PLANAR COMPOSITE MATERIAL

Abstract

A sheetlike composite material including at least one layer A of a nonwoven thermoplastic fiber web or a thermoplastic film, and at least two unidirectional oriented-fiber layers B and B′, the layers B and B′ having a bidirectional fiber orientation. The layers are not only needled but also stitched to one another.

Claims

1-20. (canceled)

21. A planar composite material comprising a) at least one layer A comprising a fiber nonwoven comprising 40 to 100 wt.-% thermoplastic fibers and 60 to 0 wt.-% reinforcing fibers, or comprising a thermoplastic foil, and b) at least two unidirectionally oriented fiber layers B and B′ comprising parallel reinforcing fiber bundles, wherein at least two layers B and B′ have different fiber orientations relative to at least one other B or B′ layer prior to stitching and needling, wherein all layers are both stitched together and also subsequently needled.

22. The composite material of claim 21, wherein a layer arrangement is B-A-B′ or B-A-B′-A-B.

23. The composite material of claim 21, wherein the fiber orientation of the layers B and B′ with respect to a reference direction of the composite material is 0°/90°, 30°/−30°, 45°/−45° or 60°/−60°.

24. The composite material of claim 21, the areal weights of the individual layers each are 20 to 1,000 g/m.sup.2.

25. The composite material of claim 21, the areal weights of the individual layers each are 30 to 1,000 g/m.sup.2.

26. The composite material of claim 21, the areal weights of the individual layers each are 150 to 3,000 g/m.sup.2.

27. The composite material of claim 21, wherein the total amount of reinforcing fibers in the composite material is 20 to 80 wt.-%, based on the total weight of the composite material.

28. The composite material of claim 21, wherein the reinforcing fibers comprise glass fibers or carbon fibers.

29. The composite material of claim 21, wherein the thermoplastic fibers or the thermoplastic foil of the layer A comprise polypropylene.

30. The composite material of claim 29, wherein threads used for stitching comprise polypropylene.

31. The composite material of claim 21, wherein the thermoplastic fibers or the thermoplastic foil of the layer A comprise polyamide.

32. The composite material of claim 31, wherein the threads used for stitching comprise polyamide.

33. The composite material of claim 21, wherein the thermoplastic fibers or the thermoplastic foil of the layer A comprise polyether ketone.

34. The composite material of claim 33, the threads used for stitching comprise polyether ketone.

35. A method for producing a composite material of claim 21, comprising: a) continuously merging together fiber nonwoven layer(s) A produced by a carding, airlay or spunbond nonwoven process, with oriented fiber layers B and B′, and subsequently stitching the layers to each other and thereafter needling the layers; or b) continuously merging together thermoplastic foil(s) of the layer(s) A with the oriented fiber layers B and B′, stiching the layers to each other, and thereafter needling the layers.

36. A process for producing three-dimensional components comprising heat pressing a composite material of claim 21 in a mold.

37. A process for producing a planar semifinished product with a thickness of 0.5 to 5 mm comprising of heat pressing a composite material of claim 21 in a double band press.

38. A planar heat-moldable semi-finished product comprising a molding having a thickness of 0.5 to 5 mm prepared by thermally consolidating a composite material of claim 21 in a double band press.

39. The composite material of claim 21, wherein the at least one layer A consists of a thermoplastic foil.

40. The composite material of claim 21, wherein an acute angle between fiber directions of the fiber layers B and B′ is 60°.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] FIG. 1 shows a schematic perspective view of an example composite material according to one or more embodiments; and

[0015] FIG. 2 shows a cross-sectional view of the composite material depicted in FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0016] The term “thermoplastic” as generally known in the technical field is to be understood in such manner that the corresponding materials can be melted and thermoplastically molded under conventional processing conditions.

[0017] According to an advantageous embodiment the fiber nonwoven of the layer A contains up to 50 wt.-% reinforcing fibers. According to another advantageous embodiment the fiber nonwoven of the layer A contains no reinforcing fibers and is, therefore, only made of thermoplastic fibers. According to a further advantageous embodiment the layer A is made of a thermoplastic foil.

[0018] “Bidirectional” in the context with two oriented fiber layers B and B′ means that the longitudinal axis of the oriented fiber layer B is not parallel to the longitudinal axis of the oriented fiber layer B′.

[0019] Further objects of the invention are processes for producing such composite materials. There are two variants therefor:

[0020] In the first variant, initially the fiber nonwoven-layer(s) A are produced according to the carding, airlay or spunbound nonwoven process or according to so-called paper making process, and subsequently the oriented fiber layers B and B′, which are bidirectionally aligned to each other, are continuously joined together with the layer(s) A. The layers are subsequently stitched to each other and thereafter needled.

[0021] In the second variant, the thermoplastic foil(s) of the layer A and the oriented fiber layers of the layers B and B′, which are bidirectionally aligned to each other, are continuously joined, stitched to each other and are thereafter needled. Preferred layer arrangements are B-A-B′ and B-A-B′-A-B. Further arrangements with a plurality of up to 20 layers are possible. It is preferred that always a fiber nonwoven or a thermoplastic foil layer A is arranged between two oriented layers B or B′. For specific applications, an arrangement in which one layer A is arranged at the outside is also possible.

[0022] The fiber orientation of the layers B or B′ is bidirectional, and preferred orientations are 0°/90°, 30°/−30° , 45°/−45° and 60°/−60° with respect to a reference direction in the layer arrangement such as, for example, its longitudinal axis L. Accordingly, the acute angle between the respective fiber directions is preferably 60° or 90°. Thereby, the layers are preferably arranged symmetrically.

[0023] FIG. 1 shows in a perspective view a layer arrangement B-A-B′ with a bidirectional fiber orientation 45°/−45° of the layers B and B′, respectively, with respect to a longitudinal axis L.

[0024] The areal weights of the individual layers are preferably between 20 to 1,000 g/m.sup.2, particularly between 30 to 1,000 g/m.sup.2, more particularly between 150 and 300 g/m.sup.2. The individual oriented fiber layers may also have different areal weights. The areal weights are to be selected in such manner that the portion of the total reinforcing fibers in the composite material is preferably 20 to 80 wt.-%, more preferably 30 to 70 wt.-% and most preferably about 60 wt.-%.

[0025] Preferred reinforcing fibers are glass fibers and carbon fibers; but also aramide fibers, basalt fibers, natural fibers, and fibers from higher melting polymers, as well as hybrid fibers, for example from glass fibers and polypropylene fibers, are suitable. Preferably, the fiber types are in each case the same in the individual layers. The reinforcing fibers of the oriented fiber layer are preferably present as fiber bundle with a titer between 300 and 4,800 tex.

[0026] Preferred thermoplastics in the fiber nonwoven or in the thermoplastic foil are polypropylene and meltable polyamides, particularly aliphatic polyamides; in addition, other thermoplastics such as polyester, polyether sulfone, polyether ketones and polyether imide are also suitable. Polyether ketones stand out particularly by a good heat resistance. Composite materials having a particularly good flowability can be obtained if the thermoplastic is polypropylene with a melt flow index (melt flow index, MFI) (230° C., 2.16 kg) between 10 and 400, particularly at about 120 g/10 min. The thermoplastics for producing the fiber nonwoven of the layer A can be provided in many different dimensions and geometries.

[0027] The individual layers of the composite material are both stitched to each other and also needled.

[0028] Upon stitching, the fiber bundles of the oriented fiber layer are connected to each other by means of a stitching thread which forms meshes. Thereby, the reinforcing fibers are fixed in their parallel orientation. Suitable stitching threads can be made of glass, polypropylene, polyamide, and also of PET or polyether ketones. Acetate and viscose threads can also be used.

[0029] Preferably, the stitching threads are made of the same thermoplastic as the thermoplastic fibers or the thermoplastic foil of the layer A, that is, preferably also of polypropylene or polyamide.

[0030] FIG. 2 show the layer arrangement B-A-B′ of FIG. 1 in a cross section along the fiber orientation of the layer B after stitching. Thereby, the stitching thread N connects the fiber bundles of the layers B′ and B. Subsequently, this layer arrangement is also needled.

[0031] Upon needling, as already explained, the fiber bundles are opened and the fibers are partially broken. Moreover, thermoplastic fibers are drawn out of the nonwoven into the oriented fiber layer by the barbs of the needles. The same happens also upon needling the thermoplastic foil, where fragments or threads are torn out of the foil and drawn into the oriented fiber layer by the barbs. The needling can be carried out on conventional needling looms with felting needles. The number of needle stitches may vary between 5 and 100 per cm.sup.2, particularly between 20 and 40 punctures per cm.sup.2.

[0032] All this has the result that by the subsequent hot pressing the thermoplastic melt penetrates from the fiber nonwoven or from the thermoplastic foil into the oriented fiber layers and can impregnate the same uniformly. If the stitching thread consists of the same thermoplast, it will also melt during the hot pressing; thereafter it is no longer needed.

[0033] Due to the fact that the fiber bundles are additionally stitched to each other, they keep their orientation upon needling, and because by the needling also the oriented fiber layer is connected to the fiber nonwoven layer or to the thermoplastic foil, there is also no risk for the layers to slip out of position during the transport and the subsequent processing.

[0034] At temperatures above the softening range of the thermoplastic the planar composite materials of the present invention can be directly pressed in molds to form three-dimensional components, or they can be consolidated by means of heat pressing, for example, in a double band press, to planar semifinished products, preferably with a thickness of 0.5 to 5 mm.

[0035] While embodiments of the invention have been illustrated and described, it is not intended that these embodiments illustrate and describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention.