Glass composition for substrates and process for its production
View Patent ↗A glass composition for substrates excellent in productivity is provided by lowering the high temperature viscosity while securing characteristics and quality required for FPD substrates, particularly for PDP substrates. A glass composition for substrates, which is characterized by comprising, as represented by mass% based on oxides, from 55 to 75% of SiO 2 , from 5 to 15% of Al 2 O 3 , from 4 to 18% of MgO, from 3 to 12% of CaO, from 4 to 18% of SrO, from 0 to 20% of BaO, from 6 to 20% of Na 2 O+K 2 O, from 0.5 to 6% of ZrO 2 and from 18 to 25% of MgO+CaO+SrO+BaO, as a glass matrix composition, and containing from 0.001 to 0.6% of SO 3 , and which is further characterized in that when the viscosity is represented by η, the temperature satisfying logη=2 is at most 1,545° C. and the devitrification temperature is at most the temperature satisfying logη=4, the thermal expansion coefficient is from 75×10 −7 to 90×10 −7 /° C., the specific gravity is at most 2.8, and the glass transition point is at least 600° C.
1. A glass composition for substrates, which is characterized by comprising, as represented by mass% based on oxides,
from 55 to 75% of SiO 2 ,
from 5 to 15% of Al 2 O 3 ,
from 4 to 18% of MgO,
from 3 to 12% of CaO,
from 4 to 18% of SrO,
from 0 to 20% of BaO,
from 6 to 20% of Na 2 O+K 2 O,
from 0.5 to 6% of ZrO 2 and
from 18 to 25% of MgO+CaO+SrO+BaO,
as a glass matrix composition,
and containing from 0.001 to 0.6% of SO 3 , and which is further characterized in that
when the viscosity is represented by η, the temperature satisfying logη=2 is at most 1,545° C. and the devitrification temperature is at most the temperature satisfying logη=4,
the thermal expansion coefficient is from 75×10 −7 to 90×10 −7 /° C.,
the specific gravity is at most 2.8, and
the glass transition point is at least 600° C.
2. The glass composition for substrates according to claim 1 , which is characterized by comprising, as represented by mass % based on oxides,
from 55 to 70% of SiO 2 ,
from 5 to 10% of Al 2 O 3 ,
from 4 to 10% of MgO,
from 3 to 8% of CaO,
from 4 to 13% of SrO,
from 0 to 11% of BaO,
from 6 to 15% of Na 2 O+K 2 O,
from 0.5 to 4% of ZrO 2 and
from 18 to 25% of MgO+CaO+SrO+BaO,
as a glass matrix composition,
and containing from 0.01 to 0.4% of SO 3 .
3. The glass composition for substrates according to claim 1 , wherein the difference between
the SO 3 content in a glass obtained by adding a sulfate in an amount of from 0.5 to 10 mass % as calculated as SO 3 to the glass matrix composition material to prepare a glass material, melting and holding the glass material at a temperature of 1,350° C. for from 30 minutes to 2 hours and then cooling it to a temperature of from 20 to 30° C. in from 30 seconds to 1 minute, and
the SO 3 content in a glass obtained by melting and holding the above glass material at a temperature of 1,500° C. for from 30 minutes to 2 hours and then cooling it to a temperature of from 20 to 30° C. in from 30 seconds to 1 minute,
is at least 0.17.
4. The glass composition for substrates according to claim 1 , which has a fracture toughness of at least 0.7 MPa·m 1/2 .
5. The glass composition for substrates according to claim 1 , which has a volume resistivity of at least 10 11 Ω·cm at 150° C.
6. The glass composition for substrates according to claim 1 , wherein the temperature satisfying logη=4 is at most 1,200° C.
7. The glass composition for substrates according to claim 1 , wherein the content of K 2 O is from 1 to 10%.
8. A process for producing a glass composition for substrates, which comprises preparing a material so as to obtain a glass comprising, as represented by mass % based on oxides, from 55 to 75% of SiO 2 , from 5 to 15% of Al 2 O 3 , from 4 to 18% of MgO, from 3 to 12% of CaO, from 4 to 18% of SrO, from 0 to 20% of BaO, from 6 to 20% of Na 2 O+K 2 O, from 0.5 to 6% of ZrO 2 and from 18 to 25% of MgO+CaO+SrO+BaO, as a glass matrix composition, adding a sulfate in an amount of from 0.5 to 10 mass % as calculated as SO 3 to the material to prepare a glass material, melting the glass material at from 1,200 to 1,400° C., then fining it at from 1,400 to 1,700° C., and forming it into a plate glass by a float process to obtain the glass composition for substrates as defined in claim 1 .
9. A process for producing a glass composition for substrates, which comprises preparing a material so as to obtain a glass comprising, as represented by mass% based on oxides, from 55 to 70% of SiO 2 , from 5 to 10% of Al 2 O 3 , from 4 to 10% of MgO, from 3 to 8% of CaO, from 4 to 13% of SrO, from 0 to 11% of BaO, from 6 to 15% of Na 2 O+K 2 O, from 0.5 to 4% of ZrO 2 and from 18 to 25% of MgO+CaO+SrO+BaO, as a glass matrix composition, adding a sulfate in an amount of from 0.5 to 10 mass % as calculated as SO 3 to the material to prepare a glass material, melting the glass material at from 1,200to 1,400° C., then fining it at from 1,400 to 1,700° C., and forming it into a plate glass by a float process to obtain the glass composition for substrates as defined in claim 2 .