On press cleaning is easy?

Cleaning on press is probably seen as one of the easiest cleaning processes in screen printing. After all, you just take a rag/tissue soaked in solvent and re-open the mesh ready for printing. William Shorter of SPT Sales + Marketing GmbH takes us through this process and explains the technical problems that can occur.

When it comes to screen cleaning on the press, the operators look for the cheapest press wash that has a quickest evaporation rate and cuts through the dried inks quickly. Why do they want this? Time lost on press can affect the profits, the quicker they can get back to printing, the more money can be made. Is this false economy though?

General purpose press wash solvents tend to be rich in solvents such as Cyclohexanone, Solvent Naphta’s and other petroleum distillates (check section 3 of your safety data sheet and don’t forget to pay attention to their hazard classifications, DANGER!) and it is these solvents that break down the dried in inks quickly and open up the mesh. They also have a very low flash point and evaporate very quickly. They really do meet the expectations of the press operator’s needs.

However, low flash point solvents can also be a risk and there is a European directive that stipulates that on press wash solvents should have a flash point of greater than 40°C to avoid the possibility of a fire. If you fail to comply with this directive and subsequently have a fire in your factory (not uncommon especially with the use of flash cure units in textile screen printing), your insurance will no longer be valid!

Complications from on press screen cleaning typically do not show up until later on in the process and most commonly at the reclamation stages. It is here that the headaches begin and the extra costs that will affect your profits are often over looked. That fast evaporating press wash that has been excellent at opening up the mesh is also very effective at getting into the emulsion and has changed its properties (Does the stencil on the print side show signs of whitening? If it does, this is a sign of acetate fusing). Your screen printing emulsion that was originally easy to reclaim with your stencil remover, has become very difficult to remove unless you increase the concentration of your stencil remover or use lots of elbow grease to break down the stencil with your brush or scrub pad. This means, you are using more screen cleaning chemicals and the process of cleaning the screens is taking longer. This fusing often results in a layer of the emulsion being left on the mesh and the only way to remove this is to use Haze Removers. Continued use of high caustic and fast acting haze removers can damage that all important mesh which governs your ink deposit, increasing the likelihood of you experiencing a split screen during printing.

Heavy ink staining is also a symptom from the use of fast evaporating press washes, the solvent is evaporating very fast and the binders from the ink are being removed and absorbed into the rags. Where as the pigments and the dyes of the inks are left behind and start to bond to the mesh. Slower evaporating solvents reduce the likelihood of this occurring and you end up using less rags, less solvents and add approximately 30 seconds more to your cleaning time. But reduce the need for high caustic haze removers.

Take a look at your press wash that you are using today and ask yourself. Is the press wash solvent that I am using free of Cyclohexanone, Solvent Naphtha and petroleum distillates? Have I added costs into my process further down the line and created a false economy in screen printing? If this is true for you, then now is the time to change and have a bigger impact on your profits moving forward than purchasing the cheapest press wash in the market place.