JPS6366236A - Optical disk substrate - Google Patents

Abstract

PURPOSE:To obtain an optical disk substrate, by molding a resin consisting of an aromatic polyester and polyolefin and exposing the molded resin to radiation and improved heat resistance as well as transparency and small birefringence. CONSTITUTION:An optical disk substrate produced by kneading (A) 70-95wt%, preferably 80-90wt% aromatic polyester with (B) 5-30wt%, preferably 10-20wt% low-molecular weight polyolefin having 1,000-10,000, preferably 2,000-5,000mol.wt. while heating, pelletizing the kneaded blend, molding the resultant pellets with an injection molding machine, heating the molded article, preferably in a vacuum at about the melting point of the polyolefin (B), exposing the article to radiation, e.g. at 90-110 deg.C in an atmosphere under 2X10<-4>-5X10<-6>Torr vacuum degree, and irradiating the heated article with electron rays at 20-70Mrad using an electron accelerator.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a substrate for an optical disk on which information is reproduced, recorded, and erased by irradiation with light such as a laser.

[Conventional technology]

Substrates for optical disks can be roughly divided into (1) inorganic glass, (2)
) thermosetting resin eboxy), (3) thermoplastic resin 3
It can be divided into types. Each of these substrates has significant advantages and disadvantages, but thermoplastic resin is mainly being considered for adoption. This is due to the following reasons. In the future, as the construction of four-cal networks such as advanced information communication systems and value-added communication networks progresses, the demand for optical discs capable of high-density recording is expected to increase rapidly. In this case, it is essential to have excellent mass productivity. It is also necessary that groups for tracking guidance can be formed on the substrate with high precision. In view of these points, injection molding of thermoplastic resin is suitable for eel as well. This thermoplastic resin is
Publication No. 978, "Nikkei Electronics" No. 292,
Main examples include polymethyl methacrylate, polystyrene, and polycarbonate, which are described on page 133 (1982).

[Problem to be Solved by the Invention 3] Polymethyl methacrylate and polystyrene have a problem in that they have poor heat resistance, typified by heat distortion temperature, and cannot withstand use under high temperature conditions. Since polycarbonate has poor fluidity, it tends to generate internal stress in the substrate and has a problem of large birefringence.

In particular, magneto-optical disks, which have been attracting attention recently, have a structure that captures subtle differences due to the Kerr effect and Faraday effect as binary signals, so a large birefringence would be fatal.

The present invention is intended to solve these problems, and its purpose is to provide an optical disk substrate that has excellent heat resistance, transparency, and low birefringence.

[Means to solve the problem]

In order to solve the above problems, the optical disc substrate of the present invention (
1) Using a resin consisting of 70 to 95% aromatic polyester and 5 to 30% by weight of polyol/fin, irradiation is performed after molding. (2) The polyolefin has molecules [1000 to 1
Using low molecular weight polyolefin of 00fIO, (3)
It is characterized in that the radiation irradiation is carried out in a vacuum and by heating to around the melting point of the polyolefin. The proportion (content) of the polyolefin used in the invention is 5 to 30% by weight, preferably 10 to 200 to 20% by weight. If the content is less than 5%, the effect of improving fluidity is small, resulting in large birefringence and unstable group formation. If it exceeds 30%, both the heat deformation temperature and the brightness decrease, so the effect of the present invention is small. The molecular migration of the polyolefin is 1000 to 1°000, preferably 2000 = 5000.

If the molecular weight is less than 1,000, the heat distortion temperature is low (if it exceeds 10,000, there is little effect on improving fluidity and the birefringence is large and the formation of groups is unfortunate.There is a conflict between the polyolefin content and the size of the molecular weight. Therefore, the optimal point differs depending on the combination.If 1 contains polyolefin and is not subjected to radiation treatment, the heat distortion temperature will be significantly lower and the birefringence will also increase.By the way, if only aromatic y +) ester does not contain polyolefin, When irradiated with radiation, the heat distortion temperature tends to be lower than before irradiation. When radiation irradiation is performed in air, oxygen is diffused and absorbed and the main chain is severed due to oxidation, so it is preferable to perform radiation irradiation in vacuum or in an inert gas. Furthermore, heating at a temperature near the melting point of the polyolefin improves the crosslinking efficiency of the polymer, which is preferable.

〔Example〕

The present invention will be explained below with reference to Examples.

Example-1 The aromatic polyester shown in formula (1) with a viscosity average molecular weight of 25,000 to 40,000 and low molecular weight polyethylene were
Pellets were obtained by heating and kneading under the conditions shown in the table.

Next, using an injection molding machine, the pellets are molded into a cylinder at a temperature of 2.
90υ～,! Molded under the conditions of +40'O, injection pressure of 200ν/d, and mold temperature of 40℃ to 120℃ to φ120? +
-71L 1.2 mm thick optical disc substrate and thermal deformation temperature
A test piece for measuring light transmittance was obtained. Next, these molded products were heated to 90° C. to 110° C. in an atmosphere with a vacuum degree of 2Xi O””-5×10” TOrr, and then irradiated with an electron beam of 20 to 70 Mrad using an electron beam accelerator.

Table 1 (Here, the lowercase letters in the resin abbreviations indicate polyethylene, and the uppercase letters indicate polypropylene.) Example 2 Low molecular weight polypropylene was used as the polyolefin resin, and the aromatic polyester resin shown in formula (2) was used. Using resin, kneading and injection molding were performed under the same conditions as in Example 1. In addition, the viscosity average molecular weight of the aromatic polyester used here was 3
It is 0000.

-O-o-0- (2) Next, the 12 Mrad molded product was irradiated with gamma rays using Cobalt 30 in an atmosphere with a degree of vacuum of 2 x 10-'TOrr. Since polypropylene is used here, the molded product is not heated during r-ray irradiation.Example-1 and Example-2
A molded article (sample) was evaluated under the following conditions.

Heat distortion temperature: ASTM D-648 Light transmittance: ASTM D-1003 (633 lumens) Birefringence: Ellipsometer single pass (63
3n yL) The value of birefringence here is the highest value within the usage range of the substrate.

The measurement results are shown in Tables 2 and 3. Table 2 is Example 1
．． Table 3 is Example 2. Comparative examples (Table 4) include polymethyl methacrylate (comparative example 1), polystyrene (comparative example 2), polycarbonate (comparative example 3), 9 without radiation irradiation (comparative example 4), and irradiation in the air. (Comparative Example 5) and one in which the molded article was not heated during radiation irradiation (Comparative Example 6: room temperature, vacuum). Comparative Examples 4 to 6 use the b-s resins shown in Table 1.

As can be seen from the table, Example 1. Both Example 2 and this Example have a high heat deformation temperature, excellent transparency, and low birefringence. In contrast, polymethyl methacrylate has a low heat distortion temperature. Zarystyrene has poor heat distortion temperature and birefringence, while polycarbonate has high birefringence.

In addition, in the case of a mixed system of aromatic polyester and polyolefin, the heat distortion temperature will decrease unless radiation is applied.

Both birefringence is inferior. Even if the fluidity is improved and the generation of internal stress is suppressed, the birefringence tends to be small but large because the polyolefin used is of a crystalline type. This crystallinity depends on the polyolefin content and may not be exhibited if the polyolefin content is small.

! Even if it exhibits crystallinity, it disappears upon irradiation with radiation. Furthermore, when irradiation with radiation is performed in air, the heat distortion temperature is higher than when irradiation is not performed, but lower than when irradiation is performed in vacuum, and the heating of the molded product is similarly lower when irradiation is not performed.

Table 2 [Effects of the Invention] As described above, according to the present invention, it is possible to obtain an optical disk substrate that has excellent heat resistance represented by heat distortion temperature, excellent transparency, and low birefringence.

that's all

Claims (3)

[Claims] (1) An optical disc substrate characterized in that it is molded using a resin consisting of 70 to 95% by weight of aromatic polyester and 5 to 30% by weight of polyolefin and then irradiated with radiation. (2) The optical disc substrate according to claim 1, wherein the polyolefin is a low molecular weight polyolefin having a molecular weight of 1,000 to 10,000. (3) The optical disc substrate according to claim 1, wherein the radiation irradiation is performed in a vacuum and by heating near the melting point of the low molecular weight polyolefin.