JPH0359833A - Optical disk substrate - Google Patents

Abstract

PURPOSE:To obtain a substrate having excellent adhesion to recording film, heat resistance and small water absorption by constituting the substrate of a specific hydrocarbon resin and treating the substrate with a sulfuric-chromic acid mixture in a manner that the surface after treated has a specified contact angle for water. CONSTITUTION:The substrate consists of a transparent hydrocarbon resin having >=100 deg.C softening point and the surface of the substrate is treated within a sulfuric-chromic acid mixture in a manner that the treated surface has 60 - 100 deg. contact angle for water. It is supposed that adhesion to the recording film can be increased with increase of polarity of the substrate surface due to oxidation by the acid mixture which has high oxidation power. However, it is required that treatment with the acid mixture is carried out lightly so as to obtain 60 - 100 deg. contact angle of the treated surface for water. Thereby, the obtd. optical disk substrate has excellent adhesion to the recording layer, heat resistance and little water absorption.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an optical disk substrate, particularly an optical disc substrate having a softening point of 100°C.
Made of the above hydrocarbon resin, the contact angle of the substrate surface to water after being treated with a sulfuric acid chromic acid mixture is 60 to 1.
The present invention relates to an optical disc substrate that has been subjected to contact treatment so as to have an angle of 00 degrees and has excellent adhesion with a surface recording film layer.

(Prior technology) Optical recording using lasers is a method of high-density information recording, storage,
Since it can be recycled and regenerated, its development has been actively carried out in recent years. 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.

Colorless and transparent synthetic resins are often used for the transparent substrates of optical discs, and typical examples include polycarbonate (hereinafter referred to as rPCJ) or polymethyl methacrylate (hereinafter referred to as rPMMA). I can do it. In addition to being colorless and transparent, these resins each have their own unique properties;
It does not meet all the requirements for an optical material, especially an optical disk substrate, and there are problems that need to be solved. 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. In this way, each of these resins is used with its own inherent problems, but in reality, there are also problems with the relationship with recording media coated on transparent substrates made of these resins. However, new problems have arisen as described below.

On the other hand, regarding recording media, a wide variety of developments have been made in the past depending on the uses of optical discs. For example, there is a write-once type that is dedicated to recording and playback, and there is a hole-drilling type that is called an erasable type.
As recording-reproducing, erasing, and re-recording devices, there are known phase change types that utilize crystal transition phenomena, magneto-optical types that utilize magneto-optical effects, and the like. These recording medium materials include tellurium or its oxide, alloy compound, etc. for the write-once type, and GdFe for the erasable type.

Inorganic materials such as rare earth-transition metal amorphous alloy compounds such as TbFe, GdFeCo, and TbFeCo are mainstream, and are generally formed by forming a film on a transparent substrate by dry processing such as sputtering under high vacuum. has been done.

By the way, the hygroscopicity and water permeability of PC and PMMA, on the one hand, cause the problem of warpage due to expansion of the substrate itself when it absorbs moisture, but on the other hand, it causes corrosion of the recording medium due to moisture permeation through the substrate. This causes the lifespan of optical discs to be shortened.

Further, regarding the heat resistance of the substrate resin, there are the following problems. That is, optical discs, especially light discs,
For optical discs such as once type and erasable type,
The temperature of the recording medium during writing and erasing of records reaches 200° C. or higher. For this reason, 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 resins with low heat resistance may cause deformation of the substrate or group formation. Problems such as deformation may occur.

On the other hand, in the production process of optical discs, a heat treatment process is often incorporated in order to prevent aging of the substrate or recording medium. It is desirable to shorten the time.

Even from this point of view, there is a problem that if the heat resistance of the resin is low, a high processing temperature cannot be used and productivity cannot be increased.

For these reasons, PMMA, which has low heat resistance, is completely insufficient to withstand the high temperatures of the optical disc production process and usage conditions, and conventionally, PC, which has higher heat resistance, has been exclusively considered as a transparent substrate material. has been done. However, even PC is not necessarily evaluated as having sufficient heat resistance, and the emergence of resin materials with higher heat resistance is desired.

To compensate for the shortcomings of conventional resins such as PC, PMMA, etc., there is a method of using transparent resins that mainly consist of only carbon and hydrogen and have a high softening point, and this method has been proposed in JP-A-63-43910, etc. .

(Problems to be Solved by the Invention) However, hydrocarbon resins with a high softening point have poor adhesion to the recording layer, as is the case with so-called polyolefins, and do not have a sufficient lifespan as optical discs. The problem was that I couldn't do it.

(Means for Solving the Problem) Therefore, as a result of intensive study on a method for improving the adhesion with the above-mentioned recording film layer, the inventors of the present invention discovered that the surface of the finished product was treated with a sulfuric acid chromic acid mixture, and then the substrate It was discovered that the adhesion to the recording film was significantly improved by treating the surface so that the contact angle with water was 60 to 100 degrees, and the present invention was achieved based on this finding.

That is, the optical disc substrate of the present invention has a softening point of 100
It is made of transparent hydrocarbon resin with a temperature of ℃ or above, and its surface is lightly contact-treated with a mixture of sulfuric acid and chromic acid.

The present invention will be explained in detail below.

In the present invention, the transparent hydrocarbon resin with a softening point of 100'C or higher may be a non-grade resin with a high glass transition point and having an alicyclic structure in the main chain or side chain, but it may be crystalline. However, as long as a high level of transparency is maintained, this is not necessarily excluded.

The non-grade resin having an alicyclic structure with a softening point of 100° C. or higher in its main chain or side chain used in the present invention is firstly polyvinylcyclohexane resin.

The polyvinylcyclohexane resin used in the present invention is preferably obtained by nuclear hydrogenation of a styrene resin (styrene polymer).

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"). ).

Examples of the vinyl aromatic hydrocarbon used as a monomer include styrene, p-methylstyrene, and α-methylstyrene, with styrene being a particularly representative example.

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.

In addition, a copolymer obtained by copolymerizing the vinyl aromatic hydrocarbon and other unsaturated monomers copolymerizable with the vinyl aromatic hydrocarbon to the extent that the properties of the vinyl aromatic hydrocarbon polymer are not lost. You can also use fusion.

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. Further, examples of the conjugated diene of the B segment in the block copolymer include 1,3-butadiene, isoprene, 2,3. Examples include dimethyl-1,3-phtadiene, 1,3-pentadiene, 1,3-hexadiene, and 1,3-butadiene and isoprene are particularly 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. The content of the A segment in such a block copolymer is 80% by weight or more, preferably 90% by weight or more, and more preferably 93% by weight or more. 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 disc 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 hydrogenated resin 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.

Polyvinylcyclohexane resin can be obtained by nuclear hydrogenating such a styrene polymer in the presence of a hydrogenation catalyst capable of aromatic hydrogenation. Examples of hydrogenation catalysts used here include metals such as nickel, cobalt, ruthenium, rhodium, platinum, and palladium, or their oxides, salts, and complexes, and these on activated carbon, diatom, etc.
Examples include those supported on a carrier such as 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.

The nuclear hydrogenation reaction requires a pressure of 50 to 250 kg/cm2,
At a temperature of 100 to 200°C, a saturated hydrocarbon solvent such as cyclohexane, methylcyclohexane, n-octane, decalin, tetralin, naphtha, etc., or
It is preferable to use an ether solvent such as THF.

It is preferable that the nuclear hydrogenation rate of the aromatic nucleus by the nuclear hydrogenation reaction is 90% or more, particularly 95% or more. Nuclear hydrogenation rate is low, 9
If it is less than 0%, there are problems such as a decrease in the heat resistance of the resulting resin and an increase in birefringence, which is not preferable.

Other non-grade polymers of the present invention include 0-
Examples include a random copolymer of an olefin and a cyclic monoolefin using a Ziegler catalyst, and a hydrogenated ring-opening polymer of a cyclic olefin using a metathesis catalyst.

The a-olefins used for the former include ethylene,
Examples include propylene, and ethylene is particularly preferred. In addition, as the cyclic monoolefin, 2J rubornene, 5-methyl-2J rubornene, 1,4,5.8-tetramethano-1,2,3,4,4a, 5,8,8a-octahydronaphthalene, 2-methyl -1,4,5,8-tetramethano-1,2,3,4,4a, 5,8,8a-octahydronaphthalene 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 non-quality polymers are described in JP-A-60-168708, 61-115912, etc., and the latter non-quality polymers are described in JP-A-60-26024, 63-218726, etc. ing.

Even if the resin is crystalline, it is possible to use a transparent polymer such as 4-methylpentene-1 polymer polymerized using a stereoregular catalyst.

The optical disc 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 greater than 20,000 and less than 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 is measured using a thermomechanical analyzer using a probe for needle insertion mode, and a load of 5
g, 100℃ or more when measured at a temperature increase rate of 5℃ minutes,
Preferably it is 120″C or higher.If the softening temperature is low,
There are problems such as deformation of the substrate and grape.

In the present invention, a heat stabilizer is blended with the resin obtained as described above and injection molding is performed.

As heat stabilizers, hindered phenol heat stabilizers,
Examples include sulfur-based heat stabilizers and phosphorus-based heat stabilizers.

A combination of a hindered phenol heat stabilizer and a phosphorus heat stabilizer is preferred from the standpoint of improving heat deterioration resistance.

The hindered phenol heat stabilizer employed in the present invention includes tetrakis[methylene-3-(3,5-di-t
-butyl-4-hydroxyphenyl)propionate methane, 3,9-bis[1,1-dimethyl-2-(13-
(3-t-butyl-4-hydroxy5-methylphenyl)propionyloxy)ethyl]-2.4,8.10
-tetraoxaspiro[5,5]undecane, 1,3.
5-) Lis(3,5-di-t-butyl-4-hydroxybenzyl-5-)riazine-2,4,6(IH,3H
,5H)-trione, 1.3.5-trimethyl-2,4
, 6-) lis(3,5-di-t-butyl4-hydroxybenzyl)benzene and the like.

In addition, as a phosphorus-based heat stabilizer, tetrakis (2,4-
Examples include t-detalphenyl)-4,4'-biphenylene phosphonite and bis(2,6-di-t-butyl-4-methylphenyl)pentaerythryl di-phosphite.

The suitable amount of each of these stabilizers added is 0.01 to 1 part by weight.

There are no particular restrictions on the method of mixing these stabilizers with the hydrocarbon resin of the present invention having a softening point of 100° C. or higher, but usually the resin and stabilizer are mixed using a ribbon blender, tumbler blender, Henschel mixer, etc. Thereafter, the mixture is melt-kneaded using a Panbury mixer-screw extruder, twin-screw extruder, etc. to form pellets. Using the pellets thus obtained, the molding temperature was 2.
By injection molding at 70 to 350°C, especially 280 to 340°C, it is possible to obtain an optical disc substrate that has excellent transparency, heat resistance, etc., is free from coloring, and has extremely small optical distortion.

In the present invention, it is important to impregnate the optical disc substrate obtained in the manner described above in a sulfuric acid chromic acid mixture and to subject the surface to a slight contact treatment.

The sulfuric acid chromic acid mixture used is a mixture of an alkali dichromate salt, pure water, and concentrated sulfuric acid, and the ratio of pure water and concentrated sulfuric acid to dichromate is 1/1 in terms of weight ratio of Itoun water/chromate.
1 to 20/1, preferably 171 to 311° Concentrated sulfuric acid monobichromic acid weight ratio of 1011 to 200/1, preferably 101
It is 1 to 30/1. Sodium or potassium is usually used as the alkali metal.

The contact treatment with the sulfuric acid chromic acid mixture is mild, and is defined by the contact angle of the substrate surface with water after the treatment, and in the present invention, the contact angle is 60.
It is processed so that the temperature is within the range of ~100 degrees.

After treatment, the contact angle with water decreases because the surface is oxidized by the sulfuric acid chromic acid mixture, which has strong oxidizing power, and C-OH,
It is presumed that this is due to the formation of oxygen-containing groups such as C=O and COOH. It is thought that the adhesion of the recording film increases as the polarity of the surface increases.

The treatment temperature is usually room temperature to 80°C, but room temperature is sufficient to achieve the purpose of the present invention.

The treatment time may be relatively short, less than 1 hour when treated at room temperature, preferably less than IO minutes, more preferably 3
Within minutes.

If the processing time is not long, the surface will become rough and it is thought that this will have an adverse effect on the noise level, etc.

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 then a recording layer of TbFeCo, etc. is formed on the film. However, it is also possible to adopt a method such as providing a reflective film such as AI or covering it with a protective film.

[Examples] The present invention will be described in more detail with reference to Examples and Comparative Examples below, 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.

■Number average molecular weight Nigel permeation chromatography (GPC)
) was measured in the same manner as polystyrene using THF as a solvent, and the number average molecular weight in terms of polystyrene was determined.

(2) Nuclear hydrogenation rate (%): Polyvinylcyclohexane resin was dissolved in tetrahydrofuran (THF) and measured by UV absorption.

(1) Softening temperature (°C): Using a thermomechanical analyzer manufactured by Seiko Electronics Co., Ltd., the softening temperature was measured using a needle insertion mode probe at a heating rate corresponding to a load of 585°C. The thickness of the test piece was 3 mm.

■Light transmittance of optical disc substrate (%): JISK671
Measured according to 4.

(2) Measurement of contact angle The contact angle was measured by the droplet method using Kyowa Kaimen Kagaku Co., Ltd. (A-DT, type A) at a room temperature of 23° C. and 50% RH.

A sample was set, and demineralized distilled water was formed into a liquid sphere with a diameter of 1.5 mm and dropped onto the sample. Measure the contact angle between the droplet and the sample surface on the left and right sides of the droplet, calculate the average value, and repeat the measurement several times at different measurement points.
The contact angle was calculated from the average value.

Substrate production example 1,3.5-trimethyl-2, 1,3.5-trimethyl-2,
4,6-Dolis(3,5-di-t-butyl-4-hydroxybenzyl)benzene (manufactured by Ciba Geigy Japan)
Irganox1330 J) 0.2 parts by weight, screws (
Add 2 parts by weight of 2,6-di-t-butyl-4,methylphenyl)-pentaerythritol-diphosphite (manufactured by Adeka Argus Co., Ltd. r MARK PEP-36J O, and perform melt mixing at 260°C using an extruder. Pelleted.

This pellet is molded using an injection molding machine (rM140AJ manufactured by Meiki Co., Ltd.)
Attach a stub bar with a grape to the movable mold side using
A disk-shaped optical disk substrate of m 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 109°C.

Example 1 Thoroughly grind 5 g of potassium dichromate in an agate mortar. 5 g of this pulverized potassium dichromate was placed in 8 g of sizable water, and 100 g of concentrated sulfuric acid was added little by little while stirring.

Continue stirring for 1 hour to completely dissolve the potassium dichromate. The optical disk substrate obtained in the substrate manufacturing example was impregnated in this sulfuric acid/chromic acid mixture at room temperature, and after 2 minutes, it was taken out and thoroughly washed with water. This substrate was dried at 100° C. for 1 hour and the contact angle with water was measured and found to be 69°. The obtained substrate was loaded into a sputtering device, and first 8X10-7
Evacuate to below Torr and perform reactive sputtering of Ta target using a mixed gas of Ar and 02.
An interference layer (thickness: 50A) consisting of 5 was formed. Next, Ar using Tb target and FeCo target
A TbFeCo recording layer (thickness: 300 Å) was provided by dual-source simultaneous sputtering using gas. Further, an A1 target on which Ti chips were placed was sputtered in Ar gas to form a reflective layer with a thickness of 300 Å. On the mirror surface of the substrate coated with this film, draw 10 lines each in an area of 1 cm x 1 cm. Apply Teraoka's adhesive tape (imide film base) to the resulting grout area of the substrate. The adhesion strength between the substrate and the tantalum oxide film was evaluated by peeling it off.

As a result, out of 100 substrate grain test pieces measuring 1 mm x 1 mm square, not a single piece peeled off. Furthermore, in a peel test after a 100-hour high-temperature, high-humidity test of a substrate provided with a tantalum oxide film at a temperature of 85° C. and a humidity of 85% RH, not a single film peeled off. In this way, the adhesion of the tantalum oxide film was good. The surface treated for 2 minutes was examined using an electron microscope (
When observed under a magnification of 1,000 times, no surface roughness was observed.

Example-2 In Example-1, the immersion time in the chromic acid mixture was 9
The process was carried out in the same manner as in Example-1 except that the time was changed to minutes.

As a result of the tape peeling test, not a single piece out of 100 peeled off. The surface treated for 9 minutes was examined using an electron microscope (10 minutes).
When observed under a magnification of 00 times), no surface roughness was observed.

Comparative Example 1 When a tape peeling test was conducted on untreated substrates, 100 sheets out of 100 were peeled off.

The results of Examples and Comparative Examples are summarized in Table 1.

Table 1 (Effects of the Invention) As detailed above, the present invention is an invention of an optical disk substrate that has excellent adhesion with a surface recording film layer and heat resistance, and has low water absorption, and has extremely high industrial utility value.

Claims (2)

[Claims] (1) Made of hydrocarbon resin with a softening point of 100°C or higher,
An optical disk substrate, the surface of which has been contact-treated with a sulfuric acid chromic acid mixture so that the contact angle of the substrate surface to water after treatment is 60 to 100 degrees. (2) The ratio of pure water and concentrated sulfuric acid to dichromate in the sulfuric acid chromic acid mixture is 1/1 in terms of pure water/dichromate weight ratio.
~3/1, concentrated sulfuric acid/dichromic acid weight ratio 10/1~30
The optical disc substrate according to claim 1, which is /1