JP2002220259A5 - Glass substrate for magnetic recording medium, method for manufacturing glass substrate for magnetic recording medium, and method for manufacturing recording medium - Google Patents

Description

[Claims]
1. A glass substrate for a magnetic recording medium, which is subjected to a treatment for suppressing elution of a glass component,
A glass substrate for a magnetic recording medium , wherein the treatment is a treatment in which the treatment is brought into contact with an aqueous solution containing a lithium salt.
2. A method for producing a glass substrate for a magnetic recording medium, comprising: bringing a substrate made of a glass material into contact with an aqueous solution containing a lithium salt to perform a treatment for suppressing elution of glass components.
3. The method for producing a glass substrate for a magnetic recording medium according to claim 2, wherein the treatment is a treatment in which the substrate made of a glass material is immersed in an aqueous solution of lithium nitrate at 100 ° C. or more and 200 ° C. or less.
4. The method for producing a glass substrate for a magnetic recording medium according to claim 2, wherein the treatment is a treatment of bringing the substrate made of a glass material into contact with an aqueous solution containing a lithium salt and having a pH of 5 to 9.
5. subjected to chemical strengthening treatment on the substrate made of a glass material, a magnetic recording according to any one of claims 2-4 is subjected to suppress the process the elution of the glass component on the substrate after the chemical strengthening treatment A method for manufacturing a glass substrate for a medium .
Wherein said glass component suppressing elution method of producing a glass substrate for a magnetic recording medium according to any one of claims 2-5 is an alkali ion.
7. The glass substrate for a magnetic recording medium manufactured by the manufacturing method of the magnetic recording medium glass substrate according to any one of claims 2-6, recording medium and forming at least a recording layer Manufacturing method.

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention is a glass substrate for a magnetic recording medium, a method of manufacturing a recording medium using the same manufacturing method and a glass substrate for a magnetic recording medium.

Conventionally, aluminum substrates plated with Ni-P have been mainly used as the substrate material for magnetic disks. However, due to demands for smaller, thinner magnetic disks and lower flying heights of magnetic disks, high rigidity and high-speed rotation are required. However, the rate of use of glass substrates for magnetic recording media that are difficult to deform and have high surface smoothness is increasing.

The glass material used for such a glass substrate for a magnetic recording medium contains an alkali metal in an amount of several percent to several tens percent in order to lower the melting point and improve vitrification and moldability. However, since these alkali metals have a small atomic radius and easily migrate, they gradually precipitate on the surface and combine with carbon dioxide and halogen in the atmosphere to precipitate as carbonates and chlorides. This phenomenon of alkali component elution is remarkable under high temperature and high humidity, and recording and reproduction cannot be performed directly, resulting in an error, or transfer to a magnetic head to hinder or corrode the floating, resulting in poor reliability. Cause you to

In order to enhance the effect of suppressing alkali elution, in Japanese Patent Application Laid-Open No. Hei 10-226439 in which an acid treatment is performed, the glass skeleton itself is also destroyed and the amount of alkali ions eluted increases, and the treatment with a molten salt is also performed. According to 2000-82211, since the treatment is performed at a high temperature, in a glass substrate for magnetic recording that has been subjected to a chemical strengthening treatment, diffusion of ions forming a compressive stress on the surface and relaxation of strain due to heat occur, and strength of the glass substrate is reduced. There is a problem that deterioration is likely to occur.

The present invention was made in view of the above, long-term use at high temperature and high humidity, in storage, no strength deterioration, magnetism can be suppressed dissolution such as an alkali component at a high level It is an object to provide a glass substrate for a recording medium, a method for manufacturing the same, and a method for manufacturing a recording medium using the same.

That is, a glass substrate for a magnetic recording medium of the present invention is a glass substrate for a magnetic recording medium processing of suppressing elution of the glass component is being subjected, wherein the process is contacted with an aqueous solution containing a lithium salt treatment It is.

[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
Aqueous glass substrate for a magnetic recording medium according to claim 1 of the present invention is a glass substrate for a magnetic recording medium processing of suppressing elution of the glass component is being subjected, the process, containing a lithium salt Li + in an aqueous solution having an ionic radius smaller than that of Na + and K + is ion-exchanged with Na + and K + on the glass surface to strongly bind to non-crosslinked oxygen in the glass. Elution of glass components can be effectively suppressed, and there is no deterioration in strength as in the conventional example in which a high-temperature treatment is performed using a molten salt.

The method for producing a glass substrate for a magnetic recording medium according to claim 2 of the present invention comprises subjecting a substrate made of a glass material to an aqueous solution containing a lithium salt to perform a treatment for suppressing elution of glass components. Li + in an aqueous solution with a smaller ionic radius than that of + and K + ion-exchanges with Na + and K + on the glass surface and binds strongly to non-crosslinked oxygen in the glass, effectively dissolving the glass components. It can be suppressed, and there is no deterioration in strength as in the conventional example in which high-temperature treatment is performed using a molten salt.

The invention according to claim 3 is the method for manufacturing a glass substrate for a magnetic recording medium according to claim 2, wherein the treatment is performed by subjecting the substrate made of a glass material to an aqueous solution of lithium nitrate at 100 ° C. or more and 200 ° C. or less. This is a treatment for immersion. Since the solubility of lithium nitrate is high and the boiling point of the aqueous solution is also increased, it is possible to perform a treatment for efficiently suppressing elution at a high concentration and at a high temperature. In addition, since the treatment is performed at a temperature of 200 ° C. or less, even for a glass substrate for a magnetic recording medium that has been subjected to a chemical strengthening treatment, there is almost no influence on the compressive stress layer on the surface, and the strength hardly decreases.

The invention according to claim 4 is the method for producing a glass substrate for a magnetic recording medium according to claim 2 or 3, wherein the treatment is performed by adjusting the substrate made of a glass material to a pH of 5 to 9 containing a lithium salt. This treatment is to bring the glass skeleton into contact with an aqueous solution, and by using an almost neutral aqueous solution, the glass skeleton is not broken.

The invention according to claim 5 is the method for producing a glass substrate for a magnetic recording medium according to any one of claims 2 to 4 , wherein the substrate made of a glass material is subjected to a chemical strengthening process, The above-mentioned substrate is subjected to the treatment for suppressing the elution of the glass component, whereby the elution of the glass component can be suppressed and the glass surface can be strengthened.

The invention of claim 6 is a manufacturing method of a glass substrate for a magnetic recording medium according to any one of claims 2-5, wherein the glass component suppressing elution, an alkali ion, Na + Ya Elution of K + can be suppressed.

According to a seventh aspect of the present invention, there is provided a method of manufacturing a recording medium, comprising forming at least a recording layer on a glass substrate for a magnetic recording medium manufactured by the method of manufacturing a glass substrate for a magnetic recording medium according to any one of the second to sixth aspects. Since the recording medium is manufactured using a glass substrate for a magnetic recording medium that does not deteriorate in strength and effectively suppresses elution of glass components, a highly reliable recording medium can be obtained.

The present invention is characterized in that a glass substrate for a magnetic recording medium is brought into contact with an aqueous solution containing a lithium salt to perform a treatment for suppressing the elution of glass components (hereinafter also referred to as “elution suppression treatment”).

Here, the term “contact” includes not only immersion in an aqueous solution but also contact with only one surface of a glass substrate for a magnetic recording medium .

By bringing the glass substrate for a magnetic recording medium into contact with an aqueous solution containing a lithium salt, Li + in the aqueous solution performs ion exchange with Na + and K + on the glass surface. Li + has a smaller ionic radius than Na + and K +, is strongly associated with non-crosslinked oxygen in glass, and has less elution than other alkali ions, thereby effectively dissolving alkali ions. Can be suppressed. In addition, since the elution is suppressed by an aqueous solution, there is no deterioration in strength as in the conventional example in which a high temperature treatment is performed using a molten salt.

The glass composition of the magnetic recording medium glass substrate surface of an embodiment example that a dissolution inhibiting treatment with an aqueous solution containing the Li salt, was analyzed by X-ray photoelectron spectroscopy, K glass substrate surface for a magnetic recording medium and It was confirmed that the composition of Na was 0.5% (atomic ratio) or less.

FIG. 1 is a diagram showing the relationship between the depth of the surface portion and the metal ion concentration in the glass substrate for a magnetic recording medium of this embodiment. Lithium ions are converted to sodium ions and potassium ions on the glass surface by the elution suppression treatment. It can be seen that a layer rich in lithium ions is formed on the outermost surface of the glass.

It is preferable that the glass substrate for a magnetic recording medium is immersed in these aqueous solutions. Among these lithium salts, nitrates are preferred because of their high solubility in water. When the lithium salt is present at a high concentration, the boiling point of the aqueous solution is increased, and the treatment at 100 ° C. or more can be performed while being an aqueous solution. In the case of lithium nitrate, treatment at 180 ° C. is possible by adding 2600 g of lithium nitrate to 1000 g of water.

The effect of suppressing alkali ion elution is more effective when the processing temperature is higher. However, when the processing temperature is too high , the glass substrate for a magnetic recording medium that has been subjected to a chemical strengthening treatment has an ion forming a surface compressive stress. Diffusion and relaxation of strain due to heat occur, resulting in a decrease in strength. For this reason, the processing temperature is preferably 100 ° C to 200 ° C, more preferably 130 ° C to 180 ° C.

In the present invention, before treating the glass substrate for a magnetic recording medium with a heated Li salt aqueous solution, the glass substrate for a magnetic recording medium is preheated to 100 ° C. to 150 ° C. in order to prevent the glass substrate for the magnetic recording medium from cracking. It is preferable to keep it.

During the immersion in the aqueous solution of the elution suppression treatment, i.e., the treatment liquid, the magnetic recording medium glass substrate is held at the end face so that the entire surface of the magnetic recording medium glass substrate can be uniformly ion-exchanged, i.e., In a state where the surface in the thickness direction is supported at a plurality of locations and is substantially vertically set, it is desirable that a portion of the main surface that does not come into contact with the processing liquid is minimized.

Examples of the glass material of the glass substrate for a magnetic recording medium used in the present invention include soda lime glass, aluminosilicate glass, aluminoborosilicate glass, and borosilicate glass. Aluminosilicate glass is preferable because the effect of the chemical strengthening treatment is large and a high-strength substrate can be obtained.

The elution suppression treatment of the glass component of the present invention is effective for a magnetic recording medium glass substrate produced by a polishing method, but is more effective for a pressure-formed magnetic recording medium glass substrate. That is, the glass substrate for a magnetic recording medium manufactured by pressure molding has a higher alkali component concentration than that of a glass substrate for a magnetic recording medium obtained by normal polishing, because the alkali component on the surface is higher than that of the glass substrate during pressure molding. This is because alkali ions, such as sodium ions and potassium ions, diffuse into the glass surface. Therefore, a large amount of sodium ions and potassium ions that can be exchanged with Li + in the elution suppression treatment are present on the surface, and the ion exchange ability is high and effective.

The present invention is also effective for a glass substrate for a magnetic recording medium that has been subjected to a chemical strengthening treatment as required. Chemical strengthening treatment is a method of immersing a glass substrate for a magnetic recording medium in a chemical strengthening treatment liquid that has been melted by heating, and ion-exchanging ions of the magnetic recording medium glass substrate surface layer with ions in the chemical strengthening treatment liquid, that is, This is performed by an ion exchange method. As the ion exchange method, there are a low-temperature ion exchange method and a high-temperature ion exchange method. Considering energy efficiency and damage to the glass surface, it is preferable to employ a low-temperature ion exchange method. In the low-temperature ion exchange method, an alkali ion, for example, Li + or Na + near the surface of a glass substrate for a magnetic recording medium , is immersed in a chemical strengthening treatment solution in a temperature range of a glass transition temperature (Tg) or lower. It substitutes for alkali ions having a large radius, for example, Na + or K +, and generates a strong compressive stress on the glass surface by increasing the volume of the ion-exchanged portion, thereby strengthening the glass surface.

The temperature of the chemical strengthening treatment liquid is preferably high in order to promote ion exchange, but is preferably equal to or lower than the glass transition temperature in order to prevent deformation of the glass substrate for a magnetic recording medium . For example, when processing a glass substrate for a magnetic recording medium made of a glass material having a glass transition point of 450 ° C. to 800 ° C., the temperature of the chemical strengthening treatment solution is 350 ° C. to 700 ° C., particularly 350 ° C. to 450 ° C. Is preferred.

When chemical strengthening, in order to prevent cracking and cracks the glass substrate for a magnetic recording medium, and to prevent the molten salt of the chemical strengthening treatment solution to crystallize the glass substrate surface for a magnetic recording medium, a magnetic It is desirable to preheat the glass substrate for a magnetic recording medium to 200 ° C. to 350 ° C. before immersing the glass substrate for a recording medium in the chemical strengthening treatment liquid.

During immersion in the chemical strengthening treatment liquid, the entire surface of the magnetic recording medium glass substrate is chemically strengthened uniformly, so that the magnetic recording medium glass substrate is held at the end face, that is, the surface in the thickness direction of the substrate is supported at a plurality of locations. Then, it is desirable that a portion that does not come into contact with the processing liquid on the main surface is as small as possible in a state where the processing solution stands substantially vertically.

The magnetic recording medium as the recording medium of the present invention is characterized in that at least a magnetic recording layer as a recording layer is formed on a glass substrate for a magnetic recording medium that has been subjected to the elution suppression process as described above. Here, known magnetic recording layers and other layers can be used.

Since the magnetic recording medium of the present invention uses a glass substrate for a magnetic recording medium in which elution of alkali ions is significantly suppressed, the magnetic recording medium is excellent in weather resistance and life, and exhibits high reliability.

Further, the glass substrate for a magnetic recording medium obtained by the present invention can be applied to optical materials, building materials, mechanical parts, and the like.

[0047]
【Example】
Hereinafter, specific examples of the present invention will be described.
(Example 1)
The glass substrate for a magnetic recording medium in this example was manufactured by the following forming step and elution suppression processing step, and further, a magnetic recording medium was manufactured through a film forming step.
(1) Forming Step A cylindrical glass material made of alumina silicate glass having a softening point of 690 ° C. was prepared as a substrate material. In addition, a pair of molds made of a tungsten carbide cemented carbide was prepared as a mold for pressure molding. The press surface of this mold was flat, and a surface having a center line average roughness of 1 nm was obtained by sputtering a platinum alloy as a protective film on the surface mirror-finished by polishing so as to have a thickness of 1 μm. The pressure molding was performed by sandwiching a glass material on the pressing surface of a mold, heating the material to 690 ° C., and applying a pressure of 350 kg / cm 2 until the glass material had a predetermined thickness. Pressing time was about 1 minute. After pressure molding, the substrate was cooled to obtain a disk glass substrate having a thickness of 0.64 mm and a diameter of 84 mm.
(2) Elution Suppression Treatment Step The glass substrate for a magnetic recording medium after the above-mentioned pressure molding step was treated with an aqueous solution containing a Li salt. A treatment solution prepared by heating an aqueous solution obtained by adding 2600 g of LiNO 3 to 1000 g of pure water and heating to 130 ° C. was prepared. The glass substrate for a magnetic recording medium was preheated to 100 ° C. and then immersed for 1 hour. During immersion, it was held at the end surface of the glass substrate for a magnetic recording medium so that the magnetic recording medium glass substrate surface is uniformly processed. The glass substrate for a magnetic recording medium after the above-mentioned elution suppression treatment is scrub-washed with a neutral detergent and PVA sponge, washed with an alkaline detergent (2% semi-clean (trade name), pH = 12, manufactured by Yokohama Yushi), 18 MΩ The above-mentioned ultrapure water was sufficiently rinsed, and isopropyl alcohol vapor drying was performed.
(3) Film-forming step A Cr underlayer, a Co-Cr-Pt-based magnetic layer, and a C protective layer are sequentially formed on the glass substrate for a magnetic recording medium that has been subjected to the above processing by a sputtering method, and a dip coating method is used. Then, a fluorine-based liquid lubricant was applied to obtain a magnetic recording medium.

The glass substrate for a magnetic recording medium and the magnetic recording medium manufactured as described above were evaluated as follows. That is, the measurement was performed by measuring the bending strength, the alkali elution amount, the surface roughness and the number of errors in the magnetic recording medium on the glass substrate for the magnetic recording medium . Table 1 shows the evaluation methods.

(実施例2)
実施例２は、溶出抑制処理において、処理液の温度を１７０℃とし、処理時間を１０分とした以外は実施例１と同じ条件で製造し、評価した。
(実施例3,4)
実施例３，４は、成形工程を研磨工程で行った以外はそれぞれ実施例１、２と同じ条件で製造し、評価した。研磨による磁気記録媒体用ガラス基板は、実施例１で使用したものと同じガラス材料からなる厚さ１ｍｍのガラス板をφ６５ｍｍに切り出した後、酸化セリウムを用いて厚みが０.６４ｍｍとなるまで研磨した後、コロイダルシリカを用い中心線平均粗さが1ｎｍ以下となるように研磨することにより得た。
(実施例5)
実施例５は、成形工程と溶出抑制処理工程との間に、化学強化処理を施した以外は実施例１と同じである。すなわち、成形工程を終えた磁気記録媒体用ガラス基板を洗浄後、化学強化処理を施したものである。化学強化処理は、硝酸カリウム（６０％）硝酸ナトリウム（４０％）を混合した化学強化処理液を用意し、この化学強化処理液を４００℃に加熱し、３５０℃で予熱した上記磁気記録媒体用ガラス基板を２時間浸漬して行った。浸漬の際には、ガラス表面が均一に処理されるように磁気記録媒体用ガラス基板の端面で保持した。上記化学強化処理を終えた磁気記録媒体用ガラス基板を２００℃まで徐冷し、２０℃の水槽に浸漬して急冷し約２０分間放置した。その後、中性洗剤とＰＶＡスポンジを用いたスクラブ洗浄，１８ＭΩ以上の超純水を用いて十分に濯ぎ、イソプロピルアルコール蒸気乾燥を行なった。
(実施例6)
実施例６は、成形工程を研磨工程で行ったこと以外は実施例５と同じ条件で製造し、評価を行った。研磨による磁気記録媒体用ガラス基板は、実施例２と同じものを用意した。
(比較例)
溶出抑制処理工程における処理以外は実施例１と同じである。比較例として行った溶出抑制処理条件を表２に示す。比較例１は、溶出抑制処理を行なっていない以外は、実施例１と同じである。比較例２は、溶出抑制処理の処理温度を１００℃以下の８０℃としたこと以外は実施例１と同じである。比較例３は、実施例１の処理液に硝酸を添加しｐＨを５以下の２に調整したもの以外は実施例１と同じである。比較例４は、実施例１の処理液に水酸化リチウムを添加しｐＨを９以上の１２に調整したもの以外は実施例１と同じである。

(Example 2)
Example 2 was manufactured and evaluated under the same conditions as in Example 1 except that the temperature of the treatment liquid was set to 170 ° C. and the treatment time was set to 10 minutes in the elution suppression treatment.
(Examples 3, 4)
Examples 3 and 4 were manufactured and evaluated under the same conditions as Examples 1 and 2, respectively, except that the forming step was performed by a polishing step. A glass substrate for a magnetic recording medium was polished by cutting a 1 mm thick glass plate made of the same glass material as that used in Example 1 into φ65 mm, and then polishing it to a thickness of 0.64 mm using cerium oxide. Then, it was obtained by polishing using colloidal silica so that the center line average roughness was 1 nm or less.
(Example 5)
Example 5 is the same as Example 1 except that a chemical strengthening treatment was performed between the molding step and the elution suppression processing step. That is, the glass substrate for a magnetic recording medium after the molding step is washed and then subjected to a chemical strengthening treatment. For the chemical strengthening treatment, a glass for the magnetic recording medium pre-heated at 350 ° C. by heating the chemical strengthening solution to 400 ° C. by preparing a chemical strengthening treatment solution in which potassium nitrate (60%) and sodium nitrate (40%) are mixed. This was performed by immersing the substrate for 2 hours. During the immersion, the glass surface was held on the end surface of the glass substrate for a magnetic recording medium so that the glass surface was uniformly treated. The glass substrate for a magnetic recording medium after the chemical strengthening treatment was gradually cooled to 200 ° C., immersed in a water bath at 20 ° C., rapidly cooled, and left for about 20 minutes. Then, scrub cleaning using a neutral detergent and PVA sponge, sufficiently rinsed using the above ultrapure water 18 M [Omega, becomes the row of isopropyl alcohol vapor drying.
(Example 6)
Example 6 was manufactured and evaluated under the same conditions as Example 5 except that the forming step was performed by a polishing step. The same glass substrate as in Example 2 was prepared by polishing the magnetic recording medium glass substrate.
(Comparative example)
It is the same as Example 1 except for the process in the elution suppression process. Table 2 shows elution suppression treatment conditions performed as comparative examples. Comparative Example 1 is the same as Example 1 except that the elution suppression treatment was not performed. Comparative Example 2 is the same as Example 1 except that the treatment temperature of the elution suppression treatment was set to 80 ° C. which was 100 ° C. or less. Comparative Example 3 is the same as Example 1 except that nitric acid was added to the treatment liquid of Example 1 to adjust the pH to 2 of 5 or less. Comparative Example 4 is the same as Example 1 except that the pH was adjusted to 9 or more to 12 by adding lithium hydroxide to the treatment liquid of Example 1.

実施例1〜６は溶出抑制処理によってアルカリ溶出量は激減しており、エラー数の増加は殆どみられない。成形ガラス基板を用いたもの（実施例１，２）は、研磨基板（実施例３，４）よりもアルカリ溶出量が少なく、成形ガラス基板が有効であることがわかる。また、化学強化処理を施すことによって（実施例５，６）さらにアルカリ溶出量が減少し本処理の併用が極めて有効であることがわかる。

In Examples 1 to 6, the amount of alkali elution was drastically reduced by the elution suppression treatment, and the number of errors hardly increased. Those using a molded glass substrate (Examples 1 and 2) have a smaller amount of alkali elution than the polished substrates (Examples 3 and 4), indicating that the molded glass substrate is effective. In addition, by performing the chemical strengthening treatment (Examples 5 and 6), the alkali elution amount was further reduced, and it was found that the combined use of this treatment was extremely effective.

As described above, by bringing the glass substrate for a magnetic recording medium into contact with an aqueous solution containing a lithium salt, there is no deterioration in the surface properties or strength of the glass, and it is possible to prevent the elution of glass components, particularly alkali ion components. it can. Further, it was confirmed that a glass substrate for a magnetic recording medium obtained by press-molding a heat-softened glass material had a high effect. This process is also effective for chemically strengthened glass substrates for magnetic recording media . Further glass substrate for a magnetic recording medium subjected to the present process, i.e., since the production of magnetic recording medium using a magnetic recording medium glass substrate without eluting effectively suppress the deterioration of strength of glass component, high reliability A magnetic recording medium can be obtained.

[0057]
【The invention's effect】
As described above, according to the present invention, by bringing the glass substrate for a magnetic recording medium into contact with an aqueous solution containing a lithium salt, elution of glass components can be effectively suppressed, and there is almost no deterioration in strength. . Furthermore, a highly reliable recording medium can be obtained by using a glass substrate for a magnetic recording medium that has been subjected to a glass component elution suppression treatment.

[Brief description of the drawings]
FIG.
FIG. 3 is a diagram showing the relationship between the depth of the surface portion and the metal ion concentration in the glass substrate for a magnetic recording medium according to one embodiment of the present invention.