Ink transfer time

The color transfer time is the shortest interval from the moment of pickup to the complete color transfer by the pad and is the most important measurement parameter in pad printing.

 

When the ink cup moves away from the printing image and releases the recessed image filled with ink, the thinner in the ink begins to dry, making it tacky. The pad lowers onto the cliché and picks up the ink. When lifted, it carries the ink along. As soon as the underside of the ink layer is exposed, the color transfer time starts. The thinner on the exposed side evaporates, which also makes the ink tacky there. When it is tacky enough, the pad completely transfers the ink upon contact with the product. The measurement ends when the ink is entirely transferred.

 

Why must the entire ink be transferred?
In most cases, it is necessary for the pad to transfer all the ink to achieve a homogeneous ink film. The ink remaining on the pad is missing from the print. Ideally, the cleaning tape should show no ink residues after cleaning.

 

Why is the color transfer time so important?
It plays a crucial role in optimizing the printing process. Often, a predetermined quantity must be achieved. In this context, not only the maximum speed of the machine counts – the color transfer time of the ink used must also be considered. A fast machine offers no advantage if the ink cannot be transferred quickly enough.

 

What should be done if the entire ink is not transferred?
First, the waiting time before ink release should be increased until the point is reached where the entire ink is transferred.

 

Is this value constant?
No, the waiting time varies depending on the air temperature and humidity, as the thinner evaporates faster or slower.

 

What happens if the waiting time is too long?
If the waiting time is extended too much, too much thinner evaporates, making the ink too dry for a successful transfer and preventing it from being released from the pad.

 

What should be done if the color transfer time is too long and the required production count is not reached?

  • An alternative ink line or a faster-evaporating thinner (accelerator) can be used.
  • The pad can be blown with air to accelerate the evaporation of the thinner. However, this method is rarely used, as it is not fully reproducible – even a slight change in nozzle position or air volume affects the process.
  • A lesser-known method is to reduce the ink layer thickness by using a cliché etched at a shallower depth. A thinner layer dries faster, thereby shortening the waiting time in the air before ink release. Alternatively, the pad may dwell directly on the product rather than waiting in the air – for some inks, this method is more efficient and shortens the transfer time.