FR2675097A1 - COVER FOR RECEIVING A PNEUMATIC SAFETY CUSHION. - Google Patents

Abstract

The invention relates to a cover (1) for receiving an air bag (2), and provided on its inner surface with a thin portion intended to break easily at the start of actuation of the air bag. The cover is made of olefinic and / or styrenic type thermoplastic elastomer, having a JIS A hardness of at least 80, in accordance with JIS K-6301 and a flexural modulus of at most 5. 000 kg / cm2 (4.9.108 Pa) in accordance with JIS K-7203.

Description

Lid for receiving a pneumatic cushion

of security.

  The present invention relates to a cover for receiving a pneumatic safety cushion mounted in a vehicle and adapted to be inflated abruptly in the event of detecting an impact or deformation on the cover when the vehicle collides

  against another vehicle or hard object.

  Lids of this type are fractured at the moment when the pneumatic cushion they contain is inflated abruptly. Since the broken fragments of these lids are thrown by the pneumatic cushion during inflation, they can inflict injuries to the face, vehicle occupant eyes etc. Conventional lids were thus made impossible to fracture by inserting a reinforcing element, such as a net, for example (Japanese Published and Unreviewed Patent Nos. 234,764 / 1987 and 127). 336/1975 and published and unexamined Japanese utility models No. 80,928/1977,

  Nos. 43,454 / 1975 and No. 25,342 / 1976).

  The lid, containing a reticular insert, is generally produced by molding a material of the polyurethane foam type, which is resistant to a relatively low temperature, a reinforcing thread then being embedded in the entire volume of the lid In this case this cover is generally provided with a line along which no reinforcing thread has been inserted, so that the air cushion, during its swelling,

  can expand and easily fracture the lid.

  Published Japanese Unexamined Utility Model No. 76,042 / 1977 provides a cover adapted to receive a pneumatic safety cushion, said cover being composed of two layers, i.e., a foam shell surface layer. of hard urethane intended to form a surface with clean finishes, and a central layer of low density (high expansion ratio) urethane foam, provided to give the general flexibility to the lid, and provided with a slot (a line allowing the lid to expand smoothly during swelling) from the middle layer and through a portion of the envelope

of surface.

  In the aforementioned conventional lids intended to contain a pneumatic cushion, the lid reinforced with a reticular insert, because of the presence of this insert, has the disadvantage of requiring a lot of hours of work and labor. work and proves risky, since it only works with difficulty with precision despite the use of a formed urethane foam (RIM) and that it has a yield

low for a high price.

  The lid described in Japanese Unexamined Utility Model No. 76,042 / 1977 discloses a urethane foam head surface shell (the degree of Shore hardness is in the range of 30 to 40, measured in accordance with to ASTM D-2240) and is not particularly provided with a reinforcing material, which poses a problem of low safety of use because it is impossible to completely avoid the risk of projection of broken fragments during swelling

  abrupt pneumatic cushion, especially at -40 'C.

  Japanese Published and Unexamined Patents Nos. 202,550 / 1989 and No. 171,362,1990 disclose inventions

designed to overcome this problem.

  The lids proposed in these inventions consist of a surface envelope producing a soft feel and a hard core layer having a capacity of preserving its shape, provided with a portion, a perforated slot for example, which can be easily torn during inflation of the airbag The surface envelope and the core layer are described as being made of a thermoplastic material and produced by the insert molding process or the two-color injection molding process. Although the lid of this kind serving to contain a pneumatic cushion gives an excellent feeling of flexibility and has a very good ability to expand at temperatures ranging from a low temperature (-40 C) to a high temperature (+ 800 C ), it nevertheless has the following two drawbacks: to manufacture a formed article (finished product), it is necessary to use two metal molds, one to mold the central layer, the other to mold a surface envelope This results in a economic problem, since manufacturing requires a specific molding apparatus and the molding cycle is long; when materials with different molding shrinkage are subjected to multilayer molding, the product inevitably undergoes deformation and a crease occurs along the slotted portion (such as, for example, a perforated slot) provided in the central element This fold is visible to the naked eye through the surface envelope This appearance of the fold affects the appearance of the lid as an interior decoration element, since the air cushion is placed in a visible place such as

  center of a steering wheel or the front of a dashboard.

  The present invention aims to solve the problems posed by the above-mentioned cover for containing an airbag and provides a cushion cover with moderate flexibility and sufficient strength to withstand external pressure, which is not crushed during inflation of the air cushion and that opens

easily.

  The present invention also aims to provide a cover for receiving a pneumatic cushion that can be reproduced by a simple molding process, such as injection molding, which method avoids rejects and ensures high profitability, high accuracy, high productivity

and an ideal economy.

  The lid of the present invention for receiving a pneumatic cushion is provided on its inner surface with a portion having a small thickness which

  can be easily torn when the tire cushion

  tick will begin to swell, this lid being

  in that it is made of a thermoplastic elastomer (ETP) of an olefinic and / or styrenic type material having a hardness JIS A (Japanese industry standard) of at least 70, as determined according to the standard JIS K-6301, and a modulus of flexural elasticity of not more than 5,000 kg / cm 2 (4.9 108 Pa) as determined in accordance with

the JIS K-7203 standard.

  The lid of the present invention serves to

  to receive a pneumatic cushion is preferably

  characterized in that it is a shaped article obtained by injection molding into a color of the material mentioned

  above with a coating applied on its surface.

  The inventors of the present invention have diligently studied the means of fulfilling the objectives described above, and have found that these objectives are achieved by means of a cover made of a specific thermoplastic elastomer and provided, on its internal surface, of a part having a small thickness intended to be broken The present invention is the result of

this discovery.

  In the accompanying figures, Fig. 1 is a schematic front view partially in section illustrating a cover according to an embodiment of the present invention for receiving an airbag, the cover being attached to the airbag; and FIG. 2 is a rear view of the cover for receiving a pneumatic cushion, illustrating an example of the thin portion provided for

fracture easily.

  In the figures, the references denote in 1, a cover for receiving a pneumatic cushion, in 2 a pneumatic cushion, in 3 a swelling device, in 4 an annular retention device, in 5 a basic retention device, in 6 a plate

metal and in 7 a rivet.

  The lid 1 of the present invention is made of a single layer of styrene and / or olefinic type ETP thermoplastic elastomer having a JIS A hardness (Japanese industry standard) of at least 70, as determined according to the JIS standard. K-6301, and a bending modulus of elasticity of not more than 5,000 kg / cm 2 (4.9 108 Pa) as determined in accordance with JIS K-7203. This cover is provided on its inner surface with a thin IC part designed to break easily when the airbag starts to

to inflate.

  The styrenic type elastomer to be used in the present invention is a composite material formed of a conjugated styrene diene block polymer and a hydrogenated version of the block polymer serving as matrix material, said matrix material incorporating a component selected from the group consisting of thermoplastic resins, such as olefinic and styrenic type resins, various rubber plasticizers, such as hydrocarbon-type rubber (e.g. oils) plasticizers, and synthetic plasticizers ( for example polybutene),

  mineral fillers, waxes and other various additives.

  The conjugated dienes which it is desirable to use in the above-mentioned conjugated styrene-diene block polymer include butadiene and isoprene. For the present invention, a hydrogenated version of the block polymer is used which offers as advantages a longer life (resistance to heat and weather conditions) and stability

during shaping.

  The thermoplastic elastomer of the olefinic type which can be used in the present invention is a composite material using a rubbery copolymer of ethylene and olefin of 3 to 6 carbon atoms and a plasticized polymer as a material for the matrix. , the latter containing a component selected from the group consisting of the same resins, plasticizers, mineral fillers, waxes and additives as those listed above for the styrenic type elastomer.It may be incorporated into the rubbery ethylene copolymer and o & -olefin-conjugated diene a quantity

  moderated diene component, such as dicyclopenta

  diene or ethylidene norbornene in a copoly-

  The X-olefins that can be used in the present invention to achieve performance and cost advantages include ample products.

  marketed using C 3: propylene and C 4: butene-1.

  The olefin elastomer is melted and mixed with an organic peroxide, a rubber vulcanizer and a variable crosslinking aid in a Banbury mixer or in a device for

  extrusion and, during the process of smelting and melting

  lange, dynamic crosslinking can also be used

  that partial or substantially total of the copolymer of ethylene and o-olefin rubber The elastomer of olefin type thus worked proves particularly interesting when it has a hardness JIS A understood

between 70 and 95.

  The styrene type elastomer and the olefin type elastomer mentioned above can be used alone

  or combined to a suitable percentage.

  Specifically, the elastomeric products of the

  styrene type available today on the common market

  for example, the following products: "Clayton", produced by Shell Chemical, "Rubberon" produced by Mitsubishi Petrochemical, "Elastomer-AR" produced by Aron Kasei, "Sumitomo TPE-SB" produced by Sumitomo

  Chemical, and "Tuftex" produced by Asahi Chemical.

  The olefin-type ETP products available today on the market include, for example, the following products: "Thermolan", "SPX" and "Yukaron Cell" produced by Mitsubishi Petrochemical, "Sumitomo TPE" produced by Sumitomo Chemical , "Milastomer" and Goodmer "produced by Mitsui Petrochemical," Santoprene "produced by Mistubishi-Monsanto," Softlex "produced by Nihon Sekiyu Kagaku," Oleflex "produced by Showa Denko and

"Hi-Fax" produced by Himont.

  The elastomer of the olefinic type and / or the styrene type

  of the present invention is selected using the criterion of hardness, so that

  its JIS A hardness is at least 70 as determined by

  in accordance with JIS K-6301 and that its modu-

  the flexural elasticity is not more than 5000 kg / cm 2 (4.9 108 Pa) as determined in accordance with JIS K-7203, since this FTE must produce good

  feeling of flexibility, having important characteristics

  of form retention and that its ability to

  regular expansion of a pneumatic cushion should

to be stable.

  Preferably, the hardness JIS A is not inferior

  at 75 and the modulus of elasticity in flexion is not greater than

  It is even more preferable for the JIS A hardness to be at least 80 and for the modulus of elasticity not to exceed 2000 kg / cm 2 to be 3 000 kg / cm 2 (2.94 108 Pa).

(1.96 108 Pa).

  If the hardness JIS A is less than 70, although the ETP has a significant feeling of flexibility, it is deficient, not only in its ability to keep a shape and its ability to allow a solid attachment of a rivet, but also with regard to its ability to allow expansion of the pneumatic cushion

  at high temperatures (+ 80 C) If the coefficient of

  bending elasticity exceeds 5 000 kg / cm 2 (4.9 108 Pa), the ETP can not be used since it does not give the desired feeling of flexibility and does not allow the expansion of the low air cushion temperature

(-40 C).

  The average thickness of the cover wall of the present invention for receiving a pneumatic cushion (the average of the wall thickness of the cover representing at least 60% of the area) is approximately in the range of 0, 5 to mm It does not need to be uniform for the entire area Properly, the cover is designed such that the portions intended to receive a rivet will have a relatively large thickness and that the parts intended to fracture will have a relatively small thickness, about 50% less than

at the average thickness.

  Although, to produce a cover of the present invention for receiving a pneumatic cushion, conventional known molding methods for thermoplastic resins may be used, the one-color molding process may be referred to as a particularly desirable choice of view of the design. It is desirable that the cover of the present invention for receiving a pneumatic cushion be covered with a coating in order to increase the aesthetic appearance of the interior of an automobile, to allow good color matching with the other elements. Decorative interior and enhance the feel The coating is also desirable to prevent dust deposits and ensure scratch resistance For this coating, we can use different coating materials already used for

lids of this type.

  Since the cover of the present invention for receiving a pneumatic cushion gives a general feeling of flexibility, it does not provide any unpleasant feeling to the occupant of the car in contact with it, and it avoids any distortion or breakage.

because of an external force.

  The lid of the present invention is fractured along the thin portion located on its inner surface, at the moment when the airbag contained in the lid is expanded in the event of collision of the automobile against a hard object during its fracture. , the lid will not be broken into small pieces and will not

will produce no projection.

  The present invention will now be described more specifically below with reference to practical examples and comparative experiments. Of course, this invention is not limited to the examples given below but can be used otherwise without

  deviate from the spirit of the invention.

  Examples 1 to 3 and Comparative Experiments 1 and 2: A variable material, indicated in Table 1, and used to make the core, was developed with an injection molding device of the screw type in line with a mold pressure of 350 tonnes to form a product containing a thin H-part (lmm) to be fractured and measuring 3 mm in overall thickness and 5 mm in the parts intended to allow the fastening of a rivet Examples 1 and 2 and Comparative Experiments 1 and 2 were

received a coating.

  The coating was obtained by cleaning the molded injection molded lid surface with isopropyl alcohol and then applying a primer, (MEX 5440 and methyl ethyl ketone = 1: 1) produced by Sakai Kagaku KK. about 7 to 10 microns thick, on

  the surface cleaned by spraying.

  The applied primer layer was dried at room temperature for 10 minutes, then a surface layer of urethane (MEX 6047: drying agent F-3: thinner was sprayed onto the primer layer). 58 microns = 100: 50) produced by Sakai Kagaku KK over 20 to 25 microns thick. The applied surface layer was then dried at room temperature for 10 minutes, and the coating layer was cured.

  Dry surface at 800 C for 30 to 45 minutes.

  Comparative Experiment 3 represents a case of manufacturing a cover with reinforcing mesh The casting of the urethane edge containing the net was carried out by placing a polyester net in a urethane putty except for the thin part intended for to be fractured, by fixing metal parts of hooks lining) allowing the fixing of the hooks to a metal mold RIM, and molding the urethane putty In this molding, was used freon as foaming agent The molded product was removed from the mold and allowed to dry at 100 ° C. for 30 minutes. By this method, it proved difficult to obtain a stable lid, because of the insertion of the net. The molding required a very long cycle and generated heavy losses. The materials used indicated by symbols in Table 1 were as follows: TPS-1: styrene-type ETP based on hydrogenated SBS, produced by Mitsubishi Petrochemical and marketed under the trademark "Rubberon MJ 8300 C", hardness

  JIS A of 85 and density 0.90 g / cm 3.

  TPS-2: Styrene type ETP based on hydrogenated SBS, produced by Mitsubishi Petrochemical and marketed under the brand name "Rubberon MJ 8300 B", hardness

JIS A of 55 and density 1.1 g / cm 3.

  TP 0-1: olefinic type ETP (partially crosslinked type) based on ethylenepropylene rubber, produced by Mitsubishi Petrochemical and marketed under the trademark "Thermolan 3980 B", JIS A hardness of 93, density

0.89 g / cm 3.

  TPO-2: ETP of the olefinic type (non-crosslinked type)

  based on an ethylenepropylene / polypropylene rubber

  ne / poly-ethylene, produced by Mitsubishi Petrochemical and marketed under the trademark "Thermolan 2920 B", modulus of elasticity in flexion 2000 kg / cm 2 (1.96 108 Pa) and

density 0.90 g / cm 3.

  TP 0-3: mixture of polypropylene BC 8 D produced by Mitsubishi Petrochemical, MFR 1.8 g / 10 min (230 C, 2.16 kg) and specific gravity 0.90 g / cm 3 with 10% of EPO 2 P produced by Nippon Synthetic Rubber, Mooney viscosity module 24 (ML 1 + 4100), and 26% propylene by using a fusion-mixing device, the mixture having a flexural modulus of elasticity of 7 000

  kg / cm 2 (6.8 108 Pa) and a density of 0.89 g / cm 3.

Method used for the tests.

  (1) Sensation of flexibility. A module cover or cover unit consisting of a pneumatic cushion 2, a cover 1 for receiving the airbag, retention devices (metal fittings) 4 and 5, and a swelling device 3 has been left in an ambient temperature ranging from -1% C to 601 C until the temperature of the module cover reached room air temperature. Then, a panel of 10 people tested the modulus cover to define softness to the touch A sample whose feeling of flexibility had been assessed as satisfactory by at least seven members of the panel was designated by o and a sample whose feeling of flexibility had been estimated satisfactory by

  plus six of the panel members was designated by x.

  (2) Ability to retain a form.

  An airbag module housing mounted as described above was heated to 1101 C for 1000 hours. Furthermore, a similar module package was subjected to two cycles of temperature fluctuations between -401 C and 1000 C. virtually undistorted sample was designated by o and a sample

  with marked deformation has been designated x.

  (3) Expansion capacity test.

  An airbag module housing mounted as in (1) was attached to a flywheel and tested for expansion capability at -401 ° C and + 801 ° C. A broken and projected sample in all directions, broken into sharp edges and thus preventing the cushion from operating normally, or torn at the point of riveting the parts on the cages was found to be inadequate and designated by

  x A sample free from the drawbacks mentioned above

  above and working normally has been designated by o.

  (Appearance of the product) A cover coming out of the injection molding, either in its unmodified form or after coating, was examined for signs of cracking, peeling, non-uniform varnish and deformation in the part showing thin A sample with questionable cracking has been designated x and a sample with no defects has been designated

by o.

  (Productivity) The appearance and size of a set of 20 products formed one after the other were examined. A group of products whose levels were generally acceptable was designated by o and a product group containing a sample can be

  considered missed was designated by x.

(Table 1)

  As is clear from the working examples cited above, the lids of the present invention for receiving a pneumatic cushion were very pleasing to the touch because of the comfortable feeling of softness imparted to human bodies in contact therewith. Moderate rigidity and, consequently, an excellent ability to maintain their shape Due to the low resistance portion intended to break, the lid was quickly broken at

  when the airbag began to inflate.

  The lid had a good appearance despite the party to

  thick on its inner surface.

  The lid of the present invention for receiving a pneumatic cushion can be manufactured by a streamlined injection molding process which allows for simplicity of procedure, high accuracy, very little scrap, high profitability and efficient and reliable operation. These advantages are

  translate into a sharp decrease in costs.

  The coating on the lid not only helps to enhance the aesthetics of the interior of the car, allows for an assortment of the color with other decorative elements of the cabin and gives the feeling of flexibility, but ensures also cover protection against dust deposits and damages.

Claims (7)

  1 cover (1) for receiving a pneumatic cushion (2) and provided on its inner surface with a portion having a small thickness which can be easily torn when the airbag begins to swell, this cover being characterized in that it is made of a thermoplastic elastomer (ETP) of the olefinic and / or styrenic type having a hardness JIS A (Japanese industry standard) of at least 70, as determined in accordance with JIS K-6301, and a module flexural elasticity of not more than 5,000 kg / cm 2 (4.9 108 Pa) as determined in accordance with JIS K-7203.   2 Lid according to claim 1, characterized in that it is obtained by injection molding said material which is colored and by applying a coating on its surface.   Lid according to claim 1, characterized in that said styrene-type elastomer is a   composite material comprising a styrene block polymer   conjugated diene and a hydrogenated version of the block polymer serving as a material for the matrix, and integrating into the matrix material a component selected from the group consisting of thermoplastic resins of the olefinic and / or styrenic type, rubber plasticizers, charging materials   minerals, waxes and other various additives.   Lid according to claim 3, characterized in that said conjugated diene is butadiene and / or isoprene.   Lid according to claim 1, characterized in that the olefin type ETP is a composite material using a rubbery copolymer of ethylene and olefin of 3 to 6 carbon atoms and a plasticized polymer as a material for the matrix , the latter containing a component selected from the group consisting of the same resins, plasticizers, mineral fillers, waxes and additives. Lid according to claim 5, characterized in that said ethylene rubber of conjugated diene and olefin contains a moderate amount of a diene component, such as dicyclopentadiene or   ethylidene norbornene in a copolymerized form.   Lid according to Claim 5, characterized in that the said olefin is C 3: propylene and / or C 4: butene-1.   Lid according to claim 1, characterized in that said olefin type ETP is melted and mixed with an organic peroxide, a vulcanization product of the rubber and a variable crosslinking aid in a Banbury mixer or a device for extrusion and, during the melting and mixing process, partial or substantially total dynamic crosslinking of the copolymer rubber may also be used ethylene zolefin.   9 lid according to claim 1, characterized in that the hardness JIS A is at least 75 and in that the elasticity coefficient in flexion is equal to   more at 3000 kg / cm 2 (2.94 108 Pa).   Lid according to Claim 1, characterized in that the hardness JIS A is at least 80 and the flexural elasticity coefficient is equal to   more at 2,000 kg / cm 2 (1.96 108 Pa).