# Patent

## Title
Composition for high performance glass fibers and fibers formed therewith

## Abstract

A composition for the manufacture of high strength glass fibers suitable for manufacture in both precious metal lined furnaces and refractory lined glass melter is disclosed. The glass composition of the present invention includes 62-68 weight % SiO2, 22-26 weight % Al2O3, 8-15 weight % MgO and 0.1 to 3.0 weight % Li2O. One suitable composition of the present invention includes 64-66.5 weight percent SiO2, 23-24.5 weight percent Al2O3, 9-11 weight percent MgO and 0.3-0.35 weight percent Li2O. Another suitable composition includes 66.5 weight percent SiO2, 23.4 weight percent Al2O3, 9.8 weight percent MgO and 0.3 weight percent Li2O. Yet another suitable composition is about 66 weight percent SiO2, about 23 weight percent Al2O3, about 10.5 weight percent MgO and about 0.3 weight percent Li2O. Fibers formed by the present invention are also disclosed. The fibers have a fiberizing temperature of less than 2650° F., a ΔT of at least 25° F. Further, the glass fibers of the present invention typically have a strength in excess of 700 KPSI, in one embodiment, a strength in excess of about 730 KPSI, and, in yet another embodiment, a strength in excess of about 750 KPSI. The glass fibers will typically have a modulus greater than 12.8 MPSI, in one embodiment, greater than about 13 MPSI, and, in yet another embodiment, greater than about 13.2 MPSI.

## Background
TECHNICAL FIELD AND INDUSTRIAL APPLICABILITY OF THE INVENTION
The present invention is generally directed to a composition for use in manufacturing continuous high strength glass fibers and fibers formed from the composition.
BACKGROUND OF THE INVENTION
A common glass composition for making continuous high-strength glass fiber strands is “S-Glass.” The term S-Glass defines a family of glasses composed primarily of the oxides of magnesium, aluminum, and silicon with a chemical composition that produces glass fibers having a higher mechanical strength than E-Glass fibers. The chemical composition of the S-glass family produces high strength glass fiber and enables these glasses to be used in high strength applications such as ballistic armor. ASTM International defines S-Glass as family of glasses composed primarily of the oxides of magnesium, aluminum, and silicon with a certified chemical composition which conforms to an applicable material specification and which produces high mechanical strength (D578-05). The Deutsches Institut für Normung (DIN) defines S-Glass as an aluminosilicate glass without added CaO and having a partial mass of MgO where MgO is about 10% by weight (An alumino-silicate glass is defined as a glass which consists largely of aluminum trioxide and silicon dioxide and other oxides) (DIN 1259-1).
U.S. Pat. No. 3,402,055, describes a composition for forming a high strength glass within the S-Glass family. A commercially available high strength S-Glass composition is S-2 Glass. As described in publication WO/2004/094794, assigned on its face to 3M Innovative Properties Company, S-2 glass fibers typically have a composition of about 65% Of SiO2, 25% of Al2O3, and 10% of MgO. S-2 Glass is manufactured by Advanced Glass Yarns, of Aiken S.C., USA. S-2 Glass has high compressive and tensile strength and good high temperature properties. S-2 Glass is used in helicopter blades, armor and windings for high pressure tanks, such as scuba tanks.
R-Glass is another family of high strength, high modulus glasses that is typically formed into fibers for use in aerospace composite applications. The R-Glass family is primarily composed of silicon oxide, aluminum oxide, magnesium oxide, and calcium oxide with a chemical composition that produces glass fibers with mechanical strength which is generally lower than S-Glass fibers. R-Glass generally contains less silica and greater calcium oxide (CaO) than S-Glass which requires higher melting and processing temperatures during fiber forming. As also described in publication WO/2004/094794, R-glass fibers typically have a composition of 60% of SiO2, 25% of Al2O3, 9% of CaO and 6% of MgO.
Tables IA-IE set forth the compositions for a number of conventional high strength glass compositions.











TABLE I-A









NITTOBO



Chinese
RUSSIAN
NITTOBO
“T” Glass



High
CONTINUOUS
“T”
Fabric



Strength
ROVING MAGNESIUM
Glass
(Yarn)


Constituent
glass
ALUMINOSILICATE
Fabric “B”
“C”



















SiO2
55.08
55.81
64.58
64.64


CaO
0.33
0.38
0.44
0.40


Al2O3
25.22
23.78
24.44
24.57


B2O3
1.85

0.03
0.03


MgO
15.96
15.08
9.95
9.92


Na2O
0.12
0.063
0.08
0.09


Fluorine
0.03

0.034
0.037


TiO2
0.023
2.33
0.019
0.018


Fe2O3
1.1
0.388
0.187
0.180


K2O
0.039
0.56
0.007
0.010


ZrO2
0.007
0.15


Cr2O3

0.011
0.003
0.003


Li2O

1.63


CeO2





















TABLE I-B






Nitto
Nitto

Vetrotex Saint




Boseki
Boseki
Nitto Boseki TE
Gobain SR Glass
Polotsk



A&P
NT6030
Glass RST-
Stratifils SR CG
STEKLOVOLOKNO


Constituent
Yarn
Yarn
220PA-535CS
250 P109
High Strength Glass




















SiO2
65.51
64.60
64.20
63.90
58.64


CaO
0.44
0.58
0.63
0.26
0.61


Al2O3
24.06
24.60
25.10
24.40
25.41


B2O3




0.04


MgO
9.73
9.90
9.90
10.00
14.18


Na2O
0.04
0.06
0.020
0.039
0.05


Fluorine
0.07



0.02


TiO2
0.016
0.000
0.000
0.210
0.624


Fe2O3
0.067
0.079
0.083
0.520
0.253


K2O
0.020
0.020
0.020
0.540
0.35


ZrO2
0.079


Cr2O3
0.0010


0.001
0.023


Li2O


CeO2




















TABLE I-C







Chinese
Advanced





High
Glass



Chinese High
Strength
Yarns



Strength Yarn
Glass
Zentron S-2
SOLAIS Glass


Constituent
(8 micron)
Roving
Glass Roving
Sample



















SiO2
55.22
55.49
64.74
64.81


CaO
0.73
0.29
0.14
0.55


Al2O3
24.42
24.88
24.70
24.51


B2O3
3.46
3.52

0.02


MgO
12.46
12.28
10.24
9.35


Na2O
0.104
0.06
0.17
0.16


Fluorine
0.07


0.02


TiO2
0.32
0.36
0.015
0.04


Fe2O3
0.980
0.930
0.045
0.238


K2O
0.240
0.150
0.005
0.03


ZrO2


Cr2O3
0.0050


0.007


Li2O
0.59
0.63


CeO2
1.23
1.25





















TABLE I-D






Advanced



IVG Vertex



Glass Yarns
Culimeta
IVG Vertex B96
IVG Vertex
Outside #1 Glass


Constituent
S Glass
Roving
675 Yarn
Glass Roving
Roving




















SiO2
64.61
59.37
58.34
58.58
58.12


CaO
0.17
0.27
0.31
0.30
0.31


Al2O3
24.84
25.49
23.81
24.26
24.09


B2O3
0.04
0.05


MgO
10.11
13.47
14.99
15.02
15.36


Na2O
0.118
0.024
0.05
0.02
0.03


Fluorine
0.03

0.04
0.04
0.04


TiO2
0.011
0.530
1.380
0.67
0.91


Fe2O3
0.042
0.374
0.333
0.336
0.303


K2O

0.48
0.42
0.28
0.29


ZrO2

0.152
0.129
0.165
0.157


Cr2O3
0.0050
0.0120
0.0100
0.0120
0.0120


Li2O


CeO2




















TABLE I-E








IVG Vertex
RH CG250 P109




Outside #2
Glass Fiber



Constituent
Glass Roving
Strand




















SiO2
58.69
58.54



CaO
0.29
9.35



Al2O3
24.3
25.39



B2O3



MgO
15.06
6.15



Na2O
0.03
0.10



Fluorine
0.04
0.16



TiO2
0.64
0.008



Fe2O3
0.331
0.069



K2O
0.36
0.14



ZrO2
0.187
0.006



Cr2O3
0.0130



Li2O



CeO2










SUMMARY OF THE INVENTION
The present invention is a glass composition for the formation of continuous glass fibers suitable for use in high strength applications. Once formed into fibers, the glass composition provides the strength characteristics of S-Glass. One composition of the present invention includes 62-68 weight percent SiO2, 22-26 weight percent Al2O3, 8-15 weight percent MgO and 0.1-2 weight percent Li2O. In certain embodiments, the glass composition is composed of 64-66.5 weight percent SiO2, 23-24.5 weight percent Al2O3, 9-11 weight percent MgO and 0.3-0.35 weight percent Li2O. In another embodiment, the glass composition is composed of 66.5 weight percent SiO2, 23.4 weight percent Al2O3, 9.8 weight percent MgO and 0.3 weight percent Li2O. In another embodiment the fiber is composed of about 66 weight percent SiO2, about 23 weight percent Al2O3, about 10.5 weight percent MgO and about 0.3 weight percent Li2O. In certain embodiments, the composition does not contain more than about 2.0 weight % of oxides or compounds selected from the group consisting of CaO, P2O5, ZnO, ZrO2, SrO, BaO, SO3, F2, B2O3, TiO2 and Fe2O3. In certain embodiments the fiber has a modulus greater than 12.8 MPsi and a pristine tensile strength of 700 KPsi. In another embodiment, the fiber has a modulus greater than about 13 MPsi and a pristine tensile strength of about 750 KPsi.
The desired properties of the high performance composite fibers manufactured by the present invention include a composition having a fiberizing temperature of less than about 2650° F., or in one embodiment less than about 2625° F., in another embodiment less than about 2600° F. and in yet another embodiment less than about 2575° F. and a liquidus temperature that is, in one embodiment, below the fiberizing temperature by at least 25° F., in another embodiment, by at least about 50° F., and, in yet another embodiment, by at least about 75° F.


DETAILED DESCRIPTION AND PREFERRED EMBODIMENTS OF THE INVENTION
The fiberizing properties of the glass batch composition of the present invention include the fiberizing temperature, the liquidus, and delta-T (ΔT). The fiberizing temperature is defined as the temperature that corresponds to a viscosity of 1000 Poise. As discussed in more detail below, a lowered fiberizing temperature reduces the production cost of the fibers, allows for a longer bushing life, increases throughput and reduces energy consumption. For example, at a lower fiberizing temperature, a bushing operates at a cooler temperature and does not “sag” as quickly. Sag is a phenomenon that occurs in bushings that are held at an elevated temperature for extended periods of time. By lowering the fiberizing temperature, the sag rate of the bushing may be reduced and the bushing life can be increased. In addition, a lower fiberizing temperature allows for a higher throughput since more glass can be melted in a given period at a given energy input. As a result, production cost is reduced.
The liquidus of a glass is defined as the highest temperature at which equilibrium exists between liquid glass and its primary crystalline phase. At all temperatures above the liquidus, the glass is free from crystals in its primary phase. At temperatures below the liquidus, crystals may form. Crystals in the melt will cause blockages in the bushing and weakness in the fibers.
Another fiberizing property is delta-T (ΔT), which is defined as the difference between the fiberizing temperature and the liquidus. A larger ΔT offers a greater degree of flexibility during the formation of the glass fibers and helps to inhibit devitrification of the glass (that is, the formation of crystals within the melt) during melting and fiberizing. Increasing the ΔT also reduces the production cost of the glass fibers by allowing for a greater bushing life and by providing a wider process window for forming fibers.
The glasses of the present invention are typically continuously melted in precious metal lined containers using a platinum electric heater. The glasses may be suitable for melting in traditional commercially available refractory-lined glass melters that are widely used in the manufacture of glass reinforcement fibers. Starting batch components typically include SiO2 (ground silica sand), and Al2O3 (calcined alumina) or pyrophyllite, as well as chain modifiers from source materials such as talc, magnesite or dolomite. The carbon included in materials such as magnesite is off gassed as oxides of carbon such as CO2.
A fiber formed in accordance with the present invention will typically include 62-68 weight percent SiO2, 22-26 weight percent Al2O3, 8-15 weight percent MgO and 0.1-2 weight percent Li2O. In certain embodiments, the glass composition is composed of 64-66.5 weight percent SiO2, 23-24.5 weight percent Al2O3, 9-11 weight percent MgO and 0.3-0.35 weight percent Li2O. In another embodiment, the glass composition is composed of 66.5 weight percent SiO2, 23.4 weight percent Al2O3, 9.8 weight percent MgO and 0.3 weight percent Li2O. In another embodiment the fiber is composed of about 66 weight percent SiO2, about 23 weight percent Al2O3, about 10.5 weight percent MgO and about 0.3 weight percent Li2O. In certain embodiments, the composition does not contain more than about 2.0 weight % of oxides or compounds selected from the group consisting of CaO, P2O5, ZnO, ZrO2, SrO, BaO, SO3, F2, B2O3, TiO2 and Fe2O3. A fiber formed in accordance with the present invention will typically include small amounts of CaO, P2O5, ZnO, ZrO2, SrO, Ba, SO3, F2, B2O3, TiO2 and Fe2O3, typically in a total amount of less than 3 weight percent, and in another embodiment less than about 2 weight percent. In addition, a fiber formed in accordance with the method and composition of the present invention will typically have a fiberizing temperature of less than 2650° F., in another embodiment less than about 2625° F., in yet another embodiment less than about 2600° F. and, in yet another embodiment, less than about 2575° F. and a liquidus temperature that is typically below the fiberizing temperature by at least 25° F., in one embodiment, by at least about 50° F., and, in yet another embodiment, by at least about 75° F. Further, the glass of the present invention typically will have a pristine fiber tensile strength in excess of 700 KPSI, in one embodiment, a strength in excess of about 730 KPSI, and, in yet another embodiment, a strength in excess of about 750 KPSI. Further, the glass fibers will typically have a modulus greater than 12.8 MPSI, in one embodiment, greater than about 13.0 MPSI, and in yet another embodiment, greater than about 13.2 MPSI.
The melted glass is delivered to a bushing assembly from a platinum lined melting chamber which is heated electrically. The bushing includes a tip plate with a plurality of nozzles; each nozzle discharges a stream of molten glass, which is mechanically drawn to form continuous filaments. Typically, the filaments are coated with a protective sizing, gathered into a single continuous strand and wound onto a rotating collet of a winder device to form a package. The filaments may also be processed into other forms including, without limitation, wet used chopped strand fibers, dry use chopped strand fibers, continuous filament mats, chopped strand mats, wet formed mats or air laid mats.
Having generally described this invention, a further understanding can be obtained by reference to certain specific examples illustrated below which are provided for purposes of illustration only and are not intended to be all inclusive or limiting unless otherwise specified.
EXAMPLES
The glasses in the examples listed in Tables IIA-IID were melted in platinum crucibles or in a continuous platintim-lined melter for determining the mechanical and physical properties of the glass and fibers produced there from. The units of measurement for the physical properties are: Viscosity (° F.), Liquidus temperature (° F.) and ΔT (° F.). In some examples the glasses were fiberized and Strength (KPsi), Density (g/cc), Modulus (MPsi) were measured.
The fiberizing temperature was measured using a rotating spindle viscometer. The fiberizing viscosity is defined as 1000 Poise. The liquidus was measured by placing a platinum container filled with glass in a thermal gradient furnace for 16 hours. The greatest temperature at which crystals were present was considered the liquidus temperature. The modulus was measured using the sonic technique on a single fiber of glass. The tensile strength was measured on a pristine single fiber.













TABLE IIA





Glass
Ex. 1
Ex. 3
Ex. 4
Ex. 5
Ex. 6
Ex. 7





















SiO2
62
62
66.05
63.05
66.05
66.05


Al2O3
22
22
24.05
23.55
23.05
23.05


MgO
14
15
9.55
13.05
9.55
10.55


Li2O
2
1
0.35
0.35
1.35
0.35


Measured
2389
2433
2626
2499
2506
2603


Viscosity (° F.)


1st Measured
2410
2466
2609
2551
2571
2577


Liquidus (° F.)


2nd Measured
2426
2491
2623
2545
2545
2574


Liquidus (° F.)


ΔT (° F.)
−29
−45.5
10
−49
−52
27.5


Measured
2.5333
2.5418
2.4773
2.5251
2.4745
2.4845


Density (g/cc)






















TABLE II-B





Glass
Ex. 8
Ex. 9
Ex. 10
Ex. 11
Ex. 12
Ex. 13





















SiO2
63.05
62
63.55
64.1
64
63.05


Al2O3
23.05
28
23.05
24.1
26
23.05


MgO
13.05
8
13.05
11.1
9.55
12.55


Li2O
0.85
2
0.35
0.7
0.35
1.35


Measured
2486
2513
2510
2549
2619
2479


Viscosity


(° F.)


1st Measured
2539
2646
2581
2594
2696
2502


Liquidus (° F.)


2nd Measured
2566
2636
2566
2564
2664
2535


Liquidus (° F.)


ΔT (° F.)
−66.5
−128
−63.5
−30
−61
−39.5


Measured
2.5239
2.4910
2.5205
2.5013
2.5004
2.5160


Density (g/cc)




















TABLE II-C





Glass
Ex. 14
Ex. 15
Ex. 16
Ex. 17



















SiO2
63.05
66.5
66.5
63.05


Al2O3
26.05
23.4
23.4
26.05


MgO
10.55
9.8
9.8
9.55


Li2O
0.35
0.3
0.3
1.35


Measured
2564
2651
2659
2550


Viscosity


(° F.)


1st Measured
2616
2587
2540
2521


Liquidus (° F.)


2nd Measured
2627
2600
2562
2550


Liquidus (° F.)


ΔT (° F.)
−57.5
57.5
108
14.5


Measured
2.5130


2.4975


Density (g/cc)









In Table II-C (above) Ex. 15 is the same composition as Ex. 16, however Ex. 15 has been formed with reagent grade raw materials.
The fibers of Example 7 have a Measured Modulus of 13.04 MPsi and a Measured Strength of 739 KPsi. The fibers of Example 12 have a Measured Modulus of 13.21 MPsi and a Measured Strength of 751 KPsi. The fibers of the present invention have superior modulus and strength characteristics. The fibers of Example 15 have a Measured Modulus of 13.04 MPsi and a Measured Strength of 753 KPsi
As is understood in the art, the above exemplary inventive compositions do not always total 100% of the listed components due to statistical conventions (such as, rounding and averaging) and the fact that some compositions may include impurities that are not listed. Of course, the actual amounts of all components, including any impurities, in a composition always total 100%. Furthermore, it should be understood that where small quantities of components are specified in the compositions, for example, quantities on the order of about 0.05 weight percent or less, those components may be present in the form of trace impurities present in the raw materials, rather than intentionally added.
Additionally, components may be added to the batch composition, for example, to facilitate processing, that are later eliminated, thereby forming a glass composition that is essentially free of such components. Thus, for instance, minute quantities of components such as fluorine and sulfate may be present as trace impurities in the raw materials providing the silica, calcia, alumina, and magnesia components in commercial practice of the invention or they may be processing aids that are essentially removed during manufacture.
As apparent from the above examples, glass fiber compositions of the invention have advantageous properties, such as low fiberizing temperatures and wide differences between the liquidus temperatures and the fiberizing temperatures (high ΔT values). Other advantages and obvious modifications of the invention will be apparent to the artisan from the above description and further through practice of the invention). The high-performance glass of the present invention melts and refines at relatively low temperatures, has a workable viscosity over a wide range of relatively low temperatures, and a low liquidus temperature range.
The invention of this application has been described above both generically and with regard to specific embodiments. Although the invention has been set forth in what is believed to be the preferred embodiments, a wide variety of alternatives known to those of skill in the art can be selected within the generic disclosure. Other advantages and obvious modifications of the invention will be apparent to the artisan from the above description and further through practice of the invention. The invention is not otherwise limited, except for the recitation of the claims set forth below.

## Claims

1. A high strength glass fiber comprising:
62-68 weight percent SiO2;
22-26 weight percent Al2O3;
8-11.1 weight percent MgO;
0.1-3.0 weight percent Li2O; and
less than 2 weight percent CaO, wherein said fiber has a pristine fiber tensile strength greater than 700 KPSI and a fiberizing temperature less than about 2650° F.

2. The high strength glass fiber of claim 1, further comprising:
less than about 3 weight percent total of one or more compounds selected from the group consisting of P2O5, ZnO, ZrO2, SrO, BaO, S03 F2, B2O3, TiO2 and Fe2O3.

3. The high strength glass fiber of claim 1, wherein said SiO2 is present in said glass in amount between 64 and 67 weight percent.

4. The high strength glass fiber of claim 1, wherein said fiber has a modulus greater than about 12.8 MPSI.

5. The high strength glass fiber of claim 1, wherein said fiber has a liquidus temperature that is at least 25° F. less than said fiberizing temperature.

6. The high strength glass fiber of claim 1, wherein:
said SiO2 is present in said fiber in an amount from about 64 to about 66.5 weight percent;
said Al2O3 is present in said fiber in an amount from about 23 to about 24.5 weight percent;
said MgO is present in said fiber in an amount from about 9 to about 11 weight percent; and
said Li2O is present in said fiber in an amount from about 0.1 to about 2.0 weight percent.

7. The high strength glass fiber of claim 1, wherein said fiber has a delta T of at least 25° F.

8. The high strength glass fiber of claim 1, wherein said Li2O is present in said fiber in an amount from 1.75 to 3.0 weight percent.

9. A composition for forming a glass fiber comprising:
SiO2 in an amount from about 62 to about 68 weight percent;
Al2O3 in an amount from about 22 to about 26 weight percent;
MgO in an amount from about 8 to about 11.1 weight percent;
Li2O in an amount from about 0.1 to about 3 weight percent; and
less than 2 weight percent CaO, wherein said fiber has a pristine fiber tensile strength greater than 700 KPSI.

10. The composition of claim 9, further comprising less than about 3 weight percent total of one or more compounds selected from the group consisting of P2O5, ZnO, ZrO2, SrO, BaO, SO3, F2, B2O3, TiO2 and Fe2O3.

11. The composition of claim 9, wherein:
said SiO2 is present in said fiber in an amount from about 64 to about 66.5 weight percent;
said Al2O3 is present in said fiber in an amount from about 23 to about 24.5 weight percent;
said MgO is present in said fiber in an amount from about 9 to about 11 weight percent; and
said Li2O is present in said fiber in an amount from about 0.1 to about 2.0 weight percent.

12. The composition of claim 9, wherein said Li2O is present in said fiber in an amount from 1.75 to 3.0 weight percent.