Laminated disc and information recording disc

Details Laminated disc and information recording disc Laminated disc and information recording disc

2000-09-28

2003-10-14

Kelly, Cynthia H. (Department: 1774)

Stock material or miscellaneous articles

Circular sheet or circular blank

C428S064200, C428S064400, C428S065200, C428S411100

Reexamination Certificate

active

06632500

ABSTRACT:

BACKGROUND OF THE INVENTION
(1) Field of the Invention
This invention relates to a laminated disc composed of supporting discs superposed upon another, made of a vinyl alicyclic hydrocarbon polymer, and to an optical information recording medium comprising the laminated disc.
(2) Description of the Related Art
Polycarbonate is known as a molding material for disc-form information recording medium including a compact disc.
As a molding material suitable for a high-density high-capacity recording medium, a polymer containing at least 30% by weight of a vinylcyclohexane ingredient in the molecule chain has been proposed, for example, in Japanese Unexamined Patent Publication No. S63-43910. It is reported that a compact disc molded from this polymer by injection molding has a greatly reduced birefringence.
However, according the study of the present inventor, the vinylcyclohexane-containing polymer has poor mechanical strengths and abrasion resistance, as compared with polycarbonate, and thus, a problem arises when a disc made therefrom is subjected to high-speed revolution. An attempt of enhancing the mechanical strengths of a disc has been made by carrying out the injection molding at a high injection rate and thus give an orientation in the molded disc. However, the birefringence became large and the mechanical strengths were not enhanced to the desired extent. Further, the vinylcyclohexane-containing polymer has a problem such that, when a recording film and a protective film were formed on one surface of a single plate disc of the polymer, the resulting disc-form recording medium easily warps due to moisture absorption.
SUMMARY OF THE INVENTION
In view of the foregoing, a primary object of the invention is to provide a laminated disc and an information recording medium, which have reduced birefringence and good abrasion resistance, and do not warp to any significant degree.
The present inventor made extensive research, and found that the above-object of the invention can be achieved by a laminated disc composed of supporting discs having a specific thickness and made of vinyl alicyclic hydrocarbon polymer, which is prepared by hydrogenation of a vinyl aromatic hydrocarbon polymer such as polystyrene.
Thus, in accordance with the present invention, there is provided a laminated disc composed of at least two supporting discs superposed upon another; each supporting disc having a thickness of 0.01 to 1 mm and being made of a vinyl alicyclic hydrocarbon polymer.
In accordance with the present invention, there is further provided an information recording medium comprising the above-mentioned laminated disc.
Preferably, each supporting disc has a recording layer on a surface thereof.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Vinyl Alicyclic Hydrocarbon Polymer
The laminated disc of the invention is made from a vinyl alicyclic hydrocarbon polymer, which preferably comprises repeating units represented by the following formula (1):
wherein X is an alicyclic hydrocarbon group; and R
1
, R
2
and R
3
independently represent (i) a hydrogen atom, (ii) a chainlike hydrocarbon group, (iii) a group selected from a halogen atom, an alkoxy group having 1 to 6 carbon atoms, a hydroxyl group, an ester group, a cyano group, an amide group, an imide group, a silyl group, or (iv) a chainlike hydrocarbon group having a polar group which is selected from a halogen atom, an alkoxy group having 1 to 6 carbon atoms, a hydroxyl group, an ester group, a cyano group, an amide group, an imide group and a silyl group.
The alicyclic hydrocarbon group for “X” usually has 4 to 20 carbon atoms, preferably 4 to 10 carbon atoms and more preferably 5 to 7 carbon atoms in view of the reduced birefringence and mechanical strengths.
The alicyclic hydrocarbon group for “X” may have carbon-carbon unsaturation, but, the content of carbon-carbon unsaturation is not larger than 20%, preferably not larger than 10% and more preferably not larger than 5% based on the total carbon-carbon bonds in the alicyclic hydrocarbon group in view of the reduced birefringence, heat resistance and transparency. The content of carbon-carbon unsaturation can be determined by
1
H-NMR measurement.
The alicyclic hydrocarbon group for “X” may have a substituent, which is (1) a hydrocarbon group, (2) a polar group selected from a halogen atom, an alkoxy group having 1 to 6 carbon atoms, a hydroxyl group, an ester group, a cyano group, an amide group, an imide group and a silyl group, or (3) chainlike hydrocarbon group having a substitutent selected from a halogen atom, an alkoxy group having 1 to 6 carbon atoms, a hydroxyl group, an ester group, a cyano group, an amide group, an imide group and a silyl group. Of these substituents (1), (2) and (3), a chainlike hydrocarbon group having 1 to 6 carbon atoms as hydrocarbon group (1) is preferable in view of the heat resistance.
R
1
, R
2
and R
3
independently represent (i) a hydrogen atom, (ii) a chainlike hydrocarbon group, (iii) a group selected from a halogen atom, an alkoxy group having 1 to 6 carbon atoms, a hydroxyl group, an aster group, a cyano group, an amide group, an imide group, a silyl group, or (iv) a chainlike hydrocarbon group having a polar group which is selected from a halogen atom, an alkoxy group having 1 to 6 carbon atoms, a hydroxyl group, an ester group, a cyano group, an amide group, an imide group and a silyl group.
As examples of the chainlike hydrocarbon group (ii), there can be mentioned alkyl groups having 1 to 20 carbon atoms, preferably 1 to 10 carbon atoms and more preferably 1 to 6 carbon atoms, and alkenyl groups having 2 to 20 carbon atoms, preferably 2 to 10 carbon atoms and more preferably 2 to 6 carbon atoms.
As examples of the chainlike hydrocarbon group (iv) having a substituent comprising a polar group, there can be mentioned alkyl groups having 1 to 20 carbon atoms, preferably 1 to 10 carbon atoms and more preferably 1 to 6 carbon atoms.
R
1
, R
2
and R
3
are preferably selected from a hydrogen atom and a chainlike hydrocarbon group having 1 to 6 carbon atoms in view of the heat resistance, reduced birefringence and mechanical strengths.
The vinyl alicyclic hydrocarbon polymer contains the repeating unit represented by the formula (1) in an amount of usually at least 50% by weight, preferably at least 70% by weight, more preferably at least 80% by weight and most preferably at least 90% by weight.
The vinyl alicyclic hydrocarbon polymer has a weight average molecular weight (Mw), as measured by gel permeation chromatography (GPC) and expressed in terms of polystyrene, of usually 10,000 to 1,000,000, preferably 50,000 to 500,000 and more preferably 100,000 to 300,000, and has a molecular weight distribution, as expressed by the ratio (Mw/Mn) of weight average molecular weight (Mw) to number average molecular weight (Mn), which are measured by GPC and expressed in terms of polystyrene, of usually not larger than 5, preferably not larger than 3, more preferably not larger than 2.5 and most preferably not larger than 2. When the ratio (Mw/Mn) is within the above-specified range, the polymer exhibits good mechanical strengths and heat resistance. When the weight average molecular weight (Mw) is within the above-specified range, the polymer exhibits good and balanced mechanical strengths, moldability and birefringence.
The vinyl alicyclic hydrocarbon polymer usually has a glass transition temperature (Tg) of 50° C. to 250° C., preferably 70° C. to 200° C. and more preferably 90° C. to 180° C.
The vinyl alicyclic hydrocarbon polymer can be produced by (A) a process of polymerizing a vinyl aromatic compound, and then, hydrogenating the aromatic ring of the resultant vinyl aromatic polymer, or (B) a process of polymerizing a vinyl alicyclic hydrocarbon such as a vinylcycloalkane or a vinylcycloalkene, and then, when the resultant polymer has a carbon-carbon unsaturation, hydrogenating the carbon-carbon unsaturation of the polymer.
The vinyl aromatic compounds used in the production process (A) include styrene and substituted styrenes, and, as specifi

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