JPH05205326A - Manufacture of optical disk substrate - Google Patents

Abstract

PURPOSE:To provide a manufacturing method of an optical disk substrate using a 4-methyl-1-pentene polymer or a 4-methyl-1-pentene copolymer superior in a transfer property. CONSTITUTION:The optical disk substrate is manufactured by a method that pellets of the 4-methyl-1-pentene polymer or the 4-methyl-1-pentene copolymer whose (a) melt flow rate (MFR) measured, based on ASTM D1238, at 5kg load and 260 deg.C temp. is 240-1200g/10min. and whose (b) m.p. by DSC is 234-240 deg.C, are molded by injection at a temp. of 320-370 deg.C at least at one part of the cylinder and at <=55 deg.C of metallic mold temp.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an optical disk substrate, and more specifically, 4-methyl-1 having excellent transferability.
The present invention relates to a method for producing an optical disk substrate made of a pentene polymer or a 4-methyl-1-pentene copolymer.

[0002]

BACKGROUND OF THE INVENTION Optical discs are widely used in the information recording field such as recording and recording of CDs, LDs, write-once optical discs, MO discs, etc. because of their large storage capacity and portability.

For an optical disk, a stamper is attached to a mold of an injection molding machine, injection molding is performed, an optical disk substrate having pits or tracks transferred to the surface thereof is prepared, and an optical recording layer or an optical recording layer is formed on the substrate. It is manufactured by forming a reflective layer (metal layer) and a protective layer, or by molding a substrate by injection molding and simultaneously forming information pits, and then forming a reflective layer and, if necessary, a protective layer thereon. Then, in order to obtain an optical disk having good recording and reproducing sensitivity, it is necessary to faithfully reproduce the fine irregularities of the stamper when molding the substrate. In addition, such an optical disk substrate has excellent transparency, low birefringence, no distortion during molding, excellent dimensional stability, no warpage after molding, and metal vapor deposition property. Various properties such as excellent wettability of the organic film and excellent heat resistance and moisture resistance are required.

In recent years, it has been required to further increase the storage capacity of an optical disk, and in order to increase the storage capacity with a substrate having the same diameter, it is necessary to increase the recording density by narrowing the track pitch or the pit pitch. is there. In order to manufacture such an optical disc having a high recording density, there is a demand for a substrate molding method having the above-mentioned characteristics and further excellent in transferability.

[0005]

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above-mentioned prior art, and is composed of a 4-methyl-1-pentene polymer or a 4-methyl-1-pentene copolymer and is excellent in transferability. Moreover, it is an object of the present invention to provide a method for manufacturing a substrate for an optical disc with less warpage.

[0006]

SUMMARY OF THE INVENTION A method for manufacturing an optical disk substrate according to the present invention comprises: (a) ASTM 5 load, temperature 260 ° C.
Melt flow rate measured according to D 1238 (M
FR) is 240 to 1200 g / 10 minutes, and (b) the melting point by DSC is 234 to 240 ° C. 4-methyl-1-pentene polymer or 4-methyl-1-pentene copolymer pellets It is characterized in that injection molding is performed at a temperature of at least a part of the cylinder of 320 to 370 ° C. and a mold temperature of 55 ° C. or less.

Among the polymers constituting such a substrate for an optical disk, a homopolymer of 4-methyl-1-pentene or a repeating unit derived from 4-methyl-1-pentene is 94 to 99.5% by weight. %, And the repeating unit derived from α-olefin (preferably α-olefin having 4 to 24 carbon atoms) is 6 to 0.5% by weight, 4-methyl-1-pentene / α-olefin copolymer. Is particularly preferable.

[0008]

DETAILED DESCRIPTION OF THE INVENTION A method for manufacturing an optical disk substrate according to the present invention will be described below. First, the 4-methyl-1-pentene polymer and the 4-methyl-1-pentene copolymer used in the present invention are described. Will be described.

The resin for the substrate used in the present invention is 4-methyl-1-pentene polymer or 4-methyl-1-pentene copolymer, preferably 4-methyl-1-pentene homopolymer or A copolymer of 4-methyl-1-pentene and α-olefin (preferably α-olefin having 4 to 24 carbon atoms), more preferably 94 wt% of repeating unit derived from 4-methyl-1-pentene % Of 4-methyl-1-pentene and α-olefin having 4 to 24 carbon atoms, it is necessary to obtain a substrate for an optical disc having excellent transferability, which is an object of the present invention. The repeating unit derived from -methyl-1-pentene is 94 to 99.5% by weight, particularly preferably 96 to 99.5% by weight, and the repeating unit derived from an α-olefin having 4 to 24 carbon atoms is 6 to 0.5
A 4-methyl-1-pentene / α-olefin copolymer consisting of 4% to 0.5% by weight is particularly desirable.

In the present invention, 4-methyl-1-pentene polymer means 4-methyl-1-pentene homopolymer and copolymerization of 4-methyl-1-pentene with a small amount of a monomer other than α-olefin. Means coalescence. In the present invention, 4-methyl-1-pentene copolymer (4-methyl-1-pentene / α-olefin copolymer) means a copolymer of 4-methyl-1-pentene and α-olefin. And a copolymer of 4-methyl-1-pentene, α-olefin and a small amount of a monomer other than α-olefin.

Examples of the monomers other than the above α-olefins include butadiene, dicyclopentadiene, ethylidene norbornene, methyl acrylate, methyl methacrylate, ethyl acrylate and ethyl methacrylate.

As the α-olefin used for copolymerization with 4-methyl-1-pentene, an α-olefin having 2 or more carbon atoms is used. In the present invention, an α-olefin having 4 to 24 carbon atoms is particularly preferable. It is preferably used. As the α-olefin having 2 or more carbon atoms, ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-decene, 1-tetradecene, 1-hexadecene, 1-octadecene , 1-eicosene, etc., among them, α-olefins having 4 to 24 carbon atoms are preferable, α-olefins having 6 to 18 carbon atoms are more preferable, 1-decene, 1
Most preferred are -hexadecene and 1-octadecene. These α-olefins may be used alone or in combination of two or more.

The above-mentioned 4-methyl-1-pentene polymer or 4-methyl-1-pentene copolymer is produced, for example, by using the following conventionally known catalysts and methods. (A) a highly active titanium catalyst component, (B) an organometallic compound catalyst component, and (C) an organosilicon compound catalyst component represented by the following general formula R _n Si (OR ') in _4-n (wherein, R and R'is a hydrocarbon group, and 0 <n <4
Is. 2) in the presence of a polymerization catalyst formed from
It is obtained by polymerizing 4-methyl-1-pentene or copolymerizing 4-methyl-1-pentene with the α-olefin at a temperature of 0 to 100 ° C. In this case, for example, a small amount of a monomer other than the above α-olefin may be copolymerized.

In the present invention, the 4-methyl-1-pentene polymer or the 4-methyl-1-pentene copolymer is a 4-methyl-1-pentene polymer or a 4-methyl-1-pentene copolymer. A polymer obtained by partially decomposing it by thermal decomposition or the like may be used. It is also possible to use a composition in which a 4-methyl-1-pentene polymer and a 4-methyl-1-pentene copolymer are blended.

4-methyl-1-pentene polymer and 4-methyl-1-
When blending with the pentene copolymer, 4-methyl-1
With respect to the total amount of the -pentene polymer and the 4-methyl-1-pentene copolymer, the content of the 4-methyl-1-pentene copolymer is 0.5% by weight or more, preferably 30% by weight or more, particularly preferably Four
It is preferable to mix in an amount of 0% by weight or more and to blend 4-methyl-1-pentene polymer in an amount of 99.5% by weight or less, preferably 70% by weight or less, particularly preferably 60% by weight or less.

4-methyl used in the present invention
Pellets of -1-pentene polymer or 4-methyl-1-pentene copolymer (4-methyl-1-pentene / α-olefin copolymer) were subjected to ASTM D at a load of 5 kg and a temperature of 260 ° C.
Melt flow rate measured according to 1238 (MF
R) is 240 to 1200 g / 10 minutes, preferably 24
0 to 1000 g / 10 minutes, more preferably 300 to 95
0 g / 10 minutes, most preferably 350-900 g / 10
The melting point by DSC is 234 to 240.
C., preferably in the range of 235 to 239.degree. The density of the 4-methyl-1-pentene polymer or 4-methyl-1-pentene copolymer used in the present invention is 0.830 to 0.83.
5 g / cm ³ , particularly preferably 0.831 to 0.834 g
It is preferably in the range of / cm ³ . The number average molecular weight (Mn) of the 4-methyl-1-pentene polymer or 4-methyl-1-pentene copolymer used in the present invention is 15
The molecular weight distribution (Mw / Mn) measured by gel permeation chromatography (GPC, solvent: o-dichlorobenzene, 140 ° C., polystyrene conversion) is preferably 2.3 to 5.
A range of 0 is desirable.

The melting point by DSC is measured by the following procedure using a differential scanning calorimeter. That is, using DSCII type manufactured by Perkin Elmer Co., Ltd., about 3 mg of the sample was 4 mm ×
The orientation method of the sample is restricted by winding the aluminum plate having a thickness of 4 mm and a thickness of 0.2 mm. Next, the sample wound around this aluminum plate is enclosed in an aluminum pan and used as a measurement sample. In addition, the same aluminum plate as that used for the sample is enclosed in a normally empty aluminum pan to be placed in a reference holder, which is a sample for comparison, to balance the heat of both. Then, after holding the sample at 30 ° C. for about 1 minute, the temperature is raised to 250 ° C. at a heating rate of 10 ° C./min. The maximum endothermic peak position determined by this measurement is the melting point of the sample.

4-methyl-1-pente obtained according to the invention
Consisting of a 4-methyl-1-pentene copolymer
The density of the optical disk substrate is 0.830 to 0.835g
/ Cm ³, Preferably 0.831 to 0.834 g / cm³
And the melt flow measured according to ASTM D 1238.
-Rate (MFR) is 300-3000g / 10min.
And preferably 350 to 2000 g / 10 minutes
desirable. In addition, 4-methyl-1-peptone obtained by the present invention
From 4-methyl-1-pentene copolymer
The optical disc substrate has a number average molecular weight (Mn) of 100.
The gel permeation chroma is between 0 and 80,000.
Tography (GPC, solvent: o-dichlorobenzene, 1
Molecular weight distribution (M in terms of polystyrene) at 40 ° C
It is desirable that w / Mn) is 2 to 5.

Such a 4-methyl-1-pentene polymer or a 4-methyl-1-pentene copolymer is excellent in heat resistance and transparency, and also has excellent melt flow characteristics and precision molding processability, and further has a molding process. It has characteristics such that it is difficult for distortion to occur.

The above-mentioned copolymer or composition may optionally contain various additives such as a heat resistance stabilizer, a weather resistance stabilizer, a hydrochloric acid absorbent and an antistatic agent. In the present invention,
A substrate for an optical disc is molded from the above copolymer or composition.

The optical disk substrate according to the present invention is prepared by using the above-described polymer or copolymer or composition.
The temperature of at least part of the cylinder is usually 320-37.
0 ° C., preferably 330-355 ° C., more preferably 330-350 ° C., most preferably 335-350 ° C.,
Injection molding is performed under the condition that the mold temperature is 55 ° C. or lower, preferably 10 to 50 ° C.

The cooling time during injection molding is preferably 5.0 to 11 seconds, more preferably 6.0 to 8.0 seconds, and the molding cycle is preferably 10.0 to 18.0.
Seconds, more preferably 12.0 to 18.0 seconds, particularly preferably 13.0 to 15.0 seconds.

The thickness of the optical disk substrate thus obtained is usually 0.1 to 5 mm, preferably 0.5 to 1.
It is preferably 5 mm. In order to manufacture an optical disk using the optical disk substrate obtained by the present invention, for example, a magneto-optical element containing a 3d transition metal such as Fe-Co-Tb layer or Fe-Co-Gd layer and a rare earth metal on the substrate. A recording layer or a write-once type optical recording layer such as a Te-C-H layer or a Te-Cr layer is formed, and a reflective layer or a protective layer is formed on the recording layer as required, or a recording layer is formed on a substrate. At the same time, information pits may be formed, and a reflective layer, or a reflective layer and a protective layer may be formed thereon, if necessary. (For example, a read-only optical disk) The reflective layer is not particularly limited, but Al, Cr, A
Examples thereof include a layer made of a metal such as u, Ag, Cu or a layer made of an alloy containing these metals. The thickness of such a reflective layer is 500 to 1000Å, more preferably 8
It is desirable that it is 00 to 1000Å.

Examples of the protective layer include layers made of ultraviolet curable resin, epoxy resin, methacrylic resin, silicon nitride (SiNx), silicon carbide (SiCx), aluminum nitride (AlN) and the like. The thickness of such a protective layer is 3
It is desirable that the thickness is ˜7 μm, more preferably 5 to 7 μm.

These recording layer, reflective layer and protective layer can be formed by a conventionally known method such as vapor deposition, sputtering and spin coating. According to the optical disk manufacturing method of the present invention, a low-viscosity 4-methyl-1-pentene polymer or 4-methyl-melted in a cylinder at high temperature is used.
The 1-pentene copolymer is kept at a low temperature for a short time and is filled in the mold, so that the groove groove depth is uniformly deep regardless of the disc radius, and the transferability is particularly good. Further, when the mold temperature is low, the molding cycle can be shortened, so that the productivity can be improved. further,
Since the residence time of the resin in the cylinder can be shortened, it is possible to prevent thermal degradation of the 4-methyl-1-pentene polymer or 4-methyl-1-pentene copolymer, and the resulting optical disc is It does not warp easily and has excellent dimensional stability.

[0026]

EFFECT OF THE INVENTION In the method of manufacturing an optical disk substrate according to the present invention, 4-methyl-1-pentene polymer or 4-methyl-1-pentene polymer is used.
A pentene copolymer, preferably 4-methyl-1-pentene homopolymer or 94-100% by weight of repeating units derived from 4-methyl-1-pentene, preferably 94-9.
9.5% by weight, particularly preferably 96 to 99.5% by weight, and 6 to 0% by weight, preferably 6 to 0.5% by weight, of a repeating unit derived from an α-olefin having 4 to 24 carbon atoms. , Particularly preferably 4-0.5% by weight of 4-methyl-
1-pentene copolymer, load 5 kg, temperature 260
Melt flow rate (MFR) measured according to ASTM D1238 at 240 ° C. is 240 to 1200 g / 10
And the melting point by DSC is 234 to 240 ° C.
A pellet of 4-methyl-1-pentene polymer or 4-methyl-1-pentene copolymer is used as a raw material resin pellet, and the temperature of at least a part of the cylinder is 320 to 370.
Since it is formed by injection molding at ℃ and mold temperature of 55 ℃ or less,
The transferability of the obtained optical disk substrate is particularly good. Further, the substrate of the optical disc molded by such a manufacturing method is less likely to warp, has excellent dimensional stability and heat resistance, does not generate flow marks, and has excellent transparency.
Birefringence is small.

A method of manufacturing an optical disk substrate according to the present invention is a CD, MD, CD-ROM, LD, MO disk,
It can be widely used as a method for manufacturing a transparent substrate such as a write-once disc.

[0028]

EXAMPLES The method for producing a substrate for an optical disk of the present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

In the present invention, the warp and transferability of the optical disk are evaluated as follows. [Warping] As shown in FIG. 1, the distance (n) between the surface in contact with the peripheral edge on the concave side of the optical disk and the center of the substrate was measured,
The warp (mm) of the optical disk was used. [Transferability] Modulation degree of the optical disc (I ₃ / I _Top and I ₁₁
/ I _Top ) to evaluate the transferability of the optical disk substrate.

That is, a reflective layer and a protective layer are sequentially formed on an optical disk substrate to which pits have been transferred, and when the obtained optical disk is irradiated with a reproducing laser beam, it is reflected back at a pit-free area of the optical disk. The amount of incoming laser light (I _Top ) and the amount of laser light (I ₃ ) that returns after being reflected by the pit with the shortest pit length,
The light amount (I ₁₁ ) of the laser light reflected and returned by the pit having the longest pit length was measured, and I ₃ / I _Top and I ₁₁ / I _Top were obtained. I ₃ and I _11, because the value as a good transferability is high, I ₃ / I _Top and I ₁₁ / I
_The higher the value of _Top , the better the transferability.

Generally, I ₃ / I _Top is about 40% and I ₁₁ / I _Top is about 60%.

[0032]

Example 1 A 4-methyl-1-pentene / α-olefin polymer [MFR: 400 g / 10 min (comprising 98% by weight of 4-methyl-1-pentene and 2% by weight of n-decene (1-decene)] A
STM D1238 compliant, temperature 260 ° C), melting point 235 ° C by DSC, number average molecular weight (Mn): 47,000, GPC
(Solvent: o-dichlorobenzene, 140 ° C.) molecular weight distribution (Mw / Mn): 2.38] by injection molding machine (Sumitomo-
With Nestal DISK5 M III Sumitomo Heavy Industries, Ltd., maximum cylinder temperature 350 ° C, mold temperature 40 ° C, cooling time 5 seconds, screw rotation speed 200 rpm, molding cycle 1
Molded under the condition of 3 seconds, thickness 1.2mm, diameter 120mm
A φ substrate for CD was manufactured.

Al was vapor-deposited on the obtained substrate to a thickness of 700Å by a sputtering method, and then a protective layer of an acrylic UV-curable resin (Dacure Clear SD-17; manufactured by Dainippon Ink and Chemicals, Inc.) was formed on the Al layer. It was formed by spin coating to have a thickness of 7 μm. The characteristics of the optical disk thus obtained were measured. The results are shown in Table 1.

[0034]

Example 2 4-Methyl-1-pentene 98.5% by weight and n-hexadecene (1-hexadecene) 1.5% by weight 4-
Methyl-1-pentene / α-olefin polymer [MFR: 4
20 g / 10 minutes (conforms to ASTM D 1238, temperature 260
℃), melting point 235 ℃ by DSC] with an injection molding machine (Sumitomo-Nestal DISK5 M III Sumitomo Heavy Industries, Ltd.), maximum cylinder temperature 345 ℃, mold temperature 50 ℃, cooling time 5 seconds, screw rotation Molded under conditions of several 200 rpm and molding cycle of 10 seconds, thickness 1.2 mm, diameter 120 m
An mφ CD substrate was manufactured.

Al was vapor-deposited on the obtained substrate to a thickness of 700 Å by a sputtering method, and then a protective layer of an acrylic UV curable resin (Dacure Clear SD-17; Dainippon Ink and Chemicals, Inc.) was formed on the Al layer. It was formed by spin coating to have a thickness of 7 μm. The characteristics of the optical disk thus obtained were measured. The results are shown in Table 1.

[0036]

Example 3 4-Methyl-1-pentene homopolymer [MF
R: 490 g / 10 minutes (according to ASTM D 1238, temperature 26
0 ℃), melting point 235 ℃ by DSC] injection molding machine (Sumitomo-Nestal DISK5 M III Sumitomo Heavy Industries, Ltd.)
At a cylinder maximum temperature of 355 ° C., mold temperature of 43 ° C., cooling time of 5 seconds, screw rotation speed of 200 rpm, molding cycle of 13 seconds, thickness 1.2 mm, diameter 120
A mm substrate for CD is manufactured.

Al was vapor-deposited on the obtained substrate to a thickness of 700Å by a sputtering method, and then a protective layer of an acrylic UV-curable resin (Dacure Clear SD-17; manufactured by Dainippon Ink and Chemicals, Inc.) was spun on the Al layer. It is formed with a coat to a thickness of 7 μm. The characteristics of the optical disc thus obtained are measured. The results are shown in Table 1.

[0038]

Example 4 4-Methyl-1-pentene / α-olefin polymer [MFR: 800 g / 10 minutes (98% by weight of 4-methyl-1-pentene and 2% by weight of n-decene (1-decene)] A
STM D1238 compliant, temperature 260 ℃, melting point 235 ℃ by DSC] injection molding machine (Sumitomo-Nestal DISK5 MI
II Sumitomo Heavy Industries, Ltd.) maximum cylinder temperature 35
Molded under the conditions of 0 ° C., mold temperature 40 ° C., cooling time 5 seconds, screw rotation speed 200 rpm, molding cycle 18 seconds,
A CD substrate having a thickness of 1.2 mm and a diameter of 120 mmφ was manufactured.

Al was vapor-deposited on the obtained substrate to a thickness of 700Å by a sputtering method, and then a protective layer of an acrylic UV curable resin (Dacure Clear SD-17; manufactured by Dainippon Ink and Chemicals, Inc.) was formed on the Al layer. It was formed by spin coating to have a thickness of 7 μm. The characteristics of the optical disk thus obtained were measured. The results are shown in Table 1.

[0040]

[Comparative Example 1] 4-methyl-1-pentene resin [TPX-RT18 manufactured by Mitsui Petrochemical Co., Ltd., MFR: 26 g / 10 min, DS
[Melting point 231 ° C. by C] was molded in the same manner as in Example 1 except that the cylinder temperature was 300 ° C. and the mold temperature was 60 ° C. using the same injection molding machine as that used in Example 1, and the thickness was A CD substrate having a diameter of 1.2 mm and a diameter of 120 mm was manufactured.

A reflective layer was formed on the obtained substrate in the same manner as in Example 1.
A protective layer was applied and the characteristics of the optical disc were measured. Since the MFR of the resin is small, warpage is large and it cannot be used as an optical disc. The results are shown in Table 1.

[0042]

[Comparative Example 2] Polycarbonate for disc [MFR; 5
2 g / 10 min] using an injection molding machine similar to that used in Example 1, cylinder temperature 335 ° C., mold temperature 85.
Molding was carried out at a temperature of 5 ° C., a cooling time of 5 seconds, a screw rotation speed of 200 rpm, and a molding cycle of 9 seconds, and a reflective layer and a protective layer were applied in the same manner as in Example 1 to measure the characteristics of the optical disc. The results are shown in Table 1.

[0043]

[Table 1]

As is apparent from Table 1, the optical disk having the substrate obtained by the manufacturing method of the present invention is I ₃ / I
_{Since both the Top} value and I ₁₁ / I _Top value are high, it can be seen that the substrate manufacturing method of the present invention is excellent in transferability.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a method for measuring a warp of an optical disc.

[Explanation of symbols]

 1 optical disc

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[Procedure amendment]

[Submission date] June 15, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0033

[Correction method] Change

[Correction content]

The resultant of 700Å of Al by sputtering on the substrate was deposited in a thickness, and then an acrylic type ultraviolet curing resin on the Al layer (dialog Cure Clear SD-17; produced by Dainippon Ink & Chemicals Co., Ltd.) of Protective layer is 7μm by spin coating
It was formed with a thickness of. The characteristics of the optical disk thus obtained were measured. The results are shown in Table 1.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0035

[Correction method] Change

[Correction content]

The resulting Al was deposited to a thickness of 700Å by sputtering on the substrate, and then an acrylic type ultraviolet curing resin on the Al layer (dialog Cure Clear SD-17; produced by Dainippon Ink & Chemicals Co., Ltd.) of Protective layer is 7μm by spin coating
It was formed with a thickness of. The characteristics of the optical disk thus obtained were measured. The results are shown in Table 1.

[Procedure 3]

[Document name to be amended] Statement

[Name of item to be corrected] 0037

[Correction method] Change

[Correction content]

The Al is evaporated at a thickness of 700Å by sputtering substrate obtained, then an acrylic type ultraviolet curing resin on the Al layer; Protection (dialog Cure Clear SD-17 manufactured by Dainippon Ink &) Layer 7 μm by spin coating
It is formed with the thickness of. The characteristics of the optical disc thus obtained are measured. The results are shown in Table 1.

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0039

[Correction method] Change

[Correction content]

The resultant of 700Å of Al by sputtering on the substrate was deposited in a thickness, and then an acrylic type ultraviolet curing resin on the Al layer (dialog Cure Clear SD-17; produced by Dainippon Ink & Chemicals Co., Ltd.) of Protective layer is 7μm by spin coating
It was formed with a thickness of. The characteristics of the optical disk thus obtained were measured. The results are shown in Table 1.

Claims (3)

[Claims] 1. A melt flow rate (MFR) measured according to ASTM D 1238 at a load of 5 kg and a temperature of 260 ° C. of 240 to 1200 g / 10 minutes, and (b) a melting point by DSC. Of 4-methyl-1-pentene polymer or 4-methyl-1-pentene copolymer having a temperature of 234 to 240 ° C., the temperature of at least a part of the cylinder being 320 to 370 ° C.,
A method for manufacturing a substrate for an optical disk, characterized by performing injection molding at a mold temperature of 55 ° C. or lower. 2. The method for producing an optical disk substrate according to claim 1, wherein the 4-methyl-1-pentene polymer is a 4-methyl-1-pentene homopolymer. 3. The 4-methyl-1-pentene copolymer is
It is a copolymer of methyl-1-pentene and an α-olefin having 4 to 24 carbon atoms and has 9 repeating units derived from 4-methyl-1-pentene.
The method for producing a substrate for an optical disk according to claim 1, wherein the repeating unit is 4 to 99.5% by weight, and the repeating unit derived from an α-olefin having 4 to 24 carbon atoms is 6 to 0.5% by weight.