WO2006105814A1

WO2006105814A1 - Production of fibre composite materials inclosed laminating systems and associated products

Info

Publication number: WO2006105814A1
Application number: PCT/EP2005/051507
Authority: WO
Inventors: Klaus Kölzer
Original assignee: Spheretex Gmbh
Priority date: 2005-04-04
Filing date: 2005-04-04
Publication date: 2006-10-12

Abstract

The invention relates to a method for producing fibre composite materials and associated products. The invention is based on the object of being able to produce a fibre composite material with good mechanical properties in a cost-effective and environmentally friendly manner. According to the invention, to solve the object a desired restoring force is produced in a complex by embedded micro hollow spheres or micro hollow bodies (4). This is so because it has surprisingly been found that a better controllable restoring force as compared with the prior art can be provided in this way.

Description

MANUFACTURE OF FIBER COMPOSITES IN CLOSED LAMINATION SYSTEMS AND RELATED PRODUCTS

The invention relates to a process for the production of Faserverbuπd- materials, related products and precursors.

A method of the aforementioned type is known from German Patent Application 1 03 1 4 901 Al. Fiberglass filaments, which have been voluminated by embedding thermoplastic microvoids, are sprayed onto a negative mold by means of a resin fiber spray gun. At the same time, the endless spun yarns are chopped into staple fibers of, for example, 3 cm in length by means of a cutting mechanism and sprayed onto a negative mold together with a spray jet of hardenable resin, such as unsaturated polyester.

From EP 0 222 399 A2 it is known to produce fiber composites by using suitable fiber materials with thermosetting plastic resins such as e.g. Polyester, epoxy resins or amino and phenolic drinks, forms without pressure, for example in an open negative mold and cured. It is further proposed in EP 0 222 399 A2 to spread the filaments of reinforcing materials used with the aid of hollow spheres. Adverse emissions due to the use of resins occur disadvantageously in these so-called open lamination processes. Also, the back surface of a resulting molded article is relatively uneven, especially in comparison to the front side which abutted on the inner wall of the female mold during manufacture,

Increasingly, the use of closed lamination processes is being attempted to avoid the undesirable emissions and to make the manufacturing processes more economical. It is known to bring fibers together with the resin in a negative mold and then to close them. The disadvantage of this is that emissions occur before closing. Also, the required amount of resin can not be metered accurately enough. This leads to qualitative losses in the resulting molded part.

Fibers which serve to reinforce and which are therefore called Verstarkungsfasern or Verstarkungsmaterial are therefore preferably dry inserted into a corresponding negative mold. The negative mold is first closed with a suitable counter mold. After closing with the counter mold, resin is injected or infused into the closed overall shape. Emissions can thus be prevented and the amount of resin required can be better dosed

Two processes are of importance, namely the so-called RTM process (resin transfer molding) and the so-called VIP process (vacuum infusion process).

In the RTM process, the negative mold and the counter mold, ie two mold halves, each consist of stable, ie solid parts. The parts can be made of steel or aluminum. In order to reduce costs for the provision of the molds, these are made of plastic and especially if it is produced in small quantities

In the VIP process, only one mold half is solid and the other mold half consists of a thin, inexpensive plastic film

During the RTM process, the two mold halves are mechanically closed and held closed. In the VIP process, the mold is closed by vacuum using a suitable vacuum pump. After closing the mold halves, the RTM process pressurizes the liquid resin until it is completely filled of the predetermined mold gap is pressed into the mold intermediate spaces, whereby the pressure penetrates the liquid resin through the reinforcing fibers located between the molds. later speaks the material thickness of the thus produced made of a fiber composite molding. In the VIP method, the liquid, curable resin is sucked in by the generated vacuum between the two mold halves in such a way that also in this process, the lying between the mold halves dry reinforcing fibers are completely wetted. The injection of resin by means of pressure or the infusion with the aid of negative pressure in closed overall forms for the production of composite materials is shown in German Patent DE 69003436 T2.

To be able to carry out the two aforementioned methods, a sufficiently high elasticity and Rücks.tellfederkraft of the fiber complexes used must be present. In the RTM process, the restoring force compensates for the unavoidable gap tolerances after closing the mold. Although the molds for the production of certain wall thicknesses of the molded parts produced have a SoII distance, but can vary considerably from the standard and in part by 50% and more. Only if the fiber layers are pressed reliably and with the appropriate pressing pressure on the two inner walls of the two mold parts, overflushing of the fibers with resin during subsequent injection can be avoided here.

In order to achieve such a restoring force, the actual reinforcing fibers of high modulus fibers such as glass, carbon or aramid fibers in the outer area and special fiber layers are provided with high return spring force in the core area in layered fiber layers. These spring-back layers can consist of plastic monofilaments, as described in DE 69003436 T2. As spring-back layers but also knitted or knitted fiber layers of plastic or glass fibers can be used. Furthermore, continuous glass fibers, as they are known in the market under the name "Continuous beach mat" can be used.

In the described fiber layers of glass or plastic filaments pressure is generated by the mechanically resilient core layers. The Compressibility can be controlled relatively poorly. In particular, in the vacuum process, a control of the remaining and desired material thickness is very difficult, because the degree of compression of this type of mats is very high and the material can lose up to 80% of its original strength. Fiber composites produced in this way therefore have relatively poor mechanical properties.

For reasons of economical processing, suitable fiber layers are usually delivered to the fabricators as finished, multi-layered complexes by joining together several superimposed layers of the reinforcing material by a needle punching or stitchbonding process. Such a complex is described in the patent DE 69003436 T2.

The invention has for its object to be able to produce a fiber composite material with good mechanical properties economically and environmentally friendly.

The object of the invention is achieved by a method having the features of claim 1. Advantageous embodiments emerge from the subclaims.

According to the invention, the required restoring force is generated by embedded hollow microspheres or hollow microbodies. Surprisingly, it was found that such a better controllable restoring force compared to the prior art can be provided.

In practice, it has proven useful to introduce an unexpanded precursor of the hollow microspheres into the fiber material and then to volumise the hollow microspheres. Preference is given to high-modulus fibers, such as glass fibers used. The fiber material with the therein located hollow spheres, spheres or bodies is brought into a closed Gesαmtform in the aforementioned sense. Resin is made into the overall shape, thus finally forming a molded fiber composite.

Above all, the core situation consists of volumised fibers. For cost and weight reasons, plastic fibers and / or glass fibers are provided for the core layer. Also suitable are inexpensive natural fibers such as sisal or coconut fibers. The core layer is then mainly between layers of non-volumized high modulus fibers, which are mainly responsible for the bending properties of the walls of the subsequent molding. Therefore, glass, carbon and / or aramid fibers are preferably used for the outer layers.

Within the overall shape of the fibers hollowed out with elastic hollow microspheres or bodies, a gas-hydraulic counter-pressure is generated during compression, which is easier to control not only in the percentage compressibility, but also brings with it additional additional positive properties. While control of the remaining and desired material thickness is very difficult in the above-described mechanically resilient fiber layers, especially in vacuum process, because the degree of compression of this type of mats is very high and the material can lose up to 80% of its original strength, build the hollow microspheres a gas-hydraulic Counterpressure, which is easier to control insofar as the closed-cell, filled with gas hollow spheres merely deformed, but not reduced in their gas volume, even by higher pressure or at least relatively little. This is the case, in particular, in the case of the vacuum process, in which pressures of between 0.2 and 0.8 bar are used, but also, above all, in the case of an RTM process in which the two mold halves are made of plastic. The result is that, compared with the above-described mechanically acting fiber packages, which can lose up to 80-85% of their original strength, the Fαserpαketθ with hollow microspheres at a comparable pressure only between 25 and max. Losing 40% of its original strength The result is composite materials that, for example, result in considerably higher wall thicknesses in the vacuum process and thus composite materials with much higher bending stiffnesses.

Another significant advantage of using the volumized fibers is that the soft, conformable contact pressure of the hollow microspheres does not result in a print through effect on the mold surface. This results in far optically better molding surfaces. By the method according to the invention result in contrast to the prior art moldings with smooth walls on the front and back with micro hollow spheres or hollow bodies in the molding. In particular, the core layer has the volumized fibers. The layers on the surface are usually made of high modulus fibers.

With increasing compression is further reduced by the compression of the hollow microspheres, the amount of resin matrix and the specific gravity of such a molded part also reduced. In the case of fiber mats, which use mechanical restoring stresses, the reverse effect occurs, in that, depending on the pressure, the fiber compaction becomes ever higher and thus also the specific weight.

In an advantageous embodiment of the method, a complex comprising a core layer with hollow microspheres or micro-hollow bodies located therein has a pre-compression. In particular, the various layers or layers of the complex have been connected to one another in such a way that, in the connected state, the hollow microspheres or bodies exert a gas-hydraulic pressure. The hollow microspheres are then preloaded. This pre-compression can be achieved by compressing the volumised fiber layers be targeted. It can be controlled so specifically desired properties of the molded part to be produced therefrom.

In any case, the embedding of the hollow microspheres has the considerable advantage of reducing the resin absorption capacity in accordance with the volume of the microspheres and thus reducing the specific weight of a molded part produced therefrom. The higher the degree of compression in the complex preparation, the lower the resin absorption and thus the weight of the molded part produced therefrom. The result is either thicker molded parts with a comparable total weight, compared to the molded parts produced from non-volumized fiber layers described above have a significantly higher flexural rigidity or molded parts with the same wall thickness and similar mechanical strengths with a weight saving of 30-50%.

In an advantageous embodiment, in the mat complexes used with the hollow microspheres located therein, it is achieved by a predetermined arrangement of the fibers that sufficient penetration of the liquid resins is ensured. Thus, in one embodiment, drainage gaps are created between parallel volumized endless fiber strands. The generation of the drainage gap succeeds in an embodiment of the invention by volumisierte fiber strands, ie fiber strands embedded therein hollow microspheres or micro hollow bodies are not placed directly next to each other, but on the gap. In another embodiment, bulked, cut staple fibers are used and, due to the coarseness of the structure produced, suitable drainage openings are created. This is achieved, in particular, by stacking volumized fiber strands in disordered and two-dimensional stacked stacks. As with the accumulation of matches, the result is a very open structure, which in this state becomes a complex. The use of layers of needled monofilaments of eg glass or plastic fibers (polyester, polyamide, polypropylene, etc.) is able to increase the penetration rate of the resin. Further examples are given in the claims.

In one embodiment of the invention, in addition to hollow microspheres, further elements are used which are intended and suitable for increasing the penetration rate of the resin in the reinforcing material. Short pieces of tubing can be used, especially within cut fiber stacks. Particularly preferred are thin perforated hollow tubes, and in particular so-called endless tubes. Such endless hoses are preferably used in the case of located.

Twisted monofilaments are also suitable. The arrangement of such drainage aids may be between the volumized fibers or adjacent to the volumized fibers.

Drainage aids such as the aforementioned hoses or monofilaments are particularly advantageous if a higher drainage rate is desired for process-technical reasons or if the reinforcing material, for example a complex, has been compressed very strongly. By a strong compression namely creates a high compression of the volumized fibers. The permeability to resin is thus reduced. This can be counteracted by adding additional drainage aids.

example 1

A scrim made of volumised fiberglass yarns (core area) with a fiber diameter of 2.0 mm and a weight of 200 lex is coated on both sides with layers of Glasfaserrovings (each + 45 / - 45 ° about 400 g / m ² ) and by a Nahwirkprozess with suitable Nahgarnen of 1 70 dtex connected to a ready-to-use complex. A volumized yarn is understood to mean a yarn having hollow microspheres or microcavities therein. The complex is placed in a closed Gesαmtform and resin introduced. After curing of the resin, the desired fiber-reinforced molding is present.

Example 2

A complex as described under 1 is provided with an additional drainage aid in the core area, consisting of needled plastic monofilaments with a weight of approximately 1 50 g / m ² . The complex is placed in a closed overall mold and resin introduced. After curing of the resin, the desired fiber-reinforced molding is present.

Example 3

A complex is made of two 5 mm thick core layers of microsphere volumisierten and mechanically pre-compressed glass fiber webs with a weight of about 150 g per layer and an intermediate additional drainage aid made of needle-punched monofilaments of about 150 g / m ² . Through a Nähwirkprozess with suitable sewing thread of 1 70 d-tex, the layers are joined together.

The complex is placed in a closed overall mold and resin introduced. After curing of the resin, the desired fiber-reinforced molding is present.

Figure 1 shows schematically a negative mold 1, which is closed by a film 2. Within this overall shape there is a core layer 3 formed of fibers with hollow microspheres 4. The core layer is enveloped by regions 5 formed by high modulus fibers. Within such a mold, a vacuum is created and resin infused. After curing of the resin, the molding is removed from the overall shape. The molded part produced in this way has smooth walls on the front and back sides. Inside the molding are then the hollow microspheres.

Claims

claims

1 . Process for the production of fiber composites with the steps:

Providing fibers with hollow microspheres or microcircuit (4) located therein

Introducing the fibers with the hollow microspheres therein in a closed overall shape (1, 2), supplying resin in the overall form (1, 2).

2. The method of claim 1, wherein before the supply of resin, a negative pressure in the overall shape (1, 2) is generated.

3. The method of claim 1 or 2, wherein the overall shape by a solid mold half (l) and a film (2) is formed.

4. The method of claim 1, wherein the closed overall shape is formed by two solid mold halves, which in particular consist of plastic.

5, Method according to one of the preceding claims, in which by closing a mold half with a further mold half, the fibers therein are compressed.

A method according to any one of the preceding claims, wherein fibers having hollow microspheres therein are provided so that the hollow microspheres are biased.

7. The method according to any one of the preceding claims in the fibers are placed therein with hollow microspheres or micro hollow bodies and Dralnagehilfen in the overall form and in particular in the form of hoses or Kuπststoffmonofilamenten in the core area

Method according to one of the preceding claims, in which voluminized threads or yarns are used, in particular for a core layer (3).

A method according to any one of the preceding claims, wherein mat blends of parallel plastic, glass, carbon or aramid yarns having a diameter of 0.5-1 mm, volumed with thermoplastic hollow microspheres, are bonded and used by a seaming process with suitable sewing yarns

10. The method according to any one of the preceding claims, are used in which Mattengelege consisting of several layers of fibers in which the individual layers are arranged at different angles to each other.

1 1. A method according to any one of the preceding claims, wherein mat loops of microballoon-volume staple fibers with a diameter of 0.5-5 mm joined by a close-knit process with suitable sewing yarns are used

2. Method according to one of the preceding claims, in which the outer layers of a complex are not voluminous slert are and preferably made of high modulus fibers such as glass fibers, carbon fibers and / or aramid fibers.

1 3. Mattengelege for performing a method according to any one of the preceding claims consisting of one or more layers of hollow microspheres volumisierten fibers, in particular nonwoven fabrics, preferably consisting of glass fibers, plastic fibers or natural fibers such as coconut fibers or sisal fibers.

1 4. Matting according to the preceding claim with drainage nets consisting of perforated hollow tube or perforated tubes between the volumized fibers or adjacent to volumized fibers.

15. Matting mat according to one of the two preceding claims with drainage layers of twisted monofilaments between volumized fibers.

16. Mattengelege according to one of the four preceding claims with drainage layers of needled glass fiber or plastic filaments of preferably about 50 -500 g / m ² between the volumized fibers.

1 7. Mattengelege according to one of the five preceding claims, in which the additional drainage aids are placed in one layer next to the fiber layers of volumized fibers.

1 8. Mαttengelege according to one of the preceding physical claims, in which the additional Drαinαgehilfen are placed on both sides of the volumized fibers

1 9. Matting according to one of the preceding claims, wherein the individual layers are interconnected by a needling process.

20 matting according to one of the preceding claims, wherein the individual layers are joined together by a Nahwirkprozess

21 Mattengelege according to one of the preceding physical claims, in which the individual layers are joined together by an adhesive process.

22. Mattengelege according to one of the preceding claims, wherein the individual mat layers are connected to each other under a defined precompression of 1-50% of the starting starch.

23. Molding, producible according to one of the preceding Verfahrensanspruche, consisting of a fiber composite material with hollow microspheres or Mikrohohlkorpern inside the molding and the same smooth front and back

24. Molding according to the preceding claim with Wandbere- chen of Galsfasern, carbon fibers and / or Aramidfa- be formed and a core area, which is formed of plastic fibers, glass fibers, sisal fibers and / or coconut fibers with embedded Mlkrohohlkörpern.

25. Molding according to one of the two preceding claims with befindlichem hose, which is in particular perforated.