Carpet underlay having pad and perforated plastic film
This application is a continuation of application Ser. No. 519,220 filed 8/3/83, now abandoned, which is a continuation of application Ser. No. 331,038 filed 12/19/81 now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to underlays for carpets and the combination of the underlays and the carpet. 
     It is known in the art to provide pads to underlay carpets to provide a soft cushioned effect. One problem encountered in laying carpet over pads is that the carpet tends to stick to the pad during installation due to the frictional force between the two. One solution to this problem is to provide a loosely woven or non-woven scrim fabric between the pad and the carpet to reduce this friction. 
     However, this fabric has marginal flame retardant properties; and the potential for even tighter regulation in the area of building materials poses a threat to this solution. 
     Nylon film has very good slip characteristics, good heat seal adhesion to foam padding and excellent flame retardant properties, but produces a crinkling sound, similar to that produced by crumpling paper, when the carpet is walked on. 
     It is one object of this invention to provide an improved pad-film combination which will overcome the above-noted deficiencies while retaining the desired slip, adhesion and flame retardant characteristics. 
     Other objects and features of the invention will become apparent from the following specification. 
     SUMMARY OF THE INVENTION 
     The invention accordingly comprises a quiet carpet underlay comprising: a pad; and a perforated plastic film overlaying said pad; said film being perforated with holes having an average diameter ranging from 0.001 to 0.5 inches and a density ranging from 3 to 100,000 holes per square inch. In a presently preferred embodiment, the film is made from nylon and the ratio of: (a) the Percent Open Area encompassed by the holes to (b) the hole diameter (expressed as number of holes per square inch) is above about 140. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The invention is more clearly illustrated in the following description in which: 
     FIG. 1 illustrates a cross-section of the padfilm underlay-carpet combination of this invention. 
     FIG. 2 is a plan view of the pad covered by the film underlay showing the holes punched in the film. 
    
    
     FIG. 1 shows a cross-section of a carpet and underlay construction, comprising conventional carpet 11, peforated nylon film underlay 12 and foam pad 13. 
     As can be seen from FIG. 2, the film 12 has a series of holes 14 distributed generally uniformly through the film 12. 
     These holes or perforations are preferably round, having a diameter ranging from 0.001 to 0.5 inches, preferably 0.010 to 0.045 inches, and a density ranging from 3 to 100,000, preferably 100 to 400 holes per square inch. 
     The film should range in thickness from 0.00025 to 0.010 inches, preferably 0.0004 to 0.001 inches. 
     Surprisingly, we have found that not only the hole size and density are critical factors, but also the ratio of the Percent Open Area of the film to the hole diameter. This calculation can be found from the following formula: ##EQU1## wherein &#34;D&#34; is the average diameter of the holes expressed in inches and Density is the hole density expressed in number of holes per square inch. 
     As can be seen from the following examples, there is a definite relationship between this ratio and the noise generated by pressure simulating the walking of someone on the carpet. In these examples, holes of various sizes and density were punched in a film laminated to a foam pad and the film pad sample &#34;crinkled&#34; to simulate walking. The noise level was estimated empircally on a scale of 0-10 with 10 representing the loudest noise generated by an unpunched film and 0 representing essentially no noise generated by the crinkling. From these examples it can be seen that as the ratio of the &#34;Percent Open Area&#34; to the &#34;Hole Diameter&#34; increases the noise level gets lower. A noise level above 7 is considered unacceptable with the preferred level being below 2-3. Based on this correlation, we find tht the Ratio of the Percent Open Area to the hole diameter (D) should be above about 128, preferably above about 140, and more preferably above about 240. 
     In the following Examples, a 0.0006 inch nylon film was formed with hole sizes and densities as indicated. 
     The film was bonded to foam backing which was then &#34;crinkled&#34; to simulate walking and noise level recorded on a scale of 0-10. 
     
                       TABLE I                                                     
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                         % Open                                           
                Hole     Area (100 ×                                
                                  % Open                                  
                Density  Den. ×                                     
                                  Area                                    
       Hole     (No. of  Cross    divided                                 
       Diameter Holes    Sec. of  by hole                                 
                                         Noise                            
Ex.    in Inches                                                          
                per in.sup.2.)                                            
                         each Hole)                                       
                                  diameter                                
                                         Rating                           
______________________________________                                    
Comp. 1                                                                   
       unmodified nylon film                                              
Ex. 1  .045&#34;    113       16%     399    0                                
Comp. 2                                                                   
       .010&#34;    100       .8%      79    8                                
Ex. 2  .010&#34;    200      1.4%     157    5                                
Ex. 3  .010&#34;    300      2.3%     236    2                                
Ex. 4  .010&#34;    400      3.1%     314    0                                
Ex. 5  .016&#34;    256      2.9%     241    0                                
Comp. 3                                                                   
       .100&#34;     16      12.8%    126    7                                
Ex. 6  .100&#34;     20       16%     157    5                                
Ex. 7  .100&#34;     25       20%     196    3                                
Comp. 4                                                                   
       .156&#34;     1       1.9%      12    10                               
Comp. 5                                                                   
       .156&#34;     5       9.5%      61    9                                
Ex. 8  .156&#34;     9       17.1%    110    5                                
Ex. 9  .156&#34;     16       30%     196    3                                
Ex. 10 .016&#34;     64       .7%      60    5                                
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     While hole area has been expressed as a function of diameter &#34;D&#34; in this case, it is understood that the theory is equally applicable to apertures or holes of any cross-section configuration. In cases other than circular cross-sections, the diameter &#34;D&#34; would be the average diameter, such as the average between the longest and the shortest axis in the case of an ellipse or a rectangle. 
     Although nylon is the preferred plastic material because of its fire retardant characteristics and adhesion to foam pad properties, other plastic films of high noise level could be used in non-critical applications. Examplatory of these are polypropylene, polyester, polyvinyl chloride and others.