JP6963444B2 - Magnetic recording medium board, magnetic recording medium, hard disk drive - Google Patents

Description

The present invention relates to a magnetic recording medium substrate, a magnetic recording medium, and a hard disk drive.

In recent years, the magnetic recording medium used for a hard disk drive has been remarkably improved in recording density. In particular, since the introduction of MR (magneto magnetized) heads and PRML (Partial Response Maximum Likelihood) technology, the increase in the surface recording density of magnetic recording media has become even more intense.

In addition, the amount of data accumulated in data centers continues to increase due to the recent development of the Internet network and the expansion of the use of big data. And, due to the space problem of the data center, it is necessary to increase the storage capacity per unit volume of the data center. That is, in order to increase the storage capacity per standardized hard disk drive, in addition to increasing the storage capacity per magnetic recording medium, it is possible to increase the number of magnetic recording media stored inside the drive case. Attempted.

As the substrate for the magnetic recording medium, an aluminum alloy substrate and a glass substrate are mainly used. Of these, the aluminum alloy substrate is used as a magnetic recording medium having a relatively large outer diameter because it has higher toughness and is easier to manufacture than the glass substrate. Since the thickness of the aluminum alloy substrate used for the magnetic recording medium of a 3.5-inch hard disk drive is usually 1.27 mm, a maximum of five magnetic recording media can be stored inside the drive case. can.

In order to increase the number of magnetic recording media stored inside the drive case, attempts have been made to make the substrate used for the magnetic recording medium thinner.

However, when the substrate is made thin, the aluminum alloy substrate is more likely to cause fluttering than the glass substrate.

Fluttering is the fluttering of the magnetic recording medium that occurs when the magnetic recording medium is rotated at high speed, and when the fluttering becomes large, stable reading in the hard disk drive becomes difficult.

For example, in a glass substrate, it is known to use a material having high specific elasticity (specific Young's modulus) as a material for a substrate for a magnetic recording medium in order to suppress fluttering (see, for example, Patent Document 1). ).

In addition, by filling the inside of the drive case of a 3.5-inch hard disk drive with helium gas, fluttering is reduced, which makes the aluminum alloy substrate thinner and records 6 or more magnetic sheets inside the drive case. Attempts have been made to store the medium.

The magnetic recording medium substrate is generally manufactured by the following steps. First, an aluminum alloy ingot is rolled to obtain an aluminum alloy plate having a thickness of about 2 mm or less, and the obtained aluminum alloy plate is punched into a disk shape to obtain a desired size. Next, after chamfering the inner and outer diameters and turning the data surface of the punched aluminum alloy plate disk, a grindstone is used to reduce the surface roughness and waviness of the turned aluminum alloy plate. Grind to make an aluminum alloy substrate. Then, NiP plating is applied to the surface of the aluminum alloy substrate for the purpose of imparting surface hardness and suppressing surface defects. Next, both sides (data surfaces) of the aluminum alloy substrate on which the NiP plating film is formed are polished.

Substrates for magnetic recording media are mass-produced products and are required to have high cost performance. Therefore, aluminum alloys are required to have high machinability and low cost.

Patent Document 2 contains Mg: 0.3 to 6% by mass, Si: 0.3 to 10% by mass, Zn: 0.05 to 1% by mass, and Sr: 0.001 to 0.3% by mass. An aluminum alloy in which the balance is composed of Al and impurities is disclosed.

Further, Patent Document 3 contains Si of 0.5% by mass or more and 24.0% by mass or less and Fe of 0.01% by mass or more and 3.00% by mass or less, and is composed of the balance Al and unavoidable impurities. An aluminum alloy substrate for a magnetic disk is disclosed.

Further, in Patent Document 4, an Al—Mg-based alloy containing 0.1 wt% or less of Zr is continuously cast on a thin plate having a plate thickness of 4 to 10 mm, and the cast plate is 50% or more without subjecting heat treatment. An Al-Mg alloy rolled plate for magnetic disks that is cold-rolled at a high processing rate and then annealed at a temperature of 300 to 400 ° C. to produce a rolled plate with an average crystal grain size of 15 μm or less on the surface layer. The manufacturing method is disclosed. Here, the Al—Mg-based alloy contains Mg 2.0 to 6.0 wt%, one or two types of Ti and B 0.01 to 0.1 wt%, and further contains Cr 0.03 to 0.3 wt%. Contains one or two types of Mn 0.03 to 0.3 wt%.

Further, in Patent Document 5, in order to provide a substrate for a magnetic recording medium having a high Young's modulus and excellent machinability, Mg is in the range of 0.2 to 6% by mass and Si is in the range of 3 to 17% by mass. Among them, Zn is contained in the range of 0.05 to 2% by mass and Sr is contained in the range of 0.001 to 1% by mass, and the average particle size of Si particles in the alloy structure of the aluminum alloy substrate may be 2 μm or less. It is disclosed.

Japanese Unexamined Patent Publication No. 2015-26414 Japanese Unexamined Patent Publication No. 2009-24265 International Publication No. 2016/068293 Japanese Unexamined Patent Publication No. 6-145927 JP-A-2017-120680

The substrate for a magnetic recording medium used as a base material for a magnetic recording medium for a hard disk drive has suppressed fluttering, that is, the width of displacement due to fluttering: NRRO (None Repeatable Run-Out) is small, and It is desired that the plating property is excellent, that is, the NiP-based plating film is uniformly formed. As described in Patent Documents 2 to 5, it has been actively studied to add various elements to an aluminum alloy substrate in order to improve these performances.

However, according to the study by the inventors of the present invention, the composition of the conventional aluminum alloy described in Patent Documents 2 to 5 is 6 or more in the drive case of a hard disk drive such as 3.5 inch size. If the drive case of a standardized hard disk drive has a thin shape that can accommodate a larger number of hard disks than before, it is difficult to improve the plating property while suppressing fluttering. In addition, the castability when casting an aluminum alloy ingot and the workability when cutting a disk of an aluminum alloy plate material may deteriorate, and it may be difficult to industrially stably manufacture an aluminum alloy substrate. there were.

The present invention has been made in view of the above-mentioned circumstances, and fluttering is suppressed even in a thin shape capable of accommodating a large number of sheets in a standardized hard disk drive drive case as compared with the conventional case. An object of the present invention is to provide a substrate for a magnetic recording medium having improved plating property. It is also an object of the present invention to provide a magnetic recording medium having the above-mentioned substrate for a magnetic recording medium and a hard disk drive including the magnetic recording medium.

As a result of diligent research conducted by the inventors of the present invention in order to solve the above problems, the rigidity of the aluminum alloy substrate containing Si and Cu in a predetermined range is improved, and the aluminum alloy substrate is coated with a NiP-based plating film. It was found that the increase in NRRO due to fluttering can be suppressed even if the substrate for the magnetic recording medium in which the above is formed has a thin shape. However, it has been found that the aluminum alloy substrate containing Si and Cu tends to generate coarse Si particles, and it is difficult to uniformly form a NiP-based plating film. As a result of further research, by adding Sr to the aluminum alloy substrate in a predetermined range, it is possible to suppress the formation of coarse Si particles, and it is possible to uniformly form a NiP-based plating film on the aluminum alloy substrate. I found that

Further, it has been found that the aluminum alloy having the above composition tends to generate scratches during the grinding process when manufacturing the aluminum alloy substrate. As a result of further research, it was found that the occurrence of scratches during grinding can be suppressed by reducing the Fe content of the aluminum alloy. Then, by forming a NiP-based plating film on an aluminum alloy substrate containing each element of Si, Cu, Sr, and Fe in a predetermined amount, a substrate for a magnetic recording medium having improved plating property while suppressing fluttering can be obtained. The present invention was completed after confirming that it was possible to obtain it.

Furthermore, according to the study by the present inventors, in a magnetic recording medium that rotates at an extremely high rotation speed of 5000 rpm or more during normal use, NRRO due to fluttering depends not only on the rigidity of the substrate for the magnetic recording medium but also on the density. Turned out to fluctuate. Then, paying attention to Young's modulus, which is one physical property value that indicates the rigidity of the material, ^{the relationship between Young's modulus E (unit: GPa), density ρ (unit: g / cm 3} ), and NRRO is examined, and Young's modulus is examined. The present invention has been completed by finding that the increase in NRRO is suppressed when the ratio E / ρ of E and the density ρ becomes a predetermined value or more.
That is, the present invention provides the following means for solving the above problems.

(1) The substrate for a magnetic recording medium according to one aspect of the present invention is a substrate for a magnetic recording medium including an aluminum alloy substrate and a NiP-based plating film formed on at least one surface of the aluminum alloy substrate. The ratio E / ρ of the Young's ratio E represented by GPa ^{and the density ρ represented by g / cm 3} is 29 or more, and the aluminum alloy substrate contains 9.5 mass of Si. % Or more and 13.0% by mass or less, Cu in the range of 0.5% by mass or more and 3.0% by mass or less, and Sr in the range of 0.005% by mass or more and 0.1% by mass or less. The Fe content is less than 0.01% by mass, the balance is Al, the diameter is in the range of 53 mm or more and 97 mm or less, and the thickness is in the range of 0.4 mm or more and 0.9 mm or less. It is characterized by that.

(2) The magnetic recording medium according to one aspect of the present invention is a magnetic recording medium having a magnetic recording medium substrate and a magnetic layer provided on the surface of the magnetic recording medium substrate, and the magnetic recording medium. The medium substrate is the magnetic recording medium substrate according to (1) above, and the magnetic layer is provided on the surface of the magnetic recording medium substrate on the side where the NiP-based plating film is formed. It is characterized by being.

(3) The hard disk drive according to one aspect of the present invention is a hard disk drive including a magnetic recording medium, and the magnetic recording medium is the magnetic recording medium according to the above (2).

According to the present invention, even if the drive case of a standardized hard disk drive has a thin shape that can accommodate a larger number of sheets than before, a substrate for a magnetic recording medium in which fluttering is suppressed and the plating property is improved can be obtained. Can be provided. Further, according to the present invention, it is possible to provide a magnetic recording medium having the above-mentioned substrate for a magnetic recording medium and a hard disk drive including the magnetic recording medium.

It is sectional drawing which shows an example of the substrate for magnetic recording medium in this embodiment. It is a perspective view which shows an example of the polishing machine which can be used in the manufacture of the substrate for a magnetic recording medium in this embodiment. It is sectional drawing which shows an example of the magnetic recording medium in this embodiment. It is a perspective view which shows an example of the hard disk drive in this embodiment.

Hereinafter, the magnetic recording medium substrate, the magnetic recording medium, and the hard disk drive according to the embodiment of the present invention will be described in detail with reference to the drawings as appropriate. In addition, in the drawings used in the following description, in order to make the features of the present invention easy to understand, the featured portions may be enlarged and shown, and the dimensional ratios of the respective components are different from the actual ones. Sometimes.

<Substrate for magnetic recording medium>
FIG. 1 is a cross-sectional view of an example of a magnetic recording medium substrate according to the present embodiment.
As shown in FIG. 1, the magnetic recording medium substrate 10 has an aluminum alloy substrate 11 and a NiP-based plating film 12 formed on at least one surface of the aluminum alloy substrate 11. In the magnetic recording medium substrate 10 of the present embodiment, the ratio E / ρ of the ^{Young's modulus E whose unit is expressed in GPa and the density ρ whose unit is expressed in g / cm 3 is 29 or more.}

[Ratio of Young's modulus E and density ρ E / ρ]
It is said that increasing the rigidity of the magnetic recording medium substrate is one of the effective methods in order to suppress the fluttering characteristics of the magnetic recording medium substrate and suppress the increase in the displacement width (NRRO) due to fluttering. Conceivable. On the other hand, according to the study by the present inventors, in a magnetic recording medium that is rotated at an extremely high rotation speed of 5000 rpm or more during normal use, the fluttering characteristics may fluctuate depending on the density of the magnetic recording medium substrate. found. Then, paying attention to Young's modulus, which is one physical property value that indicates the rigidity of the material, Young's modulus E (unit: GPa), density ρ (unit: g / cm ³ ), and fluttering characteristics of the substrate for the magnetic recording medium are used. It was found that when the ratio E / ρ of Young's modulus E and density ρ is 29 or more, the fluttering characteristic is improved, that is, the fluttering is reduced.
Therefore, in the present embodiment, the ratio E / ρ of the Young's modulus E and the density ρ is 29 or more. The ratio E / ρ is preferably 32 or less.

The substrate 10 for a magnetic recording medium of the present embodiment has a Young's modulus E in the range of 79 GPa or more and 87 GPa or less, and a density ρ in the range of 2.6 g / cm ³ or more and 3.0 g / cm ³ or less. Therefore, it is preferable that the ratio E / ρ is 29 or more.

[Aluminum alloy substrate]
The aluminum alloy substrate 11 contains Si in the range of 9.5% by mass or more and 13.0% by mass or less, Cu in the range of 0.5% by mass or more and 3.0% by mass or less, and Sr in the range of 0.005% by mass or more. Included within the range of 0.1% by mass or less. Further, the aluminum alloy substrate 11 contains at least one metal element selected from the group consisting of Cr, Ti and Ni in a range of 0.01% by mass or more and 0.4% by mass or less of Zn in total. In the range of 005% by mass or more and 1.0% by mass or less, Mn in the range of 0.05% by mass or more and 0.4% by mass or less, and Zr in the range of 0.03% by mass or more and 0.3% by mass or less. It may be included in each.

The aluminum alloy substrate 11 is composed of the above metal elements, unavoidable impurities, and the remaining Al. Inevitable impurities are impurities that are unavoidably mixed from the raw materials and the manufacturing process. In the present embodiment, the Fe content is less than 0.01% by mass as an unavoidable impurity. Further, it is preferable that the Mg content is less than 0.05% by mass, the B content is less than 0.001% by mass, and the P content is less than 0.001% by mass.

Further, in the aluminum alloy substrate 11, it is preferable that the average particle size of Si particles having a maximum diameter of 0.5 μm or more is 2 μm or less.

Further, the aluminum alloy substrate 11 has a disk shape having an opening in the center. The size of the aluminum alloy substrate 11 is within the range of 53 mm or more and 97 mm or less in diameter, and 0.4 mm or more and 0.9 mm or less in thickness.
Hereinafter, the average particle diameter and size (diameter, thickness) of each element and Si particles contained in the aluminum alloy substrate 11 having such a configuration will be described.

(Si)
Since Si has a small amount of solid solution in Al, it is mainly dispersed in the aluminum alloy structure as Si particles of Si alone. The rigidity of the aluminum alloy substrate in which the Si particles are dispersed is improved. Further, during machining with a cutting tool, chips are easily divided, that is, chip fragmentability is improved by crushing Si particles or peeling at the interface between Si particles and the Al matrix. Therefore, the workability when manufacturing the aluminum alloy substrate is improved.

If the Si content is less than 9.5% by mass, it may be difficult to obtain the above effect. On the other hand, when the Si content exceeds 13.0% by mass, the average particle size of the Si particles dispersed in the aluminum alloy structure becomes large, and the chip breakability of the aluminum alloy is improved, but the cutting tool after machining is improved. There is a risk that the wear of the aluminum alloy substrate will increase significantly and the productivity of the aluminum alloy substrate will decrease. Further, since Si particles are difficult to form a NiP-based plating film, an aluminum alloy substrate in which Si particles having an excessively large average particle diameter are dispersed is difficult to form a uniform NiP-based plating film. The substrate for the magnetic recording medium used may have reduced plating properties.
Therefore, in the present embodiment, the Si content is in the range of 9.5% by mass or more and 13.0% by mass or less. The Si content is preferably in the range of 10.0% by mass or more and 12.0% by mass or less.

(Cu)
Cu has the effect of improving the rigidity of the aluminum alloy substrate by being dissolved in the aluminum alloy structure. Further, Cu has an effect of further improving the rigidity of the aluminum alloy substrate by forming an _{Al 2 Cu phase in the aluminum alloy structure.}

If the Cu content is less than 0.5% by mass, it may be difficult to obtain the above effect. On the other hand, if the Cu content exceeds 3.0% by mass, the density of the aluminum alloy substrate becomes high, and the substrate for a magnetic recording medium using this may deteriorate fluttering.
Therefore, in the present embodiment, the Cu content is in the range of 0.5% by mass or more and 3.0% by mass or less. The Cu content is preferably in the range of 1.0% by mass or more and 2.8% by mass or less.

(Sr)
By coexisting with Si, Sr has the effect of spheroidizing eutectic Si and primary Si at the time of solidification and miniaturizing Si particles. Due to the effect of miniaturizing the Si particles, the chip breakability of the aluminum alloy is indirectly improved, the workability of the aluminum alloy is improved, and the wear and damage of the cutting tool during machining can be suppressed. In addition, it has the effect of uniformly and finely dispersing Si particles in steps such as casting, extrusion, and drawing to further improve the machinability of the alloy. In addition, it has the effect of making the structure of the NiP-based plating film formed on the surface of the aluminum alloy substrate uniform, and also making the film quality of the NiP-based plating film uniform.

If the Sr content is less than 0.005% by mass, the above effect may be difficult to obtain. That is, since the Si particles do not become spheroidized and sharp corners are formed, there is a possibility that the cutting tool is easily worn or damaged during machining. On the other hand, when the content of Sr exceeds 0.1% by mass, the effect of improving the machinability of the alloy is saturated, and it becomes meaningless to add more. Further, when the content of Sr is increased, SrAl ₄ is generated, and this SrAl ₄ acts as a nucleus, the Si of the primary crystal becomes coarse, and the average particle size of the Si particles may become large.
Therefore, in the present embodiment, the Sr content is in the range of 0.005% by mass or more and 0.1% by mass or less. The content of Sr is preferably in the range of 0.01% by mass or more and 0.05% by mass or less.

(Zn)
Zn dissolves in the aluminum alloy structure as a solid solution, combines with other additives, and disperses in the aluminum alloy structure as a precipitate. As a result, the mechanical strength of the aluminum alloy is increased, and the synergistic effect with other solid solution type elements improves the workability (cutability) when manufacturing the aluminum alloy substrate, and also forms a NiP-based plating film. It has the effect of promoting.

If the Zn content is less than 0.01% by mass, it may be difficult to obtain the above effect. On the other hand, if the Zn content exceeds 0.4% by mass, the corrosion resistance of the alloy may decrease.
Therefore, in the present embodiment, the Zn content is in the range of 0.01% by mass or more and 0.4% by mass or less.

(Cr, Ti and Ni)
Cr can improve the strength because the rolled structure is miniaturized, Ti is effective in preventing leakage during casting because the cast structure can be miniaturized, and Ni is effective in improving Young's modulus. Due to these effects, by adding one of Cr, Ti and Ni, the castability (fluidity of molten metal of raw material mixture, shrinkage property, heat-resistant cracking property) when casting an aluminum alloy ingot is improved. At the same time, the mechanical strength is increased, and the workability (cutability) when manufacturing an aluminum alloy substrate is improved. One type of Cr, Ti and Ni may be used alone, or two or more types may be used in combination.

If the total content of Cr, Ti and Ni is less than 0.005% by mass, the above effect may be difficult to obtain. On the other hand, when the total content of Cr, Ti and Ni exceeds 1.0% by mass, the above effect is saturated and it becomes meaningless to add more.
Therefore, in the present embodiment, the total content of Cr, Ti, and Ni is in the range of 0.005% by mass or more and 1.0% by mass or less.

(Mn)
Mn has the effect of finely precipitating in the aluminum alloy structure, increasing the mechanical strength of the alloy, and improving the workability when manufacturing the aluminum alloy substrate.
If the Mn content is less than 0.05% by mass, it may be difficult to obtain the above effect. On the other hand, when the Mn content exceeds 0.4% by mass, the above effect is saturated and the meaning of adding more is lost.
Therefore, in the present embodiment, the Mn content is in the range of 0.05% by mass or more and 0.4% by mass or less.

(Zr)
Zr has the effect of miniaturizing Si particles in the same manner as Sr. _{Further, by forming a fine Si 2} Zr compound in the aluminum alloy structure, there is an effect of improving the rigidity of the aluminum alloy substrate.

If the Zr content is less than 0.03% by mass, the above effect may be difficult to obtain. On the other hand, when the content of Zr exceeds 0.3% by mass, the above effect is saturated and the meaning of adding more is lost.
Therefore, in the present embodiment, the Zr content is in the range of 0.03% by mass or more and 0.3% by mass or less.

(Fe)
Fe is an impurity that is unavoidably mixed from the raw material. When the Fe content is 0.01% by mass or more, coarse crystals of the Al—Si—Fe compound may be formed in the aluminum alloy structure. When coarse Al-Si-Fe compound crystallization is generated, a large number of scratches are generated during grinding when manufacturing an aluminum alloy substrate, and many parts that cannot be used for a magnetic recording medium are generated. May decrease. Further, in the substrate for a magnetic recording medium using an aluminum alloy substrate in which a crystallized product of a coarse Al—Si—Fe compound is generated, the Al—Si—Fe compound falls off during processing to form a dent, and the plating property is deteriorated. There is a risk of
Therefore, in the present embodiment, the Fe content is less than 0.01% by mass.

(Mg)
Mg is an impurity that is unavoidably mixed from the raw material. If the Mg content is 0.05% by mass or more, the castability at the time of casting an aluminum alloy ingot may decrease.
Therefore, in the present embodiment, the Mg content is less than 0.05% by mass.

(B)
B is an impurity that is unavoidably mixed from the raw material. If the B content is 0.001% by mass or more, the effect of miniaturizing Si particles by adding Sr may decrease.
Therefore, in the present embodiment, the content of B is less than 0.001% by mass.

(P)
P is an impurity that is unavoidably mixed from the raw material. When the P content is 0.001% by mass or more, coarse Si particles having AlP particles as nuclei are generated, and there is a possibility that the processability and plating property at the time of manufacturing the aluminum alloy substrate may be deteriorated.
Therefore, in the present embodiment, the content of P is less than 0.001% by mass.

(Average particle size of Si particles)
As described above, a substrate for a magnetic recording medium using an aluminum alloy substrate in which Si particles having an excessively large average particle diameter are dispersed may have a reduced plating property.
According to the study by the present inventors, a substrate for a magnetic recording medium using an aluminum alloy substrate having an average particle diameter of Si particles having a maximum diameter of 0.5 μm or more and an average particle diameter of more than 2 μm tends to have a significantly reduced plating property. Ranged.
Therefore, in the present embodiment, the average particle size of Si particles having the longest diameter of 0.5 μm or more is 2 μm or less.

The average particle size of the Si particles is a value obtained by an image analysis method from a cross-sectional image of an aluminum alloy substrate. More specifically, the average particle size of Si particles has a maximum diameter of 0 by an image analysis method after taking a cross-sectional image of an aluminum alloy substrate using an electron microscope such as FE-SEM. It is a value obtained by extracting Si particles of .5 μm or more, measuring the longest diameter of the extracted Si particles, and calculating the average value of the measured longest diameters.

(Size: diameter, thickness)
The magnetic recording medium substrate 10 is mainly used for a magnetic recording medium of a hard disk drive. The magnetic recording medium needs to be able to be stored in a standardized hard disk drive, that is, a 2.5-inch hard disk drive, a 3.5-inch hard disk drive, or the like. For example, a 2.5-inch hard disk drive uses a magnetic recording medium with a maximum diameter of about 67 mm, and a 3.5-inch hard disk drive uses a magnetic recording medium with a maximum diameter of about 97 mm.
Therefore, in the present embodiment, the diameter of the aluminum alloy substrate 11 is set to be within the range of 53 mm or more and 97 mm or less.

Further, in the hard disk drive, it is effective to increase the number of magnetic recording media stored in the case in order to increase the recording capacity. For example, a normal 3.5-inch hard disk drive can store up to five magnetic recording media with a thickness of 1.27 mm, but if six or more magnetic recording media can be stored, the recording capacity will increase. It becomes possible to make it.
Therefore, in the present embodiment, the thickness of the aluminum alloy substrate 11 is set to be within the range of 0.4 mm or more and 0.9 mm or less.

[Manufacturing method of aluminum alloy substrate]
The aluminum alloy substrate 11 includes, for example, a casting step of producing an aluminum alloy ingot containing the above-mentioned elements, a rolling step of rolling an aluminum alloy ingot into a plate shape to obtain an aluminum alloy plate material, and an aluminum alloy plate material of aluminum. It can be manufactured by a method including a processing step of forming into an alloy substrate.

(Casting process)
In the casting step, a mixture of raw materials containing the above-mentioned elements is cast to produce an aluminum alloy ingot.
As a method for casting a mixture of raw materials, for example, a direct chill casting method (DC casting method) can be used. The direct chill casting method is a method in which a molten metal of a raw material mixture is poured into a mold, and then the mold is brought into direct contact with cooling water to cast an aluminum alloy ingot.

The obtained aluminum alloy ingot is preferably homogenized. The homogenization treatment is performed, for example, by heating an aluminum alloy ingot at a temperature of 300 ° C. or higher and 600 ° C. or lower within a range of 1 hour or more and 5 hours or less.

(Rolling process)
In the rolling step, the aluminum alloy ingot obtained in the above casting step is rolled into a plate shape to obtain an aluminum alloy plate material. The rolling method is not particularly limited, and a hot rolling method and a cold rolling method can be used. The rolling conditions are not particularly limited, and can be the normal conditions used for rolling an aluminum alloy ingot.

(Processing process)
In the processing step, first, the aluminum alloy plate material obtained in the rolling step is punched into a disk shape to obtain an aluminum alloy disk. Next, the aluminum alloy disk is heated at a temperature of 300 ° C. or higher and 500 ° C. or lower within a range of 0.5 hours or more and 5 hours or less to be annealed. By performing annealing, the strain inherent in the aluminum alloy disk substrate can be alleviated, and the rigidity of the obtained aluminum alloy substrate can be adjusted within an appropriate range. Next, the surface and end face of the annealed aluminum alloy disk are cut using a cutting tool. As the cutting tool, for example, a diamond bite can be used. Annealing may be performed after cutting.

[NiP-based plating film]
The NiP-based plating film 12 has the effect of improving the rigidity (Young's modulus) of the magnetic recording medium substrate 10.
The NiP-based plating film 12 may contain elements other than Ni and P. The NiP-based plating film 12 is preferably formed of a NiP alloy containing Ni and P, or a NiWP alloy containing Ni, W and P. It is preferable that the NiP alloy contains P in the range of 10% by mass or more and 15% by mass or less, and the balance is Ni and unavoidable impurities. The NiWP alloy preferably contains W in the range of 15% by mass or more and 22% by mass or less, P in the range of 3% by mass or more and 10% by mass or less, and the balance is Ni and unavoidable impurities. By forming the NiP-based plating film 12 with a NiP alloy or a NiWP alloy having the above composition, the rigidity of the magnetic recording medium substrate 10 can be reliably improved.

The thickness of the NiP-based plating film 12 is preferably 7 μm or more, and particularly preferably 9 μm or more. By setting the thickness of the NiP-based plating film 12 to this thickness, the rigidity of the magnetic recording medium substrate 10 can be reliably improved.
The thickness of the NiP-based plating film 12 is preferably 20 μm or less, and particularly preferably 17 μm or less. By setting the thickness of the NiP-based plating film 12 to this thickness, the flatness and light weight of the magnetic recording medium substrate 10 can be achieved at the same time.

[Manufacturing method of substrate for magnetic recording medium]
The substrate for a magnetic recording medium of the present embodiment is, for example, a plating step of forming a NiP-based plating film on an aluminum alloy substrate 11 by a plating method and polishing of the surface of an aluminum alloy substrate with a NiP-based plating film. It can be manufactured by a method including a processing step.

(Plating process)
In the plating step, it is preferable to use an electroless plating method as a method for forming a NiP-based plating film on an aluminum alloy substrate. The plating film made of NiP alloy can be formed by using a conventionally used method. As the plating film made of NiWP alloy, a plating solution obtained by adding a tungsten salt to the plating solution for NiP alloy can be used. As the tungsten salt, for example, sodium tungstate, potassium tungstate, ammonium tungstate and the like can be used.

The thickness of the NiP-based plating film can be adjusted by the immersion time in the plating solution and the temperature of the plating solution. The plating conditions are not particularly limited, but the pH of the plating solution is 5.0 to 8.6, the temperature of the plating solution is 70 to 100 ° C., preferably 85 to 95 ° C., and the plating solution is immersed in the plating solution. The time is preferably 90 to 150 minutes.

The obtained aluminum alloy substrate with a NiP-based plating film is preferably heat-treated. As a result, the hardness of the NiP-based plating film can be further increased, and the Young's modulus of the substrate for the magnetic recording medium can be further increased. The temperature of the heat treatment is preferably 300 ° C. or higher.

(Polishing process)
In the polishing process, the surface of the aluminum alloy substrate with a NiP-based plating film obtained in the plating process is polished. The polishing process is a multi-step polishing method that has two or more stages of polishing using multiple independent polishing machines from the viewpoint of achieving both improvement in surface quality such as smoothness and few scratches and improvement in productivity. It is preferable to adopt it. For example, a rough polishing step of polishing while supplying a polishing liquid containing alumina abrasive grains using a first polishing machine, and a colloidal using a second polishing machine after cleaning the polished aluminum alloy substrate. A finish polishing step is performed in which polishing is performed while supplying a polishing liquid containing silica abrasive grains.

FIG. 2 is a perspective view showing an example of a polishing machine that can be used in the polishing process.
As shown in FIG. 2, the first and second polishing machines 20 include a pair of upper and lower surface plates 21 and 22, and sandwich a plurality of substrates W between the surface plates 21 and 22 rotating in opposite directions. However, both sides of the substrate W are polished by the polishing pads 23 provided on the surface plates 21 and 22.

<Magnetic recording medium>
FIG. 3 is a schematic cross-sectional view showing an example of the magnetic recording medium according to the present embodiment.
As shown in FIG. 3, the magnetic recording medium 30 includes the above-mentioned magnetic recording medium substrate 10 and a magnetic layer 31 provided on the surface of the NiP-based plating film 12 of the magnetic recording medium substrate 10. The protective layer 32 and the lubricant layer 33 are further laminated on the surface of the magnetic layer 31 in this order.

The magnetic layer 31 is made of a magnetic film whose axis for easy magnetization is oriented perpendicular to the substrate surface. The magnetic layer 31 contains Co and Pt, and may contain oxides, Cr, B, Cu, Ta, Zr, and the like in order to further improve the SNR characteristics. Examples of the oxide contained in the magnetic layer 31 include SiO ₂ , SiO, Cr ₂ O ₃ , CoO, Ta ₂ O ₃ , and TiO ₂ . The magnetic layer 31 may be composed of one layer or may be composed of a plurality of layers made of materials having different compositions.
The thickness of the magnetic layer 31 is preferably 5 to 25 nm.

The protective layer 32 protects the magnetic layer 31. As the material of the protective layer 32, for example, carbon nitride can be used. The protective layer 32 may be composed of one layer or may be composed of a plurality of layers.
The film thickness of the protective layer 32 is preferably in the range of 1 nm to 10 nm.

The lubricant layer 33 prevents the magnetic recording medium 30 from being contaminated and reduces the frictional force of the magnetic head of the magnetic recording / reproducing device that slides on the magnetic recording medium 30 to improve the durability of the magnetic recording medium 30. It is something that makes you. As the material of the lubricant layer 33, for example, a perfluoropolyether-based lubricant or an aliphatic hydrocarbon-based lubricant can be used.
The film thickness of the lubricant layer 33 is preferably in the range of 0.5 nm to 2 nm.

The layer structure of the magnetic recording medium 30 in the present embodiment is not particularly limited, and a known laminated structure can be applied. For example, the magnetic recording medium 30 has an adhesion layer (not shown), a soft magnetic base layer (not shown), a seed layer (not shown), and an orientation control layer (not shown) between the magnetic recording medium substrate 10 and the magnetic layer 31. (Not shown) may be laminated in this order.

<Hard disk drive>
FIG. 4 is a perspective view showing an example of the hard disk drive in the present embodiment.
As shown in FIG. 4, the hard disk drive 40 includes the above-mentioned magnetic recording medium 30, a medium drive unit 41 for driving the magnetic recording medium 30 in the recording direction, a magnetic head 42 including a recording unit and a playback unit, and a magnetic head. It includes a head moving unit 43 that moves the 42 relative to the magnetic recording medium 30, and a recording / reproducing signal processing unit 44 that processes the recording / reproducing signal from the magnetic head 42.

The magnetic recording medium substrate 10 can be made thinner because fluttering is reduced. Therefore, by increasing the number of magnetic recording media 30 housed inside the drive case of the standardized hard disk drive, it is possible to provide the hard disk drive 40 having a high recording capacity.

Further, since the magnetic recording medium substrate 10 has high machinability and can be manufactured at low cost, the bit unit price of a hard disk drive having a high recording capacity can be reduced.

Further, since the magnetic recording medium substrate 10 reduces fluttering in the atmosphere, it is not necessary to enclose a low molecular weight gas such as helium inside the hard disk drive case, and the hard disk drive 40 having a high recording capacity has a high recording capacity. The manufacturing cost can be reduced.

Further, the hard disk drive 40 is particularly preferably used for a 3.5-inch hard disk drive having a high recording capacity.

In the magnetic recording medium substrate 10 of the present embodiment having the above configuration, since the aluminum alloy substrate of the base material contains Si, Cu, and Sr in the above amounts, the rigidity is high and the coarse Si Since the content of particles is small, it is easy to form a uniform NiP type plating film.

The substrate for a magnetic recording medium of the present embodiment having the above configuration has the above-mentioned aluminum alloy substrate and NiP-based plating film, and further has a ratio E / ρ of Young's modulus E and density ρ of 29 or more. Therefore, even if the thin shape has a diameter in the range of 53 mm or more and 97 mm or less and a thickness in the range of 0.4 mm or more and 0.9 mm or less, the plating property can be improved while suppressing fluttering. Can be improved.

Further, since the magnetic recording medium of the present embodiment is provided with a magnetic layer on the surface of the above-mentioned magnetic recording medium substrate, it has a thin shape that can accommodate a larger number of sheets in a standardized hard disk drive drive case than before. Can be.

Since the hard disk drive of the present embodiment includes the above-mentioned magnetic recording medium, a larger number of magnetic recording media than before can be stored in the drive case, which increases the recording capacity.

<Examples 1 to 24, Comparative Examples 1 to 7>
Hereinafter, the effects of the present invention will be made clearer by examples. The present invention is not limited to the following examples, and can be appropriately modified and implemented without changing the gist thereof.

[Manufacturing of aluminum alloy substrate]
Pure Al lumps as Al raw materials, Si, Cu, Sr, Zn, Cr, Ti, Ni, Mn, Zr, Fe, Mg, B raw materials are simple substances or alloy lumps with Al, and P is a mixture lump with Si. I prepared. For each raw material of Al, Si, Cu, Sr, Zn, Cr, Ti, Ni, Mn, and Zr, the Fe content is less than 0.01% by mass and the Mg content is less than 0.05% by mass. , B content was less than 0.001% by mass, and P content was less than 0.001% by mass.

The raw materials of each of the prepared elements are weighed so that the composition after casting becomes the composition shown in Table 1, these are melted in the air at 820 ° C., and aluminum is used by the direct chill casting method (DC casting method). An alloy ingot was prepared. The casting temperature was 700 ° C. and the casting speed was 40 to 60 mm / min. Next, the obtained aluminum alloy ingot was held at 460 ° C. for 2 hours for homogenization treatment. Then, it was rolled into a plate material having a thickness of 1.2 mm. The obtained aluminum alloy plate was punched into a disk shape having a diameter of 97 mm having an opening in the center, and annealed at 380 ° C. for 1 hour. Then, the surface and the end face of the aluminum alloy disk were cut with a diamond tool to obtain an aluminum alloy substrate having a diameter of 96 mm and a thickness of 0.8 mm. However, Example 4 is not an example of the present invention.

[Manufacturing of substrates for magnetic recording media]
_{The aluminum alloy substrate is immersed in a NiP-based plating solution, and a Ni 88} P ₁₂ (P content 12% by mass, balance Ni) film is formed as a NiP-based plating film on the surface of the aluminum alloy substrate using an electroless plating method. bottom.

The NiP-based plating solution contains nickel sulfate (nickel source) and sodium hypophosphite (phosphorus source), and lead acetate, sodium citrate, and sodium borate are appropriately added to form a NiP-based plating film having the above composition. The amount of the component adjusted was used so that The pH of the NiP-based plating solution at the time of forming the NiP-based plating film was adjusted to 6, and the solution temperature was adjusted to 90 ° C. The immersion time of the aluminum alloy substrate in the NiP-based plating solution was 2 hours.
Next, the aluminum alloy substrate on which the NiP-based plating film was formed was heated at 300 ° C. for 3 minutes to obtain an aluminum alloy substrate with a NiP-based plating film.

Next, using a three-stage lapping machine equipped with a pair of upper and lower surface plates as a polishing machine, the surface of an aluminum alloy substrate with a NiP-based plating film was polished to prepare a substrate for a magnetic recording medium. .. At this time, a suede type (manufactured by Filwel) was used as the polishing pad. Alumina abrasive grains with a D50 of 0.5 μm are used for the first-stage polishing, colloidal silica abrasive grains with a D50 of 30 nm are used for the second-stage polishing, and colloidal silica abrasive grains with a D50 of 30 nm are used for the third-stage polishing. Colloidal silica abrasive grains having a D50 of 10 nm were used. The polishing time was set to 5 minutes for each stage.

[evaluation]
The following items were evaluated.
(Composition of aluminum alloy substrate)
The composition of the obtained aluminum substrate was confirmed by wet analysis for Sr and cantlet analysis for other elements. As a result, it was confirmed that the content of each metal element was the same as the content shown in Table 1.

(Castability)
The castability was visually evaluated for the shapes of the aluminum alloy ingot before rolling and the aluminum alloy plate after rolling. ◎ when there is no abnormality in the shape of both the aluminum alloy ingot and the aluminum alloy plate, ○ when there are fine cracks and cracks at the end of the aluminum alloy plate but there is no problem in practical use, and the end of the aluminum alloy plate is distorted. However, the case where there is no problem in practical use was judged as Δ. The results are shown in Table 2 below.

Table in which the mate 17P01003 table to be applied is incorporated (workability)
The processability of the aluminum alloy substrate during production was evaluated from the flatness of the surface of the aluminum alloy substrate after cutting by observing it with a 1000-fold differential interference contrast optical microscope. The case where the flatness was excellent was judged as ⊚, the case where a slight scratch was observed but there was no problem in practical use was evaluated as ◯, and the case where a large number of scratches were observed and many unusable parts were generated was evaluated as ×. The results are shown in Table 2 below.
In addition, the surface of the cutting tool after processing was visually observed. As a result, those with large wear of the cutting tool are described in Table 2 as "large wear of the cutting tool".

(Average particle size of Si particles)
The alloy structure of the aluminum alloy substrate was observed in cross section, and the distribution density of Si particles having the longest diameter and the longest diameter of 0.5 μm or more was measured. Then, the average particle size was calculated from the distributed density of the measured particles having the longest diameter of 0.5 μm or more.

Specifically, an aluminum alloy substrate was cut into 10 mm squares and embedded in resin to prepare a sample. At this time, as the embedding resin, Demotoc 20 (manufactured by Bodson Quality Control Co., Ltd.) (powder: liquid = 2: 1 (mass ratio) mixed, room temperature curing type) was used. Next, the sample was subjected to wet polishing to form a cross section in a direction horizontal to the rolling direction, and then the sample was etched. At this time, the sample was etched by immersing the sample in a 2.3 mass% hydrofluoric acid aqueous solution at room temperature for 30 seconds, taking it out, and then washing it with running water for 1 minute.

Here, a reflected electron image of the alloy structure of the sample after etching was photographed using JSM-7000F (manufactured by JEOL Ltd.) of FE-SEM. At this time, the sample was subjected to conductive treatment by carbon vapor deposition in advance, the magnification was set to 2000 times, and a reflected electron image was taken. From this reflected electron image having a visual field area of 2774 μm ² , binarization treatment was performed using WinROOF (Ver6.5), and the distribution density of the Si particles having the longest diameter and the longest diameter of 0.5 μm or more was measured. .. Specifically, the threshold value was set to 200 to 255 (135 to 255 when binarization did not work) by the discriminant analysis method, and the binarization process was performed. The obtained image was subjected to a hole filling treatment and a treatment for removing particles having a particle size of 0.5 μm or less, and the distribution density of the longest diameter of Si particles having a maximum diameter of 0.5 μm or more was measured. ..

(Plating property)
_{The aluminum alloy substrate is immersed in a NiP-based plating solution to form a Ni 88} P ₁₂ film as a NiP-based plating film on the surface of the aluminum alloy substrate using an electroless plating method, and then the aluminum alloy substrate is 3 at 300 ° C. It was heated for a minute to produce an aluminum alloy substrate with a NiP-based plating film. The conditions for forming the NiP-based plating film were the same as those for manufacturing the substrate for the magnetic recording medium.

The surface of the NiP-based plating film of the aluminum alloy substrate with the NiP-based plating film was observed with a differential interference type optical microscope having a magnification of 1000 times, and the plating property was evaluated from the flatness and the presence or absence of fine holes. The case where the plating property was particularly excellent was evaluated as ⊚, the case where the plating property was particularly excellent was evaluated as ◯, the case where the plating property was within the usable range was evaluated as Δ, and the case where the plating property was inferior was evaluated as ×. The results are shown in Table 2 below.

(Young's modulus E, density ρ, ratio E / ρ)
The Young's modulus of the magnetic recording medium substrate was measured at room temperature based on the Japanese Industrial Standards JIS Z 2280-1993. The Young's modulus was measured by cutting a substrate for a magnetic recording medium into strips having a length of 50 mm, a width of 10 mm, and a thickness of 0.8 mm, which were used as test pieces.

The density of the substrate for the magnetic recording medium was determined using the literature values of the densities of the constituent elements.
Then, the ratio E / ρ of the Young's modulus E and the density ρ was calculated. The results are shown in Table 2 below.

(Fluttering characteristics)
Fluttering was evaluated by measuring NRRO. NRRO rotates the magnetic recording medium substrate at 10000 rpm for 1 minute, measures the width of displacement due to fluttering occurring on the outermost peripheral surface of the magnetic recording medium substrate using a He-Ne laser displacement meter, and obtains the displacement. The maximum value of the width of is NRRO.
NRRO of 3.2 μm or less is ◎, that is more than 3.2 μm and 3.4 μm or less is ○, that is more than 3.4 μm and 3.6 μm or less is Δ, and that is more than 3.6 μm. It was evaluated as x. The results are shown in Table 2 below.

In Comparative Example 1, the ratio E / ρ was 29 or less, and the fluttering characteristics deteriorated. In addition, the workability at the time of manufacturing the aluminum alloy substrate was lowered. It is considered that this is because the content of Si is less than the range of the present invention. On the other hand, in Comparative Example 2, the average particle size of the Si particles of the aluminum alloy substrate was as large as 3.0 μm, and the substrate for the magnetic recording medium had reduced plating property. In addition, the wear of the cutting tool during machining (cutting) has increased. It is considered that this is because the content of Si exceeds the range of the present invention.

In Comparative Example 3, the ratio E / ρ was 29 or less, and the fluttering deteriorated. It is presumed that this is because the Cu content is less than the range of the present invention and the Young's modulus is lowered. On the other hand, in Comparative Example 4, the ratio E / ρ was 29 or less, and the fluttering characteristic was lowered. It is presumed that this is because the Cu content exceeds the range of the present invention and the density ρ of the magnetic recording medium substrate becomes too high.

In Comparative Example 5, the average particle size of the Si particles of the aluminum alloy substrate was as large as 5.0 μm, and the substrate for the magnetic recording medium had reduced plating property. In addition, the wear of the cutting tool during machining (cutting) has increased. It is considered that this is because the Si particles became coarse due to the low content of Sr. On the other hand, in Comparative Example 6, the average particle size of the Si particles of the aluminum alloy substrate was as large as 11.0 μm, and the substrate for the magnetic recording medium had reduced plating property. In addition, the wear of the cutting tool during machining (cutting) has increased. This is because the content of Sr is large, SrAl ₄ becomes a nucleus, Si particles primary crystal is considered to be because became coarse.

In Comparative Example 7, many scratches were generated during processing during the production of the aluminum alloy substrate, and the processability was lowered. Further, the substrate for the magnetic recording medium has deteriorated plating property. It is considered that this is because the content of Fe exceeds the range of the present invention, so that coarse crystallization of the Al—Si—Fe compound is generated.

On the other hand, in Examples 1 to 24 in which the aluminum alloy substrate contains Si, Cu, and Sr within the scope of the present invention and the ratio E / ρ is 29 or more, the substrate for the magnetic recording medium suppresses fluttering. However, the plating property was improved.

Further, in Example 8 in which each element of Zn, Cr, Ti, Mn, Zr, Mg, B, and P is contained in a predetermined range, the castability and workability are further improved, and the plating property of the substrate for the magnetic recording medium is further improved. Was further improved, and fluttering was further suppressed.

Further, in Examples 9 to 10 containing Zn in a predetermined range, the workability was further improved, and the fluttering of the magnetic recording medium substrate was further suppressed.

Further, in Examples 11 to 17 containing Cr, Ti, and Ni in a predetermined range, castability and workability were further improved.

Further, in Examples 18 to 19 in which Mn was contained in a predetermined range, the workability was further improved.

Further, in Examples 20 to 21 containing Zr in a predetermined range, the plating property of the magnetic recording medium substrate was further improved, and fluttering was further suppressed.

Further, in Example 22 in which the Mg content was slightly high, the castability was slightly lowered.
Further, in Example 23 in which the B content was slightly high, the average particle size of Si was large.
Then, in Example 24 in which the P content was slightly high, the processability and the plating property were slightly lowered.

10 ... Magnetic recording medium substrate, 11 ... Aluminum alloy substrate, 12 ... NiP-based plating film, 20 ... Polishing machine, 21, 22 ... Standard plate, 23 ... Polishing pad, 30 ... Magnetic recording medium, 31 ... Magnetic layer, 32 ... protective layer, 33 ... lubricant layer, hard disk drive 40 ..., 41 ... medium drive unit, 42 ... magnetic head, 43 ... head moving unit, 44 ... recording / playback signal processing unit

Claims (3)

A substrate for a magnetic recording medium including an aluminum alloy substrate and a NiP-based plating film formed on at least one surface of the aluminum alloy substrate.
The ratio E / ρ of the Young's modulus E whose unit is expressed in GPa ^{and the density ρ whose unit is expressed in g / cm 3} is 29 or more and 32 or less .
The aluminum alloy substrate contains Si in the range of 9.5% by mass or more and 13.0% by mass or less, Cu in the range of 2.0 % by mass or more and 3.0% by mass or less, and Sr in the range of 0.005% by mass or more. It is contained within the range of 0.1% by mass or less, the Fe content is less than 0.01% by mass, and the balance is Al.
A substrate for a magnetic recording medium, characterized in that the diameter is within the range of 53 mm or more and 97 mm or less, and the thickness is within the range of 0.4 mm or more and 0.9 mm or less. A magnetic recording medium having a magnetic recording medium substrate and a magnetic layer provided on the surface of the magnetic recording medium substrate.
The magnetic recording medium substrate is the magnetic recording medium substrate according to claim 1, and the magnetic layer is provided on the surface of the magnetic recording medium substrate on the side on which the NiP-based plating film is formed. A magnetic recording medium characterized by being plated. A hard disk drive equipped with a magnetic recording medium
A hard disk drive, wherein the magnetic recording medium is the magnetic recording medium according to claim 2.

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