JPH0321968B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention particularly relates to a magnetic recording medium for a magnetic encoder that enables high coercivity. The magnetic films of magnetic disks and magnetic drums for magnetic encoders are required to maintain high magnetic force because the distance between the magnetic detection element and the magnetic recording body must be large, ranging from several micrometers to several hundred micrometers. For this reason, while magnetic tapes and magnetic disks for computers are made of thin magnetic films of several micrometers, magnetic films for magnetic encoders require thick films of 50 to 100 micrometers or more. On the other hand, a method for forming a magnetic film uses a magnetic paint made by kneading magnetic powder (usually metal powder), an organic binder such as epoxy or polyurethane, and a solvent that dissolves the binder, and then applies this onto a substrate using a spinner. It is applied by spraying, printing, etc., and then, after baking, it is oriented and magnetized. This magnetic film must be smooth and thick with no defects such as bubbles or film cracks, but magnetic films formed with conventional magnetic paints cannot produce high-quality films without film defects, and are difficult to obtain. However, the yield was poor and stable products could not be produced. SUMMARY OF THE INVENTION An object of the present invention is to provide a magnetic recording medium in which a magnetic film is formed using a magnetic paint that does not cause film defects even when the film is thick. It has been found that obtaining a high-quality magnetic recording medium for a magnetic encoder depends on the quality of the magnetic paint used to form the magnetic film. That is, since it has been found that the filling amount of magnetic powder in the magnetic paint has a close relationship with magnetic film defects, the gist of the present invention is to set this to a predetermined value. An embodiment of the present invention will be described in detail regarding a magnetic disk. After cleaning the magnetic disk substrate made of non-magnetic material such as aluminum, a metal magnetic paint using an epoxy binder is applied to the thickness using a spinner method.
Deposit 100μm. Next, in order to harden the deposited magnetic film, baking is performed at 120° C. for 2 hours, resulting in a complete magnetic film. Here, the composition (weight ratio) of the magnetic paint used is as follows. Metal powder 65 parts Epoxy resin 35 parts Solvent (toluene) 20 parts The most important point in the above composition is the weight ratio of the metal powder and the epoxy resin as a binder.
Note that the solvent disappears after baking. That is, as shown in the table, it was confirmed that when the metal filling amount was less than 57%, air bubbles were generated in the magnetic film due to the large resin content, and when it was more than 70%, cracks occurred in the coating film. These coating film defects are not a problem when the film is thin, such as a magnetic tape, of a few micrometers, but they are an important factor when making a thick film of several tens of micrometers or more, such as a magnetic film for a magnetic encoder. .

[Table] The numbers for bubbles and cracks are the defect occurrence rate (%). As described above, when the metal filling amount is in the range of 60 to 70 wt%, a good magnetic film with almost no bubbles or cracks can be obtained. As described above, by using the magnetic paint having the metal filling amount of the present invention, industrially stable products can be mass-produced. In the above embodiments, epoxy resin was used as the binder for the magnetic paint, but the same results could also be obtained with polyurethane, phenol resin, etc. Also, although the explanation has been made using disks, it goes without saying that the same applies to drums.

Claims (1)

[Claims] 1. A rotating body attached to a rotating shaft, a magnetic film containing a binder and magnetic powder provided on a non-magnetic substrate of the rotating body, and a magnetic detection element that detects a magnetic field leaking from the rotating body. In the magnetic encoder, the magnetic film is a thick film of several tens of micrometers or more, and the amount of magnetic powder in the magnetic film is 60 wt% or more and less than 70 wt% with respect to the magnetic film. encoder.