Journal of the Japan Society of Colour Material

As one of the mechanisms which a pigment does not settle but be stabilized in a pigment dispersion, the electrical repulsive force due to the surface charges of the pigment is considered, and the surface charges are believed one of the important factors to suspend the pigment particles. Authors made experiment for investigating the relationship of the suspensions and the zeta potential.
The zeta potential was measured with glass U tube for the combination of 22 kinds of pigment and distilled water, alcohol, aromatic hydrocarbon media by the electrophoresis method.
As a result, three different tendencies were observed in the boundary movement phenomena as follows :
1. The boundary moves to only one electrode.
2. The boundary does not move to the electrode but descend.
1) The movement velocities of the descended boundary were not equal.
2) They were equal.
The signal of surface charges for the same pigment was not different by the difference of medium. For titanium dioxide pigments used in this experiment, the signal of surface charges was different by the presence of added aluminium compound. It was positive in case of addition, and was negative in case of absence. It was found that in a good suspended dispersion the zeta potential was high and this contributed on pigment dispersions as one of the factors of the stabilization.

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The effect of organic titanium compounds as crosslinking agent for water soluble resins was investigated.
As model resins, acrylic polymers of organic solvent system having various functional groups were prepared to select the most suitable combination of organic titanium compounds and functional groups. Functional groups cmployed were OAC, -COOH, -OH-CO, -CO> O and-CONH₂.
Films were prepared from the mixture of above resins and organic titanium compounds including alkoxide, acylate and chelate type by baking on steel panels.
The results of resistance for organic solvents of the baked films were as follows :
1) Carboxyl and hydroxyl groups in resins were excellcnt functional groups for organic titanium compounds. other groups had little function for organic titanium compounds.
2) Chelate compounds, especially diisopropoxy titanium bis acetylacetone, were most excellent as crosslinking agent. Alkoxide type was not suitable because they cause gel when mixed with above resins. Acylate type was inferior than chelate type in resistance for organic solvents.
3) The suitable amount of organic titanium compounds to be added to resins was twice in mole ratio for functional groups contained in resins.
Above results indicate that when organic titanium compounds are applied for water soluble resin system as crosslinking agent, resins should have carboxyl or hydroxyl group as functional group. Hence water soluble alkyd resins were prepared because they have both carboxyl and hydroxyl group. Chelate type was selected from organic titanium compounds to investigate crosslinking effect and water soluble melamine-formaldehyde resins were adopted to compare with organic titanium compounds in crosslinking effect for water soluble alkyd resins.
The films were prepared by baking on steel panels from the mixture 80 parts of water soluble alkyd resins and 20 parts of organic titanium compounds or water soluble melamine-formaldehyde resins.
Water resistance, chemical resistance, and salt spray resistance were investigated and the results were as follows :
1) The films prepared from water soluble resins were improved in water resistance, chemical resistance and salt spray resistance by using organic titanium compounds as crosslinking agent.
2) As comparing with water soluble melamine-formaldehyde resins, films crosslinked with organic titanium compounds were superior than that of melamine-formaldehyde resins in water resistance, chemical resistance and salt spray resistance when baked at lower temperature as conventional. This indicate that water soluble resin may be baked at lower temperature than usual if organic titanium compounds are used as crosslinking agent.
Melamine-formaldehyde resin system was superior than organic titanium compound system when sufficiently baked, but parallel use of organic titanium compounds and water soluble melamine-formaldehyde resins gave more excellent results.

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