Never approach problems thinking there is a “one-size-fits-all” solution. This philosophy is key to success in providing solutions for printing white ink on flexibles.
Innovation after innovation has focused on printing whiter whites for years. The story continues to this day. The goal: provide customers with the benefits of optimized white printing. Namely:
- Improved overprints and trapping
- Improved color saturation
- Improved consistency in color matching
- Reduced ink consumption
- Increased press speed
Application experts help printers optimize their workflows for white ink printing every day. How? By analyzing plate making, workflows and printed samples to help create a path forward. To find the best printed white solution, it’s essential that plate manufacturers work with customers to set goals, choose the right package, and finally, optimize the package for their workflow.
One such manufacturer, MacDermid Graphics Solutions, has offered innovations focused on printing whiter whites since 2014, including its collaborative project with CSW Inc, launched at FTA’s FORUM 2014—Digital MWW, a plate optimized for white ink in combination with advanced screening.
We continue our innovations today. Most recently, we’ve found success with LUX ITP M, LUX ITP 60, and Digital RAVE, exposed with UV LED in combination with further advancements of surface screening.
Set Your Goals
Understanding where you are and knowing what you want to achieve is the first step. For white ink, you must decide if you want to increase opacity, improve ink coverage, improve print performance or a combination of all three.
- If you want to increase opacity or improve ink coverage, what is the target?
- For improved printability, are you focused on efficiency, ink savings, productivity or increased quality?
Once you set your goal, it’s time to plan. Are there practical limitations that need to be addressed?
You must factor in the white ink dry rate for opacity and the ink film thickness you will use. These factors affect ghosting or rewetting, cost, and possible solvent limitations. Your press speed and the anilox used are also factors that make a difference in white ink printing.
The Right Package
Remember, there is no one-size-fits-all solution, so when a customer comes to a supplier with a white ink problem, the partner must work to find the best print package for that client’s needs. The print packages include the following:
- Surface screening
- Mounting tape
- Press speed
Mottle and opacity are two points we measure to determine the effectiveness of a package. For mottle, we measure the density variations in a sample where white density variations down to zero are prioritized over higher density values. Opacity is calculated by the average size of the pinholes in the sample and excludes values smaller than the human eye can see.
We’ve tried multiple combinations to optimize white ink to reduce mottle and increase opacity. To analyze our tests, we created a calculation called “The White Function.” The White Function is a calculation of mottle, or mottle and opacity.
In Figure 1, we focus on three combinations—standard, reduced mottle and a package optimized for both mottle and opacity. The goal was to find a combination with a mottle less than six and an opacity greater than 54.
- For the standard combination, we used a 250 volume anilox with a medium-durometer plate, hard tape and no surface treatment. With this combination, we measured a mottle of 20.09
- In the reduced-mottle combination, we used a higher anilox volume (360), a soft durometer plate, the same hard tape and applied a surface treatment. Changing those same plate characteristics resulted in dramatically reduced mottle and pinholing
- We then used a lower volume anilox (250), a soft durometer plate, hard tape and a surface treatment. This combination seems to be ideal and could potentially become a “game-changer” when it comes to absolutely smooth, pinhole-free white ink coverage on transparent film
Continued advances in plate technology and surface screening make choosing a technology package easier, but optimizing the technologies makes them more effective.
To optimize, you must set values for the technology available, press data availability, anilox availability and their condition, and ink requirements and maintenance. After setting the optimized values, you must verify the results. To do this, you should determine the appropriate mask value and tolerance based on printed results for plate quality control.
To properly optimize the trials, you must set the correct power setting for each screening technique you would like to use. For example: Ablation power varies, depending on the screening used.
- For 3x3C, decreased power is used
- For WSI and WSI-White, once the power level is set to achieve the density value of 0.30 at the 50 percent tone, the pixel boost settings work in opposite directions
- WSI uses a lower boost and WSI-White uses a higher boost. Lower for WSI, 200 to 245 range and higher for WSI White in the 320 to 355 range
Our test shows the production window is wider using 3X3C. For the 3x3C testing, the power test is in 0.2 joule increments from 2.8 to 3.8. Plates are then made with strip tests and printed with various anilox configurations (see Figure 2).
The print samples are read for coverage, mottle and opacity using the proper analytical tools, (opacimeter, spectrophotometer, or flexographic plate analyzer). Choosing the optimized settings results in a significant quality increase in all three aspects, as shown in Figure 3.
As printed white screening technology has evolved, plate manufacturers, like MacDermid, have been true partners that customers depend on to transform their printed white workflow. From early plate development and screening options to today’s latest technology, we have a procedure to optimize your printed whites that will work with your workflow.