DE20201902U1 - prepreg - Google Patents

Description

Gesthuysen, by Rohr & Eggert

02.0116 Ase

Essen, 6 February 2002

Utility model application

epo gmbh Siemensring 31-33

47877 Willich

with the label

Prepreg

Prepreg

The present invention relates to a prepreg according to the preamble of claim 1, an arrangement of prepregs and a component according to the preamble of claim 24.

The term "prepreg" refers to a fiber mat, particularly in the form of a scrim, which is or can be impregnated (soaked) with a resin, particularly a thermosetting resin. Prepregs are further processed, particularly by hot pressing, to form molded parts or semi-finished products, among other things. Thick-walled components can be made from prepregs layered on top of one another.

The term "resins" refers here in particular to liquid to solid organic products, preferably in accordance with DIN 55958, which can be cured or cross-linked to strengthen the fiber mat. In general, however, it can also be another binding agent for strengthening the impregnated fiber mat during curing.

Prepregs with fiber mats, unidirectional fabrics, multiaxial fabrics, fabrics and the like are used in particular in the manufacture of components when defined mechanical properties are important. By defining the alignment and uniform loading of the filaments, very high-load components can be achieved.

To produce a component, several prepregs are usually placed on top of each other, pressed together under vacuum and evacuated, and then heated to liquefy and harden the resin. This is problematic when air is trapped in the individual prepregs themselves or between adjacent prepregs and cannot escape during evacuation. This leads to an undesirable, undefined arrangement of the filaments. In particular, this can cause uneven loading or tension on the filaments and thus a deterioration in the mechanical properties of the finished component.

In order to avoid air inclusions, it is already known from practice to alternately layer dry fabrics, woven fabrics, mats, etc. - i.e. layers without resin and prepregs or resin films impregnated with resin - on top of each other so that air can escape laterally through the dry layers during evacuation.

The disadvantage of the above-mentioned procedure is that it is relatively laborious and particular attention must be paid to the appropriate layering. It has also been shown that thick dry layers are often not properly impregnated or saturated when the resin liquefies and hardens. This leads to poor mechanical properties in the finished component.

Furthermore, sandwich-like prepregs are already known from practice. For example, a resin layer is placed between a dry upper layer and a dry lower layer.

The disadvantage of the above-mentioned structure is that it requires a complex production of the prepreg. Furthermore, with thicker layers, which are particularly desirable for the production of thick-walled components, the individual filaments are often not properly impregnated or saturated when the resin liquefies and hardens.

The present invention is based on the object of specifying a prepreg and an arrangement of prepregs as well as a component made from prepregs, so that with simple production of the prepreg a simple, cost-effective production of in particular thick-walled components is possible, in particular while avoiding undesirable air inclusions.

The above object is achieved by a prepreg according to claim 1, an arrangement according to claim 20 or a component according to claim 24. Advantageous further developments are the subject of the subclaims.

A fundamental idea of the present invention is to impregnate a prepreg with a fabric only partially in the thickness direction - in a first thickness range - with resin, so that a

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A layer is formed in a second thickness range of the fabric that extends over the entire surface area of the prepreg and is not impregnated (soaked) with resin or at least to a much lesser extent than the first thickness range. The partial impregnation therefore means that the dry filaments or those that are only slightly in contact with resin in the second thickness range form an air-permeable layer that allows air to escape sideways when prepregs lying on top of each other are evacuated and/or pressed together.

The proposed prepreg is very simple and cost-effective to produce.

A further advantage is that, if required, particularly thick walls of components can be constructed exclusively from the proposed prepregs.

For example, especially with high basis weights, intermediate layers of prepregs that are impregnated with a high resin content can also be used.

The partial impregnation leads to a desired dual function in a way that is surprisingly simple in retrospect: on the one hand, it leads to extensive impregnation of the fabric before the prepreg is finished, as is particularly necessary for thicker fabrics, and on the other hand, it leads to reliable ventilation in order to avoid unwanted air pockets when layering on top of one another and then pressing or evacuating them. Up to now, a prepreg or fabric layer has always been impregnated at least essentially uniformly or not impregnated at all. The present invention is based on the idea of deliberately varying the resin content across the thickness of the fabric in order to obtain the desired properties.

Preferably, the resin content of the proposed prepreg (ventilation prepreg) is so high or dosed that the entire fabric, including the second thickness range of the fabric, is impregnated or saturated during processing. By adjusting the resin content of the proposed prepreg accordingly, a desired resin content or fiber content can be achieved.

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proportion in the finished component. In particular, when producing a particularly thick-walled component, only the proposed, preferably relatively thick prepregs can be layered on top of one another without any intervening resin films or layers, dry layers or the like.

Preferably, the second thickness region is directly adjacent to an (outer) flat side of the fabric. In particular, according to a particularly preferred embodiment, the outer "loose" filaments are then fixed on the outer flat side of the second thickness region by means of a fixing element arranged exclusively on the flat side. For example, the fixing can be designed according to DE 31 32 697 A1, EP 0 072 453 A2 or DE 197 07 125 A1. In a particularly preferred embodiment, the fixing element is formed by a relatively large-mesh, very thin net or grid that is connected at least at certain points to at least some of the outer filaments. If required, a fixing element or a fixing can also be provided on both flat sides of the fabric.

Further advantages, properties, features and aspects of the present invention will become apparent from the following description of a preferred embodiment with reference to the drawing. The single figure shows

a schematic representation of a proposed prepreg.

The prepreg 1, which is shown only very schematically and not to scale, has a fabric 2 made of filaments 3.

The fabric 2 is unidirectional, i.e. all filaments 3 run parallel to each other, here in the longitudinal extension L of the prepreg 1.

If required, the fabric 2 can also be multidirectional or multiaxial, i.e. have superimposed layers of filaments 3 with different extension directions.

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The lay-up thickness D is preferably at least 0.3 mm, in particular at least 0.5 mm. For example, the lay-up thickness is even 1 mm or more. This is particularly desirable or advantageous when producing thick-walled components.

Instead of a particularly undirectional scrim 2, the filaments 3 can also be in the form of a Malimo scrim, fabric or the like.

The filaments 3 are preferably made of glass fibers, plastic fibers and/or carbon fibers. In particular, filaments 3 made of carbon (carbon fibers), ε-glass, R-glass or aramid are used.

The diameter of the filaments 3 is preferably 2 to 20 μm, in particular substantially 5 to 12 μm.

Preferably, the filaments 3 lie very closely and evenly against one another, wherein the filaments 3 preferably run very straight with regard to a uniform tension or load when a component made from the prepreg 1 (not shown) is loaded.

The oblique hatching indicates a resin 4 with which the proposed prepreg 1 or its fabric 2 is only partially impregnated (soaked) over the fabric thickness D. The part impregnated with the resin 4 forms a first thickness range 5 of the fabric 2. The first thickness range 5 is followed by a second thickness range 6 of the fabric 2, which is preferably not impregnated or possibly only slightly impregnated with the resin 4 or another resin or binder.

The resin 4 is in particular a duroplastic or thermoplastic, preferably an epoxy resin.

The basis weight of the fabric 2 without resin 4 is preferably 200 to 5000 g/m ² , in particular 500 to 2000 g/m ² , for example substantially 1000 g/m ² .

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An essential aspect of the present invention is that the second thickness region 6 of the layup 2 forms a layer of "dry" or at least relatively loose filaments 3 that are not glued together in an airtight manner, which extends over the entire width B of the layup 2 and along the longitudinal extent L of the prepreg 1, preferably over or on a flat side 7 of the layup 2 and is sufficiently permeable to air to allow air located between the prepregs 1 or air from the first thickness region 5 of the layup 2 to escape sideways when prepregs 1 layered on top of one another are evacuated and/or pressed together.

The second thickness range 6 preferably has at least a thickness of one filament 3, in particular at least 5%, 10% or 20% of the total lay thickness D. The thickness is preferably at most 50%, in particular at most 40%, of the lay thickness D.

Preferably, the proposed prepreg 1 is formed only from a preferably "one-piece" fabric 2, which may also be multidirectional.

The fabric 2 preferably consists only of the first thickness region 5 and the second thickness region 6, which in particular - as far as possible - merge into one another in a defined manner.

According to a particularly preferred embodiment, the fabric 2 is impregnated with the resin 4 to a predetermined depth or thickness starting only from one side - in the example shown, from the lower flat side. This depth or thickness therefore determines the first thickness range 5.

If required, a layer of pure resin 4 can be applied to the outer flat side of the prepreg 1 directly adjacent to the first thickness region 5 - in the example shown, the lower flat side. Preferably, however, the resin 4 is at least substantially completely contained or absorbed in the fabric 2, i.e. in the first thickness region 5.

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The proportion of resin 4 in the fabric 2 or prepreg 1 is selected such that after processing into a component, the desired mechanical properties are achieved, in particular that the second thickness region 6 is then sufficiently impregnated or saturated.

In particular, the prepreg (venting prepreg) 1 or the scrim 2 contains essentially 35 to 60 vol.%, preferably 40 to 45 vol.% of resin 4 based on all filaments 3 of the scrim 2. When the resin 4 liquefies during processing of the prepreg 1, the resin 4 is then distributed at least substantially evenly over the thickness of the scrim 2, so that the often desired, ideal fiber content of 55 to 60 vol.% can be achieved.

During processing or during the manufacture of a component, the proposed prepregs 1 are preferably layered directly on top of one another, i.e. without the interposition of other layers, films, mats or the like, in such a way that at the transition from one prepreg 1 to the next, a first thickness range 5 and a second thickness range 6 lie on top of one another. This ensures that during the subsequent evacuation and/or pressing together of the prepreg stack, air between the flat sides of adjacent prepregs 1 can escape laterally through the respective second thickness range 6 - i.e. transversely to the longitudinal extension L. The same applies to the escape of air from the first thickness range 5 during the evacuation and/or pressing together of the prepreg stack. The second thickness range 6 thus prevents unwanted air inclusions in the prepreg stack, so that the consequences for the finished component caused by air inclusions, as already explained at the beginning, can be avoided.

Subsequently, the preferably thermosetting resin 4 is liquefied and hardened or crosslinked, in particular by heating, for example to about 6O ⁰ C to 180 ⁰ C, in particular 6O ⁰ C to 100 ⁰ C.

The proposed structure of the prepreg 1 enables, even with a very thick fabric 2, the second thickness region 6 to be sufficiently impregnated or saturated with the liquefied resin 4 before it hardens, since the thickness of the second thickness region 6 is chosen to be relatively small in relation to the total thickness D of the fabric 2 and can be adjusted as required - for example

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depending on the resin 4 used, the filament material, the filament diameter, etc.
For production or intermediate storage or transport, the proposed prepreg 1 can be provided with a carrier (not shown), for example silicone paper, in particular on the impregnation side - in the example shown, therefore on the lower flat side.

Preferably, the proposed prepreg 1 has a fixing element 8 on its flat side 7, to which the second thickness region 6 of the fabric 2 adjoins, or on the outside of the second thickness region 6.

The fixing element 8 is preferably arranged exclusively on the flat side 7 in order not to disturb the course of the filaments 3 in the scrim 2. In the example shown, the fixing element 8 is formed by a preferably coarse-meshed net or grid which is connected, for example glued, at least at certain points to at least some of the outer filaments 3 on the flat side 7 in order to stabilize the scrim 2, in particular the second thickness region 6 of the scrim 2.

It is essential that in the proposed prepreg 1 no elements such as quilting seams or the like penetrate or constrict the fabric 2, so that an optimal alignment and an optimal course of the filaments 3 in the component to be manufactured can be easily achieved.

Claims (24)

1. Prepreg ( 1 ) with a web-shaped fabric ( 2 ) made of filaments ( 3 ) and with a resin ( 4 ) for impregnation, characterized in that the fabric ( 2 ) is impregnated over the fabric thickness (D) in a first thickness range ( 5 ) and is not impregnated or is impregnated to a significantly lesser extent in a second thickness range ( 6 ), and that the first and second thickness ranges ( 5 , 6 ) each extend over the entire fabric width (B), so that the filaments ( 3 ) in the second thickness range ( 6 ) are permeable to air transversely to the longitudinal extent (L) of the prepreg ( 1 ). 2. Prepreg according to claim 1, characterized in that the second thickness region ( 6 ) adjoins a flat side ( 7 ) of the fabric ( 2 ). 3. Prepreg according to claim 2, characterized in that the prepreg ( 1 ) has a fixing element ( 8 ) arranged exclusively on the flat side ( 7 ), which fixes the filaments ( 3 ) of the second thickness region ( 6 ) arranged on the flat side ( 7 ) at least partially and/or at certain points. 4. Prepreg according to claim 3, characterized in that the fixing element ( 8 ) is designed like a net. 5. Prepreg according to claim 3 or 4, characterized in that the fixing element ( 8 ) has a basis weight of 0.5 to 4 g/m ² , in particular of 1 to 1.5 g/m ² . 6. Prepreg according to one of the preceding claims, characterized in that the filaments ( 3 ) of the fabric ( 2 ) run undisturbed, in particular no elements extending through the fabric ( 2 ) are provided. 7. Prepreg according to one of the preceding claims, characterized in that the filaments ( 3 ) run unidirectionally or multidirectionally. 8. Prepreg according to one of the preceding claims, characterized in that the filaments ( 3 ) have a diameter of 2 to 20 µm, in particular substantially 5 to 12 µm. 9. Prepreg according to one of the preceding claims, characterized in that the filaments ( 3 ) are formed from glass fibers, plastic fibers and/or carbon fibers. 10. Prepreg according to one of the preceding claims, characterized in that the prepreg ( 1 ) has only a single layer ( 2 ). 11. Prepreg according to one of the preceding claims, characterized in that the second thickness region ( 6 ) has at least a thickness of one filament ( 3 ). 12. Prepreg according to one of the preceding claims, characterized in that the second thickness range ( 6 ) has a thickness of 5% to 50%, in particular 10% to 40%, based on the total fabric thickness (D). 13. Prepreg according to one of the preceding claims, characterized in that the lay-up thickness (D) is at least 0.3 mm, preferably at least 0.5 mm, and in particular substantially 1 mm or more. 14. Prepreg according to one of the preceding claims, characterized in that the fabric ( 2 ) without resin ( 4 ) has a basis weight of 200 to 5000 g/m ² , in particular of 500 to 2000 g/m ² . 15. Prepreg according to one of the preceding claims, characterized in that the first thickness region ( 5 ) immediately adjoins the second thickness region ( 6 ), in particular wherein the fabric ( 2 ) is formed only from the first and second thickness regions ( 5 , 6 ). 16. Prepreg according to one of the preceding claims, characterized in that the resin ( 4 ) is arranged at least substantially exclusively in the fabric ( 2 ), in particular in the first thickness region ( 5 ). 17. Prepreg according to one of the preceding claims, characterized in that the prepreg ( 1 ) contains 35 to 60 vol.%, in particular 40 to 45 vol.%, resin ( 4 ) based on all filaments ( 3 ) of the fabric ( 2 ). 18. Prepreg according to one of the preceding claims, characterized in that the fabric ( 2 ) is impregnated on one side with the resin ( 4 ). 19. Prepreg according to one of the preceding claims, characterized in that the resin ( 4 ) is thermally curable and/or is a thermosetting plastic and/or a thermally crosslinkable thermoplastic. 20. Arrangement of prepregs ( 1 ) for producing a component, wherein preferably each prepreg ( 1 ) has a web-shaped fabric ( 2 ) made of filaments ( 3 ), wherein the fabric ( 2 ) is impregnated with a resin (4) over the fabric thickness (D) in a first thickness range ( 5 ) and is not impregnated with the resin ( 4 ) or is impregnated to a much lesser extent in a second thickness range ( 6 ), wherein the first and second thickness ranges ( 5 , 6 ) each extend over the entire fabric width (B) so that the filaments ( 3 ) in the second thickness range ( 6 ) are permeable to air transversely to the longitudinal extent (L) of the prepreg ( 1 ), wherein several prepregs ( 1 ) are layered on top of one another so that in the evacuated and/or compressed state the resin ( 4 ) can be liquefied and finally cured or crosslinked to even out the impregnation over the thickness ranges ( 5 , 6 ). 21. Arrangement according to claim 20, characterized in that only prepregs ( 1 ) according to one of claims 1 to 19 are used. 22. Arrangement according to claim 20 or 21, characterized in that the resin ( 4 ) can be liquefied and/or cured by heating. 23. Arrangement according to one of claims 20 to 22, characterized in that the prepregs ( 1 ) are layered one above the other in such a way that at the transition from one prepreg ( 1 ) to the next a first thickness region ( 5 ) and a second thickness region ( 6 ) lie on top of one another or that a fully impregnated prepreg lies between the second thickness regions ( 6 ) of two prepregs ( 1 ) facing one another. 24. Component made from prepregs ( 1 ), characterized in that the prepregs ( 1 ) are designed according to one of claims 1 to 19 and/or that the component is made from an arrangement according to one of claims 20 to 23.