Abstract:
Abrasive articles are disclosed that may be used in dry sanding applications. The abrasive articles disclosed may be made entirely from abrasive materials or alternatively may be made by fastening abrasive surfaces to handles or tools. The abrasive articles of the present invention have abrasive surfaces with controlled wear rates that renew themselves during use. The self renewing abrasive surfaces of the present invention may be prepared by pressing a mixture of abrasive particles and a minimal amount of a foam binder together into a mold and subsequently allowing the mixture to foam, break down, and harden. Alternatively, high loading densities of abrasive with larger amounts of foam binder may be employed that retain their foam integrity. The resulting abrasive articles are long lasting and may be made low in cost.

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
       [0001]    This is a Continuation-in-Part of prior application Ser. No. 11/929,963 filed on Oct. 30, 2007 which is a Continuation-in-Part of Ser. No. 11/846,073 filed on Aug. 28, 2007 which is a Continuation-in-Part of Ser. No. 11/828,270 filed on Jul. 25, 2007 which is a Continuation-in-Part of Ser. No. 11/503,058 filed Aug. 14, 2006, which claimed priority to provisional application No. 60/764,110 filed on Feb. 1, 2006 and provisional application No. 60/818,571 filed on Jul. 5, 2006. Each of the above listed applications are incorporated herein by reference in their entirety. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    This invention relates to abrasive articles. More particularly this invention relates to abrasive articles having wearable abrasive surfaces. The wearable abrasive surfaces of the present invention are comprised of rigid closed cell polymeric foam materials having very high loading densities of abrasive materials such as aluminum oxide and silicon carbide. The density of the polymeric foam may be adjusted for optimum controlled rates of wear. The wearable abrasive articles of the present invention may be used on power sanding tools for automotive applications such as straight-line and dual action sanders. 
         [0004]    2. Description of the Related Art 
         [0005]    There are numerous methods that may be employed to sand surfaces. One of the more common methods employs sand paper. Sand paper is a thin sheet material usually made of paper that has an abrasive material securely bonded onto one side. Despite its name, the abrasive is rarely if ever sand. Commonly used abrasives such as aluminum oxide and silicon carbide are significantly harder than sand and are therefore more effective. This may be especially true when sanding hard materials such as glass or steel. 
         [0006]    Sand paper may be used by hand. This process is often referred to as hand sanding. The process of hand sanding involves using manual labor to repeatedly slide the sand paper back and forth and/or in a circular motion over the surface until smooth. Numerous textures of abrasives are available. Often sanding starts out with a relatively course grade of sand paper of about 80 grit followed by finer grades of several hundred grit to finish the job. 
         [0007]    One drawback often associated with sand paper is the tendency of producing dust that clogs the sand paper. One way to alleviate this problem is by using wet or dry Emery cloth. Wet or dry Emery cloth is an abrasive coated cloth having a wide variety of grades. It is designed for use with water thereby reducing clogging effects. 
         [0008]    Another drawback with using sand paper is the tendency for the abrasive to become dull and fall off from the sand paper backing surface. 
         [0009]    Sanding by hand using sand paper is not always practical owing to the amount of labor required. This is especially true for large jobs that may take a long time resulting in fatigue. 
         [0010]    In order to alleviate the worker fatigue issue in hand sanding operations, numerous power sanding techniques and/or equipment have been developed. Drum sanding, belt sanding, disc sanding, and orbital sanding are commonplace. These standard power sanding tools often employ some form of sand paper and therefore often suffer from many of the previously mentioned drawbacks. In particular is the need to change the sanding surface at regular intervals. 
         [0011]    Numerous modifications to ordinary sand paper have been made in order to improve the overall process. For example, sand paper having a lowered surface density of abrasive particles is available. This particular sand paper is made by 3M Corporation of ST. Paul Minn. and is designed for use in sanding relatively soft materials that quickly gum up ordinary sand paper. Significant improvements in sand paper life may be realized by reducing the tendency of particulate matter to clog the needed spaces between adjacent abrasive particles. 
         [0012]    Another improvement that may be made to ordinary sand paper involves the use of flexible and conformable foam backing. Such backing materials allow the sand paper to conform to surface contours thereby more rapidly smoothing contoured surfaces. Individual pieces of sand paper may be applied to foam pads or conversely, foam pads having previously attached sand paper may be employed. For example, Finishing Buddies (Mona Lisa Products 10770 Moss Ridge Road Houston, Tex., 77043) is a complete sanding tool kit consisting of a steel wool pad, oval sanding disc, and coarse, medium, and fine sanding pads. The oval pad is relatively rigid, and the three other sanding pads have a softer foam backing that has a greater degree of flexibility. This sanding kit is designed for slow hand sanding and finishing operations. 
         [0013]    There are numerous flexible sanding surfaces, components, and articles comprised of abrasive materials fixedly attached to flexible foam backings. Of particular interest is a sanding system employing a relatively thin rigid foam backing disclosed in U.S. Pat. No. 6,923,840 and assigned to 3M Innovative Properties Company, St. Paul Minn. (US). U.S. Pat. No. 6,923,840 discloses a flexible abrasive product comprised of an open cell foam backing, a foraminous barrier coating, and a shaped foraminous abrasive coating. The top abrasive coating is discontinuous and allows for holding lubricants such as water as well as spaces for removal of debris. 
         [0014]    U.S. Pat. No. 6,949,128 also assigned to 3M, discloses a method for making a foam backed abrasive article having embossed raised areas. 
         [0015]    U.S. Pat. No. 3,401,490 discloses a method for forming an abrasive article having a resiliently yielding open cell meltable base which is passed under a heated roll to melt the surface to a desired depth followed by application of abrasive particles to the melted surface. The result is a flexible foam based abrasive article capable of following irregular, uneven, or sunken surfaces. 
         [0016]    U.S. Pat. No. 6,997,794 by James Matthew Pontieri discloses a disposable sanding device fabricated as a continuous rope like article adapted for selective segmentation. This device may employ a foam central portion along with an abrasive outer portion. In particular the flexible cylindrical geometry illustrated in several embodiments of the invention lends itself to the hand sanding of difficult to reach contours and may prove especially useful in woodworking applications. 
         [0017]    There are numerous flexible foam based cleansing and scouring pads having added abrasive materials. An example of this can be found in U.S. Pat. No. 3,377,151. U.S. Pat. No. 3,377,151 discloses a method for making flexible resilient cleansing and scouring pads having an abrasive surface. A thermoplastic foam web material is hot laminated to abrasive web material. In addition, one or more cleansing materials may be added. 
         [0018]    U.S. Pat. No. 3,619,843 discloses sponges having dry impregnated materials. In this invention, impregnated sponges are prepared by a process that deposits particulate material on one surface of the sponge and subsequently pierces the sponge with spikes to form crevices followed by drawing particulate material into the crevices. The result is a modified sponge suitable for surgical and sanitizing applications. 
         [0019]    Also of interest are flexible open cell foam scouring and cleaning pads having numerous protrusions. These pads are disclosed in U.S. Pat. No. 4,055,029 by Heinz Kalbow, Lichgasse. The flexible pad has numerous protrusions on the working surface having an abrasive layer. U.S. Pat. No. 4,111,666 also by Heinz Kalbow discloses a method of manufacturing flexible abrasive cleaning pads along with improvements in tear resistance. 
         [0020]    U.S. Pat. No. 4,421,526 discloses polyurethane foam cleaning pads composed of a densified flexible sponge like polyurethane foam material impregnated with various cleansing additives. Excessive mixing of the freshly blended polymers inhibits foam formation long enough to add the cleansing ingredients. The resulting pads have added strength due to collapsed, ruptured, and distorted cells along with fibers that result from the specific mixing process employed. The result is an unusually strong dense flexible cleaning pad capable of absorbing substantial amounts of water that releases additives along with absorbed water on gentle squeezing. 
         [0021]    U.S. Pat. No. 4,594,362 discloses a dry type textile cleaning article comprised of a friable hydrophilic polyurethane foam with incorporated abrasive particles as well as other additives. The abrasive particles are chemically bonded to the foam using silane coupling agents thereby reducing their tendency to separate from the mass and subsequently damage cloth material. 
         [0022]    Wet sanding abrasive foam compositions are disclosed in U.S. patent application # 20080020678 titled “Discontinuous Abrasive Particle Releasing Surfaces” having serial # 828270. In this invention, water softening properties are imparted to an abrasive loaded foam surface to prevent deep scratches from coarse abrasive particles, and to aid in abrasive paste formation. Attempting to use these wet abrasive compositions in dry sanding operations results in an abrasive surface that dulls, clogs up and may not have the proper controlled rate of wear. 
         [0023]    While the above described examples of foam based abrasive articles provide a wide variety of uses, there exists a need in the art for semi-rigid or rigid abrasive articles having a wearable surface that renews itself during use that may be employed in hand and/or low speed dry abrasive operations including dry sanding, and/or dry grinding operations. 
         [0024]    Many of the above described examples outline the use of foam with abrasive materials in order to achieve certain advantageous and desirable properties. Still others outline some of the more simple methods and materials commonly employed in dry sanding, and grinding. While generally effective for dry sanding, and grinding, there exists a need in the industry for further improvements in dry abrasive operations. 
         [0025]    For example, improvements in dry abrasive operations may be realized in the area of dual action sanding tools. Dual action sanding tools employ the action of simultaneous spinning and vibration. This dual action results in rapid and relatively uniform sanding. Dual action sanding tools may be used with the dry sanding compositions outlined in the present invention to provide continuous non-clogging use. Additionally, The action of straight-line sanding tools tends to reduce clogging effects when sanding surfaces with the dry sanding compositions outlined in the present invention as well. 
         [0026]    Despite numerous advancements in the field of abrasives there is a need for abrasive articles having a wearable surface that renews itself during use that may be employed in dry abrasive operations. 
         [0027]    It is an object of this invention to provide abrasive surfaces for dry hand sanding applications. 
         [0028]    It is a further object of this invention to provide numerous grades of abrasive surfaces for low dry hand sanding applications. 
         [0029]    It is a further object of this invention to provide abrasive surfaces dry sanding applications employing dual action and straight-line sanding tools resistant to excess build up of debris. 
         [0030]    It is a further object of this invention to provide abrasive surfaces for both hand and power dry sanding applications having a controlled level of rigidity. 
         [0031]    It is a further object of this invention to provide abrasive surfaces for both hand and power dry sanding applications that are low in cost. 
         [0032]    It is a further object of this invention to provide simple methods for producing abrasive surfaces for hand and power dry sanding applications. 
         [0033]    It is a further object of this invention to provide abrasive surfaces for hand and power dry sanding applications that may be used for extended periods of time without wearing out. 
         [0034]    Finally, it is an object of this invention to provide abrasive surfaces for hand and power dry sanding applications that have wear rates that result in continuous renewal of working surfaces during use. 
       SUMMARY OF THE INVENTION 
       [0035]    This invention proposes articles for dry sanding applications employing wearable abrasive surfaces that renew themselves on continued use. The dry sanding articles of the present invention have wearable abrasive surfaces comprised of closed cell rigid polymeric foam loaded with large amounts of abrasive particles. Dense wearable abrasive surfaces may be formed by compressing a mixture of abrasive particles with a minimal amount of liquid polyurethane foam resin together. Compression of the above described wearable abrasive surfaces may be take place in a mold thereby forming them into specific shapes. Wearable abrasive surfaces of a lower density may be formed by mixing substantial amounts of abrasive particles together with liquid polyurethane foam resins having a density of 8 or more pounds per cubic foot. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0036]    A more complete appreciation of the invention and many of the advantages thereof will be readily obtained as the same becomes better understood by reference to the detailed description when considered in connection with the accompanying drawings, wherein: 
           [0037]      FIG. 1  shows an abrasive surface suitable for Velcro attachment to a straight-line sander. 
           [0038]      FIG. 2  shows a cross sectional view of a dense abrasive composition of the present invention. 
           [0039]      FIG. 3  shows an abrasive article suitable for Velcro attachment to a dual action sander. 
           [0040]      FIG. 4  shows a cross sectional view of a foam based abrasive surface suitable dry sanding applications. 
           [0041]      FIG. 5  shows a cross sectional view of a sanding disk having Velcro attachment means for a rotary or dual action tool. 
           [0042]      FIG. 6  shows a hand held abrasive article suitable for dry hand sanding applications comprised of a handle portion fixedly attached to wearable abrasive surface. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0043]      FIG. 1  shows an abrasive surface suitable for Velcro attachment to a straight-line sander. Abrasive straight line sanding pad  2  is shown having top abrasive pad portion  4  attached to soft Velcro attachment portion  6 . Also shown is top exposed major sanding surface portion  8 . Straight line sanding pad  2  attaches to a straight line sanding tool with Velcro attachment portion  6 . 
         [0044]      FIG. 2  shows a cross sectional view of a dense abrasive composition of the present invention. Dense abrasive composition  10  is shown having hard abrasive particles  12  along with spaces  14  between hard abrasive particles  12 . Spaces  14  between hard abrasive particles  12  provide separation between hard abrasive particles  12 . This separation allows for exposure of individual hard abrasive particles  12  while at the same time providing space for debris generated during the sanding process. 
         [0045]    The dense abrasive composition of  FIG. 2  forms when there is not enough liquid polymeric foam resin in the mix to properly foam. Dense abrasive compositions form at an abrasive loading density of about 90% by weight of the mix. This value is dependent on the polymeric resin system, the abrasive material, and the abrasive particle size. Dense abrasive compositions of the present invention may used to produce working tools having a controlled rate of wear. Abrasive compositions of this nature may be made to work for hand sanding as well as power sanding applications. Abrasive compositions employing 92% by weight of silicon carbide abrasive to 8% by weight of liquid polymeric foam resin exhibit desirable sanding properties having surfaces that renew themselves at a good rate and are resistant to clogging effects from prolonged use. The following examples will now be given in detail. 
       EXAMPLE 1 
       [0046]    8 grams of polyurethane resin A SP-328-8 from Silpak (Silpak INC 470 East Bonita AVE Pomona, Calif. 91767 Tel # (909) 625-0056) were placed into a 1 liter polyethylene wide mouthed container. To this were added 8 grams of polyurethane resin B SP-328-8 from Silpak. These two resins were then blended together and mixed thoroughly. 184 grams of 120 grit silicon carbide abrasive were then added and mixed thoroughly with an electric mixer to form a damp powder. This damp powder was then placed into a 2½″×4½″×1″ deep cavity of a silicone mold. This mixture was then compressed with a wooden block by applying about 40 pounds of pressure for a period of one minute. The wooden block was then removed and the mixture allowed to cure for 20 minutes. The partially cured part was then removed from the mold. The bottom surface was then sanded down to open expose an abrasive surface. The part was then allowed to stand for 24 hours to thoroughly cure. This part was then attached to a plastic handle with polyurethane adhesive. Once cured, the tool was used to sand automotive paint and primer from a metal surface. Sanding was rapid. The sanding surface released abrasive particles at a rate sufficient to renew the surface without dulling. The working surface of the tool had little tendency toward plugging up. This tool behaved in a similar manner to 320 grit sandpaper. Furthermore, despite the fact that 120 grit abrasive was used to make the tool, deep scratches were not observed. 
       EXAMPLE 2 
       [0047]    The above experiment was repeated using 46 grit silicon carbide abrasive. Results were substantially the same with the sanding surface of the tool behaving like 100 grit sandpaper. 
         [0048]    Samples of both abrasive materials outlined above were broken off from the tools. Microscopic examination revealed about 50% void space with no evidence of closed cells. No foam structure was present. The abrasive particles were spaced uniformly throughout the mix forming an aggressive abrasive composition. This clearly shows that the 92% abrasive loading density in the mix was sufficient to disrupt the formation of foam. Disruption of the foam may be said to have occurred when bubbles normally present in the foam are no longer discernable under microscopic examination. 
         [0049]      FIG. 3  shows an abrasive article suitable for Velcro attachment to a dual action sander. Abrasive dual action sanding pad  18  is shown having top abrasive pad portion  20  attached to soft Velcro attachment portion  22 . Also shown is top exposed major sanding surface portion  24 . Dual action sanding pad  18  attaches to a Dual action sanding tool with Velcro attachment portion  22 . Dual action sanding pads attach to dual action sanding tools. Dual action sanding tools combine the simultaneous actions of both spinning and vibration. These two combined actions help to remove debris from the sanding area thereby reducing clogging effects that may occur at exposed major sanding surface portion  24  during use. 
         [0050]      FIG. 4  shows a cross sectional view of a foam based abrasive surface suitable dry sanding applications. 
         [0051]    Abrasive material  26  is shown in cross sectional view. Abrasive material  26  is shown having abrasive particles  28  embedded within high density foam matrix material  30 . Abrasive particles  26  may comprise a material selected from the group consisting of aluminum oxide, silicon carbide, zirconia, diamond, ceria, cubic boron nitride, garnet, ground glass, quartz, and combinations thereof. Also shown are voids  32 . Voids  32  result from the foaming action of the polymeric foam based resin materials employed. 
         [0052]    Foam based dry sanding compositions may be prepared by blending substantial amounts of silicon carbide abrasive with liquid polyurethane foam resins having a density of 8 or more pounds per cubic foot. These higher density foam compositions may be loaded with larger amounts of abrasive without falling apart. This may require the use of low viscosity resin materials or alternatively may be prepared by thinning down higher viscosity resin materials with a non-reactive solvent. Additionally, solvents having some reactivity toward the isocyanate portion of the mix may be added to modify the foaming characteristics of the mix. Non-reactive solvents include solvents having enough polarity do be compatible with both the polyol and isocyanate resins but lacking reactive functional groups. Generally speaking, hydroxyl groups are reactive toward isocyanate resins. Alcohols and ketones having enol alcohols (enol keto tautomerization) may react with isocyanate resins and should be considered reactive with the system. 
         [0053]    Additionally, the resin ratio of polyol resin to isocyanate resin should be close to stoicheometric. One practice used in the industry is to use a very slight excess of isocyanate resin in the mix of about one percent by weight. Although both flex agents as well as stiffening agents may be added to modify resin properties, working abrasive compositions have been made that work in straight-line sanding tools without these additives. Additionally, Working compositions have been prepared for dual action sanding tools by limiting the thickness of the abrasive surface to 0.2″. This limited thickness allows for some tool flexibility without the need to use flex agents. Abrasive loading density and foam density may then be used to provide a suitable tool life without the need to increase the thickness of the abrasive surface. 
         [0054]    The density of polyurethane foam materials may be increased by blending non-foaming polyurethane resins with foaming polyurethane resins. In certain circumstances it may be desirable to blend foaming polyurethane resins with non-foaming polyurethane resins in order to increase foam density, modify surface hardness, and control bubble size and uniformity. This blending is easily carried out by thoroughly mixing the resins prior to adding the abrasive. 
         [0055]    The abrasive loading density needed for these tools requires about 270 grams of silicon carbide abrasive for each 100 grams of resin mix. Below this value, sanding is slow and surface clogging may occur. This ratio of abrasive to resin mix results in structural integrity. A foam may be considered to have structural integrity if bubbles in the foam remain intact once cured. 
         [0056]    The abrasives themselves may have various particle shapes. Silicon carbide abrasives tend to be somewhat planar. Because of this, there is a tendency of silicon carbide abrasive particles to align themselves in the direction of foam growth during manufacture. Sanding surfaces cut at right angles to foam growth may therefore exhibit better sanding properties that sanding surfaces cut along the direction of foam growth. Additionally, it may be desirable to blend different abrasive materials having the same grit value together to provide sanding surfaces having improved properties. 
         [0057]      FIG. 5  shows a cross sectional view of a sanding disk having Velcro attachment means for a rotary or dual action tool. Abrasive dual action sanding pad  34  is shown having top abrasive pad portion  36  attached to soft Velcro attachment portion  38 . Also shown is top exposed major sanding surface portion, on the opposite side of the Velcro attachment  38 . Dual action sanding pad  34  attaches to a Dual action sanding tool with Velcro attachment portion  38 . Dual action sanding pads attach to dual action sanding tools. Dual action sanding tools combine the simultaneous actions of both spinning and vibration. These two combined actions help to remove debris from the sanding area thereby reducing clogging effects that may occur at exposed major sanding surface portion during use. Exposed abrasive particles  42  are shown protruding from major sanding surface. 
         [0058]      FIG. 6  shows a hand held abrasive article suitable for dry hand sanding applications comprised of a handle portion fixedly attached to wearable abrasive surface. 
         [0059]      FIG. 6  shows a hand held abrasive article that may be used to dry sand automotive surfaces. Hand held abrasive article  44  is shown comprising a main handle portion  46  and a major abrasive surface working portion  48 . Also shown is side groove  50 . Side groove  50  provides an ergonomic fit to the hand for easier use. Hand held abrasive article  44  is shown having major abrasive surface portion  48  fixedly attached to main handle portion  46 . Major abrasive surface portion  48  may be comprised of the abrasive dry sanding composition of  FIG. 4 . 
         [0060]    Those skilled in the art will understand that the preceding exemplary embodiments of the present invention provide foundation for numerous alternatives and modifications. These other modifications are also within the scope of the limiting technology of the present invention. Accordingly, the present invention is not limited to that precisely shown and described herein but only to that outlined in the appended claims.