JPH01271936A - Optical information recording medium - Google Patents

Abstract

PURPOSE:To prevent or limit bleeding of corrosive elements from a substrate and to prolong the life of the recording medium by subjecting the resin substrate formed with a thin film layer for recording or reproducing on one face to a reforming treatment by irradiation of energy. CONSTITUTION:The substrate 1 is formed of a transparent resin material such as polycarbonate, polymethyl methacrylate or epoxy. The recording layer or reflecting layer 3 is laminated on one face of the substrate 1 and signal patterns consisting of pregrooves 4 and prepits 5 are formed on the layer 3. A chemical change of crosslinking or decomposition arises on the surface layer of the substrate 1 and the corrosive elements are taken into a hydrocarbon group when the substrate 1 is irradiated by the energy such as oxygen plasma, sputter etching, glow discharge, electron beam or UV rays. The bleeding of the corrosive elements from the substrate is thereby prevented or limited and the life of the recording medium is prolonged.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an optical information recording medium, and particularly to a means for preventing corrosion of a recording layer or a reflective layer formed on a substrate.

[Conventional technology]

2. Description of the Related Art Conventionally, optical information recording media have been known in which a thin film layer such as a reflective film or a recording film is formed on a signal pattern forming surface of a resin substrate. For example, taking a compact disc as an example, an aluminum reflective film is formed on the signal pattern forming surface of a polycarbonate substrate, and a protective film made of a urethane acrylate photocurable resin is further laminated on top of this aluminum reflective film. There is.

In the case of the compact disc, if no anti-corrosion treatment is applied to the aluminum reflective film on the substrate, the temperature at 60°C
When an accelerated environmental test is performed by leaving the device in an atmosphere of 90% RH, the aluminum reflective film corrodes in 200 to 300 hours, and the reflectance decreases, making it difficult to read information.

Although the above description has been made using a compact disc having an aluminum reflective film as an example, similar problems exist with all optical information recording media having a reflective layer or recording layer made of other materials.

Conventionally, it has been recognized that this type of corrosion of thin film layers is caused by water penetrating through the substrate or protective film, forming a waterproof film on the surface of the thin film layer.

Alternatively, if the thin film layer is made of metal, corrosion-resistant treatments such as forming an oxide film of the metal have been proposed (
JP-A No. 62-62445).

An optical information recording medium that has been subjected to such waterproofing or corrosion-resistant treatment has a longer lifespan effect than an optical information recording medium that has not been subjected to any such treatment. For example, in the case of a compact disc, if an alumina layer is formed on the surface layer of the aluminum reflective film, when an accelerated environmental test is conducted under the same conditions as above, the corrosion start time of the aluminum reflective film will be extended to about 1500 hours. .

[Problem to be solved by the invention]

However, this type of optical information recording medium is required to have a longer lifespan, and conventional corrosion protection measures are still insufficient.

As a result of research, the applicant of the present application has learned the following facts regarding corrosion of thin film layers.

■The thin film layer is easily corroded in a high temperature, high humidity atmosphere, but hardly corroded in a high temperature, low humidity atmosphere.

When a glass substrate is used, the thin film layer is less likely to corrode even in a high temperature and high humidity atmosphere.

■As a result of analysis, it was confirmed that the corroded thin film layer was composed of hydroxide.

■Corrosive elements such as chlorine, sulfur, and fluorine are detected in the corroded thin film layer.

■Corrosion of thin film layers occurs from the interface with the substrate.

■Corrosive elements such as chlorine, sulfur, and fluorine are detected in the resin substrate.

From these facts, it is estimated that the corrosion mechanism of the thin film layer is as follows.

First, a corrosive element contained in a resin substrate causes a chemical reaction with the thin film layer material. Taking the case where the corrosive element is chlorine (C1) as an example, this chemical reaction will be explained using a chemical formula.
It is as follows.

M (thin film material) +4 C1-→MC14-+ 3 e
- (1) Next, the MC14- generated by this reaction and the moisture that has entered from the outside through the protective film cause the following chemical reaction.

MC14-+ 3 Hz O → M(○H) 3+38" +4C1-...(2) Furthermore, C1- generated by this reaction again causes the chemical reaction of formula (1) above, and corrosion continues. Proceed to.

Therefore, corrosion of the thin film layer can be prevented by preventing the intrusion of at least one of corrosive elements and moisture. However, resin substrates have some degree of water permeability, and it is difficult to completely prevent water permeability, and if treatments are applied to prevent this, the cost of the optical information recording medium will increase significantly. On the other hand, it has been found that the corrosive elements can penetrate into the thin film layer from the resin substrate relatively easily by modifying at least the surface layer of the resin substrate.

The present invention has been made based on this knowledge, and by modifying the resin substrate, it is possible to prevent corrosive elements from entering the thin film layer from the resin substrate, thereby achieving a long-life optical information recording medium. The purpose is to provide the following.

[Means for Solving the Problem A] In order to achieve the above-mentioned object, the present invention provides a resin substrate for an optical information recording medium that is physically modified at least on the surface on which the thin film layer is formed. It is characterized by the use of objects.

Here, the physical modification treatment refers to a treatment in which a resin substrate is irradiated with energy such as oxygen plasma, sputtered particles, glow discharge, electron beam, or ultraviolet rays.

[Effect]

Oxygen plasma and sputtered particles on a resin substrate.

When irradiated with energy such as glow discharge, electron beam, or ultraviolet light, the energy causes chemical changes such as crosslinking and decomposition in at least the surface layer of the substrate.

A corrosive element is incorporated into the hydrocarbon group (CnHm; where n and m are positive integers). Therefore, the free movement of the corrosive element in the substrate is restricted, and the elements constituting the thin film layer and the corrosive element are not combined.

Corrosion of the thin film layer is prevented.

Hereinafter, using a case where polycarbonate (PC) is used as the substrate material and chlorine is contained in the substrate, changes in the substrate structure caused by the above-mentioned means will be explained using chemical formulas.

It is presumed that even if a resin material other than PC polycarbonate contains a corrosive element other than chlorine, corrosion of the thin film layer will be prevented in the same way.

〔Example〕

First, the schematic structure of the optical information recording medium according to the present invention will be explained.

FIG. 1 is a sectional view of a main part showing a typical example of an optical information recording medium according to the present invention, in which a recording layer or a reflective layer 3 is laminated on a signal pattern forming surface of a substrate 1. As shown in FIG.

The substrate 1 is made of polycarbonate (PC), for example.

It is formed from a transparent resin material such as polymethyl methacrylate (PMMA), polymethylpentene, or epoxy. On one side of the substrate 1, a signal pattern such as a pre-group 4 for guiding a recording/reproducing radiation beam (for example, a laser beam) along a recording track and a pre-pit 5 for modulating an address signal is formed in the form of an uneven shape. ing.

These signal patterns 4 and 5 are formed by an appropriate method depending on the type of substrate material. For example, injection molding is suitable for thermoplastic resins such as PC and PMMA, and for thermosetting resins such as epoxy. In this case, the fi2P method (photocurable resin method) and the casting method are suitable.

This substrate 1 is subjected to physical modification treatment such as oxygen plasma irradiation, sputter etching, glow discharge irradiation, electron beam irradiation, and ultraviolet irradiation, and at least the signal patterns 4 and 5 are coated with corrosive elements. has been modified to restrict the free movement of This modification treatment is performed after the signal patterns 4 and 5 are transferred when the substrate 1 is molded by injection molding or casting. Further, when the substrate 1 is molded using the 2P method, the step can be performed before or after the signal patterns 4 and 5 are transferred.

In addition, the outer surface of the board (the surface opposite to the signal pattern formation surface)
It has been widely known as a method of forming a hard coat layer to apply an ultraviolet curable resin liquid to a substrate and irradiate the coated surface with ultraviolet rays in order to cure the resin liquid. However, such ultraviolet irradiation does not have the effect of inhibiting corrosion of the recording layer or reflective layer, and although the substrate is similarly irradiated with ultraviolet rays, it is not prior art to the present invention. The optical information recording medium on which the hard coat layer was formed by irradiation was heated at 80°C
When an accelerated environmental test was conducted under the condition of 0% RH, 58
It was found that the light reflectance decreased to 18% to 40% after a period of time, and the environmental resistance was almost the same as that of a product that was not irradiated with ultraviolet rays.

The recording layer 3 is formed of a desired recording material selected from known heat mode recording materials.

In addition, for read-only optical information recording media, zero reflective layer materials in which a reflective layer is formed instead of a recording layer include:
Although any high reflectance material can be used, it is relatively inexpensive and easy to form a film, so
Aluminum is particularly preferred.

As a means for forming the recording layer 3, a spin coating method is used for organic dye-based recording materials, and a vacuum film forming method such as a vacuum evaporation method or a sputtering method is used for other recording materials.

Hereinafter, specific examples of the present invention will be shown, and the effects of the present invention will be discussed.

First Example> A polycarbonate substrate with a signal pattern transferred onto one side was irradiated with oxygen plasma as a modification treatment, and then an aluminum reflective film was formed on the signal pattern surface by electron beam evaporation. A protective film of urethane acrylate photocurable resin was laminated on the aluminum reflective film.

The oxygen plasma irradiation conditions are as shown in Table 1.

The deposition conditions for the aluminum reflective film were as follows: using aluminum as a target with a purity of 5N, the ultimate degree of vacuum being 6.6710-'PaPa or less, the substrate temperature being 5°C, and the deposition rate being lnm/sec. The film thickness was 1100n.

The optical information recording medium thus produced and the optical information recording medium (3 of each) that had not been subjected to any anti-corrosion treatment were left in an atmosphere of 60°C x 90% RH to conduct an accelerated environmental test. . In Figure 2.

The results of this accelerated environmental test are shown below. The horizontal axis of this graph is the test time, and the vertical axis is the reflectance of the reflective layer.1 The solid line is the data for the optical information recording medium according to the present invention, and the data for the optical information recording medium according to the conventional example. The data is shown with a two-dot chain line. however.

The measurement light is a laser with a wavelength of 780 nm, and each line showing the measurement results is the average value of three samples of the same type.

As is clear from the graph in Figure 2, the optical information recording medium whose substrate is not irradiated with oxygen plasma has a
The reflectance decreases rapidly over time.

After 3000 hours, the reflectance is about 16%, whereas in the optical information recording medium of this example in which the substrate was irradiated with oxygen plasma, no decrease in reflectance was observed even after 3000 hours.

<Second Example> A polycarbonate substrate with a signal pattern transferred onto one side was subjected to sputter etching as a decorrosive element treatment, and then an aluminum reflective film and an aluminum reflective film were applied under the same conditions as in the first example. A protective film of urethane acrylate photocurable resin was laminated.

The sputter etching conditions are as shown in Table 2.

Table 2: Accelerated environmental test by leaving the optical information recording medium thus prepared and the optical information recording medium (3 each) without any anti-corrosion treatment in an atmosphere of 60°C x 90% RH. I did it. FIG. 3 shows the results of this accelerated environmental test. The measurement conditions were the same as in the first embodiment.

As is clear from this graph, the optical information recording medium whose substrate is not sputter-etched has a
The reflectance rapidly decreases during 0 hours and reaches 15% after 3000 hours, whereas the optical information recording medium of this example in which the substrate was subjected to sputter etching treatment 6. Third Example in which no decrease in reflectance is observed even after the passage of time> A polycarbonate substrate with a signal pattern transferred to one side was subjected to glow discharge treatment as a decorrosive element treatment, and then An aluminum reflective film and a protective film of a urethane acrylate photocurable resin were laminated under the same conditions as in the first example and the second example. The number of samples was three.

The glow discharge conditions are as shown in Table 3.

Table 3 Optical information recording media produced in this way and optical information recording media (3 pieces) that have not been subjected to any anti-corrosion treatment.
An accelerated environmental test was conducted by leaving the sample in an atmosphere of 0° C. and 90% RH. FIG. 4 shows the results of this accelerated environmental test, provided that the measurement conditions were the same as in the first and second examples.

As is clear from this graph, the reflectance of optical information recording media whose substrates have not been subjected to glow discharge treatment decreases rapidly between 200 and 300 hours, and the reflectance reaches 15% after 3000 hours. On the other hand, the optical information recording medium of this example in which the substrate was subjected to glow discharge treatment
No decrease in reflectance was observed even after 00 hours had elapsed.

<Fourth Example> After irradiating a polycarbonate substrate with a signal pattern transferred onto one side with ultraviolet rays as a decorrosive element treatment,
Under the same conditions as the first to third examples,
An aluminum reflective film and a protective film of urethane acrylate photocurable resin were laminated. The number of samples was three.

The ultraviolet irradiation conditions are as shown in Table 4.

The optical information recording medium thus produced and the optical information recording medium (3 pieces) without any anti-corrosion treatment were
An accelerated environmental test was conducted by leaving the sample in an atmosphere of 0°C be.

As is clear from this graph, the reflectance of an optical information recording medium whose substrate is not irradiated with ultraviolet rays rapidly decreases between 22 and 45 hours, and after 2000 hours, the reflectance reaches approximately 1005%. On the other hand, in the optical information recording media of this example in which the substrate was irradiated with ultraviolet rays, no decrease in reflectance was observed even after 2000 hours had passed.

Fifth Example> After irradiating a polycarbonate substrate with a signal pattern transferred onto one side with an electron beam as a decorrosive element treatment, under the same conditions as in the first to fourth examples, An aluminum reflective film and a protective film of urethane acrylate photocurable resin were laminated. The number of samples was three.

The electron beam irradiation method and irradiation conditions are as follows.

First, the substrate was set in a vacuum chamber of an electron beam irradiation processing apparatus and evacuated. The degree of vacuum in the vacuum chamber is 6.67
When the temperature was below X10-'Pa, the signal pattern surface of the substrate was irradiated with an electron beam from an electron gun. At this time, the electron beam was scanned so that the entire surface of the substrate was uniformly irradiated with the electron beam. Furthermore, in order to prevent the substrate surface from being charged up, an ion gun was used to irradiate Ar+ ions toward the substrate surface to neutralize the charges on the substrate surface.

Note that the acceleration voltage during electron beam irradiation was 20 KV, and the irradiation current was 2 mA.

The optical information recording medium of this example that was irradiated with the electron beam in this way and the optical information recording medium that had not been subjected to any anti-corrosion treatment were left in an atmosphere of 80°C x 90% RH to perform an accelerated environmental test. Ta. FIG. 6 shows the results of this accelerated environmental test. The measurement conditions are the same as those of the first to fourth embodiments.

As is clear from this graph, the reflectance of the optical information recording medium whose substrate is not irradiated with an electron beam rapidly decreases between 22 and 45 hours, and after 2000 hours, the reflectance is approximately 10.5%. In contrast, the optical information recording medium of this example in which the substrate was irradiated with an electron beam had a
No decrease in reflectance was observed even after 0 hours had elapsed.

From the above test results, it can be seen that the optical information recording medium of the present invention has a remarkable effect on improving the corrosion resistance of the reflective layer.

In each of the above embodiments, a polycarbonate substrate was used as an example of the resin substrate, but epoxy resin or polymethyl methacrylate may also be used.

Similar effects can be obtained with other resin substrates such as polymethylpentene and polyolefin.

Further, in each of the above embodiments, an aluminum reflective layer was used as an example of a thin film layer to be corrosion-protected, but the same effect can be obtained for a heat mode recording material.

Further, in each of the above embodiments, only the influence of chlorine as a corrosive element has been described, but a similar effect is also exerted on corrosion of a metal layer caused by, for example, sulfur or fluorine.

The gist of the present invention is that at least the surface layer of the substrate is modified by irradiating the substrate with energy so that the free movement of corrosive elements within the substrate is restricted. , and other corrosion protection treatments may be optionally combined. Other anti-corrosion treatments include (1) forming an intermediate layer between the substrate and the recording layer or reflective layer using a material that is difficult to transmit corrosive elements; ■Baking the board.

■Select a substrate material that originally has a low content of corrosive elements. There are ways to do this.

Further, in each of the above embodiments, only the case where the intermediate layer 2 and the reflective layer or the recording layer 3 are laminated as two layers on the substrate 1 has been described, but any thin film structure may be used, for example, by omitting the intermediate layer 2. It can be applied to optical information recording media that have

〔Effect of the invention〕

As described above, according to the present invention, at least the surface layer portion of the resin substrate is modified, and the seepage of corrosive elements from the substrate can be prevented or significantly restricted. Therefore, even if the thin film layer is left in a high-temperature atmosphere, chemical reactions between the thin film layer and corrosive elements do not occur, or the progress of these chemical reactions is slowed down, significantly extending the life of the optical information recording medium. be able to.

[Brief explanation of the drawing]

The figures are all for explaining the present invention, and FIG. 1 is a sectional view of a main part showing a schematic structure of an optical information recording medium, and FIGS. 2 to 6 are optical information recording media according to each embodiment. This is a graph explaining the effect of 1: Substrate, 3: Recording layer or reflective layer, 4 Nibli groove, 5: Blibit. Figure 1: 3;
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Claims (6)

[Claims] (1) In an optical information recording medium in which a thin film layer including at least one of a recording layer and a reflective layer is formed on one side of a resin substrate, at least the surface on which the thin film layer is formed is modified as the resin substrate. An optical information recording medium characterized by using an optical information recording medium that has been subjected to quality treatment. (2) The optical information recording medium according to claim 1, wherein the surface of the substrate is irradiated with oxygen plasma as the modification treatment. (3) The optical information recording medium according to claim 1, wherein as the modification treatment, a sputter etching treatment is performed on the surface of the substrate. (4) The optical information recording medium according to claim 1, wherein the surface of the substrate is subjected to glow discharge treatment as the modification treatment. (5) The optical information recording medium according to claim 1, wherein the surface of the substrate is irradiated with an electron beam as the modification treatment. (6) The optical information recording medium according to claim 1, wherein the surface of the substrate is irradiated with ultraviolet rays as the modification treatment.