Part 7 - Improving Plate Longevity and Reuse
Sustainability can come from environmentally friendly raw materials as well as the elimination of waste in your manufacturing process. In printing it can also come by increasing plate longevity or the ability to reuse plates multiple times on press. Photopolymer plates are a costly investment, so we want them to last as long as possible both on press and in storage.
In this article, you will find some tips and tools that will offer you proven means to increase plate longevity on press. You will also find some suggestions to improve highlight reproduction, obtain excellent solid ink density and improve ink transfer along the way. All you need to do is optimize the process around you by selecting manufacturing variables that truly compliment the printing plate.
So how does one begin this pursuit for increasing press uptime and plate longevity? For starters, consider selecting a thermal or environmentally friendly plate offering. Whether you prefer a flat top or a round top dot, you can select the firmness or durometer of the plate you wish to use.
Here are some common prepress and platemaking variables that you should consider evaluating in your manufacturing operation to improve plate longevity on press.
Select a minimum dot size on the finished plate that offers a stable, consistent, and repeatable dot. This can be achieved by selecting the proper bump curve and highlight screening options. Keep in mind that dots which are too small or not properly formed, as seen here, will fold over when put under impression, leading to premature plate wear and dirty printing. There are prepress tools out there to help make this process easier.
When selecting an optimal cushion/plate combination, you want to use the firmest tape possible (density) that offers the least amount of impression without influencing dot gain (slur). If your tape of choice is too hard you can introduce excess pressure and wear on your plate. Contrary, if your tape is too soft then the press operator might feel the urge to over impress the plate to fill in any unwanted print voids.
It is best to clean your plates (solids) with 100% alcohol and a lint-free cloth to remove any third-party debris from the print surface prior to inking. This once-over removes any contaminants such as dust and debris, oil and grease due to handling, remains, or contamination from plate cleaners, press sprays, lubricated press wipes, hand sanitizers, or lotions.
Have you ever mentioned that your used plates no longer come up to color, or they fill in with ink after only a short while on press? If so, you should revisit your plate cleaning, handling, and storage methodologies. Keep in mind that once a plate has been subjected to excessive ambient UV light, ozone, or a surfactant, the ink transfer characteristics will dramatically change. So how can we help this?
Please use a soft sponge or natural bristle brush in conjunction with a lint free rag when cleaning plates. DuPont™ Cyrel® Solutions discourages the use of shop rags, nylons, or stiff brushes as they can prematurely. damage your plate.
Please be sure that your plate cleaning chemistry is compatible with the photopolymer plate. Certain plate cleaners are either absorbed by or deteriorate the printing plate, leading to poor ink transfer and an overall loss in solid ink density.
Whether you choose to hand wash your plates or use an automatic plate cleaner be sure that the cleaning solvent is compatible with the printing plate. Aggressive cleaning agents have been known to swell and soften the printing plate leading to poor print reproduction. Please also ensure that the printing plate is completely dry prior to storage to avoid solvent retention, cracking or curling of the photopolymer.
Ideally plates should be stored dry, flat, and interleaved with foam. Plates should also not be stacked over 6-inches high as photopolymer plates on the bottom of stack can emboss due to weight of stacked plates.
Flexographic printing plates should be protected from any external influences. Ambient UV light changes the print surface of the plate, making it less ink receptive and leading to print inconsistencies. Storing plates in a UV free environment such as in drawers, boxes, tubes, or opaque folders is recommended. The plate should also be protected from temperature extremes, sources of ozone, open doors, heat, vents, or electrical discharge.
Here are some other tips that could improve press uptime and lower overall waste in your manufacturing process.
- Work with your ink supplier of choice to select a proper ink dispersion and formulation. Too thick or thin of a viscosity, in addition to too high or low of a pH may cause dirty printing, premature plate wear, and excessive dot gain. .
- Ink temperature should be consistent per the ink manufacturer’s guidelines. Too hot/cold of an ink could lead to ghosting and other image transfer problems.
- The use of press/plate sprays or silicone for image transfer is not recommended. Such sprays inhibit ink transfer, contain oils, contaminate inks, and hide the root cause of most printing problems.
- Establish a preventative maintenance program for doctor blades. Doctor blades should be changed out regularly on a schedule rather than on an as needed basis.
- Understand the condition and capabilities of your anilox rollers. The function of the anilox roll is to control the wet ink film thickness delivered to the surface of the printing plate and should be audited on a regular basis.
In closing, work with your suppliers. Ask your DuPont™ Cyrel® Solutions Representative how we can help you achieve improved plate longevity on press. Visit cyrel.com for more!
The Sustainable Platemaker Series
Part 1 - Next Generation Plate Making and the Pursuit of Green
Part 2 - Plate considerations when working with sustainable inks and substrates
Part 3 - Changing the mindset: thinner flexo plates deliver quality and sustainability to the corrugated market
Part 4 - Plates, Plate Packaging and the 5 Rs
Part 5 - Reducing Plate Waste
Part 6 - Plateroom Habits that Affect Sustainability
Part 7 - Improving Plate Longevity and Reuse
Part 8 - Driving Pressroom Sustainability with Prepress Innovation