WHY ARE WHITE INKS DIFFICULT TO WORK WITH?
All professional printers eventually come up against the metering challenges of white inks. Throughout the industry, white inks are notorious for being inconsistent and requiring frequent changing of doctor blades often. The longer a doctor blade lasts, the more expensive it is in many cases. Weighing the cost of a doctor blade vs. the cost of press downtime is as issue printers and coaters deal with constantly. The issue with metering white inks is actually a little more complicated than just buying the right blade.
GATHER PROFESSIONAL SUPPORT:
First and foremost, ink, anilox, and doctor blade suppliers should all be consulted in a cooperative manner. When everyone knows the details of the scenario, a more comprehensive solution can be attained. Having end seal suppliers involved can also prove useful. Most people working in these industries are either printers themselves or have at least been involved in the print industry for some time – so they will most likely be able to relate to your specific challenges.
COMMON SENSE ANSWERS:
Having your press and chambers in optimum condition can provide big results. By taking care of the mechanical issue in order to optimize the setting of the chamber at the lowest amount of pressure possible, run times for both doctor blades and end seals can be significantly extended. By simply taking the extra 10-15 minutes to clean a deck and an extra 2 minutes to set it lightly and evenly, some issues may be completely resolved. It’s definitely worth investigating before moving on to more involved solutions. CAREFUL SET-UP AND MAINTENANCE: Maintaining the proper viscosity and ink/vehicle/solvent ratio is another very important consideration when it comes to working with white inks. Often, when issues come up with white inks, even though other printing functions have been problem-free for some time, viscosity and solvent ratios are a primary reason behind the problem.
In most cases radius tipped blades are used for any roller under 600 lines per inch (lpi). Switching to a radius tip blade from a lamella or bevel blade may help or eliminate many white ink challenges. Increasing the thickness of the blade may help as well. However, remember, the more steel you throw at the problem, the more it increases anilox wear – so proceed with caution. Many printers elect to use a coated blade to address the wear, quality and press downtime issue with metering white inks. These coatings are generally significantly harder than a standard doctor blade but not quite as hard as the ceramic anilox roller itself. Other ingredients in the coatings can help address coefficient of friction values (COF). These coated blades can greatly increase doctor blade wear but should also be installed in the chambers properly and care should be used setting them. They are significantly higher in cost, though proper care when using them can increase the return on your investment. In some cases, plastic blades have been used with promising results. While this has not proven to work across the board for consistent metering, it may be worth looking into.
Download the full White Inks White Paper for more information.
Source: FlexoGlobal Blog