JPH05114165A - Optical disk - Google Patents

Abstract

PURPOSE:To lessen the influence of dust sticking by specifying the surface roughness of a protective film to a specific value or below and the contact angle of the oil drop falling onto the protective film with the protective film to a specific value or below. CONSTITUTION:The surface roughness of the film 4 of the optical disk provided with the protective film 4 on the laser beam incident surface side of a substrate 1 provided with an optical recording film 2 is specified to <=0.003mum and the contact angle of the oil drop falling onto the film 4 with the film 4 to <=20 deg.. The reflection intensity of the laser beam with which the optical disk surface is irradiated does not degrade even if the optical disk is used over a long period of time in an atmosphere of inorg. dust and org. dust, by which the influence to be exerted on the recording and reproducing of information is lessened.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disc, and more particularly to an optical disc having a protective film provided on a laser light incident surface side of a resin substrate for forming an optical disc.

In recent years, optical discs have been spotlighted as information storage media for storing large-capacity document data and image information. Since an optical disc records and reproduces information with a laser beam focused to about 1 μm, it can store a large amount of information.

A transparent resin substrate is often used as a substrate for an optical disk because it is inexpensive and lightweight, and therefore scratches and dust (inorganic and organic dust) are likely to adhere to the substrate. There is.

Therefore, in order to prevent the occurrence of the scratches, a transparent organic compound protective film or a transparent inorganic compound protective film is formed on the resin substrate on the incident surface side of the laser beam.

[0005]

2. Description of the Related Art In a conventional optical disk, the surface of the laser light incident surface has a higher hardness than that of a resin substrate in order to prevent scratches, and the surface of the resin substrate has a surface hardness to prevent dust from adhering. A protective film with low resistance was used.

By the way, the above-mentioned conventional protective film has a great effect on the prevention of scratches, but it is not enough to adhere to the dust of inorganic substances and the dust of organic substances such as cigarette smoke. There is no. Therefore, the optical disc is regularly wiped with a cloth or the like for cleaning, but if organic dust such as oil mist is attached, the optical disc cannot be wiped off and cannot be cleaned.

[0007]

Therefore, in the conventional optical disc, the adverse effect of the attached dust causes an error in recording or reproducing information, and it is difficult to record or reproduce information with high accuracy.

An object of the present invention is to solve the above-mentioned problems and to provide an optical disc in which the recording and reproducing of information is hardly affected even if dust is attached to some extent.

[0009]

The optical disk of the present invention comprises:
In an optical disc having a protective film on the laser light incident surface side of a resin substrate provided with a recording film, the surface roughness of the protective film is
It is characterized in that it is 0.003 μm or less, and the contact angle of the oil droplets dropped on the protective film to the protective film is 20 degrees or less.

Further, the protective film is characterized in that it is an organic compound film formed by spin coating or an inorganic compound film formed by vacuum film forming. Further, the protective film has a surface hardness higher than that of the resin substrate, or
And surface resistance is small.

[0011]

According to the first aspect of the present invention, the protective film having a small surface roughness is formed on the laser light incident surface side of the resin substrate.

Since the surface roughness is small, the microscopic unevenness of the protective film is small, and the chances of inorganic dust adhering to the uneven surface are small. Therefore, the surface roughness is preferably small. As a result of the experiment, if the surface roughness of the protective film is 0.003 μm or less,
It was confirmed that even when used in an atmosphere of inorganic dust for a long time, the reflection intensity of the laser beam applied to the optical disc surface did not decrease, and as a result, the amount of dust adhesion decreased.

Further, as described in claim 1, oil droplets are dropped on the protective film provided on the laser light incident surface side of the resin substrate, and the contact angle is measured. If the contact angle is 20 degrees or less, Even when used for a long time in an atmosphere of organic dust such as cigarette smoke,
The reflection intensity of the laser beam applied to the optical disk surface does not decrease, which means that the smaller the contact angle, the easier the dust spreads,
Since the scattering of light is reduced, the reflection intensity of the laser light applied to the optical disk surface does not decrease.

As shown in FIGS. 4 (a) and 4 (b), this contact angle θ is the same as when the oil droplet 11 is dropped on the protective film 4 formed on the laser beam incident side of the resin substrate. It is the angle at the position where the free surface of the droplet 11 contacts the protective film 4. The larger the contact angle θ, the greater the oil repellency, and the smaller the contact angle, the smaller the oil repellency.

When the oil repellency is small, that is, when the contact angle θ is small, when organic dust such as oil mist adheres to the protective film 4, the organic dust spreads on the order of several mm. On the other hand, when the protective film 4 is irradiated with a laser beam for recording and reproduction, the diameter of this light is on the order of several μm, so when the spread organic dust is irradiated with a laser beam,
The scattering of laser light is reduced, and the occurrence of errors during recording and reproduction is reduced.

Therefore, from the viewpoint of preventing the scattering of the laser light, it is preferable that the contact angle θ is smaller. Further, this protective film preferably has a small surface resistance in order to prevent electrostatic charge and reduce adhesion of dust, and has a hardness higher than that of the resin substrate in order to prevent scratches caused by dust. desirable.

[0017]

Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a sectional view of an optical disk of the present invention. As shown in the figure, in the head guide groove (not shown) of the transparent resin substrate 1 such as polycarbonate having a diameter of 5 inches, a dielectric film of terbium-silicon dioxide (Tb-SiO ₂ ) film, terbium- The optical recording film 2 is formed by laminating a magnetic film such as iron-cobalt (Tb-Fe-Co), a dielectric film of terbium-silicon dioxide (Tb-SiO ₂ ) film and a reflective film such as aluminum (Al). This substrate 1 after film formation by the method
And the optical recording film 2 are made to face each other and bonded using an adhesive 3 (trade name: Hot Melt XW-13, manufactured by Toagosei Kagaku Co., Ltd.).

Then, an organic compound protective film 4 made of an acrylic resin is applied to the surface of the substrate 1 opposite to the surface on which the optical recording film 2 is formed, by a spin coating method. Then, a hub 5 for mounting the disc in the disc drive is attached to the center position of the optical disc to form the optical disc.

Then, the transparent inorganic filler of SiO ₂ added to the acrylic resin of the protective film is added at a ratio of 1% by weight to the acrylic resin. When the particle size is changed and added, the larger the particle size of the filler,
Since the surface roughness becomes large, the diameter of the filler to be added was changed to form the protective film with the changed surface roughness.

Then, while rotating the optical disk having the protective film thus formed, the fine powder of soil (particle size: 1 to 5 μm) in the Kanto loam layer is filled as inorganic dust to have a capacity of 0.25 m. Install in the desiccator of ³ . Then, the optical disc is left in a rotated state for 0.5 hour, and then the optical disc is taken out from the desiccator.

Then, a position P on the inner circumference at a position 35 mm from the center O of the optical disk in the radial direction, a central position Q at a position 45 mm from the center O of the optical disk in the radial direction, and the center of the optical disk Laser light was irradiated to three points at a position R on the outer periphery at a position 55 mm in the radial direction from O, and the light amount of the reflected light was measured to measure the reflectance. The larger the reflectance, the smaller the amount of dust attached, and the smaller the reflectance, the smaller the amount of dust attached.

In this optical disc, the reflectance is slightly different between the inner circumference and the outer circumference, and the amount of decrease in the reflectance after a predetermined time elapses from the initial value of the reflectance when the optical disc is not rotated. The larger the value, the larger the amount of dust attached, and therefore the fluctuation in the reflectance was measured at a predetermined position in the radial direction of the optical disc.

FIG. 2 shows a relationship diagram between the amount of change in reflectance and the surface roughness of the protective film when the protective film having the surface roughness thus changed is formed. The vertical axis of the figure indicates a predetermined position of the optical disc, that is, P, before the optical disc is installed in the desiccator filled with the inorganic dust of the Kanto loam layer.
Laser light is applied to the Q and R positions, the reflection intensity of the reflected light reflected from the optical disk surface is measured, and the reflectance is calculated.
Assume 100%. (The actual reflectance is about 20%.)
Next, this optical disk is placed in the desiccator described above, and the reflectance of the optical disk after a predetermined time has elapsed is measured, and it is assumed that the reflectance becomes R%.

Then, the change amount of the reflectance is (R / initial value × 10
It is expressed as 0)%, so this value is plotted on the vertical axis.
The horizontal axis represents the radial position of the optical disc. As shown by curves b and c in the figure, the surface roughness is 0.005 μm, 0.01 μm
As shown in, the amount of change in reflectance becomes large when the thickness is increased from 0.003 μm. However, as shown by the curve a, the optical disc on which the protective film having the surface roughness of 0.003 μm is formed shows almost no change in the reflectance. From this, the surface roughness is 0.
003 μm or less is desirable.

Silicon oil is further added to the acrylic resin of the protective film used in the above embodiment, and the addition amount of this silicone oil is changed to change the contact angle of the oil droplet 11 shown in FIG. 4 with respect to the protective film 4. The oil repellency of the protective film is changed by changing θ. Then, such a protective film having a different contact angle is attached to the optical disc, and the optical disc is placed in a desiccator filled with cigarette smoke for 2 hours while rotating the disc, and then the optical disc is taken out. Then, the reflectance was measured in the same manner as described above, and the result is shown in FIG.

As shown in FIG. 4, this contact angle θ is obtained by dropping an oil drop 11 of vacuum pump oil manufactured by Nippon Vacuum Technology Co., Ltd. under the trade name ULVOIL R-7 onto the protective film 4. θ was measured experimentally.

The vertical axis of the figure shows the amount of change in the reflectance described above, and the horizontal axis shows the position of the optical disk in the radial direction. As shown by the curve a in the figure, when the contact angle θ is 20 degrees, there is almost no change in reflectance, and as shown by the curves b and c in the figure, the contact angle θ is 25 degrees and 40 degrees. The lower the reflectance, the more.

This means that if a protective film having a contact angle of 20 degrees or less against organic dust such as cigarette smoke is used, it is unlikely to be affected by the organic dust even if it is used for a long time. It can be seen that an optical disc that is not easily affected by the recording and reproduction of information can be obtained even when used for a long time without performing a complicated cleaning work such as a wiping operation.

In this embodiment, an organic compound film of acrylic resin is used as the protective film, but in addition, an inorganic compound film such as ITO (indium tin oxide) is used as the protective film in a vacuum film forming method such as a sputtering method. You may form and use it by the method.

It is even more preferable that the protective film of the present invention described above has a surface hardness higher than that of the resin substrate, a surface resistance lower than that of the resin substrate, or has both properties.

[0031]

As described above, according to the optical disk of the present invention, even if dust adheres to the surface of the optical disk after being used for a long period of time, it does not affect the reflected light of the laser beam, so that information recording is possible. In addition, there is an effect that the reproduction is not affected, the number of wiping operations is small, and the optical disc is easy to handle and has high reliability.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of an optical disc of the present invention.

FIG. 2 is a diagram showing the relationship between the surface roughness of a protective film and the amount of change in reflectance.

FIG. 3 is a relationship diagram between a contact angle of a protective film and a change amount of reflectance.

FIG. 4 is an explanatory diagram of a contact angle.

[Explanation of symbols]

 1 substrate 2 optical recording film 3 adhesive 4 protective film 5 hub 11 oil drop

Claims (2)

[Claims] 1. An optical disc having a protective film (4) on the laser light incident surface side of a substrate (1) provided with an optical recording film (2), wherein the surface roughness of the protective film (4) is An optical disk having a contact angle of not more than 0.003 μm and an oil droplet dropped on the protective film (4) with respect to the protective film (4) is 20 degrees or less. 2. An optical disk, wherein the protective film (4) according to claim 1 is an organic compound film formed by spin coating or an inorganic compound film formed by vacuum film forming.