Note: Descriptions are shown in the official language in which they were submitted.
CA 02575900 2007-02-09
BIOSOLUBLE POT AND MARBLE-DERIVED FIBERGLASS
This application is a division of copending, commonly owned, Canadian Patent
Application No. 2,255,626 of March 20, 1998.
TECHNICAL FIELD
The present invention pertains to fiberglass products prepared from glass
compositions
suitable for fiberization by the pot and marble process. The glass fibers
exhibit enhanced
biosolubility while maintaining other desirable properties.
DESCRIPTION OF THE RELATED ART
Fiberglass has a myriad of uses, including the reinforcement of polymer matrix
composites; preparation of thermoformable intermediate products for use as
headliners and
hoodliners in vehicles; air and water filtration media; and sound and thermal
insulation
products. The preparation and/or subsequent processing of such materials often
involves
handling steps which result in cut or broken fibers which may be inhaled. As
it is impractical
or impossible to remove such fibers from the body, it has become important to
create glass
compositions which exhibit high degrees of biosolubility, i.e. which are
rapidly solubilized in
biological fluids.
If high biosolubility were the only factor which need be considered, a
solution to the
biosolubility problem would be rapidly attained. However, in addition to being
biosoluble, glass
fibers must also possess a number of other physical and chemical
characteristics. For example,
in many applications such as in battery separators, high chemical (e.g. acid)
resistance is
required. As can be readily imagined, high chemical resistance and high
biosolubility are
largely conflicting characteristics.
Glass fibers must also be strong and moisture-resistant. If moisture weakens
glass
fibers appreciably, their applicability to many uses suffers. Weakened glass
fibers not only
possess less than desired tensile strength and modulus, but also break and
fracture more
easily, thus increasing the risk of inhalation, etc. By the same token,
moisture resistant glass
fibers which have low strength to begin with also do not fulfill many
requirements. For
example, building insulation is shipped in compressed form. If the glass
fibers of the insulation
product are weak or brittle, many fibers will be broken during compression,
not only increasing
the number of small fibers which are bioavailable, but also producing an
inferior product which
may not recover a sufficient amount of its pre-compressed thickness. Strong
fibers which are
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CA 02575900 2007-02-09
not moisture resistant also exhibit a great deal of breakage, especially under
humid storage,
as illustrated hereinafter. Finally, glass fibers must be prepared from glass
compositions which
can be economically processed.
The two principal methods of glass wool fiber production are the pot and
marble process
and the centrifugal or "rotary" process. In the latter, molten glass enters a
centrifugal spinner
from the forehearth of a glass melting furnace. As the centrifugal spinner
rotates, relatively
large diameter glass strands stream from orifices located in the spinner's
periphery. These
large diameter strands immediately contact an intense hot gas jet produced by
burners located
around the spinner. The hot gas attenuates the large diameter strands into
fine, elongated
fibers, which may be collected on a moving belt.
As glass is an amorphous rather than crystalline "solid", crystallization in
the melt or
during fiberization will disrupt the fiber glass forming process with
disastrous results. In the
rotary process, the glass ingredients are first melted in a glass melter prior
to their entry into
the forehearth. Thus, the feed to the forehearth is high temperature, molten
glass. From the
forehearth, the molten glass fed to the spinner is cooled to the HTV (high
temperature
viscosity) or "fiberization" temperature . Because the forehearth is fed with
hot, molten glass,
and the temperature of the glass in the forehearth is above the HTV, the
difference in
temperature between the HTV and liquidus ("AT"), the temperature which defines
the boundary
of crystallization, may be quite small in the rotary process.
In the pot and marble process, relatively large diameter "primary" strands of
glass
(primaries) exude from holes located in the bottom of the pot. Because room
temperature
marbles are continuously or incrementally added to the pot, numerous locations
will exist within
the pot where the temperature might fall below the liquidus temperature,
thermodynamically
favoring crystallization and disrupting the process. To ensure that the
process is not disrupted,
glass compositions must be used which exhibit a significant difference,
minimally 300 F.,
between the HTV and liquidus temperatures. Thus, glass compositions formulated
for the rotary
process, having low AT, are not suitable for use in pot and marble process.
The primaries exiting the pot from the pot and marble process are flame
attenuated
rather than hot gas attenuated, thus exposing the glass fibers to higher
temperatures than in
the rotary process. These higher temperatures cause a loss of the more
volatile compounds of
the glass composition from the outside of the fibers, resulting in a "shell"
which has a different
composition than the fiber interior. As a result, the biosolubility of glass
fibers prepared from
pot and marble fiberglass is not the same as that derived from the rotary
process. As glass
fibers must necessarily dissolve from the fiber ends or the cylindrical
exterior, more highly
resistant shell will drastically impede the biodissolution rate.
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CA 02575900 2007-02-09
SUMMARY OF THE INVENTION
It has now been surprisingly discovered that glass fibers of enhanced
biosolubility may
be prepared from glass compositions suitable for pot and marble processing,
which exhibit
minimally about a 350 F. difference in HTV and liquidus, and which have well
defined
formulations meeting both narrow mol percentage composition as well as meeting
each of three
specific "C-ratios" which govern chemical resistance, moisture resistance, and
biosolubility.
The invention according to the parent application generally provides glass
fibers
exhibiting chemical resistance, moisture resistance, and biosolubility, the
glass fibers having
a shell exterior which has a different composition than the fiber interior,
and with the glass
fibers being prepared from a glass composition consisting essentially of, in
mol percent:
Si0Z 66 - 69.7
A1203 0 - 2.2
RO 7 - 18
R20 9 - 20
B203 0 - 7.1
the glass composition having a C (acid) _ 1.95, a C (bio) <_ 2.30, a C (moist)
_ 2.46, a
difference, OT, between HTV (103 poise) and liquidus in excess of 350 F, and
the fibers
exhibiting a biodissolution in excess of 150 ng/cmZ/hr.
The invention of the parent application also may be considered as providing
flame
attenuated pot and marble fiberized glass fibers, the fibers having an outer
shell depleted of
a position of volatile oxides, the fibers prepared from a glass composition
comprising, in mol
percent:
Si0Z 66 - 69.0
A1203 0 - 2.2
RO 7 - 16
R20 9 - 19
B203 0 - 7.1
characterized by a C (acid) _ 2.00, a C (bio) <_ 2.23, a C (moist) _ 2.50, a
difference OT between
the HTV (103 poise) and liquidus greater than 300 F, the fibers exhibiting a
biodissolution
greater than about 150 ng/cmZ/hr.
Additionally, the invention of the parent application provides an acid an
moisture
resistant glass fiber having a shell exterior which has a different
composition than the fiber
interior, and with the glass fiber being prepared from a glass composition
consisting essentially
of, in mol percent:
Si0Z 66.5 - 67.8
A1203 0.5 - 1.5
BZ03 5.0 - 7.0
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CaO 3.0 - 7.0
Mg0 3.0-7.0
NazO 14.0 - 17.0
K20 0.1 - 0.4
wherein the sum of CaO and MgO is between 8.0 and 12.0, the glass fiber
exhibiting a AT,
greater than 400 F, and a biodissolution greater or equal to about 150
ng/cmZ/hr.
The present invention, on the other hand provides a glass marble suitable for
melting
and forming fibers exhibiting chemical resistance, moisture resistance, and
biosolubility, the
glass marble composition comprising, in mo( percent:
SiOz 66 - 69.7
A1203 0 - 2.2
RO 7 -18
R20 9 - 20
B203 0 - 7.1
and the glass marble composition having a difference, oT, between HTV (103
poise) and liquidus in excess
of 350 F, an HTV (103 poise) of 1800 F to 2100 F; the glass marble composition
has a c(acid) > 1.95, c(bio)
s 2.30 and a c(moist) _ 2.40; and fibers prepared therefrom exhibit a
biosolubility in excess of 150 ng/cm2/hr_
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The subject invention glasses have HTV and liquidus which are suitable for
production of glass
fibers in the pot and marble process. Such glass generally must have an HTV
(103 poise) of 1800 F to
2100 F, preferably 1900 F to 2000 F, and exhibit a liquidus which is minimally
about 350 F, preferably
425 F, and more preferably 500 F or more lower than the HTV. These
characteristics are necessary to
prepare glass fibers economically on a continuous basis.
The glass composition must fall within the following range of composition, in
mol
percent:
Si02 66 - 69.7
A1203 0- 2.2
RO 7 - 18
R20 9 - 20
Bz03 0-7.1
where R20 is an alkali metal oxide and RO is an alkaline earth metal oxide.
RZ0 is preferably
Na20 in most substantial part, while RO may be MgO and/or CaO, preferably
both, in a molar
ratio of MgO/CaO of 1:3 to 3:1, more preferably 2:3 to 3:2. The chemical
behavior of the glass
is dictated by three ratios which the glass composition must meet, C(acid),
C(bio), and
C(moist). These ratios are defined compositionally as follows, all amounts
being in mol
percent:
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C(acid) = [Si0Z] / ([AI203] + [B203] + [RZ0] + [RO])
C(bio) = ([Si02] + [A1203]) / ([B203] + [RZ0] + [RO])
C(moist) = (Si0z] + [AI203] + [B203])/ ([RZ0] + [RO])
In these ratios, C(acid) is the ratio which pertains to chemical resistance in
acid environments,
C(bio) is the ratio which is most closely linked to biosolubility, and
C(moist) is the ratio which
relates to retention of properties in moist environments. It is desired that
C(acid) and C(moist)
be as large as possible, while C(bio) should be as low as possible. At the
same time, the HTV
and liquidus of the overall composition must be suitable for glass fiber
processing. It has been
found that pot and marble glass of high biosolubility, while yet maintaining
other necessary
physical properties such as chemical resistance and moisture resistance, is
obtained when
C(acid) _1.95, C(bio) < 2.30, and C(moist) > 2.40.
Preferably, the biosoluble fiberglass of the subject invention has a
composition which
falls within the following ranges (in mol percent):
Si02 66 - 69.0
A1203 0 - 2.2
RO 7 - 16
R20 9 - 19
B203 0 - 7.1
Most preferably, the biosoluble glass fibers of the subject invention have a
composition which
falls within the following most preferred range:
Si0Z 66 - 68.25
A1203 0 - 2.2
RO 7 - 13
R20 11 - 18
B203 0 - 7.1
With respect to the performance characteristics of the glass fibers of the
subject
invention, it is preferred that C(acid) be greater than or equal to 2.00;
C(bio) be less than or
equal to 2.23, more preferably less than or equal to 2.20; and that C(moist)
be greater than
or equal to 2.50, preferably greater than or equal to 2.60. As discussed
previously, it is most
desirable that C(acid) and C(moist) be as high as possible. For example,
C(moist) values of
3.00 or greater are particularly preferred. It should be noted also, that the
various C-ratios are
independent in the sense that a more preferred glass need not have all "more
preferred"
C-ratios.
Acid resistance may be measured by battery industry standard tests. For
example, a
typical test involves addition of 5 grams of nominally 3 pm diameter fiber in
50 mL of sulfuric
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CA 02575900 2007-02-09
acid having a specific gravity of 1.26. Following refluxing for 3 hours, the
acid phase may be
separated by filtration and analyzed for dissolved metals or other elements.
The procedure used to evaluate biodissolution rate is similar to that
described in Law
et al. (1990). The procedure consists essentially of leaching a 0.5 gram
aliquant of the
candidate fibers in a synthetic physiological fluid, known as Gamble's fluid,
or synthetic
extracellular fluid (SEF) at a temperature of 37 C and a rate adjusted to
achieve a ratio of flow
rate to fiber surface area of 0.02 cm/hr to 0.04 cm/hr for a period of up to
1,000 hours
duration. Fibers are held in a thin layer between 0.2 pm polycarbonate filter
media backed by
plastic support mesh and the entire assembly placed within a polycarbonate
sample cell through
which the fluid may be percolated. Fluid pH is regulated to 7.4+0.1 through
the use of positive
pressure of 5% COZ /95% N2 throughout the flow system.
Elemental analysis using inductively coupled plasma spectroscopy (ICP) of
fluid samples
taken at specific time intervals are used to calculate the total mass of glass
dissolved. From
this data, an overall rate constant could be calculated for each fiber type
from the relation:
K = LdoP(1 - (M/M(,)0.5] )/2t
where k is the dissolution rate constant in SEF, do the initial fiber
diameter, p the initial
density of the glass comprising the fiber, Mo the initial mass of the fibers,
M the final mass of
the fibers (M/Mo = the mass fraction remaining), and t the time over which the
data was taken.
Details of the derivation of this relation is given in Leineweber (1982) and
Potter and Mattson
(1991). Values for k may be reported in ng/cm2 /hr and preferably exceed a
value of 150.
Replicate runs on several fibers in a given sample set show that k values are
consistent to
within 3 percent for a given composition.
Data obtained from this evaluation can be effectively correlated within the
sample set
chosen - dissolution data used to derive k's were obtained only from
experimental samples of
uniform (3.0 pm) diameter and under identical conditions of initial sample
surface area per
volume of fluid per unit time, and sample permeability. Data was obtained from
runs of up to
days to obtain an accurate representation of the long term dissolution of the
fibers.
Preferred biodissolution rate constants in ng/cmZ/hr are greater than 150
ng/cmz/hr, preferably
greater than 200 ng/cmz/hr, more preferably greater than 300 ng/cmZ /hr, and
most preferably
30 greater than 400 ng/cmZ/hr.
Having generally described this invention, a further understanding can be
obtained by
reference to certain specific examples which are provided herein for purposes
of illustration only
and are not intended to be limiting unless otherwise specified.
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CA 02575900 2007-02-09
EXAMPLES
Comparative Cl and C2
C-ratios are calculated for a conventional C-glass (chemically resistant
glass) and a
"soluble" glass as disclosed in Examples la and 2b in Table 1 of U.S. Patent
No. 5,055,428.
The glass composition is in weight percent. HTV (103 poise) and liquidus are
as reported in the
'428 patent.
TABLE 1
Comparative Example 1 Comparative Example 2
(Wt%) (Wt%)
SiOz 66.4 66.7
A1203 1.2 1.0
B203 11.0 10.0
Na20 12.9 13.9
K20 0.2 0.2
CaO 4.8 5.5
MgO 3.2 2.5
C(acid) 2.03 2.07
C(bio) 2.09 2.13
C(moist) 3.41 3.29
HTV
(103 poise) 1965 F 1949 F
Li uidus 1738 F 1702 F
As can be seen from Table 1, the C-ratios of these rotary process glasses
indicate that
they should both have good performance with respect to acid resistance,
moisture resistance,
and biosolubility. The Comparative Example 2 glass is reported by the patentee
to have a
dissolution rate in model physiological saline (composition not disclosed) of
211 ng/cmZ/hr.
However, examination of the HTV and liquidus temperatures reveals that these
differ only by
227 F. and 247 F., respectively. Thus, these glass compositions cannot be
used in pot and
marble fiberization. These Comparative Examples serve to illustrate the ease
with which higher
biosolubility can be obtained in rotary processable glass. These glasses
cannot be used to
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CA 02575900 2007-02-09
manufacture fiberglass by the pot and marble process. However, even were this
possible, the
flame attenuation and consequent loss of volatile oxides from the fiber
surface would be
expected to lower the measured biodissolution rate by a factor of from about 2
to 4.
Examples 1 and 2
Two glass formulations were processed into marbles for use in pot and marble
fiberization, and glass fibers prepared in the conventional manner. The
formulations, C-ratios,
HTV (103 poise), liquidus, and measured biosolubility are presented in Table
2. The ingredients
are in mol percent.
TABLE 2
Example 1 (mol %) Example 2 mol %
Si02 67.24 67.18
A1203 1.04 1.02
B203 6.08 5.99
CaO 4.99 5.26
Mg0 5.24 5.26
Na20 15.22 15.45
K20 0.26 0.23
C(acid) 2.05 2.05
C(bio) 2.15 2.14
C(moist) 2.89 2.87
Biosol K(dis) 350 426
HTV 1972 1981
Liquidus 1435 <1325
The C-ratios indicate that the glasses of Table 2 should exhibit desirable
chemical
resistance (both acid and moisture) as well as high biodissolution. The high
biodissolution is
confirmed by actual tests, being in both cases, considerably greater than 300
ng/cmZ /hr.
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Example 3, Comparative Examples C3 and C4
A subject invention glass is compared with two commercial glasses for acid
resistance
and moisture resistance, respectively. The formulations (mol percent) are as
follows.
TABLE 3
Exam le 3 Exam le C3 Exam le C4
Si0Z 67.28 65.36 57.53
A1203 1.04 1.83 3.11
B203 6.00 4.59 7.23
CaO 4.00 6.27 8.82
Na20 15.20 15.56 16.24
K20 0.26 0.45 0.71
F2 -- 1.43 --
C(acid) 2.06 1.96 1.35
C(bio) 2.16 2.14 1.54
C(moist) 2.89 2.67 2.11
M 0 5.23 4.52 6.36
The acid resistance of the Example 3 glass was compared with that of
Comparative
Example C3. It is noted that the Comparative Example C3 glass meets the C-
ratio requirements
but not the compositional limitations. The results of the acid resistance test
are presented
below in Table 3a.
TABLE 3a
Glass Example 3 Example C3
Element Quantity Dissolved Quantity Dissolved
(ppm) (ppm)
Al 187 453
Ca 2831 4110
Mg 854 938
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To determine moisture resistance, a stress corrosion test is used in which the
fibers are
stressed by bending in a controlled humidity and temperature test chamber.
Fibers which
exhibit moisture resistance under these conditions take longer to break. The
Example 3 glass
was compared to Comparative Example C4 glass, a glass used commercially for
building
insulation where compression of insulation and storage generates the potential
for fiber
breakage as a result. After 50 hours, only 12% of the Example 3 glass had
broken, while all
of the Comparative Example C4 fibers had failed.
Comparative Examples C5 and C6
C-ratios are calculated for the rotary process glasses of Example 3 of U.S.
Patent No.
4,510,252, and Example 2 of U.S. Patent No. 4,628,038. Composition, calculated
C-ratios,
liquidus, and estimated HTV (103 poise) are given below in Table 4, in mol
percent.
TABLE 4
Example C5 Example C6
Si0z 68.2 66.67
A1203 2.2 2.25
B203 5.0 4.78
Na20 9.2 8.68
K20 -- 0.26
CaO 11.9 14.77
Mg0 3.5 3.6
C(acid) 1.85 1.94
C(bio) 2.03 2.15
C(moist) 2.54 2.70
HTV
(103 poise), est. 2280 F 2210 F
Li uidus 1983 F F 2035 F
As can be seen from the table, the acid resistance of Comparative Example C5
is
expected to be low, and the biodissolution is expected also to be low,
although the glass should
display good moisture resistance. However, the difference between HTV (103
poise) and
CA 02575900 2007-02-09
liquidus is only about 297 F, and thus this glass is not suitable for use in
a pot and marble
process. The glass of Comparative Example C6 exhibits C(acid) close to an
acceptable value,
although C(bio) is too high. The glass should have good moisture resistance.
However, the
glass cannot be used in a pot and marble process as the difference between
liquidus and HTV
(103 poise) is only 175 F.
Comparative Example 7
C-ratios and composition data (mol percent) are presented for Example 6 of
U.S. Patent
No. 5,108,957.
TABLE 5
Exam le C7
Si02 69.55
AIz03 0.08
CaO 7.46
Mg0 4.30
Na20 15.05
K20 0.04
B203 3.52
C(acid) 2.28
C(bio) 2.29
C(moist) 2.72
HTV
(103 poise) 2003 F
Liquidus 1706 F
The biodissolution for this glass should be marginal, however the moisture and
acid
resistance should be acceptable. However, the difference in HTV and liquidus
(AT) indicates
that this glass is unsuitable for pot and marble fiberization.
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Examples 4-12
Additional glass compositions which fall within the subject invention
parameters are
presented in the following table.
EXAMPLES 4-12
Ex.4 Ex.5 Ex.6 Ex.7 Ex.8 Ex.9 Ex.10 Ex.11 Ex.12
MoI % Mol % Mol % Mol % Mol % Mol % Mol % Mol % Mol %
Si0Z 67.28 67.4 66.38 66.9 65.96 68.03 69.08 67.96 68.61
A1203 1.04 1.03 2.35 2.37 2.33 0 0 0 0
B203 6.00 6.06 3.49 7.03 6.93 0.75 3.42 3.37 6.8
Na20 15.20 15.25 17.13 16.08 9.25 16.08 17.58 11.63 9.83
K20 0.26 0.19 0.52 0 0.51 0 0 0 0
CaO 4.99 4.83 4.87 3.76 7.42 7.43 4.89 8.46 7.28
M O 5.23 5.23 5.27 3.87 7.63 7.71 5.02 8.58 7.48
By the term "consisting essentially of" is meant that additional ingredients
may be added
provided they do not substantially alter the nature of the composition.
Substances which cause
the biodissolution rate to drop below 150 ng/cmz/hr or which lower the AT to a
value below
350 F are substances which do substantially alter the composition.
Preferably, the glass
compositions are free of iron oxides, lead oxides, fluorine, phosphates
(P205), zirconia, and
other expensive oxides, except as unavoidable impurities. It should be noted
that while rotary
process glass compositions are in general unsuitable for pot and marble
fiberization, the reverse
is not true, and the subject invention glass compositions should yield fibers
prepared by the
rotary process which have yet higher rates of biodissolution.
Having now fully described the invention, it will be apparent to one of
ordinary skill in
the art that many changes and modifications can be made thereto without
departing from the
spirit or scope of the invention as set forth herein.
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