BACKGROUND ART As a glass sheet manufactured so as to suppress the transmission of heat rays to decrease a cooling load and a degree of sensed heat due to solar light, a glass sheet with a heat shading film (a heat shading glass sheet) or a glass sheet with a colorant (a heat absorbing glass sheet) has been used. A multiple-glazing unit using such a glass sheet also has been used.

As the transparent heat shading glass sheet, one obtained by forming a multilayer film of a silver layer and a dielectric layer on a glass sheet by sputtering has been known. In addition, a transparent heat shading glass sheet obtained by forming a metal oxide film such as a tin oxide film or the like on the surface of a glass sheet also has been known.

In order to suppress interference colors (iridescence) due to the tin oxide film, for example, JP 3-72586 B proposes to provide two intermediate layers between a tin oxide film and a glass sheet. In JP 3-72586 B, the two intermediate layers enable reflected or transmitted light to have an achromatic color tone.

In the heat-absorbing glass sheet, the amounts of coloring components in the glass sheet are adjusted to obtain a desired color tone or solar heat gain coefficient. As the coloring components, iron, nickel, selenium, cobalt, or the like is added.

Window glass is required to have a high visible light transmittance and a high solar heat shading rate (a low solar heat gain coefficient).

However, when the solar heat shading rate is intended to be improved merely by the addition of trace components as in the heat-absorbing glass sheet, the visible light transmittance decreases. On the other hand, in the heat shading glass sheet with a metal oxide film, even if transmitted light is allowed to have an achromatic color by forming intermediate layers as proposed in JP 3-72586, the visible light transmittance decreases with the increase in thickness of the metal oxide film to improve the solar heat shading rate in view of the dependence of the efficiency on the metal oxide film on the outermost side. Furthermore, the transparent heat shading glass sheet with the multilayer film of a silver layer and a dielectric layer has a high solar heat shading rate, but the multilayer film does not have a sufficient durability.

DISCLOSURE OF THE INVENTION The present invention is intended to provide a transparent heat shading glass sheet including metal oxide films and having a high visible light transmittance and a high solar heat shading rate, and a multiple- glazing unit using this transparent heat shading glass sheet. Particularly,

the present invention is intended to provide a transparent heat shading glass sheet not only having the high visible light transmittance and the high solar heat shading rate but also causing no harm to natural color tones of a landscape, and a multiple-glazing unit with preferable characteristics for low latitude areas where the climate is relatively mild.

In order to achieve the aforementioned objects, the present invention employs a glass sheet containing the following base components and coloring components.

Base Components SiO2: 65 wt. % to 80 wt. % AI, 03: 5 wt. % or less B203: 5 wt. % or less MgO: 10 wt. % or less CaO: 5 wt. % to 15 wt. % Na2O: 10 wt. % to 18 wt. % K2O: 5 wt. % or less Total amount of MgO and CaO: 5 wt. % to 15 wt. % Total amount of Na20 and K20: 10 wt. % to 20 wt. % Coloring Components FeO: 0.090 wt. % to 0. 14 wt. % Total amount of iron oxide based on Fe203: at least 0.31 wt. % and below 0.46 wt. % According to the present invention, the transparent heat shading glass sheet is obtained by forming a plurality of metal oxide films on the

surface of the glass sheet, wherein the visible light transmittance is set to be at least 70% and the absolute values of both the psychometric chroma coordinates a* and b* of transmitted light are set to be 5 or less.

According to the present invention, a transparent heat shading glass sheet having a high solar heat shading rate while maintaining the visible light transmittance to be at least 70% can be obtained. In the transparent heat shading glass sheet, a preferable solar heat shading rate is 60% or lower when being indicated as a solar radiation transmittance. In the transparent heat shading glass sheet of the present invention, transmitted light has an achromatic color. Therefore, the transparent heat shading glass sheet causes no harm to natural color tones of a landscape when being used as window glass.

In order to achieve the aforementioned object, the multiple-glazing unit of the present invention includes a plurality of glass sheets and at least one inner layer selected from an air layer, a reduced pressure layer, and an inert gas layer. The plurality of glass sheets are positioned so as to oppose each other via the at least one inner layer. In the multiple-glazing unit, at least one of the glass sheets is formed of the transparent heat shading glass sheet of the present invention. This multiple-glazing unit is suitable for use particularly in low latitude areas, since preferably, the solar heat gain coefficient can be suppressed to 0.58 or lower.

The visible light transmittance and solar radiation transmittance of the glass sheet and the solar heat gain coefficient of the multiple-glazing unit are determined according to Japanese Industrial Standard (JIS)

R3106-1985. In addition, the psychometric chroma coordinates a* and b* of transmitted light are determined based on a* and b* of the L*a*b* color system prescribed in JIS Z8729-1982.

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a partial sectional view of an embodiment of a transparent heat shading glass sheet according to the present invention.

FIG. 2 is a structural view of an example of a device used for forming metal oxide films on the surface of a transparent heat shading glass sheet according to the present invention.

FIG. 3 is a partial sectional view of an embodiment of a double- glazing unit according to the present invention.

FIG. 4 is a sectional view of another embodiment of a double- glazing unit according to the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION Preferable embodiments of the present invention are described as follows.

In the transparent heat shading glass sheet of the present invention, a glass sheet contains iron components as coloring components, wherein the total amount of iron oxide based on Fe203 is at least 0.31 wt. % and below 0.46 wt. % and the amount of FeO is in the range between 0.090 wt. % and 0.14 wt. %.

The component Fe203 improves UV absorption efficiency and the

component FeO improves infrared-ray absorption efficiency. It is not preferred to increase the ratio of FeO to improve the infrared-ray absorption efficiency on the condition that the total amount of iron oxide based on Fe203 is below 0.31 wt. %, since this causes difficulty in melting glass and allows the color tone of transmitted light in the glass sheet to have blueness.

When the total amount of iron oxide based on Fe203 is at least 0.46 wt. %, the visible light transmittance decreases. When the ratio of FeO is lowered to prevent the decrease in the visible light transmittance, a large amount of bubbles is produced when the glass is melted, which deteriorates the quality of the glass. From such viewpoints, the total amount of iron oxide based on Fie203 ils set to be at least 0.31 wt. % and below 0.46 wt. % and preferably in the range between 0.35 wt. % and 0.40 wt. %.

In order to obtain a desired solar heat shading rate and a desired efficiency in visible light transmittance on the condition that the total amount of iron oxide based on Fe203 is at least 0.31 wt. % and below 0.46 wt. %, the amount of FeO is set to be in the range between 0.090 wt. % and 0.14 wt. %. When the amount of FeO is below this range, the infrared absorption efficiency deteriorates excessively. On the other hand, an amount of FeO exceeding the range results in an excessive decrease in the visible light transmittance.

The amounts of iron components to be added as coloring components are set to be in the above-mentioned range and metal oxide films are formed on the surface of the glass sheet to have a suitable structure, thus obtaining a transparent heat shading glass sheet in which

while the visible light transmittance is maintained to be at least 70%, preferably at least 75%, the solar radiation transmittance is restricted to be 60% or lower. In this transparent heat shading glass sheet, the color tone of transmitted light is adjusted to be an achromatic color, while iron components are contained as coloring components.

It is preferable that the metal oxide films include a film containing tin oxide as a main component. Preferably, in this film containing tin oxide as a main component, at least one selected from fluorine and antimony is added. It is preferable that the metal oxide films include at least one film containing tin oxide as a main component to which fluorine is added in an amount in the range between 0.01 wt. % and 1 wt. %. A further preferable amount of fluorine to be added is in the range between 0.1 wt. % and 0.5 wt. %. In addition, it is preferable that the metal oxide films include a film containing tin oxide as a main component to which antimony is added at a ratio in the range between 0.01 and 0.1 where the ratio is indicated by a mole ratio to tin. In this specification, the"main component"denotes a component accounting for at least 50 wt. % of the whole amount.

It is preferable that the film containing tin oxide as a main component is positioned as the outermost layer when being seen from the glass sheet side. This film may be formed of a single layer or a plurality of layers.

A preferable structure of the metal oxide films is described with reference to FIG. 1. It is preferable that a metal oxide film 2 as the first layer (hereinafter referred to as a"first metal oxide film") formed directly on

a glass sheet 1 contains tin oxide as a main component and has a thickness in the range between 10 nm and 50 nm, preferably between 20 nm and 40 nm. It is preferable that a metal oxide film 3 as the second layer (hereinafter referred to as a"second metal oxide film") formed on the first metal oxide film contains silicon oxide as a main component and has a thickness in the range between 10 nm and 40 nm, preferably between 20 nm and 30 nm. It is preferable that at least one metal oxide film 4 as the third layer and layers formed thereon, which is formed on the second metal oxide film, contains tin oxide as a main component and has a total thickness in the range between 150 nm and 450 nm, preferably between 300 nm and 400 nm.

When the total thickness of the metal oxide film as the third layer and layers formed thereon is too thin, the solar heat shading rate and the heat insulation efficiency deteriorate. On the other hand, when the total thickness is too thick, the color of transmitted light may become cloudy in some cases. In this structural example, it is preferred to add at least one selected from fluorine and antimony to the film as the third layer and layers formed thereon containing tin oxide as a main component.

Besides fluorine and antimony, the film containing tin oxide as a main component may contain silicon, aluminum, zinc, copper, indium, bismuth, gallium, boron, vanadium, manganese, zirconium, niobium, iron, cobalt, chromium, nickel, tungsten, titanium, or the like. In addition, halogen such as chlorine, bromine, or the like may be contained.

The properties and preferable amounts of base components of the glass sheet are described as follows.

A component SiO2 is a main component forming the network (skeleton) of the glass. When the amount of SiO2 is below 65 wt. %, the durability of the glass sheet deteriorates. On the other hand, an amount of SiO exceeding 80 wt. % causes difficulty in melting the glass. Therefore, the amount of SiO2 is set in the range between 65 wt. % and 80 wt. %. A component Al203 is not an essential component but improves the durability of the glass sheet. When the amount of A1203 exceeds 5 wt. %, it becomes difficult to melt the glass. Therefore, the amount of Al203 is set to be 5 wt. % or less. A component B203 also is not an essential component but improves the durability of the glass sheet and is used as a solubilizer.

However, an amount of B203 exceeding 5 wt. % causes inconvenience in forming the glass sheet due to volatilization of B203 or the like and therefore the amount of B203 is set to be 5 wt. % or less.

Components MgO and CaO improve the durability of the glass sheet and also are used for adjusting the devitrification temperature and viscosity in forming the glass sheet. The amount of MgO is set to be 10 wt. % or less, since the devitrification temperature increases when the amount exceeds 10 wt. %. The amount of CaO is set to be in the range between 5 wt. % and 15 wt. %, since the devitrification temperature increases when the amount is below 5 wt. % or exceeds 15 wt. %. When the total amount of MgO and CaO is below 5 wt. %, the durability of the glass sheet deteriorates, and when the total amount exceeds 15 wt. %, the devitrification temperature increases. Therefore, the total amount of MgO and CaO is set to be in the range between 5 wt. % and 15 wt. %.

Components Na2O and K2O are used as a dissolution accelerator for glass. When the amount of Na2O is below 10 wt. % or the total amount of Na2O and K2O is below 10 wt. %, the dissolution acceleration effect is poor.

On the other hand, when the amount of Na2O exceeds 18 wt. % or the total amount of Na2O and K2O exceeds 20 wt. %, the durability of the glass sheet deteriorates. Therefore, the total amount of Na2O and K20 is set to be in the range between 10 wt. % and 20 wt. %. Since K20 is more expensive than Na2O, it is preferable that the amount of K2O is 5 wt. % or less.

Other trace components may be added in the glass sheet. For instance, the color tone or the degree of reduction may be adjusted by adding at least one component selected from CoO, NiO, Se, Cr203, ZnO, MnO, SnO2, and MoO3, preferably in a total amount of 1 wt. % or less, or by adding S based on S03, preferably in an amount of 1 wt. % or less.

A method of forming the metal oxide films is described as follows.

The metal oxide films may be formed by a vacuum evaporation method, a sputtering method, a coating method, or the like. However, in view of the productivity and the durability of coating films and further the practicability of air cooling and chemical strengthening of the glass sheet after the film formation, methods accompanied by thermal decomposition (pyrolysis) of coating film materials are preferable, which include a chemical vapor deposition method (a CVD method) and a spray method such as a solution spray method, a dispersion spray method, a powder spray method, or the like.

In the CVD method, vapor for forming a coating film containing a

metal compound to be a metal oxide film is used as a raw material. As a raw material, a solution containing a metal component is used in the solution spray method, a dispersion in which fine grains of a metal compound are dispersed is used in the dispersion spray method, and powder of a metal compound is used in the powder spray method. Such a raw material is supplied to the surface of a high-temperature glass sheet and is thermally decomposed (pyrolyzed), thus forming a metal oxide film.

In the spray method, a liquid in which respective components have been premixed may be sprayed as fine droplets or powder, or respective components may be sprayed separately as droplets or powder at the same time to react with one another. In the spray method, however, a uniform film thickness cannot be obtained easily due to the difficulty in controlling droplets or products to be exhausted such as a reaction product, an undecomposed product, or the like. In addition, distortion occurs in the glass sheet. Therefore, the film formation by the CVD method is more preferable.

When the respective metal oxide films are formed by a method accompanied by pyrolysis of coating film materials, generally, metal oxide is supplied to a precut and heated glass sheet. However, when the films are formed on a glass ribbon in the manufacture of the glass sheet by a float glass process, thermal energy in forming the glass sheet (float formation) can be utilized and therefore the step of heating the glass sheet for forming the films can be omitted. Particularly, when the CVD method is carried out inside a float bath, a film can be formed even on a glass surface having a

temperature equal to or higher than the annealing point, thus improving the film performance, the film growth rate, and the film formation reaction efficiency. In addition, defects such as pinholes can be suppressed.

FIG. 2 shows an embodiment of a device used for depositing metal oxide films by the CVD method on a glass ribbon in the float glass process.

As shown in FIG. 2, in this device, a predetermined number of coaters 16 (three coaters 16a, 16b, and 16c in the embodiment shown in the figure) are placed inside a float bath 12 at a predetermined distance from the surface of a glass ribbon 10. The glass ribbon 10 is formed from molten glass, which flows from a furnace 11 into a float bath 12 in a belt-like form on a tin bath 15 while traversing the length of the float bath 12. These coaters supply gaseous materials to form coating films on the glass ribbon 10 continuously.

The temperature of the glass ribbon is adjusted by a heater and a cooler (not shown in the figure) installed inside the float bath so that the glass ribbon has a predetermined temperature directly before reaching the coaters 16.

The glass ribbon 10 on which respective films have been formed is lifted by a roller 17 and is carried into an annealing furnace 13. The glass ribbon annealed in the annealing furnace 13 is cut to form a glass sheet with a predetermined size by a cutting device used widely in the float glass process, which is not shown in the figure.

The film formation on the glass ribbon may be carried out using the CVD method and the spray method together. For instance, by using the CVD method and the spray method in this order (for instance, by forming a film by the CVD method inside the float bath and a film by the spray method

using a spray gun 18 installed on the downstream side from the float bath in the moving direction of the glass ribbon), predetermined stacked layers may be obtained. According to this method, the stacked films exhibiting excellent characteristics can be formed efficiently.

Examples of materials used for forming the metal oxide films by the CVD method and the spray method are described as follows.

Silicon materials of a silicon oxide film formed by the CVD method include silane (monosilane), disilane, trisilane, monochlorosilane, 1,2- dimethylsilane, 1,1,2-trimethyldisilane, 1,1,2,2-tetramethyl disilane, tetramethyl orthosilicate, tetraethyl orthosilicate, or the like. In this case, oxidation materials include oxygen, water vapor, dry air, carbon dioxide, carbon monoxide, nitrogen dioxide, ozone, or the like. When silane is used, for the purpose of preventing the silane from being oxidized before reaching the glass surface and controlling the refractive index of the silicon oxide film, unsaturated hydrocarbon such as ethylene, acetylene, toluene, or the like may be added. In addition, when, for example, tetramethyl orthosilicate or tetraethyl orthosilicate is used, aluminium isopropoxide or the like may be added to improve the film growth rate.

Examples of tin materials of a tin oxide film formed by the CVD method include monobutyltin trichloride (MBTC), tin tetrachloride, dimethyltin dichloride, dibutyltin dichloride, dioctyltin dichloride, tetramethyltin, tetrabutyltin, tetraoctyltin, or the like. In this case, oxidation materials include oxygen, water vapor, dry air, or the like.

When antimony is to be added to the tin oxide film, antimony

trichloride, antimony pentachloride, or the like may be used also. When fluorine is to be added, hydrogen fluoride, trifluoroacetic acid, bromotrifluoromethane, chlorodifluoromethane, difluoromethane, or the like may be used also.

Silicon materials used for forming films by the spray method include tetramethyl orthosilicate, tetraethyl orthosilicate, or the like. In order to improve the film growth rate, zirconium acetyl acetate, or the like may be added.

Examples of the tin materials used for forming tin oxide films by the spray method include tin tetrachloride, dibutyltin dichloride, tetramethyltin, dioctyltin dichloride, dimethyltin dichloride, tetraoctyltin, dibutyltin oxide, dibutyltin dilaurate, dibutyltin fatty acid, monobutyltin fatty acid, monobutyltin trichloride, dibutyltin diacetate, dioctyltin dilaurate, or the like.

A double-glazing unit according to the present invention is described with reference to FIG. 3 as follows.

When the double-glazing unit of the present invention is installed in an opening, it is preferable that a transparent heat shading glass sheet 21 is placed as the glass sheet positioned outside a room. As a glass sheet positioned inside a room, the transparent heat shading glass sheet may be used, but a general glass sheet 22 provided with no film serves sufficiently.

The transparent heat shading glass sheet 21 and the glass sheet 22 are bonded at their peripheries with a sealant 25 via a spacer 23 containing a desiccant as in a general method. It is preferable that the transparent heat

shading glass sheet 21 is placed so that a metal oxide film 26 formed on the surface of the glass sheet 21 is positioned on the side of an air layer 24. The air layer 24 may be an inert gas layer. Suitable intervals between the glass sheets 21 and 22 are in the range between about 6 mm and 12 mm.

As shown in FIG. 4, a space between a transparent heat shading glass sheet 31 on which a metal oxide film 36 is formed and a glass sheet 32 may be a reduced pressure layer 34. In a vacuum insulating glazing unit with a reduced pressure layer, great heat insulating and shading effects can be obtained even when the interval between glass sheets is narrow.

Therefore, a multiple-glazing unit also can be manufactured so as to be used without requiring to change an existing window frame by reducing its total thickness. The vacuum insulating glazing unit is produced by providing a number of minute columnar spacers 33 between the pair of glass sheets 31 and 32 to maintain the interval between them and reducing the pressure between them via a through hole used for reducing the pressure, which is not shown in the figure. A preferable air pressure in the reduced pressure layer 34 is 1.0 Pa or lower, for example, in the range between about 0.01 and 1.0 Pa. The reduced pressure layer 34 is pre-sealed with a sealant 35 positioned along the peripheries of the glass sheets 31 and 32. As the sealant 35, a low melting point glass (with, for example, a melting point of 400 to 600°C) is suitable. This low melting point glass is heated to a temperature exceeding the softening point when the reduced pressure layer 34 is sealed. Similarly in the vacuum insulating glazing unit, it is preferable that the transparent heat shading glass sheet 31 is placed as the

glass sheet positioned outside a room while the metal oxide film 36 faces the reduced pressure layer 34.

When the main purpose is to suppress the heat release from the inside to the outside of a room, generally the glass sheet on which a metal oxide film is formed is positioned inside the room. In this case, however, the transparent heat shading glass sheet is used for suppressing the ingress of solar radiation from the outside to the inside of a room and therefore is placed to be positioned outside a room with the film facing the interior. In this double-glazing unit, particularly infrared rays from the outside are absorbed by the glass sheet in which trace components are added and the flow of the energy reradiated from the glass sheet toward the inside is suppressed by the metal oxide film. Therefore, a high solar heat shading rate can be obtained.

According to the above-mentioned double-glazing unit, specifically, a solar heat gain coefficient based on JIS of 0.58 or lower, preferably 0.49 or lower and a SHGC value in the United States of 0.57 or lower, preferably 0.48 or lower can be obtained. The"SHGC" (solar heat gain coefficient) value in the United States also denotes an index of shading solar heat and corresponds to the solar heat gain coefficient prescribed in JIS. The U. S.

Department of Energy has provided"ENERGYSTAR Windows Criteria"as a standard corresponding to the next-generation energy saving standard in Japan. According to the"ENERGYSTAR Windows Criteria", the standard applied to the mild climate (southern climate) of the southern area in the United States is 0.40 or lower with respect to a window as a whole. From

the standard value, a value with respect to glass alone is calculated and is 0.57 or lower. This value can be calculated using a software program"WINDOWS 4.1" provided by the U. S. Department of Energy.

Examples The present invention is described further in detail using examples as follows, but is not limited by the following examples.

Samples 1 to 3. 7 to 10. and 12 to 14 In order to obtain a predetermined glass composition, silica, dolomite, limestone, soda lime, mirabilite, ferric oxide, and a carbon-based reducing agent were mixed suitably. This material was then heated at 1450°C in an electric furnace to be melted for 4 hours. After that, the material was poured onto a stainless steel sheet and then was annealed to have a room temperature, thus obtaining a glass sheet with a thickness of about 5 mm. Further, the glass sheet was polished to have a thickness of 3 mm. The base compositions other than the coloring components of the glass sheet included: 71 wt. % SiO2,1.5 wt. % Al203,4 wt. % MgO, 8 wt. % CaO, 15 wt. % Na2O, and 0.8 wt. % K2O.

As a next step, the glass sheet, which had been washed and dried, was placed on a mesh belt in a belt furnace and was passed through a heating furnace to be heated up to about 570°C. Then, to the surface of the glass sheet, a mixed gas containing vapor of monobutyltin trichloride and oxygen, a mixed gas containing monosilane, oxygen, and nitrogen, and a mixed gas containing vapor of monobutyltin trichloride, oxygen, water vapor, nitrogen, and hydrogen fluoride were supplied sequentially. Thus, on the

glass sheet, a tin oxide film (SnO2 film), a silicon oxide film (SiO2 film), and a tin oxide film (SnOF 61m) to which fluorine was added were deposited in this order. The content of fluorine was adjusted to be 0.2 wt. %.

With respect to each transparent heat shading glass sheet thus obtained, Table 1 shows the iron components, thicknesses of respective metal oxide films, visible light transmittance, solar radiation transmittance, and color tones of transmitted light.

Samples 4 to 6 and 11 A glass sheet produced as in the above was placed on a mesh belt in a belt furnace and was passed through a heating furnace to be heated up to about 570°C. Then, to the surface of the glass sheet, a mixed gas containing vapor of monobutyltin trichloride and oxygen, a mixed gas containing monosilane, oxygen, and nitrogen, a mixed gas containing vapor of monobutyltin trichloride, oxygen, water vapor, nitrogen, and vapor of antimony trichloride, and a mixed gas containing vapor of monobutyltin trichloride, oxygen, water vapor, nitrogen, and hydrogen fluoride were supplied sequentially. Thus, on the glass sheet, a tin oxide film (SnO2 film), a silicon oxide film (SiO film), a tin oxide film (SnO2 : Sb film) to which antimony was added, and a tin oxide film (SnO2: F film) to which fluorine was added were deposited in this order. The mole ratio of the added antimony to tin was 0.02, and the content of fluorine was set to be the same (i. e. 0.2 wt. %) as in the above.

Table 1 also shows the iron components, thicknesses of respective metal oxide films, visible light transmittance, solar radiation transmittance,

and color tones of transmitted light with respect to each transparent heat shading glass sheet thus obtained.

Using each transparent heat shading glass sheet of the samples 1 to 8 and 10 to 14 and a float glass sheet with a general composition with a thickness of 3 mm, a double-glazing unit as shown in FIG. 3 was produced.

Specifically, the glass sheets are sealed with isobutylene-isoprene rubber with an aluminum spacer filled with a desiccant being positioned at the peripheries of the glass sheets so that an air layer with a predetermined thickness is maintained therebetween. The thickness of the air layer was set to be 6 mm in the sample 6 and to be 12 mm in the other samples. The transparent heat shading glass sheet was placed as the glass sheet positioned inside a room in the sample 14, but was placed as the glass sheet positioned outside a room in the samples other than the sample 14. The transparent heat shading glass sheet was placed so that its metal oxide films were positioned on the air layer side in every case.

Furthermore, using the transparent heat shading glass sheet of the sample 9 and a general float glass sheet with a thickness of 3 mm, a double- glazing unit including a reduced pressure layer as shown in FIG. 4 was produced. The thickness of the reduced pressure layer was maintained to be 0.3 mm and the pressure of the reduced pressure layer was reduced to be about 0.01 Pa. The transparent heat shading glass sheet was placed as a glass sheet positioned outside a room.

Table 1 also shows SHGC values in the United States and solar heat gain coefficients (acquisition rates; n) based on JIS of solar radiation heat of the respective double-glazing units thus obtained. In Table 1, the values that are not preferable for achieving the objects of the present invention are underlined. However, the underlines in Table 1 merely are added for reference and do not limit the present invention.

Table 1 Characteristics of Single-Layer Glass Sheet (Transparent Heat shading Glass Sheet) Iron Visible Solar- Color of Sample Component Film Material/Trickness (nm) Light Light Transmitted No. (wt.%) Trans- Trans- Light Total First Second Fourth mittance mittance FeO Third Layer a* b* @ Lron Layer Layer Layer (%) (%) 1 0.31 0.096 SnO2/32 SiO2/22 SnO2:F/350 - 78.9 59.4 -2.6 0.2 2 0.38 0.095 SnO2/32 SiO2/22 SnO2:F/850 - 78.4 59.4 -2.8 0.9 3 0.38 0.095 SnO2/40 SiO2/22 SnO2:F/450 - 79.1 57.1 -3.4 1.6 4 0.38 0.095 SnO2/32 SiO2/22 SnO2:Sb/50 SnO2:F/300 78.9 57.1 -8.8 0.8 5 0.31 0.090 SnO2/40 SiO2/22 SnO2:Sb/210 SnO2:F/220 75.6 51.6 -2.2 1.9 6 0.45 0.140 SnO2/40 SiO2/22 SnO2:Sb/210 SnO2:F/240 71.5 45.3 -4.1 -0.2 7 0.45 0.097 SnO2/32 SiO2/22 SnO2:F/350 - 78.2 59.4 -3.0 1.5 8 0.45 0.115 SnO2/25 SiO2/25 SnO2:F/200 - 77.1 56.4 -3.4 1.7 9 0.38 0.095 SnO2/32 SiO2/22 SnO2:F/350 - 78.8 59.4 -2.8 0.9 10 0.30 0.088 SnO2/32 siO2/22 SnO2:F/350 - 79.7 61.9 -2.5 0.2 11 0.48 0.150 SnO2/40 SiO2/22 SnO2:Sb/210 SnO2:F/240 69.7 42.2 -4.5 -0.1 12 0.38 0.095 SnO2/52 SiO2/20 SnO2:F/350 - 79.2 59.4 -5.2 2.6 13 0.38 0.095 SnO2/25 SiO2/25 SnO2:F/130 - 80.0 60.7 -2.8 0.1 14 0.38 0.095 SnO2/32 SiO2/22 SnO2:F/350 - 78.4 59.4 -2.8 0.9

The visible light transmittance of the glass sheets obtained in the above and the solar heat gain coefficients of solar radiation heat in the double-glazing units obtained in the above were measured according to JIS R3106-1985. The color of transmitted light was measured according to JIS Z8722-1982 using a spectrophotometer 330 manufactured by Hitachi, Ltd.

In addition, a* and b* of the L*a*b* color system psychometric chroma coordinates, which are prescribed in JIS Z8729-1980, were calculated. The "SHGC"values of the double-glazing units were calculated using the software program"WINDOW4.1" provided by the U. S. Department of Energy.

As shown in Table 1, the transparent heat shading glass sheets (single-layer glass sheets) of the samples 1 to 9 have visible light transmittances of at least 70% and solar radiation transmittances of below 60%, and the double-glazing units using the samples 1 to 9 have solar heat gain coefficients of 0.58 or lower and SHGC values of 0.57 or less. On the other hand, in the sample 10, since excessively small amounts of total iron and FeO are present, the solar radiation transmittance of the transparent heat shading glass sheet and the solar heat gain coefficient of the double- glazing unit are excessively high. In the sample 11, excessive amounts of total iron and FeO are contained, and the visible light transmittance of the transparent heat shading glass sheet is too low. In the sample 12, mainly the first layer is too thick and therefore the absolute value of a* exceeds 5.

In the sample 13, preferable results were obtained with respect to the visible light transmittance and the color of transmitted light in the transparent

heat shading glass sheet. However, mainly the third layer is too thin and thus the solar radiation transmittance and the solar heat gain coefficient of the double-glazing unit are excessively high. In the sample 14, preferable characteristics were obtained with respect to the transparent heat shading glass sheet. However, since the transparent heat shading glass sheet in the double-glazing unit was placed to be positioned inside a room, the solar heat gain coefficient was excessively high.

In the samples 1 to 9 in which preferable results were obtained with respect to the respective characteristics of the transparent heat shading glass sheets and the double-glazing units, the visible light transmittance of every double-glazing unit was at least 64%.

INDUSTRIAL APPLICABILITY As described above, according to the present invention, the transparent heat shading glass sheet is provided by suitably combining a glass sheet and metal oxide films formed thereon to obtain a high efficiency in visible light transmittance and a high solar heat shading rate.

Furthermore, in the transparent heat shading glass sheet of the present invention, an achromatic color tone of transmitted light is obtained not only by employing the suitable stacked structure of the metal oxide films shown in the above as an example but also by suitably adjusting the total amount and valence of iron components in the glass sheet, thus improving its quality as window glass.