Rough Ink Surface
- Post by: Bill Hood
- September 1, 2020
- Comments off
The number one complaint in the textile segment of screenprinting is that the ink deposit is not smooth. Although you surmised that the ink attributed to the problem, I would venture that the problem may lie elsewhere.
Several things can cause a rough ink surface. First, let’s get the ink out of the way. Inks formulated for resistance to bleeding often have a small amount of “blowing agent.” The blowing agent is also used to make puff inks. When using inks with a blowing agent, you should expect a slight puffing effect if you over-flash or over-cure only slightly. This puffing can result in a rough ink surface. Even if the outcome is very subtle, it can be aggravated by multiple flashing and subsequent overprinting.
Related: Rough Ink Surface and Fibrillation
Low Tension Mesh
One of the most prevalent reasons for rough ink surfaces is the use of stretch and glue wood screens that have lost their tension. Any screens with a tension level below approximately 20N/cm2 should be replaced or stretched with a new mesh. Usually, it is less expensive to replace the screens in the long run with retensionable screens.
The loose mesh will sit in the wet ink deposit after being transferred to the substrate. Some ink is pulled back towards the mesh when lifting the screen, creating small peaks for each mesh opening. Using 158 mesh creates almost 25,000 of these peaks per square inch and a very rough surface.
All textile printing requires a certain amount of off-contact. Off contact refers to the distance between the mesh and the substrate and is usually only just a bit more than the thickness of the ink deposit. However, more space is necessary when using low tension mesh to pull the loose mesh from the ink deposit while the ink is still flowing. If the off-contact distance is too small, the mesh will sit in the wet ink deposit after transfer.
Related: Eliminating Rough Ink on Textiles
A print-flash-print technique is necessary when the screenmaker chose a high mesh count to lay down a sufficient amount of ink in the first place. However, there are times when an incorrect screen gets to the press and needs a print-flash-print technique. If the time required to make the double stroke was more than the time necessary to replace the screen, it might be time to consider exposing the correct screen while the operator prints another job.
When using a print-flash-print technique, the second print only exacerbates the roughness of the first print. For instance, if the ink has small peaks on the first print, the second pass only increases the peaks’ height.
Small Mesh Opening
Think about what is happening within one single mesh opening. Keeping in mind that what is happening there can be multiplied by 25,000 to create severe problems. Even with perfect ink, off contact, flood, and squeegee control, you can still get a rough ink surface whenever there are peaks. If an ink doesn’t release quickly from the mesh, roughness may appear. When a stencil is too thick, it may be challenging to create a proper ink release without high tension levels.