Method of manufacturing a sheet-like composite part with improved compression strength

Abstract

Sheet-like composite parts are manufactured by: a) providing a substantially planar arrangement (A, B, A′) comprising a core layer (B) comprising a fleece material made of fleece thermoplastic fibers and reinforcement fibers, sandwiched between a pair of skin layers (A, A′), each comprising a skin thermoplastic and optionally reinforcement fibers, one face of the core layer being adjacent and substantially parallel to a skin layer and a second face of the core layer being adjacent and substantially parallel to the other skin layer, b) heating and pressing the sandwich arrangement (A,B,A′) followed by cooling, thereby obtaining the composite part, wherein the compression strength of the composite part is improved with a core layer (B) which is a Z-oriented core layer having reinforcement fibers that are predominantly oriented in a direction (Z) perpendicular to the first and second faces, produced by multiple folding.

Claims

1. A method of manufacturing a sheet-like composite part, comprising the following process steps: a) providing a substantially planar sandwich arrangement (A, B, A′) comprising a core layer (B) sandwiched between a pair of skin layers (A, A′), a first face of the core layer being adjacent and substantially parallel to a first one (A) of said skin layers and a second face of the core layer being adjacent and substantially parallel to the other one (A″) of said skin layers, the skin layers (A, A′) each comprising a skin thermoplastic and optionally reinforcement fibers, the core layer (B) comprising a fleece material made of fleece thermoplastic fibers and reinforcement fibers, wherein said fleece material is prepared with the fleece thermoplastic fibers and the reinforcement fibers in an airlaying or carding process, b) heating to melt the skin layers and pressing the sandwich arrangement (A,B,A′) followed by cooling, thereby obtaining the sheet-like composite part, wherein the core layer (B) is a Z-oriented core layer having the reinforcement fibers predominantly oriented in an orientation direction (Z) perpendicular to the first and second faces, and wherein the core layer (B) comprises a stacked plurality of continuously folded arrangements of said fleece material.

2. The method according to claim 1, wherein one of the continuously folded arrangements of said Z-oriented core layer (B) is provided by multiply folding a sheet of said fleece material into a continuously folded arrangement of mutually parallel and adjacent sheet portions pairwise connected by a first or a second folding edge located, respectively, along a first face or a second face of the continuously folded arrangement, thereby yielding said Z-oriented core layer with exposed first and second faces for applying thereto the skin layers (A) and (A′) to form said sandwich arrangement (A, B, A′) for subsequent process step b).

3. The method according to claim 2, wherein said multiply folding is carried out as a continuous process wherein the sheet of said fleece material is supplied along a processing direction (X) with a first velocity (v1) and subsequently slowed down to a second velocity (v2) which is slower than said first velocity (v1), thereby causing said multiply folding.

4. The method according to claim 2, wherein said core layer (B) further comprises at least one unfolded layer of said fleece material.

5. The method according to claim 1, wherein said reinforcement fibers are selected from the group consisting of glass fibers, carbon fibers, aramid fibers, basalt fibers, natural fibers, high-melting thermoplastic fibers, and mixtures thereof.

6. The method of claim 1, wherein said fleece thermoplastic and said skin thermoplastic are independently selected from the group consisting of polypropylene, polyethermide, polyethersulfone, polysulfone, polyphenylenesulfone, polyphthalamide, polyphenylether, polyetheretherketone, polyphenylene sulfide, polyamide, polyaryletherketone, polyetherketoneketone, polycarbonate and mixtures thereof.

7. The method of claim 1, wherein at least one skin layer (A, A′) comprises a reinforcement sheet consisting of a woven fabric, non-crimp fabric or a unidirectional fiber arrangement.

8. The method of claim 1, wherein the core layer (B) provided before processing step b) has an areal weight of 50 to 10,000 g/m.sup.2.

9. The method of claim 1, wherein the fleece material is prepared by the airlaying process.

10. The method of claim 1, wherein the fleece material is prepared by the carding process.

11. The method of claim 1, wherein the thermoplastic of the skin layers is the same as the fleece thermoplastic.

12. The method of claim 1, wherein the thermoplastic of the skin layer and the fleece thermoplastic are mutually compatible.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The above mentioned and other features and objects of this invention and the manner of achieving them will become more apparent and this invention itself will be better understood by reference to the following description of various embodiments of this invention taken in conjunction with the accompanying drawings, wherein:

(2) FIG. 1 shows an arrangement to be processed according to prior art, as a perspective view;

(3) FIG. 2 shows a core layer of the arrangement of FIG. 1, also as a perspective view;

(4) FIG. 3 shows an arrangement processed according to a first embodiment with foldings, as a vertical section perpendicular to the sheet-plane;

(5) FIG. 4 shows an arrangement processed according to a second embodiment with foldings, as a vertical section perpendicular to the sheet-plane;

(6) FIG. 5 shows an arrangement processed according to a third embodiment with foldings, as a vertical section perpendicular to the sheet-plane;

(7) FIG. 6 shows an arrangement processed according to a fourth embodiment with foldings, as a vertical section perpendicular to the sheet-plane;

(8) FIGS. 7 to 10 show various processing steps according to a fifth embodiment with longitudinal compression, as a vertical section perpendicular to the sheet-plane; and

(9) FIG. 11 shows an arrangement for a process according to a sixth embodiment with needling, as a vertical section perpendicular to the sheet-plane.

(10) It will be understood that the figures are not necessarily drawn to scale. In some instances, relative dimensions are substantially distorted for ease of visualization. Identical or corresponding features in the various figures will generally be denoted with the same reference numerals.

DETAILED DESCRIPTION OF THE INVENTION

(11) It will be understood that the figures are not necessarily drawn to scale. In some instances, relative dimensions are substantially distorted for ease of visualization. Identical or corresponding features in the various figures will generally be denoted with the same reference numerals.

(12) A method of manufacturing a sheet-like composite part according to prior art is shown in FIGS. 1 to 3. As generally shown in FIG. 1, the method starts by providing a substantially planar arrangement (A, B, A′) comprising a core layer B sandwiched between a pair of skin layers, namely an upper skin layer A and a lower skin layer A′. In the example shown, the core layer B is made up of two individual layers B1 and B2 stacked on top of each other.

(13) A first face of the core layer B is adjacent and substantially parallel to the upper skin layer A whereas the second face of the core layer is adjacent and substantially parallel to the lower skin layer A′.

(14) The two skin layers A, A′ each comprise a skin thermoplastic and optionally reinforcement fibers. The core layer B, i.e. each one of the individual layers B1 and B2, comprises a fleece material F made of fleece thermoplastic fibers and further comprising reinforcement fibers R1, R2, etc.

(15) As illustrated in FIG. 2, the orientation of reinforcement fibers R1, R2, etc. in each core layer is predominantly in the layer plane, i.e. in the plane spanned by directional vectors X and Y. More precisely, the reinforcement fibers are oriented in such manner that their longitudinal fiber direction does not have a substantial component in the out-of-plane direction Z. It should be noted that this also applies to curved fibers, in which case one has to consider the local fiber direction at any point along the fiber.

(16) The basic concept of the present invention is now illustrated in FIG. 3. In contrast to the situation shown in FIGS. 1 and 2, there is now a substantial amount of reinforcement fibers R1, R2, etc. having a directional component perpendicular to the faces of the core layer, i.e. along the out-of-plane direction Z.

(17) In the example shown in FIG. 3, this is achieved by having the core layer (B) made up by multiply folding a sheet 2 of fleece material into a continuously folded arrangement of mutually parallel and adjacent sheet portions 2a, 2b, 2c etc. pairwise connected by a first folding edge 4 or a second folding edge 6 located, respectively, along a first face 8 or a second face 10 of the continuously folded arrangement. More specifically, in the example of FIG. 3 sheet portions 2a and 2b are connected by first folding edge 4, whereas sheet portions 2b and 2c are connected by second folding edge 6. This yields a Z-oriented core layer with exposed first and second faces 8, 10 onto which the surface layers A and A′ are then applied to form a sandwich arrangement A, B, A′.

(18) The sandwich arrangement A, B, A′ thus obtained can then be subjected to a heating and pressing step followed by cooling, thereby obtaining a sheet-like composite part with excellent compression strength properties.

(19) Further embodiments based on the same principle using a folded fleece sheet material are shown in FIGS. 4 to 6.

(20) In the example of FIG. 4, the core layer B comprises one continuously folded arrangement 12a and a pair of unfolded layers 12b and 12c of the same fleece material. In this particular example, the folded layer 12a is positioned between unfolded layers 12b and 12c.

(21) In the example of FIG. 5, the core layer B comprises two continuously folded arrangements 12d and 12e stacked on top of each other and forming a double layer located between the upper skin layer A and the lower skin layer A′. In the arrangement shown here, the two stacked continuously folded layers 12d and 12e are substantially “out of phase”, thereby shifting and thus minimizing the protruding effect of the folding edges.

(22) In the example of FIG. 6, the core layer B comprises a triple stack comprising two continuously folded arrangements 12d and 12e and an unfolded layers 12f located therebetween.

(23) In certain embodiments, the multiply folded layer is carried out as a continuous process wherein the sheet of said fleece material is supplied along a processing direction (X) with a first velocity (v1) and subsequently slowed down to a second velocity (v2) which is slower than said first velocity (v1), thereby causing said multiply folding.

(24) A different approach for providing a Z-oriented core layer is used in a fifth embodiment, which is illustrated in FIGS. 7 to 10. Here, the required Z-oriented core layer B is formed by filling the fleece material 102, which comprises fleece thermoplastic fibers and reinforcement fibers, into a compression unit 104 with a fixed upper wall 106, lower wall 108, lateral walls (not shown) and terminal walls 110 and 112. Initially, in the situation shown in FIG. 7, the orientation of the reinforcement fibers is substantially isotropic. By applying a longitudinal mechanical compression step, achieved in this case by reducing the distance between the terminal walls, yields a laterally confined and longitudinally compressed fleece material 102a as shown in FIG. 8. In this situation, the reinforcement fibers are preferentially oriented perpendicular to the direction X of compression. Removal of the upper and lower walls provides a Z-oriented core layer with exposed first (upper) face 114 and second (lower) face 116. This is followed by applying thereon an upper surface layer A and a lower surface A′ to form a sandwich arrangement A, B, A′ as shown in FIG. 9. Finally, as shown in FIG. 10, the sandwich arrangement A, B, A′ is subjected to a heating and pressing with an appropriate tool 118 step followed by cooling, thereby obtaining a sheet-like composite part with excellent compression strength properties.

(25) A further approach for providing a Z-oriented core layer is used in a sixth embodiment, which is illustrated in FIG. 11. In this case, the required Z-oriented core layer B is produced continuously by passing the fleece material 202, which comprises fleece thermoplastic fibers and reinforcement fibers R, through a processing unit 204. The latter comprises, sequentially along a processing direction X, a compression station 206, an expansion station 208, and a needling station 210. More specifically, the compression station 206 comprises a first roller pair 212 spaced apart by a first distance d1 and running at a first velocity v1. The subsequent expansion station 208 comprises a second roller pair 214 spaced apart by a second distance d2 which is substantially larger than the first distance 1. The second roller pair runs at a second velocity v2 which is substantially smaller than the first velocity v1. As illustrated in FIG. 11, the fleece material follows the diverging cross-sectional profile of the processing unit, effectively leading to an expansion. The latter phenomenon leads to a reorientation of the reinforcement fibers R contained in the fleece material so as to be preferentially oriented perpendicular to the processing direction X. In order to maintain the resulting Z-orientation, the material passes the needling station 210 comprising a plurality of needle elements 216 reciprocating perpendicularly to the processing direction X. The Z-oriented core layer thus obtained has an exposed first (upper) face 218 and second (lower) face 220.

(26) Because the core layer is produced as a substantially endless material, the following application of an upper surface layer A and a lower surface A′ to form a sandwich arrangement A, B, A′ for subsequent heating and pressing followed by cooling can be carried out in a continuous process. Alternatively, the Z-oriented core material can be cut in sections and processed by applying corresponding sections of surface layer material.