Negative Pre-sensitized Offset Printing Plate
Introduction
Jinyan negative PS plates have high pressrun, proper exposure rate, simple plate making,
and perfect dot reproduction advantages and so on. In order to make the plate reach its best
printing efficiency, please use it under the following conditions.
1. Printing down(Exposure):
Negative ps plate’ exposure is finished by negative film jointing nearly with sensitive plate,
spectrum range is between blue ray and ultraviolet ray (320-450nm), while exposing, the iodine
gallium lamp is the most proper lamp-house and around 150mJ/sqm exposure quantum is
recommended, in the actual operation, the exposure time can be different according to different
exposure equipment and different film sort. So the exposure time must be decided by actual
experiment result.
(1) Put FUJI gray scale (0.15 tier) on the edge of plate and under the film, choose the
proper exposure quantum to expose the plate, after finishing exposing, wash the plate,
the optimum exposure quantum can be determined on the ninth step without
printing ink.
(2) Use UGRA PCW82 control strip, choose proper exposure quantum to expose it, when
the 15-20um weenie line appear on the control strip, the exposure quantum reach its
optimum state.
15~20μ
Weenie line sketch map
(3) Remark:
In order to reach the most pressrun, the exposure quantum must be enough;
In order to prevent halftone (net dot) being scale-up, the exposure quantum can’t be
added or decreased optionally. Avoid the tone value, transferred from film with
halftone to printing plate, increasing excessively and decreasing excessively so that
the thin part of the dark area disappearing; the tone value must be controlled in the
permitted range.
(4) Before using our plate to print, please operate it under the yellow safe light to
prevent exposing before printing for fear it influences quality.
2. Develop
Kodak -956 developer and our company’s negative developer are strongly
recommended.
Develop temperature: 25±2°C developer’s dilution ratio: 1:1(developer: water)
Develop time: 30-60 seconds.
Manual develop: must scrub, wash off remnant developer on the surface of plate.
Automatic develop: develop machine must be equipped with brush to reinforce
developing efficiency.
Introduction:
(1) Because the developer from different area is of diversity, some of negative plate will
appear shallow yellow on the surface after developing, with the plate substrate being
using, the shallow yellow will disappear automatically, it won’t influence printing
effect (Kodak -956 developer has no such problem).
(2) In order to solve the problem, you can expose the developed plate once again, that
will not only eliminate the shallow yellow but also enhance pressrun.
3. Correction:
In order to wipe off the excrescent image and stain, you can lay right quantity negative
remover on the surface of image or stain. 15 seconds later, wash the surface.
4. Inking up (Dip ink):
The function of dipping ink to negative plate is to enhance the image area’s capability of
absorbing ink and enduring fretting. The negative plate must be laid a layer of sensitive
colophony additionally on the image area.
5. Lay on gum.
The gum must be diluted under the manufacturer’s requirements, and the layer should
be well-distributed. Too thin or too thick all will influence the effect, and if you lay on
gum automatically, please control the drying temperature.
6. Storage
(1) Before using: The negative plates should be stored in the cool (10—30°C), dark and
dry place. Relative humidity ≤60%.
(2) Storage life: six months.