Irregularly-shaped glass fibers and insulation therefrom

Irregularly-shaped glass fibers and insulation therefrom comprising two different glasses having differing coefficients of thermal expansion. The irregularly-shaped dual-glass fibers exhibit a substantially uniform volume filling nature, and provide improved recovery and thermal conductivity abilities even in the absence of a binder material.

TECHNICAL FIELD 
This invention relates to irregularly-shaped glass fibers suitable for 
insulation. Each glass fiber comprises two distinct glasses. 
BACKGROUND OF THE INVENTION 
Glass fibers, mineral fibers and other wool materials have been insulating 
buildings for some time. Insulation easily fits into the spaces in attics, 
ceilings, walls, floors and the like. 
The common prior art methods for producing glass fiber insulation products 
involve producing glass fibers from a rotary process. A single molten 
glass composition is forced through the orifices in the outer wall of a 
centrifuge or spinner, producing primarily straight glass fibers. The 
fibers are drawn downward by a blower. The binder required to bond the 
fibers into a wool product is sprayed onto the fibers as they are drawn 
downward. The fibers are then collected and formed into a wool pack. 
Recent developments include insulation which installs rapidly and 
effectively between the studs of a building. An exterior layer covers the 
fibrous batt. Preferably, the exterior layer covering comprises a 
polyethylene package which receives the fibrous batt. Another focal point 
of recent developments in insulation is one in which all the binder or 
essentially all the binder is no longer present in the fibrous batt. 
Evolution of processes for producing low density insulation provide 
satisfactory resiliency without a binder in the batt. 
Still other developments are insulations of mineral fibers which are 
irregular in shape. Fibers that are irregular, rather than straight, 
kinked or even curly, provide a more uniform lattice structure. This 
uniform volume filling allows for higher recovery ratios. More 
importantly, uniform volume filling also results in significantly lower 
thermal conductivity. Also, the greater entanglement of irregularly-shaped 
fibers provides better wool pack integrity. By sufficient integrity, it is 
meant that the fibers of the wool batt will remain entangled and not 
separate. 
DISCLOSURE OF THE INVENTION 
The present invention provides irregularly-shaped glass fibers suitable for 
insulation. Each glass fiber comprises two distinct glasses. Each glass 
has a different coefficient of thermal expansion (CTE). Each glass has a 
different glass composition and is boron-free. The first boron-free glass 
composition by weight percent consists essentially of: 
______________________________________ 
Higher 
Most Dissolution 
Ingredients 
Broad Preferred 
Preferred 
Rate Glasses 
______________________________________ 
SiO.sub.2 35-65 40-64 45-63 40-64 
Al.sub.2 O.sub.3 
0-17 0-16 0-15 0-5 
MgO 0-30 1-27 2-25 0-30 
CaO 5-40 10-37 15-35 5-40 
FeO 0-17 0-16 0-15 0-17 
Na.sub.2 O + K.sub.2 O 
0-10 0-5 0-2.5 0-10 
SiO.sub.2 + Al.sub.2 O.sub.3 
.gtoreq.45 
.gtoreq.47 
.gtoreq.50 
.gtoreq.45 
.ltoreq.70 
.ltoreq.67 
.ltoreq.65 
.ltoreq.69 
Temperature for a 
&gt;2350 &gt;2400 &gt;2450 &gt;2350 
Viscosity of 10 
&lt;3400 &lt;3200 &lt;3000 &lt;3400 
Poise; .degree.F. 
______________________________________ 
FeO+Fe.sub.2 O.sub.3 is expressed as FeO. 
Generally, TiO.sub.2, MnO, and other impurities can be present in amounts 
up to several percent. It is generally desirable that the Na.sub.2 
O+K.sub.2 O be less than several percent to keep the CTE low. 
The second boron-free glass composition consists by weight percent 
essentially of: 
______________________________________ 
Higher 
Most Dissolution 
Ingredients 
Broad Preferred 
Preferred 
Rate Glasses 
______________________________________ 
SiO.sub.2 35-65 40-64 45-63 40-64 
Al.sub.2 O.sub.3 
0-17 0-16 0-15 0-5 
MgO 0-30 1-27 2-25 0-30 
CaO 5-40 10-37 15-35 5-40 
FeO 0-17 0-16 0-15 0-17 
Na.sub.2 O + K.sub.2 O 
0-25 7-22 10-20 0-25 
SiO.sub.2 + Al.sub.2 O.sub.3 
.gtoreq.45 
.gtoreq.47 
.gtoreq.50 
.gtoreq.45 
.ltoreq.70 
.ltoreq.67 
.ltoreq.65 
.ltoreq.69 
Temperature for a 
&gt;2350 &gt;2400 &gt;2450 &gt;2350 
Viscosity of 10 
&lt;3400 &lt;3200 &lt;3000 &lt;3400 
Poise; .degree.F. 
______________________________________ 
FeO+Fe.sub.2 O.sub.3 is expressed as FeO. 
Generally, TiO.sub.2, MnO, and other impurities can be present in amounts 
up to several percent. It is generally desirable that the Na.sub.2 
O+K.sub.2 O be greater than several percent to increase the CTE. 
Relatively high amounts of FeO (greater then about 5%) is desirable in 
applications where a high fire resistance or high temperature performance 
is needed. 
The glasses have a viscosity of 10 poise at a temperature ranging from 
2350.degree. to 3400.degree. F. and have a liquidus at least 50.degree. F. 
below the 10 poise viscosity temperature. 
This invention produces two component glass fibers from CaO--MgO--Al.sub.2 
O.sub.3 --FeO--SiO.sub.2 and/or Na.sub.2 O--CaO--MgO--Al.sub.2 O.sub.3 
--FeO--SiO.sub.2 type glasses by a "mineral wool" process. The two 
components have different thermal contractions so that the fiber curls on 
cooling. Glasses used previously to produce two component fibers by the 
rotary process were based on the Na.sub.2 O--B.sub.2 O.sub.3 --Al.sub.2 
O.sub.3 --MgO--CaO--SiO.sub.2 system. "Mineral wool" type glasses are 
generally lower cost. However, they are more difficult to form into fiber 
because of their low viscosity at their liquidus temperature. In this 
invention, we discovered that two component glass fibers could be formed 
from "mineral wool" type glasses by feeding the glasses through a single 
hole and blowing them with a gas jet.

BEST MODE OF CARRYING OUT INVENTION 
FIG. 1 shows two distinct molten glass compositions supplied from furnaces 
10 via forehearths 12 to fiberizers 14. Preferably, the glasses have 
coefficients of thermal expansion differing by at least 2.0 ppm/.degree.C. 
Veils of irregularly-shaped glass fibers 18 produced by the fiberizers are 
collected on conveyor 16 as wool pack 20 by means of a vacuum positioned 
beneath the conveyor. As the fibers are blown downward by air or gases to 
the conveyor by means of blowers 22 in the fiberizers, they are attenuated 
and assume their irregular shape. The wool can be used as collected as 
insulation for buildings and other purposes. Alternatively, the wool can 
be wrapped in plastic film and used as insulation. 
FIG. 2 shows fiberizer 32 which is a platinum crucible. Fiberizer 32 has a 
platinum divider 34 which keeps the molten glasses separate. The lower 
portion of fiberizer 32 is Pt tip 36 to which divider 34 extends. Blower 
22 is a "V" nozzle with air at 90 psi. The molten glasses flow out of tip 
36 and are fiberized with air from blower 22. 
FIG. 3 is a view of the V-nozzle in blower 22. 
FIG. 4 shows insulation product 30 comprised of entangled, irregularly- 
shaped glass fibers 38. 
FIG. 5 is a cross-sectional view of an ideal irregularly-shaped glass fiber 
38 having a 50:50 A/B glass ratio. Halves 40 and 42 essentially are equal 
in the ideal with point 44 being the center and line 46 being the 
diameter. 
FIG. 6 shows a more typical cross-section where halves 48 and 50 are not 
equal. Line 52 is no longer a diameter, but just a divider. Lines R and r 
are shown to locate center point 44. 
The deviation ratio is a measure of how far the A/B glass ratio is away 
from 50:50. The larger the deviation from 50:50, the larger r will be as a 
percent of R. 
The irregularly-shaped fibers of the present invention are dual-glass 
fibers, i.e. each fiber is composed of two different glass compositions, 
glass A and glass B. If one were to make a cross-section of an ideal 
irregularly-shaped glass fiber of the present invention, one half of the 
fiber would be glass A, with the other half glass B. In reality, a wide 
range of proportions of the amounts of glass A and glass B may exist in 
the various irregularly-shaped glass fibers in the wool insulating 
material (or perhaps even over the length of an individual fiber). In 
general, insulation products of the irregularly-shaped fibers will consist 
of fibers of all different combinations of the percentages of glass A and 
glass B, including a small fraction of fibers that are single component. 
Optical micrographs of the fibers easily show the two components due to 
differences in the refractive index. Also, in some cases, the two 
components can easily be seen due to the color difference if the iron 
content is significantly different in the two glasses. 
Due to a continuously changing attenuation environment, each 
irregularly-shaped fiber is twisted in a unique way. No two fibers are 
exactly alike. The fiber's final shape is one with a baseline curvature 
due to the dual-glass nature, which is modified by the twisting, irregular 
rotation of the plane of curvature caused by the continuously changing 
attenuation environment. The fiber has a baseline curvature that is 
twisted through three dimensions. It is generally not helical. The fiber's 
irregular nature allows the irregularly-shaped glass fibers to stand apart 
from one another and achieve a uniform volume filling nature. 
A number of mineral wool processes previously known can be used to produce 
fibers by the present invention. Several examples of suitable mineral wool 
processes include those found in U.S. Pat. Nos. 2,257,767, 2,206,058, 
4,243,400, 3,885,940 and 3,874,886. The primary criteria is that the 
glasses be fed parallel into a single stream which is then further 
attenuated by a gas jet. 
The following examples further demonstrate the glass fibers of the present 
invention. 
Example 1 
We produced irregularly-shaped glass fibers of the present invention having 
the following two compositions, viscosities and liquidus temperature: 
______________________________________ 
Ingredients Weight Percent 
______________________________________ 
SiO.sub.2 41.46 
Al.sub.2 O.sub.3 13.27 
Na.sub.2 O 0.61 
K.sub.2 O 0.13 
MgO 8.37 
CaO 33.18 
TiO.sub.2 0.36 
Fe.sub.2 O.sub.3 2.62 
Temperature for a 
2,524.degree. F. 
Viscosity of 10 Poise, 
Liquidus Temperature 
2,381.degree. F. 
SiO.sub.2 42 
Al.sub.2 O.sub.3 10.9 
Na.sub.2 O 17.44 
K.sub.2 O 0.82 
MgO 7.07 
CaO 21.20 
Temperature for a 
2,480.degree. F. 
Viscosity of 10 poise 
Liquidus Temperature 
2,427.degree. F. 
______________________________________ 
Irregular-shaped glass fibers of the present invention were produced in a 
batch-mode laboratory fiberizer. The two glasses were melted in a Pt 
crucible with a Pt divider to keep the glasses separate. The glasses had a 
viscosity of less than 10 poise at 2,550.degree. F. The two coefficients 
of thermal expansion were 12.2 and 7.5.times.10.sup.-6 /.degree.C. 
respectively. After being well melted, a Pt plug at the bottom of this 
crucible was removed and fiber was blown with a "V nozzle" with air at 
about 90 psi. Two component fiber was produced. Optical micrographs showed 
the two component fiber and curl of the fiber. 
The irregular glass fibers were collected and formed into standard 
insulation products in the shape of wool batts.