Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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This invention relates to compositions containing a
thickener which are useful as joint sealing materials for
the installation of wallboard paneling. More
specifically, it relates to compositions wherein the
thickener is an aqueous suspension of a cellulose ether in
an inorganic salt.
For many years, the use of wallboard has all but
displaced plaster in erection of interior walls in the
construction of buildings. Wallboard is generally
installed in large panels which are nailed and glued to
the studding of the wall and fitted together until the
entire section of wall is covered. The joints where
sections of the board are butted together are covered with
joint compound, then with tape and then the taped joints
and all nails are covered with a joint compound which,
upon hardening, can be sanded smooth so that it is
imperceptible under paint or wallpaper.
Joint compounds employed with wallboard contain a
resinous binder, limestone, clay, mica, lubricant,
stabilizer and a thickener as the principal dry
ingredients which are mixed with water to form a dope
which is applied normally by troweling, as described in
U.S. Patent 3,891,582.
Typically, the water-soluble polymer used to
thicken the product joint compound is a cellulose ether,
e.g., hydroxyethylcellulose, hydroxypropylmethyl
cellulose, etc. One of the factors limiting the output of
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large quantities of a joint compound in a commercial plant
is the relatively long time necessary to completely
dissolve the water-soluble polymer thickener. Because of
this, the ingredients are usually blended for times
ranging from 15 to 20 minutes. The water-soluble polymer
may be dry-blended with the other ingredients, or added as
an aqueous slurry. In the latter case, the hydration rate
of the water-soluble polymer must be chemically retarded
so that the slurry does not thicken prior to being added
to the remaining ingredients.
It is the object of this invention to provide a new
aqueous joint compound formulation, and a process for its
preparation. One of the advantages of this new
formulation is that it reduces the time needed to blend
all of the joint compound ingredients into a homogeneous,
ready-to-use joint compound formulation to as little as
about 5 minutes, resulting in considerable cost savings
and convenience for the user. This is accomplished by
preparing the water soluble polymer thickener in fluidized
suspension form and adding it directly to the mixture of
other joint compound ingredients. It is not necessary to
chemically retard the hydration rate of the water soluble
polymer thickener.
An aqueous joint compound formulation comprises
calcium carbonate, clay, binder, mica. clay lubricant and
thickener, characterized in that the thickener is an
aqueous suspension of a nonionic cellulose ether in an
inorganic salt, wherein the suspension consists of 15% or
more by weight of the cellulose ether based on the total
weight of the suspension and the weight ratio of the
inorganic salt to water in the suspension is at least 0.15.
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203912
Fluidized Suspension of P
The stable fluidized suspension of the nonionic
thickener comprises 15% or more, by total weight, of a
nonionic water soluble polymer dispersed in a aqueous
solution of an inorganic salt preferably having a
multivalent anion, wherein the weight ratio of the
inorganic salt to the water is at least 0.15. Its
composition and preparation are described in U.S. Patents
4,883,536 and 4,883,537.
For the thickener, useful water soluble polymers
are nonionic and contain hydrophilic substituents such as
hydroxyl. Illustrative are hydroxyethylcellulose,
hydrophobically modified hydroxyethylcellulose,
hydroxypropylcellulose, methyl hydroxypropylcellulose, and
hydroxyethyl hydroxypropylcellulose. U.S. Patents
4,338,277, 4,243,802 and 4,826,970 describe some suitable
hydrophobically modified cellulosics~.
The concentration of water soluble polymer in the
aqueous suspension added as the thickener will be 15% or
more. Preferably, the concentration will be in the range
of 17 to 50%, and more preferably in the range of 20 to
35%.
Any inorganic salt which may be dissolved in water
to a sufficiently high concentration that it will render
the water-soluble polymer insoluble with minimal swelling,
can be used in this invention. Suitable inorganic salts
are diammonium sulfate (also known as ammonium sulfate),
diammonium phosphate, ammonium polyphosphate, potassium
carbonate, epsom salts (magnesium sulfate hydrate), sodium
formate and mixtures thereof.
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The weight ratio of inorganic salt to the water in
the suspension is at least 0.15 and is preferably 0.18 to
0.6. The desired concentration of salt in water varies
with the polymer to be suspended. For
hydroxyethylcellulose, a salt to water ratio of 0.18 to
0.25 is preferred.
A number of other additives have been found to
provide beneficial properties to the fluidized
suspension. Preferred additives are stabilizers, such as
hydrophilic fumed silica, and clays such as attapulgite
clay. They increase the time over which the suspension
will remain stable. Also useful for stabilization, in
certain circumstances, are carboxymethylcellulose (CMC),
xanthan gum and other water-soluble polymers. For
instance, the most preferred stabilizers for hydroxyethyl
cellulose suspensions are sodium carboxymethyl cellulose
and xanthan gum. Stabilizers are generally used in
amounts up to about 2%, and are preferably used in an
amount of 0.2% to 1%, by weight of total suspension.
Other additives which can be used include pigments,
dispersants, surfactants, glycols and thickening agents.
These are generally used in amounts up to 10%. preferably
0.5% to 2%, by weight of the total suspension.
The fluidized suspensions can be prepared by
dissolving the inorganic salt in water to form an aqueous
salt solution and, then, dispersing with agitation the
water-soluble polymer therein. In the case where other
additives are employed, these are typically added to the
water before the salt. The slurry may comprise a blend of
one or more of hydroxyethylcellulose (HEC),
methylhydroxypropylcellulose (MHPC) and hydrophobically
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modified hydroxyethylcellulose (HMHEC) or other similar
modified cellulosic polymers.
Joint Compound
Most commercial joint compound formulations contain
limestone, clay, mica, resinous binder, thickener,
lubricant and stabilizer in varying amounts. In some
cases, other additives are included to give the
composition sufficient body for application to a vertical
wall without sagging or melt down. Materials useful for
this purpose include, e.g., cellulose fibers in various
forms, treated clays, and porous stone flour. When
structure additives of this type are added, they normally
replace a portion of the inert fillers, i.e., the
limestone, mica or clay.
The resinous binder is normally a coalescable vinyl
material, such as polyvinyl acetate) which upon drying or
curing of the cement forms a thin matrix to hold the clay,
limestone, etc. When a fully formulated mix is being
prepared, the binder is usually added as an aqueous
latex. In the case of dry mixes it is added as
spray-dried latex particles. Other materials useful as
the binder include, e.g., starch, casein, polyacrylamide,
copolymers of acrylamide and acrylic acid.
In addition to the principal ingredients mentioned
above, a typical joint compound will frequently also
contain a dispersant, a defoamer, and a preservative.
Typically, joint compounds are prepared by
combining all of the wet ingredients (and K2C03, if used)
and mixing for one minute to homogenize. A blend of all
the solids is then added to the mixing bowl, with
continuing mixing. The entire mass is blended for a total
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of about 20 minutes. This procedure may be modified by
different manufacturers.
Mixing time cannot simply be shortened in order to
increase production. For example, with only 10 minutes
mixing, a slightly pasty mixture results. and adhesion
suffers. However, the use of a fluidized suspension of
the water soluble thickener, as described in this
invention, results in easy dispersion throughout the
mixture, and faster hydration of the thickener.
Consequently, the mixing time is shortened to about 5
minutes and the production rate is 2 to 3 times that of
the usual output.
r
The following general procedure was employed to mix
the ingredients:
(1) Add all of the liquid ingredients (and K2C03)
to the mixing bowl and mix for one minute to
obtain a uniform dispersion.
(2) Dry blend the limestone, clay and mica, and
add it to the mixing bowl over 15 seconds.
(3) Add the polymer slurry to the mixing bowl.
Mix for a total of six minutes, stopping at
the end of one and three minutes to rid the
sides of the bowl and the paddle of any
materials.
(4) Evaluate the joint compound, comparing it to
one made by the standard procedure (20 minutes
mixing time).
Product Characterization
To characterize the products prepared in the
examples, the following tests were used.
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Viscosity: Measured in Brabender units (B. U.)
determined by ASTM C 474-67.
Cracking: Panels are dried in an essentially
vertical position with a current of air from a 14
inch oscillating fan forced across their face from
about 30 inches for 45 minutes. the panels are
then allowed to dry overnight in the vertical
position without the air current. Ratings are
assigned subjectively as: none (N), very slight
(V.S.), slight (S), moderate (M), or heavy (H).
Sag_ Resistance: Panels of the cement about 4 x 5 x
1/8 inch are cast. Sag is observed at the edges of
the panels. Ratings: Excellent: structure of
cast panel is retained with sharp edges. Slight:
edges of panel are slightly rounded. Poor: edges
of panel smooth and tapered.
Adhesion: By ASTM test C 474-67.
The Invention is illustrated in the following
Examples. Parts and percentages are by weight, unless
otherwise indicated.
Example 1
Fluidized Suspension of Hydro~hobically Modified
Hydroxyethyl Cellulose (HMHEC)
A fluidized suspension of HMHEC available from
Aqualon Company, Wilmington, DE as AQA D-3082, was
prepared as described in U.S. Patent 4,883,537 using the
following ingredients.
CA 02039124 2001-O1-22
22124-I_776
_g_
Ingredients Weight
WatE~r 63.79
Diarnmonium Sulfate (available from
Agway, Inc., Syracuse, New York) 16.0
HMHEC (available from Aqualon Company) 20.0
Xani=han Gum 0.20
Pro:~el* GXL Stabilizer 0.01
The hydrophobic modifier in AQA D-3082 was
3-n-butoxy-2-hydroxypropyl at a molar substitution level
of 0.10. It had a hydroxyethyl molar substitution of
3.2. Brookfield viscosity was 500 mPas.
Joint Compound
Using the general procedure described previously,
a joint compound was prepared from the following
formulation.
Joint Compound Formulation
- Ing!redients Weight
Limestone (Georgia White No. 9) 60.22
A~ttapulgite (Gel B) Clay 1.85
Latex (Ucar*131) Binder 2.25
Mica (P80K)*(available from Unimin Corp.,
Spruce Pine, North Carolina) 2.75
Propylene Glycol(available from East
Falls Corp., Frazer, Pennsylvania) 0.40
Biocides 0.05
Tlhickener 0.48
Water 32.0
* Trade -mark
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The amount of thickener listed corresponds to the
amount of polymer present in the fluidized suspension.
The amount of water in the formulation was then
decreased to compensate for the water added with the
suspension. Likewise, the limestone was decreased to
compensate for the salt (DAS) added with the
suspension. The joint compound was prepared by the
method described above in the section titled "Mixing
Procedure".
The joint compound prepared in this manner had very
good properties, as demonstrated by the following:
Appearance: Creamy
Viscosity: 500 B.U.
Adhesion: Excellent
Sag Resistance: Excellent
Cracking: Very Slight
Example 2
The joint compound formulation of Example 1 was
prepared with dry HMHEC, instead of the fluidized
suspension of HMHEC; after mixing for 6 minutes by the
general procedures described previously, the product was
grainy in appearance and gave poor adhesion, indicative
of incomplete dissolution of the polymer. It contained
many partially hydrated water-soluble polymer gel
particles, which prevented troweling to a smooth finish.
Example 3
Using the procedures described in Example 1, a
fluidized suspension of a mixture of methyl
hydroxypropylcellulose and hydroxyethylcellulose
(Natrosol~ 250 HXR from Aqualon Company) was prepared.
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A joint compound was prepared utilizing this
fluidized suspension in the joint compound formulation
given for Example 1, but with 0.56% thickener. The
joint compound had very good properties, as demonstrated
by the following:
Appearance: Creamy
Viscosity: 570 B.U.
Adhesion: Excellent
Sag Resistance: Excellent
Cracking: Very Slight
Example 4
Using the procedures described for Example 1, a
fluidized suspension of mixture of methyl
hydroxypropylcellulose and hydroxyethylcellulose polymer
(Natrosol~ 250HHXR) was prepared. A joint compound was
prepared utilizing this fluidized suspension in the joint
compound formulation given for Example 1, but with 0.40%
polymer and 2.0% Attapulgite. The joint compound had very
good properties, as demonstrated by the following:
Appearance: Creamy
Viscosity: 540 B.U.
Adhesion: Excellent
Sag Resistance: Excellent
Cracking: Slight
These examples demonstrate a new aqueous joint
compound formulation and a process for its preparation and
use, utilizing a particulate water soluble polymer
thickener in an aqueous suspension in a solution of an
ammonium salt, which provides much more rapid thickening
and equilibration of the joint compound formulation than
prior art thickeners employed in their dry form. In
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addition, less cracking and shrinkage of the joint compound
was evident.
Example 5
A fluidized suspension of HMHEC was prepared
utilizing the following ingredients:
Ingredients Weight
Water 63.7
Diammonium phosphate 16.0
HMHEC (available from Aqualon Company) 20.0
Xanthan gum 0.2
Proxel GXL 0.1
The so-formed suspension was observed to be fluid,
pourable and stable to particle settling with time.
Joint Compound
A joint compound was prepared utilizing this fluid
suspension as a thickening agent with a 5 minute
thickening time as practiced in Example 1. The joint
compound prepared in this manner had the following
properties:
Appearance: Creamy
Viscosity: 550 B.U.
Adhesion: Excellent
Sag Resistance: Excellent
Cracking: Very Slight
The above example showed that ammonium phosphate
was a suitable salt for joint compounds of the present
invention.
Example 6
A fluidized suspension of HMHEC was prepared
according to the method of example 1 with the following
compositions:
__T.._~.___._ _ __.__.._ ._.
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2039124
Ingredients Weight
Water 4g,~
Sodium formate 20.0
HMHEC (available from Aqualon Company) 30.0
Xanthan gum 0.2
Proxel GXL 0.1
The so-formed suspension was observed to be fluid
and pourable and to show minimal solids settling upon
standing with time.
Joint Compound
A joint compound was prepared according to the
method of Example 1 employing the above polymer suspension
as the thickening agent. The joint compound prepared in
this manner had the following properties:
Appearance: Creamy
Viscosity: 480 B.U.
Adhesion: Excellent
Sag Resistance: Excellent
Cracking: Slight
The above example showed that sodium formate was an
effective salt for preparing joint compounds of the present
invention.
Example 7
A fluidized suspension was prepared according to
the method of Example 1 which employed the the following
composition:
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Ingredients Weight
Water 63.8
Culminalm 20,000 PFR (Aqualon) 20.0
Epsom Salt (magnesium sulfate hydrate) 16.0
Xanthan gum (available from Ashland
Chemical Corp.) 0.2
The so-formed suspension was observed to be fluid,
pourable and stable.
Joint Compound
A joint compound was prepared according to the
method of example 1 that employed the above fluid
suspension as the thickening agent. The joint compound
prepared in this manner had the following properties:
Appearance: Smooth
Viscosity: 470 B.U.
Adhesion: Excellent
Sag Resistance: Excellent
Cracking: Slight
This example demonstrated that epsom salts could be
employed as the salt ingredient in the present invention.
360
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