HK1000861B

HK1000861B - Soda-lime-silica glass compositions and uses thereof

Info

Publication number: HK1000861B
Application number: HK97102389.9A
Authority: HK
Inventors: Koch Stephanie; Jousse Didier; Gy Rene; Courtemanche Gilles
Original assignee: Saint-Gobain Glass France
Priority date: 1994-10-13
Filing date: 1995-10-13
Publication date: 2005-01-14

Abstract

A heat-stable glass composition including 45-68 wt. % , 0-20 wt. % , 0-20 wt. % , 0-10 wt. % , 2-12 wt. % , 3.5-9 wt. % , 1-13 wt. % CaO and 0-8 wt. % MgO, wherein the total content of , and oxides is no more than 70 %, the total content of and oxides is no less than 2 %, the total content of alkaline oxides and is no less than 8 %, and said composition optionally includes BaO and/or SrO oxides in proportions selected so that 11 % MgO + CaO + BaO + SrO 30 %. Said glass composition is useful for making an emissive screen substrate or fireproof glazing.

Description

The present invention relates to glass compositions which can be transformed into glass tape into which plates can be cut and which are well resistant to heat, and which can be used to make fire-proof glazing or as substrates for the manufacture of plasma displays, electroluminescent displays and cold cathode displays.

The glass currently used to make such substrates is a glass belonging to the family of silico-sodo-calcium glasses, commonly used to make glass for buildings or automobile vehicles. Such glass also includes at least one lithium or zinc oxide (see SU-A-998 401, SU-A-975 618, SU-A-1 604 763 and JP-A-01 148 730). While this type of glass is generally satisfactory in terms of its chemical resistance, flatness and defects, its temperature holding is sometimes poor.

In the manufacture of the emission shields, the substrate is subjected to several thermal treatments with the aim of stabilizing the dimensions of the substrate and fixing a series of layers of different compounds, such as enamels, deposited on its surface. The fixing of these layers of varying thicknesses requires the substrate to be brought to temperatures above 550°C. If the coefficient of expansion of the silico-sodium-calcium glass is used to the same extent as that of the compounds deposited on its surface, its temperature holding is insufficient and it is necessary to lay it on a smooth slab during heat treatments to avoid any deformation.

The glass used for the manufacture of fireproof glass is generally borosilicate glass, which has very good resistance to heat and thermal shock, and is generally characterized by a low expansion coefficient, which prevents the development of high thermal stresses in the glass and thus limits the increase in mechanical strength.

The present invention is intended to address the limitations of the use of these known lenses for any of the above applications.

Thus, the present invention is concerned with a glass composition which allows the manufacture of a plate or substrate with virtually no deformation when subjected to temperatures between 550 and 600°C.

The present invention relates in particular to a glass composition which allows the manufacture of a plate within which, by heat treatment, stresses at least as high as those arising in an ordinary silicon-sodium-calcium glass plate can be established.

The present invention is intended to produce a glass composition that allows the manufacture of a substrate with a lower surface depletion of alkaline ions than that observed on a substrate made from ordinary silico-sodium-calcium glass.

The present invention also concerns a glass composition which can be melted and transformed into a float glass tape on a metal bath under conditions of temperatures close to those of ordinary silico-sodium-calcium glass.

These objectives are achieved by means of a glass composition which includes exclusively the following constituents in the following proportions by weight:

	45 à 68 %
	0 à 20 %
	0 à 20 %
	0,5 à 4 %
	2 à 12 %
	3, 5 à 9 %
CaO	1 à 13 %
MgO	0 à 8 %

The sum of the oxides SiO2, Al2O3 and ZrO2 remaining at or below 70%, the sum of the oxides Al2O3 and ZrO2 remaining at or above 2%, the sum of the alkaline oxides Na2O and K2O remaining at or above 8%, the said composition possibly including the oxides BaO and/or SrO in such proportions as: - What? The following is the list of active substances: - What? a thickness of not more than 0,05 mm and a thickness of not more than 0,05 mm,

It is generally accepted that glass has no viscous behaviour below a characteristic temperature called the lower recrystallization temperature (strain point), which corresponds to a viscosity of the order of 1014.5 Poise. This temperature is therefore an interesting benchmark for assessing the temperature holding of glass. By combining the constituents as resulting from the invention, glasses meeting this definition have a lower recrystallization temperature of at least 25°C above that of a classical silico-sodo-calcium glass.

This combination of constituents also makes it possible to obtain glasses with a coefficient of expansion of the same order of magnitude as that of a traditional silica-sodium-calcium glass.

The glass according to the invention also has the advantage of being able to be melted and transformed into glass ribbon at temperatures close to those used for the manufacture of conventional silico-sodium-calcium glass.

In the context of the invention the SiO2 content must not exceed about 68%; furthermore, the melting of the vitrifiable mixture and the refining of the glass require high temperatures which cause accelerated wear of the refractories of the furnaces. Furthermore, it has been observed in the context of the invention that the increase in the SiO2 content does not favour the elevation of the lower boiling temperature of the glass. Below 45% by weight of SiO2, the stability of the glass according to the invention is insufficient. The glasses according to the invention which melt the most, the fluctuations are best suited to the boiling temperatures of the glass, which are between 59% and 45O2 and contain higher boiling viscosities.

The Al2O3 content must not exceed 20% or it will make melting too difficult and increase the viscosity of the glass to an unacceptable extent at high temperatures.

ZrO2 also plays a stabilizing role. This oxide increases the chemical strength of the glass to some extent and promotes the increase in the lower boiling temperature. The percentage of ZrO2 should not exceed 20% or it will make melting too difficult. If this oxide is difficult to melt, it has the advantage of not increasing the viscosity of the glass according to the invention at high temperatures.

The melting of the glass according to the invention is generally within acceptable temperature limits, provided that the sum of the SiO2, Al2O3 and ZrO2 oxides is equal to or less than 70%.

The glasses of the present invention shall preferably contain the following constituents in the following proportions by weight: - What?

	45 à 68 %
	2 à 20 %
	0 à 20 %
	0,5 à 4 %
	4 à 11 %
	3,5 à 7 %
CaO	1 à 13 %
MgO	1 à 8 %

the sum of the contents of SiO2, Al2O3 and ZrO2 oxides remaining equal to or less than 70%, the sum of the contents of the alkaline oxides Na2O and K2O remaining equal to or more than 8%, the said composition possibly including the oxides BaO and/or SrO in such proportions as: - What? The following substances are added to the product: - What? - What?

The glass of the present invention is characterized by the systematic presence of B2O3, which, as a network-forming oxide, can be added to or substituted for SiO2, which reduces the melting temperature of the vitrifiable mixture and the viscosity of the glass at high temperatures. It also reduces the ability of the glass to devitrify, in particular by preventing the rise in the temperature of liquids. This effect, together with the decrease in viscosity, must maintain a sufficient gap between the glass's forming temperature and its liquid temperature. In the float glass technique in particular, it is important that the temperature of the liquids remain equal to or less than the corresponding room temperature of 3.5°C or 11°C. In this case, a more precise temperature of the glass is preferably equal to or less than the room temperature of 3.5°C or 11°C.

The content of B2O3 does not exceed about 4%, since above this value the volatilization of boron in the presence of alkaline oxides during glass making can become significant. In this family of glasses according to the invention, the sum of the oxides Al2O3 and ZrO2 is advantageously equal to or greater than 5%.

The glass compositions of the preferred invention include the following constituents in the following proportions by weight: - What?

	45 à 59 %
	5 à 18 %
	0 à 17 %
	0,5 à 4 %
	4 à 10 %
	3,5 à 7 %
CaO	1 à 12 %
MgO	1 à 7 %

The sum of the contents of SiO2, Al2O3 and ZrO2 oxides remaining at or above 70%, the sum of the contents of the alkaline oxides remaining at or above 10%, the said compositions possibly containing BaO and/or SrO oxides in such proportions as: - What? The total amount of the product obtained shall be calculated as follows: - What? glass compositions having a lower recrystallization temperature (strain point) of 550°C or more and a coefficient of expansion (α25-300°C) of between 85 and 95.10-7/°C.

In general, the influence of other oxides on the suitability of the glasses of the invention to be melted and floated on a metal bath, and on their properties, is as follows:

The oxides Na2O and K2O allow the glass of the invention to maintain its melting temperature and viscosity at high temperatures within the limits indicated above. To do this, the sum of the oxide contents remains equal to or greater than about 8%.[2] Compared to ordinary silico-sodium-calcium glass, the simultaneous presence of these two oxides in the glass of the invention, sometimes in close proportions, allows to significantly increase their chemical resistance, specifically their hydrolytic resistance, as well as their resistivity.

The alkaline earth oxides introduced into the glass according to the invention have the overall effect of raising the lower boiling point, which is why the sum of their weight contents must be at least 11%. Above about 24%, the ability of the glass to devitrify can be increased to proportions incompatible with the metal bath flotation process. To maintain the devitrifying of the glass within acceptable limits, their weight contents of CaO and MgO must not exceed 13 and 8%, respectively. The MgO content is preferably equal to or less than 5%.

MgO, CaO and to a lesser extent SrO increase the lower boiling point; BaO and SrO increase the chemical resistance and resistivity of the glass according to the invention.

The advantages of the glass compositions of the invention will be better appreciated by the examples given in the table in the annex.

Glass No. 1 is a classical composition of silico-sodium-calcium glass used to make a glass ribbon by the process of float glass on a molten metal bath; glass No. 2 is a known borosilicate glass. Lenses No. 3 to 8 illustrate the glass compositions according to the invention.

As the examples show, the viscosity and liquid characteristics of the glasses of the invention are sufficiently close to those of the reference glass to enable them to be made and processed into ribbon under virtually the same conditions as the latter.

Thus, by the float glass technique, the glass according to the invention is obtained in the form of a strip of strictly controlled thickness, which may vary from 0.5 mm to 10 mm. Sheets are cut into the desired size in the strip, before being subjected to a heat treatment to stabilize the dimensions of the said sheets. These sheets are then ready to serve as a substrate that will withstand the deposition of different layers and the heat treatments required for their fixation.

These insulating panes consist of two or more panes joined together by means of a glued interlayer profile and their mounting technique in the supporting chassis is such that when exposed to flames, the edge of the plate on the fire side is exposed instantly or, in any case, shortly, to thermal radiation and the flames themselves, thus limiting the thermal stresses which usually arise in a plate when it is heated more centrally than on its edges. The combination of a good quality thermal insulation and mounting in such a place allows it to remain in place for a long time to satisfy the standards in force.

The laminated glass is made by joining plates together using an interlayered plastic film; in general, the glass plates used are also heat-soaked.

Claims

Glass composition for use in the manufacture of a thermally stable plate or substrate, characterized in that it exclusively comprises the following constituents in the weight proportions given hereinafter: 45 to 68% 0 to 20% 0 to 20% 0.5 to 4% Na20 2 to 12% 3.5 to 9% CaO 1 to 13% MgO 0 to 8%

the sum of the contents of the oxides SiO₂, Al₂O₃ and ZrO₂ remaining equal to or below 70%, the sum of the contents of the oxides Al₂O₃ and ZrO₂ being equal to or above 2%, the sum of the contents of the alkali metal oxides Na₂O and K₂O being equal to or above 8%, said composition optionally comprising the oxides BaO and/or SrO in proportions such that: 11% ≤ MgO + CaO + BaO + SrO ≤ 24% said composition having a strain point equal to or above approximately 53°C and an expansion coefficient (α_25-300°C) between 80 and 95.10^-7/°C.
Glass composition according to claim 1, characterized in that it comprises the following constituents in the following weight proportions: 45 to 68% 2 to 20% 0 to 20% 0.5 to 4% 4 to 11% 3.5 to 7% CaO 1 to 13%
Glass composition according to any one of the preceding claims, characterized in that the sum of the contents of the oxides Al₂O₃ and Zr02 contained therein is equal to or above 5%.
Glass composition according to any one of the preceding claims, characterized in that its SiO₂ weight content is between 45 and 59%.
Glass composition according to any one of the preceding claims, characterized in that it comprises the following constituents in the following weight proportions: 45 to 59% 5 to 18% 0 to 17% 0.5 to 4% Na20 4 to 10% 3.5 to 7% CaO 1 to 12% MgO 1 to 7%

the sum of the contents of the alkali metal oxides remaining equal to or above 10% and said composition can also comprise the oxides BaO and/or SrO in proportions such that: 14% ≤ CaO + MgO + BaO + SrO ≤ 22% said composition having a strain point equal to or above approximately 550°C and an expansion coefficient (α_25-300°C) between 85 and 95.10^-7/°C.
Glass composition according to any one of the preceding claims, characterized in that the sum of the contents of the oxides ZrO₂ and Al₂O₃ contained therein is between 8 and 22%.
Glass composition according to any one of the preceding claims, characterized in that it has a viscosity corresponding to logη = 1.6 at a temperature equal to or below 1630°C and preferably 1590°C.
Glass composition according to any one of the preceding claims, characterized in that it has a viscosity corresponding to logη = 3.5 at a temperature equal to or below 1220°C and preferably 1170°C.
Glass composition according to claim 8, characterized in that it has a liquidus temperature equal to or below the temperature corresponding to the viscosity logη = 3.5.
Use of glass compositions as defined by any one of the claims 1 to 6 for the manufacture of a substrate for an emissive screen from a glass sheet cut in a glass ribbon obtained by floating glass on a molten metal bath.
Use of glass compositions as defined by any one of the claims 1 to 6 for the manufacture of fire-retarding glazings produced from a glass sheet or plate cut from a glass ribbon obtained by floating glass on a molten metal bath.