Method for manufacturing a moulded part comprising a decorative layer

Abstract

The invention relates to a method for manufacturing a part (1) shaped by at least one moulding operation, the moulded part comprising at least one decorative layer (2) made at least partly with a synthetic material, comprising the following successive steps: - a step of positioning the decorative layer (2) in a mould (7), and - a step of injecting a plastics material (8) into the mould (7), characterized in that the injection step is carried out under the following conditions: - the injection pressure varies between 300 and 500 bar, - the temperature of the injected plastics material (8) is between 200 and 250°C, - the temperature of the mould (7) is kept at 25°C + / - 5°C.

Description

[0001] Title: Method of manufacturing a molded part comprising a decorative layer

[0002] The present invention relates to the field of motor vehicles, and more particularly to parts produced by molding a plastic material, present within the passenger compartments of these motor vehicles.

[0003] Automotive interiors are often equipped with various plastic parts, which are frequently enhanced with a decorative layer for aesthetic and functional reasons. This decorative layer is not limited to the visual appearance of the vehicle's interior; it also helps improve the tactile experience for the driver and passengers. For example, adding a decorative layer that includes a foam layer can provide a soft and comfortable feel to the touch, which can increase overall comfort. In addition, the decorative layer of these parts can be customized to the owner's taste, offering a wide range of textures, colors, and patterns to create a unique and personalized interior.

[0004] To achieve the decorative layer on plastic parts without compromising its quality, a specific manufacturing process is required. This process must ensure that the decorative layer remains intact and is not damaged during manufacturing.

[0005] The most commonly used process is gluing, which is broken down into several steps. The first step involves injecting a plastic material into a mold, which forms the basic structure of the part. Once the structural part has cooled, the mold is opened and the part is removed. The decorative layer, previously cut to fit the shape of the part, is then coated with glue and then glued to the structural part. A finishing step is then implemented to perfectly match the decorative layer to the structural part.

[0006] This process ensures that the decorative layer does not undergo excessive compression or mechanical stresses that could damage it.

[0007] The method discussed above has several disadvantages. First, this process involves many steps, which lengthens manufacturing time and results in high energy consumption. In addition, this method requires the use of a large amount of glue. EP1798112B1 presents an alternative to gluing, describing an injection molding process for creating a part including a facing surface. This process involves placing a decorative sheet in a mold, then closing it to create an injection cavity where the plastic material is injected, thus forming the part which is then removed from the mold. This process eliminates the need for glue and simplifies production steps by integrating the facing surface directly during injection.

[0008] However, this process has the major disadvantage of compromising the quality of special facing surfaces. Indeed, the injection step causes intense compression of the facing surface, which deteriorates its qualities, especially when this facing surface includes a layer of foam.

[0009] The objective of the invention described in this document is therefore to overcome the disadvantages of the prior art by presenting a method for manufacturing a plastic part which does not alter the decorative layer.

[0010] To this end, the present invention proposes a method which avoids overcompression and therefore degradation of the quality of the decorative layer.

[0011] The main subject of the present invention is thus a method for manufacturing a part shaped by at least one molding operation, the molded part comprising at least one decorative layer made at least in part with a synthetic material, comprising the following successive steps: step of positioning the decorative layer in a mold, step of injecting a plastic material into the mold, characterized in that the injection step is carried out according to the following conditions: an injection pressure varying between 300 and 500 bars, a temperature of the injected plastic material between 200 and 250 °C, a mold temperature maintained at 25 °C + / - 5 °C.

[0012] The step of positioning the decorative layer in the mold involves placing the decorative layer, previously cut, in the mold when it is open.

[0013] The mold is then closed, and then the step of injecting the plastic material into the mold is carried out. At this stage, the plastic material is therefore injected and will mechanically or chemically bond to the decorative layer. After the injection step, the formed molded part is extracted from the mold. The molded part then includes the decorative layer and a part forming a structural element of the part, this structural element conferring its mechanical properties after cooling of the plastic material.

[0014] During the injection stage, certain conditions are necessary to preserve the integrity of the decorative layer and prevent it from suffering damage that could alter its characteristics, such as its softness, feel or aesthetic appearance.

[0015] The injection pressure of the plastic material must be between 300 and 500 bars.

[0016] Injection pressure can, for example, be determined using pressure sensors integrated into an injection machine, which provide real-time data on the applied pressure.

[0017] According to the invention, the temperature of the injected plastic material must be between 200 and 250°C. This range of values ​​guarantees the flow of the plastic material during the injection step and also guarantees a perfect bond with the decorative layer, without altering the latter.

[0018] Finally, the mold temperature should be around 25°C, with a tolerance of + / - 5°C. This temperature control also aims to protect the decorative layer from potential damage that could be caused by too high a mold temperature.

[0019] The temperature of the plastic material injected into the mold and the temperature of the mold can be controlled using temperature sensors integrated into the mold and / or the injection machine which is connected to the mold.

[0020] This process offers the advantage of eliminating certain additional steps, typical of gluing. Indeed, in the gluing technique, a step is necessary to apply glue to the decorative layer. The process according to the invention makes it possible to do without this step since the bond between the decorative layer and the injected plastic material is carried out during the injection step. The manufacturing process is therefore simplified, offering both a reduction in production time and a saving in materials, in particular by eliminating the use of glue. This process also has the advantage of preserving the aesthetic and tactile properties of the decorative layer, thanks to the specific conditions maintained during the injection step.

[0021] It is important to understand that the term "plastic" does not refer to the deformation properties of an object but rather to a category of materials. Therefore, any type of plastic material can be used, regardless of its deformation properties.

[0022] According to an optional feature, the decorative layer comprises an appearance layer, a foam layer and a barrier layer.

[0023] The appearance layer of the decorative layer constitutes the visible surface of the finished molded part by the user. This layer must provide an attractive visual appearance and a pleasant touch for the user because this part is a direct interface with the user.

[0024] The foam layer is a component of the decorative layer, located between the appearance layer and the barrier layer. It gives the decorative layer its characteristic softness, thus providing a soft and comfortable touch sensation for the user.

[0025] The barrier layer, on the other hand, is in contact with the plastic structural element of the molded part. This barrier layer limits the temperature rise of the foam layer during injection, which helps maintain an appropriate residual foam thickness and flexibility of the foam layer. The barrier layer also ensures adhesion between the plastic structural element and the decorative layer.

[0026] According to an optional feature, the barrier layer of the decorative layer is between 0.2 mm and 1 mm thick, measured before the injection step.

[0027] This thickness ensures protection of the decorative layer against the heat of the plastic material during the injection stage and also guarantees a solid bond of the decorative layer with the injected plastic material which forms the structural element once finished.

[0028] To measure the thickness of the barrier layer, a cross-section must be made in the decorative layer before the injection step. The thickness of the barrier layer is then measured in this section to ensure that it is between 0.2 mm and 1 mm.

[0029] According to an optional feature, the barrier layer of the decorative layer is made of polyester or polypropylene.

[0030] During the injection stage, the properties of the barrier layer material allow the barrier layer to blend with the plastic, while protecting the foam layer. This phenomenon thus ensures a strong adhesion between the decorative layer and the plastic structural element.

[0031] According to an optional feature, the foam layer of the decorative layer is between 2 mm and 8 mm thick, measured before the injection step.

[0032] This thickness of the foam layer ensures that, even after the injection step and the fusion of the barrier layer with the plastic material, there remains a sufficient residual thickness of the foam layer to maintain the soft feel of the decorative layer.

[0033] In order to measure the thickness of the foam layer, a cross-section is made before the injection step in the thickness of the decorative layer. This cut then makes it possible to measure the thickness of the foam layer to check that it is between 2 mm and 8 mm.

[0034] According to an optional feature, the foam layer of the decorative layer has a density between 60 kg / m 3 and 100 kg / m 3 determined before the injection step.

[0035] By choosing a foam layer with a density between 60 kg / m 3 and 100 kg / m 3, we ensure that it has the necessary strength to withstand the pressure exerted during the injection stage, without compressing excessively. The decorative layer thus retains its soft appearance at the end of this stage. Thanks to this characteristic and the injection conditions of the manufacturing process, the foam layer compresses to a maximum of 20 to 25% of its initial thickness during the injection stage.

[0036] To measure the percentage of compression of the foam layer, a cross-section of the finished molded part is first taken. The thickness of the residual foam layer is then measured. If the foam layer varies in thickness, an average of several measurements is taken to obtain a representative value. This measurement is then compared to the thickness of the foam layer before injection to calculate the percentage of compression.

[0037] According to an optional feature, the appearance layer of the decorative layer has a thickness between 0.7 mm and 1.4 mm, measured before the injection step.

[0038] A decorative layer with a thickness between 0.7 mm and 1.4 mm is strong enough to withstand the effects of heat and pressure during the injection stage, ensuring a pleasant feel and visual appearance of the decorative layer.

[0039] To determine the thickness of the decorative layer before the injection step, it is necessary to make a cross-section in the thickness of the decorative layer. The thickness of the decorative layer is then measured in this section, ensuring that it complies with the values ​​previously mentioned.

[0040] According to an optional feature, the appearance layer of the decorative layer is a plastic-coated fabric, genuine leather or synthetic leather.

[0041] These materials are particularly suitable for the surface coating, as they combine several essential properties: they are strong, pleasant to the touch, and visually attractive.

[0042] According to an optional feature, the barrier layer of the decorative layer is in contact with the plastic material during injection while the appearance layer of the decorative layer is in direct contact with the mold.

[0043] During the injection stage, positioning the barrier layer so as to face the injected plastic material allows the bonding between the plastic material and the barrier layer of the decorative layer during this stage.

[0044] Positioning the finish layer in direct contact with the mold prevents its aesthetic and tactile properties from being altered. Indeed, by being far from the injected plastic material, the finish layer is less exposed to high temperatures.

[0045] According to an optional feature, the plastic material injected during the injection step is polypropylene, polycarbonate, acrylonitrile butadiene styrene or a mixture of these materials. The use of these materials has several advantages in the manufacture of plastic parts.

[0046] Polypropylene, whether filled or not, is known for its lightness, resistance to bending and wear, as well as its ability to resist various chemicals.

[0047] Polycarbonate is valued for its high impact resistance and its ability to be molded, machined, or thermoformed.

[0048] Acrylonitrile butadiene styrene, on the other hand, combines rigidity, impact resistance and a smooth finished surface, making it perfect for applications where aesthetics are important.

[0049] Using a blend of these materials allows the specific properties of each component to be optimized to meet the particular requirements of an application.

[0050] According to a variant of the invention, the plastic material injected during the injection step is a loaded polypropylene.

[0051] Filled polypropylene, for example with additives such as glass, carbon or mineral fibres, offers increased mechanical strength.

[0052] According to another variant of the invention, the plastic material injected during the injection step is an unfilled polypropylene.

[0053] Unfilled polypropylene, on the other hand, retains more flexibility than filled polypropylene.

[0054] According to an optional feature, the method as described herein comprises a cutting step before the positioning step.

[0055] The cutting stage involves cutting the decorative layer according to the specific shape and dimensions of the finished part, thus ensuring a precise fit during the injection stage.

[0056] According to an optional feature, the method as described herein comprises a finishing step after the injection step.

[0057] A finishing step may indeed occur after the injection step. This can involve various post-molding treatments of the molded part, such as machining to remove residual pieces of plastic or resizing the decorative layer as needed. This step ensures that the final part meets the required quality standards and specifications, both aesthetically and functionally.

[0058] According to another aspect of the invention, a molded part for a motor vehicle is obtained by the manufacturing method as described herein.

[0059] This molded part thus comprises at least one structural element made of plastic material and a decorative layer which comprises an appearance layer, a foam layer and a barrier layer.

[0060] According to an optional characteristic, the thickness of the foam layer of the molded part is between 30% and 60% of its initial thickness before molding.

[0061] In order to determine the thicknesses of the various layers in the finished part, it is necessary to make a cross-section through the thickness of the casting. The thickness of the various layers is then measured in this section.

[0062] The barrier layer of the molded part is melted into the plastic structural element. This feature can be seen with some high-precision imaging instruments.

[0063] Thanks to this process, the molded parts can integrate a decorative layer offering both a pleasant visual appearance and a soft and pleasant feel.

[0064] Other characteristics, details and advantages of the invention will emerge more clearly on reading the description which follows on the one hand, and examples of embodiment given for informational and non-limiting purposes with reference to the appended drawings on the other hand, in which:

[0065] [Fig. 1] is a cross-section of a portion of a casting manufactured by the manufacturing method according to the invention.

[0066] [Fig. 2] is a cross-section of a decorative layer before its use in the manufacturing method according to the invention.

[0067] [Fig. 3] is a schematic representation of a mold and a decorative layer positioning step of the manufacturing method according to the invention.

[0068] [Fig. 4] is a schematic representation of an injection step of the manufacturing method according to the invention.

[0069] [Fig. 5] is a schematic representation of the molded part as obtained once the manufacturing method according to the invention has been implemented. The characteristics and variants of the invention may be combined with each other, in various combinations, provided that they are not incompatible or mutually exclusive. In particular, variants of the invention may be imagined comprising only a selection of characteristics described below in isolation from the other characteristics described, if this selection of characteristics is sufficient to confer a technical advantage and / or to differentiate the invention from the state of the prior art.

[0070] In the figures, elements common to several figures retain the same reference.

[0071] Figure 1 is a partial cross-section of a molded part 1 manufactured by the manufacturing method according to the invention.

[0072] The molded part 1 is a part of a motor vehicle interior. The molded part 1 may be any type of part of the motor vehicle interior, for example an armrest, a console or an element of a dashboard or a dashboard.

[0073] This molded part 1 comprises a decorative layer 2 and a plastic structural element 3. The decorative layer 2 gives the molded part 1 an aesthetic appearance and a specific texture. In this embodiment, the decorative layer 2 is applied to one of the surfaces of the plastic structural element 3. As a general rule, the surface provided with the decorative layer 2 is the one visible and / or accessible to the user. The other surface is called technical and is oriented towards volumes inaccessible to the user of the vehicle.

[0074] The manufacturing process of this molded part 1 is broken down into several consecutive steps: a step of positioning the decorative layer 2 in a mold 7 and a step of injecting the plastic material 8 into the mold 7, which will form the plastic structural element 3 of the molded part 1 and bond this plastic structural element 3 to the decorative layer 2.

[0075] The method may also optionally include two additional steps: a step of cutting the decorative layer 2 before the positioning step, as well as a finishing step after the injection step.

[0076] The decorative layer 2 is made up of three sub-layers: an appearance layer 4, a foam layer 5 and a barrier layer 6. The appearance layer 4 is positioned facing the exterior so as to constitute the part visible to the user of the decorative layer 2. The barrier layer 6 is a sheet of the decorative layer 2 which is in contact with the plastic structural element 3. The foam layer 5 is located between the barrier layer 6 and the appearance layer 4.

[0077] The 4th layer of appearance aims to provide a pleasant visual and tactile experience for the user. Different materials can be used for this, such as plastic-coated fabric, genuine leather, or synthetic leather.

[0078] The foam layer 5 is essential to ensure a soft feel to the touch of the molded part 1; it can be made from a variety of materials commonly used in foam production. The minimum residual thickness of this foam layer 5 after implementing the method of the invention is on average 2.25 mm for an initial thickness of 3 mm, i.e. a compression of around 25%. This minimum residual thickness makes it possible to maintain a soft texture of the decorative layer 2.

[0079] The barrier layer 6 is represented by a dotted line in Figure 1. This barrier layer 6 fuses with the plastic material 8 during the injection step. This characteristic can be visible in particular using certain high-precision imaging instruments.

[0080] It is also possible to verify that the molded part 1 was manufactured by the method of the invention, rather than by gluing, by taking a tab, then carrying out delamination to remove the decorative layer 2 from the molded part 1, and by observing the absence of glue residue on the plastic structural element 3.

[0081] The plastic structural element 3 makes it possible to give the shape to the molded part 1. This plastic structural element 3 is composed of the plastic material 8. Various types of plastic material can be used, for example filled or unfilled polypropylene, polycarbonate, acrylonitrile butadiene styrene (ABS) or a mixture of these materials.

[0082] Figure 2 is a cross-section of the decorative layer 2 before its use in the manufacturing method according to the invention.

[0083] The decorative layer 2 has a thickness between 2.9 mm and 10.4 mm. This thickness is the result of adding the thicknesses of the different layers that compose it. Among these components is the appearance layer 4, which must have a thickness between 0.7 mm and 1.4 mm, which ensures its strength during injection molding while preserving its aesthetic appeal and tactile comfort. This appearance layer 4 can be made of plastic-coated fabric, genuine leather, or synthetic leather. These materials are ideal for forming the appearance layer 4 due to their robustness, tactile comfort, and visual appeal.

[0084] Next is the foam layer 5, which has a thickness between 3 mm and 8 mm. Its density must be between 60 kg / m3 and 100 kg / m3. These characteristics guarantee optimal resistance to compression during the injection stage, thus preserving its soft appearance and improving the comfort and aesthetics of the final molded part 1.

[0085] Finally, the barrier layer 6 has a thickness between 0.2 mm and 1 mm. It can be made from different types of synthetic material, such as polyester or polypropylene. These materials provide effective protection against heat during the injection step and promote robust adhesion with the plastic structural element 3.

[0086] Figure 3 is a schematic representation of the positioning step of the manufacturing method according to the invention.

[0087] During this step, a mold must be used. The mold 7 shown in this figure is not the only possible model, and other types of molds can be used to carry out the different steps of the process.

[0088] The mold 7 illustrated comprises at least two parts: a first part 9 and a second part 10. The first part 9 of the mold is equipped with an injection orifice 11. Although there is only one injection orifice 11 in this embodiment, it is possible to have several injection orifices 11 in other configurations, in particular for the manufacture of large molded parts 1, in order to ensure that the plastic material 8 completely fills the mold 7.

[0089] The first part 9 of the mold also includes a container 12 for plastic material 8, fluidly connected to the injection orifice 11. This container 12 contains the plastic material 8 which, in a subsequent step, will form the plastic structural element 3 of the molded part 1. The plastic material 8 used may be of different types, such as polypropylene (filled or not), polycarbonate, acrylonitrile butadiene styrene (ABS), or a mixture of these materials.

[0090] The first part 9 of the mold 7 comprises a first molding surface 13, as well as a first connecting surface 14 and a second connecting surface 15. The second part 10 of the mold 7 also comprises a second molding surface 16, as well as a third connecting surface 17 and a fourth connecting surface 18.

[0091] During the positioning step, the first part 9 and the second part 10 of the mold 7 are spaced apart from each other to allow the placement of the decorative layer 2. This decorative layer 2, previously cut to correspond to the shape of the mold, is placed in the mold 7. The appearance layer 4 of the decorative layer 2 is arranged in contact with the mold 7, more precisely, in contact with the second molding surface 16. The barrier layer 6 is positioned facing the first molding surface 16 so as to be in contact with the plastic material 8 during the injection step.

[0092] Figure 4 is a schematic representation of the injection step of the manufacturing method according to the invention.

[0093] During this injection step, the first part 9 and the second part 10 of the mold are positioned in contact with each other. More precisely, the connecting surfaces are in mutual contact. It should thus be understood that the first connecting surface 14 is in contact with the third connecting surface 17, and the second connecting surface 15 is in contact with the fourth connecting surface 18. This connection makes it possible to create a closed space between the first molding surface 13 and the second molding surface 16, thus forming a molding zone 19.

[0094] During this step, the plastic material 8 contained in the reservoir 12 of plastic material 8 is injected into this molding zone 19 via the injection orifice 11. The plastic material 8 will then fill the molding zone 19 by matching the decorative layer 2 and will form the plastic structural element 3 of the molded part 1.

[0095] During the injection step, certain conditions must be met. The injection pressure must be between 300 and 500 bars. The choice of pressure results from an analysis carried out by the inventors with the aim of correcting the appearance defects of the parts manufactured according to the prior art methods. This maximum pressure of 500 bars can be problematic, in particular when manufacturing large molded parts 1. Indeed, the plastic material 8 might not correctly fill the molding zone 19, particularly in the areas far from the injection orifices 11, or in the areas with fine details or thin walls.

[0096] To overcome this problem, several injection ports 11 could be used on the mold 7. This would allow the plastic material 8 to be distributed more uniformly across the molding zone 19, thus ensuring complete and uniform filling of this molding zone 19.

[0097] The temperature of the injected plastic material 8 must be maintained within a range of 200 to 250°C, at the time it is injected. This temperature must not be too low in order to allow adequate fusion of the plastic material 8 with the barrier layer 6, but it must not be too high in order to avoid damaging the foam layer 5 and to preserve the soft feel of the decorative layer 2.

[0098] Regarding the temperature of mold 7, it must be maintained around 25°C, with a tolerance of + / - 5°C, in order to preserve the properties of decorative layer 2 such as its appearance and softness.

[0099] After the injection step, the molded part 1 is cooled and then extracted from the mold 7.

[0100] Figure 5 is a schematic representation of the molded part 1 as obtained after the injection step of the manufacturing method according to the invention.

[0101] A molded part 1 in accordance with the invention is thus obtained, which comprises a decorative layer 2. This decorative layer 2 retains its characteristics, such as its soft feel. Indeed, after using the method according to the invention, an average compression of 20 to 25% of the initial thickness of the foam layer 5 is observed.

[0102] After the molded part 1 is removed from the mold, the molded part 1 may undergo a finishing step. During this step, the molded part 1 may be machined to remove unwanted plastic residue 8 from the molded part 1. This finishing step may also include precise cutting processes to perfect the shape and contours of the decorative layer 2.

[0103] The molded part 1 as obtained after the manufacturing process thus comprises at least one structural element made of plastic material 3 and a decorative layer 2 which comprises an appearance layer 4 made of synthetic material, a foam layer 5 and a barrier layer 6.

[0104] The decorative layer 2 of the molded part 1 has a thickness of between 30% and 60% of its initial thickness before molding. The present invention thus proposes a method for manufacturing a molded part comprising at least one decorative layer. The method makes it possible to limit the number of steps while retaining the tactile and visual properties of the decorative layer.

[0105] The present invention cannot, however, be limited to the means and configurations described and illustrated here and it also extends to any equivalent means and configuration as well as to any technically effective combination of such means.

Claims

CLAIMS:

1. Method for manufacturing a part (1) shaped by at least one molding operation, the molded part (1) comprising at least one decorative layer (2) made at least in part with a synthetic material, comprising the following successive steps: step of positioning the decorative layer (2) in a mold (7), step of injecting a plastic material (8) into the mold (7), characterized in that the injection step is carried out according to the following conditions: an injection pressure varying between 300 and 500 bars, a temperature of the injected plastic material (8) between 200 and 250 °C, a temperature of the mold (7) maintained at 25 °C + / - 5 °C.

2. Method according to claim 1, wherein the decorative layer (2) comprises an appearance layer (4), a foam layer (5) and a barrier layer (6).

3. Method according to claim 2, in which the barrier layer (6) of the decorative layer (2) has a thickness of between 0.2 mm and 1 mm, measured before the injection step.

4. Method according to any one of claims 2 or 3, in which the barrier layer (6) of the decorative layer (2) is made of polyester or polypropylene.

5. Method according to any one of claims 2 to 4, in which the foam layer (5) of the decorative layer (2) has a thickness of between 2 mm and 8 mm, measured before the injection step.

6. Method according to any one of claims 2 to 5, wherein the foam layer (5) of the decorative layer (2) has a density of between 60 kg / m 3 and 100 kg / m 3 , determined before the injection step.

7. Method according to any one of claims 2 to 6, in which the appearance layer (4) of the decorative layer (2) has a thickness of between 0.7 mm and 1.4 mm, measured before the injection step.

8. A method according to any one of claims 2 to 7, wherein the appearance layer (4) of the decorative layer (2) is a plastic-coated fabric, genuine leather or synthetic leather.

9. Method according to any one of claims 2 to 8, in which the barrier layer (6) of the decorative layer (2) is in contact with the plastic material (8) during injection while the appearance layer (4) of the decorative layer (2) is in direct contact with the mold (7).

10. Molded part (1) for a vehicle obtained by the manufacturing method according to any one of claims 1 to 9.

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