Toner and process for developing electrostatic latent images

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The toner for developing electrostatic latent images according to the present invention is produced by the following procedure: a mixture of 5 to 90 mol % of an unsaturated dibasic acid having unsaturated carbon-carbon double bonds with another polybasic acid such as a saturated dibasic acid is condensed with a corresponding amount of polyvalent alcohol to form an unsaturated polyester; 99.
5 to 92 parts by weight of a vinyl polymer is graft-polymerized to 0.
5 to 8 parts by weight of this unsaturated polyester; the resulting graft-polymer is ground into fine particles, and a coloring agent and other necessary additives are dispersed in these toner particles to form a toner.
Using such graftpolymer as the binder component, the toner of the present invention has the following advantages, as will be illustrated in the examples that follow later in this specification.
The graftpolymer contains at least 90 parts by weight of the vinyl monomer base component, so its softening point is significantly lower than that of resins having the same molecular weight.
Because of this low softening point of the binder, the toner of the present invention melts at low temperatures and is fluidized sufficiently to penetrate deep into paper which is typically used as a printing sheet.
This great "anchor effect" reduces the possibility of the toner separating from the paper once it is fixed thereto.
Furthermore, the high molecular weight of the binder increases the toner strength and eliminates the chance of a blurred toner image or its adhesion to fingers due to abrasion that may occur after the fixing.
The toner has high releasability in molten state, so it will not stick to the heated rollers and thus prevents the occurrence of offsetting.
As a further advantage, the graftpolymer has a relatively high elasticity by the nature of its molecular chain, and, therefore, the toner of the present invention will not part from the printing sheet even if it is bent or otherwise deformed after the fixing operation