Glass substrate for an inorganic el display

A glass substrate for an inorganic EL display comprises an aluminosilicate glass, contains CaO, SrO, BaO, and ZrO 2 the contents of which fall within ranges of, by mass percent, 0-13% CaO, 0-13% SrO, 0-13% BaO, 0-10% ZrO 2 , and 0-13% CaO&plus;SrO&plus;BaO&plus;ZrO 2 , and has the strain point not lower than 520° C.

BEST MODE FOR EMBODYING THE INVENTION Now, examples of this invention will be described in detail. Table 1 and 2 show examples (samples Nos. 1-10) of an inorganic EL display glass substrate of this invention and comparative examples (samples Nos. 11 and 12). The sample No. 12 as the comparative example is a soda lime glass substrate commercially available as a window panel glass for a building. 1 TABLE 1 Examples No. 1 No. 2 No. 3 No. 4 No. 5 No. 6 Composition (mass %) SiO 2 63.7 63.8 67.8 67.5 63.8 62.6 Al 2 O 3 6.0 7.9 7.9 2.8 7.9 10.0 MgO 3.6 3.6 3.6 4.5 3.6 6.2 CaO 2.5 2.5 5.5 6.0 2.5 1.0 SrO 7.5 6.5 3.5 — — 6.5 BaO — — — 3.1 6.5 — Li 2 O — — 0.4 — — — Na 2 O 2.5 2.5 2.5 4.9 2.5 5.0 K 2 O 12.5 12.5 7.1 7.9 12.5 8.0 ZrO 2 0.5 0.5 0.5 2.1 0.5 0.5 TiO 2 — — — — — — P 2 O 5 1.0 — 1.0 1.0 — — SO 3 0.2 0.2 0.2 0.2 0.2 0.2 CaO &plus; SrO &plus; 10.5 9.5 9.5 11.2 9.5 8.0 BaO &plus; ZrO 2 strain point 578 585 589 558 573 589 (° C.) volume 11.3 11.2 10.7 11.2 11.2 10.6 resistivity log &rgr; (&OHgr; · cm) crack 1030 1500 880 730 2100 1500 resistance (mN) coefficient 85 84 71 80 81 79 of thermal expansion &lsqb;30-380° C.&rsqb; (×10 −7 /° C.) density (g/cm 3 ) 2.55 2.53 2.49 2.54 2.54 2.55 2 TABLE 2 Examples No. 7 No. 8 No. 9 No. 10 No. 11 No. 12 Composition (mass %) SiO 2 68.3 67.2 67.2 62.6 57.1 73.0 Al 2 O 3 2.1 2.8 7.2 7.9 7.0 2.0 MgO 3.8 4.5 1.9 3.6 1.5 4.0 CaO 5.0 6.3 7.6 7.5 2.0 7.0 SrO — — — — 7.0 — BaO — 3.1 — — 8.5 — Li 2 O 1.0 — 1.0 0.5 — — Na 2 O 3.6 4.9 2.0 1.9 4.5 13.0 K 2 O 10.0 7.9 12.3 12.8 7.5 1.0 ZrO 2 6.0 2.1 0.6 1.9 4.5 — TiO 2 — — — — — — P 2 O 5 — 1.0 — 1.1 — — SO 3 0.2 0.2 0.2 0.2 0.2 — CaO &plus; SrO &plus; 11.0 11.5 8.2 9.4 22.0 7.0 BaO &plus; ZrO 2 strain point 533 558 535 578 587 500 (° C.) volume 12.0 11.3 12.0 11.4 11.9 8.5 resistivity log &rgr; (&OHgr; · cm) crack 680 700 880 1030 490 880 resistance (mN) coefficient 79 81 84 83 82 89 of thermal expansion &lsqb;30-380° C.&rsqb; (×10 −7 /° C.) density (g/cm 3 ) 2.54 2.54 2.47 2.51 2.80 2.50 Each of the samples Nos. 1-11 in Tables was produced in the following manner. A glass material batch was prepared to have each glass composition in Tables, melted in a platinum pot at 1550° C. for 5 hours, and then poured out onto a carbon plate. Thus, a glass substrate was produced. Each sample thus obtained was evaluated for various characteristics. The result is shown in Tables. As is obvious from Tables, each of the samples Nos. 1-10 as examples of this invention has a strain point not lower than 533° C., a volume resistivity not lower than 10.6, and a coefficient of thermal expansion of 71-85×10 −7 /° C. and is thus suitable as a rear substrate of an inorganic EL display. In addition, since the density is not higher than 2.55 g/cm −3 , the weight can be reduced. Furthermore, since each of these samples has a crack resistance as high as 680 mN or more, it is assumed that cracks will hardly occur in a production process. On the other hand, the sample No. 11 as a comparative example has a crack resistance as low as 490 mN. It is therefore assumed that cracks will easily occur in a production process. The sample No. 12 has a low strain point. Therefore, if it is used as a rear substrate of an inorganic EL display and fired at 650-700° C., thermal deformation will occur. Since the volume resistivity is as low as 8.5, it is anticipated that the electric resistance of the electrode material will unfavorably be changed. The strain point in Tables was measured according to ASTM C336-71. The volume resistivity was measured according to ASTM C657-78 as a value at 150° C. For the crack-resistant characteristic, use was made of a method proposed by Wada et al (M. Wada et al, Proc., the Xth ICG, vol. 11, Ceram. Soc., Japan, Kyoto, 1974, p.39). In this method, a sample glass is placed on a stage of a Vickers hardness tester. A square pyramid diamond indenter was pressed against the surface of the sample glass for 15 seconds under various loads. Then, the number of cracks produced from four indentation corners within 15 seconds after the removal of the load is counted. As a crack occurrence ratio, the ratio with respect to the number of maximum possible occurrences of cracks (four) is calculated and the ratio with respect to the number of maximum possible occurrences of cracks (four) is calculated. The load when the crack occurrence ratio is equal to 50% is taken as a “crack resistance”. The crack resistance being great means that cracks hardly occur even under a high load, i.e., the crack-resistant characteristic is excellent. The measurement of the crack occurrence ratio was carried out 20 times under the same load and the average was calculated. The measurement was carried out under the conditions of the temperature of 25° C. and the humidity of 30%. The coefficient of thermal expansion was measured by the use of a dilatometer as an average coefficient of thermal expansion within a range of 30-380° C. The density was measured by the known Archimedes method. As described above, the inorganic EL display glass substrate of this invention has a high strain point not lower than 520° C. as well as a high volume resistivity and a high crack resistance and is therefore suitable as the rear substrate of the inorganic EL display. The inorganic EL display glass substrate of this invention has a low density and therefore can be reduced in weight. In addition, since a large-sized substrate can easily be produced, it is possible to produce a large-sized home television of 40-inch to 60-inch models. If it is used in a small-sized display, the productivity is considerably improved. Furthermore, if the inorganic EL display glass substrate of this invention has a coefficient of thermal expansion of 50-100×10 −7 /° C. within a temperature range of 30-380° C., thermal stress is hardly produced between the glass substrate and the front substrate or the dielectric material.