JP2014127219A - Aluminum substrate for magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an aluminum substrate for a magnetic recording medium having high-temperature heat resistance, and excellent in hardness and flaw resistance.SOLUTION: An aluminum substrate for a magnetic recording medium is an aluminum substrate where a SiOfilm of thickness of 6 μm or more is formed. The SiOfilm is formed by a gas phase film formation method where the aluminum substrate is heated at from 150°C to 370°C.

Description

The present invention relates to an aluminum substrate which is used as a substrate for a magnetic recording medium (magnetic disk) and on which an SiO ₂ film suitable for forming a magnetic film (recording layer) is formed at a high temperature.

  As an information recording medium, a magnetic recording medium is a versatile medium. As characteristics required for a magnetic recording medium, it is required to have excellent hardness and scratch resistance. For example, when a magnetic recording medium is subjected to an impact during manufacture or use, the magnetic head and the magnetic recording medium may come into contact with each other. If a physical defect such as a wrinkle or a depression occurs on the surface of the magnetic recording medium due to the contact, the magnetic recording medium Defects cause defective recording media. For this reason, the magnetic recording medium is required to have sufficient hardness and scratch resistance.

  It is also required that the surface of the magnetic recording medium be smooth. Recording / reading of information to / from the magnetic recording medium is performed via a magnetic head moving on the recording medium, but the distance between the magnetic head and the magnetic recording medium (the flying height of the magnetic head) is at most several nm. It is. Therefore, in order to prevent contact with the magnetic head and recording / reading failure, the magnetic recording medium is required to have excellent surface smoothness at the sub-nanometer level.

  As a substrate for a magnetic recording medium, an aluminum substrate is known. However, an aluminum substrate alone has insufficient hardness and scratch resistance, and it is difficult to realize smoothness by polishing. Therefore, a NiP plated aluminum substrate having an electroless NiP plating on the surface of the aluminum substrate is used. The NiP plating film has high hardness and scratch resistance, and can achieve excellent smoothness by polishing.

  NiP-plated aluminum substrate is made by rolling a coiled aluminum plate into a disk shape, turning the inner and outer circumferences and grinding the main surface (grinding), and then electrolessly plating NiP Are further manufactured by polishing (polishing) and washing (Non-patent Document 1).

  For example, the magnetic recording medium has a NiP plated aluminum substrate on which a soft magnetic backing layer, an intermediate layer (crystal grain control layer, crystal orientation control layer, etc.), etc. are formed, and a magnetic film is formed thereon as a recording layer. Furthermore, a surface protective layer (such as hard carbon) is formed.

  In recent years, the capacity of magnetic recording media has been increasing, and next-generation magnetic recording media that dramatically increase recording density have been developed. For example, when trying to increase the density of magnetic recording media, it is necessary to make the magnetic particles finer, which causes the problem of thermal fluctuations in which part of the magnetic recording data disappears due to the influence of ambient heat. A magnetic recording medium having an increased film coercivity has been proposed. However, increasing the coercive force makes it difficult to record data with a conventional head. Therefore, a heat-assisted recording method that records data while heating a recording medium with a laser is attracting attention. In this recording method, data can be recorded because the coercivity of the heated portion of the magnetic film formed on the magnetic recording medium is reduced, and thermal fluctuation can be eliminated because the non-heated portion has high coercivity.

  In the process of manufacturing a magnetic recording medium suitable for such a heat-assisted recording method, the thermal history during manufacturing, such as the film formation temperature of the magnetic film, may be 300 ° C. or higher, and further 350 ° C. or higher. In the case of an aluminum substrate formed with a NiP plating film that is currently widely used, the heat resistance of the underlying aluminum substrate is 370 ° C. or higher, but the NiP plating film crystallizes and becomes magnetic when heated to 300 ° C. or higher. Therefore, it is practically possible to cope with only up to about 300 ° C., and the heat-resistant temperature of the substrate is a great restriction on the production of the magnetic recording medium.

  In order to solve this problem, an attempt has been made to improve the heat resistance of the NiP plating film by adding a third component (Patent Document 1), but it has a heat resistance of up to about 320 ° C. and has a sufficient heat resistance improvement effect. Is not obtained.

For this reason, it is necessary to develop a substrate film that is non-magnetic, has high hardness, is excellent in scratch resistance, and is excellent in heat resistance in place of the current NiP plating. An amorphous SiO ₂ film has attracted attention as a film that meets such conditions.

For example, Patent Document 2 proposes a SiO ₂ film by a sol-gel method. However, when a film is formed by the sol-gel method, mass reduction and volume shrinkage during the film formation process are large, and it is difficult to secure a required film thickness.

Further, Patent Document 3 proposes a technique for forming a SiO ₂ film of about 0.6 μm by sputtering. Although surface accuracy, hardness, and wear resistance can be achieved, a film thickness of 0.6 μm is insufficient to achieve scratch resistance. If the SiO ₂ film is thickened to improve the soldering resistance, the difference in thermal expansion coefficient between the SiO ₂ film and the aluminum substrate is large, so that the SiO ₂ film is likely to crack when exposed to a high temperature environment. Problems arise.

Although SiO ₂ itself is non-magnetic and has high temperature heat resistance, when it is actually formed on an aluminum substrate, problems such as cracks as described above occur. Therefore, no practical SiO ₂ film has yet been provided that does not cause cracks or the like even when exposed to a high temperature environment.

  On the other hand, as for the heat resistance of the aluminum substrate itself (base material) used for the magnetic recording medium, for example, 5086 alloy (JIS H4000) has excellent high temperature heat resistance at 300 ° C. or higher, and recently, 500 ° C. There has also been proposed an aluminum alloy substrate that can maintain surface smoothness and the like even to the extent (Patent Document 4).

Therefore, if an SiO ₂ film suitable for an aluminum substrate excellent in high temperature heat resistance can be realized, restrictions on the use of the aluminum alloy substrate in the magnetic recording field such as the above-described thermally assisted recording method can be greatly relaxed.

JP 2012-195021 A Japanese Patent No. 2552682 Japanese Patent Publication No.53-37202 JP2012-99179A

Journal of Abrasive Technology, Vol. 43, no. 11, November 1999, p. 475-479

  The present invention has been made paying attention to the above-described circumstances, and an object thereof is to provide an aluminum substrate for a magnetic recording medium excellent in heat resistance, hardness, and scratch resistance. Furthermore, an object of the present invention is to provide an aluminum substrate for a magnetic recording medium that can be polished to reduce the surface roughness as required in addition to these characteristics and is excellent in surface smoothness after polishing. That is.

An aluminum substrate for a magnetic recording medium according to the present invention that can solve the above-mentioned problems is an aluminum substrate on which a SiO ₂ film having a thickness of 6.0 μm or more is formed, and the SiO ₂ film is formed at 150 ° C. The main point is that the film is formed by heating at ˜370 ° C. and vapor phase film formation.

  As a preferred embodiment of the present invention, it is recommended that the vapor deposition method is a plasma CVD method.

The aluminum substrate for a magnetic recording medium of the present invention is nonmagnetic and heat resistant (preferably 300 ° C. or more, preferably) because a SiO ₂ film having a predetermined thickness is formed on an aluminum substrate heated to a predetermined temperature range. More preferably 350 ° C. or higher, more preferably 400 ° C. or higher) and hardness (preferably 4.0 GPa or higher, more preferably 7.0 GPa or higher), and scratch resistance (preferably equal to or higher than NiP plating). Has characteristics. Further, the SiO ₂ film according to the present invention can be applied with a conventional glass substrate polishing technique as a polishing means after film formation. By polishing, the SiO ₂ film can be used for a magnetic recording medium having superior surface smoothness. An aluminum substrate can be provided.

Therefore, the aluminum substrate on which the SiO ₂ film of the present invention is formed is suitable as a magnetic recording medium, and can greatly relax restrictions on the use of the aluminum alloy substrate in the magnetic recording field such as a heat-assisted recording method. it can.

FIG. 1 is a graph showing the relationship between the substrate temperature during film formation and [heat resistance evaluation temperature-substrate temperature during film formation]. FIG. 2 is a graph showing the relationship between various coatings (test materials 1 to 4 (SiO ₂ film) and Reference Examples 1 and 2 (without SiO ₂ film and NiP plating film) and wrinkle depth. Figure 3 is a graph showing the surface roughness of the SiO ₂ film before and after polishing of the SiO ₂ film. FIG. 4 is a graph showing changes in the surface roughness of the aluminum substrate surface before forming the SiO ₂ film and the surface roughness of the SiO ₂ film after forming the SiO ₂ film.

Hereinafter, the present invention will be described. In the present invention, the “substrate temperature at the time of film formation” refers to the temperature of the aluminum substrate itself when the SiO ₂ film is formed, and is measured by installing a thermocouple on the substrate. The temperature of the substrate. In this specification, “substrate temperature at the time of film formation” may be simply referred to as “film formation temperature” or “substrate temperature”.

  The “substrate temperature during heating” refers to the temperature of the substrate itself when exposed to a high temperature environment in the process of manufacturing a magnetic recording medium such as the formation of a magnetic film or surface protective layer, and is measured with a thermocouple as described above. The temperature of the substrate to be processed. In this specification, the “substrate temperature at the time of heating” may be simply referred to as “heating temperature” or “heat resistance evaluation temperature”.

  Further, the “heating temperature difference” means a temperature difference between the “substrate temperature during heating” and the “substrate temperature during film formation”.

In the present invention, since the temperature of the substrate is measured, the set temperature of the apparatus or atmosphere when the SiO ₂ film or magnetic film is formed does not match the substrate temperature (substrate temperature during heating). Sometimes. For example, in the embodiment of the present invention, in order to evaluate the heat resistance of the substrate on which the SiO ₂ film is formed, a thermocouple is attached to the substrate in advance, and the relationship between the temperature in the heating furnace and the temperature of the substrate is examined. Since the temperature of the heating furnace is set so that the temperature becomes a temperature simulating the thermal history of the manufacturing process, the temperature of the heating furnace may not match the temperature of the substrate.

  The inventors of the present invention have made extensive studies on a film having hardness and scratch resistance that can be substituted for a conventional NiP plating film and having excellent heat resistance that surpasses that of a NiP plating film.

In general, the thermal expansion coefficient of aluminum (including pure aluminum and aluminum alloy) is about 24 × 10 ⁻⁶ / K, and it is known that linear expansion occurs by about 1% with a temperature increase of 400 ° C. On the other hand, the thermal expansion coefficient of the SiO ₂ is ^{approximately, 1 × 10 -7 ~1 × 10} -6 / are known to be the thermal expansion coefficient of about K, the linear expansion of the SiO ₂ film of linear expansion of aluminum Is a few tenths.

The present inventors examined an aluminum substrate on which a SiO ₂ film was formed under various conditions.

First, the temperature of the aluminum substrate when forming the SiO ₂ film is set to about room temperature (25 ° C.) to form a SiO ₂ film having a thickness of 3.5 μm, and then the aluminum substrate is inserted into an electric furnace and heated. As a result, it has been found that when the heating temperature reaches about 250 ° C. (substrate temperature during heating), the SiO ₂ film cracks or the SiO ₂ film peels off from the aluminum substrate.

On the other hand, when the substrate temperature during film formation of the SiO ₂ film was increased to 150 ° C. or higher, no cracks or peeling were observed in the SiO ₂ film even when the substrate heating temperature (heat resistance evaluation temperature) was 300 ° C. or higher. (Nos. 3 to 24 in Table 1). From this, it was found that the substrate temperature at the time of film formation should be at least 150 ° C. or higher in order to ensure heat resistance of 300 ° C. or higher (substrate temperature during heating).

The reason for exhibiting excellent high temperature heat resistance at 300 ° C. or higher (heat resistance evaluation temperature) when the SiO ₂ film is formed at such a high temperature is considered as follows.

Although the shape and size are affected, SiO ₂ generally has a property of being easily broken by a tensile force but hardly broken by a compressive force. Therefore, when the SiO ₂ film is formed with the aluminum substrate heated as described above, the SiO ₂ film is compressed when cooled from the film forming temperature to room temperature, and the shrinkage difference between the SiO ₂ film and the aluminum substrate However, the SiO ₂ film is excellent in durability against the compressive force, and it is considered that the SiO ₂ film is not cracked or peeled off.

On the other hand, if such a SiO ₂ film compressive force is applied at room temperature was heated aluminum substrate that has been deposited, but the aluminum substrate is a SiO ₂ film is stretched by thermal expansion, a compressive force acts at room temperature they were divided, for up to the deposition temperature of SiO ₂ film which acts in the direction of compression is relaxed, is eased actually tensile force acting on the SiO ₂ film, as a result, cracks and peeling of the SiO ₂ film It is unlikely to occur and is considered to exhibit excellent heat resistance.

That is, since the thermal expansion of the SiO ₂ film is mainly governed by the difference between the heating temperature and the film forming temperature, when the film is formed at a high temperature, the SiO ₂ film does not reach the film forming temperature from room temperature to the film forming temperature even after reheating. The tensile force does not substantially act, and when the substrate is heated beyond the film formation temperature, the tensile force acts on the SiO ₂ film within the range up to the film formation temperature and the heating temperature. Therefore, if the deposition temperature of the SiO ₂ film is high, to produce a difference tension between the heating temperature after the film formation temperature and the SiO ₂ film formation of SiO ₂ film, and the case of forming the SiO ₂ film at room temperature In comparison, it is considered that cracking and peeling of the SiO ₂ film due to the difference in thermal expansion coefficient are less likely to occur.

In addition, the hardness of the SiO ₂ film at room temperature tended to increase as the substrate temperature during film formation increased. For example, when the substrate temperature during film formation is 150 ° C., the hardness of the SiO ₂ film is 8.0 GPa. However, as the substrate temperature increases, the hardness also increases to 8.4 GPa (200 ° C.) and 8.8 Gpa (250 ° C) (Nos. 13 to 18). The same applies when the film thickness is different. For example, when the film thickness is 10.5 μm (No. 19 to 24), as the temperature increases (200 ° C. → 250 ° C. → 300 ° C.), The hardness also tended to increase (8.5 GPa → 8.8 GPa → 9.2 GPa).

Therefore, it was found that the film formation temperature of the SiO ₂ film should be increased to give sufficient hardness.

Further, it was found that when the SiO ₂ film was thin, the function as a protective film for the aluminum substrate surface (brazing resistance) was insufficient, and a certain film thickness was required. That is, in the examples where the film thickness is less than 6 μm (Nos. 1 to 12), the scuff resistance was poor, but in the examples where the film thickness was 6 μm or more, it has a satisfactory level of scuff resistance. (No. 13 or later), in particular, in the case where the film thickness is 10 μm or more (No. 19 to 24), more excellent scratch resistance was provided.

The present invention was made based on the above finding, a aluminum substrate or thickness 6.0μm of SiO ₂ film is formed, the SiO ₂ film 0.99 ° C. the aluminum substrate to 370 ° C. The present invention is summarized in that the film is formed by vapor phase film formation method.

  Hereinafter, the structure of the aluminum substrate for magnetic recording media of the present invention will be specifically described.

[Thickness of SiO ₂ film: 6.0 μm or more]
When the thickness of the SiO ₂ film formed on the aluminum substrate is thin, the scratch resistance is insufficient even if the hardness is high, and defects are likely to occur in the magnetic recording medium. On the other hand, when a SiO ₂ film having a film thickness of 6.0 μm or more is formed in the substrate temperature range during the predetermined film formation, even if the surface of the magnetic recording medium is subjected to an impact during manufacture or use, physical defects such as wrinkles and dents are removed. Sufficient scratch resistance that can be suppressed can be imparted. Therefore, the thickness of the SiO ₂ film needs to be 6.0 μm or more, preferably 9.0 μm or more, and more preferably 10.0 μm or more. On the other hand, the upper limit of the film thickness is not particularly limited from the viewpoint of scratch resistance, but since the proof stress against the tensile stress caused by thermal expansion decreases as described later when the film thickness of the SiO ₂ film becomes too thick, 15.0 μm or less.

When polishing the SiO ₂ film to ensure the desired surface smoothness, the film thickness of the SiO ₂ film to be formed is determined in consideration of the polishing amount so that the film thickness after polishing is within the above range. It is desirable to make it.

[Aluminum substrate temperature during SiO ₂ film formation: 150 ° C. to 370 ° C.]
When the SiO ₂ film is formed at a temperature lower than 150 ° C. of the aluminum substrate, the SiO ₂ film may crack before the substrate heating temperature reaches 300 ° C. The heat resistance exceeding 300 ° C. cannot be imparted. On the other hand, if the temperature of the aluminum substrate at the time of film formation exceeds 370 ° C., the strength (tensile strength) and 0.2% proof stress of the aluminum substrate itself are lowered, and thus the substrate characteristics required for the magnetic recording medium are poor. Become. In particular, when the substrate temperature exceeds 370 ° C., the strength of the aluminum substrate is reduced to ¼ or less of the strength at room temperature, and the aluminum substrate is deformed during the cooling process during the film formation or after the film formation. Unevenness may occur. As a result, there is a case where a sufficient compressive force cannot be applied to the SiO ₂ film even if it is cooled to room temperature. Therefore, when heated again, a tensile force is generated in the SiO ₂ film from a temperature lower than the film forming temperature, and the desired high temperature heat resistance may not be obtained.

From the viewpoint of improving heat resistance, the temperature of the aluminum substrate at the time of forming the SiO ₂ film is preferably high. Therefore, the aluminum substrate temperature is 150 ° C. or higher, preferably 200 ° C. or higher. If the temperature of the aluminum substrate is too high, the properties such as the strength of the aluminum substrate deteriorate as described above, and therefore the temperature is 370 ° C. or lower, preferably 350 ° C. or lower.

By forming the SiO ₂ film by the vapor deposition method in the temperature range with the temperature of the aluminum substrate raised to 150 ° C. to 370 ° C., as described above, the SiO ₂ film is thermally expanded by heating. Since the temperature at which the resulting tensile force begins to act can be increased, cracking and peeling of the SiO ₂ film can be prevented.

Further deposition temperature of SiO ₂ film in the present invention, it is also a preferred embodiment be determined in consideration of the heat resistance temperature required the film thickness of the SiO ₂ film (temperature at the time of heating). The present inventors have SiO ₂ film having a thickness, the heating temperature difference ([substrate temperature during the heating] - [substrate temperature during film formation]), the result of examining the relationship between the heat resistance, the film thickness of the SiO ₂ film thick will also increases the heating temperature difference, crack SiO ₂ film strength becomes lower with respect to the tensile force caused by the difference in thermal expansion between the SiO ₂ film and an aluminum substrate caused by heating the temperature difference between the SiO ₂ film and peeling (Table 1 and FIG. 1). Therefore, in order to suppress the occurrence of defects such as cracks in relation to the film forming temperature and tensile stress, it is desirable to appropriately control the manufacturing conditions.

  For example, in the case of a film thickness of 6.1 μm (Nos. 13 to 18 in Table 1), the substrate temperature during film formation (“substrate temperature during film formation” in Table 1) is any of 150 ° C., 200 ° C., and 250 ° C. In the case of, excellent heat resistance ("Heat resistance evaluation" in Table 1) is obtained if the difference in heating temperature (in Table 1, "heat resistance evaluation temperature-substrate temperature during film formation") is in the range of 150 to 175 ° C. Although obtained (No. 13, 15, 17), when the heating temperature difference was 200 ° C., the heat resistance was poor (No. 14, 16, 18). On the other hand, in the case where the film thickness is 10.5 μm (No. 19 to 24 in Table 1), the heating temperature difference is 100 to 125 when the substrate temperature during film formation is any of 200 ° C., 250 ° C., and 300 ° C. Excellent heat resistance was obtained in the range of ° C. (No. 19, 21, 23), but when the heating temperature difference was 150 ° C., the heat resistance was inferior (No. 20, 22, 24). Among these examples, the substrate temperature during film formation is 200 ° C. 15 (film thickness: 6.1 μm), 19 (film thickness 10.5 μm) No. 15 exhibited heat resistance even when the heating temperature difference was 175 ° C. In 19, the temperature at which the heat resistance was exhibited was up to 125 ° C. Therefore, no. In the case of No. 15, the substrate temperature during heating (in Table 1, “heat resistance evaluation temperature”) has heat resistance up to 375 ° C., but no. In the case of No. 19, the temperature is up to 325 ° C. In order to exhibit heat resistance at the substrate temperature (375 ° C.) at the time of heating equivalent to 15, it is necessary to raise the substrate temperature during film formation to 250 ° C. (No. 21).

Such a tendency is summarized in FIG. 1. For example, in order to set the substrate temperature during heating having heat resistance to 350 ° C. or higher (in FIG. 1, the right side of the “350 ° C. line”), SiO ₂ When the film thickness is 6.1 μm, the substrate temperature at the time of film formation may be 200 ° C. or higher, but when the film thickness is 10.5 μm, it is 250 ° C. or higher. There is a tendency that the substrate temperature during film formation is increased and the heating temperature difference is reduced.

Therefore, in order to exhibit heat resistance at high temperatures, it is desirable to increase the substrate temperature during film formation and reduce the difference from the substrate temperature during heating as the thickness of the SiO ₂ film increases.

  In addition, since the relationship between such a film thickness and a heating temperature difference shows the same tendency if it is the same film thickness irrespective of the substrate temperature at the time of heating as mentioned above, it is the substrate temperature at the time of desired heating. What is necessary is just to raise the substrate temperature at the time of film-forming so that heat resistance may be acquired.

[Hardness of SiO ₂ film: preferably 4.0 GPa or more]
The hardness of the SiO ₂ film is not particularly limited, but a higher hardness is desirable from the viewpoint of improving the durability of the aluminum substrate against physical impacts. Further, it is desirable to increase the film thickness after securing sufficient hardness to improve the scratch resistance. The hardness of the SiO ₂ film is preferably 4.0 GPa or more, more preferably 7.0 GPa or more.

Incidentally, the hardness of the SiO ₂ film, as the substrate temperature during the deposition of the SiO ₂ film is high, since there is a tendency that the hardness becomes higher, the desired range of the substrate temperature during the deposition (150 ℃ ~370 ℃) The substrate temperature may be set so as to obtain a hardness of.

[Deposition of SiO ₂ film: Vapor deposition method]
Furthermore, the SiO ₂ film of the present invention is formed by a vapor deposition method. The vapor deposition method is desirable because the film thickness can be easily controlled and uniform and precise film formation is easy. The vapor deposition method is a physical vapor deposition method (PVD) such as sputtering or vapor deposition, or a chemical vapor deposition method (CVD) such as plasma CVD. Among these, the chemical vapor phase method is preferable because it is easy to form a film having a desired film thickness of 6 μm or more. Furthermore, as the chemical vapor phase method, the plasma CVD method is particularly preferable. Since the plasma CVD method is easy to control the film formation speed, it is suitable as a method for forming a SiO ₂ film having a desired film thickness, and because it is easy to form a uniform and dense film, the surface of the SiO ₂ film This is desirable because it is easy to adjust the smoothness to a predetermined range.

The reason why the plasma CVD method is particularly preferable with respect to the surface smoothness is as follows. That is, FIG. 4 is a diagram showing a general trend of the roughness of the SiO ₂ film surface after forming a SiO ₂ film with roughness and a plasma CVD method of the SiO ₂ film formation prior to the aluminum substrate surface, FIG. In FIG. 4, the “stylus method” is a result of measuring a plurality of samples using Intra manufactured by Taylor / Hobson, “AMF1” is Nano Science EasyScan (viewing angle 10 μm) manufactured by Nano Science Instrument, and “AMF2” is Nano Science. It is the result of having measured using Nanosurf EasyScan (viewing angle 2 micrometers) by Instrument. Regardless of the measurement method, the surface roughness before and after the formation of the SiO ₂ film (center line surface roughness Ra (nm)) is substantially the same, so that when the SiO ₂ film is formed by the plasma CVD method, the film is formed. The surface roughness of the previous aluminum substrate surface is considered to be reflected in the surface roughness of the SiO ₂ film surface formed almost as it is.

However, as shown in the examples below, the SiO ₂ film formed by the plasma CVD method can be easily polished by a known glass substrate surface polishing method, and the surface roughness can be reduced to a desired value. This is because excellent smoothness can be easily obtained (FIG. 3).

When a SiO ₂ film is formed by sputtering, reactive sputtering is used in which sputtering is performed using RF plasma or pulsed DC discharge plasma, using Si as a target and adding O ₂ to Ar. However, the film forming speed is fast and practical.

When a SiO ₂ film is formed by vapor deposition, the mixed powder of Si and SiO ₂ is heated in a furnace, vaporized as SiO having a low sublimation temperature, and a small amount of O ₂ is added to the vicinity of the substrate surface. _Two films can be formed.

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

  First, an aluminum substrate is prepared. The aluminum substrate (base material) used in the present invention is not particularly limited, but preferably has a tensile strength at room temperature and a 0.2% proof stress equivalent to or higher than those of 5086 alloy. The thickness of the aluminum substrate is not particularly limited, and various thicknesses can be used. However, the thickness may be appropriately set so as to be finished to a predetermined thickness required for a magnetic recording medium. For example, an aluminum substrate having a thickness of 1.270 mm or a thickness of 1.753 mm may be used for an aluminum substrate for a magnetic recording medium of φ95 mm, and an aluminum substrate for a magnetic recording medium of φ65 mm may have a thickness of 0.635 mm or An aluminum substrate with a thickness of 0.800 mm may be used.

  It is recommended that the aluminum substrate 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 a processing method such as chamfering or grinding using a lathe, or a combination of both, and the surface of the aluminum substrate is removed. Is preferably smoothed. Further, if the surface roughness of the aluminum substrate is too large, there is a possibility that the desired surface roughness (surface smoothness) may not be obtained even if the SiO ₂ film is polished. Therefore, it is preferable to keep the surface smooth.

  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. Moreover, you may perform wet grinding using a PVA grindstone after chamfering.

  The surface roughness of the aluminum substrate is, for example, preferably 20 nm or less, more preferably 12 nm or less in terms of the centerline average roughness Ra defined by JIS B0601 (2001).

[Deposition of SiO ₂ film]
In the present invention, an SiO ₂ film having a thickness of 6.0 μm or more may be formed on an aluminum substrate heated to 150 ° C. to 370 ° C. by a vapor deposition method.

For example, when a SiO ₂ film is formed by a chemical vapor deposition method, which is desirable as a vapor deposition method, an organic siloxane gas (having a Si—O—Si bond in the molecular skeleton) is formed on the surface of an aluminum substrate heated to a predetermined temperature. Compound 2) or a silane gas and an oxygen-containing gas can be used to form a SiO ₂ film.

The good quality, i.e., dense and hard, for deposition of and smooth SiO ₂ film, it is preferable to convert completely SiO ₂ to Si contained in the organic siloxane gas. For this purpose, SiO ₂ When forming the film, it is necessary to use an oxygen-containing gas in an amount of 1.2 times or more the stoichiometric amount of oxygen gas necessary for converting Si contained in the organosiloxane gas into SiO _2. Recommended. Theoretically, if a stoichiometric amount of oxygen-containing gas necessary to convert Si contained in the organosiloxane gas to SiO ₂ is used, Si should be completely converted to SiO _2. , Affected by reaction loss and by-products. Therefore, in order to completely convert Si into SiO ₂ , it is desirable to use an excess amount (specifically, 1.2 times or more) of oxygen gas with respect to the stoichiometric amount. In the present invention, it is recommended to control the flow rate of the oxygen-containing gas within the above range so that the flow rate ratio of the oxygen gas during film formation is within the above range.

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 speed, and hardness of the SiO ₂ film to be formed, it is preferable to use HMDSO.

As the silane gas, _{e.g., SiH 4, SiHCl 3, SiH} 2 Cl 2, SiH 3 Cl, SiCl 4, SiBr 4, SiI 4, SiF 4, Si (OC 2 H 5) 2 , etc. may be used, these May be used in combination. Of these, SiH ₄ is particularly preferred.

Examples of the oxygen-containing gas include O ₂ and N ₂ O. The oxygen-containing gas also includes a mixed gas with H ₂ gas or the like added as necessary to form the SiO ₂ film. Among these, a mixed gas of O ₂ or N ₂ O gas is particularly preferable.

[About polishing process]
The surface roughness of the SiO ₂ film after the film formation is preferably 0.5 nm or less, more preferably 0.3 nm or less, with a centerline average roughness Ra specified by, for example, JIS B0601 (2001). Preferably there is.

However, when the SiO ₂ film is formed by the plasma CVD method as described above, the surface roughness of the aluminum substrate surface is directly reflected as the surface roughness of the SiO ₂ film. Therefore, the surface smoothness of the SiO ₂ film is also high, and in order to reduce the load required for polishing the SiO ₂ film, the surface smoothness of the aluminum substrate should be increased in advance before the SiO ₂ film is formed as described above. Is desirable.

When the SiO ₂ film is polished after film formation, the surface of the SiO ₂ film may be polished under known conditions so as to achieve the desired smoothness (the surface roughness). For polishing the SiO ₂ film of the present invention, a conventionally used method or apparatus for polishing a glass plate can be used as it is. 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.

[Usage]
The aluminum substrate on which the SiO ₂ film of the present invention is formed can be suitably used as a magnetic recording medium. In particular, the aluminum substrate on which the SiO ₂ film of the present invention with improved heat resistance is formed contributes to the relaxation of the substrate temperature restriction during the formation of the magnetic film. When manufacturing a magnetic recording medium using an aluminum substrate on which the SiO ₂ film of the present invention is formed, a magnetic recording film or the like is formed on the surface of the SiO ₂ film of the aluminum substrate under known conditions. In addition, a magnetic recording medium can be manufactured by further forming a protective film and a lubricating film.

  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, it was examined the relationship between the characteristics of the deposition temperature and the SiO ₂ film of the SiO ₂ film.

An aluminum substrate (aluminum alloy (4.2% by mass Mg—the balance: Al and inevitable impurities), size: a disk-shaped disk having an outer diameter of 65 mm, an inner diameter of 20 mm, and a thickness of about 0.84 mm) is ground with a PVA grindstone and rolled. The altered layer due to was removed. For grinding, a Speed Fam 16B double-sided machine was used, grinding pressure: 80 gf / cm ² , sliding speed: 80 cm / second, removal amount per surface: about 20 μm, polished aluminum substrate The thickness was set to 0.800 mm. When the surface roughness of the ground aluminum substrate was measured by a stylus method, Ra = 12 nm. Thereafter, the substrate temperature during film formation is changed between 80 ° C. and 350 ° C. (in Table 1, “substrate temperature during film formation (° C.)”), and a film thickness of 3.5 μm or more is formed by plasma CVD under the following conditions. A 10.5 μm SiO ₂ film was formed. At this time, the substrate temperature at the time of film formation is obtained by calculating the correlation between the set temperature of the film formation apparatus and the substrate temperature using an aluminum substrate to which a thermocouple is previously attached, and the substrate temperature at the time of film formation is a predetermined temperature accordingly. It was controlled to become. After the film formation, it was allowed to cool to room temperature to obtain a test material in which a SiO ₂ film was formed on the surface of the aluminum substrate.

(Deposition conditions for plasma CVD)
Carrier gas: mixed gas of monosilane and nitrogen and nitrous oxide Gas ratio: SiH ₄ / N ₂ = 1/9 Flow rate: 80 sccm, N ₂ O flow rate: 56 sccm
Pressure: 133Pa
RF power: 150W

(Surface properties of SiO ₂ film)
The surface properties of the obtained test materials were examined at room temperature. It was visually confirmed whether the SiO ₂ film of each test material was cracked or peeled off from the substrate. As a result, there was no test material in which cracks or peeling occurred, and the surface properties of all the test materials were good.

(Thickness of SiO ₂ film)
The film thickness of the SiO ₂ film of each test material was measured using a nanospec / AFTmodel 5100 manufactured by nanometrics.

(Hardness of SiO ₂ film)
The hardness of the SiO ₂ film of each test material was measured by the nanoindentation method. Specifically, it measured using the nano indenter (Nano Indenter XP / DCM made from Agilent Technology). The measurement was performed at an excitation frequency: 45 Hz, an excitation vibration amplitude: 2 nm, a strain rate: 0.05 / second, and an indentation depth: 2000 nm.

(Heat resistance evaluation)
In order to evaluate the heat resistance, using a substrate with a thermocouple attached in advance, the correlation between the set temperature of the heating furnace and the substrate temperature was examined, and the temperature of the heating furnace was set accordingly. The test material was inserted into a heating furnace heated to a temperature corresponding to the heat resistance evaluation temperature (the substrate temperature during heating) shown in Table 1 and held for 30 minutes, and then the test material was taken out of the furnace and room temperature (25 ° C. ) Until cooled.

After allowing to cool, the surface properties of the test material were observed at room temperature. Specifically, the SiO ₂ film was visually observed under fluorescent light illumination and an optical microscope (magnification: 50 times and 200 times, any one of the inner peripheral portion, the central portion, and the outer peripheral portion of the substrate hitting one side). The presence or absence of cracks and the presence or absence of peeling between the aluminum substrate and the SiO ₂ film were examined and evaluated according to the following criteria (“Heat resistance evaluation” in Table 1).
○: crack or peeling was not observed on the SiO ₂ film ○ Note 1: cracking or peeling in the SiO ₂ film was observed, Example × Note 2 of the heat resistant temperature is lower than 300 ° C.: Aluminum substrate deformation occurs ×: Cracks and delamination were observed in the SiO ₂ film

  The heat resistance evaluation temperature is raised from 250 ° C. to several tens of degrees C., and the heat resistance is evaluated. The example of “○” evaluation indicates the highest temperature at which no crack or peeling is observed, and the “×” evaluation indicates crack or peeling. Indicates the temperature at which was observed. For example, no. 13 and 14, although the heat resistance evaluation up to 325 ° C. was “◯” (No. 13), it was further “x” (No. 14) at 350 ° C. where the temperature was raised by 25 ° C.

(Scratch resistance evaluation)
The tip of a stylus (diamond sphere having a radius of 0.1 mm) to which a load of 10 g or 50 g was applied was brought into contact with the test material surface (film formation surface side) and slid. The sliding speed was a constant speed (5 mm / second), and the sliding distance was 15 mm. After sliding, the depth of the sliding trace on the surface of the test material was measured with a non-contact optical roughness meter and evaluated according to the following criteria.

○: Wrinkle depth equal to or less than NiP plating at both load 10g and 50g Δ: Wrinkle depth equal to or lower than NiP plating at 10g load, but wrinkle deeper than NiP plating at 50g ×: From NiP plating even at 10g load The wrinkle becomes deeper--: Since sufficient heat resistance was not obtained (heat resistance evaluation “×”), the scratch resistance was not evaluated.

  The test results are shown in Table 1.

Further, the relationship between the substrate temperature during film formation and [heat resistance evaluation temperature-substrate temperature during film formation] is shown in FIG. 1 for each film thickness of the SiO ₂ film based on the example of “◯” evaluation in Table 1. In FIG. 1, diagonal lines (“300 ° C. line”, “350 ° C. line”, “substrate deformation”) correspond to the heat-resistant temperature.

No. satisfying the film thickness and film forming conditions of the present invention. Nos. 13 to 24 were excellent in heat resistance (heat resistance evaluation temperature: 300 ° C. or higher), scratch resistance (Δ or higher), and hardness (4.0 GPa or higher). In particular, the film thickness of the SiO ₂ film is 10 μm or more. In Nos. 19 to 24, the film thickness was 6.1 μm. Better scuff resistance was obtained compared with 13-18.

  On the other hand, in an example not satisfying the requirements of the present invention, desired characteristics could not be obtained.

  When the substrate temperature (80 ° C.) during film formation was low (No. 1, 2), heat resistance at 275 ° C. was obtained (No. 1), but high temperature heat resistance of 300 ° C. or higher was not obtained. (No. 2).

Moreover, when the film thickness (3.5 μm) of the SiO ₂ film was thin (Nos. 3 to 12), although heat resistance of 300 ° C. or higher was obtained, the scratch resistance was low.

Experiment 2
In Experiment 2, the relationship between the SiO ₂ film and the scratch resistance was examined.

The aluminum substrate used in Experiment 1 was heated to 250 ° C., and the thickness of the SiO ₂ film was 3.5 μm (test material 1), 6.1 μm (test material 2), 9 μm (test material 3), 10.5 μm. A test material was prepared by forming a SiO ₂ film on an aluminum alloy substrate (disc-shaped disk) by plasma CVD in the same manner as in Example 1 except that (Test material 4) was used.

  For reference, an aluminum substrate on which the film used in Experiment 1 was not formed was prepared as Reference Example 1 and a NiP plated substrate as Reference Example 2.

  NiP plating is performed by degreasing (Uemura Kogyo: AD-68F), acid cleaning (Uemura Kogyo: AD-107F), zincate treatment (Uemura Kogyo: AD-301 F3-X), and NiP plating ( Uemura Kogyo: Nimuden HDX-7G and Uemura Kogyo: HDX-A mixed solution). The plating thickness was 10 μm.

(Scratch resistance test)
The tip of a stylus (diamond sphere having a radius of 0.1 mm) to which a load of 10 g or 50 g was applied was brought into contact with the test material surface (film formation surface side) and slid. The sliding speed was a constant speed (5 mm / second), and the sliding distance was 15 mm. After sliding, the depth of the sliding mark on the surface of the test material was measured with a non-contact optical roughness meter. The results are shown in FIG.

The following was found from FIG. First, the sliding trace depth of the test material 1 having a SiO ₂ film thickness of 3.5 μm was better than that of Reference Example 1 (aluminum alloy substrate), but from Reference Example 2 (NiP plating substrate). It was also inferior and did not have sufficient scratch resistance.

On the other hand, when the film thickness of the SiO ₂ film was 6.1 μm (test material 2), 9 μm (test material 3), and 10.5 μm (test material 4), it was superior to Reference Example 1 (aluminum alloy substrate). It had scratch resistance. Further, in the case of a load of 10 g, the sliding trace depths of the test materials 2 to 4 were equivalent to those of Reference Example 2, and had excellent scratch resistance. Further, when the load was 50 g, the sliding trace depth of the test material 2 (film thickness 6 μm) was worse than that of the reference example 2, but the test material 3 (film thickness 9 μm) and the test material 4 (film thickness 10.5 μm). It was found that the sliding trace depth was better than that of Reference Example 2 and had better scratch resistance.

Experiment 3
In Experiment 3, the effect of the presence or absence of SiO ₂ film polishing on the surface roughness (centerline average roughness Ra) of the SiO ₂ film formed on the surface of the aluminum alloy substrate was examined.

Except that the thickness of the SiO ₂ film was 7 μm and the substrate temperature was 250 ° C., a test material was manufactured by forming a SiO ₂ film on the aluminum substrate used in Experiment 1 by the plasma CVD method.

At that time, the surface roughness of the aluminum substrate to be used was measured before forming the SiO ₂ film. First, the centerline average roughness Ra as the surface roughness of the aluminum substrate was measured with an atomic force microscope (AFM). As the AFM, “Nanosurf easyScan2 FlexAFM” manufactured by Nano Science Instrument was used (viewing field: 2 μm square).

The centerline average roughness Ra was measured based on the centerline average roughness Ra [JIS B0601 (2001)] measured in two dimensions. As a result of measuring the center line average roughness Ra, the center line average roughness Ra of the aluminum substrate before forming the SiO ₂ film was 8.9 nm.

Next, the center line average roughness Ra of the SiO ₂ film formed on the aluminum substrate was measured. As a result, the center line average roughness Ra of the SiO ₂ film was 8.9 nm (“polishing amount 0 μm” in FIG. 3), and the surface roughness was the same before and after the SiO ₂ film was formed.

Subsequently, the surface of the SiO ₂ film was polished with a polishing machine (9B double-side polishing machine manufactured by SPEED Fam). Polishing was performed using a commercially available polishing pad for glass substrates (RN-H pad manufactured by Rodel Nitta) and polishing slurry (Compol 20 polishing slurry manufactured by Fujimi). The polishing conditions are a polishing pressure of 100 gf / cm ² , a sliding speed of 60 cm / second, and the polishing amount assumes a silica film density (2.2 g / cm ³ ) based on weight change before and after polishing. Estimated.

The center line average roughness Ra measured after polishing the SiO ₂ film by 0.39 μm was 0.45 nm, and the surface smoothness of the SiO ₂ film formation could be greatly improved by polishing.

Further, the center line average roughness Ra measured after polishing the SiO ₂ film by 0.60 μm is 0.27 nm, and it is confirmed that a sufficiently smooth surface can be obtained by applying a polishing method for a glass substrate. It was.

Claims (2)

An aluminum substrate on which a SiO ₂ film having a thickness of 6.0 μm or more is formed,
The aluminum substrate for a magnetic recording medium, wherein the SiO ₂ film is formed by heating the aluminum substrate to 150 ° C. to 370 ° C. to form a vapor phase film formation method. The aluminum substrate according to claim 1, wherein the vapor deposition method is a plasma CVD method.