Photoirradiation on the suspension of TiO2 particles in 1,3,5,7-tetramethylcyclotetrasiloxane led to the graft polymerization from the particles, forming a linear poly (methylsiloxane) (PMS) layer. Transmission electron micrograph of the particles obtained after 2 h of photoirradiation clearly showed the polymer layer with a thickness ranging from 10 to 20 nm. The amount of the grafted polymer determined by diffuse reflectance IR measurements increased with an increase in the photoirradiation time, reaching a plateau value of ca. 27 wt% above 15 h. The dispersion stability of the particles in poly (dimethylsiloxane) was remarkably improved by the coating of PMS. In order to estimate the van der Waals potential energy in this system, a single layer model was applied. The results of the calculation revealed that the decrease of van der Waals potential energy accompanied by the graft polymerization was partly responsible for the better dispersion stability.
The preparation of silica gel powder having functional groups by sol-gel process and the grafting of polyesters onto the silica gel surface were investigated. Silica gel having carboxyl groups was prepared by copolycondensation of tetraethoxysilane with 4-trimethoxysilyltetrahydrophthalic anhydride. The silica gel was ground into a powder : The average diameter determined by SEM and carboxyl group content of the powder were 4 μm and 1.07 mmol/g, respectively. Then the carboxyl groups on the surface were converted into potassium carboxylate groups by the neutralization with dilute aqueous solution of potassium carbonate. It was found that the anionic alternating copolymerization of epoxides with cyclic acid anhydrides was successfully initiated by potassium carboxylate groups on the silica gel surface. In the copolymerization, the corresponding polyester was grafted onto the silica gel based on the propagation of the polymer from the surface : The percentage of polyester grafting onto silica gel obtained from the copolymerization of styrene oxide with phthalic anhydride and chloromethyloxirane with succinic anhydride was determined to be 37.1% and 42.2%, respectively. The copolymerization rate and percentage of polyester grafting increased with an increase in the polymerization temperature. The stability of silica gel dispersion in organic solvent was found to be remarkably improved by the grafting of polyesters onto the surface.
The preparation of silica gel powder having reducing groups such as alcoholic hydroxyl and mercapto groups by sol-gel process and its application to the grafting of vinyl polymers onto the silica gel surface were investigated. Silica gels having alcoholic hydroxyl groups and mercapto groups were prepared by the copolycondensation of tetraethoxysilane with γ-glycidoxypropyltrimethoxysilane and γ-mercaptopropyltrimethoxysilane, respectively. The obtained silica gel was ground into a powder : The average diameter determined by SEM was 4 μm. It was found that the radical polymerization of acrylamide was initiated by a redox system consisting of silica gel having alcoholic hydroxyl groups and ceric ion to give polyacrylamide-grafted silica gel powder. The redox system consisting of silica gel having mercapto groups and ceric ion also had an ability to initiate the radical polymerization of acrylamide. The percentage of polyacrylamide grafting onto the silica gel surface was determined to be 15-45%. These results indicate that the polymerization is initiated by radicals formed on the silica gel surface by the redox reaction of these reducing groups with ceric ion. The percentage of grafting obtained from the alcoholic hydroxyl groups/ceric ion initiating system was larger than that from the mercapto groups/ceric ion system. This may be due to the chain transfer reaction of growing polymer radical to mercapto groups on the surface. The polyacrylamide-grafted silica gel powder was found to have a higher hydrophilic property and to disperse stably in water.
The control of the diameter and the sahpe of pigment during the process of preparation by using W/O emulsion has been attempted in order to increase dispersing and tinting abilities of the pigments. The pigment was prepared by reacting an acid dye with multinuclear aluminum salt within the aqueous phase of a W/O emulsion which was prepared by using a nonionic surfactant. This pigment consisted of fine spherical particles with diameters of less than 0.5 μm ; it also had excellent dispersing ability and good tinting properties. The diameter of spherical particles could be controlled by varying the concentrations of surfactant within the W/O emulsions. Due to the presence of a surfactant on the surface of pigment, the prepared pigments exhibited excellent dispersing ability.
Spherical pigment was obtained by the reaction of an acid dye wih a multinuclear aluminum salt within the aqueous phase in a W/O emulsion prepared with using a nonionic surfactant. The diameter of the pigment was less than 0.5 μm. The pigment had excellent dispersing and good tinting properties. An investigation of the formation mechanism of the spherical pigments revealed that the diameter of the pigment was related to the concentration of the pigment in the W/O emulsion as well as the diameter of water droplets in the W/O emulsion. In addition, the smaller the diameter of the pigment was, the larger the tinting strength of the pigment and saturation of colored films became. These results are explained by an increase in absorption and a decrease in scattering due to decreased sizes of pigments used.
White inks were prepared with six kinds of titanium dioxide and a polyurethane as a binder. Lamination strength of Extruded Polyethylene/Ink/Nylon Film laminated stock, and peeling strength and internal stress of white ink films were measured. Results in this study are as follows : (1) Peeling strength of the ink films and internal stress of the films induced by heating and cooling in laminating process affect lamination strength. (2) Degree of polymer adsorption on pigments and internal stress of the ink films caused by drying affect peeling strength. (3) Internal stress shows strong relation to 1% Modulus of the ink films and reduces peeling and lamination strength. (4) Acid/base amount and particle size of pigments affect polymer adsorption on pigments and internal stress of the ink films caused by drying and heating-cooling processes, which results in the difference in lamination strength, Of all the pigments evaluated in this study, basic and large particle size titanium dioxide digment provided good lamination strength.
The relationships between surface properties and surface compositions have been investigated for two types of polyestermelamine paint films. The surface content of melamine has been estimated from XPS nitrogen-peak intensities. The surface segregation of melamine on the paint films was observed under hightemperature and short-time curing as a practical condition. The contact angle of water and the adhesiveness to urethan adhesive depended not upon polyester resin but upon surface melamine content. The stain resistance of marker ink was improved as surface melamine content increased. The stain resistance also depended upon the type of polyester resin. These phenomena indicate that the surface properties such as the contact angle of water and the adhesiveness are effected by the surface composition within the sampling depth of XPS (-10 nm), and that the stain resistance is influenced by the interior structure of paint films.