Abstract:
The invention relates to a process for the production of a composite part with a multi-part outer layer and with a foam layer bonded on the reverse side to the outer layer, in particular internal cladding of a vehicle, and also to a composite part. The inventive process comprises the following steps: a) arrangement of a first skin and of a second skin with angled-off end regions on the surface of a mold in such a way that the angled-off end regions of the first and second skin have firstly been oriented away from the surface of the mold and secondly are adjacent to one another; b) application of a reduced pressure in the region of the position of the angled-off end regions, in such a way that the angled-off end regions are pressed two-dimensionally against one another; c) reverse-side foaming of the first and second skin with a foam composition. The inventive process permits the simple production of visually attractive composite parts with multi-part outer layer.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a method for the production of a composite part, in particular an interior trim part for vehicles, with a multipart cover layer, and also to a composite part. 
     Composite parts which have a carrier, a decorative layer and a foam layer, which is situated between carrier and decorative layer and connects carrier and decorative layer to each other, are known. 
     Furthermore, it is known to construct the decorative layer to be multipart comprising at least two skins which are situated adjacently relative to each other. 
     It is problematic in the production of a component with a multipart decorative layer that, during the rear-foaming, foam can escape in the region of the separating line between the adjacent skins. 
     In order to prevent this, the patent JP 3347850 discloses a method according to which two skins with angled-off end regions are disposed on the surface of a tool in such a manner that the angled-off end regions of the first and second skin are directed away from the surface of the tool. The end region of one skin has at least one sealed portion in the form of a protuberance which can engage into a corresponding opening or hollow of the oppositely situated end region of the other skin. Correspondingly, the two skins are connected to each other to form a seal. Thereafter, the skins are foamed to each other. 
     The disadvantage of this solution is that, in order to ensure sufficient impermeability, the sealed portions must be configured in a relatively complex manner, that the skins must have a certain degree of rigidity in order to retain their shape and that an exact arrangement of the skins must be ensured. 
     It is the object of the present invention to produce a method with which composite parts can be produced with a rear-foamed multipart cover layer, which method enables an uncomplicated arrangement of the skins forming the cover layers and also can ensure sufficient impermeability during the rear-foaming. It is a further object to produce a composite part with a rear-foamed optically attractive, multipart cover layer. 
     These objects are achieved by a method and a composite part according to the independent claims. 
     Advantageous developments are described in the dependent claims. 
     BRIEF SUMMARY OF THE INVENTION 
     The invention produces a method for the production of a composite part, in particular an interior trim, with a multipart cover layer and a foam layer which is connected to the cover layer on the rear-side, containing the steps: a) arrangement of a first skin and of a second skin with angled-off end regions on the surface of a tool in such a manner that the angled-off end regions of the first and second skin are directed, on the one hand, away from the surface of the tool and, on the other hand, are adjacent to each other; b) application of a low pressure in the region of the position of the angled-off end regions so that the angled-off end regions are pressed against each other flatly; c) rear-foaming of the first and second skin with a foam material. 
     There is intended to be understood by “skin” within the scope of the invention in particular the flat elements used for decorative layers of interior trim parts of vehicles, such as slush skins, cast skins, sprayed skins, single or multilayer films, textiles or woven fabric and/or leather or imitation leather. The layer thicknesses of such skins are in particular in the range of 0.5 to 1.5 mm. 
     Due to the low pressure, the end regions of both skins are pressed against each other, a possible gap between the end regions is closed. Due to the active pressing of the end regions against each other, it is possible to prevent foam material being able to penetrate through a gap between the end regions to the visible surface of the skins during rear-foaming. 
     The low pressure is preferably applied without interruption along the entire visible-side separating line of the two skins which are to be sealed and are produced on the visible side by the angled-off end regions in order to achieve an effective uniform sealing effect along the entire separating line. In order to apply a low pressure along the entire course of the separating line to be sealed, a vacuum groove and/or borings can be introduced for example on the tool surface directly at the intended position of the separating line, or a projection which is capable of creating a vacuum can be provided. 
     The low pressure applied in the region of the angled-off end regions or of the separating line (sealing low pressure) differs qualitatively from the low pressure which can be applied when inserting the skins in order to fix the skin within the tool and to retain it in position (fixing low pressure). 
     Within the method, the fixing low pressure of the first and second skin is only a partial step and is not sufficient to produce the required sealing between the angled-off end regions. Reference should be made at the same time to the fact that the presence of a fixing low pressure merely represents an advantageous extension of the method, i.e. is not absolutely necessary. 
     Since the skins are fixed to each other via the foam, any combinations of different types of skins can be used. 
     Between the tool surface and the skins, a low pressure is likewise applied preferably over a large area in order to keep the skins in position in the tool. In order to apply such a low pressure, suitable air evacuation channels and/or borings can be provided in the tool. 
     The composite parts produced in this manner are suitable in particular as interior trims for the interior of vehicles, for example as instrument panel, as central console or as door trim. 
     An advantageous development of the invention provides that at least the first skin is configured in the end region thereof with one or more sealing lips, and the at least one sealing lip is orientated, during arrangement of the skin in the tool, towards the end region of the other skin. 
     By applying the low pressure, the sealing lips are pressed against the surface of the oppositely situated end region of the other skin. In addition, it is possible to use the foam pressure in order to press the end regions against each other. The number of sealing lips depends upon the required impermeability. 
     Preferably, the one skin at least in the region of the sealing lips, preferably at least in the end region thereof, comprises a soft, elastic material and the other skin, in the end region thereof, a hard, firm material. As a result, the sealing effect is increased, on the one hand, and also the position of the end regions is stabilised in particular during the rear-foaming. In particular, also the sealing lips can hence comprise the firm material, the elastic region in this case would be formed by the other skin. 
     Advantageously, the low pressure in the region of the angled-off end regions is between 40%-100% of a total vacuum, in particular preferably greater than 60% and less than 90% of a total vacuum. The percentage details relate to the air volume which must be evacuated in order to produce a vacuum, i.e. 100% of a total vacuum means complete evacuation of the air volume. 
     In a particularly advantageous manner, a low pressure applied for positioning the skins is weaker than the low pressure in the region of the angled-off end regions. Preferably, the low pressure for the positioning is up to 50% of a total vacuum. 
     It can also be the case that two skins made of the same material (with different colours) are combined. 
     An advantageous development of the invention provides that the first skin and the second skin are disposed on the right and left-hand side of a projection situated on the tool surface. 
     By providing a projection of this type, the positioning of the skins and hence the course of the separating line of the two skins can be fixed exactly. The projection preferably follows the entire course of the desired separating line. 
     Preferably, a low pressure is applied for positioning (sealing pressure) via the projection, which low pressure fixes the skin on the projection and makes possible a sealing effect between the angled-off end regions. For this purpose, the projection preferably has a porous, gas-permeable material or is provided with vacuum borings and/or with a vacuum groove. 
     In addition to the sealing low pressure, a further low pressure (fixing low pressure) ensures a large-area fixing of the skins in the surface of the tool. 
     Advantageously, the fixing low pressure is weaker than the sealing low pressure. Firstly the sealing low pressure and subsequently the fixing low pressure are thereby applied. In this way, the skins can be placed in the tool, subsequently drawn into position by the low pressure applied in the region of the subsequent separating line and thereafter fixed in their entirety. 
     Advantageously, the tool in which the first and second skin can be inserted has therefore two low pressure cycles: a fixing low pressure and, in the region of the angled-off end regions, a sealing low pressure for sealing the separating line. 
     Because of the different low pressure cycles, the low pressure cycles being actuated at least independently of each other, the method can be implemented or the composite part can be produced particularly advantageously. In the case of a suitable tool with a large number of air evacuation channels, it is thus possible, by means of suitable allocation of the air evacuation channels to the sealing cycle, for a large number of different separating line courses to be defined, such as S-shaped or curved separating lines or spatially, i.e. separating lines extending also in the third spatial dimension. 
     Of course, these separating line geometries can be produced by means of a corresponding projection or protrusion. 
     An advantageous development of the invention provides that the projection is lowered at least partially in the tool during curing of the foam material. 
     By lowering the projection during the curing of the foam material, a gap is opened between the two first angled-off regions of the two skins. By means of the foam material, the skins are pressed against each other so that this opened space is sealed at least partially by the skins which move up. 
     The projection can be lowered completely or be loaded in order to produce a design groove in a position in which it protrudes at least partially into the cavity. 
     An advantageous development of the invention provides that the end region of one of the two skins is angled-off for a second time and is disposed in such a manner that the second angled-off region of the end region, after arrangement of the skins in the tool, completely covers the gap between the end regions of the first and second skin. 
     The end region of one of the two skins is preferably configured and disposed in such a manner that the latter covers not only the gap between the end regions but in addition at least a part of the rear-side of the oppositely situated end region. The one end region is surrounded in this way by the other end region. In this way, the path which the foam material must overcome in order to emerge on the visible side of the cover layer is lengthened on the one hand. On the other hand, it is possible to use the foam which penetrates between a gap which is formed by the rear-side of the surrounded end region and the oppositely situated inner surface of the externally situated end region for mutual pressing together of the two end regions, as result of which the sealing effect can likewise be increased. 
     The skins are preferably preformed before arrangement in the tool corresponding to the described shapes of the end regions. 
     An advantageous development of the invention provides that the foam material is introduced on both sides of the end regions of the two skins in such a manner that the foam fronts reach the end regions of the skins at the same time. 
     This prevents the end regions being tilted by too strong pressure of the foam material on the end regions on one side. 
     It is possible in particular to introduce different foam materials on the right and left-hand side. Haptics which are different in regions for example can be produced herewith. 
    
    
     
       The invention is now explained in more detail with reference to embodiments which are represented by several Figures. There are thereby shown: 
         FIG. 1  an embodiment of a method according to the invention after completion of the foaming process and also a composite part according to the invention, 
         FIG. 2  a first embodiment of the end regions of two skins, 
         FIG. 3  a second embodiment of the end regions of two skins, 
         FIG. 4  a third embodiment of the end regions of two skins, 
         FIG. 5  a fourth embodiment of the end regions of two skins, 
         FIG. 6  different possible configurations of sealing lips, 
         FIG. 7  a variant of the angled-off end regions. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     According to one embodiment of a method according to the invention, an interior trim with a multipart cover layer is produced. 
     A carrier  5  is firstly disposed in an upper tool  6  of a foaming tool. 
     In a lower tool, a first skin  1  and a second skin  2  with their end regions which are angled-off respectively inwardly by 90° are disposed on the right and left-hand side of a protrusion  4  which is situated in the lower tool, protrudes partially beyond the tool surface and can be lowered. The skins  1 ,  2  are disposed in such a manner that the angled-off end regions  11 ,  12  are adjacent to each other and directed away from the surface of the lower tool  3 . In this case, the first angled-off regions  11 ,  12  are orientated perpendicular to the surface of the lower tool  3 . 
     The ends of the skins  1 ,  2  extend almost up to the height of the surface of the carrier  5 . In order not to impede the flow of foam during the subsequent foaming process, the carrier  5  in the region which is situated opposite the regions  11 ,  12  which are angled-off to the ends is configured with a recess in the form of a convexity  17 . 
     The first skin  1  is configured in its end region  11  with three sealing lips  13 . The sealing lips are disposed such that these are orientated towards the end region of the second skin  2  during arrangement of the skins  1 ,  2  in the tool. 
     By applying a low pressure via air evacuation openings in the lower tool  3 , which are not illustrated in more detail, the skins  1 ,  2  disposed in the lower tool are fixed in their position. On the protrusion  4 , which comprises a microporous material in this case (alternatively or additionally the protrusion can be provided with vacuum borings and/or a vacuum groove), a low pressure is likewise applied via a vacuum groove  7  which is situated on the surface of the lower tool  3 , as a result of which the skins  1 ,  2  are pressed against the protrusion  4  on the one hand and, on the other hand a possible  16  between the first angled-off regions  11 ,  12  is closed. In particular, the sealing lips  13  are pressed against the oppositely situated surface of the end region  12  of the second skin  2  when the low pressure is applied. Protrusion  4  and vacuum groove  7  are configured in such a manner that these extend continuously along the entire region, to be sealed, of the separating line of the two skins  1 ,  2 , as a result of which it is ensured that a uniform contact pressure is present along the mentioned course of the separating line. 
     Alternatively, for example a solid protrusion  4  can be used. The pressing of the two end regions  11 ,  12  together is effected in this case by applying a low pressure in the vacuum groove  7 . 
     Thereafter, the tool is closed. 
     A foam material  8  is introduced into the cavity defined by carrier  5  and skins  1 ,  2  via two foam mixer heads (not illustrated) on the right and left-hand side of the boundary region of the two skins  1 ,  2  defined by the protrusion  4 . In this case, the foam material is identical on the right and left-hand side and is introduced at the same time. Alternatively, also different foam materials are possible for example in order to produce different haptics of the composite part. Furthermore, the foam materials can be introduced with a time delay dependent upon the desired spreading of the foam. According to the component to be produced, also only one foam head can be provided (simultaneous introduction of foam on the right and left-hand side of the protrusion is of course no longer possible in this case) or more than only two foam heads can be provided. 
     The point of entry and time of introduction of the foam materials is chosen in this case such that the foam material with the foam fronts thereof reach the end regions  11 ,  12  at the same time. Alternatively, it would however also be possible to introduce the foam material in such a manner that the foam fronts reach the end regions with a time delay. 
     The foam material  8 , when impinging on the end regions  11 ,  12  of the two skins, presses these against each other, in particular the sealing lips  13  against the surface of the oppositely situated end region  12 . As a result of the curing of the foam material  8 , the pressing of the first angled-off regions  11 ,  12  against each other and hence the sealing effect in the sealing region  9  is increased in addition. The foam  8  penetrates between the end regions  11 ,  12  merely in the region of the ends of the skins  1 ,  2 . 
       FIG. 1  shows this state of the method. 
     During curing of the foam material  8 , the protrusion  4  is lowered completely in the lower tool  3 . As a result of the pressure of the foam material, the skins  1 ,  2  move up into the space opened up by the protrusion  4 . The visible-side groove between the skins  1 ,  2  is closed almost completely. 
     After the foam material  8  has acquired sufficient rigidity due to the curing process, the thus produced composite part  10  with a multipart cover layer formed by the skins  1 ,  2 , here an instrument panel  10 , can be removed from the foaming tool. 
     The carrier  5  in this embodiment is made of PP with a glass fibre component. Of course, other materials are possible, in particular thermoplastic materials, such as POM or ABS/PC, including supplements, such as for example fibres or minerals. The thickness of the carrier is approx. 2.4 mm. 
     The first skin  1  is a soft, flexible PVC slush skin with a thickness of 1.0 mm. The hardness is approx. 50 Shore A. The second skin  2  is a firm TPU slush skin with a thickness likewise of 1.0 mm. The hardness is approx. 80 Shore A. The angled-off end regions of both skins were preformed within the scope of the slush process. 
     A PU foam is used as foam material  8  in this case. 
     As an alternative to the above foaming methods, it is likewise possible to introduce the foam material when the tool is open and only then to close the tool. 
     In a second embodiment of the method according to the invention, in contrast to the first embodiment, the protrusion  4  remains in its position, is therefore not lowered. The thus produced composite part has a design groove in the region of the separating line of both skins  1 ,  2 . 
       FIGS. 2 to 5  show different embodiments of end regions  11 ,  12  of the two skins  1 ,  2 . The above-described methods can be transferred to these embodiments analogously. 
       FIG. 2  shows a first embodiment of end regions  11   a ,  12   a  of two skins which was described within the scope of the above method. The end region  11   a  of the first skin comprises a flexible material, the end region  12   a  of the second skin a firm material. The sealing lips  13  of the end region  11   a  are placed against the surface of the end region  12   a  of the second skin when the low pressure is applied and because of the foam pressure, which second skin offers sufficient resistance because of the rigidity thereof. The skin geometry  4   a  allows penetration of the foam  8  into the joint  16 , as a result of which adhesion of the two skins on the contact surface also can be effected. The number of sealing lips  13  is designed to be dependent upon the foam system, in particular upon the pressure. 
       FIG. 3  shows a second embodiment of end regions  11   b ,  12   b . In contrast to the first embodiment, the gap or the joint  16  is covered by the end region  11   b  of the first skin, as a result of which flowing of the foam material  8  into the joint  16  is prevented. The end region  11   b  is configured for this purpose to be slightly longer than the end region  12   b  of the second skin and is angled-off for second time. The joint  16  is closed with the angled-off second region. In order to produce this skin geometry  14   b  of the end region  11   b  with this exact contour, a tearing seam can be provided for example in the slush process in order to produce the skin. 
       FIG. 4  shows a third embodiment of end regions  11   c ,  12   c  of two skins  1 ,  2 . The end region  11   c  of the first skin  1  is drawn over the joint  16  up to the rear-side  17  of the end region  12   c  of the second skin. For this purpose, the end region is angled-off three times and forms a U-shaped region which is open in the direction of the surface of the lower tool  3  and in which the end region  12   c , angled-off once, of the second skin is disposed. With this skin geometry  14   c , the joint  16  between the end regions  11   c ,  12   c  is sealed analogously to the second embodiment. Furthermore, via a desired penetration of the foam material into the gap c) between the end of the end region  11   c  of the first skin and the rear-side  17  of the second skin, this geometry makes it possible to use the movement resulting therefrom of the second end region  12   c  against the sealing lips  13  of the first end region  11   c  in order to assist the sealing effect. In order to produce this skin geometry  14   c  of the end region  11   c  with this exact contour, a tearing seam can be provided for example in the slush process for producing the skin. 
       FIG. 5  shows a fourth embodiment of end regions  11   c ,  12   c  of two skins  1 ,  2 . Deviating from the previous embodiments, the separation of the skins  1 ,  2  is produced by a step  15  in the lower tool. Both end regions  11   c ,  12   c  are angled-off once at right angles analogously to the first embodiment and end at a common height, as a result of which the end region  12   d  of the second skin is shortened in its length corresponding to the height of the step  15 . 
     The step  15  can be disposed both in the region of the first skin  1  and in the region of the second skin  2 . Furthermore, a protrusion is introduced in this embodiment in order to produce a design groove. It is likewise possible to provide such a step within the scope of the above-described embodiments. 
       FIG. 6  shows different shapes of sealing lips  13 . 
     According to the above-described methods, see also  FIG. 1 , an interior trim  10  with a multipart cover layer comprising a first skin  1  and a second skin  2  and a foam layer  8  which is connected to the cover layer on the rear-side is produced, the end regions  11 ,  12  of the first skin  1  and of the second skin  2  being angled-off, the skins being disposed in such a manner that the angled-off end regions  11 ,  12  are adjacent to each other and protrude into the foam layer  8 , and the first skin  1  in its end region  11  having sealing lips  13  which are pressed against the end region  12  of the other skin  2 , the first skin  1  comprising a soft material with a hardness of approx. 50 Shore A, and the second skin  2  comprising a firm material with a hardness of approx 80 Shore A, and the wall thickness of the first skin  1  and of the second skin  2  respectively being 1.0 mm. In the case of the first embodiment of the method, almost no separating joint is visible in the region of the separating line of the two skins  1 ,  2 , in the case of the second embodiment of the method, the composite part has a design groove in the region of the separating line. The features described within the scope of the embodiments of the different end regions, see  FIGS. 2 to 5 , are transferred correspondingly to the composite part produced in this manner. 
     In  FIG. 7 , an advantageous development of the geometry of the angled-off end regions is represented. The state of the end regions of the skins  1  and  2  which are brought in contact by applying the sealing low pressure is hereby represented. 
     The angled-off end regions  11   e  and  12   e  of the first skin  1  and of the second skin  2  have, in addition to the regions angled off inwards respectively by 90°, an additional angled-off portion  21  or  22  which is angled-off opposite the first angled-off region  20  in a range between 30°-60°, here 45°. Of course, this variant can be combined with the other embodiments. 
     The advantage of the second angled-off portion resides in the fact that a greatly improved sealing effect can be achieved for the end regions  11   e ,  12   e  having additional intrinsic tension which occurs because of the second angled-off portion of the first skin  1 . A composite part with end regions which are angled-off twice in this manner has a greatly improved separating line, which leads to a longer lifespan of the composite part. 
     The angled-off portions  21  and  23 , which can be introduced already in the original form or reforming process, are in total three angled-off portions. The double angled-off portion  23 —although twice in the region of the first skin  1 —should be understood as part of the first angled-off portion  20 . The second angled-off portion  21 ,  22  is distinguished in that the end regions of the first and of the second skin abut against each other both in front of and after the second angled-off portion. 
     The advantages of the method according to the invention and of the composite part which can be produced therewith reside in particular in the possibility of combining different skins, for example high-quality with lesser quality, in easy insertion and positioning of the skins, in the automatically sealing skin geometry, in the visible material transition with visible joint, in the increase in appearance value and in the integration of the joining process of the skins within the scope of the foaming process.