JPH04315832A - Optical disk substrate - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to an optical disc substrate.
In particular, it is made of a hydrocarbon resin with a softening point of 100°C or higher, the substrate surface is contact-treated with a fluorine and oxygen-containing gas, and the contact angle of the substrate surface to water after treatment is 70° or less, and the oxygen to fluorine element on the substrate surface is The present invention relates to an optical disk substrate having improved heat resistance and adhesiveness, having a ratio of 0.1 to 1 and a fluorine penetration depth of 100 to 2000 Å.

0002

2. Description of the Related Art Optical recording using lasers has been actively developed in recent years because it enables high-density information recording, storage, and reproduction. An optical disk can be cited as an example of such optical recording. In general, an optical disk basically consists of a transparent substrate and various recording media coated thereon.

[0003] Colorless and transparent synthetic resins are often used for the transparent substrates of optical discs, and typical examples include polycarbonate (hereinafter referred to as "PC") or polymethyl methacrylate (hereinafter referred to as "PMMA"). ) can be mentioned. These resins are colorless and transparent, and each has unique and excellent properties, but they do not meet all the requirements for optical materials, especially optical disk substrates, and there are problems that need to be solved. have. For example, PC has a problem with birefringence due to its aromatic ring, and also has problems with water absorption or water permeability. On the other hand, problems with PMMA in terms of heat resistance, water absorption, and toughness have been pointed out for some time.

[0004] As described above, each of these resins is used with its own inherent problems, but in reality, recording media coated on transparent substrates made of these resins are In relation to this, new problems have arisen as described below. On the other hand, regarding recording media, a wide variety of developments have been carried out in response to the uses of optical discs. For example, the write-once type, which is dedicated to recording and playback, is a hole-pull type, and the erasable type, which is used for recording, playback, erasing, and re-recording, is a phase change type that uses crystal transition phenomena. There are also known magneto-optical types that utilize the magneto-optical effect. These recording media materials include tellurium or its oxide, alloy compound, etc. for the write-once type, and GdFe, TbFe, GdFeCo, TbF for the erasable type.
Inorganic materials such as rare earth-transition metal amorphous alloy compounds such as eCo are mainstream, and are generally formed by forming a film on a transparent substrate using a dry processing method such as sputtering under a high vacuum.

By the way, the hygroscopicity and water permeability of PC and PMMA, on the one hand, cause the problem of warping due to expansion of the substrate itself when it absorbs moisture, but on the other hand, it also causes corrosion of the recording medium due to moisture permeation through the substrate. This causes problems and shortens the lifespan of optical discs. Further, regarding the heat resistance of the substrate resin, there are the following problems. That is, in optical discs, especially write-once type optical discs, erasable type optical discs, etc., the temperature of the recording medium during writing and erasing of records reaches 200° C. or higher. Therefore, even though this heat is not directly applied to the disk substrate, it is expected that the substrate will reach a considerably high temperature when writing and erasing records, and with resins with low heat resistance, the substrate may be deformed or the grooves may be deformed. problems may occur.

On the other hand, in the production process of optical discs,
A heat treatment step is often incorporated for the purpose of preventing aging of the substrate or recording medium, but in order to improve productivity, it is desirable to shorten the processing time by processing at as high a processing temperature as possible. From this perspective,
If the heat resistance of the resin is low, a high processing temperature cannot be used and productivity cannot be increased.

[0007] For these reasons, PMMA, which has low heat resistance, is completely insufficient to withstand the high temperatures encountered in the production process or usage conditions of optical discs;
PC, which has higher heat resistance, is being considered as a transparent substrate material. However, even PC is not necessarily evaluated as having sufficient heat resistance, and the emergence of resin materials with higher heat resistance is desired.

[0008] In order to compensate for the drawbacks of conventional resins such as PC and PMMA, there is a method of using a transparent resin that mainly consists of only carbon and hydrogen and has a high softening point.
3-43910 etc. However, hydrocarbon resins with a high softening point have poor adhesion to the recording film layer, just like polyolefins that have low adhesion.
There was a problem that a sufficient lifespan as an optical disk could not be obtained. The present inventors have discovered that by treating the surface of a molded product with fluorine gas, the adhesion to the recording film can be improved (Japanese Patent Application No. 2-200893).

[0009]

[Problems to be Solved by the Invention] However, even with the above-mentioned method of treatment with fluorine gas, the adhesion was still not sufficient. Another problem was that it was difficult to control the fluorine gas treatment. Therefore, as a result of intensive research into ways to improve the treatment with fluorine gas, it was discovered that the adhesion to the recording film layer could be dramatically improved by performing a specific treatment with fluorine gas and oxygen gas, and the present invention was achieved.

0010

[Means for Solving the Problems] The optical disk substrate of the present invention is made of a transparent hydrocarbon resin with a softening point of 100°C or higher, and the surface thereof is contact-treated with a fluorine and oxygen-containing gas, and the substrate surface after the treatment is The contact angle with water is 70 degrees or less, the elemental composition of the substrate surface measured by electron spectroscopy (ESCA), the elemental ratio of oxygen to fluorine is 0.1 to 1, and the SIM
It is characterized by a fluorine penetration depth of 100 to 2000 Å as measured by S (secondary ion mass spectrometer).

[0011] In the present invention, the transparent carbon resin having a softening point of 100°C or higher is mainly an amorphous resin having a high glass transition point and having an alicyclic structure in the main chain or side chain. However, even if it is crystalline, it is not necessarily excluded as long as it maintains high transparency. In addition, the fluorine and oxygen-containing gas in the present invention includes a mixed gas of F2 gas and oxygen gas or air, and a mixture of these gases with nitrogen gas.
2. A mixed gas diluted with an inert gas such as Ar can be used.

The present invention will be explained in detail below. A first example of the amorphous resin having an alicyclic structure with a softening point of 100° C. or higher in the main chain or side chain used in the present invention is polyvinylcyclohexane resin. The polyvinylcyclohexane resin used in the present invention is preferably obtained by nuclear hydrogenation of a styrene resin (styrene polymer).

[0013] Examples of the raw material styrenic polymer include vinyl aromatic hydrocarbon polymers and vinyl aromatic hydrocarbon block copolymers. The latter vinyl aromatic hydrocarbon block copolymer includes a vinyl aromatic hydrocarbon polymer segment (hereinafter referred to as "A segment") and at least one conjugated diene polymer segment (hereinafter referred to as "B segment"). ).

Vinyl aromatic hydrocarbons used as monomers include styrene, p-methylstyrene, α-
Examples include methylstyrene, and a particularly representative example is styrene. Examples of the vinyl aromatic hydrocarbon polymer include a homopolymer of one kind of these vinyl aromatic hydrocarbons or a copolymer of two or more kinds thereof.

[0015] Furthermore, the above-mentioned vinyl aromatic hydrocarbon and another unsaturated monomer copolymerizable with the vinyl aromatic hydrocarbon may be copolymerized to the extent that the properties of the vinyl aromatic hydrocarbon polymer are not lost. It is also possible to use a copolymer. Next, examples of the A segment in the vinyl aromatic hydrocarbon block copolymer include those similar to those of the vinyl aromatic hydrocarbon polymer described above. In addition, the conjugated diene of the B segment in the block copolymer includes 1,3-butadiene, isoprene,
Examples include 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, 1,3-hexadiene, and especially,
1,3-butadiene and isoprene are common. A block copolymer consisting of an A segment and a B segment can be easily produced by a known method called living anion polymerization, such as a method in which polymerization is performed using an organic lithium compound as an initiator in a hydrocarbon solvent such as hexane or heptane. can be obtained. In addition, the content of A segment in such a block copolymer is 80% by weight or more,
Preferably 90% by weight or more, more preferably 93% by weight
That's all. When the content of the A segment is less than 80% by weight, the heat resistance of the resin obtained after hydrogenation decreases, making it unsuitable for use as an optical disk substrate.

In the present invention, the molecular weight of such raw material styrenic polymer is preferably 50,000 or more in terms of number average molecular weight. If the molecular weight of the styrenic polymer is too low, the heat resistance and toughness of the resin obtained after hydrogenation will decrease. On the other hand, there is no particular restriction on the upper limit of the molecular weight, but it is usually preferably 400,000 or less.

The polyvinylcyclohexane resin can be obtained by nuclear hydrogenation of such a styrene polymer in the presence of a hydrogenation catalyst capable of hydrogenating aromatics. Examples of hydrogenation catalysts used here include nickel,
Metals such as cobalt, ruthenium, rhodium, platinum, and palladium, or their oxides, salts, and complexes, and activated carbon,
Examples include those supported on carriers such as diatomaceous earth, alumina, silica, and silica alumina. Among these, Raney nickel, Raney cobalt, stabilized nickel and ruthenium, rhodium or platinum supported catalysts on carbon or alumina are particularly preferred from the viewpoint of reactivity.

[0018] Nuclear hydrogenation reaction is carried out at 50 to 250 kg/cm2.
The process is carried out at a pressure of 100 to 200°C using a saturated hydrocarbon solvent such as cyclohexane, methylcyclohexane, n-octane, decalin, tetralin, naphtha, or an ether solvent such as THF. preferable. Nuclear hydrogenation rate of aromatic nuclei due to nuclear hydrogenation reaction is 60%
or more, preferably 70% or more, more preferably 95% or more. If the nuclear hydrogenation rate is low, less than 60%, the resulting resin may have problems such as a decrease in heat resistance and an increase in birefringence, which is not preferable.

Other amorphous polymers of the present invention include random copolymers of α-olefins such as ethylene and cyclic monoolefins using a Ziegler catalyst, and hydrogenated ring-opening polymers of cyclic olefins using a metathesis catalyst. Examples include those that have been made. Examples of the α-olefin used in the former include ethylene and propylene, with ethylene being particularly preferred. Further, examples of the cyclic monoolefin include norbornene, methylnorbornene, dimetanooctahydronaphthalene, methyldimethanooctahydronaphthalene, and the like.

As the cyclic olefin used in the latter, in addition to the cyclic monoolefins mentioned in the former, cyclic polyenes such as dicyclopentadiene and tricyclopentadiene can also be used. The resulting metathesis-catalyzed ring-opened polymer is hydrogenated under similar conditions using a hydrogenation catalyst similar to that used to produce the polyvinylcyclohexane-based resins described above.

The former amorphous polymer is disclosed in Japanese Unexamined Patent Application Publication No. 60-16
8708, 61-115912, etc., the latter amorphous polymer is described in 60-26024, 63-21, etc.
It is described in Publication No. 8726 and the like. In addition, even if the resin is crystalline, 4-
Transparent polymers such as methylpentene-1 polymers can also be used.

The optical disk substrate in the present invention is molded by injection molding. In order to maintain the fluidity necessary for injection molding, the hydrocarbon resin of the present invention has a number average molecular weight of 2.
It is greater than 0,000 and less than or equal to 200,000. The lower limit of the molecular weight is determined by the strength of the resin. In the present invention, the softening point of the resin was measured using a thermomechanical analyzer using a needle insertion mode probe at a load of 5 g and 5 g.
When measured at a heating rate of °C/min, the temperature is 100°C or higher, preferably 120°C or higher. If the softening temperature is low, there are problems such as deformation of the substrate and groove.

In the present invention, a heat stabilizer is blended with the resin obtained as described above and injection molding is performed. Examples of the heat stabilizer include hindered phenol heat stabilizers, sulfur heat stabilizers, phosphorus heat stabilizers, and the like. A combination of a hindered phenol heat stabilizer and a phosphorus heat stabilizer is preferred from the viewpoint of improving heat deterioration resistance.

The hindered phenol heat stabilizer employed in the present invention is tetrakis[methylene-3-(3
, 5-di-t-butyl-4-hydroxyphenyl)propionate methane, 3,9-bis[1,1-dimethyl-
2-{β-(3-t-butyl-4-hydroxy-5-methylphenyl)propionyloxy}ethyl]-2,4
, 8,10-tetraoxaspiro[5,5]undecane, 1,3,5-tris(3,5-di-t-butyl-4-
Hydroxybenzyl-s-triazine-2,4,6(1
H,3H,5H)-trione, 1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-
Examples include hydroxybenzyl)benzene and the like.

Further, as the phosphorus-based heat stabilizer, tetrakis(2,4-di-t-butylphenyl)-4,4-biphenylenephosphonite, bis(2,6-di-t-butyl-4 -methylphenyl)pentaerythritol di-phosphite and the like. The suitable amount of each of these stabilizers added is 0.01 to 1% by weight.

These stabilizers and the softening point of the present invention are 100
There are no particular restrictions on the method of mixing the hydrocarbon resin at a temperature of ℃ or higher, but the resin and stabilizer are usually mixed using a ribbon blender,
The mixture is mixed using a tumbler blender, a Henschel mixer, etc., and then melt-kneaded using a Banbury mixer, single-screw extruder, twin-screw extruder, etc. to form pellets. Using the pellets thus obtained, the molding temperature is 270 to 350°C, particularly 280 to 340°C.
By injection molding, it has excellent transparency, heat resistance, etc.
It is possible to obtain an optical disk substrate that is free from coloring and has extremely small optical distortion.

In the present invention, the surface of the optical disc substrate obtained as described above is lightly contacted with a fluorine and oxygen containing gas. The partial pressure of fluorine during treatment is not particularly limited in relation to treatment time, but is usually below normal pressure, preferably below 100 mmHg, and more preferably below 20 mmH.
g or less. If the fluorine partial pressure is too high, it is difficult to control the treatment level, and in some cases, the reaction between the fluorine and the substrate surface proceeds excessively, causing roughening of the substrate surface.

The partial pressure of oxygen is determined in relation to the partial pressure of fluorine, and is usually 0.3 to 10, preferably 0.5 to 5 as a value of oxygen partial pressure/fluorine partial pressure. . Even when the value of oxygen partial pressure/fluorine partial pressure is smaller than 0.3, some improvement in adhesion is observed, but the improvement effect cannot be said to be sufficient. Furthermore, when the value of oxygen partial pressure/fluorine partial pressure is greater than 10, the effect of improving adhesion is poor.

The total pressure during processing, that is, the pressure of the total mixed gas when inert gases such as N2 and Ar are mixed, is not particularly limited and may be a pressurized system, but usually it depends on the degree of dilution of the inert gas. Depending on the situation, a value below normal pressure is used. Regarding fluorine gas, since pure fluorine gas is dangerous to handle, it is preferable to use one diluted with an inert gas to a concentration of 20 mol % or less.

Although the mechanism of action during the contact treatment with fluorine and oxygen-containing gas in the method of the present invention is not clear, it is clear that after the treatment, the contact angle with water decreases and the surface polarity increases. This is presumed to be the cause of the increase in recording film adhesion. Particularly when a gas with a low oxygen content is used, if the contact treatment is performed excessively, the contact angle that has once decreased tends to increase again, and as the contact angle increases, the adhesion decreases again. Excessive treatment is believed to lead to excessive surface fluorination, reducing surface polarity.

[0031] The treatment equipment with fluorine and oxygen-containing gas is as follows:
There are no particular limitations, as long as the fluorine- and oxygen-containing gas can come into uniform contact with the optical disc substrate. Room temperature is usually sufficient for the treatment temperature. The treatment time may be relatively short, ranging from 1 minute to 10 hours. It is carried out for a long time when the fluorine partial pressure is relatively low, and for a short time when it is relatively high. If the treatment time is too short, the adhesion will not be improved, and if the treatment time is too long, problems such as surface roughness will occur.

When the fluorine partial pressure is in the range of 1 to 20 mmHg, the treatment time is preferably longer than 10 minutes and shorter than 2 hours. More preferably, it is longer than 30 minutes and shorter than 2 hours. The fluorine-containing gas treatment in the present invention is mild, and the weight increase of the optical disk substrate due to the treatment in the present invention is 1 wt% or less, preferably 0.1 wt% or less. Further, the contact angle of the surface of the optical disk substrate with water after the fluorine gas treatment is 70° or less, preferably 65° or less.

[0033] Also, ESCA (Electron Sp
Electroscopy for Chemical
The ratio of fluorine content to oxygen content obtained by elemental analysis of a region up to a surface depth of 5 nm is preferably in the range of 0.1 to 1.0, and this value is more preferably 0.1 to 1.0. It is 2 to 0.8. Moreover, it is preferable that the fluorine treatment depth measured by SIMS (secondary ion mass spectrometer) is 100 to 2000 Å. Furthermore, the thickness is preferably 150 to 1000 Å. The measurement method will be described in the Examples section.

When manufacturing an optical disc using the optical disc substrate of the present invention, a film of SNx, TaOx, etc. is formed on the surface of the substrate by a method such as sputtering or vapor deposition, and a recording layer of TbFeCo, etc. is further formed on the film. form,
Furthermore, it is possible to adopt a method such as providing a reflective film such as Al and finally covering with a protective film.

[0035]

[Examples] The present invention will be explained in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples unless it exceeds the gist thereof. In addition, various physical properties in the following Examples and Comparative Examples were measured by the following methods. (2) Number average molecular weight: Measured by gel permeation chromatography (GPC) in the same manner as polystyrene using THF as a solvent to determine the number average molecular weight in terms of polystyrene. (2) Nuclear hydrogenation rate (%): Polyvinylcyclohexane resin was dissolved in tetrahydrofuran (THF) and measured by UV absorption. ■Softening temperature (°C): Using a thermomechanical analyzer manufactured by Daini Seiko Co., Ltd., using a probe for needle insertion mode, a load of 5
g, the softening temperature was measured at a heating rate of 5° C./min. The thickness of the test piece was 3 mm. ■Light transmittance of optical disc substrate (%): JISK671
Measured according to 4. ■Measurement of the carrier level (C/N ratio) of an optical disk An optical disk with a recording medium and a protective film is measured using a dynamic characteristic detector equipped with a PIN photodiode differential detector to measure the C/N ratio (when using an Al film). OdB
) was measured.

The recording and reproducing conditions were as follows. Recording conditions: CAV (constant angular velocity) 1800 rpm radius 30
mm position, recording on the groove Recording frequency 0.5 MHZ duty 50% Reproducing conditions: CAV 1800 rpm Reproducing power 0.8 mW ■Measurement of contact angle Under conditions of room temperature 23°C and 50% RH, the CA-DT/A type manufactured by Kyowa Interface Science Co., Ltd. was used. The contact angle was measured using the droplet method.

A sample was set, and desalinated distilled water was formed into a liquid sphere with a diameter of about 1.5 mm and dropped onto the sample. The contact angle between the droplet and the sample surface was measured on the left and right sides of the droplet, the average value was calculated, the measurement was repeated several times at different measurement points, and the contact angle was calculated from the average value. . ■Measurement of surface composition Using Kratos Xsam800, Kα of Al was measured.
It was measured at 14KV x 20mA. 10 in C, O, F
Converted as 0. ■Measurement of F penetration depth Using ATOMIKA's A-DIDA3000 secondary ion mass spectrometer, primary ion species: O2 +, acceleration voltage 12KeV, acceleration current 100nA, scan width 40
Under the measurement conditions of 0μm□, E-Gun: 1.0KV, 2.5A, the depth profiles of C and F were determined, and F-/
The F penetration depth was defined as the point at which the C-value attenuated to 1/2.

On the horizontal axis of the depth profile, the depth of the flator after measurement was measured using a stylus meter, and the sputtering rate was determined and calibrated. Substrate structure example 1,3,5-trimethyl-2, 1,3,5-trimethyl-2,
0.2 parts by weight of 4,6-tris-(3,5-di-t-butyl-4-hydroxybenzyl)benzenemethane (“Irganox 1330” manufactured by Ciba Geigy Japan), bis(
0.2 parts by weight of 2,6-di-t-butyl-4-methylphenyl)-pentaerythritol-di-phosphite (MARK PEP-36 manufactured by Adeka Argus) was added, and the mixture was heated at 260°C using an extruder. The mixture was melt-kneaded and pelletized.

[0039] The pellets were molded using an injection molding machine ("M" manufactured by each machine company).
140A''), attach a grooved stambar to the movable mold side, and mold the mold to a thickness of 1.2 mm at a resin temperature of 300°C.
A disc-shaped optical disc substrate with a diameter of 130 mm was molded. The softening temperature of the substrate resin was 172° C., and the light transmittance of the substrate was 90%. The contact angle with water was 103°. Example 1 The optical disc substrate obtained in Substrate Production Example was subjected to contact treatment with a fluorine and oxygen-containing gas.

First, the substrate was placed in a cylindrical chamber with a diameter of 18 cm, and the inside of the chamber was evacuated. Next, a mixed gas diluted with N2 gas such that the fluorine partial pressure was 3 mmHg and the oxygen partial pressure was 3 mmHg was introduced into the chamber so that the internal pressure returned to 110 mmHg. The temperature inside the chamber at this time was 17°C. After 1 hour, the F2/O2/N2 mixed gas in the system was evacuated and replaced with air, and then the substrate was taken out.

[0041] The contact angle of this substrate with water was 50°. The elemental analysis result of the substrate surface measured by ESCA is C/0/F=51/16/33 (element ratio), and O/F=51/16/33 (element ratio).
F=0.48. Further, the F penetration depth measured by SIMS was 210 Å. Also, the weight increase after treatment is 0.1
It was less than wt%.

The obtained substrate is placed in a sputtering device, the exhaust is first evacuated to below 8×10 −7 torr, and a Ta target is reactively sputtered using a mixed gas of Ar and O 2 to form an interference layer made of Ta 2 O 5 . (thickness 8
00 Å) was formed. Then, Tb target and Fe
A TbFeCo recording layer (thickness: 300 Å) was provided by dual simultaneous sputtering using Ar gas using a Co target. Further, an Al target with a Ti chip placed thereon was sputtered in Ar gas to form a reflective layer with a thickness of 300 Å.

The C/N ratio of the obtained optical disc was 60.5.
It was dB. Draw 10 lines each in an area of 1 cm x 1 cm on the mirror surface of the substrate with this film,
Adhesion strength between the substrate and the recording film was evaluated by pasting adhesive tape (imide film base) manufactured by Teraoka Co., Ltd. on the resulting grid-shaped area and peeling it off.

[0044] As a result, out of 100 1 mm x 1 mm square test pieces in the form of a checkerboard, not a single piece was peeled off. Example 2 The same treatment as in Example 1 was carried out except that the oxygen partial pressure in Example 1 was changed to 6 mmHg. The results are shown in Table 1. Comparative Example 1 When a tape peeling test was conducted on a substrate that was not subjected to fluorine and oxygen-containing gas contact treatment, peeling was 10
It was 100 out of 0. Also, the C/N ratio is 60.8dB
Met. The results are shown in Table 1. Comparative Example 2 Example 1 except that the processing time was 3 minutes in Example 1.
The same process was carried out. The results are shown in Table 1. Comparative Example 3 Fluorine partial pressure is 20 mmHg, oxygen partial pressure is approximately 0.02 mm
The treatment was carried out in the same manner as in Example 1 except that the total pressure including Hg and nitrogen was 400 mmHg and the treatment time was 30 minutes. The results are shown in Table 1. Comparative Example 4 The same process as in Example 1 was carried out except that the oxygen partial pressure was 33 mmHg and the total pressure was 600 mmHg. The results are shown in Table 1.

[0045]

[Table 1]

[0046]

Effects of the Invention The present invention provides an optical disk substrate that has superior heat resistance and low water absorption compared to conventional materials such as PC and PMMA, and has improved adhesion to the recording film layer by treatment with fluorine and oxygen-containing gas. has improved significantly.

Claims (1)

[Claims] Claim 1: The substrate is made of a hydrocarbon resin with a softening point of 100°C or higher, the surface of which is contact-treated with a fluorine and oxygen-containing gas, and the contact angle of the substrate surface with water after the treatment is 70°.
Below, regarding the elemental composition of the substrate surface, the elemental ratio of oxygen to fluorine is 0.1 to 1, and the fluorine penetration depth is 100 to 2000.
An optical disc substrate characterized by: .