JPH09131777A - Injection molding method of information recording disc - Google Patents

Abstract

PROBLEM TO BE SOLVED: To mold an information recording disc out of a resin having low heat history by supplying a material resin to an injection device having a venting opening by omitting preliminary drying and melting and kneading the material resin by the injection device. SOLUTION: A green material resin is supplied into a cylinder 1 from a supplying opening 4. The pelletized material resin is sent to the front part of the cylinder 1 by rotation of an injection screw 2, compressed, melted, and kneaded. Moisture and volatile vaporized by heat compression are sucked together with inert gas by a venting opening 5 whose pressure is always being reduced, and exhausted to the outside of the cylinder 1. The resin which is measured in the front part of the cylinder 1 is moved by the forward movement of the injection screw 2 so as to fill a cavity 9 in a mold 8 with it from a nozzle 7 at the head end of the cylinder 1 through a hot runner 10.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of injection molding an information recording disk by omitting predrying of a material resin.

[0002]

2. Description of the Related Art Synthesized resins are small particles (granular sugar-like) and contain unreacted monomers, so they are difficult to use for molding. Therefore, they are heated and melted into pellets of a certain particle size before being used as a material. Used as a resin.

[0003] Even when prepared into pellets, synthetic resins are generally large and small, but are hygroscopic, so most of them are pre-dried before being used for molding. This pre-drying takes time, and if the dryer is not properly controlled, fine foreign matter in the air adheres and carbonizes, which may appear as black spots on the molded product, resulting in a defective product. Especially molded products are optical disks, magnetic disks,
In an information recording disk such as a magneto-optical disk, even a very small black spot will be an obstacle to reproduction.

[0004]

For this reason, the material resin is heated at least three times including the time of injection molding, which tends to cause deterioration of physical properties, particularly strength deterioration, and transparency. May cause problems, so
It is not preferable for molding information recording disks such as optical disks and magneto-optical disks.

The present invention has been conceived in view of the above circumstances, and its purpose is to reduce the number of times the resin is melted by heating to suppress the heat history, thereby making it possible to mold a high quality information recording disk. A simple injection molding method may be provided.

[0006]

According to the present invention for the above object, a material resin such as polycarbonate is supplied to an injection apparatus having a vent port without predrying, and the material resin is melted and kneaded by the injection apparatus. At the same time, the water content of the resin is vaporized by heating and discharged from the vent port to the outside of the cylinder, and the molten resin is weighed in the front part of the heating cylinder, and then a mold having a cavity for forming the information recording disk inside is formed. Injection filling is performed to form a thin information recording disk.

In the molding method according to the present invention, since heating by pre-drying before molding is omitted, the heat history of the resin is extremely small, deterioration of the resin due to heating, particularly strength reduction, is suppressed, and in addition, foreign matter Since there are few chances of mixing, generation of black spots due to carbonization of foreign matters, which has been a problem up to now, is solved, and molding defects due to hydrolysis are also solved, so that a high quality information recording disk can be obtained.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a vent type injection molding machine capable of carrying out the injection molding method of the present invention. In FIG. 1, reference numeral 1 denotes a heating cylinder, which is not shown in the drawing, but a band heater is attached to the outer circumference. . This heating cylinder has an injection screw 2
Is installed so as to be rotatable and movable back and forth, and a material supply port 4 is provided upward at the rear end of the cylinder fitted with the holding cylinder 3.

A vent port 5 is formed in the upper part of the cylinder in front of the supply port 4. Although not shown in the drawing, a decompression suction device and an inert gas pressure feeding device are connected to the vent port 5 and the supply port 4, respectively.

In such a vent type injection apparatus, the injection screw 2 is rotated as usual, and an inert gas such as nitrogen gas is pressure-fed from the supply port 4 into the cylinder. At the vent port 5, the pressure inside the cylinder is reduced.

In this state, when the undried material resin, which has been sent to the hopper 6 in advance, such as polycarbonate, is supplied from the supply port 4 into the cylinder, the material resin of the pellet is sent to the front of the cylinder by the rotation of the injection screw 2. Compressed.

In the process leading to this compression, the material resin is kneaded while being melted by the heat from the heating cylinder 1 and the breaking heat generated by the rotation of the screw. Since the melt-kneading is performed in the inert gas atmosphere generated in the cylinder between the supply port 4 and the vent port 5, oxidation due to heating is prevented, and moisture and volatile components vaporized by heating and compression are removed from the cylinder. Occurs within.

These gases are sucked together with the inert gas into the vent port 5 which is constantly decompressed and removed outside the cylinder, and do not remain in the plasticized resin ahead of the vent port 5. Therefore, even if the material resin absorbs moisture, the resin measured in the front portion of the cylinder due to the backward movement of the injection screw 2 due to the resin pressure does not cause yellowing due to oxidation or deterioration due to hydrolysis.

The measured resin is filled by the forward movement of the injection screw 2 through the hot runner 10 from the nozzle 7 at the tip of the cylinder into the cavity 9 inside the mold 8. This cavity 10 is for a thin information recording disk. Since a stamper is stretched on one side of the cavity, the pits formed on the stamper are transferred to one side of the disk molded there, and the thin wall made of polycarbonate is used. It becomes an information recording disk (about 0.6 to 1.2 mm).

As described above, even if the material resin used for injection molding is an undried resin, there is no problem in performing injection molding, and the resin itself has a smaller heat history than the material resin predried. Therefore, it is preferable in terms of physical properties, and since polycarbonate does not impair transparency, it becomes possible to perform injection molding of high-quality optical discs, magneto-optical discs, etc. with improved birefringence as compared with conventional ones. Moreover, since the preliminary drying is omitted, the molding cost can be reduced.

[Brief description of the drawings]

FIG. 1 is a vertical cross-sectional side view of a main part of an injection molding machine with a vent type screw used to carry out an information recording disk injection molding method according to the present invention.

[Explanation of symbols]

 1 Injection Cylinder 2 Injection Screw 4 Supply Port 5 Vent Port 7 Nozzle 8 Mold 9 Cavity

Claims (2)

[Claims] 1. A material resin is supplied to an injection device provided with a vent port while omitting preliminary drying, and the material resin is melted and kneaded by the injection device, and moisture of the resin is vaporized by heating to vent the port. From the cylinder to the outside of the heating cylinder, the molten resin is weighed in the front part of the heating cylinder, and then injection-filled into a mold that has a cavity for molding the information recording disk to form a thin information recording disk. A method for injection-molding a characteristic information recording disk. 2. The method of injection molding an information recording disk according to claim 1, wherein the material resin is polycarbonate.