WO2023066800A1

WO2023066800A1 - Method for producing sandwich components from a plate-shaped sandwich semi-finished product

Info

Publication number: WO2023066800A1
Application number: PCT/EP2022/078642
Authority: WO
Inventors: Thomas Gläßer; Peter Michel; Peter Stache
Original assignee: Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e. V.
Priority date: 2021-10-18
Filing date: 2022-10-14
Publication date: 2023-04-27
Also published as: DE102021126912A1

Abstract

The invention relates to a method for producing sandwich components from a plate-shaped sandwich semi-finished product (1) which is manufactured from a thermoplastic material of a first type and is fibre-reinforced at least in a partial region by means of continuous fibres of a second type and is joined with at least one functional component (8), said method comprising the following method steps: - separating the plate-shaped sandwich semi-finished product into at least a sandwich cut-out piece (2, 7) and a cutting waste part (3), - processing the cutting waste part in order to obtain a material resource containing the thermoplastic material of the first type and components of the continuous fibres of the second type, - thermoforming the sandwich cut-out piece in order to obtain a shaped sandwich intermediate product (7), and - producing at least one functional component (8) manufactured from the material resource, and joining the at least one functional component (8) to the sandwich intermediate product (7) in order to obtain the sandwich component consisting of the thermoplastic material of the first type and the continuous fibres and components of the continuous fibres of the second type.

Description

Process for the production of sandwich components from a panel-shaped semi-finished sandwich product

technical field

The invention relates to a method for producing sandwich components from a plate-shaped semi-finished sandwich product made from a thermoplastic material of a first type and fiber-reinforced at least in a partial area using endless fibers of a second type and joined with at least one functional component.

The sandwich construction based on continuous fiber-reinforced plastics is one of the most efficient lightweight construction technologies for the production of large-scale structural components. Usually, sandwich components, which are characterized by high mechanical performance, i.e. resilience, with minimal weight at the same time, consist of two high-strength cover layers or cover layers in which continuous fibers, for example made of carbon, glass or aramid, are embedded in a plastic matrix made of duroplastic or thermoplastic material present.

Between the cover layers there is a predominantly air-filled and therefore very light core layer, which can also be structured, e.g. in the form of honeycombs, or homogeneously porous, e.g. as foam. In addition to the material processed in the cover layers and the core layer, i.e. fiber and plastic material, ready-to-use sandwich components usually contain at least one other material system, which should have sufficiently good flowability during production and from which complex-shaped and/or pressure-resistant functional components are produced, which with or are mostly bonded in the sandwich composite of the sandwich component. Such functional components are, for example, housings, domes, clips, connection profiles, insert potting systems, etc.

The sandwich construction method has been used for decades, primarily in high-price segments such as aerospace, in boat and yacht building or various sports such as winter or water sports.

The matrix material used in the above-mentioned areas of application is thermoset plastics such as epoxy or polyester resins in comparatively small quantities. However, due to their irreversible cross-linking reaction after component manufacture, duroplastics are only poorly recyclable and are incinerated after their use in the context of fossil energy generation. In contrast, modern processing technologies make it possible to cost-effectively manufacture sandwich composites from thermoplastics in the form of continuous fiber-reinforced sandwich components, even in large series. In a large number of mass markets, such as in the automotive sector, sandwich components of this type are increasingly replacing flat structural components made of steel in order to reduce weight.

In order to improve these products in terms of sustainability and resource conservation, solutions are being sought that go beyond the already mentioned burning for the purpose of energy generation and simple recycling.

For example, the production-related waste in the form of offcuts is unfavorable for the sustainable use of thermoplastic sandwich components result for component production from sandwich or cover layer material produced in panels or webs; on the other hand, after the sandwich components have been in use, very large quantities of thermoplastic, fiber-mixed plastic material accumulate, which cannot be recycled or can only be recycled with great financial and energy expenditure. Due to the hybrid production methods of the sandwich and functional components, the finished, functionalized sandwich components each contain different material compositions, which make sustainable recycling almost impossible. But even if an identical plastic is used in sandwich and functional components, every component design with different volume fractions of sandwich and functional components leads to different proportions of plastic and fiber in the sandwich components. This results in a different overall material composition per component type and thus, after material recycling, a recyclate that is materially dependent on the component type. With regard to the fiber content, these different compositions cause differences in the mechanical material properties, such as E-modulus and strength. Especially in the case of material flows that are difficult or impossible to trace when recycling different components, this leads to a material quality with sometimes strongly fluctuating mechanical properties. Such fiber-reinforced composite materials obtained in the course of recycling represent a high safety-specific and therefore also economic risk when reused for the production of new, resilient structural components.

Both the fluctuations in the property profile of the recyclate material-recycled continuous fiber-reinforced sandwich components and the large amounts of offcuts in the production of such components represent the problem of the underlying invention. State of the art

One process that has come into focus in recent years is the production of sandwich-like structural components made of thermoplastic, continuous fiber-reinforced prepregs, so-called organo sheets. As part of hybrid manufacturing technology, a thermoforming process is used in the first step to process the organo sheets into the final multi-curved shell geometry. In the second directly subsequent process step, a ribbed structure is produced in the same tool by means of injection molding or extrusion. The ribs assume the same mechanical support function on the component as the core structure in a sandwich with two outer layers. In addition to the production of the supporting ribs, functionalizations such as load introduction elements are also integrated directly on the component. Machines that are suitable for this process are marketed by "KraussMaffei Group GmbH" under the brand name "FiberForm" or by "ENGEL AUSTRIA GmbH" under "Organomelt". It is true that reference is made here to the good recyclability of the components produced in a thermoforming/injection molding combination. The general problem with this technology is that different starting composite materials always have to be used to produce the hybrid components. The reason for this is that an organo sheet composite cannot be processed by injection molding without material additives. Thus, after recycling, the problem explained in section 1 arises with regard to the fluctuations in the property profile of the recovered fiber-mixed recyclate after material recycling. In addition, offcuts that occur during the processing of the flat organic sheet semi-finished products must also be recycled, which is not possible without further processing steps with additional plastic admixtures due to the high proportion of fiber mass.

In the "Project MAI sandwich" funded by the Federal Ministry of Education and Research, three processes for the production of single-variety thermoplastic sandwich components were derived. The differences in the processing routes are basically due to the examined manufacturing processes for the core material. The different core materials are respectively as part of component production during the hot forming of the core directly with the previously thermoformed cover layers to form a sandwich component in the forming tool. The functional component, designed as an edge finish and additional rib reinforcement, is also injection molded in the same tool and is directly bonded to the sandwich component. The processing of PP and PA foam cores has proven advantageous for large-scale component production. The processes published in the final report rely on thermoplastic base polymers of the same type or of the same type as the matrix system of the core and cover layer within the sandwich component and the injection-molded functional component in favor of the recyclability of the sandwich component. As with the previously described hybrid processes for processing organo sheet, the material mix resulting from the differences in the bond between the two components is neglected. This in turn leads to the problem described in Section 1 with regard to offcuts, in this case the top layer material and property fluctuations in the fiber-mixed recyclate in the production of different types of components.

A similar process for manufacturing sandwich components with a foam core is foam injection molding, which is marketed under the brand name MuCell®. As with the technology from the "Mai Sandwich" project, organic sheets can also be processed in one tool to form sandwich components in conjunction with injection molding. The difference is that core production takes place directly during molding within a physical foaming process. There are the same problems with regard to offcuts, from the fiber-reinforced top layer material and the fluctuations in properties in the fiber-mixed recyclate in the production of different types of components. The patents listed in the table include further processes for the production of fiber-reinforced thermoplastic sandwich components for large-scale applications. However, none of the documents listed contain approaches to increasing the recyclability of the sandwich components with which a mix of materials via the composite materials contained in the sandwich and functional components can be avoided. The publication DE 102014218 305 A1 describes a sandwich element which is easy to produce and stable and comprises two cover layers and a core layer arranged between the cover layers, the sandwich element having at least one compressed section, preferably at the edge, on which a functional plastic injection molded element is arranged .

The document DE 10 2000401 682 B3 discloses a manufacturing process for a sound-absorbing composite body, in which a foam blank together with a plastic mass used to form a carrier part are introduced into a compression mold or injection molding tool, in which the mass is formed into the carrier part and used to Formation of the composite part is connected to the foam, which forms the absorber layer in the composite body.

The publication DE 102010 008 370 A1 discloses a method for producing a plate-shaped semi-finished product made of fiber composite material, which contains carbon fibers and at least one thermoplastic matrix material, the carbon fibers being isolated from unspecified carbon fiber-containing waste and these being mixed with thermoplastic fibers. In a subsequent carding process, the fibers are laid flat and aligned so that a fibrous web with a specific fiber orientation is obtained, which is then pressed under the action of heat to form a panel material. In this way, carbon fibers from textile production waste can be reused as reinforcement fibers.

Presentation of the invention

The invention is based on the object of producing fiber-reinforced sandwich components provided with at least one functional component, preferably for lightweight construction applications, in a way that should enable the sandwich component to be fully recycled after its intended use or use, ie without loss of material to supply The goal should be to realize the sandwich component in the form of a recyclate that is as pure as possible in order to create the conditions for a closed, material recycling economy. The process should also be usable in large-scale industrial production in order to be able to produce large numbers of single-variety sandwich components at competitive unit costs.

The solution to the problem on which the invention is based is specified in claim 1. Features that advantageously further develop the idea of the invention are the subject matter of the subclaims and the further description, in particular with reference to the exemplary embodiments.

The inventive method for the production of sandwich components uses as a starting product a large-area, plate-shaped semi-finished sandwich product, which is made of a thermoplastic material of a first type and is fiber-reinforced at least in a partial area by means of endless fibers of a second type.

Particularly suitable plate-shaped semi-finished sandwich products are composite structures which have at least two layers, of which in at least one layer the continuous fibers of the second type are embedded in a matrix of thermoplastic material of the first type. In particular for the production of thermoplastic continuous fiber-reinforced sandwich components for large-scale applications, which are usually able to withstand large static and dynamic surface loads, composite structures are used as a plate-shaped semi-finished sandwich product, which have at least two cover layers in which continuous fibers are in a matrix of thermoplastic material of the first Sort are embedded and the one, arranged between the two outer layers core layer of the thermoplastic material of the first type limit on both sides and are integrally connected with this. The core layer is preferably structured and delimits cavities, for example in the form of a honeycomb structure, or is in the form of a foam. This semi-finished product consists of a cover layer-core-cover layer composite whose plastic matrix contains a thermoplastic base polymer of the same type. The respective modification of the base polymer is carried out differently according to the necessary properties of the core and cover layer in the composite.

The invention is based on the idea of exclusively using the composite material that is built into or contained in the semi-finished sandwich product, preferably in its entirety, to produce the sandwich component together with the at least one functional component. This makes it possible for different sandwich components, which are produced from a composite material but have different volume fractions of both components, to be materially recycled after they have been used to form a recyclate with the same composition as the starting material. Since the process aims to produce sandwich components in the sense of a closed recycling economy, waste can also be avoided and fluctuations in properties in the recycled recyclate can be significantly reduced.

For this purpose, the method according to the solution is made up of the following method steps: The stored semi-finished sandwich product, which is a large-area, plate-shaped composite structure, is separated into at least one sandwich cut part and a scrap residue. In particular, for economic reasons, the largest possible sandwich semi-finished products are stored, from which more than two, preferably a large number of individual sandwich components can be produced. Not necessarily, but preferably, all the so-called sandwich blanks separated from a semi-finished sandwich product have the same shape and size. Depending on the procedural objective, the number, shape and size of the sandwich blanks to be separated from a plate-shaped semi-finished sandwich product must be selected in a suitable manner, for example in order to generate the lowest possible, but unavoidable, proportion of waste residues. The process of separating, which can be carried out with known, suitable means, e.g. by means of separating, cutting or stamping processes, should preferably be carried out in such a way that the at least one sandwich blank part and the remainder of the offcut each have an identical proportion of thermoplastic material of the first type and Possess continuous fibers or components of the continuous fibers of the second type.

The scrap residue obtained by way of the separation is subjected to processing in order to obtain a material resource, which only contains the thermoplastic material of the first type and components of the continuous fibers of the second type. The processing of the waste residue is preferably carried out by means of a mechanical and/or thermal material processing, by which the waste residue is converted into the material resource, which is present in a particulate form that can be portioned or in a free-flowing form after the thermoplastic material has been melted.

A functional component can be produced by thermally assisted softening of the material resource obtained from the waste residue, preferably by means of a thermoplastic injection molding or extrusion process.

The at least one pre-cut sandwich part, which is also obtained by way of separation, is converted into a shaped intermediate sandwich product by way of thermoforming, preferably as part of a thermally assisted press forming process. Preferably separately from this, at least one of the functional components to be manufactured from the material resource is produced, e.g. in the form of a housing, dome, clip, connection profiling, insert-potting system, etc., which, due to their material identity with the material of the intermediate sandwich product, has the same material properties has, so that the desired sandwich component is obtained by materially joining the at least one finished functional component to the intermediate sandwich product, which consists of the thermoplastic material of the first type and the continuous fiber and components of the continuous fiber second variety exists. The preferably thermally supported joining process leads to a monolithic connection between the two components. As a result, a sandwich component that appears uniform in terms of material and is functionalized by the at least one functional component is obtained.

Alternative procedures are conceivable and can be implemented to produce the at least one functional component and the sandwich intermediate product as well as their materially bonded connection:

Thus, the at least one functional component and the intermediate sandwich product can be produced in a common thermoforming process using a press forming tool designed appropriately for this purpose. In this case, the joining of the two components is not necessary or takes place in situ, i.e. during the production of both component sections within the press forming tool.

If the at least one functional component and the intermediate sandwich product are manufactured separately by means of a thermoforming process, which can be carried out consecutively or in parallel, the at least one functional component is joined to the intermediate sandwich product after thermoforming. In this case, the joining of the at least one functional component to the intermediate sandwich product is preferably carried out by means of a suitably selected thermal joining technique, preferably by means of thermoplastic welding.

The continuous fiber or fiber content of the second type in the entire panel-shaped semi-finished sandwich product should not exceed a maximum value of 50 percent by mass, preferably 40 percent by mass, in relation to the thermoplastic material of the first type, in order to ensure material recycling of the waste by means of thermoplastic injection molding or To be able to ensure extrusion to obtain the functional component. Preferably, the fiber content of the continuous fiber-reinforced cover layers of the sandwich semi-finished product is always higher, than that of the core layer. Therefore, the maximum fiber or particle proportions of the core must be selected to be correspondingly small in order to balance out the total of the cover layers.

For reasons of improved separation of the sandwich component from the press forming tool after thermoforming, it is advantageous to add talc to the composite material made of thermoplastic material of the first type and the fibers of the second type, and this in a proportion of fiber content to talc of greater than (>) 75%.

As a result, with the method explained above, a pure recyclate is obtained in the form of a sandwich component having at least one functional component, the purity of which is also retained in various other components when recycled in suitable material recycling processes at the end of the product life cycle. The process according to the solution contributes, in particular when using large-scale industrial production lines for sandwich components, to promoting the recycling of such recylates suitable for large-scale production and opening the way to a sustainable and resource-saving production method.

Brief description of the invention

The invention is described below by way of example, without restricting the general inventive concept, using exemplary embodiments with reference to the drawings. Show it:

Fig. 1a-h Process steps for the production of a sorted recyclate

Ways of carrying out the invention, industrial applicability

In the figures 1 a - h is an example of a process path for the production of a single-variety sandwich component, which serves as recyclate, illustrated. In FIG. 1a, the starting product forms a continuous-fiber-reinforced semi-finished sandwich product 1, which represents a composite structure of two continuous-fiber-reinforced cover layers and a structured core layer arranged in between. The semi-finished sandwich product 1 consists entirely of a thermoplastic material of a first type and continuous fibers or fiber components of a second type. The semi-finished sandwich product 1 preferably consists of a total of 40% fiber and 60% plastic.

In a first process step, the plate-shaped semi-finished sandwich product 1 is subjected to a separation step corresponding to a later desired component geometry of a sandwich component, in which at least one sandwich blank part 2, preferably a large number of sandwich blanks 2, which are not necessarily identical in shape and size, is obtained, see Fig. 1b. The separation can be done, for example, using cutting, cutting or punching technologies.

In addition to the sandwich blanks 2 fall after the separation waste residues 3, see Fig. 1c., Which are materially processed in a further process step, e.g. subjected to mechanical crushing 4 to obtain portionable particles 5. The material processing can be adapted to the needs As an alternative to purely mechanical comminution, portioning or dosing can also be done thermomechanically, e.g. by compounding in a suitable extruder. The material composition of the waste residues 3 to be processed must not be changed as part of the material processing.

A further process step includes the processing of the prefabricated sandwich blank 2 as part of a thermally assisted pressing or thermoforming process to obtain a shaped intermediate sandwich product 7, the shape of which largely corresponds to the shape of the final sandwich component, see Fig. 1e, which shows the sandwich blank inserted within a press forming tool 6 2 and 1f showing the formed intermediate sandwich product 7 within the stamping die. In a final process step, the intermediate sandwich product 7 produced is completed by at least one functional component 8, e.g. in the form of a holder framing the intermediate sandwich product, see FIG. 1g, in which the final functionalized sandwich component 9 is shown.

The material of the at least one functional component 8 consists exclusively of the portionable particles 5, which are obtained from the leftover waste 3.

Depending on the component requirements for the final sandwich component, the functional component can be manufactured, e.g. by means of thermoplastic injection molding or the extrusion process. For this purpose, the portionable particles 5, which consist of the thermoplastic material of the first type and the fiber components of the second type, are converted into a flowable state and serve as a material resource that can be metered.

In a first variant for the production of the at least one functional component 8 and its connection to the intermediate sandwich product 7 , this measure can be combined with the shaping process for producing the intermediate sandwich product 7 . In this case, the flowable and meterable material resource is added to the sandwich blank 7 in the press-forming tool 6 or in a press-forming tool arrangement suitable for this purpose, in which the functionalized, final sandwich component 9 is obtained as part of a joint thermal press-forming process, see Fig. 1g.

In a second variant, the functional component 8 is produced separately from the production of the sandwich intermediate product 7, preferably by means of thermoplastic injection molding or an extrusion process. The separate functional component can then be bonded to the intermediate sandwich product 7 by means of thermal joining technology, such as thermoplastic welding. The process steps illustrated in the sequence images of FIGS. 1a to g are, if necessary, carried out at the same time in real large-scale production in order to meet the demands of industrial production.

Subsequent processing or finishing of the sandwich components 9 produced in the manner described, for example by laminating or coating the produced sandwich components, is still possible, but should be detachable or removable with regard to later recycling. In this way, a pure recyclate can be guaranteed for different components when used in suitable material recycling processes at the end of the product's service life. At the end of the service life of a sandwich component 9 that has been produced according to type, it can be reused by means of material processing, e.g. by mechanical crushing 4 into portionable particles 5, see Fig. 1h, material recycling within the framework of a closed cycle, while maintaining the original type purity .

The sandwich component produced according to the solution and having at least one functional component is particularly suitable as a flat, load-bearing component in the field of electromobility, automotive, caravan, ship, rail and aircraft construction, sports equipment, e.g. in the form of long boards, surfboards and kites -Boards, skis, etc. or as a support structure for photovoltaic modules. The purity of the component, e.g. in the form of a PV supporting structure, obtained through the component production according to the solution, enables the component material to be completely returned to a recycling process after the end of the supporting structure’s use as a material resource for the production of new short- or long-fiber-reinforced thermoplastic components. Reference List

sandwich semi-finished product

sandwich blank

Waste remainder, mechanical comminution, portionable particles

press forming tool

sandwich intermediate

Functional component functionalized sandwich component

Claims

patent claims

1 . Method for producing sandwich components (9) from a plate-shaped semi-finished sandwich product (1), which is made from a thermoplastic material of a first type and is fiber-reinforced at least in a partial area by means of continuous fibers of a second type and is joined with at least one functional component (8). the following procedural steps:

Separation of the plate-shaped semi-finished sandwich product (1) into at least one sandwich blank part (2) and a leftover scrap (3),

Processing the waste residue (3) to obtain a material resource containing the thermoplastic material of the first type and components of the continuous fibers of the second type,

thermoforming the sandwich blank (2) to obtain a shaped intermediate sandwich product (7), and

Producing at least one of the functional components (8) made from the material resource and joining the at least one functional component (8) to the intermediate sandwich product (7) to obtain the sandwich component (9) consisting of the thermoplastic material of the first type and the continuous fibers and components of the continuous fibers of the second variety.

2. The method according to claim 1, characterized in that the separation takes place in such a way that the at least one sandwich blank part (2) and the offcut (3) each contain at least one continuous fiber-reinforced partial area.

3. The method according to claim 1 or 2, characterized in that the separation is carried out in such a way that the at least one sandwich blank (2) and the leftover waste (3) each have an identical quantity ratio of thermoplastic material of the first type and continuous fibers or components of the continuous fibers of the own second kind.

4. The method according to any one of claims 1 to 3, characterized in that the processing of the waste residue (3) takes place by way of a mechanical and / or thermal material processing, through which the waste residue (3) is converted into the material resource that can be portioned in particulate form is present or can be metered free-flowing or free-flowing by melting the thermoplastic material.

5. The method according to any one of claims 1 to 4, characterized in that the thermoforming of the sandwich blank (2) to obtain a shaped intermediate sandwich product (7) is carried out in the context of a thermally assisted compression molding process.

6. The method as claimed in one of claims 1 to 5, characterized in that the at least one functional component (8) produced from the material resource is produced separately from the production of the intermediate sandwich product (2).

7. The method as claimed in one of claims 1 to 6, characterized in that the at least one functional component (8) produced from the material resource is produced by means of a thermoplastic injection molding or extrusion process.

8. The method according to any one of claims 1 to 7, characterized in that the production of the at least one functional component (8) and the joining to the intermediate sandwich product (7) is carried out coupled with the thermoforming of the sandwich blank part (2).

9. The method according to any one of claims 1 to 7, characterized in that the production of the at least one functional component (8) and the joining of the functional component (8) to the intermediate sandwich product (7) is carried out after the thermoforming of the sandwich blank part (2). 18

10. The method according to any one of claims 1 to 9, characterized in that the joining of the at least one functional component (8) to the intermediate sandwich product (7) is carried out by means of material joining technology.

11 . Method according to Claim 10, characterized in that the at least one functional component (8) is joined to the intermediate sandwich product (7) by means of thermoplastic welding.

12. The method according to any one of claims 1 to 11, characterized in that a thermoplastic, continuous fiber-reinforced composite structure is provided as the plate-shaped semi-finished sandwich product (1), which has at least two layers, of which in at least one layer continuous fibers in a matrix of thermoplastic material of the first variety are embedded.

13. The method according to any one of claims 1 to 11, characterized in that a thermoplastic, continuous fiber-reinforced composite structure is provided as the plate-shaped semi-finished sandwich product (1), which has at least two cover layers in each of which continuous fibers are embedded in a matrix of thermoplastic material of the first type , and that the two outer layers delimit an intermediate core layer made of the thermoplastic material of the first type on both sides and are connected to it in a materially bonded manner.

14. The method as claimed in claim 13, characterized in that the core layer is structured and cavities are delimited or formed in the form of a foam. 19

15. The method according to any one of claims 1 to 14, characterized in that the plate-shaped sandwich semi-finished product (1) has the following weight proportions: greater than (>) 50% thermoplastic material of the first type and less than (<) 50% fiber content of the second type.

16. The method according to any one of claims 1 to 15, characterized in that the plate-shaped semi-finished sandwich product (1) has the following proportions by weight: greater than (>) 60% thermoplastic material of the first type and less than (<) 40% fiber content of the second type and Talc having a fiber to talc ratio of greater than or equal (>) 75%.

17. Sorted recyclate in the form of a sandwich component (9) having at least one functional component (8) produced with a method according to one of claims 1 to 16.

18. Use of the single-variety recyclate according to claim 17 as a flat, load-bearing component in the field of electromobility, automotive, caravan, ship, rail and aircraft construction, sports equipment, or as a supporting structure for photovoltaic modules.