JPS62219248A - Ventilation type optical disk - Google Patents

Abstract

PURPOSE:To suppress the deformation of a disk substrate, and to eliminate troubles such as the deterioration in S/N due to the deformation of the disk substrate, the breakage of the disk substrate, and the breakage of a recording film by boring a vent hole in an area where the value obtained by subtracting the surface pressure of the disk substrate from the pressure in a gap is specific. CONSTITUTION:The vent hole 8 should be bored within a range of 73-113mm from the center of the disk substrates 1 and 1 so that the hole is bored in an area where the pressure difference between the gap 6 and the surfaces of the disk substrates 1 and 1 is -5-+2 millibars when the optical disk is rotated at 1,200r.p.m. Similarly, when the optical disk is rotated at 1,800r.p.m., the hole should be bored in an area of 93-108mm from the center of the substrate 1 and 1. Further, when the optical disk is rotated at 3,600r.p.m., the vent hole 8 should be bored in an area of 101-105mm from the center of the disk substrates 1 and 1. Thus, the vent hole 8 is bored in said area.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention has an air sandwich structure, and by communicating the air gap formed inside with the outside air, it is possible to allow the outside air to flow into the air gap. This invention relates to a vented optical disc.

[Conventional technology]

In the conventionally well-known optical disk with air sandwich structure, the inner and outer circumferential parts of two disk substrates are bonded with the recording film on which information signals are recorded inside, and the inner and outer peripheral parts are bonded to each other on the surface side of the recording film. The formed void is kept isolated from the outside air.

In this way, optical discs with sealed air gaps do not allow foreign objects such as dust to enter into the air gaps, so the recording film is always in contact with clean air, which prevents foreign objects from adhering to the recording film and causing abnormal conditions. There is no risk of problems such as information recording being obstructed. However, since the gap in such optical disks is sealed, when environmental conditions such as temperature and pressure change, a pressure difference occurs between the air in the gap and the outside air, causing the two bonded disk substrates to face outward. It protrudes or curves inward. For this reason, there is a risk that tracking and focusing of the laser beam for recording and reproduction may be hindered, and in the worst case, the optical device itself may be damaged.

In order to avoid such a risk, an optical disc has been proposed in the past, as shown in FIGS. 9 to 11, in which a ventilation hole is provided to communicate the air gap with the outside air. 106204. Japanese Unexamined Patent Publication No. 59-171049).

In these figures, 11 is a disk substrate formed of a transparent material, 12 is an uneven pattern for tracking and access formed on the inner surface of the disk substrate 11,
13 is a recording film made of a heat mode recording material formed on the uneven pattern forming surface side of the disk substrate 11; 14 is a gap formed between the recording films 13 and 13; and 15 is an opening in the center of the disk substrate 11. central hole, 16 is void 1
4 is a ventilation hole communicating with the outside air, and 17 is a filter attached to the ventilation hole 16.

In the optical disc of the first conventional example shown in FIG.
6 is opened at a position where the inner circumferential end of the cavity 14 and the central hole 15 communicate with each other. Further, in the optical disc of the second conventional example shown in FIG. 10, the ventilation hole 16 is opened at a position where the outer peripheral end of the gap 14 and the outer peripheral part of the disc substrate 11 communicate with each other. In addition, in the optical disc of the third embodiment shown in FIG.
It is opened at both positions communicating with the outer peripheral part of 1.

[Problem that the invention seeks to solve]

By the way, information is recorded and reproduced on such an optical disc by mounting it on a recording/reproducing device equipped with a rotating spindle. When the optical disk is driven to rotate, the centrifugal force causes the inside of the gap 14 and the disk substrate 11 to
The distribution of air pressure on the surface becomes uneven. That is, within the void 14, the pressure at the inner circumference is the lowest (the pressure increases exponentially as it reaches the outer circumference. In this case, the pressure at the inner circumference is lower than atmospheric pressure, and the pressure at the outer circumference is the lowest). On the other hand, on the surface of the disk substrate 11, the pressure on the center hole 15 side is highest, and the pressure decreases exponentially toward the outer periphery.In this case, The pressure at the center (rotation center) of the central hole 15 is approximately equal to atmospheric pressure.

Therefore, among the above-mentioned conventional optical disks, the first conventional optical disk in which the ventilation holes 16 are formed in the inner circumferential portion of the disk substrate 11 has a low pressure inside the air gap 14 when it is rotated by a recording/reproducing device. Outside air flows in, causing a phenomenon in which the two bonded disk substrates 11, 11 bulge outward.

The optical disc records and reproduces information by vertically irradiating the recording film 13 with laser light from the outer surface of the disc substrate 1 and detecting changes in the intensity of reflected light due to the uneven pattern 12. Therefore, when the disk substrate 11 is deformed as described above, the incident angle and reflection angle of the laser beam on the disk substrate 11 become small, causing a problem that normal recording and reproduction of information signals cannot be performed. In this case, in order to record and reproduce normal information signals, it is necessary to keep the tilt angle due to deformation of the disk substrate to 0.5 degrees or less. Furthermore, if the disk substrate 11 is made of a material with a large photoelastic coefficient, such as epoxy or polycarbonate, birefringence of the laser beam occurs every time the disk substrate 11 is deformed, and the S/N ratio further decreases. to degrade.

On the other hand, among the conventional optical disks described above, the second conventional optical disk in which the ventilation hole 16 is provided on the outer periphery of the disk substrate 11 is such that the air in the gap 14 is discharged to the outside when the disk substrate 11 is driven to rotate. Two disk boards combined! 1.
11 is bent inward. If the disk substrate IL 11 warps in this way, not only will it cause the same problems as in the first conventional example, but also the disk substrate IL 11.
A problem arises in that the recording film 13.13 formed on the inner surface of the recording film 11 interferes with the recording film 13 and becomes easily peeled off.

In addition, in the optical disc of the third conventional example in which the ventilation holes 16 are provided in both the inner and outer peripheral portions of the disc substrate 11, the air gaps 16 are
Since an air flow is generated passing through the vent holes provided in the outer circumferential portion of the disk substrate 11, the balance of air conductance between the inner and outer circumferential filter portions becomes a problem. That is, when the air conductance at the inner periphery is higher than that at the outer periphery, the amount of air flowing into the gap 14 exceeds the amount of air being discharged from the gap 14, causing the disk substrates 11, 11 to bulge outward, and the opposite effect occurs. When the air conductance at the outer circumference becomes higher than that at the inner circumference, the amount of air discharged from the gap 14 exceeds the amount of air flowing into the gap 14, and the disk substrate 11,
11 turns inward.

In recent years, in this type of optical disk, there has been a tendency to increase the rotational drive speed to a large extent due to the demand for increased access speed. As the difference in atmospheric pressure increases, the various adverse effects described above become even more pronounced.

In the above-mentioned conventional ventilated optical discs, such problems are not taken into account at all, and when the discs are rotated at high speeds of 120Qr, p, n+ or higher, the difference in atmospheric pressure becomes 2 millibar or more, causing Practicality is lost.

Means for Solving Problem C] As a result of intensive research, the inventor of the present application has found that when an optical disk is driven to rotate, the air pressure in the gap and the air pressure in the disk substrate are If there is a region where the pressure on the outer surface is equal, and if the above-mentioned pressure difference at the opening of the vent is between 15 mbar and +2 mbar, the tilt angle due to warpage of the disk substrate will be approximately 0.5 degrees or less, making it practical. I learned that the above rarely causes problems.

The present invention has been made based on the above-mentioned findings, and includes a vent hole that communicates the air gap formed between two disk substrates with the outside air, extending from the inner circumference of the disk substrate to the outer circumference. It is characterized in that it is located in an intermediate region at a position where the air pressure in the gap minus the air pressure on the outer surface of the disk substrate during rotational driving is 15 mbar to +2 mbar.

〔Example〕

FIG. 1 shows an example of an optical disc according to the present invention. In this figure, 1 is a disk substrate, 2 is an uneven pattern, and 3 is a disk substrate.
4 is a recording film, and 4 is two disk substrates 1. 1 is an inner periphery spacer provided on the inner periphery of the disk substrate 1.1, 5 is an outer periphery spacer provided on the outer periphery of the disk substrate 1.1, 6 is a gap, 7 is a central hole, 8 is a ventilation hole, and 9 is a filter. be.

The disk substrate 1 is made of a transparent material such as polymethyl acrylate polycarbonate, polyprotylene, polyester, epoxy, or glass, and has an inner diameter of 35 mm.
It is formed into a donut shape with a diameter of φ and an outer diameter of 300φ.

The uneven pattern 2 can be formed on one side of the disk substrate 1 by an injection method when the disk substrate 1 is made of synthetic resin, or by a 2P method when the disk substrate 1 is made of glass. can.

The recording film 3 is made of a known heat mode recording material, such as a TeSe-based recording material, by vacuum deposition, for example.
It is formed on the surface of the uneven pattern 2 by using a known thin film forming means such as sputtering.

The inner spacer 4 and the outer spacer 5 have a thickness of 0 and 6.
It is formed from a thin aluminum plate or the like of mm.

Among these spacers, the inner spacer 4 has an inner diameter of 35 mm.
The spacer 5 is formed into a ring shape with an inner diameter of 290φ and an outer diameter of 300φ. Both of these spacers 4 and 5 are
For example, the disk substrate 1 is
is glued in place.

The gap 6 is formed between the two disk substrates 1. 1, an inner circumferential spacer 4, and an outer circumferential spacer 5.

The ventilation hole 8 is located 6811 points from the center of the disk substrate 1.
It will be established in the areas from II+ to 85III11. The opening position of the ventilation hole 8 is determined as follows. That is, when an air-sandwiched optical disk is driven to rotate, the pressure distribution within the gap 6 follows the following equation.

p = CB+/2-T”
”' (11 However, P: Pressure inside the cavity (Pa) r: Distance from the disk center (m) ω: Rotational angular velocity of the disk (rad/sec) k
: Constant of proportionality between air pressure and density [in g/pa-m'') C: Constant of integration [Pa) a: Innermost radius of void (m) b: Outermost radius of void (m) Po: Stationary Internal pressure of the gap (Pa) at the time (from equation 11, the rotational speed of the optical disc is 60 Orpm).

120Orpm, 1800rpm, 3600rpm
Also, the temperature was set to 20℃ (k = 1.19X10-'
Kg/pa,,l), the pressure distribution inside the gap 6 was calculated when the internal pressure P0 of the gap 6 at rest was 1013 mbar, and the calculation results shown in FIG. 2 were obtained.

On the other hand, when the optical disc is driven to rotate, the pressure distribution on the surface of the disc substrate 1.1 is given by the following equation.

However, Pl: pressure on the surface of the disk substrate (Pa)Po
: External pressure (Pa) M : Matsuha number : Adiabatic index (=1.4) From equation (2), the rotation speed of the optical disc is 60 Orpm.

1200rpI11.1800rpm, 3600rpm
When the pressure distribution on the surface of the disk substrates 1, 1 was calculated when m was calculated, the calculation results shown in FIG. 3 were obtained.

From the calculation results shown in FIGS. 2 and 3, the pressure difference between the air gap 6 and the surfaces of the disk substrates 1 and 1 at each rotation speed is determined as follows:
The calculation results shown in FIG. 4 are obtained. Figure 5 shows a disk substrate with a bending rigidity of 40 kg/mm.
2 is a graph showing the relationship between the pressure difference between the inside of the air gap and the outer surface of the disk substrate in the vent forming portion of the 2-inch air sandwich disk and the 8-inch air sandwich disk and the warpage (tilt angle) of the disk substrate, and the warpage of the disk substrate. This shows that in order to keep the temperature below 0.5 degrees, which is the limit that allows normal recording and playback, the vent hole must be set in a range where the pressure difference is between 15 millibar and +2 millibar. As is clear from the graph in FIG. 4, when the optical disc is rotated at 120 rpm, the vent hole 8 is opened in a region where the pressure difference between the gap 6 and the surface of the disc substrate 1.1 is 15 mbar to +2 mbar. In order to
It can be seen that the opening must be in the range of mm. Similarly, when an optical disk is rotated at 180 rpm,
It should not be opened in an area of 93 mm to 108 cm from the center of the disk substrate 1.1. Furthermore, when the optical disk is rotated at 360 rpm, the disk substrate 1
．． It can be seen that the ventilation hole 8 must be opened in an area of 101 mm to 105 mm from the center of the hole 1.

The present invention is characterized in that ventilation holes 8 are provided in the above region.

Furthermore, from FIG. 4, for an optical disk that is rotationally driven at 600 rpm, the pressure difference between the gap 6 and the surface of the disk substrates 1, 1 is 2 millibar or less in the entire area, and the ventilation hole 8 should not be opened at any position. Even when the disk substrate is deformed, problems caused by deformation of the disk substrate do not occur.

The filter 9 is made of, for example, porous ceramics, foamed plastic, or the like, and is attached at a position facing the ventilation hole 8 in the cavity 6 .

In the vented optical disc of the above embodiment, the vent hole 8 is opened in a region where the value obtained by subtracting the external pressure on the surface of the disc substrate 1 from the internal pressure of the gap 6 is 15 mbar to +2 mbar, so that the vent hole 8 is bonded in opposite directions. It is possible to eliminate all problems caused by the deformation of the disk substrate 1.1, such as deterioration of the S/N ratio, destruction of the disk substrate, and damage to the recording film 3.

In the above embodiment, a case has been described in which two disk substrates 1.1 each having a concave-convex pattern 2 and a recording film 3 formed on one side are bonded together, but the gist of the present invention is not limited to this. Instead, as shown in FIG. 6, a so-called single-sided recording type is formed by joining a disk substrate 1 on which a concavo-convex pattern 2 and a recording film 3 are formed and a disk substrate 1a on which a concavo-convex pattern and a recording film are not formed. The same method can be applied to optical discs.

In this case, by opening the ventilation hole 8 on the side of the disk substrate la, it is possible to avoid the problem of the recording area being reduced.

Further, in the above embodiment, two disk substrates 1.
1 through the spacers 4 and 5, the gist of the present invention is not limited to this, and as shown in the conventional example (FIGS. 9 to 11), The gap 6 can also be formed by integrally forming joining protrusions on the inner and outer circumferential parts and abutting them.

Further, in the above embodiment, a case has been described in which a filter 9 is attached to a position facing the ventilation hole 8 in the cavity 6, but the gist of the present invention is not limited to this, and as shown in FIG. Similarly, the filter 9 can also be embedded within the ventilation hole 8.

Further, in the above embodiment, the case where the ventilation hole 8 is penetrated in the front and back directions of the disk substrate 1 has been described, but the gist of the present invention is not limited to this, and as shown in FIG. Ventilation holes 8 may also be provided in the circumferential spacer 4.

〔Effect of the invention〕

As explained above, since the ventilation holes are opened in the area where the pressure inside the gap minus the pressure on the surface of the disk substrate is 15 mbar to +2 mbar or less, deformation of the disk substrate is suppressed and the disk Deterioration of S/N ratio due to substrate deformation.

Problems such as destruction of the disk substrate and damage to the recording film can be solved.

[Brief explanation of drawings]

FIG. 1 is a central sectional view of an optical disk showing an embodiment of the present invention, FIG. 2 is a graph showing the pressure distribution within the gap caused by the rotational drive of the optical disk, and FIG. 3 is a graph showing the pressure distribution generated on the surface of the disk substrate. Figure 4 is a graph showing the pressure difference between the gap and the surface of the disk substrate, and Figure 5 is a graph showing the relationship between the pressure difference between the inside of the gap and the outside of the disk substrate at the vent forming part and the maximum tilt angle of the substrate warp. Graph showing, No. 6
The figure is a sectional view showing a second embodiment of the invention, FIG. 7 is a plan view showing a third embodiment of the invention, FIG. 8 is a sectional view showing a fourth embodiment of the invention, and FIG. 9 is a sectional view showing a fourth embodiment of the invention. FIG. 10 is a cross-sectional view showing an example of a conventionally known vented optical disc, FIG. 10 is a cross-sectional view showing a second conventional example, and FIG. 11 is a cross-sectional view showing a third conventional example. 1... Disc substrate, 2... Uneven pattern, 3...
- Recording film, 4... Inner spacer, 5... Outer spacer, 6... Void, 7... Center hole, 8... Vent hole,
9... Filter. Figure 1 1: Disk substrate 6 Two chambers Gap 2: Concave and convex pattern 7: Center hole 3: Recording film
8: Ventilation hole 4: Inner circumference 4-1 g: Filter 5:
Outer circumference space 7 Distance between cb and others in Fig. 2 (mm) Fig. 3 Distance between l and +%! ('mm) Fig. 4 Rotation, distance of D゛5 (mm) Fig. 5 Fig. 6 Fig. 7 Fig. 8 Fig. 9 Fig. 10 Fig. 11

Claims (1)

[Claims] It has an air sandwich structure, and a ventilation hole is opened to communicate the gap formed inside the two disk substrates with the outside air, and the difference in air pressure between the inside of the gap and the outside surface of the disk substrate that occurs during rotational drive is eliminated. In a ventilated optical disc that is applied to a recording and reproducing apparatus having a rotational condition of 2 millibar or more at both the inner and outer peripheries of the disc substrate, the air vents are formed so that the air pressure inside the gap is removed from the air pressure of the disc during rotational driving. 1. A vented optical disc, characterized in that the optical disc is opened at a position where the atmospheric pressure on the outer surface of the substrate is -5 millibar to +2 millibar.