JPS6232522B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for demagnetizing a magnetic tape with a metal reel.

Magnetic tapes used in cassettes, audio, video, electronic computers, etc. are oriented along the length of the tape to increase sensitivity, so a high residual magnetism remains in the magnetic tape after manufacture. It's on. Additionally, the tape is magnetized for some reason during the tape manufacturing process, which also causes residual magnetism. If residual magnetism remains on the tape, it cannot be used as is, so tape manufacturers demagnetize the tape to a level below a specified level (for example, below -60 dB) before shipping.

Conventionally, as shown in FIG. 1, a magnetic tape demagnetization method involves transporting a magnetic tape 5 at a predetermined speed V in the direction of arrow A by a conveyor 4 between magnetic poles 2 and 3 of an electromagnet 1 generating an alternating magnetic field H. It was moved and demagnetized.

However, in such a demagnetizing method, the portions on both sides 5a and 5b parallel to the conveying direction A of the tape 5 are well demagnetized, but the front and rear portions 5c and 5d perpendicular to the conveying direction A are not well demagnetized. Not demagnetized. This is because the tape 5 is oriented in the longitudinal direction (arrow BB' direction) as described above. That is, as shown in Figure 2a,
Since the tape 5 moves in the direction of the arrow A at a constant speed V with respect to the alternating magnetic field H, both sides 5 of the tape 5
The alternating magnetic field H' is applied from an oblique direction to parts a and 5b, and therefore these parts 5a and 5b
is often demagnetized. On the other hand, the direction of the alternating magnetic field H applied to the front and rear portions 5c and 5d of the tape 5 is always in the vertical direction (Fig. 2b) regardless of the movement of the tape 5. These front and rear portions 5c and 5d are difficult to demagnetize, and residual magnetism inevitably remains above the specified value.

If such an incompletely demagnetized tape 5 is used, for example, as a music tape and double-speed recording is performed, the residual magnetism remains as a noise component because the double-speed recording device is not equipped with a degaussing device. It gets hot and appears as periodic noise during playback.

And, like conventional tape, the coercive force Hc is
If the tape is about 300 Oe, the demagnetization method (first method)
(Figure), it is possible to somehow demagnetize it to the specified level. However, in order to demagnetize a tape with a very high coercive force Hc of approximately 700 Oe, such as recent metal tapes, to the specified level, it is necessary to apply a high magnetic field of approximately 2000 to 2200 Oe using conventional demagnetization methods. It is.

When such a high alternating magnetic field is applied, a large eddy current i is generated in the metal reels 6a and 6b due to the alternating magnetic field φ (Fig. 1), and as a result, the surface temperature of these metal reels 6a and 6b becomes extremely low. The temperature reaches a high temperature of 50° C. or more, and the wrapped tape 5 becomes useless due to this high heat.

The present invention was made in view of the above-mentioned points, and demagnetizes the tape with a low magnetic field by applying an alternating magnetic field in the winding direction of the tape and repeating the application twice with the applied direction shifted by 90 degrees. A method for demagnetizing a magnetic tape with a metal reel is provided.

The present invention will be described in detail below based on one embodiment of the accompanying drawings.

In FIG. 3, a turntable 12 is rotatably supported horizontally on a support 11 of a conveyance device 10 via a shaft 13.
3 has a gear 14 fixedly attached thereto. The support body 11 can be moved horizontally by a predetermined distance in the directions of arrows C and C'. Further, a driving belt 15 is installed between the gear 14 and a driving device (not shown). And this drive device is a belt 15
The turntable 12 is sequentially rotated, for example, by 90 degrees clockwise (in the direction of arrow D) at fixed time intervals. A magnetic tape 7 with a metal reel is placed horizontally on the turntable 12.

The demagnetizing coil 20 is an air-core coil arranged at a predetermined position so that its axial direction coincides with the direction of movement of the support 11 of the conveying device 10 (arrow C, C' direction).
When the support body 11 is retracted in the direction of arrow C, the turntable 12 is placed at a predetermined position outside the opening 20a on one side of the demagnetizing coil 20, and when it is extended in the direction of arrow C', the turntable 12 is positioned inside the opening 20c of the demagnetizing coil 20. They are each held at an approximately central position. This demagnetizing coil 20 is connected to a predetermined AC power source (not shown).
, and is designed to generate a predetermined alternating magnetic field H in the axial direction.

Further, each part of the conveying device 10, such as the support 11, turntable 12, shaft 13, gear 14, etc., does not impart residual magnetism to the magnetic tape 9 and does not adversely affect the alternating magnetic field H generated by the demagnetizing coil 20. It is made of a non-ferrous metal member or a non-metallic member to ensure that there is no metal. In order to prevent the generation of eddy currents caused by the alternating magnetic field H and to prevent heat generation, each of these parts is desirably made of a non-metallic material such as synthetic resin.

Now, after retracting the support body 11 of the conveyance device 10 in the direction of arrow C, the magnetic tape 7 with metal reel to be demagnetized is placed on the turntable 12 (third
(shown in dashed lines in Figure 4a).

Next, the support body 11 is extended in the direction of arrow C',
The tape 7 is inserted approximately at the center of the demagnetizing coil 20 (FIG. 4a). In this state, the alternating magnetic field H of the demagnetizing coil 20 and the both sides 9a, 9 of the tape 9
The alignment direction B--B' of the portion b is parallel (FIG. 5), and therefore the portions on both sides 9a and 9b are demagnetized. However, in the front and rear portions 9c and 9d of the tape 9, the alternating magnetic field H and the tape orientation direction are perpendicular to each other, and therefore, these portions 9c, 9d
9d is not demagnetized much.

After demagnetizing for a certain period of time, the turntable 12 is rotated 90 degrees to the state shown in FIG. 4b. In this state, the orientation processing direction of the front and rear portions 9c and 9d of the tape 9 is now directed by the alternating magnetic field H.
is parallel to Therefore, these portions 9c and 9d (FIG. 4c) are demagnetized. After demagnetizing for a certain period of time, the support body 11 is retracted and the turntable 12 is extracted from the demagnetizing coil 20.

By aligning the orientation process direction of the tape 9 with the direction of the demagnetizing alternating magnetic field H in this way, approximately 1200 ~
The tape 9 can be demagnetized to below a specified level with a relatively low magnetic field of 1300 Oe.

On the other hand, the metal reel 8 of the magnetic tape 7 is made of a non-ferrous metal member such as aluminum, and therefore, while the magnetic tape 7 is inserted into the coil 20, the metal reel 8 is naturally exposed to an alternating magnetic field H. Eddy currents occur. However, both side surfaces 8a and 8b (FIGS. 3 and 5) of the metal reel 8 are always parallel to the direction of the alternating magnetic field H, and therefore, the eddy currents generated are very small and there is also little heat generation. Therefore, the heat generated in the metal reel 8 will not damage the tape 9.

In this way, the tape 9 can be demagnetized below a specified level without causing any thermal damage.

Note that an alternating current power source applied to the demagnetizing coil 20 may be used to continuously supply current, or a damping type power source that attenuates over a predetermined period of time may be used. When using a damping type power supply, turntable 1 is turned off after the decay time has elapsed.
Needless to say, 2 should be rotated.

As explained above, according to the present invention, it is possible to easily demagnetize the tape below a specified level with a relatively low magnetic field, and furthermore, the heat generation in the metal reel portion can be extremely reduced, so that there is no damage to the tape. Does not cause thermal damage. It is also extremely effective in demagnetizing metal tapes with particularly high coercive force. Furthermore,
There are excellent effects such as the ability to downsize the power supply and the like and the ability to construct the demagnetizing device at low cost.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram showing a conventional method of demagnetizing a magnetic tape with a metal reel, Fig. 2 a and b are explanatory diagrams of a magnetic field applied to a magnetic tape by the demagnetizing method shown in Fig. 1, and Fig. 3 4 is a partially cutaway perspective view showing an embodiment of a demagnetizing device used in the method of demagnetizing a magnetic tape with a metal reel according to the present invention, and FIGS. FIG. 5 is an explanatory diagram showing the relationship between the magnetic tape orientation processing direction applied to the magnetic tape by the demagnetization method according to the present invention. 7... Magnetic tape with metal reel, 8... Metal reel, 9... Magnetic tape, 10... Conveyance device, 11... Support body, 12... Turntable, 15... Belt, 2
0... Demagnetizing coil.

Claims (1)

[Claims] 1. When demagnetizing a magnetic tape with a metal reel, place the tape with a metal reel in a demagnetizing magnetic coil that generates a predetermined alternating magnetic field so that both sides of the metal reel are parallel to the direction of the alternating magnetic field, and After demagnetizing a portion of the tape that is parallel to the alternating magnetic field, the magnetic tape is rotated at a predetermined angle within the same plane to make the portion that was orthogonal to the alternating magnetic field parallel, and the parallel portion is demagnetized; A method for demagnetizing a magnetic tape with a metal reel, which suppresses heat generation of the metal reel and demagnetizes the entire magnetic tape below a specified level.