JPS59108012A - Resin for optical high-density information recording medium, and medium for optical high-density information recording - Google Patents

Abstract

PURPOSE:To provide a resin for an optical high-density information recording medium, having a specific physical properties, and composed mainly of a copolymer obtained by the copolymerization of methyl methacrylate monomer, a specific ester monomer and a monoalkenylaromatic monomer at specific ratios. CONSTITUTION:The objective resin for an optical high-density information recording medium, having a solution viscosity of 3-10cps as 10% methyl ethyl ketone solution at 25 deg.C and a birefringence of <=100nm, is prepared by copolymerizing (A) 40-70pts.wt. of methyl methacrylate monomer, (B) 5-20pts.wt. of an ester monomer of methacrylic acid and a 3-6C monohydric saturated aliphatic alcohol (e.g. propyl methacrylate) and (C) 25-40pts.wt. of a monoalkenylaromatic monomer (e.g. styrene). The information recording meduim can be obtained by applying microscopic unevenness to a surface of a plate made of said resin, and depositing a metallic film to the surface.

Description

[Detailed description of the invention]

Regarding resins for optical high-density information recording media such as audio discs, video discs, and read-only discs, and optical high-density information recording media using this resin, in recent years, consumer Optimal resin and optics using this resin for use in high-density information recording media of high-density information recording and reproducing devices that digitize information using laser beams, which are attracting worldwide attention for their convenience as equipment. This relates to a type high-density information recording medium. A digital audio disk (DAD), which is an example of an optical high-density information recording medium, divides the music signal into small pieces, simply converts them into numerical values, and replaces them with a binary pattern of rOJ and rLl, using a metal surface that can reflect laser beams. The pattern is recorded as unevenness, then picked up by a laser beam, and the binary signal of the laser beam is converted into an electrical signal, which is then reproduced as sound. Such a disk with an uneven metal surface that can reflect laser beams is generally made by molding a transparent resin disk with an uneven surface on one side.
It is obtained by forming a metal film on the uneven surface of this by metal vapor deposition or the like. If the signal related to the image is recorded as a digital uneven disc, it becomes a video disc (VD). Furthermore, by recording computer programs and data in a concave-convex pattern, it can be used as a recording board for programs and data.
(abbreviated as DRAW) has been attracting attention. However, since the optical high-density information recording medium as described above uses a laser beam to detect and reproduce interference light based on a very small optical path difference and phase difference, its optical characteristics are as follows: ) The laser beam transmittance of the resin layer is high.11) The orientation of the polymer in the resin layer is small, and the birefringence is small.1ii) The variation in refractive index is small.iv)
It is required to be free of dust, turbidity, etc., and its physical properties include ■) High heat deformation temperature vi) Good metal deposition properties vii) Excellent formability and ability to form fine irregularities sharply etc. are required, and dimensional accuracy and stability are viii)
It is required to have a small wall thickness distribution, 1x) a small warp, and a) small water absorption rate and dimensional change due to water absorption. When using polymethyl methacrylate resin, the water absorption rate is high (because of this, the molded plate-like object will warp due to changes over time due to water absorption etc., which is fatal.) In order to improve this, polymethyl methacrylate resin was used. Attempts have also been made to laminate a resin with excellent barrier properties such as vinylidene chloride resin on the surface. However, lamination has the drawback of increasing the number of complicated steps.
There was a desire for a resin that satisfies the requirements (X) (2) and can be molded all at once. As an attempt at information recording media, a copolymer resin of methyl methacrylate/styrene = 60,740 (weight ratio) (Japanese Patent Application No. 57-33446, Japanese Patent Application No. 57-162135-
Examples of using copolymer resins such as 1 and methyl methacrylate/styrene=30/70 (weight ratio) (Japanese Unexamined Patent Publication Nos. 57-162135) in information recording media are known. However, methyl methacrylate/styrene = 60.
7'40 copolymer resin has a large water absorption rate (and when molded into a disk, it tends to warp due to water absorption), and has high birefringence for DRAW use, and methacrylic acid When a methyl/styrene = 30/70 copolymer resin is injection molded into a disc, it has a low water absorption rate but a large birefringence, making it difficult to use for DRAW.Meanwhile, the present inventors , A specific resin characterized by a copolymer obtained by copolymerizing a methacrylic acid ester monomer and a monoalkenyl aromatic monomer as a resin that basically satisfies the required performances such as 1) to x) above. (Japanese Patent Application No. 56-184381), but the resin mainly composed of this copolymer is DAD ('W diameter 120tAm, thickness 12mm).
mm ) gives satisfactory results, but D
RAW (diameter 300 mm, thickness), 2 mm
), it has become difficult to meet the standard values. In other words, the diameter has increased from 120 mm to 300 mm, and the ratio of diameter to thickness (L/T) has changed from 100 to 250, so the distance that resin flows from the center to the periphery during injection molding has increased significantly. Molecular orientation occurs easily due to flow, making it difficult to bring the birefringence value to the standard value required for DRAW, leading to problems such as difficulty in moldability and increased molding defect rate. .In addition, the value of warp due to water absorption increases by the amount of increase in diameter, and DRAW
It has become difficult to meet the standard values required for commercial use. Therefore, the inventors of the present invention have arrived at the present invention as a result of intensive studies to obtain a resin that satisfies the standards for DRA and W substrates. Thus, according to the invention, methyl methacrylate monomer 40
~70 parts by weight of methacrylic acid, monovalent saturated aliphatic alcohol 08-C6, ester monomer 5-20 parts by weight, and monoalkenyl aromatic monomer 25-40 parts copolymerized. The viscosity of a 10% methyl ethyl ketone solution of the copolymer at 25°C is 3-10 cps.
In the present invention, the ester monomer of methacrylic acid with a monovalent saturated aliphatic alcohol 08 to C6 is propyl methacrylate, butyl methacrylate, hydroxypropyl methacrylate, hexyl methacrylate, cyclohexyl methacrylate, or A mixture of the following may be mentioned. Further, examples of the monoalkenyl aromatic monomer include styrene, α-methylstyrene, p-methylstyrene, or a mixture thereof. In addition, as a copolymer, methyl methacrylate monomer 40
A ternary copolymer obtained by copolymerizing ~70 parts by weight of methacrylic acid with a monovalent saturated aliphatic alcohol 08 to C6, 5 to 20 parts by weight of an ester monomer, and 25 to 40 parts by weight of a monoalkenyl aromatic monomer. It has to be a combination. (Of course, monoalkenyl aromatic monomers and ester monomers with monovalent saturated aliphatic alcohols 03 to C6 of methacrylic acid are, respectively,
Strictly speaking, when they are used as a mixture, they are quaternary or higher multi-component copolymers, but they are basically understood as ternary copolymers. ) That is, the objective cannot be achieved with a binary copolymer. For example, in the case of a copolymer containing 35 parts by weight of a monoalkenyl aromatic monomer and 65 parts by weight of methyl methacrylate monomer alone, the saturated water absorption rate becomes large, which is undesirable because warping occurs due to water absorption. . As monomers for esters of methacrylic acid with monovalent saturated aliphatic alcohols, saturated aliphatic alcohols with less than 0.3 carbon atoms have little effect on reducing the saturated water absorption rate, and monomers with carbon atoms exceeding C6 are less effective. It is not preferable because it lowers the T8 of the copolymer resin and lowers the heat deformation temperature.
8 to C6 are used. In addition, when the methyl methacrylate monomer is less than 40 parts by weight, the saturated water absorption rate is low, but since there are many other monomer components, the birefringence becomes large and the heat distortion temperature becomes low. Undesirable. If the amount of the methyl methacrylate monomer used exceeds 70 parts by weight, the saturated water absorption rate will increase, making it easy to cause sori due to water absorption, which is not preferable. The monoalkenyl aromatic monomer contributes to raising the heat distortion temperature and lowering the saturated water absorption rate of the copolymer resin, but if it is used in an amount exceeding 40 parts by weight, it increases the birefringence of the copolymer resin, which is preferable. do not have. Further, if it is less than 25 parts by weight, it is not preferable because the saturated water absorption rate is less likely to decrease. For copolymer resins obtained from methyl methacrylate monomer and monoalkenyl aromatic monomer, simply changing the ratio of the two components results in good heat distortion temperature, but problems with birefringence or saturated water absorption. Although one or both of them will not meet the standards for DRAW, if an ester monomer of methacrylic acid with a monovalent saturated aliphatic alcohol (03-Ca) is used in addition to the former two monomers, , birefringence, and saturated water absorption can both be improved in a well-balanced manner. However, monohydric saturated aliphatic alcohol of methacrylic acid -/l/(08~c6)
If the amount of the ester exceeds 20 parts by weight, it is undesirable because it lowers the heat distortion temperature of the copolymer resin, and if it is in a small amount of less than 5 parts by weight, either birefringence or saturated water absorption will be insufficient and it is not preferable. do not have. Further, if the viscosity of the 10% methyl ethyl ketone solution at 25°C of the copolymer is 3 cps or less (measured with a Cannon-Fenske viscometer in a water tank at 25°C), it becomes brittle, which is not preferable. Also, the viscosity of the same solution is 10 cp
If it exceeds s, birefringence increases, moldability deteriorates, and fine irregularities cannot be accurately transferred, which is not preferable. The viscosity of the 10% methyl ethyl ketone solution of the copolymer is 3.
If the molecular weight is in the range of ~10 cps, the moldability will be very good, the fine irregularities of the mold can be accurately transferred to the molded product, and there will be no brittleness, which is preferable. If the birefringence is too high, the reflection efficiency of the laser beam will decrease when information recorded on the information recording medium is reproduced in an optical high-density information reproducing apparatus, resulting in poor reproduction performance, which is not preferable. Furthermore, due to various limitations of the device, it is desirable that the birefringence of the resin portion of the information recording medium is 1001"1m or less. Birefringence is determined by various factors, but the factors and their effects on birefringence are still unclear. As a result of various studies, the inventors have investigated the type of resin, the composition molecular weight of the resin, etc.
This invention has clarified the relationship with birefringence, and has invented a resin that satisfies the various performance requirements mentioned above and is relatively inexpensive, that is, an industrially optimal resin. In addition to the basic composition of the resin described above, when producing an actual high-density information recording medium, the influence of the manufacturing method (molding method) of the recording medium on birefringence cannot be ignored. Although various molding methods are possible, injection molding is considered to be the best in terms of productivity, dimensional accuracy, etc. Considering the molding principle of injection molding, there are differences in various physical properties and optical properties depending on the flow direction of the resin and the direction perpendicular to the flow. That is, there is a difference between the refractive index in the flow direction (nl) of the resin and the refractive index in the direction perpendicular to the flow (nQ), and the difference Δn=n1-n2 is the birefringence. In other words, the birefringence Δn and the birefringence R increase or decrease depending on the molding conditions. The relationship between the two is expressed by the following equation. R5 Δn It is impossible to do so. As a result of examining the general trends and the molding temperature, which is thought to have the greatest effect on birefringence, we found that birefringence decreases as the molding temperature increases. just,
It is impossible to raise the molding temperature infinitely; the upper limit of the cylinder temperature is the thermal decomposition temperature of the resin, and the upper limit of the mold temperature is the heating deformation temperature in consideration of mold releasability. Therefore, the inventors set the following conditions to optimize the composition of the resin, and set the ko molding temperature to a temperature close to the upper limit temperature of the resin. CC50Qn diameter disc, l, 2mm thickness) Cylinder temperature: 300°C Mold temperature = 70°C Injection pressure Nijiiodine shot point) + 5
kg/cm 2 To give an example, in the copolymer of the present invention, MMA/B
MA/Styrene-50/15/35.10% by weight methyl ethyl ketone solution When a polymer with a viscosity of 5 cps is molded under the above molding conditions, the cylinder temperature is changed to 280°C and 300°C, the average birefringence R is 60, 40nm
Met. The resin of the present invention can be obtained by copolymerizing the above methacrylic acid ester and a monoalkenyl aromatic monomer using known polymerization methods such as suspension polymerization, bulk polymerization, and solution polymerization. In the case of bulk polymerization, the polymerization can be initiated by thermal monomeric free radicals or irradiation with ionizing radiation, but it can be initiated by any free radical-generating catalyst. Specifically, diacyl oxides such as acetyl peroxide, lauroyl peroxide, and benzoyl peroxide, hydroperoxides such as cumene hydroperoxide, alkyl peroxides such as di-tert-butyl peroxide, and t-butyl peroxide. Oxyacetate, t-butyl baroxylaurate, t-
Examples include peroxy esters such as butyl peroxybenzoate, azo compounds such as 2,2'-azobyl inbutyronitrile, and the like. In this case, toluene, xylene,
Diluents such as ethylbenzene, ethyltoluene, ethylxylene, diethylbenzene, benzene, etc. can be added in amounts of 2 to 20% of the monomers. In addition, when polymerizing by suspension polymerization, a polymerization initiator that is sparingly soluble in the medium (mainly water) and easily soluble in the monomer is used. Examples of such polymerization initiators include diacyl peroxides such as acetyl peroxide, lauroyl peroxide, and benzoyl peroxide, and 2,2'-azobisisobutyronitrile. A dispersion stabilizer or co-stabilizer may be added to stir and disperse the monomer in water. When such a stabilizer is used, a water-soluble polymer is used. Slightly soluble fine powder inorganic compounds used as dispersion stabilizers in normal suspension polymerization cannot be used. This is because the resin of the present invention is required to have a high degree of transparency. In addition, in the various polymerization methods mentioned above, it is often desirable to incorporate molecular weight regulators such as mercaptans, disulfides, halides, and terpenes, as well as stabilizers and the like. In addition, a hindered phenol compound having a molecular weight of 350 or more is added to the above-mentioned specific copolymer. OOppm~1000
Adding 0 ppm suppresses foaming properties during molding, making it even more preferable. A hindered phenol compound refers to a compound in which one of the two ortho positions of a phenolic hydroxyl group is substituted with a bulky substituent. Preferred examples include the general formula (■): R, R2 (wherein R1 is a hydrogen atom or an alkyl group, R2 is a hydrogen atom or an alkyl group, R3 is an organic substituent, R4 is a hydrogen atom,
R5 is a t-butyl group) Phenol compounds having a molecular weight of 350 or more are exemplified. This organic substituent R8 is preferably one having a structure further having one or more heated phenol structure in the organic substituent. Further, specific compound names are as follows. Pentaerythrityl-tetrakis [3-(3,5-di-
t-butyl-4-hydroxyphenyl) flobionate] (molecular weight 1176.6) 1.1.3-tris(2-methyl-4-hydroxy-5
=, t-butyl-phenyl)butane (molecule i
544.83) n-octadecy/I/-3-(4,
'-Hydroxy-3', 5'-di-t-butyl-phenyl) propionate, (molecular weight 520.'9)
Tet+Jsu(3,5-sheett,-phthyl-4-hydroxy-benzyl)in cyanurate (molecular weight 712) triethylene glycol-bis-3-(3-
t,-Butyl-4-hydroxy-5-methyl-phenyl)propionate (molecular weight 586.8) 4,4'-butylidene-bis(3-methyl-6-t-butyl-phenol) (molecular weight 38
2.6) Tris[β-(3,5-di-t-butyl-4-
Hydroxy-phene = /l/ ) 7'ropionyloxyethyl]isocyanurate (molecular weight 1045) 4.4'-methylene-bis(2,6-di-t-butyl)
Phenol (molecular weight 425) 1.3.5-trimethyl-2,4,6-)lis(3,
5-di-t-phthyl-4-hydroxy-benzyl)benzene (molecular weight 761.1) hexamethylene glycol bis[β-(3,5-di-t
-butyl-4-hydroxyphenyl) flobionate (
Molecular weight: 524.8) Bis[3,3-bis(4'-hydroxy-3'-1-butyl-phenyl)butyric acid coglycol ester (molecular weight: 795) As long as transparency and other physical properties are not impaired, It is free to add release agents, antistatic agents, antistatic agents, and other additives to the resin. Further, according to the present invention, methyl methacrylate monomer 40
~70 parts by weight of methacrylic acid and monovalent saturated fatty acid alcohol C3 to C6 A copolymer copolymerized with 5 to 20 parts by weight of monomer and 25 to 40 parts by weight of monoalkenyl aromatic monomer. An optical high-density information recording medium is mainly composed of a 10% methyl form of the copolymer at 25°C, one side of which has minute irregularities, and a metal film is laminated on the uneven surface. provided. Next, the present invention will be described with reference to embodiments shown in the drawings. 1st
The figure is an explanatory diagram showing the operating state of the optical high-density information recording medium according to the present invention, and FIG. 2 is an enlarged top view of the recording medium according to the present invention. In FIG. 1, (1) is a resin layer made of the above-mentioned specific resin, and (2) is a metal film laminated by metal vapor deposition or the like. (3) is a convex portion of the resin layer (1). Focusing on the metal film (2) and considering the metal film (2) as one layer, the convex portions (3) of the resin layer (1) are similar to the pits (4) in the metal film (2). Become a part. This pit (4) has a width of about 1.0 to 15μ, a depth of 0.1 to 0.2μ,
The minimum length is 1 to 16μ. Such pits (4) are densely arranged along a spiral line when viewed from the entire board surface. An enlarged top view showing this arrangement is shown in FIG. 2. Next, in Fig. 1, the laser beam (5) is
), half of the light beam goes straight, the other half enters the resin layer (1) perpendicularly, passes through the resin layer (1), and is then reflected by the metal film (2), and half of the reflected light is Transparent mirror (
It is further reflected at step 6) and follows the same optical path as the light that went straight. This causes the bald head and metal film (2) to move straight, and the semi-transparent mirror (
6) An optical path difference (therefore, a phase difference) is created in the reflected light that has passed through the laser beam reflection site due to the unevenness of the metal film (2). Therefore, if you rotate the entire plate-shaped body, there will be pits (4
) and flat portions (7) appear at various intervals, the optical path difference changes accordingly, and based on the change in the optical path difference, the straight light and the reflected light interfere with each other, resulting in optical high-density information processing. Information about the shape of the unevenness of the recording medium is converted into a signal indicating the intensity of the laser beam and the time length of the intensity. This signal is converted into an electrical signal and further reproduced as sound. To manufacture this optical high-density information recording medium, first,
The above-mentioned specific resin is molded by a molding method such as injection molding to obtain a plate-shaped body having minute irregularities on one side. Next, a metal film is formed on the uneven surface of the obtained plate-shaped body. In order to form a metal film on a resin plate, a method using metal vapor deposition is suitably applied. Aluminum, gold, platinum, silver, copper, etc. are used as the metal for the metal film, and aluminum is inexpensive and practical. Furthermore, according to the present invention, methyl methacrylate monomer 40-
A terpolymer copolymerized with 70 parts by weight of methacrylic acid, monovalent saturated fatty acid alcohol 08-C6, 5-20 parts by weight of any ester monomer, and 25-40 parts by weight of monoalkenyl aromatic monomer. Mainly, the viscosity of a 10% methyl ethyl ketone solution of the copolymer at 25°C is 3 to 10
cps range and a birefringence of 100 nm or less, one side of which is made of a resin plate with minute irregularities, and a metal film laminated on the uneven surface, two laminates are placed with the metal film surfaces on the inside. An optical high-density information recording medium is provided, which is characterized in that it is formed by laminating and integrating two layers. FIG. 3 shows a cross-sectional view of an optical high-density recording medium in which both the front and back sides can be used as recording surfaces. The recording medium shown in Fig. 3 is produced by bonding two plate-shaped laminates with one side as the recording surface obtained as described above, with the metal film (2) sides of each other, using, for example, an adhesive (8). It can be manufactured by integrating the two. It should be noted that the physical properties of the optical high-density information recording medium according to the present invention in Table 1 above and the following Examples were measured as follows. 300 ff1l11, 1.2 mm thick disc without groove)
Therefore, retardation (
12mm thickness double pass) was measured. The judgment criteria are as follows. Birefringence (nm) ◎' 100 nm or less ○: 100~l50nmX'15
0 nm or more [2] Saturated water absorption DAD molded product (diameter 1.20 rnm, thickness), 2
Using a grooveless disk of mm, immerse it in distilled water at 23°C ± 05°C, measure the water absorption rate every 24 hours, and measure the point at which the water absorption curve is saturated as the saturated water absorption rate. The judgment criteria are as follows. Saturated water absorption ◎: 07 or less ○: 07 to 0.9 × River O or more [3] Heat resistance According to JIS K 7207, 18.5 kg/cm2
Measure the heating deformation temperature under the load of The judgment criteria are as follows. Heating deformation temperature (°C) ◎ 75°C or more x near less than 5°C [4] Thermal stability test injection molding machine [Kato Seisakusho (KTS), type: K
], 70S, capacity: 2.500Z, screw structure. When molding a molded product (chip) with a length of 90 mm, a width of 4 (1 mm, and a thickness of 3 tnm) using the Dullmage two-stage tip method L/D = 20', the resin composition was added with a screw while retracting the nozzle. After the pellets are plasticized, the screw rotation is stopped and the pellets are allowed to stay for a predetermined time.Then, the nozzle is moved forward and injection molding is carried out after touching the nozzle.Voids or silver marks due to bubbles in the chip.
Check for presence and condition. Judgment is based on the following criteria. [5] Mechanical strength (1) Measured with bending strength AS'l'M' D 790. Judgment criteria: 650 kj9/cm2 or more ◎650k
Less than g/cm2 × (2) Tensile strength Measured according to JIS K 6871 Judgment criteria: 500 kg/cm2 or more ◎500 kg
//Less than cm2 × [6] Transferability Determine whether mold surface pits of 1μ width × 1 to 1.6μ length × 01 to 02μ depth will be reproduced in the molded product (information recording medium resin). The judgment criteria are as follows. Transferability ◎, If the mold can be clearly reproduced ×° If the mold reproduction is slightly uneven [7] Transparency (laser light transmittance) Use an integrating sphere light transmittance measuring device according to JIS K671.8 (Method A) and measure. Transmittance of 90% or more...◎ [8] Refractive index JIS K71.05-1981 (Testing method for optical properties of plastics) using an Atsube refractometer at a measurement temperature of 2305°C Measurements were made using natural light as the light source.

[9] Garbage ・Using the standard spot size gauge of the Onjun Wireless Communication Machinery Industry Association, injection mold a flat plate with a thickness of 25 cm, measure the size and number of dust per 200 cm2, and measure the size and number of dust with a diameter of 0.2 mm or more. If there is one or less particles of the same size, it is determined that there is substantially no dust turbidity. [10] Aluminum deposition property 1.0' to 1.0-5 Torr and thickness 1.0OO1
1 was vapor-deposited, cross-cuts were made, and a peel test was performed using cellophane tape to determine whether or not peeling occurred. Those with no peeling were considered good. [11] Wall thickness distribution The wall thickness variation of a disc (molded product) with a diameter of 30 cm and a thickness of 1.5 to 12 mm was measured using a micro gauge. [12] Place a disc (molded product) with a warpage diameter of 30 cm and a thickness of 1.5 to 12 mm on a surface plate and measure the warpage. The following examples are given to illustrate the invention. Example 1 43 parts by weight of methyl methacrylate, n-butyl methacrylate
Chill 13 parts, styrene 24 parts by weight, ethylbenzene 20 parts
Parts by weight, n-dodecylmercapkun o, 19 M,
A formulation consisting of 0.03 parts by weight of i part, t-butylperoxybenzony) was continuously fed at a rate of 0.751/hr into a jacket with an internal volume of 21 to a thorough mixing reactor. The polymerization temperature was 130°C. The obtained copolymer was colorless and transparent. The results of compositional analysis of this polymer using an infrared spectrophotometer are 50% by weight of methyl methacrylate, 15% by weight of n-butyl methacrylate, and 35% by weight of styrene.
Met. This copolymer was dissolved in methyl ethyl ketone to create a 10% by weight methyl ethyl ketone solution, and the solution viscosity of the solution was measured using a Cannon-Fenske viscometer as a guide to the molecular weight of the polymer in a water bath at 25°C. 5
It was cps. In the above copolymer, n-octadecyl-3 is added as a heat stabilizer.
A resin prepared by adding 2000 ppm of -(4,'-hydroxy-37.5/-di-t-butylphenyl)propionate and 2000 ppm of stearic acid as a mold release agent was put into a cylinder in a 13-ounce in-line injection molding machine. When we set the temperature to 300'C and the mold temperature to 60'C, we molded a disc for a disc with a molded product wall thickness of 12 mm and a diameter of 300 mm that can be written on and played immediately.The laser beam transmittance was 91% and the birefringence was 50~ 60m saturated water absorption rate was 0.50%. Examples 2 to 6 Copolymers with different contents of methyl methacrylate and n-butyl methacrylate were produced in the same manner as in Example 1, except that the amounts of methyl methacrylate, n-butyl methacrylate and styrene were changed. 1 of the resulting resin at 25°C
0 wt% methyl ethyl ketone solution viscosity is 5-7 cps
Met. Example 7 The same procedure as in Example 1 was carried out except that n-butyl methacrylate was changed to inbutyl methacrylate, and the contents were 15% by weight of isobutyl methacrylate and 35% by weight of styrene. The resulting resin had a 10% by weight methyl ethyl ketone solution viscosity of 48 cps at 25°C. Example 8 A copolymer was obtained in the same manner as in Example 1 except that n-butyl methacrylate was changed to cyclohexyl methacrylate. A composition analysis of this polymer using a red phosphorus spectrophotometer revealed that it contained 50% methyl methacrylate, 15% by weight cyclohexyl methacrylate, and 35% by weight styrene. The resulting resin had a 10% by weight methyl ethyl ketone solution viscosity of 5.6 cps at 25°C. Comparative Examples 1 to 3 The amounts of methyl methacrylate, n-butyl methacrylate, and styrene were varied, and the molecular weight regulator (n
Copolymerization was carried out by varying the amount of methyl methacrylate and n-butyl methacrylate added and various solution viscosities. Comparative Examples 4 to 9 Methyl methacrylate-styrene copolymer (methyl methacrylate 60% by weight, styrene 40% by weight, 25°C11
0% by weight methyl ethyl ketone solution viscosity 7 cps)
(Comparative Example 4), polymethyl methacrylate (25°C11
,,0% by weight methyl ethyl ketone solution viscosity 1. Ocp
s) (Comparative Example 5) Polycarbonate (Teijin Kasei Ltd. Panlite L] 250) (Comparative Example 6), polystyrene (Asahi Kasei Ltd. Stylon 666) (Comparative Example 6)
), similar physical properties were measured. The resin of the present invention is not only used for DRAW, which has the most demanding performance, but also for DAD,
It can be seen that this resin has very excellent physical properties as a resin for optical high-density information recording media such as VD. In addition, the resins of Comparative Examples 4 to 6 are generally used as resins with excellent transparency, but they have both the birefringence and saturated water absorption required for resins for optical high-density information recording media. Table 1 shows that they cannot be satisfied at the same time.
It's more obvious.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing the operating state of the optical high-density information recording medium according to the present invention, FIG. 2 is an enlarged top view of a part of an embodiment of the optical high-density recording medium of the present invention, and FIG. FIG. 1 is a cross-sectional view of an optical high-density recording medium of the present invention in which both the front and back sides can be used as recording surfaces. (1)・Resin layer, (2)・Metal film, (3) Convex portion, (
4)...bit, (5)...-laser beam, (6)...
・Semi-transparent mirror, (7) ・Flat part, (8) ・Adhesive. Applicant Asahi Kasei Industries Co., Ltd. Agent Yutaka 1) Yoshio Figure 1 Figure 2 Figure 3

Claims (2)

[Claims] (1) 40 to 70 parts by weight of methyl methacrylate monomer and monohydric saturated aliphatic alcohol 08 to C of methacrylic acid
The viscosity of a 10% methyl ethyl ketone solution of the copolymer at 25 ° C. It is in the range of 3 to 10 CpS,
An optical high-density information recording medium resin characterized in that the resin has birefringence of 1.00 nm or less. (2) The ester monomer of methacrylic acid with a monohydric saturated aliphatic alcohol C8 to C6 is propyl methacrylate, butyl methacrylate, hydroxyglopyl methacrylate, hexyl methacrylate, cyclohexyl methacrylate or the like (3) Mono Alkenyl aromatic monomers are styrene, α-methylstyrene, p-methylstyrene and methacrylic acid monohydric saturated aliphatic alcohol C3-C
A 10% methyl ethyl ketone solution of the copolymer at 25°C, mainly consisting of a copolymer copolymerized with 5 to 20 parts by weight of ester monomer 6 and 25 to 40 parts by weight of monoalkenyl aromatic monomer. It is characterized by having minute irregularities on one side of a plate-shaped body made of a resin having a viscosity in the range of 3 to 10 cps and a birefringence of 1'oonm or less, and a metal film laminated on the irregular surface. An optical high-density information recording medium.