JPH1158474A - Manufacture of optical disk substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing an optical disk substrate of high quality in which a warpage is hard to be formed. SOLUTION: For manufacturing an optical disk substrate from a transparent thermoplastic resin, as raw material, by an injection molding method, a difference in temperatures between cooling water passed through water grooves 15 provided in a fixed side die 2 and cooling water passed through water grooves 16 provided in a movable side die 4 is made equal to or higher than 5 deg.C. And for releasing the substrate from the dies, the duration of blowing air from the side of the die, in which the temperature of cooling water is made lower, is made 0.2 seconds or more longer than that of blowing air from the side of the die, in which the temperature of cooling water is made higher.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for manufacturing an optical disk substrate. More specifically, CD (compact disk), CD-R (recordable), CD-RW
(Rewritable), CD-ROM, MO (magneto-optical disk), PD (phase change disk), DVD-ROM, D
The present invention relates to a method for manufacturing a transparent substrate of an optical disk such as a VD-R or a DVD-RAM using a transparent resin as a raw material.

[0002]

2. Description of the Related Art CD, CD-R, CD-RW, CD-R
OM, MO, PD, DVD-ROM, DVD-R, DV
A transparent substrate of an optical disk such as a D-RAM is usually manufactured by injection molding using a transparent thermoplastic resin such as a polycarbonate resin as a raw material. In the injection mold, a signal composed of irregularities such as pits and grooves is engraved on a nickel master called a stamper, and this is arranged in the mold cavity, and the signal composed of these irregularities is Transfer to the surface of the transparent resin molded product,
The target optical disc substrate is manufactured.

[0003] Since signals such as pits and grooves are extremely fine irregularities on the order of submicrons, in order to accurately transfer them to the surface of a resin molded product, the raw material resin is melted at a high temperature to improve the fluidity. Must be injected into the mold cavity. In particular, DVDs with high signal recording density
In high-density optical disc media such as CDs, MOs, and CD-Rs, pits and grooves themselves are reduced, and the distance between adjacent pits and grooves is also reduced, so that a high-accuracy transfer technique is required.

As a thermoplastic resin for manufacturing an optical disk substrate, a polycarbonate resin is mainly used.
This is because it has excellent transparency, heat resistance, strength, and low water absorption. On the other hand, since the intrinsic birefringence and photoelastic coefficient are high, the birefringence increases due to the residual stress during molding in the substrate. There is a disadvantage that. In order to compensate for this drawback, when manufacturing a substrate by an injection molding method, the temperature of the raw material resin or the set temperature of the mold cavity must be increased.

[0005]

As described above, when the raw resin temperature and the set temperature of the mold cavity are increased, the substrate molded product is released from the mold at a relatively high temperature.
After being taken out of the mold in a high temperature state, "warpage" tends to occur easily. Here, the “warp” of the substrate molded product means that the substrate molded product becomes bowl-shaped or twisted. If the “warpage” of the board molded product is large, when reading the signal of the board product with a laser after processing it into the final product,
Reading errors are likely to occur.

In order to reduce the "warpage" of a molded substrate,
(a) lowering the set temperature of the mold cavity; (b) elongating the cooling time and sufficiently cooling the product before taking it out of the mold. However, the method (a) is not preferable because it causes a problem that transferability of pits and grooves is reduced. Further, although the method (b) can reduce the “warpage” of the substrate molded product, there is a problem that productivity is significantly reduced. In particular, in the case of manufacturing CDs and DVDs in which productivity is regarded as important, the goal is to shorten the molding cycle as much as possible, and the actual situation is that the cooling time cannot be lengthened.

[0007]

In view of this situation, the present inventor has conducted intensive studies with the aim of providing an efficient method of manufacturing an optical disk substrate with less "slipping". By adjusting the set temperature of the water and the time during which cold air is blown onto the substrate when removing the optical disk substrate from the mold cavity, and the time at which air is blown on the front and back of the molded product substrate, the resulting warpage of the optical disk substrate is obtained. "Can be minimized,
The present invention has been completed.

In order to solve the above problems, according to the present invention, when manufacturing an optical disk substrate by using a transparent thermoplastic resin as a raw material by an injection molding method, a cavity portion between a movable mold and a fixed mold is cooled. Use a mold with cooling water flow grooves and an air blow port for blowing air to the molded product substrate when releasing the molded product substrate from the mold. Setting the temperature by providing a temperature difference of at least 5 ° C. or more from the set temperature of the other mold, and
When air is blown to the molded product substrate when the molded product substrate is released from the mold, the blowing time from the mold with the lower set temperature is longer than the spray time from the mold with the higher set temperature. Is also set to be longer by 0.2 seconds or more.

Hereinafter, the present invention will be described in detail. Examples of the transparent thermoplastic resin for manufacturing an optical disk substrate include transparent resins having excellent fluidity such as polycarbonate resin, polymethyl methacrylate, and amorphous polyolefin. Among them, a polycarbonate resin is particularly preferable.

[0010] Polycarbonate resins are polymers or copolymers obtained by the phosgene method of reacting various dihydroxydiaryl compounds with phosgene, or the transesterification method of reacting dihydroxydiaryl compounds with carbonates such as diphenyl carbonate. Say union. A typical example is a polycarbonate resin produced from 2,2-bis (4-hydroxyphenyl) propane (Hisphenol A).

The dihydroxydiaryl compounds include bisphenol A, bis (4-hydroxydiphenyl) methane, 1,1-bis (4-hydroxyphenyl) ethane, and 2,2-bis (4-hydroxy Diphenyl) butane, 2,2-bis (4-hydroxyphenyl)
Octane, bis (4-hydroxyphenyl) phenylmethane, 2,2-bis (4-hydroxy-3-methylphenyl) propane, 1,1-bis (4-hydroxy-tert-butylphenyl) propane, 2,2 Such as -bis (4-hydroxy-3-bromophenyl) propane, 2,2-bis (4-hydroxy-3,5dibromophenyl) propane, 2,2-bis (4-hydroxy-3,5dichlorophenylpropane) And bis (hydroxyaryl) alkanes.

Further, bis (hydroxyaryl) cycloalkanes such as 1,1-bis (4-hydroxyphenyl) cyclohexane, 4,4-hydroxydiphenyl ether, 4,4'-dihydroxy-3,3'-dimethyl Dihydroxy diaryl ethers such as diphenyl ether, 4,4'-dihydroxyphenyl sulfide, dihydroxy diaryl sulfides such as 4,4'-dihydroxy-3,3'-dimethyl diphenyl sulfide, 4,4'-dihydroxy diphenyl sulfoxide; Dihydroxydiarylsulfoxides such as 4,4'-dihydroxy-3,3'-dimethyldiphenylsulfoxide, 4,4'-dihydroxydiphenylsulfone, 4,4dihydroxy-3,3'-
And dihydroxydiarylsulfones such as dimethyldiphenylsulfone.

The above dihydroxydiaryl compound is
They can be used alone or in combination of two or more. A small amount of biperazine, dipiperidyl, hydroquinone, resorcin, 4,4'-dihydroxydiphenyl, and the like can be further mixed with the above dihydroxydiaryl compound.

According to experiments, the polycarbonate resin preferably has a viscosity average molecular weight of 13,000 to 22,
000, more preferably 14,000 to 20,000.
00 range. Here, the viscosity average molecular weight (M) refers to the intrinsic viscosity (η) of a solution obtained by using an Ostwald viscometer using methylene chloride as a solvent,
l, that is, (η) = 1.23 × 10 ⁻⁵ M
^0.83 refers to the molecular weight calculated from

According to the method of the present invention, the optical disk substrate is manufactured by an injection molding method. The mold for manufacturing the optical disk substrate used at this time includes a cooling water flow groove for cooling the cavity portion between the movable mold and the fixed mold, and a substrate for releasing the molded product substrate from the mold. A mold is used in which both the molds are provided with air blowing ports for blowing air to the molded product. A water passage for cooling the mold is provided between the cavity plate and the nest of the cavity. In order to rapidly cool the portion into which the molten resin has been injected, the water passage groove has a cross section cut at a right angle to the direction in which the water passage groove extends. It is preferable to increase the size and to reduce the size at a portion away from the injection portion.

The air (compressed air) blowing port has a function of blowing air to the substrate molded product when the substrate molded product is released from the mold. In the fixed mold, for example, along the periphery of the sprue bush, provided at the tip of the sprue bush and opened in the mold cavity portion, in the movable mold,
For example, it is provided between the mold block and the stamper fixture and opened at the mold cavity. The size of the air blowing port is a size that allows air to pass but does not allow molten resin to pass.

According to the method of the present invention, the set temperature of the cooling water passing through the cooling water passage is set at least 5 ° C., preferably at least 5 ° C., higher than the set temperature of the other mold. Is set by providing a temperature difference of 10 ° C. or more. The mold cavity portion is heated to a high temperature by injecting the molten resin, but can be lowered by flowing water through a cooling water passage. The temperature of the mold is adjusted by passing cooling water at a constant temperature at a specific water flow rate. As a cooling method of the mold cavity portion, it is preferable to adopt a method of circulating pressurized hot water when the temperature of the cooling water exceeds 90 ° C, and to adopt a method of circulating hot water when the temperature of the cooling water is less than 90 ° C.

According to an experiment, the time for blowing air to the front and back of the molded substrate is set to be shorter than the time for blowing from a mold having a higher set temperature. It has been found that when the length is set longer than 0.2 seconds, preferably longer than 0.3 seconds, and particularly preferably longer than 0.5 seconds, the "warpage" of the finally obtained molded product substrate can be greatly reduced.

For the air blown to the front and back of the molded substrate, an air (pressurized air) tank is installed at a location remote from the mold, and the air is stored in advance in this tank and guided to a predetermined location of the mold by piping. Is preferred. It is preferable that a cooling mechanism is installed in the tank for storing the air to cool the air, and the cooling temperature is set to 10 ° C. or lower.

According to an experiment, when the raw material is polycarbonate, the production temperature of the cylinder of the molding machine is set to 280 ° C. to 400 ° C.
℃, the set temperature of the movable mold cavity 50 ℃ ~ 105
℃, set temperature of fixed side mold cavity 50 ~ 140
It has been found that it is particularly preferable to select the air blowing time from the movable mold cavity at about 3.0 ° C. and the air blowing time from the fixed mold cavity at about 3.4 to 8.0 seconds. . The optical disk substrate molded product is one or two laminated substrates, and has a thickness of 0.6 mm to 1.0 mm.
A range of 2 mm is preferred.

Hereinafter, the present invention will be described with reference to the drawings.
FIG. 1 shows a partially enlarged side sectional view of an example of a mold for manufacturing a CD substrate. In the figure, 1 is a fixed plate, 2 is a fixed plate side mold, 3 is a movable plate, 4 is a movable plate side mold, 5 is a tip of an injection molding machine cylinder, 6 is a sprue bush, 7 is a sprue, and 8 is a sprue part. The cooling water passage is connected to a cooling water circulation device (not shown). 9, 10
Is a nest, and the stamper 12 is mounted on one surface of the mold cavity 11 by the stamper fixtures 13 and 14.

Cooling water passage groove 15 provided in the fixed mold
Are provided on the back of the nest 9 and cooling water passages 16 provided on the movable mold are provided on the back of the nest 10, respectively. It is articulated. The water groove for cooling the sprue portion is formed, for example, in a spiral shape on the surface of the sprue bush as described above, but the number of turns of the spiral can be changed by the length of the sprue bush. The fixed plate side mold 2 and the movable plate side mold 4 abut on the contact surfaces 17 and 18 when the molds are clamped to form a mold cavity 11 for an optical disk substrate.

The air blowing port 19 is introduced from the air pipe 21 and is provided at the tip of the sprue bush and opened at the mold cavity. The air blowing port 20 is introduced from the air pipe 22. Are provided along a fixture for fixing the stamper to the nest, and are opened at the mold cavity portion. The air pipes 21 and 22 are connected to an unillustrated air (pressurized air) tank, and the time for blowing the air to the substrate molded product can be set and adjusted by a control mechanism of the molding machine.

[0024]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the following description unless it departs from the gist.

[Example 1] <Molding mold> Injection molding machine (Model: DTS, manufactured by Sumitomo Heavy Industries, Ltd.)
K3) A mold for manufacturing a CD substrate having a diameter of 12 cm and a thickness of 0.6 mm, as shown in FIG. 1, having a radius of 10 mm at a position 20 mm away from the cavity surface with the cavity interposed therebetween.
Three cooling water passages are formed concentrically, and one cooling water passage having a radius of 4 mm is formed at the outer periphery of the root of the sprue bush. Air blow port 19 is provided and stamper fixture 1
A mold provided with an air blowing port 20 on the inner peripheral portion of each of Nos. 3 and 14 was mounted.

<Production of CD Substrate> A polycarbonate resin (having a viscosity average molecular weight of 16,000) for producing an optical disk substrate was heated at 250 ° C., 320 ° C., 330 ° C., 330 ° C, 3
20 ° C, 250 ° C, mold clamping pressure 25 tons, injection peak pressure 98 kgf / cm ² (ram), injection time 0.3 sec
And The set temperatures of the cooling water for the fixed mold and the movable mold were as shown in Table 1. Further, after cooling the substrate molded product in the mold for 2.0 seconds, blowing of 8 ° C. air from the fixed mold and the movable mold to the front and back of the substrate molded product was started, as shown in Table-1. The time for blowing air was changed as described above to manufacture a CD substrate.

<Measurement of "Warpage" of CD Substrate>
The "warp" amount of the D substrate was measured as follows. Place the convex side of the bowl-shaped sled of the CD substrate on the surface plate,
Radiation was drawn from the center of the circumference of the D-substrate, and the displacement amounts of the 22.0 mm radius portion and the 59.0 mm radius portion on the radiation were measured by a laser displacement meter manufactured by Keyence Corporation. The measured values are average values of eight measured values obtained by drawing four radiations from the center of the circumference of the CD substrate, and the results are shown in Table 1.

[Examples 2 to 4 and Comparative Examples 1 to 3] In the example described in Example 1, the set temperatures of the cooling water for the fixed mold and the movable mold are shown in Table 1. And the blowing time of air from the fixed mold and the movable mold to the front and back surfaces of the substrate molded product was changed as shown in Table 1, except that described in Table 1. A CD substrate was manufactured in the same procedure as described above. The amount of “warpage” of the obtained CD substrate was determined in Example 1.
The measurement was carried out according to the method described in (1). Table 1 shows the results.

[0029]

[Table 1]

From Table 1, the following is clear. (1) The difference between the set temperature of the cooling water between the fixed mold and the movable mold is set to 5 ° C. or more, and the time for blowing air to the surface of the substrate molded product in which the set temperature of the cooling water is lowered is set to 0. When the length is set to 5 seconds or more, the "warp" amount of the obtained CD substrate molded product is small (see Examples 1 to 3). (2) On the other hand, when the set temperature of the cooling water of the fixed mold and the movable mold was set to be the same, and the time of blowing air to the surface of the substrate molded product was set to the same value, the obtained value was obtained. The amount of "warp" of the molded CD substrate is large (see Comparative Example 1). (3) Even when the set temperature difference of the cooling water between the fixed mold and the movable mold was set to 5 ° C. or more, when the blowing time of the air to the surface of the substrate molded product was the same, it was obtained. The amount of “warpage” of the molded CD substrate is large (see Comparative Example 2). (4) Further, even if the time for blowing air to the surface of the substrate molded product in which the set temperature of the cooling water is lowered is extended by 0.5 seconds or more, the setting of the cooling water for the fixed mold and the movable mold is performed. If the temperature difference is the same, the "warp" of the obtained CD substrate molded product
The amount is large (see Comparative Example 3).

[0031]

The method of the present invention has the following particularly advantageous effects, and its industrial value is extremely large.
1. According to the method of the present invention, a high-quality optical disk substrate with little "warpage" can be manufactured very easily. 2. Since the optical disk substrate obtained by the method of the present invention has a small amount of "warpage" and is of high quality, it is unlikely that a reading failure by a laser or the like occurs.

[Brief description of the drawings]

FIG. 1 is a partially enlarged side sectional view of an example of a mold for manufacturing a CD substrate.

[Explanation of symbols]

 1: fixed plate 2: fixed plate side mold 3: movable plate 4: movable plate side mold 5: cylinder end of injection molding machine 6: sprue bush 7: sprue 8: water groove for cooling the sprue part 9, 10: Nesting 11: Mold cavity 12: Stamper 13, 14: Stamper fixing device 15, 16: Cooling water passage groove 17, 18: Contact surface 19, 20: Air blowing port 21, 22: Air pipe

Claims (3)

[Claims] 1. A cooling water flow groove for cooling a cavity between a movable mold and a fixed mold when manufacturing an optical disc substrate by injection molding using a transparent thermoplastic resin as a raw material. When releasing the substrate from the mold, use a mold that has air blowing ports for both molds to blow air to the molded product substrate, set the temperature of one mold and the setting of the other mold A temperature difference of at least 5 ° C. or more than the temperature is set, and when air is blown to the molded product substrate when the molded product substrate is released from the mold, the temperature is set to be lower than the temperature set by the mold. A method for manufacturing an optical disk substrate, characterized in that the application time is set to be 0.2 seconds or more longer than the time of spraying from a mold having a higher set temperature. 2. The method according to claim 1, wherein the transparent thermoplastic resin is a polycarbonate resin having a viscosity average molecular weight of 13,000 to 22,000. 3. The method according to claim 1, wherein the temperature of the air blown to the molded product substrate when the molded product substrate is released from the mold is set at 10 ° C. or less in advance. Method of manufacturing optical disk substrate.