JP2001213633A - Glass for press forming and substrate glass for information recording media - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide glass which has low softening point, is easily press formed at a low temperature capable of forming precise surface following the press mold, is capable of approximating its coefficient of thermal expansion to that of the press mold without getting out of shape, has low transition temperature, is capable of exchanging alkalline ion at a low temperature, and is highly strengthened chemically. SOLUTION: This is lithium-sodium-alminosilicate glass for a press formed article which is press formed of glass in a thermally softened state and chemically toughened by exchanging alkalline ion of that article, where the softening point is 700 deg.C or lower, the transition point is 481 deg.C or lower, and the coefficient of thermal expansion between 30 deg.C and the transition point is 100 to 130 (×10-7/ deg.C).

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, the glass can be easily melted, can be easily press-molded at a relatively low temperature, can form a precise surface similar to a press mold, and can be used together with a press mold. It is required that the thermal expansion coefficients are close to each other, the shape is not easily deformed, 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 the prior art, US Pat. No. 4,156,755
The description states that SiO_Two−Al_TwoO_Three−Li_TwoO-Na _TwoFurther Z in O system
rO_TwoA glass containing, strengthened by ion exchange
Melting and molding temperatures are high,
Problems remain in the formability and moldability (especially press molding).

[0005] JP-A-11-199267 discloses SiO ₂ -Al ₂ O
In ₃ -Li ₂ O-Na ₂ O-based, as a glass for a magnetic disk substrate comprising ZrO ₂ and / or TiO ₂ is disclosed, which has been described that the transition point is 490 ° C. or higher, It does not focus on the transition point.

JP-A-5-32431, JP-A-10-1329 and the like disclose SiO ₂ —Al ₂ O ₃ —Li ₂ O—Na ₂ O-based glass for chemical strengthening. It does not focus on the point and mention it.

[0007] Japanese Patent Application No. 11-80809, filed by the present applicant, discloses a press forming method for press-forming glass in a heat-softened state and further subjecting the formed product to chemical strengthening by alkali ion exchange. in-body glass, chemical composition of the glass, in _{wt%, SiO 2 58~65, Al} 2 O 3 10~15, Li 2 O
_{4~6, Na 2 O 10~13, K} 2 O 0~3, MgO 0~4, C
aO 0-4, SrO 0-2, BaO 1-10, TiO ₂ 0
5, the press-molding glass and ZrO ₂ 1 to 5 ranges, further of the glass 10 ² poises equivalent temperature 1450
° C. or less, 10 ⁴ poises corresponding temperature is 1000 ° C. or less, a softening point of 700
° C or lower, and the temperature equivalent to 10 ¹⁰ poise
It is described that the temperature is 600 ° C. or less. The above glass is applied as a substrate glass for an information recording medium. However,
The transition point is 492 ° C. or higher as described in the specification. In the present invention, this is improved, and the transition point is 481 ° C. or lower, and the coefficient of thermal expansion between 30 ° C. and the transition point is 100 to 130 (× 10 ⁻⁷ / ° C.).

[0008]

That is, the present invention provides:
Low softening point, easy to press mold, can form a precise surface following the press mold, and can approximate the thermal expansion coefficient of both press molds, making it difficult for the mold to collapse, and has a low transition point, alkali ion exchange It is an object of the present invention to provide a press-molding glass which is easily strengthened by so-called chemical strengthening and has a high degree of strengthening, and particularly to provide a substrate glass for an information recording medium which can be suitably used as a magnetic recording medium or the like.

[0009]

According to the present invention, there is provided a lithium-sodium aluminosilicate system for press-molding a glass in a heat-softened state and further subjecting the molded product to chemical strengthening by alkali ion exchange. In glass, the softening point of glass is 700 ° C. or less, the transition point is 481 ° C. or less, and the coefficient of thermal expansion between 30 ° C. and the transition point is 100 to 130 (× 10 ⁻⁷ /
C).

[0010] In the above, the component composition of the glass is
Fraction (%), SiO_Two 59-66, Al_TwoO _Three 7-12, Li_TwoO
4-7, Na_TwoO 12-15, K_TwoO 0-3, MgO 0-4, Ca
O 0-4, SrO 0-2, BaO 1-10, TiO_Two 0 to
5, ZrO_Two The range is 3 to 6.

[0011] The present invention also relates to an information recording medium for press-forming the above-mentioned glass for press-forming in a heat-softened state, and further subjecting the formed product to chemical strengthening by alkali ion exchange in a molten salt containing a potassium salt. Substrate glass.

[0012]

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, the preformed shape may be used, and it may be produced in a continuous operation by subjecting it to a press molding after slightly adjusting the temperature while keeping the heat in a state.

When the glass is melted, the glass viscosity is 10 ²
In poise, the glass is rich in extremely flowability, melt, is effective in helping to homogenize, thus 10 ² poise corresponds temperature is also referred to as the melting temperature. The viscosity 10 ² poise corresponds temperature in soda-lime-silica glass typically melt is facilitated is in the range of from 1,400 to 1,450 ° C., it is also equivalent to that or lower temperatures in the glass of the present invention.

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
It is also preferable that the temperature is equal to or less than that,
New

In the present invention, the press base material used 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, even if glass is once formed, the surface of the formed glass is polished to obtain an optical surface. However, by performing the above-described treatment, the desired optical surface can be formed with almost no subsequent polishing. Obtainable.

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 performing ion exchange and chemical strengthening. It is what you need.

[0017] The glass viscosity in the press molding, the glass
10 equivalent to softening point^7.6Poise or 10 ¹²Poise, even better
Or 10^TenIt is good to be near poise. Ten^7.6Poise not yet
At low viscosity (high temperature), the glass to be molded
It is easy to adhere to the surface of the mold, peeling is not easy, and
The glass is likely to lose its shape during peeling. Also, press die loss
Wear becomes severe. Ten¹²High viscosity over poise (low temperature
Degree), it is difficult for the glass to be molded
(It is hard to be familiar), and optics that closely follows the press mold surface
It becomes difficult to obtain a surface.

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, abrasion resistance and erosion resistance, when pressed repeatedly at a high temperature, the optical surface is easily damaged by abrasion. . Thus glass 10 ^7.6 poise corresponds temperature (softening point), compared ordinary soda-lime-silica based glass in the range of about seven hundred twenty to seven hundred and forty ° C., preferably to the 700 ° C. or less, more preferably a viscosity, i.e. 10 ¹⁰ poise In this case, the temperature is preferably 600 ° C. or less.

The press forming pressure is 10 kgf to 50 kgf / cm.
² (about 1 to 5 MPa). When the press forming pressure is set to a high pressure exceeding 50 kgf / cm ² , the glass is easily cracked and broken, 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 becomes difficult to obtain an optical surface following the surface of the press die.

In the above glass viscosity (temperature) -forming pressure range, 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 thermal expansion coefficient of the glass is 100 to 130 × 10 ⁻⁷ / ° C. as an average value between 30 ° C. and the transition point. This matches or approximates the coefficients of thermal expansion of heat resistant steels used as press dies and most heat resistant ceramics. If the coefficient of thermal expansion is higher or lower than the above range, wrinkles, distortions and other problems occur on the glass surface in the process of cooling while maintaining the pressed state after the start of pressing.

The chemical strengthening treatment after press-molding the glass is carried out by melting the glass in a melt of a potassium nitrate salt or a mixed salt thereof with sodium nitrate at a temperature lower than or close to the transition point at which the glass is less likely to be thermally deformed. It is immersed and applied by ion exchange on the order of several hours. Above the transition point, the glass loses its rigidity and develops viscoelastic properties, and then softens when the temperature is further increased.Therefore, ion exchange at a temperature above the transition point increases the glass strength. Therefore, even if the ion exchange is performed at a temperature much lower than the transition point, efficient ion exchange cannot be performed and an increase in strength cannot be expected. By setting the transition point to a temperature as low as possible, the ion exchange can be efficiently performed at a low temperature close to the temperature. The ion exchange temperature is
This significantly affects the cost of chemical strengthening treatment. In the present invention, by setting the transition point to 481 ° C. or lower, ion exchange at a low temperature according to the transition point is enabled. The substrate glass for an information recording medium has a three-point bending strength after chemical strengthening of 1500 kgf / cm ^2.
The above (approximately 147 MPa or more) is considered effective, but in the present invention, in view of further improvement in strength and ease of handling of the substrate glass, 2000 kgf / cm ² or more (approximately 196 MPa or more) is preferable. is there.

The glass for press molding has the following composition.

SiO ₂ is a main component in forming glass as a glass network former, and
It is contained in the range of 59 to 66% (mass percentage; the same applies hereinafter). If it is less than 59%, the glass is not easily formed, devitrification is likely to occur, and the glass after chemical strengthening by ion exchange is inferior in water resistance. If it exceeds 66%, 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 used to increase the ion exchange rate during chemical strengthening and to improve the water resistance of glass after chemical strengthening. It is an essential component in glass and is 7 ~ 12wt%
Content within the range. If it is less than 7%, the above effect is insufficient. If it exceeds 12%, the glass viscosity is increased, and the temperature and transition point of preforming and press forming are increased. Al ₂ O ₃ is more preferably 7% or more and less than 10% in consideration of thermophysical properties and the like.

Li ₂ O is an essential component for performing chemical strengthening by ion exchange, and is also an essential component for facilitating glass melting and forming at a relatively low temperature and lowering the softening point and the transition point. Is contained in the glass in the range of 4 to 7%. If it is less than 4%, the viscosity of the glass increases, and the melting and molding temperatures increase. If it exceeds 7%, the viscosity of the glass is unnecessarily lowered, and the water resistance of the glass after chemical strengthening by ion exchange deteriorates.

Na ₂ O, like Li ₂ O, is an essential component for performing chemical strengthening by ion exchange, and is a component that facilitates glass melting and moldability and lowers the softening point and the transition point. Also, it can be obtained at lower cost than other alkali metal component raw materials. Na ₂ O is contained in the glass in a range of 12 to 15%. If the content is less than 12%, the viscosity of the glass increases, and the melting,
Increase molding temperature. If it exceeds 15%, the viscosity of the glass is lowered unnecessarily, and the water resistance of the glass after chemical strengthening by ion exchange deteriorates.

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 3% in the glass, the coefficient of thermal expansion becomes excessive, the viscosity of the glass is lowered unnecessarily, and the water resistance of the glass deteriorates.

MgO 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% in the glass, the ion exchange rate is reduced, so that the content is preferably 4% 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 4% in the glass, the ion exchange rate is reduced.

BaO is an effective component for increasing the melting property of the glass and lowering the liquidus temperature of the glass. Also, Na ₂ O
And K lowering the molding temperature without enough alkali metal component ₂ O such that excessive thermal expansion coefficient of the glass, and easy moldability,
In addition, the transition point is not lowered, and the water resistance is not deteriorated unlike the alkali metal component. BaO is 1-10 in glass
%, The effect is small if it is less than 1%, it is not necessary to contain more than 10%, and the thermal expansion coefficient of the glass tends to be excessive.

TiO ₂ is a component that is appropriately contained in order to adjust the viscosity and coefficient of thermal expansion of the glass and to improve the chemical durability of the glass after chemical strengthening by ion exchange.
However, if the content exceeds 5% in the glass, the viscosity of the glass is increased, and the melting and moldability of the glass are deteriorated. Therefore, the content is preferably 5% or less.

ZrO ₂ is essential for increasing the ion exchange rate and improving the water resistance after ion exchange.
It is contained in a range of 3 to 6% in glass. If the amount is less than 3% by weight, the effects are insufficient. If the amount exceeds 6%, the viscosity of the glass is increased, and the melting and molding temperatures are undesirably increased.

[0034]

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 a potassium oxide source, magnesium oxide was used as a magnesia source, calcium carbonate was used as a calcia source, barium carbonate was used as a barium oxide source, titanium dioxide was used as a titania source, and zircon sand was used as a zirconia source. Each raw material was weighed and prepared.

2L of a mixed batch equivalent to 3.5 kg of glass weight
And then preliminarily melted in an electric furnace at 1300 ° C for 5 hours, then melted while stirring with a stirrer at 1450 ° C for 5 hours, then cooled down to 1300 ° C for 2 hours Then, the crucible was taken out and poured into a carbon mold to obtain a glass block. The glass block was set in an electric furnace preliminarily heated to 500 ° C. and maintained for 60 minutes, and then gradually cooled.

[Measurement of Viscosity of Glass] A part of the obtained glass is cut out, heat-formed into a predetermined thin line shape, and softened by a known fiber elongation method and beam bending method (temperature equivalent to ^107,6 poise). , Annealing point (10 ¹³
(Poise equivalent temperature) and strain point (10 ^14,5 Poise equivalent temperature) were measured. Also, heated and melted in a platinum crucible, by a known ball pulling method 10 ² poises corresponding temperature (melting temperature) were measured 10 ⁴ poises corresponding temperature (working temperature). From the above-mentioned respective characteristic viscosities and temperatures, a known viscosity-temperature relational expression by Fulcher, log η = −A + B / (T−T _O ) [where A, B and T _O are constants, η
10 ¹⁰ poise corresponds temperature viscosity, T the absolute temperature (preferably press-molding temperature)
I asked.

The softening point is preferably 700 ° C. or less, and more preferably, the press forming temperature is 600 ° C.
It is desirable to do the following. Although the strain point is not specified, press forming is no longer possible at a temperature lower than this.

[Measurement of thermal expansion coefficient and transition point of glass] A part of a glass block is cut out and formed into a predetermined rod shape.
The transition point and the average coefficient of thermal expansion from room temperature to the transition point were determined by a differential thermal dilatometer.

[Preparation of ion exchange glass and measurement of bending strength and water resistance] Separately, a glass block was cut and mirror-polished to have a bending strength of size 50 × 10 × 3 mm (thickness) and a water resistance of size 50 ×. The sample having a size of 20 × 3 mm (thickness) was immersed in an alkaline solution for ion exchange and subjected to an ion exchange treatment. The conditions are as follows. Ion exchange liquid: 40% sodium nitrate, 60% potassium nitrate (mass%) molten salt (100% potassium nitrate is used for the soda-lime glass of Comparative Example 3) Immersion conditions: temperature Transition point (° C) × about 0.8 (° C) Time 2 hr After the treatment, a sample was taken out, and after cooling and washing, the bending strength and the water resistance were measured. Each condition is as follows. Bending strength: The strength (kgf / cm ² ) is shown as an average value with n = 10 according to JIS R 1601 (Testing method for bending strength of fine ceramics) (standard deviation: about ±
200kgf / cm ² ) In three-point bending strength, strength 2000kgf / cm ² (196MPa)
Good water resistance performance: immersed in pure water of 1 L, 95 ° C for 40 hours. From the sample weight before and after immersion, determine the weight loss (mg) per unit surface area (1 cm ² ). Reduction 0.05 mg / cm ² Good in

[Press Formability of Glass] A glass block is put into a platinum crucible with a nozzle, reheated and defoamed.
The temperature of the nozzle portion was raised to the working temperature or higher, and glass was dropped onto the preforming frame from the end of the nozzle to prepare a preformed body having a free upper surface (a dropping sample having a size of 20 mmφ and a thickness of 5 mm). This is sandwiched between a pair of upper and lower concave molds made of austenitic steel and having a molded optical surface coated with a Pt-Rh film, and hot-pressed under the conditions of 600 ° C for 10 minutes and a press pressure of 30 kg / cm ^2. While being pressed, it was cooled down to 400 ° C., and then the pressure was released to allow it to cool down, taken out, 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 ○), those having a surface roughness of 4 nm or more or wrinkles. Those having any defects such as cracks were rejected (indicated by X). Tables 1 and 2 show the composition of the glass and the results of the above measurements and evaluations.

[Table 1] Examples and Comparative Examples Example 1 Example 2 Example 3 Example 4 Example 5 ───────────── Composition (%) SiO ₂ 62.0 63.0 61.0 62.0 66.0 Al ₂ O ₃ 10.0 9.0 9.0 10.0 7.0 Li ₂ O 5.0 5.0 5.0 5.0 4.0 Na ₂ O 13.0 13.0 13.0 14.0 15.0 K ₂ O-----MgO-----CaO--2.0--BaO 5.0 5.0 5.0 4.0 2.0 TiO ₂ ----- - ZrO ₂ 5.0 5.0 5.0 5.0 6.0 thermal properties thermal expansion coefficient 112 111 113 112 110 melt temperature (10 ² P temperature) 1372 1372 1320 1368 1410 working temperature (10 ⁴ P temperature) 942 935 910 928 962 Press temperature (10 ¹⁰ P temperature) 566 562 564 562 583 transition 480 478 481 472 475 softening point 650 645 637 645 675 distortion point 456 449 445 445 450 chemical strengthening conditions temperature - time 385-2 385-2 385-2 380-2 380-2 Ca Bu Las of the physical and chemical resistance strength ^{(Kgf / cm 2) 2600 2500} 2400 2600 2000 water-resistant 0.02 0.03 0.02 0.02 0.02 mosquito Bu-flops less formability of Las ○ ○ ○ ○ ○ Note 1) Expansion ^{coefficient: α × 10 -7 / ℃ (} 30 ℃ ~ transition point) Note 2) Melt temperature, the working temperature, press temperature, transition point, softening point, strain point: is the same in both ° C. (Table 2)

[Table 2] Examples / Comparative Examples Example 6 Comparative Example 1 Comparative Example 2 Comparative Example 3 ───── Composition (%) SiO ₂ 59.0 63.0 64.0 72.0 Al ₂ O ₃ 11.0 6.0 3.0 2.0 Li ₂ O 6.0 5.0 8.0-Na ₂ O 12.0 18.0 12.0 13.0 K ₂ O 2.0-2.0 1.0 MgO-- --4.0 CaO-5.0-8.0 BaO 2.0 3.0 5.0-TiO ₂ 2.0-3.0-ZrO ₂ 6.0-3.0- Thermophysical thermal expansion coefficient 117 132 138 99 Transition temperature 468 395 365 556 Melting temperature (10 ² P temperature) 1302 1151 1098 1426 Working temperature (10 ⁴ P temperature) 905 772 695 1040 Free temperature (10 ¹⁰ P temperature) 558 475 431 646 Softening point 645 549 508 737 Strain point 439 360 330 513 Chemical strengthening condition temperature -Time 375-2 320-2 290-2 445-2 Physical and chemical strength of glass (Kgf / cm ² ) 2200 1100 1200 2800 Water resistance 0.03 0.09 0.08 0.02 Glass moldability of glass ○ Not performed Not performed × [Result In the range of the examples, the heat including the coefficient of thermal expansion, the transition point, and the softening point Sex is also in the preferred range, it performed by the chemical strengthening treatment is low temperature, enhance the degree of reinforcing glass, both water resistance good. Comparative Examples 1 and 2 are inferior in both the degree of reinforcement and the water resistance. Comparative Example 3 (soda-lime glass) has a high transition point.

[0044]

According to the present invention, the softening point is low, the press molding at a relatively low temperature is easy, the precise surface following the press mold can be formed, and the thermal expansion coefficient of both the press mold and the mold is approximated. It is possible to obtain a glass having a low degree of transition, a low transition point, alkali ion exchange at a relatively low temperature, and a high degree of chemical strengthening. Particularly, it is useful as a substrate glass for an information recording medium such as a magnetic recording medium.

Claims (3)

[Claims] 1. A lithium-sodium-aluminosilicate glass for press molding for press-molding glass in a heat-softened state and further subjecting the molded product to chemical strengthening by alkali ion exchange, wherein the glass has a softening point. 700
A glass for press molding, wherein the glass has a transition temperature of 481 ° C. or lower and a thermal expansion coefficient between 30 ° C. and the transition point of 100 to 130 (× 10 ⁻⁷ / ° C.). 2. The composition of glass has a mass percentage (%).
And SiO ₂ 59-66, Al ₂ O ₃ 7-12, Li ₂ O 4-7, Na ₂
O 12-15, K ₂ O 0-3, MgO 0-4, CaO 0-4,
_{SrO0~2, BaO 1~10, TiO 2 0~5} , ZrO 2 3~6
The glass for press molding characterized by the above-mentioned range. 3. The press-molding glass according to claim 1 or 2, wherein the glass is press-molded in a heat-softened state, and the molded product is chemically strengthened by alkali ion exchange in a molten salt containing a potassium salt. Characteristic substrate glass for information recording media.