Celvolit 1350 VAE Emulsion

Celvolit 1350 is a carboxylated vinyl acetate-ethylene (VAE) copolymer emulsion supplied at a solids content of 55 ± 1 %, a Brookfield RVT viscosity (spindle 3, 20 min⁻¹, 25 °C) of 500—1 500 mPa·s, and a pH of 4.0—5.5. The minimum film formation temperature (MFFT) determined per ISO 2115 is approximately 0 °C, while the glass transition temperature (Tg) by differential scanning calorimetry (DSC, midpoint) lies in the range of 0 to 5 °C. Average particle size, measured by laser diffraction, falls between 0.5 and 1.5 µm. The stabilisation system combines polyvinyl alcohol (PVOH) and a low level of anionic surfactant; no alkylphenol ethoxylates (APEO) are present. The carboxylic acid content, expressed as an acid number of approximately 5—10 mg KOH/g dry polymer, enables site-specific crosslinking and adhesion enhancement. The product meets the compositional requirements of FDA 21 CFR 175.105, 176.170, and 176.180 for indirect food-contact adhesives and is registered under REACH. Free monomer content remains below 0.5 wt%, and the product can be formulated into systems achieving volatile organic compound (VOC) levels below 1 g/L when used without coalescing agents, as determined by ASTM D6886.

How Does Celvolit 1350 Perform in Waterborne Adhesive Formulations Subjected to EN 204 Durability Classes?

Waterborne wood-adhesive compounds based on Celvolit 1350 routinely meet the wet-strength requirements of durability class D3 per EN 204 when compounded with a suitable ionic or blocked isocyanate crosslinker. In single-component formulations without post-added hardener, the emulsion’s native carboxyl functionality and ethylene copolymer content produce sufficient film coalescence and water resistance to satisfy class D2. Tensile shear strength on beech, conditioned and tested according to EN 205, exceeds 2.5 N/mm² under dry conditions for an adhesive containing 2—4 % PVOH extender and 0.3 % coalescent (Texanol) on polymer solids. After the D3 immersion sequence—7 days in standard atmosphere (23 °C, 50 % RH) followed by 4 days in water at 20 °C—wet shear values typically remain above 2.0 N/mm², with wood failure percentages exceeding 70 %. The low MFFT of 0 °C eliminates the need for aggressive film-forming auxiliaries in ambient shop-floor conditions, a point of distinction from higher-Tg VAE grades such as Celvolit 1325 (MFFT ≈ 5 °C). On production-scale nozzle application lines using a Zahn cup #2 viscosity of 25—30 s, the emulsion’s rheology allows clean transfer from a diaphragm pump at a back-pressure of 1—2 bar onto moving lamella laths without stringing. The absence of APEO surfactants minimizes foaming tendencies that otherwise disrupt automated bead placement. Adhesion tests on steam-treated beech at 80 °C for 60 min have shown no creep separation above 0.15 mm, qualifying for certain heat-resistant assembly glue specifications. The carboxylated backbone differentiates this grade from non-functional VAE dispersions, as the acid groups can complex with added zinc acetate or zirconium ammonium carbonate to further reduce cold-water whitening, a mechanism unavailable in base VAE products lacking acid functionality.

In high-speed corrugated converting lines where adhesive is applied by a curtain coater or a three‑roll applicator at 150—300 m/min, the emulsion’s rheological profile and tack development time become critical. Celvolit 1350, at the delivered solids of 55 %, exhibits a pseudoplastic flow index (n) near 0.6 when measured on a controlled-stress rheometer at 25 °C, enabling 40—50 µm wet film deposition without ribbing. The open time, as determined by a wedge test on kraft linerboard conditioned to 20 °C and 60 % RH under TAPPI T 411, ranges from 8 to 15 s, depending on relative humidity. On polyethylene-coated board, adhesion can drop below 0.5 N/25 mm when surface energy is below 36 mN/m; inline corona treatment raising the surface energy to 44—48 mN/m (ASTM D2578) restores bond strength to above 2.0 N/25 mm. Cold-set lamination at ambient temperature without auxiliary heat creates economic advantages over hot-melt alternatives, but the evaporative drying rate of the film limits line speed in completely unheated tunnel operations. Infrared moisture balance data indicate that 90 % of water is removed within 12—15 s at a web temperature of 60 °C; when ambient conditions fall below 15 °C, preheating of the substrate to 30 °C is necessary to prevent blocking on the winder. The dispersion is compatible with standard polyvinyl alcohol back-coatings but incompatible with amine-based wetting agents that prematurely raise pH above 6.5, initiating partial hydrolysis and destabilizing the colloidal system. Storage in unlined carbon steel tanks is not recommended due to corrosion-induced iron-ion pickup, which can cause brown discoloration and a drop in pH below 3.8.

When Formulating with Celvolit 1350 in the Presence of Ionic Crosslinkers, Rheological Considerations Must Be Addressed

Addition of ionic zirconium salts such as ammonium zirconium carbonate (AZC, 20 % ZrO₂ solution) initiates rapid complexation with surface carboxylates, increasing the emulsion’s low-shear viscosity by a factor of 2—4 within 5—10 min of mixing at 23 °C. A Brookfield RVT value rising from 800 mPa·s to over 3 000 mPa·s is typical for a 1.0 wt% AZC addition (based on wet emulsion). To prevent gelation in static zones, crosslinker dosing must occur in-line via a gear pump feeding a static mixer of 12—15 elements immediately before the application head. Residence time post-mixing must not exceed 20 min at 25 °C, and the pot-life, defined as the time to reach a viscosity of 5 000 mPa·s, is approximately 25—35 min. Temperature dependence is pronounced: at 10 °C the pot-life extends beyond 90 min, but the final crosslink density achieved after 7 days of curing drops by roughly 30 %, as tracked by gel content measurements in boiling MEK. For two-component application systems that must meet EN 204 class D4, isocyanate crosslinkers such as hydrophilically modified HDI trimers (NCO content 20—22 %) are preferred. At an addition rate of 5 % on polymer solids, the shear strength after the D4 boiling-water test (6 h in boiling water) can exceed 1.5 N/mm² when wood moisture content before bonding is held at 10 ± 1 %. The pot-life with isocyanates, indicated by a doubling of dynamic viscosity, is 2—3 hours at 23 °C, substantially longer than with ionic zirconium systems. Differences in water resistance become measurable: non-carboxylated VAE emulsions lack the capacity for this dual crosslinking mechanism, and even after isocyanate addition they display lower cohesive strength on water immersion, rarely exceeding 1.0 N/mm² D4 shear values. In plant trials, batches that exceeded 4 hours of pot-life showed a transition from substrate failure to cohesive failure within the adhesive layer, evidenced by a tacky film containing unreacted isocyanate. A 20‑µm stainless steel screen filter installed downstream of the static mixer captures any microgel particles that would otherwise cause nozzle clogging.

For interior wall paint formulations targeting low volatile organic compound content, Celvolit 1350 serves as the sole binder without coalescent addition, owing to its MFFT of 0 °C. Scrub resistance measured per ASTM D2486 (abrasive scrub medium, 500 g load, 12.5 mm shim) on a 20 % pigment volume concentration (PVC) formulation yields 150—250 cycles before failure, which is lower than the 400—600 cycles typical of all-acrylic binders but sufficient for flat interior ceiling paints not subject to frequent wet wiping. The emulsion achieves a contrast ratio of >90 % at 8 m²/L spreading rate when pigmented with 15 wt% titanium dioxide (rutile). A notable processing limitation is the sensitivity to high-shear viscosity loss in tinting systems using strong inorganic colorants, where dispersion pumps operating above 200 s⁻¹ shear rate can induce temporary viscosity breakdown of over 30 %. To mitigate, maximum shear rates during circulation should be kept below 150 s⁻¹. Comparative tests have shown that replacing a portion of the VAE with a pure acrylic soft polymer (Tg −10 °C) improves scrub cycles to 350 without deviating from zero-VOC status, but the dry film’s picking resistance on paper laminates declines. The balance between film integrity and water sensitivity represents the key differentiator from pure acrylic or styrene-acrylic binder platforms, which demand 1—3 % coalescent for similar film formation at 5 °C.

Processing Compatibility with High-Capacity Coating Lines: Heat Stability and Foam Control

Celvolit 1350 exhibits thermal coagulation behavior when subjected to prolonged exposure above 35 °C under static conditions. In jacketed holding tanks, recirculation at a linear velocity of 0.3 m/s through 25 mm bore piping prevents skin formation but raises bulk temperature; consequently, cooling-coil circuits must maintain the storage temperature below 30 °C. The emulsion is stabilized by PVOH, which, unlike fully surfactant-stabilized colloids, generates limited foam under low-pressure air admixing. The dynamic surface tension, measured by maximum bubble pressure method at a surface age of 100 ms, is approximately 42 mN/m, higher than that of conventional surfactant-only systems (35—38 mN/m). This property reduces the need for mineral oil defoamers, which can interfere with cling performance on high-speed label presses. When defoamer is required, a 0.1—0.2 wt% addition of a polyether siloxane (active content 20 %) reduces foam collapse time from >120 s to <15 s without crater formation in the dried adhesive line. In production, air entrapped during drum emptying into a saw-tooth disperser must be released by 10—15 min rest under vacuum (0.8 bar), otherwise microvoids in the final adhesive layer reduce peel strength on oriented polypropylene by 15—25 %.