Determination of Adhesion of Printed Plastic Films: Standards, Methods and Testing Guide

Adhesion testing of printed plastic films is a critical quality control procedure that evaluates the bond strength between printing inks and flexible polymeric substrates such as PE, PP, PET, and PVC. This article provides a comprehensive technical overview of adhesion determination methods, including cross-cut tape tests, peel tests, and rub resistance tests, with reference to internationally recognized standards such as ASTM D3359, ISO 2409, and GB/T 13217.7. Whether you manufacture flexible packaging, labels, or decorative films, understanding these testing protocols helps ensure print durability, regulatory compliance, and customer satisfaction.

Technical Overview

Adhesion determination for printed plastic films refers to the quantitative and qualitative evaluation of the bond formed between a layer of printing ink and a plastic substrate surface. Because plastic films such as polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), and polyvinyl chloride (PVC) are inherently non-polar and chemically inert, achieving durable ink adhesion is one of the most persistent challenges in the flexible packaging and printing industries. Poor adhesion leads to ink transfer, smearing, delamination, scratching, and premature print failure during converting, filling, transportation, or end use.

Adhesion performance depends on multiple interrelated factors, including the surface energy of the film (commonly enhanced by corona or plasma treatment), the ink formulation and resin chemistry, the degree of curing or drying, printing process parameters, and post-printing environmental exposure. Standardized test methods allow manufacturers, converters, and accredited third-party laboratories to verify that printed films meet specified adhesion requirements before mass production or shipment.

The most widely applied techniques include the cross-cut (cross-hatch) tape test described in ASTM D3359 and ISO 2409, the Chinese national standard GB/T 13217.7 for liquid ink adhesion on plastic films, peel strength testing per ASTM D3330 and GB/T 8808, and rub resistance and abrasion evaluations. Together, these methods cover the range from rapid qualitative screening to quantitative mechanical measurement.

Testing Samples

Surface-Printed Flexible Packaging Films

Surface-printed films, where ink is applied directly onto the treated side of the substrate, are the most common samples submitted for adhesion testing. Typical materials include mono-layer and co-extruded PE films, BOPP (biaxially oriented polypropylene), CPP (cast polypropylene), and PET films printed by flexography or rotogravure. These samples are evaluated to confirm that surface treatment levels and ink systems produce adequate initial adhesion.

Reverse-Printed Laminated Structures

In reverse printing, ink is deposited on the inside of the outer film and then laminated to a sealing layer. Adhesion is assessed both at the ink-to-substrate interface and at the laminate bond. Samples may include PET/PE, BOPP/CPP, PA/PE, and metallized film structures used for food and consumer product packaging.

Labels and Pressure-Sensitive Materials

Self-adhesive label stocks printed by flexo, offset, screen, or digital processes require adhesion verification to ensure that printed information remains legible through die-cutting, matrix stripping, application, and product lifetime. These tests are often supplemented by peel adhesion measurements of the adhesive layer itself.

Coated and Treated Films

Films carrying functional coatings, topcoats, varnishes, or primers, as well as digitally printed films using UV-curable or aqueous inkjet systems, are tested to verify intercoat adhesion and coating integrity. Barrier-coated films and films intended for high-slip or high-abrasion environments fall into this category.

Testing Items

Adhesion determination programs for printed plastic films typically include the following evaluation items:

• Cross-cut tape adhesion rating (classification 0 to 5 per ISO 2409 / ASTM D3359 / GB/T 9286)
• Ink adhesion of liquid inks on plastic films and sheets per GB/T 13217.7
• 90-degree and 180-degree peel strength of printed or laminated layers per ASTM D3330 and GB/T 8808
• Tape peel transfer assessment for digitally and UV-printed films
• Rub resistance and abrasion durability of printed surfaces
• Scratch resistance and ink cohesion evaluation
• Adhesion retention after conditioning, such as heat aging, humidity exposure, cold storage, and chemical contact
• Surface energy (dyne level) verification as a supporting indicator of printability and adhesion potential

Testing Methods

Cross-Cut Tape Test (ASTM D3359 / ISO 2409 / GB/T 9286)

The cross-cut tape test is the industry-standard rapid method for measuring adhesion of ink coatings up to approximately 250 micrometers in thickness. A cutting tool or blade is used to make a lattice pattern of parallel cuts through the ink layer to the substrate, either a 6 by 6 grid for ISO 2409 or an 11-slit pattern (Method A) or 6 by 6 grid (Method B) for ASTM D3359. Pressure-sensitive tape is then applied over the lattice, rubbed down firmly, and rapidly pulled away. The amount of ink detached is visually compared with classification illustrations, and an adhesion rating from 0 (worst, greater than 65 percent detachment) to 5 (best, no detachment) is assigned. Test conditions such as tape type, peel angle, pull speed, and substrate rigidity must be controlled because they significantly influence results.

Ink Adhesion Test per GB/T 13217.7

This Chinese national standard specifies the determination of adhesion for liquid inks printed on plastic films and sheets. Printed specimens are conditioned at standard atmosphere, after which adhesive tape is applied to the printed area with defined pressure and removed in a controlled manner. The degree of ink removal is assessed by comparing the transferred ink against standard rating scales, yielding a pass/fail or classified result. The method is widely used for incoming ink inspection and process qualification in gravure and flexographic printing operations.

Peel Strength Testing (ASTM D3330 / ASTM D903 / GB/T 8808)

Peel testing provides quantitative adhesion data expressed in force per unit width, typically newtons per 25 millimeters. For laminated printed structures, T-peel or 180-degree peel configurations measure the force required to separate the laminate at the ink interface using a universal tensile testing machine. This approach is essential for printed laminates where interlayer bond strength directly affects package integrity, and it allows numerical comparison between ink systems, primers, and treatment levels.

Tape Peel Transfer Test (ASTM F2252)

For flexible substrates where the standard cross-cut test is difficult to perform, ASTM F2252 describes a tape peel procedure suitable for thin, pliable printed webs. A strip of pressure-sensitive tape is applied to the print, burnished, and peeled at a controlled rate and angle, and the degree of ink transfer to the tape is rated. This method is particularly relevant for pressure-sensitive labels and thin flexible packaging films.

Rub and Abrasion Resistance Testing

Printed films are subjected to reciprocal rubbing action, either print against print or print against an unprinted reference surface, under a defined load and number of cycles. The extent of ink removal, scuffing, or marring is evaluated visually or instrumentally. Rub resistance complements adhesion testing because it simultaneously stresses ink cohesion and ink-to-substrate bonding under realistic mechanical abuse.

Conditioned and Environmental Adhesion Testing

Adhesion often changes after exposure to service environments. Specimens may be conditioned by heat aging, elevated humidity, refrigeration or freezing, immersion in water or product simulants, or exposure to chemicals such as oils, detergents, and sterilization agents. Cross-cut or tape tests are then repeated to determine adhesion retention, which is critical for food packaging, medical packaging, and labels exposed to harsh conditions.

Supporting Measurement: Surface Energy Determination

While not a direct adhesion measurement, surface energy testing using dyne pens or contact angle instruments verifies that the film surface has been adequately treated, typically to 38 to 42 dyne per centimeter for polyolefins. Insufficient surface energy is the most frequent root cause of adhesion failure, so this check is commonly integrated into adhesion investigation protocols.

Applications

Adhesion determination of printed plastic films supports quality assurance and product development across many industries:

• Flexible packaging for food, beverages, snacks, and confectionery, where printed information and barrier layers must survive filling, sealing, distribution, and consumer handling
• Pharmaceutical and medical device packaging requiring validated print legibility and laminate integrity
• Pressure-sensitive labels for bottles, containers, and logistics applications
• Shrink sleeves and stretch labels on PVC, PET-G, and OPS films
• Decorative and graphic films for automotive trim, appliances, and consumer electronics
• Digitally printed films and short-run packaging produced with UV inkjet, latex, or toner-based systems
• Incoming material inspection of films, inks, coatings, and primers at converters and printing houses
• Failure analysis and root cause investigation of ink transfer, smearing, and delamination complaints
• Process validation after changes in corona treatment level, ink supplier, printing speed, or curing parameters

FAQ

Why does ink fail to adhere to plastic films?

The most common cause is insufficient surface energy of the film, often due to inadequate or aged corona treatment. Polyethylene and polypropylene are naturally low-energy, non-polar surfaces, and most ink systems require a treated surface of at least 38 dyne per centimeter. Additional causes include contaminated or slip-migrated surfaces, under-cured inks, excessive slip additives blooming to the surface, and mismatched ink chemistry for the substrate.

What is the difference between ASTM D3359 and ISO 2409?

Both standards use a cross-cut lattice with pressure-sensitive tape and assign a 0 to 5 rating, but they differ in cutting geometry, blade specifications, tape requirements, and classification definitions. ASTM D3359 Method A uses two sets of eleven parallel cuts, while Method B and ISO 2409 use a six by six grid. Results from the two standards are not directly interchangeable, so the specification standard must be stated in test reports.

How should specimens be conditioned before testing?

Specimens are typically conditioned at 23 degrees Celsius and 50 percent relative humidity for a minimum of 24 hours prior to testing, unless the applicable standard or product specification states otherwise. Conditioning stabilizes the ink layer and substrate, reducing variability between measurements.

Can adhesion be tested on laminated printed films?

Yes. For laminates, peel strength testing per GB/T 8808 or ASTM D3330 quantifies the bond at the ink interface, while cross-cut methods evaluate the outer printed surface. Both approaches are often combined to fully characterize multi-layer printed structures.

How often should adhesion testing be performed?

Best practice includes adhesion verification at incoming material inspection, during initial job setup and first-article approval, periodically during production runs, and after any change to substrates, inks, treatment levels, or process conditions. Routine tape tests at the press side provide rapid feedback, while accredited third-party laboratories perform standardized verification for certification and dispute resolution purposes.

Does higher surface energy always guarantee good adhesion?

No. Surface energy is a necessary but not sufficient condition. High dyne readings measured immediately after treatment can decay over time due to additive migration and re-contamination, and ink chemistry, film chemistry, curing completeness, and printing conditions all influence the final bond. Direct adhesion testing on the actual printed specimen remains the definitive verification method.