CA1212492A - Tape joint cement compositions - Google Patents

Abstract

TAPE JOINT CEMENT COMPOSITION

Abstract of Disclosure Tape joint cement compositions suitable for use with wallboard are disclosed wherein at least one hydroxypropyl-hydroxyethylcellulose having specified substitution levels is employed as the water retention aid and thickener. Blends of hydroxypropylhydroxyethylcellulose with a) at least one cellulose ether, such as, hydroxyethylcellulose, hydroxy-propylcellulose, methylcellulose, methylhydroxyethylcellu-lose, and methylhydroxypropylcellulose or b) a hydroxy-alkylguar, such as hydroxypropylguar and hydroxyethylguar are also disclosed.

Description

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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 Jo 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.

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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:

_ 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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to D) I I-- O 1-- IT 1-- I-- 3 I-- .. I.......... .
ED I. co 1-- --I O I_ Us I O .
C
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O P CO O
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Go O
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Go OVA
If I 11 Sol` Us Jo) So O
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3'3 Jo O O I O O O O O 3 Q, O O O O O O o o to O
I ) N W I-- it a o w I

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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.

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The properties of the compositions of Examples 9 through 12 are shown in Table IIIo I w ~2~24~

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to O Jo to O Jo S 3 to (D to I I< (D
ED rut to 1- Us on n ~~-- o rut o o o o rut O
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Us O
I Jo rut n It

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3 Pi rut I: 3 n I
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ED O

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3'0' I_ O O O O O
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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.

Claims (16)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In 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 at least one hydroxypropylhydroxy-ethylcellulose having a hydroxyethyl substitution from about 0.5 to about 4.0 M.S. and a hydroxypropyl substitution great-er than 0.36 M.S. as a water retention aid and thickener.

2. The composition of claim 1 wherein the hydroxypropyl-hydroxyethylcellulose has a hydroxypropyl substitution great-er than 0.6 M.S.

3. The composition of claim 2 wherein the hydroxypropyl-hydroxyethylcellulose has a hydroxyethyl M.S. from about 0.8 to about 1.8 and a hydroxypropyl M.S. from about 0.8 to about 1.5.

4. The composition of claim 1 wherein the hydroxypropyl-hydroxyethylcellulose is present at a concentration from about 0.5% to about 1.0%.

5. In joint cement composition which comprises lime-stone; mica; a clay selected from the group consisting of attapulgite, bentonite, kaolin and mixtures thereof; 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 at least one hydroxypropylhydroxyethylcellulose having a hydroxyethyl substitution from about 0.5 to about 4.0 M.S. and a hydroxy-propyl substitution greater than 0.36 M.S. as a water reten-tion aid and thickener.

6. The composition of claim 5 wherein the hydroxypropyl-hydroxyethylcellulose, has a hydroxypropyl substitution great-er than 0.6 M.S.

7. The composition of claim 6 wherein the hydroxypropyl-hydroxyethylcellulose has a hydroxyethyl M.S. from about 0.8 to about 1.8 and a hydroxypropyl M.S. from about 0.8 to about 1.5.

8. The composition of claim 5 wherein the hydroxypropyl-hydroxyethylcellulose is present at a concentration from about 0.5% to about. 1.0%.

9. In 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 of a) at least one hydroxy-propylhydroxyethylcellulose having a hydroxyethyl substitu-tion from about 0.5 to about 4.0 M.S. and a hydroxypropyl substitution greater than 0.36 M.S., and b) a cellulose ether selected from the group consisting of hydroxyethylcellulose, hydroxypropylcellulose, methylcellulose, methylhydroxyethyl-cellulose and methylhydroxypropylcellulose having a total M.S. from about 1.5 to about 4.0 as a water retention aid and thickener.

10. The composition of claim 9 wherein the hydroxy-propylhydroxyethylcellulose has a hydroxyethyl M.S. from about 0.8 to about 1.8 and a hydroxypropyl M.S. from about 0.8 to about 1.5, and the cellulose ether is a hydroxyethyl-cellulose having a hydroxyethyl M.S. from about 1.8 M.S. to about 3Ø

11. In joint cement composition which comprises lime-stone; mica; a clay selected from the group consisting of attapulgite, bentonite, kaolin and mixtures thereof; 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 of a) at least one hydroxypropylhydroxyethylcellulose having a hydroxyethyl substitution from about 0.5 to about 4.0 M.S.
and a hydroxypropyl substitution greater than 0.36 M.S., and b) a cellulose ether selected from the group consisting of hydroxyethylcellulose, hydroxypropylcellulose, methyl-cellulose, methylhydroxyethylcellulose and methylhydroxy-propylcellulose having a total M.S. from about 1.5 to about 4.0 as a water retention aid and thickener.

12. The composition of claim 11 wherein the hydroxy-propylhydroxyethylcellulose has a hydroxyethyl M.S. from about 0.8 to about 1.8 and a hydroxypropyl M.S. from about 0.8 to about 1.5, and the cellulose ether is the hydroxyethyl-cellulose having a hydroxyethyl M.S. fxom about 1.8 M.S. to about 3Ø

13. In 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 of a) at least one hydroxy-propylhydroxyethylcellulose having a hydroxyethyl substitu-tion from about 0.5 to about 4.0 M.S. and a hydroxypropyl substitution greater than 0.36 M.S., and b) a hydroxyalkyl-guar selected from the group consisting of hydroxypropylguar and hydroxyethylguar having an M.S. from about 0.1 to about 1.2 as a water retention aid and thickener.

14. The composition of claim 13 wherein the hydroxy-alkylguar is a hydroxypropylguar having a hydroxypropyl M.S.
from about 0.1 to about 0.5.

15. In joint cement composition which comprises lime-stone; mica; a clay selected from the group consisting of attapulgite, bentonite, kaolin and mixtures thereof; and a latex binder as its principal ingredients, the improvement which comprises the addition of from ahout 0.2% to about 2.0%, by weight based on the dry ingredients, of a mixture of a) at least one hydroxypropylhydroxyethylcellulose having a hydroxyethyl substitution from about 0.5 to about 4.0 M.S.
and a hydroxypropyl substitution greater than 0.36 M.S., and b) a hydroxyalkylguar selected from the group consisting of hydroxypropylguar and hydroxyethylguar having an M.S. from about 0.1 to about 1.2 as a water retention aid and thickener.

16. The composition of claim 15 wherein the hydroxy-alkylguar is a hydroxypropylguar having a hydroxypropyl M.S.
from about 0.1 to about 0.5.