JPH01290137A - Optical disk - Google Patents

Abstract

PURPOSE:To provide a disk substrate which is economically advantageous in cost, has excellent moldability in injection molding, decreases double refractions and is less cambered under high humidity after formation of a reflecting film on one face by using a copolymerized polymer of methyl methacrylate and styrene as the material of the disk substrate. CONSTITUTION:The disk substrate on which information pits are recorded is formed of the copolymerized resin of the methyl methacrylate (MMA) and styrene. This disk has the good stability at the time of molding, is economically low in material cost and has excellent transparency. However, this material contains the styrene system as the copolymer component and, therefore, the bending strength is weak in terms of physical strength with the disks having >=150mm diameter, but the material has the strength sufficient for practicable use with the disk substrates such as CD-single and CDs (12mm width) which are main applications and are inexpensively mass-produced. The optical disk which has the excellent moldability, decreases the double refractions, particularly decreases the camber of the disk formed with the reflecting film on one face and is extremely advantageous in cost is thereby obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to an optical disc on which information is recorded.

<Prior art and its problems> Conventionally, polycarbonate has been used as the base material of optical discs on which information is recorded in advance, such as compact discs (CDs).

In other words, polycarbonate has good transparency and does not warp even under high temperatures, so it is used for discs such as CDs, which have information pits formed on only one side and are coated with an aluminum vapor-deposited reflective film.

Next, polymethyl methacrylate, which is used as a base material for laser discs with information stored on both sides, has less birefringence than polycarbonate during disc molding and has good fluidity, so it can be used for large optical discs with a diameter of 300III11. It is used.

However, a disk made of acrylic as a base material, aluminum vapor-deposited on one side, and then coated with a protective coating will not work well in a high-temperature atmosphere.
The acrylic polymer (P?1MA) absorbs moisture from the reading surface side, and the reflective film surface is less likely to absorb moisture, so the disc is likely to warp.

In addition, in order to deal with this warping in discs with information pits transferred using polymethyl methacrylate (PMMA), after depositing an aluminum reflective film on the information pit side and applying a protective coating, a protective coating is applied to both sides of the reading area. There are methods such as sputtering of an inorganic material such as a moisture barrier, and thin film coating of vinylidene chloride, epoxy, UV-curable acrylic resin, etc.

However, this method is not suitable for C
Compared to the manufacturing process of D, there is a problem in terms of price reduction because the number of steps is increased and the cost is high.

Therefore, polycarbonate is currently used for small discs such as CDs with a diameter of 150 cm or less.

Since 8-polycarbonate is synthesized by polycondensation of bisphenol A and phosgene, it has higher material cost and higher melt viscosity than radical polymerization polymers.Moreover, the melt viscosity has a high temperature dependence, and the solidification rate is fast. For this reason, a method of duplicating disks by injection molding has conventionally been used as a method of manufacturing a large quantity of optical disk substrates, but this method has the disadvantage that bibending bonding tends to occur due to the characteristics of the PC material.

<Means for Solving the Problems> The present invention has been made in view of the above-mentioned current situation, and by using a copolymer of methyl methacrylate and styrene as the material of the disk substrate, the above-mentioned problems can be solved. It is an object of the present invention to provide an optical disk that has an economically advantageous disk substrate cost, has excellent moldability in injection molding, has little birefringence, and has little warpage at high temperatures after forming a reflective film on one side.

<Cloud fJ Pi example> The optical disc of the present invention has information pits formed on the disc substrate, and aluminum (1000 people) is formed on the information pit surface.
A reflective film such as the above is formed as a single layer or by sputtering, and an acrylic ultraviolet curing resin is protectively coated on the reflective film by spin coating.

The disk substrate on which the information pits are recorded is made of a copolymer resin of methyl methacrylate (?1MA) and styrene.

This disc has good stability during molding, low economical material cost, and excellent transparency, so it is expected that CD-singles with a diameter of 80 mm and 1-diameter discs will be manufactured in large quantities in the future.
Suitable as a material for CD in 20 m.

However, since this material contains styrene as a copolymer component, its physical strength is weak for discs with a diameter of 150 m or more, but it is not suitable for large quantities of CD-singles and CDs (120 yen), which are the main applications mentioned above. Disk substrates manufactured at low cost have sufficient strength for practical use, so they are highly effective as disk substrate materials.

Here, as shown in Table 1 (conventional polycarbonate).

The results of performance experiments on polymethyl acrylate and the methyl methacrylate-styrene copolymer according to the present invention are shown.

That is, the optical disc made of the methylmethacrylate-styrene copolymer according to the present invention has birefringence and moldability of 1.
It has stable performance in terms of warpage and transparency.

Table 1 *1 High temperature (40”C9
0%) warping after 7 pow seek.

*2 Can be covered by molding conditions.

*3 Due to the nature of the substrate, it is not possible to use a single-sided information pit transfer substrate/aluminum reflective film/protective sheet structure → Possible to use other physical methods (add more steps to prevent warping or laminate the disks together) <Effects> As described above, the present invention provides an optical disk which has excellent moldability, has little birefringence, and especially has little warpage in a disk formed with a reflective film on one side, and is extremely excellent and advantageous in terms of cost.

Special permission person Toppan Printing Co., Ltd. Representative: Kazuo Suzuki

Claims (1)

[Claims] (1) Information pits are formed on the disk substrate, a reflective film such as aluminum is formed on the information pit surface by vapor deposition or sputtering, and an acrylic ultraviolet curing resin is protectively coated on the reflective film by spin coating. An optical disc characterized in that a disc substrate on which information pits are recorded is made of a copolymer resin of methyl methacrylate (MMA) and styrene.