JPH07118093B2 - Optical information recording medium - Google Patents

Description

The present invention relates to an optical information recording medium such as a magneto-optical disc, a write-once type optical disc, a compact disc, etc., and particularly, the improvement of long-term reliability and substrate strength thereof. It is about.

[Outline of Invention]

The present invention is an optical information recording medium having an information recording layer on a polycarbonate resin substrate, wherein the amount of residual free chlorine remaining on the substrate is 1.0 ppm or less, and the phosphorus content is 5 to 10 ppm to prevent oxidation or It is intended to suppress the occurrence of deterioration due to decomposition and improve long-term reliability, and at the same time, suppress thermal decomposition during molding to improve substrate strength.

[Conventional technology]

The optical recording system has features such as non-contact recording / reproducing, easy handling, and resistance to scratches and stains. Furthermore, the optical recording system has a storage capacity of several tens as compared with the magnetic recording system. Since it has the advantage of being several to several hundred times larger, it is expected to be put to practical use as so-called compact discs and video discs for recording audio signals and image signals, and also expected to be used for large capacity files such as code information and image information. ing.

As the information recording medium of the optical recording system, there are various types of media such as a write-only optical disc and a magneto-optical disc in addition to a read-only medium such as the compact disc described above.
In any case, it is configured by forming an information recording layer on a transparent substrate made of polycarbonate resin or the like.

Polycarbonate resin has characteristics such as heat resistance during melt molding and easy molding, little deformation and deterioration after disk molding, and excellent mechanical properties.
It is useful as a substrate material for the above-mentioned optical information recording medium.

On the other hand, as a recording material for the information recording layer, a metal-based recording material is being developed, as represented by a rare earth element-transition metal amorphous alloy film in a magneto-optical disk,
For example, it has been reported that materials such as TbFeCo, TbFe, and GdFe can obtain good characteristics in terms of sensitivity and read performance.

[Problems to be solved by the invention]

By the way, in an optical information recording medium having an information recording layer formed of the above-mentioned metal-based recording material, improvement of long-term reliability becomes a major issue in putting it into practical use.

For example, when an optical information recording medium having a polycarbonate resin molded body as a substrate (for example, a compact disc or a magneto-optical disc) is stored under high temperature and high humidity, the recording film or the reflective film is corroded due to local oxidation. The occurrence of this corrosion causes defective reproduction and the like, which is a serious problem in the optical information recording medium for which reliability must be guaranteed.
Alternatively, the substrate also deteriorates due to local hydrolysis or the like, and the number of bite errors increases correspondingly, which causes the commercial value of the optical information recording medium to decrease.

Therefore, the present invention has been proposed in view of such conventional circumstances, and aims to improve long-term reliability in an optical information recording medium having a polycarbonate resin molded body as a substrate, and a machine with less occurrence of reproduction defects It is an object of the present invention to provide an optical information recording medium which is excellent in dynamic strength and has high reliability.

[Means for solving problems]

The present inventors have made extensive studies over a long period of time to investigate the mechanism of occurrence of defects in an optical information recording medium using a polycarbonate resin as a substrate material, and as a result, the amount of residual free chlorine and phosphorus content remaining on the substrate. Has come to gain the knowledge that they are deeply involved.

The present invention has been completed based on such findings, and in an optical information recording medium comprising an information recording layer on which a signal is optically read is provided on a substrate made of a polycarbonate resin, the substrate is left free. The chlorine content is 1.0 ppm or less, and the phosphorus content is 5 to 10 ppm.

In the optical information recording medium of the present invention, the polycarbonate resin used as the substrate material comprises a dihydric phenol compound (for example, bisphenol A), an acid binder (for example, alkali such as sodium hydroxide) and a solvent (methylene chloride). It is produced by the phosgene method of synthesizing by reacting with phosgene in the presence, and uses a normal polycarbonate resin and a trifunctional or higher polyfunctional organic compound having a phenolic hydroxyl group as a branching agent. Branched polycarbonate resin, a terminal long-chain alkyl polycarbonate resin using a monofunctional organic compound such as a long-chain alkyl acid chloride or a long-chain alkyl ester-substituted phenol as a terminal stopper, both the branching agent and the terminal stopper described above. Long-chain alkyl branched polycarbonate resin used, Etc. These mixtures are used in al.

Then, these polycarbonate resins are put into an injection molding machine in the form of pellets, fluidized by a heater, and then extruded into a mold to be molded into a substrate. In the present invention, first, they were obtained by this injection molding. The amount of residual free chlorine remaining in the substrate in the state of the molded body is 1.0 ppm or less. According to the experiments conducted by the present inventors, the amount of residual free chlorine is
When it exceeded 1.0 ppm, the error rate increased.

In order to reduce the above-mentioned residual free chlorine, the purification of the polycarbonate resin produced by the phosgene method may be sufficient, and for example, salts of salts such as impurities and electrolyte substances such as alkalis from the polymer solution produced by the phosgene method are It is possible to suppress the amount of chlorine contained in the polycarbonate resin by repeating the water washing step for removing them completely and completely expelling the solvent methylene chloride from the polycarbonate resin. As a result, the amount of residual free chlorine at the time of molding the substrate can be reduced.

On the other hand, in order to improve the thermal stability of the polycarbonate resin, a phosphorus compound (for example, phosphite ester) is added during the production of the polycarbonate resin, and as a result, the phosphorus content contained in the substrate is still corroded or altered. It will have a great effect on the temperature, so the amount should be kept below 10ppm. According to experiments conducted by the present inventors, it was confirmed that defects (due to corrosion, deterioration, etc.) rapidly increase when the phosphorus content exceeds 10 ppm.

In this case, it is preferable not to add the phosphorus compound to the polycarbonate resin in order to prevent the above defects, but if the phosphorus compound is not added, a difference occurs in the strength deterioration of the injection-molded substrate, for example. This is because if the phosphorus compound is not added, the resin is hydrolyzed at a high temperature during injection molding and the molecular weight is lowered. The decrease in molecular weight is
It deteriorates the mechanical strength of the material. According to experiments conducted by the present inventors, it was found that a phosphorus content of 5 ppm or more exerts a sufficient effect of preventing thermal decomposition.

Therefore, it was concluded that the phosphorus content is preferably 5 to 10 ppm in order to exert sufficient heat stability performance and prevent the occurrence of defects.

[Operation] In general, a considerable amount of free chlorine remains in commercially available polycarbonate resins, and the residual free chlorine amount becomes about 1.3 to 1.6 ppm at the time of molding on a substrate.

This residual free chlorine originates from, for example, the electrolyte (sodium chloride) remaining in the polycarbonate resin polymer, methylene chloride which is a solvent, and chlorine bonded to the end of the polymer. Remarkably adversely affects the corrosion resistance.

As a method of suppressing the influence of residual free chlorine, for example, a method of cleaning the substrate can be considered, but it is only an emergency measure and is not a fundamental solution. Further, it has been considered to provide a protective film, but when a slight crack is generated, corrosion starts, which is also difficult to say as a fundamental solution.

In the present invention, the purification process of the polycarbonate resin is reviewed, chlorine-containing components contained in the polycarbonate resin of the substrate material are thoroughly removed, and the residual free chlorine amount in the substrate state is set to 1.0 ppm or less. Corrosion that occurs in the information recording layer of the information recording medium is suppressed.

On the other hand, a phosphorus compound is added to the polycarbonate resin from the viewpoint of thermal stability, but when it is molded into a substrate, the content of this phosphorus compound also causes corrosion and alteration of the substrate. However, if the phosphorus compound is not added at all, the thermal stability of the polycarbonate resin is insufficient and a problem occurs in terms of strength. Therefore, in the present invention, by suppressing the phosphorus content within the range of 5 to 10 ppm, defects occurring in the information recording layer are suppressed, and at the same time, the mechanical strength of the substrate is secured.

〔Example〕

 Hereinafter, the present invention will be described based on specific experimental results.

First, prepare polycarbonate resin pellets with different chlorine removal processes, put them in an injection molding machine,
Injection molding was performed at a heater temperature of 320 to 360 ° C and a mold temperature of 80 to 115 ° C to form a disk-shaped substrate having a thickness of 1.2 mm. These will be referred to as substrates A to D.

Next, the amount of residual free chlorine remaining on these substrates A to D was quantified. Quantification was by potentiometric titration. That is,
Cut 5g of sample from each substrate, precisely weigh it and dissolve it in 150ml of methylene chloride, add acetone to it and immediately quantitate chlorine by potentiometric titration with 0.005M silver nitrate / acetone solution using an automatic titrator. I asked. The amount of chloride ions liberated by this method was quantified. The automatic titrator used was the Hiranuma Reporting Titler COMTITE-7.

As a result, the residual free chlorine amount of the substrate A was 0.9 ppm, the residual free chlorine amount of the substrate B was 1.2 ppm, and the residual free chlorine amount of the substrate C was 1.
The amount of residual free chlorine of the substrate D was 3 ppm and 1.9 ppm.

Therefore, next, as shown in FIG. 1, these substrates (1)
[Substrate A to substrate D] A Si ₃ N ₄ film (2) with a film thickness of 500Å and a TbFeCo film (3) with a film thickness of 600Å [This TbFeCo film (3) serves as a recording layer. ] And an ultraviolet curable resin layer (4) having a thickness of 5 μm were successively deposited and formed to produce a magneto-optical disk.

For each of the obtained magneto-optical disks, the increase in error rate was evaluated. As an evaluation method, 90 ℃, relative humidity 85%
Each magneto-optical disk was stored under the condition of, and the increase in error rate with time was expressed as a ratio to the initial error rate. Results are shown in FIG. In the figure, a curve A is a magneto-optical disk using the substrate A, a curve B is a magneto-optical disk using the substrate B, a curve C is a magneto-optical disk using the substrate C, and a curve D is a substrate D. Represents the original magneto-optical disk.

From FIG. 2, it can be seen that in the case where the amount of residual free chlorine remaining on the substrate (1) is 1.0 ppm or less [a magneto-optical disk using the substrate A], the error rate hardly increases, and good corrosivity is exhibited. You can see that. On the other hand, when the residual free chlorine content of the substrate exceeded 1.0 ppm, the error rate increased with the occurrence of corrosion, and this tendency was confirmed to be more remarkable as the residual free chlorine content increased.

Based on the above results, in order to investigate the influence of phosphorus content, several polycarbonate resins with different phosphorus contents were prepared through a purification process such that the amount of free chlorine was 0.9 ppm, and the usual method was used. Injection molding was carried out to prepare a substrate. A phosphorous acid ester was used as the phosphorus compound.

Fluorescent X-ray analysis was performed on each molded substrate to determine the phosphorus content in each sample. As a result, the phosphorus contents were 0, 5, 10, 15, 22 ppm, respectively.

Next, in order to investigate the thermal stability of the substrate, each polycarbonate resin (phosphorus content 0, 5, 10, 15, 22 ppm) before molding the substrate
Was measured and evaluated as thermal decomposition data. Results are shown in FIG. Liquidity is measured by the flow tester method (JI
According to the S standard), the change ΔQ in the flow value between the pellet state and the molded substrate was measured. If the change ΔQ in the flow value is large, it means that the decrease in the molecular weight is large.

As a result, if the phosphorus content in the substrate is 5 ppm or more, Δ
It was found that Q was suppressed and was sufficient for preventing thermal oxidation.

Further, a magneto-optical disk as shown in FIG. 1 was manufactured using these substrates.

Then, first, an initial visual inspection was performed on these magneto-optical disks, and it was confirmed that there was no defect.

Next, each magneto-optical disk was stored in a thermo-hygrostat at 90 ° C and 85% relative humidity for 150 hours, and the appearance was inspected after the storage. The relationship between the number of defects and the phosphorus content confirmed by this visual inspection is shown in FIG. The number of defects generated in FIG. 3 represents the number of defects found in eight magneto-optical disk samples.

As a result, in a magneto-optical disk using a polycarbonate resin containing phosphorus exceeding 10 ppm, 90 ° C,
In a reliability test under constant temperature and humidity with a relative humidity of 80%, it was found that a visually observable defect occurred after 150 hours, affecting bite error. On the other hand, by setting the phosphorus content in the substrate to 10 ppm or less, no defect was observed in the visual test after 150 hours.

The present invention has been described above with reference to specific experimental results. However, the scope of application of the present invention is not limited to the above-described magneto-optical discs, and so-called compact discs, write-once optical discs, and all other types of optical information recording media. The structure of the medium is not limited at all.

〔The invention's effect〕

As is clear from the above description, in the optical information recording medium of the present invention, the residual free chlorine amount remaining on the polycarbonate resin substrate is 1.0 ppm or less, and the phosphorus content is 10 pp.
Since the thickness is set to m or less, it is possible to provide an optical information recording medium in which corrosion of the information recording layer and deterioration of the substrate are significantly suppressed, reproduction defects are small, and long-term reliability is excellent.

Further, since the phosphorus content is 5 ppm or more, it is advantageous in terms of the thermal stability of the polycarbonate resin, and the mechanical strength of the substrate can be secured.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of an essential part showing an example of the structure of a magneto-optical disk, and FIG. 2 is a characteristic showing the change with time of the error rate of each magneto-optical disk when the amount of residual chlorine remaining on the substrate is changed. It is a figure. FIG. 3 is a characteristic diagram showing the relationship between the phosphorus content of the substrate and the number of defects generated after storage, and FIG. 4 is a characteristic showing the relationship between the phosphorus content in the polycarbonate resin and the magnitude of the flow value change ΔQ. It is a figure. 1 ... Substrate 3 ... TbFeCo film (information recording layer) 5 ... Recording layer

Claims (1)

[Claims] 1. An optical information recording medium comprising an information recording layer for optically reading signals on a substrate made of a polycarbonate resin, wherein the substrate has a residual free chlorine amount.
An optical information medium having a phosphorus content of 5 to 10 ppm and 1.0 ppm or less.