JP5396859B2 - Glass for information recording medium substrate - Google Patents

Description

  The present invention relates to a glass substrate for an information recording medium such as a glass substrate for a magnetic disk and a glass for an information recording medium substrate suitable for a glass substrate for an information recording medium.

A glass substrate is widely used as an information recording medium substrate, particularly a magnetic disk (hard disk) substrate, and there are chemically strengthened and non-chemically strengthened glass substrates for magnetic disks.
As a glass substrate for a magnetic disk that is not chemically strengthened, a glass substrate made of SiO ₂ —Al ₂ O ₃ —Li ₂ O—Na ₂ O—K ₂ O—TiO ₂ glass has been proposed (see Patent Document 1). ).

JP 2004-161597 A (Tables 1 to 12)

The glass of Patent Document 1 has a maximum glass transition point (Tg) of 567 ° C. When this glass is used for a glass substrate for a magnetic disk, the temperature at which a magnetic layer is formed on the glass substrate may be increased. As a result, the coercive force of the magnetic layer may not be increased.
An object of the present invention is to provide a glass for an information recording medium substrate and a glass substrate for an information recording medium using the same, which can solve such problems.

The present invention is expressed in terms of mol% based on the following oxides: SiO ₂ is 55 to 75%, Al ₂ O ₃ is 1 to 12%, MgO is 2 to 15%, CaO is 0 to 1.5%, Na ₂ The total content of O or K ₂ O is 1 to 20%, the content of TiO ₂ is 0 to 8%, and the content of BaO is 2% or less, and the content of Li ₂ O is 1 or less. %, And when ZrO ₂ is contained, the content of the glass for an information recording medium substrate is 0.5% or less.
Moreover, the glass substrate for information recording media which consists of said glass for information recording media substrates is provided.

According to the present invention, a glass for an information recording medium substrate having a Tg of 600 ° C. or higher can be obtained.
Further, it is possible to obtain an information recording medium substrate glass or an information recording medium glass substrate having high strength, low density, or float forming.
In addition, since a glass substrate for an information recording medium having high weather resistance can be obtained, the surface properties of the glass substrate change remarkably during inventory, and films such as a base film, a magnetic film, and a protective film formed on the substrate. The problem of easy peeling is less likely to occur.
Moreover, since the glass substrate for information recording media can be manufactured without performing the chemical strengthening treatment, the number of processes can be reduced, and the problem of dirt adhesion to the substrate surface after the chemical strengthening treatment can be solved.

  The Tg of the glass for an information recording medium substrate of the present invention (hereinafter referred to as the glass of the present invention) is preferably 600 ° C. or higher. If it is less than 600 ° C., the heat treatment temperature for forming the magnetic layer cannot be sufficiently increased, and it may be difficult to increase the coercive force of the magnetic layer. More preferably, it is 610 degreeC or more, Most preferably, it is 620 degreeC or more.

It is preferable that the average linear expansion coefficient ((alpha)) in 50-350 degreeC of the glass of this invention is 70x10 < ^-7 > / degreeC or more. If it is less than 70 × 10 ⁻⁷ / ° C., the difference between the thermal expansion coefficient of the metal of the hub attached to the substrate (typically 70 × 10 ^{−7 to} 100 × 10 ⁻⁷ / ° C.) becomes large, and the substrate cracks. It tends to happen. More preferably, it is 75 × 10 ⁻⁷ / ° C. or more, and particularly preferably 80 × 10 ⁻⁷ / ° C. or more. Α is typically 95 × 10 ⁻⁷ / ° C. or less.

In the glass of the present invention, when the liquidus temperature is _TL and the temperature at which the viscosity is 10 ⁴ P (poise) is T ₄ , ( _TL- T ₄ ) is preferably less than 50 ° C. If (T _L -T ₄ ) is 50 ° C. or higher, float molding may be difficult, more preferably less than 40 ° C., and particularly preferably less than 30 ° C.
The temperature T _{2 at} which the viscosity of the glass of the present invention becomes 10 ² P is preferably 1700 ° C. or lower. If T ₂ exceeds 1700 ° C., it may be difficult to dissolve or clarify the glass.

Glass substrates for magnetic disks are widely used for 2.5 inch substrates (outer diameter of glass substrate: 65 mm) used for notebook personal computers and 1.8 inch substrates (outer diameter of glass substrate: 48 mm) used for portable MP3 players, etc. The market is growing year by year, while low-cost supply is required. It is preferable that the glass used for such a glass substrate is suitable for mass production.
Mass production of sheet glass is widely performed by continuous molding methods such as the float method, fusion method, and downdraw method. As described above, the glass of the present invention can be produced in large quantities because it can be made, for example, glass that can be float molded. It is suitable for.

Preferably the density of the glass of the present invention is 2.50 g / cm ³ or less, more preferably 2.48 g / cm ³ or less, particularly preferably 2.47 g / cm ³ or less.

  The glass substrate for information recording media of the present invention (hereinafter referred to as the glass substrate of the present invention) is a generally circular glass plate made of the glass of the present invention. An example of the information recording medium is a magnetic disk.

When the glass substrate of the present invention is held in a steam atmosphere at 120 ° C. and 2 atm for 20 hours, the number N _{L of} deposits having a size of 10 μm or more present on the surface is 1 piece / cm ² or less. or, it is preferable that the size adheres the number _{N S} of less than 10μm or 1μm is 10 ⁵ / cm ² or less. The N _L is 1 / cm ² or greater than _{N S} 10 ⁵ cells / cm ^2, greater than the base film which deposits on the surface of the glass substrate in the glass substrate stock (dimming) is generated, are formed on a glass substrate In addition, films such as magnetic films and protective films are easily peeled off. This deposit is considered to be a reaction product produced and adhered to the glass substrate due to the influence of moisture and carbon dioxide in the air, and cannot be removed by wiping. N _L is more preferably 0.8 pieces / cm ² or less, particularly preferably 0.5 pieces / cm ² or less. N _S is more preferably 0.8 × 10 ⁵ / cm ² or less, particularly preferably 0.6 × 10 ⁵ / cm ² or less.

The crack occurrence rate of the glass of the present invention is preferably 70% or less. If it exceeds 70%, the glass strength may be insufficient. More preferably, it is 60% or less, and particularly preferably 50% or less.
The crack occurrence rate is obtained as follows. That is, in a room controlled at 23 ° C. and a relative humidity of 70%, a Vickers indenter is driven with a load of 500 g on the surface of a mirror-polished glass plate having a thickness of 1 to 2 mm and a size of 4 cm × 4 cm. Measure the number of cracks generated. This measurement is repeated 10 times, and 100 × (total number of cracks generated) / 40 is defined as the crack occurrence rate.
When the crack generation rate is small, the glass surface is hardly scratched, so that stress concentration is difficult to occur, and brittle fracture does not occur or is reduced by weak stress.

  The method for producing the glass and glass substrate of the present invention is not particularly limited, and various methods can be applied. For example, the raw materials of each component normally used are prepared so as to have a target composition, and this is heated and melted in a glass melting kiln. Homogenize the glass by bubbling, stirring, adding a clarifying agent, etc., and forming it into a sheet glass of a predetermined thickness by methods such as the well-known float method, press method, fusion method or down draw method, and after slow cooling, as necessary After processing such as grinding and polishing, a glass substrate having a predetermined size and shape is obtained. As the molding method, a float method suitable for mass production is particularly suitable. Further, continuous molding methods other than the float method, that is, the fusion method and the downdraw method are also suitable.

Next, the composition of the glass of the present invention will be described using mol% display.
SiO ₂ is a component that forms a glass skeleton and is essential. If it is less than 55%, the glass tends to be scratched, and the _TL rises and the glass becomes unstable. Preferably it is 58% or more, more preferably 60% or more, particularly preferably 62% or more, typically 64% or more, more typically 65% or more. If it exceeds 75%, the high-temperature viscosity rises and it becomes difficult to melt the glass. Preferably it is 72% or less, More preferably, it is 71% or less.

Al ₂ O ₃ has an effect of increasing Tg and improving weather resistance, and is essential. If it is less than 1%, the effect is small. Preferably it is 1.5% or more, More preferably, it is 2% or more, Most preferably, it is 2.5% or more. If it exceeds 12%, the high-temperature viscosity will increase, making it difficult to melt the glass, and _TL will be too high. It is preferably 10% or less, more preferably 8% or less, particularly preferably 7% or less, and typically 6.5% or less.

  MgO is an essential component with the effect of increasing α while maintaining the weather resistance, making the glass less susceptible to damage, and improving the solubility of the glass. If it is less than 2%, the effect is small. Preferably it is 5% or more, more preferably 7% or more, and most preferably 8% or more. If it exceeds 15%, the TL becomes too high. Preferably it is 14% or less, More preferably, it is 13% or less.

  CaO is not essential, but may be contained up to 1.5% in order to increase α while maintaining the weather resistance or to improve the solubility of the glass. If it exceeds 1.5%, the glass may be easily damaged. Preferably it is 1% or less, more preferably less than 0.5%, typically 0.3% or less.

Na ₂ O and K ₂ O are components having an effect of increasing α and improving the solubility of glass, and must contain at least one of them. The effect is small when the total Na ₂ O + K ₂ O content of Na ₂ O and K ₂ O is less than 1%. It is preferably more than 2%, more preferably 5% or more, particularly preferably 7% or more, and typically 10% or more. If it exceeds 20%, the weather resistance is lowered and the glass transition point is lowered. It is preferably 17% or less, more preferably 15% or less, particularly preferably 14% or less, and typically 13.5% or less. Typically, Na ₂ O is 2 to 8% and K ₂ O is 3 to 10%.
It is preferable that SiO ₂ is more than 60%, Al ₂ O ₃ is 10% or less, and Na ₂ O + K ₂ O is more than 2% and 17% or less.

TiO ₂ is not an essential component, but has the effect of increasing Tg, increasing weather resistance, or improving glass solubility, and may be contained up to 8%. If it exceeds 8%, _TL may be too high, or a phase separation phenomenon may easily occur. Preferably it is 7% or less, More preferably, it is 6% or less, Most preferably, it is 5% or less. Further, when containing TiO _2, its content is preferably at least 1%. More preferably, it is 1.5% or more, particularly preferably 2% or more, and most preferably 3% or more.
The total MgO + TiO ₂ content of MgO and TiO ₂ is preferably 10% or more. If it is less than 10%, the glass may be easily damaged, or the high-temperature viscosity may increase and it may be difficult to melt the glass. MgO + TiO ₂ is typically at least 13%.
Typically, SiO ₂ is 62~72%, _Al 2 _{O 3} is 2 to 8%, MgO is _{7~14%, Na 2 O + K} 2 O is 10 to 14%, TiO ₂ is 6% .

The glass of the present invention consists essentially of the above components, but may contain other components as long as the object of the present invention is not impaired. In that case, the total content of the other components is preferably 10% or less, more preferably 5% or less, and typically 2% or less.
For example, clarifiers such as SO ₃ , Cl, As ₂ O ₃ , Sb ₂ O ₃ and SnO ₂ may be contained up to 2% in total, but As ₂ O ₃ , Sb ₂ O ₃ and SnO ₂ are not contained. It is preferable.
It may also be contained in order to improve the solubility and stability of the glass up to 3% B ₂ O ₃ in total.
However, B ₂ O ₃ is from the following viewpoints are preferably substantially free. That is, when B ₂ O ₃ coexists with an alkali metal oxide component, it tends to form an alkali borate compound having a low vapor pressure, and the same component is very easily volatilized from the glass melt. This causes inhomogeneities such as striae and causes glass quality deterioration, and at the same time, the volatilized material is condensed into the brick material used in the glass melting kiln, which significantly reduces the strength of the volatilized material. Therefore, it is preferable that B ₂ O ₃ is not substantially contained when it is desired to suppress the occurrence of such a problem.

In some cases, SrO or BaO may be contained within a total range of 4% or less in order to increase α while maintaining the weather resistance and to improve the solubility of the glass. If it exceeds 4%, the glass may be easily damaged. Preferably it is 2% or less. However, when it contains BaO, the content must be 2 mol% or less.
In addition, when it is desired to make the glass more difficult to be damaged, SrO is not contained, or even if it is contained, it is preferably less than 0.1%. In such a case, BaO is not contained, or even if contained, it is preferably less than 0.1%.
Li ₂ O may be contained up to 1% in order to increase α or improve the solubility of glass. If it exceeds 1%, the Tg is lowered, the weather resistance is lowered, or the glass is easily damaged. Typically, it is 0.6% or less, but it is often preferable not to contain it substantially.
In order to increase Tg, ZrO ₂ may be contained up to 0.5%. If it exceeds 0.5%, the glass tends to be damaged.

  When CaO, SrO or BaO is contained, the molar ratio of MgO content to (total content of MgO, CaO, SrO and BaO): (MgO) / (MgO + CaO + SrO + BaO) is preferably 0.6 or more. . If it is less than 0.6, the glass tends to be damaged.

The total content of Li ₂ O, Na ₂ O and K ₂ O is R ′ ₂ O, the total content of alkaline earth metal oxides is RO, and R ′ ₂ O and (R ′ ₂ O + RO) the molar ratio of, _{i.e., (R '2 O) /} (R' 2 O + RO) is preferably 0.25 to 0.75. Outside this range, the weather resistance may be reduced, α may be small, or the glass may be easily damaged. More preferably, it is 0.3-0.7.
When containing _{K 2} O, K ₂ O content and _Li 2 O, molar ratio of the sum of the content of Na ₂ O and _{K 2} O, _{i.e., K 2 O / (Li 2} O + Na 2 O + K 2 O ) Is preferably 0.2 or more. If it is less than 0.2, Tg may be lowered, or the weather resistance may be lowered. More preferably, it is 0.3 or more, and particularly preferably 0.4 or more.
Since oxides of atoms having atomic numbers larger than Ti (such as V) may easily damage the glass, when these are contained, the total content thereof is preferably 0.5% or less. . More preferably, it is 0.3% or less, particularly preferably 0.2% or less, and most preferably 0.1% or less.

The raw materials of each component were prepared so as to have a composition expressed in mol% in the columns from SiO ₂ to ZrO ₂ in the “Table”, and dissolved at a temperature of 1550 to 1600 ° C. for 3 to 5 hours using a platinum crucible. did. In melting, a platinum stirrer was inserted into the molten glass and stirred for 2 hours to homogenize the glass. Next, the molten glass was poured out, formed into a plate shape, and gradually cooled. In Tables, RO is the total content of MgO, CaO, SrO and BaO (unit: mol%), and R ′ ₂ O is the content of Li ₂ O, Na ₂ O and K ₂ O ( (Unit: mol%).
The glass of Examples 1-11 is an Example, The glass of Examples 12-25 is a comparative example.

About the glass plate obtained in this way, crack generation rate (unit:%), glass transition point Tg (unit: ° C.), thermal expansion coefficient α (unit: × 10 ⁻⁷ / ° C.), liquidus temperature T _L (unit: ° C.), the temperature _{T 4} at which the viscosity becomes 10 ⁴ P (unit: ° C.), the temperature _{T 2} (unit viscosity becomes 10 ² P: ℃), wherein _{N L} (unit: pieces / ^cm 2), said _{N S} (Unit: 10 ⁵ pieces / cm ² ) and density (unit: g / cm ³ ) were measured. The results in "table" indicates _{Tg, α, T L, T} 4, T 2, N L, the _{N S} measurement methods below, respectively. In addition, the item shown by "-" in a "table" was not measured.
Tg: Using a differential thermal dilatometer, the elongation rate of the glass when the temperature is raised from room temperature at a rate of 5 ° C./minute using quartz glass as a reference sample is the temperature at which the glass softens and no longer can be observed. Measurement was made up to the yield point, and the temperature corresponding to the inflection point in the obtained thermal expansion curve was taken as the glass transition point.

  α: Using a differential thermal dilatometer, the elongation of the glass was measured from quartz glass as a reference sample at a rate of 5 ° C./min from room temperature to the yield point. The average linear expansion coefficient at ˜350 ° C. was calculated.

T _L : The glass was crushed into glass particles of about 2 mm with a mortar, and these glass particles were placed side by side on a platinum boat and heat-treated in a temperature gradient furnace for 24 hours. The maximum value of the temperature of the glass grains on which the crystals were precipitated was taken as the liquidus temperature.
T ₄ , T ₂ : Measured with a rotational viscometer.

N _L , N _S : Both sides of a glass plate having a thickness of 1 to 2 mm and a size of 4 cm × 4 cm are mirror-polished, washed with calcium carbonate and a neutral detergent, and then a super accelerated life tester (unsaturated) Was placed in a mold pressure cooker TPC-410, Tabai Espec Co., Ltd.) and allowed to stand in a steam atmosphere at 120 ° C. and 2 atmospheres for 20 hours. The surface of the surface of the glass plate taken out was observed with a differential interference microscope, and the number of deposits having a size of 10 μm or more and the number of deposits having a size of 1 μm or more and less than 10 μm were counted.

It can be used for manufacturing information recording medium substrates such as magnetic disk substrates and information recording media such as magnetic disks.

It should be noted that the entire contents of the specification, claims, drawings and abstract of Japanese Patent Application No. 2006-315122 filed on November 22, 2006 are cited herein as disclosure of the specification of the present invention. Incorporated.

Claims (14)

In terms of mol% based on the following oxide standards, SiO ₂ is 55 to 75%, Al ₂ O ₃ is 1 to 8%, MgO is 7 to 15%, CaO is less than 0 to less than 0.5%, Na ₂ O or K 1-20% of ₂ O in total, the TiO ₂ containing 0-8%, the content of the case containing BaO is 2% or less, the content of the case containing Li ₂ O is 1% or less There, its content if it contains ZrO ₂ is Ri der less 0.5%, MgO content and MgO, CaO, molar ratio of the sum of the content of SrO and BaO is 0.9 or more information Glass for recording medium substrate. In terms of mol% based on the following oxides, SiO ₂ is 55 to 75%, Al ₂ O ₃ is 1 to 8%, MgO is 7 to 15%, CaO is 0 to 1.5%, Na ₂ O or K _2. When O is contained in a total of 1 to 20%, TiO ₂ is contained in an amount of 0 to 8%, and BaO is contained, its content is 2% or less, and when it contains Li ₂ O, its content is 1% or less. , its content if it contains ZrO ₂ is Ri der 0.5%, the information recording MgO content and MgO, CaO, molar ratio of the sum of the content of SrO and BaO is 0.9 or more Glass for medium substrate (excluding those containing 0.5% by mass or more of ZrO ₂ ).   The glass for an information recording medium substrate according to claim 2, wherein the content of CaO is less than 0.5%. The glass for an information recording medium substrate according to claim 1, wherein SiO ₂ is more than 60% and Na ₂ O + K ₂ O is more than 2% and 17% or less. The SiO ₂ is 62 to 72%, the Al ₂ O ₃ is 2 to 8%, the MgO is 7 to 14%, the Na ₂ O + K ₂ O is 10 to 14%, and the TiO ₂ is 0 to 6%. Or the glass for an information recording medium substrate according to 3. MgO + information recording medium glass substrate according to claim 1, 2, 3, 4 or 5 TiO ₂ is 10% or more. The total content of Li ₂ O, Na ₂ O and K ₂ O is R ′ ₂ O, and the total content of alkaline earth metal oxides is RO, and R ′ ₂ O and (R ′ ₂ O + RO) information recording medium glass substrate according to any one of claims 1 to 6 molar ratio of 0.25 to 0.75. Containing K ₂ O, any one of the content of _{K 2} O and _Li 2 O, claim 1-7 molar ratio of the sum of the content of Na ₂ O and _{K 2} O is 0.2 or more The glass for information recording medium substrates as described in the paragraph . B ₂ O ₃ containing substantially no claim 1-8 information recording medium glass substrate according to any one of. Information recording medium glass substrate according to any one of claims 1-9 glass transition point of 600 ° C. or higher. The average linear expansion coefficient of 70 × ^{10 -7} / ℃ higher than it claims 1-10 information recording medium glass substrate according to any one of the 50 to 350 ° C.. The liquidus temperature of _{T L,} the temperature at which the viscosity becomes 10 ⁴ P as _{T 4, (T L -T 4} ) < information recording medium substrate according to any one of claims 1 to 11 which is 50 ° C. Glass. Density 2.50 g / cm ³ or less information recording medium glass substrate according to any one of claims 1 to 12. Glass substrate for an information recording medium comprising a recording medium glass substrate according to any one of claims 1 to 13.