JP2002210784A - Mold for molding optical disk substrate and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a mold for molding an optical disk substrate which can produce the substrate having stable mechanical properties by controlling the generation of warpage, waving, etc., even when a small-size thin optical disk substrate is molded, and to provide a method for producing the optical disk substrate. SOLUTION: The thickness of a cavity space 4 in the mold, when the temperature of the mold is increased close, to the temperature of a molten resin 5 when the resin is injected/packed in the cavity space 4, is adjusted to be equal to or smaller by a prescribed thickness than the thickness of the optical disk substrate 7 as a molding.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mold for molding an optical disk substrate used as a recording medium and a method for manufacturing an optical disk substrate, and more particularly to a method for injection compression molding of an optical disk substrate formed by injection compression molding. The present invention relates to a mold and a method for manufacturing an optical disk substrate using the mold.

[0002]

2. Description of the Related Art In recent years, as a recording medium for recording information,
Optical disks excellent in storage capacity and storage stability have been actively used. The substrate of the optical disk is usually manufactured by injection molding using a thermoplastic resin as a raw material.

[0003] In general injection molding, in order to obtain a desired shape, a mold designed in consideration of a certain degree of heat shrinkage is used, an actual molded product is measured by injection molding, and then the cavity size is finely adjusted. By doing so, the dimensional accuracy is maintained.

However, when molding a precision thin-walled molded product such as a substrate of an optical disk, mainly, a step of filling a mold cavity space with a thermoplastic resin in a molten state, a mold clamping mechanism of an injection molding machine or a mold. It is manufactured by injection compression molding comprising a step of compressing a resin filled in a mold by a mechanism for applying a compressive force only to a cavity space by a movable core in the mold.

[0005] Injection compression molding is a type of injection molding performed for the purpose of stabilizing the optical characteristics, mechanical characteristics, and mechanical shape of a molded product, and manufactures a precision thin molded product such as an optical disk substrate as a molded product. It is a suitable molding method.

The process of manufacturing an optical disk substrate by the injection compression molding will be described below with reference to FIGS. 9 (a) to 9 (e).

As shown in FIG. 9A, the molding of the optical disk substrate is roughly divided into two mold parts, a first mold part 81 on the movable side and a second mold part 82 on the fixed side. Mold 8
This is done using 0.

First, as shown in FIG. 9 (a), the first mold part 81 attached to the movable platen (not shown) moves in the direction A indicated by an arrow together with the operation of the movable platen. The mold 80 is closed by the second mold part 82, and in this state, the mold 80 is clamped by a mold clamping force set to a predetermined pressure.

At this time, the mirror surface mold portion (not shown) attached to the first mold portion 81 and the second mold portion 82 are attached to a position facing the mirror surface mold portion. By regulating the outer diameter of the information recording stamper (not shown) and the two surfaces thereof with a cavity ring, a cavity space 84 is formed in the mold 80 as shown in FIG. 9B.

Next, as shown in FIG. 9C, a predetermined amount of the thermoplastic resin 85 plasticized and measured is supplied to the injection nozzle 8.
From 3, the cavity space 84 of the mold 80 is injected and filled. At this time, the first mold portion 81 of the closed pair of molds 80, or a compression mechanism (core) (not shown) installed to allow the first mold portion 81 to slide, is made of resin. 0.01 to 0.5 m in the direction of arrow B
Pushed back about m.

Thereafter, the thermoplastic resin 85 formed by filling the center hole of the disk substrate is sealed in the cavity space 84 by a spool gate forming member (not shown).

As shown in FIG. 9D, the thermoplastic resin 85 sealed in the cavity space 84 has a mold clamping force or a pressure for pressing the core (hereinafter, referred to as a stamping pressure).
As a result, a compressive force in the direction C indicated by the arrow is received. By the compression force, the orientation and internal stress of the thermoplastic resin 85 in the mold 80 can be adjusted, and the optical and mechanical properties of the formed transparent disk substrate can be controlled.

Finally, as shown in FIG. 9E, both or one of the first mold portion 81 and the second mold portion 82 is moved to remove the cooled and solidified optical disc substrate 87. Take out.

Here, the more detailed movement of the movable-side first mold portion 81 of the optical disk substrate molding die used in the optical disk substrate manufacturing process will be described with reference to FIG. It is on the street.

In the graph shown in FIG. 10, the vertical axis indicates the position of the first mold part 81, and the horizontal axis indicates time. Note that the periods a to e described on the horizontal axis correspond to the respective steps in the above-described optical disk substrate manufacturing method of FIGS. 9A to 9E.

When the production is started, in the mold closing step shown in FIG. 9A, the first mold portion 81 moves from the mold opening side to the mold closing side, and furthermore, in the present embodiment. The first mold portion 81 moves until the thickness of the cavity space 84 at the mold temperature at the time of molding set in advance (compression advance limit 201) is reached (period a).

Next, in the mold clamping step shown in FIG. 9B, mold clamping is performed by applying a predetermined pressure (period b).

Further, in the filling step shown in FIG. 9C, the plasticized thermoplastic resin 8
When 5 is injected at a high pressure, the first mold part 81 is pushed and retreats to the retreat limit 202 (period c).

Then, in the cooling / compression step shown in FIG. 9D, the mold filled with the thermoplastic resin 85 is cooled, but the thermoplastic resin 85 and the mold shrink with the cooling. Then, the first mold part 81 is moved in the mold clamping direction. At this time, the first mold portion 81 is under pressure until it moves to the compression advance limit 201, and is kept under pressure until the thermoplastic resin 85 is solidified and can be taken out (period d). ).

Finally, in the mold opening / removing step shown in FIG. 9 (e), when the thermoplastic resin 85 is solidified and ready to be removed, the first mold portion 81 is moved to the mold opening side to remove the mold. With the mold open, the molded optical disc substrate 8
7 is taken out (period e).

When transferring the information signal or the tracking guide groove formed on the surface of the information recording stamper to the surface of the molded substrate, the molded optical disk substrate 87 should be given a uniform compressive force. Cavity space 84
Is set to be about 0.00 mm to 0.05 mm thinner than a predetermined molded substrate thickness in a cold design.

Further, with the increase in the density of the optical disk, a thinner optical disk substrate than before has been demanded so as to be compatible with a pickup lens having a higher NA than before.

[0023]

However, in the above-mentioned conventional method for manufacturing an optical disk substrate, the thickness of the optical disk substrate is reduced to 0.
When a thin optical disk substrate 87 having a thickness of 7 mm or less is formed, the following problem occurs.

That is, the optical disk substrate 87 is formed with a guide groove for performing information recording pre-recorded on the surface of the information recording stamper or performing tracking during recording. In order to transfer the shape of the guide groove to the optical disk substrate 87, during molding, the glass transition point Tg (° C.) of the thermoplastic resin 85 is usually Tg−50 (° C.) to Tg
The temperature of the mold is stabilized at about −5 (° C.). In this manner, by forming the mold 80 while stabilizing the temperature within the above-mentioned temperature range and molding, the flow distortion of the molten thermoplastic resin 85 can be reduced while the flowability of the molten thermoplastic resin 85 can be reduced. It can be carried out.

However, when the temperature of the mold 80 is raised to the above temperature range, the mold 80 thermally expands, and the thickness of the cavity space 84 is reduced by about 0.03 mm to 0.07 mm. Further, as described above, the thickness of the cavity space 84 is set to be about 0.00 mm to 0.05 mm thinner than a predetermined product thickness of the optical disc substrate 87 in a cold design. Therefore, by raising the temperature of the mold 80, the thickness of the cavity space 84 at the time of molding becomes 0.1 mm.
It is about 03 mm to 0.12 mm, which is thinner than the product thickness.

As a result, as the product thickness becomes thinner,
The amount of shrinkage of the optical disk substrate 87 due to cooling also decreases,
Further, the reduction in the size of the cavity space 84 due to the expansion of the mold has a great effect. Especially, the product thickness is 0.7m
In the case of a thin optical disk substrate having a thickness of not more than m, if a mold clamping force or a stamping pressure is applied to the cavity space 84 using a mold similar to the conventional one, an excessive compressive force is applied to the thermoplastic resin 85. .

When the thermoplastic resin 85 is filled, a mold clamping force or a stamping pressure is easily applied to the cavity space 84 in order to obtain a desired thickness of the optical disk substrate in the cavity space 84 narrowed by heating and heating. It is set to be weak enough to increase the thickness. Therefore, when the thermoplastic resin 85 is injected into the mold 80 at a high pressure, FIG.
As shown in (c), the cavity space 84 in the direction of arrow B
Is spread out. Thereafter, according to the dimensional change (shrinkage) due to the cooling of the thermoplastic resin 85, a mold clamping force or a stamping pressure for tightening the mold 80 is applied.

Further, in the case of the above conventional mold structure,
At the time of cooling / compression shown in FIG. 9D, the first mold part 81 moves in the direction C indicated by the arrow, and attempts to close to the thickness of the cavity space 84 which is further reduced by the temperature rise of the mold 80. For this reason, excessive compressive stress remains in the optical disk substrate 87, causing distortion such as warpage or undulation of the molded product.

Still another conventional method for manufacturing an optical disk substrate is to control the shape of the optical disk substrate by controlling a mold clamping force or a stamping pressure in a mold in which an excessive compressive stress is applied. Has also been proposed. However, the shape of a small and thin optical disk substrate is sensitive to excessive compressive force, and warpage and undulation are likely to occur. Therefore, the variation between shots tends to increase, and it has been difficult to suppress the variation in the mechanical shape such as warpage or undulation and perform stable manufacturing by only mechanical control.

For example, in an optical disk substrate molding die for molding a CD (compact disk) having a diameter of 120 mm or a magneto-optical disk having a diameter of 90 mm (both having a thickness of about 1.2 mm), the information recording stamper is engraved. In order to transfer the obtained information satisfactorily, the thickness of the cavity space at the time of cold (room temperature) is designed to be smaller than the thickness of the molded substrate of 1.2 mm. Further, the resin filled at a position where the first mold part position 205 in the cooling / compression step in the period d shown in FIG. 10 is wider than the compression advance limit 201 at the time of the mold clamping in the period b shown in FIG. It will be compressed. In this case, all of the compression force excluding the pressure loss due to the friction of the mold is applied only to the directly filled resin. However, unless a mold having a size smaller than the product size and thickness is used and molding conditions are not applied to the resin filled with a sufficient compressive force, the information stamped on the information recording stamper is transferred to the optical disc substrate. Insufficient transfer pressure or partial shrinkage of the disk surface due to heat shrinkage made it impossible to produce an optical disk substrate efficiently.

When a small and thin optical disk substrate having a thickness of 0.7 mm or less is manufactured using the above-described mold as it is, the thickness is smaller than that of a conventional optical disk substrate.
The amount of expansion and contraction of the thermoplastic resin when pressure is applied to the cavity space is reduced, and an excessive compressive force is applied to the thermoplastic resin. Therefore, the excessive compressive force remains in the molded product as a residual stress, and causes distortion such as warpage or undulation of the manufactured optical disk substrate.

The present invention has been made in view of the above-mentioned problems, and has as its object to suppress the occurrence of distortion such as warpage and undulation even when molding a small and thin optical disk substrate, and to achieve stable mechanical characteristics. An object of the present invention is to provide a mold for molding an optical disk substrate and a method of manufacturing an optical disk substrate, which can manufacture an optical disk substrate having the following.

[0033]

In order to solve the above-mentioned problems, a mold for molding an optical disk substrate according to the present invention determines the shape of a molded product when a pair of openable and closable mold parts is closed. A mold used for injection compression molding for forming an optical disc substrate by forming a cavity space therein, and injecting and filling a molten thermoplastic resin into the cavity space, and then cooling and compressing the mold. The thickness of the cavity space when the mold is heated to a temperature close to the temperature at the time of injection filling of the molten thermoplastic resin into the cavity space is the same thickness as the optical disc substrate as a molded product or a predetermined amount smaller. It is characterized by being adjusted to.

According to the present invention, the thickness of the cavity space when the temperature is raised to near the temperature at the time of injection filling of the molten thermoplastic resin into the cavity space is the same as that of the optical disk substrate as a molded product. Are adjusted so as to be smaller by a predetermined amount. Therefore, it is not necessary to consider a decrease in the thickness of the cavity space due to the thermal expansion of the mold when the molten thermoplastic resin is filled in the cavity space, and the thickness of the cavity space is smaller than that of the conventional mold. Cooling with increased
It will be compressed.

That is, in the optical disk substrate molding die of the present invention, the thickness of the cavity space at the time of injection filling is set to be equal to or smaller than the thickness of the optical disk substrate as a molded product as described above. Is set,
The compression force applied to the thermoplastic resin in the cavity space at the beginning of the cooling / compression process is maximized. Then, as the inside of the mold is cooled, the mold and the thermoplastic resin shrink, and the compressive force applied to the thermoplastic resin in the cavity space decreases.

On the other hand, in the conventional mold, the compressive force applied to the thermoplastic resin in the cavity space during the cooling / compression step is applied until the mold is opened. Therefore, if the optical disk substrate has a thickness of about 1.2 mm, the amount of shrinkage of the thermoplastic resin is large, and excessive compressive force is not applied. Since the amount of shrinkage of the plastic resin is small, it causes distortion such as warpage or undulation of the molded product.

Thus, if the mold of the present invention is used,
In the cooling / compression step, no excessive compressive force is applied to the optical disk substrate as a molded product, so that an optical disk substrate free from distortion such as warpage or undulation due to residual stress can be obtained.

Further, the thickness of the cavity space in the mold when the temperature is raised to near the temperature at the time of injection filling of the molten thermoplastic resin into the cavity space is T, and the thickness of the optical disk substrate as a molded product. Is t, the following relational expression (1)
It is preferable to satisfy the following.

0.96t ≦ T ≦ t (1) Accordingly, the mold for molding the optical disc substrate is filled with the molten thermoplastic resin at the time of injection filling into the cavity space. The thickness T of the cavity space when the temperature is raised to a temperature close to the temperature (hereinafter, referred to as molding) is set in a range from 0.96 t (mm) to t (mm) with respect to the product thickness t of the optical disk substrate. Because it is limited, even when molding a thin optical disk substrate with a thickness of 0.7 mm or less,
Excessive pressure can be prevented from being applied to the thermoplastic resin filled in the cavity space. As a result, even when a thin optical disk substrate having a thickness of 0.7 mm or less is formed, occurrence of molding defects such as warpage and undulation can be reduced, and an optical disk substrate having stable mechanical characteristics can be obtained.

That is, in the cooling / compressing step in the manufacturing process of the optical disk substrate, a compressive force is applied in a direction to reduce the thickness of the cavity space as the thermoplastic resin filled in the cavity space shrinks.

In the present invention, in particular, the thickness T of the cavity space is set at the mold temperature at the time of molding, and the range of the thickness is reduced from the dimension of 4% reduction of the product thickness of the optical disk substrate to the optical disk. It is limited to a size equal to the product thickness of the substrate. For this reason, it is not necessary to consider the decrease in the thickness of the cavity space due to the expansion of the mold due to the temperature rise, and the cavity is cooled, compressed and molded with the thickness of the cavity space increased compared to the conventional case.

The reason for setting the lower limit of the thickness T of the cavity space at the time of molding to 0.96 × (product thickness t of the optical disk substrate) is as follows.

If the thickness is 4% of the product thickness, it is a stress region where elastic strain is generated, and residual strain due to excessive compression does not remain, so that it is possible to manufacture a molded substrate without impairing the flatness of the substrate. done.

On the other hand, the upper limit of the thickness T of the cavity space at the time of molding is set to the product thickness t of the optical disk substrate for the following reason.

If the upper limit of the thickness T of the cavity space is included to a dimension larger than the product thickness t of the optical disk substrate, the filled resin material is cooled and contracted, so that the space between the mold and the molded product is reduced. This is because a gap is formed in the hole and sink marks and the like are generated, so that the predetermined shape cannot be maintained. Thus, the upper limit of the thickness of the cavity space during molding is limited to the product thickness t of the optical disk substrate.

As described above, even when a thin optical disk substrate is molded, the occurrence of distortion such as warpage or undulation of the optical disk substrate is suppressed by preventing excessive pressure from being applied to the cavity space during molding. An optical disk substrate molding die having good dimensional accuracy can be obtained.

In other words, according to the present invention, even when a thin optical disk substrate is manufactured by applying the conventional method for manufacturing an optical disk substrate having a thickness of 1.2 mm, generation of distortion such as warpage or undulation cannot be suppressed. And a mold for forming a thin optical disk substrate having a thickness of 0.7 mm or less and a method of manufacturing the same.

The optical disk substrate molding die is
It is roughly composed of two parts, a first mold part and a second mold part. The cavity space is composed of the first mold part and the second mold part.
This is a space into which the thermoplastic resin is poured when the mold part is closed, that is, when the mold part is in the pressed state. By designing the mold in consideration of the dimensions of the cavity space and the shrinkage of the thermoplastic resin, molding with required product dimensions becomes possible.

It is more preferable that an information recording stamper on which an information signal to be recorded on an optical disk is formed is provided on at least one of the opposing surfaces of the pair of mold parts.

Thus, since the thickness of the cavity space at the time of molding is set within the above range, an appropriate pressure for transferring recording information is applied to the cavity space, and the guide formed on the information recording stamper is applied. Recorded information such as grooves can be transferred to the optical disk substrate simultaneously with molding.

That is, when the molten thermoplastic resin is injected and filled into the cavity space, and enters the cooling / compression step,
A compressive force is applied to the thermoplastic resin in the cavity space. At this time, since the information recording stamper is provided in at least one of the first mold part and the second mold part,
When a compressive force is applied, the recording information formed on the information recording stamper is transferred to one or both surfaces of the optical disk substrate. Thereby, the recorded information is transferred at the same time as the molding,
An optical disk substrate free of distortion such as warpage and undulation can be obtained.

The information recording stamper is a member on which recording information to be transferred to an optical disk substrate and guide grooves for performing tracking during recording are formed. It is provided to transfer recorded information to an optical disk substrate at the same time as molding by the pressure applied during molding.

The temperature of the mold when the temperature is raised to a temperature close to the injection filling of the molten thermoplastic resin into the cavity space is Td (° C.), and the glass transition point of the thermoplastic resin is Tg. (° C.), it is more preferable to satisfy the following relational expression (2).

Tg−50 ≦ Td ≦ Tg−5 (2) As a result, the flow distortion can be reduced while the flowability of the thermoplastic resin is ensured during molding. The groove or the like formed on the information recording stamper on which the information signal is formed can be accurately transferred to the optical disk substrate.

As described above, in addition to defining the thickness of the cavity space of the heated mold, the thickness of the cavity space of the mold when cold (room temperature) may be defined.

For example, assuming that the thickness of the cavity space of the mold at room temperature is T ₁ and the thickness of the optical disk substrate as a molded product is t, it is more preferable to satisfy the following relational expression (3). Here, t indicates the product thickness of the optical disk substrate.

1.04t ≦ T ₁ ≦ 1.12t (3) Accordingly, the thickness T of the cavity space at the temperature at the time of molding and the thickness of the cavity space at the room temperature To T ₁
By controlling the thickness of the cavity space at both temperatures, more accurate molding can be performed.

It should be noted that the range expressed by the above relational expression (3) is
The maximum value and the minimum value are calculated by taking into account the change in the thickness of the cavity space due to the shrinkage of the mold with respect to the setting of the thickness of the cavity space at the temperature during molding.

It is more preferable to mold the optical disc substrate using the above-described mold for molding an optical disc substrate.

As a result, even when a thin optical disk substrate is molded, the occurrence of distortion such as warpage or undulation of the optical disk substrate is suppressed by preventing excessive pressure from being applied to the cavity space during molding, and the product yield is reduced. Can be improved.

The thickness of the cavity space when the thermoplastic resin filled in the cavity space in the optical disk substrate molding die is cooled and compressed is represented by T ₂ , and the molten heat flowing into the cavity space is represented by T ₂ . Assuming that the thickness of the cavity space in the mold when the temperature is raised to near the temperature at the time of injection and filling of the plastic resin is T, the thermoplastic resin is filled into the cavity space so as to satisfy the following relational expression (4). It is more preferable to adjust the filling amount of the resin. In addition, T indicates the thickness of the cavity space in the mold when the temperature is raised to a temperature close to the temperature at the time of injection filling of the molten thermoplastic resin into the cavity space.

T ≦ T ₂ ≦ 1.04T (4) Thereby, by controlling the filling amount of the thermoplastic resin,
Variations in the filling amount can be eliminated, and an excessive compression force can be prevented from being applied to the thermoplastic resin during the cooling / compression step. Therefore, it is possible to more reliably prevent excessive pressure from being applied to the thermoplastic resin together with the setting of the thickness of the cavity space.

Further, the thickness of the cavity space is taken into consideration in consideration of a variation due to an error in the thickness of the information recording stamper provided on at least one of the opposing surfaces of the pair of mold parts and on which the information signal to be recorded on the optical disk is formed. More preferably, the setting is adjusted according to the thickness of the information recording stamper.

Normally, the thickness of the information recording stamper is allowed to have a tolerance of about ± 0.005 mm. Therefore, even if the thickness tolerance of the optical disk substrate is strictly controlled, the thickness variation of the information recording stamper is not affected. However, it may still affect the cavity spacing, that is, the excessive compression during cooling.

Therefore, as in the present invention, by adjusting the thickness of the cavity space by following the fluctuation of the thickness of the information recording stamper, the excess amount of the thermoplastic resin filled in the cavity space can be more reliably obtained. Pressure can be prevented from being applied. As a result, it is possible to mold an optical disk substrate free from distortion such as warpage or undulation.

Further, it is more preferable that the pair of mold parts in the cooling / compressing step be opened stepwise with the passage of time.

Thus, by gradually reducing the pressure for compressing the filled thermoplastic resin, it is possible to remove an excessive compressive force. Thus, by gradually removing the compressive force in this manner, the excessive compressive stress remaining in the optical disk substrate can be more reliably removed, and an optical disk substrate free from distortion such as warpage or undulation can be formed.

[0068]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of a mold for molding an optical disk substrate and a method of manufacturing an optical disk substrate according to the present invention will be described below with reference to FIGS.

The method for manufacturing an optical disk substrate according to the present embodiment is a manufacturing method by injection compression molding.

The optical disk substrate manufactured in this embodiment has a flat disk shape having a diameter of about 50 mm and a thickness of about 0.5 mm, and a metal hub for engaging with the drive unit is mounted at the center. A central hole having a diameter of about 7 mm is formed.

In the method for manufacturing an optical disk substrate by injection compression molding according to the present embodiment, as shown in FIG.
Molding is performed by opening and closing a mold that is roughly divided into two parts. That is, the two parts are the first mold part 1 on the movable side and the second mold part 2 on the fixed side. Also,
An injection nozzle 3 for injecting the plasticized thermoplastic resin 5 into the cavity space 4 is attached to the second mold part 2. The detailed configuration of the mold will be described later.

In the method of manufacturing an optical disk substrate according to the present embodiment, first, as shown in FIG. 2A, the first mold part 1 is moved along with the movement of the movable platen (not shown). The mold part 1 and the second mold part 2 are moved in the direction A for closing (mold closing step).

Next, as shown in FIG. 2B, the first mold part 1 is fixed to a second platen (not shown) fixed to a second platen.
The mold is closed so as to face the mold part 2, and a predetermined pressure is applied (mold clamping step). At this time, the cavity space 4 is formed by the first mold part 1 and the second mold part 2.

Further, as shown in FIG. 2C, the thermoplastic resin 5 plasticized in a flowable state by the plasticizing device (not shown) is supplied through the injection nozzle 3 to the cavity space 4. (Filling step). In this filling process, when the filling pressure of the plasticizing device shows the highest value, the first mold part 1 moves in the direction of arrow B, that is, the mold opening side due to the filling pressure of the filled thermoplastic resin 5. .

Then, as shown in FIG. 2D, the first mold part 1 and the second mold part are so arranged that the pressure in the cavity space 4 does not decrease with cooling of the filled thermoplastic resin 5. Pressure is applied to the first mold part 1 in the direction C in which the part 2 is closed. In this state, the thermoplastic resin 5 filled in the cavity space 4 is cooled and compressed until it can be taken out and solidified (cooling / compression step).

Finally, as shown in FIG. 2E, when the thermoplastic resin 5 has been cooled to a temperature at which it can be taken out, the compressive force compressing the cavity space 4 is reduced, and the first metal is further cooled. By moving the mold part 1 in the direction D, the cavity is opened and the optical disc substrate 7 as a molded product is taken out (mold opening / take-out step).

By the above five steps, the optical disk substrate 7
Is manufactured by injection compression molding.

Here, the more detailed movement of the first mold part 1 on the movable side of the mold for forming an optical disk substrate used in the above-described method for manufacturing an optical disk substrate will be described with reference to FIG. It is on the street.

In the graph shown in FIG. 1, the vertical axis indicates the position of the first mold part 1, and the horizontal axis indicates time. Note that the periods a to e described on the horizontal axis correspond to the respective steps in the method for manufacturing the optical disk substrate of FIGS. 2A to 2E described above.

When the production is started, in the mold closing step shown in FIG. 2A, the first mold part 1 moves from the mold opening side to the mold closing side, and further according to the present embodiment. The first mold part 1 moves until the thickness (compression advance limit 101) of the cavity space 4 at the mold temperature at the time of molding set in advance (period a). The mold temperature at the time of molding refers to the temperature of the mold 10 for molding an optical disk substrate when the temperature is raised to near the temperature at the time of injection filling of the molten thermoplastic resin 5 into the cavity space 4. Hereinafter, when the mold is heated to the above temperature is referred to as molding.

Next, in the mold clamping step shown in FIG. 2B, mold clamping is performed by applying a predetermined pressure (period b).

Further, in the filling step shown in FIG. 2C, when the plasticized thermoplastic resin 5 is injected into the cavity space 4 at a high pressure, the first mold part 1 is pushed to reach the retreat limit 102. Retreat (period c).

Then, in the cooling / compression step shown in FIG. 2D, the mold filled with the thermoplastic resin 5 is cooled, but the thermoplastic resin 5 and the mold shrink with the cooling. Then, the first mold part 1 is moved in the mold clamping direction. At this time, the first mold part 1 moves to the compression advance limit 101 and is held until the thermoplastic resin 5 is solidified and can be taken out (period d).

Finally, in the mold opening / removing step shown in FIG. 2 (e), when the thermoplastic resin 5 is solidified and can be removed, the first mold part 1 is moved to the mold opening side to remove the mold. The mold is opened, and the molded optical disk substrate 7 is taken out (period e).

In the above-described method of manufacturing an optical disk substrate, in the present embodiment, assuming that the thickness of the optical disk substrate, which is a molded product, is t, the period b shown in FIG.
The range of the thickness T of the cavity space 4 when the mold is clamped in (b) is set to 0.96t ≦ T ≦ t. In particular, in the present embodiment, attention is paid not to the thickness dimension of the cavity space 4 at the mold temperature at the time of molding (period bc shown in FIG. 1) but at the time of molding (period d shown in FIG. 1).

In the present embodiment, the thickness of the cavity space 4 in the mold is set to be substantially the same as the product thickness of the optical disc substrate at the mold temperature during continuous molding.
As shown in the figure, period b (clamping process) and period d (cooling
The position of the first mold part 1 in the compression step) is almost the same.

According to the method of manufacturing an optical disk substrate using the optical disk substrate molding die of the present embodiment as described above, the thickness of the cavity 4 in the clamped die is a molded product. Since the thickness is set to be equal to or slightly smaller than the thickness of the optical disk substrate 7, the thickness of the cavity space 4 in the mold does not become unnecessarily small in the cooling / compression step, and excessive compressive force is generated during the hardening. Of the thermoplastic resin 5. As a result, the optical disk substrate 7 free from distortion such as warpage or undulation can be formed. In particular, in molding the thin optical disk substrate 7 having a thickness of about 0.5 mm manufactured in the present embodiment, accurate molding conditions that do not apply excessive pressure are required. The manufacturing method used is very effective.

Here, the detailed structure of the mold used in the present embodiment will be described below with reference to FIG.

As shown in FIG. 3, the optical disk substrate molding die 10 used in the present embodiment includes a first die part 11, a second die part 12, a spacer ring 13, and an inner diameter punching means 1.
4. Movable mirror surface product protrusion 15, spool protrusion 1
6, an information recording stamper 17, a fixed-side mirror surface mold portion 18, a movable-side mirror surface mold portion 19, a cavity ring 20, and a stamper inner diameter holder 25.

The first mold part 11 and the second mold part 12 are
This is a main part of the optical disk substrate molding die 10 corresponding to the first die portion 1 and the second die portion 2 shown in FIG.

The spacer ring 13 is connected to the first mold 1
The member is provided on the outer peripheral portion of the surface facing the first mold portion 12 and regulates the limit of the movement of the first mold portion 11 together with the cavity ring 20. The spacer ring 13 may be provided on the second mold part 12 side.

The inner diameter punching means 14 is provided at the center of the first mold portion 11 and is a member for forming a center hole of about 7 mm formed at the center of the optical disk substrate.

The movable mirror surface product protrusion 15 is provided concentrically with the inner diameter punching means 14 and outside the inner diameter punching means 14, and when the first mold part 11 reaches the mold opening limit set arbitrarily. This is provided to take out the optical disk substrate formed by sliding away from the first mold portion 11.

The spool protrusion 16 is provided concentrically with the inner diameter punching means 14 and inside the inner diameter punching means 14 to take out a spool runner (not shown) which has become a path between the thermoplastic resin when the thermoplastic resin is filled. It is provided in.

The information recording stamper 17 is provided in the second mold 12
The first mold portion 11 is provided with a recording groove for transferring to an optical disk substrate and a guide groove for performing tracking at the time of recording. It is provided for transferring.

When the information recording stamper 17 is attached to the surface of the fixed-side mirror surface mold portion 18, the fixed-side mirror surface mold portion 18 comes into contact with the molded product via the information recording stamper 17, and the movable-side mirror surface mold portion 19.
Is a mold member located in a portion directly in contact with a molded product, and both surfaces have a mirror surface in order to improve the surface finish of the molded product.

The cavity ring 20 is installed in a substantially circular shape between the fixed-side mirror surface mold portion 18 provided with the information recording stamper 17 and the movable-side mirror surface mold portion 19, and the movable ring on the fixed-side mirror surface mold portion 18 side is provided. A member that forms a cavity space by regulating the outer peripheral end of the gap formed by the side mirror surface mold portion 19, but in a mold shown in another embodiment as shown in FIG. With the thickness of 20, the thickness of the cavity space can be adjusted.

Note that the cavity space corresponds to the first mold part 11.
And the second mold part 12 are closed, that is,
The figure shows a space surrounded by the cavity ring 20, the fixed-side mirror surface mold portion 18, and the movable side mirror surface mold portion 19 when the mold is clamped.

The stamper inner diameter holder 25 is a member for holding the information recording stamper 17, and is not shown.
It is located at the inner diameter of the stamper and holds the inner diameter of the stamper by vacuum or mechanical tightening.

In this embodiment, the information recording stamper 1 is used.
7 is used in a state provided on the surface of the fixed-side mirror surface mold portion 18, but is not limited thereto, and the same applies to the case where it is provided on the surface of the movable side mirror surface mold portion 19. .

In the optical disk substrate molding die 10 configured as described above, the thickness dimension T of the cavity space formed by the fixed-side mirror surface mold portion 18, the movable side mirror surface mold portion 19, and the cavity ring 20 is reduced. It is designed so that 0.96t ≦ T ≦ t with respect to the product thickness t of the optical disk substrate. That is, the thickness of the cavity space at the time of molding is limited to a range from a thickness 4% smaller than the thickness of the optical disk substrate as a molded product to a thickness equal to the optical disk substrate. The thickness of the cavity space in the mold when the temperature is raised to near the temperature at the time of injection filling of the molten thermoplastic resin into the cavity space is denoted by T.

The reason why the lower limit of the thickness of the cavity space is 4% smaller than the thickness of the optical disk substrate which is a molded product is as follows.

That is, at the time of molding, the mold 10 for molding an optical disk substrate is stabilized by raising the temperature to about Tg-50 ° C. to Tg-5 ° C. with respect to the glass transition point Tg of the thermoplastic resin as the molding material. . Thereby, the thermoplastic resin can reduce the flow distortion while securing the flowability, so that the groove or the like formed in the information recording stamper on which the information signal of the disk is formed can be accurately transferred to the optical disk substrate.
At this time, the optical disk substrate molding die 10 thermally expands, and the thickness of the cavity space is 0.03 mm to 0.07 mm.
mm. Here, the lower limit of the thickness of the cavity space is, as described above, 4 mm of the molded optical disk substrate.
% Reduced thickness (0.96 t). If the product thickness of the small and thin optical disk substrate is 0.7 mm or less, 4% of that
Corresponds to about 0.028 mm. When the thickness is 4% of the product thickness, the stress region is such that elastic distortion occurs, and no residual distortion due to excessive compression remains. Therefore, a molded substrate can be manufactured without impairing the flatness of the substrate.

Therefore, if the thickness of the cavity space at the time of molding is set within the above range, an excessive compressive force is not applied to the thermoplastic resin during the cooling / compressing step, and distortion such as warpage or undulation can be prevented. No optical disc substrate can be molded.

On the other hand, the reason why the thickness of the cavity space at the time of molding is limited to the same size as the optical disk substrate is as follows.

When the upper limit is set to a value equal to or larger than the size of the optical disk substrate, the cooling / compression step is completed, and the thickness of the cavity space when the thermoplastic resin is solidified increases due to shrinkage of the mold. The thickness becomes larger than the target thickness of the optical disk substrate, and if the target is manufactured as intended, the thickness of the cavity space becomes larger than the thickness of the optical disk substrate. A gap is formed between the mirror surface mold portion 19 and the information recording stamper 17, so that the optical disk substrate cannot be manufactured in an accurate shape. Further, in order to transfer the recording information formed on the information recording stamper 17 provided on the fixed side mirror surface mold portion 18 to the optical disk substrate simultaneously with molding, it is necessary to apply a certain pressure to the cavity space. For this reason, the upper limit of the thickness of the cavity space at the time of molding is set to a dimension equal to the product thickness of the optical disk substrate.

That is, if the thickness of the cavity space is equal to or smaller than the product thickness of the optical disk substrate, but the amount of shrinkage due to pressure does not become residual stress, an optical disk substrate free from distortion such as warpage or undulation can be used. Can be manufactured. Further, it becomes possible to accurately transfer the recording information of the information recording stamper to the optical disk substrate simultaneously with the molding.

For example, a diameter of about 50 mm and a thickness of about 0.5 m
In the case of an optical disk substrate having a thickness of about 20 μm, by using a mold having a thin cavity space having a thickness of about 20 μm (4% of the product thickness), even if an excessive compression force is applied, the compression force is reduced. Since it is absorbed by the shrinkage of the mold, it is possible to obtain an optical disk substrate having good mechanical characteristics with less distortion such as warpage or undulation, and an optical disk substrate on which recorded information is accurately transferred.

Further, since the thickness of the cavity space at the time of molding can be set within the above range and the optical disk substrate can be molded with high precision, the room temperature is taken into consideration in consideration of expansion of the cavity space due to shrinkage at the time of cooling. The thickness T ₁ of the cavity space at _{1 is set} to be 1.
04t ≦ T ₁ ≦ 1.12t may be set. Thus, by controlling the thickness of the cavity space at room temperature, the same effect as in the present embodiment can be obtained.

The range of T ₁ is defined as the above range in consideration of the amount of expansion and contraction of the mold due to a change in temperature.

More specifically, when a thermoplastic resin having a glass transition point Tg of 120 ≦ Tg ≦ 150 (° C.) is used in consideration of heat resistance, the mold temperature Td at the time of injection filling is as described in the above (2). From the formula, 120-50 ≦ Td ≦ 150-5
(° C.), that is, 70 ≦ Td ≦ 145 (° C.).

The mold most suitable for obtaining an optical disk substrate having a product thickness of 0.5 mm has a cavity space thickness of 0.55 mm at 25 ° C., and the cavity space thickness is increased when the mold is heated to 125 ° C. The length was 0.49 mm due to the thermal expansion of the members constituting the mold. Therefore, from the proportional relationship, the shrinkage amount of the cavity space per 1 ° C. is 0.0
It turns out that it is 006 mm / ° C.

As described above, the thickness of the cavity space, which was 0.49 mm at 70 ° C., was 0.52 mm at room temperature (25 ° C.).
mm, and the thickness of the cavity space, which was 0.49 mm at 145 ° C., becomes 0.56 mm at room temperature (25 ° C.). Therefore, since 0.52 ≦ T ≦ 0.56, if the thickness t of the optical disk substrate is 0.5 mm, then 1.04 t
≦ T ₁ ≦ 1.12t could be calculated.

Further, the thickness T ₁ of the cavity space at room temperature is set in the above range. In this range, the thickness of the optical disk substrate to be formed is larger than the target optical disk product thickness t. For this reason, for example, the thickness of the cavity space of the mold when molding an optical disc substrate having a thickness of about 0.5 mm is preferably designed to be 0.49 ± 0.01 (mm). By centering the crossing range at 0.49 mm, an optical disk substrate having a thickness closer to 0.5 mm can be formed.

The present invention focuses on the compression behavior during cooling that the filled thermoplastic resin undergoes while it becomes an optical disk substrate. Period d shown in FIG. 1 and FIG.
As is clear from (d), in order to minimize the compressive force applied to the disk substrate during cooling, the cavity space at the mold temperature during continuous molding has a thickness similar to that of the optical disk substrate after completion of cooling. Is set to In addition, it is assumed that the first mold portion 11 on the movable side in the cooling / compression process is located at substantially the same position as the position in the mold clamping process due to the contraction of the thermoplastic resin.

In addition to the optical disk substrate molding dies 10 used in the present embodiment, the optical disk substrate molding dies 30 and 40 as shown in FIGS.
By limiting the thickness dimension of the cavity space to the above range, it is possible to mold an optical disk substrate without distortion that causes undulation.

That is, FIG. 4 shows a mold of a system for controlling a compression force for compressing an optical disk substrate by a mold clamping force applied from a movable platen (not shown). Further, FIG. 5 shows that the compression core 21 (shaded portion) attached to the movable first mold portion 11 so as to be able to advance and retreat is moved in accordance with the advance and retreat of a compression piston (not shown) provided in the movable platen. 3 shows a core mold for compressing the cavity. In any of these dies, if the dimensions of the cavity space are set within the above range by improving the components (spacer ring 13, cavity ring 20, and core mold cavity ring 22) that limit the limit of the compression advancement, it is easy to perform The effects of the embodiment can be obtained.

When the molded optical disk substrate is taken out, one of the fixed mirror surface mold portion 18 and the stamper inner diameter holder (spool bush) 25 is provided on the surface of the cavity space on the second mold portion 12 side. The optical disc substrate is released from the mold by blowing a mold release gas introduced from the gap formed by the concentric parts or the gap formed by another concentric part provided exclusively between the molds. May be. On the surface of the cavity space on the first mold portion 11 side, another concentric circle provided between or between any one of the gaps between the movable mirror surface product protrusion 15 and the product protrusion holding cylinder (not shown). The mold release may be performed by using the same method as that for the above-described one side of the fixed side.
Further, when the mold opening limit reaches an arbitrarily set mold opening limit, the product protrusion 15 is slid so that the optical disk substrate is moved away from the die, and the optical disk substrate is taken out. At the same time, it is possible to take out the optical disk substrate by using a spool runner provided at the position of the hole passing through the optical disk substrate as the spool protrusion 16.

Further, it can be seen that the thickness dimension of the cavity space inside the mold largely depends on the thickness of the information recording stamper 17, as shown in FIG. In particular, thickness 0.7
In the case of a thin optical disk substrate having a thickness of less than 1 mm, the ratio of the optical disk substrate becomes large.

The thickness fluctuation of the information recording stamper 17 is generally allowed to have a tolerance of about ± 0.005 mm as a target value. Therefore, even if the thickness tolerance of the optical disk substrate to be formed is strictly controlled, the thickness variation of the information recording stamper 17 still causes the thickness of the cavity space 26, that is,
In some cases, excessive compression during the compression step may be affected. Accordingly, even when the optical disk substrate molding die of the present embodiment is used, it is desirable to adopt a molding method for further causing the target value of the optical disk substrate thickness to follow the variation in the thickness of the information recording stamper 17.

For example, when the information recording stamper 17 is 0.005 mm thicker than the reference thickness (upper limit),
The center value of the target thickness of the optical disk substrate to be manufactured is 0.49
5mm, and conversely, 0.005mm thinner (lower limit)
By setting the center value of the target thickness to 0.505 mm, it is possible to perform molding such that residual stress due to excessive compression does not remain on the molded optical disk substrate.

FIG. 7 is a graph showing an example of the improvement effect of the optical disk substrate formed by the present embodiment and the optical disk substrate formed by the conventional manufacturing method.

The vertical axis of the graph shown in FIG. 7 is the maximum height difference of the surface of the optical disk substrate during one round of an arbitrary radial position when the optical disk substrate is rotated while holding the center of the optical disk substrate. This is called whirling. This is used as an index indicating the degree of distortion that causes undulation of the optical disk substrate.

That is, from the graph shown in FIG. 7, in the prior art, the dynamic whirling is improved by reducing the compressive force to the thermoplastic resin in the cooling / compressing step to about 10 MPa. It can be seen that the dynamic whirling increases as the compression force increases. On the other hand, in the case where the optical disk substrate molding die and the manufacturing method of the present embodiment are adopted, as described above, the influence on the optical disk substrate which is a molded product due to the fluctuation of the compression force can be suppressed. It can be seen that the dynamic whirling does not increase so much even if the compression force is increased.

From the above results, the difference between the optical disk substrate manufactured according to the prior art and the optical disk substrate manufactured according to the present embodiment is apparent.

Also, when an optical disk substrate having a diameter of about 64 mm and a thickness of about 0.5 mm is formed and manufactured by the same manufacturing method as described above, the same effect as the present result is obtained. If the optical disk substrate is of the order of magnitude, when the optical disk substrate molding die of the present embodiment is used,
An optical disc substrate having good mechanical characteristics with little distortion such as warpage or undulation can be manufactured.

In the present embodiment, as shown in FIGS. 1 and 2, the case where the position of the first mold part 1 is constant during the cooling / compression step after filling the thermoplastic resin 5 has been described. However, the present invention is not limited to this. For example, as shown in FIG. 8, the compression of the first mold part 1 during the cooling / compression process in the period d may be gradually released.

That is, after filling the thermoplastic resin,
Excessive compression force can be removed by gradually reducing the compression force at the time of compression to about 60% and about 40% of the compression force given during filling and gradually reducing it. Become. Thus, by gradually removing the compressive force in this manner, it is possible to remove the excessive compressive stress remaining in the optical disk substrate.

When the compressive force is reduced during cooling, the first mold part position 103 has a compressive force of about 60% of the initial compressive force, and the first mold part position 104 has a compressive force of about 40% of the initial compressive force. 2 shows the position of the first mold part 1 shown in FIG. 2 when the mold is closed. It is preferable that the first mold part positions 103 and 104 at this time indicate positions close to the limit of the compression advance when a compression force is applied to the empty cavity space 4 not filled with the thermoplastic resin. .

That is, the first mold part positions 103 and 104
Is the position of the first mold part 1 for forming the thickness of the cavity space 4 that satisfies the range of the present invention with each compressive force. As a modified example of the present embodiment, an example in which the compression force at the time of cooling is reduced to 60% and 40% of the initial compression force in two stages has been described, but the present invention is not limited to this reduced pressure amount. Any compressive force that does not open the cavity space 4 during cooling can be arbitrarily selected. Also,
In the step of reducing the pressure, the pressure may be reduced in one to a plurality of steps, may be reduced stepwise as in the present embodiment, or may be controlled so as to continuously change the compressive force. Is also good.

Also, the thickness T ₂ of the cavity space 4 in the cooling / compression step is set so that T ≦ T ₂ ≦ 1.04T with respect to the thickness T (mm) of the cavity space 4 at the time of molding. It is preferable to control the filling amount of the thermoplastic resin.
This suppresses variation in the filling amount of the thermoplastic resin filling the cavity space 4 and applies a stable pressure to the cavity space 4. Therefore, it is possible to stably form an optical disc substrate having accurate dimensional accuracy.

In the present invention, it is not necessary to limit the thermoplastic resin used for molding the optical disk substrate. However, in consideration of transferability or birefringence, the absolute value of the photoelastic coefficient is 1 × 10 ⁻¹¹ cm. ² / dyne or less, more preferably 5 × 10 ⁻¹² cm ² / dyne or less.

Further, the MFR (Melt Flow Rate) at a resin temperature of 260 to 280 ° C., which is an index of the fluidity of the resin material,
(Rate) is preferably 20 g / 10 min or more.

The thermoplastic resin described in this embodiment includes, for example, PC (Polycarbonate), PMMA (Polymethyl me
thacrylate), PET (Polyethylene telephthalat)
e), a thermoplastic resin generally used as a raw material of an optical disk substrate, such as polyolefin or polyester, may be used.

An injection molding mold for producing an optical disk substrate is provided. The mold half (hereinafter, referred to as a second mold portion) attached to a fixed platen is provided on a movable side opposite to the second mold portion. A mold which is attached to a platen and includes two or more mold halves (hereinafter, referred to as a first mold part), wherein an information recording stamper on which an information signal of an optical disc is formed is a second mold part or a first mold part. It is attached to the part,
In addition, a part (hereinafter, referred to as a cavity ring), in which the mold halves on the fixed side and the movable side are combined and which forms an approximately cylindrical space (hereinafter referred to as a cavity space) for forming an optical disk, is formed. Is provided so as to face the information recording stamper and cover the outer peripheral end of the information recording stamper. (1) A mold having an optical disk inner peripheral hole forming means which is incorporated in a mold portion and protrudes so as to engage with a fixed-side concave portion, wherein signal recording of the stamper in a cavity space formed by the cavity ring is performed. The surface of the mold facing the part is mirror-finished, or a plain stamper is attached to a glass molding die with a glass transition point (T ) To, Tg-50~Tg-5 ℃
The thickness T of the minimum cavity space, which is the limit of the advance of compression when performing continuous molding by raising the mold temperature to (24/25) × t ≦ T with respect to the thickness t (mm) of the optical disk substrate. ≤t
(Mm).

The above mold was used, and the thickness was 0.7 mm.
When molding the following optical disc substrate, the behavior of opening and closing the mold or moving the core back and forth is monitored by a displacement meter, and when the filled resin is compressed at a constant pressure, the cavity space thickness T ₂ at the end of the cooling / compression step is calculated. May be a method of manufacturing an optical disc substrate in which the filling amount is controlled so that T ≦ T ₂ ≦ 1.04 T (μm) with respect to the minimum cavity space thickness T.

Further, the outer diameter of the disk of the optical disk substrate manufactured by the above-described method for manufacturing an optical disk substrate may be 70 mm or less.

When an optical disk substrate having a thickness t (mm) is manufactured by injection molding, the minimum cavity space thickness T ₁ (mm), which is the limit of compression advance at room temperature, is set to 1.04.
t ≦ T ₁ ≦ 1.12t (mm) may be set.

In the mold for producing an optical disk substrate having a thickness of 0.5 ± αmm, the minimum cavity space thickness T ₁ , which is a compression advance limit at room temperature, is 1.04 × (0.
5 ± α) ≦ T ₁ ≦ 1.12 × (0.5 ± α) (mm).

When forming an optical disk substrate having a substrate thickness of about 0.5 mm, the glass transition point (Tg) is
The thickness of the minimum cavity space at the limit of the compression advance when the mold is heated to a temperature of -50 ° C to Tg-5 ° C is 0.49.
It may be ± 0.01 mm.

Further, the thickness of the cavity space set at the time of molding an optical disk substrate having a substrate thickness of about 0.5 mm is set to 0.1 mm.
When using a mold of 49 ± 0.01 mm, increase or decrease of the cavity space due to fluctuation of the thickness of the information recording stamper loaded on the movable side or the fixed side is determined by the target optical disk substrate thickness by the filling amount or the compressive force during injection. By adjusting,
The compression force applied to the resin after filling the cavity during cooling may be a constant value corresponding to the mold clamping force or the stamping pressure.

When a pair of mold parts that can be opened and closed are closed, a cavity space that determines the shape of the molded product is formed inside, and the cavity space is filled with a molten thermoplastic resin by injection. A mold used for injection compression molding for molding an optical disc substrate by being cooled and compressed, wherein the mold is heated to a temperature close to the temperature at the time of injection filling of the molten thermoplastic resin into the cavity space. The thickness of the cavity space is adjusted so as to be in the range from the same thickness as the optical disk substrate as a molded product to a thickness smaller by the amount corresponding to the contraction amount of the mold in the cooling / compression process. An optical disk substrate molding die characterized by the following.

As a result, the thickness of the cavity space when the temperature is raised to near the temperature at the time of injection and filling of the molten thermoplastic resin into the cavity space is reduced from the same thickness as the optical disk substrate as a molded product to the cooling. -The thickness is adjusted so as to be in a range up to a small thickness corresponding to the shrinkage amount of the mold in the compression step. Therefore, it is not necessary to consider the decrease in the thickness of the cavity space due to the thermal expansion of the mold when the molten thermoplastic resin is filled in the cavity space, and the thickness of the cavity space is smaller than that of the conventional mold. It will be cooled and compressed in the increased state. In addition, since a small thickness corresponding to the amount of contraction of the mold in the cooling / compression step is set to the lower limit of the thickness of the cavity space at the time of the molding, the cavity space is shrunk by the contraction of the mold due to cooling. The thickness is increased so that no excessive pressure is applied to the thermoplastic resin. As a result, in the cooling / compression step, since an excessive compressive force is not applied to the optical disk substrate as a molded product, it is possible to obtain an optical disk substrate free from warping or undulation due to residual stress.

When a pair of mold parts which can be freely opened and closed are closed, a cavity space for determining the shape of the molded product is formed therein, and the cavity space is filled with a molten thermoplastic resin by injection. A mold used for injection compression molding for molding an optical disc substrate by being cooled and compressed, wherein the thickness of the cavity space when the mold is heated to the molding temperature of the thermoplastic resin is Characterized in that the thickness is adjusted to be in the range from the same thickness as the optical disk substrate as a product to a thickness smaller by an amount corresponding to the amount of shrinkage of the die after the cooling / compression process. It may be.

As a result, the thickness of the cavity space when the temperature is raised to the molding temperature of the thermoplastic resin is changed from the same thickness as the optical disk substrate as a molded product to the shrinkage amount of the mold after the cooling / compression step. It has been adjusted to a range corresponding to a smaller thickness. Therefore, it is not necessary to consider a decrease in the thickness of the cavity space due to the thermal expansion of the mold when the molten thermoplastic resin is filled in the cavity space, and the thickness of the cavity space is smaller than that of the conventional mold. It will be cooled and compressed in the increased state. In addition, a small thickness corresponding to the amount of shrinkage of the mold in the cooling / compression process,
Since the lower limit of the thickness of the cavity space at the time of molding is set, the thickness of the cavity space increases with shrinkage of the mold due to cooling, so that no excessive pressure is applied to the thermoplastic resin. As a result, in the cooling / compression step, since an excessive compressive force is not applied to the optical disk substrate as a molded product, it is possible to obtain an optical disk substrate free from warping or undulation due to residual stress.

[0146]

The mold for molding an optical disk substrate of the present invention is:
As described above, the thickness of the cavity space when the temperature of the mold is raised to near the temperature at the time of injection filling of the molten thermoplastic resin into the cavity space is the same thickness as the optical disc substrate as a molded product, It is characterized by being adjusted so as to be smaller by a predetermined amount.

Therefore, when the temperature of the cavity space is raised to a temperature close to the temperature at the time of injection filling of the molten thermoplastic resin into the cavity space, the thickness of the cavity space is the same as that of the optical disk substrate as a molded product, or a predetermined amount. It has been adjusted to be smaller. Therefore, it is not necessary to consider a decrease in the thickness of the cavity space due to the thermal expansion of the mold when the molten thermoplastic resin is filled in the cavity space, and the thickness of the cavity space is smaller than that of the conventional mold. It will be cooled and compressed in the increased state. Therefore, in the cooling / compression step, no excessive compressive force is applied to the optical disk substrate to be a molded product, so that an optical disk substrate free from distortion such as warpage or undulation due to residual stress can be obtained.

Further, the thickness of the cavity space when the temperature was raised to near the temperature at the time of injection filling of the molten thermoplastic resin into the cavity space was defined as T, and the thickness of the optical disk substrate as a molded product was defined as t. At this time, it is preferable to satisfy the following relational expression (1).

0.96t ≦ T ≦ t (1) Therefore, the temperature at which the mold for molding the optical disc substrate is injected and filled with the molten thermoplastic resin into the cavity space. The thickness T of the cavity space when the temperature is raised close to (hereinafter, referred to as molding) is defined as:
Since it is limited to the range of 0.96 t (mm) or more and t (mm) or less, even when a thin optical disc substrate having a thickness of 0.7 mm or less is formed, the cavity space is filled in the cooling / compression process. Excessive pressure can be prevented from being applied to the thermoplastic resin. As a result, the thickness is 0.1 mm.
Even when a thin optical disk substrate having a thickness of 7 mm or less is formed, it is possible to reduce the occurrence of molding defects such as warpage and undulation, and to obtain an optical disk substrate having stable mechanical characteristics.

It is more preferable that an information recording stamper on which an information signal to be recorded on an optical disk is formed is provided on at least one of the opposing surfaces of the pair of mold parts.

Therefore, since the thickness of the cavity space at the time of molding is set within the above range, an appropriate pressure for transferring recording information is applied to the cavity space, and the guide formed on the information recording stamper is applied. There is an effect that recorded information such as grooves can be transferred onto the optical disk substrate simultaneously with molding.

Further, the temperature of the mold when the temperature is raised to near the temperature at the time of injection filling of the molten thermoplastic resin into the cavity space is Td (° C.), and the glass transition point of the thermoplastic resin is Tg (Tg). (° C.), it is more preferable to satisfy the following relational expression (2).

Tg−50 ≦ Td ≦ Tg−5 (2) Therefore, the flow distortion can be reduced while the flowability of the thermoplastic resin is ensured during molding. Thus, an effect is obtained that a groove or the like formed on the information recording stamper on which the information signal is formed can be transferred to the optical disk substrate with high accuracy.

It is more preferable that the following relational expression (3) is satisfied, where T _{1 is} the thickness of the cavity space at room temperature of the mold and t is the thickness of the optical disk substrate as a molded product.

1.04t ≦ T ₁ ≦ 1.12t (3) Therefore, the thickness T of the cavity space at the temperature during molding and the thickness of the cavity space at room temperature of the by managing the temperature of both T _1, an effect that it is possible to perform more accurate molding.

It is more preferable to mold an optical disk substrate using the above-described mold for molding an optical disk substrate.

Therefore, even when a thin optical disk substrate is molded, by preventing excessive pressure from being applied to the cavity space at the time of molding, the occurrence of distortion such as warpage or undulation of the optical disk substrate is suppressed, and the product yield is reduced. The effect that it can improve is produced.

Further, the thickness of the cavity space when the thermoplastic resin filled in the cavity space in the optical disk substrate molding die is cooled and compressed is represented by T ₂ , and the molten heat flowing into the cavity space is T ₂ . Assuming that the thickness of the cavity space in the mold when the temperature is raised to near the temperature at the time of injection and filling of the plastic resin is T, the thermoplastic resin is filled into the cavity space so as to satisfy the following relational expression (4). It is more preferable to adjust the filling amount of the resin.

T ≦ T ₂ ≦ 1.04T (4) Therefore, by controlling the filling amount of the thermoplastic resin, the dispersion of the filling amount is eliminated, and Excessive compressive force can be prevented from being applied to the thermoplastic resin during the compression step. Therefore, in addition to the setting of the thickness of the cavity space, there is an effect that an excessive pressure can be more reliably prevented from being applied to the thermoplastic resin.

The thickness of the cavity space is taken into consideration in consideration of a variation due to an error in the thickness of the information recording stamper provided on at least one of the opposing surfaces of the pair of mold portions and on which the information signal to be recorded on the optical disk is formed. More preferably, the setting is adjusted according to the thickness of the information recording stamper.

Therefore, by adjusting the thickness of the cavity according to the change in the thickness of the information recording stamper, an excessive pressure can be more reliably applied to the thermoplastic resin filled in the cavity. Can be prevented. As a result, there is an effect that an optical disk substrate without distortion such as warpage or undulation can be formed.

It is more preferable that the pair of mold parts in the cooling / compressing step be opened stepwise with the passage of time.

Therefore, by gradually reducing the pressure for compressing the filled thermoplastic resin, it is possible to remove the excessive compressive force. Therefore, by gradually opening the mold in this manner, it is possible to more reliably remove the excessive compressive stress remaining in the optical disk substrate, and it is possible to mold an optical disk substrate without distortion such as warpage or undulation. It works.

[Brief description of the drawings]

FIG. 1 is a graph showing the operation of a movable-side first mold part in an optical disk substrate molding mold according to the present invention.

FIGS. 2A to 2E are explanatory views showing a manufacturing method by an injection compression step using a mold for molding an optical disk substrate of the present invention.

FIG. 3 is a cross-sectional view showing the internal structure of the optical disk substrate molding die of the present invention.

FIG. 4 is a sectional view showing the internal structure of another optical disk substrate molding die according to the present invention.

FIG. 5 is a sectional view showing the internal structure of still another optical disk substrate molding die according to the present invention.

FIG. 6 is an enlarged view showing a cavity space of the optical disk substrate molding die of the present invention.

FIG. 7 is a graph comparing dynamic whirling between an optical disk substrate manufactured according to the present invention and an optical disk substrate manufactured according to the related art.

FIG. 8 is an explanatory view showing another operation of the first mold portion on the movable side of the optical disc substrate molding mold of the present invention.

FIGS. 9A to 9E are conceptual diagrams showing a conventional injection compression molding process.

FIG. 10 is a graph showing the operation of a first mold portion on the movable side of a conventional optical disc substrate molding mold.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 first mold part (mold part) 2 second mold part (mold part) 4 cavity space 5 thermoplastic resin 7 optical disc substrate 10 mold for molding optical disc substrate 11 first mold part (mold part) Reference Signs List 12 Second mold part (mold part) 13 Spacer ring 17 Information recording stamper 18 Fixed-side mirror-surface mold part 19 Movable-side mirror-surface mold part 20 Cavity ring 21 Compression core 26 Cavity space

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Miyuki Nagahara 22-22 Nagaikecho, Abeno-ku, Osaka City, Osaka Inside (72) Inventor Akira Takahashi 22-22-22 Nagaikecho, Abeno-ku, Osaka City, Osaka F-term (for reference) 4F202 AH79 CA11 CB01 CK18 CN05 4F206 AH79 JA03 JM05 JN22 JQ81

Claims (9)

[Claims] When a pair of mold parts which can be freely opened and closed are closed, a cavity space for determining a shape of a molded product is formed therein, and after a molten thermoplastic resin is injected and filled in the cavity space. A mold used for injection compression molding for molding an optical disc substrate by being cooled and compressed, wherein the mold is heated to a temperature close to the temperature at the time of injection filling of the molten thermoplastic resin into the cavity space. The mold for molding an optical disk substrate, wherein the thickness of the cavity space when adjusted is adjusted to be the same thickness as the optical disk substrate as a molded product or to be smaller by a predetermined amount. 2. The thickness of the cavity space in the mold when the temperature is raised to near the temperature at the time of injection filling of the molten thermoplastic resin into the cavity space, and the thickness of the optical disk substrate as a molded product. The optical disk substrate molding die according to claim 1, wherein the following relational expression (1) is satisfied, where t is t. 0.96t ≦ T ≦ t (1) 3. An information recording stamper on which an information signal to be recorded on an optical disk is formed on at least one of the opposing surfaces of the pair of mold parts. For molding optical disc substrates. 4. The temperature of the mold when the temperature is raised to a temperature close to the temperature at the time of injection filling of the molten thermoplastic resin into the cavity space is Td (° C.), and the glass transition point of the thermoplastic resin is Tg. The optical disk substrate molding die according to any one of claims 1 to 3, wherein the following relational expression (2) is satisfied when the temperature is set to (° C). Tg-50 ≦ Td ≦ Tg-5 (2) 5. The thickness of the cavity space at room temperature of the mold is T ₁ , and the thickness of an optical disc substrate as a molded product is t.
The mold for molding an optical disk substrate according to any one of claims 1 to 4, wherein the following relational expression (3) is satisfied: 1.04t ≦ T ₁ ≦ 1.12t (3) 6. A method for manufacturing an optical disk substrate, comprising molding an optical disk substrate using the optical disk substrate molding die according to any one of claims 1 to 5. 7. The thickness of the cavity space when the thermoplastic resin filled in the cavity space in the optical disk substrate molding die is cooled and compressed is T ₂ , and the heat of the molten state in the cavity space is T ₂ . The thickness of the cavity space in the mold when the temperature is raised to near the temperature at the time of injection filling of the plastic resin is represented by T
7. The method according to claim 6, wherein the filling amount of the thermoplastic resin in the cavity is adjusted so as to satisfy the following relational expression (4). T ≦ T ₂ ≦ 1.04T (4) 8. A thickness of a cavity space, which is provided on at least one of the opposing surfaces of the pair of mold portions and has an information recording stamper on which an information signal to be recorded on an optical disk is formed, in consideration of a variation due to a thickness error. 8. The apparatus according to claim 6, wherein the setting is adjusted according to the thickness of the information recording stamper.
3. The method for manufacturing an optical disc substrate according to claim 1. 9. The pair of mold parts during the cooling / compressing step,
9. The method for manufacturing an optical disk substrate according to claim 6, wherein the optical disk substrate is opened stepwise as time elapses.