JP2000007372A - Glass for chemical tempering and glass base for magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce glass for chemical tempering capable of producing glass of high homogeneity, having the low melting temperature and exhibiting excellent weather resistance even after chemical tempering by specifying the glass composition consisting of SiO2, Al2O3, Li2O, Na2O, ZrO2, ZnO and P2O5. SOLUTION: The composition of this glass is set by maintaining the content of ZrO2 for increasing viscosity at high temperatures within a relatively low level and by including ZnO and P2O5 in a preferred quantity respectively for increasing resistance to weather and for promoting chemical tempering. The glass contains 58-65 wt.% SiO2, 8-15 wt.% Al2O3, 4-10 wt.% Li2O, 9-13 wt.% Na2O, 0.5-2 wt.% ZrO2, 2-5 wt.% ZnO and 0.5-2 wt.% P2O5. The glass is prepared by throwing a raw material mixture into a platinum crucible, by heating it in an electric furnace at 1,450 deg.C for 6 h, by molding the resulting glass into a preferred product form and by the ion-exchange treatment through dipping the glass in a mixed fused salt consisting of 40 wt.% sodium nitrate and 60 wt.% potassium nitrate and through retaining the glass at 380 deg.C for 3 h.

Description

DETAILED DESCRIPTION OF THE INVENTION

TECHNICAL FIELD The present invention relates to a chemically strengthened glass, a chemically strengthened glass obtained by strengthening the chemically strengthened glass,
Further, the present invention relates to a glass substrate for an information recording medium using the chemically strengthened glass.

2. Description of the Related Art In general, chemically strengthened glass is prepared by immersing glass in a molten salt containing monovalent ions having a larger ionic radius than the alkali metal contained in the glass composition, so that the alkali metal ions in the glass are eliminated. High strength glass is obtained by exchanging ions in the molten salt and forming a compressive stress layer on the glass surface. Therefore, in the glass for chemical strengthening, a composition containing appropriate amounts of Li and Na as ions to be exchanged is used. Conventionally known chemically strengthened glasses include those described in U.S. Pat. No. 4,156,755, JP-A-62-187140, JP-A-5-32431, and JP-A-8-48537. U.S. Pat. No. 4,156,755 discloses that in weight percent S
iO2 59-63%, Al2O3 15-23%, Li2
O 4 to 5.5%, Na2O 10 to 13%, ZrO2
2-5%, and the weight ratio of Na2 O / ZrO2 is 2.
Disclosed are glasses that are 2-5.5. The above JP
JP-A 62-187140 discloses that SiO2 is 64 to 70% by weight.
%, Al2 O3 14-20%, Li2 O 4-6%, N
a2 O 7-10%, ZrO2 0-1.5%, MgO
Glasses containing 0-4% are disclosed. Japanese Patent Application Laid-Open No. 5-32431 discloses that SiO2 62 to 75% by weight.
%, Al2 O3 5 to 15%, Li2 O 4 to 10%, N
a2 O 4-12%, ZrO2 5.5-15%, the weight ratio of Na2 O / ZrO2 is 0.5-2.0, and the weight ratio of Al2 O3 / ZrO2 is 0.4-2. No. 5 is disclosed. Further, JP-A-8-48537
In the publication, 58 to 70% by weight of SiO2, Al2 O3
13-22%, Li2 O 6-10%, Na2 O5
Glasses having a composition of about 12% and 2-5% ZrO2 are disclosed.

Although chemically strengthened glass has various uses, in recent years it has been used as a substrate for an information recording medium, particularly a magnetic disk substrate.
In such applications, excellent weather resistance that does not cause surface deterioration for a long time even under high temperature and high humidity is required. Conventionally,
Float glass having a soda-lime composition has been widely used as a glass for chemical strengthening.However, this glass is significantly deteriorated in weather resistance when subjected to chemical strengthening treatment. Was not sufficiently reliable. The above-mentioned glass is known as a glass for chemical strengthening having improved weather resistance, and is also applied to a substrate for an information recording medium. On the other hand, the recording density of a recording medium such as a magnetic disk has been dramatically improved, and the flying height of the magnetic head with respect to the magnetic recording medium has become extremely low. For this reason, magnetic disk substrates are required to have extremely high flatness and smoothness on the substrate surface. Normally, the surface of an information recording medium substrate is precisely polished to obtain a predetermined surface property, but the homogeneity of the glass has reached such a level as to affect the product characteristics. In other words, in the case of glass having a high degree of homogeneity, after the polishing treatment, uniform flatness / smoothness can be obtained over the entire substrate,
Glass with low homogeneity may cause partial unevenness in flatness and smoothness and variation between substrates. This may be an obstacle to increasing the density of the recording medium, and may be a serious problem in quality assurance. In light of this background, US Pat. No. 4,156,755 and US Pat.
The glass disclosed in JP 2-187140 is melted at 1600 ° C.
Since high and low temperatures are required, production of highly homogeneous glass has drawbacks accompanied by difficulties. Further, in the glasses described in JP-A-5-32431 and JP-A-8-48537, although a decrease in the melting temperature is observed, the surface of the substrate after the polishing treatment is caused by the inhomogeneity of the glass. There may be variations in roughness. Generally, mass-produced glass is often melted in a continuous melting furnace made of refractories, but refractories are eroded by high-temperature molten glass, and foreign matter and inhomogeneous parts are generated in the glass due to mixing of refractory components. There are drawbacks. For this reason, in glass for electronic and optical applications that require high homogeneity,
When the amount is small, a platinum crucible is used, and when the amount is large, a melting furnace in which the inner wall of the melting tank is covered with platinum is used. Thereby, contact between the refractory and the molten glass is eliminated, and a glass excellent in homogeneity without the above-mentioned glass defects can be obtained. However, since there is a limit to the temperature that platinum itself can withstand, it is desirable that the glass to be melted in a platinum melting furnace can be melted at a temperature of 1460 ° C. or less. The present invention has been made in view of such circumstances, and provides a glass for chemical strengthening that has a low melting temperature at which a highly homogeneous glass can be easily produced and has excellent weather resistance after chemical strengthening. With the goal.

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention suppresses the content of ZrO2, which has the effect of increasing the viscosity at high temperatures, while increasing the amount of ZrO2 to increase weather resistance and promote chemical strengthening. Of ZnO and P2 O5. That is, the present invention relates to a method for producing SiO 2 by mass%.
2 58-65%, Al2 O3 8-15%, Li2 O4
-10%, Na2O 9-13%, ZrO2 0.5-2
%, ZnO 2 to 5%, and P2 O5 0.5 to 2%. Preferably, in mass%, SiO2 58-65%, Al2 O3
9-12%, Li2 O 5-9%, Na2 O 10-1
3%, ZrO2 0.5-1.8%, ZnO 2.5-4.
It is characterized in that it has a composition of 5% and P2 O5 0.7 to 1.8%. Explaining the action of the components constituting the glass and the reasons for limiting the composition range, SiO2 is the main component forming the glass. If it is less than 58%, the chemical durability is poor, and if it exceeds 65%, the melting temperature is high. In any case, it does not meet the purpose of the present invention. A
l2 O3 has the effect of increasing the ion exchange rate and improving the water resistance of the glass. However, if it is less than 8%, the effect is not sufficient, and if it exceeds 15%, the viscosity of the glass melt becomes too high and melting is difficult. Becomes Preferably it is in the range of 9 to 12%. Li2O is a component necessary for ion exchange and has an effect of enhancing the meltability. However, if it is less than 4%, sufficient compressive stress after ion exchange cannot be obtained, and the meltability is poor.
On the other hand, if the content exceeds 10%, the chemical durability deteriorates, which is not preferable. Preferably it is in the range of 5 to 9%.
Na2O is a component necessary for ion exchange like Li2O and is a component for improving the melting property. However, if it is less than 9%, its effect is insufficient, and if it exceeds 13%, the chemical durability deteriorates. ZrO2 increases the ion exchange rate and also contributes to improving the water resistance of the glass. However, if it is less than 0.5%, the effect cannot be obtained. If it exceeds 2%, the melting temperature becomes too high, and it is difficult to obtain a homogeneous glass. Become. Preferably the upper limit is 1.8%
Up to. ZnO increases the ion exchange rate without increasing the melting temperature and improves the water resistance. However, if it is less than 2%, the effect cannot be obtained, and if it exceeds 5%, the workability deteriorates. Preferably, it is in the range of 2.5 to 4.5%. P2
O5 can be expected to act as a melting aid to increase the ion exchange rate and promote uniform vitrification.
If it is less than 5%, the effect is not obtained, and if it exceeds 2%, the glass tends to be devitrified, which is not preferable. Preferably 0.7
範 囲 1.8%. In addition to the above, the glass of the present invention can contain As2 O3, Sb2 O3, F, Cl, etc., which are usually used as fining agents, as long as the desired properties are not impaired. The glass of the present invention adjusted to fall within the above-mentioned composition range is easily ion-exchanged and shows excellent weather resistance even after strengthening treatment by ion exchange. Further, the glass of the present invention is characterized in that the temperature at which the viscosity of the glass becomes 10 Pa · s is 1460 ° C. or less. This temperature is
Normally, the melting point is almost the upper limit of the melting temperature in a platinum glass melting furnace using a silicon carbide heating element, and it is possible to melt at 1460 ° C or less, making it possible to produce highly homogeneous glass with conventional general melting equipment. Becomes On the other hand, if the temperature at which the viscosity of the glass becomes 10 Pa · s is higher than this, the homogeneity of the glass is impaired due to volatilization of components and the like, and it is difficult to achieve the object of the present invention. Further, the present invention is characterized in that the glass for chemical strengthening according to any one of claims 1 and 2 is chemically strengthened by ion exchange in a treatment bath containing at least one of Na ions and K ions. It is chemically strengthened glass. This chemically strengthened glass is obtained by subjecting the glass for chemical strengthening to an ion exchange treatment. The glass for chemical strengthening is Li2O,
Since Na 2 O is contained, in a treatment bath containing Na ions, Li ions in glass are Na ions, and in a treatment bath containing K ions, Na ions in glass are K ions, Na,
In a treatment bath containing both K ions, a both ion exchange reaction similar to the above occurs, and a chemical stress is easily strengthened by forming a compressive stress layer on the glass surface due to a difference in ionic radius. The present invention further provides an information recording medium substrate using the above-mentioned glass. As described above, since the substrate for an information recording medium of the present invention can be melted at a relatively low temperature, an extremely homogeneous glass can be obtained, and thus a very high flatness and smoothness can be obtained even on the substrate surface after polishing. Can be Further, since it has excellent water resistance, the reliability as a substrate for an information recording medium is also high.

Embodiments of the present invention will be described below. The glass for chemical strengthening of the present invention can be produced as follows. First, the above composition range, for example, SiO 2
262.5%, Al2O3 13.0%, Li2O6.
0%, Na2O 12.0%, ZrO2 1.5%, Z
nO 3.0%, P2 O5 1.5%, Sb2 O3 0.5
%, Oxides, carbonates, nitrates, hydroxides and the like, which are usually used as glass raw materials, are weighed and mixed so as to have a composition of%. 1 kg of this raw material mixture is placed in a 1-liter platinum crucible, and heated and melted at 1450 ° C. for 6 hours in an electric furnace. After sufficiently stirring and refining, the mixture is cast into a mold and slowly cooled to obtain a glass. The resulting glass is
It is formed into a predetermined product shape through processing such as slicing and polishing. Next, the ion exchange treatment is performed by immersing the glass in a mixed molten salt of 40% of the reagent first-grade sodium nitrate and 60% of the reagent first-grade potassium nitrate, and holding the glass at 380 ° C. for 3 hours. The treatment bath for performing the ion exchange may use a sulfate, a carbonate, a halide or the like other than the nitrate.
In the case of a substrate for an information recording medium, for example, a magnetic disk substrate, the above-mentioned glass for chemical strengthening is formed into a disk having a hole at the center, and the disk surface is polished. A magnetic disk substrate made of tempered glass is obtained.

EXAMPLES Further, the present invention will be described in detail with reference to examples. Table 1 shows Examples of the present invention, and Table 2 shows Comparative Examples made of conventional glass. Comparative Example 1 in Table 2 is described in US Pat. No. 4,156,755.
Comparative Example 2 is the glass of Example 1 of JP-A-62-187140, and Comparative Example 3 is the glass of Example 4 of JP-A-5-32431. Comparative Example 4 is the glass of Example 3 in JP-A-8-48537. The compositions in the table are shown in mass%, and the raw materials weighed and mixed to obtain the compositions in the table are melted in a platinum crucible and cast into a mold in the same manner as in the above-described embodiment, and the glass for chemical strengthening is used. Sample was obtained. In addition, the platinum rotor was inserted into the molten glass, the high-temperature viscosity was determined from the rotation torque, and the temperature at which the viscosity of the glass became 10 Pa · s was described as “melting point” in the table. The obtained glass sample for chemical strengthening was formed into a disk shape having a thickness of 0.635 mm, an outer diameter of 65 mm, and a hole having a diameter of 20 mm in the center, and the plate surface was mirror-polished, and then the same as in the above embodiment. The sample was ion-exchanged to obtain a chemically strengthened glass sample on a magnetic disk substrate. The surface stress and the surface stress layer depth of each sample of the chemically strengthened glass were measured using a polarizing microscope. The water resistance was measured according to the powder method specified by the Optical Glass Industry Association. The results of these measurements are also shown in the table.

[Table 1]

[Table 2] From the above results, the glass of this example exhibits excellent properties equivalent to those of the comparative example in terms of water resistance, surface stress layer depth, and surface stress, and has practically improved ion exchangeability, strength after chemical strengthening, and water resistance. It turns out that it has sufficient performance. Further, each of the glasses of this example has a low melting point of 1460 ° C. or less, and a highly homogeneous glass can be obtained in a platinum melting furnace. On the other hand, since the glass of the comparative example has a high melting point, the quality tends to vary, and melting in a platinum melting furnace is also difficult.

As described above, according to the present invention, it is possible to obtain a glass for chemical strengthening which has excellent water resistance after chemical strengthening and has sufficient strength at a low melting temperature.
Highly homogeneous glass can be produced economically. Further, the chemically strengthened glass of the present invention obtained by chemically strengthening the glass for chemical strengthening has good water resistance, and has sufficient strength even with a thin plate. Furthermore, since the substrate for information recording media using this chemically strengthened glass has a high homogeneity of the glass, an extremely high flatness and smoothness of the substrate surface can be obtained, and a low flying height of the magnetic head,
It can contribute to higher recording density. In addition, since it is excellent in water resistance, there is no deterioration in quality during storage, the influence on the magnetic recording film formed on the substrate surface is suppressed, and the reliability as a recording medium is improved.

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[Procedure amendment]

[Submission date] August 20, 1998 (1998.8.2
0)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Name of invention

[Correction method] Change

[Correction contents]

Patent application title: Chemical strengthening glass and glass substrate for magnetic recording medium

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4G059 AA20 AC30 HB03 HB13 HB14 4G062 AA01 BB01 DA06 DB03 DB04 DC01 DD02 DD03 DE03 DF01 EA03 EB03 EB04 EC01 ED01 EE01 EF01 EG01 FA01 FB01 FC02 FC03 FD01 FG01 F01 GA10 GB01 GC01 GD01 GE01 HH01 HH03 HH05 HH07 HH09 HH11 HH13 HH15 HH17 HH20 JJ01 JJ03 JJ05 JJ07 JJ10 KK01 KK03 KK05 KK07 KK10 MM27 NN34 5D006 CB04 CB07 DA03 FA03 FA09

Claims (7)

[Claims] 1. A method according to claim 1, wherein the content of SiO2 is from 58 to 65% by mass,
2 O3 8-15%, Li2 O 4-10%, Na2 O
9-13%, ZrO2 0.5-2%, ZnO 2-5
%, P2O5 0.5 to 2%. 2. The composition according to claim 1, wherein the content of SiO2 is from 58 to 65% by weight,
2 O3 9-12%, Li2 O 5-9%, Na2 O1
0-13%, ZrO2 0.5-1.8%, ZnO2.5
Glass for chemical strengthening characterized by having a composition of about 4.5% and P2 O5 of 0.7 to 1.8%. 3. The glass for chemical strengthening according to claim 1, wherein the temperature at which the viscosity of the glass becomes 10 Pa · s is 1460 ° C. or less. 4. The chemical strengthening glass according to claim 1, wherein the glass for chemical strengthening is ion-exchanged in a treatment bath containing at least one of Na ions and K ions. Tempered glass. 5. A glass substrate for a magnetic recording medium having the composition according to claim 1. 6. A glass substrate for a magnetic recording medium having the composition according to claim 2. 7. A glass substrate for a magnetic recording medium, wherein the chemically strengthened glass according to claim 4 is used.