JPH0896407A - Optical information recording medium - Google Patents

Abstract

(57) [Abstract] [Purpose] An inorganic thin film formed on an acrylic resin substrate has excellent characteristics required for an optical information recording medium, and it is not easily deformed by moisture absorption and has excellent reliability under high temperature and high humidity conditions. And an optical information recording medium. [Structure] When stored in an environment of 60 ° C. and 90% RH, 0.5 in a region of 20 mm or more from the center of the optical information recording medium substrate and a region of 100 μm in depth from the surface of the recording medium substrate. When the dimension after time is L1 and the dimension after 5 hours is L2, (L1-L2) / L1
An optical information recording medium in which an inorganic thin film is laminated on an acrylic resin substrate with ≦ 1.0 × 10 ⁻³ .

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical information recording medium such as an optical disc.

[0002]

2. Description of the Related Art Optical discs, optical cards, etc. are known as optical information recording media, but these can read information in a non-contact manner and record signals at high density for recording and reproducing by narrowing down laser light. Since it has a feature that it can be used, it has been remarkably spread in recent years. Especially, as typified by compact discs and video discs, the growth of optical discs is remarkable, and it is expected that they will be used more and more in the future.

In these optical information recording media, an inorganic thin film such as metal or metal oxide is formed as a reflective film or a recording film on a transparent substrate having fine grooves or pits formed on the surface thereof. The thickness and composition of the thin film differ depending on the application of the optical information recording medium, and include, for example, compact discs,
In a read-only optical disc such as a video disc, an aluminum film is formed with a thickness of about 60 to 100 nm.

Glass and resin are used as the transparent substrate for the optical information recording medium, but from the viewpoint of mass productivity, it is the mainstream to use a transparent thermoplastic resin and manufacture it by an injection molding method. Has become.

Examples of the transparent thermoplastic resin used as the transparent substrate include acrylic resin, polycarbonate resin, and amorphous polyolefin. Among them, the acrylic resin has the best optical characteristics and moldability. Widely used for video discs.

However, the acrylic resin has a large water absorption rate, and when an inorganic thin film is formed on one surface such as an optical disk, moisture is absorbed mainly from one side of the substrate, and thus moisture absorption tends to cause warpage, which results in long-term use. Improvement is required in terms of reliability. As a way to avoid this problem,
For video discs, a method of bonding two substrates has been attempted, but it is not always sufficient, and if left under high temperature and high humidity, it may deform and become unreproducible, or the bonded surface may peel off. There was an occasion. Further, the size of the optical information recording medium tends to decrease, and it is expected that the thickness of the base material will decrease accordingly. In that case, due to the decrease in the strength of the substrate,
Deformation due to moisture absorption also increases.

[0007]

The object of the present invention is to form an inorganic thin film on an acrylic resin substrate,
An object of the present invention is to provide an optical information recording medium which has excellent characteristics required as an optical information recording medium, has a small deformation due to moisture absorption, and has excellent reliability under high temperature and high humidity.

[0008]

SUMMARY OF THE INVENTION The gist of the present invention is that, when stored in an environment of 60 ° C. and 90% RH, the area is 20 mm or more from the center of an optical information recording medium substrate, and the recording medium. When the dimension after 0.5 hour is L1 and the dimension after 5 hours is L2 in a region of a depth of 100 .mu.m from the substrate surface, (L1-L2) /L1.ltoreq.1.
It is an optical information recording medium in which an inorganic thin film is laminated on a 0.times.10.sup.- ³ acrylic resin substrate.

As the acrylic resin used in the present invention, when the base material is stored in an environment of 60 ° C. and 90% RH, an area of 20 mm or more from the center of the base material and 10 from the surface of the substrate is used.
When the dimension after 0.5 hours is L1 and the dimension after 5 hours is L2 in the depth range up to 0 μm, (L
It is necessary that 1−L2) /L1≦1.0×10 ⁻³ , and it is difficult to improve the warp of the substrate if the condition is not satisfied.

As the acrylic resin satisfying the above conditions, for example, one having a glass transition temperature of 110 ° C. or more, one having a water absorption rate of 1.0% or less, or a molded substrate having a glass transition temperature of ± 30 ° C. or less is used. Examples include those that have been annealed in the environment.

Although the monomer composition of the acrylic resin is not particularly limited, for example, methyl methacrylate and other methacrylic acid esters,
Examples thereof include acrylic acid esters or copolymers of other vinyl monomers having copolymerizability with these monomers.

Examples of the methacrylic acid ester monomer include methyl methacrylate, ethyl methacrylate, cyclohexyl methacrylate, phenyl methacrylate, benzyl methacrylate, norbornyl methacrylate, isobornyl methacrylate, tricyclo [5,2, methacrylate].
1,0 ^2.6 ] deca-8-yl and the like can be mentioned.

As the acrylic acid ester monomer, methyl acrylate, ethyl acrylate, cyclohexyl acrylate, phenyl acrylate, benzyl acrylate, norbornyl acrylate, isobornyl acrylate, tricyclo [5,2, acrylate] 1,0 ^2.6 ] deca-8-yl and the like can be mentioned.

Further, as other monomers, N-cyclohexylmaleimide, N-phenylmaleimide, N-
Examples thereof include maleimides such as chlorophenylmaleimide, aromatic vinyl compounds such as styrene and α-methylstyrene, and vinyl cyanide compounds such as acrylonitrile methacrylonitrile.

Examples of the inorganic thin film in the present invention include simple metals such as aluminum and gold, metals containing these as the main components, and inorganic dielectrics such as silicon oxide, silicon nitride, zirconium oxide and zinc sulfide. Here, the type and thickness of the inorganic thin film to be formed, the film composition, etc. are determined by the type of the optical information recording medium. For example, in a normal read-only optical disc, in order to obtain sufficient reflectance and durability, the aluminum film has a thickness of 50 nm or more, preferably 70 n or more.
Form at least m thick. In a write-once type optical disc or a rewritable type optical disc, it is usual to form a dielectric and a metal by laminating.

Further, the optical information recording medium of the present invention comprises:
An ultraviolet-curable resin or a wax-based protective film may be formed on the inorganic thin film according to the purpose, and it may be used in the form of a single plate or may be used as a double-sided type by laminating.

[0017]

EXAMPLES The present invention will be described in more detail below with reference to examples, but the gist and scope of application of the present invention are not limited to these examples.

The production, molding, aluminum thin film formation, shrinkage and warpage deformation of the optical disk molding materials in Examples and Comparative Examples were all carried out by the following methods unless otherwise specified.

Preparation of Molding Material Bead-like copolymers of various acrylic resins shown in Table 1 were obtained by suspension polymerization using various monomer mixtures shown in Table 1.

The obtained copolymer was PCM manufactured by Ikegai Co., Ltd.
The mixture was kneaded with a -30 twin-screw extruder and pelletized.

Substrate molding An optical disc substrate with a signal was manufactured under the following conditions.

-Substrate specifications: Disc with a diameter of 120 mm x plate thickness of 0.6 mm-Stamper used: stamper with a CD signal with a pitch of 1.6 μm and pit depth of 110 nm-Molding machine name machine M-70A-DM-Mold for disk Mold Substrate Annealing Treatment Only the samples of Example 3 and Comparative Example 3 were subjected to substrate annealing treatment under the following conditions.

Example 3: The glass transition temperature of the resin was kept at -20 ° C for 2 hours in a constant temperature bath and then gradually cooled.

Comparative Example 3: The glass transition temperature of the resin was kept at -50 ° C. for 5 hours in a constant temperature bath and then gradually cooled.

Formation of Inorganic Thin Film Aluminum was formed into a film by a vacuum deposition method. Specifically, it was performed under the following conditions.

Equipment used: HCU-12 manufactured by Shibaura Manufacturing Co., Ltd.
P-55 ・ Preliminary evacuation: Evacuation time 0.5 hr, Arrival vacuum degree 1 × 10
^-5 Torr-Evaporation method: resistance heating-Film forming rate: 0.8 to 1.2 nm / sec-Film thickness: 70 nm Evaluation <Material characteristics> [Weight average molecular weight] Measurement was carried out by an ordinary method by GPC.

[Glass transition temperature] JIS according to DSC
It was measured according to K7121.

[Equilibrium water absorption rate]
After drying in vacuum for an hour, the initial weight (W0) is measured and 60
The sample was stored in a thermo-hygrostat at 90 ° C. and 90% RH until the weight of the sample became constant. From the weight (W) at that time, the equilibrium water absorption is given by the following formula.

Equilibrium water absorption rate [%] = (W−W0) / W0 × 100 <Substrate characteristics> [Shrinkage rate] 3.5 c from the center of the molded disc substrate
A test piece is cut out in a range of m to 4.5 cm, and the thickness of the test piece is 70 μm to 10
A test piece was obtained by polishing so as to have a thickness of 0 μm or less.

After determining two arbitrary points on a straight line along the radial direction of the disk, the test piece was left in an environment of 60 ° C. and 90% RH. Then, the distance (L1) between the two points when 0.5 hours had passed was measured with an optical microscope, and after 5 hours, the distance (L2) between the two points was measured again. The shrinkage ratio (X) at this time is as follows.

X = (L1−L2) / L1 <Amount of warp deformation> The warp was measured on both a single plate disk and a double-sided bonded disk.

1) In the case of a single plate disk A protective film having the following moisture resistance was applied onto the surface of a substrate on which an aluminum thin film had been formed to prepare a measurement sample. This is 60 ℃, 9
It was supported by a spacer having an outer diameter of 25 mmφ in an environment of 0% RH, and left with the aluminum thin film and the protective film forming surface facing upward.
After 200 hours, the displacement of the outermost periphery of the sample was measured with a clearance gauge.

Material of protective film used: P manufactured by ACI Japan
K-441 2) In the case of bonded disk The single plate disk manufactured by the method of 1) was bonded to its metal film sides with the following hot melt adhesive to give a measurement sample. The warp measurement method was the same as that for the single plate.

Adhesive used: PS-made by ACI Japan
16 In the following Examples and Comparative Examples, the monomer names used are abbreviated as follows.

Methyl methacrylate: MMA N-cyclohexylmaleimide: CHMI Cyclohexyl acrylate: CHA Styrene: ST Cyclohexyl methacrylate: CHMA Methyl acrylate: MA [Examples 1 to 3 and Comparative Examples 1 to 3] A copolymer having a monomer composition was injection-molded by the method described above, and an aluminum film having a thickness of 70 nm was formed on the obtained substrate. The obtained evaluation results are shown in Table 1.

[0036]

[Table 1]

[0037]

Industrial Applicability As described above in detail, the acrylic resin optical disk substrate of the present invention has little deformation due to moisture absorption and is excellent in reliability under high temperature and high humidity. Therefore, its industrial significance is extremely large. is there.

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[Procedure amendment]

[Submission date] November 24, 1994

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0036

[Correction method] Change

[Correction content]

[0036]

[Table 1]

Claims (4)

[Claims] 1. When stored in an environment of 60 ° C. and 90% RH, 0 in a region of 20 mm or more from the center of the optical information recording medium substrate and a region of 100 μm in depth from the surface of the recording medium substrate. Assuming that the dimension after 5 hours is L1 and the dimension after 5 hours is L2, (L1-L2) /
An optical information recording medium in which an inorganic thin film is laminated on an acrylic resin substrate having L1 ≤ 1.0 x 10 ^-3 . 2. The optical information recording medium according to claim 1, wherein the acrylic resin constituting the substrate has a glass transition temperature of 110 ° C. or higher. 3. The optical information recording medium according to claim 1, wherein the acrylic resin forming the substrate has a water absorption of 1.0% or less. 4. The substrate has a glass transition temperature ± of the substrate resin.
The optical information recording medium according to claim 1, wherein the optical information recording medium is annealed in a temperature environment within 30 ° C.