JPS613317A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To form an underlying layer having excellent smoothness without generating magnetism even if a magnetic recording medium is heated to a high temp. and to form the medium suitable for high-density recording by providing a magnetic layer via the underlying layer consisting of Ni-Cu-P contg. Ni at a specific ratio or below onto a non-magnetic metallic substrate. CONSTITUTION:The underlying layer 2 consisting of the Ni-Cu-P contg. <=88wt% Ni, >=9wt% Cu and >=3wt% P is provided by using an alkaline electroless plating bath on the surface of the non-magnetic metallic substrate 1 consisting of Al (alloy), etc. The surface of the underlying layer may be mechanochemically polished, if necessary, to improve further the surface smoothness. Co-Ni-P is plated on the underlying layer to form the magnetic layer 3. A gamma-Fe2O3 magnetic layer 3 is otherwise formed by a sputtering method, etc. on the underlying layer. The underlying layer is not magnetized at all even if said layer is exposed to the high temp. in the stage of forming the magnetic layer and since the low- purity Al alloy is usable as the substrate, the magnetic recording medium is obtd. at a low cost.

Description

[Detailed description of the invention] [Technical field to which the invention pertains]

The present invention relates to a magnetic recording medium having a magnetic layer on a nonmagnetic metal substrate used in magnetic disks and magnetic drums of magnetic recording devices.

[Prior art and its problems]

In recent years, magnetic recording devices have achieved higher recording densities. Due to the requirement for high rotation performance, the use of a contact start/stop type head flotation system has become common. In addition, recording media have been made thinner, have improved magnetic properties, and have improved substrate surface precision, replacing the coated media formed by coating γ-1'e20*6 particles that have been widely used in the past. Ururen Vt thin film media, plated media in which a magnetic film is formed by plating, and ferrite continuous film media, in which a ferrite magnetic film is formed by reactive sputtering, vapor deposition, etc., are rapidly being put into practical use. Improving the quality of the substrate is an essential condition for the practical application of continuous thin film media. The following conditions must be met for a substrate used in a medium for high recording density. 1) Good mechanical flatness and roughness of the surface. 2) Defects such as minute depressions and minute protrusions should be as few as possible. 3) Appropriate hardness to improve head crushing resistance. 4) The substrate must be non-magnetic after the magnetic recording medium has been manufactured. Conventionally, as magnetic disk substrates, aluminum alloy substrates have been used for coated media, N1-P plated aluminum alloy substrates have been used for plated media, and alumite-treated aluminum has been used for ferrite continuous film media. A 2um alloy substrate was used. N1-P plated aluminum alloy used for plating media has moderate hardness (400 to 500 FIV), good mirror workability, and excellent productivity, but it has a major drawback of becoming magnetic due to heat treatment. was there. As mentioned above, the underlayer of the magnetic recording medium must be non-magnetic. If magnetism exists in the substrate, it is recorded not only in the magnetic layer but also in the underlayer during magnetic recording, increasing the magnetization transition width, and during reproduction, the magnetization of the magnetic medium layer is closed by the underlying substrate, resulting in magnetic The magnetic flux generated outside the recording body decreases, and the head output decreases. This is because when magnetism appears in the substrate, the recording and reproducing characteristics are significantly degraded. Although the temperature at which magnetism appears varies depending on the P (phosphorus) content in the plating film, the heat resistance limit is approximately 260 to 275°C. There are two reasons why magnetism is generated by heating above this temperature. 1) State change from amorphous Ni state to crystalline Ni state 2) N
The appearance of Pauli magnetism due to the formation of iiP Of these two reasons, the former, the appearance of magnetism due to the crystallization of Nl, can be suppressed to some extent by increasing the P content in the plating film, but the latter, the appearance of magnetism due to the formation of Ni3P, can be suppressed to some extent. cannot be prevented with a practical N1-P plating film. For this reason, there is a major restriction that the various heat treatment temperatures in the media manufacturing process must be kept below this range. In addition, in the manufacturing process of ferrite continuous film media, for example, in the case of sputtering, the substrate is exposed to a temperature of 200 to 300°C during reactive sputtering, and the substrate is exposed to a temperature of 300 to 350°C when heated in the air to form γ-FezO. Because of the exposure to temperature for several hours, N1-P plating, which becomes magnetic at such temperatures, could not be used for ferrite sputtered or ferrite evaporated media. Furthermore, plated media require a protective film to protect the recording medium from damage caused by friction with the recording/reproducing head and corrosion due to ambient environmental conditions, but the firing temperature of this protective film has been limited. For this reason, in ferrite-containing thin film media, an alumite-treated aluminum alloy that can withstand the above-mentioned heat treatment is generally used (Japanese Unexamined Patent Publication No. 85694/1983). The alumite coated alloy substrate has excellent surface workability,
The film is also A1.0. Since the film is mainly composed of , it is a hard film with a Mohs hardness of 9, and has the advantage of being less likely to be damaged by collisions with recording/reproducing heads. Furthermore, by using high-purity AI-M and alloys as base materials, the number of surface defects has been significantly reduced. However, this alumite film has a major drawback in that if the alumite thickness is thick, cracks will occur due to the heat treatment. If a recording medium is manufactured using a cracked alumite plate as a substrate, signal errors will occur, resulting in a completely unreliable magnetic recording medium. The occurrence of this squeak is 77L/? This is due to the difference in thermal expansion coefficient between the alumite film and the aluminum alloy substrate, and the thermal expansion coefficient of the alumite film is said to be about 1/3 that of the aluminum substrate. Figure 5 shows the thickness of sulfuric acid alumite and the occurrence of cracks due to heat treatment. In the figure, the ○ mark indicates that no cracks have occurred, the x mark indicates that cracks are observed, and the Δ mark indicates that it cannot be determined. be. It is recognized that such racks are generated mainly in the black spots that appear on the surface, and as a result, it is clear that the allowable thickness of the alumite film at 320° C. must be as extremely thin as 2 μm. However, an alumite thickness of 2 μm or less is extremely insufficient for the purpose of obtaining a hard film that can withstand collision with the head, which is originally required as an underlayer for a magnetic medium layer, and in fact, the γ-Fears sputter type This is considered one of the reasons why discs lack practicality. Furthermore, in the case of alumite-treated substrates, since the alumite film has high insulating properties and is chemically passive, it cannot be applied to plating media, and its use is limited to coating media or ferrite continuous film media. In addition, since alumite treatment is a method of growing a highly insulating film by electrolysis, it is necessary to ensure a sufficient electrical current flow method that does not inhibit the growth of the alumite film, which has the disadvantage of lacking productivity compared to plating methods. had. Furthermore, for high-density alumite substrates, impurity elements other than Al-Mg must be kept below 0.01%, otherwise black spots will occur that can lead to signal errors, so it is necessary to use materials with a high purity of 99.99% or higher. This was a big problem in terms of cost.

[Purpose of the invention]

The present invention eliminates the above-mentioned drawbacks, has high heat resistance, non-magnetic stability,
The purpose of the present invention is to provide a magnetic recording medium having an underlying substrate that is excellent in processability, productivity, and economy, suitable for high recording density, has few defects, and is not limited by the type of magnetic layer formation method. do.

[Key points of the invention]

According to the present invention, the underlayer of the magnetic layer of the magnetic recording medium is made of Ni.
The above objective can be achieved by using a Ni-CuP plating film whose content is limited to 88% or less. It is desirable that the Cu content is 9% or more, and the P content is 3 or more. A one-time N1-Cu-P plating film can be easily formed using an alkaline electroless plating bath.

[Embodiments of the invention]

FIG. 1 shows a general cross-sectional structure of a magnetic disk or magnetic drum in which the present invention is implemented, and as shown in FIG. Underlayer 2. Magnetic layer 3. Protective layer 4. Lubricating layer 5 are laminated. According to the present invention, underlayer 2 is made of Ni of 88 or less.
It is an N1-Cu-P plating film containing. This plating film is formed, for example, in a process as shown in FIG. As an example, a plated film 2 was formed by electroless plating under the following conditions. N1-Cu-P plating solution composition: Nickel sulfate 0.085-0.095 mol/l Copper sulfate or cupric chloride 0.005-0.01
5 mol/1 Sodium hypophosphite 0.2 mol/β Sodium citrate 0.2 mol/1 plating solution P)
I: Approximately 10 (using sodium hydroxide) Plating solution temperature = 80 ± 2°C Plating time: wX Corresponding to thickness The composition ratio in the film was adjusted by changing the amounts of nickel sulfate and copper sulfate, and is shown in Table 1. Test pieces having three types of plating films were created. For comparison, Table 1 shows comparative sample 21 having an electroless N1-P plating film with a P content of 9%, Ni 28%, and Cu 1%. Comparative sample 22 having an electroless N1-Cu-P plating film consisting of pH% was created. Figure 3 shows the magnetic properties of these samples when heated in the atmosphere for 2 hours. The number attached to the line corresponds to the sample number. Comparative sample 21,
In contrast to sample 11, 12, and 13 in the example, magnetism appears when heated, as shown by the measured values that line up on a straight line, even when heated to 400°C. 14 is also non-magnetic up to 300°C. That is, in order to ensure high nonmagnetic stability, it is important to keep the Ni content in the film at 88% or less. The Vickers hardness of the plating film in the sample of the example of the present invention is 500 to 600 HV T at a load of 100 g, and has sufficient hardness as an underlayer of a magnetic disk. but,
This hardness is obtained by the Ni content, and the Ni content needs to be 30% or more. The change in hardness when each sample was heated in the atmosphere for 2 hours was measured as
As shown in the figure. As in FIG. 3, the numbers attached to each curve correspond to the sample numbers. As seen in the figure, a plating film with a low Ni content shows little change in hardness, and as the Ni content decreases, the hardness after heating tends to increase. But curve 2
No remarkable increase in hardness such as the maximum at around 400° C., which is characteristic of the N1-P film shown in No. 1, was observed, and it is thought that such an increase in hardness is due to the formation of N1aP. This was also confirmed by the results of X-ray diffraction. That is, in sample 11.12 of the example, Ni crystallization and N15
No formation of P was observed when heated up to 350°C;
Even after heating at .degree. C., the Ni crystal peak is smaller than in the case of N1-P plating. Regarding Ni sample 13 with 6==4>&c, formation of Ni3P is also observed for the first time when heated to 325°C. The thickness of the plating film needs to be 1μ or more to ensure a certain level of strength, and if it exceeds 30μ, workability will decrease due to increased plating time and stress in the plating film will increase during heat treatment in the post-process. This naturally results in limitations, since this causes a disadvantage in that mechanical flatness deteriorates, such as warping of the substrate due to the release of the substrate. In addition, if the surface precision is further improved by applying a certain polishing process to the surface of the base plating after applying the N1-Cu-P alloy base plating and before forming the magnetic layer, it is possible to achieve high recording density. This makes it more preferable as a substrate for magnetic recording media. For example, a disc of high-purity Al-4%Mg alloy is polished to a mirror finish by diamond turning, and pre-treated by the zincate method according to the process shown in Figure 2 to form a 20 μm thick Ni45%
, plated with 49% Cu and 6% P, with an average grain size of 1.
It was confirmed that a surface precision of Ra of 0.01 or less could be obtained by mechanochemical polishing using a suspension of 0 μm alumina fine particles with a pH of about 5, and that mirror workability was also good. Using this mirror-finished substrate, CoN1-P magnetic plating was performed under the following conditions. CoNj-P plating solution composition: Cobalt sulfate 0.06 mol/l Nickel sulfate 0.04 mol/l Sodium hypophosphite 0.2 mol/l Ammonium sulfate 0.1 mol/l Sodium succinate 0.5 mol/l Sodium malonate 0.2 mol/l plating solution pu:
9 (adjusted with ammonia). Plating solution temperature: 65±2℃ The obtained magnetic properties were as follows at a film thickness of 0.08μ-
Shows excellent value. Anti-magnetic crab 600-8000e Residual magnetic flux density: 6500-7000C. Squareness ratio: 20.7 to 0.85 Next, a γ-Fetus magnetic film was formed by sputtering on the N1-Cu-P plated film which had been mirror-finished in the same manner. The sputtering and heat treatment conditions are as follows. Sputtering conditions (RF diode type) Target Fe-2,5% by weight Co-3,0% by weight Cu Total gas pressure 2 Xl0-”Torr (Ar +Oz)
Oxygen partial pressure 7.8 Shows excellent value. Anti-magnetic crab Too ~8000e Residual magnetic flux density: 2500~3000 G squareness ratio: Example 0.7
7-0.79

【Effect of the invention】

The present invention uses Ni88 as an underlayer for a magnetic layer of a magnetic recording medium.
It has an N1-Cu-P plating film with a high Cu content of less than 9% and more than 9%, which shows no appearance of magnetism even when heated to high temperatures, and provides an underlayer with excellent mirror workability. Therefore, it can be applied extremely effectively to high recording density recording media. This type of plating film can be easily formed using an electroless plating bath using an alkaline bath, so simultaneous batch processing is possible, and it is excellent in mass production. It can also be applied to low-purity aluminum alloy plates, which reduces costs. The effects obtained are extremely large.

[Brief explanation of the drawing]

FIGS. 1(a) and (bl are cross-sectional views of a magnetic disk in which the present invention is implemented, FIG. 1(b) is an enlarged view of part A of FIG. 1(9), and FIG. 2 is a magnetic disk according to the present invention. A process diagram of an example of N1-Cu-P plating, Fig. 3 is a diagram showing the change in magnetic flux saturation density of the plating film of the example and comparative example due to heating, and Fig. 4 is a diagram showing the change in hardness of the plating film due to heating. Fig. 5 is a diagram showing the occurrence of cracks due to heating of an alumite film on an aluminum substrate.1 Aluminum substrate, 2: Base layer N1-Cu-P No. Z
Figure 3 Figure 3 Hitoshi Churokiro Kuwaka On 7! (°υ f14 figure man-made disaster - hot five wave C°C)

Claims (1)

[Claims] 1) A magnetic layer is deposited on a non-magnetic metal substrate via an underlayer consisting of a nickel-copper-phosphorus plating film, in which the nickel content of the underlayer is 88% or less. A magnetic recording medium characterized by: 2) A magnetic recording medium according to claim 1, characterized in that the copper content of the underlayer is 9% or more. 3) A magnetic recording medium according to claim 1 or 2, characterized in that the phosphorus content of the underlayer is 3% or more. 4) A magnetic recording medium according to any one of claims 1 to 3, characterized in that the underlayer is formed in an alkaline electroless plating bath.