Lab Report on Wet Trapping Lab
Lab Report on Wet Trapping Lab
To ensure proper trap the ink tack units vary by one or two units from printing unit to printing unit. The highest amount of tack should be on the first unit proceeding to lesser tack values as the paper travels to the further printing units. On the other hand as you progress printing units the ink film thickness should increase. The reason for this is because thinner ink films will not trap properly on thinner ink films.
Optical density is used as a checkpoint, therefore color strength of the ink must be carefully controlled.
Variables :
Setting- is the immediate buildup of viscosity after the ink has been applied to paper
Essential to avoid setoff.
Many printers will add quickset varnish to the ink in the second printing unit to promote setting, and trapping on the first down ink
In gravure and flexographic printing inks do not set, other methods are needed to trap the second down ink, the use of dry trap is required.
Tack- is the stickiness that can be observed when a printer taps out a thin film of ink on a slab or other flat surface
It is best to have the ink as tacky as possible without causing the paper to get damaged. Thicker tack will promote better printed lines and halftones. To find the resistance that it takes an ink film to split can be calculated by steffans equation:
F=VSA/t ³
Where F = force
V = viscosity
S = speed of the press
A= the area of film being split
t ³ = the cube of the thickness
It has been found that a thicker ink film is harder to split than a thicker ink film
Offset lithography uses the thinnest ink films therefore this process places the greatest amount of stress on the substrate being used
The graph shows that by increasing the amount of ink on the press to be printed will only increase the amount of ink on the substrate to a certain point. By this increase, the ability for the ink to be separated from the plate and the substrate is increased. When enough ink has been added to print a full solid, further additions of ink do not increase the area of contact between the ink film and the plate but, instead increase the thickness of the film and reduce the amount of force required to remove the paper.