FR3085380A1 - POLYOLEFIN-BASED COMPOSITION FOR THE MANUFACTURE OF TRANSPARENT PARTS - Google Patents

Abstract

The subject of the invention is a composition characterized in that it comprises a mixture of at least i) from 75% to 90% by total mass of the composition of a constituent chosen from: - a polypropylene-based material having a light transmission of between 55 and 75%, - an amorphous polyolefin, and ii) from 0 to 20% by total mass of the composition of at least one agent for reducing the coefficient of thermal expansion, and iii) from 0 to 20 % by total mass of the composition of an elastomeric copolymer polyolefin, provided that the concentration of at least one of the components ii) and iii) is different from 0. The invention also relates to inserts 20 for part 10 of motor vehicle body 40 and on methods of manufacturing motor vehicle body parts 40.

Description

The invention relates to a composition for the manufacture of objects in the automotive industry, and more particularly a motor vehicle body part comprising a transparent or translucent element.

An element is qualified as transparent when it allows light to pass through it in the visible region. A transparent element makes it possible to distinguish objects clearly through its thickness. An element is considered to be transparent when it has a transmittance greater than or equal to 85%. An element is called translucent when it lets light pass through it in the visible range, but without making it possible to clearly distinguish objects. A translucent element is an element through which we can see blurring. It is considered that an element having a transmittance greater than or equal to approximately 50% and less than 85% is translucent.

The transmittance or light transmission of a material is the fraction of the light flux passing through it. Thus the transmittance represents the ratio of the light intensity transmitted by the material to the incident light intensity.

There are known elements reported on a bodywork having in particular the object of enhancing a line or underlining a shape in order to strengthen the image that the manufacturer wishes to associate with his vehicle model.

For example, the chrome strips running along the side of the vehicle, the rocker panels, the brand logo, the door handle covers, the mirror caps are these elements of style whose design is the subject of particular care on the part of the vehicle designers.

In order to enhance the effect produced by these bodywork elements, it has been proposed to place a light source behind a surface of the bodywork element formed from a transparent material.

The composition which is the subject of the invention can be used to form an element, of transparent or translucent material which could be added to all the bodywork visible from the outside of the vehicle, such as an opening, a bumper, or a grille.

Body parts are known from plastic molding, and on which a transparent element is attached in a housing provided for this purpose.

These transparent elements have the drawback of having to be perfectly adapted to the housing present in the bodywork part. In addition, the assembly of such optical elements on body parts has the disadvantage of highlighting assembly clearances and significant outcrops, incompatible with the visual quality required for a motor vehicle. Finally, such added elements generate complexity in the management of the seal.

To avoid these problems of element attached to a part, body parts are also known which come from plastic molding, overmolding one or more inserts. These inserts are preformed parts incorporated in, and / or integral with said molded part, which generally serve to reinforce said molded part and / or serve for the subsequent fixing of mechanical elements. The insert can also be combined with the bodywork part.

Furthermore, the transparent material used to manufacture a transparent element must allow optimal diffusion of the light passing through it, while having a fairly large capacity to absorb shocks. It has been proposed to use polycarbonate (PC) as transparent materials in the automobile for the manufacture of large transparent body panels and PMMA (Polymethyl methacrylate) for the manufacture of parts in the optical zone, on the headlights. and around, outside the shock zone. PC and PMMA are available in tinted to achieve a smoky effect allowing to hide a light function once switched off.

However, these materials are not compatible with polypropylene (PP). However, the body parts from molding are mainly made from a material based on polypropylene (PP). As a result, there is not enough adhesion between the insert and the polypropylene part and their assembly requires fixing means.

Furthermore, PMMA is not very resistant to shocks and the PC requires a complex molding process (suitable injection system, high molding temperature, and above all a varnish casting process which does not pass through the chains. traditional painting).

As for the various plastic materials based on polypropylene, they are opaque, and therefore cannot be used to manufacture a transparent element. Conventionally, a body panel is made of a material comprising polypropylene loaded with:

- talc between 0 and 30% in order to obtain a CTE (Coefficient of Thermal Expansion) suitable for its use; the CTE is a reflection of the thermal behavior of the material, and

- carbon black (around 2%), to fight against aging and maintain color).

and includes an elastomer.

The incorporation of these additives makes it even more opaque. Currently, the use of polypropylene prevents the implementation of any light signature for exterior parts.

Furthermore, to obtain a tinted appearance, it is possible to cover a transparent body panel with a molding film or with a veil of paint on the exterior or interior face. This however involves additional and complex steps, and therefore additional costs. In addition, these techniques can be used for PC and polypropylene panels, but PMMA is too fragile to be applied with such treatments.

Finally, there are known materials as transparent as a PC and moldable under the same conditions as polypropylene or PMMA depending on the grades. However, these materials are brittle like PMMA and are therefore difficult to use in this application.

The invention aims to remedy these drawbacks. There is indeed a need to have a material which can be used to form an element which could be overmolded or co-molded in a polypropylene bodywork part, having more good qualities of light transmission, good mechanical resistance, and can be tinted.

This is why the present invention relates to a composition comprising a mixture of at least

i) from 75% to 90% by total mass of the composition of at least one constituent chosen from:

- a polypropylene-based material having a light transmission of between 55 and 75%, preferably between 58 and 65%, especially around 60%;

an amorphous polyolefin;

ii) from 0 to 20% by mass relative to the total mass of the composition of at least one agent for reducing the coefficient of thermal expansion, and iii) from 0 to 20% by mass relative to the total mass of the composition of an elastomeric copolymer polyolefin;

provided that the concentration of at least one of the components ii) and iii) is different from 0. In the description of the present invention, the limits indicated are included.

The composition according to the invention allows in particular to manufacture transparent or translucent inserts, compatible with polypropylene, the assembly of the transparent insert with the main body of the polypropylene part having the required visual quality and allowing a good sealing management. These transparent inserts are also capable of absorbing fairly large shocks and can be tinted.

This composition has a viscosity (MFI, melt flow index) between 10 and

g. 10 min ^-1 at 230 ° C on the material with a weight of 2.16 kg according to ISO 1133-1: 2011. The glass transition temperature (Tg) of the material forming this transparent element is less than or equal to the glass transition temperature of the material forming the bodywork part.

The term "polypropylene-based material" means a material comprising at least 90%, in particular 95% and in particular at least 99% of polypropylene. The material can in particular be made of 100% polypropylene.

By polypropylene within the meaning of the present invention means in particular:

- Homopolymer: a single motif in the polymer chain: - (CH (CH3) -CH2) -n (Motif A),

- Copolymer: the material also contains polyethylene (PE) monomers (CH2-CH2) - (Pattern B).

The patterns can be distributed in blocks, for example: A-A-A-A-A-B-B-B-B-B-A-A-A-A; they can be distributed randomly, for example: A-B-A-A-A-B-B-B-A-A-B-;

they can be distributed periodically, or alternately, for example: A-B-A-B-A-BA-B-A-B-A-B-A;

the polymers can be grafted, for example:

A-A-A-A-A-A-A-A-A-A-A-A-A-AI

B-B-B-B-B-B-B-B-B.

The polypropylene-based material i) can be a combination of a polypropylene and a nucleating agent; the nucleating agent makes it possible to obtain very fine crystals and a translucent material having a transmittance of approximately 70%.

Amorphous polyolefins are also called "cyclic copolymer polyolefins". In the present invention, the amorphous polyolefin can be a cycloolefin-copolymer (COC), or a cycloolefin-polymer (COP), of general developed formulas presented below:

Preferably, component i) is present at least 80% by mass relative to the total mass of the composition, and preferably at least 85%.

Preferably, the agent for reducing the coefficient of thermal expansion ii) constitutes at least 0.001% relative to the total mass of the composition, in particular at least 1%, in particular at least 5% and even more particularly at minus 10% of the total mass of the composition.

According to one embodiment of the invention, the composition contains one or more agents for reducing the coefficient of thermal expansion ii), in an amount greater than 0% by mass relative to the total mass of the composition.

Advantageously, the agent for reducing the coefficient of thermal expansion ii) is chosen from:

- crushed glass fiber with a length less than or equal to 80 μm, preferably 60 μm and with a diameter 8 to 15, preferably 13 μm,

- an elastomer, preferably ethylene-octene elastomer, or

- their mixtures in all proportions.

The compositions according to the invention containing such glass fibers have isotropic properties close to those of the polymer and allow the production of materials which are not opacified.

The presence of ethylene octene elastomer makes it possible to obtain material having very good impact resistance.

The agent for reducing the coefficient of thermal expansion ii) may in particular consist of a mixture of ground glass fiber and ethylene-octene elastomer, comprising ground glass fiber at a concentration of 0.001% to 99.999% by mass relative to the mass of said mixture, in particular from 1% to 99%, in particular from 5 to 95%. The mixture of ground glass fiber and ethylene-octene elastomer may comprise ethylene-octene elastomer at a concentration of 0.001% to 99.999% by mass relative to the mass of the mixture, in particular from 1% to 99%, in particular from 5 to 95%. According to certain embodiments of the invention, the glass fiber represents from 25 to 50% by mass of the total mass of agent for reducing the coefficient of thermal expansion and the ethyleneoctene elastomer represents from 75 to 50% by mass of the total mass of agent for reducing the coefficient of thermal expansion. According to other embodiments of the invention, the glass fiber represents from 75 to 50% by mass of the total mass of agent for reducing the coefficient of thermal expansion and the ethylene-octene elastomer represents from 25 to 50 % by mass of the total mass of agent for reducing the coefficient of thermal expansion.

Preferably, the elastomeric copolymer polyolefin iii) constitutes at least 0.001% relative to the total mass of the composition, in particular at least 1%, in particular at least 5%, and even more particularly at least 10% of the total mass of the composition.

Advantageously, the composition comprises a constituent ii) and a constituent iii).

The total mass of the components ii) and iii) in the final composition is generally less than or equal to 20% relative to the total mass of the composition, and can represent, for example, from 5 to 15% of the composition.

The composition may consist of the mixture of constituents i), ii) and iii).

Advantageously, the composition also comprises an anti-ultraviolet (anti-UV) additive. This anti-UV additive is for example bis (2,2,6,6, -tetramethyl-4piperidyl) sebacate. The presence of the anti-UV additive prevents yellowing of the polymer induced by exposure to the sun.

According to one of the embodiments, the composition comprises a light-diffusing additive. An insert containing a diffusing additive can serve as a light guide, that is to say a light deflector placed in front of a light source. The insert may take, for example, the combined form of a bodywork skin and a light guide. The light guide is therefore part of the insert which will be integrated on the bodywork part, by overmolding or co-molding.

Optionally, the composition comprises a coloring agent. It is thus possible to obtain a transparent insert tinted in the mass. All colors can be considered.

The coloring agent can be a dye. Such an agent is soluble in the material, which allows good light transmission. The dye is for example blue in color, which can compensate for the yellowing possibly induced by an anti-UV additive.

The coloring agent can also be a pigment, for example carbon black, at a concentration not exceeding 0.020% relative to the total mass of the composition, and preferably 0.015%.

The invention also relates to an insert for a motor vehicle body part, capable of being obtained from a composition according to the invention; such an insert is thus manufactured in a composition as described above.

The insert can in particular be intended to be molded into a main body of the bodywork part of a motor vehicle.

Alternatively, it can be obtained by co-molding with the main body of the motor vehicle body part.

Advantageously, the insert has a surface intended to be visible from outside the vehicle and an opposite surface, at least one of said surfaces not being covered by the plastic of the main body, preferably both surfaces not covered by the plastic material constituting the bodywork part. If one of the surfaces is covered by the plastic material constituting the bodywork part, the insert can transmit light while being lit laterally.

Optionally, the surface intended to be visible from outside the vehicle is grained. The graining adds diffraction, which increases the scattering of light.

Advantageously, the surface intended to be visible from outside the vehicle is covered with a protective varnish against scratches and ultraviolet.

The invention also relates to a motor vehicle body part comprising the insert presented above.

The invention also relates to a method of manufacturing a motor vehicle body part, into which is injected at the same time:

- In a first portion of a mold, a composition as described above to form an insert, and

- In a second portion of the mold, a plastic material based on polypropylene in order to form a main body of the bodywork part, so that the insert and the main body of the bodywork part are co-molded.

As the compositions according to the invention are compatible with polypropylene, there is sufficient adhesion between the insert and the main body of the polypropylene part. Thus their assembly does not require any fixing means. The co-molding process makes it possible to obtain an insert perfectly suited to the main body of the polypropylene part. Furthermore, this assembly is compatible with the visual quality required for a motor vehicle. Finally, such an assembly is characterized by good sealing.

The invention also relates to a process for manufacturing a motor vehicle body part, in which:

- An insert is made by injection molding in a first mold a composition as described above;

- after demolding, the insert is placed in a second mold;

- a polypropylene-based plastic material is injected into the second mold, in order to overmold the insert, while protecting the two surfaces of the insert intended to allow light to pass through.

Finally, the invention also relates to a method of manufacturing a motor vehicle body part, in which:

- An insert is produced by injection molding, in a mold comprising a cavity for molding the insert delimited by movable wedges, a composition as described in the foregoing; then, after movement of the wedges;

- a polypropylene-based plastic material is injected into the mold, comprising a molding cavity of a main body of the part, in order to overmold the insert, while protecting the two surfaces of the insert intended to allow the light.

These overmolding processes have advantages similar to those described for the co-molding process.

The inserts obtained with the compositions and methods according to the invention have good impact resistance and are compatible with polypropylene body parts. The compositions allow the manufacture of light transmitting inserts, with a transmission coefficient greater than or equal to 50%, measured according to standard NF EN ISO 13468-1 of November 1996 or NF EN ISO 13468-2 of July 2006 and in particular of around 85%. The inserts according to the invention contain at least 75% by mass of amorphous polypropylene or polyolefin.

The invention will be better understood on reading the attached Figure 1, which is provided by way of example and has no limiting character. FIG. 1 illustrates an example of a motor vehicle comprising a set of body parts according to the invention, comprising inserts according to the invention, produced in a composition according to the invention.

According to the examples of FIG. 1, the bodywork part 10 can be a front or rear bumper (not visible in the figure), a tailgate, a roof, a door or even a motor vehicle wing 40.

The bodywork part 10 has an area intended to allow, at least partially, the light from a light source placed behind said area.

To this end, the part 10 comprises at this zone a transparent or translucent element 20.

The transparent or translucent element 20 can be molded into the main body 30 of the part 10; it then constitutes an overmolded insert 20. It can also be obtained by co-molding with the main body 30 of the part 10.

The insert 20 has a surface intended to be visible from outside the vehicle 40 (surface facing the exterior of the vehicle) and an opposite surface (surface facing the interior of the vehicle). The insert 20 is partially overmolded, or co-molded, so that at least one of the two surfaces (preferably the surface intended to be visible) is not entirely covered by the material of the main body 30, in order to allow passage at least part of the light. However, the opposite surface (surface facing the interior of the vehicle) can be covered directly or indirectly by the material of the main body 30.

The main body 30 is made of a plastic material based on polypropylene. This material is opaque.

The insert 20, molded or co-molded, is transparent or translucent, and it was produced in a composition according to the invention.

The invention is not limited to the embodiments presented and other embodiments will be apparent to those skilled in the art.

Claims (15)

Claims 1. Composition characterized in that it comprises a mixture of at least i) from 75% to 90% by total mass of the composition of a constituent chosen from: - a polypropylene-based material having a light transmission of between 55 and 75%, an amorphous polyolefin, and ii) from 0 to 20% by total mass of the composition of at least one agent for reducing the coefficient of thermal expansion, and iii) from 0 to 20% by total mass of the composition of a elastomeric copolymer polyolefin, provided that the concentration of at least one of the components ii) and iii) is different from 0. 2. Composition according to the preceding claim, in which the amorphous polyolefin is a cyclo-olefin-copolymer (CGC) or a cyclo-olefin-polymer (COP). 3. Composition according to any one of the preceding claims, in which the agent for reducing the coefficient of thermal expansion ii) is chosen from: - crushed glass fiber with a length less than or equal to 80 μηι and a diameter of 8 to 15 μm, preferably 13 μm, of the ethylene-octene elastomer, or - their mixtures in all proportions. 4. Composition according to any one of the preceding claims, further comprising an anti-UV additive. 5. Composition according to any one of the preceding claims, further comprising a light-diffusing additive. 6. Composition according to any one of the preceding claims, further comprising a coloring agent. 7. Insert (20) for a part (10) of a motor vehicle body (40), made from a composition according to any one of the preceding claims. 8. Insert (20) according to the preceding claim, intended to be molded into a main body (30) of the part (10) of the motor vehicle body (40). 9. Insert (20) according to claim 7, obtained by co-molding with the main body (30) of the part (10) of the motor vehicle body (40). 10. Insert (20) according to any one of claims 7 to 9, comprising a surface intended to be visible from outside the vehicle (40) and an opposite surface, at least one of said surfaces not being covered by the plastic material of the main body (30), preferably the two surfaces not being covered by the plastic material of the main body (30). 11. Insert (20) according to the preceding claim, wherein the surface intended to be visible from outside the vehicle (40) is covered with a protective varnish against scratches and / or ultraviolet. 12. Part (10) of a motor vehicle body (40) comprising the insert (20) according to any one of claims 7 to 11. 13. Method for manufacturing a part (10) of a motor vehicle body (40), into which is injected at the same time: - in a first portion of a mold, a composition according to any one of claims 1 to 6 to form an insert (20), and - In a second portion of the mold a plastic material based on polypropylene in order to form a main body (30) of the part (10) of the bodywork, so that the insert (20) and the part (10) of bodywork are collapsed. 14. Method for manufacturing a part (10) of a motor vehicle body (40), in which: - An insert (20) is produced by injection molding in a first mold a composition according to any one of claims 1 to 6; - the insert (20) is placed in a second mold; - a plastic material based on polypropylene is injected into the second mold, in order to overmold the insert (20), while protecting the two surfaces of the insert (20) intended to allow light to pass through. 15. Method for manufacturing a part (10) of a motor vehicle body (40), in which: - An insert (20) is produced by injection molding, in a mold comprising a mold cavity for the insert (20) delimited by movable wedges, a composition according to any one of claims 1 to 6; then, after movement of the wedges; - A polypropylene-based plastic material is injected into the mold, comprising a molding cavity of a main body (30) of the part (10), in order to overmold the insert (20), while protecting the two surfaces insert (20) intended to allow light to pass through.