PROCESS AND DEVICE FOR THE PRODUCTION OF A FIBRE-COMPOSITE MATERIAL

Abstract

Very good impregnation quality is achieved by a process for production of a fiber-composite material, with introducing a fiber layer by a spreader device and thus spreading to a width greater than that of the final product, at least by a factor of 1.2, where the extent of spreading of the fiber layer is such that its average thickness is 1 to 50 times the filament diameter; applying a melt by at least one applicator nozzle to the spread material; by virtue of cross-section-narrowing, the mould brings the width of the wetted fiber layer at least to the cross section with which the product leaves the take-off die; a radius then deflects the wetted fibers by an angle of 5 to 60°; a relaxation zone renders the fiber distribution more uniform to give a uniform height; achieving the first shaping by a take-off die at the end of the mould.

Claims

1. A process for the production of a fiber-composite material, comprising: a) introducing a fiber layer by way of a spreader device and thus spreading said fiber layer to a width greater than that of the final product, at least by a factor of 1.2, where the extent of spreading of the fiber layer is such that its average thickness corresponds to 1 to 50 times the filament diameter; b) applying a melt by at least one applicator nozzle to the spread material; c) by virtue of cross-section-narrowing, the mould brings the width of the wetted fiber layer at least to the cross section with which the product leaves the take-off die; d) a radius then deflects the wetted fibers by an angle of 5 to 60°; e) a relaxation zone renders the fiber distribution more uniform to give a uniform height; f) achieving a first shaping by a take-off die at the end of the mould.

2. The process according to claim 1, wherein in the step c) the width of the wetted fiber layer is reduced to a cross section that is smaller than the cross section with which the product leaves the take-off die, and additionally either prior to or after the step d) the width of the wetted fiber layer is brought to the cross section with which the product leaves the take-off die.

3. The process according to claim 1, wherein the matrix of the composite material is a thermoplastic moulding composition, a thermoset, a thermoplastic-thermoset hybrid system, a thermoplastic elastomer or a crosslinked elastomer.

4. The process according to claim 1, wherein in the step d) the deflection radius is 2 to 90 mm.

5. The process according to claim 1, wherein the step d) comprises a single deflection.

6. The process according to claim 1, wherein the strand obtained is calendered after leaving the take-off die.

7. The process according to claim 1, wherein the strand obtained is cut to give elongate long fiber-reinforced pellets of length 4 to 60 mm.

8. The process according to claim 1, wherein the strand obtained is a film, a tape, a sheet, a round profile, a rectangular profile or a complex profile.

9. A device which is suitable for the production of a fiber-composite material and which comprises the following elements: a) a spreader device by way of which a fiber layer can be introduced into a chamber and at the same time can be spread to a width greater than that of the final product, at least by a factor of 1.2; b) following in the direction of transport, one or more applicator nozzles which can apply melt to the spread fiber layer; c) in the transport duct, a subsequent cross-section narrowing which can bring the wetted fiber layer at least to the cross section of the take-off die; d) a subsequent deflection point providing deflection by 5 to 60°; e) a relaxation zone; and f) a take-off die.

10. The device according to claim 9, wherein the spreader device can spread the fiber layer to an extent such that its average thickness corresponds to 1 to 50 times the filament diameter.

11. The device according to claim 9, wherein the element c) the width of the wetted fiber layer can be reduced to a cross section that is smaller than the cross section of the take-off die, and additionally, either prior to or after the deflection point according to element d), the width of the wetted fiber layer can be brought to the cross section of the take-off die.

12. The device according to claim 9, wherein the radius of the deflection at the deflection point is 2 to 90 mm.

13. The device according to claim 9, wherein the element d) comprises a single deflection point.

14. The device according to claim 9, which comprises a plurality of chambers, and it is possible here that the sub strands are brought together at the deflection point or after the deflection point.

Description

[0031] The take-off die does not generally comprise any integrated take-off equipment. Instead, tension is usually applied to the strand by a take-off directly after the die, or by calender rolls. This type of take-off, for example in the form of rollers or rolls, is prior art, as also are calenders.

[0032] FIG. 1 is a diagram of the system concept.

[0033] FIG. 2 shows the cross-section-narrowing system which brings the wetted fibre layer to the subsequent cross section of the product.

[0034] FIG. 3 shows an embodiment of the system.

[0035] As depicted in FIG. 1, the fibre layer is unwound, for example in the form of a roving, from a bobbin 10. It is possible here to use a plurality of bobbins 10. The fibre layer is spread on a spreader device 20 and then introduced into the mould. Conventional spreader devices can be used here. The direction of movement of the roving is characterized by 30 in FIG. 1. The fibre layer can optionally be preheated here, for example by means of IR radiation or by circulation of air. Melt is applied to the fibre layer from above and from below through two applicator nozzles 60. It is also possible, as an alternative to this, that the melt is applied only from above or only from below. The melt and the required application pressure are supplied by the extruders 40 and 50. (Melt pumps downstream of a plastifying unit can also be used as an alternative to this.) FIG. 1 does not depict the subsequent cross-section-narrowing system, the deflection radius, the relaxation zone or the take-off die. For final shaping, the profile can also be calendered by means of a calender 80 after take-off. The resultant strand is then either cooled and wound or cut to length; as an alternative to this it can be further processed immediately, e.g. by winding around a core and then cooling (in the case of a thermoplastic matrix) or then hardening (in the case of a thermoset matrix).

[0036] FIG. 2 shows how the spread fibre layer is introduced into the cross-section-narrowing system. The melt is applied by way of an applicator nozzle 63. In an alternative embodiment the positioning of the application nozzle 63 can also be, instead of as depicted in FIG. 2, at the ingoing end of the cross-section-narrowing system, at a position prior to the cross-section-narrowing, so that the first phase of wetting takes place in the fully spread condition. At the end of the cross-section-narrowing system there is a deflection system 66; the cross section of the fibre layer is reduced at this point to the width 67.

[0037] FIG. 3 views the device from the side. The spread fibre layer is introduced into the mould by way of the intake 61. The melt is applied in the inlet-and-wetting zone 62. The length of the inlet-and-wetting zone is indicated by 64. The matrix is applied by means of application nozzles in the spread condition; because of the relative movements during fibre displacement, the subsequent cross-section-narrowing allows the matrix to penetrate into the layers between fibres. At the end of the cross-section-narrowing system the wetted fibre layer is deflected by the angle α at the deflection system 65. The radius is not depicted here.

[0038] This deflection leads to further relative fibre movements, and also to a local pressure gradient from the deflection point into the remaining cavity, permitting further matrix penetration. The arrangement of the deflection system after completion of cross-section-narrowing achieves particularly good impregnation quality in comparison with the embodiments in the prior art where a deflection is implemented during cross-section-narrowing.

[0039] The subsequent relaxation zone 68 of length 69 renders the fibre distribution more uniform to give a uniform height. This procedure, and also further impregnation, are assisted by the possibility that this chamber region can have been filled with melt. Attached at the end of the mould is the die 70 that is responsible for the initial shaping of the subsequent product. The pressure here generally increases along the route from the application zone to the die; the precise pressure profile depends on the material. The final shaping here is carried out by the calender 80.

[0040] The preferred viscosity of the melt applied in the process of the invention is from 10 mPas to 400 Pas, and particularly up to 300 Pas. In the case of prepolymers or resin-hardener systems which, after curing, give thermosets or thermoplastic-thermoset hybrid systems, viscosity is in the lower range down to 10 mPas or even lower. In the case of a melt made of a thermoplastic moulding composition, a thermoplastic elastomer or a compounded elastomer material viscosity is generally at least 1 Pas. According to the invention, viscosity is the zero-shear viscosity at the temperature of the process, measured in accordance with ASTM D4400 in a mechanical spectrometer.

[0041] Operations during application of the melt generally avoid any excess of melt, in particular in the case of relatively high-viscosity melts, or use only a small excess of melt. In the case of operations using an excess of melt, precautions must be taken to ensure that the excess melt can flow out through an aperture provided for this purpose. The ratio of fibres to melt is adjusted in such a way that the proportion by volume of the fibres in the finished part is about 10 to 85%, preferably 15 to 80% and particularly preferably 20 to 75%.

[0042] If the matrix of the resultant composite material is a thermoset, the hardening reaction usually takes place mainly in the relaxation zone. The strand drawn off has then in essence already hardened.

[0043] The length of the relaxation zone depends by way of example on the melt viscosity, the intended take-off velocity and the size of the system. By way of an example, in the case of a laboratory system producing a tape of width 40 mm made of E glass or S glass and PA12, a length of 100 mm gives very good results. However, this is only an approximate guide. The relaxation zone can also be shorter or else significantly longer.

[0044] The take-off velocity can be adjusted as required. It is preferably 0.1 to 30 m/min and particularly preferably 0.5 to 25 m/min.

[0045] The strand obtained in the process of the invention can have any desired geometry. It can by way of example be a film, a tape, a sheet, a round profile, a rectangular profile or a complex profile. It is preferably a tape or a sheet; this is in particular true in the case of the process in which, in the step c), the width of the wetted fibre layer is reduced to a cross section that is smaller than the cross section with which the product leaves the take-off die, and additionally after the step d) the width of the wetted fibre layer is brought to the cross section with which the product leaves the take-off die.

[0046] In a variant of the process of the invention according to claim 1 or claim 2 the resultant strand comprising a thermoplastic matrix is cut to give elongate long-fibre-reinforced pellets of length 4 to 60 mm, preferably 5 to 50 mm, particularly preferably 6 to 40 mm, with particular preference 5 to 30 mm and very particularly preferably 6 to 25 mm. These pellets can then be used to produce mouldings by means of injection moulding, extrusion, compression moulding or other familiar shaping processes, and particularly good properties of the moulding are achieved here with non-aggressive processing methods. The meaning of non-aggressive in this context is mainly substantial avoidance of disproportionate fibre breakage and the attendant severe fibre length reduction. In the case of injection moulding this means that it is preferable to use screws with large diameter and low compression ratio, and also generously dimensioned channels in the region of nozzle and the gate. A supplementary condition that should be ensured is that the elongate pellets are melted rapidly with the aid of high cylinder temperatures (contact heating), and that the fibres are not excessively comminuted by disproportionate levels of shear. When attention is given to these measures, the mouldings obtained have higher average fibre length than comparable mouldings produced from short-fibre-reinforced moulding compositions. This gives a significant improvement of properties, in particular tensile modulus of elasticity, ultimate tensile strength and notched impact resistance.

[0047] The invention also provides a device which is intended for the production of a fibre-composite material and which comprises the following elements: [0048] a) a spreader device by way of which a fibre layer can be introduced and at the same time can be spread to a width greater than that of the final product, at least by a factor or 1.2, preferably at least a factor of 1.4 and particularly preferably at least a factor of 1.6, [0049] b) following in the direction of transport, one or more applicator nozzles which can apply melt to the spread fibre layer, [0050] c) in the transport duct, a subsequent cross-section-narrowing system which can bring the wetted fibre layer at least to the cross section of the take-off die, [0051] d) a subsequent deflection point providing deflection by 5 to 60°, preferably 8 to 50°, particularly preferably 12 to 40° and with particular preference 15 to 35°, [0052] e) a relaxation zone and [0053] f) a take-off die.

[0054] Details of the said device are apparent from the process description above, because the device serves for the conduct of the process of the invention.

[0055] As FIG. 2 shows, the construction of the device is preferably such that it has an inlet inclined at an angle determined by the deflection at the deflection point of the element d); the angle of inclination of the inlet corresponds here to the angle of deflection in the element d). Otherwise an inclined arrangement of the take-off die would have been necessary; this would require more difficult engineering of the system.

[0056] In a preferred embodiment the design of the cross-section-narrowing system of the element c) is such that the width of the wetted fibre layer can be reduced to a cross section that is smaller than the cross section of the take-off die, and additionally, either prior to or after the deflection point according to element d), the width of the wetted fibre layer can be brought to the cross section of the take-off die.

[0057] In the form described, the device comprises a chamber in which a fibre layer is wetted and the cross section is narrowed. However, in particular on the scale required for production it is advantageous for the device to comprise a plurality of chambers, and for the substrands to be brought together at the deflection point or after the deflection point. Preference is therefore given to the following embodiments of the device and of the process: [0058] There are two, three or more chambers mutually superposed; in each chamber a substrand is wetted with melt and the cross section of the transport duct is narrowed. The substrands are then brought together, mutually superposed, at the deflection point or after the deflection point. If the individual substrands comprise different fibres, a specific layer structure can be achieved here in the production of complex profiles. [0059] There are two, three or more chambers mutually superposed; in each chamber a substrand is wetted with melt and the cross section of the transport duct is narrowed. The substrands are then brought together alongside one another at the deflection point or after the deflection point. [0060] There are two, three or more chambers alongside one another; in each chamber a substrand is wetted with melt and the cross section of the transport duct is narrowed. The substrands are then brought together, mutually superposed, at the deflection point or after the deflection point. [0061] There are two, three or more chambers alongside one another; in each chamber a substrand is wetted with melt and the cross section of the transport duct is narrowed. The substrands are then brought together, alongside one another, at the deflection point or after the deflection point.

[0062] The significant difference from previous solutions is, according to the invention, the specific wetting method implemented after a high degree of spreading and the subsequent impregnation of the individual fibres via relative longitudinal and transverse movements which are caused by the cross-section narrowing, the subsequent deflection, and also optional subsequent renewed cross-section widening. Very good impregnation quality is thus achieved across a very wide viscosity range, even when take-off velocity is high.

KEY

[0063] 10 Bobbin [0064] 20 Spreader device [0065] 30 Direction of movement of fibre layer [0066] 40 Extruder [0067] 50 Extruder [0068] 60 Applicator nozzle [0069] 61 Intake [0070] 62 Inlet zone and wetting zone [0071] 63 Applicator nozzle [0072] 64 Length of inlet zone and wetting zone [0073] 65 Deflection system [0074] 66 Deflection system [0075] 67 Cross-sectional width after deflection [0076] 68 Relaxation zone [0077] 69 Length of relaxation zone [0078] 70 Die [0079] 80 Calender