JP2001180960A - Press molding method of oxynitride glass and press molded oxynitride glass obtained by press molding method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optimum mould release layer for a press molding of an oxynitride glass. SOLUTION: A press molding method of an oxynitride glass by a molding die is characterized by an existence of a mold release layer including carbon and/or boron nitride between a surface of an oxynitride glass and a surface of the molding die, in order to keep a nitrogen quantity in a molded oxynitride glass after press above 90% (mass ratio) of the nitrogen quantity in a molded oxynitride glass before press, with raising the mold release property between an oxynitride glass after press and a molding die.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a press molding method which focuses on a release layer when obtaining an oxynitride glass press molded body usable for a disk for a recording medium such as a magnetic disk.

[0002]

2. Description of the Related Art In the field of magnetic disk drives, technical developments are being made more and more rapidly in order to improve recording density and transfer speed. In recent years, there has been an urgent need to increase the speed of rotation of a disk, particularly for the purpose of improving the transfer speed, and a disk material having high specific rigidity (= Young's modulus / density) that does not vibrate even during high speed rotation is desired. . The specific rigidity of a conventionally used aluminum disk (hereinafter referred to as aluminum disk) is 26.7 (= Young's modulus: 72 GPa / density:
2.7 g / cm ³ ), and it is said that specific stiffness more than twice that of use at a high speed rotation of 10,000 rpm is required. However, in order to double the specific rigidity of the aluminum disk, it is necessary to combine it with ceramics (MM
C) and the like, and the practicality is low in terms of cost.

On the other hand, a glass disk used in a 2.5-inch size (hereinafter, referred to as a glass disk) is
Attention is drawn to the fact that high specific rigidity is easily achieved. For example, there have been many attempts to improve the Young's modulus by heat-treating the glass at an appropriate temperature to precipitate a crystal phase having a high Young's modulus to form glass ceramics. For example, Japanese Unexamined Patent Publication
JP-A-329440, JP-A-8-111024 and JP-A-8-221747 disclose examples of depositing lithium dioxide crystals and α-quartz crystals. Japanese Patent Application Laid-Open No. 9-77531 discloses that spinel crystals are precipitated to reduce the Young's modulus to 109 to 144.
An example in which GPa and specific rigidity are improved to 36 to 47 is disclosed. However, although the specific rigidity of the glass itself is increased by crystallization, a fine step occurs during polishing because it has a composite structure of a hard crystal phase and a soft glass phase,
There is a disadvantage that it is difficult to obtain a super mirror surface required for a disk.

On the other hand, as a measure for improving the specific rigidity of the glass itself, a method of adding a rare earth element which is expected to have an effect of improving the Young's modulus of the glass is known. However,
The addition of the rare earth element increases the Young's modulus of the glass and at the same time increases the density, with the result that the specific stiffness does not improve as expected.

Therefore, as a measure for improving the Young's modulus without significantly increasing the density of the glass, use of an oxynitride glass in which oxygen in the glass is replaced with nitrogen has been studied. The present applicants studied the composition of oxynitride glass giving a high Young's modulus, and filed the results of the study (Japanese Patent Application No. Hei 11-1999).
96987). Further, various studies are being conducted with the aim of establishing an industrial production method of oxynitride glass.

For example, to apply oxynitride glass to a magnetic disk or the like, adopting a press molding method is considered to be the most efficient industrially. However, oxynitride glass has a high viscosity at a high temperature and has a problem that it adheres to a molding die after pressing. In addition, even if oxynitride glass having a composition that gives a high Young's modulus is pressed, nitrogen is deprived from the glass during the pressing process depending on the type of the release agent, and the composition of the glass changes. There has also been a problem that a molded article having a high Young's modulus cannot be obtained.

[0007]

Accordingly, in the present invention, in obtaining a molded article of oxynitride glass by press molding, it is necessary to prevent the molding die from being attached to the oxynitride glass after pressing, and to further reduce the oxynitride glass. An object of the present invention was to establish a press molding method capable of maintaining a glass composition at a desired composition and to provide a press molded article of oxynitride glass having excellent performance.

[0008]

SUMMARY OF THE INVENTION The present invention is a method for press-molding oxynitride glass using a molding die, which enhances the releasability between the molded oxynitride glass and the molding die. In order to maintain the amount of nitrogen in the oxynitride glass molded body after pressing at least 90% (mass ratio) of the amount of nitrogen in the oxynitride glass before pressing, the surface of the oxynitride glass and the surface of the molding die were used. The gist lies in performing press molding in a state where a release layer containing carbon and / or boron nitride is present between them.

In order to form this release layer, an average particle diameter of 0.0
A method in which a release agent containing 1 to 100 μm of carbon powder and / or boron nitride powder is provided by applying to a surface of a molding die and / or a surface of oxynitride glass before pressing, or By depositing carbon and / or boron nitride on the surface and / or the surface of the oxynitride glass before pressing,
Any of the methods of providing a deposited film of carbon and / or boron nitride can be preferably employed.

[0010] In the case of providing a release layer using the release agent, the amount of the formed release layer, as the mass per unit surface area of the forming surface of the forming ^{material, 1 × 10 -5 ~5 × 10} - ¹ g / cm
Preferably to be ^2, the case of using a deposited film as a release layer, the thickness of the release layer, 0.001 to 10
It is preferable that the thickness be set to μm. The present invention also includes a press-formed body of oxynitride glass press-formed using the press-forming method of the present invention.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The most important feature of the present invention is that a layer containing carbon and / or boron nitride is used as a release layer when press-molding oxynitride glass. With this configuration, it is possible to prevent the oxynitride glass after pressing from adhering to the molding die. In addition, it has become possible to prevent nitrogen from being deprived from the oxynitride glass during the pressing, thereby changing the composition. Hereinafter, the present invention will be described in detail.

The release layer in the press molding method of the present invention must be a layer containing carbon and / or boron nitride. As the form of the release layer, a carbon-only layer,
Examples include a single layer of boron nitride, a mixed layer of both, or a layer in which a plurality of these layers are stacked. The temperature at which the oxynitride glass can be spread by pressing depends on the composition of the glass, but is at least 650 ° C, usually 1000 to 18 ° C.
When the present inventors examined a substance having a level of 00 ° C. and exhibiting releasability at this temperature, carbon, boron nitride, silicon carbide and the like were found. However, it has been found that silicon carbide forms a silicon nitride by removing a part of nitrogen from oxynitride glass during pressing. That is, the glass composition after pressing is different from that before pressing, and a desired glass molded body with a high Young's modulus cannot be obtained due to a decrease in the amount of nitrogen. Since oxynitride glass forcibly introduces a nitrogen atom instead of an oxygen atom into the glass skeleton, the existing state of nitrogen is never stable. For this reason, it is considered that if there is an element that easily bonds to nitrogen such as Si derived from silicon carbide around the glass during pressing, nitrogen may escape from the glass.

On the other hand, the release layer made of carbon or boron nitride exhibited good release properties without changing the glass composition (without reducing the nitrogen content). Therefore, in the present invention, a release layer containing carbon and / or boron nitride was selected. Since boron nitride has a nitrogen source, it is considered that nitrogen is not extracted from the glass, but the reason why the carbon-based release layer does not change the nitrogen amount of the glass is not clear. . However, when a carbon-based molding die such as isotropic graphite is used alone without providing a release layer, the amount of nitrogen in the glass is reduced. It has been confirmed that the decrease in the amount of nitrogen from ash can be suppressed.

[0014] The standard of the fluctuation behavior of the nitrogen content of the oxynitride glass is that when the mass of nitrogen contained in the glass before pressing is 100%, the mass of nitrogen contained in the molded product after pressing is large. When the ratio is less than 90%, the Young's modulus of the glass becomes inferior. Therefore, in the present invention, it is required that nitrogen be retained at 90% or more.

Since a release layer may adhere to the surface of the molded product after pressing, the amount of nitrogen contained in the molded product after pressing is determined by polishing the surface of the molded product and completely removing the release layer. This is done so that the release layer is not affected by the nitrogen when the release layer is formed of boron nitride.

The polishing method and the analysis of the amount of nitrogen were performed as follows. The molded body of oxynitride glass obtained by press molding is immersed in acetone and subjected to ultrasonic cleaning. A molded body is adhered to a ceramic plate (support) having a mass of 1 kg, and the molded body is set on a lapping apparatus so that the molded body is on a lower side, and a platen (flatness ± 1 μm) is brought into contact with the lower side, Polishing load 1 kg (= mass of ceramic plate)
Polishing is performed at a platen rotation speed of 60 rpm. As a polishing agent, a diamond slurry having a particle diameter of 15 μm is used for rough polishing, and a diamond slurry having a particle diameter of 1 μm is used for finishing polishing.
Spray on the surface of the platen every second. At the stage where the release layer (colored) attached to the surface of the oxynitride glass was removed, the rough polishing was changed to finish polishing.
Polishing is completed in about several minutes to several tens of minutes. The amount of nitrogen in the glass before pressing and the amount of nitrogen in the glass from which the release layer has been removed by polishing after pressing are each quantified by X-ray fluorescence analysis.

In the present invention, the layer “containing” carbon and / or boron nitride means that other substances may be contained as long as the releasability is not impaired. Further, the temperature at which the oxynitride glass is press-molded is at least 650 ° C., and is usually at a level of 1000 to 1800 ° C., so that compounds which are carbonized or volatilized in this temperature range (for example, various polymers and low molecular organic compounds) Compounds)
Is contained in the release layer before press molding, but in the above-mentioned temperature range in which press molding is performed, the “layer containing carbon and / or boron nitride” referred to in the present invention is generated.
There is no problem at all. However, substances that change the composition of the glass during pressing (for example, the silicon carbide) should not be included.

In order to provide the release layer at the time of press molding,
There are roughly two methods. In the first method, a release agent containing carbon powder and / or boron nitride powder is applied to the surface of a molding die and / or the surface of a gob of oxynitride glass (so-called glass gob) before pressing to form a coating film. Is a way to get Since it is difficult to obtain a coating film using only powder, it is preferable to use a solvent or a dispersion medium that evaporates by heating or a release agent containing a binder resin component that carbonizes at the press temperature. Further, the release agent may contain additives such as a drying accelerator and a surfactant.

The size of the carbon powder and / or boron nitride powder is preferably in the range of 0.01 to 100 μm in average particle size. When the average particle size of the powder is smaller than 0.01 μm, the releasability may not be sufficiently exhibited. Further, it is considered that when the mold is opened after pressing, a part of the release layer is peeled off and adheres to the surface of the press-formed body to exhibit the releasability. Therefore, when the average particle diameter of the powder exceeds 100 μm, the powder having such a large particle diameter adheres to the surface of the press-formed body, and the surface smoothness, dimensional accuracy and shape accuracy of the formed body are deteriorated. The more preferable average particle diameter of the powder is 0.1 to 10 μm.

The method of applying the release agent is not particularly limited.
In consideration of a coating method applied to press molding, a brush coating method, a spin coating method, a spray coating method, or the like can be employed. Among them, the spray coating method is efficient. The mold release agent is sprayed evenly with the solvent etc., if necessary, onto the surface of the molding die (glass contact surface) or the surface of the oxynitride glass gob before pressing, thereby releasing the mold. Layers can be formed.

At this time, a preferable formation amount of the release layer is 1 × as a weight per unit surface area of the surface on which the object is formed.
It is 10 ^{-5 to} 5 × 10 ^-1 g / cm ² . 1 × 10 ^-5 g /
If it is less than cm ² , the glass after pressing and the molding die will be undesirably adhered. Also, the amount of nitrogen in the glass may decrease. A more preferred lower limit is 0.0001 g / cm ² . A more preferred lower limit is 0.0004 g / cm ² . On the other hand, 5 × 10
^Even if the release layer is formed in excess of ^-1 g / cm ² , the releasability is saturated, so that it is economically useless. Also, if the amount of the release layer formed is too large, the thickness of the release layer that adheres to the surface of the press-formed body also increases, which causes problems in the surface smoothness, dimensional accuracy, and shape accuracy of the formed body. It is not preferable because of fear. The amount of the release layer formed is determined by measuring the mass before the formation of the release layer and the mass after the formation of the release layer for the object to be formed (the molding die or the glass gob before pressing).
The mass of the release layer was determined from the difference between the latter and the former, and the result was divided by the total area of the portion of the object on which the release layer was formed to calculate the release layer formation amount [g / cm ² ].

A second method for providing a release layer is a method utilizing vapor deposition. That is, this is a method in which a vapor deposited film of carbon and / or boron nitride is formed on the surface of a molding die and / or the surface of an oxynitride glass gob before pressing to form a release layer. Known methods such as a CVD method, a sputtering method, and an ion plating method can be employed as the vapor deposition method. At this time, the thickness (film thickness) of the release layer (evaporated film) is preferably set to 0.001 to 10 μm.
If the thickness is too small, the pressed glass and the molding die may adhere to each other, or the amount of nitrogen in the glass may decrease.If the thickness is too large, the releasability is saturated as described above, so that waste is lost. In addition, there is a possibility that problems may occur in the surface smoothness, dimensional accuracy, and shape accuracy of the molded body.

The release layer may be formed only on the surface of the molding die, only on the surface of the oxynitride glass (glass gob) before pressing, or on both of them. It can be appropriately selected such as a case where a release layer is provided and a vapor deposition layer is provided on any of them, or a layer is alternately laminated.

The temperature at which the oxynitride glass can be spread by pressing is at least 650 ° C., usually 100 ° C.
It is at a level of 0 to 1800 ° C., and as a material of a molding die usable at this temperature, there are exemplified isotropic graphite, impermeable carbon, glassy carbon and the like.

Although the composition of the oxynitride glass that can be used in the present invention is not particularly limited, M ¹ -Al-Si-ON (M ¹ is Ca, Mg, Y,
An oxynitride glass represented by one or more of Gd, Ce and La); M ² —Si—ON (M ² is Ca and / or M
Any of the oxynitride glass represented by g) and the oxynitride glass obtained by mixing two or more of these glasses are preferable.

In general, M ¹ is Ca, Mg,
A composition that is one of Y, Gd, Ce and La is known, but two or more metal elements may be mixed. Also, both Mg and Ca may be mixed. Is a case where two or more types of glass are mixed before pressing.

The oxynitride glass preferably used in the method of the present invention has an amount of nitrogen of 5 equivalent% ≦ N ≦ 25 equivalent% when O + N = 100 equivalent%. If the amount of nitrogen is less than 5 equivalent%, it is difficult to obtain a molded body having a high Young's modulus, and if the amount of nitrogen exceeds 25 equivalent%, silicon nitride or the like may precipitate during pressing, which is not preferable as a molded body. It is. A particularly preferred composition of the metal component capable of obtaining a homogeneous glass with a high Young's modulus is disclosed in Japanese Patent Application No. 11-96987 filed by the present applicant. Further, preferable conditions for press-molding a glass having the above composition have been separately filed by the present applicant.

The oxynitride glass is prepared by reducing a metal oxide (SiO ₂ , Al ₂ O ₃ , MgO, CaO, etc.) and a nitride serving as a nitrogen source (Si ₃ N ₄ , AlN, BN, etc.) in a reducing atmosphere. It can be manufactured by a method of mixing below, melting at a high temperature and then quenching. In addition, a method of melting a metal oxide in N ₂ gas or NH ₃ gas, and adding N ₂ gas or N
A method of blowing H ₃ gas by bubbling, a method of baking porous glass in NH ₃ gas, and the like can also be adopted.

It is preferable that the pressed body is subjected to a polishing step in order to remove the release layer adhering to the surface, increase dimensional accuracy and smooth the surface.

[0030]

The present invention will be described in more detail with reference to the following examples. However, the following examples do not limit the present invention, and all changes and modifications within the scope of the present invention are included in the present invention. It is.

Experimental Example 1 A press molding experiment of a reheat press method was performed using Ca-Al-Si-ON-based oxynitride glass. Composition: Ca: 20 equivalent%, Al: 20 equivalent%, S
i: 60 equivalent%, O: 80 equivalent%, N: 20 equivalent%. The pressing was performed at a pressing temperature of 1200 ° C., a pressing load of 14220 (N), and a pressing time of 10 seconds. The molding die is made of isotropic graphite and has a diameter of 96 mm and a thickness of 1.
One that can form a 2 mm glass disk was used.

As a release agent, carbon powder (average particle size 20
μm) spray or “Toyoka Ace BN spray” (both manufactured by Oriental Sangyo Co., Ltd.) containing boron nitride powder (average particle diameter 10 μm). Formed. For comparison, an example in which a release layer made of silicon carbide powder and silicon nitride powder was provided was also examined. Silicon carbide powder (average particle size 1
0 μm) and a release layer made of silicon nitride powder (average particle diameter: 10 μm) are formed by applying a solution in which these powders are dispersed in n-hexane to the surface of a molding die by a spin coating method, and then naturally drying. did. In each case, the adhesion amount of the release layer was 0.001 g / cm ² . The releasability and the amount of nitrogen after press (reduced amount of nitrogen) were evaluated according to the following criteria. Table 1 shows the results.

Releasability: The glass disk after pressing and the molding die do not adhere during opening of the mold, and when the mold is cleanly released, ○: when partially adhered, Δ: when adhered entirely, ×: when entirely adhered. And

Nitrogen content after pressing The pressed oxynitride glass compact was immersed in acetone, subjected to ultrasonic cleaning, and then adhered to a ceramic plate (support) having a mass of 1 kg. It was set in a lapping device so that the molded body was on the lower side. A platen (flatness: ± 1 μm) was brought into contact with the molded body from below, and polished at a polishing load of 1 kg (= mass of the ceramic plate) and a platen rotation speed of 60 rpm. As a polishing agent, a diamond slurry having a particle diameter of 15 μm was used for rough polishing, and a diamond slurry having a particle diameter of 1 μm was used for finish polishing, and was sprayed on the surface of the platen at intervals of 30 seconds together with a lubricant during polishing. At the stage where the release layer (colored) adhering to the oxynitride glass surface was almost removed, the polishing was changed from rough polishing to finish polishing, and the polishing was completed in about several minutes to several tens of minutes. The amount of nitrogen in the glass before pressing, and the amount of nitrogen in the glass from which the release layer was removed by polishing after pressing,
It was quantified by X-ray fluorescence analysis.

As a result of the above analysis, assuming that the nitrogen content (mass) of the glass before press molding is 100%, 90% (mass) or more of the nitrogen content in the glass after press molding (after polishing) remains. The sample was rated as 、, 80 to 90% as Δ, and less than 80% as ×.

[0036]

[Table 1]

As is clear from Table 1, No. 1 was pressed in the presence of a release layer containing carbon. No. 4 which was pressed in the presence of a release layer containing boron nitride and boron nitride. For 5,
Good release properties were exhibited, and no decrease in the amount of nitrogen was observed. However, no. In No. 1, no releasability was exhibited, and the amount of nitrogen also decreased. No. 1 using silicon carbide. In No. 2, although the releasability was exhibited, the amount of nitrogen was reduced, and No. 2 using silicon nitride was used. In No. 3, no decrease in the amount of nitrogen was observed, but there was a problem in the releasability.

Experimental Example 2 Using an oxynitride glass having the same composition as in Experimental Example 1,
Experimental Example 1 except that the average particle diameter of the powder, the amount of the release layer formed, and the location of the release layer were changed as shown in Table 2 (carbon-based) and Table 3 (boron nitride-based: BN-based). A press molding experiment was performed under the same conditions. The glass gob is the glass before pressing, and in this embodiment, the diameter is 37.5.
A disk-shaped one having a thickness of ± 2.5 mm and a thickness of 8.0 ± 1.0 mm was used. The releasability and the amount of nitrogen after pressing were evaluated as described above. Formability is thickness 1.2mm ± 0.1
When a disc of mm was obtained, it was evaluated as ○, and when it was not obtained, as ×.

[0039]

[Table 2]

[0040]

[Table 3]

As is apparent from Tables 2 and 3, the average particle diameter of the powder is preferably 0.01 to 100 μm.
It can be seen that the release layer formation amount is preferably 1 × 10 ^{−5 to} 5 × 10 ⁻¹ g / cm ² . The examples of the present invention satisfying the preferred ranges were excellent in the releasability, the amount of nitrogen after pressing, and the moldability in both carbon-based and BN-based.

Experimental Example 3 An evaporation film was provided as a release layer on the surface of a glass gob having the same composition as in Experimental Example 1, and a press molding experiment was performed. The deposition was performed using a plasma CVD apparatus at a pressure of 2666.4 Pa (2
0 Torr), substrate temperature: 400 ° C., μ-wave power: 90
Performed at 0W. For the composition of the source gas, for example, a mixed gas of CH ₄ and H ₂ was used for a carbon vapor deposition film, and the other components were appropriately changed in composition using a known method.

The conditions for the press molding experiment are the same as those in the experimental example 1. Table 4 shows the results. The same results as in the case of the powder system in Table 1 were obtained.

[0044]

[Table 4]

EXPERIMENTAL EXAMPLE 4 The type, thickness (film thickness) and release layer disposing portion of the release layer formed of a vapor-deposited film were changed as shown in Table 5, and the other conditions were the same as those of Experimental Example 1. A press molding experiment was performed under the conditions. Table 5 shows the evaluation results. Similar results were obtained when glassy carbon was used as the molding die.

[0046]

[Table 5]

As apparent from Table 5, the most suitable thickness (film thickness) of the release layer (deposited film) was 0.001 to 10 μm.

[0048]

According to the method of the present invention, when press-molding oxynitride glass, a release layer containing carbon and / or boron nitride is interposed between the surface of the glass gob and the surface of the molding die. By pressing in this manner, the inconvenience that the pressed glass adheres to the mold was eliminated. In addition, it is possible to press without changing the composition of the glass, and to obtain a press-formed body having a desired shape and dimensions.

Therefore, according to the present invention, a press-formed body of oxynitride glass can be efficiently produced on an industrial scale. Further, the press-formed body of oxynitride glass obtained by the method of the present invention is particularly useful for a high specific rigidity disk for a recording medium such as a magnetic disk.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kazutaka Kunii 1-5-5 Takatsukadai, Nishi-ku, Kobe In the Kobe Research Institute, Kobe Steel Ltd. (72) Inventor Naoya Fujiwara 1, Takatsukadai, Nishi-ku, Kobe City No.5 No.5 F-term in Kobe Steel Research Institute, Kobe Research Institute, Ltd. (reference) 4G015 HA02

Claims (6)

[Claims] 1. A method for press-molding an oxynitride glass using a molding die, wherein the mold release property between the molded oxynitride glass and the molding die is improved.
The amount of nitrogen in the oxynitride glass molded body after pressing was 9 times the amount of nitrogen in the oxynitride glass before pressing.
In order to maintain 0% (mass ratio) or more, carbon and / or carbon between the surface of the oxynitride glass and the surface of the molding die.
Alternatively, a press forming method for oxynitride glass, comprising press forming in a state where a release layer containing boron nitride is present. 2. A method of applying a release agent containing carbon powder and / or boron nitride powder having an average particle diameter of 0.01 to 100 μm to the surface of a molding die and / or the surface of oxynitride glass before pressing. The press molding method according to claim 1, wherein the release layer is provided. 3. The formation amount of the release layer is 1 × 10 ^{−5 to} 5 × 10 ⁵ as a mass per unit surface area of a formation surface of an object.
The press molding method according to claim ² , wherein the weight is ^-1 g / cm2. 4. By depositing carbon and / or boron nitride on the surface of a molding die and / or the surface of oxynitride glass before pressing, to form a deposited film of carbon and / or boron nitride. The press molding method according to claim 1, wherein the release layer according to claim 1 is provided. 5. The release layer has a thickness of 0.001 to 10 μm.
The press molding method according to claim 4, wherein 6. A press-formed body of oxynitride glass formed by press-forming using the press-forming method according to claim 1.