Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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HIGH TEMPERATURE SAG RESISTANT LIGHTWEIGHT GYPSUM BOARD
FIELD OF THE INVENTION
100011 The present invention relates to a high temperature sag
resistant lightweight board.
The addition of urea significantly improves the thermal sag on Type X gypsum
boards.
These gypsum boards may have a board weight of less than 2100 lbs/msf, and may
comprise
glass fibers and/or mineral wool. The present invention also provides methods
of making the
gypsum board and a wall system for employing the gypsum board.
BACKGROUND OF THE INVENTION
100021 In the construction of buildings, one of the more common
building elements for
construction and remodeling is gypsum board, often known as drywall, gypsum
wallboards,
gypsum panels, gypsum paneling, and ceiling tiles. Gypsum (calcium sulfate
dihydrate and
any impurities) suitable for use in wallboard may be obtained from both
natural and synthetic
sources, followed by further processing. In chemical terms, gypsum contains
calcium sulfate
dihydrate (CaSO4=2H20).
100031 Set gypsum is a well-known material that is used in such products.
Panels
containing set gypsum are often referred to as gypsum boards, which contain a
board core
layer (set gypsum core) sandwiched between two cover sheets, particularly
paper cover
sheets. Such panels are commonly used in drywall construction of the interior
walls and
ceilings of buildings. One or more denser regions, often referred to as "skim
coats," may be
included as layers on either face of the board core layer, usually at an
interface (bond surface)
between the board core layer and an inner surface of a cover sheet. The denser
regions may
be contiguous with a less dense region of the gypsum core following setting of
the gypsum.
100041 During manufacture of a gypsum board, stucco (containing
calcium sulfate
hemihydrate and any impurities, also known as calcined gypsum), water, and
other
ingredients as appropriate may be mixed, typically in a mixer to form an
aqueous gypsum
slurry. As used herein, the terms "stucco" and "calcined gypsum" refer to both
the
hemihydrate and anhydrite forms of calcium sulfate that may be contained
therein. The terms
of art aqueous gypsum slurry or aqueous slurry or gypsum slurry are typically
employed for
the slurry both before and after the calcium sulfate hemihydrate converts to
calcium sulfate
dihydrate. The gypsum slurry is formed and discharged from the mixer onto a
moving
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conveyor carrying an optional first cover sheet, optionally bearing a skim
coat. If present, the
skim coat is applied upstream from the location where the gypsum slurry is
discharged onto
the first cover sheet. After applying the gypsum slurry to the first cover
sheet, a second cover
sheet, again optionally bearing a skim coat, is applied onto the gypsum slurry
to form a
sandwich assembly having a desired thickness. A forming plate, roller or the
like may aid in
setting the desired thickness. The gypsum slurry is then allowed to harden by
forming set
(i.e., rehydrated) gypsum through a reaction between the calcined gypsum and
water to form
a matrix of crystalline hydrated gypsum. The desired hydration of the calcined
gypsum
promotes formation of an interlocking matrix of set gypsum crystals, thereby
imparting
strength to the gypsum board. The resulting set gypsum product may then be cut
into
standard lengths as known in the art. Heat may be applied (e.g., using a kiln)
to drive off the
remaining free (i.e., unreacted) water to yield a dry product.
100051 When calcium sulfate dihydrate is heated sufficiently, in a
process called calcining
or calcination, the water of hydration is at least partially driven off and
there can be formed
either calcium sulfate hemihydrate (CaSO4=1/2H20) or calcium sulfate anhydrite
(CaSO4)
depending on the temperature and duration of exposure. Calcination of the
gypsum to
produce the hemihydrate form takes place by the following equation:
CaSO4-2E170¨>CaSO4-0.5H20+1.5H70
[0006] Calcined gypsum is capable of reacting with water to form
calcium sulfate
dihydrate, which is a rigid product and is referred to herein as -set gypsum.-
[0007] Should a finished gypsum product be exposed to relatively
high temperatures,
such as those produced by high temperature flames or gases, portions of the
gypsum may
absorb sufficient heat to start the release of water from the gypsum dihydrate
crystals of the
core. The absorption of heat and release of water from the gypsum dihydrate
may be
sufficient to retard heat transmission through or within the gypsum product
for a time. The
gypsum product can act as a barrier to prevent high temperature from passing
directly
therethrough. The heat absorbed by the gypsum product can be sufficient to
essentially
recalcine portions of the gypsum, depending on the heat source temperatures
and exposure
time. At certain temperature levels, the heat applied to a gypsum product also
may cause
phase changes to the anhydrite of the gypsum and rearrangement of the
crystalline structures.
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In some instances, the presence of salts and impurities may affect the phase
transition
temperatures, resulting in a difference in crystal morphologies
100081 Gypsum panels have been produced that resist the effects of
relatively high
temperatures for a period of time, which may inherently delay passage of high
heat levels
through or between the panels, and into (or through) systems using them.
Gypsum panels
referred to as fire resistant or "fire rated" typically are formulated to
enhance the panels'
ability to delay the passage of heat though wall or ceiling structures and
play an important
role in controlling the spread of fire within buildings. As a result, building
code authorities
and other concerned public and private entities typically set stringent
standards for the fire
resistance performance of fire rated gypsum panels.
100091 The ability of gypsum panels to resist fire and the
associated extreme heat may be
evaluated by carrying out generally accepted tests. Examples of such tests are
routinely used
in the construction industry, such as the procedures described in the
specifications of E119-
20, Standard Test Methods for Fire Tests of Building Construction and
Materials, published
by the American Society for Testing and Materials (ASTM International), West
Conshohocken, PA, 2020. Some of such tests comprise constructing test
assemblies using
gypsum panels, normally a single-layer application of the panels on each face
of a wall frame
formed by wood or steel studs. Depending on the test, the assembly may or may
not be
subjected to load forces. The face of one side of the assembly, such as an
assembly
constructed according to those published by Underwriters Laboratories ("UL")
as UL U305,
U419 and U423, for example, is exposed to increasing temperatures for a period
of time in
accordance with a heating curve, such as those discussed in the ASTM El 19-20
procedures
100101 The temperatures proximate the heated side and the
temperatures at the surface of
the unheated side of the assembly are monitored during the tests to evaluate
the temperatures
experienced by the exposed gypsum panels and the heat transmitted through the
assembly to
the unexposed panels. The tests are terminated upon one or more structural
failures of the
panels and/or when the temperatures on the unexposed side of the assembly
exceed a
predetermined threshold. Typically, these threshold temperatures are based on
the maximum
temperature at any one of such sensors and/or the average of the temperature
sensors on the
unheated side of the assembly.
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100111 Test procedures, such as those set forth in ASTM E119-20,
are directed to an
assembly's resistance to the transmission of heat through the assembly as a
whole. The tests
also provide, in one aspect, a measure of the resistance of the gypsum panels
used in the
assembly to shrinkage in the x-y direction (width and length) as the assembly
is subjected to
high temperature heating. Such tests also provide a measure of the panels'
resistance to losses
in structural integrity that result in opening gaps or spaces between panels
in a wall assembly,
with the resulting passage of high temperatures into the interior cavity of
the assembly. In
another aspect, the tests provide a measure of the gypsum panels' ability to
resist the
transmission of heat through the panels and the assembly. It is believed that
such tests reflect
the specified system's capability for providing building occupants and
firemen/fire control
systems a window of opportunity to address or escape fire conditions.
100121 In the past, various strategies were employed to improve the
fire resistance of fire
rated gypsum panels. For example, thicker, denser panel cores have been
provided which use
more gypsum relative to less dense gypsum panels, and therefore include an
increased
amount of water chemically bound within the gypsum (calcium sulfate
dihydrate), to act as a
heat sink, to reduce panel shrinkage, and to increase the structural stability
and strength of the
panels. Alternatively, various ingredients including glass fiber and other
fibers have been
incorporated into the gypsum core to enhance the gypsum panel's fire
resistance by increasing
the core's tensile strength and by distributing shrinkage stresses throughout
the core matrix.
Similarly, amounts of certain clays, such as those of less than about one
micrometer size, and
colloidal silica or alumina additives, such as those of less than one
micrometer size, have
been used in the past to provide increased fire resistance (and high
temperature shrinkage
resistance) in a gypsum panel core. It has been recognized, however, that
reducing the weight
and/or density of the core of gypsum panels by reducing the amount of gypsum
in the core
will adversely affect the structural integrity of the panels and their
resistance to fire and high
heat conditions.
100131 Another approach, has been to add unexpanded vermiculite
(also referred to as
vermiculite ore) and mineral or glass fibers into the core of gypsum panels.
In such
approaches, the vermiculite is expected to expand under heated conditions to
compensate for
the shrinkage of the gypsum components of the core. The mineral/glass fibers
were believed
to hold portions of the gypsum matrix together. US Patent No. 3,454,456 to
Willey discloses
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distributing unexpanded vermiculite (also referred to as vermiculite ore) of
specified particle
size throughout a core of gypsum wallboard. At least about 0.1%, by weight of
mineral fibers
and boric acid may also be dispersed throughout the core.
[0014] US Patent No. 8,323,785 to Yu et al., incorporated herein by
reference, discloses a
reduced weight, reduced density gypsum panel that includes high expansion
vermiculite with
fire resistance capabilities that are at least comparable to (if not better
than) commercial fire
rated gypsum panels with a much greater gypsum content, weight and density.
[0015] US Patent No. 10,377,108 to Yu et al., incorporated herein
by reference, teaches
that at least one high efficiency heat sink additive, e.g., aluminum
trihydrate is incorporated
into a gypsum product to increase heat resistance. Further, phosphate salt or
other source of
phosphate ions is added to the gypsum slurry used to produce the gypsum
product, e.g., a
panel gypsum core. The use of such phosphates can contribute to providing a
gypsum core
with increased strength, resistance to permanent deformation (e.g., sag
resistance), and
dimensional stability, compared with set gypsum formed from a mixture
containing no
phosphate.
[0016] There is a continuing need to develop gypsum products, e.g.,
at lower weight, that
are less susceptible to the damaging effects of extreme heat.
[0017] The prior art teaches the use of urea resins or urea
complexes in gypsum boards
for various reasons including increasing wall strength (for example EP0585200,
CN108947575, WO 2020/225746, US 10,377,108). Other prior art teaches starch
urea
phosphate for high strength gypsum boards (for example US 9,321,685. Phase
change
materials are used in gypsum boards with urea to provide a self-extinguishing
feature (for
example FR2779715).
[0018] Other prior art teaches applying urea as a coating for a
fire wall (DE
102006018356), or decreasing emissions from the coating (US 2010/0382589).
[0019] It will be appreciated that this background description has
been created by the
inventors to aid the reader, and is neither a reference to prior art nor an
indication that any of
the indicated problems were themselves appreciated in the art. While the
described principles
can, in some regards and embodiments, alleviate the problems inherent in other
systems, it
will be appreciated that the scope of the protected innovation is defined by
the attached
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claims, and not by the ability of the claimed invention to solve any specific
problem noted
herein.
BRIEF SUMMARY OF THE INVENTION
100201 The present invention provides the ability to reduce thermal
sag in lightweight
gypsum boards with the incorporation of 0.03-1 wt. % urea distributed
uniformly throughout
the set gypsum core.
100211 The invention provides a high temperature sag resistant,
ultralight weight gypsum
board containing urea dispersed in its gypsum core. Ultralight weight means a
5/8 inch
gypsum board having a mass of pounds per area less than 2100 lbs/msf,
preferably less than
2000 lbs/msf. For example, a gypsum board having a mass of pounds per area of
500 to less
than 2100 lbs/msf, preferably 500 to less than 2000 lbs/msf ("lbs/msf' means
pounds per
1000 square feet.) The lbs/msf is based on the entire board including the
gypsum core, any
other gypsum layer(s), any cover sheets, and any other layers. The gypsum
boards (including
the gypsum core, any other gypsum layer(s), any cover sheets, and any other
layers) typically
have a thickness of 3/8"-1" (0.95-2.54 cm), more preferably 3/8"- 6/8" (0.95-
1.90 cm),
typically 5/8 inch (1.59 cm) The gypsum board mass of pounds per area lbs/msf
values are
subject to proportional adjustment for thicker or thinner boards. For example,
a half inch
thick board has a mass of pounds per area less than 1680 lbs/msf, rather than
less than 2100
lbs/msf as in the case of the 5/8 thick board. Generally, the gypsum core
layer has a density
of about 40 pounds per cubic foot or less. For example, 15 to 40 pounds per
cubic foot, 20 to
40 pounds per cubic foot, or 30 to 40 pounds per cubic foot.
100221 The invention provides gypsum boards comprising
a gypsum core layer (also referred to as a board core layer) comprising
at least 60 wt. % calcium sulfate dihydrate, preferably at least 70 wt. %, and
more
preferably at least 80 wt. %, typically at least 90 wt. % or at least 95 wt. %
calcium sulfate dihydrate, and
0.03-1 wt. %, preferably 0.05-0.8 wt. %, more preferably 0.06-0.6 wt. %, most
preferably 0.05-0.2 wt. %, for example 0.1-0.2 wt. % or 0.1-0.5 wt. %, urea
distributed uniformly throughout the gypsum core,
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wherein the gypsum core layer has a density of about 40 pounds per cubic foot
or less,
and
wherein the gypsum board has a mass of pounds per area less than 2100 lbs/msf,
wherein the mass of pounds per area lbs/msf values are for a nominally 5/8
inch (1.59 cm)
thick board and subject to proportional adjustment for thicker or thinner
boards.
100231 Preferably the gypsum core layer is effective to provide a
Thermal Insulation
Index (TI) of about 20 minutes or greater, for example greater than 30
minutes.
100241 Preferably the gypsum core layer is effective to provide a
High Temperature
Shrinkage (S) of about 10% or less.
100251 The gypsum core may further comprise additives such as phosphate,
perlite,
starch, fiberglass, and/or vermiculite.
100261 The gypsum board may further comprise a front cover sheet
and a back cover
sheet, wherein the gypsum core layer is disposed between the front cover sheet
and the back
cover sheet. In the alternative one of the front or back cover sheets may be
omitted.
100271 The front cover sheet has an outer surface and an inner surface,
wherein its inner
surface faces a first face of the gypsum core layer. The back cover sheet has
an outer surface
and an inner surface, wherein its inner surface faces a second face of the
gypsum core layer.
Generally the outer surface of the front cover sheet faces outwardly from the
wall once the
gypsum board has been installed on a wall frame. The materials of the cover
sheets may be
independently selected from paper, fiber glass, or mineral wool fiber. The
front and back
cover sheets may be of the same or different material. For example, if both of
the cover
sheets are paper cover sheets, the paper cover sheets may be the same or
different paper
materials. Typically the front and back cover sheets materials are nonwoven
mats.
100281 Optionally, various additives may be present in the board
core layer or a gypsum
slurry used to form the board core layer. Optionally siloxane may be used to
improve water
resistance in the gypsum board. Optionally, the board core layer may further
comprise
vermiculite or other high expansion particles to improve fire resistance in
the gypsum board.
The board core layer may further comprise one or more high-density regions
(skim layers) in
contact with the inner surface of the front cover sheet or the back cover
sheet and coated
thereon. The one or more high-density regions may be in contact with a
relatively lower-
density interior of the board core layer.
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100291 The present invention also provides methods for preparing a
gypsum board which
comprises:
preparing an aqueous slurry comprising a mixture of water, stucco, and urea,
wherein
the stucco comprises calcium sulfate hemihydrate,
wherein the aqueous slurry comprises a mixture of:
at least 60 wt. 1)/0, preferably at least 70 wt. %, more preferably at least
80 wt.
%, typically at least 90 wt. % or typically at least 95 wt. % said calcium
sulfate
hemihydrate on a dry (water free) basis,
0.03-1 wt. %, preferably 0.05-0.8 wt. %, more preferably 0.06-0.6 wt. %, most
preferably 0.05-0.2 wt. %, for example 0.1-0.2 wt. % or 0.1-0.5 wt. %, said
urea on a
dry (water free) basis, and
the water at a weight ratio of water to the calcium sulfate hemihydrate of
0.2:1
to 1.2:1; and
disposing a layer of the aqueous slurry on a surface and setting the calcium
sulfate
hemihydrate to form a set gypsum core layer comprising calcium sulfate
dihydrate and the
urea distributed uniformly throughout the set gypsum core layer; and
cutting the set gypsum core layer into a gypsum board of pre-determined
dimensions;
and
drying the gypsum board;
wherein the set gypsum core layer has a density (D) of about 40 pounds per
cubic foot
or less, and the gypsum board has a mass of pounds per area less than 2100 lb
s/msf, wherein
the lbs/msf values are for a 5/8 inch (1.59 cm) thick gypsum board and subject
to
proportional adjustment for thicker or thinner gypsum boards.
100301 Preferably the set gypsum core layer is effective to provide
a Thermal Insulation
Index (TI) of about 20 minutes or greater, for example greater than 30
minutes.
100311 Preferably the set gypsum core layer is effective to provide
a High Temperature
Shrinkage (S) of about 10% or less.
100321 The deposited aqueous slurry may include calcium sulfate
anhydrite, although it is
preferably used in small amounts of less than 20 wt. % of the dry (water-free)
materials of the
aqueous slurry.
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100331 Typically, the gypsum core and the aqueous gypsum slurry
have less than 10 wt.
%, typically an absence, of Portland cement or other hydraulic cement on a dry
(water-free)
basis. Typically, the gypsum core and the aqueous gypsum slurry has less than
10 wt. %,
more typically an absence, of fly ash on a dry (water-free) basis. Typically,
the gypsum core
and the aqueous gypsum slurry has less than 10 wt. %, more typically an
absence, of calcium
carbonate on a dry (water-free) basis.
100341 The board core layer of the gypsum board resulting from
setting the aqueous
slurry comprises at least 60 wt. % calcium sulfate dihydrate, preferably at
least 70 wt. %, and
more preferably at least 80 wt. %, typically at least 90 wt. % or at least 95
wt. % calcium
sulfate dihydrate, and 0.03-1 wt. %, preferably 0.05-0.8 wt. %, more
preferably 0.06-0.6 wt.
%, most preferably 0.05-0.2 wt. %, for example 0.1-0.2 wt. % or 0.1-0.5 wt. %,
urea
distributed uniformly throughout the gypsum core.
100351 The gypsum boards of the invention may exhibit significant
adhesion between the
board core layer and the back cover sheet even when the gypsum board was
prepared from
gypsum sources having significant quantities of one or more extraneous
chloride salts.
100361 In one or more other aspects of the invention, the invention
provides a wall system
comprising framing to which is attached at least one gypsum board of the
invention, wherein
the outer surface of the front cover sheet faces away from the framing. In the
wall system,
the gypsum board may be on an interior wall or ceiling of a building.
Typically, the framing
is wood or metal. Typically, the at least one gypsum board is attached to the
framing by any
one or more of screws, nails, glue, or other mechanical fasteners.
100371 Advantages of the present invention may become apparent to
those having
ordinary skill in the art from a review of the following detailed description,
taken in
conjunction with the examples, and the appended claims. It should be noted,
however, that
while the invention is susceptible of various forms, the present disclosure is
intended as
illustrative, and is not intended to limit the invention.
100381 For purposes of this disclosure a dry basis is a water-free
basis. For example, a
dry wt. % amount of an ingredient of the aqueous slurry is the wt. % of the
ingredient based
on the dry (water-free) materials of the aqueous slurry.
100391 For purposes of this disclosure all average molecular weights,
percentages and
ratios used herein, are by weight (i.e., wt. %) unless otherwise indicated.
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BRIEF DESCRIPTION OF THE DRAWINGS
[0040] FIG. 1 shows a cross-sectional view of a gypsum board of the
invention, in which
a board core layer (gypsum core) is sandwiched between a front cover sheet and
a back cover
sheet, with the back cover sheet.
[0041] FIG. 2 shows a cross-sectional view of a gypsum board of the
invention, in which
a board core layer (gypsum core) with a skim layer is sandwiched between a
front cover sheet
and a back cover sheet, with the back cover sheet.
[0042] FIG. 3 shows a perspective view of a wall system of the
present invention
including the tile backer panel of the present invention attached to one side
of a metal stud
wall.
[0043] FIG. 4 is a two dimensional image developed from a micro CT-
X-ray scan, as
further discussed below, of a core section of a specimen comprising
vermiculite from a
nominal 5/8 inch thick, about 1880 lbs./msf exemplary panel.
[0044] FIG. 5 shows a process flow diagram of the present method.
[0045] FIG. 6 shows a photograph of a sample with a 2 inch thermal
sag and another
sample with a 13/16 inch thermal sag.
DETAILED DESCRIPTION OF THE INVENTION
[0046] FIG. 1 schematically shows an embodiment of a gypsum board 10 of the
present
invention comprising:
a gypsum core layer 24 (also referred to as a board core layer) comprising
at least 60 wt. % calcium sulfate dihydrate, preferably at least 70 wt. %, and
more
preferably at least 80 wt. %, typically at least 90 wt. % or at least 95 wt. %
calcium sulfate dihydrate, and
0.03-1 wt. %, preferably 0.05-0.8 wt. %, more preferably 0.06-0.6 wt. %, most
preferably 0.05-0.2 wt. %, for example 0.1-0.2 wt. % or 0.1-0.5 wt. %, urea
distributed uniformly throughout the gypsum core,
wherein the gypsum core layer has a density of about 40 pounds per cubic foot
or less,
and
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wherein the gypsum board has a mass of pounds per area less than 2100 lbs/msf,
wherein the lbs/msf values are for a 5/8 inch (1.59 cm) thick gypsum board and
subject to
proportional adjustment for thicker or thinner gypsum boards.
[0047] Preferably the set gypsum core layer is effective to provide
a Thermal Insulation
Index (TI) of about 20 minutes or greater, for example greater than 30
minutes.
[0048] Preferably the set gypsum core layer is effective to provide
a High Temperature
Shrinkage (S) of about 10% or less.
[0049] Thermal Insulation Index (TI) is measured as described in
Example 4D of US
Patent No. 8,323,785 B2 to Yu et al. High Temperature Thermal Insulation Index
testing,
pursuant to the procedures discussed in ASTM Pub. WK25392-Revision of C473-09
Standard Test Methods for Physical Testing of Gypsum Panel Products (herein
after "ASTM
Pub. WK25392-) available from ASTM International, provides a simple,
representative test
of the high temperature thermal insulating characteristics of gypsum panels.
The heat transfer
conditions reflected in this test can be described by the energy equation (1)
for one
dimensional unsteady heat conduction through the board thickness:
A/Ax(k(AT/z1x))-Fq¨pc p(AT/At) (1)
where T is the temperature at a given time t and depth x in the board. The
thermal
conductivity (k), density (p), and specific heat (cp) are nonlinear
temperature dependent
functions at elevated temperatures. The heat generation rate q represents a
variety of
endothermic and exothermic reactions, e.g., gypsum phase changes and face
paper
combustion, which occur at different temperatures and, correspondingly, at
different times.
[0050] For the purpose of evaluating the total heat conduction
through the gypsum board
and, hence its thermal insulating performance, it typically is not necessary
to separately
measure and describe each variable mentioned above. It is sufficient to
evaluate their net
cumulative effect on heat transfer. For that purpose, the simple High
Temperature Thermal
Insulation Index test discussed in ASTM Pub. WK25392 was developed. "High
Temperature
Thermal Insulation Index" as used herein refers to a measure of the thermal
insulation
characteristics of gypsum panels under high temperature testing and sample
conditions
consistent with those described herein. Each test specimen consists of two 4
inch (100 mm)
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diameter disks clamped together by type G bugle head screws. A thermocouple is
placed at
the center of the specimen. The specimen then is mounted on edge in a rack
designed to
insure uniform heating over its surface and placed in a furnace pre-heated to
about 930 F.
(500 C.). The temperature rise at the center of the test specimen is recorded
and a Thermal
Insulation Index, TI, computed as the time, in minutes, required for the test
specimen to heat
from about 105 F. (40 C.) to about 390 F. (200 C.). The Thermal Insulation
Index of the
test specimen is calculated according to equation (2) as:
TI=t 200 C. -t 40 C. (2)
100511 A temperature profile developed from data collected by this
procedure often
shows the transition from gypsum to hemihydrate at about 212 F. (100 C.) and
the
conversion of hemihydrate to the first anhydrite phase near about 285 F. (140
C.). Such
data also often shows that once these phase transitions are completed, the
temperature rises
rapidly in a linear fashion as no further chemical or phase change reactions
of significance
typically occur below the oven temperature of about 930 F. (500 C.). By
waiting until the
specimen's core temperature has reached about 105 F. (40 C.) to begin
timing, acceptable
repeatability and reproducibility may be achieved.
100521 FIG. 1 also shows optional front and back cover sheets on
front and back sides of
the gypsum core layer 24 of the board 10.
100531 Typically the board 10 has a thickness of 3/8
inch to 1 inch (0.9525 to 2.54
cm).
100541 The optional front (top) cover sheet 12 and/or the optional
back (bottom) cover
sheet 30 may be made from any suitable paper material having any suitable
basis weight,
woven or nonwoven glass fiber (fiberglass), woven or nonwoven mineral wool
fiber, or
woven or nonwoven other fibrous materials, or combination of fibrous
materials.
100551 When the back and front cover sheets are made of paper the
paper materials for
each cover sheet may be the same or different. Various paper grades can be
used in gypsum
panels, including Manila grade paper with a smooth calendared finish is often
used as the
facer paper cover sheet, and newsline paper with a rougher finish is often
used as the backer
paper cover sheet. Typically both paper grades are multi-ply with at least one
liner ply and
several filler plies. However, if desired, at least one paper cover sheet or
both paper cover
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sheets may be made of single-ply paper. Newsline is similar to Manila, but it
is thinner
because of its lighter weight.
100561 Optionally, the cover sheets may incorporate and may have
added to their exposed
surfaces, coatings of materials providing surfaces for specific construction
applications such
as exterior sheathing, roofing, tile backing, etc. Thus, they may be uncoated
or, for example,
coated with a polymer coating and/or a hydrophobic finish
100571 The gypsum core layer 24 may also include optional
ingredients, for example,
phosphate such as sodium trimetaphosphate, potassium trimetaphosphate,
ammonium
trimetaphosphate, lithium trimetaphosphate, or any combination thereof.
100581 Gypsum and Stucco (calcined gypsum)
100591 The calcium sulfate hemihydrate (typically provided in the
raw material known as
stucco or calcined gypsum) component used to form the crystalline matrix of
the gypsum
panel core typically comprises beta calcium sulfate hemihydrate, water-soluble
calcium
sulfate anhydrite, alpha calcium sulfate hemihydrate, or mixtures of any or
all of these, and
obtained from natural or synthetic sources. In some aspects, the stucco may
include non-
gypsum minerals, such as minor amounts of clays or other components that are
associated
with the gypsum source or are added during the calcination, processing and/or
delivery of the
stucco to the mixer. Typically the raw gypsum has at least 60 wt. %,
preferably at least 70
wt. %, more preferably at least 80 wt. %, typically at least 90 wt. % or
typically at least 95
wt. % calcium sulfate dihydrate.
100601 Urea
100611 Urea used in the invention has the formula of NH2CONH2. It
may be used in
crystalline form or as an aqueous solution and is present in the gypsum board
at 0.03-1 wt. %,
preferably 0.05-0.8 wt. %, more preferably 0.06-0.6 wt. %, most preferably
0.05-0.2 wt. %,
for example 0.01-0.02 wt. % or 0.01-0.05 wt. %. Urea does not include urea
resins, urea
formaldehyde or urea complexes.
100621 The invention includes urea incorporated into the gypsum
board. The gypsum
board of the invention preferably has an absence of urea resins, urea
formaldehyde and urea
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complexes. The gypsum board of the invention preferably has an absence of urea
applied as
a coating of the gypsum board.
[0063] Gypsum Board With a Skim Layer
[0064] In an embodiment the gypsum board of the invention is a composite
gypsum
board that comprises a gypsum core layer of the invention comprising set
gypsum formed
from at least water, stucco, and urea, as described above, and further
optionally comprises a
skim layer disposed in bonding relation to a first face of the gypsum core
layer. If a first face
of the gypsum core layer is also provided with a first cover sheet then the
skim layer is
between the first face of the gypsum core layer and the first cover sheet.
[0065] FIG. 2 shows a schematic cross-sectional view of an
embodiment of the
composite gypsum board 10 having the set gypsum core 24 comprising calcium
sulfate
dihydrate and urea according to the invention, and further including a skim
layer 18 and the
front (top) cover sheet 12 and the back (bottom) cover sheet 30. The materials
of the cover
sheets 12, 30 are as described above. The front (top) cover sheet 12 has a
first face 14 and a
second face 16. The optional skim layer 18 is in bonding relation to front
(top) cover sheet
12. The skim layer 18 has a first face 20 and a second face 22. The board core
24 has a first
face 26 and a second face 28. The back (bottom) cover sheet 30 has a first
face 32 and a
second face 34.
[0066] FIG. 2 shows the composite gypsum board 10 is arranged such that
face 16 of the
front (top) cover sheet 12 faces the first face 20 of the skim layer 18 and
the second face 22
of the skim layer 18 faces the first face 26 of the core 24. The second face
28 of the core 24
faces the first face 32 of the back cover sheet 30.
[0067] Typically, the skim layer 18 has the same composition as the
core layer 24. Thus,
typically the skim layer has at least 60 wt. % calcium sulfate dihydrate,
preferably at least 70
wt. %, and more preferably at least 80 wt. %, typically at least 90 wt. % or
at least 95 wt. %
calcium sulfate dihydrate, and 0.03-1 wt. %, preferably 0.05-0.8 wt. %, more
preferably 0.06-
0.6 wt. %, most preferably 0.05-0.2 wt. %, for example 0.01-0.02 wt. % or 0.01-
0.05 wt. %,
urea distributed uniformly throughout the skim layer. Typically, the skim
layer has a density
of at least about 1.1 times higher than a density of the gypsum core layer.
The board has an
overall thickness "T" of about 3/8 inch to about 1 inch (0.9525 cm to 2.54
cm). The gypsum
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core layer 24 may have a thickness "T2" of about 3/8 inch to about 1 inch
minus the
thicknesses of any skim layer and/or cover sheet, for example "T2" of about
2/8 inch to about
7/8 inch (0.635 cm to 1.2225 cm), if one or more skim layers and / or cover
sheets are
present. The thickness "T2- of the gypsum core layer 24 is greater than the
thickness "Ti" of
the skim layer 18. Typically, the skim layer has a thickness ("Ti") of from
about 0.02 inches
(about 0.05 cm) to about 0.2 inches (about 0.5 cm). Optionally a second skim
layer (not
shown), of the same or different composition, and the same or different
thickness, as the first
skim layer 18, may be applied to the second face 28 of the core 24. If the
back (bottom) cover
sheet 30 is present then the second skim layer is between the second face 28
of the core 24
and the back (bottom) cover sheet 30.
100681 Another option is to have no first skim layer 18 but have a
skim layer (not shown),
of the same or different composition, and the same or different thickness, as
described above
for the first skim layer 18, that may be applied to the second face 28 of the
core 24. If the
back (bottom) cover sheet 30 is present then this skim layer is between the
second face 28 of
the core 24 and the back (bottom) cover sheet 30.
100691 The higher density gypsum layer (or skim layer) may be
formed at or about the
first cover sheet and/or along the peripheral edges of the cover sheet. The
higher density layer
typically provides beneficial properties to the board surfaces, such as
increased hardness
improved nail pull strength etc. The higher density along the peripheral edges
of the cover
sheet typically provides improved edge hardness and other beneficial
properties. In yet other
embodiments, a higher density layer is applied to either or both cover sheets,
or to the
equivalent portions of the core/cover sheet construction.
100701 Optionally, the core layer and/or skim layer includes an
enhancing additive. The
optional enhancing additive includes a strength-imparting additive, such as
pregelatinized
starches, boric acid, nano-cellulose, micro-cellulose, or any combination
thereof, that helps
produce desired strength properties. The core layer 24 and skim layer 18 may
also include
phosphate such as sodium trimetaphosphate, potassium trimetaphosphate,
ammonium
trimetaphosphate, lithium trimetaphosphate, or any combination thereof.
100711 Siloxanes
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100721 In some embodiments, the water resistance (moisture
resistance) of gypsum
boards formed according to the principles of the present disclosure can be
improved by
adding a polymerizable siloxane, typically in the form of a stable emulsion,
to the slurry used
to make the gypsum boards. Thus, the present invention also relates to making
the gypsum
boards 10 as moisture resistant gypsum based boards, for example, exterior
sheathing,
roofing, tile backer board, gypsum wall boards, or reinforced gypsum composite
boards. The
moisture resistant board has a gypsum core layer (such as gypsum core layer 24
of FIG. 1)
comprising calcium sulfate dihydrate and urea according to the invention.
Preferably a
catalyst which promotes the polymerization of the siloxane is also added to
the aqueous
gypsum slurry. For example, the aqueous gypsum slurry to make the gypsum core
may
include 0.4-1.0 wt. % siloxane and optionally 0.1-0.5 wt. % of a magnesium
oxide catalyst,
preferably dead burned magnesium oxide catalyst or blends of dead burned
magnesium oxide
and fly ash catalyst to enhance the polymerization of the siloxane to form a
highly cross-
linked silicone resin. Siloxane and dead burned magnesium oxide catalyst are
disclosed in
US 7,892,472 to Veeramasuneni et al, which is incorporated herein by
reference. The
aqueous gypsum slurry is then shaped and dried under conditions which promote
the
polymerization of the siloxane to form a highly cross-linked silicone resin.
Such moisture
resistant boards may absorb less than 10 % of its own weight in water when
immersed at 70
F. for two hours in accordance with ASTM Standard 1396 within 24 hours.
100731 In some embodiments, embodiments of the core slurry formulation for
use in
preparing gypsum boards in accordance with principles of the present
disclosure can
comprise a combination of pre-gelatinized starch (or functionally equivalent
starch) in an
amount greater than about 2 by wt. % based on the weight of stucco and
siloxane in an
amount of at least 0.4 % based on the weight of the stucco, which can produce
gypsum panels
with less than about 5% water absorption.
100741 Expansion Particles
100751 In some embodiments, the fire resistance of gypsum boards
formed according to
the principles of the present disclosure can be improved by adding expansion
particles, such
as vermiculite to the aqueous slurry used to make the gypsum boards. Such fire
resistant
gypsum based board, also known as fire rated board, has a gypsum core layer
(such as
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gypsum core layer 24 of FIG. 1) comprising calcium sulfate dihydrate and urea
according to
the invention disposed between two cover sheets plus the expansion particles
in the core. The
gypsum core of the fire rated gypsum panels comprises a crystalline matrix of
set gypsum
and high expansion particles, such as high expansion vermiculite, expandable
at least about
200 %, preferably at least about 300% or more, of their original volume after
being heated for
about one hour at about 1560 F. (about 850 C). Typically the gypsum core 24
comprises
about 5 to about 10 wt. % high expansion particles, preferably high expansion
vermiculite.
100761 The high expansion particles are distributed throughout the
gypsum core 24 in
amounts effective to provide fire resistance in terms of shrinkage resistance
comparable to
commercial Type X gypsum panels and other much heavier and denser gypsum
panels. Such
high expansion particles are disclosed in US Patent 8,323,785 to Yu et al,
which is
incorporated herein by reference.
100771 The gypsum core layer can have a density (D) of about 40
pounds per cubic foot
or less and a core hardness of at least about 11 pounds (5 kg). The gypsum
core can be
effective to provide a Thermal Insulation Index (TI) of about 20 minutes or
greater, for
example greater than 30 minutes.
100781 Preferably the gypsum core layer is effective to provide the
panel with a ratio of
TI/D of about 0.6 minutes/pounds per cubic foot (0.038 minutes/(kg/m3)) or
more, wherein D
is density of the gypsum core and TI is Thermal Insulation Index. Preferably
the panel
satisfies the at least one hour fire-rated panel standards in assemblies UL
U305 and / or UL
U419. Preferably the gypsum core layer and the high expansion particles are
effective to
provide the panel with a High Temperature Shrinkage (S) of about 10% or less.
100791 The fire resistant board optionally has a higher density
gypsum layer (skim layer)
formed at or about the first cover sheet or peripheral edges thereof and/or
the second cover
sheet or peripheral edges thereof. In some embodiments the higher density
layer comprise
about 3% to about 4 % of the board weight.
100801 Typical methods for making fire resistant gypsum boards are
described in US
Patent No. 8,323,785 to Yu et al. herein incorporated by reference.
100811 As mentioned in US Patent No. 8,323,785 to Yu et al, Example
4B, a test for
measuring "High Temperature Shrinkage" (S) was developed and reported in ASTM
Pub.
WK25392 , to provide a quantitative measure of the shrinkage characteristics
of gypsum
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panels under high temperature conditions. This test procedure reflects the
fact that the High
Temperature Shrinkage that gypsum panels may experience under fire conditions
is
influenced by factors in addition to calcining reactions that may occur in the
panel gypsum
cores under high temperature conditions. The test protocol, accordingly, uses
an unvented
furnace so that there is no airflow from outside of the furnace that might
cool the test
specimens. The furnace temperature also is about 1560 F. (850 C.) to account
for the
shrinkage that may occur in the anhydrite phases of the gypsum core
structures, as well as
calcining and other high temperature effects, when exposed to the high
temperatures fire
conditions. The test specimens are about 4 inches (100 mm) diameter disks cut
from gypsum
board samples using a drill press with a hole saw blade. Six specimens are
typically
employed for each test. The specimens are placed in the furnace side by side
without
touching each other, Test specimens were placed on small pedestals to allow
them to heat and
vent uniformly on both faces so that they remained relatively flat,
cylindrical disks.
100821 In order to prevent thermal shock to the test specimens,
which might produce
invalid test results due to spalling and breakage, the test protocol was
modified to place the
test specimens in the furnace before it was heated to about 1560 F. (850
C.). The specimens
were held at that temperature for a minimum of about 20 minutes before the
furnace was shut
off The furnace door remained closed while the furnace cooled. The specimens
were not
removed for measurement until after the temperature had dropped to near room
temperature.
100831 As gypsum board is anisotropic, the amount of shrinkage will vary
slightly in the
length and width directions. Therefore, two orthogonal measurements were taken
and
averaged to compute the mean diameter of the disk. In these tests, two
measurements at 90
degrees to each other were taken as it has been found that this approach
provides a consistent
mean diameter measurement from specimen to specimen. It has been found that
the
orientation of the specimens in terms of "machine direction" and "cross
machine direction" is
not a significant concern for the purposes of this test. Typically, if the two
measurements for
a disk differed by more than 0.01 inches (0.25 mm), then the disk was rejected
and the
measurements excluded from the reported results. High Temperature Shrinkage
was
calculated as the percent change in mean diameter after heat exposure, and
denoted "S,"
typically to the nearest 0.1% for the group of six test specimens.
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100841 The amount of x, y (width, height) High Temperature
Shrinkage is calculated as
the percent change in mean diameter after heat exposure, and denoted "S".
"High
Temperature Shrinkage" as used herein refers to a measure of the shrinkage
characteristics of
gypsum panels under high temperature testing and sample conditions consistent
with those
described in ASTM Pub. WK25392 and US Patent No. 8,323,785 to Yu et al,
Example 4B.
ASTM Pub. WK25392 is incorporated herein.
100851 The expansion particles can have a first unexpanded phase
and a second expanded
phase when heated. This can provide fire performance. Such industry standard
fire tests
include, without limitation, those set forth in the procedures and
specifications of UL U305,
U419 and U423 full scale fire tests and fire tests that are equivalent to
those. In other
embodiments, reduced weight and density gypsum panels formed according to
principles of
the present disclosure, and the methods for making same, can provide a shrink
resistance of
greater than about 85% in the x-y directions at temperatures of in excess of
about 1800 F.
(980 C).
100861 An embodiment of the fire rated board of the invention has a
set gypsum core
layer that has a density of from about 30 pounds per cubic foot (pcf) to about
40 pcf, and
comprises set gypsum in an amount from about 1150 lbs/msf to about 1600
lbs/msf, wherein
the lbs/msf values are for a 5/8 inch (1.59 cm) thick gypsum board and subject
to
proportional adjustment for thicker or thinner gypsum core layers, wherein the
set gypsum
comprises calcium sulfate dihydrate, and
wherein the set gypsum core layer comprises:
at least 60 wt. % said calcium sulfate dihydrate, preferably at least 70 wt.
%, and more
preferably at least 80 wt. %, typically at least 90 wt. % or at least 95 wt. %
calcium sulfate
dihydrate,
0.03-1 wt. %, preferably 0.05-0.8 wt. %, more preferably 0.06-0.6 wt. %, most
preferably 0.05-0.2 wt. %, for example 0.01-0.02 wt. % or 0.01-0.05 wt. %,
urea,
about 2 to about 10 wt.%, for example about 2 to about 5 wt. %, high expansion
vermiculite having a volume expansion of about 200% or more of their original
volume after
being heated for about one hour at about 1560 F., and
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0.1 to about 1.0 wt.%, for example about 0.1 to about 0.3 wt.% or about 0.3 to
about
0.9 wt.% glass fiber, or
0.5 to about 10 wt. %, for example about 0.8 to about 3.0 wt% or about 1.0 to
about
2.0 wt.% mineral wool, and
0 to about 3 wt.%, for example about 0.3 to about 3 wt.%, starch, and
0 to about 0.4 wt.%, for example about 0.03 to about 0.4 wt.% or about 0.10 to
about
0.15 wt.%, phosphate,
0 to about 1.0 wt. %, for example about 0.1 to about 1.0 wt. % dispersant.
100871 Preferably the set gypsum core layer is effective to provide
a Thermal Insulation
Index (TI) of about 20 minutes or greater, for example greater than 30
minutes.
100881 Preferably the set gypsum core layer is effective to provide
a High Temperature
Shrinkage (S) of about 10% or less.
100891 Assemblies made using the 5/8 inch (1.59 cm) thick fire
rated gypsum panels
formed of the present disclosure can provide fire resistance when tested in
assemblies UL
U305, U419 and U423 in accordance with the fire test procedures of ASTM E119-
20. The
fire resistance of fire rated gypsum panels of the present disclosure can be
reflected by the
maximum single sensor temperature or the average sensor temperature on the
unexposed
surface of such assemblies made pursuant to such fire test procedures (and
equivalent fire test
procedures). Assemblies made using panels formed according to principles of
the present
disclosure and tested in assemblies UL U419 may provide:
a maximum single sensor temperature of less than about 500 F. (260 C) and/or
an
average sensor temperature of less than about 380 F. (195 C) at about 60
minutes elapsed
time;
a maximum single sensor temperature of less than about 260 F. and/or an
average
sensor temperature of less than about 250 F. at about 50 minutes elapsed
time; a maximum
single sensor temperature of less than about 410 F. and/or an average sensor
temperature of
less than about 320 F. at about 55 minutes;
a maximum single sensor temperature of less than about 300 F. and/or an
average
sensor temperature of less than about 280 F. at about 55 minutes elapsed
time' and/ or
a maximum single sensor temperature of less than about 415 F. and/or an
average
sensor temperature of less than about 320 F. at about 60 minutes elapsed
time.
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100901 In certain of such embodiments, gypsum panels formed
according to principles of
the present disclosure can have a core with a density of less than about 40
pcf that satisfies
the requirements for a 60 minute fire rated gypsum panel under one or more of
the UL U305,
U419 and U423 assemblies tested in accordance with ASTM E119-20 and other fire
test
procedures that are equivalent to any one of those.
100911 The high expansion particulates are typically in the form of
vermiculite with a
high volume of expansion relative to conventional, relatively low expansion
vermiculite, such
as that referred to as "Grade No. 5" unexpanded vermiculite (U.S. grading
system) (with a
typical particle size of less than about 0.0157 inches (0.40 mm)) and other
low expansion
vermiculites which have been used in commercial fire rated gypsum panels.
100921 The vermiculites also referred to herein have a volume
expansion after heating for
one hour at about 1560 F. (about 850 C.) of about 200% or more, preferably
about 300% or
more, of their original volume. For example, Grade No. 5 unexpanded
vermiculite typically
has a volume expansion at about 1560 F. (about 850 C.) of about 225%. Other
particulates
with properties comparable to high expansion vermiculite also may be utilized
in
embodiments of panels formed according to principles of the present
disclosure, as well. In
some embodiments, high expansion vermiculites can be used that have a volume
expansion
of about 300% to about 380% of their original volume after being placed for
one hour in a
chamber having a temperature of about 1560 F (about 850 C).
100931 Another suitable vermiculite is often referred to as Grade No. 4
unexpanded
vermiculite (U.S. grading system) (such high expansion vermiculites were
rejected as a useful
ingredient in fire rated gypsum wallboard in U.S. Pat. No. 3,454,456 discussed
above). In
some embodiments, at least about 50% of the particles in the high expansion
vermiculite used
in panels formed according to principles of the present disclosure will be
larger than about 50
mesh (i.e. greater than about 0.0117 inch (0.297 mm) openings). In other
embodiments, at
least about 70% of the particles will be larger than about 70 mesh (i.e.
larger than about
0.0083 inch (0.210 mm) openings).
100941 In other embodiments, vermiculites can be used that are
classified under different
and/or foreign grading systems. Such vermiculites should have substantially
similar
expansion and/or thermal resistance characteristics typical of those discussed
herein. For
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example, in some embodiments, a vermiculite classified as European, South
American, or
South African Grade 0 (micron) or Grade 1 (superfine) can be used.
[0095] TABLE 1 lists typical particle distributions A, B or C
suitable for high expansion
vermiculite in embodiments of the present invention.
TABLE 1 (all % are wt. %)
Particle Size A
less than about 500 up to about 50% between about 25% between
about 5% and
micrometers and about 45% about 20%
between about 500 and up to about 60% about 40% to 60% about 35% to about 60%
about 1000
between about 1000 and up to about 40% up to about 20% about 20% to
about 40%
about 1500 micrometers
between about 1500 and up to about 20% up to about 10% up to about
20%
about 3000 micrometers
[0096] Systems
[0097] It will be understood that gypsum boards in accordance with some
embodiments
can be constructed and used in an assembly as will be understood in the art.
Generally, as will
be understood, the composite boards can be affixed in any suitable arrangement
to studs
formed of any suitable material such as wood, metal or the like. The top or
face cover sheet
of the board faces out and is generally decorated (e.g., with paint, texture,
wallpaper, tile,
etc.) in use while the bottom or back cover sheet faces the studs. A cavity is
normally present
behind the stud, facing the back paper, in use. If desired, insulation
material as known in the
art optionally can be placed in the cavity. In one embodiment, the assembly
comprises two
composite boards connected by studs with a cavity there between, facing the
bottom cover
sheets of the respective boards.
[0098] FIG. 3 is a perspective view of a typical wall system 40 that may
employed
gypsum wallboard made from the treated gypsum. FIG. 3 shows the gypsum board
10 of the
present invention attached to one side of a metal stud wall with a metal stud
wall "skeleton"
42 which includes a plurality of metal studs 43, an upper track 44, and a
lower track 45. The
gypsum board 10 may be secured in any known manner to one or both sides of the
metal
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studs 43 to close the wall and form the wall surface. A typical metal stud
wall "skeleton"
may be fabricated according to U.S. Patent No. 6,694,695 to Collins et al.,
incorporated
herein by reference, which is suitable for combination with an exterior
sheathing panel to
achieve an exterior wall system of the present invention. This metal stud wall
"skeleton"
system is merely provided as illustrative as other framing systems may also be
employed,
such as wood framing.
100991 In the system the gypsum panels are typically attached to
the framing by any one
or more of screws, nails, or glue. Also, in the system the gypsum panel
typically has no
perforations except for perforations made by the screws or nails.
1001001 Methods for Manufacturing Gypsum Board
1001011 Various methods can be employed for preparing a gypsum board of the
present
invention from an aqueous gypsum slurry comprising calcium sulfate hemihydrate
and urea.
1001021 The base material from which gypsum wallboard and other gypsum
products are
manufactured is the hemihydrate form of calcium sulfate (CaSO4-1/2H20),
commonly termed
"calcined gypsum" or "stucco," which is produced by heat conversion
(calcination) of the
dihydrate form of calcium sulfate (CaSO4).
1001031 The present invention covers methods making a gypsum board,
comprising:
preparing an aqueous slurry comprising a mixture of water, stucco, and urea,
wherein
the stucco comprises calcium sulfate hemihydrate,
wherein the aqueous slurry comprises a mixture of:
at least 60 wt. %, preferably at least 70 wt. %, more preferably at least 80
wt.
%, typically at least 90 wt. % or typically at least 95 wt. % said calcium
sulfate
hemihydrate on a dry (water free) basis,
0.03-1 wt. %, preferably 0.05-0.8 wt. %, more preferably 0.06-0.6 wt. %, most
preferably 0.05-0.2 wt. %, for example 0.1-0.2 wt. % or 0.1-0.5 wt. %, said
urea on a
dry (water free) basis, and
the water at a weight ratio of water to the calcium sulfate hemihydrate of
0.2:1
to 1.2:1; and
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disposing a layer of the aqueous slurry on a surface and setting the calcium
sulfate
hemihydrate to form a set gypsum core layer comprising calcium sulfate di
hydrate and the
urea distributed uniformly throughout the set gypsum core layer; and
cutting the set gypsum core layer into a gypsum board of pre-determined
dimensions;
and
drying the gypsum board;
wherein the set gypsum core layer has a density (D) of about 40 pounds per
cubic foot
or less, and the set gypsum core layer has a mass of pounds per area less than
2100 lbs/msf,
wherein the lbs/msf values are for a 5/8 inch (1.59 cm) thick panel and
subject to proportional
adjustment for thicker or thinner panels.
1001041 Preferably the set gypsum core layer is effective to provide a Thermal
Insulation
Index (TI) of about 20 minutes or greater, for example 30 minutes or greater.
1001051 Preferably the set gypsum core layer is effective to provide a High
Temperature
Shrinkage (S) of about 10% or less.
1001061 The present invention encompasses methods for making a gypsum board,
comprising:
preparing an aqueous slurry comprising a mixture of water and stucco, wherein
the stucco comprises calcium sulfate hemihydrate, and the aqueous slurry
comprises a
mixture of:
at least 60 weight percent said calcium sulfate hemihydrate on a dry basis,
0.03-1 weight percent urea on a dry basis,
optionally about 500 ppm to about 3000 ppm chloride anions per 1,000,000
parts by weight (pbw) said calcium sulfate hemihydrate, and
the water at a weight ratio of water to the calcium sulfate hemihydrate of
0.2:1
to 1.2:1, and
disposing the aqueous slurry between a front paper cover sheet and a back
paper cover
sheet, each paper cover sheet having an inner surface and an outer surface,
and the aqueous
slurry contacts the inner surfaces of the front paper cover sheet and the back
paper cover
sheet;
setting the calcium sulfate hemihydrate to form a panel comprising a board
core layer
comprising calcium sulfate dihydrate; and
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drying the panel and cutting the panel into a gypsum board having one or more
pre-
determined dimensions.
1001071 The term about 500 ppm to about 3000 ppm chloride anions per 1,000,000
parts
by weight (pbw) said calcium sulfate hemihydrate means about 500 parts by
weight to about
3000 parts by weight chloride anions per 1,000,000 parts by weight (pbw) said
calcium
sulfate hemihydrate. The present invention encompasses a gypsum core layer
that has at least
one of a thermal sag of less than 1 inch as measured according to the thermal
sag test in
examples of the present specification, a density of about 40 pounds per cubic
foot or less, and
a mass of pounds per area less than 2100 lbs/msf, wherein the mass of pounds
per area
lbs/msf values are for a 5/8 inch (1.59 cm) thick board and subject to
proportional adjustment
for thicker or thinner boards.
1001081 Illustrative manufacturing techniques and equipment suitable for
forming gypsum
board according to the present invention can be found, for example, in U.S.
Patent 7,364,676
and U.S. Patent Application Publication 2010/0247937, each of which is
incorporated herein
by reference in its entirety. Briefly, such processes may optionally involve
discharging a
cover sheet onto a moving conveyor. Since gypsum board is normally formed
"face down,"
this cover sheet corresponds to facer cover sheet 12 upon completion of the
fabrication
process. The gypsum slurry can be made with any suitable water/calcium sulfate
hemihydrate ratio for disposition onto the cover sheet.
1001091 FIG. 5 illustrates an example of a wet end 80 (upstream portion) of a
manufacturing production line for producing a layered gypsum board of the
present invention
having a gypsum layer optionally between two cover sheets. The cover sheets
are, for
example, made of paper, for example manila paper or kraft paper, non-woven
glass scrims,
woven glass mats, other synthetic fiber mats such as polyester, metallic foil
such as
aluminum, and the like, and combinations thereof.
1001101 The wet end 80 includes a gypsum slurry mixing and dispensing assembly
82 and
a forming station 86. A first moving and web 90 of first cover sheet material
which moves in
a longitudinal direction of travel "T" along the forming table 92. The gypsum
core slurry 94
is mixed in the gypsum slurry mixing and dispensing assembly 82 where
additives and
optional foaming of the slurry occurs. While the gypsum slurry mixing and
dispensing
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assembly 82 is illustrated as a single component of the wet end 80, there can
be multiple
components that comprise the gypsum slurry mixing and dispensing assembly 82.
1001111 A first gypsum skim layer slurry 70 may be applied to the first cover
sheet
material 90 to form a gypsum skim layer on the first cover sheet material 90,
and passes
under a first gypsum skim coat roller 72, before depositing the gypsum core
slurry 94. The
gypsum skim layer is relatively denser than the gypsum core slurry which may
be a foamed
gypsum slurry. As is known in the art, the skim layer can be achieved by
directing a portion
of the slurry out of the mixer and into a skim layer mixer prior to
introduction of foam or by
beating foam out of the slurry. Thus, the gypsum core slurry 94 for the gypsum
core layer of
the board is deposited onto either the first moving web 90 (e.g., to form the
gypsum core) or
the gypsum skim layer slurry 70, if applied. In a preferred embodiment of the
invention, such
as for gypsum wallboard or acoustical panel production, including but not
limited to ceiling
tile, wall panel, and partitions for office cubicles, the slurry for forming
the core of the board
is deposited onto a densified layer (i.e., a skim coat layer) of aqueous
slurry carried by the
backing layer, as described, for example, in U.S. Pat. Nos. 4,327,146 and
5,718,797, each of
which is incorporated by reference herein.
1001121 As is also known in the art, a second skim layer can optionally be
applied on top
of the core slurry, particularly in embodiments where a cover layer is
employed such as with
gypsum drywall. The skim layer(s) can have any suitable thickness, such as,
for example,
from about 0.0625 inch to about 0.125 inch.
1001131 A second moving web 96 of cover sheet material (namely the material
for the
above-described rear facing 6 which may be uncoated or coated with a pre-
applied polymer
coating and a hydrophobic finish) is applied to the gypsum slurry 94, or
applied to the second
skim lay slurry 76 if present as described below, and passed through the
forming station 86 to
compress the layers into a desired total thickness (e.g., about 0.25 inches to
about 1.0 inches
thick, preferably 0.25 inches to about 0.625 inches thick). The resultant
structure is a gypsum
board preform 98.
1001141 Typically the outer surface of the applied moving web 96 is in contact
with no
additional layers.
1001151 Additional components can be included in the wet end 80 of the
manufacturing
line. For example, a calcined gypsum slurry 76 for forming a second skim layer
may be
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applied to the layer of deposited gypsum core slurry 94, and then passes under
a second
gypsum skim coat roller 74. The first and second gypsum skim layers will
typically be
thinner and denser than the gypsum core layer. Typically the calcined gypsum
(calcium
sulfate hemihydrate) slurry for the gypsum core layer is foamed to be less
dense than the
slurry 70 of the first skim layer, as well as less dense than the slurry 76 of
the second skim
layer. Thus if desired, calcined gypsum core slurry stream 94 may pass through
a former
device (not shown), which for instance mixes the calcined gypsum core slurry
stream 94 with
foam and/or air, prior to deposition on the first coated nonwoven glass fiber
cover sheet
material 90. Typically the slurry streams for the gypsum skim layers 70, 76
have the same
composition and density. However if desired, the slurry streams for the gypsum
skim layers
70, 76 can have different compositions and/or densities. FIG. 5 shows both
gypsum slurries
70, 76, 94 coming from the same calcined gypsum slurry mixing and dispensing
assembly 82.
However, the calcined gypsum slurries 70, 76, 94 can come from different
mixing and
dispensing assemblies to have different properties, such as different
densities.
[00116] The first gypsum skim coat roller 72, the second gypsum skim coat
roller 74, the
forming table 92, the forming station 86 can all comprise conventional
equipment suitable for
their intended purposes as is known in the art. The wet end 80 can be equipped
with other
conventional equipment as is known in the art.
[00117] The calcined gypsum in the gypsum slurries 70, 76, 94 reacts with the
water and
sets as a conveyor moves the gypsum board preform 98 down a manufacturing
line. The
gypsum board preform 98 is dried and cut into segments of predetermined
dimensions at a
point along the line where the gypsum board preform 98 has set sufficiently.
The segments
can be dried (e.g., in a kiln) to drive off excess water, and processed to
provide the final
layered wallboard of desired dimensions.
[00118] The gypsum layer (including the core and skim layers) resulting from
the set
gypsum core slurries 70, 76, 94 generally has a thickness of 0.25 inches to
1.0 inches and an
overall density of 40 pounds/cubic foot or less. When foamed, the portion of
the gypsum core
layer resulting from the set foamed gypsum slurry has a total void volume of
30 to 90 volume
percent, preferably a void volume of 45 to 80 volume percent. The first skim
layer and
second skim layer (if present) resulting from setting the gypsum slurries 70,
76 have a total
void volume of less than 30 volume percent, preferably less than 10 volume %.
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1001191 The forming station is the location in the board line where wet board
precursor is
sized to a pre-determined width and thickness, and optionally, length. Thus,
the forming
station includes, or can be, any device capable of performing a final
mechanical spreading
and/or shaping of the slurry across the width of the backing layer, many of
which are known
in the art. The forming station comprises a means of conforming the slurry
thickness and
width to the final desired thickness and width of a wet board precursor that,
when set, will
produce the cementitious board product. The final desired slurry thickness and
width
produced at the forming station can, of course, differ from the final
thickness and width of the
finished board product. For example, the slurry thickness and/or width can
expand and/or
contract during crystallization (i.e., setting) and drying of the slurry.
Typically, the desired
slurry thickness is substantially equal to the desired board thickness (e.g.,
about 0.375", about
0.5, about 0.625, about 0.75", or about 1"). By way of illustration only, the
final board
thickness typically is within about -P-1/8" or less of the final slurry
thickness.
1001201 The forming station includes any device that is capable of creating
the desired
slurry thickness and width of the wet board precursor. Suitable devices
include, for example,
a forming plate, a forming roller, a forming press, a screed, and the like.
The particular device
used will depend, in part, on the type of cementitious board being produced.
In a preferred
embodiment, for example when the board forming system is a gypsum board or
acoustical
panel forming system, the board forming station comprises a forming plate as
is known in the
art. The board forming system of any of the above embodiments optionally
further comprises
a blade for cutting wet board precursor or dry cementitious board product to
the desired
lengths, and/or a drying region capable of removing water from the set
cementitious board.
1001211 In an embodiment, to produce gypsum board having front and back paper
cover
sheets, the stucco is mixed with water and additives to form an aqueous slurry
which is
continuously fed between continuous layers of paper on a board machine. As the
board
moves down a conveyer line to form a panel, the calcium sulfate recrystallizes
or rehydrates,
reverting to its original rock state. The paper becomes bonded to the board
core layer as the
gypsum sets. The panel is then cut to length and conveyed through dryers to
remove any free
moisture.
1001221 Dry and/or wet components of the gypsum slurry are fed to a mixer,
where they
are agitated to form the gypsum slurry. The mixer comprises a main body and a
discharge
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conduit (e.g., a gate-canister-boot arrangement as known in the art, or an
alternative
arrangement, such as that described in U.S. Patents 6,494,609 and 6,874,930,
which are
incorporated herein by reference in their entirety). In some process
configurations, the
discharge conduit may include a slurry distributor with either a single feed
inlet or multiple
feed inlets, such as those described in U.S. Patent Application Publication
2012/0168527 and
2012/0170403, which are incorporated herein by reference in their entirety.
When using a
slurry distributor with multiple feed inlets, the discharge conduit can
include a suitable flow
splitter, such as those described in U.S. Patent Application Publication
2012/0170403.
Foaming agent (typically soap) can be added in the discharge conduit of the
mixer (e.g., in
the gate as described, for example, in U.S. Patents 5,683,635 and 6,494,609,
which are
incorporated herein by reference) or in the main body, if desired. Slurry
discharged from the
discharge conduit after all ingredients have been added, including foaming
agent, is the
primary gypsum slurry and is used to form the board core layer. This gypsum
slurry is
discharged onto the moving cover sheet.
1001231 In some embodiments, the aqueous slurry optionally has foam added to
decrease
the product density. Foam is typically generated by combining soap and water.
The foam
may be injected into the aqueous slurry as it exits the mixer through a gate,
hose or chute or
shortly afterwards, as is known in the art. Foam is typically added to the
portion of slurry for
the less dense core layer, but not for the portion of slurry for the skim
coat.
1001241 When the foam and the slurry have been brought together, the resulting
slurry
moves toward and is poured onto a conveyor lined with a first piece of facing
material which
is typically the front cover sheet (e.g., facer paper cover sheet 12). Another
piece of facing
material which is the back cover sheet (e.g., backer paper cover sheet 30) is
placed on top of
the slurry, forming a sandwich assembly with the slurry between the two facing
materials.
The sandwich assembly is fed to a forming plate, the height of which
determines the
thickness of the board. Next the continuous sandwich assembly is cut into
appropriate lengths
at a cutting knife, usually eight feet to twelve feet. During this processing
the slurry is
allowed to harden (set) to form a board core comprising an interlocking
crystalline matrix of
set gypsum.
1001251 The boards are then moved to a kiln for drying. Temperatures in the
kiln typically
range from 450 F to 500 F. Preferably there are three or more temperature
zones in the kiln.
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In the first zone contacted by the wet board, the temperature increases to the
maximum
temperature, while the temperature slowly decreases in the last two zones. The
blower for
the first zone is positioned at the exit of the zone, blowing the air
countercurrent to the
direction of board travel. In the second and third zones, the blowers are
located at the
entrance to the zone, directing the hot air co-current with board travel.
Heating that is less
severe in the last zone prevents calcination of dry areas of the board,
causing poor paper
bond. A typical residence time in the kiln is about forty minutes, but the
time will vary
depending on the line capacity, the wetness of the board and other factors.
1001261 As described above, one or both of the cover sheets in a gypsum board
may
optionally be in interfacial contact with a high-density region or layer of
the board core layer,
also known as a skim coat. The skim coat may be contiguous with the board core
layer after
setting. Where foam is inserted into the discharge conduit, a stream of
secondary gypsum
slurry can be removed from the mixer body before foaming to provide a slurry
for forming
the skim coat. If present, the skim coat may be deposited onto the moving
front cover sheet
before the main portion of the gypsum slurry is deposited for forming the
board core layer,
with deposition of the skim coat usually occurring upstream of the mixer.
After being
discharged from the discharge conduit, the gypsum slurry is spread, as
necessary, over the
front cover sheet (optionally bearing a skim coat). At this point, the spread
gypsum slurry is
contacted with a second cover sheet, which may correspond to the back cover
sheet. The
resulting wet assembly is in the form of a sandwich assembly, which is a
precursor to the
final gypsum board product. The back cover sheet may optionally bear a second
skim coat,
which can be formed from the same or different secondary gypsum slurry as for
the skim coat
on the front cover sheet, if present.
1001271 The gypsum core (e.g., gypsum core 24 of FIG. 1) resulting from the
set gypsum
core slurry generally has a thickness of about 0.25 inches to about 1.0,
typically about 0.375
inches to about 1.0 inches and a density of 15 to 40 pounds/cubic foot. When
foamed, the
gypsum core resulting from the set foamed gypsum slurry has a total void
volume of 10 to 92
volume percent, particularly 25 to 90 volume percent, and more particularly 30
to 85 volume
percent. In contrast, the resulting skim layer, if present, has a total void
volume of less than
30 volume percent.
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1001281 Optional Additives
1001291 Other additives that may be present in the gypsum slurry used to form
the board
core layer include, but are not limited to, strengthening agents, foam
(prepared from a
suitable foaming agent), dispersants, polyphosphates (e.g., sodium
trimetaphosphate),
retarders, accelerators, recalcination inhibitors, binders, adhesives,
secondary dispersing aids,
leveling or non-leveling agents, thickeners, bactericides, fungicides, pH
adjusters, buffers,
colorants, reinforcing materials, fire retardants, water repellants (for
example siloxane),
fillers, starches, and mixtures thereof
1001301 Additives and other components of the gypsum slurry may be added to
the mixer
in various ways. For example, various combinations of components may be pre-
mixed
before entering the mixer, either as one or more dry components and/or as one
or more wet
components. Singular components may similarly be introduced to the mixer in
wet or dry
form. If introduced in a wet form, the components may be included in a carrier
fluid, such as
water, in any suitable concentration.
1001311 Fibers can optionally be used in the methods and composition of the
present
invention. The fibers may include mineral fibers (also known as mineral wool),
glass fibers,
carbon fibers, and mixtures of such fibers, as well as other comparable fibers
providing
comparable benefits to the wallboard. For example, glass fibers can be
incorporated in the
gypsum core slurry and/or the skim layer slurry and resulting crystalline core
structure. The
glass fibers in such aspects may have an average length of about 0.5 to about
0.75 inches and
a diameter of about 11 to about 17 microns. In other aspects, such glass
fibers may have an
average length of about 0.5 to about 0.675 inches and a diameter of about 13
to about 16
microns. In yet other aspects, E-glass fibers are utilized having a softening
point above about
800 C or above at least about 900 C. Mineral wool or carbon fibers such as
those known to
those of ordinary skill may be used in place of or in combination with glass
fibers.
1001321 Fibers, when included, can be present in the gypsum core slurry and/or
the skim
layer slurry in amounts on a dry basis per 100 pbw (pbw=parts by weight) of
calcium sulfate
hemihydrate of about 0.5 to about 10 pbw; preferably about 1 to about 8 pbw;
more
preferably about 2 to about 7 pbw; and most preferably about 3 to about 6 pbw.
There may
also be an absence of fibers.
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1001331 Optionally, one or more phosphate-containing compounds can also be
included in
the slurry, if desired. For example, these phosphate-containing components can
include
water-soluble components and can be in the form of an ion, a salt, or an acid,
namely,
condensed phosphoric acids, each of which comprises two or more phosphoric
acid units;
salts or ions of condensed phosphates, each of which comprises two or more
phosphate units;
and monobasic salts or monovalent ions of orthophosphates as well as water-
soluble acyclic
polyphosphate salts. Illustrative examples are described in U.S. Patents
6,342,284;
6,632,550; 6,815,049; and 6,822,033, which are incorporated herein by
reference in their
entirety.
1001341 Phosphate-containing components can enhance green strength, resistance
to
permanent deformation (e.g., sag), dimensional stability, and the like.
Trimetaphosphate
compounds can be used, including, for example, sodium trimetaphosphate,
potassium
trimetaphosphate, lithium trimetaphosphate, and ammonium trimetaphosphate.
Sodium
trimetaphosphate (STMP) is commonly used, although other phosphates may be
suitable,
including for example sodium tetrametaphosphate, sodium hexametaphosphate
having from
about 6 to about 27 repeating phosphate units and having the molecular formula
Nan-h2Pn03n+1
wherein n=6-27, tetrapotassium pyrophosphate having the molecular formula
K4P207,
trisodium dipotassium tripolyphosphate having the molecular formula
Na3K7133010, sodium
tripolyphosphate having the molecular formula Na5P3010, tetrasodium
pyrophosphate having
the molecular formula Na4P207, aluminum trimetaphosphate having the molecular
formula
Al(P03)3, sodium acid pyrophosphate having the molecular formula Na2H2P507,
ammonium
polyphosphate having 1000-3000 repeating phosphate units and having the
molecular
formula (NIT
P n¨ 3n+1 wherein n=1000-3000, or polyphosphoric acid having two or more
repeating phosphoric acid units and having the molecular formula fin+2PnO3n+1
wherein n is
two or more.
1001351 The phosphates usually are added in a dry form and/or an aqueous
solution liquid
form, with the dry ingredients added to the slurry mixer, with the liquid
ingredients added to
the mixer, or in other stages or procedures.
1001361 When present, the phosphate can be included in the gypsum slurry in a
dry form
or in a form in water (e.g., a phosphate solution from about 5% to about 20%,
such as about a
10% solution). If included, the phosphate can be present in any suitable
amount (solids/solids
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basis), such as from about 0.01% to about 0.5% by weight of the stucco, e.g.,
from about
0.03% to about 0.4%, from about 0.1% to about 0.3%, or from about 0.12% to
about 0.4% by
weight of the stucco. There may also be an absence of phosphate.
[00137] The gypsum slurry can optionally include at least one dispersant to
enhance
fluidity. The dispersant(s) may be introduced to the gypsum slurry in a dry
form, optionally
with other additives, and/or in a liquid form, optionally with other liquid
components.
Examples of suitable dispersants include naphthalene sulfonates, such as
polynaphthalene
sulfonic acid and its salts (polynaphthalene sulfonates) and derivatives,
which are
condensation products of naphthalene sulfonic acids and formaldehyde, as well
as
polycarboxylate dispersants, such as polycarboxylic ethers, for example. Other
examples of
suitable dispersants include lignosulfonates or sulfonated lignin.
Lignosulfonates are water-
soluble anionic polyelectrolyte polymers, which are byproducts from the
production of wood
pulp using sulfite pulping.
1001381 Lower molecular weight dispersants may be desirable. Lower molecular
weight
naphthalene sulfonate dispersants may be favored because they trend to a lower
water
demand than higher viscosity, higher molecular weight dispersants. Thus,
molecular weights
from about 3,000 to about 10,000 (e.g., about 8,000 to about 10,000) may be
desirable
molecular weights for a dispersant. If desired, the molecular weight of the
polycarboxylate
dispersants can be from about 20,000 to about 60,000, which may exhibit less
retardation
than dispersants having molecular weights above about 60,000.
[00139] Typical naphthalene sulfonates are a naphthalene sulfonate solution in
water,
having a range of about 35% to about 55% by weight naphthalene sulfonate
solids content.
However, if desired the naphthalene sulfonates can be used in dry solid or
powder form.
[00140] When present, the dispersant can be included in the gypsum slurry in
any suitable
(solids/solids) amount, such as, for example, about 0.1% to about 5% by weight
of the stucco,
e.g., about 0.1% to about 4%, about 0.1% to about 3%, about 0.2% to about 3%,
about 0.5%
to about 3%, about 0.5% to about 2.5%, about 0.5% to about 2%, about 0.5% to
about 1.5%,
or the like. There may also be an absence of any one or more of
polynaphthalene sulfonates,
polycarboxylic ethers or lignosulfonates.
[00141] Accelerators and/or retarders may be added to the gypsum core slurry
and/or the
skim layer slurry to modify the rate at which the calcium sulfate hemihydrate
hydration
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reactions take place. When present, the accelerator and/or retarder each can
be incorporated
in the gypsum slurry in an amount on a solid basis of, e.g., about 0% to about
10% by weight
of the stucco (e.g., about 0.1% to about 10%), such as, for example, from
about 0% to about
5% by weight of the stucco (e.g., about 0.1% to about 5%). Suitable
accelerators may
include, for example, calcium sulfate dihydrate, carbohydrate-coated calcium
sulfate, calcium
sulfate dihydrate/organic phosphonate, and calcium sulfate dihydrate/organic
phosphate.
There may also be an absence of accelerators and/or retarders.
1001421 Foam (also known as foam water) may optionally be introduced into the
gypsum
core slurry and/or the skim layer slurry (preferably the gypsum core slurry)
in amounts that
provide the above mentioned reduced core density and panel weight. The foaming
agent to
produce the foam is typically a soap or other suitable surfactant. The
introduction of foam in
the gypsum core slurry in the proper amounts, formulations, and process will
produce a
desired network and distribution of voids within the core of the final dried
wallboards. This
void structure permits the reduction of the gypsum and other core constituents
and the core
density and weight, while maintaining desired panel structural and strength
properties. If
present, foaming agents may comprise a major weight portion of unstable
component and a
minor weight portion of stable component (e.g., where unstable and blend of
stable/unstable
are combined). The weight ratio of unstable component to stable component is
effective to
form an air void distribution within the set gypsum core, as described in U.S.
Patents
5,643,510; 6,342,284; and 6,632,550, which are incorporated herein by
reference in their
entirety. The approaches for adding foam to a gypsum core slurry are known in
the art and
one example of such an approach is discussed in U.S. Patent No. 5,683,635, the
disclosure of
which is incorporated by reference herein. Evaporative water voids, generally
having voids
of about 5 p.m or less in diameter, also contribute to the total void
distribution along with the
aforementioned air (foam) voids. The volume ratio of voids with a pore size
greater than
about 5 microns to the voids with a pore size of about 5 microns or less, is
from about 0.5:1
to about 9:1, such as, for example, about 0.7:1 to about 9:1, about 1.8:1 to
about 2.3:1, or the
like. The foaming agent is present in the gypsum slurry in an amount, for
example, of less
than about 0.5% by weight of the stucco, such as about 0.01% to about 0.5%,
about 0.01% to
about 0.2%, about 0.02% to about 0.4%, about 0.02% to about 0.2%, about 0.01%
to about
0.1%, or the like. There may also be an absence of foaming agents.
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1001431 Components for fire and/or water resistance can also be included in
the gypsum
slurry. Examples include, for instance, siloxanes (water resistance); fiber;
heat sink additives
such as aluminum trihydrite (ATH), magnesium hydroxide or the like; and/or
high expansion
particles as discussed above (e.g., expandable to about 300% or more of
original volume
when heated for about one hour at 1560 F) Further disclosure on such additives
may be
found in U.S. Patent 8,323,785, which is incorporated by reference in its
entirety. High
expansion vermiculite may be included, although other fire resistant materials
can be
included. If present, fire or water resistance additives can be included in
any suitable amount
as desired depending, e.g., on fire rating, and like performance parameters.
For example, if
included, the fire or water resistance additives can be individually present
in an amount from
about 0.5% to about 10% by weight of the stucco, such as from about 1% to
about 10%,
about 1% to about 8%, about 2% to about 10%, about 2% to about 8%, or the
like. If
included, the siloxane may desirably be introduced in the form of an emulsion.
The slurry
may then be shaped and dried under conditions which promote the polymerization
of the
siloxane to form a highly crosslinked silicone resin. A catalyst which
promotes the
polymerization of the siloxane to form a highly crosslinked silicone resin can
be added to the
gypsum slurry. Solventless methyl hydrogen siloxane fluid can be used as the
siloxane.
This product is a siloxane fluid containing no water or solvents. It is
contemplated that about
0.3% to about 1.0% of the siloxane may be used if desired, based on the weight
of the dry
ingredients. For example, if desired, about 0.4% to about 0.8% siloxane may be
present in
the gypsum slurry based on the dry stucco weight. There may also be an absence
of any one
or more of these components for fire and/or water resistance. For example,
there may be an
absence of siloxane.
1001441 The starch, when present, can be a pre-gelatinized (cooked)
starch and/or an
uncooked starch. In this regard, starches are classified as carbohydrates and
contain two
types of polysaccharides: linear amylose and branched amylopectin. Starch
granules are
semi-crystalline, e.g., as seen under polarized light, and are insoluble in
water at room
temperature or near room temperature. Uncooked starches are characterized as
being cold
water insoluble and having a semi-crystalline structure. Typically, uncooked
starches are
obtained by wet milling and are not modified by heating wet starch as in the
case of cooked
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starches. Pre-gelatinized, or cooked, starches are characterized as being cold
water soluble
and having a non-crystalline structure. There may also be an absence of
starch.
[00145] Water
[00146] Water is added to the slurry in any amount that makes the slurry
flowable. The
amount of water to be used varies greatly according to the application with
which it is being
used, the exact dispersant being used, the properties of the calcium sulfate
hemihydrate, and
the additives being used.
[00147] Water used to make the slurry should be as pure as practical for best
control of the
properties of both the slurry and the set plaster. Salts and organic compounds
are well known
to modify the set time of the slurry, varying widely from accelerators to set
inhibitors. Some
impurities lead to irregularities in the structure as the interlocking matrix
of dihydrate crystals
forms, reducing the strength of the set product. Product strength and
consistency is thus
enhanced by the use of water that is as contaminant-free as practical.
[00148] The water can be present in the gypsum core slurry and/or the skim
layer slurry of
the present invention at a weight ratio of water to calcium sulfate
hemihydrate of about 0.2:1
to about 1.2:1; preferably, about 0.3:1 to about 1.1:1; more preferably, about
0.6:1 to about
1:1; most preferably 0.7:1 to 0.95:1, typically about 0.6 to about 1.2, or
about 0.8 to about
1.0, or about 0.85:1.
[00149] The following examples further illustrate the invention but, of
course, should not
be construed as in any way limiting its scope.
[00150] EXAMPLES:
[00151] Thermal Sa2 Test and Shrinka2e Test
[00152] Samples were produced and a thermal sag test was conducted on the
samples. For
all of the examples, this thermal sag test procedure was used. 10"x1.5" x 5/8"
strips were cut
from the cast boards. The samples were placed horizontally in a furnace on
bricks (2.5- high)
spaced 8" apart in the middle of the heated space. The furnace was heated from
ambient
temperature to 1600 F (870 C)(taking about 75 min), and then maintained at
1600 F (870
C) for 15 mins. The total heating time was 90 minutes. Sag performance was
observed every
30 minutes after 30 minutes of heating. Thermal sag is the distance the sample
dips from its
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original height due to exposure to fire during the test. Thus, it is the
difference between the
gap before exposure to the fire and the gap from original height after the
fire testing. As the
board is flat before the fire, the initial gap is zero. The maximum dip
(distance) after the fire
is the gap after the fire. A High-Temperature Thermal Sag of 2 inches means
that the 10-
x1.5" x 5/8" strip test sample placed horizontally in a furnace on bricks
(2.5" high) spaced 8"
apart in the middle of the heated space dipped 2 inches at the center of the
strip. For
example, FIG. 6 shows a photograph of a sample with a 2 inch thermal sag and
another
sample with a 13/16 inch thermal sag.
1001531 In this invention, the thermal sag (as measured according to the above-
described
thermal sag test) observed in gypsum boards with urea is 10-80%, preferably 15-
70 %, more
preferably 20-60 %, most preferably 30%, of the thermal sag observed in
control boards (the
same gypsum board composition without the urea).
1001541 Shrinkage in the examples of the present specification was
tested according to the
test described above for measuring "High Temperature Shrinkage" (S) of ASTM
Pub.
WK25392 as described above. Thus, shrinkage was tested at about 1560 F. (850
C.) on six
test specimens that were about 4 inches (100 mm) diameter disks cut from
gypsum board
samples using a drill press with a hole saw blade as specified above. As
specified above, in
order to prevent thermal shock to the test specimens, which might produce
invalid test results
due to spalling and breakage, the test protocol was modified to place the test
specimens in the
furnace before it was heated to about 1560 F. (850 C.). The specimens were
held at that
temperature for a minimum of about 20 minutes before the furnace was shut off.
The furnace
door remained closed while the furnace cooled. The specimens were not removed
for
measurement until after the temperature had dropped to near room temperature.
1001551 Example 1: GF-added Type X board with and without Urea
1001561 Urea can be introduced to the slurry as a dry form or an aqueous
solution. The dry
powders soaked in the liquid solution for 10 seconds and blended for 10
seconds in a Hobart
mixer, followed by injecting the foam for 13 or 7 seconds and mixing another 2
seconds. The
slurry was poured into the 12"x13"x 5/8" envelope.
1001571 After the slurry was set and hardened, the board dried at 450 F for
15 mins, then
dried at 360 F for another 15 mins. At last, the board dried at 110 F
overnight.
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1001581 Table 2 is the formula for making ultralight gypsum glass fiber ("GF")
board with
and without urea.
1001591
Table 2
Sample ID GF GF-Urea
Thickness (inches) 5/8" (1.5875 cm) 5/8"
Stucco (g) 900 900
Accelerator (g) 9 9
Pregelatinized, partially hydrolyzed starch (g) 5 5
Glass Fiber (g) 4.65
4.65
Grade 4 Vermiculite (g) 31 31
Urea (g) 0
0.9
10% STMP (g) 3 3
Retarder 1% (g) 12 12
Dispersant (g) 3 3
Water (g) 855 855
Air flow (L/min) 40 40
Soap flow (L/min) 5 5
Foam time (sec) 15 15
1001601 Table 3 summarizes the thermal performance of the boards made from
Table 2.
The glass fiber board shows a similar thermal shrinkage as the glass fiber-
urea board.
However, the high-temperature sag of glass fiber-board is higher than that of
Glass Fiber-
Urea board, 2" vs. 1 5/16". The addition of urea improved the high-temperature
sag
resistance.
Table 3: Thermal performance of GF-Type X Board with and without Urea
Sample GF GF-Urea
Thermal shrinkage X-Y% 4.58+0.41 4.67+0.35
Thermal Shrinkage Z% 5.86+0.47 5.38+0.61
High-Temperature Sag (inches) 2" 1 5/16"
Board Weight (lbs/msf) 1820 1837
1001611 Example 2: Mineral Wool-added ultralight board with and without urea
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1001621 For mineral wool (MW) added board, MW was added in the wet slurry
form. 5%
of MW slurry prepared by mixing MW with water in the Waring blender for 5
seconds. Urea
was introduced as a dry form or an aqueous solution. Dry powders and the MW
slurry were
soaked in the solution for 10 seconds and blended for 10 seconds, followed by
injecting the
foam for 13 or 7 seconds and mixing another 2 seconds. The slurry was poured
into the
12"x13"x 5/8" envelope.
1001631 Table 4 is the formula for making MW-added ultralight board
with and without
urea.
Table 4: ultralight board formula with and without Urea
Sample ID MW MW-Urea
Thickness (inches) 5/8" (1.5875 cm) 5/8"
Stucco (g) 900 900
Accelerator (g) 9 9
Pregelatinized, partially hydrolyzed starch (g) 5 5
Mineral Wool (g) 11.2 11.2
Grade 4 Vermiculite (g) 31 31
Jrea (g) 0 0.9
10% STMP (g) 3 3
Retarder 1% (g) 12 12
Dispersant (g) 3 3
Water (g) 855 855
Air flow (L/min) 40 40
Soap flow (L/min) 5 5
Foam time (sec) 15 15
1001641 Table 5 summarizes the thermal performance of the boards made from
Table 4.
The MW-board shows a similar thermal shrinkage as the MW-Urea board. However,
the
high-temperature sag of MW-board is higher than that of MW-Urea board, 15/16"
vs. 11/16".
Therefore, the addition of Urea improves the high-temperature sag resistance
of the MW-
board.
Table 5: Thermal performance of MW-Type X Board with and without Urea
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Sample ID MW MW-
Urea
Thermal shrinkage X-Y% 4.34+0.22
4.38+0.34
Thermal Shrinkage Z% 8.32 0.39
8.68 0.42
Thermal Sag (") 15/16" 11/16"
Board Weight (lbs/msf) 1837 1825
1001651 Example 3: Heavy board (>2100#/msf) with and without Urea
GF-High Salt and MW-High Salt boards were prepared with and without Urea.
Table 6 is the
formula for making High Salt boards with GF and MW.
Table 6: Formula for High Salt boards with and without Urea
High Salt
Sample ID
GF GF-Urea MW MW-Urea
Thickness (inches) 5/8" (1.5875 cm) 5/8" 5/8"
5/8"
Stucco (g) 900 900 900 900
Accelerator (g) 9 9 9 9
Pregelatinized, partially
2 2 2 2
hydrolyzed starch (g)
Fiber Glass (g) 2.8 2.8 0 0
Mineral Wool (g) 0 0 6.7
6.7
Urea (g) 0 0.9 0 0.9
10% STMP (g) 3 3 3 3
Retarder 1% (g) 12 12 12 12
Dispersant (g) 3 3 3 3
Water (g) 845 845 845 845
Air flow (L/min) 40 40 40 40
Soap flow (L/min) 5 5 5 5
Foam time (sec) 6 6 6 6
1001661 Table 7 summarizes the thermal performance of the boards made from
Table 6.
Irrespective of the GF-added or the MW-added boards, the addition of urea
seems no impact
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on the high-temperature sag performance. Therefore, urea is used for making
wallboard with
a board weight less than 2100 lbs/msf (that is, ultralight weight boards).
Table 7: Thermal Shrinkage and High-Temperature Sag of Type X with and without
Urea
Type X
Sample ID
GF GF-Urea MW MW-Urea
Thermal shrinkage X-Y% 5.28+0.25 5.34+0.28 5.22+0.32
4.95+0.22
Thermal Shrinkage Z% 10.71+0.14 11.23+0.58 10.68+0.71
11.31+0.62
Thermal Sag (") 2 1/16" 2 3/16" 1 3/16"
1 2/16"
Board Weight (lbs/msf) 2141 2113 2135
2129
[00167] Example 4: High Salt, Ultralight weight boards with and without Urea
[00168] Table 8 is the formula for making the high salt, ultralight weight
boards with and
without Urea. Chloride source is from a mixture of sodium chloride and
magnesium chloride.
The total chloride concentration is 1000 ppm to Stucco.
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Table 8: Formula for high salt ultralight weight board with and without Urea
GF-Clay- MW- MW- MW-Clay-
GF- GF-Clay-
Sample ID Urea-1000 1000 Clay-1000 Urea-1000
1000ppm 1000ppm
ppm ppm ppm
ppm
Thickness (inches) 5/8" 5/8" 5/8" 5/8" 5/8"
5/8"
Stucco (g) 900 900 900 900 900
900
Accelerator (g) 9 9 9 9 9
9
pregelatinized
5 5 5 5 5
starch (g)
Fiber Glass (g) 4.65 4.65 4.65 0 0
0
Grade 4
31 31 31 31 31
31
Vermiculite (g)
Mineral Wool (g) 0 0 0 11.2 11.2
11.2
NaCl (g) 0.62 0.62 0.62 0.62 0.62
0.62
MgCl2 (g) 0.6 0.6 0.6 0.6 0.6
0.6
Clay (g) 0 11 11 0 11
11
Urea (g) 0 0 0.9 0 0
0.9
10% STMP (g) 3 3 3 3 3
3
Retarder 1% (g) 12 12 12 12 12
12
Dispersant (g) 3 3 3 3 3
3
Water (g) 855 855 855 855 855
855
Air flow (L/min) 40 40 40 40 40
40
Soap flow (L/min) 5 5 5 5 5
5
Foam time (sec) 15 15 15 15 15
15
1001691 Table 9 summarizes the thermal performance from the high salt
ultralight weight
boards in Table 8. The chloride salts severely reduce the thermal shrinkage
and the high-
temperature sag, as shown as GF-1000 ppm and MW-1000 ppm in Table 9. The
addition of
5 clay improves the thermal shrinkage and the high- temperature sag, as
shown as GF-Clay-
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1000ppm and MW-Clay-1000ppm. The addition of urea further improves the high-
temperature sag performance, as shown as GF-Clay
_________________________________ Urea-1000ppm and MW-Clay-Urea-
1000ppm in Table 9.
Table 9: Thermal Shrinkage and High-Temperature Sag of high salt Ultralight
weight boards
with and without Urea
GF-Clay- MW- MW-
Clay-
GF- GF-Clay- MW-
Sample ID Urea- Clay-
Urea-
1000ppm 1000ppm 1000ppm
1000ppm
1000ppm 1000ppm
Thermal
6.79+0.21 4.58+0.15 4.78+0.47 6.81+0.12 4.26+0.46 4.85+0.22
shrinkage X-Y%
Thermal
Shrinkage Z% 12.31+0.02 6.76+0.44
6.93+0.58 11.18+1.30 6.45+0.31 6.49+0.53
Thermal Sag
>2" (fell) 1 5/16" 15/16" >2" (fell)
14/16" 10/16"
(inches)
Board Weight
1848 1827 1809 1811 1817
1821
(lbs/msf)
[00170] Example 5: Glass Fiber Boards without STMP
[00171] Table 10 shows the formula for making glass fiber boards without STMP.
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Table 10
Sample Glass Fiber Glass
Fiber-Urea
Thickness (inches) 5/8" 5/8"
Stucco (g) 900 900
Accelerator (g) 9 9
Pregelatinized, partially hydrolyzed starch (g) 5 5
Glass fiber (g) 4.65 4.65
Grade 4 vermiculite (g) 31 31
Urea (g) 0 0.9
10% sodium trimetaphosphate (STMP) (g) 0 0
Retarder 1% (g) 12 12
Dispersant (g) 3 3
Water (g) 906 906
Air flow (L/min) 40 40
Soap flow (L/min) 5 5
Foam time (sec) 15 15
1001721 Table 11 shows the thermal performance of the boards in
Table 10. The addition
of urea improves the high temperature sag resistance of the glass fiber ("GF")
added board
even when STMP is not added.
Table 11
Sample Glass fiber Glass fiber-
Urea
Thermal shrinkage X-y% 4.67 0.41 5.24 0.32
Thermal shrinkage Z% 7.28 0.11 8.17 0.71
High temperature sage (") 1 1/16" 13/16"
Board weight (lbs/msf) 1832 1851
1001731 Example 6: Glass fiber gypsum board with and without urea
1001741 Table 12 shows the composition of the gypsum core of this example. The
boards
were made at a plant.
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Table 12
Sample Glass Fiber Glass
Fiber-Urea
Thickness (inches) 5/8" 5/8"
Stucco (lbs/msf) 1485 1487
Accelerator (lbs/msf) 3.5 3.5
Pregelatinized, partially hydrolyzed starch (lbs/msf) 12.1 12.1
Glass fiber (lbs/msf) 7.6 7.6
Grade 4 vermiculite (lbs/msf) 55 55
Urea (lbs/msf) 0 1.5
Sodium trimetaphosphate (lbs/msf) 1.0 1.0
Retarder 1% (lbs/msf) 0.235 0.234
Dispersant (lbs/msf) 4.0 4.0
Water (lbs/msf) 1261 1260
Soap (lbs/msf) 0.521 0.518
Foam Air (cubic feet/msf) 17.29 17.40
Water to Stucco Ratio (%) 85.1 85.2
1001751 Table 13 shows the thermal performance of the boards in Table 12. The
addition
of urea improves the high temperature sag resistance.
Table 13
Plant Boards Glass fiber Glass fiber-
Urea
Thermal shrinkage X-Y% 6.63+0.40 6.44+0.41
Thermal shrinkage Z% 3.37+0.81 2.27+0.44
High temperature sag (inches) 1 15/16" 1 2/16"
Board weight (lbs/msf) 1886 1856
1001761 CLAUSES OF THE INVENTION
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1001771 The following clauses describe various aspects of the invention.
1001781 Clause 1. A gypsum board comprising:
a gypsum core layer (also referred to as a board core layer) comprising
at least 60 wt. % calcium sulfate dihydrate, preferably at least 70 wt. %, and
more
preferably at least 80 wt. %, typically at least 90 wt. % or at least 95 wt. %
calcium sulfate dihydrate, and
0.03-1 wt. %, preferably 0.05-0.8 wt. %, more preferably 0.06-0.6 wt. %, most
preferably 0.05-0.2 wt. % for example 0.05-0.1 wt. % or 0.1-0.2 wt. %, urea
distributed uniformly throughout the gypsum core,
wherein the gypsum core layer has a density of about 40 pounds per cubic foot
or less,
and
wherein the gypsum board has a mass of pounds per area less than 2100 lbs/msf,
wherein the mass of pounds per area lbs/msf values are for a 5/8 inch (1.59
cm) thick board
and subject to proportional adjustment for thicker or thinner boards.
1001791 Clause 2. The gypsum board of clause 1, wherein the gypsum core layer
further
comprises high expansion particles having a volume expansion of about 200% or
more of
their original volume after being heated for about one hour at about 1500 F
1001801 Clause 3. The gypsum board of clause 2, wherein the gypsum core layer
further
comprises 0-0.1% sodium trimetaphosphate, typically 0.02-0.05% sodium
trimetaphosphate.
1001811 Clause 4. The gypsum board of any of clauses 1-3, further comprising
less than
120 parts by weight chloride per 1,000,000 parts by weight of said calcium
sulfate dihydrate.
1001821 Clause 5. The gypsum board of any of clauses 1-3, further comprising
about 120
parts by weight to about 3000 parts by weight chloride per 1,000,000 parts by
weight of said
calcium sulfate dihydrate.
1001831 Clause 6. The gypsum board of clause 1, wherein the gypsum core layer
has
opposed front and back outer surfaces, further comprising a front cover sheet
on the gypsum
core front surface and a back cover sheet on the gypsum core back surface.
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[00184] Clause 7. The gypsum board of clause 1, wherein the front and/or back
cover
sheets are made of paper or fiberglass.
[00185] Clause 8. The gypsum board of clause 1, wherein the gypsum core layer
further
comprises about 0.1-3.0% by weight of fiber-reinforced such as mineral wool,
glass fiber or
carbon fiber.
[00186] Clause 9. The gypsum board of clause 1, further comprising a skim
layer
comprising at least 60 wt. % calcium sulfate dihydrate on at least one side of
the gypsum core
layer, said skim layer having a density at least 1.1 times higher than the
density of the
gypsum core layer.
[00187] Clause 10. The gypsum board of clause 9, wherein the skim layer
further
comprises 0.03-1 wt. %, 0.05-0.8 wt. %, 0.06-0.6 wt. %, 0.05-0.2 wt. % urea.
[00188] Clause 11. The gypsum board of clause 1, wherein the board has a
thickness of
3/8"-1", preferably 5/8".
[00189] Clause 12. The gypsum board of clause 1, further comprising a skim
layer
comprising at least 60 wt. % calcium sulfate dihydrate, and 0.03-1 wt. %, 0.05-
0.8 wt. %,
0.06-0.6 wt. %, 0.05-0.2 wt. % urea.
[00190] Clause 13. The gypsum board of clause 1, wherein the gypsum core layer
is
effective to provide a Thermal Insulation Index (TI) of about 20 minute, for
example greater
than 30.0 minutes.
[00191] Clause 14. The gypsum board of clause 1, wherein the gypsum core layer
is
effective to provide a High Temperature Shrinkage (S) of about 10% or less.
[00192] Clause 15. A gypsum board having a gypsum core layer made from a
mixture of:
at least 60 wt. % on a dry basis calcium sulfate hemihydrate,
0.03-1 wt. %, preferably 0.05-0.8 wt. %, more preferably 0.06-0.6 wt. %, most
preferably 0.05-0.2 wt. `)/0, for example 0.05-0.1 wt. % or 0.1-0.2 wt. %, on
a dry basis
urea,
an accelerator,
glass fiber or mineral wool,
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pregelatinized, partially hydrolyzed starch,
vermiculite,
retarder,
dispersant,
optionally sodium trimetaphosphate,
optionally clay,
optionally sodium chloride,
optionally magnesium chloride, and
water.
[00193] Clause 16. The gypsum board of clause 15, wherein the gypsum core
layer has a
density of about 40 pounds per cubic foot or less, and
wherein the gypsum board has a mass of pounds per area less than 2100 lbs/msf,
wherein the mass of pounds per area lbs/msf values are for a 5/8 inch (1.59
cm) thick board
and subject to proportional adjustment for thicker or thinner boards.
[00194] Clause 17. The gypsum board of clause 15 or 16, wherein the gypsum
core layer
further comprises 0-0.1% sodium trimetaphosphate, typically 0.02-0.05% sodium
trimetaphosphate.
[00195] Clause 18. The gypsum board of clause 15, 16 or 17, further comprising
less than
120 parts by weight chloride per 1,000,000 parts by weight of said calcium
sulfate
hemihydrate.
[00196] Clause 19. The gypsum board of clause 15, 16 or 17, further comprising
about 120
parts by weight to about 3000 parts by weight chloride per 1,000,000 parts by
weight of said
calcium sulfate hemihydrate.
[00197] Clause 20. The gypsum board of clause 15, 16 or 17, wherein the gypsum
core
layer has opposed front and back outer surfaces, further comprising a front
cover sheet on the
gypsum core front surface and a back cover sheet on the gypsum core back
surface.
[00198] Clause 21. The gypsum board of clause 15, 16 or 17, wherein the front
and/or
back cover sheets are made of paper or fiberglass.
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1001991 Clause 22. The gypsum board of clause 15, 16 or 17, wherein the gypsum
core
layer further comprises about 0.1-3.0% by weight of fiber-reinforced such as
mineral wool,
glass fiber or carbon fiber.
1002001 Clause 23. The gypsum board of clause 15, 16 or 17, further comprising
a skim
layer comprising at least 60 wt. % calcium sulfate dihydrate on at least one
side of the
gypsum core layer, said skim layer having a density at least 1.1 times higher
than the density
of the gypsum core layer.
1002011 Clause 24. The gypsum board of clause 23, wherein the skim layer
further
comprises 0.03-1 wt. %, 0.05-0.8 wt. %, 0.06-0.6 wt. %, 0.05-0.2 wt. % urea.
1002021 Clause 25. The gypsum board of clause 15, 16 or 17, wherein the board
has a
thickness of 3/8"-1", preferably 5/8".
1002031 Clause 26. The gypsum board of clause 15, 16 or 17, further comprising
a skim
layer comprising at least 60 wt. % calcium sulfate dihydrate, and 0.03-1 wt.
%, 0.05-0.8 wt.
%, 0.06-0.6 wt. %, 0.05-0.2 wt. % urea.
1002041 Clause 27. The gypsum board of clause 15, 16 or 17, wherein the gypsum
core
layer is effective to provide a Thermal Insulation Index (TI) of about 20
minute, for example
greater than 30.0 minutes.
1002051 Clause 28. The gypsum board of clause 15, 16 or 17, wherein the gypsum
core
layer is effective to provide a High Temperature Shrinkage (S) of about 10% or
less.
1002061 Clause 29. A method of making a gypsum board of any of clauses 1-28,
comprising:
preparing an aqueous gypsum slurry comprising a mixture of water and
stucco, wherein the stucco comprises calcium sulfate hemihydrate, and
wherein the aqueous gypsum slurry comprises a mixture of:
at least 60 weight percent of said calcium sulfate hemihydrate on a dry basis,
0.03-1 wt. % urea on a dry basis, and
the water at a weight ratio of water to the calcium sulfate hemihydrate of
0.2:1
to 1.2:1;
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disposing the aqueous gypsum slurry onto a surface and allowing the aqueous
gypsum slurry to set to form a set gypsum core layer comprising calcium
sulfate
dihydrate;
cutting the set gypsum core layer into a panel of predetermined dimensions;
and
drying the panel,
wherein the gypsum core layer has a density of about 40 pounds per cubic foot
or less,
wherein the gypsum board has a mass of pounds per area less than 2100
lbs/msf, wherein the mass of pounds per area lbs/msf values are for a 5/8 inch
(1.59
cm) thick board and subject to proportional adjustment for thicker or thinner
boards.
1002071 Clause 30. The method of clause 29, wherein the aqueous slurry is
disposed
between a front cover sheet and a back cover sheet, each cover sheet having an
inner surface
and an outer surface;
wherein the aqueous slurry contacts the inner surface of the front cover sheet
and the back cover sheet, and
at least a portion of the aqueous slurry is in a foamed state while being
disposed between the front cover sheet and the back cover sheet.
1002081 Clause 31. The method of clause 29, wherein the front and back cover
sheets
comprise woven fibers.
1002091 Clause 32. The method of clause 29, wherein the front and back cover
sheets
comprise non-woven fibers.
1002101 Clause 33. The method of clause 29, wherein the front and back cover
sheets
comprise paper.
1002111 Variations of the specifically disclosed invention may become apparent
to those of
ordinary skill in the art upon reading the foregoing description. The
inventors expect skilled
artisans to employ such variations as appropriate, and the inventors intend
for the invention to
be practiced otherwise than as specifically described herein. Accordingly,
this invention
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includes all modifications and equivalents of the subject matter recited in
the claims
appended hereto as permitted by applicable law. Moreover, any combination of
the above-
described elements in all possible variations thereof is encompassed by the
invention unless
otherwise indicated herein or otherwise clearly contradicted by context.
1002121 All references cited herein are hereby incorporated by reference to
the same extent
as if each reference were individually and specifically indicated to be
incorporated by
reference and were set forth in its entirety herein.
1002131 The use of the terms -a" and -an" and -the" and -at least one" and
similar
referents in the context of describing the invention (especially in the
context of the following
claims) are to be construed to cover both the singular and the plural, unless
otherwise
indicated herein or clearly contradicted by context. The use of the term -at
least one"
followed by a list of one or more items (for example, "at least one of A and B-
) is to be
construed to mean one item selected from the listed items (A or B) or any
combination of two
or more of the listed items (A and B), unless otherwise indicated herein or
clearly
contradicted by context. "Bonding relation" does not mean that two layers are
in direct
contact. The terms "comprising," "having," "including," and "containing" are
to be
construed as open-ended terms (i.e., meaning "including, but not limited to,")
unless
otherwise noted. Recitation of ranges of values herein are intended to serve
as a shorthand
method of referring individually to each separate value falling within the
range, unless
otherwise indicated herein, and each separate value is incorporated into the
specification as if
it were individually recited herein. All methods described herein can be
performed in any
suitable order unless otherwise indicated herein or otherwise clearly
contradicted by context.
The use of any and all examples, or exemplary language (e.g., "such as")
provided herein, is
intended merely to better illuminate the invention and does not pose a
limitation on the scope
of the invention unless otherwise claimed. No language in the specification
should be
construed as indicating any non-claimed element as essential to the practice
of the invention.
The claims set forth below are also part of the disclosure of the invention.
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