A Brief Discussion on Causes and Improvements for Ink Adhesion Failure in Labels
Self-adhesive label printing encompasses various methods, classified by equipment: letterpress printing, flexographic printing, offset (planographic) printing, digital printing, gravure printing, screen printing, and combination printing (e.g., offset + screen, flexo + screen, etc.).
Different processes vary in printing effects, costs, applicable materials, and order quantities. During production, various issues frequently arise, among which ink adhesion failure (ink flaking) is a relatively common problem. Ink adhesion failure is a performance issue, with test methods including cross-hatch adhesion test, abrasion resistance test, 3M tape test, manual scraping test, and pseudo-dry ink test.
Based on relevant experience and industry standards, the causes of ink adhesion failure primarily concentrate in four dimensions: substrate film, ink, printing process, and external environment. Below is a systematic analysis of causes and improvement countermeasures:

I. Substrate Surface Issues (Non-ink-absorbing substrate, poor adhesion)
For general ink adhesion failure, the first consideration is usually substrate surface issues. Indeed, many material printing failures are indeed caused by substrate problems.
1. Insufficient Substrate Surface Tension (Inadequate Corona Treatment)
Common plastic films (such as PET, PP, etc.) have smooth surfaces and low polarity. If the surface tension is lower than that of the ink, the ink cannot properly wet and adhere to the surface.
Standard requirement: Corona value on printing side ≥ 38 dyn; below 38 dyn, ink adhesion failure is highly likely.
Improvement measures: If the company printing press is equipped with a corona treater, perform corona treatment on the film before printing, ensuring the treated film surface tension reaches 38–40 dyn/cm or above. Meanwhile, note the storage period after corona treatment, as the dyne value will decay over time; it is recommended to reduce long-term raw material storage. If no corona equipment is available, a primer (undercoat) can be printed before the color layers to enhance ink adhesion. If the process does not allow this, arrange to return the material to the supplier for corona or coating treatment.
Note: If neither corona treatment nor primer printing is effective, return the material to the supplier for coating treatment.
2. Substrate Surface Contaminated with Release Agent, Silicone Oil, or Dust
During label film production, silicone oil is applied for anti-stick purposes; residual silicone oil on the surface will isolate the ink, causing complete flaking upon scraping.
Improvement: Select low-silicone printing-grade synthetic paper; perform dust and oil removal before printing; prohibit printing on the release film side.

II. Ink Selection and Condition Factors
1. Ink Performance and Compatibility
The performance and matching degree of the ink itself is the core of adhesion.
•  Ink model incompatible with substrate: PE, PP, PVC, and synthetic paper are difficult-to-adhere substrates; using ordinary paper-based water-based ink will not penetrate. Using soft PVC dedicated ink on coated paper will cause delamination.
•  Excessive ink dilution reduces the resin carrier proportion, weakening bonding strength.
•  Expired, separated, or precipitated ink causes resin failure.
•  Insufficient UV ink curing energy results in incomplete curing; the surface layer flakes off with hand scraping.
Improvement: Select dedicated inks by material: use polyolefin dedicated inks for PP/PE; use PVC soft inks for PVC; use general adhesion inks for coated paper/matte silver. Control dilution ratios: water-based ink dilution with water ≤ 10%; solvent ink dilution not to exceed manufacturer standards. Stir ink evenly; replace expired ink directly; for UV inks, regularly replace lamp tubes and increase curing energy.
Note: If necessary, add a small amount of adhesion promoter to the ink to improve surface slip and hardness, making it easier to pass the 3M tape test.
2. Poor Ink Abrasion / Friction Resistance
Cause: Low-grade inks contain no abrasion-resistant additives; during finished product transportation friction, hand contact, and packaging friction, the surface ink layer is directly worn off.
Improvement: Add abrasion-resistant additives; switch to high abrasion-resistant printing inks; apply abrasion-resistant varnish / film lamination after printing.
To enhance ink abrasion resistance, a layer of abrasion-resistant matte/gloss varnish can be printed, with the proportion appropriately adjusted according to abrasion requirements.

III. Printing Process Defects
1. Incomplete Drying / Curing (High Incidence)
•  Water-based / solvent inks: Low oven temperature, fast running speed, insufficient air volume lead to residual solvent inside the ink, incomplete film formation; ink fails upon water contact or friction.
•  UV inks: Lamp aging, excessive printing speed, insufficient UV lamp power cause surface dryness with internal uncuring. UV lamp service life expiration.
Improvement:
•  Water-based inks: Oven at 60–90°C, reduce machine speed, increase hot air circulation, ensure complete drying before rewinding.
•  UV printing: Regularly replace UV lamp tubes, reduce running speed, increase lamp group power.
2. Excessive Ink Layer Thickness
When the ink layer is too thick, the surface dries while the bottom remains uncured; high internal stress causes complete flaking upon slight friction.
Improvement: Reduce doctor blade gap, decrease ink supply, use thin ink multi-pass printing, avoid single-pass heavy ink deposition.
3. Dampening Solution / Additive Interference (Offset Printing)
Excessive dampening solution, high alcohol proportion destroys ink resin, reducing adhesion.
Improvement: Control dampening solution dosage, reduce alcohol addition, select low-corrosion dampening solution.

IV. External Environment and Post-Processing Protection Factors
1. No Varnish, No Lamination
Matte silver, PP, PET, and synthetic paper labels with bare ink and no protective layer have increased risk of friction-induced ink adhesion failure during transportation.
Improvement: Apply water-based abrasion-resistant varnish / UV varnish after printing; for large-volume abrasion-resistant requirements, apply BOPP matte film / gloss film lamination.
2. Poor Varnish Adhesion Itself
Varnish incompatible with ink causes varnish peeling, taking the ink layer with it.
Improvement: Use varnish and ink from the same manufacturer as a set; conduct small-batch sample testing for adhesion before production.
3. Color Fading Upon Water, Oil, or Alcohol Wiping
Insufficient ink water resistance and chemical resistance cause rapid color fading in household chemical, food, and oily environments.
Improvement: Switch to alcohol-resistant, water-resistant dedicated inks; increase varnish layer thickness; apply film lamination protection.
4. Low / High Temperature Environment Ink Adhesion Failure
•  High temperature: Ink resin softens and friction causes flaking.
•  Low temperature: Ink becomes brittle and easily scraped off (especially when combined with low-temperature hot-melt adhesive substrates).

Improvement: Select industrial-grade inks resistant to high and low temperatures; avoid using soft low-temperature inks for outdoor / cold storage labels.

cold storage labels，outdoor labels，self-adhesive label printing，digital printing labels，gravure printing labels, screen printing labels, combination printing labels