Method for manufacturing a natural fiber reinforced interior lining part

Abstract

Method for producing a natural fiber reinforced interior lining part (1) by pressing, heating and forming a semi-finished product (H), wherein at least the pressing and heating takes place in a press tool device (10), wherein, prior to the compression and heating of the semi-finished product (H), the semi-finished product (H) comprises a first and a second fiber composite mat (2, 4), each with a plastic matrix (K) and natural fibers (N) embedded therein, having a first thickness (T21, T41), and a foaming film (3) located between them, having a thickness (T3) in a range between 0.1 mm and 3 mm, wherein the foaming film comprises a blowing agent (3f) enclosed therein, which foams up when heated to a minimum temperature, wherein the heating of the semi-finished product (H) to a temperature between 150°C and 250°C is carried out by heating the press tool device (10), wherein the compression and heating of the semi-finished product (H) reduces the thickness of the first and second fiber composite mats (2, 4) and creates a foam layer (30) formed by the foaming film (3) with a thickness (T30) greater than the thickness (T3) of the foaming film (3) and which lies in a range between 2 mm and 6 mm, and connects the first and second fiber composite mats (2, 4) together, wherein during compression and heating a transition layer (5) is formed which is in contact with the foam layer and with the respective first or second fiber composite mat, which has material of the foam layer (30) and material of the plastic matrix (K) of the respective fiber composite mat (2, 4) and after compression and heating of the semi-finished product (H) has a thickness (T5) which is a maximum of 80 percent of a second thickness (T22, T42) of the first or second fiber composite mat (2, 4).

Description

[0001] The invention relates to a method for manufacturing a natural fiber reinforced interior trim part, in particular a natural fiber reinforced interior trim part for the interior of a motor vehicle.

[0002] Natural fiber-reinforced interior trim components are used in motor vehicles, for example as door panels or instrument panels. These components must meet certain requirements regarding strength, particularly bending and breaking strength. At the same time, the interior trim components should be as lightweight as possible.

[0003] From DE 10 2014 212 287 A1, a method for manufacturing a plastic component is known in which two outer cover layers, designed as fiber mats with natural and plastic fibers, are pressed together with a core layer arranged between them under heat and then formed. The core layer is designed as a plastic fiber nonwoven fabric that forms a carrier for thermoplastic hollow spheres, which are applied to both sides of the plastic fiber nonwoven fabric. A blowing gas is diffusion-tightly encapsulated in the thermoplastic hollow spheres. Due to the heating, the thermoplastic hollow spheres expand and penetrate the outer cover layers.

[0004] German patent DE 10 2010 014 398 A1 describes a process for manufacturing "SMC multilayer components" comprising two SMC surface layers and a foam material layer sandwiched between them. The starting material consists of two thermosetting reaction resins in film form with fibers. The two SMC surface layers are placed in a forming press together with a foamable, dimensionally stable mold body. This mold body acts as a separator. The foamable mold body 3' lies between the SMC surface layers while they are formed by applying the appropriate pressing pressure. The first and second SMC surface layers are each formed into a single SMC surface layer with the desired final geometry. This is achieved by forcing the SMC material to flow under pressure. The SMC material hardens due to the heat applied by the heated tool.The punch and die are spaced apart, and then the foaming process is initiated, causing the mold to expand and form the molded foam that completely fills the space between the two top layers.

[0005] German patent DE 10 2013 223 353 A1 describes a one-shot manufacturing process for composites. In this process, a pre-foamed foam core is transferred between two mold shells of a press, in which the mold shells are already coated with a fiber matrix or prepreg top layer consisting of a fiber material and a resin. The mold shells are then heated to a curing temperature and cooled to a demolding temperature.

[0006] DE 10 2013 213 681 A1 describes the production of a composite component with two cover layers and an intermediate foam layer using a foaming tool.

[0007] JP S61 102 347 A also describes the production of a composite component with two outer layers and an intermediate foam layer.

[0008] The object of the present invention is to provide a method by which a natural fiber reinforced interior lining part, which has high strength at low weight, can be manufactured in a simple and efficient manner.

[0009] This problem is solved by a method having the features of claim 1. Further embodiments are specified in the dependent claims relating to it.

[0010] According to the invention, a method for manufacturing a natural fiber reinforced interior lining part is provided, wherein the method comprises the following steps: - Compressing a semi-finished product to form the inner lining part between a first and a second tool part of a press tool device, wherein the semi-finished product comprises a first and a second fiber composite mat, each having natural fibers embedded in a plastic matrix, and a foaming film located between them, wherein the foaming film has a blowing agent enclosed therein which foams up when heated to a minimum temperature, - Heating the semi-finished product to the minimum temperature by heating the press tool device and thereby creating a foam layer formed by the foaming film, which connects the first and the second fiber composite mat together, and - Forming the semi-finished product into the interior trim part.

[0011] By using a foaming film containing an enclosed blowing agent that foams up when heated to a minimum temperature, a very good bond is achieved between the film material enclosing the blowing agent and the fiber composite mats. At the same time, the penetration of gas inclusions released during foaming into the fiber composite mats can be at least largely, and preferably completely, prevented. This creates a foam layer between the fiber composite mats that has an extremely low weight per unit area. As a result, for a given thickness of the interior trim panel, the fiber composite mats can be made thinner than usual, thus reducing the overall weight of the interior trim panel.Since the foam forms a mechanically stable layer after hardening, the interior trim part, given its thickness, exhibits the desired mechanical properties for that thickness, while significantly reducing its weight.

[0012] The foaming film has a first thickness before compression and heating, and the foam layer formed by the foaming film has a second thickness after compression and heating, the second thickness being greater than the first thickness.

[0013] The first thickness is in a range between 0.1 mm and 3 mm, and the second thickness is in a range between 2 mm and 6 mm.

[0014] Furthermore, in the method according to the invention, it is provided that the first and the second fiber composite mat each have a first thickness before compression and heating and a second thickness after compression and heating, wherein the second thickness is smaller than the first thickness.

[0015] The first thickness is preferably in a range between 2 mm and 15 mm and the second thickness in a range between 0.4 mm and 2.2 mm.

[0016] Generally, the semi-finished product is heated to a temperature at which a transition layer is formed adjacent to the foam layer and to the respective first or second fiber composite mat, wherein the transition layer comprises material of the foam layer and material of the plastic matrix of the respective fiber composite mat.

[0017] The transition layer has a thickness that is a maximum of 80 percent of the second thickness of the respective first or second fiber composite mat after the semi-finished product has been compressed and heated.

[0018] During the heating step, the semi-finished product is heated to a temperature between 150°C and 250°C. Within this temperature range, reliable melting of the plastic matrix is ​​ensured.

[0019] According to the invention, it can also be provided that the semi-finished product is formed after compression and heating between a first contour surface of a first tool part of a forming device and a second contour surface of a second tool part of the forming device.

[0020] Alternatively, the semi-finished product can be formed between a first contour surface of the first tool part of the press tool fixture and a second contour surface of the second tool part of the press tool fixture. For example, it can also be provided that the forming takes place partly in the press tool fixture and partly in a separate forming device.

[0021] In the process according to the invention, it is particularly advantageous if the semi-finished product is cooled during forming. This results in rapid hardening of the individual layers. In this case, the forming of the semi-finished product preferably takes place in a forming device separate from the press tool. This keeps the energy consumption for cooling low, since only the heat needs to be dissipated from the semi-finished product. When forming the semi-finished product in the press tool, the tool can be designed to be both heated and cooled. This offers the advantage that fewer devices are required to carry out the process.

[0022] Cooling the semi-finished product during forming can be carried out, in particular, to a temperature between 20°C and 70°C.

[0023] According to a further embodiment of the method according to the invention, the density of the foam layer can be provided that it decreases in one thickness direction of the foam layer from the first and the second fiber composite mats towards a center of the foam layer located in the thickness direction between the first and the second fiber composite mats. This results in a mechanically particularly stable foam layer which, due to the low porosity of the area in contact with the fiber composite mats, is particularly reliably bonded to them.

[0024] The term "along" in the context of the directional specifications mentioned herein, which may relate to the course of a contour line or a surface, or which may relate to a direction of a mechanical component such as an axle or shaft, may in particular mean that the tangent to the respective contour line or to the respective surface in its course according to the directional specification, or the longitudinal extent and, for example, central axis of the mechanical component, deviates locally by an angle of at most 45 degrees and preferably at most 30 degrees from a reference direction or reference axis to which the respective directional specification refers.

[0025] The following describes embodiments of the invention with reference to the accompanying figures. They show: Fig. 1 an initial situation of the method according to the invention, in which a semi-finished product for the formation of an inner lining part is located in a press tool device, Fig. 2 a broken sectional view along line AA through the press tooling device and the semi-finished product inserted into it, Fig. 3 the semi-finished product during compression and heating in the press tool device, Fig. 4 a broken sectional view along line BB through the semi-finished product after it has been compressed and heated, Fig. 5. the semi-finished product after compression and heating before forming the semi-finished product in a forming device, Fig. 6 the forming of the semi-finished product in the forming device, Fig. 7 a perspective view of an interior lining part produced by the method according to the invention.

[0026] Fig. Figure 1 shows an initial situation of the inventive method for producing a natural fiber reinforced interior lining part 1. According to the invention, the interior lining part 1 is formed from a semi-finished product H, which has a first fiber composite mat 2 and a second fiber composite mat 4 and a foaming film 3 located between the fiber composite mats 2, 4 with respect to a respective thickness direction D2, D4.

[0027] The fiber composite mats 2, 4 each have natural fibers N embedded in a plastic matrix K.

[0028] Within the scope of the invention, the term fiber composite mat refers to a textile sheet, i.e., in particular a woven, knitted, or nonwoven fabric, comprising fibers, chips, shavings, or mixtures thereof. Examples of fiber composite mats are wet-laid, air-laid, or carded nonwovens. The nonwovens can contain natural or synthetic fibers or mixtures of natural and synthetic fibers, as well as wood chips or shavings. Examples of suitable natural fibers include fruit fibers, seed fibers, and stem fibers such as sisal, jute, hemp, kenaf, flax, cellulose, and cotton, as well as banana fibers and wool. Furthermore, synthetic fibers made of polyester, polyacrylonitrile, polyamide, carbon, polyvinyl chloride, polyolefins such as polyethylene and polypropylene, and inorganic materials such as aramid and glass are provided for the formation of the polymer matrix K.

[0029] The foaming film 3 comprises a blowing agent 3f enclosed within it, which foams up when heated to a minimum temperature. The foaming film 3 is designed as a sheet-like mat. In particular, the foaming film 3 can be formed from a sheet-like polypropylene film or, more generally, from a thermoplastic film, wherein the thermoplastic film forms a carrier layer 3c for the blowing agent 3f. The blowing agent 3f is enclosed within the foaming film 3. In particular, the blowing agent 3f can be in the form of granules embedded in the carrier layer 3c. It can also be provided that the blowing agent 3f is chemically bonded to the molecules forming the thermoplastic film.

[0030] The blowing agent 3f is a chemical blowing agent that foams up above a certain minimum temperature, e.g., above 120°C. Specifically, heating to the minimum temperature supplies the blowing agent with the activation energy necessary to initiate a chemical reaction. This reaction releases a gas, which forms gas inclusions in the foaming film 3, particularly in the support layer 3c.

[0031] With the foaming film 3, a foam layer 30 can be produced which solidifies after foaming and, in its solidified state, exhibits high mechanical strength, e.g., a high modulus of elasticity.

[0032] According to the invention, the semi-finished product H is pressed together between a first tool part 11 and a second tool part 12 of a press tool device 10, which can in particular be designed as a contact heating press. This is described in the Fig. Figure 3 illustrates this. In particular, the first fiber composite mat 2, with a first surface 2a, rests against a first tool surface 11a of the first tool part 11 of the press tool device 10. The foaming film 3, with a first surface 3a, rests against a second surface 2b of the first fiber composite mat 2, located opposite the first surface 2a of the first fiber composite mat 2, and with a second surface 3b, located opposite the first surface 3a, rests against a first surface 4a of the second fiber composite mat 4. The second fiber composite mat 4, with a second surface 4b located opposite the first surface 4a, rests against a second tool surface 12a of the second tool part 12.

[0033] The first and second tool parts 11, 12 are movable relative to each other along a tool opening direction W10 by means of movement devices 13, 14. The movement devices 13, 14 can, for example, each be designed as a hydraulic cylinder that can be actuated by means of a control device. In particular, it can be provided that one of the two tool parts, e.g., the first tool part 11, is fixed in place, and the other tool part, e.g., the second tool part 12, is movable relative to the fixed tool part in and against the tool opening direction W10. It can also be provided that both the first and the second tool parts 11, 12 are movable in and against the tool opening direction W10.

[0034] Fig. Figure 1 shows the press tool device in a closed state, wherein the first and second tool parts 11, 12 each apply an opposing force to the semi-finished product H and press it together.

[0035] Fig. Figure 2 shows an enlarged cross-sectional view through the semi-finished product H before compression. In this initial state, the plastic fibers are located in Fig. 2, which are not shown individually, are represented as individual interwoven fibers. The natural fibers N are embedded in the polymer matrix K formed by the polymer fibers. The first fiber composite mat 2 has a first thickness T21 in the thickness direction D2 of the first fiber composite mat 2. The second fiber composite mat 4 has a first thickness T41 in the thickness direction D4 of the second fiber composite mat 4. The foaming film 3 is located between the first and the second fiber composite mat 2, 4 with respect to the semi-finished product thickness direction DH. As in Fig. Figure 2 schematically shows that the blowing agent 3f is enclosed inside the foaming film 3 and, in particular, inside the carrier layer 3c of the foaming film 3, e.g., in the form of granules. Before compression, the foaming film 3 has a first thickness T3 in the thickness direction D3 of the foaming film 3.

[0036] Simultaneously with the compression, the semi-finished product H is heated in the press tool 10. Alternatively, the semi-finished product H can also be heated before compression, e.g., in a separate heating device. Generally, the semi-finished product H is heated to the minimum temperature at which the foaming film 3 foams up, or to a temperature above the minimum temperature. The heating melts the plastic fibers of the plastic matrix K of the fiber composite mats 2, 4. Furthermore, the carrier layer 3c of the foaming film 3 is at least plasticized, and activation energy is supplied to the blowing agent 3f. As a result, the blowing agent 3f reacts, releasing gas, and gas inclusions are formed in the foaming film 3. This creates a foam layer 30 formed by the foaming film 3, which bonds the first and second fiber composite mats 2, 4 together.

[0037] The amount of gas released can be controlled by adjusting the temperature and the amount of propellant in the foaming film 3, whereby a high temperature and a large amount of propellant each lead to a high amount of gas released.

[0038] Heating can be achieved, in particular, by heating the press tool 10. For this purpose, the press tool 10 is designed as a contact heating press. It can be provided that at least one of the tool parts 11, 12 is heated. To heat the press tool 10, the first tool part 11 and, alternatively or additionally, the second tool part 12 can each have a heating device 15, 16. The heating devices 15, 16 can, for example, each be designed as electrically operated heating wires or as heating lines through which a heating fluid flows, and which, when viewed from above, run beneath the respective first or second tool surface 11a, 12a. During pressing, a control device activates the heating devices 15, 16, thereby heating the press tool and the semi-finished product H.

[0039] According to the invention, the semi-finished product H is preferably heated to a temperature between 150°C and 250°C. Within this temperature range, the fibers of the plastic matrix K reliably melt. Furthermore, within this temperature range, the foaming of the foaming film 3, in particular its diameter and the distribution of the gas inclusions, can be specifically controlled.

[0040] Fig. Figure 4 shows the semi-finished product H after heating and compression. The heating process melts the plastic fibers of the plastic matrix K, and the blowing agent 3f reacts, releasing gas. This results in the formation of gas inclusions G within the foamed film 3, particularly within the support layer 3c.

[0041] Fig. Figure 4 shows that the first and second fiber composite mats 2, 4, after compression and heating, each exhibit a second thickness T22, T42 in the respective thickness direction D2 and D4, respectively. This second thickness T22, T42 is smaller than the first thickness T21, T41 before compression and heating.

[0042] The first thicknesses T21, T41 of the first and second fiber composite mats 2, 4 are in a range between 2 mm and 15 mm, and preferably in a range between 2 mm and 10 mm. The second thicknesses T22, T42 are in a range between 0.4 mm and 2.2 mm, and preferably between 0.4 mm and 1.5 mm. In this thickness range, particularly in the latter, the fiber composite mats 2, 4 exhibit only very low strength in a cooled state in which the polymer matrix K has solidified. However, the weight per unit area of ​​the respective fiber composite mat is very low in this thickness range.

[0043] The foam layer 30 formed by the foaming film 3 exhibits, after compression and heating, a second thickness T30 in the thickness direction D3, which is greater than the first thickness T3 of the foaming film 3 before compression. The first thickness T3 is in a range between 0.1 mm and 3 mm, and the second thickness T30 is in a range between 2 mm and 6 mm.

[0044] In general, it can be provided that the semi-finished product H is heated in such a way that a foam layer 30 formed by the foaming film 3 is produced with a thickness T30 that is greater than the thickness T3 of the foaming film 3 before compression and heating.

[0045] Because the second thickness T30 of the foam layer 30 is relatively large and connects the first and second fiber composite mats 2, 4, the second thicknesses T42, T22 of the fiber composite mats 2, 4 can be reduced, while simultaneously maintaining or increasing the strength of the interior cladding part 1 manufactured from the semi-finished product H. This results from the fact that the overall component thickness of the interior cladding part remains the same, and thus the area moment of inertia and bending stiffness remain unchanged despite the reduced thicknesses T42 and T22 of the fiber composite mats 2, 4. A particular advantage is that the foam layer 30 has an extremely low weight per unit area. This significantly reduces the overall weight of the interior cladding part while maintaining the same component thickness and thus the same mechanical properties.

[0046] According to the invention, the semi-finished product H is heated to a temperature at which transition layers 5 are formed. The transition layers are located, as shown in Fig. The transition layers 5 are shown in Figure 4, each at the foam layer 30 and the respective fiber composite mat 2, 4. These transition layers are formed by the penetration of material from the foam layer 30 and the fiber composite mats 2, 4 into one another as a result of heating and compression of the semi-finished product H. Each transition layer 5 therefore contains material from the foam layer 30 and material from the respective fiber composite mat 2, 4, in particular material from the plastic matrix K thereof. Specifically, the semi-finished product H can be heated to a temperature at which the transition layer consists exclusively of material from the carrier layer 3c of the foaming film 3 and material from the respective fiber composite mat 2, 4. In this case, each transition layer 5 contains no gas inclusions G. This results in a particularly reliable and mechanically stable connection between the foam layer 30 and the respective fiber composite mat 2, 4.

[0047] The transition layer 5 is designed to have a thickness T5 in the semi-finished product thickness direction DH, which is a maximum of 80 percent of the second thickness T22, T42 of the respective first or second fiber composite mat 2, 4 after the semi-finished product H has been compressed and heated. Within this thickness range of the transition layer 5, a reliable bond between the foam layer 30 and the fiber composite mats 2, 4 is ensured, while simultaneously maintaining high stability of the foam layer 30.

[0048] In a further step of the inventive method, the semi-finished product H is formed into the inner lining part 1. During the forming step, the fiber composite mats 2, 4 and the foam layer 30 are plastically deformed such that a surface and cross-sectional profile of the inner lining part 1 is formed.

[0049] According to one embodiment of the method according to the invention, it can be provided that the forming of the semi-finished product takes place in a forming device 20 that is different from the press tool device 10 (contact heating press), as in the Fig. 3 and Fig. 4 shown.

[0050] Accordingly, after compression and heating, the press tool device 10 is opened, e.g., by moving the second tool part 12 in the tool opening direction W10 by means of the movement device 14, and the semi-finished product H is removed from the press tool device 10. The semi-finished product H is in a plastically deformable state in which the plastic fibers of the plastic matrix K of the fiber composite mats are at least partially melted. In this state, the foaming film 3 has also already foamed into a foam layer 30. In particular, gas inclusions G are formed in the plastically deformable support layer 3c of the foaming film 3 due to the reaction of the blowing agent 3f (see Fig. 4).

[0051] For further forming, the semi-finished product H can then be cut into a Fig. The forming device 20 shown in Figure 5 is inserted, which has a first tool part 21 with a first contour surface 21a and a second tool part 22 with a second contour surface 22a. The first and the second contour surfaces 21a and 22a are formed complementarily to each other and are in a closed state of the forming device 20 ( Fig. 6) facing each other. The first and second contour surfaces 21a and 22a are designed as three-dimensionally describable surfaces and each defines the surface profile of the surfaces of the inner cladding part 1.

[0052] The first and second tool parts 21, 22 of the forming device 20 are movable relative to each other along a forming device opening direction W20 by means of motion devices 23, 24. The motion devices 23, 24 can, for example, each be designed as a hydraulic cylinder that can be actuated by means of a control device. In particular, it can be provided that one of the two tool parts, e.g., the first tool part 21, is stationary, and the other tool part, e.g., the second tool part 22, is movable relative to the stationary tool part in and against the forming device opening direction W20. It can also be provided that both the first and the second tool parts 21, 22 are movable in and against the forming device opening direction W20.

[0053] After the semi-finished product H is placed in the forming device 20, the device is closed by moving the first and second tool parts 21, 22 relative to each other, as shown in Fig. Figure 6 shows that the semi-finished product H is formed between the first contour surface 21a of the first tool part 21 and the second contour surface 22a of the second tool part 22 of the forming device 20. The first surface 2a of the first fiber composite mat 2 lies flat against the first contour surface 21a, and the second surface 4b of the second fiber composite mat 4 lies flat against the second contour surface 22a.

[0054] According to another embodiment of the method according to the invention, the semi-finished product H is formed between the first tool surface 11a of the first tool part 11 of the press tool device 10 and the second tool surface 12a of the second tool part 12 of the press tool device 10. In this case, the first and second tool surfaces 11a and 12a are each designed as three-dimensional surfaces and each defines the surface profile of the surfaces of the inner lining part 1.

[0055] After the semi-finished product H was formed into the interior trim part 1, the components forming the semi-finished product solidified. In particular, the plasticized polymer matrix K and the foam layer 30 solidified.

[0056] Fig. Figure 7 shows an interior trim part 1 produced using the inventive method, which may be, for example, a door trim panel or a support part for an instrument panel for a motor vehicle. The first and second fiber composite mats 2, 4 each form surfaces of the interior trim part 1 that are opposite to each other with the first surface 2a and the second surface 4b, respectively. For example, it can be provided that the second surface 4b of the second fiber composite mat 4 defines a visible side S of the interior trim part 1 and the first surface 2a a rear side R of the interior trim part 1.

[0057] By creating a high-strength, bonding foam layer 30 between the fiber composite mats 2 and 4, the fiber composite mats 2 and 4 can have smaller wall thicknesses in the thickness directions D2 and D4 of the interior panel 1, given a given interior panel thickness T1, while maintaining the same component strength. Since the foam layer 30 has a lower density than the fiber composite mats 2 and 4, creating the foam layer simultaneously reduces the weight of the interior panel 1.

[0058] Generally, the semi-finished product H can be cooled during forming. This causes the plasticized polymer matrix K to solidify. The foam layer 30 also solidifies or hardens as a result. Cooling, in particular, stops the reaction of the blowing agent 3f and thus allows the thickness T30 of the foam layer 30 to be adjusted. Preferably, the semi-finished product H is cooled to a temperature between 20°C and 70°C during forming. Within this temperature range, reliable solidification of the materials of the fiber composite mats 2, 4 and the foam layer 30 is achieved. In particular, the process can be accelerated by setting a temperature in the range of 40°C to 60°C, since these temperatures are reached quickly by cooling and the formed inner lining part 1 is already easily handled at this temperature, minimizing the risk of unintentional deformation or damage to the surfaces of the inner lining part.

[0059] Depending on the embodiment, the heating device 15, 16 of the press tool device 10 can simultaneously form a cooling device for cooling the inner lining part 1, or the forming device 20 can have at least one cooling device 25, 26.

[0060] In the first case, the cooling device can be designed, for example, by having a cooling fluid flow through the heating lines after the semi-finished product has been heated, whereby the heating and cooling fluids can be identical if, for example, this is heated and cooled in an external device (not shown).

[0061] In the case that the forming of the semi-finished product H takes place in the forming device 20, it may be provided that at least one of the tool parts 21, 22 is cooled. For cooling the forming device 20, it may be provided that the first tool part 21 and, alternatively or additionally, the second tool part 22 have a cooling device 25, 26. The cooling devices 25, 26 may, for example, each be designed as cooling lines through which a cooling fluid flows, and which, when viewed from above, run beneath the respective first or second contour surface 21a, 22a.

[0062] Generally, the cooling device is activated by a control device during forming, and the forming device is cooled, thereby cooling the semi-finished product H.

[0063] According to the invention, it can further be provided that the density of the foam layer 30, i.e. the weight per unit volume, decreases in the thickness direction D30 of the foam layer 30 from the first and the second fiber composite mat towards a center 31m or a central region of the foam layer 30 located in the thickness direction D30 between the first and the second fiber composite mat 2, 4, as Fig. 4 shown.

[0064] In particular, it can be provided that in the central region 31m, the gas inclusions have a larger volume than in the area of ​​the foam layer 30 adjoining the fiber composite mats 2, 4 or the transition layers 5 in the thickness direction D30. In this area, a particularly high number of small-volume gas inclusions can be provided. This density structure of the foam layer can be achieved, for example, by the spatial distribution of the blowing agent 3f within the carrier layer 3c and the control of the temperature during the heating and forming of the semi-finished product H. Reference symbol list 1 Interior trim panel 2 first fiber composite mat 2a first surface of the first fiber composite mat 2b second surface of the second fiber composite mat 3 Foam film 3a first surface of the foam film 3b second surface of the foam film 3c carrier layer 3f propellant 4 second fiber composite mat 4a first surface of the second fiber composite mat 4b second surface of the second fiber composite mat 5 Transition layer 10 Press tool device 11 First tool part of the press tool device 11a First tool surface of the first tool part of the press tool device 12 second tool part of the press tool device 12a Second tool surface of the second tool part of the press tool device 13, 14 Motion devices 15, 16 Heating device 20 forming device 21 first tool part of the forming device 21a First contour surface of the first tool part of the forming device 22 second tool part of the forming device 22a second contour surface of the second tool part of the forming device 23, 24 Motion devices 25, 26 Cooling device 30 foam layer 31m middle of the foam layer D1 Thickness direction of the interior trim part D2, D4 Thickness direction of the first and second fiber composite mat respectively D3 Thickness direction of the foam film DH Semi-finished product thickness direction G Gas inclusions H Semi-finished product for forming the interior trim part K plastic matrix Natural fibers T1 Interior trim panel thickness T3 first thickness of the foam film T30 second thickness of the foam layer T5 Transition layer thickness T21, T41 first thickness of the first or second fiber composite mat before compression and heating T22, T42 second thickness of the first or second fiber composite mat after compression and heating W10 tool opening direction W20 forming device opening direction R Rear of the interior trim panel S Visible side of the interior trim panel

Claims

[1] Method for producing a natural fiber reinforced interior lining part (1) by pressing, heating and forming a semi-finished product (H), wherein at least the pressing and heating takes place in a press tool device (10), wherein, prior to the compression and heating of the semi-finished product (H), the semi-finished product (H) comprises a first and a second fiber composite mat (2, 4), each with a plastic matrix (K) and natural fibers (N) embedded therein, having a first thickness (T21, T41), and a foaming film (3) located between them, having a thickness (T3) in a range between 0.1 mm and 3 mm, wherein the foaming film comprises a blowing agent (3f) enclosed therein, which foams up when heated to a minimum temperature, wherein the heating of the semi-finished product (H) to a temperature between 150°C and 250°C is carried out by heating the press tool device (10), wherein the compression and heating of the semi-finished product (H) reduces the thickness of the first and second fiber composite mats (2, 4) and creates a foam layer (30) formed by the foaming film (3) with a thickness (T30) greater than the thickness (T3) of the foaming film (3) and which lies in a range between 2 mm and 6 mm, and connects the first and second fiber composite mats (2, 4) together, wherein during compression and heating a transition layer (5) is formed which is in contact with the foam layer and with the respective first or second fiber composite mat, which has material of the foam layer (30) and material of the plastic matrix (K) of the respective fiber composite mat (2, 4) and after compression and heating of the semi-finished product (H) has a thickness (T5) which is a maximum of 80 percent of a second thickness (T22, T42) of the first or second fiber composite mat (2, 4). [2] Method according to claim 1, wherein the first and second fiber composite mat (2, 4) each have a first thickness (T21, T41) in a range between 2 mm and 15 mm before compression and heating and a second thickness (T22, T42) in a range between 0.4 mm and 2.2 mm after compression and heating. [3] Method according to one of claims 1 or 2, wherein the compression and heating of the semi-finished product (H) in the press tool device (10) and subsequent forming of the semi-finished product (H) takes place between a first contour surface (21a) of a first tool part (21) of a forming device (20) and a second contour surface (22a) of a second tool part (22) of the forming device (20). [4] Method according to one of claims 1 or 2, wherein the semi-finished product (H) is formed between a first contour surface (11a) of the first tool part (11) of the press tool device (10) and a second contour surface (12a) of the second tool part (12) of the press tool device (10). [5] Method according to one of the preceding claims, wherein the semi-finished product (H) is cooled during forming. [6] Method according to claim 3, wherein the semi-finished product (H) is cooled to a temperature between 20°C and 70°C during forming.

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