JPH0421939A - Optical disk - Google Patents

Abstract

PURPOSE:To prevent the warpage at the time of a change in temp. and humid ity, the sticking of dust and the generation of flaws by forming an optical recording layer and coating the optical recording layer with a fluororesin film, particularly a trifluorochloroethylene copolymer film, then forming an SiO2 layer. CONSTITUTION:An SiNx enhancement layer 20, a TbFeCo recording layer 30 and an SiNx protective layer 40 are successively laminated on a polycarbonate substrate 10 by a sputtering method. The layers are then coated with the tetrafluoroethylene/hexafluoropropylene copolymer resin which is the fluororesin to form the fluororesin layer 50. The SiO2 layer 60 is thereafter formed over the entire surface at 1500Angstrom by an LDP method. The trifluorochloroethylene copolymer may be used particularly for the above-mentioned fluororesin layer 50. The warpage of the substrate at the time of the abrupt change in the temp. and humidity is prevented in this way and the hardness and antistatic function of the substrate surface are enhanced so that the substrate surface is resistant to dust pick-up and flawing. The reliability is thus enhanced.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to an optical disc for recording and reproducing information using light.

<Conventional technology> Transparent plastic substrates are used as substrate materials for optical disks.
Reproduction is easy and low cost, especially for polycarbonate 1 substrates.

However, when a plastic substrate having a relatively high moisture permeability coefficient, such as a polycarbonate substrate, is used, the substrate warps due to water being supplied only to the side on which the recording surface is not formed. Especially when used in environments with significant changes in temperature and humidity.
A large warpage occurs, and as a result, the focus tracking servo of the actuator cannot follow it stably, causing malfunctions and errors, which poses a serious problem in practice.

As a method for preventing warpage, it is known to form a moisture-proof film on the surface of the substrate opposite to the surface on which the recording film is formed. FIG. 3 is a cross-sectional view of an optical disc showing a conventional method disclosed in, for example, Japanese Patent Application Laid-Open No. 1-292639.
In the figure, 1 is a plastic substrate, 3 is a recording film, 7 is an ultraviolet curing resin layer, and 8 is a moisture-proof film.

The moisture-proof film may be either organic or inorganic, and if it is an organic film, coating or the like is used, and if it is an inorganic film, a sputtering method, a vacuum evaporation method, a CVD method, etc. are used.

However, when a moisture-proof film is formed on a portion of the disk, although it is possible to prevent warping when the temperature and humidity change with a gentle gradient, it is not possible to prevent warping that occurs when the temperature and humidity change with a steep gradient. This is because moisture is rapidly absorbed from the parts of the substrate where the moisture-proof film is not formed, and the moisture distribution inside the substrate becomes temporarily uneven, causing warping due to local expansion.

<Problems to be Solved by the Invention> Therefore, it is necessary to form a light-transmitting moisture-proof film over the entire surface of the disk so that the material of the substrate is not exposed to the atmosphere. However, as shown in the above-mentioned Japanese Patent Application Publication No. 1-292639, it is known that it is very difficult to uniformly form a film over the entire surface. In other words, in conventional spin codes, sputtering methods, vapor deposition methods, etc., the use of masks during the manufacturing process creates film boundaries and microscopic holes (voids, pinholes) in the film. There have been problems in that the moisture-proofing effect cannot be improved due to boundaries and holes, and the protective film may peel off or deteriorate.

Furthermore, in the case of an optical disc, since the laser light is incident from the substrate side, the light also passes through the moisture-proof film formed on the substrate. Therefore, it is necessary to form a moisture-proof film without impairing the necessary characteristics of the optical disk, such as the enhancement effect of the magneto-optical disk and the reduction of incident light intensity and noise. Surface roughness and other factors must be controlled, and performing this with conventional film forming methods requires advanced technology and increases manufacturing costs.

In addition, dust accumulates on the optical disc, and scratches occur when wiping it. To prevent this, it is known to form a Bartcoat 1 film or an antistatic film on the surface of the substrate, but adding an antistatic function to the conventional hard coat material Its function as a material is halved. For example, in the case of polycarbonate substrates, what used to be 3H for the substrate and 7H for Bartco-1 later became 4H for the film with antistatic function, which has both hard coat function and antistatic function at the same time. The problem was that there was no membrane.

In order to solve these problems, a method has been proposed in which silicon dioxide (S i 02 ) M is formed on a substrate by a liquid phase thin film forming method, as shown in Japanese Patent Application Laid-Open No. 63-112632. The film formed using this method has not only good moisture resistance but also high surface hardness and antistatic function as shown in FIG. 4.

Furthermore, a method has been proposed in which a silicon dioxide (S10□) film is formed on the entire surface of an optical recording medium by a liquid phase thin film forming method, as shown in Japanese Patent Application Laid-Open No. 2-18729. Fifth
In the figure, 1 is a plastic substrate, 2 is a dielectric film, and 3 is a plastic substrate.
is a recording film, 4 is a dielectric protective film, 5 is a U/V effect resin, 6
(This is a SiO2 layer. When forming a Si2 layer using the LPD method, a hydrofluoric acid solution is used as the solution, so the recording film, which is a metal, is eroded. Therefore, an optical recording film is formed on the substrate. After forming a film to protect the recording film from a hydrofluoric acid solution which is a processing solution of the LPD method, it is necessary to form an SiO□ layer over the entire surface by LPD processing.

Conventionally, U/v hardening resin Hu has been used because films formed by sputtering or vapor deposition have poor film density, generate countless pinholes, and erode the recording film over almost the entire surface. However, the liquid phase thin film formation method (=Li
Quid Phase Deposition (
When forming a Sin layer using the LPD method (abbreviated as LPDl method), since a hydrofluoric acid solution is used as a solution, the recording film, which is a metal, is eroded, making it difficult to form a recording film and then perform the mustard PD treatment. Can not. Conventionally, a method was used in which the substrate was subjected to LPD treatment to form a 5iOz layer on the entire surface of the substrate, and then a recording film was formed.However, with this method, grooves and pre-pits were formed on the substrate. If there is, a layer of Sin will be formed in that part as well, resulting in a change in their shape. Although it is possible to make a slight correction by adjusting the settings of the standber that molds the substrate, it is difficult to make a complete correction because it requires sophisticated technology.Therefore, it is difficult to apply the liquid phase thin film formation method described in Part B to optical discs. There was a problem that.

Therefore, an optical recording film is formed on the substrate, and the recording film is used as an LPD.
It is conceivable that after forming a film for protection from a hydrofluoric acid solution, which is a processing solution of the method, an SiO□ layer is formed on the entire surface by LPD processing.

However, in films formed by sputtering or vapor deposition, the density of the film is poor and countless pinholes are generated, resulting in the recording film being eroded over almost the entire surface.

In addition, many of the commonly known coating resins are
The adhesion with the recording film may be poor and the liquid may penetrate from the interface, or there may be pinholes in the film and the liquid may reach the recording film.
The recording film may be eroded, or the film may be deformed due to the heat applied to the film when the resin is cured.
Birefringence increased due to distortion, and cracks appeared in the resin layer and recording film during the LPD process.

The present invention has been made in order to solve the above-mentioned problems, and aims to provide an optical disc that does not warp even when there is a sudden change in temperature and humidity, and is also resistant to dust and scratches. ing.

Means for Solving the Problems> The optical disc of the present invention includes forming an optical recording film, covering the optical recording film with a fluororesin film, particularly a chlorine trifluoride ethylene copolymer film, and then forming a 5102 layer. It is characterized by

By forming the 8102 layer after coating the optical recording layer with fluororesin, it not only prevents the plastic substrate from warping due to rapid changes in temperature and humidity (it also provides high hardness and hardness to the substrate surface). By using trifluorinated chlorine ethylene copolymer for the fluorine-based resin that coats the optical recording layer, we can obtain an optical disc that has excellent antistatic properties and is resistant to dust and scratches, and is resistant to changes in environmental temperature and humidity cycles. A strong and highly reliable optical disc can be obtained.

In addition, since the 5i02 layer can be cured at a very thin thickness of 1000 to 200 oA, it does not affect the laser light incident from the substrate side, so strict control of the refractive index and thickness is required. The number of processes and costs can be reduced without having to do this.

<Example> An example of the present invention will be described below. In FIG. 1, 10 is a polycarbonate substrate, 20 is a 5INx processing layer, 30 is a TbFeCo recording layer, and 40 is a SiNx
The protective layer 50 is a fluororesin and 60 is a 5IO2 layer. After sequentially laminating 20, 30, and 40 on a polycarbonate substrate by sputtering, a fluorine-based resin, tetrafluoroethylene hexafluoropropylene copolymer resin (Daikin Industries, Ltd.)
Coated with Neoflon FEP (manufactured by Co., Ltd.), and then
In the LPD method shown in Special Kai No. 63-112632,
A SiO□ layer of 1.500 A was formed on the entire surface. Various test results for this example are shown in the Example 1 section of Table 1.

When the environment was changed from 60℃ 50%RH to 60℃ 90%RH in 30 minutes, the warping that occurred was 0.5m when tilted.
It was a very small value of rad.

In addition, a test was conducted for 500 hours at 80°C and 90% RH, but there was no change in the C7N bit error rate, the surface hardness was 7H before and after the test, and the charging property was almost unchanged before and after the test, indicating good reliability. I got sex.

Next, other embodiments will be described. In Figure 1,
An optical disc was prepared under exactly the same conditions as in the previous example, except that a trifluorinated chlorine ethylene copolymer (Lumifucin, manufactured by Asahi Glass Co., Ltd.) was used as the fluororesin No. 50. The results of various tests for this example are shown in the Example 2 section of Table 1.

Tilt change when changing from 60℃50%RH to 90%RH is 0
．． There was no change in each characteristic in the 500-hour input test at 3 mrad, 80° C., 90% RH.

Furthermore, Z/AD (
As a result of testing (temperature and humidity), there was no change in each characteristic, and high reliability was obtained.

Other embodiments will be described. In FIG. 2, 11 is a polycarbonate substrate, 21 is a SiNx enhancement layer,
31 is a TbFeCo recording layer, 41 is a S i N x protective layer, and 51 is a trifluorinated chlorine ethylene copolymer, and Lumiflon manufactured by Asahi Glass Co., Ltd. was used. 11 to 21.31.4
1 was sequentially laminated by sputtering method, and then JP-A-63-1
In the method shown in No. 12632, a SiO□ layer 61 for polycarbonate having a thickness of 1500 mm was formed on the exposed portion of the polycarbonate substrate by a liquid phase thin film forming method. The results of various tests for this example are shown in the Example 3 section of Table 1.

As a result, the tilt change when changing from 60°C 50%RH to 90%RH is 0.7mrad, and the C/N and bit in the 80°C 90%RH 500-hour test and Z/AD test (JIs-C5024 method I). There was no change in the error rate, and no change was observed in the pencil hardness of 7H on the substrate surface.

Furthermore, the charging properties were good on both sides, and no deterioration was observed in reliability tests.

Therefore, after coating the optical recording layer with a fluororesin, a t+siO□ layer is formed by the LPD method on the exposed portion of the substrate material, thereby preventing the substrate from absorbing moisture.
It is possible to prevent the plastic substrate from warping, to obtain an optical disk that is resistant to dust and scratches, has both high surface hardness and excellent antistatic function, and it is also possible to reduce the number of LPD processing steps. Furthermore, by using a trifluorinated chlorine ethylene polymer as the fluororesin that coats the optical recording film, a highly reliable optical disc can be obtained with a small number of steps and at a low cost. Further, the present invention is not limited to the contents of the above embodiments, and the substrate may be made of glass or plastic other than polycarbonate.

Table <Effects of the Invention> In this way, after coating the optical recording layer with a fluororesin, the S
By forming an iO3 layer, it not only prevents the plastic substrate from warping due to rapid changes in temperature and humidity, but also provides the substrate surface with high hardness and excellent antistatic properties, making it resistant to dust and scratches. By using a trifluorinated chlorine ethylene copolymer as the fluororesin that coats the optical recording layer, it is possible to obtain a highly reliable optical disc that is resistant to changes in environmental temperature and humidity cycles and with a small process cost. can.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of an optical disc showing one embodiment of the present invention, FIG. 2 is a sectional view of an optical disc showing another embodiment of the invention, and FIG. 3 is a sectional view of a conventional optical disc. □ Fig. 4 is a diagram comparing the charging properties of the surface of a polycarbonate substrate with and without an SiO □ layer, and Fig. 5 is a cross-sectional view showing another conventional disk. In the figure, 50 is a fluororesin, and 51 is a trifluorinated chlorine ethylene copolymer. In addition, the same symbols in the figures indicate the same or equivalent parts.

Claims (2)

[Claims] (1) In an optical recording medium consisting of a substrate and an optical recording layer having a memory function, after forming the optical recording layer on the substrate and forming a fluororesin layer covering the optical recording layer, SiO
An optical disc characterized by forming two layers. (2) Claim 1, characterized in that a trifluorinated chlorine ethylene copolymer is used for the fluororesin layer.
Section optical disc.