JP2003095673A - Method and apparatus for producing substrate, method for heating mold, glass substrate and information recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve such problems that heating blocks fastened to soaking members with bolts are deformed due to the difference of thermal expansions, a space is formed between the heating blocks and the soaking members, thereby the temperature increase of molds is slower than that of the heating blocks, and useless energy consumption is increased. SOLUTION: The method includes a heating step for heating the molds 16a and 16b to a predetermined temperature through soaking members 15a and 15b by driving the heating blocks 13a and 13b, while clamping a glass material 30 by a lower mold 16a and an upper mold 16b, and a pressing step for press- molding the molding material 30 by bringing a pair of molds 16a and 16b closer to each other. Heat transfer is achieved by pressing compression springs 21a and 21b such that the heating blocks 13a and 13b are brought into intimate contact with the soaking members 15a and 15b from their backs. The lag of the temperature increase of the mold to that of the heating block is improved, thereby decreasing the time required and the energy consumed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a substrate by heating a molding material such as a glass material to a predetermined temperature and then pressure-molding the material. The present invention relates to a method for manufacturing a substrate in which a soaking member is interposed therebetween. The present invention also relates to a substrate manufacturing apparatus, a mold heating method, a glass substrate, and an information recording medium, which are related thereto.

[0002]

2. Description of the Related Art In recent years, a glass substrate has received a great deal of attention as a substrate for an information recording medium. This is because the glass substrate has high rigidity, high hardness, easy smoothing, is advantageous for downsizing and thinning, and is also advantageous for high density and high reliability. Has been done.

In the glass substrate manufacturing method, a press molding method is effective instead of the polishing method, which has a low productivity and is expensive. The press molding method transfers the molding surface of the mold to the glass material with high accuracy by going through the steps of heating, pressure molding, and cooling the glass material, and does not require post-processing. . Therefore, the press molding method is inexpensive, high in productivity, and high in quality.

The press molding method has already been put to practical use in the field of optical element manufacturing, but even if it is simply applied as it is to a glass substrate for an information recording medium such as a magnetic disk,
The reality is that the desired results are not obtained. One of the reasons is that the ratio of the substrate outer diameter to the substrate thickness is large.
For example, a glass substrate for a 2.5-inch size magnetic disk has a substrate outer diameter of 65 mm and a substrate thickness of 0.635 mm, and the ratio of the outer diameter to the thickness is about 100: 1. Molding such a glass substrate has a problem different from that of an optical element having a relatively small ratio and having a curvature.

The heat generating block is for generating heat and transmitting the heat to the mold. The mold is basically for applying pressure to the glass material to perform molding, and also for transferring heat to the glass material to soften the glass material from the pre-pressing stage. In this heating and pressing process,
Molds are required to manage temperature distribution with high accuracy. The mold material and the heat generating block are different from each other in constituent materials and shapes. It is difficult for the heat transferred from the heat generating block to the mold to bring about the desired temperature distribution on the mold molding surface.

Therefore, it is conceivable to interpose a heat equalizing member between the heat generating block and the mold. The heat equalizing member is for adjusting the state of heat transfer so as to bring about the desired temperature distribution when the heat from the heat generating block reaches the die molding surface.

An outline of a conventional glass substrate manufacturing apparatus having a soaking member will be described with reference to the drawings.

In FIG. 9, 40a is a lower mold element, 40b is an upper mold element, 41a and 41b are cooling members in both upper and lower mold elements 40a and 40b, 42a and 42b are heat insulating members, and 43a and 43b are Heat generating blocks, 44a and 44b are heating elements (heaters), 4
5a and 45b are heat equalizing members, 46a and 46b are molds, 47
a and 47b are mold fixing rings, 48 is a molding machine housing, and 49
Is a cylinder piston. Those abutting in the vertical direction are fixedly connected to each other via bolts. Among these, the bolts 50a and 50b that fixedly connect the heat generating block and the heat equalizing member, which are related to the task, are illustrated in an emphasized manner.

The lower mold element 40a will be described below, but the same applies to the upper mold element 40b.

In the lower die element 40a, the cooling member 41a is fixed to the molding machine housing 48, and the heat insulating member 42 is used.
a is fixed to the cooling member 41a, the heat generating block 43a is fixed to the heat insulating member 42a, the heat equalizing member 45a is fixed to the heat generating block 43a, and the die 46a is brought into contact with the heat equalizing member 45a and presses the die 46a. Mold fixing ring 47a
Are fixed to the heat equalizing member 45a. Although these are fixed by bolts, the bolt 50a for fixing the heat equalizing member 45a to the heat generating block 43a is highlighted. In addition, in the upper mold element 40b, the cooling member 41b is fixed to the cylinder piston 49.
FIG. 10 is a schematic plan view showing the arrangement of the bolts 50a.

The heat equalizing member 45a has the same coefficient of thermal expansion as that of the die 46a, that is, is made of the same material as that of the die 46a in order to uniformly heat the die 46a. On the other hand, the heat equalizing member 45a and the heat generating block 43a are made of different materials. For example, the mold 46a
In the case of a cemented carbide such as tungsten carbide, the heat equalizing member 45a is also a cemented carbide of the same material, but the heat generating block 43a is stainless steel. The bolt 50a is also stainless steel.

FIG. 11 shows a temperature profile when molding a glass substrate in the conventional structure. The heater temperature indicates the output of the thermocouple installed near the heater, and the glass internal temperature indicates the output of the thermocouple inserted inside the glass material. The pressing force during heating is set to 10 kg, the pressing pressure is set to 15,000 kg, and the cooling pressure is set to 10,000 kg. The heater temperature is set to a temperature equal to or higher than the glass softening point Ts.

In this case, aluminosilicate glass was used as the glass material. Aluminosilicate glass
Transition point temperature Tg = 460 ° C., softening point temperature Ts = 580
C., linear expansion coefficient α = 95 × 10 ⁻⁷ / ° C.

Mold 4 in lower mold element 40a
The glass material 51 is placed on 6a. By extending and driving the hydraulic cylinder, the cylinder piston 49 is moved downward together with the upper mold element 40b, and the upper mold 4 is moved.
The molding surface of 6b is brought into contact with the glass material 51 and pressed with a relatively small pressure. Specifically, a force of 10 kg (pressure: about 26 g / cm ² ) was applied. By preliminarily energizing the heating elements 44a and 44b, the upper and lower molds 46a and 46b are moved to 30
The temperature is raised to 0 ° C.

The process following this preliminary process is roughly divided into three stages. These are a heating step, a pressing step, and a cooling step.

First, the heating process will be described. Upper and lower mold 4
6a, 46b starts to be heated from 300 ° C., and the softening point temperature T
Temperature rises above s and keeps at 590 ° C. The rate of increase of the internal temperature of the glass material 51 is considerably lower than the rate of temperature increase of the heat generating block 43a. The reason will be described later.

The internal temperature of the glass material 51 does not reach the vicinity of the glass softening point Ts. Therefore, at a certain stage, that is, at a stage where the temperature is raised to an intermediate point between the glass transition point Tg and the glass softening point Ts (after about 21 minutes from the start of heating), the press process is started.

In the pressing step, the cylinder piston 49 is further moved downward to move the upper die 46b.
And the lower mold 46a presses the glass material 51 strongly enough (15000 kg≅390 kg / cm ² ). The rate of rise of the internal temperature of the glass material increases. That is, the heat generating blocks 43a and 43b and the heat equalizing members 45a and 45, respectively.
This is because the state of close contact with each of b is stronger.

After about 4 minutes, the internal temperature of the glass material 51 becomes close to the glass softening point Ts, at which point the heating elements 44a,
At the same time when the power supply to 44b was stopped, the pressing force was reduced (10000 kg≅260 kg / cm ² ). The subsequent steps are the cooling step. And the temperature monitor of the heating element is 30
The mold was opened when 0 ° C was indicated.

As described above, a glass substrate for a magnetic disk having an outer diameter of 70 mm and a thickness of 0.635 mm was obtained.

[0021]

The apparatus for manufacturing a glass substrate in the above prior art has the following problems.

Heat generating blocks 43a and 43b and die 46
In the press molding apparatus in which the heat equalizing members 45a and 45b are interposed between the heat generating blocks 43a and 43b and the heat equalizing members 45a and 45b, the bolts 5 are commonly used.
It is fastened with 0a and 50b.

The lower mold element 40a will be described below, but the same applies to the upper mold element 40b.

In the lower die element 40a, the heat equalizing member 45a has a heat equalizing effect on the die 46a.
The coefficient of thermal expansion is the same as that of the mold 46a, and as a result, the mold 46a is made of the same material. On the other hand, the heat equalizing member 45a and the heat generating block 43a are made of different materials. For example, when the die 46a is made of cemented carbide, the soaking member 45a is also made of cemented carbide, but the heat generating block 43a is made of stainless steel.

In the initial state, that is, when the heating element 44a is not energized, the soaking member 45a and the heating block 43
The entire surface is in close contact with a. Even in the stage of preheating up to 300 ° C, it is in a close contact state. However, if the temperature of the heat generating block 43a is further increased while increasing the temperature increasing rate with the start of the heating step shown in FIG. 11, the internal temperature of the glass material 51 cannot follow the temperature increasing rate of the heat generating block 43a. .

The reasons that the present inventor recognizes will be explained below as the reasons why the above cannot be followed.

The heat generating block 43a and the heat equalizing member 45a, which are fastened to each other by the bolts 50a, are in close contact with each other at room temperature and the stage of initial preheating, but as the temperature becomes higher, the heat generating block 43a and the heat equalizing member 45a become more stable. Four
There is a difference in the amount of thermal expansion with 5a. This is because the coefficients of thermal expansion differ from each other.

Regarding the amount of thermal expansion, the heat generating block 43a made of stainless steel is larger than the heat equalizing member 45a made of cemented carbide such as tungsten carbide. Due to this difference in the amount of thermal expansion, in the heating process,
As shown in FIG. 12, the heat generating block 43 a and the heat equalizing member 4
A gap 52a is generated at the boundary surface with 5a. Outside air enters the gap 52a or becomes a vacuum or an ultra low pressure,
Both increase the heat insulation. If the heat generating block 43a and the heat equalizing member 45a are not fastened with the bolt 50a,
The heat generating block 43a only expands along its original plane, and does not significantly affect the adhesion with the heat equalizing member 45a. However, if the bolts 50a are not fastened, the horizontal positional relationship between the heat generating block 43a and the heat equalizing member 45a cannot be determined, and the glass material 51
It interferes with the press forming. Unless there is another means for fixing the heat equalizing member 45a in the horizontal direction, the bolt 5
The fastening by 0a cannot be omitted.

Since there is a difference in the amount of thermal expansion and there is a fastening, the heat generating block 43a is curved with respect to its own plane. As a result of the thermal deformation of the heat generating block 43a, as shown in FIG. 12, a gap 52a is generated at the boundary surface between the heat generating block 43a and the heat equalizing member 45a. In addition, 52b is the upper mold element 40.
In b, for the same reason, it is a gap generated at the boundary surface between the heating element 44b and the heat equalizing member 45b.

The formation of the gap 52a means that the adhesion between the heat generating block 43a and the heat equalizing member 45a deteriorates. Heat generating block 43a and heat equalizing member 45a
The area of contact with each other at the boundary surface between the heat generating block 43a and the heat equalizing member 45 increases from the heat dissipation block 43a to the outside air, the vacuum, or the ultra-low pressure that increases the heat insulating property.
The heat conductivity to a is deteriorated, the followability of the temperature inside the glass material to the temperature of the heating element in the heating step is poor, and the temperature rising rate becomes extremely slow.

That is, it takes too long a predetermined time from the start of the heating step to the shift to the pressing step. And this has been a factor that causes an increase in extra energy consumption. In other words, the energization time to the heating element is long, and the set temperature of the heating element is set to a temperature higher than the softening point temperature, resulting in a great waste of energy consumption. . Combined with the fact that the predetermined time is too long and the productivity is low, the cost of molding is high, which is a big problem.

Such a problem is not limited to the glass substrate,
It is generally considered to be widely applicable to the method of interposing a heat equalizing member between the mold and the heat generating block for press molding.

The present invention was devised in view of the above circumstances, and aims to improve the followability of the temperature rise of the mold with respect to the temperature rise of the heat generating block, shorten the required time and reduce the energy consumption. Has an aim.

[0034]

The present invention solves the above problems by taking the following means.

The present invention regarding the method of manufacturing a substrate is premised on the following. It includes a heating step and a pressing step. In the heating step, at least one of the molds is heated to a predetermined temperature through the heat equalizing member by driving the heat generating block, that is, heat while the molding material is sandwiched by the pair of molds. Of the pair of molds, the mold having the heat generating block and the heat equalizing member may be one mold or both molds. In the pressing step, a pair of molds are brought relatively close to each other to press-mold a molding material. One of the pair of molds may be fixed and the other may be movable, or both may be movable.

In such a substrate manufacturing method, according to the present invention, at least in the heating step, the heat generating block is pressed from behind so as to be in close contact with the heat equalizing member to perform heat transfer.

At least in the heating step, a state in which the heat generating block is pressed to bring the heat generating block into close contact with the heat equalizing member is ensured. When the coefficient of thermal expansion is different, the amount of thermal expansion is different between the heat generating block and the heat equalizing member. Conventionally, since the heat generating block and the heat equalizing member are fastened together with bolts or the like, a gap is generated between the heat generating block and the heat equalizing member in the heating process. However, in the present invention, at least in the heating step, the heat generating block is pressed from the rear side so that the heat generating block is brought into close contact with the heat equalizing member. Therefore, even if the heat generating block is deformed due to the difference in the amount of thermal expansion, the deformation can be canceled by the pressing.

Since the deformation of the heat generating block is prevented by pressing in the heating step, the close contact between the heat generating block and the heat equalizing member can be ensured and the contact area between the heat generating block and the heat equalizing member can be maximized. . As a result, the performance of heat conduction from the heat generating block to the mold via the heat equalizing member is improved, and the followability of the temperature rising speed of the molding material to the mold with respect to the temperature rising speed of the heat generating block is improved.

Therefore, the time required to raise the temperature of the mold to the predetermined temperature in the heating step can be shortened. In addition, the performance of heat conduction from the heat generating block to the mold via the heat equalizing member can be satisfactorily exhibited, and the quality of the molded product of the molding material can be advantageously improved. And since the follow-up characteristic of temperature rise is excellent,
Energy consumption can be significantly reduced. Therefore, it is possible to provide a method of manufacturing a substrate having excellent cost performance.

In the above, as a preferred embodiment, the predetermined temperature of the mold in the heating step is set near the softening point temperature in the range of the softening point temperature of the molding material or lower, and in the heating step This means that heat is generated until the temperature rises to a predetermined temperature near the softening point temperature, and when the temperature reaches the predetermined temperature, the predetermined temperature is maintained before proceeding to the pressing step.

The effect of this is as follows.

In the prior art, since the temperature of the mold (molding material) with respect to the temperature rise of the heating block is low, the molding material does not easily reach the predetermined temperature. To make up for this,
The limit of temperature rise of the heating block is set to a level above the softening point temperature. However, in practice, setting the temperature rise limit of the heating block to a level exceeding the softening point temperature is
It is hard to say that it is normal. This is because when the molding material exceeds the softening point temperature, the molding material may deteriorate. When the molding material is a glass material, water may come out and react with the protective film of the mold, which may deteriorate the protective film.

Further, conventionally, the pressing process has been started from the stage before the molding material reaches a predetermined temperature, and the die (molding material) is further heated in the pressing process. That is, in the pressing process, temperature fluctuations occur in the mold (molding material). Therefore, it is difficult to control the duration of the pressing process.

On the other hand, in the substrate manufacturing method of the present invention configured as described above, since the temperature rising characteristic is excellent, the predetermined temperature of the mold in the heating step is ideal. It becomes possible to set the temperature in the vicinity of the softening point temperature within the range of the softening point temperature of the forming material or lower. In the heating step, the heat generating block generates heat until the mold (molding material) reaches a predetermined temperature near the softening point temperature, and when the predetermined temperature is reached, the predetermined temperature is maintained and then the pressing step. Proceed to.

This avoids the inconvenience of having to set the temperature of the mold (molding material) above the softening point temperature. It is also free from the fear of deterioration of the molding material. When the molding material is a glass material, generation of water can be avoided and deterioration of the mold protective film can be avoided. During the pressing process, it is not necessary to actively raise the temperature of the mold (forming material), and it is easy to control the temperature during the pressing process. Through the above synergies, it is possible to improve the quality of the molded product.

There is a time lag (time lag) between the heat generation block reaching a predetermined temperature and the die (molding material) reaching a predetermined temperature. It is after the heating block reaches the predetermined temperature that the pressing process proceeds, but it is also possible to control the time at which it is done, such as after the required time elapses. If monitoring is performed and the pressing process is performed on the condition that the temperature of the forming material reaches a predetermined temperature, more strict temperature control can be performed. Here, of course, regarding the temperature monitoring of the molding material, it is of course better to directly measure the molding material, but if it is difficult, the temperature of the mold may be measured instead.

In the above, in a preferred embodiment, the temperature distribution on the molding surface of the mold in the heating step is a temperature distribution which is axisymmetric with respect to the center of the mold. Axisymmetric means that in any arc around the center, the temperature is substantially equal at any point on the arc. The circumferences of different radii may have different temperatures. However, it is preferable to change monotonically along the radial direction. The axial symmetry here is a broad concept and includes the case of uniform temperature distribution over the entire surface.

In the case where the temperature distribution on the die molding surface is axisymmetric, the axial symmetry of the molded product is guaranteed. Particularly, in the case of a substrate of an information recording medium (particularly a glass substrate), a medium for recording / reproducing that moves in a substantially radial direction with respect to a medium rotating at high speed and floats on an air flow generated by the medium rotating at high speed It is desirable to be axisymmetric in relation to the head. This is because the relative speed in the circumferential direction is overwhelmingly larger than the relative speed in the radial direction, and axial symmetry of the shape is extremely strictly required in the circumferential direction. The ability to guarantee the axial symmetry of the molded glass substrate exactly meets this requirement.

In the above, in a preferred embodiment, when the heat generating block is pressed against the heat equalizing member, the heat generating block is pressed with a bias. A compression spring, a leaf spring, or the like is used as the means for urging. A reliable and simple means of pressing is urging.

When a compression spring or a leaf spring is used, the pressing points against the heat generating block are partial. In particular, when a plurality of springs having relatively small spring constants are used, the pressing points are likely to be partial. In the pressing process, the pair of molds are pressed against each other with a strong pressing force with the forming material sandwiched between them, but at this time, the heat equalizing member that is pressed partially rather than entirely is due to the large pressing force. It tends to cause deformation. The deformation of the soaking member causes the deformation of the mold, which may result in deterioration of the shape of the molded product.

Therefore, in order to counter the deformation of the heat generating block, it is an effective measure to support the heat equalizing member from behind. Particularly, when the pressing force is applied by the biasing means, the heat equalizing member is likely to be deformed by the pressing force.
By supporting the heat equalizing member from behind by a suitable supporting member, deformation of the heat equalizing member can be avoided.
Therefore, it is possible to prevent the deformation of the mold and ensure the shape accuracy of the molded product. From a different perspective, it can be said as follows. By supporting the heat equalizing member from the back side, deformation of the heat equalizing member is prevented, so that a sufficiently large pressing force can be applied. as a result,
It is possible to obtain a molded product having extremely excellent flatness and surface smoothness.

In the above-mentioned substrate manufacturing method, after the pressing step, driving of the heat generating block (heat generating operation) is stopped, and molding is performed with a pressure smaller than the pressure applied to the molding material by the pair of molds in the heating step. A cooling process for lowering the temperature of the molding material while maintaining a state of pressurizing the material may be performed. After pressing by heating and pressurizing, it is general to lower the temperature of the molding material and the mold by natural cooling or forced cooling, but in that case, the mold should not be opened entirely. It is preferable to lower the temperature while maintaining the pressurized state. Until the temperature falls below the transition point,
This is because there is still the possibility that the shape will change. By lowering the temperature while maintaining the pressurized state, it is possible to prevent an unexpected change in the shape and ensure the shape accuracy of the molded product. Further, if the pressure applied in the cooling step is the same as that in the pressing step, the heat generation associated with pressurization is large and the rate of temperature decrease is low.
Further, since it becomes difficult to release the molded product, it is desirable to make the pressure smaller than the pressing force in the pressing step. The time required for cooling the temperature can be shortened and the mold can be released easily when the mold is opened.

The above method of manufacturing a substrate is extremely useful when the molding material is a glass material. Glass substrates for information recording media such as magnetic recording media have many problems at present, but the present invention is extremely effective for breakthrough (breakthrough of technology).

In the case where the above-mentioned molding material is a glass material, in a preferred embodiment, a cemented carbide mold containing tungsten carbide as a main component is used as the mold and aluminum nitride is used as the heating block. It is possible to use a heat-generating block made of silicon carbide or silicon carbide, and to use, as the soaking member, a soaking member made of the same cemented carbide as the die. This specifically describes that the heat equalizing member is made of the same material as the mold and has the same coefficient of thermal expansion, and that the material of the heat generating block is different from that of the heat equalizing member. Is.

In the above, in a preferred embodiment, the pressure applied to press the heat generating block from behind is 0.5 to 2.5 kg / cm ² , preferably 1.0 to
It may be set to 2.0 kg / cm ² .
On the contrary, if it exceeds 2.5 kg / cm ² , the soaking member tends to warp, and if it is less than 0.5 kg / cm ² , the generation of gaps tends to be unable to be suppressed. And
If the applied pressure is in the range of 1.0 to 2.0 kg / cm ² ,
Both flatness and efficiency can be satisfied.

The present invention is also applicable as a mold heating method. In heat transfer from the heat generating block to the mold, a heat equalizing member is interposed between the heat generating block and the mold to perform heat transfer, and the heat generating block is brought into close contact with the heat equalizing member from behind. In this way, heat is transferred by pressing. In this case, the manufacturing of the substrate does not matter. In other words, the object of molding is not necessarily limited to the substrate, and any object may be used.

The present invention also relates to a substrate manufacturing apparatus.

The present invention regarding the apparatus for manufacturing a substrate has, as its constituent elements, at least a pair of molds for heating and molding a molding material to mold, and a heating block for heating at least one of the pair of molds. A heat equalizing member interposed between the heat generating block and the mold, and mold driving means for relatively moving the pair of molds toward and away from each other. It further comprises a pressing means for pressing the heat equalizing member so as to come into close contact with it from behind.

In the above, one of the pair of molds may be provided with the heat generating block, but more preferably, both molds are provided with the heat generating blocks. That is. In a die having a heat generating block, a heat equalizing member is interposed between the die and the heat generating block. Regarding the mold driving means for relatively moving the pair of molds closer to and away from each other, only one of the molds is a movable type and the other is a fixed type, and both molds are both movable types. There is. In the combination of the mold, the heat generating block and the heat equalizing member, since the pressing means for pressing the heat generating block is provided so as to be in close contact with the heat equalizing member, the difference in the thermal expansion amount is caused by Even if the heat generating block is about to be deformed, the deformation can be canceled.
That is, the adhesion between the heat generating block and the heat equalizing member can be ensured to a high degree, and the contact area between the heat generating block and the heat equalizing member can be maximized. As a result, the performance of heat conduction from the heat generating block to the mold via the heat equalizing member is improved,
The mold is improved in conformity with the rate of temperature rise of the heat generating block, and thus the rate of temperature rise of the molding material.

Therefore, the time required to raise the temperature of the mold to the predetermined temperature in the heating step can be shortened. In addition, the performance of heat conduction from the heat generating block to the mold via the heat equalizing member can be satisfactorily exhibited, and the quality of the molded product of the molding material can be advantageously improved. And since the follow-up characteristic of temperature rise is excellent,
Energy consumption can be significantly reduced. That is, the substrate can be manufactured with excellent cost performance.

In the above, the pressing means is preferably a biasing means such as a compression spring or a leaf spring. The structure and control are simple, and the pressing action is reliable, and moreover, constant pressing is possible.

Further, it is preferable that a circular heating block is adopted and the center of the circular heating block is arranged coaxially with the center of the mold. It is easy to obtain the axial symmetry of the temperature distribution.

Alternatively, it is preferable that the heat generating block has a through hole formed in the center thereof and that the center of the heat generating block is arranged coaxially with the center of the mold. In this case, in order to counter the deformation of the heat equalizing member, it is preferable to provide a supporting member that supports the heat equalizing member from the back in a state of being inserted into the through hole of the heat generating block.

The glass substrate obtained by the above-described substrate manufacturing method or manufacturing apparatus of the present invention can have a center line average roughness of 1.0 nm or less at most. The center line average roughness can be 0.7 nm or less, which is more preferable.

Regarding the glass substrate, it is preferable that the main component of the glass substrate is soda lime glass, aluminosilicate glass, aluminoborosilicate glass, borosilicate glass, or zinc silicate glass.

The present invention also relates to an information recording medium, in which at least a recording layer is formed on the surface of any of the above glass substrates. In the case of magnetic recording media,
Generally, an underlayer, a magnetic recording layer, a protective layer, and a lubricant layer are formed in this order. Since the glass substrate is excellent in smoothness and flatness as described above, the information recording medium using the same can advantageously develop its high-speed rotation property and high recording density.

[0067]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1) FIG. 1 is a schematic sectional view showing the structure of a glass substrate manufacturing apparatus according to Embodiment 1 of the present invention.

In FIG. 1, reference numeral 1 is a molding machine, 2 is a casing of the molding machine, 3 is a hydraulic cylinder as a mold driving means, and 4 is a hydraulic cylinder.
Is a conveying means. 10a is a lower mold element, 10
b is an upper mold element, 11a and 11b are cooling members in the upper and lower mold elements 10a and 10b, respectively.
12a and 12b are heat insulating members, 13a and 13b are heating blocks, 14a and 14b are heating elements (heaters), and 15a and 1
5b is a soaking member, 16a is a lower mold, 16b is an upper mold, 1
7a and 17b are mold fixing rings, 18 is a heat retaining cylinder type, 19
Is a restriction ring, 20a, 20b are heat insulating members, 21a, 2
Reference numeral 1b is a compression spring as a pressing means.

FIG. 2 shows a lower die 16a, a soaking member 15a and a heat generating block 13 in the lower die element 10a.
It is a schematic plan view which shows the shape and arrangement of a.

First, the structure of the lower mold element 10a will be described.

An annular cooling member 11a is fixed on the base 2a of the molding machine housing 2, an annular heat insulating member 12a is fixed on the cooling member 11a, and a circular heat equalizing member 15a is fixed on the heat insulating member 12a. The circular lower die 16a is placed on the heat equalizing member 15a, and the die fixing ring 17a is fixed to the heat equalizing member 15a in a state where the circular lower die 16a is externally fitted and engaged with the lower die 16a. Lower mold 16a by ring 17a
Is fixed, and the heat retaining cylinder die 18 is placed on the die fixing ring 17a in a state of being externally fitted to the forming portion of the lower die 16a, and the forming thickness for regulating the thickness of the glass substrate to be press-formed. The regulating ring 19 is mounted on the lower mold 16a in a state where the regulating ring 19 is fitted into the heat retaining cylinder mold 18 and the position thereof is regulated. Then, in the inner space of the annular cooling member 11a and the annular heat insulating member 12a, the circular heat generating block 13a is arranged in contact with the lower surface of the heat equalizing member 15a, and the heat insulating member 20a contacts the lower surface of the heat generating block 13a. The plurality of compression springs 21a are interposed between the heat insulating member 20a and the base portion 2a. Lower die 16a, heat equalizing member 15a, heat generating block 13a, heat insulating members 12a, 20
a and the cooling member 11a are arranged coaxially with each other.

Next, the structure of the upper mold element 10b will be described.

An annular cooling member 11b is fixed to the lower surface of the piston body (cylinder head) 3a of the hydraulic cylinder 3, an annular heat insulating member 12b is fixed to the lower surface of the cooling member 11b, and a heat equalizing member is attached to the lower surface of the heat insulating member 12b. 15b is fixed, and the upper die 16b is brought into contact with the lower surface of the heat equalizing member 15b, and the die fixing ring 17b is fixed to the heat equalizing member 15b in a state of being externally fitted and engaged with the upper die 16b. The upper die 16b is fixed by the die fixing ring 17b. Then, in the inner space of the annular cooling member 11b and the annular heat insulating member 12b, the heat generating block 13b is placed on the upper surface of the heat equalizing member 15b, the heat insulating member 20b is placed on the upper surface of the heat generating block 13b, and the heat insulating member 20b. And piston body 3
A plurality of compression springs 21b are interposed between the lower surface of a and the compression spring 21b. Upper die 16b, heat equalizing member 15b, heat generating block 13
b, the heat insulating members 12b and 20b, and the cooling member 11b are arranged coaxially with each other.

Here, each of the above fixings is performed by a bolt. Use co-fastening if necessary. The heat retaining body mold 18 is not fixed and is simply placed. The same applies to the molding thickness control ring 19.

In the lower mold element 10a, the heat equalizing member 15a is fixed to the base portion 2a via the heat insulating member 12a and the cooling member 11a. In this way, the peripheral portion is fixed and the heat equalizing member 15a supported in a horizontal posture.
Is the heat generating block 1 on the lower surface inside the periphery
3a is in contact with the compression spring 21 through the heat insulating member 20a.
The heat generating block 13a is moved by the urging force of a.
It is pressed by a. Cooling member 11a and heat insulating member 1
The ring 2a has a heating block 13 inside.
This is because a, the heat insulating member 20a, and the plurality of compression springs 21a are arranged.

Similarly, in the upper mold element 10b, the heat equalizing member 15b includes the heat insulating member 12b and the cooling member 1.
It is fixed to the piston body 3a via 1b. The heat equalizing member 15b whose peripheral portion is fixed in this way and which is supported in a horizontal posture has the heat generating block 13b abutted on the upper surface of a portion inside the peripheral portion, and the compression spring 21b of the compression spring 21b is interposed via the heat insulating member 20b. The heat generating block 13b is pressed against the heat equalizing member 15b by the urging force. The cooling member 11b and the heat insulating member 12b are annular because the heat generating block 13b, the heat insulating member 20b and the plurality of compression springs 21 are provided inside.
This is because b is arranged.

The lower mold 16a and the upper mold 16b are each made of a material excellent in mechanical strength at high temperature, such as cemented carbide whose main material is tungsten carbide (WC) or quartz glass. It has become a thing. Furthermore, those having a small coefficient of thermal expansion are desirable. A thin protective film of a noble metal-based metal or a noble metal-based alloy is formed on the press molding surfaces 16a ₁ and 16b ₁ of the lower mold 16a and the upper mold 16b, respectively. The protective film is formed by sputtering a target made of a noble metal-based metal or a noble metal-based alloy material such as platinum (Pt), ruthenium (Ru), or iridium (Ir). Such a protective film prevents the glass material from adhering to the press-molded surface due to repeated press-molding under high temperature and high pressure and the deterioration of the surface smoothness due to the surface roughness of the press-molded surface. For a glass substrate for a magnetic recording medium, the protective film preferably has a smoothness of 5 nm or less. Such a smooth surface can be obtained by polishing with fine particles of cerium oxide.

Heat insulating members 12a and 12b and heat insulating member 2
0a and 20b are made of a material such as ceramic having a low thermal conductivity.

In the lower die element 10a, the heat equalizing member 15a has the same coefficient of thermal expansion as that of the lower die 16a because of the soaking action on the lower die 16a. Composed of the same material.
On the other hand, the heat equalizing member 15a and the heat generating block 13a are made of different materials. For example, when the lower die 16a is a cemented carbide such as tungsten carbide, the heat equalizing member 15a is also a cemented carbide of the same material, but the heating block 1
3a is aluminum nitride (AlN) or silicon carbide (S
The heat generating element 14 is formed on the base material having high heat conductivity and high rigidity such as iC).
a is built in. As the heating element 14a, a plurality of straight tubular heaters embedded in parallel is shown in the figure. The heating element 14a is more preferably a disc-shaped one.

Although the above description is for the lower mold element 10a, the same applies to the upper mold element 10b.

The operation of the glass substrate manufacturing apparatus configured as described above will be described below.

The glass material 30 is preheated to a predetermined temperature by a preheating block (not shown) before being loaded into the casing 2 of the molding machine. The preheated glass material 30 is adsorbed to the adsorption portion 4a at the tip of the conveying means 4, the shutter 22 of the side wall 2c of the molding machine housing 2 is opened, and the conveying means 4 is moved to the molding machine housing 2 through the opening 2d. The glass material 30 is placed on the press-molding surface 16a ₁ of the lower mold 16a by entering the inside, stopping the suction portion 4a at the tip immediately above the press-molding surface 16a ₁ of the lower mold 16a, and then moving it downward. Place. Then, the transporting means 4 is retracted from the opening 2d to the outside by the route opposite to the above, and the shutter 22 is closed. See FIG.

The molding machine 1 performs a heating process, a pressing process and a cooling process in this order. Hereinafter, description will be made step by step.

(1) Heating Step With the preheated glass material 30 placed on the press molding surface 16a ₁ of the lower mold 16a, the hydraulic cylinder 3 is extended and driven, and the upper mold element 10b together with the piston body 3a. And press down to move the upper mold 16b to the press forming surface 16b.
_{The 1} is pressed against the glass material 30 with a small force, and the downward movement of the piston body 3a is stopped when the press molding surface 16b ₁ reaches a predetermined height position.

Then, the upper and lower mold elements 10a, 1
Heating element 14 of heating blocks 13a, 13b at 0b
Power supply to a and 14b is started, and heating of the glass material 30 is started. As shown in FIG. 5, the rate of increase of the internal temperature of the glass material 30 is slower than the rate of temperature increase of the heat generating blocks 13a and 13b. Heating block 13
When the temperature of a, 13b reaches the predetermined temperature To set near the softening point temperature within the range of the softening point temperature Ts or lower, the temperature control for the heating elements 14a, 14b is performed at the predetermined temperature To.
Switch to the state of maintaining. Late, glass material 30
The internal temperature of reaches the predetermined molding temperature To. After the internal temperature of the glass material 30 is stabilized at the predetermined molding temperature To, the press process is started.

In this heating step, the heat equalizing members 15a and 15b and the heat generating block 13a, due to the difference in the coefficient of thermal expansion,
13b has a difference in the amount of thermal expansion. When the two are fastened together with a fastening member such as a bolt as in the prior art, a gap is generated between the two and the heat transfer property from the heat generating block to the heat equalizing member is deteriorated. On the other hand, in the present embodiment, the heat generating block 1 is formed by the compression springs 21a and 21b.
Since 3a and 13b are configured to be pressed against the heat equalizing members 15a and 15b, while maintaining high adhesion between the heat equalizing members 15a and 15b and the heat generating blocks 13a and 13b,
The heat generating blocks 13a, 15b
13b can be relatively displaced along the boundary surface between the two. This is the so-called “escape”. As a result, it is possible to prevent a gap from being formed on the boundary surface. As a result, the performance of heat transfer from the heat generating blocks 13a and 13b to the molds 16a and 16b via the heat equalizing members 15a and 15b is improved. That is, the molds 16a, 16 are controlled with respect to the heating rate of the heat generating blocks 13a, 13b.
b. Consequently, the followability of the temperature rising rate of the glass material 30 becomes good. In addition, the time from the start of the heating step to the shift to the pressing step can be significantly shortened as compared with the prior art.

(2) Pressing Step As shown in FIG. 4, the piston body 3a is further extended and driven in the hydraulic cylinder 3 to heat and press the glass material 30 at the predetermined temperature To. In this state, the heat generating block 13
The heating elements 14a and 14b of a and 13b are temperature-controlled so that a predetermined molding temperature To is maintained. Piston body 3
The extension drive of a is performed by the press forming surface 16b ₁ of the upper die 16b.
Is brought into contact with the regulation ring 19 to regulate the position.
Thereby, the thickness of the obtained glass molded body is determined. Glass material 30 is deformed by the pressing force is strongly held between the press forming surface 16b ₁ of the upper mold 16b to move downward and press-molding surface 16a ₁ of the lower die 16a of the stationary. When the press forming of the glass material 30 with heating and pressurization is completed in this way, a cooling step is performed next.

(3) Cooling Step Heating is stopped by stopping energization to the heating elements 14a and 14b, and the pressure applied by the piston body 3a of the hydraulic cylinder 3 is slightly reduced. Upper and lower mold elements 10a,
Natural cooling is performed on each component in 10b, and the glass molded body obtained by molding is cooled and cooled. In the cooling step, the temperature decrease of the glass molded body is delayed as compared with the temperature decrease of the heat generating blocks 13a and 13b. When the internal temperature of the glass molded body reaches the glass strain point Ps or lower, which is set lower than the transition temperature Tg, the piston body 3a of the hydraulic cylinder 3 is contractively driven to raise the upper mold element 10b. Open the mold.

When the cooling process is completed and the mold is opened,
Eject the glass molding. The shutter 22 is opened, the conveying means 4 is made to enter through the opening 2d, the glass molded body is adsorbed to the tip portion, and the glass molding is retracted from the opening 2d.

Subsequently, the next glass material 30 is carried in by the carrying means 4, and the same processing as described above is repeated.

From the above heating step to the pressing step,
Since the temperature distributions on the press molding surfaces 16a ₁ and 16b ₁ of the molds 16a and 16b are axially symmetrical with respect to the centers of the molds 16a and 16b, the shape of the glass molded body is axially symmetrical. This makes the flying characteristics of the magnetic head excellent in the magnetic recording medium manufactured using the obtained glass substrate.

(Example 1) Next, a method of manufacturing a magnetic recording medium according to the present invention will be specifically described with reference to FIGS.

The molding material 30 is a glass material. As the glass material 30, aluminosilicate glass was used. In the aluminosilicate glass, the transition point temperature Tg is 460 ° C., the softening point temperature Ts is 580 ° C., and the linear expansion coefficient α is 95 × 10 ⁻⁷ / ° C. The weight of this aluminosilicate glass is 6.5 g ± 0.5 g, and the outer diameter is 2
The thickness was 2.3 mm ± 0.3 mm and the thickness was 8 mm ± 0.5 mm.

As shown in FIG. 5, as the molding conditions, the preheating temperature for the glass material was 300 ° C., the mold 16a,
16b is heated from 300 ° C. and maintained at 570 ° C. The pressing step was started 13 minutes after the start of the temperature rise, the molding pressure was set to 15,000 Kg (390 Kg / cm ² ), and the molding time was set to 3 minutes. In the cooling step, the press pressure was set to 10,000 kg (260 kg / cm ² ) and the heating element 14
It cooled until the temperature monitor of a, 14b showed 300 degreeC.

The glass substrate for a magnetic recording medium thus obtained had an outer diameter of 70 mm and a thickness of 0.
It was 635 mm.

The smoothness of the glass substrate was Ra = 0.5n.
It was m ± 0.2 nm, and it was confirmed that the smoothness of the press molding surfaces 16a ₁ and 16b ₁ of the dies 16a and 16b was transferred almost as it was.

(Second Embodiment) FIG. 6 is a schematic view showing an apparatus for manufacturing a glass substrate according to a second embodiment of the present invention. 6, since the same reference numerals as those in FIG. 1 of the first embodiment refer to the same constituent elements, detailed description thereof will be omitted. FIG. 7 shows a lower die 16a, a heat equalizing member 15a and a heat generating block 13a in the lower die element 10a.
It is a schematic plan view showing the shape and arrangement of the. FIG. 8 is a schematic view of the pressing process.

Hereinafter, in the second embodiment, the first embodiment will be described.
The description will focus on the configuration that is different from.

In the lower mold element 10a, through holes 13a ₁ and 20a ₁ are formed in the central portions of the heat generating block 13a and the heat insulating member 20a, respectively. The support member 23a inserted into the through holes 13a ₁ and 20a ₁ is interposed between the base portion 2a of the molding machine housing 2 and the heat equalizing member 15a. That is, the soaking member 15a is supported by the supporting member 23a, and the soaking member 15a is prevented from being deformed by a strong pressing force in the pressing process. The support member 23a is composed of a heat insulating member, but the upper side may be a heat insulating member and the lower side may be a cooling member.

Similarly, in the upper mold element 10b, through holes 13b ₁ and 20b ₁ are formed in the central portions of the heat generating block 13b and the heat insulating member 20b, respectively.
Support member 23 inserted into the through holes 13b ₁ and 20b ₁
b is interposed between the piston body 3a and the heat equalizing member 15b. That is, the soaking member 15 is supported by the supporting member 23b.
It supports b and prevents the soaking member 15b from being deformed by a strong pressing force in the pressing process. Support member 23
Although b is composed of a heat insulating member, the lower side may be a heat insulating member and the upper side may be a cooling member.

In the second embodiment, the support member 23
Since a and 23b are added, even if an extremely large pressing force is applied during mold clamping in the pressing process, this can be counteracted, and the heat equalizing members 15a and 15b and the mold 16a,
The deformation of 16b can be prevented. This allows an increase in the maximum pressing force, which advantageously develops a press-moldable glass substrate having a large diameter.

In each of the above embodiments, the case where the compression spring is used as the pressing means has been described, but the present invention is not limited to this, and a pressing means using a leaf spring may be used. Alternatively, a hydraulic cylinder or an air cylinder may be used. When a spring is used, the action of pressing the heat generating block against the heat equalizing member is constant, but it is not necessarily required to be constant, and the pressing action may be exhibited at least in the heating step. Therefore, when a cylinder is used, it may be configured so that the stretching operation is performed at least in the heating step. However, the stretching operation may be continued from the heating step to the pressing step, and further, the stretching operation may be continued even in the cooling step.

[0104]

According to the present invention, when press-molding a molding material with a heat equalizing member interposed between the heat generating block and the mold, the amount of thermal expansion is equal to that of the heat generating block due to the difference in thermal expansion coefficient. Even if the heating member is different from the heating member, the heating block is pressed against the heating member to prevent the heating block from being deformed and to prevent a gap from being generated between the heating block and the heating member. That is, at least in the heating step, the adhesion of the heat generating block to the heat equalizing member can be secured, and heat can be efficiently conducted from the heat generating block to the heat equalizing member, and further to the mold and the molding material. That is, the followability of the temperature rise rate of the molding material with respect to the temperature rise rate of the heat generating block and the molding material is improved.

Therefore, the time required for raising the temperature of the mold to the predetermined temperature in the heating step can be shortened. Further, since the heat conductivity from the heat generating block to the mold via the soaking member is good, the quality of the molded product can be improved advantageously. Further, since the follow-up characteristic of temperature rise is excellent, it is possible to greatly reduce energy consumption. Therefore, it is possible to manufacture the substrate with excellent cost performance.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of a glass substrate manufacturing apparatus according to a first embodiment of the present invention.

FIG. 2 is a schematic plan view showing the arrangement of a lower mold, a heat equalizing member, and a heat generating block in the lower mold element in the glass substrate manufacturing apparatus according to the first embodiment.

FIG. 3 is a schematic cross-sectional view showing a state of a heating step of the glass substrate manufacturing apparatus in the first embodiment.

FIG. 4 is a schematic cross-sectional view showing a state of a pressing step of the glass substrate manufacturing apparatus in the first embodiment.

FIG. 5 is a temperature profile of glass material molding according to Embodiment 1 of the present invention.

FIG. 6 is a schematic sectional view of a glass substrate manufacturing apparatus according to a second embodiment of the present invention.

FIG. 7 is a schematic plan view showing the arrangement of a lower mold, a heat equalizing member and a heat generating block in the lower mold element in the glass substrate manufacturing apparatus according to the second embodiment.

FIG. 8 is a schematic cross-sectional view showing a state of a pressing step of the glass substrate manufacturing apparatus in the first embodiment.

FIG. 9 is a schematic cross-sectional view of a main part of a glass substrate manufacturing apparatus in the related art.

FIG. 10 is a schematic plan view showing the arrangement of bolts in the related art.

FIG. 11: Temperature profile of glass material molding in the prior art

FIG. 12 is a schematic cross-sectional view for pointing out a problem in the conventional technique.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Molding machine 2 ... Molding machine housing 3 ... Hydraulic cylinder (mold drive means) 4 ... Conveying means 10a ... Lower mold element 10b ... Upper mold elements 11a, 11b ... Cooling members 12a, 12b ... Thermal insulation member 13a , 13b ... heating block 13a _1, 13b ₁ ... through hole 14a, 14b ... heating element (heater) 15a, 15b ... soaking member 16a ... lower die 16b ... upper die 16a _1, 16b ₁ ... press forming surface 17a, 17b ... die fastening ring 18 ... insulation barrel die 19 ... restricting ring 20a, 20b ... heat insulating member 20a _1, 20b ₁ ... through hole 21a, 21b ... compression spring (pressing means) 22 ... shutter 23a, 23b ... support member 30 ... Glass material

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Kengo Kainuma             1-1 Tanabe Nitta, Kawasaki-ku, Kawasaki-shi, Kanagawa             Within Fuji Electric Co., Ltd. F-term (reference) 5D006 CB04 DA03

Claims (18)

[Claims] 1. A heating step of heating at least one of the molds to a predetermined temperature via a heat equalizing member by driving a heat generating block while sandwiching the molding material between the pair of molds, and the pair of molds are opposed to each other. In the method for manufacturing a substrate, which includes a pressing step of press-forming a molding material by closely approaching each other, at least in the heating step, the heat generating block is pressed from behind so as to be in close contact with the heat equalizing member to transfer heat. A method for manufacturing a substrate, which is performed. 2. The substrate manufacturing method according to claim 1, wherein the predetermined temperature is set near a softening point temperature within a range of the softening point temperature of the molding material or lower, and in the heating step, the heat generating block is used. Is carried out until the temperature rises to a predetermined temperature near the softening point temperature, and when the predetermined temperature is reached, the predetermined temperature is maintained and then the pressing step is performed. 3. The method of manufacturing a substrate according to claim 2, wherein the temperature of the forming material reaches a predetermined temperature near the softening point temperature or a temperature near the predetermined temperature, and then the pressing step is performed. Production method. 4. The method for manufacturing a substrate according to claim 1, wherein the temperature distribution on the molding surface of the mold in the heating step is an axially symmetric temperature with respect to the center of the mold. A method for manufacturing a substrate, which is characterized by a distribution. 5. The method of manufacturing a substrate according to claim 1, wherein the heat generating block is pressed against the heat equalizing member with a bias. Production method. 6. The method for manufacturing a substrate according to claim 1, wherein when the pressing portion against the heat generating block is partial, at least in the pressing step, A method for manufacturing a substrate, characterized in that the heat equalizing member is supported from behind to resist deformation. 7. The method of manufacturing a substrate according to claim 1, wherein, after the pressing step, driving of the heat generating block is stopped and the pair of the heating step is performed in the heating step. A method for manufacturing a substrate, comprising a cooling step of lowering the temperature of the molding material while maintaining a state in which the molding material is pressed with a pressure smaller than a pressure applied to the molding material by a mold. 8. The method of manufacturing a substrate according to claim 1, wherein the glass substrate is manufactured using a glass material as the molding material. 9. The method of manufacturing a substrate according to claim 8, wherein a die made of a cemented carbide containing tungsten carbide as a main component is used as the die, and the heating block is made of aluminum nitride or silicon carbide. 2. The method for manufacturing a substrate, wherein the heat generating block is used, and as the soaking member, a soaking member made of the same cemented carbide as the die is used. 10. The method for manufacturing a substrate according to claim 9, wherein the pressing force for pressing the heat generating block from behind is 0.5 to 2.5 kg / cm ² , and preferably 1.0 to
A method for manufacturing a substrate, which is 2.0 kg / cm ² . 11. A method of heating a mold, wherein a heat equalizing member is interposed between the heat generating block and the mold to transfer the heat from the heat generating block to the mold. A method for heating a mold, characterized by pressing from the back so as to be in close contact with the soaking member to transfer heat. 12. A pair of molds for molding a molding material by heating and pressurizing, a heat generating block for heating at least one of the pair of molds, and a heat generating block interposed between the heat generating block and the mold. In a substrate manufacturing apparatus including a heat equalizing member and a mold driving unit that relatively moves the pair of molds toward and away from each other, a press for pressing the heat generating block from behind so as to closely contact the heat equalizing member. An apparatus for manufacturing a substrate, which is provided with a means. 13. The substrate manufacturing apparatus according to claim 12, wherein the pressing means is a biasing means such as a compression spring. 14. The substrate manufacturing apparatus according to claim 12 or 13, wherein the heat generating block is circular, and the center of the circular heat generating block is arranged coaxially with the center of the mold. A substrate manufacturing apparatus characterized by the above. 15. The substrate manufacturing apparatus according to claim 12 or 13, wherein the heat generating block has a through hole formed in the center thereof, and the center of the heat generating block is coaxial with the center of the mold. An apparatus for manufacturing a substrate, comprising: a support member that is arranged in a circular shape and is inserted into the through hole to counter the deformation of the heat equalizing member and supports the heat equalizing member from behind. 16. Even if the center line average roughness is large, 1.0n
A glass substrate having a thickness of m or less, preferably 0.7 nm or less. 17. The glass substrate according to claim 16, wherein the main component of the glass substrate is soda lime glass, aluminosilicate glass, aluminoborosilicate glass, borosilicate glass or zinc silicate glass. A glass substrate for recording media. 18. An information recording medium in which at least a recording layer is formed on the surface of a glass substrate, wherein the glass substrate comprises the glass substrate according to claim 16 or 17.