JP3527933B2 - Injection molding method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an injection molding method for molding an information recording disk using polycarbonate before pelletizing as a molding material. [0002] Resin before pelletizing is inexpensive, but it is difficult to use it as it is as a material resin for injection molding. Therefore, in injection molding, pellets having a certain particle size are processed and then used as a forming material. The pelletizing of the resin is performed using a vented extruder. After the molten resin is extruded into a strand in a heating cylinder, the resin is cut into a predetermined size. Further, during melting in a heating cylinder of an extruder, volatile matters such as water and unreacted monomers in a material resin, which cause molding failure, are discharged by a vent, and any use of the pelletized material resin is unsatisfactory. So as not to cause any trouble. [0004] However, most of the resin is pre-dried before it is used for molding because the resin is hygroscopic even though its size is large. This pre-drying requires a long time, and poor control of the dryer may cause fine foreign matters in the air to adhere and carbonize the fine foreign substances to appear as black spots on the molded product, resulting in a defective product. In particular, when the molded article is an information recording disk such as an optical disk, a magnetic disk, and a magneto-optical disk, even a very small black spot can cause a reproduction obstacle. The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an injection molding method in which inexpensive polycarbonate before pelletizing is directly used as a material resin for an information recording disk. SUMMARY OF THE INVENTION The present invention according to the above-mentioned object is directed to a method for removing polycarbonate before pelletizing by using a vent port.
The material resin to be fed into the hopper of the injection molding machine equipped with, without pre-drying before using the polycarbonate for molding, melt kneading in an inert gas atmosphere, in a mold with a stamper stretched on one side To form a thin information recording disk. In the molding method according to the present invention, the heating during pelletizing of the polycarbonate and the heating by preliminary drying before the molding are omitted, so that the heat history of the polycarbonate is extremely small, and the deterioration of the polycarbonate due to the heating, particularly, the decrease in strength, is reduced. Not only is it suppressed, but also there are few opportunities for foreign matter to be mixed in, which solves the problems of black spots caused by carbonization of foreign matter, and prevents oxidation during melt-kneading. Molding defects due to decomposition are also resolved. In addition, the material price is extremely low as compared with the case where the material price is adjusted to the pellet, and the molding cost is reduced. FIG. 1 shows a vent type injection molding machine which can carry out the injection molding method of the present invention. In the figure, reference numeral 1 denotes a heating cylinder, which is not shown in the figure, and has a band heater attached to the outer periphery. An injection screw 2 is provided inside the heating cylinder 1 so as to rotate and move forward and backward, and a material supply port 4 is provided upward at a 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, the vent port 5 and the supply port 4 are connected to a reduced pressure suction device and an inert gas pressure feeding device, respectively. In such a vent-type injection device, the injection screw 2 is rotated as usual, and an inert gas such as nitrogen gas is fed from the supply port 4 into the cylinder. At the vent port 5, the pressure in the cylinder is reduced. In this state, the polycarbonate before pelletizing previously fed into the hopper 6 is supplied to the supply port 4.
When the injection screw 2 is supplied to the inside of the cylinder, the polycarbonate of small particles (granule sugar) is sent to the front of the cylinder and compressed by rotation of the injection screw 2. In the course of the compression, the polycarbonate is melted and kneaded by the heat from the heating cylinder 1 and the shear heat generated by the rotation of the screw. Since the melt-kneading is performed in an inert gas atmosphere generated in the cylinder between the supply port 4 and the vent port 5, oxidation by heating is prevented. In the cylinder, steam and residual monomer gases are generated by the heating and compression. These gases are sucked together with the inert gas through the vent port 5, which is constantly depressurized, and are discharged out of the cylinder. No longer remains in the plasticized resin ahead of the vent port 5. Therefore, even if the polycarbonate before pelletizing contains water, residual monomers, etc., the retreating of the injection screw 2 due to the resin pressure causes the polycarbonate measured in the front part of the cylinder to have yellowing due to oxidation and hydrolysis due to hydrolysis. Deterioration does not occur, and the same physical properties as when polycarbonate prepared as pellets are pre-dried and used are maintained. The polycarbonate weighed in the front part of the cylinder is injected and filled by the advancement of the injection screw 2 from the nozzle 7 at the tip of the cylinder into the disk molding cavity 9 inside the mold 8 through the hot runner 10. Is done. A stamper (omitted in the figure) is stretched on one side of the cavity 9, and a disk formed by the stamper is thin (about 0.6 to 1.2 mm) in which pits on the stamper surface are transferred on one side. It becomes an information recording disk. As described above, according to the present invention, the material resin of the information recording disk used for injection molding is polycarbonate before pelletizing, and the preliminary drying before use for molding is also omitted. Even if it is, there is no problem in performing injection molding, and the polycarbonate itself also has a smaller heat history than the material after being adjusted to pellets, so it is preferable from the viewpoint of physical properties, and the inherent transparency of polycarbonate is also impaired. Therefore, it is possible to perform injection molding of a high-quality optical disk, a magneto-optical disk or the like with low cost and improved birefringence. In the above description, a vent-type screw-injection molding machine is used. However, the present invention is practiced using a vent-type pre-plastic injection device having a vent port on the plasticizing cylinder side. Is also possible. Therefore, the present invention is not generally limited to injection molding by an in-line screw type injection device.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a vertical sectional side view of a main part of a vent-type screw-injection molding machine used for carrying out an information recording disk injection molding method according to the present invention. [Description of Signs] 1 Heating cylinder 2 Injection screw 4 Supply port 5 Vent port 7 Nozzle 8 Mold 9 Cavity

──────────────────────────────────────────────────続 き Continuation of the front page (51) Int.Cl. ⁷ Identification code FI B29L 17:00 B29L 17:00 (56) References JP-A-62-124923 (JP, A) JP-A-3-34820 (JP) JP-A-3-34821 (JP, A) JP-A-6-293021 (JP, A) JP-A-57-167230 (JP, A) JP-A-63-21019 (JP, U) (58) Field surveyed (Int. Cl. ⁷ , DB name) B29C 45/00-45/84

Claims (1)

(57) [Claims] [Claim 1] Polycarbonate before pelletizing
Is fed into a hopper of an injection molding machine having a vent port. <br/> A material resin is used , and the polycarbonate is used for molding.
Melting and kneading in an inert gas atmosphere without pre-drying before injection filling into a cavity in a mold with a stamper stretched on one side to form a thin information recording disk Injection molding method.