Patent Publication Number: US-2006016128-A1

Title: Abrasive material having an antiloading coating

Description:
CROSS-REFERENCE TO PRIORITY APPLICATION  
      This application claims priority from Japanese patent application Serial No. 2004-203510, filed Jul. 9, 2004.  
     BACKGROUND  
      The present invention relates to an abrasive material having an antiloading coating on an outermost surface thereof, and particularly an abrasive material having an antiloading coating whose entire surface is reticulately cracked.  
     SUMMARY  
      In an abrasive material obtained by applying a multitude of abrasive particles together with binding resin, there is some degree of space between the abrasive particles. During the abrading process, material abraded from a body to be abraded, also known as swarf, tends to fill spaces between abrasive particles.  
      The filling of spaces between abrasive particles with swarf and the subsequent build-up of swarf is known as loading. Loading causes a problem because the function of abrasive particles is hindered and the cut rate of abrasive particles is decreased (thus, more force may be required to abrade). In addition, loading is an exponential problem; once swarf begins to fill in spaces between abrasive particles, the initial swarf acts as a “seed” or “nucleus” for additional loading.  
      The abrasive material industry has sought antiloading materials to use in as abrasives. Examples of antiloading materials which have been used include metal salts of fatty acids, urea-formaldehyde resins, waxes, mineral oils, crosslinked silanes, crosslinked silicones, and fluorohydrocarbons.  
      For example, antiloading agents for abrasives have been known, which comprise metal salts of carboxylic acids having hydrocarbon chain, phosphates having hydrocarbon chain and ammonium having hydrocarbon chain, amines, imines and carboxylic acids having hydrocarbon chain, and acid anhydrides, and quaternary ammonium anti-static compounds. These antiloading agents are borne on an outermost surface of coated abrasives so as to serve for the abrading work. The antiloading agents are occasionally applied with a binder in order to assist in being retained on the surface.  
      Also, in the case where an abrasive article has a size coat and a supersize coat on abrasive particles, antiloading agents are occasionally contained therein.  
      In the case where antiloading agents are applied to abrasives, it has been conventionally thought that the function of antiloading agents is sufficiently performed by retaining the antiloading agents between an abrasive surface of abrasive materials and a body to be abraded. Thus, in the case where antiloading agents are applied on an abrasive surface or contained in an outermost resin layer, sufficient studies have not been made so far on a state in which the antiloading agents are retained on the abrasive surface. Also, it has not been known what influence a fine structure of the surface on which antiloading agents are applied has on abrasive performance. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is an electron micrograph showing a surface of an antiloading coating of an abrasive material in Example 1.  
       FIG. 2  is an electron micrograph showing a surface of an antiloading coating of an abrasive material in Example 1 after being used.  
       FIG. 3  is an electron micrograph showing a surface of an antiloading coating of an abrasive material in Example 2.  
       FIG. 4  is an electron micrograph showing a surface of an antiloading coating of an abrasive material in Example 2 after being used.  
       FIG. 5  is an electron micrograph showing a surface of an antiloading coating of an abrasive material in Comparative Example 1.  
       FIG. 6  is an electron micrograph showing a surface of an antiloading coating of an abrasive material in Comparative Example 1 after being used.  
       FIG. 7  is an electron micrograph showing a surface of an antiloading coating of an abrasive material in Comparative Example 2.  
       FIG. 8  is an electron micrograph showing a surface of an antiloading coating of an abrasive material in Comparative Example 2 after being used. 
    
    
     DETAILED DESCRIPTION  
      The present invention solves the above-mentioned conventional problem, and the object thereof is to determine what fine structure of the surface on which antiloading agents are applied performs the function of antiloading agents sufficiently.  
      The present invention provides an abrasive material having an antiloading coating on an outermost surface thereof, in which 
          the antiloading coating contains an antiloading agent and a binding resin;     the binding resin is formed into a film with cracks; and     a reticulate fine structure is formed on an entire surface of the antiloading coating by the cracks, whereby the above-mentioned object is achieved.        

      An abrasive material of the present invention is preferably produced by a method comprising the steps of: 
          providing an abrasive material;     applying an antiloading agent composition containing an antiloading agent and a binding resin on an outermost surface of the abrasive material; and     forming the binding resin into a film with cracks by heating the abrasive material to form a reticulate fine structure on an entire surface of an antiloading coating by the cracks.        

      An abrasive material of the present invention has a superior capability of discharging swarf and a markedly improved cutting performance.  
      An abrasive material having an antiloading coating on an outermost surface thereof of the present invention comprises an antiloading agent composition coated on an outermost surface of a generally known abrasive material. Kinds of abrasives on which an antiloading agent composition is coated are not particularly limited and may be such that an antiloading agent has been conventionally used for the abrading work. Such abrasives include many kinds such as a bonded abrasive material, a coated abrasive material and a nonwoven abrasive material.  
      For example, a bonded abrasive material comprises a multitude of abrasive particles fixed by a binding resin. A coated abrasive material comprises abrasive particles stuck to a substrate by a binding resin. A nonwoven abrasive material comprises abrasive particles stuck into or onto a three-dimensional nonwoven substrate by a binding resin. Each type of the abrasives may be in a variety of forms. For example, a coated abrasive material may comprise a first layer (also known as a make coat), a plurality of abrasive particles stuck to or into the first layer, and a second layer (also known as a size coat). In some cases, a third layer (also known as a supersize coat) may be applied onto the size coat. In addition, a coated abrasive material can be of forms such as a belt, a disk and a seat.  
      An outermost surface of an abrasive material denotes a surface of an abrasive material which will touch a body to be abraded in the case of not coating an antiloading agent composition thereon. That is, the outermost surface signifies a surface on the size coat in the presence of the make coat and the size coat, and meanwhile a surface on the make coat and the abrasive particles in the presence of only the make coat. Also, the outermost surface denotes a surface of resin used for the bonding in the case of a nonwoven abrasive product and a bonded abrasive product.  
      An antiloading agent composition denotes a coating solution containing an antiloading agent, a binding resin and a solvent. The antiloading agent may be such as to be conventionally used; typically including metallic soap having the antiloading effect, particularly stearates such as zinc stearate, calcium stearate and lithium stearate, metal salts of fatty acids, waxes and graphite. An additive such as fluorohydrocarbon may be used together.  
      A binding resin may be such as to be formed into a film with cracks, by which a reticulate fine structure can be formed on an entire surface of the coating. The cracks of the coating and the reticulate fine structure can be generally formed by adjusting hardness of resin and film-forming conditions. The hardness of resin is adjusted by changing glass transition temperature (Tg). The film-forming conditions are adjusted by changing heating temperature and time. particulate resin dispersed into a solvent is generally used for the binding resin. The solvent may be an aqueous solvent consisting essentially of water. The binding resin is preferably in a form of an aqueous latex or an aqueous resin emulsion.  
      The binding resin has a Tg value of 35° C. or more, preferably 40 to 150° C. and more preferably 50 to 130° C. A Tg value of less than 35° C. in the binding resin brings a possibility of rendering the formed antiloading coating so sticky as to lose antiloading function. Kinds of the binding resin include latexes such as natural rubber, butadiene rubber, styrene-butadiene rubber, styrene-butadiene-acrylonitrile rubber, chloroprene rubber and methyl-butadiene rubber, and acrylic and vinyl acetate emulsions. Preferable binding resins are styrene-butadiene-acrylonitrile rubber and styrene-butadiene rubber.  
      An antiloading agent composition is prepared by mixing an antiloading agent, a binding resin and a solvent. With regard to components of the antiloading agent composition, conventionally known additives may be mixed thereinto in the quantities typically used, such as a surface-active agent, a plasticizer, an antistatic agent, a humidifying agent, an antifoaming agent, a coloring matter, a pigment and a filler. Each of the components may also be mixed in a form of being previously dispersed into a solvent in a proper quantity.  
      A binding resin is contained in the antiloading agent composition in the quantity occupying 5 to 50% of the formed antiloading coating on the basis of solid content weight, preferably 10 to 40% and more preferably 15 to 35%. A binding resin content of less than 5% in the antiloading coating decreases the proportion of the binding resin component so extremely as to deteriorate the retention of an antiloading agent on a surface of a coated abrasive material, while a binding resin content of more than 50% therein renders the proportion of the binding resin component more than the antiloading coating to deteriorate an original function of the antiloading agent for preventing swarf from adhering.  
      An antiloading agent composition is applied on an outermost surface of an abrasive material by methods such as brush coating, roll coating, flow coating, die coating and spray coating. The applied quantity may properly vary with the size and quantity of abrasive grains to be used and the use of the abrasive material, generally being approximately 1 to 75 g/m 2  as dried coating weight, preferably approximately 9 to 40 g/m 2 .  
      Then, an abrasive material on which an antiloading agent composition is applied is preferably heated and dried at temperature and time appropriate for forming a selected binding resin into a film with cracks to form a reticulate fine structure on an entire surface of the coating by the cracks. The heating conditions can be properly determined by those skilled in the art.  
      For example, an abrasive material is heated at a temperature higher than Tg of a binding resin, preferably a temperature 1 to 60° C. higher than Tg of a binding resin and more preferably a temperature 10 to 40° C. higher than Tg of a binding resin. A heating temperature lower than Tg of a binding resin dries the binding resin with a granular state retained not to be formed into a film or to be insufficiently formed into a film, while a heating temperature more than 60° C. higher than Tg of a binding resin makes an antiloading agent composition into so uniform film as to be incapable of obtaining a reticulate fine structure by the cracks.  
      The heating time is 0.5 to 30 minutes, preferably 1 to 15 minutes. A heating time of less than 0.5 minute does not sufficiently volatilize and dry a solvent to perform no antiloading function, while a heating time of more than 30 minutes results in the deterioration and discoloration of an antiloading agent composition and the uniformalization of a film.  
      The obtained antiloading coating is formed into a film by fusing the particles of a binding resin and the appearance of the coating is transparent. That is, the antiloading coating obtained by a method of the present invention exhibits light transmission properties. The relative transmittance thereof is 1% or more, preferably 2 to 50% and more preferably 10 to 40%. A relative transmittance of less than 1% in the antiloading coating determines that an antiloading agent composition is not formed into a film, whereby the effect of the present invention is not obtained.  
      Also, with regard to a reticulate fine structure formed on an entire surface of the coating by the cracks, the longest diameter of the largest one among reticulations is 1000 μm or less, preferably 1 to 700 μm and more preferably 5 to 500 μm. A longest diameter of more than 1000 μm in the largest reticulation deteriorates capability of discharging swarf which is exhibited by peeling off of an antiloading agent composition having a fine structure with the cracks. A reticulate fine structure of the coating by the cracks varies also with the size of abrasive particles. The dimensions of reticulations are determined by observing with a microscope.  
      Incidentally, an abrasive material on which an antiloading agent composition is applied has been conventionally heated only at temperature and time sufficient for drying a selected solvent; consequently, a binding resin is retained in a granular state and not formed into a film, and the appearance of the coating is opaque. The reason therefor is that it has been thought that the formation of the antiloading coating into a film drops the antiloading agent off an abrasive material surface with such difficulty as to deteriorate a function of discharging swarf, and thus the heating has been restricted to a minimum performance.  
      An abrasive material of the present invention having an antiloading coating on an outermost surface thereof can be used for abrading various workpieces, woody materials such as wood, fiberboards and particle boards, fiberglass, varnish, polyester coatings, stainless surfaces, car body fillers, ceramics, glass, paints starting with latexes and oil paints, primers including oily primers and aqueous primers, and metals containing aluminum, stainless steel and mild steel.  
      The present invention is further detailed by the following examples and is not limited thereto. “Part” and “%” in the examples are on the basis of weight unless otherwise specified.  
     EXAMPLES  
     Example 1  
      The Production of an Antiloading Agent Composition  
      While stirring calcium stearate dispersion (a solid content of 55%), brand name of NOPCO 1097-AH, manufactured by San Nopco Co. Ltd., Japan, with a mixer, LABO-STIRRER MODEL LR-518, manufactured by Yamato Scientific Co. Ltd., Japan, at a number of revolutions of 500 rpm, styrene-butadiene-acrylonitrile latex (an aqueous dispersion, solid content of 49%, Tg of 105° C.), brand name of NIPOL LX311 manufactured by Zeon Corp., Japan, was charged thereinto and stirred at room temperature for 10 minutes. The mixture ratio thereof was adjusted so that the solid content weight ratio of calcium stearate to acrylonitrile-butadiene rubber is 8/2.  
      The production of an abrasive material having an antiloading coating on an outermost surface thereof  
      A coated abrasive material “Uni” (P120 grade) manufactured by 3M Ltd. was prepared. The antiloading agent composition was applied on a surface of a size coat of this coated abrasive material by using a hand rubber roller. The applied quantity was 0.3 g with respect to an area of 4 inches×6 inches as dry coating weight. The temperature of an oven was set at 120° C. and then the abrasive material on which the antiloading agent composition was applied was put thereinto and heated for 2.5 minutes. Thereafter, the abrasive material was taken out and cooled.  
      A surface of the formed antiloading coating was observed under a magnification of 150 times by using an electron microscope.  FIG. 1  is an electron micrograph showing a surface of the antiloading coating of the abrasive material in Example 1. The antiloading coating is formed into a film with cracks and a reticulate fine structure is confirmed. The relative transmittance of the antiloading coating measures 35% by using a spectrophotometer “U-4000” manufactured by Hitachi, Ltd., Japan. The longest diameter of the largest one among reticulations by the cracks is approximately 200 μm.  
      Abrasion Test  
      The obtained coated abrasive material was stamped into a disk having a diameter of 125 mm for an evaluation sample. A putty “High Soft Super” manufactured by 3M Ltd. was applied to a steel panel substrate, and it was dried and cured. The cured putty was abraded by using a double action sander “3965” manufactured by 3M Ltd., under the conditions of an abrasion load of 5 kg, an abrasion time of 3 minutes and an abrasion number of 3 times. The abraded quantity was converted into 118% with respect to 100%, which was the abraded quantity (weight) obtained by using an abrasive disk in Comparative Example 1 produced on current heating conditions.  
      Next, a surface of the antiloading coating after being used for abrading was observed under a magnification of 150 times by using an electron microscope.  FIG. 2  is an electron micrograph showing a surface of the antiloading coating of the abrasive material in Example 1 after being used. A fine structure of the antiloading coating is crushed and an antiloading agent is effectively dropped off.  
     Example 2  
      An abrasive material having an antiloading coating on an outermost surface thereof was obtained for performing the abrasion test in the same manner as Example 1 except for modifying the preset temperature of an oven into 110° C. The properties and test results of the antiloading coating are shown in Table 1.  FIG. 3  is an electron micrograph showing a surface of the antiloading coating of the abrasive material in Example 2.  FIG. 4  is an electron micrograph showing a surface of the antiloading coating of the abrasive material in Example 2 after being used.  
     Comparative Example 1  
      An abrasive material having an antiloading coating on an outermost surface thereof was obtained in the same manner as Example 1 except for modifying the preset temperature of an oven into 100° C.  FIG. 5  is an electron micrograph showing a surface of the antiloading coating of the abrasive material in Comparative Example 1. The antiloading coating is not formed into a film and offers no appearance of transparency. The relative transmittance of the antiloading coating measures 0% by using a spectrophotometer “U-4000” manufactured by Hitachi, Ltd. Reticulations by the clear cracks are not formed.  
      The abrasion test was performed in the same manner as Example 1 except for using the obtained coated abrasive material. The abraded quantity (weight) obtained herein was determined at 100%, which was a benchmark of the abraded quantities obtained in other examples and another comparative example.  FIG. 6  is an electron micrograph showing a surface of the antiloading coating of the abrasive material in Comparative Example 1 after being used. Particles of an antiloading agent are partially dropped off and the antiloading coating is not crushed.  
     Comparative Example 2  
      An abrasive material having an antiloading coating on an outermost surface thereof was obtained for performing the abrasion test in the same manner as Example 1 except for modifying the preset temperature of an oven into 90° C. The properties and test results of the antiloading coating are shown in Table 1.  FIG. 7  is an electron micrograph showing a surface of the antiloading coating of the abrasive material in Comparative Example 2.  FIG. 8  is an electron micrograph showing a surface of the antiloading coating of the abrasive material in Comparative Example 2 after being used.  
                                   TABLE 1                                           Comparative   Comparative           Example 1   Example 2   Example 1   Example 2                                                        Heating   120   110   100   90       Temperature       (° C.)       Transmittance   35   2   0   0       (%)       Longest   About 200   About 500   Not   Not       Diameter of           Observed   Observed       Reticulations       (μm)       Abraded   118   108   100   98       Quantity (%)