Note: Descriptions are shown in the official language in which they were submitted.
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OPEN-CELLED GYPSUM CORE, GYPSUM ACOUSTIC PANEL, AND METHOD FOR
MAKING SAME
REFERENCE TO RELATED APPLICATIONS
[0001] The present application claims priority to U.S. Provisional Application
Serial
No. 63/136,977, filed January 13, 2021, entitled OPEN-CELLED GYPSUM CORE,
GYPSUM ACOUSTIC PANEL, AND METHOD FOR MAKING SAME. U.S.
Provisional Application Serial No. 63/136,977 is incorporated by reference in
its
entirety herein.
FIELD
[0002] The present disclosure relates to gypsum structures having improved
acoustical properties. More specifically, the present disclosure relates to
open-
celled gypsum cores, gypsum acoustic panels, and methods for making same.
BACKGROUND
[0003] Acoustic panels, such as but not limited to ceiling tiles, wall panels
and other
building panels, and partitions, can be used as acoustic absorbers in various
environments. Acoustic panels include an acoustic layer that is selected for
acoustic absorbency as well as factors such as durability. For absorbing
noise,
sound enters a matrix of an acoustic layer, which matrix is defined by the
acoustic
layer's structure. Once the sound is inside, the matrix traps and dissipates
the
sound energy therein. NRC (noise reduction coefficient) of building panels can
be
used to define their acoustic absorption capacity.
[0004] Ideally, the panels combine acoustic absorbency with durability for
long life.
Mineral wool is commonly used because it provides a porous fibrous structure
for
absorbing sound. Other common materials used in the manufacture of acoustic
panels include fiberglass, expanded perlite, clay, gypsum, stucco, calcium
carbonate, paper fiber, and binder (e.g., starch or latex).
[0005] Some acoustic panels are made using a water-felting process. An aqueous
dispersion of fibers, aggregates, binders, and other additives is dispensed
onto a
porous surface or wire where the furnish is dewatered, both by gravity and by
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vacuum suction. The wet mat is typically dried in a convection oven, fissured,
and/or perforated to impart acoustical absorbency and then cut into desired
lengths. If desired, the surface is painted to produce a finished panel.
[0006] Another process for making acoustic panels is disclosed in U.S. Patent
No.
1,769,519. A composition of mineral wool fibers, fillers, colorants, a binder
such as
cooked starch, and water is placed in trays covered with paper or paper-backed
foil. The composition is then screeded with a forming plate to the desired
thickness.
A decorative surface, such as an embossed pattern, may be obtained by
imparting
a pattern into the surface of the cast material by use of a screed bar or a
patterned
roll.
[0007] Such methods of making acoustic panels utilize large amounts of water
and
energy. Additionally, hygroscopic binders, such as paper or starch, can result
in
panels that are susceptible to sag. Panel sagging can be accentuated when the
panel supports insulation or other loads or when subjected to high levels of
humidity and temperature. Additional process steps, such as perforation, may
also
increase the manufacturing cost.
[0008] Gypsum panels are less prone to sag and can be manufactured efficiently
in
a high-speed process. There has accordingly been a great need and potential to
provide an acoustic absorber on the platform of conventional gypsum wallboard.
However, gypsum is a dense material, and is not inherently an especially
acoustically absorbent material. Gypsum panels can lack sufficient acoustical
absorbency for use as an acoustic absorber. Gypsum panels have a very limited
noise reduction function, mainly due to the closed air cells in conventional
gypsum
panels.
[0009] Some gypsum wallboards have been adapted for use as acoustical panels
by
including perforations (holes) and positioning a sound-absorbing backing sheet
on
the back of the perforated panel. This allows some sound to pass through the
perforations to improve the noise reduction performance. An example
perforation
process includes formation of large (e.g., 1 cm or more in diameter) holes
that are
mechanically formed (e.g_, drilled, bored, punched) to extend through the
entire
panel by an external device.
[0010] Perforating introduces several drawbacks. For example, perforation is
typically an offline process, in that it is performed externally, that is, in
addition to
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and separate from the formation of the gypsum wallboard itself. Perforation
also
may produce a significant amount of dust. Perforation further increases
manufacturing costs of the gypsum wallboards. Additionally, while the
perforations
provide some weight reduction and sound absorbance, they may not be acceptable
by consumers as being aesthetically pleasing.
[0011] U.S. Pat. Nos. 6,387,172 and 6,481,171 disclose acoustic gypsum
compositions. Both describe the use of both fibrous calcined gypsum and non-
fibrous calcined gypsum in gypsum products. Another gypsum panel having an
acoustical layer is disclosed in U.S. Patent Publication No. 2004/0231916. One
embodiment of this panel has an acoustic layer of foamed gypsum formed on
denser gypsum material for strength. U.S. Pat. No. 7,503,430 discloses a
ceiling
tile manufactured on a gypsum board line that reduces dusting when cut. U.S.
Pat.
No. 7,851,057 discloses an acoustic panel including an interlocking matrix of
set
gypsum and an additive such as cellulosic fiber or lightweight aggregate. U.S.
Pat.
No. 8,057,915 discloses an acoustic gypsum board including a matrix of calcium
dihydrate crystals and expanded perlite distributed throughout the matrix.
SUMMARY
[0012] According to one aspect of the disclosed embodiments, an open cell set
gypsum core is provided. An interlocking matrix of gypsum and, optionally,
reinforcing fiber has air voids distributed therein. The air voids define
cells having
cell walls formed by the interlocking matrix. The interlocking matrix further
includes
channels distributed therein. The channels interconnect the air voids and
comprise
openings in the cell walls.
[0013] The core may further include a reinforcing fiber distributed throughout
the
interlocking matrix. The gypsum may include synthetic gypsum, natural gypsum,
or a combination.
[0014] According to another aspect of the disclosed embodiments, a set gypsum
core
is provided. The core is formed from an air-foamed stucco slurry comprising
stucco,
at least one uncooked starch, and an aqueous foam, the uncooked starch being
in
the amount of at least 4% by weight of the dry stucco. The air-foamed stucco
slurry
has air bubbles distributed therein. The core is set to provide an
interlocking matrix
of set gypsum, wherein the air bubbles form air voids distributed within the
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interlocking matrix, and wherein granules of the uncooked starch are
distributed
within the interlocking matrix between the air voids and within cell walls of
the air
voids. The set core is heated to at least a gelatinizing temperature, wherein
the
granules of the uncooked starch gelatinize to provide channels distributed
within
the interlocking matrix and interconnecting the air voids.
[0015] The air-foamed stucco optionally may further include reinforcing fiber.
The
gypsum may include synthetic gypsum, natural gypsum, or a combination.
[0016] According to yet another aspect of the disclosed embodiments, a gypsum
acoustic panel is provided. The panel comprises an acoustic layer comprising
an
open cell set gypsum core. The open cell set gypsum core comprises an
interlocking matrix of gypsum having air voids distributed therein. The air
voids
define cells having cell walls formed by the interlocking matrix. The
interlocking
matrix further has channels distributed therein, where the channels
interconnect
the air voids, and the channels comprise openings in the cell walls. At least
one
backing sheet faces an outer surface of the acoustic layer.
[0017] The open cell set gypsum core may further include reinforcing fiber
disposed
within the interlocking matrix. The gypsum may include synthetic gypsum,
natural
gypsum, or a combination.
[0018] According to yet another aspect of the disclosed embodiments, an air-
foamed
slurry is provided for making an acoustic panel. A slurry is formed from a
mixture.
The mixture comprises stucco, water, and at least one uncooked starch, the
uncooked starch being in the amount of at least 4% by weight of the dry
stucco. An
aqueous foam comprises a foaming agent, water, and air. The water to stucco
ratio
(wt/wt) in the air-foamed slurry is between about 65% and about 120%.
[0019] The air-foamed slurry may further include reinforcing fiber, such as
but not
limited to glass fiber. The stucco may be formed from synthetic gypsum,
natural
gypsum, or a combination.
[0020] According to yet another aspect of the disclosed embodiments, a method
for
making a set gypsum core is provided An air-foamed stucco slurry is formed
comprising stucco, at least one uncooked starch, water, and an aqueous foam,
the
uncooked starch being in the amount of at least 4% by weight of the dry
stucco,
the air-foamed stucco slurry having air bubbles distributed therein. A core is
formed
from the air-foamed slurry. The core is allowed to set to provide an
interlocking
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matrix of set gypsum, wherein the air bubbles form air voids distributed
within the
interlocking matrix, and wherein granules of the uncooked starch are
distributed
within the interlocking matrix between the air voids and within cell walls of
the air
voids. The set core is heated to at least a gelatinizing temperature, wherein
the
granules of the uncooked starch gelatinize and dissolve into the water to
provide
channels distributed within the interlocking matrix and interconnecting the
air voids.
[0021] The air-foamed stucco slurry may include reinforcing fiber, which is
disposed
within the interlocking matrix of the set gypsum core. The stucco may be
formed
from synthetic gypsum, natural gypsum, or a combination.
[0022] According to yet another aspect of the disclosed embodiments, a method
for
making an acoustic panel is provided. A slurry comprises stucco at least one
uncooked starch, and water, the uncooked starch being in the amount of at
least
4% by weight of the dry stucco. A foam is added to the slurry to provide an
air-
foamed slurry, the air-foamed stucco slurry having air bubbles distributed
therein.
A continuous strip of the air-foamed slurry may be formed, and the strip may
be
cut to form the acoustic panel. The gypsum is allowed to set to provide an
interlocking matrix of set gypsum, wherein the air bubbles form air voids
distributed
within the interlocking matrix, and wherein granules of the uncooked starch
are
distributed within the interlocking matrix between the air voids and within
cell walls
of the air voids. The set gypsum matrix is heated to at least a gelatinizing
temperature, wherein the granules of the uncooked starch gelatinize to provide
channels distributed within the interlocking matrix and interconnecting the
air voids.
[0023] The slurry may include reinforcing fiber, which is disposed within the
interlocking matrix of the set gypsum core. The stucco may be formed from
synthetic gypsum, natural gypsum, or a combination.
[0024] Other features and advantages of the invention will be apparent from
the
following specification taken in conjunction with the following figure.
BRIEF DESCRIPTION OF THE DRAWING
[0025] The present disclosure will become more fully understood from the
detailed
description and the accompanying figure, wherein:
[0026] Figure 1 is a scanning electron microscope (SEM) of a cross-section of
a
gypsum core having open cells, according to an embodiment of the present
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disclosure.
DETAILED DESCRIPTION
[0027] Introduction
[0028] While this invention is susceptible of embodiments in many different
forms,
there is shown in the drawings and will herein be described in detail
preferred
embodiments of the invention with the understanding that the present
disclosure is
to be considered as an exemplification of the principles of the invention and
is not
intended to limit the broad aspects of the invention to the embodiments
illustrated.
[0029] Unless otherwise noted, concentrations used in this description refer
to
percentages by weight based on the dry weight of stucco (calcium sulfate
hem ihydrate).
[0030] Embodiments disclosed herein provide, among other things, an open cell
set
gypsum core, and methods for making and using the same. The open cell set
gypsum core can provide an acoustical product alone, e.g., as a mold or core,
or
as an acoustic component, such as an acoustic layer sandwiched between two
layers such as glassmats, of an acoustic product such as an acoustic panel.
The
open cell set gypsum core includes an interlocking matrix including gypsum. As
the
interlocking matrix includes gypsum, it can also be referred to as an
interlocking
gypsum matrix. An "open-cell" structure with respect to an example set gypsum
core refers to a structure having a plurality of voids (cells) formed
internally in the
structure (e.g., distributed throughout an interior of the structure), which
voids
individually are not completely closed to neighboring voids, but instead are
interconnected with one or more neighboring voids via channels that are also
formed internally in the structure.
[0031] The open cell gypsum core may optionally include reinforcing fiber
disposed
within the interlocking gypsum matrix. An example reinforcing fiber is made
from a
material that does not set as does the set gypsum. Setting of the gypsum
results
in the reinforcing fibers being bound by and distributed throughout the set
gypsum.
This can improve the flexural strength and acoustical performance of the
matrix.
[0032] An acoustic path is provided in the interior of the open-cell
structure, i.e., from
one void through a channel to at least another, neighboring void, and often
through
yet another channel to yet another void, then to another void, etc. The
resulting
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paths, which can be complex or tortuous paths through the structure, provide
improved sound absorption capacity in an interlocking gypsum matrix, without
the
need to externally perforate the interlocking matrix as in some conventional
gypsum panels (though perforation can be provided if desired). Sound
absorption
capacity can be verified by, for instance, measuring an estimated noise
reduction
coefficient (e-NRC).
[0033] Additionally, example open cell set gypsum cores and acoustic panels
incorporating such gypsum cores can have a relatively low density, while
exhibiting
good compressive strength. Example open cell set gypsum cores and acoustic
panels incorporating such gypsum cores can be produced in batches using
continuous methods generally analogous to those for producing gypsum wallboard
and acoustic panels, but without the need to separately perforate the finished
cores
or panels.
[0034] To form an open-cell structure, uncooked starch is added to an air-
foamed
stucco slurry including stucco. For instance, the uncooked starch can be added
to
the air-foamed stucco slurry after, during, or prior to air-foaming, or in any
combination. The uncooked starch is distributed through the air-foamed stucco
slurry.
[0035] The stucco in the air-foamed stucco slurry sets (that is, hydrates or
rehydrates)
due to reaction of the stucco with water to harden, forming a set gypsum core
having an interlocking matrix therein. The interlocking matrix includes air
voids due
to the air bubbles provided by the air foam, and these air voids define cell
walls in
the set gypsum core. Air bubble size can be controlled to provide, among other
things, an optimal opening for sound to enter the core as well as optimal
paths to
provide optimal attenuation.
[0036] The uncooked starch can be in the form of granules. When the stucco
sets to
form a set gypsum core the uncooked starch granules are distributed in the set
gypsum cell walls. When the set gypsum is then dried at a temperature
sufficient
to gelatinize the uncooked starch ("gelatinizing temperature") the starch
granules
are gelatinized, dissolved in water, forming openings (holes) in the cell wall
[0037] The openings in the cell wall provide channels connecting neighboring
air
voids, resulting in an open-celled structure for absorbing sound. This open-
cell
structure can define tortuous (e.g., complex or maze-like) acoustic paths for
sound
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impinging on the set gypsum core, providing an acoustic absorbing structure
having good noise reduction performance. Example acoustic absorbing structures
can operate similarly to Helmholtz resonators.
[0038] Open Cell Set Gypsum Core
[0039] Example open cell set gypsum cores that exhibit acoustic properties
will now
be described. Example set gypsum cores can be provided as a monolithic product
(e.g., as a mold or monolithic core) or incorporated as one or more acoustic
layers
in an acoustic product such as an acoustic panel, including any acoustic
panels
described herein or any other suitable acoustic panel.
[0040] An example set gypsum core includes an interlocking matrix of gypsum
(calcium sulfate dihydrate) and optionally reinforcing fiber. For example, the
interlocking matrix can include a crystalline gypsum matrix; that is, a matrix
of
calcium sulfate dihydrate crystals (also referred to as crystalline hydrated
gypsum).
The crystalline gypsum matrix imparts strength to the set gypsum core.
[0041] Calcined gypsum, also known as stucco or calcium sulfate hemihydrate,
can
be used in a slurry that sets to make the example set gypsum core in example
methods. Any calcined gypsum comprising calcium sulfate hemihydrate or water-
soluble calcium sulfate anhydrite or both can be useful. Synthetic gypsum,
natural
gypsum, or a combination may be used to provide (e.g., form) the calcined
gypsum.
Example synthetic gypsum includes but is not limited to gypsum from sulfide
oxidation such as may be recovered flue gas desulfurization. Natural gypsum
includes but is not limited to gypsum from natural rock or minerals such as
clay,
dolomite, limestone, alabaster, selenite, etc.
[0042] Calcium sulfate hemihydrate produces at least two crystal forms, the
alpha
and beta forms. Beta calcium sulfate hemihydrate is commonly used in gypsum
board panels, but it is also contemplated that layers made of alpha calcium
sulfate
hem ihydrate are also useful for example set gypsum cores. Either or both of
these
forms may be used to create an example set gypsum core. The gypsum in the set
gypsum core in example embodiments can be at least 80% gypsum based on the
weight of the set gypsum core, but greater or smaller percentages of gypsum
may
be used.
[0043] Reinforcing fibers optionally may be provided or included in the
interlocking
matrix, e.g., distributed throughout the matrix. The reinforcing fibers are
non-setting
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components that improve the set gypsum core and enhance the green strength of
the core and/or an acoustic product (e.g., acoustic panel) incorporating the
core.
Example reinforcing fibers such as organic fiber, cellulosic fiber, glass
fiber or
mineral wool fiber may be used. Reinforcing fibers add strength to the set
gypsum
core while minimizing overall weight.
[0044] The interlocking matrix has air voids distributed therein, e.g.,
throughout the
interlocking matrix. Air voids, also referred to as foam voids, are voids
(openings)
disposed throughout the interlocking matrix that result from stable air
bubbles in an
air-foamed slurry that are present when the stucco sets so that the
interlocking
matrix forms around the air bubbles. Figure 1 shows an interior portion of a
core
100 showing example air voids 102.
[0045] The air voids respectively define cells having cell walls formed by the
structure
of the interlocking matrix. For example, the cell walls of each cell can
generally
surround an air void, defining a volume of the air void. Most of the air
bubbles are
generally spherical in shape, resulting in generally spherical air voids
(generally
circular in cross-section), though some of the air bubbles may be partially
compressed, resulting in various ovoid shapes (oval or elliptical in cross-
section).
[0046] Air voids enhance acoustic properties of the set gypsum core by
providing an
increased surface area, defined by the inner cell walls of the air voids, over
which
impinging sound waves that enter the air voids can travel. Additionally, air
voids
reduce the density of the set gypsum core, and thus lower the overall weight
of the
set gypsum core as compared to a set gypsum core lacking air voids.
[0047] The size and/or number of air bubbles in the air-foamed slurry can be
configured, such as by control of an air rate and/or a flow rate of an air
foam,
selection of a foaming agent, etc., to control the air void sizes and/or
proportion of
air voids (e.g., a proportion of volume) in the interlocking matrix. Both the
density
and the acoustic properties of the set gypsum core can be configured by
controlling
the size and/or number of air bubbles. For instance, the size and/or
proportion of
air voids can be controlled to provide a longer and more complex path for
entering
sound waves. Water reducing agents, e.g., dispersants, can also be selected
and
included in the air-foamed slurry to affect density and acoustic properties in
the set
gypsum core.
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[0048] In some example set gypsum cores, the air voids have a distribution of
diameters having a mean (average) of between about 20 microns and about 200
microns. For instance, the mean air void diameter may have a lower bound that
can be any of at least about 20pm, 30pm, 40pm, 50pm, 60pm, 70pm, 80pm, 90pm,
100pm, 110pm, 120pm, 130pm, 140pm, 150pm, 160pm, 170pm, 180pm, or
190pm, in combination with an upper bound that is greater than the lower bound
and at most about 200pm, 190pm, 180pm, 170pm, 160pm, 150pm, 140pm,
130pm, 120pm, 110pm, 100pm, 90pm, 80pm, 70pm, 60pm, 50pm, 40pm, or
30pm. The distribution of air void diameters can be configured such that a
majority
of the air voids have a diameter at or near the mean diameter, though this is
not
required in all embodiments. The air voids collectively may have, in some
embodiments, a volume proportion of from about 60% to about 80% of the overall
volume of the set gypsum core. For instance, the volume proportion may have a
lower bound that can be any of at least about 60%, 62%, 64%, 66%, 68%, 70%,
72%, 74%, 76%, or 78%, in combination with an upper bound that is greater than
the lower bound and at most about 80%, 78%, 76%, 74%, 72%, 70%, 68%, 66%,
64%, or 62%. Proportion of air voids can be determined, for instance, based on
density. The shape, diameter and proportion of air voids can be evaluated, for
example, using a scanning electron microscope (SEM) at a suitable
magnification
(e.g., 40x (Figure 1), 100x, etc.).
[0049] Conventionally, air voids formed in gypsum cores are closed cell, in
that they
are generally not interconnected with one another, but instead they
essentially
completely enclose their respective air voids within the interlocking matrix.
In such
conventional acoustic products, it can be difficult or impossible for external
sound
impinging on a facing surface of the set gypsum core (or acoustic product
incorporating the set gypsum core) to enter the interlocking matrix and thus
enter
most or all of the air voids, or for sound to travel between neighboring air
voids,
without at least an additional perforation step. Other openings that may be
present
within a gypsum matrix, such as water voids, are too small (e.g., 5 microns or
less),
few in number, and/or otherwise insufficient to address the above problems.
[0050] It is known to externally perforate set gypsum cores and/or acoustic
products
to open some of the air voids to facing surfaces and/or to neighboring air
voids,
e.g., along a direction of perforation. For example, pin-hole sized
perforations are
known, and often are combined with positioning a sound-absorbing backing on an
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acoustic layer. However, the holes created by external perforations are
relatively
large and are consistent in their size, orientation, and/or positioning due to
the
perforation methods used (resulting in relatively less complex acoustical
paths),
which negatively affects acoustic absorption. Further, such perforations
require
additional manufacturing steps, and generally are not aesthetically pleasing.
[0051] By contrast, in example embodiments disclosed herein, the interlocking
matrix
further includes channels distributed therein that interconnect the air voids.
For
example, as shown in the core 100 in Figure 1, the channels pass through the
structure of the interlocking matrix include openings 104 that are formed in
the cell
walls of the air voids 102 within the interlocking matrix. For example, a
channel can
include at least a first opening formed in a cell wall of one of the air voids
and a
second opening formed in a cell wall of another one of the air voids, e.g., a
neighboring (adjacent) air void. The channel optionally may include a third
opening
formed in a cell wall of a third air void, a fourth wall formed in a cell wall
of a fifth
air void, etc.
[0052] The channels can be formed within and pass through the structure of the
interlocking matrix, terminating at the cell wall openings. In this way, the
channels
interconnect the air voids to one another. For instance, a channel may define
a
continuous path from a first opening in a cell wall of a first air void,
through the
channel within the interlocking matrix, and to a second opening in a cell wall
of a
second air void. This interconnects the first and second air voids. If the
channel
also terminates at cell wall openings of third, fourth, etc. air voids, the
channel can
interconnect each of these air voids (first, second, third, fourth, etc.).
Individual
channels can define multiple continuous paths. Any combination of neighboring
air
voids can include cell wall openings and be continuously connected via one or
more channels.
[0053] The distribution of such air voids, openings, and channels in various
positions
and orientations throughout the set gypsum core, creates complex, maze-like
open
structures within and throughout the set gypsum core, internally connecting a
large
portion of the air voids to other air voids. These open structures provide
acoustic
paths for sound waves to travel, increasing the acoustic properties of the set
gypsum core. Further, continuous paths (that is, paths not completely broken
by
the interlocking matrix) can be provided between the channels, air voids, and
one
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or more facing surfaces of the set gypsum core. For instance, the air voids,
which
may be generally spherical or ovoid in shape, may be configured to absorb
sound,
and further the channels may define multiple paths for sound to travel among
and
within the air voids, e.g., in a complex distribution.
[0054] The distribution of air voids and interconnecting channels (including
cell wall
openings) can vary. The position and orientation of the interconnecting
channels,
for instance, can be less consistent and more varied (e.g., more complex, more
random, and/or less predictable) than the throughholes made using external
perforation. In some embodiments, this distribution of air voids and
interconnecting
channels may approach a random or pseudorandom distribution. The paths for
sound to travel may be complex paths, for instance providing a generally maze-
like structure, through the interior of the set gypsum core. In some
embodiments,
the defined path(s) may provide or perform similarly to a Helmholtz resonator
or
other acoustic damper.
[0055] As shown by example in Figure 1, a large proportion of the air voids
can be
interconnected to one another by channels having openings in the cell walls of
the
air voids. For example, at least 30% of the air voids may be interconnected to
at
least one other of the air cells by at least one of the channels. For
instance, the
percentage of interconnected air voids may be at least about 30%, 35%, 40%,
45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, or 95%. In some example
embodiments, substantially all (i.e., about 100%) of the air voids may be
interconnected to at least one other of the air cells by at least one of the
channels.
[0056] As another example, at least 30% of the air voids may have at least one
of the
openings of a channel formed on a cell wall. For instance, the percentage of
air
voids having at least opening of a channel may be at least about 30%, 35%,
40%,
45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, or 95%.
In some example
embodiments, the cell walls of substantially all (i.e., about 100%) of the air
cells
may have at least one of the openings of a channel formed therein.
[0057] The acoustic properties of the set gypsum core may be affected by the
relative
size of the openings to those of the air voids. Larger channel openings
relative to
the size of the air voids may provide improved sound travel between the air
voids
and thus within the interlocking matrix, with a possible trade-off of overall
strength
of the set gypsum core. For instance, the channels may include openings in the
air
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voids having a first mean size, e.g., a mean diameter between about 10 microns
and about 50 microns. For instance, the mean channel diameter may have a lower
bound that is at least about 10pm, 15pm, 20pm, 25pm, 30pm, 35pm, 40pm, or
45pm, in combination with an upper bound that is greater than the lower bound
and at most about 50pm, 45pm, 40pm, 35pm, 30pm, or 25pm.The air voids may
have diameters in a first distribution having a second mean size, e.g., a mean
diameter between about 20 microns and about 200 microns. For instance, the
mean air void diameter may have a lower bound that is at least about 20pm,
30pm,
40pm, 50pm, 60pm, 70pm, 80pm, 90pm, 100pm, 110pm, 120pm, 130pm, 140pm,
150pm, 160pm, 170pm, 130pm, or 190pm, in combination with an upper bound
that is greater than the lower bound and at most about 200pm, 190pm, 180pm,
170pm, 160pm, 150pm, 140pm, 130pm, 120pm, 110pm, 100pm, 90pm, 80pm,
70pm, or 60pm , 50pm, 40pm, or 30pm. Alternatively or additionally, the mean
of
the first distribution may be, for instance, at least 25% of the mean of the
second
distribution. For instance, the mean of the first distribution may be a
percentage of
the mean of the second distribution that that is at least about 25%, 30%, 35%,
40%,
45%, or 50%.
[0058] Openings in the cell walls may be generally circular or elliptical in
cross-
sectional shape. For instance, the openings may be generally elliptical in
cross-
sectional shape with an eccentricity less than 0.5. For instance, the
eccentricity of
the openings may have an upper bound that is less than or equal to about 0.5,
0.45, 0.40, 0.35, 0.30, 0.25, 0.20, 0.15, 0.10, or 0.05, with a lower bound of
about
0.00. In some embodiments, openings may be substantially circular in cross-
sectional shape (eccentricity of about 0.00).
[0059] As example embodiments provide air voids and connecting channels that
can
connect the air voids to one another and to a facing surface of the set gypsum
core,
it is not required to externally perforate the set gypsum core to allow
impinging
sound waves to travel within the channels and air voids. Thus, the example set
gypsum core may be free of external perforations, such as those provided by
pin
holes in some conventional acoustic panels. However, if desired, the set
gypsum
core may be additionally perforated.
[0060] Example set gypsum cores can have improved acoustic properties relative
to
conventional acoustic products, and have a relatively low density, while still
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exhibiting sufficient strength. In some embodiments, the set gypsum may have a
density of from about 15 pound-force per cubic feet (pcf) to about 25 pcf, or
greater.
For instance, the density may have a lower bound that is at least about 15
pcf, 16
pcf, 17 pcf, 18 pcf, 19 pcf, 20 pcf, 21 pcf, 22 pcf, 23 pcf, or 24 pcf, in
combination
with an upper bound that is greater than the lower bound and at most about 25
pcf,
24 pcf, 23 pcf, 22 pcf, 21 pcf, 20 pcf, 19 pcf, 18 pcf, 17 pcf, or 16 pcf. The
example
set gypsum core may further have a compressive strength of at least about 50
pounds-force per square inch (psi), and in some examples is at least about 210
psi. For instance, the compressive strength may have a lower bound that is at
least
about 50 psi, 60 psi, 70 psi, 80 psi, 90 psi, 100 psi, 110 psi, 120 psi, 130
psi, 140
psi, 150 psi, 160 psi, 170 psi, 180 psi, 190 psi, 200 psi, 210 psi, 220 psi,
230 psi,
240 psi, or 250 psi, and an upper bound that is greater than the lower bound
and
at most 250 psi, 240 psi, 230 psi, 220 psi, 210 psi, 200 psi, 190 psi, 180
psi, 170
psi, 160 psi, 150 psi, 140 psi, 130 psi, 120 psi, 110 psi, 100 psi, 90 psi, 80
psi, 70
psi, or 60 psi. The example set gypsum core (as a nonlimiting example, a set
gypsum core having a thickness of between about 0.5 inch and about 0.75 inch)
may further have an estimated noise reduction coefficient (e-NRC) of at least
about
0.30, according to ASTM E1050-98, and in some examples is at least about 0.46.
For instance, the e-NRC may have a lower bound that is at least about 0.30,
0.35,
0.40, 0.45, 0.50, 0.55, 0.60, 0.65, 0.70, or 0.75, with an upper bound that is
greater
than the lower bound and at most about 0.75, 0.70, 0.65, 0.60, 0.55, 0.50,
0.45,
0.40, or 0.35.
[0061] The set gypsum core having acoustic properties may be formed from a
composition embodied in an air-foamed stucco slurry. This mixture provides a
precursor for the set gypsum core. Generally, the air-foamed stucco slurry
includes
a stucco slurry, which may be combined with an aqueous foam.
[0062] Stucco Slurry
[0063] Stucco slurry (also referred to as gypsum slurry) may be formed, for
instance,
inside a mixer such as but not limited to a pin or pinless main mixer during a
manufacturing process. However, the mode of introduction of ingredients into
the
mixer may vary. For example, various combinations of components may be pre-
mixed before entering the mixer, e.g., one or more dry ingredients and/or one
or
more wet ingredients may be pre-mixed in any suitable manner prior to entry
into
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the mixer where the stucco slurry is formed as set forth herein. By "added
to," or
"included in" it will be understood that ingredients may be combined with one
or
more other ingredients in any suitable manner within the mixer, prior to
entering
the mixer, subsequent to leaving the mixer, or in any combination of within
the
mixer, prior to entering the mixer, or subsequent to leaving the mixer. A
mixer can
be embodied in one or multiple mixers, and references herein to a mixer can
likewise refer to multiple mixers.
[0064] The stucco slurry includes calcium sulfate hemihydrate (stucco), water,
at
least one uncooked starch, and optionally one or more additional components as
discussed below. Stucco may be added to the stucco slurry in an amount that
is,
as a nonlimiting example, between about 80% and about 90% by weight of the
total
solids in the stucco slurry.
[0065] Optional reinforcing fibers can be added to the stucco slurry in an
amount of
at least about 0.5% by weight of the dry stucco. In some embodiments,
reinforcing
fibers can be added in an amount between about 0.5% and about 5% by weight of
the dry stucco. For instance, the reinforcing fibers may be added to the
stucco
slurry in an amount by weight of the dry stucco having a lower bound that is
at least
about 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, or 5.0%, with an
upper bound that is greater than the lower bound and is at most about 5.0%,
4.5%,
4.0%, 3.5%, 3.0%, 2.5%, 2.0%, 1.5%, or 1.0%. Example materials for stucco and
reinforcing fibers that may be added to the stucco slurry are provided herein.
In
some example stucco slurries, up to 5% glass fiber by weight of the dry stucco
is
added to the stucco slurry to provide the reinforcing fibers.
[0066] The size of the reinforcing fibers may be selected to have a sufficient
length
to improve strength while limiting build up in a mixer during manufacture.
[0067] Example long reinforcing fibers are from about 1/4" in length to about
1 inch,
though it is contemplated that such fibers may be outside of this range. Some
natural fibers, such as cellulose, may be limited in size. They can be
considered
reinforcing fibers if they are longer than average for that fiber type.
[0068] Starches are carbohydrates containing two types of polysaccharides:
linear
amylose and branched amylopectin. Starches generally are known in the art to
be
added to a stucco slurry for binding a resulting gypsum panel core to facing
materials described herein and/or to enhance compressive strength of the final
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product. For instance, since starch contains glucose monomers containing three
hydroxy groups, starch can provide multiple sites for hydrogen bonding to
gypsum
crystals. However, according to example embodiments herein, uncooked starches
are included in the stucco slurry to provide channels interconnecting air
voids in
the set gypsum core.
[0069] Uncooked as used in example compositions and methods herein refers to
the
starches being in granular form. Starches can be classified as either cooked
or
uncooked. Uncooked starches are cold water insoluble and have a semi-
crystalline
structure. Starch granules are semicrystalline, e.g., as seen under polarized
light,
and are insoluble at room temperatures. By contrast, in cooked starches (also
referred to as pregelatinized starches), the starch in placed in water and
heated (or
cooked) so that the crystalline structure of the starch granules melts and
dissolves
in water (gelatinization). Gelatinization can be determined, e.g., by the
disappearance of birefringence under a microscope with a polarized light.
"Uncooked" as used herein means that the starch has a degree of gelatinization
of
less than about 5% (e.g., less than about 3%, or less than about 1%, or about
zero)
before being added into the stucco slurry.
[0070] Some example uncooked starches can be provided, for instance, by wet
milling. Example uncooked starches include cereal starches, root starches, and
tuber starches, such as but not limited to corn starch, wheat starch (e.g., A
type, B
type), pea starch, tapioca starch, or potato starch. Starches may be native
starches, chemically modified (e.g., acid-modified), substituted starches
having
substituted groups, or a combination.
[0071] In some example embodiments, the uncooked starches in the stucco slurry
may have a hot water viscosity between about 20 Brabender Units (BU) and about
300 BU, and/or a mid-range peak viscosity between about 120 BU and about 1000
BU. For instance, uncooked starches may have a hot water viscosity having a
lower
bound that is at least about 20 BU, 30 BU, 40 BU, 50 BU, 60 BU, 70 BU, 80 BU,
90 BU, 100 BU, 110 BU, 120 BU, 130 BU, 140 BU, 150 BU, 160 BU, 170 BU, 180
BU, 190 BU, 200 BU, 210 BU, 220 BU, 230 BU, 240 BU, 250 BU, 260 BU, 270 BU,
280 BU, or 290 BU, with an upper bound that is greater than the lower bound
and
at most about 300 BU, 290 BU, 280 BU, 270 BU, 260 BU, 250 BU, 240 BU, 230
BU, 220 BU, 210 BU, 200 BU, 190 BU, 180 BU, 170 BU, 160 BU, 150 BU, 140 BU,
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or 130 BU, and/or a mid-range peak viscosity with a lower bound that is at
least
about 120 BU, 160 BU, 200 BU, 240 BU, 280 BU, 320 BU, 360 BU, 400 BU, 440
BU, 480 BU, 520 BU, 560 BU, 600 BU, 640 BU, 680 BU, 720 BU, 760 BU, 800 BU,
840 BU, 880 BU, 920 BU, or 960 BU, with an upper bound that is greater than
the
lower bound and at most about 1000 BU, 960 BU, 920 BU, 880 BU, 840 BU, 800
BU, 760 BU, 720 BU, 680 BU, 640 BU, 600 BU, 560 BU, 520 BU, 480 BU, 440 BU,
400 BU, 360 BU, 320 BU, 280 BU, 240 BU, 200 BU, or 160 BU. Examples of such
uncooked starches and example methods for determining hot water viscosity
and/or peak viscosity are disclosed in U.S. Pat. Pub. 2019/0023612, which is
incorporated by reference. Including uncooked starches having hot water and/or
peak viscosities in this range in an example stucco slurry may improve core
strength of the set gypsum core or acoustic product including the acoustic
layer.
Some uncooked starches can natively exhibit such hot water and/or peak
viscosity,
or be provided, for instance, by modifying (e.g., acid-modifying or otherwise
modifying) starches (e.g., native uncooked starches or starches modified in
other
ways), for instance as disclosed in U.S. Pat. Pub. 2019/0023612, including any
combination of such uncooked starches. However, uncooked starches may be
used in example stucco slurries herein that exhibit hot water viscosities
outside of
this example range; e.g., less than about 20 BU or greater than about 300 BU,
and/or midrange peak viscosities less than about 120 BU or greater than about
1000 BU, including in some examples one or more of the uncooked starches
disclosed in U.S. Pat. Pub. 2019/0023612 that have not been modified to fall
within
or otherwise do not fall within this range. Combinations of uncooked starches
within
this hot water viscosity range and/or midrange peak viscosity and beyond such
ranges may also be used in example stucco slurries.
[0072] The uncooked starch granules may be combined in the stucco slurry with
other
starches, including one or more additional uncooked (non-gelatinized) starches
and/or cooked (gelatinized) starches. For instance, additional starch may be
added
to the stucco slurry for use as a binder during hydration of the stucco.
Additionally
or alternatively, a portion of the uncooked starch itself may provide a binder
for the
stucco slurry, while another portion provides channels. Example pregelatinized
starches that may be used for binders are provided in U.S. Pat. App. Pub. No.
2019/0023612, which is incorporated by reference.
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[0073] It is possible that some portion of the starch used in an example air-
foamed
stucco slurry may be cooked when the stucco slurry sets, even though another
portion of the starch will be uncooked and in granular form. As further
described
herein, during manufacture of example set gypsum cores and acoustic products
incorporating set gypsum cores, the uncooked starch in the air-foamed stucco
slurry provided for forming channels will undergo gelatinization after the
gypsum
sets and the interlocking matrix is formed.
[0074] In a stucco slurry according to example embodiments, the uncooked
starch is
in the amount of at least about 4% by weight of the dry stucco. For instance,
the
amount of uncooked starch by weight of the dry stucco may have a lower bound
that is any of at least about 4.0%, 4.5%, 5.0%, 5.5%, 6.0%, 6.5%, 7.0%, 7.5%,
8.0%, 8.5%,
u /0 9.5%, or 10%.
[0075] Properties of the set gypsum core can optionally be modified by the use
of
one or more additives added to the stucco slurry, as in other gypsum precursor
compositions. For example, a set accelerator can be an optional component of
an
example stucco slurry. One such gypsum set accelerator includes 95% calcium
sulfate dihydrate co-ground with 5% sugar and heated to 250 F (121 C) to
caramelize the sugar and can be made according to U.S. Pat. No. 3,573,947,
herein incorporated by reference. Another typical gypsum set accelerator is
calcium sulfate dihydrate freshly ground with sugar or dextrose at a ratio of
about
2.5 to 7.5 pounds of sugar per 100 pounds of calcium sulfate dihydrate and can
be
made according to U.S. Pat. No. 2,078,199, herein incorporated by reference.
The
use of any gypsum set accelerator, or combinations thereof, in appropriate
amounts is contemplated for use in example embodiments.
[0076] Set accelerators may be provided in the stucco slurry in amounts such
as
between about 0.5% and about 4% by weight of the dry stucco.
[0077] Binders may optionally be added to the stucco slurry (in addition to
the
granular uncooked starch described above) to improve the integrity of the
interlocking matrix. Binders may also be provided in some embodiments to
improve
bonding of the acoustic product to an optional facing material_
[0078] Example binders include starches, such as corn or wheat starch, a
latex, such
as polyvinyl acetate, acrylic, or styrene butadiene latexes, or combinations
thereof.
One example useful binder is an acrylic binder that forms a self-linking
acrylic
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emulsion, such as RHOPLEX HA-16, available from Rohm and Haas (Philadelphia,
PA). Acrylic binders are optionally used in amounts of from about 0.5% to
about
5%, and in some examples from about 0.8% to about 1.5%, by weight of the dry
stucco.
[0079] Either migrating or non-migrating starches may be useful. Non-migrating
starches are also applicable by solution directly to a backing layer (e.g.,
paper) to
enhance bonding with the set gypsum core. Starch used for binding in the
stucco
slurry, which can be provided in addition to the uncooked starch disclosed
above,
can be present in amounts of from about 0.5 to about 10 by weight based on the
dry stucco weight. Examples of pregelatinized, non-migrating starches useful
for
an acoustic layer include GemGel Starch (Manildra Group USA, Shawnee Mission,
Kans.) and PCF1000 (Bunge North America, St. Louis, MO). Examples of non-
pregelatinized (uncooked), non-migrating starches include Minstar 2000 and
Clinton 106 Corn Starch, acid-modified corn starch Clinton 260 (from Archer
Daniels Midland Co., Decatur, IL). Examples of migrating starches include Hi-
Bond
Starch and LC-211 starch (both from Archer Daniels Midland Co., Decatur, IL).
[0080] In some examples, binders may be provided in the stucco slurry in
amounts
less than about 4% by dry weight of the stucco, such as between about 0.5% and
about 3% by dry weight of the stucco.
[0081] explained above, it will be appreciated that the granular uncooked
starch
described above may bind the interlocking matrix as well as generate openings
in
the cell walls of air voids in the interlocking matrix as disclosed herein. In
some
example embodiments, the uncooked granular starch may be provided in the
stucco slurry in an amount (e.g., by weight) of at least a 2x multiple of an
amount
used for binding the interlocking matrix, as provided above.
[0082] The stucco slurry may further include a water reducing agent or
dispersant
that enhances the fluidity of the slurry and makes it flowable when less water
is
added. The selection of water reducing agent (dispersant) can affect sound
adsorption performance of the set gypsum core. Naphthalene sulfonates,
polynaphthalene sulfates, melamine compounds, and polycarboxylate ethers
(PCEs) are examples of water reducing agents that may be included in the
slurry,
though other water reducing agents can be used. Example water reducing agents
include PCEs such as Coatex (Arkema) and EthaCryl (Lyondell Chemical Co.,
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Houston, TX), and polynaphthalene sulfates such as DiloFlo GW (GEO Specialty
Chemical, Lafayette, IN).
[0083] Water reducing agents or dispersants may be provided in the stucco
slurry in
amounts such as, as nonlimiting examples, between about 0.01% and about 2%
by dry weight of the stucco. Where the water reducing agent is added in the
form
of a liquid, amounts can be calculated based on the dry solids weight.
[0084] The stucco slurry may optionally include a sagging-resistant agent to
promote
green (wet) strength and/or dimensional stability. Example sagging-resistant
agents may include organic acids. An example sagging-resistant agent is a
trimetaphosphate compound, an ammonium phosphate having 500-3000
repeating units, and a tetrametaphosphate compound, including salts or anionic
portions of any of these compounds. Some example sagging-resistant agents are
disclosed in commonly-owned U.S. Pat. No. 6,342,284. In some embodiments, a
sagging-resistant agent includes sodium trimetaphosphate. The sagging-
resistant
agent can be used in any suitable amount, for example, in a range having a
lower
bound from about 0.004%, 0.01%, or higher, and an upper bound of about 0.3%,
about 0.5%, about 1%, about 2% or lower, by weight based on the dry weight of
the ingredients. Boric acids, tartaric acids and combinations thereof also can
be
used as sagging resistant agents, as is known in the art.
[0085] The stucco slurry may further comprise a retarder. For instance, salts
and
organic compounds are known to modify a set time of a slurry, varying widely
from
accelerating to retarding gypsum hydration. Example retarders include a 1%
solution of pentasodium salt of diethylenetriaminepentaacetic acid (Versanex
TM 80,
commercially available from Dow Chemical Company, Midland, Michigan). Some
example retarders are disclosed in U.S. Pat. Nos. 3,573,947 and 6,409,825.
[0086] The retarder may be added to the stucco slurry, as a nonlimiting
example, in
an amount on a solid basis of about 0.01% to about 0.05% by weight based on
the
dry weight of the stucco.
[0087] Forming the Stucco Slurry
[0088] To form the stucco slurry, dry ingredients may be combined including
calcium
sulfate hem ihydrate (stucco), the uncooked starch, and optionally one or more
additional dry ingredients (such as but not limited to the reinforcing fiber),
examples
of which are disclosed herein, to provide a mixture. Dry ingredients can be
blended,
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e.g., in a mixer such as but not limited to a powder mixer to provide a dry
mixture.
In some example embodiments, dry components other than stucco may be
dispersed over the dry stucco as it moves along a conveyor.
[0089] The dry ingredients may be added in a slurry mixer to water and/or to a
wet
mixture including water and one or more optional liquid ingredients (disclosed
herein) to obtain the stucco slurry. For instance, water may be provided in an
example stucco slurry in a water to solid ratio (by weight) between about 0.60
and
about 1.20). For instance, the water to solid ratio may have a lower bound
that is
at least about 0.60, 0.65, 0.70, 0.75, 0.80, 0.85, 0.90, 0.95, 1.00, 1.05,
1.10, or
1.15, in combination with an upper bound that is greater than the lower bound
and
at most about 1.20, 1.15, 1.10, 1.05, 1.00, 0.95, 0.90, 0.85, 0.80, 0.75,
0.70, or
0.65.
[0090] Sufficient water can be added to make a flowable slurry. It has been
found
that an amount of water used to slurry the stucco is sufficient to gelatinize
the
uncooked starch to form the openings as described herein. However, a greater
amount of water can be used. For example, an amount of water in the stucco
slurry
may be provided that exceeds 20% of the amount needed to hydrate all of the
calcined gypsum to form calcium sulfate dihydrate, so that excess water is
provided
after this hydration. For instance, the excess percentage of water (by weight)
in the
stucco slurry may have a lower bound that is any of at least about 20%, 25%,
30%,
35%, 40%, 45%, or 50%.
[0091] An example water-to-solid ratio for hydrating the calcined gypsum can
be
determined based on the weight of the water compared to the weight of the
total
solids in the formulation. An optimal amount of water may also be determined,
at
least in part, by the type of calcined gypsum that is used. For instance,
alpha-
calcined stucco uses less water to achieve the same flowability as beta-
calcined
stucco. A water to solid ratio in an example stucco slurry ranges from about
0.6:1
to about 1.2:1. If the calcined gypsum is primarily a beta hem ihydrate, the
water to
solid ratio may be, for example, from about 0.7:1 to about 2:1, and in some
examples from about 0.9:1 to 1.5:1.
[0092] In some embodiments, one or more of the dry ingredients (e.g., all or a
portion
of the dry ingredients) can be blended in a mixer, e.g., powder mixer, to
provide a
dry mixture prior to addition to the water or wet mixture. Additional dry
ingredients
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can be added to the dry or wet mixture after mixing of other ingredients such
that
mixing is provided in multiple stages. All or a portion of the liquid
ingredients, if any,
can be added directly to the water or wet mixture before, during, or after
addition
of one or more of the dry ingredients. For example, one or more of the liquid
ingredients can be added to the water to form a wet mixture, which can then be
combined with the dry mixture in the slurry mixer to provide the stucco
slurry. As
another example, water may be combined with the dry mixture, and during or
after
combining with the water, one of more of the liquid ingredients can be added
in the
slurry mixer to provide the stucco slurry.
[0093] The process water can affect the properties of both the slurry and the
set
gypsum matrix. Salts and organic compounds can modify the set time of the
slurry,
varying widely from accelerating to retarding gypsum hydration. Some
impurities
lead to irregularities in the structure as the interlocking matrix of
dihydrate crystals
forms, reducing the strength of the set product. Good quality water without
contamination can be used to improve product strength and consistency.
However,
lower-quality water, such as but not limited to tap water, can also be used.
[0094] Aqueous Foam
[0095] The aqueous foam can be added to the stucco slurry to provide the air-
foamed
stucco slurry before, after, or as the stucco slurry is mixed (e.g., to obtain
a
homogeneous slurry). In some embodiments, an aqueous foam may be
pregenerated by combining a foaming agent with water and air, for instance in
a
foam generator, and then combined with the stucco slurry downstream of the
slurry
mixer, e.g., at a discharge of the slurry mixer. For instance, aqueous foam
can be
added to the stucco slurry as it exits (discharges from) the slurry mixer or
thereafter
to provide fluidity to the mix. In other embodiments, the aqueous foam can be
combined in situ. For instance, the foaming agent can be added to the stucco
slurry
in the slurry mixer, where high shear agitation or mixing generates bubbles.
Example methods for combining stucco slurries with aqueous foam are disclosed
in U.S. Pat. Nos. 5,643,510, 6,494,609, and 7,851,057, each of which is
incorporated by reference herein. Other methods for combining stucco slurries
with
aqueous foam may be used, as will be appreciated by those of ordinary skill in
the
art.
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[0096] The total mixing time for providing the stucco slurry and the air-
foamed slurry
should be sufficient to yield a substantially uniform mixture. However, the
total
mixing time should be less than the set time of the slurry.
[0097] Air bubbles in the aqueous foam promote the formation of air voids in
the set
gypsum matrix to improve the acoustic absorption. Additionally, the air
bubbles
reduce the density of the set gypsum core. Providing a density equal to or
less than
about 25 pcf for the set gypsum core or the acoustic layer of an acoustic
product,
as a nonlimiting example, further provides a sufficient thinness to the cell
walls of
the air cells to allow the uncooked starch to form the channels connecting the
air
cells.
[0098] The aqueous foam can be provided by combining a foaming agent with
water
and air. For instance, the foaming agent, water, and air can be combined in a
high
shear foam mixing apparatus, such as a foam generator. Conventional foaming
agents known to be useful in gypsum products may be added to the aqueous foam.
The foaming agent may be selected so that stable air bubbles (foam cells) are
distributed in the aqueous foam and the air-foamed stucco slurry to form
stable air
voids in the set gypsum core. Any suitable foaming agent for providing stable
air
bubbles may be used. An example foaming agent is a surfactant such as stable
soap, so that a stable soap solution is provided. Other surfactants such as
unstable
soaps can be added to the aqueous foam in addition to the stable soap. Example
foaming agents include alkyl ether sulfates and sodium laureth sulfates, such
as
STEOLO CS-230 (Stepan Chemical, Northfield, IL), foaming agents available
commercially from GEO Specialty Chemicals in Ambler, PA, and others disclosed
in, for example, U.S. Pat. Nos. 4,676,835; 5,158,612; 5,240,639; and
5,643,510,
as well as in PCT Intl. Pub. WO 95/16515 (Jun. 22, 1995).
[0099] The foaming agent is added to the aqueous foam in an amount sufficient
to
obtain the desired density in the set gypsum core. For example, the foaming
agent
may be present in amounts of about 0.003% to about 2.0%, and in some examples
from about 0.005% to about 1.5% by weight, based on the weight of the dry
stucco.
[0100] A foam stabilizer may be added to the air-foamed stucco slurry in a
suitable
amount. Example foam stabilizers are disclosed in U.S. Pat. No. 7,851,057,
which
is incorporated by reference herein.
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[0101] The foaming agent and the water can be combined (e.g., mixed) to
provide a
foaming agent solution in the aqueous foam. For example, an example aqueous
foam can include a foaming agent solution having a foaming agent concentration
of, as a nonlimiting example, between about 0.5% and about 2.5% by weight.
Some
example foaming agent solutions include a 1% soap solution (stable soap,
unstable
soap, or a combination of stable and unstable soap). A combination of stable
soap
and unstable soap, for instance, can be used to control the amount of air
added
and the size of the air bubbles. The water in the foaming agent solution may
be
any suitable water, e.g., filtered water, tap water, etc. In some embodiments,
the
combined water in the air-foamed slurry, including the water from the stucco
slurry
and the additional water in the foaming agent solution, can be provided in a
water
to stucco ratio between about 60% and about 150% by weight. For instance, the
water to stucco ratio (by weight) may have a lower bound that is at least
about
60%, 70%, 80%, 90%, 100%, 110%, 120%, 130%, 01 140%, in combination with
an upper bound that is greater than the lower bound and at most about 150%,
140%, 130%, 120%, 110%, 100%, 90%, 80%, or 70%.
[0102] To provide air-foaming with stable air bubbles, an example aqueous foam
includes a mixture of air and the foaming agent solution, such as but not
limited to
a stable soap solution. The air rate and flow rate can be selected to provide
an
optimal air bubble size and air bubble proportion in the air-foamed stucco
slurry.
The air rate and/or flow rate can be adjusted according to a target core
density, as
will be appreciated by those of ordinary skill in the art. The amount and/or
type of
foaming agent used can affect how much air is incorporated into the set gypsum
core.
[0103] Preparinq a Set Gypsum Core
[0104] The prepared air-foamed slurry can provide a composition that can be
formed
into a gypsum core using a molding or casting process. In an example method,
after the aqueous foam is added to the slurry (or at least a portion thereof)
to
provide (at least a portion of) the air-foamed slurry, the air-foamed slurry
can be
poured between two glassmat facing sheets to make an acoustic product. As
another example, the provided air-foamed slurry can be dispersed, e.g,
discharged, poured, etc., into a mold or otherwise between and/or onto one or
more
surfaces, which may be sized and arranged based on the desired configuration.
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Any suitable molding or casting process known for forming gypsum molds, gypsum
panels, or acoustic products may be used to distribute the air-foamed slurry,
illustrative examples of which are provided herein.
[0105] The dispersed air-foamed stucco slurry is allowed to set (hydrate) to
provide
a set gypsum core including the interlocking matrix of set gypsum. For
instance,
the precursor core can be maintained under conditions that are sufficient for
the
calcined gypsum in the air-foamed stucco slurry to hydrate, curing or
hardening to
form the interlocking matrix of set calcium sulfate dihydrate in the set
gypsum core.
If non-setting reinforcing fibers are included in the air-foamed slurry the
reinforcing
fibers are distributed within the interlocking matrix to strengthen the
matrix.
[0106] The stable air bubbles in the air-foamed slurry form stable air voids
in the set
gypsum core that are distributed within the interlocking matrix. For instance,
when
the calcium sulfate hemihydrate (stucco) sets to form calcium sulfate
dihydrate, air
voids are left behind from the foam after the gypsum is set or interlocking
gypsum
crystals are formed. The air voids also result in a lower density (lighter
weight)
product.
[0107] Additionally, when the stucco has set, all the uncooked starch
granules, which
were mixed in the (liquid) air-foamed slurry, are distributed within the
interlocking
matrix of the set core. These uncooked starch granules are disposed between
the
air voids and within cell walls of the air voids. Without wishing to be bound
or limited
by theory, it is believed that the interlocking matrix, including the cell
walls of the
air voids, forms around the uncooked starch granules. Additionally, and
without
wishing to be bound by theory, the uncooked starch granules are believed to be
disposed in excess water that itself is disposed within the interlocking
matrix.
[0108] The gypsum core, e.g., the set gypsum core, is heated to at least a
gelatinizing
temperature, such that the granules of the uncooked starch gelatinize to
provide
the channels that are distributed within the interlocking matrix and
interconnect the
air voids. The gelatinizing temperature is a temperature sufficient to cause
the
uncooked starch within the interlocking matrix to gelatinize. The gelatinizing
temperature can depend on the uncooked granular starch that is added to the
stucco slurry.
[0109] The temperature for heating the gypsum product, including the set
gypsum
matrix, should be sufficient to heat the granules of the uncooked starch to
the
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gelatinizing temperature, but less than a temperature that results in
calcination of
the hydrated gypsum of the set gypsum matrix back to the calcium sulfate
hem ihydrate or anhydrite form. For example, the gelatinizing temperature for
the
uncooked starch may be at least 170 F. For instance, the gelatinizing
temperature
may have a lower bound that is at least about 170 F, 180 F, 190 F, 200 F, 210
F,
220 F, 230 F, 240 F, 250 F, 260 F, 270 F, 280 F, 290 F, 300 F, 310 F, 320 F,
330 F, 340 F, 350 F, 360 F, 370 F, 380 F, 390 F, 400 F, 410 F, 420 F, 430 F,
440 F, 450 F, 460 F, 470 F, 480 F, 490 F, 500 F, 510 F, 520 F, 530 F, 540 F,
or
550 F.
[0110] As another example, the heating temperature may be at least about 170 F
but
less than or equal to about 550 F, and in some example embodiments the heating
temperature may be between about 350 F and about 450 F. For instance, the
heating temperature may have a lower bound that is at least about 170 F, 180
F,
190 F, 200 F, 210 F, 220 F, 230 F, 240 F, 250 F, 260 F, 270 F, 280 F, 290 F,
300 F, 310 F, 320 F, 330 F, 340 F, 350 F, 360 F, 370 F, 380 F, 390 F, 400 F,
410 F, 420 F, 430 F, 440 F, 450 F, 460 F, 470 F, 480 F, 490 F, 500 F, 510 F,
520 F, 530 F, or 540 F, in combination with an upper bound that is greater
than
the lower bound and at most about 550 F, 540 F, 530 F, 520 F, 510 F, 500 F,
490 F, 480 F, 470 F, 460 F, 450 F, 440 F, 430 F, 420 F, 410 F, 390 F 380 F,
370 F, 360 F, 350 F, 340 F, 330 F, 320 F, 310 F, 300 F, 290 F, 280 F 270 F,
260 F, 250 F, 240 F, 230 F, 220 F, 210 F, 200 F, 190 F, or 180 F.
[0111] Heating may take place in a single stage or in multiple stages, each of
which
may occur at heating temperatures in the ranges disclosed above. If multiple
heating stages are used, an example heating may include a first heating at a
first
heating temperature such as (as a nonlimiting example) between 350 F and 450
F,
and a second heating at a second heating temperature, which optionally may be
a
lower temperature than the first temperature, such as (as a nonlimiting
example)
between 300 F and 400 F The amount of heating time (single stage or multiple
stages) can be determined based on, for instance, the heating temperature, the
size/weight of the set gypsum matrix, and/or the amount of excessive water.
[0112] Without wishing to be bound by theory, it is believed that excess water
from
the slurry (that is, water in excess of that needed for hydration of the
calcium sulfate
hemihydrate to calcium sulfate dihydrate) may be present after the gypsum is
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allowed to set, so that heating the set gypsum matrix to at least the
gelatinization
temperature may cause the gelatinized starch granules to dissolve in the
excess
water, and that the dissolved starch granules migrate into the gypsum matrix.
This
excess water may be driven off by evaporation at the end of drying.
[0113] Set gypsum cores having an open cell structure according to example
embodiments can be embodied in monolithic products such as molds or
sandwiched between two glassmats having desired acoustic properties.
Additionally, example set gypsum cores having an open cell structure can be
embodied in one or more acoustic layers for an acoustic product such as but
not
limited to a gypsum acoustic panel, e.g., acoustic ceiling tile, wall panel,
other
surface panel, etc.
[0114] For example, gypsum acoustic panels may optionally include one or more
facing materials coupled to the acoustic layer to support the acoustic layer
during
manufacture by transferring stresses across the facing material, especially
while
the acoustic panel is wet. Such facing materials can be analogous to face
paper
commonly used in gypsum wallboard manufacture. As used herein, a "front face"
is an outer surface or face of an acoustic layer that is adjacent to the space
where
sound absorption is desired (e.g., it faces the direction of incoming sound to
be
absorbed). Example acoustic layers may include more than one face that can
provide the front face. A "back face" is the outer surface or face that is
opposite the
front face. Because of the open-cell structure of example acoustic layers
disclosed
herein, sound impinging on an outer surface of the acoustic layer can travel
to the
acoustic layer's interior, including the interior air voids, without the need
to
perforate one or more surfaces. Further, as opposed to some conventional
acoustic panels that include perforated surfaces, a sound-absorbing backing
sheet
is not required.
[0115] The facing material can include a front facing material, a back facing
material,
or both. In some embodiments, the back facing material may be a normal
wallboard
paper, such as manila paper or kraft paper, non-woven glass, metallic foil, or
combinations thereof. An example of a non-woven glass facing material is Johns
Manville Dura-Glass Mat Series 5000 (Denver, CO). Where paper is selected as a
back face facing material, multi-ply paper, such as conventional wallboard
paper,
may be useful. The number of plies optionally varies, e.g., from 1-8 plies,
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depending on the paper chosen. For example, at least one backing sheet may
face
an outer surface of the acoustic layer such as the back face. The backing
sheet
may be disposed directly on the acoustic layer, or indirectly, with one or
more
additional layers disposed between the acoustic layer and the backing sheet.
[0116] Another example facing material is a scrim layer. The scrim layer can
be
positioned, for example, on the front face adjacent to the acoustic layer (the
set
gypsum core). A scrim layer can also be provided on the back face. For
example,
the scrim layer may be porous to facilitate attachment of the set gypsum core
and
to facilitate drying. Any suitable material that provides support for the
acoustic layer
and has expansion properties compatible with the facing material (if used) can
be
useful as scrim material. Example embodiments include non-woven fiberglass
scrims, woven fiberglass mats, other synthetic fiber mats such as polyester,
and
combinations thereof.
[0117] Other embodiments can include facing materials that are acoustically
transparent. A non-woven glass or fabric is an example of an acoustically
transparent material useful as front face facing material. The front face
facing
material can be bondable to a gypsum core formed by the slurry using any known
binder. An example facing material is a non-woven glass mat JM 5022 (Johns
Manville, Denver, CO).
[0118] Some example embodiments use a single type of material for both front
and
back facing material. In other example embodiments, a scrim layer and
optionally
one or more additional layers may be provided on the front face and a paper
sheet
and optionally one or more additional layers may be provided on the back face.
[0119] The gypsum acoustic panel may include a densified layer, described in
more
detail below, that has a greater density than the acoustic layer. The
densified layer
can be positioned between the acoustic layer and the backing sheet, and can
include set gypsum.
[0120] Additional example methods for making an acoustic product, such as but
not
limited to an acoustic panel, will now be described. An example method in some
embodiments can be a batch process. In other embodiments the method may be
an individual process.
[0121] In an example method, an air-foamed slurry is prepared for a set gypsum
core
as described above. For instance, or more liquid materials, e.g., dispersant,
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retarder, sagging-resistant materials, etc., may be pre-mixed in a slurry
mixer or
other mixer with water to provide a wet mixture and combined with another
(e.g.,
dry) mixture, e.g., including stucco, uncooked granular starch, and optional
dry
materials such as reinforcing fibers, set accelerators, etc., prepared in, for
instance,
a powder mixer, to provide the stucco slurry. Liquid and dry ingredients can
be
combined in various orders and/or stages. Some materials may be provided as
either liquid or dry ingredients, and such ingredients can be combined
appropriately
with other ingredients.
[0122] The aqueous foam including water, air, and the foaming agent, can be
pregenerated, for instance in a foam generator, and added to the slurry, e.g.,
at the
discharge of the mixer, to provide an air-foamed slurry. The mixing time for
the
stucco slurry and the air-foamed slurry should be sufficient to yield a
uniform slurry,
but less than the set time of the slurry.
[0123] In other example methods, the wet mixture can be mixed with the aqueous
foam (pregenerated or mixed in situ) to form a process solution. The process
solution can then be combined with the dry mixture to provide the air-foamed
slurry.
In both examples, the mixing time to provide the air-foamed slurry should be
sufficient to yield a uniform slurry, but less than the set time of the
slurry.
[0124] A continuous strip of the air-foamed slurry may be formed. For example,
the
wet slurry mixture may be dispersed, e.g., poured, from the mixer containing
the
wet slurry mixture (e.g., a slurry mixer), combined with the aqueous foam to
form
the air-foamed slurry, and the air-foamed slurry may then be spread evenly
onto a
facing material that is positioned to receive the slurry. This continuous
strip forms
the acoustic layer (set gypsum core layer) when set. Additional layers may be
added.
[0125] The facing material can be provided (e.g., formed, sized, etc.) to
provide one
or more facing layers. Example materials for the facing layers include one or
more
sheets such as backing sheets, scrim layers, etc. A nonlimiting example facing
material is glass-mat. The facing material may be disposed (directly or
indirectly)
on any surface to receive the slurry, a nonlimiting example of which being an
upper
surface of a conveyor belt.
[0126] For instance, the facing material, if used, can be positioned on the
conveyor
belt to receive the gypsum slurry. The (air-foamed) gypsum slurry can be
poured
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onto the facing material using a continuous process similar to that used to
make
other gypsum panels. From the slurry mixer, the slurry can be transferred to
the
facing material using a flexible conduit. The gypsum slurry can be made
sufficiently
fluid so that it will spread over the surface of the backing material with
little or no
spreading necessary. If a facing material is applied to another face, it can
be
applied next, for instance while the gypsum slurry is still fluid, sandwiching
the
slurry between the two facing materials. The gypsum core, and any optional
covering materials, if present, can then pass under a forming bar to make the
gypsum core a uniform thickness.
[0127] If an optional densified layer is to be provided, the stucco slurry may
be divided
into a main stream and a slip stream, where the stucco slurry in the slip
stream has
a greater density than that of the main stream, and then both the stucco
slurry in
the main stream and the slip stream can be combined with the aqueous foam. In
some example embodiments, the densified layer may be formed by forming a
continuous strip from (either) slip stream on the facing material. The
acoustic layer
can then be formed on (e.g., over) the facing material, from the main stream.
[0128] The gypsum in the air-foamed slurry material is allowed to set, as
explained
above, to provide an interlocking matrix of set gypsum. As a result of this
setting,
the air bubbles form air voids distributed within the interlocking matrix, and
granules
of the uncooked starch are distributed within the interlocking matrix between
the
air voids and within cell walls of the air voids. If reinforcing fiber is
included in the
dispersed air-foamed slurry, the reinforcing fiber is distributed throughout
the
interlocking matrix.
[0129] When the gypsum core has set sufficiently to achieve desired green
strength
to be easily handled, the gypsum product, e.g., the acoustic panel, can be cut
and
transferred (e.g., using a conveyor) to a heater such as but not limited to a
kiln for
heating and drying. The kiln may optionally include multiple zones to achieve
selected heating and drying conditions. Alternatively, multiple heaters and
dryers
may be used, e.g., in series, with the gypsum product being transferred among
the
multiple heaters/dryers.
[0130] By heating the gypsum product in the heater, the set gypsum matrix is
heated
to at least the gelatinizing temperature so that the granules of the uncooked
starch
gelatinize. As explained herein, the gelatinization of the uncooked starch
granules
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provides channels that are distributed within the interlocking matrix and
interconnect the air voids. To remove additional excess water if needed, the
gypsum product, including the set gypsum matrix, may be dried at a suitable
drying
temperature.
[0131] The gypsum product (e.g., acoustic panel) can be formed (e.g., cut) to
any
desirable size. Sizes can vary as needed. Example areas for the cut panels can
be
m x n, where m is any width between about 4 ft and about 5.4 ft, and n is any
length
between about 8 ft and about 12 ft. A nonlimiting example size for the formed
acoustic panel is about 4 ft x 12 ft. Example thicknesses for the formed
acoustic
panel are between about 0.5 inches and about 1.0 inches. However, these
dimensions (m, n, thickness) can be greater or smaller.
[0132] As mentioned above, it is not necessary to separately (externally)
perforate
the acoustic material (set gypsum core) or the acoustic panel incorporating
the set
gypsum core to obtain good sound absorbency. Thus, perforation of the set
gypsum core and/or one or more facing materials in the acoustic panel is
optional
and can be omitted to reduce the number of steps taken to manufacture the
acoustic product. This reduces time, waste material, and cost. However, if
additional, external perforation is desired, such perforation can optionally
be
performed, e.g., using perforations having depth and spacing similar to those
known to an artisan.
[0133] The resulting gypsum product can be embodied in, for instance, acoustic
ceiling tiles (acoustic ceiling panels) or acoustic gypsum panels (e.g., wall
panels
or other surface panels). Acoustic ceiling panels can be applied to a ceiling
using
methods known to those of ordinary skill in the art. Similarly, acoustic wall
panels
or other acoustic surface panels can be applied to a wall or other surface
using
methods known to those of ordinary skill in the art.
[0134] Example 1
[0135] A foamed gypsum core was made from an air-foamed stucco slurry
according
to the formulation listed in Table 1 below. The water to stucco ratio in the
air-
foamed stucco slurry was 0.85 by weight. The dry ingredients (stucco,
accelerator,
starch, and glass fiber) in Table 1 were mixed and added into the liquid
ingredients
to provide the stucco slurry. The mixture was soaked for five seconds, and
then
mixed at Speed II using a Hobart mixer for twenty seconds.
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[0136] Air bubbles were made in a pregenerated aqueous foam by mixing air and
a
1`)/0 of stable and 1% of unstable soap solution in a foam generator. The air
rate
was 5.0 L/m in, and the flow rate of soap solution was 40 lb/min. The aqueous
foam
was combined with the wet mixture in the Hobart mixer to provide the air-
foamed
stucco slurry.
Table 1 - Foamed Gypsum Core Formulation
Stucco (g) 250
Accelerator (g) 2.5
Uncooked starch (Clinton 260) (g) 15
Glass fiber, 1/2" (g) 4.75
Sodium trimetaphosphate 10% solution (g) 5
Dispersant (Coatex) (g) 0.5
Retarder (Versenex 80) (g) 0.06
Water (g) 163
Foam time (sec) 10
[0137] The air-foamed stucco slurry was poured from the Hobart mixer into a
glass-
mat envelope with a thickness of 3/4 inches (3/4"), and was allowed to set.
The set
gypsum core was heated at 440 F for 12 min, followed by 380 F for 13 min. The
sample heated gypsum core was then dried at 110 F overnight.
[0138] The cross-section of the sample was then examined using scanning
electron
microscopy (SEM). As shown by example in Figure 1, openings (holes) (- 30 pm
diameter) were formed on the cell wall of the air voids.
[0139] The openings on the cell wall of the air voids were demonstrated to
provide
channels between the air voids, changing the closed-cell structure into an
open-
cell structure. The example open-cell structure provided a tortuous or complex
path
between the air voids formed by the air bubbles. The tortuous or complex path
among the open-celled air voids provided improved sound absorption capacity
and
provide a significant improvement of the noise reduction performance of the
gypsum core, as illustrated by the measured e-NRC value in Table 2, below.
[0140] The Noise Reduction Coefficient (NRC) is a measure of sound absorption
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property for a product. For instance, an NRC value of 0.7 means that
approximately
70% of sound was absorbed by the product, while 30% was reflected back into
the
environment. The estimated noise reduction coefficient (e-NRC) of the dried
gypsum core sample was measured using an impedance tube and is a direct
correlator of NRC. e-NRC was measured by ASTM E1050-98, and compressive
strength was measured using an MTS system (Model #SATEC). The load was
applied continuously and without a shock at a speed of 0.04 inch/min (with a
constant rate between 15 to 40 psi/s).
[0141] Results of the measurements are listed in Table 2, below. Without
perforation,
the sample had a good e-NRC of 0.46 at a density of 22.8 pcf. The sample also
had a good compressive strength of 210 psi.
Table 2 ¨ Measurements of Set Gypsum Core
Density (pcf) Compressive strength e-NRC
(psi)
22.8 210 0.46
[0142] Example 2
[0143] To compare the influence of different water reducing agents
(dispersants) on
sound adsorption performance, foamed gypsum cores having either
polycarboxylate ether (PCE) or polynaphthalene sulfate as a dispersant were
made
from an air-foamed stucco slurry according to the formulations listed in Table
3
below and using the method described above in Example 1.
Table 3 - Foamed Gypsum Core Formulation with Different Dispersants
Ingredients Slurry A Slurry B
Stucco (g) 250 250
Accelerator (g) 2.5 2.5
Uncooked starch (Clinton 260) (g) 15 15
Glass fiber, 1/2" (g) 4.75 4.75
Sodium trimetaphosphate 10% 5 5
solution (g)
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Dispersant (g) Polycarboxylate
Polynaphthalene
ether (Coatex) sulfate
(DiloFlo)
0.5 2.5
Retarder (Versenex 80) (g) 0.06 0.06
Water (g) 163 163
Foam time (sec) 10 10
[0144] Results of the measurements are listed in Table 4, below. Changing the
water
reducing agent (dispersant) from polycarboxylate ether to polynaphthalene
sulfate
lowered the e-NRC from 0.50 to 0.36 at a comparable density, demonstrating
that
particular dispersants such as PCE may provide improved acoustic absorption
performance in set gypsum cores and acoustic panels.
Table 4 ¨ Measurements of Set Gypsum Core
Dispersant Density (pcf) e-NRC
Slurry A: 21.8 0.50
Polycarboxylate ether
(Coatex)
Slurry B: 21.90 0.36
PolyNaphthalene sulfate
(DiloFlo)
[0145] Embodiments disclosed herein provide, among other things, open cell set
gypsum cores, set gypsum cores, methods for making set gypsum cores, gypsum
acoustic panels, methods for making acoustic panels, and air-foamed slurries,
as
described herein. Example methods can be used to produce gypsum-based
acoustic tiles, such as but not limited to acoustic ceiling and wall tiles.
[0146] Embodiments disclosed herein provide, among other things, an open cell
set
gypsum core comprising: an interlocking matrix of gypsum, the interlocking
matrix
having air voids distributed therein, the air voids defining cells having cell
walls
formed by the interlocking matrix; the interlocking matrix further having
channels
distributed therein, the channels interconnecting the air voids, the channels
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comprising openings in the cell walls. The core may optionally further include
reinforcing fiber that is distributed throughout the interlocking matrix. In
addition to
any of the above features in this paragraph, at least 30% of the air cells may
be
interconnected to another of the air cells by at least one of the channels. In
addition
to any of the above features in this paragraph, the cell walls of at least 30%
of the
air cells may have at least one of the openings formed therein. In addition to
any
of the above features in this paragraph, the cell walls of substantially all
of the air
cells may have at least one of the openings formed therein. In addition to any
of
the above features in this paragraph, the openings may be generally circular
or
elliptical in cross-sectional shape. In addition to any of the above features
in this
paragraph, the openings may be substantially elliptical in cross-sectional
shape
with an eccentricity less than 0.5. In addition to any of the above features
in this
paragraph, the openings may be generally circular in cross-sectional shape. In
addition to any of the above features in this paragraph, each of the channels
may
terminate in at least one opening in one or more of the cell walls. In
addition to any
of the above features in this paragraph, each of a plurality of the channels
may
comprise a first opening in a first cell wall of a first air void and a second
opening
in a second cell wall of a second air void. In addition to any of the above
features
in this paragraph, at least 30% of the channels may be connected to at least
one
other of the channels via the air voids. In addition to any of the above
features in
this paragraph, the air voids may be configured to absorb sound, and the
channels
may define a path for sound among the air voids. In addition to any of the
above
features in this paragraph, the path for sound may be a generally maze-like
structure. In addition to any of the above features in this paragraph, the
defined
path may provide a Helmholtz resonator. In addition to any of the above
features
in this paragraph, the core may be free of external perforations. In addition
to any
of the above features in this paragraph, the air void volume may be at least
60%
of the core volume. In addition to any of the above features in this
paragraph, the
air voids may have diameters in a first distribution having a mean; wherein
the
channels have diameters in a second distribution having a mean; and wherein
the
mean of the first distribution is at least 25% of the mean of the second
distribution.
In addition to any of the above features in this paragraph, the mean of the
first
distribution may be between about 20 microns and about 200 microns; and the
mean of the second distribution may be between about 10 microns and about 50
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microns. In addition to any of the above features in this paragraph, the mean
of the
first distribution may be between about 20 microns and about 200 microns; and
the
mean of the second distribution may be between about 20 microns and about 50
microns. In addition to any of the above features in this paragraph, the
gypsum
may comprise calcium sulfate dihydrate. In addition to any of the above
features in
this paragraph, the gypsum may comprise synthetic gypsum, natural gypsum, or a
combination of synthetic and natural gypsum. In addition to any of the above
features in this paragraph, the reinforcing fiber, if included, may comprise
glass
fiber. In addition to any of the above features in this paragraph, the
uncooked starch
may comprise an acid-modified starch. In addition to any of the above features
in
this paragraph, the set gypsum core may have a density between about 15 pcf to
about 25 pcf, and an e-NRC of at least about 0.3, according to ASTM E1050-98.
In addition to any of the above features in this paragraph, the set gypsum
core may
have a compressive strength of at least about 100 psi.
[0147] Additional embodiments disclosed herein provide, among other things, a
set
gypsum core, the core being formed from an air-foamed stucco slurry comprising
stucco, at least one uncooked starch and an aqueous foam, the uncooked starch
being in the amount of at least 4% by weight of the dry stucco, the air-foamed
stucco slurry having air bubbles distributed therein; wherein the core is set
to
provide an interlocking matrix of set gypsum, wherein the air bubbles form air
voids
distributed within the interlocking matrix, and wherein granules of the
uncooked
starch are distributed within the interlocking matrix between the air voids
and within
cell walls of the air voids; and wherein the set core is heated to at least a
gelatinizing temperature, wherein the granules of the uncooked starch
gelatinize
to provide channels distributed within the interlocking matrix and
interconnecting
the air voids. In addition to any of the above features in this paragraph, the
gelatinized granules may migrate into the set gypsum matrix when the set core
is
heated to the at least a gelatinizing temperature. In addition to any of the
above
features in this paragraph, the uncooked starch may be in an amount of at
least a
2x multiple of a binding amount of the uncooked starch for the interlocking
matrix.
In addition to any of the above features in this paragraph, the air-foamed
stucco
slurry may comprise: a slurry comprising stucco and at least one uncooked
starch,
the uncooked starch being in the amount of at least 4% or, alternatively, at
least
6% by weight of the dry stucco; the slurry being combined with an aqueous foam
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comprising the foaming agent, water, and air. In addition to any of the above
features in this paragraph, the air-foamed stucco slurry may further comprise
a
reinforcing fiber. In addition to any of the above features in this paragraph,
the
reinforcing fiber may be distributed throughout the interlocking matrix of the
set
gypsum core. In addition to any of the above features in this paragraph, the
stucco
may comprise calcium sulfate hem ihydrate. In addition to any of the above
features
in this paragraph, the stucco may be formed from synthetic gypsum, natural
gypsum, or a combination of synthetic and natural gypsum. In addition to any
of
the above features in this paragraph, the water to stucco ratio
(weight/weight) in
the air-foamed stucco slurry may be between about 70% and about 120%. In
addition to any of the above features in this paragraph, the foaming agent and
the
water may comprise a 1% (weight) solution of the foaming agent. In addition to
any
of the above features in this paragraph, the foaming agent may comprise a
stable
soap. In addition to any of the above features in this paragraph, the slurry
may
further comprise a water reducing agent. In addition to any of the above
features
in this paragraph, the water reducing agent may comprise polycarboxylate ether
(PCE). In addition to any of the above features in this paragraph, the water
reducing
agent may comprise polynaphthalene sulfate. In addition to any of the above
features in this paragraph, the slurry may further comprise a sagging-
resistant
agent. In addition to any of the above features in this paragraph, the sagging-
resistant agent may comprise sodium trimetaphosphate, boric acid and/or
tartaric
acid. In addition to any of the above features in this paragraph, the slurry
may
further comprise a stabilizer.
[0148] Additional embodiments of the invention provide, among other things, a
gypsum acoustic panel, comprising: an acoustic layer comprising an open cell
set
gypsum core, the open cell set gypsum core comprising an interlocking matrix
of
gypsum, the interlocking matrix having air voids distributed therein, the air
voids
defining cells having cell walls formed by the interlocking matrix, the
interlocking
matrix further having channels distributed therein, the channels
interconnecting the
air voids, the channels comprising openings in the cell walls; and at least
one
backing sheet facing an outer surface of the acoustic layer. In addition to
any of
the above features in this paragraph, at least 30% of the air cells may be
interconnected to another of the air cells by at least one of the channels. In
addition
to any of the above features in this paragraph, the cell walls of at least 30%
of the
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air cells may have at least one of the openings formed therein. In addition to
any
of the above features in this paragraph, the cell walls of substantially all
of the air
cells may have at least one of the openings formed therein. In addition to any
of
the above features in this paragraph, the openings may be generally circular
in
cross-sectional shape. In addition to any of the above features in this
paragraph,
the set gypsum core may further comprise reinforcing fiber distributed
throughout
the reinforcing matrix. In addition to any of the above features in this
paragraph,
the gypsum may comprise synthetic gypsum, natural gypsum, or a combination of
synthetic and natural gypsum. In addition to any of the above features in this
paragraph, the gypsum may be synthetic gypsum. In addition to any of the above
features in this paragraph, the gypsum may be natural gypsum. In addition to
any
of the above features in this paragraph, the backing sheet may comprise one or
more of non-woven glass face, metallic foil, paper, a laminate comprising
paper
and a metallic foil, or combinations thereof. In addition to any of the above
features
in this paragraph, the backing sheet may be disposed directly on the acoustic
layer.
In addition to any of the above features in this paragraph, the gypsum
acoustic
panel may further comprise: a densified layer being denser than the open cell
gypsum core, the densified layer being positioned between the acoustic layer
and
the backing sheet, wherein the densified layer comprises an interlocking
matrix of
set gypsum. In addition to any of the above features in this paragraph, the
gypsum
acoustic panel may further comprise: an additional layer disposed between the
densified layer and the backing sheet. In addition to any of the above
features in
this paragraph, the additional layer may comprise one or more of paper, non-
woven
fiberglass, woven fiberglass, synthetic fiber, or a combination.
[0149] Additional embodiments provide, among other things, an air-foamed
slurry for
making an acoustic panel comprising: a slurry formed from a dry mixture
combined
with water, the dry mixture comprising stucco, reinforcing fiber, and at least
one
uncooked starch, the uncooked starch being in the amount of at least 6% by
weight
of the dry stucco; and an aqueous foam comprising a foaming agent, additional
water, and air; wherein the water to stucco ratio in the air-foamed slurry is
between
about 60% and about 120%. In addition to any of the above features in this
paragraph, the water to stucco ratio in the air-foamed slurry may be about
85%. In
addition to any of the above features in this paragraph, the dry mixture may
be
combined with a wet mixture comprising the water. In addition to any of the
above
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features in this paragraph, the wet mixture may further comprise at least one
of a
dispersant, a retarder, a sagging-resistant agent, or a combination. In
addition to
any of the above features in this paragraph, the wet mixture may further
comprise
a dispersant. In addition to any of the above features in this paragraph, the
dispersant comprises polycarboxylate ether (PCE). In addition to any of the
above
features in this paragraph, the reinforcing fiber comprises glass fiber. In
addition to
any of the above features in this paragraph, the stucco comprises calcium
sulfate
hem ihydrate. In addition to any of the above features in this paragraph, the
stucco
may be formed from synthetic gypsum, natural gypsum, or a combination of
synthetic and natural gypsum. In addition to any of the above features in this
paragraph, the aqueous foam may comprise air combined with a solution of a
foaming agent and the additional water. In addition to any of the above
features in
this paragraph, the foaming agent may comprise a stable soap. In addition to
any
of the above features in this paragraph, the foaming agent may further
comprise
an unstable soap.
[0150] Additional embodiments provide a method for making a set gypsum core,
the
method comprising: forming an air-foamed stucco slurry comprising stucco, at
least
one uncooked starch, and an aqueous foam, the uncooked starch being in the
amount of at least 4% by weight of the dry stucco, the air-foamed stucco
slurry
having air bubbles distributed therein; forming a core from the air-foamed
slurry;
allowing the core to set to provide an interlocking matrix of set gypsum,
wherein
the air bubbles form air voids distributed within the interlocking matrix, and
wherein
granules of the uncooked starch are distributed within the interlocking matrix
between the air voids and within cell walls of the air voids; and heating the
set core
to at least a gelatinizing temperature, wherein the granules of the uncooked
starch
gelatinize to provide channels distributed within the interlocking matrix and
interconnecting the air voids. In addition to any of the above features in
this
paragraph, the gelatinized granules may migrate into the set gypsum matrix
when
the set core is heated to the at least a gelatinizing temperature. In addition
to any
of the above features in this paragraph, the uncooked starch may be in an
amount
of at least a 2x multiple of a binding amount of the uncooked starch for the
interlocking matrix. In addition to any of the above features in this
paragraph,
forming the air-foamed stucco slurry may comprise: forming a slurry comprising
the
stucco, the at least one uncooked starch, and water; and combining the formed
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slurry with an aqueous foam comprising foaming agent, additional water, and
air.
In addition to any of the above features in this paragraph, the air-foamed
slurry
may further comprise reinforcing fiber. In addition to any of the above
features in
this paragraph, the stucco may comprise calcium sulfate hemihydrate. In
addition
to any of the above features in this paragraph, the stucco may be formed from
synthetic gypsum, natural gypsum, or a combination of synthetic and natural
gypsum. In addition to any of the above features in this paragraph, the slurry
may
further comprise a reinforcing fiber. In addition to any of the above features
in this
paragraph, the water to stucco ratio in the air-foamed stucco slurry
(weight/weight)
may be between about 70% and about 120%. In addition to any of the above
features in this paragraph, the foaming agent and the water may comprise a 1%
(by weight) foaming agent solution. In addition to any of the above features
in this
paragraph, the foaming agent may comprise a stable soap. In addition to any of
the above features in this paragraph, the method may further comprise: mixing
the
foaming agent, additional water, and air to provide the aqueous foam. In
addition
to any of the above features in this paragraph, the air may be introduced at
an air
rate of 5.0 L/m in. In addition to any of the above features in this
paragraph, the
foaming agent and the water may comprise an about 1% (by weight) foaming agent
solution, and wherein a flow rate of the foaming agent solution may be about
40
lb/min. In addition to any of the above features in this paragraph, the slurry
may
further comprise a sagging-resistant agent. In addition to any of the above
features
in this paragraph, the slurry may further comprise a dispersant. In addition
to any
of the above features in this paragraph, the dispersant may comprise
polycarboxylate ether (PCE). In addition to any of the above features in this
paragraph, the gelatinizing temperature may be at least 170 F. In addition to
any
of the above features in this paragraph, the heating may be at a temperature
of at
least 350 F. In addition to any of the above features in this paragraph, the
heating
may be at a temperature between about 350 F and about 450 F.
[0151] Additional embodiments provide, among other things, a method for making
an
acoustic panel, the method comprising: forming a slurry comprising stucco, at
least
one uncooked starch, and water, the uncooked starch being in the amount of at
least 4% by weight of the dry stucco; adding a foam to the slurry to provide
an air-
foamed slurry, the air-foamed stucco slurry having air bubbles distributed
therein;
forming a continuous strip of the air-foamed slurry; cutting the strip to form
the
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acoustic panel; allowing the gypsum to set to provide an interlocking matrix
of set
gypsum, wherein the air bubbles form air voids distributed within the
interlocking
matrix, and wherein granules of the uncooked starch are distributed within the
interlocking matrix between the air voids and within cell walls of the air
voids; and
heating the set gypsum matrix to at least a gelatinizing temperature, wherein
the
granules of the uncooked starch gelatinize to provide channels distributed
within
the interlocking matrix and interconnecting the air voids. In addition to any
of the
above features in this paragraph, the uncooked starch may be in an amount of
at
least a 2x multiple of a binding amount of the uncooked starch for the
interlocking
matrix. In addition to any of the above features in this paragraph, excess
water
from the slurry may be present after allowing the gypsum to set, wherein
heating
the set gypsum may cause the gelatinized starch granules to dissolve in the
excess
water, wherein the dissolved starch granules migrate into the gypsum matrix.
In
addition to any of the above features in this paragraph, the gelatinizing
temperature
may be at least 170 F. In addition to any of the above features in this
paragraph,
the heating may be at a temperature of at least 350 F. In addition to any of
the
above features in this paragraph, the heating may be at a temperature between
about 350 F and about 450 F. In addition to any of the above features in this
paragraph, the heating may comprise: first heating at a temperature between
400 F and 450 F; and second heating at a temperature between 350 F and 400 F.
In addition to any of the above features in this paragraph, the stucco may be
formed
from synthetic gypsum, natural gypsum, or a combination of synthetic and
natural
gypsum. In addition to any of the above features in this paragraph, the slurry
may
further comprise a reinforcing fiber. In addition to any of the above features
in this
paragraph, the method may further comprise: positioning a scrim layer to
receive
the slurry, wherein the continuous strip of said forming is formed by
distributing the
slurry over the scrim layer. In addition to any of the above features in this
paragraph, the method may further comprise: dividing the slurry into a main
stream
and a slip stream prior to the forming; and making a densified layer from the
slip
stream; wherein the continuous strip of said forming is formed by distributing
the
slurry over the densified layer. In addition to any of the above features in
this
paragraph, the method may further comprise: positioning a backing layer to
receive
the slurry, wherein the continuous strip of said forming is formed by
distributing the
slurry over the backing layer. In addition to any of the above features in
this
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paragraph, the method may further comprise: applying the acoustic panel to a
ceiling. In addition to any of the above features in this paragraph, the
method may
further comprise: applying the acoustic panel to a wall.
[0152] Additional embodiments provide, among other things, a set gypsum core
as
described herein.
[0153] Additional embodiments provide, among other things, a method for making
a
set gypsum core as described herein.
[0154] Additional embodiments provide, among other things, a set gypsum core
made using a method as described herein.
[0155] Additional embodiments provide, among other things, an acoustic panel
as
described herein.
[0156] General
[0157] The foregoing description is merely illustrative in nature and is in no
way
intended to limit the disclosure, its application, or uses. The broad
teachings of the
disclosure may be implemented in a variety of forms. Therefore, while this
disclosure includes particular examples, the true scope of the disclosure
should
not be so limited since other modifications will become apparent upon a study
of
the drawings, the specification, and the following claims. It should be
understood
that one or more steps within a method may be executed in different order (or
concurrently) without altering the principles of the present disclosure.
Further,
although each of the embodiments is described above as having certain
features,
any one or more of those features described with respect to any embodiment of
the disclosure may be implemented in and/or combined with features of any of
the
other embodiments, even if that combination is not explicitly described. It
will be
readily understood that the aspects of the present disclosure, as generally
described herein, and illustrated in the figures, can be arranged,
substituted,
combined, separated, and designed in a wide variety of different
configurations, all
of which are explicitly contemplated herein. In other words, the described
embodiments are not mutually exclusive, and permutations of one or more
embodiments with one another remain within the scope of this disclosure. Other
embodiments may be utilized, and other changes may be made, without departing
from the scope of the subject matter presented herein.
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[0158] Any of the above aspects and embodiments can be combined with any other
aspect or embodiment as disclosed here in the Summary, Figures and/or Detailed
Description sections, except where such combinations would be infeasible as
will
be appreciated by an artisan.
[0159] As used in this specification and the claims, the singular forms "a,"
"an" and
"the" include plural referents unless the context clearly dictates otherwise.
[0160] Unless specifically stated or obvious from context, as used herein, the
term
"or" is understood to be inclusive and covers both "or" and "and."
[0161] Unless specifically stated or obvious from context, as used herein, the
term
"about" is understood as within a range of normal tolerance in the art, for
example
within 2 standard deviations of the mean. About can be understood as within
20%,
19%, 18%, 17%, 16%, 15%, 14%, 13%, 12%, 11%, 10%, 9%, 8%, 7%, 8%, 5%,
4%, 3%, 2%, 1%, 0.5%, 0.1%, 0.05%, or 0.01% of the stated value. Unless
otherwise clear from the context, all numerical values provided herein are
modified
by the term "about."
[0162] Unless specifically stated or obvious from context, as used herein, the
terms
"substantially all", "substantially most of", "substantially all of" or
"majority of"
encompass at least about 90%, 95%, 97%, 98%, 99% or 99.5%, or more of a
referenced amount of a composition.
[0163] The entirety of each patent, patent application, publication and
document
referenced herein hereby is incorporated by reference. Citation of the above
patents, patent applications, publications and documents is not an admission
that
any of the foregoing is pertinent prior art, nor does it constitute any
admission as
to the contents or date of these publications or documents. Incorporation by
reference of these documents, standing alone, should not be construed as an
assertion or admission that any portion of the contents of any document is
considered to be essential material for satisfying any national or regional
statutory
disclosure requirement for patent applications. Notwithstanding, the right is
reserved for relying upon any of such documents, where appropriate, for
providing
material deemed essential to the claimed subject matter by an examining
authority
or court.
[0164] Modifications may be made to the foregoing without departing from the
basic
aspects of the invention. Although the invention has been described in
substantial
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detail with reference to one or more specific embodiments, those of ordinary
skill
in the art will recognize that changes may be made to the embodiments
specifically
disclosed in this application, and yet these modifications and improvements
are
within the scope and spirit of the invention. The invention illustratively
described
herein suitably may be practiced in the absence of any element(s) not
specifically
disclosed herein. Thus, for example, in each instance herein any of the terms
"comprising", "consisting essentially of", and "consisting of" may be replaced
with
either of the other two terms. Thus, the terms and expressions which have been
employed are used as terms of description and not of limitation, equivalents
of the
features shown and described, or portions thereof, are not excluded, and it is
recognized that various modifications are possible within the scope of the
invention. Embodiments of the invention are set forth in the following claims.
[0165] It will be appreciated that variations of the above-disclosed
embodiments and
other features and functions, or alternatives thereof, may be desirably
combined
into many other different systems or applications. Also, various presently
unforeseen or unanticipated alternatives, modifications, variations, or
improvements therein may be subsequently made by those skilled in the art
which
are also intended to be encompassed by the description above and the following
claims.
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