Note: Descriptions are shown in the official language in which they were submitted.
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GYPSUM BOARD CONTAINING HIGH ABSORPTION
PAPER AND RELATED METHODS
BACKGROUND OF THE INVENTION
[0001] In the construction of buildings, one of the more common building
elements for
construction and remodeling is gypsum wallboard, often known as drywall,
gypsum boards,
gypsum panels, gypsum paneling, and ceiling tiles. In chemical terms, gypsum
is calcium
sulfate dihydrate (CaSO4=2H20).
[0002] Set gypsum (calcium sulfate dihydrate) 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 (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, usually at
an interface
between the board core and an inner surface of a cover sheet or a coating
thereon. The denser
regions may be contiguous with a less dense region of the gypsum layer which
provides the
gypsum core layer of the gypsum board.
[0003] During manufacture of a gypsum board, the stucco (containing
calcium sulfate
hemihydrate), water, and other ingredients as appropriate may be mixed,
typically in a mixer
to form an aqueous gypsum slurry. 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 conveyor carrying a 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
(i.e., calcium
sulfate dihydrate, also known as set 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. Heat may be applied (e.g., using a kiln) to
drive off the
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remaining free (i.e., unreacted) water to yield a dry product. Then the set
gypsum product is
cut to form gypsum boards having a desired length.
[0004] Gypsum (calcium sulfate dihydrate and any impurities) suitable
for use in
wallboard may be obtained from both natural sources and synthetic sources,
followed by
further processing.
[0005] Natural gypsum may be used by calcining its calcium sulfate
dihydrate to produce
the hemihydrate form. Gypsum from natural sources is a naturally occurring
mineral and can
be mined in rock form. Naturally occurring Gypsum is a mineral that is
typically found in
old salt-lake beds, volcanic deposits, and clay beds. When it is mined, raw
gypsum is
generally found in the dihydrate form Gypsum is also known as calcium sulfate
dihydrate,
terra alba or landplaster. This material is also produced as a by-product in
various industrial
processes. For example, synthetic gypsum is a byproduct of flue gas
desulfurization processes
from power plants. In gypsum, there are approximately two molecules of water
associated
with each molecule of calcium sulfate.
[0006] Plaster of Paris is also known as calcined gypsum, stucco, calcium
sulfate
semihydrate, calcium sulfate half-hydrate or calcium sulfate hemihydrate.
[0007] When calcium sulfate dihydrate from either source 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)
(typically
provided in the material commonly referred to as "stucco") or calcium sulfate
anhydrite
(CaSO4) depending on the temperature and duration of exposure. 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. Calcination of the gypsum to
produce the
hemihydrate form takes place by the following equation:
CaSO4=2H20¨>CaSO4Ø5H20+1.5H20
[0008] 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."
[0009] Gypsum may also be obtained synthetically (referred to as
"syngyp" in the art) as
a by-product of industrial processes such as flue gas desulfurization from
power plants, for
example. Natural or synthetic gypsum can be calcined at high temperatures,
typically above
150 C, to form stucco (i.e., calcined gypsum in the form of calcium sulfate
hemihydrate
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and/or calcium sulfate anhydrite), which may undergo subsequent rehydration to
form set
gypsum in a desired shape, such as a board.
[0010] Synthetic gypsum obtained from power plants is usually suitable
for use in
gypsum panels intended for construction projects. Synthetic gypsum is a
byproduct of flue
gas desulfurization processes from power plants (also known as
desulphurisation gypsum or
desulphogyspum or DSG). In particular, flue gas including sulfur dioxide is
wet scrubbed
with lime or limestone, which produces calcium sulfite in the following
reaction.
CaCO3+S02¨>CaS03+CO2
The calcium sulfite is then converted to calcium sulfate in the following
reaction.
CaS03+2H20+1/202¨>C aSO4.2H20
The hemihydrate form may then be produced by calcination in a similar manner
to that used
for natural gypsum.
[0011] However, many conventional coal-fired power plants are being shut
down in favor
of more environmentally friendly sources of energy. The shutdown of coal-fired
power
plants has created a growing shortage of synthetic gypsum suitable for
producing gypsum
panels. Lower quality synthetic gypsum is available from power plants and
other sources, but
this alternatively sourced gypsum often contains fairly high concentrations of
extraneous
salts, particularly magnesium or sodium salts, more particularly magnesium
chloride and
sodium chloride. Small amounts of potassium chloride and calcium chloride may
also be
present in alternatively sourced synthetic gypsum. The extraneous salts can be
problematic
due to their tendency to decrease adhesion between the board core and the
cover sheets,
particularly a back paper cover sheet.
[0012] 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
claims, and not by the ability of the claimed invention to solve any specific
problem noted
herein.
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BRIEF SUMMARY OF THE INVENTION
[0013] The invention relates to gypsum board and a method of preparing
gypsum board
where the board exhibits good adhesion between a set gypsum layer and a cover
sheet of the
board. The invention has particular applicability with boards formed from
stucco containing
a high content of salt impurities. Generally, stucco is formed by calcining
gypsum from
natural or synthetic sources. In nature, it is a common abundant mineral that
can be mined
from the earth. The synthetic form of gypsum can be derived as a byproduct
from flue gas
desulfurization (FGD) processes associated with coal-fired electric
powerplants that burn
high sulfur coals. In the powerplants, sulfur dioxide emissions are removed
through a wet
scrubbing process. A limestone slurry injection results in precipitation of
synthetic gypsum
following fly ash removal. For example, some forms of synthetic gypsum contain
the high
content of salt impurities, which then remain in the stucco formed as calcined
gypsum. The
salt impurities in the synthetic gypsum can result from, for example high salt
coals. These
salt impurities have been found to deleteriously affect bonding between a
cover sheet (e.g.,
formed from paper) and a set gypsum layer (e.g., the board core) in the board.
[0014] The invention provides for a product and method of manufacture
where at least
one set gypsum layer is sandwiched between two cover sheets, wherein at least
one of the
cover sheets is a high absorption paper. In this manner, the invention allows
for improved
adhesion even when the set gypsum layers are formed from stucco derived from
low quality
synthetic gypsum, e.g., containing undesirable extraneous salts, including
chloride salts such
as NaCl, KC1, MgCl2, and/or CaCl2, which previously were found to interfere
with paper-
core bonding.
[0015] Thus, in one aspect, the invention provides a gypsum board
comprising a set
gypsum core disposed between a face cover sheet and a back cover sheet, the
set gypsum
core formed from a slurry comprising water, stucco, and a high salt impurity
content (e.g.,
chloride salt). At least one of the cover sheets is a high absorption paper.
As used herein,
high absorption paper refers to paper that absorbs more water as compared to
conventional
paper grades. If desired, a face skim coat layer can be disposed between a
first face of the set
gypsum core and the face cover sheet, and a back skim coat layer can be
disposed between a
second face of the set gypsum core and the back cover sheet. In some
embodiments, at least
the back cover sheet is high absorption paper.
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[0016] In another aspect, the invention provides a method of making
gypsum board. The
method comprises mixing at least water and stucco containing a high salt
impurity content to
form a first slurry. The first slurry is applied to form a set gypsum board
core in a bonding
relation to a face cover sheet. The board core has a first face and a second
face. The first face
5 faces the face cover sheet. A back cover sheet is applied in bonding
relation to the second
face of the board core to form a board precursor. At least one of the cover
sheets is a high
absorption paper (e.g., at least the back cover sheet in some embodiments).
The board
precursor is dried to form a board. If desired, a face skim coat layer and a
back skim coat
layer can be provided in any suitable manner on either side of the board core.
For example,
in some embodiments, a second slurry comprising at least stucco and water is
applied to the
face paper prior to the first slurry being applied over the face paper. The
second slurry forms
a face skim coat disposed between the face cover sheet and the board core.
Similarly, if
desired, a third slurry comprising at least stucco and water can be applied to
the back paper
before the back cover sheet is applied over the board core. The third slurry
forms a back
skim coat disposed between the back cover sheet and the board core. The second
and third
slurries can be the same or different and generally have a higher density than
the first slurry
in preferred embodiments.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)
[0017] FIG. 1 are photographs of three boards after bond testing as
discussed in Example
1.
[0018] FIG. 2 are photographs of three boards after bond testing as
discussed in Example
1.
DETAILED DESCRIPTION OF THE INVENTION
[0019] The invention is predicated, at least in part, on a board
containing at least one set
gypsum layer sandwiched between two cover sheets, wherein at least one of the
cover sheets
is in the form of a high absorption paper in order to enhance adhesion between
the set
gypsum layer and the cover sheet. The invention is particularly useful for
gypsum boards
where the set gypsum layer(s) is formed from a stucco slurry containing
appreciable
quantities of extraneous salts. For example, in some embodiments, the salts
are chloride
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salts, e.g., sodium chloride (NaCl), potassium chloride (KC1), magnesium
chloride (MgCl2),
and/or calcium chloride (CaCl2).
[0020] Such salts can be found, for example, in stucco slurries where
the stucco is
derived from a low quality synthetic gypsum. In this regard, normally, a board
manufacturing facility is sourced with gypsum that is then calcined to form
stucco. The
stucco is then reacted with water to form the gypsum (i.e., calcium sulfate
dihydrate) layer of
desired dimensions. If the low quality synthetic gypsum contains the
appreciable quantities
of salt impurities, such salts have been found to remain with the stucco after
calcining and
hence are present in the stucco slurry. In some embodiments, the stucco slurry
comprises
.. high qualities of the salts, e.g., at least about 150 ppm chloride anion
per 1,000,000 parts by
weight of said calcium sulfate hemihydrate, such as about 150 ppm to about
2000 ppm
chloride anion per 1,000,000 parts by weight of said calcium sulfate
hemihydrate. The
presence of the salt impurities in appreciable amounts has been found to
interfere with
adhesion between the board core and the paper cover sheet.
[0021] The high absorption paper absorbs more water than conventional
paper. When
high salt stucco is used, the salt migrates to surface of a paper cover sheet,
between plies of
the paper cover sheet, and the interface between the paper cover sheet and the
board core,
thereby resulting in poor adhesion and potentially delamination. While not
wishing to be
bound by any particular theory, it is believed that the use of high absorption
paper increases
the amount of salt impurities migrating to the outer side of the cover paper
and
correspondingly reduces the amount of salt migrating to the cover sheet-core
interface. It is
further believed that, during the drying process in the kiln, when the water
evaporates from
the surface of board, the high absorption paper tends to absorb water and
evaporate water
faster than conventional paper, resulting in more salt migrating to the outer
side of the paper.
[0022] The high absorption paper can have any suitable weight and
thickness. Generally,
the weight of paper is determined by basis weight, which refers to the weight
per unit area.
This can be expressed as pounds per 1000 sq. ft as paper weight. In some
embodiments, the
high absorption paper has a basis weight of from about 30 lb/MSF to about 70
lb/MSF, such
as from about 42 lb/MSF to about 60 lb/MSF, e.g., from about 45 lb/MSF to
about 55
.. lb/MSF. In some embodiments, the high absorption paper has a caliper of
from about 7 mils
to about 20 mils, e.g., from about 10 mils to about 15 mils (such as about 12
mils). The
surface water absorption over 60 seconds, expressed in g/m2, measured by Cobb
Test. The
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test determines, on the surface of 100 cm2 of paper, how many grams of water
is absorbed
based on the Cobb test. The procedural standards for the Cobb Test are
explained in TAPPI
T441.
10023] The high absorption paper can have any suitable water
absorptivity higher than
that of conventional paper. The bond side Cobb value refers to the inner side
of the paper
that is in contact with the gypsum slurry, while the liner side Cobb refers to
the outer side of
the paper which is not in contact with the slurry, where the Cobb values are
measured
according to TAPPI standards as set forth in the TAPPI T441 test procedure.
For example, in
some embodiments, the high absorption paper has a bond side Cobb value of at
least about
1.8 g/100 cm2, e.g., from about 1.8 g/100 cm2 to about 3 g/100 cm2, such as
from about 1.8
g/100 cm2 to about 2.9 g/100 cm2, from about 1.8 g/100 cm2 to about 2.7 g/100
cm2, from
about 1.8 g/100 cm2 to about 2.5 g/100 cm2, from about 2 g/100 cm2 to about 3
g/100 cm2,
from about 2 g/100 cm2 to about 2.9 g/100 cm2, from about 2 g/100 cm2 to about
2.7 g/100
cm2, from about 2 g/100 cm2 to about 2.5 g/100 cm2, from about 2.1 g/100 cm2
to about 3
g/100 cm2, from about 2.1 g/100 cm2 to about 2.9 g/100 cm2, from about 2.1
g/100 cm2 to
about 2.7 g/100 cm2, from about 2.1 g/100 cm2 to about 2.5 g/100 cm2, from
about 2.2 g/100
cm2 to about 3 g/100 cm2, from about 2 g/100 cm2 to about 2.9 g/100 cm2, from
about 2.2
g/100 cm2 to about 2.7 g/100 cm2, or from about 2.2 g/100 cm2 to about 2.5
g/100 cm2, from
about 2.4 g/100 cm2 to about 3 g/100 cm2, from about 2.4 g/100 cm2 to about
2.9 g/100 cm2,
from about 2.4 g/100 cm2 to about 2.7 g/100 cm2, etc.
[0024] In some embodiments, the high absorption paper has a liner side
Cobb value of at
least about 0.5 g/100 cm2, e.g., from about 0.5 g/100 cm2 to about 1.5 g/100
cm2, such as
from about 0.5 g/100 cm2 to about 1.2 g/100 cm2, from about 0.7 g/100 cm2 to
about 1.5
g/100 cm2, from about 0.7 g/100 cm2 to about 1.2 g/100 cm2, from about 0.9
g/100 cm2 to
about 1.5 g/100 cm2, from about 0.9 g/100 cm2 to about 1.2 g/100 cm2, etc.
Examples of high
absorption paper include Newsline Hi-Abs and News SHW HiAbs from USG. Newsline
Hi
Abs has a basis weight of from about 45 lb/MSF to about 48 lb/MSF. Newsline
SHW Hi Abs
is a super heavy high absorption paper, having a basis weight of from about 53
to about 63.5
lb/MSF.
[0025] In embodiments in which the board has only one high absorption cover
sheet (e.g.,
the back cover sheet), the other cover sheet (e.g., the face cover sheet) can
have any suitable
basis weight and thickness. For example, in some embodiments, the other cover
sheet can
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have a basis weight of from about 10 lb/msf to about 60 lb/msf, e.g., from
about 10 lb/msf to
about 55 lb/msf, from about 10 lb/msf to about 50 lb/msf, from about 10 lb/msf
to about 40
lb/msf, from about 20 lb/msf to about 60 lb/msf, from about 20 lb/msf to about
55 lb/msf,
from about 20 lb/msf to about 50 lb/msf, from about 20 lb/msf to about 40
lb/msf, from about
30 lb/msf to about 60 lb/msf, from about 30 lb/msf to about 55 lb/msf, from
about 30 lb/msf
to about 50 lb/msf, from about 30 lb/msf to about 40 lb/msf, etc. In some
embodiments, the
other cover sheet has a weight of from about 15 lb/MSF to about 35 lb/msf,
such as from
about 20 lb/MSF to about 33 lb/msf, from about 20 lb/MSF to about 31 lb/msf,
from about 20
lb/MSF to about 29 lb/msf, from about 20 lb/MSF to about 27 lb/msf, from about
15 lb/MSF
to about 31 lb/msf, etc. Paper at such weights can have a nominal thickness of
about 0.005
inch to about 0.015 inch thick, e.g., 0.007 to about 0.03 inch (e.g., about
0.01 inch). In some
embodiments, the other cover sheet can be in the form of paper having a
thickness of from
about 0.008 inch to about 0.013 inch.
[0026] If desired, the board can include a face skim coat and/or a back
skim coat. In
preferred embodiments, the skim coat layers generally have higher density and
are very thin
relative to the set gypsum core. In some embodiments, the layer(s) forming the
set gypsum
core is the largest contributor to thickness of the gypsum layers
cumulatively, and to the
board as a whole. In some embodiments, the set gypsum core makes up a
substantial
thickness (e.g., at least about 90%, at least about 92%, at least about 95%,
or at least about
97%) of the total thickness of all the gypsum layers. In some embodiments, the
face and/or
back skim coat layer has a dry thickness of from about 0.125 inches (1/8 inch)
to about 0.016
inches (1/64 inch). In preferred embodiments, at least one skim coat layer has
a thickness of
from about 0.08 inches to about 0.02 inches, such as from about 0.08 inches to
about 0.03
inches, from about 0.07 inches to about 0.02 inches, from about 0.07 inches to
about 0.03
inches, from about 0.06 inches to about 0.02 inches, from about 0.06 inches to
about 0.03
inches, from about 0.05 inches to about 0.02 inches, from about 0.05 inches to
about 0.03
inches, from about 0.04 inches to about 0.02 inches, or from about 0.04 inches
to about 0.03
inches.
[0027] In some embodiments, one or both skim coats can be prepared from
a slurry
containing skim coat starch, as described in U.S. Patent Application
62/930,965, filed
November 5, 2019, incorporated herein by reference. Surprisingly and
unexpectedly,
including skim coat starch in the very thin back skim coat has been found to
further provide
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enhanced bonding between the core and the back cover sheet. While not wishing
to be found
by any particular theory, the presence of the skim coat starch in the thin
skim coat is effective
for enhancing cover sheet-gypsum core bonding because it is believed the
starch acts as glue
to bind the paper fibers and gypsum crystals in the core tightly.
[0028] In a wall assembly, the board can be affixed to a substrate,
typically studs in a
framing construction. In the wall assembly, the back surface of the board
(i.e., the outer
surface of the back cover sheet) faces inward toward the studs while the face
surface of the
board (i.e., the outer surface of the face cover sheet) is visible when the
board is hanging
when installed in use.
[0029] The stucco slurry used in making the set gypsum layer(s) of the
board contains
stucco, e.g., in the form of calcium sulfate alpha hemihydrate, calcium
sulfate beta
hemihydrate, and/or calcium sulfate anhydrite. In addition to the stucco and
water, the board
core is preferably formed from an agent that contributes to its lower density,
preferably
foaming agents, although in some embodiments low density filler (e.g.,
perlite, low density
aggregate or the like) can be employed. Various foaming agent regimes are well
known in
the art. Foaming agent can be included to form an air void distribution within
a crystalline
matrix of set gypsum. In some embodiments, the foaming agent comprises 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.
See, e.g., U.S. Patents 5,643,510; 6,342,284; and 6,632,550. In some
embodiments, the
foaming agent comprises an alkyl sulfate surfactant.
[0030] Many commercially known foaming agents are available and can be
used in
accordance with embodiments of the disclosure, such as the HYONIC line (e.g.,
25A5) of
soap products from GEO Specialty Chemicals, Ambler, PA. Other commercially
available
soaps include the Polystep B25, from Stepan Company, Northfield, Illinois. The
foaming
agents described herein can be used alone or in combination with other foaming
agents. The
foam can be pregenerated and then added to the stucco slurry. The
pregeneration can occur
by inserting air into the aqueous foaming agent. Methods and apparatus for
generating foam
are well known. See, e.g., U.S. Patents 4,518,652; 2,080,009; and 2,017,022.
[0031] In some embodiments, the foaming agent comprises, consists of, or
consists
essentially of at least one alkyl sulfate, at least one alkyl ether sulfate,
or any combination
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thereof but is essentially free of an olefin (e.g., olefin sulfate) and/or
alkyne. Essentially free
of olefin or alkyne means that the foaming agent contains either (i) 0 wt.%
based on the
weight of stucco, or no olefin and/or alkyne, or (ii) an ineffective or (iii)
an immaterial
amount of olefin and/or alkyne. An example of an ineffective amount is an
amount below the
5 .. threshold amount to achieve the intended purpose of using olefin and/or
alkyne foaming
agent, as one of ordinary skill in the art will appreciate. An immaterial
amount may be, e.g.,
below about 0.001 wt.%, such as below about 0.0005 wt.%, below about 0.001
wt.%, below
about 0.00001 wt.%, etc., based on the weight of stucco, as one of ordinary
skill in the art
will appreciate.
10 [0032] Some types of unstable soaps, in accordance with
embodiments of the disclosure,
are alkyl sulfate surfactants with varying chain length and varying cations.
Suitable chain
lengths, can be, for example, C8-C12, e.g., C8-Cio, or Cio-C12. Suitable
cations include, for
example, sodium, ammonium, magnesium, or potassium. Examples of unstable soaps
include, for example, sodium dodecyl sulfate, magnesium dodecyl sulfate,
sodium decyl
sulfate, ammonium dodecyl sulfate, potassium dodecyl sulfate, potassium decyl
sulfate,
sodium octyl sulfate, magnesium decyl sulfate, ammonium decyl sulfate, blends
thereof, and
any combination thereof.
[0033] Some types of stable soaps, in accordance with embodiments of the
disclosure, are
alkoxylated (e.g., ethoxylated) alkyl sulfate surfactants with varying
(generally longer) chain
length and varying cations. Suitable chain lengths can be, for example, Cio-
C14, e.g., C12-C14,
or Cio-C12. Suitable cations include, for example, sodium, ammonium,
magnesium, or
potassium. Examples of stable soaps include, for example, sodium laureth
sulfate, potassium
laureth sulfate, magnesium laureth sulfate, ammonium laureth sulfate, blends
thereof, and any
combination thereof. In some embodiments, any combination of stable and
unstable soaps
from these lists can be used.
[0034] Examples of combinations of foaming agents and their addition in
preparation of
foamed gypsum products are disclosed in U.S. Patent 5,643,510, herein
incorporated by
reference. For example, a first foaming agent which forms a stable foam and a
second
foaming agent which forms an unstable foam can be combined. In some
embodiments, the
first foaming agent is a soap, e.g., with an alkoxylated alkyl sulfate soap
with an alkyl chain
length of 8-12 carbon atoms and an alkoxy (e.g., ethoxy) group chain length of
1-4 units.
The second foaming agent is optionally an unalkoxylated (e.g., unethoxylated)
alkyl sulfate
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11
soap with an alkyl chain length of 6-20 carbon atoms, e.g., 6-18 or 6-16
carbon atoms.
Regulating the respective amounts of these two soaps, in accordance with some
embodiments, is believed to allow for control of the board foam structure
until about 100%
stable soap or about 100% unstable soap is reached.
[0035] In some embodiments, a fatty alcohol optionally can be included with
the foaming
agent, e.g., in a pre-mix to prepare the foam, as described in U.S. Patent
Publications US
2017/0096369 Al, US 2017/0096366 Al, and US 2017/0152177 Al. This can result
in an
improvement in the stability of the foam, thereby allowing better control of
foam (air) void
size and distribution. The fatty alcohol can be any suitable aliphatic fatty
alcohol. It will be
understood that, as defined herein throughout, "aliphatic" refers to alkyl,
alkenyl, or alkynyl,
and can be substituted or unsubstituted, branched or unbranched, and saturated
or
unsaturated, and in relation to some embodiments, is denoted by the carbon
chains set forth
herein, e.g., Cx-Cy, where x and y are integers. The term aliphatic thus also
refers to chains
with heteroatom substitution that preserves the hydrophobicity of the group.
The fatty
alcohol can be a single compound, or can be a combination of two or more
compounds. In
some embodiments, the optional fatty alcohol is a C6-C20 fatty alcohol (e.g.,
C6-C18, C6-C116,
C6-C14, C6-C12, C6-C10, C6-C8, C8-C16, C8-C14, C8-C12, C8-C10, C10-C16, C10-
C14, c10-c12, C12-
C16, C12-C14, or C14-C16 aliphatic fatty alcohol, etc.). Examples include
octanol, nonanol,
decanol, undecanol, dodecanol, or any combination thereof.
[0036] In some embodiments, the optional foam stabilizing agent comprises
the fatty
alcohol and is essentially free of fatty acid alkyloamides or carboxylic acid
taurides. In some
embodiments, the optional foam stabilizing agent is essentially free of a
glycol, although
glycols can be included in some embodiments, e.g., to allow for higher
surfactant content.
Essentially free of any of the aforementioned ingredients means that the foam
stabilizer
contains either (i) 0 wt.% based on the weight of any of these ingredients, or
(ii) an
ineffective or (iii) an immaterial amount of any of these ingredients. An
example of an
ineffective amount is an amount below the threshold amount to achieve the
intended purpose
of using any of these ingredients, as one of ordinary skill in the art will
appreciate. An
immaterial amount may be, e.g., below about 0.0001 wt.%, such as below about
0.00005
wt.%, below about 0.00001 wt.%, below about 0.000001 wt.%, etc., based on the
weight of
stucco, as one of ordinary skill in the art will appreciate.
Date Recue/Date Received 2020-06-26
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12
[0037] It has been found that suitable void distribution and wall
thickness
(independently) can be effective to enhance strength, especially in lower
density board (e.g.,
below about 35 pcf). See, e.g., US 2007/0048490 and US 2008/0090068.
Evaporative water
voids, generally having voids of about 5 gm or less in diameter, also
contribute to the total
void distribution along with the aforementioned air (foam) voids. In some
embodiments, 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, from
about 0.7:1 to about 9:1, from about 0.8:1 to about 9:1, from about 1.4:1 to
about 9:1, from
about 1.8:1 to about 9:1, from about 2.3:1 to about 9:1, from about 0.7:1 to
about 6:1, from
about 1.4:1 to about 6:1, from about 1.8:1 to about 6:1, from about 0.7:1 to
about 4:1, from
about 1.4:1 to about 4:1, from about 1.8:1 to about 4:1, from about 0.5:1 to
about 2.3:1, from
about 0.7:1 to about 2.3:1, from about 0.8:1 to about 2.3:1, from about 1.4:1
to about 2.3:1,
from about 1.8:1 to about 2.3:1, etc.
[0038] As used herein, a void size is calculated from the largest
diameter of an individual
void in the core. The largest diameter is the same as the Feret diameter. The
largest diameter
of each defined void can be obtained from an image of a sample. Images can be
taken using
any suitable technique, such as scanning electron microscopy (SEM), which
provides two-
dimensional images. A large number of pore sizes of voids can be measured in
an SEM
image, such that the randomness of the cross sections (pores) of the voids can
provide the
.. average diameter. Taking measurements of voids in multiple images randomly
situated
throughout the core of a sample can improve this calculation. Additionally,
building a three-
dimensional stereological model of the core based on several two-dimensional
SEM images
can also improve the calculation of the void sizes. Another technique is X-ray
CT-scanning
analysis (XMT), which provides a three-dimensional image. Another technique is
optical
microscopy, where light contrasting can be used to assist in determining,
e.g., the depth of
voids. The voids can be measured either manually or by using image analysis
software, e.g.,
ImageJ, developed by NIH. One of ordinary skill in the art will appreciate
that manual
determination of void sizes and distribution from the images can be determined
by visual
observation of dimensions of each void. The sample can be obtained by
sectioning a gypsum
board.
[0039] The foaming agent can be included in the stucco slurry in any
suitable amount,
e.g., depending on the desired density. A solution of foaming agent is
prepared at, for
Date Recue/Date Received 2020-06-26
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13
example, about 0.5% (w/w). Proper amount of air is mixed with the proper
amount of the
solution of foaming agent, and added into slurry. Depending on the amount of
air required,
the concentration of the solution of the foaming agent can vary from about
0.1% to about 1%
(w/w). Since the skim coat layers have a higher density, the slurry for
forming the skim coat
layers can be made with less (or no) foam.
[0040] The fatty alcohol can be present, if included, in the stucco
slurry in any suitable
amount. In some embodiments, the fatty alcohol is present in the core slurry
in an amount of
from about 0.0001% to about 0.03% by weight of the stucco, e.g., from about
0.0001% to
about 0.025% by weight of the stucco, from about 0.0001% to about 0.02% by
weight of the
stucco, or from about 0.0001% to about 0.01% by weight of the stucco. Since
the slurries for
the skim coat layers can have less or no foam, the fatty alcohol is not
required in the skim
coat layers, or else can be included in a lower amount, such as from about
0.0001% to about
0.004% by weight of the stucco, e.g., from about 0.00001% to about 0.003% by
weight of the
stucco, from about 0.00001% to about 0.0015% by weight of the stucco, or from
about
0.00001 % to about 0.001% by weight of the stucco.
[0041] Other ingredients as known in the art can also be included in the
board core slurry,
including, for example, accelerators, retarders, etc. Accelerator can be in
various forms (e.g.,
wet gypsum accelerator, heat resistant accelerator, and climate stabilized
accelerator). See,
e.g., U.S. Patents 3,573,947 and 6,409,825. In some embodiments where
accelerator and/or
retarder are included, the accelerator and/or retarder each can be in the
stucco slurry in an
amount on a solid basis of, such as, from 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%).
[0042] In addition, the gypsum layer(s) can be further formed from at
least one dispersant
to enhance fluidity in some embodiments. The dispersants may be included in a
dry form
with other dry ingredients and/or in a liquid form with other liquid
ingredients in stucco
slurry. Examples of dispersants include naphthalenesulfonates, such as
polynaphthalenesulfonic acid and its salts (polynaphthalenesulfonates) and
derivatives, which
are condensation products of naphthalenesulfonic acids and formaldehyde; as
well as
polycarboxylate dispersants, such as polycarboxylic ethers, for example,
PCE211, PCE111,
1641, 1641F, or PCE 2641-Type Dispersants, e.g., MELFLUX 2641F, MELFLUX 2651F,
MELFLUX 1641F, MELFLUX 2500L dispersants (BASF), and COATEX Ethacryl M,
Date Recue/Date Received 2020-06-26
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14
available from Coatex, Inc.; and/or lignosulfonates or sulfonated lignin.
Lignosulfonates are
water-soluble anionic polyelectrolyte polymers, byproducts from the production
of wood
pulp using sulfite pulping. One example of a lignin useful in the practice of
principles of
embodiments of the present disclosure is Marasperse C-21 available from Reed
Lignin Inc.
[0043] Lower molecular weight dispersants are generally preferred. For
naphthalenesulfonate dispersants, in some embodiments, they are selected to
have molecular
weights from about 3,000 to about 10,000 (e.g., about 8,000 to about 10,000).
In some
embodiments, higher water demand naphthalenesulfonates can be used, e.g.,
having
molecular weights above 10,000. As another illustration, for PCE211 type
dispersants, in
some embodiments, the molecular weight can be from about 20,000 to about
60,000, which
exhibit less retardation than dispersants having molecular weight above
60,000.
[0044] One example of a naphthalenesulfonate is DILOFLO, available from
GEO
Specialty Chemicals. DILOFLO is a 45% naphthalenesulfonate solution in water,
although
other aqueous solutions, for example, in the range of about 35% to about 55%
by weight
solids content, are also readily available. Naphthalenesulfonates can be used
in dry solid or
powder form, such as LOMAR D, available from GEO Specialty Chemicals, for
example.
Another example of naphthalenesulfonate is DAXAD, available from GEO Specialty
Chemicals, Ambler, PA.
[0045] If included, the dispersant can be provided in any suitable
amount. In some
embodiments, for example, the dispersant can be present in the stucco slurry
in an amount,
for example, from about 0% to about 0.5%, e.g., from about 0.01% to about
0.7%, e.g., from
about 0.01% to about 0.4% by weight of the stucco, from about 0.1% to about
0.2%, etc.
[0046] In some embodiments, the gypsum layer(s) can be further formed
from at least
one phosphate-containing compound, if desired, to enhance green strength,
dimensional
stability, and/or sag resistance. For example, phosphate-containing components
useful in
some embodiments 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 salt. See, e.g., U.S. Patents 6,342,284;
6,632,550;
6,815,049; and 6,822,033.
Date Recue/Date Received 2020-06-26
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[0047] Phosphate compositions if added in some embodiments can enhance
green
strength, resistance to permanent deformation (e.g., sag), dimensional
stability, etc. Green
strength refers to the strength of the board while still wet during
manufacture. Due to the
rigors of the manufacturing process, without sufficient green strength, a
board precursor can
5 become damaged on a manufacturing line.
[0048] Trimetaphosphate compounds can be used, including, for example,
sodium
trimetaphosphate, potassium trimetaphosphate, lithium trimetaphosphate, and
ammonium
trimetaphosphate. Sodium trimetaphosphate (STMP) is preferred, although other
phosphates
may be suitable, including for example sodium tetrametaphosphate, sodium
10 hexametaphosphate having from about 6 to about 27 repeating phosphate
units and having
the molecular formula Nan 2PnO3n q wherein n=6-27, tetrapotassium
pyrophosphate having
the molecular formula ICIP207, trisodium dipotassium tripolyphosphate having
the molecular
formula Na3K2P3010, sodium tripolyphosphate having the molecular formula
Na5P3010,
tetrasodium pyrophosphate having the molecular formula Na4P207, aluminum
15 .. trimetaphosphate having the molecular formula Al(P03)3, sodium acid
pyrophosphate having
the molecular formula Na2H2P207, ammonium polyphosphate having 1,000-3,000
repeating
phosphate units and having the molecular formula +2-1
INI44, P o ,- ¨n n ¨ 3n+1 wherein n=1,000-3,000,
or polyphosphoric acid having two or more repeating phosphoric acid units and
having the
molecular formula Hn+2PnO3n+1 wherein n is two or more.
[0049] If included, the polyphosphate can be present in any suitable
amount. To
illustrate, in some embodiments, the polyphosphate can be present in the
slurry in an amount,
for example, from about 0.1% to about 1%, e.g., about 0.2% to about 0.4% by
weight of the
stucco, from about 0% to about 0.5%, e.g., from about 0% to about 0.2% by
weight of the
stucco. Thus, the dispersant and polyphosphate optionally can be in any
suitable amount in
the stucco slurry.
[0050] The board core can have any suitable density useful in
contributing to a desired
total composite board density, such as, for example, a core density of from
about 16 pcf
(about 260 kg/m3) to about 40 pcf, e.g., from about 18 pcf to about 40 pcf, 18
pcf to about 38
pcf, 18 pcf to about 36 pcf, 18 pcf to about 32 pcf, 20 pcf to about 40 pcf,
20 pcf to about 36
pcf, 20 pcf to about 32 pcf, 22 pcf to about 40 pcf, 22 pcf to about 36 pcf,
22 pcf to about 32
pcf, 26 pcf to about 40 pcf, 26 pcf to about 36 pcf, or 26 pcf to about 32
pcf. In some
embodiments, the board core has an even lower density, e.g., about 30 pcf or
less, about 29
Date Recue/Date Received 2020-06-26
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16
pcf (about 460 kg/m3) or less, about 28 pcf or less, about 27 pcf (about 430
kg/m3) or less,
about 26 pcf or less, etc. For example, in some embodiments, the core density
is from about
12 pcf (about 190 kg/m3) to about 30 pcf, from about 14 pcf (about 220 kg/m3)
to about 30
pcf, 16 pcf to about 30 pcf, 16 pcf to about 28 pcf, 16 pcf to about 26 pcf,
16 pcf to about 22
pcf (about 350 kg/m3), 18 pcf to about 30 pcf, 18 pcf to about 28 pcf, 18 pcf
to about 26 pcf,
18 pcf to about 24 pcf, 20 pcf to about 30 pcf, 20 pcf to about 28 pcf, 20 pcf
to about 26 pcf,
20 pcf to about 24 pcf, 22 pcf to about 28 pcf, etc.
[0051] In some embodiments, composite board made according to the
disclosure meets
test protocols according to ASTM Standard C473-10. For example, in some
embodiments,
when the board is cast at a thickness of 1/2 inch, the dry board has a nail
pull resistance of at
least about 67 lbe (pounds force) as determined according to ASTM C473-10
(method B),
e.g., at least about 68 lbe, at least about 70 lbe, at least about 72 lbe, at
least about 74 lbe, at
least about 75 lbe, at least about 76 lbe, at least about 77 lbe, etc. In
various embodiments, the
nail pull resistance can be from about 67 lbe to about 100 lbe, from about 67
lbe to about
95 lbe, from about 67 lbe to about 90 lbe, from about 67 lbe to about 85 lbe,
from about 67 lbe to
about 80 lbe, from about 67 lbe to about 75 lbe, from about 68 lbe to about
100 lbe, from about
68 lbe to about 95 lbe, from about 68 lbe to about 90 lbe, from about 68 lbe
to about 85 lbe, from
about 68 lbe to about 80 lbe, from about 70 lbe to about 100 lbe, from about
70 lbe to about
95 lbe, from about 70 lbe to about 90 lbe, from about 70 lbe to about 85 lbe,
from about 70 lbe to
about 80 lbe, from about 72 lbe to about 100 lbe, from about 72 lbe to about
95 lbe, from about
72 lbe to about 90 lbe, from about 72 lbe to about 85 lbe, from about 72 lbe
to about 80 lbe, from
about 72 lbe to about 77 lbe, from about 72 lbe to about 75 lbe, from about 75
lbe to about
100 lbe, from about 75 lbe to about 95 lbe, from about 75 lbe to about 90 lbe,
from about 75 lbe
to about 85 lbe, from about 75 lbe to about 80 lbe, from about 75 lbe to about
77 lbe, from about
77 lbe to about 100 lbe, from about 77 lbe to about 95 lbe, from about 77 lbe
to about 90 lbe,
from about 77 lbe to about 85 lbe, or from about 77 lbe to about 80 lbe.
[0052] In some embodiments, the composite gypsum board can have an
average core
hardness of at least about 11 lbe, e.g., at least about 12 lbe, at least about
13 lbe, at least about
14 lbe, at least about 15 lbe, at least about 16 lbe, at least about 17 lbe,
at least about 18 lbe, at
least about 19 lbe, at least about 20 lbe, at least about 21 lbe, or at least
about 22 lbe, as
determined according to ASTM C473-10, method B. In some embodiments, board can
have
a core hardness of from about 11 lbe to about 25 lbe, e.g., from about 11 lbe
to about 22 lbe,
Date Recue/Date Received 2020-06-26
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17
from about 11 lbe to about 21 lbe, from about 11 lbe to about 20 lbe, from
about 11 lbe to about
19 lbe, from about 11 lbe to about 18 lbe, from about 11 lbe to about 17 lbe,
from about 11 lbe to
about 16 lbe, from about 11 lbe to about 15 lbe, from about 11 lbe to about 14
lbe, from about
11 lbe to about 13 lbe, from about 11 lbe to about 12 lbe, from about 12 lbe
to about 25 lbe, from
about 12 lbe to about 22 lbe, from about 12 lbe to about 21 lbe, from about 12
lbe to about
20 lbe, from about 12 lbe to about 19 lbe, from about 12 lbe to about 18 lbe,
from about 12 lbe to
about 17 lbe, from about 12 lbe to about 16 lbe, from about 12 lbe to about 15
lbe, from about
12 lbe to about 14 lbe, from about 12 lbe to about 13 lbe, from about 13 lbe
to about 25 lbe, from
about 13 lbe to about 22 lbe, from about 13 lbe to about 21 lbe, from about 13
lbe to about
.. 20 lbe, from about 13 lbe to about 19 lbe, from about 13 lbe to about 18
lbe, from about 13 lbe to
about 17 lbe, from about 13 lbe to about 16 lbe, from about 13 lbe to about 15
lbe, from about
13 lbe to about 14 lbe, from about 14 lbe to about 25 lbe, from about 14 lbe
to about 22 lbe,
from about 14 lbe to about 21 lbe, from about 14 lbe to about 20 lbe, from
about 14 lbe to about
19 lbe, from about 14 lbe to about 18 lbe, from about 14 lbe to about 17 lbe,
from about 14 lbe to
about 16 lbe, from about 14 lbe to about 15 lbe, from about 15 lbe to about 25
lbe, from about
15 lbe to about 22 lbe, from about 15 lbe to about 21 lbe, from about 15 lbe
to about 20 lbe, from
about 15 lbe to about 19 lbe, from about 15 lbe to about 18 lbe, from about 15
lbe to about
17 lbe, from about 15 lbe to about 16 lbe, from about 16 lbe to about 25 lbe,
from about 16 lbe to
about 22 lbe, from about 16 lbe to about 21 lbe, from about 16 lbe to about 20
lbe, from about
16 lbe to about 19 lbe, from about 16 lbe to about 18 lbe, from about 16 lbe
to about 17 lbe, from
about 17 lbe to about 25 lbe, from about 17 lbe to about 22 lbe, from about 17
lbe to about
21 lbe, from about 17 lbe to about 20 lbe, from about 17 lbe to about 19 lbe,
from about 17 lbe to
about 18 lbe, from about 18 lbe to about 25 lbe, from about 18 lbe to about 22
lbe, from about
18 lbe to about 21 lbe, from about 18 lbe to about 20 lbe, from about 18 lbe
to about 19 lbe, from
about 19 lbe to about 25 lbe, from about 19 lbe to about 22 lbe, from about 19
lbe to about
21 lbe, from about 19 lbe to about 20 lbe, from about 21 lbe to about 25 lbe,
from about 21 lbe to
about 22 lbe, or from about 22 lbe to about 25 lbe.
[0053] With respect to flexural strength, in some embodiments, when cast
in a board of 1/2
inch thickness, the dry board has a flexural strength of at least about 36 lbe
in a machine
.. direction (e.g., at least about 38 lbe, at least about 40 lbe, etc.) and/or
at least about 107 lbe
(e.g., at least about 110 lbe, at least about 112 lbe, etc.) in a cross-
machine direction as
determined according to the ASTM standard C473-10. In various embodiments, the
board
Date Recue/Date Received 2020-06-26
4993 CA GYP
18
can have a flexural strength in a machine direction of from about 36 lbe to
about 60 lbe, e.g.,
from about 36 lbe to about 55 lbe, from about 36 lbe to about 50 lbe, from
about 36 lbe to about
45 lbe, from about 36 lbe to about 40 lbe, from about 36 lbe to about 38 lbe,
from about 38 lbe to
about 60 lbe, from about 38 lbe to about 55 lbe, from about 38 lbe to about 50
lbe, from about
38 lbe to about 45 lbe, from about 38 lbe to about 40 lbe, from about 40 lbe
to about 60 lbe, from
about 40 lbe to about 55 lbe, from about 40 lbe to about 50 lbe, or from about
40 lbe to about
45 lbe. In various embodiments, the board can have a flexural strength in a
cross-machine
direction of from about 107 lbe to about 130 lbe, e.g., from about 107 lbe to
about 125 lbe, from
about 107 lbe to about 120 lbe, from about 107 lbe to about 115 lbe, from
about 107 lbe to about
112 lbe, from about 107 lbe to about 110 lbe, from about 110 lbe to about 130
lbe, from about
110 lbe to about 125 lbe, from about 110 lbe to about 120 lbe, from about 110
lbe to about
115 lbe, from about 110 lbe to about 112 lbe, from about 112 lbe to about 130
lbe, from about
112 lbe to about 125 lbe, from about 112 lbe to about 120 lbe, or from about
112 lbe to about
115 lbe.
[0054] Advantageously, in various embodiments at various board densities as
described
herein, the dry composite gypsum board can have a compressive strength of at
least about
170 psi (1,170 kPa), e.g., from about 170 psi to about 1,000 psi (6,900 kPa),
from about 170
psi to about 900 psi (6,200 kPa), from about 170 psi to about 800 psi (5,500
kPa), from about
170 psi to about 700 psi (4,800 kPa), from about 170 psi to about 600 psi
(4,100 kPa), from
about 170 psi to about 500 psi (3,450 kPa), from about 170 psi to about 450
psi (3,100 kPa),
from about 170 psi to about 400 psi (2,760 kPa), from about 170 psi to about
350 psi (2,410
kPa), from about 170 psi to about 300 psi (2,070 kPa), or from about 170 psi
to about 250 psi
(1,720 kPa). In some embodiments, the board has a compressive strength of at
least about
450 psi (3,100 kPa), at least about 500 psi (3,450 kPa), at least about 550
psi (3,800 kPa), at
least about 600 psi (4,100 kPa), at least about 650 psi (4,500 kPa), at least
about 700 psi
(4,800 kPa), at least about 750 psi (5,200 kPa), at least about 800 psi (5,500
kPa), at least
about 850 psi (5,850 kPa), at least about 900 psi (6,200 kPa), at least about
950 psi
(6,550 kPa), or at least about 1,000 psi (6,900 kPa). In addition, in some
embodiments, the
compressive strength can be bound by any two of the foregoing points. For
example, the
compressive strength can be between about 450 psi and about 1,000 psi (e.g.,
between about
500 psi and about 900 psi, between about 600 psi and about 800 psi, etc.). The
compressive
strength as used herein is measured using a materials testing system
commercially available
Date Recue/Date Received 2020-06-26
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19
as ATS machine model 1610, from Applied Test Systems in Butler, PA. The load
is applied
continuously and without a shock at speed of 1 inch/min.
[0055] Gypsum board according to embodiments of the invention can be
made on typical
gypsum wallboard manufacturing lines. For example, board manufacturing
techniques are
described in, for example, U.S. Patent 7,364,676, U.S. Patent Application
Publication
2010/0247937, and U.S. Patent Application Number 16/581,070. Briefly, the
process
typically involves discharging a cover sheet onto a moving conveyor. Since
gypsum board is
normally formed "face down," this cover sheet is the "face" cover sheet in
such
embodiments. Face and/or back skim coats as known in the art can be included
as desired.
[0056] In some embodiments, one or both skim coat layers has an average dry
core
hardness that is at least about 1.5 times greater than the average dry core
hardness of the
board core, wherein the average core hardness is measured according to ASTM C-
473-07,
e.g., at least about 2 times greater, 2.5 times greater, 3 times greater, 3.5
times greater, 4
times greater, 4.5 times greater, etc., wherein each of these ranges can have
any
mathematically appropriate upper limit, such as, for example, 8, 7, 6, 5, 4,
3, or 2.
[0057] The slurries for forming the board core and for forming the skim
coat layer can be
formed in any suitable manner. For example, one mixer can be used to develop
both slurry
streams. The mixer can be e.g., in the form of "pin mixers" or "pin-less
mixers" as desired
where the raw materials are agitated. Alternatively, two or more separate
mixers can be used.
The multiple mixers can be in series or unconnected. Examples of mixers are
described in
European Patent 1 637 302 Bl, European Patent 2 929 996 Bl, European Patent
Application
3 342 571 Al, and U.S. Patent Application 2017/0008192 Al. If desired for
efficiency, the
mixer used for the skim coat layer(s) can have a smaller mixing volume
capacity in some
embodiments since the amount of slurry needed to be applied for the skim coat
layer is less
than the amount of slurry that is applied to form the board core. The "main"
mixer (i.e., for
forming the board core slurry) comprises a main body and a discharge conduit
(e.g., a gate-
canister-boot arrangement as known in the art, or a modified outlet design
(MOD)
arrangement as described in U.S. Patents 6,494,609 and 6,874,930). Foaming
agent 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).
[0058] In some embodiments, it will be understood that the discharge
conduit can include
a slurry distributor with either a single feed inlet or multiple feed inlets,
such as those
Date Recue/Date Received 2020-06-26
4993 CA GYP
described in U.S. Patent Application Publication 2012/0168527 Al (Application
No.
13/341,016) and U.S. Patent Application Publication 2012/0170403 Al
(Application No.
13/341,209), for example. In those embodiments, using a slurry distributor
with multiple
feed inlets, the discharge conduit can include a suitable flow splitter, such
as those described
5 in U.S. Patent Application Publication 2012/0170403 Al.
[0059] Board is formed in a sandwich structure, normally concurrently
and continuously,
as will be understood in the art. The face cover sheet travels as a continuous
ribbon on a
moving conveyor. After being discharged from its mixer, a face skim coat layer
slurry is
applied to the (e.g., moving) face cover sheet. Also, hard edges, as known in
the art, can be
10 formed, e.g., from the same slurry stream forming the skim coat layer
(e.g., the face and/or
back skim coat layer) for convenience, if desired.
[0060] The board core slurry is then applied over the skim coat layer
and covered with a
second cover sheet (typically the "back" cover sheet) to form a wet assembly
in the form of a
sandwich structure that is a board precursor to the final product. The back
(bottom) cover
15 sheet can bear a back skim coat layer, which can optionally contain the
skim coat starch as
described herein to enhance bonding between the back paper and the board core.
The back
skim coat layer can be formed from the same or different gypsum slurry as for
the face skim
coat layer. In some embodiments, the skim coat layer is applied on the back
side of the
board, i.e., in bonding relation to the bottom (back) cover sheet but no skim
coat layer is
20 applied between the core and the top cover sheet.
[0061] In some embodiments, the face paper (which is face down at the
wet end of the
board machine) can be made to be slightly wider than the width of the final
board product
since the edges of the paper can be folded up and over the edges of the board
to meet the back
paper (face up at the wet end of the board machine) to form a board envelope.
For example,
for nominal 48 inch wide board, the face paper can have a width of about 50
inches or more
(e.g., from about 50 to about 52 inches, such as about 50.375 inches).
Correspondingly, in
some embodiments, the back paper can be made to be narrower than the width of
the board.
Thus, for nominal 48 inch wide board, the back paper can have a width of less
than about 48
inches (e.g., from about 46.5 inches to about 47.5 inches, such as about
47.125 inches).
[0062] The wet assembly thereby provided is conveyed to a forming station
where the
product is sized to a desired thickness (e.g., via forming plate), and to one
or more knife
sections where it is cut to a desired length. The wet assembly is allowed to
harden to form
Date Recue/Date Received 2020-06-26
4993 CA GYP
21
the interlocking crystalline matrix of set gypsum, and excess water is removed
using a drying
process (e.g., by transporting the assembly through a kiln).
[0063] It also is common in the manufacture of gypsum board to use
vibration in order to
eliminate large voids or air pockets from the deposited slurry. Each of the
above steps, as
.. well as processes and equipment for performing such steps, are known in the
art.
[0064] The invention is further illustrated by the following exemplary
clauses. However,
the invention is not limited by the following clauses.
[0065] (1) Gypsum board or method of making gypsum board as described
herein.
[0066] (2) A gypsum board comprising a set gypsum core disposed between
a face cover
sheet and a back cover sheet, the set gypsum core formed from a slurry
comprising water,
stucco, and a high salt impurity content, at least one of the cover sheets
being high absorption
paper.
[0067] (3) The gypsum board of clause 2, further comprising a face skim
coat disposed
between the face cover sheet and the set gypsum core.
[0068] (4) The gypsum board of clause 2 or 3, further comprising a back
skim coat
disposed between the back cover sheet and the set gypsum core.
[0069] (5) The gypsum board of any one of clauses 2-4, wherein the back
cover sheet is
high absorption paper.
[0070] (6) The gypsum board of any one of clauses 3-5, wherein the face
and/or back
skim coat has a dry thickness of from about 0.125 inches (1/8 inch) to about
0.016 inches
(1/64 inch), such as from about 0.08 inches (1/12 inch) to about 0.03 inches
(1/32 inch).
[0071] (7) The gypsum board of any one of clauses 2-6, wherein the high
salt impurity
comprises at least about 150 ppm chloride anion per 1,000,000 parts by weight
of said stucco.
[0072] (8) The gypsum board of any one of clauses 2-7, wherein the salt
impurity
comprises a chloride salt, such as sodium chloride, potassium chloride,
magnesium chloride,
or calcium chloride.
[0073] (9) The gypsum board of any one of clauses 2-8, wherein the high
absorption
paper has a bond side Cobb value of at least about 2.1 g/100 cm2 according to
the Cobb test.
[0074] (10) The gypsum board of any one of clauses 2-9, wherein the high
absorption
paper has a bond side Cobb value of from about 2.1 g/100 cm2 to about 3.1
g/100 cm2
according to the Cobb test.
Date Recue/Date Received 2020-06-26
4993 CA GYP
22
[0075] (11) The gypsum board of any one of clauses 2-10, wherein the
high absorption
paper has a basis weight of from about 35 lb/MSF to about 65 lb/MSF, such as
from about 38
lb/MSF to about 60 lb/MSF, e.g., from about 42 lb/MSF to about 55 lb/MSF.
[0076] (12) The gypsum board of any one of clauses 2-11, wherein the
high absorption
paper has a caliper of from about 10 mils to about 15 mils.
[0077] (13) A method of making gypsum board, the method comprising: (a)
mixing at
least water and stucco containing a high salt impurity content to form a first
slurry; (b)
applying the first slurry to form a board core in a bonding relation to a face
cover sheet, the
board core having a first face and a second face, the first face facing the
face cover sheet; (c)
applying a back cover sheet in bonding relation to the second face of the
board core to form a
board precursor, at least one of the cover sheets being high absorption paper;
(d) drying the
board precursor to form a board.
[0078] (14) The method of clause 13, further comprising applying a
second slurry
comprising at least stucco and water to the face paper to form a face skim
coat disposed
between the face cover sheet and the board core.
[0079] (15) The method of clause 13 or 14, further comprising applying a
third slurry
comprising at least stucco and water to the back paper to form a back skim
coat disposed
between the back cover sheet and the board core, the second and third slurries
being the same
or different.
[0080] (16) The method of any one of clauses 13-15, wherein the back cover
sheet is
high absorption paper.
[0081] (17) The method of any one of clauses 13-16, wherein the face
and/or back skim
coat has a dry thickness of from about 0.125 inches (1/8 inch) to about 0.016
inches (1/64
inch), such as from about 0.08 inches (1/12 inch) to about 0.03 inches (1/32
inch).
[0082] (18) The method of any one of clauses 13-17, wherein the high salt
impurity
comprises at least about 150 ppm chloride anion per 1,000,000 parts by weight
of said stucco.
[0083] (19) The method of any one of clauses 13-18, wherein the salt
impurity comprises
a chloride salt, such as sodium chloride, potassium chloride, magnesium
chloride, or calcium
chloride.
[0084] (20) The method of any one of clauses 13-19, wherein the high
absorption paper
has a bond side Cobb value of at least about 2.1 g/100 cm2 according to the
Cobb test.
Date Recue/Date Received 2020-06-26
4993 CA GYP
23
[0085] (21) The method of any one of clauses 13-20, wherein the high
absorption paper
has a bond side Cobb value of from about 2.1 g/100 cm2 to about 3.1 g/100 cm2
according to
the Cobb test.
[0086] (22) The method of any one of clauses 13-21, wherein the high
absorption paper
has a basis weight of from about 40 lb/MSF to about 65 lb/MSF, such as from
about 42
lb/MSF to about 60 lb/MSF, e.g., from about 45 lb/MSF to about 55 lb/MSF.
[0087] (23) The method of any one of clauses 13-22, wherein the high
absorption paper
has a caliper of from about 10 mils to about 15 mils.
[0088] It shall be noted that the preceding clauses are illustrative and
not limiting.
Other exemplary embodiments are apparent from the entirety of the description
herein. It
will also be understood by one of ordinary skill in the art that each of these
embodiments may
be used in various combinations with the other embodiments provided herein.
[0089] The following examples further illustrate the invention but, of
course, should not
be construed as in any way limiting its scope.
EXAMPLE 1
[0090] This example demonstrates the effect of using high absorption
paper as a cover
sheet in a wallboard containing a set gypsum layer prepared from stucco
containing a high
content of salt impurities. The high absorption paper enhances the bond
between the paper
and the set gypsum core when the set gypsum layer is formed from a slurry
containing a high
concentration of salt.
[0091] In particular, three 1/2" thick boards (1A-1C) were prepared on a
wallboard
manufacturing production line. The boards contained a set gypsum layer
prepared according
to the formulation of Table 1, sandwiched between face and back cover sheets.
Board 1A
was a control board such that the set gypsum core was prepared without any
high salt
impurities. The set gypsum cores of Boards 1B and 1C, respectively, were
prepared with the
introduction of 600 ppm of chloride ions, via addition of a mixture of sodium
chloride and
magnesium chloride into the formulation listed in Table 1. The amounts for the
ingredients
in Table 1 are provided in lb/MSF.
Table 1: Formulation for Set Gypsum Layer of Boards 1A-1C
Board lA
Ingredient Board 1B Board 1C
(control)
Date Recue/Date Received 2020-06-26
4993 CA GYP
24
Stucco 961 961 961
HRA 13 13 13
Pregelatinized
15 15 15
Starch
Uncooked Starch 20 20 20
NaCl 0 0.48 0.48
MgC12=6H20 0 0.83 0.83
Dispersant 0.3 0.3 0.3
Retarder 0.48 0.48 0.48
10% STMP 10 10 10
Foam weight 3.7 3.7 3.7
Water 811 820 820
[0092] In Table 1, HRA refers to heat resistant accelerator. The
pregelatinized starch is a
pregelatinized corn flour starch with a cold water viscosity of 90 centipoise.
The uncooked
starch is an uncooked acid-modified corn starch having a hot water viscosity
of 180 BU. The
dispersant is naphthalenesulfonic acids. The retarder is pentasodium
diethylenetriaminepentaacetate. STMP refers to sodium trimetaphosphate. The
foam was
prepared using HYONIC line (e.g., 25A5) of soap products from GEO Specialty
Chemicals,
Ambler, PA. and Polystep B25, from Stepan Company, Northfield, Illinois.
[0093] The face cover sheet (Manila) for each of boards 1A-1C was paper
having a 50 lb
basis weight, and were of conventional (regular) composition without a high
absorption
property. The back cover sheet (Newsline) for Comparative Board 1A and Board
1B was
paper having a 47 lb basis weight of conventional composition, while the back
cover sheet for
Board 1C was a high absorption paper having a basis weight of 47 lb.
Comparative Board
1A had a weight of 1307 lb/MSF, while Boards 1B and 1C had a weight of 1305
lb/MSF.
[0094] A test was conducted to determine the effect on the bond
between each cover
sheet and the set gypsum layer in the respective boards. After the boards came
out of the kiln
of the manufacturing line, they were cut into 5.5" x 5.875" samples. A one
eighth inch-deep
straight score was made in the face surface of each board 1.0" from and
parallel to one of the
5.875 inch edges, and each board was conditioned in a 75 F/50 % relative
humidity ("RH")
room overnight. The conditioned samples were then placed in a 90 F/90 % RH
room. A
humidified bond test was conducted on both the face and back side of the
boards after three
hours, sixteen hours, and one week in a 90 F/90 % RH room, respectively. The
humidified
boards were tested according to the humidified board test as follows.
Date Recue/Date Received 2020-06-26
4993 CA GYP
[0095] The humidified board was snapped along the score without breaking
or stressing
the paper on the back side of the board, and the larger (4.5" x 5.875") piece
of the board
sample was then rotated and forced downward with its face surface up, in an
attempt to force
the back paper on the back side of the board to peel away from the larger
pieces. The force
5 was increased until the two board pieces came completely apart. A higher
humidified bond
load indicates a better bond between the paper-to-core. The back surface of
the larger piece
was then examined to determine the percentage of the surface of the back paper
that had
pulled completely away from the core (referred to as "% failure").
[0096] The face side of the boards from all three conditions showed a
similar number of
10 the humidified bond load and 0% of failure between the paper-to-core
bond as shown in
Table 2. FIG. 1 shows the pictures of all three conditions after the bond
test. As seen in FIG.
1, a good bond between the paper-to-core was observed in each condition.
Table 2: Humidified Bond and Failure Percentage of
15 Face Side of Boards Under 90 F/90 % RH Conditions
Three Hours Sixteen Hours One Week
Board Humidified Humidified Humidified
Failure % Failure % Failure %
Bond (lbs) Bond (lbs) Bond (lbs)
1A
19.5 0 16.6 0 15.4 0
(control)
1B 22.8 0 16.6 0 15.9 0
1C 18.9 0 16.4 0 15.2 0
[0097] However, the humidified bond from the back side of the boards had
different
results as shown in Table 3. FIG. 2 shows pictures of all three conditions
after the bond test.
20 As seen in FIG. 2, conditioned Board 1B showed a poor bond between the
paper-to-core,
while conditioned Boards 1A and 1C showed good bond between the paper-to-core.
Control
Board 1A, without the addition of salt, had a high humidified bond load and 0%
of failure
between the regular back paper and the gypsum core. However, when 600 ppm of
chloride
was added into the gypsum slurry, Board 1B showed much lower humidified bond
load and
25 >60% failure between the regular Newsline back paper and the gypsum
core.
Table 3: Humidified Bond and Failure Percentage of
Back Side of Boards Under 90 F/90% RH Conditions
Board I Three Hours I Sixteen Hours I One Week
Date Recue/Date Received 2020-06-26
4993 CA GYP
26
Humidified Failure Humidified Failure Humidified
Failure
Bond (lbs) (%) Bond (lbs) (%) Bond (lbs) (%)
1A
19 0 14.2 0 14.7 0
(control)
1B 7.31 60% 4.9 80% 3.8
100%
1C 19.3 0 14.5 0 14.1 0
[0098] Unlike Board 1B, when high absorption paper was used as the back
paper, Board
1C, which was formed from the same stucco slurry formulation as Board 1B,
showed much
higher humidified bond load and 0% failure between the paper-to-core bond.
This indicates
that high absorption paper increases the paper-to-core bond, in particular,
when the wallboard
contains high concentration of salt.
[0100] All references, including publications, patent applications, and
patents, 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.
[0101] 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. 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 merely 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
Date Recue/Date Received 2020-06-26
4993 CA GYP
27
specification should be construed as indicating any non-claimed element as
essential to the
practice of the invention.
[0102] Preferred embodiments of this invention are described herein,
including the best
mode known to the inventors for carrying out the invention. Variations of
those preferred
.. embodiments 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 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.
Date Recue/Date Received 2020-06-26
