JPH0366129B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention is applicable to video discs, draw discs,
This invention relates to an injection molding method for disc-shaped recording media such as compact discs.

[Prior Art] In general, disc-shaped recording media such as video discs and compact discs are produced by inserting a disc (stamper) having protrusions corresponding to minute signal bits into a mold cavity, and injecting molten resin into the cavity. It was molded using so-called injection molding, which involves injection-filling.

However, compact disks with a small diameter of 12 cm and good moldability, and video disks made of acrylic resin with good fluidity even though they have a large diameter of 20 to 30 cm compared to compact disks, are conventional. Although it can be molded by injection molding without much problem,
A disk with a diameter of 20 to 30 cm is made of polycarbonate resin (compared to acrylic resin, it is less fluid, but it has less moisture absorption, so it has good adhesion to the aluminum reflective film that is deposited after molding, has high heat resistance, and has good impact resistance. Excellent.Also, polycarbonate resin has traditionally been used for compact discs.
DISK (abbreviation for Direct Read After Write) that both writes and reads signals, and requires low birefringence due to internal distortion, is difficult, and in that case, low distortion is required. This is done by injection compression molding, which has excellent transferability.

There are two types of injection compression molding methods used for disk molding:

One is to increase the mold cavity volume before starting the injection process, perform injection filling in that state, and then clamp the mold again after filling is completed to apply compressive force to the resin. In this method, molten resin is injected into a completely closed mold under low pressure, the mold is opened by the injection pressure, and after injection and filling, the mold is strongly clamped to apply clamping force to the resin. be. In either of these methods, the mold is opened to an excess amount for compression, and the resin filled therein is compressed by clamping the mold.

[Problems to be Solved by the Invention] However, even with the injection compression molding described above, the molded draw disk is on the edge of the practical range, and when setting stable molding conditions,
Disc molding requires advanced molding technology and a great deal of time, and requires even higher density.
I still wasn't satisfied with it.

This invention has been made in view of the above circumstances, and an object of the present invention is to provide a new injection compression molding method that can increase the filling speed and improve transferability compared to conventional methods, and can also reduce the orientation of resin. With the goal.

[Means for Solving the Problems] This invention for the above purpose provides a video disk,
A cavity for molding a disk-shaped recording medium such as a compact disk is variably formed from a fixed mold and a movable mold that fit together, and when the volume of the cavity becomes large, injection and filling of molten resin is started. When the amount reaches the required amount that does not fill the cavity, the movable mold is moved at a predetermined speed while injection filling is continued to start reducing the cavity volume, and injection filling is started immediately before the molten resin is completely filled. After stopping, a predetermined pressure is applied to the movable mold to completely fill it with molten resin and control the pressure, and the movable mold is kept cooled under that pressure.

[Function] In this invention, injection filling is started in a state where the cavity volume is formed larger than the cavity volume taking into account the compression allowance of the cavity, so injection can be started at low pressure and high speed, and a predetermined amount of resin is filled. The movable mold is moved forward again at the point where the mold is moved forward, so the resin in the cavity is spread out, and the decrease in the spreading speed of the resin as injection filling progresses is alleviated.
Since the force is applied in a direction perpendicular to the resin flow direction, flow direction orientation is reduced.

Injection is completed immediately before the cavity is filled, and the cavity is filled by the advancement of the movable mold, so that no unnecessary stress is left on the gate portion.

Furthermore, after that, pressure is applied to the movable mold to uniformly apply compressive force to the entire surface of the molten resin, and by controlling the compressive force, low distortion and relaxation of cooling shrinkage are achieved.

[Embodiment] In the figure, 1 is a movable mold, 2 is a fixed mold, and a cavity 3 for molding a disc-shaped recording medium (eg, a video disc, a compact disc, etc.) is formed by fitting the two molds.

The volume of this cavity 3 can be changed by moving the movable mold 1, and while the movable mold 1 presses the molten resin 5 injected and filled into the cavity 3 from the passage 4 provided in the fixed mold 2. , the cavity 3 has a depth sufficient to reduce the volume and form the recording medium 6 in a disk shape.

As shown in FIG. 5, the movable mold 1 has a movable platen 7.
The stationary mold 2 is attached to a stationary platen 8.

The movable platen 7 is provided so as to be able to slide back and forth on a tie bar 10 that is horizontally suspended between the fixed platen 8 and the mold clamping cylinder 9, and its back side is connected to a mold clamping ram 11 inserted into the mold clamping cylinder. has been done.

The mold clamping ram 11 has a small diameter cylinder part inside, and the booster ram 1 is inserted into the cylinder part from the rear.
2 is inserted, and the cylinder portion is divided into oil chambers 13 and 14 by the large diameter portion at the tip of the booster ram 12.

Further, the mold clamping ram 11 divides the interior of the mold clamping cylinder 9 into oil chambers 15 and 16.

Next, the molding method will be explained.

The movable mold 1 and fixed mold 2 in the open state shown in FIG. 1 are closed to the state shown in FIG. 2 by moving the movable platen 7 at high speed.

The depth of the cavity 3 formed by closing the mold is preferably within 3 times the wall thickness of the molded product, and once the cavity 3 of a predetermined volume is formed by closing the mold, the movable platen 7 is stopped. , the cavity 3 is filled with molten resin 5 from an injection device 17 whose nozzle touches the resin path 4 of the fixed mold 2. When the molten resin 5 reaches a predetermined filling amount (40 to 80%) before filling the cavity 3, the movable platen 7 is moved forward again at a predetermined speed without stopping the injection filling. Move mold 1 toward fixed platen 2.

In this state, the cavity volume is reduced as the mold closes, and the molten resin 15 in the cavity 3 is spread out, so that the decrease in the spreading speed of the molten resin tip due to the progress of injection filling is alleviated, and the molten resin is applied a force perpendicular to the flow direction, thereby reducing orientation in the flow direction.

Further, the spreading speed of the molten resin 5 in this state is controlled by controlling the forward speed of the movable platen 7.

Then, the injection is completed just before the cavity 3 is completely filled, and as the movable platen moves forward further, the cavity 3 has a volume that takes into account the compression, as shown in Figure 3, and the cavity 3 is filled with molten resin. is satisfied by.

Filling with molten resin 5 is stopped immediately before complete filling. Then, pressure is applied to the movable mold 1 together with the movable platen 7, the molten resin 5 is pressurized and compressed, and the disc-shaped recording medium 6 is molded therein. In addition, cooling solidification is similar to the compression process in ordinary injection compression molding.
V-T curve (a property of plastic materials that shows the relationship between pressure, specific volume, and temperature; the horizontal axis is temperature, the vertical axis is specific volume, and the specific volume at each temperature under a given pressure is plotted there) This is done by controlling the compressive force in multiple stages according to the plot.As a result, when the temperature is lowered under a certain pressure, it can be seen how the specific volume decreases accordingly. This further reduces distortion due to residual stress, alleviates cooling shrinkage and orientation, and improves transferability.

[Effects] According to the present invention, in addition to inheriting the effects of conventional injection compression molding, the fluidity at the start of injection and during the injection process is increased, and high-speed, low-pressure filling is possible. This further improves transferability and reduces orientation. Moreover, they are synergistically improved by the next compression process, so molding quality can be greatly improved.
Since the molding conditions can be expanded, even when molding a thin-walled, large-diameter molded product using a material with poor fluidity, it is possible to easily mold the molded product.

[Brief explanation of drawings]

The drawings illustrate the injection molding method for a disk-shaped recording medium according to the present invention, and FIGS. 1 to 4 are cross-sectional views of a mold showing the steps in order, and FIG. 5 is a schematic cross-sectional view of an injection molding machine. It is. 1... Movable type, 2... Fixed type, 3... Cavity, 5... Molten resin, 6... Disk-shaped recording medium.

Claims (1)

[Claims] 1. A cavity for molding a disc-shaped recording medium such as a video disc or a compact disc is variably formed from a fixed mold and a movable mold that fit into each other,
Injection filling of the molten resin is started when the volume of the cavity is large, and when the filling amount reaches the required amount that does not fill the cavity, the movable mold is moved at a predetermined speed while continuing injection filling. Then, injection filling is stopped just before the molten resin is completely filled, and a predetermined pressure is applied to the movable mold to completely fill the molten resin and the pressure is controlled. A method for injection molding a disc-shaped recording medium, which is characterized by performing cooling maintenance.