This article is part of the FLEXO FLAW FIXING series

Blocking in flexo printing occurs when adjacent dots are connected together during the transfer process, resulting in a bridge between them. A blockage is most common in the mid-tones and the highlights, about 40% and 10%, respectively.

Light pressure printing plays a significant role in print quality. One crucial factor is adjusting the pressure when printing.

Inking mechanisms of flexo printing machines are rubber roller and anilox roller inking systems, blade-anilox roller inking systems, and closed blade inking systems.

Below are the significant factors that cause blocking in flexo printing.

  • The surface of the substrate is pulled off the powder. The shape of the dot is irregular.
  • The printing speed is too low.
  • Improper adjustment of the angle of the doctor’s blade.
  • Heat and weight are the two leading causes of ink blocking in the summertime. Prints are more likely to stop when temperatures are higher.
  • A glossier ink is also more likely to block. Flexible, soft inks are more susceptible to clogging than rigid inks. Curing fast-curing inks tend to cause less heat buildup during curing, leading to fewer blocks than slow-curing inks. 
  • Ink films can be made more flexible and less likely to clog by increasing the curing level during the processing process. It is more challenging to block ink when the curing level is increased.

 Adjustments to Prevent Ink Blocking several methods exist to reduce heat within stacks, but heat can be a constant battle throughout the summer. Reduce the amount of energy exposed to the print (while ensuring a complete cure occurs) to reduce the amount of heat buildup in each stack.

 Additionally, cooling prints before stacking will help lower the amount of heat. The problem of blocked ink is caused by pressure points. By stacking fewer parts together in smaller stacks, using spacers within a stack, or vertically stacking, you can reduce the weight of the ink film. It is easier to prevent blocking if piles are stacked flat and in even piles (see picture).

Reducing ink gloss can help remove ink-blocking. An additional 5% by weight of this product allows the ink film to have some “tooth,” preventing 100% ink-to-ink contact; it does not negatively impact gloss while still reducing the likelihood of ink blocking.