Bodywork part comprising polypropylene and exhibiting optical properties for decorative lighting

Abstract

A motor vehicle (40) body part (20) having: - a transmittance measured at a thickness of 3 mm greater than or equal to 50%, - a haze measured at a thickness of 30% to 90%, and said body part (20) being made of a material comprising at least: - from 73.5% to 79.5% by mass of polypropylene, and - a styrenic block copolymer comprising ethylene and propylene medial blocks. Figure for the abbreviation: Figure 1

Description

Title of the invention: Bodywork part comprising polypropylene and having optical properties for light decoration

[0001] The invention relates to the field of the automotive industry, and in particular to the field of plastic bodywork parts which allow light to pass through them, in particular transparent or translucent parts, used in particular for light decoration. It relates in particular to a bodywork part. It also relates to a bodywork panel comprising the bodywork part and to a motor vehicle comprising the bodywork panel and / or the bodywork part.

[0002] An element is generally described as transparent when it allows light to pass through it in the visible range. A transparent element allows objects to be clearly distinguished through its thickness. An element is considered to be transparent when it has a transmittance greater than or equal to 85%. The transmittance or total light transmission is the fraction of the light flux passing through it; the transmittance represents the ratio of the light intensity transmitted by the material to the incident light intensity. An element is generally described as translucent when it has a transmittance greater than or equal to 50%, but less than 85%. Throughout the description below, the term "transparent" is used to mean that the element it describes allows light to pass through, whether it is transparent or translucent.

[0003] Elements are known which are added to a bodywork panel and which are intended in particular to highlight the style of a vehicle, such as a line or a shape, in order to reinforce the image that the manufacturer wishes to associate with its vehicle model. For example, there are chrome-plated strips, or rods, placed on the edge of a panel or equipment. In order to reinforce the aesthetic effect produced by these bodywork parts, it has been proposed to place a light source behind a surface of the bodywork part which lets the light pass through.

[0004] Body panels are known which are made from plastic molding, and on which a transparent body part is attached in a housing provided for this purpose. These attached transparent body parts have the disadvantage of not being able to be perfectly adjusted to the housing present in the body panel, because the assembly of such optical parts on body panels has the disadvantage of presenting assembly clearances and flushnesses of lower visual quality than that required for a motor vehicle. Finally, such parts reported generate complexity in the management of sealing against liquids, such as water (rain, washing, etc.).

[0005] To avoid these problems of parts being attached to a panel, body panels are also known which are made from plastic molding, overmolding one or more transparent body parts. These body parts are preformed and incorporated by overmolding into said molded body panel, and serve to protect an optical device or a light source. The body part can also be co-molded with the body panel.

[0006] It has been proposed to use PC (polycarbonate) as transparent materials in the automobile industry for the manufacture of transparent body panels and PMMA (polymethyl methacrylate) for the manufacture of parts in the optical zone, on the headlights and around them, outside the impact zone. However, these materials are not compatible in molding with polypropylene. However, body panels resulting from molding are mainly made from a polypropylene-based material. As a result, there is not sufficient molding adhesion between the body part and the polypropylene panel and their assembly requires fixing means.Furthermore, PMMA is not very shock resistant and PC requires a complex molding process (adapted injection system, high molding temperature, and above all a protective varnish process on the outer face which requires significant industrial equipment to be added after the traditional painting lines). As for the different plastic materials based on polypropylene, they are not used in light decoration because they do not have the desired light transmission properties.

[0007] The invention aims in particular to provide a bodywork part for the luminous decoration of bodywork panels, compatible in molding adhesion with polypropylene.

[0008] To this end, the invention relates to a motor vehicle body part, having: - a transmittance measured at 3 mm thickness greater than or equal to 50%, - a haze measured at 3 mm thickness ranging from 30% to 90%, and said bodywork part is manufactured from a material comprising at least: - from 73.5% to 79.5% by mass of polypropylene, and - a styrenic block copolymer comprising ethylene and propylene midblocks.

[0009] The bodywork part can thus be used for light decoration. Indeed, for light decoration, transparent elements are generally sought, that is to say elements having a transmittance greater than or equal to 85%. The inventors have imagined another method of light decoration, not requiring a transparent element, but a translucent element. This is the case for non-transparent elements with a transmittance greater than or equal to 50%, and less than 85%. The bodywork part according to the invention also has a haze (or veil, or turbidity, or "haze" in English), ranging from 30 to 90%. With these optical properties, the bodywork part has a milky appearance which allows for diffused lighting of a brand, logo or pattern. Thus, surprisingly, a polypropylene-based bodywork part is used for light decoration, whereas other materials are traditionally used for light decoration.Thanks to its milky appearance, the bodywork part allows the emitted light to be diffused more evenly and to mask the technical components located behind the wall of the part (for example the components of the lighting system or the reinforcing ribs of the part which are molded and located on the hidden face).

[0010] This polypropylene-based bodywork part can therefore be integrated by molding (co-molding or overmolding) into a main body of a bodywork panel, also molded in polypropylene, or added, for example by screwing, clipping, riveting, riveting, gluing or stapling, onto the bodywork panel. The bodywork part can be a medium-sized bodywork panel, such as for example an outer skin of a tailgate, the "grill" of an electric vehicle, the external surface of a trim module ("black panel"), or the external surface of an added light module interfacing by assembly with the other bodywork panels located around it.

[0011] The term "body panel" means an exterior trim part (also called "exterior skin") of a motor vehicle opening, bumper, wing, hood or roof.

[0012] The styrenic block copolymer comprising ethylene and propylene midblocks is a styrene-ethylene-propylene-styrene (SEPS).

[0013] Advantageously, the bodywork part must be capable of absorbing significant impacts. Thus, it is highly desirable that the bodywork part according to the invention has one of the following mechanical properties: - Flexural modulus at 23°C according to ISO 178, at 0°, 3 mm, ranging from 1000 to 1800 MPa, - Melt flow index according to ISO 1133, 230°C, 2.16 kg, ranging from 10 to 25 g / 10 min, - Linear thermal expansion coefficient according to ISO 11359-2, 3 mm, 0°, ranging from 90 / °C to 130 / °C, - Charpy impact strength with notch at 23°C according to ISO 179, 3 mm, iso, greater than or equal to 35 kJ / m2, Charpy impact strength with notch at -20°C according to ISO 179, 3 mm, iso, greater than or equal to 5 kJ / m2, - Brittle - ductile transition temperature according to ISO 6603-2, 3 mm, less than or equal to - 10 °C. Preferably, the body part must have all of its properties.

[0014] The bodywork part according to the invention has a transmittance measured at 3 mm thickness greater than or equal to 50%, that is to say that when the material constituting the bodywork part is molded and tested at 3 mm thickness according to the ASTM D1003 standard, the transmittance is greater than or equal to 50%.

[0015] The bodywork part according to the invention has a haze measured at 3 mm thickness ranging from 30% to 90%, that is to say that when the material constituting the bodywork part is molded and tested at 3 mm thickness according to the ASTM DI003 standard, the haze ranges from 30% to 90%.

[0016] According to one embodiment, the transmittance measured at 3 mm thickness is less than or equal to 95%.

[0017] In one embodiment, the bodywork part has a thickness ranging from 1 mm to 5 mm, preferably from 2 mm to 4 mm, and preferably being approximately 3 mm.

[0018] Advantageously, the material comprises between 74% and 78% by mass, inclusive, of polypropylene, preferably between 74.5% and 77%, and more preferably approximately 75%.

[0019] Preferably, the polypropylene is a homopolymer. It advantageously has a melt flow index ranging from 10 to 25 g / lOmin (ISO 1133, 230°C, 16 kg), preferably ranging from 15 to 22.5 g / lOmin, and more preferably approximately 20 g / lOmin. Its density is, for example, approximately 905 kg / m3 (ISO 1183). The polypropylene advantageously has a flexural modulus of approximately 2000 MPa (ISO 178). For example, it has a tensile modulus of approximately 2200 MPa (ISO 527-2, 1 mm / min). Preferably, it has a tensile elongation of approximately 6% and approximately 40 MPa (ISO 527-2, 50 mm / min). It advantageously has a heat deflection temperature of about 115°C (ISO 75-2, 0.45 N / mm2). In one example, it has a Charpy notch impact strength of about 2.5 kJ / m2 (ISO 179 / leA, 23°C). Advantageously, the polypropylene of the body part is a polypropylene α-nucleated by polyvinyl cyclohexane (polyVCH).For example, the polypropylene of the body part is HF955MO from Borealis AG.

[0020] Advantageously, the material of the bodywork part comprises approximately 75% by mass of polypropylene and approximately 25% by mass of the styrene block copolymer comprising midblocks of ethylene and propylene.

[0021] Advantageously, the styrenic block copolymer has a mass content of 21% of polystyrene. In one embodiment, the styrenic block copolymer has a specific gravity of about 0.90 (ASTM D 792). It advantageously has a melt flow rate of about 13 g / 10 min (ASTM D 1238, 230 °C, 5 kg). In one embodiment, it has a Shore A hardness of about 61 (ASTM D 2240, 10 sec.). For example, the styrenic block copolymer is KRATON™ G1730 M Polymer from KRATON Corporation.

[0022] The invention also relates to a bodywork panel comprising a bodywork part as described above.

[0023] The invention also relates to a motor vehicle comprising a body panel as described above and / or a body part as described above.

[0024] Another object of the invention relates to the composition described above and its use for parts inside a vehicle, or for the interior lining of a vehicle opening. Brief description of the figures

[0025] The invention will be better understood on reading the following description given solely by way of example and with reference to the appended figure in which:

[0026] [Fig-1] is a view of a motor vehicle comprising a set of parts of bodywork according to the invention. Detailed description

[0027] According to the examples of [Fig.l], the motor vehicle 40 comprises a bodywork panel 10 which may be a bumper, a roof, a door or even a wing. This bodywork panel 10 comprises a main body 30 and a bodywork part 20 according to the invention. The motor vehicle 40 also comprises an external surface of an attached light module interfacing by assembly with the other bodywork panels located around it. The external surface is also a bodywork part 20 according to the invention. The bodywork parts 20 have:

[0028] - a transmittance measured at 3 mm thickness greater than or equal to 50%, - a cloudiness measured at 3 mm thickness ranging from 30% to 90%, and they are made from a material comprising at least: - from 73.5% to 79.5% by mass of polypropylene, and - a styrenic block copolymer comprising ethylene and propylene midblocks.

[0029] Different compositions were tested under the conditions set out below.

[0030] For each composition, the different constituents composing it, in the form of granules, were weighed then mixed mechanically, under standard conditions, so as to obtain a homogeneous preparation to feed the injection press. Standard molding conditions for a polypropylene-based material were used to produce a test plate from which standard specimens (defined according to the test to be carried out and the corresponding standard) 3 mm thick were cut.

[0031] On these 3 mm plates or test pieces, the following parameters were measured, under the following conditions: - the total light transmission was measured on the 3 mm plates according to ASTM D1003-2021 (“Standard Test Method for Haze and Luminous Transmittance of Transparent Plastics”); - the haze was measured on the 3 mm plates according to the same standard, ASTM D1003-2021; - the flexural modulus was measured according to ISO 178 of 2018 (“Plastics - Determination of flexural properties”), at 23°C, on 3 mm specimens, the long dimension of which was cut at 0° to the direction of flow of the material in the mold; - the melt flow index (MFI) was measured according to ISO 1133 (Plastics - Determination of the melt flow index of thermoplastics, by mass (MFR) and by volume (MVR)), at 230°C and for 2.16 kg of composition; - the coefficient of linear thermal expansion (CLTE) was measured from 23 to 80°C, according to ISO 11359-2 (Plastics - Thermomechanical Analysis (TMA) - Part 2: Determination of the coefficient of linear thermal expansion and the glass transition temperature), on 3 mm thick specimens, the long dimension of which was cut at 0° to the direction of material flow in the mold; - the Charpy impact strength notched was measured according to ISO 179 (Plastics - Determination of Charpy impact strength), at 23°C and -20°C, on 3 mm thick specimens; the measurement was carried out on the one hand on specimens whose long dimension was cut at 0° to the direction of flow of the material in the mold, and on the other hand on specimens whose long dimension was cut at 90° to the direction of flow of the material in the mold, then the average of these two measurements, 0° and 90°, was calculated to obtain the "iso" (isotropic) value; - the brittle-ductile transition temperature was measured on 3 mm plates according to ISO 6603-2. These eight parameters are particularly significant and discriminating in establishing the correct suitability of the molded material for the production of bodywork parts meeting the required conditions of use.

[0032] The following table summarizes the criteria that the polymer must advantageously fulfill to manufacture a part having the characteristics according to the invention, the values ​​being measured under the conditions described above.

[0033] [Tables 1] Parameter Minimum accepted value Maximum accepted value Total light transmission at 3 mm thickness ASTM D1003 50% No limit Haze at 3 mm thickness ASTM D1003 30% 90% Flexural modulus ISO 178, 0°, 3 mm 1000 MPa 1800 MPa Melt flow rate ISO 1133, 230°C, 2.16 kg 10 g / 10 min 25 g / 10 min Coefficient of linear thermal expansion ISO 11359-2, 0°, 3 mm 90 / °C 130 / C Charpy impact strength with notch at 23°C ISO 179, iso, 3 mm 35 kJ / m2 Not applicable Charpy impact strength with notch at -20°C ISO 179, iso, 3 mm 5 kJ / m2 Not applicable Brittle-ductile transition temperature ISO 6603-2 No limit -10°C

[0034] Example 1 (Witness): polypropylenes without fillers Polypropylenes with both interesting mechanical and light transmission performance were tested. The following commercial polypropylenes were tested, without additives or fillers.

[0035] - Daplen™ EE002AE from Borealis: this is a reactor polypropylene, "reactor elastomer modified polypropylene”, with good mechanical properties and good surface quality.

[0036] - Hifax EP3080 from LyondellBasell: this is a non-polypropylene copolymer loaded and with good impact resistance. It is used for the manufacture of painted parts. - HF955MO from Borealis AG, Wagramer Strasse 17-19, 1220 Vienna, Austria: it is a polypropylene homopolymer with good stiffness, transparency and impact resistance. It has a melt flow rate of 20 g / lOmin (ISO 1133, 230°C, 16 kg), a density of 905 kg / m3 (ISO 1183), a flexural modulus of 2000 MPa (ISO 178), tensile modulus of 2200 MPa (ISO 527-2, 1 mm / min), tensile elongation of 6% and 40 MPa (ISO 527-2, 50 mm / min), heat deflection temperature of 115°C (ISO 75-2, 0.45 N / mm2) and Charpy notch impact strength of 2.5 kJ / m2 (ISO 179 / leA, 23°C). According to Borealis company EP3495422, HF955MO is a polypropylene a-nucleated by polyvinyl cyclohexane (polyVCH). - Moplen RP340N from LyondellBasell: it is a random copolymer of polypropylene with a melt flow rate of 11 g / lOmin (ISO 1133, 230°C, 2.16 kg), good transparency and gloss. It has a density of 0.90 g / cm3.

[0037] These products were used to manufacture plates and test pieces as presented above, and different parameters were measured for each composition, under the conditions described above. The following table summarizes the results obtained for each of these polypropylenes.

[0038] [Tables2] Parameter EE002AE EP3080 HF955MO RP340N Total Light Transmission, 3 mm, ASTM D1003 39% 42% 71% 76% Haze, 3 mm, ASTM D1003 86% 99% 90% 90% Flexural Modulus ISO 178, 0° 1000 MPa 950 MPa Coefficient of Linear Thermal Expansion ISO 11359-2, 0° 145 / °C 139 / °C Charpy Impact Strength with Notch at 23°C, ISO 179, iso 45 kJ / m2 65 kJ / m2 2.5 kJ / m2 6 kJ / m2 Thus, out of the five criteria measured, these polypropylenes do not have all the required mechanical characteristics or optical values. In particular, it is noted that only HF955MO and RP340N have the required optical values. However, these commercial polypropylenes could not be selected because the only measured mechanical property, Charpy impact strength, is not sufficient. None of these commercial polypropylenes was therefore selected to manufacture parts according to the invention.

[0039] Example 2 (Witness): commercial compositions based on polypropylene and comprising fillers and / or additives Polypropylene-based materials, adapted to improve their characteristics mechanical, and which are not completely opaque, have been tested.

[0040] These are the following commercial compositions.

[0041] - Daplen™ EE103AE from Borealis: this is a polypropylene comprising 10% of mineral filler, presenting both good impact resistance and good rigidity.

[0042] - Daplen™ EE112AE from Borealis: this is a mineral-filled polypropylene, presenting both good impact resistance and good rigidity, and ease of painting.

[0043] - Daplen™ EE001AI from Borealis: this is a polypropylene comprising 7% of mineral filler, presenting both good impact resistance and good rigidity.

[0044] - S AB IC PPcompound 1761: this is a polypropylene modified for resistance to shocks.

[0045] These compositions were used to manufacture plates and test pieces as presented above, and different parameters were measured for each composition, under the conditions described above. The following table summarizes the results obtained for each of the compositions.

[0046] [Tables3] Parameter EE103AE EE112AE EE001AI PPcompound 1761 Total Light Transmission ASTMD1003, 3 mm 15% 17% 20% 44% Haze ASTM D1003, 3 mm 100% 86% Flexural Modulus, ISO 178, 0° 1178 MPa 1400 MPa 1150 MPa 1026 MPa Coefficient of Linear Thermal Expansion ISO 11359-2, 0° 103 / °C 77 / °C 123 / °C 80 / °C Charpy Impact Strength with Notch at 23°C ISO 179, iso 52 kJ / m2 49 kJ / m2 35 kJ / m2 60 kJ / m2 Thus, on the only five criteria measured, these commercial compositions confirm their improved mechanical characteristics compared to example 1, but do not exhibit the required total light transmission. These commercial compositions were therefore not selected to manufacture the parts according to the invention.

[0047] Examples: Compositions according to the invention, and other comparative compositions

[0048] Not identifying any polypropylene or polypropylene-based composition that would allow parts with the required characteristics to be directly manufactured, the applicant considered preparing his own compositions. To do this, he used different components.

[0049] Several polypropylenes were used. These are HF955MO and Moplen RP340N presented and evaluated alone above. Without fillers or additives, these polypropylenes have interesting optical properties, but their mechanical characteristics are not satisfactory.

[0050] The following additives were used: - Maxlmpact™ 10238 from Milliken: This is an impact strength improving agent, specially adapted to polypropylenes, and which degrades transparency little or not at all. - KRATON™ G1643 M Polymer from KRATON Corporation: It is a linear triblock copolymer of styrene and ethylene / butylene with a mass content of 20% polystyrene (SEBS). It is an impact strength improving agent. - KRATON™ G1646 V Polymer from KRATON Corporation: It is a copolymer of styrene, ethylene and butadiene (S-EB). It is an impact resistance improving agent.

[0051] - KRATON™ G1730 M Polymer from KRATON Corporation, distributed by Kraton Polymers SPRL, 1348 Louvain-la-Neuve, Belgium: It is a styrenic block copolymer comprising ethylene and propylene midblocks (styrene-ethylene-propylene-styrene, SEPS) with a mass content of 21% polystyrene. It is an impact strength improver. It has a density of 0.90 (ASTM D 792), a melt flow rate of 13 g / 10 min (ASTM D 1238, 230 °C, 5 kg), and a Shore A hardness of 61 (ASTM D 2240, 10 sec.).

[0052] - INFUSE™ 9817 Olefin Block Copolymer from Dow: it is a reactive agent that improves the impact resistance, an olefin block copolymer. - NX™ UltraClear™ GP 120N from Milliken: clarifying agent specially adapted for polypropylenes.

[0053] The influence of the addition of Kraton G1730 M and Maxlmpact™ 10238, two impact resistance improving agents, was tested in compositions based on HF955MO polypropylene. Table 4 shows the results obtained.

[0054] [Tables4] Parameters Total light transmission Sail ("Haze") Charpy shock resistance with notch at 23°C Example Composition (%, 3mm) (%, 3mm) (23°C, kJ / m2) 3.1 75% HF955MO + 25% Kraton G1730 M 587 393%. HF955MO + 25% Kraton G1730 M + 2% NX™ UltraClear™ GP 120N 58 85 33 3.3 71%HF955MO + 25% Kraton G1730 M + 4% NX™ UltraClear™ GP 120N 25 84 254 . 90% HF955MO + 10% Maxlmpact™ 10238 74 76 5 4.2 85% HF955MO + 15 % Maxlmpact™ 10238 74 77 8 4.3 80% HF955MO + 20% Maxlmpact™ 10238 16938

[0055] Of the only three criteria measured, among examples 3.1 to 4.3 tested above, only example 3.1 (75% HF955MO, 25% Kraton G1730 M) has the values ​​required for the manufacture of a part according to the invention. Indeed, even if all examples 3.1 to 4.3 have compliant optical characteristics, the Charpy impact strength values ​​for examples 3.2 to 4.3 are not sufficient. In view of the results obtained, among two impact resistance modifying agents tested, only Kraton G1730 M, under the conditions of example 3.1, appears to make it possible to manufacture a part in accordance with the invention. In Examples 3.2 and 3.3, differing from Example 3.1 by the replacement of part of the HF955MO polypropylene with the clarifying agent NX™ UltraClear™ GP 120N, this replacement does not allow sufficient impact resistance to be maintained. These two compositions based on three components (one po- lypropylene, an impact strength improver and a clarifying agent) do not allow the required mechanical characteristics to be obtained in the proportions tested.

[0056] Table 5 shows the results obtained for compositions incorporating two other impact modifiers from KRATON Corporation, which also supplies Kraton G1730 M. RP340N polypropylene is also tested.

[0057] [Tables5] Examples 5.3 5.4 5.5 6.1 6.2 6.3 6.4 6.5 6.6 Moplen RP340N, % 95 90 85 HF955MO, % 90 80 75 90 80 75 Kraton G1646, % 10 20 25 Kraton G1643, % 5 10 15 10 20 25 Total Light Transmission, % 64.2 60.9 60.4 72 62.6 61.2 60 Charpy Impact Strength, 23°C, kJ / m2 4 27 41 5.2 27 46 4.4 35.6 41

[0058] Thus, of the only two criteria evaluated, only compositions 5.5, 6.3, 6.5 and 6.6 have the required values. To improve the impact resistance of RP340N polypropylene, it seems positive to replace 15% of RP340N polypropylene with 15% of Kraton G1643 M, while maintaining correct light transmission.

[0059] As regards HF955MO polypropylene, replacing 25% of polypropylene with Kraton G1646 (composition 5.5) and Kraton G1643 (composition 6.6) agents, or even with 20% of Kraton G1643 also appears to give acceptable results in terms of Charpy impact strength, while maintaining correct light transmission. Kraton G1646 V gives acceptable light transmission and impact resistance values ​​in Example 5.5, used at 25%. Kraton G1643 M gives acceptable values ​​in Examples 6.3 and 6.6, used at 15 and 25% respectively. Kraton G1643 appears to be more effective because replacing 20% ​​of HF955MO polypropylene with 20% of Kraton G1643 is sufficient to achieve the required impact resistance.

[0060] Table 6 shows the results obtained for compositions incorporating Dow's impact modifier, Infuse 9817.

[0061] [Tableauxô] Examples 7.1 7.2 7.3 7.5 7.6 7.7 7.8 Moplen RP340N 90 85 80 HF955MO 90 85 80 75 Infuse 9817 10 15 20 10 15 20 25 Total Light Transmission, % 63.7 58.2 54.4 51.5 45.3 43 43.1 Charpy Impact Strength, 23°C, kJ / m2 7.6 14.9 53.7 3.5 4.7 6.9 17.3

[0062] Unlike agents G1730, G1646 and G1643, replacing 25% of HF955MO with 25% of Infuse 9817 (composition 7.8) does not provide the required impact resistance. Furthermore, in this example, the light transmission is also not acceptable. Furthermore, unlike agent G1643, replacing 20% ​​of HF955MO polypropylene with 20% of Infuse 9817 (composition 7.7) does not provide sufficient total light transmission. Also, unlike agent G1643, replacing 15% RP340N polypropylene with 15% Infuse 9817 (composition 7.2) does not provide sufficient impact resistance. In contrast, this agent gives acceptable values ​​in Example 7.3, replacing 20% ​​of RP340N polypropylene.

[0063] Thus, following initial tests carried out on numerous polypropylene-based compositions, with or without additives, commercial or prepared on purpose by the applicant, with variable levels of additives, only six of these compositions, compositions 3.1, 5.5, 6.3, 6.5, 6.6 and 7.3, obtained suitable results on the criteria evaluated.

[0064] Table 7 gives additional results for Examples 3.1, 5.5, 6.3, 6.5, 6.6 and 7.3 selected from Tables 4, 5 and 6. It also presents the results of new examples. These new examples, which all include the Kraton G1730 M additive, relate to the following compositions: - 3.4: 85% Moplen RP340N 15% Kraton G1730 M - 3.5: 83% Moplen RP340N 17% Kraton G1730 M - 3.6: 80% Moplen RP340N 20% Kraton G1730 M - 3.7: 90% Moplen RP340N 10% Kraton G1730 M - 3.8: 80% HF955MO 20% Kraton G1730 M - 3.9: 72% HF955MO 28% Kraton G1730 M.

[0065] [Tables7] Properties Total Light Transmission Haze Flexural Modulus Charpy Notched Impact Strength CLTE (%, 3mm) (%, 3mm) (23°C, MPa) (23°C, kJ / m2) (23°C to 80°C, 1 / °C) 6.3 72 30 600 46 130 7.3 59 99 707 54 124 6.5 61 71 960 36 120 6.6 60 70 950 41 117 3.4 69 51 26 3.5 64 46 705 41 140 3.6 64 47 736 46 139 3.7 70 45 6.4 3.8 59 86 18 3.1 58 87 1340 39 103 3.9 57 94 45 5.5 60.4 70 950 41 117

[0066] Table 7 shows that of the only five criteria evaluated, only composition 3.1, corresponding to 75% HF955MO, 25% Kraton G1730 M, gives acceptable results. In particular, replacing 25% RP340N polypropylene with 25% Kraton G1730 M (composition 3.4) does not, contrary to what is observed with composition 3.1, sufficiently improve impact strength. Even if replacing 27% RP340N polypropylene with 27% Kraton G1730 (composition 3.5) sufficiently improves impact strength, the flexural modulus and CLTE values ​​are not sufficient. Similarly, among the agents tested (G1730, G1646 and G1643, compositions 3.1, 5.5 and 6.6 respectively), only G1730 is capable, by replacing 25% HF955MO polypropylene, of providing an acceptable flexural modulus.

[0067] It is also observed that by replacing 28% of HF955MO polypropylene with 28% of Kraton G1730 (composition 3.9), an acceptable impact resistance is obtained, but the haze value is no longer acceptable. On the other hand, if 20% of HF955MO polypropylene is replaced with 20% of Kraton G1730 (composition 3.8), the impact resistance is not acceptable, while the haze value is acceptable.

[0068] Thus, a composition 3.1 is identified, comprising polypropylene HF955MO and the additive Kraton G1730, which, on the basis of the results set out in Tables 4 and 7, appears to give acceptable results. But other compositions comprising the same polypropylene HF955MO and the same additive Kraton G1730 do not give acceptable results, as shown in Table 4 for compositions 3.2 and 3.3, and in Table 7 for compositions 3.8 and 3.9. The results obtained with the compositions comprising polypropylene HF955MO and the agent Kraton G1730 are summarized in Table 8 below, on the basis of the results presented in Tables 4 and 7. This Table 8 shows the relative concentrations making it possible to obtain, or not to obtain, acceptable results.

[0069] [Tables8] Examples 3.1 3.2 3.3 3.8 3.9 HF955MO, % 75 73 71 80 72 Kraton G1730, % 25 25 25 20 28 Haze acceptable acceptable acceptable acceptable not acceptable Charpy impact strength, 23°C, kJ / m2 acceptable not acceptable not acceptable not acceptable acceptable

[0070] Example 3.1 was finally tested for all the criteria listed in Table 1, thus making it possible to know whether this composition has the values ​​required to manufacture a part having the characteristics according to the invention. The following table summarizes the results obtained.

[0071] [Tables9] Parameter Minimum accepted value Maximum accepted value Example 3.1 Total light transmission 50% No limit 58% Haze 30% 90% 87% Flexural modulus 1000 MPa 1800 MPa 1256 MPa Melt flow rate 10 g / 10 min 25 g / 10 min 16 g / 10 min Coefficient of linear thermal expansion 90 / °C 130 / °C 103 / °C Charpy impact strength with notch at 23 °C 35 kJ / m2 Not applicable 39 kJ / m2 Charpy impact strength with notch at -20 °C 5 kJ / m2 Not applicable 11 kJ / m2 Brittle - ductile transition temperature No limit -10 °C -25 °C

[0072] Thus, it appears that the selections made, in particular in terms of additives and their relative concentrations, make it possible to have a particular composition, which has the values ​​required to manufacture parts according to the invention. This highlights in particular that the styrene block copolymer comprising middle blocks of ethylene and propylene Kraton G1730 M, used in combination with the polypropylene homopolymer HF955MO, at a mass percentage of 25%, makes it possible to obtain a part in accordance with the invention.

[0073] The results also show that other additives tested, used in the same proportions, do not make it possible to obtain a part conforming to the invention.

[0074] Furthermore, in the examples tested, a mass percentage of 73% does not allow an acceptable Charpy impact strength to be obtained (composition 3.2). It is also observed that a mass percentage of 80% also does not allow an acceptable Charpy impact strength to be obtained (composition 3.8).

[0075] Thus, in view of the results obtained, it is advantageous for the composition to comprise between 73.5% and 79.5% by mass of polypropylene.

[0076] The invention is not limited to the embodiments presented and other embodiments will become clear to those skilled in the art. In particular, even if only a two-component composition made it possible to manufacture a material associated with the desired values, it is possible that a composition comprising a number Higher components also allow the manufacture of a material associated with the desired values.

Claims

Claims

1. Bodywork part (20) of a motor vehicle (40) having: - a transmittance measured at 3 mm thickness greater than or equal to 50%, - a haze measured at 3 mm thickness ranging from 30% to 90%, and said bodywork part (20) being manufactured from a material comprising at least: - from 73.5% to 79.5% by mass of polypropylene, and - a styrene block copolymer comprising middle blocks of ethylene and propylene.

2. Bodywork part (20) according to claim 1, having a thickness ranging from 1 mm to 5 mm, preferably from 2 mm to 4 mm, and preferably being approximately 3 mm.

3. A body part according to any one of claims 1 and 2, wherein the material comprises between 74% and 78% by mass, inclusive, of polypropylene, preferably between 74.5% and 77%, and more preferably approximately 75%.

4. A body part according to any one of claims 1 to 3, wherein the polypropylene is a homopolymer.

5. A body part according to one of claims 1 to 4, wherein the material comprises approximately 75% by mass of polypropylene and approximately 25% by mass of the styrene block copolymer comprising midblocks of ethylene and propylene.

6. A body part according to the preceding claim, wherein the styrene block copolymer has a mass content of 21% polystyrene.

7. A body panel (10) comprising a body part according to any preceding claim.

8. A motor vehicle (40) comprising a body part (20) according to any one of claims 1 to 6.

Images