JP4200422B2 - Glass blank, information recording medium substrate, and information recording medium manufacturing method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a glass blank, an information recording medium substrate, and an information recording medium manufacturing method. More specifically, the present invention is a thin glass blank that is used as an intermediate molded body of an information recording medium substrate, has a stable outer diameter and thickness, and has excellent accuracy with suppressed occurrence of waviness and the like. In particular, the present invention relates to a method for producing a substrate for information recording medium from the glass blank, and a method for producing an information recording medium using the substrate.
[0002]
[Prior art]
As a hard disk substrate used as a large-capacity recording means in a personal computer or the like, a glass or glass ceramic substrate is widely used as a high performance and high reliability substrate. With the spread of personal computers and the development of an information network society, the demand for such information recording media substrates and information recording media made of glass or glass ceramics has increased rapidly in recent years, and the demand for such information recording media has been increased. Therefore, a substrate manufacturing technique having high productivity is desired. Among these techniques, the most promising method is the intermediate molding made of glass having a shape that approximates to the substrate in anticipation of volume changes during crystallization, etc. There can be mentioned a so-called direct press method in which the body is produced by press molding of molten glass with a mold.
[0003]
As a method for producing an intermediate molded body of an information recording medium substrate by direct pressing, a method disclosed in Japanese Patent Laid-Open No. 12-53431 is known. In this method, a groove called a notch is provided in a portion where the inner hole is opened 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 molten glass supplied is excessive, the peripheral part of the intermediate molded body is not regulated by a barrel mold or the like, and the volume of glass supplied varies by letting the excess volume of glass escape to the peripheral part. Even if there is, an intermediate molded body having a stable thickness is obtained every time.
[0004]
Apart from the intermediate molded body described in the above publication, a disk-shaped intermediate body in which notches are not formed is also known as orthodox. In this case, the peripheral edge portion 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 are strong demands for sludge reduction from the viewpoints of resource saving, reduction of environmental load by reducing waste, and cost reduction. Therefore, in the direct press method, it is required to produce an intermediate molded body having a thickness close to that of the substrate.
[0006]
Under such circumstances, the present applicant has previously proposed a method for producing a glass blank, which is an intermediate molded body of an information recording medium substrate with good accuracy in which the occurrence of swell and the like is suppressed (special feature). Application No. 2001-20379). This method prevents the peripheral edge of the glass blank from coming into contact with the press mold in press molding, suppresses heat dissipation due to heat conduction from the peripheral edge of the glass blank to the mold, reduces the temperature distribution in the glass blank surface, This is intended to reduce the waviness of the blank.
[0007]
In the above method, the peripheral edge of the glass blank, that is, the disk-shaped side surface is not defined by the press mold. Therefore, if the amount of the softened glass supplied to the press mold is slightly changed, the outer diameter of the glass blank is also changed accordingly. After the glass blank is annealed, the periphery is machined to finish to the desired outer diameter. However, if the outer diameter of the press-molded glass blank fluctuates, the allowance to be processed by the outer diameter processing varies depending on the individual blank, and as a result, the allowance for outer diameter processing should be set uniformly. The problem that it is difficult to do occurs.
[0008]
[Problems to be solved by the invention]
Under such circumstances, the present invention is used as an intermediate molded body of an information recording medium substrate, has a stable outer diameter and thickness, and has a thin plate shape with good accuracy with suppressed occurrence of waviness and the like. It is an object of the present invention to provide a method for producing a glass blank by direct pressing, a method for producing an information recording medium substrate from the glass blank, and a method for producing an information recording medium using the substrate.
[0009]
[Means for Solving the Problems]
As a result of intensive research to achieve the above object, the present inventor has used a molding die having an upper die and a lower die, and press-molded a predetermined amount of molten glass by a specific method to form a glass blank. It has been found that a thin glass blank having no desired undulation and good accuracy can be obtained by manufacturing sequentially, and that the object can be achieved, and the present invention has been completed based on this finding. .
[0010]
That is, the present invention
(1) Information having a predetermined outer diameter by repeating a step of supplying a predetermined amount of molten glass onto the lower mold and press-molding using the press mold including the lower mold and the upper mold facing the lower mold. In the method for producing a glass blank for sequentially forming a glass blank for a recording medium substrate,
A glass blank is formed so that the peripheral edge of the glass does not come into contact with the press mold during pressing and the minimum distance between the upper and lower mold forming surfaces is regulated, and the outer diameter of the molded glass blank is placed on the lower mold. A glass blank manufacturing method, characterized by measuring with a non-contact measuring instrument, and adjusting the amount of molten glass supplied based on the measurement result,
[0011]
(2) At the time of press molding, the method for producing a glass blank according to the above (1), which uses a press mold having a means for regulating the interval between the upper and lower mold surfaces,
(3) Sequentially forming a glass blank by circulating and transferring a plurality of lower molds 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 taking out the glass blank from the lower mold. The method for producing a glass blank according to (1) or (2) above,
[0012]
(4) By the method described in (1), (2) or (3) above Glass blank was made and obtained A method for producing an information recording medium substrate, comprising: machining a glass blank to produce an information recording medium substrate; and
(5) By the method described in (4) above An information recording medium substrate was produced and obtained. An information recording medium manufacturing method comprising forming an information recording layer on an information recording medium substrate;
Is to provide.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
In the method for producing a glass blank of the present invention (hereinafter sometimes simply referred to as “blank”), the blank is made of softened glass (hereinafter sometimes referred to as “gob”) as an upper mold and a lower mold. It is manufactured by press-molding with a mold equipped with Both main surfaces of the thin glass blank are transferred and molded by the upper mold surface and the lower mold surface, respectively. Note that both the upper mold and the lower mold are constituted by one or a plurality of members as required.
[0014]
In this invention, the gob which is a raw material of a glass blank is normally supplied on a lower mold | type in the state of a molten glass, and weight management is carried out so that a glass blank may become a predetermined shape. When the gob is supplied onto the lower mold (hereinafter referred to as casting), the lower mold temperature is adjusted so that the gob is not cooled rapidly due to contact with the lower mold and cannot be press-molded. 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 press-molded and the molded glass is removed from the press mold (hereinafter referred to as take-out). The amount of heat is lost. Furthermore, although the upper mold temperature is adjusted even during press molding, it is generally lower than the temperature of the gob. Therefore, while the upper mold is in contact with the gob or the molded product, the gob and the glass molding are also performed by the upper mold. The amount of heat that the product has is deprived.
[0015]
It is considered that the undulation of the molded product is caused by a large distribution of heat radiation generated in a plane perpendicular to the pressing direction by the upper and lower molds in the process of cooling the thin plate-shaped molded product. In the direct press method, heat distribution can be achieved in the inside of the molded product and the surface of the molded product, in the center and outer periphery of the molded product, and in the thick and thin parts during the cooling process. The following factors can be considered as factors that further increase the heat radiation distribution.
[0016]
(1) The gob is pressed by the upper and lower molds and spreads in the space between the upper and lower molds. When the peripheral part touches the body mold, etc., heat dissipation from the peripheral part increases, and the temperature at the outer peripheral part of the glass increases rapidly. The heat dissipation distribution increases.
(2) The notch described in the above-mentioned publication introduced as the prior art is a groove having an extremely small area compared to the main surface of the molded product. Such a portion has a large die contact area per unit area perpendicular to the pressurizing direction, and the heat radiation from the glass is locally increased as compared with the peripheral portion of the notch, which causes a large heat radiation distribution.
Further, when the notch is formed in the vicinity of the peripheral portion by press molding, the heat radiation from the peripheral portion is increased by the contact with the notch forming portion of the mold, and the result is similar to (1).
[0017]
(3) Since the notch is used during inner diameter processing and outer diameter processing, the thickness of the notch portion is not described in the above publication, but it is advantageous that the thickness of the notch is thinner than the target substrate thickness in performing the processing. It is guessed. On the other hand, when performing inner diameter processing, the thickness of the main body of the publication is naturally larger than the thickness of the target substrate. Thus, if the thickness of the notch part is thinner than the maximum value of the target substrate thickness, the heat conduction from the main body part or inner hole part to the notch part cannot catch up with the heat dissipation speed from the notch part to the mold, and the above The heat distribution becomes even larger.
[0018]
(4) When the glass blank has a thick part and a thin part with the thinnest thickness, if the area of the thin part is smaller than the area of the thick part, the thin part becomes a local temperature-decreasing part, similar to the above notch. , The heat dissipation distribution becomes larger.
(5) When 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 remove such factors, in the blank manufacturing method of the present invention, the gob is press-molded so that the peripheral edge of the blank to be formed does not contact the mold, and a blank having at least a notch is produced. It is good to do. In the production method of the present invention, as a preferred embodiment, for example, the following three types of glass blanks can be produced.
[0020]
First, a 1st aspect is a method of producing the glass blank which has the surface which consists of a flat front and back surface and a peripheral part. Here, the flat surface means a surface on which intentional unevenness is not provided, apart from minute warpage and inevitable formation of uneven 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 the second aspect, the minimum thickness of the glass blank, that is, the thickness of the thinnest portion of the glass blank is greater than the thickness of the thickest portion of the target glass substrate (maximum value of the thickness of the substrate). This is a method for producing a thick glass blank. As such a molding, a thick wall portion and a thin wall portion are formed like a glass blank suitable for producing a flat glass having excellent flatness disclosed in Japanese Patent Application Laid-Open No. 10-194760 previously filed by the present applicant. An example of forming a glass blank is shown.
[0022]
Furthermore, as a third aspect, there is a method of producing a glass blank having a thick part and a thin part having the thinnest thickness, and the area of the thin part is larger than the area of the thick part. As such molding, there can be exemplified molding of a glass blank suitable for production of a sheet glass having excellent flatness disclosed in JP-A-10-194760.
[0023]
In this way, direct press molding with suppressed generation of undulation is possible. At this time, the peripheral edge of the glass blank does not contact the press mold. Therefore, although the amount of heat radiation due to heat conduction from the peripheral edge of the glass blank to the press mold is reduced, the outer diameter of the glass blank is not defined by the press mold, so that variations in molding conditions appear as changes in the outer diameter of the glass blank. It will be. In particular, the present invention regulates the minimum distance between the upper and lower mold forming surfaces during pressing. That is, the interval between the upper and lower mold forming surfaces when the press mold is clamped is regulated to be always constant. This restriction 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, the upper and lower mold forming surfaces are regulated so that the interval between them is always constant. Therefore, if the amount of molten glass supplied to the lower mold varies, the variation 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 with a non-contact type measuring instrument, and if the measurement result is deviated from the outer diameter of the target glass blank, the amount of deviation is determined. Feedback is applied to the mechanism that controls the amount of molten glass supplied onto the lower mold. That is, when the glass blank outer diameter is larger than the required value, control is performed to decrease the supply amount of the molten glass, and when the glass blank outer diameter is smaller than the required value, control is performed to increase the supply amount of the molten glass. . When the required outer diameter is obtained, the supply amount of the molten glass is maintained 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 is caused to flow down from a pipe called a feeder at a constant flow rate. The molten glass flow is cut using a cutting blade maintained at a temperature at which the molten glass is not fused, and the tip of the cut molten glass flow is received on the lower mold. At this time, the supply amount of the molten glass can be adjusted by controlling the time interval of cutting with the cutting blade. That is, if the time interval is lengthened, the amount of molten glass supplied increases, and if the time interval is shortened, the amount of molten glass supplied 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 method 1, 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 molten glass to be prepared is also kept constant. And the outflow rate of a molten glass flow is changed by controlling the temperature of a feeder. By raising the temperature of the feeder, the viscosity of the molten glass is lowered and the outflow rate is increased, so that the supply amount of the molten glass is increased. Conversely, by lowering the temperature of the feeder, the viscosity of the molten glass rises and the outflow rate decreases, so that the amount of molten glass supplied decreases. Thus, the supply amount of molten glass can be increased / decreased by changing the temperature of a feeder.
As a specific example, a heater is provided around the feeder, and the temperature of the feeder is controlled by changing or maintaining the current value flowing through the heater.
[0027]
<Method 3>
The supply amount of 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 be careful not to cause striae or devitrification in the flowing glass.
[0028]
Moreover, the following method can be illustrated as a method of regulation of the minimum space | interval of the upper and lower mold forming surfaces at the time of a press. A preferred method is to provide contact portions that contact each other at the time of pressing around the lower mold forming surface and the upper mold forming surface. It is a means to regulate not to become narrower than the state. In this case, a contact part is provided in the position which does not contact a glass blank. The lower mold contact portion may be the same height as the lower mold molding surface, may be provided below, or may be provided above. However, considering the ease of measuring the outer diameter of the glass blank, which will be described later, the peripheral edge of the glass blank is positioned higher than the lower mold contact portion with the glass blank on the lower mold forming surface being placed. It is desirable to do. By doing in this way, an outer diameter measurement can be made easy, without hiding a glass blank peripheral part by a lower mold | type contact part.
[0029]
As another method, a method of controlling the interval between the upper and lower mold surfaces to a predetermined value using a mold having a structure as shown in FIG. The molding die is composed of a lower die 3, an upper die 4, a barrel die 5 and an upper barrel die 6, and the upper die 4 is slidable inside the upper barrel die 6. 2 is a gob. A body mold 5 that accommodates the lower mold 3 and a cylinder mold 6 that accommodates the upper mold 4 are used, and the two cylinder molds are brought into contact with each other during pressing. Then go down the gap between the molding surfaces of the upper and lower molds and press the gob. 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 if the shape of the press mold is set, since 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 cylinder mold together with the glass blank and perform an operation such that the peripheral edge of the glass blank is above the upper end of the cylinder mold. .
[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 location may be deformed when contact measurement is performed. In addition, since the contact-type measurement needs to be performed while the measurement target is stationary, the production efficiency is lowered when applied to the present invention in which supply of molten glass and press molding are repeated. Furthermore, since non-contact measurement can be performed at higher speed than contact measurement, fluctuations in the outer diameter of the glass blank can be quickly fed back to adjustment of the molten glass supply amount.
[0032]
As the non-contact measurement method, an optical measurement method using a laser beam is most suitable, but other methods such as a measurement method using 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 forming a glass blank sequentially by circulating and transferring a plurality of lower molds 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 taking out the glass blank from the lower mold, 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 the above-mentioned circulation transfer is performed by arranging a plurality of lower molds on a turntable and rotating the turntable with an index, it is preferable to measure the outer diameter in the section next to the press molding section (stop position). In addition, in order to correct the curvature of the glass blank after press molding or to accelerate the cooling of the glass blank, when the upper surface of the glass blank on the lower mold is pressed with a pressing member, the outer diameter of the glass blank after the pressing It is preferable to perform the measurement.
In addition, although the outer diameter measurement of a glass blank may be performed only in one place, you may perform in several places and you may control the said supply amount based on the measurement result in a respectively different place.
[0034]
The measurement data of the outer diameter is processed by a computer, a sequencer, etc., and the supply amount of the molten glass is adjusted at any time based on the data by the above method.
In addition, it is desirable to perform the said control so that the change of the said outer diameter may fall within the range of 0.05 to 0.1% with respect to the outer diameter of a glass blank.
[0035]
In the manufacturing method of the glass blank of the present invention, as described above, the peripheral portion of the glass blank formed at the time of press molding is not brought into contact with the mold, that is, the peripheral portion is not restricted. Becomes a free surface. Since the molding surface of the mold is not transferred to the free surface, the processing marks existing on the molding surface are not transferred. In addition, when molding is performed by applying a powder release agent to the molding surface, the free surface is not pressurized by the molding surface to which the powder is applied, so that this portion cannot be roughened by the release agent.
[0036]
In addition, the peripheral portion can maintain a relatively low viscosity in the press molding process as compared with the conventional case, and the peripheral portion can be plastically deformed even when the molded product is sinked. 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 a decrease in the shape accuracy of the blank due to sink marks can be reduced.
[0037]
If the amount of gob is made exactly the same every time, or the excess glass is protruded from the outer periphery as in the above publication, the variation in the total height corresponding to the maximum thickness of the molded product increases due to the sink. On the other hand, as in the present invention, in the method of dispersing sink marks on the peripheral edge of the molded product, the total height for each molding can be kept within ± 5 to 10 μm.
[0038]
When providing a thick part and a thin part in a blank, it is desirable to shape the thick part so that the thick part receives pressure from both main surface sides of the blank. To do so, either form a thick part on the outer periphery of the blank and a thin part on the part surrounded by the outer periphery, or form a thick part on the center of the blank and a thin part around it, or It is preferable to form a thick part at the center and the central part and a thin part between the outer peripheral part and the central part. And it is preferable to make uniform the thickness of a thin part, and the thickness of a thick part, respectively.
As the shape of the blank, a shape that is symmetrical in the pressurizing direction like a magnetic disk substrate, that is, a disk shape is preferable. In a disk-shaped blank, the side surface of the disk is the peripheral edge.
[0039]
The present invention is suitable for producing a glass blank having a thickness of 0.8 to 2.2 mm. Even a blank having a thick part and a thin part is suitable for producing a glass blank in which both the maximum value and the minimum value of the thickness of the blank are in the above range.
[0040]
Fig.1 (a)-(d) is the vertical cross-sectional schematic with respect to the main surface which shows the example from which the shape of the disk-shaped glass blank obtained by the method of this invention differs, Comprising: The code | symbol 1 shows a glass blank.
[0041]
(A) in FIG. 1 shows a disk-shaped glass blank having a uniform thickness without a thick part and a thin part, and the thickness is preferably 0.8 to 1.8 mm, and 0.9 to 1.7 mm. Particularly preferred. Moreover, the blank which has the said thickness and an outer diameter of 60-100 mm is suitable. (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 enclosed by the outer peripheral part, (c) shows the outer peripheral part and center part of the glass blank 1 The glass blank which has the thick part 11 and 11 'and the thin part 12 between the outer peripheral part and the center part is shown, respectively. Moreover, (d) glass shows the glass blank which has the thick part 11 'in the center part of the blank 1, and has the thin part 12 around the thick part 11'. Thus, in the case of the 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 denotes a peripheral edge.
[0042]
By performing press molding in accordance with the method for producing a glass blank of the present invention, the gob is likely to spread, and it is not necessary to excessively increase the press pressure for thinning the molded product. As a result, the press failure is reduced, and a powdery mold release agent is not required, and the surface roughness of the molded product due to the mold release agent is reduced. Further, in order to prevent damage to the molded product in the notch forming portion, it is advantageous not to form a local thin portion like the notch.
The manufacturing method of the glass blank of this invention is applied to preparation of the glass blank for information recording media.
[0043]
Next, the structure of the mold 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 mold is composed of a lower mold 3 and an upper mold 4. The upper mold 4 is provided with a stopper that abuts the lower mold 3 during mold clamping so as to surround the molding surface and regulate the interval between the upper and lower mold molding surfaces. As shown in FIG. 2, in the casting process, the molten glass flow 6 flows out from 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 where the molding surface of the lower mold | type 3 is formed is flat (except the part which shape | molds the thick part of a glass blank). In the next cutting step, the molten glass flow is cut with the cutting blade 7 to obtain a gob 2 having a predetermined weight on the lower mold surface. Subsequently, the gob is pressed by the upper mold 4 and the lower mold 3, and the distance between the upper and lower mold forming surfaces is regulated by the stopper when the mold is clamped. The gob 2 is pressed by the upper and lower molds, and is expanded into a cavity formed by the upper and lower molds, and is formed into the press-formed product 1. The peripheral edge of the molded product does not contact either the upper mold 4 or the lower mold 3 and remains on the molded product 1 as a free surface. After press molding, the upper die 4 is separated from the press-formed product 1 on the lower die 3 and retracts upward. The outer diameter of the press-formed product 1 is measured when the molded product is released from the upper die 4 and is on the lower die 3. FIG. 2 shows an example of the outer diameter measurement of the molded product. In this example, optical means is used as a non-contact measurement method. That is, the light projecting 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 mold 3 on which the press-formed product 1 is placed. Sensor light is emitted from the light projecting side 8 toward the light receiving side 9. When the lower mold 3 stops between the light projecting 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 this unreachable width, the outer diameter of the press-formed product 1 can be measured quickly. As described above, the measurement data of the outer diameter is fed back to the flow rate of the glass flowing out from the outflow pipe 5 and the glass cutting cycle. After the outer diameter is measured, the press-formed product 1 is cooled to a temperature at which it does not deform 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 glass blanks shown in FIGS. 1B, 1C, and 1D are manufactured in the same manner as described above only by changing the shape of the transfer molding surface of the mold according to the shape of the blank. A glass blank having a free surface at the peripheral edge 13 is obtained.
[0045]
Next, preparation of the glass blank using the said shaping | molding die is demonstrated.
As a material for the substrate for information recording media, for example, a glass containing an alkali metal oxide that can be chemically strengthened, a glass having a high Young's modulus with little deflection during high-speed rotation, and the Young's modulus can be increased by crystallization and grinding. Glass that can obtain a flat and smooth crystallized glass substrate surface by polishing finish, or glass suitable for a substrate material that becomes an optical filter by providing an optical thin film on the substrate itself or on the surface is used. Examples of such 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 produced by the following method. First, molten glass made of these glass materials that has been melted, clarified, and stirred and homogenized is continuously discharged from an outflow nozzle at a constant outflow rate, and this molten glass flow is always kept at a constant weight by a cutting machine called shear. Cut periodically to get gob. The cut gob is received by the lower mold waiting just under 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, but it is heated to a temperature at which the gob temperature suddenly drops so that pressing becomes impossible. The temperature is adjusted.
[0047]
The lower die on which the gob is placed after the casting is finished is transferred to a press position where the upper die is waiting, and is press-formed by the upper die and the lower die. In this case, the upper and lower mold temperatures, the press pressure, and the press time are appropriately set under conditions such that the peripheral portion of the formed product does not touch the mold. For example, the upper mold temperature may be set to 250 to 550 ° C., the lower mold temperature may be set to 350 to 650 ° C., and the upper mold temperature may be set within a range of the lower mold temperature to [lower mold temperature−100 ° C.]. it can. The pressing force at the time of pressing can be 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, the minimum distance between the upper and lower mold forming surfaces is regulated, and the outer diameter of the molded glass blank is measured on the lower mold with a non-contact type measuring instrument, Based on the measurement result, the supply amount of the molten glass is adjusted.
[0049]
When the press molding is completed, the upper surface of the molded product is released from the upper mold, and the lower mold on which the molded product is placed is transferred to a take-out 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 the pressing mold, the warpage of the molded product is corrected, and each lower mold is transferred to the take-out position. May be. The molded product is cooled to near the glass transition temperature or lower than the glass transition temperature before being transferred to the take-out position. This is to prevent the molded product from being deformed by the force applied during take-out. Take-out is performed by adsorbing and holding the upper surface of the molded product with an adsorbing means. The take-out molded product is quenched in the atmosphere and then placed in an annealing furnace for annealing. The glass blank which has been subjected to strain removal by annealing is transferred to a grinding process, an inner diameter outer diameter processing, or a heat treatment process for crystallization.
[0050]
The parallelism and flatness of the glass blank thus produced are both within a range of 10 μm even if the minimum thickness of the disc blank is 2.2 mm or less and the outer diameter is about 100 mm. The generation of large swells in the process has been eliminated. This parallelism and flatness are obtained by reducing the minimum thickness of the blank to about 1.2 mm in order to obtain a substrate having an outer diameter of 95 mm and a thickness of 1 mm, and a substrate having an outer diameter of 65 mm and a thickness of 0.63 mm. Therefore, it can be seen that the minimum thickness of the glass blank is reduced to 1.0 mm so that the method of the present invention is effective.
[0051]
When the glass blank is disk-shaped, the method of the present invention is suitable for one having a diameter in the range of 60 to 100 mm, and in the case of a polygon such as a quadrangle, one having a side length in the range of 60 to 100 mm. However, it is particularly suitable for the production of a disk-shaped glass blank that is rotationally symmetric with respect to the pressing direction.
[0052]
Next, a method for producing a glass substrate will be described by taking as an example a process for producing an information recording medium substrate using the glass blank. After the inner and outer diameters of the glass blank are subjected to grinding and polishing, the substrate is adjusted to a substrate shape and a flat and smooth main surface is provided to form a substrate. In the case of a substrate made of glass containing an alkali metal oxide, chemical strengthening by ion exchange may be performed by immersing the substrate in an alkali metal molten salt. In each of the above steps, a step such as washing can be appropriately added.
[0053]
When obtaining a crystallized glass substrate, heat treatment is performed on a blank that has been subjected to processing such as grinding and inner and outer diameter processing, and crystallization is performed to precipitate the crystal phase in the amorphous phase, which is then ground and polished. Alternatively, the inner and outer diameters are processed to obtain a substrate. 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 blank having a stable outer diameter and wall thickness and small waviness can be used. Therefore, the grinding and polishing margins can be reduced by approximately 40% almost uniformly. It is possible to obtain merits such as resource saving, reduction of environmental load, cost reduction, grinding, and shortening of polishing time.
[0055]
An information recording layer, such as a magnetic recording layer, is formed on the main surface of the information recording medium substrate thus obtained to obtain a magnetic recording medium. In addition to the magnetic recording medium, an information recording medium such as a magneto-optical recording medium or an optical memory can be obtained by providing a recording layer in the same manner.
In addition to the information recording medium, an optical filter substrate, an optical element provided with an optical thin film (including a multilayer film) on the substrate surface, and the like can also be obtained.
[0056]
【Example】
EXAMPLES Next, although an Example demonstrates this invention further in detail, this invention is not limited at all by these examples.
[0057]
Example 1
A gob made of aluminosilicate glass containing lithium oxide and zirconium oxide was press-molded using the mold shown in FIG. 2 to produce a glass blank for a magnetic disk substrate.
[0058]
However, after press molding, a lower die having a flat upper surface including the molding surface was used so that the outer periphery of the glass blank was exposed in a state where the glass blank released from the upper die was placed on the lower die molding surface. . The lower mold is arranged on a turntable that rotates with an index and is transferred together with the glass blank. The distance between the frontmost part and the rearmost part of the glass blank with respect to the transfer direction is defined as the outer diameter of the glass blank. The distance between the foremost part and the last part was measured without contacting the object by a measuring device using a laser beam. Based on the measurement data signal of the outer diameter, the supply amount of the molten glass was controlled, 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 an outer diameter variation of 0.1 mm or less could be mass-produced.
[0060]
These glass blanks were subjected to center drilling, outer diameter processing, chamfering processing, lapping processing, polishing processing, 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 machining could be smoothly performed because the glass blank had the same outer diameter and thickness. In addition, you may chemically strengthen this glass substrate as needed.
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
Although the glass blank of the target value similar to Example 1 was shape | molded, the feedback to the supply amount of the molten glass based on an outer diameter measurement was not performed. As a result, the variation of the glass blank outer diameter was 0.4 mm.
[0062]
Example 2
In the same manner as in Example 1, when forming a glass blank having an outer diameter target value of 85 mm and a wall thickness target value of 1.3 mm, the outer diameter change was controlled to be 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 fluctuation of 0.075 mm or less could be mass-produced.
[0063]
These glass blanks were subjected to center drilling, outer diameter processing, chamfering processing, lapping processing, polishing processing, and the like to produce a magnetic disk substrate. The above machining could be smoothly performed because the glass blank had the same outer diameter and thickness. In addition, you may chemically strengthen this glass substrate as needed.
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
Although the glass blank of the target value similar to Example 2 was shape | molded, the feedback to the supply amount of the molten glass based on an outer diameter measurement was not performed. As a result, the variation of the glass blank outer diameter 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, the outer diameter change was controlled to be 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 drilling, outer diameter processing, chamfering processing, lapping processing, polishing processing, 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 machining could be smoothly performed because the glass blank had the same outer diameter and thickness. In addition, you may chemically strengthen this glass substrate as needed.
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
Although the glass blank of the target value similar to Example 3 was shape | molded, the feedback to the supply amount of the molten glass based on an outer diameter measurement was not performed. As a result, the variation of the glass blank outer diameter 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 the thin plate-shaped glass blank with a sufficient precision by which generation | occurrence | production of the wave | undulation etc. was suppressed can be produced by direct press.
Therefore, since good glass blanks having a uniform outer diameter can be mass-produced, machining including the outer diameter processing of these glass blanks becomes easy, and a substrate for an information recording medium can be produced 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 with respect to a main surface showing examples of different shapes of a disk-shaped glass blank.
FIG. 2 is a schematic diagram 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-molded product)
2 Gob
3 Lower mold
4 Upper mold
5 Outflow pipe
6 Molten glass flow
7 Cutting blade
8 Light emitting side of outer diameter measuring sensor
9 Light receiving side of outer diameter measuring sensor
11, 11 'Thick part
12 Thin section
13 Perimeter

Claims (5)

An information recording medium substrate having a predetermined outer diameter by repeating a step of supplying a predetermined amount of molten glass onto the lower mold and press-molding using the press mold including the lower mold and the upper mold facing the lower mold In the glass blank manufacturing method of sequentially forming glass blanks for use,
A glass blank is formed so that the peripheral edge of the glass does not come into contact with the press mold during pressing and the minimum distance between the upper and lower mold forming surfaces is regulated, and the outer diameter of the molded glass blank is placed on the lower mold. And measuring with a non-contact type measuring device, and adjusting the supply amount of the molten glass based on the measurement result.   The manufacturing method of the glass blank of Claim 1 using the press-molding die provided with the means to regulate the space | interval of an upper-and-lower mold-forming surface at the time of press molding.   A plurality of lower molds are sequentially formed by sequentially circulating and transferring a glass blank 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 taking out the glass blank from the lower mold. The manufacturing method of the glass blank of 1 or 2. A method for producing an information recording medium substrate, comprising: producing a glass blank by the method according to claim 1, and machining the obtained glass blank to produce an information recording medium substrate. A method for producing an information recording medium , comprising producing an information recording medium substrate by the method according to claim 4 and forming an information recording layer on the obtained information recording medium substrate.

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