Abstract:
A baffle may conform to and be magnetically coupled to a body having a ferromagnetic component in proximity to the baffle. The baffle includes a first layer of a flexible thermally expansible baffle material which expands when subjected to an elevated temperature, and a second layer of a flexible magnetic material. The baffle may thereby be flexed to conform to an irregular or curved surface. In addition, the baffle may be preformed to provide an irregular or arcuate portion to conform to the body on which it is placed. The magnetic attachment facilitates attachment and removal without the need to provide holes in the body, and upon heating and expansion of the baffle, the baffle material expands to fill cavities and adhere to the inside wall surface of the body on which it is received.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention concerns baffle assemblies useful inside cavities or other open areas of metal structures wherein the baffle assembly may be readily temporarily held in place by magnetic attachment. More particularly, the present invention concerns a baffle assembly having a layer of flexible thermally expandible material and an adjacent layer of flexible magnetic material which permits the baffle to be made into a desired shape and temporarily held against a ferromagnetic metal prior to expansion. 
     2. Description of the Prior Art 
     The use of baffle assemblies in automobiles is well known to inhibit sound transmission through panels, pillars, rails and the like of a chassis or unibody structure. While rigid foam materials were initially employed in the cavities, it is now known to use thermally expansible baffle compositions which undergo heat induced expansion to expand in the cavity. Such heat activation may occur when the automobile is passed through a paint baking oven forming a part of the primer or paint curing step of the automobile manufacturing process. Various types of materials have been used, including the dry expansible sealant and baffle composition and product disclosed in U.S. Pat. Nos. 5,266,133 and 5,373,027. 
     However, the thermally expansible baffle composition must typically be placed in a particular location within the cavity of the vehicle to be effective. After activation and expansion of the baffle composition, it readily conforms to the surrounding panels and adheres thereto, but prior to activation the composition must be at least temporarily held in place. This has required the use of a separate carrier or component on which the thermally expansible baffle composition is mounted, and which in turn is mounted on the vehicle. Examples disclosing various types of parts and components for retaining a baffle composition in place include those shown in U.S. Pat. Nos. 5,506,025 and 5,806,915. These carriers attach to the expansible baffle composition, but require a hole in the surrounding structure for mounting. Such holes may therefore permit the intrusion of corrosion forming agents therethrough. In addition, primer and other coatings applied to the metal inhibit adhesive attachment. 
     There have also been developed mounts for insertion into a hollow space of a hollow structure such as a vehicle pillar, which mounts include an expandable foam substrate and at least one support panel secured to the substrate using a tack as shown in U.S. Pat. No. 5,904,024. The mount is then secured to the interior wall of the hollow space through either a clip, a magnet, or a suction disc. However, this construction uses a magnet to hold the support panel to the interior wall and not the expansible material itself. There have also been developed magnetized hot melt adhesive articles such as shown in U.S. Pat. Nos. 5,985,435, 4,427,481, 4,724,243 and 4,749,434 which are used to seal a gap or opening in an automobile part, which include thermoplastic resins, tackifiers and the like with magnetized particles to form an extruded mixture. However, these adhesive articles do not satisfy the needs hereof for an initially non-tacky expansible baffle composition. 
     Thus, there has developed a real need for a baffle composition which may be temporarily secured in place prior to activation, may conform to the surrounding structure prior to activation, is inexpensive to produce, and does not require holes through the structure. 
     SUMMARY OF THE INVENTION 
     These needs have largely been met by the expansible synthetic resin baffle with magnetic attachment of the present composition. That is to say, the baffle hereof is simple, inexpensive to manufacture, convenient to install, requires no additional mounting structure or holes in the wall of the structure forming the cavity, and may be cut or formed to a desired shape. 
     Broadly speaking, the baffle of the present invention is provided as adjacent layers of magnetic material and expansible baffle material. The layers may be co-extruded to form the baffle, or molded into layers. The expansible baffle material is preferably an initially non-tacky thermally expansible material which activates at a temperature preferably within the range of about 100° C. to about 200° C., and which is resilient and flexible prior to expansion. Such a baffle material is disclosed in U.S. Pat. Nos. 5,266,133 and 5,373,027, the disclosure of which is incorporated herein by reference. The expansible material preferably expands to at least 300% and preferably 400% or more of its initial volume during baking. The baffle material may be provided as a relatively thin layer which may be conformed to irregular surfaces, or formed into a three dimensional part of a greater thickness which is pre-conformed to an irregular shape. 
     The magnetic material is in laminated relationship to the baffle material, whereby the baffle material and magnetic material is side-by-side. The magnetic material may be provided as strips which may cover all or only a portion of the baffle material. Further, the magnetic material is preferably flexible to conform to irregular shapes. The magnetic material may also be perforated to permit enhanced bonding between the baffle material and the wall of the structure after activation and cooling, thereby providing an enhanced bonding between the expanding baffle material and the structure. Advantageously, the magnetic material retains its position in proximity to the wall of the structure throughout the expansion period, and thus the magnetic attachment of the magnetic layer is unaffected by the expansion. 
     The baffle of the present invention is simple to install, and involves merely placement in a desired position and permitting the magnetic material to attach to the wall of the structure. The structure needs only some ferromagnetic material in sufficient proximity to the baffle to permit magnetic attraction, and thus its use includes not only application to steel and other ferromagnetic metals, but also to compositions with a ferromagnetic metal backing or core. Because no adhesive or holes are required, there is no problem with reapplying or repositioning the baffle. The baffle&#39;s application is not limited to automotive uses, but may include placement in marine environments as well as in appliances or the like where sound deadening is desired. These and other advantages will be readily appreciated by those skilled in the art with reference to the drawings and description which follow. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of an automobile chassis showing some possible placements for the baffle hereof; 
     FIG. 2 is a vertical cross sectional view of one embodiment of the baffle hereof prior to placement in a cavity showing both the layer of baffle material and the layer of magnetic material in a substantially flat orientation; 
     FIG. 3 is a vertical cross sectional view of the embodiment of FIG. 2 after placement on the interior of a wall of a structural member prior to expansion; 
     FIG. 4 is a vertical cross-sectional view similar to FIG. 3 showing the baffle within the structural member after expansion; 
     FIG. 5 is a top plan view of another embodiment of the baffle prior to expansion showing the use of two parallel and spaced strips of magnetic material located beneath a block of the baffle material, the strips being shown in broken lines; 
     FIG. 6 is atop plan view of the embodiment of FIG. 5 after activation and expansion of the baffle material; 
     FIG. 7 is a top plan view of a fourth embodiment of the baffle hereof, showing the use of a perforated strip of magnetic material located beneath the block of baffle material and shown in dotted lines, the perforated strip having its perimeter relatively inboard of the peripheral margin of the baffle material; and 
     FIG. 8 is a vertical cross-sectional view of a fifth embodiment of the baffle hereof, wherein the magnetic material is provided as parallel strips magnetically attached to walls of the structural member oriented at right angles to one another, and the baffle material has a groove prior to expansion to facilitate folding and conformance to the walls. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the drawing, an automobile body  10  is one structure which may receive the expansible synthetic resin baffle with magnetic attachment  12  hereof. The body  10  includes a plurality of walls  14 , rails  16 , pillars  18  and channels  20  of steel or other ferromagnetic material which may receive the baffle  12  thereon or therein. 
     The baffle  12  includes a first layer  22  of baffle material  24  and a second layer  26  of magnetic material  28 . The baffle material  24  is preferably a dry, flexible, initially non-tacky, thermally expansible sealant and baffle composition. Two examples of such baffle material are described in U.S. Pat. No. 5,373,027 and as Sikabaffle by Sika Corporation of Madison Heights, Michigan, and in co-pending and allowed U.S. Application Ser. No. 09/407,820 filed Sep. 28, 1999, now U.S. Pat. No. 6,150,428 both assigned to the assignee hereof and the disclosure of which is incorporated herein by reference. 
     For example, a composition useful for preparing a sealant and baffle composition having the desired characteristics of the present invention includes a quantity of a grafted anhydride polymer, and an amount of polymer additive containing a terminal epoxide group which reacts with at least a part of the anhydride polymer when the component is heated to a temperature experienced by an automobile body cavity receiving the baffle material as the automobile body is conveyed through a conventional paint and/or primer bake oven forming a part of the automotive manufacturing operation, e.g. about 100° C. to about 200° C.. In addition, the baffle material  24  includes a suitable blowing agent which effects expansion of the baffle material  24  when the material  24  is subjected to heat during baking of the automobile body in the bake oven. Desirably, the baffle material  24  also includes a tackifier which imparts tackiness to the outer surface of the dry, initially non-tacky baffle material  24  as it expands when subjected to bake oven heat. The grafted anhydride polymer present in the baffle material  24 , which functions somewhat in the manner of an adhesive when heated in the bake oven, increases the tackiness properties of the baffle material  24  as it undergoes expansion. 
     The grafted anhydride polymers useful in the present invention include ethylene-vinyl acetate, ethylene-n-butyl acrylate, ethylene-octane copolymer, polyethylene, polypropylene and ethylene-rubber, each grafted with an acid anhydride functionally; a preferred acid anhydride would be maleic anhydride. The grafted anhydride polymer is preferably present in the baffle material on a wt % basis of from about 10% to about 60%. A epoxide terminated polymer additive, such as solid Bisphenol A or F diglycidyl ether polymer (derived from Bisphenol A or Bisphenol F and epichlorhydrin) characterized by an epoxide equivalent greater than about 400, is preferably present in the composition on a wt % basis of from about 1% to 10%. The baffle material  24  is also provided with a blowing agent, selected from the group of a modified or unmodified azodicarbonamide, p,p′-oxybis(benzene-sulfonyl) hydrazide, p-toluene sulfonyl hyddrazide, and dinitroso pentamethylene tertamine, present in the baffle material  24  on a wt % basis of from about 1% to 10%. A filler polymer, such as, for example, ethylene-vinyl acetate, ethylene n-butyl acrylate, ethylene-octane copolymer, polyethylene, polypropylene, and ethylene methacrylic acid copolymer, is present on a wt % basis of from about 1% to about 50%. A rubber-like constituent may also be included in the baffle material  24 , which is selected from, e.g., styrene-butadiene rubber, ethylene-propylene rubber, ethylene-propylene-diene rubber, butadiene rubber, styrene isoprenet-styrene Block copolymer, styrene-butadiene-styrene Block copolymer, styrene-ethylene/butylene-styrene Block copolymer, styrene-ethlylene/propylene Block copolymer, nitrile rubber and chlorinated polyethylene is present on a wt % basis of from about 1 to 15. A molding and processing aid may be included in the baffle material  24 , selected from the group including as paraffin wax, microcrystalline wax, polyethylene wax, polyamide wax, and natural wax, and may be present in an amount on a wt % basis of from about 1% to about 15%. A tackifier for enhancing tackiness of the baffle material  24  after activation may be provided and selected from a group of aliphatic hydrocarbon resins, aromatic hydrocarbon resins, aliphatic/aromatic hydrocarbon resins, hydrogenated hydrocarbon resins, polyterpene resins, rosin ester resins, coumarone indene resins, α-methyl styrene resins and polystyrene resins, and is present on a wt % basis of from about 1% to about 15%. An inorganic or organic filler may be included in the baffle material  24  on a wt % basis of from about 1% to about 20%, and selected from the group of calcium carbonate, barium sulfate, silica, calcium sulfate, aluminum silicate, magnesium silicate, potassium aluminum silicate, calcium metasilicate, pumice, glass spheres, and organic fillers. 
     The baffle material  24  is preferably prepared by introducing the individual constituents into a conventional continuously operable machine such as a screw or reciprocating extruder or compounding machine. Where multiple inlets are presented on the extruding machine or the like, the constituents of the baffle material, except for the reactive agents, and including the blowing agent, are added at the first entrance port, and the reactive agents and the blowing agents are added at a downstream port. A nominal processing time is about 2 minutes. Upon emerging from the extruder, the baffle material may be cut into pellets for molding or co-extruded with the magnetic material. 
     The magnetic material  28  is preferably a flexible and conformable material which will readily attach to ferromagnetic surfaces. The magnetic material  28  may be provided as particles of barium ferrite which are oriented and embedded in nitrile rubber. An example of such magnetic material useful in accordance with the present invention is sold as Plastiform® 1033 by The Arnold Engineering Company of Marengo, Illinois. The Plastiform® 1033 material measured at 23° C. has an advertised elongation of 18% under ASTM D-412, flexibility sufficient to meet 180° bending on a mandrel equal to 7 times the sample thickness, maximum energy product (Bd Hd max) of 1.6 MGOe/12.7×10 3  kJ/m 3 , residual induction of 2500 Gauss/255 mT, and coercive force (pole-core hysteresigraph) of 2300 Oersteds/183 kA/m. 
     The baffle  12  may be formed in a variety of configurations. Initially, it may be appreciated that the baffle may be formed in co-extruded sheets with the baffle material  24  layered with the magnetic material  28 . The thicknesses of the respective layers may be varied depending on the amount of magnetic attraction required and the volume of the area to be filled. As shown in FIG. 2, the baffle  12  is provided as a laminated sheet  30 , with the baffle  12  being substantially flat and the thicknesses of the baffle material  24  and magnetic material  28  being relatively equal. The baffle  12  may also be formed by molding, whereby the magnetic material  28  may be introduced into a mold cavity and pellets of the baffle material  24  thereafter introduced, heated to a temperature in the range of about 80° C. to 100° C., and usually no more than about 120° C. It may thus be appreciated that the magnetic material  28  has a melting temperature in excess not only of the melting temperature of the baffle material  24 , but also preferably above its activation temperature and the temperature encountered in the bake oven. 
     While the baffle  12  may be provided in sheet form  30  which is sufficiently flexible to conform to irregular shapes, it may be desirable to mold or extrude the baffle  12  into a pre-formed three-dimensional shape such as the embodiment of baffle  12   a  shown in FIGS. 3 and 4. Baffle  12   a  may more readily attach to curved surfaces of a structural member, such as channel  32  as shown in FIGS. 3 and 4. As shown in FIG. 3, the channel  32  includes a lower panel  34  having an arcuate ridge  36 , and an upper panel  38  configured to cap or cover the end legs  40  of the generally U shaped lower panel  34 . The upper panel  38  is affixed to the lower panel  34  to define therein a cavity  42  into which a pre-configured baffle  12   a  is placed. As may be seen in FIGS. 3 and 4, the magnetic material  28  and the baffle material  24  are formed to present a groove  44  complemental in configuration to the ridge  36  of the lower panel  34 . The baffle material  24 , while flexible, is typically more rigid than the magnetic material  28 , and thus a thicker layer of the baffle material  24  will not only fill a larger cavity, but will also serve to retain the shape of the baffle  42 . As shown in FIG. 4, upon heating of the cavity  40  to a sufficient activation temperature, typically about 110° C. to 190° C., the baffle material expands to block and seal a cross-section of the cavity  40 . 
     Furthermore, as shown by the embodiment of the baffle  12   b  of FIGS. 5 and 6, the baffle  12   b  can be configured whereby the magnetic material  28  may be provided as strips  46  and  48  which are small than the overlying block  50  of the baffle material  24 . The strips  46  and  48  are shown as positioned in substantially parallel and spaced-apart orientation, presenting a gap  52  therebetween and with the perimeter of each of the strips inboard of peripheral margin  56  of the block  50  to provide for adhesion by the baffle material  24  after activation between the perimeter  54  of the strips and the initial peripheral margin  56  of the block  50 . This arrangement may be advantageous where only limited magnetic attachment may be needed to hold the baffle to the adjacent structure and where improved post-expansion adhesion is desired between the baffle material  24  and the body  10 . As shown in FIG. 6, after expansion, the baffle material  24  expands substantially to adhere to the body  10  and provide an acoustical baffle. 
     FIG. 7 illustrates a fourth embodiment of the baffle  12   c,  where a strip  58  of magnetic material  28  is perforated. Holes  60  enable the baffle material  24  of block  50  to flow therethrough for improved adhesion after activation. 
     FIG. 8 illustrates a further embodiment as baffle  12   d,  wherein the baffle material  24  may be provided as a sheet  62  having an elongated groove  64  formed or cut therein to promote folding therealong, with the sheet  62  thus having panels  66  and  68  separated by the groove  64 . The magnetic material  28  is provided in two separate members as spaced apart strips  70  and  72  and, as shown in FIG. 8, positioned between the panels  66  and  68  and the adjacent walls  74  and  76  of the body  10 . Such an application may be particularly useful in applications such as the engine well of the body  10  shown in FIG. 1, where the baffle  12   d  may be applied in sharp comers. Further, the groove  64  may be provided on the upper surface  78  of the sheet  62  away from the strips  70  and  72  as shown in FIG. 8 to facilitate placement on an inside corner, or the groove  64  may be provided on the bottom surface  80  of the sheet  62  which receives the strips  70  and  72  to facilitate mounting on an outside comer. 
     The baffle  12  of the present invention thus presents considerable flexibility in use. As shown, the magnetic material  28  itself is flexible to conform to the underlying wall surface and may be perforated to permit passage of the activated baffle material  24  therethrough. Sheets of the baffle  12  may be cut into desired shapes, such as with dies, to thereby permit placement of the baffle  12  into desired positions of complex configuration. The thickness of the baffle material  24  may be varied according to the volume of the cavity to be filled. In addition, the baffle  12  may be removed or repositioned at any time prior to bake-out without any adverse affects on the body  10 . It may be readily appreciated that the use of the automobile body  10  is illustrative of the uses of the baffle  12  hereof, and not intended to be limiting. 
     Although preferred forms of the invention have been described above, it is to be recognized that such disclosure is by way of illustration only, and should not be utilized in a limiting sense in interpreting the scope of the present invention. Obvious modifications to the exemplary embodiments, as hereinabove set forth, could be readily made by those skilled in the art without departing from the spirit of the present invention. 
     The inventor hereby states his intent to rely on the Doctrine of Equivalents to determine and assess the reasonably fair scope of his invention as pertains to any apparatus not materially departing from but outside the literal scope of the invention as set out in the following claims.