Abstract:
A slip resistant step stool includes a step surface with four legs extending downward. A slip resistant surface is bonded to the step surface. The slip resistant surface may be disposed in a pocket and have a ridge surrounding it. The slip resistant surface can be a thermoplastic elastomer. The stool can be manufactured by inserting the slip resistant surface in a mold adapted to form a step stool, then injecting molten resin into the mold, thereby bonding the resin to the slip resistant step stool.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. Provisional Application 60/382,720, filed on May 23, 2002. 
    
    
     TECHNICAL FIELD 
     The technical field generally relates to step stools and, more particularly, relates to injection molded step stools having a slip-resistant insert formed thereon. 
     BACKGROUND 
     Step stools for commercial and consumer utility are well-known. Such step stools are typically constructed from stamped or otherwise formed metal or from a plastic molded by an injection molding process. Generally, a step stool includes a step portion forming a planar surface supported by a plurality of legs fixedly attached to a bottom surface of the step portion.  FIG. 1  illustrates a prior art metal step stool  2  including a step portion  4  having a substantially rectangular configuration. The step portion  4  further includes a plurality of rounded corners  6  and a skirt  8  fixedly attached or integrally formed along the periphery  10  of the support portion  4 . The step portion  4  further includes a top surface  12 , a bottom surface  14  and a plurality of support legs  16  fixedly attached to the bottom surface  14 . The support legs  16  have a substantially circular cross section and extend a uniform distance from the bottom surface  14  such that the bottom surface  14  is substantially parallel to a reference surface such as a floor or other horizontal surface. The support legs  16  further including a footer  18  fixedly attached to an end of the support leg  16   a  distal to the bottom surface  14 . The footer  18  may be constructed from any appropriate plastic or rubber material and configured to be firmly attached at the end of the support leg  16   a . The top surface  12  can be formed to have a variety of configurations including a textured or uneven surface such as a plurality of raised ridges  20   a-   20   c  formed integrally with the top surface  12 . The raised ridges  20   a-   20   c  can be formed to provide additional traction for the top surface  12 . 
       FIG. 2  illustrates another embodiment of a prior art metal step stool  2  wherein the top surface  12  includes a non-skid surface  22  fixedly adhered to the top surface  12 . The non-skid surface  22  may be a self-adhesive material having a textured or irregular surface  22   a  to provide a high coefficient of friction such that a person using the step stool will not slip or skid on the stool. The non-skid surface  22  may be formed in a substantially rectangular configuration having a plurality of filleted corners  24 , as illustrated in  FIG. 2 , or may be formed as a plurality of longitudinal strips similar to the raised ridges  20   a-   20   c  illustrated in FIG.  1 . 
     Further embodiments of the prior art step stool may include injection molded step stools formed from plastic and resin materials having a configuration substantially similar to the step stool  2  described above. The top surface of the injection molded step stool is often formed with a knurled or a textured surface to provide slip resistance. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a prior art step stool; 
         FIG. 2  is a perspective view of another embodiment of the prior art step stool; 
         FIG. 3  is a perspective view of a step stool providing a non-skid surface in accordance with the teachings of this disclosure; 
         FIG. 4  is a sectional view of the step stool taken along the line  4 — 4 ; 
         FIG. 5  is an enlarged cross-sectional view of the slip-resistant surface highlighted in  FIG. 4 ; and 
         FIG. 6  is an enlarged cross-sectional view of another embodiment of a slip-resistant surface similar to that highlighted in FIG.  4 . 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 3  illustrates an injection-molded step stool  30  that includes a support structure  31  and a slip resistant surface  64 . The support structure  31  has a step surface  32  with a substantially rectangular configuration. The rectangular step surface  32  has a plurality of edges  34   a - 34   d  wherein each of the edges is connected by a concave edge  36  located proximately to the intersection of any two of the edges  34   a - 34   b ,  34   b - 34   c ,  34   c - 34   d ,  34   d - 34   a , respectively. A plurality of side-walls  38   a - 38   d  may be formed adjacent to the edges  34   a - 34   d , wherein the side walls  38   a - 38   d  are aligned generally orthogonal to a plane defined by the step surface  32 . The plurality of edges in this example have a smooth transition or radius between the top surface  32  and the side-walls  38   a - 38   d . These sidewalls  38   a - 38   d  can be arranged to define a downwardly depending skirt for the step surface  32 . 
     In this example, the side-walls  38   a - 38   d  are interconnected, each in the same fashion as the edges  34   a - 34   d , by legs  56 , each having a concave surface  40 , respectively, located proximate to the intersection of any two of the side-walls and extending downward a greater distance than the remaining portions of the sidewalls  38   a - 38   d . Each concave surface  40  terminates at a convex footer  42 . The convex footer  42  transitions to each concave surface  40  at a ledge surface  44  formed substantially parallel to the step surface  32 . Each side-wall  38   a - 38   d  and its adjacent concave surfaces  40  define a cut-out generally indicated by the numeral  48 . The cutout  48  comprises a pair of substantially parallel edges  50  of the adjacent respective concave surfaces  40  that intersect a transverse edge  52  via a pair of curved corners  54 . The above structure of a single leg  56  has been described herein for the sake of brevity, but one skilled in the art will understand that the structure is exemplary of the construction of the remaining legs  56 . 
       FIG. 4  illustrates a cross-sectional view of the step stool  30  described above. An interior surface of the side-wall  38   c  and the concave surfaces  40  are illustrated. The side-walls  38   b ,  38   d  and the step surface  32  are illustrated having a thickness “t.” A bead  58  can circumnavigate each cut-out  48  providing a strengthened edge. As shown in  FIG. 4 , the stool  30  may be positioned on a reference surface  62  such as the floor of a house. 
     Disposed on top of the step surface  32  is a slip-resistant surface  64  that provides a high friction surface such that a person standing on the stool  30  will be safer and less likely to fall off. The slip resistant surface  64  is disposed in a pocket  68  within the step surface  32 . The step surface  32  further includes a ridge  70  circumnavigating the outside edge of the slip resistant surface  64 . 
     The support structure  31  can be manufactured from any of a variety of plastic materials such as polypropylene, polyethylene, acrylonitrile-butadiene-styrene (ABS) plastic, nylon, polyvinyl chloride (PVC) or any other material suitable for use in an injection molding process. Typically, in an injection molding process, a multi-piece mold is constructed defining an inverse representation of the item to be molded. A pressurized melted plastic material, such as the plastics listed above, is injected into the mold to form a completed item. When the melted plastic has sufficiently cooled, the multi-piece mold is separated into its component pieces and the resulting item is removed. 
       FIG. 5  illustrates an enlarged view, in a first example, taken from circle  5  in  FIG. 4 , of the support structure  31  and the slip-resistant surface  64 . The slip resistant surface  64  can be manufactured from virtually any thermoplastic elastomer (TPE) or thermoplastic vulcanizate (TPV). SANTOPRENE® thermoplastic elastomer, and VYRAM® thermoplastic elastomer, both manufactured by Advanced Elastomer Systems (AES) of Akron Ohio, styrene-butadiene-styrene (SBS) and ethylene vinyl acetate (EVA) are examples of suitable materials for this application. 
     First, the slip-resistant surface  64  can be manufactured by extrusion or the like. Extrusion is a process by which raw material, generally in the form of small pellets, or resin, such as SANTOPRENE®, is heated in a chamber to the point where it will flow under moderate pressure and can be extruded through a flat die and subsequently cooled and cut to size to form the slip-resistant surface  64 . 
     Next, the slip-resistant surface  64  can be affixed to the support structure in a number of ways such as insert molding or in-mold labeling. Using insert molding process to form the support structure  31  involves pre-positioning an insert, in this case the slip-resistant surface  64 , within a multi-piece mold prior to the injection of melted plastic material. The multi-piece stool mold is generally made up of two vertically separable halves, and a vacuum system or static charger is incorporated to ensure the slip-resistant surface  64  remains in position throughout the formation process. Upon injection of the resin in a liquefied state into the stool mold, the slip-resistant surface  64  and the liquefied resin come into contact. The heat of the melted plastic is transferred to the slip resistant surface  64 , thereby slightly melting the slip resistant surface, allowing the two materials to flow within each other, and thereby forming a heat bond or thermoplastic weld  74  between the two materials. 
     In a first example, it has been found that a slip resistant surface  64  can be created using a high viscosity resin such that the slip resistant surface  64  maintains its integrity and does not flow into the support structure  31  under the heat and pressure of the insert molding process. An example is a slip resistant surface  64  created by a plate extrusion of a mixture of 79.5% VYRAM® grade 9101-45, a thermoplastic elastomer, 15% EXACT® 2101, an ethylene octene copolymer manufactured by Exxon Mobile Chemicals, 5% VECTOR® styrene-isoprene-styrene block co-polymer manufactured by DexCo Polymers, and 0.5% SP 1045, a phenolic resin manufactured by Schenectady International, Inc., each percentage by weight. It is believed that the EXACT® and phenolic resin provide cross-linking action to the VYRAM® to increase its viscosity. Further, the VECTOR® adds to the processability of the extrusion. When this higher viscosity material extruded insert is placed within the stool mold and the molten resin is injected under pressure, the extruded insert does not bleed into the resin. Instead, the extrusion maintains its shape. While this example puts forth specific parameters, it is clear that one skilled in the art would recognize product equivalents. Furthermore, it has been found that the ratios of the ingredients can be varied substantially and the same or substantially similar results can be achieved. 
     In a second example, a SANTOPRENE® or VYRAM® insert  64  is placed and held within the mold. The hot molten resin is injected under pressure into the mold. In this example, the SANTOPRENE® has been found to bleed into the resin due to the pressure and the heat which in some applications may provide an aesthetically pleasing marbled effect. 
     In-mold labeling, a process similar to the insert molding, involves pre-positioning a plastic label within the multi-piece mold, and affixing the label to the item while it is still being formed within the multi-piece mold. In this example, the slip-resistant surface  64  can be manufactured of the same material as the support structure  31  or of a substantially homogenous material such that the two components, in the presence of sufficient heat, form a continuous bond  74  with each other. The use of plastic film labels for in-mold labels provide a recycling advantage by allowing the whole item to be reground for reuse without having to remove the label. 
     Another example of a slip-resistant surface  64  is illustrated in FIG  6 . In this example, a separate layer  66 , not shown in  FIGS. 4  or  5 , is used to affix the slip-resistant surface  64  to the step surface  32 , whereby the layer  66  operatively connects or adheres the slip-resistant surface  64  to the step surface  32 . The layer  66  may be an adhesive applied to an undersurface  64   a  of the slip-resistant surface  64 . The adhesive can removably or fixedly join the slip-resistant surface  64  within the pocket  68 . Further, the layer can be any other material known in the art to affix materials together. For example, the slip resistant surface  64  and the step surface  32  may be incompatible, and therefore unable to form a heat bond. In this case, it is possible that the layer  66  will be compatible with both, thereby making it possible to bond the incompatible surfaces  32 ,  64 . 
     Another embodiment provides for the slip-resistant surface  64  to be affixed within the pocket  68  after the formation of the support structure  31  has been completed within the multi-piece mold. During one such post-molding operation, the slip-resistant surface  64  can be affixed using a heat transfer process which combines heat and pressure to thermally bond the slip-resistant surface  64  to the top surface  32 , either with or without a layer  66 . Another post-molding operation may include coating of the step surface  32  with a slip resistant coating such as a commercially available textured epoxy coating. 
     In the illustrated examples, only a single slip resistant surface  64  is shown. However, it is clear that a plurality of strips of slip resistant surfaces  64  can used. Further, it is illustrated that a portion of the step surface  32  is covered by the slip resistant surface  64 . Additionally, it is illustrated that a majority, or over 50%, of the step surface  32  is covered by the slip resistant surface  64 . Others may find it useful to cover the entire step surface  32  with the slip resistant surface  64 . Others may find it cost efficient to cover less than the majority of the step surface  32  with the slip resistant surface  64 . 
     While the step stool  30  has been described with reference to specific examples which are intended to be illustrative only and not to be limiting of the invention, it will be apparent to those of ordinary skill in the art that changes, additions or deletions may be made to the disclosed embodiments without departing from the spirit and scope of the invention.