JPS63111024A - Mold for resin plate - Google Patents

Abstract

PURPOSE:To prevent a backward flow of resin by cooling the gates of narrow gap formed in between the end surface of the heat absorbing part of a cooling body and the peripheral edge of sprue hole, when a high mold clamping pressure is applied to a mold. CONSTITUTION:A protrusion 40 is provided at the heat absorbing part of a heat pipe 37, i.e. the central part of the end surface of a sprue bush 36-side. Narrow gaps 41 and 12 are formed in between the end surface of this heat absorbing part and the peripheral edge of the resin pouring hole of the sprue bush 36 and in between the protrusion 40 and the inner part of the resin pouring hole in the condition where a high mold clamping pressure in compression molding is applied, thereby constructing the gate for injecting resin. The resin is injected into a molding cavity 35 from the sprue bush 36. After injection, cooling blast is sent into a space 43, from the time when the resin flow in the gate part begins to stop, and the heat radiation from the radiation part of the heat pipe 37 is accelerated. Then, since the resin in the gate part is cooled and solidified, the backward flow of the resin from the gate may be prevented in the compression molding following said solidification and having a heightened mold clamping pressure.

Description

[Detailed description of the invention] [Technical field to which the invention pertains] The present invention relates to the structure of a mold for injection compression molding of a resin plate such as an optical disk substrate, and in particular to a method for preventing backflow of resin at a gate portion where resin is injected into a molding cavity. This relates to the structure of a mechanism for preventing this.

[Prior art and its problems] The substrate of an optical disk that uses light as a means of recording, erasing, and reproducing information is a transparent thin plate with an information track, which is an area where information is recorded, on one side. . The width of this information track is approximately 1 μm.

These are extremely fine grooves with a depth of 0.1 μm or less, and are formed in a spiral or concentric shape with a pitch of around 1.6 μm. The other surface is smooth, and light enters from this smooth surface, passes through the inside of the optical disk, and is projected from the inside so as to be focused onto the information track. Information is recorded as minute indentations formed on the information track or minute dots with different reflectances in a thin film formed on the surface of the information track, and is read as changes in the amount of reflected light caused by these points. This reflected light passes through the inside of the optical disk substrate and exits from the smooth surface.

The reason why light is applied to the information track from inside the optical disk in this manner is to prevent the recording, erasing, and reproduction of information from being hindered even if foreign matter such as dust adheres to the information track. Optical disk substrates with extremely fine uneven patterns such as the information tracks and information depressions described above are
It can be mass-produced by molding resin. Injection compression molding is suitable for obtaining a substrate in which a fine uneven pattern is formed with high precision and is free from distortion. In the injection compression molding method, a mold with a fine concavo-convex pattern is closed to create a molding cavity with narrow gaps, and molten resin is injected and filled into the molding cavity through a gate with a gap smaller than the thickness of the optical disk substrate. . At this time, the force for closing the mold, that is, the mold clamping pressure, is set slightly lower than the resin injection pressure to reduce the stress generated in the resin being injected. Therefore, at this time, the mold opens by 1 mm. After filling the resin, a large clamping pressure is applied to the mold to close the mold, and the resin is compression molded. Since the mold clamping pressure at this time is uniformly applied to the entire resin in the molding cavity, it is possible to eliminate nonuniform stress in the resin that causes distortion and optical birefringence after molding. However, as mentioned above, the injection pressure of the resin is not very high, so during compression molding where high mold clamping pressure is applied, the resin may flow back from the gate part. When molecular chains are oriented along the direction of flow due to this reverse flow, birefringence of light occurs, which interferes with recording, erasing, and reproducing information.

Furthermore, anisotropy in properties occurs, particularly anisotropy in thermal properties, which causes deformation of the optical disk substrate, thereby eliminating the advantages of injection compression molding.

As a conventional technique for preventing backflow, there is a method of mechanically closing the gate immediately after filling with resin. FIG. 5 shows an example of a mold for injection compression molding using this method. FIG. 6 is an enlarged view of the vicinity of the gate portion. The mold consists of a fixed mold 1 and a movable mold 2, and in the joint portion of the fixed mold 1 and the movable mold 2, there is a gap between the fixed mold plate 3 and the movable mold plate 4 provided on each mold. Annular molding cavities 5 with narrow intervals are formed. Movable mold plate 4 of molding cavity 5
A stamper 6, which serves as a mold for fine uneven patterns such as information tracks and information depressions, is fixed on the side by an inner stamper holder 7 and an outer stamper holder 8. A sprue bushing 9 having a sprue hole for resin injection is provided in the center of the fixed mold 1 on the molding cavity 5 side.

This sprue bush: L9 is provided with a certain amount of room to move in the vertical direction within the fixed mold 1. On the other hand, the movable mold 2 has a cylindrical sprue bushing 9 which faces the sprue bushing 9 and fits into the sprue lock pin 10 and the outside thereof.
A gate pin 11 having the same outer diameter as the sprue bushing 9 is arranged so as to share the same central axis as the sprue bushing 9.

The sprue lock pin 10 is fixed to the movable mold 2, but the gate pin 11 is designed to slide on the outside of the sprue lock pin 10. It is pressed against the periphery of the opening at the tip of the sprue bush 9 by a compression spring 13 via the three projections 12 shown. The height of the protrusion 12 is smaller than the height of the molding cavity 5, and three slits 14 for resin injection are formed at the contact area between the sprue bush 9 and the gate pin 11, as shown in FIG. . At the center of the tip of the sprue lock pin 1O, there is provided an abacus bead-shaped protrusion 15 having a maximum diameter at the middle part and decreasing in diameter toward both sides. This is for drawing out the resin in the sprocket 9 when opening the mold after molding.

This protrusion 15 also forms a slit 16 with the inner wall of the opening of the sprue bush L9, and the ejector cylinder 17 is fitted into the slit 14, and after molding, a piston (not shown) The molded resin plate is extruded through the ejector plate 18 and released from the mold. Furthermore, the movable mold 2 is provided with a heat insulating plate 26 for keeping the molding cavity 5 warm.

When filling with resin, a heating cylinder 1 containing molten resin is used.
9 is pressed against the sprue bush 9, and molten resin is injected and filled into the molding cavity 5 through the sprue bush 9 and through the gaps 14 and 16 in the gate portion. When the filling is completed, the heating cylinder 19 moves back and the sprue tooth: L
9, the gate pin 11 is pushed in the direction of the fixed mold 1 by the action of the compression spring 13 extending, and the sprue pin
The sprue bushing 9 of the stationary side mold plate 3 enters the inserted hole together with the slit 14 while maintaining contact with the sprue bushing 9 and closes the gate portion, blocking the resin passage and preventing backflow.

Compression molding is performed in this state. In this configuration, the force for closing the gate is applied by the compression spring 13, so if compression and expansion are repeated many times for mass production, reliability of operation will be lost due to fatigue. Therefore, maintenance such as checking the operation of the compression spring 13 and replacing it is required. Although there is a method of operating the ejector cylinder 17 by hydraulic drive or the like to avoid this, the mold structure becomes even more complicated. Therefore, as a conventional technique to avoid the complexity of providing these movable mechanisms and prevent the backflow of resin, a cooling fluid is used to cool and solidify the resin near the gate, as shown in the example shown in Figure 7. Some have structures that prevent backflow. This is a sprue with the outer diameter excluding the gate pin 11 in Figures 5 and 6:
The gate portion is cooled by flowing a cooling fluid through a sprue lock pin 20 having a double tube structure that is approximately equal to L9. In this structure, the base 21 of the sprue lock pin 20
, a double pipe 22, a 23° cooling fluid artificial pipe 24, an outlet pipe 25, etc., are respectively joined by welding or brazing. Since the outer diameter of the sprue lock pin 20 is only about 1 cm, there are many joints compared to the overall size, and the parts to be joined are small, so the build-up of each joint is also small. Fluid may leak from the joint. Additionally, a fluid circulation device and piping between the circulation device and the mold are required.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and provide a mold for injection compression molding which has high reliability and has a simpler structure, which cools the gate part and prevents the backflow of resin.

[Key points of the invention]

This invention includes an ejector tube coupled to an ejector mechanism in one of a pair of molds constituting a mold for injection compression molding, and a cooling body configured as a heat pipe fitted inside the ejector tube. The end face of the heat absorbing part of this cooling body is arranged so as to face the sprue hole for resin injection provided in the other mold, and due to its compressed bottom shape, cooling occurs when high mold clamping pressure is applied to the mold. By creating a structure in which a slit-like gate is formed between the end face of the heat-absorbing part of the body and the peripheral edge of the sprue hole, the flow of resin at the gate part stops after the molding cavity is filled with resin. The resin in the gate part is rapidly cooled and solidified by the heat pipe action of the cooling body from around the time when the molding starts, thereby preventing the resin from flowing backward from the molding cavity toward the sprue hole. For this reason, a heat dissipating part of a heat pipe serving as a cooling body is positioned in a space inside a mold provided with a cooling body, and cooling is performed so as to dissipate the heat taken from the resin.

[Embodiments of the invention]

FIG. 1 shows an embodiment of the present invention, and FIG. 2 is an enlarged view of the vicinity of the gate portion. A sprue spout 36 is fixed to the fixed mold 31 and is arranged at the center of the fixed mold plate 33. In the center of the movable mold plate 34 of the movable mold 32, there is a sprue pusher 3.
6, a heat pipe 37 serving as a rod-shaped cooling body having a heat absorbing portion on the side of the sprue bush L36 is fixed. An ejector tube 38 that releases a resin plate such as an optical disk substrate molded in the annular molding cavity 35 is slidably fitted on the outside of the heat pipe 37 . The ejector cylinder 38 is in contact with the heat pipe 37 on sliding surfaces at both ends, and a gap 39 is formed between the heat pipe 37 and the middle part to suppress heat conduction in the radial direction of the ejector cylinder 38. This prevents an increase in the apparent heat capacity of the heat pipe 37. heat pipe 3
The sprue lock pin 1 shown in FIG. 5 and FIG.
A protrusion 40 having the same shape and function as the protrusion 15 of 0.
is the provision. The end face of this heat absorbing part and the sprue bush 2 3
6 and the periphery of the resin injection port, as well as between the protrusion 40 and the inside of the resin injection port, as shown in FIG. Small gaps 41 and 42 are formed to form gates for resin injection. In this embodiment of the invention, the sprue bush 36 is fixed to the fixed mold 31, and the heat pipe 37 is fixed to the movable mold 2, so that the gaps 41 and 42 are fixed to each other.
Since the 0 dimension can be inevitably determined by the relative positions of the fixed mold 31 and the movable mold 32 during mold clamping, there is no need to ensure a narrow gap with the protrusion 12 as in the prior art.

Inside the heat pipe 37, as partially shown in FIG. 2, a wick 44 is provided, which has a network of slits along both end faces and the inner wall, and a working fluid such as water as a heat medium is provided. A suitable amount is included. This working fluid is in a state where every corner of the wick 44 is impregnated by capillary action. When the heat absorption part is heated, the working fluid impregnated in the wick 44 absorbs the latent heat of vaporization and vaporizes.
The pressure in the heat absorption section is higher than that in the cooling section. This pressure difference causes the steam to move at high speed to the heat radiation section. In the heat dissipation section, the steam is cooled and condensed, releasing the same amount of latent heat of condensation as during vaporization. The working fluid condensed in the heat radiating section is returned to the heat absorbing section by the capillary action of the wick 44.

Heat transport occurs through the cycle of evaporation → vapor movement → U condensation ring reflux as described above, and the apparent thermal conductivity is extremely high and the thermal response is fast.Moreover, heat transfer from the heat absorption part to the heat radiation part Since no mechanical power is required for the cooling system, the configuration of the cooling system is extremely simple.
3 and sends forced cooling air into the space 43 to promote heat radiation from the heat radiation section.

Molding of the optical disc substrate in this example is carried out as follows. Spruce pusher 36 to molding cavity 3
The procedure in which resin is injected into 5 is similar to the prior art. However, since there is nothing obstructing the flow of the resin in the circumferential direction of the narrow gap 41, the resin can be uniformly filled around the narrow gap 41. Heat from the resin being injected is taken away from the end of the heat pipe 37, but since the resin is flowing and the high temperature resin is continuously transferred, the resin being injected does not solidify. If the cooling air is sent to the space 43 from the time when the resin injection is finished and the flow of resin in the gate part starts to stop, and the heat radiation from the heat radiation part of the heat pipe 37 is promoted, the amount of resin in the gate part is small. Since the heat capacity is small and a large amount of that heat is taken away by the heat pipe 37, the resin in this area rapidly cools and solidifies, and during the subsequent compression molding with increased mold clamping pressure, the resin flows back from the gate. It is possible to prevent this from happening. The compression molding procedure and the subsequent procedure of moving the ejector cylinder 38 to release the molded optical disk substrate are the same as in the prior art.

FIG. 3 shows a second embodiment of the invention.

In this embodiment, in addition to the gap 39 at the boundary between the ejector tube 51 and the heat pipe 37, the ejector tube 51.
Inner stand bar presser foot 52. There are also gaps 53, 54, and 55 at the boundaries between the inner stamper holder 52 and the movable die 32, respectively.
This is provided. With this configuration, the heat insulation from the surface of the heat pipe 37 toward the movable mold 32 is further improved, the apparent heat capacity of the heat pipe 37 is further reduced, and the thermal response characteristics of the heat pipe 37 are accelerated.
The property of solidifying and cooling the resin near the gate portion can be improved.

FIG. 4 shows a third embodiment of the present invention, in which a cooling pipe 56 is provided in the heat dissipation section of the heat pipe 37 in the space 43, and a cooling fluid is allowed to flow inside, thereby further improving the cooling characteristics in the heat absorption section. It has been improved. Also in this embodiment, the ejector cylinder 38. Inner stamper holder 7. The characteristics can be further improved by providing a gap as shown in the second embodiment at each boundary between the inner star: the nozzle presser 7 and the movable mold 32. Although this embodiment requires a cooling fluid circulation device, since the heat dissipating portion of the heat pipe 37 is cooled from the outside, the cooling system can be made highly reliable and robust.

〔Effect of the invention〕

In this invention, a rod-shaped cooling body configured as a heat pipe is provided inside the ejector cylinder of one of a pair of molds constituting a mold for injection compression molding, and a rod-shaped cooling body configured as a heat pipe is provided on the heat absorption side. When compression molding is performed by applying high mold clamping pressure to the mold, the end face of the cooling body is placed so that it faces the sprue hole for resin injection provided in the other mold. Since the structure is such that a slit-like gate is formed between the sprue hole and the peripheral edge of the sprue hole, the gate part starts to close to the point where the molding cavity is filled with resin and the flow of resin starts to stop at the gate part. The heat of the resin near the slits is rapidly removed by the heat pipe action of the cooling body. Since the resin in the above part is small, its heat capacity is small.
Therefore, the resin quickly cools and solidifies, thereby providing a slit-blocking effect and preventing the resin in the gate portion from flowing back from the molding cavity toward the sprue hole. A heat pipe is a thermal conductor with extremely high thermal conductivity that transfers heat by the rapid movement of vaporized working fluid inside, so in this invention, a cooling pipe is installed directly inside the small part that touches the resin near the gate. Without flowing fluid, it is possible to quickly remove the heat from the resin in the gate section by simply cooling the heat dissipation section of the heat pipe located in a relatively wide space from the outside. In addition, since the gate part does not have a movable mechanism, the mold can be easily constructed, and there is almost no need to maintain the part that prevents the backflow of the resin.

Further, since the resin is uniformly injected around the sprue hole from the slit in the gate portion, uneven stress is prevented from being generated in the resin during resin injection.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of an embodiment of the present invention, FIG. 2 is an enlarged view of the vicinity of the gate portion in the embodiment of the present invention, and FIGS.
The figures are sectional views of the second and third embodiments of the present invention, FIG. 5 is a sectional view of a mold according to the prior art, FIG. FIG. 7 is a partial sectional view of a mold according to a different prior art. 1.31. Fixed type, 2.32-Movable type, 5,35 Molding cavity, 9.36 Sprue bush, 14°16.41.42 Slit, 15.40-Protrusion, 17,
38.51 Ejector cylinder, 37 Heat pipe, 39
．． 53.54°55 void. Ij 244 Lilag Fig. 2 τ Fig. 3 Sei Fig. 4

Claims (1)

[Scope of Claims] 1) It is constructed as a split mold comprising first and second mold parts, a sprue hole for injecting molten resin, and an ejector mechanism for releasing the molded resin, and the mold parts are joined together. A molding cavity with a narrow gap between both molds is formed at the eye part, and resin is forcibly injected into the molding cavity from the sprue hole provided in the first mold part under low mold clamping pressure, and then high mold clamping pressure is applied to the split mold. In a mold for compression molding a resin in a molding cavity by imparting a A rod-shaped cooling body configured as a heat pipe that is fixed and has one end on the sprue hole side as a heat absorption part and the other end as a heat radiation part is provided, and the end face of the one end side of the cooling body and the first mold part side are arranged. When high mold clamping pressure is applied to the mold, a slit-like gate is formed between the peripheral edge of the outlet side opening of the sprue hole, and the resin in the gate part is heated by the heat pipe action of the cooling body. A mold for molding a resin plate, characterized in that the mold is cooled to prevent backflow from the molding cavity toward the sprue hole. 2) In the mold according to claim 1, the cooling body is arranged on the central axis of one end on the side of the sprue hole, and the diameter thereof is maximum at the middle part and decreases toward the sprue side and the one end side, respectively. A mold for molding a resin plate characterized by having a shaped protrusion. 3) In the mold according to claim 1 or 2, the molding cavity is formed in a flat ring shape, the sprue hole is in the center of the first mold part, and the ejector cylinder is in the second mold part. A mold for molding a resin plate, characterized in that each mold is placed in the center. 4) In the mold according to any one of claims 1 to 3, the diameter at which the inner wall surface of the ejector cylinder fits into the cooling body is smaller than that at both ends in the axially intermediate part of the ejector cylinder. A mold for molding resin plates that is characterized by its large size. 5) A mold for molding a resin plate according to any one of claims 1 to 4, characterized in that a void is provided inside the cylindrical wall of the ejector cylinder. 6) A mold for molding a resin plate according to any one of claims 1 to 5, wherein the resin is a transparent resin. 7) A mold for molding a resin plate according to claim 6, wherein the resin plate is an optical disk substrate.