JP2009280461A - Glass substrate for information recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a glass substrate for an information recording medium, which has no bubble in glass even though an arsenic component or an antimony component is not used and has physical properties for use as a substrate for the next-generation information recording medium, in particular, which has a good balance between specific gravity and mechanical strength applicable as the substrate for the next-generation information recording medium, in which reboil does not occur when the glass substrate is pressed, and which is suitable when a direct press method is used. <P>SOLUTION: The glass substrate for the information recording medium contains an SiO<SB>2</SB>component, Al<SB>2</SB>O<SB>3</SB>and a R<SB>2</SB>O component (wherein R is one or more elements selected from Li, Na and K) as essential components in terms of oxides, further contains an α element as a clarifying component and has <0.1 molar ratio βm/αm, a compound of a β element to an oxide of the α element in the glass, and <2.7 specific gravity. The α element is one of Sn and Ce and the β element is one or more elements selected from Sn, Ce, Mn, W, Ta, Bi, S, Cl and F but is not the same as the α element. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

The present invention relates to a glass substrate for information magnetic recording media.
In particular, the present invention provides a glass substrate having physical properties for use as an information recording medium substrate without using an arsenic component or an antimony component that adversely affects the human body and the environment.

  In the present invention, the “information recording medium” refers to a fixed hard disk, a removable hard disk, a card hard disk, a digital video camera, a digital camera, an audio hard disk, or a car navigation hard disk used as a hard disk of a personal computer. It means an information magnetic recording medium that can be used in a mobile phone hard disk or a hard disk for various electronic devices.

  In recent years, large-capacity information magnetic recording devices have come to handle large amounts of data such as moving images and voices in digital video cameras, digital cameras, and portable audio devices in order to cope with the multimediaization of personal computers. Is required. As a result, information magnetic recording media are increasingly required to have a higher recording density year by year.

  In order to cope with this, the adoption of the perpendicular magnetic recording system and the mass production are being promoted. In this perpendicular magnetic recording system, the heat resistance of the substrate and the smoothness of the surface, which are superior to those of the prior art, are required. Conventionally, information magnetic recording devices have been mostly used in a static environment such as for personal computers. However, in recent years, information magnetic recording devices have been used in a dynamic environment such as a portable audio device. There is a lot to be done. Therefore, it is more important than ever for next-generation information recording media substrates to have low specific gravity to reduce the burden on the spindle motor and high mechanical strength to prevent disk crashes. It has become. However, low specific gravity, high mechanical strength, and excellent mass productivity are in conflict with each other. In the next generation of information recording media substrates that are considered for use in dynamic environments, There is research on how to balance elements.

Glass materials have been studied as one of materials for information recording medium substrates that satisfy the above requirements. When using a glass material, in order to manufacture a disk-shaped substrate having a thickness of 1 mm or less at a low cost, a direct press method of directly pressing molten glass is used.
In the direct press method, when melting glass, arsenic and antimony components have been used as fining agents to remove bubbles from the molten glass, but in recent years there is a risk of adverse effects on the human body and the environment. Therefore, it is required to reduce the content or not to use it.

Patent Document 1 discloses an aluminosilicate glass that uses an SnO ₂ component, a CeO ₂ component, and an F ₂ component without using an arsenic component or an antimony component. However, when this glass is cast into a mold, the presence of bubbles can be suppressed to some extent. However, when it is formed into a disk using the direct press method, reboiling (glass after clarification) is caused due to impact during pressing. From which the bubbles are generated again), and the clarification effect cannot be obtained.

Patent Document 2 discloses a glass substrate for an information recording medium that does not use an arsenic component or an antimony component. However, there is a problem of reboil generation during pressing, and a specific gravity that can be applied as a substrate for a next-generation information recording medium. The balance of mechanical strength has not been studied. Therefore, a glass that has a balance between specific gravity and mechanical strength that can be applied as a next-generation information recording medium substrate and that can suppress the occurrence of reboil during pressing is not disclosed.
Japanese Patent Laid-Open No. 10-72238 JP 2001-76336 A

  The object of the present invention is to produce the next generation represented by a perpendicular magnetic recording system and the like without bubbles in the glass without substantially using an arsenic component or an antimony component which may adversely affect the human body and the environment. An object of the present invention is to provide a glass substrate having physical properties for use as an information recording medium substrate. In particular, it has a balance between specific gravity and mechanical strength that can be applied as a substrate for next-generation information recording media assuming use in a dynamic environment, and has high strength that can withstand high-speed rotation and drop impact. An object of the present invention is to provide a glass substrate for an information recording medium which is free from reboil during pressing and has a high productivity suitable for the direct pressing method.

  As a result of intensive studies and studies to achieve the above object, the present inventor achieved a balance between specific gravity and mechanical strength that can be applied as a next-generation information recording medium substrate by setting the specific gravity to a specific value. Furthermore, by limiting the content of the components used as a clarifier to a specific range, it was found that reboiling was suppressed even during direct pressing, high productivity and a sufficient clarification effect were obtained. It was. In addition, it has been found that it has an extremely smooth substrate surface that can cope with chemical durability and low flying height of the magnetic head, and has excellent drop strength when mounted on a drive (> 1200 G). More specifically, the present invention provides the following.

(Configuration 1)
In terms of oxide, it contains SiO ₂ component, Al ₂ O _3, R ₂ O component as essential components, further contains α element as a refining component, and a molar ratio βm / β of α element oxide and β element compound in glass. A glass substrate for information recording media, wherein αm is less than 0.1 and specific gravity is less than 2.70. However, the α element is one of Sn and Ce, and the β element is one or more selected from Sn, Ce, Mn, W, Ta, Bi, S, Cl, and F. Does not overlap with α element. R is at least one selected from Li, Na, and K.
(Configuration 2)
The content of the α element is mass% based on oxide,
SnO ₂ 0.01~2.3%, or,
CeO ₂ 0.01-2.5%,
The glass substrate for information recording media of the structure 1 which is.
(Configuration 3)
SiO ₂ : 55 to 80% and Al ₂ O ₃ : 2 to 20% and R ₂ O: 3 to 20% by mass% based on oxide
The glass substrate for information recording media of the structure 1 or 2 containing each component of these.
(Configuration 4)
P ₂ O ₅ : 0 to 3.0% and / or ZrO ₂ : 0 to 10% and / or B ₂ O ₃ : 0 to 15% and / or BaO: 0 to 0% by mass based on oxide 15%, and / or SrO: 0-15%, and / or
MgO: 0 to 20%, and / or CaO: 0 to 20%, and / or ZnO: 0 to 20%, and / or TiO _2: 0~10%, and / or Gd ₂ O ₃ components, _La 2 O Total content of one or more selected from _three components, Y ₂ O ₃ component, Nb ₂ O ₅ component Ga ₂ O ₃ component: 0 to 15%,
The glass substrate for information recording media in any one of the structures 1-3 containing each component of these.
(Configuration 5)
The glass substrate for an information recording medium according to any one of configurations 1 to 4, wherein the Young's modulus is 81 GPa or more and the specific elastic modulus, which is a ratio of Young's modulus and specific gravity, is 30 or more.
(Configuration 6)
The glass substrate for information recording media according to any one of configurations 1 to 5, which does not substantially contain the β element.
(Configuration 7)
A glass substrate for an information recording medium according to any of the 1-6 that is substantially free of _As 2 _{O 3} component and _Sb 2 _{O 3} component on an oxide basis.
(Configuration 8)
The glass substrate for information recording media which provided the compressive-stress layer on the surface of the board | substrate in any one of the structures 1-7.
(Configuration 9)
The glass substrate for an information recording medium according to Configuration 8, wherein the compressive stress layer is formed by substituting with an alkali component having an ionic radius larger than that of an alkali component present in the surface layer.
(Configuration 10)
The glass substrate for an information recording medium according to Configuration 8 or 9, wherein the compressive stress layer is formed by heating the substrate and then rapidly cooling the substrate.
(Configuration 11)
11. The glass substrate for an information recording medium according to any one of constitutions 1 to 10, wherein the surface roughness Ra (arithmetic average roughness) is 2 mm or less.
(Configuration 12)
An information recording medium using the glass substrate for information recording medium according to any one of Structures 1 to 11.

  According to the present invention, it is possible to provide a balance between specific gravity and mechanical strength that can be applied as a next-generation information recording medium substrate, and use an arsenic component or an antimony component that may adversely affect the human body and the environment. Even if it is not, glass with a limited content of components used as fining agents is highly productive and has physical properties that can withstand information recording medium substrate applications. It is possible to provide a glass substrate that has a refining action equivalent to the case of containing bismuth and exhibits an effect superior to that of the prior art in suppressing reboil generation in the case of direct press molding or the like.

Next, specific embodiments of the present invention will be described.
In this specification, the glass substrate of the present invention is a generic term for an amorphous glass substrate and a crystallized glass substrate, and when describing each component constituting the glass substrate, unless otherwise specified, the content of each component is It is expressed as mass% based on oxide. Here, the “oxide standard” is contained in the glass on the assumption that oxides, nitrates, etc. used as raw materials of the constituent components of the glass of the present invention are all decomposed and changed into oxides when melted. This is a method of expressing the composition of each component, and the amount of each component contained in the glass is described with the total mass of the generated oxides being 100% by mass.

The glass of the present invention essentially contains an SiO ₂ component, an Al ₂ O _{3, and an} R ₂ O component, and further contains an α element as a refining component. Here, the α element is a main clarification component and is any one element selected from Sn and Ce. By using these as a clarification component, a high clarification effect can be obtained while maintaining the physical properties required for an information recording medium substrate.

Although it is possible to use other clarification components in combination with the clarification component of Sn or Ce selected as the α element, the mixture of clarification agents tends to cancel the clarification effect or cause reboiling during direct pressing. . In the present invention, it was found that by making the amount of the clarification component other than the clarification component selected as the α element below a specific range, it becomes difficult to cause reboil generation during direct pressing without canceling the clarification effect. is there. Specifically, when the content of any one element of Sn and Ce selected as the α element is αm mol% and the content of the β element as the other fining component is β m mol%, The effect described above can be obtained by setting the content range of the other clarified components so that the upper limit of the molar ratio βm / αm of the α element oxide and β element compound is less than 0.1. In order to make it easier to obtain the above effect, the βm / αm value is more preferably 0.095 or less, and most preferably 0.09 or less.

Here, the β element corresponds to one or more elements selected from Sn, Ce, Mn, W, Ta, Bi, S, Cl, and F that can provide a glass refining effect, but was selected as the α element. Does not overlap with elements. That is, for example, when Ce is selected as the main clarification component (α element), the content of Ce is excluded when calculating the content of β element.
The molar ratio is calculated as follows. First, excluding components contained as β elements, assuming that the constituent components of glass including α elements exist in the glass as oxides, α elements when the total number of oxides is 100 mol% The mole% of the oxide is αm, and the mole% of the β element compound with respect to the total number of oxides constituting the glass excluding the β element is βm.
In the case of calculating the mol% of an α element as an oxide, Sn is SnO ₂ and Ce is CeO ₂ . In the case of calculating the mol% of β element as a compound, Sn is SnO ₂ , Ce is CeO ₂ , Mn is MnO ₂ , W is WO ₃ , Ta is Ta ₂ O ₅ , Bi is Bi ₂ O ₃ , S is SO ₃ , Cl is Cl ₂ , and F is F ₂ .
The β element is most preferably not substantially contained in order to suppress reboil during direct pressing.

  In order to reduce the load applied to the spindle motor and to obtain a balance between specific gravity and mechanical strength that can be applied as a next-generation information recording medium substrate, the present inventors set the specific gravity of the glass to less than 2.70. Found that is preferable. In order to improve the balance, the specific gravity is most preferably 2.69 or less. On the other hand, when the specific gravity is less than 2.20, it is substantially difficult to obtain a substrate having a desired rigidity. Therefore, the specific gravity is preferably 2.20 or more, more preferably 2.30 or more, and 2.35 or more. Is most preferable.

In order to obtain a high clarification effect while maintaining the physical properties required for the information recording medium substrate, it is preferable to contain one element selected from Sn and Ce as the α element as the main clarification component. In order to obtain a high clarification effect, the lower limit of the content of the SnO ₂ component or CeO ₂ component on the oxide basis is preferably 0.01%, more preferably 0.05%, % Is most preferred.
On the other hand, to maintain the mechanical strength, lower the specific gravity, obtain a high clarification effect, and increase the reboil suppression effect during direct pressing, the upper limit of the SnO ₂ component content is 2.3% Preferably, 2.2% is more preferable, 2.0% is most preferable, and the upper limit of the CeO ₂ component is preferably 2.5%, more preferably 2.3%, and most preferably 2.1%.
Only one of the SnO ₂ component and the CeO ₂ component is contained as the α element, but the other element not contained as the α element satisfies the ratio βm / αm defined above as the β element. If it is in the range, it can be contained.

As ₂ O ₃ component and Sb ₂ O ₃ component act as fining agents, but they can be harmful to the environment, and their use should be refrained. The glass of the present invention can obtain a clarification effect even if it does not contain an As ₂ O ₃ component or an Sb ₂ O ₃ component, and when these components and the clarifier component of the present application are added, the clarification effect is achieved between the clarifiers. Will be offset.

The SiO ₂ component is an essential component for forming a glass network structure and achieving an improvement in chemical stability and a reduction in specific gravity. If the amount is less than 55%, the chemical durability of the obtained glass is poor, and the specific gravity tends to increase with an increase in the content of other components, so the lower limit of the content may be 55%. Preferably, 57% is more preferable, and 58% is most preferable. Further, if it exceeds 80%, dissolution and moldability are likely to be difficult as the viscosity increases, and as a result, the homogeneity and clarification effect of the material are likely to be lowered. Therefore, the upper limit of the content is preferably 80%, 78% is more preferred and 77% is most preferred.

Al ₂ O ₃ component is an important component that contributes to stabilization of glass and improvement of chemical durability, but if its amount is less than 2%, its effect is poor, so the lower limit of the content is 2%. Preferably 2.5%, more preferably 3.4%. On the other hand, if it exceeds 20%, dissolution, moldability, and devitrification resistance are deteriorated, and as a result, homogeneity and clarification effect are likely to be lowered. Therefore, the upper limit of the content is preferably 20%, 19% Is more preferable, and 18.5% is most preferable.

R in the R ₂ O component indicates one or more alkali metals selected from Li, Na, and K, but is an essential component for reducing the viscosity of the glass, improving moldability, improving homogeneity, and chemical strengthening. On the other hand, for information recording medium substrate applications, it is preferable that the chemical durability is high, that is, the alkaline component elution amount is as small as possible. Li ₂ O component, Na ₂ O component, K ₂ O contained as necessary in order to obtain an elution amount of an alkali component that can be used as a next-generation information recording medium application typified by a perpendicular magnetic recording system. The total amount of one or more components is preferably 20% or less, more preferably 18% or less, and most preferably 17% or less. On the other hand, regarding the lower limit, the total amount of one or more of these is preferably 3% or more, more preferably 5% or more, and most preferably 8% or more.

The P ₂ O ₅ component is a component that can be used as a nucleating agent when the glass is heat-treated into a crystallized glass, and can be optionally added. This component contributes to lower viscosity and improves the melting and clarity of the original glass by coexistence with SiO _2. However, if this component is added excessively, it becomes difficult to vitrify, and devitrification and phase separation tend to occur. Therefore, the upper limit of the content is preferably 3.0%, more preferably 2.7%, and most preferably 2.6%.

The ZrO ₂ component contributes to the improvement of the chemical durability and physical properties of the glass and can be optionally added. However, if the amount of this component exceeds 10%, it remains undissolved or ZrSiO ₄ (zircon). Since the glass specific gravity is high, the upper limit of the content is preferably 10%, more preferably 8%, and most preferably 6%.

The B ₂ O ₃ component contributes to lowering the viscosity of the glass and improves melting and moldability, so it can be added as an optional component. However, if this component is 15% or more, the original glass tends to phase-separate and it is difficult to vitrify, so the upper limit of the content is preferably 15%. A more preferred upper limit is 12%, and a more preferred upper limit is 10%.

  The BaO component and the SrO component can be added as an optional component as an effective component for reducing the viscosity of the glass and improving the chemical durability. However, if added excessively, the glass specific gravity increases, so the BaO component or the SrO component. The upper limit of each content is preferably 15% or less, more preferably 14% or less, and most preferably 13% or less in order to set the specific gravity to an appropriate value.

  Since MgO, CaO, and ZnO components are effective in reducing the viscosity of glass, they can be added as optional components. However, when MgO exceeds 20%, CaO exceeds 20%, or ZnO exceeds 20%, the original glass tends to be devitrified. Therefore, the upper limit of the content of these components is 20% for MgO, 20% for CaO, and 20% for ZnO, and more preferable upper limit values are 15% for MgO, 15% for CaO, and 15% for ZnO. Further, more preferable upper limit values are 8% for MgO, 10% for CaO, and 10% for ZnO.

The TiO ₂ component can be arbitrarily added as a component that contributes to lowering the viscosity of glass and improving chemical durability. However, if the added amount of this component exceeds 10%, the specific gravity value of the glass increases, and further vitrification becomes difficult, so the upper limit of the content is preferably 10%, more preferably 8%, 6% is most preferred.

Gd ₂ O ₃ , La ₂ O ₃ , Y ₂ O ₃ , Nb ₂ O ₅ , Ga ₂ O ₃ components contribute to lowering the viscosity of glass, improving mechanical properties by improving Young's modulus, and improving heat resistance. Although it can be added as an optional component, an increase in the amount added causes an increase in specific gravity and an increase in raw material cost. Accordingly, the total amount of one or more of these components is sufficient up to 15%. If the total amount exceeds 15%, vitrification and crystallization are difficult. Therefore, the upper limit of the total amount of these components is preferably 15%, more preferably 10%, and most preferably 8%.

  Components such as V, Cu, Mn, Cr, Co, Mo, Ni, Fe, Te, Pr, Nd, Er, Eu, and Sm, which are used as glass coloring components, can be added for the purpose of preventing glass mixture. However, since the specific gravity increases, the raw material costs increase, and the glass forming ability decreases, the total amount of one or more of these components is sufficient up to 5%. Therefore, the upper limit of the total amount of these components is preferably 5% on the oxide basis, more preferably 4%, and most preferably 3%.

  The Young's modulus is described. As described above, in order to improve the recording density and the data transfer speed, the tendency of high-speed rotation of the information recording medium disk substrate is progressing. To cope with this trend, the substrate material is bent at the time of high-speed rotation. In order to prevent disc vibration due to, it must have high rigidity and low specific gravity. In addition, when used in a portable recording apparatus such as a head contact or a removable recording apparatus, it is preferable to have sufficient mechanical strength, high Young's modulus, and surface hardness that can withstand it. The rate is preferably 81 GPa or more, more preferably 81.5 GPa or more, and most preferably 82 GPa or more.

However, even if the rigidity is simply high, if the specific gravity is large, the weight is large at the time of high-speed rotation, so that bending occurs and vibration is generated. On the other hand, if the rigidity is small even at a low specific gravity, vibration will occur in the same manner. If the specific gravity is too low, it becomes difficult to obtain a desired mechanical strength as a result. Therefore, it is necessary to balance the seemingly contradictory characteristics of low specific gravity while having high rigidity, and a preferable range thereof is a Young's modulus [GPa] / specific gravity expressed by specific gravity of 30 or more, and a more preferable range is 31 or more, and the most preferable range is 32 or more.
The Young's modulus and the value of specific modulus expressed by Young's modulus [GPa] / specific gravity can be achieved by limiting the specific gravity value to a specific range.

  The glass substrate of the present invention can obtain the effect of further improving the mechanical strength by providing a compressive stress layer on the surface.

  As a method for forming the compressive stress layer, for example, there is a chemical strengthening method by performing an exchange reaction with an alkali component having an ionic radius larger than that of the alkali component present in the surface layer of the glass substrate before forming the compressive stress layer. Further, there are a heat strengthening method in which a glass substrate is heated and then rapidly cooled, and an ion implantation method in which ions are implanted into the surface layer of the glass substrate.

As the chemical strengthening method, for example, a salt containing potassium or sodium, for example, potassium nitrate (KNO ₃ ), sodium nitrate (NaNO ₃ ), or a molten salt thereof is used at a temperature of 300 to 600 ° C. for 0.5 to 12 hours. Immerse. As a result, the lithium component (Li ⁺ ion) present in the glass component near the substrate surface exchanges with a sodium component (Na ⁺ ion) or potassium component (K ⁺ ion), which is an alkali component having an ionic radius larger than that of Li. Alternatively, an exchange reaction with a potassium component which is an alkali component having an ionic radius larger than that of a sodium component (Na ⁺ ion) present in the glass component near the substrate surface proceeds, thereby increasing the volume of crystallized glass. Compressive stress is generated in the substrate surface layer, and as a result, the ring bending strength, which is an index of impact characteristics, increases.

  Although it does not specifically limit about the heat-strengthening method, For example, it heats from 300 degreeC-600 degreeC, and then implements rapid cooling, such as water cooling and / or air cooling, and arises by the temperature difference between the surface of a glass substrate and an inside. A compressive stress layer can be formed. In addition, a compression stress layer can be formed more effectively by combining with the above chemical treatment method.

  About the glass substrate of this invention, mechanical strength and a Young's modulus can also be improved by producing | generating a crystal | crystallization inside glass by a crystallization process. In order to produce crystallized glass, a glass raw material containing the above-mentioned raw materials is melted and rapidly cooled to prepare a raw glass, and the raw glass is heat-treated to perform a nucleation step. The crystal growth step is performed by heat treatment at a higher temperature than the nucleation step.

  Moreover, in order to produce the information recording medium substrate of the present invention, the molten glass produced under the above conditions is dropped onto a lower mold and pressed into an upper and lower mold to form a disk, and if necessary, shape processing And lapping and polishing may be performed by a known method.

More specifically, it is produced by the following method.
First, mix the raw materials such as oxides, carbonates and nitrates so as to have the glass components in the above composition range, and use a normal melting apparatus using a crucible such as platinum or quartz, the viscosity of the glass melt Is dissolved at a temperature of 2.3 to 3.0 dPa · s.
Next, the temperature of the glass melt is raised to a temperature at which the viscosity is 1.5 to 2.3 dPa · s, preferably 1.9 to 2.2 dPa · s, and bubbles are generated in the glass melt and stirred. Causes effects and improves homogeneity.
Thereafter, the temperature of the glass melt is lowered to a temperature at which the viscosity becomes 2.2 to 2.6 dPa · s, preferably 2.3 to 2.5 dPa · s, and the defoaming of bubbles generated inside the glass is performed. Clarify, then maintain this temperature.

Next, the upper mold temperature is set to 300 ± 100 ° C., preferably 300 ± 50 ° C., and the lower mold temperature is set to Tg ± 50 ° C., preferably Tg ± 30 ° C. of the glass.
Further, the temperature of the glass outlet pipe for guiding the glass from the crucible to the press-molded shape is set to a temperature at which the viscosity of the glass is 2.2 to 2.6 dPa · s, preferably 2.3 to 2.5 dPa · s. Then, a predetermined amount of glass is dropped on the lower mold, and the upper mold and the lower mold are brought close to each other and pressed to obtain a glass molded body.
In manufacturing information recording medium substrates, cost reduction per sheet is required, so press speeds of 150 to 700 mm / sec, cycle time (time from the start of press to the start of the next press) of 1 to 2 sec. However, even in such an impact during pressing, the glass of the present invention is used, and by controlling the temperature of the glass melt and the temperature of the manufacturing apparatus as described above, the occurrence of reboil during pressing can be suppressed. Is possible.

  When the obtained glass molded body is crystallized glass, the glass molded body after press molding is nucleated at 500 to 650 ° C. for 0.5 to 10 hours, and the crystal growth is 600 to 750 ° C. at 2 to 20 hours. Heat treatment for hours. The heat treatment temperature for crystal growth is preferably higher than the heat treatment temperature for nucleation.

  Next, lapping is performed for about 10 to 60 minutes with abrasive grains having an average particle diameter of 5 to 30 μm, and after processing of the inner and outer diameters, free abrasive grains such as cerium oxide having an average particle diameter of 0.5 to 2 μm are used for about 30 minutes to By polishing for 60 minutes, an information recording medium substrate can be obtained. The lapping and polishing steps are not limited to the above, and known methods may be used as appropriate.

  Next, preferred embodiments of the present invention will be described. The present invention is not limited to these examples.

All the glasses of the above-mentioned embodiments of the present invention are mixed with raw materials such as oxides, carbonates, nitrates, etc., and melted at a temperature of about 1300-1400 ° C. using a quartz crucible to melt the raw material batch. After sufficiently dissolving so that no residue is generated, the temperature is raised to a temperature of about 1400 to 1500 ° C., then the temperature is lowered to a temperature of 1,450 to 1,300 ° C., and the bubbles generated inside the glass are defoamed and clarified. Went. After that, a predetermined amount of glass flows out while maintaining the temperature, and the upper mold temperature is set to 300 ± 100 ° C. and the lower mold temperature is set to Tg ± 50 ° C. by the direct press method. A glass molded body was obtained. Subsequently, a part was crystallized, and the obtained glass molded body was lapped and polished by the above-described method to obtain a substrate for an information recording medium. At this time, the surface roughness Ra (arithmetic mean roughness) of the substrate was all 2 mm or less. In addition, 100 manufactured substrates were randomly extracted, and an internal defect inspection was performed using a microscope to obtain a yield rate (%). Here, the non-defective product rate refers to the ratio of non-defective products in which no bubbles are present in the pressed substrate, and the proportion of non-defective products.
The surface roughness Ra (arithmetic average roughness) was measured with an atomic force microscope (AFM).

Tables 1 to 7 show glass compositions of Examples 1 to 30 and Comparative Examples 1 to 3, non-defective ratio of substrate after press molding, specific gravity, Young's modulus, Young's modulus / specific gravity, average linear expansion coefficient at 25 ° C to 100 ° C. (CTE).
Moreover, the temperature-viscosity graph of the glass of this invention is shown in FIG.
The viscosity of the glass was measured using a ball pulling viscometer (BVM-13LH manufactured by Opto Corporation).
The average linear expansion coefficient was measured by changing the temperature range from 25 ° C. to 100 ° C. according to JOGIS (Japan Optical Glass Industry Association Standard) 16-2003 “Measurement Method of Average Linear Expansion Coefficient of Optical Glass Near Room Temperature”. Value.
Specific gravity was measured using Archimedes method, and Young's modulus was measured using ultrasonic method.

  As shown in Tables 1 to 7, in the examples of the present invention, the presence of bubbles due to reboil generation during pressing was effectively suppressed, and the yield rate was in the range of 78 to 97%.

(Example 31)
The 2.5-inch HDD polishing substrate (65φ × 0.635 mmt) of Example 1 was immersed in a mixed salt of potassium nitrate and sodium nitrate (KNO ₃ : NaNO ₃ = 1: 3) at 400 ° C. for 0.5 hour to obtain a surface. A compressive stress layer was formed. It was confirmed that the ring bending strength of this substrate was improved to 7 times that before formation of the compressive stress layer (260 MPa). The ring bending strength was measured by a concentric bending method in which a thin disk sample having a diameter of 65 mm and a thickness of 0.635 mm was prepared, and the strength of the disk sample was measured with a circular support ring and a load ring. Refers to bending strength.

(Example 32)
The 2.5-inch HDD polishing substrate (65φ × 0.635 mmt) of Example 10 was immersed in a mixed salt of potassium nitrate and sodium nitrate (KNO ₃ : NaNO ₃ = 1: 3) at 400 ° C. for 0.5 hour, A compressive stress layer was formed on the surface. It was confirmed that the ring bending strength of this substrate was improved 5 times that before the compression stress layer was formed (280 MPa).

(Example 33)
The 2.5-inch HDD polishing substrate (65φ × 0.635 mmt) of Example 1 was heated to 300 ° C. to 600 ° C. and then rapidly cooled by an air cooling method to form a compressive stress layer on the surface. This substrate was confirmed to have improved ring bending strength.

  In the glass of the present invention, fine crystal particles can be uniformly deposited in the glass by heat treatment, and the mechanical strength can be improved. In particular, since the precipitated crystal particles prevent the growth of fine cracks, fine chips caused by chipping during polishing can be remarkably reduced.

(Example 34)
The glass of Example 1 is heat treated at 500 ° C. to 650 ° C. to perform a nucleation step, and after this nucleation step, a crystal growth step is performed by heat treatment at a temperature higher than the nucleation step in the range of 600 ° C. to 850 ° C. By carrying out, lithium disilicate and lithium disilicate solid solution, α-quartz, α-quartz solid solution were precipitated, specific gravity 2.48 g / cm ³ , Young's modulus 102 GPa, Young's modulus / specific gravity 41.1, CTE 85 × 10 ⁻⁷ / A glass at 0 ° C. could be produced. In addition, the identification of the crystal phase was calculated | required from the X-ray-diffraction figure obtained with the X-ray-diffraction apparatus (The product made by Panalical, brand name: X'pert-MPD).

(Example 35)
Also, a 2.5-inch HDD polishing substrate (65φ × 0.635 mmt) of Example 34 was prepared by a known method, and a mixed salt of potassium nitrate and sodium nitrate at 400 ° C. (KNO ₃ : NaNO ₃ = 1: 3). For 0.5 hour to form a compressive stress layer on the surface. It was confirmed that the ring bending strength of this substrate was improved to 3 times that before the compression stress layer was formed (500 MPa).

(Example 36)
Further, a chromium alloy underlayer and a cobalt alloy magnetic layer are formed on the substrate obtained by the above-described example by DC sputtering, and further a diamond-like carbon layer is formed, and then a perfluoropolyether lubricant is added. This was coated to obtain an information magnetic recording medium.

  The substrate such as the magnetic recording medium substrate of the present invention can increase the surface recording density, and even if the substrate itself is rotated at a high speed in order to improve the recording density, there is no occurrence of bending or deformation. Vibration due to rotation is reduced, and the number of data reading errors (TMR) due to vibration and deflection is reduced. In addition, since it has excellent impact resistance characteristics, it is difficult to cause head crashes and substrate breakage particularly as an information recording medium for mobile applications, and as a result, excellent stable operation is exhibited.

It is a temperature-viscosity graph of Example 1 of this invention, a vertical axis | shaft is the value of logarithmic log (eta) of a viscosity (dPa * s), and a horizontal axis | shaft is the temperature (degreeC) of the glass which a ball pulling-type viscometer shows.

Claims (12)

In terms of oxide, it contains SiO ₂ component, Al ₂ O _3, R ₂ O component as essential components, further contains α element as a refining component, and a molar ratio βm / β of α element oxide and β element compound in glass. A glass substrate for information recording media, wherein αm is less than 0.1 and specific gravity is less than 2.70. However, the α element is one of Sn and Ce, and the β element is one or more selected from Sn, Ce, Mn, W, Ta, Bi, S, Cl, and F. Does not overlap with α element. R is at least one selected from Li, Na, and K. The content of the α element is mass% based on oxide,
SnO ₂ 0.01~2.3%, or,
CeO ₂ 0.01-2.5%,
The glass substrate for an information recording medium according to claim 1. SiO ₂ : 55 to 80% and Al ₂ O ₃ : 2 to 20% and R ₂ O: 3 to 20% by mass% based on oxide
The glass substrate for information recording media of Claim 1 or 2 containing each component of these. P ₂ O ₅ : 0 to 3.0% and / or ZrO ₂ : 0 to 10% and / or B ₂ O ₃ : 0 to 15% and / or BaO: 0 to 0% by mass based on oxide 15%, and / or SrO: 0-15%, and / or
MgO: 0 to 20%, and / or CaO: 0 to 20%, and / or ZnO: 0 to 20%, and / or TiO _2: 0~10%, and / or Gd ₂ O ₃ component, _La 2 O Total content of one or more selected from _three components, Y ₂ O ₃ component, Nb ₂ O ₅ component, and Ga ₂ O ₃ component: 0 to 15%,
The glass substrate for information recording media in any one of Claims 1-3 containing each component of these. The glass substrate for an information recording medium according to any one of claims 1 to 4, wherein the Young's modulus is 81 GPa or more and the specific elastic modulus, which is the ratio of Young's modulus and specific gravity, is 30 or more. The glass substrate for information recording media according to any one of claims 1 to 5, which does not substantially contain the β element. The glass substrate for information recording media according to any one of claims 1 to 6, which contains substantially no As ₂ O ₃ component and no Sb ₂ O ₃ component on an oxide basis.   The glass substrate for information recording media which provided the compressive-stress layer on the surface of the board | substrate in any one of Claims 1-7.   9. The glass substrate for an information recording medium according to claim 8, wherein the compressive stress layer is formed by substituting with an alkali component having an ionic radius larger than that of an alkali component present in the surface layer.   The glass substrate for an information recording medium according to claim 8 or 9, wherein the compressive stress layer is formed by heating the substrate and then rapidly cooling the substrate.   11. The glass substrate for an information recording medium according to claim 1, wherein the surface roughness Ra (arithmetic average roughness) is 2 mm or less.   An information recording medium using the glass substrate for an information recording medium according to claim 1.