JPS62289939A - Optical recording medium - Google Patents

Abstract

PURPOSE:To improve the solvent resistance of a surface while the tracking performance of a pregrooved plate is maintained by forming a transparent film consisting of a cyclohexane and optical recording film consisting of an org. die successively on a transparent plastic having grooves for tracking servocontrol. CONSTITUTION:The transparent film 2 consisting of the cyclohexane and the optical recording film 3 consisting of the org. dye are formed on the transparent plastic substrate 1 provided with the grooves 4 for tracking servocontrol. Transparent resins such as polycarbonate and methacrylic resins are usable as the substrate 1. Of cyanine and squarium resins, a dye having >=20% spectral absorptivity and >=8% spectral reflectivity at 830nm is more preferable as the resins for recording by a semiconductor laser.

Description

DETAILED DESCRIPTION OF THE INVENTION 3. DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an optical recording medium that can be written by a laser.

Conventional Technology Optical disks are considered to be the mainstay of future external memory and have been actively researched in recent years. Up until now, many recording materials have been made by vapor-depositing thin films of inorganic or metal materials.

These recording materials are manufactured by vapor deposition under vacuum, and unlike simple aluminum vapor deposition, the speed of vapor deposition and contamination of the vapor deposition equipment must be controlled very carefully. Therefore, there was a limit to reducing manufacturing costs through mass production. In addition, when plastic is used as a transparent substrate, it has been observed that the substrate is significantly deformed due to the presence of a layer of metal etc. due to the unavoidable thermal and humidity expansion of plastic, which significantly affects the reliability of recording and reproduction. In many cases, this resulted in a significant decrease. Recently, many studies have been published on the use of organic dyes as recording materials. (Reference: Organic Synthetic Chemistry, Vol. 43, No. 4 (1985), P334-343) The advantage of using organic dyes is that it is possible to form a recording film by wet coating, and compared to forming thin films of inorganic materials or metals, manufacturing equipment costs are low. , can be suppressed to 1/10 or less.

By the way, dyes are generally soluble only in organic solvents, and therefore it is extremely difficult to coat them onto plastic substrates, and there have been many reports of cases in which they were directly coated onto glass plates. (Reference: Japanese Unexamined Patent Publication No. 58-219090) The problem to be solved by the present invention is that the plastic substrate is easily attacked by organic solvents, so it has often been impossible to directly apply a dye thereon. In particular, in the case of a substrate on which fine grooves are formed for tracking servo (hereinafter referred to as a pregroup plate), the grooves easily disappear even if the substrate comes into contact with an organic solvent for a very short time. The present invention uses a transparent resin substrate such as methacrylic resin or polycarbonate as a pregroup plate, and improves the tracking performance of the pregroup plate in order to realize an optical recording medium having an optical recording layer made of a highly sensitive organic dye on the substrate. The objective is to improve the solvent resistance of the surface while maintaining the properties.

Means for Solving the Problems In order to produce optical discs at low cost, it is necessary to introduce an injection molding method that allows mass production of discs with grooves. However, as transparent plastics that can be molded and have good optical performance, only materials with poor solvent resistance such as polycarbonate and methacrylic resin are commercially available. When trying to apply a dye directly to the surface of a substrate molded with grooves, at most only alcohol can be used as a solvent, so the range of dye selection is extremely limited, and it is often difficult to find an appropriate dye. If a ketone, halogen, or ester solvent other than alcohol is used, the formed grooves will instantly disappear without a trace when they come into contact with the solvent.

Therefore, improving the solvent resistance of the surface of these general-purpose transparent plastics and making injection-molded transparent substrates usable as optical disks is an important factor in reducing costs. In the present invention, a siloxane-based thin film 2 made of an alcohol-based solution is applied to the surface of the molded substrate 1 so that a general-purpose resin can be used as the pre-group plate. The thickness of the siloxane-based thin film is required to be 5 nm or more, and desirably does not exceed 1/2 of the tracking groove depth. If it is less than 5 nm, the effect of improving solvent resistance will be poor, and if it exceeds 1/2 of the groove depth, the tracking servo will easily fail. However, this does not apply if the grooves on the plastic are made deep in advance in consideration of the shallowness of the grooves. After uniformly forming a polysiloxane film with an appropriate thickness in this manner, the siloxane film is cured. The curing method involves heating at 40° C. to 60° C. for several hours, but it may be left for one day after application. After the crosslinked polysiloxane film is formed on the pregroup plate, an organic dye is dissolved in a suitable solvent and formed on the siloxane film 2 by spin coating to form a dye layer 3.

The dye used here may be any dye as long as it absorbs laser light, generates heat, and can record electrical signals as a row of perforated pits. Cyanine dyes are dyes that can be recorded by semiconductor lasers.

Among squasolium dyes, cholines, organometallic complex compounds, and the like, any dye that has a spectral absorption rate of 20% or more at 830 nm and a spectral reflectance of 8% or more can be used. The suitable thickness of the dye is within 1/4 to 1/2 of the wavelength of the reproduction laser beam, and if it deviates from this range, the C/N ratio of the reproduction signal will deteriorate.

Function As described above, the present invention allows the use of general-purpose transparent resins such as polycarbonate and methacrylic resin as the pregroup plate, and the ability to form the dye as the recording layer by a coating method. Since the thermal conductivity is lower than when a film is used as a recording film, the distance between pits can be narrowed, and an optical recording medium that is inexpensive and easy to handle can be provided.

Example An embodiment of the present invention will be described below with reference to the drawings.

(Example 1) The present invention will be explained using a cross-sectional view of an optical recording medium of the present invention. That is, on a polycarbonate resin molded substrate 1 with a thickness of 1.2 mm and a diameter of 120 nm, a groove for tracking servo with a depth of 0.07 μm and a width of 0.7 μm was formed in a spiral shape with a 1.6 μm pinch on the surface. A siloxane film was applied to each thickness shown in Table 1 on the surface having the grooves 4 by a spin coating method. The solution used for coating was a mixed solution of commercially available terminal acetylated polysiloxane containing isopropanol and n-butanol. After coating, evaporate the solvent and heat at 60°C.
A crosslinked siloxane film 2 was formed by curing for a period of time. A trichloroethane solution of trimethine compound (1) shown by the following formula was applied on top of this to form an optical recording layer 3 having a thickness of 75 nm.

The optical disc medium manufactured in this way has an oscillation wavelength of 830n.
A signal was recorded on the recording film while applying focus servo and tracking servo using a semiconductor laser of m.

Recording conditions are as follows; Recording power: 5 m
w ・Line continuous 4 m/s・Spatial frequency
IMHz・Duty-50150 After recording, C/N and C/N when reproduced using a semiconductor laser with 0.5 mW output and reproduced with a bandwidth of 30 kHz,
Table 1 shows the results of measuring the bit error rate.

(Table 1) (Example 2) A transparent substrate having the same shape as in Example 1 was molded using methacrylic resin, and a terminal acetylated polysiloxane coating was formed thereon to a thickness of 20 nm in the same manner as in Example 1. It was heat cured at 50°C for 3 hours. On top of this, the organic dye of Example 1 (
A solution of 1) dissolved in methyl ethyl ketone was applied to form an 80 nm layer of the dye. The thin film of dye thus formed was smooth and had almost no pinholes. Under the same recording and playback conditions as Example 1, C/N 56dB, BER 4×
I got 105.

(Example 3) A polycarbonate resin molded product having the same shape as in Example 1 is used as a transparent substrate. Next, fine colloidal particles of a partial hydrolyzate obtained by hydrolyzing a portion of silicon tetrachloride with a small amount of water are added to a mixed solvent of n-butanol and isopropanol at 0.00%.
A 4% by weight dispersed solution was prepared and spin-coated onto the transparent substrate to form a 20 nm siloxane film.
It was dried and cured at 0° C. for 4 hours. On top of this, apply a methylene chloride solution of trimethine dye (II) below and dye it at 90 nm.
The film thickness was set to . The coated surface formed was smooth and had almost no pinholes. C/ under the same recording and playback conditions as in Example 1.
N54dB and BER5xlOJi were obtained.

...... (It) Effects of the Invention As mentioned above, the present invention originally involves forming a thin film of siloxane on a plastic transparent substrate with poor solvent resistance, thereby improving fine tracking formed on the substrate. Since various dyes can be applied using various solvents without damaging the grooves, the most suitable dye can be selected.

Additionally, a spin coater is all that is required to form the siloxane film, and compared to forming an inorganic transparent film such as S i 02 by sputtering or vapor deposition, equipment costs and process time can be significantly reduced.

[Brief explanation of the drawing]

The figure is a sectional view of the optical disc of the present invention. ■... Transparent substrate, 2... Siloxane film, 3... Optical recording film, 4... Groove.

Claims (2)

[Claims] (1) An optical recording medium comprising a siloxane-based transparent film as a first layer on a plastic transparent substrate, and an organic dye-based optical recording film formed thereon as a second layer. (2) The optical recording medium according to claim (1), which uses a plastic transparent substrate on which grooves for tracking servo are formed in advance.