Previously, in producing a high density magnetic recording tape, the magnetic layer was subjected to a calendering treatment, so as to lessen the Ra value as far as possible; (Ra value is the average surface roughness of centerline measured according to JIS 8060.) Preferably the Ra value is about 15 nm or less improves the electromagnetic conversion characteristics (Japanese Unexamined Patent Publication (Kokai) No. 5-54367). However, when the value of Ra is lessened, the coefficient of friction of the magnetic layer increases, and the trafficability of the magnetic tape is noticeably impaired. "Trafficability" means that coefficient of kinetic friction is small at the first pass of low speed running of a tape (10 to 1,000 cm/min.) and that adhesion of the tape at the start of running the tape is prevented.
To avoid the increase in friction, high molecular weight fatty acids or fatty acid esters have generally been used as lubricants. However, when fatty acids and fatty acid esters are added in small amounts, the trafficability of the magnetic tape remains poor. When these substances are added in large amounts, the strength of the magnetic layer decreases substantially, potentially lowering the durability of the magnetic tape (Japanese Unexamined Patent Publication (Kokai) No. 58-130435). While a high molecular weight fatty acid is especially effective for lessening the coefficient of kinetic friction of a magnetic tape when the tape is running at a low speed, if it is used in a large amounts, it disturbs the mutual adsorption between the ferromagnetic powder and the binder, and the strength of the magnetic layer as a coating is lowered.
Japanese Unexamined Patent Publication (Kokai) No. 3-224123 discloses a process for the production of a magnetic tape, comprising subjecting a magnetic layer to a calendering treatment, so as to harden the magnetic layer, and thereafter subjecting the magnetic layer to contact slide action by use of a plate-like or rod-like hard metal such as carbon steel or super steel, for the purpose of reducing the abrasion characteristics and drop-out, and improving the durability of static images.
However, this process has the following problems: (1) in order to form an effective lubricant film (especially a film of a fatty acid) on the surface of a magnetic layer, contact sliding procedures must be repeated several times; (2) when the contact sliding is effected by use of a metal having an Ra value higher than the roughness of the magnetic layer surface, flaws are produced such as scratches, and many errors are caused; (3) with a contact slide action in only one direction, the lubricant film of the magnetic layer becomes non-uniform or causes anisotropy, so that the coefficient of kinetic friction varies depending on the running direction (the direction in which the contact slide action was effected, and the direction contrary thereto); and (4) when put into practical use, the magnetic tape is brought into frictional contact, in the forward and reverse directions, with the magnetic head, rotary cylinder, and the like of a recording reproduction device, so that it becomes difficult to realize stable running of a tape in any of the directions.