JP5552501B2 - Manufacturing method of substrate for information recording medium - Google Patents

Description

  The present invention corresponds to the future increase in the density of information magnetic recording media, has a low specific gravity, a high Young's modulus, excellent fracture toughness, extremely smooth surface roughness after processing, and head sliding characteristics. The present invention also relates to a method for manufacturing an information recording medium substrate having excellent impact resistance and having physical properties necessary for future information recording medium substrate applications.

  In the present invention, the “information recording medium” means an information magnetic recording medium that can be used in hard disks for various electronic devices.

  In recent years, large amounts of data such as moving images and sounds have been handled in personal computers and various electronic devices, and large-capacity information recording apparatuses are 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, in the next-generation magnetic recording system, the heat resistance and surface smoothness of the substrate are required to be higher than those of the current substrate. It also has a low specific gravity to reduce the burden on the spindle motor, a high mechanical strength to prevent disk crashes, and a high fracture toughness that can withstand the impact with the head when dropped. More important.
Furthermore, in recent years, a part of the hard disk market is being replaced by SSD (solid state drive), which is an information recording device using flash memory, in order to appeal the unit price per storage capacity, which is an advantage over SSD. Therefore, there is a demand for further reduction in manufacturing costs.

Examples of the material used for the information recording medium substrate include an Al alloy substrate, a glass substrate, and a crystallized glass substrate.
A glass-based material substrate of glass or crystallized glass is superior in that it has higher Vickers hardness and higher surface smoothness than an Al alloy, and is currently widely used in applications that are expected to be used dynamically.

  A glass-based material substrate is generally produced by the following method. That is, a glass raw material is melted to form molten glass, and this molten glass is formed into a plate shape. As a method for forming a plate, there are a direct press method and a float method for pressing molten glass. In the case of crystallized glass, crystals are precipitated inside by heat-treating the plate glass. Next, plate glass or crystallized glass is processed into a disk shape, and then subjected to a grinding process to bring the plate thickness and flatness close to the final shape, and a polishing process to obtain a smooth surface property, and the glass substrate is crystallized. A glass substrate is used.

  The grinding process is performed by holding the plate glass between the upper and lower platens and rotating the platen and the plate glass while relatively moving while rotating the platen and the slurry containing free abrasive grains in the grinding liquid. Rotating the platen and plate glass while supplying grinding fluid (coolant) with a platen with a plurality of pellets made of diamond, using a method, resin, metal, vitrified bond, etc. Conventionally, it is generally performed by a fixed abrasive method performed by moving.

  As in the grinding process, the polishing process holds the plate glass between the upper and lower surface plates, affixes a polishing pad to the surface plate, and supplies slurry containing free abrasive grains made of cerium oxide etc. This is done by rotating the glass relative to it.

  Both the grinding process and the polishing process are performed in a plurality of stages, and it is common to make the abrasive grains smaller each time the process is performed.

  According to such a conventional manufacturing method, the following problems occur when an attempt is made to produce a substrate corresponding to the next-generation magnetic recording system. For example, in the case of a crystallized glass substrate, the type of crystal phase precipitated in the glass phase, the crystal grain size, the crystal amount, and the like greatly affect the mechanical strength. Taking advantage of this, if the crystal grain size or amount is controlled in order to increase the mechanical strength, or if the crystal phase to be precipitated is a crystal with high hardness, the processing rate of grinding or polishing will be significantly deteriorated or desired. There was a problem that it was difficult to obtain a smooth surface. The deterioration of the processing rate is a factor that greatly affects the increase in manufacturing cost.

  Patent Document 1 discloses an information recording medium substrate made of crystallized glass having a garnite crystal phase. When crystallized under the crystallization conditions disclosed in this document, the crystallinity becomes high. This has high mechanical strength and high fracture toughness, but the surface roughness after polishing does not satisfy the next-generation required level. Also, because the surface hardness is too high, the processing rate in the grinding and polishing processes is low, the grinding and polishing process takes a long time, the productivity is poor, and it is impossible to meet the required cost of the market. is there.

  Crystallized glass having a spinel compound or a solid solution thereof as a main crystal phase has been proposed in the past as a material having high mechanical strength, as an information recording medium substrate or a building material. However, in order to have high mechanical strength in the past, it has been considered necessary to increase the crystallinity. Accordingly, crystals of the garnite-based crystallized glass proposed in the past have been deposited so as not to transmit visible light, and the surface properties applied to the next-generation information recording medium substrate cannot be obtained by the conventional processing method.

  Patent Document 2 discloses an information recording medium substrate made of crystallized glass having an enstatite crystal phase. Even if the crystallized glass disclosed in this document is processed by a conventional processing method, the processing rate of the grinding step is low, and the surface properties after the polishing step are Ra 0.2 nm to 0.3 nm, and a smooth surface is obtained. I can't.

Japanese Patent Laid-Open No. 07-300340 JP 2004-220719 A

  An object of the present invention is to provide various physical properties required for next-generation information recording medium substrate applications such as a perpendicular magnetic recording method, and in particular, to reduce an information recording medium substrate having high fracture toughness and a smooth surface. The object is to provide a manufacturing method for manufacturing at a low cost.

As a result of intensive studies and studies to achieve the above object, the present inventors have found that SiO ₂ component, Al ₂ O ₃ component, R ′ ₂ O component (where R ′ is Li, Na, K) as glass-based materials. The above-mentioned problem is solved by a manufacturing method including a step of selecting a plate-like glass containing any one or more of the above and preparing the same and a grinding step of grinding the plate-like glass material with a diamond pad. I found it.
Specifically, the present invention provides the following production method.

(Configuration 1)
A step of preparing a plate-like glass-based material containing a SiO ₂ component, an Al ₂ O ₃ component, and an R ′ ₂ O component (where R ′ is one or more of Li, Na, and K);
The manufacturing method of the board | substrate for information recording media including the grinding process of grinding the said plate-shaped glass-type material, and the said grinding process has a sub process of grinding at least the said plate-like glass-type material with a diamond pad.
(Configuration 2)
2. The method of manufacturing a substrate for an information recording medium according to Configuration 1, wherein the sub-step of grinding with the diamond pad comprises grinding with a diamond pad having an average diameter of diamond particles of 0.1 to 5 [mu] m.
(Configuration 3)
3. The method for manufacturing a substrate for an information recording medium according to claim 2, wherein the sub-step of grinding with the diamond pad comprises grinding with a diamond pad having an average diameter of diamond particles of 2 to 5 [mu] m.
(Configuration 4)
The method for producing a substrate for an information recording medium according to Configuration 2, wherein the final sub-step of grinding with the diamond pad comprises grinding with a diamond pad having an average diameter of diamond particles of less than 0.1 to 2 μm.
(Configuration 5)
The method for manufacturing a substrate for an information recording medium according to any one of claims 1 to 4, wherein the plate-like glass material is a material in which crystals having a Mohs hardness of 6 or more and less than 10 are precipitated as a crystal phase.
(Configuration 6)
The plate-like glass-based material contains at least one selected from MAl ₂ O ₄ , M ₂ TiO ₄ (wherein M is one or more selected from Zn, Mg, Fe) as the main crystal phase, and the main crystal phase 6. The substrate for an information recording medium according to claim 1, wherein the crystal grain size is in the range of 0.5 nm to 20 nm and the crystallinity is 15% or less. Manufacturing method.
(Configuration 7)
In the grinding step, when the target thickness after the final polishing is t1, and the thickness t2 of the plate-like glass material at the time of processing, if t2 / t1 ≦ 1.2, the grinding is performed with a diamond pad. The method for manufacturing a substrate for an information recording medium according to claim 1, comprising at least a step.
(Configuration 8)
The plate-like glass-based material is an oxide-based mass%,
SiO ₂ : 40 to 60%, and Al ₂ O ₃ : 7 to 20%, and R ′ ₂ O: 2 to 15% (where R ′ is one or more selected from Li, Na, and K)
The manufacturing method of the board | substrate for information recording media in any one of Claim 1 to 7 containing each component of these.
(Configuration 9)
The plate-like glass-based material is an oxide-based mass%,
TiO ₂ : 1 to 15%, and RO: 5 to 35% (where R is one or more selected from Mg, Ca, Sr, Ba, Zn, Fe)
The manufacturing method of the board | substrate for information recording media in any one of Claim 1 to 8 containing each component of these.
(Configuration 10)
The plate-like glass-based material is an oxide-based mass%,
The method for producing a substrate for an information recording medium according to any one of claims 1 to 9, comprising 5 to 25% of a ZnO component.
(Configuration 11)
11. The information recording medium according to claim 1, wherein the grinding step uses a double-sided processing machine that holds and polishes a material to be ground between upper and lower surface plates, and has a maximum processing pressure of 3 kPa to 6 kPa. A method for manufacturing a substrate.
(Configuration 12)
The method for manufacturing a substrate for an information recording medium according to claim 1, wherein a processing rate in the grinding step is 5 μm / min or more.
(Configuration 13)
The method for producing a substrate for an information recording medium according to any one of claims 1 to 12, wherein a surface roughness Ra after the grinding step is 0.001 µm to 0.085 µm.

  According to the present invention, the processing time in the grinding process is shortened and the surface roughness Ra after the grinding process is completed even for a substrate having high mechanical strength as required for the next generation information recording medium substrate application. Since this value is small, the time required for the polishing process is also shortened because it requires less allowance for obtaining a desired Ra value in the polishing process. Therefore, it has various physical properties required for next-generation information recording medium substrate applications as typified by perpendicular magnetic recording methods, etc. compared to conventional methods, especially for information recording media having high fracture toughness and a smooth surface. The substrate can be manufactured at low cost.

  In the present invention, the “main crystal phase” refers to a crystal phase corresponding to the main peak (highest peak) in XRD diffraction.

  “Crystallinity” can be obtained by adding up the amount (mass%) of crystals calculated from the diffraction intensity obtained from powder XRD using the Rietveld method. Regarding the Rietveld method, the “Crystal Analysis Handbook” Editorial Committee edited by the Crystallographic Society of Japan, “Crystal Analysis Handbook”, Kyoritsu Publishing Co., Ltd., September 1999, p. The method described in 492-499 was used.

“Crystal grain size” means that an image of an arbitrary part at a magnification of 100,000 to 500,000 is acquired by a TEM (transmission electron microscope), and the crystals appearing in the obtained image are sandwiched between two parallel straight lines. It is the average value of the longest distance. At this time, the n number is 100.
“Maximum crystal grain size” means that an image of an arbitrary part at a magnification of 100,000 to 500,000 is acquired by a TEM (transmission electron microscope), and crystals appearing in the obtained image are expressed by two parallel straight lines. The maximum value of the longest distance when sandwiched. At this time, the n number is 100.

  “Ra” refers to the average surface roughness specified in JIS B0601.

The Vickers hardness is a value representing the hardness of the substrate surface, and is specifically a value obtained by measurement by the following method. That is, by pressing a diamond square cone indenter with a face angle of 136 ° at a load of 4.90 N for 15 seconds and dividing the test load of 4.90 (N) by the surface area (mm ² ) calculated from the length of the indentation. Desired. For the measurement, a micro hardness tester MVK-E manufactured by Akashi Seisakusho Co., Ltd. can be used.

  The Mohs hardness is a numerical value for hardness based on how the standard material is scratched. Specifically, the sample is sequentially scratched with a standard substance, and if the sample is scratched, it is measured that the hardness is lower than that of the mineral. Standard materials from 1 to 10 are specified in order from soft ones. Specifically, 1 is talc, 2 is gypsum, 3 is calcite, 4 is fluorite, 5 is apatite, and 6 is positive. Feldspar, 7 is quartz, 8 is topaz, 9 is corundum, and 10 is diamond.

  The physical properties required for the next-generation information recording medium substrate are generally as follows.

[Young's modulus]
In order to improve the recording density and data transfer speed, the information recording medium disk substrate is being rotated at a high speed. To cope with this trend, the substrate material prevents disk vibration due to bending during high-speed rotation. Therefore, it must have high rigidity and low specific gravity. Further, when used in a portable recording device such as a head contact or a removable recording device, it preferably has mechanical strength, high Young's modulus, and surface hardness that can sufficiently withstand it, and the Young's modulus is 85 GPa or more. It is preferable to do.

[Young's modulus [GPa] / specific gravity]
Even if the information recording medium substrate is merely high in rigidity, if the specific gravity is large, the substrate is bent due to its large weight during high-speed rotation and generates vibration. On the other hand, if the rigidity is small even at a low specific gravity, vibration will occur in the same manner. In addition, there is a problem that power consumption increases due to an increase in weight. 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 properties of high rigidity and low specific gravity. In addition, in order to cope with future high speed rotation, a preferable range thereof is a value represented by Young's modulus [GPa] / specific gravity of 31.4 or more.

[Fracture toughness]
Fracture toughness is an index representing resistance to crack propagation based on slight scratches on the substrate surface. In particular, information recording medium substrates used in next-generation hard disks are required to have high fracture toughness because the magnetic disk rotational speed tends to increase as the recording density increases.
The value obtained by the SEPB method (JIS R1607) is used for the fracture toughness (K _1C ).
The fracture toughness value K _1C is preferably 1.0 or more, more preferably 1.1 or more, and preferably 1.2 or more in order to be applicable as a next-generation information recording medium substrate. Most preferred.

[specific gravity]
In order to improve the balance between rigidity and specific gravity, the specific gravity of the substrate is preferably 3.00 or less, more preferably 2.95 or less, and most preferably 2.90 or less. . On the other hand, when the specific gravity is less than 2.45, it is substantially difficult to obtain a substrate having a desired rigidity. Therefore, the specific gravity is preferably 2.45 or more, more preferably 2.48 or more, and 2.50 or more. Is most preferable.

As a glass-based material capable of realizing the above physical properties, in the present invention, SiO ₂ component, Al ₂ O ₃ component, R ′ ₂ O component (where R ′ is one or more of Li, Na, and K). Or crystallized glass is selected.
In at least one sub-process of the grinding process, this glass-based material is ground using a diamond pad, so that the processing rate in the grinding process is increased and the processing can be performed in a short time. Further, the value of the surface roughness Ra at the end of the grinding process can be reduced. Therefore, it is possible to shorten the processing time until the desired surface roughness is reached by polishing, and it is possible to shorten the entire processing time.

  In those skilled in the art of grinding glass or the like, a diamond pad is also called a diamond sheet, and diamond abrasive grains are fixed to a resin on a flexible sheet. The surface of the diamond pad is provided with a groove for supplying coolant to the grinding surface and discharging grinding debris. The grooves are provided in a lattice shape, a spiral shape, a radial shape, a concentric shape, or a combination thereof.

  The grinding process of the present invention may be divided into a plurality of sub-processes, but in at least one sub-process, preferably in the final sub-process, the average diameter of the fixed diamond abrasive grains is 2 μm to 5 μm. It is preferable to grind with a certain diamond pad. By grinding using the diamond pad as described above, the surface roughness Ra after the grinding process can be reduced without deteriorating the processing rate, and the processing time including the grinding process and the polishing process can be reduced. Can be shortened. A more preferable average diameter of diamond abrasive grains for obtaining the above effect is 2 μm to 4.5 μm. The diamond abrasive grains fixed to the diamond pad are preferably 10 wt% or less. At this time, in the sub-step prior to the final sub-step, the average diameter of the diamond pad abrasive grains is preferably in the range of 6 μm to 10 μm.

  When the conventional first polishing step (rough polishing step) is omitted, grinding is performed with a diamond pad having an average diameter of diamond abrasive grains of 0.1 μm or more and less than 2 μm in the final sub-step of the grinding step. Is preferred. Conventionally, the polishing process after the grinding process is divided into two or more stages, and processing is performed while changing the type of abrasive grains and the average grain size for each stage. At this time, if the rough polishing process can be omitted, the manufacturing process can be shortened, and the cost can be greatly reduced. In the present invention, the rough polishing step is performed while maintaining the processing speed required in the grinding step by grinding with a diamond pad having an average diameter of diamond abrasive grains of 0.1 μm or more and less than 2 μm in the final sub-step of the grinding step. Since the necessary surface smoothness can be obtained, the rough polishing step can be omitted. For example, it is possible to obtain the surface properties necessary for an information recording medium substrate even in only one polishing step. More preferably, the average diameter of the diamond abrasive grains is 0.2 μm or more and 1.8 μm or less. This effect is particularly remarkable when processing a glass-based material (1) described later. This is also considered to be one of the factors that the grindability of the glass-based material (1) to be described later by the diamond pad is less likely to cause scratches. In this case, although not essential, in order to improve the efficiency of the entire processing, in the sub-process before the final sub-process in the grinding process, the diamond abrasive grains may be ground with a diamond pad having an average diameter of 2 μm to 5 μm. preferable.

Therefore, as the diamond pad used in the grinding process, a diamond diamond having an average diameter of 0.1 μm to 5 μm can be used.
The average diameter of the diamond abrasive grains fixed to the diamond pad may be a volume-based d50 value measured by a laser diffraction confusion method. Usually, it is grasped by the particle size distribution of diamond abrasive grains managed in the manufacturing stage, but it is also possible to measure only diamond abrasive grains by dissolving the diamond pad with a chemical solution.

  When the glass-based material is crystallized glass, it is more preferable that the crystal having a Mohs hardness of 6 or more and less than 10 is precipitated as a crystal phase. The diamond pad is clogged by grinding scraps of the material to be ground, and the shape of diamond particles exposed on the surface of the diamond pad is rounded as the grinding process proceeds. When a glass-based material whose crystal phase crystal grains are specified by Mohs' hardness is ground with a diamond pad, the grinding particles clogged on the surface of the diamond pad with the crystal particles detached from the crystallized glass by grinding are eliminated. The dressing effect that makes the shape of the diamond particles exposed on the surface an acute angle is obtained, and the processing rate is improved. In order to obtain the above effect more effectively, the Mohs hardness of the crystal in the crystal phase is more preferably more than 6, and most preferably 7 or more. However, if the Mohs hardness becomes too high, the hardness of the glass-based material increases and the processing rate decreases, and a large difference occurs in the processing rate between the glass phase and the crystal phase, making it difficult to obtain a smooth surface. End up. Therefore, the Mohs hardness of the crystal in the crystal phase is most preferably 9 or less.

  In particular, when the glass-based material is glass, the grinding process in a range thinner than 1.2 times the target thickness after the final polishing is finished is not performed with diamond pellets or with a sanding method. It is preferable to grind only with a diamond pad. That is, in the grinding step, when the target thickness after the final polishing is t1, and the thickness t2 of the plate-like glass material at the time of processing, when t2 / t1 ≦ 1.2, all are ground with a diamond pad. It is preferable to do. In the case of glass, if grinding is performed with diamond pellets or sanding in a range thinner than 1.2 times the target thickness after the final polishing, the surface roughness after the grinding process and before the polishing process This is because the processing time in the subsequent polishing process becomes long, and it becomes difficult to obtain the surface roughness necessary for the next-generation substrate.

The composition of the sheet glass material containing the SiO ₂ component, Al ₂ O ₃ component, and R ′ ₂ O component will be described.
In the present specification, when each composition component constituting the plate-like glass-based material is described, the content of each component is represented by mass% based on the oxide unless otherwise specified. Here, the “oxide standard” is assumed that oxides, carbonates, and the like used as raw materials of the constituent components of the glass-based material of the present invention are all decomposed when melted and changed to the indicated oxides. This is a method for expressing the composition of each component contained in the plate-like glass-based material. The total amount of the generated oxide is 100% by mass, and the amount of each component contained in the plate-like glass-based material is write.

[Glass-based material (1)]
The glass material (1) is at least one selected from MAl ₂ O ₄ and M ₂ TiO ₄ (where M is one or more selected from Zn, Mg and Fe) (hereinafter also referred to as “spinel compound”). It is a crystallized glass as the main crystal phase. Analysis by X-ray diffraction makes it difficult to distinguish garnite and spinel (MgAl ₂ O ₄ ) because the peaks appear at the same angle. This _is the same case of R 2 TiO _4, in these cases, in the composition i.e. the composition of the raw glass of the crystallized glass to compare the content of ZnO component and MgO component, the more ZnO component gahnite (ZnAl ₂ It is suggested that O ₄ ) or zinc titanate compound (Zn ₂ TiO ₄ ) is the main crystal phase.

  Since the crystal made of the spinel compound has a Mohs hardness of 8, when the crystallized glass having the spinel compound as the main crystal phase is ground, the above-mentioned diamond pad dressing effect is particularly prominent, and the processing rate is high. It is preferable because it is extremely high.

  The glass-based material of the present invention is particularly preferably a crystallized glass having a crystallinity of 1% to 15% and a crystal grain size of 0.5 nm to 20 nm. Since the crystallized glass having a spinel compound as the main crystal phase has an excellent Mohs hardness of 8 as described above, excellent mechanical strength can be obtained. The crystallinity of the precipitated crystals (including precipitated crystals other than the main crystal phase) and the crystal grain size are in the above-mentioned range, and the next-generation information recording is achieved by using the diamond pad defined in the present invention in the grinding process. Balanced mechanical strength such as surface smoothness and Young's modulus, Vickers hardness, fracture toughness, etc. required for the substrate for media, and a good balance between the diamond pad dressing effect and the processing rate in the grinding process, This makes it possible to process at a high processing rate. If the crystallinity is too high, it becomes difficult to obtain the desired surface properties, and since the hard crystal phase is increased compared to the glass phase, the processing rate tends to be deteriorated. Is more preferably 14% or less, and most preferably 13% or less. Similarly, the crystal grain size is more preferably 15 nm or less, and most preferably 10 nm or less. Similarly, in order to obtain the above effect, the maximum grain size of the main crystal phase is preferably 30 μm or less, more preferably 20 μm or less, and most preferably 15 μm or less.

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 40%, the resulting glass has poor chemical durability, 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 40%. Preferably, 41% is more preferable and 42% is preferable. Further, if it exceeds 60%, dissolution and press molding are likely to be difficult as the viscosity increases, and the homogeneity and clarification effect of the material are likely to be lowered. Therefore, the upper limit of the content is preferably 60%. 59% is more preferable, and 58% is most preferable.

The Al ₂ O ₃ component is one of the components constituting the main crystal phase by heat treatment of the original glass, and is an important component that contributes to stabilization of the glass and improvement of chemical durability. If it is less than%, the effect is poor, so the lower limit of the content is preferably 7%, more preferably 9%, and most preferably 11%. On the other hand, if it exceeds 20%, dissolution, moldability and devitrification resistance are deteriorated, and homogeneity and clarification effect are liable to be lowered. Therefore, the upper limit of the content is preferably 20%, 19% Is more preferred and 18% is most preferred.

  The RO component (where R is one or more selected from Mg, Ca, Sr, Ba, Zn, and Fe) includes a component that forms the main crystal phase by heat treatment of the original glass, and contributes to glass stabilization. However, if the total amount is insufficient, the current glass viscosity becomes high, and the mass productivity is impaired, and furthermore, a desired crystal phase cannot be obtained. The lower limit of the content is preferably 5%, more preferably 8%, and most preferably 11%. On the other hand, when the total amount exceeds 35%, not only vitrification becomes difficult, but also precipitation of insoluble matter and increase in devitrification temperature are caused. The upper limit of the content is preferably 35%, more preferably 33%, and most preferably 31%.

  The ZnO component is one of the components that constitute the main crystal phase by heat treatment of the original glass, and contributes to lowering the specific gravity and Young's modulus of the glass and is also effective for lowering the viscosity of the glass. However, if the content is less than 5%, the above effect cannot be obtained. Therefore, the lower limit of the content is preferably 5%, more preferably 6%, and most preferably 8%. On the other hand, if the content of the ZnO component exceeds 25%, the precipitation of crystals from the original glass becomes unstable and the crystal grains are likely to be coarsened, so the upper limit of the content is preferably 25%. % Is more preferred and 21% is most preferred.

  The MgO component is a component that contributes to lowering the specific gravity of the glass and improving the Young's modulus, and is an optional component that can be optionally added to lower the viscosity of the glass. However, if the content exceeds 15%, the specific gravity of the original glass becomes high and it becomes difficult to obtain the desired glass, and it may be precipitated as an insoluble matter. Therefore, the upper limit of the content of these components is preferably 15%, more preferably 14%, and most preferably 13%.

The FeO component is one of the components constituting the main crystal phase by heat treatment of the original glass, and generates a spinel compound together with the Al ₂ O ₃ component and the TiO ₂ component. Moreover, although it is a compound which acts also as a clarifier, platinum generally used at the time of glass melting will be alloyed. Therefore, the upper limit of the content is preferably 8%, more preferably 6%, and most preferably 4%.

The TiO ₂ component plays a role of nucleation for precipitating the spinel compound and is a component that contributes to improvement of Young's modulus, low viscosity, and chemical durability of the glass. In addition, it is one of the components constituting the main crystal phase by heat treatment of the raw glass. However, if the added amount of this component exceeds 10%, the specific gravity value of the glass becomes high, and further vitrification becomes difficult, so the upper limit of the content is preferably 10%, more preferably 9%, 8% is most preferred.
If the content of the TiO ₂ component is less than 1%, nucleation due to heat treatment does not occur. Therefore, the lower limit of the content is preferably 1%, more preferably 2%, and most preferably 3%.

ZrO ₂ component, like TiO ₂ component, plays the role of nucleation for precipitating the main crystal phase and contributes to the improvement of the Young's modulus and chemical durability of the glass, so it can be optionally added. When the addition amount of this component exceeds 2%, undissolved or ZrSiO ₄ (zircon) is likely to be generated when the glass is melted, and the glass specific gravity becomes high, so the upper limit of the content is preferably 10%. 8% is more preferable, and 6% is most preferable.

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 8% or more, it will be difficult to satisfy the mechanical properties, and the glass will be difficult to phase separate, making it difficult to vitrify. Therefore, the upper limit of the content should be less than 8%. Is preferred. A more preferred upper limit is 7%.

The R ′ ₂ O component (where R is one or more selected from Li, Na, and K) is a component that brings about low viscosity of glass, improved formability, and improved homogeneity. Further, by containing the R ′ ₂ O component, it is possible to exchange the alkali metal ions on the surface after forming the substrate and to impart additional characteristics. When the content of the R ′ ₂ O component (total of each component of Li ₂ O, Na ₂ O, and K ₂ O) is less than 2%, the above effect cannot be obtained, so the lower limit of the content Is preferably 2%. Moreover, since it is necessary to limit the elution of the alkaline component from the surface of the information recording medium substrate, the upper limit of the content of the R ₂ O component is preferably 15% in order to minimize the alkaline component elution amount. 13% is more preferred and 11% is most preferred.

The individual contents of each component of Li ₂ O, Na ₂ O, and K ₂ O will be described.
The Li ₂ O component can be optionally contained, but if it is contained in a large amount, it becomes difficult to obtain a desired crystal phase, so the upper limit is preferably 2%.
The Na ₂ O component can be optionally contained, but if it is contained in a large amount, it becomes difficult to obtain a desired crystal phase. Therefore, the upper limit is preferably 15%, more preferably 12%. % Is most preferred.
The K ₂ O component can be optionally contained, but if it is contained in a large amount, it becomes difficult to obtain a desired crystal phase. Therefore, the upper limit is preferably 10%, more preferably 8%. Most preferably it is.

  The CaO component is a component that contributes to lowering the specific gravity of the glass and improving the Young's modulus, and is effective in lowering the viscosity of the glass, so it can be added as an optional component. However, when the CaO component exceeds 15%, the specific gravity of the original glass increases and it becomes difficult to obtain the desired glass. Therefore, the upper limit of the content of these components is preferably 15%, more preferably 12%, and most preferably 9%.

  BaO component and SrO component have the same function as MgO, CaO, etc. as effective components for lowering glass viscosity and improving chemical durability and mechanical improvement, but the glass specific gravity tends to increase. The upper limit of the content is preferably 5%, more preferably 4%, and most preferably 3%.

The P ₂ O ₅ component has an effect of suppressing the progress of cracks in the glass, and thus can contribute to an increase in Vickers hardness. Moreover, it contributes to lowering the viscosity and improves the melting and clarifying properties of the original glass by coexistence with SiO ₂ . In order to obtain these effects, the P ₂ O ₅ component can be optionally contained. However, when this component is added excessively, vitrification becomes difficult and devitrification and phase separation are likely to occur. Therefore, the upper limit of the content is preferably 7%, more preferably 6%, and most preferably 5%. .

Gd ₂ O ₃ , La ₂ O ₃ , Y ₂ O ₃ , Nb ₂ O ₅ , Ga ₂ O ₃ , and WO ₃ components contribute to lowering the viscosity of glass, improving mechanical properties by improving Young's modulus, and improving heat resistance Therefore, 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 5%, and if the total amount exceeds 5%, the specific gravity, Young's modulus and specific rigidity cannot be satisfied. Therefore, the upper limit of the total amount of these components is preferably 5%, more preferably 4%, and most preferably 3%.

  Components such as V, Cu, Mn, Cr, Co, Mo, Ni, Te, Pr, Nd, Er, Eu, and Sm, which are used as coloring components of glass, are obtained by utilizing the fluorescence characteristics resulting from these components. Can be added for the purpose of preventing mixing with other types of glass at a factory, etc., but this causes an increase in specific gravity, an increase in raw material costs, and a decrease in glass forming ability. 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%.

[Glass-based material (2)]
The glass material (2) is an amorphous glass containing a SiO ₂ component, an Al ₂ O ₃ component, and an R ′ ₂ O component.

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 refers to one or more alkali metals selected from Li, Na, and K, but is an essential component for reducing glass viscosity, improving formability, improving homogeneity, and chemical strengthening. On the other hand, it is preferable for the information recording medium substrate to have high chemical durability, that is, to reduce the elution amount of the alkali component as much 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%. When 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%.

In order to obtain a high clarification effect while maintaining the physical properties required for the information recording medium substrate for both the glass-based materials (1) and (2), the main clarification component is selected from a SnO ₂ component and a CeO ₂ component. It is preferable to contain one or more components. In order to obtain a high clarification effect, the lower limit of the total content of SnO ₂ component, CeO ₂ component, or both on the oxide basis is preferably 0.01%, more preferably 0.1% Preferably, 0.15% is most preferable.
On the other hand, one or more selected from SnO ₂ component or CeO ₂ component is used to maintain the mechanical strength, to lower the specific gravity, to obtain a high clarification effect and to enhance the reboil suppression effect at the time of direct pressing. The upper limit of the content of is preferably 1%, more preferably 0.8%, and most preferably 0.6%.

Both the glass-based materials (1) and (2) are As ₂ O ₃ components, Sb ₂ O ₃ components and Cl ⁻ , NO ⁻ , SO 2 ⁻ and F ⁻ components, which act as fining agents, but can be harmful to the environment. Yes, its 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.

Forsterite (Mg ₂ SiO ₄ ), enstatite (MgSiO ₃ ), and these, which are crystals that deteriorate the polishing processability and lower the chemical durability in both the glass-based materials (1) and (2) of the present invention. The solid solution is preferably not contained.

  Moreover, the glass substrate of this invention can acquire the effect which improves a mechanical strength more by providing a compressive-stress layer in 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 0.1 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.

More specifically, the information recording medium substrate of the present invention is manufactured by the following method.
[Process for preparing plate-like glass-based material]
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 Dissolves at a temperature of 1.5 to 3.0 dPa · s.
Next, the temperature of the glass melt is raised to a temperature at which the viscosity becomes 1.0 to 2.3 dPa · s, preferably 1.2 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 1.8 to 2.6 dPa · s, preferably 2.0 to 2.5 dPa · s, and the defoaming of bubbles generated inside the glass is eliminated. Clarify, then maintain this temperature.

The molten glass produced under the above conditions is dropped onto the lower mold, and the molten glass is pressed (direct press) with the upper and lower molds to form a disk having a thickness of about 0.7 mm to 1.2 mm.
Specifically, 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.
Furthermore, 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 2.0 to 2.6 dPa · s, preferably 2.1 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 disk-shaped plate glass.

  In addition, it can also be produced by a method of slicing a glass body formed into a cylindrical shape, a method of cutting out a glass sheet produced by a float method, or the like. However, the production by direct press is most preferable in terms of production efficiency.

Next, when the glass-based material is crystallized glass, crystals are produced from the obtained disk-shaped glass by heat treatment. This heat treatment is preferably performed at two stages. That is, first, a nucleation step is performed by heat treatment at a first temperature, and after this nucleation step, a crystal growth step is performed by heat treatment at a second temperature higher than the nucleation step.
In this crystallization process, it is preferable that the disk-shaped ceramic setter and the disk-shaped glass are alternately stacked and sandwiched between the setters (the number of setters is the number of glass + 1) because the flatness of the disk is improved.
In order to obtain the grain size and crystallinity of the precipitated crystal of the present invention, preferable heat treatment conditions are as follows.
The maximum temperature of the first heat treatment is preferably 600 ° C to 750 ° C. The first stage heat treatment may be omitted. The maximum temperature of the second stage heat treatment is preferably 650 ° C to 850 ° C.
The holding time of the first temperature is preferably 1 hour to 10 hours.
The holding time of the second temperature is preferably 1 hour to 10 hours.

[Pre-processing process]
Next, chamfering is performed by drilling the center portion, grinding the end surfaces of the outer peripheral portion and the inner peripheral portion, or the like.

[Grinding process]
The grinding process is a process for bringing a desired plate thickness and flatness close to the final shape, and it is preferable to use a double-sided processing machine that holds a plate-like glass material between upper and lower surface plates and relatively moves by rotation. The grinding process may be a process of at least one stage, but is preferably divided into at least two stages of sub-processes, and the count of the abrasive grains is made finer as the process goes through.

The first stage sub-process may be a sanding method using loose abrasive grains such as alumina, a fixed abrasive method using diamond pellets, or a method using a diamond pad. In this case, the count when using diamond pellets is preferably # 800 to # 1200, and the average diameter of diamond abrasive grains when using a diamond pad is preferably 6 μm to 10 μm. As described above, when the rough polishing step is omitted, the average diameter of the diamond abrasive grains of the diamond pad is preferably 2 μm to 5 μm.
Further, the processing pressure in the first stage sub-process is preferably 3 kPa to 6 kPa, and more preferably 3.5 kPa to 5.5 kPa. The rotation speed is preferably 20 to 50 rpm. The supply amount of the coolant is preferably 0.5 cc to 1 cc per 1 cm ² of the processing surface of the double-side processing machine.

A diamond pad is used in the final sub-process including the case where the grinding process is only one stage. By using a diamond pad at least in the final sub-process, the surface roughness Ra after the grinding process can be reduced without deteriorating the processing rate, and the processing time including the grinding process and the polishing process can be reduced. It can be a short time.
In this case, the average diameter of the diamond abrasive grains of the diamond pad is preferably 2 μm to 5 μm, and more preferably 2 μm to 4.5 μm. As described above, when the rough polishing step is omitted, the average diameter of the diamond abrasive grains of the diamond pad is preferably 0.1 μm or more and less than 2 μm, and preferably 0.2 μm to 1.8 μm. .
The processing pressure in the final sub-process is preferably 3 kPa to 6 kPa, and more preferably 3.5 kPa to 5.5 kPa. The rotation speed is preferably 20 to 50 rpm. The supply amount of the coolant is preferably 0.5 cc to 1 cc per 1 cm ² of the processing surface of the double-side processing machine. The surface roughness Ra after completion of the final sub-process is preferably 0.001 μm to 0.085 μm because the processing time can be shortened from the viewpoint of the total time of the grinding process and the time of the polishing process.

[Inner and outer periphery polishing process]
After the grinding step, the end surface is polished as necessary to smooth the end surface.

[Polishing process]
After the grinding step or the inner and outer peripheral polishing step, the main surfaces of the front and back surfaces are polished to obtain a desired surface property. The polishing process may be a single-stage process, but is divided into two or more sub-processes. It is preferable to use a double-sided processing machine as in the grinding process, as well as the grinding process, using free abrasive grains such as colloidal silica, cerium oxide, zirconia, alumina, diamond, etc. The polishing pad is changed from a hard one to a soft one.

  By sufficiently smoothing the polishing roughness after completion of the grinding process, the polishing process can be limited to only the final sub-process (finish polishing process).

The first sub-process is preferably processed using a polishing pad while supplying a polishing slurry containing free abrasive grains of cerium oxide. In this case, the average grain size of the free abrasive grains is preferably 0.3 μm to 1 μm. The content of the free abrasive grains in the polishing slurry can be appropriately adjusted between 5% by mass and 80% by mass. The polishing pad is preferably made of hard foamed urethane in which fine cerium oxide abrasive grains are dispersed or hard foamed urethane. The hardness of the pad is preferably 75 to 95 in JIS K 6253, more preferably more than 85 and 95 or less.
The pH of the polishing slurry is preferably 9 to 13, and more preferably 10 to 13. Usually, in the case of polishing a glass-based material, the pH of the polishing slurry is in the vicinity of the neutral region. This is because if the polishing slurry has a strong acid or alkali pH, the chemical action becomes too strong and the surface of the glass-based material becomes rough. However, when the polishing slurry is in the above pH range for the glass-based material of the present invention, a high polishing rate can be obtained while obtaining smooth surface properties. In particular, with a crystallized glass having a spinel compound as a main crystal phase, a high polishing rate can be obtained.
Further, the processing pressure in the first stage sub-process is preferably 8 kPa to 15 kPa, and more preferably 9 kPa to 13 kPa. The rotation speed is preferably 20 to 50 rpm.
In this step, a processing rate of 0.3 μm / min to 1 μm / min can be obtained.

It is preferable to use a polishing pad in the final sub-process, including the case where the polishing process is only one stage, and process while supplying a polishing slurry containing free abrasive grains of cerium oxide or colloidal silica. The content of the free abrasive grains in the polishing slurry can be appropriately adjusted between 0.1% by mass and 60% by mass. In this case, the free abrasive grains preferably have a distribution in the range of 10 nm to 100 nm. The polishing pad is preferably a soft nonwoven fabric (preferably Asker C hardness of 55 to 80) or a suede polishing pad.
In addition, the pH of the polishing slurry is preferably 1 to 5 or 9 to 13, in other words, more than 5 and not less than 9.
By setting the pH of such a polishing slurry, it becomes easier to increase the processing rate of the polishing step and obtain a very smooth surface property.
Further, the processing pressure in the final sub-process is preferably 8 kPa to 15 kPa, and more preferably 9 kPa to 13 kPa. The rotation speed is preferably 20 to 50 rpm.
In this step, a processing rate of 0.05 μm / min to 0.20 μm / min can be obtained.
Also, two types of polishing slurries having different pHs may be prepared, and different pHs may be set before and after the sub-process. For example, it is possible to supply a polishing slurry of pH 3 from the tank A of the polishing slurry, and then stop supplying the polishing slurry and supply a rinsing liquid, and supply a polishing slurry of pH 1 from the tank B. By this operation, a smoother surface property can be obtained while further improving the processing rate.

  The particle size distribution of the free abrasive grains is measured on a volume basis by the laser diffraction confusion method, and the average particle diameter is the value of d50.

  The pH of the polishing slurry may be adjusted by adding an acid solution such as nitric acid, sulfuric acid, acetic acid, organic acid, caustic soda, or organic alkali, or an alkaline solution to the abrasive slurry. Since the processing rate may vary depending on the type of solution even at the same pH depending on the composition of the glass material, an optimal solution can be selected.

  In the polishing step, when the supply of the polishing slurry is a supply by circulation, the pH of the polishing slurry may gradually change due to the influence of the polishing sludge. In such a case, a means for adding the acid solution or the alkali solution to adjust the pH in a timely manner may be provided. In this case, it is preferable to control by a signal from the pH measuring device.

  According to the present invention, the surface roughness Ra after completion of the final sub-step, that is, the finish polishing step, can be made 1.5 mm or less.

  Further, the Ra value can be further reduced by treating with an acid or alkali solution after polishing.

  Next, preferred embodiments of the present invention will be described.

[Process for preparing plate-like glass-based material]
Oxide and carbonate raw materials are mixed so as to have the composition of Table 1, and this is melted at a temperature of about 1250 to 1450 ° C. using a quartz or platinum crucible, and the raw material batch remains undissolved. After dissolving sufficiently so as not to occur, the temperature is raised to about 1350 to 1500 ° C., then the temperature is lowered to 1,450 to 1,250 ° C., and the bubbles generated in the glass are defoamed and clarified. It was. Thereafter, a predetermined amount of glass was poured out while maintaining the temperature, and the upper mold temperature was set to 300 ± 100 ° C. and the lower mold temperature was set to Tg ± 50 ° C. by a direct press method. Molded into a 95 mm disk. Next, in the case of crystallized glass, a disk-shaped ceramic setter and the obtained glass disk are alternately stacked, and crystals are precipitated by holding at a nucleation temperature of 670 ° C. for 3 hours and holding at a crystal growth temperature of 750 ° C. for 7 hours. I let you.

Each item in Table 1 includes crystallized glass and glass composition (mass%), specific gravity of the substrate after press molding, Vickers hardness, Young's modulus, average linear expansion coefficient (α) at 25 ° C to 100 ° C, crystallinity ( Mass%), crystal grain size (nm), and maximum crystal grain size (nm).
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.
The Vickers hardness was obtained by dividing a load (N) when a pyramid-shaped depression was made on a test surface by using a diamond square cone indenter having a facing angle of 136 ° by a surface area (mm ² ) calculated from the length of the depression. Indicated by value. Using a micro hardness tester MVK-E manufactured by Akashi Seisakusho Co., Ltd., the test load was 4.90 (N) and the holding time was 15 (seconds).

[Pre-processing process]
Next, a hole having a diameter of 18.7 mm was formed in the central portion with a core drill, and chamfering was performed by end face grinding of the outer peripheral portion and the inner peripheral portion.

[Grinding process]
1) Sub-step of the first stage Grinding was performed using a 16B double-side processing machine manufactured by Speed Fam Co., Ltd., diamond pellets or diamond pads of # 1000.
In some cases, the first sub-step is omitted, and the grinding step is only the final sub-step.
2) Second stage sub-process (final sub-process or only grinding process)
Grinding was performed using a 16B double-sided processing machine and a diamond pad manufactured by Speed Fam.

[Inner and outer periphery polishing process]
After the grinding step, the inner and outer peripheral end surfaces were polished smoothly.

[Polishing process]
1) Sub-process of the first stage Using a 16B double-sided processing machine manufactured by Speed Fam Co., Ltd., and a hard urethane foam polishing pad (hardness 90), a polishing slurry containing loose abrasive grains is supplied to perform the first-stage polishing process. did.
2) Second stage sub-process (final sub-process or only polishing process)
Using a 16B double-sided processing machine and a suede polishing pad manufactured by Speed Fem Co., the second stage polishing was performed while supplying a polishing slurry containing loose abrasive grains.

  Other processing conditions and processing results are shown in Tables 2 to 5. In the table, in the case of diamond pellets, the count of pellet abrasive grains is shown, and in the case of diamond pads, the average diameter of diamond particles is shown. Tables 6 and 7 show the polishing process performed after the grinding process of the present invention and the results thereof. In addition, Example 1 and Example 10 in Table 2 to Table 5 are reference examples of the present application.

Claims (11)

SiO ₂ component, Al ₂ O ₃ component, R ′ ₂ O component (where R ′ is any one or more of Li, Na, K), and MAl ₂ O ₄ , M ₂ TiO ₄ (however, M is a step of preparing a plate-like crystallized glass containing at least one selected from Zn, Mg, and Fe)
A grinding step of grinding the crystallized glass,
The grinding step consists only of grinding the crystallized glass with a diamond pad,
The grinding step is a method for manufacturing a substrate for information recording media to be ground with a diamond pad having an average diameter of diamond particles of 0.1 to 5 μm (however, before the step of grinding with the diamond pad, the main surface of the crystallized glass) Except those having a roughening step to roughen the surface) .   The method for manufacturing a substrate for an information recording medium according to claim 1, wherein the grinding step includes a sub-step of grinding with a diamond pad having an average diameter of diamond particles of 2 to 5 μm.   The method for manufacturing a substrate for an information recording medium according to claim 1, wherein the grinding step includes a final sub-step of grinding with a diamond pad having an average diameter of diamond particles of less than 0.1 to 2 μm.   4. The information according to claim 1, wherein the crystallized glass has a crystal grain size of a main crystal phase in a range of 0.5 nm to 20 nm and a crystallinity of 15% or less. 5. A method for manufacturing a substrate for a recording medium. The crystallized glass is mass% based on oxide,
SiO ₂ : 40 to 60%, and Al ₂ O ₃ : 7 to 20%, and R ′ ₂ O: 2 to 15% (where R ′ is one or more selected from Li, Na, and K)
The manufacturing method of the board | substrate for information recording media in any one of Claim 1 to 4 containing each component of these. The crystallized glass is mass% based on oxide,
TiO ₂ : 1 to 15%, and RO: 5 to 35% (where R is one or more selected from Mg, Ca, Sr, Ba, Zn, Fe)
The manufacturing method of the board | substrate for information recording media in any one of Claim 1 to 5 containing each component of these. The crystallized glass is mass% based on oxide,
The method for producing a substrate for an information recording medium according to any one of claims 1 to 6, comprising 5 to 25% of a ZnO component.   8. The information recording medium according to claim 1, wherein the grinding step uses a double-sided processing machine that holds and polishes a material to be ground between upper and lower surface plates, and has a maximum processing pressure of 3 kPa to 6 kPa. A method for manufacturing a substrate.   The method for manufacturing a substrate for an information recording medium according to claim 1, wherein a processing rate in the grinding step is 5 μm / min or more. Method of manufacturing a substrate for information recording medium according to any one of claims 1 to 9 surface roughness Ra after the grinding step is completed is 0.001Myuemu～0.085Myuemu. The information recording according to any one of claims 1 to 10, wherein a polishing step using free abrasive grains having a volume-based average particle diameter d50 of 10 nm to 100 nm is performed on the crystallized glass subjected to the grinding step. A method for manufacturing a medium substrate.