibration and wherein the polycarbonate is selected from homopolycarbonate or copolycarbonate, introducing the at least one inner ply of fibre composite between the outer fibre composite plies, wherein the inner plies of fibre composite have the same orientation and their orientation relative to the outer plies of fibre composite is rotated by 30° to 90°, joining the layered plies of fibre composite to afford the multilayer composite.

11. An electronic device or housing part suitable for use as or employment in a housing of an electronic device, wherein the electronic device or housing part comprises a multilayer composite according to claim 1.

12. The electronic device according to claim 11, wherein the electronic device is a monitor, tablet, mobile telephone or a computer.

13. The housing part according to claim 11, wherein the housing of an electronic device is the monitor backside or the underside of a laptop.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a schematic and perspective depiction of a multilayer composite made of three superposed plies of fibre composite with enlarged detail, wherein the inner ply is rotated by 90° relative to the outer plies of fibre composite,

(2) FIG. 2 shows a schematic and perspective depiction of a multilayer composite made of five superposed plies of fibre composite, wherein the inner plies have the same orientation and their orientations relative to the outer plies of fibre composite are rotated by 90°,

(3) FIG. 3a shows a schematic and perspective depiction of a multilayer composite made of six superposed plies of fibre composite, wherein the inner plies have the same orientation and their orientations relative to the outer plies of fibre composite are rotated by 90°,

(4) FIG. 3b shows a schematic and perspective depiction of a multilayer composite made of three superposed plies of fibre composite, wherein the inner ply has a greater thickness than the sum of the two outer plies. The thickness ratio of the inner ply to the sum of the two outer plies is the same as the thickness ratio of the sum of all inner plies to the sum of the two outer plies of the multilayer composite from FIG. 3A,

(5) FIG. 4 shows a schematic and perspective depiction of a multilayer composite made of three superposed plies of fibre composite, wherein the outer plies of fibre composite have a lower fibre volume content than the inner plies of fibre composite,

(6) FIG. 5a shows a schematic and perspective depiction of a multilayer composite made of three superposed plies of fibre composite and an additional material ply on an outer ply of fibre composite,

(7) FIG. 5b shows a schematic and perspective depiction of a multilayer composite made of three superposed plies of fibre composite and two additional inner further material plies, for example plastic layers, wherein an inner further material ply is located between each outer ply of fibre composite and the inner ply of fibre composite,

(8) FIG. 6 shows a schematic and perspective depiction of a laptop.

(9) FIG. 1 shows a portion of a multilayer composite 1 made of three superposed plies of fibre composite 2, 3, wherein the inner ply of fibre composite 2 is rotated by 90° relative to the outer plies 3 of fibre composite. The enlarged detail in FIG. 1 shows that each of the plies 2, 3 of the multilayer composite comprises endless fibres 4 which are unidirectionally aligned within the respective ply and are embedded in polycarbonate-based plastic 5. The orientation of the respective ply of fibre composite 2, 3 is determined by the orientation of the unidirectionally aligned endless fibres 4 present therein. The endless fibres 4 extend over the entire length/width of the multilayer composite. The layers 2, 3 are uniformly interjoined.

(10) The multilayer composite 1 as per FIG. 2 is made of five superposed plies of fibre composite 2, 3, wherein the inner plies of fibre composite 2 have the same orientation and their orientation relative to the outer plies of fibre composite 3 are rotated by 90°.

(11) The multilayer composite 1 as per FIG. 3a is made of six superposed plies of fibre composite 2, 3, wherein the inner plies of fibre composite 2 have the same orientation and their orientation relative to the outer plies of fibre composite 3 are rotated by 90°. For a thickness of each individual ply of the outer plies 3, and a thickness of each individual ply of the inner plies 2, of 170 μm for example, the thickness ratio of the sum of the two outer plies 3 to the sum of the inner plies 2 is (2.Math.170 μm)/(4.Math.170 μm)=0.5.

(12) FIG. 3b shows a multilayer composite 1 made of three superposed plies of fibre composite 2, 3, wherein the inner ply 2 has a greater thickness than the sum of the two outer plies 3. For a thickness of each individual ply of the outer plies 3 of 170 μm and a thickness of the inner ply 2 of 680 μm for example, the thickness ratio of the sum of the two outer plies 3 to the sum of the inner ply 2 is (2.Math.170 μm)/680 μm=0.5. The thickness ratio of the sum of the two outer plies 3 to a thick inner ply 2 as per FIG. 3b is thus the same as the thickness ratio of the sum of the two outer plies 3 to the sum of the four inner plies 2 of the multilayer composite 1 from FIG. 3a.

(13) The multilayer composite 1 as per FIG. 4 is made of three superposed plies of fibre composite 2, 3, wherein the outer plies of fibre composite 3 have a lower fibre volume content than the inner plies of fibre composite 2. This is shown here in schematic form such that the density of the endless fibres 4 in the outer plies of fibre composite 3 is lower compared to the fibre density in the inner ply of fibre composite 2/that the proportion of the plastic 5 in the outer plies of fibre composite 3 is correspondingly higher compared to the proportion of the plastic in the inner fibre composite plies 2.

(14) FIG. 5a shows the multilayer composite 1 made of three superposed plies of fibre composite 2, 3 as described for FIG. 1 but with an additional further outer material ply 6 atop one of the outer plies of fibre composite 3. The outer material ply 6 may for example comprise one or more fibre-free plastic plies and/or a thin facing, for example a coating layer or a veneer.

(15) FIG. 5b shows a multilayer composite 1 made of three superposed plies of fibre composite 2, 3 as described for FIG. 1 but with two additional further inner material plies 7, wherein a respective inner further material ply 7 is located between one of the outer plies 3 of fibre composite and the inner ply 2 of fibre composite respectively. The further inner material plies 7 may have an identical or different construction and may comprise for example one or more fibre-free plastic plies.

(16) FIG. 6 shows a schematic representation of a laptop. The housing part of the laptop which forms the monitor backside a of the monitor b is also referred to in the art as an “a-cover”. The housing part of the laptop which forms the underside d of the keyboard c is typically referred to as a “d-cover”. The monitor backside a and the underside d of the laptop comprise the multilayer composite according to the invention.

LIST OF REFERENCE SYMBOLS

(17) 1: multilayer composite 2: inner plies of fibre composite 3: outer plies of fibre composite 4: endless fibre 5: polycarbonate-based plastic 6: further outer material ply 7: further inner material ply a: laptop monitor backside b: laptop monitor c: laptop keyboard d: laptop underside

(18) The invention is hereinafter more particularly elucidated with reference to examples.

EXAMPLES

(19) 1. Description of Raw Materials and Test Methods

(20) Component A

(21) Linear polycarbonate based on bisphenol A having a melt volume flow rate MVR of 6.0 cm.sup.3/10 min (as per ISO 1133 at a test temperature of 300° C. and 1.2 kg loading).

(22) Component B

(23) Pyrofil TRH50 60M carbon fibre from Mitsubishi Rayon CO., LtD. having an individual filament diameter of 7 μm, a density of 1.81 g/cm.sup.3 and a tensile modulus of 250 GPa. 60,000 individual filaments are obtained in a roving as an endless spool.

(24) Methods of Measurement

(25) The methods detailed hereinafter for determining the relevant parameters were employed for performing/evaluating the examples and are also the methods for determining the parameters relevant in accordance with the invention in general.

(26) Determination of Thickness and Thickness Ratio

(27) The thickness determination of the fibre composite plies and of the multilayer composites that result after joining was effected using a commercially available micrometer. The reported result was the arithmetic mean of 5 individual measurements at different positions.

(28) The thickness ratio of the two outer fibre composite plies to the sum of the inner fibre composite plies may be determined in the course of production by determination of the individual thicknesses of the plies of fibre composite prior to the joining of the plies to afford the multilayer composite. Practical tests have shown that in the customary processes for joining the plies (for example lamination under the action of pressure and heat) the ratio of the thicknesses to one another does not substantially change even in the case of compression and concomitant reduction in thicknesses. The thickness ratios described here relate to the individual thicknesses of the plies of fibre composite determined in the course of production before joining of the plies to afford the multilayer composite.

(29) Alternatively, the determination of the thickness ratio may also be effected in the finished multilayer composite. This is achieved by examination of a cross section of the material by microscopy. The change in orientation of the fibre running direction upon transition from the inner to the two outer plies of fibre composite makes these plies readily identifiable by microscopy. For layer thickness determination a plane running parallel to the planes determined by the fibre running direction halfway between the last endless fibre belonging to an outer ply of the fibre composite and the first endless fibre belonging to an inner ply of the fibre composite is used as the layer boundary.

(30) Void Content Determination

(31) The void content was determined by means of the thickness difference method as described above on the test specimens previously joined by means of an interval heating press. Determination of the actual specimen thickness was effected at 5 points of measurement distributed over the component. Computation of the void content used the arithmetic mean of the 5 individual determinations of the actual sample thickness.

(32) Determination of Waviness Parameters

(33) The waviness parameters on surfaces were determined using a KLA Tencor P16+™ instrument using Profiler 7.21 control software and Apex 3D evaluation software.

(34) Differentiation between roughness profile and waviness profile from the determined primary profile was effected by utilization of a digital Gaussian filter as per DIN EN ISO 11562:1998 with a threshold wavelength of 0.08 mm.

(35) The waviness profile was used to calculate arithmetic mean waviness (Wa), quadratic mean waviness (Wq) and the total height of the waviness profile over the calculation length (Wt) as defined in DIN EN ISO 4287:2010.

(36) A tracking weight of the sensor of 2 mg and a feed rate of the sensor of 200 μm/sec were chosen for determination of the parameters. The measurement distance was 30 mm in each case. The computation length corresponded to the measurement distance.

(37) The parameters reported hereinbelow were meaned from 3 individual measurements orthogonal to the fibre orientation. The measurements were taken at room temperature (23° C.).

(38) Flexural Modulus of Elasticity

(39) To determine the flexural modulus of elasticity 5 test specimens per orientation (0°, 90°) were first prepared from the produced multilayer composite sheets with a Mutronic Diadisc 5200 cut-off saw using Dia cutting discs CFK fine blades. An outside micrometer was then used to determine the exact specimen dimensions (width and thickness) relevant for the tests. The test was performed as per ASTM D790-10 method A. The slope of the resulting force-distance diagram corresponds to the flexural modulus of elasticity. The reported result was the arithmetic mean of the 5 individual measurements.

(40) Determining Fibre Volume Content

(41) In the present process the fibres are passed through the thermoplastic melt at a constant wetting rate. The fibre volume content of a fibre composite ply is thus calculated from the difference in the melt volume flow of the thermoplastic melt and the product of the production rate of the fibre composite ply and the cross section of the fibre composite ply to be produced.

(42) 2. Production and Results

(43) Production of the Fibre Composite Plies

(44) Production of the fibre composite ply from the above-described components A and B was effected according to the process described in DE 10 2011 005 462 B3. The dry fibre band composed of spread rovings was heated to a temperature of about 220° C. before the molten polymer was applied to both sides of the plane of the dry fibre band. Once application of pressure-shear vibration had been effected the following compositions of the fibre composite plies were obtained as an endless tape.

(45) TABLE-US-00001 TABLE 1 Overview of properties of the individual fibre composite plies content of content of layer composite component A in component B in thickness in ply [vol %] [vol %] [μm] 1 63 37 230 2 55 45 150 3 55 45 180 4 55 45 190 5 53 47 190 6 57 43 210 7 50 50 185 8 50 50 180

(46) Production of the Multilayer Composites

(47) Test specimens of multilayer composite used for further characterization were obtained by specific layup of the fibre composite plies in the following orientations.

(48) TABLE-US-00002 TABLE 2 Overview of type, orientation and number of employed fibre composite plies in the multilayer composites test specimen inner plies outer plies composite ori- total composite total ply entation number ply orientation number A 4 90° 3 4 0° 2 (comp.) B 3 90° 4 3 0° 2 C 5 90° 4 2 0° 2 D 7 90° 2 1 0° 2 (comp.) E 7 90° 2 6 0° 2 (comp.) F 7 90° 2 7 0° 2 (comp.) G 8 90° 4 1 0° 2 H 8 90° 4 6 0° 2 I 8 90° 4 8 0° 2

(49) After layup the test specimens were semicontinuously interjoined in an interval heating press. The surficially applied moulding pressure was 10 bar. The temperature in the heating zone was 280° C. and the temperature in the cooling zone was 100° C. Furthermore, the feed per cycle was 30 mm and the cycle time was 10 sec. The thicknesses of the individual tape specimens were retained after joining to afford a test specimen.

(50) Results of Waviness Profile Measurement

(51) TABLE-US-00003 TABLE 3 Parameters for multilayer composites having different ply constructions thickness ratio Σ of test number Wa Wq Wt outer plies/Σ of specimen of plies [in μm] [in μm] [in μm] inner plies D (comp.) 4 8.58 10.58 60.10 1.24 F (comp.) 4 9.35 11.81 65.27 1.00 G 6 7.31 9.05 52.90 0.64 H 6 6.89 8.70 54.97 0.58 I 6 7.38 9.13 55.47 0.50

(52) The comparison of the comparative examples (D, F) with the inventive examples (G-I) shows that for a thickness ratio of the sum of the two outer plies to the sum of all inner plies of less than 0.65 markedly lower parameters are achieved for the arithmetic and quadratic average waviness (Wa, Wq) and for the total height of the waviness profile (Wt), resulting in improved optics, smoothness and an improved coatability of the surfaces.

(53) Results of Flexural Modulus of Elasticity and Void Content Determination

(54) TABLE-US-00004 TABLE 4 Flexural modulus of elasticity in 0° and 90° orientation of multilayer composites having different layer constructions flexural flexural modulus of modulus of test elasticity in elasticity in test specimen void speci- 90° orientation 0° orientation thickness in content in men in [GPa] in [GPa] [μm] [%] A (comp.) 11.4 77.9 950 <0.5 B 30.2 64.5 1080 <0.5 C 37.5 55.9 1060 <0.5 D (comp.) 12.3 71.9 830 <0.5 E (comp.) 14.1 80.9 790 <0.5 F (comp.) 15.3 97.2 740 <0.5 G 28.1 66.9 1280 <0.5 H 28.0 72.3 1200 <0.5 I 32.4 75.8 1080 <0.5

(55) The tests show that the inventive multilayer composites B, C, D, G, H and I exhibit a sufficient flexural modulus of elasticity both in the 90° orientation and in the 0° orientation, whereas the comparative specimens A, D, E and F in 90° orientation in each case exhibit too low a flexural modulus of elasticity. This ensures that the inventive specimens are resistant to a multiaxial load, such as a dropping of the relevant component or an unintentional surficial loading. It is all the more evident that the content of voids is minimized by the production process and is below 0.5 for all specimens tested.