Celvolit 1408 Emulsão de VAE com alto teor de etileno para substratos difíceis

The introduction of Celvolit 1408, a high-ethylene vinyl acetate-ethylene (VAE) dispersion with a nominal solids content of 55% and a Brookfield viscosity at 25 °C between 2 000 and 4 000 mPa·s, addresses a persistent limitation in waterborne adhesive technology: the reliable, primer-free bonding of low-surface-energy substrates. The polymer backbone contains an ethylene weight fraction exceeding 25%, which depresses the glass transition temperature (Tg) to approximately -30 °C as measured by differential scanning calorimetry according to ISO 11357-2:2020. This depression enables spontaneous film formation at ambient conditions without external coalescing agents and reduces the interfacial energy gap between the dried adhesive layer and substrates such as untreated polyethylene, polypropylene, and polystyrene. In contrast to standard-grade VAE copolymers limited to ethylene levels below 18%, Celvolit 1408 maintains cohesive integrity under static shear loads of >72 h on high-density polyethylene (ASTM D3654, Procedure A) while delivering a 180° peel adhesion on unprimed LDPE exceeding 2.0 N/cm after 24 h conditioning at 23 °C and 50% RH.

How Does Elevated Ethylene Content Modify Adhesive Wetting on Critically Low-Energy Surfaces?

The adhesion mechanism of Celvolit 1408 to substrates with surface free energy below 30 mN/m departs from the acid-base or mechanical interlocking models that dominate acrylic and polyurethane dispersions. The high ethylene segment density lowers the critical surface tension of the dried polymer to approximately 27–29 mN/m, as determined by contact angle goniometry using Owens–Wendt theory with diiodomethane and water probe liquids. This value falls beneath the surface energy of corona-treated polyethylene (38–42 mN/m) and approaches that of untreated polypropylene (29–31 mN/m). During the coalescence phase, the partially hydrolyzed vinyl acetate sequences contribute a small polar component, but film formation is dominated by the ethylenic domains, which exhibit high chain mobility at processing temperatures. Published data for this specific configuration is limited, yet comparative measurements on a Krüss DSA100 drop shape analyzer confirm that the polar fraction of Celvolit 1408 accounts for less than 15% of the total surface energy, whereas a conventional VAE with 12% ethylene registers a polar contribution above 30%. This shift enables an autophobic wetting transition that prevents retraction of the adhesive film on low-polarity substrates during drying, even when applied at web speeds of 150 m/min on a Bachofen rod coater.

Peel Strength Evolution on Uncorona-Treated Polyolefin Films

Comparative 180° peel testing per FINAT FTM 1 (equivalent to ASTM D3330) on 50 µm untreated low-density polyethylene film reveals a time-dependent adhesion build-up unique to the high-ethylene architecture. After 15 minutes dwell at 23 °C, Celvolit 1408 registers an average peel force of 0.8 N/cm with a clean cohesive failure mode, while a standard VAE containing 15% ethylene yields 0.2 N/cm with adhesive delamination at the interface. At 24 hours, the value for Celvolit 1408 climbs to 2.1 N/cm with a transition to substrate fiber-tear or film yield, whereas the standard VAE plateaus at 0.6 N/cm and continues to fail adhesively. The difference is attributable to a combination of lower interfacial energy mismatch and rapid development of macromolecular entanglement across the interphase, facilitated by the free volume induced by polyethylene-like segments. On a Cheminstruments AR-1000 adhesion/release tester, the average energy to debond (integration of the force–displacement curve) shows a 4.5× increase for Celvolit 1408 between 15 min and 24 h, a factor not reproduced in any lower-ethylene homologue tested under identical lamination conditions.

When Celvolit 1408 Substitutes for Solution Acrylics in Pressure-Sensitive Label Coatings

In the conversion of paper face stocks for pressure-sensitive labels, the shift from solvent-borne acrylics to high-ethylene VAE dispersions imposes changes on both coating rheology and the final adhesive performance fingerprint. Celvolit 1408 exhibits a shear-thinning profile with a low-shear (Brookfield) viscosity of 3 200 mPa·s and a high-shear (ICI cone and plate at 10 000 s⁻¹) viscosity of approximately 90 mPa·s, enabling transfer-coating through a 150-mesh anilox roller without stringing or misting on a 300 mm wide pilot coater-laminator operating at 50 m/min. The absence of volatile organic solvents eliminates the explosive lower limit monitoring required for solvent-based lines, and the calculated VOC content of <0.1% per EPA Method 24 simplifies the site environmental permit. Compared to a typical solvent acrylic yielding 22 N/25 mm loop tack on stainless steel, Celvolit 1408 delivers 18–20 N/25 mm (FINAT FTM 9) on the same substrate but surpasses the acrylic on low-energy polyethylene where the acrylic drops below 5 N/25 mm due to interfacial failure. The cohesive performance at elevated temperature (60 °C), measured via static shear holding 500 g on 25 mm × 25 mm area per FINAT FTM 8, exceeds 100 h for Celvolit 1408, provided the dry film weight remains above 20 g/m². Drying below this threshold leads to a measurable loss of cohesive integrity and an unacceptable drop in shear resistance to <10 h.

On a flatbed laboratory laminator equipped with a #22 Meyer rod, the emulsion’s minimum film-forming temperature (MFFT) of <0 °C permits coating at ambient conditions down to 8 °C without the addition of coalescents, a processing advantage not shared by acrylic dispersions that typically demand 3–5% of a high-boiling ester such as texanol when processed below 12 °C. However, substrate pre-heating to 35–40 °C via infrared panels is recommended when line speed exceeds 80 m/min to ensure complete water evaporation within the dryer tunnel and prevent residual moisture from plasticizing the interlayer, which manifests as a creep failure during shear testing. The pH of the as-supplied emulsion is buffered to 4.5–5.5 using a proprietary colloid system; addition of ammonia to raise pH above 7.0 results in a sharp increase in particle size distribution width, detectable as a shoulder in the D(0.9) measurement on a Malvern Mastersizer, and a correlated decrease in peel adhesion by approximately 30% after 24 h drying. The shear stability under recirculation in a piston pump configuration (Waukesha Cherry-Burrell SPX) is acceptable for runs of up to 8 h when the back-pressure is maintained below 2 bar; beyond this, observed gel count exceeds 50 particles per 100 mL on a 25 µm filter, indicating the onset of mechanically induced coagulation.

Film Elastic Recovery and Resistance to Plasticizer Migration in Laminated Lidding

When Celvolit 1408 is employed as the tie layer for PET-lidded polystyrene trays containing oily food simulants, the high ethylene mole fraction imparts an elastic recovery characteristically superior to that of conventional VAEs. Cyclic tensile testing on free films (ISO 527-3, specimen type 5, crosshead speed 100 mm/min) records a hysteresis ratio of <15% after ten cycles to 100% strain, whereas a VAE with 15% ethylene exhibits a hysteresis exceeding 35%, indicative of energy dissipation through irreversible viscous flow. This elasticity ensures that the seal remains hermetic during the post-filling thermal shock when the tray temperature drops from 95 °C to 4 °C within 30 minutes. In a migrant resistance challenge using the EU food simulant Tenax TA (modified PPO) per Regulation (EU) No 10/2011, migration of the adhesive components remains below 50 µg/dm² after 10 days at 40 °C when the dry film weight is controlled within 12–15 g/m². This value falls within the established safe margin for non-listed substances when a functional barrier layer is present; however, direct food contact compliance requires a case-by-case evaluation because Celvolit 1408 is not formulated with explicit FDA 21 CFR 175.105 clearance for all constituents, and the formulator must verify the specific end-use with the manufacturer’s food contact statement.

In contrast to acrylic-based heat-seal coatings that often require precise activation windows of ±3 °C to prevent blushing or burn-through, Celvolit 1408 provides a broader hot-tack plateau. Measured on a Theller heat-sealing unit at 1 bar sealing pressure and 0.5 s dwell, a 1.5 N/15 mm hot-tack strength is sustained over a temperature range of 75–105 °C when sealed against an amorphous PET (APET) sheet. The ethylene-rich domains undergo segmental melting above 75 °C, creating a transient melt-like layer that diffuses into the APET surface without requiring a separate tie resin. Post-cooling, the ethylenic segments recrystallise, contributing to an immediate bond strength of 2.5 N/15 mm (ASTM F88) that resists delamination during gravity-fed packaging line drop tests of 1.2 m.

In applications where the lamination line is equipped with a closed-loop gravimetric feed system, batch-to-batch viscosity variations of up to ±500 mPa·s can be automatically compensated by a 0.5–1.5% adjustment in addition water. Operator intervention is required, however, when relative humidity in the coating bay exceeds 85%, because the delayed water release from the drying film causes micro-bubble nucleation in the interlayer visible under 50× microscopy. Pre-drying of the secondary web with a hot-air knife set to 50 °C and air velocity 20 m/s mitigates this effect. The emulsion is also incompatible with borate-based buffer additives; contact with sodium tetraborate at levels above 0.1 wt% of wet adhesive triggers instantaneous shear thickening that clogs the gravure cylinders within 2 minutes of circulation.