JPS60247532A - Formation of disc-shaped recording medium - Google Patents

Abstract

PURPOSE:To permit high-cycle molding to be performed as well as to raise the accuracy of a disc molding by a gate cutting method by a method in which under the condition that the molding in the gate portion is in a semi-hardened state and the same gate capacity is maintained, the gate portion is relatively moved. CONSTITUTION:In the first gate 32 and the clamping region in the surrounding of the gate 32 in the least, the molding is preferably in a semi-hardened state. In the gate cutting, the tip face 143 of the sprue bush 4 becomes a no-load state or a negative pressure state by drawing pressure oil from an operating chamber 14. The situation can be optionally obtained by regulatively drawing the pressure oil. In short, the sprue bush side becomes a movable state by a slight force. When a cut pin 5 is advanced at the timing, the tip face 143 of the sprue bush 4 is retracted at the same gate volume correspondingly to the advancing force. As a result, cutting can be performed without application of compression force to the first gate 32.

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Technical field to which the invention pertains The present invention relates to a method for molding a disc-shaped recording medium (hereinafter referred to as a disc) such as a video disc or an audio disc. The present invention relates to a method of forming a disk center hole.

(2) Prior art and its problems Regarding disk molding, injection molding has been attempted in consideration of production efficiency. During injection molding, the center hole of the disk is formed by a gate cut method using thermoplastic synthetic resin, as shown in Japanese Patent Publication No. 58-58214. As shown in the same publication, the gate cut method is
Generally, by advancing a cut pin fixed to the ejector plate, the sprue bush is retreated through the resin component solidified in the gate gap, and by varying the position of the gate gap with respect to the cavity cross section, shearing of the center hole is prevented. It was something to do.

However, according to the above method, gate cutting is not performed until the molten resin has solidified on the information track surface and the gate portion has been sealed. In gate seal bending, the gap between the gate parts is compressed as the cut pin moves, creating a stress gradient in the product around the gate part, forming a disk with approximately the same value of birefringence. It's impossible. the result,
The molding cycle was lengthened because of the waiting time required for the product to solidify. Normally, one cycle took about 20 to 30 seconds.

Second, due to repeated cutting after the product has solidified, it is inevitable that the tip end surface of the canting pin will become rounded. Due to the sagging, the disk center hole has a cross section that is oriented toward or away from the center of rotation, resulting in a decrease in concentricity accuracy. With continued use, the accuracy described above gradually deteriorated. Currently, cut pins continue to be used even if there are defective products, regardless of the decrease in concentricity accuracy, and they are replaced only when there are a large number of defective products.

” - In view of the actual situation, the present inventors conducted repeated research and obtained the first finding. One of the reasons for the decrease in disc accuracy is gate cuts. That is, when gate cutting is performed in a solidified state of the product, chips, which are fine particles of the product, are generated from the cut portion, and these chips get mixed into the information track surface, causing a major cause of erroneous signals. It is well known that fine particles left over from the previous molding cycle get mixed into the information track and cause a difference in birefringence.
It was confirmed that the biggest cause was chips. The chips are
The amount increases due to the wobbling of the cut pin,
This further reduced accuracy.

It has been found that in order to prevent the generation of the chips mentioned above, it is sufficient to shear the product in a semi-solidified state at the gate portion. Here, the semi-solid state refers to a state in which the molten resin has been cooled to below its softening point and formed into a single shape, and it also refers to a state in which it has a viscosity that does not generate chips when cutting the product. , force 4z), it was necessary to avoid stress.

(3) Purpose of the invention The present invention has been further developed based on the above knowledge, and aims to further improve the precision of gate-cut disk products and enable high-cycle molding. This is its main purpose.

(4) Features of the Invention The feature of the method for molding a disk-shaped recording medium according to the present invention is that relative movement of the gate portion is obtained while the gate volume remains the same while the product is in a semi-solidified state at the gate portion.

Hereinafter, the present invention will be explained in detail based on the drawings.

(5) An Embodiment of the Invention The drawings show an embodiment of the method for molding a disc-shaped recording medium according to the present invention, and FIG. The figure is a perspective view of the cut pin of the same mold, Figure 3 is a sectional view of the main part of the same mold, Figure 4 is a sectional view of the main part showing the gate cut state, and Figure 5 shows the protruding state of the cut part. It is a sectional view of the same main part.

Thus, the mold comprises a fixed mold plate 1 and a movable mold plate 2 to form a cavity 3 having a disk molding space, a sprue bush 4 is attached to the cylinder structure on the fixed side, and a cut pin 5 is opposed to the movable side. installed.

To explain in detail from the fixed side, the head side and barrel side of the cylinder are composed of the fixed receiving plate 11 and the hole 13 of the fixed mounting plate 12, and the bottom side is composed of the bush cylinder 41,
The remaining space where the protrusion 42 of the bushing cylinder 41 is fitted into the hole 13 forms an action chamber 14 for pressurized oil.

The sprue bush 4 includes a large diameter portion 43 mounted in the cylinder space and a small diameter portion 44 extending from the large diameter portion 43.
It consists of The large diameter portion 43 is formed by a stepped portion 46 having a larger diameter than the spherical portion 45, and a sealing material is provided in a groove 47 on the outer peripheral surface of the large diameter portion 43. The stepped portion 46 is
It faces the action chamber 14 and receives pressure oil from the flow path 15. As the sealing material, a wear-resistant wear ring or the like is used. In the figure, 49 is a sprue hole, 141. , , is a sealing material between each member, 142 is a bushing cylinder 41
This is a fixing bolt.

Furthermore, the small diameter portion 44 of the sprue bush 4 is connected to the fixed receiving plate 1.
It is inserted into the hole 1B of No. 1 so as to be movable forward and backward, and its tip end surface 143 is normally aligned with the core surface of the cavity 3 and protrudes. Note that 17 is a refrigerant passage in the fixed mold plate l.

Next, to explain the movable side, the sprue ejector pin 6 and cut pin 5 located in the center of the cavity 3,
The ejector pin 7, the cylindrical member 21, and the stamper inner periphery pressing member 8, which constitute the clamping area of the product and are respectively fitted onto the outer periphery of the cut pin 5, and the stamper 31 and the outer periphery pressing member 9, which constitute the information track surface area. Consists of.

”-The distribution pin 5 has an elongated small diameter portion 51 and a large diameter portion 52.
The large diameter portion 52 is a cut pin cylinder 53.
The small diameter portions 51 are fitted inside the ejector pins 7 so as to be movable forward and backward, and the rear ends are fixed to an ejector plate (not shown). The small diameter portion 51 has the same cross section as the small diameter portion 44 of the sprue bushing 4, and is arranged to face each other so as to be movable back and forth, and its tip surface 54 protrudes beyond the movable mold surface of the cavity 3 and is connected to the sprue tip surface +43. A first gate 32 is configured. Inside the cut pin 5, from the tip side, there is a slack well portion 55, a small hole 56. This small hole 56
A communication hole 57 with a larger diameter and a cylinder hole 5 with an even larger diameter.
8, and a sprue ejector pin 6 is fitted into each hole 5B, 57.58 so as to be movable forward and backward. The large diameter portion 52
An end surface 59 of the cut pin cylinder 53 faces an action chamber 151 defined by the cut pin cylinder 53. In addition, 152 is a flow path provided in the cut pin cylinder 53 and communicates with the action chamber 151, 153 is a refrigerant flow path provided in the large diameter portion 52,
1549. is a sealing material.

The sprue ejector pin 6 consists of a pin-shaped protruding pin part 61, a blade-shaped flat part 62, and a large-diameter piston 63.
are inserted into each hole 5B, 57.58. The flat portion 62 extends a blade portion 64 so as to vertically block the communication hole 57 along its length, and a reduced taper portion 65 is formed at the tip of the blade portion 64. The tapered portion 65 forms a communication passage with the inner wall of the communication hole 57. As a result, the passage blocked above and below the communication hole 57 communicates with the refrigerant flow paths 153, 153, and a circuit is constructed in which the passage connects the tapered portion 65 and is supplied with the refrigerant. . This circuit is sprue ejector pin 8
Functions regardless of forward or backward movements. Moreover, the piston 63 is
Although its rear end is locked and it always moves following the cut pin 5, it can move independently by receiving a pressure medium in the cylinder hole 58. In the figure, 6B is a sealing material.

The ejector pin 7 has a large diameter piston 71 and a body portion 7.
The piston 71 is fitted into the cut cylinder 53, and the body 72 is fitted into the cylindrical member 21 so as to be movable forward and backward. The cylindrical member 21 is fixed and positioned on the cut pin cylinder 53. The ejector pin 7 is provided with V-shaped grooves 73 and 74 on the inner peripheral surface of the rear half and the outer peripheral surface of the front half on the piston side, respectively. 3.74 is a through hole 75 to the inner and outer peripheral surfaces. It is communicated with. Groove 7 on the front half
4 is terminated at a slight distance from the distal end surface. 7 in the diagram
8.7.7 are working chambers before and after the piston 71, and 78 is a sealing material. This ejector pin 7 functions to blow out air at the same time when it is ejected by pneumatic pressure.

Further, the stamper inner periphery pressing member 8 is configured to be movable back and forth by operating means from outside the mold, and has a claw 8 at its tip 81.
2 to press the stamper 31, and the tip 81 protrudes annularly from the movable mold surface to form the second gate 33. The tip 83 is provided with a tapered surface 83 that reduces the cavity cross section. The second gate 33 is configured to be wider than the first gate 32 when the gate 32 is the first gate. A pressure sensor 18 is attached inside the second gate 33.

Next, explaining the area around the cavity, the mold surfaces of the information track surfaces are each mirror-finished.

The outer periphery holding member 9 of the stamper is composed of an outer periphery holding claw 91 of the stamper 31, a circumferential surface 92 extending perpendicularly from the claw 91, and a guide surface 93 inclined from the circumferential surface 92 in the outer circumferential direction. The mold surface end of the fixed mold plate l fits into the circumferential surface 92 to form the cavity 3.

Only the effects unique to the present invention based on the above configuration will be explained.

■When filling cavity 3 with molten resin,
Since the molten resin is sheared and heated at the first gate 32, it flows radially in a flowable state, and is filled along the stamper 31 on the information track surface while absorbing stress at the second gate 33.

q) Since high resin pressure is generated at the first gate 32, pressurized oil is applied to the action chamber 14 at the timing of this generation. As a result, linear hydraulic pressure can be applied from the stepped portion 46 with less nozzle touch force in response to linear resin pressure, and linear pressure can be applied to the tip surface 143 to face it. Become.

・■ Holding pressure is applied after filling. The holding force mainly acts on the inside of the clamping area. That is, the second gate 33
This is because the holding force that causes residual stress does not spread to the information track surface. Although it is not fully understood whether the cooling of the molten resin starts from the outer periphery of the cavity 3, it is sufficient that the molten resin exhibits a semi-solidified state at least in the first gate 32 and the clamping area around it.

(2) When cutting the gate, by removing the pressure oil from the action chamber 14, the front end surface 143 of the sprue bush 4 is placed in a no-load state or a negative pressure state. The above state can be adjusted arbitrarily by adjusting the release of pressure oil. That is, the suzurubutsu side becomes movable with little force. If the cut pin 5 is advanced at this timing, the tip surface 143 of the sprue bush 4 will retreat in response to this forward force while maintaining the same gate volume. As a result, the first gate 32 is cut without any compressive force acting on it. During cutting, the sprue ejector pin 6 moves simultaneously with the cut pin 5.

As the mold is opened after cutting of type 7, the sprue ejector pin 6 moves forward, thereby ejecting the remaining product of the slough well portion 31.

According to the above-mentioned embodiment, one of the causes of tip sagging of the cut pin 5, which is a cause of generation of chips, can be eliminated. In other words, the cylinder structure of the sprue bushing 4 made it possible to suppress the nozzle touch force dispersed by the spherical part of the bushing against linear resin pressure, thereby avoiding distortion of the sprue bushing, which would occur during gate carting. car/
This is because problems such as galling of the toppin 5 could be resolved.

Furthermore, cutting in a semi-solidified state does not require a large shearing force, and tip sag is less likely to occur.

Further, since the cylinder structure of the sprue bush 4 is used as a means to ensure the same gate volume, relative movement can be performed accurately.

(6) Other Embodiments of the Invention Drawings FIG. 6 is a sectional view of essential parts showing a mold applied to another molding method. The same reference numerals as those in FIGS. 1 to 4 in the drawings have the same functions, so repeated explanation will be omitted.

Thus, the barrel portion and the bottom side of the cylinder are composed of a bushing cylinder 144, and a return action chamber 149 is formed between the tip side end face 145 of the large diameter portion 43 and the thick bushing cylinder cover 146. Ru.

In the figure, 148 is a flow path provided in the bushing cylinder cover 148.

When molding is performed using this mold structure, gate cutting can be performed by supplying pressure oil to the working chamber 14 and moving the sprue bush 4 forward, making it suitable for molding large-sized discs. Furthermore, by applying pressure oil to the action chamber 147, it becomes possible to move the sprue bush 4 backward, so that the movements of the canting pin 5 and the sprue ejector pin 7 can be synchronized.

In each of the above embodiments, a sprue bushing cylinder is illustrated as a means for not changing the gate volume, but other means may be used. Further, the semi-solidified state can be applied to any material that is at a melting level that does not generate chips when cutting. Furthermore, the implementation of the present invention is not limited to the above-mentioned mold structures, and may be applied to other mold structures.

(7) As described in detail, the present invention provides the following effects.

■Since the gate was cut in a semi-solid state without applying compressive force, it was possible to prevent the generation of chips and to prevent stress from spreading to the information track surface.

As a result, it was possible to eliminate the most significant factor that causes differences in birefringence values and to form highly accurate disc-shaped recording media.

Since no compressive force is applied to the gate part when cutting, there is no need to wait until the product is solidified before gate cutting, and gate cutting can be performed while the clamping area is semi-solidified, reducing the cost by less than half that of conventional methods. It was made possible to mold at high cycles.

[Brief explanation of drawings]

The drawings show an embodiment of the method for molding a disc-shaped recording medium according to the present invention, and FIG. 1 is a perspective view of a main part of a mold used in the molding method, and FIG. bin perspective view,
Fig. 3 is a sectional view of the main part of the mold, Fig. 4 is a sectional view of the main part showing the gate cut state, Fig. 5 is a sectional view of the main part showing the protruding state of the cut part, and Fig. 6 is the other part. FIG. 2 is a cross-sectional view showing a mold applied to the molding method. l 1. Fixed template, 29. Movable template 30. Cavity, 41. Sprubutush 58. Cut pin 69. Sprue ejector pin 79. Ejector pin, 32. , (first) gate 33
1. second gate

Claims (1)

[Claims] A gate portion is arranged at the center of the disc-shaped cavity space,
” - In a method for forming a disk-shaped recording medium in which a center hole is formed by relative movement of a gate part with respect to a cavity, relative movement of the gate part is obtained while the gate volume remains the same while the product is in a semi-solidified state at the gate part. A method for forming a disc-shaped recording medium characterized by: