JPS6364297B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a recording disk forming device, and more particularly to a device that prevents burrs formed around the center hole of the disk from interfering with correct rotation of the disk.

High packing density recording discs such as video discs, which have a groove density of about 3937 grooves per cm, have much narrower grooves and rotate at much higher speeds than audio recording discs. In other words, the grooves of the high packing density disk have a width of about 2.7μ compared to the 50 to 60μ of the audio recording disk, a depth of about 4000Å, and a rotation speed of about 450 revolutions per minute compared to 33 rotations for the audio recording disk. . Because the grooves are narrow and rotate quickly, the disc must be stably supported so that the accumulator needles can accurately track the grooves. One way to increase this stability is to use a relatively large-diameter disk with a diameter of approx.
It has a 3.3cm center hole and fits into the truncated conical shaft of the player.

A commonly used method for manufacturing discs is pressure molding. It has been found desirable to form the center hole of the disc during molding of the disc. Apparatus suitable for such a process is described in U.S. Patent Application No. 9, November 1979.
Specification and drawings of No. 93012 (Japanese Unexamined Patent Publication No. 55-148130
(corresponding to the publication). The problem with this device is that burrs remain around the center hole on both sides of the disk. The burr projects radially inwardly from the edge of the center hole on one side, and projects along and perpendicularly from the edge of the center hole on the other side. Therefore, no matter how the disk is fitted onto the pivot, the burr will come into contact with the surface of the pivot and interfere with proper fitting. Thus, burrs can cause the disk support to become unstable during playback.

The recording disk forming device has a pair of templates configured to form a disk mold space between them, and can move forward and backward through one of the templates with respect to the other template at the center of the mold space. It has a center hole forming pin. This center hole forming pin has a diameter larger than the hole to be formed, and has a cylindrical protrusion having the same diameter as the hole to be formed and protruding from its end face. This projection has a length such that when its end engages with the other mold plate to form a hole in the disc, the end face of the pin around it forms an extension of the inner surface of the mold space.

FIG. 1 shows a conventional recording disk press forming machine 10 as described in the specification of the above-mentioned US patent application. Generally, the molding machine 10 has an upper mold plate 12 and a lower mold plate 14, at least one of which is mounted so as to move forward and backward relative to the other. These templates 12, 14
have aligned center openings 16, 18 into which center plates 20, 22 are fitted, respectively. Push molds 24 and 26 are mounted on opposing surfaces of the mold plates 12 and 14. This stamping die is a thin metal plate having an intaglio pattern of concave and convex patterns to be formed on the surface of the recording disk.
is fixed.

A center hole forming pin 2 is provided on the center plate 20 of the upper mold plate 12.
8 through which it can be slid. This center hole forming pin 28 is cylindrical and has an outer diameter corresponding to the required center hole diameter of the recording disk.
A recess 30 is provided on the end face facing the center plate 22 of the lower mold. The top surface 32 of the lower mold center plate 22 can be completely flat or can have a raised portion to assist in forming the center hole of the molded disk.

To manufacture recording discs in press molding machine 10, templates 12 and 14 are separated (i.e., opened) and a preform of plastic material for the recording disc is placed between them. The heated mold plates 12,14 are then brought closer together (i.e., closed) and pressed against the preform, causing the material to flow radially outwardly from between the molds 24,26. Place the templates 12 and 14 on the required recording disk 3.
4, and while closed, the center hole forming pin 28 is forced into the preform to force plastic material out of the center hole area. The center hole forming pin 28 is advanced until it contacts the top surface 32 of the lower die center plate 22. In this way, a molding disk 34 having a center hole 36 is formed in the mold space between the press molds 24, 26.

During the molding of the recording disc 34, some of the plastic material is deposited on the ends of the center hole forming pins 28 and the lower mold center plate 22.
A thin annular burr 38 is formed on one surface of the disk 34 and protrudes radially inward from the periphery of the center hole 36. In addition, some of the plastic material leaks between the center hole forming pin 28 and the upper mold center plate 20, forming a short cylindrical burr 40 that protrudes upward from the edge of the center hole 36 on the other surface of the disk 34. do. When the recording disc 34 is fitted onto the truncated conical shaft 42 of the record player, the burr 3
8 may come into contact with the surface of the pivot 42 as shown in FIG. 2a, making it difficult for the disc 34 to sit on the pivot 42. Further, when the disc 34 is inverted and fitted onto the pivot, the burr 40 may come into contact with the pivot surface as shown in FIG. 2b, making it difficult for the disc 34 to sit on the pivot. In this way, the burr in the center hole 36 of the disc 34 interferes with correct reproduction of the recording disc 34.

This invention will be explained below with reference to FIGS. 3 to 4b.

FIG. 3 shows a disk pressure molding machine 100 according to the present invention.
shows. Similar to pressure forming machine 10 of FIG. 1, this pressure forming machine 100 also has aligned center openings 116, 118.
It has upper and lower mold plates 112, 114, respectively, and center plates 120, 122 are fitted into their center openings 116, 118, respectively. Template 11
Pressing molds 124 and 126 are mounted on opposing surfaces of molds 2 and 114, and these are fixed to mold plates 112 and 114 by center plates 120 and 122.

A center hole forming pin 128 slidably extends through the center plate 120 of the upper mold plate 112 . The center hole forming pin 128 is cylindrical, has an outer diameter slightly larger than the diameter of the hole to be formed in the disk, and has a cylindrical protrusion 129 protruding from the end surface facing the lower mold center plate 122. This protrusion 129 has an outer diameter corresponding to the required diameter of the disk center hole and a length slightly less than 1/2 the thickness of the disk. This protrusion 129
is the center hole forming pin 28 of the pressure molding machine 10 in FIG.
It has a recess 130 at its end corresponding to the recess 30 of. The lower die center plate 122 has a cylindrical protrusion 133 protruding from the center of its top surface 132. The diameter of this protrusion 133 corresponds to the diameter of the hole to be formed in the recording disk, and the length is equal to 1/2 the thickness of the disk.

In the pressure molding machine 100, the recording disk 1 is prepared in the same manner as described for the pressure molding machine 10 in FIG.
34 is manufactured, with the center hole forming pin 128 advancing through the plastic material to form the center hole 1 into the disk 134.
36, the protrusion 129 of the pin 128
and the protrusion 133 of the lower mold center plate 122 are connected to the center hole 1.
36 at approximately the midpoint in the length direction, and at this time, the end surface 131 of the pin 128 and the top surface of the lower mold center plate 122 approximately coincide with the surfaces of the upper and lower pressing molds 124, 126, respectively, and the protruding portions 129, Together with the outer surface of 133, it forms an extension of the mold space.
The protrusions 129 and 133 are located in the center hole 13 of the disk 134.
6 abut at the midpoint in the longitudinal direction, so the burr 138 formed therebetween projects radially inward from the inner surface of the center hole 136 at the midpoint in the length direction of the center hole. In addition, the center hole forming pin 128 and the upper mold center plate 1
The burr 140 formed between the central hole 1
36 protrudes from the surface of the disk 134 at a position outwardly away from the edge thereof. Projection 12 of center hole pin 128
9 has a length slightly shorter than 1/2 of the thickness of the recording disk, so the end surface 131 slightly presses the surface of the disk to form a recess 135 around the center hole 136. This ensures that the burr 140 is removed from the center hole 13.
It is formed at a position outwardly away from the edge of 6.

When this recording disc 134 is fitted onto the pivot of the player, the burr 138 protruding from the inner surface of the center hole 136 separates from the pivot surface and does not interfere with the seating of the disc on the pivot, as shown in FIG. 4a. Similarly, when the disk 134 is reversed and fitted onto the pivot 42, the center hole 1
burr 138 and disk 13 protruding from the surface of 36
Since the burr 140 protruding from the surface of 4 is spaced from the pivot plane, neither will interfere with the proper seating of the disc on the pivot. As described above, the recording disk pressure molding machine of the present invention forms a disk in which the positions of all burrs existing in or near the center hole of the disk are set so as not to interfere with the correct seating of the disk with respect to the pivot axis of the player.

[Brief explanation of drawings]

Fig. 1 is a partial vertical cross-sectional view of a conventional processing molding machine having a center hole forming pin, and Figs. 2a and 2b show a state in which a recording disk manufactured by the molding machine of Fig. 1 is fitted to the pivot of the player. 3 is a partial longitudinal sectional view of a pressure forming machine having a center hole forming pin according to the present invention; FIGS. 4a and 4b are 3
FIG. 3 is a partial vertical cross-sectional view of a recording disc manufactured by the molding machine shown in the figure, which is fitted onto the pivot of the player. 100...recording disk forming device, 112, 114
...Pair of templates, 128...Center hole forming pin, 1
30...Protrusion.

Claims (1)

[Claims] 1. A pair of templates configured to form a disk-shaped mold space between them, and a central hole forming which passes through one of the templates and moves forward and backward relative to the other template at the center of the mold space. The central hole forming pin has a diameter larger than the hole to be formed, and has a cylindrical protrusion having a diameter equal to that of the hole to be formed and protruding from its end surface, and this protrusion has a diameter larger than that of the hole to be formed. A recording disc forming apparatus characterized in that when the pin engages with the other template to form a hole in the disc, the end face of the pin around the pin has a length such that it forms an extension of the inner surface of the mold space. .