Alkali-Free Aluminoborosilicate Glass

Abstract

Provided is alkali-free aluminoborosilicate glass. The glass is prepared by the following raw materials in percentage by weight: 60-72% SiO.sub.2, 13-18% of Al.sub.2O.sub.3, 8.5-10% of B.sub.2O.sub.3, 1-4.5% of MgO, 3-8% of CaO, 1-5% of SrO, 0.5-2% of ZrO.sub.2, 1-5% of P.sub.2O.sub.5, and 0.1-0.5% of SnO.sub.2, wherein SiO.sub.2+Al.sub.2O.sub.3 is 76-85%; (MgO+CaO+SrO)/Al.sub.2O.sub.3 is 0.4-0.7; the total amount of alkaline earth metal oxide is 5-11.5%; B.sub.2O.sub.3/(B.sub.2O.sub.3+ZrO.sub.2+P.sub.2O.sub.5) is 0.6-0.9; and (ZrO.sub.2+P.sub.2O.sub.5)/(MgO+CaO+SrO) is 0.15-0.8. The glass has the characteristics such as higher strain point, high Young modulus, high hardness, high specific modulus, proper thermal expansion coefficient, and low thermal shrinkage; the boron volatilization rate is as low as 5.6-10.5%, so that the phenomenon of component nonuniformity due to boron volatilization can be effectively controlled; and the glass is suitable for a float forming process, does not contain toxic substances such as As.sub.2O.sub.3 and Sb.sub.2O.sub.3, is environment-friendly, is suitable for large-scale industrial production, and is particularly suitable for glass substrates for LCD/OLED displays.

Claims

1. An alkali-free aluminoborosilicate glass, wherein the alkali-free aluminoborosilicate glass is made of raw materials in following weight percentages: 60-72% of SiO.sub.2, 13-18% of Al.sub.2O.sub.3, 8.5-10% of B.sub.2O.sub.3, 1-4.5% of MgO, 3-8% of CaO, 1-5% of SrO, 0.5-2% of ZrO.sub.2, 1-5% of P.sub.2O.sub.5, and 0.1-0.5% of SnO.sub.2, and a total weight percentage of the raw materials is 100%; wherein SiO.sub.2+Al.sub.2O.sub.3 is 76-85%; (MgO+CaO+SrO)/Al.sub.2O.sub.3 is 0.4-0.7; a total amount of alkaline earth metal oxides is 5-11.5%; B.sub.2O.sub.3/(B.sub.2O.sub.3+ZrO.sub.2+P.sub.2O.sub.5) is 0.6-0.9; and (ZrO.sub.2+P.sub.2O.sub.5)/(MgO+CaO+SrO) is 0.15-0.8.

2. The alkali-free aluminoborosilicate glass according to claim 1, wherein the alkali-free aluminoborosilicate glass is made of raw materials in following weight percentages: 61.8-70.5% of SiO.sub.2, 13-17.5% of Al.sub.2O.sub.3, 8.5-10% of B.sub.2O.sub.3, 1-4.02% of MgO, 3.05-6.2% of CaO, 1.05-4.4% of SrO, 0.5-1.96% of ZrO.sub.2, 1-4.93% of P.sub.2O.sub.5, and 0.1-0.5% of SnO.sub.2; wherein SiO.sub.2+Al.sub.2O.sub.3 is 77.4-83.5%; (MgO+CaO+SrO)/Al.sub.2O.sub.3 is 0.42-0.65; a total amount of alkaline earth metal oxides is 5.45-10.3%; B.sub.2O.sub.3/(B.sub.2O.sub.3+ZrO.sub.2+P.sub.2O.sub.5) is 0.62-0.83; and (ZrO.sub.2+P.sub.2O.sub.5)/(MgO+CaO+SrO) is 0.15-0.7.

3. The alkali-free aluminoborosilicate glass according to claim 1, wherein the glass has a β-OH value lower than 0.5%, a boron volatilization rate lower than 11%, a thermal expansion coefficient lower than 39.5×10.sup.−7/° C. in the range of 50-350° C., a Young's modulus higher than 78 GPa, a strain point higher than 690° C., a melting temperature lower than 1662° C., and a thermal shrinkage rate lower than 11.5 ppm.

4. The alkali-free aluminoborosilicate glass according to claim 1, wherein the glass has 0.11-0.47% of a β-OH value, 5.67-10.37% of a boron volatilization rate, 33.70-39.5×10.sup.−7/° C. of a thermal expansion coefficient in the range of 50-350° C., 78.2-84.1 GPa of a Young's modulus, 690-739° C. of a strain point, a melting temperature lower than 1662° C., and 7.68-11.45 ppm of a thermal shrinkage rate.

5. The alkali-free aluminoborosilicate glass according to claim 2, wherein the glass has a β-OH value lower than 0.5%, a boron volatilization rate lower than 11%, a thermal expansion coefficient lower than 39.5×10.sup.−7/° C. in the range of 50-350° C., a Young's modulus higher than 78 GPa, a strain point higher than 690° C., a melting temperature lower than 1662° C., and a thermal shrinkage rate lower than 11.5 ppm.

6. The alkali-free aluminoborosilicate glass according to claim 2, wherein the glass has 0.11-0.47% of a β-OH value, 5.67-10.37% of a boron volatilization rate, 33.70-39.5×10.sup.−7/° C. of a thermal expansion coefficient in the range of 50-350° C., 78.2-84.1 GPa of a Young's modulus, 690-739° C. of a strain point, a melting temperature lower than 1662° C., and 7.68-11.45 ppm of a thermal shrinkage rate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0035] In order to make the objects, technical solutions, and advantages of the present invention more clear, the present invention will be described in detail with reference to following examples. Obviously, the described examples are only a part of the examples of the present invention, rather than all of the examples. All other examples obtained by those skilled in the art based on the examples in the present application will fall within the protection scope of the application.

[0036] The present invention provides a method for preparing an alkali-free aluminoborosilicate glass, using the formula described in Table 1-5, wherein SiO.sub.2, Al.sub.2O.sub.3, B.sub.2O.sub.3, MgO, CaO, SrO, ZrO.sub.2, and P.sub.2O.sub.5 mean that the composition contains Si-containing compounds, Al-containing compounds, B-containing compounds, Mg-containing compounds, Ca-containing compounds, Sr-containing compounds, Zr-containing compounds, and P-containing compounds, such as carbonate, nitrate, sulfate, oxide, etc. of the aforementioned elements. The content of each component is measured in the oxide of each element. According to different glass preparation processes, the composition contains a clarifying agent. There is no particular limitation on the specific choice of clarifying agent, and various clarifying agents commonly used in the field can be selected. Under heating conditions, the SiO.sub.2, Al.sub.2O.sub.3, B.sub.2O.sub.3, MgO, CaO, SrO, ZrO.sub.2 and P.sub.2O.sub.5 are evenly mixed and then subjected to high-temperature melting (1450-1650° C.), clarification and homogenization, molding, and annealing (higher than 600° C.) to obtain an alkali-free aluminoborosilicate glass substrate, which is then such as cutted, grinded, and polished.

[0037] The glass does not substantially contain alkali metal oxides and does not substantially contain BaO.

[0038] The clarifying agent may be any one of calcium sulfate, strontium nitrate, and calcium chloride, or may be a composite clarifying agent, such as containing at least one of sulfate, nitrate, and chloride.

[0039] Those skilled in the art should understand that the method of controlling the β-OH value of the present invention includes: selecting raw materials with low water content; adding components that reduce the water content in the glass (such as adding sulfates, chlorides, etc.); reducing the water content in the furnace environment; bubbling with nitrogen in the molten glass; adopting a small furnace; accelerating the flow of the molten glass; and using an electric melting method. These methods are well known to those skilled in the art, and will not be detailed here.

[0040] In an embodiment of the present invention, the alkali-free aluminoborosilicate glass of the present application can be prepared by the following steps:

[0041] (1) weighing the batch materials and mixing them thoroughly;

[0042] (2) smelting the mixed glass batch materials at 1450-1650° C. for 7-12 h, and then clarifying at 1600-1700° C. for 60-120 minutes; and

[0043] (3) slip casting, annealing at 600-750° C. for 5-10 h.

[0044] Preferably, the glass composition of the present invention has 0.11-0.47% of a β-OH value, 5.67-10.37% of a boron volatilization rate, 33.70-39.5×10.sup.−7/° C. of a thermal expansion coefficient in the range of 50-350° C., 690-739° C. of a strain point, a melting temperature lower than 1662° C., and 7.68-11.45 ppm of a thermal shrinkage rate.

[0045] The present invention provides the use of the glass composition of the present invention as an alkali-free aluminosilicate glass in the preparation of display devices and/or optoelectronic devices, preferably in the preparation of TFT-LCD glass substrates and/or OLED glass substrates.

[0046] In the following examples and comparative examples:

[0047] the alkali-free aluminoborosilicate glass is prepared by the following steps:

[0048] (1) weighing the batch materials according to the proportions in Table 1 to Table 5, and mixing them thoroughly;

[0049] (2) smelting the mixed glass batch at 1500° C. for 10 h, and then clarifying at 1650° C. for 90 minutes;

[0050] (3) slip casting, annealing at 650° C. for 10 h; and

[0051] (4) processing and subjecting to performance tests.

[0052] The performance tests include:

[0053] analyzing and calculating the hydroxyl content in the glass by using Fourier transform infrared spectrometer, in %;

[0054] obtaining the boron volatilization rate by comparing the boron content with the amount of boron in the glass raw material, in %;

[0055] measuring the thermal expansion coefficient of glass at 50-350° C. with a horizontal dilatometer according to ASTME-228, in 10.sup.−7/° C.;

[0056] determining the Vickers hardness (HV) with an automatic turret digital micro Vickers hardness tester according to GB/T4340.2-2012;

[0057] measure the Young's modulus of glass with a material mechanics testing machine according to ASTM C-623, in GPa; calculating and obtaining the specific modulus from the ratio of Young's modulus and density, in GPa/(g×cm.sup.−3);

[0058] measuring the annealing point and strain point of the glass using a three-point tester according to ASTMC-336 and ASTMC-338 , in ° C.;

[0059] measuring the high-temperature viscosity-temperature curve of glass with a rotary high-temperature viscometer according to ASTMC-965, where the corresponding temperature at 200 P viscosity is the melting temperature, and the unit is ° C.; and

[0060] obtaining the thermal shrinkage with the difference calculation method. The method comprise: a glass substrate without any defects is used and the initial length is marked as L0, after a certain condition of heat treatment (for example, the heat treatment process conditions of the present invention are: heating the glass from room temperature to 600° C. at a heating rate of 10° C./min and holding it for 10 minutes, and then lowering the temperature to the room temperature at a cooling rate of 10° C./min), the length of the substrate shrinks by a certain amount, and the length is measured again, marked as Lt, and the thermal shrinkage Yt is expressed as:

[00001]$\mathrm{Yt}=\frac{L0-\mathrm{Lt}}{L0}\times 100\%.$

[0061] Specific examples and comparative examples are given below, in which each component in the formula is measured by weight percentage, see Tables 1, 2, 3, 4, and 5:

TABLE-US-00001 TABLE 1 Exam- Exam- Exam- Exam- Exam- Exam- Exam- Exam- Component wt % ple 1 ple 2 ple 3 ple 4 ple 5 ple 6 ple 7 ple 8 SiO.sub.2 60.15 60.26 60.39 60.53 61.45 61.57 61.64 61.89 Al.sub.2O.sub.3 17.59 16.50 17.01 16.42 16.56 16.22 18.00 16.44 B.sub.2O.sub.3 8.94 9.81 9.92 8.53 8.81 9.13 8.50 8.73 MgO 1.86 2.53 1.26 2.57 2.78 2.04 2.48 3.47 CaO 4.11 3.38 6.43 5.56 6.19 5.35 3.56 3.25 SrO 1.42 1.53 2.37 3.08 1.19 2.30 2.32 4.32 ZrO.sub.2 0.50 0.80 1.00 1.71 0.71 1.51 1.36 0.79 P.sub.2O.sub.5 4.93 4.89 1.12 1.10 2.20 1.75 1.99 1.01 SnO.sub.2 0.50 0.30 0.50 0.50 0.11 0.13 0.15 0.10 SiO.sub.2 + Al.sub.2O.sub.3 77.74 76.76 77.40 76.95 78.01 77.79 79.64 78.33 (MgO + CaO + SrO)/Al.sub.2O.sub.3 0.42 0.45 0.59 0.68 0.61 0.60 0.46 0.67 Total amount of alkaline earth 7.39 7.44 10.06 11.21 10.16 9.69 8.36 11.04 metals B.sub.2O.sub.3/(B.sub.2O.sub.3 + ZrO.sub.2 + P.sub.2O.sub.5) 0.62 0.63 0.82 0.75 0.75 0.74 0.72 0.83 (ZrO.sub.2 + P.sub.2O.sub.5)/(MgO + CaO + SrO) 0.73 0.76 0.21 0.25 0.29 0.34 0.40 0.16 β-OH 0.36 0.29 0.19 0.24 0.3 0.39 0.38 0.4 Volatilization rate of boron, % 9.56 10.33 10.17 9.23 8.42 9.71 10.35 10.06 Thermal expansion coefficient 39.5 38.1 38.8 35.9 36.6 35.7 39.4 36.8 (50-350° C.), 10.sup.−7/° C. Young's modulus, GPa 78.90 80.6 79.8 81.2 80.4 79.9 81.8 78.3 Vickers hardness, Hv 679.7 677.1 676.3 673.8 674.7 679.4 680.8 678.3 Specific modulus, GPa/g × cm.sup.−3 30.46 31.24 30.69 31.21 32.83 31.49 32.04 31.63 Strain point, ° C. 711.00 706 690 712 720 704 693 726 Melting temperature, T.sub.2.3 ° C. 1601 1612 1606 1613 1608 1632 1613 1622 Thermal shrinkage 10.84 11.03 9.05 10.74 11.37 7.68 11.29 10.48 (600° C., 10 min), ppm

TABLE-US-00002 TABLE 2 Exam- Exam- Exam- Exam- Exam- Exam- Exam- Exam- Component wt % ple 9 ple 10 ple 11 ple 12 ple 13 ple 14 ple 15 ple 16 SiO.sub.2 62.35 62.51 62.73 62.80 63.24 63.73 63.81 64.17 Al.sub.2O.sub.3 16.11 16.03 15.30 15.19 15.52 14.32 14.52 14.05 B.sub.2O.sub.3 9.23 8.62 10.00 9.31 8.72 8.81 9.01 8.55 MgO 4.02 2.85 4.01 3.25 3.13 1.65 2.56 1.95 CaO 3.66 4.69 5.14 4.17 3.25 4.16 5.03 4.14 SrO 2.61 1.83 1.15 1.14 1.19 3.55 2.15 2.08 ZrO.sub.2 0.58 1.21 0.55 1.10 0.55 1.59 1.31 1.21 P.sub.2O.sub.5 1.29 2.14 1.01 2.89 4.27 2.07 1.46 3.74 SnO.sub.2 0.15 0.12 0.11 0.15 0.13 0.12 0.15 0.11 SiO.sub.2 + Al.sub.2O.sub.3 78.46 78.54 78.03 77.99 78.76 78.05 78.33 78.22 (MgO + CaO + SrO)/Al.sub.2O.sub.3 0.64 0.58 0.67 0.56 0.49 0.65 0.67 0.58 Total amount of alkaline earth 10.29 9.37 10.30 8.56 7.57 9.36 9.74 8.17 metals B.sub.2O.sub.3/(B.sub.2O.sub.3 + ZrO.sub.2 + P.sub.2O.sub.5) 0.83 0.72 0.87 0.70 0.64 0.71 0.76 0.63 (ZrO.sub.2 + P.sub.2O.sub.5)/(MgO + CaO + SrO) 0.18 0.36 0.15 0.47 0.64 0.39 0.28 0.61 β-OH 0.37 0.34 0.32 0.28 0.31 0.35 0.24 0.18 Volatilization rate of boron, % 9.52 10.37 9.19 8.62 7.06 8.87 9.45 10.23 Thermal expansion coefficient 37.1 38.5 36.4 39.3 37.9 35.2 34.6 36.9 (50-350° C.), 10.sup.−7/° C. Young's modulus, GPa 80.6 78.2 79.4 81.7 79.6 81.2 79.7 80.3 Vickers hardness, Hv 677.4 673.9 678.5 668.6 680.3 679.4 677.1 676.9 Specific modulus, GPa/g × cm.sup.−3 30.7 31.34 32.06 30.65 31.27 30.25 30.94 31.83 Strain point, ° C. 706 694 725 718 724 708 713 725 Melting temperature, T.sub.2.3 ° C. 1634 1609 1614 1621 1626 1618 1605 1622 Thermal shrinkage 10.83 8.75 10.71 8.35 9.56 11.25 10.76 8.89 (600° C., 10 min), ppm

TABLE-US-00003 TABLE 3 Exam- Exam- Exam- Exam- Exam- Exam- Exam- Exam- Component wt % ple 17 ple 18 ple 19 ple 20 ple 21 ple 22 ple 23 ple 24 SiO.sub.2 64.55 65.39 65.61 65.82 66.41 66.83 67.17 67.42 Al.sub.2O.sub.3 14.26 14.61 14.14 14.09 13.86 13.29 13.02 13.15 B.sub.2O.sub.3 8.91 9.15 8.64 9.26 8.55 8.75 9.03 9.59 MgO 2.08 1.99 2.15 1.64 1.95 2.17 3.05 1.15 CaO 3.65 4.17 3.55 4.86 4.91 4.05 4.22 3.64 SrO 2.87 2.06 2.18 1.09 2.37 1.96 1.25 1.47 ZrO.sub.2 1.96 1.32 1.35 0.85 0.75 1.63 0.79 1.95 P.sub.2O.sub.5 1.60 1.21 2.23 2.27 1.05 1.20 1.36 1.48 SnO.sub.2 0.12 0.10 0.15 0.12 0.15 0.12 0.11 0.15 SiO.sub.2 + Al.sub.2O.sub.3 78.81 80.00 79.75 79.91 80.27 80.12 80.19 80.57 (MgO + CaO + SrO)/Al.sub.2O.sub.3 0.60 0.56 0.56 0.54 0.67 0.62 0.65 0.48 Total amount of alkaline earth 8.60 8.22 7.88 7.59 9.23 8.18 8.52 6.26 metals B.sub.2O.sub.3/(B.sub.2O.sub.3 + ZrO.sub.2 + P.sub.2O.sub.5) 0.71 0.78 0.71 0.75 0.83 0.76 0.81 0.74 (ZrO.sub.2 + P.sub.2O.sub.5)/(MgO + CaO + SrO) 0.41 0.31 0.45 0.41 0.20 0.35 0.25 0.55 β-OH 0.21 0.26 0.22 0.17 0.11 0.2 0.14 0.16 Volatilization rate of boron, % 6.92 8.35 10.24 10.22 9.95 5.67 6.52 9.57 Thermal expansion coefficient 35.6 34.7 35.1 36.3 35.7 34.4 33.7 35.6 (50-350° C.), 10.sup.−7/° C. Young's modulus, GPa 81.6 80.7 79.2 81.5 84.1 81.3 82.4 80.9 Vickers hardness, Hv 668.3 673.8 669.4 678.4 679.1 682.2 681.6 678.6 Specific modulus, GPa/g × cm.sup.−3 32.31 30.97 31.62 30.76 33.29 31.62 32.97 31.86 Strain point, ° C. 719 716 720 709 721 719 724 722 Melting temperature, T.sub.2.3 ° C. 1618 1628 1632 1638 1619 1633 1621 1636 Thermal shrinkage 9.42 10.59 7.83 8.92 9.21 10.34 9.11 11.45 (600° C., 10 min), ppm

TABLE-US-00004 TABLE 4 Exam- Exam- Exam- Exam- Exam- Exam- Exam- Exam- Component wt % ple 25 ple 26 ple 27 ple 28 ple 29 ple 30 ple 31 ple 32 SiO.sub.2 67.78 68.14 68.63 68.85 69.31 69.79 70.33 70.71 Al.sub.2O.sub.3 13.05 14.21 13.04 13.17 13.35 13.07 13.01 13.00 B.sub.2O.sub.3 8.83 8.62 8.57 8.74 8.74 8.85 8.55 8.67 MgO 1.42 1.03 2.25 1.19 2.12 1.92 1.38 1.16 CaO 3.11 3.28 3.08 3.13 3.35 3.34 3.45 3.25 SrO 3.06 1.87 1.72 1.38 1.16 1.02 1.17 1.04 ZrO.sub.2 0.97 0.95 0.73 1.33 0.63 0.55 0.75 1.01 P.sub.2O.sub.5 1.64 1.79 1.86 2.06 1.21 1.31 1.21 1.02 SnO.sub.2 0.14 0.11 0.12 0.15 0.13 0.15 0.15 0.14 SiO.sub.2 + Al.sub.2O.sub.3 80.83 82.35 81.67 82.02 82.66 82.86 83.34 83.71 (MgO + CaO + SrO)/Al.sub.2O.sub.3 0.58 0.43 0.54 0.43 0.50 0.48 0.46 0.42 Total amount of alkaline earth 7.59 6.18 7.05 5.70 6.63 6.28 6.00 5.45 metals B.sub.2O.sub.3/(B.sub.2O.sub.3 + ZrO.sub.2 + P.sub.2O.sub.5) 0.77 0.76 0.77 0.72 0.83 0.83 0.81 0.81 (ZrO.sub.2 + P.sub.2O.sub.5)/(MgO + CaO + SrO) 0.34 0.44 0.37 0.59 0.28 0.30 0.33 0.37 β-OH 0.2 0.25 0.19 0.22 0.24 0.23 0.33 0.24 Volatilization rate of boron, % 8.63 7.39 10.36 7.18 10.06 7.25 9.03 10.24 Thermal expansion coefficient 34.2 36.6 35.5 36.3 34.8 37.1 37.4 36.2 (50-350° C.), 10.sup.−7/° C. Young's modulus, GPa 81.5 79.6 80.4 81.7 80.3 82.6 79.8 80.9 Vickers hardness, Hv 680.5 678.9 679.5 680.8 669.4 679.3 680.1 677.4 Specific modulus, GPa/g × cm.sup.−3 30.4 32.64 31.32 30.24 32.69 31.93 31.44 32.36 Strain point, ° C. 714 727 731 739 733 736 728 730 Melting temperature, T.sub.2.3 ° C. 1628 1634 1648 1652 1643 1660 1639 1651 Thermal shrinkage 9.97 10.63 9.03 11.31 9.66 10.23 11.02 10.76 (600° C., 10 min), ppm

TABLE-US-00005 TABLE 5 Compar- Compar- Compar- Compar- ative ative ative ative Exam- Exam- Exam- exam- exam- exam- exam- Component wt % ple 33 ple 34 ple 35 ple 1 ple 2 ple 3 ple 4 SiO.sub.2 71.23 71.66 71.90 59.03 73.84 66.42 66.5 Al.sub.2O.sub.3 13.09 13.00 13.00 19.23 12.42 13.51 13.45 B.sub.2O.sub.3 8.65 8.51 8.50 11.64 8.01 8.37 8.51 MgO 1.00 1.09 1.00 6.17 0.56 2.01 1.95 CaO 3.03 3.05 3.00 2.07 1.83 4.98 5.05 SrO 1.01 1.02 1.00 0.50 0.72 2.85 2.8 ZrO.sub.2 0.62 0.51 0.50 0.45 0.47 1.59 P.sub.2O.sub.5 1.24 1.06 1.00 0.76 2.00 1.71 SnO.sub.2 0.13 0.10 0.10 0.15 0.15 0.15 0.15 SiO.sub.2 + Al.sub.2O.sub.3 84.32 84.66 84.90 78.26 86.26 79.93 79.95 (MgO + CaO + SrO)/Al.sub.2O.sub.3 0.39 0.40 0.38 0.45 0.25 0.73 0.73 Total amount of alkaline earth 5.04 5.16 5.00 8.74 3.11 9.84 9.80 metals B.sub.2O.sub.3/(B.sub.2O.sub.3 + ZrO.sub.2 + P.sub.2O.sub.5) 0.82 0.84 0.85 0.91 0.76 0.83 0.84 (ZrO.sub.2 + P.sub.2O.sub.5)/(MgO + CaO + SrO) 0.37 0.30 0.30 0.14 0.79 0.17 0.16 β-OH 0.34 0.47 0.41 0.61 0.53 0.78 0.86 Volatilization rate of boron, % 10.31 9.86 10.11 14.8 13.5 12.76 12.31 Thermal expansion coefficient 35.9 37.3 38.1 38.1 36.5 36.3 35.8 (50-350° C.), 10.sup.−7/° C. Young's modulus, GPa 81.7 80.3 82.1 73.3 76.9 77.6 75.4 Vickers hardness, Hv 679.5 671.7 676.6 642.4 659.2 650.7 639.6 Specific modulus, GPa/g × cm.sup.−3 30.04 31.72 30.95 27.93 32.67 28.14 29.92 Strain point, ° C. 735 726 729 658 684 662 675 Melting temperature, T.sub.2.3 ° C. 1649 1658 1662 1603 1672 1621 1618 Thermal shrinkage 8.48 11.08 9.73 20.16 14.28 15.04 9.52 (600° C., 10 min), ppm

[0062] The above examples are only preferred examples of the present invention and are not intended to limit the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.