Patent Abstract:
The present disclosure relates to an anti-fatigue flooring article having inherent properties of electrostatic dissipation. Further, this disclosure relates to flooring article having at least two layers, wherein a first layer (comprised of dense rubber) is calendered to a second layer (comprised of foam rubber). Each layer has a different electrical conductivity, thereby creating a mat having an appropriate range of conductivity when combined. The present flooring article may also include a layer of static dissipating scrim, a grounding means, and/or a colored marking.

Full Description:
TECHNICAL FIELD 
     The present disclosure relates to an anti-fatigue flooring article having inherent properties of electrostatic dissipation. Further, this disclosure relates to flooring article having at least two layers, wherein a first layer (comprised of dense rubber) is calendered to a second layer (comprised of foam rubber). Each layer has a different electrical conductivity, thereby creating a mat having an appropriate range of conductivity when combined. The present flooring article may also include a layer of static dissipating scrim, a grounding means, and/or a colored marking. 
     BACKGROUND 
     Static dissipating floor articles are useful in manufacturing locations and in areas where computers or other sensitive electronic equipment is used. The objective of such flooring articles is to reduce static electricity on a person when that person is performing job tasks related to the manufacture of textiles, electronic components, or other products. It is known that static electricity can be generated by rubbing articles together, such as fibers or plastic components. Static electricity can be accumulated on a person&#39;s body and be discharged when the person touches a metal or grounded object. Such discharge can be unpleasant or painful to the person and may result in damage to nearby electronic devices or computer-aided instruments. Thus, an ideal flooring article for this situation should provide static dissipating properties to reduce static associated with persons standing on the article and insulating properties to prevent the mat from conducting electricity to persons standing on the article. 
     SUMMARY 
     The present flooring article functions as a static dissipating article and may include a grounding means (such as a snap, grommet, or the like) to prevent a person standing on the article from being shocked. A layer of static dissipating scrim may also be incorporated onto the flooring article. Alternatively, the flooring article can function as an insulating mat and be inherently grounded for use on conductive flooring. A flooring article having an appropriate range of conductivity is described herein. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 is a plan view of the face side of the static dissipating flooring article of the present invention, including a grounding means attached thereto; 
     FIG. 2 is a plan view of the face side of the static dissipating flooring article of the present invention, including a grounding means attached thereto and a border marking around the perimeter thereof; 
     FIG. 3 is a plan view of the static dissipating flooring article of the present invention, secured to a ground via a wire from the grounding means incorporated on the flooring article to the ground; and 
     FIG. 4 is a cross-sectional view of the static dissipating flooring article of the present invention, further including an anti-static scrim that covers the lower surface of the article; and 
     FIG. 5 is a cross-sectional schematic view of the static dissipating flooring article of the present invention, wherein the anti-static scrim covers the upper surface of the article. 
    
    
     DETAILED DESCRIPTION 
     As used herein, the term “flooring article” shall refer to a vulcanized rubber article that covers the floor but may be easily removed by the user. A flooring article is intended to encompass a mat (having a defined shape and integrated border area) and a flooring tile (a substantially square flooring article having cut edges rather than a molded and defined border). 
     FIG. 1 shows a plan view of the face side of one embodiment of the present flooring article. This is the side that would typically be seen by persons using article  10 . The face side includes a plurality of protrusions  12  positioned in a patternwise arrangement across the surface. Article  10  also includes a border area  14  around the perimeter, in which a grounding means  16  may incorporated. Although shown as a mat-type flooring article, article  10  might also comprise a flooring tile (thus lacking border area  14 ). 
     The particular pattern of protrusions  12  is not critical to the performance characteristics of flooring article  10 . Any spaced arrangement that provides a heightened surface may be used. More critical is the rubber formulation that is used. A dense rubber layer  24  is calendered to a foam rubber layer  26 . A die mold or molding plate is placed over dense rubber layer  24 , and foam rubber layer  26  is allowed to expand through a patternwise arrangement of openings. As the rubber is cured, foam layer  26  expands to create protrusions  12  that are “capped” by the dense rubber layer. The rubber formulation is a proprietary compound, sold under the name HM-8 from Hoover Hanes Custom Rubber Mixing Corporation, a subsidiary of RBX of Roanoke, Va. It contains from 20 parts to 70 parts by weight carbon black particles in both layers, which enhance the static dissipating qualities of article  10 . 
     Resultant flooring article  10  comprises unique features. First, protrusions  12 , in combination with the formulation used, produce a mat having desirable anti-fatigue qualities. Cumulative Standing Trauma (CST) is the result of excessive stress on the back, legs, and various muscles of a person who stands for long periods of time. CST can lead to varicose veins and to arch and heel pain from flattened feet. Flooring article  10  combats these problems. Persons standing for long periods of time on such a flooring article  10  (as described herein) are less likely to suffer from CST and other muscular disorders than those standing on concrete or other flooring surfaces. 
     More importantly, article  10 , because of its conductivity level, is capable of dissipating electrostatic charges from persons standing thereon. This conductivity is important in dissipating charges created in manufacturing locations, clean rooms, and areas where sensitive electronic equipment is in use. Electrical resistance is the property of a material whereby it opposes the flow of an electric current. Electrical resistance is measured in ohms (Ω); one such test for measuring electrical resistance is ASTM F-150. A range of values from that test is shown in Table 1, along with the affiliated industry nomenclature. 
     
       
         
               
             
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Industry Nomenclature for Electrical Conductivity of Floor Coverings 
               
             
          
           
               
                   
                   
                 Electrical Resistance range (Ohms) 
               
               
                   
                 Classification 
                 ASTM F-150 
               
               
                   
                   
               
               
                   
                  Insulative 
                 1 × 10 13 -1 × 10 15   
               
               
                   
                 Static Dissipative 
                     1 × 10 6 -1 × 10 11   
               
               
                   
                 Conductive 
                 2.54 × 10 4 -1 × 10 6    
               
               
                   
                 Super Conductive 
                 1 × 10 1 -1 × 10 4   
               
               
                   
                   
               
             
          
         
       
     
     Founded in 1982, the Electrostatic Discharge (ESD) Association is a professional voluntary association dedicated to advancing the theory and practice of electrostatic discharge (ESD) avoidance. From fewer than 100 members, the Association has grown to more than 2,000 members throughout the world. From an initial emphasis on the effects of ESD on electronic components, the Association has broadened its horizons to include areas such as textiles, plastics, web processing, explosives, clean rooms, and graphic arts. To meet the needs of a continually changing environment, the Association is chartered to expand ESD awareness through standards development, educational programs, local chapters, publications, tutorials, certification, and symposia. Their mailing address is 7900 Turin Road, Bldg. 3, Suite 2, Rome, N.Y. 13440-2069, and their web-site is www.esda.org. 
     Tests, conducted according to the ESD Association&#39;s Test Method S7.1, of two embodiments of article  10  are documented in Table 2. Samples 1 and 2 were comprised of a dense rubber layer and a foam rubber layer, in which each layer contained between 20 and 70 parts by weight of carbon black particles. 
     
       
         
               
             
               
               
               
             
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 Resistance ESD 7.1 
               
               
                 RESISTANCE ESD 7.1 
               
               
                 100 Volts, 72° F., 50% Relative Humidity - Measured in Ohms (Ω) 
               
             
          
           
               
                   
                   
                 Surface to Ground 
               
               
                   
                 Point to Point 
                 (Al foil underneath) 
               
               
                   
                   
               
             
          
           
               
                  Dense Rubber Layer - Sample 1 
                 1.43 × 10 6   
                 1.04 × 10 6   
               
               
                 Foam Rubber Layer - Sample 1 
                 1.08 × 10 9   
                 1.09 × 10 9   
               
               
                 Dense Rubber Layer - Sample 2 
                 1.06 × 10 6   
                 1.00 × 10 6   
               
               
                 Foam Rubber Layer - Sample 2 
                 2.73 × 10 9   
                 2.40 × 10 9   
               
               
                   
               
             
          
         
       
     
     The above table indicates that dense rubber layer  24  is more conductive than foam rubber layer  26 . The combination of rubber layers and the resulting combination of conductivity levels make article  10  well-suited for static dissipation. When comparing the values from Table 2 with the industry definitions listed in Table 1, it is clear that article  10  falls within the definition of “static dissipative.” 
     Turning again to the drawings, FIG. 2 shows border area  14  on which a distinctive colored marking  18  may be included. Marking  18  may consist of a solid color different from that of article  10  or any geometric or organic pattern, including, but not limited to, stripes of varying widths, designs, or logos. In one embodiment, marking  18  approximates the dimensions of border area  14 , in order to differentiate article  10  from other mats that may be in use in a given facility. Royal blue is one example of a color accepted by the industry for such marking, although other colors may be equally acceptable to other industry groups or countries. 
     Marking  18  may be comprised of thermoplastic elastomer (TPE), thermoset rubber, vinyl, polyvinyl chloride (PVC), thermoplastic olefins, or any other colored sheet that will permanently laminate to the rubber during the vulcanization process. PVC must be thermoprinted onto article  10  and is currently available only in white. The preferred material is TPE, such as is available in a variety of colors and thicknesses from Specialty Adhesive Film of Cleves, Ohio. A suitable thickness of colored material used for marking  18  is in the range of 3 to 200 mils (1 mil=0.001 inches). The colored material can be cut by any cutting means appropriate for the application; for instance, if a precision cut is required, a cutting means capable of precision is required. Any cutting means known in the industry, including, but without limitation, an X-Y plotter, a rotary die cutter, or any other die cutters, may be used. 
     To laminate the colored material used in marking  18  to flooring article  10 , the material is placed on top of the uncured rubber. The colored material may be laminated to either the dense rubber or foam rubber side of article  10 . A die mold (such as has been previously described) is positioned over the layers. The rubber is vulcanized to create flooring article  10 , to which marking  18  is then permanently laminated. Multiple layers of colored material may be used. These colored layers can be laminated one upon the other or in registration with each other to create multi-color sheeting, graphics, patterns, or the like. Graphics, logos, geometries, diagonal stripes of varying widths, and/or alphanumeric figures can each be produced using this lamination technique. Marking  18  may be applied to border area  14  or, in an alternate embodiment, at any position in the center panel of article  10 . If marking  18  is applied to the center of mat  10  (that is, in an area in which protrusions  12  will be created), then marking  18  will become attached to the tops and sides of protrusions  12 . 
     By using the lamination technique described herein, flooring articles  10  are given a distinctive appearance with less cost than would be associated with colored rubber. First, the colored material (e.g., TPE) provides the same colored effect as a co-calendered colored rubber, with a much thinner film and much less weight. Accordingly, the thinner film needs a shorter cure time, contributing to a decrease in manufacturing costs. Unlike rubber, which tends to cure over time even in inventory at room temperature, TPE is already cured and therefore does not have a limited shelf-life. 
     Turning now to FIG. 3, grounding means  16  is comprised of a snap, grommet, probe, or other conductive device to which a ground wire may be connected. Although shown as a snap or grommet, grounding means  16  could consist of a wire protruding from the edge of article  10 , a flat metal blade inserted through the edge of article  10 , or any other grounding means known in the industry. Both the wire and the blade-style grounding means would be attached to a ground wire  20  that connects article  10  with a ground  22 . 
     FIG. 4 shows a cross-sectional view of article  10 , further including a layer of static-dissipating scrim  28 . Scrim  28 , comprised of conductive fibers configured in a substantially open construction, provides a conductive path from the upper surface of article  10  (that is, dense rubber layer  24 ) to the ground. Scrim  28  is laminated to article  10  during the vulcanization process, in such a way as to complete a circuit between article  10  and the ground. In a preferred embodiment, scrim  28  is laminated over the rear side of article  10  and onto border area  14  located on the face side of article  10 . The vulcanization process protects scrim  28  while article  10  is in use and prevents scrim  28  from being damaged in multiple washings. 
     An alternate embodiment is shown in FIG. 5, in which scrim  28  is attached to dense rubber layer  24  that comprises the face layer of article  10 . Scrim  24  is then wrapped around the edge portion(s) of article  10  to complete the circuit between article  10  and the ground. 
     Alternatively, scrim  28  can be integrated between the dense rubber layer and the foam rubber layer during calendering and prior to vulcanization, if scrim  28  is allowed to wrap around foam layer  26 . Wherever it is positioned, scrim  28  must make good electrical contact with the rubber components of article  10 .

Technology Classification (CPC): 4