Emulsão Dairen DA-265 VAE

Dairen DA-265 is a carboxylated vinyl acetate-ethylene (VAE) copolymer emulsion stabilized with a polyvinyl alcohol protective colloid, supplied at a nominal solids content of 55.0% by weight and a Brookfield RV viscosity (spindle #3, 20 rpm, 23 °C) typically in the range of 2 500–4 500 mPa·s. The dispersed phase carries a glass transition temperature (T_g) centered at −3 °C by differential scanning calorimetry, which translates to a minimum film-forming temperature (MFFT) of 0 °C without external coalescent addition, measured according to ISO 2115. The built‑in ethylene comonomer fraction imparts permanent chain flexibility, eliminating the need for phthalate or benzoate plasticizers in many ambient‑cure adhesive and coating systems. The grade is positioned as a low‑odour, low‑VOC base binder for formulations requiring high wet tack on porous and non‑porous surfaces, alkaline stability in cementitious matrices, and hydrolytic resistance under intermittent moisture load.

What Distinguishes DA-265 from Conventional VA Homopolymer Dispersions?

A straight vinyl acetate homopolymer emulsion typically exhibits a T_g near 28–33 °C and an MFFT above 15 °C, demanding significant coalescent dosage to form a coherent film at ambient temperature. DA-265, by virtue of its ethylene segments, lowers the T_g into the sub‑zero domain while retaining sufficient cohesive strength for structural adhesives and renders. The ethylene‑rich backbone also reduces the oxygen‑sensitive acetate group concentration per unit mass, slowing the carbonyl‑to‑carboxyl hydrolysis pathway that accelerates ageing embrittlement in VA homopolymer films. In accelerated QUV‑B weathering (ASTM G154, cycle 1, 1 000 h), films cast from DA-265 retain more than 70% of original elongation at break, whereas a plasticised VA homopolymer control typically falls below 40% under identical exposure.

The carboxylation of the polymer backbone, achieved through the incorporation of a low level of acrylic acid monomer during emulsion polymerization, introduces pendent carboxylic acid groups that enhance colloidal stability, promote adhesion to metallic and mineral substrates, and provide reactive sites for post‑addition ionic crosslinking. This differentiates DA-265 from non‑carboxylated conventional VAE grades, which rely solely on steric and interfacial tension mechanisms for dispersion stability and may exhibit lower wet adhesion to aluminium or galvanized steel.

Tensile Adhesion Strength After Water Immersion and Thermal Ageing

When formulated into a cementitious tile adhesive (CTA) in accordance with EN 12004, the emulsion is typically added at 3–6% on cement weight, replacing a portion of the batch water. The polymer‑to‑cement ratio, water‑to‑cement ratio, and superplasticizer demand must be rebalanced because the colloidal solids contribute to the continuous phase viscosity and retard early C₃S hydration by surface adsorption. Isothermal calorimetry at 20 °C shows a shift of the main silicate hydration peak by 60–90 minutes at a 5% polymer addition level, which is consistent across VAE latices with polyvinyl alcohol protective colloids. Post‑cure adhesion measured by the pull‑off method (EN 1348) on fully vitrified ceramic tiles after 7‑day standard climate storage followed by 21‑day water immersion at 23 °C yields values in excess of 1.0 MPa for formulations based on DA-265, with cohesive failure predominantly within the mortar. By comparison, non‑redispersible VA homopolymer‑modified mortars rarely exceed 0.5 MPa under the same water immersion protocol and typically exhibit adhesive failure at the tile‑mortar interface.

Thermal ageing at 70 °C for 14 days (EN 1348, heat resistance condition) results in adhesion recovery to above 1.5 MPa as the cement matrix continues to hydrate and the latex coalesces further within capillary pores. The alkaline hydrolysis resistance of the ethylene‑rich VAE structure is critical here: when immersed in a saturated Ca(OH)₂ solution at 50 °C for 28 days, the isolated polymer film retains more than 80% of its initial tensile strength (ASTM D882), whereas VA homopolymer films dissolve or disintegrate within 72 hours.

The table below collates the standard specification parameters and their corresponding test methodologies.

The relatively coarse particle size distribution, characteristic of polyvinyl alcohol‑stabilized emulsions, contributes to high‑shear stability under violent pumping conditions but imposes a shear‑thinning rheology that must be accounted for in blade‑coating and roller‑application viscosity curves. Pseudoplasticity indices (ratio of viscosity at 2 rpm to 20 rpm) typically fall between 3.5 and 5.0.

When DA-265 Is Formulated into Pressure-Sensitive Adhesives

The low T_g and inherent tack of the ethylene‑modified backbone allow DA-265 to serve as the primary binder in water‑based pressure‑sensitive adhesives (PSAs) for paper labelling tapes and repositionable films without the addition of tackifying resin dispersions, thereby maintaining optical clarity and reducing volatile bleed‑out. Lab‑coated PET films (coat weight 22–25 g/m² dry, dried at 80 °C for 3 min) exhibit 180° peel adhesion to stainless steel (ASTM D3330, test method A) of 4.5–6.0 N/25 mm and a static shear holding time exceeding 100 h (1 kg load, 25 mm × 25 mm overlap, 23 °C). When a post‑added crosslinker such as an ammonium zirconium carbonate or a polyfunctional aziridine is introduced at 0.3–0.5 wt% on dry polymer, the static shear resistance increases beyond 500 h with only a minor peel penalty (peel decreases to 3.8–5.0 N/25 mm), the exact balance depending on the degree of carboxylic acid neutralization prior to crosslinker addition.

The compatibility with rosin ester and hydrocarbon tackifier dispersions is limited due to the anionic‑nonionic stabilization package; hydrogenated rosin ester dispersions with an average particle size below 300 nm can be incorporated up to 10 phr without coagulation, but higher loadings provoke viscosity buildup and microscopic grit formation detectable on a Hegman gauge. Published data for high‑solids PSA formulations using DA-265 paired with alkylphenol‑free surfactants for enhanced food‑contact compliance (EU No 10/2011, overall migration limit) indicate satisfactory migration values below 10 mg/dm² when the film is conditioned at 40 °C for 10 days with the simulant Tenax.

In woodworking assembly and profile wrapping, DA-265 is combined with polyvinyl alcohol solution extenders at 15–25% dry weight ratio to adjust open time and initial green strength. The high‑molecular‑weight PVA co‑binder raises the wet‑tack plateau, enabling a vertical assembly hold without clamping longer than 20 seconds, which is critical on short‑cycle edgebanding machines operating at feed speeds above 12 m/min. D3 water resistance classification (EN 204) is obtainable with 10–12% of a blocked isocyanate or polymeric MDI dispersion co‑reactant; without the crosslinker, the bond line fails after 4 hours of cold‑water immersion at the prescribed 23 °C.

Maintaining Colloidal Stability Under Mechanical Shear and Freeze‑Thaw Cycling

VAE emulsions with polyvinyl alcohol colloids are susceptible to shear‑induced coagulation when processed through high‑pressure piston pumps or toothed colloid mills operating above critical shear stress thresholds. DA-265 tolerates recirculation through a centrifugal pump at 1 500 rpm for 30 minutes with < 0.1% screen residue on a 40 µm filter, but twin‑screw compounding with a filler loading above 30 wt% calcium carbonate can generate local thermal‑mechanical hot spots that raise the surface temperature of the metal barrel beyond the emulsion’s thermal coagulation onset, which is approximately 75 °C under moderate shear. Barrel cooling to 40 °C is therefore essential during continuous processing.

Freeze‑thaw stability of DA-265 in its as‑supplied state is limited; the emulsion coagulates irreversibly after a single freeze‑thaw cycle (−15 °C to +23 °C). If winter transport or unheated warehouse storage is anticipated, 5–7% of a freeze‑thaw stabilizer such as a low‑HLB nonylphenol‑free alkoxylate or polypropylene glycol must be post‑added, which drops the freezing point below −10 °C and permits up to 3 cycles without viscosity drift beyond 20% of the initial value. Avoid combination with multivalent cationic additives (Al³⁺, Ca²⁺, Zn²⁺ at concentrations above 0.1 % of the liquid phase) in the absence of a complexing agent such as tetrasodium pyrophosphate; otherwise, carboxylate bridging causes instantaneous gelation. Direct contact with strong oxidizers, strong mineral acids, and amines that raise the pH above 9.0 will destabilize the protective colloid shell and must be avoided.

In contrast to DA-102, which sacrifices low‑temperature flexibility for elevated heat resistance and a higher Wet-Grab Test shear value on porous paper, DA-265 provides a broader service‑temperature window for exterior applications without volatile coalescents. DA-305 pushes the glass transition even lower but requires careful formulation to control creep under load; DA-265 occupies the midpoint where structural integrity and permanent tack coexist, making it the default starting point when transitioning a rigid styrene‑acrylic or VA‑homopolymer system toward a non‑toxic, plasticizer‑free compliance profile under REACH and EU Ecolabel for indoor adhesives (limit values for TVOC ≤ 1 000 µg/m³ after 3 days, EN 16516).