Formulating Water-Based Systems y,ith Propylene-Oxide Based Glycol Ethers
Carmen l. Rodriguez and Julia Weathers-lyondell Chemical Company· Bernadette Corujo-Engineered Polymer Solutions Patricia Peterson-Avecia
To camply with environmental regulations, formulators have reformulated to water-based systems using non-hazardous air pollutants (non-HAP) cosolvents and developed new resin technology. In fully formulated water-based systems, however, changing the solvent system to meet environmental regulations has wide ranging effects on viscosity, surface defects, film shrinkage, adhesion, and durability. Formulators often adjust paint viscosity by balancing the levels of cosolvents, surfactants, and rheology modifiers. Reformulating with non-HAPs solvents such as propylene oxide-based glycol ethers (PG-glycol ethers) helps reduce volah1e organic content WOC) to meet environmental compliance and eliminates HAPs reporting requirements. When replacing ethylene oxide-based glycol ethers (EG-glycol ethers) with their PG-glycol ethers, reformulation seems simple enough, particularly if evaporation rates and solubility parameters are matched. A drop-in replacement, however, requires optimization. This study compares the use ofPG-glycol ethers in four architectural latex paints and assesses their effects on rheology, drying, and some key performance attributes.
INTRODUCTION ing a suitable coalescent solvent for a solvent in the filmis stronglydependent waterborne coating.1 However, chang on the end use. The principal positive The primary reason for reformulating a ing the solvent package in a coating for effect of solvent entrapment is the in solventsystemis to meet environmental mulation may also necessitate optimiza creased fleXIbility of the cured coating compliance in volatile organic content tion of the other paint components. and possibly superior cure. Negative ef (VOC) reduction and reporting require First, the viscosity of paint can be fects include slow hardness develop ments. The development of new resins affected by the solvent package depend ment, poor blocking resistance, low to produce less toxic coatings formula ing on the thickener used. Paints thick gloss, and poor water and chemical re tions can also be explored but it is often ened with hydroxyethylcellulose sistance. Losing solvent prematurely costly and requires time. Whether deal (HMHEC) show viscosities that are not leads to inadequate film formation and ing with old or new formulations, all too susceptible to changes in the sol poor ultimate performance. If we con formulators should use non-hazardous vent. However, paints thickened with sider a dried paint film as one which no air pollutants (non-HAPs) solvents to hydrophobically modified thickeners are longer flows, the importance of the vis insure compliance with future regula highly dependent on interactions be cosity on the drying paint is apparent. tions and to lower the toxicity of the tween thecosolvent and otherpaintcom Formulated paintviscosity is dependent product. Propylene oxide-based glycol ponents.2 Formulators are cognizant of on the viscosity of the external phase, ethers (PG-glycol ethers) are one such these effects and often optimize paint which is water and anything dissolved example of non-HAPs solvents that can viscosity by balancing the levels of in it; the volume of the internal phase, beused inreformulating coatings. Inad cosolvent, surfactants, and rheology including pigment, resin, and agglom dition, glycol ethers based on propylene modifiers. In the past, many formula erates; and a packing factor, equal to the oxide can offer improved property de tors have added diethylene glycol n-bu internalphasevolume atcritical pigment velopment versus their HAPs listed tyl ether (DB), a 100% water miscible volume concentration (ePVC). This re counterparts based on ethylene oxide lationship has been summarized in the coalescent, to achieve high shear (ICI) 3 (EG-glycol ethers). viscosity development. This approach Mooney Equation. Ke Vi Replacing CUIIently used EG-glycol has lost popularity due to the increased /n'll=/n'lle ethers with the PG-glycol ethers seems VOC requirements, the higher cost of +(1_ Vi) simple enough, particularly if evapora rheology additives, and some water sus f where tion rates and solubility parameters are cepbbility issues. matched. Table 1 compiles key physical 'lle is the viscosity of the continuous, properties that are important in choos- Second, in this industry, each formu external phase lationis different, therefore each coating I Table l-Key Properties of Some Propylene and Ethylene Glycol Ethers as Compared to Water Evaporation Rate Surface Tension Glycol Ether Nomenclature nBuAc=l00 % in Water@ 25°C Flash Point OF dynes/cm@25°C PM Propylene glycol monomethyl ether 66.0 100.0 89 27.0 PE Propylene glycol monoethyl ether 47.0 100.0 92 29.7 PNP Propylene glycol n-propyl ether 22.0 100.0 119 27.0 PTB Propylene glycol t-butyl ether 25.0 17.5 113 24.4 PNB Propylene glycol n-butyl ether 7.0 6.4 138 26.3 DPM Dipropylene glycol monomethyl ether 2.0 100.0 167 29.0 DPNP Dipropylene glycol n-propyl ether 1.3 18.0 190 25.3 DPNB Dipropylene glycol n-butyl ether 0.4 5.0 212 28.8 TPM Tripropylene glycol monomethyl ether 0.2 100.0 242 30.0 PMA Propylene glycol methyl acetate 34.0 18.0 114 28.0 PEA Propylene glycol ethyl acetate 26.0 10.0 129 26.3 DPMA Dipropylene glycol methyl acetate 1.0 12.0 186 28.3 EM Ethylene glycol monomethyl ether 53.0 100.0 105 30.8 EMA Ethylene glycol methyl acetate 35.0 100.0 120 34.0 EB Ethylene glycol n-butyl ether 6.0 100.0 143 26.6 DB Diethylene glycol n-butyl ether 0.3 100.0 232 30.0 Water . 36.0 100.0 None 72.0 Temperature, substrate porosity, film In this experiment, we hope to give paints used were: a high scrub polyvi build, and air flow also affect paint dry the starting point formulations of four nyl acrylic (PVA) interior flat latex, a ing.4 In waterborne systems, both tem main types of waterborne architectural PVA/acrylic blend interior semi-gloss perature and humidity greatly affect the coatings and to provide an indication of latex, styrenated acrylic interior/exterior rate of evaporation of water from the expected effects on paint properties high gloss latex, and an acrylic exterior paint. The rate of evaporation of the when glycol ethers are used as coalesc flat latex. cosolvent is dependent on the tempera ing solvents. By studying the effect of Master batch formulations were pre ture. the coalescent solvent on the rheology, pared according to Table 2 with the ex Finally, short- and long-term stabil gloss, freeze/thaw, heat stability, dry ception that each batch was made with ity of the paint can be affected with a time, and block resistance in four archi out coalescent or thickener. Preparing a change in solvent. For example, in a tectural paint systems, general guide master batch helped minimize experi waterborne system, the water freezes lines can be developed to lead to suc mental variance, as well as shorten the during freeze/thaw testing. This forces cessful reformulation of other similar time needed to make the coatings. This the polymer particles to agglomerate in coatings systems. masterbatch was divided into three sub an irreversible manner. This is more batches. Each sub-batch was thickened likely to occur with surfactant starved EXPERIMENTAL with four dry pounds of one of three resins. Glycol ethers will suppress the classes ofhydrophobicallymodified thick freezing of water and should overcome Suitable Formulating eners: hydrophobically modified alkali freeze/thaw problems. Heat-aged test swellable emulsion (HASE); hydro ing and pH drifts are good screening In this study, the effect of various phobically modified ethoxylated ure tools for changes in stability due to coalescents was investigated in water thane rheology modifier (HEUR); and changes in the solvent package. borne architectural coatings. The four hydrophobically modified hydroxy- Table 2-Masterbatch Formulations of Waterborne Coatings Using Four Architectural Acrylic Latex Paints Main Components Function Interior Flat Interior Semigloss Int/Ext High Gloss Exterior Flot Grind Base (ppw) Water Diluent 350 100 50 40 Colloid 643lB1 Defoamer 3 2 1.5 2 Propylene glycol Freeze/thaw 40 65 50 35 Ethylene glycol Freeze/thaw 25 Tamoje 1124 Dispersant 6 8 7 7 TritanlBl CF 10 Surfactant 4 3 1 14% ammonia Stabilizer 4 4 4 1.5 Titanium dioxide Hiding pigment 120 250 200 225 Clay Extender pigment 200 50 Carbonate Extender pigment 150 Altapulgite clay Extender pigment 35 UF clay Extender pigment 50 NaK alumino silicate Extender pigment 150 Letdown Acrylic resin Binder 130 500 350 PVA Binder 265 340 Colloid 643lB1 Defoamer 3 2 2 Water Diluent 80 115 225 Coalescent Film former 12 14 25 9.5 PVC . 48 28 18 45 68 Journal of Coatings Technology Propylene-Oxide-Based Glycol Ethers ethylcellulose (HMHEC) werepickedbe cause they are representative examples DHMHEC DHMHEC 011 of this class of thickeners. 011 aMEUR aHEUR aHASE aHASE The sub-batches were further subdi ON ON vided into seven paints. A suitable .... amountof coalescentwas added to each. .... The coalescents selected for this study ..- ...... were: diethylene glycol n-butyl ether ...... (DB); an EG-glycol ether, dipropylene .... glycol monopropyl ether (DPNP); .... dipropylene glycol monobutyl ether T_ (DPNB); propylene glycol monopropyl - 1 2 3 4 30 10 to 120 150 ether (PNP); propyleneglycol monobutyl __Ity(l Vol. 72, No. 905, June 2000 69 c.L. Rodriguez et 01. Inthese same interior formulations, how iting the amount ofadditional thickener Despite the overall trends observed, ever, thereis a significant-25to50 KU that can be added, which falls short of there are specific examples throughout Stormer viscosity difference between the amountrequired for high-shear (ICI) the experimental series that should be those containing the solvents DB and viscosity development. Consequently, discussed separately. The 25/75 blend Texanol. Formulations containing PG DB is often recommended as the solvent ofacrylic PVA, witha six percent coales glycol ethers, on the other hand, devel to use in these formulations. Paints for cent level used as the interior semi-gloss oped Stormer viscosity that fell between mulated with the PG-glycol ethers and formulation, showed the range differ the formulations using DB and Texanol. the HMHEC thickener showed high ence in Stormer viscosity between for With HMHEC thickener, the difference shear (lCI) viscosities falling between mulations containing DB and Texanol inthe range ofStormerviscosity is small, Texanol and DB, with the exception of using the HASE thickener was not as 10 KU units, in the interior paints. The PNPin the interior flat paint, which was large as in the interior flat coating (Fig interior flat formulations containing DB only slightlyhigher than Texanol. HEUR ure 2). The PG-glycol ethers-based paints HMHEC developed a higher high-shear thickeners are less efficient than the other again fell between these two. There were (ICI) viscosity than the one containing rheology modifiers for PVA systems. no significant differences in high-shear Texanol. One explanation for this be Texanol-based formulations developed (ICI) viscosity between the coalescents. havior is that Texanol often builds low the highestStormer and high shear (lCI) Additionally, when using the HMHEC shearviscosity too quickly, possibly lim- viscosity with this thickener. thickener, the PG-glycol ether contain ing paints showed low-shear viscosities between those formulations using DB DHMHEC I DHMHEC and Texanol. DB containing formulations IIHEUR I E1HEUR did not have the advantage ofincreased .HASE I.HASE high-shear viscosity development inthis - case. In the HEUR thickened example, - the PG-glycol ether paints developed Stormer and high-shear (lCI) viscosities .M11 similar to DB-based paints. The Stormer viscosity for the blended PVAIacrylic - Texanol formulation was 24 KU higher than DB; this possibly limits the high shear (lCI) development of the formula. o 30 eo 80 120 1110 O~ OA O~ 12 ...... VIeoeIr IIW) H'",_lICIl_\POi_} Only four dry pounds of thickener were used in all the formulations; there Figure 3-Rheology evaluations of styrenated acrylic interior or exterior - fore, the interiorI exterior high gloss coat high gloss paint using PG-glycol ethers as coalescents and comparing these ing did not have the required viscosity to Texano/ and DB. for high gloss paint. However, the data does show viscosity trends with the dif ferent solvents (Figure 3). With both aHMHEC DHMHEC Illl HMHEC and HASE thickeners, the gly I!IHEUR o. aHEUR .HASE .HASE col ethers-based paints significantly de OPM press the low- and high-shear viscosity - ... relative to Texanol-based paints. HEUR - thickeners are recommended in these - - high gloss systems. The glycol ethers - based and HEUR formulations sup -P•• T__••• pressed low-shear viscosity and, there T_ fore, none showed sufficient high-shear viscosity development. In this case, for 1 2 :I • • 0 30 '0 80 120 H..... _tIClI*_IIr(Poilll mulators must balance low- and high .-_lIWl shear development with a blend of gly col ether and Texanol. Figure 4-Rhe%gyevaluations ofacrylic exterior Hat paint using PG-g/ycol ethers as coa/escents and comparing these to Texano/ and DB. Usually exterior paints contain HMHEC and HEUR rheology modifi ers. They are based onsoft, flexible poly mers and onlyrequire a five percentcoa • cold & hwnld ecoid & moderate EJ moderate lescent level (Figure 4). The HASE thick 30 -r------l ened sample showed lower Stormer vis .hot& humid " hot & dry 25 H:tt-----U~---'=====-======r_-----l cosities for all the glycol ether-based paints as compared to Texanol. On the g 20 Htl----m------,.-j other hand, the PG-glycol ethers-based '1I-t~D----Ul------ll------1 paintsimprovedhigh-shear (10) viscos ity developmentversus DB-based paints. g 10Htl----m------l·.I------l With the HMHEC thickener, the PG-gly col ether paints have better Stormer and high-shear (lCI) viscosity than DB-based paints. Additionl,\lly, the PC-glycol DPNB DPM DB PHS ethers performed comparably to Texanol-based formulations. Using Figure 5-Coa/escent effect on dry time of a styrenated acrylic inte"'ior/ DPNB as the coalescent afforded the exterior high gloss paint. highest high-shear (10) viscosity. Also, 70 Journal of Coatings Technology Propylene-Oxide-Based Glycol Ethers the differences in drying under several conditions. Inbothformulations, we ob laT~1 served that substituting DB with DPNB improves film formation of the paints. DPNB also offers increased open time hot & humid ~_;._;.~ h::h::'mi'.. · .- for the high gloss paint. moderate : ,! ! cold & moderate l' '! cold & mode... ~.~.iiiiiIr • , I ' cold&humld 'I I i i cold & humid L~iiiiiiii~iiiiiiB I -1-._··---;.----- PERFORMANCE o 30 80 90 120 o 30 90 110 120 Gloas20" Gloss 60" Gloss under Marginal Drying Conditions Figure 6-Effectofthe coalescent on gloss ofa styrenated acrylic interior/ We evaluated the 20° and 60° gloss of exterior high gloss paint under changing drying conditions. the HEUR thickened high gloss paints after they reached dry-through under in the HEUR thickened paint, the DPNB under most conditions. The DB failures the various drying conditions (Figure 6). coalescent showed viscosity develop suggest that it has coupled with the wa These paints were evaluated for 3 mil ment similar to Texanol. ter and has left too quickly to provide drawdowns on Leneta charts. A corre adequate film formation. The Texanol lation between gloss and drying condi coalesced paint had dried-through by tion was observed. When dried under Film Formation the first hour, suggesting a need for the hot/dryconditions, DPNB-based formu improved "open time," a property at lations showed apprOXimately 100% DRYING UNDER MARGINAL CONDmONs: tributed to glycol ethers. gloss retention, while those based on The effects of different simulated Texanollost about 12% of the 20° gloss. weather conditions on drying were ex DRYING OF ExTERIOR HMHEC TmCK This may be a result of snap drying of amined for several coalescents in two ENED FLAT PAINT: We repeated the same the Texanol-based paint. Under hot and exterior latex paint formulations (Figure experiment with the exterior flat formu humid conditions, the 20° gloss for the 5). Five drying conditions were evalu lation. This time only DPNB and Texanol DPNB-based paint fell 30% and both ated by noting the time it took the paint were included. Under all five of the con coalescents showed 60° gloss loss of 10%. to dry (Table 3). The range of coalescents ditions evaluated, the DPNB andTexanol Both Texanol and DPNB were at 35% of examined had different water miscibil dried the same as in the interior/ exte their 20° gloss, and 25% oftheir 60° gloss, ity and evaporation rates (Table 1). rior paint. DB showed poor drying under cold andmoderate conditions. Fi Overall, the PG-glycol ethers contain throughout the entire spectrum artd was nally, under cold andhumid conditions, ing a butyl group show low solubility in eliminated from the test results. both DPNB and Texanol formulations water and possess the slowest relative The mostsignificant observation was were at 50% of their 20° gloss and 75% of evaporation rates. DB is totally water during drying under cold and humid their 60° gloss. miscible and slower than the PG-glycol conditions. The paints took four days to ethers. Texanol is not miscible in water dry-through. Additionally, the films ex Shelf Stability, Freeze/Thaw and is the slowest to evaporate. lubited a loss of adhesion during this time, indicating a susceptibility to rain Resistance, Scrub Resistance DRYING OF HIGH GLOSS HEUR TmCK and dew. One explanation is that the The formulated paints were evalu- ENED PAINT: The films' drying time was higher pigment volume concentration evaluated using the ASTM Method D ated for shelf stability, freeze/thaw re tends to increase the paint porosity. The sistance, block resistance, and scrub re 1640 as well as visual inspection of the exterior paint was the only paint that sistance using conventional test meth- film for cracking, peeling, and other sur contained both face defects. Under cold and humid con EG-glycol ethers ditions, the high gloss exterior paints and PG-glycol CIS cycle freezellhaw stability coalesced withTexanol andDPNB while ethers in the same .6 mo shelf stability DB, DPM, and PNB failed to form a film formulation. It is PNP within 24 hr dry time. The combination well known that offaster evaporationrates andwatermis EG-glycol ethers cibility contributed to the failures. Early are very hygro DPM drying of the paint was fairly consistent scopic.6 With the for all of the coalescents evaluated. increased porosity Texanole At lower humidity, only the PN13 andhighhumidity paint failed to form a film at low tem and low tempera perature. Cracking occurred within the ture conditions, DPNB first three hours of drying. The PNB the water in the evaporation rate was too rapid. DB and ambient can easily DB DPNB showed a slight loss of adhesion migrate into the between four and six hours' dry time, unformed film, r----f---!----·--ll----l---+I---il but they both ultimately formed films. saturate it, and ·20 -10 o 10 20 30 40 Again, early drying of all of the paints hinder the drying Change in Stonner Viscosity, KU was fairly consistent for the coalescent:> process. evaluated. Overall, the ex Figure 7-Effect ofcoalescent on shelf and freeze/ In fact, the evaporation rate of PNB periment was de thaw stability for a PVA interior Rat paint employing an HMHEC thickener. was too fast and failed to form films signedto highlight Vol. 72, No. 905, June 2000 71 c.L. Rodriguez et 01. 05 cycle freeze/thaw stability formulating l ods. In many tests, the formulations be CONCLUSIONS haved equally and were not reported. ACKNOWLEDGMENTS There were, however, results that clearly In all four formulations evaluated, the separated some PC-glycol ether The authors express their gratitude 10 low shear, Stormer viscosities of the PC coalescents from the DB and Texanol Daniel Pourreau who offered assistance. benchmarks. glycol ethers were between DB and In interior flat paint using HMHEC, Texanol regardless of the thixotrope the six-month shelf stability for DPNB-, used. Texanol-based formulations References DPM-, and Texanol-based paints was showed the higher Stormer viscosity excellent. Using DB as the coalescent while DB was at the low end. In com (1) Sullivan, P.A., "Water and Solvent was acceptable while the PNP based parison, the PC-glycol ethers provided Evaporation from Latex and Latex Paint enhancement in KU development with Films," JOURNAL OF PAlNT TECHNOLOGY, 47, formulation was only marginal (Fig No. 610, 60 (1975). ure 7). The five-cycle freeze/thaw sta the propyl and butyl ethers contributing the most to this enhancement. PC-glycol (2) Thibeault, J.e., Sperry, P.R., and Shaller, bility was excellent with DPNB as the E.J., "Effect of Surfactants and Co-sol coalescent and marginal with DPM-, ethers formulated paints also presented vents on the Behavior of Associative PNP-, and DB-based formulations. The improved high-shear viscosity overthose Thickeners in Latex System," ACS Divi Texanol formulation failed the freeze/ using Texanol, when either HMHEC or sion of Polymeric Materials: Science and thaw stability test. The abrasive scrub HASE was used in the formulation. Like Engineering, 51, 353 (1984). results for paints based on DB, DPNB, wise, the same behavior is observed in (3) Wicks, Z.W., Jones, EN., and Pappas, and Texanol were equivalent while the exterior paints. In this case, a combi S.P., Organic Coatings: Science and Tech nology, John Wiley and Sons, New York, those based on DPM and PNP were nation of PG-glycol ethers and Texanol would be desirable. Vol 1., p. 28, 1992. only slightly, 20%, lower. (4) Croll, S.G., "Heat and Mass Transfer in In the interior semi-gloss paint, the Drying time in the exterior formula Latex Paints during Drying," JOURNAL OF DB-based formulation had poor shelf tions that were evaluated showed im COAnNGS TECHNOLOGY, 59, No. 751, 81 and freeze/ thaw stability, while both the provement with DPNB. PNB showed (1987). DPNB and Texanol formulation showed cracking and failure to dry under most (5) 1996 Annual Book ofASTM Standards Vols. excellent shelf and freeze/thaw stability weather conditions. DPM presented a 6.01,6.02, Storer, R.A. (Mgr. Ed.), Ameri (Figure 8). Texanol-based paintproduced midpoint between DB and DPNB. DB can Society for Testing and Materials, West Conshohocken, PA. superior scrubs to formulations based failed to dry under cold and humid and (6) Andrews, M.D., "Influence of Ethylene on DB and DPNB, these being equiva hot and humid conditions. Only two for and Propylene Glycols on Drying Char lent. The DPNB-based formulation, how mulations dried under extreme cold and acteristics of Latex Paints," JOURNAL OF ever, significantly improved the over humid conditions; DPNB dried not un PAINT TECHNOLOGY, 46, No. 598, 45 (1974). night, ambient block resistance rating to like TexanoI. DPNB performs similarly eight versus six for DB and five for to Texanol under cold conditions and Texanol. Oven block resistance was offered a slight improvement in gloss equivalent for all formulations. under hot conditions. Again, the widest 72 Journal of Coatings Technology