WO2011095232A1

WO2011095232A1 - Plastic skin

Info

Publication number: WO2011095232A1
Application number: PCT/EP2010/051519
Authority: WO
Inventors: Ryan J. Forman; Anca Paula Iordachianu; Doug Allen Stout; Yvan Vanluchene; Omar Ahmed
Original assignee: Recticel Automobilsysteme Gmbh
Priority date: 2010-02-08
Filing date: 2010-02-08
Publication date: 2011-08-11

Abstract

A plastic skin 1 for a lining part, such as a trim panel for a vehicle interior application shows at least one decorative element 4, 4.1 resembling a design element of three-dimensional shape. The decorative element 4, 4.1 is formed as part of said skin 1 and has at least at its visible margin towards the adjacent parts of said skin 1 at least partially a coating 14 applied thereon providing a contrasting aspect of the decorative element 4, 4.1 relative to the adjacent parts of the skin 1.

Description

Plastic skin

The invention relates to a plastic skin for a lining part, such as a trim panel for a vehicle interior application showing at least one decorative element resembling a design element of three-dimensional shape.

Plastic skins are used for example in interior linings of motor vehicles. Typical applications of such skins in motor vehicle applications are instrument panels, door panels, consoles, glove compartment covers, etc. In such applications the plastic skin, which forms the visibly exposed outer layer of such interior linings, is adhered to a rigid support structure, typically a hard plastic, usually by means of a intermediate foam layer, the so- called backfoam layer. Typically these plastic skins show elastomeric properties and are thus also flexible.

Such elastomeric plastic skins are typically manufactured by way of a moulding process, for example by a spraying process. In a spraying process, a liquid skin forming composition is sprayed on the mould surface of the mould, and is allowed to cure on the mould surface. Such spraying process is for instance disclosed in WO 95/32850A1 . Polyurethane reactive compositions are suitable for producing moulded skins by a spraying process. Another moulding process for producing a moulded plastic skin is for instance powder slush moulding. In such a process, a powder of a thermoplastic material such as PVC or TPU (thermoplastic polyurethane) is applied in a heated rotating mould, forming upon cooling a skin against the mould surface.

In order to enhance the design quality of such moulded skins, a method for manufacturing such skins with one or more areas of different design is disclosed for instance in WO95/32850A1 and in WO02/09977A1 . WO 95/32850A1 allows to produce elastomeric moulded skins with visibly exposed surface areas of a different colour, whilst WO02/09977A1 allows to produce elastomeric moulded skins with ornamental elements. The different design qualities may be related to the material used (the plastic compound), the colour, and/or the front surface structural design. With the method disclosed in WO02/09977A1 it is possible to manufacture plastic skins with areas showing a different design whereas each area of such different design is manufactured in the conventional manner, for example by spraying a plastic compound on the mould surface of a mould.

The moulded plastic skins are usually manufactured against a mould surface, the surface structure of which is grained in order to give the visibly exposed surface of such moulded skins the look of natural leather.

In order to further enhance the look of natural leather, further design elements typical for hand-wrapped real leather automotive components, may be replicated. Such design elements are for example the typical seams, with which the individual pieces of leather are joined to each other. By engagement of the thread with the leather, a three-dimensional design element is established. The seams as such and the locations of the seams on a hand-wrapped leather automotive component have traditionally become representative of a stylish look. Typically two pieces of leather are sewed to each other by means of a cross-stitch consisting of two threads - a needle thread and a bobbin thread. In order to enhance the resemblance look of natural leather of such skins, attempts have been made to replicate such seams together with the leather grained surface in moulded elas- tomeric skins, produced for instance by injection moulding, vacuum forming or slush moulding processes. The mould surface of the mould used for the manufacturing of such skins is itself the negative replication of the original lining, in this case the leather wrapping material with its at least one design element, for instance the seam. The manufacturing of the mould usually involves the steps of obtaining a negative of a master leather wrap model. Typically silicone is used as compound to obtain the master model's negative form. After the master model has been removed, the side of the silicon skin having faced to the master model is used to manufacture a positive replication of the master to provide support, on which a metal mould surface may be built up. The metal mould surface is achieved for example by a metallic deposition process, such as a galvanic process, by which the metal used, for example nickel is deposited on the support. The nickel then represents a female duplication of the original master model. Plastic skins produced on that mould surface represent the male duplication of the master model. The results however achieved with this method are not very plausible with the effect that, due to the lower quality replication of the seams, it may be evident at first sight that the skin is not real leather but a plastic replication. Due to the lower replication quality of the seams, the presence of such seams even enhances the fake leather look of these plastic skins. A high- quality replication of seams as design element is basically not impossible. However, the effort needed to be undertaken in order to replicate such design element with a very high quality in an interior trim part manufacturing process is so high, that in practice this is not implemented, in particular when trying to keep the costs of such manufacturing process low. Therefore, plastic skins with a leather grained structural surface are typically manufactured without any seam replications.

It is therefore an object of the invention to provide a plastic skin with replicated decorative elements of three-dimensional shape, such as stitches forming a seam, of which the resemblance is more plausible and thus more natural leather-looking, without basically increasing the manufacturing costs.

According to the invention this object is achieved by way of a plastic skin according to the preamble of independent claim 1 in that the decorative element is formed as part of said skin and in that the decorative element has at least at its visible margin towards the adjacent parts of said skin at least partially a coating applied thereon providing a contrasting aspect of the decorative element relative to the adjacent parts of the skin.

In contrast to previous approaches, the invention is based on a manufacturing process, in which the main emphasis is not directed to provide a replication of the design element, such as stitches of a seam in connection with joined lining pieces, with more detail. Moreover, the plastic skin according to the invention, typically manufactured by way of a moulding process, is provided with a replication, which in certain aspects does not need to be as accurate as possible. In order to obtain a highly plausible appearance quality of the decorative element, this element is formed as part of the skin and shows at least at its visible margin towards the adjacent parts of the skin a different, contrasting aspect provided by a coating applied on the decorative element of the skin. Thus, according to the invention, a contrast between the decorative element and the skin is used to create a highly plausible replication. Such kind of coating, without restricting to the mentioned examples, could be a colour coating, a gloss coating, a transparent coating enhancing the visual effect of deepness.

According to a preferred embodiment, said coating is a colour coating, thus providing a colour contrast between the decorative element and the adjacent parts of the skin. This result indeed comes unexpected, in particular having in mind that, although the shape of the replication does not need to be very accurate in certain features, the plausibility of the replicated original design element is a lot better compared to prior art replications. It seems that, in order to obtain a high plausibility of a replication, in particular the visible margins of the decorative element towards the adjacent parts of the skin are of major relevance. Therefore it has been found that highly plausible replications may be achieved, when in particular the visible margins of the decorative element have a contrasting aspect relative to the adjacent parts of the skin. The coating responsible for the contrasting aspect of the decorative element does not necessarily need to be applied onto the decorative element in total, but only as far as to the visible margin of the decorative element towards the adjacent parts of the skin. This does not necessarily need to be the exact bordering between the decorative element and the parts of the skin. This, for example counts for decorative elements showing undercuts. Highly plausible replications of design elements showing an undercut may be achieved without basically applying a coating on the undercut side of the decorative element.

It is surprising to discover that decorative elements may resemble the original design element a lot better even when using a conventional manufacturing process, without the need to spend efforts to optimise the replication process in order to replicate features of the original design in more and more detail. In particular this is the case with original design elements showing undercuts, such as stitches or the like, giving the typical three- dimensional appearance resembling real leather stitches. The same or almost the same appearance may thus be achieved with a plastic skin according to the invention, in which the undercuts of the replicated stitches are limited to a certain degree or are omitted at all. Thus, it was very surprising to discover that even without or with reduced undercuts compared to the original design element, the undercuts of which are prominently responsible for the design effect, a resemblance to the original design shows a very high plausibility. With regard to the invention, it may be observed that, compared to prior art efforts to enhance the quality of replications of design elements to be incorporated as replications in plastic moulded skins, this goal is achieved in a total different way.

As indicated above, according to a preferred embodiment, the decorative element shows a colour contrast relative to the adjacent parts of the skin, which is achieved by a colour coating. Such colour coating may be applied as in-mould coating and/or as coating which is applied after the moulding process; coating. In case of an in-mould coating, the colour coating is applied in the mould before the moulding process of the skin takes place. In case the decorative element is upstanding, it can be more appropriate to apply the coating after the moulding process in case the decorative element is recessed in the surface it could be more appropriate to apply the coating in the mould before the moulding process.

Such a coating can be applied, without being element of restriction, by pad printing, inkjet printing, heat pressing, transfer coating, or the like. Such colour coating may be applied for instance by a pad printing process, which may be conducted by means of a pad printing robot. In order to guide the printing arm with the printing pad of the robot during the process of print, the decorative element may comprise one or more fiduciary markers, which help the robot in detecting the exact position of the art work. They allow the robot to position separate pads on the flexible skin with a very high accuracy, even as high as 0.3 mm, allowing to catch up certain tolerances on the dimensions of the art work due to e.g. shrinkage. Such markers are according to one embodiment markers, which are detectable with optical means, for example a digital camera. Such fiduciary markers may be part of the decorative element itself but may also be supplementary elements of the decorative element. The decorative element according to the invention shows a three-dimensional shape. Examples of decorative elements for instance are, without being bound to any limitation: buttons, zippers, letters, stitches, art work, or the like. In certain cases, for example when the skin having the decorative element is part of a vehicle interior application and thus being subject to be touched, it may be desirable to protect the decorative element from abrasion. This may be worked in such a way that the decorative element is arranged in a recess between at least two shoulders of the plastic skin, that are adjacent to the decora- tive element. An enhanced protection from abrasion may be achieved when arranging the decorative element in a recess as described before but in such a way, that the decorative element is not touched by a virtual tangent line or plane bridging the recess and connecting the two adjacent shoulders. Touching of the decorative element can however not totally be prevented by arranging it in a recess in the manner described, but abrasion due to movements in a direction lateral to the longitudinal extension of the decorative element, which are typically more abrasive than touching movements in the longitudinal extension, are at least reduced.

According to a specific embodiment of the invention, the decorative element on the plastic skin is an assembly of stitches, typically forming a stitch line. Such stitch lines may be arranged as decorative stitches or as a replication of a seam, by which for example two lining elements are joined with each other. When wishing to resemble a seam, typically two parallel stitch lines are used. Thus, such seam could be the replication of two leather pieces joined with each other by a seam using a thread.

Threads used for such purposes generally show visible grooves between the individual yarns twisted to form the thread. In connection with the claimed invention it has been discovered that, similar to the undercuts mentioned above, also these grooves may be replicated with a reduced depth or undercut. Due to the contrasting aspect they still resemble the original thread in a highly plausible way.

Having found out that in spite of reduced undercuts and/or reduced groove depth, the decorative element resembles very much to the original design element due to the different, contrasting aspect of said decorative element relative to the adjacent parts of the skin. According to the invention, it is now possible to manufacture plastic skins with replicated design elements having a very high resemblance to the original design elements, by using conventional manufacturing processes. Such plastic skins are typically manufactured by way of a moulding process. In order to achieve enhanced replication of a design element in a plastic moulded skin, a spray process is preferably used. The advantage of such spray process, which is for instance disclosed in EP0379246A1 , is that, due to the use of a relatively low viscous reactive mixture, this mixture is allowed to penetrate into the surface texture of the mould surface against which it is sprayed. The advantage of having reduced undercuts and/or less deep grooves in the mould surface enables easier demoulding of the cured skin. Due to the typically elastomeric property of such moulded skin it may be easily de- moulded out of undercuts, if these do not exceed a certain depth. Further, providing decorative elements such as stitch arrangements showing a less amount of undercut then provided by the thread of the original design feature, the mechanical stability of the decorative element - the replicated stitch line for instance - as part of the skin is enhanced. Further, reducing undercuts gives the decorative element, for example a stitch line, a more stable abutment for a coating process, thus enhancing the preciseness and quality of this process.

Further embodiments and benefits of the invention will become apparent from the following description of an embodiment with reference to the figures, whereas

Fig. 1 : is a photograph showing a replicate seam with two parallel stitch lines as decorative element on a plastic skin,

Fig. 2: is a schematic cross-section through the skin of figure 1 ,

Figs. 3a-c: are photographs showing embodiments of fiduciary markers as part of the seam, and

Fig. 4: is a photograph showing the plastic skin with a replicated seam as part of a trim panel for a motor vehicle after applying a colour coat to the visible surface of the stitches of the seam.

A segment of a moulded plastic skin, in particular a polyurethane skin, formed by way of a spray moulding process, is shown in figure 1 . The moulded skin 1 of the depicted embodiment shows a leather imitation surface 2 resembling the grain structure of leather. The segment shown in figure 1 further shows the replication of a seam 3, resembling the joining of two leather pieces. The seam 3 is resembled by two parallel stitch lines 4, 4.1 . The stitch lines 4, 4.1 are in terms of these descriptions decorative elements. The stitch lines 4, 4.1 follow a groove 5 resembling the abutting edges of the two joined leather pieces. Crossing the groove 5 are replica- tions of cross-stitches 6. As to be seen from figure 1 , the replicated seam 3 shows all typical features of a seam of an original leather lining with such seam.

Figure 2 shows a schematic cross-section of the seam 3 of the plastic skin 1 of figure 1 . In the following, the stitch line 4 is described in more detail. The stitch line 4.1 is arranged and built up in the same manner. The stitch line 4 is arranged in a recess 7 of the skin 1 . The recess 7 is bordered by two shoulders 8, 8.1 of the skin 1 . The shoulders 8, 8.1 resemble the bulging of original leather used for lining due to the tension of the thread applied. The depth of the recess 7 and/or the height of the stitch line 4 are provided in such a way, that a virtual tangent line 9 bridging the recess 7 and connecting the two shoulders 8, 8.1 , does not touch the stitch line 4. Therefore, the stitch line 4 is protected in respect of objects moving in a lateral direction there too. Abrasion of the stitch line 4 is thus reduced. Also visible in figure 2 is a cross-stitch 6 crossing the groove 5.

In the enlargement of the cross-section of the stitch line 4 in figure 2 the replication of the individual yarns 10 used to resemble the thread 1 1 forming a stitch may be identified. The yarns 10 are indicated with hatched lines in order to indicate the replication. The thread 1 1 is a replication of a more-ply thread used in the original design element. Figure 2a shows for means of comparison a cross section of the original thread 1 1 '. By way of comparison it is evident that the replicated thread 1 1 shows reduced undercuts 12 with the adjacent parts of the moulded skin 1 , compared to the undercuts 12', produced by thread 1 1 '. Further, a comparison between the enlarged stitch of figure 2 and the cross-section of an original stitch of figure 2a shows, that the grooves 13 of the replicated stitch are less deep compared to the grooves 13' between the yarns 10' of the original thread 1 1 '. Reducing the undercuts 12 and the grooves 13 facilitates the process of demoulding the cured skin from the mould surface of a mould. Thus, a minor amount of a demoulding agent, if used at all, is necessary and basically no further steps of cleaning the decorative elements 4, 4.1 in order to remove the demoulding agent before the step of applying a coating are necessary. Further, due to the reduced depth of the grooves 13 of the thread 1 1 and the reduced undercuts 12 the amount of cured polyurethane rests remaining in the grooves or undercuts of the mould surface is minimised, thus facilitating the mould cleaning after demoulding a cured moulded skin.

The stitch line 4 is coated on its visibly exposed surface with a colour in order to obtain a different, contrasting aspect relative to the adjacent parts of the skin 1 . The colour coating is identified in the enlarged cross section of figure 2 with reference numeral 14. The colour of the colour coating 14 is different than and is thus in contrast to the colour of the moulded skin 1 in its parts adjacent to the stitch line 4.

As to be seen from figure 2 the thread 1 1 is formed to the moulded skin 1 almost with its complete width. The undercuts 12 reduce the connecting area between thread 1 1 and the rest of the moulded skin 1 only by about 10-15 %. It is thus evident that the stitch lines 4, 4.1 are attached to the rest of the moulded skin 1 with a good mechanical strength. Preferably undercuts should typically not exceed an amount of 20 % of the width of the decorative element in order to optimise the mechanical stability of the decorative element such as a stitch line, so that the skin can be optimally demoulded without the need to use a large amount of demoulding agent.

The colour coating 14 may be applied on the decorative element of the skin by a pad printing process, for instance after the skin has been moulded. Other coating processes are possible, such as transfer printing, inkjet printing. The colour coating may also be applied as in-mould coating. The pad printing process is well-known in the art. Only roughly: In such pad printing process at first a cliche with art work representing the look of the stitch or other art work to be deposit is provided. The recess of the art work of the cliche will have a surface tension relative low compared to the other materials coming into contact with the colour to be used, typically ink or paint. The successive increase in surface tension is the key to moving the colour to various materials in order to accurately place the colour on to the final product, here the replicated stitches. Ink or paint is deposited on to the cliche. A doctor blade is moved across the smooth surface of the cliche leaving only ink or paint deposited into the recesses of the cliche. A pad, typically a silicon pad is located above the edged art work of the cliche and placed down on the plate. The silicon pad will have a surface tension which is higher compared to the surface tension of the cliche. Thus the ink or paint is picked up on to the pad upon contact with the surface. The pad is then deposited over the part to be coated with the colour, here; the stitch, and placed down on to the surface of the part. The part surface (the replicated stitch) has a surface tension which is greater than the surface tension of the pad and will thus draw the ink or the paint on to its surface. As a result the colour - the ink or the paint - is left on the part.

For the pad printing preferably a pad printing robot is used. In order to guide the pad printing arm of the robot during the process of pad printing the decorative elements - the stitch lines 4, 4.1 in this embodiment - within the seam 3 fiduciary markers are provided. Figures 3a to 3c show by way of examples possible embodiments of different fiduciary markers. Figure 3a shows a centre dot 15 designed in the embodiment depicted as a wart-like protrusion. The fiduciary marker depicted in figure 3b is provided as a side dot of lentil-like shape provided within the stitch line 4 and/or 4.1 respectively. Still another example of such fiduciary marker is shown in figure 3c. In this embodiment an elevated cross-stitch 17 (elevated in respect to the other cross-stitches 16 of the seam 3) is provided in the groove 5 between the two replicated lining pieces joined by the seam. The examples depicted in figures in 3a to 3c show, that fiduciary markers may be arranged within the decorative element (fiduciary marker according to figure 3b) or associated with decorative element (fiduciary marks according to figures 3a and 3c).

Figure 4 shows in a photograph of the moulded skin 1 applied on a backing structure with a foam layer sandwiched between the backing structure and the moulded skin 1 . The moulded skin 1 is part of a trim panel for an interior part to be mounted in a motor vehicle. Due to the different aspect of the stitch lines 4, 4.1 , which is achieved in this embodiment by providing the stitch lines in a different colour as a coating applied by a pad printing process the resemblance of the seam 3 is almost indistinguishable from an original seam joining two leather pieces. From figure 4 it may be seen, that the colour of the stitch lines 4, 4.1 , which is in this embodiment rather white coloured, is in quite some contrast to the colour of the other parts of the moulded skin 1 (here: dark coloured).

Reducing the depth of the grooves 13 of the replicated thread 1 1 allows a colour application by way of pad printing process virtually over all the visibly exposed surface of the stitch lines 4, 4.1 . The grooves 13 between the individual yarns 10 of thread 1 1 are still present to a certain amount, thus, supplying an enlarged surface for the colour coating application. Due to the reduced depth of the grooves 13 these are easily coloured. In particular the creation of colour bridge connecting the two walls defining such groove and thus bridging the base of the groove is omitted. Such colour bridges are likely to break and impair the overall good resemblance of the original design element.

With the plastic skin described and claimed, it is possible to arrange decorative elements, such as stitch lines, seams or the like in virtual any posi- tion, also in positions on a trim panel, in which leather seams would most likely not be arranged.

Reference numerals

1 moulded skin

2 leather imitation surface

3 seam

, 4.1 stitch line

5 groove

6 cross-stitch

7 recess

, 8.1 shoulder

9 tangent line

, 10' yarn

, 1 1 ' thread

, 12' undercut

, 13' groove

14 colour coating

15 center dot

16 side dot

17 cross-stitch

Claims

A plastic skin for a lining part, such as a trim panel for a vehicle interior application showing at least one decorative element (4, 4.1 ) resembling a design element of three-dimensional shape, characterized in, that the decorative element (4, 4.1 ) is formed as part of said skin (1 ) and in that the decorative element (4, 4.1 ) has at least at its visible margin towards the adjacent parts of said skin (1 ) at least partially a coating (14) applied thereon providing a contrasting aspect of the decorative element (4, 4.1 ) relative to the adjacent parts of the skin (1 ).

The skin according to claim 1 , characterized in, that said coating is a colour coating providing a contrasting colour of the decorative element (4, 4.1 ) in respect to the adjacent parts of the skin (1 ).

The skin according to claim 2, characterized in, that the colour coating (14) has been applied onto the visibly exposed surface of the decorative element (4, 4.1 ) by way of a printing process.

The skin according to claim 3, characterized in, that the colour coating has been applied by way of a pad printing process.

The skin according to one of the claims 1 or 4, characterized in, that the decorative element (4, 4.1 ) comprises one or more fiduciary markers (14, 15, 16) for orientation of a robot applying the coating to the decorative element.

The skin according to one of the claims 1 to 5, characterized in, that the decorative element (4, 4.1 ) resembles a design element with an undercut surface and that it has substantially no or a smaller undercut than said design element.

The skin according to one of the preceding claims, characterized in, that the decorative element (4, 4.1 ) is arranged recessed between at least two shoulders (8, 8.1 ) of the skin.

8. The skin according to claim 7, characterized in, that the decorative element (4, 4.1 ) is recessed between the at least two shoulders (8, 8.1 ) in such a way that the decorative element (4, 4.1 ) is not touched by a virtual tangent line (9) bridging the recess (7) and connecting the two shoulders (8, 8.1 ).

9. The skin according to one of the claims 1 to 8, characterized in, that the decorative element is a stitch line (4, 4.1 ).

10. The skin according to claim 9, characterized in, that the stitch line (4, 4.1 ) is arranged in such way and that the adjacent parts of the skin (1 ) are formed in such a way as to resemble a seam (3).

11. The skin according to claim 10, characterized in, that the decora- tive element comprises at least two stitch lines (4, 4.1 ), which are arranged such a way and the adjacent parts of the skin (1 ) are formed in such a way as to resemble a seam (3) joining two or more pieces of a lining with each other.