EP0954426A1

EP0954426A1 - Method for inserting decorations in a thermoplastic part

Info

Publication number: EP0954426A1
Application number: EP98955682A
Authority: EP
Inventors: Jack Boulbon
Original assignee: Eurostyle SAS
Current assignee: Eurostyle SAS
Priority date: 1997-11-18
Filing date: 1998-11-18
Publication date: 1999-11-10
Also published as: FR2771045A1; FR2771045B1; BR9806779A; WO1999025535A1; JP2001508373A

Abstract

The invention concerns a method for inserting flexible decorations (1, 2) in a thermoplastic support, by low pressure overmoulding, the mould (20, 21) having cavities (10) wherein the injected melting plastic penetrates, passing through the decorations (1 or 2), cutting edges (15) being provided on the matrix (20) and/or the punching die (21) cutting out the decoration (1) in the inset zones (3) to reveal the decorative.

Description

METHOD FOR INSERTING DECORATIONS INTO A THERMOPLASTIC PART

The present invention relates to a delimited insertion process of at least one decoration in a thermoplastic support during a low pressure molding and the parts obtained by this process.

FR-A-2 702 990 describes a process for decorating a thermoplastic support by low-pressure overmolding, according to which:

- The thermoplastic material is introduced in the molten state into the mold below the decoration;

- The material is injected at low pressure through at least one nozzle while an inert low pressure gas is simultaneously injected by means of a nozzle working sequentially to orient the molten material in the desired locations of the mold.

This low pressure injection has the advantage of not deteriorating the decor. The folding, or covering of the edges by the decoration, can be carried out in the mold but it requires, most of the time, a subsequent operation of manual or automatic recovery.

In the traditional technique, the decoration is placed on the side of the mold matrix, then the material is injected in the molten state against the back of the decoration. It is the injection pressure which places the decoration in the cavity of the matrix. The decoration thus perfectly fits the cavity of the matrix but frequently overflows from it. Therefore, it is necessary to cut the edges of the decoration after demolding. And humidity can pass from the back side to the front side decorated by capillary action in the decor.

To obtain a part partially covered by a decoration, it is known to proceed in two stages. In a first step, a part is coated with a decoration which will be called a medallion. In a second step, the medallion (s) are assembled by conventional connecting means (gluing, welding, clipping, etc.) to form the partially decorated part. But, despite the quality of modern adhesives, it is still possible that there will be delamination on the edges of the pieces thus decorated and, of course, a lack of sealing.

The object of the present invention is to overcome these drawbacks and to eliminate recovery operations. For this purpose, the decoration is inserted into the thermoplastic material in very precise delimited areas of finishing or semi-finishing to avoid any additional recovery. It makes it possible to obtain a plastic part having a finishing face, integrating different decorations, by successive stages of plastic injection, without one of them being added by gluing, welding or clipping.

It is already known to overmold thermoplastic material on small canvas parts or on grids for the purpose of reinforcement. EP-A-332 889 relates to the injection molding of plastic material on a canvas diaphragm. Beads of thermoplastic material are formed on two circumferences, the assembly then being cut inside the smallest of the circumferences and outside the largest. This document does not describe a process for obtaining parts made of thermoplastic material, decorated with at least one decoration, perfectly sealed, and obtained by chemical bonding of parts injected in one or two stages.

EP-A-636 464 describes a method of overlapping making it possible to integrate the periphery of a decoration in the injected plastic material making it possible to avoid costly manual rework on the edges of the part. This process makes it possible to obtain a good seal by integrating the edge of the decoration in the plastic material. A second object of the invention is to propose a method of integrating several different decorations, juxtaposed or not, on an injected thermoplastic part. This process allows various decorations to appear on a thermoplastic part, in different zones, also by integrating functional shapes of said part. It implements specially adapted tools making it possible to integrate in transfer parts of pieces (medallions) previously produced or to obtain these decorations in a single operation comprising sequential phases, without having to open the mold.

This result is obtained by making use of the chemical bonding of the injected materials passing through one or more textile or other decorations.

According to the invention, the method of delimited insertion of a decoration in a rigid thermoplastic support by low-pressure overmolding of the textile decoration placed in a mold, in at least two parts, having cavities reserving between them at least one molding cavity , a first decoration being disposed against a part of the mold and pressed against it by the injection pressure is characterized in that the material is injected below the first decoration and penetrates, during the injection, into said cavity through the first decoration to integrate, by chemical bond, the edges of the adjoining pieces of the panel, some of the pieces being covered by a second decoration placed below the first decoration which is then cut opposite said certain pieces.

In a particular embodiment, the medallions previously made and decorated are introduced into the mold where they are precisely positioned, as well as a general decoration covering the entire external surface of the panel or of the part. Plastic material is injected in the molten state at low pressure with sequential nozzles behind the surface of the general decor to bring together the different medallions and form the panel or the room. After polymerization of the material, cutting blades in front and at the periphery of the medallions cut the general decor to reveal the local decorations of the medallions. This cutting operation can, of course, be carried out using different cutting techniques.

In another embodiment, a first injection is carried out sequentially behind the local decorations arranged and maintained in the mold by mechanical systems, behind the main decor.

Then, after moving the mechanisms, a second sequential injection is made behind the main decor. During these injections, the material passes through the decoration on the periphery of the local areas (medallions) which makes it possible to obtain the chemical connections for securing the elements. It is thus possible to simply obtain rigid one-piece and waterproof parts without opening the mold.

This setting up of the decoration makes it possible, in certain zones, to pass the thermoplastic material through the decoration and to obtain an overmolded assembly in which the components are perfectly integrated and waterproof. In all cases, the edge of the textile is inserted into the plastic in the overlap zones, with, if necessary, automatic cutting of the textile or other decorative material in the mold. The part obtained can be used as is with local decoration or reinserted in another mold in order to undergo an additional overmolding to obtain an assembly of several parts, flexible-hard, two-tone or any other arrangement.

Other characteristics and advantages of the invention will appear during the description which follows, of particular embodiments, given solely by way of nonlimiting examples, with reference to the drawings which represent: - Figure 1, a sectional view of a semi-finished part resulting from the assembly of two adjacent parts;

- Figure 2, a detailed view of a mold in which it is used mobile blocks. - Figure 3, a view of a thermoplastic part comprising two local decorations on a general surface having a third decoration;

- Figure 4, a sectional view along the line IV-IV of Figure 3, a mold for implementing the method according to the invention in a first embodiment with transfer of medallions;

- Figure 5, a sectional view along the line IV-IV of Figure 3, a mold for implementing the method according to the invention in a second embodiment without transfer of medallions;

- Figure 6, an enlarged view of the area of a medallion.

- Figure 7, a detailed view of the connection area between a medallion and the rest of the panel.

Figure 1 is a section of a part obtained by the method according to the invention. Two pieces of compatible thermoplastic materials 3 and 7 are joined by chemical bond during overmolding.

In a first step, the part 3 is coated with a local decoration 2 in a first mold (not shown) as indicated above. The part 3 includes a peripheral centering 4 for its precise positioning in a second mold. It is noted that during this first injection, the molten plastic material is passed through the decoration 2 to form the peripheral centering pins 4 and the chemical bond, as symbolized by the arrows, which ensures a tight overlap. In a second step, the part 3 previously obtained is positioned in the cavity of the second mold (not shown). The thermoplastic material, such as polypropylene or any other suitable thermoplastic material, is injected in the molten state, to constitute the part 7 in the cavity of the second mold. possibly on the back of a general decoration 1 which is stretched in the matrix of this second mold. The connection between the two parts 3 and 7 is obtained by chemical welding along the surfaces 6 of the parts 7 which are sufficiently dimensioned to maintain a temperature making it possible to heat the corresponding profile of the part 3 and ensure the chemical bond between the two parts. Of course, this chemical bond is independent of the presence or not of the decoration 1 covering the entire panel. Similarly, in the example shown, the part 3 is surrounded by a part 7 which is injected into the second mold. But it could be two independent parts 7.7a. The materials injected for the constitution of parts 7 and 3 can be the same or different but with chemical compatibility.

It is thus possible to obtain a homogeneous and integral assembly of multiple parts. The decoration 1 may consist of a textile with or without foam or of a carpet or any other suitable material. Thanks to this method, the part 7a can also be coated with an identical or different decoration from the general decoration 1 which is, beforehand, stretched in the mold or from the local decoration 2. This method allows the insertion of several decorations by realization successive operations. The medallions 3 are then cut at their periphery and the decoration 1 removed to reveal the decoration 2.

FIG. 2 represents another embodiment of the invention, intended for relatively simple parts, in which, as in the case of FIG. 1, a decoration 2 is inserted locally. In this embodiment, the mold comprises a first part or punch 21 and a die 20 inside which is mounted movable in translation at least one shim 8 in which a molding cavity 10 is formed. In this embodiment, in a first phase, the wedges 8 being closed, the plastic material 7 is injected below the decoration 1 which is centered in the mold by a pecking system referenced 4. Then, after having moved the wedges 8, the part or medallion 3 is injected below the decoration 2, the injection of the material 3 making a chemical connection with the part 7.

After insertion of the local decoration 2, between the punch 21 and the movable wedge 8 of the matrix 20, the mold is closed and the part 8 is applied against the punch 21 by hydraulic means (not shown) by pinching the decoration 2 against the punch 21 as it appears on the left side of the figure. This gives a sealed closure between the bead or peripheral centering.

After closing the mold, phase I consists of injecting a peripheral part 7 under low pressure and sequentially as described in the aforementioned patent. This injection is carried out from the punch 21 below the decoration 1 and outside the movable wedge 8. The excess part of the decoration 2 is thus included in the lower part of the thermoplastic part 7.

During phase II of the process, (represented on the right-hand side of FIG. 2), the shim 8 rises inside the matrix 20 which frees up a space of thickness determined by the height of displacement of the shim 8. A second injection is then carried out, below the decoration 2, this second injection pressing the decoration 2 against the cavity 10 formed in the wedge 8. The plastic material injected during this second injection can be of the same nature as the material introduced into the mold during the first injection. But it can also be different provided that it is chemically compatible with the first material. During phases I and II, the thermoplastic material passes through the decoration by capillary action and the integration of parts 3 and 7 is obtained by chemical bonding between the two plastic parts in zone 6.

FIG. 3 is a diagram showing in perspective a thermoplastic part obtained according to the method of the invention and, in the example shown, this part constitutes the internal wall of a motor vehicle door. It comprises a panel A, an upper medallion forming an armrest B and a lower medallion C. In the example shown, the panel is coated with a decoration 1 and the armrest B with medallion and the medallion C are coated with a second decor 2 with or without foam under the decor. The method according to the invention thus makes it possible to carry out additional finishes enriching the product. The final part has a general decor embellished with one or more localized decorations which can be integrated into functional parts such as an armrest in the example shown.

The present invention achieves this result in one or two steps.

In the embodiment of a door panel such as that shown in FIG. 4, the desired result is obtained in two distinct steps. The medallions or glasses 3 are firstly formed by injection according to a conventional process. For this purpose, the local decoration is placed in a first mold (not shown) with or without a layer of padding or “soft” and the medallion is preferably molded by low pressure injection as indicated in the aforementioned French patent which allows spare the decor. The medallion (s) are then transferred manually or by an automaton to the male part or punch 21 of a second mold which is schematically represented in FIG. 4, in which an overmolding is carried out. Each medallion is held very precisely by small plastic centralizers 4 protruding from the rear of the medallion, formed during the first step of the process, these centralizers coming to be housed in housings (not shown) made in the mold. Of course, several medallions can thus be mounted on the punch and, in the example shown, two medallions B and C are thus integrated. The general decoration 1 of the panel is then deposited in the female part or matrix 20 of the mold, and positioned outside the molding cavity by small needles (not shown) which pierce it outside of the molding part and maintain it when closing the mold. The press is progressively locked and the general decor follows, by known tension systems (blank press), the shapes of the part by pressing against the reliefs of the core. Depending on the shape of the medallions and in order to obtain a suitable plating thereof as well as a good peripheral seal, there is preferably added for each medallion, a movable wedge 8, having an appropriate relief, which is hydraulically locked in the areas before the injection phase of the main panel area. The mold being made watertight, the plastic is injected onto the back of the decoration 1 and a chemical bond is obtained between the main part 7 and the inclusions 3. This injection is carried out at low pressure so as not to not alter the decor and, preferably, using a sequential injection.

After the plastic has cooled and polymerized, the part and its local decorations are semi-finished; the mold is opened and the part is ejected. The entire surface of the room is covered by the general decoration 1. It is therefore necessary to clear the surface of the medallions so that their local decoration 2 appears and to level the periphery.

If the shape of the mold allows it, webs 15 whose movements are synchronized with those of the press perform a peripheral cutting around the medallion (s) B or C. In the case of more complex shapes, these cuts are made in recovery by cutting tools on a hydraulic press which can perform the peripheral leveling if the part does not include a rebound. These cuts can also be made in recovery in a device controlled by a 5-axis robot which can follow all the profiles to be resumed on the part, whatever the form of these resumes or any other cutting system such as high frequency front cutting machines etc. Peripheral cutting of the panel can be avoided by using the method described in EP-A-636,464 mentioned above. The presence of movable shims 8 is not necessary in this embodiment insofar as only one injection of the layer 7 is carried out.

The advantage of this first embodiment results from the fact that it is possible to change the decorations of the medallions using the same mold and to produce parts with or without foam.

In the second embodiment called “one-shot”, shown in FIGS. 5 to 7, the medallion (s) 3 are produced in a single operation with the main panel 7. First, the local decor 2 is stretched on frames 17,18, the local decoration being plated with a certain elasticity by sliding on the core of the mold 21. The mold, including the two decorations is then closed and we proceed, firstly, to the injection of the medallions 3 behind the decoration 2 The decorations 1 and 2 are thus placed inside the mold cavity. The injection continues until the injected material crosses the periphery of the decoration 2 at the level of the frames 17, 18. The sequential nozzles are then closed and the injection of the rest of the panel 7 begins using a second series of nozzles (not shown) until the panel and its medallions are completely formed

Figure 5 shows in section a mold in which the method is implemented. In this case, around each medallion and in the punch part, a small frame 17 or 18 is provided which surrounds the location of the future medallion and frees up a space in which the localized decoration (s) 2 will be deposited. After closing the mold, the frame 17.18 makes it possible to tension the local decoration 2 on the shape of the core which corresponds to the medallion to be produced. We extract the small mobile frame in a movement of the mold. This small frame frees up a space or housing in which the local decoration 2 is deposited and fixed on the small needles 16 which pierce the decoration and ensure its maintenance during the injection phase. The medallion (s) being thus positioned, the general decoration 1 is deposited in the matrix 20 which is held there by needles (not shown) external to the molding zone. Then, the mold is closed and the movable wedge 8 which ensures the shape of the medallion is locked which seals its periphery and prevents the passage of plastic.

In the first injection phase, the part 7 is injected with the exception of the medallions 3. Cavities 10 corresponding to the medallions B and C are formed in the wedges or cores 8, on the back of the decoration general 1.

In a second phase, after polymerization of the injected material, the movable wedge 8 is unlocked which is raised in the matrix to clear the space necessary for the injection of the medallion or parts or local areas of the part. After unlocking the wedges, the local areas are injected in cascade according to the teachings of the aforementioned French patent. After polymerization and the formation of chemical bonds between the different parts of the panel and the cooling of these, the mold is opened and the part injected is ejected and coated with the two decorations 1 totally and 2 locally, the decor 1 covering the parts of pieces coated with decor 2. There is generally an excess of decor 1 at the periphery of the room. The excess decoration around the medallions is folded inwards and can remain as it is. The finish of the part is obtained by leveling the periphery of the part and by cutting the general decoration 1 opposite the medallions, as described above in the first embodiment in two stages. The part can also be finished as indicated in EP-A-636 464. It is also possible to inject in a first phase the medallions and, in a second phase the rest of the part. FIG. 6 represents, on an enlarged scale, the zone of the medallion C in the mold 20,21. This figure shows the frame 17 which appears in section at the periphery of the medallion zone C, the movable wedge 8 comprising the mold cavity 10. The dashed line 2a symbolizes the position of the frame after it has been released.

FIG. 7 is a detailed view of the connection between a plastic medallion 3 and the panel 7. As it appears in the figure, part of the medallion 3 has passed through the decoration 2 to form a chemical connection between the parts 3 and 7. The decoration 1 is cut by a blade 15 whose movement in the direction of the medallion is synchronized with the opening of the mold. The decoration 1 is thus cut around the medallion (s) after polymerization of the last molded part 3 or 7.

The process which has just been described makes it possible to produce, in a single operation, a thermoplastic part coated with an integrated decoration which does not require rework for the overlapping inside the part. The connection between the different materials is perfectly sealed. The transfer of humidity by capillary action is suppressed whereas in the case of a traditional ply, the humidity can pass from the rear part of the part to the front face thereof.

The decorations can be constituted as indicated above by textiles covered or not with synthetic foam, by carpet or by leather, leatherette or any other decoration. It is also possible by the method according to the invention to imitate padding. The general surface of the panel may have, for example a seed appearance. The combination of the different decors makes it possible, for example, to enrich an enriched car door panel and at a lower cost. Compared to conventional manufacturing processes, it provides rigidity, tightness and flexibility in manufacturing.

Claims

1 ° Method of inserting a decoration into a rigid thermoplastic support by low-pressure overmolding of the textile decoration placed in a mold in at least two parts having, cavities reserving between them at least one molding cavity, the general decoration (1 ) being disposed against a part of the mold (20) and pressed against it by the injection pressure, characterized in that the material is injected below the decoration (1) and penetrates, during the injection, into said cavity, through the decoration, to integrate two contiguous parts (3,7) of the panel assembled by chemical bond, the parts (3) being covered by at least a second local decoration (2), arranged below the decoration ( 1) which is then cut to reveal the decoration locally (2).

2 ° Method according to claim 1, characterized in that in a first step, the medallions are coated with a local decoration (2) in a first mold, then transferred to a second mold in which the general decoration (1) is applied on the face of one of the parts of the mold, the parts of the general decoration (1) corresponding to the medallions being cut out after injection of the panel (7), after which the part is ejected from the mold and finished by leveling off its periphery or wrapping .

3 ° A method according to claim 1, characterized in that the parts (3,7) constituting the medallions and- the panel are successively injected respectively on the back of the local decor (2) and on the back of the general decor (1 ) in two phases, the second phase occurring after polymerization of the material injected in the first phase.

4 ° Method according to one of claims 2 or 3, characterized in that during injection operations under the decoration (1), the decoration (2) is maintained in the stretched position by at least one mobile wedge (8), the wedge being moved to allow the second injection. 5 ° Method according to claim 3 or 4, characterized in that the thermoplastic part is produced in two phases without opening the mold:

- During phase I, the peripheral part (7) is injected below the decoration (1) by integrating the edges of the latter by passing the material through the decoration;

- during phase II, the cavity (10) of the matrix (20) and the decoration (1) are distant from the punch (21) and a new injection is carried out, the two injected parts being connected by chemical bond (6 ).

6 ° Method according to claim 2 or 3, characterized in that the decoration (1) surrounding the medallions (3) is cut at the periphery thereof by blades (15) whose movements are synchronized with those of the mold ( 20.21).

7 ° Method according to claim 3, characterized in that during assembly in the mold (20,21), the decor (2) is stretched on frames (17,18) movable, then hung on needles (16).

8 ° thermoplastic parts obtained by the process according to any one of the preceding claims.