JP2006327936A - Glass substrate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a glass substrate which has a high coefficient of liner thermal expansion and is excellent in cost effectiveness and from which alkaline components are hardly eluted. <P>SOLUTION: The glass substrate has a constitution comprising each glass component of, by weight, 45-70% SiO<SB>2</SB>, 1-5.0% Al<SB>2</SB>O<SB>3</SB>, 1.0-8% B<SB>2</SB>O<SB>3</SB>, 0.7-20% of Li<SB>2</SB>O+Na<SB>2</SB>O+K<SB>2</SB>O, 0.1-10% MgO, 0.1-10% CaO, 1-15% of MgO+CaO, 0.5-10% TiO<SB>2</SB>, 0.5-10% ZrO<SB>2</SB>, 0-5% ZnO and 0-8% La<SB>2</SB>O<SB>3</SB>. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a glass substrate, and more particularly to a glass substrate used as a substrate for information recording media such as magnetic disks, magneto-optical disks, DVDs, MDs, and optical communication elements.

  Conventionally, as a substrate for a magnetic disk, an aluminum alloy is generally used for a stationary type such as a desktop computer or a server, while a glass substrate is generally used for a portable type such as a notebook computer or a mobile computer. Was easily deformed and its hardness was insufficient, so that the substrate surface after polishing was not sufficiently smooth. Further, when the head mechanically contacts the magnetic disk, there is a problem that the magnetic film is easily peeled off from the substrate. Therefore, it is predicted that a glass substrate with little deformation, good smoothness and high mechanical strength will be widely used not only for portable devices but also for stationary devices and other household information devices in the future. .

  As a glass substrate, a chemically strengthened glass is known in which a compressive strain is generated by replacing an alkali element on the surface of the substrate with another alkali element and mechanical strength is improved. However, chemically tempered glass requires a complicated ion exchange process, and rework after ion exchange is impossible, making it difficult to increase the production yield. Moreover, in order to give ion exchange property to the glass substrate, movement of alkali ions in the substrate has been facilitated. For this reason, there is a problem that alkali ions on the surface of the substrate move to the surface during the heating process when the magnetic film is formed and are eluted, or the magnetic film is eroded and the adhesion strength of the magnetic film is deteriorated. It was.

  On the other hand, as a general glass substrate not subjected to chemical strengthening treatment, there is a soda lime substrate, but mechanical strength and chemical durability are insufficient to use this soda lime substrate as an information recording substrate. In addition, glass materials used for liquid crystal substrates, etc. have a low coefficient of linear expansion by alkali-free or low alkali to maintain thermal stability at high temperatures, so clamps and spindles made of SUS steel, etc. The difference between the coefficient of linear thermal expansion of the motor member is large, and problems may occur when the recording medium is attached to the recording apparatus or when information is recorded. In addition, since the mechanical strength is insufficient, it is difficult to apply to an information recording substrate.

  In addition, although a glass substrate is used as a substrate in an optical communication element such as an optical filter or an optical switch, the element may be deteriorated by an alkali component eluted from the glass substrate. In addition, as the density of the film formed on the glass substrate increases, the wavelength shift due to changes in temperature and humidity is suppressed, but there is a limit to the density of the film that can be formed by the conventionally widely used vacuum deposition method. .

  The present invention has been made in view of such conventional problems. The object of the present invention is to have a high mechanical strength without performing a strengthening treatment and to have a linear thermal expansion coefficient close to that of a motor member. Another object of the present invention is to provide a glass substrate having excellent chemical durability.

  Another object of the present invention is to provide a glass substrate with a small alkali elution amount and capable of forming a high-density film.

The glass substrate according to the present invention for achieving the above object, in _{weight%, SiO 2: 45~70%,} Al 2 O 3: 1~10%, B 2 O 3: 0.5~8%, Li 2 O + Na ₂ O + K ₂ O: 7 to 20%, MgO: 0.1 to 10%, CaO: 0.1 to 10%, MgO + CaO: 1 to 15%, TiO ₂ : 0.5 to 10%, ZrO ₂ : 0 .5~10%, ZnO: 0~5%, La 2 O 3: was configured to have 0 to 8% of each glass component. Hereinafter, “%” means “% by weight” unless otherwise specified.

Here, the linear thermal expansion coefficient A of the glass substrate is 60 × 10 ⁻⁷ / ° C. or more, the alkali elution amount B is 250 ppb or less per 2.5 inch disk, the Young's modulus E is 85 GPa or more, and the following formula (1) It is preferable that the surface and the internal composition are uniform and have an amorphous structure.
(A / B) × E × 10 ⁷ ≧ 30 (1)

  The linear thermal expansion coefficient A is a value measured using a differential expansion measuring device under the conditions of load: 5 g, temperature range: 25 to 100 ° C., temperature increase rate: 5 ° C./min. The alkali elution amount B was determined by immersing a sample glass whose surface was polished with cerium oxide to a smooth surface with an Ra value of 2 nm or less and then washed for 24 hours in 50 ml of reverse osmosis membrane water at 80 ° C. It is a value calculated by analyzing the eluate with an emission spectroscopic analyzer. Accordingly, the alkali elution amount is the total amount of Li, Na, and K elution amounts. The sample glass used had a surface area substantially the same as that of the 2.5-inch disk substrate. The Young's modulus E is a value measured according to the dynamic elastic modulus test method of the elastic test method of JIS R 1602 fine ceramics. Moreover, that the composition of the surface and the interior is homogeneous and has an amorphous structure means that no strengthening treatment is performed.

Further, from the viewpoint of durability, productivity, etc., the Vickers hardness Hv is larger than 550, the liquidus temperature TL is 1,300 ° C. or less, and the temperature T _log η _{= 2 at} which the glass melt viscosity _log η _{= 2} is 1 , 450 ° C. or lower, and the glass transition temperature Tg is preferably 600 ° C. or lower. The Vickers hardness Hv is a value measured using a Vickers hardness tester under conditions of a load of 100 g and a load time of 15 sec. The liquidus temperature _TL was determined by checking the presence or absence of devitrified substances on the surface and inside of the glass after melting and holding at 1,550 ° C. for 2 hours, holding at 1,300 ° C. for 10 hours and quenching. is there. The temperature T _log η _{= 2} is a temperature at which _log η _{= 2} when the viscosity of the molten glass is measured using a stirring type viscosity measuring machine. The glass transition point Tg is a value measured by heating a glass sample adjusted to a powder form in a temperature range of room temperature to 900 ° C. at a rate of temperature increase of 10 ° C./min using a differential calorimeter.

In addition, from the viewpoint of improving density recording when the glass substrate of the present invention is used as a substrate for an information recording medium, in a glass substrate produced through a polishing process and a cleaning process, pure water, acid, and alkali are used. When the glass substrate is washed with at least one liquid, the surface roughness Ra after the polishing step and the surface roughness Ra ′ after the washing step are expressed by the following formula:
Ra ′ / Ra ≦ 1.5 (2)
Ra ≦ 1nm (3)
Is preferably satisfied. The surface roughness Ra, Ra ′ of the glass substrate is a value measured with an atomic force microscope (AFM).

  Since the glass substrate according to the present invention has a specific glass composition, it has high rigidity without performing a strengthening treatment, has a high linear thermal expansion coefficient, and has little elution of alkali components. Can be suppressed.

  When the glass substrate according to the present invention is used for an information recording medium, it has excellent durability and a high recording density.

  Further, when the glass substrate according to the present invention is used for an optical communication element, there is little change with time, and wavelength shift due to changes in temperature and humidity can be suppressed.

  The glass substrate according to the present invention will be described. The present inventor has intensively studied to increase the rigidity of the glass substrate without performing a strengthening treatment, to reduce the amount of alkali elution while increasing the linear thermal expansion coefficient than before, and to further improve the chemical durability. Repeated. As a result, silicon oxide is used as the matrix component of the glass, and a specific rigidity such as MgO or CaO can be contained therein, whereby a predetermined rigidity can be obtained, and the total content of a specific alkali metal oxide can be specified. By making it into the range, it was found that the linear thermal expansion coefficient can be increased and at the same time the amount of alkali elution can be suppressed, and the present invention has been made.

Hereinafter, the reason why the components of the glass substrate according to the present invention are limited will be described. First, SiO ₂ is a component that forms a glass matrix. If its content is less than 45%, the structure of the glass becomes unstable and the chemical durability deteriorates, and at the same time the viscosity characteristics at the time of melting deteriorate and the moldability is hindered. On the other hand, if the content exceeds 70%, the meltability is deteriorated, the productivity is lowered, and sufficient rigidity cannot be obtained. Therefore, the content is determined to be in the range of 45 to 70%. A more preferred range is from 50 to 65%.

Al ₂ O ₃ enters the glass matrix, stabilizes the glass structure, and improves the chemical durability. If the content is less than 1%, a sufficient stabilizing effect cannot be obtained. On the other hand, if it exceeds 10%, the meltability deteriorates and the productivity is hindered. Therefore, the content is determined to be in the range of 1 to 10%. A more preferred range is from 2 to 8%.

B ₂ O ₃ improves meltability and productivity, and has the effect of entering the glass matrix, stabilizing the glass structure, and improving chemical durability. If the content is less than 0.5%, the effect of improving the meltability is poor and the stabilization of the matrix becomes insufficient. On the other hand, if the content exceeds 8%, the viscosity property at the time of melting deteriorates, and the moldability is hindered and sufficient rigidity cannot be obtained. Therefore, the content is determined to be in the range of 0.5 to 8%. A more preferred range is from 1 to 6%.

Alkali metal oxide R ₂ O (R = Li, Na, K) has the effect of improving the meltability and increasing the linear expansion coefficient. If the total amount of alkali metal oxides is less than 7%, the effects of improving the meltability and increasing the linear thermal expansion coefficient cannot be obtained sufficiently. On the other hand, if the total amount exceeds 20%, the amount of alkali dispersed between the glass skeletons becomes excessive and the amount of alkali elution increases. Therefore, the total amount of alkali metal oxides was determined to be in the range of 7 to 20%. A more preferable range is 8 to 15%. Further, in order to obtain a so-called alkali mixing effect that reduces the alkali elution amount, it is desirable that the content of each component of the alkali metal oxide is 0.5% or more.

  MgO has the effect of increasing the rigidity and improving the meltability. If the content is less than 0.1%, sufficient effects are not obtained for improvement of rigidity and improvement of meltability. On the other hand, if the content exceeds 10%, the glass structure becomes unstable, and the melt productivity is lowered and the chemical durability is lowered. Therefore, the content is determined to be in the range of 0.1 to 10%. A more preferable range is 0.5 to 8%.

  CaO has the effect of increasing the linear thermal expansion coefficient and rigidity and improving the meltability. If the content is less than 0.1%, a sufficient effect is not exerted with respect to improvement of linear thermal expansion coefficient and rigidity and improvement of meltability. On the other hand, if the content exceeds 10%, the glass structure becomes unstable, the melt productivity is lowered, and the chemical durability is lowered. Therefore, the content is set in the range of 0.1 to 10%. A more preferable range is 0.5 to 8%.

  And the total amount of MgO and CaO was made into the range of 1-15%. If this total amount is less than 1%, the effect of increasing the rigidity and improving the meltability will be insufficient, while if it exceeds 15%, the glass structure will become unstable and the melt productivity will decrease and the chemical durability will decrease. is there. A more preferable total amount is in the range of 2 to 12%.

TiO ₂ has the effect of strengthening the glass structure, improving the rigidity and improving the meltability. If the content is less than 0.5%, sufficient effects are not exerted for improving rigidity and improving meltability. On the other hand, if the content exceeds 10%, the glass structure becomes unstable, and the melt productivity is lowered and the chemical durability is lowered. Therefore, the content is determined to be in the range of 0.5 to 10%. A more preferred range is from 1 to 8%.

ZrO ₂ has the effect of strengthening the glass structure and improving the rigidity and chemical durability. When the content is less than 0.5%, sufficient effects are not exerted with respect to improvement in rigidity and improvement in chemical durability. On the other hand, if the content exceeds 10%, the meltability is lowered and the productivity cannot be improved. Therefore, the content is set in the range of 0.5 to 10%. A more preferred range is from 1 to 8%.

  ZnO has the effect of improving chemical durability and rigidity and improving meltability. If the content exceeds 5%, the glass structure becomes unstable and the melt productivity is lowered and the chemical durability may be lowered. For this reason, the content is preferably 5% or less. More preferably, it is 4% or less.

La ₂ O ₃ has the effect of improving the rigidity by strengthening the structure of the glass. If the content exceeds 8%, the glass structure becomes unstable, and the melt productivity is lowered and the chemical durability may be lowered. For this reason, the content is preferably 8% or less. More preferably, it is 6% or less. In order to improve the rigidity, instead of La ₂ O ₃ , lanthanoid oxides other than Ta ₂ O ₅ , Nb ₂ O ₅ , Y ₂ O ₃ , and La may be used, but compared with La ₂ O ₃ In view of production cost, it is desirable to use a small amount.

In order to improve the meltability, SrO and BaO may be added to the glass substrate of the present invention in less than 5% each. The fining agents such as Sb ₂ O ₃ may be added in the range of 2% or less. If necessary, conventionally known glass components and additives may be added within a range not impairing the effects of the present invention.

  There is no limitation in particular in the manufacturing method of the glass substrate of this invention, A conventionally well-known manufacturing method can be used. For example, the corresponding oxides, carbonates, nitrates, hydroxides, etc. are used as raw materials for each component, weighed to a desired ratio, and thoroughly mixed with powder to obtain a blended raw material. This is put into, for example, a platinum crucible in an electric furnace heated to 1,300 to 1,550 ° C., melted and clarified, homogenized with stirring, cast into a preheated mold, and gradually cooled to a glass block. . Next, it is reheated to the vicinity of the glass transition point, and is slowly cooled to remove strain. Then, the obtained glass block is sliced into a disk shape, and the inner periphery and the outer periphery are concentrically cut out using a core drill. Alternatively, the molten glass is press-molded into a disk shape. The disk-shaped glass substrate thus obtained is further subjected to rough polishing and polishing on both surfaces, and then washed with at least one of water, acid, and alkali to form a final glass substrate. .

  Here, when the glass substrate of the present invention is used as, for example, a substrate for an information recording medium, the surface roughness Ra of the glass substrate after the polishing step is determined from the viewpoint of reducing the flying height of the head or the film thickness of the recording medium. The surface roughness Ra ′ after the cleaning step is preferably 1.5 nm or less of the surface roughness Ra. In the case of a glass substrate that has been subjected to a tempering treatment, it is possible to reduce the surface roughness Ra to 1 nm or less by polishing, but when the surface of the substrate is cleaned with water, acid, or alkali in the next cleaning step. Since the chemical durability is low, the surface is severely eroded, resulting in an increase in the surface roughness Ra ′ after the cleaning process. On the other hand, since the glass substrate that is not tempered generally has a uniform surface and internal composition, the surface roughness Ra 'of the substrate does not change significantly even in the cleaning process. Therefore, by optimizing the glass component, the surface roughness Ra ′ after the cleaning process can be made 1.5 times or less of the surface roughness Ra after the polishing process.

Moreover, it is preferable that the glass substrate which concerns on this invention has a predetermined | prescribed glass physical property. First, the linear thermal expansion coefficient is preferably 60 × 10 ⁻⁷ / ° C. or higher. If the linear thermal expansion coefficient is out of this range, the difference between the linear thermal expansion coefficient of the material of the drive unit to which the information recording medium using the glass substrate is attached becomes large, and stress is generated in the fixed part of the information recording medium. This is because the recording position is shifted due to the breakage of the substrate or the deformation of the substrate, making it impossible to read / write the record. A more preferable lower limit value of the linear thermal expansion coefficient is 62 × 10 ⁻⁷ / ° C., and a preferable upper limit value is 90 × 10 ⁻⁷ / ° C.

  In the glass substrate according to the present invention, the alkali elution amount is preferably 250 ppb or less per 2.5 inch disk. This is because when the alkali elution amount is more than 250 ppb, when a glass substrate is used as an information recording medium, a recording film such as a magnetic film formed on the surface of the glass substrate is deteriorated by the eluted alkali component. A more preferable alkali elution amount is 230 ppb or less.

  Furthermore, in a glass substrate having a uniform surface and internal composition and an amorphous structure according to the present invention, the Young's modulus is preferably 85 GPa or more because the mechanical strength depends on the rigidity of the substrate. This is because when the Young's modulus is less than 85 GPa, the mechanical strength of the substrate becomes insufficient, and when it is subjected to an impact from the outside when the HDD is mounted, it tends to be damaged from the fastening portion with the HDD member. A more preferable Young's modulus is 87 GPa or more.

  The glass substrate according to the present invention preferably further satisfies the formula (1) while satisfying the various physical properties. If the formula (1) is not satisfied, the balance of the physical properties is poor even if the various physical properties are satisfied, the productivity at the time of melt molding is reduced, and the productivity at the time of polishing / cleaning / processing is remarkable. This is because problems occur in actual production such as deterioration. The left side of the formula (1) is more preferably 33 or more. On the other hand, a preferable upper limit is 70.

  Furthermore, the glass substrate of the present invention preferably has a Vickers hardness Hv of more than 550 in terms of impact resistance of the recording surface and prevention of damage in the process. In order to set the Vickers hardness in such a range, for example, the component ratio may be adjusted so as to increase the ion filling rate in the glass within a range in which the intended main physical properties are not deteriorated.

In the glass substrate of the present invention, from the viewpoint of productivity during melt molding, the liquidus temperature TL is 1,300 ° C. or lower, and the temperature T _log η _{= 2 at} which the glass melt viscosity _log η _{= 2} is 1,450 ° C. The glass transition temperature Tg is preferably 600 ° C. or lower. In order to set the liquid phase temperature, T _log η _{= 2} , and the glass transition temperature in such a range, for example, the liquid phase temperature of the glass can be adjusted by adjusting the total amount and ratio of components that cause the glass to become unstable when added excessively. That's fine. For T _log η _{= 2} , the addition ratio of SiO ₂ , which is the main component for increasing the viscosity, and the component for improving the viscosity may be adjusted within a range in which the intended main physical properties are not deteriorated. Regarding the glass transition temperature, the total amount and ratio of SiO ₂ , B ₂ O ₃ , and Al ₂ O ₃ that are skeleton components, and the amount of alkali metal oxide that is a component that greatly reduces the glass transition temperature, The main physical properties may be adjusted within a range not deteriorating.

  The glass substrate of the present invention is not limited in size, and can be a small-diameter disk of 3.5, 2.5, 1.8 inches or less, and the thickness thereof is 2 mm, 1 mm, 0. It can be as thin as 63 mm or less.

  Next, an information recording medium using the glass substrate of the present invention will be described. When the glass substrate of the present invention is used as a substrate for an information recording medium, durability and high recording density are realized. Hereinafter, an information recording medium will be described with reference to the drawings.

  FIG. 1 is a perspective view of a magnetic disk. This magnetic disk D is obtained by directly forming a magnetic film 2 on the surface of a circular glass substrate 1. As a method for forming the magnetic film 2, a conventionally known method can be used. For example, a method in which a thermosetting resin in which magnetic particles are dispersed is spin-coated on a substrate, or a method by sputtering or electroless plating is used. A method is mentioned. The film thickness by spin coating is about 0.3 to 1.2 μm, the film thickness by sputtering is about 0.04 to 0.08 μm, and the film thickness by electroless plating is 0.05 to 0.1 μm. From the viewpoint of thinning and densification, film formation by sputtering and electroless plating is preferable.

The magnetic material used for the magnetic film is not particularly limited, and a conventionally known material can be used. However, in order to obtain a high coercive force, Ni having a high crystal anisotropy is basically used, and Ni or A Co-based alloy to which Cr is added is suitable. Specific examples include CoPt, CoCr, CoNi, CoNiCr, CoCrTa, CoPtCr, and CoNiPt containing Co as a main component, CoNiCrPt, CoNiCrTa, CoCrPtTa, CoCrPtB, and CoCrPtSiO. The magnetic film may have a multilayer structure (for example, CoPtCr / CrMo / CoPtCr, CoCrPtTa / CrMo / CoCrPtTa) that is divided by a nonmagnetic film (for example, Cr, CrMo, CrV, etc.) to reduce noise. Addition to the above magnetic material, ferrite, iron - rare-earth or be in a non-magnetic film made of _{SiO 2, BN Fe, Co,} FeCo, etc. granular structure magnetic particles are dispersed, such CoNiPt Also good. Further, the magnetic film may be either an inner surface type or a vertical type recording format.

  In addition, a lubricant may be thinly coated on the surface of the magnetic film in order to improve the sliding of the magnetic head. Examples of the lubricant include those obtained by diluting perfluoropolyether (PFPE), which is a liquid lubricant, with a freon-based solvent.

  Furthermore, you may provide a base layer and a protective layer as needed. The underlayer in the magnetic disk is selected according to the magnetic film. Examples of the material for the underlayer include at least one material selected from nonmagnetic metals such as Cr, Mo, Ta, Ti, W, V, B, Al, and Ni. In the case of a magnetic film containing Co as a main component, Cr alone or a Cr alloy is preferable from the viewpoint of improving magnetic characteristics. Further, the underlayer is not limited to a single layer, and may have a multi-layer structure in which the same or different layers are stacked. For example, a multilayer underlayer such as Cr / Cr, Cr / CrMo, Cr / CrV, NiAl / Cr, NiAl / CrMo, or NiAl / CrV may be used.

Examples of the protective layer that prevents wear and corrosion of the magnetic film include a Cr layer, a Cr alloy layer, a carbon layer, a hydrogenated carbon layer, a zirconia layer, and a silica layer. These protective layers can be formed continuously with an in-line type sputtering apparatus, such as an underlayer and a magnetic film. In addition, these protective layers may be a single layer, or may have a multilayer structure including the same or different layers. Note that another protective layer may be formed on the protective layer or instead of the protective layer. For example, in place of the protective layer, tetraalkoxylane is diluted with an alcohol-based solvent on the Cr layer, and then colloidal silica fine particles are dispersed and applied, and then baked to form a silicon oxide (SiO ₂ ) layer. It may be formed.

  The magnetic disk has been described above as one embodiment of the information recording medium. However, the information recording medium is not limited to this, and the glass substrate of the present invention can be used for a magneto-optical disk, an optical disk, and the like. .

Moreover, the glass substrate of this invention can be used conveniently also for the element for optical communications. In the glass substrate of the present invention, the alkali elution amount is as small as 250 ppb or less per 2.5 inch disk, and the film on the substrate is not deteriorated by the alkali component eluted from the substrate. In addition, since the linear thermal expansion coefficient is as large as 60 × 10 ⁻⁷ / ° C. or more as compared with the conventional glass substrate, the glass substrate heated in the vapor deposition process is cooled and shrunk, and the shrinkage of the glass substrate The film formed on the substrate surface is compressed to increase its density. As a result, wavelength shift due to changes in temperature and humidity is suppressed.

Hereinafter, an optical communication element using the glass substrate of the present invention will be described taking an optical filter for wavelength division division (“DWDM”) as an example. An optical filter using a dielectric multilayer film has a high refractive index layer and a low refractive index layer, and has a structure in which these layers are laminated. A method for forming these layers is not particularly limited, and a conventionally known method such as a vacuum deposition method, a sputtering method, an ion plating method, or an ion beam assist method can be used. Among these, vacuum deposition is recommended because of its high productivity. Vacuum deposition is a method of forming a thin film by heating a deposition material in vacuum and condensing and adhering the generated vapor onto a substrate. There are various methods such as resistance heating, an external heating crucible, an electron beam, a high frequency, and a laser as a method for heating the vapor deposition material. As specific vapor deposition conditions, the degree of vacuum is about 1 × 10 ^{−3 to} 5 × 10 ⁻³ Pa. During the deposition, the amount of introduced oxygen is adjusted by controlling the solenoid valve so that the degree of vacuum is constant. Then, when the predetermined layer thickness is reached by the layer thickness monitor, the shutter is closed and the deposition is finished.

  Each film thickness is not particularly limited, but the optical film thickness is basically ¼ of the wavelength, and is generally about 1 μm. Moreover, the total number of layers generally exceeds 100 layers. Examples of the film material to be used include dielectrics, semiconductors, and metals. Among these, dielectrics are particularly preferable.

  As mentioned above, although the optical filter for DWDM was demonstrated as one embodiment of the element for optical communications using the glass substrate of this invention, the element for optical communications is not limited to this, The glass substrate of this invention is optical. It can also be used for optical communication elements such as switches and multiplexing / demultiplexing elements.

Examples 1 to 59, Comparative Examples 1 to 11
A specified amount of raw material powder was weighed into a platinum crucible, mixed, and then melted at 1,550 ° C. in an electric furnace. After the raw materials were sufficiently dissolved, a stirring blade was inserted into the glass melt and stirred for about 1 hour. Thereafter, the stirring blade was taken out and allowed to stand for 30 minutes, and then the melt was poured into a jig to obtain a glass block. Thereafter, the glass block was reheated to near the glass transition point of each glass, and slowly cooled to remove strain. The obtained glass block was sliced into a disc shape of about 1.5 mm in thickness and 2.5 inches, and the inner periphery and outer periphery were cut out using a cutter with concentric circles. And both surfaces were subjected to rough polishing, polishing, and cleaning to produce glass substrates of Examples and Comparative Examples. The following physical property evaluation was performed about the produced glass substrate. The results are shown in Tables 1 to 6.

(Linear thermal expansion coefficient A)
Using a differential expansion measuring device, the measurement was performed under the conditions of load: 5 g, temperature range: 25 to 100 ° C., temperature increase rate: 5 ° C./min.

(Alkaline elution amount B)
After polishing the surface of the glass substrate with cerium oxide to obtain a smooth surface with an Ra value of 2 nm or less, the surface is washed, immersed in 50 ml of reverse osmosis membrane water at 80 ° C. for 24 hours, and then subjected to an ICP emission spectroscopic analyzer. The eluate was analyzed and calculated.

(Young's modulus E)
It measured according to the dynamic elastic modulus test method of the elastic test method of JIS R 1602 fine ceramics.

(Glass transition point Tg)
Using a differential heat measuring device, a glass sample adjusted to a powder form was measured in a temperature range from room temperature to 900 ° C. at a rate of temperature increase of 10 ° C./min.

(Vickers hardness Hv)
The measurement was performed using a Vickers hardness tester under conditions of a load of 100 g and a load time of 15 sec.

(Liquid phase temperature T _L )
After melting and holding at 1,550 ° C. for 2 hours, holding at 1,300 ° C. for 10 hours and rapid cooling, the presence or absence of devitrified material was observed on the surface and inside of the glass. “,” When there was a devitrified material, “×”.

(Temperature T _log η _{= 2} )
The viscosity of the melted glass was measured using a stirring-type viscometer, and the temperature at which _log η _{= 2} was obtained. When T _log η _{= 2} was 1450 ° C. or less, “◯” was exceeded and 1450 ° C. was exceeded. The case was set as “x”.

(Surface roughness)
The sample surface was polished for 1 hour using cerium oxide as the abrasive and using hard urethane as the polishing pad. Next, the polished sample was subjected to ultrasonic cleaning with pure water in a wet state. Then, the surface of the sample was observed using an AFM (atomic force microscope, “D3100 system” manufactured by Digital Instruments), and the surface roughness Ra after the polishing step was measured. The measurement area is a visual field of 10 μm × 10 μm, and the number of measurement points is 5 per sample. Next, the polished sample was immersed in a 5 wt% sodium hydroxide aqueous solution at 50 ° C. for 10 minutes, and then ultrasonically cleaned with pure water. In the same manner as described above, the surface roughness Ra ′ of the sample was measured using AMF.

According to Tables 1 to 4, in the glass substrates of Examples 1 to 59, the linear thermal expansion coefficient was in the range of 62 × 10 ⁻⁷ / ° C., which was a large value compared to the conventional glass substrate. Moreover, the alkali elution amount was 235 ppb or less, which was smaller than that of the conventional glass substrate. In addition, the Young's modulus was 85 GPa or more, and all of them were practically no problem. Furthermore, the meltability of the glass was also at a good level.

According to Table 5, in the glass substrate of Comparative Example 1, since the content of SiO ₂ was as low as 42.9%, the glass structure was weak and the alkali elution amount increased and the Young's modulus decreased. In addition, devitrification was observed in the glass. On the other hand, in the glass substrate of Comparative Example 2 having a high SiO ₂ content of 72.1%, the coefficient of linear thermal expansion decreased and the Young's modulus also decreased. The glass substrate of Comparative Example 3 having a high Al ₂ O ₃ content of 12.9% and a B ₂ O ₃ content of 8.8% and an Al ₂ O ₃ content of 16.9% In many glass substrates of Comparative Example 4, the coefficient of linear thermal expansion decreased and the Young's modulus also decreased. Furthermore, the temperature T _log η _{= 2} was high and the meltability of the glass was poor.

In the glass substrate of Comparative Example 5 containing a large amount of B ₂ O ₃ of 13.8%, the coefficient of linear thermal expansion was small, the amount of alkali elution was large, the Young's modulus was small, and the Vickers hardness was low. On the contrary, in the glass substrate of Comparative Example 6 containing no B ₂ O ₃ , the amount of alkali elution was large. The glass substrate of Comparative Example 7 containing no Al ₂ O ₃ was devitrified and did not vitrify. In the glass substrate of Comparative Example 8 containing a large amount of CaO as 12.3%, the alkali elution amount was large and the Vickers hardness was low. In addition, devitrification was observed in the glass. Moreover, in the glass substrate of the comparative example 9 which contained MgO as much as 12.3%, there was much alkali elution amount and the devitrification thing was seen by glass. In the glass substrate of Comparative Example 10 containing 13.5% of ZrO ₂ , undissolved substances were observed when the glass was melted. Moreover, in the glass substrate of Comparative Example 11 containing a large amount of TiO ₂ as 13.0%, the amount of alkali elution was large, and devitrified substances were observed in the glass.

  As shown in Table 6, in each glass substrate of the example and the glass substrate of the comparative example, the surface roughness Ra after the polishing step was 1.0 nm or less, but after washing with a sodium hydroxide solution, In each glass substrate of the example, Ra ′ / Ra was 1.3 or less, whereas in the glass substrate of Comparative Example 1, Ra ′ / Ra was 1.9, and the glass surface after the cleaning step The roughness Ra ′ was increased, causing a problem in practical use.

It is a perspective view which shows an example of the information recording medium using the glass substrate of this invention.

Explanation of symbols

1 Glass substrate 2 Magnetic film D Magnetic disk

Claims (4)

% By weight
SiO _2: 45~70%,
Al ₂ O ₃ : 1 to 5.0%,
B ₂ O ₃ : 1.0-8%,
Li ₂ O + Na ₂ O + K ₂ O: 7-20%,
MgO: 0.1 to 10%,
CaO: 0.1 to 10%,
MgO + CaO: 1 to 15%,
TiO ₂ : 0.5 to 10%,
ZrO ₂ : 0.5 to 10%,
ZnO: 0 to 5%,
La ₂ O ₃ : 0 to 8%
A glass substrate characterized by having each glass component. The linear thermal expansion coefficient A is 60 × 10 ⁻⁷ / ° C. or more, the alkali elution amount B is 250 ppb or less per 2.5 inch disk, the Young's modulus E is 85 GPa or more, and the following formula is satisfied. The glass substrate according to claim 1, wherein the internal composition is uniform and has an amorphous structure.
(A / B) × E × 10 ⁷ ≧ 30 (1) Vickers hardness Hv is greater than 550, liquidus temperature T _L is 1,300 ° C. or less, temperature T _log η _{= 2 at} which glass melt viscosity _log η _{= 2} is 1,450 ° C. or less, and glass transition temperature Tg is 600 The glass substrate according to claim 1 or 2, wherein the glass substrate has a temperature of ° C or less. A glass substrate manufactured through a polishing step and a cleaning step, wherein the glass substrate is cleaned with at least one liquid of pure water, acid, and alkali in the cleaning step, and the surface roughness Ra after the polishing step and after the cleaning step The surface roughness Ra ′ is the following formula (2), (3)
Ra ′ / Ra ≦ 1.5 (2)
Ra ≦ 1.0nm (3)
The glass substrate in any one of Claims 1-3 which satisfy | fills.

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