Digital video disk substrate

Details Digital video disk substrate Digital video disk substrate

1998-09-25

2001-02-06

Thibodeau, Paul (Department: 1773)

Stock material or miscellaneous articles

Circular sheet or circular blank

Recording medium or carrier

C428S065100

Reexamination Certificate

active

06183830

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a digital video disk substrate, and more precisely, to that of a polycarbonate which is cracked little at the time of molding and exhibits small birefringence and excellent transcriptional ability.
BACKGROUND ART
The standards of CDs, CD-ROMs and the like which are conventional optical disks are disk diameter=120 mm, disk thickness=1.2 mm, and structure=a single plate utilizing one surface. On the contrary, the standards of digital video disks (DVDs) are disk diameter=120 mm, disk thickness=1.2 mm, and structure=both surfaces stuck. Accordingly, the thickness of each disk substrate is 0.6 mm. As materials of these disk substrates, polycarbonates are much used in recent years, as having high transparency, good heat resistance, good impact resistance and good water resistance.
However, thin disk substrates, of which the thickness is reduced from 1.2 mm to 0.6 mm as so mentioned in the above, are often problematic in that they will be cracked or broken during molding and that their birefringence may increase. In order to prevent the disks from being cracked during molding, the molecular weight of the polycarbonate which Ls the substrate material can be increased, but in this case, the birefringence of the disks further increases. On the other hand, in order to reduce the birefringence, it has been attempted to mold the digital video disk substrates by the use of techniques such as ultrasonic molding, multi-stage compression molding and high-speed filling molding. Even by these techniques, however, the reduction in the birefringence is not sufficient, and what is worse, the breakage of the disks more often occurs as compared with usual molding techniques.
Under such circumstances, the present invention has been attained, and an object of the invention is to provide a digital video disk substrate which is cracked little during molding and which exhibits small birefringence and excellent transcriptional ability.
DISCLOSURE OF THE INVENTION
The present inventors have intensively researched on digital video disk substrates which are cracked little during molding and which exhibit small birefringence, and, as a result, have found that the above-mentioned object can be achieved by the use of a polycarbonate of which the molecular weight falls within a specific range and which has a broad molecular weight distribution, or a polycarbonate which is obtained by transesterification to have a molecular weight falling within a specific range, as the substrate material. The present invention has been completed on the basis of the thus-found knowledge.
Specifically, the present invention provides the following:
1. A digital video disk substrate of a polycarbonate having a viscosity-average molecular weight (Mv) of from 10,000 to 17,000 and a weight-average molecular weight (Mw)
umber-average molecular weight (Mn) of not smaller than 2.3.
2. A digital video disk substrate of a polycarbonate obtained by the transesterification of a diphenol and a carbonic acid diester to have a viscosity-average molecular weight (Mv) of from 10,000 to 17,000.
3. The digital video disk substrate of 2, wherein a nitrogen-containing basic compound and a nitrogen-free basic compound are used as the catalyst for the transesterification.
4. The digital video disk substrate of 3, wherein the nitrogen-containing basic compound is a quaternary ammonium salt.
5. The digital video disk substrate of 3, wherein the nitrogen-free basic compound is a quaternary phosphonium salt.
6. The digital video disk substrate of 4, wherein the quaternary ammonium salt is tetramethylammonium hydroxide.
7. The digital video disk substrate of 5, wherein the quaternary phosphonium salt is tetraphenylphosphonium tetraphenylborate.
8. The digital video disk substrate of 1 or 2, wherein the polycarbonate has a viscosity-average molecular weight (Mv) of from 12,000 to 16,000.
9. The digital video disk substrate of 1 or 2, wherein the polycarbonate has a viscosity-average molecular weight (Mv) of from 13,500 to 15,500.
BEST MODES OF CARRYING OUT THE INVENTION
The polycarbonate which is used as the material for the DVD substrate of the invention can be produced in any conventional manner of a solution method (interfacial polymerization method, pyridine method), a transesterification method and the like. In general, it can be produced by reacting a diphenol with a polycarbonate precursor such as phosgene, a carbonic acid ester or the like. Concretely, for example, the polycarbonate is produced by reacting a diphenol with a carbonate precursor such as phosgene in a solvent such as methylene chloride or the like in the presence of a known acid receptor or a molecular weight regulator, to which is optionally added a branching agent (interfacial polymerization); or by transesterifying a carbonic acid diester such as diphenyl carbonate with a diphenol (transesterification). Preferred is the polycarbonate as produced by transesterification of a diphenol with a carbonic acid diester.
Preferred examples of the diphenol to be used for producing the polycarbonate include compounds of a general formula (I):
In formula (I), R
1
and R
2
each represent a halogen atom, an alkyl group having from 1 to 6 carbon atoms, or aphenyl group. The halogen atom includes chlorine, bromine, fluorine and iodine atoms. The alkyl group having from 1 to 6 carbon atoms may be any of linear, branched or cyclic ones, and includes, for example, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, t-butyl, amyl, isoamyl, hexyl, isohexyl and cyclohexyl groups, etc. R
1
and R
2
maybe the same or different. Plural R
1
's, if any, may be the same or different; and plural R
2
's, if any, may be the same or different. p and q each represent an integer of from 0 to 4. Z represents a single bond, an alkylene or alkylidene group having from 1 to 20 carbon atoms, a cycloalkylene or cycloalkylidene group having from 5 to 20 carbon atoms, —O—, —S—, —SO—, —SO
2
—, or —CO—. The alkylene or alkylidene group having from 1 to 20 carbon atoms includes, for example, methylene, ethylene, propylene, butylene, pentylene, hexylene, ethylidene and isopropylidene groups, etc. The cycloalkylene or cycloalkylidene group having from 5 to 20 carbon atoms includes, for example, cyclopentylene, cyclohexylene, cyclopentylidene and cyclohexylidene groups, etc.
A variety of diphenols of formula (I) are known. Of those, especially preferred is 2,2-bis(4-hydroxyphenyl)propane [bisphenol A]. Other examples of the diphenols except bisphenol A include dihydroxydiarylalkanes such as bis(4-hydroxyphenyl)methane, bis(3,5-dichloro-4-hydroxyphenyl)methane, bis(3,5-dimethyl-4-hydroxyphenyl)methane, 1,1-bis(4-hydroxyphenyl)ethane, 1,2-bis(4-hydroxyphenyl)ethane, 2-methyl-1,1-bis(4-hydroxyphenyl)propane, 2,2-bis(3,5-dimethyl-4-hydroxyphenyl)propane, 1-ethyl-1,1-bis(4-hydroxyphenyl)propane, 2,2-bis(3,5-dichloro-4-hydroxyphenyl)propane, 2,2-bis(3,5-dibromo-4-hydroxyphenyl)propane, 2,2-bis(3-chloro-4-hydroxyphenyl)propane, 2,2-bis(3-methyl-4-hydroxyphenyl)propane, 2,2-bis(3-fluoro-4-hydroxyphenyl)propane, 1,1-bis(4-hydroxyphenyl)butane, 2,2-bis(4-hydroxyphenyl)butane, 1,4-bis(4-hydroxyphenyl)butane, 2,2-bis(4-hydioxyphenyl)pentane, 4-methyl-2,2-bis(4-hydroxyphenyl pentane, 2,2-bis(4-hyiroxyphenyl)hexane, 4,4-bis (4-hydroxyphenyl)heptane, 2,2-bis(4-hydroxyphenyl)nonane, 1,10-bis(4-hydroxyphenyl)decane, 1,1-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane, 2,2-bis(4-hydroxyphenyl)-1,1,1,3,3,3-hexafluoropropane, etc.; dihydroxydiarylcycloalkanes such as 1,1-bis(4-hydroxyphenyl)cyclohexane, 1,1-bis(3,5-dichloro-4-hydroxyphenyl)cyclohexane, 1,1-bis(4-hydroxyphenyl)cyclodecane, etc.; dihydroxydiarylsulfones such as bis(4-hydroxyphenyl)sulfone, bis(3,5-dimethyl-4-hydroxyphenyl) sulfone, bis(3-chloro-4-hydroxyphenyl) sulfone, etc.; dihydroxydiaryl ethers such as bis(4-hydroxyphenyl) ether, bis (3,5-dimethyl-4-hydroxyphenyl) ether, etc.; dihydroxydiaryl ketones such as 4,4′-dihydroxybenzophenone, 3,3′,5,5′-tetr

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