Improved hydrolytic stability of waterborne polyester resins with Eastman 1,4-CHDA and Eastman TMPD glycol

Transcription

1 Improved hydrolytic stbility of wterborne polyester resins with Estmn nd Estmn glycol Introduction Wterborne cotings provide vible mens of complying with VOC (voltile orgnic compound) requirements. An inherent problem with mine-neutrlized wterborne polyester resins is their hydrolytic instbility due to hydrolysis of the ester linkges in the ph rnge of 8 9. This hydrolysis reduces the moleculr weight of the resin, leding to poor cotings performnce nd/or precipittion of the resin from the dispersion. Storge temperture, ph, degree of neutrliztion, hydrophobicity, polr (inductive) effects, steric fctors, nd nchimeric effects re ll thought to be importnt vribles tht control the rte of ester hydrolysis. Severl of these vribles cn be controlled by monomer selection. Estmn (1,4-cyclohexnedicrboxylic ) nd Estmn glycol (2,2,4-trimethyl-1,3-pentnediol) hve been shown to hve numerous benefits in resins for solution cotings 1 s listed in the following. 1 See Estmn publiction N-329 (Estmn tringle glycol study).

2 Benefits of Estmn bsed cotings Cotings performnce Hrdness/flexibility blnce Chemicl, corrosion, detergent, nd stin resistnce Rpid rectivity Resin processing Low resin color Excellent solubility in common glycols Benefits of Estmn glycol bsed cotings Cotings performnce Lower viscosity (VOC) Chemicl resistnce Excellent solubility Resin processing Rpid rectivity Low resin color Low melting point This study shows tht nd glycol lso offer improved hydrolytic stbility for polyester resin dispersions compred with other common dis nd glycols. The superior stbility of the ester bonds derived from glycol nd Estmn mkes these intermedites the monomers of choice for wterborne polyester resins. Experimentl di study Dis studied Estmn ws compred to Estmn purified isophthlic (PIA) nd dipic (AD) for hydrolytic stbility. Estmn PIA nd AD re widely used in combintion with ech other to mke sturted polyesters for cotings pplictions. PIA, being n romtic di, hs the highest dissocition constnts, K (lowest pk ) of the dis studied, indicting tht it should hve the lest resistnce to bse-ctlyzed hydrolysis. PIA is lso the most hydrophobic of the dis. AD is the most soluble of the three in wter, but it hs much lower dissocition constnts. Estmn hs cycloliphtic structure tht llows for better steric shielding thn AD s well s low dissocition constnts. It is lso much more hydrophobic thn AD. Experimentl design The dis were evluted using sttisticlly designed mixture study. The resin compositions re represented s dots on Figure 1. Ech pex of the tringle indictes 100 weight % usge of the di in tht resin composition. The midpoint of ech leg represents 1:1 molr blend of two dis, nd the center point is resin composition tht contins n equimolr blend of ll three dis. Attempts to mke 100 weight % PIA resin were unsuccessful due to incomplete rection; therefore, blend of PIA//AD (75/12.5/12.5) ws substituted. Figure 1 Experimentl design Isophthlic 2

3 Synthesis Five resins were prepred for ech dot on the tringle using wterborne resin formultion bsed on Estmn glycol. All resins were prepred with the sme di/glycol equivlent rtio nd the sme Estmn /TMA rtio s shown in Tble 5. Vrition in glycol moleculr weight resulted in some vrition in resin moleculr weight, number, nd hydroxyl number. Resin compositions nd properties re shown in Tble 1. The resins were prepred s ctlyzed two-stge cooks with the lest rective di being in the first stge. Resins contining only one di were single-stged. Tble 1 Resin composition nd properties Resin composition Estmn glycol/trimethylolpropne/di intermedites Molr rtio: 8.7/2.8/11.6 Fsct 4102 ctlyst: 0.1% of resin chrge Resin properties Finl number, mg KOH/g resin Moleculr weight (M n, number verge), clculted 1,800 2,200 Hydroxyl number, mg KOH/g resin, clculted Weight % solids in solvent blend b 75 Atofin Chemicls b Estmn EB/Estmn DE glycol ethers t 90/10 weight % rtio Dispersion preprtion nd stbility testing The dispersions were prepred ccording to the formultion in Tble 2. Stbility studies were crried out on the dispersions both t mbient tempertures (c. 23 C [73 F]) nd t 52 C (126 F). Chnges in M w (weight verge), dispersion ppernce, nd ph were monitored. Tble 2 Typicl dispersion composition Ingredients Weight, g Polyester resin (75% N.V.) dimethylminoethnol 2.6 Wter (deionized) Resulted in ph rnge of Results di study Resin processbility Cook times were shorter for resins contining Estmn thn for those contining Estmn PIA nd AD (Figure 2). While AD hs the fstest rection rte, it required lower rection temperture to minimize foming. Figure 2 Cook times (hours) Isophthlic Resin solution viscosity At 75 weight % solids, the mjor contributor to solution viscosity is Estmn PIA (Figure 3). Figure 3 Resin solution viscosity (P s) t 75 weight % solids in cosolvent Isophthlic 3

4 Resin dispersion stbility ppernce The lest chnge in ppernce, which cn be viewed s one indiction of dispersion stbility, ws chieved s the Estmn content ws incresed. All dispersions were initilly cler nd homogeneous. Dispersion clrity fter 13 weeks t 52 C (126 F) is illustrted in the cover photogrph. Resin dispersions shown in the photogrph re identified in Tble 3. Tble 3 Resin dispersions fter 13 weeks t 52 C (126 F) Dispersion PIA AD Appernce Cler Hzy Hzy Seprted Hzy Seprted Seprted See the following key. 1 Figure 4 Percent reduction in ph fter 13 weeks t 52 C (126 F) Isophthlic Figure 5 Percent reduction in ph fter 12 months t mbient temperture P IA AD 14 Resin dispersion stbility ph Chnge in dispersion ph occurs when polyester resins re hydrolyzed. The ph chnge in dispersions contining Estmn ws less thn with Estmn PIA- nd AD-contining systems (Figures 4 nd 5). The higher the level of in the system, the lower the chnge in ph. Isophthlic 4

5 Resin dispersion stbility moleculr weight Hydrolysis of polyester resin results in clevge of the polymer chin nd corresponding decrese in moleculr weight (M w, weight verge). The resin dispersions contining showed less decrese in M w thn those contining PIA nd/or AD the more used, the less chnge in M w (Figures 6 nd 7). Figure 6 Percent reduction in Mw fter 4 weeks t 52 C (126 F) Isophthlic Conclusion di study nd AD hd the best processbility nd the lowest solution viscosity. PIA rnked third. imprted the best dispersion stbility, followed by PIA, nd finlly AD. offers good processbility, low viscosity, nd excellent wterborne dispersion stbility, in ddition to the unique blnce of hrdness nd flexibility s previously demonstrted in solution cotings. 1 would mke idel polyester dispersion for modifying crylic dispersion nd still mintin cceptble storge stbility. Tble 4 Effect of dis on wterborne polyester resins nd dispersions Resin properties Dispersion stbility 1 = best; 3 = worst PIA AD Processbility Solution viscosity Appernce ph M w Figure 7 Percent reduction in M w fter 13 weeks t 52 C (126 F) Isophthlic 1 See Estmn publiction N-335 (A sttisticl comprison of Estmn, Estmn PIA, AD, nd HHPA in high-solids resin system bsed on Estmn glycol). 5

6 Experimentl glycol study Glycols studied In the present study, three glycols re evluted for their effects on the hydrolytic stbility of Estmn bsed mine-neutrlized wterborne polyester resins. The effects of glycol structure were determined for Estmn glycol, Estmn 1,4-, nd glycol (2-butyl-2-ethyl-1,3-propnediol). Experimentl design Glycol effects on the hydrolytic stbility of polyester dispersions were evluted utilizing sttisticlly designed three-component mixture experiment. The pices of the tringle represent 100 mole % of tht glycol in the resin, while ech midpoint represents 1:1 molr blend of the two glycols on tht leg of the tringle. The center point represents n equimolr blend of the three glycols nd is duplicted for sttisticl nlysis (Figure 8). Figure 8 Experimentl design Resin synthesis All resins were mde with the sme di/glycol equivlents rtio keeping the di (/TMA) constnt nd synthesized to the sme extent of rection. Vrition in glycol moleculr weight resulted in some vrition in resin moleculr weight, number, nd hydroxyl number. The superior hydrolytic stbility of polyester resins bsed on Estmn 1,4-cyclohexnedicrboxylic mkes it the di of choice in designing resin formultions for evlution of glycol effects on hydrolytic stbility. Resin composition nd properties re shown in Tble 5. The polyester resins were synthesized using two-stge rections with the glycols nd trimellitic nhydride chrged to the first stge. For resins contining glycol, it is importnt to chrge the trimellitic nhydride to the molten glycol rther thn melting both simultneously. This substntilly reduces color formtion nd glycol decomposition. The first-stge rection mixture ws mintined t 180 C (356 F) until number nlysis indicted the first two crboxyl groups of the TMA were esterified. The ws then chrged to the mixture, nd the second-stge rection ws mintined t 180 C (356 F) until the desired number ws reched. Incorporting the TMA in the bckbone of the resin molecules, rther thn t the ends, nd processing the resins to the sme extent of rection resulted in identicl resins except for the glycol moieties in the bckbone. These processing techniques llowed isoltion of the effect of glycol structure on the hydrolytic stbility of the resins. 6

7 Tble 5 Composition nd properties Resin composition Glycol intermedites/estmn /TMA b Equiv. rtios: 1.06:0.63:0.37 Resin properties R vlue 1.06 Functionlity, foh 2 Extent of rection, P 0.87 Mn, moleculr weight rnge c 1,382 1,468 Acid number rnge, c mg KOH/g resin Mximum rection temperture, C ( F) 180 (356) Weight % solids in Estmn EB 80 1,4-cyclohexnedicrboxylic chrged to second stge of two-stge rection. b Trimellitic nhydride chrged to first stge with 100 mole % of glycol intermedites. c Rnges reported becuse of differences in glycol moleculr weight. Dispersion preprtion Resin dispersions were prepred ccording to the formultion in Tble 6. A 100 weight % neutrliztion of the polyester ws chieved by ddition of 2-dimethylminoethnol ccording to the eqution: Wt mine, g = Tble 6 Resin dispersion formultion Component Wt% Polyester resin (net) 35.0 Estmn EB 8.8 Deionized wter Dimethylminoethnol Resulted in ph rnge of (wt resin, g) ( number) (mine M w ) 56,100 Clculted Enmel formultion Pigmented enmels were prepred from ech resin ccording to the formultion in Tble 7. Enmels were prepred immeditely fter dispersion of the resins in wter nd fter ging the dispersions t 52 C (126 F) for 4 weeks. The enmels were djusted to #4 Ford cup viscosity of 30 seconds nd spryed onto unprimed, Bonderite 1000 pretreted, cold-rolled steel test pnels. The enmels were then cured for 30 minutes t 163 C (325 F). Tble 7 Enmel composition Ingredient Wt% Msterbtch Cymel 303 melmine resin 16.8 Ti-Pure R-900 TiO 2 pigment b 48.9 Fluord FC-430 c 3.3 Disperbyk 181 d 0.1 Estmn EB 2.1 Deionized wter 28.2 Coting (200 g) Msterbtch 65 (g) Dispersed resin (35% solids) 135 (g) Cytec b DuPont c 3M d BYK Chemie Results glycol study Stbility testing A portion of ech resin dispersion ws subjected to ccelerted ging t 52 C (126 F) for 4 weeks. The dispersions were checked weekly for ph drift nd increse in number. Pigmented enmels from ech resin dispersion were prepred initilly nd t the end of 4 weeks. In ddition, portion of ech resin dispersion ws ged under mbient conditions for 1 yer. Acid number nd ph were monitored once every 3 months. The responses from both sets of ged dispersions were then plotted s percent number increse, percent ph decrese. Chnges in enmel properties were plotted s percent increse in MEK double rubs. 7

8 Resin dispersion stbility 4 weeks ccelerted ging The reltive stbilities of the resin dispersions were determined by monitoring the increse in number nd the decrese in ph. Both responses re directly proportionl to the mount of hydrolysis of the polyester chins tht occurred during ging. The percent increse in number of the dispersions fter ccelerted ging for 4 weeks t 52 C is shown in Figure 9. The ph responses re plotted in Figure 10. The dt shows tht Estmn glycol imprts superior hydrolytic stbility to the resin dispersions. The resin contining 100 mole % glycol ws clerly the most stble to hydrolysis, nd the dt shows direct correltion between hydrolytic stbility nd glycol content in ny given resin formultion. Thus, glycol cn be blended with other glycols to improve the hydrolytic stbility of given resin formultion. Figure 9 Estmn /TMA/glycol dispersions (Percent increse in number fter 4 52 C [126 F]) Figure 10 Estmn /TMA/glycol dispersions (Percent reduction in ph fter 4 52 C [126 F]) Enmel properties Polyester chin hydrolysis results in n increse in both hydroxyl nd crboxyl functionl groups nd should result in higher cross-link density for the corresponding melmine cross-linked films. Thus, there should be correltion between the mount of resin hydrolysis nd film hrdness. To confirm this, the resin dispersions subjected to ccelerted ging were formulted into pigmented enmels t the end of 4 weeks ccording to the formultion in Tble 6. The percent increse in MEK (methyl ethyl ketone) double rubs ws determined nd is shown in Figure 11. These results correlte well with the number nd ph results, with the cured enmels prepred from resins bsed on Estmn glycol exhibiting the smllest increse in MEK double-rub resistnce

9 Figure 11 Chnges in enmel properties (percent increse in MEK double rubs fter 4 52 C [126 F]) Figure 12 Percent increse in number (12 months mbient conditions) Resin dispersion stbility 12 months mbient ging A portion of ech dispersion ws ged t mbient conditions for 12 months. Acid number nd ph mesurements were tken every 3 months during this time. The percent number increse (Figure 12) nd the percent ph decrese (Figure 13) correlted well with the ccelerted ging results. Agin, resins contining incresing mounts of Estmn glycol exhibit incresing resistnce to hydrolysis with the resin contining 100 mole % glycol giving the best performnce. Figure 13 Percent reduction in ph (12 months mbient conditions)

10 Conclusion glycol study Estmn is the glycol of choice for formulting wterborne polyester resins. The hydrophobicity, becuse of its bulky symmetricl structure nd the stericlly shielded secondry hydroxyl group, results in ester linkges tht re extremely resistnt to hydrolysis. cn lso be used s modifying glycol to improve the hydrolytic stbility of polyester resins bsed on other glycol intermedites. The combintion of Estmn nd Estmn glycol is n excellent choice for hydrolyticlly stble polyester resins nd polyester polyols for wterborne polyurethnes. Summry Proper selection of resin intermedites cn minimize the tendency of polyester resins to undergo hydrolysis. When formulted into typicl wterborne cotings, Estmn -bsed polyesters will resist hydrolysis much better thn Estmn PIA- nd/or AD-bsed resins. 1,4- CHDA nd Estmn glycol cn be used lone or in combintion to mke polyesters tht re much more hydrolyticlly stble thn current systems. Estmn nd Estmn glycol were shown to provide the following benefits to wterborne resins: Benefits of Estmn Excellent resin stbility in wter Better rectivity thn PIA during resin synthesis Lower resin viscosity in cosolvent compred with PIA Benefits of Estmn gycol Excellent resin stbility in wter Lower resin viscosity in cosolvent 10

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