JP2000319036A - Glass for press forming and substrate glass for information recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a glass for press forming which can be easily molten, which is easily press-formed, which can form a precise face identical to the press die, which hardly loses shape, and which has a high so-called chemical reinforcement degree by alkali ion exchange. SOLUTION: The glass is prepared so as to obtain a press-formed product by press forming while the glass is in a thermally softened state, and further to subject the formed body to chemical reinforcement by alkali ion exchange. The compsn. of the component of the glass consists of, by wt.%, 51 to 58 SiO2, 10 to 15 Al2O3, 0 to 3 Li2O, 15 to 25 Na2O, 0 to 4 K2O, 0 to 4 MgO, 0 to 3 CaO, 0 to 3 SrO, 1 to 10 BaO, 0 to 5 TiO2 and 0.5 to 4 ZrO2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for press-molding heat-softened glass and further chemically strengthening the same by alkali ion exchange to obtain glass molded articles such as optical glasses such as lenses and small-sized substrate glasses. The present invention relates to glass for press molding, and particularly to a substrate glass for an information recording medium which can be suitably employed as a magnetic recording medium.

[0002]

2. Description of the Related Art For example, as a substrate glass for an information recording medium, it can be easily melted at a temperature equal to or lower than that of soda-lime-silica glass, has a softening temperature lower than that of soda-lime-silica glass, and is easy to press-mold. Therefore, it is required that a precise surface similar to that of a press die can be formed, the thermal expansion coefficient of both press molds is close to that of the press die, the shape of the press die does not easily collapse, and the degree of so-called chemical strengthening by alkali ion exchange is high.

[0003] Conventionally, once press-molded glass,
Although it is common to employ a polishing method to obtain surface smoothness, polishing is time-consuming and troublesome, and costs are increased, which is not preferable. Although there is another proposal to form a smooth surface by the float molding method, the float molding method is suitable for mass-producing relatively large-sized glass such as a window glass. And not suitable for producing precise substrates.

In known examples, for example, US Pat. No. 4,156,755
In the official gazette, SiO_Two−Al_TwoO_Three−Li_TwoO-Na _TwoFurther Z in O system
rO_TwoIs a glass containing, by ion exchange
Although tempered glass is disclosed, this glass is made of SiO_TwoAnd
And Al_TwoO_Three+ ZrO_TwoRelatively high melting, high molding temperature
And imposed on the formability including press forming
Leave a title.

Japanese Patent Application Laid-Open No. Hei 10-1329 discloses that SiO ₂ —Al ₂ O ₃
-Li A ₂ O-Na ₂ O-CaO-based (ZrO ₂ free), chemically strengthened glass composition suitable for float forming and is chemically strengthened glass article is disclosed. Generally, chemically strengthened glass is likely to be degraded by moisture (moisture), and particularly when used for precision electronic devices such as information recording media, severe weather resistance and moisture resistance are required. It is known that the content of the ZrO ₂ component is excellent in weather resistance and moisture resistance. However, in the known examples, since the ZrO ₂ is not contained, it is difficult to satisfy the above-mentioned properties.

[0006] JP-A-5-32431 discloses SiO ₂ -Al ₂ O ₃
Disclosed is a glass for chemical strengthening composed of —Li ₂ O—Na ₂ O—ZrO ₂ system and a chemically strengthened glass using the same. Conversely, the glass for chemical strengthening of this known example contains ZrO ₂ in an excessive amount. However, an excessive amount increases the melting temperature of the glass and makes molding, particularly press molding, difficult.

Japanese Patent Application Laid-Open No. Hei 10-158028 discloses SiO ₂ —Al ₂ O
_{3 -Na 2 O-K 2 O} -RO-ZrO 2 based glass (the RO is, MgO, Ca
A glass substrate for a magnetic disk and a magnetic disk which are made of O, SrO, and BaO), are hardly damaged, and are suitable for float molding are disclosed. The known glass is made of Na ₂ O
It contains a larger amount of K ₂ O than that of glass, but from the viewpoint of ion exchange of the sodium in the glass by the molten potassium salt, it seems difficult to perform efficient ion exchange. In addition, the melting temperature and the molding temperature are high.

[0008]

That is, there is a problem in the conventional formability such as easy solubility and press molding, insufficient weather resistance and moisture resistance, and satisfactory chemical strengthening by ion exchange. In some cases, the present invention can be easily melted, can be easily press-formed, can form a precise surface following the press mold, and can approximate the thermal expansion coefficient of both the press mold and the mold collapse. It is an object of the present invention to provide a glass for press forming, which is difficult to perform and has a high degree of so-called chemical strengthening by alkali ion exchange, and particularly to provide a substrate glass for an information recording medium which can be suitably employed as a magnetic recording medium.

[0009]

SUMMARY OF THE INVENTION The present invention relates to a glass for press-forming glass in a heat-softened state and further obtaining the above-mentioned press-formed body for subjecting the molded product to chemical strengthening by alkali ion exchange. , composition of the glass, in _{wt%, SiO 2 51~58, Al} 2 O 3 10~15, Li 2 O 0~
_{3, Na 2 O 15~25, K} 2 O 0~4, MgO 0~4, CaO 0~
3, SrO 0-3, BaO 1-10, TiO ₂ 0-5, ZrO ₂ 0.5
It is a glass for press molding in the range of ~ 4.

In the above, it is preferable that the glass has a temperature equivalent to 10 ² poises of 1450 ° C. or less, a temperature equivalent to 10 ⁴ poises of 1000 ° C. or less, and a softening point of 700 ° C. or less.

In addition, the temperature corresponding to 10 ¹⁰ poise of glass is 60
It is desirable that the temperature be 0 ° C or lower.

In addition, the thermal expansion coefficient of the glass (from room temperature to
(Transition point) is preferably 110 to 140 × 10 ⁻⁷ / ° C.

According to the present invention, there is also provided information obtained by press-forming the above-mentioned glass for press-forming at a temperature not higher than its softening point, and further subjecting the formed product to alkali ion exchange in a molten salt containing a potassium salt to chemically strengthen the glass. This is a substrate glass for a recording medium.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The glass for press molding according to the present invention comprises:
From a molten glass obtained by melting, refining, and homogenizing a glass raw material, a preformed body having a shape similar to a target shape is once manufactured by, for example, casting, and then heated again and subjected to press forming. It is manufactured at a stage.
Alternatively, it is also possible to produce the above preformed shape, and in a state of keeping the heat as it is, subject it to press molding after slightly adjusting the heating, and to produce it by a continuous operation.

When the glass is melted, the glass viscosity is 10 ²
In poise, the glass is extremely fluid and effective in melting and homogenizing. Thus 10 ² poise corresponds temperature is also referred to as the melting temperature. The temperature corresponding to a viscosity of 10 ² poise in a general soda-lime-silica glass that is easily melted is in the range of 1400 to 1450 ° C., but the glass of the present invention is equivalent to or less than that, that is, 1450 ° C. or less. .

The temperature for the preforming, that is, the working
The operating temperature is generally 10 ^FourPoise but glass
With a viscosity that is an indicator for thermal processing of
Yes, it also applies to the preforming in the present invention.
You. 10 above^FourPoise equivalent temperature is ordinary soda lime silica
In the system glass is about 1000 ℃, the glass of the present invention
Is also equal to or less than that, that is, 1000 ° C. or less.

In the present invention, the press die base material for press forming is made of a material having heat resistance and excellent wear resistance, that is, alloy steel (for example, austenitic steel), cermet (for example,
TiC-Mo-Ni type), ceramics (for example, alumina, zirconia) and the like are employed. The press-type base material is processed and polished into a desired shape and an optical surface, and furthermore, a heat-softened glass for molding (glass for press molding) can be in close contact with the glass and is hardly eroded by the glass for molding. Thermally and chemically stable thin film, that is, noble metal film, tungsten film,
A forming surface is formed by forming a tantalum film or an alloy film of these metals by, for example, a sputtering method or the like. Conventionally, once the glass is formed, the surface of the formed glass is polished in order to obtain an optical surface, but by performing the above treatment, it is possible to obtain a desired optical surface without polishing. it can.

Of course, the glass to be molded also needs properties suitable for press molding in terms of thermophysical properties and the like in order to obtain the above-mentioned optical surface, and also has properties suitable for further performing ion exchange and chemical strengthening. It is what you need.

The glass viscosity in the press molding, from 10 ^7.6 poise corresponds glass softening point 10 ^{1 2} poise, and more preferably preferably set to 10 ¹⁰ near poise. At a low viscosity of less than 10 ^7.6 poise, the glass to be molded easily adheres to the surface of the press die, and the glass is not easily peeled off, and the glass is easily deformed at the time of peeling. In addition, the press die becomes severely worn. If the viscosity is higher than 10 ¹² poise, the glass to be molded is less likely to be in close contact with the surface of the press die (it is difficult to adapt), and it is difficult to obtain an optical surface that closely follows the surface of the press die.

Regarding the temperature at the time of the press molding, although the press mold base material and the thin film are excellent in heat resistance and abrasion resistance and are excellent in erosion resistance, the optical surface is easily damaged by abrasion when repeatedly pressed at a high temperature. . Therefore, the temperature equivalent to 10 ^7.6 poise (softening point) is 720% for ordinary soda-lime-silica glass.
About 740 ° C., preferably 700 ° C. or less, more preferably viscosity of 60 ° C. at 10 ¹⁰ poise.
The temperature is preferably set to 0 ° C. or lower.

The press forming pressure is 10 kgf / cm ² to 50 kg.
It is better to be in the range of f / cm ² . Press forming pressure 50Kgf / c
If the pressure is higher than m ² , the glass is liable to crack and break, and the press die itself is worn. When the press forming pressure is set to a low pressure of less than 10 kgf / cm ² , it is difficult to obtain an optical surface following the surface of the press die.

In the glass viscosity (temperature) -forming pressure range described above, the glass to be formed is in close contact with the press die (thin film), so that it is possible to obtain an optical surface that is fine and matches the optical surface of the base material.

The coefficient of thermal expansion of glass is similar to that of a press mold. Thermal expansion coefficient is the average value between room temperature and transition point
The temperature is appropriately set within a range of 110 to 140 × 10 ⁻⁷ / ° C. For example, when the press die is a heat-resistant steel represented by austenitic steel, the temperature is set to approximately 110 to 120 × 10 ⁻⁷ / ° C.

In the press-molding glass of the present invention, the chemical strengthening by alkali ion exchange does not specify the conditions, and the strain is not higher than the strain point at which the glass is hardly thermally deformed, and the melting point of the potassium nitrate salt or the mixed salt of sodium nitrate. The glass is immersed in the molten salt at the above temperature, and the ion exchange treatment is performed on the order of several hours. In addition, as a substrate glass for an information recording medium, after a chemical strengthening, in a bending strength test by a three-point bending test in accordance with JIS R 1601 (Bending strength test method of fine ceramics), it is 2.5 × 10 ³ Kgf / cm ² or more. Is preferred.

The glass for press molding has the following composition.

SiO ₂ is a main component forming glass,
It is contained in the glass in the range of 51 to 58% by weight. If the content is less than 51 wt%, glass formation is not easy, devitrification tends to occur, and the weather resistance and water resistance of the glass itself deteriorate. If it exceeds 58% by weight, the glass melting temperature is increased, and the forming temperature is increased in forming including preforming, especially in press forming.

Al ₂ O ₃ is also a component that forms glass together with SiO ₂ , but is an essential component for increasing the ion exchange rate during chemical strengthening. To be contained. If the amount is less than 10% by weight, the above effect is insufficient. If the amount exceeds 15% by weight, the viscosity of the glass is increased, and the temperature of preforming and press forming is increased.

Na ₂ O is an essential component for performing chemical strengthening by ion exchange, and is a component that facilitates glass melting and moldability. Furthermore, there is an advantage that it can be obtained easily and at a lower cost than other alkali metal component raw materials. Na ₂ O is intended to be contained within a range in 15-25 wt% glass, it is less than 15 wt% increases the viscosity of the glass, the melting, increasing the molding temperature. If it exceeds 25% by weight, the viscosity of the glass is lowered unnecessarily, and the weather resistance and water resistance of the glass deteriorate. More preferably, it is in the range of 20 to 25 wt%.

K ₂ O is appropriately introduced as necessary to enhance the melting property of the glass and to adjust the viscosity and the coefficient of thermal expansion of the glass. If the content exceeds 4 wt% in the glass, the coefficient of thermal expansion becomes excessive or the viscosity of the glass becomes unnecessarily low.

Li ₂ O (Li ⁺ ) is a component involved in chemical strengthening by ion exchange with K ⁺ , Na ⁺ and the like. In the component system of the present invention, the above Na ₂ O (Na ⁺ ) is converted to K 2 It is not essential since ion exchange with ⁺ enables sufficient reinforcement. However, Li ₂ O reduces glass melting,
Further, since it has an effect of facilitating molding, it can be appropriately contained in a range of 3 wt% or less. If it exceeds 3% by weight, the viscosity of the glass is lowered unnecessarily, and the cost of raw materials rises.

MgO is a component that is appropriately introduced as necessary to enhance the solubility of the glass and to adjust the viscosity and the coefficient of thermal expansion of the glass. MgO, like CaO, has the advantage of being available at a lower cost than alkali metal component raw materials. However, if the content exceeds 4% by weight in the glass, the ion exchange rate is reduced, so the content is preferably 4% by weight or less.

CaO is also a component that is appropriately introduced as necessary in order to enhance the meltability of the glass and adjust the viscosity and the coefficient of thermal expansion of the glass. If the content exceeds 3% by weight in the glass, the ion exchange rate is reduced.

BaO is an effective component for increasing the meltability of the glass and lowering the liquidus temperature of the glass. Also, Na ₂ O
And K ₂ O or the like to lower the molding temperature without the thermal expansion coefficient of the glass excessively large as alkali metal component, to facilitate the moldability. BaO is contained in the glass in the range of 1 to 10% by weight. If the content is less than 1% by weight, the above-mentioned effect is small, and it is not necessary to contain more than 10% by weight.

TiO ₂ is a component that is appropriately contained in order to adjust the viscosity and the coefficient of thermal expansion of the glass and to improve the weather resistance and the water resistance of the glass. However, if the content exceeds 5% by weight in the glass, the viscosity of the glass is increased, and the melting and formability of the glass are deteriorated.

ZrO ₂ is essential for increasing the ion exchange rate and improving the weather resistance and water resistance of the glass.
It is contained in the glass in the range of 0.5 to 4% by weight. If the content is less than 0.5 wt%, the effects are insufficient, and if it exceeds 4 wt%, the viscosity of the glass is increased, and the melting and molding temperatures are undesirably increased.

[0036]

EXAMPLE [Glass melting] Optical silica sand as a silica source, aluminum oxide as an alumina source, lithium carbonate as a lithium oxide source, sodium carbonate as a sodium oxide source,
Potassium carbonate was used as the potassium oxide source, magnesium oxide was used as the magnesia source, calcium carbonate was used as the calcia source, barium carbonate was used as the barium oxide source, titanium dioxide was used as the titania source, and zircon sand was used as the zirconia source. Each raw material was weighed and prepared.

A blended batch equivalent to 3 kg in terms of glass weight is filled in a 2 L platinum crucible, and preliminarily melted in an electric furnace at 1300 ° C. for 5 hours, and then melted while stirring with a stirrer at 1480 ° C. for 5 hours. The temperature was lowered and clarification was performed at 1300 ° C. for 2 hours. The crucible was taken out and poured into a carbon mold to obtain a glass block. The glass block was further set in an electric furnace preliminarily heated to 600 ° C., maintained for 60 minutes, and then gradually cooled by stopping heating and allowing the furnace to cool.

The cut out portion of the glass obtained Viscosimetry glass], and heated and melted in again a platinum crucible, by a known ball pulling method 10 ² poises corresponding temperature (melting temperature), 10 ⁴ poises corresponding temperature (Working temperature) was measured. Also, cutting out a portion of the glass to heat molding to a predetermined thin line, the softening point by a known fiber elongation method (10 ^7,6 poises equivalent temperature) was measured annealing point (10 ¹³ poises equivalent temperature) . The melting temperature is 1450 ° C or less, the working temperature is 1000 ° C or less, and the softening point is 700 ° C or less.

The above characteristic temperatures (softening point, annealing point)
From the viscosity by known Fulcher - temperature relationship, logη = -A + B / ( T-T O) [ where A, B, T _O is a constant, eta
10 ¹⁰ poise corresponds temperature viscosity, T the absolute temperature (preferably press-molding temperature)
I asked. The press molding temperature is desirably 600 ° C. or less.

[Measurement of Coefficient of Thermal Expansion and Transition Point of Glass] A part of a glass block was cut out and formed into a predetermined rod shape, and the average thermal expansion coefficient between the transition point and room temperature to the transition point was measured with a suggestive thermal dilatometer. I asked.

[Preparation of ion-exchange glass and measurement of bending strength and weather resistance] Further, a glass block was cut and polished to a size of 50 × 10 × 3 mm (thickness). Exchange, then
The bending strength was measured by a three-point bending test in accordance with JIS R 1601 (Testing method for bending strength of fine ceramics).
Good at a strength of 2500 kgf / cm ² or more.

The glass subjected to the same alkali ion exchange treatment was subjected to a continuous 100-hour weather resistance test using a sunshine weather meter. After the test, the surface of the glass is wiped lightly and observed, and no fogging or foreign matter is deposited (mainly due to the reaction between alkali ions on the glass surface and acidic gases such as carbon dioxide and sulfur dioxide in the atmosphere via moisture). Was good and evaluated as passing (indicated by ○), and otherwise unacceptable (indicated by ×).

In the alkali ion exchange, the glass sample was mixed with a molten salt of 100 wt% of potassium nitrate for each sample.
The immersion treatment was performed at 30 ° C. for 4 hours.

[Glass moldability] A glass block is put into a platinum crucible with a nozzle, reheated and defoamed. Then, the nozzle is raised to a molding temperature or higher, and a glass dripping sample (approximately 6 g) on the upper free surface from the nozzle. Was prepared.
This is made of austenitic steel, and the formed optical surface is Pt-
After being coated with a Rh film, it is sandwiched between a pair of lower flat molds, cooled to 400 ° C while hot pressed at 600 ° C for 10 minutes at a pressing pressure of 30 kg / cm ² , and then the pressure is released. And allowed to cool, removed and evaluated.

As evaluation criteria, those having a surface roughness of 4 nm or less according to the stylus method and having no wrinkles or cracks were accepted (indicated by ○), and those having a surface roughness of 4 nm or more or wrinkles. Those having any defects such as cracks were rejected (indicated by X).

The composition of the glass is shown in Table 1, and the results of the above measurements are shown in Table 2.

[0047]

[Table 1]

[0048]

[Table 2]

[Results] In Example Samples Nos. 1 to 10, the thermal properties and moldability of the glass and the bending strength of the ion-exchanged glass were 2700 kgf / cm ² or more in the range of this example, which was considered to be good. Over 2500 Kgf / cm ² ), good in all weather resistance, and comparative sample Nos. 1 to 6
Is inferior in one or more of the above items.

[0050]

According to the present invention, the glass can be easily melted, the press forming is easy, a precise surface following the press mold can be formed, and the thermal expansion coefficient of both the press mold and the mold can be approximated. It is difficult to perform, and it is a glass with a high degree of so-called chemical strengthening by alkali ion exchange,
In particular, it is a substrate glass for an information recording medium that can be suitably used as a magnetic recording medium or the like.

Continued on the front page F term (reference) 4G059 AA09 AB01 AC16 HB03 HB14 HB23 4G062 AA18 BB01 DA06 DB04 DC01 DD01 DE01 DF01 EA01 EA02 EA03 EB04 EC01 EC02 EC03 ED01 ED02 ED03 EE01 EE02 EE03 FC03 EF01 FB02 FF01 FG01 FH01 FJ01 FK01 FL01 GA01 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 GA03 NN30 03A30 GBA 03A30 GAA

Claims (5)

[Claims] 1. A glass for press-molding a glass in a heat-softened state, and further for obtaining said press-formed body for subjecting said molded product to chemical strengthening by alkali ion exchange, wherein the glass has a composition of wt. percent, SiO ₂ 51~58, Al
₂ O ₃ 10-15, Li ₂ O 0-3, Na ₂ O 15-25, K ₂ O 0
4, MgO 0-4, CaO 0-3, SrO 0-3, BaO 1-1
0, TiO ₂ 0~5, the press-molding glass which is a range of ZrO ₂ 0.5 to 4. 2. The glass for press molding according to claim 1, wherein the glass has a temperature equivalent to 10 ² poises of 1450 ° C. or less, a temperature equivalent to 10 ⁴ poises of 1000 ° C. or less, and a softening point of 700 ° C. or less. 3. The glass for press molding according to claim 1, wherein a temperature corresponding to 10 ¹⁰ poises of the glass is 600 ° C. or less. 4. A glass having a coefficient of thermal expansion (room temperature to transition point) of 11
3. The temperature range of 0 to 140 × 10 ⁻⁷ / ° C.
Or the glass for press molding according to 3. 5. The press-molding glass according to claim 1, 2, 3 or 4, which is press-molded at a temperature not higher than its softening point,
The substrate glass for information recording media, wherein the molded product is subjected to chemical strengthening by alkali ion exchange in a molten salt containing a potassium salt.