Silica-based particle dispersion, polishing slurry for polishing magnetic disk substrates, polishing composition for polishing magnetic disk substrates, and method for producing silica-based particles

Abstract

To provide a silica-based particle dispersion capable of reducing undulation and increasing polishing speed when used as a polishing slurry.SOLUTION: A silica-based particle dispersion according to the present invention contains a group of silica-based particles consisting of deformed silica-based particles and spherical silica-based particles. The silica-based particle group satisfies the following requirements. [1] A weight-average particle size, etc., is within a prescribed range. [2] An average aspect ratio of a first particle with a major diameter of 10 nm or more and less than 50 nm, a second particle with a major diameter of 50 nm or more and less than 100 nm, and a third particle with a major diameter of 100 nm or more is a prescribed value or more. [3] When an area ratio (S1 / S2) between a projected area (S1) in the particles and an area (S2) of a circle with a circumference equal to the projection perimeter is measured, an average value of the area ratio (S1 / S2) is a prescribed value or less. [4] In a weight equivalent particle size distribution, a particle size ratio (D10 / D90) between D10 and D90 from the particles with a larger diameter is a prescribed value or more.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a silica-based particle dispersion liquid, a polishing slurry for polishing a magnetic disk substrate, a composition for polishing a magnetic disk substrate, and a method for producing a silica-based particle group.

Background Art

[0002] Conventionally, silica sol, fumed silica, fumed alumina, etc. have been used as polishing particles. In the production of a substrate with an integrated circuit of a semiconductor, an aluminum wiring is formed on a silicon wafer, and an oxide film such as silica is provided thereon as an insulating film. In this case, unevenness is generated due to the wiring, so this oxide film is polished and flattened. In the polishing of such a substrate, the surface after polishing is flat without steps or unevenness, and is smooth without micro scratches or the like, and a high polishing rate is required.

[0003] As a method for obtaining a high polishing rate, it is common to use abrasive grains with a large size. However, if the particle diameter of the abrasive grains becomes too large, the flatness of the substrate surface after polishing tends to deteriorate. Therefore, in order to obtain a high polishing rate without deteriorating the flatness of the surface, it is known that it is effective to make the abrasive grains non-spherical, that is, to make the abrasive grains into particles with a deformed shape (deformed particles). As a method for obtaining large-sized deformed particles, as in Patent Document 1, porous silica gel is pulverized by a bead mill or the like to prepare a deformed porous gel, and this deformed porous gel is grown into particles by silicic acid or the like, thereby obtaining a method for obtaining deformed particles with a large size and a high degree of deformation.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, the polishing composition described in Patent Document 1 has a high polishing rate, but when a high flatness is to be obtained on the substrate surface after polishing, it is necessary to prepare the particle size of the irregular particles smaller. When trying to reduce the particle size using the method of Patent Document 1, it is necessary to repeatedly grind the porous silica gel used as the raw material to further reduce the size. Although the size of the irregular porous gel can be reduced by repeatedly grinding, the irregularity of the irregular porous gel is also reduced at the same time. As a result, the irregularity of the irregular silica particles after particle growth using silicic acid or the like is also reduced, which causes a problem of a decrease in the polishing rate. In addition, in order to grind the irregular porous gel to a predetermined size, it is necessary to repeatedly grind it, which is inefficient and uneconomical.

[0006] The present invention aims to provide a silica-based particle dispersion that can reduce waviness and increase the polishing rate when used as a polishing slurry, as well as a polishing slurry for polishing magnetic disk substrates, a polishing composition for polishing magnetic disk substrates, and a method for producing silica-based particles. [Means for solving the problem]

[0007] According to one aspect of the present invention, there is provided a silica-based particle dispersion liquid containing a silica-based particle group consisting of irregular silica-based particles and spherical silica-based particles, wherein the silica-based particle group satisfies the following conditions [1] to [4]: [1] The weight average particle diameter is 50 nm or more and 600 nm or less, and the specific surface area converted particle diameter is 10 nm or more and 300 nm or less. [2] When the aspect ratios of first particles having a major axis of 10 nm or more and less than 50 nm, second particles having a major axis of 50 nm or more and less than 100 nm, and third particles having a major axis of 100 nm or more are measured by SEM image analysis, the average aspect ratio of the first particles is 1.3 or more, the average aspect ratio of the second particles is 1.35 or more, and the average aspect ratio of the third particles is 1.43 or more. [3] When the area ratio (S1 / S2) of the projected area (S1) of the first particles, the second particles and the third particles to the area (S2) of a circle having a circumference equal to the projected perimeter is measured by SEM image analysis, the average area ratio (S1 / S2) of the first particles is 0.84 or less, the average area ratio (S1 / S2) of the second particles is 0.77 or less, and the average area ratio (S1 / S2) of the third particles is 0.66 or less. [4] The particle size ratio (D10 / D90) of the cumulative 10% particle size (D10) from the larger particles to the cumulative 90% particle size (D90) from the larger particles, calculated from the weight-converted particle size distribution, is 5 or more.

[0008] According to one aspect of the present invention, there is provided a polishing slurry for polishing magnetic disk substrates, which contains the silica-based particle dispersion liquid according to the above aspect of the present invention.

[0009] According to one aspect of the present invention, there is provided a composition for polishing magnetic disk substrates, comprising the silica-based particle dispersion liquid according to the above aspect of the present invention.

[0010] According to one aspect of the present invention, there is provided a method for producing a silica-based particle group consisting of irregular silica-based particles and spherical silica-based particles, the method including the following steps 1 to 3: (Step 1) A step of wet-grinding a silica-based gel having a powder strength of 15 GPa or less, represented by the following formula (F1), under alkaline conditions to obtain a first solution containing particles made of irregularly shaped silica-based gel. (Step 2) A step of adding a silicic acid liquid under alkaline conditions to the first solution containing particles made of the irregular silica-based gel, filling the pores between the primary particles of the particles made of the irregular silica-based gel by reacting with the silicic acid contained in the silicic acid liquid, thereby growing the particles while maintaining their irregular shape to form irregular silica-based particles, thereby obtaining a second solution containing the irregular silica-based particles. (Step 3) A step of concentrating the second solution containing the irregularly shaped silica-based particles to recover the silica-based particles. σ = [(1-ε) / π] K H / d 2 (F1) (where σ, d, K, ε, π, and H are: σ: powder strength [Pa], d: average particle size [m], K: average coordination number of the particle, ε: porosity of powder, π: pi, H: Adhesion force of particles [N]) In the description of the manufacturing method of the present application, unless otherwise specified, when referring to the silica-based gel (silica powder) used as the raw material, the term "particles" refers to primary particles, and when referring to the silica-based gel (silica powder), the term "powder" refers to secondary particles formed by aggregation of the primary particles. Effect of the Invention

[0011] According to the present invention, it is possible to provide a silica-based particle dispersion liquid which, when used as a polishing slurry, can reduce waviness and increase the polishing rate, as well as a polishing slurry for polishing magnetic disk substrates, a polishing composition for polishing magnetic disk substrates, and a method for producing silica-based particle groups. [Brief description of the drawings]

[0012]

Figure 1

[0013] [Silica-based particle dispersion] First, the silica-based particle dispersion liquid according to this embodiment will be described. The silica-based particle dispersion according to this embodiment contains a silica-based particle group consisting of irregularly shaped silica-based particles and spherical silica-based particles, and is characterized in that the silica-based particle group satisfies the following conditions [1] to [4]. Here, the spherical silica-based particles refer to silica-based particles that are spherical in shape. Also, the irregular silica-based particles refer to particles that are irregular (non-spherical) in shape other than spherical silica-based particles. More specifically, in the present application, in the SEM image of silica-based particles, the aspect ratio value of the particles is 1.1 or more is considered to be irregular silica-based particles, and the aspect ratio value of the particles is less than 1.1 is considered to be spherical silica-based particles. Examples of the irregular silica particles include primary silica particles obtained by crushing silica particles, and particles in which these primary silica particles are linked together. The linking of primary silica particles means that adjacent primary silica particles are fixed together by the bond formed between them. The type of bond is not particularly limited, but examples include chemical bonds such as siloxane bonds formed by condensation reaction between the surface silanol groups of adjacent primary silica particles.

[0014] [1] The weight average particle diameter is 50 nm or more and 600 nm or less, and the specific surface area converted particle diameter is 10 nm or more and 300 nm or less. When the weight average particle diameter of silica-based particle group is less than 50nm, when used as polishing slurry, the polishing speed becomes low.On the other hand, when the weight average particle diameter of silica-based particle group is more than 600nm, there is a problem that waviness, scratch, etc. worsen.In addition, from the same viewpoint, the weight average particle diameter of silica-based particle group is preferably 100nm or more and 500nm or less, more preferably 120nm or more and 300nm or less. In this specification, the weight average particle diameter of a silica-based particle group or the like is the average particle diameter determined from the weight-based particle distribution obtained by diluting the silica-based particle dispersion to be measured with a 0.05 mass % aqueous solution of sodium dodecyl sulfate to make the solid concentration 2 mass %, injecting 0.1 mL of the diluted solution into a conventionally known disk centrifugal particle size distribution measuring device (e.g., manufactured by CPS Instruments) with a syringe, and measuring in a density gradient solution of 8% to 24% sucrose at a measurement condition of 18,000 rpm.

[0015] When the particle size in terms of specific surface area of the silica-based particle group is less than 10 nm, it is difficult to obtain the required polishing rate, and the particles tend to remain on the substrate. On the other hand, when the particle size in terms of specific surface area of the silica-based particle group exceeds 300 nm, scratches tend to occur and the surface roughness of the substrate after polishing tends to deteriorate. Also, from the same viewpoint, the particle size in terms of specific surface area of the silica-based particle group is preferably 15 nm or more and 200 nm or less, more preferably 20 nm or more and 150 nm or less, and particularly preferably 30 nm or more and 100 nm or less. In this specification, the particle size in terms of specific surface area of a silica-based particle group or the like means the primary particle size of the silica particles, and is a value converted from the specific surface area measured by the nitrogen adsorption method or the titration method.

[0016] [2] When the aspect ratios of the first particles with a major axis of 10 nm or more and less than 50 nm, the second particles with a major axis of 50 nm or more and less than 100 nm, and the third particles with a major axis of 100 nm or more are measured by SEM image analysis, the average aspect ratio of the first particles is 1.3 or more, the average aspect ratio of the second particles is 1.35 or more, and the average aspect ratio of the third particles is 1.43 or more. In the present embodiment, after classifying the silica-based particle group into first particles (small particles), second particles (medium particles), and third particles (large particles) according to the particle size, by adjusting the average aspect ratio of each of the small particles, medium particles, and large particles to a predetermined value or more, it is possible to reduce the waviness while improving the polishing rate. Generally, it is known that particles with a large size have a high polishing rate, and it is also known that the polishing rate increases as the degree of particle irregularity or aspect ratio increases. On the other hand, particles with a large size or a high degree of irregularity or aspect ratio deteriorate the surface roughness and waviness of the polished substrate. In contrast, although the polishing rate of small-sized particles is slow, the surface roughness and waviness of the substrate tend to improve. Also, it is known that spherical particles have a slower polishing rate compared to irregular particles, but the waviness and surface roughness improve. From this, it is considered that the third particles of 100 nm or more have a high polishing rate, but at the same time, they worsen the surface roughness and waviness of the substrate. In contrast, the first particles of 10 nm or more and less than 50 nm have a low polishing rate due to their small size, but improve the surface roughness and waviness of the substrate. Therefore, the first particles play a role in repairing the waviness caused by the third particles. In addition, the second particles of 50 nm or more and less than 100 nm have a polishing performance intermediate between the first and second particles, and play a role in contributing to a certain degree of polishing rate and the elimination of waviness on the substrate surface. In this way, the coexistence of these three components makes it possible to obtain a polished surface that is smooth and has low waviness, while having a high polishing rate. In particular, the first particles of 10 nm or more and less than 50 nm are irregular particles with an aspect ratio of 1.3 or more, and therefore have a certain degree of high polishing rate, and it is presumed that the repair effect of the first particles is enhanced. Here, the SEM image analysis refers to analyzing a planar image of a silica-based particle group using a scanning electron microscope (SEM). At this time, the magnification of the scanning electron microscope is not particularly limited, but is preferably 200,000 times.

[0017] The first particles having a major axis of 10 nm or more and less than 50 nm play a role in reducing the waviness caused by polishing the third particles to the final target waviness in order to achieve low waviness. In addition, by making the average aspect ratio of the first particles 1.3 or more, the polishing speed can be kept high compared to spherical particles. From the viewpoint of improving the polishing speed while reducing the waviness, the average aspect ratio of the first particles is preferably 1.32 or more and 3 or less, more preferably 1.35 or more and 2 or less. This is because the polishing speed is insufficient when the aspect ratio is less than 1.32. In addition, when the aspect ratio is more than 3, the waviness tends to worsen.

[0018] The second particle with a major axis of 50nm or more and less than 100nm plays an intermediate role between the first particle and the third particle, making up for the lack of polishing speed of the first particle and eliminating the waviness that the third particle worsens to some extent.If the average aspect ratio of the second particle is less than 1.35, the particle shape becomes close to a spherical particle, and when used as a polishing slurry, the polishing speed decreases.In addition, the average aspect ratio of this second particle is preferably 1.4 or more and 3 or less, more preferably 1.45 or more and 2 or less, from the viewpoint of reducing moderate waviness and improving polishing speed.

[0019] The third particles having a major axis of 100 nm or more have a high degree of irregularity, and therefore play a role in showing a high polishing rate. That is, a high polishing rate can be achieved by making the average aspect ratio of the third particles 1.43 or more. Moreover, from the viewpoint of improving the polishing rate without excessively worsening the waviness, the average aspect ratio of the third particles is preferably 1.45 or more and 3 or less, and more preferably 1.5 or more and 2 or less.

[0020] [3] When the area ratio (S1 / S2) of the projected area (S1) of the first particles, the second particles and the third particles to the area (S2) of a circle having a circumference equal to the projected perimeter is measured by SEM image analysis, the average area ratio (S1 / S2) of the first particles is 0.84 or less, the average area ratio (S1 / S2) of the second particles is 0.77 or less, and the average area ratio (S1 / S2) of the third particles is 0.66 or less. The ratio of S1 / S2 is a parameter indicating the smoothness of the particle surface, and when the value of S1 / S2 is 1, the particle is spherical, and the smaller the value is, the more minute the unevenness of the particle surface is. When S1 / S2 is close to 1, the particle is spherical, and the polishing speed is slower. The smaller S1 / S2 is than 1, the more uneven protrusions tend to be formed on the particle surface. When the particle surface is uneven, the protrusions selectively contact the substrate, so that stress is concentrated on the substrate and the polishing speed tends to increase. On the other hand, the unevenness does not have a significant effect on the waviness of the substrate surface. In this embodiment, the silica-based particle group is classified into first particles (small particles), second particles (medium particles), and third particles (large particles) according to the particle diameter, and the average value of the area ratio (S1 / S2) of each of the small particles, medium particles, and large particles is adjusted to a predetermined value or less, thereby obtaining abrasive grains with small waviness and high polishing speed.

[0021] Although the primary particles having a major axis of 10 nm or more and less than 50 nm have a low aspect ratio and therefore a slow polishing rate, the polishing rate can be increased to a certain extent by setting the average area ratio (S1 / S2) to 0.84 or less. From the viewpoint of improving the polishing rate, the average area ratio (S1 / S2) of the primary particles is preferably 0.2 or more and 0.8 or less, and more preferably 0.3 or more and 0.75 or less.

[0022] The second particles having a major axis of 50 nm or more and less than 100 nm have a higher aspect ratio than the first particles, and therefore have a relatively high polishing rate. Furthermore, the polishing rate can be further increased by setting the average value of the area ratio (S1 / S2) to 0.77 or less. From the viewpoint of improving the polishing rate, the average value of the area ratio (S1 / S2) of the second particles is preferably 0.2 or more and 0.7 or less, and more preferably 0.3 or more and 0.65 or less.

[0023] The third particles having a major axis of 100 nm or more have the highest aspect ratio and the largest size, and therefore exhibit a high polishing rate, but when the average value of the area ratio (S1 / S2) is 0.66 or less, the polishing rate can be further improved. From the viewpoint of improving the polishing rate, the average value of the area ratio (S1 / S2) of the third particles is preferably 0.2 or more and 0.64 or less, and more preferably 0.3 or more and 0.6 or less.

[0024] [4] The particle size ratio (D10 / D90) of the cumulative 10% particle size (D10) and cumulative 90% particle size (D90) from the large particle size particles, calculated from the weight conversion particle size distribution, is 5 or more. Here, the D10 / D90 ratio indicates the breadth of the particle size distribution, and the larger the D10 / D90 ratio, the broader the particle size distribution. In other words, when the D10 / D90 ratio is high, it means that small and large particles are present at the same time. Therefore, while large particles show a high polishing speed, they worsen waviness, but the small particles present at the same time have the effect of repairing the worsened waviness. From the viewpoint of reducing waviness and improving the polishing speed, the particle size ratio (D10 / D90) of the silica-based particle group is preferably 6 to 15, more preferably 7 to 12. If the D10 / D90 ratio is too small, the number of large particles will be too small, resulting in an insufficient polishing rate, whereas if it is too large, the small particles will not be able to repair the undulations caused by the large particles. The weight-converted particle size distribution of silica-based particles and the like can be measured using a disk centrifugal particle size distribution measuring device (eg, manufactured by CPS Instruments, etc.).

[0025] In the present embodiment, it is preferable that the first particles are particles not having a pore structure, and the second particles and the third particles are both particles having a pore structure. Specifically, the silica-based particle group of this embodiment preferably has pores inside the particle. More specifically, it is preferable that the silica-based particle group has a gradient structure of pores depending on the particle size (particle diameter). The silica-based particle group of this embodiment is classified into first particles (small particles) with a major axis of 10 nm or more and less than 50 nm, second particles (medium particles) with a major axis of 50 nm or more and less than 100 nm, and third particles (large particles) with a major axis of 100 nm or more, but the small particles with a small particle size do not have pores inside the particle. In contrast, the medium particles and large particles have a pore structure inside the particle. Also, as the particle size of the medium particles and large particles increases, the number of pores provided inside the particle tends to increase. In this application, the presence or absence of pores inside the particle and the number of pores depending on the particle size are called a gradient structure of pores inside the particle.

[0026] The reason why the above-mentioned gradient structure of pores occurs is presumed to be due to the following mechanism. The silica-based gel (silica powder) which is the raw material of the method for producing silica-based particles of the present embodiment described later has an external shape on the order of microns, for example, tens to hundreds of microns. 2 / g and is an agglomerate structure of primary particles of several nm to several tens of nm in size, i.e., a silica-based gel. Agglomerates of this type have voids between the primary particles. In the method for producing silica-based particles of the present embodiment described later, a raw silica-based gel (silica powder) having such a structure is adjusted to an irregular silica-based gel of a desired particle size in a crushing process, but the structure of the primary particles and their voids is maintained. After this crushing process, the pores between the primary particles of the irregular silica-based gel are filled with silicic acid to improve the strength, and the particles are grown to a desired size. At this time, the irregular silica-based gel before particle growth contains particles of various particle sizes from 10 nm to 100 nm or more, and when these particles are grown by silicic acid, the particle growth proceeds while the silicic acid penetrates into the interior of the irregular silica gel particles. The penetration depth of the silicic acid depends on the particle growth conditions, pore size, and particle shape, but generally reaches a depth of several tens of nm. Therefore, the first particles having a particle size of 10 nm or more and less than 50 nm do not have pores inside the particles. On the other hand, when the second particles have a particle size of 50 nm or more and less than 100 nm, and the particle size is relatively small and the pore size is relatively large, the silicic acid penetrates into the inside of the irregular silica-based gel. Therefore, pores are unlikely to remain inside, but when the particle size is relatively large and the pore size is small, pores tend to remain inside. In the end, the number of second particles with pores tends to be smaller than that of the third particles described below. Silica does not penetrate easily into the third particles with a particle size of 100 nm or more. Therefore, the internal pores tend to remain, and the number of pores tends to be greater than that of the first and second particles. Also, because of this mechanism, the pores inside the particles tend to be located at the center of the particles.

[0027] When particles having a gradient structure of pores according to particle size are used for polishing purposes, the polishing rate tends to increase and waviness and surface roughness tend to improve. The reason for the improved polishing performance is that the medium and large particles having internal pores have a low particle density due to the presence of internal pores, and the number of particles per unit weight increases compared to particles that do not have internal pores. On the other hand, the primary particles are sufficiently reinforced by silicic acid, so the strength of the particles is high and they do not collapse during polishing. Therefore, it is assumed that the polishing speed is improved by increasing the contact area between the substrate and the particles. Also, when the number of particles increases, the load on each particle decreases, so local stress concentration on the polishing substrate is alleviated. Therefore, excessive digging of the polishing substrate is unlikely to occur, and surface roughness and waviness tend to improve. In addition, small particles do not have pores inside, so the hardness of the particles is relatively high, which tends to improve the polishing speed.

[0028] In this embodiment, when the aspect ratio of the silica-based particles is measured by SEM image analysis, the average aspect ratio of the silica-based particles is preferably 1.35 or more. If the average aspect ratio of silica-based particle group is 1.35 or more, when used as polishing slurry, it can increase the polishing speed.From the same viewpoint, the average aspect ratio of silica-based particle group is more preferably 1.4 or more and 3 or less, and particularly preferably 1.42 or more and 2 or less.When the average aspect ratio is more than 3, the polishing speed is improved, but scratches tend to occur frequently.

[0029] The silica-based particle dispersion according to this embodiment (wherein the silica-based particles satisfy the above conditions [1] to [4]) can be prepared, for example, by the method for producing a silica-based particle dispersion described below.

[0030] [Method of producing silica-based particle dispersion and silica-based particle group] A method for producing the silica-based particle dispersion liquid and the silica-based particle group according to this embodiment will be described. The silica-based particle dispersion liquid according to this embodiment can be produced when producing the silica-based particle group according to this embodiment. The method for producing silica-based particle groups according to this embodiment is a method for producing silica-based particle groups consisting of irregularly shaped silica-based particles and spherical silica-based particles, and is characterized by including the following steps 1 to 3. According to this manufacturing method, it is possible to prepare a silica-based particle group that satisfies the above conditions [1] to [4].

[0031] (Step 1) A step of wet-grinding a silica-based gel having a powder strength of 15 GPa or less, represented by the following formula (F1), under alkaline conditions to obtain a first solution containing particles made of irregularly shaped silica-based gel. σ = [(1-ε) / π] K H / d 2 (F1) (where σ, d, K, ε, π, and H are: σ: powder strength [Pa], d: average particle size [m], K: average coordination number of the particle, ε: porosity of powder, π: pi, H: Adhesion force of particles [N]) If the powder (secondary particles) is a silica-based gel having a strength of 15 GPa or less, it can be made into particles made of irregularly shaped silica-based gel by wet pulverization under alkaline conditions. The strength of a powder can be calculated from the Rumpf equation, which indicates the compressive or tensile strength of a powder. According to the Rumpf equation, the strength of a powder is expressed by equation (F1). The crushing mechanism is classified into surface crushing, which is performed by friction and shear forces, and volume crushing, which breaks down the powder by impact and compression forces. In actual crushing, these occur simultaneously to some extent, and it is thought that whether surface crushing or volume crushing occurs mainly depends on the type of raw material and the crushing conditions. In volume crushing, the entire powder breaks down, so the particles obtained tend to have a high degree of irregularity. In surface crushing, the particles are gradually crushed from the surface, so the convex parts of the surface are easily crushed, and the particles tend to gradually become closer to spherical, decreasing the degree of irregularity of the particles. At the same time, fine particles are generated by the crushing of the convex parts of the surface, and these fine particles tend not to have a high degree of irregularity. In wet milling using beads, beads of a certain size are used, and the suspension slurry is introduced into a mill to perform milling, and the desired size is obtained by adjusting the residence time inside the mill. In this case, depending on the milling conditions and the type of raw material, it is thought that volumetric milling is likely to occur in those whose size rapidly decreases. On the other hand, it is thought that surface milling occurs in those whose size changes gradually. In this case, if the strength of the raw material silica-based gel is high, it is necessary to extend the residence time to mill to the desired size, so surface milling tends to occur easily. For the reasons mentioned above, particles generated by surface milling tend to have a small degree of irregularity. Therefore, by selecting a raw material with a silica-based gel strength of 15 GPa or less and ending the milling at the stage where the mechanism of volumetric milling mainly occurs, particles with a high degree of irregularity can be obtained. Here, the average particle size of the particles is a specific surface area converted particle size (d) determined by the BET method, and is calculated by the following formula (F2). d = 6000 / (ρs × SA1) (F2) (where d, ρs and SA are: d: Specific surface area equivalent particle diameter [nm], ρs: silica density (= 2.2 [g / mL]), SA1: Specific surface area of ​​silica powder [m 2 / g]) The porosity (ε) of the powder was calculated from the pore volume (PV) and silica volume (SV) of the powder by the following formula (F3). ε=(PV) / (PV+SV)×100...(F3) (where ε, PV, and SV are: ε: Porosity of powder [unitless], PV: Pore volume of powder [mL / g], SV: Silica volume, calculated by the following formula: SV=1 / ρs=1 / 2.2=0.4545) The method for determining the pore volume (PV) of the powder is described later. The average coordination number (K) of the primary particles was calculated using the value of the powder porosity (ε) from the following formula (F4) (known as the Ridgway-Tarbuck formula), which expresses the relationship between the powder porosity (ε) in random packing of uniform spherical particles and the average coordination number (K) of the primary particles. ε=1.072-0.1192K+0.00431K 2 (F4) The adhesive strength (H) was calculated from the theoretical strength of glass (Q) and the cross-sectional area of ​​the adhesion between primary particles in the raw silica powder using the following formula (F5). The "cross-sectional area of ​​the adhesion portion between primary particles in the raw silica powder" is also referred to as the "cross-sectional area of ​​the adhesion portion between particles." Also, the "length of the adhesion portion between primary particles in the raw silica powder" is also referred to as the "length of the adhesion portion between particles." The theoretical strength of glass (Q) is 20 [GN / m 2 ]. The cross-sectional area of ​​the particle attachment portion was determined by image analysis of a scanning electron microscope photograph, where the length (L) of the particle attachment portion was regarded as the diameter of the cross section of the attachment portion, the area of ​​the circle was calculated, and the cross-sectional area of ​​the particle attachment portion was determined by multiplying the area of ​​the circle by the theoretical strength (Q) of the glass. The length (L) of the adhering portion of the particle in the present invention means a value obtained by the following measurement. In this specification, the "length (L) of the adhering portion of the particle" is also referred to as the "cross-sectional diameter (L) of the particle." A planar SEM image (magnification: 200,000) of the dispersion of the present invention (silica concentration: 40% by mass) is taken using a scanning electron microscope (SEM) (e.g., an ultra-high resolution field emission scanning electron microscope S-5500 [STEM observation possible] (manufactured by Hitachi High-Technologies Corporation)), and the lengths of 50 or more points where primary particles are attached to each other in the obtained image or photograph are measured. The value obtained by simply averaging the lengths of all the points obtained is the length (L) of the particle attachment portion. H=(L / 2) 2 ×π×Q (F5) (where H, L, π, and Q are: H: Adhesion strength [N], L: length of the particle attachment part [nm], π: Pi (=3.14), Q: Theoretical strength of glass (=20[GN / m 2 ]) In this way, the strength (σ) of the raw silica powder is calculated from the above formula (F1) (as well as formulas (F2), (F3), (F4) and (F5)). The strength (σ) of the raw silica powder is desirably 15 GPa or less for the reasons described below. Regarding the raw silica powder, the porosity of the powder, the specific surface area of ​​the powder, and the length of the particle adhesion part are not particularly limited, but the porosity of the silica powder is usually 0.5 to 0.9, and the specific surface area of ​​the silica powder is 200 to 550 m. 2 / g, and the length of the attached portion is preferably in the range of 5 to 15 nm. Within this range, the strength of the raw material silica powder is likely to be 15 GPa or less.

[0032] The strength σ of the silica-based gel calculated by the formula (F1) is preferably 15 GPa or less, more preferably 10 GPa or less, and even more preferably 5 GPa or less, because the strength of the raw material powder is weak, volumetric crushing is likely to occur during crushing, and a highly irregular silica-based gel is likely to be obtained. The size of the silica gel, which is the raw material, is not particularly limited as long as the strength is 15 GPa or less, but from the viewpoint of crushing efficiency, it is preferably 100 μm or less, more preferably 10 μm to 60 μm, and particularly preferably 20 μm to 50 μm. If the size is less than 10 μm, the viscosity of the suspension is high and handling is poor, and if the size exceeds 100 μm, the large size is likely to cause clogging of the screen or gap of the crusher.

[0033] For the wet grinding, a conventionally known wet grinder can be used, such as a ball mill or a bead mill. Materials of media used in wet grinding include zirconia, glass, and alumina. Among these, zirconia and glass are preferred from the viewpoint of crushing particles finer. The size of the media is not particularly limited as long as it is a size that can obtain the desired irregular silica-based gel, but a size of 1 mm or less is preferred in order to efficiently prepare an irregular silica-based gel of 40 nm to 550 nm.

[0034] The wet grinding must be performed under alkaline conditions. If the conditions are not alkaline, there is a problem in that the crushed particles will re-aggregate. However, if the pH is too high, the irregular silica gel after grinding is likely to dissolve or change over time, so the pH during wet grinding is preferably 8 to 11.5, more preferably 9 to 10.5. The wet grinding may be carried out in one stage from the viewpoint of efficiently grinding to the desired particle size, or may be carried out in two or more stages by changing the grinding conditions according to the particle size during the grinding process.

[0035] In the solution obtained in step 1, the particles made of the irregular silica-based gel preferably have a weight average particle size of 40 nm or more and 550 nm or less, and more preferably 70 nm or more and 250 nm or less. In the first solution containing particles made of irregular silica-based gel obtained in step 1, the shape of the particles made of silica-based gel is usually irregularized (non-sphericalized) through wet grinding. The degree of irregularization is not particularly limited.

[0036] (Step 2) A step of adding a silicic acid liquid under alkaline conditions to a first solution containing particles made of the irregular silica-based gel, filling the pores between the primary particles of the particles made of the irregular silica-based gel by reacting with the silicic acid contained in the silicic acid liquid, thereby growing the particles while maintaining their irregular shape to form irregular silica-based particles, thereby obtaining a second solution containing the irregular silica-based particles. As the silicic acid liquid, a conventionally known silicic acid liquid can be used. The concentration of the silicic acid liquid is preferably 1% by mass or more and 10% by mass or less. The amount of silicic acid solution added is determined by the SiO 2 Molar concentration of SiO in silicate solution 2 The molar concentration is preferably in the range of 0.5 to 20 times. If the amount of silicic acid solution added is more than 20 times, self-nucleation by silicic acid is likely to occur. If the amount is less than 0.5 times, the particles cannot grow to the desired size, and the polishing speed tends to decrease.

[0037] The addition of the silicic acid liquid needs to be carried out under alkaline conditions. If the conditions are not alkaline, the particles cannot grow, and problems such as the generation of small particles due to self-nucleation occur. In addition, from the viewpoint of growing the particles, the pH when adding the silicic acid liquid is preferably 9 or more and 12.5 or less, more preferably 9 or more and 11 or less. It is preferable to heat the solution before or after the addition of the silicic acid solution. From the viewpoint of growing particles, the temperature of the solution after heating is preferably 60° C. or more and 170° C. or less, and more preferably 80° C. or more and 120° C. or less. SiO after adding silicate liquid 2 The concentration is preferably from 1% by mass to 10% by mass.

[0038] In the second solution obtained in step 2, the specific surface area of ​​the silica-based particle group including the irregular silica-based particles is 270 m 2 / g or less, and 2 / g or more 182m 2 It is more preferable that the molecular weight is not more than 1 / g. In the second solution obtained in step 2, the weight average particle size of the silica-based particle group including the irregular shaped silica-based particles is preferably 50 nm or more and 600 nm or less, and more preferably 100 nm or more and 200 nm or less. The second solution obtained in step 2 is a silica-based particle dispersion liquid.

[0039] (Step 3) A step of concentrating the second solution containing the irregularly shaped silica-based particles and recovering the silica-based particle group. When concentrating the second solution, a known concentration method such as an ultrafiltration membrane or an evaporator can be used. In this manner, a silica-based particle group that satisfies the above conditions [1] to [4] can be produced.

[0040] [Polishing slurry and composition for polishing magnetic disk substrates] Next, the polishing slurry and composition for polishing magnetic disk substrates according to this embodiment will be described. The polishing composition for magnetic disk substrates according to this embodiment (also referred to as "polishing composition") contains the silica-based particle dispersion liquid according to this embodiment. The polishing slurry for polishing magnetic disk substrates according to this embodiment can be prepared by diluting this polishing composition with water or the like.

[0041] The polishing composition according to this embodiment may further contain other components. As the other components, one or more components selected from a polishing accelerator, a surfactant, a hydrophilic compound, a heterocyclic compound, a pH adjuster, and a pH buffering agent can be used.

[0042] Examples of the polishing accelerator include acids such as sulfuric acid, nitric acid, phosphoric acid, oxalic acid, and hydrofluoric acid, or the sodium salts, potassium salts, and ammonium salts of these acids, and mixtures thereof. In the case of a polishing composition containing such a polishing accelerator, when polishing a material to be polished that is composed of multiple components, the polishing rate of a specific component of the material to be polished can be accelerated, and a flat polished surface can be finally obtained.

[0043] When the polishing composition according to the present embodiment contains a polishing accelerator, the content is preferably 0.1% by mass or more and 10% by mass or less, and more preferably 0.5% by mass or more and 5% by mass or less. Surfactant and / or hydrophilic compound In order to improve the dispersibility and stability of the polishing composition, a cationic, anionic, nonionic, or amphoteric surfactant or hydrophilic compound can be added.

[0044] Both the surfactant and the hydrophilic compound have the effect of reducing the contact angle with the surface to be polished and promoting uniform polishing. As the surfactant and / or hydrophilic compound, for example, those selected from the following group can be used.

[0045] Examples of anionic surfactants include carboxylates, sulfonates, sulfates, and phosphates. Examples of carboxylates include soaps, N-acylamino acid salts, polyoxyethylene or polyoxypropylene alkyl ether carboxylates, and acylated peptides. Examples of sulfonates include alkylsulfonates, alkylbenzene and alkylnaphthalenesulfonates, naphthalenesulfonates, sulfosuccinates, α-olefinsulfonates, and N-acylsulfonates. Examples of sulfate ester salts include sulfated oils, alkyl sulfates, alkyl ether sulfates, polyoxyethylene or polyoxypropylene alkyl allyl ether sulfates, and alkyl amide sulfates. Examples of phosphate ester salts include alkyl phosphates, polyoxyethylene or polyoxypropylene alkyl allyl ether phosphates, and the like.

[0046] Examples of cationic surfactants include aliphatic amine salts, aliphatic quaternary ammonium salts, benzalkonium chloride salts, benzethonium chloride, pyridinium salts, and imidazolinium salts. Examples of amphoteric surfactants include carboxybetaine type, sulfobetaine type, aminocarboxylate salts, imidazolinium betaine, lecithin, and alkylamine oxide.

[0047] Examples of nonionic surfactants include ether type, ether ester type, ester type, and nitrogen-containing type, and examples of ether type include polyoxyethylene alkyl and alkylphenyl ether, alkylaryl formaldehyde condensed polyoxyethylene ether, polyoxyethylene polyoxypropylene block polymer, and polyoxyethylene polyoxypropylene alkyl ether, examples of ether ester type include polyoxyethylene ether of glycerin ester, polyoxyethylene ether of sorbitan ester, and polyoxyethylene ether of sorbitol ester, examples of ester type include polyethylene glycol fatty acid ester, glycerin ester, polyglycerin ester, sorbitan ester, propylene glycol ester, and sucrose ester, and examples of nitrogen-containing type include fatty acid alkanolamide, polyoxyethylene fatty acid amide, and polyoxyethylene alkylamide. Other examples include fluorine-based surfactants, etc.

[0048] The surfactant is preferably an anionic surfactant or a nonionic surfactant, and the salt includes ammonium salts, potassium salts, sodium salts, etc., and ammonium salts and potassium salts are particularly preferred.

[0049] Further, other surfactants, hydrophilic compounds, etc., include esters (glycerin esters, sorbitan esters, alanine ethyl esters, etc.), ethers (polyethylene glycol, polypropylene glycol, polytetramethylene glycol, polyethylene glycol alkyl ethers, polyethylene glycol alkenyl ethers, alkyl polyethylene glycols, alkyl polyethylene glycol alkyl ethers, alkyl polyethylene glycol alkenyl ethers, alkenyl polyethylene glycols, alkenyl polyethylene glycol alkyl ethers, alkenyl polyethylene glycol alkenyl ethers, polypropylene glycol alkyl ethers, polypropylene glycol alkenyl ethers, alkyl polypropylene glycols, alkyl polypropylene glycol alkyl ethers, alkyl polypropylene glycol alkenyl ethers, and alkenyl polypropylene glycols, etc.), polysaccharides (alginic acid, pectinic acid, carboxymethylcellulose, curdlan, pullulan, etc.), amino acid salts (glycine ammonium salt, glycine sodium salt ... polysaccharides (alginic acid, pectinic acid, carboxymethylcellulose, curdlan, pullulan, etc.), polysaccharides (alginic acid, pectinic acid, carboxymethylcellulose, curdlan, pullulan, etc.), polysaccharides (alginic acid, pectinic acid, polytetramethylene glycol, polyethylene glycol alkyl ethers, polyethylene glycol alkenyl ethers, alkyl polyethylene glycol alkyl ethers, alkyl polyethylene glycol alkenyl ethers, alkenyl polypropylene glycols, polysaccharides (polysaccharides (polysaccharides (polysaccharides))), polysaccharides (polysaccharides (polysaccharides)), polysaccharides (polysaccharides (polysaccharides)), polysaccharides (polysaccharides)), polysaccharides (polysaccharides (polysaccharides) Polycarboxylic acids and their salts (polyaspartic acid, polyglutamic acid, polylysine, polymalic acid, polymethacrylic acid, ammonium salts of polymethacrylic acid, sodium salts of polymethacrylic acid, polyamic acid, polymaleic acid, polyitaconic acid, polyfumaric acid, poly(p-styrene carboxylic acid), polyacrylic acid, polyacrylamide, aminopolyacrylamide, ammonium salts of polyacrylic acid, sodium salts of polyacrylic acid, polyamic acid, ammonium salts of polyamic acid, sodium salts of polyamic acid, and polyglyoxylic acid, etc.), vinyl polymers (polyvinyl chloride, polyvinyl alcohol, polyvinyl ether, polyvinyl alcohol ... alcohol, polyvinylpyrrolidone and polyacrolein, etc.), sulfonic acids and their salts (ammonium methyl taurate, sodium methyl taurate, sodium methyl sulfate, ethyl ammonium sulfate, butyl ammonium sulfate, sodium vinyl sulfonate, sodium 1-allyl sulfonate, sodium 2-allyl sulfonate, sodium methoxymethyl sulfonate, ammonium ethoxymethyl sulfonate, sodium 3-ethoxypropyl sulfonate, etc.), and amides (propionamide, acrylamide,methylurea, nicotinamide, succinamide, sulfanilamide, etc.

[0050] When the substrate to be polished is a glass substrate or the like, any surfactant can be suitably used. However, when the substrate is a silicon substrate for a semiconductor integrated circuit or the like, and the influence of contamination by alkali metals, alkaline earth metals, halides, or the like must be avoided, it is preferable to use an acid or an ammonium salt-based surfactant.

[0051] When the polishing composition of this embodiment contains a surfactant and / or a hydrophilic compound, the total content thereof is preferably 0.001 g or more and 10 g or less, more preferably 0.01 g or more and 5 g or less, and particularly preferably 0.1 g or more and 3 g or less, per 1 L of the polishing composition.

[0052] The content of the surfactant and / or hydrophilic compound is preferably 0.001 g or more per liter of the polishing composition in order to obtain a sufficient effect, and is preferably 10 g or less in order to prevent a decrease in the polishing rate.

[0053] The surfactant or hydrophilic compound may be used alone or in combination with two or more kinds.

[0054] In the polishing composition according to this embodiment, when the substrate to be polished contains a metal, a heterocyclic compound may be contained in the composition in order to form a passivation layer or a dissolution-suppressing layer on the metal and suppress the erosion of the substrate to be polished. Here, the term "heterocyclic compound" refers to a compound having a heterocycle containing one or more heteroatoms. The term "heteroatom" refers to an atom other than a carbon atom or a hydrogen atom. The term "heterocycle" refers to a cyclic compound having at least one heteroatom. The term "heteroatom" refers only to an atom that forms a part of the ring system of a heterocycle, and does not refer to an atom that is located outside the ring system, that is separated from the ring system by at least one non-conjugated single bond, or that is a part of a further substituent of the ring system. Preferred examples of heteroatoms include, but are not limited to, nitrogen atoms, sulfur atoms, oxygen atoms, selenium atoms, tellurium atoms, phosphorus atoms, silicon atoms, and boron atoms. Examples of heterocyclic compounds that can be used include imidazole, benzotriazole, benzothiazole, and tetrazole. More specific examples include 1,2,3,4-tetrazole, 5-amino-1,2,3,4-tetrazole, 5-methyl-1,2,3,4-tetrazole, 1,2,3-triazole, 4-amino-1,2,3-triazole, 4,5-diamino-1,2,3-triazole, 1,2,4-triazole, 3-amino-1,2,4-triazole, and 3,5-diamino-1,2,4-triazole, but are not limited to these.

[0055] When a heterocyclic compound is blended in the polishing composition of this embodiment, the content is preferably 0.001 mass% or more and 1.0 mass% or less, more preferably 0.001 mass% or more and 0.7 mass% or less, and even more preferably 0.002 mass% or more and 0.4 mass% or less.

[0056] In order to enhance the effects of the above-mentioned additives, etc., the pH of the polishing composition can be adjusted by adding an acid or a base as necessary.

[0057] When the polishing composition according to this embodiment is adjusted to a pH of 7 or more, an alkaline pH adjuster is used. Desirably, sodium hydroxide, aqueous ammonia, ammonium carbonate, or an amine such as ethylamine, methylamine, triethylamine, or tetramethylamine is used.

[0058] When the polishing composition is adjusted to a pH of less than 7, an acidic pH adjuster is used, such as hydroxy acids such as lactic acid, citric acid, malic acid, tartaric acid, and glyceric acid.

[0059] In order to keep the pH value of the polishing composition constant, a pH buffer may be used. Examples of the pH buffer include phosphates and borates such as ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and ammonium tetraborate tetrahydrate, or organic acids.

[0060] For the polishing composition according to the present embodiment, solvent can be used as necessary. As the solvent, water is usually used, but alcohols such as methyl alcohol, ethyl alcohol, isopropyl alcohol, etc. can be used as necessary, and water-soluble organic solvents such as ethers, esters, ketones, etc. can be used. In addition, it may be a mixed solvent consisting of water and organic solvent.

[0061] The concentration of the polishing particles in the polishing composition according to this embodiment is preferably in the range of 0.5% by mass or more and 50% by mass or less, more preferably 5% by mass or more and 30% by mass or less. If the concentration is less than 0.5% by mass, depending on the type of substrate or insulating film, the concentration is too low, and the polishing speed is slow, which may cause productivity problems. If the concentration of the polishing particles exceeds 50% by mass, the stability of the polishing material becomes insufficient, and the polishing speed and polishing efficiency are not further improved, and in the process of supplying the dispersion liquid for polishing treatment, dried matter may be generated and adhered, which may cause scratches. EXAMPLES

[0062] [Example 1] (Preparation of Silica Powder (Silica-Based Gel)) Add pure water to 462.5 g of sodium silicate to obtain SiO 2 A 24% by mass sodium silicate aqueous solution was prepared, and an aqueous sulfuric acid solution (concentration 25% by mass) was added to adjust the pH to 7.1 to obtain a solution containing silica hydrogel. This solution containing silica hydrogel was kept at 21°C in a thermostatic chamber and left to stand for 5.75 hours for aging. Thereafter, the SiO 2 The silica hydrogel was washed with pure water until the content of sodium sulfate was 0.05% by mass to obtain a purified silica hydrogel. 2 The concentration is 5.0% by mass, and the specific surface area is 350 m 2 The purified silica hydrogel thus obtained was dried at 120° C. and pulverized in a mortar to obtain silica powder (silica-based gel) having a volume-based particle size of about 12 μm after pulverization. The measurement or calculation results of the particle diameter (d) converted into specific surface area, the specific surface area of ​​the powder, the pore volume of the powder, the porosity of the powder (ε), the average coordination number of the particle (K), the cross-sectional diameter of the particle (L), the adhesive force of the particle (H), and the strength of the powder (σ) for this silica powder (silica-based gel) are shown in "(1) Physical properties of the silica-based gel" in Table 1. Note that in the examples and comparative examples described later, these measurement or calculation results are also shown in "(1) Physical properties of the silica-based gel" in Table 1 (the same applies to the following examples and comparative examples). Note that in Table 1, for convenience, the unit of the value of the average particle diameter (particle diameter converted into specific surface area) (d) of the particles is shown in "nm". Similarly, the unit of the value of the powder strength (σ) is shown in "GPa".

[0063] (Preparation of a solution containing particles made of irregular silica-based gel) 5.01 kg of water was weighed into a 10 L container, and 84 g of 48% sodium hydroxide solution was added to prepare a sodium hydroxide solution with a pH of 9.7. 1.87 kg of the silica powder (silica-based gel) was added, followed by the addition of 48% sodium hydroxide solution to adjust the pH, to obtain a silica powder suspension with a pH of 10.3. This silica powder suspension was passed through a grinder equipped with zirconia media of 1.0 mmφ, and ground until the weight average particle diameter became 800 nm, and SiO 2 A solution (1) containing particles made of irregular silica-based gel with a concentration of 21.7% by mass was obtained. Next, the solution (1) containing the obtained particles made of irregular silica-based gel is passed through a grinder equipped with glass media of 0.35 mmφ, and ground until the weight average particle diameter becomes 98 nm, to obtain SiO 2 A solution (2) containing particles made of irregular silica-based gel with a concentration of 18.7% by mass was obtained.

[0064] (Growth of particles made of irregular silica-based gel and concentration of the preparation) 1.9 kg of the solution (2) containing particles made of the irregular silica gel obtained was weighed out, and 10.5 kg of water was added to obtain SiO 2 12.4 kg of a solution with a concentration of 3.0% by mass was obtained. Next, a 4.8% by mass aqueous solution of sodium hydroxide and water were added to adjust the pH to 10.4. The temperature was then raised to 98°C and maintained at 98°C for 30 minutes. Next, 25.7 kg of a 4.6% by mass acidic silicic acid solution was added over 16 hours while maintaining the temperature at 98°C, and stirring was continued for another hour while maintaining the temperature at 98°C to grow particles made of irregular silica-based gel, thereby obtaining a preparation liquid (A) (a solution containing irregular silica-based particles). The SiO of this preparation liquid (A) 2 The concentration is 4.0% by mass, and the SiO 2 of added silicate solution to 2 The molar ratio of the silica particles was 3.33. The specific surface area of ​​the silica particles was 87 m 2 / g and the weight average particle size was 137 nm. The first particle, the second particle, and the third particle were each examined for the presence or absence of pores using the method described below. As a result, no pores were found in the first particle, but pores were found to exist in both the second particle and the third particle. After cooling the mixture (A) to room temperature, it was filtered through an ultrafiltration membrane (manufactured by Asahi Kasei Corporation, "SIP-1013") to remove SiO 2 The mixture was concentrated to a concentration of 12% by mass. 2 The mixture was concentrated to a concentration of 50% by mass to obtain a silica-based particle group consisting of irregular shaped silica-based particles and spherical silica-based particles. The measurement or calculation results of the physical properties of the silica-based particle group thus obtained (weight average particle size, specific surface area converted particle size, average aspect ratio of each particle, total particle average aspect ratio, area ratio of each particle, particle size ratio calculated from weight converted particle size distribution, cumulative 10% particle sizes (D10) and (D90) calculated from weight converted particle size distribution) are shown in “(2) Physical Properties of Silica-Based Particle Group” in Table 1 (the same applies to the following Examples and Comparative Examples). Regarding steps 1 and 2, the particle properties, physical properties, and production conditions are shown in Table 2 (the same applies to the following examples and comparative examples).

[0065] [Example 2] (Preparation of a solution containing particles made of irregular silica-based gel) The solution (1) containing particles made of the irregular silica-based gel obtained in Example 1 was passed through a grinder equipped with glass media of 0.5 mmφ, and ground until the weight average particle diameter became 185 nm, to obtain SiO 2 A solution (3) containing particles made of irregular silica-based gel with a concentration of 19.1% by mass was obtained. Next, the solution (3) containing particles made of irregular silica-based gel is passed through a grinder equipped with glass media of 0.25 mmφ, and ground until the weight average particle diameter becomes 85 nm, to obtain SiO 2 A solution (4) containing particles made of irregular silica-based gel with a concentration of 16.7% by mass was obtained. (Growth of particles made of irregular silica-based gel and concentration of the preparation) Next, 1.9 kg of the solution (4) containing particles made of irregular silica-based gel was weighed in the same manner as in Example 1, and 10.5 kg of water was added to obtain SiO 212.4 kg of a solution with a concentration of 3.0 mass% was obtained. Next, an aqueous sodium hydroxide solution of 4.8 mass% and water were added to adjust the pH to 10.4. Then, the temperature was raised to 98 °C and maintained at 98 °C for 30 minutes. Next, while maintaining the temperature at 98 °C, 25.7 kg of an acidic silicic acid solution of 4.6 mass% was added over 16 hours, and stirring was continued for 1 hour while maintaining the temperature at 98 °C to grow particles composed of irregular silica-based gel, and a preparation liquid (B) (a solution containing irregular silica-based particles) was obtained. The SiO 2 concentration of this preparation liquid (B) was 4.0 mass%, and the molar ratio of SiO 2 in the added silicic acid solution to SiO 2 in the irregular silica-based gel was 3.33. Also, the specific surface area of the obtained silica-based particle group was 88 m 2 / g, and the weight average particle diameter was 148 nm. When the presence or absence of pores in the first particle, the second particle, and the third particle was confirmed by the method described below, the presence of pores was not confirmed in the first particle, and the presence of pores was confirmed in both the second particle and the third particle. The obtained preparation liquid (B) was cooled to room temperature in the same manner as in Example 1, and concentrated to a SiO 2 concentration of 12 mass% using an ultrafiltration membrane, and further concentrated to a SiO 2 concentration of 50 mass% using a rotary evaporator to prepare a silica-based particle group composed of irregular silica-based particles and spherical silica-based particles.

[0066] [Comparative Example 1] (Preparation of silica powder (silica-based gel)) Pure water was added to 462.5 g of sodium silicate to prepare an aqueous sodium silicate solution with a SiO 2 equivalent concentration of 24 mass%. An aqueous sulfuric acid solution (concentration 25 mass%) was added so that the pH became 4.5 to obtain a solution containing a silica hydrogel solution. This silica hydrogel solution was maintained at a temperature of 21 °C in a constant temperature bath and allowed to stand for 5.75 hours for aging. Then, it was washed with pure water until the sodium sulfate content with respect to SiO 2 contained in the silica hydrogel became 0.05 mass% to obtain a purified silica hydrogel. The concentration of this purified silica hydrogel was 5.0 mass%, and the specific surface area was 600 m 2The purified silica hydrogel thus obtained was dried at 120° C. and pulverized in a mortar to obtain silica powder (silica-based gel) having a volume-based particle size of about 100 μm after pulverization.

[0067] (Preparation of a solution containing particles made of irregular silica-based gel) The silica powder (silica-based gel) was suspended in water in a 2 L glass beaker to a concentration of 5.0 mass %, to obtain 500 g of silica powder suspension. A 4.8 mass % aqueous sodium hydroxide solution was added to adjust the pH to 9.8. 2390 g of zirconia media with a diameter of 1.0 mm was added, and the mixture was crushed in a sand mill until the weight average diameter became 530 nm, to obtain SiO 2 A solution (5) containing particles made of irregular silica-based gel with a concentration of 4.0% by mass was obtained. Next, 1,135 g of glass media having a diameter of 0.25 mm was added to the solution (5) containing particles made of irregular silica-based gel, and the mixture was crushed until the weight average particle diameter became 224 nm to obtain SiO 2 A solution (6) containing particles made of irregular silica gel with a concentration of 3.5% was obtained. (Growth of particles made of irregular silica-based gel and concentration of the preparation) Ion-exchanged water was added to the solution (6) containing the particles made of the irregular silica gel to obtain SiO 2 2716 g of a solution with a concentration of 2.76% by mass was obtained. Next, a 4.8% by mass aqueous solution of sodium hydroxide and ion-exchanged water were added to obtain a solution with a pH of 10.0 and SiO 2 The solution was adjusted to a concentration of 2.5% by mass. The temperature was then raised to 98°C and maintained at 98°C for 30 minutes. Next, while maintaining the temperature at 98°C, 5573.1 g of 4.6% by mass acidic silicic acid solution was added over 20 hours, and stirring was continued for another hour while maintaining the temperature at 98°C to obtain Preparation (C) (a solution containing irregularly shaped silica-based particles). The SiO 2 The concentration is 4.0% by mass, and the SiO 2 of added silicate solution to 2 The molar ratio of the silica particles was 3.42. The specific surface area of ​​the silica particles was 30 m 2 / g and the weight average particle size was 217 nm. The first particle, the second particle, and the third particle were each examined for the presence or absence of pores using the method described below. As a result, no pores were found in the first particle, but pores were found to exist in both the second particle and the third particle. In the same manner as in Example 1, the mixture was cooled to room temperature and filtered through an ultrafiltration membrane using SiO 2 The mixture was concentrated to a concentration of 12% by mass and then further evaporated to SiO 2 The mixture was concentrated to a concentration of 50% by mass to prepare a silica-based particle group consisting of irregularly shaped silica-based particles and spherical silica-based particles.

[0068] [Comparative Example 2] (Preparation of a solution containing particles made of irregular silica-based gel) A solution (5) containing particles made of irregular silica-based gel was prepared in the same manner as in Comparative Example 1, and 1,135 g of glass media having a diameter of 0.25 mm was added thereto, followed by crushing until the weight average particle diameter became 244 nm to obtain SiO 2 A solution (7) containing particles made of irregular silica-based gel with a concentration of 3.5% was obtained. Ion-exchanged water was added to the solution (7) containing the particles made of the irregular silica gel to obtain SiO 2 2716 g of a solution with a concentration of 2.76% by weight was obtained. (Growth of particles made of irregular silica-based gel and concentration of the preparation) Next, a 4.8% by mass aqueous solution of sodium hydroxide and ion-exchanged water were added to obtain a solution with a pH of 10.0 and a SiO 2 The solution was adjusted to a concentration of 2.5% by mass. The temperature was then raised to 98°C and maintained at 98°C for 30 minutes. Next, while maintaining the temperature at 98°C, 5573.1 g of 4.6% by mass acidic silicic acid solution was added over 20 hours, and stirring was continued for another hour while maintaining the temperature at 98°C to obtain Preparation (D). The SiO 2 The concentration is 4.0% by mass, and the SiO 2 of added silicate solution to 2 The molar ratio of the silica particles was 3.42. The specific surface area of ​​the silica particles was 30 m 2 / g and the weight average particle size was 261 nm. The first particle, the second particle, and the third particle were each examined for the presence or absence of pores using the method described below. As a result, no pores were found in the first particle, but pores were found to exist in both the second particle and the third particle. In the same manner as in Example 1, the mixture was cooled to room temperature and filtered through an ultrafiltration membrane using SiO 2 The mixture was concentrated to a concentration of 12% by mass and then further evaporated to SiO 2 The mixture was concentrated to a concentration of 50% by mass to prepare a silica-based particle group consisting of irregular silica-based particles and spherical silica-based particles. A silica-based particle group consisting of irregular silica-based particles and spherical silica-based particles was obtained. The weight average particle diameter of the obtained silica-based particle group was 261 nm.

[0069] [Comparative Example 3] The preparation liquid (A) (a solution containing irregularly shaped silica particles) obtained in Example 1 was diluted with water to 12%, and 500 g was introduced into a 500 mL centrifuge tube. The mixture was placed in a centrifuge (Hitachi's "CR21G Rotor R12A") and centrifuged at 3000 rpm for 90 minutes. After centrifugation, 450 g of the supernatant (light liquid) was collected to obtain preparation liquid (E). The obtained preparation (E) was subjected to a rotary evaporator to remove SiO 2 The silica-based particle group consisting of irregular silica-based particles and spherical silica-based particles was prepared by concentrating the mixture to a concentration of 50% by mass. The weight-average particle diameter of the obtained silica-based particle group was 59 nm, but the particle diameter ratio (D10 / D90) of the cumulative 10% particle diameter (D10) and cumulative 90% particle diameter (D90) from the large particle diameter particles, calculated from the weight-converted particle diameter distribution, was 2.4.

[0070] [Comparative Example 4] The precipitate not collected in Comparative Example 3 was redispersed by adding 75 g of water to obtain 125 g of a silica redispersion. The same process was repeated four times to obtain a total of 500 g of a silica redispersion. The obtained redispersion was introduced into a 500 mL centrifuge tube. It was placed in a centrifuge (Hitachi "CR21G Rotor R12A") and centrifuged at 1500 rpm for 90 minutes. After centrifugation, 300 g of the supernatant was extracted from the top of the centrifuge tube with a syringe and discarded, and 150 g was further extracted from the top after the extraction to obtain a preparation (F). The obtained preparation (F) was subjected to a rotary evaporator to remove SiO 2 The silica-based particle group consisting of irregular silica-based particles and spherical silica-based particles was prepared by concentrating the mixture to a concentration of 50% by mass. The weight-average particle diameter of the obtained silica-based particle group was 192 nm, but the particle diameter ratio (D10 / D90) of the cumulative 10% particle diameter (D10) and cumulative 90% particle diameter (D90) from the large particle diameter particles, calculated from the weight-converted particle diameter distribution, was 4.6.

[0071] [Comparative Example 5] To the preparation liquid (F) obtained in Comparative Example 4, spherical silica particles (weight average particle diameter 60 nm) were added in an amount of 65 mass % based on the silica solid content to prepare preparation liquid (G). The obtained preparation liquid (G) was subjected to SiO 2 removal by a rotary evaporator in the same manner as in Example 1. 2 The silica-based particle group consisting of irregular silica-based particles and spherical silica-based particles was prepared by concentrating the mixture to a concentration of 50% by mass. The weight-average particle diameter of the obtained silica-based particle group was 113 nm, but the particle diameter ratio (D10 / D90) of the cumulative 10% particle diameter (D10) and cumulative 90% particle diameter (D90) from the large particle diameter particles, calculated from the weight-converted particle diameter distribution, was 4.2.

[0072] [Evaluation of Silica-Based Particles and Polishing Composition] The following evaluations were carried out for the silica-based particles and polishing compositions obtained in each Example and Comparative Example. The results are shown in Table 1 ("(2) Physical properties of silica-based particles" and "(3) Evaluation results"). The physical properties of the raw material (silica powder (silica-based gel)) in each Example and Comparative Example are shown in Table 1. (1) Weight average particle size of silica-based particles The measurement was carried out using a disk centrifugal particle size distribution measuring device (eg, manufactured by CPS Instruments, etc.).

[0073] (2) Particle size converted into specific surface area of ​​silica-based particles 50 mL of silica particle dispersion containing silica-based particles was dissolved in HNO 3 The pH was adjusted to 3.5 with 1-propanol, 40 mL was added, and the sample was dried at 110°C for 16 hours. The sample was then crushed in a mortar and baked in a muffle furnace at 500°C for 1 hour to prepare a measurement sample. The specific surface area was calculated from the amount of nitrogen adsorption by the BET single point method using a specific surface area measuring device (Yuasa Ionics, model number Multisorb 12) using the nitrogen adsorption method (BET method). Specifically, 0.5 g of sample is placed in a measurement cell, and degassed for 20 minutes at 300°C in a mixed gas flow of 30v% nitrogen and 70v% helium, and then the sample is kept at liquid nitrogen temperature in the mixed gas flow to allow the nitrogen to be adsorbed in equilibrium on the sample. Next, the sample temperature is gradually raised to room temperature while the mixed gas is being passed, and the amount of nitrogen desorbed during this period is detected, and the specific surface area of ​​the irregularly shaped silica particles is calculated using a calibration curve created in advance. The specific surface area (SA) obtained is then substituted into the following formula to determine the specific surface area converted particle diameter D1. Specific surface area equivalent particle diameter D1 (nm) = 6000 / (ρ×SA) (where ρ is the density of the silica particles, 2.2 [g / cm 3 ].)

[0074] (3) Average aspect ratio and area ratio (S1 / S2) of silica-based particle groups, etc. A planar image of the silica-based particle group was taken using a scanning electron microscope (SEM) and analyzed using RADIUS 2.0 manufactured by Emsis. The magnification of the scanning electron microscope was set to 200,000 times. A scanning electron microscope photograph of the silica-based particle group obtained in Example 2 is shown in FIG. 1. In addition, when classifying the silica-based particle group, first particles with a long diameter of 10 nm or more and less than 50 nm, second particles with a long diameter of 50 nm or more and less than 100 nm, and third particles with a long diameter of 100 nm or more were classified, and other particles (long diameter less than 10 nm) were also classified. Then, the average aspect ratios of the first, second and third particles, and the average aspect ratio of the silica-based particle group were measured by SEM image analysis. Specifically, for 50 first, second and third particles, the aspect ratio of the particle was determined to be the maximum ratio of the major axis to minor axis of the circumscribed rectangle, and the average was calculated to obtain the average aspect ratio. The average aspect ratio of the silica-based particle group was determined by averaging the average aspect ratios of the first, second and third particles. In addition, the area ratio (S1 / S2) between the projected area (S1) of the first particle, the second particle, and the third particle and the area (S2) of a circle having a circumference equal to the projected perimeter was measured by SEM image analysis. Specifically, the projected area (S1) and the area (S2) of a circle having a circumference equal to the projected perimeter were measured for 50 first particles, 50 second particles, and the third particle, and the individual area ratio (S1 / S2) was calculated for each. The area ratio (S1 / S2) was calculated as the average of the 50 particles. As described above, 20 randomly selected first particles, second particles, and third particles were identified using transmission electron microscope images (200,000 times magnification) and visually inspected for the presence or absence of pores inside the particles. When no pores were confirmed in 20 particles each of the first particles, second particles, and third particles, the first particles, second particles, or third particles were determined to have no pores, and when one or more pores were confirmed, the first particles, second particles, or third particles were determined to have pores. Regarding the presence or absence of pores, when pores having an inner diameter of 1 nm or more were confirmed, pores were deemed to be present.

[0075] (4) Particle size ratio (D10 / D90) calculated from the weight-converted particle size distribution of silica-based particle groups The weight-equivalent particle size distribution was measured using a disk centrifugal particle size distribution measuring device (e.g., manufactured by CPS Instruments, Inc., etc.). Using this weight-equivalent particle size distribution, the cumulative 10% particle size (D10) and cumulative 90% particle size (D90) from the particles with the larger particle size were read, and the particle size ratio (D10 / D90) was calculated.

[0076] (5) Polishing test method (polishing speed ratio and waviness ratio) An aluminum substrate coated with nickel plating for hard disks (nickel-plated substrate manufactured by Toyo Kohan Co., Ltd.) was prepared as the substrate to be polished. This substrate to be polished was set in a polishing device (NF300 manufactured by Nanofactor Co., Ltd.) and polished 1 μm using a polishing pad (Bellatrix NO178 manufactured by FILWEL) with a substrate load of 0.05 MPa, a platen rotation speed of 50 rpm, a head rotation speed of 50 rpm, and a polishing slurry supplied at a rate of 40 g / min. ·Polishing speed ratio The polishing rate was determined from the difference in weight of the polished substrate before and after polishing and the polishing time, and a relative value was calculated with the result of Comparative Example 2 taken as 100. Waviness ratio The amplitude of minute irregularities with a waviness wavelength of several tens to several hundreds of μm was measured at any point dividing the outer and inner circles of a polished doughnut-shaped aluminum substrate into two equal parts. Next, the amplitude of minute irregularities with a waviness wavelength of several tens to several hundreds of μm was also measured at a point on a line connecting the measurement point and the center point of the doughnut-shaped aluminum substrate, where the center point is a bisecting point of the measurement point.Then, a relative value was calculated from the average value of these two values, with Comparative Example 2 being taken as 100. The measurement conditions are as follows. Equipment: Zygo NewView 7200 Lens: 2.5x Zoom ratio: 1.0 Filter: 50-500μm Measurement area: 3.75mm x 2.81mm

[0077] (6) SiO contained in silica hydrogel 2 Method for determining sodium sulfate content in It was measured by high performance liquid chromatography (HPLC). Specifically, the sodium sulfate content was determined by HPLC (manufactured by Dionex Corporation, ICS-1100).

[0078] (7) Analysis of components [SiO 2 Measurement of content] Regarding the SiO 2 content in the purified silica hydrogel, for 5 g of the purified silica hydrogel, it was calcined at 1000 °C to determine the loss on ignition and weighed. Assuming that all of the obtained product was SiO 2 the SiO 2 content was determined.

[0079] (8) Measurement of volume-based particle diameter of dried and pulverized purified silica hydrogel The volume-based particle diameter (μm) of the dried and pulverized purified silica hydrogel was measured using a laser diffraction / scattering particle size distribution analyzer LA950 manufactured by HORIBA, after adjusting the sample concentration so that the transmittance R was 90 ± 0.5%.

[0080] (9) Method for measuring pore volume 10 g of the sample powder was placed in a crucible, dried at a temperature of 105 °C for 1 hour, then placed in a desiccator and cooled to room temperature. Next, 1 g of the sample was taken in a well-washed cell, nitrogen was adsorbed using a nitrogen adsorption apparatus, and the pore volume was calculated from the following formula. Pore volume (mL / g) = (0.001567 × (V - Vc) / W) In the above formula, V represents the adsorption amount (mL) in the standard state at a pressure of 735 mmHg, Vc represents the cell blank volume (mL) at a pressure of 735 mmHg, and W represents the mass (g) of the sample. Also, the ratio of the density of nitrogen gas to liquid nitrogen was taken as 0.001567.

[0081]

Table 1

[0082]

Table 2

Claims

1. A silica-based particle dispersion liquid containing a silica-based particle group consisting of irregularly shaped silica-based particles and spherical silica-based particles, The silica-based particle dispersion liquid, wherein the silica-based particles satisfy the following conditions [1] to [4]: [1] The weight average particle diameter is 50 nm or more and 600 nm or less, and the specific surface area converted particle diameter is 10 nm or more and 300 nm or less. [2] When the aspect ratios of first particles having a major axis of 10 nm or more and less than 50 nm, second particles having a major axis of 50 nm or more and less than 100 nm, and third particles having a major axis of 100 nm or more are measured by SEM image analysis, the average aspect ratio of the first particles is 1.3 or more, the average aspect ratio of the second particles is 1.35 or more, and the average aspect ratio of the third particles is 1.43 or more. [3] When the area ratio (S1 / S2) of the projected area (S1) of the first particle, the second particle, and the third particle to the area (S2) of a circle having a circumference equal to the projected peripheral length is measured by SEM image analysis, the average area ratio (S1 / S2) of the first particles is 0.84 or less, the average area ratio (S1 / S2) of the second particles is 0.77 or less, and the average area ratio (S1 / S2) of the third particles is 0.66 or less. [4] The particle size ratio (D10 / D90) of the cumulative 10% particle size (D10) from particles with large particle sizes to the cumulative 90% particle size (D90) as determined from the weight-converted particle size distribution is 5 or more.

2. 2. The silica-based particle dispersion liquid according to claim 1, wherein the first particles are particles having no pore structure, and the second particles and the third particles are both particles having a pore structure.

3. 2. The silica-based particle dispersion liquid according to claim 1, wherein, when the aspect ratio of the silica-based particle group is measured by SEM image analysis, the average aspect ratio of the silica-based particle group is 1.35 or more.

4. 4. An abrasive slurry for polishing magnetic disk substrates, comprising the silica-based particle dispersion liquid according to claim 1.

5. A composition for polishing magnetic disk substrates, comprising the silica-based particle dispersion liquid according to claim 1 .

6. A method for producing a silica-based particle group consisting of irregularly shaped silica-based particles and spherical silica-based particles, comprising the steps of: A method for producing a silica-based particle group, comprising the following steps 1 to 3: (Step 1) A step of wet-grinding a silica-based gel having a powder strength of 15 GPa or less, represented by the following mathematical formula (F1), under alkaline conditions to obtain a first solution containing particles made of irregularly shaped silica-based gel. (Step 2) A step of adding a silicic acid liquid under alkaline conditions to the first solution containing particles made of the irregular silica-based gel, filling the pores between the primary particles of the particles made of the irregular silica-based gel by reacting with the silicic acid contained in the silicic acid liquid, thereby growing the particles while maintaining their irregular shape to form irregular silica-based particles, thereby obtaining a second solution containing the irregular silica-based particles. (Step 3) A step of concentrating the second solution containing the irregularly shaped silica-based particles to recover the silica-based particles. σ=[(1-e) / π]・K・H / d ２ ・・・(F1) (where σ, d, K, ε, π and H are: σ: powder strength [Pa], d: average particle diameter of particles [m], K: average coordination number of the particle, ε: porosity of powder, π: pi H: adhesive force of particles [N])

7. In the step 1, the specific surface area of ​​the silica-based gel is 50 m ２ / g or more 800m ２ / g or less, and the weight average particle diameter of the particles made of the irregular shaped silica-based gel is 40 nm or more and 550 nm or less, In the step 2, the silica-based particle group including the irregular shaped silica-based particles has a specific surface area of ​​270 m ２ The method for producing a silica-based particle group according to claim 6, wherein the weight average particle diameter is 50 nm or more and 600 nm or less.

8. In the step 1, the pH during wet grinding is 8 or more and 11.5 or less, In the step 2, the pH when the silicic acid liquid is added is 9 or more and 12.5 or less, and the SiO ２ The method for producing a silica-based particle group according to claim 6 or 7, wherein the concentration is from 1% by mass to 10% by mass, and the temperature after heating is from 60° C. to 170° C.

Images