JPS63275654A - Optical disc - Google Patents

Abstract

PURPOSE:To obtain an optical disc free of flashes, silver streaks and voids and excellent in pit transfer and transparency, wherein the base comprises a thermoplastic transparent resin containing a polyalcohol fatty acid ester and a specified antioxidant. CONSTITUTION:An optical disc comprising a base comprising a thermoplastic resin and a reflective film or a recording film provided thereon, wherein said thermoplastic transparent resin contains at least a phenolic antioxidant {e.g., tetrakis [ methylene( 3,5-di-tert-butyl-4-hydroxyphenyl )propionate ] methane}, a polyalcohol fatty acid ester formed by esterifying part of the alcoholic hydrox yl groups of an at least trihydric polyalcohol (e.g., partially esterified glycerol). Said optical disc is freed of flashes, silver streaks or voids, good in pit transfer, excellent in transparency, good in adhesion to a recording film or a reflective film and further has advantages such as a low possibility of being adversely affected by dust in reproduction because of difficult adhesion of dust to its surface.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical disc using a plastic substrate.

[Conventional technology]

Optical discs are read-only optical discs and writeable discs in which a reflective film made of metal is formed on a disc substrate that has been provided with irregularities corresponding to information signals in advance, and a laser beam is scanned along the irregularities to read and reproduce changes in the reflected light. Alternatively, there are rewritable optical discs. The latter type of writable or rewritable optical disks is further divided into three types: hole-forming type, phase change type, and magneto-optical type. The hole-forming type is a type in which a recording layer made of a thin metal or organic film is irradiated with a laser beam, and holes are created in the recording layer by the heat of the beam.
A number of ancient Te-based recording layers have been developed. In phase-change type recording layers, when the temperature rises due to laser beam irradiation and the temperature rises above a characteristic transition temperature, the area becomes amorphous. →It takes advantage of the property that the reflectance changes by causing a change in crystal structure, such as TeOx and 5n-Te-S.
e has been proposed as the recording layer. The magneto-optical type irradiates a perpendicularly magnetized film with a laser beam and heats it above the compensation temperature of the film-forming material or the Curie temperature to cause magnetization reversal, and utilizes magneto-optical phenomena such as the Kerr effect or Faraday effect. A rare earth element-transition metal amorphous alloy film such as Tb-Fe has been proposed as a recording layer.

By the way, glass, metal, thermosetting resin, and thermoplastic resin have been proposed as substrate raw materials for these optical disks. Among these, glass is heavy and brittle, has poor impact resistance, and is not suitable for mass production of substrates.

Metals and thermosetting resins also have poor mass production. On the other hand, thermoplastic resins can be mass-produced by injection molding, are lightweight, and have impact resistance, so they have the best conditions among these materials for optical disk substrates.

[Problems with conventional technology]

However, even if thermoplastic resin is applied to the substrate of an optical disk, various problems actually occur.

For example, transparent thermoplastic resins such as polymethyl methacrylate (PMM^), which can be used for optical disk substrates,
Polycarbonate (PC), poly4 methylpentene 1
(PMI') and the like have high viscosity, and therefore, during injection molding, it is necessary to raise the resin temperature to lower the viscosity and improve fluidity.

However, optical disk substrates with a large projected area (but thin thickness) have a small amount of resin, so the residence time of the resin in the injection molding machine is longer.Also, in the mold, the resin passes through thin areas at high speed. As a result, mechanical shear heat is likely to occur.In this way, resins that remain at high temperatures due to external heating for a long time and also experience internal heating such as shear heat naturally decompose and deteriorate, resulting in There are problems in that the mechanical strength of the product is weakened, scorch inclusions occur, and the product cannot be used as an optical disk substrate.

Another problem is the fact that manufactured disk substrates often have small voids. Although it can be accepted that this phenomenon applies to injection molding in general, methods such as pre-drying the material resin or adding air vents to the mold, which have been considered effective in solving this type of problem, cannot achieve the low flow rate described above. The production of disk substrates by high-temperature injection molding using plastic resins is insufficient.

Another problem is that the pits and guide grooves of the disk are not accurately transferred from the stamper to the disk substrate.

Yet another problem is that a phenomenon called flash may occur on or inside the disk substrate. Here, flash is a phenomenon that produces irregularly shaped clouds along the radial direction of the disk, and is a completely different phenomenon from silver streaks, which have a relatively clear striped shape.

Although such a phenomenon may not be much of a problem with ordinary molded products, it must never occur in applications such as optical disk substrates. This phenomenon often occurs even after sufficient time has been taken to pre-dry the material resin, which is said to be effective in preventing, for example, common silver streaks, and is a source of headache for those skilled in the art.

Yet another problem is that the transparent substrate obtained by molding becomes yellow (colored).

Still another problem is that if a recording film is formed on a substrate to form an optical disc and then left for a long period of time under high temperature and high humidity conditions, the area will be extremely small and can only be seen with a microscope. There is a problem in that the recording film partially peels off from the substrate.

[Problem that the invention seeks to solve]

In view of the current situation, the present inventors have discovered that by using a specific antioxidant and a specific compound in combination, it is possible to prevent thermal deterioration during substrate molding of the thermoplastic resin that makes up the optical disk, and also prevent voids, flash, and silver streaks. The inventors have discovered that the transferability is good, there is no coloration, and partial peeling of the recording film can be prevented, and the present invention has been achieved.

[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 transparent thermoplastic resin, in which the transparent thermoplastic resin contains a small amount (both 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 aliphatic ester in which a part of the polyhydric alcohol hydroxyl group having a valence of 3 or more is esterified.

[For production]

As the transparent thermoplastic resin, the above-mentioned PMMA and PC are used.
, In addition to PMP, polystyrene (PS), or hydrogenated ring-opening polymers of tetracyclododecenes or ring-opening copolymers with norbornenes as shown in JP-A-60-26024, In addition, copolymers of ethylene and cyclic olefins such as norbornene, tetracyclododecene, and methyltetracyclododecene (for example,
0-168708, 61-115912 61-1
15916, 6l-120816), etc.

Transparent thermoplastic resins that are particularly useful in the present invention are those with relatively high glass transition temperatures (Tg) of about 100
℃ or higher, especially 120"C or higher. In other words, if the Tg is high, the temperature of the resin surface that comes into contact with the mold when it flows into the mold during injection molding decreases, and the surface hardens relatively quickly. For this reason, it is assumed that volatile components, etc., which are presumed to be due to oxidative deterioration of the resin, are trapped inside the resin and cause the flash mentioned above.In other words, the higher the Tg, the faster the surface solidification occurs. Therefore, applying the present invention to such resins is useful because flash can be prevented.

Therefore, the resin preferably used is a copolymer of ethylene and cyclic olefin.

To explain the ethylene/cyclic olefin copolymer in more detail, the copolymer is obtained by copolymerizing ethylene and a cyclic olefin monomer represented by the following formula (1). Among them, the cyclic olefin monomer has a structure substantially represented by formula (2).

(In the formula, R1 to RI2 are hydrogen, an alkyl group, or a halogen, and may be the same or different, and R9 or RIG and R or RI2 may mutually form a ring. n is 0 or an integer of 1 or more, and when R5-R6 is repeated multiple times, they may be the same or different.) Ethylene/cyclic olefin copolymer particularly suitable for forming the substrate of an optical disk. As for the coalescence, the ethylene content is 50 to 90 mol% based on the total number of moles of ethylene and cyclic olefin, and in the above formula, even if it is the n-1 cyclic olefin, R1 to R12 are hydrogen. Preferred is a copolymer of

In addition, although it is possible to use only one type of ethylene/cyclic olefin copolymer alone, it is also possible to use ethylene/cyclic olefin copolymers of different types, that is, those with different types of cyclic olefin monomers or with different ethylene contents. A mixture of a plurality of them may be used. Furthermore, other copolymerizable monomer components may be copolymerized in amounts that do not impair its properties.

Phenol antioxidants, when added to thermoplastic transparent resins, not only provide heat resistance stability during substrate molding, but also provide an appearance that is sufficient for use as optical disk substrates, i.e. It reduces voids, silver streaks, and flash, and also stabilizes the hue to some extent. Of course, the pit transferability is also improved.

Such phenolic antioxidants include, for example, tetrakis[methylene(3,5-di-tert-butyl-4-hydroxyphenyl)propionate comethane,
β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid alkyl ester or 2.
2'-oxamidobis(ethyl-3-(3,5-di-t)
er t-butyl-4-hydroxyphenyl)propionate] and the like. β-(3,5-di-ter
As the t-butyl-4-hydroxyphenyl)propionic acid alkyl ester, an alkyl ester having 18 or less carbon atoms is particularly preferred.

Fatty acid esters of trihydric or higher polyhydric alcohols can significantly prevent coloring when used in combination with the phenolic antioxidant, and provide uncolored transparent substrates, which are important as optical disk substrates. Furthermore, the present invention provides an optical disc that prevents partial peeling of a recording film provided on a substrate under high temperature and high humidity conditions, and has excellent dust adhesion prevention properties.

As the fatty acid ester of a trihydric or higher polyhydric alcohol, one in which a part of the alcoholic hydroxyl group is esterified is used. Therefore, some specific examples of polyhydric alcohol fatty acid esters used include glycerin monostearate,
Glycerin fatty acid esters such as glycerin monolaurate, glycerin monomyristate, glycerin monopalmitate, glycerin distearate, glycerin dilaurate, pentaerythritol monostearate, pentaerythritol monolaurate, pentaerythritol distearate, pentaerythritol dilaurate, Examples include fatty acid esters of pentaerythritol such as 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, and more preferably 0.1 to 1 part by weight based on 100 parts by weight of the resin. and the fatty acid ester of polyhydric alcohol is 0.01 to 10 parts by weight, preferably 0.05 to 3 parts by weight.
Parts by weight.

It should be noted that the range of the compounding amount of the above compound is such that if it is too large, the initial physical properties of the optical disk substrate may not be maintained stably over a long period of time, and if it is too small, the desired effect of the present invention may not be achieved. This was set because even if it were to occur, it would not be effective enough to endure in practical terms.

In the present invention, a phosphorus stabilizer, a sulfur stabilizer, a light absorber, a hindered amine weathering stabilizer, etc. may be further added as necessary.

Furthermore, when using a transparent resin made with a halogen-containing catalyst such as Ziegler's catalyst, it is necessary to use fatty acid metal salts to prevent the halogen contained in the remaining catalyst residue from damaging the molding machine. A halogen scavenger should be used in combination.

To manufacture an optical disk substrate, first, resin and the above compounds,
If necessary, it may be mixed with other stabilizers in an amount that does not impair the effects of the present invention using a ribbon blender, tumbler blender, Henschel mixer, etc., or after mixing, it may be melt-mixed using an extruder, Banbury mixer 1/2 roll, etc. Dissolved in hydrocarbon or aromatic solvent and mixed into polymer solution, then single screw extruder, bent two extruder, double screw extruder,
Three-screw extruder, conical two-screw extruder,
Injection molding is performed using a co-kneader, plateifier, mixtruder, twin-screw conical screw extruder, planetary screw extruder, gear type extruder, screwless extruder, etc., and a mold for disc molding (information pit or (including those equipped with a stub bar for forming guide grooves).

Various known gates may be used for injection molding, but in view of shrinkage and warping, center bin gates, center disc gates, and preferably gate diameters of 3.
Center pin gate of mm or less, especially 0.5 to 2.0 mm, gate thickness ILIII11 or less, especially 0.2 to 0
．． It is better to use an 8mm center disc gate.

On the optical disk substrate obtained by injection molding, a recording layer or a metal layer for reflecting laser beams is then formed by a known method such as vapor deposition or sputtering, and a protective layer or an enhancement layer is further provided as necessary. completed.

As a metal reflective layer formed by fusion bonding, A! is typical, and Te-C185- is a typical hole-forming recording layer.
Te-5e, Te-5e-C system, T as phase change type
e0xXSn-Te-Ses Te7Sb-Ge, 5
b-Se /B1-Te system, magneto-optical type Tb-Fe,
, Tb-Fe-Co, Nb-Dy-Fe.

Nb-Dy-Fe-Co, Nb-Dy-CoXPt
-Tb-Fe-Co type etc. are typically used. However, there is no problem even if reflective layers and recording layers other than those exemplified here are applied.

〔Example〕

The content of the present invention will be illustrated below using preferred examples, but the present invention is not limited to these examples unless otherwise specified.

Examples 1-2 Melt flow rate 1- (MFR: ASTM D 1238) at a load of 2.15 kg and a temperature of 260°C is 3
Tetrakis [
Methylene-3-(3,5-di-tert-butyl-4
-Hydroxyphenyl)propionate comethane (A)
, glycerin monostearate (B) and zinc stearate (C) are blended, and after mixing with a Henschel mixer,
230℃ using a twin-screw extruder with a screw diameter of 40mm
Pellets were made at a temperature of

Using this pellet as a raw material, using a Jujuki P40/25A injection molding machine and a center disk gate mold (a mold equipped with a stub bar for forming information pits), it was molded at a temperature of 280°C to a diameter of 80 mm and a thickness. A disk substrate of No. 1.01 was molded, and the items shown in Table 1 (voids, silver streaks, flash, bit transferability) were evaluated. Note that these items were evaluated visually, and the evaluation criteria were 1 to 5 good.

In addition, the disk plate obtained in this way was used as Freon T.
After ultrasonic cleaning with E (manufactured by Mitsui DuPont Fluorochemical), Si:+ was applied as an information recording film by sputtering.
A 3-layer film of Na/TbFeCo/5iJ4 (no pretreatment such as press sputtering, film thickness: 500 layers for each layer) was formed. The film formation condition observed under a microscope was good. The 80mmφ disc plate with the film obtained above was heated at a humidity of 85%.
, and left in a constant temperature and humidity chamber at a temperature of 60° C. for 48 hours. When the state of the film after the test was observed under a microscope, there was no change in the appearance of the recording film compared to before the test, and the density of the film was also good.

The amount of the stabilizer is expressed in parts by weight based on 100 parts by weight of the raw material resin.

Example 3 The same procedure as in Example 1 was carried out except that pentaerythritol distearate (D) was used instead of (B).

Comparative Example 1 The same procedure as Example 1 was carried out except that (B) was not used. As a result of observing the film surface after the environmental test using a microscope, as shown in Table 1, peeling of the recording film was observed in areas where foreign matter was present near the substrate surface and in areas where liquid dripped during substrate cleaning.

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

Comparative Example 3 Comparative example 3 was carried out in the same manner as in Example 1 except that glycerin tristearate (F) in which all of the alcoholic hydroxyl groups were esterified was used instead of (B).

Comparative example 4 The same procedure as in Example 1 was carried out except that (A) was not used.

〔Effect of the invention〕

The optical disc of the present invention has no flash, silver streak, or void, has good pit transferability, has excellent transparency, and has good adhesion to the recording film and reflective film. Since it does not adhere to the surface, there is less possibility that dust will cause an adverse effect during playback.

Claims (4)

[Claims] (1) In an optical disc in which a reflective film or a recording film is provided on a substrate made of a transparent thermoplastic resin, the transparent thermoplastic resin contains at least a phenolic antioxidant and a fatty acid ester of a polyhydric alcohol. ,
An optical disc characterized in that the polyhydric alcohol fatty acid ester is a polyhydric alcohol fatty acid ester in which a part of the alcoholic hydroxyl groups of a trihydric alcohol or more is esterified. (2) The optical disc 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) Phenolic antioxidants include tetrakis[methylene(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]methane, β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate,
ert-butyl-4-hydroxyphenyl)propionic acid alkyl ester and 2,2'-oxamide bis[
The optical disc according to claim 1 or 2, wherein the optical disc is selected from ethyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate. (4) The optical disc according to any one of claims 1 to 3, wherein the fatty acid ester of a polyhydric alcohol is obtained by esterifying a portion of glycerin or pentaerythritol.