JP2007223884A - Inorganic composition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inorganic composition for use in information recording medium disc substrate which has an excellent surface property sufficiently corresponding to a ramp load system for high density recording in both of the horizontal magnetic recording system and perpendicular magnetic recording system, high strength durable to high speed rotation, both of heat expansion property and heat resistance suitable with each drive component, a low melting point, and high productivity. <P>SOLUTION: The inorganic composition contains one or more crystal phases selected from the group consisting of α-quartz (α-SiO<SB>2</SB>), lithium disilicate (Li<SB>2</SB>Si<SB>2</SB>O<SB>5</SB>) and lithium monosilicate (Li<SB>2</SB>SiO<SB>3</SB>) or contains one crystal phase of at least lithium monosilicate (Li<SB>2</SB>SiO<SB>3</SB>). The average particle diameter of particles each showing a crystal phase, contained in the inorganic composition, is 1 μm or less. The inorganic composition has a ring flexural strength of 300 MPa or more, and a surface roughness Ra (an arithmetic average roughness) after being polished of 10 Å or less. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention has a fine particle size, good mechanical strength, excellent surface roughness with little change in substrate surface roughness after acid or alkali surface treatment, and compatibility with other materials. Relates to an inorganic composition having good thermal expansion characteristics. More particularly, the present invention relates to a substrate for a magnetic recording medium used in various information magnetic recording apparatuses, and more particularly to a disk-shaped information recording medium substrate that has super smoothness of the surface, cleanability, and high strength in a perpendicular magnetic recording medium. In the present invention, the “information recording medium” means a fixed hard disk, a removable hard disk, a card hard disk, a digital video camera or digital camera, an audio hard disk, a car navigation hard disk, a portable hard disk used as a hard disk of a personal computer. It means an information magnetic recording medium that can be used in a telephone hard disk.

  In recent years, the use of multimedia in personal computers and the handling of large data such as moving images and sounds such as digital video cameras and digital cameras have led to the need for large-capacity information magnetic recording devices. As a result, the information magnetic recording medium tends to increase the bit and track density and reduce the size of the bit cell in order to increase the surface recording density. In order to cope with this, the magnetic head is operated closer to the disk surface as the bit cell is reduced. As described above, when the magnetic head operates in a low floating state or a contact state (contact) with respect to the information magnetic recording medium disk substrate, a specific portion of the information magnetic recording medium disk substrate ( It is important to develop a landing zone method or the like that performs adsorption prevention processing (texture processing or the like) on the disk inner diameter side or outer diameter side unrecorded portion) and starts and stops the magnetic head there.

  In the current information magnetic recording apparatus, the magnetic head is in contact with the information magnetic recording medium disk substrate before the apparatus is started, and is repeatedly lifted from the information magnetic recording medium disk substrate when the apparatus is started. Stop) method. At this time, if both contact surfaces are mirror surfaces more than necessary, adsorption occurs, causing problems such as unsmooth rotation start and damage to the surface of the information magnetic recording medium due to an increase in the friction coefficient. As described above, the information magnetic recording medium disk substrate is required to have conflicting demands for lowering the flying height of the magnetic head as the recording capacity increases and preventing the magnetic head from adsorbing on the information magnetic recording medium disk substrate. In response to these conflicting demands, development of a landing zone technique for producing a magnetic head start / stop unit in a specific area of an information magnetic recording medium disk substrate is underway.

Further, when the recording density exceeds 100 Gb / in ² , such a small magnetization unit becomes thermally unstable. Therefore, the in-plane recording method is in response to the demand for higher recording density exceeding 100 Gb / in ^2. The physical limit has been reached.

On the other hand, a perpendicular magnetic recording method has been adopted. In this perpendicular magnetic recording method, since the easy axis of magnetization is in the vertical direction, the bit size can be extremely small, and a desired medium film thickness ( 5 to 10 times the in-plane recording method), the effect of reducing the demagnetizing field and shape magnetic anisotropy can also be desired. It can solve the problems of energy reduction and thermal instability, and can achieve much higher recording density than in-plane magnetic recording. For this reason, in the perpendicular magnetic recording system, it is already possible to achieve a recording density of 100 Gb / in ² or more at a practical level at a mass production level, and research on a recording density exceeding 300 Gb / in ² has already been conducted. It has been broken.

In this perpendicular magnetic recording system, since magnetization is performed in a direction perpendicular to the medium surface, a medium having an easy magnetization axis in the perpendicular direction is used unlike a conventional medium having an easy magnetization axis in the in-plane direction. Research and practical application of perpendicular magnetic recording layers are Cr-based alloys such as CoCrPt, CoCrPt—Si, and CoCrPt—SiO ₂ , and Fe-based alloys such as FePt.

  However, oxide-based media such as FePt and the like need to increase the film formation temperature in order to refine the magnetic crystal grains and to generate them in the vertical direction. In some cases, annealing is performed at a high temperature (about 300 to 900 ° C.) in order to improve magnetic properties. Therefore, the substrate material must be able to withstand such high temperatures, and should not cause deformation of the substrate or change in surface roughness.

  Also, perpendicular magnetic recording media tend to have a low flying height of 15 nm or less as the recording density increases, and are in the direction of near contact recording or contact recording. On the other hand, in order to effectively use the medium surface as a data area, a ramp loading system without a landing area is changed from a conventional system in which a landing area is provided. Therefore, the data area on the disk surface or the entire surface of the substrate surface must be an ultra-smooth surface in order to reduce the flying height and enable contact recording.

  These magnetic recording medium substrates must be free of crystal anisotropy, foreign matter, impurities, etc., affecting the medium crystal to be deposited, and must have a dense, homogeneous, and fine structure. It must have chemical durability that can withstand chemical cleaning and etching.

  In addition, technology development is progressing by rotating the information magnetic recording medium disk substrate of the magnetic recording device at high speed in order to increase the speed of information today, but because bending and deformation occur by rotating at high speed, A substrate material is required to have high mechanical strength. In addition to the current fixed information magnetic recording devices, information magnetic recording devices such as a removable method and a card method are being studied and put into practical use, and application development to digital video cameras, digital cameras, and the like is beginning.

  By the way, aluminum alloy is often used for the magnetic disk substrate material in the past, but in the case of aluminum alloy substrate, protrusions or spot-like irregularities are likely to be generated on the substrate surface in the polishing process, and in terms of flatness and smoothness. It is difficult to get enough. In addition, since aluminum alloy is a soft material and easily deforms, it is difficult to cope with thinning. Furthermore, there are problems such as head crushing due to bending during high-speed rotation and damage of the media, and it is not a material that can sufficiently cope with future high-density recording. Moreover, since the heat-resistant temperature during film formation, which is most important in the magnetic recording system, is less than 300 ° C., when film formation is performed at 300 ° C. or higher, or annealing at a high temperature of about 500 to 900 ° C. is performed, the substrate Will be thermally deformed. Therefore, it is difficult to apply as a substrate for a magnetic recording medium that requires such a high temperature treatment.

Further, as a material for solving the problems of the aluminum alloy substrate, chemically strengthened soda lime glass (SiO ₂ —CaO—Na ₂ O) and aluminosilicate glass (SiO ₂ —Al ₂ O ₃ —Na ₂ O) are known. ing.

  In these cases, since polishing is performed after the chemical strengthening treatment, unstable elements of the reinforcing layer in thinning the disk are high, and the heat resistance of the substrate itself is low. That is, the flatness measured by a predetermined method is deteriorated after a magnetic recording medium is formed on a predetermined sample at a high temperature of 300 ° C. or higher. It becomes a source of a problem that dissolves and damages the film, and the deterioration of the reinforced layer and the unreinforced layer becomes a serious problem.

As a material for overcoming the disadvantages of the chemically strengthened glass substrate, SiO ₂ —Li ₂ O—P ₂ containing lithium disilicate (Li ₂ Si ₂ O ₅ ) crystal and α-quartz (α-SiO ₂ ) crystal. Various types such as O ₅ -based crystallized glass, SiO ₂ -Al ₂ O ₃ -Li ₂ O-based crystallized glass including lithium disilicate (Li ₂ Si ₂ O ₅ ) crystal and β-spodumene (LiAlSi ₂ O ₆ ) crystal The crystallized glass has been developed (for example, Patent Document 1 to Patent Document 11).
JP-A-62-72547 JP-A-6-329440 Japanese Patent Laid-Open No. 7-169048 Japanese Patent Laid-Open No. 9-35234 US Pat. No. 5,336,643 US Pat. No. 5,028,567 Japanese Patent Laid-Open No. 10-45426 Japanese Patent Laid-Open No. 11-16143 JP 2000-233941 A JP 2000-302481 A JP 2001-184624 A

However, Li ₂ O—Al ₂ O ₃ —SiO ₂ -based crystallized glass described in Patent Document 1 has lithium disilicate (Li ₂ Si ₂ O ₅ ) and α-cristobalite as crystal phases, and this crystal phase Is advantageous in controlling the thermal expansion coefficient within an appropriate range, and a high-strength magnetic disk substrate can be obtained. However, it has a large and rapid surface roughness (Ra). Therefore, it is impossible to sufficiently cope with the low flying height of the head accompanying the improvement in recording capacity.

Further, the SiO ₂ —Li ₂ O—MgO—P ₂ O ₅ -based crystallized glass described in Patent Document 2 has lithium disilicate (Li ₂ Si ₂ O ₅ ) and α-quartz (α-SiO ₂ ) as crystal phases. By controlling the spherical particle size of α-quartz (α-SiO ₂ ), the conventional mechanical texture and chemical texture are not required, and the surface roughness (Ra) after polishing is in the range of 15 to 50 mm. It is an excellent material as a texture material for the entire surface of the substrate that can be controlled. However, the target surface roughness (Ra) is too large compared to 10 mm or less, and cannot sufficiently cope with the low flying height of the head accompanying the rapid increase in recording capacity. In addition, as with tempered glass, since heat resistance is low, there is a problem of deformation of the substrate after film formation or annealing, and a change in surface roughness.

Patent Document 3 discloses photosensitive crystallized glass containing photosensitive metals Au and Ag in SiO ₂ —Li ₂ O-based glass. Patent Document 4 discloses SiO ₂ —Al ₂ O ₃ —Li ₂ O. Magnetic glass substrates in which the main crystal phase is composed of lithium disilicate (Li ₂ Si ₂ O ₃ ) and β-spodumene (LiAlSi ₂ O ₆ ) are disclosed in the system glass, respectively, Similar to the crystallized glass, since the heat resistance is low, there is a problem of deformation of the substrate after film formation or annealing, and a change in surface roughness.

Patent Document 4 discloses a magnetic material in which the main crystal phase is composed of lithium disilicate (Li ₂ Si ₂ O ₃ ) and β-spodumene (LiAlSi ₂ O ₆ ) in SiO ₂ —Al ₂ O ₃ —Li ₂ O-based glass. It is a substrate for a disk, and the crystallization heat treatment is newly reduced in temperature (680 to 770 ° C.) to precipitate β-eucryptite (Li ₂ Al ₂ Si ₂ O ₈ ). However, although these crystallized glass substrates have less alkali elution than chemically strengthened amorphous glass, they still generate alkali elution. Even in the case of a glass substrate, “deterioration of magnetic properties of storage medium”, “deposition of defects on the substrate surface”, “problem of recording skip”, and the like due to alkali elution are becoming problems.

Patent Document 5 discloses SiO ₂ —Al ₂ O ₃ —Li ₂ O-based low expansion transparent crystallized glass, and Patent Document 6 discloses SiO ₂ —Al ₂ O ₃ —ZnO-based crystallized glass. However, each glass ceramic material was measured by a predetermined method after undergoing the above heat resistance (ie, at a predetermined temperature environment (500 ° C. or higher for 5 minutes or longer)) as a substrate material for a perpendicular magnetic recording medium. There has been no study or suggestion regarding the level of flatness. There is no discussion on the maintenance of ultra-smoothness of the substrate surface after high-temperature film formation or annealing, which is particularly important.

Patent Document 7 and Patent Document 8 describe SiO ₂ —Li ₂ O—K ₂ O—P ₂ O ₅ —Al ₂ O ₃ based crystallized glass, and Patent Document 10 describes SiO ₂ —Li ₂ O—P. _{As a} crystal phase from ₂ O ₅ -Al ₂ O ₃ based crystallized glass, lithium disilicate (Li ₂ Si ₂ O ₅ ), a mixed crystal of lithium disilicate and α-quartz (α-SiO ₂ ), or lithium disilicate and Introducing the technology of crystallized glass for laser texture, characterized by depositing a mixed crystal of α-cristobalite (α-SiO ₂ ) or a mixed crystal of lithium disilicate and α-cristobalite and α-quartz. However, today's target surface roughness Ra (arithmetic mean roughness) is 10 mm or less, preferably 5.0 mm or less, more preferably 3.0 mm or less, and most preferably 2.0 mm or less, and recording that proceeds rapidly. It is not possible to sufficiently cope with the low flying height in accordance with the capacity increase.

In _{SiO 2 -Li 2 O-K 2} O-P 2 O 5 -ZrO 2 -Al 2 O 3 system glass-ceramics in Patent Document 9, lithium disilicate _{(Li 2 Si 2 O 5)} , lithium disilicate And a mixed crystal of α-quartz (α-SiO ₂ ), a mixed crystal of lithium disilicate and α-cristobalite (α-SiO ₂ ), or a mixed crystal of lithium disilicate and α-cristobalite and α-quartz. in _{SiO 2 -Li 2 O-K 2} O-P 2 O 5 -ZrO 2 -Al 2 O 3 -Na 2 O based crystallized glass 11, the lithium disilicate and α- quartz (α-SiO ₂₎ This paper introduces the technology of crystallized glass substrates for high recording density characterized by depositing mixed crystals, mixed crystals of lithium disilicate and β-spodium (β-Li ₂ Al ₂ Si ₄ O ₁₂ ). Crystallized glass produced by this technology can ensure smoothness at the atomic level by polishing. However, as a result of various types of cleaning performed during the film formation process of the magnetic film, there is a large smoothness change in the surface properties and fine protrusions. It is causing problems.

  And since these crystallized glasses have different hardness between the crystalline phase and the amorphous phase, minute irregularities are inevitably generated between the crystalline phase and the amorphous phase even after polishing. However, the unevenness played a role in preventing the magnetic head from adsorbing to the disk substrate.

  On the other hand, the information magnetic recording apparatus is a ramp load technique (contact recording of a magnetic head) in which the magnetic head is completely brought into contact with the above landing zone technology and the start / stop of the head is removed from the information magnetic recording medium disk substrate. ) Has also been developed, and the unevenness that prevents the magnetic head from adsorbing to the disk substrate is no longer necessary. Therefore, by making the surface of the substrate ultra-smooth, it becomes possible to operate in a state extremely close to the surface of the information recording medium, and the bit cell size can be reduced and the recording density can be increased.

  Therefore, in order not to cause head breakage or medium breakage even in this extremely low flying height or contact state, the surface roughness Ra (arithmetic mean roughness) of the substrate is preferably 10 mm or less. In order to obtain such an ultra-smooth polished surface, one having a fine average crystal particle diameter is required.

Further, as the recording density is improved, high accuracy is required for positioning of the magnetic head and the medium. Therefore, high dimensional accuracy is required for each component of the disk substrate and the magnetic information recording apparatus. For this reason, the influence of the difference in average thermal expansion coefficient on these components cannot be ignored. Therefore, the difference in these average thermal expansion coefficients must be minimized. More precisely, it is often preferred that the average thermal expansion coefficient of the disk substrate is slightly greater than the average linear expansion coefficient of these components. In particular, the thermal expansion coefficient of a component used for a small magnetic information recording medium is often about +90 to +100 (× 10 ⁻⁷ · ° C. ⁻¹ ), and the disk substrate has a thermal expansion coefficient of this level. Even if the thermal expansion coefficient is required to be 1 (× 10 ⁻⁷ · ° C. ⁻¹ ), there is a disadvantage that a write error occurs. However, the design of the drive increases the width of this thermal expansion coefficient, and the thermal expansion The coefficient has become more flexible, and even a low thermal expansion coefficient can be applied to drive design. That is, even if the thermal expansion coefficient is about +60 to +80 (× 10 ⁻⁷ · ° C. ⁻¹ ), it can be used for a component.

  The object of the present invention is to sufficiently cope with the ramp load method for high density recording in both the in-plane magnetic recording method and the perpendicular magnetic recording method in response to the design improvement of the magnetic information recording apparatus as described above. For information recording media with low melting temperature and high productivity that have good surface characteristics that can be used, high strength that can withstand high-speed rotation, and thermal expansion characteristics and heat resistance that match each drive member An object of the present invention is to provide an inorganic composition for a disk substrate or the like.

As a result of intensive studies and studies to achieve the above object, the present inventors have obtained lithium monosilicate (Li ₂ SiO ₃ ), lithium disilicate (Li ₂ Si ₂ O ₅ ), α-quartz (α-SiO ₂ ) containing one or more crystal phases selected from ₂ ), or containing at least a lithium monosilicate (Li ₂ SiO ₃ ) crystal phase, and the polished surface is extremely smooth. Excellent in strength, capable of supporting high-speed rotation of information recording devices, and also having thermal expansion characteristics that match drive components, such as crystallized glass used in conventional information recording media, etc. It has been found that a more advantageous inorganic composition can be obtained compared to the inorganic composition, and the present invention has been achieved. In particular, a disk substrate for an information recording medium using an inorganic composition such as crystallized glass that achieves the object of the present invention is suitable for use in a ramp load system because of its surface smoothness. More specifically, the present invention provides the following.

(1) It includes one or more crystal phases selected from α-quartz (α-SiO ₂ ), lithium disilicate (Li ₂ Si ₂ O ₅ ), and lithium monosilicate (Li ₂ SiO ₃ ). Inorganic composition.

An inorganic composition containing one or more crystalline phases selected from α-quartz (α-SiO ₂ ), lithium disilicate (Li ₂ Si ₂ O ₅ ), and lithium monosilicate (Li ₂ SiO ₃ ), especially In most SiO ₂ —Li ₂ O-based crystallized glass, the crystallinity increases as the crystallization temperature increases, and the crystal transitions to a SiO ₂ rich phase. When heating (heating) to crystallize the inorganic composition, phase separation occurs in the inorganic composition, crystal nuclei are formed at the phase separation interface, and then Li ₂ SiO ₃ (lithium monosilicate) is formed. Li ₂ Si ₂ O ₅ (lithium disilicate), and in some cases, α-quartz (α-SiO ₂ ), which is transferred to a β-quartz compound by solid solution of Al ions or the like.

Since these crystal phases are precipitated at a relatively low temperature, fine crystal particles are precipitated, and those having excellent surface properties and physical characteristics can be easily obtained. In the crystallization temperature region where the above-described crystal phase of lithium monosilicate (Li ₂ SiO ₃ ) and lithium disilicate (Li ₂ Si ₂ O ₅ ) coexist, the crystal particle diameter is small. Since it is very fine, it can obtain extremely good surface roughness and ring bending strength, and the proportion of precipitated fine particles of α-quartz (α-SiO ₂ ) having a large particle diameter is small. The smoothness of the will be more excellent. However, if the surface becomes ultra-smooth, the adsorbing force between the head and the medium becomes large, and medium damage is caused. Therefore, when appropriate smoothness other than the ultra-smooth surface is required, α-quartz (α-SiO ₂ ) is moderately used. By precipitating, the desired smooth surface can be obtained without causing medium damage.

In general, the same compound may slightly change depending on the temperature range, but Li ₂ SiO ₃ <Li ₂ Si ₂ O ₅ <α-SiO ₂ holds in relation to the thermal expansion coefficient, and α-SiO ₂ The thermal expansion coefficient of exceeds 200 (× 10 ⁻⁷ · ° C. ⁻¹ ) in the high temperature region. Since the thermal expansion coefficient of the original glass of this system is about +60 to +100 (× 10 ⁻⁷ · ° C. ⁻¹ ), when α-SiO ₂ or the like having a large difference in thermal expansion coefficient is precipitated, the crystal and the original glass are separated. Strain is likely to increase, and the strength is easily affected. Therefore, Li ₂ SiO ₃ has an advantage in that the difference in thermal expansion coefficient from the original glass is smaller than that of α-SiO ₂ .

Furthermore, it is known that the relationship of Li ₂ SiO ₃ <original glass <Li ₂ Si ₂ O ₅ <α-SiO ₂ is generally satisfied in the acid resistance between the original glass and the crystal. After polishing with CeO ₂ (cerium oxide) or the like, surface cleaning by permeation of hydrofluoric acid is performed in order to clean the remaining abrasive attached to the surface. As a result, if the acid resistance difference from the original glass, particularly the difference in dissolution speed due to hydrofluoric acid, is large, the surface roughness after surface cleaning deteriorates. Li ₂ SiO ₃ has a lower acid resistance than the original glass, and there is a difference in the dissolution speed with respect to hydrofluoric acid. However, crystals grow from a relatively low temperature such as 600 ° C., and the crystal grain size is very fine, so that even if there is a difference in dissolution speed for hydrofluoric acid, a much better surface roughness can be obtained. it can. On the other hand, Li ₂ Si ₂ O ₅ and α-SiO ₂ are strong in acid resistance and have a relatively slow dissolution rate in hydrofluoric acid, so that a good surface roughness can be obtained. The main crystal phase of the glass ceramic of the present invention includes β-spodumene, β-eucryptite, β-cristobalite (β-SiO ₂ ) having negative thermal expansion characteristics, diopsite, enstar It is preferable that tight, mica, α-tridymite, fluorrichite and the like are not contained as much as possible.

  The crystallized glass refers to a polycrystal composed of a polycrystalline crystal and a vitreous crystallized by reheating an original glass having a specific composition.

(2) An inorganic composition containing a crystalline phase of lithium monosilicate (Li ₂ SiO ₃ ).

Most of the SiO ₂ —Li ₂ O-based crystallized glass has a crystallinity that increases as the crystallization temperature increases, and the crystal transitions to a SiO ₂ rich phase. When the glass is heated (heated) to crystallize, phase separation occurs in the glass, crystal nuclei are generated at the phase separation interface, and then Li ₂ SiO ₃ is generated, and Li ₂ Si ₂ O ₅ In some cases, this results in α-SiO ₂ , which is transferred to a β-Quartz compound by solid solution of Al ions or the like. In general, there is a possibility that the temperature varies slightly between the same compounds, but Li ₂ SiO ₃ <Li ₂ Si ₂ O ₅ <α-SiO ₂ holds in the relationship of the thermal expansion coefficient, and the heat of α-SiO ₂ The expansion coefficient exceeds ⁺²⁰⁰ (× 10 ⁻⁷ · ° C. ⁻¹ ) in the high temperature region. Since the raw glass has a thermal expansion coefficient of about +60 to +100 (× 10 ⁻⁷ · ° C. ⁻¹ ) in this system, when α-SiO ₂ or the like having a large difference in thermal expansion coefficient is precipitated, the strain between the crystal and the original glass is increased. Tends to be large and has an effect on strength. Therefore, Li ₂ SiO ₃ has an advantage in that the difference in thermal expansion coefficient from the original glass is smaller than that of α-SiO ₂ .

Furthermore, it is known that the relationship of Li ₂ SiO ₃ <original glass <Li ₂ Si ₂ O ₅ <α-SiO ₂ is generally satisfied in the acid resistance between the original glass and the crystal. After polishing with CeO ₂ (cerium oxide) or the like, surface cleaning by permeation of hydrofluoric acid is performed in order to clean the remaining abrasive attached to the surface. As a result, if the acid resistance difference from the original glass, particularly the difference in dissolution speed due to hydrofluoric acid, is large, the surface roughness after surface cleaning deteriorates. Li ₂ SiO ₃ has lower acid resistance than the original glass and there is a difference in the dissolution rate in hydrofluoric acid, but crystals grow from a relatively low temperature such as 600 ° C., and the crystal grain size is very fine. In addition, it does not significantly affect the dissolution speed with respect to hydrofluoric acid, and it is possible to obtain surface roughness much better than that of depositing Li ₂ Si ₂ O ₅ or α-SiO ₂ .
(3) The inorganic composition according to (2), further including at least one crystal layer of lithium disilicate (Li ₂ Si ₂ O ₅ ) and α-quartz (α-SiO ₂ ).

According to the inorganic composition of the present invention, since the crystal particle diameter is fine, the polished surface is extremely smooth and has a high ring bending strength. That is, since lithium disilicate (Li ₂ Si ₂ O ₅ ) begins to form crystals at a temperature of 700 ° C., crystallized glass can be generated at a temperature lower than that of conventional crystallized glass. In addition, since it has the same characteristics as lithium monosilicate (Li ₂ SiO ₃ ), such as the fine particle diameter of the crystals to be precipitated and the thermal expansion coefficient approximate to that of the original glass, an ultra-smooth polished surface can be obtained. Can do. However, when the surface is super smooth, the adsorbing force between the head and the medium increases, and the medium is damaged. Therefore, moderate smoothness other than the super smooth surface is required. Thus, by appropriately depositing α-quartz (α-SiO ₂ ) having a large particle size, a desired smooth surface can be obtained without causing medium damage.

  (4) The inorganic composition according to any one of (1) to (3), wherein an average particle diameter of particles exhibiting the crystal phase is 1 μm or less.

  (5) The inorganic composition according to any one of (1) to (3), wherein an average particle diameter of particles exhibiting the crystal phase is 100 nm or less.

  (6) The inorganic composition according to any one of (1) to (3), wherein an average particle diameter of particles exhibiting the crystal phase is 50 nm or less.

  (7) The inorganic composition according to any one of (1) to (3), wherein an average particle diameter of particles exhibiting the crystal phase is 1 nm or more and 50 nm or less.

  According to the inventions of (4) to (7), the average particle size of the particles showing the crystal phase is 1 μm or less, preferably 100 nm or less, more preferably 50 nm or less, and most preferably 1 nm or more and 50 nm or less. A polished surface can be obtained. Therefore, when a substrate such as a disk substrate for an information recording medium is used, the surface roughness Ra (arithmetic average roughness) of the substrate is 10 mm or less, preferably 5 mm or less, more preferably 3 mm or less, and most preferably 2 mm or less. Therefore, even if the distance between the magnetic head and the substrate is small, the projection on the substrate and the magnetic head do not collide to cause damage to the magnetic head or the substrate. For this reason, the recording density can be increased. Further, by uniformly depositing such fine crystals, the mechanical strength of the inorganic composition is improved, and the lower limit of the ring bending strength is 300 MPa or more, preferably 450 MPa or more, more preferably 500 MPa or more, most preferably 750 MPa or more, and the upper limit is preferably 1600 MPa or less. For this reason, for example, when a substrate such as a disk substrate for a magnetic recording medium is used, the surface recording density can be increased, and even if the substrate itself is rotated at a high speed in order to improve the recording density, bending or deformation occurs. Therefore, vibration due to this rotation is reduced, and the number of data reading errors (TMR) due to vibration and deflection is reduced. Here, the particles showing the crystal phase are particles constituting the crystal phase and include crystalline particles and amorphous particles.

  Here, the average particle diameter of the particles exhibiting the crystal phase refers to the particle diameter of the center-based cumulative value (“median diameter” d50) of the particle diameter measured by a transmission electron microscope (TEM) image. The ring bending strength is a concentric bending method in which a thin disk sample having a diameter of about 65 mm and a thickness of about 0.6 mm is prepared, and the in-plane strength of the disk sample is measured with a circular support ring and a load ring. The bending strength measured by the method.

  (8) The inorganic composition according to any one of (1) to (7), wherein the content of the particles exhibiting the crystal phase is 1 to 44% by mass.

  According to the aspect of (8), when the inorganic composition is formed on a substrate such as a disk substrate for information recording media, a reduction in the surface roughness (Ra) of the substrate after polishing and excellent mechanical properties are realized. The In addition, as a quantitative handling of the amount of crystals, a diffraction peak area is obtained from an X-ray diffraction diagram obtained by an X-ray diffractometer (manufactured by Philips, trade name: X'pert-MPD), and the content is determined based on a calibration curve. evaluated.

  (9) The inorganic composition according to any one of (1) to (8), wherein the ring bending strength is 300 MPa or more.

  (10) The inorganic composition according to any one of (1) to (8), wherein the ring bending strength is 450 MPa or more.

  (11) The inorganic composition according to any one of (1) to (8), wherein the ring bending strength is 750 MPa to 1600 MPa.

  According to the inventions of (9) to (11), since the bending strength is high, when the inorganic composition is used as a substrate such as a disk substrate for an information recording medium, the substrate itself is bent or deformed due to high rotation. As a result, the distance between the magnetic head and the substrate can be reduced. Thereby, the surface recording density can be increased, vibration due to rotation is reduced, and the number of data reading errors (TMR) due to vibration and deflection is reduced.

  (12) The inorganic composition according to any one of (1) to (11), wherein the surface roughness (Ra) is 10 mm or less.

  According to this aspect, since the surface is extremely smooth, when the inorganic composition is used as a substrate such as a disk substrate for an information recording medium, the distance between the magnetic head and the substrate can be reduced. Therefore, the surface density for data writing or the like can be increased.

  (13) When the surface roughness (Ra) after polishing is Ra1, and the surface roughness by acid cleaning and / or alkali cleaning after polishing is Ra2, the surface roughness change rate (| Ra2-Ra1 | / Ra1) The inorganic composition according to any one of (1) to (12), having a value of less than 0.62.

  (14) The surface roughness (Ra) after polishing is 0.5 to 10 mm, and the amount of change in surface roughness due to acid cleaning and / or alkali cleaning after polishing is within 2.0 mm (1) The inorganic composition according to any one of (13).

  (15) The surface roughness (Ra) after polishing is from 0.5 to 10 mm, and the amount of change in surface roughness by cleaning with hydrofluoric acid after polishing is within 2.0 mm. (1) to (13) The inorganic composition in any one.

  According to the embodiments of (14) and (15), after polishing a substrate such as a disk substrate for an information recording medium made of an inorganic composition, particularly crystallized glass, the substrate surface is subjected to a cleaning treatment with acid, alkali or hydrofluoric acid. Etching rate difference between crystal and glass due to cleaning treatment with acid or alkali, even if it removes adhering glass debris and abrasives, especially crystallized glass where crystals and glass components are mixed in the glass matrix Therefore, the surface roughness (Ra) is not impaired.

  Here, the amount of change in surface roughness means the amount of change in surface roughness of the substrate after the substrate has been subjected to the above-described cleaning treatment relative to the surface roughness of the substrate after polishing. Degree of change = surface roughness after cleaning treatment−surface roughness of substrate after polishing.

  The surface roughness change rate is the ratio between the surface roughness of the substrate after polishing and the surface roughness change amount, and the surface roughness change rate = surface roughness change amount / surface roughness of the substrate after polishing. Indicated.

(16) The inorganic composition according to any one of (1) to (15), wherein the inorganic composition contains the following components in mass% in terms of oxide.
SiO _2: 50~90%, and / or _Li 2 O: _5~15%, and / or _Al 2 _O 3: _0~20%, and / or MgO: 0 to 3%, and / or ZnO: 0 to 3% and / or P ₂ O ₅ : 0 to 3% and / or ZrO ₂ : 0 to 3% and / or K ₂ O: 0 to 2% and / or Sb ₂ O ₃ + As ₂ O ₃ : 0 to 2%

(17) The inorganic composition according to any one of (1) to (15), wherein the inorganic composition contains the following components in mass% in terms of oxide.
SiO _2: 70~82%, and / or _Li 2 O: _7~13%, and / or _Al 2 _O 3: _3~10%, and / or MgO: 0 to 3%, and / or ZnO: 0 to 3% and / or P ₂ O ₅ : 1 to 3% and / or ZrO ₂ : 0 to 3% and / or K ₂ O: 0 to 2% and / or Sb ₂ O ₃ + As ₂ O ₃ : 0 to 2%

According to this aspect, a crystal layer of lithium monosilicate and lithium disilicate is easily selectively generated. In the inorganic composition of the present invention, particularly crystallized glass, the SiO ₂ component, LiO ₂ component and Al ₂ O ₃ component play an important role. That is, the SiO ₂ component and the LiO ₂ component are obtained by heat-treating a composition (hereinafter referred to as a raw inorganic composition) obtained by melting, molding, and cooling the above-described composition, as a crystalline phase, such as lithium disilicate, mono Lithium silicate and α-quartz are extremely important components, and the lower limit of the amount of SiO ₂ component is preferably 50% or more, more preferably 70% or more, and the upper limit is preferably 90% or less. Preferably it is 82% or less. The lower limit of the amount of LiO ₂ component is preferably 5% or more, more preferably 7% or more, and the upper limit is preferably 15% or less, more preferably 13% or less.

Further, the Al ₂ O ₃ component has an effect to improve the chemical durability and mechanical strength of the inorganic composition, particularly the hardness, and can be arbitrarily added. The lower limit of the amount of ₂ O ₃ component is preferably 0% or more, more preferably 3% or more, and the upper limit is 20% or less, more preferably 10% or less.

  Here, “mass% in terms of oxide” means that oxides, nitrates, and the like used as raw materials of the inorganic composition constituents of the present invention are all decomposed and changed into oxides when melted. It is the composition which described each component contained in an inorganic composition by making the sum total of the mass of a production | generation oxide into 100 mass%.

(18) The inorganic composition according to (16) or (17), wherein in the component, a mass ratio of Li ₂ O / K ₂ O is 5.5 or more.

The silicate inorganic composition, which is said to be easily crystallized compared to the general borate inorganic composition and phosphate inorganic composition, is low in cost due to the high melting point of SiO ₂ . It is very difficult to melt. In order to solve this problem, in order to produce an inorganic composition at a low cost in the inorganic composition range of this system, it is necessary to dope a certain amount of alkali components, but other components also have important roles. Therefore, in this composition range, the mass ratio of Li ₂ O / K ₂ O is preferably 5.5 or more, more preferably 9.0 or more, and most preferably 9.5 or more. Productivity can be improved while maintaining the characteristics.

  (19) The inorganic composition according to any one of (1) to (18), which is crystallized glass.

  (20) From (1) obtained by performing a nucleation process at 450 ° C. to 620 ° C., and performing a nucleation process by performing a heat treatment at 620 ° C. to 800 ° C. after the nucleation process. 19) The inorganic composition according to any one of

  The inorganic composition of the present invention melts the above composition, performs molding and cooling, and then performs heat treatment for crystal phase precipitation. In this heat treatment, nuclei are formed at 450 ° C. to 620 ° C., Thereafter, crystals are grown by heat treatment at 620 ° C. to 800 ° C., so that the precipitated crystal phase is mainly composed of lithium monosilicate and lithium disilicate. In addition, since the temperature of nucleation and crystal growth is relatively low, crystals are gradually precipitated, and crystals with a fine particle diameter are uniformly generated. Further, since the productivity is high and the temperature of the heat treatment is relatively low, it can be manufactured at low cost and is economical.

  (21) The inorganic composition according to any one of (1) to (20), which is a glass ceramic substrate for information recording media.

  (22) An information recording medium using the glass ceramic substrate for information recording medium according to (21).

  (23) The inorganic composition according to any one of (1) to (20), which is an electronic circuit board.

  (24) An electronic circuit using the electronic circuit board according to (23).

  (25) The inorganic composition according to any one of (1) to (20), which is a substrate for optical filters.

  (26) An optical filter comprising a dielectric multilayer film formed on the optical filter substrate according to (25).

  (27) A method of using the inorganic composition according to any one of (1) to (20) as a substrate for manufacturing a magnetic disk.

Since crystal grains of α-quartz (α-SiO ₂ ), lithium disilicate (Li ₂ Si ₂ O ₅ ), and lithium monosilicate (Li ₂ SiO ₃ ) are very small, these crystal particles The substrate made of an inorganic composition containing the material has extremely excellent surface roughness, excellent mechanical strength, and thermal expansion characteristics that match each drive member, and is useful as a substrate for manufacturing magnetic disks. It will be possible.

The inorganic composition of the present invention includes one or more crystals selected from lithium monosilicate (Li ₂ SiO ₃ ), lithium disilicate (Li ₂ Si ₂ O ₅ ), and α-quartz (α-SiO ₂ ). One containing a phase or at least a crystalline layer of lithium monosilicate (Li ₂ SiO ₃ ) having a particle size of 1 μm or less, preferably 100 nm or less, more preferably 50 nm or less, most preferably 1 to Since it is as small as 50 nm and the content ratio of the particles showing a crystal phase is 1 to 35% by mass, the surface roughness desirable for a substrate such as a disk substrate for a magnetic recording medium can be obtained only by polishing without requiring texture treatment. Further, the ring bending strength of the material can be dramatically improved, and the material has high mechanical strength that can withstand high speed rotation. In addition, since the deterioration of the substrate surface roughness after etching the surface with acid, alkali, or hydrofluoric acid can be suppressed as much as possible, a substrate suitable for a substrate, particularly an information recording medium, an electronic circuit, an optical filter, etc. is provided. it can.

  Next, specific embodiments of the inorganic composition of the present invention will be described.

The inorganic composition of the present invention has one or more crystal phases of lithium monosilicate (Li ₂ SiO ₃ ), lithium disilicate (Li ₂ Si ₂ O ₅ ), or α-quartz (α-SiO ₂ ). Or at least lithium monosilicate (Li ₂ SiO ₃ ), and the average particle size of particles showing these crystal phases is 1 μm or less, preferably 100 nm or less, more preferably 50 nm or less, most preferably 1 to 50 nm. It consists of a crystal phase in which crystals are uniformly deposited.

This inorganic composition is used, for example, for a substrate such as a disk substrate for a magnetic recording medium. Since the inorganic composition has the above properties, the surface roughness (Ra) is 10 mm or less, preferably 5 mm. Or less, more preferably 3 mm or less, and most preferably 2 mm or less, and a ring bending strength of 300 MPa or more, preferably 450 MPa or more, more preferably 500 MPa or more, still more preferably 750 MPa or more, most preferably 750 MPa or more and 1600 MPa. The high mechanical strength of the following and the thermal expansion coefficient in the temperature range of 25 to 100 ° C. have a lower limit of +50 (× 10 ⁻⁷ · ° C. ⁻¹ ) or more and an upper limit of +120 (× 10 ⁻⁷ · ° C. ⁻¹ ) Hereinafter, it preferably has +100 (× 10 ⁻⁷ · ° C. ⁻¹ ) or less. The Young's modulus is 80 GPa or more and the specific gravity is 2.7 or less.

  In addition, after polishing this substrate, cleaning with acid or alkali is performed to remove glass scraps and abrasives adhering to the substrate surface. Especially in the case of crystallized glass, crystals and glass components are contained in the glass matrix. Therefore, when a cleaning treatment with acid, alkali, or hydrofluoric acid is performed, the surface roughness tends to deteriorate due to a difference in etching rate between the crystal and the glass. Therefore, in the present invention, the deterioration of the surface roughness due to the cleaning treatment is reduced by 2.0% by extremely reducing the particle diameter of the particles showing the contained crystal phase and lowering the existence ratio of the particles showing the crystal phase. The following can be reduced. The upper limit is more preferably 1.5 mm, and still more preferably 1.0 mm.

  Hydrofluoric acid (HF) was used for the etching test. The polishing substrate was immersed in a solution containing HF (0.48 wt%) for 1 minute. Thereafter, the substrate was washed, and the surface roughness (Ra) of the substrate was confirmed with an atomic force microscope (AFM).

The inorganic composition of the present invention, SiO ₂ 50 to 90% by weight percent on the oxide basis, preferably 70-82%, and / or _Li 2 O: 5 to 15%, preferably 7-13% , and / or _Al 2 _O 3: _0~20% preferably 3-10%, and / or MgO: 0 to 3% and / or ZnO: 0 to 3%, and / or _P 2 _O 5: _0~ 3% and / or ZrO ₂ : 0 to 3%, and / or K ₂ O: 0 to 2%, and / or Sb ₂ O ₃ + As ₂ O ₃ : After cooling, it is obtained by further heat treatment and crystallization. Then, a crystalline phase of lithium monosilicate and / or lithium disilicate and / or α-quartz is selectively generated.

  The reason why the particle diameter, surface characteristics, physical characteristics, and composition of the particles showing the crystal phase of the inorganic composition of the present invention are limited as described above will be described below.

First, regarding the crystalline phase, in order to obtain a desired surface roughness, lithium monosilicate (Li ₂ SiO ₃ ) in which the precipitation ratio is relatively large and the crystalline phase is in the form of fine spherical particles, and / or two It is preferable to contain lithium silicate (Li ₂ Si ₂ O ₅ ) and / or α-quartz (α-SiO ₂ ), more preferably lithium monosilicate, and most preferably lithium monosilicate or lithium disilicate. And α-quartz. Since these crystal phases are precipitated at a relatively low temperature, fine crystal particles are precipitated, and those having excellent surface properties and physical characteristics can be easily obtained. In the crystallization temperature region where the above-mentioned crystal phases of lithium monosilicate and lithium disilicate coexist, the crystal particle diameter is very fine in the relatively low temperature region. Roughness can be obtained, and since the proportion of α-quartz (α-SiO ₂ ) particles having a large particle diameter is small, the surface smoothness is further improved. However, when the surface becomes super smooth, the adsorbing force between the head and the medium becomes large, and medium damage is caused. Therefore, moderate smoothness that is not the super smooth surface is required. Therefore, α-quartz is appropriately precipitated to obtain the desired smooth surface. The technology for obtaining is established in the present application.

  The abundance ratio of the particles exhibiting the crystal phase is preferably set to 1% by mass% in order to realize a reduction in surface roughness after polishing and excellent mechanical properties, which will be described later. %, More preferably 5%, and the upper limit is preferably 44%, more preferably 30%, and most preferably 25%.

  Next, regarding the surface characteristics, as described above, with the improvement of the surface recording density of the information recording medium, the flying height of the head has recently become 15 nm or less, and in the near future from 10 nm or less. In order to cope with this, the smoothness of the surface of a substrate such as a disk substrate must be better than that of a conventional product.

  Even if high-density input / output to / from the magnetic recording medium is performed with the smoothness of the conventional level, the magnetic signal cannot be input / output because the distance between the head and the medium is large. If this distance is reduced, the projection of the medium (disk substrate) and the head collide with each other, causing head damage or medium damage. Therefore, in order not to cause head damage or disk substrate damage even at this extremely low flying height or contact state, and to prevent adsorption of the head and the medium, the upper limit of the surface roughness Ra (arithmetic average roughness) is: The current magnetic recording medium is preferably 10 mm or less, more preferably 5 mm or less, and most preferably 4 mm or less. In the future magnetic recording medium, since smoothing is required, it is preferably 7 mm or less, more preferably 3 or less, most preferably 2 or less, and the lower limit is preferably 0.5 or more. In order to obtain such a smooth polished surface, and in order to obtain a desired ring bending strength, the upper limit of the average particle diameter of particles showing the crystalline phase of the inorganic composition in the current magnetic recording medium is 1 μm or less. More preferably, it is 100 nm or less, most preferably 50 nm or less. In future magnetic recording media, it is preferably 70 nm or less, most preferably 40 nm or less for the above-mentioned reasons, and the lower limit is preferably 1 nm or more. .

  Furthermore, the mechanical strength of the inorganic composition can be improved by depositing fine crystal particles uniformly. In particular, since the precipitated crystal particles prevent the growth of fine cracks, fine chips caused by chipping during polishing can be remarkably reduced. Also from such a viewpoint, the upper limit of the precipitation average particle diameter of the particles exhibiting the crystal phase is preferably 1 μm or less as described above, more preferably 100 nm or less, still more preferably 50 nm or less, and the lower limit. Is preferably 1 nm or more.

  The abundance ratio of the particles showing the crystalline phase is 1% or more, preferably 3% or more in terms of mass% in order to realize the above-described reduction in surface roughness after polishing and excellent mechanical properties. Most preferably, it is 5% or more, and the upper limit is 44% or less, preferably 34% or less, and most preferably 33% or less.

  In addition, after polishing the substrate, cleaning with acid or alkali is performed to remove glass scraps and abrasives adhering to the substrate surface. Especially in the case of crystallized glass, crystals and glass components are contained in the glass matrix. Since they are mixed, when the cleaning treatment with acid or alkali is performed, the surface roughness tends to deteriorate due to the difference in the etching rate between the crystal and the glass. Therefore, in the present invention, the deterioration of the surface roughness due to the cleaning treatment is reduced by 2.0% by extremely reducing the particle diameter of the particles showing the crystal phase to be contained and reducing the abundance ratio of the particles showing the crystal phase. It has succeeded in reducing to the following. The upper limit is more preferably 1.5 mm or less, and further preferably 1.0 mm or less.

  Further, when the surface roughness (Ra) after polishing is Ra1, and the surface roughness by acid cleaning and / or alkali cleaning after polishing is Ra2, the surface roughness change rate (| Ra2-Ra1 | / Ra1) The value is preferably less than 0.62.

  Next, ring bending strength and specific gravity will be 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 device such as a head contact or a removable recording device, it is necessary to have sufficient mechanical strength, high Young's modulus, and surface hardness that can withstand it. The bending strength is preferably 300 MPa or more and the Young's modulus is preferably 80 GPa or more. Therefore, also from this aspect, the mechanical strength is such that the lower limit of the ring bending strength is 300 MPa or more, preferably 450 MPa or more, more preferably 500 MPa or more, further preferably 750 MPa or more, and most preferably 750 MPa or more and 1600 MPa or less. The Young's modulus is 80 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. On the other hand, 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. A preferable range thereof is Young's modulus (GPa) / specific gravity of 30 or more, and a more preferable range is 33 or more. A preferable range is 35 or more. Also, the specific gravity needs to be 2.7 or less even if it is highly rigid, but if it is below 2.2, it is difficult to obtain a substrate having the desired rigidity with this type of inorganic composition. Become.

As for the coefficient of thermal expansion, as the recording density is improved, high precision is required for positioning the magnetic head and the medium. Therefore, high dimensional accuracy is required for each component of the medium substrate and the disk. For this reason, since the influence of the difference in thermal expansion coefficient with these components cannot be ignored, the difference in these thermal expansion coefficients must be minimized. In particular, the thermal expansion coefficient of components used for small magnetic information recording media is often about +90 to +100 (× 10 ⁻⁷ · ° C. ⁻¹ ), and the substrate also needs this thermal expansion coefficient. However, depending on the drive manufacturer, a material having a thermal expansion coefficient (about +70 to about +125 (× 10 ⁻⁷ · ° C. ⁻¹ )) deviating from this range may be used for the component parts. For the above reasons, the upper limit of the coefficient of thermal expansion is in the range of 25 to 100 ° C. so that it can be widely used for the material of the component to be used while balancing the strength with the crystal system of the inorganic composition of the present invention. The upper limit is preferably +50 (× 10 ⁻⁷ · ° C. ⁻¹ ) or more, and the lower limit is preferably +120 (× 10 ⁻⁷ · ° C. ⁻¹ ) or less, more preferably 100 (× 10 ⁻⁷ · ° C. ⁻¹ ). It is as follows.

  Next, the reason why the composition range of the inorganic composition is limited as described above will be described below. In addition, each component of the composition of the inorganic composition is expressed by mass%. In the present specification, the composition of the inorganic composition represented by mass% is all represented by mass% in terms of oxide.

The inorganic composition of the present invention is produced by, for example, melting the above composition, forming and removing the cooling, and then performing a heat treatment, but the SiO ₂ component is a monolith that precipitates as a crystalline phase by the heat treatment. Lithium silicate (Li ₂ SiO ₃ ), lithium disilicate (Li ₂ Si ₂ O ₅ ), and α-quartz (α-SiO ₂ ) crystals are very important components, but if the amount is less than 50% The precipitated crystals of the resulting inorganic composition are unstable and the structure tends to become coarse, and if it exceeds 90%, it becomes difficult to melt and mold the inorganic composition before heat treatment (referred to as the original inorganic composition). Therefore, the lower limit is preferably 50%, more preferably 65%, most preferably 70%, the upper limit is preferably 90%, and more preferably 85%. Preferably, 8 % And it is the most preferred range be.

The Li ₂ O component is a very important component that generates lithium monosilicate (Li ₂ SiO ₃ ) and lithium disilicate (Li ₂ Si ₂ O ₅ ) that precipitate as a crystalline phase by heat treatment of the raw inorganic composition. If the amount is less than 5%, it is difficult to precipitate the crystals, and it is difficult to melt the raw inorganic composition, and if it exceeds 15%, the resulting crystals are unstable and the structure is likely to be coarse. Since chemical durability tends to decrease, the lower limit is preferably 5%, more preferably 6%, most preferably 7%, and the upper limit is preferably 15%. 14% is more preferable, and 13% is the most preferable range.

The Al ₂ O ₃ component is suitable for improving the chemical durability and mechanical hardness of the inorganic composition. In order to precipitate lithium monosilicate (Li ₂ SiO ₃ ) and lithium disilicate (Li ₂ Si ₂ O ₅ ) even if various heat treatment conditions are taken into consideration, the type of precipitated crystals varies depending on the heat treatment conditions. Al ₂ O ₃ preferably has an upper limit of 20%, more preferably 15%, most preferably 10%, and a lower limit of 1%, preferably 2%. More preferably, 3% is the most preferable range.

The MgO and ZnO components are components that improve the meltability of the inorganic composition and at the same time prevent coarsening of the precipitated crystals. Further, lithium monosilicate (Li ₂ SiO ₃ ) and lithium disilicate (Li ₂ Si) are used as crystal phases. ₂ O ₅ ), which is effective for precipitating each crystal particle in a spherical shape. However, if it is excessively contained, the resulting crystal is unstable and the structure tends to be coarsened. Therefore, the MgO component is 3% or less, More preferably, it is 2% or less, and most preferably 1% or less. Further, the ZnO component is 3% or less, more preferably 2% or less, and most preferably 1% or less.

In the present invention, the P ₂ O ₅ component is a useful component that acts as a crystal nucleating agent of the inorganic composition. However, if the amount exceeds 3%, the milky white devitrification of the raw inorganic composition is caused. It is preferable that: If it is less than 1%, the formation of crystal nuclei may be insufficient and the precipitated crystal phase may grow abnormally. Therefore, the upper limit is preferably 3%, and the lower limit is preferably 1%. is there.

ZrO ₂ component, like P ₂ O ₅ component, functions as a crystal nucleating agent for inorganic compositions, and has remarkable effects on refinement of precipitated crystals, improvement of mechanical strength of materials, and improvement of chemical durability. However, if it exceeds 3%, melting of the raw inorganic composition tends to be difficult, so it must be 3% or less. More preferably, it is 2.7% or less, and most preferably 2.5%.

The K ₂ O component is a component that improves the meltability of the inorganic composition and prevents coarsening of the precipitated crystal, but its amount is 2% or less, more preferably 1.7% or less, and most preferably. Is 1.5% or less.

Sb ₂ O ₃ component and As ₂ O ₃ component are added as fining agents when melting the inorganic composition, but the sum of these components is 2% or less, more preferably 1.5% or less, most preferably 1%. It is as follows.

Incidentally, the Na ₂ O component is a component that tends to be a problem in increasing the accuracy and miniaturization of the magnetic film. When this component is present in the substrate, Na ions diffuse into the magnetic film during film formation, leading to abnormal growth of the magnetic film particles and a decrease in orientation, which tends to deteriorate the magnetic properties. Furthermore, it is preferable not to include Na ions because they gradually diffuse into the magnetic film and deteriorate the long-term stability of the magnetic properties. Further, since the PbO component is an environmentally undesirable component, it is preferable to avoid using it as much as possible.

  In addition, components composed of metal oxides such as V, Cu, Mn, Cr, Co, Mo, Ni, Fe, Te, Ce, Pr, Nd, and Er may color the glass and impair other properties. Therefore, it is preferable not to contain substantially.

  Next, in order to produce the inorganic composition of the present invention, first, the raw material having the above composition is melted, and after hot forming and / or cold working, the lower limit is 450 ° C., preferably 480 ° C., More preferably 520 ° C. or higher, the upper limit is 620 ° C., preferably 580 ° C., more preferably 560 ° C., heat treatment for about 1 to 20 hours to form crystal nuclei, and subsequently the lower limit is 620 ° C. or higher. Crystallization is performed by heat treatment for about 0.5 to 10 hours in a temperature range where the upper limit is 800 ° C., preferably 750 ° C., more preferably 685 ° C. Note that the upper limit of the nucleation temperature is preferably 700 ° C., more preferably 680 ° C., and most preferably 670 ° C. in order to realize further smoothing to cope with future high-density recording.

  At this time, when the crystal nucleation temperature is 450 ° C. or lower, nuclei are not formed and crystallization does not start. When the crystal nucleation temperature is 620 ° C. or higher, growth occurs simultaneously with nucleation, and crystallization cannot be controlled. Further, when the crystallization temperature is lowered from 620 ° C., it is difficult to grow a crystal having a preferable thermal expansion coefficient, and when it is 800 ° C. or higher, a crystal having a low expansion property is precipitated.

Crystalline phase of the crystallized inorganic composition by heat treatment thus, mono lithium silicate containing at least mono-lithium silicate _{(Li 2 SiO 3) (Li} 2 SiO 3), lithium disilicate _{(Li 2 Si 2 O 5)} , α -Quartz (α-SiO ₂ ) having an average particle size of 1 μm or less, more preferably 100 nm or less, and even more preferably 50 nm or less, and fine crystals are uniformly deposited and applied as a disk substrate for information magnetic recording. A crystallized glass having excellent surface roughness and mechanical strength can be obtained.

Here, the higher the crystallization temperature, the more α-quartz precipitates increase. However, since α-quartz has a large difference in thermal expansion coefficient from the original inorganic composition, the presence of α-quartz exists. If the ratio is too high, the strength decreases. On the other hand, if the crystallization temperature is too low, a large amount of Li ₂ SiO ₃ precipitates, resulting in problems of deterioration in surface roughness and reduction in strength due to an increase in particle diameter. In the present application, in order to obtain an inorganic composition such as crystallized glass having excellent surface roughness and mechanical strength, the strongest powder XRD peak intensity in each crystal is preferably represented by the following formula 1. However, the strength of the lithium disilicate _{I Li2Si2O5,} its mono-lithium silicate _{I Li2SiO3,} the sum of the strongest peak intensity of the crystalline phase other coexisting with _{I S.}

  Next, the substrate made of this heat-crystallized inorganic composition is lapped by a conventional method and then polished to have a surface roughness Ra (arithmetic average roughness) of 10 mm or less, more preferably 5 mm or less, and still more preferably A disk substrate, an electronic circuit substrate, and an optical disk substrate material of an inorganic composition of 3 mm or less, most preferably 2 mm or less are obtained. An information magnetic recording medium disk capable of high density recording is obtained by forming a magnetic film and, if necessary, Ni-P plating, or an underlayer, a protective layer, a lubricating film, etc. on the disk substrate material. . Further, an optical disk can be obtained by forming a dielectric multilayer film on an optical disk substrate material.

  EXAMPLES Hereinafter, although this invention is demonstrated further in detail using an Example, this invention is not limited to a following example.

<Examples 1-3> and <Comparative Examples 1-4>
Table 1 shows examples (No. 1 to 3) of crystallized glass, which is an inorganic composition of the present invention, and three types of conventional Li ₂ SiO ₃ -based crystallized glasses (Comparative Example 1: Japanese Patent Laid-Open No. Sho 62) as comparative composition examples. -72547, comparative example 2: disclosed in JP-A-9-35234, comparative example 3: disclosed in JP-A-12-302481, and conventional Li ₂ O—SiO ₂ The ratio of the component composition, the nucleation temperature of the crystallized glass, the crystallization temperature, the crystal phase, the crystallinity, the average crystal particle diameter, the ring bending strength, and the surface roughness obtained by polishing the amorphous amorphous glass (Comparative Example 4) It is shown together with Ra (arithmetic average roughness), surface roughness change amount and surface roughness change rate, specific gravity, Young's modulus, and thermal expansion coefficient due to hydrofluoric acid cleaning after polishing. Here, specific gravity was measured by Archimedes method, Young's modulus was measured by ultrasonic method, and thermal expansion coefficient was measured by optical interference method.

  The crystallized glass of Examples 1 to 3 and the crystallized glass of Comparative Examples 1 to 3 are all mixed with raw materials such as oxides, carbonates and nitrates in the ratios shown in Table 1, and this is mixed with a normal melting apparatus. It was melted at a temperature of about 1200 to 1550 ° C. and stirred and homogenized, then formed into a disk shape and cooled to obtain a glass molded body. Thereafter, this glass molded body was crystallized by heat treatment under the nucleation conditions and crystallization conditions shown in Table 1 to obtain a desired crystallized glass. Next, this crystallized glass is lapped with 800 # to 2000 # diamond pellets for about 1 to 20 minutes, and then polished with an abrasive (cerium oxide) having an average particle diameter of 3 μm or less for about 10 to 120 minutes to finish. It was. The amorphous glass of Comparative Example 4 was mixed with raw materials such as oxides, carbonates and nitrates in the proportions shown in Table 1, and melted at a temperature of about 1200 to 1550 ° C. using a normal melting apparatus and stirred. After homogenization, it was molded into a disk shape and cooled to obtain a glass molded body.

  About the average particle diameter of the particle | grains which show the crystal phase of each obtained crystallized glass, it calculated | required with the transmission electron microscope (TEM). Moreover, the crystal seed | species of each crystal grain was identified by the XRD analysis.

  Further, the surface roughness Ra (arithmetic average roughness) was determined by an atomic force microscope (AFM).

  Moreover, hydrofluoric acid (HF) was used for the surface roughness (Ra) fluctuation | variation by an etching test. The polishing substrate was immersed in a solution containing HF (0.48 mass%) for 1 minute. Thereafter, the substrate was washed, and the surface roughness (Ra) of the substrate was confirmed with an atomic force microscope (AFM). Table 1 shows the surface roughness after the hydrofluoric acid treatment (HF treatment) of oxide crystals, the amount of change and the rate of change.

  Regarding the ring bending strength, a thin disk sample having a diameter of about 65 mm and a thickness of about 0.6 mm is prepared, and the in-plane strength of the disk sample is measured by a circular support ring and a load ring. The breaking load was obtained and calculated from the following equation 2 from the inner diameter / outer diameter / plate thickness / Poisson's ratio / breaking load of the disk.

Here, P is the breaking load, a is the outer diameter of the disk, b is the inner diameter of the disk, h is the plate thickness, and ν is the Poisson's ratio.

  Precipitation crystal phase and crystallization rate (existence ratio of particles showing crystal phase) are X-ray diffractometer (manufactured by Philips, trade name: X'Pert-MPD) and energy dispersive analyzer (trade name, manufactured by Hitachi, Ltd.). : S-4000N, manufactured by HORIBA, Ltd., trade name: EX420).

  Moreover, the TEM photograph of the crystal grain shape of Example 1, 2 is shown in FIG. 1, FIG. In FIG. 1 and FIG. 2, the crystal particles are both fine and approximately spherical, and the average crystal particle diameter is 10 nm and 20 nm.

As shown in Table 1, in Examples 1 and 2 of the present invention and the comparative example of the conventional Li ₂ SiO ₃ based crystallized glass, the average particle diameter and crystallinity of the particles showing the crystal phase are different. In the crystallized glass of the present invention, the crystal phase is composed of lithium monosilicate (Li ₂ SiO ₃ ) and lithium disilicate (Li ₂ Si ₂ O ₅ ), and the average crystal particle diameter is The crystallized glass of Comparative Example 1 has an average crystal particle size of 1.5 μm of lithium disilicate and an average crystal particle size of α-cristobalite of 0. 0.02 μm or less, both fine and roughly spherical. 3 μm, the crystallized glass of Comparative Example 2 has an average crystal particle diameter of lithium disilicate of 0.1 μm, the average crystal particle diameter of β-spodumene is 0.2 μm, and the crystallized glass of Comparative Example 3 has lithium disilicate and α-quartz Average crystal grain size and 0.15 [mu] m, all of which are relatively large needle-like or rice grain spherical. This affects the surface roughness and defects obtained by polishing in a situation where more smoothness is required, and the crystallized glass of Comparative Examples 1 and 2 has a surface roughness Ra (arithmetic average roughness) of 10 mm. The above shows that it is difficult to obtain surface characteristics with excellent smoothness. Further, the crystallized glass of Comparative Examples 1 and 2 having a ring bending strength of 320 MPa or less and a Young's modulus of 86 GPa or less is a low strength, low Young's modulus material. Moreover, the surface roughness of the glass of Comparative Example 3 is 5.28 mm, which is lower than Comparative Examples 1 and 2. On the other hand, the amount of change in surface roughness after cleaning is 14 mm or more, the rate of change in surface roughness is as high as 2.68, and the ring bending strength is less than 750 MPa.

In Example 3 of the present invention, the crystal phase is composed of lithium disilicate (Li ₂ Si ₂ O ₅ ) and α-quartz (α-SiO ₂ ), the average crystal particle is 0.03 μm, and the crystallinity is 33. While the crystallized glass of Comparative Example 3 is composed of lithium disilicate and α-quartz, the average crystal particle diameter is 0.1 μm, and the degree of crystallinity is about 45%. %, Which is a relatively large needle shape or rice grain sphere. This affects the ring bending strength, the ring bending strength of the crystallized glass of Comparative Example 3 is less than 750 MPa, and the crystallized glass of Comparative Example 3 has a lower strength than Examples 1-3. It is a material. Moreover, since the comparative example 4 has not performed the crystallization process, it is a low strength material with a ring bending strength of 280 MPa or less.

  In addition, a Cr intermediate layer (80 nm), a Co—Cr magnetic layer (50 nm), and a SiC protective film (10 nm) were formed on the crystallized glass obtained in the above example by DC sputtering.

  Next, a perfluoropolyether lubricant (5 nm) was applied to obtain an information magnetic recording medium.

  The information magnetic recording medium obtained by this method can reduce the flying height of the head as compared with the conventional because of its good surface roughness, and the ramp loading method allows input and output when the head and the medium are in contact. Even if the test was performed, magnetic signals could be input and output without causing head damage or medium damage. Furthermore, the crystallized glass of the present invention exhibits a stable bump shape even in a laser texture performed by a landing zone method.

  The inorganic composition of the present invention has excellent heat resistance and mechanical strength that are necessary to cope with higher recording density by the future magnetic recording method, particularly higher recording density by the perpendicular magnetic recording method. And the inorganic composition which achieves the ultra smooth surface required in order to improve the crystal orientation of a film | membrane material in the case of film-forming can be provided. As a result, not only is it suitable for use as a substrate for perpendicular magnetic recording media for HDDs, but also a dielectric multilayer film is formed on a substrate for information recording media, an electronic circuit substrate, an optical filter substrate, and an optical filter substrate. It can also be used as an optical filter.

2 is a TEM photograph of crystallized glass of Example 1. 4 is a TEM photograph of crystallized glass of Example 2.

Claims (27)

Inorganic composition containing one or more crystalline phases selected from α-quartz (α-SiO ₂ ), lithium disilicate (Li ₂ Si ₂ O ₅ ), and lithium monosilicate (Li ₂ SiO ₃ ) . An inorganic composition containing a crystalline phase of lithium monosilicate (Li ₂ SiO ₃ ). Further, lithium disilicate _{(Li 2 Si 2 O 5)} , α- quartz (alpha-SiO ₂₎ inorganic composition of claim 2 comprising at least one crystalline phase.   The inorganic composition according to any one of claims 1 to 3, wherein an average particle diameter of the particles exhibiting the crystal phase is 1 µm or less.   The inorganic composition according to any one of claims 1 to 3, wherein an average particle diameter of the particles exhibiting the crystal phase is 100 nm or less.   The inorganic composition according to any one of claims 1 to 3, wherein an average particle diameter of the particles exhibiting the crystal phase is 50 nm or less.   The inorganic composition according to any one of claims 1 to 3, wherein an average particle diameter of the particles exhibiting the crystal phase is 1 nm or more and 50 nm or less.   The inorganic composition according to any one of claims 1 to 7, wherein the content of the particles exhibiting the crystal phase is 1 to 44% by mass.   The inorganic composition according to any one of claims 1 to 8, wherein the ring bending strength is 300 MPa or more.   The inorganic composition according to any one of claims 1 to 8, wherein the ring bending strength is 450 MPa or more.   The inorganic composition according to any one of claims 1 to 8, which has a ring bending strength of 750 MPa to 1600 MPa.   The inorganic composition according to any one of claims 1 to 11, wherein the surface roughness (Ra) is 10 Å or less.   When the surface roughness (Ra) after polishing is Ra1, and the surface roughness by acid cleaning and / or alkali cleaning after polishing is Ra2, the value of the surface roughness change rate (| Ra2-Ra1 | / Ra1) is The inorganic composition according to any one of claims 1 to 12, which is less than 0.62.   14. The surface roughness (Ra) after polishing is 0.5 to 10 mm, and the amount of change in surface roughness due to acid cleaning and / or alkali cleaning after polishing is within 2.0 mm. An inorganic composition as described in 1.   14. The surface roughness (Ra) after polishing is 0.5 to 10 mm, and the amount of change in surface roughness after cleaning with hydrofluoric acid after polishing is within 2.0 mm. Inorganic composition. The said inorganic composition is an inorganic composition in any one of Claim 1 to 15 containing the following component in the mass% of oxide conversion.
SiO _2: 50~90%, and / or _Li 2 O: _5~15%, and / or _Al 2 _O 3: _0~20%, and / or MgO: 0 to 3%, and / or ZnO: 0 to 3% and / or P ₂ O ₅ : 0 to 3% and / or ZrO ₂ : 0 to 3% and / or K ₂ O: 0 to 2% and / or Sb ₂ O ₃ + As ₂ O ₃ : 0 to 2% The said inorganic composition is an inorganic composition in any one of Claim 1 to 15 containing the following component in the mass% of oxide conversion.
SiO _2: 70~82%, and / or _Li 2 O: _7~13%, and / or _Al 2 _O 3: _3~10%, and / or MgO: 0 to 3%, and / or ZnO: 0 to 3% and / or P ₂ O ₅ : 1 to 3% and / or ZrO ₂ : 0 to 3% and / or K ₂ O: 0 to 2% and / or Sb ₂ O ₃ + As ₂ O ₃ : 0 to 2% The inorganic composition according to claim 16 or 17, wherein a mass ratio of Li ₂ O / K ₂ O is 5.5 or more.   The inorganic composition according to any one of claims 1 to 18, which is crystallized glass.   The nucleation step is performed on the raw glass at 450 ° C to 620 ° C, and the nucleation step is performed after the nucleation step by heat treatment at 620 ° C to 800 ° C. The inorganic composition as described.   The inorganic composition according to any one of claims 1 to 20, which is a glass ceramic substrate for an information recording medium.   An information recording medium using the glass ceramic substrate for information recording medium according to claim 21.   The inorganic composition according to any one of claims 1 to 20, which is an electronic circuit board.   An electronic circuit using the electronic circuit board according to claim 23.   The inorganic composition according to any one of claims 1 to 20, which is an optical filter substrate.   An optical filter comprising a dielectric multilayer film formed on the optical filter substrate according to claim 25.   A method of using the inorganic composition according to any one of claims 1 to 20 as a substrate for manufacturing a magnetic disk.