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. 

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. 

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. 

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 

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. 

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. 

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. 

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. 

