JP2685092B2 - Optical information recording medium and manufacturing method thereof - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an optical information recording medium and a manufacturing method thereof,
More specifically, the present invention relates to a transparent substrate particularly suitable for an optical information recording medium that reads information by using linearly polarized light, and a manufacturing method thereof. [Prior Art] In recent years, a recording film such as a magneto-optical recording film, a phase change recording film, a write-once recording film, or a reflective film is provided on one surface of a transparent substrate, and a light beam is applied to the recording film or the reflective film. An optical information recording medium, which records / reproduces information by irradiating light, has attracted attention as a large-capacity recording medium. In this type of optical information recording medium, linearly polarized light or circular light is used as a recording / reproducing light beam. (Akihiko Yoshizawa "PC for magneto-optical recording
Analysis of optical anisotropy of substrates ", Optics, October 1986). By the way, when linearly polarized light or circularly polarized light passes through a birefringent medium, it becomes elliptically polarized light, and one of two linearly polarized light components whose vibration directions are orthogonal to each other has a phase delay (retardation) with respect to the other. Occurs. Therefore, when the transparent substrate is made of a birefringent medium, normal reading of information is hindered by the influence of the retardation, and the SN ratio of the detection signal deteriorates. In particular, it is formed by forming a magneto-optical recording film on one surface of a transparent substrate, and the Kerr rotation angle of the portion where the inverted magnetic domain is formed on the magneto-optical recording film and the portion where it is not formed are linearly polarized. In magneto-optical recording media that detect changes (rotational direction of the plane of polarization), retardation directly contributes to the noise component of the detection signal, so the detection signal
The deterioration of the SN ratio is particularly remarkable. Conventionally, in order to reduce or eliminate the deterioration of the SN ratio of the detection signal due to retardation, a transparent substrate with a minimum retardation is produced by selecting a substrate material or devising a method for producing the substrate. Research is being conducted in that direction. As a result, although productivity is good, thermoplastic resins such as polycarbonate resins are unsuitable as transparent substrate materials for magneto-optical recording media, and at present, thermosetting resins such as ceramics such as glass and epoxy resins. Has been proposed as a suitable transparent substrate material. [Problems of the prior art] However, ceramics such as glass are likely to be cracked or chipped and difficult to handle during manufacturing, use and transportation, and guide tracks corresponding to tracking signals and prepit corresponding to address signals, etc. When transferring the signal pattern of, the so-called 2P method (photo polymerization) has to be applied, which causes a problem of poor productivity. In addition, since thermosetting resins such as epoxy resins can be formed only by a casting method (a method of injecting a resin in a fluid state into a mold having a predetermined shape and heating and curing),
There is a problem that productivity is remarkably poor as compared with a thermoplastic resin to which an injection molding method can be applied. [Means for Solving Problems] The applicant of the present invention has proposed an optical device for an optical information recording medium, which uses linearly polarized light as recording / reproducing light, based on a mathematical analysis described in detail in the section of Examples below. Is capable of reducing the noise component of the detection signal due to retardation to zero by adjusting the polarization plane of the recording / reproducing light to be parallel to, or perpendicular to, the main refractive index axis of the transparent substrate, or 45 degrees. ,
And the deviation between the polarization plane of the recording / reproducing light and each of the above directions is ±
It has been found that the noise component of the detection signal can be made equal to or lower than the allowable level if the angle is 3 degrees or less. In order to realize an optical device for an optical information recording medium having the above function, an optical information recording medium in which the main refractive index axes are aligned in a fixed direction is indispensable. The present invention has been made to address such technical requirements, and comprises a recording film or a reflective film provided on one surface of a transparent substrate, and the information is obtained by irradiating the recording film or the reflective film with a light beam. In the optical information recording medium for recording or reproducing, the main refractive index axis of the transparent substrate is in a scanning direction of the light beam with respect to the transparent substrate or a direction perpendicular thereto or a direction forming 45 degrees with the scanning direction of the light beam. To ± 3
It is characterized in that it is within the range of degrees or less. Further, in a method for manufacturing an optical information recording medium, including a step of forming a transparent substrate by injecting a molten polymer substance into a mold in which a part of a cavity surface is formed by a signal surface of a stamper, a cold mold is used as the mold. Manufactured by using a slum provided with a gate width of 1 mm or less, and controlling the injection speed of the molten polymer substance so that it is slow at the injection start timing and the injection end timing and fast at the intermediate timing. It is a feature of the above. [Operation] When it is assured that the main refractive index axes of the transparent substrate are aligned in a certain direction, a fixed light source and an optical circuit are provided to change the polarization plane of the recording / reproducing light to the main refractive index. It is possible to set parallel to the axis, perpendicular to the axis, or set to 45 degrees. Further, since the main refractive index axis is set to be within ± 3 degrees with respect to the arbitrarily set constant direction, the noise component of the detection signal can be set to the allowable level or less. As a result, an optical information recording medium driving device capable of reading information with a high SN ratio from an optical information recording medium provided with a transparent substrate made of a high retardation material is realized. [Embodiment] FIGS. 1 to 3 show a first embodiment of the present invention. The first embodiment of the present invention is an application of the present invention to a disk-shaped recording medium. As shown in FIG. 3, this disk-shaped recording medium is formed on a transparent substrate 2 on one side of which a signal pattern 1 such as a guide track or a prepit is formed, and on the surface of the transparent substrate 2 on which the signal pattern 1 is formed. And the film 3. The transparent substrate 2 is formed, for example, by injection molding a polycarbonate resin, an acrylic resin layer, or a thermoplastic resin such as a methacrylate resin.
At the same time when the transparent substrate 2 is injection-molded, the signal pattern 1 is transferred to one surface of the transparent substrate 2 in a spiral or concentric pattern centered on the rotation center of the disk-shaped recording medium. On this transparent substrate 2, as shown in FIG.
The main refractive index axis extends in the radial direction (x-x direction) of the transparent substrate 2 and the direction (y-y direction) perpendicular thereto. Said y
The −y direction is the scanning direction of the light beam on the disk-shaped recording medium, and the formation direction of the signal pattern 1. The direction of the main refractive index axis is, as shown in detail in FIG. 2, the radial direction (xx direction) of the transparent substrate 2.
And ± 3 around the direction (y-y direction) perpendicular to this
Allowed up to a range of degrees. The recording film 3 is formed of any known recording material such as a magneto-optical recording film, a phase change recording film and a write-once recording film. For a read-only disc such as a compact disc, a reflective film may be provided instead of the recording film. However, the transparent substrate of the optical information recording medium of the present invention is particularly suitable when applied to an optical information recording medium such as a magneto-optical recording medium which uses linearly polarized light as the information reading light. As the magneto-optical recording material, for example, a TbFeCo-based alloy or the like can be used. Of course, not only when the recording film 3 is composed of a single layer of this magneto-optical recording material, a laminated body of this magneto-optical recording material and an enhancement film for improving reproduction sensitivity,
Alternatively, the recording film 3 may be configured by including a laminated body of these and a protective film. In the optical information recording medium of the first embodiment, the main refractive index axis of the transparent substrate is set to the scanning direction of the light beam with respect to the optical information recording medium, the direction perpendicular thereto, or the scanning direction of the light beam.
Since it is adjusted to ± 3 degrees or less with respect to the direction forming 45 degrees, the polarization plane of the recording / reproducing light is in the direction of the light beam scanning direction or at a right angle thereto or in the direction forming 45 degrees with the scanning direction of the light beam. By adjusting the above, the deviation of the polarization plane of the recording / reproducing light from the main refractive index axis of the transparent substrate can be set within a range of ± 3 degrees or less. Therefore, an optical information recording medium equipped with a transparent substrate made of a high retardation material has a high SN ratio.
It is possible to put into practical use a drive device that can read information in a ratio. Hereinafter, a method of manufacturing the transparent substrate 2 according to the first embodiment will be described. FIG. 4 is a cross-sectional view of a main part of a mold applied to the manufacture of the transparent substrate according to the first embodiment. Mold 11 and
It consists of a movable mold 12 and a punch 13. On the surface of the fixed mold 11 facing the movable mold 12, there is provided a recess 14 forming a part of the cavity, and in the center of the recess 14, a spool 16 communicating with the injection port 15 is provided. Has been established. On the surface of the movable mold 12 facing the fixed mold 11,
A stamper 17 having an inverted pattern of a desired signal pattern to be transferred to a transparent substrate is attached, and is fixed by a stamper retainer 18 so that the center of the inverted pattern matches the center of the recess 14. There is. The stamper 17 and the recess 14 form a doughnut-shaped cavity 19 in a plan view. The punch 13 is slidably attached to a portion of the movable die 12 that faces the spool 16, and a gap d between the inner periphery of the recess 14 of the fixed die 11 is appropriately provided on the outer peripheral portion of the tip. The center gate 20 is configured by the adjustment. The gate thickness d of the center gate 20 is adjusted to 1 mm or less, more preferably 0.1 mm to 0.6 mm. In addition, a cold slam for accumulating a low-temperature molten polymer substance at the beginning of injection is formed on the inner circumference of the tip of the punch 13.
21 is recessed. The capacity of this cold slam 21 is
It is preferable that it is as large as possible to align the main refractive index axes in a certain direction, but in order to reduce the loss of fuel for heating the resin material and the mold, it may be about 1/5 of the capacity of the spool 16. More preferable. Before the molten polymer substance is injected into the cavity 19, the temperature of the resin is adjusted so that the viscosity of the molten polymer substance is 500 poise to 2000 poise. In addition, the temperature distribution on the circumference of the cavity surfaces 14 and 17 centering on the spooth 16 is within ± 5 ° C, and when the glass transition temperature of the resin is Tg, the cavity surfaces of the mold are 14,1
The temperatures of the molds 11 and 12 are adjusted so that the temperature Tc of 7 is Tg−80 ≦ Tc ≦ Tg. When injecting the molten high-molecular substance into the cavity 19, instead of injecting at a constant injection speed from the start of injection to the end of injection, the following multistage injection speed control can be performed. That is, first, the molten high-molecular substance is injected at a relatively low injection speed, and the resin cooled at the stage of passing through the spool 16 is accumulated in the cold slam 21. Next, in order to prevent the temperature of the resin from decreasing in the process of filling the cavity 19 with the molten high-molecular substance, the resin is injected at a relatively high injection speed. Finally, the injection speed is reduced to prevent resin rebound at the end of the cavity. The multi-step control of the injection speed is not limited to the three-step control as described above, and can be set to an arbitrary number of steps. However,
From the viewpoint of productivity improvement, the injection time is 0 in any case.
It is preferably within 2 sec to 1 sec. In FIG. 5, using the mold of FIG. 4 in which the gate thickness d was adjusted to 0.3 mm, the mold temperature and the resin temperature were set to the conditions of the above-mentioned example, and the injection speed of the molten polymer substance was changed in multiple stages. A transparent substrate (control product) that was controlled and molded, and a transparent substrate that was molded using the same mold as this product and under the same temperature conditions without controlling the injection speed in multiple stages (first comparison). Example)
And a transparent substrate formed by controlling the injection speed in multiple stages under the same temperature conditions as the product of the present invention, using a mold having no cold slam and a gate thickness d adjusted to 1 mm (second comparative example). ) Of the main refractive index axis is compared. The horizontal axis of FIG. 5 is the radius of the transparent substrate, and the vertical axis is the deviation of the main refractive index axis with respect to the radius line. This product is a white circle, the first comparative example is a white triangle, and the second comparative example. Two examples are shown as black circles. As is clear from this graph, in the transparent substrate of the present invention, the deviation of the main refractive index axis from the radial line is within ± 1 degree in the inner and outer circumferences. On the other hand, in the transparent substrate of the first comparative example, the deviation of the main refractive index axis with respect to the radial line is within ± 2 degrees in one of the two examples, but is ± 2.5 degrees in the other example. Further, in the transparent substrate of the second comparative example, the deviation of the main refractive index axis from the radial line is about ± 3.5 degrees. Therefore, the transparent substrate of this product makes it easy to adjust the polarization plane of the reading light,
It can be seen that the SN ratio of the detection signal can be reduced. FIG. 6 shows a second embodiment of the present invention. The second embodiment of the present invention is an application of the present invention to a card-shaped recording medium. In this card-shaped recording medium, as shown in FIG. 6, a recording area 33 having a signal pattern and a recording film (not shown) is formed on a part of a transparent substrate 32 on which a predetermined display 31 is made. ing. In this card-shaped recording medium, the longitudinal direction (xx direction) of the transparent substrate 32 is the scanning direction, and the signal pattern is also formed along this direction. Further, the main refractive index axis of the transparent substrate 32 is the longitudinal direction (x−
It is allowed up to a range of ± 3 degrees centered on the x direction) and the direction (y-y direction) perpendicular thereto. As the transparent substrate material and the recording film material, the same materials as in the first embodiment can be used. The optical information recording medium of the second embodiment also has the same effect as the optical information recording medium of the first embodiment. Hereinafter, a method of manufacturing the transparent substrate 32 according to the second embodiment will be described. FIG. 7 is a cross-sectional view of a main part of a mold used for manufacturing the transparent substrate according to the second embodiment, in which 41 is a fixed mold, 42 is a movable mold, and 43 is a gate member. On the surface of the fixed mold 41 facing the movable mold 42, a concave portion 44 having a rectangular planar shape forming a part of the cavity is provided, and a portion communicating with one end of the concave portion 44 is projected. A spool 46 extending from the exit 45 is opened. On the surface of the movable mold 42 facing the fixed mold 41,
A stamper 47 on which an inverted pattern of a desired signal pattern to be transferred is formed is attached to a transparent substrate, and the stamper 47 and the recess 44 constitute a cavity 48 having a rectangular planar shape. The gate member 43 is provided on a side surface of the movable mold 42 on the resin injection side, and a cold slam 49 is recessed in a portion facing the spool 46, and the portion in contact with the movable mold 42 and the fixed portion. Gate between the inner surface of the recess 44 of the mold 41
It is supposed to make up 50. The temperature conditions of the molds 41 and 42, the temperature condition of the molten polymer material injected into the molds 41 and 42, the gate thickness d, the capacity of the cold slam 49, and the injection speed at the time of multi-stage control are as follows. It is set as in the case of the first embodiment. Regarding the transparent substrate of the second embodiment, the gate thickness d is 0.
Using the mold of FIG. 7 adjusted to 3 mm, the mold temperature and the resin temperature were set to the conditions of the above-mentioned example, and the injection speed of the molten polymer substance was controlled in multiple stages to form a transparent substrate (the present invention). Product) and a mold similar to the product of the present invention, and under the same temperature condition, without being controlled by a multi-stage control of the injection speed, without a cold slam, and without a gate thickness d.
Fig. 5 shows the variation of the main refractive index axis of the transparent substrate formed by controlling the injection speed in multiple stages under the same temperature condition as the product of the present invention, using the mold with the diameter adjusted to 1 mm. And almost the same result was obtained. Below, if the polarization plane of the recording / reproducing light is adjusted to be parallel, perpendicular, or 45 ° to the main refractive index axis of the transparent substrate, the noise component of the read signal will be generated regardless of the retardation of the transparent substrate. The reason why the size can be reduced will be described. FIG. 8 is an optical circuit diagram of an optical information recording medium driving device for recording / reproducing information with respect to the optical information recording medium, which mainly includes a laser 51, a half prism 52, and a condenser lens 53. An incident optical path 55 including the optical information recording medium 54
An optical information recording medium 54, a condenser lens 53, a half prism 52, a polarized beam splitter 56, and a detector.
And a reflection optical path 58 including 57 and 57a. As the laser 51, a semiconductor laser or a laser provided with a linear polarization device is used, and the optical information recording medium 54 is irradiated with linearly polarized light through the incident optical path 55. Further, the polarized beam splitter 56,
It is configured with an analyzer and is set at an appropriate angle with respect to the reflection optical path 58. First, as shown in FIG. 9, the polarization plane p-p of linearly polarized light
Is an angle formed by the plane r-r perpendicular to the plane r-r and the transmitted light plane s-s of the polarized beam splitter, and the plane r-r perpendicular to the plane p-p of the linearly polarized light is transparent. The intensity I of the light incident on the detectors 57 and 57a is represented by the following formula (1), where β is the angle formed by the main refractive index axis mm of the substrate. In the equation, δ represents the retardation size, and θ _κ represents the Kerr rotation angle. ^{I = (sin 2 αcos 2 θ} κ + cos 2 αsin 2 θ κ) + sin2βsin (2α + 2β) sin 2 δcos 2 θ κ - (1/2) · cosδsin2αsin2θ κ ...... (1) said first (1) the first term of Is a DC component that does not depend on the sign of the Kerr rotation angle θ _κ , the second term is a noise component due to retardation, and the third term is a signal component that can extract a change in θ as a signal. Therefore, sin (2α + 2β) =
The noise component of the second term can be removed by adjusting the polarization plane of the information reading light so that 0 or sin2β = 0. As is clear from the third term of the above equation (1), the signal strength can be maximized by adjusting the angle α to 45 degrees. Further, when the difference between the intensities I (α) and I (−α) of the light incident on the two detectors 57, 57a shown in FIG. 8 is calculated, the DC component becomes as shown in the following formula (2). Can be removed. I (α) = I (−α) = sin ² δsin2αsin4βcos ² θ _κ− cos δsin2αsin2θ
_κ (2) It should be noted that the formulas (1) and (2) are expressed by the condenser lens 53
The transparent substrate 2 (32) of the optical information recording medium 54 that passes through the center of the
This is true for light having a component that is incident perpendicularly to, but is not true for light that obliquely enters the transparent substrate 2 (32) from the peripheral portion of the condenser lens 53. Less than,
The influence of retardation on this obliquely incident light component will be examined. The retardation for the obliquely incident light component obliquely incident on the transparent substrate 2 (32) from the periphery of the condenser lens 53 is
As shown in FIGS. 10 and 11, by imagining a refractive index ellipsoid (normal ellipsoid) given in the transparent substrate 2 (32) as a function of the main refractive index peculiar to the transparent substrate material. You can ask for it. That is, when the main refractive index in the circumferential direction of the transparent substrate 2 (32) is nx, the main refractive index in the radial direction is ny, and the main refractive index in the vertical direction is nz, the refractive index ellipsoid is represented by the formula (3). Given to you. This refractive index ellipsoid E is used as a transparent substrate 2 as shown in FIG.
It is hypothesized in (32) that, as shown in FIG. 11, when light with an intensity of k is incident from the direction in which the angle with respect to the main refractive index axis nz is θ and the angle with respect to the main refractive index axis nx is φ, The retardation can be expressed by the difference between the major axis and the minor axis of the ellipse e formed by cutting the index ellipsoid E on a plane that is perpendicular to the plane and passes through the origin O. The retardation value fluctuates depending on the angle between the polarization direction of the incident light k and the principal axis of the ellipse e of the cut surface, but its magnitude Ω is a function of the θ and φ Ω (θ, φ). Can be found at. By the way, when attention is paid to the circumferential direction of the condenser lens 53 (the incident angle θ in FIG. 10 is constant), the light condensed by the condenser lens 53 is from any direction φ (0 ≦ φ <2π). It is estimated that the intensity of each oblique incident light is almost constant, including the oblique incident component of. Since the signals detected by the detectors 57 and 57a are obtained by the sum of these, the influence of the oblique incident light as a noise component on the detection signal of the retardation is canceled in the circumferential direction of the condenser lens 53. Expected to be possible. Below, the validity of the above assumption will be examined with reference to FIG.
In FIG. 12, 53 is a condenser lens, E and E'are incident planes of polarization, E is an index ellipsoid virtual on a transparent substrate arranged perpendicularly to the incident light (direction of paper surface), xx Indicates the main refractive index axis of the transparent substrate. Now, as shown in FIG. 12, it is assumed that the linearly polarized light is irradiated so that the incident polarization plane E is parallel to the main refractive index axis xx of the transparent substrate. In this case, the light obliquely incident on the transparent substrate through the two points P and Q which are points on the condenser lens 53 and which are symmetrical with respect to the main refractive index axis xx, has an incident angle θ. Since the incident angle φ is the same and the absolute value is the same, when the refractive index ellipsoid E is cut in a plane perpendicular to this and passing through the origin of the refractive index ellipsoid E, ellipses e ₁ and e ₂ is isomorphic and the retardation δ is equal. By the way, when light passes through the condenser lens 53,
As shown in FIG. 13, it is known that the incident polarization plane changes from E to E '. As shown in FIG. 13, the wavefront of the linearly polarized light before incidence is Σ, the polarization plane of the linearly polarized light before incidence is E, the angle between the polarization plane E on the wavefront Σ and the direction Ep of the p-wave is φ, and the transmission is φ. The plane of polarization of the subsequent linearly polarized light is Σ ′, the plane of polarization of the linearly polarized light after transmission is E ′, and the planes of polarization E ′ and p on the wavefront Σ ′ are
The angle formed by the wave direction Ep ′ is φ ′, the angle formed by the normal line of the incident surface and the incident direction of the linearly polarized light is θ ₁ , and the angle formed by the perpendicular line of the incident surface and the traveling direction of the linearly polarized light is θ ₂ , The angle between the perpendicular of the exit surface and the linearly polarized light traveling in the condenser lens is θ
_{3. If} the angle formed by the normal line of the exit surface and the linearly polarized light after transmission is θ ₄ , the variation of the plane of incident polarization can be obtained by the equation (4). tanφ ′ = tanφcos (θ ₁ −θ ₂ ) cos (θ ₃ −θ ₄ ) ... (4) Since points P and Q are on the same circumference on the lens, θ _{1 in} FIG. 13 is equal, and therefore θ ₂ , θ ₃ , and θ ₄ are also equal.
Therefore, the coefficients for tan φ in the equation (4) are equal. Further, since the angle φ is represented by the angle Δ in FIG. 12 and has the same absolute value and the opposite sign, φ ′ in the equation (4) also has the same absolute value and the opposite sign (± β). When the angles β and −β have such a relationship, when the respective sums are taken, the first term of the equation (2) becomes zero. As described above, the light condensed by the condenser lens 53 includes oblique incident components from all directions, and the intensity of each oblique incident light is estimated to be substantially constant. Therefore, the point P, The relationship of Q holds for all light transmitting portions on the condenser lens 3. Therefore, the first term of the equation (2) becomes zero even if integration is performed for all the light transmitting portions on the condenser lens 53, and the noise component due to the retardation of the oblique incident component is removed. I understand. On the other hand, as shown by E ′ in FIG. 12, when the light is incident non-parallel to the main refractive index axis, the absolute values of the angles β and −β are not equal as shown by e ₁ and e ₂ in the same figure. , Second (2)
The sum of the first term in the equation cannot be zero. A differential detection method is used for the magnitude of noise due to retardation of the optical circuit of the present invention, using the equations (1) to (4) and assuming that the intensity distribution of the recording / reproducing light is Gaussian. When the calculation was performed for the above case, the results shown in FIG. 14 were obtained. In this graph, the horizontal axis represents the angle between the polarization plane of the recording / reproducing light that is linearly polarized light and the main refractive index axis of the transparent substrate,
The vertical axis shows the detection signal level, which is shown by the solid line when the analyzer angle of the polarized beam splitter is set to 45 degrees, and by the broken line when the analyzer angle of the polarized beam splitter is set to 70 degrees. . As is clear from this graph, regardless of the analyzer angle, the angle between the polarization plane of the recording / reproducing light and the main refractive index axis of the transparent substrate should be set to 0 degree, 45 degrees, or 90 degrees. Therefore, it was found that the noise component of the detection signal can be made zero. Also, from this graph,
When the deviation between the polarization plane of the recording / reproducing light and the main refractive index axis of the transparent substrate is suppressed to ± 3 degrees, the noise of the detection signal and the case where the glass transparent substrate is irradiated without adjusting the polarization plane of the linearly polarized light It turns out that the levels are about the same. In the embodiment, the main refractive index axis of the transparent substrate is ± with respect to the scanning direction of the light beam with respect to the optical information recording medium or the direction perpendicular thereto or the direction forming 45 degrees with the scanning direction of the light beam. Although the case of adjusting the angle to 3 degrees or less has been described, the gist of the present invention is not limited to this, and a direction parallel to or perpendicular to the reference direction set in any direction on the optical information recording medium. Alternatively, it can be adjusted to ± 3 degrees or less with respect to a direction forming 45 degrees with the scanning direction of the light beam. [Effects of the Invention] As described above, the optical information recording medium of the present invention has the main refractive index axis of the transparent substrate, the scanning direction of the light beam with respect to the transparent substrate, the direction perpendicular thereto, or the scanning of the light beam. Since it is aligned within a range of ± 3 degrees or less with respect to the direction forming the 45 degree direction, the polarization plane of the recording / reproducing light is the scanning direction of the light beam or the direction perpendicular thereto or the scanning direction of the light beam.
By using a driving device adjusted to a direction of forming 45 degrees, the deviation between the polarization plane of the recording / reproducing light and the main refractive index axis can be controlled within ± 3 degrees, and a high retardation material can be obtained. Information with a high SN ratio can be read from an optical information recording medium provided with a molded transparent substrate. According to the method for producing an optical information recording medium of the present invention, a molten polymer substance is used, which is provided with a cold slam as a mold and a gate width of 1 mm or less when a transparent substrate is injection-molded. Since the injection speed is controlled to be slow at the injection start time and the injection end time and fast at the intermediate time, the direction of the main refractive index axis of the transparent substrate can be aligned in a fixed direction within ± 3 degrees.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a plan view of a transparent substrate according to a first embodiment, FIG. 2 is a partial plan view of a transparent substrate according to a first embodiment showing an allowable range of a main refractive index axis, FIG. 3 is a sectional view of an essential part of an optical information recording medium,
FIG. 4 is a cross-sectional view of a mold applied to manufacture the transparent substrate according to the first embodiment, FIG. 5 is a graph showing the effect of the transparent substrate manufactured by the method of the present invention, and FIG. FIG. 7 is a plan view of an optical information recording medium according to the second embodiment, FIG. 7 is a cross-sectional view of a mold applied to manufacture a transparent substrate according to the second embodiment, and FIG. 8 is an optical information recording medium of the present invention. FIG. 9 is an optical circuit diagram of an applied driving device, FIG. 9 is an explanatory diagram showing each parameter of the calculation formula,
10 and 11 are explanatory views for explaining the index ellipsoid, and FIG.
Figure is an explanatory view showing the relationship between the incident point on the lens and retardation, Figure 13 is an explanatory view explaining the change of the polarization plane due to light collection, and Figure 14 is the polarization plane of the information readout light and the transparent substrate. 6 is a graph showing a relationship between an angle formed by the main refractive index axis and noise caused by retardation. 1: Signal pattern, 2: Transparent substrate, 3: Recording film, 11,41: Fixed mold, 12,42: Movable mold, 13: Punch, 14:44: Recessed part, 15,45:
Ejection port, 16,46: Spool, 17,47: Stamper, 19,48: Cavity, 20,50: Gate, 21,49: Cold slam, 51: Laser, 52: Half prism, 53: Condenser lens, 54 : Optical information recording medium, 55: Incident optical path, 56: Polarized beam splitter, 5
7,57a: Detector, 58: Reflected light path

   ────────────────────────────────────────────────── ─── Continuation of front page    (72) Inventor Mitsuru Shimizu               Hitachi Maxe, 1-188 Ushitora, Ibaraki City               Le Co., Ltd. (72) Inventor Kintane Tsuburaya               Hitachi, 1-88, Torora, Ibaraki City, Osaka Prefecture               Maxell, Inc.                (56) References JP-A-59-60747 (JP, A)

Claims (1)

(57) [Claims] A transparent substrate with a recording film or reflective film on one side,
In an optical information recording medium for recording or reproducing information by irradiating the recording film or the reflective film with a light beam,
The main refractive index axis of the transparent substrate is within a range of ± 3 degrees or less with respect to the scanning direction of the light beam with respect to the transparent substrate, the direction perpendicular thereto, or the direction forming 45 degrees with the scanning direction of the light beam. An optical information recording medium characterized by: 2. The optical information recording medium according to claim 1, wherein the transparent substrate is formed in a disk shape or a card shape. 3. In a method of manufacturing an optical information recording medium, including a step of injecting a molten polymer substance into a mold in which a part of a cavity surface is constituted by a signal surface of a stamper to mold a transparent substrate, a cold slam is used as the mold. It is characterized in that it is provided and has a gate width of 1 mm or less, and that the injection speed of the molten polymer substance is controlled to be slow at the injection start timing and the injection end timing and fast at the intermediate time. Manufacturing method of optical information recording medium. 4. The method for manufacturing an optical information recording medium according to claim 3, wherein the cavity is formed in a disk shape, and the molten polymer substance is filled from the center of the cavity. Medium manufacturing method. 5. The method for manufacturing an optical information recording medium according to claim 3, wherein the cavity is formed in a card shape,
A method for manufacturing an optical information recording medium, characterized in that the molten polymer substance is filled from the side of the cavity.