JPH0622055B2 - Magnetic disk manufacturing method - Google Patents
Magnetic disk manufacturing methodInfo
- Publication number
- JPH0622055B2 JPH0622055B2 JP59163683A JP16368384A JPH0622055B2 JP H0622055 B2 JPH0622055 B2 JP H0622055B2 JP 59163683 A JP59163683 A JP 59163683A JP 16368384 A JP16368384 A JP 16368384A JP H0622055 B2 JPH0622055 B2 JP H0622055B2
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- substrate
- magnetic disk
- magnetic
- less
- alumina
- Prior art date
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Description
【発明の詳細な説明】 本発明は、アルミナセラミック基板を支持体とした磁気
ディスクの製造方法に関するものである。DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a magnetic disk using an alumina ceramic substrate as a support.
磁気ディスク装置はコンピュータの情報処理システムの
中で情報記憶の中心的な役割を果しているが、近時、こ
の磁気記録は高密度化及び大容量化の傾向にあるため、
スパッタリングなどの薄膜技術を利用して磁気記録媒体
の薄層化及び高面精度化をおこない、その要求に答えよ
うとしている。The magnetic disk device plays a central role of information storage in the information processing system of a computer, but recently, since this magnetic recording tends to have a high density and a large capacity,
By using thin film technology such as sputtering, the magnetic recording medium has been made thinner and the surface accuracy has been improved, and it is trying to meet the demand.
かかる磁気記録媒体が形成される基板にはアルミニウム
合金が使用され、その表面を酸化して得られたアルマイ
ト層が2μ〜15μの厚みで被覆されており、このアルマ
イト層によって基板表面の硬度が大きくなっているが、
この硬貨アルマイト層の厚みが小さく、且つアルミニウ
ム合金とアルマイトの熱膨張係数が異なっているため、
基板温度が上昇するに従い、基板に歪みが発生し易かっ
た。即ち、スパッタリングによって基板上に磁気記録媒
体を形成する際には、スパッタ粒子や電子が基板上に衝
突するため、その衝突エネルギによって基板温度が上昇
し、更に、γ−Fe2O3 から成る磁気記録媒体の場合で
は、通常、300 ℃以上に加熱処理することが行われてお
り、かように基板が被る温度上昇に伴って、アルミニウ
ム基板に歪みが発生し易くなり、これにより、このアル
ミニウム基板に磁気記録媒体を形成して高密度磁気記録
に用いた場合、正確な書き込みや読み取りが出来にくい
という問題があった。An aluminum alloy is used for a substrate on which such a magnetic recording medium is formed, and an alumite layer obtained by oxidizing the surface thereof is coated with a thickness of 2 μ to 15 μ, and the hardness of the substrate surface is large due to the alumite layer. Has become
Since the thickness of this coin alumite layer is small and the aluminum alloy and alumite have different thermal expansion coefficients,
As the substrate temperature increased, the substrate was likely to be distorted. That is, when forming a magnetic recording medium on a substrate by sputtering, since the sputtering particles and electrons impinging on the substrate, the substrate temperature is increased by the collision energy, further consisting of γ-Fe 2 O 3 magnetic In the case of a recording medium, heat treatment is usually performed at 300 ° C. or higher, and the aluminum substrate is likely to be distorted due to the temperature rise of the substrate. When a magnetic recording medium is formed in and used for high density magnetic recording, there is a problem that it is difficult to perform accurate writing and reading.
更に、磁気ディスク装置は、同一の回転軸に複数の磁気
ディスクを配置して1000 〜3000 rmp 位までの高速回転
をさせて、読み取り及び書き込みのデータ処理をおこな
っており、この磁気ディスク用基板がアルミニウム合金
から形成されていると、基板自体が遠心力によって伸び
易くなり、これによっても、高密度磁気記録に適した正
確な書き込み及び読み取りが出来ず、このような書き込
み誤差や読み取り誤差の解決が望まれていた。Further, the magnetic disk device arranges a plurality of magnetic disks on the same rotating shaft and rotates them at a high speed of about 1000 to 3000 rmp to perform read and write data processing. If the substrate is made of an aluminum alloy, the substrate itself tends to expand due to centrifugal force, and this also makes it impossible to perform accurate writing and reading suitable for high-density magnetic recording, and to solve such writing errors and reading errors. Was wanted.
その上、アルミニウム合金製磁気ディスク用基板には、
通常、表面がアルマイト処理されているが、最大5μ位
のボイドが10個位あっても使用されている。そのため
に、高密度記録用磁気ディスク装置にとっては、このボ
イド欠陥に起因して正確な書き込み及び読み取りが出来
ないという問題もあり、ボイド欠陥の少ない磁気ディス
ク用基板材料が望まれていた。In addition, the aluminum alloy magnetic disk substrate,
Normally, the surface is anodized, but it is used even if there are about 10 voids with a maximum of 5μ. Therefore, the magnetic disk device for high-density recording has a problem that accurate writing and reading cannot be performed due to the void defect, and a magnetic disk substrate material having few void defects has been desired.
また、他のディスク基板用材料としてプラスチックやガ
ラスが検討されているが、プラスチックは透湿性が高い
こと、ガラスは割れ易いことと割れた場合の危険性が高
いことが最大の弱点と言われている。そして、プラスチ
ック材料を用いた基板を高速回転させると、ヤング率が
小さいため基板自体が遠心力によって伸び易くなり、前
述と同様な問題があった。Further, although plastics and glass have been studied as other materials for disk substrates, it is said that the plastics have high moisture permeability, the glass is easily broken, and the risk of breaking is high, which is the greatest weakness. There is. When a substrate made of a plastic material is rotated at a high speed, the Young's modulus is small and the substrate itself tends to expand due to centrifugal force, which causes the same problem as described above.
さらに、磁気ディスク基板として、セラミックスを用い
ることも考えられているが、セラミック基板には、1〜
20μmの気孔が多数存在するという問題があった。その
ため、厚み0.5 μm以下の磁性体薄膜を形成した場合
に、被膜欠陥の原因となったり、あるいはヘッドと磁性
膜との距離が遠くなるために記録密度が低下するといっ
た不都合があった。Further, although it is considered to use ceramics as the magnetic disk substrate, the ceramic substrate has
There was a problem that many pores of 20 μm existed. Therefore, when a magnetic thin film having a thickness of 0.5 μm or less is formed, it causes a film defect, or the distance between the head and the magnetic film becomes long, so that the recording density is lowered.
本発明は上述の難点をすべて解消するために完成された
ものであり、その目的はスパッタリングや熱処理に対し
て基板に何ら歪みが発生せず、且つ基板に加えられる遠
心力に対して基板自体の伸びが全く生じることもなく、
更に基板表面にボイド欠陥の少ない材料を用いることに
より、高密度磁気記録に相応しい書き込みや読み取りが
できる磁気ディスク用基板を提供することにある。The present invention has been completed in order to eliminate all the above-mentioned difficulties, and the purpose thereof is to prevent any distortion in the substrate due to sputtering or heat treatment, and to prevent the centrifugal force applied to the substrate from affecting the substrate itself. There is no elongation at all,
Another object of the present invention is to provide a magnetic disk substrate capable of writing and reading suitable for high-density magnetic recording by using a material having few void defects on the substrate surface.
本発明に係る磁気ディスクの製造方法は、平均粒子径1
μm以下で、純度97%以上のアルミナ原料粉末を所定形
状に成形し焼成した後、1000気圧以上の圧力下でHIP 処
理することで、1.0 μ以下の平均ボイド径と、0.01μm
以下の中心線平均粗さを有するアルミナセラミック基板
を作製し、該基板上に磁性膜を形成する工程から成るも
のである。The method of manufacturing a magnetic disk according to the present invention has an average particle size of 1
Alumina raw material powder with a purity of 97% or more at a size of less than μm is molded into a predetermined shape, fired, and then subjected to HIP treatment at a pressure of at least 1000 atm to obtain an average void diameter of 1.0 μ or less and 0.01 μm
It comprises the steps of producing an alumina ceramic substrate having the following centerline average roughness and forming a magnetic film on the substrate.
以下、本発明のアルミナ多結晶体から成る磁気ディスク
の製造方法について詳細に説明する。The method for producing a magnetic disk made of the polycrystalline alumina of the present invention will be described in detail below.
本発明の磁気デイスク用基板はアルミニウム合金製基板
に発生したような欠陥を低減するためアルミナディスク
用基板の製作に際してHIP (Hot Isostatic Pressing、
熱間静水圧加圧)処理することを特徴とするものであ
る。The magnetic disk substrate of the present invention is manufactured by HIP (Hot Isostatic Pressing) when manufacturing the alumina disk substrate in order to reduce defects such as those generated in the aluminum alloy substrate.
Hot isostatic pressing).
即ち、後述する通りにHIP 処理したアルミナディスク用
基板はボイドが著しく少なくなり且つそのボイドの径も
一段と小さくなり、本発明者が繰り返し実験を行ったと
ころ、平均ボイド径を1.0μ以下にすることができ
た。これにより正確な書き込み及び読み取りの出来る高
密度磁気ディスク用基板と成る。That is, as described below, the HIP-treated alumina disk substrate had significantly less voids and the diameter of the voids was further reduced, and when the present inventor repeatedly performed the experiment, the average void diameter was reduced to 1.0 μm or less. I was able to. As a result, a high-density magnetic disk substrate capable of accurate writing and reading is obtained.
本発明のアルミナディスク用基板はアルミニウムなどの
金属やプラスチック等に比べて著しく弾性率が小さいた
め、かかる基板を3000rpm の高速回転を行っても基板自
体が被る遠心力によって基板に全く伸びが生じることも
なかった。Since the alumina disk substrate of the present invention has a significantly smaller elastic modulus than metals such as aluminum and plastics, even if the substrate is rotated at a high speed of 3000 rpm, the substrate itself is stretched due to the centrifugal force applied to the substrate. There was no.
更に本発明によれば、磁気ディスク用基板の高速回転に
伴って生じる板面のうねりが基板自体の高硬度化によっ
て完全に防止できるものであり、殊にHIP 処理アルミナ
基板では後述の実施例で示す通りビッカース硬度Hvで21
00kg/mm2という値を得ている。Furthermore, according to the present invention, the waviness of the plate surface caused by the high-speed rotation of the magnetic disk substrate can be completely prevented by increasing the hardness of the substrate itself. 21 as indicated by Vickers hardness Hv
The value of 00kg / mm 2 is obtained.
本発明の磁気ディスク用基板はHIP 処理アルミナディス
ク用基板を表面研摩することにより中心線平均粗さ(R
a)で0.01μ以下の表面粗さにまで達成でき、その結
果、スパッタリングなどによって形成された磁気記録媒
体が著しく薄くなっても基板表面の表面粗さに起因して
記録媒体の表面に凹凸がほとんど発生せず高密度磁気記
録に向く磁気ディスク用基板となることが判った。The magnetic disk substrate of the present invention has a center line average roughness (R
With a), a surface roughness of 0.01μ or less can be achieved, and as a result, even if the magnetic recording medium formed by sputtering etc. becomes extremely thin, the surface roughness of the substrate surface causes unevenness on the surface of the recording medium. It has been found that it is a substrate for a magnetic disk that is suitable for high-density magnetic recording with almost no occurrence.
更にまた、本発明の磁気ディスク用基板を用いるに当っ
て、磁気記録媒体をその基板表面に被着させる以前に、
高密度磁気記録に効果のある介在層を設けることは何ら
差支えない。Furthermore, in using the magnetic disk substrate of the present invention, before applying the magnetic recording medium to the substrate surface,
There is no problem in providing an intervening layer effective for high density magnetic recording.
次に本発明の磁気ディスク用基板の製法を述べる。Next, a method for manufacturing the magnetic disk substrate of the present invention will be described.
本発明の磁気ディスク用基板を得んがためにはアルミナ
原料粉末の1次平均粒子径及び純度が所定の範囲に設定
することが重要である。即ち、本発明者が種々の実験を
繰り返し行った結果、製造上の他の種々の条件にも関連
するが、1次平均粒子径を1μ以下、且つその純度を97
%以上にしたアルミナ原料粉末を用いてHIP 処理すれば
ディスク用基板表面の平均ボイド径を1.0 μ以下にまで
することができる。In order to obtain the magnetic disk substrate of the present invention, it is important to set the primary average particle diameter and the purity of the alumina raw material powder within a predetermined range. That is, as a result of repeated experiments conducted by the present inventor, although it is related to other various manufacturing conditions, the average primary particle size is 1 μm or less and the purity is 97% or less.
If HIP treatment is performed using alumina raw material powder of which the content is at least 100%, the average void diameter on the disk substrate surface can be reduced to 1.0 μ or less.
斯様なアルミナ原料粉末を用いてWAX エマルジョン、PV
A ,PEG 等の有機物系バインダ、及びSiO2,MgO 等の焼
結助剤を添加し、十分に混合した後、スプレードライヤ
にて乾燥・造粒を行う。次いで、0.6kg/cm2以上の圧力
にてディスク状にプレス成形し、1450〜1750℃の温度範
囲内に設定した雰囲気にて焼成を2〜6時間行う。この
焼成品を窒素もしくはアルゴン雰囲気中、1000〜2000気
圧(ゲージ圧)で、1300〜1800℃の温度範囲内に設定し
て0.5 〜3時間HIP 処理を行う。WAX emulsion, PV using such alumina raw material powder
Add organic binders such as A and PEG, and sintering aids such as SiO 2 and MgO, mix thoroughly, and then dry and granulate with a spray dryer. Then, it is press-molded into a disc shape at a pressure of 0.6 kg / cm 2 or more, and firing is performed for 2 to 6 hours in an atmosphere set within a temperature range of 1450 to 1750 ° C. The fired product is subjected to HIP treatment in a nitrogen or argon atmosphere at a pressure of 1000 to 2000 atm (gauge pressure) within a temperature range of 1300 to 1800 ° C for 0.5 to 3 hours.
かくして得られたHIP 処理アルミナ焼結体は処理前のア
ルミナ焼結体に比べて透明感が顕著に現われる。このHI
P 処理品をラップ、ポリッシ、ファイナルポリッシの研
摩を行って本発明の磁気ディスク用基板を得る。The HIP-treated alumina sintered body thus obtained shows a clearer transparency than the unsintered alumina sintered body. This HI
The P-treated product is lapped, polished and polished to obtain a magnetic disk substrate of the present invention.
また、上記基板上に設ける磁気記録媒体はそれ自体公知
の任意のものであればよく、その膜形成手段も任意のも
のであればよいが、本発明では、磁性膜をスパッタリン
グあるいはメッキにより、連続薄膜の形で設けるのが望
ましい。Further, the magnetic recording medium provided on the above-mentioned substrate may be any known per se, and its film forming means may be any, but in the present invention, the magnetic film is continuously formed by sputtering or plating. It is preferably provided in the form of a thin film.
次に本発明の実施例を述べる。Next, examples of the present invention will be described.
〔実施例1〕 アルミナ粉末(1次平均粒子径0.6 μ、純度99.7%)に
有機物系バインダーとともに焼結助剤MgO を0.2 重量%
加え、ミリングした後、スプレードライヤにて乾燥・造
粒を行った。この粉体の油圧プレス(圧力1.2ton/cm2)
でドーナツ状の円板(外径114 mm、内径30mm、厚み2.4
mm)に成型した。この成型品を1600℃の温度にて3時間
焼成を行ってディスク状焼成品を得た。然る後、アルゴ
ン雰囲気中2000atm 、1500℃にて1時間HIP 処理を行っ
て磁気ディスク用基板(外径95mm、内径25mm、厚み2m
m)を得た。[Example 1] 0.2% by weight of alumina powder (first average particle size: 0.6 µ, purity: 99.7%) and sintering aid MgO together with an organic binder.
In addition, after milling, it was dried and granulated with a spray dryer. This powder hydraulic press (pressure 1.2ton / cm 2 )
A donut-shaped disc (outer diameter 114 mm, inner diameter 30 mm, thickness 2.4
mm). This molded product was baked at a temperature of 1600 ° C. for 3 hours to obtain a disk-shaped baked product. After that, HIP treatment was performed in an argon atmosphere at 2000 atm at 1500 ° C for 1 hour, and a magnetic disk substrate (95 mm outer diameter, 25 mm inner diameter, 2 m thickness)
m) got.
この基板をダイヤモンド砥石(#220 )で研摩したとこ
ろ、表面粗さ3〜6Sが得られた。次いでこの基板の表
面をラッピング及びポリシングによって研摩したとこ
ろ、中心線平均粗さ(Ra)で0.01μの表面粗さにするこ
とができた。When this substrate was polished with a diamond grindstone (# 220), a surface roughness of 3 to 6S was obtained. Then, the surface of this substrate was polished by lapping and polishing, and a center line average roughness (Ra) of 0.01 μ was obtained.
かくして得られた本発明の磁気ディスク用基板につい
て、片面の表面に発生した平均ボイド数、平均ボイド占
有面積比、平均ボイド径及び最大ボイド径をイメージア
ナライザーにより測定したところ、それぞれ順に55個、
0.002 %、0.8 μ及び1.2 μとなり、従来のアルミニウ
ム基板が片面全面に2〜3μのボイドが100 個以上もあ
り、またHIP 処理のないアルミナ多結晶体から成るディ
スク用基板が最大ボイド径50μ位、平均ボイド径15μ位
であることと比較すればボイド欠陥が著しく改善してい
る。Thus obtained magnetic disk substrate of the present invention, the average number of voids generated on the surface of one side, the average void occupation area ratio, the average void diameter and the maximum void diameter was measured by an image analyzer, 55 in each order,
0.002%, 0.8 μ and 1.2 μ, the conventional aluminum substrate has 100 or more voids of 2 to 3 μ on one side, and the disk substrate made of alumina polycrystal without HIP treatment has a maximum void diameter of about 50 μ. The void defects are remarkably improved as compared with the average void diameter of about 15 μm.
更に本発明のディスク用基板はビッカース硬度が2100kg
/mm2、曲げ強度が60kg/mm2とHIP 処理のないアルミナ
多結晶ディスク用基板(ビッカース硬度1800kg/mm2、
曲げ強度33kg/mm2)に比べ、一段と高強度且つ高硬度
であり、ディスク用基板の高速回転に伴って生じる板面
のうねりが全く生じなかった。Furthermore, the disk substrate of the present invention has a Vickers hardness of 2100 kg.
/ mm 2 , flexural strength 60kg / mm 2 and HIP-free substrate for alumina polycrystalline disk (Vickers hardness 1800kg / mm 2 ,
The bending strength was 33 kg / mm 2 ) and the strength and hardness were much higher, and the waviness of the plate surface caused by the high speed rotation of the disk substrate did not occur at all.
本実施例を更に詳述すると、本発明の磁気ディスク用基
板上に、それぞれCoを含んだFeをターゲットとした反応
スパッタリングによってα-Fe2O3膜(厚さ0.2μ)を被
着し、次いで、水素雰囲気中にて320 ℃で還元するのに
伴って、Fe3O4 膜に変換し、空気中にて320 ℃で酸化し
てγ-Fe2O3膜に変換し、高密度磁気ディスクを作成し
た。かようにして得られた磁気ディスクについて、浮上
量が0.2 μでヘッドを浮上させたところ、ヘッドが磁気
ディスクに衝突せず、そして、それぞれについて、信号
エラーを確かめたところ高密度記録の実用上、何ら支障
がないことが判った。This example will be described in more detail. On the magnetic disk substrate of the present invention, an α-Fe 2 O 3 film (thickness 0.2 μm) was deposited by reactive sputtering targeting Fe containing Co, Then, as it is reduced at 320 ℃ in hydrogen atmosphere, it is converted into Fe 3 O 4 film, oxidized in air at 320 ℃ and converted into γ-Fe 2 O 3 film. I made a disc. For the magnetic disks thus obtained, when the head was levitated at a flying height of 0.2 μ, the head did not collide with the magnetic disk, and the signal error was confirmed for each, and it was found that high-density recording was practically used. , I found that there was no problem.
〔実施例2〕 実施例1においてアルミナ原料粉末の1次平均粒子径及
び純度を第1表に示す通りにし、その他は全く実施例1
と同じにしてアルミナディスク用基板を製作した。そし
てこれらの基板の平均ボイド径を測定した。[Example 2] The primary average particle diameter and purity of the alumina raw material powder in Example 1 were as shown in Table 1, and the others were completely Example 1.
A substrate for an alumina disk was manufactured in the same manner as in. And the average void diameter of these substrates was measured.
第1表より明らかな通り、試料番号1,2,4は所定の
アルミナ原料粉を用いたため、平均ボイド径を1.0 μ以
下にすることができた。また比較例として試料番号3,
5,6においては平均ボイド径が大きく、アルミニウム
基板の平均ボイド径に近くなっており、本発明の目的が
達成できなかった。 As is clear from Table 1, since the sample Nos. 1, 2, and 4 used the predetermined alumina raw material powder, the average void diameter could be set to 1.0 μ or less. As a comparative example, sample number 3,
In Nos. 5 and 6 , the average void diameter was large and was close to the average void diameter of the aluminum substrate, and the object of the present invention could not be achieved.
上述の通り、本発明の磁気ディスク用基板では磁気記録
媒体の形成に伴って基体自体に歪みが発生せず、且つ基
板に加わる遠心力に対して基板自体が伸びることもな
く、加えて、中心線平均粗さ(Ra)で0.01μ以下の表
面粗さにまで表面処理できて、その表面に現出したボイ
ド欠陥がアルミニウム合金製基板に比べて著しく小さく
なり、その結果、正確に高密度記録の書き込みや読み取
りができる高信頼性の磁気ディスク用基板が提供でき
る。As described above, in the magnetic disk substrate of the present invention, the substrate itself is not distorted due to the formation of the magnetic recording medium, and the substrate itself is not elongated by the centrifugal force applied to the substrate. The surface roughness can be as low as 0.01μ or less in the line average roughness (Ra), and the void defects appearing on the surface are significantly smaller than those of the aluminum alloy substrate, resulting in accurate high density recording. It is possible to provide a highly reliable magnetic disk substrate capable of writing and reading.
Claims (1)
アルミナ原料粉末を所定形状に成形し焼成した後、1000
気圧より高い圧力下でHIP 処理を施して、平均ボイド径
1.0μm以下で、中心線平均粗さ(Ra)0.01μm以下の
表面を持ったアルミナセラミック基板を作製するととも
に、該基板上に磁性膜を形成する工程からなる磁気ディ
スクの製造方法。1. An alumina raw material powder having an average particle size of 1 μm or less and a purity of 97% or more is molded into a predetermined shape and fired, and then 1000
Alumina ceramic substrate with average void diameter 1.0μm or less and center line average roughness (Ra) 0.01μm or less was prepared by HIP treatment under pressure higher than atmospheric pressure, and magnetic A method of manufacturing a magnetic disk, which comprises the step of forming a film.
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
JP59163683A JPH0622055B2 (en) | 1984-08-02 | 1984-08-02 | Magnetic disk manufacturing method |
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
JP59163683A JPH0622055B2 (en) | 1984-08-02 | 1984-08-02 | Magnetic disk manufacturing method |
Publications (2)
Publication Number | Publication Date |
---|---|
JPS6142730A JPS6142730A (en) | 1986-03-01 |
JPH0622055B2 true JPH0622055B2 (en) | 1994-03-23 |
Family
ID=15778612
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
JP59163683A Expired - Lifetime JPH0622055B2 (en) | 1984-08-02 | 1984-08-02 | Magnetic disk manufacturing method |
Country Status (1)
Country | Link |
---|---|
JP (1) | JPH0622055B2 (en) |
Families Citing this family (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JP2924094B2 (en) * | 1989-06-19 | 1999-07-26 | 住友化学工業株式会社 | Magnetic recording media |
EP0407627A1 (en) * | 1989-07-10 | 1991-01-16 | Leybold Aktiengesellschaft | Process for the treatment of the surface of a substrate |
EP0673023B1 (en) * | 1992-05-26 | 1999-05-19 | Nihon Cement Co., Ltd. | Vacuum-clamping device using ceramic vacuum-clamping board |
Family Cites Families (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JPS514088B2 (en) * | 1971-09-13 | 1976-02-09 | ||
JPS604263B2 (en) * | 1980-10-28 | 1985-02-02 | 株式会社神戸製鋼所 | Manufacturing method of Al alloy plate for magnetic disk substrate |
JPS6022733A (en) * | 1983-07-19 | 1985-02-05 | Hitachi Metals Ltd | Substrate for magnetic disc |
-
1984
- 1984-08-02 JP JP59163683A patent/JPH0622055B2/en not_active Expired - Lifetime
Also Published As
Publication number | Publication date |
---|---|
JPS6142730A (en) | 1986-03-01 |
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