Ultraviolet/infrared absorbent low transmittance glass

[0002] This is a continuation-in-part application of patent application Ser. No. 09/817,119 filed on March 27, 2001, abandoned, which is a continuation-in-part application of patent application Ser. No. 09/266,628 filed on Mar. 11, 1999, abandoned.

[0003] The present invention relates to an ultraviolet/infrared absorbent low transmittance glass. More particularly, it relates to an ultraviolet/infrared absorbent low transmittance glass having a grayish green shade, a low visible light transmittance, a low solar energy transmittance, and a low ultraviolet transmittance, so that it is useful for windows of vehicles or buildings particularly for a privacy protecting glass in a rear window of a vehicle.

[0004] Recently, a variety of glasses with capable of absorbing ultraviolet/infrared light to be used as a vehicle windshield has been proposed for preventing degradation of luxurious interior materials and reducing cooling load of the vehicle. In view of privacy protection, a glass with relatively low visible light transmittance is preferably used for a rear window glass of a vehicle. Such kinds of glass include the followings.

[0005] For example, a dark gray colored infrared absorbent glass disclosed in Japanese Patent Publication No. 07-29813B consists of the soda-lime-silica glass including colorants consisting of 1.00 to 1.7 weight percent of Fe₂O₃(total iron), at least 0.27 weight percent of FeO, 0.002 to 0.005 weight percent of Se, and 0.01 to 0.02 weight percent of CoO. The glass exhibits less than 32 percent of the luminous transmittance and less than 15 percent of the total solar infrared transmittance at 3.9 mm thickness.

[0006] A dark gray colored glass disclosed in Japanese Patent Publication No. 08-157232A consists of a soda-lime-silica glass including colorants consisting of 0.8 to 1.4 weight percent of Fe₂O₃(total iron), less than 0.21 weight percent of FeO, 0.05 to 1.0 weight percent of TiO₂, 0.02 to 0.05 weight percent of CoO, and 0.0005 to 0.015 weight percent of Se.

[0007] A neutral gray colored glass disclosed in claim 25 of U.S. Pat. No. 5,393,593 consists of a soda-lime-silica glass including colorants consisting of 1.00 to 2.2 weight percent of Fe₂O₃(total iron), at least 0.20 weight percent of FeO, 0.0005 to 0.005 weight percent of Se, and 0.010 to 0.030 weight percent of CoO. The glass exhibits less than 35 percent of the luminous transmittance and less than 20 percent of the total solar infrared transmittance at 3.9 mm thickness.

[0008] A glass disclosed in PCT (Japanese phase) No. 07-508971 consists of a soda-lime-silica glass including colorants consisting of 1.3 to 2.0 weight percent of Fe₂O₃(total iron), about 0.01 to 0.05 weight percent of NiO, about 0.02 to 0.04 weight percent of Co₃O₄, about 0.0002 to 0.003 weight percent of Se and 18 to 30 weight percent of a ferrous iron value, resulting in less than 0.53 of a light and shade coefficient.

[0009] In both the dark gray colored infrared absorbent glass disclosed in Japanese Patent Publication No. 07-29813B and the neutral gray colored glass disclosed in U.S. Pat. No. 5,393,593, a great quantity of Se is used for providing a desirable color. However, such a great quantity of Se is not favorable for the environment because Se is toxic and easy to vaporize. The above dark gray glass disclosed in Japanese Patent Publication No. 08-157232A including 0.05 to 1.0 weight percent of TiO₂as an essential component is not preferable because TiO₂is expensive to thereby increase a cost.

[0010] The aforementioned glass includes the high concentration of selenium to provide optical properties, essentially without including nickel.

[0011] The glass disclosed in PCT (Japanese phase) No. 07-508971 is prepared from a standard soda-lime-silica glass, to which iron oxide, cobalt oxide, nickel oxide and selenium are added in a specific ratio. However, the glass composition disclosed therein has the great concentration of selenium and a small amount of nickel oxide.

[0012] It is an object of the present invention to provide an ultraviolet/infrared absorbent low transmittance glass having a grayish green shade, a low visible light transmittance, a low solar energy transmittance and a low ultraviolet transmittance, thus it is useful for a window of a vehicle or a building, particularly for a privacy protecting glass of a rear window of a vehicle.

[0013] An ultraviolet/infrared absorbent low transmittance glass of the present invention is formed of a base glass and a colorant, wherein major constituents of the base glass are 65 to 80 wt. % of SiO₂; 0 to 5 wt. % of Al₂O₃; 0 to 10 wt. % of MgO and 5 to 15 wt. % of CaO wherein a total amount of MgO and CaO is between 5 and 15 wt. %; 10 to 18 wt. % of Na₂O and 0 to 5 wt. % K₂O wherein a total amount of Na₂O and K₂O is between 10 and 20 wt. %; and 0 to 5 wt. % of B₂O

[0014] Also, the colorant includes more than 0.95 and less than 1.2 wt. % of total iron oxide (T-Fe₂O₃) expressed as Fe₂O3, i.e. 0.95<T-Fe₂O₃<1.2; 0.001 to 0.03 wt. % of CoO; and 0.003 to 0.2% of NiO.

[0015] The glass of the present invention does not substantially contain Se. The glass of the present invention is preferable to be reinforced by blasting air cooling for a desired color shade.

[0016] Hereunder, embodiments of an ultraviolet/infrared absorbent low transmittance glass composition will be explained. It should be noted that components are represented in weight percentage.

[0017] SiO₂(silica) is a principal component of the ultraviolet/infrared absorbent low transmittance glass. Less than 65% of SiO₂lowers durability of a glass and more than 80% of SiO₂raises a melting temperature of a glass too high.

[0018] Al₂O₃is a component for improving the durability of the glass. More than 5% Al₂O₃raises a melting temperature of a glass too high. A preferable range of Al₂O₃is between 0.1% and 2%.

[0019] MgO and CaO are used to improve the durability of a glass and adjust a devitrification temperature and a viscosity of a glass during molding. More than 10% of MgO raises the devitrification temperature. Less than 5% or more than 15% CaO raises the devitrification temperature of a glass. The durability of a glass is lowered when the total amount of MgO and CaO is less than 5%, while the devitrification temperature is increased when the total amount of MgO and CaO exceeds 15%.

[0020] Na₂O and K₂O prompt a glass to melt. An efficiency of promoting the melting becomes poor when Na₂O is less than 10% or the total of Na₂O and K₂O is less than 10%, while the durability of a glass is lowered when Na₂O exceeds 18% or the total of Na₂O and K₂O exceeds 20%. It is preferable for K₂O not to exceed 5% because of a cost.

[0021] B₂O₃is a component for improving the durability of a glass, prompting to melt, and yet enhancing the ultraviolet absorption. B₂O₃should be less than 5%, since it becomes difficult to mold due to vaporization of B₂O₃.

[0022] Iron oxide is present in the form of Fe₂O₃and FeO in the glass. Fe₂O₃is a component for improving the ultraviolet absorption and FeO is a component for improving the heat rays absorption. The iron in the composition of the glass makes the glass green tint.

[0023] When a total amount of iron oxide (T-Fe₂O₃) expressed as Fe₂O₃is less than 0.95%, the efficiency of ultraviolet and infrared absorption becomes too small to provide desired optical properties. On the other hand, when T-Fe₂O₃exceeds 1.2%, it is difficult to obtain a desired grayish color shade because a large amount of iron makes the color green tint too much.

[0024] When T-Fe₂O₃is not greater than 1.1%, iron in the composition is effective in coloring the glass green tint and improves the visible light transmittance, thus other colorants can be added to adjust the shade. T-Fe₂O₃is therefore contained in an amount between 0.95% and 1.2%, preferably not more than 1.1%.

[0025] Fe₂O₃particularly has a function of increasing the light absorption in the ultraviolet range when the glass is reinforced by air blast cooling. This means that the glass of this invention can obtain enough efficiency of the ultraviolet absorption without using expensive ultraviolet absorbent such as CeO₂and TiO₂. When T-Fe₂O₃is in the range mentioned above, the desired color shade of the glass can be obtained after discoloration due to the reinforcement process by the air blast cooling.

[0026] When the FeO/T-Fe₂O₃ratio (a weight of FeO expressed as Fe₂O₃against T-Fe₂O₃) is too low, sufficient heat ray absorption can not be achieved because the amount of FeO is too small. Also, many bubbles can be formed in a molten glass because the molten glass is relatively reactive with oxygen, so that a product yield is lowered. When the FeO/T-Fe₂O₃ratio is too high, the visible light transmittance is reduced and the color becomes blue tint. In addition, nickel sulfide stones are sometimes present in the molten glass because the molten glass is relatively reductive. Too high ratio of FeO/T-Fe₂O₃is also not preferable since it causes streaks with enough silica and silica scum.

[0027] In the present invention, the FeO/T-Fe₂O₃ratio in a range between 0.15 and 0.4 brings a green shade, which is an almost neutral color having high ultraviolet absorption and high heat ray absorption. In this case, values expressed as Fe₂O₃are used for the content of FeO.

[0028] CoO is a component for obtaining an almost neutral color such as greenish gray shade in cooperating with Se and/or NiO, and Fe₂O₃for controlling the visible light transmittance. Less than 0.001% CoO can not form a desired color shade and makes the visible light transmittance too high. More than 0.03% CoO makes the color too blue tint and reduces the visible light transmittance. A content of CoO is preferable to be in a range of 0.001% to 0.018%.

[0029] NiO is a component for controlling the visible light transmittance and for reducing the excitation purity as like as CoO. It should be understood that NiO may not be always included when Se is included. When NiO is included more than 0.2%, nickel sulfide stones are sometimes present in a product and the visible light transmittance is reduced. In addition, the obtained shade becomes too greenish. When using NiO, the content thereof is preferably in a range between equal to or more than 0.003% and less than 0.05% for middle visible light transmittance, or in a range between 0.05% and 0.2% for low visible light transmittance.

[0030] When a concentration of NiO in the glass is too high, there is a possibility that NiO coagulates to form a nickel sulfide stone. However, when NiO is in the range defined by this invention, the desired color shade can be obtained without producing the nickel sulfide stone.

[0031] It is known that the coordination number of NiO varies according to a rate of cooling a glass so that the color of the glass varies. This is because the cooling rate changes the coordination number of oxide around Ni²⁺from 6 to 4 and thus changes the optical absorption. The absorption of Ni²⁺ with octahedral coordination exists around 430 nanometer to thereby impart yellow to the glass, while the absorption of Ni²⁺with tetrahedral coordination exists between 500 and 640 nanometers. Therefore, the excitation purity would be reduced to obtain the preferable shade when using Ni²⁺with tetrahedral coordination. A windshield of a passenger car is normally reinforced by air blast cooling for safety. The reinforcement process by air blast cooling also changes the coloring condition of NiO. In the present invention, the desired color shade can be obtained through the discoloration from the reinforcement process by the air blast cooling without adding Se.

[0032] CeO₂is a component for improving the ultraviolet absorption and is present in the form of Ce³⁺ or Ce⁴⁺ in the glass. Particularly, Ce³⁺is effective in absorbing ultraviolet light with less absorption of the visible light. In the present invention, an oxide of Ce³⁺ is also expressed in terms of CeO₂and is included in the total amount of CeO₂.

[0033] TiO₂is a component for improving the ultraviolet absorption particularly by interaction with FeO. TiO₂can be added to improve the ultraviolet absorption within such a range as not to lose the grayish green color shade, or to add a yellow tint in order to obtain the desired color shade. The use of expensive CeO₂and TiO₂increases the cost so that it is not preferable to use more than 2% CeO₂and TiO₂.

[0034] One or more than two ingredients among MnO, V₂O₅, MoO₃, CuO, and the like may be added as colorant, and SnO₂within a rang from 0% to 1% in total amount may be added as a reducing agent in such a range as not to lose middle transmittance and the grayish green shade. There is substantially no Cr₂O₃contained except a trace amount from raw materials as an impurity, which is very difficult to eliminate. To further securely prevent the formation of nickel sulfide stones, ZnO may be added in a range from 0% to 1%.

[0035] In the present invention, the glass is preferable to be reinforced by the air blasting. The desired color shade and optical properties are obtained in the reinforced process when the glass has a composition of the present invention comprising NiO and Fe₂O₃in the specific amount.

[0036] In the reinforcement process, the glass plate produced from the molten glass is reheated at 600 to 750° C. for 2 to 5 minutes, and then, cooled by blasting air of 10 to 30° C. at a cooling rate of 100 to 300° C./sec.

[0037] The air blasting reinforcement process makes the glass plate comprising NiO and Fe₂O₃have the greenish gray and almost neutral shade, and have the low visible light transmittance and the low ultraviolet transmittance while keeping an ability of absorbing the high heat rays.

[0038] In the present invention, when measured by using C.I.E standard illuminant “A”, the glass with a thickness between 2 to 5 mm has a visible light transmittance (YA) in a range from 10% to 50%, a solar energy transmittance (TG) of not greater than 30% and an ultraviolet transmittance (Tuv) defined by ISO of not greater than 12%.

[0039] When using the color system of L*, a*, b*, the chromaticity, expressed as a* and b* of the glass color, is preferably in a range of −8≦a*≦−2 and −2≦b*≦4, respectively.

[0040] When measured by using C.I.E. standard illuminant “C” over the wavelength range between 380 and 770 nanometers, the glass of the present invention preferably has optical properties with a dominant wavelength (λd) in a range between 480 and 580 nanometers and an excitation purity (Pe) of less than 9% in a case the glass has a thickness of 4 mm.

[0041] Hereinafter, a mode of carrying out the present invention will be described with reference to examples.

[0042] A glass raw material is prepared by adding required ingredients consisting of ferric oxide, titanium oxide, cerium oxide, cobalt oxide, metallic selenium, and nickel oxide into a standard soda-lime-silica glass batch composition, also by adding carbonaceous reducing agent (concretely, coke powder etc.) at a ratio of about 0.01 parts by weight per 100 parts of the glass raw material therein, and mixing them. The glass raw material thus prepared is heated and melted in an electric furnace at 1500° C. for 4 hours. The molten glass is flowed onto a stainless plate and annealed to the room temperature to obtain a 6 mm thick glass plate. After polishing the glass plate so that the thickness reduces to 4 mm, the glass plate is reinforced with reheating it at 700° C. for 5 minutes and then cooling it with 20° C. air blast at 3.2 to 2.1 kgf/mm²wind flow to obtain a sample. Each sample is measured for the visible light transmittance by the C.I.E. illuminant A (YA), the solar energy transmittance (TG), the ultraviolet transmittance by ISO 9050(Tuv), the dominant wavelength by the illuminant C(λd), and the excitation purity (Pe). And, L*, a* and b* are measured in accordance with C.I.E.L.A.B.

[0043] Table 1 shows the base glass compositions of the obtained samples, T-Fe₂O₃concentration, FeO (expressed as Fe₂O₃) concentration, FeO. (expressed as Fe₂O₃) /T-Fe₂O₃ratio, CoO concentration, Se concentration, NiO concentration, CeO₂concentration, and TiO₂concentration. The numerals in Table are indicated as a weight percentage except that CoO concentration, Se concentration, and NiO concentration are expressed in ppm. Table 1 also shows the optical properties of the respective samples.

[0044] Table 1 shows that all glasses having thicknesses of about 3-4 mm of Examples 1 through 8 have the visible light transmittance (YA) between 10% and 50%, the solar energy transmittance (TG) of less than 30%, and the ultraviolet transmittance (Tuv) of less than 12%. Each of the glasses has the FeO/T-Fe₂O₃ratio in a range from 0.15 to 0.4.

[0045] These samples show the chromaticity expressed by a* and b* in the ranges −8≦a*≦−2 and −2≦b*≦4, the dominant wavelength (λd) measured by using the illuminant “C” between 480 and 580 nanometers, and the excitation purity (Pe) of less than 9%.

[0046] The glasses having large values of a* have preferable grayish green shade. A relatively small amount of CoO does not reduce the visible light transmittance of these samples or does not make these glasses too blue tint.

[0047] These samples farther include CeO₂and/or TiO₂to improve the ultraviolet transmittance. Therefore, when the glass compositions of the examples mentioned above are used for windshields of vehicles and windows of buildings, good effects of preventing degradation of interior materials and of privacy protecting can be obtained.

[0048] Table 2 shows glass components and optical properties of comparative examples made in the same manner as in Examples 1-8 but the glass components are different.

[0049] All of Comparative Examples 1-5 have compositions out of the range of the present invention. The comparative example 1 has the same composition as the example in Japanese Patent Publication No. 07-29813B, which shows the glass produced by the vacuum refining process, as referred to in the prior art description. The comparative example 2 has the same composition as the example in Japanese Patent Publication No. 08-157232A as referred above. The comparative example 3 has the same composition as the example in PCT (Japanese phase) No. 07-508971 as referred to above.

[0050] It should be noted that the optical properties of the comparative example 1 are indicated in converted values based on a glass thickness of 3.9 mm and the optical properties of the comparative example 2 are indicated in converted values based on a glass thickness of 5 mm.

[0051] The comparative examples 4 and 5 contain T-Fe₂O₃of an amount that is out of the claimed range.

[0052] As detailed above, according to the present invention, an ultraviolet/infrared absorbent low transmittance glass, which exhibits low visible light transmittance, low solar energy transmittance, and low ultraviolet transmittance and has grayish green shade can be provided.

[0053] The ultraviolet/infrared absorbent low transmittance glass having the greenish gray shade can exhibit the effect of preventing degradation and discoloration of interior materials and the privacy protecting effect when the glass is used for a rear window glass of a vehicle, a window of a building, or the like.