JP2003064484A - Aluminum alloy sheet for cover of electronic equipment, cover of electronic equipment having the aluminum alloy sheet, and electronic equipment having the cover - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a low-cost aluminum alloy sheet for a cover of an electronic equipment, which prevents the falling of fine particles having high dangeousness of causing the malfunction of the electronic equipment, can secure the electric conductivity of the surface of the cover required for the removal of static electricity, and can reduce a load on the environment in its production process. SOLUTION: A substrate layer containing 5 to 50 mg/m<2> Cr or Zr is formed on at least one surface of an aluminum alloy sheet stock 1 having a surface mean average roughness Ra of 0.1 to 0.5 μm. A resin film 2 having a mean film thickness of 0.1 to 0.5 μm is formed on the substrate layer. Thus, the falling of fine particles by an aluminum oxide film can be reduced, and a part of the aluminum alloy sheet stock 1 exposes from the resin film 2, so that the electric conductivity of the surface of the cover can be secured.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aluminum alloy plate for a cover of an electronic device used for a cover of a hard disk drive (HDD), a cover of an electronic device having the same, and an electronic device having the same, and more particularly to an HDD The present invention relates to an aluminum alloy plate for a cover of an electronic device, which prevents malfunction and facilitates grounding, a cover of an electronic device including the same, and an electronic device including the cover.

[0002]

2. Description of the Related Art With the development of information networks such as the Internet, it is possible to instantly exchange characters and image information in a wide range in the world. Along with this, a huge amount of information is generated, and a large-capacity recording medium for accumulating and recording such information is required. In response to this situation, recently, 1 square inch (6.45 cm)
² ) A hard disk drive equipped with a magnetic disk having a recording density of about 32.6 Gbits has been put on the market. In this case, about 40 GB of information can be recorded on one 3.5-inch type magnetic disk. Generally, an aluminum alloy substrate is used for a magnetic disk, and in order to achieve such a high density, the surface of the aluminum alloy substrate is required to have extremely severe mechanical precision. The hard disk drive cover plays an important role in preventing the magnetic disk, which requires such strict accuracy, from being contaminated by fine particles from the outside world. Therefore, aluminum alloy, stainless steel, brass or the like has been conventionally used as the material for the cover. However, in recent years, the demand for aluminum alloy covers is increasing in fields requiring lightness such as hard disk drives for notebook personal computers and space-saving desktop personal computers and hard disk drives for portable devices.

However, when a case and a cover for mounting such a magnetic disk are formed from an aluminum alloy plate, an aluminum oxide film which is naturally formed on the surface thereof is cracked during press molding to generate fine particles and the like. There is a risk of When such fine particles collide with the magnetic head, the information recorded up to that point may be erased.
Therefore, especially in the case of increasing the density, it is required to prevent the fine particles from falling off the cover surface.

Therefore, for example, there has been proposed an aluminum alloy cover having a surface similar to the electroless NiP plating film formed on the magnetic disk substrate.
The plating method is the same as that used for the magnetic disk substrate. For example, JP-A-8-158060.
It is described in Japanese Patent Publication No. By forming such an electroless NiP plating film, the number of fine particles that may fall off the hard disk drive cover surface can be significantly reduced. This prevents the danger that the recorded information will be instantly destroyed by the collision of the fine particles dropped from the cover surface to the magnetic head, that is, the head crash, during the operation of the hard disk drive. Is possible.

[0005]

However, since the electroless NiP plating film is an extremely hard film, there is a problem that the film may be cracked when press working after plating. For this reason, it is necessary to collectively perform the batch processing of the molded products after pressing, which takes time and labor, resulting in an extremely high cost. Further, since the adhesion (adhesion) of the plating film is greatly influenced by the surface condition of the molded product before plating, the quality variation is large. In order to suppress variations, it is necessary to perform pretreatment such as alkaline degreasing, acid etching and zincate treatment on the aluminum alloy base plate as pretreatment, but these pretreatments are alkali waste liquid and acid waste liquid, and further Zn and Al etc. A large amount of waste liquid containing the above metal is discharged. Further, since the plating solution itself contains a harmful Ni compound, there is a great environmental problem.

In order to solve such a drawback, a method of forming a resin film on the surface of an aluminum alloy plate has been disclosed (for example, JP-A-11-25653, JP-A-2000-67570 and JP-A-2000-67570). 2000-675
No. 71).

However, in these conventional covers, the resin film formed on the surface thereof is thick, and the surface of the hard disk drive cover is insulative. If the surface of the hard disk drive cover is insulative, it cannot be grounded to remove static electricity, and it is difficult to remove static electricity, which is one of the causes of malfunction in the hard disk drive. There is a problem. Therefore, in order to secure conductivity on the surface, conductive fine particles such as nickel are added to the resin film, but generally, the size of such conductive fine particles is 2 μm or more. large. Therefore, even if the conductive fine particles fall off from the resin film, even if compared with the fine particles (the particle diameter of the fine particles is 2 μm or less in most cases) generated by the crack of the aluminum oxide film, The risk of malfunctioning is even greater.

The present invention has been made in view of the above problems, and it is possible to secure the conductivity of the surface necessary for static electricity removal while preventing the fine particles from falling off. An object of the present invention is to provide an aluminum alloy plate for a cover of an electronic device capable of reducing a load, a cover of an electronic device having the same, and an electronic device having the same.

[0009]

An aluminum alloy plate for a cover of an electronic device according to the present invention comprises an aluminum alloy base plate having a surface average roughness Ra of 0.1 to 0.5 μm,
An undercoat layer containing 5 to 50 mg / m ² of Cr or Zr formed on at least one surface of the aluminum alloy base plate, and an average film thickness of 0.1 to 0.5 μm formed on the undercoat layer. And a resin film of.

The thickness of the resin film is determined as follows. That is, the mass (A) of a fixed area (for example, 10 cm × 10 cm) of the aluminum alloy base plate on which the resin film is formed and the mass (B) of the aluminum alloy base plate after the resin film is peeled off are measured. (A)-(B)
The mass (C) of the resin film is calculated according to, and the thickness of the resin film is obtained by dividing this (C) by the specific gravity of the resin film. Further, it is preferable that the resin film does not contain particles having a particle diameter of 2 μm or more.

Further, the resin film may be made of one resin selected from the group consisting of polyester resins, epoxy resins and polyurethane resins.

The cover of the electronic device according to the present invention is molded so that the surface of the aluminum alloy plate for the cover of any one of the above electronic devices on which the resin film is formed is the inside. Characterize.

An electronic device according to the present invention includes a case in which a recording medium is stored, and a cover for the electronic device according to claim 4 which covers the case.

In the present invention, since the average surface roughness Ra of the aluminum alloy base plate, the thickness of the resin film and the Cr or Zr content of the undercoat layer are properly specified, the fine particles of the aluminum oxide film are It is possible to secure high conductivity while preventing generation.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION The aluminum alloy plate for a hard disk drive cover according to the present invention will be described below.

First, a suitable raw material is subjected to melting, casting, hot rolling, cold rolling, heat treatment and the like to produce an aluminum alloy base plate on which a base treatment layer and a resin film have not yet been formed. . In this case, a desired aluminum alloy ingot can be obtained by adding various elements to aluminum during melting. Further, by appropriately changing the conditions such as rolling and heat treatment, it is possible to change the plate thickness, strength, surface roughness and the like.

The inventors of the present application have aimed to remove the static electricity, which is one of the causes of the malfunction of the hard disk drive and the prevention of the dropping of fine particles from the surface of the hard disk drive cover, which causes a head crash during the operation of the hard disk drive. As a result of an experimental study on the relationship between the surface roughness of the alloy base plate and the thickness of the resin film, the following facts were found. That is, when a resin film having an average film thickness of 0.1 to 0.5 μm is formed on the surface of an aluminum alloy base plate having a surface average roughness Ra of 0.1 to 0.5 μm, the fine particles are prevented from falling off. It has been found that the conductivity of the cover surface can be increased to the extent that static electricity can be removed. The reason for this is considered as follows. FIG. 1 is a sectional view showing the relationship between an aluminum alloy base plate and a resin film. As shown in FIG. 1, the average film thickness is 0.1 to 0.5 μm on the surface of the aluminum alloy base plate having the surface average roughness Ra of 0.1 to 0.5 μm.
It is considered that when the resin film of (1) is formed, a part of the surface of the aluminum alloy base plate is exposed from the resin film, and as a result, high conductivity can be secured.

In the present invention, since the surface of the aluminum alloy base plate 1 is covered with the resin film 2, even if the aluminum oxide film is cracked during press molding, the dropout of fine particles due to the aluminum oxide film is significantly reduced. It becomes possible. Further, due to the relationship between the average surface roughness of the aluminum alloy base plate 1 and the average film thickness of the resin film 2, a part of the aluminum alloy base plate 1 is exposed, so that the conductivity of the hard disk drive cover surface is ensured and static electricity is generated. It is possible to prevent malfunction of the hard disk drive. In this way, according to the present invention, the risk of malfunction of the hard disk drive due to the loss of fine particles is significantly reduced while ensuring conductivity. The surface conductivity required for grounding to prevent static electricity differs depending on the grounding method, but the surface resistance is generally 1Ω.
It is said that all ground connection methods can be supported if

The size and number of fine particles that can be removed from the entire hard disk drive cover are generally 3.5 inch type, provided that the number of fine particles having a size of 2 μm or more is less than 100,000. The frequency of malfunctions when actually using a hard disk drive is at a level that does not cause a problem. The number of the fine particles is large immediately after press molding, but is reduced by repeating washing with an acid, alkali or organic solvent, and at the same time, the cleanliness is improved. However, these cleanings are costly and
There is concern about adverse effects on the environment, such as the generation of harmful waste liquid. In the present invention, such cleaning is unnecessary, and the cleaning degree required for the hard disk drive cover can be obtained by performing cleaning with a water-based cleaning agent that has little effect on the environment and simple hot water cleaning.

Next, the reasons for limiting the numerical values of the surface average roughness of the aluminum alloy base plate and the thickness of the resin film will be described.

Thickness of resin film: 0.1 to 0.5 μm,
Surface average roughness: Ra (center line average roughness) of 0.1 to
When the surface average roughness of the 0.5 μm aluminum alloy base plate is less than 0.1 μm in terms of the center line average roughness Ra, the unevenness of the surface of the aluminum alloy base plate becomes too small. As a result, a very small portion (projection) of the aluminum alloy base plate is secured to ensure conductivity.
To expose only the above on the resin film,
It becomes too thin as less than μm, and the resin film having such a thickness cannot prevent the fine particles from falling off due to the aluminum oxide film on the surface of the aluminum alloy base plate. On the other hand, when the average surface roughness Ra exceeds 0.5 μm, the unevenness of the surface of the aluminum alloy base plate becomes too large. In this case, in order to prevent the fine particles from falling off, it is necessary to make the thickness of the resin film thicker than 0.5 μm, and as a result, it becomes difficult to secure the conductivity of the hard disk drive cover surface. Therefore, it is necessary to control the surface average roughness Ra of the aluminum alloy base plate to be 0.1 to 0.5 μm and the thickness of the resin coating to be 0.1 to 0.5 μm. This makes it possible to prevent the fine particles from falling off and to secure the surface conductivity, which is necessary for the hard disk drive cover.

By prescribing these numerical values, it is possible to achieve both prevention of fine particles required for the hard disk drive cover and ensuring of surface conductivity.

The aluminum alloy base plate may be any one as long as it satisfies the surface roughness, and the effect of the present invention can be obtained. For example, a high-purity aluminum base plate may be used. The alloy type, plate thickness and strength can be selected according to the design strength of the hard disk drive.

In the present invention, the aluminum alloy is
Between the gold plate and the resin film, for example, phosphoric acid chromate treatment
There is a base treatment layer formed by the method. This groundwork
The physical layer can be formed by the following method.
It First, the table of the aluminum alloy base plate that has been rolled, etc.
The oil remaining on the surface is treated with an alkaline chemical (for example, Nippon Pay
Degrease with a Surf Cleaner 360)
Wash. Then, for example, by chromate phosphate treatment
Apply groundwork. At this time, the resin film and the aluminum alloy
In order to ensure adhesion with the base plate, the amount of the surface treatment layer attached
Is 5 to 50 mg / m in terms of chromium^TwoAdjust to the range
Need to Adhesion amount of base treatment layer is 5 mg in terms of Cr
/ M^TwoIf it is less than, resin film and aluminum alloy base plate
Adhesiveness with
Film peeling occurs. On the other hand, the mass of the surface treatment layer is 50 m
g / m^TwoAbove the surface treatment layer, e.g.
Cracks easily form on the coating film. This results in cracks
There is a high risk that the undercoat layer itself will fall off as fine particles.
Therefore, it induces a malfunction of the hard disk drive,
The object of the present invention cannot be achieved. The groundwork
As an example of the physical layer, in addition to the phosphoric acid chromate treatment,
For example, by coating chromate treatment or coating zircon treatment
The same effect can be obtained by the formed film. However
However, in any of the treatments, the adhesion amount of the base treatment layer is
5 to 50 mg / m in terms of Cr or Zr ^TwoAnd
Also, in the above description, application as a method of forming the resin film
The method of forming a resin film has been described above
Is not limited to the coating method.

After that, a resin is applied, for example, by a roll coater on the undercoating layer formed on at least one surface of the aluminum alloy base plate, and the oven (baking furnace) is used.
A strong resin film can be formed by carrying out a heat curing reaction inside. FIG. 2 is a schematic view showing an example of an apparatus for forming a resin film. In this apparatus, a paint tank 11 containing a resin paint as a raw material, a roller 12 whose surface is partially immersed in the paint tank 11 and discharges the resin paint, and an aluminum alloy which is in contact with the roller 12 to apply the resin paint A roller 15 is provided for applying the aluminum alloy base plate 14 unwound from the coil 13. Further, a roller 16 is arranged so as to sandwich the aluminum alloy base plate 14 between the roller 15 and the roller 15 and changes the traveling direction of the aluminum alloy base plate 14 by 90 to 180 °. Further, in the subsequent stage of the roller 16, another paint tank 21 containing the resin paint as a raw material, a roller 22 for discharging a resin paint by partially immersing the surface in the paint tank 21 and the roller 22 are contacted. A roller 23 for applying the resin paint to the aluminum alloy base plate 14 is provided. Further, a baking furnace 24 is arranged in the latter stage of these. It should be noted that, as a raw material of the resin film, as a material satisfying the above-mentioned conditions (one that can be uniformly applied and can be cured by heating to form a strong resin film), for example, a polyester resin, an epoxy resin, or a polyurethane resin Can be used, but is not limited thereto.

With respect to such an aluminum alloy plate, the surface on which the resin film is formed is set to the inner surface side of the hard disk drive, that is, the side where both the prevention of the fine particles from falling off and the conductivity are required, and a desired value is obtained. A hard disk drive cover can be obtained by pressing into a shape. Further, a hard disk drive can be obtained by mounting a recording medium, a recording head, etc. inside such a hard disk drive cover.

It should be noted that although the above description is of a hard disk drive, the electronic equipment to which the present invention is applied is not limited to a hard disk, and has the same structure as a hard disk drive, that is, a case and a cover. It can also be applied to electronic devices that are combined, such as removable hard disk drives, large capacity flexible disk drives, various CD drives, and DVD drives.

[0028]

EXAMPLES Examples of the present invention will be specifically described below in comparison with comparative examples outside the scope of the claims.

First Experimental Example First, various aluminum alloy base plates shown in Table 1 were prepared while adjusting the surface average roughness Ra obtained by changing the surface roughness of the finish rolling roll. The plate thickness of these aluminum alloy base plates is 0.8 mm, and the product type is temper AA5052-H34. After that, alkali degreasing is applied to the entire surface, and the amount of deposited chromium is 20 mg / m.
^A ground treatment layer was formed by performing a phosphoric acid chromate treatment so as to be ² . Then, a resin film having a film thickness shown in Table 1 was formed on both the base treatment layers to manufacture an aluminum alloy plate.

[0030]

[Table 1]

After that, the surface resistance value, which is an index of conductivity, was measured for each of these aluminum alloy plates by using a tester. Further, press-molding was performed into the shape of a 3.5-inch type hard disk drive cover, and then the adhesion between the aluminum alloy plate and the resin film was investigated. Further, this molded product is washed with a water-soluble cleaning agent, water and hot water to be mounted on a hard disk drive, and then generated from one hard disk drive cover using a liquid particle counter.
The number of fine particles of μm or more was measured, and it was evaluated whether the number was less than 100,000 or 100,000 or more. Here, as the water used for extracting the fine particles, 0.
Pure water filtered with a 05 μm filter was used. The results are shown in Table 2. In the evaluation of the moldability, the case where the peeling of the film did not occur was evaluated as ◯, and the case where it did occur was evaluated as x. In the evaluation of the number of fine particles generated (fine particles after pressing), those having a number of less than 100,000 were evaluated as ◯, and those having a number of 100,000 or more were evaluated as x.

[0032]

[Table 2]

As shown in Table 2 above, Example No. In Nos. 1 to 4, good results were obtained in all evaluations of moldability, surface conductivity, and dust after pressing (number of fine particles generated). In addition, these Example Nos. When the cover formed from 1 to 4 was used, there was no particular problem with the performance of the hard disk drive.

On the other hand, in Comparative Example No. In No. 11, since the average surface roughness Ra and the thickness of the resin film were less than the lower limit value of the range of the present invention, a large amount of fine particles were generated.

Comparative Example No. In Nos. 12 to 14, the surface average roughness Ra is less than the lower limit value of the range of the present invention.
The exposure of the aluminum alloy base plate was extremely reduced and the surface resistance value was increased. In particular, Comparative Example No. In No. 14, since the thickness of the resin film further exceeded the upper limit of the range of the present invention, the surface resistance value was extremely high.

Comparative Example No. In Nos. 15 and 17, since the thickness of the resin film was less than the lower limit value of the range of the present invention, a large amount of fine particles were generated.

Comparative Example No. In Nos. 16 and 18, since the thickness of the resin film exceeds the upper limit value of the range of the present invention,
The surface resistance value became high.

Comparative Example No. In 19 and 20, the surface average roughness Ra exceeds the upper limit of the range of the present invention,
Good electrical conductivity was obtained because the resin film was relatively thin. However, a large amount of fine particles were generated. In addition, Comparative Example No. In Nos. 21 and 22, since the resin film was relatively thick, the generation of fine particles was small, but the surface resistance value was high.

Second Experimental Example Similar to the first experimental example, an aluminum alloy base plate (thickness:
0.8 mm, product type: temper AA5052-H34) was prepared. However, the surface average roughness (center line average roughness) is R
It was unified to 0.3 μm in a. After that, alkali degreasing was applied to the entire surface, and phosphoric acid chromate treatment was performed so that the chromium deposition amount shown in Table 3 was obtained, thereby forming a base treatment layer. Next, a film such as a resin film having a film thickness of 0.2 μm was formed on each of the base treatment layers to manufacture an aluminum alloy plate.

[0040]

[Table 3]

Then, by the same method as in the first experimental example, the moldability, the surface conductivity and the amount of fine particles generated were evaluated. The results are shown in Table 4.

[0042]

[Table 4]

As shown in Table 4, Example No. In 5 to 10, in any of the evaluations of moldability, surface conductivity, and dust after pressing (number of fine particles generated),
Good results have been obtained. In addition, these Example Nos. 5
When the covers formed from Nos. 10 to 10 were used, there was no particular problem with the performance of the hard disk drive.

On the other hand, in Comparative Example No. In Nos. 23 to 26, since the amount of Cr in the base treatment layer was less than the lower limit value of the range of the present invention, the adhesion between the resin film and the aluminum alloy base plate was low, and the resin film peeled off, resulting in low formability. ,
Also, a large amount of fine particles were generated.

Comparative Example No. In Nos. 27 and 28, since a film made of water glass was formed as a film, not a resin film, a large amount of fine particles were generated.

Comparative Example No. In Nos. 29 to 32, the amount of deposited chromium in the undercoat layer exceeded the upper limit of the range of the present invention, so that the phosphoric acid chromate film itself was cracked and a large amount of fine particles were generated.

Regarding surface conductivity, Example N was used.
o. 5 to 10 and Comparative Example No. In each of Nos. 23 to 32, the target surface resistance value of 1Ω or less was obtained.

[0048]

As described in detail above, according to the present invention,
Generation of fine particles from the aluminum alloy plate can be significantly reduced, and desired conductivity can be secured on the surface. Furthermore, by using this aluminum alloy plate, it is possible to obtain a cover for electronic equipment such as a hard disk drive and the electronic equipment itself, which is low in cost, has a small variation in quality, and is environmentally friendly.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a relationship between an aluminum alloy base plate and a resin film.

FIG. 2 is a schematic view showing an example of an apparatus for forming a resin film.

[Explanation of symbols]

1; Aluminum alloy base plate 1a; convex part 2; Resin film 11, 21; paint tank 12, 15, 16, 22, 23; rollers 13; Aluminum alloy coil 14; Aluminum alloy base plate

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 4E360 AB02 EE12 EE13 EE15 FA09                       GA35 GB43 GC04 GC08 GC13                 4K044 AA06 AB10 BA12 BA15 BA17                       BA21 BB03 CA16 CA53

Claims (5)

[Claims] 1. The average surface roughness Ra is 0.1 to 0.5 μm.
an aluminum alloy base plate of m, and 5 to 50 mg formed on at least one surface of the aluminum alloy base plate
/ M ² Cr or Zr-containing underlayer, and an average film thickness of 0.1 to 0.5 μ formed on the underlayer.
An aluminum alloy plate for a cover of an electronic device, which has a resin film of m. 2. The aluminum alloy plate for a cover of electronic equipment according to claim 1, wherein the resin film does not contain particles having a particle size of 2 μm or more. 3. The resin film is a polyester resin,
The aluminum alloy plate for a cover of an electronic device according to claim 1 or 2, comprising one kind of resin selected from the group consisting of an epoxy resin and a polyurethane resin. 4. The aluminum alloy plate for a cover of an electronic device according to claim 1, wherein the surface of the aluminum alloy plate on which the resin film is formed is formed inside. Characteristic electronic device cover. 5. An electronic device comprising: a case in which a recording medium is stored; and the electronic device cover according to claim 4, which covers the case.