A printing process for applying or transferring a ferroelectric image pattern to a web or substrate using electrically-charged toner particles is disclosed in German patent publication DE 38 35 091 C2. In accordance with that process, the ferroelectric material may be polarized in different directions within unusually narrow regions; this permits the attainment of very high-resolution printing using monochrome toners and, using two colors of toner having differently charged particles--i.e. one containing positively-charged particles and the other containing negatively-charged particles--both colors may be applied simultaneously to the ferroelectric surface in a single printing step or pass thereby minimizing the number of passes required to transfer or apply the image to the substrate. The priming form and therein-disclosed process are suitable for use with dry toners as well as with toners that are dissolved in moistening agents that serve as carriers for the toner. This reference does not specify particular temperatures at which the printing form is operatively polarized.
U.S. Pat. No. 3,899,969, on the other hand, discloses a method for printing an image on a substrate using a pyroelectric material upon which a charge pattern representing the image to be reproduced has been established through the application of an electric field. The placement of the image-representing charge pattern to the pyroelectric material, which is also a ferroelectric material, is carried out by polarizing the material at very high temperatures, e.g. 150.degree. C., while the electric field is applied. For this purpose the material to be polarized must, for example, be placed in a bath of hot oil.
German patent publication DT 25 30 290 A1 teaches a one-time application of an external electric field to a ferroelectric material after a polarization process for producing a latent image on the surface of the ferroelectric material. However, the charges applied to the surface of the ferroelectric material by the electric field are only proportional to the field strength of the applied field, as in the case of a capacitor, and are therefore limited in magnitude. Moreover, since the surface-carried charges are transferred along with the toner image to the substrate upon which the image is to be reproduced, only a limited number of copies can be thus printed from the latent image carried on the ferroelectric material before all of the free charges that were generated by the applied external field have been consumed. This is similarly true with respect to the use of the pyroelectric or piezoelectric effect which is produced by heating the ferroelectric material or by applying pressure thereto. As a consequence, the process taught in German publication DT 25 30 290 A1 is not a continuous printing process but, rather, a mere copying process useful for producing only a limited number of copies.