Method for producing a support element for a vehicle

Abstract

The invention relates to a method for producing a support element for a means of transport, wherein the method comprises: providing a polypropylene/natural fiber mat (106), wherein the mat (106) has a basis weight of less than 1150 g/m.sup.2, wherein the polypropylene/natural fiber mat (106) comprises a first type of natural fibers, preheating the mat (106), placing the mat (106) in a mold (100), wherein the mold (100) has a rib-shaped cavity (112), pressing the mat (106) into a predefined form by the mold (100), so that the thickness of the mat (106) after the pressing is less than 1.5 mmimmediately and directly after the pressing, insert molding the mat (106) by injecting a polypropylene-containing material into the rib-shaped cavity, wherein the insert molding has the effect that the material forms stiffening ribs (200) that are integrally bonded with the mat (106), demolding the mat (106) comprising the stiffening ribs (200).

Claims

1. A method for producing a support element for a transport means, wherein the method comprises the steps of: providing a polypropylene-natural fiber mat, wherein the mat has a basis weight below 1150 g/m.sup.2, wherein the polypropylene-natural fiber mat comprises a first type of natural fibers, pre-heating the mat, placing the mat in a tool, wherein the tool has a rib-shaped cavity, pressing the mat into a predefined form by the tool such that the thickness of the mat after the pressing is less than 1.5 mm, immediately and directly after the pressing, insert molding the mat by injecting a polypropylene-containing material into the rib-shaped cavity, wherein, on account of the insert molding, the material forms stiffening ribs bonded integrally to the mat, demolding the mat comprising the stiffening ribs.

2. The method according to claim 1, wherein the polypropylene-containing material has a second type of natural fibers.

3. The method according to claim 1, wherein the polypropylene-containing material is heated for the insert molding process to 180-200 C. and the mat is pre-heated to 180-220 C.

4. The method according to claim 1, wherein the pressed mat has a basis weight below 850 g/m.sup.2 and a density above 0.8 g/cm.sup.3.

5. The method according to claim 1, wherein the tool forms depressions in the mat during the pressing, wherein the depressions extend parallel to the rib-shaped cavity, wherein the stiffening ribs completely fill out the depressions and protrude from the depressions in a rib-shaped manner on account of the insert molding.

6. The method according to claim 1, wherein the ratio of rib height to rib width of the stiffening ribs is greater than 3.

7. The method according to claim 1, wherein the distance between stiffening ribs extending parallel to one another is between 2.5 times to 5 times the height of the stiffening ribs.

8. The method according to claim 1, wherein the tool has two mutually opposed parts, wherein on one of the parts there is arranged a punch movable relative to this part in the direction of the opposite part, wherein the mat is placed in the tool between the two parts, wherein the pressing is performed by closing the tool on account of a reduction of the distance between the parts, wherein, once the mat has been placed in position and before the punch has been pressed, the mat is pressed at predefined points onto the part opposite the punch, wherein the points are selected such that a stretching of the mat as the tool is closed is avoided.

9. The method according to claim 1, wherein the mat comprises inner and/or outer edges to recesses of the mat, wherein the predefined form comprises bulged regions of the edges.

10. The method according to claim 9, wherein the recesses comprise holes, wherein the bulged regions surround the holes fully.

11. The method according to claim 1, wherein the mat is pressed such that, at points at which the stiffening ribs are insert molded, the mat is pressed to a lesser extent than at points which are free from stiffening ribs.

12. A support element for a transport means, produced in accordance with claim 1.

13. The support element according to claim 12, wherein the support element is a motor vehicle interior trim part.

14. The support element according to claim 13, wherein the support element has a basis weight below 1250 g/m.sup.2.

15. The method according to claim 1, wherein the time between the end of the step of pre-heating and the start of the step of pressing is no longer than 10 seconds.

16. The method according to claim 1, wherein the tool is unheated.

17. The method according to claim 1, wherein the rib-shaped cavity is covered by the mat when the mat is placed in the tool and during the step of insert molding such that the pressing of the mat is less at the rib-shaped cavity than away from the rib-shaped cavity, whereby the bonding of the polypropylene-containing material to the mat is enhanced at the cavity due to looser pressing of the fibers and better penetration of the polypropylene-containing material into the fibers at the rib-shaped cavity.

18. The method according to claim 8, wherein the pre-heated mat has a contour different from said opposite part of the tool such that a portion of the mat is spaced away from said opposite part of the tool when placed in the tool, and wherein the punch presses said portion of the mat toward said opposite part of the tool before the tool is closed so that said portion of the mat is less spaced away from said opposite part of the tool while the tool is closing.

Description

(1) Preferred embodiments of the invention will be explained in greater detail hereinafter on the basis of the drawings.

(2) In the drawings:

(3) FIG. 1 shows a schematic view of a device for carrying out the above-described method,

(4) FIG. 2 shows a schematic view of a support element,

(5) FIG. 3 shows a schematic view of a device for producing a support element in the open state,

(6) FIG. 4 shows a schematic view of the device of FIG. 3 with additional punch,

(7) FIG. 5 shows a flow diagram of a method for producing a support element for a transport means,

(8) FIG. 6 shows a schematic view of part of a device for carrying out the above-described method.

(9) Like elements will be designated hereinafter using like reference signs.

(10) FIG. 1 shows a schematic view of a device 100 for producing a support element for a transport means. The support element here comprises a polypropylene-natural fiber mat 106, wherein the mat has a basis weight below 850 g/m.sup.2. The polypropylene-natural fiber mat preferably comprises:

(11) (a) 28-95% by weight of polypropylene/polyethylene copolymer;

(12) (b) 0-10% by weight of fluxing agent;

(13) (c) 1-20% by weight of shock modifier;

(14) (d) 1-20% by weight of compatibility agent;

(15) (e) 3-70% by weight of natural fibers,

(16) wherein the polypropylene/polyethylene copolymer forms a matrix in the natural fiber mat.

(17) By way of example, the fluxing agent is a polymer having a cup flow figure between 200 and 2000 g/10 min at a temperature of 230 C. and a load of 2.16 kg.

(18) By way of example, the fluxing agent is a polyolefin which for example has been produced by catalysis of a metallocene.

(19) By way of example, the fluxing agent originates from the group comprising a polypropylene homopolymer, a polypropylene copolymer, a polyethylene homopolymer, or a polyethylene copolymer.

(20) By way of example, the polypropylene-polyethylene copolymer comprises 10 to 90 mol % of ethylene. By way of example, the shock modifier originates form the group comprising the monomer ethylene-propylene-diene (EPdM), the monomer ethylene-propylene (EPM), ethylene-propylene rubber (EPR), polyolefin elastomers (POE), copolymers and terpolymers based on ethylene and propylene, nitrile-butadiene rubber (NBR), isobutylene (IB), chlorinated rubber, poly(styrene-butadiene-styrene) (SBS), styrene-ethyl ene-butene-styrene (SEB S) copolymer, isobutylene-isoprene rubber (IIR), styrene-isoprene-styrene (SIS) copolymer, chloro-polyethylene (CM), isoprene, ethylene-butene, and mixtures and derivatives thereof.

(21) By way of example, the compatibility agent originates from the group of polyolefins trickled through carboxylic acid or through esters or anhydrides.

(22) By way of example the natural fibers originate from the group comprising cotton, linen, flax, hemp, flax or hemp from manila or abaca, banana, jute, ramie, bast, sisal, gorse, wool, alpaca, mohair, cashmere, angora, silk, bamboo, miscanthus, kenaf, coconut, agave, sorghum, switchgrass and wood.

(23) By way of example, the polypropylene-natural fiber mat comprises 10-30% by weight of the natural fibers. 30-70%/NFPP has 50% natural fibers.

(24) Such a polypropylene-natural fiber mat provides the challenge that a high mechanical stability, in particular a high modulus of elasticity, must be ensured in spite of the very low basis weight. For this purpose the mat 106 is firstly placed in the device, referred to hereinafter as a tool. The tool 100 here has two mutually opposed parts 102 and 104. It is assumed hereinafter, without limitation of the generality, that the part 104 is rigid, whereas the part 102 can be moved in the direction 108 and against the direction 108 towards the part 104 and away from the part 104 respectively. In the open state a distance between the part 102 and the part 104 is provided such that the mat 106 can be positioned in the gap defined as a result.

(25) Before the mat 106 is placed in position, the mat is heated to a predefined temperature, in particular to a temperature of 200 C. The polypropylene material of the mat is thus made soft, such that a deformation process is possible. It should be noted that the tool itself is unheated. The following step of closing the tool and of pressing the mat must therefore be carried out quickly.

(26) The tool 100 is closed by moving the part 102 in the direction 108 towards the part 104. This causes the mat 106 to assume the desired form on account of this pressing process. After the pressing of the mat into the predefined form by the tool 100, the thickness of the mat is less than 1 mm.

(27) Such a pressed mat is shown by way of example in FIG. 2. As can also be seen in FIG. 2, the mat on the rear side thereof has stiffening ribs 200. These are used to provide the mat with a high modulus of elasticity, although said mat is extremely lightweight and thin.

(28) In order to form the rib structure on the rear side of the mat, a polypropylene-containing material approximately 190 hot is injected into a cavity 112 immediately and directly after the pressing of the mat. The cavity is a rib-shaped cavity 112 beneath the mat 106. This polypropylene-containing material will contact the surface of the polypropylene-natural fiber mat 106 and bond integrally thereto. Said stiffening ribs are thus formed in the cavity 112 and are also shown in greater detail in FIG. 2.

(29) It should be noted at this juncture that the cavity 112 has a very small cross section. It is thus ensured during the pressing process, even at the points of the cavity, that the mat experiences a high pressing, even in the region of the cavity. The fact that the pressing in the region of the cavity 112 does not correspond here to 100% of the pressing in which the part 102 and the part 104 could contact one another without cavity could be advantageous: due to the slightly looser pressing in the region of the cavity, the bonding of the polypropylene-containing material to the natural fiber mat could be strengthened. This is because the liquid material of the polypropylene-containing material here could better penetrate the natural fiber mat, whereby the bonding of the created stiffening ribs to the mat could be improved.

(30) In order to now further increase the bonding strength of the stiffening ribs 200 to the mat 106, the tool 100 for example can introduce depressions in the mat 106 during the pressing. During the pressing process a depression 120 can be generated in the mat 106. The mat 106 provides side walls 122 in the depression. If the polypropylene-containing material is now injected into the depression 120 for the insert molding process, these side walls thus additionally provide contact faces for an integrally bonded connection between mat 106 and the material. The ultimately formed stiffening ribs will protrude beyond the lower edge of the depression 120. On the whole, stiffening ribs produced hereby are fixedly embedded in the mat 106.

(31) Following the insert molding of the mat by the injection of the polypropylene-containing material into the rib-shaped cavity 112, a demolding and removal of the mat 106 comprising the stiffening ribs can take place following a suitable cooling process.

(32) If polypropylene-containing material containing natural fibers is used for the insert molding process d, the mat also consisting of said natural fibers for example, the coefficient of thermal expansion will thus be lower than in the case of a material without natural fibers, on account of the natural fiber proportion. Experiments have revealed that, with use of the above-described material composition (which is also used for the mat), a very small shrinkage of the stiffening ribs of just 0.38-0.83% has taken place 3 hours after the demolding and exposure of the insert-molded mat to a room temperature environment. If here a conventional polypropylene-containing material were used, the shrinkage would usually be twice as great.

(33) A warping of the mat during the cooling process is avoided as a result of the low shrinkage.

(34) In order to now further increase the stability of the mat 106, it is possible for corresponding inner edges 202 or outer edges 204 of the mat to corresponding recesses of the mat to comprise predefined bulged regions. These bulged regions may result from the pressing process, i.e. may be defined by the pressing process itself. However, the bulged regions 202 and 204 are preferably defined as a result of said above-described insert molding process of the mat by injection of the polypropylene-containing material into cavities to be defined accordingly. Besides the hollow cavity 112, as shown in FIG. 1, the workpiece 100 thus comprises further cavities and further corresponding slide bars in order to define these bulged regions 202 and 204. The slide bars do not define the cavities, the cavities are contained in the tool form. The slide bars release bulged regions or ribs with undercuts in order to better demold these.

(35) FIG. 3 shows an exemplary tool 100 having two parts 102 and 104, which correspond substantially to the corresponding parts of FIG. 1, but have a slightly more complicated shaping. If the mat 106 is now placed in the space between part 102 and 104 and the part 102 is moved theretowards in the direction 108, the mat 106 would be overstretched between the points designated by reference signs 300 and 302 during the closing process of the tool. The reason for this lies in the fact that, during the closing process, parts of the mat 106 are already fixed between the parts 102 and 104, whereas other parts still continue to be moved during the closing process as a result of the movement of the part 102. On the whole, an inhomogeneity of the density of the mat and of the basis weight could thus result. An inhomogeneity, however, corresponds to a different mechanical load-bearing capability of the mat at different points.

(36) In order to avoid this a pneumatic punch 400 is provided on the upper part 102, as shown in FIG. 4. The punch 400 can press the mat 106 onto the part 104 before the closing process of the tool 100. This pressing process is merely local here, such that parts of the mat 106 located to the left and right of the punch may shift in the direction of the punch 400. There is thus no stretching of the mat 106 during the pressing process of the mat 106 via the punch 400.

(37) If the tool 100 is now closed by moving the part 102 in the direction 108 of the punch 104, the part 102 will press the other regions of the mat 106 onto the part 102 without stretching the mat 106 as the tool is closed.

(38) It should be noted that a punch 400 as shown in FIG. 4 can exert a force onto the mat 106, both starting from the part 102 in the direction of the part 104 and conversely starting from the part 104 in the direction of the part 102 against the direction 108. Stretching of the mat as the tool 100 is closed can thus be reliably avoided in a versatile manner in accordance with the respective geometric form of the parts 102 and 104.

(39) FIG. 5 shows a flow diagram of a method for producing a support element for a transport means. The method starts with step 500 and the provision of the mat in the unpressed state. The mat is pre-heated in step 502 and is then immediately placed in the unheated tool (step 504). In step 508 a punch can now be moved towards the mat so as to thus fix the mat in the tool at predefined points. The predefined points are selected here such that a stretching of the mat as the tool is closed is avoided. Directly following the closure of the tool the mat is pressed in step 510, such that said mat has the desired density following the pressing process.

(40) Immediately and directly after the completion of the pressing process in step 510, the mat is insert molded by injection of a polypropylene-containing material into a rib-shaped cavity, which is arranged on the tool. The material and the mat form an integrally bonded connection on account of the insert molding, whereby corresponding integrally bonded stiffening ribs are formed.

(41) In step 514, lastly, the mat comprising the stiffening ribs is then demolded.

(42) FIG. 6 shows a schematic view of part of a device for carrying out the above-described method. In contrast to FIG. 1, with regard to the part 102, an indentation 606 is provided in the part 102, wherein protrusions protrude from the part 102 to the left and right in the direction 108 of the mat 106 to be pressed. During the pressing process, i.e. force effect in the direction 108, the protrusions are pressed into the mat 106, whereby small notches 604 are created in the mat. The protrusions, in the state pressed onto the mat, cause a lateral sealing of the indentation, such that a discharge of the soft polypropylene from the indentation during the pressing process is prevented. This is true in particular also in the case of the optional foaming of the polypropylene, as a result of which the polypropylene additionally attempts to expand in the indentation 606.

(43) The protrusions 602 could be particularly advantageous in the case of the Core-Back Expansion (CBE) method, in which, following the injection of a gas, the foaming tool is opened a little in the direction 600 so as to give the material space to foam up. With a slight opening of the foaming tool the side walls of the stiffening ribs are still stabilized a little by the downwardly protruding protrusions and are therefore protected against lateral deformation (caused by expansion).

LIST OF REFERENCE SIGNS

(44) 102 part 104 part 160 mat 108 direction 112 cavity 120 depression 122 edge of the mat 200 stiffening rib 202 bulged region 204 bulged region 300 point 302 point 400 punch (advancer) 600 direction 602 protrusion 604 notch 606 indentation