UD TAPE WITH IMPROVED PROCESSING CHARACTERISTICS AND ROUGHENED SURFACE AND METHOD FOR PRODUCTION THEREOF

Abstract

The present invention relates to a method for producing a unidirectional tape with a surface polymer layer, the method comprising the steps of a) providing an impregnation slurry comprising particles of a polymer, water, optionally a surfactant, optionally an organic carrying medium, optionally organic compounds and optionally surface active compounds, and providing a pressing tool having a surface profile structure, the surface profile structure having a surface roughness Ra of 1 to 20 μm, preferably of 2 to 10 μm, more preferably 3 to 7 μm, b) impregnating a unidirectional fiber layer comprising unidirectional fibers with the impregnation slurry to obtain an impregnated unidirectional fiber layer comprising the particles of the polymer, c) pressing at a surface of the impregnated unidirectional fiber layer with the surface profile structure to move at least some of the particles of the polymer within the impregnated unidirectional fiber layer onto the surface to form a surface polymer layer on the unidirectional fiber layer, and d) obtaining a unidirec

Claims

1. A method for producing a unidirectional tape with a surface polymer layer, the method comprising the steps of a) providing an impregnation slurry comprising particles of a polymer, water, optionally a surfactant, optionally an organic carrying medium, optionally organic compounds and optionally surface active compounds, and providing a pressing tool having a surface profile structure, the surface profile structure having a surface roughness Ra of 1 to 20 μm, b) impregnating a unidirectional fiber layer comprising unidirectional fibers with the impregnation slurry to obtain an impregnated unidirectional fiber layer comprising the particles of the polymer, c) pressing at a surface of the impregnated unidirectional fiber layer with the surface profile structure to move at least some of the particles of the polymer within the impregnated unidirectional fiber layer onto the surface to form a surface polymer layer on the unidirectional fiber layer, d) obtaining a unidirectional tape with a surface polymer layer.

2. The method according to claim 1, wherein the polymer is a thermoplastic polymer.

3. The method according to claim 2, wherein the thermoplastic polymer comprises, or consists of, polyaryletherketone (PAEK)-based polymeric material, polyphenylene sulphide (PPS), polyetherimide (PEI), polyethersulfone (PESLI, PES) or polysulfone (PSU).

4. The method according to claim 3, wherein the polyaryletherketone (PAEK)-based polymeric material is selected from the group consisting of poly-ether-ketone (PEK), polyether-ether-ketone (PEEK), poly-ether-ether-ketone-ketone (PEEKK), poly-ether-ether-ketone-ketone (PEKK), poly-ether-ketone-ether-ketone-ketone (PEKEKK), poly-ether-ether-ketone-ether-ketone (PEEKEK), poly-ether-ether-ether-ketone (PEEEK), and poly-ether-diphenyl-ether-ketone (PEDEK), meta-polyether-ether-ketone (PEmEK), copolymers thereof and blends thereof.

5. The method according to claim 1, wherein the unidirectional fibers are carbon fibers and/or glass fibers and/or quartz.

6. The method according to claim 1, wherein the surface polymer layer has a surface roughness Ra of 1 to 20 pm.

7. The method according to claim 1, further comprising the step of e) drying the unidirectional fiber layer, wherein step e) is performed between impregnating step b) and pressing step c).

8. The method according to claim 1, further comprising the step of f) cooling the unidirectional fiber layer before or while performing pressing step c).

9. The method according to claim 1, wherein pressing step c) is performed while the unidirectional fiber layer is at a temperature T being in the range
(Tc−150° C.)<T<(Tc+150° C.) wherein Tc is the crystallization temperature of the polymer.

10. The method according to claim 1, wherein the surface profile structure comprises protrusions for pressing the impregnated unidirectional fiber layer and recesses for receiving the polymer pressed out of the impregnated unidirectional fiber layer.

11. The method according to claim 1, further comprising step g) of electrostatically depositing secondary particles on the surface polymer layer.

12. Unidirectional tape with a surface polymer layer obtained by the method according to claim 1.

13. Unidirectional tape comprising a unidirectional fiber layer and a surface polymer layer, wherein the unidirectional fiber layer comprises unidirectional fibers and particles of a polymer and wherein the surface polymer layer comprises particles of the polymer, characterized by the surface polymer layer having a surface roughness Ra of 1 to 20 pm and having a thickness of less than 15 pm.

14. Unidirectional tape according to claim 13, further comprising a transition zone, wherein the transition zone is located between the unidirectional fiber layer and the surface polymer layer, wherein a thickness of the transition zone is between 2 to 15 pm, and/or wherein a thickness variation of the surface polymer layer is between 0 and 75% of an average surface polymer layer thickness, and/or wherein the surface polymer layer comprises voids, wherein the amount of voids in the surface polymer layer is between 1 to 10 vol. % based on the total volume of the surface polymer layer.

15. Unidirectional tape according to claim 13, wherein the polymer is a thermoplastic polymer and the unidirectional fibers are carbon fibers.

Description

[0066] The figures show

[0067] FIG. 1a Schematic drawing of friction testing,

[0068] FIG. 1b Schematic drawing of the friction testing specimen,

[0069] FIG. 2 Results of the shear stress measurements,

[0070] FIG. 3 Micrograph image of the comparative example, and

[0071] FIG. 4 Micrograph image of the inventive example.

[0072] The invention is further illustrated by way of a non-limiting example below.

EXAMPLES

Material and Sample Preparation

[0073] Material tested was carbon fiber reinforced (PAEK)-based polymer 145 gsm UD tape. In addition to a reference UD tape, two additional tapes were prepared. The comparative tape was made by pressing between normal smooth surfaces, whereas the inventive tape was made by pressing between roughened surfaces in accordance with the present invention.

Ply-Ply Friction Testing Set-Up

[0074] Ply-ply friction tests were performed on a benchmarked friction tester schematically shown in FIG. 1a. A specimen consists of two outer plies and a middle ply with all fibers aligned in the longitudinal direction, as visualized in FIG. 1b. FIG. 1b schematically shows the specimen with dimensions given in millimeter. The specimen was mounted in a universal testing machine. The velocity V of the upper clamp can be controlled resulting in a relative movement between the middle ply and the outer plies. The resulting pull force, Fp, was measured using a 1 kN loadcell, which was used to calculate the shear stress:

[00001]$\tau =\frac{F_p}{2A}$

[0075] With A the area of the heated pressure plates (50×50 mm.sup.2). A normal force Fn can be applied on the plates, which was measured using three loadcells. The pressurized area remained constant by using an additional overlap of 15 mm as shown in FIG. 1a.

[0076] As can be seen from FIG. 2, a clear drop in shear stress is observed for both the peak value as well as the plateau for the inventive example (rough surface).

[0077] A lower shear stress results in better processing behavior.

Micrographs

[0078] Micrographs of a cross section of both the comparative example with smooth surface (FIG. 3) as well as the inventive example with rough surface (FIG. 4) were taken with a microscope with a magnification of ×20. FIGS. 3 and 4 show each the polished surface perpendicular to the carbon fiber direction.