JPH02173953A - Substrate for optical recording medium - Google Patents

Abstract

PURPOSE:To obtain a substrate with very little double refraction, excellent light permeability, little warpage due to water absorption, excellent mechanical strength and heat resistance by forming the substrate from specific polyester, polyester carbonate or polycarbonate resin. CONSTITUTION:The substrate consists of polyester, polycarbonate or polyester carbonate having recurrent units expressed by formula I. In the formula, R1 and R2 represent a bond or alkylene group, alkylidene group, etc., having <=8 carbons. There may be a bond or cross-linkage comprising alkylene group or alkylidene group with <=6 carbons between R1 and R2. It is inhibited that both of R1 and R2 are bonds. R3 and R4 represent hydrogen atom or alkyl group with <=4 carbons. x and y represent the proportion of copolymerization, x:y=100:0 to 0:100 (in molar ratio). (n) is 0, 1 or 2. By this method, the obtd. substrate has very little double refraction, excellent light permeability, little warpage due to water absorption, and excellent heat resistance and mechanical strength.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides an optical recording medium with extremely low birefringence, excellent light transmittance, and very little warpage or deformation due to water absorption, and excellent mechanical properties and heat resistance. The present invention relates to a substrate for media.

[Conventional technology]

So-called optical discs such as digital audio discs and laser vision are rapidly becoming popular due to their advantages such as long life based on high-density, large-capacity recording and non-contact playback.

In recent years, write-once types and erasable types that allow users to record information have also appeared, and with the development of recording methods, the level of demand for the properties of the base material has also increased. Especially low water absorption (low water absorption resistance), low birefringence, and high heat resistance.
Items are important characteristics. Currently, glass and plastic materials are mainly used as substrate materials, but glass has disadvantages such as low mass production, high cost, heavy weight, and breakability, so plastic materials are more mainstream.

The plastic materials currently particularly used as substrates for optical recording media are polymethyl methacrylate (PMMA) and polycarbonate (PC). Although PMMA has extremely low birefringence, it has high water absorption (moisture absorption) and is susceptible to warping and deformation due to water absorption. This has the disadvantage that it tends to cause deterioration of optical properties.

In particular, when used in an optical recording medium consisting of a single substrate such as a digital audio disc, faithful reproduction of information may be difficult. In addition, further improvement in thermal properties is desired. On the other hand, PC has low water absorption, hardly any water absorption warping, and has no problem with heat resistance, but it has the disadvantage of high birefringence. For relatively small diameter products such as digital audio discs, it is possible to suppress birefringence below the required level by controlling the molding conditions with high precision, but for laser vision with a diameter of 30 cm and magneto-optical recording. It is nearly impossible to support media that require extremely high optical properties.

The application of resins other than PMMA and PC is also being considered;
) has the problem of high birefringence and very low surface hardness, making it easy to scratch. Furthermore, polyester resins (JP-A-58-150147) have particular drawbacks regarding birefringence.

It has been pointed out that in resins having aromatic rings, such as the above-mentioned PC1 styrene resins and polyester resins, birefringence occurs due to the optical anisotropy of the aromatic rings. Therefore, in order to obtain a resin with low birefringence, a material design policy that does not use aromatic rings can be considered, but not using aromatic rings causes the problem of reduced heat resistance.

As a material with low birefringence and good heat resistance, alicyclic polyester or polycarbonate can be considered. As examples of such resins, polyester or polycarbonate derived from 2.2.4.4-tetramethyl-1,3-cyclobutanediol is proposed in British Patent No. 962.913 and Japanese Patent Publication No. 38-26798. ing. Japanese Unexamined Patent Publication No. 63-92644 discloses 2, 2.
The possibility of a polycarbonate resin derived from 4,4-tetramethyl-1,3-cyclobutanediol as a molding material for optical parts is disclosed. Furthermore, the present inventors have proposed, in Japanese Patent Application No. 62-293639, an alicyclic polyester carbonate which is excellent in properties required when used as a substrate for an optical recording medium. Furthermore, Journal of Polymer 5cie
nce.

Polymer Chemistry Edition
, Vol. 10, p. 3191 (1972) and US Pat.

Furthermore, JP-A-63-122729 discloses a polycarbonate having a norbornane skeleton.

[Problems to be solved by the invention] As mentioned above, PMMA and PC have problems when used as substrates for optical recording media, and even if new materials are used, there are still some problems. The current situation is that there is.

The object of the present invention is to provide a substrate that is excellent in all the properties required when used as a substrate for optical recording media, that is, has extremely low birefringence, excellent light transmittance, and has extremely low water absorption warping (deformation). An object of the present invention is to provide a substrate for an optical recording medium having good mechanical properties and heat resistance.

[Means for solving problems]

As a result of intensive studies in view of the above objectives, the present inventors found that a specific polyester resin has extremely low birefringence, excellent light transmittance, very little warping when water is absorbed, and has high heat resistance and mechanical strength. The inventors have discovered that this is a good result and have arrived at the present invention. That is, the present invention is a substrate for an optical recording medium characterized in that the repeating unit is made of polyester, polycarbonate, or polyester carbonate resin represented by the following general formula <1).

The following are specifically exemplified.

Among these, preferably in general formula (I), the ratio of X to y is not particularly limited and may be any value between 0:100 and 1oo:o. Furthermore, n may be 0, 1 or 2, but is preferably 1 or 2 in terms of heat resistance and low water absorption.

As mentioned above, J, Polymer ScilPol
ymer C1+emistryEdiLion,
10, p. 3191 (1972), and more preferably a polyester derived from a dihydroxy compound and an aromatic sicarphonic acid such as terephthalic acid.
It may be a mixture of two or more types. Further, it may have any other structure in an amount within a range that does not impair the effects of the present invention, for example, in an amount of about 10 mol % or less based on the total amount.

Polyesters derived from aromatic or cycloaliphatic dicarboxylic acids are disclosed. However, these prior documents merely state that the above-mentioned polyesters can be used to form films, and molded products obtained from these polyesters do not have the characteristics particularly required as substrates for optical recording media. Nothing is stated or even suggested that everything is satisfied.

Furthermore, in JP-A-63-122729, bis(hydroxymethyl ) Norbornane or dihydroxynorbornane is exemplified.

However, the diols having a norbornane skeleton used in the examples in the publication include a mixture of 2,5- and 2,6-bis(hydroxymethyl)norbornane and a mixture of 2,5- and 2,6-dihydroxynorbornane. It is thought that the diol having a norbornane skeleton in this publication is intended to be a compound in which a hydroxymethyl group and a hydroxyl group are bonded to the two rings of norbornane, respectively. All of these compounds are derived from norbornadiene,
It is usually obtained as a mixture of 2,5- and 2,6. Therefore, in the Examples of the publication, a mixture of isomers is used, but since it is a mixture of isomers, the glass transition point of the resulting resin is relatively low. Furthermore, in the resin, the norbornane skeleton is located in the polymer main chain. On the other hand, in 2,3-bis(hydroquinemethyl)norbornane, which corresponds to the case where n = O in the present invention, two hydroquinemethyl groups are bonded to one ring of norbornane. In resins derived from diols, the norbornane ring is located in the side chain of the polymer main chain and acts effectively to reduce the mobility of the main chain, so the glass transition point is 2.5 or 2.
6 is higher than when using one piece. This high glass transition point is essential for practical physical properties desired for a substrate for an optical recording medium.

Furthermore, in the present invention, by introducing carbonate in addition to bonding, the glass transition ratio of the resulting resin increases, which is desirable.

The resin of the present invention can be produced according to any known suitable method. For example, dephenol reaction from a mixture of diphenyl carbonate and diphenyl ester of dicarboxylic acid and diol, dealcoholization reaction from a mixture of dialkyl carbonate and dialkyl ester of dicarboxylic acid and diol, de-alcoholization reaction from phosgene and dicarboxylic acid chloride and diol. It can be produced by carrying out reactions such as hydrogen chloride reaction, dealkali metal chloride reaction from a mixture of phosgene, dicarboxylic acid chloride, and alkali metal salt of diol, etc. in the presence of an appropriate catalyst as necessary. . As for the form of the reaction, methods such as a melt method and a solution method can be adopted depending on the reaction method, but the melt method is preferable from the viewpoint of ease of reaction.

When the resin of the present invention is produced by a melting method using diphenyl carbonate and/or diphenyl ester of a dicarboxylic acid as a raw material, metal lithium or various lithium compounds are preferable as catalysts because of their high spreading properties. Preferred are metal lithium, lithium hydride, lithium nitride, lithium hydroxide, and lithium alkoxides such as lithium ethoxide and butoxide, and more preferred are metal lithium and lithium hydride. In addition, when diphenyl ester is not used as a raw material, ordinary transesterification catalysts such as tetraalkylorthotitanate, diptyltin oxide, germanium oxide, zinc acetate, etc. can be used in addition to the lithium compounds mentioned above. Tetraalkyl orthotitanate is preferred because of its high properties.

The amount of catalyst used is usually 010001 to 1 based on the total raw material.
% by mole, preferably from 0.001 to 0.1 mol%. If the amount of catalyst used is too small, the reaction rate will be extremely reduced, and if the amount of catalyst used is too large, the water absorption rate of the resulting resin will increase.

The polycondensation reaction can be advanced by heating and stirring the raw materials and catalyst in an atmosphere of an inert gas such as nitrogen, argon, or carbon dioxide, and distilling off the generated alcohol or phenol.

The reaction temperature varies depending on the raw materials, the boiling point of the alcohol or phenol generated, and the required reaction rate, but is usually in the range of 150 to 300°C.

In the latter half of the reaction, the pressure of the system is reduced as necessary to drive the reaction. The pressure at this time is in the range of 0.001 to 100 mmHy.

Regarding the molecular weight of the resin of the present invention, the number average molecule i (
(in terms of polystyrene) is preferably 3,000 or more and 100,000 or less, preferably 5,000 or more and 100,000 or less, and even more preferably 10,000 or more and 100,000 or less. As the molecular weight decreases, mechanical strength decreases. Furthermore, when the molecular weight becomes high, synthesis becomes difficult.

When the resin of the present invention is used as a substrate for an optical recording medium, molding can be carried out by any known method such as extrusion molding, injection molding, compression molding, injection compression molding, and the like. At this time, the resin temperature is usually set in the range of 200 to 400°C, and the mold temperature is set in the range of 40 to 200°C. Known additives such as heat stabilizers, light stabilizers, antistatic agents, lubricants, inorganic or organic fillers, dyes, etc. may be added as necessary during molding.
Pigments etc. may also be added. It is also possible to blend other resins.

The substrate for optical recording media of the present invention can be formed into a simple shape such as a flat plate, then laminated with an inorganic or organic material, laminated by adhesion or fusion, or embossed on the surface. It is also possible to perform processing.

For example, when using the resin of the present invention as a substrate for a read-only optical recording medium, the substrate is obtained by injection molding or the like using a mold in which groups, signals, etc. are recorded as necessary. A film of metal such as aluminum or platinum is then formed on the information surface by a method such as vacuum evaporation, and then a protective polymer layer is formed or two layers are bonded together. The information recording layer may be provided on a flat substrate using the molding material of the present invention using a photocurable resin by the so-called 2P method. Further, the information recording section can be constructed using any other known method. For example, a thin film of an inorganic material such as tellurium oxide or a terbium-iron-cobalt alloy, or an organic material such as a cyanine dye is provided on the surface of a molded substrate. In addition,
Here, the term "substrate for optical recording media" specifically refers to a medium for physically or chemically recording and/or reading information using a laser beam passing through the substrate, such as an optical recording medium substrate or an optical card substrate. refers to the substrate used for Further, the shape thereof may be arbitrary, such as a sheet, a film, a disk, or a card.

The following margins [Examples] The present invention will be explained in more detail by way of Examples below. In addition, the physical property values were measured according to the following method.

■Number average molecular weight: Determined by GPC (polystyrene equivalent).

■Glass transition point: Differential thermal analysis method (in nitrogen, heating rate 10
°C/min).

(2) Light transmission rate: The transmittance of light at a wavelength of 400.600 and 800 um was measured using a spectrophotometer for a sample molded to a thickness of 2rffr+ by heat pressing.

■Birefringence (retardation): Diameter 40 mrn
, A sample molded to a thickness of 6 mrrI was heated through a hot press.
It was rolled to a thickness of mm and measured using a polarizing microscope (wavelength: 589 nm) at a point 3 Q mm from the center.

■Photoelastic coefficient: heat press 2 cm x 10 cm
X Soejima et al.'s method using a helium-neon laser as a light source for a plate formed to a thickness of 2 plates (Komunshi Experimental Science, edited by the Editorial Committee of the Society of Polymer Science and Technology, Vol. 10, P, 296)
(1983) Kyoritsu Shuppan).

■Surface hardness: Pencil hardness test (J I S K 540
0).

(2) Saturated water absorption rate: Measured by determining the weight increase rate when no time change in weight increase due to water absorption was observed in distilled water at 23°C. Note that the saturated water absorption rate of bisphenol A polycarbonate obtained by the powder method was 0.40%.

■Water absorption warpage: 2 crr + × 10 cm It absorbs water and becomes warped.

Polymer synthesis example 1 Inner diameter 44 Q mm, internal volume 70P, material S U
2.3-di(hydroxymethy/L/) was placed in a reaction tank with a double helical ribbon type stirring blade and a clearance of 5 plates between the wall of the reaction tank and the stirring blade.
-berhydro-1,4:5.8-dimethanonaphthalene 1
9.39kg, diphenyl carbonate 14.95
kg, 5,66 kg of diphenyl 1,4-cyclohexanedicarboxylate and 0.6 kg of lithium hydride as catalyst.
9. After charging Q and sufficiently purging the system with nitrogen gas, the temperature of the oil bath in the reaction tank was set to 220°C and maintained for 60 minutes.

Then, while stirring at a rotational speed of 70 revolutions per minute, the temperature was 230°C for 60 minutes, 240"C for 80 minutes, and 250°C.
The reaction was carried out for 90 minutes. The amount of phenol distilled out at this point was 15.17 kg (92% of the theoretical amount).

The system was then heated to 28 mmH while maintaining the temperature at 250°C.
The reaction was carried out for 15 minutes at a reduced pressure of 1.5 g. Next, the contents of this reaction tank are
The mixture was supplied to a reaction tank having an inner diameter of 100 mm and a tank length of 1000 mm, and forced polymerization was carried out under the conditions of 250°C, a rotation speed of 90 times per minute, and a residence time of 15 minutes per ml of vacuum. The polymer was taken out in the form of strands and cut into pellets. The obtained polymer was pale yellow and transparent, and had a number average molecular weight of 39,000. Moreover, the polymer yield was 21.26 kQ. Table 1 shows the composition and various physical properties of the obtained polymer.

Synthesis Example 2 Into the reaction tank used in Synthesis Example 1, 23,61 kg% of 2,3-di(hydroxymethyl)-berhydro-1,4:5.10:6.9-trimethanoanthracene/dimethylene 114-cyclohexanedicarboxylate/ L'16.39 and tetrabutylorontitane as catalyst) 4.0
After the system was sufficiently purged with nitrogen gas, the temperature of the oil bath in the reaction tank was set to 180°C and maintained for 60 minutes. Then, while stirring at a rotational speed of 70 revolutions per minute,
60 minutes at 0°C, 80 minutes at 230°C, 60 minutes at 250°C
I responded accordingly. The amount of methanol distilled at this point is 4.7
It was 7 kg (91% of the theoretical amount). Then increase the temperature to 25
While maintaining the temperature at 0°C, the system was reduced in pressure to 30 mmHg and allowed to react for 15 minutes. Next, the contents of this reaction tank were synthesized in Synthesis Example 1.
In the same manner as above, it was supplied to the next reaction tank and heated at 250°C and 90% per minute.
rotational speed, degree of vacuum 6 rrtnHg, residence time 1
Drive polymerization was carried out under conditions of 5 minutes. The polymer was taken out in the form of strands and cut into pellets. The obtained polymer was pale yellow and transparent, and the number average molecular weight was 34.00.
It was 0. Moreover, the polymer yield was 30.92 kQ. Table 1 shows various physical properties of the obtained polymer.

Synthesis Example 3 As a raw material, 2,3-di(hydroxyne-F-)L/)
-berhydro-1,4:5.8-dimethanonaphthalene 2
0,0572 g, dimethylene perhydro-4,7-methanoindene-2,5-dicarboxylic acid/L' 9.11 kQ
, 1,4-cyclohexanedicarboxylic acid dimethy/l/
Using the reaction apparatus of Synthesis Example 1 and the same reaction conditions as Synthesis Example 2, using 10.84 kg and 4.0 g of tetrabutyl orthotitanate as a catalyst, 30.16 kg of pale yellow transparent pellet-shaped polymer was obtained. . The number average molecular weight of this polymer was 40,000. Table 1 shows the composition and various physical properties of the obtained polymer.

Synthesis Example 4 Starting materials, 2.3-norbornane dimethanol-iV 1
4.89 kg, Schiff x 2) v carbonate 14.29&g.

2.7-zocahydronafcleandicarponic acid diphenylene/
Using 10.82 kg of L' and 0.66 g of metallic lithium powder as a catalyst, 20.30 kg of pale yellow transparent pellet-shaped polymer was obtained using the reaction apparatus of Synthesis Example 1 under the same reaction conditions as Synthesis Example 2. . Number average of this polymer +
1 was 37.000.

obtained polymer The composition and various physical properties are shown in Table 1.

Characteristics as a blank optical recording medium Example 1 Using the resin of Synthesis Example 1, SIM-47 manufactured by Technoplus Co., Ltd.
Outer diameter 13cm, inner diameter 1.5cm by 49A injection molding machine
A substrate was obtained which was injection molded to a thickness of 1.2rrlrr+.

Films of aluminum silicon nitride/terbium iron-cobalt/aluminum silicon nitride were sequentially formed on this substrate by sputtering, and the writing/reading/erasing characteristics as a magneto-optical disk were evaluated. As a result, the C/N ratio of the read signal was 50 dB. there were. Furthermore, the C/N ratio after writing/reading/erasing 1 million times was 46 dB. Furthermore, the C/N ratio after storage for 1000 hours at 75'C and 85% RH was as good as 47 dB.

Example 2 Using the resin of Synthesis Example 2, the characteristics as a magneto-optical disk were evaluated in the same manner as in Example 1. As a result, the C/N ratio was 51.
dB, 48dB, 75'C after 1 million repeated tests
After storage for 1000 hours at 185% RH, the i was good at 6 dB.

Example 3 Using the resin of Synthesis Example 3, the characteristics of the magneto-optical disk were evaluated in the same manner as in Example 1. As a result, the C/N ratio was 5.
0dB, repeated test 100'7i times, then 47dB,
45dB after 1000 hours storage at 75°C 185%RH
It was good.

Polycarbonate (Panrai manufactured by Ondai Kasei) A as a comparative example resin
D5503), and as a result of evaluating the characteristics as a magneto-optical disk in the same manner as in Example 1, the C/N ratio was 45d.
B, 40dB after 1 million times repeated test, 75°C1
After being stored for 1000 hours at 8596RH, it was 40 dB.

〔Effect of the invention〕

As described above, by using the resin of the present invention, a substrate excellent as a substrate for an optical recording medium, that is, a substrate having the following characteristics can be provided.

■Light transmittance is 9096 or more (2nu4, wavelength 800ru
n) and high.

■It exhibits good heat resistance with a glass transition point of 110°C or higher.

■Saturated water absorption rate is low at 0.3% or less.

(2) When used as a magneto-optical disk substrate, the C7N ratio of the read signal is 5 dB or more higher than when a substrate made of bispheno-/I/A polycarbonate is used.

Patent applicant RiRashi Co., Ltd.

Claims (3)

[Claims] (1) A substrate for an optical recording device comprising polyester, polyester carbonate or polycarbonate resin in which repeating units are represented by the following general formula (I). ▲There are mathematical formulas, chemical formulas, tables, etc.▼ (I) (R_1 and R_2 are a bond or an alkylene group, alkylidene group, or cycloalkylene group with 8 or less carbon atoms, and between R_1 and R_2 there is a bond or a carbon number of 6 or less There may be a bridged structure with an alkylene group or an alkylidene group. R_1 and R_2 are not bonds at the same time. R_3 and R_4 are hydrogen atoms or alkyl groups having 4 or less carbon atoms. It is a number indicating the polymerization ratio, and is in the range of x:y = 100:0 to 0:100 (molar ratio). Also, n is 0, 1 or 2.) (2) A substrate for an optical recording medium comprising polyester, polycarbonate, or polyester carbonate resin in which the repeating unit is represented by the following general formula (Ia). ▲There are mathematical formulas, chemical formulas, tables, etc.▼ (I a) (x, y are numbers indicating the copolymerization ratio, x:y=100
:0 to 0:100 (molar ratio). Further, n is 0, 1 or 2. ) (3) A substrate for an optical recording medium comprising polyester, polycarbonate or polyester carbonate resin in which the repeating unit is represented by the following general formula (Ib). ▲There are mathematical formulas, chemical formulas, tables, etc.▼ (I b) (x, y are numbers indicating the copolymerization ratio, x:y, = 10
The range is 0:0 to 0:100 (molar ratio). Further, n is 0, 1 or 2. )