| 摘要 |
PURPOSE:To obtain a hard magnetic grain difficult to crack, good in dispersibility of amino resin powder, dispersion stability and affinity for binder resin and excellent in resistance to heat and friction, etc., by treating the amino resin powder with a vinyl monomer containing an isocyanate group to introduce the vinyl group into the surface. CONSTITUTION:A monomer phase contg. a magnetic powder, an amino resin powder which has been treated with an isocyanate group-contg. vinyl monomer to introduce a vinyl group into the surface and vinyl monomer is dispersed in a dispersion medium in the form of droplets and polymerized. Even if the isocyanate group-contg. vinyl monomer used in the treatment of the amino resin powder is left, the excess monomer is polymerized with another vinyl monomer in the succeeding suspension polymerization, hence the vinyl monomer is not left in the magnetic grain as a low-mol.wt. monomer. Accordingly, the magnetic grain is excellent in resistance to heat and friction, hard and difficult to crack. |
