JPH0199001A - Optical disk substrate made of polyester system - Google Patents

Abstract

PURPOSE:To lessen double refraction and hygroscopicity and to improve transparency, heat resistance and molding workability by using specific transparent polyester as a base material. CONSTITUTION:The transparent polyester consisting of a dionyl unit having an arom. ring in the side chain and dibasic acid unit having an arom. ring in the main chain is used as the base material of an optical disk substrate. The dibasic acid is preferably terephthalic acid and/or isophthalic acid and >=50% of the acid component thereof is preferably the terephthalic acid and/or isophthalic acid. Arom. dibasic acids such as phthalic acid and diphenyl carboxylic acid are preferably used in combination so that the heat resistance of the resulted polymer is improved and the amorphous polymer is obtd. The diol component has the polystyrene deriv. segment of <=5,000mol.wt. expressed by the formula and is preferably copolymerized with the diol at 5-40wt.% of the dibasic acid. In the formula, R is H, Cl, Br, alkyl group of 1-4C.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a polyester-based optical disk substrate that has low birefringence and excellent dimensional and morphological stability and heat resistance.

[Prior Art] Optical disks are a recording medium that is characterized by non-contact, high-density recording, and their uses have been rapidly expanding in recent years.

Optical disks are ultra-high precision technology systems that require precision on the order of submicrons, and the disk substrates used there must also have strict performance and precision requirements such as transparency, low birefringence, low moisture absorption, and dimensional stability. required.

Conventionally, methacrylic resin (Japanese Unexamined Patent Publication No. 56-131
Transparent plastics such as JP-A-654, etc.) and polycarbonate resins (JP-A-58-126119, etc.) are used. In addition, heat-resistant polyester resins (Japanese Unexamined Patent Publication No. 57-208645), resins such as polystyrene and polycarbonate having a specific difference in principal polarizability (Japanese Unexamined Patent Publication No. 61-108617), and thermosetting epoxy resins It has also been proposed to apply resins to optical discs.

[Problems to be Solved by the Invention] However, although methacrylic resin exhibits good performance in terms of transparency and birefringence, it is highly hygroscopic and may cause the disk to absorb moisture in the air and cause warping. There is a problem that the dimensions change or the recording material changes or deteriorates. On the other hand, polycarbonate resin has a drawback of low hygroscopicity but high birefringence, which causes a problem that accurate recording and reproduction becomes difficult when used as a disc substrate material. Similarly to polycarbonate, polyester resins have the problem of large birefringence even if their heat resistance is simply improved, and epoxy resins cannot be injection molded, resulting in productivity problems.

In other words, a fully satisfactory optical disk substrate with low birefringence and low hygroscopicity has not yet been obtained, and it is desired to develop an optical disk substrate that has all of transparency, low birefringence, and low hygroscopicity. ing.

The inventors of the present invention have conducted extensive studies with the aim of providing a high-performance optical disc substrate that satisfies the above requirements, and have found that a specific polyester resin has extremely low birefringence, excellent transparency, heat resistance, and hygroscopicity. The inventors have discovered that the present invention is also small.

Means for Solving Problem U] In order to achieve the above object, the present invention has the following configuration.

"An optical disc substrate characterized by having a transparent polyester base material consisting of a diol unit having an aromatic ring in the side chain and a dibasic acid unit having an aromatic ring in the main chain." As the dibasic acid having a ring, terephthalic acid and/or isophthalic acid are suitable, and it is desirable that 50% or more of the acid component is terephthalic acid and/or isophthalic acid. In addition, aromatic dibases such as phthalic acid, diphenyldicarboxylic acid, diphenylsulfonedicarboxylic acid, diphenoxyethanedicarboxylic acid, etc. It is also preferable to use an acid in combination. These dibasic acids are
It may be used as a dicarboxylic acid as it is, or as an ester-forming derivative such as dimethyl terephthalate or dichloride terephthalate.

In addition, the diol having an aromatic ring in the side chain as used in the present invention is
Regardless of the length of the molecular chain, the main chain is a molecular chain having OH groups at both ends, and this is a diol substituted with a molecular chain containing an aromatic ring as a side chain.

Examples of aromatic rings include not only benzene rings but also fused rings such as indene, naphthalene, tetralin, anthracene, and phenanthrene, biphenyl, p-terphenyl,
Multiple rings such as diphenylmethane, pyridine, thiophene,
Examples include heterocycles such as pyrrole, furan, indole, quinoline, inquinoline, and acridine, and derivatives thereof. In practical use, a diol having a polystyrene derivative segment represented by (R is a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, and (1, selected from Br)) is preferably used.The molecular weight of the polystyrene derivative segment is 5,
000 or less, particularly preferably 1,000 or less. When the molecular weight exceeds 5,000, the transparency of the resulting polyester decreases.

In the diol of the present invention, any of the polystyrene segments can be applied since the phenyl groups, which are aromatic rings, are arranged in a side chain pendant shape. In addition, in the polystyrene derivative segment, for example, acrylonitrile,
A copolymer component such as butadiene may be included.

The reason why the polyester of the present invention exhibits extremely small birefringence is that the diol having an aromatic ring in the side chain exhibits negative birefringence in the polymer, and the dibasic acid component having an aromatic ring in the main chain exhibits positive birefringence. This is thought to be to offset the The diol having an aromatic ring in the side chain has an amount of 5 to 4 based on the weight of the dibasic acid component.
0% copolymerization.

If the copolymerization ratio is less than 5%, the birefringence will increase, and the birefringence will increase to 40%.
If it exceeds this amount, the heat resistance and transparency of the polyester will decrease.

In addition to the diol having an aromatic ring in the side chain, any diol that can be copolymerized with the dibasic acid is used as the third component, but in order to improve the heat resistance of the resulting polyester, for example, 1,4-cyclohexane dimetatool, Tricyclodecane dimetatool, alicyclic dihydroxy compounds such as cyclohexanediol, bisphenols such as 2,2-bis(4-hydroxyphenyl)propane, bis(4-hydroxyphenyl)sulfone, bisphenols and alkylene glycols ( For example, aromatic dihydroxy compounds such as ether diols obtained from ethylene glycol) are preferably used. In order to roughly improve melt fluidity during injection molding, aliphatic diol compounds such as ethylene glycol, trimethylene glycol, tetramethylene glycol, hexamethylene glycol, etc. can also be used in combination. These diols may be used alone or in combination of two or more.

The polyester of the present invention must be an amorphous polymer having no oriented portions, ie, crystalline regions, in the molecule. In crystalline polymers, a difference in refractive index occurs between the crystalline portion and the amorphous portion, resulting in poor transparency. As a measure of such transparency, a transmittance of 80% or more is preferable.

The polyester of the present invention can be produced by conventionally known methods, such as melt polycondensation, solution polycondensation, interfacial polycondensation, and the like. Additives that impair transparency must be avoided in polymers for optical disk substrates, but additives such as lubricants, antistatic agents, ultraviolet absorbers,
Additives of inorganic and organic compounds, such as antioxidants, can be used if desired.

Polyester resin has lower hygroscopicity than methacrylic resin, and does not cause warping or deterioration of the recording material due to moisture absorption.

Further, by using the above-mentioned rigid diol as the third component, a polymer having higher heat resistance than general polyethylene terephthalate can be obtained.

The constituent units of the polyester of the present invention can be analyzed by hydrolyzing it according to a conventional method.

The present invention will be explained below with reference to Examples. Note that parts in the examples mean parts by weight.

[Example] Example 1 A 47.2q/ff THF solution of α-methylstyrene was
The mixture was poured onto a sodium mirror, and the reaction solution was allowed to react at room temperature for 6 hours while shaking. A THF solution of 8.8 g of ethylene oxide was added to this reaction solution. The reaction product was poured into 0.5% hydrochloric acid-acidic methanol 3a to obtain a diol having hydroxyethyl groups attached to both ends of an α-methylstyrene tetramer.

The molecular weight of the styrene derivative segment was 472.

38.8 parts of dimethyl terephthalate, 7 parts of the above diol.
8 parts (20% based on the weight of the acid component), 47°3 parts of bis(4-hydroxyethoxyphenyl)sulfone, 18 parts of ethylene glycol, and 0.0% of manganese acetate tetrahydrate as a catalyst.
0.05 parts, antimony trioxide 0.04 parts, and initially 1
The reaction was carried out while gradually increasing the temperature from 80'C to -0-250°C, and methanol and excess ethylene glycol produced as a result of the transesterification reaction were distilled out of the system. Then 15 at 280'C
After stirring for several minutes, the pressure in the system was gradually reduced, and the mixture was reduced to 0.5 mm (11 g) over about 1 hour, and the reaction was further continued for 3 hours.

This polyester was made into pellets and molded using an injection molding machine to obtain discs with a thickness of 1 and 2 mm and a diameter of 130 mm. The birefringence of the obtained disc is 3 parts m when vertical and 15 parts when incident at 30'.
The transmittance is 91%, the saturated moisture absorption rate at 60'C95%RH is 0.6% (1.8% for PMMA), and the dimensional change during moisture absorption and when left at 75°C is 0. It was less than .01%.

Example 2 Styrene (ST) using thioglycol as a chain transfer agent
, acrylonitrile (AN>) is radically polymerized to form the molecule f
A diol having f15,000 styrene/acrylonitrile copolymer in the side chain was obtained.

38.8 parts of dimethyl terephthalate, 7.8 parts of the above diol
In the same manner as in Example 1, a catalyst was added to 1 part, 27° 4 parts of tricyclodecane dimetatool, and 18 parts of ethylene glycol, and transesterification, polycondensation, and injection molding were performed to obtain a copolyester disk.

The birefringence of the obtained disk is 1 nm at normal incidence and 1 at 30' incidence.
0nm, the transmittance is 92%, and the saturated moisture absorption rate at 60'C95%RH is 0.4%.
All dimensional changes due to standing at 5°C were less than 0.01%.

[Effects of the Invention] According to the present invention described above, it is possible to produce a polyester optical disk substrate that has extremely low birefringence and moisture absorption, high transparency and heat resistance, and excellent moldability.

Claims (2)

[Claims] (1) An optical disc substrate characterized in that its base material is transparent polyester consisting of a diol unit having an aromatic ring in its side chain and a dibasic acid unit having an aromatic ring in its main chain. (2) The dibasic acid component is mainly terephthalic acid and/or isophthalic acid, and the diol component is a diol having a polystyrene derivative segment with a molecular weight of 5,000 or less represented by the general formula ▲ Numerical formula, chemical formula, table, etc. ▼ However, R represents a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, Cl, or Br.)
and the diol is 5 to 5% based on the weight of the dibasic acid.
The optical disc substrate according to claim (1), characterized in that it is 40% copolymerized.