JPS6372705A - Optical disc material - Google Patents

Abstract

PURPOSE:To improve the moisture distortion resistance, heat resistance, mechanical strength, reliability, etc., of an optical disc, by using an ultrahigh-MW methyl methacrylate polymer of a viscosity-average MW in a specific range as an optical disc material. CONSTITUTION:An ultrahigh-MW methyl methacrylate polymer of a viscosity- average MW of 5X10<5>-5X10<7> and, preferably, of a water absorptivity <=0.2%, a heat distortion temperature >=150 deg.C and a total transmittance >=90% is used as an optical disc material for a base of a disc of a type which optically reads information, such as video disc. This polymer can be obtained by adding a radical polymerization initiator (e.g, benzoyl peroxide) to a vapor phase containing monomer vapor, irradiating this phase with plasma, leading the generated polymerization-initiating active species to a monomer coagulation phase and performing chain-growth polymerization of the monomer.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to optical disc materials. More specifically, the present invention relates to an optical disc material which is preferably used as a base for optically readable discs such as video discs, digital audio discs or memory discs.

(Prior Art) In recent years, so-called optical disks that read information using laser light have been attracting attention as information recording media. As shown in FIG. 1, such an optical disc normally has a recording pit group 2 sequentially arranged in a track shape on the surface of a main body 1 of a disc 11 serving as an information recording carrier, and a recording pit group 2 is formed to cover the pit group. A highly reflective metal vapor deposited film 3 and a protective coating 4 that roughly covers the metal vapor deposited film are integrated into a groove. To read information, a reading beam enters from the bottom surface of the disk substrate main body 1, passes through the disk substrate main body 1, enters the recording pit 2, and returns the reflected light modulated by the information held in the recording pit 2. This is performed by passing through the base body 1 and returning to the incident direction for detection and reproduction. In another method, the reading beam is incident from the protective coating 4 side, passes through the protective coating 4, and enters the recording pit 2.
This is also done by extracting reflected light that is incident on the recording pit 2 and modulated by the information held in the recording pit 2.

In the above-mentioned optical disc, the performance of the material that makes up the disc, especially the V1 quality that makes up the disc base body as an information recording carrier that records information as minute changes in surface conditions, that is, pits, is important for information recording. This has a significant impact on the quality of the media. The material constituting the disk base body must be transparent, have good light transmittance, and have extremely low warpage and birefringence.

Currently, polymethyl methacrylate and polycarbonate are mainly used as materials for forming the disk base body. Polymethyl methacrylate is a material with excellent transparency, durability, and scratch resistance, but it is highly hygroscopic and absorbs moisture, causing changes in size and shape and warping. For this reason, attempts have been made to improve the hygroscopicity by changing the type and amount of (meth)acrylic acid ester, but this has not yet been put to practical use. On the other hand, polycarbonate has excellent heat resistance and impact resistance, and has low moisture absorption, but it is more prone to birefringence than (meth)acrylic resins such as polymethyl methacrylate, and it also has problems in terms of molding processing, surface hardness, etc. However, problems remain.

Furthermore, the use of other light-transmitting resins such as rigid polyvinyl chloride and polystyrene is being considered, but rigid polyvinyl chloride is inexpensive and has excellent moisture resistance, but is inferior in durability, heat resistance, and moldability. Polystyrene is not very suitable as a disc material, and although polystyrene is excellent in terms of moldability and cost, it is also unsuitable as a disc material because it is an interference film and has large birefringence. there were.

(Problems to be Solved by the Invention) As described above, a material that is fully satisfactory for forming the disk base body of an optical disk has not yet been obtained. Therefore, it has high transparency, optical properties such as birefringence are within certain limits, and has good moldability for accurately transferring recording pitches from the mold. It is desired to develop materials that are excellent in all of the required performances such as mechanical strength, heat resistance, resistance to moisture absorption and deformation, surface hardness, and durability.

It is therefore an object of the present invention to provide a new optical disc material. The present invention also provides an lf of an optical disc.
It is an object of the present invention to provide an optical disc material preferably used as i. A further object of the present invention is to provide a (meth)acrylic resin-based optical disc material with improved moisture absorption deformation resistance, heat resistance, mechanical strength, etc.

(Means for solving the problem) The above-mentioned development purpose is to
This is accomplished with an optical disc material made of methyl methacrylate polymer.

The present invention also has a water absorption rate of 0.2% or less, a heat ☆ humidity temperature of 1
This indicates an optical disc material having a temperature of 50° C. or higher and a total light transmittance of 90% or higher.

The present invention generally provides an optical disc in which the methyl methacrylate polymer is a copolymer with a (meth)acrylic acid ester, (meth)acrylic acid, or (meth)acrylamide whose main component is methyl methacrylate. Indicates the material. The present invention also provides that the methyl methacrylate polymer
By allowing a radical polymerization initiator to exist in a gas phase containing monomer vapor, and irradiating plasma into this gas phase, the generated polymerization initiating active species are guided to the monomer solidification phase to perform chain growth polymerization of the monomers. The resulting optical disc material is shown.

(Function) Therefore, unlike the conventionally used general-purpose methyl methacrylate polymer having an average molecular weight of 104, the optical disc material according to the present invention has a viscosity average molecular weight of 5×105 to 5× Since it is an ultra-high molecular weight methyl methacrylate polymer with a molecular weight of about 107, it has excellent transparency, durability, and is similar to or better than general-purpose methyl methacrylate polymers.
It has low birefringence, as well as heat resistance, moisture absorption deformation resistance,
It has extremely excellent performance in terms of surface hardness and mechanical strength such as tensile strength and impact strength, making it extremely preferable as a material constituting the base body of an optical disc.

The ultra-high molecular weight methyl methacrylate polymer, which is the optical disc material according to the present invention, can be obtained by a plasma-initiated polymerization method, and in particular,
It can be obtained easily and in high yield by the plasma-initiated polymerization method (Japanese Patent Application No. 60-22.001) using a radical polymerization initiator. That is, plasma is irradiated into a gas phase containing monomer vapor to generate A plasma-initiated polymerization method in which a radical polymerization initiator is present at least in the gas phase in a plasma-initiated polymerization method in which a polymerization-initiating active species is introduced into a coagulation phase of monomers to perform chain growth polymerization of monomers. Viscosity average molecule u5×105 by
-5x107 methyl methacrylate polymer can be obtained easily and in high yield.

In addition, in this specification, "methyl methacrylate polymer"
The term does not mean only methyl methacrylate homopolymer, but also refers to co-polymerization with other (meth)acrylic esters, (meth)acrylic acid, or (meth)acrylamide whose main component is methyl methacrylate. It also includes polymers.

Hereinafter, the present invention will be explained in more detail based on embodiments.

The optical disc material of the present invention preferably has a viscosity Iff average molecular weight of 5 x 105 to 5 x 107, more preferably 5 x 10B to 5 x 107, particularly preferably 1 x 10
It consists of a 7 to 2 x 107 methyl methacrylate polymer. In this way, the viscosity average molecular weight is 5 x 105~5
×107, which is an ultra-high molecular weight V, so the average molecular weight is 10
It has excellent transparency, durability, and low birefringence comparable to or better than that of general-purpose methyl methacrylate polymers of the order of 4. At the same time, it has excellent heat resistance, moisture absorption deformation resistance, surface hardness, tensile strength, and impact resistance. It also has extremely excellent performance in terms of mechanical strength such as strength. If the viscosity average molecular weight is less than 5 x 105, such ultra-high molecular weight properties will not be sufficient; on the other hand, if the viscosity average molecular weight is less than 5 x 10
If it exceeds 20%, it becomes difficult to perform molding process that involves melting and hardening.

In particular, in the optical disc material of the present invention, the water absorption rate is 0.
．． 2% or less, the thermal deformation temperature is 150°C or more, and the total light transmittance is 90% or more, which guarantees long-term reliability of recording and reading by the optical system when forming the disk base body of an optical disk. This is a desirable characteristic in order to maintain a high level of performance.

As the ultra-high molecular weight methyl methacrylate polymer which is the optical disc material of the present invention, in addition to methyl methacrylate homopolymer, polymers containing methyl methacrylate as a main component and other copolymerizable polymers can be used. Contains polymers. Other copolymerizable polymers include, for example, methacrylic esters such as ethyl methacrylate and in-butyl methacrylate, acrylic esters such as ethyl acrylate and n-butyl acrylate, methacrylic acid, acrylic acid, and methacrylic acid. Examples include amide and acrylamide.

Such an ultra-high molecular weight methyl methacrylate polymer can be easily obtained in high yield by a plasma initiation method using a radical polymerization initiator.

In other words, a radical polymerization initiator is made to exist in a gas phase containing the above-mentioned vapor, and plasma is irradiated into this gas phase, and the generated polymerization initiating active species are transferred to the monomer solidification phase. An ultra-high molecular weight methyl methacrylate polymer is obtained by conducting chain growth polymerization of monomers. Additionally, as previously discovered by the present inventors, if alcohol is present in the coagulation phase during the chain growth polymerization of seven polymers, the polymerization time can be shortened and the yield can be increased. Can be done (Patent Application No. 1988-224.892)
.

The radical polymerization initiator used in this plasma-initiated polymerization method may be any one used in the general radical polymerization of -Ezmer, such as acetyl cyclohexyl sulfonyl peroxide, isobutyryl peroxide, Cumyl peroxyneodecanoate, diisopropyl peroxydicarbonate, di-n-propyl peroxydicarbonate, dicyclohexyl peroxydicarbonate, dimyristylno<-
Oxydicarbonate, -di(2-ethoxyethyl)
peroxydicarbonate, di(methoxyisopropyl)peroxy)dicarbonate, di(2-ethylhexylperoxy)dicarbonate, di(3-methyl-3-methoxybutyl)peroxydicarbonate, t
- peroxides such as butyl peroxyneodecanoate, potassium persulfate, ammonium per5IILM, 2,2'
- Low temperature active radical polymerization initiators such as azo compounds such as azobis(4-methoxy-2,4-dimethylvaleronitrile) and 2,2'-azobis(2,4-dimethylvaleronitrile), and t-butylcumylper oxide, diisopropylbenzene hydroperoxide, di-t-
Butyl peroxide, p-menthane hydroperoxide, 2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3,1,1,3,3-tetramethylbutyl hydroperoxide, 2. 5-dimethylhexane-2,5-cybidroba-oxide, cumene hydroperoxide, t-butyl hydroperoxide, 1.
1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, 1,1-bis([-butylperoxy)cyclohexane, t-butylperoxymaleate, t-butylperoxylaurate, t-butylperoxy-3,5,5-trimethylhexanoate,
t-Butylperoxy-2-ethylhexanoate, cyclohexanone peroxide, t-butylperoxyisopropyl carbonate, 2,5-dimethyl-2,5
-di(benzoylperoxy)hexane, 2,2-bis(t-butylperoxy)octane, t-butylperoxyacetate, 2,2-bis(t-butylperoxy)butane, t-butylperoxybenzoate , n-butyl-4,4-bis(t-butylperoxy)valerate, di-1-butylshiba-oxyisophthalate, methyl ethyl ketone peroxide, α,α′-bis(t-
butylperoxyisopropyl)benzene, dicumylperoxide, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, t-butylhydroperoxide, m-1-luoylperoxide, benzoylperoxide oxide, peroxides such as t-butyl peroxyisobutyrate, octanoyl peroxide, decanoyl peroxide, lauroyl peroxide, stearoyl peroxide, propionyl peroxide, succinic acid peroxide, 1,1'-azobis There are high temperature active radical polymerization initiators such as azo compounds such as (cyclohexane-1-carbonitrile) and azobisisobutyronitrile. Here, as the low temperature active radical polymerization initiator,
The decomposition temperature for obtaining a half-life of 10 hours is 50°C or less, while the high temperature active radical polymerization initiator
Decomposition temperature to obtain 0 hour half-life is 60-220'C
It is of a certain degree.

The addition of these radical polymerization initiators to monomers is as follows:
It is difficult to make a general statement because it largely depends on the degree of polymerization of the polymer to be obtained and the type of hexamer and radical polymerization initiator. However, it is not preferable to add more radical polymerization initiator than necessary because the radical polymerization initiator will not disappear during the polymer combination period and will remain in the resulting polymer. For example, when trying to obtain polymethyl methacrylate with a molecular weight of the order of 107, benzoyl peroxide (BPO) is used at 4×10°5 to 2×10−2 mol/Q.

Also, azobisisobutyronitrile (AIBN> is 6X
10'~6X10°3More L//Q Culm 1fi Te (T) Le.

The plasma used for polymerization initiation is preferably non-equilibrium plasma, especially low-temperature plasma generated by glow discharge.
It is obtained by applying a voltage of 20 to 100 W, preferably 30 to 50 W, to a gas under a pressure of 11111H. The electrodes used include external or internal parallel plate electrodes or coiled electrodes, preferably external parallel plate electrodes. The plasma source gas may be any gas such as hydrogen, methane, nitrogen, argon, ethylene, or the monomer gas itself.

In addition, in the plasma initiated polymerization method, generally the second a-
As shown in figure b, during plasma irradiation, the monomer solidification phase 1
1 and the monomer gas phase 12 are not separated by partition walls or the like and are maintained in an equilibrium state in the container 13, and polymerization active species generated by plasma irradiation on the gas phase 12 come into contact with the solidified phase surface. By doing so, post-polymerization is initiated.

However, as is known, for example, in a plasma initiated polymerization method, as shown in FIGS. 3a-b, during plasma irradiation, the monomer solidified phase 11 and the monomer gas phase 12 are separated by, for example, a partition wall 13. After plasma irradiation has been performed on the gas phase 12, the partition wall 13 may be removed, the gas phase 12 containing polymerization active species may be guided to the solidification phase 11, and the polymerization may be initiated after the polymerization active species is brought into contact with the solidification phase 11. , also the fourth
As shown in figures a to d, during plasma irradiation, only the gas phase 12 containing monomer vapor is sealed in the plasma reactor 14, and after plasma irradiation, the gas phase 12 is discharged from the reactor 14 to the outside of the system. Reactor 14 that was removed and then subjected to plasma irradiation
It is also possible to enclose old and new monomers therein and carry out post-polymerization in the coagulation phase 11. This method is possible because even during plasma-initiated polymerization, an extremely thin film of polymer is coated on the surface of the plasma reactor 14 made of a material such as glass, and the polymerization active species are absorbed by this polymer. This is because fine powder plasma-polymerized polymers with similar polymerization active species trapped in the gas phase 12 also exist (Masayuki Kuzuya,
"Plasma Initiated Polymerization Tree", Proceedings of the Plasma Chemistry Symposium (November 14, 1984)).

In addition, when carrying out the plasma-initiated polymerization method by the method shown in FIGS. 2a-b or 4a-c, the material of the plasma reactor 14 used is particularly the above-mentioned ultra-Fa thin polymer coating. things that are easy to do,
Various types of glass such as quartz glass and Pyrex glass,
Preferably, it is Pyrex glass.

Note that in Figures 2a, 3a, and 4a, the symbol @
15 is an electrode, 16 is an RF''Q imaging device δ, and 17 is a control unit.

Therefore, plasma irradiation to the gas phase 12 is carried out at a temperature such that monomer vapor exists in the reduced pressure gas phase 12, generally around room temperature, and the irradiation time is particularly limited. However, a short period of time is sufficient to generate polymerization active species, and is usually about several seconds to several minutes. The reaction in the coagulation phase 12 is carried out at about room temperature, although it depends on the type of radical polymerization initiator used. That is, if the post-polymerization is carried out under too high a temperature condition, the reaction may proceed thermally and a polymer having a low degree of polymerization may be produced. In addition, if the polymerization is carried out under too low a temperature condition f, there is a risk that the polymerization will not proceed well. However, when a low-temperature active radical polymerization initiator is used as a radical polymerization initiator, the post-polymerization in the coagulation phase is carried out in a low-temperature range that is difficult to proceed in the conventional plasma-initiated polymerization method. It progresses satisfactorily even at -20°C.

Furthermore, the degree of polymerization of the polymer obtained in this plasma-initiated polymerization method can be adjusted by generating a stoichiometric amount of the polymerization active species when the polymerization active species are obtained by plasma irradiation.

In addition, when alcohol is added to the reaction system, examples of this alcohol include methanol, ethanol, n-propanol, isopropanol, n-butanol, 5ec
-Alcohols having about 1 to 10 carbon atoms such as -butanol, tert-butanol, n-amyl alcohol, isoamyl alcohol, hexanol, heptatool, octatool, caprylic alcohol, nonyl alcohol, and decyl alcohol are mentioned, but among them, Lower alcohols, especially methanol, are preferred. The amount of these alcohols added to the monomer is such that the heptanomer:alcohol (volume ratio) is about 3 to 7:3, more preferably about 4:6 to
The ratio is preferably about 6:4, more preferably about 1:1. Furthermore, these alcohols may or may not be present in the gas phase during plasma irradiation.

In order to obtain an optical disc using the ultra-high molecular weight methyl methacrylate polymer obtained in this way, the ultra-high molecular weight methyl methacrylate polymer is placed in a disc standby at a temperature of about 150 to 300°C. For example, when obtaining a digital audio disc having a group of pits on one side of the disc, more specifically, a stand bar is attached to one side of the molding die of a press machine, and steam heats both sides of the molding die. 150-30
A compression molding method in which the ultra-high molecular weight methyl methacrylate polymer heated to 0° C. is placed and pressed at 100 to 200 kg/cd, or the ultra-high molecular weight methyl methacrylate polymer is placed in a mold containing a stand bar at about 150 to 200 kg/cd. This is carried out by an injection molding method or the like in which the material is inserted at a temperature of 300° C. and maintained at a pressure of about 500 to 1500 kO/Cl7t. In this way, a disk base body made of ultra-high molecular weight methyl methacrylate polymer with a group of pits transferred to its surface is formed, and then a metal film for reflection, such as an aluminum thin film, is applied to this pit surface using a conventional method. The metal is deposited by vacuum evaporation, and the metal evaporation film is used to form a protective coating made of hard resin.

Further, the optical disc material of the present invention may be subjected to a conventional method as long as it does not affect the vacuum deposition of metal as a post-treatment.
It is also possible to configure the disk base body by appropriately adding a mold release agent, a lubricant, an antioxidant, an ultraviolet absorber, an antistatic agent, and the like.

(Example) Hereinafter, the present invention will be explained in more detail based on Examples.

Example 1 Methyl methacrylate monomer 20- and benzoyl peroxide 4.13X as a radical single initiator were placed in a Pyrex glass polymerization tube (capacity 42 d) with an inner diameter of 15 II and 1 m.
10-3 mol/Q was added, and then the second I '1 was connected to a vacuum line, and freezing and degassing with liquid nitrogen was repeated three times. The seven polymers in the polymerization tube were again sufficiently cooled and frozen using liquid nitrogen. At the point when a portion of the hexamer in the polymerization tube began to dissolve at around room temperature, plasma was generated in the gas phase as shown in FIG. The electrodes used were made of copper.
The electrodes were parallel plate electrodes with an interelectrode distance of 0×10,0 cm and an interelectrode distance of 1 all Im, and a power of 50 W was applied to the electrodes by a radio frequency (RF) transmitter with a 13.56 MHz control unit. The plasma irradiation time was 60 seconds,
Further, the degree of pressure reduction was 10''l rorr.

After this, sufficient freeze-deaeration is performed, and then the polymerization tube is separated from the vacuum system by melt-sealing, and post-polymerization is carried out at 20'C for 55 minutes.
I did it for days. The reaction mixture was dissolved in benzene and reprecipitated in methanol to remove impurities, and polymethyl methacrylate was obtained with a yield of 80%. Various physical properties of the obtained polymethyl methacrylate were measured by the methods described below. The results are shown in Table 1.

Comparative Examples 1 and 2 Commercially available polymethyl methacrylate (Kyowa Gas Chemical Industry ■
The physical properties of Parapet [F]G, manufactured by Mitsubishi Gas Chemical Co., Ltd. (Comparative Example 1) and polycarbonate (Niepilon ■, manufactured by Mitsubishi Gas Chemical Company) (Comparative Example 2) were measured by the methods described below. The results are shown in Table 1.

Viscosity Average Molecular Weight The viscosity average molecular weights of polymethyl methacrylate and polycarbonate were determined from the intrinsic viscosity η using the Markuhouinck equation η-KM. (However, η is measured at 30°C using benzene for polymethyl methacrylate and methylene chloride for polycarbonate, and = 5
．． Calculated as 2×10 −3 and α=0.76. ) Molecular weight (MW/MN) Molecular weight (MW/MN) was measured using a tetrahydrofuran (8 days old) solution of each polymer by GPC method.

Melting temperature The melting temperature of the polymer powder was measured using a micromelting point measuring device.

heat deformed warm hemp Measurements were made using ASTM D648 test method.

flooded soil Measurement was performed using ASrM D570 test method.

Changes in each polymer were observed through weather resistance outdoor exposure tests.

Hirogon bean melon Measurements were made using ASTM D63B test method.

wild goose Δ51-M Measurement was performed using the D256 test method.

Measurements were made using ASTM D542 test method.

Konbe Keiyu 5y Measurements were made using ASTM D1003 test method.

(Margin below) Table 1 Examples] Comparative example 1 Comparative example 2 Molecular weight 1.68 x 107 1.3
xl[F] 5 x Italian molecular half cloth (M,,/MN) approx. 2.0 20-30 2-3 Melting fl'l' temperature (°C) 273-287 163-18
4 230-260 heat distortion temperature ('C) ≧
170 ~100 ~135 Water absorption rate (%)
0.20 0.30 0.15 Weather resistance Excellent Excellent Tensile strength (kg/C scrap) 730 68
0 6ri 0100 bulletproof 1”u (kg-cm/cm)
2.7 1.6 75-102 Refractive index (nI) > 1.49 1.
49 1. b9 Total light transmittance (%)
93 93 87 (Effect of the invention) As described above, the present invention has an average molecular weight of 5 x 105 to 5
Since it is an optical disc material made of x107 methyl methacrylate polymer, it is used as a material for forming the base body of optically readable discs such as video discs, digital audio discs, and memory discs. Compared to general-purpose methyl methacrylate immobilizers, it has improved properties such as moisture absorption deformation resistance, heat resistance, and mechanical strength, and at the same time has excellent performance such as transparency, durability, and low birefringence. Because it has the same or better quality, the optical system of the resulting optical disc can read information more accurately and with less noise, and can be maintained highly reliable over a long period of time. Ru.

Furthermore, the optical disc material of the present invention has a water absorption rate of % or less,
Heat deformation temperature 150'C or higher and total light transmittance 90%
If this is the case, the reliability of the optical disc obtained will be even higher. In addition, in the optical disc material of the present invention, a radical polymerization initiator is present in a gas phase containing monomer vapor, and plasma is irradiated into this gas phase to transfer the generated polymerization initiating active species to the monomer solidification phase. Since it can be obtained easily and in a high yield by carrying out chain growth polymerization of the monomers introduced into the polymer, it is completely satisfactory in terms of cost.

[Brief explanation of the drawing]

FIG. 1 is a sectional view schematically showing the basic structure of an optical disc, and FIGS. It is a diagram showing one embodiment of a plasma-initiated polymerization method that can be used for preparing the material. 1... Disc substrate main body part, 2... Recording bit group,
3...Konflex n film, 4...protective coating. Patent Applicant Chiru Seven Co., Ltd. Figure 1 Figure 2 Ship a 3rd ship (a) 4th (b) (b) □

Claims (4)

[Claims] (1) An optical disc material comprising a methyl methacrylate polymer having a viscosity average molecular weight of 5 x 10^5 to 5 x 10^7. (2) The optical disc material according to claim 1, which has a water absorption rate of 0.2% or less, a heat distortion temperature of 150° C. or more, and a total light transmittance of 90% or more. (3) The methyl methacrylate polymer contains other (meth)acrylic esters containing methyl methacrylate as the main component, (
The optical disc material according to claim 1 or 2, which is a copolymer with meth)acrylic acid or (meth)acrylamide. (4) A radical polymerization initiator is present in the gas phase containing monomer vapor in the methyl methacrylate polymer, and plasma is irradiated into this gas phase to transfer the generated polymerization initiating active species to the solidification phase of the monomer. The optical disc material according to any one of claims 1 to 3, which is obtained by conducting chain growth polymerization of a guide monomer.