JPH11300842A - Optical disk substrate - Google Patents

Abstract

(57) [Summary] [PROBLEMS] A transparent substrate for optical discs having excellent transferability. The glass transition temperature of a polycarbonate resin injection-molded to form a transparent substrate is 120 to 14.
An optical disc substrate manufactured at 2 ° C., wherein a difference between the glass transition temperature and a set temperature of a mold on which a stamper is mounted is 0 to 7 ° C. Further, it can be obtained by a molding method in which a mold clamping pressure of 20 T or more is applied to the substrate during cooling during injection molding of the substrate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transparent substrate of an optical disk which is a high-density storage medium, and more particularly to a transparent substrate of an optical disk having excellent performance of a molded substrate, particularly, good signal transferability and mechanical characteristics. .

[0002]

2. Description of the Related Art The recording capacity of an optical disk has been rapidly increasing in recent years with the spread of DVD (digital versatile disk). This is because an increase in the storage capacity enables high-quality signal recording. In recent years, the market development of this optical disk has been remarkable, and high quality and productivity of the transparent substrate have been regarded as important.

[0003]

The transparent substrate of an optical disk is usually manufactured by injection molding of a polycarbonate resin for optics, and pits or grooves (guide grooves) of a submicron size are stamped in advance on a stamper. Must be faithfully transferred to the substrate. In particular, the recording capacity of a high-density optical disc such as a DVD (digital versatile disc) is 4.7 GB or more, which is seven times or more that of a CD (compact disc). High-density recording is achieved by increasing the depth of the pits and grooves, or by reducing the pitch of the grooves.However, in order to faithfully transfer the signal engraved on the stamper to the substrate However, more advanced technology is required. For example, in the case of a DVD-R (write-once DVD), the groove depth is 150 nm or more, and the pitch is 0.85 μm or less. . Further, the thickness of a single plate of a substrate such as a DVD-ROM, -R, -RAM, and ASMO (next-generation high-density magneto-optical disk) is 0.6 mm, which is different from the conventional CD of 1.2 mm. And the transfer becomes more difficult.

Usually, thermoplastic amorphous resins used for a transparent substrate of an optical disc include polycarbonate, polymethyl methacrylate, and amorphous polyolefin.
Polycarbonate is generally used in terms of strength, heat resistance and the like. First to transfer high density signals to substrate
As a means of reducing the viscosity average molecular weight of polycarbonate, it has been performed. Thereby, the melt viscosity at the time of molding decreases and the fluidity improves. However, the viscosity average molecular weight of polycarbonate for optical use, which is currently used for transparent substrates of CDs (compact disks) and DVD-ROMs, is already about 15,000, and even if the molecular weight is further reduced, the transferability is remarkable. No improvement can be expected. Because,
Injection molding of optical disc substrate is usually 5,000 / sec
This is because the molding is performed at the high shear rate described above, and the effect of reducing the viscosity by the shearing force is great. Further, when the molecular weight is further reduced, another adverse effect that the strength of the substrate is reduced also occurs.

As a second means, raising the cylinder temperature of a molding machine to 380 ° C. or higher and the mold temperature to 135 ° C. or higher when injection molding a transparent substrate is effective to some extent. However, in such high-temperature molding, there is a problem that the warp of the substrate becomes large, gas is generated in the mold, and the cooling time in the mold becomes long, so that the molding cycle is extended and the productivity is deteriorated. . As a third measure,
The method of adding an additive such as a plasticizer is not desirable because gas is easily generated in the mold. In addition, impurities in the additive may impair long-term reliability of the substrate. Therefore, there is a need for a technique for producing a transparent substrate on which the signal of a stamper is faithfully transferred without lowering the molecular weight of polycarbonate, without increasing the molding temperature, and without depending on additives.

[0006]

Means for Solving the Problems As a result of intensive studies, the present inventors have selected a polycarbonate resin having a glass transition temperature closer to the set temperature of the mold on which the stamper on which the signal is imprinted is mounted. By doing so, it has been found that it is possible to obtain a transparent substrate that ensures high-accuracy transferability without increasing the molding temperature. That is, it has been found that the use of polycarbonate having a low glass transition temperature even at the same mold temperature improves the signal transferability. Also, since molding can be performed without increasing the mold temperature,
It became clear that the warpage of the substrate was small, the molding cycle could be shortened, and the productivity of the transparent substrate also improved.

The present invention has been accomplished on the basis of the above findings, and the gist of the present invention is that the glass transition temperature of a polycarbonate resin injection-molded to form a transparent substrate is one.
An optical disc substrate manufactured at 20 to 142 ° C., wherein the difference between the glass transition temperature and the set temperature of the mold on which the stamper is mounted is 0 to 7 ° C. Also, the present invention relates to an optical disk substrate obtained by a molding method in which a mold clamping pressure of 20 T or more is applied to a substrate during cooling during injection molding of the substrate.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.
Since the polycarbonate resin used in the present invention is required to have a small optical distortion, it is desirable to improve the fluidity by reducing the molecular weight, but when the strength exceeds a certain limit, the strength sharply decreases. Its viscosity average molecular weight is usually 13,000 to 20,000, preferably 1
It is desirable to be in the range of 3,000 to 18,000. The viscosity average molecular weight (M) here is calculated from the following Schnell's viscosity formula by measuring the intrinsic viscosity (η) of a solution using methylene chloride as a solvent using an Ostwald viscometer.

[0009]

(Η) = 1.23 × 10 ⁻⁵ M ^0.83

The polycarbonate resin is a polymer or copolymer obtained by a phosgene method of reacting various dihydroxydiaryl compounds with phosgene, or a transesterification method of reacting a dihydroxydiaryl compound with a carbonate such as diphenyl carbonate. Yes, a typical example is a polycarbonate resin produced from 2,2-bis (4-hydroxyphenyl) propane [= bisphenol A].

Examples of the dihydroxydiaryl compound include bisphenol A, bis (4-hydroxydiphenyl) methane, 1,1-bis (4-hydroxyphenyl) ethane, 2,2-bis (4-hydroxydiphenyl) butane, 2,2-bis (4-hydroxyphenyl)
Octane, bis (4-hydroxyphenyl) phenylmethane, 2,2-bis (4-hydroxy-3-methylphenyl) propane, 1,1-bis (4-hydroxy-3-
Tert-butylphenyl) propane, 2,2-bis (4-hydroxy-3-bromophenyl) propane, 2,2-bis (4-hydroxy-3,5-dibromophenyl) propane, 2,2-bis (4 Bis (hydroxyaryl) alkanes such as -hydroxy-3,5-dichlorophenyl) propane, bis (hydroxyaryl) cycloalkanes such as 1,1-bis (4-hydroxyphenyl) cyclohexane, 4,4′- Dihydroxy diphenyl ethers, dihydroxy diaryl ethers such as 4,4'-dihydroxy-3,3'-dimethyldiphenyl ether, 4,4'-dihydroxyphenyl sulfide, 4,4'-dihydroxy-3,3'-dimethyl Dihydroxydiaryl sulfides such as diphenyl sulfide; Dihydroxydiarylsulfoxides such as droxydiphenylsulfoxide, 4,4′-dihydroxy-3,3′-dimethyldiphenylsulfoxide, 4,4′-dihydroxydiphenylsulfone, 4,4′-dihydroxy-3, 3 '
Dihydroxydiarylsulfones such as -dimethyldiphenylsulfone;

These may be used alone or as a mixture of two or more. In addition to these, piperazine, dipiperidyl,
Hydroquinone, resorcin, 4,4'-dihydroxydiphenyl and the like may be used as a mixture.

It is important to select a polycarbonate resin having an appropriate glass transition temperature. That is, in order to mold a high recording density optical disc, the polycarbonate resin is heated at 120 to 142 ° C.
It is necessary to have a glass transition temperature of preferably 120 to 137 ° C. With a resin having a glass transition temperature exceeding this range, it is extremely difficult to improve transferability. Further, the glass transition temperature of the resin is preferably closer to the set temperature of the mold on which the stamper is mounted. Specifically, it is preferable to use a polycarbonate resin having a glass transition temperature higher by 0 to 7 ° C. than the set temperature of the mold.

The reason why the transferability can be improved by bringing the glass transition temperature of the polycarbonate close to the mold temperature is considered as follows. Usually, the injection molding of the optical disk substrate
Since the injection compression method is used as described later, a constant mold clamping pressure is applied even during cooling inside the mold. If the glass transition temperature is lowered to approach the mold temperature, the rate of cooling and solidification is low, so the viscosity of the resin is low even during cooling inside the mold,
It is considered that the transfer is promoted while the stamper is pressed against the resin during cooling.

To this end, the molecular terminal of the polycarbonate resin is an alkyl ester of alkylphenol having 5 or more, preferably 8 or more alkyl groups, or an alkyl ester of parahydroxybenzoic acid, wherein the alkyl group has 3 or more carbon atoms. It is important that it is sealed with. That is, when the alkyl group of the alkyl phenol used as the terminal blocking agent used in the present invention has 4 or less carbon atoms, the length of the molecular chain provided to the terminal is short, so that the plasticizing effect is small and the glass transition temperature is low. The effect of lowering is small.
Further, if the alkyl group of the parahydroxybenzoic acid alkyl ester has 2 or less carbon atoms, for the same reason as above,
The effect of lowering the glass transition temperature is small. Specific examples of the terminal blocking agent include alkylphenols such as amylphenol, hexylphenol, heptylphenol, octylphenol, nonylphenol, decylphenol, dodecylphenol, myristylphenol, palmitylphenol, stearylphenol, and behenylphenol, and parahydroxybenzoate. Alkyl esters of parahydroxybenzoic acid such as propyl ester, butyl ester, amyl ester, hexyl ester, heptyl ester, octyl ester, nonyl ester, decyl ester, dodecyl ester, myristyl ester, palmityl ester, stearyl ester and behenyl ester of acids No. Further, the alkyl group of the alkyl phenol or the alkyl ester of parahydroxybenzoic acid has an o-,
It may be at any position of m- and p-, and may be linear or branched. Preferred terminal blocking agents include
Octyl phenol, nonyl phenol, decyl phenol, dodecyl phenol, butyl ester of parahydroxybenzoic acid, amyl ester, hexyl ester and the like can be mentioned. The end cap of polycarbonate is originally
It is performed for the purpose of adjusting the degree of polymerization and improving the thermal stability and hydrolysis resistance of the terminal, and usually, 98 mol% or more of the terminal is sealed with respect to all molecular terminals.

The optical disk substrate of the present invention is manufactured by injection molding, specifically, by the following injection compression method. In other words, the injection compression method is a mold clamping process in which a thin disk made of pure nickel called a stamper having information to be transferred to an optical disk substrate is engraved on one surface of an injection molding die and the die is closed, and a predetermined process is performed. An injection step of injecting a polycarbonate resin having physical properties, a pressure holding step of operating the injection cylinder for a certain period of time after the injection to maintain the pressure, a cooling step of stopping the operation of the injection cylinder and cooling without reducing the mold clamping pressure, and The operation of the mold clamping cylinder also includes a mold opening step of opening the stopper mold and taking out the optical disc substrate to which the information of the stamper has been transferred as an injection molded product.

In the above injection step, a polycarbonate resin having a predetermined glass transition temperature and having a molecular end sealed with a predetermined sealing agent is used, and the mold temperature on the side where the stamper is mounted is adjusted. Set to 130-135 ° C,
Further, by maintaining a constant mold clamping pressure in the cooling step after the injection step and the pressure holding step are completed, and preferably by setting the mold clamping pressure to 20 T or more for at least 3 seconds from the start of cooling, An optical disk substrate with good transfer to the outer periphery can be obtained. If the temperature of the mold on the side where the stamper is mounted is increased to 135 ° C. or more in the injection step, a problem occurs that the warpage of the substrate increases. Furthermore, productivity is inferior because the molding cycle is extended. When the mold temperature is lowered to 130 ° C. or lower, the transferability deteriorates.

After the above-described injection molding, the optical disk substrate taken out of the mold has a recording layer and a reflective layer formed on the surface thereof, a protective film formed thereon, and, if necessary, a plurality of substrates. Affixed to an optical disc. The recording layer may be formed using any of a metallic material such as tellurium or thallium, or an organic material such as cyanine dye or naphthoquinone dye. The reflective layer can be formed by depositing a thin film of aluminum or the like, and the protective layer can be formed by applying a conventional material and solidifying it by a curing reaction.

In particular, in the case of a DVD, a reflective film, a translucent film, a dye film, and the like are formed on an injection-molded substrate, and two obtained single plates are bonded together to obtain high transferability and high transferability. A quality optical disc is obtained. The present invention relates to a high recording density substrate having a groove depth of 150 nm or more and a groove pitch of 0.85 μm or less, particularly a DVD-R or DVD-RAM.
It is useful for molding. In addition, the thickness of the veneer to be bonded is usually 0.6 mm or 1.2 mm.

[0020]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, which, however, are not intended to limit the scope of the invention.

Examples 1-3 and Comparative Examples 1-3 Molding Materials In Examples and Comparative Examples, polycarbonate molding materials were prepared as follows. At the time of polymerization by a usual phosgene method, an alkylphenol or an alkyl ester of parahydroxybenzoate shown in Table 1 was present as a terminal blocking agent together with a polycarbonate oligomer and bisphenol A to obtain a granular polycarbonate. At that time, the addition ratio of each terminal blocking agent was adjusted so that the viscosity average molecular weight was 14,800. The obtained granular polycarbonate was prepared by adding stearic acid monoglyceride as a releasing agent and tris (mono- and di-mixed nonylphenyl) phosphite as a heat stabilizer to 500 ppm and 100 pp, respectively, based on the polycarbonate.
After adding at a ratio of m, the mixture was melt-extruded into pellets to obtain a molding material.

Molding conditions The polycarbonate molding material prepared as described above was
Using a mold equipped with a stamper, an optical disk substrate for DVD was molded according to the injection compression molding method. The equipment, specifications and molding conditions used for molding were as follows. Molding machine: Sumitomo Heavy Industries DISK3 Mold: 12 cmφ DVD mold Molded substrate thickness: 0.6 mm Stamper groove depth: 160 nm Stamper groove pitch: 0.80 μm Injection time: 0.1 second Cooling time: 7.0 seconds Screw rotation speed: 360 rpm Screw diameter: 25 mmφ Mold clamping pressure: Injection, 20T during holding pressure, 25T during cooling Also, the glass transition temperature of the polycarbonate molding material, the set temperature of the mold on which the stamper is mounted, and during cooling (cooling) The mold clamping pressure (for 7.0 seconds from the start) is as shown in Table 1.

Evaluation Method The optical disk substrates formed in the examples and comparative examples were evaluated for the following items based on the following criteria. Table 1 shows the results. (1) Glass transition temperature: For a polycarbonate molding material constituting a substrate, using DSC (manufactured by Seiko Co., Ltd.), in accordance with JIS K7121, under a nitrogen stream at 10 ° C.
/ Min, determined from the inflection point of the DSC curve measured at a heating rate of / min.

(2) Transfer rate at the outermost periphery of the optical disk substrate: radius 57 corresponding to almost the outermost periphery of the recording layer of the substrate
The groove depth at four points equally dividing the circumference of mm was measured using an atomic force microscope (NV2000, manufactured by Olympus Corporation), and the average of the measured values was obtained. This is the design value of the stamper. The percentage with respect to 160 nm was calculated and used as the transfer rate.

(3) Warpage of the substrate:
Displacement in the vertical direction of a point on a circle with a radius of 58 mm with reference to a point on a circle with a radius of 23 mm near the inner / outer boundary of the recording layer of the substrate after acclimation for 1 hour in an environment of 55% RH Was measured using a laser displacement meter (manufactured by Keyence Corporation) at four pairs of points that equally divide the circumference, and the average value thereof was obtained to determine the warpage of the substrate.

[0026]

[Table 1]

As shown in Table 1, in Examples 1 to 3 using an end capping agent having an alkyl group having a predetermined number of carbon atoms, a predetermined glass transition temperature and a high transfer rate can be obtained. On the other hand, when the number of carbon atoms is small, as shown in Comparative Examples 1 and 3, the transfer rate is greatly reduced, and is not practical. Further, as shown in Comparative Example 2, when the mold temperature is increased to increase the fluidity, the warpage of the substrate increases sharply, which is not practical.

[0028]

According to the present invention, by using a polycarbonate resin having an appropriate glass transition temperature,
Since the temperature can be approached to the mold temperature, it is possible to provide an optical disc substrate having excellent transferability. Therefore,
INDUSTRIAL APPLICABILITY The present invention has an extremely high utility value for an optical disk substrate having a high recording density such as a DVD.

[Procedure amendment]

[Submission date] May 8, 1998

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claim 5

[Correction method] Change

[Correction contents]

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Michio Nakata 5-6-1, Higashi-Hachiman, Hiratsuka-shi, Kanagawa Prefecture Inside the Technology Center of Mitsubishi Engineering-Plastics Co., Ltd. (72) Hiroyoshi Maruyama 5-chome, Higashi-Yawata, Hiratsuka-shi, Kanagawa No. 6-2 Mitsubishi Engineering Plastics Co., Ltd. Technology Center

Claims (6)

[Claims] The glass transition temperature of a polycarbonate resin injection-molded to form a transparent substrate is 120 to 14.
An optical disc substrate manufactured at 2 ° C., wherein a difference between the glass transition temperature and a set temperature of a mold on which a stamper is mounted is 0 to 7 ° C. 2. The optical disc substrate according to claim 1, wherein the viscosity average molecular weight of the polycarbonate resin is 13,000 to 20,000. 3. An optical disk is formed by laminating a 1.2 mm-thick veneer, a 1.2 mm-thick veneer, a 0.6 mm veneer or a 0.6 mm veneer. 3. The optical disc substrate according to claim 1, wherein 4. The optical disk substrate according to claim 1, wherein a signal of the optical disk has a guide groove having a depth of 150 nm or more and a pitch of 0.85 μm or less. 5. The method according to claim 1, wherein the molecular terminal of the polycarbonate resin is blocked with an alkylphenol having 5 or more carbon atoms or an alkyl ester having 3 or more carbon atoms of parahydroxybenzoic acid. An optical disk substrate according to claim 1. 6. When performing injection molding of an optical disk substrate, at least three hours from the start of cooling after the injection and pressure-holding steps are completed.
6. The method according to claim 1, wherein a mold clamping pressure of 20 T or more is applied to the substrate for at least 20 seconds.
An optical disc substrate according to any one of the above.