JP2507132B2 - Play-only optical disc - Google Patents

Description

The present invention relates to a read-only optical disc that performs optical reading.

[Conventional technology and its problems]

The read-only optical disc has been widely put into practical use as a low-cost, large-capacity recording medium. It is especially popular for music playback and image playback.

The structure of the read-only type optical disc is such that a reflective film (usually Al) is vapor-deposited on a transparent substrate having pits (concavities and convexities) corresponding to recording signals formed on the surface, and a protective coat made of resin is further applied.

However, this structure still has a problem in weather resistance. For example, the expansion and shrinkage of the substrate when a sudden change in temperature and humidity is applied, or peeling of the reflective film due to contraction or high temperature, corrosion of the reflective film under high humidity, etc. directly leads to an increase in error rate,
It greatly reduces the reliability of the optical disc.

Especially when used in a special environment such as high temperature or low temperature, the problem of weather resistance becomes extremely important.

[Means for solving the problem]

In view of the above problems, the inventors of the present invention have made earnest studies to provide a read-only optical disc having high weather resistance, and as a result, a disc having extremely excellent weather resistance can be obtained by selecting a specific structure. Found.

[Structure of Invention]

The gist of the present invention is to provide a read-only optical disc comprising a transparent substrate made of polycarbonate having an annular shape on which concave and convex information is formed, and a reflective layer and a protective layer provided on the transparent substrate. It is provided only in an intermediate portion between the protective layer and the protective layer so as to cover the upper surface portion of the reflective layer and the outer peripheral edge portion and the inner peripheral edge portion of the substrate, and a polycarbonate substrate with residual halogen of 20 ppm or less is used as the polycarbonate substrate. The reflective layer is an Al alloy containing 0.1 to 15 at% Ta, the protective layer is a curable resin, the residual alkali metal or alkaline earth metal is 10 ppm or less, and the residual halogen is a resin of 20 ppm or less. The present invention resides in a read-only optical disc characterized by.

 The present invention will be described in detail below.

The substrate used in the present invention is transparent for transmitting reproduction light, and polycarbonate is used.

Polycarbonate is usually molded into a substrate by so-called injection molding in which a polycarbonate is melted and injected into a mold. At this time, by installing a stamper in which unevenness information is recorded in advance in the mold, the unevenness information is transferred to the substrate. Diameter 130m
For mφ or 86 mmφ substrates, the standard thickness of the substrate is 1.2 mm.

Polycarbonate is optically unfavorable if the residual strain upon injection molding is too large. Therefore, it is usually preferable to injection-mold a polycarbonate having a weight average molecular weight of about 13,000 to 16000 at a resin temperature of about 320 to 380 ° C.

In order to prevent corrosion and deterioration of the reflective layer provided on the polycarbonate again, the residual halogen content in the polycarbonate is preferably 20 ppm or less, more preferably 5 ppm or less.

Polycarbonate is obtained by reacting a phenolic compound (Bethphenol A) with phosgene using a halogenated hydrocarbon as a solvent, and the halogen (chlorine) compound used during this reaction forms a reflective layer if it remains in the polycarbonate. Reacts with the metal to cause corrosion of the reflective layer.

The removal of the halogen compound is carried out by adding a non-solvent for the resin to the produced polycarbonate solution, spraying it into warm water to cause gelation, and distilling off the solvent, or purification by washing with water.

A reflective layer for reflecting the reproduction light is usually formed on the substrate, but in the present invention, Ta is contained as the reflective layer.
Use an Al alloy. The Al alloy containing Ta is superior in corrosion resistance to the film of Al alone and ensures high reliability of the disk. The content of Ta is preferably 0.1 to 15 atomic% (a
The thickness of the reflective layer is preferably 0.5 to 10 at%, more preferably 300 Å or more and 1 μm or less, and further preferably 500 Å or more and 3000 Å or less.

The reflective layer is not provided on the outer peripheral edge portion and the inner peripheral edge portion of the substrate, but is provided only on the intermediate portion between the both peripheral edge portions. This is performed by covering the outer peripheral edge portion and the inner peripheral edge portion of the substrate with a cover when providing the reflective layer by sputtering or the like.

It is also considered that the surface of the substrate is treated before the formation of the reflective layer to improve the adhesiveness and temporal stability of the reflective layer.

Plasma treatment, ultraviolet irradiation treatment, etc. can be considered as the method of surface treatment, but in any case, it is enough to remove water adsorbed on the surface of the substrate and organic substances adhering to the surface of the substrate that cause corrosion and peeling. Process, that is, a process called a water removal process.

The degree of treatment cannot be unconditionally determined depending on the treatment method, but in the case of plasma treatment, the contact angle of water on the substrate surface is less than 60 °, and in the case of ultraviolet irradiation treatment, the contact angle of water on the substrate surface is It is better to treat so that the wettability is less than 60 °.

Since the surface treatment of this substrate is a treatment for removing water and organic substances attached to the reflective layer after forming the substrate, the reflecting layer is formed within 120 minutes, preferably within 30 minutes after forming the substrate. In some cases, it may not be necessary to start the formation.

A protective layer is further provided on the reflective layer. The protective layer is
For example, a so-called curable resin that cures upon irradiation with energy rays (ultraviolet rays), such as a system containing epoxy acrylate or urethane acrylate as a main component, or a thermosetting resin such as a silicone system is preferably used. Of these, UV curable resins are preferred.

The protective layer made of these curable resins is usually applied directly on the reflective layer by spin coating, coating by a coating method such as a bar coater, and is cured, so that the Al-Ta reflective layer of the present invention is corroded or deteriorated. It is necessary that the substrate and the protective layer are normally in direct contact with each other at the outer peripheral edge portion and the inner peripheral edge portion of the substrate where the reflective layer is not provided. Therefore, properties such as good adhesion to the substrate and no deterioration of the substrate are required.

Therefore, as the curable resin, the content of alkali metals or alkaline earth metals such as Na, K, and Ca and halogens such as Cl, Br, and F, which cause deterioration of the reflective layer, are alkali metals or alkaline earth metals. As, i.e., Na in the compound
It is preferable that the content of Ca or Ca is 10 ppm or less and the content of halogen, that is, Cl or Br in the compound is 20 ppm or less. As a method of obtaining these resins, there are a method of performing sufficient washing in the manufacturing process (washing with water or a solvent), a method of performing crystallization with a solvent (crystal folding), and the like.

The thickness of the protective layer (after curing) is preferably about 1 to 20 μ,
If the thickness is made thicker than this, the substrate may be deformed due to the shrinkage of the protective layer and the like, and it is necessary to take measures against this, and if it is too thin, the durability is deteriorated.

The protective layer after curing has a pencil hardness of HB or higher, and a shrinkage rate of about 0 to 15% from the time of curing to the time of curing, protection against external force, consideration of substrate deformation, ease of handling, etc. From the point of, it is preferable.

〔Example〕

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to the following Examples as long as the gist thereof is not exceeded.

The methods for measuring the content and the like in the present specification and examples are as follows.

1) Measurement of alkali metal content-Measured by atomic absorption spectrometry. (N, not as a compound
Content as a, K, etc. ) 3) Measurement of halogen content ・ Oxidative decomposition of 30 mg of sample (combustion in oxygen stream and coulometric titration of generated hydrogen halide using silver electrode. Content is converted to Cl (chlorine)).

Equipment used "Chlorine and sulfur analyzer manufactured by Mitsubishi Kasei Co., TSX
-10 ”3) Measurement of contact angle-Measured using the FACE contact angle meter CA-S150 type manufactured by Kyowa Interface Science Co., Ltd.

4) Measurement of shrinkage rate-Determination of density before and after curing It is the value obtained in%.

ρ ₁ : Density before curing (liquid) ρ ₁ : Density after curing Example 1 Polycarbonate having a weight average molecular weight of 15,000 and residual chlorine of 5 ppm is used, injection molding is performed at a resin temperature of 350 ° C. into a mold having a built-in stamper, and tracking is performed. A polycarbonate substrate of 130 mmmφ having a groove and irregularity information for use was obtained.

After this substrate was introduced into a sputtering apparatus and evacuated to 8 × 10 ⁻⁷ Torr or less, plasma treatment was performed on the side of the substrate on which irregularity information was formed under conditions of 5 mm Torr, 100 w, and 30 seconds. Then, an alloy target having a composition of Al ₉₇ Ta ₃ (at%) was DC-sputtered on the substrate with Ar gas. A reflective layer with a composition of Al ₉₆ Ta ₄ (at%) is 1000 on the substrate.
Å formed. The composition was analyzed by X-ray fluorescence analysis.

The reflective layer is provided from a position with a radius of 22 mm to a position of 62 mm from the center of the substrate, with a width of 14.5 mm at the inner peripheral edge of the substrate and a width at the outer peripheral edge.
A portion having no 3 mm reflective layer was formed.

Alkali metal content 3ppm on the substrate provided with this reflective layer,
An epoxy UV curable resin having a halogen compound content of 5 ppm was spin-coated and irradiated with UV to cure the resin to form a protective layer of 5 μm. The hardness of the protective layer was H and the shrinkage rate was 8%. The disc thus obtained is 70 ° C, 90%
An acceleration test was performed for 1000 hours under RH conditions, and when the drop-in error rate was measured over time, the increase stopped at 1.6 times.

Example 2 Instead of the plasma treatment, an ultraviolet irradiation treatment was carried out so that the contact angle of water was 45 °. A disk was obtained in the same manner as in Example 1 except for the above.

When an accelerated test was performed, the drop-in error rate stopped at 1.4 times.

Examples 3, 4, 5 Al ₉₉ Ta ₁ , Al _97.5 Ta _2.5 , Al ₉₅ Ta ₅ by placing Ta chip or Al chip on the target of Al ₉₇ ta ₃ (at%).
A disk was obtained in the same manner as in Example 1 except that the reflective layer was formed.

When the accelerated test was performed, the drop-in error rates were 1.7, 1.4 and 1.2 times, respectively.

Comparative Example 1 In the same manner as in Example 1, 1000 Å a film of Al alone was formed on the substrate.
A disk was obtained in the same manner as in Example 1 except that the film was formed.
When this disk was subjected to an acceleration test in the same manner as in Example 1, corrosion occurred on the entire surface and the error rate could not be measured.

〔The invention's effect〕

Since the optical disk of the present invention has excellent weather resistance, it is suitable as an optical disk for use under severe conditions and for long-term storage.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Takashi Hashimoto Inventor Takashi Hashimoto 1000 Kamoshida-cho, Midori-ku, Yokohama, Kanagawa Mitsubishi Kasei Corp. Research Institute (72) Toshifumi Kawano 1000 Kamoshida-cho, Midori-ku, Yokohama, Kanagawa Mitsubishi Kasei Research Institute Co., Ltd. (56) Reference JP-A-1-169751 (JP, A) JP-A-58-137151 (JP, A) JP-A-2-101649 (JP, A) Jitsukoku Sho-63-27298 ( JP, Y2)

Claims (1)

(57) [Claims] 1. A read-only optical disc comprising a transparent polycarbonate substrate having an annular shape on which uneven information is formed, and a reflective layer and a protective layer provided on the transparent substrate, the reflective layer having an outer peripheral edge and an inner peripheral edge. Provided only in the intermediate portion between, the protective layer is provided so as to cover the upper surface portion of the reflective layer and the outer peripheral edge portion and the inner peripheral edge portion of the substrate, the remaining halogen as a polycarbonate substrate using a polycarbonate substrate of 20ppm or less, The reflective layer is an Al alloy containing 0.1 to 15 at% Ta, the protective layer is a curable resin, the residual alkali metal or alkaline earth metal is 10 ppm or less, and the residual halogen is 20 p
A read-only optical disc characterized by using a resin of pm or less.