Various techniques for electrostatic image transfer are known. One method includes the use of an intermediate transfer member. A liquid image, which includes a liquid carrier having ink particles dispersed therein, is transferred from a photoconductive surface of a photoconductive member or drum to a surface (e.g., a release layer or blanket) of the intermediate transfer member. The liquid image is attracted from the photoconductive surface to the surface of the intermediate transfer member. The liquid carrier is removed from the surface of the intermediate transfer member and the ink particles are compacted on the surface in the image configuration. Thereafter, the ink particles are transferred from the surface of the intermediate transfer member to a substrate in the image configuration by thermal attraction.
Modern liquid toner electrostatic imaging began with the invention of a new class of toners referred to as ElectroInk™. This type of toner (also referred to as ink formulation) is characterized by its toner particles being dispersed in a carrier liquid, where the toner particles include a core of a polymer with fibrous extensions extending from the core. When the toner particles are dispersed in the carrier liquid in a low concentration, the particles remain separate. When the toner develops an electrostatic image, the toner particles come together and the fibrous extensions interlock. A large number of patents and patent applications are directed toward this type of toner (e.g., U.S. Pat. Nos. 4,794,651; 5,047,306; and 5,208,130). It has been discovered that this type of toner allows for high quality offset printing at high speed. This type of printing is described in the following U.S. Pat. Nos. 4,678,317; 4,860,924; 4,980,259; 4,985,732; 5,028,964; and 5,034,778.
However, the electrostatic imaging inks can suffer from deficiencies relating to agglomeration of PTFE in the electrostatic imaging ink. The agglomeration of PTFE under an electrical field is a known process. The agglomeration of the PTFE can cause print quality defects called white spots (1 to 2 micron voids, FIG. 1). This deficiency is exhibited in solid prints, which can show a large number of white spots or voids. The voids significantly reduce the quality of print, and in some industries, the prints are not usable. Therefore, a need exists in the art for ink formulations to overcome at least this deficiency.
USPTO Backgrounds
USPTO Backgrounds