PROCESS FOR OVERMOULDING OVER A PLASTIC INSERT AND AUTOMOBILE PART OBTAINED BY THIS PROCESS

Abstract

A process for manufacturing a composite automobile part by overmoulding, over at least one surface of an insert (1) comprising a first plastic material, a layer of a second thermoplastic material, comprises the following successive steps: a) a step of positioning said insert (1) 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 comprises an additive, said additive comprising a polymer to which carboxylic anhydride monomers are grafted. Said first and second materials are respectively based on polyamide and based on polypropylene, or vice versa and said second material comprises talc as mineral filler.

Claims

1. A process for manufacturing a composite automobile part by overmoulding, a layer of a second thermoplastic material over at least one surface of an insert comprising a first plastic 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, wherein at least one of said first plastic material and said second thermoplastic materials comprises an additive, said additive comprising a polymer to which carboxylic anhydride monomers are grafted; wherein said first plastic material and said second thermoplastic materials are respectively based on polyamide and based on polypropylene, or vice versa; and wherein said second thermoplastic material comprises talc as mineral filler.

2. The process according to claim 1, wherein said moulding step is an injection moulding step.

3. The process according to claim 1, wherein said additive is maleic anhydride and/or one of its derivatives.

4. The process according to claim 1, wherein said polymer to which carboxylic anhydride monomers are grafted is selected from the group consisting of polypropylene, high or low density polyethylene, copolymers of propylene and ethylene, a thermoplastic elastomer based on styrene-block-copolymers, and combinations thereof.

5. The process according to claim 1, wherein said second thermoplastic material comprises said additive.

6. The process according to claim 1, wherein said first plastic material or said second thermoplastic material further comprises another additive comprising a thermoplastic polymer to which carboxylic anhydride monomers are grafted.

7. The process according to claim 1, wherein said first plastic material and said second thermoplastic material are materials of different type.

8. The process according to claim 1, wherein the second thermoplastic material comprises a propylene/ethylene copolymer and/or an elastomer.

9. The process according to claim 1, wherein during the positioning step, the insert is not in a molten state and/or is at ambient temperature.

10. The process according to claim 1, wherein said second thermoplastic 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.

11. A composite automobile part comprising an insert comprising a first plastic material and a layer of a second thermoplastic material, wherein at least one of said first plastic material and said second thermoplastic material comprises an additive, said additive comprising a polymer to which carboxylic anhydride monomers are grafted, wherein said first plastic material and said second thermoplastic materials is respectively based on polyamide and based on polypropylene, or vice versa; and wherein said second thermoplastic material comprises talc as mineral filler.

12. The process according to claim 3, wherein said maleic anhydride or its derivative is present in a proportion ranging from 0.1% to 20% by weight compared with the total weight of said first plastic material and/or said second thermoplastic material.

13. The process according to claim 12, wherein said maleic anhydride or its derivative is present in a proportion ranging from 2% to 20% by weight compared with the total weight of said first plastic material and/or said second thermoplastic material.

14. The process according to claim 4, wherein the polymer is (polystyrene-b-poly(ethylene-butylene)-b-polystyrene.

15. The process according to claim 7, wherein said first plastic material and said second thermoplastic material are materials not likely to adhere to each other satisfactorily when subjected to typical injection moulding pressure and temperature conditions.

16. The process according to claim 10, wherein said second thermoplastic material is made of a polymer consisting of 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.

Description

EXAMPLES OF EMBODIMENT

[0042] An Overmoulding Material According to the Invention is Made as Follows:

[0043] Granules of a propylene/ethylene copolymer, of respective proportions P/E 80/20, are poured into the input hopper of a standard twin-screw extruder. The extruder can be used to add compounds about one third of the way along the extrusion path when the initial polymer has melted. Thus, the following are added: [0044] 12% by weight of talc; [0045] 10% by weight of EPR (PP 108MF10 sold by Saudi Basic Industries Corporation (SABIC), Le Monge-22 Place des Vosges, La Défense 5, 92979 Paris La Defense cedex, France); [0046] 0.2% by weight of SEBS grafted with maleic anhydride (type KRATON FG 1901G); and [0047] 10% by weight of PP grafted with AM of type Orevac CA 100.

[0048] Kraton FG type polymers are polymers grafted by adding maleic anhydride. The grafting rate of these polymers is about 1.0% to 1.7% by weight. These polymers are sold by Kraton Performance Polymer Inc, 15710 John F Kennedy Blvd, Houston, Tex. 77032, USA.

[0049] The polymer OREVAC® CA100 is a highly functionalised polymer with a high proportion of maleic anhydride sold by ARKEMA, Immeuble Défense Ouest 420, rue d'Estienne d'Orves 92705 COLOMBES Cedex, France.

[0050] The granules obtained after granulation at the extruder output (temperature about 220° C.) therefore contain the above-mentioned percentages.

[0051] Manufacture of a Composite Part According to the Invention:

[0052] A composite beam intended to be positioned behind a motor vehicle bumper is manufactured.

[0053] A part, or beam, made of polyamide PA-6 PA is produced by pultrusion. It contains 80% by weight of glass fibres. This insert is heated to 150° C. on the surface and is placed in a standard injection mould used for the manufacture of automobile parts.

[0054] The overmoulding material described above is poured into the hopper to supply the plasticising screw (worm screw type). It is heated and temperature-controlled by the plasticising barrel at 250° C. to change to molten state (deformable).

[0055] The material moves to the front of the plasticising screw to be metered and injected at high pressure inside the mould which has the shape of the required part. This material is injected directly onto the surfaces of the insert exposed by the mould. The mould temperature is controlled at a temperature below the transformation temperature, i.e. at about 40° C. to 50° C. The pressure is maintained for 10 to 20 seconds (in this case 10 seconds) to compensate for shrinkage of the material during cooling. The part is cooled for a few seconds and then ejected.

[0056] The composite beam is thus obtained directly at the output of the injection mould and comprises a more rigid section (the insert) and a more flexible section which is attached directly to the insert by overmoulding. The adhesion of these two components together meets the required criteria. For example, the adhesion is considered satisfactory when there is no decohesion between the overmoulded beam and the overmoulding material after impact tests.

[0057] A protocol which can be applied to ensure cohesion of the composite part is application on specimens (tabs) of an international standard lap shear test such as that of standard ASTM D5868. The test specimens are made of the same materials as those of the composite parts. The shapes of the parts used are shown in FIG. 1.

[0058] Thus, rectangular PA bars (1) of dimensions 125×25 mm and thickness 2 mm comprising a proportion of 83% glass fibres by weight are introduced into a mould. A plastic composition according to the invention comprising a polymer grafted with maleic anhydride is injected. A 200 T press is used and the moulding temperature is 80° C. The overmoulded part is a rectangular bar (2) of the same dimensions 125×25 mm as the bar (1) but of thickness 3 mm. Overmoulding only covers one of the surfaces of the bars and is as shown on the diagram of FIG. 1. The coverage area is 25×25 mm. The tensile characteristics of these specimens are then measured (using a tensile testing machine) at a speed of 13 mm/min. The stress must be greater than 1 MPa. The test must be repeated successfully at least 5 times.

[0059] The invention is not limited to the embodiments described and other embodiments will be clearly apparent to those skilled in the art. In particular, other plastic materials can be used to make the insert or the injectable material, possibly with the materials described above. This material may be selected from the thermosetting materials based on, or comprising, polyester, epoxy or vinyl ester (VE). This material may also be selected from 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 polyethylenes (HDPE), low density polyethylenes (LDPE), amorphous or crystalline poly(ethylene terephthalates) (PET), poly(methyl methacrylates) (PMMA), polypropylenes (PP), “crystal” polystyrenes (PS), rigid polyvinyl chloride (PVC) and mixtures thereof. Compression moulding may also be used instead of injection moulding. This alternative uses a prepreg material such as a fabric preimpregnated with resin (also called matrix) which is applied over the insert and moulded.