CA1330128C - Drywall coating composition - Google Patents

Abstract

Abstract of the Disclosure The unequal porosity ant different textures of a drywall reinforced with joint tape and joint compound are concealed by a paint made from a low cost, easily dispersible powder in which the pigment volume concen-tration is about 70% to about 75%. A vinyl acetate/ethylene copolymer serves as the principle binder and a water soluble cellulose ether thickens the water dispersion of kaolin, attapulgus clay, mica, sodium potassium aluminum silicate and calcium carbonate.

Description

-- ` 1330128 ,:-. ;.
.,,., ~ ,~ ".
- ' .'~ . "'~
,, .; - ~
, . . ,, ~ ,...

DRYWALL COATING COMPOSITION
: ,:.' , , .
This invention relates to the problem of painting a wall newly erected by fastening wpsum drywall panels to a framework, taping the seams, covering the tape and fastener dimples with ~Oint compound and then smoothing the surface. The invention relates more particularly to an easily dispersible powder for making a water based paint which, as a first coat, will conceal the tifferences in the textures of the drywall face paper and the ~oint compound and also equali~e the porosities of ~ ~ ;
the paper and the ~oint compound.
The problem of "~oint banding" or "photographing" when decorating a drywall with a gloss or semi-gloss paint remains a concern for the ' -industry. Raised paper fibers, caused by the inadvertent roughening of the drywall paper when sandin8 the ~oint compound, are difficult to hide.
Unless the differences between the poro~ities and surface textures of the face paper and the ~oint compound are concealed beforehand, the ~ `
glossy coating will reveal all the irregularities of the underlying wall.
One of the methods recommended by ~oint compound.suppliers for overcoming the Joint banding problem is to apply a skim coat of the Joint compound over the entire surface of the newly erected wall. Thus, the porosity and texture presented to the glossy paint is that of the ~oint compound. In skim coating the ~oint compound is slightly thinned ~ -out with water and applied with a trowel or a broadknife, or with a long nap roller followed by troweling. Loss of ~oint compound as droppings ~ `
during application and smoothing iB almost inevitable. The skim coat of ~oint compound does not provide sufficient "hold out" to prevent the ; ;
~ " :

penetration of water or solvent from the finish coat of paint. Shu8, the suppliers of ~oint compound recommend a primer ant sealer over the skim coat.
Ready mixed compositions are often packaged and promoted a8 com-bination primers/sealers. A sealer should have a resin content high enough to lay town a fllm which provides good "hold out" to both the face paper and ~oint compound surfaces. Sealers usually do not have adequate amounts and kinds of pigments and fillerg to build up the film 80 that texture differences are concealed. Primers are primarily de-signed for the latter purpose but some do contain enough resin to equalize porosity. The cost of providing adequate resin along with the adequate amounts and proper types of plgments and fillers to do both ~obs, when added to the cost of large scale dispersing equlpment and the cost of transporting water-heavy compositlons results in prices of about $8.00 or re per gallon to the contractor. A low cost alternative which imparts equal or superior properties to the drywall is thus very desirable.
Flat paints are the st commonly used untercoating compositions even though they contain lesser amounts of resin than do the ready mixed primer/ sealer combinations.
There still remains, however, a need for a low cost method for pre-paring a newly erected drywall 80 that the occupants of a room cannot tell where the ~oint compound and raised paper flbers are after decoration wlth a gloss or semi-gloss palnt.
The coating composltion used ln such a method 18 the key to the cost savings in that lts cost as supplled to the contractor must be low and the cost of preparing and applying the compositlon must not negate the lnltial ~-low cost. As may be seen from the above, a high ~uallty undercoatlng com~
positlon for drywall should have a high resin content for seallng the pores of Wth the Joint compound and the face paper and also a hlgh pigment/
. 30 filler content for building up the film ln order to conceal the varying -~
textures of the ~olnt compound, smooth face paper and roughened face paper.
But, the nature of the various reslns, plgments and fillers must be taken into account when they are to be combined ag a dry powder for sale to con- ~ -tractors who then will choose to disperse the powder in local tap water at ,,' ' -, the job site. The contractor wants to get thorough dispersion in as little time as possible. Some contractors prefer to spray the undercoating and cannot abide poorly dispersed paint. Thu~, the components of the dry powder must be selected and combined in proportions designed to maxlmize the dispersibility of the dry powder while providing good film build up -properties to the water-based paint and high hiding power along with good "hold out" properties and hardness to the dried film of paint.
It is an ob~ect of this invention, therefore, to provide an easily dispersible dry powder for use in making a water based undercoat paint for drywall at the ~ob site.
It i9 a related ob~ect of this invention to provide a low cost -;
method for equalizing the porosities and concealing the differences in texture of a drywall having ~oint compound at its seams and fasteners.
It is yet another ob~ect of this invention to provide a method for - - -applying a thick undercoating film on a drywall which is sufficiently smooth without sanding for decoration with a finish coat to give a plea-singly fine texture.
It i9 a further related ob~ect of this invention to provide a low cost undercoating composition for newly erected drywall which i9 equal or superior to high cost, ready-mixed primer/sealer compositions in its ability to provide for a monolithic appearance of the wall when finished -with a gloss or semi-gloss paint.
These and other ob~ects of this invention which will become apparent are achieved by a powder consisting essentially of, on a weight basis: -from about 16% to about 24Z calcium carbonate, ~
from about 20% to about 30% kaolin, ~ -from about 3% to about 5% attapulgus clay, from about 8% to about 12% mica, from about 16% to about 24% sodium potassium aluminum silicate, from about 4.5% to about 10% vinyl acetate/ethylene copolymer, from about l% to about 3% of a water soluble cellulose ether, -and a dispersant.

The calcium carbonate i8 a very finely divided filler having a mean particle size of about 0.7 micron. Preferably, about 90% of the particles are smaller than 2 microns. The powder of this lnvention preferably con-tains from about 18% to about 22% of the calcium carbonate; a particularly preferred powder contains about 20% of this filler by weight.
A rather large amount of the kaolin i9 used despite its high oil absorption value of 40 to 42 because it has good hiding power and is easily dispersible in water. Titanium dioxide, being a true pigment rather than an extender or filler, has much greater hiding power and a much lower oil demand (about 20l but it is difficult to disperse in water.
The dry powder preferably contains from about 23X to about 28X of the kaolin by weight and more preferably from about 25 to about 28%. It is preferred that about 96% by weight of the kaolin particles are smaller than 10 microns - ~-and at least about 20% of them are smaller than 1 micron. -~
Because the extenders and fillers do not opacify the film deposited on the drywall according to this invention, the worker who applies the coating may have difficulty ln distingulshing the coated area of the drywall from the non-coated area. For that reason, a true plgment such as titanium dioxide which does opacify or a dispersible colorant of some kind may be added to the dry powder. When using tltanium dioxide, the amount may be up to about lOX, preferably up to about 8Z, of the total weight of the -powder.
The levelling properties of the water based paint are such that the ~ ~ -undercoated drywall will have a smooth surface ready for finish coating without sanding belng necessary even when the undercoating is applied with a roller. The attapulgus clay and the cellulose ether work together to lmpart such deslrable levelllng propertles. Attapulgus clay is known to impart non-levelllng propertles to water based coatlng materlals and itslpresence helps to make possible a thick, non-sagglng undercoae on the drywall. The vlscoslty at low shear rates lmparted to the water based paint by the water soluble cellulose ether balances the effect of the attapulgus clay as to the levelling properties of the paint. The viscosity at high shear rates affects the thickness of the film that can be applled on each stroke of a roller or each pass of a spray gun.

A water soluble cellulose ether 19, for the purposes of this invention, one which forms a transparent colloidal solution in water at a concentration of about 6% by weight of the solution. A 2% aqueous solution of tbe -;
cellulose ether of this invention has a viscosity of from about 5000 to about 50,000 cps at a shear rate of 2 reciprocal seconds as meaæured with a Brookfield viscometer type LV. At a shear rate of 10,000 sec 1, a 2% solution of the ether has a viscosity of from about S0 to about 90 cps.
The cellulose backbone of the ether has from about 100 to about 1200 anhydroglucose units. A hydroxyalkyl cellulose and particularly, an --alkyl hydroxyalkyl cellulose, is preferred. An ethyl hydroxyethyl cellulose i~ preferred among the latter types and one in which there are an average of about two hydroxyethyl groups on each anhydroglucose unit is especially preferred. The cellulose ether preferably amounts to from about l.SZ to about 2.5% of the weight of the dry powder and a particularly lS preferred amount is 2%. A preferred amount of the attapulgus clay, on the other hand, is from about 3Z to about 4Z, the latter being more preferable.
The mica platelets help to hide the varying textures of the drywall paper and ~oint compound. The mean particle size of the platelets is from about 20 to about 25 microns. A preferred powder of this in~ention - contains about lOZ mica.
The sodium potassium aluminum silicate is a non-argillaceous mineral ~ :
which acts as an extender pigment. Unlike the rather soft mlca platelet~
the irregular nodules of this mineral are relatively hard (5.5-6 on the Mohs scale). Thus, although sanding of the undercoating film is not ;~
necessary for a satisfactory smoothness, this extender imparts a hardness to the film 80 that if light sanding i~ done the integrity of the film will not be disturbed. The mean particle size of the nodules is 4.5 microns and' the largest nodules are about 17 microns, as determined by the sedimen- `
tation method. It has an oil absorption value of 28 to 29. A preferred amount of this alkali aluminum silicate is from about 18% to about 22Z
of the weight of the dry powder. About 20% is especially preferred.
The primary binder in this system is a vinyl acetate/ethylene copoly-mer in which the ethylene portion is from about 10% to about 30% of the weight. It is in the form of a redispersible powder whose predominant partlcle Bi~e i8 in the 1-5 micron range wlth only about 2% of the particles ~eing larger than 40 mesh. It forms a tough film which adheres well to the drywall and to the filler~ and pigments of the coating composition. Preferably, the dry powder of this invention contains from about 6 to about 8% of the copolymer.
Overpigmentation of a coating composition can lead to 10~9 of adhesion especially when one or more of the pigments or extenders has a high oil absorption value. Pigment volume concentration, commonly called the PVC, is the ratio of the volume of the pigment, including extenders and filler~, to the total volume of non-volatile components (i.e., pigment ant vehicle). In this invention, the volu~e of the binder plu9 the ~ ~`
thickener and the miscellsneous additlves such as defoa~ers, dispersants -~ -ant preservatives is less than half of the volume of the pigment. The adhesion of the undercoating film to the drywall is very good despite the fact that the PVC is from about 70Z to about 75%.
The dry powder may be dispersed easily and quickly in water by a -painter at the ~ob site. A hand-held mixer powered by a 3/4 inch drill motor and equipped with a cage type paddle or similar paddle is well suited to the ~ob. It is preferred that the initial proportion of powder to water is about 10 pounds per gallon and that the powder is stirred into the water at a m~er speed of about 550 r.p.m. until the d xture becomes lu~p free. After soaking of the mixture for from about i 5 to about 10 minutes, stirring is resu~ed and up to about 1.6 gallons of water per lO pounds of powder is added to obtain the desired con-sistency. The water content of the paint may be from about 60X to about -~
70~ by weight or 75-~5X by volume. The paint may be sprayed, brushed, `
or rolled onto the drywall without further delay although the customary praçtice of straining the paint through a ~ock or the like before putting it into the spray gun may be followed if desired. Usually, the wet thickness of the coating so applied is about 4 mils or more and it may be up to about 12 mils without runs or sags.
The following examples illustrate the invention more specifically ; and are not intended to be limiting.

'~. ' . '~' "` ' '''`','~ ~ -~7~ 1 330 1 28 , A dry powder was prepared according to the following formula~
Ingredient Weight Percent Calcium carbonate 20.0 Calcined kaolin 25.0 ~ -Attapulgus clay 4.0 Titanium dioxide 8.0 Mica 10.0 Sodium potassium aluminum silicate 20.2 Vinyl acetate/ethylene copolymer 8.0 Ethyl hydroxyethyl cellulose 2.0 Defoamer (Nopco PD-l) * 2.0 Dispersant (Daxad 30S)* 0.7 Fungicide (Vancide MZ-96) * 0.1 ::
The calcium carbonate was the high purity, ultrafine product sold by Omya, Inc. under its trademark Omyacarb. Its bulking value is 0.0444 gallon ~ -~
per pound.
The calcined kaolin used was the product 301d under the trademark Snow-Tex 45 by the Texas Industrial Minerals Company. Its bulking value ~ ~-is 0.0465 gallon per pound and its oil absorption value is 40-42 lbs.
per 100 lbs. by the spatula rub out method of ASTM D-281-31. --The attapulgus clay was Attagel M-8214 from Engelhard Minerals and Chemical Co. Its bulking value is 0.0508 gallon per pound.
The titanium dioxide was the rutile type sold by American Cyanamid ~ -under its Unitane OR-600 trademark. Its bulking value is 0.0293 gallon per pound.
The mica has a bulking value of 0.0418 gallon per pound. Sold by United States Gypsum Company under the designation P80F-K, its mean particle size is 22.8 microns, as determined by Stokes sedimentation by sedigraph, and 97.5X by weight is smaller than 150 microns.
The sodium potassium aluminum silicate is available from Indusmin, Ltd.
under its trademark Minex 7. It has a bulking value of 0.0459 gallon per ~ -pound.
The vinyl acetate/ethylene copolymer used was a redispersible powder sold by Air Products and Chemicals, Inc. under its trademark Airflex RP-245 -~
which contains about 10% each of an inert filler and polyvinyl alcohol by ~-weight.
*trade-marks - `~

Thus, the copolymer itself, constituted about 6.47~ of the powder of thls example. The bulking value of the RP-245 powder i9 0.1091. ~ -The ethyl hydroxyethyl cellulose was the Bermocoll E-351 water soluble cellulose ether solt in powder form by Berol Kemi AB. The average number of hydroxyl groups ln each anhydroglucose unlt that have been replaced by hydroxyethyl groups is 2 and the average number of ethyl substituents per unit is 0.9. The Brookfield viscogity of a 2X aqueous solutlon at 20C
is from 4000 to 6000 cps as measured with a type LV viscometer and a No. 3 spindle at a speed setting of 12. With a specific gravity of 1.33, the bulking value of the cellulose ether 19 0.0903 gallon per pound.
The powder of this example, havlng a pigment volume concentration of 74.6~ as calculated from the bulking values, was added to water wlth stirring ln the proportlon of 25 pounds of powder to 2.5 gallons of water. A cage type paddle mixer driven by a 3/4 inch drill motor at 550 r.p.m. was used to dlsperse the powder ln the water. The thlck, lump-free slurry was then diluted with 4 gallons of water. The resulting paint was ready to use about 15 minutes after the powder was flrst added to the water. It was strained through a sock in keeping with standard ;
practlce before belng sprayed through an alrless spray gun havlng a 0.019 inch atomizing tlp onto a newly erected drywall having ~olnt tape ~-and ~olnt compound at the seams between each panel. The result was a -~
monollthlc undercoat with no ~oint flashing vlslble under critical lighting. The wall was painted with a finish coat later without sanding ~-the undercoat.
. .:
,~ ,, 25 EXAMPLE 2 ~ - -~ -The procedure of Example 1 was followed generally except that the -- -paint was applied with a roller with similarly good results. ~ ~ -'' " ~, ,.
': ` .' ~
: ~. :
: . , .: . . . .. - . ... -. . .. , ,- , .

Claims (18)

1. A dry powder easily dispersible in water to make a coating compo-sition at a job site for a drywall having varying porosities and surface textures, said powder consisting essentially of, on a weight basis:
from about 16% to about 24% calcium carbonate, from about 20% to about 30% kaolin, from about 3% to about 5% attapulgus clay, from about 8% to about 12% mica, from about 16% to about 24% sodium potassium aluminum silicate, from about 4.5% to about 10% vinyl acetate/ethylene copolymer, from about 1% to about 3% of a water soluble cellulose ether, and a dispersant.

2. The powder of claim 1 wherein the kaolin is about 25%.

3. The powder of claim 2 wherein the silicate is about 20% and the mica is about 10% of the weight.

4. The powder of claim 3 wherein the copolymer is from about 6%
to about 8% and the attapulgus clay is about 4% of the weight.

5. The powder of claim 4 wherein the cellulose ether is a hydroxyalkyl cellulose.

6. The powder of claim 5 wherein the cellulose ether is ethyl hydroxyethyl cellulose.

7. The powder of claim l further characterized by the presence of an opacifying pigment in an amount from greater than 0% to about 10%.

8. A method for equalizing the porosity and concealing differences in texture of a joint compound reinforced drywall comprising blending a dry powder consisting essentially of:
from about 16% to about 24% calcium carbonate, from about 20% to about 30% kaolin, from about 3% to about 5% attapulgus clay, from about 8% to about 12% mica, from about 16% to about 24% sodium potassium aluminum silicate, from about 4.5% to about 10% vinyl acetate/ethylene copolymer, from about 1% to about 3% of a water soluble cellulose ether, and a dispersant;

dispersing the dry powder in a sufficient amount of water to make a paint containing from about 60% to about 70% water by weight, and coating the drywall with the paint.

9. The method of claim 8 wherein the dispersing step is completed in about 15 minutes.

10. The method of claim 8 wherein the coating step is commenced promptly after the dispersing step is completed.

11. The method of claim 8 wherein the kaolin is about 25% of the weight of the dry powder.

12. The method of claim 8 wherein the silicate is about 20% and the mica is about 10% of the weight of the dry powder.

13. The method of claim 8 wherein the copolymer is from about 6%
to about 8% and the attapulgus clay is about 4% of the weight of the dry powder.

14. The method of claim 13 wherein the cellulose ether is a hydroxy-alkyl cellulose.

15. The method of claim 14 wherein the cellulose ether is ethyl hydroxyethyl cellulose.

16. The method of claim 8 wherein the powder contains from greater than 0% to about 10% of an opacifying pigment.

17. The method of claim 8 wherein the paint has a pigment volume concentration of from about 70% to about 75%.

18. The method of claim 8 wherein the drywall is coated to a wet thickness from about 4 mils to about 12 mils.