JP3131138B2 - Crystallized glass substrate for magnetic disk - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic disk substrate, and more particularly to a magnetic disk glass ceramic substrate suitable for contact recording.

[0002]

2. Description of the Related Art With the development of multimedia in personal computers, large-capacity magnetic disk drives are required. As a result, in the magnetic disk, it is necessary to increase the bit and track densities and reduce the size of the bit cells in order to increase the areal recording density. In response to the shrinkage of bit cells, the magnetic head needs to operate closer to the disk surface. The flying height of the magnetic head from the disk surface is set to 0.025 μm or less, and recording is performed with the magnetic head almost in contact with the disk. Is required.

[0003]

In such a contact recording system, a magnetic disk is
In order to enable a flying height of the magnetic head of 0.025 μm or less, the surface roughness (Ra) is required to be 10 ° or less, and a sufficiently high wear resistance to withstand contact with the magnetic head is required. Required to have.

Conventionally, an aluminum alloy has been used for a magnetic disk substrate material. However, in the case of an aluminum alloy substrate, projections or spot-like irregularities are formed on the substrate surface in a polishing process due to the influence of various material defects. Smoothness is not sufficient, and aluminum alloy is a soft material, so it is easy to deform and it is difficult to cope with thinning, and furthermore, deformation of the head due to contact with the head causes damage to the media For example, it cannot sufficiently cope with today's high-density recording.

Further, as materials for solving the problems of the aluminum alloy substrate, soda lime glass (SiO ₂ —CaO—Na ₂ O) and aluminosilicate glass (SiO ₂ —Al ₂ O—Na ₂ O) of chemically strengthened glass are used. As is known, in this case, (a) polishing is performed after chemical strengthening, and the unstable element of the strengthening layer in thinning the disk is high.
(B) Since the glass contains the Na ₂ O component as an essential component, the film-forming properties are deteriorated, and it is necessary to perform a barrier coating treatment on the entire surface to prevent Na ₂ O from being eluted. There is a disadvantage that.

Further, some crystallized glasses are known for aluminum alloy substrates and chemically strengthened glass substrates. For example, as described in JP-A-6-329440,
iO ₂ —Li ₂ O—MgO—P ₂ O ₅ -based crystallized glass has lithium disilicate (Li ₂ O · 2Si) as a main crystal phase.
O ₂ ) and α-quartz (α-SiO ₂ );
The spherical particle size of quartz (α-SiO ₂ ) can be controlled, but the surface roughness (R
a) is in the range of 15 ° to 50 °, and the target surface roughness (Ra) is 10 ° or less.

An object of the present invention is to provide a magnetic disk having a surface roughness of 10 ° or less and high abrasion resistance by solving the above-mentioned disadvantages of the prior art in order to cope with a contact recording method by increasing the density of a hard disk. It is to provide a crystallized glass substrate for use.

[0008]

The inventor of the present invention has conducted research and experiments to achieve the above object, and has found that SiO ₂ —Li
₂ O-Al ₂ O ₃ MgO component in -P ₂ O ₅ system and Z
The main crystal phases obtained by heat-treating raw glass containing nO as an essential component under strictly limited heat treatment conditions are α-cristobalite (α-SiO ₂ ) and lithium disilicate (Li ₂ O · 2SiO ₂ ). By limiting the composition ratio of α-cristobalite to lithium disilicate to a narrow range of 0.25 to 0.35, the surface roughness (Ra) of the polished magnetic disk substrate is reduced. 2 to 10 ° and the degree of wear (A
The present inventors have found that a magnetic disk substrate ideal for contact recording in which a) is within the range of 5 to 15 can be obtained, and have reached the present invention.

That is, in the crystallized glass substrate for a magnetic disk according to the first aspect of the present invention, the main crystal phase of the crystallized glass is α-cristobalite (α-Si
O ₂ , wherein the object of the present invention is achieved.
Crystallized glass substrates for magnetic disks are mainly made of crystallized glass.
The crystalline phase is α-cristobalite (α-SiO ₂ ) and
Lithium disilicate (Li ₂ O.2 SiO ₂ )
The composition ratio of the crystal phase is α-cristobalite / lithium disilicate
Is 0.25 to 0.35, and the particle size of the crystal particles is
Having a value in the range of 0.1 to 1.0 μm,
The surface roughness (Ra) obtained by polishing the plate is 2 to 10 °
And the degree of wear (Aa) is in the range of 5 to 15.
And is characterized by the following.
You.

The crystallized glass substrate for a magnetic disk according to claim 1 or 2 is a substrate for a magnetic disk according to claim 1, wherein the crystallized glass is SiO 2 by weight percentage.
_Two

The composition of the crystallized glass of the present invention can be expressed on an oxide basis as in the case of the original glass. The reason why the composition range of the original glass is limited as described above will be described below.

The SiO ₂ component is converted into lithium disilicate (Li ₂ O · 2Si) as a main crystal phase by heat treatment of the raw glass.
O ₂ ) and α-cristobalite are very important components, but if the amount is less than 75.0%, the precipitated crystals of the obtained glass are unstable, the structure is liable to become coarse, and 83.0% If it exceeds, melting of the raw glass becomes difficult.

The Li ₂ O component is converted into lithium disilicate (Li ₂ O · 2Si) as a main crystal phase by heat treatment of glass.
O ₂ ) is a very important component for producing crystals, but if the amount is less than 7%, it becomes difficult to precipitate the above crystals, and at the same time, it becomes difficult to melt the raw glass. Deposited crystals of fossilized glass become unstable,
The structure is easily coarsened, and the chemical durability and hardness are deteriorated. The K ₂ O component is a component for improving the melting property of glass, and can be contained up to 5%.

MgO is an important component for defining the precipitated crystals. If its amount is less than 0.5%, the precipitation of α-cristobalite increases and the wear resistance deteriorates. 3%
If it exceeds 300, precipitation of α-quartz increases, and the particles become coarse, so that the surface roughness deteriorates. ZnO also has the same effect and can be added, but should be added up to 3%.

The P ₂ O ₅ component is indispensable as a crystal nucleating agent for glass, but if its content is less than 1%, Li ₂ O 5
-The particles of 2SiO ₂ and α-SiO ₂ crystals are coarsened, and desired surface roughness and abrasion cannot be obtained. On the other hand, if it exceeds 3%, the glass tends to be devitrified at the time of glass molding, and the devitrification causes coarsening of particles.

The Al ₂ O ₃ component is an effective component for improving the chemical durability of the crystallized glass, but if its content is less than 1%, its purpose cannot be achieved, and its content is 5%. %, The meltability deteriorates. The As ₂ O ₃ and / or Sb ₂ O ₃ component can be added as a fining agent in melting the glass, but a total amount of one or two of them is not more than 2%.

In the present invention, in addition to the above components, a small amount of B is used in the glass to be used so as not to impair the desired properties.
₂ O ₃ , CaO, SrO, BaO, TiO ₂ , SnO,
And ZrO ₂ component.

In the crystallized glass substrate of the present invention, the ratio of the constituent crystal phases at the time of crystallization is defined as α-cristobalite / lithium disilicate = 0.25 to 0.35. This is because the ratio of each crystal phase is determined by the XRD peak height, and α
-Cristobalite (101), lithium disilicate (13
The ratio was determined using each of the peak surfaces of 0). The reason for limiting this ratio to 0.25 to 0.35 is that when the composition ratio is in the range of 0.25 to 0.35, the ideal surface roughness of the substrate after polishing is 2 to 10 °. In addition to that, as shown in FIG. 1, when the composition ratio is less than 0.25 or exceeds 0.35, the degree of wear (Aa) rapidly deteriorates, and within a range of 0.25 to 0.35. In the degree of wear (A
This is because many experiments have revealed that the desired surface characteristics of a) can be obtained in the order of 15 or less.

The crystallized glass substrate of the present invention has a degree of wear (A
a) is in the range of 5 to 15, preferably 5 to 12,
As a result, the magnetic head has sufficient wear resistance even in contact recording where the flying height of the magnetic head is 0.025 μm or less.

Next, in order to produce the crystallized glass for a magnetic disk according to the present invention, the glass having the above composition is melted, hot and / or cold formed, and then nucleation is performed at 400 ° C. to 550 ° C. A crystallization heat treatment is performed at a temperature of 720 ° C. to 820 ° C., and the heat treated crystallized glass is usually wrapped and polished by a generally well-known method so that the surface roughness (Ra) is in the range of 2 to 10 °. And

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, preferred embodiments according to the present invention will be described. Tables 1 to 4 show working composition examples (Nos. 1 to 10) of a crystallized glass substrate for a magnetic disk of the present invention and conventional SiO ₂ —Li ₂ O—Al ₂ O ₃ —P ₂ O ₅ -based crystallized glass. Are shown together with the measurement results of the nucleation temperature, crystallization temperature, precipitated crystal phase, crystal grain size, surface roughness (Ra) after polishing, and abrasion degree of these crystallized glasses. The composition is shown by weight percentage.

[0022]

[Table 1]

[0023]

[Table 2]

[0024]

[Table 3]

[0025]

[Table 4]

Further, Example 3 of the present invention and Comparative Examples 1 and 2
2 and 3 show electron micrographs showing the particle state of
And FIG.

The glasses of the above embodiments are all oxides,
Raw materials such as carbonates and nitrates are mixed and melted at a temperature of about 1350 ° C. to 1500 ° C. using a usual melting apparatus,
After stirring and homogenizing, the mixture was formed into a desired shape and cooled to obtain a glass molded body. Thereafter, this is heat-treated and after nucleation (4)
00 ° C. to 550 ° C.), crystallization temperature (720 ° C. to 820
C.) for about 1-5 hours to obtain the desired crystallized glass. In preparing the surface roughness measurement sample, the above crystallized glass was treated with abrasive grains having an average particle size of 9 to 12 μm for about 10 minutes.
Finished by polishing for 20 minutes to 20 minutes. The degree of wear was measured by the method specified by the Japan Optical Glass Industrial Association. That is, a flat plate made of cast iron (25 in which a glass square plate of 30 × 30 × 10 mm in sample size is horizontally rotated 60 times per minute.
0mmφ) at the fixed position of 80mm from the center, 9.8
While applying a load of N {1kgf} vertically, # 800
Wrap material (Alumina A abrasive) with (average particle size 20 μm)
Was added and uniformly worn for 5 minutes with 20 ml of water added thereto, and the sample was measured before and after the lap to determine the wear mass. Similarly, the abrasion mass of a standard sample specified by the Japan Engineering Glass Industry Association was determined, and the value calculated by the following equation was used as the abrasion degree (Aa).

[0028]

As can be seen from Table 1, the crystallized glasses of the examples all had a surface roughness (Ra) value of less than 10 ° compared to the comparative examples, and were excellent in the surface characteristics, and the effect of the objective improvement. Is remarkable. In addition, the degree of wear was 12
It shows the following small values, which indicates that it has excellent wear resistance.

[0030]

As described above, according to the present invention, the main crystal phase of the crystallized glass is α-cristobalite (α-S
iO ₂ ) and lithium disilicate (Li ₂ O.2Si)
O ₂ ), wherein the composition ratio of the crystal phase is 0.25 to 0.35 of α-cristobalite / lithium disilicate;
The surface roughness (Ra) obtained by polishing the magnetic disk substrate, wherein the crystal particles have a value in the range of 0.1 to 1.0 μm.
Is 2 to 10 °, and the degree of wear (Aa) is 5 to 15 °.
Within this range, a crystallized glass substrate for a magnetic disk suitable for contact recording can be obtained.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between α-cristobalite / lithium disilicate composition ratio and degree of wear.

FIG. 2 is an electron micrograph showing a particle state of an example of the present invention.

FIG. 3 is an electron micrograph showing the particle state of Comparative Example 1.

FIG. 4 is an electron micrograph showing the particle state of Comparative Example 2.

Claims (3)

(57) [Claims] The main crystal phase of the crystallized glass is α-cristo.
Barite (α-SiO ₂ ) and lithium disilicate (Li
₂ O. 2SiO ₂ ), and the composition ratio of the crystal phase is α
-Cristobalite / lithium disilicate in the range of 0.25-0.
35, and the diameter of the crystal grains is in the range of 0.1 to 1.0 μm.
Surface roughness of the magnetic disk substrate
A magnetic disk having a degree (Ra) of 2 to 10 °.
Crystallized glass substrate for disk. 2. The main crystal phase of the crystallized glass is α-cristobalite (α-SiO ₂ ) and lithium disilicate (Li).
₂ O. 2SiO ₂ ), and the composition ratio of the crystal phase is α
-Cristobalite / lithium disilicate in the range of 0.25-0.
35, the crystal grain diameter has a value in the range of 0.1 to 1.0 μm, the magnetic disk substrate has a polished surface roughness (Ra) of 2 to 10 °, and the abrasion degree (Aa)
Is in the range of 5 to 15. 3. The crystallized glass is in weight percent Si
O ₂ 75 to 83%, Li ₂ O 7 to 13%, Al ₂ O
_{3 1~5%, P 2 O 5} 1~3%, MgO0.5~3
_{%, 0.5~3% ZnO, K 2} O 0~5%, As 2
O ₃ and / or Sb ₂ O ₃ crystallized glass substrate according to claim 1 or 2, characterized in that it is obtained by heat-treating a raw glass consisting 0-2%.