Processing the positive-working presensitized plate on the market in the screenless lithography, the density range of tone reproduction is too narrow to meet actual use. So, we have investigated the procedure to increase the density range of tone reproduction by the flash exposure on the plate.
We have studied three flash exposure methods such as the flash before the main exposure, the flash after the main exposure and the flash after devlopment of the plate.
The results are as follow;
1. In the both case of the flash exposure before and after the main exposure, the density range of tone reproduction could be increased proportional to the amount of the flash exposure. At the best, the resulted density range was almost twice as the range without the flash.
2. The flash exposure after development also increased the density range, but the rate of increase is less than others.
3. The amount of flash exposure is so critical and overexposure reduces the solid density, making the plate inadequate to use.
4. Alternation of the amount of main exposure has entirely no effects for improvements on the density range and value.
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