JP2013004132A - Manufacturing method for aluminum substrate for magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technique which improves productivity and reduces cost when manufacturing an aluminum substrate for magnetic recording medium having smooth surfaces by reducing surface roughness before polishing and reducing the amount of polishing.SOLUTION: A manufacturing method for an aluminum substrate for magnetic recording medium includes a step for performing a phosphoric acid treatment on an aluminum substrate and a step for forming SiOfilm on the surfaces of the aluminum substrate after the phosphoric acid treatment by a plasma-enhanced chemical vapor deposition process using oxygen gas and organic siloxane gas.

Description

  The present invention relates to a method of manufacturing an aluminum substrate used as a substrate of a magnetic recording medium (magnetic disk).

  A substrate of a magnetic recording medium is required to have a smooth surface and high hardness. As such a substrate, a glass substrate or a NiP aluminum substrate obtained by performing nickel phosphorous plating on an aluminum substrate is used. Among these substrates, NiP aluminum substrate is made by rolling a coiled aluminum plate into a disk shape, lathes on the inner and outer periphery and grinding (grinding) on the main surface, and then electroless It is manufactured by performing NiP plating by plating, further polishing (polishing) and washing (Non-patent Document 1). Polishing is usually performed in two stages (first polishing and second polishing), and the polishing amount is approximately 1 to 2 μm per side.

  There is an increasing need for cost reduction for the substrate of the magnetic recording medium, and in order to reduce the amount of polishing at the time of polishing for the NiP aluminum substrate and to reduce the cost, immediately after NiP plating before polishing processing is performed. There is a strong demand to smooth the substrate surface in stages (Non-Patent Document 2). The surface roughness immediately after NiP plating is affected by the roughness of the aluminum substrate surface before NiP plating (that is, the aluminum substrate surface after grinding). For this reason, it is effective to prepare an aluminum substrate having a surface roughness as small as possible by grinding and to apply NiP plating to reduce the amount of polishing in the subsequent polishing process and to reduce the cost.

  By the way, when performing NiP plating, alkali degreasing, acid etching, desmutting, and zincate treatment are usually performed as pretreatment on an aluminum substrate after grinding. The zincate process is a process performed to remove a strong oxide film formed on the surface of the aluminum substrate and to obtain good plating adhesion. This zincate treatment is usually repeated twice in order to uniformly form the NiP plating layer. Specifically, the first zincate treatment is performed, and after washing with nitric acid, the second zincate treatment is performed. However, in the zincate treatment, the surface of the aluminum substrate is etched and the surface roughness is increased. Therefore, even if the surface roughness of the aluminum substrate is reduced by grinding, the surface of the aluminum substrate becomes rough by the subsequent zincate treatment. In order to smooth the NiP plating surface after zincate treatment, it is necessary to newly polish the NiP plating surface, which is sufficient for the need to reduce the amount of polishing at the time of polishing processing, increase productivity, and reduce costs. There was a problem that we could not respond.

Journal of Abrasive Technology, Vol. 43, no. 11, November 1999, p. 475-479 Kobe Steel Engineering Reports, Vol. 48, no. 3, December 1998, p. 5-8

  The present invention has been made by paying attention to the above-described circumstances, and its purpose is to reduce the surface roughness before polishing in manufacturing an aluminum substrate for a magnetic recording medium having a smooth surface. The purpose is to provide a technology capable of reducing the amount to increase productivity and reducing the cost.

The method for producing an aluminum substrate for a magnetic recording medium according to the present invention that has solved the above problems includes a step of subjecting an aluminum substrate to a phosphoric acid treatment, and an oxygen gas and an organic siloxane on the surface of the aluminum substrate after the phosphoric acid treatment. And a step of forming a SiO ₂ film by a plasma chemical vapor deposition method using a gas.

As the oxygen gas, it is preferable to use an oxygen gas in an amount of 1.2 times or more with respect to the stoichiometric amount of oxygen gas necessary for converting Si contained in the organosiloxane gas into SiO ₂ .

  As the organic siloxane gas, for example, hexamethyldisiloxane gas can be used.

When the FT-IR (Fourier transform infrared spectrophotometer) spectrum of the SiO ₂ film formed on the surface of the aluminum substrate was measured, the aluminum substrate for a magnetic recording medium obtained by the above production method was 1220. the maximum absorption peak intensity P ₁ observed in the range of ~1280cm ^-1, the ratio between the maximum absorption peak intensity P ₂ observed in the range of 1000 to 1200 ^-1 (P ₁ / P ₂₎ is 0.10 or less It is recommended that

According to the present invention, an aluminum substrate is not subjected to zincate treatment and NiP plating treatment as in the prior art, but is smooth and high hardness SiO ₂ film by a predetermined plasma chemical vapor deposition method after phosphoric acid treatment. Therefore, the problem of conventional NiP plating treatment (decrease in smoothness of aluminum substrate surface due to zincate treatment) can be avoided, and the amount of subsequent polishing can be reduced, the surface is smooth and high hardness. The aluminum substrate for magnetic recording media can be easily produced.

FIG. 1 shows an SiO ₂ film formed with a flow rate ratio of oxygen gas to hexamethyldisiloxane (HMDSO) of 10.4: 1 (0.87 times the stoichiometric amount of oxygen gas is used) and polished. 3 shows an FT-IR spectrum of the SiO ₂ film after the process. FIG. 2 shows the FT of the SiO ₂ film after forming and polishing the SiO ₂ film with a flow ratio of oxygen gas to HMDSO of 16: 1 (using oxygen gas 1.33 times the stoichiometric amount). -IR spectrum is shown.

The present inventors can replace the conventional NiP plating process, can reduce the amount of polishing at the time of polishing without losing the smoothness of the aluminum substrate surface after grinding, the surface is smooth, We have intensively studied to provide a technology that can produce aluminum substrates for magnetic recording media with high hardness. As a result, it is possible to reduce the surface roughness of the aluminum substrate obtained by grinding, rather than deteriorating the surface roughness of the aluminum substrate obtained by grinding the aluminum substrate after grinding. By forming a SiO ₂ film on the surface of an aluminum substrate that has been subjected to phosphoric acid treatment by a plasma chemical vapor deposition method using oxygen gas and organosiloxane gas, the amount of polishing during the subsequent polishing process can be reduced, and the surface becomes smooth. Thus, the inventors have found that an aluminum substrate for a magnetic recording medium with high hardness can be produced, and completed the present invention.

That is, in the present invention, phosphoric acid is used as an etching solution that can selectively dissolve and remove burrs and grinding marks on a grinded (ground) aluminum substrate (hereinafter sometimes referred to as a ground aluminum substrate). The smoothness of the ground aluminum substrate surface can be improved. If the SiO ₂ film is formed on the surface of the ground aluminum substrate thus obtained by the above-described plasma chemical vapor deposition method, the nucleation of SiO ₂ is performed almost uniformly over the entire surface, so that the surface roughness is low. A small and high hardness SiO ₂ film can be formed.

  Thus, the present invention is characterized in that a grinded aluminum substrate is etched using phosphoric acid. If phosphoric acid is used as an etching solution, the natural oxide film formed on the surface of the aluminum substrate can be etched, pits are not generated during etching, and the surface roughness does not increase after etching.

  Aluminum is an amphoteric metal and is soluble in both acid and alkali aqueous solutions. However, according to the examination results of the present inventors, when an alkaline aqueous solution (for example, an aqueous sodium hydroxide solution) is used as an etching solution, pits are generated on the surface, as shown in the examples described later. It was found that the surface roughness was higher than before. In addition, since aluminum has a higher ionization tendency than hydrogen, even if a strong oxide film is formed, it should generally be easily etched with acid. However, when the present inventors examined the case where an acid was used as an etching solution, it was actually found that it can be etched efficiently only with a specific type of acid because of a natural oxide film formed on the surface. did. For example, sulfuric acid or nitric acid could not etch an aluminum substrate, and even if the aluminum substrate was immersed in sulfuric acid or nitric acid, no decrease in mass was observed before and after immersion. In addition, an acid containing halogen ions (for example, hydrochloric acid or nitric acid containing potassium fluoride) can easily dissolve the natural oxide film formed on the aluminum surface, so that the aluminum substrate can be etched. Occurs, and the surface changes to a satin state, so that the surface roughness becomes larger than before etching.

  In contrast, phosphoric acid can etch an aluminum substrate and does not generate pits. Accordingly, when the aluminum substrate is immersed in phosphoric acid, the surface roughness can be reduced rather than impairing the smoothness of the surface of the aluminum substrate as compared with before the immersion, and etching can be effectively performed.

  Hereinafter, the manufacturing method of the aluminum substrate for magnetic recording media which concerns on this invention is demonstrated.

[Preparation of test materials]
First, an aluminum plate is prepared. As the aluminum plate, 5086 alloy (international aluminum alloy name) can be used. Also, alloy types other than 5086 alloy may be used.

  The plate thickness of the aluminum plate is not particularly limited, and various thicknesses can be used. Usually, the aluminum plate is set to have a predetermined thickness after film formation of the media. For example, when manufacturing an aluminum substrate for a magnetic recording medium having a diameter of φ95 mm, an aluminum plate having a thickness of 1.270 mm or a thickness of 1.753 mm is usually used. When manufacturing an aluminum substrate for a magnetic recording medium having a diameter of 65 mm, An aluminum plate having a thickness of 0.635 mm or a thickness of 0.800 mm is usually used.

  It is recommended that the aluminum plate is punched into a desired shape and annealed. By performing the annealing treatment, distortion due to processing can be removed and the flatness can be improved.

  Since the surface altered layer resulting from rolling or the like is formed on the surface of the aluminum substrate, the surface altered layer is removed by chamfering with a lathe or grinding, or a combination of both to smooth the surface of the aluminum substrate. It is preferable to keep it.

  The said processing method is not specifically limited, Generally, the wet grinding using a PVA grindstone and the face cutting using a diamond bite are employable. In addition, wet grinding using a PVA grindstone may be performed after chamfering.

  For example, the surface roughness of the aluminum substrate is preferably 20 nm or less in terms of the centerline average roughness Ra defined by JIS B0601 (2001).

[About phosphoric acid treatment]
In the present invention, it is important to perform phosphoric acid treatment on the aluminum substrate. As described above, by dipping the aluminum substrate in phosphoric acid, fine protrusions formed during burrs and grinding can be dissolved and removed, so that the surface of the aluminum substrate can be smoothed. On the other hand, when an etching solution other than phosphoric acid is used, the aluminum substrate cannot be etched or even if it can be etched, pits are generated and the surface roughness increases.

  As the phosphoric acid, for example, an aqueous solution having a phosphoric acid concentration of 5 to 60% by mass is preferably used.

  The immersion conditions can be appropriately adjusted depending on the type of aluminum substrate or phosphoric acid used so that fine protrusions formed during burrs and grinding can be dissolved and removed.

  It is preferable that the liquid temperature of the said phosphoric acid shall be 35-60 degreeC, for example. The time for immersing the aluminum substrate in phosphoric acid is preferably about 1 to 10 minutes, for example.

  When immersing the aluminum substrate in phosphoric acid, rotate the aluminum substrate, circulate phosphoric acid, or stir the phosphoric acid to prevent the reaction product from staying near the substrate surface. Is preferred.

  After immersion, it is preferable to wash the phosphoric acid adhering to the aluminum substrate with, for example, pure water.

[Formation of SiO ₂ film]
In the present invention, it is important to form an SiO ₂ film by plasma chemical vapor deposition using oxygen gas and organosiloxane gas after performing phosphoric acid treatment on the aluminum substrate.

The organosiloxane is a compound having a Si—O—Si bond in the molecular skeleton, and is used for forming a SiO ₂ film.

As said organic siloxane, hexamethyldisiloxane (HMDSO), octamethyltrisiloxane, etc. can be used, for example, These may be used together. In consideration of appropriate vapor pressure, safety, availability, film formation rate, and hardness of the formed SiO ₂ film, it is preferable to use HMDSO.

According to the plasma chemical vapor deposition method, a dense SiO ₂ film with few defects can be formed at a high deposition rate. That is, it is known that the SiO ₂ film can be formed not only by the plasma chemical vapor deposition method but also by a vacuum deposition method or a sputtering method. However, it is known that in the vacuum deposition method, defects are likely to occur in the film, and local defects in surface roughness are caused by the exposure of defects on the polished surface. In addition, the sputtering method can obtain a film with fewer surface defects than the vacuum deposition method, but the film formation rate cannot be increased, and the productivity is deteriorated. On the other hand, the SiO ₂ film formed by the plasma enhanced chemical vapor deposition method is a dense and hard film, and thereafter, the surface of the SiO ₂ film can be polished by employing a technique for polishing a conventional glass plate. .

Film quality good, that is, in order to form a dense and hard, and smooth SiO ₂ film is preferably converted to fully SiO ₂ to Si contained in the organic siloxane gas. For this purpose, the SiO ₂ film In film formation, it is recommended to use oxygen gas in an amount of 1.2 times or more with respect to the stoichiometric amount of oxygen gas necessary to convert Si contained in the organosiloxane gas into SiO _2. . Theoretically, Si should be completely converted to SiO ₂ if the stoichiometric amount of oxygen gas required to convert Si contained in the organosiloxane gas to SiO ₂ is used. In order to completely convert Si to SiO ₂ due to the effects of reaction loss and by-products, it is necessary to use an excess amount (specifically, 1.2 times or more) of oxygen gas relative to the stoichiometric amount. However, it became clear by experiment of the present inventors. In the present invention, it is recommended that the gas flow rate ratio during film formation be controlled within the above range.

Here, the case where HMDSO is used as the organic siloxane gas will be specifically described. HMDSO is a compound represented by the structural formula: (CH ₃ ) ₃ —SiO—Si (CH ₃ ) ₃ . When this HMDSO reacts with oxygen, a chemical reaction represented by the following formula occurs to generate SiO ₂ , CO ₂ , and H ₂ O. From this reaction formula, 1 mol of HMDSO and 12 mol of O ₂ react to produce 2 mol of SiO ₂ , 6 mol of CO ₂ , and 9 mol of H ₂ O.
_{C 6 H 18 Si 2 O +} 12O 2 → 2SiO 2 + 6CO 2 + 9H 2 O

When this is converted into a gas flow rate, the oxygen gas flow rate may be 12 times or more of the HMDSO flow rate. The flow rate of the oxygen gas is less than 12 times, can not be converted completely SiO ₂ film HMDSO even if all the oxygen is used in the reaction, a methyl group in the SiO ₂ film was large amount residual organic It becomes an inorganic hybrid structure. In this case, since a part of the bond of Si atoms is terminated with a methyl group, a strong three-dimensional skeleton of -Si-O-Si- cannot be formed, and the film quality is low and hardness is inappropriate for polishing. It becomes.

However, in reality, since a reaction efficiency of 100% is not realized, the amount is 1.2 times or more than the stoichiometric amount of oxygen gas necessary for converting Si contained in the organosiloxane gas into SiO _2. It is preferable to use an oxygen gas of 1.5 times or more.

In forming the SiO ₂ film by the plasma chemical vapor deposition method, oxygen plasma is generated on the upstream side in the plasma CVD apparatus, an organic siloxane gas is supplied from the downstream side, and oxygen plasma and organosiloxane are formed on the aluminum substrate surface. May be reacted to form a SiO ₂ film.

  As other conditions in the plasma chemical vapor deposition method, known conditions can be adopted.

The temperature of the aluminum substrate charged in the plasma CVD apparatus may be, for example, about room temperature to 80 ° C. By raising the temperature of the aluminum substrate from room temperature, a SiO ₂ film with good heat resistance can be formed.

The SiO ₂ film after the film formation preferably has a surface roughness of 20 nm or less in terms of the center line average roughness Ra defined by JIS B0601 (2001), for example.

[About polishing process]
After forming the SiO ₂ film, the surface of the SiO ₂ film is polished by a known condition may be a surface smooth. According to the present invention, since the surface of the aluminum substrate is smoothed by performing phosphoric acid treatment before polishing, the amount of polishing can be reduced as compared with the prior art, productivity can be increased, and cost reduction can be realized. In the present invention, since the SiO ₂ film formed on the surface of the aluminum substrate is hard, a conventionally used method or apparatus for polishing a glass plate can be used as it is.

The method for polishing the SiO ₂ film is not particularly limited, and a known method may be adopted. For example, wet polishing may be performed using a polishing pad and a polishing slurry. The polishing pressure may be, for example, 40 to 150 gf / cm ² , and the sliding speed may be, for example, about 40 to 160 cm / second.

[About polished SiO ₂ film]
In the present invention, when an FT-IR (Fourier transform infrared spectrophotometer) spectrum is measured for the polished SiO ₂ film formed on the surface of the aluminum substrate for magnetic recording media, 1220-1280 cm ^−1. The ratio (P ₁ / P ₂ ) between the maximum absorption peak intensity P ₁ observed in the range of ₁ and the maximum absorption peak intensity P ₂ observed in the range of 1000 to 1200 cm ⁻¹ is 0.10 or less. preferable.

The maximum absorption peak P ₁ observed in the above range of 1220 to 1280 cm ⁻¹ is a Si—CH ₃ group or a Si—CH ₂ —R group (R is a lower alkyl having 1 to 3 carbon atoms) that causes a decrease in hardness. The maximum absorption peak P ₂ observed in the range of 1000 to 1200 cm ⁻¹ indicates the characteristic absorption due to the Si—O group that brings about an improvement in hardness.

The maximum absorption peak intensity P ₁ observed in the above range 1220～1280Cm ^-1, a ratio of the maximum absorption peak intensity P ₂ observed in the above range 1000 to 1200 ^-1 (hereinafter referred to as P ₁ / P ₂ ratio May be used as an index indirectly indicating the amount of SiO ₂ contained in the SiO ₂ film. That is, the P ₁ / P ₂ ratio is 0.10 or less means that the Si—CH ₃ group or the Si—CH ₂ —R group (R is R is a lower alkyl group having 1 to 3 carbon atoms). This means that the Si—O group converted to SiO ₂ is remarkably small, and almost all of the organosiloxane is converted to SiO ₂ , and the methyl groups contained in the organosiloxane remain almost unchanged. It means not.

In the above spectrum, characteristic absorption due to the Si—CH ₃ group or the Si—CH ₂ —R group (R is a lower alkyl group having 1 to 3 carbon atoms) is also observed around 2960 cm ^−1. However, in the present invention, the peak intensity observed in this range is ignored. This is characteristic absorption due to Si—CH ₃ group or Si—CH ₂ —R group (R is a lower alkyl group having 1 to 3 carbon atoms) observed in the range of 1220 to 1280 cm ⁻¹ . Compared with the characteristic absorption due to the Si—O group (maximum absorption peak observed in the range of 1000 to 1200 cm ⁻¹ ), the error is generally smaller when comparing the peak intensities of the characteristic absorptions close to each other. Therefore, in the present invention, the P ₁ / P ₂ ratio is calculated using the maximum absorption peak intensity P ₁ observed in the range of 1220 to 1280 cm ⁻¹ . The P ₁ / P ₂ ratio is preferably 0.08 or less.

The FT-IR spectrum uses a germanium crystal (Ge crystal) as a prism, the incident angle is 48 °, the resolution is 4 cm ⁻¹ , and the number of integration is 16 times. The reflection method may be used for measurement.

[Usage]
The aluminum substrate of the present invention can be suitably used as a substrate for a magnetic recording medium (magnetic disk). In manufacturing a magnetic recording medium using the aluminum substrate of the present invention, a magnetic recording film is formed on the surface of the aluminum substrate under known conditions, and if necessary, a protective film and a lubricating film are further formed. Good.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples, but may be appropriately modified within a range that can meet the purpose described above and below. Of course, it is possible to implement them, and they are all included in the technical scope of the present invention.

[Experiment 1]
In Experiment 1, the influence of the etching solution on the surface roughness of the ground aluminum substrate was examined.

  A disk-shaped ground aluminum substrate (Kobe Steel KS5D86 alloy) having an outer diameter of 65 mm, an inner diameter of 20 mm, and a thickness of 0.630 mm was prepared. The centerline average roughness Ra was measured as the surface roughness of the ground aluminum substrate using a stylus roughness meter “Tarisurf Intra” manufactured by Taylor Hobson. The measurement was performed using a stylus having a tip diameter of 2.5 μm and a measurement length of 1.5 mm. As a result, the center line average roughness Ra was 14 nm.

  Next, the ground aluminum substrate is etched by immersing it in an etching solution shown in the following Table 1 (both liquid temperatures are 35 ° C.) for 10 minutes, and the centerline average roughness Ra after etching and the surface state after etching are etched. I investigated. The centerline average roughness Ra after etching was measured under the above-described conditions. The surface state after etching was examined using visual observation and an optical microscope (observation magnification was 200 times).

  The following table 1 can be considered as follows. No. As shown in 1 and 2, even when 10% by mass sulfuric acid or 10% by mass nitric acid was used as the etching solution, the aluminum substrate was not etched, and no mass decrease was observed. No. As shown in 3, 4, and 5, the surface was etched when 10 mass% hydrochloric acid, 10 mass% sulfuric acid containing 1 mass% potassium fluoride, or 10 mass% sodium hydroxide aqueous solution was used as an etching solution. However, pits occurred on the surface, and the centerline average roughness Ra after etching was larger than the centerline average roughness Ra before etching (Ra = 14 nm).

  On the other hand, no. As shown in FIG. 6, when 10 mass% phosphoric acid is used as the etching solution, the center line average roughness Ra after etching becomes smaller than the center line average roughness (Ra = 14 nm) before etching, and the surface is smooth. You can see that Moreover, no pits were generated even when the surface of the aluminum substrate after etching was observed visually and with an optical microscope.

  From the above results, it can be seen that if phosphoric acid is used as the etching solution, the surface of the aluminum substrate can be made smoother than before etching without generating pits.

[Experiment 2]
In Experiment 2, the effect of the presence or absence of phosphoric acid treatment on the surface roughness (center surface average roughness Sa) of the SiO ₂ film formed on the surface of the aluminum substrate was examined.

(Invention)
After subjecting the disk-shaped ground aluminum substrate used in Experiment 1 to phosphoric acid treatment, an SiO ₂ film was formed by plasma chemical vapor deposition to produce an aluminum substrate. Detailed manufacturing conditions are as follows.

  First, as the surface roughness of the disk-shaped ground aluminum substrate, the central surface average roughness Sa is measured using an atomic force microscope (AFM), and the measurement visual field is 3 μm square, 2 μm square, 10 μm square, or 60 μm square. Measured as type. As the AFM, “Nanosurf easyScan2 FlexAFM” manufactured by Nanosurf was used.

The center plane average roughness Sa is a three-dimensional extension of the centerline average roughness Ra [JIS B0601 (2001)] measured in two dimensions, and is defined by the following formula (2). That is, the center surface average roughness Sa is a portion surrounded by the surface shape curved surface and the average surface when the average surface is the xy plane, the vertical direction is the z axis, and the measured surface shape curve is represented by the following equation (1). Is divided by the measurement area, and is calculated by the following equation (2). In the following formula (2), L _x and L _y are measurement lengths in the x direction and the y direction, respectively. The measurement results of the center plane average roughness Sa are shown in Table 2 below.

  Next, the aluminum substrate was subjected to phosphoric acid treatment. Specifically, the aluminum substrate was immersed in 10% by mass phosphoric acid at a temperature of 35 ° C. for 4 minutes, and then washed with pure water.

A phosphoric acid-treated aluminum substrate is placed in a plasma CVD apparatus, and an SiO ₂ film is formed on the surface of the aluminum substrate by plasma chemical vapor deposition using oxygen gas and organosiloxane gas to produce an SiO ₂ film-coated aluminum substrate. did. Specifically, an aluminum substrate heated to 80 ° C. is put in a plasma CVD apparatus, oxygen plasma is generated by a hollow cathode type radio wave discharge, and an organic siloxane gas is supplied to the generated oxygen plasma to form an SiO ₂ film. Formed. Hexamethyldisiloxane (HMDSO) was used as the organic siloxane. The flow ratio of oxygen gas to HMDSO was 16: 1. That is, 1.33 times as much oxygen gas as the stoichiometric amount of oxygen gas necessary for converting Si contained in the organosiloxane gas into SiO ₂ was used.

The thickness of the formed SiO ₂ film was measured by applying a refractive index (1.46) of SiO ₂ using an optical interference film thickness meter (“Nano Spec / AFT Model 5100” manufactured by Nanometrics). As a result, the thickness was 3 μm.

(Comparison material)
As a comparative material, a SiO ₂ film (thickness 3 μm) was formed by plasma chemical vapor deposition under the same conditions as the above-described invention material without subjecting the disk-shaped ground aluminum substrate used in Experiment 1 to phosphoric acid treatment. Thus, an aluminum substrate coated with SiO ₂ film was produced.

The center plane average roughness Sa of the obtained SiO ₂ film-coated aluminum substrate (invention material, comparative material) was measured under the same conditions as when the center plane average roughness Sa of the disk-shaped ground aluminum substrate was measured. The measurement results are shown in Table 2 below.

It can be considered as follows from Table 2 below. The measurement area As is clear from the result of observation of the surface roughness (center plane average roughness Sa) as 60μm angle relative to the aluminum substrate, by forming a SiO ₂ film after subjected to the phosphate treatment, SiO ₂ It can be seen that the center plane average roughness Sa of the film surface can be reduced.

Further, comparing the case where the aluminum substrate was subjected to the phosphoric acid treatment and the case where the aluminum substrate was not subjected to the phosphoric acid treatment, the surface roughness (center surface average roughness Sa) of the SiO ₂ film was phosphoric acid in any measurement range. It can be seen that the treatment is relatively small. Specifically, when the measurement area is 2 μm square or 10 μm square, the center plane average roughness Sa of the SiO ₂ film surface is equal to the center plane average roughness Sa of the ground aluminum substrate regardless of the presence or absence of phosphoric acid treatment. However, the increase in Sa is smaller when the phosphoric acid treatment is performed. On the other hand, when the central area average roughness Sa of the SiO ₂ film surface in a wide area is measured with a measurement area of 60 μm square, the central plane average roughness Sa of the SiO ₂ film surface is obtained by performing phosphoric acid treatment. It turns out that it becomes small compared with the case where acid treatment is not performed.

The phenomenon in which the surface roughness (center surface average roughness Sa) of the SiO ₂ film formed on the surface of the aluminum substrate changes depending on the presence or absence of phosphoric acid treatment is considered to be caused by the following mechanism. The formation of the SiO ₂ film by the reaction between the remote oxygen plasma and the organic siloxane is performed by first generating nuclei along the grinding marks and sequentially growing the nuclei. In the case of a mechanically ground surface, a lot of minute protrusions are generated on the surface, and this tends to be a nucleation base point. Therefore, when the measurement area is narrowed, the roughness of the film formation surface becomes It is thought that it will be significantly larger than On the other hand, when the phosphoric acid treatment is performed, minute protrusions on the ground surface are selectively dissolved and removed, so that nucleation is performed substantially uniformly over the entire surface. As a result, an increase in roughness due to film formation can be suppressed.

From the above results, it can be seen that the surface roughness (center plane average roughness Sa) of the SiO ₂ film surface can be reduced by forming the SiO ₂ film after performing phosphoric acid treatment on the aluminum substrate.

[Experiment 3]
In Experiment 3, the influence of the flow rate ratio of oxygen gas and organosiloxane gas on the surface roughness (center surface average roughness Sa) after polishing the SiO ₂ film formed on the aluminum substrate surface was examined.

The disc-shaped ground aluminum substrate used in Experiment 1 was subjected to phosphoric acid treatment under the same conditions as in Experiment 2. The aluminum substrate subjected to the phosphoric acid treatment is put into a plasma CVD apparatus, and an SiO ₂ film is formed on the surface of the aluminum substrate by plasma chemical vapor deposition using oxygen gas and organosiloxane gas to form an SiO ₂ film-coated aluminum substrate. Manufactured. Specifically, an oxygen plasma was generated by a hollow cathode type radio wave discharge, and an organosiloxane gas was supplied to the generated oxygen plasma to form a SiO ₂ film. Hexamethyldisiloxane (HMDSO) was used as the organic siloxane. The flow ratio of oxygen gas to HMDSO was 10.4: 1 or 16: 1. When the flow rate ratio of oxygen gas to HMDSO is 10.4: 1, 0.87 times as much oxygen gas as the stoichiometric amount of oxygen gas required to convert Si contained in HMDSO to SiO ₂ is used. It means that it is used. When the flow ratio of oxygen gas to HMDSO is 16: 1, 1.33 times as much oxygen gas as the stoichiometric amount of oxygen gas required to convert Si contained in HMDSO into SiO ₂ is used. It means that

When the thickness of the SiO ₂ film was measured under the same conditions as in Experiment 2, the thickness was 3 μm in any case.

As the surface roughness of the obtained SiO ₂ film-coated aluminum substrate, the center plane average roughness Sa was measured under the same conditions as in Experiment 2 above. The measurement results are shown in Table 3 below.

Next, the obtained aluminum substrate surface was grind | polished and the surface roughness after grinding | polishing (center-plane average roughness Sa) was measured. Polishing uses “Suede type RN-H” manufactured by Nitta Haas as a polishing pad and “Compol-80” manufactured by Fujimi as a polishing slurry diluted 1: 1 with water, and polishing pressure: 6.9 kPa ( 70 gf / cm ² ), sliding speed: 70 cm / second, and the polishing amount per side was set to 0.6 μm. The surface roughness after polishing (central surface average roughness Sa) was measured using AFM in the same manner as in Experiment 2 above, and the measurement area was measured with three types of 2 μm square, 10 μm square, and 60 μm square. Table 3 below shows the center surface average roughness Sa after polishing.

Next, the FT-IR spectrum was measured for the SiO ₂ film after polishing. The FT-IR spectrum was measured by a single reflection ATR method. The measurement was performed using a Ge crystal prism, an incident angle of 48 °, a resolution of 4 cm ⁻¹ , and an integration count of 16. The measurement results are shown in FIGS.

FIG. 1 shows an FT-IR spectrum after polishing a SiO ₂ film formed with a flow rate ratio of oxygen gas to HMDSO of 10.4: 1 (0.87 times the stoichiometric amount of oxygen gas is used). Is shown. Based on FIG 1, the maximum absorption peak intensity P ₁ observed in the range of 1220～1280Cm ^-1, the ratio between the maximum absorption peak intensity P ₂ observed in the range of 1000 to 1200 ^-1 (P ₁ / P As a result of calculating ₂ ), the ratio was 0.11.

FIG. 2 shows an FT-IR spectrum after polishing a SiO ₂ film formed with a flow rate ratio of oxygen gas to HMDSO of 16: 1 (using oxygen gas 1.33 times the stoichiometric amount). ing. Based on FIG. 2, the maximum absorption peak intensity P ₁ observed in the range of 1220～1280Cm ^-1, the ratio between the maximum absorption peak intensity P ₂ observed in the range of 1000 to 1200 ^-1 (P ₁ / P As a result of calculating ₂ ), the ratio was 0.06.

When the P ₁ / P ₂ ratio is 0.06, there is almost no methyl group remaining in the SiO ₂ film, so it is considered that a strong three-dimensional skeleton of —Si—O—Si— is formed. It is done. Accordingly, it is considered that the hardness of the SiO ₂ film having a P ₁ / P ₂ ratio of 0.06 is higher than the hardness of the SiO ₂ film having a P ₁ / P ₂ ratio of 0.11.

Next, it can be considered as follows from Table 3 below. The oxygen gas and HMDSO flow ratio of 10.4: 1 than a SiO ₂ film is formed as (using 0.87-fold of the oxygen gas relative to the stoichiometric amount), the flow ratio of oxygen gas and HMDSO 16 : 1 better to form a SiO ₂ film as (using 1.33-fold of the oxygen gas relative to the stoichiometric amount) has lower center surface average roughness Sa of the SiO ₂ film surface after polishing, SiO ₂ It can be seen that the film surface can be smoothed.

From the above results, it is included in the SiO ₂ film by using 1.2 times or more of oxygen gas stoichiometric amount necessary for converting Si contained in HMDSO to SiO _2. The amount of Si—CH ₃ groups to be reduced can be reduced, the P ₁ / P ₂ ratio can be suppressed to 0.10 or less, and the hardness of the SiO ₂ film can be increased. Therefore, it can be seen that the SiO ₂ film is easily polished and the surface can be easily smoothed.

Claims (4)

A step of subjecting the aluminum substrate to phosphoric acid treatment;
Forming a SiO ₂ film on the surface of the aluminum substrate after the phosphoric acid treatment by plasma chemical vapor deposition using oxygen gas and organosiloxane gas. . The oxygen gas is used in an amount of 1.2 times or more of the stoichiometric amount of oxygen gas required to convert Si contained in the organosiloxane gas into SiO ₂ as the oxygen gas. Manufacturing method. The manufacturing method according to claim 1, wherein hexamethyldisiloxane gas is used as the organic siloxane gas. An aluminum substrate for a magnetic recording medium obtained by the manufacturing method according to claim 1, wherein an FT-IR spectrum of a SiO ₂ film formed on the surface of the aluminum substrate is measured. ,
Maximum absorption peak intensity P ₁ observed in the range of 1220-1280 cm ⁻¹ ;
An aluminum substrate for a magnetic recording medium, wherein a ratio (P ₁ / P ₂ ) with a maximum absorption peak intensity P ₂ observed in a range of 1000 to 1200 cm ⁻¹ is 0.10 or less.

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