CELLULOSE ETHER COMPOSITIONS WITH IMPROVED WORKABILITY FOR USE IN GYPSUM SMOOTHING MORTAR AND JOINT FILLER APPLICATIONS

Abstract

The present invention provides additives for dry mix or tape joint compound compositions comprising one or more cellulose ether powders containing on its surface one or more hydrophobic alkali swellable emulsion polymer (HASE), preferably, one that is not crosslinked or which comprises, in copolymerized form, no multi-ethylenically unsaturated monomer, and, optionally, an inorganic basic filler. The present invention also provides methods to make the additive comprising kneading at from 50 to 120 C. a wet cellulose ether mixture containing from 50 to 80 wt. % of water with from 0.5 to 25 wt. %, based on total cellulose ether solids, of the hydrophobic alkali swellable emulsion polymer; if desired, adding an inorganic basic filler, and drying and grinding. The additive can be combined with 0.1 to 20 wt. %, based on total cellulose ether solids, of a dry polyacrylamide.

Claims

1. A method for making compositions for use as gypsum dry mix or gypsum tape joint compound additives comprise kneading at elevated temperature of from 50 to 120 C. a wet cellulose ether mixture containing from 60 to 80 wt. % of water, one or more cellulose ether, and from 0.5 to 25 wt. %, as solids, based on the total weight of cellulose ether solids, of a hydrophobic alkali swellable emulsion (HASE) polymer additive to form an additive; drying and grinding the additive to an average particle size of at least 50 wt. %<200 m (measured by light scattering) wherein tie cellulose ether becomes coated with the HASE polymer.

2. The method as claimed in claim 1, wherein the kneading device comprises an extruder, a kneader, a banbury mixer; a high shear mixer, or a homogenizer.

3. The method as claimed in claim 1, wherein the cellulose ether is hydroxyethyl methyl cellulose.

4. The method as claimed in claim 1, wherein the amount of the hydrophobic alkali swellable emulsion polymer ranges from 2.5 to 20 wt. %, as solids, based on the total weight of cellulose ether solids.

5. The method as claimed in claim 1, wherein the hydrophobic alkali swellable emulsion polymer comprises, in copolymerized form, (i) from 45 to 55 wt. % of at least one C.sub.1 to C.sub.4 alkyl (meth)acrylate, (ii) from 35 to 45 wt. % of at least one ethylenically unsaturated carboxylic acid or salt thereof, and (iii) from 2.5 to 20 wt. %, of a surfactant monomer that contains a hydrophobic group, a nonionic hydrophilic group, all weights based on the total weight of monomers used to make hydrophobic alkali swellable emulsion polymer.

6. The method as claimed in claim 5, wherein the hydrophobic alkali swellable emulsion polymer comprises, in copolymerized form (i) ethyl acrylate (EA), (ii) methacrylic acid (MAA), and (iii) a surfactant monomer that contains as a hydrophobic group a C.sub.12 to C.sub.18 alkyl group and as a nonionic hydrophilic group a poly(oxyethylene) group having 6 to 25 oxyethylene repeating units.

7. The method as claimed in claim 1, wherein the hydrophobic alkali swellable emulsion polymer is not crosslinked or comprises, in copolymerized form, no multi-ethylenically unsaturated monomer.

8. A dry mix composition comprising gypsum or calcium sulfate and a dry mix additive comprising one or more cellulose ether powders wherein the powder of cellulose ethers contains on its surface from 2.5 to 20 wt. %, as solids, based on the total weight of cellulose ether solids, of a hydrophobic alkali swellable emulsion (HASE) polymer additive.

9. The dry mix additive as claimed in claim 8, further comprising a polyacrylamide in the amount of from 0.1 to 20 wt. %, based on total cellulose ether solids, an inorganic basic filler that readily disperses into water, or a combination thereof.

10. The dry mix additive as claimed in claim 8 wherein the hydrophobic alkali swellable emulsion polymer is not crosslinked and has a weight average molecular weight of from 250,000 to 1,000,000.

Description

EXAMPLES

[0063] The following materials were used.

[0064] Setting gypsum dry powder (CASUTEC WS Casea GmbH, Ellrich, DE), containing no cellulose ether, pH7.

[0065] The cellulose ether was a hydroxyethyl methylcellulose (HEMC) available as WALOCEL MKX 40000 PP 01 cellulose ether (Dow Deutschland Anlagengesellschaft mbH, DE). Viscosity given below.

[0066] The polyacrylamide 1 has 30% of repeat units as anionic (carboxylic acid) groups and a viscosity at room temperature as a 1.0 wt. % solution in water at 10 rpm (Brookfield; Spindle 2) with 10 wt. % NaCl of from 1600-2200 mPa.Math.s. Polyacrylamide 1 has an average particle size of <50 wt. % passing through a 63 micron sieve.

[0067] The hydrophobic alkali swellable emulsion polymer (HASE) was a copolymer of 50 wt. % ethyl acrylate (EA), 40 wt. % methacrylic acid (MAA) and 10 wt. % of Cm to C.sub.18 alkyl poly(oxyalkylene).sub.20(meth)acrylate having a weight average molecular weight (Mw) of 558,000. The aqueous emulsion copolymer had a 30 wt. % solids content and a viscosity (Brookfield LV, spindle 1@ 60 rpm, 25 C.) of 26 mPa s.

Examples 1 to 3, 1C and 3C: Incorporation of Hydrophobic Alkali Swellable Emulsion Polymer onto a Cellulose Ether

[0068] 263.4 g Hydroxyethyl methylcellulose (HEMC, 5.1 wt. % moisture content) was placed into a kitchen mixing machine (Bosch ProfiMixx 44, Munich, Germany, 4-6 liter volume). In order to mimic the wet filter cake at the plant, water was added and adjusted to a total moisture content of 65%. Here the water content of the HASE suspension (30% aq. solution) as well as the moisture content of the hydroxyethyl methylcellulose has been included. HASE suspension was added within 1 hour using a dropping funnel. During the addition the composition was mixed at a shear rate of from 35 to 45 rpm. Then the HASE-HEMC batch was removed from the kitchen mixing machine and placed into a heated laboratory scale (4-6 liter volume) kneading machine (Werner & Pfleiderer Masch.Typ: LUK 4 III-1, Coperion, Stuttgart, DE) set at 70 C. The HASE-HEMC batch was then finally kneaded continually for 60 minutes at a shear rate of from 25 to 50 rpm; and the product afterwards dried in a drying cabinet at 55 C. and ground in an Alpine mill (Hosokawa Alpine Aktiengesellschaft, Augsburg, DE) equipped with an 0.5 mm sieve for a time sufficient that 100 wt. % of the product passes through the sieve to form a dry mix additive.

[0069] Then, the particle size was adjusted with a standard sieve so that the product has an average particle size of 40-60%<63 m and >99.5%<200 m.

[0070] As shown in Table 1, below, the grade of HEMC used and compared had consistent viscosities.

TABLE-US-00001 TABLE 1 Wet Viscosity of Polymeric Fluidizer Cellulose Ether Mix Examples 1C.sup.1 1 2 3 HEMC or HEMC 46770 29120 37880 31020 composition with HASE (mPa s*) HASE (wt. % 0 15.0 5.0 10.0 based on HEMC) *Viscosity: 2 wt. % aq. solution, Haake Rotovisko RV 100, shear rate 2.55 s.sup.1, 20 C.; .sup.1Denotes Comparative Example.

[0071] Not shown in Table 1, above, the polyacrylamide was included in the composition by adding it to the ground cellulose ether dry mix additive and dry mixing to make the final additive product. The dry polyacrylamide has an average particle size of <50% through 63 m and >98% through 315 m.

[0072] Test Methods:

[0073] 200 g of drying gypsum smoothing mortar and joint filler raw material was dry blended with 1.0 g of the dry mix additive and mixed in a plastic cup with tap water and, if included, the indicated amount of lime hydrate; the mortar was mixed after a waiting time of 15 sec for 45 sec with a wooden stick. The thickening behavior was evaluated immediately after stirring and expressed in narrative form, as shown in Tables 2A and 2B, below. The quality of thickening is indicated in narrative form: 1 is best (slow and gradual); 6 is worst (uneven and/or rapid), 2 is good. After a 10 min. resting time, the mortar was stirred again and the workability was evaluated, as shown in Table 2A, below. Paste quality was evaluated visually for the formation of lumps. It is indicated whether or not lumps are present and if so to what degree: 1 is best; 6 is worst, 2 is good. Ease of movement and the stirring test refers to thickening power which is evaluated at the start and end of observed thickening and after stirring; this is judged in comparison to the comparative Example. Standing strength refers to anti sagging.

[0074] As shown in Table 2B, below, thickening behavior, standing strength, ease of movement and surface conditions were also evaluated in comparison to a control. In these tests, a number larger than 100 indicates better performance than the control, while a number smaller than 100 indicates lesser performance than the control.

[0075] Tables 2A and 2B, below, show workability results and performance for various inventive compositions and the control, Example 10.

TABLE-US-00002 TABLE 2A Workability Results (at pH 11-adjusted using 2% lime hydrate) 1C 1 1A Dim Materials: HEMC 96 Wt. % Polyacrylamide 1 4 4 Wt. % HEMC with HASE 100 96 Wt. % water demand 0.56 0.56 0.56 Stirring test as described above start of thickening 12 10 8 sec end of thickening 38 38 40 sec Thickening Behavior weaker noticeably less Strong thickening = thickening = thickening = % grade 2 grade 1 grade 3 Lumps in gypsum none visible none visible none visible mortar Application Performance Ease of Movement.sup.1 3 3 3 Workability (10 min) normal, normal, normal, good good good sliding sliding sliding Surface Rating.sup.1 4 3 3 Surface Quality standard/ very good, very good, some no lumps no lumps on lumps mix.sup.2 .sup.1Grades for rating: 1 = best; 6 = worst; .sup.2One lump appeared after setting (~24 hrs).

[0076] As shown in Table 2A, above, the composition of Example 1, with no polyacrylamide showed better thickening behavior and much better lump control performance than the control in Comparative Example 1C. Further, the mortar in Example 1 A with polyacrylamide behaved in the same manner as the inventive Example 1; and, the surface having applied on it mortars in Examples 1 and 1A had fewer lumps than the control in 1C.

TABLE-US-00003 TABLE 2B Workability Results (at neutral pH, no lime hydrate except in 3C) 1C.sup.2 2 3 1 3C* Dim Materials: HEMC 96 Wt. % Polyacrylamide 1 4 4 4 4 4 Wt. % HEMC with HASE 96 96 96 96 Wt. % water demand 0.50 0.50 0.50 0.50 0.50 Stirring test start of thickening 5 5 5 8 nm.sup.3 sec end of thickening 35 23 20 30 nm.sup.3 sec Thickening Behavior 100 90 90 90 >120 Application Performance Ease of Movement (1 min) 100 90 100 95 ~80 % Ease of Movement (10 min) 100 90-95 95 95-100 ~80 % Standing Strength (1 min) 100 110 100 105-110 ~120 Standing Strength (10 min) 100 105 105 105 ~120 % Surface Rating.sup.1 3 2 1 2 nm.sup.3 Surface Quality Some lumps Only few No Few Impossible lumps lumps lumps to apply .sup.1Grades for rating: 1 = best; 6 = worst; 2. nm = Not possible to measure; 2. Denotes comparative Example; 3. nm = Not measurable. *Contains 2 wt. % lime, based on the total weight of cellulose ether and HASE.

[0077] As shown in Table 2B, above, under more challenging neutral pH conditions, the composition of Examples 1, 2 and 3 provided a surface with fewer lumps than comparative 10. The composition of Examples 1, 2 and 3 also provided gentler thickening and greater ease of movement than did the comparative Examples of 10 and 3C. Thickening of the composition with 2 wt. % lime in Example 3C drastically increased as pH increased as the HASE additive became overly viscous with water demand set at 0.50; thus, the mortar made with the additive of 3C, which is the same as the additive in Example 1 A with a lower water demand, could not even be applied to a substrate. Example 3C demonstrates the important of adding sufficient water to more basic (higher pH) versions of the dry mix compositions of the present invention. Further, the compositions in Example 2 containing 10 wt. % of the HASE on the basis of cellulose ether provided the best lump free applied gypsum mortar.