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Magnetic recording medium
| Details |
Inventors: Ryoke, Katsumi; Takahashi, Masatoshi; Izaki, Tsugio; Suzuki, Masaki;
Assignee: Fuji Photo Film Co., Ltd. (Kanagawa, JP)
Primary Examiner: Thibodeau; Paul J.
Assistant Examiner:
Attorney, Agent or Firm: Sughrue, Mion, Zinn, Macpeak & Seas
A magnetic recording medium composed of a non-magnetic support having thereon at least one magnetic layer containing a ferromagnetic fine powder dispersed in a binder, wherein (a) the magnetic layer further contains at least one of (i) carbon black having a sodium content of at most 100 ppm, (ii) carbon black having a chlorine content of less than 400 ppm, and (iii) an abrasive having a Mohn' hardness of at least 8 and a mean particle size of 0.05 to 0.5 .mu.m and a sodium content of at most 100 ppm; (b) the ferromagnetic fine powder is a magnetic metal powder having a sodium content of at most 200 ppm; and/or (c) the magnetic recording medium further has a back layer provided on the side of the non-magnetic support opposite to the magnetic layer, containing carbon black having a chlorine content of at most 300 ppm dispersed in a binder. The magnetic recording medium has superior storage stability, with remarkably limited dropout increase, head clogging, C S/N decrease and RF output decrease. |
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DETAILED DESCRIPTION OF THE INVENTION The present inventors have markedly improved the storage stability characteristics of magnetic recording media by identifying the previously unknown sources of inorganic salts and clarifying the relationship between inorganic salts and storage stability characteristics.
Thus such problems as dropouts, head clogging, C S/N decrease and RF output decrease have been overcome in the present invention by further reducing the very low content of water-soluble Na remaining in carbon black, abrasives, other powders (fillers) and ferromagnetic powders (in particular, magnetic metal powders) contained in the magnetic layer and back coat layer of magnetic recording media, and/or by further reducing the very low content of water-soluble Cl remaining in carbon black.
The terms "Na content" and "Cl content" as used herein are relative to the respective water-soluble components.
Such Na content and C1 content are determined in the following manner.
A specified quantity (5 g) of each sample is weighed and suspended in 100 ml of deionized water, and the suspension is shaken or heated under reflux and then filtered or decanted to give a sample solution, which is subjected to atomic absorption analysis or plasma ion spectro-photometry, for instance, followed by calculation with reference to calibration curves constructed by using standard samples.
X-ray fluorescence analysis is also applicable.
In the magnetic recording medium according to the invention, the formation and crystal growth of NaCl occurring in the process of magnetic recording medium manufacture, for example, in the steps of mixing, dispersing and application of magnetic coating mixes, or during long-term storage of the magnetic recording medium are prevented or suppressed as a result of the reduction of at least one of the water-soluble Na content and water-soluble C1 content of magnetic layer-constituting powders, such as carbon black, abrasives and magnetic metal powders, and of carbon black used in the back coat layer
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