The industry is always looking for ways to predict how long photopolymer flat plates and ITR (in-the-round) photopolymer sleeves will last in a press. How many times can plates and ITR polymer sleeves be reused?
From experience, there is no standard to the predictability of plate life or the reuse of plates or sleeves. Twenty years ago, the goal was to get 1 million feet of production on one run or over several runs. The next question becomes: Why can one printer get 2 million feet of production and the next printer with the same plate material only get 500,000 feet? Every printer you ask will give you a different number it expects to get.
The problem is there are so many factors that influence the life of photopolymer plate material. It is completely up to printers and the choices they make, based on their needs.
Plate Variables Revealed
Some of the factors that influence plate life are:
- Plate material used
- Type of ink/coating being used (solvent/water)
- pH, in the case of water-based ink
- Type of solvent/blend
- Plate mounting tape
- Plate durometer
- Plate cylinder and anilox roll concentricity (TIR)
- Anilox roll surface characteristics
- Substrate surface characteristics
- Plate demounting and removal techniques
- Type of plate cleaner used
- Plate storage conditions (exposure to ozone, UV and temperatures in storage area)
- Mounting room conditions
- Plate lift
- Design layout
- Gear pitch line
- Deck setting or impression setting between plate and anilox
- Mismatched speeds—plates to impression cylinder/anilox to plate/plates to substrate
- Harmonics (bounce)
- Plate processing conditions
- Press speed
- Press maintenance
- Reusing mounting tape
- Backing impression off after the start of the run to accommodate plate swell
This list has many important operating conditions and things to think about when managing your own facility. Flat top dots and surface screen technology have also improved plate life in many operations. If you are not using these technologies, it may be worth looking into for your process. This list can always be expanded; the factors affecting plate life are many and deserve some careful study.
Optimize for Fit
Performing press optimization for the best run conditions of the press is needed to identify best plate material. In today’s environment with the constant changing of technologies in both the plates and press accessories, it is more important than ever to work on continuous improvement of the plates. The payback can be huge on quality of print and life of the plates. Therefore, allotting press time for plate testing is critical to success.
Photopolymer ITR sleeves can be a way to improve both the quality of print and plate life. It is normally expected that you will see two to three times the life of flat plates. If you take a job that you have a history of running and track the plate life from flat plate to polymer ITR, it’s not uncommon to experience better life using polymer ITR sleeves when run under the same conditions as flat plates. The upfront cost comparison does not show the total picture until the total cost savings in plate life and runability is reviewed.
Today’s photopolymer sleeves have many advantages that offer cost savings and quality improvements. There are different durometer plate materials that can be used. Some processes use an open cell mounting tape so that the tape can handle plate bounce better. The tape also does not collapse as easily from over impression. Some printers will reuse the close cell mounting tape to cut costs. This does shorten the life of the flat because the cushion is gone. Manufacturers have a number of different durometer tapes to match the printing conditions.
Polymer ITR sleeves also have flat top dots and HD screening can be applied. On long runs and short runs that require the sleeve to be taken on and off the plate cylinder, plate edge lift is eliminated. ITR does not have to be mounted, saving time, material and labor costs. Stripping flat plates with the plan to reuse can result in damaged plates not being discovered until remounting. Then new plates have to be produced, delaying the press schedule. The ITR of today can be used on any type of substrate, allowing all markets to take advantage of its benefits.
Plate life comes down to the handling and care given to the photopolymer material. From plate processing to plate handling before going on press and after being in the press, to running in the press—all steps make a difference.
Plate Prep & Placement
Below are some of the recommended cleaning and storage tips for photopolymer plates. It is widely known how important it is to have clean plates to run quality print.
- Plates should be cleaned before mounting. The solvent that is used to wash the plates off after the plate making processing should be removed for better adhesion to the mounting tape and better ink transfer
- The plate mandrel or sleeve you are mounting should also be cleaned before placing the mounting tape on the surface
- After mounting onto the plate cylinder, the plates should be wrapped with opaque film, often times black film. When the film is wrapped around the plates, minimum pressure should be used. Any exposed backing should be avoided, or corn starch should be applied to take the backing tape tack away. Caution should be used when wrapping the film around the plates. If wrapped too tightly, it will leave low spots in the plates. Wrapping the plates after mounting will help the plates to adhere to the backing and protect the plates from the ozone and UV light
- Plates should only be cleaned with a soft brush, horse hair brush, sponge or lint-free soft rag. The plates should be air-dried or blotted with a lint-free rag. When cleaning plates, great care needs to be taken not to damage the dots of the screens
- When the job is complete, if the plates are going to be stored for the next run, they should be cleaned as soon as possible to keep the ink from drying onto the plates. This is especially true for water-based inks. Water-based inks are designed not to break back down. Once water-based ink hardens, it is required to scrub harder, risking damaging the plates
- Automated plate cleaners are also an excellent method to ensure increased plate life. These devices clean plates in a thorough and consistent manner, allowing for increased utilization and optimal conditions in which to store the cleaned plate
- Before storage, the plates should be allowed to dry, so all the solvents can flash off. If the solvents are trapped in storage, it can lead to plate swelling and other damage
- In the case of photopolymer sleeves, after cleaning the sleeves, they should be carefully put back into the core packaging the sleeve was received in. Without its original packaging, photopolymer sleeves should be wrapped in the same manner as flat plates
- Flat plates should be stored in the flat to be kept out of the UV light and away from any ozone that is present. Best practice is to place paper or the foam from the packaging the plates came with, in between each plate. Plates should not be stacked more than 6-in. high and kept away from any heat source. Plates should be stored between 40 degrees and 100 degrees Fahrenheit
With good care and management, today’s plates can last far longer than they could just a short four or five years ago. Working closely with your plate supplier as technologies change, you will benefit from the continuous improvement of print quality and plate life that will give you a competitive edge in your chosen market.