SLI P RHEOLOGY OF COATI NG COLORS CONTAI NI NG CALCI UM CARBONATE PI GMENTS WI TH NARROW PARTI CLE SI ZE DI STRI BUTI ONS Nick Triantafillopoulos Kaj Backfolk Tom Grankvist Stora Enso Oyj Research Centre I matra I matra, Finland Laboratory of Paper Chemistry Åbo Akademi University Turku, Finland RohmNova LLC Akron, USA SLI P RHEOLOGY “Slip “Slip velocity velocity isis the the unpredictably unpredictably high high velocity velocity next next to to aa bounding bounding wall wall of of “flow” “flow” within within aa thin thin liquid liquid layer, layer, or or particle-free particle-free zone” zone” Lubricity Lubricity of of coating coating colours colours in in blade blade coating coating may may be be associated associated with: with: -Less -Less blade blade wear wear -I-Improved mproved coater coater runnability runnability -Less -Less blade blade deposits deposits Blade Coating colour/ Paper Previous Work High Slip Velocity associated with lowsolids coatings that have good coater runnability n Slip velocity Increases with shear stress n Decreases with increasing coating solids n n Slip layer thickness n Decreases with increasing coating solids Previous Work Calcium Stearate lubricant increases slip velocity of a high-solids (63%) coating n Makes coating to have same high slip velocities as with lower solids coatings n Lower solids coatings have better runnability n Can differentiate between coatings that have the same viscosities and water retention STEEP CALCI UM CARBONATE The calcium carbonate suspension is lacking of fine particles (< 0.2 um ) Optical and physical properties of the final coating layer improve, while this is attained at the cost of rheological properties / coater runnability OBJECTI VE “ To improve flow and to minimize w ater release at a given high-shear viscosity for coating colours containing steep calcium carbonate particles “ DETERMI NI NG SLI P VELOCI TY n Slip velocity for coating colours can be calculated and estimated from high-shear capillary viscometric data 8V ∆ 1 D Vs = 8 ∆ 1 D Shearrate rate(1/s) (1/s) Shear ( Kokko, A., et al.2001 ) 700000 700000 500000 500000 2 2 yy==0,0002x 0,0002x ++16,685x 16,685x++33311 33311 300000 300000 100000 100000 1000 1000 2 2 yy==0,0002x 0,0002x ++13,707x 13,707x++53792 53792 6000 6000 11000 11000 16000 16000 21000 21000 22 Shear stress (N/m Shear stress (N/m )) 26000 26000 31000 31000 METHODS n Brookfield viscometer n 100 rpm, spindle # 5, room temperature n High-shear capillary viscometer 2 different capillaries of same length, but different diameters, 0.525 and 0.735 mm, respectively, to calculate Slip Velocity n ÅAGWR Water release n n TAPPI Standard Method MATERI ALS MATERI AL Abbrevation Calcium carbonate, steep Calcium carbonate, fine Styrene/ butadiene latex Carboxymethylcellulose Polymer 1 Acrylamide/ ammonium polyacrylate Polymer 2 Ethyl acrylate/ carboxylic acid Polymer 3 Calcium stearate 1 Castea 1 Calcium stearate 2 Castea 2 FORMULATI ONS n n The reference coating formulations w ere prepared to attain a high-shear viscosity value of 50 and 70 mPas, respectively, at 500,000 1/ s. The influence of: n Fine carbonate particles n Solids content n Calcium stearate type & level n Thickener chemistry n Amount of thickener … w here determined to clarify the slip rheology RESULTS The I nfluence of fine CaCO3 particles Particle size distributions w t% < 2 µ w t% < 1 µ w t% < 0.2 µ Steep CaCO3 95 75 - Fine CaCO3 97 80 ? RESULTS The I nfluence of CaCO3 particles Distribution Materials CaCO3, Steep 1 2 3 4 5 6 7 100 100 100 85 85 70 70 15 15 30 30 CaCO3, Fine 11 11 11 11 11 11 11 0.35 0.5 1.2 0.9 0.9 1.1 1.1 - - - - 0.8 - 0.8 Solids Content, w t-% 64.3 64.3 64.0 64.2 64.0 64.1 64.0 Water release, g/ m 2 254 248 164 177 175 152 153 Brookfield viscosity, mPas 999 High-shear viscosity, mPas 50 SB Latex Polymer 1 ( CMC) CaStea 1 1180 2230 1740 1820 1990 57 74 52 54 51 1990 51 Apparent slip velocity (m/s) SLI P VELOCI TY DOES NOT I NCREASE WI TH ADDI TI ON OF FI NE CaCO3 PARTI CLES 30 85 pph Steep CaCO3 15 pph Fine CaCO3 11 pph Latex 0.35 pph CMC 0.8 pph CaStea1 20 70 pph Steep CaCO3 30 pph Fine CaCO3 11 pph Latex 0.35 pph CMC 0.8 pph CaStea1 10 0 0 5000 10000 15000 20000 25000 2 Shear stress (N/m ) 30000 35000 THE I NFLUENCE OF TYPE AND LEVEL OF CALCI UM STEARATE nn CaStea CaStea 11 nn nn nn nn nn 50% 50% active activesolids solids Free Freefrom from hydrocolloid hydrocolloid Contains Containssurfactants surfactants Mean Mean particle particlesize: size: 9.5 9.5µµ Median Median particle particlesize: size: 9.25 9.25µµ nn CaStea CaStea 22 nn nn nn nn nn 55% 55% active activesolids solids Contains Containsaahydrocolloid hydrocolloid Contains Containssurfactants surfactants Mean Mean particle particlesize: size: 11.0 11.0µµ Median Median particle particlesize: size: 13.0 13.0µµ RESULTS The I nfluence of Type and Level of Calcium Stearate MaterialS 1 8 9 10 11 12 13 100 100 100 100 100 100 100 11 11 11 11 11 11 11 0.35 0.35 0.35 0.35 0.35 0.35 0.35 CaStea 1 - 0.4 0.8 1.2 - - - CaStea 2 - - - - 0.4 0.8 1.2 Solids Content, w t-% 64.3 64.3 64.0 64.1 63.9 64.0 64.0 Water release, g/ m 2 254 254 241 261 229 241 233 Brookfield viscosity, mPas 999 894 904 796 768 784 756 High-shear viscosity, mPas 50 48 50 48 50 50 47 CaCO3, Steep SB Latex Polymer 1 ( CMC) 0.8 PARTS OF CALCI UM STEARATE GAVE HI GHEST SLI P VELOCI TY ( particucalry w ith CaStea 2) Apparent slip velocity (m/s) 50 0.4 pph CaStea 1 40 0.8 pph 30 20 1.2 pph 10 Apparent slip velocity (m/s) 0 50 CaStea 2 40 0.8 pph 30 1.2 pph 20 0.4 pph 10 0 0 5000 10000 15000 20000 Shear stress (N/m2) 25000 30000 35000 RESULTS The I nfluence of Solids Content Materials 14 15 16 1 9 12 17 18 19 CaCO3, Steep 100 100 100 100 100 100 100 100 100 11 11 11 11 11 11 11 11 11 SB Latex Polymer 1 ( CMC) 0.35 0.35 0.35 0.35 0.35 0.35 0.35 0.35 0.35 CaStea 1 CaStea 2 Solids Content, w t-% 0.8 0.8 0.8 0.8 0.8 0.8 62.7 62.7 62.7 64.0 64.0 64.0 65.5 65.5 65.5 Brookfield viscosity (mPas) CALCI UM STEARATE REDUCES BOTH BROOKFI ELD VI SCOSI TY AND WATER RELEASE 1300 Reference 65.8 % 0.8 pph CaStea 1 1200 1100 1000 65.7 % 64.3 % 0.8 pph CaStea 2 62.7 % 64.0 % 800 700 62.7 % 64.0 % 65.5 % 900 62.7 % 600 200 220 240 260 2 Water release (g/m ) 280 300 High shear viscosity (mPas) CALCI UM STEARATE HAS LESS I MPACT ON HI GH-SHEAR VI SCOSI TY, BUT … 75 70 65 60 55 50 45 40 35 30 25 100000 65.5 % 64.0 % 62.7 % 300000 500000 700000 900000 Shear rate (1/s) 1100000 … SI GNI FI CANTLY RAI SES SLI P VELOCI TY, ESPECI ALLY AT LOWER SOLI DS 62.7 wt% CaStea 1 40 62.4 wt% 30 65.5 wt% 20 10 Apparent slip velocity (m/s) Apparent slip velocity (m/s) 50 0 50 40 30 20 10 0 62.7 wt% CaStea 2 64.0 wt% 65.5 wt% 0 5000 10000 15000 20000 Shear stress (N/m2) 25000 30000 35000 RESULTS The I nfluence of Type and Level of Thickeners Materials 23 24 25 26 27 28 CaCO3, Steep 100 100 100 100 100 100 SB Latex 11 11 11 11 11 11 Polymer 2 0.1 0.1 0.1 0.3 0.3 0.3 CaStea 1 0.8 0.8 0.8 CaStea 2 0.8 Solids Content, w t-% 64.4 64.2 64 64.5 64.5 64.1 Water release, g/ m 2 203 242 253 171 170 195 Brookfield viscosity, mPas 404 360 216 688 673 848 High-shear viscosity, mPas 50 60 51 67 70 66 RESULTS The I nfluence of Type and Level of Thickeners Materials 23 24 25 26 27 28 CaCO3, Steep 100 100 100 100 100 100 SB Latex 11 11 11 11 11 11 Polymer 3 0.1 0.1 0.1 0.3 0.3 0.3 CaStea 1 0.8 0.8 0.8 CaStea 2 0.8 Solids Content, w t-% 64.3 64.2 64.0 64.5 64.3 64.0 Water release, g/ m 2 211 225 209 123 123 141 Brookfield viscosity, mPas 560 532 288 872 848 756 High-shear viscosity, mPas 50 58 52 68 68 67 RESULTS The I nfluence of Type and Level of Thickeners Materials CaCO3, Steep SB Latex Polymer 1 ( CMC) 1 9 12 20 21 22 100 100 100 100 100 100 11 11 11 11 11 11 0.35 0.35 0.35 0.9 0.9 0.9 CaStea 1 0.8 0.8 0.8 CaStea 2 0.8 Solids Content, w t-% 64.3 64.0 64.0 64.1 64.0 64.0 Water release, g/ m 2 254 241 225 180 178 183 Brookfield viscosity, mPas 999 920 784 1860 1760 1710 High-shear viscosity, mPas 50 50 50 69 63 62 None 0.8 pph CaSte 1 0.8 pph CaSte 2 2000 0.8 pph 1500 0.35 pph 0.3 pph 1000 0.3 pph 0.1 pph 0.1 pph 500 3 (7 0) m Po ly m er Po ly er 2 (7 0) m er Po ly m er Po ly m er Po ly 1 (5 0) 3 (5 0) 2 (5 0) 1 er m (7 0) 0 Po ly Brookfield viscosity (mPas) RHEOLOGY I NVESTI GATED AT HI GH-SHEAR RATES NEEDS CORRECT THI CKENER CONCENTRATI ONS CALCI UM STEARATE-THI CKENER ASSOCI ATI ONS I NFLUENCE DEVELOPMENT OF SLI P LAYERS Reference no Lub CaStea 1, 0.8 pph CaStea 2, 0.8 pph Polymer 1, 0.35 pph - + +++ Polymer 1, 0.9 pph - + + Polymer 2, 0.1 pph ++ - ++ Polymer 2, 0.3 pph + - - Polymer 3, 0.1 pph - - ++ Polymer 3, 0.3 pph + - - - = no slip observed + = 5-10 m/ s at shear stresses betw een 20,000-30,000 N/ m 2 + + = 10-30 m/ s at shear stresses betw een 20,000-30,000 N/ m 2 + + + = > 30 m/ s at shear stresses betw een 20,000-30,000 N/ m 2 DI SCUSSI ONS AFM ( PHASE) I MAGES OF LATEX FI LMS SHOWS EVI DENCE OF DI SSOLVED SPECI ES FROM CALCI UM STEARATE Source: Backfolk et al., 2003 Latex film prepared from SB latex substantially free from surfactants • Latex film prepared from SB latex emulsion containing 10 w t-% Calcium Stearate emulsion • SUPERNATANT FROM CALCI UM STEARATE EMULSI ON I NDUCES SLI P VELOCI TY Apparent slip velocity (m/s) 40 0.8 pph Supernatant from CaStea1 ''0.8 pph CaStea 1'' 35 30 25 20 15 10 5 0 0 5000 10000 15000 20000 2 Shear stress (N/m ) 25000 30000 35000 ORI GI N OF SLI P VELOCI TY Potential Mechanisms Previous Previous work work has has shown shown that that species species from from calcium calcium stearate stearate are are oleic, oleic, surface surface active active that that accumulate accumulate at at interfaces, interfaces, e.g., e.g., at at latex latex particle particle surfaces surfaces This This agrees agrees with with our our observations observations suggesting suggesting that that components components migrate migrate towards towards aa boundary boundary wall wall and and give give slip-> slip-> lowering lowering surface surface tension tension and and interfacial interfacial viscosity viscosity Slip layer formation is promoted by calcium stearate species ORI GI N OF SLI P VELOCI TY Potential Mechanisms IIncrease ncrease in in slip slip velocity velocity not not associated associated with with substitution substitution of of pigment pigment particles particles by by calcium calcium stearate stearate particles particles at at constant constant TSC TSC Besides Besides surface surface active active species, species, low low MW MW oleic oleic species species are are also also present present in in the the water water phase phase of of aa calcium calcium stearate stearate lubricant lubricant Slip layer formation is promoted by calcium stearate species CONCLUSI ONS Slip Rheology n n The liquid phase from Calcium Stearate emulsion promotes slip velocity Slip velocity is strongly dependent on n Thickener chemistry Level of thickener n Solids content (lower at higher solids) n CONCLUSI ONS Formulation Strategy n Slip rheology of coating colours containing 100 parts of a steep calcium carbonate at high solids can be adjusted through: n Choice of thickener and calcium stearate Selective choice of levels to maximize slip n Avoidance of strong associative interactions n ACKNOWLEDGEMENTS n Bj örn Sj östr öm, Laboratory of Paper Chemistry, Åbo Akademi, Finland n Dr. Patrick Gane, OMYA AG, Switzerland n Robert Flowers, OMNOVA Solutions, USA