JPH077529B2 - optical disk - Google Patents

Description

The present invention relates to an optical disk using a plastic substrate.

[Prior Art] On an optical disc, a reflective film made of metal is formed on a disk substrate having irregularities corresponding to information signals in advance, and a laser beam is scanned along the irregularities to read and reproduce changes in reflected light. There are a read-only optical disk and a writable or rewritable optical disk. The latter writable or rewritable optical disk is further classified into three types: a hole forming type, a phase change type and a magneto-optical type. The hole forming type is a type in which a recording layer made of a metal or organic thin film is irradiated with a laser beam and holes are formed in the recording layer by heat of the beam.
Many Te-based recording layers have been developed as the recording layer. The phase-change type utilizes the property that when it is cooled by exceeding the peculiar transition temperature due to the temperature rise due to laser beam irradiation, that part undergoes a structural change of the amorphous crystal and the reflectance changes. And Sn-Te-Se have been proposed as the recording layer. In the magneto-optical type, a perpendicularly magnetized film is irradiated with a laser beam and heated above the compensation temperature or the Curie temperature of the film forming material to cause magnetization reversal, and the Kerr effect or Faraday effect and the magneto-optical phenomenon are used. Amorphous alloy film of Tb-Fe and rare earth element-transition metal has been proposed as the recording layer.

By the way, glass, metal, thermosetting resin, and thermoplastic resin have been conventionally proposed as the substrate material for these optical disks. Of these, glass is heavy and brittle, has poor impact resistance, and has poor mass productivity for substrates. Metals and thermosetting resins also have poor mass productivity. On the other hand, the thermoplastic resin is excellent in quantity production by utilizing injection molding, and is lightweight and has impact resistance, so that it has optimum conditions among these materials as an optical disk substrate.

[Problems with conventional technology]

However, even if an attempt is made to apply a thermoplastic resin to a substrate of an optical disc, various problems actually occur.

For example, transparent thermoplastic resins that can be used for optical disk substrates such as polymethylmethacrylate (PMMA), polycarbonate (PC), poly-4methylpentene-1 (PMP)
In many cases, the viscosity is high, and therefore, in injection molding, the resin temperature must be raised to lower the viscosity and improve the fluidity. However, even if the projected area is large, the optical disc substrate having a small thickness has a small amount of resin, and thus the residence time of the resin in the injection molding machine becomes long. In addition, mechanical shearing is likely to occur because the material passes through a thin portion at a high speed in the mold. In this way, resins that stay for a long time under high temperature due to external heating and experience internal heating such as shearing heat will naturally decompose and deteriorate, weakening the mechanical strength of the resulting product and mixing burns. However, there is a problem in that it cannot be used as an optical disk substrate due to such problems.

Another problem is the fact that minute voids are often generated in the manufactured disk substrate. It can be said that this phenomenon can be said to be applicable to injection molding in general, but in the method of predrying the material resin and bleeding air in the mold, which has been said to be effective for solving this type of problem, the low fluidity resin described above is used. It is not sufficient to manufacture a disk substrate by high-temperature injection molding using.

Another problem is that the pit portion and the guide groove of the disk are not accurately transferred from the stamper to the disk substrate.

Yet another problem is that a phenomenon called flashing may occur on the surface or inside the disk substrate. Here, flashlash is a phenomenon that produces an irregularly shaped cloud along the radial direction of the disk, and is a phenomenon completely different from silver streak, which has a relatively clear streak shape. Although such a phenomenon may be less problematic in an ordinary molded product, it is absolutely not necessary in an application such as an optical disk substrate. This phenomenon often occurs even if it takes sufficient time to pre-dry the material resin, which is said to be effective for preventing ordinary silver streaks, and is a headache for those skilled in the art.

Still another problem is that the transparent substrate obtained by molding is colored yellow.

Still another problem is that when a recording film is formed on a substrate to form an optical disc and then left under high temperature and high humidity conditions for a long period of time, it is an extremely minute region that can be finally confirmed with a microscope. However, there is a problem that the recording film is partially peeled from the substrate.

[Problems to be solved by the invention]

In view of such a current situation, the present inventors can prevent thermal deterioration at the time of molding a substrate of a thermoplastic resin that constitutes an optical disk, and can also prevent voids, flash, and silver streaks by using a specific antioxidant together with a specific compound. They have found that they can be prevented, the transferability is good, they are not colored, and that partial peeling of the recording film can be prevented, and the present invention has been completed.

[Means for solving problems]

That is, the present invention provides an optical disc in which a reflective film or a recording film is provided on a substrate made of a thermoplastic transparent resin, wherein the thermoplastic transparent resin contains at least a phenolic antioxidant and a fatty acid ester of a polyhydric alcohol. The polyhydric alcohol fatty acid ester is a polyhydric alcohol fatty acid ester obtained by esterifying a part of the alcoholic hydroxyl groups of a trihydric or higher polyhydric alcohol.

[Work]

As the transparent thermoplastic resin, the above-mentioned PMMA, PC, PMP
In addition to polystyrene (PS), or JP-A-60-26024
Hydrogenated ring-opening copolymers of tetracyclodotecenes and norbornenes as shown in
Alternatively, copolymers of ethylene with cyclic olefins such as norbornene, tetracyclododecene, and methyltetracyclododecene (for example, JP-A-60-168708 and JP-A-61-1159).
12, 61-115916, 61-120816) and the like.

Particularly useful transparent thermoplastic resins in the present invention are those having a relatively high glass transition temperature (Tg), that is, those having a glass transition temperature (Tg) of about 100 ° C. or higher, particularly those having a temperature of 120 ° C. or higher. That is, Tg
In the case where the temperature is high, the resin temperature of the resin surface that comes into contact with the mold when flowing into the mold by injection molding decreases, and the surface solidifies relatively quickly. Therefore, volatile components that are presumed to be due to oxidative deterioration of the resin are trapped inside the resin,
It is presumed to be the cause of the flash. That is,
The higher the Tg, the faster the solidification of the surface occurs and the more the flash becomes. Therefore, when the present invention is applied to such a resin, the flash is prevented and useful. Therefore, the resin preferably used is a copolymer of ethylene and cyclic olefin.

The ethylene / cyclic olefin copolymer will be described in more detail. The copolymer was obtained by copolymerizing ethylene and a cyclic olefin monomer represented by the following formula (1). The cyclic olefin monomer therein has a structure substantially represented by the formula (2).

(Formula, R ^{1 to} R ¹² are hydrogen, an alkyl group or a halogen, which may be the same or different, and further R ⁹ or R ¹⁰ and R ¹¹
Alternatively, R ^{12 s} may form a ring with each other. n is an integer of 0 or 1 or more, and when R ^{5 to} R ⁶ are repeated a plurality of times, these may be the same or different. ) Particularly, as an ethylene / cyclic olefin copolymer suitable for constituting a substrate of an optical disk, the ethylene content is based on the total number of moles of ethylene and cyclic olefin.
A copolymer using 50 to 90 mol% of the cyclic olefins having n = 1 in the above formula and R ^{1 to} R ¹² being hydrogen is preferable. In addition, only one type of ethylene / cyclic olefin copolymer may be used alone, but different types, that is, different types of cyclic olefin monomers and ethylene / cyclic olefin copolymers with different ethylene contents may be used. A plurality of them may be mixed and used. Further, other copolymerizable monomer components which do not impair the properties thereof may be copolymerized.

The phenolic antioxidant is added to the thermoplastic transparent resin to give it heat resistance and stability during molding of the substrate, and it has an external appearance that is sufficient for use as an optical disk substrate. That is, it reduces voids, siriburst leaks, and flashes, and stabilizes the hue to some extent. Of course, the transferability of the pit is also improved.

Examples of such phenol-based antioxidants include tetrakis [methylene (3,5-di-tert-butyl-4-hydroxyphenyl) propionate] methane, β-3,5-di-tert-butyl-4- Examples thereof include hydroxyphenyl) propionic acid alkyl ester and 2,2'-oxamide bis [ethyl-3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate]. β- (3,5-di-te
As the rt-butyl-4-hydroxyphenyl) propionic acid alkyl ester, an alkyl ester having 18 or less carbon atoms is particularly preferable.

The fatty acid ester of a trihydric or higher polyhydric alcohol, when used in combination with the above-mentioned phenol-based antioxidant, significantly prevents coloring, and provides an uncolored transparent substrate which is important as an optical disc substrate. Further, the present invention provides an optical disc which is excellent in dust adhesion prevention while preventing partial peeling of a recording film provided on a substrate under high temperature and high humidity.

As the fatty acid ester of trihydric or higher polyhydric alcohol, one in which a part of the alcoholic hydroxyl group is esterified is used. Therefore, as a part of the specific examples of the polyhydric alcohol fatty acid ester used, glycerin fatty acid such as glycerin monostearate, glycerin monolaurate, glycerin monomyristate, glycerin monopalmitate, glycerin distearate, glycerin dilaurate, etc. Examples thereof include fatty acid esters of pentaerythritol such as ester, pentaerythritol monostearate, pentaerythritol monolaurate, pentaerythritol distearate, pentaerythritol dilaurate, pentaerythritol tristearate.

The blending ratio of the phenolic antioxidant to the transparent thermoplastic resin is 0.01 to 10 parts by weight, preferably 0.05 to 3 parts by weight, more preferably 0.1 to 1 part by weight, based on 100 parts by weight of the resin, and the polyhydric alcohol is used. The fatty acid ester of 0.01-10
Parts by weight, preferably 0.05 to 3 parts by weight.

If the compounding amount of the above compound is too large, the initial physical properties of the optical disk substrate cannot be stably maintained for a long time, or if it is too small, the intended effect of the present invention is exhibited. It was difficult to do, or even if it appeared, it was set because it is not effective enough to withstand practical use.

In the present invention, if necessary, a phosphorus-based stabilizer, a sulfur-based stabilizer, a light absorber, a hindered amine-based weathering stabilizer, etc. may be added. Further, when a transparent resin made of a halogen-containing catalyst such as a Ziegler catalyst is used, the halogen contained in the residual catalyst residue is represented by a fatty acid metal salt so as not to damage the molding machine. A halogen scavenger should be used in combination.

In order to manufacture an optical disk substrate, first, the resin and the above compound,
If necessary, an amount of other stabilizer that does not impair the effects of the present invention is mixed with a ribbon blender, a tumbler blender, a Hensiel mixer or the like, or after the mixture is melt-mixed with an extruder, a Banbury mixer, a twin roll, Dissolved in hydrocarbon or aromatic solvent and mixed with polymer solution, then single screw extruder, vent type extruder, twin screw extruder,
Three-screw extruder, conical two-screw extruder,
Cokneader, Plate equator, Mixtruder, Twin-screw conical screw extruder, Planetary screw extruder,
Injection molding is performed using a gear type extruder, a screwless extruder, or the like, and molding is performed using a die for disk molding (including a set of stan bars for forming information pits and guide grooves).

The gate used in the injection molding may be various known ones, but from the viewpoint of shrinkage and warpage, a center pin gate or a center disk gate, preferably a gate diameter of 3 m
It is preferable to use a center pin gate of m or less, particularly 0.5 to 2.0 mm, and a center disk gate of 1 mm or less, particularly 0.2 to 0.8 mm.

The optical disk substrate obtained by injection molding is then formed with a recording layer or a metal layer for reflecting a laser beam by a known method such as a vapor deposition method or a sputtering method, and further, if necessary, a protective layer or a protective layer. Completed with an enhancement layer.

Al is a typical metal reflective layer formed by fusion, and Te-C, As-Te-Se, Te are used as hole-forming recording layers.
-Se-C system, TeOx, Sn-Te-Se, Te-Sb-G as phase change type
e, Sb-Se / Bi-Te system, Tb-Fe, Tb-Fe-Co, Nb- for magneto-optical type
Dy-Fe, Nb-Dy-Fe-Co, Nb-Dy-Co, Pt-Tb-Fe-Co, etc. are typically used. However, there is no problem even if a reflective layer or a recording layer other than those exemplified here is applied.

〔Example〕

The contents of the present invention will be shown below by way of preferred examples, but the present invention is not limited to these examples unless otherwise specified.

Examples 1-2 Melt flow rate at a load of 2.15 kg and a temperature of 260 ° C (M
FR: ASTM D 1238) is 35kg / 10min ethylene-tetracyclododecene copolymer (ethylene content 60mol%),
Tetrakis [ethylene-3- (3,5-di-tert-butyl-4-
Hydroxyphenyl) propionate] methane (A),
Glycerin monostearate (B) and zinc stearate (C) were blended and mixed with a Henschel mixer, and then a pellet was prepared at a temperature of 230 ° C. using a twin screw extruder having a screw diameter of 40 mm.

Using this pellet as a raw material, a Sumitomo Heavy Industries P40 / 25A injection molding machine and a center disk gate mold (mold with a stamper for forming information pits) are used.
A disk substrate having a diameter of 80 mm and a thickness of 1.0 mm was formed at a temperature of ℃, and the items shown in Table 1 (void, silver streak,
Flash and pit transferability) were evaluated. In addition, these items were visually evaluated, and the evaluation standard was set as bad 1 → 5 good.

In addition, the disk plate obtained in this way was used for Freon TE.
After ultrasonic cleaning with (Mitsui-Dyupon Fluorochemical Co., Ltd.), Si ₃ N ₄ / Tb was used as an information recording film by the sputter method.
A FeCo / Si ₃ N ₄ three-layer film (without pretreatment such as press patterning, the film thickness of each layer is 500Å) was formed. The film formation condition observed by a microscope was good. 80 with membrane obtained above
Place the mmφ disk in a thermo-hygrostat at a humidity of 85% and a temperature of 60 ° C.
It was left for 48 hours. When observing the state of the film after the test with a microscope, there is no change in the appearance of the recording film compared to before the test,
Also, the density of the film was good.

The compounding amount of the stabilizer is shown in parts by weight with respect to 100 parts by weight of the raw material resin.

Example 3 Example 3 was repeated except that pentaerythritol distearate (D) was used instead of (B).

Comparative Example 1 The procedure of Example 1 was repeated except that (B) was not used. As a result of observing the surface of the film after the environmental test with a microscope, as shown in Table 1, peeling of the recording film was observed in a portion where a foreign substance was present near the surface of the substrate and in a liquid dripping portion during cleaning of the substrate.

Comparative Example 2 The procedure of Example 1 was repeated except that N, N'-di (p-hydroxyethyl) laurylamine (E) was used instead of (B).

Comparative Example 3 The procedure of Example 1 was repeated except that glycerin tristearate (F) in which all alcoholic hydroxyl groups were esterified was used instead of (B).

Comparative Example 4 The procedure of Example 1 was repeated except that (A) was not used.

[Effects of the Invention] The optical disk of the present invention can provide an optical disk having no flash, silver streaks or voids, good pit transfer property and excellent transparency, and further having good adhesion to a recording film or a reflective film, Moreover, since dust is unlikely to adhere to the surface of the optical disc, there is less possibility that dust will adversely affect reproduction.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location C08L 101/00

Claims (4)

[Claims] 1. An optical disc having a reflective film or a recording film provided on a substrate made of a thermoplastic transparent resin, wherein the thermoplastic transparent resin contains at least a phenolic antioxidant and a fatty acid ester of a polyhydric alcohol. The optical disc is characterized in that the polyhydric alcohol fatty acid ester is a polyhydric alcohol fatty acid ester in which a part of alcoholic hydroxyl groups of a polyhydric alcohol having a valence of 3 or more is esterified. 2. The optical disk according to claim 1, wherein 0.01 to 10 parts by weight of a phenolic antioxidant and 0.01 to 10 parts by weight of a fatty acid ester of a polyhydric alcohol are blended. 3. A phenolic antioxidant is tetrakis [methylene (3,5-di-tert-butyl-4-hydroxyphenyl) propionate] methane, β- (3,5-di-tert-butyl-4-). Hydroxyphenyl) propionic acid alkyl ester and 2,2'-oxamide bis [ethyl-3- (3,5
-Di-tert-butyl-4-hydroxyphenyl) propionate], the optical disc according to claim 1 or 2. 4. The optical disc according to any one of claims 1 to 3, wherein the fatty acid ester of polyhydric alcohol is obtained by esterifying a part of glycerin or pentaerythritol.