Bodywork part comprising polypropylene and having optical properties for luminous decoration

Abstract

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

Description

Body 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 transparent when it has a transmittance greater than or equal to 85%. The transmittance or total light transmission is the fraction of the luminous flux passing through it; transmittance represents the ratio of the luminous intensity transmitted by the material to the incident luminous 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] We know of elements added to a body panel whose purpose is 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 strips, or beadings, placed on the edge of a panel or equipment. In order to reinforce the aesthetic effect produced by these body parts, it has been proposed to place a light source behind a surface of the body part that lets the light pass through.

[0004] Body panels are known that are made from plastic molding, and on which a transparent body part is added in a housing provided for this purpose. These added 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 added parts create 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 automotive industry for the manufacture of transparent body panels and PMMA (polymethyl methacrylate) for the manufacture of parts in the optical zone, on and around headlights, outside the impact zone. However, these materials are not compatible with polypropylene in molding. However, body panels resulting from molding are mainly made of a polypropylene-based material. As a result, there is insufficient molding adhesion between the body part and the polypropylene panel and their assembly requires fixing means.Furthermore, PMMA is not very impact resistant and PC requires a complex molding process (adapted injection system, high molding temperature, and especially a protective varnish process on the outer face which requires significant industrial equipment to be added after traditional painting lines). As for the various polypropylene-based plastic materials, 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] For this purpose, 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%, andsaid body part is 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.

[0009] The bodywork part can thus be used for light decoration. Indeed, for light decoration, transparent elements are generally sought, that is, elements having a transmittance greater than or equal to 85%. The inventors have imagined another mode of light decoration, not requiring a transparent element, but a translucent element. This is the case for non-transparent elements having 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 makes it possible to obtain diffuse lighting of a brand, a logo or a pattern.Surprisingly, a polypropylene-based body part is used for light decoration, whereas other materials are traditionally used for light decoration. Thanks to its milky appearance, the body part allows the emitted light to be diffused more evenly and to mask the technical components located behind the wall of the room (for example, the components of the lighting system or the reinforcement ribs of the part, molded and located on the hidden side).

[0010] This polypropylene-based body part can therefore be integrated by molding (co-molding or overmolding) into a main body of a body panel, also molded in polypropylene, or added, for example by screwing, clipping, riveting, riveting, gluing or stapling, onto the body panel. The body part can be a medium-sized body panel, such as for example an outer skin of a tailgate, the "grille" 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 body panels located around it.

[0011] A "body panel" means an exterior trim portion (also called an "outer skin") of a motor vehicle opening, bumper, fender, hood, or roof.

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

[0013] Advantageously, the body part must be able to withstand 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 of 2018, at 0°, 3 mm, ranging from 1000 to 1800 MPa, - Melt flow index according to ISO 1133 of 2022, 230°C, 2.16 kg, ranging from 10 to 25 g / 10 min, - Linear thermal expansion coefficient according to ISO 11359-2 of 2021, 3 mm, 0°, ranging from 90 / °C to 130 / °C, - Charpy impact strength with notch at 23°C according to ISO 179 of 2010, 3 mm, iso, greater than or equal to 35 kJ / m 2 , - Charpy impact strength with notch at -20°C according to ISO 179 of 2010, 3 mm, iso, greater than or equal to 5 kJ / m 2,- Brittle-ductile transition temperature according to ISO 6603-2 of 2000, 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 of 2021, the transmittance is greater than or equal to 50%, preferably the transmittance is 50 to 62%, more particularly 55 to 60%, and more particularly 57 to 59%, for example 58%.

[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 D1003 standard of 2021, the haze ranges from 30% to 90%, more particularly from 50 to 89%, even more particularly from 60 to 88%, for example 87%.

[0016] By the expression "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 body part 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", it is meant that the same area of ​​the part manufactured from the composition mentioned above has said optical characteristics.

[0017] According to one embodiment, the transmittance measured at 3 mm thickness is less than or equal to 95%.

[0018] The transmittance measured at 3 mm thickness can be less than or equal to 90%, it can be less than or equal to 85%.

[0019] In one embodiment, the body part has a thickness ranging from 1 mm to 5 mm, preferably from 2 mm to 4 mm, and preferably being approximately 3 mm.

[0020] Advantageously, the material comprises between 74% and 78% by mass, inclusive, of polypropylene, preferably between 74.5% and 77%, and more preferably approximately 75%.

[0021] Preferably, the polypropylene is a homopolymer. It advantageously has a melt flow index ranging from 10 to 25 g / 10 min (ISO 1133, 230°C, 16 kg), preferably ranging from 15 to 22.5 g / 10 min, and more preferably around 20 g / 10 min. Its density is, for example, around 905 kg / m3 (ISO 1183). Polypropylene advantageously has a flexural modulus of about 2000 MPa (ISO 178). For example, it has a tensile modulus of about 2200 MPa (ISO 527-2, 1 mm / min). Preferably, it has a tensile elongation of about 6% and about 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 / mm 2 ). According to one example, it has a Charpy notch impact strength of about 2.5 kJ / m 2 (ISO 179 / 1eA, 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.

[0022] Advantageously, the body part material comprises about 75% by mass of polypropylene and about 25% by mass of the styrenic block copolymer comprising midblocks of ethylene and propylene.

[0023] Advantageously, the styrenic block copolymer has a polystyrene mass content of from 20 to 22%, preferably 21%. In one embodiment, the styrenic block copolymer has a density of about 0.90 (ASTM D 792). It advantageously has a melt flow index 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 TM G1730 M Polymer from KRATON Corporation.

[0024] The invention also relates to a bodywork panel comprising a bodywork part as described above.

[0025] The invention also relates to a motor vehicle comprising a body panel as described above and / or a body part as described above.

[0026] Another subject 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

[0027] The invention will be better understood by reading the following description, given solely by way of example and with reference to the appended figure in which:

[0028] is a view of a motor vehicle comprising a set of body parts according to the invention. Detailed description

[0029] According to the examples of the, the motor vehicle 40 comprises a body panel 10 which may be a bumper, a roof, a door or even a wing. This body panel 10 comprises a main body 30 and a body 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 body panels located around. The external surface is also a body part 20 according to the invention. The body parts 20 have:

[0030] - 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%, andthey are manufactured from a material comprising at least:- from 73.5% to 79.5% by mass of polypropylene, and- a styrene block copolymer comprising midblocks of ethylene and propylene.

[0031] Different compositions were tested under the conditions stated below.

[0032] For each composition, the various constituents composing it, in the form of granules, were weighed and then mechanically mixed, under standard conditions, in order 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 test pieces (defined according to the test to be carried out and the corresponding standard) of 3 mm thickness were cut.

[0033] On these 3 mm plates or specimens, the following parameters were measured, under the following conditions:- the total light transmission was measured on the 3 mm plates according to the ASTM D1003-2021 standard (“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 the ISO 178 standard of 2018 (“Plastics - Determination of flexural properties”), at 23°C, on the 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 the ISO 1133 standard (Plastics - Determination of the melt flow index of thermoplastics, by mass) (MFR) and in 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 at -20°C, on 3 mm thick specimens;the measurement was carried out on the one hand on test pieces whose long dimension was cut at 0° to the direction of flow of the material in the mold, and on the other hand on test pieces 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 the 3 mm plates according to the ISO 6603-2 standard. These eight parameters are particularly significant and discriminating in establishing the good suitability of the molded material for the production of bodywork parts satisfying the required conditions of use.;

[0034] 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.

[0035] ParameterMinimum accepted valueMaximum accepted valueTotal light transmission at 3 mm thickness ASTM D100350%No limitHaze at 3 mm thickness ASTM D100330%90%Flexural modulus ISO 178, 0°, 3 mm1000 MPa1800 MPaMelt flow rate ISO 1133, 230°C, 2.16 kg10 g / 10 min25 g / 10 minCoefficient of linear thermal expansion ISO 11359-2, 0°, 3 mm90 / °C130 / CCharpy impact strength with notch at 23°C ISO 179, iso, 3 mm35 kJ / m 2 Not applicableCharpy impact strength with notch at -20°C ISO 179, iso, 3 mm5 kJ / m 2 Not applicableBrittle-ductile transition temperature ISO 6603-2No limit-10°C

[0036] Example 1 (Control): Polypropylenes without fillersPolypropylenes with both interesting mechanical and light transmission performances were tested. The following commercial polypropylenes were tested, without additives or fillers.

[0037] - Daplen TM EE002AE from Borealis: this is a reactor elastomer modified polypropylene, with good mechanical properties and good surface quality.

[0038] - Hifax EP3080 from LyondellBasell: This is an unfilled polypropylene copolymer with good impact resistance. It is used for the manufacture of painted parts.- HF955MO from Borealis AG, Wagramer Strasse 17-19, 1220 Vienna, Austria: This is a polypropylene homopolymer with good stiffness, transparency and impact resistance. It has a melt flow rate of 20 g / 10 min (ISO 1133, 230°C, 16 kg), a density of 905 kg / m 3 (ISO 1183), a flexural modulus of 2000 MPa (ISO 178), a tensile modulus of 2200 MPa (ISO 527-2, 1 mm / min), a tensile elongation of 6% and 40 MPa (ISO 527-2, 50 mm / min), a heat deflection temperature of 115°C (ISO 75-2, 0.45 N / mm 2) and a Charpy notch impact strength of 2.5 kJ / m 2 (ISO 179 / 1eA, 23°C). According to Borealis company EP3495422, HF955MO is a polypropylene α-nucleated by polyvinyl cyclohexane (polyVCH).- Moplen RP340N from LyondellBasell: it is a polypropylene random copolymer with a melt flow rate of 11 g / 10 min (ISO 1133, 230°C, 2.16 kg), good transparency and gloss. It has a density of 0.90 g / cm 3 .

[0039] These products were used to manufacture plates and test specimens 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.

[0040] ParameterEE002AEEP3080HF955MORP340NTotal light transmission, 3 mm, ASTM D100339 %42 %71 %76 %Haze, 3 mm, ASTM D100386 %99 %90 %90 %Flexural modulus ISO 178, 0°1000 MPa950 MPaCoefficient of linear thermal expansion ISO 11359-2, 0°145 / °C139 / °CCharpy impact strength with notch at 23°C, ISO 179, iso45 kJ / m 2 65 kJ / m 2 2.5 kJ / m 2 6 kJ / m 2 Thus, out of the five criteria measured alone, these polypropylenes do not exhibit all the required mechanical characteristics or optical values. In particular, it is noted that only HF955MO and RP340N exhibit the required optical values. However, these commercial polypropylenes could not be selected because the only mechanical property measured, Charpy impact strength, is not sufficient. None of these commercial polypropylenes was therefore selected to manufacture parts according to the invention.

[0041] Example 2 (Control): Commercial compositions based on polypropylene and containing fillers and / or additivesPolypropylene-based materials, adapted to improve their mechanical characteristics, and which are not completely opaque, were tested.

[0042] These are the following commercial compositions.

[0043] - Daplen TM EE103AE from Borealis: this is a polypropylene with 10% mineral filler, offering both good impact resistance and good rigidity.

[0044] - Daplen TM EE112AE from Borealis: this is a mineral-filled polypropylene, offering both good impact resistance and rigidity, and ease of painting.

[0045] - Daplen TM EE001AI from Borealis: this is a polypropylene with 7% mineral filler, offering both good impact resistance and good rigidity.

[0046] - SABIC PPcompound 1761: This is a polypropylene modified for impact resistance.

[0047] These compositions were used to manufacture plates and test specimens 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.

[0048] ParameterEE103AEEE112AEEE001AIPPcompound1761Total light transmission ASTM D1003, 3 mm15%17%20%44%Haze ASTM D1003, 3 mm100%86%Flexural modulus, ISO 178, 0°1178 MPa1400 MPa1150 MPa1026 MPaCoefficient of linear thermal expansion ISO 11359-2, 0°103 / °C77 / °C123 / °C80 / °CCharpy impact strength with notch at 23°C ISO 179, iso52 kJ / m 2 49 kJ / m 2 35 kJ / m 2 60 kJ / m 2Thus, on the only five criteria measured, these commercial compositions confirm their improved mechanical characteristics compared to example 1, but do not present the total light transmission required. These commercial compositions were therefore not selected to manufacture the parts according to the invention.

[0049] Examples: Compositions according to the invention, and other comparative compositions

[0050] Since no polypropylene or polypropylene-based composition could be identified that would allow parts with the required characteristics to be directly manufactured, the applicant considered preparing his own compositions. To do this, he used various components.

[0051] 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.

[0052] The following additives were used:- MaxImpact™ 10238 from Milliken: This is an impact strength improving agent, especially suited to polypropylenes, and which degrades transparency little or not at all.- KRATON TM 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 TM G1646 V Polymer from KRATON Corporation: It is a copolymer of styrene, ethylene and butadiene (S-EB). It is an impact resistance improving agent.

[0053] - KRATON TMG1730 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.).

[0054] - INFUSE TM 9817 Olefin Block Copolymer from Dow: It is an impact strength improver, an olefin block copolymer.- NX TM UltraClear TM Milliken GP 120N: clarifying agent specially adapted for polypropylenes.

[0055] The influence of adding Kraton G1730 M and MaxImpact™ 10238, two impact strength enhancers, was tested in compositions based on HF955MO polypropylene. Table 4 shows the results obtained.

[0056] ParametersTotal light transmissionSail (“Haze”)Charpy impact resistance with notch at 23°CExampleComposition(%, 3mm)(%, 3mm)(23°C, kJ / m²)3.175% HF955MO+ 25% Kraton G1730 M5887393.273% HF955MO+ 25% Kraton G1730 M + 2%NX™ UltraClear™ GP 120N5885333.371% HF955MO+ 25% Kraton G1730 M+ 4% NX™ UltraClear™ GP 120N5884254.190% HF955MO+ 10% MaxImpact™ 10238747654.285% HF955MO+ 15 % MaxImpact™ 10238747784.380% HF955MO+ 20% MaxImpact™ 10238698914

[0057] 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 modifiers 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 (a polypropylene, an agent improving impact resistance and a clarifying agent) do not allow the required mechanical characteristics to be obtained in the proportions tested.

[0058] 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.

[0059] Examples5.35.45.56.16.26.36.46.56.6Moplen RP340N, %959085HF955MO, %908075908075Kraton G1646, %102025Kraton G1643, %51015102025Total Light Transmission, %64.260.960.47262.661.260Charpy Impact Strength, 23°C, kJ / m²427415.227464.435.641

[0060] Thus, of the 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.

[0061] For HF955MO polypropylene, replacing 25% of the polypropylene with Kraton G1646 (composition 5.5) and Kraton G1643 (composition 6.6), or even with 20% of Kraton G1643, also appears to give acceptable results in terms of Charpy impact strength, while maintaining good light transmission. Kraton G1646 V gives acceptable light transmission and impact strength 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 strength.

[0062] Table 6 presents the results obtained for compositions incorporating Dow's impact modifier, Infuse 9817.

[0063] Examples7.17.27.37.57.67.77.8Moplen RP340N908580HF955MO90858075Infuse 981710152010152025Total Light Transmission, %63.758.254.451.545.34343.1Charpy Impact Strength, 23°C, kJ / m²7.614.953.73.54.76.917.3

[0064] Unlike agents G1730, G1646 and G1643, replacing 25% HF955MO with 25% Infuse 9817 (composition 7.8) does not achieve the required impact resistance. In addition, in this example, the light transmission is also not acceptable. Furthermore, unlike agent G1643, replacing 20% ​​HF955MO polypropylene with 20% Infuse 9817 (composition 7.7) does not maintain 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. However, this agent gives acceptable values ​​in Example 7.3, replacing 20% ​​RP340N polypropylene.

[0065] 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.

[0066] 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.

[0067] 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) 6.372 30 600 461 30 7.35 999 707 541 24 6.561 719 603 612 0 6.660 709 504 111 7 3.469 51 26 3.564 467 054 114 0 3.664 47 7 364 61 39 3.770 45 6.43.85 98 61 8 3.15 88 7 1340 391 0 33.95 79 44 5 5.560 470 9 504 111 7

[0068] Table 7 shows that of the five criteria evaluated, only composition 3.1, corresponding to 75% HF955MO, 25% Kraton G1730 M, gives acceptable results. In particular, the replacement of 25% RP340N polypropylene by 25% Kraton G1730 M (composition 3.4) does not, contrary to what is observed with composition 3.1, sufficiently improve the impact resistance. Even if the replacement of 27% RP340N polypropylene by 27% Kraton G1730 (composition 3.5) sufficiently improves the impact resistance, the flexural modulus and CLTE values ​​are not sufficient. Similarly, among the agents tested (G1730, G1646 and G1643, respectively compositions 3.1, 5.5 and 6.6), only G1730 is capable, by replacing 25% of HF955MO polypropylene, of conferring an acceptable flexural modulus.

[0069] It is also observed that by replacing 28% of HF955MO polypropylene with 28% of Kraton G1730 (composition 3.9), an acceptable impact strength 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 strength is not acceptable, while the haze value is acceptable.

[0070] 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.

[0071] Examples3.13.23.33.83.9HF955MO, %7573718072Kraton G1730, %2525252028HazeacceptableacceptableacceptableacceptablenotacceptableCharpy impact resistance, 23°C, kJ / m²acceptablenotacceptablenotacceptablenotacceptableacceptable

[0072] 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.

[0073] ParameterMinimum accepted valueMaximum accepted valueExample 3.1Total light transmission50%No limit58%Haze30%90%87%Flexural modulus1000 MPa1800 MPa1256 MPaMelt flow rate10 g / 10 min25 g / 10 min16 g / 10 minCoefficient of linear thermal expansion90 / °C130 / °C103 / °CCharpy impact strength with notch at 23°C35 kJ / m 2 Not applicable 39 kJ / m 2Charpy impact strength with notch at -20°C 5 kJ / m 2 Not applicable 11 kJ / m 2 Brittle - ductile transition temperatureNo limit -10°C-25°C

[0074] Thus, it appears that the selections made, particularly 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 styrenic block copolymer comprising midblocks 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.

[0075] 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.

[0076] Furthermore, in the tested examples, 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% does not allow an acceptable Charpy impact strength to be obtained (composition 3.8).

[0077] 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.

[0078] The invention is not limited to the embodiments presented and other embodiments will become apparent 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 greater number of components would also make it possible to manufacture a material associated with the desired values.

Claims

Bodywork part (20) of a motor vehicle (40) having:- a transmittance measured at 3 mm thickness greater than or equal to 50% and less than or equal to 95%,- a haze measured at 3 mm thickness ranging from 30% to 90%, andsaid 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. 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. Body part according to any one of claims 1 and 2, in which the material comprises between 74% and 78% by mass, inclusive, of polypropylene, preferably between 74.5% and 77%, and more preferably approximately 75%. A body part according to any one of claims 1 to 3, wherein the polypropylene is a homopolymer. Body part according to one of claims 1 to 4, in which 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. Bodywork part according to the preceding claim, in which the styrene block copolymer has a mass content ranging from 20 to 22% of polystyrene, preferably 21%. A body panel (10) comprising a body part according to any preceding claim. Motor vehicle (40) comprising a body part (20) according to any one of claims 1 to 6.

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