JP2012142060A - Substrate for magnetic recording medium and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a substrate for a magnetic recording medium which enhances the hardness of a substrate while maintaining non-magnetic properties even when being subjected to a heat treatment at high temperature for a long period of time.SOLUTION: In the substrate for the magnetic recording medium including an aluminum alloy layer and an Ni-P-Mo plated layer formed on the aluminum alloy layer and the method for manufacturing the same, the Ni-P-Mo plated layer consists of 0.05-1.0 wt% of Mo, 9-15 wt% of P and the balance Ni, the substrate for the magnetic recording medium has a hardness of 650 Hv or more and a saturation magnetic flux density of 0.2 mT or less, and the method includes subjecting the Ni-P-Mo plated layer to a heat treatment in an inert atmosphere.

Description

  The present invention relates to a magnetic recording medium substrate and a manufacturing method thereof, and more preferably to a magnetic recording medium substrate mounted on a hard disk drive (HDD) and a manufacturing method thereof.

  Currently, HDDs are widely used as recording devices for personal computers (PCs). A substrate for a magnetic recording medium used in this HDD is mainly one in which a Ni—P plating layer is formed on the surface of an aluminum alloy layer that is inexpensive and has good workability. Such a substrate is less expensive than a semiconductor medium and is suitable for increasing the capacity.

  Recently, the use of HDDs has been expanded to portable PCs. In the case of a portable PC, the magnetic head may damage the magnetic layer on the substrate surface due to a drop or impact during transportation or use. Therefore, the HDD of the portable PC is required to have good impact resistance against dropping or impact during transportation or use.

  In connection with the above-described Ni-P plating, an electroless Ni-P-Mo plating bath and a plating method in which Mo is added to Ni-P plating have been proposed (see Patent Document 1). In this electroless Ni—P—Mo plating bath and plating method, even when the Ni—P—Mo plating layer is heat-treated at 300 ° C. for 3 hours, it maintains non-magnetism and can be obtained well at a high deposition rate. It has been found. In order to maintain the nonmagnetic property of the magnetic recording medium substrate, a magnetic recording medium substrate in which an amorphous Ni—P—Mo alloy layer is formed on the nonmagnetic layer has also been proposed (see Patent Document 2). ).

JP-A-5-263259 JP-A-5-266457

  However, the impact resistance required for recent magnetic recording media is high, and the required impact resistance cannot be sufficiently met by just using the substrate. Neither Patent Document 1 nor Patent Document 2 presents explicit solution means for improving hardness. On the other hand, it is necessary to solve the problem that the substrate is easily magnetized when heated at a high temperature.

  An object of the present invention is to provide a substrate for a magnetic recording medium that has improved surface hardness while maintaining non-magnetism even after heat treatment at a high temperature for a long time.

  A magnetic recording medium substrate (hereinafter also simply referred to as a substrate) according to a first aspect of the present invention includes an aluminum alloy layer and a Ni-P-Mo plating layer formed on the aluminum alloy layer, The Ni—P—Mo plating layer is made of 0.05 to 1.0 wt% Mo, 9 to 15 wt% P and the balance Ni, and the magnetic recording medium substrate has a hardness of 650 Hv or more and 0.2 mT ( 2 Gauss) or less. Here, the Ni—P—Mo plating layer preferably has a thickness of 5 μm or more and less than 15 μm. Moreover, it is preferable that the said Ni-P-Mo plating layer contains 0.6-1.0 wt% Mo.

  The method for manufacturing a magnetic recording medium substrate according to the second aspect of the present invention includes a step of forming a Ni—P—Mo plating layer on an aluminum alloy layer by a plating method, and the Ni—P—Mo plating layer. The Ni—P—Mo plating layer is composed of 0.05 to 1.0 wt% Mo, 9 to 15 wt% P, and the balance Ni. Here, the heat treatment is preferably performed at 300 ° C. or higher and 320 ° C. or lower. Moreover, it is preferable that a Ni-P-Mo plating layer contains 0.6-1.0 wt% Mo.

  According to the present invention, it is possible to provide a magnetic recording medium substrate having improved surface hardness while maintaining non-magnetism. In particular, when the Ni—P—Mo plating layer has a thickness of 5 μm or more and less than 15 μm, there are few plating defects (pits) from the initial stage of deposition and defects after polishing. In particular, when the Ni—P—Mo plating layer contains 0.6 to 1.0 wt% of Mo, the magnetic recording medium has improved surface hardness while maintaining non-magnetism even at 320 ° C. heat treatment. A substrate can be provided.

It is the schematic diagram which showed the example of the board | substrate for magnetic recording media of this invention. It is the figure which showed the relationship between Mo density | concentration (wt%) of a Ni-P-Mo plating layer, and a saturation magnetic flux density (mT). It is the figure which showed the relationship between Mo density | concentration (wt%) and hardness (Hv) of a Ni-P-Mo plating layer.

  A magnetic recording medium substrate (hereinafter also simply referred to as a substrate) according to the first embodiment of the present invention includes an aluminum alloy layer and a Ni—P—Mo plating layer formed on the aluminum alloy layer. As shown in FIG. 1 as an example, the magnetic recording medium substrate 10 is obtained by forming a Ni—P—Mo plating layer 14 on an aluminum alloy layer 12 mainly composed of aluminum. Normally, the magnetic recording medium 20 is configured by forming the magnetic layer 16 and the like on the Ni—P—Mo plating layer 14. The magnetic recording medium 20 is normally used for a hard disk or the like.

  The aluminum alloy layer 12 can be formed from, for example, an aluminum alloy blank material that has been rolled and heat-annealed and then processed to a specified size after being heated and melted. Examples of the aluminum alloy that can be used include an Al—Mg alloy and an Al—Cu alloy. The aluminum concentration of the aluminum alloy layer 12 mainly composed of aluminum is preferably 90.0 to 99.8 wt%.

  The Ni—P—Mo plating layer 14 formed on the aluminum alloy layer 12 includes 0.05 to 1.0 wt% Mo, 9 to 15 wt% P, and 84 to 90.95 wt% Ni. Since the Ni—P—Mo plating layer 14 contains 0.05 wt% or more of Mo, magnetic deterioration (increase in saturation magnetic flux density) due to heat treatment is prevented. Since the Ni—P—Mo plating layer 14 contains 1.0 wt% or less of Mo, the film formation rate is not slow particularly in the electroless plating method, which is suitable for practical use. Since the Ni—P—Mo plating layer 14 contains 9 wt% or more of P, an amorphous film can be obtained. The Ni—P—Mo plating layer preferably has a thickness of 5 μm or more and less than 15 μm. Since the Ni—P—Mo plating layer has a thickness of 5 μm or more, there are few plating defects (pits) from the initial stage of deposition and defects after polishing.

  The magnetic recording medium substrate of the present invention has a hardness of 650 Hv or more. The “hardness” of the magnetic recording medium substrate in the present invention means micro Vickers hardness. By having the hardness within the above-mentioned range, the magnetic recording medium substrate of the present invention exhibits desired impact resistance.

  The magnetic recording medium substrate of the present invention has a saturation magnetic flux density of 0.2 mT (2 Gauss) or less. By having the saturation magnetic flux density within the above-mentioned range, the magnetic recording medium substrate of the present invention exhibits desired non-magnetism.

  The method for manufacturing a magnetic recording medium substrate according to the second aspect of the present invention includes a step of forming a Ni—P—Mo plating layer on an aluminum alloy layer by a plating method, and the Ni—P—Mo plating layer. The Ni—P—Mo plating layer is composed of 0.05 to 1.0 wt% Mo, 9 to 15 wt% P, and the balance Ni. . The inert atmosphere can be, for example, an inert gas such as nitrogen or argon.

  For the formation of the Ni—P—Mo plating layer, a Ni—P—Mo plating solution obtained by adding Mo salt to a NiP plating solution of a conventionally used magnetic recording medium substrate is used. As the Mo salt, sodium molybdate, ammonium molybdate, potassium molybdate, calcium molybdate, phosphomolybdic acid, ammonium phosphomolybdate, or the like can be used. Plating is preferably performed by electroless plating. The thickness of the Ni—P—Mo plating layer formed by plating (electroless plating) can be adjusted by the immersion time in the plating solution and the temperature of the plating solution. Although the conditions at the time of plating are not particularly limited, as a preferred embodiment, the pH of the plating bath is 4.5 to 6.5, the bath temperature is 70 to 100 ° C, preferably 85 to 95 ° C, Immersion time is 30 to 60 minutes.

  The heat treatment is preferably performed at 300 ° C. or higher and 320 ° C. or lower. Since the heat treatment is 300 ° C. or higher, the desired hardness of the substrate can be obtained, and since the heat treatment is 320 ° C. or lower, the non-magnetic property of the substrate can be maintained.

  An important characteristic of a magnetic recording medium substrate is that it is non-magnetic, that is, the saturation magnetic flux density is 0.2 mT (2 Gauss) or less. For this reason, in the prior art, for the surface treatment of the aluminum alloy layer, a NiP plating layer containing 9 to 15 wt% of P, and in electroless plating containing a high concentration (high content) of P of about 12 wt%, Ensures non-magnetism. However, when the temperature of the heat treatment is increased and when the heat treatment is performed for a long time, the magnetism of the NiP plating layer is deteriorated (saturation magnetic flux density is increased), and non-magnetism cannot be ensured. In order to prevent the deterioration of magnetism due to this heat treatment, it is known to add Mo. On the other hand, it is known that NiP plating containing a high concentration of P is heat-treated (annealed) to improve the hardness. The inventor of the present application has found that the addition of Mo significantly increases the hardness of the magnetic recording medium substrate. Specifically, the inventor of the present application includes a predetermined amount of Mo in the plating layer of the magnetic recording medium substrate and heat-treats it in a predetermined temperature range, so that the non-magnetism of the substrate is ensured only. In addition, the inventors have found that the hardness of the substrate is also significantly improved.

  EXAMPLES Hereinafter, although an experiment example and a comparative example are shown and this invention is demonstrated concretely, this invention is not restrict | limited to an experiment example and a comparative example.

(Experimental Examples 1-5)
Al alloy / Ni-P-Mo substrate Al-Mg alloy annular aluminum alloy layer with inner diameter φ20mm, outer diameter φ65mm, thickness 0.8mm is subjected to alkali degreasing, acid etching and zincate treatment according to conventional conditions We went sequentially. Next, this aluminum alloy layer was immersed in a plating solution having the composition shown in Table 1 (pH 4.5 adjusted with sulfuric acid and ammonia water and heated to 90 ° C.) for 90 minutes, and Ni—P—Mo plating was performed. A layer was formed. The thickness of the Ni—P—Mo plating layer was measured using a fluorescent X-ray analyzer. The thickness was 12 μm.

  Next, this Ni—P—Mo plating layer was heat-treated in a nitrogen gas atmosphere using a clean oven under the conditions shown in Table 2 to obtain a magnetic recording medium substrate. Next, the micro Vickers hardness (Hv) and saturation magnetic flux density (mT) of the obtained magnetic recording medium substrate were measured.

  Micro Vickers hardness (Hv) was measured by a micro Vickers method (square pyramid indenter) with a load of 5 g.

  The saturation magnetic flux density (mT) was measured using a VSM-P7-15 type with a magnetization measurement sensitivity of about 2 × 10 −6 emu, a maximum applied magnetic field of 5 kOe, and a sample 8 mm square.

  FIG. 2 shows the relationship between the Mo concentration (wt%) and the saturation magnetic flux density (mT) of the Ni—P—Mo plating layer. In the magnetic recording medium substrate, the saturation magnetic flux density was significantly reduced by adding 0.05 wt% or more of Mo. In the heat treatment at a high temperature of 300 ° C. or higher and 320 ° C. or lower, the effect of reducing the saturation magnetic flux density was great. In particular, it was confirmed that when Mo was added in an amount of 0.6 to 1.0 wt%, non-magnetism could be maintained even by heat treatment at 320 ° C. However, it was not non-magnetic at 330 ° C.

  FIG. 3 shows the relationship between the Mo concentration (wt%) and the hardness (Hv) of the Ni—P—Mo plating layer. This figure shows the change in hardness after heat treatment (annealing) of the magnetic recording medium substrate. The Ni—P—Mo plating layer to which 0.05 wt% or more of Mo was added was significantly improved in hardness as compared with the Ni—P plating layer (Mo is 0 wt%) by heat treatment.

Claims (6)

A magnetic recording medium substrate comprising an aluminum alloy layer and a Ni-P-Mo plating layer formed on the aluminum alloy layer,
The Ni-P-Mo plating layer is composed of 0.05 to 1.0 wt% Mo, 9 to 15 wt% P and the balance Ni,
The magnetic recording medium substrate has a hardness of 650 Hv or more and a saturation magnetic flux density of 0.2 mT or less.   The magnetic recording medium substrate according to claim 1, wherein the Ni—P—Mo plating layer has a thickness of 5 μm or more and less than 15 μm.   The magnetic recording medium substrate according to claim 1, wherein the Ni—P—Mo plating layer contains 0.6 to 1.0 wt% of Mo. A method for manufacturing a substrate for a magnetic recording medium, comprising:
Forming a Ni-P-Mo plating layer on the aluminum alloy layer by a plating method;
Heat-treating the Ni-P-Mo plating layer in an inert atmosphere,
The Ni-P-Mo plating layer is composed of 0.05 to 1.0 wt% Mo, 9 to 15 wt% P and the balance Ni.   The method according to claim 4, wherein the heat treatment is performed at 300 ° C. or higher and 320 ° C. or lower.   The method according to claim 4 or 5, wherein the Ni-P-Mo plating layer contains 0.6 to 1.0 wt% of Mo.

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