Dispersion of hydrophobic pigments (Cu-phthalocyanine) and that of hydrophilic pigments (Titanium dioxide), both in water-soluble acrylic resins were studied. As for the dispersion of hydrophobic pigments in water soluble resins, their hydrophilicity (the degree of hydrophilic character) was an important factor, while for the hydrophilic pigments, their hydrophobicity was an important factor of dispersion (in the same water soluble resins). These experimental results indicate that the wetting process (in the hydrophobic pigment dispersion) and the stabilization process (in the hydrophilic pigment dispersion) are the determining process of the dispersion of each pigments, and that these dispersion systems are stabilized by the hydrophobic interaction between pigments and resins. Selection of a hydrophilic pigment leads to a higer rate of wetting but results in lower level of stabilization. For the fine pigment dispersion in aqueous solution of acrylic resins, the most favorable hydrophilicity value of pigment, which was masured by the heat of immersion in water, was considered to be between 0.1 and 0.2 J/m2.
This paper describes the results of attempts at preparing fine metallic cobalt particles through reducing reaction in liquid phase. The materials used were : cobalt chloride (II) and tris (acetyl acetonate) cobalt (III) (abbreviated as [Co(acac)3], hereafter) as cobalt compound ; water, anisole and diphenylether as solvent ; hydrazine, hydroquinone and sodium borohydride as reducing agent. Although the reduction in water or anisole was impossible, the black and strongly magnetic cobalt particles were formed through the procedure : refluxing diphenylether containing [Co(acac)3] at its boiling point with an addition of sodium borohydride, and filtration after cooling and decomposition of sodium borohydride with an addition of methanol. Since the obtained particles were observed to be remarkably flocculated, refluxing with N2 gas flow was attempted to prevent this flocculation. The result was that the flocculation was considerably suppressed. Although the formation of cobalt particles covered with thin oxide layer required the amount of sodium borohydride 20 times as much as that of [Co(acac)3] in the molar ratio, the former amount was reduced to 1/2 with N2 gas flow. The cobalt particles obtained by this method were in flocculated state of primary particles of 5 to 10 nm. The purity of this product was about 93 percent.