JPH01182323A - Optical disc - Google Patents

Abstract

PURPOSE:To obtain the title disc having small optical strain and excellent adhesion with recording film and suitable for videodisc., etc., by forming the surface of signal face substrate with a polyamide resin layer having an aromatic ring. CONSTITUTION:A polyamide resin expressed by the formula (either one of R<1> and R<2> is aromatic ring) is molded by e.g., injection molding to a disc substrate 12, preferably having 1.2mm thickness and 130mm diameter, which is preferably washed and dried under vacuum at 70-100 deg.C and then fed into a sputtering apparatus, where intermediate film 11, recording film 10 and then protecting film 13 are formed by sputtering to provide the aimed disc.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to an optical disc and a method for manufacturing the same, and more particularly, to an optical disc having a plastic substrate with small optical distortion and good adhesion to a recording film. .

[Conventional technology]

In general, the cross-sectional structure of optical discs such as video discs and digital audio discs is
There is an air sandwich method disclosed in No. 8636.

FIG. 4 shows an example of the cross-sectional structure of the optical disc.

According to the configuration of the optical disc shown in FIG. 4, the substrates 12 are arranged facing each other with a spacer 14 in between, and the intermediate 1 (
11° recording film 10 and protective film 13 (also referred to as heat absorption film)
(not shown) is formed.

Depending on the type and properties of the recording film 10, optical discs may be produced by forming holes in the recording film 10 using thermal energy such as a laser beam, changing the structure of the recording film 10, or by using light. There are many methods such as changing the reflectance of light by using magnetism. In either method, there is no difference in that reproduction or recording and reproduction is performed using thermal energy such as a laser beam.

The intermediate film 11 is made of nitrocellulose, beer mass compound, acrylic resin, SiN, Sin, 5ift.

It is composed of Zr0z, etc., and prevents heat from escaping to the outside, increasing the conversion efficiency of thermal energy such as laser beams.

Further, the spacer 14 is made of metal or plastic and a plastic composite material, and performs functions such as gap adjustment and matching with the center drive shaft.

There are two types of rewritable optical disk systems: one that uses a recording material that changes phase between a crystalline state and an amorphous state, and one that uses magneto-optical technology. It is difficult to judge the merits and demerits of both types, but it seems likely that they will appear as a product soon.

In the case of a video disc, the substrate 12 is generally a PM
It is made of acrylic resin such as MA, audio discs are generally made of PC resin (polycarbonate resin) or PMMA, and write-once discs are generally made of PMMA, PC resin, or tempered glass. However, the above-mentioned substrate materials have advantages and disadvantages, and although tempered glass is excellent in long-term reliability, it has the problem of high specific gravity and high cost. Furthermore, although plastic substrates have a low specific gravity and are inexpensive, they have low heat resistance and high moisture absorption, resulting in poor long-term reliability.

For example, an acrylic resin substrate has good birefringence, but has low heat resistance, high hygroscopicity, and poor impact strength. In recent years, acrylic resin manufacturers have been actively conducting research and prototyping, and ultra-heat-resistant acrylic resins have been developed.Although the heat resistance is improved compared to conventional acrylic resins, moisture absorption and impact strength are poor. The reality is that little has been improved.

On the other hand, with PC resin, by lowering the molecular weight and improving fluidity, although there are some problems with birefringence, moisture absorption and impact strength are good, and there are almost no problems as a playback-only or write-once disk substrate. It is said that

However, many new recording materials are being developed as the types of optical discs move from the current read-only and write-once types to rewritable types. Along with these,
The required characteristics of the plastic substrates used in these rewritable types are also becoming more stringent. One of them is the shelf life, which is thought to be caused by the adhesion between the recording film and the plastic substrate.

Currently, PC resin seems to be the most promising material for rewritable optical disk substrates. In addition, various companies, academic conferences, newspapers, etc. have announced rewritable discs, but they have not yet been commercialized. If we consider the main causes of this, we think that there are the following problems. (1) Problems with birefringence, such as a large change in birefringence due to the oblique incident angle of the PC resin.

(2) The problem of short shelf life.

Regarding (1), 1. The problem is being solved by improvements on the drive side, such as changing the optical system of the disk drive to a differential optical system.

Regarding (2), it is said that the 2P method, in which a glass substrate is used and the signal transfer layer is made of ultraviolet curing resin, etc., or discs that use light and thermosetting resin, have a considerably long lifespan. There is also information. However, when considering mass-produced products, it is necessary to mold disk substrates by injection molding, which is highly productive, but there is currently no information on molding disk substrates to produce long-life optical disks. This suggests that for rewritable optical discs, the storage life is a very important issue, which is thought to be caused by the adhesion between the recording film and the substrate. It is inferred that the shelf life of new non-grade polyolefin resins that have appeared with great fanfare in recent years is also a problem.

[Problem to be solved by the invention]

As shown in the above-mentioned prior art, PC resin is seen as promising as a blue-changeable optical disc substrate, but it has problems in terms of optical distortion and shelf life.

Furthermore, polyamide resins that can be easily injection molded have not been considered for use as plastic substrates for optical applications, particularly for optical disks, because conventional polyamide resins are generally opaque and water absorbent. This is because the substrate performs recording and reproduction using a laser beam, so a transmittance of 80% or more (measured at 827) is required for, for example, a 1.2mm substrate. The transmittance is preferably 90% or more. When the transmittance is less than 80%, the loss becomes large, so the power of the semiconductor laser used must be increased, which causes a disadvantage in terms of energy. Furthermore, although a recording film is sputtered onto the substrate, the adhesion between the substrate and the recording film affects the storage life.Furthermore, the glass transition temperature of the substrate ( If Tg (hereinafter referred to as Tg) is less than 100° C., the optical disc will be deformed and there is a problem that the C/N ratio, which is the ratio of signal to noise, cannot be measured as an optical disc.

An object of the present invention is to provide an optical disc that is suitable for mass production and easy to injection mold, is transparent and heat resistant, has high adhesion strength between the substrate and recording film, has low optical distortion, and has a long shelf life. There is a particular thing.

[Means to solve the problem]

The above object is achieved by an optical disc having a substrate, in which the material of the substrate is represented by the following general formula and at least one of R1 and R2 is an aromatic ring.

−+R1-Co-NH-R"-NH-Co+-.

〔Example〕

The optical disk substrate according to the present invention is a polyamide resin that has an aromatic ring in its chemical structure, and by adding a certain type of diamine to make it amorphous, it is transparent and heat resistant, and has great adhesion strength with the recording film. However, for slightly higher water absorption, an organic or inorganic moisture-proof coating is applied to the surface of the substrate to eliminate the influence of moisture from the outside. Before detailed explanation of the present invention based on examples, improvement of the adhesion between a recording film and a substrate according to the present invention will be explained.

In the process of sputtering a recording film onto a plastic substrate of an optical disk, as shown in FIG. 2, an intermediate film 11 of SiN, SiO, etc. is first sputtered onto a substrate 12, and then a recording film 1o is sputtered thereon.

Therefore, the adhesion between the substrate 12 and the recording film 10 becomes a problem, as does the adhesion between the substrate 12 and the intermediate film 11, such as SiN. Furthermore, as a pre-process for sputtering, the substrate 12
There is a pre-drying process to reduce moisture and other volatile components.

Below, we will consider how the adsorbed water adhering to the surfaces of the aromatic polyamide material (substrate 12A) and other relatively low water absorption materials (substrate 12B) will fly.

First, as shown in FIG. 3b, the adsorbed water on the surface of the substrate 12B consists of three molecular layers, and the adsorbed water 120 is relatively easy to fly. It is thought that it will not disappear completely until the temperature reaches 300°C. Therefore, in preliminary drying of the disk substrate 12B, adsorbed water I20 and adsorbed water lI
About half of 21 is lost, and the adsorbed water is 11123
I can't imagine that it will remain completely. Even if the intermediate film 11 is sputtered onto the substrate 12B with such a surface condition, it is estimated that the adhesion will be poor and the storage life of the disk will be shortened because of the presence of several molecular layers of adsorbed water.

On the other hand, in the case of the substrate 12A made of aromatic polyamide material, as shown in FIG. 3a, one molecular layer of adsorbed water 20
There is only one. Adsorbed water 120 can be eliminated relatively easily by pre-drying the disk substrate 12A. Although this is not very clear at present, it is presumed that such a tendency exists for materials that have a certain degree of water absorption, or in other words, materials that have good water retention.

As described above, the substrate 1 made of aromatic polyamide material
In 2A, almost no adsorbed water is lost in the pre-drying process, and the amide group (-Go-NH-) is highly active and easily reacts with active hydrogen groups and attached water contained in many substances. Furthermore, if the intermediate film 11 is SiN, the affinity between N and N increases the adhesion between the SiN and the substrate 12A, or in other words, the adhesion between the recording film 10 and the substrate 12A, increasing the storage life of the disk. I can reason.

Furthermore, thermal history is added during preliminary drying and sputtering, and if the glass transition temperature (Tg) of the substrate 12 is less than 100°C, it will deform and the C/N ratio of the optical disc cannot be measured. It is preferable that 'rg is 100° C. or higher, preferably 140° C. or higher.Among polyamide resins, the aromatic polyamide resin according to the present invention is a material that satisfies this requirement.

The present invention will be explained in more detail below based on Examples.

<Example 1> An aromatic polyamide resin (manufactured by Dynamite Nobel) having the chemical structure shown in Example 1 in Table 1 was used as a plastic material for the disk substrate. Using this resin, a signal grooved disk substrate having a thickness of 1.2 mm and a diameter of 130 mm was produced using an injection molding machine.

In order to measure the heat resistance of the obtained disk substrate, the glass transition temperature (Tg) was determined using a TMA-1500 type thermophysical tester manufactured by Shinku Riko Co., Ltd., and is shown in Table 1. In addition, a tensile test piece was cut from this disk substrate, a load was applied to the test piece in stages, and the retardation (birefringence) was measured each time using an ellipsometer. The photoelastic constants were determined by calculation and are shown in Table 1.

Next, the disk substrate is thoroughly cleaned by sequentially passing through various cleaning tanks such as a surfactant aqueous solution cleaning tank with an ultrasonic oscillator and an ultrapure water cleaning tank with an ultrasonic oscillator.
Temperature 70~100℃, degree of vacuum 10''''2~10-8mH
Dry thoroughly in a vacuum dryer. Thereafter, an intermediate film 11 (SiN), a recording film 10 (TbFeCo), and a protective film 13 (SiN) as shown in FIG. 2 are successively formed in a sputtering apparatus. In addition, zero warpage, which is measured using a three-dimensional coordinate measuring device, is the initial value immediately after injection molding, and the amount of change in warpage after vacuum drying and sputtering of the recording film 10 is expressed in μm. It is shown in Table 1.

Next, using an epoxy adhesive, the plastic substrate with a recording film formed above was bonded to each other via a spacer 14 to produce an optical disc. Approximately 1,000 to 5,000 people vapor-deposited an organic moisture-proof layer such as parylene resin on the surface of this optical disk, and further, to protect the surface, SiN was applied by sputtering to obtain a finished product.

Further, an adhesion test of the recording film was conducted using a small test piece on which a recording film was sputtered in the same manner. That is, 30μm
A 90@beer test was conducted by bonding a copper plate and a plastic substrate using an epoxy adhesive. Tensile speed 20
Table 1 shows the load per 1 mm width in m/win as the adhesion strength.

Put the completed optical disc into the disc drive C7
The N ratio (a type of SN ratio that is the ratio of signal output to noise output) was measured, and the results are shown in Table 1.

In addition, as a simple method for evaluating the lifespan of optical discs, 60°C/9
The plastic substrate with a recording film prepared above was stored in an environment of 5% RH for a certain period of time, then taken out, the reflectance of the recording film was measured at room temperature, and the disc life was determined when the reflectance of light became 70% or less. did.

These results are shown in FIG.

<Examples 2 to 5> Disc substrates were molded using aromatic polyamide resins having the chemical structural formulas shown in Examples 2 to 5 in Table 1 as the substrate material, and the two sheets were bonded together to form an optical disc. Created,
For further surface protection.

The same procedure as in Example 1 was performed except that SiN or SiOx was sputtered. The results are shown in Table 1 and
Shown in the figure.

Comparative Examples 1 to 4> The same procedure as Examples 2 to 5 was carried out except that the chemical structural formulas shown in Comparative Examples 1 to 3 in Table 1 and the heat-resistant acrylic resin of Comparative Example 4 were used as the substrate materials. Ta.

The results are shown in Table 1 and FIG. Comparative Examples 1 and 2 are polyamide resins, but the glass transition temperature (Tg
) is low, and Comparative Examples 3 and 4 are based on conventional materials, substrate structures, and I[methods] used in boat fishing.

According to Table 1 above, the C/N ratios of the optical discs manufactured using the disc substrates molded using the substrate materials of Examples 1 to 5 were very good values of 50 to 57 dB. this is,
Because the photoelastic constants of the resins of Examples 1 to 5 were small, stress relaxation occurred during the flow process of the resin! It is presumed that the glue tarpsion was reduced and the C/N ratio was improved. Furthermore, the changes in warpage of the substrates after thermal history were both as small as 100 μm, but this can be presumed to be due to the high heat resistance of the aromatic polyamide resin substrates at Tg of 102 to 155° C. Furthermore, looking at the □ storage life curve in Figure 1, in the case of Examples 1 to 4, the temperature was 60°C, 795% RH.
Under such an environment, the lifespan is extremely long at 103 hours, and this is due to the good adhesion between the substrate and the recording film.

On the contrary, the lifetimes of Comparative Examples 1 and 2 are as long as Examples 1 to 4 due to the good adhesion between the substrate and the recording film, but both have lower Tg of the substrate than the Examples. Therefore, the substrate was deformed due to thermal history, and therefore tracking was not performed and the C/N ratio could not be measured. Furthermore, Comparative Examples 3 and 4 had poor adhesion between the substrate and the recording film, resulting in short lifespans.

However, in both cases, the 'rg of the substrate is high at 140°C and 147°C, so there is little deformation due to the thermal history of the board, but in Comparative Example 3, the photoelastic constant is large, so the turbulence of the board becomes large and C/ The N ratio has become smaller. Comparative example 4 is
Since the photoelastic constant was small, the substrate adhesive tarpsion was small, and a C/N ratio close to that of Examples 1 to 4 was obtained.

From Table 1 and FIG. 1 showing the characteristics of the above examples, it is clear that the substrate using aromatic polyamide resin has small optical distortion and good adhesion of the recording film.
This has the effect of making it possible to obtain an optical disc with a long shelf life.

〔Effect of the invention〕

As explained above, in the optical disc using the plastic substrate according to the present invention, the optical distortion is small, so there is less risk of errors occurring during recording and reproduction, and the adhesion between the substrate and the recording film is improved, so the disc It has an excellent effect of extending the storage life of the product.

[Brief explanation of the drawing]

Fig. 1 is a life curve of a small optical disk substrate with a recording film according to the present invention, Fig. 2 is a cross-sectional structural diagram of the optical disk, Figs. 3a and 3b are diagrams showing adsorbed water on the substrate surface, and Fig. 4 is an air FIG. 2 is a cross-sectional structural diagram of a sandwich type optical disc.
. 1... Data of Example 1, 2... Data of Example 2, 3... Data of Example 3, 4... Data of Example 4. 5... Data of Example 5, 6... Data of Comparative Example 1, 7... Data of Comparative Example 2, 8... Data of Comparative Example 3, 9... Data of Comparative Example 4, 10...Recording film, 1
DESCRIPTION OF SYMBOLS 1... Intermediate film, 12... Substrate, 13... Protective film,
14...Spacer. No. 1 Usho 8 Makima (It) Early 2nd day 3a [I 3rd Toro 4th mouth / 11th midway

Claims (1)

[Claims] 1. An optical disc having a substrate, characterized in that the material of the substrate is represented by the following general formula, and at least one of R^1 and R^2 is constituted by an aromatic ring. optical disc. 2. The optical disc according to claim 1, wherein the surface of the substrate is covered with an organic or inorganic moisture-proof film. 3. The optical disc according to claim 1, wherein the substrate and the surface of the signal plane substrate are made of different resins, and the surface of the signal plane substrate is made of a polyamide resin layer. 4. The optical disk according to claim 1 or 2, wherein the substrate has a glass transition temperature of 140° C. or higher. 5. The optical disc according to claim 1 or 2, wherein the composition of the intermediate film disposed between the substrate and the recording film for recording information is SiN.