JP2003226529A - Method and apparatus for manufacturing glass substrate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method by which temperature control of high precision can be attained without being influenced by a position of a metallic mold, distortion and warp due to residual stress in a formed substrate can be suppressed to the minimum and glass substrate excellent in flatness can be obtained and to provide an apparatus for manufacturing a glass substrate. <P>SOLUTION: The apparatus is provided with upper and lower metallic molds (1) respectively having a mold surface, upper and lower induction coils (8U, 8L) disposed integrally with the respective upper and lower metallic molds, a press forming means for pressurizing a glass raw material between the mold surfaces by moving at least one among the upper and lower metallic molds and respective high frequency power sources 11 connected with respective upper and lower induction coils. Further a heating process is performed by performing induction-heating of the metallic mold by making alternating current flow through the upper and lower induction coils disposed integrally with the respective upper and lower metallic molds. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for manufacturing a glass substrate, and more particularly to a method and an apparatus for manufacturing a glass substrate for a magnetic disk which is most suitable for manufacturing a storage medium such as a magnetic disk.

[0002]

2. Description of the Related Art Conventionally, glass substrates for magnetic disks are
After being cut into a predetermined size, it has been manufactured by a polishing method in which a substrate is polished to obtain a smooth surface. However, in recent years, the substrate is required to have ultra-smoothness, and the polishing process is required to have high precision, which is technically very difficult. Therefore, a manufacturing method for polishing each substrate requires many steps. Therefore, there is a drawback that the product becomes expensive.

On the other hand, a glass material is heated, shaped and cooled,
Since the press molding method for transferring the mold surface to the glass material with high accuracy does not require post-processing, it can be obtained at low cost, high productivity and high quality. Many studies have already been made and commercialized.

By the way, in press molding of high-precision glass products such as magnetic disks and optical elements, temperature control of the mold is one of the important control items, and nichrome heaters and induction heating are mainly used as heating means. , Radiant heaters, etc. are used. In the field of optical element molding where press molding has been used in the past, cleanness, heating efficiency,
Induction heating is often used because of its high controllability (see JP-A-5-24869).

Since induction heating heats an object to be heated in a non-contact manner, it is easy to save heat capacity and to make it clean. Further, in a press molding machine, it is not necessary to place a heater in a system under pressure, so design and maintenance are required. Is advantageous to. Further, when the object to be heated is an electric conductor, it can be directly heated, so that it is excellent in efficiency and heating rate.

[0006] As an example using such induction heating, "optical glass lens molding apparatus" disclosed in Japanese Patent Laid-Open No. 6-64932 and "manufacture of a glass molded body" disclosed in Japanese Patent Laid-Open No. 11-171564. There is a way. The former is
A first high-frequency oscillation coil wound around the outer periphery of the upper mold, a second high-frequency oscillation coil wound around the outer periphery of the lower mold, and induction heating of the mold by these first and second high-frequency oscillation coils. A high-frequency oscillator and a control circuit for changing the oscillation frequency of the high-frequency oscillator according to the position of the mold during press molding to control the temperature of the upper and lower molds of the mold so as to maintain a predetermined value. It has and. Also, the latter is
At least one of the upper mold and the lower mold is movable, preheated by induction heating in a state where the upper mold and the lower mold are separated from each other, and the preheated glass material is supplied to the lower mold which is preheated in the separated condition. After that, one of the upper die and the lower die moves to perform the pressurizing step. Both of the former and the latter are intended for molding small parts such as an optical glass lens so that the relative positions of the mold and the coil are changed.

[0007]

By the way, molding a glass substrate for a magnetic disk, which has a large outer shape, a thin substrate thickness, and a large ratio of the outer shape to the plate thickness, is required.
It has a problem different from that of the optical element. That is, the shape required for the glass substrate for the magnetic disk is
The surface waviness should be as small as possible (flatness), especially in order to improve the followability of the magnetic head during high-speed rotation.
It is required to suppress waviness on the same radius and to have high dimensional accuracy of inner and outer diameters.

However, when the relative positions of the mold and the coil change as described above, the controllability (deviation from setting) of the upper and lower mold temperatures during movement of the mold becomes a problem.
Especially when using thick glass materials such as spheres and marble shapes, the amount of mold movement during molding increases, so the input power to the upper and lower molds changes due to the change in the relative position of the mold and the induction coil. The distribution changes, which causes a temperature difference between the upper and lower molds, which hinders highly accurate molding.

In order to adjust the temperature of the upper and lower molds as described above, the induction coil is moved in the vertical direction, and the method described in JP-A-6-
As disclosed in Japanese Patent No. 64932, there is a method of utilizing current balance adjustment of upper and lower coils and change of frequency. However, these methods use a single power source and a coil, and thus have problems such as poor control followability and a complicated control circuit.

The present invention pays attention to such a problem and enables highly accurate temperature control without depending on the position of the mold, and as a result, distortion and warpage due to residual stress of the molded substrate can be minimized, An object of the present invention is to provide a glass substrate manufacturing method and apparatus capable of obtaining a glass substrate having excellent flatness.

[0011]

In order to achieve the above object, a method of manufacturing a glass substrate according to an aspect of the present invention is to place a glass material between molding surfaces of upper and lower molds and heat the upper and lower molds. A method of manufacturing a glass substrate through a step of moving at least one of the upper and lower molds by a press machine to pressurize the glass material, wherein the heating step is integrated with each of the upper and lower molds. It is characterized in that it is carried out by inductively heating the mold by passing an alternating current through the arranged upper and lower induction coils.

Here, it is preferable that the upper and lower induction coils are connected to different power supplies, and the output of the power supply is adjusted separately while monitoring the temperatures of the upper and lower molds.

Further, it is preferable that the separate power supplies have the same frequency, and the upper and lower induction coils are respectively arranged on the opposite sides of the molding surfaces of the upper and lower molds.

Further, an apparatus for manufacturing a glass substrate according to another aspect of the present invention which achieves the above object is provided with upper and lower molds each having a molding surface and upper and lower molds integrally provided in the upper and lower molds, respectively. An induction coil, a press molding unit that moves at least one of the upper and lower molds to press the glass material between the molding surfaces, and a separate high-frequency power source connected to each of the upper and lower induction coils. And

Here, each of the upper and lower induction coils is
It is preferably arranged on the opposite side of the molding surface of the upper and lower molds.

Further, among the upper and lower induction coils, at least the induction coil arranged in the moving mold is preferably connected to a power source through a flexible lead.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of a glass substrate manufacturing apparatus for carrying out the present invention will be described below with reference to the accompanying drawings.

This manufacturing apparatus is composed of an upper mold 1U and a lower mold 1L each having a molding surface, and is equipped with a mold 1 made of an electrically conductive material such as WC, and the upper mold 1U is tubular. To the upper fixed plate 3U via the upper mold support 2U, and the lower mold 1L to the lower movable plate 3 via the cylindrical lower mold support 2L.
Each is fixedly supported by L. The mold support for mounting the mold 1 may be a metal such as stainless steel, but an electrical insulator such as a ceramic is preferable in consideration of efficiency. Reference numeral 4 is a restriction ring for determining the distance between the molding surfaces of the upper mold 1U and the lower mold 1L. In the present embodiment, the lower movable plate 3L is connected to the cylinder 6 of the pressing machine 5, and constitutes the press molding means for moving the lower mold 1L to press the glass material between the molding surfaces.

On the opposite side of the molding surface of the upper mold 1U, that is, on the back surface, the upper induction coil 8U is provided on the opposite side of the molding surface of the lower mold 1L, that is, the back surface, through the annular upper insulator 7U. A lower induction coil 8L is integrally provided in each of the lower insulation coils 7L via a lower insulator 7L. Upper and lower induction coils 8U, 8L
Are arranged so that their coil center axes coincide with the center axis of the mold 1, and the upper and lower induction coils 8 are
U and 8L are respectively upper and lower inverter power supplies 11U and 11L as high frequency power supplies, and upper and lower current leads 12U and 12L.
Connected through. Here, lower mold 1L on the movable side
The current lead 12L connected to the lower induction coil 8L has a flexible lead 12F in the middle thereof, and the flexible lead 12F is bent to bend the lower induction coil 8L.
However, it can be moved up and down integrally with the lower mold 1L.

Further, temperature measuring elements 13U and 13L such as thermocouples are attached to the center of the back surface of the upper mold 1U and the lower mold 1L (or may be a peripheral part where the mold temperature can be estimated).
The temperature measuring elements 13U and 13L are connected to the temperature controllers 14U and 14L, and while monitoring the temperatures of the upper and lower molds 1U and 1L, the temperature controllers 14U and 14L are used so that the respective temperatures become set patterns. The upper and lower inverter power supplies 11
It is possible to adjust the current (output) of U and 11L.

Note that 15U and 15L are upper and lower cooling units, respectively, and in the present embodiment, they are formed of a material having good heat conductivity and are provided with passages for passing a cooling medium therein. The upper cooling unit 15U is for the upper fixed plate 3U, and the lower cooling unit 15L is for the lower movable plate 3L.
On the other hand, they are attached so as to be movable relative to each other.

The above-mentioned manufacturing apparatus is installed in a chamber, and in order to prevent deterioration of the mold 1 and other components due to oxidation in a high temperature atmosphere, the chamber has a mechanism capable of evacuating or purging with an inert gas. There is.

The glass material M is formed on the molding surface of the lower mold 1L with the upper mold 1U and the lower mold 1L separated from each other by the transfer arm 10 of the transfer machine (not shown) as shown in FIG. Placed on top. An alternating magnetic field is generated by passing an alternating current from the inverter power supplies 11U and 11L to the upper and lower induction coils 8U and 8L, and heating of the upper mold 1U and the lower mold 1L by electromagnetic induction is started. At the same time, the temperatures of the upper mold 1U and the lower mold 1L are controlled by the temperature controllers 14U and 14L while being measured by the temperature measuring elements 13U and 13L, and heated to near the softening point of the glass material M.

The heated glass material M is held in the vicinity of the softening point for a certain period of time, and thereafter, is pressurized by a press 5 through a cylinder 6 and its thickness is regulated by a regulating ring 4 as shown in FIG. Molded into a glass substrate. After the molding, the upper and lower molds 1 are cooled to the glass transition temperature of the glass material M or less by passing the cooling medium through the cooling units 15U and 15L which are in contact with the upper mold 1U and the lower mold 1L, respectively ( (See FIG. 3), then the lower die 1L is lowered and the die is opened. The molded glass substrate is taken out of the chamber by a transfer machine (not shown). During this time, the inside of the chamber is kept in a vacuum or an inert atmosphere.

In the case of this embodiment, the glass material M
Since the mold 1 can be heated even during the conveying operation of the mold 1, its temperature control is easy, and even when the amount of movement of the lower mold 1L for closing the mold and the amount of deformation of the glass material M are large. Since the relative positions of the die 1 and the induction coil 8 do not change during the pressing operation, the input balance to the upper and lower dies does not change, and there is no need to adjust the current distribution between the upper part and the lower part of the induction coil. Is.

Incidentally, FIG. 4 shows another embodiment of the present invention. In contrast to the cylindrical mold support 2 in the previous embodiment, it is a cylindrical mold support 20 having upper and lower flanges, and a cooling gas passage is formed therein to serve also as a cooling unit. Has been done. The upper and lower induction coils 8U and 8L are the upper mold 1U and the lower mold 1L on the front surface side.
Is arranged on the back surface side of the flange where is arranged.
Note that the other configuration is the same as that of the previous embodiment, and thus a duplicate description will be omitted.

The actions and effects of the characteristic configuration of the present invention are listed below.

(1) Induction heating-2 induction coil dual power supply system An induction coil connected to an inverter power supply generates an alternating magnetic field to heat a mold by electromagnetic induction. The upper and lower molds are connected to different coils and power supplies, respectively, so as to have a 2-coil 2-power supply structure that can be heated independently. Using a temperature controller, the mold temperature is monitored so that the power supply has a predetermined temperature pattern. Adjust the output.

The induction coil, which has conventionally been around the mold, is arranged on the back surfaces of the upper and lower molds by being insulated with an insulator, and the mold is heated from the back side by passing an alternating current there. Since the induction coil is circular along the shape of the mold, the mold can be heated uniformly (axisymmetrically). The induction coils arranged independently on the top and bottom have a two-coil, two-power supply configuration in which separate inverter power supplies are connected with current leads, and a temperature measuring element such as a thermocouple is attached to the mold or the peripheral part where the mold temperature can be estimated. While monitoring this temperature, a temperature regulator is used to adjust the current (output) of the inverter power supply so that the temperature of the mold becomes a set pattern. By attaching separate temperature control heating systems to the upper and lower molds, highly accurate temperature control becomes possible.

(2) Mold part / induction coil integrated movement structure On the movable side, the induction coil can operate integrally with the mold by using a current lead capable of absorbing the movement stroke of the mold. As a result, since the mutual inductance between the die and the induction coil does not change during pressing, high precision control of die temperature becomes easy. Further, since the upper and lower molds can be temperature-controlled separately, temperature control can be performed without depending on the mold position, and temperature control can also be performed when the position of the mold is greatly different from that during molding, such as during transportation.

The current lead connected to the coil of the movable die is connected via a flexible lead. Due to the bending of the flexible lead, the induction coil
It has a structure that moves up and down together with the lower mold part. That is, the relative positions of the mold and the induction coil do not change regardless of the position of the mold when the mold of FIG. 1 is released and the pressing operation of FIG. Therefore, the temperature controller becomes a simple control circuit that controls the output of the inverter power supply while monitoring the mold temperature, and the mold temperature adjustment becomes easy.

(3) Mold backside heating-elimination of power supply interference When two inverter power supplies with the same frequency are used, the operation of the power supply becomes unstable if the magnetic fields generated from the coils of both interfere with each other, and the operation of the molding machine becomes unstable. Influence. In the present invention, since the induction coil is installed on the back side of the mold, the magnetic field generated from the coil is shielded by the mold, so that the power supply can operate stably without magnetic field interference.

Further, in the present invention, since the mold exists between the upper and lower induction coils, the magnetic field created by the coil on one side is shielded by the mold, and the two inverter power supplies do not interfere with each other. This effect stabilizes operation and improves productivity.

[0034]

As is apparent from the above description, according to the present invention, it is possible to accurately adjust a mold in which uneven heat is less likely to occur due to highly accurate temperature control of upper and lower molds with respect to a predetermined temperature pattern. Therefore, it is possible to minimize distortion and warpage due to residual stress of the molded substrate, and obtain a glass substrate having excellent flatness. As a result, when this substrate is used as an information recording medium, a high density and highly reliable one can be stably produced.
Also, since the temperature control of the mold is independent for the upper and lower molds,
The control circuit can also be simplified.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an embodiment of a glass substrate manufacturing apparatus according to the present invention, showing a state when a mold is opened.

FIG. 2 is a cross-sectional view showing an embodiment of an apparatus for manufacturing a glass substrate according to the present invention, showing a mold closed state.

FIG. 3 is a time chart showing an example of a molding process of the glass substrate manufacturing method according to the present invention.

FIG. 4 is a cross-sectional view showing another embodiment of the glass substrate manufacturing apparatus according to the present invention.

[Explanation of symbols]

1 mold 1U upper mold 1L lower mold 2U upper mold support 2L lower mold support 3U upper fixed plate 3L lower movable plate 4 regulation ring 5 Press machine 6 cylinders 7U upper insulator 7L lower insulator 8U upper induction coil 8L lower induction coil 10 Transport arm 11U, 11L inverter power supply 12U, 12L current lead 12F flexible lead 13U, 13L temperature measuring element 14U, 14L temperature controller 15U, 15L cooling unit

Claims (6)

[Claims] 1. A step of arranging a glass material between the molding surfaces of the upper and lower molds, heating the upper and lower molds, and moving at least one of the upper and lower molds by a press to press the glass material. A method of manufacturing a glass substrate, wherein the heating step is performed by inductively heating the mold by applying an alternating current to upper and lower induction coils integrally arranged in each of the upper and lower molds. And a method for manufacturing a glass substrate. 2. The upper and lower induction coils are respectively connected to different power sources, and the output of the power source is separately adjusted while monitoring the temperatures of the upper and lower molds. Method for manufacturing glass substrate. 3. The separate power supplies have the same frequency, and the upper and lower induction coils are respectively arranged on opposite sides of a molding surface of the upper and lower molds. Of manufacturing glass substrate of. 4. An upper and lower molds each having a molding surface, an upper and lower induction coil integrally arranged in each of the upper and lower molds, and a glass material between the molding surfaces by moving at least one of the upper and lower molds. An apparatus for manufacturing a glass substrate, comprising: a press molding unit that pressurizes the glass substrate; and a separate high-frequency power source connected to each of the upper and lower induction coils. 5. The glass substrate manufacturing apparatus according to claim 4, wherein each of the upper and lower induction coils is arranged on a side opposite to a molding surface of the upper and lower molds. 6. The upper and lower induction coils, wherein at least the induction coil disposed in the moving mold is connected to a power source via a flexible lead. Glass substrate manufacturing equipment.