FR2768961A1 - Blow molded and extruded component - Google Patents

Abstract

In the production of a hollow component by blow molding, the plastics material is reinforced by additives and/or it has a relatively low stretch. The material is co-extruded with a layer of another plastics material containing the reinforcement additives and/or with a relatively high stretch. In an Independent claim the molded product is a tank or an internal combustion motor air intake channel (10), molded with the silencer (12) and/or resonator. Preferred Features: The second plastics material, which can be free of the reinforcement additives, is the same as the initial material, or it can be incompatible with the first material to be co-extruded with an intermediate film to bond them together in layers. The second layer is at the inner or outer surface of the first layer, or it can be extruded between two layers of the first material. The reinforcement additive is pref. talc, at a rate of 5-50 wt.%. The second plastics material can be extruded between a layer of the first material and a plastics layer formed by recycled plastics materials. The materials can be extruded with a dampening layer. The technique uses an extruder which gives a continuous extrusion of the plastics layers.

Description

PROCESS FOR THE MANUFACTURE OF HOLLOW PRODUCTS BY EXTRUSION
BLOWING AND PRODUCTS THUS OBTAINED.

 The invention relates to a method of manufacturing hollow products by extrusion blow molding, as well as the products obtained by carrying out this method, in particular air intake ducts for internal combustion engine, tanks, and in general all products. or hollow body whose walls must have a certain rigidity.

 Document EP-A-0761 413 discloses a method of manufacturing by extrusion blow molding products such as air intake ducts which, for molding, are produced with silencers and / or resonators allowing 'absorb certain sound frequencies and reduce "mouth" noises on internal combustion engines in operation.

 The silencers and resonators used must comply with criteria of geometry, volume rigidity (ratio of a variation in volume and a variation in pressure, the variation in volume being caused by the variation in pressure) and natural frequency to absorb the sound energy at the desired frequencies, which makes it necessary to use for their molding plastics reinforced by inert fillers such as fibers, particles, etc. These reinforced materials, however, have a relatively low elongation capacity in the molten state (for example of the order of 100%), which does not allow them to be used in extrusion-blowing to manufacture conduits formed with silencers and / or integrated resonators.

 These products could be made of reinforced material using other means than extrusion-blowing, but the advantages linked to this technique would then be lost.

 The invention aims to provide a simple, effective and economical solution to this problem.

 It relates to a method of manufacturing by extrusion blow molding of products comprising hollow parts of relatively large volume made of reinforced plastic to have optimal characteristics of rigidity, mechanical resistance and / or natural frequency.

 It also relates to hollow bodies having the desired characteristics of geometry, rigidity, mechanical strength and / or natural frequency and which benefit from the advantages associated with manufacturing by extrusion blow molding.

 To this end, it proposes a method consisting in extruding a parison of plastic material inside a mold, closing the mold on the parison and injecting a pressurized gas into the parison to apply it to the walls. of the mold, characterized in that, said plastic material being reinforced by fillers and / or having a relatively low elongation capacity, it consists in co-extruding with this plastic material a layer of another plastic material comprising less filler of reinforcement and / or having a relatively high elongation capacity.

 It is noted, in the method according to the invention, that the loaded material is somehow carried by the other plastic material, which makes it possible to produce by extrusion blow-molding the same hollow products as with an unfilled plastic material, so that extrusion-blowing under the same conditions of a parison of charged material would result in holes in the areas where the material is greatly elongated during blowing.

 The co-extrusion of a layer of reinforced material and a layer of non-reinforced material or with a high elongation capacity, makes it possible to mold hollow products by extrusion blow-molding, at least some parts of which are formed of reinforced material. which is stretched clearly beyond its elongation limit and which however retains a desired rigidity and mechanical strength.

 Advantageously, the two aforementioned plastics are of the same nature or of the same type, so that they naturally adhere to one another. They can also be of different types or types, which generally leads to co-extruding them with an intermediate layer of a material ensuring adhesion.

According to another characteristic of the invention, the method also consists in co-extruding more than two layers of plastic material and for example
- a layer of uncharged material or with a high elongation capacity between two layers of charged material,
a layer of uncharged material or with a high elongation capacity between a layer of charged material and a layer of material obtained by recovering and grinding off plastic scraps from previously manufactured products, this layer of recycled material preferably being covered with 'a layer of the aforementioned charged material,
- A layer of a shock absorbing plastic material (comprising for example an elastomer) between a layer of the uncharged material or with a high elongation capacity and a layer of the abovementioned recycled material.

 The invention also provides hollow products produced by carrying out this method, which in particular constitute reservoirs or air intake ducts for an internal combustion engine, these ducts being formed by molding with silencers and / or resonators.

 These products are advantageously made of polypropylene and comprise at least one layer of polypropylene loaded with a reinforcing material and a layer of unfilled polypropylene.

 The reinforcing filler for the polypropylene is, for example, talc, in an amount of between 5 and 50% approximately, preferably between 15 and 30% approximately, by weight and the polypropylene is of the very high molecular weight type.

In general, the advantages of the products according to the invention are as follows:
- high mechanical rigidity,
- high volume rigidity,
- high mechanical resistance,
- lower wall thickness, resulting in weight and price savings,
- shorter cooling time, hence an increase in the production rate,
- manufacturing by extrusion blow molding.

The invention will be better understood and other characteristics, details and advantages thereof will appear more clearly on reading the description which follows, given by way of example with reference to the appended drawings in which
- Figure 1 is a schematic half-view in axial section of an air intake duct according to the invention
- Figure 2 is a schematic top view of an alternative embodiment of this conduit
- Figures 3, 4 and 5 are schematic sectional views of various embodiments of the walls of the products according to the invention.

 The duct 10 of FIG. 1 is an air intake duct for an internal combustion engine of a motor vehicle and comprises a substantially U-shaped part, made of rigid plastic material and coming from molding with a silencer 12 whose geometry , the rigidity and the natural frequency are determined as a function of the sound frequencies to be absorbed, the internal volume of the silencer 12 being connected to the internal volume of the conduit 10 by a series of orifices 14 formed in the material connecting the conduit 10 to the silencer 12, the number and dimensions of these orifices also being determined according to the characteristics of the sound energy to be absorbed.

 In known manner and as indicated in document EP-A-0 761 413, the ends 16 of the duct part 10 shown can be made of a more flexible material or connected to duct parts made of a more flexible material than the part of the conduit 10 comprising the silencer 12, by means of a sequential extrusion technique of rigid sub-material-flexible material.

In practice, the volume of the silencer 12 can be between 0.3 and 6.10-3 m3 approximately, depending on the sound frequencies to be absorbed, the small volume silencers being more particularly intended for the absorption of high frequencies (for example 400 -500
Hz) and the larger volume silencers being more particularly intended for the absorption of lower sound frequencies (for example 50-100 Hz).

 The volume rigidities of these silencers must be less than approximately 100-300 cm3 / bar, and their natural frequencies must be greater than a few hundred Hz, as the case may be.

 This requires the use of relatively rigid plastics to produce the silencers 12.

 For cost reasons, it is preferable to use polypropylene which must be reinforced with a filler, for example talc, in an amount of between 5 and 50% by weight approximately and preferably between 15 and 30% by weight.

 The loaded polypropylene however has too low an elongation capacity in the molten state for it to be possible to form the duct 10 with the silencer 12 by extrusion blow molding.

 The invention solves this problem by co-extruding a layer of reinforced polypropylene and a layer of polypropylene which is not reinforced or has a high elongation capacity (for example 1000 or more) in the molten state.

 The invention then consists in forming a parison comprising an inner layer of unfilled polypropylene and an outer layer of charged polypropylene, closing around this parison a mold in the form of the duct and the silencer to be produced, possibly moving the ends of the parison to give the duct a general U shape if necessary, to close parts of the mold on the corresponding ends of the parison, and to inject a gas under pressure to apply the parison to the walls of the mold, this injection of gas under pressure can be done at once or twice as described in the aforementioned prior European patent.

 During the elongation of the material which results from the injection of pressurized gas into the parison, the layer of loaded polypropylene is carried by the layer of unfilled polypropylene and, because of its adhesion thereto, can follow the elongation of the layer of unfilled polypropylene without tearing.

 It is therefore possible to produce by extrusion-blowing conduits provided with silencers in a charged material which gives the conduits and the silencers the desired characteristics of mechanical resistance, rigidity and natural frequency.

 Preferably, the polypropylene used is of the UHMW (Ultra High Molecular Weight) type to present a high viscosity in the molten state, so that the parison does not deform too much and does not fall inside the mold before the injection of blowing gas.

 Furthermore, it is preferable to use a continuous extrusion machine, rather than an accumulation chamber extrusion machine with which it is difficult to extrude products with a multilayer wall of approximately constant thickness.

 There is shown schematically in FIG. 2 an alternative embodiment of the invention, in which the air intake duct 10 is associated, by molding, not only with a silencer 12, but also with a resonator 18, such as a HELMHOLTZ resonator connected to line 10 by a single gas passage line 20.

 As already indicated and as shown diagrammatically in FIG. 3, the walls of the silencer 12 (as well as that of the resonator 18) may comprise an outer layer 22 of a material such as polypropylene reinforced by a filler and an inner layer 24 of non-polypropylene loaded, the layer 22 having for example a thickness twice that of the layer 24. Conversely, the layer 24 of uncharged material can be outside the silencer 12, and the layer 22 of charged material inside.

 It is also possible, as shown in FIG. 4, that the wall of the silencer 12 (and that of the resonator 18) comprises two layers 22 of charged material and an intermediate layer 24 of uncharged material, the thicknesses of these three layers being for example substantially equal.

 As a variant, and as shown diagrammatically in FIG. 5, this wall may comprise an inner layer and an outer layer 22 of charged material, an intermediate layer 24 of uncharged material and an intermediate layer 26 of a material obtained by recovery and grinding of the falls of material from previously manufactured ducts (these falls of material coming essentially from the webs of material which are located between the duct 10, the silencer 12 and / or the resonator 18).

 In a first embodiment, this layer 26 of recycled material can be located between a layer 22 of charged material and layer 24 of uncharged material.

 In another embodiment, a layer 28 of damping material can be provided between layer 24 of uncharged material and layer 26 of recycled material, as shown in FIG. 5, this damping material being obtained by adding an appropriate elastomer to the plastic used for the other layers.

 In general, the wall thicknesses of the silencers and of the resonators formed in accordance with the invention are between 1.5 and 3.5 mm (they vary from point to point of the same silencer or of a same resonator due to the stretching of the material) and are therefore significantly less than the wall thicknesses of traditionally manufactured silencers and resonators, which are 4 to 5 mm. This results in a gain in weight and also in a reduction in the cooling time during manufacture, the cooling time being a function of the square of the thickness of the parts produced.

All thermoplastic materials in general can be used in the process according to the invention, and in particular:
- polypropylenes,
- polyamides,
- polyesters,
- polyamide-polypropylene alloys.

 The materials of the different layers of a product with a multilayer wall are preferably of the same nature or compatible, they can also be of different natures if one or more intermediate films of an adhesion material or other means are provided. ensuring the adhesion of the layers together.

 In general, the invention is applicable to the manufacture of air intake ducts for the engine of a motor vehicle, of tanks and of all products or hollow bodies which must have minimum characteristics of resistance and rigidity.

Claims (14)

 1) Method for manufacturing hollow products by extrusion blow molding, consisting of extruding a parison of plastic material inside a mold, closing the mold on the parison and injecting a pressurized gas into the parison to applying to the walls of the mold, characterized in that, said plastic material being reinforced by fillers and / or having a relatively low elongation capacity, it consists in coextruding with this material a layer of another plastic material comprising less reinforcing load and / or having a relatively high elongation capacity.  2) Method according to claim 1, characterized in that said other plastic material does not include a reinforcing filler.  3) Method according to claim 1 or 2, characterized in that said other plastic material is of the same nature or the same type as the first material mentioned.  4) Method according to claim 1 or 2, characterized in that said other plastic material is not compatible with the first cited material and is co-extruded with an intermediate film of a material ensuring adhesion between the two layers of plastic material.  5) Method according to one of the preceding claims, characterized in that said other plastic material is on the inner face of the layer of the first plastic material mentioned.  6) Method according to one of claims 1 to 4, characterized in that said other material is on the outer face of the layer of the first plastic material mentioned.  7) Method according to one of the preceding claims, characterized in that it consists in extruding said other plastic material between two layers (22) of the first plastic material mentioned.  8) Method according to claim 7, characterized in that it consists in extruding said other plastic material between a layer (22) of the first cited material and a layer (26) of plastic material formed by recovery and grinding of scrap material previously manufactured products.  9) Method according to one of the preceding claims, characterized in that it consists in co-extruding with the above-mentioned plastic layers a layer (28) of damping material.  10) Method according to one of the preceding claims, characterized in that it consists in using a continuous extrusion machine to extrude said layers of material.  11) Products manufactured by carrying out the process described in one of the preceding claims, characterized in that they constitute reservoirs or ducts (10) for air intake for an internal combustion engine, these ducts (10) being formed by molding with silencers (12) and / or resonators (18)  12) Products according to claim 11, characterized in that they are made of polypropylene and comprise at least one layer (22) of polypropylene loaded with a reinforcing material and a layer (24) of unfilled polypropylene.  13) Products according to claim 12, characterized in that the polypropylene is reinforced with a talc filler, the amount of which is between 5 and 508 by weight approximately.  14) Products according to claim 12 or 13, characterized in that the polypropylene is of the very high molecular weight type to have a high viscosity in the molten state.