Method for producing a planar composite component and composite component produced thereby

Abstract

A method for producing a planar composite component having a core layer (B), which is arranged between and integrally bonded to two cover layers (A, A′), wherein the cover layers contain a cover-layer thermoplastic and wherein the core layer contains a core-layer thermoplastic, comprises the following steps: a) a heated stack with layer sequence A-B-A′ is provided; b) the heated stack (A-B-A′) is pressed; c) the pressed stack is cooled, whereby the planar composite component with consolidated layers integrally bonded to each other is formed. To improve the production method including the producibility of planar 3D components, it is proposed, that at least one of the cover layers (A, A′) in unconsolidated form comprises a fibrous nonwoven layer of 10 to 100 wt.-% thermoplastic fibers of the cover-layer thermo-plastic and 0 to 90 wt.-% of reinforcing fibers having an areal weight of 300 to 3,000 g/m.sup.2; the core layer (B) in unconsolidated form comprises at least one randomly-oriented-fiber nonwoven layer (D) formed from reinforcing fibers and thermoplastic fibers of the core-layer thermoplastic,
and that after the pressing the consolidated core layer(s) has/have an air pore content of <5 vol.-% and the consolidated core layer has an air pore content of 20 to 80 vol-%.

Claims

1. A method for producing a planar composite component having a core layer (B) arranged between and integrally bonded to two cover layers (A, A′), wherein the cover layers contain a cover-layer thermoplastic and wherein the core layer contains a core-layer thermoplastic, comprising the following steps: a) providing corresponding pre-cut parts of the two cover layers and of the core layer and forming therefrom a stack with layer sequence A-B-A′ is heated to a temperature above the melting temperature of both the cover-layer thermoplastic and the core-layer thermoplastic; b) pressing the heated stack A-B-A; c) cooling the pressed stack, whereby the planar composite component with consolidated layers integrally bonded to each other is formed; and wherein in step a) the initially provided pre-cut parts of the two cover layers (A, A′) are provided in unconsolidated flexible form, at least one cover layer (A) comprising an unconsolidated flexible fibrous nonwoven layer (C) of 10 to 100 wt.-% thermoplastic fibers of the cover-layer thermoplastic and 0 to 90 wt.-% of reinforcing fibers having an areal weight of 300 to 3000 g/m.sup.2, and in step a) the initially provided pre-cut parts of the core layer (B) comprise at least one randomly-oriented-fiber nonwoven layer (D) formed from reinforcing fibers and thermoplastic fibers of the core-layer thermoplastic, and having an areal weight of 500 to 10,000 g/m.sup.2, and after step c) the consolidated cover layer(s) has/have an air pore content of <5 vol.-% and the consolidated core layer has an air pore content of 20 to 80 vol-%.

2. The method of claim 1, wherein the randomly-oriented-fiber nonwoven layer (D) of the core layer (B) provided in step a) is needled.

3. The method of claim 1, wherein the cover-layer thermoplastic and the core-layer thermoplastic are independently selected from the group consisting of PP, PEI, PEEK, PPS, PA, PEAK, PEKK, PC, and mixtures thereof.

4. The method of claim 1, wherein the reinforcing fibers are selected from the group consisting of carbon fibers, glass fibers, aramid fibers, basalt fibers, high-melting thermoplastic fibers, and mixtures thereof.

5. The method of claim 1, wherein in step a) the pre-cut parts of the two cover layers (A, A′) and the core layer (B) are stacked onto each other in a cold state with layer sequence A-B-A′, and the stack (A-B-A′) thus formed is heated to a temperature above the melting temperature of both the cover-layer thermoplastic and the cover-layer thermoplastic, whereby a heated stack (A-B-A′) is formed to then carry out the pressing step b).

6. The method of claim 5, wherein the cover-layer thermoplastic and the core-layer thermoplastic are identical.

7. The method of claim 1, wherein in step a) the pre-cut parts of the core layer (B) and of the cover layers (A, A′) are heated independently of one another to a temperature above the melting temperature of the corresponding thermoplastic, and then stacked onto each other in the heated state with layer sequence A-B-A to form a heated stack (A-B-A′) which is then subjected to the pressing step b).

8. The method of claim 1, wherein the at least one cover layer (A) in unconsolidated form comprises a woven layer or an oriented-fiber layer (E) comprising reinforcing fibers, which has an areal weight of 100 to 2,000 g/m.sup.2 and which is needled, stitched or thermally connected to the fibrous nonwoven layer (C).

9. The method of claim 8, wherein the at least one cover layer (A) comprises several woven layers or oriented-fiber layers comprising different reinforcing fiber materials.

10. The method of claim 1, wherein the core layer (B) in unconsolidated form comprises at least one further structural layer (F) which is adjacent to the randomly-oriented-fiber nonwoven layer (D).

11. The method of claim 1, wherein the core layer (B) in unconsolidated form comprises at least one further structural layer (F) which is adjacent to the randomly-oriented-fiber nonwoven layer (D) and is further randomly-oriented-fiber nonwoven layer with a different content of reinforcing fibers, a honeycomb layer, or a foamed plastic layer.

12. The method of claim 10, wherein the structural layer (F) is provided only in selected regions of the core layer.

13. The method of claim 1, wherein the pressing of the heated stack (A-B-A′) is carried out in a non-planar pressing tool.

14. The method of claim 1, wherein the cover-layer thermoplastic and the core-layer thermoplastic are PEEK, wherein the reinforcing fibers are carbon fibers, and wherein the cover layers (A, A′) have a density of 1.0 to 2.0 g/cm.sup.3, and wherein the core layer (B) has a density of 0.2 to 1.0 g/cm.sup.3.

15. The method of claim 1, wherein the cover-layer thermoplastic and the core-layer thermoplastic are PEI, wherein the reinforcing fibers are carbon fibers, and wherein the cover layers (A, A′) have a density of 1.0 to 2.0 g/cm.sup.3, wherein the core layer (B) has a density of 0.2 to 1.0 g/cm.sup.3.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Examples of the invention will henceforth be described in more detail by reference to the drawings, which show;

(2) FIG. 1 a first planar composite component, in a schematic, perspective view;

(3) FIG. 2 an embodiment of an unconsolidated cover layer, in a schematic sectional view;

(4) FIG. 3 a second planar composite component, in a schematic, perspective view;

(5) FIG. 4 a third planar composite component, in a schematic, perspective view;

(6) FIG. 5 a fourth planar composite component, in a schematic, perspective view;

(7) FIG. 6 a combined heating, pressing and cooling device for processing a layer stack, in a schematic, perspective view;

(8) FIG. 7 a device with a heating station and a follow-up pressing and cooling device for processing a layer stack, in a schematic, perspective view; and

(9) FIG. 8 a device with separate heating stations for individual layers and a follow-up pressing and cooling device for processing a layer stack, in a schematic, perspective view.

MODES FOR CARRYING OUT THE INVENTION

(10) Only to clarify the layer structure, the planar composite components of FIGS. 1 to 5 are shown with layers offset in the longitudinal direction. In practical use, however, the individual layer edges are usually arranged in justified manner. Moreover, FIGS. 1 to 5 are intended to illustrate the principal layer structure only, and not relative thicknesses of the layers. Accordingly, the arrangements shown in FIGS. 1 to 5 basically represent both each provided layer stack and also the composite components formed after the pressing process.

(11) The composite component shown in FIG. 1 comprises a core layer B which is arranged between two cover layers A and A′.

(12) A possible embodiment of the cover layer A is illustrated in FIG. 2. It comprises, in its initially provided form, a fibrous nonwoven layer C and a woven layer E made of reinforcing fibers which is needled therewith. Such a layer can be produced, for example, by adjacently laying out and needling of the layers C and E, with a part of the nonwoven fibers C being pushed through the reinforcing fiber layer E during needling. Accordingly, the reinforcing fiber layer E is surrounded on both sides by nonwoven fibers C.

(13) In the composite component shown in FIG. 3, each of the two cover layers A and A′ is formed from two woven layers E1 and E2 comprising different reinforcing fiber materials.

(14) In the composite component shown in FIG. 4, the core layer B in its unconsolidated form comprises at both sides thereof a structure layer F with the shape of a honeycomb plate or of a randomly oriented fiber layer with a different content of reinforcing fibers arranged in the interior of the randomly-oriented-fiber nonwoven layer D. In the example shown, the structural layer is formed so as to cover the whole area and is thus embedded in sandwich-like manner between two randomly oriented fiber layers.

(15) In the composite component shown in FIG. 5, the structure layer F is present only in selected regions of the core layer B. As shown in FIG. 5, in the example shown the structure layer F is arranged as a central strip in the interior of the core layer B and is embedded between upper and lower randomly-oriented-fiber nonwoven layers D1 and D2 and between lateral randomly-oriented-fiber nonwoven layers D3 and D4.

(16) In an embodiment of the production method, as shown in FIG. 6, an initially provided cold layer stack A-B-A′ is introduced into a combined heating, pressing and cooling device 2, where it is heated and pressed to a planar composite component.

(17) In a further embodiment, as illustrated in FIG. 7, a previously provided flexible cold layer stack A-B-A′ is introduced into a contact heating device 4 where it is heated. The heated layer stack thus formed is subsequently pressed to a planar composite component in a pressing device 6.

(18) In still another embodiment, as illustrated in FIG. 8, a core layer B in non-consolidated form, which in the example shown consists of several layers, is introduced into a first heating device 4a where it is heated. At substantially the same time, a cover layer A in unconsolidated form is introduced into a contact heating device 4b where it is also heated. A further cover layer A′, not shown, is also heated either in a third heating device or immediately afterwards in the second heating device. From the heated cover layers and core layers thus formed, a hot stack A-B-A is formed, which is subsequently pressed to a planar composite component in the pressing device 6. By using separate heating devices, different heating temperatures can be used for the core layer B on the one hand and for the cover layers A and A′ on the other hand. This allows the use of different thermoplastic materials in the core layer and in the cover layers.

Example 1: Remarks on Maximum Fiber Contents and Thicknesses

(19) The following table gives an overview of correlated quantities for various combinations of PP and PEEK as thermoplastics and for glass fibers (GF) and carbon fibers (CF) as reinforcing fibers:

(20) TABLE-US-00001 TABLE 1 Per- centage Percentage volume Content of weight propor- reinforcing proportion tion fibers 0% 10% 90% 75% PP-GF density g/cm3 0.9 0.963 2.187 2.187 PP-GF weight — 0 0.1 0.897 0.897 proportion PP-GF volume — 0 0.037 0.7499 0.7499 proportion Thicknesses at given areal weights (g/m2) 300 mm 0.33 0.31 0.14 0.14 3000 mm 3.33 3.12 1.37 1.37 PP-CF density g/cm3 0.9 0.947 1.638 1.575 PP-CF weight — 0 0.1 0.9 0.857 proportion PP-CF volume — 0 0.0526 0.8182 0.75 proportion Thicknesses at given areal weights (g/m2) 300 mm 0.33 0.32 0.18 0.19 3000 mm 3.33 3.17 1.83 1.90 PEEK-GF g/cm3 1.3 1.368 2.364 2.275 density PEEK-GF — 0 0.1 0.9 0.857 weight proportion PEEK-GF — 0 0.526 0.8182 0.7498 volume proportion Thicknesses at given areal weights (g/m2) 300 mm 0.23 0.22 0.13 0.13 3000 mm 2.31 2.19 1.27 1.32 PP-GF density g/cm3 1.3 0.9257 1.733 1.675 PEEK-CF — 0 0.1 0.9 0.806 weight proportion PEEK-CF — 0 0.0743 0.8667 0.75 volume proportion Thicknesses at given v (g/m2) 300 mm 0.23 0.32 0.17 0.18 3000 mm 2.31 3.24 1.73 1.79 Density g/cm3 PP 0.9 PEEK 1.3 GF 2.6 CF 1.8
wherein the following relationship were used for calculation:
Volume proportions:

(21) $V_F=\frac{W_F}{D_F.Math.\left(\frac{W_F}{D_F}+\frac{W_P}{D_P}\right)}$ with: VF Volume proportion of the fibers WF Weight proportion of the fibers WP Weight proportion of the polymer DF Density of the fibers (kg/m3) DP Density of the polymer (kg/m3)
Density:
D.sub.C=V.sub.F.Math.D.sub.F+(1−V.sub.F).Math.D.sub.P with: DC Density to the composite (kg/m3)
Thickness:

(22) $t_C=\frac{A_C}{D_C}$ with: tC Thickness to the composite (m) AC Areal weight to the composite

(23) It should be noted that due to geometrical reasons the volume proportions amount to a maximum of 79% in the case of a square arrangement and to a maximum of 91% in case of a hexagonal arrangement. In Table 1 above, a maximum fiber volume proportion of 75% was assumed.

Example 2: Composite Component with a Constant Thickness

(24) A flexurally rigid composite component according to the present invention and having the layer structure A-B-A was produced. The two cover layers A were each provided from a fibrous nonwoven pre-cut part made of carbon fibers and PEI thermoplastic fibers having an areal weight of 440 g/m2. The core layer B was provided from a total of four layers of a randomly-oriented-fiber nonwoven made of carbon fibers with PEI thermoplastic fibers having an areal weight of 4×500 g/m2.

(25) The non-planar flexurally rigid composite component thus produced had a thickness of about 4 mm, an areal weight of 2,880 g/m2 and a density of 0.7 g/m3.

Example 3: Composite Component Having Areas of Different Thickness

(26) A composite component according to the invention and having the layer structure A-B-A was produced. The two cover layers A were each provided from a fibrous nonwoven precut part made of carbon fibers and PEI thermoplastic fibers having an areal weight of 440 g/m2. The core layer B was provided from a total of seven layers of a randomly-oriented-fiber nonwoven made of carbon fibers with PEI thermoplastic fibers having an areal weight of 7×500 g/m2.

(27) The flexurally rigid composite component having regions of different thickness thus produced had a thickness of about 3.5 mm in the more strongly consolidated regions and a thickness of about 8 mm in the in the less strongly consolidated regions. The areal weight was 4,380 g/m2 and the density was 1.26 g/m3 and 0.55 g/m3 in the more strongly and the less strongly consolidated regions, respectively.

Example 4: Results of Material Testing

(28) The following table shows measured mechanical properties of various composite components according to the present invention.

(29) TABLE-US-00002 TABLE 2 Layer 1x 1x 1x 1x 1x 2x structure *) 2x 5x 5x 5x 6x 6x A-B-A 1x 1x 1x 1x 1x 2x Density 0.34 0.43 0.43 0.62 0.72 1.01 (g/cm3) Thickness 4.9 4.9 5.7 4.86 4.87 4.54 (mm) Areal weight 1,880 2,380 2,380 3,380 3,380 4,760 (g/m2) Flexural 8.2 28.4 22.6 74 94 195 rigidity 0° (MPa) Flexural 82 164 208 rigidity 90° (MPa) Flexural 1,351 4,285 3,100 6,381 8,245 17,173 rigidity E module 0° (MPa) Flexural 8,178 12,313 18,271 rigidity E module 90° (MPa) *) Cover layers A with CF woven and PEI matrix, core layer made of CF randomly-oriented-fibers and PEI matrix