Abstract:
The present invention provides an abrasive material comprising a base surface having a plurality of pyramidal shapes protruding therefrom the base surface and the protrusions being formed of the same material, each protrusion having a substantially triangular, square, or polygonal base and triangular sides which meet at an apex which substantially forms a point. The pyramidal shapes have apexes in at least two distinct planes with a portion of the pyramidal shapes extending further from the base surface than others, with the apexes of the protrusions providing intermixing cutting and planning edges in a pattern such that the material is capable of abrading independent of direction of use.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to an abrasive material produced by an etching process and suitable for sanding or smoothing a variety of surfaces and to a method of forming the abrasive material.  
       BACKGROUND OF THE INVENTION  
       [0002]     Various abrading surfaces have been suggested over the years. Such surfaces include those wherein abrasive particles such as gamet, aluminum oxide, silicon carbide, grit of zirconia and alpha aluminum oxide monohydrate, single crystals of diamond or cubic boron nitride are adhered to a substrate. Also known are abrasive surfaces which are scored to provide grooves or punched to provide holes or openings with projections or burs surrounding the holes. Where grooves have been formed in metal sheets such as steel sheets, coating the surface or the cutting edge formed by the groove are also known. Metal abrasive sheets are known which are prepared by forming a cured polyvinylchloride negative master using a sheet of sandpaper and, then, electroplating the master to form the sheet.  
         [0003]     Etching processes using a suitable resist to form a desired pattern in a metal substrate are also known. In one such technique, a resist pattern is applied to a thin flat steel plate in a predetermined pattern such as equal sized spots which can be round, elongate or polygonal. The plate is etched which with an etchant such as an aqueous solution of ferric chloride to remove the desired amount of metal and form the pattern elements. It is reported that through variations of spraying mode, composition and temperature of the etching solution, the angle between the side of the protruding cutting elements and the original plate surface, as I well as how far under the edge of the protecting pattern elements the etching will reach. One improvement suggested is to provide parallel ridges on the etched side of the plate in the form of rhombic quadrangles either tangentially or helically to prevent the plate from curling.  
         [0004]     Another improvement suggested is a resist pattern which is reported to give an even intermixing of fast working sharp points with smooth planing edges. The cutting teeth are formed in the shape of triangles or squares which come out of the etch process still sharp and usable due to the resist pattern which accentuates the corner points and eliminates under cutting of the upper surfaces of the cutting teeth. Each tooth bears an upper flat surface and is amenable to hardening by heat treating without excessive brittleness due to the tooth configuration. The upper flat surface of each tooth is reported to be typically about 3 mils with the width of the base and the height of the tooth being about twice that of the upper flat surface.  
         [0005]     A process for producing cutting dies, particularly for use such as, for example, cutting adhesive tape to form labels, has been disclosed wherein multiple etching steps are used. A resist corresponding to the contour of a label to be propertied is formed on a steel plate and a first etching step is carried out, thereby forming a convex portion of a prescribed height. A second etching step is carried out whereby the resist extending from both sides of the top off of the convex portion is removed and the steel plate is subjected to further etching. This second etching step may be carried out multiple times. The resist remaining on the top of the convex portion is then removed.  
         [0006]     A metal abrasive has been described having substantially uniform pyramidal protrusions extending from a base surface which is formed by etching of metal sheet material.  
       SUMMARY OF THE INVENTION  
       [0007]     The present invention, in one aspect, provides an abrasive material comprising a base surface having a plurality of pyramidal shapes protruding therefrom, the base surface and the protrusions being formed of the same material, each protrusion having a substantially triangular, square, or polygonal base and triangular sides which meet at an apex which substantially forms a point, the pyramidal shapes having apexes in at least two distinct planes with a portion of the pyramidal shapes extending further from the base surface than others, with the apexes of the protrusions providing intermixing cutting and planing edges in a pattern such that the material is capable of abrading independent of direction of use.  
         [0008]     The apexes of the pyramidal shapes extending a lesser distance from the base surface retaining their apexes which substantially form points after a period of use during which the pyramidal shapes extending a further distance from the base material may have their apexes worn to less than substantially a point. This retention of the apexes of those pyramidal shapes extending a lesser distance from the base material provides the abrasive material with greater length of service life and effectiveness.  
         [0009]     Preferably, the pyramidal shapes extending a lesser distance from the base material, extend at least about ten percent less, more preferably at least about twenty percent less, most preferably at least about thirty percent less, than those of the pyramidal shapes extending a further distance from the base material.  
         [0010]     The pyramidal shapes of an abrasive material of the invention may be the same or different in shape. For example, various pyramidal shapes may have different bases configurations, i.e., different numbers of sides, and/or different degrees of slope.  
         [0011]     Optional performance enhancing surface treatments may be applied to the protrusions and/or the base surface to improve abrasive performance, aid in non-loading characteristics due to the lubricity of certain coatings, and reduce surface porosity.  
         [0012]     Preferably, the triangular sides of the pyramidal protrusions have an inward arcuate slope. Such a slope provides greater longevity of the abrasive material due to lack of loading of material being abraded. The present invention provides rapid material removal from a workpiece, yet leaves a smooth surface on the workpiece.  
         [0013]     The abrasive material of the invention can be provided with protrusions on both surfaces of the base material to prevent curling when the material is thin. Alternatively, to prevent curling of thin materials, i.e., relieve internal stress or tension, protrusions can be provided on one surface and the opposing surface can simply be etched.  
         [0014]     The present invention, in a further aspect, provides a method of forming an abrasive material comprising the steps of: 
        (a) providing a base material;     (b) applying to at least one surface of the base material a photoresist coating;     (c) placing over the photoresist a mask having a randomly directional triangular, square or polygonal pattern thereon, the individual elements forming the pattern having at least two different surface areas;     (d) curing the photoresist not covered by the mask;     (e) removing said mask and unexposed photoresist;     (f) applying an etchant suitable for etching the base material for a time sufficient to provide a plurality of pyramidal protrusions on the base surface, each protrusion having a substantially triangular, square or polygonal base and triangular sides which meet at an apex which substantially forms a point, the pyramidal shapes having apexes in at least two distinct planes with a portion of the pyramidal shapes extending further from the base surface than others.        
 
         [0021]     The surface of the protrusions and the base surface can optionally be provided with performance enhancing coatings or treatments to improve abrasive performance, aid in non-loading characteristics due to the lubricity of certain coatings, and reduce surface porosity. Plating can be used to provide such enhanced surfaces. The surface can be heat treated or metallurically altered to form a thin harder layer on the surface of the base surface and protrusions to improve hardness as is well known to those skilled in the art. Other performance enhancing treatments such as, for example, diamond surface treatments can be useful. A particularly useful diamond surface treatment using laser technology is described in U.S. Pat. No. 5,620,754. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0022]     FIGS.  1 [ a ]A,  1 [ b ]B, and  1 [ c ]C are perspective views of pyramidal protrusions useful in the invention.  
         [0023]      FIG. 2  is a perspective view of a preferred pyramidal protrusion of the invention having inward arcuate triangular sides.  
         [0024]      FIG. 3  is a top view showing a preferred pyramidal protrusion of the invention having inward arcuate triangular sides.  
         [0025]      FIG. 4 [ a ]A is a top view of a portion of a photoresist mask suitable for use in producing an abrasive material of the invention.  
         [0026]      FIG. 4 [ b ]B is a top view of a portion of another photoresist mask suitable for use in producing an abrasive material of the invention.  
         [0027]      FIG. 5  is side view of a pyramidal protrusion useful in the invention having a performance enhancing coating thereon.  
         [0028]      FIG. 6  is a fragmented cross-section of an abrasive material of the present invention having pyramidal protrusions on each surface thereof. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0029]     The abrasive material of the invention can be formed from any material susceptible to etching including, for example, stainless steel, carbon steel, aluminum alloys, iron-nickel-chrome alloys, and titanium; boron-filled elastomers, silica composites, fluorocarbon materials, graphite alloys, plastics, and the like.  
         [0030]     Stainless steel is a particularly preferred base material in the present invention due to the intrinsic resistance of the material to corrosion, the good high and excellent low temperature strength and toughness over a broad range of temperatures, the non-magnetic properties of austenitic grades, and aesthetic appeal. Stainless steel can also be readily reproducibly etched to form the abrasive material of the invention.  
         [0031]     The thickness of the material is not particularly limited, but after etching should be suitably flexible where it will be used over a roller or suitably stiff when used as a flat abrasive. Of course, stiffness can be provided, if necessary, by attachment to a stiff substrate such as, for example, a metal plate or synthetic resin plate having suitable stiffness.  
         [0032]     Typical surface treatments particularly preferred for stainless steel base material include, but are not limited to, nickel or chrome plating or diamond coating or plating in combination with diamond dust or boron nitride. The base and pyramidal protrusions can be exposed to heat treatment or metallurical alteration, e.g., case hardening, to effect, for example, surface hardness by forming a thin harder layer on the base surface and protrusions to improve performance.  
         [0033]     With respect to the drawings, like references number will be used with reference to like parts. FIGS.  1 [ a ]A,  1 [ b ]B, and  1 [ c ]C depict various possible embodiments of the pyramidal protrusions of the abrading material of the invention with the bases of the pyramidal protrusions being triangular, square and pentagonal, respectively. Of course, other polygonal shapes can be used. In  FIG. 1 [ a ]A, protrusion  10   a  is shown having triangular base  12   a , triangular side  14   a , and apex  16   a . In  FIG. 1 [ b ]B, protrusion  10 b is shown having square base  12   b , triangular side  14   b  and apex  16   b . In  FIG. 1 [ c ]C, protrusion  10   c  is shown having polygonal base  12   c , triangular side  14   c  and apex  16   c.    
         [0034]     The apex of each protrusion need not form a true point as shown in the FIGS., although this is the preferred configuration. The apexes of the protrusions may be slightly rounded or flat. However, this portion of the apexes should preferably be no greater in width than 20 percent of edges L, more preferably no more than 10 percent of edges L, edges L being shown in  FIG. 5 .  
         [0035]     The depth of the inward arcuate slope on the triangular sides of the pyramidal protrusions which are found in the preferred embodiments of the invention can be from very slight, e.g., 1 μm, to as great as about 175 μm. Such actuate slopes can readily be seen in  FIGS. 2 and 3  wherein protrusion  20  has actuate sloped surfaces  22 . The greater the size of the protrusions, the deeper the inward actuate slope can be formed.  
         [0036]     Preferably, the height H of the pyramidal protrusions from the etched surface can be in the range of about 25 μm to 1.5 mm, with higher pyramidal protrusions for normal coarse abrading, i.e., from about 125 μm to 375 μm, and lower pyramidal protrusions for finer abrading, i.e., from about 75 μm to 125 μm. The length of the edges L of the base is dependent on the height of the protrusions. Preferably, the ratio of the height of the protrusions from the etched surface to the length of the edge of the base is in the range of about 1:1 to 1:5, more preferably about 1:2 to 1:4, most preferably about 1:3. The thickness of the remaining base material B can vary widely and is not critical, with thinner base materials being used for more flexible abrasive materials and thicker base materials being used for stiffer abrasive materials as is well known to those skilled in the art. Such dimensions are indicated in the enlarged view of a portion of a hard coated abrasive material, seen in cross-section in  FIG. 5 .  
         [0037]     The spacing S of the pyramidal protrusions can also vary widely, from about 0.75 mm to 30 mm apart, as measured from center to center of the pyramidal protrusions, with greater spacing for coarse abrading, i.e., 2 to 10 mm or more apart and less spacing for finer abrading, i.e., from about 0.75 to 1.5 mm apart.  
         [0038]     The fineness or coarseness of the abrasive material can also be adjusted by maintaining the height of the protrusions and the length of the base of the protrusions and adjusting the size of the resist pattern. Greater spacing between the protrusions provides coarser abrading material, while lesser spacing between the protrusions provides finer abrading material.  
         [0039]     A photoresist mask suitable for a fine abrasive grit is shown in  FIG. 4 [ b ]B. A photoresist mask suitable for a coarse abrasive grit is shown in  FIG. 4A .  
         [0040]     It is important that the pyramidal protrusions be oriented such that the cutting edges of the individual protrusions are oriented in different directions to provide the capability of abrading independent of direction of use. The pyramidal protrusions can be randomly oriented in various directions such as by designing the etching mask through the use of a computer-based random generator or an etching mask can be patterned which ensures random orientation as is well known to those skilled in the art. Examples of a randomly oriented patterns are shown in  FIGS. 4   a  and  4   b .  
         [0041]     As previously described, a coating such as nickel or chrome plating; a diamond coating; or nickel or chrome plating in combination with diamond dust or Teflon®, tungsten, carbide or boron nitride particles can be applied to the surface of the abrasive material such as is shown in  FIG. 5 , wherein a portion of abrasive material  59  has protrusion  52 , remaining base material  54 , and coating  56 .  
         [0042]     The etching process can be carried out using well-known resist and etching materials and processes. Prior to application of the photoresist to the base material, cleaning of the base material is preferably carried out. Where the base material is stainless steel, such cleaning may involve rinsing with deionized water and drying. Alternatively, or in addition to such rinsing, the stainless steel surface may also be subjected to a pumice scrub or passivation treatment. Passivation which removes free iron contaminants, if present, as well as other contaminants is generally carried out with the use of solutions of ferric chloride, nitric acid or other solutions know to those skilled in the art.  
         [0043]     The resist coating can be applied using, for example, hot roll lamination, screen printing, gravure printing, dip coating and the like. When a resist is applied in the form of a polymeric film to a stainless steel base material, the base material is preferably pre-heated and the film is applied using sufficient heat and pressure to ensure good adhesion. Curing of the resist must be avoided at this point in the process.  
         [0044]     The mask which is used to provide the desired abrasive pattern surface is then placed on the resist covered base material. Good, i.e., intimate, contact between the resist coating and the mask is needed to achieve the desired pattern on the base material when the photoresist not covered by the mask is cured. Such contact can be enhanced by use of vacuum techniques.  
         [0045]     Curing, or imaging, is achieved by exposure to light sufficient to cure, i.e., cross-link, the polymeric resist. The mask is then removed from the base material/photoresistmask composite and the uncured, photoresist is removed from the base material using a developing solution, or developer. The selection of the developer is dependent on the composition of the photoresist. If desired, the photoresist then remaining on the base material may be imaged again prior to etching to further ensure good adhesion of the photoresist to the base material during etching.  
         [0046]     Etching is then performed on those portions of the base material not protected by the photoresist. For example, when the substrate is stainless steel, carbon steel, or the like, suitable etchants include ferric chloride, hydrochloric acid, nitric acid, mixtures of these acids and sodium hydroxide; for aluminum or aluminum alloys, suitable etchants include sodium hydroxide; for titanium, suitable etchants include hydrofluoric acid; and plastics are generally etchable using various acids. The degree of etching can be adjusted by altering the concentration and temperature of the etchant solution and the method of application as is known to those skilled in the art. For example, when the base material, or substrate, is stainless steel, an aqueous ferric chloride solution of about 37° to 42° Baume can be used, the lower the Baume of the solution, generally the more arcuate the slope of the sides of the protrusions.  
         [0047]     After etching, any remaining photoresist may optionally be removed by techniques well known to those skilled in the art. In some cases with certain mask patterns and etching parameters, much of the photoresist is removed in the etching process. Removal of remaining photoresist is generally preferable, particularly when the pyramidal protrusions are to be plated and the photoresist may act as a plating resist.  
         [0048]     Alternatively, the resist can be retained on the surface of the resultant abrasive material, particularly on the non-abrasive side of the material when only one side is masked and pattern etched, which aids in prevention of curling. A suitable method of preventing curling involves etching both surfaces of the base material as shown in  FIG. 6 , wherein abrasive material  60  has protrusions  62   a ,  62   b  on each surface  61 ,  63  extending from the remaining base material  64 .  
         [0049]     Objects and advantages of this invention are further illustrated by the following examples, but the particular materials and amounts thereof recited in these examples, as well as other conditions and details, should not be construed to unduly limit this invention. All parts and percentages are by weight unless otherwise indicated.  
       EXAMPLES  
     Example 1  
       [0050]     A sheet of  301  high tensile stainless steel having a thickness of about 0.02000 inch was cleaned using a pumice scrub and passivated for 30 seconds with a 40° Baume solution of ferric chloride. A 0.0013 inch thick photoresist film, Type EM213, available from DuPont Co., was adhered to the passivated stainless steel and a mask having a pattern like that shown in  FIG. 4   a  was applied over the photoresist.  
         [0051]     The stainless steel/photoresist/mask composite was exposed to 60 millijoules of light to effect initial imaging of the photoresist. The uncrosslinked photoresist was removed by rinsing with a developer solution of 1% aqueous potassium carbonate at pH 10.5. The stainless steel having the photoresist pattern thereon was re-exposed to 100 millijoules light to ensure adherence of the photoresist to the stainless steel during etching.  
         [0052]     The stainless steel was etched to a depth of about 0.011 inches using a 40° Baume ferric chloride solution. The resulting etched sheet was rinsed with water and remaining photoresist was removed using a 15% potassium hydroxide aqueous stripping solution.  
         [0053]     The pyramidal protrusions had a triangular base. The height of the protrusions whose apexes were the greatest distance from the base material was about 0.004. The resulting sheet performed excellently in a manner similar to a coarse grit sandpaper, but without loading problems typical with sandpaper.  
       Example 2  
       [0054]     A sheet of  302  full hard stainless steel having a thickness of about 0.006 inch, available from Ulbrich of California, was cleaned using a pumice scrub and passivated for 30 seconds with a 40° Baume solution of ferric chloride as in Example 1. A photoresist film was adhered to the passivated stainless steel and a mask having a pattern like that shown in FIG[S].  4 [B] was applied over the photoresist. The stainless steel was etched to a depth of about 0.0040±0.0005 inches using a 40° Baume ferric chloride solution over a period of about 4 minutes. The resulting etched sheet was rinsed with water and remaining photoresist was removed using a 15% potassium hydroxide aqueous stripping solution.  
         [0055]     The pyramidal protrusions had a triangular base. The height of the protrusions whose apexes were the greatest distance from the base material was about 0.004 inch. The resulting abrasive material performed in a manner similar to fine sandpaper but significantly more efficiently and with greater longevity than standard sandpaper.  
         [0056]     Various modifications and alterations of this invention will become apparent to those skilled in the art without departing from the scope and spirit of this invention, and it should be understood that this invention is not to be unduly limited to the illustrative embodiments set forth herein.