U.S. patent application number 11/152323 was filed with the patent office on 2006-12-14 for method of making a gypsum slurry with modifiers and dispersants.
This patent application is currently assigned to United States Gypsum Company. Invention is credited to David R. Blackburn, Dennis M. Lettkeman, Qingxia Liu, Brian S. Randall, Michael P. Shake, John W. Wilson.
Application Number | 20060280899 11/152323 |
Document ID | / |
Family ID | 37522960 |
Filed Date | 2006-12-14 |
United States Patent
Application |
20060280899 |
Kind Code |
A1 |
Liu; Qingxia ; et
al. |
December 14, 2006 |
Method of making a gypsum slurry with modifiers and dispersants
Abstract
In a method of making a gypsum slurry, a polycarboxylate
dispersant, a modifier and a hydraulic material comprising stucco
are selected for use in the slurry. These components are then
combined with water to form a slurry, where the modifier is added
to the slurry prior to formation of a slurry phase by the water,
the stucco and the dispersant. The modifier has been shown to be
less effective when added after the dispersant and stucco have been
contacted in an aqueous slurry. In a preferred embodiment, an
amount of stucco is obtained and the modifier and dispersant are
selected. A predissolved solution of a dispersant and modifier is
prepared in water to form a solution prior to the addition of the
stucco. After mixing the solution, the stucco is added to form the
slurry. Optionally, the slurry is then shaped into a product and
allowed to set.
Inventors: |
Liu; Qingxia; (Vernon Hills,
IL) ; Blackburn; David R.; (Barrington, IL) ;
Shake; Michael P.; (Johnsburg, IL) ; Randall; Brian
S.; (Fairview, OK) ; Wilson; John W.;
(Fairview, OK) ; Lettkeman; Dennis M.; (Watonga,
OK) |
Correspondence
Address: |
GREER, BURNS & CRAIN
300 S WACKER DR
25TH FLOOR
CHICAGO
IL
60606
US
|
Assignee: |
United States Gypsum
Company
|
Family ID: |
37522960 |
Appl. No.: |
11/152323 |
Filed: |
June 14, 2005 |
Current U.S.
Class: |
428/70 ; 106/772;
106/778; 106/781; 106/783; 106/785; 106/788 |
Current CPC
Class: |
C04B 28/26 20130101;
C04B 2111/60 20130101; C04B 22/16 20130101; C04B 24/38 20130101;
C04B 24/38 20130101; C04B 24/2647 20130101; C04B 20/0048 20130101;
C04B 22/064 20130101; C04B 2103/67 20130101; C04B 22/10 20130101;
C04B 2103/22 20130101; C04B 22/10 20130101; C04B 24/2647 20130101;
C04B 2103/12 20130101; C04B 22/16 20130101; C04B 22/143 20130101;
C04B 14/06 20130101; C04B 40/0028 20130101; C04B 2103/22 20130101;
C04B 40/0028 20130101; C04B 2103/12 20130101; C04B 20/0048
20130101; C04B 22/064 20130101; C04B 12/04 20130101; C04B 2103/67
20130101; C04B 28/145 20130101; C04B 2111/0062 20130101; C04B
28/145 20130101; C04B 28/26 20130101; Y10T 428/232 20150115 |
Class at
Publication: |
428/070 ;
106/778; 106/783; 106/772; 106/781; 106/785; 106/788 |
International
Class: |
C04B 28/14 20060101
C04B028/14; C04B 11/00 20060101 C04B011/00; B32B 1/04 20060101
B32B001/04 |
Claims
1. A method of making a gypsum slurry comprising: obtaining an
amount of dry components comprising stucco, predissolving a
modifier and a dispersant in water to form a solution, and mixing
the solution and the dry components to form a gypsum slurry.
2. The method of claim 1 wherein the modifier in said predissolving
step comprises at least one of the group consisting of lime,
quicklime, a silicate, a phosphate, a phosphonate and a
carbonate.
3. The method of claim 2 wherein the modifier comprises at least
one of the group consisting of sodium carbonate, potassium
carbonate, calcium oxide and sodium silicate.
4. The method of claim 1 wherein said predissolving step comprises
adding the modifier and the dispersant to the water essentially
simultaneously.
5. The method of claim 1 wherein the modifier is added to the water
before the dispersant in said predissolving step.
6. The method of claim 1 wherein the dispersant in said
predissolving step is a polycarboxylic ether dispersant.
7. The method of claim 6 wherein the dispersant in said
predissolving step comprises vinyl ether repeating units.
8. The method of claim 1 wherein said predissolving step further
comprises combining the modifier with a portion of the water to
form a modifier slurry, prior to predissolving the modifier slurry
and dispersant in the remaining portion of water.
9. The method of claim 1 wherein the dry components comprise at
least 50% stucco by weight.
10. A method of making a gypsum product comprising: obtaining an
amount of dry components comprising stucco, predissolving a
modifier and a dispersant into water to form a solution, mixing the
solution and the dry components to form a gypsum slurry, shaping
the gypsum slurry into a product, and allowing the slurry to
set.
11. The method of claim 10 further comprising drying the product in
a kiln.
12. The method of claim 10 wherein the dry components comprise at
least 50% stucco by weight.
13. The method of claim 10 wherein the product is a gypsum
panel.
14. The method of claim 13 wherein said shaping step further
comprises sandwiching the slurry between two pieces of facing
material.
15. The method of claim 13 wherein the dispersant comprises an
acrylic repeating unit and a vinyl ether repeating unit.
16. The method of claim 10 wherein the dispersant comprises a
polycarboxylic ether.
17. The method of claim 10 wherein the dry components further
comprise at least one selected from the group consisting of
strength enhancers, set accelerators, set retarders, starch, fibers
and biocides.
18. A method of making a gypsum slurry comprising: selecting a
polycarboxylate dispersant, a modifier and a hydraulic material
comprising stucco; and combining the polycarboxylate dispersant,
the modifier, the hydraulic material and water together to form a
slurry, wherein the modifier is added to at least one of the water,
stucco and dispersant prior to formation of the slurry phase by the
water, the stucco and the dispersant.
19. The method of claim 18 wherein the dispersant is in a dry form
and said combining step further comprises predissolving the
modifier in the water and the dispersant is added to the stucco to
make a stucco-dispersant mixture, then adding the stucco-dispersant
mixture to the predissolved modifier in the water.
20. A product made by the method of claim 10.
21. The product of claim 20 wherein the product is a gypsum
panel.
22. The product of claim 20 wherein the product is a floor or floor
underlayment.
23. The product of claim 20 wherein the product is a cast product.
Description
CROSS REFERENCES TO RELATED APPLICATIONS
[0001] This application is related to co-pending U.S. Ser. No.
11/______ (Attorney Ref. No. 2033.72380) entitled "Fast Drying
Wallboard"; U.S. Ser. No.11/______ (Attorney Ref. No. 2033.72740),
entitled "Gypsum Products Utilizing a Two-Repeating Unit Dispersant
and Process for Making Them"; U.S. Ser. No. 11/______ (Attorney
Ref. No. 2033.72739), entitled "Modifiers for Gypsum Products and
Methods of Using Them" and U.S. Ser. No. 11/______ (Attorney Ref.
No. 2033.73130), entitled, "Effective Use of Dispersants in
Wallboard Containing Foam", all filed concurrently herewith and all
hereby incorporated by reference.
BACKGROUND OF THE INVENTION
[0002] This invention relates to a method for making gypsum
products using a modifier and polycarboxylate dispersant. More
specifically, it relates to the making a gypsum slurry and a gypsum
panel that adds the dispersant and modifier in a specific
sequence.
[0003] Gypsum-based building products are commonly used in
construction. A gypsum panel made of gypsum is fire retardant and
can be used in the construction of walls of almost any shape. It is
used primarily as an interior wall and ceiling product. Gypsum has
sound-deadening properties. It is relatively easily patched or
replaced if it becomes damaged. There are a variety of decorative
finishes that can be applied to the gypsum panel, including paint
and wallpaper. Even with all of these advantages, it is still a
relatively inexpensive building material.
[0004] One reason for the reasonable cost of gypsum panels is that
they are manufactured by a process that is fast and efficient. A
slurry, including calcium sulfate hemihydrate and water, is used to
form the core, and is continuously deposited on a paper cover sheet
moving beneath a mixer. A second paper cover sheet is applied
thereover and the resultant assembly is formed into the shape of a
panel. Calcium sulfate hemihydrate reacts with a sufficient amount
of the water to convert the hemihydrate into a matrix of
interlocking calcium sulfate dihydrate crystals, causing it to set
and to become firm. The continuous strip thus formed is conveyed on
a belt until the calcined gypsum is set, and the strip is
thereafter cut to form boards of desired length, which boards are
conveyed through a drying kiln to remove excess moisture. Since
each of these steps takes only minutes, small changes in any of the
process steps can lead to gross inefficiencies in the manufacturing
process.
[0005] The amount of water added to form the slurry is in excess of
that needed to complete the hydration reactions. Some of the water
that is added to the gypsum slurry is used to hydrate the calcined
gypsum, also known as calcium sulfate hemihydrate, to form an
interlocking matrix of calcium sulfate dihydrate crystals. Excess
water gives the slurry sufficient fluidity to flow out of the mixer
and into the facing material to be shaped to an appropriate width
and thickness. While the product is wet, it is very heavy to move
and relatively fragile. The excess water is removed from the board
by evaporation. If the excess water were allowed to evaporate at
room temperature, it would take a great deal of space to stack and
store the gypsum panel while it was allowed to air dry or to have a
conveyor long enough to provide adequate drying time. Until the
board is set and relatively dry, it is somewhat fragile, so it must
be protected from being crushed or damaged.
[0006] To dry the boards in a relatively short period of time, the
gypsum panel product is usually dried by evaporating the extra
water at elevated temperatures, for example, in an oven or kiln. It
is relatively expensive to build and operate the kiln at elevated
temperatures, particularly when the cost of fossil fuel rises. A
reduction in production costs could be realized by reducing the
amount of excess water present in set gypsum boards that is later
removed by evaporation.
[0007] Another reason to decrease water is that the strength of
gypsum products is inversely proportional to the amount of water
used in its manufacture in full density products. As the excess
water evaporates, it leaves voids in the matrix once occupied by
the water. Where large amounts of water were used to fluidize the
gypsum slurry, more and larger voids remain in the product when it
is completely dry. These voids decrease the product density and
strength in a finished product such as poured flooring.
[0008] Dispersants are known for use with gypsum that helps
fluidize the mixture of water and calcium sulfate hemihydrate so
that less water is needed to make a flowable slurry. Naphthalene
sulfonate dispersants are well known, but have limited efficacy.
Polycarboxylate dispersants are commonly used with cements and, to
a lesser degree, with gypsum. The class of compounds represented by
the term "polycarboxylate dispersants" is huge, and it is very
difficult to predict how individual compounds react in different
media.
[0009] Modifiers can be added to a gypsum slurry to increase the
efficacy of the dispersant. Salts, including silicates and
carbonates, are particularly effective modifiers. More
specifically, quicklime, lime and soda ash are especially effective
with polycarboxylic ether dispersants. Modifiers are disclosed in
greater detail in copending U.S. Ser. No. 11/______ (Attorney Ref.
No. 2033.72739), entitled, "Modifiers for Gypsum Products and
Methods of Using Them", previously incorporated by reference.
[0010] It has been found, however, that the methods used to make
mixtures of gypsum, dispersants and modifiers do not consistently
produce highly fluid slurries. In some instances, the efficacy of
the dispersant is dramatically increased, but in other cases, the
same combination of components had little effect on the fluidity of
the slurry. This inability to predict the fluidity of the slurry
can lead to increased dispersant use to ensure that a minimum
fluidity is achieved. In a process where the dispersant can be one
of the most expensive component, dispersant overdose unnecessarily
increases the product cost at a rapid rate.
[0011] Another property of polycarboxylate dispersants is their
tendency to retard the set of a gypsum slurry. If high doses of
dispersants are used to accommodate uncertain dispersant efficacy,
set may be retarded to the degree where certain products, such as
the gypsum panel, cannot be produced on current, high-speed
equipment.
[0012] Thus there is a need for a method to make a gypsum slurry,
and products therewith, that consistently generate a highly fluid
mixture without excessive dosages of dispersants. Use of such a
method would keep the cost reasonable where expensive dispersants
were used, and would minimize set retardation of the slurry.
SUMMARY OF THE INVENTION
[0013] Solutions to these and other problems are met by the current
method which consistently produces a highly fluid slurry from
gypsum, a dispersant and a modifier.
[0014] More specifically, in a method of making a gypsum slurry, a
polycarboxylate dispersant, a modifier and a hydraulic material
comprising stucco are selected for use in the slurry. These
components are then combined with water to form a slurry, where the
modifier is added to the slurry prior to formation of a slurry
phase by the water, the stucco and the dispersant. The modifier has
been shown to be less effective when added after the dispersant and
stucco have been contacted in an aqueous slurry.
[0015] In a preferred embodiment, an amount of stucco is obtained
and the modifier and dispersant are selected. A predissolved
solution of a dispersant and modifier is prepared in water to form
a solution prior to the addition of the stucco. After mixing the
solution, the stucco is added to form the slurry. Optionally, the
slurry is then shaped into a product and allowed to set.
[0016] This method of combining the modifier, dispersant, stucco
and water leads to consistency in using the modifier to its best
advantage. If the slurry fluidity is consistent, there is less need
to use high dosages of the dispersant to assure a mixture of
sufficient fluidity to pour easily. Less product is lost that does
not meet specifications. Reduced dispersant dosages lead to reduced
dispersant cost and improved product set times.
DETAILED DESCRIPTION OF THE INVENTION
[0017] These and other problems are improved by the present
invention that includes a method for making a slurry of water, a
polycarboxylate dispersant, a modifier and calcium sulfate
hemihydrate, by combining the components in a particular order. As
is discussed in greater detail below, a modifier is an additive
that enhances the efficacy of the dispersant.
[0018] It has been discovered that if the calcium sulfate
hemihydrate, or stucco, is exposed to the dispersant before the
modifier is exposed to the dispersant, then the modifier is
rendered less effective. Preferably the modifier and the dispersant
are both predissolved in the gauge water, forming a solution. In
this case, the modifier and the dispersant are added in any order,
either sequentially or essentially simultaneously. After the
solution is formed, the stucco is mixed with the solution, exposing
the stucco to both the dispersant and the modifier
simultaneously.
[0019] In another embodiment, the modifier is mixed with a portion
of the gauge water to form a modifier slurry. The modifier slurry
is then mixed with the remaining gauge water and the dispersant,
either simultaneously or sequentially, to form the three component
solution. In either case, both the modifier and the dispersant are
blended in the gauge water prior to introduction of the dry
components.
[0020] If both the dispersant and the modifier are in dry or
powdered form, in another preferred embodiment the modifier and
dispersant are combined with the stucco, then all of the dry
components are added to the water at once. Alternately, the
dispersant is added to the stucco to make a dispersant-stucco
mixture, while the modifier is predissolved in the water. The
dispersant-stucco mixture is then added to the predissolved
modifier in the water. These embodiments are particularly
advantageous where powdered dispersants are preferred.
[0021] As in the other embodiments, since the modifier and the
dispersant are added at the same time, the dispersant has not had
the opportunity to interact with the stucco in water prior to
addition of the modifier.
[0022] The stucco, also known as calcium sulfate hemihydrate or
calcined gypsum, in present amounts of at least 50% of the dry
materials. Preferably, the amount of stucco is at least 80%. In
many gypsum formulations, the dry component material is more than
90% or even 95% calcium sulfate hemihydrate. The method of
calcination is not important, and either alpha or beta-calcined
stucco is suitable. Use of calcium sulfate anhydrite and/or calcium
sulfate dihydrate is also contemplated, although preferably in
small amounts of less than 20%.
[0023] Stuccos from different sources include different amounts and
types of salt and impurities. The slurry of this invention is most
effective when calcium sulfate hemihydrate having small
concentrations of naturally occurring salts. Low-salt stuccos are
defined as those having soluble salts of less than 300 parts per
million. High salt content stuccos that include those having at
least 600 parts per million soluble salts are most likely to
interfere with the action of the modifier. Stuccos such as those in
deposits found in Southard, Okla., Little Narrows, Nova Scotia,
Fort Dodge, Iowa, Sweetwater, Tex., Plaster City, Calif. or many
other locations are suitable for use with this slurry.
[0024] In some embodiments of the invention, additives are included
in the gypsum slurry to modify one or more properties of the final
product. Additives are used in the manner and amounts as are known
in the art. Frequently these and other additives are in solid,
powder or granular form and are added to the dry components before
the slurry is mixed. Concentrations are reported in amounts per
1000 square feet of finished board panels ("MSF").
[0025] Additional additives are also added to the slurry as are
typical for the particular application to which the gypsum slurry
will be put. Set retarders (up to about 2 lb./MSF (9.8 g/m2)) or
dry accelerators (up to about 35 lb./MSF (170 g/m2)) are added to
modify the rate at which the hydration reactions take place. "CSA"
is a set accelerator comprising 95% calcium sulfate dihydrate
co-ground with 5% sugar and heated to 250.degree. F. (121.degree.
C.) to caramelize the sugar. CSA is available from USG Corporation,
Southard, Okla. plant, and is made according to U.S. Pat. No.
3,573,947, herein incorporated by reference. Potassium sulfate is
another preferred accelerator. HRA is calcium sulfate dihydrate
freshly ground with sugar at a ratio of about 5 to 25 pounds of
sugar per 100 pounds of calcium sulfate dihydrate. It is further
described in U.S. Pat. No. 2,078,199, herein incorporated by
reference. Both of these are preferred accelerators.
[0026] Another accelerator, known as wet gypsum accelerator, is
also a preferred accelerator. A description of the use of and a
method for making wet gypsum accelerator are disclosed in U.S. Pat.
No. 6,409,825, herein incorporated by reference. This accelerator
includes at least one additive selected from the group consisting
of an organic phosphonic compound, a phosphate-containing compound
or mixtures thereof. This particular accelerator exhibits
substantial longevity and maintains its effectiveness over time
such that the wet gypsum accelerator can be made, stored, and even
transported over long distances prior to use. The wet gypsum
accelerator is used in amounts ranging from about 5 to about 80
pounds per thousand square feet (24.3 to 390 g/m.sup.2) of board
product.
[0027] Starches are used in amounts from about 3 to about 20
lbs./MSF (15.6 to 97.6 g/m.sup.2) to increase bond strength and
strengthen the product. Glass fibers are optionally added to the
slurry in amounts of up to 11 lb./MSF (54 g/m.sup.2). Up to 11
lb./MSF (53.7 g/m.sup.2) of paper fibers are also added to the
slurry. Wax emulsions are added to the gypsum slurry in amounts up
to 90 lb./MSF (439 g/m.sup.2) to improve the water-resistency of
the finished gypsum board panel.
[0028] In embodiments of the invention that employ a foaming agent
to yield voids in the set gypsum-containing product to provide
lighter weight, any of the conventional foaming agents known to be
useful in preparing foamed set gypsum products can be employed.
Many such foaming agents are well known and readily available
commercially, e.g. the HYONIC line of soap products from GEO
Specialty Chemicals, Ambler, Pa. Foams and a preferred method for
preparing foamed gypsum products are disclosed in U.S. Pat. No.
5,683,635, herein incorporated by reference. If foam is added to
the product, the polycarboxylate dispersant is optionally divided
between the process water and the foam water prior to its addition
to the calcium sulfate hemihydrate. This preferred method of
combining stucco, modifiers and dispersants is disclosed in U.S.
Ser. No. 11/______ (Attorney Ref. No. 2033.73130), entitled,
"Method of Controlling Core Properties in Wallboard", previously
incorporated by reference.
[0029] A trimetphosphate compound is added to the gypsum slurry in
some embodiments to enhance the strength of the product and to
reduce sag resistance of the set gypsum. Preferably the
concentration of the trimetaphosphate compound is from about 0.07%
to about 2.0% based on the weight of the calcined gypsum. Gypsum
compositions including trimetaphosphate compounds are disclosed in
U.S. Pat. Nos. 6,342,284 and 6,632,550, both herein incorporated by
reference. Exemplary trimetaphosphate salts include sodium,
potassium or lithium salts of trimetaphosphate, such as those
available from Astaris, LLC., St. Louis, Mo. Care must be exercised
when using trimetaphosphate with lime or other modifiers that raise
the pH of the slurry. Above a pH of about 9.5, the trimetaphosphate
looses its ability to strengthen the product and the slurry becomes
severely retardive.
[0030] Other potential additives to the gypsum panel are biocides
to reduce growth of mold, mildew or fungi. Depending on the biocide
selected and the intended use for the gypsum panel, the biocide can
be added to the facing, the gypsum core or both. Examples of
biocides include boric acid, pyrithione salts and copper salts.
Biocides can be added to either the facing or the gypsum core. When
used, biocides are used in the facings in amounts of less than
about 500 ppm.
[0031] In addition, the gypsum composition optionally can include a
starch, such as a pregelatinized starch or an acid-modified starch.
The inclusion of the pregelatinized starch increases the strength
of the set and dried gypsum cast and minimizes or avoids the risk
of paper delamination in wallboard under conditions of increased
moisture (e.g., with regard to elevated ratios of water to calcined
gypsum). In cast gypsum products, starch improves the product
surface hardness. One of ordinary skill in the art will appreciate
methods of pregelatinizing raw starch, such as, for example,
cooking raw starch in water at temperatures of at least about
185.degree. F. (85.degree. C.) or other methods. Suitable examples
of pregelatinized starch include, but are not limited to, PCF 1000
starch, commercially available from Lauhoff Grain Company and
AMERIKOR 818 and HQM PREGEL starches, both commercially available
from Archer Daniels Midland Company. If included, the
pregelatinized starch is present in any suitable amount. For
example, if included, the pregelatinized starch can be added to the
mixture used to form the set gypsum composition such that it is
present in an amount of from about 0.5% to about 10% percent by
weight of the set gypsum composition. Starches such as USG95
(United States Gypsum Company, Chicago, Ill.) are also optionally
added for core strength.
[0032] A number of dispersants are useful in this invention.
Polycarboxlate dispersants are a preferred type of dispersant. More
preferred are polycarboxylic ether dispersants. When used in gypsum
panel and other slurries high in stucco content, polycarboxylic
ether dispersants that are the least effective for fluidizing the
slurry alone, in many cases are most responsive to modifiers.
[0033] One of the preferred class of dispersants used in the slurry
includes two repeating units. It is described further in co-pending
U.S. Ser. No. 11/______ (Attorney Ref. No 2033.72740), entitled
"Gypsum Products Utilizing a Two-Repeating Unit Dispersant and
Process for Making Them", previously incorporated by reference.
These dispersants are products of Degussa Construction Polymers,
GmbH (Trostberg Germany) and are supplied by Degussa Corp.
(Kennesaw, Ga.) (hereafter "Degussa"), and are hereafter referenced
as the "PCE211-Type Dispersants".
[0034] The first repeating unit is an olefinic unsaturated
mono-carboxylic acid repeating unit, an ester or salt thereof, or
an olefinic unsaturated sulphuric acid repeating unit or a salt
thereof. Preferred repeating units include acrylic acid or
methacrylic acid. Mono- or divalent salts are suitable in place of
the hydrogen of the acid group. The hydrogen can also be replaced
by hydrocarbon group to form the ester.
[0035] The second repeating unit satisfies Formula I, R.sup.113
O--R.sup.2 I
[0036] where R.sup.1 is an alkenyl group of Formula II ##STR1##
[0037] and R.sup.2 is derived from an unsaturated (poly)alkylene
glycol ether group according to Formula III.
--(C.sub.mH.sub.2mO).sub.x--(C.sub.nH.sub.2nO).sub.y--R.sub.4
[0038] Referring to Formula II, the alkenyl repeating unit
optionally includes a C.sub.1 to C.sub.3 alkyl group between the
polymer backbone and the ether linkage. The value of p is an
integer from 0-3, inclusive. Preferably, p is either 0 or 1.
R.sub.3 is either a hydrogen atom or an aliphatic C.sub.1 to
C.sub.5 hydrocarbon group, which may be linear, branched, saturated
or unsaturated. Examples of preferred repeating units include
acrylic acid and methacrylic acid.
[0039] The polyether group of Formula III contains multiple
C.sub.2-C.sub.4 alkyl groups, including at least two different
alkyl groups, connected by oxygen atoms. M and n are integers from
2 to 4, inclusive, preferably, at least one of m and n is 2. X and
y are integers from 55 to 350, inclusive. R.sup.4 is hydrogen or an
aliphatic C.sub.1 to C.sub.20 hydrocarbon group, a cycloaliphatic
C.sub.5 to C.sub.8 hydrocarbon group, a substituted C.sub.6 to
C.sub.14 aryl group or a group conforming at least one of Formula
IV(a), IV(b) and VI(c). ##STR2##
[0040] In the above formulas, R.sup.5 and R.sup.7, independently of
each other, represent an alkyl, aryl, aralkyl or alkylaryl group.
R.sup.6 is a bivalent alkyl, aryl, aralkyl or alkylaryl group.
[0041] A particularly useful dispersant of the PCE211-Type
Dispersants is designated PCE211 (hereafter "211"). Other polymers
in this series known to be useful in the gypsum panel include
PCE111.
[0042] The molecular weight of the PCE211-Type Dispersant is
preferably from about 20,000 to about 60,000 Daltons. Surprisingly,
it has been found that the lower molecular weight dispersants cause
less retardation of set time than dispersants having a molecular
weight greater than 60,000 Daltons. Generally longer side chain
length, which results in an increase in overall molecular weight,
provides better dispersibility. However, tests with gypsum indicate
that efficacy of the dispersant is reduced at molecular weights
above 60,000 Daltons.
[0043] Another class of polycarboxylate compounds that are useful
in this invention is disclosed in U.S. Pat. No. 6,777,517, herein
incorporated by reference and hereafter referenced as the
"2641-Type Dispersant". Use of the 2641-Type dispersants in gypsum
slurries and wallboard is further described in U.S. Ser. No.
11/______, entitled, "Fast Drying Gypsum Products", (Attorney Ref.
No. 2033.72380), previously incorporated by reference.
[0044] Preferably, the 2641-Type dispersant includes at least three
repeating units shown in Formula V(a), V(b) and V(c). ##STR3##
[0045] In this case, both acrylic and maleic acid repeating units
are present, yielding a higher ratio of acid groups to vinyl ether
groups. R.sup.1 represents a hydrogen atom or an aliphatic
hydrocarbon radical having from 1 to 20 carbon atoms. X represents
OM, where M is a hydrogen atom, a monovalent metal cation, an
ammonium ion or an organic amine radical. R.sup.2 can be hydrogen,
an aliphatic hydrocarbon radical having from 1 to 20 carbon atoms,
a cycloaliphatic hydrocarbon radical having from 6 to 14 carbon
atoms, which may be substituted. R.sup.3 is hydrogen or an
aliphatic hydrocarbon radical having from 1 to 5 carbon atoms,
which are optionally linear or branched, saturated or unsaturated.
R.sup.4 is hydrogen or a methyl group, depending on whether the
structural units are acrylic or methacrylic. P can be from 0 to 3.
M is an integer from 2 to 4, inclusive, and n is an integer from 0
to 200, inclusive. Some preferred 2641-Type Dispersants are sold by
Degussa as MELFLUX 2641F, MELFLUX 2651F and MELFLUX 2500L
dispersants. (MELFLUX is a registered trademark of Degussa
Construction Polymers, GmbH, Trostberg, Germany)
[0046] Yet another preferred dispersant family is sold by Degussa
and referenced as "1641-Type Dispersants". This dispersant is
described in U.S. Pat. No. 5,798,425, herein incorporated by
reference. A particularly preferred 1641-Type Dispersant is shown
in Formula VI and marketed as MELFLUX 1641F dispersant by Degussa.
This dispersant is made primarily of two repeating units, one a
vinyl ether and the other a vinyl ester. An example of a 1641-Type
Dispersant, shown in Formula VI, m and n are the mole ratios of the
component repeating units, which can be randomly positioned along
the polymer chain. ##STR4##
[0047] These dispersants are particularly well-suited for use with
gypsum. While not wishing to be bound by theory, it is believed
that the acid repeating units bind to the gypsum crystals while the
long polyether chains of the second repeating unit perform the
dispersing function. Since it is less retardive than other
disperants, it is less disruptive to the manufacturing process of
gypsum products such as the gypsum panel. The dispersant is used in
any effective amount. To a large extent, the amount of dispersant
selected is dependant on the desired fluidity of the slurry. As the
amount of water decreases, more dispersant is required to maintain
a constant slurry fluidity. Since polycarboxylate dispersants are
relatively expensive components, it is preferred to use a small
dose, preferably less than 2% or more preferably less than 1% by
weight based on the dry weight of the gypsum. Preferably, the
dispersant is used in amounts of about 0.05% to about 0.5% based on
the dry weight of the stucco. More preferably, the dispersant is
used in amounts of about 0.05% to about 0.2% on the same basis. In
measuring a liquid dispersant, only the polymer solids are
considered in calculating the dosage of the dispersant, and the
water from the dispersant is considered when a water/stucco ratio
is calculated.
[0048] Many polymers can be made with the same repeating units
using different distributions of them. The ratio of the
acid-containing repeating units to the polyether-containing
repeating unit is directly related to the charge density.
Preferably, the charge density of the co-polymer is in the range of
about 300 to about 3000 .mu.equiv. charges/g co-polymer. It has
been found that the most effective dispersant tested for water
reduction in this class of dispersants, MELFLUX 2651F, has the
highest charge density.
[0049] However, it has also been discovered that the increase in
charge density further results in an increase in the retardive
effect of the dispersant. Dispersants with a low charge density,
such as MELFLUX 2500L, retard the set times less than the MELFLUX
2651F dispersant having a high charge density. Since retardation in
set times increases with the increase in efficacy obtained with
dispersants of high charge density, making a slurry with low water,
good flowability and reasonable set times requires keeping of the
charge density in a mid-range. More preferably, the charge density
of the co-polymer is in the range of about 600 to about 2000
.mu.equiv. charges/g co-polymer.
[0050] The gypsum slurry also optionally includes one or more
modifiers that enhance the action of the polycarboxylate
dispersant. The two-repeating unit dispersant used here is
particularly susceptible to the effects of the modifiers. Preferred
modifiers include cement, lime, also known as quicklime or calcium
oxide, slaked lime, also known as calcium hydroxide, soda ash, also
known a sodium carbonate, potassium carbonate, also known as
potash, and other carbonates, silicates, hydroxides, phosphonates
and phosphates. When modifiers are used, the efficacy of the
dispersant is boosted to achieve a new level of fluidity, or the
amount of polycarboxylate dispersant can be decreased to reduce the
polycarboxylate expense. Additional information on modifiers and
their use is found in U.S. Ser. No. 11/_______ entitled "Modifiers
For Polycarboxylate Disperants" filed concurrently herewith and
previously incorporated by reference.
[0051] The modifiers are used in the gypsum slurry in any suitable
amount. Preferably, the modifiers are used in amounts from about
0.01% to about 2% by weight based on the dry stucco. More
preferably, the modifiers are used in amounts of about 0.03% to
about 0.5% and even more preferably, from about 0.05% to about
0.5%.
[0052] Water is added to the slurry in any amount that makes a
flowable slurry. The amount of water to be used varies greatly
according to the application with which it is being used, the exact
dispersant being used, the properties of the stucco and the
additives being used. The water to stucco ratio ("WSR") with is
preferably about 0.1 to about 0.8 based on the dry weight of the
stucco. Commonly a WSR of about 0.2 to about 0.6 is preferred.
Flooring compositions preferably use a WSR from about 0.17 to about
0.45, preferably from about 0.17 to about 0.34. Moldable or
castable products preferably use water in a WSR of from about 0.1
to about 0.3, preferably from about 0.16 to about 0.25. The WSR can
be reduced to 0.1 or less in laboratory tests based on the moderate
addition of the PCE211-Type dispersants.
[0053] Water used to make the slurry should be as pure as practical
for best control of the properties of both the slurry and the set
plaster. Salts and organic compounds are well known to modify the
set time of the slurry, varying widely from accelerators to set
inhibitors. Some impurities lead to irregularities in the structure
as the interlocking matrix of dihydrate crystals forms, reducing
the strength of the set product. Product strength and consistency
is thus enhanced by the use of water that is as contaminant-free as
practical.
[0054] In a preferred wallboard operation, the gypsum is moved on a
conveyor toward a mixer. Prior to entry into the mixer, dry
additives, such as defoamers, or set accelerators, are added to the
powdered gypsum. Some additives are added directly to the mixer via
a separate line. Trimetaphosphate was added using this method in
the examples described below. Other additives may also be added to
the water. This is particularly convenient where the additives are
in liquid form. For most additives, there is no criticality
regarding placing the additives in the slurry, and they may be
added using whatever equipment or method is convenient.
[0055] However, when using the dispersant of this invention, it is
important to add the dispersant to the water prior to addition of
the stucco. Gauge water or make-up water is added at the mixer a
rate needed to meet the target water to stucco ratio when water
from other sources has been taken into account.
[0056] Other known additives may be used as needed to modify
specific properties of the product, such as wallboard, flooring or
cast products. Sugars, such as dextrose, are used to improve the
paper bond at the ends of the boards. Wax emulsions or
polysiloxanes are used for water resistance. If stiffness is
needed, boric acid is commonly added. Fire retardancy can be
improved by the addition of vermiculite and/or glass fiber. These
and other known additives are useful in the present slurry and
gypsum panel formulations.
[0057] Unless otherwise noted in the examples that follow, a 400
gram sample was prepared based on the dry components. All dry
components, including aggregate, were weighed and dry blended
together. The predetermined amount of deionized water was measured
and poured into a mixing bowl. The dry blended material was added
to the water and the time noted as the starting point to determine
the set time. The mixing bowl was placed onto a Hobart mixer and
jogged for approximately five seconds. After one minute of soaking,
the material was mixed at low speed for two minutes. The bowl was
removed from the mixer and the contents stirred for about 15
seconds with a wisk to assure that all material was evenly
mixed.
[0058] The initial slump sample was poured into a damp
2''.times.4'' (5 cm.times.10 cm) cylinder placed on a plastic
sheet, slightly overfilling the cylinder. Excess material was
screeded from the top, then the cylinder was lifted up smoothly,
allowing the slurry to flow out the bottom, making the patty. The
patty was measured (.+-.1/8'') in two directions 90.degree. apart,
and the average reported as the patty diameter.
[0059] References to set time refer to Vicat set time per ASTM
C-472, herein incorporated by reference. The Vicat set time started
from the time the plaster was added to the water for hand mixes and
from the time the slurry came off the mixer for machine mixes. A
sample was made up of 50 grams of dry, aggregate-free material and
sufficient water to make a normal consistency for the desired
application. The sample was poured onto an acrylic sheet to form a
patty. A 300 gram Vicat needle was held half way between the center
and the outer edge of the patty, perpendicular to the patty
surface. The needle was held to the patty surface and released to
fall freely of it's own weight. Set time was determined when the
needle failed to penetrate to the bottom of the patty. If the
degree of penetration was unclear, the needle was given a little
push to determine if it had touched the underlying surface.
EXAMPLE I
[0060] This example demonstrates the importance of the order of
addition of the modifier and the dispersant. Four hundred grams of
stucco from Southard, Okla., 220 g of water, 0.7 g of HRA set
accelerator and 0.89 g of MELFLUX 2500L dispersant that includes
45% solids were used in each of the following tests. Additionally,
0.6 g soda ash was added to two of the samples as described below.
The water and dispersant were added to the water prior to the
addition of the stucco and modifier (if present) in all cases.
After addition of the stucco, the mixture was allowed to soak for
15 seconds, then mixed for 30 seconds to form a slurry. The
modifier was added as described below.
[0061] Condition 1 was the control sample, to which no soda ash
modifier was added. In Condition 2, soda ash was added to the
mixing water prior to stucco addition to the water. The soda ash
was added after the stucco was added to the mixing water in
Condition 3, just prior to turning on the mixer after the soak
time.
[0062] Patty size, stiffening rate and Vicat Set times are reported
in Table I for each of the three process conditions. TABLE-US-00001
TABLE I Condition 1 2 3 Patty Size 19.5 cm 27 cm 24.8 cm Stiffening
Rate 2:10 5:50 5:10 Vicat Set 6:10 10:00 9:30
[0063] Conditions 2 and 3 clearly show that better fluidity is
obtained when the modifier and dispersant are both added, compared
to no modifier addition. However, Condition 3, where the modifier
is added to the slurry of contact each other prior to introduction
of the stucco.
EXAMPLE 2
[0064] In this comparative example, lime was added to a gypsum
slurry used to make gypsum panels and resulted in little
improvement in fluidity. All component amounts are expressed as
pounds per 1000 square feet (104 m.sup.2) of gypsum panel
("lbs/MSF"). Twelve hundred eighty five pounds of stucco was
combined with other dry components, including three pounds of
starch, three pounds of cerelose, and 0.32 pounds (145 g) of
retarder. Ivory lime was premixed with water and added directly to
the mixer through one of several water injection orifices adjacent
to the stucco inlet. The dispersant, Melflux 2500L, was added
directly to the gauge water and blended until homogenous, and the
mixture then was added to the mixer through the remaining water
injection orifices adjacent to the stucco inlet. The dry components
were blended with the stucco, which was then added to the mixer
through the stucco downspout. TABLE-US-00002 TABLE II Sample With
0.18% Lime No Lime HRA Accelerator 32 lbs/MSF 38.8 lbs/MSF Water
831 855 WSR 0.65 0.67
[0065] As shown in Table II, the use of 0.18% lime in this process
allowed a modest reduction in water. However, the water reduction
was not nearly as large as was indicated in laboratory tests, and
it is believed that because the modifier was added in such a way
that it was not well dispersed in the stucco before the PCE was,
the interaction between the modifier and the dispersant was
limited.
EXAMPLE 3
[0066] A plant trial was held whereby the dispersant and the
modifier were both dissolved in the gauging water. The modifier,
soda ash, was dissolved in water to make a 10% solution by weight.
3.9 lbs/msf of Melflux 2500L, diluted to 32% solids, was added to
the gauging water, then 11.3 lb/msf of the soda ash slurry was
added to the gauging water, and all components were mixed to form a
homogeneous solution. Twelve hundred fifty-seven pounds of stucco
was added to the mixer to form the gypsum slurry. TABLE-US-00003
TABLE III Sample With 0.1% Soda Ash No Soda Ash HRA Accelerator 35
lbs/MSF 29 lbs/MSF Potassium Sulfate 0 lbs/MSF 4 lbs/MSF Water 861
965 WSR 0.69 0.77
[0067] As shown in Table III, the use of 0.1% soda ash in this
process allowed a signficant reduction in water.
[0068] While particular embodiments of the method for making a
slurry of gypsum, modifiers, dispersants and water has been shown
and described, it will be appreciated by those skilled in the art
that changes and modifications may be made thereto without
departing from the invention in its broader aspects and as set
forth in the following claims.
* * * * *