JP6330628B2 - Manufacturing method of glass substrate - Google Patents

Description

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

  Conventionally, an aluminum alloy substrate has been used as a glass substrate for a magnetic recording medium used in a magnetic recording apparatus or the like, but it is harder, flatter and smoother than an aluminum alloy substrate due to the demand for higher recording density. Glass substrates having excellent properties are becoming mainstream.

  A glass substrate for a magnetic recording medium is manufactured by cutting a glass base substrate into a predetermined shape and then polishing the end face and the main plane. In the polishing step in the method of manufacturing the glass substrate for magnetic recording medium, the glass substrate is held by a polishing carrier, and a polishing liquid (slurry) containing abrasive grains is interposed between the glass substrate and the polishing pad using a polishing pad. Polish while feeding.

  In the polishing step, scratches (the polishing carrier scratches the polishing surface of the polishing pad) occur on the polishing surface of the polishing pad during polishing of the glass substrate. Polishing the glass substrate with scratches on the polishing surface of the polishing pad may cause product quality problems. If the glass substrate is damaged during polishing and the polishing surface is damaged, the polishing pad must be replaced. , Etc. may occur. In addition, the use time of the polishing pad is shortened, resulting in inferior productivity and increased cost.

  When the polishing rate is lowered, the surface of the polishing pad is scraped to adjust the polishing surface (dressing process). Further, when the glass substrate manufactured using the polishing pad does not satisfy the desired quality, it is regarded as a service life limit and is replaced with a new polishing pad.

  The polishing process must be temporarily stopped by dressing or changing the polishing pad, resulting in a problem that the productivity of the glass substrate is lowered and the cost is increased. Further, since the dressing process is an operation for trimming and adjusting the polishing surface of the polishing pad, the life of the polishing pad is shortened as the dressing process is performed.

  Further, in Patent Document 1, in the method for manufacturing a glass substrate for a magnetic disk having a polishing process using a planetary gear mechanism, it is possible to suppress the occurrence of one-side scraping (uneven wear) on the polishing pad attached to the upper and lower surface plates. In order to reduce the drop in productivity due to the polishing pad, the polishing step includes a first polishing period in which the upper and lower surface plates are rotated in a predetermined direction to polish the main surface of the glass substrate; It describes that a second polishing period for polishing the main surface of the glass substrate by rotating the upper and lower surface plates in a direction opposite to the predetermined direction is provided.

JP 2011-67901 A

  However, the technique disclosed in Patent Document 1 is insufficient from the viewpoint of sufficiently preventing scratches on the polishing surface of the polishing pad during polishing of the glass substrate and extending the life of the polishing pad. .

  Therefore, an object of the present invention is to provide a method for producing a glass substrate that can prevent the polishing surface of the polishing pad from being scratched during polishing of the glass substrate and extend the life of the polishing pad.

  The inventors of the present invention have used a polishing pad and a polishing liquid at which the contact angle of the polishing liquid after 50 seconds after dropping 1 μl of the polishing liquid on the polishing surface of the polishing pad is 50 ° or less, and It has been found that by polishing the main surface of the glass substrate with improved permeability, scratches on the polishing surface of the polishing pad can be prevented during polishing of the glass substrate, and the life of the polishing pad can be extended. Completed the invention.

That is, the present invention is as follows.
(1) Holding a polishing carrier using a polishing pad having a foamed resin polishing layer having a Shore D hardness of 40 or less and a polishing liquid containing silica having a primary particle diameter of 3 to 50 nm as abrasive grains A method for producing a glass substrate, comprising: a polishing step for polishing a main plane of a glass substrate held in a hole; and a cleaning step for cleaning the surface of the glass substrate,
In the polishing step, the main surface of the glass substrate is polished by using the polishing pad and the polishing liquid at which the contact angle of the polishing liquid is 50 ° or less after 50 seconds from dropping 1 μl of the polishing liquid onto the polishing surface of the polishing pad. A method for producing a glass substrate, comprising:
(2) In the polishing carrier, the glass substrate according to (1), wherein a contact angle of the polishing liquid 0.1 seconds after dropping 1 μl of the polishing liquid onto the surface of the polishing carrier is 75 ° or less. Method.
(3) The said polishing liquid is a manufacturing method of the glass substrate as described in (1) or (2) whose viscosity in 25 degreeC is 1.7 mPa * s or less.
(4) The method for producing a glass substrate according to any one of (1) to (3), wherein the polishing liquid has a pH of 1 to 6 and a silica content of 5 to 25 mass%.
(5) The method for producing a glass substrate according to any one of (1) to (4), wherein the glass substrate is a glass substrate for a magnetic recording medium having a circular hole in a central portion.

  According to the method for producing a glass substrate of the present invention, it is possible to improve the permeability of the polishing liquid with respect to the polishing pad and to prevent the polishing pad from being scratched in the final polishing step. As a result, the life of the polishing pad can be lengthened, and the productivity can be improved and the cost can be reduced in the manufacturing process of the glass substrate for magnetic recording medium.

FIG. 1 is a diagram for explaining a double-side polishing apparatus for a glass substrate on which a polishing carrier can be mounted. FIG. 2 is a perspective view of the glass substrate.

[Outline of glass substrate production method]
The outline of the manufacturing method of the glass substrate of this embodiment is demonstrated.

  In the present invention, the glass substrate may be amorphous glass, crystallized glass, or tempered glass (for example, chemically tempered glass) having a tempered layer on the surface layer of the glass substrate.

  Specifically, for example, when high mechanical strength is required for the glass substrate, it is preferable to perform a strengthening step (for example, a chemical strengthening step) for forming a reinforcing layer on the surface layer of the glass substrate. The strengthening step may be performed either before the first polishing step, after the last polishing step, or between each polishing step.

  The glass substrate of the glass substrate of the present invention is formed by a method such as a float method, a fusion method, a press molding method, a down draw method, or a redraw method, but the present invention is not limited in this respect.

The glass substrate is a glass substrate formed by the above-described method,
(Step 1) A shape imparting step of chamfering the inner peripheral side surface and the outer peripheral side surface after processing the glass substrate into a disk shape having a circular hole in the center portion;
(Step 2) An end surface polishing step for polishing the end surfaces (the inner peripheral end surface and the outer peripheral end surface) of the glass substrate;
(Step 3) Main surface polishing step for polishing the upper and lower main surfaces of the glass substrate;
(Step 4) A cleaning step of precisely cleaning and drying the glass substrate;
It is manufactured by performing the process including.

  And the glass substrate obtained by the manufacturing method including the above-mentioned process can be used as a magnetic recording medium (magnetic disk) by further forming an underlayer, a magnetic layer, a protective layer or a lubricating film on the surface thereof. it can.

  Prior to the main surface polishing step, main surface lapping (for example, loose abrasive lapping, fixed abrasive lapping, etc.) may be performed, and glass substrate cleaning (inter-step cleaning) or glass between each step Etching of the substrate surface (inter-process etching) may be performed.

  Note that the main plane lapping here is polishing of the main plane in a broad sense. Further, the polishing step may be only primary polishing, primary polishing and secondary polishing may be performed, or tertiary polishing may be performed after secondary polishing.

Next, each step will be described.
(Step 1) Shape imparting step In the shape imparting step, the glass base substrate is processed into a disk shape having a circular hole in the center, and then the inner peripheral side surface and the outer peripheral side surface are chamfered. The chamfering processing of the inner and outer peripheral side surfaces in the shape imparting step is generally performed using a grindstone to which diamond abrasive grains are fixed.

(Step 2) End Surface Polishing Step In the end surface polishing step, the inner peripheral end surface and the outer peripheral end surface of the glass substrate are end polished. Either the outer peripheral end face or the inner peripheral end face may be polished first.

(Step 3) Main surface polishing step In the main surface polishing step, the upper and lower main planes of the glass substrate are polished using a double-side polishing apparatus while supplying a polishing liquid to the main plane of the glass substrate. The double-side polishing apparatus is not particularly limited. For example, a double-side polishing machine that can use a carrier having a diameter of 16 inches, 20 inches, or 22 inches (for example, a 16B type double-side polishing apparatus or a 20B type double-side polishing apparatus). And a 22B type double-side polishing apparatus).

  The polishing step may be one-step polishing with only primary polishing (finish polishing), two-step polishing in which primary polishing and secondary polishing (finish polishing) are performed, or three after first polishing and second polishing. Three-stage polishing in which next polishing (finish polishing) is performed may be used. Usually, a cleaning process (inter-process cleaning) is provided between each polishing process.

  Prior to the main surface polishing step, main surface lapping (for example, loose abrasive lapping and fixed abrasive lapping) may be performed. The main plane lap mentioned here is polishing of the main plane in a broad sense.

  The method for producing a glass substrate of the present invention improves the ease of adapting the polishing liquid to the polishing pad by performing a specific method described later in the final polishing, so that the polishing surface of the polishing pad is polished during the polishing of the glass substrate. This prevents the generation of scratches and extends the life of the polishing pad. Details of the main surface polishing step will be described later.

  In the main surface polishing step, a polishing apparatus is used that holds a glass substrate on a polishing carrier and uses a polishing pad to polish while supplying a polishing liquid containing abrasive grains between the glass substrate and the polishing pad. .

  In the polishing apparatus, the main surface of the glass substrate is polished by attaching the polishing pad to the upper and lower surface plates, sandwiching the glass substrate, and moving the glass substrate and the polishing pad relatively by using the planetary gear mechanism. Yes. Polishing by the polishing apparatus is an excellent method in terms of production efficiency because a plurality of glass substrates can be simultaneously polished.

  The polishing apparatus will be described with reference to FIG.

  As shown in FIG. 1, the polishing apparatus 12 is configured to set a polishing carrier 10 on which a glass substrate 30 can be set between a stainless sun gear 13 and a ring gear 14. The gear portion 10a formed on the outer peripheral surface of the sun gear 13, the ring gear 14 and the polishing carrier 10 constitutes a planetary gear mechanism, and the sun gear 13 and the ring gear 14 are rotationally driven at a predetermined rotation ratio, whereby the polishing carrier 10 Revolves around the sun gear 13 while rotating.

  At this time, the polishing carrier 10 has a polishing pad 16 on the surface facing the glass substrate 30 in a state where the glass substrate 30 is held in the glass substrate holding hole 11 formed in the glass substrate holding portion 10b inside the gear portion 10a. , 18 are sandwiched and pressed between the upper surface plate 15 and the lower surface plate 17. A polishing liquid containing abrasive grains is supplied between the polishing pads 16 and 18 and the polishing carrier 10 and the glass substrate 30, and both main planes of the glass substrate held by the polishing carrier 10 are simultaneously polished. The

  For example, the dynamic friction coefficient on the upper surface plate 15 side increases and the glass substrate 30 does not rotate or revolve smoothly, or the dynamic friction coefficient on the lower surface plate 17 side increases, and the glass substrate 30 rotates or revolves smoothly. It is considered that the scratches are generated on the polishing pads 16 and 18 when the glass substrate 30 rides on the polishing carrier 10 or goes under the polishing carrier 10 when it does not break.

  As shown in FIG. 2, the glass substrate 30 is formed in a disk shape having a circular hole at the center of both main planes 31, and has an inner peripheral side surface 32 and an outer peripheral side surface 33. The plate thickness of the polished glass substrate 30 is preferably 0.5 mm to 1.0 mm.

  The polishing pads 16 and 18 are polishing pads (hereinafter also referred to as polishing pads) having a foamed resin polishing layer having a Shore D hardness of 40 or less. A polishing pad having a polishing layer of a foamed resin having a Shore D hardness of 40 or less is thinner than a hard urethane pad (typically 1.5 mm to 2.0 mm), typically 0.3 mm. It has a thickness of about 1.2 mm.

  Also, the groove depth formed on the pad surface is shallower than the groove depth of the hard urethane pad (typically 1.2 mm to 1.7 mm), typically 0.2 mm to 1.0 mm. Has a depth of about.

  Accordingly, a polishing pad having a foamed resin polishing layer having a Shore D hardness of 40 or less tends to have a non-uniform supply of polishing liquid to the polishing surface when the groove depth is shallower than a hard urethane pad. Tend.

  The number of glass substrates 30 that can be polished simultaneously varies depending on the size of the polishing carrier 10 and the double-side polishing apparatus 12. Specifically, for example, in a 16B type double-side polishing apparatus using a polishing carrier having a diameter of 16 inches, 80 to 110 glass substrates 30 can be simultaneously polished per batch, and a polishing carrier having a diameter of 22 inches is used. In the 22B double-side polishing apparatus, 115 to 222 glass substrates 30 can be simultaneously polished per batch. When polishing, it is not necessary to set the glass substrate 30 in all the glass substrate holding holes 11 of the polishing carrier 10.

(Process 4) Cleaning process In the cleaning process, for example, scrub cleaning using a detergent, ultrasonic cleaning in a state of immersing in a detergent solution, and ultrasonic cleaning in a state of immersing in pure water. Etc. are sequentially performed and dried with steam such as isopropyl alcohol.

[Method for Manufacturing Glass Substrate of the Present Invention]
In the method for producing a glass substrate of the present invention, in the main surface polishing step of (Step 3) described above, a polishing pad having a foamed resin polishing layer having a Shore D hardness of 40 or less and a primary particle size as abrasive grains The main plane of the glass substrate held in the holding hole of the polishing carrier is polished with a polishing liquid containing silica having a thickness of 3 to 50 nm.

  The polishing pad is laminated to a thickness of 0.3 to 1.2 mm, and the hardness is 40 or less, preferably 30 or less in Shore D hardness. If the Shore D hardness is more than 40, there is a possibility that fine scratches may be caused on the glass by pressing the abrasive grains. Moreover, it is preferable that Shore A hardness is 20 or more, More preferably, it is 30 or more. A sufficient polishing rate can be obtained by setting the Shore A hardness to 30 or more.

  The material of the polishing pad satisfying such conditions typically includes a suede pad having a foamed resin on the polishing surface, an unemployed fabric pad, a woven fabric pad, etc., of which the suede pad is most preferable. .

  Specific examples of the structure of the polishing pad include a structure having a base layer and a surface layer (generally called a NAP layer) made of plastic foam or the like. It is preferable that the polishing pad is ground and removed by a dressing process. Thereby, the bubble contained in a plastic foam is opened, and the grinding | polishing surface which grind | polishes a glass substrate is formed.

  Thus, the polishing pad in which the skin of the surface layer is removed by grinding to open the bubbles of the plastic foam is also referred to as a suede type polishing pad. A polishing pad is often used for finish polishing of a glass substrate.

  The polishing pad is preferably subjected to dressing using a dresser in advance before polishing the glass substrate to adjust the shape and surface roughness of the polishing surface of the polishing pad.

  For example, a polishing pad made of urethane has a configuration in which a foam layer is formed inside and abrasive particles are temporarily held therein. Therefore, in order to open the foamed layer on the polishing surface of the polishing pad, it is necessary to perform dressing using a dresser and to grind and remove the surface layer of the polishing pad to form a polishing surface. The dressing process is a process of grinding and removing the surface layer of the polishing pad using a dresser after mounting the polishing pad on the surface plate of the polishing apparatus.

  The primary particle diameter of silica contained as abrasive grains in the polishing liquid is 3 to 50 nm, preferably 5 to 40 nm, and more preferably 7 to 30 nm. When the primary particle diameter of silica is less than 3 nm, it is difficult to obtain a high polishing rate, and productivity may be deteriorated. This is because the activity of the silica surface becomes strong and it is easy to adhere to the substrate surface without being polished. Further, when the primary particle diameter of silica is more than 50 nm, it becomes difficult to polish to a surface roughness of the main plane that can cope with a higher recording density of the magnetic recording medium.

  The polishing liquid is preferably pH 1 to pH 6, more preferably pH 2 to pH 6, and further preferably pH 3 to pH 5.5. By setting the pH of the polishing liquid to 6 or less, friction between the polishing pad and the glass substrate is less likely to occur, so that the polishing pad can be prevented from being scratched and the rate can be prevented from dropping. By setting the pH of the polishing liquid to 1 or more, the surface of the glass substrate is hardly roughened, and the polishing apparatus can be prevented from being rusted.

  The pH of the polishing solution is a pH standard solution [phthalate pH standard solution (pH 4.01), neutral phosphate pH standard solution (pH 6.86), borate pH standard solution (pH 9.18)]. Then, after three-point calibration, the pH electrode is washed with pure water, and then the pH of the polishing liquid is measured using a pH measuring machine. As the pH measuring device, a pH measuring device (model: D-53S) manufactured by HORIBA, Ltd. can be used.

  It is preferable that content of the silica which is an abrasive grain is 5-25 mass%, More preferably, it is 5-20 mass%, More preferably, it is 5-15 mass%. By setting the content of silica to 25% by mass or less, it is possible to prevent the viscosity of the polishing liquid from increasing excessively and to suppress a decrease in the permeability of the polishing liquid to the polishing pad. A sufficient polishing rate can be obtained by setting the silica content to 5 mass% or more.

  The polishing pad and the polishing liquid are combined such that the contact angle of the polishing liquid after 50 seconds after dropping 1 μl of the polishing liquid onto the polishing surface of the polishing pad is 50 ° or less. The contact angle is preferably 45 ° or less, more preferably 40 ° or less, and still more preferably 38 ° or less.

  The main surface of the glass substrate is polished with a combination of the polishing liquid and the polishing pad that satisfies the relationship that the contact angle of the polishing liquid after 50 seconds after dropping 1 μl of the polishing liquid on the polishing surface of the polishing pad is 50 ° or less. As a result, it is possible to prevent the polishing pad from being damaged during the polishing of the glass substrate, to prolong the life of the polishing pad, to improve productivity, and to reduce costs.

  When 1 μl of the polishing liquid is dropped on the polishing surface of the polishing pad and the glass substrate is polished using a polishing pad and a polishing liquid with a contact angle of the polishing liquid exceeding 50 ° after 50 seconds, polishing is performed during polishing of the glass substrate. There is a problem that the surface of the pad is easily damaged, and the life of the polishing pad is shortened.

  The permeability of the polishing liquid to the polishing pad is evaluated as follows. The polishing surface of the polishing pad is dressed and washed with pure water, and then the polishing pad is dried at room temperature for 1 day. 1 μl of polishing liquid is dropped on the polishing surface of the dried polishing pad, and the contact angle 50 seconds after the polishing liquid is dropped is measured using a contact angle measuring device. As the contact angle measuring device, a contact angle measuring device (manufacturer: manufactured by Kyowa Interface Science, model: PCA-1) can be used.

  In order to make the contact angle of the polishing liquid 50 seconds or less after dropping 1 μl of the polishing liquid on the polishing surface of the polishing pad, specifically, for example, the particle diameter of the abrasive grains is small, Even if the content is 5 to 25% by mass, it is possible to select a polishing liquid having excellent dispersibility and a polishing pad having excellent affinity for such a polishing liquid.

  For the polishing carrier and the polishing liquid, the contact angle of the polishing liquid 0.1 seconds after dropping 1 μl of the polishing liquid onto the surface of the polishing carrier is preferably 75 ° or less, more preferably 70 ° or less. More preferably, the combination is 65 ° or less.

  By dripping 1 μl of the polishing liquid onto the surface of the polishing carrier, the main surface of the glass substrate is polished by a combination of a polishing liquid and a carrier whose polishing liquid contact angle is 75 ° or less after 0.1 seconds. The polishing pad can be prevented from being damaged during the polishing of the substrate, the life of the polishing pad can be extended, the productivity can be improved, and the cost can be reduced.

  The contact angle of the polishing liquid with respect to the polishing carrier is evaluated as follows. 1 μl of the polishing liquid is dropped on the surface of the dried polishing carrier, and the contact angle 0.1 seconds after the polishing liquid is dropped is measured using a contact angle measuring device. As the contact angle measuring device, a contact angle measuring device (manufacturer: manufactured by Kyowa Interface Science, model: PCA-1) can be used.

  The polishing liquid preferably has a viscosity at 25 ° C. of 1.7 mPa · s or less, more preferably 1.6 mPa · s or less. Moreover, it is preferable that it is 1.1 mPa * s or more normally, More preferably, it is 1.2 mPa * s or more. By setting the viscosity of the polishing liquid to 1.7 mPa · s or less, the surface of the polishing pad is hardly damaged during polishing of the glass substrate, and the life of the polishing pad can be extended. On the other hand, if it is less than 1.1 mPa · s, the liquid film formed between the glass and the polishing pad becomes too thin, the frictional force becomes high, and the vibration of the polishing machine is generated, which is not preferable.

  In order that the contact angle of the polishing liquid after 0.1 second after dropping 1 μl of the polishing liquid on the surface of the polishing carrier is preferably 75 ° or less, specifically, for example, the particle size is small and the abrasive grains Even if the concentration is 5 to 25% by mass, it is possible to select a polishing liquid that is highly dispersible and a polishing carrier that is not too hydrophobic.

  Examples of the present invention will be specifically described below, but the present invention is not limited to these.

[Manufacture of glass substrates]
(Process 1) Shape imparting process The silicate glass plate shape | molded by the float process was processed into the disk shaped glass substrate which has a circular hole in the center part. The inner peripheral side surface and the outer peripheral side surface of this disk-shaped glass substrate were chamfered. Thereafter, lapping of the upper and lower surfaces of the glass substrate was performed using aluminum oxide abrasive grains, and the abrasive grains were washed and removed.

(Step 2) End surface polishing step The inner peripheral side surface and the inner peripheral chamfered portion were polished with a polishing brush and cerium oxide abrasive grains, and scratches on the inner peripheral side surface and the inner peripheral chamfered portion were removed to make a mirror surface. . Next, the outer peripheral side surface and the outer peripheral chamfered portion are polished with a polishing brush and a cerium oxide abrasive grain, and the outer peripheral side surface and the outer peripheral chamfered portion are removed from scratches to become a mirror surface. It was processed into. The glass substrate that had been subjected to inner peripheral end surface polishing and outer peripheral end surface polishing was cleaned and removed by ultrasonic cleaning.

(Step 3) Main Surface Polishing Step Next, using the double-side polishing apparatus of FIG. 2, the main surface of the glass substrate was subjected to primary polishing, then washed and dried. Thereafter, the main plane of the glass substrate was secondarily polished, then washed and dried.

Tertiary polishing (final polishing) was performed on the cleaned glass substrate. As a polishing tool for final polishing, a polishing pad made of soft urethane after being subjected to the above-mentioned dressing treatment (laminated to a thickness of 0.65 mm, hardness is 24 for Shore D hardness, 72 for Shore A hardness), and average primary The upper and lower main planes were polished using a 16B double-side polishing apparatus (DSM-16B-5PV manufactured by Speedfam Co., Ltd.) using a polishing liquid containing colloidal silica having a particle diameter of 20 to 30 nm. The polishing time was set so that the total polishing amount was 1 μm in total in the thickness direction of the upper and lower main planes.
The polishing pad used in Examples 1 to 7 will be described. In Examples 1 to 7, three types of polishing pads were used. In Examples 1 and 2, polishing pad A having high hydrophilicity was used. In Examples 3 to 5, polishing pad B having lower hydrophilicity than polishing pad A was used. In Examples 6 and 7, polishing pad C, which is lower in hydrophilicity than polishing pad B, was used.
Moreover, the polishing liquid used in Examples 1 to 7 will be described. In Examples 1 to 7, three types of polishing liquids were used. In Examples 1, 3, and 6, polishing liquid A was used. In Example 2, Example 4, and Example 7, the polishing liquid B was used. In Example 5, the polishing liquid C was used. The contact angle of the polishing liquid with respect to the polishing carrier is large when the polishing liquid C is used and is small when the polishing liquid B is used. This is considered to be due to the difference in the electrolyte concentration of the polishing liquid. That is, the polishing liquid C has a high electrolyte concentration, the polishing liquid A has an electrolyte concentration next to the polishing liquid C, and the polishing liquid B has an electrolyte concentration lower than the polishing liquid A.

  The polishing liquid used in the main surface polishing step had a viscosity at 25 ° C. of 1.6 mPa · s, and the content of abrasive grains (silica) in the polishing liquid was 7% by mass. The pH of the polishing liquid was adjusted with citric acid so as to be 4.

[Evaluation method]
(1) Contact angle of polishing liquid with respect to polishing pad The polishing pad used in Examples 1 to 7 was dressed on the polishing surface, washed with pure water, and then dried at room temperature for 1 day. 1 μl of polishing liquid was dropped onto the polishing surface of the dried polishing pad, and the contact angle 50 seconds after the polishing liquid was dropped was measured with a contact angle measuring device (manufactured by Kyowa Interface Science, model: PCA-1). .

(2) Contact angle of polishing liquid with respect to polishing carrier 1 μl of polishing liquid is dropped onto the surface of the dried polishing carrier, and the contact angle 0.1 seconds after dropping the polishing liquid is measured with a contact angle measuring device ( It was measured by Kyowa Interface Science, model: PCA-1.

(3) Life of the polishing pad The life of the polishing pad is the same as that in the third polishing (finish polishing) in the above-described step 3, since the polishing surface of the polishing pad is damaged or glass is damaged when polishing is started. The integration of the time for polishing the main surface of the glass substrate with the polishing pad up to the point of time when the scratch was generated and the use was stopped was measured and evaluated according to the criteria shown in the following AC.
A: Accumulation time of polishing main surface of glass substrate with polishing pad is 1200 minutes or more B: Accumulation time of polishing main surface of glass substrate with polishing pad is 800 minutes or more and less than 1200 minutes C: Glass with polishing pad The accumulated time for polishing the main surface of the substrate is less than 800 minutes.

(4) Viscosity of polishing liquid The viscosity of the polishing liquid was measured with a viscometer (manufacturer: manufactured by Toki Sangyo Co., Ltd., model: rotary viscometer RE80L) at a rotational speed of 100 rpm with respect to the polishing liquid at 25 ° C.

(5) pH of polishing liquid
The pH of the polishing solution is a pH standard solution manufactured by Pure Chemical [phthalate pH standard solution (pH 4.01), neutral phosphate pH standard solution (pH 6.86), borate pH standard solution (pH 9.18). ], The pH electrode was washed with pure water, and then the pH of the polishing liquid was measured using a pH measuring machine (Horiba, Ltd., model: D-53S).

  The results are shown in Table 1.

  As shown in Table 1, Examples 1 to 5 in which the contact angle of the polishing liquid to the polishing pad 50 seconds after dropping 1 μl of the polishing liquid onto the polishing surface of the polishing pad is 50 ° or less have a contact angle of 50 The life of the polishing pad was longer compared to Examples 6 and 7, which were above °.

  From this result, the polishing liquid and the polishing pad having a contact angle of 50 ° or less with respect to the polishing pad 50 seconds after dropping 1 μl of the polishing liquid onto the polishing surface of the polishing pad, that is, the polishing liquid to the polishing pad It has been found that the life of the polishing pad can be extended by using a combination of a polishing liquid and a polishing pad with good permeability.

  In addition, in Examples 1 to 4 in which the contact angle of the polishing liquid to the polishing carrier 0.1 seconds after dropping 1 μl of the polishing liquid on the surface of the polishing carrier is 75 ° or less, the contact angle exceeds 75 °. The life of the polishing pad was longer than that of Example 5 which is

  From this result, by using a polishing liquid and a polishing carrier in which the contact angle of the polishing liquid with respect to the polishing carrier 0.1 seconds after dropping 1 μl of the polishing liquid on the surface of the polishing carrier is 75 ° or less, It has been found that the life of the polishing pad can be further extended.

Claims (5)

Using a polishing pad having a foamed resin polishing layer having a Shore D hardness of 40 or less, and a polishing liquid containing silica having a primary particle diameter of 3 to 50 nm as abrasive grains, held in the holding holes of the polishing carrier A method for producing a glass substrate, comprising: a polishing step for polishing a principal plane of the glass substrate, and a cleaning step for cleaning the surface of the glass substrate,
In the polishing step, the main surface of the glass substrate is polished by using the polishing pad and the polishing liquid at which the contact angle of the polishing liquid is 50 ° or less after 50 seconds from dropping 1 μl of the polishing liquid onto the polishing surface of the polishing pad. A method for producing a glass substrate, comprising:   2. The method for producing a glass substrate according to claim 1, wherein in the polishing carrier, the contact angle of the polishing solution after 0.1 seconds after dropping 1 μl of the polishing solution on the surface of the polishing carrier is 75 ° or less.   The method for producing a glass substrate according to claim 1, wherein the polishing liquid has a viscosity at 25 ° C. of 1.7 mPa · s or less.   The said polishing liquid is pH1-pH6, and content of the silica which is an abrasive grain is 5-25 mass%, The manufacturing method of the glass substrate of any one of Claims 1-3.   The said glass substrate is a glass substrate for magnetic recording media which has a circular hole in the center part, The manufacturing method of the glass substrate of any one of Claims 1-4.

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