EP1206375A1

EP1206375A1 - Outer covering for the inside panel of a vehicle including a device for accommodating a safety air cushion

Info

Publication number: EP1206375A1
Application number: EP00956587A
Authority: EP
Inventors: Dominique Valligny; Benoít MENARD
Original assignee: Visteon Systemes Interieurs SAS
Current assignee: SMRC Automotive Modules France SAS
Priority date: 1999-08-02
Filing date: 2000-08-01
Publication date: 2002-05-22
Also published as: WO2001008934A1; FR2797240B1; FR2797240A1; US6896962B1; JP2003522068A

Abstract

An outer covering for the inside panel of a vehicle, whereby said panel includes a device for the accommodation and deployment of a safety air cushion, comprising the following: a support which includes a device for the accommodation and deployment of a safety air cushion; an inner layer consisting of a thermoplastic or thermosetting polymer foam material covering said support and fixed thereto; an outer covering or skin made from a thermoplastic polymer material covering the inner layer and fixed thereto. The inventive covering is characterized in that it does not have any incipient ruptures on the part of the panel which is used to accommodate and deploy the safety air cushion; it is made of a thermoplastic polymer material in the form of a powder by means of a free flow and by means of molding in a hot mold; the chemical composition is indicated for the entire panel and is obtained from a thermoplastic elastomer composition.

Description

Skin for vehicle interior panel including a device for housing a safety air bag

The present invention relates to a skin for a vehicle interior panel, this panel including a part for housing an air cushion or safety bag, this panel successively comprising:

- a support or insert including a cover and a device for housing and deploying the air bag,

an internal layer consisting of a foam of thermoplastic or thermosetting polymer material, covering said support, which is fixed to the support,

- An outer layer or skin, of thermoplastic polymer material, covering said inner layer which is fixed to this layer.

Such a panel is more particularly intended to serve as a dashboard, door panel or seat backs.

Commonly, there is provided in the skin a zone of weakness or of less resistance intended to open easily during the deployment of the air cushion of safety following an impact, undergone by the vehicle. The zone of least resistance generally has the form of a rupture line and is most often obtained by thinning the internal side of the skin, for example using a hot knife, or aligned rupture primers, at the using a laser.

Pre-cut skin processes require very precise and complex adjustment and control operations for the thickness of the thinned skin, in order to prevent excessive reduction and weakening of the skin. In the long term, under the repeated effect of thermal variations to which the passenger compartment of a vehicle is subjected, the skin may lose its flexibility and become brittle, in particular at the level of the rupture line.

However, for psychological reasons, it is desirable that the passenger does not see the zone of least resistance corresponding to the air bag.

In addition, this zone of least resistance must be able to retain, in the long term, despite variations in the temperature of the passenger compartment of the vehicle, an interior decorative appearance (soft and flexible surface) and sufficient mechanical properties so as not to deteriorate, including deforming and stretching, or else cracking.

The Applicant has now developed a simplified structure for a vehicle interior panel comprising an outer layer or skin free of fracture primers situated at the part of the panel serving to house the safety air cushion, these fracture primers may have the form of a line of rupture, by partial or punctual cutting of the skin, or even by local thinning along one or more lines of the skin.

More specifically, the invention relates to a skin for a vehicle interior panel including a device for housing and deploying a safety air cushion and successively comprising:

- a support including a device for housing and deploying the air bag,

an internal layer consisting of a foam of thermoplastic or thermosetting polymer material, covering the support and fixed to the latter, - an outer layer or skin, of thermoplastic polymer material, covering the inner layer and fixed to the latter,

the skin being characterized in that:

- it does not have any incipient fractures at the part of the panel used for housing and deploying the air bag,

its thickness, over the entire panel, varies from 0.2 mm to 5 mm, preferably from 0.6 mm to 1.7 mm, more preferably from 0.8 mm to 1.4 mm,

- it is made from a thermoplastic polymer material, in the form of a powder, by free flow and molding on a hot mold,

- its chemical composition is identical on the entire panel and is obtained from a thermoplastic elastomer composition mainly comprising a mixture of:

• at least one propylene homopolymer; and / or at least one copolymer based essentially on propylene, and based on at least one other olefin

(ethylene or alpha-olefin other than propylene, for example butene); and / or at least one copolymer based essentially on ethylene and based on at least one alpha-olefin;

• and at least one at least partially crosslinked polyolefin elastomer;

• possibly, a mineral or organic oil.

Preferably, the copolymer based essentially on propylene contains at least 50 mol% of propylene, and the copolymer based essentially on ethylene contains at least 50 mol% of ethylene. Thanks to the invention, the manufacture of a vehicle interior panel intended to be associated with a safety air cushion system does not require a pretreatment of the skin, subject to respecting the conditions set out in the claim 1.

The thickness of the skin may be thinner at most of the surface of the panel located above the air bag.

According to an advantageous variant of the present invention, the thickness of the skin is substantially equal over the entire panel.

The skin for the interior panel of a vehicle, in accordance with the invention, can be easily torn when the air bag begins to swell, but has sufficient mechanical strength to allow demolding of the skin without damage, in the context of '' manufacturing using the slush molding technique, and normal use in an automobile interior.

The technique of manufacturing the skin, from a powder, by free flow and molding on a hot mold, is known under the English name SLUSH MOLDING. A description of this technique can be found, in particular in European patent application 96943150.1.

The thermoplastic polymer material used to make the skin can be a powder composition comprising at least one polypropylene or a copolymer based essentially on propylene, and at least one polyolefin elastomer, at least partially crosslinked, as well as a mineral oil as 'softener.

According to a preferred variant of the invention, the skin is made from a thermoplastic polymer material consisting of an alloy of particular polyolefins, in the form of a powder, by free flow over a hot mold, preferably at a temperature variant from 220 ° C to 350 ° C. This particular polyolefin alloy includes:

a) approximately 97 to approximately 20 parts by weight of a matrix composed of at least one polymer containing at least 50 mol% of polypropylene, and, dispersed in this matrix, of at least one at least partially crosslinked polyolefin elastomer;

b) from about 3 to about 80 parts by weight of at least one polymer containing at least 50 mol% of ethylene;

c) optionally, at least one internal mold release agent.

It is not necessary to provide, in the aforementioned preferred thermoplastic polymeric material, mineral or organic oil to promote fluidity in the molten state and improve the flexibility of the molded skin.

The best results, related to the aforementioned objectives, have been obtained with a thermoplastic polymer material which is an alloy:

a) from approximately 80 to approximately 50 parts by weight of a matrix composed of at least one polymer containing at least 50 mol% of polypropylene, and, dispersed in this matrix, of at least one polyolefin elastomer at least partially crosslinked;

b) from about 20 to about 50 parts by weight of at least one polymer containing at least 50 mol% of ethylene;

c) optionally, at least one internal mold release agent.

The melt index (MFI), defined by standard ASTM D1238 L (230 ° C and 2.16 kg), of the matrix (a) is advantageously between 5 and 100 g in 10 minutes, even better, between 25 and 70 g in 10 minutes. The melt index of the matrix (a) corresponds substantially to the melt index of the thermoplastic polymer material.

The polymer containing at least 50 mol% of polypropylene, constituting the matrix (a) of one of the abovementioned families of thermoplastic polymer material is preferably semi-crystalline, that is to say its crystallinity is at least equal to 5%, determined by differential thermal analysis (ATD or DSC). The polymer can be chosen from the group comprising polypropylene semi-crystalline homopolymer, a semi-crystalline propylene-ethylene copolymer, a mixture of polypropylene semi-crystalline homopolymer and a semi-crystalline propylene-ethylene copolymer, polypropylene ( homopolymer) with amorphous and semi-crystalline blocks, propylene-ethylene or alpha-olefin copolymers with amorphous and semi-crystalline blocks. Advantageously, the semi-crystalline propylene-ethylene copolymer used to form the matrix (a) contains small amounts of ethylene, generally between 2% and 5% by weight, so that essential properties such as ease of processing work by a drop in the melting temperature of the matrix, the absence of bleaching in shock and rain, and the ease of demolding for parts undercut.

The at least partially crosslinked polyolefin elastomer contributes to improving the impact resistance of the skin at low temperature (down to -35 ° C.).

The at least partially crosslinked polyolefin elastomer dispersed in the matrix (a) is preferably semi-crystalline, that is to say its crystallinity is at least 5%, determined by differential thermal analysis. It can be chosen from thermoplastic elastomers: - used alone, such as: ethylene-propylene-rubber (EPR), ethylene-propylene-diene-monomer (EPDM), styrene-butadiene-styrene (SBS), styrene-ethylene-butadiene- styrene (SEBS), styrene-butadiene-rubber (SBR),

- or used according to a mixture, either in a reactor or by extrusion, of polypropylene with at least one elastomer, such as for example propylene / ethylene- propylene-rubber (PP / EPR), propylene / ethylene- propylene- diene monomer (PP / EPDM), the elastomeric fraction of which is at least partially crosslinked.

Advantageously, the components of the matrix (a) are subjected to a crosslinking reaction, partial or complete, by means of an appropriate agent, such as a peroxide or a silane, or to a chemical grafting by means of acrylic acid. or methacrylic acid or maleic anhydride or alkyl acrylates or methacrylates in which the alkyl is a C1 to C8 hydrocarbon chain.

The matrix can be prepared by introduction and mixing in a reactor or in an extruder of at least one polymer containing at least 50 mol% of propylene and at least one polyolefin elastomer at least partially crosslinked.

The polymer containing at least 50 mol% of ethylene, constituting component (b) of one of the aforementioned families of thermoplastic polymer material can be amorphous or semi-crystalline. It is preferably semi-crystalline, that is to say its crystallinity is at least equal to 5%, determined by differential thermal analysis. It can be chosen from the group comprising low density polyethylene (LDPE), linear low density polyethylene (LDPE), a mixture of low density polyethylene (LDPE) with a high density polyethylene (HDPE), this mixture containing at most 50% HDPE, an ethylene-alpha-olefin copolymer, in which the alpha-olefin is a C3 to

CIO and, more specifically, ethylene-octene copolymers (POE) comprising between 5 and 40% by weight of octene, ethylene-terephthalate (PET), d ¹ ethylene-vinyl acetate

(EVA), ethylene alkyl acrylate, ethylene alkyl methacrylate, in which the alkyl is a C1 to C8 hydrocarbon chain optionally modified with maleic anhydride, an ethylene copolymer and of tetrafluoroethylene, ionomers of ethylene, salified or not. Preferably, the polymer comprising at least 50 mol% of ethylene, of component (b), has a start of melting range at most equal to 140 ° C.

Various adjuvants of known type and commonly used in compositions intended for the slush molding process can also be introduced during the preparation of the mixture of the constituents of the matrix, or even subsequently, during the preparation of the thermoplastic polymeric material of the skin. , by the implementation of its various constituents (a), (b) and, possibly (c).

These various adjuvants are, for example, thermal or photochemical stabilizers, lubricants (used in much lower quantities than those of oils used to improve flexibility), antistatics, flame retardants, antioxidants.

Pulverulent mineral materials can also be introduced into the thermoplastic polymeric materials constituting the skin according to the invention in an amount of 0.1 to 10 parts and preferably from 0.1 to 5 parts by weight per 100 parts by weight of components "a" and B" . The dimensions of these mineral materials are generally between 0.01 and 300 μ and preferably between 0, 1 and 100 μm.

However, in the context of the present invention, it is preferable not to add or to limit the quantity of certain adjuvants:

- which can make the slush molding process more difficult, such as powdery mineral materials,

- which may exude and lead, in the long term, to a reduction in the mechanical properties of the skin, such as oils (or lubricants).

In the thermoplastic polymer material corresponding to the preferred variant, it is preferable to exclude the presence of powdery mineral materials serving as fillers, such as talc. Also preferably, oils are excluded as a softener.

According to the invention, the thermoplastic skin polymer material can comprise at least one internal mold release agent.

The internal release agent can be chosen from one of the conventionally known agents belonging to the group comprising the family of montane derivatives and of montane ester, stearate salts, amines, amides, hydrogenated hydrocarbon resins, waxes polyolefins such as polyethylene waxes, polypropylene waxes and ethylene-propylene copolymer waxes, copolymerization resins of aliphatic and / or aromatic monomers.

Preferably, the internal mold release agent can be chosen from the group formed by alkaline earth stearates, the most used of which is calcium stearate, and the aids of stearic acid (C17H35-CONH ₂ ) such as ethylene-bis-stearamide (EBS) used alone or as a mixture.

The internal release agent which, ultimately, is preferably used to manufacture the skin according to the invention, is magnesium stearate.

The internal release agent can be introduced into the thermoplastic polymer matrix during a mixing operation, either at the time of the preparation of the matrix constituting the component "a", or even at the time when the mixing of said matrix with the ethylene-based polymer constituting component "b".

The internal mold release agent is preferably introduced into the composition at a rate of 0.1 to 12 parts by weight and very preferably at a rate of 0.5 to 10 parts by weight per 100 parts by weight of the components "a" and "b ".

The powdered thermoplastic polymer material used to make the skin can be prepared by following the following steps:

- mixing of the constituents of the thermoplastic polymer material in an extrusion zone,

- cryogenic grinding of the granules from the extrusion, in order to reduce them to powder.

Preferably, the powdered thermoplastic polymer material used to make the skin is prepared by microgranulation, which consists of an extrusion through a microfilter and a grazing cut in an aqueous medium from which a thermoplastic polyolefin powder having particles of almost spherical shape results. or microbeads. The thermoplastic polyolefin powder suitable for the invention, obtained according to a suitable process, such as, for example, those mentioned above, has a particle size varying from 0.01 to 2000 μm, preferably ranging from 100 μm to 1000 μm.

In order to promote the best flow of the powder on the mold during the manufacture of the skin, and thus avoid local overloads of the material, whatever the shape of the mold, and achieve the small thicknesses of skin targeted within the framework of the The invention is preferably introduced into the thermoplastic polymer material, at least one flow agent, such as a precipitated silica or an alumina, optionally grafted with a silicone or with a silicone oil.

The amount of flow agent which can be provided in the thermoplastic polymer material according to the invention is between 0.01 and 10 parts, preferably between 0.01 and 5 parts by weight per 100 parts of the components

(a) and (b) matter.

Finally, other organic pulverulent materials of natural or synthetic origin can also be introduced, such as for example dyes, carbon black or a finely ground polypropylene wax. All these pulverulent materials can be used alone or in combination, and optionally introduced during extrusion before granulation (compounding).

Generally, the quantity of organic pulverulent materials which can be provided in the thermoplastic polymeric material according to the invention does not preferably exceed 6 parts per 100 parts of the components

(a) and (b) matter. The thermoplastic polymeric materials constituting the skin according to the invention can be prepared in a reactor or by extrusion or by powder-powder mixture. They can also be subjected to a partial crosslinking operation, preferably using a peroxide or a silane, or to a grafting reaction with acrylic acid, methacrylic acid, maleic anhydride or the alkyl acrylates or methacrylates in which the alkyl is a C 1 to C ₈ hydrocarbon chain.

As indicated above, the skin according to the invention is intended for an interior panel of a vehicle, including a device for housing and deploying a safety air cushion.

Such a panel therefore successively comprises:

- a support, or insert, including a device for housing and deploying a cousin of safety air. In the context of the present invention, the device can be any. In particular, the cover provided in the support to open under the pressure of the safety air cushion when it swells may or may not include means for cutting the internal layer consisting of a foam of thermoplastic polymer material and the outer layer or skin,

- Covering the support and fixed to it, an internal layer consisting of a foam of thermoplastic or thermosetting polymer material, preferably of polyurethane or polypropylene. This internal layer may or may not include a rupture line corresponding to the opening of the support during deployment of the air bag. The thickness of this internal mouse layer generally varies from 1 to 20 mm, preferably 5 to 15 mm. Its density generally varies from 20 to 500 g / 1, - Covering this internal layer and fixed thereto, a skin according to the invention.

A vehicle interior panel according to the invention can be prepared as follows:

1) manufacture of the skin by the slush molding technique,

2) fixing of the skin to the support by means of an internal layer of a foam of thermoplastic or thermosetting polymer material by placing the skin and the support in a mold and forming, inside this mold, the internal foam layer,

3) demolding and possible finishing operations of the resulting interior panel,

4) optionally, coating the skin of the interior panel.

The skin according to the invention achieves the following performances:

- an exterior decorative appearance, in particular a supple and soft touch,

- with or without paint, good thermal resistance to light, to scratching, to abrasion, to chemical agents, despite variations in the temperature of the passenger compartment of the vehicle, subject to normal use, these properties being significantly preserved over the long term,

- sufficient mechanical strength to allow excellent release of the skin without damage. But mechanical strengths (elongation at break when hot (about 90 ° C) and when cold (about -40 ° C), yield strength and tear strength) sufficiently limited to be able to open easily during inflation of the cushion safety air in case of collision with another vehicle or hard object without projection of broken fragments of the interior panel. Thus, thanks to the invention, the rupture and the projection of fragments of the interior panel are avoided due to the deployment of the air cushion. In fact, it is known that broken and projected fragments of the interior panel can injure the passenger, in particular when the vehicle just before the collision is traveling at high speed, and when the temperature of the panel is low.

the formation of a substantially rectilinear opening of the skin at the place where the stress is greatest when the support or insert is opened when the safety air cushion is deployed, under temperature conditions of the skin varying from -35 ° C to + 85 ° C.

More specifically, the performances achieved within the framework of the invention are as follows:

- test de__ _ésis_tanc_e__en tr_acti_n: this test consists in applying a traction speed of 100 mm per minute (more or less 10 mm per minute) according to the length of a skin test piece of 150 mm X 25 mm. In the context of the present invention, the tensile strength of the skin generally varies from 0.5 to 80 Newton. The best tensile strength values obtained with an alloy of different polyolefin polymers are in the range of 3 to 12 Newton.

Still within the framework of this tensile test, the elongation of the test piece generally varies from 5 to 250%. The best elongation values obtained with an alloy of different polyolefin polymers are in the range from 15 to 150%. tejst_ie__rési_s_tan: e__au _ ^^: this test consists in applying a force with a speed of 100 mm per minute (more or less 10 mm per minute) on a skin test tube of 200 mm X 50 mm comprising a rectilinear primer of 80 mm .

In the context of the present invention, the tear resistance of the skin generally varies from 20 to 100 Newton. The best tear resistance values obtained with an alloy of different polyolefin polymers are in the range from 5 to 17 Newton.

Claims

claims

1. Skin for vehicle interior panel, this panel including a device for housing and deploying a safety air cushion and successively comprising:

- a support including a device for housing and deploying the air bag,

an internal layer consisting of a foam of thermoplastic or thermosetting polymer material, covering the support and fixed to the latter,

- an outer layer or skin, of thermoplastic polymer material, covering the inner layer and fixed to the latter,

the skin being characterized in that:

- its thickness, on the whole panel varies from 0.2 mm to 5 mm,

- its chemical composition is identical on the entire panel and is obtained from a thermoplastic elastomer composition mainly comprising ^¬ a mixture of:

• at least one propylene homopolymer; and / or at least one copolymer based essentially on propylene, and based on at least one other olefin; and / or at least one copolymer based essentially ethylene and based on at least one alpha-olefin;

• and at least one at least partially crosslinked polyolefin elastomer;

optionally, a mineral or organic oil.

2. Skin for vehicle interior panel according to claim 1, characterized in that the thickness of the skin, on the entire panel, varies from 0.6 to 1.7 mm.

3. Skin for vehicle interior panel according to claim 2, characterized in that the thickness of the skin, on the entire panel, varies from 0.8 to 1.4 mm.

4. Skin for vehicle interior panel according to any one of claims 1, 2 or 3, characterized in that the thermoplastic polymeric material is in the form of a powder resulting from cryogenic grinding, or in the form of a powder composed of microbeads from an extrusion in a micro-die.

5. Skin according to claim 1, characterized in that the thermoplastic polymeric material of the skin is based:

a) from approximately 97 to approximately 20 parts by weight of a matrix composed of at least one polymer containing at least 50 mol% of polypropylene, and, dispersed in this matrix, of at least one polyolefin elastomer at least partially crosslinked;

b) from about 3 to about 80 parts by weight of at least one polymer containing at least 50 mol% of ethylene; c) optionally, at least one internal mold release agent.

6. Skin according to claim 5, characterized in that the thermoplastic polymeric material of the skin is based:

c) optionally, at least one internal mold release agent.

7. Skin according to claim 5 or 6, characterized in that the matrix (a) has a melt index (MFI: ASTM D 1238L - 230 ° C - 2.16 kg) of between 5 and 100 g in 10 minutes .

8. Skin according to claim 7, characterized in that the matrix (a) has a melt index (MFI: ASTM D 1238L - 230 ° C - 2.16 kg) of between 25 and 70 g in 10 minutes.

9. Skin according to any one of claims 5 to 8, characterized in that the polymer containing at least 50 mol% of propylene of the polymer matrix "a" is semi-crystalline.

10. Skin according to any one of claims 5 to 9, characterized in that the polymer containing at least 50 mol% of propylene of the polymer matrix "a" is chosen from the group consisting of polypropylene semi-crystalline homopolymer, a semi-crystalline propylene-ethylene copolymer, a blend of semi-crystalline polypropylene homopolymer and a semi-crystalline propylene-ethylene copolymer, polypropylene (homopolymer) with amorphous and semi-crystalline blocks, propylene-ethylene copolymers or alpha-olefin with amorphous and semi-crystalline blocks.

11. Skin according to any one of claims 5 to 10, characterized in that the polyolefin elastomer, at least partially crosslinked, of the polymer matrix "a" is semi-crystalline.

12. Skin according to any one of claims 5 to 11, characterized in that the polyolefinic elastomer, at least partially crosslinked, of the polymer matrix "a" is one of the elastomers belonging to the group consisting of ethylene- propylene-rubber (EPR), ethylene-propylene-diene-monomer (EPDM), styrene-butadiene-styrene (SBS), styrene-ethylene-butadiene-styrene (SEBS), styrene-butadiene-rubber (SBR) ).

13. Skin according to any one of claims 5 to 11, characterized in that the polyolefinic elastomer, at least partially crosslinked, of the polymer matrix "a" is a mixture of polypropylene with at least one of the ethylene-propylene elastomers rubber (EPR), ethylene-propylene-diene monomer (EPDM).

14. Skin according to any one of claims 5 to 13, characterized in that the components of the polymer matrix "a" are subjected to a chemical grafting by means of acrylic acid or methacrylic acid or maleic anhydride or alkyl acrylates or methacrylates in which the alkyl is a C1 to C8 hydrocarbon chain.

15. Skin according to any one of claims 5 to 13, characterized in that the components of the polymer matrix "a" are subjected to a partial or complete crosslinking reaction, using a crosslinking agent such as a peroxide or silane.

16. Skin according to any one of claims 5 to 15, characterized in that the polymer containing at least 50 mol% of ethylene forming component "b", is semi-crystalline.

17. Skin according to any one of claims 5 to 16, characterized in that the polymer containing at least 50 mol% of ethylene forming component "b" is chosen from the group consisting of low density polyethylene ( LDPE), linear low density polyethylene (LDPE), a mixture of low density polyethylene (LDPE) with high density polyethylene (HDPE), this mixture containing at most 50% HDPE, an ethylene-alpha copolymer -olefin, in which the alpha-olefin is a C3 to C10 unit and, more specifically, ethylene-octene copolymers

(POE) comprising between 5 and 40% by weight of octene, ethylene terephthalate (PET), ethylene vinyl acetate

(EVA), ethylene alkyl acrylate, ethylene alkyl methacrylate, in which the alkyl is a C1 to C8 hydrocarbon chain optionally modified with maleic anhydride, an ethylene copolymer and of tetrafluoroethylene, ionomers of ethylene, salified or not.

18. Skin according to claim 16 or 17, characterized in that the polymer containing at least 50 mol% of ethylene, of component "b", has an onset of melting range at most equal to 140 ° C.

19. Skin according to any one of claims 5 to 18, characterized in that all of the thermoplastic polymeric material is subjected to a partial crosslinking operation.