U.S. patent application number 10/878862 was filed with the patent office on 2005-03-10 for gypsum wallboard.
Invention is credited to Westerman, Ira John.
Application Number | 20050054760 10/878862 |
Document ID | / |
Family ID | 22894039 |
Filed Date | 2005-03-10 |
United States Patent
Application |
20050054760 |
Kind Code |
A1 |
Westerman, Ira John |
March 10, 2005 |
Gypsum wallboard
Abstract
Gypsum wallboard can be made lighter and less dense, without
sacrificing strength, by adding to the gypsum slurry used in making
the board a styrene butadiene polymer latex substantially stable
against divalent ions in which the styrene butadiene polymer
includes at least 0.25 wt. % of an ionic monomer.
Inventors: |
Westerman, Ira John;
(Wadsworth, OH) |
Correspondence
Address: |
David G. Burleson
Omnova Solutions, Inc.
175 Ghent Road
Fairlawn
OH
44333
US
|
Family ID: |
22894039 |
Appl. No.: |
10/878862 |
Filed: |
June 28, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10878862 |
Jun 28, 2004 |
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09464174 |
Dec 16, 1999 |
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6755907 |
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09464174 |
Dec 16, 1999 |
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09237512 |
Jan 26, 1999 |
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6184287 |
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Current U.S.
Class: |
524/423 ;
524/556; 524/571 |
Current CPC
Class: |
E04C 2/043 20130101;
Y10S 526/923 20130101; C08F 212/08 20130101; C08F 236/10 20130101;
C08F 236/06 20130101; C04B 24/163 20130101; C08F 236/10 20130101;
C08F 291/00 20130101; C08F 257/02 20130101; C08F 257/02 20130101;
C04B 2103/0063 20130101; C04B 2111/0062 20130101; C04B 24/163
20130101; C08F 291/00 20130101; C04B 24/2676 20130101; C04B 24/2688
20130101; C04B 2103/0062 20130101; C09K 8/46 20130101; C04B 28/145
20130101; Y10S 525/902 20130101; C08F 257/02 20130101; C04B 28/145
20130101; C08F 257/02 20130101 |
Class at
Publication: |
524/423 ;
524/571; 524/556 |
International
Class: |
G03C 005/18 |
Claims
1. A composition for making gypsum products comprising water,
calcium sulfate hemihydrate, and a styrene butadiene polymer latex
substantially stable against divalent ions in which the styrene
butadiene polymer includes at least 0.25 wt. % of an ionic
monomer.
2-22. (Cancelled)
23. A styrene butadiene polymer latex comprising: about 4 to 70 wt.
% butadiene; about 20 to 95 wt. % styrene; and at least 0.25 wt. %
of an ionic monomer comprised of 2-acrylamido-2-methyl
propanesulfonic acid salt, wherein said polymer is substantially
free of surfactants that impart stability against divalent
ions.
24. The styrene butadiene polymer latex of claim 23, wherein the
latex is substantially stable against divalent ions.
25. The styrene butadiene polymer latex of claim 23, further
comprising a hydrophilic adjunct comonomer selected from the group
consisting of hydroxyethyl acrylate, hydroxyethyl methacrylate,
acrylonitrile, methacrylocitrile, acrylamide, methacrylamide, and
mixtures thereof.
26. The styrene butadiene polymer latex of claim 25, wherein the
hydrophilic adjunct comonomer is hydroxyethyl acrylate.
27. The styrene butadiene polymer latex of claim 23, wherein the
ratio of styrene to butadiene is in the range of 10:1 to 1:1.
28. The styrene butadiene latex of claim 23, wherein the
2-acrylamido-2-methyl propanesulfonic acid salt is sodium
2-acrylamido-2-methyl propanesulfonic acid.
29. A styrene butadiene polymer latex that is substantially stable
against divalent ions, said latex comprising: about 7 to 40 wt. %
butadiene; about 45 to 90 wt. % styrene; about 0.25 to 20 wt. % of
an ionic monomer comprised of 2-acrylamido-2-methyl propanesulfonic
acid salt; wherein the ratio of styrene to butadiene is in a range
of 7:1 to 1.5:1.
30. The styrene butadiene polymer latex of claim 29, wherein said
2-acrylamido-2-methyl propanesulfonic acid salt is sodium
2-acrylamido-2-methyl propanesulfonic acid.
31. The styrene butadiene polymer latex of claim 29, further
comprising a hydrophilic adjunct comonomer selected from the group
consisting of hydroxyethyl acrylate, hydroxyethyl methacrylate,
acrylonitrile, methacrylonitrile, acrylamide, methacrylamide, and
mixtures thereof.
32. The styrene butadiene polymer latex of claim 31, wherein the
hydrophilic adjunct comonomer is present in an amount of about 0.25
to 20 wt. % based on the weight of the polymer.
33. The styrene butadiene polymer latex of claim 31, wherein the
hydrophilic adjunct comonomer is hydroxyethyl acrylate.
34. The styrene butadiene latex polymer of claim 31, wherein the
polymer is substantially free of surfactants that impart stability
against divalent ions.
35. An aqueous styrene butadiene polymer latex comprising: about 10
to 30 wt. % butadiene; about 65 to 85 wt. % styrene; about 0.5 to
10 wt. % of an ionic monomer comprised of 2-acrylamido-2-methyl
propanesulfonic acid salt; and a hydrophilic adjunct comonomer
selected from the group consisting of hydroxyethyl acrylate,
hydroxyethyl methacrylate, acrylonitrile, methyacrylonitrile,
acrylamide, methacrylamide and combinations thereof, wherein said
polymer latex is substantially stable against divalent ions.
36. The polymer latex of claim 35, wherein the hydrophilic adjunct
comonomer is present in an amount of about 0.5 to 10 wt. %.
37. The polymer latex of claim 35, wherein the hydrophilic adjunct
comonomer is hydroxyethyl acrylate.
38. The polymer latex of claim 35, wherein the hydrophilic adjunct
comonomer is hydroxyethyl acrylate in an amount of about 0.5 to
about 10 wt. %.
39. The polymer latex of claim 35, wherein the weight ratio styrene
to butadiene is 7:1 to 1.5:1.
40. The polymer latex of claim 35, further comprising: at least one
monomer selected from the group consisting of isoprene,
chloroprene, alpha-methylstyrene, 4-methylstyrene,
4-tert-butylstyrene, 4-ethylstyrene, divinylbenzene, vinylidene
chloride, 2-vinylpyridene, 4-vinylpyridene, acrylic acid,
methyacrylic acid, metal salts of acrylic acid and methyacrylic
acid, ammonium salts of acrylic acid and methacrylic acid,
substituted and unsubstituted amides of acrylic acid and
methacrylic acid other than acrylamide and methacrylamide, nitriles
of acrylic acid and methacrylic acid other than acrylonitrile and
methacrylonitrile, and C.sub.1 to C.sub.12 esters of acrylic acid
and methacrylic acid.
41. The polymer latex of claim 35, wherein the ratio of styrene to
butadiene is in a range of 6:1 to 2:1.
42. The polymer latex of claim 35, wherein the hydrophilic adjunct
is present in an amount of about 1 to about 4 wt. %.
43. The polymer latex of claim 35, wherein the
2-acrylamido-2-methyl propanesulfonic acid salt is present in an
amount of about 1 to 5 wt. %.
44. The polymer latex of claim 35, wherein said polymer is
substantially free of surfactants that impart stability against
divalent ions.
45. The polymer latex of claim 35, wherein said
2-acrylamido-2-methyl propanesulfonic acid salt is sodium
2-acrylamido-2-methyl propanesulfonic acid.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] The application on which this patent is based is a
continuation-in-part of prior, commonly-assigned application Ser.
No. 09/237,512, filed Jan. 26, 1999, now U.S. patent Ser. No.
______ (atty docket no GT-5100), the disclosure of which is
incorporated herein by reference.
BACKGROUND OF THE INVENTION
FIELD OF INVENTION
[0002] The present invention relates to improved gypsum wallboard
and to materials and processes for making such products.
BACKGROUND
[0003] Gypsum wallboard is conventionally made by depositing an
aqueous slurry of calcined gypsum ("gypsum slurry") between large
sheets of paper or other material and allowing the slurry to dry.
Calcined gypsum is composed of calcium sulfate hemihydrate
(CaSO.sub.4 1/2H.sub.2O) which rehydrates to gypsum (CaSO.sub.4
2H.sub.2O) during the drying process. See Kirk Othmer, Encyclopedia
of Chemical Technology, Second edition, 1970, Vol. 21, Pages
621-624, the disclosure of which is also incorporated herein by
reference.
[0004] In order to achieve sufficient strength, traditional,
commercial wallboard has been made with a density of about 1700
pounds (.about.772 kg.) per thousand square feet of 1/2 inch thick
board. Although it would be desirable to reduce this density and
hence overall board weight, previous attempts have met with limited
success, primarily due to loss of strength.
[0005] U.S. Pat. No. 5,879,825 to Burke et al., the disclosure of
which is also incorporated herein by reference, describes an
approach for reducing gypsum wallboard density without sacrificing
strength by including in the gypsum core an acrylic latex having a
particular combination of properties. Acrylic latexes are
expensive, and therefore commercially unattractive. Therefore, it
is desirable to develop an alternate and less expensive approach to
accomplishing this objective.
SUMMARY OF THE INVENTION
[0006] In accordance with the present invention, it has been
discovered that certain styrene butadiene latexes, modified to be
substantially stable against divalent ions, can also reduce gypsum
wallboard density without sacrificing strength. Because these
latexes are generally less expensive to manufacture than acrylic
latexes, it has also been found that commercial use of these
latexes is feasible.
[0007] Accordingly, the present invention provides a new
composition for making gypsum products comprising water, calcium
sulfate hemihydrate and a styrene butadiene polymer latex
substantially stable against divalent ions in which the styrene
butadiene polymer includes at least 0.25 wt. % of an ionic monomer.
In addition, the present invention also provides a new process for
making gypsum wallboard from this composition as well as the
wallboard so made. Preferably, the styrene butadiene polymer of the
latex used in the present invention includes copolymerized sodium
2-acrylamido-2-methyl propanesulfonic acid salt, known industrially
as "sodium AMPS."
DETAILED DESCRIPTION
[0008] In accordance with the present invention, gypsum wall board
can be made lighter in weight without sacrificing strength by
including in the gypsum slurry used to make the board a styrene
butadiene polymer latex substantially stable against divalent ions
in which the styrene butadiene polymer includes at least 0.25 wt. %
of an ionic monomer.
[0009] The styrene butadiene latexes used in accordance with the
present invention are substantially stable against divalent ions.
By "substantially stable against divalent ions" is meant that a
latex will exhibit no significant coagulation or flocculation when
10 ml (milliliters) of a 2 wt. % calcium chloride aqueous solution
is slowly added to 50 ml of the latex. By slowly added is meant
that the calcium chloride solution is added to 50 ml of the latex
with stirring over a period of time between 5 and 30 seconds.
[0010] The amount of styrene and butadiene in the polymers of these
latexes can vary widely. For example, these polymers may contain 4
to 60 wt. % butadiene, more normally 7 to 40 wt. % butadiene and
especially 10 to 30 wt. % butadiene. In addition, they may contain
20 to 95 wt. % styrene, more normally 45 to 90 wt. % styrene and
especially 65 to 85 wt. % styrene. Moreover, in these polymers, the
ratio of styrene to butadiene is typically in the range of 10/1 to
1/1, more usually 7/1 to 1.5/1, and even more typically 6/1 to
2/1.
[0011] In addition to styrene and butadiene, the styrene butadiene
polymers of the present invention also include an ionic monomer. By
"ionic monomer" is meant a monomer which addition polymerizes to
form a homopolymerwhich is water soluble when having a molecular
weight of 5000. In other words, if a 5000 molecular weight
homopolymer formed by addition polymerizing a monomer is water
soluble, that monomer is "ionic" in the context of this invention.
Examples of suitable ionic monomers are 2-acrylamido-2-methyl
propanesulfonic acid salt, styrene sulfate salt, styrene sulfonate
salt, allyl sulfonate salt, 3-sulfopropyl acrylate salt,
3-sulfopropyl methacrylate salt, 2-sulfoethyl acrylate salt,
2-sulfoethyl methacrylate salt, maleic acid, itaconic acid and
salts of maleic acid and itaconic acid. The cations of these salt
are normally sodium, potassium or ammonium, more typically sodium
or potassium. 2-acrylamido-2-methyl propanesulfonic acid salt is
the preferred ionic monomer, with sodium 2-acrylamido-2-methyl
propanesulfonic acid salt being especially preferred.
2-acrylamido-2-methyl propanesulfonic acid is known in industry as
"AMPS," which is a trademark of The Lubrizol Company.
[0012] The amount of ionic monomer in the styrene butadiene
polymers of the invention can vary widely. As little as about 0.25
wt. % to as much as about 20 wt. %, based on the weight of the
polymer, are effective. Typically, the polymers will contain about
0.5 to 10, more often about 1 to 5 wt. %, ionic monomer based on
the weight of the polymer.
[0013] In addition to styrene, butadiene and the ionic monomer, the
polymers of the invention may also include 0.25 to 20 wt. % of
hydroxyethyl acrylate, hydroxyethyl methacrylate, acrylonitrile,
methacrylonitrile, acrylamide and/or methacrylamide. These
"hydrophilic adjunct comonomers" have been found to enhance the
effect of the ionic monomers in that the overall stability against
divalent ions exhibited by a polymer including an ionic monomer as
well as a hydrophilic adjunct comonomer is greater than would have
been predicted by the rule of mixtures. A hydrophilic adjunct
comonomer content of 0.5 to 10 wt. %, or even 1 to 4 wt. %, is more
typical.
[0014] In addition to the foregoing monomers, the styrene butadiene
polymers of the present invention may also include other addition
monomers. Examples are isoprene, chloroprene, alpha-methylstyrene,
4-methylstyrene, 4-tert-butylstyrene, 4-ethylstyrene,
divinylbenzene, vinylidene chloride, 2-vinylpyridene,
4-vinylpyridene and especially acrylic acid, methacrylic acid and
their derivatives such as metal and ammonium salts, substituted and
unsubstituted amides (other than acrylamide which is an hydrophilic
adjunct comonomer), nitriles, and C.sub.1 to C.sub.12 esters. In
such cases, the polymer should contain no more than about 30 wt. %,
more typically no more than 15 wt. %, other addition monomer.
[0015] Styrene butadiene polymer latexes are typically made by
aqueous emulsion polymerization. In carrying out such processes,
the monomers forming the polymer are emulsified in water using
suitable surfactants, usually anionic or non-ionic. Other
ingredients such as free-radical initiators, chelating agents,
chain transfer agents, biocides, defoamers and antioxidants can
also be added. Once the free-radical initiator is activated, the
monomers polymerize together producing the product polymer. As is
well known, the arrangement of multiple monomers in a product
polymer can be determined, at least to some degree, by controlling
the manner which the monomers are added to the system. If all the
monomers are added at the same time, the product polymer will have
a more random distribution of monomers. If added in stages, the
polymer will have a more ordered distribution of monomers.
[0016] A typical polymer latex produced by emulsion polymerization
contains enough surfactants and other ingredients to prevent the
product polymer from separating out from the water phase upon
standing. However, these surfactants and other ingredients are
usually insufficient to prevent coagulation or flocculation of the
polymer if the latex is contaminated with significant amounts of
divalent or trivalent ions. Therefore, such latexes can be expected
to coagulate or flocculate prematurely if contacted with gypsum
slurries used in the manufacture of gypsum wallboard, since such
slurries contain significant concentrations of calcium ions, which
are divalent.
[0017] In order to avoid this problem, additional surfactants can
be incorporated into the latexes to keep them stable against
calcium ions. However, gypsum slurries already contain significant
concentrations of particular types of surfactants and other
ingredients to enable the slurries to be frothed (foamed) during
manufacture. Accordingly, it is desirable to avoid adding still
additional surfactants to these systems, since different surfactant
packages can interact with one another and thereby become
ineffective.
[0018] In accordance with the present invention, therefore, the
styrene butadiene latex includes a significant amount of a monomer,
the ionic monomer, which imparts its own surface active properties
to the polymer. As a result, additional surfactants for imparting
calcium ion stability to a latex of the polymer can be reduced or
even eliminated entirely. Therefore, when such latexes are added to
gypsum slurries in the manufacture of gypsum wallboard, problems
occurring from mixing incompatible surfactant packages can be
avoided.
[0019] Styrene butadiene latexes which are especially useful in
accordance with the present invention are described in
commonly-assigned application Ser. No. 09/237,512, filed Jan. 26,
1999, now U.S. patent Ser. No. ______ (atty docket no. GT-5100),
the disclosure of which is incorporated herein by reference. In
general, these latexes are formed by emulsion polymerization of
styrene and butadiene in the presence of an in situ seed polymer
composed of polymerized styrene and an AMPS salt, preferably
Na-AMPS. Normally, the seed polymer is made by emulsion
polymerization of styrene and Na-AMPS only, although butadiene may
be included as an additional comonomer if desired. These latexes
have been designed for mixing with cement used for cementing oil
wells and are particularly stable against divalent ions. The
conditions encountered in gypsum slurries are less severe than
those in oil well cementing, and so less ionic monomer may be
acceptable when these polymers are used in the present invention as
compared to oil well cementing applications.
[0020] Styrene butadiene latexes of particular utility in
accordance with the present invention are formed by emulsion
polymerizing the monomers identified in the following Table 1 in
accordance with the general procedure described in the above-noted
U.S. patent Ser. No. ______ (application Ser. No. 09/237,512, filed
Jan. 26, 1999, atty docket no. GT-5100):
1TABLE 1 Components of Styrene Butadiene Polymers, wt. % Example
NaAMPS Styrene Butadiene HEA.sup.1 Acrylo.sup.2 Results 1 2.5 77.5
15 3 2 2.5 67.5 15 3 10 3 5.5 67.2 26 1.3 .sup.1Hydroxyethyl
acrylate .sup.2Acrylonitrile
[0021] The amount of styrene butadiene latex that should be
incorporated into a gypsum slurry in accordance with the present
invention can vary widely, and essentially any amount can be used.
From a practical standpoint, the amount of latex should be enough
so that a noticeable decrease in density of product gypsum
wallboard can be achieved without sacrificing strength but not so
much that the product wallboard product becomes economically
unattractive. In general, this means that the amount of latex added
should be enough so that the styrene butadiene polymer is present
in the product composition is about 0.1 to 10 wt. %, based on the
weight of calcium sulfate hemihydrate in the composition. More
typically, the amount of styrene butadiene polymer in the
composition is 0.25 to 5 wt. %, and especially 0.5 to 1.5 wt. %,
based on the weight of calcium sulfate hemihydrate in the
composition.
[0022] Gypsum slurries for manufacture of wallboard typically
contain various additional ingredients, as well known to those
skilled in the art. Examples of such ingredients are accelerators,
starch, retarders, paper pulp and so forth. See the above-noted
Burke et al. patent, U.S. Pat. No. 5,879,825, especially Table I.
Such components can also be included in the compositions produced
in accordance with the present invention.
[0023] The gypsum-containing compositions of the present invention
are used in the same way as conventional gypsum slurries to
manufacture gypsum wallboard product. That is, they are deposited
between large sheets of paper or other material and allowed the dry
whereby the calcium sulfate hemihydrate in the system rehydrates
into the dihydrate, i.e. gypsum, thereby forming the completed
wallboard product. In commercial practice, the process is carried
out in high volume using machines having traveling webs which
rapidly move the incipiently-formed product through ovens under
precisely controlled heating conditions for removing exactly the
right amount of water. In this environment, it is desirable that
the amount of water in the starting gypsum slurry be controlled so
that the wallboard product is dried to the right amount when it
leaves the oven.
[0024] To this end, conventional gypsum slurries for making
wallboard typically contain about 40 to 60 wt. %, more typically
about 48 to 55 wt. % calcium sulfate hemihydrate and less than 60
wt. %, more typically less than 50 wt. % water, based on the weight
of the composition. See Table I of the above-noted Burke et. al.
patent. The gypsum slurries of the present invention may also
contain the same amounts of calcium sulfate hemihydrate and water,
especially when intended for use in making gypsum wallboard in
modern high speed equipment.
[0025] In this connection, it should be appreciated that the amount
of water which a styrene butadiene styrene butadiene latex adds to
a gypsum slurry in accordance with the present invention is
essentially trivial when making wallboard product under normal
practice. This is because the amount of latex added will typically
be small, e.g. 5 wt. % or less, and the amount of water in this
latex will usually be less than 50 wt. %. Also, less gypsum slurry
is needed to make a wallboard product of a given dimension, since
its density is less, and hence less water derived from the gypsum
slurry is present in the inventive gypsum slurries in the first
place. This means that the net effect of including a styrene
butadiene latex in a gypsum slurry in accordance with the present
invention may actually be to reduce the overall water content of
the slurry by a slight amount for a wallboard product of a given
dimension. In any event, those skilled in the art can readily
determine by routine experimentation the precise amount of calcium
sulfate hemihydrate and water to include in a particular embodiment
of the inventive gypsum slurries in order that it can be used
without problem in making gypsum wallboard in modern high speed
equipment.
[0026] It should also be appreciated that the gypsum slurries of
the present invention can be used in applications other than in
making gypsum wallboard. For example, the inventive gypsum slurries
can also be used in making molding plasters. In these applications,
more or less water than indicated above can be included in the
composition depending on the particular application desired.
Indeed, the only real upper limit on the water content of the
inventive gypsum slurry is that too much water may make its
viscosity too low for practical application or may cause water to
separate out. Similarly, the only real lower limit on the water
content is stoichiometric--that is, enough water should be present
to allow substantially complete hydration of the calcium sulfate
hemihydrate to the dihydrate form. Within these broad limits, those
skilled in the art can readily determine by routine experimentation
the precise amount of water to use in a particular application.
[0027] Although only a few embodiments of the present invention
have been described above, it should be appreciated that many
modifications can be made without departing from the spirit and
scope of the invention. All such modifications are intended to be
included within the scope of the present invention, which is to be
limited only by the following claims.
* * * * *