Abstract:
A polymeric foam buffing pad is made from a foam preform that has a convex outer working surface slit and compressed. Preferably, the working face is slit to form a pattern of foam fingers. The slit convex preform is flattened to place the outer working surface in compression and the flattened pad is attached, in use, to a flat backing surface to maintain the compressed surface state. The invention can also be applied to an unslit preform.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention pertains to polymeric foam pads used to buff, polish or finish painted or clear coat or other solid surfaces. In particular, the invention pertains to a unique method of making and resulting buffing pad made from polyurethane foam in which, in the preferred embodiment, the working face of the pad is slit or slotted and compressed. 
         [0002]    As a result of the compression of the slit working face, more working foam material is forced into a given area. This has been found to substantially enhance performance of a pad made from the compressed foam and also results in a longer pad life. This is important because the preferred open cell polyurethane foam is relatively expensive. The wavy shape imparted to the compressed working face also changes the directional forces applied to the surface being finished. This, in turn, changes the angle of attack to the surface being finished, the angle being selectively variable by choice of the slitting pattern in the working face and the curvature of the foam preform from which the pads are cut. 
       SUMMARY OF THE INVENTION 
       [0003]    In accordance with the present invention, a buffing, polishing and finishing pad is made from a body of polyurethane foam that has a working face characterized by a pattern of slits in the working face which, when compressed, reduces substantially the cell structure and increases the density of the foam body in the area of the working face. The slits in the working face of the pad are preferably bidirectional and extend only partially through the thickness of the pad to form a pattern of short foam fingers. As a result of the manner in which the front face is compressed, the opposite rear face of the pad, which is unslit, is placed in tension. The bidirectional slits typically comprise two sets of parallel and mutually perpendicular slits. Alternately, the sets of slits may intersect at acute angles or the slit lines may be curved or non-linear. Unidirectional slits may also be used. 
         [0004]    In accordance with a presently preferred embodiment of the invention, a large piece of polymeric foam material is cut to form a plurality of C-shaped foam bodies, each having a concave inner surface and a convex outer surface; the curved body is cut to form one or more pads having a working face on the outer surface; the working face of the pad is slit less than the distance to the inner surface with a pattern of multiple slits; and, the body is then flattened to cause the working face to be compressed. 
         [0005]    Preferably, the method also includes the step of attaching the inner surface of the pad to a backing member in a substantially flattened state with the working face substantially compressed. The slitting step preferably comprises providing two sets of intersecting slits. 
         [0006]    An alternate method comprises the steps of (1) forming a curved body from a polymeric foam material, such as open cell polyurethane foam, the body having a concave inner surface and a convex outer surface, (2) slitting the outer surface of the body less than the distance to the inner surface to form a selected pattern of slits, (3) flattening the body to cause the outer surfaces to be compressed, (4) cutting the flattened body to form a pad, and (5) attaching the inner surface of the pad to a backing member to hold the pad in the substantially flattened state and maintaining the outer surface substantially compressed. The slit pattern preferably comprises two sets of intersecting bidirectional slits that form foam fingers. 
         [0007]    In the presently preferred method, a plurality of curved preform bodies used in making the buffing pad are made by a method including the steps of (1) providing a large bun of polyurethane foam, (2) cutting the bun on multiple spaced curved lines of generally the same shape to form a plurality of back-to-back C-shaped bodies. The curved bodies provide the preforms for the preferred pad making method. 
         [0008]    In accordance with another method of making a buffing pad, the method includes the steps of (1) forming a hollow cylinder of polymeric foam, such as polyurethane, such that the cylinder has a cylindrical outer surface and an open core defining a cylindrical inner surface, (2) slitting the outer surface of the cylinder less than the distance to the inner surface in a pattern of bidirectional slits that define foam fingers, (3) cutting the cylinder in an axial direction along its full length to define a cylindrical piece having axially extending end faces and opposite circular edge faces, (4) opening and flattening the cylindrical piece to cause the foam fingers to be compressed, (5) cutting the flattened piece to a desired pad shape, and (6) attaching the inner surface of the pad to a backing member to hold the pad in a substantially flattened state. Preferably, the slitting step comprises forming two sets of parallel and mutually perpendicular slits. The mutually perpendicular slit sets may be positioned to be perpendicular, respectively, to the end faces and the edge faces. 
         [0009]    In a simplified embodiment of the invention, the foam pad disk may be attached directly to the backing plate without slitting the working face. In this construction, the working face is still compressed. However, loss of the unique action provided by the slit face makes this embodiment considerably less attractive. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is an end view of a large monolithic piece (bun) of polymeric foam showing the pattern of cuts used to form the C-shaped preform bodies from which the pads are cut. 
           [0011]      FIG. 2  is a perspective view of one preform body cut from the foam piece of  FIG. 1 . 
           [0012]      FIG. 3  shows the foam preform of  FIG. 2  flattened and cut to form a plurality of buffing pads. 
           [0013]      FIG. 4  is one of the circular pads cut from the flattened preform of  FIG. 3 . 
           [0014]      FIG. 5  is a perspective view of a pad shown in  FIG. 4  after the outer surface has been slit with a pattern of bi-directional slits parallel to the preform edges. 
           [0015]      FIG. 6A  is a top plan view of a pad formed with a preferred pattern of slits in the working face. 
           [0016]      FIG. 6B  is a top plan view of a pad formed with a pattern of diagonal bi-directional slits. 
           [0017]      FIG. 7  is a side elevation view of a buffing pad of the present invention prior to attachment to a backing plate. 
           [0018]      FIG. 8  is a bottom plan view of the pad shown in  FIG. 7 . 
           [0019]      FIG. 9  is a side elevation view showing the pad attached to the backing plate. 
           [0020]      FIG. 10  is a perspective view of a pad preform made in accordance with an alternate embodiment of the invention. 
           [0021]      FIG. 11  is a perspective view showing the cut-out center portion to form the preform. 
           [0022]      FIG. 12  is a top plan view showing the circular pad die cut from the flattened preform of  FIG. 10 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0023]    In  FIG. 1 , a foam slab or bun  10  is of polyurethane foam is formed in a conventional foaming process. The foam bun  10  is cut, by water jet, laser, knife or other suitable cutting tool, to form a plurality of C-shaped foam bodies  11 , which are of the same shape and size. The C-shaped bodies  11  are typically 1 to 1½ inches (25-38 mm) thick, but the thickness could be varied as desired. The radius of curvature of the cut lines  12  can also vary considerably, but may, for example, be in the range of about 5 to 10 inches (127-254 mm). Further, although the cut lines  12  are preferably circular, an elliptical, oval or other cut line shape may be used. The foam bodies  11 , however, must be curved as shown to provide the necessary preform for the pad forming method and resulting pad. In the indicated cut line pattern on the foam bun  10 , there are waste foam trimmings  14 , resulting in full semi-cylindrical bodies  11 . 
         [0024]    Although the foam preforms  11  are substantially semi-cylindrical in shape, they could also be cut to be shorter in the circumferential direction and/or flatter. Although this would increase the yield (and reduce the waste trimmings), full semi-cylindrical preforms  11  are presently preferred. In  FIG. 2 , there is shown a free standing preform  11 . Referring also to  FIGS. 3 and 4 , the preform is die cut to form one or more foam pad disks  15 . The number of disks  15  that can be cut from a foam preform  11 , of course, depends on its length in a direction perpendicular to the plane of  FIG. 1 . After die cutting, the pad disks  15 , when unconfined, resume a curved or arched shape, as shown in  FIG. 4  as a result of the memory or spring back tending to return the shape to that of the preform  11 . 
         [0025]    Each foam pad disk  15  is then slit on its outer (convex) surface, which surface becomes the working face of the pad. In the embodiment shown, the slit lines comprise two bi-directional patterns of parallel slits which preferably extend in the direction of the axis of the semi-cylindrical preform  11  and perpendicular thereto. The slits  16  extend only partially through the disk  15 , for example, about one-half the thickness of the disk. However, shallower and deeper slits may also be utilized and one pattern of parallel slits may be formed to a different depth than the other pattern perpendicular thereto. In  FIG. 6A , there is shown a die cut and flattened foam pad disk  15  in which one set of slits  17  is more widely spaced than the other set of slits  18 . This pattern has been found to perform well as a buffing pad as will be described in more detail below. In  FIG. 6B , similar patterns of slits are shown in a die cut and slit disk that are formed diagonally with respect to the rectangular preform body from which the disk  20  is cut. It should be noted that in both of the flattened disks  19  and  20  of  FIGS. 6A and 6B , respectively, the slits  17  and  18  result in a pattern of foam fingers  21  in the working face of the pad. Further, the fingers  21  are compressed when the pads are flattened from their curved preformed state for operation as a buffing, polishing or finishing pad. 
         [0026]    In  FIG. 7 , there is shown in side elevation a slit disk ( FIG. 5 ,  FIG. 6A  or  FIG. 6B ) in which a laminated structure has been attached to the rear mounting face  22  to permit the pad to be attached to a backing plate  23 . Referring also to  FIG. 8 , the laminated mounting face  22  of the pad  6 A or  6 B includes a polyethylene layer that provides a mounting medium between the mounting face of the pad and the loop half  25  of a hook and loop fastening system. The laminated polyethylene and loop half layer is heat sealed to the mounting face of the pad in a flattened state and, when the pad is relaxed, the pad assumes a semi-arched shape, but one that is significantly less curved than the free form of  FIG. 5 . The backing plate  23  carries the hook half  26  of the hook-and-loop fastening system. The pad is attached to the backing plate  23  which is of a rigid or semi-rigid construction, causing the pad to flatten and to again compress the pad outer working face  27 . Referring again to  FIGS. 6A and 6B , the working face  27  in these examples comprise short fingers  21  formed by the slitting step, previously described, and the compression causes the fingers, particularly at or near their outer ends, to be compressed together and distorted. 
         [0027]    As a result of the compression of the foam fingers  21  when the slit disk  6 A,  6 B is flattened, more working foam material is forced into a given area. This has been found to substantially enhance performance and, in addition, results in a longer life pad. This is important because the preferred open cell polyurethane foam is among the most expensive foam material used in buffing, polishing and finishing operations. The wavy shape imparted to the compressed foam fingers  21  also changes the directional forces applied to the surface being finished. This, in turn, changes the angle of attack to the surface being finished, the angle being selectively variable by choice of slitting pattern. 
         [0028]    In  FIG. 10 , there is shown another foam preform  21  that may be used to make pads of the present invention. A monolithic foam cylinder  22  is cut to remove a central cylindrical core  23 , as shown in  FIG. 11 . After removal of the core, a hollow foam cylinder  24  remains. The hollow cylinder  24  (or alternately the foam cylinder  22  before removal of the core  23 ) is provided with patterns of spaced circumferential slits  25  and spaced axial slits  26  (in a manner similar to the previously described embodiment). 
         [0029]    The slit hollow cylinder  24  is then cut along a separation line  27  to completely cut the hollow cylinder. The slit cylindrical preform  24  is then flattened, as shown in  FIG. 12 , and cut on a cut line  18  just as the previously described embodiment to form a circular pad  17 . This method is not as attractive as the first method described above because of potential waste of the unused core cylinder  23 . However, the resulting buffing pad  17  is virtually the same in both methods. 
         [0030]    Many variations in slit line position and spacing may be utilized to provide many variations in the resulting performance of the buffing pad. Indeed, a unidirectional pattern of slits, one or the other of slits  25  and  26 , may be used and provide the benefits described, but at a somewhat reduced scale. Although the compression of the foam fingers  28  as a result of flattening the preform is generally unidirectional, the unidirectional compression is most apparent when the slit lines are circumferential as at  25  and axial as at  26 . The longer circumferential dimension of the fingers  16  in the preferred embodiment also results in more lateral distortion of the fingers when compressed. As mentioned previously, variations in compression and resultant distortion of the fingers  28  beneficially enhance the finishing capabilities of the pad. 
         [0031]    In a simplified but less desirable embodiment of the invention, the foam pad disk  15  of  FIG. 4  may be attached directly to the backing plate, as shown in  FIGS. 7 and 9 , without slitting the working face. In this construction, the working face is still compressed and the attachment face correspondingly placed in tension. However, loss of the unique action provided by the slit face ( FIG. 5 ) makes this embodiment considerably less attractive.