Glass for chemical tempering and chemically tempered glass

Abstract

To provide chemically tempered glass which is less likely to break even if scratched. Chemically tempered glass, which comprises, as represented by mole percentage based on the following oxides, from 56 to 72% of SiO.sub.2, from 8 to 20% of Al.sub.2O.sub.3, from 9 to 25% of Na.sub.2O, from 0 to 2% of K.sub.2O, and from 0 to 15% of MgO, and which has a surface compressive stress of at least 900 MPa and an internal tensile stress of at most 30 MPa. Glass for chemical tempering, which comprises, as represented by mole percentage based on the following oxides, from 56 to 69% of SiO.sub.2, from 8 to 16% of Al.sub.2O.sub.3, from 9 to 22% of Na.sub.2O, from 0 to 1% of K.sub.2O, from 5.5 to 14% of MgO, from 0 to 2% of ZrO.sub.2, and from 0 to 6% of B.sub.2O.sub.3.

Claims

1. A glass comprising, as represented by mole percentage based on the following oxides: from 56 to 69% of SiO.sub.2; from 8 to 16% of Al.sub.2O.sub.3; from 9 to 22% of Na.sub.2O; from 0 to 2% of K.sub.2O; from 7 to 15% of MgO; from 0 to less than 1% of CaO; and from 0 to 1% of ZrO.sub.2, wherein the glass contains no B.sub.2O.sub.3, the glass has a glass transition temperature of at least 627 C., the glass has a temperature at which a viscosity of the glass is 10.sup.4 dPa.Math.s of 1333 C. or less, and Z calculated by the following formula by using the contents, as represented by mole percentage, of SiO.sub.2, Al.sub.2O.sub.3, Na.sub.2O, MgO, and K.sub.2O is at least 870:
Z=2SiO.sub.2+55Al.sub.2O.sub.3+22Na.sub.2O+15MgO126K.sub.2O.

2. The glass according to claim 1, wherein X calculated by the following formula by using the contents, as represented by mole percentage, of SiO.sub.2, Al.sub.2O.sub.3, Na.sub.2O and MgO is at most 1:
X=0.4SiO.sub.20.5Al.sub.2O.sub.30.4Na.sub.2O0.4MgO+41.5.

3. The glass according to claim 1, wherein Z3 calculated by the following formula by using the contents, as represented by mole percentage, of SiO.sub.2, Al.sub.2O.sub.3, Na.sub.2O, MgO and ZrO.sub.2 is at most 0.150:
Z3=0.00722SiO.sub.2+0.0264Al.sub.2O.sub.3+0.0149Na.sub.2O+0.0035MgO0.0204ZrO.sub.2.

4. The glass according to claim 1, wherein the content of SiO.sub.2 is from 62 to 66%, the content of Al.sub.2O.sub.3 is from 10.5 to 13%, the content of Na.sub.2O is from 14 to 17%, and the content of MgO is at most 9%.

5. The glass according to claim 4, wherein the content of SiO.sub.2 is from 63 to 66%, and the content of ZrO.sub.2 is from 0.2 to 1%.

6. The glass according to claim 1, wherein the difference obtained by subtracting the content of Al.sub.2O.sub.3 from the content of Na.sub.2O is less than 5%.

7. The glass according to claim 1, wherein the total content of SiO.sub.2, Al.sub.2O.sub.3, Na.sub.2O and MgO is at least 98%.

8. The glass according to claim 1, wherein the content of ZrO.sub.2 is from 0 to 0.5%.

9. The glass according to claim 1, wherein the liquid phase temperature of the glass is at most a temperature at which the viscosity of the glass becomes 10.sup.4 dPa.Math.s.

10. The glass according to claim 1, wherein Z is at least 1,000.

11. The glass according to claim 1, wherein no CaO is contained.

12. The glass according to claim 1, wherein the content of MgO is 9%.

13. A chemically tempered glass, which is obtained by chemically tempering the glass as defined in claim 1.

14. The chemically tempered glass according to claim 13, wherein the chemically tempered glass has a surface compressive stress of at least 1,000 MPa.

15. The chemically tempered glass according to claim 14, wherein the chemically tempered glass has a compressive stress layer thickness of at least 20 m.

16. A cover glass made of the chemically tempered glass as defined in claim 13.

17. A display device comprising the cover glass as in claim 16.

18. A touch panel comprising: a glass substrate made of the chemically tempered glass as defined in claim 13; and an electrode for detecting an input position formed on the glass substrate.

19. A glass comprising, as represented by mole percentage based on the following oxides: from 56 to 69% of SiO.sub.2; from 8 to 16% of Al.sub.2O.sub.3; from 9 to 22% of Na.sub.2O; from 0 to 2% of K.sub.2O; from 7 to 15% of MgO; from 0 to less than 1% of CaO; and from 0 to 1% of ZrO.sub.2, wherein the glass contains no B.sub.2O.sub.3, the glass has a glass transition temperature of at least 627 C., the glass has a temperature at which a viscosity of the glass is 10.sup.4 dPa.Math.s of 1333 C. or less, and Z4 calculated by the following formula by using the contents, as represented by mole percentage, of Al.sub.2O.sub.3, K.sub.2O and MgO is at least 24:
Z4=3Al.sub.2O.sub.310K.sub.2O+MgO.

20. The glass according to claim 19, wherein Z4 is at least 35.

21. The glass according to claim 19, wherein X calculated by the following formula by using the contents, as represented by mole percentage, of SiO.sub.2, Al.sub.2O.sub.3, Na.sub.2O and MgO is at most 1:
X=0.4SiO.sub.20.5Al.sub.2O.sub.30.4Na.sub.2O0.4MgO+41.5.

22. The glass according to claim 19, wherein Z3 calculated by the following formula by using the contents, as represented by mole percentage, of SiO.sub.2, Al.sub.2O.sub.3, Na.sub.2O, MgO and ZrO.sub.2 is at most 0.150:
Z3=0.00722SiO.sub.2+0.0264Al.sub.2O.sub.3+0.0149Na.sub.2O+0.0035MgO0.0204ZrO.sub.2.

23. The glass according to claim 19, wherein no CaO is contained.

24. The glass according to claim 19, wherein the content of MgO is 9%.

25. A glass comprising, as represented by mole percentage based on the following oxides: from 56 to 69% of SiO.sub.2; from 8 to 16% of Al.sub.2O.sub.3; from 9 to 22% of Na.sub.2O; from 0 to 2% of K.sub.2O; from 7 to 15% of MgO; from 0 to less than 1% of CaO; and from 0 to 1% of ZrO.sub.2, wherein the glass contains no B.sub.2O.sub.3, the glass has a glass transition temperature of at least 627 C., the glass has a temperature at which a viscosity of the glass is 10.sup.4 dPa.Math.s of 1333 C. or less, and Z2 calculated by the following formula by using the contents, as represented by mole percentage, of SiO.sub.2, Al.sub.2O.sub.3, Na.sub.2O, MgO and ZrO.sub.2 is at least 860:
Z2=3.5SiO.sub.2+85Al.sub.2O.sub.3+0.80Na.sub.2O+2.0MgO+81ZrO.sub.2.

26. The glass according to claim 25, wherein Z2 is at least 1,300.

27. The glass according to claim 25, wherein X calculated by the following formula by using the contents, as represented by mole percentage, of SiO.sub.2, Al.sub.2O.sub.3, Na.sub.2O and MgO is at most 1:
X=0.4SiO.sub.20.5Al.sub.2O.sub.30.4Na.sub.2O0.4MgO+41.5.

28. The glass according to claim 25, wherein Z3 calculated by the following formula by using contents, as represented by mole percentage, of SiO.sub.2, Al.sub.2O.sub.3, Na.sub.2O, MgO and ZrO.sub.2 is at most 0.150:
Z3=0.00722SiO.sub.2+0.0264Al.sub.2O.sub.3+0.0149Na.sub.2O+0.0035MgO0.0204ZrO.sub.2.

29. The glass according to claim 25, wherein no CaO is contained.

30. The glass according to claim 25, wherein the content of MgO is 9%.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a graph showing the relation between the internal tensile stress and the impact failure height in a sand paper drop test.

(2) FIG. 2 is a graph showing the relation between the thickness of the compressive stress layer and the four point bending fracture stress.

(3) FIG. 3 is a graph showing the relation between the above Z and the surface compressive stress.

(4) FIG. 4 is a graph showing the relation between the above Z4 and the surface compressive stress.

(5) FIG. 5 is a graph showing the relation between the above X and the cracking probability.

(6) FIG. 6 is a graph showing the relation between the above Z2 and the surface compressive stress.

(7) FIG. 7 is a graph showing the relation between the above Z3 and the acid resistance index.

(8) FIG. 8 is an enlarged view of the vicinity of the origin in FIG. 7.

DESCRIPTION OF EMBODIMENTS

(9) Each of the chemically tempered glass and the glass plate for a display device of the present invention is one obtainable by chemically tempering glass for chemical tempering of the present invention, and will hereinafter be generally referred to as the tempered glass of the present invention.

(10) To be used for e.g. a display device, the surface compressive stress S of the tempered glass of the present invention is preferably at least 800 MPa, more preferably at least 900 MPa, particularly preferably at least 1,000 MPa. S may be at least 1,300 MPa. Further, in a case where the thickness of the glass is less than 2 mm, S is preferably at most 1,600 MPa. If S exceeds 1,600 MPa, the internal tensile stress tends to be too large.

(11) To be used for e.g. a display device, the thickness t of the compressive stress layer of the tempered glass of the present invention is preferably more than 10 m, more preferably more than 15 m, typically more than 20 m or at least 30 m. Further, in a case where the thickness is less than 2 mm, t is preferably at most 90 m. If t exceeds 90 m, the internal tensile stress tends to be too large. More preferably, t is at most 80 m, typically at most 70 m.

(12) The method for chemical tempering treatment to obtain the tempered glass of the present invention is not particularly limited so long as it is capable of ion-exchanging Na in the glass surface layer with K in the molten salt, and for example, a method of immersing the glass in a heated potassium nitrate molten salt may be mentioned. Here, in the present invention, a potassium nitrate molten salt or a potassium nitrate salt includes not only KNO.sub.3 but also one containing KNO.sub.3 and at most 10 mass % of NaNO.sub.3.

(13) The conditions for chemical tempering treatment to form a chemically tempered layer (compressive stress layer) having a desired surface compressive stress in glass vary also depending upon e.g. the thickness in the case of a glass plate, but it is typical that a glass substrate is immersed in a potassium nitrate molten salt of from 350 to 550 C. for from 2 to 20 hours. From an economical viewpoint, the immersion is preferably conducted under conditions of from 350 to 500 C. for from 2 to 16 hours, and the immersion time is more preferably from 2 to 10 hours.

(14) The chemically tempered glass of the present invention, particularly the glass plate for a display device of the present invention, is preferably such that no cracking takes place i.e. the breakage rate is 0, even when a force of 0.1 kgf=0.98N is exerted thereto by a test by means of a Vickers hardness meter having a pyramid-shaped diamond indenter with a vertex angle of 110 mounted.

(15) Further, it is preferred that the breakage rate is less than 1 even when a force of 0.2 kgf=1.96N is exerted, and it is more preferred that the breakage rate is at most 0.8 when a force of 1.96N is exerted.

(16) The glass plate for a display device of the present invention is usually obtainable by chemically tempering a glass plate obtained by subjecting a glass plate made of glass for chemical tempering of the present invention to processing by cutting, drilling, polishing, etc.

(17) The thickness of the glass plate for a display device of the present invention is usually from 0.3 to 2 mm, typically at most 1.5 mm.

(18) The glass plate for a display device of the present invention is typically a cover glass.

(19) The method for producing a glass plate made of the above glass for chemical tempering is not particularly limited. For example, it is produced by mixing various raw materials in proper amounts, heating and melting the mixture at from about 1,400 to 1,800 C. and homogenizing the melt by defoaming, stirring, etc., forming it into a plate by a well-known float process, down draw process, pressing process, or the like, annealing it and then cutting it in a desired size.

(20) The glass transition temperature of glass for chemical tempering of the present invention i.e. the glass of the present invention, is preferably at least 400 C. If it is less than 400 C., the surface compressive strain tends to be relaxed at the time of ion exchange, whereby no adequate stress may be obtainable. It is more preferably at least 550 C.

(21) The temperature T2 at which the viscosity of the glass of the present invention becomes 10.sup.2 dPa.Math.s, is preferably at most 1,800 C., more preferably at most 1,750 C.

(22) The temperature T4 at which the viscosity of the glass of the present invention becomes 10.sup.4 dPa.Math.s, is preferably at most 1,350 C.

(23) The liquid phase temperature of the glass of the present invention is preferably lower than T4, more preferably lower by at least 20 C. than T4, with a view to preventing devitrification during formation of the glass.

(24) The specific gravity p of the glass of the present invention is preferably from 2.43 to 2.49.

(25) The Young's modulus of the glass of the present invention is preferably at least 68 GPa. If it is less than 68 GPa, the cracking resistance or fracture strength of the glass is likely to be inadequate.

(26) The Poisson's ratio of the glass of the present invention is preferably at most 0.25. If it exceeds 0.25, the cracking resistance of the glass is likely to be inadequate.

(27) Now, the composition of the glass of the present invention and glass A will be described by using contents represented by mole percentage unless otherwise specified.

(28) SiO.sub.2 is an essential component to constitute a glass matrix and also is a component to reduce cracking when a flaw (an indentation) is formed on the glass surface, or to reduce the breakage rate when an indentation is imparted after chemical tempering. If the SiO.sub.2 content is less than 56%, the stability, acid resistance, weather resistance or chipping resistance, as glass, tends to be low. SiO.sub.2 is preferably at least 58%, more preferably at least 60%. If SiO.sub.2 exceeds 73%, the viscosity of the glass tends to increase, whereby the melting property of the glass tends to be low, or it tends to be difficult to increase the surface compressive stress. SiO.sub.2 is preferably at most 72%, more preferably at most 69%, and in glass A, it is at most 69%.

(29) Al.sub.2O.sub.3 is a component effective to improve the ion exchange performance and the chipping resistance, a component to increase the surface compressive stress, or an essential component to reduce cracking when an indentation is imparted by a 110 indenter. If Al.sub.2O.sub.3 is less than 6%, it tends to be difficult to obtain the desired surface compressive stress value or compressive stress layer thickness by ion exchange. Al.sub.2O.sub.3 is preferably at least 8%, more preferably at least 9%. If Al.sub.2O.sub.3 exceeds 20%, the viscosity of the glass tends to be high, whereby uniform melting tends to be difficult, or the acid resistance tends to be low. Al.sub.2O.sub.3 is preferably at most 16%, more preferably at most 15%, typically at most 14%, and in glass A, it is preferably at most 16%.

(30) The total content of SiO.sub.2 and Al.sub.2O.sub.3 i.e. SiO.sub.2+Al.sub.2O.sub.3 is preferably at most 80%. If the total content exceeds 80%, the viscosity of the glass tends to increase at a high temperature, whereby melting tends to be difficult, and it is preferably at most 79%, more preferably at most 78%. Further, SiO.sub.2+Al.sub.2O.sub.3 is preferably at least 70%. If it is less than 70%, the cracking resistance when an indentation is imparted, tends to be low, and it is more preferably at least 72%.

(31) Na.sub.2O is an essential component to form a surface compressive stress layer by ion exchange and to improve the melting property of the glass. If Na.sub.2O is less than 9%, it tends to be difficult to form a desired surface compressive stress layer by ion exchange, and it is preferably at least 10%, more preferably at least 10.5% or at least 11%. If Na.sub.2O exceeds 25%, the weather resistance or acid resistance tends to decrease, or cracking is likely to start from an indentation. It is preferably at most 22%, more preferably at most 21%, and in glass A, it is at most 22%. In a case where it is desired to improve the acid resistance, Na.sub.2O is preferably at most 17%, more preferably at most 16.5%.

(32) K.sub.2O is not essential but is a component to increase the ion exchange rate, and thus, it may be contained up to 2%. If it exceeds 2%, cracking tends to start from an indentation, or a change in the surface compressive stress due to the concentration of NaNO.sub.3 in the potassium nitrate molten salt tends to be large. K.sub.2O is preferably less than 2%, more preferably at most 1%, further preferably at most 0.8%, particularly preferably at most 0.5%, typically at most 0.3%, and in glass A, it is at most 1%. In a case where it is desired to reduce the change in the surface compressive stress due to the concentration of NaNO.sub.3 in the potassium nitrate molten salt, K.sub.2O should better be not contained.

(33) MgO is not essential, but is a component to increase the surface compressive stress and to improve the melting property. In a case where MgO is contained, its content is preferably at least 5.5%, more preferably at least 7%. In glass A, MgO is essential and is at least 5.5%, preferably at least 7%. In a case where it is desired to prevent stress relaxation, MgO is preferably at least 8%. If MgO is less than 8%, the degree of stress relaxation tends to vary depending upon the location in the chemical tempering treatment tank due to a fluctuation of the temperature of the molten salt during the chemical tempering treatment, and consequently, it is likely to be difficult to obtain a stabilized compressive stress value. On the other hand, if MgO exceeds 15%, the glass is likely to undergo devitrification, or a change in the surface compressive stress due to the concentration of NaNO.sub.3 in the potassium nitrate molten salt tends to be large, and it is preferably at most 14%, more preferably at most 13%. In glass A, it is at most 14%.

(34) The difference (SiO.sub.2MgO) obtained by subtracting the content of MgO from the content of SiO.sub.2 is preferably at most 64%, more preferably at most 62%, typically at most 61%.

(35) The difference (Al.sub.2O.sub.3MgO) obtained by subtracting the content of MgO from the content of Al.sub.2O.sub.3 is preferably at most 9%, more preferably at most 8%.

(36) The total content of SiO.sub.2, Al.sub.2O.sub.3, Na.sub.2O and MgO is preferably at least 98%. If the total content is less than 98%, it tends to be difficult to obtain the desired compressive stress layer while maintaining the cracking resistance. It is typically at least 98.3%.

(37) In a case where it is desired to increase the surface compressive stress and at the same time to improve the acid resistance, for example in a case where it is desired to make the above S to be at least 1,150 MPa and the above W to be at most 0.15 mg/cm.sup.2, it is preferred that SiO.sub.2 is from 62 to 66%, Al.sub.2O.sub.3 is from 10.5 to 13%, Na.sub.2O is from 14 to 17% and MgO is from 6 to 9%, and the total content of these components is more preferably at least 97%.

(38) In a case where it is desired to more increase the surface compressive stress and at the same time to more improve the acid resistance, for example in a case where it is desired to make the above S to be at least 1,300 MPa and the above W to be at most 0.1 mg/cm.sup.2, it is preferred that SiO.sub.2 is from 63 to 66%, Al.sub.2O.sub.3 is from 10.5 to 13%, Na.sub.2O is from 14 to 17%, MgO is from 6 to 9% and ZrO.sub.2 is from 0.2 to 2%, and the total content of these components is more preferably at least 97.5%.

(39) The glass of the present invention consists essentially of the above-described components, but may contain other components within a range not to impair the purpose of the present invention. In a case where such other components are contained, the total content of such other components is preferably at most 5%, more preferably at most 2%, typically at most 1%.

(40) ZrO.sub.2 is not essential, but may be contained within a range of up to 2% in order to lower the viscosity at a high temperature or to increase the surface compressive stress, or to improve the acid resistance, and in a case where it is contained for the purpose of increasing the surface compressive stress, its content is preferably at least 0.2%, for example at least 0.5% or more than 0.5%. If ZrO.sub.2 exceeds 2%, the possibility of cracking to start from an indentation may increase. In a case where it is desired to prevent cracking, ZrO.sub.2 is preferably at most 1%, more preferably at most 0.5%, or typically no ZrO.sub.2 is contained.

(41) B.sub.2O.sub.3 is not essential but may be contained within a range of at most 6% in order to improve the melting property of glass at a high temperature or to improve the glass strength. If B.sub.2O.sub.3 exceeds 6%, homogeneous glass tends to be hardly obtainable, and the glass forming may be difficult, or the cracking resistance may deteriorate. Typically no B.sub.2O.sub.3 is contained.

(42) The total content of SiO.sub.2, Al.sub.2O.sub.3, Na.sub.2O and MgO is preferably at least 98%. The above Z is preferably at least 1,000, more preferably at least 1,050, typically at least 1,100.

(43) The above Z4 is preferably at least 35, more preferably at least 38.

(44) The above X is preferably at most 1, more preferably at most 0.8.

(45) The above Y1 is preferably less than 600, more preferably at most 650.

(46) The above Y2 is preferably less than 245, more preferably at most 260.

(47) The difference (Na.sub.2OAl.sub.2O.sub.3) obtained by subtracting Al.sub.2O.sub.3 from the content of Na.sub.2O is preferably less than 5%.

(48) The above R is preferably at least 100, more preferably at least 70.

(49) Glass A of the present invention consists essentially of the above-described components, but may contain other components within a range not to impair the object of the present invention. In a case where such other components are contained, the total content of such components is preferably less than 2%, more preferably at most 1%. Now, such other components will be exemplified.

(50) ZnO may be contained in a certain case, for example, up to 2% in order to improve the melting property of glass at a high temperature, but preferably at most 1%. In a case of production by a float process, ZnO is preferably at most 0.5%. If ZnO exceeds 0.5%, it is likely to be reduced during the float forming to form a product defect. Typically, no ZnO is contained.

(51) TiO.sub.2 is likely to deteriorate the visible light transmittance and likely to color glass to be brown when it is coexistent with Fe ions in the glass, and therefore, its content is preferably at most 1% if contained, and typically, it is not contained.

(52) Li.sub.2O is a component to lower the strain point and to bring about a stress relaxation thereby to make it difficult to obtain a stable surface compressive stress layer and therefore it is preferably not contained, and even if contained, its content is preferably less than 1%, more preferably at most 0.05%, particularly preferably less than 0.01%.

(53) Further, Li.sub.2O may elute into a molten salt of e.g. KNO.sub.3 during chemical tempering treatment, and if chemical tempering is carried out by using the molten salt containing Li, the surface compressive stress decreases remarkably. From this viewpoint, Li.sub.2O is preferably not contained.

(54) CaO may be contained in a range of less than 1% in order to improve the melting property at a high temperature or to prevent devitrification. If CaO is 1% or more, the ion exchange rate or the resistance against cracking tends to be low. Typically, no CaO is contained.

(55) SrO may be contained as the case requires, but it has a large effect to lower the ion exchange rate as compared with MgO or CaO, and therefore, even if it is contained, its content should preferably be less than 1%. Typically, no SrO is contained.

(56) BaO has the largest effect to lower the ion exchange rate among alkaline earth metal oxides, and therefore, it is preferred that no BaO is contained, or even if contained, its content is less than 1%.

(57) When SrO and/or BaO is contained, their total content should preferably be at most 1%, more preferably less than 0.3%.

(58) When at least one member of CaO, SrO, BaO and ZrO is contained, the total content of these four components should preferably be less than 1.5%. If the total content is 1.5% or more, the ion exchange rate is likely to be low, and typically, the total content is at most 1%.

(59) As a clarifying agent at the time of melting glass, SO.sub.3, a chloride, a fluoride or the like may suitably be contained. However, in order to increase the visibility of display devices such as touch panels, it is preferred to reduce components which may be included as impurities in raw materials such as Fe.sub.2O.sub.3, NiO, Cr.sub.2O.sub.3, etc. having an absorption in a visible light range as far as possible, and the content of each of them is preferably at most 0.15%, more preferably at most 0.05%, as represented by mass percentage.

Examples

(60) With respect to Ex. 1 to 21, 25, 29, 30, 31 to 48 and 52 to 56 in Tables, glass raw materials commonly used, such as oxides, hydroxides, carbonates, nitrates, etc., were suitably selected to have a composition as represented by mol % in columns for SiO.sub.2 to K.sub.2O, and weighed so that they became 400 g as glass. To the weighed raw materials, sodium sulfate was added in an amount by mass corresponding to 0.2% of the mass thereof, followed by mixing. Then, the mixed raw materials were put into a platinum crucible and melted, defoamed and homogenized in a resistance heating type electric furnace at a temperature of 1,650 C. for 6 hours. The obtained molten glass was cast into a mold material, held at a temperature of Tg+50 C. for one hour and then cooled to room temperature at a rate of 0.5 C./min to obtain a glass block.

(61) Further, Ex. 49 is soda lime glass separately prepared, and in Ex. 22 to 24, 32 and 33, melting of glass as described above was not carried out. Further, in Tables, data identified with * are ones obtained by calculation or assumption from the compositions.

(62) Ex. 1 to 47 and 52 to 56 are Examples for chemically tempered glass of the present invention, Ex. 48 is a Reference Example, Ex. 49 to 51 are Comparative Examples, and Ex. 1 to 25, 29 to 46, and 52 to 56 are Examples for glass A of the present invention.

(63) Further, in Tables, values of the above Z are shown which were calculated by using the contents, as represented by mole percentage, of the respective components such as SiO.sub.2, etc. For example, in the calculation of Z in Ex. 1 (the SiO.sub.2 content of glass was 64 mol %), SiO.sub.2 was taken as 64.

(64) Further, in Tables, values of the above Z2, Z3, Z4 and X are shown.

(65) With respect to these glasses, the Young's modulus E (unit: GPa), the specific gravity d, the glass transition point Tg (unit: C.), the temperature T2 (unit: C.) at which the viscosity becomes to be 10.sup.2 dPa.Math.s, the temperature T4 (unit: C.) at which the viscosity becomes to be 10.sup.4 dPa.Math.s, the liquid phase temperature TL (unit: C.), the average linear expansion coefficient (unit: .sup.7/ C.) at from 50 to 350 C., the acid resistance (unit: mg/cm.sup.2) and the cracking probability P are shown in Tables. Here, in Tables, indicates that no measurement or calculation was made, and * indicates that the calculation was made from the glass composition, etc.

(66) The acid resistance was measured as follows. That is, the glass block was cut, ground and finally processed to have both surfaces mirror-polished to obtain a plate glass having a size of 40 mm40 mm and a thickness of from 1.0 mm to 1.3 mm. The process up to the mirror polishing was such that glass in a plate-form was ground for 300 to 1,000 m by means of a grinding stone of #1,000 to obtain a plate glass, which was then polished by means of cerium oxide to have its surfaces mirror-polished. The obtained plate glass was immersed in 0.1 mol/l hydrochloric acid warmed to 90 C. for 20 hours, whereby the mass decrease as between before and after the immersion was measured, and it was divided by the plate glass surface area to calculate the acid resistance.

(67) The glass block was cut, ground and finally processed to have both surfaces mirror-polished to obtain a plate glass having a size of 30 mm30 mm and a thickness of 1.0 mm and 3.0 mm. The process up to the mirror polishing was such that glass in a plate-form was ground for 300 to 1,000 m by means of a grinding stone of #1,000 to obtain a plate glass, which was then polished by means of cerium oxide to have its surfaces mirror-polished.

(68) The liquid phase temperature was measured as follows. That is, 10 g of glass having a size of from about 1 to 4 mm was placed on a platinum dish, melted in an electric furnace maintained at a constant temperature for at least 17 hours and then taken out, whereupon the glass was quenched at room temperature. This glass sample was observed by a polarized-light microscope to confirm the presence or absence of crystals thereby to obtain a temperature at which crystals were confirmed and a temperature at which no crystals were confirmed. The result is shown in such a form that these two temperatures are connected by -, and the liquid phase temperature is present between these two temperatures. Further, in Ex. 55 and 56, the presence or absence of crystals was confirmed only at 1,250 C., whereby crystals were confirmed at that temperature, and therefore, the liquid phase temperature was found to be higher than 1,250 C.

(69) Then, with respect to plate glasses in Ex. 1, 3, 5 to 7, 11 to 24, 29 to 49 and 52 to 56, the following chemical tempering treatment was carried out. That is, each of these glasses was immersed for 10 hours in a KNO.sub.3 molten salt of 425 C. to carry out the chemical tempering treatment. Here, in the KNO.sub.3 molten salt, the KNO.sub.3 content was from 99.7 to 100 mass %, and the NaNO.sub.3 content was from 0 to 0.3 mass %.

(70) With respect to each glass after the chemical tempering treatment, the surface compressive stress S (unit: MPa) and the compressive stress layer depth t (unit: m) were measured by means of a surface stress meter FSM-6000 manufactured by Orihara Manufacturing Co., Ltd. The results are shown in the corresponding columns in Tables.

(71) Further, each of glasses in Ex. 1 to 10, 12 to 20 and 21 to 51 was immersed for 2 hours in a KNO.sub.3 molten salt of 425 C., and glass in Ex. 11 was immersed for 1 hour in a KNO.sub.3 molten salt of 425 C., whereupon the surface compressive stress, the compressive stress layer depth and the internal tensile stress calculated from these values are shown in the columns for CS (unit: MPa), DOL (unit: m) and CT (unit: MPa), respectively, in Tables.

(72) Separately, with respect to plate glasses in Ex. 1, 3, 5 to 7, 11 to 24 and 47 to 49, the following chemical tempering treatment was carried out. That is, each of these glasses was immersed in a molten salt of 450 C. having a KNO.sub.3 content of 95 mass % and a NaNO.sub.3 content of 5 mass % to carry out chemical tempering treatment.

(73) With respect to each glass after the chemical tempering treatment, the surface compressive stress and the compressive stress layer depth were measured. The results are shown in the columns for CS for P (unit: MPa) and DOL for P (unit: m) in Tables.

(74) By using such a sample subjected to the chemical tempering treatment at 450 C., the cracking probability P was measured when a load of 200 gf (=1.96N) was exerted by means of a Vickers hardness meter using a pyramid-shaped diamond indenter with a vertex angle of 110. That is, under conditions of a temperature of 24 C. and a dew point of from 35 to 45 C. in the atmosphere, the Vickers indenter was pressed at 10 points with a load of the Vickers hardness meter adjusted to 200 g, whereby the number of cracks formed at the four corners of indentations was measured. One obtained by dividing this number of cracks formed, by 40 i.e. the possible number of cracks expected, was taken as the cracking probability P. Here, P in Ex. 22 to 25, 28, 50 and 51 is one when the thickness is 3.0 mm, CS for P is 800 MPa and DOL for P is 45 m.

(75) The lower the cracking probability P, the better. Specifically, P is preferably at most 0.80. With glasses in working Examples of the present invention, P does not exceed 0.80, thus indicating that cracking is less likely to occur.

(76) Further, when CT is the same, P becomes small when CS is large. The reason is as follows. That is, when a pyramid-shaped diamond indenter with a vertex angle of 110 is pressed against the glass, cracks will be formed in a direction perpendicular to the pressing direction. An internal tensile stress will work as a force to tear the formed cracks and to break the glass, and therefore, if cracks are formed in glass having a large CT, the glass tends to undergo breakage. On the other hand, if CT is the same, glass having a larger CS working against the tearing force of the internal tensile stress, tends to be less likely to break.

(77) Further, when CT is small, P becomes small. The reason is as follows. That is, cracks formed by pressing of the pyramid-shaped diamond indenter are mainly of a type extending in a perpendicular direction from the surface, and therefore, such cracking is attributable to a stress distribution formed by elastic deformation during the pressing. Therefore, with respect to a tempered glass, the surface compressive stress and the tensile stress distributed in the thickness direction are influential over its cracking, and particularly the stress site due to elastic deformation is widely distributed in the thickness direction, and therefore, the influence of the tensile stress layer formed in a wide region is substantial.

(78) With respect to glasses in Ex. 12, 17 and 49 after the chemical tempering treatment, the acid resistance was measured as described above and found to be 12.35, 0.04 and 0.02 mg/cm.sup.2, respectively. When these data are compared with the acid resistance data before the chemical tempering treatment in Tables 2 and 6, there is a positive correlation between the two, and it is evident that the acid resistance after the chemical tempering treatment becomes 1.02 times the acid resistance before the chemical tempering treatment.

(79) TABLE-US-00001 TABLE 1 Ex. 1 2 3 4 5 6 SiO.sub.2 64 62 64 62 60 62 Al.sub.2O.sub.3 12 14 14 12 14 14 B.sub.2O.sub.3 0 0 0 0 0 0 MgO 8 8 8 10 10 10 CaO 0 0 0 0 0 0 ZrO.sub.2 0 0 0 0 0 0 Na.sub.2O 16 16 14 16 16 14 K.sub.2O 0 0 0 0 0 0 E 72 75 75 74 75 75 d 2.46 2.47 2.46 2.47 2.48 2.47 Tg 659* 689* 724* 661* 691* 726* T2 1657* 1691* 1783* 1611* 1645* 1737* T4 1242* 1292* 1370* 1221* 1271* 1349* TL 87* 87* 80* 88* 89* 82* Acid 0.12* 0.19* 0.14* 0.14* 0.21* 0.16* resistance S 1321 1431* 1334 1374* 1439 1341 t 41 42* 43 42* 34 31 CS 1400 1512 1393 1448 1514 1419 DOL 18 17 17 16 15 14 CT 27 27 24 23 23 21 CS for P 924 954 890 916 923 892 DOL for P 43 41 45 43 41 43 P 0.15 0.2 0.05 0.05 0.1 0.1 Z 1260 1366 1326 1286 1392 1352 Z2 1273 1436 1441 1270 1433 1438 Z3 0.121 0.188 0.144 0.143 0.210 0.166 Z4 44 50 50 46 52 52 X 0.3 0.1 0.1 0.3 0.1 0.1 Ex. 7 8 9 10 SiO.sub.2 60 58 60 60 Al.sub.2O.sub.3 12 14 14 12 B.sub.2O.sub.3 0 0 0 0 MgO 12 12 12 8 CaO 0 0 0 0 ZrO.sub.2 0 0 0 0 Na.sub.2O 16 16 14 20 K.sub.2O 0 0 0 0 E 75 77 78* 72 d 2.49 2.49 2.49* 2.48 Tg 663* 693* 728* 589* T2 1565 1598 1691 1473* T4 1200 1250 1328 1086* TL 90* 90* 83* 100* Acid 0.16* 0.23* 0.19* 0.21* resistance S 1346 1287* 1364 1343* t 26 24* 25 40* CS 1400* 1338* 1419* 1397* DOL 12* 11* 11* 18* CT 17* 15* 16* 26* CS for P 883 858 909 895 DOL for P 44 44 42 30 P 0.55 0.3 0.3 0.25 Z 1312 1418 1378 1340 Z2 1267 1430 1435 1262 Z3 0.164 0.231 0.187 0.210 Z4 48 54 54 44 X 0.3 0.1 0.1 0.3

(80) TABLE-US-00002 TABLE 2 Ex. 11 12 13 14 15 16 SiO.sub.2 58 60 66 66 66 68 Al.sub.2O.sub.3 14 14 11 12 13 9 B.sub.2O.sub.3 0 0 0 0 0 0 MgO 8 8 8 8 8 8 CaO 0 0 0 0 0 0 ZrO.sub.2 0 0 0 0 0 0 Na.sub.2O 20 18 15 14 13 15 K.sub.2O 0 0 0 0 0 0 E 73 73 72 73 75 71 d 2.49 2.48 2.45 2.45 2.45 2.44 Tg 619* 654* 662* 694* 727* 632* T2 1507* 1645 1687* 1750* 1812* 1687* T4 1136* 1227 1255* 1319* 1384* 1225* TL 1200-1220 101* 94* 83* 80* 77* 82* Acid 0.28* 11.54 0.06* 0.08* 0.09* 0* resistance S 1373 1446 1269 1307 1242 1078 t 46 42 40 40 38 44 CS 1524 1530 1324 1355 1352 1165 DOL 10 13 18 18 17 20 CT 16 20 25 25 23 24 CS for P 929 968 894 903 875 827 DOL for P 42 45 44 43 45 46 P 0.65 0.4 0.25 0.15 0.1 0.8 Z 1446 1406 1187 1220 1253 1081 Z2 1425 1430 1194 1278 1362 1031 Z3 0.277 0.233 0.065 0.077 0.088 .sup.0.002 Z4 50 50 41 44 47 35 X 0.1 0.1 0.4 0.3 0.2 0.6 Ex. 17 18 19 20 SiO.sub.2 68 68 68 68 Al.sub.2O.sub.3 10 11 9 10 B.sub.2O.sub.3 0 0 0 0 MgO 8 8 10 10 CaO 0 0 0 0 ZrO.sub.2 0 0 0 0 Na.sub.2O 14 13 13 12 K.sub.2O 0 0 0 0 E 72 73 73 74 d 2.44 2.43 2.44 2.44 Tg 665* 697* 669* 702* T2 1716 1779* 1699* 1762* T4 1263 1333* 1261* 1326* TL 1220-1230 79* 76* 77* 74* Acid 0.01 0.02* 0* 0* resistance S 1117 1201 1143 1131 t 42 40 34 33 CS 1248 1272 1198 1182 DOL 18 18 15 15 CT 23 24 19 18 CS for P 858 847 811 800 DOL for P 44 42 41 40 P 0.45 0.5 0.55 0.45 Z 1114 1147 1067 1100 Z2 1115 1199 1033 1118 Z3 0.010 0.021 .sup.0.025 .sup.0.013 Z4 38 41 37 40 X 0.5 0.4 0.6 0.5

(81) TABLE-US-00003 TABLE 3 Ex. 21 22 23 24 25 26 SiO.sub.2 68 61 60 58 55 63 Al.sub.2O.sub.3 11 15 15 15 20 14 B.sub.2O.sub.3 0 1 3 5 0 7.4 MgO 10 8 7 7 10 0.1 CaO 0 0 0 0 0 0.1 ZrO.sub.2 0 0 0 0 0 0 Na.sub.2O 11 15 15 15 15 15 K.sub.2O 0 0 0 0 0 0.6 E 75 80* 78* 76* 79* 64 d 2.44 2.47* 2.46* 2.46* 2.50* 2.38 Tg 734* 716* 704* 693* 696* 628 T2 1825* 1734* 1717* 1677* 1791* 1932 T4 1390* 1344* 1331* 1307* 1462* 1426 TL 71* 83* 82* 81* 82* 79 Acid 0* 0.21* 0.21* 0.22* 0.39* 0.14* resistance S 1069 1318* 1244* 1175* 1348* 954 t 33 38* 34* 25* 19* 44 CS 1117 1371* 1294* 1222* 1402* 992* DOL 14 16* 20* 14* 11* 25* CT 17 22* 26* 18* 16* 27* CS for P 773 954 DOL for P 39 44 P 0.6 0* .sup.0.3* .sup.0.7* 1* 1 Z 1133 1367 1290 1226 1690 932 Z2 1202 1925 Z3 .sup.0.002 .sup.0.389 Z4 43 53 52 52 70 36 X 0.4 0.4 1.2 2 0.5 3.26 Ex. 27 28 29 30 SiO.sub.2 70 65 66 64 Al.sub.2O.sub.3 9 15 11 12 B.sub.2O.sub.3 0 0 0 0 MgO 7 5 8 8 CaO 0 0 0 0 ZrO.sub.2 0 0 0 0 Na.sub.2O 14 15 15 16 K.sub.2O 0 0 0 0 E 72 78* 76 77 d 2.42 2.45* 2.45 2.47 Tg 649 719* 662 659 T2 1723 1823* 1707 1677 T4 1254 1388* 1285 1272 TL 78 82* 83 87 Acid 0* 0.17* 0.06 0.14 resistance S 991 1398* 1235 1317 t 47 56* 41 43 CS 1031* 1454* 1320 1399 DOL 27* 16* 20 18 CT 30* 24* 27 26 CS for P 1101 DOL for P 33 P 0.8 0.1* Z 1048 1360 1187 1260 Z2 1035 1525 1194 1273 Z3 .sup.0.035 0.168 0.065 0.121 Z4 34 50 41 44 X 0.6 0 0.4 0.3

(82) TABLE-US-00004 TABLE 4 Ex. 31 32 33 34 35 36 SiO.sub.2 62 61.4 62.7 64.1 65.4 61.2 Al.sub.2O.sub.3 13 12.9 11.8 10.7 9.6 14.3 B.sub.2O.sub.3 0 0 0 0 0 0 MgO 8 7.9 7.8 7.8 7.7 8.2 CaO 0 0 0 0 0 0 ZrO.sub.2 0 0 0 0 0 0 Na.sub.2O 17 17.8 17.6 17.5 17.3 16.3 K.sub.2O 0 0 0 0 0 0 E 78* 77* 76* 74* 73* 80* d 2.48* 2.49* 2.48* 2.47* 2.46* 2.48* Tg 657* 640* 627* 614* 601* 688* T2 1648* 1610* 1601* 1593* 1585* 1697* T4 1258* 1223* 1203* 1183* 1163* 1315* TL 90* 93* 92* 91* 90* 88* Acid 1.88 3.92 0.31 0.11 0.06 11.3 resistance S 1352 1300 1226 1120 1012 1414 t 42 43 46 46 47 40 CS 1482 1424 1319 1204 1107 1502 DOL 19 20 21 22 22 18 CT 30 30 28 27 26 28 CS for P DOL for P P Z 1333 1342 1278 1217 1156 1390 Z2 1352 1341 1252 1163 1074 1459 Z3 0.177 0.190 0.148 0.108 0.066 0.207 Z4 47 47 43 40 37 51 X 0.2 0.2 0.3 0.4 0.5 0.1 Ex. 37 38 39 40 SiO.sub.2 62.6 65.3 66.7 63.7 Al.sub.2O.sub.3 13.1 10.9 9.8 11.4 B.sub.2O.sub.3 0 0 0 0 MgO 8.1 7.9 7.8 8.0 CaO 0 0 0 0 ZrO.sub.2 0 0 0 1.0 Na.sub.2O 16.2 15.8 15.7 15.9 K.sub.2O 0 0 0 0 E 78* 75* 74* 75 d 2.47* 2.46* 2.45* 2.49 Tg 673* 646* 632* 667 T2 1687* 1668* 1659* 1665 T4 1293* 1250* 1230* 1245 TL 1210-1220 87* 86* 85* 85 Acid 0.67 0.07 0.04 0.07 resistance S 1369 1210 1115 1337 t 40 43 44 37 CS 1446 1299 1201 1426 DOL 18 19 20 17 CT 28 26 25 25 CS for P DOL for P P Z 1324 1197 1135 1226 Z2 1362 1183 1095 1302 Z3 0.164 0.079 0.038 0.086 Z4 47 41 37 42 X 0.2 0.4 0.5 0.8

(83) TABLE-US-00005 TABLE 5 Ex. 41 42 43 44 45 46 SiO.sub.2 63.4 64 64 64 64 68.2 Al.sub.2O.sub.3 10.9 12 12 12 12 10.9 B.sub.2O.sub.3 0 0 0 0 0 0 MgO 7.9 8 8 7 6 5.8 CaO 0 0 0 0 0 0.1 ZrO.sub.2 2.0 1 2 1 2 0 Na.sub.2O 15.8 15 14 16 16 15.1 K.sub.2O 0 0 0 0 0 0 E 77* 78 75 76 76 73* d 2.53* 2.51 2.48 2.51 2.48 2.44* Tg 645* 705 676 693 689 644* T2 1668* 1724* 1770* 1701* 1724* 1752* T4 1250* 1310* 1349* 1282* 1292* 1303* TL 1250-1260 88* 77 86 81 80 82* Acid 0.06 0.06 0.06 0.11 0.07 1.1 resistance S 1418 1325 1344 1356 1437 1044 t 34.3 50 31.4 40 39.6 49 CS 1488 1420 1406 1439 1514 1085 DOL 15 17 14 18 18 22 CT 24 24 21 28 28 25 CS for P DOL for P P Z 1193 1238 1216 1245 1230 1154 Z2 1339 1353 1433 1352 1431 Z3 0.052 0.086 0.051 0.097 0.073 Z4 41 44 44 43 42 38 X 1.2 0.7 1.1 0.7 1.1 0.4

(84) TABLE-US-00006 TABLE 6 Ex. 47 48 49 50 51 SiO.sub.2 67 72.5 72 73 84 Al.sub.2O.sub.3 11 6.2 1.1 9 3 B.sub.2O.sub.3 0 0 0 0 0 MgO 6 8.5 5.5 6 1 CaO 0 0 8.6 0 0 ZrO.sub.2 0 0 0 0 0 Na.sub.2O 13 12.8 12.8 12 12 K.sub.2O 2 0 0.2 0 0 E 71 71 73 72 59 d 2.44 2.41 2.49 2.40 2.33 Tg 595 627 540 683 589 T2 1825 1697 1681 1838 1853 T4 1354 1214 1116 1342 1242 TL 93 74 88 71 66 Acid resistance 0.02* 0* 0.02 0* 0* S 884 864 600 1011 275 t 48 31 14 52 74 CS 919 899 624 1051* 286* DOL 28 18 8 30* 43* CT 27 17 5 34* 13* CS for P 899 790 500 DOL for P 46 45 34 P 0.75 0.75 1 0.9* 1* Z 863 895 995 612 Z2 808 1042 561 Z3 0.139 0.090 0.345 Z4 19 27.1 6.8 33 10 X 1.6 0.88 4.83 0.6 1.2

(85) TABLE-US-00007 TABLE 7 Ex. 52 53 54 55 56 SiO.sub.2 64.5 64 64.5 65 64.6 Al.sub.2O.sub.3 12 12 11.5 12.5 12.1 B.sub.2O.sub.3 0 0 0 0 0 MgO 8 8 8 8 8 CaO 0 0 0 0 0 ZrO.sub.2 0.5 0.5 1 0.5 0.7 Na.sub.2O 15 15.5 15 14 14.6 K.sub.2O 0 0 0 0 0 E 75* 75* 76* 76 76 d 2.47* 2.47* 2.5* 2.47* 2.48* Tg 678* 672* 679* 694* 686* T2 1713* 1695* 1708* 1754* 1729* T4 1276* 1260* 1269* 1317* 1291* TL 1250-1260 1240-1250 1230-1240 >1250 >1250 82* 84* 82* 78* 80* Acid 0.056 0.07 0.03 0.04 0.04 resistance S 1337 1361 1351 1316 1345 t 38.7 36.3 38.6 36.6 36.4 CS DOL CT CS for P DOL for P P Z 1230 1239 1249 1211 1245 Z2 1314 1313 1312 1358 1339 Z3 0.092 0.103 0.069 0.087 0.084 Z4 42 44 44 42.5 45.5 X

INDUSTRIAL APPLICABILITY

(86) The glass for chemical tempering and the chemically tempered glass of the present invention are useful for e.g. cover glasses for display devices. Further, they are useful for solar cell substrates, window glasses for aircrafts, etc.

(87) This application is a continuation of PCT Application No. PCT/JP2012/079849, filed on Nov. 16, 2012, which is based upon and claims the benefit of priority from Japanese Patent Application No. 2011-253102 filed on Nov. 18, 2011 and Japanese Patent Application No. 2012-126388 filed on Jun. 1, 2012. The contents of those applications are incorporated herein by reference in their entireties.