JPH01271939A - Optical information recording medium - Google Patents

Abstract

PURPOSE:To prevent or suppress the chemical reaction of a thin film layer and corrosive elements and to obtain the optical information recording medium having excellent corrosion resistance and a long life by forming a substrate by using a polycarbonate resin contg. the corrosive element at a specific ratio or below. CONSTITUTION:The thin film layer 1 is formed of the polycarbonate resin adjusted to <=35ppm content of the corrosive elements and a recording layer or reflecting layer 3 is laminated on one face thereof. Pregrooves 4 for guiding radiation beams for recording or reproducing along recording tracks and prepits 5 where address signals are subjected to signal modulation are provided on the signal pattern forming surface. Since the total content of the corrosive elements incorporated into the substrate 1 is low, the chemical reaction of the thin film layer 3 and the corrosive elements does not take place even when the medium is rested in a high-temp. and high-humidity atmosphere. The rate of progression of the reaction is low even if such reaction takes place. The recording medium having the excellent corrosion resistance and the long life is thereby obtd.

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 is 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.

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 and high humidity atmosphere, but hardly corroded in a high temperature and low humidity atmosphere. However, 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, corrosive elements contained in the resin substrate cause a chemical reaction with the thin film layer material. Taking the case where the corrosive element is chlorine (CI) as an example, this chemical reaction is explained using a chemical formula:
It is as follows.

M (thin film material) + 4 C1--+MC1--+ 3
e - (1) Next, the MC14- produced by this reaction and the moisture that has entered from the outside through the protective film cause the following chemical reaction.

MC14-+3820 → M(OH) 3+38" +4C1-...(2) ゛Furthermore, CI- generated by this reaction again causes the chemical reaction of formula (1) above, and corrosion progresses continuously. .

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 this, so treatment is required.

The cost of optical information recording media will increase significantly. On the other hand, among various resins that are substrate materials, polycarbonate resin can be relatively easily produced with a low content of the corrosive element.

The present invention has been made based on this knowledge, and has an object to suppress corrosion of a thin film layer by reducing the total amount of corrosive elements contained in a substrate, thereby providing a long-life optical information recording medium. The purpose is to

[Means to solve the problem]

In order to achieve the above object, the present invention provides a resin substrate for an optical information recording medium with a corrosive element content of 35 PPM.
It is characterized by using a polycarbonate substrate adjusted as follows.

[Effect]

When a polycarbonate substrate with a content of corrosive elements of 35 PPM or less is used, the total amount of corrosive elements is small, so the reaction between the thin film layer and the corrosive elements either does not occur at all, or even if it does occur, the rate of reaction is slow enough to be practical. It slows down to the point where it's not a problem.

Therefore, it is possible to provide an optical information recording medium with excellent corrosion resistance and long life.

〔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 resin whose content of corrosive elements is adjusted to 35 PPM or less,
On one side thereof, 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 signal modulating an address signal is formed in the form of an uneven shape. These signal patterns 4 and 5 are transferred from a master called a stamper placed in a mold when injection molding the substrate 1.

Hereinafter, a method for producing polycarbonate with a low content of corrosive elements will be explained.

Methods for producing polycarbonate can be broadly classified into the phosgene method and the transesterification method.

The phosgene method is a method in which dichloromethane is added as a solvent to an alkaline aqueous solution or suspension of sodium salt of bisphenol A, and phosgene is blown into the solution while stirring, as shown in the following formula.

Na Salt of Bisphenol A Phosgene As is clear from the above equation, according to the phosgene method, a large amount of sodium chloride is contained in the substrate, and chlorine in this sodium chloride is involved in the corrosion of the thin film layer. It is also possible that methylene chloride as a solvent and unreacted phosgene remain in the resin, and chlorine generated by decomposition during subsequent heating during substrate molding is involved in the corrosion of the thin film layer.

However, if the paste produced by the above process is trickled into boiling water, the electrolyte can be removed and at the same time the CHz Cl 2 can be recovered. Therefore, by adjusting the time of this exposure step, the diameter of the paste trickle, etc., polycarbonates with different chlorine contents can be produced.

Moreover, the transesterification method is a method in which bisphenol A and diphenyl carbonate are mixed, heated and melted without using a solvent, and polycondensed by transesterification at high temperature and reduced pressure to obtain a polymer, as shown in the following formula.

Bisphenol A Diphenyl Carbonate Polycarbonate As is clear from the above formula, chlorine-free polycarbonate can be obtained by the transesterification method.

Five types of polycarbonate resins with different chlorine contents were selected from the various polycarbonate resins produced in this way, and a polycarbonate substrate with a desired signal pattern formed on one side was produced by injection molding. The chlorine content of each polycarbonate substrate is shown in Table 1. Note that the chlorine content was measured by activation analysis.

Table 1 Next, an aluminum reflective layer was formed on the signal pattern surface of these substrates. The conditions for forming the aluminum reflective layer are that the purity of the aluminum ingot is 5N, and the ultimate vacuum is 6.
The substrate temperature was 25° C., the film formation rate was 1 nm 7 seconds, and the film thickness was about 1100 nm.

Finally, a protective layer of urethane acrylate photocurable resin was laminated on the aluminum reflective layer.

The optical information recording medium thus obtained was heated at 60°C x 90%RH.
An accelerated environmental test was conducted by leaving the sample in an atmosphere. FIG. 2 shows the results of an accelerated environmental test of the optical information recording medium according to this example. The horizontal axis of this graph is the test time, and the vertical axis is the reflectance of the reflective layer.The solid line represents the data of the optical information recording medium according to the present invention, and the optical information that has not been subjected to any anti-corrosion treatment. Data on the recording medium is indicated by a two-dot chain line.

However, a laser with a wavelength of 780 nm was used as the measurement light, and the line indicating the measurement results was the average value of three samples of the same type.

As is clear from this graph, the chlorine content is 170p.
The optical information recording medium using the pm substrate (E) is approximately 200 yen
As time passes, the reflectance begins to decrease rapidly, and 30
After 00 hours have elapsed, the 1 reflectance decreases to about 15%.

In addition, in the optical information recording medium using the substrate (D) with a chlorine content of 90 ppm, the reflectance starts to decrease after about 300 hours, and after 3000 hours, the reflectance decreases to about 1.
It drops to 5%.

In contrast, an optical information recording medium using a substrate (C) with a chlorine content of 35 ppm and an optical information recording medium using a substrate (C) with a chlorine content of 28 ppm
In the optical information recording medium using the substrate (B), the reflectance did not decrease until after 2000 hours had passed, and a remarkable anticorrosion effect was observed.

Furthermore, the optical information recording medium using the substrate (A) containing no chlorine showed no decrease in reflectance at all even after 3000 hours had passed, proving to be particularly effective.

In 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.

The gist of the present invention is to form a substrate using a resin material with a low content of corrosive elements, but in addition to this, other anti-corrosion treatments can be optionally performed in combination. Other anti-corrosion treatments include: 1) irradiating the substrate with energy such as oxygen plasma, sputter etching, glow discharge, electron beam, or ultraviolet rays; 2) transmitting an M-contact element between the substrate and the recording layer or reflective layer. Form the intermediate layer using a material that is difficult to use. ■
There is a method of baking the substrate.

〔Effect of the invention〕

As explained above, according to the present invention, since the total amount of corrosive elements contained in the resin substrate is small, chemical reactions between the thin film layer and the corrosive elements do not occur even when left in a high temperature and high humidity atmosphere. Otherwise, the speed of progress of these chemical reactions is slowed down, and the life of the optical information recording medium can be significantly extended.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a main part showing a schematic structure of an optical information recording medium according to the present invention, and FIG. 2 is a graph explaining the present invention in detail. 3: recording layer or reflective layer; 4: nibli groove;
5: Prepit.

Claims (1)

[Claims] An optical information recording medium comprising a thin film layer including at least one of a recording layer and a reflective layer formed on one side of a substrate, wherein the substrate has a content of a corrosive element of 35%.
An optical information recording medium characterized by using a polycarbonate substrate adjusted to PPM or less.