GLASS COMPOSITION, GLASS SHEET AND METHOD FOR PRODUCING SAME, AND SUBSTRATE FOR INFORMATION RECORDING MEDIUM

Abstract

The present invention provides a glass composition having a low density and having a specific elastic modulus high enough to reduce deflection. The glass composition includes, as components, in mol %: 60 to 75% SiO.sub.2; 5 to 15% Al.sub.2O.sub.3; 0.5 to 5% MgO; 0.5 to 10% CaO; 5 to 20% Li.sub.2O; 2 to 10% Na.sub.2O; and 0 to 5% K.sub.2O, and has a density of 2.48 g/cm.sup.3 or less. The glass composition has a specific elastic modulus of, for example, 33.5×10.sup.6 Nm/kg or more.

Claims

1. A glass composition comprising, as components, in mol %: 60 to 75% SiO.sub.2; 5 to 15% Al.sub.2O.sub.3; 0.5 to 5% MgO; 0.5 to 10% CaO; 5 to 20% Li.sub.2O; 2 to 10% Na.sub.2O; and 0 to 5% K.sub.2O, wherein the glass composition has a density of 2.48 g/cm.sup.3 or less.

2. The glass composition according to claim 1, comprising, as components, in mol %: 64 to 71% SiO.sub.2; 7.9 to 11.3% Al.sub.2O.sub.3; 1.1 to 2.8% MgO; 1.8 to 7.4% CaO; 7.0 to 14.3% Li.sub.2O; 3.5 to 8.2% Na.sub.2O; and 0 to 2% K.sub.2O.

3. The glass composition according to claim 1, wherein when a content of a component X in mol % is expressed as [X], [SiO.sub.2]—[Al.sub.2O.sub.3] is 54.0% or more.

4. The glass composition according to claim 1, wherein when a content of a component X in mol % is expressed as [X], ([MgO]+[CaO]) is 2 to 10%.

5. The glass composition according to claim 1, being substantially free of SrO and BaO.

6. The glass composition according to claim 1, wherein when a content of a component X in mol % is expressed as [X], [R.sub.2O] is 12 to 20%, where [R.sub.2O] is the sum of [Li.sub.2O], [Na.sub.2O], and [K.sub.2O].

7. The glass composition according to claim 1, wherein when a content of a component X in mol % is expressed as [X], [Li.sub.2O]>[Na.sub.2O] is satisfied.

8. The glass composition according to claim 1, wherein when a content of a component X in mol % is expressed as [X], ([Na.sub.2O]/([Na.sub.2O]+[Li.sub.2O]) is 0.45 or less.

9. The glass composition according to claim 1, wherein when a content of a component X in mol % is expressed as [X], [R.sub.2O]/([R.sub.2O]+[MgO]+[CaO]) is 0.61 to 0.84, where [R.sub.2O] is the sum of [Li.sub.2O], [Na.sub.2O], and [K.sub.2O].

10. The glass composition according to claim 1, wherein when a content of a component X in mol % is expressed as [X], ([R.sub.2O]+[MgO]+[CaO])/([R.sub.2O]+[MgO]+[CaO]+[Al.sub.2O.sub.3]) is 0.68 to 0.73, where [R.sub.2O] is the sum of [Li.sub.2O], [Na.sub.2O], and [K.sub.2O].

11. The glass composition according to claim 1, wherein a Young's modulus is 80 GPa or more, and a specific modulus is 33.5×10.sup.6 Nm/kg or more.

12. The glass composition according to claim 2, wherein when a content of a component X in mol % is expressed as [X], [SiO.sub.2]—[Al.sub.2O.sub.3] is 56.0% or more, ([R.sub.2O]+[MgO]+[CaO])/([R.sub.2O]+[MgO]+[CaO]+[Al.sub.2O.sub.3]) is 0.68 to 0.73, ([Na.sub.2O]/([Na.sub.2O]+[Li.sub.2O]) is 0.2 to 0.49, and a specific modulus is 33.5×10.sup.6 Nm/kg or more.

13. A glass sheet formed of the glass composition according to claim 1.

14. The glass sheet according to claim 13 being float glass.

15. A substrate for an information recording medium, the substrate comprising the glass sheet according to claim 13.

16. A method for producing a glass sheet, comprising: melting glass raw materials; and shaping the molten glass raw materials into a glass sheet by a float process, wherein the glass raw materials are prepared so that the glass sheet is formed of the glass composition according to claim 1.

Description

EXAMPLES

[0083] Hereinafter, the present invention will be described in more detail using specific examples. The examples given below are not intended to limit the present invention, either.

[0084] Batches were prepared to give compositions shown in Tables 1 to 3 using silica, alumina, lithium carbonate, sodium carbonate, magnesium oxide, calcium carbonate, potassium carbonate, etc. which are common glass raw materials. Each of the prepared batches was put in a platinum crucible, held at 1580° C. for 4 hours, and then poured onto an iron plate. This glass was held in an electric furnace at 650° C. for 30 minutes, after which the furnace was turned off to cool the glass to room temperature. A glass specimen was thus obtained. Properties of thus-obtained glass specimens were measured by the following methods. Tables 1 to 3 show the results. It should be noted that Table 2 show Examples 13 to 16 whose compositions differ from each other in stages between Examples 4 and 8 and Examples 17 to 20 whose compositions differ from each other in stages between Examples 1 and 6.

[0085] [Density ρ and Young's Modulus E]

[0086] Plate-shaped samples having dimensions of 25×25×5 mm were fabricated by cutting the glass specimens and mirror-polishing every surface thereof. The density ρ of each sample was measured by Archimedes' principle. The Young's modulus of each sample was measured according to the ultrasonic pulse method in JIS R 1602-1995. Specifically, each sample used in the above density measurement was used to measure, for longitudinal and transverse waves, the sound speed at which an ultrasonic pulse propagates. The sound speeds and the above density were substituted in the formula defined in JIS R 1602-1995 to calculate the Young's modulus E. The propagation speeds were evaluated using an ultrasonic thickness gage MODEL 25DL PLUS manufactured by Olympus Corporation by dividing the time required by a 20 kHz ultrasonic pulse to propagate in the thickness direction of the sample, be reflected, and then come back by the propagation distance (twice the thickness of the sample).

[0087] [Glass-Transition Point Tg and Linear Thermal Expansion Coefficient CTE]

[0088] A cylindrical specimen having a diameter of 5 mm and a length of 18 mm was fabricated from each glass specimen. The cylindrical specimen was heated at 5° C./minute using a TMA apparatus to measure a thermal expansion curve. From this curve, the glass-transition point Tg and the average linear thermal expansion coefficient CTE in the temperature range of 50 to 350° C. were obtained.

[0089] [Measurement of Devitrification Temperature TL]

[0090] Each glass specimen was crushed into particles, which were sieved to obtain particles that pass through a sieve having an opening size of 2.83 mm and are left on a sieve having an opening size of 1.00 mm. These particles were washed to remove fine powder thereon, followed by drying to prepare a sample for devitrification temperature measurement. An amount of 25 g of the sample for devitrification temperature measurement was put in a platinum boat (a lidless rectangular platinum container) to have an approximately uniform thickness, held in a temperature-gradient furnace for 2 hours, and then taken out of the furnace. The highest temperature at which devitrification was observed in the glass was employed as the devitrification temperature TL of the sample.

[0091] [Measurement of Shaping Temperature T4]

[0092] The viscosity was measured by a platinum ball-drawing method, and a temperature at which the thus-measured viscosity was 10.sup.4 dPas was employed as the shaping temperature T4.

[0093] In each of Examples 1 to 31, the Young's modulus is 80 GPa or more, the density is 2.48 g/cm.sup.3 or less, and the specific elastic modulus is 33.5×10.sup.6 Nm/kg or more. On the other hand, the specific elastic modulus is as low as 33.1×10.sup.6 Nm/kg in Example 32, and the density is beyond 2.48 g/cm.sup.3 in each of Examples 33 to 35. In Tables 1 to 3, the content of the component X is expressed not as [X] but simply as X, and every content is in mol %.

TABLE-US-00001 TABLE 1 Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Ex. 7 Ex. 8 Ex. 9 Ex. 10 Ex. 11 Ex. 12 SiO.sub.2 67.52 67.52 67.52 67.52 67.52 67.52 67.52 67.52 67.92 68.32 68.72 69.12 Al.sub.2O.sub.3 9.21 9.21 9.21 9.21 9.21 9.21 9.21 9.21 9.21 9.21 9.21 9.21 MgO 1.98 1.98 1.98 1.98 1.98 1.60 1.60 1.60 1.98 1.98 1.98 2.0 CaO 5.94 5.94 5.94 5.94 5.94 2.32 2.32 2.32 5.94 5.94 5.94 5.94 Li.sub.2O 7.89 9.10 9.86 10.62 11.38 11.50 12.46 13.42 9.10 9.10 9.10 9.10 Na.sub.2O 7.27 6.07 5.31 4.55 3.79 7.67 6.71 5.75 5.67 5.27 4.87 4.47 K.sub.2O 0.18 0.18 0.18 0.18 0.18 0.18 0.18 0.18 0.18 0.18 0.18 0.18 TiO.sub.2 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Fe2O3 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Total 100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00 Tg (° C.) 527 526 523 521 521 489 491 491 527 531 537 540 CTE (10.sup.−7/° C.) 80 78 77 75 74 86 85 83 75 73 73 71 ρ (g/cm.sup.3) 2.466 2.462 2.460 2.457 2.455 2.435 2.432 2.429 2.459 2.456 2.453 2.449 E (GPa) 82.8 83.7 84.1 84.7 85.2 82.3 83.0 83.4 83.8 84.0 84.0 84.0 E/p (10.sup.6 N .Math. m/kg) 33.6 34.0 34.2 34.5 34.7 33.8 34.1 34.3 34.1 34.2 34.2 34.3 T4 (° C.) 1025 TL (° C.) 1015 1009 1120 1068 1101 959 994 1040 1018 1038 1062 1083 Al.sub.2O.sub.3/(Al.sub.2O.sub.3 + SiO.sub.2) 0.120 0.120 0.120 0.120 0.120 0.120 0.120 0.120 0.119 0.119 0.118 0.118 (R.sub.2O + MgO + CaO)/ 0.716 0.716 0.716 0.716 0.716 0.716 0.716 0.716 0.713 0.709 0.705 0.702 (R.sub.2O + MgO + CaO + Al.sub.2O.sub.3) R.sub.2O/(R.sub.2O + MgO + CaO) 0.660 0.660 0.660 0.660 0.660 0.831 0.831 0.831 0.654 0.647 0.641 0.634 CaO/(CaO + MgO) 0.750 0.750 0.750 0.750 0.750 0.592 0.592 0.592 0.750 0.750 0.750 0.750 Na.sub.2O/(Na.sub.2O + Li.sub.2O) 0.480 0.400 0.350 0.300 0.250 0.400 0.350 0.300 0.384 0.367 0.348 0.329 SiO.sub.2 − Al.sub.2Os 58.3 58.3 58.3 58.3 58.3 58.3 58.3 58.3 58.7 59.1 59.5 59.9 Blanks indicate “not measured”.

TABLE-US-00002 TABLE 2 Ex. 4 Ex. 13 Ex. 14 Ex. 15 Ex. 16 Ex. 8 Ex. 1 Ex. 17 Ex. 18 Ex. 19 Ex. 20 Ex. 6 SiO.sub.2 67.52 67.52 67.52 67.52 67.52 67.52 67.52 67.52 67.52 67.52 67.52 67.52 Al.sub.2O.sub.3 9.21 9.21 9.21 9.21 9.21 9.21 9.21 9.21 9.21 9.21 9.21 9.21 MgO 1.98 1.90 1.83 1.75 1.68 1.60 1.98 1.90 1.83 1.75 1.68 1.60 CaO 5.94 5.22 4.49 3.77 3.05 2.32 5.94 5.22 4.49 3.77 3.05 2.32 Li.sub.2O 10.62 11.18 11.74 12.30 12.86 13.42 7.89 8.61 9.34 10.06 10.78 11.50 Na2O 4.55 4.79 5.03 5.27 5.51 5.75 7.27 7.35 7.43 7.51 7.59 7.67 K.sub.2O 0.18 0.18 0.18 0.18 0.18 0.18 0.18 0.18 0.18 0.18 0.18 0.18 TiO.sub.2 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Fe.sub.2O.sub.3 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Total 100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00 Tg (°C) 521 522 514 509 506 491 527 529 512 507 502 489 CTE (10.sup.−7/° C.) 75 76 78 79 80 83 80 80 81 82 84 86 p (g/cm.sup.3) 2.457 2.451 2.446 2.440 2.434 2.429 2.466 2.459 2.453 2.447 2.440 2.435 E (GPa) 84.7 84.6 84.3 84.0 83.7 83.4 82.8 82.9 82.7 82.6 82.4 82.3 E/p (10.sup.6 N .Math. m/kg) 34.5 34.5 34.5 34.4 34.4 34.3 33.6 33.7 33.7 33.8 33.8 33.8 TL (° C.) 1068 1070 1060 1047 1049 1040 1015 989 958 946 948 959 Al.sub.2O.sub.3/(Al.sub.2O.sub.3 + SiO.sub.2) 0.120 0.120 0.120 0.120 0.120 0.120 0.120 0.120 0.120 0.120 0.120 0.120 (R.sub.2O + MgO + CaO)/ 0.716 0.716 0.716 0.716 0.716 0.716 0.716 0.716 0.716 0.716 0.716 0.716 (R.sub.2O + MgO + CaO + Al.sub.2O.sub.3) R.sub.2O/(R.sub.2O + MgO + CaO) 0.660 0.694 0.728 0.763 0.797 0.831 0.660 0.694 0.728 0.763 0.797 0.831 CaO/(CaO + MgO) 0.750 0.733 0.711 0.683 0.645 0.592 0.750 0.733 0.711 0.683 0.645 0.592 Na.sub.2O/(Na.sub.2O + Li.sub.2O) 0.300 0.300 0.300 0.300 0.300 0.300 0.480 0.460 0.443 0.427 0.413 0.400 SiO.sub.2 − Al.sub.2Os 58.3 58.3 58.3 58.3 58.3 58.3 58.3 58.3 58.3 58.3 58.3 58.3

TABLE-US-00003 TABLE 3 Ex. 21 Ex. 22 Ex. 23 Ex. 24 Ex. 25 Ex. 26 Ex. 27 SiO.sub.2 67.92 68.32 68.72 69.12 69.40 67.90 66.41 Al.sub.2O.sub.3 9.21 9.21 9.21 9.21 8.44 9.21 9.98 MgO 1.60 1.60 1.60 1.60 1.84 1.98 2.12 CaO 2.32 2.32 2.32 2.32 5.51 5.94 6.37 Li.sub.2O 11.98 11.98 11.98 11.98 9.29 9.10 8.91 Na.sub.2O 6.79 6.39 5.99 5.59 5.33 5.67 6.00 K.sub.2O 0.18 0.18 0.18 0.18 0.18 0.18 0.18 TiO.sub.2 0.00 0.00 0.00 0.00 0.01 0.01 0.01 Fe.sub.2O.sub.3 0.00 0.00 0.00 0.00 0.01 0.01 0.01 Total 100.00 100.00 100.00 100.00 100.00 100.00 100.00 Tg (° C.) 494 496 498 499 523 527 531 Td (° C.) 571 579 580 586 608 609 617 CTE (10.sup.−7/° C.) 83 82 80 78 75 76 78 ρ (g/cm.sup.3) 2.432 2.428 2.425 2.422 2.448 2.462 2.474 E (GPa) 82.7 82.9 82.7 82.9 83.3 83.9 84.5 E/p(10.sup.6 N-m/kg) 34.0 34.1 34.1 34.2 340 34.1 34.2 T4 (° C.) 1079 1071 TL (° C.) 1006 1012 1029 1050 1015 1018 1032 Al.sub.2O.sub.3/(Al.sub.2O.sub.3 + SiO.sub.2) 0.119 0.119 0.118 0.118 0.108 0.119 0.131 (R.sub.2O + MgO + CaO)/ 0.713 0.709 0.705 0.702 0.724 0.713 0.703 (RO + MgO + CaO + Al.sub.2O.sub.3) R.sub.2O/(R.sub.2O + MgO + CaO) 0.829 0.825 0.822 0.819 0.668 0.654 0.640 CaO/(CaO + MgO) 0.592 0.592 0.592 0.592 0.750 0.750 0.750 Na.sub.2O/(Na.sub.2O + Li.sub.2O) 0.362 0.348 0.333 0.318 0.365 0.384 0.403 SiO.sub.2 − Al.sub.2O.sub.3 58.7 59.1 59.5 59.9 61.0 58.7 56.4 Ex. 28 Ex. 29 Ex. 30 Ex. 31 Ex. 32 Ex. 33 Ex. 34 Ex. 35 SiO.sub.2 67.60 67.62 67.64 67.66 67.52 65.52 63.52 64.91 Al.sub.2O.sub.3 9.21 9.21 9.21 9.21 9.21 10.21 11.21 10.75 MgO 1.70 1.71 1.73 1.75 1.60 2.17 2.36 2.27 CaO 3.23 3.41 3.59 3.77 2.32 6.50 7.07 6.81 Li.sub.2O 11.62 11.45 11.28 11.11 7.89 8.02 8.15 8.72 Na.sub.2O 6.45 6.40 6.34 6.29 11.27 7.39 7.51 6.34 K.sub.2O 0.18 0.18 0.18 0.18 0.18 0.18 0.18 0.18 TiO.sub.2 0.01 0.01 0.01 0.01 0.00 0.00 0.00 0.01 Fe.sub.2O.sub.3 0.01 0.01 0.01 0.01 0.00 0.00 0.00 0.01 Total 100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00 Tg (° C.) 500 502 504 505 496 529 538 540 Td (° C.) 577 583 584 587 576 607 614 616 CTE (10.sup.−7/° C.) 82 82 82 81 91 82 83 80 ρ (g/cm.sup.3) 2.440 2.441 2.443 2.445 2.447 2.481 2.496 2.486 E (GPa) 83.2 83.4 83.1 83.3 80.9 83.9 85.8 85.1 E/p(10.sup.6 N-m/kg) 34.1 34.2 34.0 34.1 33.1 33.8 34.4 34.2 T4 (° C.) 1032 1036 1054 TL (° C.) 1003 984 995 1010 948 1021 1033 1032 Al.sub.2O.sub.3/(Al.sub.2O.sub.3 + SiO.sub.2) 0.120 0.120 0.120 0.120 0.120 0.135 0.150 0.142 (R.sub.2O + MgO + CaO)/ 0.716 0.715 0.715 0.715 0.716 0.704 0.693 0.694 (RO + MgO + CaO + Al.sub.2O.sub.3) R.sub.2O/(R.sub.2O + MgO + CaO) 0.788 0.779 0.770 0.761 0.831 0.643 0.627 0.627 CaO/(CaO + MgO) 0.655 0.665 0.674 0.683 0.592 0.750 0.750 0.750 Na.sub.2O/(Na.sub.2O + Li.sub.2O) 0.357 0.358 0.360 0.361 0.588 0.480 0.480 0.421 SiO.sub.2 − Al.sub.2O.sub.3 58.4 58.4 58.4 58.5 58.3 55.3 52.3 54.2 Blanks indicate “not measured”. Examples 32 to 35 are Comparative Examples.