JPH0729346B2 - Method of manufacturing optical disk substrate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to an injection molding method of a plastic substrate used for optical discs such as compact discs (hereinafter abbreviated as CD) and video discs (hereinafter abbreviated as VD). Is.

[Conventional technology]

Optical recording discs such as CDs, VDs, etc. are used to rotate the discs at high speed when recording and reproducing information, signals, etc.
A drive hole is provided in the center of the disc. The center hole maintains roundness in order to minimize recording and reproduction errors, and strict machining is required during drilling so as not to cause eccentricity. Conventionally, when molding a disk by injection molding, after injecting resin into the cavity of the mold,
A so-called gate cut method has been adopted in which a resin portion corresponding to a gate portion is cut and punched. 4 and 5 show examples of conventional gate cuts. In order to punch holes by this gate cutting method, after the cavity is filled with resin, the sprue bush 9 on the fixed side of the mold is retracted or the punch plate 23 on the fixed side is lifted up to cut the margin. 21, 24 are provided, and then the gate cutter is projected from the movable side of the mold to cut the resin existing in the gate portion.

[Problems to be solved by the invention]

According to the conventional gate cut method, when retracting the sprue bush, the injection cylinder must be temporarily retracted by a slight distance, for example, about several mm, in which case the nozzle touch portion 11 of the injection cylinder is sprue bushed. Since it separates from No. 9, the resin leaks from the tip of the nozzle, which causes a defective product such as silver and thread on the next shot. Further, when the fixed punch plate 23 is floated and the gate is cut, the cutting operation can be started only after the cooling of the injected resin is completed. In order to cut the completely solidified resin, the blade of the cutter was worn and the molded product was distorted or cracked, and many cutting wastes were the cause of defective molding. Both methods involve the above-mentioned troublesome operations for cutting margins.

[Means for solving problems]

The present invention provides a method for eliminating the drawbacks of conventional methods.

A method of manufacturing an optical disc substrate having an opening in the center of the present invention is a first mold including a sprue bush and a punch base, and a first mold that is disposed so as to face the first mold. And a second die for holding a gate cutter having a ring-shaped cross section concentrically so as to be slidable in the direction of the cavity. A method of manufacturing an optical disc substrate having an opening in the center by using a mold, wherein the sprue bush is concentrically and immovably held by the first mold as the first mold, and A punch table is arranged around the sprue bush so as to concentrically hold the sprue bush, and the end surface of the sprue bush and the end surface of the punch table constitute a part of the cavity. That cab A step of preparing a die having a step on the constituent surface so that the tip of the gate cutter can be fitted when the gate cutter is advanced toward the cavity, the first die and the die A step of clamping the second mold with a predetermined clamping force to form a cavity, a step of pouring a molten material for forming a disk substrate through the sprue bush toward the cavity, and a step of forming a cavity in the cavity. Before the molten material is solidified, the gate cutter is advanced in a state of being clamped and fitted into the stepped portion of the punch table, and the step of advancing the gate cutter includes the step of moving the gate cutter. It is characterized in that it is carried out without causing a change in the volume of the cavity for accommodating the molten material which is displaced along with the forward movement. At that time, it is preferable that the cutting edge at the outer peripheral portion of the gate cutter is formed at an acute angle of 90 ° or less, preferably 60 ° or less, in order to facilitate the drilling operation. Further, in punching, in order to prevent the cutting edge of the gate cutter from being chipped, an abutting prevention interval of the cutter is provided between the fixed punch table 26 and the fixed punch table 26.

Thus, in the present invention, when the resin is injected into the cavity, only the gate cutter is driven and the holes are punched while the fixed and movable plates are fixed. Therefore, it is no longer necessary to retreat the fixed-side sprue bush and float the fixed-side punch plate to provide a cutting allowance as in the prior art. Immediately after the mold is filled with resin, the gate cut moves immediately and the gate part is cut, so there is no adverse effect on the properties of the molded product, maintenance of the cutter, easy operation, reduction of cutting residue, etc. It provides an excellent gate cut method.

Next, an embodiment of the present invention will be described with reference to FIGS.

FIG. 1 shows a mold structure of an injection molding machine used in the present invention. First, the molten resin passes through the nozzle touch portion 11 from the injection cylinder 10, and the movable side mirror surface plate 6 and the fixed side mirror surface plate 8
It is filled in the cavity 19 formed by.

FIG. 2 shows an enlarged view of the gate portion of the resin flowing into the cavity 19. When molding a disk substrate, the holding pressure is several hundred kg / cm ² , and the holding time is about 0.1 seconds, so the gate part 1
5 is not completely filled and has some voids 16. In the present invention, this gap is used as a cutting margin for the gate cut portion. That is, the gate-cut step portion 20 is provided so that the volume of the gate-cut margin 15 is substantially equal to that of the unfilled void portion 16. FIG. 3 shows a state where the gate portion is cut by driving the gate cutter 4. As shown in FIG. 2, when the resin is filled, the gate cutter 4 is driven by the hydraulic pressure from the gate cutter hydraulic unit 12 to punch the cross section of the product unit (disk substrate), and then the unit 18 is shown. Enter up to the gate cutter abutment prevention interval.
The gate cutter has a ring shape having a diameter corresponding to the punched portion and has an appropriate thickness. The blade edge of the gate cutter is directed inward, and the blade angle is kept at an appropriate acute angle in the ring-shaped outer periphery, so the resin removed by the progress of the cutter flows toward the product part 14 of the molded product. Instead, it is designed to flow only into the gate portion 17.

Thus, the gate portion can be cut without causing a large internal stress in the product portion of the molded product, that is, the intended disc substrate main body portion. Further, by providing a step portion for gate cutting so that the volume of the gate cutting margin 15 is equal to the unfilled void portion 16, the sprue bush is retracted, and the gate portion is cut without floating the fixed side punch plate. be able to.

〔The invention's effect〕

The method of the present invention utilizes the gate cutting mechanism as described above, and the following effects can be expected by implementing the present invention.

(1) In the present invention, the operation of retracting the sprue bush or floating the fixed-side punch plate is unnecessary, and the mold structure can be greatly simplified.

(2) When the conventional sprue bush is retracted and the gate is cut, it is necessary to temporarily release the nozzle touch of the injection cylinder, so the resin may leak from the tip of the nozzle and a defective phenomenon such as silver or thread pulling on the next shot. However, since it is not necessary to release the nozzle touch in the present invention,
Such defects have disappeared at all.

(3) When retracting the conventional sprue bush or floating the fixed side punch plate to perform gate cutting, there is a time constraint that it must be after the next shot is weighed or after cooling is completed. In the present invention, it is possible to cut the gate at any timing independently of them, and if the gate is cut in a state where the resin is sufficiently melted, there is no gate cutting slag and the blade of the cutter is extremely worn. .

(4) The blade edge of the cutter is turned to the side opposite to the product side,
Since the blade is provided at an acute angle, the cut resin flows only into the gate portion, and the resin does not flow back to the product portion side, so that stress due to gate cutting does not occur on the product side. Therefore, the product is not affected by the birefringence due to the gate cut.

[Brief description of drawings]

1 to 3 are drawings showing an embodiment of the present invention. First
The figure shows the mold structure, FIG. 2 shows an enlarged view of the gate portion of the resin injected into the cavity, and FIG. 3 shows the injected resin cut by a gate cutter. 4th and 5th
The figure shows a conventional example of gate cutting. 1 ... Molding machine ejector rod, 2 ... Molded product sprue lock ejector pin, 3 ... Molded part ejector sleeve, 4 ... Gate cutter, 5 ... Positioning sleeve, 6 ... Movable mirror surface plate, 7 ... … Inner stamper foot, 8
...... Fixed plate on fixed side, 9 ...... Sprue bush, 10 ...... Injection cylinder, 11 ...... Nozzle touch part, 12 ...... Hydraulic part for ejecting gate cutter, 13 ...... Hydraulic part for returning gate cutter, 14 ...... Product Part, 15 ... Gate cut margin, 16 ...
… Unfilled part, 17 …… Gate part, 18 …… Gate cutter abutment prevention interval, 19 …… Cavity, 20 …… Step part for gate cut, 21 …… Gate cut allowance by retracting sprue bush, 22 …… Gate Cutter, 23 …… Punch plate, 24 …… Gate cut fee by floating punch plate,
25 …… Punch plate floating allowance, 26 …… Punch stand 26.

Claims (3)

[Claims] 1. A first device having a sprue bush and a punch base.
And a first mold, which are arranged so as to face each other to form a disc-shaped cavity, and a gate cutter having a ring-shaped cross section is used as the cavity. A method for manufacturing an optical disc substrate having an opening at the center by using an injection molding die having a second die which is concentrically held so as to be slidable in the direction, the first die As a die, the sprue bush is concentrically and immovably held by the first die, and the punch base is arranged around the sprue bush so as to concentrically hold the sprue bush. End surface of the punch table and the end surface of the punch table constitute a part of the cavity, and the tip of the gate cutter can be fitted to the cavity table surface of the punch table when the gate cutter is advanced toward the cavity. A step of preparing a mold configured to have a large step, a step of clamping the first mold and the second mold with a predetermined mold clamping force to form a cavity, and facing the cavity A step of pouring a molten material for forming a disk substrate through the sprue bush, and advancing the gate cutter in a mold clamped state before the molten material in the cavity is solidified to move to a stepped portion of the punch table. And the step of advancing the gate cutter is performed without causing a change in the cavity volume for containing the molten material displaced with the advance of the gate cutter. A method for manufacturing a characteristic optical disc substrate. 2. The method for manufacturing an optical disk substrate according to claim 1, wherein the edge of the ring-shaped gate cutter has an acute angle of 90 ° or less. 3. An abutment prevention interval is provided to prevent the tip of the gate cutter from abutting against the punch table when the gate cutter is most advanced. Manufacturing method of optical disc substrate.