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CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Non-Provisional application Ser. No. 14/281,238 filed May 19, 2014, which is a continuation of U.S. Pat. No. 8,764,101 issued Jul. 1, 2014, which is a divisional application of U.S. Pat. No. 8,221,673 issued Jul. 17, 2012, which claims priority to expired U.S. Provisional Application No. 60/691,790 filed Jun. 17, 2005, each hereby incorporated by reference in its entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention is drawn to a load bearing panel member formed by a method of injection molding. 
       BACKGROUND 
       [0003]    There are numerous known systems for plastic injection molding. In conventional plastic injection molding systems, plastic pellets are melted in an injection molding machine and advanced by a screw ram through an injection nozzle and into a mold cavity. The mold cavity is preferably formed between two mold halves. The molten plastic material in the cavity is allowed to cool and harden in the cavity. When the plastic material has cooled and sufficiently hardened, the two halves of the mold are separated or opened and the part is removed, typically by one or more ejector pins. 
         [0004]    Some injection molding systems utilize a gas in the injection molding process and are commonly known as “gas-assisted injection molding” systems. In these systems, the gas is injected into the molten plastic material through the plastic injection nozzle itself, or through one or more pin mechanisms strategically positioned in the mold. It is also possible to inject the gas directly into the molten plastic in the barrel of the injection molding machine. The gas, which typically is an inert gas such as nitrogen, is injected under pressure and forms one or more hollow cavities or channels in the molded part. 
         [0005]    Gas-assisted injected molding produces a structure having a hollow interior portion which results in saving weight and material, thereby reducing costs. The pressurized gas applies an outward pressure to force the plastic against the mold surfaces while the article solidifies. This helps provide a better surface on the molded article and reduces or eliminates sink marks and other surface defects. The use of pressurized gas also reduces the cycle time as the gas is introduced and/or migrates to the most fluent inner volume of the plastic and replaces the plastic in those areas which would otherwise require an extended cooling cycle. The pressure of the gas pushing the plastic against the mold surfaces further increases the cooling effect of the mold on the part, thus solidifying the part in a faster manner and reducing the overall cycle time. 
       SUMMARY 
       [0006]    The present invention provides a method for producing a structural or load bearing injection molded panel member. According to a preferred embodiment, the panel member is a floor panel for a van having retractable rear seats wherein the panel member is adapted to cover the rear seats when fully retracted and act as a load floor. The panel member preferably includes a first portion, a second portion and an interior surface portion. The present invention will hereinafter be described according to the preferred embodiment wherein the interior surface portion is a carpet material; however, it should be appreciated that according to alternate embodiments the interior surface portion could also include, for example, a vinyl material or a textile material. 
         [0007]    The preferred method of the present invention includes placing the carpet material into a mold cavity configured to produce the panel member. The mold cavity preferably includes a first chamber adapted to form the first portion of the panel member, and a second chamber adapted to form the second portion of the panel member. After the carpet material is inserted into the mold, molten plastic material and pressurized gas are injected into the first chamber of the mold cavity. After the molten plastic material is injected into the first chamber of the mold, molten plastic material is injected into the second chamber of the mold cavity. A sequential gating process is used to achieve this sequence of operations. The molten plastic is then cooled until it solidifies. After the molten plastic is sufficiently cooled, the pressurized gas is vented and the panel member is removed from the mold. 
         [0008]    It should be appreciated that the order in which the steps of the preferred embodiment are performed may be varied according to alternate embodiments. For example, according to one alternate embodiment of the present invention, the molten plastic material may be injected into the second chamber of the mold cavity before molten plastic material is injected into the first chamber of the mold cavity. According to yet another alternate embodiment, molten plastic may be injected into the first and second chambers of the mold cavity simultaneously. 
         [0009]    The present invention also provides a structural or load bearing panel member and a product by process. The load bearing panel member preferably includes a generally rectangular first portion, a generally rectangular second portion, and a carpet material. The carpet material is attached to the first portion and the second portion such that the carpet material forms an integral or living hinge at a gap therebetween. The first portion of the panel member defines a plurality of solid horizontally disposed ribs and a plurality of solid vertically disposed ribs. The first portion of the load bearing panel member also includes a plurality of hollow ribs formed by the gas assisted injection molding process. The hollow ribs are generally located around the periphery of the first portion of the load bearing panel member as well as in an X-shape originating at the center of the first portion and extending toward the corners thereof. The solid ribs and hollow ribs are adapted to increase strength and rigidity and provide substantial structural or load-bearing capability 
         [0010]    The above features and advantages and other features and advantages of the present invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in connection with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  is a bottom view of a load bearing panel member in accordance with the present invention; 
           [0012]      FIG. 2  is a block diagram illustrating a method of the present invention; 
           [0013]      FIG. 3  is a sectional view of the panel member taken along line A-A of  FIG. 1 ; 
           [0014]      FIG. 4   a  is a schematic sectional view of an injection molding nozzle and a plurality of valves; and 
           [0015]      FIG. 4   b  is a schematic plan view of a mold cavity. 
       
    
    
     DESCRIPTION 
       [0016]    Referring to the drawings, wherein like reference numbers refer to like components,  FIG. 1  shows a panel member  10  produced according to a method of the present invention. The panel member  10  will hereinafter be described as a floor panel for a van having retractable rear seats (not shown), wherein the panel member  10  is adapted to cover the rear seats when the seats are fully retracted and also to act as a load floor. It should be appreciated, however, that the method of the present invention may be implemented to produce other conventional panel members as well. 
         [0017]    The panel member  10  includes a generally rectangular first portion  12 , a generally rectangular second portion  14 , and an interior or appearance surface portion  16  (shown in  FIG. 3 ). The present invention will hereinafter be described according to the preferred embodiment wherein the interior surface portion  16  is carpet material; however, it should be appreciated that according to alternate embodiments the interior surface portion  16  could also include, for example, a vinyl material or a textile material. According to a preferred embodiment, the carpet material  16  is a polypropylene material with a polyester backing The carpet material  16  is attached to the first portion  12  and the second portion  14  such that the carpet material  16  forms an integral or living hinge  18  at a gap  19  between the first portion  12  and the second portion  14 . The first portion  12  of the panel member  10  defines a plurality of solid horizontally disposed ribs  20  and solid vertically disposed ribs  21 . The solid ribs  20  and  21  are normal to each other so as to increase strength and rigidity and provide substantial load-bearing capability. According to a preferred embodiment of the present invention, the second portion  14  of the panel member  10  includes a plurality of up-standing clip attach members  22 . 
         [0018]    The clip attach members  22  preferably each retain a metallic attachment clip (not shown) configured to mount the second portion  14  of the panel member  10  to a seat assembly (not shown). When the seat assembly is in an upright position, the hinge  18  allows the second portion  14  of the panel member  10  to fold underneath the first portion  12  and below the seat. 
         [0019]    When the seat assembly (not shown) is fully retracted, the first portion  12  of panel member  10  is rotatable about the integral hinge  18  from an open position exposing the seat assembly to a closed position at which the seat assembly is covered. When the seat assembly is fully retracted and the first portion  12  of panel member  10  is in the closed position, the carpet material  16  (shown in  FIG. 3 ) is exposed and the seat assembly is completely hidden. In this manner, the panel member  10  is adapted to provide an aesthetically pleasing carpeted interior when the seat assembly is retracted, and also provide substantial floor-strength. 
         [0020]    Referring to  FIG. 2 , a method for manufacturing the panel member  10  according to the present invention is shown. At step  50 , the carpet material  16  is placed into a mold cavity  70  (shown in  FIG. 4   b ) configured to produce the panel member  10 . Optionally, at step  50 , metal inserts such as bars and/or tubes (not shown) can also be placed into the mold cavity  70  with the carpet material  16  to produce a panel member  10  with increased strength and rigidity. The mold cavity  70  of the present invention preferably includes a first chamber  72  (shown in  FIG. 4   b ) adapted to form the first portion  12  of the panel member  10 , and a second chamber  74  (shown in  FIG. 4   b ) adapted to form the second portion  14  of the panel member  10 . The first and second chambers  72 ,  74  are preferably separated by an insert or feature  75  (shown in  FIG. 4   b ) configured to produce the integral hinge  18  (shown in  FIG. 3 ). At step  52 , molten plastic material  76  (shown in  FIG. 4   a ) is injected into the first chamber  72  of the mold cavity  70 . The molten plastic material  76  is preferably injected in a conventional manner, such as, for example, by a reciprocating screw type injection device (not shown), through an injector nozzle  40  (shown in  FIG. 4   a ), through a valve gate  42   a  (shown in  FIG. 4   a ), and into the first chamber  72  of the mold cavity  70 . 
         [0021]    At step  54 , an inert gas  80  (shown in  FIG. 4   b ) such as nitrogen is injected into the first chamber  72  of the mold cavity  70  (shown in  FIG. 4   b ) through a plurality of gas pins  82  (shown in  FIG. 4   b ) positioned at locations predefined by the desired locations of the hollow ribs  30 . The gas  80  preferably does not mix with the molten plastic material  76 , but takes the path of least resistance through the less viscous portions of the plastic melt. The molten plastic  76  is therefore pushed against the wall portions of the mold cavity  70 , which forms channels  31  and produces the hollow ribs  30  (shown in  FIGS. 1 and 3 ). 
         [0022]    Referring to  FIG. 3 , a sectional view taken through section A-A of  FIG. 1  is shown. It can be seen in  FIG. 3  that the hollow ribs  30  define an internal channel  31  through which the gas is injected. Referring again to  FIG. 1 , the gas  80  (shown in  FIG. 4   b ) is preferably injected through the gas pins  82  (shown in  FIG. 4   b ) into the first portion  12  of the panel member  10  at the gas injection locations  32 . According to a preferred embodiment, the hollow ribs  30  are generally located around the periphery of the first portion  12  of the panel member  10  as well as in an X-shape originating at the center of the first portion  12  and extending toward the corners thereof. It has been observed that the hollow ribs  30  formed in the manner described increase the rigidity and strength of the first portion  12  of the panel member  10 . The increased strength and rigidity is particularly advantageous for the preferred embodiment wherein the panel member  10  is implemented as a load bearing floor panel. 
         [0023]    Referring again to  FIG. 2 , at step  56  molten plastic material  76  (shown in  FIG. 4   a ) is injected into the second chamber  74  of the mold  70  (shown in  FIG. 4   b ). The molten plastic material  76  is preferably injected through the injector nozzle  40  (shown in  FIG. 4   a ), through a valve gate  42   b  (shown in  FIG. 4   a ), and into the second mold chamber  74 . 
         [0024]    A sequential gating process is preferably implemented to perform previously described steps  52  and  56 . Referring to  FIGS. 4   a - 4   b,  the valve gates  42   a  and  42   b,  which are adapted to feed the first and second mold chambers  72 ,  74 , respectively, are opened using the sequential gating process. In other words, the sequential gating process is implemented to control the timing of the gates  42   a,    42   b  and to coordinate the operation of valve gate  42   b  with the operation of valve gate  42   a.  According to a preferred embodiment, the valve gates  42   a  and  42   b  are configured to open and close at a predetermined time. The predetermined time at which the valve gates  42   a  and  42   b  open and close is generally based on the needs of the specific part to be molded and type of material being used. Alternatively, the valve gates  42   a  and  42   b  may be opened and closed based on the position of a screw type injection device (not shown). 
         [0025]    Referring again to  FIG. 2 , at step  58  the molten plastic material  76  (shown in  FIG. 4   a ) that was injected into the first and second chambers  72 ,  74  of the mold cavity  70  (shown in  FIG. 4   b ) at steps  52  and  56  is allowed to cool and solidify. Thereafter, at step  60 , the pressurized gas  80  (shown in  FIG. 4   b ) that was injected in to the first chamber  72  of the mold cavity  70  at step  54  is allowed to vent through the gas pins  82  (shown in  FIG. 4   b ). At step  62 , the finished panel member  10  is removed from the mold cavity  70 . 
         [0026]    It should be appreciated that the order in which the steps  50 - 62  of the preferred embodiment are performed may be varied according to alternate embodiments. For example, according to one alternate embodiment of the present invention, step  56  at which the molten plastic material  76  (shown in  FIG. 4   a ) is be injected into the second chamber  74  (shown in  FIG. 4   b ) of the mold cavity  70  (shown in  FIG. 4   b ) may be performed before step  52  at which molten plastic material  76  is injected into the first chamber  72  (shown in  FIG. 4   b ) of the mold cavity  70 . According to yet another alternate embodiment, steps  52  and  56  may be performed simultaneously such that molten plastic  76  is injected into the first and second chambers  72 ,  74  of the mold cavity  70  simultaneously. 
         [0027]    While the best modes for carrying out the invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention within the scope of the appended claims.

Summary:
A load bearing panel member having a first portion, a second portion, and an appearance surface portion is formed by injection molding such that the first portion includes a plurality of ribs forming a grid pattern on the first portion and another plurality of ribs extending toward the periphery of the first portion which may be non-orthogonal to each other and to the ribs forming the grid pattern. An internal channel may be formed within each of the non-orthogonal ribs by injecting a gas into the rib during the molding process forming the panel. An appearance surface portion attached to the first portion and second portion of the panel member forms an integral hinge between the first and second portions of the panel member. The panel member may be configured as a floor panel of a vehicle.