GLASS PLATE AND HEATER USING SAME

Abstract

To provide a glass plate which is hardly broken and which has a high infrared transmittance.

A glass plate, which has a thickness of from 1 to 8 mm, has an infrared transmittance T3000 at a wavelength of 3,000 nm of at least 4%, an average thermal expansion coefficient a at from 50 to 350° C. of from 15 to 35×10.sup.−7/° C., and a glass composition comprising, as represented by mol% based on oxides, from 50 to 85% of SiO.sub.2, from 0.1 to 25% of Al.sub.2O.sub.3, from 0.1 to 20% of B.sub.2O.sub.3, from 0 to 20% in total of at least one member selected from MgO, CaO, SrO, BaO and ZnO, and from 0 to 20% in total of at least one member selected from Li.sub.2O, Na.sub.2O and K.sub.2O.

Claims

1. A glass plate, which has a thickness of from 1 to 8 mm, an infrared transmittance T3000 at a wavelength of 3,000 nm of at least 4%, an average thermal expansion coefficient a at from 50 to 350° C. of from 15×10.sup.−7 to 35×10.sup.−7/° C., and a composition comprising, as represented by mol % based on oxides: SiO.sub.2: 50 to 85%, Al.sub.2O.sub.3: 0.1 to 25%, B.sub.2O.sub.3: 0.1 to 20%, MgO+CaO+SrO+BaO+ZnO: 0 to 20%, and Li.sub.2O+Na.sub.2O+K.sub.2O: 0 to 20%.

2. The glass plate according to claim 1, which has an infrared transmittance T3000 at a wavelength of 3,000 nm of at least 10%.

3. The glass plate according to claim 1, wherein the crack occurrence load is higher than 1.96N.

4. The glass plate according to claim 1, which has a strain point of from 520 to 780° C.

5. The glass plate according to claim 1, which has a composition comprising, as represented by mol % based on oxides: SiO.sub.2: 60 to 70%, Al.sub.2O.sub.3: 4 to 25%, B.sub.2O.sub.3: 8 to 20%, MgO: 0 to 10%, CaO: 0 to 5%, SrO: 0 to 5%, BaO: 0 to 5%, ZnO: 0 to 5%, MgO+CaO+SrO+BaO+ZnO: 3 to 10%, Li.sub.2O: 0 to 1%, Na.sub.2O: 0 to 2%, K.sub.2O: Li.sub.2O+Na.sub.2O+K.sub.2O: 0 to 10%; and has an average thermal expansion coefficient a at from 50 to 350° C. of from 15×10.sup.−7 to 30×10.sup.−7/° C.

6. The glass plate according to claim 5, which has a composition comprising, as represented by mol % based on oxides: Al.sub.2O.sub.3: 5 to 25%, MgO: 1 to 8%, ZnO: 0 to 2%, SiO.sub.2+Al.sub.2O.sub.3+B.sub.2O.sub.3: at least 80%, MgO+CaO+SrO+BaO+ZnO: 3 to 8%, and Li.sub.2O+Na.sub.2O+K.sub.2O: 0 to 2%

7. The glass plate according to claim 5, which has a composition comprising, as represented by mol % based on oxides: B.sub.2O.sub.3+MgO+CaO+SrO+BaO+ZnO: 11 to 22%

8. The glass plate according to claim 5, wherein, as represented by mol % based on oxides, MgO/(MgO+CaO+SrO+BaO+ZnO) is from 0.6 to 1.

9. The glass plate according to claim 1, which has a compressive stress on at least a part of its surface.

10. The glass plate according to claim 1, which is a glass plate for a heater.

11. A heater comprising a top surface on which an object to be heated is to be placed, and an infrared sensor, the top surface being composed of a glass plate, wherein the glass plate has a thickness of from 1 to 8 mm, an infrared transmittance T3000 at a wavelength of 3,000 nm of at least 4%, an average thermal expansion coefficient a at from 50 to 350° C. of from 15×10.sup.−7 to 35×10.sup.−7/° C., and a composition comprising, as represented by mol % based on oxides: SiO.sub.2: 50 to 85%, Al.sub.2O.sub.3: 0.1 to 25%, B.sub.2O.sub.3: 0.1 to 20%, MgO+CaO+SrO+BaO+ZnO: 0 to 20%, and Li.sub.2O+Na.sub.2O+K.sub.2O: 0 to 20%.

12. The heater according to claim 11, wherein the glass plate has an infrared transmittance T3000 at a wavelength of 3,000 nm of at least 10%.

13. The heater according to claim 11, wherein the glass plate is chemically tempered.

Description

EXAMPLES

[0109] In the following, Ex. 1 to 10 are Examples for glass of the present invention, and Ex. 11 to 13 are Comparative Examples.

[0110] In Ex. 1 to 10, 12 and 13, raw materials of the respective components were prepared so as to achieve the desired composition, and melted in a platinum crucible at 1,550° C. As the raw materials, silica sand with a grain size of from 1 to 1,000 μm, aluminum oxide, sodium carbonate and the like were used. The glass melt was cast, formed into a plate and annealed.

[0111] Ex. 11 corresponds to commercially available crystallized glass (manufactured by Nippon Electric Glass Co., Ltd., tradename: Neoceram).

[0112] Table 1 shows the glass composition (unit: mol %), the crack occurrence load (unit: N), the infrared transmittance T2500 (unit: %) of the glass having a thickness of 4 mm at a wavelength of 2,500 nm, the infrared transmittance T3000 (unit: %) at a wavelength of 3,000 nm, the infrared transmittance T3200 (unit: %) at a wavelength of 3,200 nm, the average thermal expansion coefficient a (unit: ×10.sup.−7° C.sup.−1) at from 50° C. to 350° C., the density (unit: g.Math.cm.sup.−3), the glass transition temperature Tg (unit: ° C.), the strain point, the Young's modulus (unit: GPa) and the βOH value. The glass composition in Ex. 11 is estimated values from the literature (New Glass, Vol. 20, No. 3, p. 23, 2005). [Method of measuring βOH value]

[0113] With respect to a glass sample, the absorbance of light at a wavelength of from 2.75 to 2.95 μm is measured, and its maximum value βmax is divided by the thickness (mm) of the sample to determine the βOH value of the glass.

TABLE-US-00001 mol % Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Ex. 7 SiO.sub.2 68.0  68.7  68.3  68.0  69.0  70.0  70.0  Al.sub.2O.sub.3 15.0  10.0 10.0  10.0  10.0  12.0  10.0  B.sub.2O.sub.3 10.0  14.9 17.9  18.0  15.0  12.0  14.0  MgO 4.0 4.0 2.5 2.0 6.0 6.0 5.0 CaO 2.0 1.4 1.0 1.0 0.0 0.0 1.0 SrO 1.0 1.0 0.0 1.0 0.0 0.0 0.0 BaO 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Li.sub.2O 0.0 0.0 0.0 0.0 0.0 0.0 0.0 TiO.sub.2 0.0 0.0 0.0 0.0 0.0 0.0 0.0 ZrO.sub.2 0.0 0.0 0.0 0.0 0.0 0.0 0.0 P.sub.2O.sub.5 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Na.sub.2O 0.0 0.0 0.0 0.0 0.0 0.0 0.0 K.sub.2O 0.0 0.0 0.0 0.0 0.0 0.0 0.0 SnO.sub.2 0.0 0.3 0.3 0.0 0.0 0.0 0.0 SiO.sub.2 + Al.sub.2O.sub.3 + B.sub.2O.sub.3 93.0  93.6  96.2  96.0  94.0  94.0  94.0  MgO + CaO + SrO + 7.0 6.4 3.5 4.0 6.0 6.0 6.0 BaO + ZnO Li.sub.2O + Na.sub.2O + K.sub.2O 0.0 0.0 0.0 0.0 0.0 0.0 0.0 B.sub.2O.sub.3 + MgO + CaO + 17.0  21.3  21.4  22.0  21.0  18.0  20.0  SrO + BaO + ZnO MgO/(MgO + CaO + 0.6 0.6 0.7 0.5 1.0 1.0 0.8 SrO + BaO + ZnO) Crack occurrence load 19.6  19.6  >20    >20    19.6  19.6  19.6  T.sub.2500 [%] 80   80   73   72   >78    >78    >78    T.sub.3000 [%] 16   38   44   37   >10    >10    >10    T.sub.3200 [%] 20   33   44   39   >20    >20    >20    Average thermal 26.4  25.3  26.0  26.8  (24.7)  (23.6)  (24.7)  expansion coefficient [10.sup.−7/° C.] Density [g/cm.sup.3]  2.38  2.31  (2.24)  (2.26)  (2.29)  (2.32)  (2.29) Glass transition 745    714    711    694    719    740    716    point [° C.] Strain point [° C.] (>685)    (>654)    (>651)    (>634)    (>659)    (>680)    (>656)    Young's modulus 79   69   61   76   68.4  73.9  69.0  [GPa] βOH [mm.sup.−1]  0.26  0.13  0.11  0.15  0.07 <0.2   0.06 mol % Ex. 8 Ex. 9 Ex. 10 Ex. 11 Ex. 12 Ex. 13 SiO.sub.2 69.8  70.0  70.0  72.1  83.0  66.1  Al.sub.2O.sub.3 10.0  10.0  10.0  14.2  1.4 11.3  B.sub.2O.sub.3 15.0  15.0  15.0  0.0 11.6  7.8 MgO 5.0 4.0 3.0 0.0 0.0 5.1 CaO 0.0 1.0 2.0 0.0 0.0 4.5 SrO 0.0 0.0 0.0 0.0 0.0 5.2 BaO 0.0 0.0 0.0 0.9 0.0 0.0 Li.sub.2O 0.0 0.0 0.0 8.8 0.0 0.0 TiO.sub.2 0.0 0.0 0.0 1.6 0.0 0.0 ZrO.sub.2 0.0 0.0 0.0 1.1 0.0 0.0 P.sub.2O.sub.5 0.0 0.0 0.0 0.5 0.0 0.0 Na.sub.2O 0.0 0.0 0.0 0.4 4.0 0.0 K.sub.2O 0.0 0.0 0.0 0.4 0.0 0.0 SnO.sub.2 0.3 0.0 0.0 0.0 0.0 0.0 SiO.sub.2 + Al.sub.2O.sub.3 + B.sub.2O.sub.3 94.7  95.0  95.0  86.3  96.0  85.2  MgO + CaO + SrO + 5.0 5.0 5.0 0.9 0.0 14.8  BaO + ZnO Li.sub.2O + Na.sub.2O + K.sub.2O 0.0 0.0 0.0 9.6 4.0 0.0 B.sub.2O.sub.3 + MgO + CaO + 20.0  20.0  20.0  0.9 11.6  22.6  SrO + BaO + ZnO MgO/(MgO + CaO + 1.0 0.8 0.6 0.0 — 0.3 SrO + BaO + ZnO) Crack occurrence load 19.6  19.6  19.6   1.96 4.9 4.9 T.sub.2500 [%] 73   72   74   83   75   77   T.sub.3000 [%] 35   39   39   2   3   7   T.sub.3200 [%] 39   42   43   6   10   16   Average thermal 24.1  24.3  25.6  −3   32.5  37.5  expansion coefficient [10.sup.−7/° C.] Density [g/cm.sup.3]  2.28  2.28  2.28  2.52  2.23  2.51 Glass transition 715    712    705    — 560    720    point [° C.] Strain point [° C.] (>655)    (>652)    (>645)    Young's modulus 68   68   67   92   64   77   [GPa] βOH [mm.sup.−1]  0.16  0.14  0.14  0.66  0.72  0.41 Values in brackets in Table 1 are estimated values.

[0114] When glass in each of Ex. 1 to 10 is formed into a plate having a thickness of from 1.5 to 5 mm, a glass plate suitable for a top surface of a heater, excellent in the infrared transmittance, the crack resistance and the heat resistance is obtained.

[0115] Glass in each of Ex. 11 and 12 is not suitable for a top surface of a heater employing an infrared sensor, since the infrared transmittance T3000 of the glass having a thickness of 4 mm at a wavelength of 3,000 nm is so low as less than 4%.

[0116] Crystallized glass in Ex. 11 has a low crack occurrence load and is easily broken when hit by a hard object.

[0117] Glass in Ex. 13 is not suitable for a top surface of a heater, since it has an average thermal expansion coefficient a at from 50° C. to 350° C. of so high as 37.5×10.sup.−7° C.sup.−1, and has a low resistance to a heat shock.

[0118] Glass in Ex. 2 is processed into a 5 cm square glass plate having a thickness of 4 mm, and the glass plate was heated in an electric furnace kept at high temperature for 30 minutes or longer. Then, the glass plate was taken out from the electric furnace and moved into water kept at low temperature within 5 minutes, and whether the glass plate was broken or not was observed. As a result, t.sub.1=325° C., t.sub.2=350° C. and t.sub.3=337.5° C., and a high resistance to a thermal shock was confirmed.

INDUSTRIAL APPLICABILITY

[0119] According to the present invention, it is possible to obtain a glass plate, preferably a glass plate for a heater, which is hardly broken both by a thermal shock and by a mechanical shock, and which has a high infrared transmittance. Further, by using the glass plate, a heater excellent in convenience can be obtained.

[0120] This application is a continuation of PCT Application No. PCT/JP2015/083810, filed on Dec. 1, 2015, which is based upon and claims the benefit of priority from Japanese Patent Application No. 2014-243758 filed on Dec. 2, 2014. The contents of those applications are incorporated herein by reference in their entireties.