WO2002006027A1 - Equipment to produce continuously powder coated thermoplastic matrix prepregs (towpregs) - Google Patents

Abstract

The machine patented is shown in schematically in next figure. It has been designed for the continuous production of towpregs of fibres preimpregnated with thermoplastic powder, to be transformed into composite structures by different processing techniques. This technique gives the possibility to produce towpregs at a lower cost without using, as it is the case of the conventional processes, solvents and/or fusion of the thermoplastic. With this machine, great quantities of glass fibre/polypropylene and glass fibre/polyamide towpregs were produced having fibre weight content between 30 and 80 %. These towpregs have already been processed by hot plate press, pultrusion and filament winding. The structures produce have shown good mechanical properties.

Description

DESCRIPTION

"EQUIPMENT TO PRODUCE CONTINUOSLY POWDER COATED THERMOPLASTIC MATRIX PREPREGS (TOWPREGS)"

History previous to the invention

Due to their excelent properties, continuous fibre reinforced thermoplastic matrices composites have been successfully used in highly demanding structural applications, mainly in aerospace, aeronautical and defense industries [1]. Moreover, as the processing doesn't involve chemical reactions, the main advantages of these materials are their excellent toughness, durability and vibration behaviour, and the easines of storage, repair and recycability [1-4]. However, the high costs resulting from the use of solvents and/or polymer fusion during fibre impregnation with thermoplastics, are an obstacle to the use of these materials in more commercial applications. Hence, the use of these materials is largely dependent of more efficient methods of fibre impregnation with thermoplastic of high viscosity and the production of semi-products for the processing of composite structures.

In 1973, an attempt has been made, for the first time, to impregnate, with polymer powder, continuous fibres [8]. As the technique was not sufficiently developed, only in the eighties more interesting impregnation techniques start to be developed [9-17]. In the different developed techniques, fibre tows are spreadded and forced to pass through a deposition chamber for polymer powder deposition.

The polymer deposition dry or wet became very promising techniques for the impregnation of fibres with thermoplastics. In the dry process [11- 14, 18], the thermoplastic is deposited in the solid state by mechanical or electrostatic means or using a fluidised bed. In the wet process, the polymer is deposited in the fibres dispersed in an acquous bath [10, 15, 16, 19-21]. The last technique is more expensive, complex and less attractive, as it implies the use of an intermediate drying chamber to wipe off the humidity from the prepreg [21] and by the difficulty to find some specific additives with low hygroscopic content which are needed for the process [22].

Concerning exhisting patents, one can identify as more relevant the following: US 3 742 105, US 4 680 224, EP 0274464 and US 4 626306.

The patent US 3 742 105 is related to a fabrication process to produce thin profiled tapes made with continuous unidirectional fibres imbedded in a thermoplastic resin. The process consists in te impregnation with resin powder of superposed parallel fibres through the fusion of the resin, in order to form a profiled coated tape. The superposed part is immersed in a bath of resin powder, mechanically impregnated, passing through immersed rolls, being the remianing removed in order to get the required resi/fibre content.

The patent US 4 680 224 refers to a process to prepare the pro- dutcts moulded from fibre cables with poly sulphide arylen. The moulded products are prepared with a pultrusion process requiring the adaptation of the polymer paste to the contact with the fibres.

The patent US 3 742 105 is related with the production of pipes without weldig line, and the relevant extrusion mechanism, in tubular shape in semi-fusion conditions. It implies the introduction of the first cooling system compressed in the pipe and the projection of the fluid against the inner part of the pipe. A second manner to project the cooling fluid compressed against the external surface is by centripet effect, at the same time of the first projection.

The patent\ EP 0274464 is related with a process and mechanism to treat yarns, loose fibres or similar. They are composed of several filaments which amay be woven or stitched and treated with surface treatment agent in suspension under one or several gas or liquid currents forced, under pressure, into the material.

As can be easily seen, none of the previously referred patents show characteristics similar to the ones claimed in this process of patent request.

Henc, the polymer deposition under dry conditions used in the de- velopped machine has the following advantages: simplicity, lower cost and possibility of continuous processing of different fibres and thermoplastics.

In the following list can be seen a set of references to the subject. Some of them were already quoted in the text.

References

1. Brandt, J., Dreschler, K. e Richter, H. (1993) "The use of high-performance Thermoplastics Composites for Structural Aerospacial Applications", 9^th Int. Conf. on Composite Materials (ICCM 9), vol. 6, Madrid, Spain pp. 143-150.

2. Malcom, W. e Todd, E. (1993) "Carbon Fiber Reinforced PPS Thermoplastic Materials Implemented in Cost Sensitive Commercial", 38^th Int. SAMPE. Symposium, U.S.A. pp. 2055-2065.

3. Nunes, J., P., Bernardo, C, A., Pouzada, A. S. e Eddie, D. D. (1997) "Formation and Caracterization of Carbon-Polycarbonate Towpregs and Composites" Journal of Composite Materials, 31 (17), pp. 1758-1777. 4. Nunes, J., P. (1998) "A Study of the Processing and Properties of Sheet Molding Compounds and Unidirectional Carbon Fibre Towpregs" Tese de Doutoramento, Universidade do Minho.

5. Gantt, B. (1987) "The Thermoplastic Coating of Carbon Fibers", Master Thesis, Clemson University, Clemson, U.S.A.

6. Allen, L. E., Edie, D. D., Lickfield, G. C e McCollum, J. R. (1988) "Thermoplastic Coated Carbon Fibers for Textile Preforms", Journal of Thermoplastic Composite Materials", 1, pp. 371-379.

7. Klett, J., W., (1991) "Towpregs Formation for Carbon/Carbon Composites, Masterthesis, Clemson University, U.S.A.

8. Price, R. V., Production of Impregnated Roving, US Patent 3 742 105 (1973).

9. Gantt, B., The Thermoplastic Coating of Carbon Fibers, Master Thesis, Clemson University, Clemson, USA, (1987).

10.0' Connor, J. E., Reinforced Plastics, US Pat. 4680224 (1987).

11. Allen, L. E., Edie, D. D, Lickfield, G. C. and McCollum, J. R, Thermoplastic Coated Carbon Fibers for Textile Preforms, Journal of Thermoplastic Composite Materials, 1, pp. 371-379, (1988).

12. de Jager, G. G., Method and Apparatus for Applying powder materials to filaments, EP 0 274 464 (1990).

13. Iyer, S. and Drzal, L., Manufacture of Powder Impregnated Thermoplastic Composites, Journal of Thermoplastic Composite Materials, 3 (4), pp. 325-355 (1990).

14. Muzzy, J., Varughese, B. and Yang, P., Flexible Towpreg by Powder Fusion Coating of Filaments, SPE ANTEC 90, Vol. 36, pp. 1385-1390 (1990).

15.Ramani, K., Tryfonidis, M., Hoyle, C. and Gentry, J., Processing of Thermoplastic Composites Using a Powder Slurry Technique, in "Processing, Fabrication and Manufacturing of Composite Materials", ASME MD, Vol. 46, pp. 633-657 (1992). lδ.Vodermayer, A., Kunhert, L., Hinrichsen, G., Reichert, K., Lindner, W. and Goldmann, G., Manufacturing of Composite Materials by Polymer Powder Dispersion Impregnation, DE-OS 21915 Al (1993).

17. Johnston, N. J. and Cano, R. J., Powder- Coated Towpreg: Avenues to Near Shape Fabrication of High Performance Composites, 10th Int. Conference on Composite Materials (ICCM-10), Vol. 3, Whistler, Canada, pp. 407-412 (1995).

18. Gibson, A. G. and Manson, J. A., Impregnation Technology for Thermoplastic Matrix Composites, Composites Manufacturing, 3 (4), pp. 223-233 (1992).

19. Tang, L., Lin, L., Yi, X. and PAN, Z., Aqueous Powder Slurry Manufacture of Continuous Fiber Reinforced Polyethylene Composite, Polymer Composites, 18 (2), pp. 223-231 (1997).

20. Chabrier, C, Moine, G., Mavrion, R and Szabo, R., Process for Manufacturing Profiles Strips in Fibre-Loaded Thermoplastic Resins - Installation for the Implementation Thereof and Profile Strips Obtained, US Pat 4 626 306 (1986).

21.Vodermayer, A. M., Kaerger, J. C. and Hinrichsen, G., Manufacture of High Performance Fibre-Reinforced Thermoplastics by Aqueous Powder Impregnation, Composites Manufacturing, 4 (3), pp. 123-132 (1993).

22. Allen, L. E., A Continuous Process for Powder Coating Carbon Fibers, Master Thesis, Clemson University, Clemson, USA (1989).

Summary

The machine to which we claim the inevntion produces, continu- osly and at na industrial scale, prepregs with a thermoplastic matrix at a cost lower than the one s obtained with more common processes. In the process used, the fibre (generally, glass, carbon, or aramidic) tows are unwind from the spools. The tows are spreaded in filaments, in a spread unit and using compressed air. After separation, the fibres go to a deposition chamber where it is formed a powder thermoplastic cloud which continuosly supplied by a dodosemeter. The ther- moplstic powder is deposited on the top of the fibres , being the exceeding part recirculated. Finally, the tows with the thermoplastic powder go through an oven in to assure the required adhesion polymer/fibre, being the finished material air cooled and wound in the spools. The produced material is a thermoplastic prepare, which can be easily processed as structures having good mechanical properties, using conventional techniques such as hot plate press, pultrusion and filament winding.

Short Description of the Drawings

To understand the invention more easily, in annex can be seen several drawings with the preferred realization models which; however, don't intend to limit the invention.

Figure 1 represents, schematically, the entire machine according to the invention Figure 2 represents a pneumatic spreader for He fibre tows. Figure 3 represents the feeder of thermoplastic powder and the deposition chamber.

Detailed Description of the Invention

The machine to comtinuosly produce powder thermoplastic fibre tows has five units: i) storing of the rovings; ii) fibre spreader ; iii) feeding and polymer deposition, iv) heating and v)final winding.

The process starts with the unwinding of four fibre spools placed in the storing support bench. These spols cn be unwound external or internally ( usually at a lower cost). The tows are duly separated in filaments, at the spread unit 2 using compressed air. The spreader fibres go into the deposition chamber 3 where a powder thermoplastic cloud is formed, continuously fed by the dosimeter 4. The thermoplastic powder is deposited in both sides of the fibre tow and the exceeding recalculated. Finally, after the tow with the deposited thermoplastic powder (prepare) has pass through the oven 4 to assure the polymer/fibre adhesion, the finished material is air-cooled and wound in the spool 5.

The deposition is made without using electrical conductive systems that, independently of the electrical properties, may give a good thermoplastic powder deposition over a great variety of reinforcement fibres.

The developed equipment, relatively to the existing equipment [5-7], has the following modifications: i) New fibre storing system which allows the use of common spools, cheaper and internal unwinding; ii) Elimination of the fibre tension system allowing for the reduction in the number of electrical engines used, as well as the respective control and synchronization systems for the rotational speed; iii) Application of a new pneumatic spreader system having an effective improvement in the separation of the filaments; iv) A more advantageous project of the chamber allowing the deposition of the thermoplastic powder in both sides of the fibre tow and avoiding the polymer recirculation through the interior of the ventilator 6; v) Use of a final winding system, more compact and giving the possibility to introduce and remove the spools more easily.

The pool storing structure is made with Bosch profile 45x45 L, having the dimensions shown in figure 1. The draws are made in laminated wood.

The fibres are separated in the pneumatic spreader made with two PMMA plates 8 (Figure 2). The spreader allows for the separation of filament tows in the diverging section 9, using a compressed air flux through two injection points at the upper and lower part.

The polymer powder is fed to the deposition chamber 3, through a double helical screw dosimeter 4 Brabender, having variable speed (0-79 rpm).

After going to the deposition chamber 3 equipped with a filter 10, in PMMA, the polymer powder is recirculated with the air flux generated by a fan 6 S&P Mixvent-TD 160/100 with variable flow and positione laterally (Fig. 3). He best recirculating conditions for the polymer inside the chamber 3 must be optimized to obtain the required fibre content.

The complete polymer/adhesion in the prepreg is obtained by softening the polymer during its passage through the oven 4, specifically design to reach 1000 °C. This oven (Fig. 2) allows the prepare to be heated up to He softening temperature at the maximum speed.

The winding system 5 gives the possibility to reach linear speeds between 0 and 10 m/min (Fig. 2). It is made with a motoreducer with a variator incorporated. It gives the possibility to wind the prepreg , being the material distributed by a cam inducing na alternate lateral movement. This final winding system is compact and make easy the introduction and removal of the spools.

The machine for the continuous and automatic production of thermoplastic prepregs, aim of the invention and previously described, can use fibre tows up to 4 800 Tex. It can reach linear velocities of prepreg production up to 50m/min, as function of the required fibre content, starting from a weight content of 20%. The machine assures that the thermoplastic deposition is made regularly on both sides of the fibre tow. The preferred execution model which has been described can't be seen as limitative. The invention is limited only by the spirit and scope of the following reivmdications.

Claims

1. Machine for the continuous and automatic production of thermoplastic prepregs by dry powder polymer deposition, with grain size between 0 μm and 1000 μm, over tows of different type of fibres, mainly glass, carbon and aramidic, characterized to be divided in three modules:

- fibre storage;

- processing of the with the following units i) spreader; ii) polymer feeding and deposition and iii) final heating;

-final winding; for the continuous and automatic production of thermoplastic prepregs processed into composite structures by conventional processes such as pultrusion and filament windin, without using solvents and/or polymer fusion.

2. Machine for the continuous and automatic production of thermoplastic prepregs, according to the previous claim, characterized by the fact that the fibre tows can be unwound, internal or externally, from the four spools stored in the platform. Later, they are separated into filaments in the spreader unit using compressed air. Then, they go to the deposition chamber where a powder thermoplastic cloud is continuously fed by a dosimeter. The powder is deposited in both sides of the fibre tow, and the exceeding is recirculated without any contact with the blades of the fan. After passing through an oven to assure He required polymer/fibre adhesion, He finished material is cooled and wound.

3. Machine for the continuous and automatic production of thermoplastic prepregs, according with the previous claims, characterized by the fact that the fibres are separated in a pneumatic spreader made of two acrylic plates. It allows He separation of He filaments of He tows in a diverging section, with a compressed air flux going through two injection points at He lower and upper plates.

4. Machine for the continuous and automatic production of thermoplastic prepregs, according with the claims 1 and 2, characterized by the dosimeter from the feeding unit of the second module being of a double helical screw Brabenderhaving variable speed.

5. Machine for the continuous and automatic production of thermoplastic prepregs, according with the claims 1 and 2, characterized by the fact that, after going into the deposition chamber in, the polymer powder can be recirculated with na air flux created by a fan of variable flow, laterally placed, without any contact with the fan blades, being the better recirculating conditions for the polymer inside the deposition chamber optimised according to the required fibre content.

6. Machine for the continuous and automatic production of thermoplastic prepregs, according with the claims 1 and 2, characterized by the fact that a complete polymer/fibre adhesion is obtained through the polymer softening. This is obtained while passing in the oven of the second module designed to reach up to 1000 °C, allowing the towpreg to be heated at the softening temperature at a maximum speed.

7. Machine for the continuous and automatic production of thermoplastic prepregs, according with the claims 1 and 2, characterized by the fact that the winding module allows linear speeds between 0 and 10 m/min and is made of a motoreducer with a variator ncorporated. It possibilitates He winding of He towpreg at the final stage, being the material distributed by a cam which induces a lateral movement.

8. Machine for the continuous and automatic production of thermoplastic prepregs, according with the previous claims, characterized by not using any tensioning system, which puts the system more reliable as it reduces the number of electrical motors used and to eliminate the need for more complex control and synchronization of the rotational speed.

9. Machine for the continuous and automatic production of thermoplastic prepregs, according with the previous claims, characterized by the fact that uses fibre tows up to 4800 Tex . It allows linear production velocities of the towpreg up to 50m/min, as function of the required fibre content starting from a weight content of 20%.

10. Machine for the continuous and automatic production of thermoplastic prepregs, according with the claims 1 and 2, characterized by the possibility to produce a pre-consolidated tape (PCT) using a die specifically designed and placed in the second module.