1. Field of the Invention
This invention relates to a magnetic disk cartridge, and more particularly to a construction of an inner surface of a jacket of the magnetic disk cartridge at which a center pin of a magnetic disk driving apparatus contacts.
2. Description of the Prior Art
A magnetic disk cartridge comprises a jacket and a magnetic disk rotatably disposed within the jacket. The magnetic disk has a hub at its center, and an opening portion for permitting a center pin of a magnetic disk driving apparatus to be inserted therein is formed in the hub. The arrangement is such that when the magnetic disk is rotating within the jacket, the pin is caused to pass through the opening portion of the magnetic disk and its tip is contacted with the inner surface of the jacket. Therefore, as there is a fear that the jacket will be damaged by the tip of the pin, a pin contacting portion within the jacket is formed as a projection of a circular shape and in order to protect the projection from being damaged, a chip made of an ultra high molecular polyethylene is applied to the projection by using an adhesive agent (double coated adhesive tape, etc.). That is, the protection layer, as described above, comprises the polyethylene chip and the adhesive agent. The protection layer is formed in a circular shape or the like so as to be in good conformity with the configuration of the projection. The protection layer is formed through a plurality of steps such as, for example, a step for applying an adhesive agent to a polyethylene film such as polyethylene sheet, etc., a step for cutting the polyethylene film to form the chip, and a step for applying the chip to the projection of the jacket.
As a conventional protection layer in the magnetic disk cartridge is formed through a plurality of steps as mentioned above, it has such a problem as that a considerable labor is required in order to form the conventional protection layer.
SUMMARY OF THE INVENTION
Therefore, it is an object of the present invention to provide a magnetic disk cartridge which is excellent in antiwear property and antishock property. The protection structure of the present invention is simple and ensures a good productivity of the cartridge.
In order to achieve the above object, the inventors of the present invention have studied about protection structures of the contacting portion of a center pin of a magnetic disk driving apparatus from various angles. As a result, they have found that a satisfactory protection layer can be formed with ease by forming a hardened layer of a particular hardness made of a particular hardening resin.
The present invention has been accomplished based on the above finding. According to the present invention, there is essentially provided a magnetic disk cartridge in which a magnetic disk is rotatably disposed within a jacket, said magnetic disk cartridge being characterized in that a hardened layer of an ultraviolet ray hardening resin is formed on an inner surface of said jacket which is contacted with a tip of a center pin of a magnetic disk driving apparatus passing through an opening portion of said magnetic disk, the hardness of said hardened layer being in the range from 1.times.10.sup.10 dyn/cm.sup.2 to 1.times.10.sup.5 dyn/cm.sup.2.
According to the present invention, there can be provided a magnetic disk cartridge in which antiwear property and antishock property to the center pin of a magnetic disk driving apparatus are excellent and the protection structure of the contacting portion of the inner surface of the jacket for receiving the center pin therein is formed in a simple structure and ensures a good productivity of the cartridge.