JPH11300758A - Mold for molding optical recording disc and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the surface, which is smooth and the hardness of which is made higher and which wears little, of a mold by a method wherein the surface of the mold is mirror-polished and, at the same time, jetted with minute particle materials having the hardness more than or equal to the hardness of the finished mold so as to apply a lapping treatment to the surface part of the hardened mold. SOLUTION: In a surface heat working treatment 52, two processes such as a surface hardening treatment and a shot-peening treatment in an ordinary heat treatment are simultaneously carried out in one process. When shot-peening materials or minute particle materials becomes smaller, their jetting speeds increase and, at the same time, heat is generated on an optical disc mold as a matter to be worked, the jetted surface temperature rises in proportion to the increase of the jetting speeds, the surface temperature reaches higher than the metal transformation point of the mold, resulting in producing a quench hardening and tempering state in the mold. Accordingly, a heat treatment and a shot-peening are carried out in one process. In the lapping treatment 53 of the mold, the lapping material, the particle side of which is smaller than that of the shot-peening material, is used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mold for molding an optical recording disk and a method of manufacturing the mold.

[0002]

2. Description of the Related Art Optical recording disks for performing recording and reproduction using a laser beam are already well known for video and audio. FIG. 2 shows the principle of signal reproduction in a read-only optical disk. Information pit 1 is approximately 1.
On the 2 mm disk substrate 2 are imprinted irregular phase pits, on which a reflective film 3 of aluminum or the like is formed by a method such as vapor deposition. When reproducing information,
The laser light passes through the disk substrate 1 and irradiates the information recording surface. Then, the laser light is reflected by the reflection film 3 and returns to the opening of the lens 4. At this time, as shown in the figure, information pits (phase pits)
The laser light is diffracted by 1, and as a result, the amount of light reflected from the disk changes. By detecting this with a photodetector (not shown), a signal is reproduced.

The information pits 2 differ depending on the type of information. For example, in the case of a video disc, a video signal obtained by FM-modulating an analog signal is binarized based on a predetermined value. Since the converted analog signal is recorded, the pits have slightly different lengths and periods. In a system for directly recording a digital signal such as a compact disk, the sound level and frequency are converted into a predetermined number of "1" and "0" bits, and the "1" or "0" is processed so as not to be continuous. After performing 10-14 conversion and error correction processing for correcting errors and complementing data, the information pits are recorded as "1" and "0" information pits.

Next, a method of copying a large number of information disks will be described. As described above, the read-only disk is manufactured as a duplicate disk based on the phase pits recorded on the master disk. FIG. 3 shows a manufacturing process for a read-only disc. First, the glass disk 10 that has been subjected to optical polishing is washed and dried, and a positive photoresist 11 is uniformly applied thereto. A positive photoresist is a resist that becomes soluble when light-irradiated portions are decomposed, and a resist that becomes insoluble on the contrary is called a negative resist. The glass disk 10 coated with the photoresist 11 is placed on a turntable having an air bearing (not shown) and rotates with high precision.

A laser beam 12 such as an argon laser is applied to a photoresist 11 on the rotating glass disk 10.
By exposing the photoresist 11 to
Writing is performed. At this time, the light amount of the laser light 12 is changed by an optical modulator incorporated in an optical section, and a signal pattern having an arbitrary depth and length can be formed on the photoresist 11.

[0006] After the signal writing is completed, the photoresist 11 is dissolved in accordance with the intensity of the laser beam by a developing process using an alkaline solution, and the signal portion is formed as a concave recording 13. Next, this photoresist 1
A thin film 14 is deposited on nickel 1 by vapor deposition, and nickel plating 15 is
Form on top. Then, after plating to a predetermined thickness, the plating layer and the glass disk 10 are peeled off, and the photoresist 11 adhering to the peeled surface is removed to complete the master disk (stamper) 16 of the optical disk.

Next, a description will be given of an injection molding method for copying a large amount at low cost by using the master (stamper) manufactured as described above. FIG. 4 shows an injection molding portion in an injection molding machine for duplicating a large amount of optical disks. In the figure, reference numeral 21 denotes a fixed mold in the present embodiment. The fixed mold 21 is fixedly supported by a molding machine fixing section 23 via a mold holding member 22. The surface of the fixed mold 21 is also a side from which a signal is read, so that deformation or distortion does not occur even under pressure during molding, and further, the molded product is easily peeled off, Mirror polishing is applied to improve the quality. Reference numeral 24 denotes a movable mold on the movable side. The movable mold 24 is fixed to a molding machine via a mold holding member 25, and this mold moves back and forth during molding.
Injection of the resin material and removal of the molded product are performed. A stamper 16 is attached to and held by the movable mold 24, and a duplication optical disk is manufactured by engraving the stamper. Also, as described in the fixed mold 21, the surface of the movable mold 24 and the stamper 16
The back surface is mirror-polished for the reason described above. In this conventional example, the stamper 16 is fixedly held on the movable mold 24, but the stamper 16 may be fixedly held on the fixed mold 21.

Here, what is important in the molding dies 21 and 24 is the flatness and hardness of the surfaces of the dies, and the flatness directly affects the flatness of the optical disk. In particular, the surface of the mold 21 on the side opposite to the stamper becomes the surface of the optical disk, and the laser beam enters and exits.
This is important because it directly affects the progress of reflection, and the hardness is determined by the number of copies, and as a result, becomes a factor in determining the mold replacement time.

Reference numeral 26 denotes a sprue runner, that is, a flow path of the molding resin material. The resin material is injected into the cavity 27 through the sprue runner 26.
The cavity 27 is a space in which the molding resin material is solidified, and the shape and thickness of the disk are determined by the size of the cavity 27. As a resin material for the optical disk in this case, an acrylic resin is used for a video disk, and a polycarbonate resin or the like is used for an audio disk. Then, based on the concavities and convexities imprinted on the stamper 16, an optical disk of the same copy as that of the master (stamper) is mass-produced at low cost.

[0010]

In the conventional optical disk mold configured as described above, first, as described above, the flatness on the surface of the mold directly affects the flatness of the optical disk. In particular, on the mold that does not hold the stamper, that is, the mold on the side opposite to the stamper,
The mold itself must be precisely finished because the surface directly receives and reflects the laser light, and the planar polishing work requires a lot of time and cost. Second, the fixed side holding the stamper Alternatively, the movable mold is tensed and relaxed in the mold release direction due to expansion and contraction due to rapid heating and rapid cooling during injection, and adhesion to the molded product, and the gap between the surface of the stamper mold and the back of the stamper. Are always engaged in friction, and the stamper-side mold has a problem of abrasion resistance, in other words, durability, and therefore, in the conventional mold, compared with other molding parts, And had many problems such as short-term exchange. At the same time, the stamper itself needs to be replaced in a short period of time for the same reason as the mold, and it has been necessary to replace the stamper after molding several thousand to tens of thousands of sheets. In particular, in a conventional mold having only a polishing step, the mold hardness is extremely small, and it has been difficult to solve the above-described problems.

SUMMARY OF THE INVENTION The present invention has been made to solve such problems, and an object of the present invention is to provide a mold for an optical disk having many features such as a smooth surface, high hardness, and low wear. As a result, it has many effects such as improvement of product yield, improvement of abrasion resistance, easy cleaning of the mold, easy repair of the mold flaw, and as a result, a large number of optical discs. It is an object of the present invention to provide a mold capable of manufacturing the same.

[0012]

In order to achieve the above object, according to a first aspect of the present invention, a mold for forming an optical recording disk is provided by subjecting a surface of the mold to mirror polishing and forming a mold. By injecting a fine particle material having a hardness equal to or higher than the product hardness of the mold to the surface of the mold, the temperature near the surface is raised to a temperature equal to or higher than the metal transformation point, and the surface of the mold is cured. It is characterized in that a lapping treatment is applied to the surface of the mold thus obtained, and the effect is particularly effective when used in a mold on the stamper side. Further, the second invention is characterized by a method of manufacturing the mold, wherein in the mold for forming an optical recording disk, the surface of the mold is mirror-polished and the hardness of the product is equal to the product hardness of the mold. By injecting the above fine particle material onto the mold surface, the temperature near the surface is raised to a temperature equal to or higher than the metal transformation point, and the mold surface is cured, and a lapping process is performed on the cured mold surface. It is characterized by having been subjected to.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A method for manufacturing a mold according to the present invention will be described with reference to an embodiment shown in the drawings. FIG. 1 shows a manufacturing process of a mold according to the present invention. In the figure, reference numeral 50 denotes a mirror polishing process of a mold, and the mirror polishing process is a process for polishing the mold to a mirror surface to secure the flatness of the mold. In case (2), the flatness is lost, and in this step, polishing is performed to obtain flatness again. Reference numeral 51 denotes a surface heat processing step newly added in the present invention, and this surface heat processing enables two steps of a surface hardening treatment and a shot peening treatment in the conventional heat treatment to be performed simultaneously in one step. In the conventional mold, this step is not performed, and by adding this step, the object of the present invention can be achieved.

The method of the surface heat processing will be described below. Conventionally, in order to harden the mold surface, a heat treatment such as quenching the mold product at about 850 degrees and tempering at about 600 degrees is performed to transform the surface structure, and then air-cooled to room temperature. In general, residual stress is generated by performing shot peening. The thermal processing means in the conventional mold had to perform the heat treatment and the shot peening process separately, and required two process controls, that is, a process control involving temperature control and a shot peening process control. For this reason, the cost and time involved in these two steps have become problems. In the present invention, when the shot peening material, that is, the fine particle material, is reduced in shot peening, the ejection speed increases, and heat is generated in the optical disc mold, which is a workpiece, and the ejection surface temperature is reduced by the ejection speed. Increases as a result, the temperature reaches or exceeds the metal transformation point, and a quenched and tempered state is generated. Therefore, heating above the metal transformation point,
Shot peening and quenching and tempering are repeatedly performed on the mold surface, so that heat treatment and shot peening are performed in one process.

To further explain the method of the thermal processing, for example, when the product material is carbon steel, a steel ball (carborundum) having a particle size of about 100 to 300 μm is compressed on a mold surface together with compressed air from a nozzle by an experiment. Inject. In this case, in the case of an air type in which a steel ball (carborundum) is injected together with compressed air from a nozzle, it is possible to inject the compressed air at a speed close to the speed of sound. Also, by reducing the particle size of the steel ball (Carborundum),
It was confirmed that it became easier to get on the compressed air and the injection speed increased to about 200 m / S.

An object having a small specific heat, such as a metal, has a large temperature rise due to a small area of a temperature rising portion, but has a fast temperature drop. As the speed of the colliding substance increases, the temperature rises above the transformation point of the metal. In the observation by a microscope after corrosion of the processed product, the surface layer to be processed of the product was heated to the A3 transformation point or higher by the shot peening, and the martensitic transformation occurred, which was the same as the case where the quenching and tempering treatment was performed. A layer of a martensite structure is formed. Then, a softened layer that forms a re-tempered layer of troostite or bainite is formed at a lower portion thereof, and further, at a lower portion, a base material is present in its original state. That is, when the product is heated by shot peening and shot peening at the same time, retained austenite is transformed into martensite in the surface layer, and as a result, the surface has a tough structure with high hardness and near the lower part of the surface layer. In this case, a phenomenon similar to a kind of tempering occurs, and a bainite structure or a troostite structure is formed, and a secondary troostite structure rich in toughness is formed. This makes it possible to obtain a mold surface having high wear resistance by performing shot peening.

As the next step, a mold wrapping process 5
Do 2 Conventionally, the surface of the mold was only polished, but by performing a lapping process together with the thermal processing, that is, a particle size smaller than the size of the shot peening material in the thermal processing. By performing the lapping process using the wrapping material, a very precise flatness can be obtained.

[0018]

As described above, according to the present invention, in a mold for molding an optical recording disk, the surface of the mold is subjected to mirror polishing, and a fine particle material having a hardness equal to or higher than the product hardness of the mold is formed. By spraying onto the mold surface, the temperature near the surface is raised above the metal transformation point, and the mold surface is cured, and the cured mold surface is subjected to a lapping process. In addition, it is possible to increase the cost increase due to the management of the complicated two processes and to reduce the mold cost by extending the use time by improving the releasability. In particular, in the present invention, since the hardness of the mold is greatly improved, it is optimal to use the mold on the side that conventionally holds the stamper, that is, the mold on the stamper side. According to the invention of the present application, two problems such as flatness and hardness are improved, so that it is effective to use it for a molding die on the anti-stamper side where flatness is particularly required, not to mention durability. Becomes

In the method of manufacturing a mold for molding an optical recording disk, the surface of the mold is subjected to mirror polishing, and a fine particle material having a hardness equal to or higher than the product hardness of the mold is formed on the surface of the mold. By raising the temperature in the vicinity of the surface above the metal transformation point by spraying, and curing the mold surface portion, by performing a lapping treatment on the cured mold surface portion, by the conventional two steps Shot peening and quenching and tempering can be completed in one step, and the processing hardness can be improved, so that the conventional problems can be solved.

Further, in the stamper itself held by the mold of the present invention, since the engagement friction between the mold and the stamper is greatly reduced, no deformation distortion occurs, and The durability is improved, and the number of molded sheets is increased.

[0021]

[Brief description of the drawings]

FIG. 1 is a process chart related to a mold manufacturing process of the present invention.

FIG. 2 is an explanatory diagram of a recording / reproducing method for an optical disc.

FIG. 3 is a process chart showing a method of copying an optical disc.

FIG. 4 is a diagram illustrating a molding die and a molding machine for duplicating an optical disk.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 information pit 2 optical disk substrate 3 reflection film 4 lens 10 glass disk 11 photoresist 12 laser beam 13 concave recording 14 nickel thin film 15 nickel plating 16 stamper 21 fixed mold 22 mold holding member 23 molding machine fixing part 24 movable mold 25 Mold holding member 26 Sprul runner 27 Cavity 51 Mold mirror polishing 52 Surface heat treatment 53 Lapping

Claims (4)

[Claims] In a molding die for an optical recording disk, a surface of the molding is mirror-polished, and a fine particle material having a hardness equal to or higher than the product hardness of the molding die is jetted to the surface of the molding. By raising the temperature in the vicinity of the surface to a temperature equal to or higher than the metal transformation point, and hardening the mold surface, a lapping process is performed on the cured mold surface to form an optical recording disk. Mold. 2. The molding die for an optical recording disk according to claim 1, wherein the molding die for the optical recording disk is a die on a stamper side. 3. A molding die for an optical recording disk, wherein the surface of the die is mirror-polished and a fine particle material having a hardness equal to or higher than the product hardness of the molding die is jetted onto the surface of the molding die. By raising the temperature in the vicinity of the surface to a temperature equal to or higher than the metal transformation point, and hardening the mold surface, a lapping process is performed on the cured mold surface to form an optical recording disk. Manufacturing method of metal mold. 4. The method according to claim 3, wherein the mold for molding the optical recording disk is a mold on the stamper side.