JPH0375944B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a flexible optical disk with excellent transparency, birefringence, flexibility, surface precision, and film thickness uniformity, and a method for manufacturing the same.

<Prior Art> Optical disk recording systems that allow information to be written and read using light have shown rapid development in recent years as compact, large-capacity storage devices with high areal storage density. A typical example of this method is to form a thin layer of the recording medium on a transparent substrate made of plastic, glass, etc., and after providing a protective layer on this recording medium, a laser beam narrowed to a diameter of several micrometers is applied from the substrate side. Information is written and read by irradiating light. This optical disk recording method has a large capacity,
It has features such as non-contact recording/playback, high-speed random access, and long life.

On the other hand, like the optical disk storage system, there is a flexible optical disk storage system that has been developed for future computer peripheral devices. This method can be thought of as replacing the conventional floppy disk storage method with an optical storage method, and uses an air floating flexible type disk.
The thickness of the disk substrate is kept to a few tens of micrometers.

The structure and information recording and reproducing of this flexible type disk are basically the same as those of optical disks, and the flexible substrate of this disk also has high transparency, low birefringence, and excellent mechanical properties. , characteristics comparable to those of optical disk substrates are required, such as surface precision and uniform film thickness.

<Problems to be Solved by the Invention> Conventionally, in the case of optical disk substrates, plastic substrates such as polymethyl methacrylate and polycarbonate have been put to practical use as substrates that satisfy the above characteristics. However, in the case of flexible substrates, due to manufacturing constraints that require the plastic material to be made into a thin film of several tens of micrometers, it is difficult to make flexible substrates using conventional materials and techniques such as those mentioned above.
It is difficult to satisfy the above characteristics. That is, since polymethyl methacrylate is a brittle material, it cannot withstand use in a thin film state. In addition, polycarbonate films produced using extrusion molding methods have large birefringence due to molding distortion, and even when films are produced using the solvent casting method, which is advantageous in terms of film thickness accuracy and molding distortion, polycarbonate is susceptible to the presence of solvent. It is difficult to obtain a highly transparent film because it tends to crystallize at the bottom.

Here, the solvent cast method refers to a method in which a polymer solution is poured into a suitable mold and left as is or heated to evaporate the solvent to produce a film. Furthermore, most commercially available polycarbonates are bisphenol A type, which is usually treated as amorphous plastic, but in the presence of an appropriate solvent, the molecular chains move smoothly and easily. Even if a chlorinated hydrocarbon such as methylene chloride or a good solvent such as tetrahydrofuran is used, it will easily crystallize if left at an appropriate concentration. Therefore, when a film is produced by the solvent casting method using polycarbonate having such properties, the film must pass through a concentration range where crystallization is likely to occur during the evaporation process of the solvent, which often results in a whitening phenomenon. . Of course, a certain amount of induction time is required for crystallization, so it is sufficient to pass a concentration that is easy to crystallize within this time, but if the film becomes thick, the evaporation rate It is impossible to make it faster. Therefore, the limit of the thickness of conventional polycarbonate film that can be produced by the solvent cast method is 100~
It is said to be 200μm. This is because if the film thickness exceeds this value, the film will turn white or become brittle. However, even when the film thickness is thinner than this, although the film is transparent at first glance, it is not sufficiently transparent when viewed through light passing through the film, and there are often large differences depending on the location.

On the other hand, it is necessary to form a tracking pre-groove on the surface of the flexible substrate, but even in the formation of this pre-groove, restrictions on the substrate material and manufacturing method pose a major problem. In the case of optical disk substrates, it is possible to form pregrooves using the photopolymer method (hereinafter abbreviated as 2P method), in-die extension method, etc., but in the case of flexible substrates made using conventional techniques, they are thin films and have low strength. Therefore, such a pregroove formation method cannot be adopted.

In view of the above problems, the present invention provides a flexible optical disk that has excellent transparency, birefringence, flexibility, surface precision, and uniformity of film thickness, and that allows easy formation of tracking pregrooves, and a method for manufacturing the same. The purpose is to provide.

<Means for Solving the Problems> The present inventors have conducted various studies in order to achieve the above object. In order to solve the problems of polycarbonate in the conventional solvent casting method, it is necessary to reduce the crystallinity of polycarbonate. The method of reducing the crystallinity of polycarbonate is to increase the molecular weight.
Three methods can be considered to reduce the symmetry of the molecule, including adding bulky substituents to the side chains of the molecule. As a result of examining these methods, the present inventors found that the method of (2) does not have a significant effect, and in fact, it tends to cause a film thickness called orange peel due to the increase in solution viscosity. The following general formula has Crystallization of Z-type polycarbonate (hereinafter referred to as PC-Z), which has repeating units of It has almost no elasticity and is more flexible.
Mechanical properties such as strength are also determined by the following general formula, which is formed by extrusion molding etc. It has been found that this is almost the same as films made of A-type polycarbonate (hereinafter referred to as PC-A) having repeating units of PC-A or a copolymer of PC-A and other resins.

The present invention was completed based on these findings, and the structure of the flexible optical disk is based on the PC
A PC-Z film produced by the solvent cast method using -Z, a tracking pregroove formed on one side of this PC-Z film, and a tracking pregroove formed on the pregroove formation surface of this pregrooved PC-Z film. It is characterized by having a recording layer that can be recorded using optical energy, and an optically transparent protective layer formed to cover this recording layer, and the structure of the manufacturing method is as follows:
The Z solution is injected as a casting solution into a cast mold with a free top surface, and an inert gas containing the same solvent as the solvent constituting the casting solution at a predetermined concentration is passed through the upper part of the cast mold at a predetermined speed to perform solvent casting. A film is prepared by removing the solvent in the casting solution by a method, a tracking pregroove is formed on one side of the film, and the pregroove formation surface of the pregrooved film is recordable by optical energy. A recording layer is provided, and an optically transparent protective layer is formed to cover the recording layer.

In the present invention, a PC-Z film produced by the solvent casting method using PC-Z as described above is used as the substrate of the disk. Here, as a solvent when PC-Z is used in the solvent cast method, in addition to chlorinated hydrocarbons such as methylene chloride and tetrahydrofuran, acrylonitrile, methyl acrylate, etc. can also be used. In addition, in the process of evaporating the solvent, natural evaporation takes time, and increasing the evaporation rate by increasing the temperature tends to cause _uneven film thickness and surface roughness. It is good to control. If dry N ₂ gas is used at this time, the evaporation rate may be too fast and the surface precision may deteriorate; however, in this case, use N ₂ gas containing the same solvent as the one that makes up the casting solution at an appropriate concentration. etc. may be used. By appropriately adjusting the evaporation rate of the solvent so that it evaporates at a gentle rate, local unevenness in concentration can be eliminated and a film with a uniform thickness and excellent surface condition can be produced. can do. Further, since no residual stress exists inside the film produced by such a solvent cast method, birefringence, which is a problem in ordinary polycarbonate films made by extrusion molding or the like, can be almost ignored. In addition, near the periphery of the mold, the film thickness increases due to the solvent rising up to the wall due to surface tension, but since this area is about 10 mm from the wall surface, it is sufficient to provide a margin of that amount to obtain the desired size. A film having a uniform thickness can be produced.

The PC-Z film produced in this way is
After demolding, the residual solvent may be removed using a vacuum dryer or the like. Furthermore, in order to remove the curl of the film due to molding distortion due to solvent evaporation from one side of the film, it is sandwiched between glass plates with excellent flatness and surface precision and annealed at 90°C for about 1 to 2 hours. It's good to do that.

This PC-Z film has the following characteristics.

If the film thickness is within 100 μm, the film thickness distribution can be suppressed to ± several μm.

Birefringence is almost negligible.

Surface accuracy can be controlled to about 0.01μm by surface roughness.

The strength is almost the same as that of polycarbonate A.

Further, such a PC-Z film has a feature that the tracking pregroove can be formed integrally with film forming by a solvent casting method. In this case, a solvent casting method may be performed after pouring the bisphenol Z solution onto a mold having pregrooves on its surface.

The tracking pregroove can be easily formed on this PC-Z film by other methods, such as a transfer method such as a hot press method, a roll method, or a 2P method, as explained in the examples below. . This method could not be applied to conventional acrylic resins due to their brittleness, but with the PC of the present invention,
-Z film is flexible and strong, so
This method can now be applied.

With pre-groove formed in this way
The PC-Z film is finished into a disk shape of 3.5φ, and a recording layer is provided on the pregroove surface. This recording layer is provided, for example, by forming a carbon disulfide plasma polymerized film co-deposited with tellurium to a thickness of 300 Å. Furthermore, a transparent protective layer with a thickness of several tens of micrometers is formed on this recording layer. This transparent protective layer can be formed by, for example, an oxide film using a vapor deposition method. In this way, the flexible optical disk of the present invention can be obtained.

<Example> Hereinafter, preferred examples of the present invention will be described with reference to the drawings.

First, the solvent casting method for producing the PC-Z film of the present invention will be explained. FIG. 1 is a cross-sectional view of the apparatus for carrying out this solvent casting method, in which 1 is a cast container, 2 is a cast mold, 3 is an equilibrium level adjustment table, 4 is a cast solution, 5 is a cover, and 6 is a solvent. No, 7 is a vibration isolation table. Add cast solution 4 as shown in the figure.
A cast mold 2 for forming a PC-Z film is placed on a balance adjustment table 3 and housed in a cast container 1. This cast container 1 is almost hermetically sealed by a cover 5, and has a structure in which N ₂ gas containing a predetermined concentration of solvent that has passed through the solvent in a solvent reservoir 6 flows.
Further, the solvent in the solvent reservoir 6 is the same as the solvent constituting the cast solution. Such equipment is installed on the vibration isolation table 7. Here, as the cast mold 2, a glass mold or the like having excellent surface precision and planar precision is used.

In order to produce a PC-Z film using this apparatus, first a casting solution 4 is prepared. This cast solution 4 is prepared by dissolving PC-Z in a solvent such as methylene chloride, acrylonitrile, methyl acrylate, or tetrahydrofuran to a concentration of 15 to 20%. After filling the glass mold 2 with a predetermined amount of the casting solution 4 prepared in this way, the balance adjustment table 3 is adjusted so that the surface of the casting solution 4 is kept parallel to the bottom surface of the glass mold 2, and the cover is covered. 5, the cast container 1 is sealed. Next, the N ₂ gas that has passed through the solvent 8 is allowed to flow into the cast container 1 at a predetermined rate to adjust the evaporation rate of the solvent from the cast solution 4 . At this time, if dry _N2 gas is passed through, the solvent evaporation rate will be too high and the surface precision will deteriorate, but as in this example, if the solvent is contained in an appropriate concentration,
By circulating N ₂ gas, it becomes possible to eliminate local concentration unevenness and to produce a film with an excellent surface condition and a uniform thickness.

After the PC-Z film produced in this way was released from the cast mold 2, the residual solvent was removed in a vacuum dryer, and the film was sandwiched between glass plates with excellent surface and planar precision and heated at 90°C for 1 to 30 minutes. By annealing for 2 hours, it becomes extremely transparent, has low birefringence,
A PC-Z film with excellent surface precision and film thickness uniformity was obtained.

Next, an example of forming a tracking pregroove on one side of such a PC-Z film will be explained using the following four methods.

1 Solvent cast method In this method, a tracking pregroove is
It can be produced simultaneously and integrally with the formation of the PC-Z film.

FIG. 2 shows an explanatory diagram of this method. As shown in the figure, this method may be carried out using a pre-grooved Ni stamper 9 instead of the cast mold 2 used in the solvent casting method described above. At this time, Ni stamper 9 with pregroove is
Since the thickness is about 300 μm, a stainless steel support plate 10 with a thickness of about 8 mm is attached to the back side of the pregrooved Ni stamper 9 with an adhesive to prevent its deformation. Furthermore, a leak prevention ring 11 is provided on the outer periphery of the pre-grooved Ni stamper 9 to prevent liquid leakage. The rest of the configuration is the same as that of the device shown in FIG. 1, so redundant explanation will be omitted here. According to this method, a pre-grooved PC-Z film for tracking can be directly formed by the same operation as the solvent casting method described above.

2 Hot Press Method FIG. 3 is an explanation of this method. As shown in the figure, according to this method, the PC-Z film 13 produced by the apparatus shown in FIG. Upper hot press mold 12 with stamper 9 attached
By pressing the PC-Z film 13 using a, the tracking pre-groove is formed into a PC-Z film 13.
It can be formed on the Z film 13.

Here, if the rubber pedestal 14 is not used, the transfer of the pregroove will be mottled, but by using the rubber pedestal 14, the transfer can be performed uniformly over the entire surface.

Further, there is a certain optimum value for the pressing conditions, and in this case, good transfer could be performed under the conditions of 80° C. and 50 kg/cm ² . If the temperature or pressure is high, the PC-Z film may be deformed or the pregroove may be disturbed, whereas if the temperature or pressure is low, good transfer cannot be performed.

3. Roll method FIG. 4 is an explanatory diagram of this method. As shown in the figure, in this method, pregrooved Ni
The stamper 9 is attached to the surface of the take-up roll 15, and the PC-Z film 13 produced by the apparatus shown in FIG. Then, while dropping the ultraviolet curable resin 19 uniformly onto the surface of the PC-Z film 13 from the dispenser 17, the PC-Z film 13 is
is pushed between the take-up roll 15 and the flat mold 16. At this time, the winding roll 15 and the flat mold 1
6, the ultraviolet curable resin 19 is compressed to a constant thickness by rotating the take-up roll 15.
Here, the ultra-high pressure mercury lamp 18 irradiates ultra-violet rays from the ultra-high pressure mercury lamp 18 through the holes 16a formed in the flat surface 16 to the ultra-violet curable resin 19, which has been squeezed to a certain thickness, to harden the ultra-violet curable resin 19. The pregroove is transferred to such a cured product 20, and the cured product 20 is removed from the Ni stamper 9 with the pregroove on the take-up roll 15.
By peeling it off, a PC-Z film with a tracking pregroove can be obtained.

The PC-Z film with pregrooves for tracking produced in this way was again sandwiched between glass plates and heated at 90°C for 1 to 10 minutes to prevent curling.
It is necessary to anneal for 2 hours.

4 2P method Figures 5a and 5b are explanatory diagrams of this method. As shown in both figures, in this method, first, a predetermined amount of ultraviolet curable resin 19 is dropped onto the center of a pre-grooved Ni stamper 9 with a stainless steel support plate 10 adhered to the back surface thereof, and then the first
PC-Z film 13 made with the device shown in the figure
Set up. Next, this PC-Z film 1
After the UV curable resin 19 is spread over the entire surface of the pre-grooved Ni stamper 9 by covering the glass cover 21 on the glass cover 21, the UV curable resin 19 is cured by irradiating UV rays from the glass cover 21 side. . The pre-groove has been transferred to the cured product thus cured, and the cured product is then transferred to the pre-grooved Ni stamper 9.
With pre-groove by peeling it off from
A PC-Z film can be obtained.

Next, an example will be shown in which a pre-grooved PC-Z film produced by methods (1) to (4) is made into a flexible optical disk.

This pre-grooved PC-Z film
It was formed into a disk shape of 3.5φ, and a carbon disulfide plasma polymerized film with tellurium co-deposited as a recording solvent was formed on the pregroove formation surface to a thickness of 300 Å. Furthermore, a transparent protective layer with a thickness of several tens of micrometers was provided on this recording layer to obtain a flexible optical disk.

Place the flexible optical disk prepared as above on the turntable, and then
When recording with a semiconductor laser while rotating a mm glass plate as a holding plate and rotating at 1800 rpm,
I was able to record at 4mW. Furthermore, when this recorded flexible optical disc was reproduced at 3 mW, good reproduction characteristics were obtained.

<Comparative Example> Using A type polycarbonate, a solvent cast film was produced using the apparatus shown in FIG. 1 in the same manner as in the examples. However, even if the casting conditions such as solution concentration and casting speed are adjusted, opaque areas and non-uniform film thickness due to partial crystallization occur, making it impossible to obtain a uniform transparent film. In this case, similar results were obtained even when a copolymer type polycarbonate was used, and the film properties could not be improved.

Furthermore, when a flexible optical disk is constructed using such a non-uniform film, good recording/reproducing characteristics cannot be obtained and errors occur.

<Effects of the Invention> As described above in detail with the examples, according to the present invention, Z-type polycarbonate is made into a film by the solvent cast method and used as a flexible optical disk substrate, thereby replacing conventional materials and conventional molding. It was possible to significantly improve properties such as film thickness accuracy, surface precision, transparency, birefringence, and strength, which could not be achieved using conventional methods, and even flexible plastic substrates can now be used as optical disk substrates. Become.

Further, according to the present invention, the tracking pregroove can also be directly formed integrally with the film substrate.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an embodiment of the apparatus for producing the PC-Z film of the present invention, and FIG.
FIG. 5 is an explanatory view showing an example of forming a tracking pregroove according to the present invention. In the drawing, 1 is a cast container, 2 is a cast mold,
3 is a balance adjustment table, 4 is a cast container, and 9 is a Ni stamper with a pregroove.

Claims (1)

[Claims] 1. General formula A film produced by solvent casting using polycarbonate as a repeating unit, a tracking pregroove formed on one side of the film, and a light energy provided on the pregroove forming surface of the film with the pregroove. 1. A flexible optical disc comprising: a recording layer capable of recording data; and an optically transparent protective layer formed to cover the recording layer. 2 General formula A solution of polycarbonate having repeating units is injected as a casting solution into a cast mold with a free top surface, and an inert gas containing a predetermined concentration of the same solvent as the solvent constituting the casting liquid is applied to the upper part of the cast mold at a predetermined rate. A film is prepared by removing the solvent in the casting solution by a solvent casting method, forming a tracking pregroove on one side of the film, and applying light energy to the pregroove formation surface of the pregrooved film. 1. A method for manufacturing a flexible optical disc, comprising: providing a recording layer capable of recording data by a method of manufacturing a flexible optical disk; and forming an optically transparent protective layer to cover the recording layer. 3. The method for manufacturing a flexible optical disk according to claim 2, wherein the tracking pregroove is integrally formed on the film by a solvent casting method using a Ni stamper with a pregroove as a cast type. . 4. The method for manufacturing a flexible optical disk according to claim 2, wherein the tracking pregroove is formed on the film by a hot press method using a mold equipped with a pregrooved Ni stamper. . 5. The flexible optical disk according to claim 2, wherein the tracking pregroove is formed on the film via an ultraviolet curable resin using a roll equipped with a pregrooved Ni stamper. manufacturing method. 6. The method for manufacturing a flexible optical disk according to claim 2, wherein the tracking pregroove is formed on the film by a photopolymer method using a Ni stamper with a pregroove.