JPH09306038A - Stamper for optical disk - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make the generation of a pit decentering and a double transfer in forming a substrate for an optical disk by making a contact angle of a mirror finished part with respect to water to be in the range of 80 deg.-100 deg.. SOLUTION: A positive type photoresist layer is formed on a glass substrate and it is irradiated with a laser beam. This is developed and recesses corresponding to pits and grooves are formed. Next, a metallic film is formed on the surface of the substrate by a sputtering or the like. Then, nickel, an electroformed body or the like are formed on the metallic film and these are stripped off from the photoresist layer and the glass substrate together with the metallic film to be made to be a stamper. Next, these are subjected to a surface processing to be made to be a stamper having irregular parts corresponding to pits or guiding grooves and a mirror finished part on its surface. Then, the wettability of the surface of the obtained stamper, that is, the contact angle is adjusted to be in the range of 80 deg.-100 deg.. This adjustment is performed by leaving one part of a resin protective layer in stripping off the protective layer formed on the irregular surface of the stamper.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a stamper for optical disks. More specifically, the present invention relates to a stamper for an optical disc, which is mounted in a mold at the time of molding a resin substrate for an optical disc and used to transfer information on its surface to the substrate.

[0002]

2. Description of the Related Art In recent years, optical recording media have attracted attention as large-capacity, high-speed memory media. As the optical recording medium, a read-only type optical disc (CD, CD-ROM, etc.), a recording / playback type optical disc (write-once type), recording, reproducing, erasing,
A rewritable optical disk (rewritable type) and the like are known. A resin substrate (polycarbonate resin, acrylic resin, etc.) is generally used as the substrate of these optical recording media.

From the viewpoint of productivity, these disk substrates are usually molded by injection molding or injection compression molding.
Specifically, this is performed by mounting a thin plate / annular metal stamper in a cavity formed between a fixed mold and a movable mold, and injecting molten resin into the cavity. Then, a flat disk substrate on which preformat information such as stamper signals (pits) and tracking guide grooves is transferred is molded.

[0004]

However, in the resin-made optical disk substrate obtained by molding in this manner,
There was a problem that the pit deviation of the preformat information and the double transfer of the pit occurred during the injection molding. These pit shifts and double transfer cause ID errors in optical disks (write-once type, rewritable type). Further, in the case of an optical disc of the zone recording format, there is a problem that a pit shift or double transfer occurs in place of the zone, which causes a burst error in the recording area.

The inventors of the present invention have made diligent studies on such problems at the time of molding a substrate, and as a result, pit shift and double transfer result in uneven releasability of the substrate from the stamper transferring pits and guide grooves. It turns out that there is a major cause. As a method of improving the releasability of the substrate, (1) control of the pit depth and pit shape of the stamper (2) adjustment of the type and amount of release agent added to the resin (3) release conditions (for example, Control of release air blowing condition), etc. are known, but none of them are fully satisfactory. An object of the present invention is to provide an optical disk stamper in which pit displacement and double transfer are less likely to occur during molding of an optical disk substrate.

[0006]

SUMMARY OF THE INVENTION The gist of the present invention is an optical disk stamper that is used by being mounted in a mold when an optical disk substrate is molded, and has an uneven portion and a mirror surface portion corresponding to pits or guide grooves on the surface. And a contact angle of water on the mirror surface portion with respect to water is in the range of 80 ° to 100 °.

An example of the stamper of the present invention will be described below with reference to the drawings. An optical disk stamper is usually manufactured by the following steps. First, a positive photoresist is applied to a well-polished glass substrate to a uniform thickness to form a photoresist layer. Then, laser light is applied to the pits and grooves corresponding to the photoresist layer. The portion of the photoresist layer that is irradiated with the laser light is more easily dissolved in the alkali developing solution than the non-irradiated portion. Therefore, when applying the alkali developing solution to the photoresist layer and performing development, the portion that is irradiated with the laser light is A concave portion corresponding to a pit and a groove is formed in the. After that, a metal film imparting electric conductivity is formed on the uneven surface formed on the glass substrate by sputtering or the like. Here, examples of the metal forming the metal film include silver (Ag) and nickel (Ni). Then, for example, nickel (N) is formed on the metal film by electroforming such as plating.
i) An electroformed body is formed, and this nickel (Ni) electroformed body is separated from the photoresist layer and the glass substrate together with the metal film to form a stamper.

The stamper obtained is further duplicated,
Depending on the stage of reproduction, it is sometimes called the father stamper, mother stamper, or sun stamper. Since such a stamper is attached to a mold during molding of an optical disk substrate, the contact surface with the mold, that is, the back surface of the stamper (the opposite surface of the stamper on the side where the unevenness is formed) is polished to be a flat surface. It

Generally, the back surface of the stamper is polished by using a polishing device such as lapping or polishing tape while supplying a polishing liquid. The back surface of this stamper is polished by two methods. That is, one method is to mount a nickel electroformed body on a glass substrate in a polishing apparatus, and supply a polishing liquid to the back surface of the electroformed body (the side opposite to the side where irregularities are formed). On the other hand, polishing is performed to make the surface flat, especially mirror-finished.

In another method, after separating the nickel electroformed body from the glass substrate, a resin protective layer is formed on the surface of the resulting stamper on the side where the unevenness is formed, and the back surface is polished. In this method, the protective layer is peeled off after polishing to obtain a stamper. In the present invention, the wettability of the surface of the obtained stamper, especially the contact angle with water is 80 ° to 100 °, preferably 90 °.
It is characterized in that it is in the range of up to 95 °.

The above contact angle with respect to water is an index of the wettability of the surface of the stamper, and is a value measured on the mirror surface portion of the stamper for convenience. Misalignment is likely to occur, and if it exceeds the upper limit, double transfer and pit misalignment are likely to occur. Therefore, if the contact angle of water on the stamper surface is in the range of 80 ° to 100 °, it is possible to prevent uneven release, pit shift, and double transfer.

The material of the stamper, that is, the contact angle of water on the surface of the nickel electroformed body itself is about 50 °, and the surface treatment of the stamper is performed to adjust the wettability (contact angle) within the range of the present invention. It is necessary. The surface treatment method of the stamper is not particularly limited as long as it is a treatment method falling within the above contact angle range. One method is the latter method of polishing the back surface of the stamper, that is, when forming a protective layer of resin on the uneven surface of the stamper, the resin, especially vinyl chloride-vinyl acetate copolymer (average molecular weight of 5 10,000 or less, preferably 10,000 to 40,000)
In addition, 0.1% by weight or more of fatty acids, particularly fatty acids having 5 to 18 carbon atoms, preferably fatty acids having 8 to 15 carbon atoms, such as capric acid, lauric acid, myristic acid, palmitic acid, and preferably 0.3 to 2 There is a method in which a mixture of the components by weight% is used as a protective layer, and then the back surface of the stamper is polished and then the protective layer is peeled off from the stamper to leave a part of the fatty acid on the stamper surface. The wettability of the surface is improved, and the contact angle of water on the mirror surface portion can be adjusted within the above range. As another method, a small amount of the resin used for the above-mentioned protective layer is applied to the surface of the stamper obtained by adopting the former method of polishing the back surface of the stamper (the side on which the uneven surface is formed). The wettability of the stamper surface may be improved to adjust the contact angle to water within the above range.

[0013]

【Example】

Example 1 A protective layer (vinyl chloride-vinyl acetate copolymer (average molecular weight 20,000) to which 0.3% by weight of lauric acid was added) was formed on the surface (uneven surface) of a stamper made of a nickel electroformed body, Then, after the back surface of the stamper was polished, the protective layer on the surface of the stamper was peeled off to obtain a stamper, and the contact angle of water on the mirror surface portion of the stamper surface was 95 °.

The Ni stamper is attached to the mold surfaces, and the polycarbonate molten resin material is injected into the cavity between the molds at a mold temperature of 110 ° C., and the mold clamping pressure is set to 300 kg / cm ^{2 of the} disk surface pressure. It was cooled in a state of being pressurized and held by, then returned to normal pressure, and air was supplied between the mold and the disk substrate to separate them. The obtained disk substrate (130 mmφ × 1.2 mm thickness) had good transferability of the grooves and pits of the stamper even after a large number of molding shots (35,000 times), and no mold release uneven pit deviation or double transfer was observed. I couldn't do it.

Comparative Example 1 In Example 1, as a protective layer on the surface of the stamper,
Vinyl chloride-vinyl acetate copolymer (average molecular weight 3.9
In the same manner as above, except that 3% by weight of dioctyl phthalate was added to 10,000). The contact angle of water on the mirror surface portion of the obtained stamper surface was 70 °, and a disk substrate was molded in the same manner as in Example 1 using this stamper. As a result, the obtained disk substrate had mold release unevenness from the beginning.

Comparative Example 2 In Example 1, as a protective layer on the surface of the stamper,
Vinyl chloride-vinyl acetate copolymer (average molecular weight 3.1
In the same manner as above, except that 15% by weight of silicon oil was added. The contact angle of water on the mirror surface portion of the obtained stamper was 60 °, and a disk substrate was molded in the same manner as in Example 1 using this stamper. As a result, the obtained disc substrate had remarkably uneven release from the beginning.

Comparative Example 3 The same procedure as in Example 1 was repeated except that a fluororesin film of propylene hexafluoride plasma polymerized film was used as a protective layer on the stamper surface. The contact angle of water on the mirror surface portion of the obtained stamper was 110 °, and a disk substrate was formed in the same manner as in Example 1 using this stamper. As a result, the obtained disk substrate had pit shift and double transfer from the initial stage.

[0018]

EFFECTS OF THE INVENTION By molding an optical disk substrate using the stamper of the present invention, it is possible to stably mold a substrate free from double transfer and uneven pits for a long period of time.

Claims (2)

[Claims] 1. A stamper for an optical disk, which is used by being mounted in a mold when molding an optical disk substrate, having a concave and convex portion corresponding to a pit or a guide groove and a mirror surface portion on the surface, and for the water on the mirror surface portion. An optical disk stamper having a contact angle in the range of 80 ° to 100 °. 2. The stamper for an optical disk according to claim 1, wherein the contact angle of the mirror surface with water is 80 ° to 100 ° by allowing a fatty acid having 8 to 15 carbon atoms to exist on the surface of the stamper. .