JPWO2015115652A1 - Method for recycling used polishing slurry, method for producing glass substrate for magnetic disk - Google Patents

Abstract

Provided is a method for reclaiming a used polishing slurry that can sufficiently crush solids generated by centrifugation of a used polishing slurry, thereby suppressing the occurrence of scratches on a glass substrate in a polishing process. One aspect of the present invention is a method for reclaiming a used polishing slurry containing abrasive grains used for polishing a glass substrate, the step of adding a saccharide to the used polishing slurry to form a mixture; Centrifuging the mixture to remove at least a part of the glass component contained in the mixture, and crushing the solid content obtained by the centrifugation.

Description

  The present invention relates to a method for recycling a used polishing slurry and a method for producing a glass substrate for a magnetic disk.

In the polishing treatment of the glass substrate, for example, a cerium abrasive mainly containing cerium oxide may be used as the abrasive grains. Since cerium abrasives are expensive, it is known to recover the used slurry after the polishing process and perform a regeneration process to remove glass components such as glass sludge (glass waste) in the used polishing slurry. . In the regeneration process of the cerium abrasive using solid-liquid separation by centrifugation, the used polishing slurry is centrifuged, the solid content including the abrasive grains is collected, and the liquid including the glass component is discarded.
In the conventional recycling process of used polishing slurries, in order to easily collect abrasive grains, magnesium salt is added to the used polishing slurry before solid-liquid separation, or before and after solid-liquid separation. It is known to perform acoustic wave irradiation (for example, Patent Documents 1 and 2).

International Publication No. 2012/101868 JP 2001-9723 A

When the polishing treatment of the glass substrate was performed using the used polishing slurry regenerated by the conventional regenerating method, it was found that the main surface of the glass substrate was easily damaged. In this regard, as a result of investigations, the abrasive grains contained in the regenerated used polishing slurry contain coarse grains and those with very hard grain boundaries. It was found that the glass substrate was scratched during the polishing process. Abrasive grains having very hard grain boundaries are not crushed even if the grain size is not coarse or is subjected to a load during the polishing process, and as a result, there is a risk of causing scratches on the glass substrate.
It is an object of the present invention to provide a method for regenerating a used polishing slurry capable of sufficiently crushing solid content generated by centrifugation of a used polishing slurry, and thereby suppressing the generation of scratches on a glass substrate in a polishing process. Objective. Another object of the present invention is to provide a method for producing a glass substrate for a magnetic disk that can suppress the occurrence of scratches on the glass substrate during polishing.

The present invention provides the following (1) to (21).
(1) One aspect of the present invention is a method for regenerating a used polishing slurry containing abrasive grains used for polishing a glass substrate,
Adding sugars to the spent polishing slurry to form a mixture;
Centrifuging the mixture to remove at least a portion of the glass component contained in the mixture;
Crushing the solid content obtained by the centrifugation.

(2) In the step of crushing, after adding water, the solid content is crushed, and the used polishing slurry is regenerated according to (1).

(3) The saccharide is selected from the group consisting of cellulose, pectin, protopectin, carrageenan, galactose, xanthan gum, locust bean gum, guar gum, psyllium seed gum, tamarind seed gum, tara gum, chitin, agarose or combinations thereof. The method for regenerating a used polishing slurry according to (1) or (2).

(4) The method for regenerating a used polishing slurry according to any one of (1) to (3), wherein the saccharide is insoluble in water.

(5) The added amount of the saccharide is 0.1 to 5% by mass with respect to the weight of the polishing abrasive grains. The used polishing slurry according to any one of (1) to (4), Playback method.

(6) The method for regenerating a used polishing slurry according to any one of (1) to (5), wherein the pH of the mixture is 5.5 to 13.

(7) The used polishing slurry regeneration method according to any one of (1) to (6), wherein in the crushing step, ultrasonic waves having a frequency of 16 to 120 kHz are irradiated.

(8) The method for regenerating a used polishing slurry according to any one of (1) to (7), further comprising a step of drying the crushed solid content.

(9) Yet another aspect of the present invention is a method for reclaiming a used polishing slurry containing abrasive grains used for polishing a glass substrate,
Adding sugars to the spent polishing slurry to form a mixture;
Centrifuging the mixture to remove at least a portion of the glass component contained in the mixture;
Crushing the solid content obtained by the centrifugation, and
The used polishing slurry is a used polishing slurry regenerated by the used polishing slurry regeneration method according to any one of (1) to (8).

(10) Yet another aspect of the present invention is a method for reclaiming a used polishing slurry containing abrasive grains used for polishing a glass substrate,
Including a centrifugation process for performing centrifugation using the treatment liquid containing the used polishing slurry,
The treatment liquid is adjusted to include a lump having a surface portion swollen by contact with water and an interior surrounded by the surface portion and blocked from entering water. .

(11) Furthermore, including a crushing treatment for crushing the solid content obtained by the centrifugation process,
In the pulverization treatment step, the used polishing slurry according to (10), wherein the solid content is crushed after adding water.

(12) The used polishing slurry regeneration method according to (11), wherein in the crushing treatment, ultrasonic waves having a frequency of 16 to 120 kHz are irradiated.

(13) The method for regenerating a used polishing slurry according to (11) or (12), further comprising a drying treatment for drying the crushed solid content.

(14) The treatment liquid is selected from the group consisting of cellulose, pectin, protopectin, carrageenan, galactose, xanthan gum, locust bean gum, guar gum, psyllium seed gum, tamarind seed gum, tara gum, chitin, agarose or combinations thereof. The method for reclaiming a used polishing slurry according to any one of (10) to (13), wherein the saccharide is used to adjust to include the lump.

(15) The method for regenerating a used polishing slurry according to (14), wherein the saccharide is insoluble in water.

(16) The method for regenerating a used polishing slurry according to (14) or (15), wherein the addition amount of the saccharide is 0.1 to 5% by mass with respect to the weight of the polishing abrasive grains.

(17) The method for regenerating a used polishing slurry according to any one of (10) to (16), wherein the pH of the treatment liquid is 5.5 to 13.

(18) Yet another aspect of the present invention is a method for reclaiming a used polishing slurry containing abrasive grains used for polishing a glass substrate,
Including a centrifugation process for performing centrifugation using the treatment liquid containing the used polishing slurry,
The treatment liquid is adjusted to include a lump having a surface portion swollen by contact with water, and an interior surrounded by the surface portion and blocked from entering water,
The used polishing slurry is a used polishing slurry regenerated by the used polishing slurry regeneration method according to any one of (10) to (17).

(19) The method for reclaiming a used polishing slurry according to any one of (1) to (18), wherein the polishing abrasive grains contain cerium oxide or zirconium oxide as a main component.

(20) The method for regenerating a used polishing slurry according to any one of (1) to (19), wherein the centrifugation is performed at 500 to 3000 G.

(21) Yet another aspect of the present invention is a method for producing a glass substrate for a magnetic disk,
A polishing process for polishing the main surface of the glass plate using the abrasive grains regenerated by the method for regenerating a used polishing slurry according to any one of (1) to (20).

  According to the method for reclaiming a used polishing slurry of the present invention, it is possible to sufficiently disintegrate the solid content generated by the centrifugation of the used polishing slurry, thereby suppressing the glass substrate from being damaged in the polishing process. Moreover, according to the manufacturing method of the glass substrate for magnetic discs of this invention, generation | occurrence | production of the damage | wound of a glass substrate in a grinding | polishing process is suppressed.

Fig.1 (a) is a figure which shows notionally the state of the water-containing aggregate and polishing abrasive grain in a used polishing slurry. FIG.1 (b) is a figure which shows notionally the solid content produced by centrifugation. It is a figure which shows notionally the mode between the particle | grains of the abrasive grain after water permeate | transmits a water-containing aggregate.

  Hereinafter, the method for regenerating a used polishing slurry and the method for producing a glass substrate for a magnetic disk of the present invention will be described in detail.

(Recycle method of used polishing slurry)
The regeneration method according to this embodiment is a regeneration method of a used polishing slurry containing polishing abrasive grains (used polishing abrasive grains) used in the polishing treatment of a glass substrate, and is a saccharide (for example, insoluble in water described later) A mixture (formation step) to add a spent polishing slurry to the spent polishing slurry (to form a mixture), and to centrifuge the mixture to remove at least a portion of the glass component contained in the mixture ( A step of removing), and a step of crushing the solid content obtained by the centrifugation (step of crushing). The step of forming the mixture can be rephrased as a step of preparing or preparing the mixture, and a step of preparing a treatment liquid described later.
In this embodiment, the case where the used polishing slurry used for polishing is regenerated will be described as an example. However, the regeneration method of this embodiment regenerates the used polishing slurry (including abrasive grains) used for grinding. It can also be applied to cases.

In the polishing process, for example, the main surface of the substrate held by the carrier is sandwiched between a pair of polishing pads, and the substrate and the polishing pad are relatively moved by planetary gear movement while supplying polishing slurry between the polishing pad and the substrate. And then polishing. The glass substrate is polished using, for example, a double-side polishing apparatus described later. The glass substrate to be polished is not particularly limited in use, and is, for example, a glass substrate used for panels for various display devices such as LCD devices, mask blanks, and magnetic disks for HDD devices.
A used abrasive grain means an abrasive grain that has been used for polishing a glass substrate at least once in the past. Examples of the polishing treatment include first polishing and second polishing performed in a method for manufacturing a glass substrate for a magnetic disk described later. The abrasive grains are not particularly limited. For example, an abrasive mainly containing cerium oxide (hereinafter also referred to as cerium abrasive) and an abrasive mainly containing zirconium oxide are used. The cerium abrasive may contain oxides of other rare earth elements such as lanthanum, praseodymium and neodymium in addition to cerium. The abrasive may further contain an abrasive other than the main abrasive. The average particle size of the abrasive grains is, for example, 0.1 to 3 μm in D50 (a particle size corresponding to a cumulative particle size of 50% from the fine particle side by the laser diffraction / scattering particle size distribution measurement method).
The slurry is obtained by dispersing abrasive grains in water, and may contain a dispersing agent and a polysaccharide insoluble in water described later, in addition to the abrasive grains. The water used for the slurry may contain impurities such as tap water as well as pure water such as RO water, deionized water, and distilled water. Although a dispersing agent is not specifically limited, For example, a phosphoric acid type dispersing agent is used. In addition, what was reproduced | regenerated by the reproduction | regeneration method of the used polishing slurry of this invention may be used for a used polishing slurry. In this case, it is possible to obtain the effect of reducing the cost of the abrasive grains by repeatedly regenerating and using the used polishing slurry.

(A) Step of forming the mixture In the step of forming the mixture, saccharides (eg, polysaccharides insoluble in water) are added to the used polishing slurry to form the mixture. The saccharide is preferably a saccharide that swells upon contact with water. By having this property, a lump (so-called lumps) is easily formed in water. Moreover, it is preferable that saccharides have low solubility in neutral water (hereinafter, also simply referred to as water) at room temperature (20 ° C.), and more preferably insoluble. By having such a property, it becomes possible for a dama to exist stably for a long time. From the above viewpoints, among saccharides, cellulose, chitin; galactose, locust bean gum, tara gum; protopectin, carrageenan, xanthan gum, guar gum, psyllium seed gum, tamarind seed gum, tara gum, chitin, agarose, cellulose, chitin; Galactose, locust bean gum, and tara gum are more preferable, and cellulose and chitin are most preferable. Saccharides can be used in combination of two or more. When cellulose is used, it is more preferable to use crystalline cellulose.

Here, a polysaccharide insoluble in water will be described as an example of a sugar insoluble in water. In the present specification, the term “insoluble in water” or “insoluble” includes not only insoluble in water but also partly dissolved in water. The phrase “partially dissolved in water” specifically means that the amount dissolved in water is 30% by weight or less, or 20% by weight or less, or 10% by weight or less of the added amount. Therefore, the “water-insoluble polysaccharide” or “insoluble polysaccharide” described below is a polysaccharide in which a part of the added amount (30 wt%, 20 wt%, or 10 wt%) or less is dissolved in water. In other words, sugars. Polysaccharides that are insoluble in water have the property of absorbing water and swell without dissolving in water, and exist as aggregates (also referred to as hydrous aggregates or lumps) containing water in the used polishing slurry. Thus, those having water absorption and water retention are preferably used. Examples of such substances include cellulose, pectin, protopectin, carrageenan xanthan gum, locust bean gum, guar gum, psyllium seed gum, tamarind seed gum, tara gum, chitin, agarose and the like. Of these, cellulose, pectin, protopectin, and carrageenan are preferably used. In addition, from the viewpoint of enabling the formation of lumps in water and allowing them to exist stably for a long period of time, cellulose, chitin; locust bean gum, tara gum; protopectin, carrageenan, xanthan gum, guar gum, psyllium seed Gum, tamarind seed gum, tara gum, chitin and agarose are preferred, cellulose and chitin; galactose, locust bean gum and tara gum are more preferred, and cellulose and chitin are most preferred. In the following description, saccharides are representatively described with respect to polysaccharides that are insoluble in water (that is, polysaccharides in which a part or less of the added amount is dissolved in water).
Such a water-insoluble polysaccharide is added to the used polishing slurry, and the water-containing aggregates are contained in the mixture, so that the solid content generated by the subsequent centrifugation can be easily crushed. In addition, the water-insoluble polysaccharide has an effect of preventing the solid content (also referred to as sediment) generated by centrifugation from becoming too hard.

The addition amount of the insoluble polysaccharide is preferably 0.1 to 5% by mass with respect to the weight (dry weight) of the abrasive grains. If it is less than 0.1% by mass, it may take time to disintegrate the solid content obtained after centrifugation. Moreover, when it adds more than 5 mass%, insoluble polysaccharide will enter easily between an abrasive grain and a to-be-polished substrate, and a polishing rate may fall after reproduction | regeneration.
The type and amount of the insoluble polysaccharide are determined so that the insoluble polysaccharide present in the solid content generated by centrifugation can further absorb moisture, in other words, for example, the water-containing aggregate retains water in the outer portion and the inner portion. Is appropriately determined so as to be in a dry state (so-called “dama” state). The dry state here means a state where water can be further absorbed after centrifugation or a state where water is not sufficiently absorbed. Therefore, when the water-containing aggregate in a dama-like state is crushed by applying an external force, a dry portion appears. In the following description, when it is referred to as a water-containing aggregate, it is a state in which water is kept in the outer part and dried in the inner part, in other words, unless otherwise noted, in other words, a surface part swollen by contact with water (outer part) ) And the inside (inner part) surrounded by the surface portion and blocked from entering water.

It is preferable that the insoluble polysaccharide is added to the used polishing slurry in a state in which the water-containing aggregate is previously formed. The hydrous aggregate can be obtained, for example, by adding an insoluble polysaccharide to water and appropriately performing stirring and ultrasonic irradiation. At this time, it is desirable that the inner part of the water-containing aggregate is not sufficiently absorbed. The size of the water-containing aggregate is not particularly limited, but the maximum length is, for example, 1 to 300 μm. It is preferable that the water-containing aggregate has a particle size larger than that of the abrasive grains.
The used polishing slurry can be brought into the state shown in FIG. 1 (a) by adding insoluble polysaccharides and then stirring moderately to adhere the abrasive grains to the surface of the hydrous aggregate. it can. Fig.1 (a) is a figure which shows notionally the state of the water-containing aggregate and polishing abrasive grain in a used polishing slurry. In FIG. 1A, a large number of abrasive grains 3 are attached to the surface of the hydrous aggregate 1. In FIG. 1, the sizes of the hydrous aggregate 1 and the particles 3 are adjusted for easy understanding.
In addition, the used polishing slurry containing the water-containing aggregates (lumps) is, in other words, a processing liquid that is subjected to centrifugation in the centrifugation process of the removing step described later. In other words, the step of forming the abrasive grains and the mixture can be rephrased as adjusting the treatment liquid used in the centrifugal separation treatment to include a lump.

The pH of the mixture of the insoluble polysaccharide and the used polishing slurry obtained by adding the insoluble polysaccharide to the used polishing slurry is preferably adjusted to 5.5 or more, more preferably 7 or more, and even more preferably. Is 10 or more. When the pH is less than 5.5, the effect of removing the glass component present in the slurry and the glass component adhering to the abrasive grains is lowered, and the glass substrate is polished using the regenerated used polishing slurry. In some cases, the polishing rate cannot be sufficiently recovered. On the other hand, under strong alkalinity exceeding pH 13, alkaline earth metal ions (for example, Mg ²⁺ , Ca ²⁺ ) and aluminum ions (Al ³⁺ ), which are glass components, form hydroxides, precipitate, and are centrifuged. In some cases, it may be mixed into a later solid content, leading to a decrease in the polishing rate and the occurrence of scratches on the glass substrate. Therefore, the pH is preferably 13 or less. The adjustment of pH is performed using, for example, a strong base such as sodium hydroxide or potassium hydroxide and a strong acid such as sulfuric acid or phosphoric acid as appropriate, but the method is not particularly limited to these methods.

  In addition, it is preferable that the coarse particle | grains which are foreign materials are removed by filtering before the step which forms a mixture in a used polishing slurry. Coarse particles are, for example, solid components such as polishing pad debris, particles of abrasive grains that have been dried and coarsened, and glass pieces such as glass chips, which are mixed in the used polishing slurry by the polishing process. By removing such foreign matter, it is possible to prevent solid components other than the abrasive grains from being mixed in the solid content generated by the “removing step” performed later. Here, the coarse particles refer to particles having a maximum length (diameter) of 15 μm or more.

(B) Removing Step In the removing step, the mixture (treatment liquid) is centrifuged to remove at least a part of the glass component contained in the mixture (also referred to as a centrifugation treatment). Centrifugation is performed using a centrifuge. Centrifugation is preferably performed at 500 to 3000G. Thereby, solid content and a glass sludge component can be isolate | separated effectively. More preferably, it is performed under conditions of 600 to 1800G. The turning radius and number of revolutions of the centrifuge are selected to meet such a range of centrifugal forces. Moreover, the time of centrifugation is suitably adjusted according to the centrifugal force of centrifugation, for example, is 15 minutes-1 hour. The conditions such as the centrifugal force of centrifugation, the time of centrifugation, the time of dehydration, the time of scraper treatment, etc. are the concentration and amount of slurry to be centrifuged, the amount of glass components removed, the weight of solids, It is determined appropriately in consideration of the recovery rate and the like. The moisture content of the solid content is preferably 10 to 40% by mass for the reason that the removal amount of the glass component and the crushability are not deteriorated. The amount of water is appropriately adjusted in consideration of the slurry concentration and the amount of slurry to be centrifuged, the amount of glass components removed, the weight of solids, the recovery rate, and the like. Centrifugation may be performed while circulating and feeding the separated liquid back to the centrifuge.

  In the removing step, the mixture is separated into a solid content and a liquid containing abrasive grains (solid-liquid separation). Moreover, the liquid after the solid-liquid separation may be centrifuged again until the concentration of the abrasive grains becomes a certain value or less to recover the solid content. When performing centrifugation again, insoluble polysaccharides may be added. The liquid is finally discarded. In addition, since the glass component (two types of melt | dissolving thing and microparticles | fine-particles) originating in glass sludge (glass waste) exists in a liquid, in the step to remove, it is glass component (2 of melt | dissolving thing and microparticles | fine-particles). Type) is removed.

Here, the effect | action of the insoluble polysaccharide contained in the isolate | separated solid content is demonstrated.
As shown in FIG. 1B, the solid content is accumulated so that the abrasive grains 3 overlap each other with an insoluble polysaccharide (not shown) interposed therebetween, as will be described later. FIG.1 (b) is a figure which shows notionally the solid content produced by centrifugation. In addition, in FIG.1 (b), in order to demonstrate easily, the space | interval between the particle | grains 3 of an abrasive grain is abbreviate | omitted and shown. Also, the size of the abrasive grains is shown uniformly for convenience of explanation. The water-containing agglomerates present in the used polishing slurry in the step of forming the above mixture are subjected to centrifugal force by centrifugal separation, so that abrasive abrasive particles adhering to the surface enter the inside thereof, thereby The particles 3 of the abrasive grains approach each other and are deposited with the insoluble polysaccharide 5 interposed between the particles 3 as shown in FIG. FIG. 2 is a diagram conceptually showing the state of the abrasive grains and the insoluble polysaccharide contained in the solid content, and focusing on a part of the solid content. Note that the interval between the particles 3 of the abrasive grains in FIG. 1 and the interval between the particles 3 shown in FIG. 2 are adjusted for easy understanding. In FIG. 2, the sizes of the particles 3 and the insoluble polysaccharides 5 are adjusted for easy understanding.
FIG. 2 shows the case where cellulose is used as the insoluble polysaccharide. As shown in FIG. 2, the abrasive abrasive grains 3 are deposited in contact with the fibrous cellulose and not in contact with each other. The water-containing agglomerates gradually become smaller in the process of centrifugation from the above-mentioned lumpy form, and serve as a cushion when the spacing between the abrasive grain particles 3 is reduced. It has the effect | action which suppresses the contact of three. Due to the action of such an insoluble polysaccharide, a solid content that is easy to be crushed later is generated even if centrifugation is performed.

(C) Step of crushing In the step of crushing, the solid content obtained by centrifugation is crushed (also referred to as crushing treatment). The crushing of the solid content is preferably performed by, for example, generating ultrasonic cavitation using a homogenizer, but may be performed using an ultrasonic bath. When using a homogenizer, it is preferable to generate ultrasonic waves of 16 kHz to 120 kHz. The time for crushing with ultrasonic waves having a frequency in this range is, for example, 1 to 60 minutes. Thereby, the particle size distribution of the abrasive grains can be made good and suitable for reuse.

  The crushing of the solid content is preferably performed after adding water to the solid content. Since water-containing aggregates have room to absorb water further, the water penetrates into the dried inner part by adding water, so that the solids can be crushed more easily and polished. The particle size distribution of the abrasive grains becomes better. The amount of water added is not particularly limited, but is, for example, an amount such that the weight of the solid content is 1 to 40% by weight. Water may be added by adding water.

  The step of removing and the step of crushing may be alternately performed, for example, once or twice.

  After the crushing step, the foreign matter may be removed once or a plurality of times. For example, filtering can be used as a foreign matter removal method. The foreign matter removed here is, for example, abrasive grains that have not been sufficiently crushed. The size of the foreign matter to be removed is, for example, 15 μm or more. Moreover, when performing it several times, you may adjust the particle diameter of an abrasive grain by grinding | pulverization etc. before removing the next foreign material.

  The regenerated spent polishing slurry may be dried (drying step or drying process) in order to improve the handleability of the abrasive grains. Drying is performed, for example, by spray drying. When the abrasive grains in the used polishing slurry are allowed to stand, they may settle and aggregate at the bottom of the container, producing coarse particles. By performing drying in order to prevent such a phenomenon from occurring, it is possible to suppress the occurrence of scratches due to coarse particles.

According to the regeneration method of the present embodiment, by adding insoluble polysaccharides to the recovered used polishing slurry, it is possible to prevent solids from becoming hard due to centrifugation, and to obtain solids that are easily crushed. Can do.
In order to prevent the abrasive grains contained in the slurry from becoming hard cakes, it is known that insoluble polysaccharides are added to the slurry before the polishing treatment of the glass substrate, but insoluble added before the polishing treatment. The polysaccharide is not in a dry state because it is sufficiently dispersed in the slurry in the polishing process by the load received from the polishing pad, carrier, glass substrate, etc. during the polishing process, and is hydrated to the inside. In the regeneration method of the present embodiment, the insoluble polysaccharide is added to the used polishing slurry before centrifugation so that an insoluble polysaccharide (water-containing aggregate) in a dry state is formed. In the crushing step, moisture is absorbed into the dried portion, and a shear stress is applied thereto, whereby the solid content is easily crushed. Thus, in the regeneration method of the present embodiment, the solid content is sufficiently prevented from being hardened by adding the insoluble polysaccharide again after collecting the used polishing slurry. In addition, according to the regeneration method of the present embodiment, the solid content is easily crushed, whereby the abrasive grains having a coarse particle size and the abrasive grains having extremely hard grain boundaries remain in the slurry. Since it can suppress, when a grinding | polishing process is performed using the reproduced | regenerated used polishing slurry, it can suppress that a damage | wound arises on the main surface of a glass substrate.
The used polishing slurry regeneration method of this embodiment can be rephrased as a slurry manufacturing method in that at least the particle size of the abrasive grains is adjusted. Further, the regeneration method of the present embodiment is a case where the glass substrate to be polished is a glass substrate used for a magnetic disk, and when the abrasive grains contain cerium oxide (ceria). It can be said that this is a method for regenerating ceria slurry for disk glass substrates.

(Method for producing glass substrate for magnetic disk)
Next, the manufacturing method of the glass substrate for magnetic disks of this embodiment is demonstrated.
This manufacturing method includes a polishing process for polishing the main surface of the glass plate using the abrasive grains regenerated by the above-described method for regenerating a used polishing slurry.
In this embodiment, the case where the used polishing slurry regenerated by the method for regenerating a used polishing slurry is used for polishing will be described as an example. However, the used polishing slurry can also be used for grinding.

  If the outline of the manufacturing method of this embodiment is demonstrated, the shaping | molding process which forms the plate-shaped glass blank which has a pair of main surface first will be performed. The glass blank is a material for a glass substrate for a magnetic disk. Next, this glass blank is subjected to a rough grinding process. Thereafter, the glass blank is subjected to shape processing to form a glass substrate, and further subjected to end face polishing. Thereafter, the glass substrate is subjected to a precision grinding process using fixed abrasive grains. Thereafter, a first polishing process and a second polishing process are performed on the glass substrate. In the present embodiment, the flow is performed according to the above flow, but the flow and the type of processing are not limited, and the above processing can be appropriately omitted as necessary. Hereinafter, each process described above will be described.

(A) Molding process of glass blank In a molding process, it shape | molds, for example using the press molding method. A disk-shaped glass blank can be obtained by the press molding method. Instead of the pressing method, a glass blank may be manufactured using a known forming method such as a downdraw method, a redraw method, or a fusion method. A disk-shaped glass substrate that is a base of the magnetic disk glass substrate can be obtained by appropriately performing the shape processing described later on the plate-shaped glass blank made by these methods.

(B) Rough grinding process Next, a rough grinding process is performed. In the rough grinding process, the main surfaces on both sides of the glass blank are ground while the glass blank is held by a carrier (not shown) of a double-side grinding apparatus. Specifically, the glass blank is held in a holding hole provided in the carrier, and is sandwiched between an upper surface plate and a lower surface plate, and an upper surface plate or a lower surface plate is supplied while supplying a grinding liquid containing an abrasive. By moving either one or both, the glass substrate and each surface plate are relatively moved, and both main surfaces of the glass substrate are ground. For example, loose abrasive grains are used as the abrasive. In the rough grinding process, the glass blank is ground so as to approximate the target plate thickness dimension and the flatness of the main surface. The rough grinding process is performed according to the dimensional accuracy or surface roughness of the molded glass blank, but can be omitted as appropriate.

(C) Shape processing processing Next, shape processing processing is performed. In the shape processing, by forming a circular hole in a glass blank using a known processing method, a disk-shaped glass substrate having a circular hole is obtained. Thereafter, the end surface of the glass substrate is chamfered. Chamfering is performed on both the inner and outer end faces of the glass substrate. By performing chamfering, a side wall surface orthogonal to the main surface and a chamfered surface (intervening surface) connecting the side wall surface and the main surface are formed on the end surface of the glass substrate.

(D) End surface polishing process Next, the end surface polishing process of a glass substrate is performed. In the end surface polishing treatment, a polishing liquid containing free abrasive grains is supplied between the polishing brush and the end surface of the glass substrate, and polishing is performed by relatively moving the polishing brush and the glass substrate in the thickness direction of the glass substrate. Do. By the end surface polishing treatment, the end surfaces on the inner peripheral side and the outer peripheral side of the glass substrate are polished into a mirror state.

(E) Fine grinding process Next, a fine grinding process is performed on the main surface of the glass substrate. In the fine grinding process, it is preferable to perform grinding on the main surface of the glass substrate using a double-side grinding apparatus in which fixed abrasive grains are attached to a surface plate. Specifically, both main surfaces of the glass substrate are ground in substantially the same manner as the rough grinding process except that the fixed abrasive is used instead of the loose abrasive. The glass substrate is held by the carrier of the above embodiment and is ground while being moved by the planetary gear in the double-side grinding apparatus. In the fine grinding process, the main surface of the glass substrate is ground by bringing the ground surface of the surface plate to which the fixed abrasive particles are adhered and the main surface of the glass substrate into contact with each other, but instead of this, loose abrasive grains were used. Grinding may be performed.

(F) First polishing treatment Next, a first polishing treatment is performed on the main surface of the glass substrate. In the first polishing process, the main surface on both sides of the glass substrate is polished by holding the glass substrate on a carrier using a well-known double-side polishing apparatus. A well-known apparatus can be used for the double-side polishing apparatus for performing the first polishing process. The apparatus includes a pair of upper and lower surface plates, an internal gear sandwiched between the upper and lower surface plates, a sun gear provided on the lower surface plate, and a plurality of carriers engaged with the internal gear and the sun gear. Yes. A polishing pad is affixed to each surface plate. In this apparatus, the glass substrate is sandwiched between the upper and lower surface plates while being held in the holding holes of the carrier, and the carrier holding the glass substrate revolves while rotating by rotating the upper and lower surface plates, Perform planetary gear motion. As a result, the glass substrate and the polishing pad move relative to each other, and the main surface of the glass substrate is polished. In particular, in the first polishing treatment, polishing is performed by using a free abrasive grain so that the polishing pad attached to the surface plate is brought into contact with the main surface of the glass substrate. During the first polishing process, a slurry containing loose abrasive grains is supplied between a glass substrate and a polishing pad via a pipe (not shown) from a supply tank (not shown) of a double-side polishing apparatus. After the slurry is supplied between the glass substrate and the polishing pad, the slurry may be collected, and may be circulated and supplied again between the glass substrate and the polishing pad while performing the same or different batch of polishing processing. . The used abrasive slurry regenerated by the above-described regeneration method is used for the slurry containing loose abrasive grains. The free abrasive grains are not particularly limited, and, for example, cerium oxide abrasive grains (the cerium abrasive), zirconia abrasive grains, or a combination thereof may be used.

  In the first polishing treatment, for example, removal of cracks and distortions remaining on the main surface when grinding with fixed abrasive grains is performed as a pretreatment, or removal of minute surface irregularities (roughness and waviness) generated on the main surface. To do. By appropriately adjusting the machining allowance, it is possible to reduce the surface roughness of the main surface, for example, the arithmetic average roughness Ra, while preventing the shape of the end of the main surface from excessively dropping or protruding. Moreover, since the abrasive grains contained in the used polishing slurry used in the first polishing treatment have a good particle size distribution by the above-described regeneration method, scratches occur on the main surface of the glass substrate. Is suppressed.

  The slurry recovered in the first polishing process may be further recovered by the above-described regeneration method. The recovered slurry (used polishing slurry) is further subjected to a polishing process for another glass substrate. May be used.

(G) Second polishing (mirror polishing) process Next, a second polishing process is performed. The second polishing treatment aims at mirror polishing of the main surface. The second polishing process may use the same double-side polishing apparatus and polishing method as used in the first polishing process, but the size of the polishing abrasive grains should be smaller than the polishing abrasive grains used in the first polishing process. Is preferred. Thereby, the roughness of the main surface can be reduced while preventing the shape of the end portion of the main surface from excessively dropping or protruding. After the second polishing process, the glass substrate is taken out from the double-side polishing apparatus and cleaned.
After the second polishing process, an inspection process for inspecting the quality of the glass substrate may be performed after the glass substrate is further cleaned (final cleaning).

(Example)
In order to confirm the effect of the present invention, the following experiment was conducted. Specifically, the conditions of the used polishing slurry when performing centrifugation are varied as shown in Tables 1 to 3 (Samples 1 to 15), and the used polishing slurry is regenerated according to the following procedure. In addition to measuring the removal amount and polishing rate of the glass component in each used polishing slurry, the degree of generation of scratches generated when the glass substrate was polished using the regenerated slurry (regenerated slurry) was evaluated.

  The used polishing slurry was regenerated by sequentially performing the following steps 1 to 7. As the used polishing slurry, a slurry containing unused cerium abrasive was used, and the first polishing treatment of the above embodiment was performed once and the recovered slurry was used. The first polishing process was performed using a double-side polishing apparatus under the same polishing conditions as the first polishing process described later. The processes other than the first polishing process were performed according to the contents of the above embodiment.

Step 1: Foreign matter removal step Foreign matter such as a glass chip was removed by filtering. The size of foreign matter to be removed was set to 15 μm or more.

Step 2: Solid-liquid separation step After adding sugars to the used polishing slurry according to Tables 1 to 3 and adjusting the pH, solid-liquid separation is performed using a centrifuge, and the liquid is discarded. Was recovered. Centrifugation was performed at 1000 G for 60 minutes.
In addition, in the column of “type and amount of added saccharide” of Tables 1 to 3, the type and amount of added saccharide are shown side by side. Moreover, the addition amount of saccharides is represented by mass ratio with respect to the weight (dry weight) of an unused abrasive grain.

Step 3: Crushing step Water was added so that the solid content was 10 to 30% by weight, and ultrasonic cavitation was generated at a frequency of 20 kHz using a homogenizer, and the solid content was crushed for 30 minutes. .
Step 4: Foreign matter removal step Foreign matter was removed from the slurry obtained in Step 3 by filtering. The size of the foreign matter to be removed was set to 15 μm or more.
Process 5: Particle diameter adjustment process The particle diameter of the cerium abrasive | polishing agent contained in the slurry obtained at the process 4 was adjusted using the wet cyclone as a classifier. This step is performed to remove abrasive grains that have a particle size that is too small to contribute to polishing. Therefore, there is no significant effect even if not implemented. When not implemented, the polishing rate is slightly reduced.
Step 6: Foreign matter removal step Foreign matter was removed from the slurry obtained in Step 5 by filtering. The size of the foreign matter to be removed was set to 15 μm or more.
Step 7: Drying Step The slurry was spray dried.

(Evaluation of glass component removal)
The content of the glass component contained in the cerium abrasive of each sample obtained in step 7 was analyzed by fluorescent X-ray analysis. The content of the glass component was evaluated as a ratio of the weight of SiO _{2 to} the weight of the cerium abrasive (ratio of SiO ₂ / cerium abrasive). The SiO ₂ / cerium abrasive ratio is a parameter indicating the removal amount of the glass component, and is the weight of SiO ₂ attached to the cerium abrasive with respect to the weight of the cerium abrasive contained in the regenerated used polishing slurry. As the value of SiO 2 _/ abrasive grain ratio is small, indicating that high removal effect of the glass component. The weight ratio of SiO ₂ to cerium abrasive is shown in Table 2.

(Evaluation of polishing rate and degree of scratching)
As a double-side polishing apparatus equipped with a planetary gear mechanism using a slurry containing each sample of cerium abrasive (used polishing slurry), an apparatus 400 used in the first polishing process described in JP 2012-133882 A is used. The first polishing process of the above embodiment was performed on the glass substrate under the following polishing conditions. A suede type polishing pad made of polyurethane foam was attached to the surfaces of the upper and lower surface plates.
・ Abrasive grain concentration: 10% by weight
-Load on glass substrate by upper surface plate and lower surface plate: 100 g / cm ²
・ Polishing time: 60 minutes

As the glass substrate, an amorphous aluminosilicate glass having the following composition having a nominal size of 2.5 inches was used. That is, SiO ₂ is 58 wt% to 68 wt%, Al ₂ O ₃ is 5 wt% to 20 wt%, Li ₂ O is 0 wt% to 10 wt%, and Na ₂ O is 4 wt% to 12 wt%. A glass containing, as main components, wt% or less, K ₂ O from 0 wt% to 6 wt%, and ZrO ₂ from 1 wt% to 10 wt% is used.

  After the first polishing treatment, the glass plate was washed and dried, and the polishing rate was calculated from the difference in weight of the glass substrate before and after polishing. The glass substrate after cleaning and drying is irradiated with light from a condensing lamp in a dark room, and the number of scratches and pits on the main surface (both sides) of the glass substrate is visually counted. The case of less than one piece / single side was evaluated as level A, the case of 20 or more and less than 100 pieces / single side was evaluated as level B, and the case of 100 pieces / single side or more was evaluated as level C. If it is level A and B, generation | occurrence | production of a damage | wound can be suppressed and there is no problem practically. The polishing rate was shown as a relative value with Sample 2 as 100%. A relative value of 90% or more is practically preferable. The results are shown in Tables 1 and 3.

As shown in Table 1, it was found that when saccharides were added to the used polishing slurry during centrifugation, the generation of scratches on the glass substrate was suppressed. In particular, when the used polishing slurry is prepared by adjusting the pH to 5.5 or more in the step of forming the mixture (samples 2 to 6, 8, and 9), when the pH is adjusted to less than 5.5 ( It was found that the occurrence of scratches was suppressed as compared with Samples 11 and 12). This is presumably because the glass component that hinders polishing was sufficiently removed from the surface of the polishing abrasive grains and the original surface of the polishing abrasive grains was obtained by adjusting the pH to 5.5 or higher.
As shown in Table 2, when the used polishing slurry was prepared by adjusting the pH to 5.5 or more in the step of forming the mixture during the centrifugation, the regenerated used polishing slurry was further used. It was found that the glass component was sufficiently removed from the abrasive grains. In this case, a high polishing rate can be obtained.
As shown in Table 3, it was found that the polishing rate was high when the amount of saccharide added was 5.0% by mass or less.

In addition to the above-described experiment, a regenerated slurry was obtained in the same manner as Sample 2 except that water was not added in Step 3 and crushing was performed using a vibration dryer (Sample 16). The slurry was evaluated for level of scratches by the same method as described above. Other characteristics were the same as those of Sample 2.
A regenerated slurry was obtained in the same manner as Sample 2 except that Step 5 was not performed (Sample 17). When the polishing rate was calculated by the same method as described above for this slurry, the relative value when the sample 2 was 100 was 96. Other characteristics were the same as those of Sample 2.

(Evaluation of yield)
As shown in Table 4, the sugar added to the used polishing slurry is varied (samples 18 to 30), and a regenerated slurry is prepared by sequentially performing the above steps 1 to 7, and the regenerated slurry thus prepared is used. A glass substrate having the same size and composition as described above was subjected to the first polishing process, and processes other than the first polishing process were performed until the final cleaning in the same manner as in the above embodiment. In this way, 1000 glass substrates were produced for each sample. Using a laser-type surface defect inspection apparatus, the yield of each produced glass substrate was evaluated. In each sample, the amount of saccharide added was 0.5% by weight, and the used polishing slurry used for centrifugation was adjusted to pH = 7. Table 4 shows the yield.
In this evaluation, it is possible to detect and remove a substrate that is formed by the first polishing process and cannot be completely removed by the second polishing process and remains on the surface. The difference in degree can be expressed relatively large. That is, it is considered that the number of relatively deep scratches among the scratches formed by the first polishing process is reflected in the yield.

  As described above, the method for regenerating a used polishing slurry and the method for producing a glass substrate for a magnetic disk according to the present invention have been described in detail, but the present invention is not limited to the above-described embodiment, and the scope of the present invention is not deviated. Of course, various improvements and changes may be made.

1 Hydrous agglomerates (blocks)
3 Abrasive Grain Particles 5 Insoluble polysaccharide (polysaccharide in which a part of the added amount or less dissolves)

Claims (10)

A method for reclaiming a used polishing slurry containing polishing abrasive grains used for polishing a glass substrate,
Adding sugars to the spent polishing slurry to form a mixture;
Centrifuging the mixture to remove at least a portion of the glass component contained in the mixture;
Crushing the solid content obtained by the centrifugation, and regenerating a used polishing slurry.   The method for reclaiming a used polishing slurry according to claim 1, wherein, in the crushing step, the solid content is crushed after adding water.   The saccharide is selected from the group consisting of cellulose, pectin, protopectin, carrageenan, galactose, xanthan gum, locust bean gum, guar gum, psyllium seed gum, tamarind seed gum, tara gum, chitin, agarose or combinations thereof. A method for regenerating a used polishing slurry according to 1 or 2.   The method for regenerating a used polishing slurry according to any one of claims 1 to 3, wherein the saccharide is insoluble in water.   The method for regenerating a used polishing slurry according to any one of claims 1 to 4, wherein the addition amount of the saccharide is 0.1 to 5% by mass with respect to the weight of the polishing abrasive grains.   The method for regenerating a used polishing slurry according to any one of claims 1 to 5, wherein the pH of the mixture is 5.5 to 13. A method for reclaiming a used polishing slurry containing polishing abrasive grains used for polishing a glass substrate,
Adding sugars to the spent polishing slurry to form a mixture;
Centrifuging the mixture to remove at least a portion of the glass component contained in the mixture;
Crushing the solid content obtained by the centrifugation, and
The used polishing slurry is a used polishing slurry, which is a used polishing slurry regenerated by the used polishing slurry regeneration method according to any one of claims 1 to 6. A method for reclaiming a used polishing slurry containing polishing abrasive grains used for polishing a glass substrate,
Including a centrifugation process for performing centrifugation using the treatment liquid containing the used polishing slurry,
The treatment liquid is adjusted to include a lump having a surface portion swollen by contact with water and an interior surrounded by the surface portion and blocked from entering water. A method for reclaiming used polishing slurry.   The used polishing slurry according to any one of claims 1 to 8, wherein the polishing abrasive grains contain cerium oxide or zirconium oxide as a main component.   A glass substrate for a magnetic disk, comprising: a polishing process for polishing a main surface of a glass plate using the abrasive grains regenerated by the method for regenerating a used polishing slurry according to claim 1. Production method.

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