GB2320022A - Green solar control glass - Google Patents

Abstract

To achieve the optimum solar performance in lightweight vehicle windows, a soda-lime-silica solar control green grass has a thickness in the range 2.6 to 3.0 mm and a total iron content in the range 1.1% to 1.45% by weight providing a light transmission in the range 70% to 73% and a direct solar heat transmission of less than 46%. Automotive glazings may be produced from the glass using bending and tempering techniques appropriate for thin iron-containing glasses. The soda-lime glass may comprise by wt. 65-75% SiO 2 , 10-18% Na 2 O, 0-5% K 2 O, 0-5% MgO, 4-14% CaO and 0-5% Al 2 O 3 . Titanium may be added or be present in amount up to 0.5 wt% TiO 2 .

Description

Solar Control Glass and Glazine The invention relates to light weight high performance solar control glasses for use in automotive glazing, and to automotive glazings composed thereof.

It has previously been proposed, in EP 0 469 446B, to produce green tinted, ultra-violet absorbing glasses for use in automotive glazing by using a colourant portion containing iron in an amount of at least 0.858 by weight and up to 0.54b cerium. To achieve the desired ultra violet absorbance, this patent proposes to use either more than 0.2% by weight cerium, or an unusually low ratio of ferrous iron to ferric iron such that the ratio of ferrous iron (calculated as weight of ferrous oxide) to total iron (calculated as weight of ferric oxide) is about 0.16.

All the Examples relate to glasses 3.9 mm thick EP 0 598 305A similarly relates to green tinted, ultra-violet absorbing glasses for use in automotive glazing, but proposes to achieve the desired ultra-violet absorbance by using increased levels of titania in place of either the ceria or the low ratio of ferrous to ferric iron used in EP 0 469 446B. The twenty four Examples in this application all have total iron contents in the range 0.65% to 0.93% and twenty one of the twenty four contain titania in an amount of 0.15% by weight or more.

EP 0 644 164A also relates to an iron containing solar control glass for use in automotive glazing, and aims to produce optimum properties in a glass thickness in the range 3.0 to 3.3 mm. The single example has a colourant portion comprising 0.95% by weight of iron (calculated as ferric oxide) and a ratio of ferrous iron (calculated as weight of ferrous oxide) to total iron (calculated as weight of ferric oxide) of 0.30.

While the prior art has been particularly concerned to provide solar control glasses of low ultra-violet transmittances, the present inventors have realised that it is more important to optimise the iron content in relation to thickness of the glass, to enable the best possible solar control performance to be achieved in lightweight green glasses meeting the automotive standards for light transmission, while operating at a ferrous to ferric ratio that does not require the demanding operating conditions envisaged for some of the prior art glasses.

According to the present invention, there is provided a lightweight high performance green solar control soda lime silica glass having a thickness in the range 2.6 to 3.0 mm and a total iron content in the range 1.1% (preferably 1.2%) to 1.45% (preferably 1.35%) by weight, whereby the glass has a light transmission in the range 70 to 73% (preferably 70 to 72%) and a direct solar heat transmission of less than 46% (preferably less than 45%).

The total iron content of the glass is calculated as ferric oxide. The light transmission is rneasured using C.I.E. llluminant A over the wavelength range 380 nm to 780 nm at 10 nm intervals; the direct solar heat transmission (DSHT) is the direct solar heat transmitted at Air Mass 2 (simulating rays from the sun incident at an angle of 30Q) measured over the wavelength range 350 to 2100 nm at 50 nm intervals. All the transmissions referred to in the present specification and claims are calculated by applying the rectangular rule to the measured values.

According to a further aspect of the invention there is provided an automotive glazing composed of a glass in accordance with the invention.

The glasses of the present invention may be produced at the ferrous to total iron ratios normally associated with many modern float glass plants and do not require special conditions necessitated by particularly low (below 15%) or particularly high (above 30%) ferrous ratios.

Thus, for example, they may be conveniently be produced at ferrous iron (calculated as Fe2O3) to total iron (calculated as Fe2O3) ratios of 0.18 to 0.30, although we generally prefer to operate at a ratio of at least 0.20 and less than 0.27, especially between 0.22 and 0.26, as such ratios are most readily achieved on many float glass producing plants.

The glasses of the present invention are green in colour, and will preferably exhibit a dominant wavelength in the range 495 - 520 nm and an excitation purity of 2-5%.

The iron oxide used in accordance with the present invention may be incorporated in a standard soda lime silica glass. Such glasses typically have a composition with the following ranges: SiO2 65% - 75% (by weight) Na2O 10% - 18% K20 0% - 5% MgO 0% - 5% CaO 4% - 14% A12 3 0% - 5% In addition to the iron, they may contain other additives, including melting and refining aids such as sulphate and carbon sources and/or impurities, provided the specified properties are achieved. If desired, titanium may be added (for example by feeding iron as ilmenite), usually in amounts of up to about 0.5% by weight, although generally no more than impurity amounts, i.e. less than 0.1%, normally less than 0.05% by weight, will be present, in order to avoid the effect of yellowing the colour of the glass. When titanium is added, the dominant wavelength will rise, possibly to 540 nm, depending on the amount of titanium present, although dominant wavelengths less than 515 nm are preferred.

Cobalt may be added in trace amounts to modify the colour of the glass.

The accompanying Table 1 sets out details of the colourant composition, thickness, and corresponding properties of exemplary glasses in accordance with the invention. In each case, the colourants are incorporated in a base glass containing, in percentages by weight: 72.5% SiO2 1.0% A1203 12.9% Na2O 0.6% K20 8.3% CaO 3.9% MgO 0.2% S03 The total iron content is specified in weight percent ferric oxide (FezO) assuming all the iron is present as ferric oxide. References to the ratio of ferrous iron to total iron in the present specification and claims are reference to ratios determined optically and given by the following formula, in which Tlooou is the percentage transmission of radiation of wavelength 1000 nm through a sample of glass L mm thick, and Fe203 is the total iron content of the glass (calculated as ferric oxide) as the percentage by weight.

Ratio ferrous iron/total iron =

The resultant value represents the proportion of the iron content which is present in the ferrous (as opposed to ferric) state.

In the Table, LT represents the percentage of visible light transmitted and DSHT represents the direct solar heat transmission both measured and calculated as described above.

"UV ISO" is the ultra violet transmission of the glass over the wavelength range 280 nm to 380 nm in 10 nm intervals in accordance with ISO 9050, while "UV Parry Moon" is the ultra violet transmission measured over the wavelength range 300 nm to 400 nm at 10 nm intervals under Parry Moon 1940 Observer Conditions at Air Mass 2.

It is apparent from the properties shown in the Table that a high performance i.e. low solar heat transmission, may be achieved in a thin glass while maintaining a light transmission over 70%. The preferred glasses of the present invention have a thickness of 2.7 to 2.9 mm, especially 2.8 mm, as thinner glasses become difficult to toughen while thicker glasses are heavier in weight.

The glasses of the present invention may be produced in conventional manner for similar iron-containing glasses, with appropriate adjustment of the production conditions dependent on the precise iron content, the ferrous state, colouring contaminants in raw materials and glass thickness. The glasses may be processed to produce vehicle windows, especially side lights and back lights, in known manner, using bending and tempering techniques appropriate for thin iron-containing glasses.

\'.\ ,-= ." .. . ,.' > ., ..' Fe2O3 1.1 1.1 1.1 1.1 1.1 1.2 1.2 1.2 1.25 1.25 Ferrous | 25.5 | 26.8 30 30 30 23.9 25.4 28.1 23.1 24.0 Stale % TiO2 % Q04 0.04 0.04 0.5 0.5 0.35 0.04 0.14 0.40 0.04 Co3O4 - 14 12 7 - 8 - - - ppm Thickness 3 2.8 2.8 2. 2.8 2.8 2.8 2.8 2.8 2.8 mm LT 72.7 71.0 70.2 70.1 71.2 70.3 71.5 70.3 70.7 70.9 (III. A) DSHT 45.9 45.8 43.6 42.8 43.2 45.0 44.8 42.7 44.9 44.8 UV ISO 18.5 19.8 20.5 18.5 18.6 15.8 17.0 17.2 14.4 15.6 9050 UV Parry 40.4 41.8 42.6 37.8 37.8 35.2 37.9 34.9 33.0 36.0 Moon Dominant 498 494 493 509 515 516 502 501 537 505 Wavelength nm Colour 3.7 4.7 5.6 3.0 2.9 2.5 3.2 3.6 3.5 2.9 Purity % a* -8.3 -8.1 1 -8.7 -9.7 -9.7 -8.7 -8.5 -92 -8.9 -8.5 b* +1.1 -0.3 -1.0 +3.4 +4.1 +3.8 +1.9 +1.9 +5.5 +2.6

w Fe2O3 1.25 1.25 1.3 1.3 1.3 1.35 1.4 1.4 1.45 Ferrous 25.8 30 22.2 22.5 24 21.4 21.0 21.3 22.0 State % TiO2 % 0.02 0.04 0.30 0.05 0.04 0.05 0.2 0.04 0.02 Co3O4 - - - - - - ppm Thickness 2.8 2.6 2.8 2.8 2.8 2.8 2.7 2.7 2.6 mm LT 70.2 70.1 70.4 70.7 70.1 70.3 70.2 70.2 70.0 (III. A) DSHT 43.4 42.4 44.9 45.0 43.7 44.9 45.0 44.9 44A Uv ISO 16.0 18.4 13.6 14.3 14.6 13.1 12.3 12.7 12.6 9050 UV Parry 36.7 39.8 32.2 34.1 34.5 32.4 30.8 31.9 32.0 Moon Dominant 501 496 534 511 506.5 518 535 519 514 Wavelength nm Colour 3.5 4.8 3.3 2.5 2.9 2.5 3.3 2.5 2.5 Purity % a* -8.8 -9.0 -8.8 -8.5 -8.8 -8.5 -8.7 -8.5 -8.6 * +1.8 +0.23 +5.2 +3.3 +2.8 +3.9 +5.2 +4.1 +3.6

Claims (8)

1. Claims 1. A light weight high performance solar control soda lime silica glass having a thickness in the range 2.6 to 3.00 mm and a total iron content (calculated as Foe203) in the range 1.1% to 1.45% by weight, whereby the glass has a light transmission (Illuminant A) of at least 70% and a direct solar heat transmission of less than 46%.
2. 2. A glass as claimed in claim 1 having a total iron content of at least 1.2% by weight.
3. 3. A glass as claimed in claim 1 or claim 2 having a total iron content not exceeding 1.35% by weight
4. 4. A glass as claimed in any of the preceding claims having a direct solar heat transmission of less than 45%.
5. 5. A glass as claimed in any one of the preceding claims having a titanium content, measured as Tit2, of less than 0.1% by weight.
6. 6. A glass as claimed in any of the preceding claims having a titanium content, measured as TiOz, of at least 0.1% by weight.
7. 7. A light weight high performance solar control soda lime silica glass substantially as described in any of Examples 1 to 19.
8. 8. An automotive glazing composed of a glass according to any of the preceding claims.