by Melissa Donovan
Analog printing technologies are favored in print shops around the globe. Flexographic (flexo) printing is commonly used for longer, static print runs. There are three types of flexo presses—central impression (CI), inline, and stack. The configuration or mechanical build of each is what sets them apart physically. This influences why certain substrates are run on one type of press over another, as well as common applications produced.
CI, inline, and stack flexo presses differ based on how their print or color stations are placed in the overall setup of the machine. The variations in build effect features such as speed, printer register, color gamut, and even finishing options like coating or laminating.
CI—A Planetary Setup
A CI flexo press consists of one impression cylinder or drum, with the print stations positioned around the cylinder. Michael R. Pfaff, VP, web carton converting, Heidelberg USA, describes the setup as “print stations arrayed around the impression roll in a planetary fashion.”
According to Rodney Pennings, director of sales, Paper Converting Machine Company (PCMC), CI presses are commonly used for longer, roll-to-roll production runs at higher speeds. As a result, this set-up’s advantages center on higher output capacity—speed plus wider web width equals higher number of impressions per output; as well as a tighter print register tolerance capability.
The tighter print register found in a CI press refers to all substrates, including thin, extensible ones, adds Marco Carrara, VP of sales and marketing, Americas, business unit web fed, Bobst.
He says CI presses offer other advantages like “suitability for extended color gamut printing and the possibility to print both sides of the web with additional colors and apply varnishes.”
Alternatively, CI technology has a few disadvantages, admits Pennings. These include set maximum print decks; less production flexibility as coating, laminating, and drying options as well as backside printing and other finishing operations are limited; and more difficult access for production run changeover.
Inline—An Option of Many Colors
Another type of flexo press is an inline press. It is equipped with individual print stations placed sequentially one after the other along a web path. Pennings explains that the substrate is transferred between each print station during the print process.
PCMC offers the ELS-MAX inline press, which adapts technology from both inline and wide web CI presses to produce a fast changeover inline press that holds extremely tight register. According to the company, printers save up to 50 to 75 percent in both waste and setup time by having the capability to store and recall virtually every setting on the press. Stored jobs are shared between multiple presses with a touch of a button.
Carrara points out that each print station in an inline press is a separate color station. He says this is one of an inline press’ main advantages, since it can be manufactured with any number of colors. “It can be built as multifunctional production lines with multi-process printing and converting operations inline for the production of flexible packaging, carton packaging, and labels in a single pass.”
“An inline press offers more printing stations—on average eight colors but can go to 20 plus,” agrees Chris Baldwin, director of sales and marketing, OMET Americas, Inc. It is also able to conduct more embellishments in one pass such as foiling, laminating, die cutting, and other specialty applications.
Challenges of using an inline press include slower run speeds, narrower web widths, and higher print register tolerances, shares Pennings.
A third type of flexo press is a stack press. It features print stations or print decks arranged vertically one above the other.
“The web can be reversed to allow both sides of a substrate to be printed in one pass. A stack press provides easy accessibility to the color stations and lends itself to print inline with other machine types. However, stack presses are not suitable for thin or extensible substrates because they cannot hold the register to high precision,” explains Carrara.
Baldwin says stack press are mainly gear driven, although servo technology can be used. Most stack presses average six printing decks—eight or nine maximum, which limits color options.
To sum up the three types of flexo presses—CI, inline, and stack, “for speed and ease of setup inline presses are the most common.
When high print quality on demanding substrates—such as thin films—are a priority, the CI press is ideal. It has a small footprint but it is not as easy to setup as an inline press and does lose production speed. As print runs continue to shorten, the stack press is becoming increasingly unpopular,” comments James Barnes, sales and marketing, Focus Label Machinery Ltd.
CI, inline, and stack flexo presses are all found in print and converting houses. Placements are determined based on cost, ease of use, and application popularity.
“I suspect inline presses have the most placements because they are lower priced and the label market has the largest share in consumer packaging, although flexible packaging is gaining ground,” suggests Baldwin.
Focus Label’s inline press, the Proflex, is its most popular model, according to Barnes. Its modular build means total flexibility and new drop-in cylinders ensure fast setup and consistent quality throughout the press speed.
“If one considers the whole realm of flexo—including narrow web label printing—then inline probably has the highest number of presses in operation. This is likely because an inline press is easier to work with and work on, as everything is on the floor.
For example, CI machines are very tall—15 feet or more to the top of the big impression cylinder—and require climbing ladders to adjust or repair,” admits Pfaff.
Heidelberg’s ICS multi-process inline web-fed converting system combines process and production flexibility through the use of modular, easy-to-change units for flexo printing, hot and cold foil stamping, rotary screenprinting, film/foil laminating, and die cutting—all inline. Fixed-position rotogravure print decks are optional.
Flexo devices are used in the production of a myriad of applications from flexible packaging to labels and tags. CI, inline, and stack presses have their own application sweet spots.
CI presses are ideal for running thin, extensible films, which are the main components in manufacturing bags and pouches. “CI flexo printing is the best technology available for printing flexible packaging thanks to speed, quick changeover time, drying efficiency, and printing quality precision,” explains Carrara.
Specific application verticals benefit from CI presses including food and non-food flexible packaging, paper bags, and pet food, he continues. The EXPERT CI press from Bobst prints on film, laminates, paper, foil, and non-woven in a wide web tension range using both solvent- and water-based inks.
Barnes notes that CI presses are ideal for applications like meat casing and sweets wrappers. The layout of Focus Label’s CI press, Centraflex, makes its suitable for packaging, flexible films, papers, labels, and tickets.
Paper and paperboard are run at high speeds in inline machines, this is because of how an inline press is constructed, with dryers between each color station. “This makes them an excellent choice for folding cartons and paperboard products of all kinds,” recommends Pfaff.
“For inline production—roll-to-roll narrow web flexographic printing and converting—self-adhesive labels are the most common application. But also applications like tags, security labels, sleeves, shrink sleeves, and tube laminates are handled with narrow web flexo presses,” adds Thomas Schweizer, head of product management, Gallus Ferd, Ruesch AG.
The Gallus RCS 430 is an inline press equipped with direct drive technology. Individual printing methods can be replaced without separating the web. It features a dynamic feed, pre-settings for web tension, length and cross register, and automatic washing units.
When it comes to stack presses, Baldwin admits that while not as popular, they are used in tissue and napkin markets.
Cost of Investment
The initial investment cost or total cost of ownership for each type of flexo press is hard to put a number on. Vendors say this is because each press is highly customizable.
Machine configuration varies between each press, as its construction depends on the final application it is used to print to, according to Carrara.
That being said, Baldwin cites CI presses as starting on average above two million dollars, depending on width. OMET offers a range of printing presses in widths from 14 to 33 inches. The company offer traditional flexo, digital hybrid, and web offset, as well as combination presses that integrate flexo, digital, gravure, offset, and rotary screen all on one platform press.
Pfaff believes CI presses generally carry a savings of 15 to 20 percent on an initial investment. He adds that their slower speeds and heightened possibility of maintenance downtime may erode that savings.
Inline presses are on average between $500,000 and two million dollars, depending on the number of colors, width, and add-on options, notes Baldwin.
For inline label production, Schweizer stresses that there is more criteria to examine than the initial investment cost. “Issues like process flexibility, web path and related paper waste, ink consumption, time for setup, and cylinder changes have to be considered if investing in a new flexo press.”
Pfaff says stack presses “are generally inexpensive, perhaps another 30 percent below CI models.”
Overall, vendors agree digital printing complements flexo technology. “There is a great opportunity for digital printing applications even if at the moment by comparison to CI and stack flexo presses in terms of percentage the growth is minimal. In regards to inline flexo presses and their versatility, a hybrid machine of flexo and digital is a solution that presents good success on a global scale,” explains Carrara.
The MASTER DM5 from Bobst is a physical representation of the flexo and digital hybrid. The digital print engine is designed by Mouvent, Bobst’s digital printing competence center, using Mouvent Cluster printheads, which offer compactness and accessibility for maintenance. Analog tools found on the device—like print cylinders and flexible dies—are automatically changed.
“Digital printing complements flexo. While there are significant improvements in digital, especially with inkjet, for most print runs, flexo cannot be beaten for cost effectiveness,” adds Barnes.
Pfaff agrees, saying “to date, digital hasn’t proved to impede to any great degree. This is most likely because of its relatively slow speeds, which makes large-volume production more costly to a package producer. Digital fits well in narrow web label production, since web speeds are not all that high to begin with. Consequently, the slow speed of a digital print engine fits in with the existing process.”
It seems inline configuration is most susceptible to digital disruption because of the increase in digitally printed labels. “I would say currently digital printing is disrupting the narrow web, inline presses the most, although digital is starting to enter mid-web flexible packaging more aggressively,” admits Baldwin.
“In general, digital printing devices limit production for CI, inline, and stack through reduced speeds—data processing and print device capability—and narrowed substrate compatibility range. CI presses in particular have increased limitation, though, because of their higher speeds and typical use in printing on film, which to date has been more difficult to print on using digital printing technology,” adds Pennings.
PCMC’s newest CI press is the Fusion C, part of the Fusion series of presses. The Fusion line of machines reduces energy requirements by utilizing low power consumption components, designs, and operations. Pairing that with fast changeovers and lower ink usage enables a quick return on investment and competitive operating costs.
Need to Know
Each type of flexo machine is configured differently. It is often this physical difference that determines which environment and application a press is best suited for.
A CI press is equipped with one impression cylinder or drum, with the print stations placed around the cylinder. An inline press is compromised of individual print stations placed sequentially one after the other along a web path. A stack press features print stations or print decks arranged vertically one above the other.
Flexo presses are integral components to the packaging and label supply chains, as they serve print shops to meet the required needs of numerous market verticals. Digital printing maintains a presence in the short-run, variable niche, but have yet to match flexo technology’s ability to churn through static, longer print runs. The two technologies continue to complement each other. dps
Jul2020, DPS Magazine