17  US 6,203,934 Bl  18  All or a part of the additives to be used in the present  invention may be added to the magnetic coating solution in  any step of the preparation. For example, additives may be  blended with a ferromagnetic metal powder before the  kneading step, may be added during the step of kneading a  ferromagnetic metal powder, a binder and a solvent, may be  added during the dispersing step, may be added after the  dispersing step, or may be added immediately before coat› ing. According to the purpose, there is a case of capable of  attaining the object by coating all or a part of the additives  simultaneously with or successively after the coating of the  magnetic layer. According to the purpose, lubricants may be  coated on the surface of the magnetic layer after the calen› dering treatment or after the completion of slitting.  As additives which can be used in the present invention,  those having a lubrication effect, an antistatic effect, a  dispersing effect and a plasticizing effect may be used.  Examples of additives which can be used in the present  invention include molybdenum disulfide, tungsten disulfide,  graphite, boron nitride, fluorinated graphite, silicone oil,  polar group-containing silicons, fatty acid-modified silicons,  fluorine-containing silicons, fluorine-containing alcohols,  fluorine-containing esters, polyolefins, polyglycols, alkyl  phosphates and alkali metal salts thereof, alkyl sulfates and  alkali metal salts thereof, polyphenyl ethers, fluorine› containing alkyl sulfates and alkali metal salts thereof,  monobasic fatty acids having from 10 to 24 carbon atoms  (which may contain an unsaturated bond or which may be  branched) and metal salts thereof (e.g., with Li, Na, Kor  The kind and amount of these lubricant and surfactant for  use in the lower layer and the magnetic layer can be properly  selected in accordance with the purpose. For example, the  lower layer and the magnetic layer can separately contain  different fatty acids each having a different melting point so  as to control bleeding out of the fatty acids to the surface, or  different esters each having a different boiling point or a  different polarity so as to control bleeding out of the esters  to the surface. Also, the amounts of surfactants are con› trolled so as to improve the coating stability, or the amount  of the lubricant in the lower layer is made larger so as to  improve the lubrication effect of the surface thereof.  Examples are by no means limited thereto.  The shape of the abrasives to be used in the present  invention may be any of acicular, spherical and die-like  shapes. Preferably, the abrasives have a shape partly with  edges, because a high abrasive property is given. Specific  examples of abrasives for use in the present invention  include AKP-20, AKP-30, AKP-50, HIT-50, HIT-60, HIT- 70, HIT-80, HIT-80G, and HIT-100 (manufactured by Sumi› tomo Chemical Co., Ltd.), G-5, G-7, S-1 (manufactured by  Nippon Chemical Industrial Co., Ltd.), and TFlO0 and  TF140 (manufactured by Toda Kogyo Co., Ltd.). It is of  course possible in the present invention to select and deter› mine the kinds, the amounts and the combinations of the  abrasives to be added to the upper layer and the lower layer  according to purposes. These abrasives may be previously  dispersed in a binder before addition to the magnetic coating  solution. The number of abrasives present on the surface and  the edge surface of the magnetic layer of the magnetic  recording medium according to the present invention is  preferably 5/100  µm 2  or more.  Specific examples of such additives include lauric acid,  myristic acid, palmitic acid, stearic acid, behenic acid, butyl  stearate, oleic acid, linolic acid, linolenic acid, elaidic acid,  octyl stearate, amyl stearate, isooctyl stearate, octyl  myristate, butoxyethyl stearate, anhydro-sorbitan  monostearate, anhydro-sorbitan distearate, anhydro-sorbitan  tristearate, oleyl alcohol, and lauryl alcohol. Additionally,  examples of other additives which may be used include  nonionic surfactants such as alkylene oxides, glycerols,  glycidols and alkylphenol-ethylene oxide adducts; cationic  surfactants such as cyclic amines, ester amides, quaternary  ammonium salts, hydantoin derivatives, heterocyclic  compounds, phosphoniums and sulfoniums; anionic surfac› tants containing an acidic group such as carboxylic acid,  sulfonic acid, phosphoric acid, sulfate groups or phosphate  groups; and amphoteric surfactants such as amino acids,  aminosulfonic acids, sulfates or phosphates of amino alco› hols and alkylbetains. The details of these surfactants are  described in  Handbook of Surfactants  (published by Sangyo  Tosha Co., Ltd.). These lubricants and antistatic agents are  not always be 100% pure and may contain impurities such  as isomers, non-reacted materials, byproducts, decomposed  products and oxides, in addition to the main component.  However, the content of such impurities is preferably 30%  or less, more preferably 10% or less.  As the abrasive usable in the present invention, well› known materials essentially having a Mohs’ hardness of 6 or  more may be used alone or in combination. Examples of  such abrasives include a-alumina having an alpha› conversion rate of 90% or more, ~-alumina, silicon carbide,  chromium oxide, cerium oxide, a-iron oxide, corundum,  artificial diamond, silicon nitride, silicon carbide, titanium  carbide, titanium oxide, silicon dioxide, and boron nitride.  Composites composed of these abrasives (abrasives  obtained by surface-treating with other abrasives) may also  be used. Compounds or elements other than the main  component are often contained in these abrasives, but the  intended effect can be attained so far as the content of the  main component is 90% or more. Abrasives preferably have  an average particle size of from 0.01 to 2  µm  but a plurality  of abrasives each having a different particle size may be  combined according to necessity, or a single abrasive having  a broad particle size distribution may be employed so as to  attain the same effect as such a combination. Preferably,  abrasives for use in the present invention have a tap density  of from 0.3 to 2 g/ml, a water content of from 0.1 to 5%, a  pH value of from 2 to 11 and a specific surface area  (SsEr)  of from 1 to 30 m $^{2}$/g.  Cu), mono-, di-, tri-, tetra-, penta- or hexa-alcohols having  from 12 to 22 carbon atoms (which may contain an unsat› urated bond or which may be branched), alkoxy alcohols  having from 12 to 22 carbon atoms (which may contain an  unsaturated bond or which may be branched), mono-fatty  acid esters, di-fatty acid esters or tri-fatty acid esters com› posed of a monobasic fatty acid having from 10 to 24 carbon  atoms (which may contain an unsaturated bond or which  may be branched) and any one of mono-, di-, tri-, tetra-,  penta- and hexa-alcohols having from 2 to 12 carbon atoms  (which may contain an unsaturated bond or which may be  branched), fatty acid esters of monoalkyl ethers of alkylene  oxide polymers, fatty acid amides having from 8 to 22  carbon atoms, and aliphatic amines having from 8 to 22  carbon atoms.  possible in the present invention to select and determine the  kinds, the amounts and the combinations of the carbon  blacks to be added to the upper layer and the lower layer, on  the basis of the above mentioned various properties such as  the particle size, the oil absorption amount, the electro› conductivity and the pH value. Regarding carbon blacks for  use in the magnetic layer of the present invention, for  example, the disclosure in  Handbook of Carbon Blacks  ( edited by Carbon Black Association of Japan) can be  referred to. 