EP1187793A1

EP1187793A1 - Glass fiber composition

Info

Publication number: EP1187793A1
Application number: EP00932752A
Authority: EP
Inventors: Frederick T. Wallenberger
Original assignee: PPG Industries Ohio Inc
Current assignee: PPG Industries Ohio Inc
Priority date: 1999-05-27
Filing date: 2000-05-23
Publication date: 2002-03-20
Also published as: WO2000073232A1; CA2375015A1; JP2003505318A

Abstract

The present invention provides a glass fiber composition comprising: 55 to 63 percent by weight SiO2; 22 to 26 percent by weight CaO; 12 to 16 percent by weight Al2O3; 0 to 1 percent by weight MgO; 0.05 to 0.80 percent by weight Fe2O3; 0 to 2 percent by weight Na2O; 0 to 2 percent by weight K2O; 0 to 2 percent by weight TiO2; 0 to 2 percent by weight BaO; 0 to 2 percent by weight ZrO2; and 0 to 2 percent by weight SrO, and at least one material selected from the group consisting of: 0.05 to 2 percent by weight B2O3; 0.05 to 2 percent by weight Li2O; 0.05 to 2 percent by weight ZnO; 0.05 to 2 percent by weight MnO; and 0.05 to 2 percent by weight MnO2. In one nonlimiting embodiment of the invention, the glass composition has a forming temperature of no greater than 2300 °F based on an NIST 717A reference standard, a liquidus temperature of no greater than 2160 °F, a ratio of SiO2 to RO of no greater than 2.65, and a ΔT of at least 65 °F.

Description

GLASS FIBER COMPOSITION

Cross Reference to Related Patent Application

This application claims the benefit of U.S. Provisional Application No. 60/136,280, filed May 27, 1999.

Background of the Invention 1. Field of the Invention

This invention relates to continuous glass fibers having glass compositions useful as reinforcement and textile fibers. 2. Technical Considerations

The most common glass composition for making continuous glass fibers, designated as E-glass, dates back to 1940. As described in the British Patent Specification No. 520,427, the original E-glass fibers were boron free and were based on glass compositions at or near the eutectic in the quaternary Si0₂-AI₂O₃-CaO-MgO phase diagram. As used herein, the terms "eutectic temperature", "liquidus temperature" and "T_UQ" mean the highest temperature at which liquid phase (melt) can be in equilibrium with solid phase (crystals); the terms "forming temperature" and "T_F0RM" mean the temperature at which the glass composition has a viscosity of 1000 poise, and the term "ΔT" means the difference between the liquidus temperature and the forming temperature. Typically, in a commercial glass fiber operation, ΔT is at least 90°F (50°C), and preferably at least 100°F (56°C) so as to preclude crystal formation in the bushing tips due to inevitable temperature and viscosity fluctuations of the melt and provide for safe and uninterrupted commercial production.

The original quaternary E-glass system had a liquidus temperature that was too close to its corresponding forming temperature, i.e. ΔT was too low. As a result, U.S. Patent No. 2,334,961 modified the quaternary system by adding boron to form a quinary system that included SiO₂, AI₂O₃, CaO, MgO and B₂0₃. These particular compositions, which required 9-11 wt% B₂0₃ and about 4.5 wt% MgO, exhibited a greater ΔT. In 1954 and later, E-glass was once more redefined according to U.S. Patent 2,571 ,074, by reducing the B₂0₃ content from about 10.0% to eventually about 5.5% and by reducing the MgO content from about 4.5% to about 0.45%. In effect, current boron and fluorine containing E-glass versions with less than about 1 % MgO belong to the quaternary, Si0₂, AI₂O₃, CaO, B₂0₃ phase diagram, since such small amounts of MgO are not deliberately added but brought into the melt as impurities. Over a decade ago, it became clear that boron levels of over 2 wt% and any amount of fluorine present in a glass fiber composition could pose an environmental concern and that fluorine free and low level boron compositions, i.e. compositions of no greater than 2 wt% boron, would be preferred in order to meet the needs of the society into the twenty-first century. The effort to achieve compliance with future needs was met by a return to the original boron free quaternary Si0₂-AI₂0₃-CaO-MgO system but modifying it to achieve the required ΔT without the beneficial effect of boron. Quaternary compositions of this kind are disclosed in U.S. Patent Nos. 4,542,106 and 5,789,329. These glass compositions met the desired ΔT condition, but had a forming temperature at least 100°F greater than earlier produced boron and fluorine free E-glass compositions.

It is believed that the liquidus temperature, and therefore the forming temperature required to maintain the desired ΔT, can be reduced in the quaternary SiO₂-AI₂O₃-CaO-MgO by optimizing the amounts of each of these principle constituents. Without the addition of small amounts of other oxides, such modifications facilitate an up to 50°F reduction in the liquidus temperature, and with the addition of small amounts of liquidus temperature reducing materials, such as but not limited to B₂0₃, Li₂0, ZnO, MnO and/or Mn0₂ (up to 2 wt%), facilitates a total reduction in liquidus temperature by over 50°F. In should be noted that all these compositions are essentially modifications of the quaternary SiO₂-AI₂O₃-CaO-MgO system and offer forming temperatures which are 50-100°F above that of borosilicate E-glass. As used herein, the term "borosilicate E-glass" means quinary Si0₂-Al₂0₃- CaO-MgO-B₂0₃ system and quaternary Si0₂-AI₂0₃-CaO-B₂O₃ system E-glass compositions as discussed above that include silica as the major constituent, greater than 2 wt% boron, in the form of B₂O₃ and up to about 4.5 wt% MgO. These glasses have a forming temperature generally ranging from 2100 to 2200°F (1149 to 1204°C) and a liquidus temperature generally ranging from 1970 to 2040°F (1077 to 1116°C).

For additional information concerning glass compositions and methods for fiberizing the glass composition, see K. Loewenstein, The Manufacturing Technology of Continuous Glass Fibres, (3d Ed. 1993) at pages 30-44, 47-60, 115-122 and 126-135, and F. T. Wallenberger (editor), Advanced Inorganic Fibers: Processes, Structures, Properties, Applications, (2000) at pages 81- 102 and 129-168, which are hereby incorporated by reference.

In today's market, the dominant boron and fluorine containing E-glass compositions, according to ASTM standard D- 578-98, are based on either the essentially quaternary Si0₂-AI₂0₃-CaO-B₂0₃ system or the essentially quinary SiO₂-AI₂0₃-CaO-MgO-B₂0₃ system, and the emerging fluorine free and essentially boron free E-glass compositions, according to the same ASTM standard, are based on the essentially quaternary SiO₂-AI₂O₃-CaO- MgO system. As used herein, the terms "essentially quaternary" and "essentially quinary" mean that the four or five stated constituents are the principal constituents of the glass composition, which can also include up to 2 weight percent each of other minor constituents. It is well known that glass fibers commonly designated as high strength (HS-) fibers can be derived from compositions in the ternary or essentially ternary SiO₂-AI₂0₃-CaO phase diagram, but they require forming temperatures which are 400-500°F higher than that of conventional borosilicate E-glass. These HS-glass fibers are premium items of commerce and are aimed at specialty markets requiring high strength, high in-use temperatures, and/or low dielectric constants for premium applications, e.g. printed circuit board in a high temperature environment.

Limited attention has been paid to the possibility of developing glass fibers from ternary or essentially ternary SiO₂-AI₂0₃-CaO compositions with only moderately higher forming and liquidus temperatures than those observed with conventional borosilicate E-glass fibers. It is believed that such fiber compositions would exhibit a low dielectric constant K. As a result, it would be advantageous to provide a ternary or essentially ternary Si0₂-Al₂0₃- CaO composition with a lowered forming temperature because the low dielectric constant K would provide superior substrates for printed wiring boards while the lower forming and liquidus temperatures would reduce the energy requirements for the glass fiber.

Summary of the Invention

The present invention provides a glass fiber composition comprising: 55 to 63 percent by weight Si0₂; 22 to 26 percent by weight CaO; 12 to 16 percent by weight AI₂O₃; 0 to 1 percent by weight MgO; 0.05 to 0.80 percent by weight Fe₂0₃; 0 to 2 percent by weight Na₂O; 0 to 2 percent by weight K₂0; 0 to 2 percent by weight TiO₂; 0 to 2 percent by weight BaO; 0 to 2 percent by weight Zr0₂; andO to 2 percent by weight SrO, and at least one material selected from the group consisting of: 0.05 to 2 percent by weight B₂0₃; 0.05 to 2 percent by weight Li₂0; 0.05 to 2 percent by weight ZnO; 0.05 to 2 percent by weight MnO; andθ.05 to 2 percent by weight MnO₂. In one nonlimiting embodiment of the invention, the glass composition has a forming temperature of no greater than 2300°F based on an NIST 717A reference standard, a liquidus temperature of no greater than 2160°F, a ratio of SiO₂ to RO of no greater than 2.65, and a ΔT of at least 65°F.

Detailed Description of the Invention The ternary or essentially ternary SiO₂-AI₂0₃-CaO compositions of the present invention are formulated to provide only moderately higher forming and liquidus temperatures as compared to those observed with conventional borosilicate E-glass fibers, and more specifically a relatively low eutectic liquidus temperature, e.g. about 2140°F (1171 °C). The Si0₂-AI₂0₃-CaO ternary system of the present invention is essentially free of MgO, i.e. the composition contains no greater than 1 percent by weight MgO. A glass fiber composition with this liquidus temperature and a ΔT of at least 100°F (as discussed earlier) would in effect have a forming temperature that is only about 100°F to 150°F (56°C to 83°C) higher than that of typical commercially produced borosilicate E-glass. Given this assumption, its forming temperature would be comparable to that of the fluorine free and essentially boron free quaternary Si0₂-AI₂0₃-CaO-MgO E-glass compositions discussed earlier.

Preferred ternary Si0₂-AI₂0₃-CaO compositions of this invention are not only useful as reinforcements for composites but, as discussed earlier, should also provide superior substrates for printed wiring boards because it is believed that they should offer a low dielectric constant K, in combination with a low liquidus temperature and a ΔT of at least 100°F. More specifically, E- glass is the currently preferred high-volume low-cost reinforcement for use in the printed wiring board market. As discussed earlier, this composition is based on an inexpensive essentially quaternary SiO₂-AI₂O₃-CaO-B₂O₃ system or essentially quinary Si0₂-AI₂0₃-CaO-MgO-B₂O₃ system, as discussed above, and has a dielectric constant of about 6.11 at 10¹⁰Hz. D glass (an essentially CaO and Al₂0₃ free glass fiber and, e.g. containing about 74 wt% Si0₂ and about 22 wt% B₂0₃) has a dielectric constant of about 3.56 at 10¹⁰ Hz, and S-glass (a ternary SiO₂-AI₂0₃-MgO glass fiber, free of trace oxides) has a dielectric constant of about 4.53 at 10¹⁰ Hz (see, Wallenberger at page 150). Because of their low dielectric constant, both D-glass and S- glass afford premium performance in printed circuit boards but at a premium price. Ternary glass fiber compositions of the present invention are believed to have a dielectric constant less than conventional borosilicate glass as well as less than the fluorine and boron free glass discussed earlier. In summary, a ternary or essentially ternary SiO₂-AI₂0₃-CaO glass fiber is expected to offer the dielectric properties comparable to that of D-glass and S-glass but at much lower forming temperatures and at a lower cost.

Commercial glass fibers of the present invention can be prepared in the conventional manner well known in the art, by blending the raw materials used to supply the specific oxides that form the composition of the fibers. For example, typically sand is used for SiO₂, clay for AI₂O₃, and lime or limestone for CaO. It should be appreciated that the glass compositions disclosed herein can also include small amounts of other materials, for example melting and refining aids, tramp materials or impurities. For example and without limiting the present invention, melting and fining aids, such as SO₃, are useful during production of the glass, but their residual amounts in the glass can vary and have no material effect on the properties of the glass product. The present invention also contemplates the inclusion of other materials in the glass fiber compositions, as will be discussed later in more detail. In addition, small amounts of the materials discussed above can enter the glass composition as tramp materials or impurities included in the raw materials of the main constituents.

After the ingredients are mixed in the proper proportions to provide the desired weight of each constituent for the desired glass, the batch is melted in a conventional glass fiber melting furnace and the resulting molten glass is passed along a conventional forehearth and into a glass fiber forming bushing located along the bottom of the forehearth, as is well known to those skilled in the art. During the glass melting phase, the glass is typically heated to a temperature of at least 2550°F ( 1 400°C). The molten glass is then drawn or pulled through a plurality of holes in the bottom of the bushing. The streams of molten glass are attenuated to filaments by winding a strand of filaments on a forming tube mounted on a rotatable collet of a winding machine. Alternatively, the fiber forming apparatus can be, for example, a forming device for synthetic textile fibers or strands in which fibers are drawn from nozzles, such as but not limited to a spinneret, as is known to those skilled in the art. Typical forehearths and glass fiber forming arrangements are shown in Loewenstein at pages 85-1 07 and pages 1 1 5-1 35, which are hereby incorporated by reference. Tables 1-3 show laboratory examples of ternary and essentially ternary Si0₂-AI₂0₃-CaO glass fiber compositions of the present invention. The glass fiber compositions were prepared from reagent grade oxides (e.g., pure silica or calcia). The batch size for each example was 1000 grams. The individual batch ingredients were weighed out, combined and placed in a tightly sealed jar. The sealed jar was then placed in a paint shaker for 15 minutes to effectively mix the ingredients. A portion of the batch was then place into a platinum crucible, filling no more than 3/4 of its volume. The crucible was then placed in a furnace and heated to 2600°F (1425°C) for 15 minutes. The remaining batch was then added to the hot crucible and heated to 2600°F (1425°C) for 15 to 30 minutes. The furnace temperature was then raised to 2700°F (1482°C) and held there for 4 hours. The molten glass was then fritted in water and dried. Where indicated, the forming temperature, i.e. the glass temperature at a viscosity of 1000 poise, was determined by ASTM method C965-81 , and the liquidus temperature by ASTM method C829-81. The weight percent of the constituents of the compositions shown in Tables 1-3 are based on the weight percent of each constituent in the batch. It is believed that the batch weight percent is generally about the same as the weight percent of the melted sample, except for glass batch materials that volatilize during melting, e.g. boron and fluorine. For boron, it is believed that the weight percent of B₂0₃ in a laboratory samples will be 5 to 10 percent less than the weight percent of B₂0₃ in the batch composition. For fluorine, it is believed that the weight percent of fluorine in a lab melt will be about 50 percent less than the weight percent of fluorine in the batch composition. It is further believed that glass fiber compositions made from commercial grade materials and melted under conventional operating conditions will have similar batch and melt weight percents as discussed above, except that the batch and melt weight percents for the volatile components of the composition will actually be closer to each other than the batch and melt wt% of the laboratory melts because in a conventional melting operation, the materials are exposed to the high melting temperatures for less time than the 4 hours of exposure for the laboratory melts.

Also included in Table 1-3 is the ratio Si0₂/RO which is the ratio of the silica content of the batch, expressed as Si0₂, to the sum of the calcia and magnesia content, expressed as CaO and MgO, respectively.

It should be appreciated that numerical values discussed herein, such as but not limited to weight percent of materials, length of time or temperatures, are approximate and are subject to variations due to various factors well known to those skilled in the art such as, but not limited to measurement standards, equipment and techniques. For example, if the range for a particular constituent of the glass composition is 55 to 63 weight percent, this range is about 55 to about 63 weight percent, and if a forming temperature of a glass composition is no greater than 2200°F (1204°C), the temperature is no greater than about 2200°F. Referring to Table 1 , the ternary Si0₂-AI₂0₃-CaO composition indicates a eutectic liquidus temperature of 2134°F (1168°C).

TABLE 1

This ternary Si0₂-AI₂0₃-CaO composition would be very attractive by itself. However this composition exhibits a sharp minimum in the phase diagram surrounded by much higher liquidus temperatures on either side of the composition, and it is a only a fraction of a percentage point removed from such higher liquidus temperature, and therefore implicitly much higher forming temperatures also. While the ΔT this specific composition might be satisfactory in a laboratory process, in a typical commercial process the sensitivity toward compositional changes is high and would not well tolerate inevitable temperature and compositional changes. It should be appreciated that derivatives of the ternary glass fiber compositions of the present invention, i.e. essentially ternary compositions can include small amounts of additives that will lower the liquidus temperature and broaden the liquidus temperature range so as to facilitate formation of fibers with a low liquidus temperature and a ΔT of at least 100°F. Such additives include, but are not limited to B₂O₃, Li₂0, ZnO, MnO and/or MnO₂. In one nonlimiting embodiment of the invention, the glass composition includes 0.05 to 2 wt% of at least one of these additives, and preferably no greater than 1 wt. In another nonlimiting embodiment, the glass composition includes 0.05 to 2 wt% each of two or more of these materials, and preferably no greater than 1 wt% each. It is believed that levels of these materials less than 0.05 wt% would be considered either tramp amounts or so low that they will not materially impact the glass melt properties. The present invention also contemplates the inclusion of other materials in the glass fiber compositions such as, but not limited to, 0 to 2 wt% each of Ti0₂, BaO, ZrO₂, NaO, K₂O and SrO, and preferably no greater than 1 wt% each of these materials. It should also be appreciated that the glass fiber composition can also include small amounts of refining aids or tramp materials that enter the glass composition as impurities in the glass batch materials, as discussed earlier. For example, the glass compositions of the present invention typically include 0.05 to 0.80 wt% Fe₂0₃ as a refining aid, and preferably up to 0.5 wt%.

Table 2 shows essentially ternary compositions of the present invention that further include the addition of minor constituents. In addition, selected examples in Table 2 include a forming temperature. The determination of T_F0RM was based on the glass samples being compared against physical standards supplied by the National Institute of Standards and Testing (NIST). In Tables 2 and 3, T_F0RM is reported based on using NIST 717A which is a borosilicate glass standard. Although not used herein, it is believed that NIST 714, which is a soda lime glass standard, provides a more accurate measure of the forming temperature. It is expected that the forming temperature (and thus ΔT) of the examples shown in Table 2 based on the NIST 714 standard reference will be 20°F to 25°F (11°C to 16°C) higher than the forming temperature as reported based on the NIST 717A reference standard. The liquidus temperature is not affected by the choice of reference standard. TABLE 2

Referring to Table 2, it can be seen, for example, that the addition of up to 2 wt% B₂O₃ generally reduces the liquidus temperatures. In addition, Examples 14-16 have ΔTs between 176°F and 210°F (98°C to 1 17°C) at an Si0₂/RO ratio of 2.66-2.67, and Examples 17-19 have ΔTs between 23°F and 50°F (13°C to 28°C) at an Si0₂/RO ratio of 2.43.

As discussed earlier, in the glass fiber forming industry, ΔT should be maintained in a range sufficient to prevent devitrification of the molten glass in the bushing area of a glass fiber forming operation and stagnant areas of the glass melting furnace. In the present invention, ΔT should be at least 65°F (36°C), preferably at least 90°F (50°C), and more preferably at least 1 00°F (56°C). If required, the amounts of SiO₂ and CaO can be modified to change the forming temperature and provide a desired ΔT. More specifically, reducing the silica content while simultaneously maintaining or increasing the calcia content (thus reducing Si0₂/RO ratio) will reduce the forming temperature and thus reduce ΔT. This type of modification would be of value if, for example, ΔT was much greater than 100°F, as in Ex. 14-16, and could be reduced without adversely affecting the glass melting and forming operation. Conversely, increasing the silica content and while simultaneously maintaining or reducing the calcia content (thus increasing the Si0₂/RO ratio) will raise the forming temperature and thus increase ΔT. This type of modification would be of value if, for example, ΔT was too low and had to be increased to at least 100°F, as in Ex. 17-19. Compositional adjustments of silica and/or calcia (and the Si0₂/RO ratio) in either direction are possible until the ΔT is obtained that is deemed to facilitate the pursuit of a safe industrial melt forming process. Based on the above, the ternary glass fiber compositions of the present invention have a base glass composition comprising 55 to 63 weight percent SiO₂, 22 to 26 weight percent CaO, 12 to 16 weight percent AI₂O₃, and preferably 55 to 59 weight percent Si0₂, 22 to 24 weight percent CaO, and 12 to 14 weight percent AI₂O₃. The glass composition also includes no greater than 1 wt% MgO, and preferably no greater than 0.6 wt% MgO. The glass composition further includes 0.05 to 2 weight percent of at least one of the following additives: B₂0₃, Li₂0, ZnO, MnO and/or Mn0₂, and in nonlimiting embodiment, the glass composition includes 0.05 to 2 wt% each of two or more of these additives. In another nonlimiting embodiment of the invention, the glass composition includes no greater than 1 wt% of at least one of these additives. In another nonlimiting embodiment of the invention, the glass compositions further include 0 to 2 wt% each of Ti0₂, BaO, ZrO₂,Na₂O, K₂O and SrO, and preferably no greater than 1 wt% each of these materials. In addition, because of the environmental concerns discussed earlier, although not limiting in the present invention, the glass compositions are preferably low fluorine compositions, and more preferably are fluorine-free.

In addition, based on the desired ΔT as discussed earlier, in one nonlimiting embodiment of the invention, the forming temperature of the glass compositions of the present invention should be no greater than 2300°F (1260°C), and preferably no greater than 2250°F (1232°C), and more preferably no greater than 2220°F (1216°C), based on the NIST 717A reference standard. In addition, in one nonlimiting embodiment of the invention, the liquidus temperature of the glass compositions should be no greater than 2160°F (1182°C), and preferably no greater than 2150°F (1177°C), and more preferably no greater than 2140°F (1171°C).

As discussed above, the Si0₂/RO ratio can be manipulated to achieve the goals of lowering the overall processing temperature, and in particular lowering the forming temperature, while providing a ΔT required to facilitate continuous fiber processing. Although not limiting in the present invention, the glass fiber compositions of the present invention have a SiO₂/RO ratio of no greater than 2.65, preferably no greater than 2.60, and more preferably no greater than 2.55.

In summary, compositions with a ΔT having been properly adjusted to facilitate continuous processing of glass fibers are of great potential commercial utility as reinforcement for composites. It is believed that these compositions will provide good mechanical properties and a low dielectric constant, which is particularly advantageous for applications such as, but not limited to, printed wiring boards

The invention has been described with reference to specific embodiments, but it should be understood that variations and modifications that are known to those of skill in the art may be resorted to within the scope of the invention as defined by the claims.

Claims

I CLAIM:

1. A glass fiber composition comprising: Si0₂ 55 to 63 percent by weight; CaO 22 to 26 percent by weight; Al₂0₃ 12 to 16 percent by weight; MgO 0 to 1 percent by weight; Fe₂0₃ 0.05 to 0.80 percent by weight; Na₂0 0 to 2 percent by weight;

K₂0 0 to 2 percent by weight;

Ti0₂ 0 to 2 percent by weight;

BaO 0 to 2 percent by weight;

Zr0₂ 0 to 2 percent by weight; and

SrO 0 to 2 percent by weight, and at least one material selected from the group consisting of:

B₂0₃ 0.05 to 2 percent by weight;

Li₂O 0.05 to 2 percent by weight;

ZnO 0.05 to 2 percent by weight;

MnO 0.05 to 2 percent by weight; and

MnO₂ 0.05 to 2 percent by weight.

2. The glass fiber composition according to claim 1 , wherein the SiO₂ content is 55 to 59 percent by weight, the CaO content is 22 to 24 percent by weight, and the AI₂O₃ content is 12 to 14 percent by weight.

3. The glass fiber composition according to claim 2, wherein the glass composition has a forming temperature of no greater than 2300°F based on an NIST 717A reference standard and a liquidus temperature of no greater than 2160°F.

4. The glass fiber composition according to claim 3, wherein the glass composition has a ratio of Si0₂ to RO of no greater than 2.65, and a ΔT of at least 65°F.

5. The glass fiber composition according to claim 1 , wherein the Na₂0 content is no greater than 1 percent by weight, the K₂O content is no greater than 1 percent by weight, the Ti0₂ content is no greater than 1 percent by weight, the BaO content is no greater than 1 percent by weight, the Zr0₂content is no greater than 1 percent by weight, and the SrO content is no greater than 1 percent by weight.

6. The glass fiber composition according to claim 1 , wherein the B₂0₃content is no greater than 1 percent by weight, the Li₂O content is no greater than 1 percent by weight, the ZnO content is no greater than 1 percent by weight, the MnO content is no greater than 1 percent by weight, and the MnO₂content is no greater than 1 percent by weight.

7. The glass fiber composition according to claim 1 , wherein the MgO content is no greater than 0.60 percent by weight.

8. The glass fiber composition according to claim 1 , wherein the glass composition is essentially free of boron.

9. The glass fiber composition according to claim 1 , wherein the glass composition is essentially free of fluorine.

10. The glass fiber composition according to claim 1 , wherein the glass composition has a ratio of SiO₂ to RO of no greater than 2.65.

11. The glass fiber composition according to claim 10, wherein the glass composition has a ratio of Si0₂ to RO of no greater than 2.60.

12. The glass fiber composition according to claim 11 , wherein the glass composition has a ratio of Si0₂ to RO of no greater than 2.55.

13. The glass fiber composition according to claim 1 , wherein the glass composition has a forming temperature of no greater than 2300°F based on an NIST 717A reference standard.

14. The glass fiber composition according to claim 13, wherein the glass composition has a forming temperature of no greater than 2250°F based on an NIST 717A reference standard.

15. The glass fiber composition according to claim 14, wherein the glass composition has a forming temperature of no greater than 2220°F based on an NIST 717A reference standard.

16. The glass fiber composition according to claim 1 , wherein the glass composition has a liquidus temperature of no greater than 2160°F.

17. The glass fiber composition according to claim 16, wherein the glass composition has a liquidus temperature of no greater than 2150°F.

18. The glass fiber composition according to claim 17, wherein the glass composition has a liquidus temperature of no greater than 2140°F.

19. The glass fiber composition according to claim 1 , wherein the composition has a ΔT of at least 65°F.

20. The glass fiber composition according to claim 19, wherein the composition has a ΔT of at least 90°F.