Coemulsion and electrodeposition properties of mixtures of polyoxypropylene‐modified cationic epoxy resin and nonionic trimethylolpropane–toluene diisocyanate–2‐ethylhexanol crosslinker

Abstract

SYNOPSISThe emulsification and electrodeposition properties of mixtures of polyoxypropylene-(POP) modified cationic epoxy resin ( I11 ) and nonionic trimethylolpropane-toluene diisocyanate-2-ethylhexanol (TMP-TDI-2EH, V ) were investigated and the compositions of their electrodeposited films were obtained by Fourier Transform Infrared ( FTIR) quantitative analysis to study the effects of "soft segment" (oxypropylene groups) contained in resin 111 on the coemulsion and electrophoretic behavior. The results indicate that the deposition yield and throwing power of emulsion of resin I11 are highly dependent on its average molecular weight (Mw). Resin 111 with higher Mw has higher deposition yield but lower throwing power. Moreover, the deposition yield of V/III coemulsion also increases with increasing the M w of 111. On the other hand, the throwing power of V/III coemulsion is not related to the M w of 111 but is influenced by the amount of soft segments in 111. Increasing soft segment content in I11 increases the throwing power of the coemulsion. Furthermore, at the conditions providing stable coemulsion, the composition of the electrodeposited film is almost equal to the resin composition of the coemulsion. INTRODUCTIONTwo or multi-component cationic coatings can provide better storage stability for electrodeposition emulsions and better physical and chemical properties of the electrodeposited films than one-component systems?-'6 In the earlier papers, 1-5 most of the crosslinkers of two-component cationic coatings were uncharged resins; however, the codeposition behavior of uncharged crosslinker and cationic resin is not well understood.In our previous the compositions of the films electrodeposited from coemulsions of cationic resin /cationic crosslinker or cationic resin / CCC 0021-8995/93/C61031-09results indicate that in the "cationic resin/cationic crosslinker" coemulsion system, 6-7 the composition of the deposited film is affected by the individual deposition velocities of the main resin and crosslinker; on the other hand, in the "cationic resin! nonionic crosslinker" coemulsion system,8 the composition of the electrodeposited film is almost equal to the resin composition of the coemulsion.The cationic resins in our studies described above (TDI) .Ethylene glycol mono-n-butyl ether (butyl cellosolve, BCS, Wako EP grade) and acetic acid (Wako first grade) were used in the preparation of electrodeposition emulsion. InstrumentsAn electrodeposition apparatus and a Jasco-7000 FTIR spectrophotometer were employed. The detailed scheme of the electrodeposition apparatus was shown in a previous p~blication.'~ A copper electrode (anode) and aluminum plate (cathode) with a surface area of about 30 cm2 were used. Approximately 200 mL of emulsion was placed in the glass vessel of the electrodeposition apparatus. After deposition, the aluminum plate was rinsed with distilled water and dried in an air circulating oven at lOO"C, then reweighed to obtain the deposition yield of deposited film ( mg/cm2). Synthesis POP-Mod...