Lifting of flexographic plate edges is a problem that can affect both print quality and production continuity. If not properly managed, it can lead to register problems, printing defects, and the penetration of ink or solvents underneath the plate, potentially resulting in unplanned machine stoppages.
The causes can be numerous and depend on the interaction between the plate, the double-sided mounting tape, the cylinder or sleeve, and the production conditions. Plate thickness and stiffness, cylinder diameter, surface preparation, mounting tape selection, and mounting procedures are all factors that must be considered.
The solution therefore does not simply consist of securing the edge when the problem occurs, but above all of identifying the root cause and adopting the most appropriate preventive method. The main causes of the phenomenon and five specific solutions for improving the retention and protection of plate edges are analyzed below.
If the Plate Edge Starts to Lift
When an edge starts to lift, it is important to stop and immediately check the condition of the plate. If the separation is already visible, continuing to print may worsen the problem and encourage ink or cleaning-fluid penetration underneath the plate. In these cases, the procedure established in the pressroom for machine shutdown and subsequent remounting must be followed.
Depending on the type of job and the materials used, different methods can be adopted to improve edge retention:
• Single-sided edge-sealing tape specifically designed for flexographic plates. A single-sided tape applied over the plate edges can help prevent ink and cleaning fluids from penetrating the bonding interface. Some tapes of this type are specifically designed for long runs or plate-washing operations.
• Adhesive for sealing the plate edges. A sealant specifically formulated for flexographic plates can help keep the edges in position while also limiting liquid penetration.
• Hot-melt adhesive for flexographic printing. A suitable hot-melt product can be applied along the plate perimeter to seal the edges and protect them against the penetration of inks and solvents. It is important to use a product and application method specifically designed for the job in question: a standard general-purpose hot-melt glue is not an equivalent alternative.
• Plate mounting primer. A compatible primer, applied exclusively to the designated area, can increase adhesion at the plate edge. Since it may make repositioning and removal more difficult, it must be used selectively.
• Portable corona or cold plasma treatment. A dedicated device can be used to treat the back of the plate before mounting, increasing surface energy and, consequently, the bond strength between the double-sided mounting tape and the plate. However, this is a preventive treatment: it cannot restore an edge that has already lifted.
These methods are not interchangeable and must be evaluated according to the characteristics of the system. Compatibility with the plate, double-sided mounting tape, inks, cleaning products, and demounting process must therefore be verified, always following the manufacturer’s instructions.
In particular, single-sided edge-sealing tapes and edge-sealing adhesives are intended to limit the penetration of ink or solvents, whereas portable cold plasma treatment acts on the surface of the plate backing, improving the effectiveness of the bond between the plate and the double-sided mounting tape.
Identify the cause before the next mounting
1. Check the plate and cylinder surfaces
The presence of dust, ink, adhesive residues, oils, or residues resulting from the plate production process, either on the back of the plate or on the cylinder, can compromise adhesion. Both surfaces must be cleaned using materials and cleaning agents approved by the manufacturers of the plate, double-sided mounting tape, and sleeve or cylinder. It is advisable to use a clean, lint-free cloth and allow the surfaces to dry completely before proceeding with mounting.
It should also not be assumed that a plate washer has cleaned the back of the plate as well: automatic plate-washing systems are generally designed to work on the printing surface. The choice of solvents is also important, as some may affect the performance of the plate or double-sided mounting tape. Therefore, only products approved for the materials in question should be used.
2. Select the mounting tape according to the job
The choice of double-sided mounting tape must take into account the plate, required print quality, repeat length, cylinder or sleeve diameter, and run conditions. Thicker or stiffer plates, as well as smaller diameters, can generate greater stresses at the interface between the plate and the double-sided mounting tape. For these conditions, mounting tapes with different adhesion and foam characteristics are available, including products specifically developed to resist edge lifting in demanding applications.
If a plate continues to lift, it is advisable to review the specifications of the double-sided mounting tape together with your supplier. Simply increasing the adhesion level may, in fact, make plate removal more difficult or increase the risk of damaging the plate.
3. Apply the tape and plate uniformly
The double-sided mounting tape must be applied using uniform pressure. The cylinder and mounting tape must remain free from residues, air bubbles, raised areas, and overlaps at the tape joint.
The plate must then be applied across its entire surface, paying particular attention to the leading and trailing edges. Consistent and uniform pressure promotes full contact between the plate, double-sided mounting tape, and cylinder. The mounting tape joint must also be positioned so that it does not coincide with the plate joint, always following the specific mounting instructions for the tape being used.
4. Check plate condition and the production process
If the plate tends to curl, appears unusually stiff, or continues to lift despite clean surfaces and correct mounting, its condition must be checked and the production process reviewed.
The manufacturer’s recommendations regarding plate processing, drying, storage, and handling should be checked. Before modifying process parameters, it is also advisable to verify the cause with the plate manufacturer or your supplier.
Preventing the problem from recurring
Record the type of plate, double-sided mounting tape, cylinder or sleeve, ink and washing conditions, any edge treatment applied, and the exact point where the lifting began. This information can help distinguish a problem related to surface preparation from an incorrect double-sided mounting tape selection or a specific process condition.
A reliable procedure therefore starts with clean, dry surfaces, continues with the selection of a compatible double-sided mounting tape and uniform plate application, and, when required by the characteristics of the job, includes the use of a specific edge-treatment method.
1. Single-Sided Edge-Sealing Tape for Flexographic Plates
As printing speeds increase and cylinder diameters progressively decrease, centrifugal forces and mechanical stresses tend to concentrate along the leading and trailing edges of photopolymer plates.
Applying a single-sided edge-sealing tape creates an immediate mechanical bridge while also protecting the interface between the plate and the double-sided mounting tape from the penetration of inks and cleaning solvents. These tapes are generally manufactured using ultra-thin, dimensionally stable polyester (PET) or vinyl backings combined with highly cross-linked, solvent-resistant acrylic adhesives.
The low-profile design is essential: it prevents interference during printing and the formation of gear-related marks or artifacts, while allowing the transition between the plate bevel and the mounting cushion tape or sleeve surface to be covered evenly.
For optimum results, the single-sided edge-sealing tape must be applied uniformly, with approximately half of its width overlapping the marginal area of the plate and the other half extending onto the cylinder or sleeve. It must then be firmly bonded using a mounting roller or squeegee, eliminating micro-voids through which volatile solvents, such as ethyl acetate or alcohols, could penetrate by capillary action.
2. Liquid adhesives and Pens for sealing Plate Edges
Liquid edge sealants act as true chemical barriers designed to seal the microscopic gap at the point of contact between the photopolymer plate, the pressure-sensitive adhesive (PSA) of the double-sided mounting tape, and the mounting cushion layer.
During continuous printing and in-press plate washing, aggressive solvent-based inks, amines present in water-based inks, and low-viscosity UV monomers can attack and dissolve standard pressure-sensitive adhesives, promoting delamination.
Liquid sealants specifically formulated for flexographic applications, often applied using felt-tip pens, syringes, or fine brushes, penetrate directly into the edge joint and polymerize rapidly, forming a flexible barrier resistant to chemical agents.
Unlike generic industrial coatings, flexographic-grade sealants are formulated to provide good adhesion during the print run while also allowing softening or clean removal during demounting. This reduces the risk of tearing the plate edge and of forming solvent-hardened adhesive residues on sleeve surfaces.
3. Precision Hot-Melt Adhesives for Flexographic Printing
For applications involving high mechanical stress, such as those using thick plate packages, cylinders with short repeat lengths, or significant press vibration, hot-melt adhesives can provide strong edge retention with immediate tack. However, it is essential to use hot-melt formulations specifically developed for flexographic printing, avoiding common multi-purpose glue sticks.
Hot-melt adhesives for flexographic applications are formulated with lower melting points and optimized open times to prevent the molten adhesive from thermally deforming or causing bubbles in the biaxially oriented polyester (PET) backing of the plate.
Applied along the edge perimeter using a temperature-controlled dispensing gun equipped with a fine nozzle, the adhesive solidifies within a few seconds, forming an elastomeric bead resistant to shear forces and capable of limiting ink penetration. During demounting, high-quality flexographic hot-melts remain intact and can be removed or peeled away in a single strip without cutting into or damaging the outer polyurethane layers of the sleeve.
4. Selective Primers for Plate Mounting
Plate mounting primers, or chemical adhesion promoters, address the problem of edge lifting by modifying the surface of the plate backing and locally increasing bond strength.
Most flexographic plates have a smooth polyester backing that is chemically relatively unreactive and characterized by comparatively low surface energy. Under high peel forces, this can make it more difficult to achieve effective anchoring with removable mounting cushion tapes. Applying a thin, uniform layer of primer exclusively to the leading and trailing margins, over a width of 5–10 mm on the back of the plate, creates a high-affinity anchoring layer for the adhesive of the double-sided mounting tape.
Because primers can significantly increase peel adhesion, they must be applied sparingly and kept strictly away from the central area of the plate. Excessive primer can create excessive adhesion, making plate removal difficult and increasing the risk of tearing the photopolymer or leaving a significant amount of adhesive transfer on the double-sided mounting tape during demounting.
5. Surface Pretreatment with Cold Plasma and Portable Corona
For companies seeking a solution free from chemicals and residues, portable atmospheric cold plasma and corona discharge devices represent an effective method for surface preparation. Standard polyester plate backings generally have surface energies below 40 dyne/cm, a value that may be insufficient to achieve the wetting threshold required by high-shear-strength mounting tapes.
Passing a portable cold plasma nozzle or corona wand along the perimeter of the plate backing ionizes the atmospheric gas and promotes the introduction of polar oxygen- and nitrogen-containing functional groups onto the polymer surface, such as hydroxyl and carboxyl groups. The treatment rapidly increases surface energy, bringing it well above 40 dyne/cm and promoting improved adhesive wetting and greater anchoring strength of the double-sided mounting tape.
Since plasma treatment is exclusively a preventive surface-activation step, it must be performed on clean, dust-free backings immediately before mounting. This creates a residue-free preparation layer that helps prevent edge lifting before the cylinder even enters the printing press.
Preventing Plate Edge Lifting
Lifting of flexographic plate edges can be reduced by addressing the entire mounting process, from surface preparation to double-sided mounting tape selection and the correct application of the plate.
When working conditions require it, single-sided edge-sealing tapes, edge-sealing adhesives, hot-melts, primers, and corona or plasma treatments can provide additional edge protection. The selection must, however, always take into account compatibility between the plate, double-sided mounting tape, inks, cleaning products, and demounting process.
A preventive approach based on clean and dry surfaces, compatible materials, uniform mounting pressure, and proper control of plate condition helps improve the reliability of the mounting system, protect print quality, and reduce the risk of machine downtime.
Written by Annalisa Paltrinieri – Graphic Designer | Team Giugni®
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