Latent image surface

In the classical theory of Ostwald, Abegg, and Schaum [96] the homogeneous reduction of silver ion is assumed to be rapid and is followed by the physical deposition of silver on a latent image nucleus from a supersaturated solution of silver. The term physical development arises from this description and developers used at this time often deliberately contained soluble silver ion. It is now considered that physical and chemical development are both chemical, or electrochemical, processes in which silver ion reduction occurs at the latent image surface. 

As in chemical sensitization, spectral sensitization is usually done after precipitation but before coating, and usually is achieved by adsorbing certain organic dyes to the silver haUde surfaces (47,48,212—229). Once the dye molecule is adsorbed to the crystal surface, the effects of electromagnetic radiation absorbed by the dye can be transferred to the crystal. As a result of this transfer, mobile electrons are produced in the conduction band of the silver haUde grain. Once in the conduction band, the electrons are available to initiate latent-image formation. 

Liquid toners are suspensions of toner particles in a fluid carrier. The carrier is typically a hydrocarbon. Dielectric, chemical, and mechanical properties of the Hquid must be compatible with the photoreceptor, the suspended toner particles, and the materials of the development equipment. Liquid toners are capable of producing higher resolution than dry toners because of the smaller (3—5 -lm) particle size achievable. Development of the latent image occurs as it passes through a bath of toner and the charged particles are attracted to the oppositely charged surface. 

Exposure and latent image formation. The sensitized photoreceptor is exposed to a light and dark image pattern in the light areas the surface potential of the photoconductor is reduced due to a photoconductive discharge. Since current can only flow perpendiculai to the surface, this step produces an electrostatic-potential distribution which replicates the pattern of the image. 

Image erasure. The potential differences due to latent image formation are removed by flooding the photoreceptors with a sufficiently intense light source to drive the surface potential to some uniformly low value (typically I00V corresponding to fields of 10 Vcni ) the photoreceptor is then ready for another print cycle. 

The developable density of many photographic materials passes through a maximum at a sufficiently high exposure and subsequently decreases with further increase in exposure. This loss of developability with increasing exposure is termed solarization, and probably is caused by a superficial rehalogenation of the surface latent image centers (cf. J. H. Webb, J. Optical Soc. Am. 30, 445, 1940). 

In a laser or LED printer, modulated light is projected onto the drum surface to create a latent image. The modulated light is used only to create the positive image, hence the term black writing. ... 

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