JPH0310085A - Surface treatment for substrate - Google Patents

Abstract

PURPOSE:To improve the adhesive strength and surface characteristics of an Ni-P film to be formed in the subsequent stage by applying zinc substitution treatment to an Al substrate and then treating the surface of the above substrate with acid solution in the surface treatment for the Al substrate. CONSTITUTION:A substrate composed of Al or Al alloy is immersed in a treating bath containing zinc oxide and sodium hydroxide at a temp. in the vicinity of ordinary temp. for about 30-150sec to undergo zinc substitution treatment, by which a zinc layer of about 100-500000Angstrom thickness is formed. Subsequently, the above substrate is immersed in an acid solution of about pH2.0-3.5 in which acetic acid is used by about 10-500ml per 1l water at about 20-40 deg.C for about 15-60sec, by which a zinc hydroxide film is removed. By washing the above substrate with water and then applying usual electroless Ni-P plating to the substrate to about 10-500mu film thickness, a smooth Ni-P film can be formed with superior adhesive strength and surface characteristics and the elution of zinc ions in the Ni-P plating bath can be prevented.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for surface treatment of a substrate made of aluminum or an aluminum alloy, and particularly to a method for forming a non-magnetic base film of a magnetic disk by electroless nickel-phosphorus plating. The present invention relates to a pretreatment method.

[41 inventions! [requires] In the surface treatment of a substrate made of aluminum or an aluminum alloy, the present invention involves performing a zinc substitution treatment on the substrate and then treating the surface with an acidic solution to form a non-magnetic base film. - It is intended to improve the adhesion and surface properties of Kellin fractures.

(Prior art) In the field of magnetic recording, demands for higher density, higher speed, and higher speed are increasing. In place of the recording medium, an IwA type magnetic recording medium in which magnetic N is formed by a thin film forming technique such as sputtering or plating has been put into practical use, and further development is expected.

In an I-cavity type magnetic recording medium, a nonmagnetic underlayer is usually formed between the substrate and the magnetic layer.

This non-magnetic base film is provided to increase the hardness of the substrate, and by being interposed between the substrate and the magnetic layer, to increase the adhesion between the two and prevent problems such as the magnetic layer falling off. be. A single-magnetic magnetic recording medium has a structure in which a nickel-phosphorus film is formed as a nonmagnetic underlayer on a substrate made of aluminum or an aluminum alloy. The above-mentioned nickel-phosphorus coating is formed by plating technology, and compared to electrolytic plating, it is relatively easy to obtain a uniform and dense thin film, and - mass production is possible. Mu'If! Deplating methods are widely applied.

Furthermore, it helps the uniform precipitation of the nickel-phosphorus coating,
Electroless nickel is used to improve adhesion to the substrate.
Prior to phosphor plating, zinc replacement treatment (zincate treatment) is often performed to replace only the surface layer of the substrate with zinc.

By the way, type II magnetic recording media have a non-magnetic base film and a magnetic layer as described above, as well as a magnetic layer. ! Membrane II? It has a structure in which functional films, such as lubricating layers, with a thickness of 10-10 μm to several tens of μm are laminated. In such a configuration, the properties of the lower layer greatly affect the properties of the upper layer, so each functional film has physical and
Strict chemical and mechanical conditions are imposed. Particularly in recent years, there has been a trend to reduce the flying flatness of in-air heads for the purpose of increasing density, so in order to avoid serious problems such as signal errors, dropouts, and even head crashes, it is necessary to use these functional films. Improving the uniformity, adhesion, and smoothness of the film is an extremely important issue.

Under these circumstances, there is a need for a method that can achieve high uniformity and smoothness in the zinc replacement treatment prior to electroless nickel-phosphorus plating.
One example is repeating the process several times. This process involves quickly growing zinc with a relatively large particle size through the first zinc replacement treatment, and then using a short-time treatment with strong acids such as nitric acid to remove most of the zinc, leaving only the core zinc. However, by the second zinc substitution treatment, zinc having a smaller particle size is grown based on the above-mentioned nuclei. As a matter of course, sufficient washing with pure water is performed between each of these steps.

[Problem to be solved by the invention]

However, even if zinc replacement treatment is performed twice as described above and sufficient water washing is performed between each process,
It has been found that it is difficult to completely prevent uneven plating, decreased gloss of the plated film, and poor adhesion in electroless nickel-phosphorus plating.

Therefore, an object of the present invention is to provide a method for surface treatment of a substrate that does not cause the above-mentioned problems.

(Means for Solving the Problem) The inventors of the present invention have conducted intensive studies to achieve the above-mentioned object, and have found that after the zinc substitution treatment, the surface of the substrate is
) was formed, and it was discovered that the above-mentioned problem was caused by the elution of zinc ions from this film into the nickel-phosphorus plating bath. In other words, uneven plating and reduced gloss are the result of uneven elution of zinc ions from the surface of the substrate after zinc replacement treatment, resulting in defects and surface irregularities in the grown plating film, and poor adhesion is due to the eutectoid of zinc. This is the result of increased internal stress in the plating film. Therefore, in order to solve these problems, it is considered effective to prevent zinc ions from being eluted into the nickel-phosphorous plating bath.

The surface treatment method for 'v& board according to the present invention is proposed based on such knowledge, and after performing zinc y1 conversion treatment on a substrate made of aluminum or aluminum alloy, the substrate is immersed in an acidic solution. , further comprising electroless nickel-phosphorus plating.

In the present invention, the zinc substitution treatment can be performed by a conventionally known method. For example, 8 parts zinc oxide per 1 part water.
0 g of sodium hydroxide and 400 g of sodium hydroxide at room temperature for about 30 to 150 seconds.

41! j lead'l! It is desirable that the thickness of the zinc layer formed by the conversion treatment be between 100 and 5000. If it is thinner than the above range, it will not be deposited uniformly on the substrate, and if it is thicker than the above range, there will be many uneven thicknesses and pinholes. As a result, the adhesion with the substrate deteriorates. A more preferable range is approximately 900 to 1,500 people, although it depends on the composition of the substrate.

The subsequent immersion in an acidic solution is performed in order to dissolve and remove the zinc hydroxide film present on the surface of the substrate after the zinc substitution treatment. At this time, it is necessary to select the pH 1 component of the acidic solution and the immersion conditions so as to selectively dissolve only the zinc hydroxide coating without affecting the underlying zinc layer.

The pH of the above acidic solution is preferably 2.0 to 3.5. If the pH is lower than the above range, the zinc layer may be eroded, and if it is higher, the zinc hydroxide coating may be damaged. Removal will be insufficient. However, even if the pH is within the above range, acids with oxidizing power such as dilute nitric acid and hydrochloric acid are unsuitable. A typical example of a suitable acid is acetic acid, 10-500 rn! can be used.

In addition, aluminum sulfate of 10 to 500 g per 1N of water may be added to the above acidic solution for the purpose of promoting the decomposition of zinc hydroxide.

As for the immersion conditions, it is desirable to set the temperature to 20 to 40"C and the immersion time to 15 to 60 seconds. Outside the above range,
There is a risk that the removal of the zinc hydroxide film will be insufficient or that the zinc layer will be eroded.

After the substrate is immersed in the acidic solution in this way, it is washed with water and subjected to normal electroless nickel-phosphorus plating.01.
The composition of the nickel-phosphorus plating bath is not particularly limited, and may be the one conventionally used for the purpose of forming a non-magnetic base film for magnetic disks. Although the film thickness is not particularly limited, especially when applied to magnetic disks, if it is too thin, it will not be possible to sufficiently improve the hardness of the substrate, and if it is too thick, the surface properties will deteriorate and its In addition to having an adverse effect on the surface properties of the magnetic layer laminated thereon, this increases the internal stress of the plating film, causing cracking and poor adhesion to the substrate. From this point of view, the desirable film thickness is 10 to 500I.
! m range.

[Effect]

Since the zinc substitution treatment is performed in a strong alkaline solution, the zinc layer on the substrate surface after treatment is further covered with a film of zinc hydroxide.

Since zinc hydroxide is almost insoluble in water, this fracture n2 remains even if water is washed before nickel-phosphorus plating. However, since this film is soluble in acids, if it is immersed in a nickel-phosphorus plating bath with a low pH, it will elute unevenly, causing uneven plating and increased surface roughness. The eluted zinc ions are incorporated into the nickel-phosphorus coating, increasing its internal stress and causing poor adhesion. However, according to the present invention, the zinc hydroxide film is removed with an acidic solution prior to nickel-phosphorus plating, and a smooth zinc layer is exposed on the surface of the substrate, so that the nila gel grows on the zinc layer. - The phosphorus film is extremely uniform, has high gloss, and has excellent adhesion. Furthermore, zinc ions are nickel-
Since it does not elute into the phosphorous plating bath, there is no inhibition of nickel precipitation and the life of the plating bath is extended.

(Example) Hereinafter, preferred examples of the present invention will be described based on experimental results.

In this example, a 3.5-inch aluminum alloy disk substrate was coated with two times of zinc T! Each step of substitution treatment, immersion in an acidic solution, and electroless nickel-phosphorus plating was carried out, and the surface texture was evaluated for 31 valence after each step.

First, a 3.5-inch aluminum alloy disk substrate was subjected to zinc replacement treatment according to a conventional method, and then most of the zinc layer was removed by immersing it in nitric acid for a short time, leaving only the core zinc particles. Then, zinc ra exchange treatment was performed again under the same conditions.

After that, water lj! per acetic acid 50 mj! *Acidic solution containing 200 g of aluminum unilum sulfate (pH2
, 3) at 20° C. for 45 seconds to remove the zinc hydroxide film present on the surface.

Note that washing with pure water was always performed between each step.

Each time the above steps are completed, the surface unevenness was measured using a stylus type surface roughness meter. The results are shown in FIGS. 1(A) to 1(D). Figure 1 (A) is before treatment, Figure 1 (B) is after the first zinc replacement treatment, Figure 1 (C) is after the second zinc replacement treatment, and Figure 1 (D) is the acid state. The surface illumination of the substrate after being immersed in the solution is shown, and in each figure, the vertical direction is magnified 1000 times as much as the horizontal direction to emphasize the surface irregularities.

First, as is clear from Fig. 1(A), the aluminum alloy substrate before treatment has an extremely smooth surface due to mirror finishing, but after one zinc substitution treatment, the surface becomes very smooth as shown in Fig. 1(A).
As shown in B), the surface unevenness increases significantly due to the growth of zinc having a large particle size. However, when a second zinc replacement treatment was performed after removing the zinc oxide, the smoothness was greatly improved as shown in Figure 1 (C), and further immersion in an acidic solution resulted in a coating of zinc hydroxide. The first
As shown in Figure (D), the smoothness was extremely good.

Next, electroless nickel-phosphorus plating was performed on the substrate shown in FIG. 1(D) described above in a nickel-phosphorus plating bath having the following composition.

Nickel sulfate 25 g/1 Sodium hypophosphite 30 g/l Malic acid
30g/l Succinic acid 16g/l Sodium acetate 10g/j! Copper sulfate 0.
05 g/1 The pH of the nickel-phosphorus plating bath was adjusted to 2113.5 with ammonia water or sodium hydroxide aqueous solution.

20μmJ in such a plating bath (bath i90'c)! After growing the nickel-phosphorus film of
The size and number of defects were counted using a laser beam surface defect inspection machine.

For comparison, the same results were applied to a board that was washed with water and nickel-phosphorus plated after the first zinc replacement treatment, and a board that was washed with water and nickel-phosphorus plated after the second zinc replacement treatment. Surface defects were measured.

The above results are summarized in Table 1.

Table 1 The results shown in Table 1 are based on the results shown in Figures 1 (B) to 1 above.
This well reflects the results shown in Figure (D).

That is, nickel-phosphorus plating is applied after immersion in an acidic solution! The plated substrate has a plating film formed on its extremely smooth surface as shown in Figure 1 (D).
No defects occurred. On the other hand, for the substrate on which sub-S4>substitution processing was performed only once, as shown in Fig. 1 ([
As shown in 3), many defects with relatively small diameters were generated due to the formation of the plating film on the surface with increased surface irregularities, and the number of such defects was determined by the number of times of zinc 11 treatment. In some cases, it could not be completely suppressed.

〔Effect of the invention〕

As is clear from the above description, if the substrate surface treatment method of the present invention is applied, the surface of the substrate made of aluminum or aluminum alloy will be made extremely smooth prior to electroless nickel-phosphorus plating. The surface of the nickel-phosphorus coating becomes extremely smooth. Therefore, when the present invention is applied to the manufacture of magnetic disks, it is possible to make the surface of the magnetic layer formed on the nickel-phosphorus film highly smooth. This improvement in the surface properties of the magnetic layer means that even if the flying height of the magnetic head becomes highly miniaturized due to increased density, serious problems such as signal errors, dropouts, and even head crashes will not occur. This makes it possible to provide a magnetic disk with extremely high reliability.

In addition, in the present invention, since zinc ions are not eluted into the nickel-phosphorus plating bath, the internal stress of the nickel-phosphorus coating that is formed does not increase and the resulting decrease in vIi adhesion does not occur, resulting in improved durability. An excellent substrate can be provided. Furthermore, since the life of the plating bath is extended, productivity and economic efficiency are also improved.

[Brief explanation of drawings]

1(A) to 1(D) are characteristic diagrams showing the surface roughness at each surface treatment stage of the substrate, and FIG. 1(A)
1(B) shows the substrate before treatment, FIG. 1(B) shows the substrate after one zinc replacement treatment, FIG. 1(C) shows the substrate after two zinc replacement treatments, and FIG. 1(D) shows the substrate after being immersed in an acidic solution. correspond to each.

Claims (1)

[Claims] A method for surface treatment of a substrate, which comprises subjecting a substrate made of aluminum or an aluminum alloy to zinc substitution treatment, immersing the substrate in an acidic solution, and further performing electroless nickel-phosphorus plating.