WO2012090754A1

WO2012090754A1 - Method for producing glass substrate for recording medium

Info

Publication number: WO2012090754A1
Application number: PCT/JP2011/079330
Authority: WO
Inventors: 典子島津
Original assignee: コニカミノルタオプト株式会社
Priority date: 2010-12-28
Filing date: 2011-12-19
Publication date: 2012-07-05

Abstract

Provided is a method that is for producing a glass substrate for a recording medium and, by means of preventing splattering of a polishing agent from the end surface to the principal surface of the glass substrate, whereby it is difficult for subsequent errors to arise. The method for producing a glass substrate for a recording medium is characterized by: containing a step for polishing the end surface of a glass substrate precursor by means of a polishing brush using a polishing liquid containing a polishing agent; and in the polishing step, when the zeta potential of the polishing agent is ζpol, the zeta potential of the polishing brush is ζbrush, and the zeta potential of the glass substrate precursor is ζsub, both ζpol and ζsub being less than 0 mV, and ζsub being smaller than ζbrush.

Description

Method for producing glass substrate for recording medium

The present invention relates to a method for producing a glass substrate for a recording medium.

In recent years, in a hard disk drive (HDD), as the recording capacity of a magnetic recording medium has increased, the flying height of the recording / reading head with respect to the magnetic recording medium has been further reduced. ing. As such a head, a head equipped with a DFH (Dynamic Flying Height) mechanism is also widespread.

In the DFH mechanism, the magnetic head thermally expands due to the heat generated by the heat generating element provided in the magnetic head, and the magnetic head is operated so as to slightly protrude in the air bearing surface (ABS) direction. Flying height can be kept constant.

Since a head equipped with such a DFH mechanism has a flying height of about several nanometers, defects such as head crashes tend to occur when a magnetic recording medium is used. In order to reduce such defects, it is required to improve the surface smoothness of the magnetic recording medium.

As an attempt to increase the surface smoothness of a glass substrate, for example, in Japanese Patent Application Laid-Open No. 2010-238310 (Patent Document 1), a glass substrate is polished by traversing a polishing grindstone with a predetermined amount of movement. A technique for reducing the size and number of surface defects has been proposed.

Japanese Patent Application Laid-Open No. 2009-087441 (Patent Document 2) controls the potential difference between the glass substrate and the aggregated silica particles and impurity particles contained in the polishing liquid when the glass substrate is polished with silica particles. A technique is disclosed that suppresses the formation of surface defects on the main surface of the glass substrate by polishing while polishing. Furthermore, Japanese Patent Application Laid-Open No. 2007-254259 (Patent Document 3) discloses a technique for polishing a glass substrate under neutral liquid conditions using cerium oxide.

JP 2010-238310 A JP 2009-087441 A JP 2007-254259 A

A glass substrate for a magnetic recording medium is usually subjected to evaluation of deposits attached to the surface and end surface of the glass substrate by an optical defect inspection apparatus (OSA: Optical Surface Analyzer) after the final cleaning. The glass substrate manufactured by the methods of Patent Documents 1 and 3 has an advantage that the number of defects is determined to be small even by evaluation by OSA, and the manufacturing efficiency of the magnetic recording medium is high.

However, when the magnetic recording medium manufactured by the methods of Patent Documents 1 and 3 is used, defects such as a head crash may occur later. Further, the polishing method disclosed in Patent Document 2 can suppress surface defects caused by silica particles to some extent by controlling the potential difference between the aggregated silica particles and impurity particles contained in the polishing liquid and the glass substrate. The above-mentioned problem caused by the abrasive itself could not be solved. Further, as a result of further studies, the above problem cannot be solved by controlling only the potential difference between the glass substrate and the abrasive. If there are abrasive particles adhering to the abrasive brush, the degraded abrasive It was found that the particles were aggregated without being discharged, and the zeta potential was changed and reattached to the glass substrate.

The present inventor investigated the cause of the defect and found that the cause was that the abrasive used for polishing the end face of the glass substrate adhered to the end face of the glass substrate. That is, when the abrasive attached to the end surface of the glass substrate scatters from the end surface to the main surface during the formation of the magnetic film, and this causes a defect such as a head crash later when used as a magnetic recording medium for a recording apparatus. I got the knowledge.

The present invention has been made under such circumstances, and the object of the present invention is to prevent the scattering of the abrasive from the end surface of the glass substrate to the main surface during the formation of the magnetic film. An object of the present invention is to provide a method for manufacturing a glass substrate for a recording medium that is less likely to cause errors.

The inventors' research has revealed that the cause of adhesion of the abrasive to the glass substrate is due to polishing with a neutral polishing liquid. That is, when neutral and rough polishing was performed, it was found that the zeta potential of the polishing agent approaches the isoelectric point, so that the polishing agent easily adheres to the glass substrate.

As a result of further investigation based on the above knowledge, in the polishing step, the abrasive remains on the end surface of the glass substrate by appropriately controlling the zeta potential of the abrasive, the glass substrate precursor, and the polishing brush. It was found that it was possible to prevent the abrasive from being scattered from the end surface of the glass substrate to the main surface during the formation of the magnetic film, and this could make it difficult to cause a subsequent error, and the present invention was completed.

That is, the method for producing a glass substrate for a recording medium of the present invention uses a glass substrate precursor, and comprises a step of polishing an end surface of the glass substrate precursor with a polishing brush using a polishing liquid containing an abrasive. In the polishing step, when the zeta potential of the abrasive is ζpol, the zeta potential of the polishing brush is ζbrush, and the zeta potential of the glass substrate precursor is ζsub, both ζpol and ζsub are less than 0 mV, Ζsub is smaller than ζbrush.

Ζsub is preferably −30 mV or less. The pH of the polishing liquid is preferably 9 or more and 13 or less. The polishing liquid further contains a dispersant, and the dispersant is preferably at least one selected from the group consisting of a polycarboxylic acid, a urethane resin, and an acrylic resin.

The abrasive is preferably composed of one or more selected from the group consisting of cerium oxide, zirconium oxide, and aluminum oxide.

The polishing liquid further contains a water-soluble polymer, and the water-soluble polymer is selected from the group consisting of polyvinyl alcohol, modified polyvinyl alcohol, polyvinyl pyrrolidone, methacrylic acid copolymer, polymethacrylamide copolymer, and polyethylene glycol. It is preferable that it consists of 1 or more types.

The polishing liquid further contains a surfactant, and the surfactant preferably contains a sulfonic acid surfactant, a phosphoric acid surfactant, or a nonionic surfactant. The polishing brush is preferably made of one or more materials selected from the group consisting of aramid fibers, polybutylene terephthalate, and polypropylene.

The method for producing a glass substrate for a recording medium of the present invention has the above-described configuration, and thus can prevent the abrasive from scattering from the end surface of the glass substrate to the main surface during the formation of the magnetic film. It shows an extremely excellent effect that it is difficult for subsequent errors to occur. For this reason, the glass substrate for recording media manufactured by the manufacturing method of this invention shows the effect that a late error does not generate | occur | produce easily.

Hereinafter, the present invention will be described in more detail.
<Method for producing glass substrate for recording medium>
The method for producing a glass substrate for a recording medium of the present invention includes at least a step of polishing an end surface of a glass substrate precursor with a polishing brush using a polishing liquid containing an abrasive (hereinafter referred to as “end surface polishing step”).

The method for producing a glass substrate for a recording medium of the present invention can include other steps as long as the chemical strengthening step and the end surface polishing step are thus included. As such other processes, for example, a disk processing process for processing the glass substrate precursor into a disk shape, a lapping process for adjusting the parallelism and thickness of the glass substrate precursor, and the surface smoothness of the glass substrate precursor are improved. Rough polishing process for polishing, precision polishing process for polishing to improve the smoothness of the glass substrate precursor than polishing in the rough polishing process, chemical strengthening to form a chemically strengthened layer on the surface and end face of the glass substrate precursor Examples of the process include a cleaning process for cleaning the surface and the end face of the glass substrate precursor.

<Glass substrate for recording medium>
The glass substrate for a recording medium produced by the present invention is used as a substrate for an information recording medium in an information recording apparatus such as a hard disk drive device, and its size and shape are not particularly limited. For example, the outer diameter is 2.5 inches, 1.8 inches, 1 inch, 0.8 inches, etc., and the thickness is 2 mm, 1 mm, 0.65 mm, 0.8 mm, etc. be able to. Further, a hole for setting in the information recording apparatus may be formed in the disc-shaped central portion.

<Disk processing process>
In the disk processing step, first, a glass material is melted (glass melting step), molten glass is poured into a lower mold, and press molding is performed with an upper mold to obtain a disk-shaped glass substrate precursor (press molding process). Note that the disk-shaped glass substrate precursor may be produced by cutting a sheet glass formed by, for example, a downdraw method or a float method with a grinding stone, without using such a press molding process.

Here, the glass material is not particularly limited as long as it can be chemically strengthened by ion exchange. For example, soda lime glass mainly composed of SiO ₂ , Na ₂ O, CaO, aluminosilicate glass mainly composed of SiO ₂ , Al ₂ O ₃ , R ₂ O (R = K, Na, Li), borosilicate Glass, Li ₂ O—SiO ₂ glass, Li ₂ O—Al ₂ O ₃ —SiO ₂ glass, R′O—Al ₂ O ₃ —SiO ₂ glass (R ′ = Mg, Ca, Sr, Ba) Etc. can be used. Among these, aluminosilicate glass and borosilicate glass are particularly preferable because they are excellent in impact resistance and vibration resistance. As the composition of the glass material, the total of SiO ₂ , Al ₂ O ₃ and B ₂ O ₃ is 50 to 85% by mass, and the total of LiO ₂ , Na ₂ and K ₂ O is 0.1 to 20% by mass. %, And the total of MgO, CaO, BaO, SrO and ZnO is 2 to 20% by mass. Among them, as the glass material, SiO ₂ is 50 to 70% by mass, Al ₂ O ₃ is 0 to 20% by mass, and B ₂ O ₃ is 0 to 5% by mass. .

Next, the glass substrate precursor press-molded as described above is perforated at the center with a core drill or the like having a diamond grindstone or the like in the cutter (coring process). Hereinafter, the end face of the hole is referred to as an inner peripheral end face.

<Lapping process>
A lapping process is performed on both the front and back surfaces of the glass substrate precursor. Here, the lapping process can be performed by, for example, a grinding process, whereby the overall shape of the glass substrate precursor, that is, the parallelism, flatness, and thickness of the glass substrate precursor can be preliminarily adjusted.

<End face polishing process>
The end surface of the glass substrate precursor after the lapping step is polished with a polishing brush using a polishing liquid containing an abrasive. Specifically, a polishing liquid containing an abrasive is supplied to the polishing brush, the polishing brush is disposed so as to contact the end surface of the glass substrate precursor, and then the polishing brush is applied while rotating the glass substrate precursor. Thus, the end face of the glass substrate precursor is polished. The “end face” in the present invention means the inner peripheral end face and the outer peripheral end face of the glass substrate precursor.

According to the present invention, in the end face polishing step using the polishing brush, if the zeta potential of the abrasive is ζpol, the zeta potential of the polishing brush is ζbrush, and the zeta potential of the glass substrate precursor is ζsub, Further, the polishing is characterized in that the polishing is carried out by setting it to be less than 0 mV and ζsub to be smaller than ζbrush. Thus, adhesion of the abrasive to the glass substrate precursor can be prevented by making the zeta potential of the abrasive and the glass substrate precursor negative.

And by making the zeta potential of the glass substrate precursor lower than the zeta potential of the polishing brush, the repulsive force of the abrasive with respect to the glass substrate precursor is increased, and the abrasive is easily separated from the glass substrate precursor. (Prevents adhesion of abrasive). By preventing the adhesion of the abrasive in this way, it is possible to prevent the abrasive from being scattered from the end surface of the glass substrate to the main surface, thereby preventing the occurrence of subsequent defects when processed as a magnetic recording medium. Can do.

Here, the zeta potential (ζ potential) means that when a solid is dispersed in a solvent, charge separation occurs at the interface between the solution and the solid, and a potential difference occurs near the interface. It means the potential difference between the potential and the potential of the solvent sufficiently away from the interface. The ζ potential is repulsive between those having a positive ζ potential or between those having a negative ζ potential, and is attractive between those having a positive ζ potential and those having a negative ζ potential. As the absolute value of the ζ potential is larger, a stronger attractive force or repulsive force is applied. The present invention makes use of such ζ potential characteristics to make both the ζ potential of the glass substrate precursor and the ζ potential of the polishing agent negative, and in particular, to increase the absolute value of the ζ potential of the glass substrate precursor. Thus, the repulsive force between the glass substrate precursor and the abrasive is increased so that the abrasive does not adhere to the end face of the glass substrate precursor or even if it adheres, it can be easily removed in the cleaning process.

As a method for measuring the ζ potential of the glass substrate precursor, the abrasive, and the polishing brush, a conventionally known method can be used, but an electrophoresis method, a streaming potential method, an ultrasonic method, an ESA method, or the like is used. It is preferable.

The above ζsub is preferably −30 mV or less. By determining the zeta potential of the glass substrate precursor in this manner, the abrasive can be more easily electrically separated from the glass substrate precursor. In order to lower the ζsub, it is preferable to change the pH of the polishing liquid in which the abrasive is dispersed. However, the method is not limited to this method. For example, additives such as a dispersant and the glass composition are changed. Therefore, it is possible to change ζsub.

The abrasive contained in the above polishing liquid is preferably contained at 1 to 15% by mass, more preferably 3 to 7% by mass. Moreover, it is preferable that the average particle diameter of an abrasive | polishing agent is 1 micrometer or more and 2.5 micrometers or less, More preferably, they are 1 micrometer or more and 1.5 micrometers or less.

It is preferable that the abrasive used in the above is made of at least one selected from the group consisting of cerium oxide, zirconium oxide, and aluminum oxide. This is because such an abrasive can efficiently polish the glass substrate precursor and can easily control the zeta potential of the abrasive. The zeta potential of such an abrasive can be reduced by adding a polycarboxylic acid-based dispersant as the composition of the polishing liquid in which the abrasive is dispersed. In addition, the zeta potential of the polishing agent can be lowered by making the polishing solution liquid alkaline.

The liquid property of the polishing liquid is not particularly limited as long as the zeta potential of the polishing agent can be controlled to −30 mV or less, but is preferably alkaline, more preferably pH. 9 or more and 13 or less. By using a polishing liquid having such a liquid property, it becomes easy to adjust the zeta potential of the abrasive to minus.

The above polishing liquid preferably contains a dispersant. The dispersant is preferably at least one selected from the group consisting of polycarboxylic acids, urethane resins, and acrylic resins. By including such a dispersing agent, it is possible to uniformly disperse the abrasive in the polishing liquid, and thus it is possible to efficiently polish the end face of the glass substrate precursor.

The polishing liquid preferably further contains a water-soluble polymer. The water-soluble polymer is preferably composed of at least one selected from the group consisting of polyvinyl alcohol, modified polyvinyl alcohol, polyvinyl pyrrolidone, methacrylic acid copolymer, polymethacrylamide copolymer, and polyethylene glycol. By introducing such a water-soluble polymer into the polishing liquid, the zeta potential of the abrasive can be adjusted. That is, by using a methacrylic acid copolymer as the composition of the water-soluble polymer, the zeta potential of the abrasive can be lowered. By using polyethylene glycol as the composition of the water-soluble polymer, the zeta potential of the abrasive can be reduced. Can be raised.

The polishing liquid preferably further contains a surfactant. As the surfactant, one or more selected from the group consisting of a sulfonic acid surfactant, a phosphoric acid surfactant, or a nonionic surfactant can be used. By introducing such a surfactant into the polishing liquid, the zeta potential of the polishing agent can be adjusted. In other words, by using a surfactant such as hydroxyl group ethylidene phosphophone (HEDP: 1-Hydroxy Ethylidene-1,1-Diphosphonic Acid), the zeta potential of the abrasive tends to be increased. By using such a surfactant, the zeta potential of the abrasive tends to be lowered.

In the present invention, the polishing brush for polishing the end surface of the glass substrate precursor is preferably composed of one or more selected from the group consisting of aramid fibers, polybutylene terephthalate, and polypropylene. By using a polishing brush made of such a material, the end face shape can be created while controlling the zeta potential more easily.
In addition to changing the pH of the polishing liquid, the zeta potential of the polishing brush or the glass substrate can be adjusted by bringing the water-soluble polymer or surfactant into contact with the surface prior to the polishing treatment. It is possible to increase or decrease the value of the zeta potential by adjusting the treatment time with the surfactant and the concentration of the water-soluble polymer and the surfactant used in the treatment. For example, when the contact time with the water-soluble polymer is increased and the amount of OH groups or COOH groups introduced into the glass substrate or polishing brush is increased, the value of the zeta potential decreases, and the OH group or COOH group When the introduction amount is decreased, the zeta potential value tends to increase.

<Rough polishing process>
The front and back surfaces of the glass substrate precursor after the end face polishing step are polished with a polishing pad using a polishing liquid containing an abrasive. Specifically, a polishing liquid containing an abrasive is supplied to the surface of the glass substrate precursor, and the polishing pads are arranged so as to be in contact with both the front and back surfaces of the glass substrate precursor. By rotating in the reverse direction, the surface of the glass substrate precursor is polished. As the polishing pad used in the rough polishing step, for example, a urethane foam pad can be used, and a hard pad having a hardness A of about 80 to 90 is preferable.

Here, the same polishing agent and polishing liquid as those described in the end face polishing step can be used. Further, by controlling the zeta potential of the polishing pad, the polishing agent, and the polishing liquid in the same manner as the polishing brush, it is possible to make it difficult for the polishing agent to adhere to the front and back surfaces of the glass substrate precursor.

<Precision polishing process>
The precision polishing step is performed to further improve the surface smoothness of the glass substrate precursor, and is a step of polishing the glass substrate precursor by a polishing method with higher accuracy than the above rough polishing step. In such a precision polishing step, it is preferable to perform mirror polishing of the front and back surfaces of the glass substrate using a polishing pad of a polyurethane-based soft polisher with a double-side polishing apparatus having a planetary gear mechanism. As the polishing liquid used here, for example, a dispersion in which colloidal silica having an average particle size of 40 nm or less is dispersed in ultrapure water, more preferably colloidal silica having an average particle size of 20 to 40 nm is used. Use dispersed ones.

<Chemical strengthening process>
In the chemical strengthening step, a chemically strengthened layer is formed on the surface and the end face of the glass substrate precursor subjected to the above-described precision polishing. Such a process usually reinforces the surface of the glass substrate precursor using a chemical strengthening treatment liquid. Such a chemical strengthening process can employ | adopt without specifically limiting the conventionally well-known method known as a chemical strengthening process in the manufacturing method of the glass substrate for recording media.

Specifically, for example, a step of immersing the glass substrate precursor in a chemical strengthening treatment liquid can be exemplified. Thereby, a chemical strengthening layer is formed in the area | region of several micrometers from the surface, Preferably about 5 micrometers in the surface and end surface of a glass substrate precursor.

More specifically, in such a chemical strengthening step, by immersing the glass substrate precursor in a heated chemical strengthening treatment solution, alkali metal ions such as lithium ions and sodium ions contained in the glass substrate precursor are further reduced. This is carried out by an ion exchange method in which alkali metal ions such as potassium ions having a large ion radius are substituted. Compressive stress is generated in the ion-exchanged region due to the strain caused by the difference in ion radius, and the surface of the glass substrate precursor is strengthened in the region. Examples of such chemical strengthening treatment liquid include a solution in which potassium nitrate (60%) and sodium nitrate (40%) are mixed.

<Final cleaning process>
The glass substrate on which the chemical strengthening layer is formed is preferably washed with a neutral detergent and pure water and dried. By performing such cleaning, it is possible to wash away the adhesion of foreign substances contained in the chemical strengthening treatment liquid, and to stabilize the surface of the glass substrate for recording media and to have excellent long-term storage stability. it can. A glass substrate for a recording medium can be produced as described above.

The method of manufacturing the glass substrate for recording medium of the present invention is not limited to the above-described manufacturing method, and may be manufactured by reversing the order of the precision polishing step and the chemical strengthening step, for example. Thus, even if the glass substrate for recording media is manufactured, the same performance as the glass substrate for recording media manufactured by the above manufacturing method can be obtained.

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited thereto.

[Example 1]
In this example, a glass substrate for a recording medium was manufactured by the following steps.

<Disk processing process>
First, a multicomponent glass material made of amorphous glass was prepared. As the composition of the glass material, aluminosilicate glass was used. The chemical composition of the glass material, SiO ₂ is 50 to 70 wt%, Al ₂ O ₃ is 0 to 20 wt%, B ₂ O ₃ 0 to 5 wt% _{_{_{(however, SiO 2, Al 2 O 3}}} , and B ₂ O ₃ is 50 to 85% by mass), Li ₂ O, Na ₂ O, and K ₂ O are 0.1 to 20% by mass, MgO, CaO, BaO, SrO, and ZnO. Was 2 to 20% by mass.

A disk-shaped glass substrate precursor was formed by molding the above glass material by a direct press method. And the hole was made in the center part of the glass substrate precursor using the grindstone, and it was set as the disk-shaped glass substrate precursor which has a circular hole in the center part. Furthermore, the outer peripheral end surface and the inner peripheral end surface of the glass substrate precursor were chamfered.

<Lapping process>
The glass substrate precursor whose end face was polished as described above was ground on both the front and back surfaces of the glass substrate precursor using abrasive grains having a particle size of # 1000. Thereby, while adjusting the glass substrate precursor to the thickness of about 0.95 mm, the parallelism of the glass substrate precursor was improved.

<End face polishing process>
Subsequently, while rotating the glass substrate precursor, the surface roughness of the end surface (inner periphery, outer periphery) of the glass substrate with a polishing brush is about 1.0 μm at the maximum height (Rmax), arithmetic average roughness (Ra) Was polished to about 0.3 μm. Here, a polishing brush made of nylon 6 was used, and a polishing liquid was included in advance. In this polishing liquid, a polishing agent made of cerium oxide having an average particle diameter of 1.5 μm was mixed with water, so that the concentration of the polishing agent was 7% by mass. Further, the pH was adjusted to 10 by adding 1 mol / L potassium hydroxide.

The zeta potential ζpol of the abrasive contained in such a polishing liquid was measured by applying an applied voltage of 60 mV / cm using a flow cell unit. Further, the zeta potential ζsub of the glass substrate precursor and the zeta potential ζ brush of the polishing brush were each measured by preparing a 37 mm × 16 mm × 5 mm sample and using a flat plate cell. These zeta potentials were measured using a zeta potential / particle size measurement system (product name: ELSZ-2 (manufactured by Otsuka Electronics Co., Ltd.). As a result of the above zeta potential measurement, ζpol was −50 mV. Yes, ζsub was −40 mV, and ζbrush was −30 mV.
In this example, the zeta potential of the polishing brush and the glass substrate was adjusted to adjust the time of contact with the phosphate surfactant solution as a surfactant before polishing treatment in addition to adjusting the pH of the polishing solution. To adjust each. Specifically, it adjusted by changing the density | concentration of phosphoric acid type surfactant (monoalkyl phosphate solution). At this time, when the concentration is increased, the zeta potential decreases, and when the concentration is decreased, the zeta potential tends to increase (or remain unchanged with no treatment).

<Rough polishing process>
Next, rough polishing was performed using a polishing apparatus capable of polishing both main surfaces of the glass substrate. A hard polisher was used for the polishing pad. As this polishing pad, one containing the same polishing liquid as described above was used.

<Precision polishing process>
Using a double-side polishing apparatus having a planetary gear mechanism, the front and back surfaces of the glass substrate precursor were mirror-polished using a polishing pad of a polyurethane-based soft polisher. The polishing liquid used was a dispersion of colloidal silica having an average particle diameter of 20 nm in ultrapure water.

<Washing process>
Subsequently, the glass substrate precursor was immersed in an aqueous NaOH solution having a concentration of 3 to 5% by mass and subjected to alkali cleaning while applying ultrasonic waves. Furthermore, it wash | cleaned by immersing in each washing tank of neutral detergent, a pure water, IPA, and IPA (steam drying) sequentially.

<Chemical strengthening process>
Subsequently, potassium nitrate (60%) and sodium nitrate (40%) were mixed to prepare a chemical strengthening solution. And while heating this chemical strengthening solution to 400 degreeC and preheating the glass substrate precursor after said washing | cleaning to 300 degreeC, it is immersed in the said chemical strengthening process liquid for about 3 hours, and chemical strengthening process is carried out. Was done. The immersion here was carried out in a state where a plurality of glass substrate precursors were housed in a holder held on the end face in order to uniformly chemically strengthen the entire surface of the glass substrate precursor. In this way, a chemically strengthened layer was formed on the entire surface of the glass substrate precursor. After finishing the chemical strengthening step, the glass substrate precursor was immersed in a 20 ° C. water bath, quenched, and maintained for about 10 minutes, thereby producing a glass substrate for recording medium.

<Final cleaning process>
The glass substrate for recording medium after the rapid cooling was washed by immersing it in sulfuric acid heated to about 40 ° C. Then, the glass substrate after washing with sulfuric acid was washed by immersing it in a washing tank filled with pure water, and further, the glass substrate for recording medium was washed by immersing it in a washing tank filled with IPA.

<Examples 2 to 8, Comparative Examples 1 to 3>
Compared to Example 1 above, the zeta potentials of the abrasive, the polishing brush, and the glass substrate precursor in the rough polishing step are different as shown in Table 1, and by adding a sulfuric acid aqueous solution or potassium hydroxide to the polishing liquid. The glass substrates for recording media of Examples 2 to 8 and Comparative Examples 1 to 3 were prepared in the same manner as in Example 1 except that the pH of the polishing liquid was different as shown in Table 1.

<Evaluation of manufacturing defects>
15 glass substrates for recording media produced by the above production method were produced in each Example and each Comparative Example. By measuring the number of defects and the number of collision errors of the glass substrate for recording medium as follows, it was evaluated whether or not the glass substrate for recording medium could be chemically strengthened uniformly.

(Number of defects)
Using the optical surface inspection machine (product name: Optical Surface Analyzer: Candela 6300 (manufactured by Candela)), each of the 15 glass substrates for recording media of each of the examples and comparative examples prepared above was used. The presence or absence of foreign matter that hinders ascent or thermal asperity failure was examined. The number of foreign substances of the 15 recording medium glass substrates having the largest number of foreign substances is shown in the “number of surface defects” and “number of end face defects” columns in Table 2. In addition, it has shown that the surface smoothness of the glass substrate for recording media is excellent, so that the number of surface defects and the number of end surface defects are small.

(Number of collision errors)
The number of recording medium glass substrates in which errors were detected was counted using the TA test head equipped with the DFH mechanism for the recording medium glass substrates thus prepared. In the column of “number of collision errors” in Table 2, the number of recording medium glass substrates on which a collision error has occurred is shown. The collision error means a collision error that occurred between 5 mm from the outer peripheral end surface of the glass substrate for recording medium. The smaller the number of collision errors, the better the surface smoothness of the glass substrate for recording medium. Is shown.

As is clear from Table 2, the glass substrates for recording media manufactured by the manufacturing methods of Examples 1 to 8 had a polishing agent that scattered from the end surface to the main surface due to a decrease in the polishing agent adhering to the end surface. It was confirmed that collision errors are less likely to occur due to the decrease. In contrast, the recording medium glass substrates manufactured by the manufacturing methods of Comparative Examples 1 to 3 are likely to cause a collision error because the abrasive adhered to the end surface of the magnetic film is scattered on the main surface when the magnetic film is formed. confirmed.

Therefore, the glass substrate for a recording medium manufactured according to the manufacturing method of the present invention performs rough polishing by controlling the zeta potential of the polishing agent, the glass substrate precursor, and the polishing brush, so that the end surface of the polishing agent is removed. It is clear that it was possible to prevent adhesion and to prevent the abrasive from scattering from the end surface to the main surface, thereby making it difficult to cause a collision error.

Although the embodiments and examples of the present invention have been described above, it is also planned from the beginning to appropriately combine the configurations of the above-described embodiments and examples.

It should be considered that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

Claims

A method for producing a glass substrate for a recording medium using a glass substrate precursor,
Polishing the end surface of the glass substrate precursor with a polishing brush using a polishing liquid containing an abrasive;
In the polishing step, when the zeta potential of the abrasive is ζpol, the zeta potential of the polishing brush is ζbrush, and the zeta potential of the glass substrate precursor is ζsub, both ζpol and ζsub are less than 0 mV. And the ζsub is smaller than the ζbrush to produce a glass substrate for a recording medium.
The method for producing a glass substrate for a recording medium according to claim 1, wherein the ζsub is -30 mV or less.
The method for producing a glass substrate for a recording medium according to claim 1, wherein the pH of the polishing liquid is 9 or more and 13 or less.
The polishing liquid further contains a dispersant,
The method for producing a glass substrate for a recording medium according to claim 1, wherein the dispersant is at least one selected from the group consisting of polycarboxylic acid, urethane resin, and acrylic resin.
The method for producing a glass substrate for a recording medium according to claim 1, wherein the abrasive comprises one or more selected from the group consisting of cerium oxide, zirconium oxide, and aluminum oxide.
The polishing liquid further contains a water-soluble polymer,
The water-soluble polymer comprises at least one selected from the group consisting of polyvinyl alcohol, modified polyvinyl alcohol, polyvinyl pyrrolidone, methacrylic acid copolymer, polymethacrylamide copolymer, and polyethylene glycol. A method for producing the glass substrate for a recording medium according to the description.
The polishing liquid further contains a surfactant,
The method for producing a glass substrate for a recording medium according to claim 1, wherein the surfactant includes a sulfonic acid surfactant, a phosphoric acid surfactant, or a nonionic surfactant.
2. The method for producing a glass substrate for a recording medium according to claim 1, wherein the polishing brush is made of one or more materials selected from the group consisting of aramid fibers, polybutylene terephthalate, and polypropylene.