JPH07201091A - Molding method for substrate for magneto-optical disk - Google Patents

Abstract

PURPOSE:To prevent defect from occurring by performing the primary injection of a quantity with which resin melted in a metal molding provided with a sprue puller part reaches a cavity inner circumference mirror surface in a range of 1000 to 1,1000sec<-1> of mean shearing speed at a sprue part. CONSTITUTION:When a part with a low temperature of the nozzle 19 of a nozzle part 11 is injected at a high speed, no resin can be held in the sprue puller part 20, and not only a large number of cold slugs are generated on a substrate, but a silver streak is easy to be generated. Therefore, the primary injection in a range of 1000 to 1,1000sec<-1> more desirably, 4000 to 10,000sec<-1> is required. Also, the quantity with which the resin melted by the primary injection reaches the cavity inner circumferential mirror surface of the metal molding is required.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an injection molding method for a thin disk-shaped plastic magneto-optical disk substrate for use in a magneto-optical recording medium capable of optically writing, reading and erasing information. is there.

[0002]

2. Description of the Related Art Magneto-optical disks have concentric spiral grooves formed on the surface of a plastic substrate with a depth of about 70 to 130 nanometers (nm) and a pitch of about 1.6 μm. A magnetic thin film of Gd-Tb-Co system or the like and a protective film are formed on the surface thereof. Information is written, read, or erased by heating the magnetic film to a temperature near the Curie point and magnetizing it by applying a magnetic field in a predetermined direction, and reading information focuses on the magnetized information. When the laser light is irradiated by the laser light, the light is rotated and reflected by the magnetic field of the information pit, so that the information can be read by catching the rotation direction. Information can be erased by irradiating the magnetic film from the back side of the substrate through the lens while focusing on the magnetic film to raise the temperature of the magnetic film to the Curie point or higher.

As a substrate used for these recording media, a so-called 2P method (in which a pit-like information or guide groove is transferred by coating a glass substrate with a photoresist compound which is hardened by ultraviolet rays and irradiating with ultraviolet rays through a photomask ( Pho
to Polymerization Process) and injection molding of transparent thermoplastic synthetic resin to form pit-shaped information and guide grooves in one step. The injection molding method provides excellent mass productivity and is the mainstream substrate manufacturing method. Is believed to be. However, when a substrate obtained by injection molding a thermoplastic synthetic resin is used as a substrate for a recording medium, foreign matter or scratches on the substrate cause the laser light to be reflected or absorbed by a device with a poor appearance, so reading or Not only writing becomes impossible, but also the product value is reduced. If the birefringence of the substrate is large, it will become noise when reading and writing information, and the sensitivity will decrease, and the surface fluctuation of the substrate when rotating the magneto-optical disk If a signal is generated or the substrate is tilted, the pickup that reads or records the signal cannot follow the guide groove or the information pit.The guide groove and the information pit faithfully follow the stamper inside the substrate.
Unless it is transferred to a uniform shape and depth, it will affect the signal reading. Also, if there is a large variation in transferability depending on the location, it will cause noise and cause misreading of information, etc., and it will be free from foreign matter or scratches and has excellent appearance. There is a demand for a substrate made of a thermoplastic synthetic resin, which is excellent in mechanical properties such as small deformation and has guide grooves and information pits uniformly transferred.

[0004]

As a solution to these problems, in JP-A-58-126119, in injection molding a polycarbonate resin, a phosphite ester is added to the polycarbonate resin and mixed, and a resin temperature of 330 to 400 ° C. Mold temperature
This is a method in which the polycarbonate resin is prevented from decomposing by injection molding at 50 to 100 ° C., and a substrate having excellent transparency and having little optical distortion and little warpage is obtained. However, even when this method is used, the resin staying at the nozzle tip portion in contact with the mold is hard to flow because it is cooled and tends to form a lump, and when injected, this portion reaches the information writing portion of the substrate. Inflow, a part with a different refractive index (cold slug) locally occurs, a sparkling part (silver streak) like air entrapment occurs, or a crack like a groove is generated. Defects such as abrasion were likely to occur.

On the other hand, as a method of injection molding a substrate having a small birefringence, Japanese Patent Publication No. 03-41048 has been proposed. This method uses a polycarbonate resin with a molecular weight of 14,000 to 22,000 to determine the residence time and injection speed of the polycarbonate resin in the injection cylinder, and
This is a method of reducing the birefringence of a large-diameter substrate of mm or more.
Even when this method was used, cold slugs, silver streaks, and defective appearance such as chipped grooves occurred. In molding a substrate, a defective appearance such as cold slug or silver streak not only lowers the product value but also causes noise and defects in reading and writing information, and thus needs to be improved.

If the distortion caused by the cold slug remains on the mirror surface portion where no information is contained, there was no serious problem in quality in practical use, but the optical disk is 5.25 'type, 3.
With the emergence of 5'types, mini discs, etc., there is a trend toward smaller diameters, and the inner diameter of the part containing information is also 29.7φ, 23.53φ
Since it is getting smaller and so on, the need to suppress the occurrence of cold slug has become larger. Further, it has been required that the guide groove and the information pit have a constant shape and depth, and that the inner peripheral portion and the outer peripheral portion of the substrate do not vary from place to place and are transferred and molded. In order to obtain a substrate with high transferability, it was necessary to raise the mold temperature or to raise the molding fluid temperature to raise the molding temperature. But,
When the conventional injection-type mold molding machine shown in Fig. 2 was used, the transferability increased as the mold temperature increased up to a mold temperature of 120 ° C, but it was higher than 120 ° C. When this happens, the transferability of the grooves and pits tends to deteriorate. The birefringence and transferability are not clear as to the variation of the raw material resin lot and the size of the cause, but it also varies depending on the molding time or the molding time such as am or pm on the same molding day.
A molding method having such a small variation has been desired from the molding side. The inventor of the present application filed Japanese Patent Application No. 4-1300
No. 31 proposes a high-precision injection molding method that exceeds the standard values of birefringence, surface wobbling and tilt, and also Japanese Patent Application No. 5-9762.
No. 2 proposed a method to prevent the occurrence of cold slack and silver streaks. However, in the mass production stage, the lot of raw material resin changes, the molding date is different even for the same lot of resin, and the transferability and birefringence deviate from the target values near the start-up of the molding machine and during long operation. It was easy to happen. Therefore, the object of the present invention is to reduce the occurrence of appearance defects such as cold slugs and silver streaks even if the variation in raw resin between lots, the molding date, and the molding time are small, and the variation in birefringence is small, and the transferability is small. The establishment of high molding method.

[0007]

The inventors of the present invention thoroughly reviewed the injection molding method in order to solve the problems, and particularly, the variation between the raw resin lots and the slight variation of the molding conditions (apparently, the same setting is set). Even if the conditions vary depending on the molding date and time), a molding method for obtaining a substrate with a wide appearance, birefringence, mechanical properties, and transferability is defined by the injection conditions and the appearance of the molded product. The present invention has been completed by investigating the relationship of characteristics and the like, and the gist thereof is to set the molding of a substrate for a magneto-optical disk having a diameter of 130 mm or less at a temperature lower than the glass transition temperature Tg of a raw thermoplastic synthetic resin by 15 ° C or more. In the method of injection compression molding into a mold, the amount of resin melted in a mold having a sprue-plural portion having a volume three times the nozzle volume or more reaches the inside mirror surface of the cavity is determined by the average shear rate at the sprue portion. There was first injection molding within the 1,000～11,000Sec ^-1, then the mean shear rate is greater than the first injection molding average shear rate in the sprue portion of the cavity underfilled amount, and within a range of 10,000～30,000Sec ^-1 Secondary injection, followed by tertiary injection (holding pressure) at a pressure of 200 to 500 kg / cm ² for 0.1 to 0.5 seconds, and immediately after that, mechanically shut off the gate part to 200 kg / in the thickness direction of the molded substrate. A method of molding a substrate for a magneto-optical disk is characterized by cooling for 7 seconds or more while applying a pressure of cm ² or more.

The present invention will be described in detail below. The most important feature of the present invention is that the appearance (cold slug, silver streak, etc.), birefringence, mechanical properties, and transferability of a molded product change significantly when the molding date and time or the raw resin lot changes. However, it is a method of molding a high-quality substrate in which the quality and the characteristics are less likely to be changed by the disturbance as described above. The first barrier to board evaluation is the appearance of the molded product, and those with a good appearance are evaluated as suitable as a board. Furthermore, the second barrier of evaluation is birefringence, mechanical properties, and whether guide grooves and information pits are accurately formed (transferability). Defects in the appearance of the 1st barrier are unfilled, cold slug, silver streak, etc. Unfilled occurs when injection weighing is insufficient, injection pressure or speed is insufficient, molding temperature is low, etc. However, the cause of cold slug and silver streak is due to the delicate balance between the shape of the mold and the injection conditions, and as a method for preventing these occurrences, Japanese Patent Application No. 5-9762 filed previously by the present inventor was used.
It is possible by applying No. 2. That is, the method of preventing the generation of cold slug is to increase the temperature of the nozzle portion. Increase the temperature of the mold sprue. A method is conceivable in which the gate portion (point A in FIG. 2, the first gate portion) of the mold is thinned and the cold slug is erased by the heat generated when the molten resin passes through the gate part of the mold. However, the generation of cold slugs is reduced, but when the molded product is taken out of the mold, a threading phenomenon occurs between the sprue and the nozzle, and the thread remains on the mold and adversely affects the molded product. The temperature cannot be raised too high. For example, in the case of molding with polycarbonate, if the nozzle temperature is 310 ° C. or less with respect to the molding temperature (temperature of the heating cylinder portion) of 360 ° C., the stringing phenomenon is improved, but cold slug is likely to occur. The temperature of the mold sprue is to be kept below the glass transition temperature Tg of polycarbonate because of the punching of the gate part (the part corresponding to the center hole of the disk). If the temperature is higher than the glass transition temperature, burr is generated during punching of the gate part (point A in FIG. 2, first gate part),
The temperature of the sprue must be set below the cavity temperature as it not only sticks to the mold to make it difficult to release the molded product but also causes deformation of the molded disc. This is a condition that is likely to occur. Thinning the portion of the gate portion (point A in FIG. 2, the first gate portion) has the effect of diminishing the phenomenon of cold slug generation, but since it is enlarged thinly, the elimination effect is small.

The substrate raw material used in the present invention includes, as the thermoplastic synthetic resin, aromatic polycarbonate, amorphous polyolefin, methyl methacrylate polymer and the like, and preferably aromatic polycarbonate. Generally, when molding a thermoplastic synthetic resin magneto-optical disk substrate, the cylinder temperature of the raw material metering / plasticizing part is about 320 to 3 because it forms a very fine groove or pit (Pit).
It must be set in the range of 60 ° C. If the temperature of the cylinder is lower than 320 ° C., the melt viscosity becomes high, which not only lowers the transferability but also causes disadvantages such as a decrease in birefringence caused by a decrease in fluidity, which is not preferable.
If the temperature exceeds 60 ° C., the thermal decomposition of the raw material is promoted, discoloration or blackening is caused, and inconveniences such as generation of decomposition gas become remarkable, which is not preferable. When injection molding, if you set the temperature of the nozzle to the same temperature as the cylinder temperature,
When the molded substrate is taken out by opening the mold, the yarn is pulled by the nozzle portion and the sprue portion, and the yarn remains on the substrate during the next molding, resulting in a defective product. Therefore, it is necessary to set the temperature of the nozzle to 310 ° C or lower, which is a temperature at which the yarn is not pulled, and it is preferable to set it in the range of 270 to 310 ° C. Not only that, but there is an inconvenience such as promoting cold slug.

The mold temperature was set at a temperature lower than Tg by 15 ° C. or more as a result of a study using the mold of the present invention, that is, the injection compression method, which has improved heat transfer efficiency. However, if the mold temperature is higher than (Tg −15) ° C., the residual stress of the molded substrate tends to be small, and the birefringence of the substrate immediately after molding tends to be small. There is a drawback that it takes too much time and that when the mold is opened and taken out, the elastic modulus of the substrate is small so that it is easily deformed. Further, if the mold temperature is lower than (Tg −55) ° C., not only the cooling time can be shortened, but also when the mold is opened and taken out, the elastic modulus is increased due to the lower temperature of the substrate, so that the deformation occurs. Although there is an advantage that it is difficult, the injected molten resin is rapidly cooled in the process of flowing into the mold, so the fluidity of the molten resin is significantly reduced, and the transferability of the grooves and pits of the stamper is reduced. However, there is a drawback that a large shear force is generated in the fluidity and the absolute value of birefringence becomes large. Therefore, the mold temperature is (Tg -15) ~ (Tg -5
5) The range of ° C is preferred.

A longitudinal sectional view of the nozzle portion 11 is shown in FIG. The resin that has accumulated in part of the nozzle 19 and nozzle pool 19a in the figure tends to lower in temperature because this part is set at a temperature lower than the heating cylinder part to prevent stringing when taking out the molded product. Moreover, the cooling effect due to the nozzle touch between the mold and the nozzle portion also helps, and it tends to cause cold slug. In order to prevent the generation of cold slug, when viewed from the structure of the mold, if the volume of the sprue puller section 20 shown in the vertical cross-sectional view of the mold in FIG. However, the generation of cold slug can be reduced by setting the volume of the sprue puller portion to 3 times or more, preferably 5 times or more that of the nozzle 19. If it is 10 times or more, the reduction effect is great, but the apparent product yield is lowered, so 10 times or less is preferable.

In order to suppress the birefringence of the substrate to a low level, injection should be performed as fast as possible. However, if the low temperature portion of the nozzle 19 of the nozzle portion 11 is injected at high speed, the resin will be injected into the sprue puller portion 20. It is not possible to keep it in place, and not only cold slug remarkably occurs on the substrate, but also silver streak easily occurs due to the inclusion of gas, so the average shear rate in the sprue part 12 is 11,000 se.
It is preferable to suppress it to c ^-1 or less. If it exceeds 11,000 sec ^-1 , silver streak will be generated on the substrate due to the inclusion of cold slug and gas. Also 1,
If it is less than 000 sec ^-1, the resin exiting the nozzle 19 can be retained in the sprue puller portion 20, but not only is the melt cooled in the middle and it becomes difficult to fill the cavity, but also the pressure increases, so molding The birefringence of the product substrate increases to the negative side. Thus the range of 1,000~11,000sec ^-1, more preferably it is necessary to first injection molding within the 4,000~10,000sec ^-1. Further, it is necessary to inject a quantity of the resin melted by the primary injection to reach the inside of the inner peripheral mirror surface portion of the mold cavity (between FIG. 3B and C).

In the secondary injection, when the resin is not injected into the inner peripheral mirror surface of the cavity and the secondary injection is performed, the second gate portion (B in FIG. 3) is generated due to the fixture at the inner peripheral portion of the stamper.
Since a concave portion such as (dot) is located at the boundary with the mirror surface, inconvenience such as appearance of entraining gas occurs unless the resin melted at a slow speed is allowed to pass through the second gate portion B.
When the resin is injected in the second recording after the resin has passed through the cavity inner peripheral mirror surface and entered the information recording portion, the absolute value of the birefringence of the portion that flows at a low speed while being cooled easily increases,
There is an inconvenience such that it enters the information recording section.

Next, in order to fill the mold cavity with the insufficient filling amount, the average shear rate in the sprue part is higher than the primary injection average shear rate, and 10,000 to 30,000 sec.
^The secondary injection is performed within the range of ^-1. However, if this average shear rate is not higher than the average shear rate of the primary injection, the flow velocity in the radial direction in the information recording part decreases in inverse proportion to the radius of the substrate. Therefore, the influence of cooling becomes large, and disadvantages such as birefringence and decrease in transferability occur, which is not preferable. further
If a predetermined amount of secondary injection is performed within the range of 10,000 to 30,000 sec ^-1 , no generation of cold slug is observed on the substrate surface, and a substrate for magneto-optical disk having a small birefringence can be formed. If it is less than 10,000 sec ^-1 , it flows while being cooled, so that the influence of cooling becomes large, and not only the absolute value of birefringence becomes large, but also the transferability of grooves and pits deteriorates. On the other hand, if it exceeds 30,000 sec ^-1 , the grooves and pits of the information recording portion cannot be completely filled, resulting in gradual smoothness, which causes inconveniences such as groove breakage. The average shear rate γ '(sec ^-1 ) here is defined by the following equation. γ ′ = 4Q / πγ ³ (γ: average radius of sprue part (cm), Q: injection amount (cm ³ /
sec)) Furthermore, to prevent sink marks due to shrinkage during the cooling process,
A substrate for a magneto-optical disk having no defects can be obtained by cooling while holding pressure (third injection for supplementing shortage).

Defects in the birefringence, mechanical properties and transferability of guide grooves and information pits of the second barrier of substrate evaluation can be considered as the following causes and countermeasures, but it is easy if any one of the properties is improved. However, if one of the characteristics is improved, the other is deteriorated, and it is difficult to deal with them. For example, if the mold temperature is raised to improve the birefringence, the tilt of the mechanical properties will deteriorate. The countermeasures that are considered to be the causes are described below for each characteristic. 1) The occurrence of birefringence is considered to be due to the three-dimensional imbalance between the shear stress generated when the melt injected into the mold flows while being cooled and the three-dimensional imbalance between the shrinkage generated during the cooling process. As a result, the birefringence can be reduced by promptly stopping the flow after the melt injected into the mold is filled in the mold and relaxing the stress generated by the strain during the flow and the cooling process. It is thought that it can be done. 2) The mechanical characteristics are evaluated in terms of the axial or radial deflection of the substrate and its acceleration and the tilt (tilt) at the time of reading the signal. Therefore, if the substrate is warped or twisted, The shake and acceleration increase, and the tilt increases. Also, if the guide groove is eccentric or has no circularity, the radial runout and acceleration will be large.Therefore, the board should be flat without warping or twisting, or the guide groove should be eccentric. The question is whether or not they have been rounded off and whether or not they are round. It is considered that most of the guide groove is eccentric or whether it has a circularity due to the stamper. Therefore, it is important to manufacture the stamper with high precision. Even if the stamper is manufactured accurately and accurately, if it is eccentric when it is set in the mold, the runout in the radial direction becomes large. If the outer presser foot 3 of the stamper is tightly tightened by setting so that there is no eccentricity, the stamper will heat or flow when the molten resin at a temperature higher than 200 ℃ above the mold temperature flows in the cavity. Since it expands and deforms due to the stress at the time, the guide groove is formed in a distorted shape, and the radial deflection of the mechanical properties becomes large. Therefore, as a setting method of the stamper, the center part presser 14 of the stamper is centered with a tolerance of 10 μm or less, and further, it is pressed at intervals so that the stamper can rotate even when the stamper is pressed,
When the presser foot on the outer periphery of the stamper is pressed with the stamper presser foot 3, the gap between the stamper and the presser foot is about 1 μm or less, and it is set so that it can enter the inside of the stamper presser foot 3 without being distorted when the stamper thermally expands. That is the point of the molding for reducing the radial runout. If the distance between the stamper retainer 3 and the stamper is 1 μm or more, burrs are likely to occur, and therefore, it is preferably 1 μm or less.

In order to improve the mechanical properties, the stamper is strictly set in the mold, and the rest depends on how to flatly mold the substrate in terms of molding technology. The reason why the substrate is warped or twisted is that the shear stress caused by the flow of the tertiary injection in the cooling process remains and the density difference due to the mold temperature difference on both sides of the substrate and the thickness from the substrate surface during the cooling process. If there are various residual stresses such as or due to dimensional difference and stress that occur when the density gradient around the center of the product changes in the direction where the densities become equal as time goes by, it will expand or contract when taken out from the mold and deform. However, due to insufficient cooling, when the temperature of the molded product at the time of mold opening is equal to or higher than the glass transition point Tg or is close to Tg, the molded product is soft and therefore deformed by a slight force when taken out from the mold. In order to mold a flat substrate that satisfies the mechanical characteristics, it is necessary that both sides of the substrate are uniformly cooled and shrunk, stress is sufficiently relaxed, and sufficiently cooled so that it does not deform when taken out from the mold. Is. For this purpose, it is considered that the stress should be sufficiently relaxed near the glass transition point Tg, then cooled to room temperature and taken out from the mold. However, productivity is extremely deteriorated, and therefore, in general, Japanese Patent Application No. 5-97622. Molding is done at a low mold temperature (about 70-115 ° C) as seen in.

3) Transferability of guide grooves, information pits, etc.
It is necessary to form a uniform shape and depth at any place from the inner peripheral part to the outer peripheral part of the substrate, but since the injected melt flows in the mold while being cooled, the outer peripheral part must be transferred. In many cases, the sex becomes poor. A possible solution to this problem is to raise the mold temperature and increase the injection speed. However, if the mold temperature is raised to (Tg-15) ° C or higher, the shrinkage becomes large and the transferability is deteriorated, so that there is a limit. Since a silver streak is generated, the injection speed is limited to about 30,000 sec ^-1 at the shear rate at the sprue part. It is necessary to perform molding so that the transferred guide groove, pit, etc. contracts in the cooling process and does not deform so that even if it contracts, it is in constant contact with the mold until it is taken out from the mold. it is conceivable that. In the conventional molding technology, it is easy to satisfy each property individually, but it is a very narrow condition to satisfy all these properties. The present inventor has made the residual stress caused by flow shear after inflow and outflow into the mold uniform and small to reduce birefringence and deformation, and also to reduce birefringence and transferability due to contraction in the cooling process. In order to reduce the effect of the above, it is considered that an injection compression molding method equipped with a mechanism capable of compressing in the thickness direction of the substrate during injection is suitable. I found it to be excellent.

In order to supplement the amount of contraction caused by cooling, 2
The third injection is performed at a pressure of 00 to 500 kg / cm ² for 0.1 to 0.5 seconds, and the gate (B in FIG. 1 and A in FIG. 4) is mechanically shut off immediately without depressurizing the molded substrate. 20 in the thickness direction
Cool for 7 seconds or more while applying a pressure of 0 kg / cm ² or more.
If the pressure of the third injection is 200 kg / cm ² or less, not only is the shrinkage replenished insufficiently, but conversely, the melt passes from the cavity 1 through the gate 13 (Fig. 1) and the molding machine nozzle. In some cases, the current flows back to the 11 side, and the thickness of the substrate becomes thin, and the birefringence on the inner peripheral side of the substrate shifts significantly to the + side. 500k
When it becomes g / cm ² or more, the amount of the molten material flowing into the cavity 1 which started to cool from the molding machine nozzle 11 side through the gate portion 13 increases, so that not only the shrinkage is replenished but also the thickness is increased. As a result, burrs easily occur, and the birefringence on the inner peripheral side of the substrate shifts significantly to the "-" side. The absolute value of birefringence
If you try to hold it below 25 nm, the third injection pressure should be 200-
It is preferable to control in the range of 500 kg / cm ² . Also, 3
If the next injection time is shorter than 0.1 sec, replenishment becomes insufficient and it tends to be overwhelmed, and if it is 0.5 sec or more, the flow between the cavity 1 and the nozzle 11 in the cooling process becomes large and the absolute value of birefringence becomes large. A range of up to 0.5 sec is preferred. Three
After the next injection, if the gate 13 is shut off slowly, the cavity 1
Since the fluid continues to flow between the side and the nozzle 11 and the absolute value of birefringence increases, the hydraulic pressure 17 is immediately applied to the gate portion 13 while the pressure for the third injection is being applied, or without depressurization. The punch 5 mechanically shuts off to stop the flow between the cavity 1 and the nozzle 11. By operating the hydraulic pressure 16 and pushing the cavity block 4, the cavity 1
Cooling is performed for 7 seconds or more while applying a pressure of 200 kg / cm ² or more in the thickness direction to the molding in progress. 200 kg / cm ²
If the pressure is lower, the compression effect is smaller and the pressure is less uniform, and the transferability tends to be slightly lower. If the cooling time is shorter than 7 seconds, the residual stress is insufficiently relaxed and the inner peripheral portion of the molded product is insufficient. This is because the absolute value of birefringence tends to be 30 nm or more.

[0019]

EXAMPLES The embodiments of the present invention will be specifically described below with reference to examples, but the present invention is not limited thereto. (Example 1) (Experiment No. 1 to 18) The injection compression type mold molding machine shown in FIG. 1 was used. As shown in FIG. 3, the nozzle part 11 has a nozzle 19 of 2 mmφ × 3 mm.
The sprue section 12 has an average diameter of 3 mmφ and a volume of 0.475 cc, and the sprue puller section 20 has a volume of 0.0584 cc and 6.2 times the volume of the nozzle 19. In addition, as shown in the enlarged view around the cavity portion in FIG. 4, the stamper has an inner presser foot 3 ', a stamper outer presser foot 3'
It is installed by pressing in a ring shape. (The thickness of stamper 2 is about 1.2 mm.) Panlite AD-9000ZG (polycarbonate resin, Teijin brand name, lot No.I (melt flow 70 g / 10 min))
Was subjected to injection compression molding under the conditions shown in Table 1 using Lot No. IA dried at 120 ° C. for about 4 hours or more. The manufacturing procedure of the injection compression type mold molding machine (mold size A) shown in FIG. 1 will be described. The molding temperature conditions shown in Table 1 are set, and the primary injection and the secondary injection are performed under the conditions shown in Table 1. Injection and tertiary injection are performed, and it passes through the inside of the nozzle part 11 and inside the cavity 1
The molten resin is injected into.

After the third injection, the gate cut punch hydraulic cylinder 17 is operated and the gate cut punch 5 is operated upward to shut off the gate portion 13. Next, the cavity lock hydraulic cylinder 16 operates and the cavity lock 4 operates upward to apply pressure to the resin in the cavity 1 while cooling is in progress to cool and compress under the conditions shown in Table 1.
After the cooling is completed, the gate cut punch hydraulic cylinder 17 is activated to return the gate cut punch 5 to the original position, and at the same time, the movable die hydraulic cylinder 25 shown in FIG. The side mold mounting plate 15 is bent downward, and the movable mold 7 and the fixed mold 8 are separated from each other. Next, the hydraulic cylinder 18 for ejecting the Z-pin is actuated to actuate the Z-pin 6 upward, and then the molded product (substrate for magneto-optical disk).
To get The appearance, the groove and pit of the stamper, the transferability, the birefringence and the mechanical properties of the obtained substrate were measured and the results are shown in Table 1. Experiment Nos. 5, 6, 11 and 12
Is a comparative example corresponding to the prior art because no compressive force is applied to the cavity. In Experiments Nos. 6 and 12, it was found that a molded product (substrate) having an excellent appearance was obtained, but it was difficult to obtain a satisfactory value in transferability and birefringence (the target value was difficult to reach). On the other hand, if the gate 13 was shut off immediately after the third injection pressure was maintained and a compressive force was applied to the cavity to cool it, it was easy to obtain a substrate excellent in transferability and birefringence. Especially experiment
In Nos. 2, 3 and 4, excellent molded products (substrates) were obtained.

(Example 2) (Experiment Nos. 19 and 20) Experiment No. 19 was the same as Experiment No. 4 in Example 1 except that the injection compression type mold molding machine (Fig. 1) used in Example 1 was used. Panlite AD-90007G (polycarbonate resin,
Teijin brand name, lot No.I (melt flow 70g / 10
Min)) was dried at 120 ° C for about 4 hours or more.
-Panlite AD after continuous molding for 8 hours 30 minutes using A
-90007G (Previous: Lot No. I (melt flow 67g / 10
Min)) was dried at 120 ° C for about 4 hours or more.
It was changed to IB and molded for 3 hours and 30 minutes. The characteristics of the molded product (substrate) obtained at regular time intervals during this continuous molding were evaluated and shown in Table 2. Experiment No. 20 was performed in the same manner as Experiment No. 19 using the conventional type mold (cavity part cannot be compressed) and the injection type mold molding machine of FIG. 2 (FIG. 2). The resin was switched from Lot No. II-B to No. II-B, and the effect of the switching on molding was investigated, and the results are shown in Table 2. Injection compression type mold (Fig. 1)
The characteristics of the molded product (substrate) obtained by changing the molding time and the resin change slightly, but a molded product (substrate) with a high overall evaluation can be obtained without finely adjusting the molding conditions during molding. Was given. On the other hand, a conventional mold (Fig. 2)
With the use of, the molded products (substrates) with a high overall evaluation could not be obtained as the molding time passed and the molding conditions were finely adjusted by changing the lot number of the resin. What is more characteristic is that when an injection compression type die (Fig. 1) is used, the difference in transferability between the inner peripheral portion and the outer peripheral portion of the obtained molded product (substrate) is small, but the conventional type (Fig. With 2) there was a difference of about 5-6%.

(Evaluation Method) Appearance Evaluation: Cold slug, silver streak, burr and stringing state were evaluated according to the following criteria. Evaluation criteria: ◯: No occurrence, X: occurrence. Transferability: The transferability (%) was measured for the groove depth h of the molded product with respect to the height h _O of the mountain portion of the stamper using CLASURF 101 (trade name of Kurabo Industries). Transferability = (h / h 2 _O ) × 100 Birefringence: Radius measured with a measuring instrument manufactured by JEOL
The values of the 24 mm portion and the 40 mm portion are shown in Tables 1 and 2. Mechanical characteristics: Based on the ISO / SC23 / WG2 proposal, using the Ono Sokki optical disk mechanical characteristics measuring device Lm-100, axial and radial surface deflection, acceleration, deflection angle and tilt of deflection are measured. did. Comprehensive evaluation: One that passed the comprehensive evaluation criteria shown in Tables 1 and 2 was evaluated as ◯, and one that failed was evaluated as x.

[0023]

[Table 1]

[0024]

[Table 2]

[0025]

According to the present invention, the birefringence, which is an optical distortion due to the residual stress during molding, is reduced by preventing the generation of cold slugs, and the ejection of a substrate for a magneto-optical disk with less warpage and twisting. Molding method can be provided,
Its utility value is extremely high in industry.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a mold of an injection compression type molding machine used in the present invention.

FIG. 2 is a sectional view of a mold of a conventional injection type molding machine.

FIG. 3 is an enlarged cross-sectional view of a nozzle unit 11 of FIG.

FIG. 4 is an enlarged cross-sectional view of the periphery of a cavity portion 1 of FIG.

FIG. 5 is a schematic sectional view of an injection compression type molding machine used in the present invention.

FIG. 6 is a schematic sectional view of a conventional injection type molding machine.

[Explanation of symbols]

1 ... Cavity part 2 ... Stamper 3 ... Stamper outer circumference presser 3 '... Stamper inner circumference presser 4 ... Cavity block 5 ... Gate cut punch 6 ... Z-pin 7・ ・ ・ Movable mold 8 ・ ・ ・ Fixed mold 9 ・ ・ ・ Sprue bushing retainer 10 ・ ・ ・ Sprue bushing 11 ・ ・ ・ Nozzle part 12 ・ ・ ・ Sprue part 13 ・ ・ ・ Gate part 14 ・ ・ ・Fixed side mold mounting board 15 ・ ・ ・ Movable side mold mounting board 16 ・ ・ ・ Cavity block hydraulic cylinder 17 ・ ・ ・ Gate cut punch hydraulic cylinder 18 ・ ・ ・ Z-pin protruding hydraulic cylinder 19 ・..Nozzle (2 mmφ × 3 mml) 19a ・ ・ ・ Nozzle stay 20 ・ ・ ・ Sprupler part A ・ ・ ・ First gate part B ・ ・ ・ Second gate part (stamper presser) C ・ ・ ・ Lead-in part D ... Lead-out section E ... Outer peripheral area A-Center line ... Center hole A-B ... Clamping area B-C ... Inner peripheral mirror surface area C-D ... Information recording area D- Between E: Peripheral mirror surface

Claims (1)

[Claims] 1. A substrate for a magneto-optical disk having a diameter of 130 mm or less is molded from the glass transition temperature Tg of a raw thermoplastic synthetic resin by 15
In the method of injection compression molding in a mold set at a temperature lower than ℃, the amount of resin melted in the mold having a sprue puller part with a capacity of 3 times the nozzle capacity or more reaches the inside mirror surface of the cavity. The primary shearing is performed within the range of 1,000-11,000 sec ^-1 in the average shear rate in the sprue part, and then the cavity shortage filling amount is determined as follows.
~ Secondary injection within the range of 30,000 sec ^-1 , then 200 ~
The third injection pressure is maintained for 0.1 to 0.5 sec at a pressure of 500 kg / cm ² , and immediately after that, the gate is mechanically shut off and the pressure of 200 kg / cm ² or more is applied in the thickness direction of the molded substrate to cool it for 7 sec or more. A method of molding a substrate for a magneto-optical disk, comprising: