JPH06100683A - Polycarbonate for disk base - Google Patents

Abstract

PURPOSE:To provide a high-quality polycarbonate which gives a disk base, such as one for an optical or magnetic disk, hardly corroding a recording film formed on the base. CONSTITUTION:A polycarbonate for a disk base has a content of methylene chloride as an impurity of up to 20ppm, or it has, in addition to the content of methylene chloride of the above amt., a content of an unreacted bisphenol up to 20ppm.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polycarbonate for a disc substrate, and more particularly to a high-purity polycarbonate having a very low content of methylene chloride as an impurity and useful as a disc substrate material.

[0002]

2. Description of the Related Art Polycarbonate is generally used as a material for disk substrates such as optical disks and magnetic disks. However, when this polycarbonate is used as a disk substrate for molding, metals such as iron, gallium, and terbium present in the recording film are gradually corroded, or the adhesion between the substrate and the recording film is insufficient. There were various problems. Therefore, the present inventors have conducted various studies to solve the above problems in using polycarbonate as a disk substrate, and as a solvent used for conventional polycarbonate, particularly polycarbonate obtained by the phosgene method. It has been found that methylene chloride is contained as an impurity, and such an impurity is a major cause of the above-mentioned various problems.

[0003]

Means for Solving the Problems The inventors of the present invention continued their research on the basis of such findings. When a polycarbonate containing these impurities was treated with an organic solvent such as acetone, the methylene chloride as an impurity was treated. It has been found that the content of the polycarbonate is extremely small and high purity, which solves the above-mentioned problems, particularly the problem of corrosiveness of the recording film, and exhibits extremely excellent performance as a disk substrate. The present invention was completed through such processes, and its gist is that the content of methylene chloride as an impurity is 20 pp.
A polycarbonate for a disk substrate, which is characterized by having a size of m or less. Further, the subject matter of the present invention is a polycarbonate for a disk substrate, which further contains methylene chloride as an impurity in an amount of 20 ppm or less and unreacted bisphenols in an amount of 20 ppm or less.

The polycarbonate of the present invention contains less impurities (particularly methylene chloride) and has a higher purity than conventional polycarbonates. In general, conventional polycarbonate contains various impurities. In particular, there are many methylene chloride used as a solvent or unreacted bisphenols (bisphenol A etc.) and low molecular weight components (polycarbonate oligomer etc.). Especially, methylene chloride causes various problems as described above when polycarbonate is used as a disk substrate.

In the polycarbonate of the present invention, the content of the above-mentioned impurity methylene chloride is 20 ppm or less, preferably 15 ppm or less. A more preferred polycarbonate has a methylene chloride content of 20 ppm or less (preferably 15 ppm or less) and an unreacted bisphenol content of 20 ppm or less, preferably 10 ppm.
It is the following. Here, if the content of methylene chloride exceeds 20 ppm, the recording film is susceptible to corrosion. If the amount of unreacted bisphenols exceeds 20 ppm, the adhesion between the disk substrate and the recording film may be insufficient.

The polycarbonate of the present invention can be obtained by various methods, but it is usually obtained by subjecting powdered polycarbonate containing impurities obtained by various methods to extraction treatment with an organic solvent such as acetone. . The method for producing a powdery polycarbonate containing the impurities is not particularly limited, but is usually a phosgene method, particularly an interfacial polycondensation method using bisphenols such as bisphenol A and phosgene as raw materials and methylene chloride as a solvent, In particular, the continuous interfacial polycondensation method can be mentioned. In addition, a so-called pyridine polymerization method using pyridine as a solvent among the transesterification method and the phosgene method can be mentioned. The above-mentioned powdery polycarbonate is not limited to a powdery one in a strict sense, and includes a flake-like one and the like. That is, it includes all powdery, granular, and flake-shaped polycarbonates obtained by the phosgene method or the transesterification method and before being pelletized. For example, the powdery polycarbonate obtained by the above-mentioned continuous interfacial polycondensation is usually in a flake form, and contains 4 to 8% by weight of low molecular weight components such as oligomers of polycarbonate and unreacted bisphenols such as bisphenol A as impurities. It contains 70 to 150 ppm and about 50 to 150 ppm of methylene chloride used as a solvent.

The polycarbonate of the present invention is considered to have a weak precipitation effect on powdery polycarbonate containing such impurities against ketones such as hexane, methanol, acetone and methyl ethyl ketone, and polycarbonate such as toluene and xylene. It is obtained by an extraction treatment with an organic solvent. In the extraction process, 0.5% of powdered polycarbonate was added to the above organic solvent.
It is preferable to use in an amount of 20 to 20 times, and to set the temperature in the range of 40 ° C. or higher and the boiling point of the organic solvent used or lower.
The extraction process is usually carried out under normal pressure, but it may be carried out under pressure.

[0008]

EXAMPLES The present invention will be described in more detail with reference to Examples and Comparative Examples. Example 1 4% by weight of low molecular weight component, unreacted bisphenol A100
To 100 kg of flaky polycarbonate containing ppm and 100 ppm of methylene chloride, 225 kg of hexane was added and stirred at 40 ° C. for 1 hour to carry out contact treatment (extraction treatment). Then, hexane is removed, and the temperature is 120 ° C.
It was dried under a reduced pressure of 1 mmHg for 20 hours. The content of impurities in the obtained flaky polycarbonate was as shown in Table 1. Next, 4 ppm of phosphorus-based antioxidant (as phosphorus) and 200 ppm of aliphatic ester were added to this flaky polycarbonate, and then pelletized by an extruder, and a disk substrate having a diameter of 13 cm was molded by an injection molding machine. 800 Å thick silicon oxide (Si O _x ) layer / 1000 Å thick metal (Tb, Fe, Co) layer / 800 Å thick silicon oxide (Si
A magneto-optical film having a three-layer structure of O _x ) layers was formed on the disk substrate by a sputtering method. The performance of the obtained optical disk was evaluated by conducting the adhesion (adhesion between the magneto-optical film and the substrate) and corrosiveness tests as described below. The results are shown in Table 1.

Adhesion test After the optical disc was left in an atmosphere of 90 ° C. and 90% relative humidity for 100 hours, a pinhole pinhole test was performed using cellophane tape, and the adhesion was displayed based on the following formula. Adhesiveness = (area of remaining portion) / (test area) × 10
0 (%) Corrosion Test After the optical disc was left in an atmosphere of a temperature of 60 ° C. and a relative humidity of 90% for 300 hours, the number of pinhole corrosion in a field of view of 250 μm × 200 μm was measured 1000 times with an optical microscope. .

Example 2 The same operation as in Example 1 was carried out except that methanol was used instead of hexane in the extraction treatment. The results are shown in Table 1.

Example 3 Except that in Example 1, a flaky polycarbonate containing 4% by weight of a low molecular weight component, 10 ppm of unreacted bisphenol A and 10 ppm of methylene chloride was used as the polycarbonate, and the extraction treatment with hexane was not performed. The same operation as in Example 1 was performed. The results are shown in Table 1.

Comparative Example 1 The same operation as in Example 1 was carried out except that the extraction treatment with hexane was not carried out. The results are shown in Table 1.

Comparative Example 2 Except that in Example 1, a flaky polycarbonate containing 4% by weight of a low molecular weight component, 100 ppm of unreacted bisphenol A and 200 ppm of methylene chloride was used as the polycarbonate, and the extraction treatment with hexane was not performed. The same operation as in Example 1 was performed. The results are shown in Table 1.

[0014]

[Table 1]

[0015]

[Table 2]

* In Table 1, the content of impurities in the obtained polycarbonate was analyzed and quantified as follows. Polycarbonate as a sample was dissolved in methylene chloride 1,2-dichloroethane and quantified by gas chromatography (FID). Soxhlet extracted with low molecular weight acetone as a solvent. That is, the sample polycarbonate is crushed to 10
Cylindrical filter paper No. 15g that passed through 0 mesh wire mesh
A sample of 84 (28 × 100 mm) was collected, and this was extracted with 300 ml of acetone by refluxing once every 3 to 4 minutes (20 ml / cycle) for 8 hours. After that, the residue after evaporating 300 ml of acetone was weighed and used as a low molecular weight component. Unreacted bisphenol A The above-mentioned low molecular weight component was quantified by liquid chromatography after Soxhlet extraction using acetone as a solvent.

[0017]

INDUSTRIAL APPLICABILITY The polycarbonate of the present invention has a very low content of methylene chloride as an impurity and is of high quality. When used for a disk substrate such as an optical disk or a magnetic disk, the recording film on the substrate is Not susceptible to corrosion. Therefore, the polycarbonate of the present invention is extremely valuable in practice as a material for a disk substrate having excellent performance, and its wide use is expected.

Claims (2)

[Claims] 1. A polycarbonate for a disk substrate, wherein the content of methylene chloride as an impurity is 20 ppm or less. 2. The content of methylene chloride as an impurity is 2
The polycarbonate for a disk substrate according to claim 1, wherein the content of unreacted bisphenols is 0 ppm or less and the content of unreacted bisphenols is 20 ppm or less.