WO2003004310A2 - Couvercle d'airbag en mousse polymere presentant une zone affaiblie - Google Patents

Couvercle d'airbag en mousse polymere presentant une zone affaiblie Download PDF

Info

Publication number
WO2003004310A2
WO2003004310A2 PCT/US2002/020581 US0220581W WO03004310A2 WO 2003004310 A2 WO2003004310 A2 WO 2003004310A2 US 0220581 W US0220581 W US 0220581W WO 03004310 A2 WO03004310 A2 WO 03004310A2
Authority
WO
WIPO (PCT)
Prior art keywords
cover
cells
skin
region
density
Prior art date
Application number
PCT/US2002/020581
Other languages
English (en)
Other versions
WO2003004310A3 (fr
Inventor
Suresh Deepchand Shah
Carl Visconti
Michael William Jary
William Joseph Filipp
Original Assignee
Delphi Technologies, Inc.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Delphi Technologies, Inc. filed Critical Delphi Technologies, Inc.
Publication of WO2003004310A2 publication Critical patent/WO2003004310A2/fr
Publication of WO2003004310A3 publication Critical patent/WO2003004310A3/fr

Links

Classifications

    • BPERFORMING OPERATIONS; TRANSPORTING
    • B60VEHICLES IN GENERAL
    • B60RVEHICLES, VEHICLE FITTINGS, OR VEHICLE PARTS, NOT OTHERWISE PROVIDED FOR
    • B60R21/00Arrangements or fittings on vehicles for protecting or preventing injuries to occupants or pedestrians in case of accidents or other traffic risks
    • B60R21/02Occupant safety arrangements or fittings, e.g. crash pads
    • B60R21/16Inflatable occupant restraints or confinements designed to inflate upon impact or impending impact, e.g. air bags
    • B60R21/20Arrangements for storing inflatable members in their non-use or deflated condition; Arrangement or mounting of air bag modules or components
    • B60R21/215Arrangements for storing inflatable members in their non-use or deflated condition; Arrangement or mounting of air bag modules or components characterised by the covers for the inflatable member
    • B60R21/2165Arrangements for storing inflatable members in their non-use or deflated condition; Arrangement or mounting of air bag modules or components characterised by the covers for the inflatable member characterised by a tear line for defining a deployment opening
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B29WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29CSHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C44/00Shaping by internal pressure generated in the material, e.g. swelling or foaming ; Producing porous or cellular expanded plastics articles
    • B29C44/02Shaping by internal pressure generated in the material, e.g. swelling or foaming ; Producing porous or cellular expanded plastics articles for articles of definite length, i.e. discrete articles
    • B29C44/04Shaping by internal pressure generated in the material, e.g. swelling or foaming ; Producing porous or cellular expanded plastics articles for articles of definite length, i.e. discrete articles consisting of at least two parts of chemically or physically different materials, e.g. having different densities
    • B29C44/0407Shaping by internal pressure generated in the material, e.g. swelling or foaming ; Producing porous or cellular expanded plastics articles for articles of definite length, i.e. discrete articles consisting of at least two parts of chemically or physically different materials, e.g. having different densities by regulating the temperature of the mould or parts thereof, e.g. cold mould walls inhibiting foaming of an outer layer
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B29WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29CSHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C44/00Shaping by internal pressure generated in the material, e.g. swelling or foaming ; Producing porous or cellular expanded plastics articles
    • B29C44/02Shaping by internal pressure generated in the material, e.g. swelling or foaming ; Producing porous or cellular expanded plastics articles for articles of definite length, i.e. discrete articles
    • B29C44/04Shaping by internal pressure generated in the material, e.g. swelling or foaming ; Producing porous or cellular expanded plastics articles for articles of definite length, i.e. discrete articles consisting of at least two parts of chemically or physically different materials, e.g. having different densities
    • B29C44/0415Shaping by internal pressure generated in the material, e.g. swelling or foaming ; Producing porous or cellular expanded plastics articles for articles of definite length, i.e. discrete articles consisting of at least two parts of chemically or physically different materials, e.g. having different densities by regulating the pressure of the material during or after filling of the mould, e.g. by local venting
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B29WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29CSHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C44/00Shaping by internal pressure generated in the material, e.g. swelling or foaming ; Producing porous or cellular expanded plastics articles
    • B29C44/34Auxiliary operations
    • B29C44/60Measuring, controlling or regulating

Definitions

  • This disclosure relates generally to air bags for vehicles. More particularly, this disclosure relates to air bag covers and methods of forming air bag covers having a weakened region defined in a polymeric foam, where the weakened region allows the cover to open during air bag inflation.
  • Air bag modules have become common in modern automobiles.
  • An air bag module comprises an inflatable cushion and an inflator.
  • the module is installed in a desired position within the vehicle.
  • the cushion is stored in a folded position within the air bag module.
  • a sensor provides a signal for activating the inflator.
  • the inflator provides a supply of inflating gas to the cushion to inflate the cushion.
  • the air bag module is provided in a desired location, such as the steering wheel, the dashboard, the seat, the A-pillar, and other locations.
  • a cover is often placed over the air bag module to conceal and protect the contents of the module.
  • the inflation of the cushion applies a force on the cover to tear or open the cover along one or more weakened regions formed in the cover.
  • the weakened regions allow the cover to open during air bag inflation.
  • the weakened region has been formed as a thinned section of the cover. This thinned section can cause a restriction in the flow of the polymer material through the mold at the weakened region. This flow restriction creates a zone of high shear stress in the weakened region. The high shear stress zone may affect, for example, the finished surface of the region.
  • the elastic nature of the polymer may cause the stress in the region to rebound once the cover has been released from the molding tool, which can cause a bump on the surface of the cover.
  • the combination of the thin/thick sections caused by the weakened region also creates non-uniform shrinkage/expansion of the cover along the weakened region during the temperature cycling to which the vehicle is exposed.
  • the non-uniform shrinkage along this weakened region may show up as a bump or ridge on the surface facing the vehicle or show surface, thus providing a potentially displeasing aesthetic appearance.
  • a cover for an air bag module comprises a polymeric sheet and one or more thinned portions.
  • the polymeric sheet has a first surface and a second surface and includes a plurality of cells formed therein.
  • a skin is formed on at least the first surface.
  • the thinned portions are formed in the second surface and define a weakened region of the cover.
  • a cover for an air bag module comprising a foamed polymeric sheet and a weakened region is provided.
  • the foamed polymeric sheet has a show surface, a non-show surface, and a skin formed on at least the show surface.
  • the weakened region is formed by one or more thinned portions defined in the non-show surface.
  • An air bag module having a housing, an inflatable cushion, an inflator, and a cover comprising a foamed polymeric member.
  • the housing is positionable in a cavity of a vehicle.
  • the inflatable cushion and inflator are stored in the housing such that the inflator is in fluid communication with the inflatable cushion.
  • the foamed polymeric member has a show surface, a non-show surface, and a weakened region. The weakened region is defined by one or more thinned portions.
  • the non-show surface covers the housing proximate the inflatable cushion whereby inflation of the inflatable cushion by the inflator causes the inflatable cushion to expand into the cover, and thus to apply a force on the cover to tear or open the cover along the weakened region thereby providing an outlet for the inflatable cushion through the cover into the vehicle.
  • a method of making a cover for an air bag module comprises mixing a blowing agent and a molten polymer under a first condition, the first condition being sufficient to prevent the blowing agent from forming bubbles in the polymer; changing the first condition to a second condition, the second condition being sufficient to cause the blowing agent to form bubbles in the molten polymer; and molding the molten polymer containing the bubbles into a desired shape in a mold, the desired shape comprising a first polymer sheet having a plurality of first cells being defined therein and a thinned portion being defined in a first surface of the first polymer sheet.
  • a method of controlling the density of a region of a foamed polymer comprises mixing a blowing agent and a molten polymer under a first condition, the first condition being sufficient to prevent the blowing agent from forming bubbles in the polymer; changing the first condition to a second condition, the second condition being sufficient to cause the blowing agent to form bubbles in the molten polymer; molding the molten polymer containing the bubbles into a desired shape in a mold, the desired shape including a plurality of first cells being defined within the desired shape by the bubbles; and moving a portion of the mold disposed at the region from a first position to a second position, movement of the portion of the mold causing the first cells in the region to change to second cells without changing the first cells in remaining regions of the foamed polymer, the foamed polymer having a first density at the remaining regions caused by the first cells and a second density at the region caused by the second cells.
  • Figure 1 is a schematic depiction of an air bag module
  • Figure 2 is a front view of a steering wheel
  • Figure 3 is a sectional view of Figure 2 along lines 3-3;
  • Figure 4 is a sectional view of the weakened region of Figure 3 along circle 4-4;
  • Figure 5 is a sectional view of an exemplary embodiment of a cover having a weakened region
  • Figure 6 is schematic view of an exemplary embodiment of a manufacturing process for making the cover of Figure 5;
  • Figure 7 is a sectional view of an alternate exemplary embodiment of a cover having a weakened region
  • Figure 8 is first view of an exemplary embodiment of a manufacturing process for making the cover of Figure 7;
  • Figure 9 is second view of the manufacturing process of Figure 8.
  • Figure 10 is a sectional view of another alternate exemplary embodiment of a cover having a weakened region.
  • Figure 11 is schematic view of an exemplary embodiment of a manufacturing process for making the cover of Figure 10.
  • an air bag module 10 is illustrated.
  • the module 10 includes an inflator 12 and an inflatable cushion 14 stored in a housing 16.
  • the housing 16 is positionable in a cavity 17 defined in a vehicle (not shown).
  • the cavity 17 is defined in a steering wheel 22 of the vehicle.
  • the cushion 14 is stored in a folded position in the housing 16 and/or the cavity 17, and is in fluid communication with the inflator 12.
  • a cover 20 is placed over the housing 16 and/or the cavity 17 to protect and conceal the module 10.
  • a sensor or sensing-and-diagnostic module 18 is adapted to detect an activation event to provide an activation signal 19 to the inflator 14.
  • the inflator 12 Upon detection of an activation event by the sensor 18, the inflator 12 is activated via signal 19 such that the cushion 14 inflates and expands into the cover 20.
  • the force applied by the expanding cushion 14 on the cover 20 opens the cover along one or more weakened regions 26 to allow the cushion to expand into the vehicle's interior.
  • cavity 17 is described herein as being defined within a steering wheel 22.
  • the cavity 17 and the air bag module 10 are described herein by way of example only as being used in conjunction with the steering wheel 22.
  • air bag modules and/or cavities in other regions of the vehicle are contemplated.
  • the steering wheel 22 illustrated in Figures 2 and 3 includes a central hub 24 having the module 10 secured therein.
  • the cover 20 is placed over the hub 24 to protect and conceal the module 10.
  • the cover 20 can be used with other known steering wheel devices, such as membrane horn switches, emblems, and the like.
  • the module 10 is illustrated by way of example only as being integral with the central hub 24. Of course, it is contemplated for the module 10 to be mounted on the steering wheel 22 separate from the hub 24 or in any other known construction.
  • the cover 20 can be of one-piece construction as illustrated, or can include multiple pieces and/or layers, which are assembled to form the cover.
  • the cover can be a single layer (e.g., a single shot cover) or can comprise multiple layers (e.g., a multiple shot cover), where the multiple layers may have the same or different compositions.
  • the cover 20 includes one or more weakened regions 26.
  • the inflation of the cushion 14 by the inflator 12 causes the cushion to expand into the cover 20, and thus to apply a force on the cover.
  • the weakened regions 26 are configured to tear or open when the force applied by the cushion 14 on the cover 20 exceeds a predetermined limit.
  • the opening of the cover 20 along the weakened regions 26 provides an outlet for the cushion 14 through the cover, which allows the cushion to expand into the vehicle interior.
  • the weakened regions 26 are arranged in one or more lines, such as the generally H-shaped geometric arrangement illustrated in Figure 2. It also should be recognized that the generally H-shaped geometric arrangement of the weakened regions 26 is only one potential arrangement. It is to be understood that any number of other geometric arrangements for the weakened regions are contemplated.
  • the weakened region can be arranged in different shapes such as, but not limited to I-shaped, Y-shaped, U-shaped, and others. The shape of the weakened region can be selected depending on the part design and deployment criteria. Regardless of the configuration of the weakened regions 26, the cover 20 is opened along the weakened regions by a force above a predetermined limit applied to the cover by the expanding cushion 14.
  • the weakened region 26 comprises a thinned portion 28 defined in the cover 20.
  • the thinned portion 28 is, for example, a continuous thinned portion and/or a plurality of spaced apart-thinned portions that enable the cushion 14 to tear or open the cover 20 at the weakened region 26.
  • the thinned portion 28 is illustrated by way of example only as having a substantially rectangular cross section. Of course, other cross sections are contemplated such as, but not limited to, arcuate-shaped, V-shaped, and others. It is also contemplated for the cross section to change in cross sectional shape and/or size along the length of the thinned portion 28.
  • the thinned portion 28 is a plurality of spaced apart-thinned portions, it is contemplated for the cross section and/or length of the thinned portion 28 in the plurality of thinned portion 28 to vary.
  • a continuous surface is presented on the outside surface 21 (e.g., the vehicle facing or show surface) of the cover 20, while the thinned portion 28 is provided on the inside surface 23 (e.g., non- vehicle facing or non-show surface) of the cover.
  • the cover 20 provides a weakened region 26 that is substantially hidden from the vehicle interior, and thus provides an aesthetically pleasing appearance.
  • the thinned portion 28 can be provided on the outside surface surface 21 (e.g., show surface) of the cover 20 to take advantage of the opening consistency and other advantages of the cover described in detail below.
  • the predetermined limit of force necessary to open the weakened region 26 must take into account several different conditions to which the module 10 is exposed.
  • the module 10 is often configured to deploy the cushion 20 at one or more levels, and the vehicle in which the module is installed is often exposed to very large ambient temperature ranges.
  • the module 10 is often configured to deploy the cushion 14 at one or more deployment levels depending on the level of the activation event detected by the sensor 18.
  • the deployment levels desired for the cushion 14 affect the design of the weakened region 26.
  • the module 10 is configured to deploy the cushion 14 at variable levels by for example, varying how rapidly inflator 12 activates after detection of the activation event, or by venting, at least a portion of the inflation gases generated by the inflator during activation, away from the cushion 20.
  • the inflator 12 is often configured to deploy at two or more levels (e.g., a dual stage inflator) by varying the amount of inflation gas supplied to the cushion 14.
  • each level generates a different quantity of inflation gas, which in turn generates a different pressure within the cushion 20. All of these methods of varying the deployment level of the cushion 14 change the pressure available within the cushion to act on the cover 20.
  • a deployment of the cushion 14 at a low level applies a first force to the cover 20, while a deployment at a high level applies a second, higher force to the cover.
  • the weakened region 26 is configured to open when the force applied to the cover 20 exceeds a predetermined limit.
  • the cover 20 is designed such that the weakened region opens when the force generated during low level deployments (e.g., the first force) is above the predetermined limit. This ensures deployment of the cushion 14 during low-level actuation events.
  • vehicles are typically subjected to very large temperature variations, and such variations are known to affect performance of the weakened region 26. For example, in southern regions of the United States ambient temperatures of 100° F (degrees Fahrenheit) are often experienced (with more than about 200° F possible in the car), while in northern regions of the United States ambient temperatures of 0° F are often experienced. Testing of vehicles usually includes testing at a range of temperatures, such as from about 185° F to about -40° F.
  • the cover 20 is formed of polymeric materials such as polyolefin elastomers (e.g., polypropylene), co-polyester elastomers, and styrene-based elastomers, which are preferably injection molded to form the cover.
  • polymeric materials such as polyolefin elastomers (e.g., polypropylene), co-polyester elastomers, and styrene-based elastomers, which are preferably injection molded to form the cover.
  • polymer materials can experience a change in material properties with temperature. More specifically, these materials weaken as the temperature increases towards the material's glass transition temperature and/or melting temperature, or alternatively, these materials strengthen or harden as the temperature decreases away from the material's glass transition temperature and/or melting temperature.
  • the weakened region 26 is configured to open when the force applied to the cover 20 exceeds a predetermined limit.
  • the cover 20 is designed such that the predetermined limit of force necessary to open the weakened region 26 under lower temperature conditions is below the lowest deployment force that may be generated by the cushion 14 during inflation.
  • the weakened region 26 is exposed to various deployment levels, temperature ranges and other conditions.
  • the weakened region 26 is configured to open at the lower end of the temperature range with the lowest deployment forces generated by the cushion 14.
  • this typically results in polypropylene covers 20 having a thickness of about 0.020 inches at the thinned portion 28, while the rest of the cover has a thickness of about 0.120 inches or higher.
  • the thinned portion 28 causes a restriction in the flow of the polymeric material through the mold at the thinned portion.
  • This flow restriction can create a zone of high shear stress in the weakened region 26.
  • the zone of high shear stress may affect the weakened region 26 due to orientation, crystallization, shrinkage, and other material characteristics or properties of the thinned portion as compared to those of the rest of the cover. These inconsistencies can be found both within the same part and/or on a part-to-part basis.
  • conventional injection molding of the solid cover 20 may not provide the weakened region 26 with the desired predictability and consistency.
  • the combination of the thin/thick sections also creates non-uniform shrinkage/expansion of the cover 20 along the weakened region 26 during the temperature cycling to which the vehicle is exposed.
  • the non-uniform shrinkage along the weakened region 26 shows usually up as a bump or ridge on the show surface, thus providing a potentially displeasing aesthetic appearance.
  • the elastic nature of the polymer may cause the stress in the weakened region to rebound or spring-back once the cover has been released from the molding tool, which can cause a bump on the surface of the cover. This effect can limit the processing conditions for making the cover and can limit flexibility in the design of the cover.
  • conventional injection molded covers 20 may also not provide the desired appearance factors over long-term use.
  • the manufacture of the cover from a foamed or cellular polymer, at least along the weakened region, can provide for the desired predictable and consistent performance under various forces and temperature ranges, while also eliminating shrinkage along the weakened region, and reduces material usage. More specifically, it has been determined that a foamed or cellular weakened region provides consistent performance regardless of temperature. The foamed or cellular weakened region also provides excellent surface appearance, excellent low temperature deployment properties, and reduced material usage.
  • the foamed or cellular weakened region is a polymeric material that includes a plurality of hollows, also called cells, in the polymeric matrix.
  • a foamed polymeric matrix By replacing solid polymers with a foamed polymeric matrix, less raw materials are necessary for parts of a given volume.
  • polymeric foams in many applications instead of solid polymers, material costs and material usage are reduced.
  • a foamed polymeric cover 120 comprising a polymeric sheet 130 with a weakened region 126 defined therein is illustrated.
  • the polymeric sheet 130 comprises a plurality of cells or hollows 132.
  • the cells 132 are micro cells having a dimension of less than about 100 microns. Of course, cells having a dimension larger or smaller than 100 microns are contemplated.
  • the weakened region 126 comprises one or more thinned portions 128 formed in an inside surface 123 (e.g., non-show surface) of the sheet 130. Alternately, it is contemplated for the thinned portions 128 to be formed in the outside surface 121 (e.g., the show surface) of the sheet 130 or a combination of the inside and outside surfaces, as needed.
  • the foamed polymeric cover 120 is formed of, for example, polyolefin elastomers (e.g., polypropylene), co-polyester elastomers, and styrene-based elastomers or other materials suitable for incorporation of the cells 132.
  • polyolefin elastomers e.g., polypropylene
  • co-polyester elastomers e.g., polypropylene
  • styrene-based elastomers e.g., polystyrene-based elastomers
  • the foamed polymeric cover 120 is described as having the same dimensions as the solid cover 20 discussed above with respect to Figure 4. Specifically, the cover 120 has a thickness of about 0.020 inches at the thinned portion 128, while the rest of the cover has a thickness of about 0.120 inches.
  • the cells 132 of the foamed polymeric cover 120 result in a reduction of the density of the weakened region 126 of about 10% as compared to the solid polymeric cover 20. The decreased density afforded by the cells 132 also weakens or reduces the force necessary to open the weakened region 126.
  • the opening force of the thinned portion 128 having the cells is lower than the opening force for a similarly sized thinned portion 28 of a solid cover.
  • the weakened region 126 in the foamed polymeric cover typically has a lower opening force than the weakened region 26 of the solid cover 20.
  • the foamed polymeric cover 120 has a lower opening force at the desired range inflation pressures and in vehicle temperatures.
  • the foamed polymeric cover 120 has a more consistent opening force than the solid cover 20 at the desired range inflation pressures and in vehicle temperatures.
  • a blowing agent can be used in the manufacture of the foamed polymeric cover. This blowing agent can cause a decrease in the viscosity of the molten polymer. This decrease in viscosity mitigates the restriction in the flow of the polymer material through the mold at the weakened region. By mitigating the flow restriction, the zone of high shear stress in the weakened region is mitigated. By reducing and/or eliminating the zone of high shear stress in the weakened region, the required opening force of the foamed polymeric cover 120 is more predictable and consistent.
  • the opening force required can be varied by varying the thickness of the foamed polymer.
  • the thickness of the thinned portion 128 can be increased while maintaining an opening force equivalent to the thinned portion in a solid cover.
  • the cells 132 of the sheet 130 result in a reduction of the density of the cover 120 at the weakened region 126 of about 10% as compared to that of the solid polymeric cover 20. This reduction in density also reduces the force necessary to open the weakened region 126. Consequently, the thickness of the thinned portion 128 can be increased while maintaining a required opening force equivalent to that of the thinned portion 28 of a solid cover 20.
  • the foamed polymeric cover typically has a weakened region 126 that is thicker than the weakened region 26 of the solid cover 20.
  • the solid cover 20 discussed above with respect to Figure 4 has a thickness at the thinned portion 28 of about 0.020 inches and at remaining portions of the cover 20 of about 0.120 inches.
  • the thinned portion 128 has a thickness of about 0.025 inches and the cover 120 has a thickness of about 0.120 inches.
  • an increase of the thickness of the thinned portion 128 (with cells 132) over the thinned portion 28 (without cells 132) of about 20% to 50% is achieved.
  • Increasing the thickness of the weakened portion 126 further increases the polymer flow through the mold at the weakened region, during injection molding of the cover. This can further reduce the high shear stress zone at the thinned portion 128. Again, by reducing and or eliminating the zone of high shear stress in the weakened region, the opening force required for the foamed polymeric cover 120 is more predictable and consistent than the opening force of covers that have such stress zones (e.g., solid covers).
  • the thickness of the weakened region 126 can mitigate the non-uniform shrinkage/expansion of the cover that can occur along the weakened region during the temperature cycling to which the vehicle is exposed. This improves the aesthetic aspects of the foamed polymeric cover 120.
  • the density reduction, which the cells 132 provide to the cover 120 allows the use less raw materials than the similarly sized solid cover 20.
  • foamed cover 120 can be lighter than a solid cover of equal volume.
  • polymeric foams have been formed through with a polymer matrix having of physical blowing agents, chemical blowing agents, super critical fluids, combinations of any of the foregoing and others.
  • the cover 120 can be produced by admixing a blowing agent with a melted polymer to form a substantially homogeneous mixture of the blowing agent in the melt.
  • the blowing agent can be introduced into molten polymer in a molding machine, can be introduced with the resin in the hopper of the molding machine, can be incorporated as part of the resin, and combinations of any of the foregoing.
  • the agent can be an inert agent, such as CO 2 , N 2j or other inert gas.
  • the agent and the melt are mixed at first conditions (usually high pressures) so that the agent mixes with melt.
  • the blowing agent can be a supercritical fluid that is solublized in the polymer melt at the first conditions (e.g., high pressure and temperature) in order to create a substantially homogeneous single-phase solution.
  • the first conditions are maintained until the formation of the cells is desired.
  • the cells can be accomplished by changing the first conditions to second conditions (usually ambient pressures).
  • the change from the first to the second conditions causes the agent to expand, forming bubbles in the melt.
  • This change in conditions can be a change in temperature, a change in pressure, or combinations thereof.
  • the melt is injected into a mold while at the second conditions or while the conditions are being changed to the second conditions.
  • the mold is cooled to return the melt to a solid state, which forms the cover.
  • the bubbles formed by the agent in the melt result in the cells or hollows being formed in the cover.
  • foamed polymers having cells of less than about 100 microns in diameter. These polymers are known as micro cellular materials.
  • the heat removed from the portion of the melt in contact with the mold causes the agent in that portion to contract such that a skin is formed on the surface of the finished part.
  • the skin is substantially free of the cells or hollows.
  • the thicl ⁇ iess of the skin is dependent upon how rapidly the heat is removed from the surfaces of the melt that are in contact with the mold. During normal molding cycle times and temperatures, the skin is formed having a minimum thickness of about 0.0002 inches. However, the thickness of the skin can be increased by removing the heat from the melt more rapidly. Alternately, the thickness of the skin can be decreased by slowing the removal of heat from the melt.
  • the polymeric sheet 130 comprises a skin 134 of a desired thickness formed on its outside surface 121 (e.g., the show surface).
  • the polymer sheet 130 may also comprise the skin 134 formed the inside surface 123 (e.g., the non-show surface).
  • the skin 134 is a unitary part of the cover that is formed during the molding of the cover 120. Namely, the skin 134 is preferably formed by removing heat from the portion of the sheet 130 in contact with the mold to cause the blowing agent in that portion of the sheet to contract such that substantially no cells are formed on the surface of the cover.
  • the sheet 130 comprises the skin 134 and the cells 132 all formed from the same polymeric material as a unitary element.
  • the cover 120 is preferably formed by injection molding molten polymeric material into a mold 138.
  • the mold 138 comprises a first portion 140 and a second portion 142 defining a cavity 141 therebetween.
  • the cavity 141 defines the shape of the cover 120.
  • the first portion 140 forms the outside or show side of the cover 120
  • the second portion 142 forms the inside or non-show side of the cover.
  • the second portion 142 is configured to provide the foamed polymeric cover 120 with the weakened region 126 (e.g., thinned portion 128). More specifically, the second portion 142 comprises a blade 144 to form the thinned portion 128.
  • a blowing agent is admixed with the polymer. The mixture is injected into the mold 138, either while being subjected to a change in conditions (e.g., first conditions to the second conditions) or after being subjected to the change in conditions, such that the cells 132 are formed in the polymer.
  • the blade 144 reduces the distance between the first and second portions (140 and 142) of the mold 138 to form the thinned portions 128.
  • blowing agent in the molten polymer causes a decrease in the viscosity of the polymer. This decrease in viscosity mitigates the restriction in the flow of the polymer material through the mold at the weakened region. Accordingly, the blowing agent allows the distance between the first and second portions (140 and 142) of the mold 138 to be minimized and/or allows the zone of high shear stress in the weakened region to be minimized.
  • the first and second portions of the mold (140 and 142) and the blade 144 are configured to provide the cover 120 with the skin 134.
  • the first and second portions (140 and 142) and the blade 144 remove heat from the portion of the sheet 130 in contact with the mold 138.
  • removing heat from the portion of the sheet 130 in contact with the mold 138 causes the blowing agent in that portion to contract such that substantially no cells are formed on the surface of the cover.
  • the mold 138 is cooled to form the skin 134 after the molten stream is injected into the mold.
  • the first portion 140 is also configured to provide the skin 134 with the desired texture and/or surface features. Namely, the skin 134 provides an aesthetically desirable outside surface 121 (e.g., the vehicle facing or show surface) to the cover 120.
  • FIG. 7 an alternate exemplary embodiment of a foamed polymeric cover 220 comprising a polymeric sheet 230 with a weakened region 226 is illustrated.
  • the polymeric sheet 230 comprises a first plurality of cells or hollows 232 and a second plurality of cells or hollows 236.
  • the weakened region 226 comprises one or more thinned portions 228 formed in an inside surface 223 (e.g., non-show surface) of the sheet 230.
  • the first cells 232 are disposed in the sheet 230 at the weakened region 226, while the second cells 236 are disposed in the sheet in the remaining regions of the cover.
  • the first cells 232 in the weakened region 226 are larger than the second cells 236 in the remaining portions of the cover.
  • the first cells make the cover 220 in the weakened region 226 less dense than the remaining portions of the cover.
  • the thickness of the thinned portion 228 can be increased without increasing the required opening force (as compared to solid covers) of the weakened region 226.
  • the first cells 232 result in a reduction of the density of the cover 220 at the weakened region 226 of about 15% to about 30% as compared to the solid polymeric cover 20.
  • the second cells 236 result in a reduction of the density of the cover 220 at the remaining regions of at least about 2% as compared to the solid polymeric cover 20, with up to about 15% contemplated.
  • This reduction in density also reduces the force necessary to open the weakened region 226. Because of the inclusion of the cells 232 in the cover 220, the thickness of the thinned portion 228 can be increased without increasing the force necessary to open the weakened region 226. Thus, when a solid cover 20 and a foamed polymeric cover 220 made of the same polymeric material and having identical opening force limits of their respective thinned portions (28 and 228) are compared to one another, the foamed polymeric cover has a weakened region 226 that is typically thicker than the weakened region 26 of the solid cover 20.
  • the solid polypropylene cover 20 discussed above with respect to Figure 4 has thinned portion 28 of about 0.020 inches and cover 20 of about 0.120 inches.
  • the thinned portion 228 has a thickness of about 0.030 inches and the cover 220 has a thickness of about 0.120 inches.
  • an increase of the thickness of the thinned portion 228 (with cells 232) over thinned portion 28 (without cells 232) of about 30% to 55% is achieved.
  • the foamed polymeric cover 220 can be provided with the same dimensions as the solid cover 20 discussed above with respect to Figure 4. Specifically, the cover 220 can have a thickness of about 0.020 inches at the thinned portion 228, while the rest of the cover has a thickness of about 0.120 inches or higher (not shown).
  • the first cells 232 result in a reduction of the density of weakened region 226 of about 15% to 30% as compared to a solid cover.
  • the second cells 236 in the remaining portions of the cover 220 result in a reduction of the density of cover 220 of between 2%-15% as compared to a solid cover.
  • the decreased density afforded by the cells 232 also reduces the force necessary to open the weakened region 226. Because of the inclusion of the cells 232 in the cover 220, the opening force of the thinned portion 228 having the cells is lower than the opening force for a similarly sized thinned portion 28 of a solid cover. Thus, when a solid cover 20 and a foamed polymeric cover 220 made of the same polymeric material and having identical dimensions of their respective thinned portions (e.g., 0.020 inches) are compared to one another, the foamed polymeric cover has a weakened region 226 with a lower opening force than the weakened region 26 of the solid cover 20.
  • cover 220 provides for weakened region 226 having a lower opening force than similar sized weakened regions without cells and requires less raw materials than similarly sized solid covers.
  • the cells 232 allow the thickness of the thinned portion 228 to be increased (as compared to a weakened region without cells) without an increase in the opening force.
  • Increasing the thickness of the weakened region 226 increases polymer flow through the mold at the weakened region. Increasing the thickness of the weakened region 226 can reduce the high shear stress zone at the thinned region 228. This provides the foamed polymeric cover 220 with a weakened region 226 that opens in a predictable and consistent manner. Additionally, increasing the thickness of the weakened region 226 mitigates the non-uniform shrinkage/expansion of the cover that can occur along the weakened region during the temperature cycling to which the vehicle is exposed, which improves the aesthetic aspects of the foamed polymeric cover 220. As an additional benefit, the density reduction the cells 232 and cells 236 provide to the cover 220 allows the use less raw materials than the similarly sized solid cover 20.
  • the polymeric sheet 230 comprises a skin 234 formed on its outside surface 221 (e.g., the show surface).
  • the polymer sheet 230 may further comprise the skin 234 formed on both the outside surface 221 (e.g., the show surface) and the inside surface 223 (e.g., the non-show surface).
  • the skin 234 is preferably formed during the molding of the cover 220.
  • the skin 234 is preferably formed by removing heat from the portion of the sheet 230 in contact with the mold to cause the blowing agent in that portion of the sheet to contract such that substantially no cells are formed on the surface of the cover.
  • the sheet 230 comprises the skin and the cells 232 all formed from the same polymeric material as a unitary element.
  • the cover 220 is preferably formed by injection molding molten polymeric material into a mold 238.
  • the mold 238 comprises a first portion 240 and a second portion 242 defining a cavity 241 therebetween.
  • the cavity 241 defines the shape of the cover 220.
  • the first portion 240 forms the outside or show side of the cover 220
  • the second portion 242 forms the inside or non-show side of the cover.
  • the second portion 242 is configured to provide the foamed polymeric cover 220 with the weakened region 226 (e.g., thinned portion 228) and with the cells 232. More specifically, the second portion 242 comprises a movable blade 244 to form the thinned portion 228.
  • the movable blade 244 is shown in a first or starting position in Figure 8, and in a second or ending position in Figure 9.
  • a liquid blowing agent is admixed with a molten polymeric stream.
  • the mixture is injected into mold 238 while movable blade 244 is in the first position ( Figure 8) and is subjected to a decrease in pressure to convert the liquid blowing agent to a gas.
  • the gas expands to form the cells 232 and 236.
  • the movable blade 244 is moved to its second position ( Figure 9). The movement of the movable blade 244 from the first to the second position allows the cells 232 in weakened region 226 to expand to a larger size than the cells 236 in the remaining regions of the cover.
  • first cells 232 to result in a reduction of the density of the cover 220 at the weakened region 226 of about 15% to about 30% as compared to the solid polymeric cover 20.
  • second cells 236 to result in a reduction of the density of the cover 220 at the remaining regions of at least about 2% as compared to the solid polymeric cover 20, with up to about 15% contemplated.
  • the movable blade 244 moves from the first position to the second position after the predetermined event. For example, the movable blade 244 moves a predetermined period of time after the molten stream is injected into mold 238.
  • the mold 238 can further include a sensor 246 configured to measure the internal gas pressure of the cells 232 at the weakened region 226.
  • sensor 246 can measure the pressure and or the temperature at the weakened region 226.
  • the sensor 246 provides information related to the internal gas pressure of the cells 232.
  • the blade 244 is configured to move from the first position to the second position when the sensor 246 detects a selected condition of the cells 232.
  • the density of the cover in the weakened region 226 is precisely controlled by relying on the internal gas pressure of the cells.232 detected by the sensor 246 to move the blade to its second position ( Figure 9).
  • the sensor 246 enables the movement of the moveable blade 244 to provide the weakened region 226 with cells 232 having a predictable and relatively consistent density.
  • This manufacturing process provides the flexibility of creating tailor-made weakened region 226 or regions in the cover without affecting the surface appearance and part performance for the rest of the cover 220.
  • the lower density cells 232 at the weakened region 226 as compared to the rest of the sheet 230 provides the weakened region with a desired opening or tear strength, while reducing the overall material usage of the cover 220.
  • the first and second portions are configured to provide the cover 220 with a skin 234 by removing heat from the portion of the sheet 230 in contact with the mold 238.
  • the mold 238 is cooled to form the skin 234 after the molten stream is injected into the mold 238.
  • the first portion 240 is also configured to provide the skin 234 with the desired texture and/or surface features. Namely, the skin 234 provides an aesthetically desirable outside surface 221 (e.g., the vehicle facing or show surface) to the cover 220.
  • the skin 234 provides an aesthetically desirable outside surface 221 (e.g., the vehicle facing or show surface) to the cover 220.
  • FIG. 10 an alternate exemplary embodiment of a foamed polymeric cover 320 comprising a polymeric sheet 330 and a weakened region 326 is illustrated.
  • the sheet comprises a first plurality of cells or hollows 332, a skin 334, a second plurality of cells or hollows 336, and a region 348 (described in detail below).
  • the first cells 332 are disposed in the sheet 330 in the weakened region 326, while the second cells 336 are disposed in the remaining regions of the sheet as described above with respect to Figure 5.
  • the skin 334 formed on the outside surface 321 and a portion of the inside surface 323 of the sheet 330 has a first thickness.
  • the skin in the region 348 which is defined on a portion of the inside surface at the weakened region 326, has a second smaller thickness.
  • the skin in the region 348 is thinner that the skin in the remaining portions of the cover.
  • the cells 332 at the region 348 can expand to a greater degree than the cells 336 in the areas having the thicker skin.
  • the skin 334 in the region 348 has a thickness that is about 5% to 10% smaller than the skin in the remaining regions of the cover. Accordingly, the cells 332 are larger than cells 336 in the remaining regions of the cover 320 by about 5% to 10%. This provides the weakened region 326 with a reduction in density of about 20% as compared to a solid cover 20. The cells 336 result in a reduction of the density of the overall cover 320 of between 2%-15% as compared to a solid cover.
  • an exemplary manufacturing process for making the cover 320 of Figure 10 is provided.
  • the process is substantially identical to the process described above with respect to Figure 6.
  • the blade 344 mitigates the cooling effects to minimize the thickness of the skin 334 in region 348.
  • the blade 344 is, for example, thermally nonconductive to insulate the region 348 from the cooling effects of the mold 338, and thus to minimize the formation of the skin 334 in the region.
  • the blade 344 can provide heat to the region 348 to minimize the formation of the skin 334 in the region 348.
  • the design of the blade 344 minimizes the formation of the skin 334 in the region in the region 348.
  • the foamed or cellular cover is described herein by way of example only as having a single layer (e.g., a single shot cover).
  • the foamed or cellular cover can be formed from multiple layers where the multiple layers have the same or different compositions.
  • the foamed or cellular cover it is contemplated for the foamed or cellular cover to be formed with a second layer during a co- molding or two-shot molding process. During this process, the foamed or cellular cover can be used as the exterior layer (e.g., the show surface) or can be covered by a second layer.

Landscapes

  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Air Bags (AREA)

Abstract

L'invention porte sur un couvercle (120, 220, 320) destiné à un module d'airbag. Ce couvercle comprend une feuille polymère (130, 230, 330) et une ou plusieurs parties rétrécies (128, 228, 328). La feuille polymère présente une première surface (121, 221, 321) et une seconde surface (123, 223, 323) et comprend plusieurs cellules (132, 232, 236, 332, 336) formées dessus. Une pellicule (134, 234, 334) est formée sur au moins la première surface. Les parties rétrécies sont formées sur la seconde surface et définissent une zone affaiblie (126, 226, 326) sur la couvercle.
PCT/US2002/020581 2001-07-02 2002-06-27 Couvercle d'airbag en mousse polymere presentant une zone affaiblie WO2003004310A2 (fr)

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
US30240801P 2001-07-02 2001-07-02
US60/302,408 2001-07-02
US30550602P 2002-06-24 2002-06-24
US305,506 2002-06-24

Publications (2)

Publication Number Publication Date
WO2003004310A2 true WO2003004310A2 (fr) 2003-01-16
WO2003004310A3 WO2003004310A3 (fr) 2003-08-14

Family

ID=27737222

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/US2002/020581 WO2003004310A2 (fr) 2001-07-02 2002-06-27 Couvercle d'airbag en mousse polymere presentant une zone affaiblie

Country Status (1)

Country Link
WO (1) WO2003004310A2 (fr)

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5082310A (en) * 1989-11-06 1992-01-21 Tip Engineering Group, Inc. Arrangement for providing an air bag deployment opening
US5316335A (en) * 1992-12-14 1994-05-31 Davidson Textron Inc. Self piercing cover assembly air bag
US5698283A (en) * 1995-06-21 1997-12-16 Toyoda Gosei Co., Ltd. Air bag cover and manufacturing method for same
US6207254B1 (en) * 1999-01-28 2001-03-27 Sealed Air Corporation Partially perforated foam
US6254122B1 (en) * 1998-02-04 2001-07-03 Johnson Controls Technology Company Reinforced trim cover for a vehicle seat assembly with a tear line for airbag deployment
US6261490B1 (en) * 1998-09-15 2001-07-17 Rotec Chemicals Limited Rotational moulding

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5082310A (en) * 1989-11-06 1992-01-21 Tip Engineering Group, Inc. Arrangement for providing an air bag deployment opening
US5316335A (en) * 1992-12-14 1994-05-31 Davidson Textron Inc. Self piercing cover assembly air bag
US5698283A (en) * 1995-06-21 1997-12-16 Toyoda Gosei Co., Ltd. Air bag cover and manufacturing method for same
US6254122B1 (en) * 1998-02-04 2001-07-03 Johnson Controls Technology Company Reinforced trim cover for a vehicle seat assembly with a tear line for airbag deployment
US6261490B1 (en) * 1998-09-15 2001-07-17 Rotec Chemicals Limited Rotational moulding
US6207254B1 (en) * 1999-01-28 2001-03-27 Sealed Air Corporation Partially perforated foam

Also Published As

Publication number Publication date
WO2003004310A3 (fr) 2003-08-14

Similar Documents

Publication Publication Date Title
US6669228B2 (en) Air bag cover of polymeric foam having weakened region
US5947511A (en) Integrally molded air-bag cover article and method of making the same
KR101664673B1 (ko) 수지 제품 제조 장치 및 방법
EP1948482B1 (fr) Motif de deploiement de coussin
US9010799B2 (en) Molding in airbag door features in a vehicle interior panel using a movable mold member
JP6713396B2 (ja) 車両のエアバッグドア及びハウジング一体型クラッシュパッド並びにその製造方法
GB2419570A (en) Moulded elastic airbag
CN101195366A (zh) 用于车辆前乘客座椅的气囊及其制造方法
WO2009124395A1 (fr) Coussin multicouche gonflable et procédé de fabrication
JP4820473B2 (ja) 自動車用内装パネル
GB2419331A (en) Automotive trim assembly and integral airbag door
US8240703B2 (en) Airbag door connecting structure of passenger seat in vehicle
GB2419320A (en) Moulding an automotive trim assembly with an integrated airbag door
JPH09226413A (ja) インストルメントパネル及びインストルメントパネルの成形方法
US20060163775A1 (en) Method and device for producing a cover for an airbag in a motor vehicle
JPH04197849A (ja) 自動車のエアバック展開開口部の構造およびその製法
WO2003004310A2 (fr) Couvercle d'airbag en mousse polymere presentant une zone affaiblie
DE102005052532B3 (de) Aufblasbares Airbagkissen, das durch einen zweischüssigen Formprozess mit einem geblasenen Elastomerkern ausgebildet ist, sowie Verfahren zum Verwenden und Herstellen solcher Airbagkissen
US5750062A (en) Method of manufacturing an air bag cover
JP3539221B2 (ja) 樹脂成形品及びその製造方法
US20060267312A1 (en) Airbag cover and method for producing airbag cover
JPH11227542A (ja) 車両内装品用表皮及びエアバッグドア構造
JP4158685B2 (ja) 表皮材付成形品の製造方法
JPH07246900A (ja) 自動車用エアバッグドアの構造
JP2004114738A (ja) 自動車用内装材及びその製造方法

Legal Events

Date Code Title Description
AK Designated states

Kind code of ref document: A2

Designated state(s): JP KR

AL Designated countries for regional patents

Kind code of ref document: A2

Designated state(s): AT BE CH CY DE DK ES FI FR GB GR IE IT LU MC NL PT SE TR

121 Ep: the epo has been informed by wipo that ep was designated in this application
DFPE Request for preliminary examination filed prior to expiration of 19th month from priority date (pct application filed before 20040101)
122 Ep: pct application non-entry in european phase
NENP Non-entry into the national phase in:

Ref country code: JP

WWW Wipo information: withdrawn in national office

Country of ref document: JP

DPE2 Request for preliminary examination filed before expiration of 19th month from priority date (pct application filed from 20040101)