Method and apparatus for image formation utilizing a blocking member for blocking an ion flow through a photosensitive screen to provide a non-image area

DETAILED DESCRIPTION Accordingly, it is a general object of the present invention to enable, in accordance with the image forming technique using a screen, to form any desired non-image area on a member to be modulated in a very simple and reliable manner.
According to the invention the above object is attained by providing, between an ion stream source for modulation and a screen photosensitive medium, an ion stream blocking member for preventing the ion stream flowing from the ion source from reaching the screen photosensitive member so as to produce a non-image area on the modulated member at the time of modulation.
The term "a member to be modulated" used herein should be understood to mean, for example, a sheet or drum member having thereon an electric charge retaining surface on which a latent image (secondary latent image) can be formed.
The latent image formed on the modulated member is later visualized by developing agent such as toner and the visualized image is brought to use directly or through a transferring step.
The term "non-image area" used herein should be understood to include: (i) fore end part of an image area; (ii) one or both side parts of an image area; (iii) surrounding area enclosing the entire image area; and (iv) any portion of an image area.
These non-image areas are sometimes contained inside the actual area of a sheet member and sometimes outside of it.
For example, there is the case in which although a non-image area is present on the dielectric drum, the non-image area does not appear on a transfer sheet on which the toner image has been transferred.
The term "non-image area" also includes such case.
The above non-image area (i) primarily prevents the toner from being scattered and prevents the sheet material from being caught into the fixing roller.
The effect attainable by (ii) is to prevent the toner from being scattered by the sheet separation belt and to prevent the belt from being soiled with toner, which in turn prevents the end portions of sheet members from being darkened