Aluminoborosilicate glass and preparation method and application thereof

Abstract

The present invention relates to the field of glass manufacturing, and discloses aluminoborosilicate glass, and a preparation method and an application thereof. Based on the total weight of components in the composition of the glass, the glass comprises: 33-60 wt % SiO.sub.2, 3-10 wt % Al.sub.2O.sub.3, 10-30 wt % B.sub.2O.sub.3, 1-15 wt % ZnO+TiO.sub.2+Sc.sub.2O.sub.3, and 7-27 wt % alkaline-earth oxide RO, wherein RO is at least one of MgO, CaO, SrO and BaO, and 0.001 wt %≤Sc.sub.2O.sub.3≤1 wt%. The aluminoborosilicate glass provided in the present invention has advantages including low density, high index of refraction, low thermal expansion coefficient, high thermostability, high flexibility, and easy bending, etc.

Claims

1. Aluminoborosilicate glass, based on the total weight of components in the composition of the glass, comprising: 33-60 wt % SiO.sub.2, 3-10 wt % Al.sub.2O.sub.3, 10-30 wt % B.sub.2O.sub.3, 1-15 wt % ZnO+TiO.sub.2+Sc.sub.2O.sub.3, and 7-27 wt % alkaline-earth oxide RO, wherein RO is at least one of MgO, CaO, SrO and BaO, and 0.001 wt %≤Sc.sub.2O.sub.3≤1 wt %.

2. The aluminoborosilicate glass of claim 1, wherein based on the total weight of components in the composition of the glass, the contents of the components of the glass measured in weight percentage meet: (MgO+BaO)/(MgO+CaO+SrO+BaO)>0.6.

3. The aluminoborosilicate glass of claim 1, wherein based on the total weight of components in the composition of the glass, the contents of the components of the glass measured in weight percentage meet: ZnO/(ZnO+TiO.sub.2+Sc.sub.2O.sub.3)>0.6.

4. The aluminoborosilicate glass of claim 1, wherein based on the total weight of components in the composition of the glass, the contents of the components of the glass measured in weight percentage meet: 0.1 wt %≤Sc.sub.2O.sub.3≤0.7 wt %.

5. The aluminoborosilicate glass of claim 1, wherein based on the total weight of components in the composition of the glass, the contents of the components of the glass measured in weight percentage meet: 40 wt %≤SiO.sub.2+Al.sub.2O.sub.3≤65 wt %.

6. The aluminoborosilicate glass of claim 1, wherein based on the total weight of components in the composition of the glass, the contents of the components of the glass measured in weight percentage meet: the brittleness coefficient D is 0-1, wherein the value D is calculated with the following formula:
D=P.sub.1*SiO.sub.2+2.0*B.sub.2O.sub.3−2.0*(Al.sub.2O.sub.3+CaO)+0.5*SrO+1.0*(MgO+BaO+ZnO+TiO.sub.2+Sc.sub.2O.sub.3)−4*ΣQ wherein SiO.sub.2, B.sub.2O.sub.3, Al.sub.2O.sub.3, MgO, CaO, SrO, BaO, ZnO, TiO.sub.2, and Sc.sub.2O.sub.3 respectively represent the weight percentages of the components in the total weight, ΣQ represents the sum of other components except SiO.sub.2, B.sub.2O.sub.3, Al.sub.2O.sub.3, MgO, CaO, SrO, BaO, ZnO, TiO.sub.2, and Sc.sub.2O.sub.3, and P.sub.1 is 0.2 if 33 wt %≤SiO.sub.2≤54 wt %, or is −0.5 if 54 wt %<SiO.sub.2≤60 wt %.

7. The aluminoborosilicate glass of claim 1, wherein the density of the aluminoborosilicate glass is lower than 3 g/cm3; the refractive index nD is greater than 1.52; the thermal expansion coefficient within 50-350° C. range is lower than 45×10−7/° C.

8. The aluminoborosilicate glass of claim 1, wherein the bending coefficient CR of aluminoborosilicate glass in thickness ≤0.5 mm meets: 0<CR<0.5 , wherein the CR value is calculated with the following formula:
CR=(R*σ)/(E*d) wherein E is the Young's modulus of the aluminoborosilicate glass, in unit of MPa; d is the thickness of the aluminoborosilicate glass, in unit of mm; R is the minimum curvature radius of the aluminoborosilicate glass when the aluminoborosilicate glass is bent, in unit of mm; σ is the bending stress in the aluminoborosilicate glass the curvature radius R, in unit of MPa.

9. The aluminoborosilicate glass of claim 1, wherein the strain point temperature of the aluminoborosilicate glass is higher than 680° C., and/or the difference between the forming temperature T4 and the liquidus temperature Tl of the aluminoborosilicate glass is greater than 100° C., and/or the Young's modulus of the aluminoborosilicate glass is smaller than 80 GPa.

10. A method for preparing aluminoborosilicate glass, comprising: providing a raw material composition according to the composition of the aluminoborosilicate glass of claim 1, and treating the raw material composition by melting, forming, annealing, and machining sequentially.

11. A method for preparing a display device and/or solar cell comprising providing the aluminoborosilicate glass of claim 1.

12. The aluminoborosilicate glass of claim 6, the contents of the components of the glass measured in weight percentage meet: the brittleness coefficient D is 0.2-0.8.

13. The aluminoborosilicate glass of claim 6, the contents of the components of the glass measured in weight percentage meet: the brittleness coefficient D is 0.3-0.6.

14. The aluminoborosilicate glass of claim 7, wherein the density of the aluminoborosilicate glass is 2.43-2.68 g/cm.sup.3; the refractive index n.sub.D is 1.52<n.sub.D<1.55; the thermal expansion coefficient within 50-350° C. range is 29×10.sup.−7/° C.−41×10.sup.−7/° C.

15. The aluminoborosilicate glass of claim 8, wherein the bending coefficient C.sub.R of aluminoborosilicate glass in thickness ≤0.5 mm meets: 0<C.sub.R<0.45.

16. The aluminoborosilicate glass of claim 8, wherein the bending coefficient C.sub.R of aluminoborosilicate glass in thickness ≤0.5 mm meets: 0<C.sub.R<0.4.

17. The method of claim 10, wherein the method further comprises treating the product obtained through the machining process by secondary melting and thinning.

18. The method of claim 10, wherein the conditions of the machining process or the secondary melting and thinning process are controlled to prepare glass in thickness smaller than 0.1 mm.

19. The method of claim 11, further comprising applying the aluminoborosilicate glass (1) as a glass substrate material and/or a glass film material to a screen surface of a flat panel display product as a screen protection, (2) as a surface packaging and/or a glass film material of a flexible display product for screen surface protection thereof, or (3) as a glass substrate material of flexible solar cell.

Description

DETAILED DESCRIPTION OF THE EMBODIMENTS

(1) The ends points and any value in the ranges disclosed in the present invention are not limited to the exact ranges or values; instead, those ranges or values shall be comprehended as encompassing values that are close to those ranges or values. For numeric ranges, the end points of the ranges, the end points of the ranges and the discrete point values, and the discrete point values may be combined with each other to obtain one or more new numeric ranges, which shall be deemed as having been disclosed specifically in this document.

(2) In a first aspect, the present invention provides aluminoborosilicate glass, based on the total weight of components in the composition of the glass, compriseing: 33-60 wt % SiO.sub.2, 3-10 wt % Al.sub.2O.sub.3, 10-30 wt % B.sub.2O.sub.3, 1-15 wt % ZnO+TiO.sub.2+Sc.sub.2O.sub.3, and 7-27 wt % alkaline-earth oxide RO, wherein RO is at least one of MgO, CaO, SrO and BaO, and 0.001 wt %≤Sc.sub.2O.sub.3≤1 wt %.

(3) Preferably, based on the total weight of components in the composition of the glass, the contents of the components of the glass measured in weight percentage meet: (MgO+BaO)/(MgO+CaO+SrO+BaO)>0.6.

(4) Preferably, based on the total weight of components in the composition of the glass, the contents of the components of the glass measured in weight percentage meet: ZnO/(ZnO+TiO.sub.2+Sc.sub.2O.sub.3)>0.6.

(5) Preferably, based on the total weight of components in the composition of the glass, the contents of the components of the glass measured in weight percentage meet: 0.1 wt %≤Sc.sub.2O.sub.3≤0.7 wt %.

(6) Preferably, based on the total weight of components in the composition of the glass, the contents of the components of the glass measured in weight percentage meet: 40 wt %≤SiO.sub.2+Al.sub.2O.sub.3≤65 wt %.

(7) Preferably, based on the total weight of components in the composition of the glass, the contents of the components of the glass measured in weight percentage meet: the brittleness coefficient D is 0-1, further preferably is 0.2-0.8, and still further preferably is 0.3-0.6, wherein the value D is calculated with the following formula:
D=P.sub.1*SiO.sub.2+2.0*B.sub.2O.sub.3−2.0*(Al.sub.2O.sub.3+CaO)+0.5*SrO+1.0*(MgO+BaO+ZnO+TiO.sub.2+Sc.sub.2O.sub.3)−4*ΣQ

(8) Wherein SiO.sub.2, B.sub.2O.sub.3, Al.sub.2O.sub.3, MgO, CaO, SrO, BaO, ZnO, TiO.sub.2, and Sc.sub.2O.sub.3 respectively represent the weight percentages of the components in the total weight, ΣQ represents the sum of other components except SiO.sub.2, B.sub.2O.sub.3, Al.sub.2O.sub.3, MgO, CaO, SrO, BaO, ZnO, TiO.sub.2, and Sc.sub.2O.sub.3, and P.sub.1 is 0.2 if 33 wt %≤SiO.sub.2≤54 wt %, or is −0.5 if 54 wt %<SiO.sub.2≤60 wt %.

(9) Preferably, the density of the aluminoborosilicate glass is lower than 3 g/cm.sup.3, further preferably is 2.43-2.68 g/cm.sup.3;

(10) Preferably, the refractive index n.sub.D of the aluminoborosilicate glass is greater than 1.52, further preferably 1.52<n.sub.D<1.55.

(11) Preferably, the thermal expansion coefficient of the aluminoborosilicate glass within 50-350° C. range is lower than 45×10.sup.−7/° C., further preferably is 29×10.sup.−7/° C.−41×10.sup.−7/° C.

(12) Preferably, the bending coefficient C.sub.R of aluminoborosilicate glass in thickness ≤0.5 mm meets: 0<C.sub.R<0.5, further preferably 0<C.sub.R<0.45, still further preferably 0<C.sub.R<0.4, wherein the C.sub.R value is calculated with the following formula:
C.sub.R=(R*σ)/(E*d)

(13) Wherein E is the Young's modulus of the aluminoborosilicate glass, in unit of MPa; d is the thickness of the aluminoborosilicate glass, in unit of mm; R is the minimum curvature radius of the aluminoborosilicate glass when the aluminoborosilicate glass is bent, in unit of mm; σ is the bending stress in the aluminoborosilicate glass in curvature radius R, in unit of MPa. Wherein the lower the C.sub.R value is, the higher the flexibility of the glass is, and the higher the bendability of the glass is.

(14) Preferably, the strain point temperature of the aluminoborosilicate glass provided in the present invention is higher than 680° C.

(15) Preferably, the difference between the forming temperature T.sub.4 and the liquidus temperature T.sub.1 of the aluminoborosilicate glass provided in the present invention is greater than 100° C. Wherein T.sub.4 is the forming temperature corresponding to 40,000 P viscosity value.

(16) Preferably, the Young's modulus of the aluminoborosilicate glass provided in the present invention is smaller than 80 GPa.

(17) Preferably, the transmittance of the aluminoborosilicate glass provided in the present invention is 91% or above.

(18) In a second aspect, the present invention provides a method for preparing aluminoborosilicate glass, comprising: providing a raw material composition according to composition of the aluminoborosilicate glass in the present invention, and treating the raw material composition by melting, forming, annealing, and machining sequentially.

(19) Wherein specifically the present invention further provides a raw material composition, based on the total weight of the composition, on an oxide basis, comprising 33-60 wt % SiO.sub.2, 3-10 wt % Al.sub.2O.sub.3, 10-30 wt % B.sub.2O.sub.3, 1-15 wt % ZnO+TiO.sub.2+Sc.sub.2O.sub.3, and 7-27 wt % alkaline-earth oxide RO, wherein RO is at least one of MgO, CaO, SrO, and BaO, and 0.001 wt %≤Sc.sub.2O.sub.3≤1 wt %.

(20) In the raw material composition in the present invention, SiO.sub.2 is a base material for forming a network structure, can improve the heat resistance and chemical durability of the glass, makes the glass resistant to devitrification, and is beneficial for the vitrification process. However, excessive SiO.sub.2 may cause increased melting temperature and increased brittleness, is adverse to improvement of the refractive index n.sub.D, and introduces extremely high requirements for the production process. The inventor of the present invention has further found in the research: when the content of SiO.sub.2 is ≥33 wt % measured in mass percentage, the mechanical properties and chemical resistance of the obtained glass can be further improved; however, the flexibility of the glass will be degraded if the content is too high. Therefore, in order to further improve the overall properties and flexibility of the obtained glass, preferably, based on the total weight of the composition and measured in oxide in weight percentage, the content of SiO.sub.2 should be: 33 wt %≤SiO.sub.2≤60 wt %. Further preferably, measured in mass percentage, 33 wt %≤SiO.sub.2≤54 wt %.

(21) In the raw material composition in the present invention, as a base material for aluminoborosilicate glass, B.sub.2O.sub.3 can form glass separately and can improve the flexibility of the glass; besides, B.sub.2O.sub.3 is an ideal solubilizer, can greatly decrease the melting temperature of the glass, and is beneficial for the vitrification process as well; however, excessively high B.sub.2O.sub.3 content is adverse to the improvement of thermostability and refractive index n.sub.D. Therefore, with comprehensive consideration, based on the total weight of the composition and measured in oxide in weight percentage, the content of B.sub.2O.sub.3 should be: 10 wt %≤B.sub.2O.sub.3≤30 wt %.

(22) In the raw material composition in the present invention, Al.sub.2O.sub.3 can promote the integrity of network connections and greatly improve the heat resistance of the glass, but make the structure of the glass tend to be rigid and increase the brittleness of the glass, and may result in devitrification of the glass and excessive high-temperature surface tension and high-temperature viscosity, inhibit the improvement of the refractive index n.sub.D and increase the difficulties in the glass production process, etc. Therefore, with comprehensive consideration, based on the total weight of the composition and measured in oxide, the content of Al.sub.2O.sub.3 is within 3-10 wt % range.

(23) In the raw material composition in the present invention, preferably, based on the total weight of the composition, on an oxide basis, 40 wt %≤SiO.sub.2+Al.sub.2O.sub.3≤65 wt %.

(24) In the raw material composition in the present invention, MgO, CaO, SrO, and BaO belong to alkaline-earth oxides, can effectively decrease the high-temperature viscosity of the glass and thereby improve the melting and forming performance of the glass, and improve the strain point and refractive index n.sub.D of the glass as well; besides, MgO and BaO can decrease the brittleness of the glass. However, if the content of these alkaline-earth oxides is excessive, the density will be increased, the occurrence rates of cracks, devitrification, and phase separation will be increased; besides, excessive CaO is adverse to the improvement of the flexibility of the glass. Therefore, with comprehensive consideration, based on the total weight of the composition and the weight of each component, on an oxide basis, the glass contains 7-27 wt % alkaline-earth oxides RO, wherein RO is one or more of MgO, CaO, SrO and BaO. Preferably, based on the total weight of the composition, on an oxide basis, (MgO+BaO)/(MgO+CaO+SrO+BaO)>0.6.

(25) In the raw material composition in the present invention, ZnO, TiO.sub.2, and Sc.sub.2O.sub.3 can effectively decrease the high-temperature viscosity and upper limit of devitrification temperature of the glass, and attain effects of improving strength, hardness, chemical resistance and flexibility of the glass and remarkably increasing the refractive index n.sub.D of the glass at temperatures lower the softening point of the glass. However, excessive ZnO, TiO.sub.2 and Sc.sub.2O.sub.3 are adverse to the improvement of the stability of glass formation. Therefore, with comprehensive consideration, based on the total weight of the composition, on an oxide basis, the content of ZnO+TiO.sub.2+Sc.sub.2O.sub.3 is within 1-15 wt % range, preferably ZnO/(ZnO+TiO.sub.2+Sc.sub.2O.sub.3)>0.6. Wherein Sc.sub.2O.sub.3 can remarkably improve the heat resistance and refractive index n.sub.D, and can improve the bending performance of the glass in the case that the glass is made into ultra-thin glass; however, excessive Sc.sub.2O.sub.3 is adverse to the stability of glass formation. Therefore, with comprehensive consideration, 0.001 wt %≤Sc.sub.2O.sub.3≤1 wt %, preferably 0.1 wt %≤Sc.sub.2O.sub.3≤0.7 wt %.

(26) In the raw material composition in the present invention, depending on the specific glass preparation process, the composition may further contain a clarifier during glass melting, wherein the clarifier preferably is at least one of sulfate, nitrate, halide, tin oxide, and stannous oxide; based on the total weight of the components, on an oxide basis, the content of the clarifier is not higher than 1 wt %. There is no particular restriction on the specific selection of the clarifier. In other words, the clarifier may be any common clarifier in the art. For example, the sulfate may be barium sulfate, the nitrate may be barium nitrate, and the halide may be barium chloride and/or calcium fluoride.

(27) Those skilled in the art should understand that the expression “the raw material composition in the present invention contains SiO.sub.2, B.sub.2O.sub.3, Al.sub.2O.sub.3, ZnO, TiO.sub.2, Sc.sub.2O.sub.3, MgO, CaO, SrO, and BaO” means that the composition contains Si-containing compounds, B-containing compounds, Al-containing compounds, Zn-containing compounds, Ti-containing compounds, Sc-containing compounds, Mg-containing compounds, Ca-containing compounds, Sr-containing compounds, and Ba-containing compounds. For example, the composition for glass contains carbonates, nitrates, sulfates, phosphates, basic carbonates and oxides, etc. of the aforesaid elements. In addition, the contents of the aforesaid components are measured in the oxides of the elements, respectively. The specific selections of the carbonates, nitrates, sulfates, phosphates, basic carbonates and oxides of the elements are well known to those skilled in the art, and will not be further detailed here.

(28) When the raw material composition in the present invention is utilized to prepare aluminoborosilicate glass, the obtained glass has the aforesaid excellent overall properties, mainly owing to the cooperation among the components, especially the cooperation among SiO.sub.2, B.sub.2O.sub.3, Al.sub.2O.sub.3, ZnO, TiO.sub.2, Sc.sub.2O.sub.3, MgO, CaO, SrO, and BaO, particularly the cooperation among the aforesaid components in specific contents.

(29) In the method provided in the present invention, preferably, the conditions for melting treatment include: temperature: lower than 1,550° C.; time: longer than 1 h. Those skilled in the art can determine the specific melting temperature and melting time according to the actual circumstance. The specific melting temperature and melting time are well known to those skilled in the art, and will not be further detailed here.

(30) In the method provided in the present invention, preferably, the conditions for annealing treatment include: temperature: higher than 720° C.; time: longer than 0.1 h. Those skilled in the art can determine the specific annealing temperature and annealing time according to the actual circumstance. The specific annealing temperature and annealing time are well known to those skilled in the art, and will not be further detailed here.

(31) In the method provided in the present invention, there is no particular restriction on the machining. In other words, the machining may be any common machining in the art. For example, the product obtained through the annealing treatment may be cut, ground, and polished, etc.

(32) Preferably, the method further comprises treating the product obtained through the machining process by secondary melting and thinning, further preferably, the conditions of the machining process or the secondary melting and thinning process are controlled to prepare glass in thickness smaller than 0.1 mm.

(33) In the method in the present invention, plate glass in thickness greater than 0.1 mm or flexible glass in thickness smaller than 0.1 mm (i.e., flexible glass in thickness <0.1 mm obtained through an one-step forming process) may be produced with a variety of common glass production methods, such as float method, overflow method, and down-drawing method, etc., or flexible glass in thickness smaller than 0.1 mm may be produced with a secondary melting and thinning method. Therefore, the method may further comprise treating the product obtained through the machining process by secondary melting and thinning to prepare flexible glass in thickness smaller than 0.1 mm. There is no particular restriction on the specific method for secondary melting and thinning. In other words, the method may be any common method in the art. For example, the method for secondary melting and thinning may comprise: producing plate glass in thickness smaller than 1 mm with a glass manufacturing method such as float method, overflow method, or down-drawing method, conveying the plate glass to a feed port of a secondary stretch forming apparatus, feeding the plate glass into a stretch forming furnace at an appropriate feeding rate V.sub.0 mm/min., controlling the viscosity in the stretch forming area to be within 10.sup.5.5˜10.sup.7 P range, performing roll-to-roll winding on the stretching machine and drum at an appropriate stretching rate V.sub.1 mm/min., so as to obtain a ultra-thin flexible glass plate material in thickness smaller than 0.1 mm, wherein the stretching rate V.sub.1 is greater than V.sub.0.

(34) In a third aspect, the present invention provides aluminoborosilicate glass prepared with the method described above.

(35) As described above, glass products different in thickness may be manufactured through different processes. Specifically, plate glass in thickness greater than 0.1 mm or flexible glass in thickness smaller than 0.1 mm may be produced with a variety of common glass production methods, such as float method, overflow method, and down-drawing method, etc., or flexible glass in thickness smaller than 0.1 mm may be produced further with a secondary melting and thinning method. Wherein the bending coefficient C.sub.R of flexible glass in thickness ≤0.5 mm is smaller than 0.5, preferably smaller than 0.45, further preferably smaller than 0.4.

(36) In a fourth aspect, the present invention provides an application of the aluminoborosilicate glass provided in the present invention in preparation of display device and/or solar cell, preferably an application in preparation of a glass substrate material and/or a glass film material for screen surface protection of flat panel display products, a glass substrate material and/or a glass material for surface packaging and/or a glass film material for screen surface protection of flexible display products, or a glass substrate material of flexible solar cell, and application in other application fields where a glass material that has higher thermostability and high flexibility and is easy to bend is required.

(37) Embodiments

(38) Hereunder the present invention will be detailed in embodiments. In the following embodiments, unless otherwise specified, all of the materials are commercially available, and all of the methods are conventional methods in the art.

(39) In the following embodiments and reference examples, the density of glass is measured as per ASTM C-693, in unit of g/cm.sup.3.

(40) The thermal expansion coefficient of the glass at 50-350° C. is measured with a horizontal dilatometer as per ASTM E-228, in unit of 10.sup.−7/° C.

(41) The Young's modulus of glass is measured with a mechanical tester for materials as per ASTM C-623, in unit of GPa.

(42) The strain point of the glass with a three-point tester as per ASTM C-336, in unit of ° C.

(43) The transmittance of the glass corresponding to 550 nm wavelength is measured with an UV-2600 UV-visible spectrophotometer.

(44) The liquidus temperature T.sub.1 of the glass is measured with a temperature gradient furnace method as per ASTM C-829, in unit of ° C.

(45) A viscosity-temperature curve of glass at high temperatures is measured with a rotary high-temperature viscosimeter as per ASTM C-965; wherein the melting temperature corresponding to 200 P viscosity is denoted as T.sub.m, in unit of ° C.; the forming temperature corresponding to 40,000 P viscosity is denoted as T.sub.4, in unit of ° C.

(46) The refractivity n.sub.D at 587.6 nm wavelength (sodium yellow laser) is measured at room temperature with a WAY-2S Abbe digital display refractometer.

(47) The minimum curvature radius and bending stress of glass in thickness ≤0.5 mm are measured with a curvature radius and bending stress tester, and the value of the bending coefficient C.sub.R is obtained through calculation.

(48) Embodiments 1-18 and Reference Examples 1-8

(49) The components of glass are weighed as indicated in Tables 1-4 and mixed to a homogeneous state, the mixture is poured into a platinum crucible, then the crucible is heated in a resistance oven at 1,530° C. for 4 h, while the mixture is stirred with a platinum rod to expel the bubbles. The molten glass is poured into a stainless steel/cast iron mold and formed into glass product in a specified shape, then the glass product is annealed in an annealing furnace for 2 h, and then the power is turned off and the glass product is cooled in the furnace to 25° C. The glass product is cut, ground and polished, and then washed with deionized water and dried. Thus, a finished glass product in 0.5 mm thickness meeting the testing requirements is produced. The properties of the glass product are tested respectively. The results are shown in Tables 1-4.

(50) TABLE-US-00001 TABLE 1 Example Example Example Example Example Example wt % 1 2 3 4 5 6 SiO.sub.2 45.0 50.2 52.3 33.3 36.8 40 Al.sub.2O.sub.3 8.4 6.7 6.1 9.8 8.9 7 B.sub.2O.sub.3 21.3 17.3 13.3 29.9 28.1 23 MgO 4.6 5.3 0 7.3 6.2 5 CaO (introduced not as clarifier) 2.6 3.8 4.7 2 5.3 5 SrO (introduced not as clarifier) 0 0.9 3.8 3 0 1.4 BaO (introduced not as clarifier) 10 6.7 13.1 5 3 14.7 ZnO 6.8 6.2 6 8.5 7.3 2.65 TiO.sub.2 0.2 2.2 0 0 3.0 0.5 Sc.sub.2O.sub.3 0.5 0.4 0.2 1 0.7 0.05 La.sub.2O.sub.3 0 0 0 0 0 0 Nb.sub.2O.sub.5 0 0 0 0 0 0 ZrO.sub.2 0 0 0 0 0 0 Clarifier Calcium oxide introduced 0.3 0 0 0 0.4 0 as calcium fluoride Strontium oxide introduced 0 0 0 0 0 0.2 as strontium chloride Barium oxide introduced as 0.3 0 0.2 0 0.3 0.5 barium sulfate SnO.sub.2 0 0.3 0 0 0 0 SnO 0 0 0.3 0.2 0 0 SiO.sub.2 + Al.sub.2O.sub.3 53.4 56.9 58.4 43.1 45.7 47.0 ZnO/(ZnO + TiO.sub.2 + Sc.sub.2O.sub.3) 0.91 0.70 0.97 0.89 0.66 0.83 (MgO + BaO)/RO 0.84 0.72 0.61 0.71 0.63 0.75 RO 17.8 16.7 21.8 17.3 15.2 26.8 ZnO + TiO.sub.2 + Sc.sub.2O.sub.3 7.5 8.8 6.2 9.5 11.0 3.2 D 0.51 0.44 0.36 0.65 0.55 0.54 Density g/cm.sup.3 2.55 2.53 2.61 2.50 2.43 2.60 Coefficient of expansion *10.sup.−7/ 29.7 29.4 38.6 33.4 29.4 30.7 (50-350□) □ Young's modulus Gpa 68.6 69.4 65.4 69.9 71.5 70.2 refractivity n.sub.D 1.528 1.545 1.536 1.543 1.538 1.523 Melting temperature T.sub.m □ 1474 1534 1511 1471 1516 1528 Molding temperature T.sub.4 □ 1238 1267 1301 1253 1235 1222 Liquidus temperature T.sub.1 □ 1080 1080 1100 1100 1070 1070 T.sub.4 − T.sub.1 □ 158 187 201 153 165 152 Strain point □ 682 715 721 698 685 686 Transmittance % 91.4 92.1 91.1 91.3 91.7 91.4

(51) It should be noted that there are five types of clarifiers enumerated in the embodiments and reference examples in the Tables 1-4: CaF.sub.2, SrCl.sub.2, BaSO.sub.4, SnO.sub.2, and SnO. After the first three raw materials are fed into the furnace, a major fraction of the anions form gasses and escape from the glass liquid, while the remaining minor fraction of the anions are dissolved into the glass network structure. Owing to a fact that F.sup.−, Cl.sup.−, and SO.sub.4.sup.2− can't form uniform grids with O.sup.2−, they reside in the gaps in the network, just like Ca, Sr, and Ba cations do. Finally, covalent balance happens between Ca, Sr, and Ba cations and more oxygen ions. Therefore, when the three types of clarifiers CaF.sub.2, SrCl.sub.2 and BaSO.sub.4 are involved in the calculation of the D value in the examples and comparative examples in the present invention, they shall be still calculated according to the corresponding CaO, SrO and BaO, and shall not be included in ΣQ; in contrast, SnO.sub.2 and SnO shall be included in ΣQ.

(52) TABLE-US-00002 TABLE 2 Example Example Example Example Example Example wt % 7 8 9 10 11 12 SiO.sub.2 43.6 47 55 57 58 60 Al.sub.2O.sub.3 8.2 5 7.5 3 3 4 B.sub.2O.sub.3 25.7 19 18 15 11 14 MgO 0.5 4 3 1 9 1 CaO (introduced not as clarifier) 2 2 3 3.5 1.8 0.6 SrO (introduced not as clarifier) 0 1.0 1 0 0 0 BaO (introduced not as clarifier) 4.6 17 11 17.7 13.4 7 ZnO 11.2 3.2 0.89 1.97 1.9 7.999 TiO.sub.2 3 1.3 0.4 0 0.9 5 Sc.sub.2O.sub.3 0.8 0.3 0.01 0.03 0.1 0.001 La.sub.2O.sub.3 0 0 0 0 0 0 Nb.sub.2O.sub.5 0 0 0 0 0 0 ZrO.sub.2 0 0 0 0 0 0 Clarifier Calcium oxide introduced as 0 0 0 0.5 0.4 0 calcium fluoride Strontium oxide introduced 0 0 0 0 0.2 0 as strontium chloride Barium oxide introduced as 0.4 0.2 0.2 0.3 0.3 0 barium sulfate SnO.sub.2 0 0 0 0 0 0 SnO 0 0 0 0 0 0.4 SiO.sub.2 + Al.sub.2O.sub.3 51.8 52.0 62.5 60.0 61.0 64.0 ZnO/(ZnO + TiO.sub.2 + Sc.sub.2O.sub.3) 0.75 0.67 0.68 0.99 0.66 0.62 (MgO + BaO)/RO 0.73 0.88 0.78 0.83 0.90 0.93 RO 7.5 24.2 18.2 23.0 25.1 8.6 ZnO + TiO.sub.2 + Sc.sub.2O.sub.3 15.0 4.8 1.3 2.0 2.9 13.0 D 0.60 0.60 0.04 0.09 0.08 0.08 Density g/cm.sup.3 2.47 2.62 2.49 2.63 2.61 2.52 Coefficient of xpansion *10.sup.−7/ 31.1 32.0 32.9 36.8 39.1 33.2 (50-350□) □ Young's modulus Gpa 60.5 68.2 68.1 65.1 78.2 67.1 refractivity n.sub.D 1.532 1.527 1.522 1.523 1.524 1.548 Melting temperature T.sub.m □ 1529 1460 1509 1534 1526 1495 Molding temperature T.sub.4 □ 1230 1215 1252 1250 1241 1280 Liquidus temperature T.sub.1 □ 1090 1070 1200 1180 1180 1210 T.sub.4 − T.sub.1 □ 140 145 52 70 61 70 Strain point □ 688 682 684 698 686 694 Transmittance % 92.4 91.0 91.6 91.1 91.7 91.7

(53) TABLE-US-00003 TABLE 3 Example Example Example Example Example Example wt % 13 14 15 16 17 18 SiO.sub.2 50.2 50.2 59.7 50.2 40 33 Al.sub.2O.sub.3 6.7 6.7 10 9.7 3 3.5 B.sub.2O.sub.3 17.3 17.3 10 10.1 28 30 MgO 3.8 5.3 0 7 4 6 CaO (introduced not as clarifier) 5.3 3.8 3.6 6.3 2 0 SrO (introduced not as clarifier) 6.7 0.9 0.9 0.9 1 3 BaO (introduced not as clarifier) 0.9 6.7 6.7 6.7 17 14.5 ZnO 6.2 2.2 6.2 6.2 3.2 6.2 TiO.sub.2 2.2 6.2 2.2 2.2 1.4 3.4 Sc.sub.2O.sub.3 0.4 0.4 0.4 0.4 0.3 0.3 La.sub.2O.sub.3 0 0 0 0 0 0 Nb.sub.2O.sub.5 0 0 0 0 0 0 ZrO.sub.2 0 0 0 0 0 0 Clarifier Calcium oxide introduced as 0 0 0 0 0 0 calcium fluoride Strontium oxide introduced 0 0 0 0 0 0 as strontium chloride Barium oxide introduced as 0 0 0 0 0 0 barium sulfate SnO2 0.3 0.3 0.3 0.3 0.1 0.1 SnO 0 0 0 0 0 0 SiO.sub.2 + Al.sub.2O.sub.3 56.9 56.9 69.7 59.9 43 36.5 ZnO/(ZnO + TiO.sub.2 + Sc.sub.2O.sub.3) 0.70 0.25 0.70 0.70 0.65 0.63 (MgO + BaO)/RO 0.28 0.72 0.60 0.66 0.88 0.87 RO 16.7 16.7 11.2 20.9 24 23.5 ZnO + TiO.sub.2 + Sc.sub.2O.sub.3 8.8 8.8 8.8 8.8 4.9 9.9 D 0.36 0.44 −0.22 0.20 0.80 0.91 Density g/cm.sup.3 2.52 2.45 2.68 2.65 2.56 2.65 Coefficient of expansion *10.sup.−7/ 30.3 33.6 41.7 33.8 30.2 29.5 (50-350□) □ Young's modulus Gpa 71.2 80.7 80.7 81.6 64.7 70.9 refractivity nD 1.524 1.542 1.521 1.552 1.509 1.531 Melting temperature T.sub.m □ 1591 1517 1619 1546 1415 1377 Molding temperature T.sub.4 □ 1272 1270 1335 1246 1180 1020 Liquidus temperature T.sub.1 □ 1230 1270 1350 1140 1080 1130 T.sub.4 − T.sub.1 □ 42 0 −15 106 100 −110 Strain point □ 677 743 787 696 609 543 Transmittance % 91.5 92.0 91.5 91.8 91.5 91.9

(54) TABLE-US-00004 TABLE 4 Compar- Compar- Compar- Compar- Compar- Compar- Compar- Compar- ative ative ative ative ative ative ative ative wt % Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Example 8 SiO.sub.2 28 72 49 57 57 45 34.9 37.5 Al.sub.2O.sub.3 17 7 18 3 3 5 1.6 8.9 B.sub.2O.sub.3 35 5.8 4 12 12 0 0 28.1 MgO 5 2 0.8 5 5 4.2 0 6.2 CaO (introduced not as clarifier) 3 8 13 5 5 5.9 5.8 5.3 SrO (introduced not as clarifier) 4 1 4 0 0 10.9 4.8 0 BaO (introduced not as clarifier) 7.8 4 4 8.7 8.7 16 26.9 3 ZnO 0 0 6 1 1 0 0 7.3 TiO.sub.2 0 0 1 8 0 7 9.6 3 Sc.sub.2O.sub.3 0 0 0 0 8 0 0 0 La.sub.2O.sub.3 0 0 0 0 0 2.9 3.8 0 Nb.sub.2O.sub.5 0 0 0 0 0 0 9.2 0 ZrO2 0 0 0 0 0 2.9 3.2 0 Clarifier Calcium oxide introduced as 0 0 0 0 0 0 0 0.4 calcium fluoride Strontium oxide introduced as 0 0 0 0 0 0 0 0 strontium chloride Barium oxide introduced as 0.2 0 0 0.3 0.3 0 0 0.3 barium sulfate SnO.sub.2 0 0 0 0 0 0.2 0.2 0 SnO 0 0.2 0.2 0 0 0 0 0 SiO.sub.2 + Al.sub.2O.sub.3 45.0 79.0 67.0 60.0 60.0 50.0 36.5 46.4 ZnO/(ZnO + TiO.sub.2 + Sc.sub.2O.sub.3) 0.00 0.00 0.86 0.11 0.11 0.00 0.00 0.71 (MgO + BaO)/RO 0.65 0.40 0.22 0.73 0.73 0.55 0.72 0.63 RO 20.0 15.0 21.8 19.0 19.0 37.0 37.5 15.2 ZnO + TiO.sub.2 + Sc.sub.2O.sub.3 0.0 0.0 7.0 9.0 9.0 7.0 9.6 10.3 D 0.51 −0.49 −0.31 0.03 0.03 −0.04 −0.35 0.54 Density g/cm.sup.3 2.39 2.44 2.70 2.50 2.51 3.34 3.73 2.42 Coefficient of expansion *10.sup.−7/ 31.1 34.7 33.6 40.4 41.9 74.2 79.1 29.2 (50-350□) □ Young's modulus Gpa 71.2 75.8 68.2 77.1 80.2 76.4 71.1 70.8 refractivity n.sub.D 1.519 1.504 1.551 1.538 1.529 1.652 1.581 1.517 Melting temperature T.sub.m □ 1375 1738 1572 1507 1493 1467 1411 1549 Molding temperature T.sub.4 □ 1149 1231 1219 1227 1196 1067 1032 1247 Liquidus temperature T.sub.1 □ 1010 1190 1170 1220 1280 1110 1031 1160 T.sub.4 − T.sub.1 □ 139 41 49 7 −84 −43 1 87 Strain point □ 558 609 675 607 596 692 700 6667 Transmittance % 90.7 91.5 91.9 92 91.4 90.9 91.8 91.2

(55) It is seen from the comparison of the data in Tables 1-4: the glass prepared according to the present invention apparently has low density, high index of refraction, high stability of glass formation, low thermal expansion coefficient, high thermostability, high flexibility, and is easy to bend.

(56) Glass is prepared with the method in some of the examples and comparative examples, and then secondary melting and thinning treatment is carried out, wherein the method for secondary melting and thinning comprises: conveying the plate glass in 0.5 mm thickness and 50 mm width obtained through cutting, grinding and polishing to the feed port of a secondary stretch forming machine, feeding the plate glass into the stretch forming furnace at a rate of V.sub.0 mm/min., controlling the viscosity P in the stretch forming area, and carrying out roll-to-roll winding with the stretching machine and drum at a rate of V.sub.1 mm/min., so as to obtain flexible glass in thickness d1 and width d2. The minimum curvature radius of the finished glass product is measured with a curvature radius and bending stress tester. The conditions and corresponding bending coefficients in some of the examples are shown in Table 5.

(57) TABLE-US-00005 TABLE 5 Curvature Bending Young's Bending Rate V.sub.0 Viscosity Rate Thickness Width radius stress modulus coefficient (mm/min) P(P) V.sub.1(mm/min) d1 (mm) d2 (mm) (mm) (MPa) (GPa) C.sub.R Example 1 — — — 0.5 50 1000 15 68.6 0.44 Example 1 5 10.sup.5.6 87 0.09 16 35 72 68.6 0.41 Example 2 5 10.sup.6.1 167 0.075 10 16 41 69.4 0.13 Example 6 5 10.sup.5.8 100 0.05 25 26 45 70.2 0.33 Example 7 5 10.sup.5.9 137 0.07 13 20 53 60.5 0.25 Example 9 5 10.sup.5.8 195 0.08 8 38 55 68.1 0.38 Comparative 5 10.sup.6.0 223 0.08 7 56 89 75.8 0.82 Example 2 Comparative 5 10.sup.5.7 250 0.05 10 45 90 68.2 1.19 Example 3 Comparative 5 10.sup.5.9 137 0.07 13 95 104 70.8 1.99 Example 8

(58) It is seen from the result in the Table 5: the method provided in the present invention can be used to prepare aluminoborosilicate glass in thickness ≤0.5 mm with bending coefficient C.sub.R smaller than 0.5. During the bending, the smaller the C.sub.R value is, the lower bending stress of the glass plate is in the same bending radius, indicating that the bending radius of the glass plate can be reduced further, i.e., the glass plate has better flexibility and bendability.

(59) While the present invention is described above in detail in some preferred embodiments, the present invention is not limited to those embodiments. Various simple variations, including combinations of the technical features in any other appropriate way, can be made to the technical scheme of the present invention within the scope of the technical concept of the present invention, but such variations and combinations shall be deemed as disclosed content in the present invention and falling in the protection scope of the present invention.