The present invention relates to photocopying systems and, more particularly, to developing apparatus for developing light sensitive paper and polyester film. The development process requires the sensitive side of the copy material to be coated with a very small amount of developer liquid, this liquid to be distributed evenly over the surface of the copy material, the quantities being in the order of 1.75 to 2.25 grams of liquid per square meter of paper. The major advantage of applying the liquid in such small quantities is that the copies emerge direct from the developing apparatus dry to the touch.
One existing system known as the "pressure diazo" system is disclosed in British Pat. Nos. 1,215,705, 1,349,597, 1,349,598, 1,349,599 and U.S. Pat. Nos. 3,626,833 and 3,640,203. Basically the "pressure diazo" system consists of a rotating roller with a rubber surface having a fine surface texture. The rubber surface effectively transports developer liquid from the developer supply to the surface of the copy material as they meet in rolling contact with each other. The quantity of developer transported is limited by a metering blade which effectively only allows the small amounts of liquid held within the "valleys" of the surface texture to reach the copy material. The transfer of developer liquid from the rubber surface to the copy material is assisted by a pressure applicator device which serves to press the copy material firmly against the rotating rubber surface.
Both the metering device and the pressure applicator device are blade members and are mounted in such a way that, under the influence of a control mechanism, they can be moved into and out of engagement with the roller surface. When engaged the metering blade traps a reservoir of developer liquid downstream of the pressure applicator blade. When a print is presented to the unit, the copy material and the developer laden roller surface meet and are pressed together under the influence of the pressure applicator blade, this causes the major part of the liquid in the "valleys" to transfer onto the activated side of the copy material thus causing it to develop.
When the machine is in operation and the roller is rotating, but the unit is not processing copy material, the pressure of both blades acts directly onto the roller surface. The points of contact are lubricated to some extent by the developer liquid, but this degree of lubrication is not adequate when the roller is rotating at the minimum speed. In order to reduce contact friction and overcome this problem, the blades have been coated with a fluoro carbon plastic such as tetrafluoroethylene polymer.
The movement of the blades, into and out of engagement with the roller surface, occurs when the machine is switched on or off respectively, which ensures that the blades do not bear down under pressure onto the surface of the roller when it is stationary. The effect of this if it should occur, for more than a few hours, would be to mark the surface of the roller with a smooth line measuring the same length as that of the blade. On a microscope scale, the "crests" of the surface texture become depressed into the space of the "valleys" of the same surface texture, thus reducing the liquid carrying capacity of the surface at the pressure set point. When the machine is then used normally, a line of poor development on the copy material will appear corresponding to the line on the roller.
It is therefore the principal object of the present invention to provide a developing apparatus in a photocopying system which overcomes the disadvantages of the prior art by including means to apply pressure on the copy paper against the surface of the application roller without causing marks on the surface of the roller and without requiring means to move the pressure application means away from the roller when the roller is stationary.
Other objects, features and advantages of the invention will become apparent from the description of the invention in connection with the accompanying drawing to be described more fully hereinafter.