Flexo printers are facing many challenges every day, with the flexo printing process itself often being one of the biggest of them all. This is caused by the huge amount of variables involved. And printing on corrugated makes it even harder to achieve the required result. Keeping the flow of ink consistent is key to getting it right.
Flexo printing on corrugated differs from other flexo processes in some important aspects. First of all: the substrate. Corrugated is more absorbent in comparison with plastic film, alu foil or other special papers. And it is also a material of poorer quality, releasing dirt into the system affecting your ink and your aniloxes – and eventually your print. Secondly: the width of the machines involved. These presses are 2,500 mm in width as common, making the process more difficult to control. And last but not least, the printing ink: almost all flexo inks for corrugated are water-based.
Substrate and ink
Let’s have closer look at the issues concerning the substrate and the inks. The biggest challenge in flexo is to achieve and control the required fixed densities in order to guarantee print quality. When you are applying a specified ink volume to a non-absorbent paper (like coated paper), the ink remains on the surface and the density will be higher than applying the same amount of ink to an absorbent corrugated paper, as the ink will penetrate the paper and the colour density will be poor. Also, the original colour of the substrate will affect the end result. If you are unable to bring the right amount of ink in a correct way to the paper, the required colour density cannot be achieved.
Dirt disrupts the process
So, getting the required ink volume to the paper in a controlled manner is crucial. Dirt-particles, released by corrugated substrates, are the main disruptors of this process. Apart from affecting the printed image quality on the substrates surface, this dirt also interferes with the consistent ink transfer to the plate, as it clogs the ink cells of the aniloxes and thus disturbs the flow of ink
Keep it clean
As dirt turns out to be one of the main disruptors in the process of flexo printing on corrugated substrates, the solution lies in keeping it clean. Here are some expert tips to getting it right and achieve the best results:
1) Choose the best paper
Although this will often prove to be more expensive in price, cheaper paper may turn out to be more costly in the end because of requiring higher ink volumes and thus causing other problems like drying capacity or wash boarding effect.
2) Select the right inks
In water-based inks, pigmentation is the factor that makes all the difference. Make sure to test your inks on specifications like density, viscosity, drying capacity and pH value. Again: the right ink may be more expensive, but may save you on time and costs.
3) Use the right anilox
This is critical, as your anilox is key to transferring the ink from A to B – the plate – and, as a result, to C – the substrate. If this fails, printing according to plan will remain an issue. Following screen types may be considered while printing onto corrugated board:
High quality flexo post- and preprint, consider open structures like GTT for more consistent ink-transfer (between jobs and over a longer period of time). Click for gtt profile specifications
Standard work, the 60 degrees closed-cell hexagonal is still a very suitable cell type -> click for conventional anilox specifications.
LongCell patterns are also an option, however, it depends very much on the application which screen and volume combination to choose; for a specific advice, contact your technical anilox expert.
4) Keep your aniloxes clean.
The surface of an anilox consists of tiny holes – the ink cells – that can easily get clogged by dirt-particles. Hardened ink clogged into the cells, is like stone and can damage the surface of your anilox. Besides, it decreases the amount of ink that can be transferred to the plate. Although cleaning your aniloxes in the right way does take some time – and printers are always short on time – you will find that it does earn you great benefits. Dependant on the usage of your anilox, a once per year deep-cleaning is advisable. It is also extremely important to know the status your rolls are in before you start printing. Every 12 months you should perform an audit of your roll/sleeve inventory.
Find out more about the challenges of printing on corrugated substrates. Understanding the process helps you in getting it right much faster: saving you time and costs and earning you better quality. Experts from Apex are ready to advice and support you on the right type of anilox and how to keep it in the best condition for as long as possible.
We developed a Use & Care Guide with detailed advice on the above mentioned topics. You want one for free? Download the guide here below!