OVERMOLDING METHOD ON A PLASTIC INSERT AND AUTOMOTIVE PART OBTAINED BY THIS METHOD

Abstract

A method for manufacturing a composite automotive part by overmolding, on at least one surface of an insert comprising a first plastic material, a layer of a second thermoplastic material, said method comprising the following successive steps: a) a step of positioning said insert in a mold, and b) a step of molding said second thermoplastic material onto said insert; at least one of said first and second materials comprising an additive, said additive comprising a polymer onto which carboxylic anhydride monomers are grafted.

Description

[0001] The present invention relates to the manufacture of automotive parts from materials based on one or more (thermo)plastic compounds. It particularly relates to a process for manufacturing automotive parts, and more specifically, body parts.

[0002] A motor vehicle may include numerous plastic parts, usually manufactured using an injection molding process, which incorporate one or more inserts. These inserts are pre-formed parts incorporated into, and / or integral with, the molded part. They generally serve to reinforce the molded part and / or to subsequently attach mechanical components. These inserts can be made of steel, aluminum, or composite plastics. The resulting parts may be structural or semi-structural components of the motor vehicle in question. Thus, the overmolding of the parts is not achieved by simultaneously injecting the insert and the layer that incorporates it. However, the overmolding can be carried out through successive injections.Overmolding can also be achieved using separate molds, each with a cavity, or a single mold with a rotating moving part (rotary cavity mold) which includes at least 2 separate cavities and which allows for the production of both an overmolded part and an insert during the same injection.

[0003] It is, of course, very important for the quality of the manufactured parts to ensure a secure bond between the insert and the plastic material that incorporates or is attached to it, a material commonly referred to as "overmolding material" due to the most frequently used manufacturing technique. This bonding can be a mechanical connection. For example, if the insert is drilled, the overmolding material flows into the hole and creates a rivet-like bond.

[0004] This bonding can be achieved through adhesion of the contacting surfaces. For example, chemical binders such as resins or adhesives can be applied, particularly to the contact surfaces of the insert. For instance, patent EP1313780B1, held by DuPont, describes a polypropylene material onto which maleic anhydride (MA) molecules are grafted. This material cannot be used as an overmolding material because its rheological characteristics prevent it from being directly injected using an injection molding machine. Furthermore, its mechanical properties are too weak for the production of a structural or semi-structural part.

[0005] These mechanical or chemical fastening methods are often weak points of the composite part, particularly when subjected to stress from impacts in the case of automotive parts.

[0006] Adhesion can also be achieved through a chemical reaction between the insert and overmolding materials. In this case, satisfactory adhesion can only be obtained between an insert and a compatible overmolding material, i.e., one of the same chemical nature (PP / PP, PA / PA), and / or by melting the materials. Thus, manufacturing composite parts with one or more inserts involves either additional steps (e.g., heating, bonding, drilling, surface treatment) or limitations in the choices and possible (compatible) combinations of materials used in the insert and overmolding. Document JP 3 377 010 B2 discloses a method for manufacturing a composite automotive part by overmolding, on at least one surface of an insert comprising a first plastic material, a layer of a second thermoplastic material. This method comprises the following successive steps: a) a step of positioning said insert in a mold, and b) a step of molding said second thermoplastic material onto said insert; at least one of said first and second materials comprising an additive, said additive comprising a polymer onto which carboxylic anhydride monomers are grafted; said first and second materials being respectively polyamide-based and polypropylene-based, or vice versa. In another example disclosed in this document, talc is used as a mineral filler. Description

[0007] The invention aims to overcome one or more of these disadvantages by providing, in particular, a method for manufacturing a composite part by overmolding it onto a plastic insert. According to one embodiment of the invention, said method relates to manufacturing a composite automotive part by overmolding, onto at least one surface of an insert comprising a first plastic material, a layer of a second thermoplastic material. Said method comprises the following successive steps: a) a step of positioning said insert in a mold, and b) a molding step preferably by injection of said second thermoplastic material onto said insert; at least one of said first and second materials comprising an additive, said additive comprising a polymer onto which carboxylic anhydride monomers are grafted.

[0008] It is thus possible to produce composite parts using chemically incompatible materials of different natures and with an insert whose material is not remelted (deformable). This process combines the adhesion step between the insert and the overmolding material with the molding step of forming the composite part. Therefore, the composite part can be produced in a single overmolding operation by injection or compression. Furthermore, the process according to the invention allows for better adaptation of the overmolding material (or "second material") to the desired requirements of the automotive part, such as its Young's modulus (by varying, for example, the type or percentage of filler) and / or its impact resistance (by varying, for example, the elastomer content) and / or its rheological behavior (by choosing, for example, the type or grade of the plastic matrix).Thus, according to a preferred aspect of the invention, the first material and the second material are materials of different natures, preferably not capable of satisfactorily adhering to each other when subjected to pressure and temperature conditions typical of injection molding. Satisfactory adhesion can be defined by the international standard ASTM D5868.

[0009] Advantageously, the said first and second materials are respectively based on polyamide and polypropylene, or vice versa.

[0010] The overmolding material is a plastic. Preferably, this material is chosen so that it can be injection molded. It can advantageously be based on a polyolefin selected from the group consisting of polypropylene (PP), high- or low-density polyethylene (PE), and / or propylene-ethylene copolymers. These materials can be virgin or recycled.

[0011] The expression "based on" designates a material comprising at least 50% by weight of the compound identified following this expression.

[0012] Preferably the plastic material comprises at least 60% polypropylene, more particularly at least 70% and preferably at least 80% by weight of olefin relative to the total weight of the overmolding material.

[0013] The additive included in the first and / or second material comprises at least one, and preferably several (for example, two), additives. This additive is selected from the group of polymers onto which carboxylic anhydride monomers, and more particularly maleic anhydride and its derivatives, are grafted. The polymer may be of a similar or identical nature or structure to the polymer forming the basis of the material to which it is attached. Advantageously, these polymers are selected from the group consisting of polypropylene, high- or low-density polyethylene (PE), propylene-ethylene copolymers, and / or a thermoplastic elastomer based on styrene block copolymers (TPS) such as Styrene Ethylene Butadiene Styrene (SEBS) (polystyrene-β-poly(ethylene-butylene)-β-polystyrene). The percentage by weight of maleic acid monomer relative to the total weight of the additive can range from 0.5% to 10%.

[0014] Preferably, the additive(s) are present in proportions ranging from 0.1 to 25%, advantageously from 2 to 25%, more particularly from 0.1 to 20%, for example 2 to 20%, by mass relative to the total weight of said material. Advantageously, this proportion is approximately 10% ± 2% by mass.

[0015] When the additive includes SEBS, it can advantageously be present in proportions ranging from 0.1 to 10% by mass relative to the total mass of the material.

[0016] When the additive includes grafted PP, it can advantageously be present in proportions ranging from 2 to 25% by mass relative to the total mass of the material.

[0017] According to a particularly preferred embodiment of the invention, the additive comprises, or is made up of, a mixture of SEBS and PP grafted with maleic acid monomers. The relative proportions of these constituents with respect to the total mass of the material may be approximately 0.1% and 15% by mass, respectively. According to a preferred embodiment, the second material (or overmolding material) comprises the additive.

[0018] Preferably the overmolding material comprises a mineral or organic filler, for example quartz, mica, kaolin, calcium phosphate, feldspar, steatite, chalk, talc, carbon black, synthetic silica, barium sulfate, barium ferrite, wood or fruit peel flour, cellulose pulp, glass fibers, carbon fibers, widely used hollow glass microspheres, synthetic silica, nanometric clay, flax, etc., as well as mixtures thereof.

[0019] This load can vary from 1 to 49.9% by weight depending on the nature of the load, for example from 3 to 30%, and more specifically from 1 to 40% by weight relative to the weight of the overmolding material. Preferably, this load, by weight, is between 5 and 40%, preferably between 5 and 30%, for example 10% and preferably 12% relative to the total weight of the overmolding material.

[0020] Preferably the filler includes a mineral filler, and in particular talc.

[0021] It is also advantageous for the overmolding material to include an elastomeric material, for example an EPR-type copolymer ( Ethylene Propylene Rubberor ethylene propylene rubber) which may be present in a proportion ranging from 5 to 35% by mass of the total mass of the overmolding material. The quantity of ethylene propylene rubber is advantageously 5 to 15%, preferably 10%, by weight relative to the total weight of the plastic. The overmolding material may also include a colorant, such as carbon black, for example, in proportions of 0.5% by mass.

[0022] The second material (or overmolding material) may therefore comprise, or consist of, a propylene / ethylene copolymer and / or an elastomer, and / or a mineral filler, such as talc. Advantageously, said overmolding material comprises, or consists of, a mixture of polypropylene, polyethylene, talc, ethylene propylene rubber, and an additive. The amount of polypropylene in the overmolding material is advantageously at least 50% by weight relative to the total weight of said material. The amount of ethylene propylene rubber is advantageously 5 to 15%, preferably 10%, by weight relative to the total weight of the plastic.

[0023] According to the invention, the overmolding layer of said composite part is made of a polymer comprising, or being made of, a propylene polyethylene-based P / E copolymer comprising 12% by mass of talc and 10% by mass of an EPR type elastomer material, 0.2% to 0.5% by mass of SEBS and 5% to 10% by mass of polypropylene grafted by maleic anhydride monomers.

[0024] Preferably, the insert and / or overmolding material does not contain substantially any metal ions. For example, it contains less than 3% of carboxylic acid functions neutralized by one or more metal ions.

[0025] Preferably, the overmolding material can be manufactured by a standard extrusion process where the base polymer is softened or liquefied and then mixed with the other components in predetermined proportions before being extruded and optionally subjected to a granulation step to obtain solid granules. Advantageously, these granules can be used directly in the manufacture of the composite part. Alternatively, the overmolding material can also be obtained during the molding of the composite part by adding and mixing its various components in the required proportions in the screw of the injection molding machine.

[0026] The insert is preferably a component made of a plastic material, advantageously based on polyamides such as polycaprolactams: [NH-(CH2)5-CO]n (PA-6), and polyhexamethylene adipamides: [NH-(CH2)6-NH-CO-(CH2)4-CO]n (PA-6,6). The plastic material (or primary material) forming all or part of the insert may also be based on polypropylene and / or polyethylene. This component may include an organic or mineral filler as described above.

[0027] When the insert has a structural, semi-structural, or reinforcing function, the filler may comprise, or be made of, a material capable of fulfilling such a function, such as glass or carbon fibers. The proportions of this filler may vary from 10 to 95%, preferably from 15 to 90%, advantageously from 20 to 85%, and more particularly from 75 to 85%, by mass of the total mass of the material of the insert thus reinforced.

[0028] As mentioned previously, the shape and function of the insert can vary. In one particular embodiment, it can be the rigid part of a beam designed to be placed behind a vehicle's bumper. Such a beam supports the bumper and absorbs deformation during an impact. The beam therefore generally comprises a rigid part (insert) and a more flexible part (moldable material). The rigid part provides support and limits deformation during high-speed impacts. The more flexible part is specifically designed to absorb low-speed impacts. Typically, the rigid part is positioned at the front, i.e., in contact with the bumper, and the flexible part is positioned between the rigid part and the car's steel body.

[0029] During the positioning step of the insert according to the process of the invention, the insert is not in a molten state and / or is at room temperature and / or is not subjected to preheating.

[0030] Advantageously, the insert is either not heated or is heated to a temperature below the melting point of the primary material. For example, the temperature of the fiberglass-reinforced PA insert when placed in the mold is ambient temperature or can reach 180°C, for example, ranging from 50 to 180°C. Heating can be achieved using infrared lamps.

[0031] To further improve the adhesion between the external surface of the insert and the overmolding material, it is possible to carry out one or more preliminary steps of treatment of this surface by chemical or mechanical means.

[0032] An example of a chemical surface treatment that enhances adhesion is flame treatment, where the treated surface is subjected to the application of a flame. This flame treatment step is known within the technical field of the invention and can be carried out using a natural gas burner under slightly oxidizing or non-oxidizing conditions.

[0033] An example of physical surface treatment of the insert that can help strengthen adhesion is the application of a sanding or sandblasting step.

[0034] The invention also relates to a composite part, in particular a part of a motor vehicle, comprising an insert, said insert comprising, or being made of, a first plastic material, and a layer of a second thermoplastic material, characterized in that at least one of said first and second materials comprises an additive, said additive comprising a polymer onto which carboxylic anhydride monomers are grafted. The materials forming said composite part and their respective proportions may be as described in this application. According to a preferred embodiment, said composite part comprises an adhesion surface between the insert and the second material, this surface substantially not comprising any materials other than the constituent materials of the first and second materials. The composite part according to the invention can take on any shape, in particular the shapes of parts used in the manufacture of motor vehicles.Preferably the part is a structural or semi-structural part, such as a beam (e.g., a bumper beam).

[0035] The invention also relates to a composite part, in particular a part of a motor vehicle, obtained directly by the process of the invention, as well as to a motor vehicle comprising said part.

[0036] Another object of the invention is a plastic composition, preferably thermoplastic, comprising a polymer and a grafted additive, as described in this application. This composition is preferably injectable and intended for use in an injection molding process, particularly for the manufacture of motor vehicle parts.

[0037] Yet another object of the invention is the use of said plastic composition in the manufacture of composite parts, in particular composite parts for motor vehicles.

[0038] The invention will be better understood upon reading the accompanying figure, which is provided for illustrative purposes only and is not intended to be limiting, in which: The figure 1 is a diagram representing the respective position of the test specimens used to test the adhesion of the materials of a composite part according to the invention. EXAMPLES OF ACHIEVEMENTS An overmolding material according to the invention is made as follows :

[0039] In a standard twin-screw extruder, granules of a propylene / ethylene copolymer, with a P / E ratio of 80 / 20, are fed into the infeed hopper. The extruder allows the addition of compounds at approximately one-third of the extrusion stroke, once the initial polymer has melted. The following compounds are added: 12% by mass of talc; 10% by mass of EPR (PP 108MF10 sold to Saudi Basic Industries Corporation (SABIC), Le Monge - 22 place des Vosges, La Défense 5, 92979 Paris La Défense cedex, France); 0.2% by mass of SEBS grafted with maleic anhydride (type KRATON FG 1901G); and 10% by mass of AM-grafted PP of type Orevac CA 100.

[0040] Kraton FG polymers are maleic anhydride-grafted polymers. The grafting rate of these polymers is approximately 1.0 to 1.7% by mass. These polymers are sold by Kraton Performance Polymer Inc., 15710 John F. Kennedy Blvd., Houston, TX 77032, USA.

[0041] The OREVAC® CA100 polymer is a highly functionalized polymer with a high proportion of maleic anhydride sold by the company ARKEMA, Immeuble Défense Ouest 420, rue d'Estienne d'Orves 92705 COLOMBES Cedex, France.

[0042] The granules obtained after granulation at the exit of the extruder (T° approx. 220°C) therefore contain the % given above. Production of a composite part according to the invention:

[0043] A composite beam intended to be positioned behind the bumper of a motor vehicle is manufactured.

[0044] A PA-6 polyamide part, or beam, is produced by pultrusion. This part contains 80% glass fibers by mass. This insert is heated to 150°C on its surface and placed in a standard injection mold used for manufacturing automotive parts.

[0045] The overmolding material described above is poured into the hopper to feed the plasticizing screw (worm type). This screw is heated and temperature-controlled via the plasticizing sleeve to 250°C to allow the material to transition to a molten (formable) state.

[0046] The material is fed to the front of the plasticizing screw to be metered and injected under high pressure into the mold, which has the shape of the desired part. This material is injected directly onto the surfaces of the insert exposed by the mold. The mold is kept at a temperature lower than the processing temperature, i.e., around 40 to 50°C. The pressure is maintained for 10 to 20 seconds (10 seconds in this case) to compensate for material shrinkage during cooling. The part is cooled for a few seconds and then ejected.

[0047] The composite beam is thus obtained directly from the injection mold and comprises a more rigid part (the insert) and a more flexible part that is fixed directly onto the insert by overmolding. The adhesion of these two components to each other meets the required criteria. For example, the adhesion is considered satisfactory when there is no decohesion between the overmolded beam and the overmolding material after impact tests.

[0048] One protocol that can be applied to ensure the cohesion of the composite part is the application of an international standard residual lap shear stress test ("lap shear test"), such as that of ASTM D5868, to test specimens (tabs). The specimens are made of the same materials as the composite parts. The shape of the parts used is shown in the diagram. figure 1 .

[0049] Thus, rectangular PA bars (1) measuring 125x25 mm and 2 mm thick, comprising 83% glass fibers by mass, are introduced into a mold. A plastic composition according to the invention, comprising a polymer grafted with maleic anhydride, is injected. The press used is 200T and the molding temperature is 80°C. The overmolded part is a rectangular bar (2) with the same dimensions (125x25 mm) as bar (1) but with a thickness of 3 mm. The overmolding occurs by covering only one of the surfaces of the bars and is as shown in the diagram. figure 1 The overlap area is 25 x 25 mm. These specimens are then characterized in tensile strength (using a tensile testing machine) at a rate of 13 mm / min. The stress value must be greater than 1 MPa. The test must be successfully repeated at least 5 times.

[0050] The invention is not limited to the embodiments presented, and other embodiments will be readily apparent to those skilled in the art. In particular, it is possible to use other plastics to produce either the insert or the injectable material, possibly in combination with the materials described above. This material may be chosen from thermosetting materials based on, or comprising, polyester, epoxy, or vinyl ester (VE).This material can also be chosen from among polyolefins, for example from the group consisting of acrylonitrile butadiene styrene (ABS), polyamides such as polycaprolactams: [NH-(CH2)5-CO]n (PA-6), and polyhexamethylene adipamides: [NH-(CH2)6-NH-CO-(CH2)4-CO]n (PA-6,6), polycarbonates (PC), high-density polyethylene (HDPE), low-density polyethylene (LDPE), amorphous or crystalline polyethylene terephthalate (PET), polymethyl methacrylate (PMMA), polypropylenes (PP), "crystal" polystyrenes (PS), rigid polyvinyl chloride (PVC), and their mixtures. It is also possible to use compression molding instead of injection. This alternative uses a pre-impregnated material such as a resin-pre-impregnated fabric (also called a matrix) which is applied to the insert and molded.

Claims

1. Process for manufacturing a composite automobile part by overmoulding, over at least one surface of an insert comprising a first plastic material, a layer of a second thermoplastic material, said process comprising the following successive steps: a) a step of positioning said insert in a mould, and b) a step of moulding said second thermoplastic material over said insert; at least one of said first and second materials comprising an additive, said additive comprising a polymer to which carboxylic anhydride monomers are grafted; said first and second materials being respectively based on polyamide and based on polypropylene, or vice versa; and said second material comprising talc as mineral filler; said process being characterised in that said second material is made of a polymer comprising a P / E copolymer based on propylene and polyethylene comprising 12 % by weight of talc and 10 % by weight of an EPR type elastomer material, from 0.2 % to 0.5 % by weight of SEBS and from 5 % to 10 % by weight of polypropylene grafted with maleic anhydride monomers.

2. Process according to claim 1, characterised in that said moulding step is an injection moulding step.

3. Process according to claim 1 or 2, characterised in that said additive is maleic anhydride and / or one of its derivatives, possibly in proportions ranging from 0.1 % to 20 %, advantageously from 2 % to 20 % by weight compared with the total weight of said first and / or said second material.

4. Process according to any one of claims 1 to 3, characterised in that said first or second material further comprises another additive comprising a thermoplastic polymer to which carboxylic anhydride monomers are grafted.

5. Process according to any one of claims 1 to 4, characterised in that said first material and said second material are materials of different type, preferably not likely to adhere to each other satisfactorily when subjected to typical injection moulding pressure and temperature conditions.

6. Process according to any one of claims 1 to 5, characterised in that the second material comprises a propylene / ethylene copolymer and / or an elastomer.

7. Process according to any one of claims 1 to 6, characterised in that during the positioning step, the insert is not in molten state and / or is at ambient temperature.

8. A composite automobile part comprising an insert comprising a first plastic material and a layer of a second thermoplastic material, characterised in that at least one of said first and second materials comprises an additive, said additive comprising a polymer to which carboxylic anhydride monomers are grafted, said first and second materials being respectively based on polyamide and based on polypropylene, or vice versa; and said second material comprising talc as mineral filler; and characterised in that said second material is made of a polymer comprising a P / E copolymer based on propylene and polyethylene comprising 12 % by weight of talc and 10 % by weight of an EPR type elastomer material, from 0.2 % to 0.5 % by weight of SEBS and from 5 % to 10 % by weight of polypropylene grafted with maleic anhydride monomers.

9. The automobile part according to Claim 8, wherein said part is a structural or semi-structural part, such as a beam, for example a bumper beam.