BACKGROUND OF THE INVENTION There is currently a great need for glass compositions having a low glass transition temperature (Tg), from about 250°C to about 450°C, good chemical durability such as resistance to attack from acids, and resistance to attack from water and humidity. Because of potentially toxic environmental factors, there is also a need for durable, low Tg glass compositions that can be made lead free without affecting durability properties such as resistance to attack from acids, water, humidity, and the like. Glass compositions that combine good chemical durability with the capability of being formed at low temperatures, i. e. compositions having low Tg, are potentially useful for a host of applications such as refractory adhesives, sealing glass frits, and overcladding material for glass fiber.

The search has been continuous to discover new durable glass compositions exhibiting low Tg and enhanced resistance to attack by water, humidity, and chemicals.

Thus, the present invention is directed towards a group of new durable Sb-stabilized

Mo + W phosphate based glass compositions that have a low Tg, and superior resistance to attack by water, humidity, and chemicals, and are suitable for use in a variety of applications, such as refractory adhesives, sealing frits, and overcladding material for glass fiber.

Additionally, the preferred Sb-stabilized Mo + W phosphate based glass compositions are essentially lead free. The expression essentially lead free indicates that no material containing a substantial concentration of lead is intentionally included in the glass.

SUMMARY OF THE INVENTION In accordance with the present invention it is provided that the addition of about 0.5 to about 60% Sb203 to Mo + W phosphate based glass compositions results in a durable, low Tg, glass compositions having unexpectedly improved resistance to attack from water, humidity and acids. The durable, low Tg, Sb-stabilized Mo + W phosphate based glass compositions of the instant invention preferably comprise, in mole percent (mol %) on the oxide basis, 0-40% R20 where R includes the alkali metals (Li, Na, K, Rb or Cs) as well as Ag and Tl, 0-20% XO where X includes the alkaline earth metals (Mg, Ca, Sr or Ba) as well as Cu, Zn, Cd and Pb, 15-80% MoO3 + W03, 0.5-60% Sb203, and 10-40% P20s. Additionally, the Sb-stabilized Mo + W phosphate based glass composition can contain a total of 0-5%, in mole percent (mol %) on the oxide basis, of glass forming oxides including, but not limited to, B203, A1203, Si02, TeO2, Ga203, GeO2, transition metal and rare earth metal oxides or mixtures thereof. In a preferred embodiment, the Sb-stabilized Mo + W phosphate based glass compositions are essentially lead free.

Additional features and advantages of the invention will be set forth in the detailed description that follows, and in part, will be readily apparent or recognized to those skilled in the art by practicing the invention as described herein.

It is to be understood that both the foregoing general discussion and the following detailed description and examples provided herein are merely exemplary of the invention, and are intended to provide an overview or framework for understanding the nature and character of the invention as it is claimed.

DETAILED DESCRIPTION OF THE INVENTION The durable, low Tg, Sb-stabilized Mo + W phosphate based glass compositions of the instant invention comprise, in mole percent (mol %) on the oxide basis, 0-40% R20 wherein R includes the alkali metals (Li, Na, K, Rb or Cs) as well as Ag and Tl ; 0- 20% XO wherein X includes the alkaline earth metals (Mg, Ca, Sr or Ba) as well as Cu, Zn, Cd and Pb; 15-80% MoO3 + W03, preferably about 20-60% Mo03 ; 0. 5-60% Sb203 ; and 10-40% P205, preferably about 15-30% P205. Additionally, the Sb- stabilized Mo + W phosphate based glass composition can contain a total of 0-5%, in mole percent (mol %) on the oxide basis, of glass forming oxides including, but not limited to, B203, Al203, Si02, Te02, Ga203, GeO2, transition metal and rare earth metal oxides or mixtures thereof.

I have observed that the presence, in mole percent (mol %) on the oxide basis, of about 0.5% to about 60% Sb203, preferably about 5% to about 40% Sb203, more preferably about 10% to about 40% Sb203, in Sb-stabilized Mo + W phosphate based glass compositions unexpectedly results in a lower Tg, and superior resistance to attack from water, humidity, and chemicals such as acids. The glass compositions encompassed by the present invention preferably exhibit a glass transition temperature (Tg) from about 250° to about 450°C ; a percentage total weight loss after exposure to 0.001N HC1 for one hour (% A (0. OOlN HC1)) less than or equal to about 0.5% ; and a percentage total weight loss after exposure to boiling distilled water for one hour (% A (H20)) less than or equal to about 0.5%.

In a preferred embodiment, the new durable Sb-stabilized Mo + W phosphate based glass compositions of the present invention are essentially Pb free.

The invention will be further clarified by the following Tables that are intended to be exemplary of the invention.

Table I summarize the data of four Mo phosphate based glass compositions, wherein the constituents of each glass composition are expressed in terms of mole percent on the oxide basis. Table I reports the glass transition temperature (Tg) in terms of °C ; the percentage of total weight loss after exposure to 0. 001N HCl for one hour (% h (0. 001N HC1)) ; and the percentage of total weight loss after exposure to boiling distilled water for one hour (% A (H20)).

In Table I, Comparative Example 1 demonstrates a Mo phosphate based glass composition without the addition of Sb203, and therefore does not fall within the purview of the present invention. Examples 2,3 and 4 representing the instant invention, demonstrate that the substitution of 10 mol% of Sb203 for either R2O, MoO3 or P205 results in an unexpectedly 60 fold to 400 fold improvement in resistance to boiling water and a comparable increase in acid durability. At the same time, Tg is reduced by about 10 °C and 60°C in Examples 2 and 4 respectively, compared to Comparative Example 1.

Table I Example 1 234 Li2O 7 7 3.5 7 Na208848 K20 5 5 2. 5 5 MoO3 60 50 60 60 Sb203-10 10 10 P205 20 20 20 10 Tg(°C) 350 338 - 290 Wt%#(H2O) 28 0.07 0.11 0.44 a (m/°C) 4 0 X 14. 9 13. 1 Wt%#(0.001N HCl) 11 0.06 0.50 0. 38 Table II summarizes the data for Mo + W phosphate based glass composition Examples 5-15, wherein the constituents of each glass composition are expressed in terms of mole percent on the oxide basis. Table II reports the glass transition temperature (Tg) in terms of °C ; the thermal expansion coefficient (a) in terms of ppm/°C ; the percentage of total weight loss after exposure to 0. 001N HCl for one hour (%#(0.001N HCl)) ; and the percentage of total weight loss after exposure to boiling distilled water for one hour (% A (H20)) for each of the Mo + W phosphate based glass compositions.

Table II Example 5 6 7 8 9 10 11 12 13 14 15 Li2O 7 7 7 3.5 3.5 7 - - 7 7 7.5 Na2O 8 8 8 4 4 8 - - 8 8 5 K2O 5 5 5 2.5 2.5 5 - - 5 5 7.5 CuO - - - - 10 - - - - 10 -- PbO - - - - - - - 10 - -- -- MoO3 40 30 20 35 30 60 60 60 20 30 -- WO3 - - - - - - - - 20 10 50 Sb2O3 20 30 40 35 30 10 20 10 20 10 10 P2O5 20 20 20 20 20 10 20 20 20 20 20 Tg(°C) 319 310 305 323 - 290 336 368 352 350 427 α (ppm/°C) 15.9 15.8 16.7 - - - 13.3 - 13.7 13.2 -- Wt%#(H2O) 0.11 0.17 0.15 0.11 0.04 0.44 0.16 0.22 0.12 0.06 0.09 Wt%#(0.001N HCl) - 0.00 0.00 0.00 0.00 0.38 0.02 0.31 0.2 0.15 --

The Sb-stabilized Mo + W phosphate glass compositions of the present invention can serve as sealing frits, refractory adhesives, and overcladding for glass fibers and the like for the purpose of enhancing the strength of the fiber, because of their low Tg and high thermal expansion coefficient.

It will be apparent to those skilled in the art that various modifications and variations can be made to the present invention without departing from the spirit and scope of the invention. Thus, it is intended that the present invention covers the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents. Accordingly, modifications are contemplated which can be made without departing from the spirit of the described invention.