JPS6345293B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for injection molding a plastic disk having an opening in the center and minute pits on the surface. The present invention is particularly applicable to the injection molding of video disc discs among plastic discs. A video disc is obtained by first manufacturing a master disc, then making a stamper from the master disc by electroforming, and attaching this stamper to a mold and performing injection molding. Video disc systems are broadly classified into laser systems and capacitance systems based on playback methods. The laser method uses acrylic resin or vinyl chloride resin with excellent optical properties, and the capacitive method uses vinyl chloride resin mixed with minute carbon particles. No matter which resin is used, when molding a disc, unless the tiny pits in microns are accurately replicated, clear images and sounds will not be reproduced. For this reason, in injection molding, the pit must be accurately replicated and distortions and variations in wall thickness must be removed from the molded disk. For this reason, in the present invention, the resin is plasticized uniformly and with good fluidity using a high compression ratio screw with a shallow metering groove depth, and then injected into the mold cavity into a small pit provided in a thin disk with high flow resistance. succeeded in filling the area with resin. On the other hand, injection molding of video discs requires a special structure in the mold. There are already US patents 3989436, 4085178 and 4260360 for molds for video discs. In both cases, the center of the disk is punched out, the sprue is pushed out, and then the disk body is pushed out.However, in the invention, the punch is fixed and the weld surface of the mold cavity is not opened, and the male and female molds of the mold cavity are fixed. is moved to cut the center part. The present invention is equipped with means different from the above-mentioned inventions so that when punching out the center of the disk in order to perform fully automatic molding of a video disk, the punched portion is always attached to the punch side. Next, one embodiment of the present invention will be described according to the drawings. 1 is a stationary plate fixed to the machine base of the injection molding machine, and 2 is a stationary side mold mounting plate fixed to the stationary plate 1. 3 is a sprue bushing provided at the center of the stationary mold mounting plate 2. The sprue bushing 3 is provided with a medium passage 4 for controlling the temperature of the molten resin. 5 is the first mold piece and 6 is the second mold piece.
The first mold piece 5 and the second mold piece 6 are fixed by screws. The tip of the sprue bushing 3 is connected to the first mold piece 5 and the second mold piece as shown in the figure.
It is fitted into the mold piece 6. Reference numeral 7 denotes a spiral cooling groove provided in the second mold piece 6, and the groove is made deeper toward the center so that the cooling effect becomes greater. 8 is an introduction pipe for injecting a medium into the cooling groove 7. 9
1 is a third mold piece, and 10 is a spiral cooling groove provided in the third mold piece 9, and the groove is made deeper toward the center so that the cooling effect becomes greater. Reference numeral 11 denotes an annular cavity of a disk provided between the second mold piece 6 and the third mold piece 9. 12 is a stamper provided on the third mold piece 9, 13 is an outer stamper holder, and 14 is an inner stamper holder. 15 is an introduction path for injecting a medium into the cooling groove 10. 16 is a fourth mold piece. 17 is a guide bush fixed to the fourth mold piece 16. 18 is a fifth mold piece. Reference numeral 19 denotes a disk ejector, the tip end 19a of which is fitted inside the guide bush 17, and the rear end 19b screwed to a flange 21 that can reciprocate within a space 20 provided in the fifth mold piece 18. . 22 is the sixth mold piece. 23
is a punch for cutting the sprue, and the punch 23
The front part 23a of the disk ejector 19 fits into the inner hole of the disc ejector 19, and the rear cylindrical part 23b of the sixth mold piece 22
and a space 25 provided in each of the seventh mold piece 24
and is inserted into the space 26. 27 is punch 2
A notch 23d is provided in the cylindrical rear end portion 23b of the rear part of No. 3.
This is an ejector bar that is reciprocatably inserted into the inside. 28 is the sixth mold piece 22 and ejector bar 2
This is a spring interposed between 7 and 7. Reference numeral 29 designates a pair of guide pins whose one end is fixed to the ejector bar 27 with a screw and the other end is loosely fitted into the flange 21 as shown. 29a is a collar fitted onto the outer periphery of the guide pin 29. A sprue ejector 30 has a sludge reservoir 30a protruding from the end face of the punch 23 from which the sprue is ejected, and the rear end of the sprue ejector 30 is fixed to the ejector bar 27. A sprue gripping rod 31 passes through the center of the sprue ejector 30 and has its rear end fixed to the cover 23c of the cylindrical rear end 23b of the punch. 32 is the eighth mold piece, and 33 is the ninth mold piece. 34
35 is a punch driving hydraulic cylinder for reciprocating the punch 23, and 35 is the hydraulic cylinder 34.
This is a hydraulic ram inserted into the 36 is a movable mold mounting plate. 37 is a movable platen of the injection molding machine.
38 is an ejector pin having one end fixed to the ejector bar 27. Reference numeral 39 is an ejector rod whose one end is fixed to the machine base 40, and the other end hits the ejector pin 38 when the movable platen 37 is retreated to a certain position. 41 is a ram of a mold clamping cylinder that reciprocates the movable platen 37. 42 is a mold separation hydraulic cylinder that separates the stationary side mold mounting plate 2 and the first mold piece 5; Fixed. Reference numeral 44 denotes a bracket fixed on the fixed platen 1, and is fixed to the tip of the ram 43a inserted into the hydraulic cylinder 42. 45 is the second mold piece 6 and the third mold piece 9
When the sprue and disk are opened, the robot arm lowers into the gap and takes out the formed sprue and disk. Next, the operation will be explained. The mold is clamped and the molten resin is injected into the annular cavity while the mold is clamped. After the resin in the annular cavity has solidified, the mold clamping side oil chamber of the mold clamping cylinder (not shown) is communicated with the atmosphere and the mold separation hydraulic cylinder is activated, and the fixed side mold is attached as shown in Figure 2. The plate 2 and the first mold piece 5 are separated. At this time, the sprue bush 3 is fixed to the fixed side mold mounting plate 2, and the annular cavity 11
Since the sprue moves to the right in the figure while being held between the second mold piece 6 and the third mold piece 9, the sprue is reliably taken out from the sprue bush. Next, oil is supplied to the port 34a of the punch driving hydraulic cylinder 34, and the punch 23 is advanced to cut the sprue (FIG. 3). When the sprue is cut and pushed out, the sprue gripping rod 31
The sprue is securely gripped by the punch. After the sprues are cut, when the movable platen 37 is moved back, the second mold piece 6 and the third mold piece 9 are separated and the mold is opened (FIG. 4). When the movable platen 37 retreats to a predetermined position, the ejector rod 39 is fixed to the machine base 40, so that the ejector pin 38 is prevented from retreating, and the ejector bar 27 is also prevented from retreating, so that the sprue cut by the sprue ejector 30 protrudes. be done. At this time, the robot arm 45 descends to an appropriate position to take out the molded product, and the robot arm 45 attracts the protruding sprue. At the same time, when the movable platen 37 further retreats, the collar 29a prevents the flange 21 from retreating, and the disk ejector 19 is operated to eject the disk and attract it to the robot arm 45. The robot arm 45 rises while adsorbing the disk and sprue and transports the disk and sprue to another predetermined position. After confirming that the disc and sprue have been removed from the mold, the mold is closed and the molding cycle ends. As explained above, in the present invention, when cutting a sprue, when separating the fixed side metal mounting plate 2 and the first mold piece 5, the punch for cutting the sprue is not fixed and cut, but the sprue is cut once from the fixed side metal plate. When the mounting plate 2 and the first mold piece 5 are separated, the punch is also moved back together with the mold, the sprue is surely taken out from the sprue bushing, and the sprue is cut later, so that no sprue remains on the sprue bushing side. Therefore, the present invention has made it possible to reliably take out the disk and sprue using a robot arm during disk injection molding, thereby making highly efficient disk injection molding possible.

Additionally, the present invention provides a spiral cooling groove for cooling the annular cavity. Cooling grooves with a constant groove depth are generally used, but heat dissipation is poor in the center of the disk, and when the molten resin cools, large differences in temperature distribution occur in the thin disk, causing sink marks and requiring high precision. It is not suitable for molding video discs. In the present invention, the cooling grooves of the annular cavity are made deeper toward the center so that cooling is performed at a uniform temperature. Furthermore, a temperature change occurs at a portion where a conduit for causing a medium to flow into or out of the spiral cooling groove crosses the cooling groove. In the present invention, as shown in FIGS. 5 and 6, the introduction pipe 8 that crosses the spiral cooling groove is inserted into the hole 8a, so that the temperature of the introduction pipe is not directly transmitted to the cooling groove. This is one of the features of the present invention.

[Brief explanation of drawings]

1 to 4 are front cross-sectional views of the device of the present invention showing different operating states, and FIG. 5 is a cross-sectional view taken along the line of FIG. 1: Fixed plate, 2: Fixed side mold mounting plate, 3: Sprue bush, 5: First mold piece, 6: Second mold piece,
9: Third mold piece, 11: Annular cavity, 19:
Disk ejector, 23: Punch, 30: Sprue ejector, 36: Movable side mold mounting plate, 37:
Movable board.

Claims (1)

[Claims] 1. A fixed side mold mounting plate is fixed to a fixed platen of an injection molding machine, a sprue butting is provided on the fixed side mold mounting plate, and the tip of the sprue butting is attached to the fixed side metal plate. A mold spacing that slides into a first mold piece adjacent to the mold mounting plate and a second mold piece fixed to the first mold piece, and separates the fixed side mold mounting plate and the first mold piece. In a mold provided with an annular cavity formed by closing a second mold piece and a third mold piece fixed to the movable plate side mold mounting plate side, the center of the annular cavity is provided with a hydraulic cylinder for A punch is provided to cut the sprue part formed in the part, a hydraulic cylinder for reciprocating the punch is fixed to a mold piece fixed to the mold mounting plate on the movable platen side, and a sprue ejector is provided which protrudes from the end face of the punch. The rear end of the sprue ejector is fixed to an ejector bar so that the sprue ejector moves forward when the punch moves forward to cut the sprue, and the ejector bar is reciprocatably inserted into a notch in the rear cylindrical end of the punch. Fixing one end of the ejector pin to the movable platen side of the ejector bar, and fixing one end of the ejector rod to the machine base, which prevents the ejector pin from moving from a predetermined position when the movable platen moves in the direction of opening the mold; On the other hand, a disk ejector is provided that slides on the outer periphery of the punch that cuts the sprue, one end of the guide pin is fixed to the fixed plate side of the ejector bar, and the other end of the guide pin is attached to the rear end of the disk ejector bar. is movably engaged, and after the sprue ejector is operated between the ejector bar and the rear end of the disk ejector, a collar is inserted into the guide pin so that the disk ejector operates. An injection device characterized in that a spiral cooling groove is provided on each back surface of the annular cavity of the mold piece. 2. A fixed side mold mounting plate is fixed to a fixed platen of an injection molding machine, a sprue butting is provided on the fixed side mold mounting plate, and the tip of the sprue butting is attached to the first side adjacent to the fixed side mounting plate. A mold separation hydraulic cylinder is provided that slides into the mold piece and a second mold piece fixed to the first mold piece and separates the fixed side mold mounting plate and the first mold piece, and a second mold piece. In a mold provided with an annular cavity formed by closing a mold piece and a third mold piece fixed to the movable mold mounting plate side, after injecting molten resin into the annular cavity and solidifying the resin. The mold separating hydraulic cylinder is operated to separate the stationary mold mounting plate and the first mold piece, and then by a punch operated by a hydraulic cylinder fixed to the movable mold mounting plate. Cut the sprue in the center of the annular cavity so that it attaches to the tip of the punch, and then
The mold piece and the third mold piece are opened to create a gap, and in order to take out the molded product, the robot arm is lowered into the gap, and the sprue attached to the punch side and the disk attached to one side of the annular cavity are moved to the sprue ejector. An injection molding method characterized in that the molded product is ejected from the robot arm side using a disk ejector.