The excellent plastic substrate adhesion of inkjet printing relies upon collaborative developments of material modification, ink formulation, and curing science. According to ASTM D3359, it is possible that the surface energy of plasma pre-treated polyethylene (PE) can be improved from 31 mN/m to 72 mN/m, such that the ink adhesion of plastic substrate for inkjet printing may reach as much as 4B class (peel area ≤5%). In 2023, HP’s UV-LED curing technology, jointly developed with Covestro, achieved 40 m/min line speed for PET bottle printing, 98% ink crosslinking, and alcohol wiping resistance more than 500 times (ISO 15720 standard). Adhesion test by 3M 610 tape peel strength ≥4.5N/cm².
The special composition of the ink is the most important factor of adhesion. The water-based acrylic ink can form a porous 3-5μm-thick layer on polypropylene (PP) by applying nanoparticle dispersion technology (particle size ≤80nm) and surface tension regulator (28-32 mN/m). Such ink is used in the Epson SurePress L-6534VW printer to print designs on auto interior ABS plastic following 85 ° C /85%RH aging test of 1,000 hours with color difference ΔE≤1.5 and adhesion retention rate of ≥95%. In 2022, Procter & Gamble (P&G) improved the energy density of UV ink curing to 1.2J/cm² in the inkjet printing on plastic line of shampoo bottles, increased the monomer conversion rate from 88% to 99%, and reduced the ink shrinkage rate from 7% to 0.8% to avoid edge peeling induced by internal stress.
The pretreatment technology greatly improves the interface bonding force. Corona treatment (power density 50-150W·min/m²) has the potential to increase the oxygen content of the surface of the BOPP film from 4% to 24%, reduce the contact Angle from 95° to 35°, and increase the diffusion coefficient of the ink by 6 times. Fujifilm Uvijet KL Series inks dry in 0.3 seconds with photoinitiator TPO-L (1.2-1.8% concentration) on corona treated PETG materials with a 5B adhesion level and steel wool friction resistance tests (500g load) for more than 2,000 times. After one medical device company employed this solution, the percentage of retention of identification after ethylene oxide sterilization (54℃/60%RH) increased from 75% to 99.9%.
Nano-coating technology breaks the non-polar material barrier. On the uncoated HDPE surface, silica sol-gel coating (50-100nm) can increase the roughness Ra on the surface from 0.02μm to 0.15μm, and ink adhesion from 0B to 4B. In 2023, Konica Minolta’s AccurioJet KM-1 machine with a nano-coating will print 10μm line width on car lampshade PC plastic without cracking after passing through thermal cycle tests of 500 times in -40℃ to 120℃. Conformance to ISO 2409 standard Class 0 (peel zone ≤0%).
Industrial applications verify technical reliability. In consumer electronics, where plastic is inkjet printed in the IML process of mobile phone cases, the Dell XPS series uses a dual curing (UV+ thermal) method, which causes the polyurethane ink to form a chemical bond with the PC substrate at the post-curing temperature of 130 ° C, and the peel strength is up to 6.8N/cm². 3 times that of traditional screen printing. The mandatory use in 2022 of EU’s REACH regulation has preferred innovation in food-grade inks: Sun Chemical’s EB curable ink meets the migration test (≤0.01mg/kg) in PP food boxes, adhesion meets the EN 71-3 safety rating for children products, and dry energy consumption drops by 62% compared to traditional UV.
The figures show that the new inkjet solution improves the adhesion qualification rate of plastic printing from the traditional 70% to 99.5%, and the pretreatment cost is reduced by 40% ($0.02 /m²). The 3C, medical and automotive sectors are driving the inkjet printing on plastic market to expand at an annual growth rate of 12.7% (Smithers 2024 forecast). These advances have transformed the quality standards for digital printing on plastic surfaces.