Note: Descriptions are shown in the official language in which they were submitted.
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GLASS FIBER COMPOSITION
s 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
io 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
is 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 AI203 Ca0-Mg0 phase diagram. As used herein, the terms
"eutectic temperature", "liquidus temperature" and "T~,o" mean the highest
2o temperature at which liquid phase (melt) can be in equilibrium with solid
phase (crystals); the terms "forming temperature" and "TFORM" mean the
temperature at which the glass composition has a viscosity of 1000 poise,
and the term "0T" means the difference between the liquidus temperature and
the forming temperature. Typically, in a commercial glass fiber operation, OT
2s 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
3o was too close to its corresponding forming temperature, i.e. 0T 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 Si02, AI203, CaO, Mg0
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and B203. These particular compositions, which required 9-11 wt% B203 and
about 4.5 wt% MgO, exhibited a greater DT. In 1954 and later, E-glass was
once more redefined according to U.S. Patent 2,571,074, by reducing the
B2O3 content from about 10.0% to eventually about 5.5% and by reducing the
s Mg0 content from about 4.5% to about 0.45%. In effect, current boron and
fluorine containing E-glass versions with less than about 1 % Mg0 belong to
the quaternary, Si02, AI203, CaO, B203 phase diagram, since such small
amounts of Mg0 are not deliberately added but brought into the melt as
impurities.
to 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
Is century. The effort to achieve compliance with future needs was met by a
return to the original boron free quaternary Si02 AI203 Ca0-Mg0 system but
modifying it to achieve the required DT 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 OT
2o 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 OT, can be reduced in the
quaternary Si02 AI203-Ca0-Mg0 by optimizing the amounts of each of these
2s 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, Mn0 and/or
Mn02 (up to 2 wt%), facilitates a total reduction in liquidus temperature by
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over 50°F. In should be noted that all these compositions are
essentially
modifications of the quaternary Si02 AI203 Ca0-Mg0 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-AI203
s Ca0-Mg0-B203 system and quaternary Si02 AI203 Ca0-B203 system E-glass
compositions as discussed above that include silica as the major constituent,
greater than 2 wt% boron, in the form of B203 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
l0 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
is 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-Ca0-B203 system or the essentially
2o quinary SiOz AI203 Ca0-Mg0-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 Si02 AI203 Ca0-
Mg0 system. As used herein, the terms "essentially quaternary" and
"essentially quinary" mean that the four or five stated constituents are the
2s 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 Si02 AI203-Ca0 phase
diagram, but they require forming temperatures which are 400-500°F
higher
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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
s environment.
Limited attention has been paid to the possibility of developing glass
fibers from ternary or essentially ternary Si02 AI203-Ca0 compositions with
only moderately higher forming and liquidus temperatures than those
observed with conventional borosilicate E-glass fibers. It is believed that
such
Io fiber compositions would exhibit a low dielectric constant K. As a result,
it
would be advantageous to provide a ternary or essentially ternary Si02 AI203-
Ca0 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
is energy requirements for the glass fiber.
Summar)i 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
2o percent by weight AI203; 0 to 1 percent by weight MgO; 0.05 to 0.80 percent
by weight Fe203; 0 to 2 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; and0 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
2s to 2 percent by weight Li20; 0.05 to 2 percent by weight ZnO; 0.05 to 2
percent by weight MnO; and0.05 to 2 percent by weight Mn02. 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
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standard, a liquidus temperature of no greater than 2160°F, a ratio of
Si02 to
RO of no greater than 2.65, and a 0T of at least 65°F.
Detailed Description of the Invention
s The ternary or essentially ternary Si02 AIz03 Ca0 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-Ca0
io 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 DT 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
is 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-Ca0-Mg0 E-glass compositions discussed
earlier.
Preferred ternary Si02 AI203-Ca0 compositions of this invention are
2o 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 OT of at least 100°F. More
specifically, E-
glass is the currently preferred high-volume low-cost reinforcement for use in
2s the printed wiring board market. As discussed earlier, this composition is
based on an inexpensive essentially quaternary Si02-AI203 Ca0-B203 system
or essentially quinary Si02 AI203 Ca0-Mg0-B203 system, as discussed
above, and has a dielectric constant of about 6.11 at 10'°Hz. D glass
(an
essentially Ca0 and AI203 free glass fiber and, e.g. containing about 74 wt%
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Si02 and about 22 wt% B203) has a dielectric constant of about 3.56 at
10'° Hz, and S-glass (a ternary Si02 AI203 Mg0 glass fiber, free of
trace
oxides) has a dielectric constant of about 4.53 at 10'° Hz (see,
Wallenberger
at page 150). Because of their low dielectric constant, both D-glass and S-
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 Si02-AI203-Ca0 glass fiber is expected to
offer
io 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
1s the fibers. For example, typically sand is used for Si02, clay for A1203,
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
2o aids, such as S03, 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
Zs 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
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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
(1400°C).
s 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
to 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
85-107 and pages 1 15-135, which are hereby incorporated by reference.
Tables 1-3 show laboratory examples of ternary and essentially ternary
Is Si02 AI203 Ca0 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
2o 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
2s 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.
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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
s 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 Bz03 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
to 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
is 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
ao magnesia content, expressed as Ca0 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
2s 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.
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Referring to Table 1, the ternary S102-AI203-Ca0 composition indicates
a eutectic liquidus temperature of 2134°F (1168°C).
TABLE 1
Ex. Ex. Ex. Ex Ex. Ex. Ex. Ex. Ex. Ex.
1 2 3 4 5 6 7 8 9 10
Si02 (wt%)62.20 62.2062.20 62.1062.1062.10 62.0062.00 62.0061.90
AIz03 14.40 14.5014.60 14.6014.5014.60 14.5014.60 14.7014.70
(wt%)
Ca0 (wt%)23.40 23.3023.20 23.3023.4023.30 23.5023.30 23.3023.40
T~~Q(F) 2194 2187 2187 2134 2196 2206 2185 2196 2169 2167
SiOz/RO 2.66 2.67 2.68 2.67 2.65 2.67 2.64 2.66 2.66 2.65
This ternary Si02-AI203-Ca0 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
to such higher liquidus temperature, and therefore implicitly much higher
forming
temperatures also. While the DT 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.
i5 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 0T of at least 100°F. Such
2o additives include, but are not limited to B203, Li20, ZnO, Mn0 and/or Mn02.
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
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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
s compositions such as, but not limited tog 0 to 2 wt% each of Ti02, BaO,
Zr02,
NaO, K20 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
io 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,
is selected examples in Table 2 include a forming temperature. The
determination of TFORnn 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, TFORnn is reported based on using NIST
717A which is a borosilicate glass standard. Although not used herein, it is
2o 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 OT) 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
2s standard. The liquidus temperature is not affected by the choice of
reference
standard.
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TABLE 2
Ex. Ex. Ex. Ex. Ex. Ex. Ex. Ex. Ex.
11 12 13 14 15 16 17 18 19
Si02 (wt%) 61.1060.50 60.4060.4060.20 59.9055.79 55.7955.79
AI203 (wt%)14.4014.20 14.2014.2014.10 14.0014.10 14.1014.10
Ca0 (wt%) 22.9022.70 22.7022.6022.60 22.5022.53 22.5322.53
Mg0 (wt%) 0.45 0.45 0.45
Ti02 (wt%) 0.50 0.50 0.50 0.50 0.50 0.50 0.60 0.60 0.60
Na20 (wt%) 0.90 0.90 0.90 0.90 0.90 0.90 0.80 0.80
F2 (wt%) 0.10 0.20
KZO (wt%) 0.07 0.07
BZ03 (wt%) 1.00 1.00 1.00 1.50 2.00 1.00 1.00
Li20 (wt%) 0.87
Fe203 (wt%)0.20 0.20 0.20 0.20 0.20 0.20 0.20 0.20 0.20
TFORM (F) 2332 2331 2343 2208 2208 2158
T~,Q (F) 2152 2125 2125 2156 2142 2133 2185 2158 2134
~T (F) 176 189 210 23 50 24
Si02/RO 2.67 2.67 2.66 2.67 2.66 2.66 2.43 2.43 2.43
Referring to Table 2, it can be seen, for example, that the addition of
up to 2 wt% B203 generally reduces the liquidus temperatures. In addition,
s Examples 14-16 have DTs between 176°F and 210°F (98°C
to 117°C) at an
Si02/RO ratio of 2.66-2.67, and Examples 17-19 have OTs 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, 0T 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, OT should be
at least 65°F (36°C), preferably at least 90°F
(50°C), and more preferably
at least 100°F (56°C). If required, the amounts of Si02 and Ca0
can be
modified to change the forming temperature and provide a desired 0T.
Is 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 OT. This type of modification would be
of value if, for example, OT was much greater than 100°F, as in Ex. 14-
16,
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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 OT. This
s type of modification would be of value if, for example, 0T 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/R~ ratio) in either direction are
possible
until the 0T is obtained that is deemed to facilitate the pursuit of a safe
industrial melt forming process.
to Based on the above, the ternary glass fiber compositions of the
present invention have a base glass composition comprising 55 to 63 weight
percent Si02, 22 to 26 weight percent CaO, 12 to 16 weight percent AI203,
and preferably 55 to 59 weight percent Si02, 22 to 24 weight percent CaO,
and 12 to 14 weight percent AI203. The glass composition also includes no
is 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, Mn0 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
2o 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,Na20, K20 and SrO, and preferably no greater than 1 wt% each of these
materials.
2s 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 4T as discussed earlier, in one
nonlimiting embodiment of the invention, the forming temperature of the glass
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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.
s 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
Io the goals of lowering the overall processing temperature, and in particular
lowering the forming temperature, while providing a ~T required to facilitate
continuous fiber processing. Although not limiting in the present invention,
the glass fiber compositions of the present invention have a Si02/RO ratio of
no greater than 2.65, preferably no greater than 2.60, and more preferably no
is greater than 2.55.
In summary, compositions with a OT 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
2o 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
2s within the scope of the invention as defined by the claims.
