Best Practices: Plate Choice: Photopolymer Versus Elastomer
When assessing the differences between photopolymer and elastomeric printing plates, there are several aspects to consider for each, including materials, speed and cost. But the biggest difference between the two is when creating the image, one requires addition while the other necessitates subtraction.
Image Building and Image Burning
With photopolymer plates, the more common of the two, exposure to UV light cures the image, with the rest being removed via washout or a thermal process, thus building the image onto the plate. When working with elastomeric plates, a laser is implemented to directly engrave the image into the material, removing any surface area that will not be printed.
While one process is not necessarily better than another in terms of print quality, package printers will need to be aware of which process best suits their needs. According to Ryan Vest, the global director of innovation for MacDermid Printing Solutions, it is essential to understand the interactions between the plate, ink and substrate, regardless of the technology employed.
Vest explains that an advantage of elastomeric plates is their ability to withstand highly aggressive inks, such as those that contain a high quantity of acetate or that use unique carrier solvents. However, in flexographic printing, Vest says that most printers are using inks that are compatible with multiple plate materials.
“The good thing in the flexo world is there are a lot of people out there who use inks that are compatible with a wide variety of materials,” he says. “We seldom come across those applications where solvent resistance matters a lot.”
According to Brian Cummins, national technical and product manager for DLE elastomer technology for Max Daetwyler Corp., the removal of material via laser engraving can be an advantage in terms of consistency and repeatability.
Because the laser used to engrave the image is the same each time, it removes the variable of the UV light exposure that printers depend on with photopolymer plates.
“Direct engraving gives you consistency, repeatability and it gives you flexibility,” Cummins says. “Every print manufacturer can create their own dot for whatever substrate and whatever type of ink they’re using. They can do all that with one type of material. With photopolymer, each type of ink and each type of substrate gets a different type of photopolymer material.”
Another major difference to keep in mind, says Rich Emmerling, a technical manager with Flint Group Flexographic Products, is that photopolymer plates are available in a variety of forms and provide a wider selection to printers using these types of plates.
“Photopolymer plates are available in many different thicknesses, from many different manufacturers and in many different hardnesses,” he says. “There’s a much broader variety to choose from for the printer.”
Advantages and Applications
Because both types of plates work well for their intended purposes, understanding what each type of plate is best at can help drive decision making in selecting the type of plate to use.
For example, Vest explains a photopolymer plate is likely a better choice when printing a corrugated package. Elastomer material is typically available only in higher durometer with limited exceptions, Vest says, which can be inhibitive when printing on corrugated substrates. Additionally, elastomeric materials, which are typically bound to a sleeve, are suitable for presses that can accept this construction only.
“With corrugated board you require a much softer material so that you don’t crush the flutes … and damage the strength and durability of the box or package that you’re printing on,” he explains.
Cummins explains however, that elastomeric plates are excellent options when printing anything with varnishes and coatings. He says it is also a great option for dry offset printing, particularly when printing on metal for cans or on plastic.
“The dot gain is minimal compared to photopolymer due to the impression that they put on those type of presses,” Cummins says. “We can hold a half percent dot with minimal dot gain.”
While these applications are where elastomeric materials shine, Cummins says they have other advantages as well. One advantage comes in reducing waste. With elastomer material, Cummins explains that since the material is not affected by UV light and nothing has been found to cause it to swell, there is a reusability element to it.
He says that once a plate is engraved, the remainder can be cut away, added back onto the drum of material and can be used for engraving again, substantially reducing waste percentage.
Emmerling explains that there have been several advancements for photopolymer plates in terms of ink laydown. This stems from a recent advancement in being able to add flat-top dot capabilities to the plate material itself, using a textured surface.
“The textured surface on these flat top dot plates provide more surface area for the ink to collect, so it lays a slightly thicker ink film down and gets rid of the pinholing issues you see in the flexible packaging industry,” Emmerling says.
Because elastomeric and photopolymer plates use such different equipment to create images, cost concerns can arise if a printer wants to switch between using one versus another.
For example, if a user of photopolymer plates wants to make the switch to elastomer, obtaining the laser engraver as well can be costly, especially when considering the expenditures put in place for all of the equipment needed to manufacture photopolymer plates.
However, Cummins states that the prices of laser engravers have come down and are comparable to the price of a CDI imager. Cummins also says that a common misconception about elastomeric plates is the idea that separate software is needed.
This is not the case, Cummins explains, and reiterates that if a printer is using Esko front end software, the engraver can read the same .tiff file that any other workflow can and no additional software needs to be acquired.
“They can keep using their Esko front end system and they can keep using whatever RIP that they want; the engraver just needs a .tiff file,” he says. “The engraver doesn’t change. A lot of people automatically assume they have to buy extra software.”
With quality fairly consistent across both types of plates, it’s the variables such as cost, applications and speed that should affect decision making. Understanding which plate best fits the most common jobs being run is essential to making the decision of what material to use.