JPS5888843A - Optical high density information recording medium resin and optical high density information recording medium - Google Patents

Abstract

PURPOSE:To obtain a recording medium having a small water absorbing factor without generation of warping, by using the resin that has the specific solution viscosity and double refraction in terms of a specific copolymer ratio between the methacrylic acid ester and a monoalkenyl aromatic monomer. CONSTITUTION:The methacrylic acid ester and a monoalkenyl aromatic monomer (styrene, chlorostyrene, etc.) are copolymerized with 30:70-70:30wt% to obtain the resin that is used as the primary element. A plate sheet 1 having a minute recessed and projected surface 3 is produced by the injection molding from the resin that has 2cps-10cps solution viscosity of 10%-methyl ethyl ketone at 25 deg.C of the above-mentioned copolymer and <=100nm double refraction. Then a metal is vapor deposited on the surface 3 to form a film 2. Thus an optical high density information recording medium is obtained. This recording medium has a large transmission factor of laser beams, >=80 deg.C heat deformation temperature, a small water absorbing factor and without generation of warping due to the water absorption. Such recording medium is suited to a digital audio disk, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a resin for optical high-density information recording media such as so-called optical digital audio discs, video discs, etc., and an optical high-density information recording medium using this resin. Regarding recording media, in more detail, high-density information recording media of high-density information recording and reproducing devices that use laser beams to digitize information, which has recently been attracting worldwide attention for its convenience as a consumer device. The present invention relates to a resin that is most suitable for use in the invention and an optical high-density information recording medium using this resin.

A digital audio disk (DAD), an example of an optical high-density information recording medium, divides the music signal into small pieces, simply converts them into numerical values, replaces them with a binary pattern of "0" and "1", and uses laser beam reflection. The pattern is recorded as possible irregularities on a metal surface, 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 unevenness on one side, and then forming a metal film on the uneven surface by metal vapor deposition. This is obtained by

If the disc is recorded as a video disc (VD), 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.

However, since the above-mentioned optical high-density information recording medium 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: I) The laser beam transmittance of the resin layer is high.Ii) The arrangement of the polymer in the resin layer is small, and the birefringence is small.M) The variation in refractive index is small. The physical properties are ■) High heat distortion temperature vi) Good metal vapor deposition properties vll) Excellent formability and ability to form fine irregularities with sharpness Vil+) Small thickness distribution lx) Small warpage thing .

×) Water absorption rate and dimensional change due to water absorption are small. etc. are required.

When polymethyl methacrylate resin is used, its water absorption rate is high, and as a result, the molded plate-like body warps due to changes over time due to water absorption, which is fatal. In order to improve this, attempts have been made to laminate a resin with excellent barrier properties, such as a vinylidene chloride resin, on the surface of the polymethyl methacrylate resin. However, lamination has the disadvantage that the process becomes more complicated. Therefore, the above (1)
There was a desire for a resin that satisfies the requirements of ~tXI and can be molded once.

The present invention has been made in view of the above points.

Thus, according to the present invention, the copolymer is mainly composed of a tutaacrylic acid ester monomer and a monoalkenyl aromatic monomer in a weight ratio of 30:0 to 70:30, and the copolymer is produced at 25°C.
Provided is an optical high-density information recording medium resin characterized in that the viscosity of a 10% methyl ethyl ketone solution of the copolymer is in the range of 2 cps to 10 cps, and the birefringence is 1100 nm or less.

In the present invention, the methacrylic acid ester monomers include methyl methacrylate, L-methyl methacrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, n-butyl methacrylate, hexyl methacrylate,
Mention may be made of cyclohexyl methacrylate, n-octyl methacrylate, nonyl methacrylate, stearyl methacrylate or mixtures thereof.

Further, examples of the monoalkenyl aromatic monomer include styrene, α-methylstyrene, chlorostyrene, dichlorostyrene, bromostyrene, dipromostyrene, or a mixture thereof.

Also, as a copolymer, 30 to 70 parts by weight of methacrylic acid ester monomer! On the other hand, it must be a copolymer containing 70 to 30 parts by weight of a monoalkenyl aromatic monomer. In the case of a copolymer in which more than 70 parts by weight of a methacrylic acid ester monomer is copolymerized with 30 parts by weight of a monoalkenyl aromatic monomer, the water absorption rate is high, and therefore warping occurs due to water absorption. Undesirable. More specifically, in the case of DAD, the information recording medium is capable of recording high-density information, so it is possible to record for a commercially sufficient length of time just by recording information on one side. be taken as a thing. In such a single-sided recording type, the uneven surface of the metal film does not absorb water and there is no dimensional change in the gold maple, but the opposite side is made of transparent resin.
The transparent resin absorbs water and causes dimensional changes. Thus,
Since a single-sided recording type information recording medium has a structure in which resin and metal are laminated, sagging occurs due to changes in temperature and humidity. The present inventors have discovered that warpage does not substantially occur when the water absorption rate is 0.2% or less.

In addition, a copolymer in which less than 30 parts by weight of methacrylic acid ester is copolymerized with 70 parts by weight of monoalkenyl aromatic monomer is preferable because it tends to cause molecular alignment in the molded gap and increases birefringence. do not have. If the weight ratio of the methacrylic acid ester monomer and monoalkenyl aromatic monomer in the copolymer is 40-60:60-40, the above (1
) to (×) can be achieved to a high degree, which is preferable.

Further, if the viscosity of the 10% methyl ether ketone solution at 25° C. of the copolymer (measured with a Cannon-Fenske viscometer in a water bath at 25° C.) is less than 20 pS, the copolymer becomes brittle, which is not preferable. Furthermore, if the viscosity of the above solution exceeds 10 cps, birefringence increases and moldability deteriorates.
Fine irregularities cannot be accurately transferred, which is undesirable. The viscosity of the 10% methyl ethyl ketone solution of the copolymer is 2 to 10.
If the molecular weight is within the cps range, moldability is very good, minute irregularities in the mold can be accurately transferred to the molded product, and there is 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 undesirable. Further, due to various limitations of the apparatus, it is desirable that the birefringence of the resin portion of the information recording medium is 1100n or less.

Birefringence is determined by various factors, but the factors and their effects on birefringence have not yet been clarified. As a result of various studies conducted by Sakaki, the present inventors have clarified the relationship with birefringence as a result of examining the type of resin, resin composition, molecular weight, etc. This invention is an inexpensive resin, 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, the refractive index in the resin flow direction (nl) and the direction perpendicular to the flow (n2)
There is a difference in refractive index, and the difference Δn w nl −n2 is the birefringence index. In other words, depending on the molding conditions, the birefringence △n
, the birefringence R increases or decreases. The relationship between the two is expressed by the following equation.

R= ΔnXd d: Test piece thickness On the other hand, we quantified all the various injection molding machines available in the world, molding temperature, mold temperature, mold design (gate design, runner diameter, runner length), etc., and investigated the relationship with birefringence. It is impossible to be clear.

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 present inventors set the following conditions to optimize the composition of the present resin. The molding temperature was set close to the upper limit temperature of the resin.

Injection molding machine: In-line injection molding machine Mold: DAl'') Mold (12 diameter circles, 1.2 mm thickness) Cylinder temperature: 300 ℃ Mold temperature near 0 ℃ Injection Pressure Nijiiodine shot point + 5KgZ
To give an example of flaws, in the combination of the present invention, MMA/
Styrene, 50150.10% by weight methyl ether ketone solution Polymer with viscosity 6 Cps Among the above molding conditions, the cylinder temperature was 240°C, 260'C, 280°C,
The average birefringence R when changed to 300°C is 60
, 30, 20, I Fl nm.

The resin of the present invention can be obtained by copolymerizing the above bittaacrylic acid ester and a monoalkenyl aromatic monomer using known polymerization methods such as suspension polymerization, bulk polymerization, and solution polymerization.

When polymerization is carried out by bulk polymerization, the undercarriage can be initiated by thermal monomeric free radicals or irradiation with ionizing radiation, but the polymerization can be initiated by any free radical-generating catalyst.

Specifically, Schiff II such as acetyl peroxide, lafuroyl peroxide, benzodilver oxide, etc.
Hydroperoxides such as ruber oxide, cumene hydroberoquinde, alkyl peroxides such as di-tert-butyl peroxide, t-phthyl peroxyacetate, t-butyl peroxylaurate, 1. Examples thereof include peroxy esters such as -butylperoxybenzoate, azo compounds such as 2,2-azobisisobuteronitrile, and the like. In this case, a diluent such as toluene, xylene dibenzene, dichlorotoluene, ethylxylene, diethylbenzene, benzene, etc. is added in an amount of 2 to 20% of the monomer in order to control the viscosity at high conversion. be able to.

Further, in the case of polymerization 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, lafuroyl peroxide, and benzoyl peroxide, and 2,2'-azobisisobutyronitrile. A dispersion stabilizer or co-stabilizer may be added or removed when the monomer is stirred into water and dispersed. When such a stabilizer is used, a water-soluble foreign molecule 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 each of the above-mentioned methods, it is often desirable to incorporate molecular weight regulators such as mercaptans, disulfides, halides, and terpenes, as well as stabilizers and the like. Furthermore, transparency and other freedoms are important.

Further, according to the present invention, the copolymer is mainly composed of a methacrylic acid ester monomer and a monoalkenyl aromatic monomer copolymerized at a ratio of 30 to 70:30, and the copolymer is copolymerized at 25°C. The viscosity of the 109 methyl ethyl ketone solution is in the range of 2 cps to 10 cps, and
Provided is an optical high-density information recording medium comprising a plate-shaped body made of a resin having a birefringence of 100 nm or less, one side of which is provided with minute irregularities, and a metal film laminated on the irregular surface. .

Next, the present invention will be described with reference to embodiments not 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 steam heating or the like. (3) is a convex portion of the resin layer (1).

If we consider the metal film (2) as one layer by looking at the texture toward the metal film (2), the convex portion (3) of the resin layer (1) is
The metal film (2) becomes the bit (4) portion. This bit (4) has a width of about 10-1.5μ, a depth of O1-02μ, and a minimum length of 1-1.6μ. These bits (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 Figure 1, the laser beam (5) is semi-transparent @ (6
), half of the light beam travels straight, the other half enters the resin layer (1) perpendicularly, passes through the resin 111# (ll, and is then reflected by the metal film (2), and half of the reflected light is It is further reflected by the transparent mirror (6) and follows the same optical path as the light that went straight.Therefore, the straight light, the metal film (2), and the reflected light that has passed through the semi-transparent mirror (6) are separated by the metal film (2). ) creates an optical path difference (therefore, a phase difference) from the laser beam reflection site.When the entire plate-shaped body is rotated, the bit (4) and the flat part (7) appear at a fine interval, Accordingly, the optical path difference becomes friendly, and based on the change in the optical path difference,
The straight light and the reflected light interfere with each other, and the information (B) of the unevenness of the optical high-density information recording medium is converted into a signal indicating the intensity of the laser beam and the temporal length of the intensity. This signal is converted into an electrical signal and further reproduced as sound1.
, ``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 form a plate-like body with small irregularities on one side. obtain. 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 a metal front cloth is suitably applied. Aluminum, gold, platinum, silver, copper, etc. are used as the metal for the metal film.
Aluminum is cheap and practical.

Further, according to the present invention, the main body is a copolymer in which a nutacrylic acid ester monomer and a heptano-alkenyl aromatic monomer are copolymerized at a weight ratio of 30:0 to 70:30, and the copolymer at 25°C. One side of a plate-shaped body made of a resin having a viscosity of a 10% notel ether ketone solution of a polymer with a viscosity in the range of 2 cps to 10 cps and a birefringence of 100 nm or less is provided with minute irregularities on one side, and the uneven surface is There is provided an optical high-density information recording medium characterized in that it is formed by laminating two laminates each having metal films stacked on top of each other with the metal film surfaces facing inside.

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, each of which has one side as a recording surface, obtained in the manner described above, with their metal film (2) surfaces together using, for example, an adhesive (8). It can be manufactured by integrating the two.

The physical properties of the optical high-density information recording medium resin according to the present invention satisfy the following values.

Table 1 In addition, each physical property in the said Table 1 and the following Example was measured as follows.

Optical properties [Laser beam transmittance] Measured using an integrating sphere type light transmittance measuring device according to JIS K 6718 (Method A).

[Birefringence]

Using an XTP-11 polarizing microscope manufactured by Nippon Kogaku Kogyo Co., Ltd., retardation was measured by the Senarmont compensator method using a He-Ne laser beam as a light source.

[Refractive index]

According to JISK7105-1981 (Plastic optical property testing method), using an Atsube refractometer, the measurement temperature was 2.
Measured at 3±0.5°C using natural light as the light source.

[Garbage/turbidity]

A flat plate with a thickness of 2.5 mm was injection molded using a standard spot size gauge of the Radio Communication Machinery Industry Association, and the size and number of debris was measured per 20 oi. If there is one or less, it is determined that there is substantially no dust turbidity.

physical properties [Heating deformation temperature] According to JIS 7207, 18. fiK9/♂ apron.

Measured in.

[Aluminum vapor deposition property]

At 10 to 10 Torr to a thickness of 1000, a cross cut was made in front, and a peel test was performed using cellophane tape to determine the presence or absence of peeling.

A sample in which no peeling occurred was rated as "good".

[Moldability]

1μ width x 1 to 1.6μ length Those that could clearly reproduce the mold were classified as "good."

Dimensional accuracy/stability [Thickness distribution] Diameter 3Qcll! , 15-12-thick disk (molded product)
Measure the variation in wall thickness using a micro gauge.0 [Warpage] Place a disc (molded product) with a diameter of 307 m and a thickness of 1.5 to 1.2 yh on a surface plate and measure warpage.

[Water absorption rate]

According to JIS K6911-1970, 23±0.
The water absorption rate was measured after being immersed in distilled water at 5° C. for 24 hours.

Example 1 38 parts by volume of methyl methacrylate, 42 parts by volume of styrene,
A liquid mixture consisting of 20 parts of ethylbenzene, n-dodecyl mercaptan, OFI, and 0.05 parts of t-butyl peroxydipenzoate was continuously added to the internal volume at a rate of It/hr. The 2t jacket was fed into a complete mixing reactor.

The polymerization reaction solution, whose polymerization temperature was 140° C., was continuously taken out and sent to an unreacted substance degassing device J.

The obtained copolymer was colorless and transparent. A composition analysis of this polymer using an infrared spectrophotometer revealed that it contained 47% by weight of methyl methacrylate and 53% by weight of styrene.

This copolymer was dissolved in methyl ether ketone to create a 10% by weight methyl 1 methyl ketone solution, and the solution viscosity of the solution was measured using a Cannon-Fenske viscometer in a water bath at 25°C as a guideline for the molecular weight of the polymer. When measured as Fl
It was cps.

Add 1 F40 stearic acid to the above copolymer as a mold release agent.
The resin containing 0 ppm was used in a 5-ounce inline injection molding machine at a cylinder temperature of 260°C and a mold temperature of 60°C.
ff1. in the molded product. zJI#i, surface diameter 12cI
When a disc for DAD of n was molded, it had a laser beam transmittance of 91%, birefringence of 20-30 nm, and a water absorption rate of 20 to 30 nm.
017% We obtained a DAD that satisfies the performance requirements for surface 1.

Example 2 Copolymers with different methyl methacrylate contents were produced in the same manner as in Example 1 by changing the amounts of methyl methacrylate and styrene. 10 of the obtained resin at 25°C
The weight percent methyl ether ketone solution viscosity was 5-8 cps.

This resin was molded using the same molding machine and molding conditions as in Example 1, with a diameter of 1 mm.
2cll! , a 12-thick disk was molded, and this disk was used as a test piece in accordance with JIS K6911-1970.
The water absorption rate was measured. The results are shown in Figure 4. As is clear from Figure 4, the performance in Table 1 is satisfied when the methyl methacrylate content in the copolymer is 70% or less, and when the methyl methacrylate content exceeds 70%, the water absorption rate rapidly decreases. The performance of Table 1 is no longer satisfied.

Example 3 The amounts of methyl methacrylate and styrene charged were varied, and the amount of the molecular weight regulator (n-dodecyl mercaptan) added was varied to co-incorporate the methyl methacrylate content and solution viscosity. God produced different copolymers.

The obtained resins were molded into similar discs under the same molding conditions as in Example 1, except that the cylinder temperature was 500°C and the mold temperature was 70°C, and the birefringence of each resin disc was measured. . The relationship between birefringence and the MMA content (wt%) of the copolymer is shown in Figure 5. In FIG. 5, the solution viscosity of each copolymer is used as a parameter, for example, 8o1n Vis
12 means that the solution viscosity of a 10'N methyl ether ketone solution of the copolymer measured in a water bath at 25°C using a Cannon-Fenske viscometer is 12 cps. As is clear from FIG. 5, the viscosity of the 10% by weight methyl ethyl ketone solution at 25°C of the resin is 2 to 10 cp.
Between s and s, the value of birefringence satisfies the required value (100 nm or less).

Example 4. Comparative Examples 1 to 4 52 parts by weight of methyl methacrylate, 28 parts by weight of styrene,
20 parts by volume of ethylbenzene, 01 parts by weight of n-dodecylmercaptan, 0.0 part by weight of t-butyl peroxybenzoate
Polymerization, degassing of unreacted substances, composition analysis, and solution viscosity measurement were carried out in the same manner as in Example 1, except that a liquid preparation consisting of 5ij parts was used.

The obtained polymer contained 60% by weight of methyl methacrylate, 40% by weight of styrene, and 10% by weight of polymer, and had a methyl ether ketone solution viscosity of Fl cps.

For comparison, acrylonitrile-styrene copolymer (styrene 75% by weight, acrylonitrile 25% by weight, 25°C, 10% by weight mether ether ketone solution viscosity s
cps) (Comparative Example 1), polymethacrylmethyl (
25°C 10% by weight methyl ether ketone solution viscosity 10 c
ps ), (Comparative Example 2), polycarbonate (Panlite L12F10 manufactured by Teijin Kasei Ltd.) (Comparative Example 3), and polystyrene (Styron 666 manufactured by Asahi Dow Co., Ltd.) (Comparative Example 4), the same physical properties were measured. It is also listed in Table 2.

Table 2 shows that the resin of the present invention has very excellent physical properties as a resin for optical high-density information recording media such as DAD and VD. In addition, the resins of Comparative Examples 1 to 4 were
Although it is generally used as a resin with excellent transparency, it cannot simultaneously satisfy both the birefringence and water absorption required for resins for optical high-density information recording media. is clear from Table 2.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing the optical high-density information recording medium according to the present invention in its operating state, FIG. 2 is an enlarged top view of a portion of an embodiment of the optical high-density recording medium of the present invention, and FIG. 4 is a cross-sectional view of the optical high-density recording medium of the present invention in which both the front and back surfaces can be used as recording surfaces, and FIG. FIG. 5 is a graph showing no relationship between the methacrylic acid content and the compound fold as described above. (1)... Resin layer, (21... Metal film, +31 ・
・Convex portion, (4) ・Beep), +51 ・Laser beam, (6) ・Semi-transparent mirror, (7) ・Flat portion, t
S+-...Adhesive. Applicant Asahi Dow Co., Ltd. Representative Yutaka Hitoshi 1) Yoshio No. 2
Figure 3 Figure 4 - MMA content (% by weight) Figure 5 - MMA content (%)

Claims (4)

[Claims] (1) The weight ratio of methacrylic acid L stell monomer and monoalkenyl aromatic monomer is 30 nia 0 to 70:3
The main component is a copolymer copolymerized with 0. An optical high-density information recording medium resin, characterized in that the viscosity of a 10% methyl L-tyl ketone solution of the copolymer at 25°C is in the range of 2 cps to 10 CpS, and the birefringence is 1100 nm or less. (2) Methacrylic acid ester monomers include methyl methacrylate, ethyl methacrylate, hydroxyl methacrylate, hydroxypropyl methacrylate, n-butyl methacrylate, hexyl methacrylate, cyclohexyl methacrylate, n-octyl methacrylate, and methacrylate. The optical high-density information recording medium resin according to claim (1), which is nonyl acid, stearyl methacrylate, or a mixture thereof. (3) The monoalkenyl aromatic monomer is styrene, α
- The high-density information recording medium resin according to claim 1 or 2, which is methylstyrene, chlorostyrene or a mixture thereof. (4) Mainly composed of a copolymer in which a methacrylic acid ester monomer and a monoalkenyl aromatic monomer are copolymerized at a bundle ratio of 30:0 to 70:30, and 10% of the copolymer at 25°C. Methyl ethyl ketone solution viscosity is 2 cps
~10 cps and birefringence is toonm
1. An optical high-density information recording medium characterized by having minute irregularities on one side of a plate-like body made of resin (B) and laminating a metal film on the irregular surface.