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To design adequate ink composition for textile printing, the relationship between the dye/additive interaction and the ink performance are investigated. In the present study, three acid dyes, C. I. Acid Red 88, 13, and 27, a water-soluble polymer poly(vinylpyrrolidone) (PVP) and three surfactants, sodium dodecyl sulfate (SDS), octaethylene glycol monododecyl ether (OGDE), and Surfynol 465 (S465) were used and the dye/additive interaction was investigated by means of visible absorption measurements. The visible absorption spectra of aqueous dye solutions changed with the addition of the nonionic surfactants, but further addition of PVP hardly changed, indicating that the strong binding of the dye molecules with the nonionic surfactant micelles is maintained even in the presence of PVP. In contrast, in the case of SDS, the spectra changed with the addition of the surfactant as well as further addition of PVP. From the above results, the behavior of the acid dyes in three species coexistence system depends on the dye structure, the surfactant structure, the molecular weight of PVP, and so on. Furthermore, to estimate the ink performance, the physical properties of the ink such as viscosity, surface tension, and ink droplet formation were determined. The composition of the ink solution having excellent ink droplet  Corresponding author. Tel.: +81 268 21 5411; fax: +81 268 21 5391 E-mail address: khamada@shinshu-u.ac.jp (K. Hamada) formation was observed, which had appropriate physicochemical properties such as viscosity and surface tension as well as PVP with lower molecular weight. In the optimized ink composition (PVP-1/S465: 1.4/0.004 mol dm -3 ), most of the dye molecules are strongly bound to the PVP chain, but the binding was hardly affected by the addition of S465.

The aggregation of an azo dye containing one trifluoromethyl and two sulphonate groups (m-FTR) in aqueous solution has been investigated by means of 19F n.m.r. and electronic absorption spectroscopy. The 19F n.m.r. signals shifted to lower magnetic field, indicating that the fluorine atoms are located outside the aromatic ring of an adjacent dye molecule in the aggregate. On the other hand, in the case of an azo dye carrying one trifluoromethyl and one sulphonate group (m-FTS), the fluorine atoms were oriented above the adjacent aromatic ring. This difference gives a different aggregate structure between m-FTR and m-FTS. The absorption spectra of m-FTR aqueous solution show a single monomer/dimer equilibrium. On the basis of the results, the aggregation constant K was determined. The value of K for m-FTR was half that for m-FTS, suggesting that the latter dye aggregates more easily than the former owing to a lower electrostatic repulsion.

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The mobility of nonionic spin probes in nylon films was investigated by electron spin resonance (ESR). Dried samples were used to avoid the effects of water in the polymer matrices. Effects of drawing were observed only for spin probes having an amino or amide group, suggesting that the orientation of the nylon chain molecules affects the interaction of these spin probes with the macromolecules. Tm, the temperature at which the extrema separation of the ESR spectra becomes 5 mT (50 G), decreased with increasing methylene chain length of the nylon. In other words, the longer the methylene chain, the larger the mobility of the spin probes. In the Arrhenius plots of rotational correlation times one or two crossover points were defined. The number of crossover points was found to vary from probe to probe. For probe molecules carrying substituent groups linked by single bonds two crossover points could be defined. The crossover point at the lower temperature, T, , ', is presumed to be the temperature at which rotation around the single bond occurs, and that at the higher temperature, T,, is considered to be the temperature at which Fotational motion of the whole probe molecule takes place. The dependence of the activation energy for rotation, in the temperature region above T,, on the methylene chain length of the nylon is influenced by the interaction of the probe molecules with the nylons and by the jumping distance of the spin probes.