WO2014156114A1 - Procédé de fabrication de substrat de verre pour un milieu d'enregistrement d'informations - Google Patents

Procédé de fabrication de substrat de verre pour un milieu d'enregistrement d'informations Download PDF

Info

Publication number
WO2014156114A1
WO2014156114A1 PCT/JP2014/001687 JP2014001687W WO2014156114A1 WO 2014156114 A1 WO2014156114 A1 WO 2014156114A1 JP 2014001687 W JP2014001687 W JP 2014001687W WO 2014156114 A1 WO2014156114 A1 WO 2014156114A1
Authority
WO
WIPO (PCT)
Prior art keywords
polishing
base plate
glass substrate
glass
information recording
Prior art date
Application number
PCT/JP2014/001687
Other languages
English (en)
Japanese (ja)
Inventor
明広 坂本
塚田　和也
Original Assignee
Hoya株式会社
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Hoya株式会社 filed Critical Hoya株式会社
Publication of WO2014156114A1 publication Critical patent/WO2014156114A1/fr

Links

Images

Classifications

    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
    • G11B5/84—Processes or apparatus specially adapted for manufacturing record carriers
    • G11B5/8404—Processes or apparatus specially adapted for manufacturing record carriers manufacturing base layers
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09G—POLISHING COMPOSITIONS; SKI WAXES
    • C09G1/00—Polishing compositions
    • C09G1/02—Polishing compositions containing abrasives or grinding agents
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
    • C09K3/00—Materials not provided for elsewhere
    • C09K3/14—Anti-slip materials; Abrasives
    • C09K3/1409—Abrasive particles per se

Definitions

  • the present invention relates to a method for producing a glass substrate for an information recording medium.
  • a typical example of such an information recording apparatus is a hard disk drive apparatus.
  • a hard disk drive device is a device that magnetically records (writes) information on a magnetic disk (hard disk) as an information recording medium having a recording layer formed on a substrate, and reproduces (reads) the recorded information. is there.
  • a so-called substrate a glass substrate is preferably used.
  • the hard disk drive device keeps the magnetic head floating above the magnetic disk without contacting the magnetic disk when information is recorded on or read from the magnetic disk. It is known that the recording density can be improved by reducing the flying height of the magnetic head. In recent years, the recording density of magnetic disks has been increased, and the flying height of the magnetic head has been reduced to about several nanometers. For these reasons, in order to further reduce the flying height of the magnetic head and increase the recording density, it is required that the glass substrate for the information recording medium has high smoothness.
  • Such a glass substrate for an information recording medium is manufactured by cutting a glass base plate (glass blank) obtained from molten glass and then polishing it.
  • this polishing process include polishing using a polishing liquid containing cerium oxide as an abrasive.
  • a polishing process using a polishing liquid containing cerium oxide as an abrasive is often applied to a rough polishing process. That is, as a method for producing a glass substrate for information recording media, for example, a rough polishing step is first performed on a cut glass base plate with a polishing liquid containing cerium oxide as an abrasive, and further colloidal. Examples thereof include a method of performing a precision polishing step of polishing with a polishing liquid containing silica as an abrasive.
  • the glass substrate for information recording media with high smoothness was obtained by performing grinding
  • a hard polishing pad such as a hard urethane pad is often used as the polishing pad.
  • a hard polishing pad such as a hard urethane pad is often used as the polishing pad.
  • a high polishing rate can be achieved, but there is a tendency that scratches generated during polishing, that is, processing marks become deep.
  • the polishing of the glass base plate has a tendency that the polishing pad hits closer to the end portion than the central portion, and polishing at the end portion proceeds preferentially.
  • the glass substrate obtained is preferentially polished near the end portion rather than the central portion, that is, a so-called edge droop occurs.
  • the processing time for polishing is set to a time that can sufficiently prevent the occurrence of edging, the processing marks cannot be made small enough to meet the smoothness quality standard of the obtained glass substrate. .
  • a suede pad which is a soft polishing pad, as a polishing pad.
  • a rough polishing process is performed using a polishing liquid containing cerium oxide polishing abrasives as a polishing liquid, and a suede pad (polyurethane type) as a polishing pad. Examples thereof include a method for producing a glass substrate for a magnetic disk using a soft polisher.
  • a polishing process using a polishing solution containing cerium oxide as an abrasive and using a suede pad as a polishing pad causes a problem in a final glass substrate even if a subsequent polishing process, for example, a precision polishing process is performed.
  • the formation of such deep processing marks can be sufficiently suppressed. That is, this polishing process provides a glass substrate with higher smoothness than when a hard polishing pad is used as the polishing pad.
  • a polishing process using a polishing liquid containing cerium oxide as an abrasive and using a suede pad as a polishing pad has a problem that the polishing rate gradually decreases depending on the polishing time. Further, the reduction in the polishing rate tended to occur preferentially in the central portion rather than the end portion of the polishing pad. For this reason, there has been a problem associated with a decrease in the polishing rate in that a difference occurs in the finish such as the thickness of the polished glass base plate depending on the position at which the glass base plate contacts the polishing pad during polishing. Specifically, the difference also occurs depending on the position of the carrier that holds the glass base plate during the polishing process, and the difference also occurs depending on the position of the holding hole that holds the glass base plate even in the same carrier. There was a problem.
  • the present invention is an invention made in view of the above-mentioned circumstances, and manufacturing a glass substrate for information recording medium capable of manufacturing a sufficiently high quality glass substrate for information recording medium while maintaining an excellent polishing rate. It aims to provide a method.
  • One aspect of the present invention is a polishing step of polishing the surface of the glass base plate by relatively moving the glass base plate and the polishing pad in a state where a polishing liquid is supplied onto the glass base plate, A polishing step of cleaning the polished glass base plate after the polishing step, wherein the polishing pad is a suede pad, the polishing liquid contains cerium oxide and an acrylic polymer, and the acrylic acid
  • FIG. 1 is a schematic cross-sectional view showing an example of a polishing apparatus used in a polishing step in a method for manufacturing a glass substrate for an information recording medium according to an embodiment of the present invention.
  • FIG. 2 is a top view showing a glass base plate used in the method for manufacturing a glass substrate for an information recording medium according to an embodiment of the present invention.
  • FIG. 3 is a partial cross-sectional perspective view showing a magnetic disk as an example of an information recording medium using the glass substrate for information recording medium manufactured by the method for manufacturing the glass substrate for information recording medium according to one embodiment of the present invention. It is.
  • the reason why the above problems occur is that agglomerates are generated by polishing, and the agglomerates enter the recesses formed on the surface of the suede pad, which is a polishing pad. This was presumed to be due to clogging of the so-called polishing pad. Further, the inventors of the present invention, as the reason for the occurrence of clogging, that the generated agglomerates reduce the fluidity of the polishing liquid existing on the glass base plate or cause unevenness in the fluidity. The agglomerates stay on the polishing pad, so that the agglomerates accumulate on the polishing pad, and pressure is applied to the agglomerates on the surface of the polishing pad.
  • the present inventors as agglomerates, agglomerated by the adhesion of glass sludge and cerium oxide generated by polishing a glass base plate, and by polishing the glass base plate using cerium oxide It was inferred that there were aggregates of cerium oxide alone generated when metal ions such as Al ions, Mg ions, and Ca ions act on cerium oxide.
  • the inventors of the present invention have arrived at the present invention as described below by examining components to be added to the polishing liquid, paying attention to the suppression of aggregates due to polishing.
  • the method for manufacturing a glass substrate for an information recording medium according to the present embodiment includes the following polishing process and a cleaning process for cleaning the polished glass base plate after the polishing process. That is, the manufacturing method of the glass substrate for information recording media according to the present embodiment is not particularly limited as long as it includes the following polishing step and then includes a cleaning step.
  • the cleaning step may be a cleaning step in a conventionally known method for manufacturing a glass substrate for information recording medium, and the method for manufacturing a glass substrate for information recording medium according to the present embodiment is specifically a polishing step. However, it is not particularly limited except that it is a process as described below, and may be any conventionally known method for producing a glass substrate for an information recording medium.
  • the polishing step is a step of polishing the surface of the glass base plate by relatively moving the glass base plate and the polishing pad in a state where the polishing liquid is supplied onto the glass base plate.
  • a suede pad is used as the polishing pad, and a polishing liquid containing cerium oxide and an acrylic acid polymer as the polishing liquid, wherein the acrylic acid polymer has a weight average molecular weight of 10,000 to 50,000. Use.
  • a suede pad which is a soft polishing pad, is used as a polishing pad. It is possible to sufficiently suppress the formation of deep processing marks that cause a problem in a glass substrate that is a product. That is, a glass substrate with higher smoothness can be obtained than when a hard polishing pad is used as the polishing step and polishing pad. For this reason, it is not necessary to perform a subsequent polishing process, for example, a polishing time (processing time) in the precision polishing process for a long time, and the occurrence of edge fringing can be suppressed.
  • an acrylic acid polymer having a weight average molecular weight of 10,000 to 50,000 is added to the polishing liquid, so that the polishing speed corresponding to the polishing time can be increased.
  • the decrease can be sufficiently suppressed.
  • an acrylic acid polymer having a weight average molecular weight of 10,000 to 50,000 is added to the polishing liquid, so that a decrease in the initial polishing rate can be suppressed, so that the polishing rate can be improved.
  • the reason why the decrease in the polishing rate according to the polishing time is suppressed is considered to be because the occurrence of clogging of the polishing pad due to the aggregates is suppressed.
  • the reason why the occurrence of clogging is suppressed is considered to be as follows.
  • the acrylic acid polymer has a carboxyl group bonded to a polymer chain. It is considered that this carboxyl group interacts with the hydroxyl group on the surface of the glass sludge and the acrylic polymer wraps the glass sludge. This is considered to suppress the generation of aggregates due to adhesion between glass sludge and cerium oxide. Moreover, it is thought that the chelate effect with respect to metal ions, such as Al ion, Mg ion, and Ca ion which generate
  • the method for manufacturing the glass substrate for information recording medium according to the present embodiment is not particularly limited as long as it includes the polishing step and the cleaning step after the polishing step as described above.
  • polishing process is not specifically limited except being the above processes.
  • the polishing step may be any polishing step, but the polishing step according to the present embodiment is performed as the rough polishing step. It is preferable to perform a precision polishing step separately.
  • the polishing step is a rough polishing step, and further includes a precision polishing step of precisely polishing the surface of the glass base plate polished in the rough polishing step. It is preferable to provide. By doing so, as the glass base plate after the rough polishing step in the polishing step, a sufficiently high-quality glass base plate can be obtained, so by further precisely polishing the glass base plate, A sufficiently high quality glass substrate for information recording media can be obtained.
  • polishing step in the method for manufacturing the glass substrate for information recording medium according to the present embodiment will be described.
  • the polishing step is not particularly limited as long as it is the above-described polishing step. Specifically, it is a step of polishing the surface of the glass base plate by relatively moving the glass base plate and the polishing pad while supplying the polishing liquid onto the glass base plate.
  • a suede pad is used as the polishing pad, and a polishing liquid containing cerium oxide and an acrylic acid polymer as the polishing liquid, wherein the acrylic acid polymer has a weight average molecular weight of 10,000 to 50,000.
  • the weight average molecular weight here can be measured using gel permeation chromatography etc., for example.
  • the polishing pad used in this polishing step is a suede pad used in the polishing step when manufacturing the glass substrate for information recording medium, that is, a suede pad used for polishing both main surfaces of the glass base plate.
  • the suede pad is a suede type soft foamed resin pad whose surface (polishing layer) is made of a soft foamed resin such as soft foamed polyurethane.
  • the suede pad is a polishing pad in which bubbles are open to the surface (pad surface), and there are relatively many soft walls separating the bubbles.
  • the pad surface hardness of the polishing pad is preferably from 60 to 90, more preferably from 70 to 84, and even more preferably from 75 to 84 in terms of Asker C hardness.
  • the diameter (open diameter) of the bubbles opened to the pad surface is preferably 20 to 80 ⁇ m.
  • the density of the polishing layer disposed on the surface of the polishing pad is preferably 0.55 to 0.62 g / m 3 .
  • a so-called non-buffing polishing pad in which the pad surface of the polishing pad is not buffed is preferable.
  • the polishing pad used in the polishing process specifically, a polyurethane suede pad is used, and for example, NP178 (Asker C hardness 82) manufactured by Filwel is used.
  • polishing liquid used in the polishing step is not particularly limited as long as it is a polishing liquid having the above configuration.
  • the cerium oxide contained in the polishing liquid is not particularly limited.
  • the oxide used as an abrasive contained in the polishing liquid used in the polishing process when manufacturing a glass substrate for an information recording medium It only has to be cerium. That is, the cerium oxide may be in the form of a powder having a shape and a particle diameter that can be used as an abrasive when producing a glass substrate for an information recording medium.
  • the polishing liquid may contain an abrasive other than cerium oxide, but it is preferable that the abrasive is only cerium oxide.
  • abrasive other than cerium oxide contains an abrasive other than cerium oxide, in order to ensure a polishing rate and obtain a glass substrate of excellent quality, the content of abrasive other than cerium oxide is polished. It is preferable that it is 20 mass% or less with respect to material whole quantity.
  • abrasives other than cerium oxide include particles (abrasive grains) such as aluminum oxide (alumina), zirconium oxide (zirconia), silicon carbide, titanium oxide (titania), and iron oxide.
  • the average particle diameter of cerium oxide may be any particle diameter that can be used as an abrasive when producing a glass substrate for information recording media, as described above.
  • the thickness is preferably 0.5 to 1.2 ⁇ m, and more preferably 0.6 to 1 ⁇ m.
  • the average particle diameter here is a median diameter (D50), and can be calculated from, for example, a particle size distribution measured using a laser diffraction scattering method or the like.
  • the content of cerium oxide varies depending on polishing conditions and the like, for example, it is preferably 6 to 20% by mass, and more preferably 10 to 15% by mass with respect to the total amount of the polishing liquid. If content of cerium oxide is in the said range, while being able to ensure an appropriate polishing rate, a higher quality glass substrate can be obtained.
  • the acrylic acid polymer contained in the polishing liquid is not particularly limited as long as the weight average molecular weight is 10,000 to 50,000. If such an acrylic acid polymer is added to the polishing liquid, it is possible to sufficiently suppress a decrease in the polishing rate corresponding to the polishing time. Further, as described above, the weight average molecular weight of the acrylic acid-based polymer is 10,000 to 50,000, more preferably 15,000 to 30,000, and further preferably 20,000 to 28,000. If the molecular weight of an acrylic acid polymer is too small or too large, the effect of containing an acrylic acid polymer, that is, the effect of suppressing the decrease in polishing rate due to the inclusion of an acrylic acid polymer will be sufficiently exerted. There is a tendency to become impossible.
  • the acrylic acid polymer is not particularly limited as long as it is a polymer obtained by polymerizing a monomer containing an acrylic acid component such as acrylic acid, acrylic acid salt or acrylic acid derivative. That is, the acrylic polymer includes a polymer obtained by polymerizing not only acrylic acid, an acrylate salt or an acrylic acid derivative as a monomer but also a monomer mixed with a monomer copolymerizable therewith. Specific examples of the acrylic acid polymer include sodium polyacrylate, acrylic acid-maleic acid copolymer, polyacrylic acid, acrylic acid-sulfonic acid monomer copolymer, and the like. As the acrylic polymer, each of the acrylic acid polymers exemplified above may be used alone, or two or more of them may be used in combination.
  • the acrylic acid-based polymer preferably contains a maleic acid component in a polymer chain such as an acrylic acid-maleic acid copolymer.
  • a polymer containing this maleic acid component as the acrylic acid-based polymer, it is possible to further suppress the decrease in the initial polishing rate and the decrease in the polishing rate according to the polishing time by adding the polymer component. Therefore, a more excellent polishing rate can be maintained. This is considered to be because the carboxyl group concentration in the acrylic acid polymer is increased, and the effect of suppressing the generation of aggregates can be further exhibited by the action of the carboxyl group. More specifically, for example, a chelating effect on metal ions such as Al ions, Mg ions, and Ca ions can be exhibited more.
  • the content of the acrylic acid polymer is preferably 0.3 to 1 part by mass and more preferably 0.6 to 0.8 part by mass with respect to 100 parts by mass of the polishing liquid. If the content of the acrylic acid polymer is within the above range, a sufficiently high quality glass substrate for information recording media can be produced while maintaining an excellent polishing rate. That is, the effect of adding the acrylic acid polymer can be suitably exhibited.
  • the polishing apparatus used in this polishing step is not particularly limited as long as it is a polishing apparatus used for manufacturing a glass substrate for an information recording medium. Specifically, there is a polishing apparatus 11 as shown in FIG. FIG. 1 is a schematic cross-sectional view showing an example of a polishing apparatus used in a polishing step in the method for manufacturing a glass substrate for information recording medium according to the present embodiment.
  • a polishing apparatus 11 as shown in FIG. 1 is an apparatus capable of simultaneously polishing both surfaces of the main surface of a glass base plate.
  • the polishing apparatus 11 also includes an apparatus main body (polishing main body) 11a and a polishing liquid supply unit 11b that supplies a polishing liquid (polishing slurry) to the apparatus main body 11a.
  • the apparatus main body 11a includes two surface plates 12 and 13 arranged to face each other.
  • the positional relationship between the respective surface plates is not limited to the upper and lower sides.
  • the surface plate disposed on the upper side is the upper surface plate 12, and the surface plate disposed on the lower side is This is referred to as the lower surface plate 13.
  • the apparatus main body 11a includes a disk-shaped upper surface plate 12 and a disk-shaped lower surface plate 13, and they are arranged at an interval in the vertical direction so that they are parallel to each other. Then, the disk-shaped upper surface plate 12 and the disk-shaped lower surface plate 13 rotate in directions opposite to each other.
  • a polishing pad 15 for polishing both the front and back surfaces of the glass base plate 10 is attached to each surface of the disk-shaped upper surface plate 12 and the disk-shaped lower surface plate 13 facing each other.
  • a rotatable carrier 14 is provided between the disk-shaped upper surface plate 12 and the disk-shaped lower surface plate 13.
  • the carrier 14 is formed with a plurality of base plate holding holes 51, and the glass base plate 10 can be fitted into the base plate holding holes 51 and disposed.
  • 100 base plate holding holes 51 may be formed, and 100 glass base plates 10 may be fitted and arranged. If it does so, 100 glass base plates can be processed by one process (1 batch).
  • the carrier 14 sandwiched between the surface plates 12 and 13 through the polishing pad 15 is the same as the lower surface plate 13 with respect to the center of rotation of the surface plates 12 and 13 while rotating while holding the glass base plate 10. Revolve in the direction.
  • the disk-shaped upper surface plate 12 and the disk-shaped lower surface plate 13 can be operated by separate driving.
  • the polishing liquid 16 is supplied between the upper surface plate 12 and the glass base plate 10 and between the lower surface plate 13 and the glass base plate 10, respectively.
  • the glass base plate 10 can be polished.
  • the polishing liquid 16 is the above-described polishing liquid.
  • the polishing liquid supply unit 11b includes a liquid storage unit 110 and a liquid recovery unit 120.
  • the liquid reservoir 110 includes a liquid reservoir main body 110a and a liquid supply pipe 110b having a discharge port 110e extending from the liquid reservoir main body 110a to the apparatus main body 11a.
  • the liquid recovery part 120 was extended from the liquid recovery part main body 120a, the liquid recovery pipe 120b extended from the liquid recovery part main body 120a to the apparatus main body 11a, and from the liquid recovery part main body 120a to the polishing liquid supply part 11b.
  • a liquid return pipe 120c was extended from the liquid recovery part main body 120a, the liquid recovery pipe 120b extended from the liquid recovery part main body 120a to the apparatus main body 11a, and from the liquid recovery part main body 120a to the polishing liquid supply part 11b.
  • a liquid return pipe 120c was extended from the liquid recovery part main body 120a, the liquid recovery pipe 120b extended from the liquid recovery part main body 120a to the apparatus main body 11a, and from the liquid recovery part main body 120a
  • the polishing liquid 16 put in the liquid storage unit main body 110a is supplied from the discharge port 110e of the liquid supply pipe 110b to the apparatus main body part 11a, and from the apparatus main body part 11a through the liquid recovery pipe 120b, the liquid recovery part main body 120a.
  • the recovered polishing liquid 16 is returned to the liquid storage part 110 via the liquid return pipe 120c, and can be supplied again to the apparatus main body part 11a.
  • polishing liquid used in a circulating manner (circulation use)
  • a new polishing liquid is always used without recovering the polishing liquid used for polishing. It may be a case where a polishing liquid is used (flowing use).
  • the reason for using the polishing liquid by pouring is that if polishing sludge (polishing waste, glass sludge) generated by polishing is present in the polishing liquid, it may cause scratches on the surface of the glass substrate.
  • the polishing pad used in the polishing process is the suede pad described above.
  • the method for manufacturing the glass substrate for information recording medium according to the present embodiment preferably performs the polishing process according to the present embodiment as a rough polishing process and separately performs a precision polishing process.
  • a precision polishing process is not particularly limited as long as it is a general precision polishing process in the method for producing a glass substrate for information recording medium.
  • the precision polishing step maintains a flat and smooth main surface obtained in the rough polishing step (the polishing step), for example, and a smooth mirror surface having a surface roughness (Rmax) of the main surface of about 0.3 nm or less. This is a mirror polishing process that finishes.
  • This precision polishing step may be performed using, for example, a polishing apparatus similar to that used in the above polishing step. Note that the surface to be polished in the precision polishing step is the main surface, similar to the surface to be polished in the polishing step.
  • polishing liquid used in the precision polishing process polishing including an abrasive that causes less scratching even if the polishing performance is lower than that of cerium oxide, which is an abrasive included in the polishing liquid used in the rough polishing process.
  • Liquid is used.
  • a polishing liquid containing silica-based abrasive grains such as colloidal silica can be used as the abrasive.
  • the average particle diameter of the silica-based abrasive is preferably about 20 nm, for example.
  • a polishing liquid (slurry liquid) containing the abrasive is supplied to the glass base plate, and the surface of the glass base plate is mirror-polished by sliding the polishing pad and the glass base plate relatively.
  • the cleaning step is not particularly limited as long as the glass base plate polished by the polishing step can be cleaned.
  • the washing step includes a washing step in a conventionally known method for producing a glass substrate for an information recording medium, and more specifically, a washing step described later.
  • the method for manufacturing a glass substrate for information recording medium may include the polishing step, but may include other steps.
  • a method including a disk machining process, a grinding process (lapping process), an internal / external grinding process, an end surface polishing process, a chemical strengthening process, a polishing process (polishing process), and a cleaning process can be used. And each said process may be performed in this order, and a chemical strengthening process may be performed after a grinding
  • a method including steps other than these may be used.
  • polishing process performs the said grinding
  • the disk processing step is a step of processing the raw glass into a disk-shaped glass base plate 10 in which a through hole 10a is formed in the center so that the inner periphery and the outer periphery are concentric circles as shown in FIG. is there.
  • a glass melting step in which raw glass is melted in a melting furnace to form molten glass
  • a forming step in which the molten glass is formed into a disc-shaped glass base plate, and the formed disc-shaped glass base plate
  • the coring process which forms the through-hole 10a in the center part of this, and is processed into the disk shaped glass base plate 10 as shown in FIG. 2 etc. is provided.
  • FIG. 2 is a top view showing a glass base plate used in the method for manufacturing a glass substrate for information recording medium according to the present embodiment.
  • the glass melting step is not particularly limited as long as raw glass can be melted in a melting furnace to obtain molten glass.
  • the starting glass is not particularly limited, for example, SiO 2, Na 2 O, and soda-lime glass composed mainly of CaO, SiO 2, Al 2 O 3, and R 1 in 2 O (wherein, R 1 is , K, Na, or Li)), aluminosilicate glass, borosilicate glass, Li 2 O—SiO 2 glass, Li 2 O—Al 2 O 3 —SiO 2 Glass, R 2 O—Al 2 O 3 —SiO 2 glass (wherein R 2 represents Mg, Ca, Sr, or Ba).
  • the glass composition is 55 to 75% by mass of SiO 2 , 5 to 18% by mass of Al 2 O 3 , 1 to 10% by mass of Li 2 O, and 3 to 15% by mass of Na 2 O. %, K 2 O is 0.1 to 5% by mass, MgO is 0.1 to 5% by mass, and CaO is 0.1 to 5% by mass.
  • aluminosilicate glass and borosilicate glass are preferable in that they are excellent in impact resistance and vibration resistance.
  • it does not specifically limit as a melting method of raw material glass, Usually, the method of fuse
  • the forming step is not particularly limited as long as the molten glass can be formed into a disk-shaped glass base plate.
  • the press process etc. which form a disk shaped glass base plate by press molding molten glass are mentioned.
  • the forming step is not limited to the pressing step, and may be a step of, for example, cutting a sheet glass formed by a downdraw method or a float method with a grinding stone to produce a disk-shaped glass base plate.
  • the float method is, for example, a method in which a molten liquid obtained by melting a glass material is poured onto molten tin and solidified as it is.
  • the smoothness is high, for example, the arithmetic average roughness Ra is 0.001 ⁇ m.
  • the following mirror surface is provided.
  • a thickness of a glass base plate a 0.95 mm thing is mentioned, for example.
  • the surface roughness of a glass base plate or a glass substrate for example, Ra or Rmax, can be measured using a general surface roughness measuring machine.
  • the coring process is a process of performing a coring process in which a through hole 10a is formed at the center of the disk-shaped glass base plate formed in the forming process.
  • the disk-shaped glass base plate 10 in which the through-hole 10a was formed in the center part as shown in FIG. 2 is obtained.
  • the coring process is not particularly limited as long as it is a drilling process that forms a through hole in the center of the glass base plate.
  • a method of forming a through hole in the center of the glass base plate by grinding with a core drill equipped with a diamond grindstone or the like, a cylindrical diamond drill, or the like can be used. By doing so, a through hole is formed in the center of the glass base plate, and an annular glass base plate is obtained in plan view.
  • the outer diameter r1 is 2.5 inches (about 64 mm), 1.8 inches (about 46 mm), 1 inch (about 25 mm), 0.8 inches (about 20 mm), etc., and the thickness is Disc-shaped glass base plates of 2 mm, 1 mm, 0.63 mm, etc. are obtained. Further, when the outer diameter r1 is 2.5 inches (about 64 mm), for example, the inner diameter r2 is processed to 0.8 inches (about 20 mm).
  • the grinding step is a step of processing the glass base plate to a predetermined plate thickness. Specifically, for example, a step of grinding (lapping) both surfaces of the glass base plate can be mentioned. By doing so, the parallelism, flatness and thickness of the glass base plate are adjusted. Further, this lapping step may be performed once or twice or more. For example, when it is performed twice, the parallelism, flatness and thickness of the glass base plate are preliminarily adjusted in the first lapping process (first lapping process), and glass is used in the second lapping process (second lapping process). Finely adjust the parallelism, flatness and thickness of the base plate. Moreover, when performing a grinding process twice, you may perform a 1st lapping process and a 2nd lapping process continuously, but perform the inside-and-outside grinding process mentioned later and an end surface grinding
  • the grinding apparatus used in the grinding process is not particularly limited as long as it can be used as a grinding apparatus used in the grinding process in the method of manufacturing the glass substrate for information recording medium. Specifically, it is the same as the polishing apparatus used in the polishing step, and includes a resin sheet (grinding sheet) using diamond as a fixed abrasive instead of the polishing pad.
  • examples of the first lapping step include a step in which the entire surface of the glass base plate has a substantially uniform surface roughness.
  • the grinding sheet used in the first lapping step for example, it is preferable to use one having an average particle diameter of 6 to 12 ⁇ m of fixed abrasive grains.
  • the difference between the minimum value and the maximum value of Ra obtained is about 0.01 to 0.4 ⁇ m. It is preferable to do.
  • examples of the second lapping step include a step in which a glass base plate from which defects such as large undulations, chips and cracks are removed can be obtained.
  • the grinding sheet used in the second lapping step for example, it is preferable to use a fixed abrasive having an average particle diameter of 0.5 to 4 ⁇ m, and preferably 1 to 2 ⁇ m.
  • Rmax of the obtained glass base plate is preferably set to 0.5 to 2 ⁇ m.
  • Ra is preferably 0.1 to 0.5 ⁇ m. If the surface of the glass base plate after the second lapping step is too rough, it is difficult to obtain a glass substrate having sufficiently high smoothness even if the polishing step is performed.
  • the glass base plate after the second lapping step is preferably as smooth as possible, that is, as Ra is small, but in the lapping step, about 0.01 ⁇ m is the limit, and 0.01 ⁇ m is the limit. This is considered to be the lower limit value of the arithmetic average roughness Ra of the glass base plate after the second lapping step.
  • the inner / outer grinding step is a step of grinding the outer peripheral end surface and the inner peripheral end surface of the glass base plate. Specifically, the process etc. which grind the outer peripheral end surface and inner peripheral end surface of a glass base plate with grinding wheels, such as a drum-shaped diamond grindstone, are mentioned.
  • the end surface polishing step is a step of polishing the outer peripheral end surface and the inner peripheral end surface of the glass base plate. Specifically, a plurality of glass base plates subjected to the inner and outer grinding steps, for example, about 100, are stacked and laminated, and in this state, the outer peripheral end surface and the inner peripheral end surface are polished using an end surface polishing machine. And the like.
  • the chemical strengthening step is not particularly limited, and specific examples include a step of immersing a glass base plate in a chemical strengthening solution (strengthening treatment solution) to form a chemical strengthening layer on the glass base plate.
  • a chemical strengthening layer can be formed in the surface of a glass base plate, for example, a 5 micrometer area
  • a chemical strengthening layer impact resistance, vibration resistance, heat resistance, etc. can be improved.
  • alkali metal ions such as lithium ions and sodium ions contained in the glass base plate are potassium having a larger ion radius. It is carried out by an ion exchange method for substituting alkali metal ions such as ions. Due to the strain caused by the difference in ion radius, compressive stress is generated in the ion-exchanged region, and the surface of the glass base plate is strengthened. That is, it is considered that the reinforcing layer is suitably formed on the glass base plate by this chemical strengthening step.
  • the chemical strengthening treatment solution is not particularly limited as long as it is a chemical strengthening treatment solution used in the chemical strengthening step in the method for producing a glass substrate for a magnetic information recording medium.
  • a melt containing potassium ions a melt containing potassium ions and sodium ions, and the like can be given.
  • melts obtained by melting potassium nitrate, sodium nitrate, potassium carbonate, sodium carbonate, and the like examples include melts obtained by melting potassium nitrate, sodium nitrate, potassium carbonate, sodium carbonate, and the like.
  • a melt obtained by melting potassium nitrate and a melt obtained by melting sodium nitrate are preferably mixed in approximately the same amount.
  • the cleaning step is a step of cleaning the glass base plate. It is preferable that the washing process is appropriately performed after each process. Moreover, scrub cleaning is mentioned as a final-cleaning process which wash
  • the apparatus for scrub cleaning (scrub cleaning apparatus) is not particularly limited as long as it is an apparatus capable of scrub cleaning an information recording medium glass substrate. Specifically, a roll scrub cleaning device in which the scrub member is a cylindrical roll scrub, a cup scrub cleaning device in which the scrub member is a cup type, and the like can be given.
  • the glass base plate or the glass substrate before the cleaning step such as the final cleaning step is kept in contact with the liquid in order to prevent foreign matter from adhering to the surface. It is preferable.
  • the final cleaning step it is preferable to perform ultrasonic cleaning after scrub cleaning.
  • the glass substrate is dried.
  • drying method include drying with IPA vapor, spin drying, and hot water drying.
  • FIG. 3 is a partial cross-sectional perspective view showing a magnetic disk as an example of a magnetic recording medium using the glass substrate for information recording medium manufactured by the method for manufacturing the glass substrate for information recording medium according to the present embodiment.
  • This magnetic disk D includes a magnetic film 102 formed on the main surface of a circular glass substrate 101 for an information recording medium. For the formation of the magnetic film 102, a known method is used.
  • a formation method for forming the magnetic film 102 by spin-coating a thermosetting resin in which magnetic particles are dispersed on the glass substrate 101 for information recording medium
  • examples thereof include a forming method for forming the magnetic film 102 by sputtering (sputtering method) and a forming method for forming the magnetic film 102 on the glass substrate 101 for information recording medium by electroless plating (electroless plating method).
  • the thickness of the magnetic film 102 is about 0.3 to 1.2 ⁇ m in the case of the spin coating method, and about 0.04 to 0.08 ⁇ m in the case of the sputtering method, and is based on the electroless plating method. In some cases, the thickness is about 0.05 to 0.1 ⁇ m. From the viewpoint of thinning and densification, film formation by sputtering is preferable, and film formation by electroless plating is preferable.
  • the magnetic material used for the magnetic film 102 can be any known material and is not particularly limited.
  • the magnetic material is preferably, for example, a Co-based alloy based on Co having high crystal anisotropy in order to obtain a high coercive force, and Ni or Cr added for the purpose of adjusting the residual magnetic flux density. More specifically, CoPt, CoCr, CoNi, CoNiCr, CoCrTa, CoPtCr, CoNiPt, CoNiCrPt, CoNiCrTa, CoCrPtB, CoCrPtSiO, and the like whose main component is Co can be given.
  • the magnetic film 102 has a multilayer structure (for example, CoPtCr / CrMo / CoPtCr, CoCrPtTa / CrMo / CoCrPtTa, etc.) divided by a nonmagnetic film (for example, Cr, CrMo, CrV, etc.) in order to reduce noise.
  • a multilayer structure for example, CoPtCr / CrMo / CoPtCr, CoCrPtTa / CrMo / CoCrPtTa, etc.
  • ferrite or iron - may be a rare earth, also, Fe in a non-magnetic film made of SiO 2, BN, etc., Co, FeCo, CoNiPt and the like
  • a granular material having a structure in which the magnetic particles are dispersed may be used.
  • either an inner surface type or a vertical type recording format may be used for recording on the magnetic film 102.
  • the surface of the magnetic film 102 may be thinly coated with a lubricant.
  • a lubricant include those obtained by diluting perfluoropolyether (PFPE), which is a liquid lubricant, with a freon-based solvent.
  • an underlayer or a protective layer may be provided on the magnetic film 102 as necessary.
  • the underlayer in the magnetic disk D is appropriately selected according to the magnetic film 102.
  • the material for the underlayer include at least one material selected from nonmagnetic metals such as Cr, Mo, Ta, Ti, W, V, B, Al, and Ni.
  • the material of the underlayer is preferably Cr alone or a Cr alloy from the viewpoint of improving magnetic characteristics.
  • the underlayer is not limited to a single layer, and may have a multilayer structure in which the same or different layers are stacked.
  • Examples of such an underlayer having a multilayer structure include multilayer underlayers such as Cr / Cr, Cr / CrMo, Cr / CrV, NiAl / Cr, NiAl / CrMo, and NiAl / CrV.
  • Examples of the protective layer that prevents wear and corrosion of the magnetic film 102 include a Cr layer, a Cr alloy layer, a carbon layer, a hydrogenated carbon layer, a zirconia layer, and a silica layer. These protective layers can be continuously formed with the underlayer and the magnetic film 102 by an in-line sputtering apparatus. These protective layers may be a single layer, or may be a multi-layer structure composed of the same or different layers.
  • a SiO 2 layer may be formed on the Cr layer.
  • Such a SiO 2 layer is formed by dispersing and applying colloidal silica fine particles in a tetraalkoxysilane diluted with an alcohol-based solvent on the Cr layer and further baking.
  • the information recording medium glass substrate 101 is formed with the above-described composition. Can be done by sex.
  • the glass substrate 101 for information recording media in this embodiment was used for a magnetic recording medium (magnetic disk) was demonstrated above, it is not limited to this, for information recording media in this embodiment
  • the glass substrate 101 can also be used for magneto-optical disks, optical disks, and the like.
  • One aspect of the present invention is a polishing step of polishing the surface of the glass base plate by relatively moving the glass base plate and the polishing pad in a state where a polishing liquid is supplied onto the glass base plate, A polishing step of cleaning the polished glass base plate after the polishing step, wherein the polishing pad is a suede pad, the polishing liquid contains cerium oxide and an acrylic polymer, and the acrylic acid
  • a suede pad which is a soft polishing pad, is used as a polishing pad. It is possible to sufficiently suppress the formation of deep processing marks that cause a problem in a glass substrate that is a product. That is, a glass substrate with higher smoothness can be obtained than when a hard polishing pad is used as the polishing step and polishing pad. For this reason, it is not necessary to perform a subsequent polishing process, for example, a polishing time (processing time) in the precision polishing process for a long time, and the occurrence of edge fringing can be suppressed.
  • an acrylic acid polymer having a weight average molecular weight of 10,000 to 50,000 is added to the polishing liquid, so that the polishing speed corresponding to the polishing time can be increased.
  • the decrease can be sufficiently suppressed.
  • a polymer component is added to the polishing liquid, it is considered that the initial polishing rate is lowered.
  • the polymer component to be added has a weight average molecular weight of 10,000 to 50,000, the polymer component may be added.
  • the polishing rate can be improved.
  • a method for manufacturing a glass substrate for information recording medium which can manufacture a sufficiently high quality glass substrate for information recording medium while maintaining an excellent polishing rate. be able to.
  • the acrylic polymer has a weight average molecular weight of 15000 to 30000.
  • the acrylic polymer contains a maleic acid component in a polymer chain.
  • the acrylic acid polymer is more preferably an acrylic acid-maleic acid copolymer.
  • the method for manufacturing the glass substrate for information recording medium preferably includes a precision polishing step for precisely polishing the surface of the glass base plate polished in the polishing step.
  • a sufficiently high-quality glass base plate can be obtained as the glass base plate after the rough polishing step in the polishing step, so that the glass base plate is further precisely polished.
  • a sufficiently high quality glass substrate for information recording media can be obtained.
  • both main surfaces of the obtained glass base plate were ground using a double-side grinding machine.
  • the coring process was given to the glass base plate which gave the grinding process, and the through-hole was formed in the center part of the glass base plate.
  • a circular center hole (through hole) having a diameter of about 19.6 mm was formed in the center of the ground glass plate using a core drill equipped with a cylindrical diamond grindstone.
  • an inner and outer grinding step was performed on the glass base plate. Specifically, the outer peripheral end face and the inner peripheral end face of the glass base plate were ground using a drum-shaped diamond grindstone so that the outer diameter of the glass base plate was 65 mm and the inner diameter was 20 mm. Then, the end surface process was performed with respect to the glass base plate. Specifically, with 100 glass base plates stacked, the outer peripheral end surface and the inner peripheral end surface of the glass base plate were polished using an end surface polishing machine. Nylon fiber having a diameter of 0.2 mm was used as the brush hair of the polishing machine. As the polishing liquid, a slurry containing cerium oxide having an average primary particle diameter of 3 ⁇ m as abrasive grains was used. Thereafter, both surfaces of the glass base plate were processed using a diamond sheet with a double-side grinding machine.
  • the glass base plate thus obtained was subjected to a polishing process. Specifically, both main surfaces of the glass base plate were polished using a polishing apparatus as shown in FIG. At that time, a suede pad (NP178 manufactured by Filwel: Asker C hardness 82) was used as a polishing pad.
  • a polishing liquid a polishing liquid containing the additives shown in Table 1 was used. Specifically, as the polishing liquid, 10% by mass of cerium oxide having an average particle diameter (D50) of 0.8 ⁇ m, and when added, acrylic acid-maleic acid copolymer (weight average molecular weight: 10,000) 0.75 mass %, And the balance was water.
  • a final cleaning process was performed on the glass substrate that had been subjected to the precision polishing process. Specifically, scrub cleaning was first performed. At that time, a liquid obtained by adding a nonionic surfactant to increase the cleaning ability was used as the cleaning liquid. Thereafter, in order to remove the cleaning liquid remaining on the surface of the lath substrate, a water rinse cleaning process was performed in an ultrasonic bath for 2 minutes, and an IPA cleaning process was performed in an ultrasonic bath for 2 minutes. Finally, the surface was dried with IPA vapor. By doing so, a glass substrate was obtained.
  • the polishing liquid in the polishing step is the same as that of Example 1 except that a polishing liquid containing the additives shown in Table 1 is used as an additive.
  • the “acrylic acid-maleic acid copolymer” in Table 1 is a copolymer obtained by polymerizing a monomer containing an acrylic acid component and maleic acid.
  • the “acrylic acid-sulfonic acid monomer copolymer” is a copolymer obtained by polymerizing a monomer containing an acrylic acid component and vinyl sulfonic acid or a salt thereof.
  • the “polyacrylic acid polymer” is a polymer obtained by polymerizing a monomer containing an acrylic acid component.
  • the thickness of the glass base plate before and after the polishing step was measured using a micrometer manufactured by Mitutoyo Corporation. If the difference in the thickness of the glass base plate before and after the polishing step is 1 ⁇ m or less, it is evaluated as “ ⁇ ”, and if it exceeds 1 ⁇ m and less than 3 ⁇ m, it is evaluated as “ ⁇ ”. “ ⁇ ”.
  • the polishing rate of the first batch in the polishing process of each example and comparative example was measured.
  • the polishing rate of the ninth batch in the polishing step of each example and comparative example was measured. If the rate of decrease of the 9th batch polishing rate relative to the 1st batch polishing rate is 10% or less, it is evaluated as “ ⁇ ”. If it was 15% or more, it was evaluated as “ ⁇ ”.
  • a polishing pad using a suede pad as a polishing pad and a polishing liquid containing cerium oxide and an acrylic acid polymer having a weight average molecular weight of 10,000 to 50,000 was used as a polishing liquid.
  • the initial polishing rate was higher than in the case of using other polishing liquids (Comparative Examples 1 to 3), and the durability of the excellent polishing rate was excellent. It was found that a high-quality glass substrate with a small amount of etc. can be obtained.
  • the present invention it is possible to provide a method for producing a glass substrate for information recording medium that can produce a sufficiently high quality glass substrate for information recording medium while maintaining an excellent polishing rate.

Landscapes

  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Organic Chemistry (AREA)
  • Manufacturing & Machinery (AREA)
  • Materials Engineering (AREA)
  • Manufacturing Of Magnetic Record Carriers (AREA)

Abstract

Un aspect de la présente invention concerne un procédé de fabrication d'un substrat de verre pour un milieu d'enregistrement d'informations, comprenant un procédé de polissage pour polir la surface de la plaque originale de verre en amenant la plaque originale de verre et un tampon de polissage à se déplacer l'un par rapport à l'autre tandis qu'un liquide de polissage est introduit sur la plaque originale de verre; et un procédé de nettoyage pour nettoyer la plaque originale de verre polie après le procédé de polissage. Le tampon de polissage est un tampon de velours; le liquide de polissage contient de l'oxyde de cérium et des polymères à base d'acide acrylique; et la masse moléculaire moyenne en poids des polymères à base d'acide acrylique est 10 000 à 50 000.
PCT/JP2014/001687 2013-03-25 2014-03-25 Procédé de fabrication de substrat de verre pour un milieu d'enregistrement d'informations WO2014156114A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
JP2013062223 2013-03-25
JP2013-062223 2013-03-25

Publications (1)

Publication Number Publication Date
WO2014156114A1 true WO2014156114A1 (fr) 2014-10-02

Family

ID=51623127

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/JP2014/001687 WO2014156114A1 (fr) 2013-03-25 2014-03-25 Procédé de fabrication de substrat de verre pour un milieu d'enregistrement d'informations

Country Status (1)

Country Link
WO (1) WO2014156114A1 (fr)

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2008515764A (ja) * 2005-10-14 2008-05-15 エルジー・ケム・リミテッド Ｃｍｐスラリー用酸化セリウム粉末の製造方法及びこれを用いたｃｍｐ用スラリー組成物の製造方法
JP2009067627A (ja) * 2007-09-13 2009-04-02 Mitsui Mining & Smelting Co Ltd 酸化セリウム及びその製造方法
JP2009084565A (ja) * 2007-09-14 2009-04-23 Kao Corp アルカリ型非イオン性界面活性剤組成物
JP2011136388A (ja) * 2009-12-28 2011-07-14 Shin-Etsu Chemical Co Ltd 合成石英ガラス基板の製造方法
JP2013039639A (ja) * 2011-08-17 2013-02-28 Asahi Glass Co Ltd 板状体研磨装置及び研磨システム

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2008515764A (ja) * 2005-10-14 2008-05-15 エルジー・ケム・リミテッド Ｃｍｐスラリー用酸化セリウム粉末の製造方法及びこれを用いたｃｍｐ用スラリー組成物の製造方法
JP2009067627A (ja) * 2007-09-13 2009-04-02 Mitsui Mining & Smelting Co Ltd 酸化セリウム及びその製造方法
JP2009084565A (ja) * 2007-09-14 2009-04-23 Kao Corp アルカリ型非イオン性界面活性剤組成物
JP2011136388A (ja) * 2009-12-28 2011-07-14 Shin-Etsu Chemical Co Ltd 合成石英ガラス基板の製造方法
JP2013039639A (ja) * 2011-08-17 2013-02-28 Asahi Glass Co Ltd 板状体研磨装置及び研磨システム

Similar Documents

Publication Publication Date Title
JP4982810B2 (ja) ガラス基板の製造方法および磁気ディスクの製造方法
JP5321594B2 (ja) ガラス基板の製造方法、および磁気記録媒体の製造方法
WO2010041536A1 (fr) Procédé pour produire un substrat de verre, et procédé pour produire un support d'enregistrement magnétique
JP2009087483A (ja) 情報記録媒体用ガラス基板の製造方法、情報記録媒体用ガラス基板及び磁気記録媒体
JP5706250B2 (ja) Ｈｄｄ用ガラス基板
JP5759171B2 (ja) ハードディスク用ガラス基板の製造方法
WO2014103284A1 (fr) Procédé pour la production de substrat en verre pour support d'enregistrement d'informations
WO2014156114A1 (fr) Procédé de fabrication de substrat de verre pour un milieu d'enregistrement d'informations
JP6104668B2 (ja) 情報記録媒体用ガラス基板の製造方法、及びキャリア
JP2008204499A (ja) 情報記録媒体用ガラス基板及び磁気記録媒体
WO2013001722A1 (fr) Procédé permettant de produire un substrat de verre pour disque dur
JP5636243B2 (ja) 情報記録媒体用ガラス基板の製造方法
JP2012079365A (ja) 情報記録媒体用ガラス基板の製造方法
JP5859757B2 (ja) Ｈｄｄ用ガラス基板の製造方法
JP5667403B2 (ja) 情報記録媒体用ガラス基板の製造方法
JP5177328B2 (ja) 磁気情報記録媒体用ガラス基板の製造方法
JP2012203960A (ja) 磁気情報記録媒体用ガラス基板の製造方法
JP5897959B2 (ja) 情報記録媒体用ガラス基板の製造方法
JP5886108B2 (ja) 情報記録媒体用ガラス基板の製造方法
JP5071603B2 (ja) 磁気情報記録媒体用ガラス基板の製造方法
WO2012042735A1 (fr) Procédé de fabrication d'un substrat en verre pour un support d'enregistrement d'informations
WO2012090426A1 (fr) Procédé de fabrication d'un substrat de verre pour disque dur
JP2012203959A (ja) 磁気情報記録媒体用ガラス基板の製造方法
JP5722618B2 (ja) 磁気情報記録媒体用ガラス基板の製造方法
JP2013012282A (ja) Ｈｄｄ用ガラス基板の製造方法

Legal Events

Date Code Title Description
121 Ep: the epo has been informed by wipo that ep was designated in this application

Ref document number: 14774643

Country of ref document: EP

Kind code of ref document: A1

NENP Non-entry into the national phase

Ref country code: DE

122 Ep: pct application non-entry in european phase

Ref document number: 14774643

Country of ref document: EP

Kind code of ref document: A1

NENP Non-entry into the national phase

Ref country code: JP