IGT W46 Information Leaflet

Introduction:
When inks are used on a two-colour offset printing press the
second ink film is printed over the first ink film while it is still
completely wet. For multi colour presses the same can be said for
the other colours. In order to do so the inks have to be trapped on
tack and/or viscosity. The systems for measuring tack and/or
viscosity measure these ones as it is in the tin, without the
influence of absorption by the paper.
On the printing press, as soon as the ink is printed on the paper
the low viscosity components of the ink will penetrate into the
paper and the viscosity and tack of the ink will increase rapidly.
The longer the ink is on the paper, the bigger this increase of
viscosity and tack will be. The time interval between individual
prints differs considerably in various types of presses. In practice
these interval times are between about 0.03 and 3 s. For proper
adjustment of ink for wet-on-wet printing a printability tester is
essential, operating from very short time intervals upwards.
Although in practice water is used and an emulsion is formed,
this method gives very good results for testing wet-on-wet
printing.
There are 2 methods:
W46 for a printing form with coated rubber of 85 Shore A for
smooth papers (described in this leaflet)
W69 for a printing form with coated rubber of 65 Shore A for
smooth and rather rough papers
Principle:
A set of two colours of offset inks is printed on each other on
paper in both the colour sequences and with different interval
times. The results are observed visually or with the help of a
densitometer. The best print quality and the best ink transfer
show the right colour sequence.
Also for a four colour series of offset inks the inks always must
be tested in sets of two colours.
Method of operation:
• It is recommended to execute the test in the standard
atmosphere; to most standards it is 23.0 ± 1.0 °C (73.4 ± 1.8 °F)
and 50 ± 2% rh.
• For the operation of the AIC2-5T2000, the High Speed Inking
Unit 4 and the ink pipette follow the instructions of the manuals,
IGT information leaflet W100 and the displays accurately.
• Handle the samples carefully.
Preparation
1. Condition the papers, inks and equipment during >6 hours in
the standard atmosphere.
2. If necessary cut the paper strips (preferable 55 x 320 mm, 4
- 6 strips per set of inks) and mark them with top and/or
bottom side, machine and/or cross direction and a code for
the type of paper.
3. Adjust the printing force of the printing disc shafts to 1000
N and pay attention for the right backlash. See W100.
4. Adjust the speed to constant (5), 1.0 m/s.
5. Check and if needed, move the slide in front of the sector
into the constant speed mode (5).
6. Check the functioning of the AIC2-5T2000 following the
instructions in the chapter "Execution".
7. Fill the ink pipettes with the inks to be tested.
8. Adjust the High Speed Inking Unit with the settings
mentioned in note 2.
9. Check the functioning of the High Speed Inking Unit.
Execution
1. Adjust the interval time in the display.
Phone +31 (0)20 409 9300, Fax +31 (0)20 697 4842, E-mail:
IGT Testing Systems, P.O.Box 12688, 1100 AR Amsterdam, The Netherlands
Keienbergweg 25, 1101 EX Amsterdam, The Netherlands
IGT Information leaflet W46
WET ON WET PRINTING (85 Shore A)
Materials / testing conditions
1 IGT AIC2-5T2000
2 IGT High Speed Inking Unit 4
(with 4 segmented top roller for
conventional inks)
3 Printing disc with coated rubber,
85 Shore A, 50 mm (2x)
4 Strips of art paper, code Ka, 55 mm
5 IGT ink pipette (2x)
6 If necessary strips of paper to be tested
(55 x 340 mm, 4 -6 strips per set of
inks)
7 Inks to be tested
8 Densitometer (if required)
9 Lint free rags
10 Cleaning naphtha
Printing force
Printing speed
Interval times between 2 colours
Ink film thickness
The numbers 1 thru 5 are available at IGT Testing Systems.
The numbers 3 thru 4 can be obtained as Wet-on-wet Printing Set
for AIC2-5T2000, article number .....
2. Attach a test strip on the sector.
3. Turn the sector into starting position.
4. Apply 2.4 µm of both inks to two separated segments of the
inking unit and distribute the inks (indication: 2.4 µm for art
paper). See note 3 or the manual of the inking unit.
5. Place the printing discs on the printing disc shafts of the
segments of
the inking
unit and ink
the discs
during the
preset time.
6. Take the
discs from
the inking
unit and
place them
on the
printing disc
shafts of the
st
tester: the 1
colour at the
top shaft and
nd
the 2 colour at
the bottom shaft.
7. Press one of the side buttons to start the motor.
8. Move the printing discs into printing position against the test
strip.
9. Press the other side button as well to make a print (also keep
both buttons pressed during the interval time).
10. After the sector has stopped in the end position, release the
side buttons.
11. Move the printing discs out of printing position
12. Remove the test strip from the sector.
13. Take off the printed paper strip from the sector.
14. Remove the printing discs from the tester and clean them
with the rags and naphtha.
15. Clean the rollers of the inking unit or use the next segments
for the following test.
16. Repeat the points 2 thru 15 for the next test strip in the
opposite colour sequence.
info@igt.nl Internet: www.igt.nl
IGT AIC2-5T2000
Version : October 2003
710
466.410.100
(466.003.003)
402.333
404.009.004
408.200 or 408.400
625 N
1m/s
at choice
2.4 µm
Fig. 1: wet-on-wet printing