Note: Descriptions are shown in the official language in which they were submitted.
49~
This invention relates to compositions useful as tape
joint sealing materials for the installation ox wallboard
paneling in residential, commercial, and industrial butt-
dings. More specifically, it refers to such compositions
wherein a cellulose derivative is employed to impart desire
able properties thereto.
Since the end of the second World jar, the use of wall-
board has all but displaced plaster in erection of interior
walls in the construction of buildings. Wallboard is goner-
lo ally installed in 4 x 8 foot 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 board are butted together are covered with tape
and then the taped joints and all nails are covered with a
joint Senate or pickling compound which, upon hardening, can
be sanded smooth so that the taped joint is imperceptible
when the wall is covered with paint or wallpaper.
At first, the joint cements employed with wallboard
contained a resinous binder, Limestone, clay, mica, a water-
soluble polymer and asbestos as the principal ingredients,
which were mixed with water to form a dope. Asbestos was
included in these formulations for several purposes. Its
primary functions however, were to impart pseudo plasticity
and to prevent sag when applied in a thick layer.
Over the past several years evidence that certain types
of asbestos appear to have carcinogenic characteristics has
led to its being banned altogether. Both prior to and when
the ban became effective, efforts were made to find subset-
lutes and many materials were evaluated as asbestos replace-
I
mints. Today, the overwhelming product of choice in the
joint cement industry to prevent sag is attapulgite clay,
although other clays are still used.
A-ttapulgite clay is acicular and has an extremely high
surface area in relationship to its weight Hence, all
water-soluble polymers used as thickeners or water retention
aids in joint cements are attracted to the surface of the
clay particles to some degree. The extent or degree of
adsorption of the water-soluble polymer on the surface of the
attapulgite clay is related to the charge of the polymer, the
density of the charge, and the hydrogen bonding capability of
top polymer.
Adsorption of the water-soluble polymer on the surface
of the attapulgite clay can lead to mild flocculation which
may manifest itself as "livening" in the joint cement. The
flocculated particles leave crevices or voids which, when the
cement is dried, result in cracks on the surface of the
cement.
Prior to the change from asbestos to attapulgite clay,
Z0 cellulose derivatives, namely, methylhydroxypropylcellulose
(MHPC) and hydroxyethylcellulose (HE) were the principal
thickeners used in joint cements. After the change to at-
tapulgite clay, MHPC became the favored thickener since HE
adsorbs on the surface of the attapulgite clay at about twice
the rate as MHPC.
According to this invention, joint cement compositions
based on a resinous hinder, mica, at lease one clay, such as
bentonite, kaolin and attapulgite clays, and limestone, are
improved by the addition of at least one water-soluble mod-
fled hydroxyethylcellulose having a hydroxyethyl substitution from about 0.5 to about 4.0 MY and a hydroxypropyl subset-
tuition greater than 0.36 MY as a water retention aid and
thickener. The hydroxypropyl substitution is preferably
greater than 0.6 MY Most preferably, the hydroxyethyl MY
will be from 0.8 to about 1.8 and the hydroxypropyl MY Jill
be from about 0.8 to about 1.5. The molecular substitution
MY is defined as the average number of moles of hydroxy-
ethyl or hydroxypropyl substituent groups present per ashy-
:~2124~
droglucose unit. The hydroxypropylhydroxyethylcellulose of this
invention has less tendency to adsorb on the surface of clays,
particularly attapulgite, than either HE or MHPC.
In another embodiment of this invention the hydra-
propylhydroxyethylcellulose is admixed with from about I to about
75% of at least one cellulose ether, based on the total thickener
weight, such as, hydroxyethylcellulose, hydroxypropylcellulose,
methyl cellulose, methylhydroxyethylcellulose and methylhydroxypro-
pylcellulose. Preferably from about 25~ to about 50% of at least
one cellulose ether is employed. Typically, the total MY of
such ethers is from about 1.5 to about 4.0, preferably from about
1.8 to about 3Ø
In yet another embodiment of this invention the hydroxy-
propylhydroxyethylcellulose is admixed with from 5% to about 75%,
based on the total thickener weight, of a hydro~yalkylguar, such
as hydroxypropylguar and hydroxyethylguar, having an MY of from
about 0.1 to about 1.2. Preferably, the hydroxyalkylguar is
present in an amount from 25~ to about 50~ and has an MY from
about 0.1 to about 0.5. ~ydroxypropylguar is preferred.
In particular, the present invention is directed to the
following three embodiments:
l) A joint cement composition which comprises limestone
mica, at least one clay, and a latex binder as its principal
ingredients, the improvement which comprises the addition of from
about I to about I by weight based on the dry ingredients,
of at least one hydroxypropylhydroxyethylcellulose having a
hydroxyethyl substitution from about 0.5 to about I MY and a
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3 -
hydroxypropyl substitution greater than 0.36 MY as a water
retention aid and thickener.
2) A joint cement composition which comprises lime stone,
mica, at least one clay, and a latex binder as its principal
ingredients, the improvement which comprises the addition of -from
about 0.2~ to about I by weight based on the dry ingredients,
ox a mixture of a) at least one hydroxypropyl hydroxyethylcellu-
lose having a hydroxyethyl substitution from about 0.5 to about
4.0 MY and a hydroxypropyl substitution greater than 0.36 MY
and b) a cellulose ether selected from the group consisting of
hydroxyethylcellulose, hydroxypropylcellulose, methylcelluLose,
methylhydroxyethylcellulose and methylhydroxypropylcellulose
having a total MY from about 1.5 to about 4.0 as a water
retention aid and thickener.
3) A joint cement composition which comprises lime stone,
mica, at least one clay, and a latex binder as its principal
ingredients, the improvement which comprises the addition of from
about 0.2% to about 2.0%, by weight based on the dry ingredients
of a mixture ox a) at least one hydroxypropylhydroxyethylcellulose
I having a hydro~yethyl substitution from about 0.5 to about I
ISSUE. and a hydroxypropyl substit-ltiorl greater than 0.3~ ISSUE., and
b) a hydroxyalkylguar selected from the group consisting of
hydroxypropylguar and hydroxyethylguar having an MY from about
0.1 to about 1.2 as a water retention aid and thickener.
Joint cements are marketed as fully formulated, ready-
to-use cement, i.e., already containing water, and as a dry powder
to which water is added at the time of use. The invention include
en such dry powders as well as the fully formulated cements.
s
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Joint cement compositions of this invention are substantially
equivalent in performance to those which are presently available
commercially.
In commercial practice the concentrations of the prince-
pal ingredients can and do vary widely between suppliers and
depending on the intended end use, i.e., whether it is for
patching holes, covering nail pops, or for initially covering
taped joints. In most commercial formulations, the principal
ingredients, which should add up to 100%, are within the following
concentration ranges:
23
_ I_
% by weight based on
Ingredients the dry ingredients
Limestone 40 to 95
Mica 2 to 10
Kaolin Clays 1 to 20
At-tapulgite Clays 1 to 8
Binder (solids) 2 to 15
Thickener 0.2 to 2.0
Bentonite clays can be used to replace all or part of
the attapulgite clay.
If the product is to be sold as a ready-mix formulation,
water in the amount of about 22% to about 35~, based on the
total weight of the composition is added and thoroughly
mixed.
All compositions within the limits described above are
suitable for manual application by troweling. When they are
to be applied mechanically, additional water can be added at
the job site just prior to use.
The modified hydroxyethylcellulose which can be used as
thickeners in the cements of this invention is prepared by
reacting ethylene oxide and propylene oxide with cellulose in
a strongly alkaline medium Specific techniques for carrying
out the etherification are well known in the art and any
known procedure can be employed.
In the alternative, a hydroxyethylcellulose can be
etherified with a propylene oxide in a strongly alkaline
medium. In this case, the hydroxyethylcellulose can be sub-
staunchly any grade having MY from about 0.5 to about
4Ø The preferred materials are those having a viscosity
30 from about 400 to about 5000 centipoise in a it water soul-
lion. Materials ox higher and lower viscosity can also be
used advantageously, however.
The concentration of 1) the hydroxypropylhydroxyethyl-
cellulose, 2) mixtures thereof, or 3) blends of the hydroxy-
propylhydroxyethylcellulose with at least one cellulose ether
or with a hydroxyalkylguar, in the compositions of this in-
mention is from about 0.2% to about 2.0~ by weight based on
the dry ingredients, desirably from about 0.5% to about 1.0%.
The resinous binder is normally a coalescable vinyl
material, preferably polyvinyl acetate) or an ethylene-vinyl
acetate copolymer, which upon drying or curing of the cement
forms a thin matrix to hold the clay, limestone, etc.
-together. When a fully formulated mix is being prepared, an
aqueous latex binder is usually added. In the case of dry
mixes, the binder is added as dried resin particles. Other
materials useful as the binder include, e.g., starch, cozen,
polyvinyl alcohol, polyacrylamide, and copolymers of acryl-
aside and acrylic acid.
In addition to the principal ingredients mentioned above, a typical joint cement will frequently also contain
small amounts of conventional additives, such as dispersants,
defamers, preservatives, pi control agents, and processing
aids to improve open time Suitable dispersants include the
polymerized alkaline salts of a sulfonic acid. Silica disk
pursed in a liquid hydrocarbon is a typical defamer. Typo
teal preservatives include 1-(3-chloroallyl-tria~a-1-
azoniaadamantane)chloride. Alkaline salts may be used as pi
control agents. Propylene glycol is a suitable process aid
to improve open time.
Small amounts of polyacrylamide can be added to further
improve the sag resistance of the cement.
The following examples are illustrative ox the invent
Zion. All parts and percentages used in this disclosure Aruba weight unless otherwise indicated.
Example 1
The following example illustrates a specific embodiment
of the joint cement composition of this invention and how to
prepare it.
A joint cement using the formulation set forth in Table
I is prepared by charging a mixing apparatus with the water
and latex binder and mixing for a short time (about 1 min.).
The defamer, preservative, and processing aid are then added.
All of the dry ingredients are dry blended by tumbling
in a tumbler, and then incrementally adding the dry mixture
to the stirred liquids.
After the addition of the dry ingredients is complete,
the mix is stirred for about 10 minutes at low speed with
occasional stopping to scrape down the tides of -the bowl or
until a homogeneous mixture is obtained.
5 _ __ TABLE I
% by weight based on
Ingredients the ingredients minus water
. . _
Limestone 83.5
Mica 6.5
10 Attapulgite clay 3.4
Latex binder (solids) 3.35
Defoarner 0.2
Preservative 0.05
Alkaline salt 0-9
15 Propylene glycol 1.5
Hydroxypropylhydroxylethylcellulose 0~6
(0.93 hydroxyethyl MY
1.17 hydroxypropyl MY
Water _ 33.6*
. _ _ _ . . _ _ _ . _ . . _ _ _ _
20 *By weight of the total composition
Examples 2-8
In Examples 2 to 8, the procedure of Example 1 and the
formulation of Table 1 are used except that a hydroxypropyl-
hydroxyethylcellulose having the hydroxyethyl MY and the
I hydroxypropyl MY shown in Table II or the particular ox-
ample in question is used instead, and except that 0.9~ of
the hydroxypropylhydroxyethylcellulose is used in Example 8
instead ox 0.6~.
To characterize the compositions of this invention, the
following tests are used:
Viscosity: measured in Bra bender units (BYWAY deter-
mined by ASTM C474-67.
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 mint
vies. The panels are then allowed to dry overnight in the
vertical position without the air current. ratings are
assigned subjectively as: 1 = none, 2 = very slight, 3 =
slight, 4 = moderate, and 5 = severe.
Sag resistance: Panels of the cement about 4 x 5 x 1/8
inch are cast. Sag resistance is rated as good, fair or poor
S by observing the degree of slump of the sharp edges of the
cast cement.
Adhesion: Determined accordions to ASTM C~74-67.
Appearance (texture): The appearance or texture is
observed and ratings are assigned as: 1 - smooth, creamy,
2 = very slight grainy, 3 = slightly grainy, = moderate
grainy, and 5 = very grainy.
Gelatin (livening): A subjective test in which the
amount of gelatin observed is rated using the same ratings
as used for the cracking test above.
Adsorption on clay: A standard curve of each polymer to
be tested is prepared by taking solutions at 0.05, 0.025,
0.01, 0.005, 0.0025, 0.0005, and 0.00025~ concentrations;
placing 1.0 ml of each solution into separate test tubes;
adding 1~0 ml of a 5.0~ phenol solution to each test tube and
mixing thoroughly by shaking; adding 5.0 ml of concentrated
S04 to each test tube and mixing thoroughly by shaking;
letting the tubes stand for 10 minutes; reshakiny; placing
the tubes in a water bath at 25C. for 20 minutes; measuring
the optical density at 490 no on a BLUE spectrometer; and
plotting the concentration vs. optical density.
The clay adsorption is measured by adding 10.0 g of a
sheared clay slurry at 10.0~ concentration plus 9.0 g disk
tilled water to a centrifuge tube; adding 18 g of a polymer
solution at 0.05~ concentration to the tube; mixing contents
by shaking; letting the tube stand for 2 hours; reshaping;
centrifuging at 10,000 RPM in a Servile centrifuge for 30
minutes; taking 1.0 ml of clear supernatant liquid and no-
peeling the procedure given in the preceding paragraph, and
determining the concentration in the supernatant by plotting
on standard curve. The concentration ox polymer adsorbed on
the clay can be determined by difference between the polymer
concentration originally and the polymer concentration in the
supernatant.
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The concentration of the clay slurry or the polymer
solution or both may have to be varied depending upon the
degree of polymer adsorption on the clay surface.
The properties of the compositions of Examples 1 through
8 are shown in Table II.
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Example 9
This Example illustrates another embodiment of this
invention.
The procedure of Example 1 and the formulation of Table
I are used except that a blend of a) 0.15% of a hydroxypropyl-
hydroxyethylcellulose having a hydroxypropyl MY of I and
a hydroxyethyl MY of 0.8, and b) 0.45% of a hydroxypropyl-
hydroxyethylcellulose having a hydroxypropyl MY of 1.30 and
a hydroxyethyl MY of 1.70 are used instead of the hydroxy-
propylhydroxyethylcellulose set forth in Table I.
Example 10
This Example illustrates another embodiment of this invention.
The procedure of Example 1 and the formulation of Table
I are used except that a blend of a) 0.15% of a hydroxyethyl-
cellulose having a hydroxyethyl MY of 2.8, and b) 0.45~ of
a hydroxypropylhydroxyethylcellulose having a hydroxypropyl
MY of 1.30 and a hydroxyethyl MY of 1.70 are used instead
of the hydroxypropylhydroxyethylcellulose set forth in Table
I.
Example 11
This Example illustrates another embodiment of this
invention.
The procedure of Example 1 and the formulation of Table
I are used except that a blend of a) 0.15~ of a hydroxypropyl-
guard having a hydroxypropyi MY of 0.?, and by 0.45% of a
hydroxypropylhydroxyethylcellulose having a hyd~oxypropyl
MY of 1~17 and a hydroxyethyl SO of 0.93 are used instead
of hydroxypropylhydroxy2thylcellulose set forth in Table I.
Example 12
This Example illustrates another embodiment of this
invention.
The procedure of Example 1 and the formulation of
Example 10 are used except that 0.3% of each of a) and h) are
35 present instead of 0.15% and 0.45%, respectively.
2~4~
The properties of the compositions of Examples 9 through
12 are shown in Table IIIo
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Features, advantages and other specific embodiments of
this invention will become readily apparent to those exercise
in ordinary skill in the art after reading the foregoing
disclosures. In this regard, while specific embodiments of
this invention have been described in considerable detail,
variations and modifications of these embodiments can be
effected without departing from the spirit and scope of the
invention as disclosed and claimed.
