JPH08156030A - Disk molding tool and disk molding method using same - Google Patents

Abstract

PURPOSE: To prevent inferiority in appearance such as a stain, haze, etc., by obtaining excellent releasability by a method wherein either the other cavity forming surface of a fixed mold or a movable mold which is positioned in opposition to a stamper is made to have a specified roughness. CONSTITUTION: A disk molding cavity 14 is formed between mating mold surfaces of a fixed mold 10 and a movable mold 12, and a stamper 44 wherein specified information is engraved on a surface is fitted to a movable side cavity forming surface 36 in the movable mold 12. A mirror surface of a fixed side mirror block 16 which is positioned in opposition to a surface of the stamper 44 composing a fixed side cavity forming surface 22 is made to have a surface roughness of Rz=50-400nm throughout the whole surface. By making coarser roughness than that of a conventional cavity forming surface thus, releasability of a disk base board is improved, and appearance inferiority and mechanical property inferiority which are caused by irregular releasing are reduced or prevented. Further, cooling time is possibly shortened, and a molding cycle is improved.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a disk molding die and a disk molding method for molding an optical disk base made of a synthetic resin on which predetermined information is transferred by a stamper.

[0002]

BACKGROUND ART Optical discs have come to be used in a wide range of fields such as audio, video, and computers.
Generally, in manufacturing the mold, a mold having a fixed mold and a movable mold which are fitted to each other to form a molding cavity is used, and a predetermined cavity is formed on a cavity forming surface of either the fixed mold or the movable mold. After setting the stamper on which information is engraved, a predetermined resin material is filled into the molding cavity to mold the base (replica) on which the stamper information is transferred. Then, the target optical disk is formed by further vapor-depositing a reflective film or the like on the substrate thus formed.

By the way, the cavity forming surfaces of the fixed mold and the movable mold for forming the optical disk substrate are both mirror-finished, and a stamper is attached to one of the cavity forming surfaces and the other cavity forming surface. However, the cavity forming surface on the side that is used as it is without the stamper is conventionally made as smooth as possible in order to improve the appearance characteristics and mechanical characteristics of the molded product. Is considered to be good, and in order to improve the surface roughness, Rz = 20 to 30 nm or less was polished to a substantially limit.

However, even if the cavity forming surface is subjected to a high degree of mirror finishing in this manner, the appearance of stains or mist on the disk molded product and the occurrence of mechanical property defects such as birefringence and warpage occur. It was not possible to suppress it sufficiently, and it was difficult to secure product quality.

Moreover, since shortening the cooling time at the time of molding further deteriorates the product quality, it is necessary to set the cooling time longer in order to secure the product quality to a certain degree. There was also the problem that improvement was difficult.

As a result of a study by the present inventors, the cause of the appearance defect and mechanical property defect in the disk molded product is mainly due to a part of the molded product which should be adhered to the stamper side when the mold is opened. It is considered that the mold may be pulled toward the mirror surface to cause uneven release. That is, 1000 to 1 is formed on the surface of the stamper that constitutes one cavity forming surface.
Since pits with an uneven height of 500 Å are engraved, it is desirable to open the mold with the molded product in close contact with the stamper side in order to prevent pit misalignment, etc. When the mold is opened, a part of the molded product comes into close contact with the mirror surface side and is partially pulled, so uneven mold release occurs and stains and mist-like appearance defects easily occur. It is considered that since the cooling effect (cooling rate) is different between the parts, the mechanical property defects such as birefringence variation in the circumferential direction, warp, and twist are likely to occur.

[0007]

The present invention has been made in view of the circumstances as described above, and the problem to be solved is to easily improve the quality conventionally required in the molding of an optical disk substrate. Another object of the present invention is to provide a disk-molding die having an improved structure and a disk-molding method that can be effectively achieved.

It is also an object of the present invention to provide a disk molding method capable of achieving not only quality improvement, but also productivity improvement (yield improvement and molding cycle increase) which has been conventionally required in molding an optical disk substrate. And

[0009]

In order to solve such a problem, a feature of the present invention is to provide a fixed mold and a movable mold in which a stamper is mounted on one of the cavity forming surfaces, and the molds are matched with each other. In the disk molding die for forming the disk molding cavity, the cavity forming surface of the other of the fixed mold and the movable mold, which is positioned to face the stamper, is
The surface roughness is z = 50 to 400 nm.

Further, according to the present invention, when a disk is formed by using the disk forming mold having the structure according to the present invention as described above, the mold clamping force of the mold is maintained at the mold clamping primary pressure to form the resin material. In the cooling step after filling the molding cavity, the mold clamping force of the mold is reduced to a mold clamping secondary pressure lower than the mold clamping primary pressure, and then again the mold clamping tertiary pressure higher than the mold clamping secondary pressure. It also features a disk forming method in which the pressure is increased.

In the disk molding method according to the present invention, concrete pressure values of the mold clamping primary pressure, the secondary pressure and the tertiary pressure are appropriately set according to the resin material, the injection pressure and the like. But is not limited to
Preferably, the mold clamping secondary pressure is set to 30 to 70% of the mold clamping primary pressure, and the mold clamping tertiary pressure is 80 to 100 of the mold clamping primary pressure.
Set to%. Further, the specific holding time of the mold clamping secondary pressure and the mold clamping tertiary pressure is also appropriately set according to the resin material, injection pressure, mold temperature, etc., and is not limited, but is preferable. Indicates that the holding time of the mold clamping secondary pressure is 20 to 5 of the total cooling time after filling the cavity of the resin material.
It is set to 0% and then kept at the third mold clamping pressure until the cooling is completed. Further, preferably, the mold opening is started at the same time when the holding time of the third mold clamping pressure is completed.

[0012]

In the disk molding die having the structure according to the present invention, since the surface roughness of the cavity forming surface (mirror surface) facing the stamper is slightly rougher than the conventional one, Since excellent mold releasability of the molded product can be obtained, the mold release of the molded product is better on the mirror surface side than on the stamper side, and the partial adhesion of the molded product to the mirror surface side when the mold is opened. Will be prevented.

In particular, the surface roughness of the mirror surface is Rz = 50.
When the thickness is not less than nm, good releasability of the molded product on the mirror surface side is obtained, and when Rz = 400 nm or less, sufficient smoothness is secured on the surface of the molded product and a good surface appearance is secured. It can be done.

Therefore, in the disk molding die having the structure according to the present invention, appearance defects such as stains and mist due to uneven release are prevented, and birefringence variation on the circumference is also prevented. It is possible to significantly reduce the deterioration of mechanical properties such as warpage and twist, and to improve product quality and yield as a whole.

Further, in the method of the present invention, since the mold clamping force of the molding die is reduced after the resin material is filled in the molding cavity and the molding die is maintained at the mold clamping secondary pressure, the resin material filled in the molding cavity is maintained. Backflow to the injection nozzle side is suppressed, the transfer of the pits transferred due to the high mold clamping primary pressure is prevented, and the transferability is improved. By increasing the pressure, the cooling effect of the skin layer of the filled resin is improved.

In addition, since the surface roughness of the cavity forming surface (mirror surface) facing the stamper in the mold is roughened to improve the mold releasability, the mold clamping force is applied before the mold is opened. Even if the height is increased to a certain level, it is possible to prevent the molded product from partially adhering to the mirror surface side when the mold is opened, which may cause problems such as poor appearance and mechanical characteristics due to the partial adherence to the mirror surface side. Absent.

Therefore, according to the method of the present invention, in addition to preventing the appearance failure and the mechanical property failure due to the partial adhesion of the molded product to the mirror surface side when the mold is opened, the backflow of the resin material is also prevented. Due to the prevention of the pit displacement due to the excellent transferability, further improvement of the product quality can be achieved, the yield can be improved, and the cooling effect of the filling resin can be improved. The molding cycle can be improved.

The mold clamping secondary pressure is 30 to 7 of the mold clamping primary pressure.
If it is set to 0%, the effect of preventing the pit displacement caused by the backflow of the resin material can be more advantageously obtained, and if the mold clamping tertiary pressure is set to 80 to 100% of the mold clamping primary pressure, the skin layer is cooled. The effect of improving the property is more advantageously obtained. Further, if the holding time of the mold clamping secondary pressure is set to 20 to 50% of the total cooling time after the cavity of the resin material is filled, the pit deviation exhibited by reducing the mold clamping force to the mold clamping secondary pressure. It is possible to obtain a sufficient prevention effect, and if the mold clamping tertiary pressure is maintained until the cooling is completed, the cooling effect of the skin layer exerted by increasing the mold clamping force to the mold clamping tertiary pressure again is achieved. Can be obtained more efficiently. Furthermore, if the mold opening is started at the same time when the holding time of the third mold clamping pressure is completed, the molding cycle can be more advantageously increased.

[0019]

EXAMPLES Examples of the present invention will now be described in detail with reference to the drawings in order to clarify the present invention more specifically.

First, FIG. 1 shows a disk molding die as an embodiment of the present invention. This molding die includes a fixed die 10 and a movable die 12, and although not shown, the fixed die 10 is attached to a fixed plate of a mold clamping device, while the movable die 12 is a die. The fixed mold 1 is attached to and supported by the movable plate of the tightening device, and moves the movable plate in the approaching / separating direction with respect to the fixed plate.
0 and the movable mold 12 are opened and closed. Then, as shown in the drawing, the fixed mold 10 and the movable mold 12 are matched with each other, so that the disk molding cavity 14 is formed between the mold matching surfaces.

More specifically, in the fixed mold 10, a fixed side mirror block 16 having a substantially thick annular plate shape is fixed to the forming side of the molding cavity 14 via a back plate 18. The center bush 20 is mounted and fixed by penetrating through the center holes of the fixed side mirror block 16 and the back plate 18, and is fixed by the mirror surface of the fixed side mirror block 16 and the axial end surface of the center bush 20. The fixed-side cavity forming surface 22 is configured. Further, the center bush 20 is provided on the central axis of the fixed mold 10.
A sprue bush 24 is attached to the molding cavity 14 through the sprue bush 24, and a resin material injected from a nozzle of an injection device (not shown) is introduced into the molding cavity 14 and filled therein.

Further, in the movable mold 12, as in the fixed mold 10, on the molding side of the molding cavity 14, a movable mirror block 28 having a substantially thick annular plate shape is provided via a rear plate 30. , Fixedly attached. Furthermore,
A substantially cylindrical stamper holder 32 is arranged so as to penetrate through the center holes of the movable side mirror block 28 and the back plate 30, and an inner bush 34 is arranged so as to penetrate through the center hole of the stamper holder 32. The movable-side cavity forming surface 36 is constituted by the mirror surface of the movable-side mirror block 28 and the axial end surfaces of the stamper holder 32 and the inner bush 34.

Further, an ejector sleeve 38 is inserted through a center hole of the inner bush 34 on the movable mold 12 side so as to be movable in the axial direction, and is ejected to the fixed mold 10 side by a drive mechanism (not shown). As a result, the optical disk substrate molded in the molding cavity 14 is projected and released from the movable mold 12 side. A punch cutter 40 is axially movably inserted through the center hole of the ejector sleeve 38, and an ejector pin 42 is axially movable on the central axis of the punch cutter 40. . And
When the punch cutter 40 is positioned in the retracted state, an annular gate is formed between the punch cutter 40 and the sprue bush 24 on the fixed mold 10 side, while the punch cutter 40 is actuated to project, so that the fixed metal The center hole of the center bush 20 on the mold 10 side is pierced to punch out the center hole of the optical disc substrate molded in the molding cavity 14, and then the punched gate portion is projected by the ejector pin 42 to be released from the mold. There is.

As shown in the drawing, the movable cavity forming surface 36 of the movable mold 12 has a thin annular plate shape, and a large number of convex pits mark predetermined information on the surface. The stamper 44 provided is placed and mounted. And such a stamper 44
The inner peripheral edge portion is held by the stamper holder 32, while the outer peripheral edge portion is held by the outer peripheral pressing ring 46 having a hook-shaped cross section fixedly mounted on the movable mold 12, so that the surface on which the pit is formed is The movable side mirror block 28, which constitutes the movable side cavity forming surface 36, is mounted on the mirror surface of the movable side mirror block 28 toward the molding cavity 14 side. As a result, by injection-filling the molding cavity 14 with the resin material to mold the optical disk substrate, the pits of the stamper 44 representing predetermined information are transferred.

On the other hand, the mirror surface of the fixed-side mirror block 16 which faces the surface of the stamper 44 and constitutes the fixed-side cavity forming surface 22 has a surface roughness of Rz = 50 to 400 nm over the entire surface. ing.
The Rz value represents the ten-point average roughness specified in JIS-B0601.

Thus, the fixed side cavity forming surface 22
Is made rougher than the cavity forming surface that has been conventionally adopted, so that the releasability of the molded disc substrate is improved, whereby the molded product adheres to the stamper 44 when the mold is opened. It is possible to prevent mold release unevenness that can be retained by the mold, and a part of which is closely attached to the fixed-side cavity forming surface 22 and pulled, and therefore, appearance defects and mechanical property defects due to mold release unevenness are reduced or reduced. It can be prevented. If the surface roughness Rz value of the mirror surface of the fixed-side mirror block 16 is smaller than 50 nm, it is difficult to obtain sufficient releasability of the disc substrate, and uneven release at the time of mold opening is sufficiently prevented. hard. On the other hand, the surface roughness of the mirror surface of the fixed side mirror block 16: Rz value,
When it is larger than 400 nm, the surface of the molded product becomes frosted glass and the appearance is liable to be deteriorated, and when it is further roughened, satisfactory optical properties of the surface may not be obtained.

Moreover, since the mold releasability of the molded product at the time of mold opening on the fixed side cavity forming surface 22 is improved,
Even if the cooling time is not so long, it is possible to prevent the appearance defect and the mechanical property defect due to the mold release unevenness from occurring, and there is also an advantage that the molding cycle can be improved.

Further, in molding the optical disk substrate using the disk molding die having such a structure, in this embodiment, injection molding of the resin material into the molding cavity 14 is performed from the mold clamping step of the molds 10 and 12. The mold clamping pressure exerted between the fixed mold 10 and the movable mold 12 is stepwise switched and controlled by the mold clamping device during one cycle from the process and the resin material cooling process to the mold opening process. That is, in a state where the molds 10 and 12 are clamped by the high-pressure mold clamping primary pressure,
The molding cavity 14 is injected and filled with a resin material, and the mold clamping pressure is dropped immediately after the completion of the filling to maintain the mold clamping secondary pressure for a predetermined time, and then the mold clamping pressure is increased again to a high pressure mold until the cooling time is completed. Clamping pressure control is performed in three stages in which the mold is clamped with the third clamping pressure.

More specifically, for example, as shown in FIG. 2, while maintaining the mold clamping pressure at a high mold clamping primary pressure: A, a resin material is molded into a cavity with a predetermined injection pressure. Immediately after a slight delay time: t1 after the injection pressure is reduced to 14 and the injection pressure is lowered to enter the cooling process, the mold clamping pressure is dropped to the low mold clamping secondary pressure: B and kept for a predetermined time: t2. After that, the mold clamping pressure is raised again to the high mold clamping tertiary pressure C, and the mold clamping pressure is maintained until the cooling process is completed. In addition, in FIG. 2, the mold opening amounts of the molds 10 and 12 are also shown.

If such a three-stage mold clamping pressure control is adopted, first, the mold clamping primary pressure: A is dropped immediately after the filling of the resin material to the mold clamping secondary pressure: B, so that a high mold clamping pressure is obtained. Since the speed and amount of the resin material flowing back from the molding cavity 14 to the injection nozzle side is suppressed, the pit deviation due to the backflow of the resin material immediately after the filling can be effectively prevented, and further, the predetermined cooling time is required. By increasing the mold clamping secondary pressure: B to the mold clamping tertiary pressure: C again after the lapse of time, the cooling effect of the skin layer (the surface layer portion in contact with the mold) in the molded article can be improved, and the cooling time can be shortened. It can be achieved. And, in particular, the fixed side cavity forming surface 22
Since the surface roughness of Rz is set to Rz = 50 to 400 nm and the mold releasability of the molded product is improved, even if the mold clamping third pressure C is set high in the cooling process, the It is possible to prevent the parts from intimately contacting the fixed side cavity forming surface 22 and prevent the deterioration of the quality of the molded product due to the unevenness of the mold release. Therefore, the product quality such as excellent appearance and mechanical characteristics is secured. At the same time, the molding cycle can be more effectively achieved by improving the cooling effect.

By the way, using the fixed mold 10 and the movable mold 12 having the above-described structure in which the surface roughness of the fixed side cavity forming surface 22 is set to various values,
Table 1 below shows the results of observing the products obtained by performing a molding test on the optical disk substrate. In addition, the molding test is performed according to the mold clamping force control shown in FIG.
= 140 kg / cm ² , mold clamping secondary pressure: B = 70 kg / cm ² , mold clamping tertiary pressure: C = 140 kg / cm ² , cooling process time is 2.0 seconds, molding cycle is 5.0 seconds. The delay time from the start of the cooling process to the reduction of the mold clamping secondary pressure is as follows:
t1 = 0.1 second, holding time of secondary pressure of mold clamping: t2 = 0.7
Mold clamping pressure is controlled in 3 stages and the mold clamping force is kept at the initial mold clamping pressure of 140 kg / cm ² during the entire molding process without reducing the mold clamping force in the cooling process. It was done for each case.

[0032]

[Table 1]

Further, in Table 1, the birefringence of the molded product of this example of Test No. 2 and the molded product of Comparative Example of Test No. 6 were measured, and the results are shown in FIG. 3 and FIG. Shown in. Note that birefringence is obtained by the following equation, where x is the refractive index in the x direction and nx is the refractive index in the y direction, and y is the light having a deflection surface parallel to the x direction. The phase difference with the y component (light having a deflection surface parallel to the y direction) is represented by δ. δ = 2π / λ · (nx-ny) d where λ: wavelength of light d: distance of medium through which light has passed Further, in FIGS. 3 and 4, birefringence is measured at each of eight radial positions. Then, the maximum, minimum, and average values of those measured values are measured by the measurement light (HeNe laser).
It was displayed at the wavelength of.

From the results shown in Table 1, the surface roughness of the fixed side cavity forming surface 22 is Rz = 50 to 50 according to the present invention.
By using a mold having a thickness of 400 nm, it is possible to stably manufacture an optical disk substrate having excellent mechanical characteristics and appearance characteristics.
It is apparent that the mechanical characteristics and the appearance characteristics of the optical disc substrate can be further improved by controlling the switching in stages. Further, the molded article according to the present example whose measurement results are shown in FIG. 3 had a birefringence within the range of ± 40 nm, while the molded article of the comparative example whose measurement results were shown in FIG.
It could not satisfy the standard of ± 80 nm, and it was a clear defective product. Further, the molded article of this example whose measurement results are shown in FIG. 3 and the molded article of the comparative example whose measurement results are shown in FIG. Almost no pit deviation was observed in the product, whereas large deviations were observed in most of the pits in the molded product of the comparative example.

The embodiments of the present invention have been described in detail above, but these are literal examples, and the present invention should not be construed as being limited to such specific examples.

For example, in the above embodiment, the stamper 44 was set on the movable mold 12 side, but it is also possible to set the stamper on the fixed mold 10 side. In such a case, the movable side cavity forming surface 36
Is processed so as to satisfy the surface roughness: Rz = 50 to 400 nm.

Also, in the cooling step after the mold clamping force of the mold is maintained at the mold clamping primary pressure and the resin material is filled in the molding cavity, the mold clamping force of the mold is lower than the mold clamping primary pressure. A disc molding die having a structure according to the present invention is advantageous even when disc molding other than the method of the present invention is adopted, such as when adopting a two-stage mold clamping pressure control in which the pressure is reduced to the secondary pressure and maintained until the end of the cooling process. It goes without saying that it can be applied.

Furthermore, the specific mold structure, such as the stamper holding structure in the mold, is not limited to the above embodiment.

Although not listed one by one, the present invention is
The present invention can be carried out in a mode in which various changes, modifications, improvements, etc. are added based on the knowledge of a person skilled in the art, and such a mode does not depart from the gist of the present invention.
Both are included within the scope of the present invention,
Needless to say.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an overall outline of a disk molding die as an embodiment of the present invention.

FIG. 2 is a graph exemplifying specific behaviors of injection pressure, mold clamping pressure and mold opening amount when the mold clamping pressure is controlled according to the method of the present invention.

FIG. 3 is a graph showing measurement results of birefringence of an optical disc substrate obtained according to the method of the present invention.

FIG. 4 is a graph showing a measurement result of birefringence of an optical disc substrate as a comparative example.

[Explanation of symbols]

 10 Fixed Mold 12 Movable Mold 14 Disk Molding Cavity 16 Fixed Side Mirror Block 22 Fixed Side Cavity Forming Surface 28 Movable Side Mirror Block 36 Movable Side Cavity Forming Surface 44 Stamper

Claims (2)

[Claims] 1. A disk molding mold, comprising a fixed mold and a movable mold to which a stamper is mounted on any one of the cavity forming surfaces, and forming a disk molding cavity by being fitted together. The cavity forming surface of the other of the fixed mold and the movable mold, which is positioned to face the stamper,
A disk-molding mold having a surface roughness of Rz = 50 to 400 nm. 2. When a disk is formed using the disk-forming mold according to claim 1, cooling is performed after the mold clamping force is maintained at the mold clamping primary pressure and the resin material is filled in the molding cavity. In the step, the mold clamping force of the mold is reduced to a mold clamping secondary pressure lower than the mold clamping primary pressure, and then raised again to a mold clamping tertiary pressure higher than the mold clamping secondary pressure. A disk molding method using the disk molding die according to claim 1.