JP2004059355A - Glass blank, and method of manufacturing substrate for information recording medium and information recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a thin plate shaped glass blank, which is used for an intermediate molding for a substrate for an information recording medium, has a stable diameter and thickness is suppressive in the occurrence of waviness or the like and is high in precision, by a direct press process. <P>SOLUTION: In the method of manufacturing the glass blank for successively molding the glass blank for the information recording medium for the substrate having a prescribe diameter by supplying a prescribed quantity of molten glass onto a lower die and repeating a process for press-molding using a press-molding die including the lower die and an upper die opposed to the lower die, the glass blank is molded so that the peripheral part of the glass is not brought into contact with the press-molding die in the pressing and the minimum interval between the upper and lower die molding surfaces is regulated. In such a case, the outside side diameter of the molded glass blank is measured on the lower die by a non-contact type measuring instrument and the feed quantity of the molten glass is controlled based on the measured result. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for manufacturing a glass blank, an information recording medium substrate, and an information recording medium. More specifically, the present invention is used as an intermediate molded article of a substrate for an information recording medium, has a stable outer diameter and thickness, and has a highly accurate thin plate-shaped glass blank in which occurrence of undulation and the like is suppressed. And a method for manufacturing an information recording medium substrate from the glass blank, and a method for manufacturing an information recording medium using the substrate.
[0002]
[Prior art]
As a substrate of a hard disk used as a large-capacity recording means in a personal computer or the like, a substrate made of glass or glass ceramic is widely used as a substrate having high performance and high reliability. With the spread of personal computers and the development of the information network society, the demand for such glass or glass-ceramic information recording medium substrates and information recording media has been growing rapidly in recent years. Therefore, a substrate manufacturing technique having high productivity is desired. The most influential method among such technologies is a glass intermediate molding that has a shape that approximates the substrate in consideration of the amount of grinding, polishing, etc., or the volume change during crystallization, etc. A so-called direct press method in which the body is produced by press molding of molten glass with a molding die can be used.
[0003]
As a method for producing an intermediate molded body of an information recording medium substrate by direct press, a method disclosed in Japanese Patent Application Laid-Open No. 12-53431 is known. In this method, a groove called a notch is provided in a portion where an inner hole is formed at the stage of forming the intermediate body so that the inner hole processing of the hard disk substrate is facilitated. And, even if the amount of the supplied molten glass is excessive, the peripheral portion of the intermediate molded body is not regulated by the body mold or the like, and the surplus volume of the glass is discharged to the peripheral portion, so that the volume of the supplied glass varies. Even if there is, an intermediate molded body having a stable thickness is obtained every time.
[0004]
Aside from the intermediate molded body described in the above publication, a disk-shaped intermediate body having no notch is also known as an orthodox one. In this case, the peripheral edge of the intermediate molded body is defined by the molding die.
[0005]
By the way, since the intermediate molded body molded by the direct press method requires grinding and polishing when producing a substrate, grinding and polishing waste called sludge is generated. There is a strong demand for sludge reduction in terms of resource saving, reduction of environmental burden by reducing waste, and cost reduction. Therefore, in the direct press method, production of an intermediate molded body having a thickness close to that of the substrate is required.
[0006]
Under such circumstances, the applicant of the present application has previously proposed a method of manufacturing a glass blank which is an intermediate molded product of a substrate for an information recording medium with high precision in which generation of undulation and the like is suppressed. Application 2001-20379). This method is to prevent the peripheral edge of the glass blank from contacting the press mold in press molding, suppress heat radiation due to heat conduction from the peripheral edge of the glass blank to the mold, reduce the temperature distribution in the glass blank plane, This is to reduce the undulation of the blank.
[0007]
In the above method, the peripheral portion of the glass blank, that is, the disk-shaped side portion is not defined by the press mold. Therefore, when the amount of the softened glass supplied to the press mold slightly changes, the outer diameter of the glass blank also changes accordingly. After the glass blank has been annealed, the periphery is machined to a desired outer diameter. However, if the outer diameter of the press-formed glass blank fluctuates, the allowance to be processed by the above outer diameter processing varies depending on the individual blank, and as a result, the allowance for the outer diameter processing must be set uniformly. Is difficult to perform.
[0008]
[Problems to be solved by the invention]
The present invention, under such circumstances, is used as an intermediate molded body of an information recording medium substrate, and has a stable outer diameter, a wall thickness, and a highly accurate thin plate shape in which occurrence of undulation is suppressed. It is an object of the present invention to provide a method for producing a glass blank by direct pressing, a method for producing a substrate for an information recording medium from the glass blank, and a method for producing an information recording medium using the substrate.
[0009]
[Means for Solving the Problems]
The present inventor has conducted extensive studies to achieve the above object, and as a result, using a mold having an upper mold and a lower mold, a predetermined amount of molten glass is press-molded by a specific method to form a glass blank. By sequentially manufacturing, a thin glass blank having no desired undulation and having good accuracy was obtained, and it was found that the object could be achieved, and based on this finding, the present invention was completed. .
[0010]
That is, the present invention
(1) A process in which a predetermined amount of molten glass is supplied onto a lower mold and press molding is performed using a press mold including the lower mold and an upper mold facing the lower mold, and information having a predetermined outer diameter is obtained. In a method for manufacturing a glass blank for sequentially forming a glass blank for a recording medium substrate,
In order to form a glass blank by pressing the peripheral portion of the glass during pressing so as not to contact the press mold, and restricting the minimum distance between the upper and lower mold forming surfaces, the outer diameter of the formed glass blank is set on the lower mold. A method for producing a glass blank, characterized by measuring by a non-contact type measuring device and adjusting the supply amount of the molten glass based on the measurement result,
[0011]
(2) The method for producing a glass blank according to the above (1), wherein a press forming die provided with a means for regulating an interval between upper and lower die forming surfaces is used during press forming.
(3) A plurality of lower molds are sequentially circulated and transferred to a position for supplying the molten glass, a position for press molding, a position for measuring the outer diameter of the glass blank, and a position for taking out the glass blank from the lower mold, thereby sequentially forming the glass blank. The method for producing a glass blank according to the above (1) or (2),
[0012]
(4) A substrate for an information recording medium, wherein the glass blank produced by the method according to the above (1), (2) or (3) is machined to produce a substrate for an information recording medium. Manufacturing method, and
(5) A method for producing an information recording medium, comprising: forming an information recording layer on an information recording medium substrate produced by the method described in (4).
Is provided.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
In the method for manufacturing a glass blank (hereinafter, may be simply referred to as a blank) according to the present invention, the blank is made of a softened glass (hereinafter, sometimes referred to as a gob) formed by an upper mold and a lower mold. It is manufactured by press molding with a molding die provided with. Both main surfaces of the thin glass blank are transfer-molded by the upper mold surface and the lower mold surface, respectively. The upper mold and the lower mold are each composed of one or more members as necessary.
[0014]
In the present invention, a gob, which is a raw material of a glass blank, is usually supplied on a lower mold in a molten glass state, and the weight is controlled so that the glass blank has a predetermined shape. When supplying the gob onto the lower mold (hereinafter referred to as casting), the lower mold temperature is adjusted so that the gob is rapidly cooled due to contact with the lower mold and press forming cannot be performed. Since the mold temperature is lower than the temperature of the gob, the gob and the glass molded product are pressed from the contact surface between the glass and the lower mold until the molded glass is removed from the press mold (hereinafter referred to as “takeout”). The amount of heat is lost. Furthermore, even during press molding, although the upper mold temperature is adjusted, it is generally lower than the temperature of the gob, so that while the upper mold is in contact with the gob or the molded product, the gob and the glass are formed by the upper mold. The heat of the product is lost.
[0015]
It is considered that the undulation of the molded product is caused by a large heat dissipation distribution generated in a plane perpendicular to the pressing direction by the upper and lower dies in the process of cooling the thin plate-shaped molded product. In the direct press method, heat distribution can be generated in the inside of the molded product and the surface of the molded product, the central portion and the outer peripheral portion, and the thick portion and the thin portion in the cooling process. Factors that can be considered as factors that further increase the heat radiation distribution are as follows.
[0016]
(1) The gob is pressed by the upper mold and the lower mold, and spreads in the space between the upper and lower molds. When the periphery touches the body mold, heat radiation from the periphery increases, and the temperature of the glass outer periphery increases rapidly. And the heat dissipation distribution increases.
(2) The notch described in the above-mentioned gazette introduced as a conventional technique is a groove having an extremely small area as compared with the main surface of a molded product. Such a portion has a large mold contact area per unit area perpendicular to the pressing direction, and locally increases the heat radiation from the glass as compared with the periphery of the notch, which is a factor of increasing the heat radiation distribution.
Also, when the notch is formed in the vicinity of the peripheral portion by press molding, heat radiation from the peripheral portion increases due to contact with the notch forming portion of the molding die, and the result is similar to (1).
[0017]
(3) Since the above-mentioned notch is used at the time of inner diameter processing or outer diameter processing, the thickness of the notch portion is not described in the above-mentioned publication, but it is advantageous that the thickness of the notch is smaller than the thickness of the target substrate from the viewpoint of performing the processing. It is inferred. On the other hand, when inner diameter processing is performed, the thickness of the main body of the above publication is naturally larger than the thickness of the target substrate. If the thickness of the notch is thinner than the maximum thickness of the target board, the heat conduction from the main body or the inner hole to the notch does not catch up with the heat radiation speed from the notch to the mold. The heat radiation distribution is further increased.
[0018]
(4) In the case where the glass blank has a thick portion and a thin portion having the smallest thickness, if the area of the thin portion becomes smaller than the area of the thick portion, the thin portion becomes a local temperature drop portion as in the case of the notch. And the heat dissipation distribution becomes larger.
(5) As the thickness of the glass blank is reduced, the heat dissipation distribution increases due to the factors (1) to (4), and the influence of the undulation due to the heat dissipation distribution also increases.
[0019]
In order to eliminate such factors, in the blank manufacturing method of the present invention, a gob is press-formed so that the peripheral edge of the blank to be formed does not come into contact with the mold, and a blank having at least a notch portion is produced. Good to do. In the production method of the present invention, as a preferred embodiment, for example, a method of producing the following three types of glass blanks can be mentioned.
[0020]
First, a first aspect is a method for producing a glass blank having a flat front and back surface and a surface including a peripheral portion. Here, the flat surface means a surface on which intentional unevenness is not provided, apart from minute warpage and inevitable minute unevenness. In this case, it is desirable that the front and back surfaces of the glass blank, that is, both main surfaces are parallel to each other.
[0021]
Next, in a second aspect, the minimum value of the thickness of the glass blank, that is, the thickness of the thinnest portion is larger than the thickness of the thickest portion of the target glass substrate (the maximum value of the thickness of the substrate). This is a method for producing a thick glass blank. As such a molding, a thick portion and a thin portion are formed as in a glass blank suitable for producing a flat glass sheet having excellent flatness disclosed in Japanese Patent Application Laid-Open No. 10-194760 previously filed by the present applicant. Forming of a glass blank having the same can be exemplified.
[0022]
Further, as a third aspect, there is provided a method of producing a glass blank having a thick portion and a thin portion having the thinnest thickness, wherein the area of the thin portion is larger than the area of the thick portion. As such a forming, a forming of a glass blank suitable for producing a plate-like glass having excellent flatness disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 10-194760 can be exemplified.
[0023]
In this way, direct press molding in which generation of undulation is suppressed can be performed. At this time, the periphery of the glass blank does not contact the press mold. Therefore, although the amount of heat radiation due to the heat conduction from the peripheral portion of the glass blank to the press mold is reduced, since the outer diameter of the glass blank is not defined by the press mold, fluctuations in the forming conditions appear as changes in the outer diameter of the glass blank. Will be. In particular, the present invention regulates the minimum distance between the upper and lower mold forming surfaces during pressing. That is, the distance between the upper and lower mold forming surfaces when the press mold is clamped is regulated to be always constant. In addition, this regulation can be performed using a press mold provided with a means for regulating the interval between the upper and lower mold forming surfaces. As described above, since the distance between the upper and lower mold forming surfaces is regulated so as to be always constant, if the amount of the molten glass supplied on the lower mold fluctuates, the fluctuation is not the thickness of the glass blank, but the outside. Appears as a variation in diameter.
[0024]
Therefore, in the present invention, the outer diameter of the glass blank is measured on the lower mold by a non-contact measuring device, and if the measurement result is shifted from the outer diameter of the target glass blank, the outer diameter is determined according to the amount of the shift. Feedback to the mechanism that controls the amount of molten glass supplied to the lower mold. That is, when the outer diameter of the glass blank is larger than a required value, control to reduce the supply amount of the molten glass is performed, and when the outer diameter of the glass blank is smaller than the required value, control to increase the supply amount of the molten glass is performed. . When the required outer diameter is obtained, the supply amount of the molten glass is kept as it is. The supply amount of the molten glass can be controlled as follows.
[0025]
<Method 1>
A homogeneous molten glass is prepared, and the molten glass flows down from a pipe called a feeder at a constant outflow speed. The molten glass stream is cut using a cutting blade maintained at a temperature at which the molten glass does not fuse, and the tip of the cut molten glass stream is received on a lower mold. At this time, the supply time of the molten glass can be adjusted by controlling the time interval of cutting by the cutting blade. That is, if the time interval is lengthened, the supply amount of the molten glass increases, and if the time interval is shortened, the supply amount of the molten glass decreases. At this time, it is desirable to control the temperature of the feeder so that the viscosity of the molten glass flowing out is kept constant.
[0026]
<Method 2>
Similar to the method 1, the homogeneous molten glass flows out of the feeder and is cut by a cutting blade. At this time, the time interval of cutting by the cutting blade is also set to be constant. The viscosity of the prepared molten glass is also kept constant. And the outflow speed of the molten glass flow is changed by controlling the temperature of the feeder. By increasing the temperature of the feeder, the viscosity of the molten glass decreases and the outflow speed increases, so that the supply amount of the molten glass increases. Conversely, by lowering the temperature of the feeder, the viscosity of the molten glass increases and the outflow speed decreases, so that the supply amount of the molten glass decreases. Thus, by changing the temperature of the feeder, the supply amount of the molten glass can be increased or decreased.
As a specific example, a heater is provided around the feeder, and the temperature of the feeder is controlled by changing or maintaining a constant current value flowing through the heater.
[0027]
<Method 3>
The supply amount of the molten glass is controlled by changing both the cutting time interval of the cutting blade and the feeder temperature. (Combination of methods 1 and 2)
However, when changing the temperature of the feeder, it is necessary to pay sufficient attention to prevent striae and devitrification of the outflowing glass.
[0028]
Further, the following method can be exemplified as a method for regulating the minimum distance between the upper and lower mold forming surfaces at the time of pressing. A preferred method is to provide a contact portion that comes into contact with each other at the time of pressing around the lower mold forming surface and the upper mold forming surface, and the upper and lower mold contact portions come into contact with each other in a mold clamped state, so that the distance between the upper and lower mold forming surfaces is reduced. This is a means for regulating the state so that it is not narrower than the state. In this case, the contact portion is provided at a position not in contact with the glass blank. The lower mold contact portion may be at the same height as the lower mold forming surface, may be provided below, or may be provided above. However, considering the easiness of measuring the outer diameter of the glass blank described below, the peripheral portion of the glass blank is positioned higher than the lower mold contact portion in a state where the glass blank on the lower mold forming surface is placed. It is desirable to do. By doing so, the outer diameter measurement can be facilitated without hiding the peripheral portion of the glass blank by the lower die contact portion.
[0029]
As another method, a method of controlling the interval between the upper and lower mold forming surfaces to a predetermined value using a mold having a structure as shown in FIG. This molding die is composed of a lower die 3, an upper die 4, a trunk die 5, and an upper trunk die 6, and the upper die 4 is slidable inside the upper trunk die 6. 2 is a gob. A body mold 5 that houses the lower mold 3 and a body mold 6 that houses the upper mold 4 are used to press the two body molds during pressing. Then, the gob is pressed by reducing the distance between the molding surfaces of the upper and lower dies. At this time, the stroke of the upper and lower molds is controlled, and the interval between the upper and lower mold forming surfaces is controlled to a predetermined value.
[0030]
The first method is preferable when the shape of the press mold is set, because the minimum distance between the molding surfaces is always kept constant by mechanical means.
In the second method, when measuring the outer diameter of the glass blank, it is desirable to raise the lower mold in the barrel together with the glass blank and perform an operation such that the peripheral edge of the glass blank is higher than the upper end of the barrel. .
[0031]
Next, a method for measuring the outer diameter of the glass blank will be described. The glass blank immediately after molding is at a high temperature, and the contact portion may be deformed when a contact measurement is performed. In addition, since the contact type measurement needs to be performed while the object to be measured is at rest, application to the present invention in which supply of molten glass and press molding are repeated reduces production efficiency. Furthermore, since the non-contact measurement can be performed at a higher speed than the contact measurement, fluctuations in the outer diameter of the glass blank can be immediately fed back to the adjustment of the supply amount of the molten glass.
[0032]
As a non-contact type measuring method, an optical measuring method using a laser beam is most preferable, but other methods such as a measuring method utilizing a temperature difference between a mold and glass can be exemplified.
[0033]
From the viewpoint of promptly feeding back the measurement result of the outer diameter, it is preferable to measure the outer diameter of the glass blank immediately after press molding. In addition, when a plurality of lower molds are supplied with molten glass, a position for press molding, a position for measuring the outer diameter of the glass blank, and a position where the glass blanks are taken out from the lower molds, when the glass blanks are sequentially circulated to form a glass blank, It is preferable to set a position for measuring the outer diameter of the glass blank near the position for press molding. In particular, when a plurality of lower dies are arranged on a turntable and the above-mentioned circulating transfer is performed by rotating the turntable by an index, it is preferable to measure the outer diameter in a section next to a section (stop position) of press molding. In addition, after press molding, to correct the warpage of the glass blank, or to accelerate the cooling of the glass blank, when pressing the upper surface of the glass blank on the lower mold with a pressing member, the outer diameter of the glass blank after the pressing Preferably, a measurement is made.
The measurement of the outer diameter of the glass blank may be performed at only one location, but may be performed at a plurality of locations, or the supply amount may be controlled based on the measurement results at different locations.
[0034]
The measurement data of the outer diameter is processed by a computer, a sequencer, or the like, and the supply amount of the molten glass is adjusted as needed based on the data by the above-described method or the like.
The above control is desirably performed so that the change of the outer diameter with respect to the outer diameter of the glass blank falls within a range of 0.05 to 0.1%.
[0035]
In the method for manufacturing a glass blank of the present invention, as described above, the peripheral edge of the glass blank formed during press molding is prevented from contacting the molding die, that is, the peripheral edge is not regulated, Is a free surface. Since the molding surface of the mold is not transferred to the free surface, processing marks existing on the molding surface are not transferred. Further, when the molding is performed by applying the powdery release agent to the molding surface, the free surface is not pressed by the molding surface to which the powder is applied, so that the roughening due to the release agent cannot occur in this portion.
[0036]
In addition, the peripheral portion can maintain a relatively low viscosity in the press forming process as compared with the conventional one, and plastic deformation of the peripheral portion is possible even when sink occurs in the molded product. On the other hand, since the surface formed by transfer molding by the upper and lower mold forming surfaces is cooled and becomes highly viscous, sink marks can be dispersed in the peripheral portion, and reduction in blank shape accuracy due to sink marks can be reduced.
[0037]
If the amount of gob is made strictly equal every time, or if the excess glass is merely protruded from the outer periphery as described in the above-mentioned publication, the variation in the total height corresponding to the maximum thickness of the molded product due to sink will increase. On the other hand, in the method of dispersing sink marks on the periphery of the molded product as in the present invention, the total height of each molding can be kept within ± 5 to 10 μm.
[0038]
When a thick portion and a thin portion are provided in the blank, it is desirable that the thick portion is formed so that the thick portion receives pressure from both main surface sides of the blank. For that purpose, a thick portion is formed on the outer peripheral portion of the blank, a thin portion is formed in a portion surrounded by the outer peripheral portion, a thick portion is formed in the center portion of the blank, and a thin portion is formed around the blank portion, or the outer periphery of the blank is formed. Preferably, a thick portion is formed at the portion and the center portion, and a thin portion is formed between the outer peripheral portion and the center portion. It is preferable to make the thickness of the thin portion and the thickness of the thick portion uniform.
The shape of the blank is preferably a shape symmetrical to the pressing direction like a substrate for a magnetic disk, that is, a disk shape. In a disk-shaped blank, the side surface of the disk is the peripheral portion.
[0039]
The present invention is suitable for producing a glass blank having a thickness of 0.8 to 2.2 mm. Even with a blank having a thick portion and a thin portion, both the maximum value and the minimum value of the thickness of the blank are suitable for producing a glass blank having the above range.
[0040]
1 (a) to 1 (d) are schematic vertical sectional views with respect to a main surface showing different examples of the shape of a disk-shaped glass blank obtained by the method of the present invention, and reference numeral 1 denotes a glass blank.
[0041]
(A) in FIG. 1 shows a disk-shaped glass blank having a uniform thickness without a thick portion or a thin portion, and preferably has a thickness of 0.8 to 1.8 mm, more preferably 0.9 to 1.7 mm. Particularly preferred. A blank having the above thickness and an outer diameter of 60 to 100 mm is preferable. (B) shows the glass blank which has the thick part 11 in the outer peripheral part of the glass blank 1, and the thin part 12 in the part surrounded by the outer peripheral part, and (c) shows the outer peripheral part and center part of the glass blank 1. 2 shows a glass blank having thick portions 11 and 11 ', respectively, and a thin portion 12 between the outer peripheral portion and the central portion. (D) Glass shows a glass blank having a thick portion 11 'at the center of the blank 1 and a thin portion 12 around the thick portion 11'. Thus, in the case of a disc-shaped blank having the thick part 11 and / or 11 'and the thin part 12, the thickness of the thick part is 1.0 to 2.2 mm and the thickness of the thin part is 0.8 to 2 0.0 mm is preferable. Further, a glass blank having an outer diameter of 60 to 100 mm in the above thickness range is preferable. Reference numeral 13 indicates a peripheral portion.
[0042]
By performing press molding according to the glass blank manufacturing method of the present invention, the gob is easily spread, and it is not necessary to excessively increase the pressing pressure even when the molded product is made thin. As a result, pressing defects are reduced, and a powdery release agent is not required, and the surface roughness of the molded article due to the release agent is reduced. In order to prevent damage to the molded product in the notch forming portion, it is advantageous not to form a local thin portion such as a notch.
The method for producing a glass blank of the present invention is applied to the production of a glass blank for an information recording medium.
[0043]
Next, the structure of the molding die and the flow of press molding will be described.
FIG. 2 is a schematic view showing an example of a state in which the disk-shaped glass blank shown in FIG. 1A is produced by press molding. The molding die includes a lower die 3 and an upper die 4. The upper mold 4 is provided with a stopper for surrounding the molding surface and abutting against the lower mold 3 at the time of mold clamping to regulate the interval between the upper and lower mold molding surfaces. As shown in FIG. 2, in the casting step, the molten glass flow 6 flows out of the outflow pipe 5 and is supplied to the center of the lower mold forming surface. In addition, as shown in FIG. 2, the upper surface of the lower mold 3 on which the molding surface is formed is flat (excluding the portion for molding the thick portion of the glass blank). In the next cutting step, the molten glass stream is cut by the cutting blade 7 to obtain a predetermined weight of the gob 2 on the lower mold forming surface. Subsequently, the gob is pressed by the upper mold 4 and the lower mold 3, and at the time of mold clamping, the distance between the upper and lower mold forming surfaces is regulated by the stopper. The gob 2 is pressurized by the upper and lower molds, pushed out into the cavity formed by the upper and lower molds, and formed into the press-formed product 1. The peripheral portion of the molded product does not come into contact with either the upper mold 4 or the lower mold 3 and remains on the molded product 1 as a free surface. After the press molding, the upper mold 4 is separated from the press molded article 1 on the lower mold 3 and retracts upward. The outer diameter of the press-formed product 1 is measured when the formed product is released from the upper mold 4 and is on the lower mold 3. FIG. 2 shows an example of measuring the outer diameter of a molded product. In this example, optical means is used as a non-contact measurement method. That is, the light emitting side 8 and the light receiving side 9 of the outer diameter measuring sensor are arranged so as to sandwich the transfer path of the lower die 3 on which the press-formed product 1 is placed. The sensor light is emitted from the light emitting side 8 to the light receiving side 9. When the lower die 3 stops between the light emitting side 8 and the light receiving side 9, part of the sensor light is blocked by the press-formed product 1 and does not reach the light receiving side 9. By measuring the width that does not reach, the outer diameter of the press-formed product 1 can be quickly measured. The measurement data of the outer diameter is fed back to the flow rate of the glass flowing out of the outflow pipe 5 and the glass cutting cycle as described above. After the outer diameter measurement, the press-formed product 1 is cooled to a temperature at which the press-formed product 1 is not deformed even when a force for taking out is applied, and then the press-formed product is taken out from the lower mold 3 (takeout).
[0044]
The production of the glass blanks shown in FIGS. 1 (b), 1 (c) and 1 (d) is performed in substantially the same manner as described above, except that the shape of the transfer molding surface of the mold is changed in accordance with the shape of the blank. Thus, a glass blank having a free surface on the peripheral portion 13 is obtained.
[0045]
Next, the production of a glass blank using the above mold will be described.
As a material of the information recording medium substrate, for example, a glass containing a chemically strengthenable alkali metal oxide, a glass having a high Young's modulus with a small deflection at a high speed rotation, and a crystallization that can increase the Young's modulus, and Glass that can obtain a flat and smooth crystallized glass substrate surface by polishing or glass suitable for a substrate material to be an optical filter by providing an optical thin film on the substrate itself or on the surface is used. Examples of such a glass include an aluminosilicate glass containing an alkali metal oxide, particularly lithium oxide, an aluminosilicate glass further containing zirconium oxide, and an aluminosilicate glass containing a divalent component such as magnesium oxide.
[0046]
The glass blank can be manufactured by the following method. First, a molten glass made of these glass materials that have been melted, clarified, and agitated and homogenized is continuously discharged from an outflow nozzle at a constant outflow speed, and the molten glass flow is constantly cut to a constant weight by a cutting machine called shear. Cut periodically to obtain a gob. The cut gob is received by the lower mold waiting just below the outflow nozzle. The viscosity of the molten glass discharged from the outflow nozzle is about 0.3 to 100 Pa · s, and the temperature of the lower mold is lower than the temperature of the gob. Temperature controlled.
[0047]
The lower mold on which the gob is placed after the casting is transferred to a press position where the upper mold is on standby, and press-formed by the upper mold and the lower mold. At this time, the upper and lower mold temperatures, the press pressure, and the press time are appropriately set under such conditions that the peripheral portion of the formed article does not touch the mold. For example, it is possible to set the temperature of the upper die to 250 to 550 ° C., the temperature of the lower die to 350 to 650 ° C., and set the upper die temperature to the range of the lower die temperature or [lower die temperature−100 ° C.] within the above range. it can. The pressing force at the time of pressing can be set to about several GPa, but is not particularly limited to this range and may be adjusted as appropriate.
[0048]
In the present invention, in forming the glass blank, while regulating the minimum distance between the upper and lower mold forming surfaces, the outer diameter of the formed glass blank is measured by a non-contact measuring instrument on the lower mold, and the The supply amount of the molten glass is adjusted based on the measurement result.
[0049]
When the press molding is completed, the upper surface of the molded product is released from the upper die, and the lower die on which the molded product is placed is transferred to a takeout position. In addition, the lower mold is stopped between the press position and the take-out position, the upper surface of the molded product on the lower mold is pressed with a press mold, the warpage of the molded product is corrected, and then the lower mold is transferred to the take-out position. May be. The molded article is cooled to a temperature near or lower than the glass transition temperature before being transferred to the takeout position. This is to prevent the molded product from being deformed by the force applied at the time of takeout. Take-out is performed by suction-holding the upper surface of the molded article by suction means. The taken-out molded article is quenched in the atmosphere, and then placed in an annealing furnace and annealed. The glass blank that has been distorted by the annealing is transferred to a grinding step, or an inner diameter / outer diameter processing, or a heat treatment step for crystallization.
[0050]
The parallelism and flatness of the glass blank thus produced are both within the range of 10 μm or less even if the minimum thickness of the disk-shaped blank is 2.2 mm or less and the outer diameter is about 100 mm. The occurrence of large swells in the process has been eliminated. The parallelism and flatness can be reduced even if the minimum thickness of the blank is reduced to about 1.2 mm in order to obtain a substrate having an outer diameter of 95 mm and a thickness of 1 mm, or a substrate having an outer diameter of 65 mm and a thickness of 0.63 mm. Even if the minimum thickness of the glass blank was reduced to 1.0 mm in order to obtain a glass blank, it was maintained, and it can be seen that the method of the present invention is effective.
[0051]
When the glass blank is a disk, the diameter is in the range of 60 to 100 mm, and in the case of a polygon such as a square, the method of the present invention is suitable for those having a side length in the range of 60 to 100 mm. Is particularly suitable for producing a disc-shaped glass blank rotationally symmetric with respect to the pressing direction.
[0052]
Next, a method for manufacturing a glass substrate will be described by taking, as an example, a step of manufacturing a substrate for an information recording medium using the glass blank. After the inner and outer diameters of the glass blank are subjected to grinding and polishing, the glass blank is formed into a substrate shape and provided with a flat and smooth main surface to form a substrate. In the case of a substrate made of glass containing an alkali metal oxide, the substrate may be immersed in an alkali metal molten salt to perform chemical strengthening by ion exchange. In each of the above steps, steps such as washing can be appropriately added.
[0053]
When obtaining a crystallized glass substrate, as appropriate, heat-treat the blank, which has been subjected to processing such as grinding and inner and outer diameter processing, perform crystallization to precipitate the crystal phase in the amorphous phase, and then subject this to grinding and polishing. Alternatively, a substrate is obtained by performing inner and outer diameter processing. In each of the above steps, a step such as washing can be appropriately added.
[0054]
In either case, the thickness of the glass blank can be reduced, and a stable outer diameter and wall thickness can be used, so that a blank with a small undulation can be used. Advantages such as resource saving, reduction of environmental load, cost reduction, and reduction of grinding and polishing processing time can be obtained.
[0055]
An information recording layer, for example, a magnetic recording layer is formed on the main surface of the information recording medium substrate thus obtained to obtain a magnetic recording medium. An information recording medium such as a magneto-optical recording medium and an optical memory can be obtained by providing a recording layer in addition to the magnetic recording medium in the same manner.
In addition to the information recording medium, an optical filter substrate, an optical element having an optical thin film (including a multilayer film) provided on the substrate surface, and the like can be obtained.
[0056]
【Example】
Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.
[0057]
Example 1
Using a mold shown in FIG. 2, a gob made of aluminosilicate glass containing lithium oxide and zirconium oxide was press-molded to produce a glass blank for a magnetic disk substrate.
[0058]
However, after press molding, in a state where the glass blank released from the upper mold is placed on the lower mold forming surface, the lower surface having a flat upper surface including the molding surface was used so that the outer periphery of the glass blank was exposed. . The lower mold is placed on a turntable that rotates by index, and is transported together with the glass blank. The distance between the frontmost portion and the rearmost portion of the glass blank in the transport direction is defined as the outer diameter of the glass blank. The measurement of the distance between the foremost part and the rearmost part was performed without contacting the object by a measuring device using a laser beam. The supply amount of the molten glass was controlled based on the measured data signal of the outer diameter, and the following results were obtained.
[0059]
That is, when forming a glass blank having an outer diameter target value of 96 mm and a wall thickness target value of 1.6 mm, the above control was performed so that the outer diameter change was within 0.05 to 0.1%. A glass blank having a thickness of 0.0 mm, a thickness of 1.6 mm, and a variation in outer diameter of 0.1 mm or less could be mass-produced.
[0060]
These glass blanks were subjected to center drilling, outer diameter processing, chamfering, lapping, polishing, and the like to produce a magnetic disk substrate having a diameter of 95.0 mm and a thickness of 1.0 mm. The above-mentioned machining could be performed smoothly because the outer diameter and thickness of the glass blank were uniform. Note that this glass substrate may be subjected to chemical strengthening as necessary.
Further, a multilayer film including an information recording layer such as a magnetic thin film was formed on the main surface of the substrate to produce a magnetic recording medium.
[0061]
Comparative Example 1
A glass blank having the same target value as in Example 1 was formed, but no feedback to the supply amount of the molten glass based on the outer diameter measurement was performed. As a result, the fluctuation of the outer diameter of the glass blank was 0.4 mm.
[0062]
Example 2
In the same manner as in Example 1, when forming a glass blank having a target outer diameter of 85 mm and a target thickness of 1.3 mm, control was performed such that the change in the outer diameter was within 0.05 to 0.1%. As a result, a glass blank having an outer diameter of 85.0 mm, a wall thickness of 1.3 mm, and an outer diameter variation of 0.075 mm or less could be mass-produced.
[0063]
These glass blanks were subjected to center hole drilling, outer diameter processing, chamfering, lapping, polishing and the like to produce magnetic disk substrates. The above-mentioned machining could be performed smoothly because the outer diameter and thickness of the glass blank were uniform. Note that this glass substrate may be subjected to chemical strengthening as necessary.
Further, a multilayer film including an information recording layer such as a magnetic thin film was formed on the main surface of the substrate to produce a magnetic recording medium.
[0064]
Comparative Example 2
A glass blank having the same target value as in Example 2 was formed, but no feedback to the supply amount of the molten glass based on the outer diameter measurement was performed. As a result, the fluctuation of the outer diameter of the glass blank was 0.4 mm.
[0065]
Example 3
In the same manner as in Example 1, when forming a glass blank having an outer diameter target value of 66 mm and a wall thickness target value of 0.9 mm, control was performed such that the outer diameter change was within 0.05 to 0.1%. As a result, a glass blank having an outer diameter of 66.0 mm, a wall thickness of 0.9 mm, and an outer diameter variation of 0.05 mm or less could be mass-produced.
[0066]
These glass blanks were subjected to center boring, outer diameter processing, chamfering, lapping, polishing, and the like to produce a magnetic disk substrate having a diameter of 65.0 mm and a thickness of 0.635 mm. The above-mentioned machining could be performed smoothly because the outer diameter and thickness of the glass blank were uniform. Note that this glass substrate may be subjected to chemical strengthening as necessary.
Further, a multilayer film including an information recording layer such as a magnetic thin film was formed on the main surface of the substrate to produce a magnetic recording medium.
[0067]
Comparative Example 3
A glass blank having the same target value as in Example 3 was formed, but no feedback to the supply amount of the molten glass based on the outer diameter measurement was performed. As a result, the fluctuation of the outer diameter of the glass blank was 0.4 mm.
[0068]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, it has a stable outer diameter and thickness, and can produce thin-plate-shaped glass blank with good precision which generation | occurrence | production of the undulation etc. was suppressed by direct press.
Therefore, a good glass blank having a uniform outer diameter can be mass-produced, so that machining including outer diameter processing of these glass blanks is facilitated, and a substrate for an information recording medium can be manufactured with high productivity. An information recording medium can also be manufactured with high productivity.
[Brief description of the drawings]
FIG. 1 is a schematic vertical sectional view of a main surface showing another example of a shape of a disc-shaped glass blank.
FIG. 2 is a schematic view showing an example of a state in which a disk-shaped glass blank is produced by press molding.
[Explanation of symbols]
1 Glass blank (press-formed product)
2 Gob
3 lower mold
4 Upper type
5 Outflow pipe
6 molten glass flow
7 Cutting blade
8 Emitting side of sensor for outer diameter measurement
9 Light-receiving side of sensor for outer diameter measurement
11, 11 'thick part
12 Thin part
13 Perimeter

Claims (5)

An information recording medium substrate having a predetermined outer diameter is supplied by supplying a predetermined amount of molten glass onto a lower mold, and repeatedly performing press molding using a press mold including the lower mold and an upper mold facing the lower mold. In a method of manufacturing a glass blank for sequentially forming a glass blank for,
In order to form a glass blank by pressing the peripheral portion of the glass during pressing so as not to contact the press mold, and restricting the minimum distance between the upper and lower mold forming surfaces, the outer diameter of the formed glass blank is set on the lower mold. A method for producing a glass blank, characterized in that the measurement is performed by a non-contact measuring instrument and the supply amount of molten glass is adjusted based on the measurement result. 2. The method for producing a glass blank according to claim 1, wherein a press mold having a means for regulating a distance between upper and lower mold forming surfaces is used during press molding. A plurality of lower molds are sequentially circulated to a position for supplying molten glass, a position for press molding, a position for measuring the outer diameter of the glass blank, and a position for removing the glass blank from the lower mold, and the glass blanks are sequentially formed. 3. The method for producing a glass blank according to 1 or 2. A method for manufacturing a substrate for an information recording medium, comprising machining a glass blank manufactured by the method according to claim 1, 2 or 3 to manufacture a substrate for an information recording medium. A method for manufacturing an information recording medium, comprising forming an information recording layer on an information recording medium substrate produced by the method according to claim 4.

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