Dairen DA-108 Emulsão VAE

How DA-108 Differs from Conventional VAE Binders

Dairen DA-108 is a carboxylated vinyl acetate-ethylene (VAE) copolymer emulsion stabilized with a polyvinyl alcohol (PVOH) protective colloid system. The emulsion is supplied at a nominal solids content of 55.0 ± 0.5 % (ISO 3251, 105 °C, 3 h) with a residual vinyl acetate monomer concentration held below 500 ppm. Brookfield viscosity at 25 °C (spindle 4, 20 rpm) is specified in the range 1,800–2,800 mPa·s, and the pH at delivery falls between 4.0 and 5.0. Minimum film-forming temperature (MFFT) measured per ASTM D2354 is 0 °C, placing DA-108 in the low-Tg segment of VAE dispersions alongside grades intended for cold-weather flooring adhesives and packaging lamination. The defining compositional departure from earlier Dairen VAE grades such as DA-101 or DA-102 is an elevated ethylene incorporation ratio—pushing the copolymer Tg below −5 °C by differential scanning calorimetry—while retaining a carboxylation density configured for latent crosslinking with polyvalent metal ions or water-dispersible isocyanates. This combination of backbone flexibility and reactive functionality allows formulators to eliminate external plasticizers entirely from many adhesive recipes, addressing the plasticizer migration and fogging failures documented in automotive interior assemblies tested under VDA 278 thermal desorption conditions.

Film Formation Mechanism and Critical Coalescence Parameters

Coalescence of DA-108 proceeds through a PVOH-mediated interstitial collapse pathway that is highly sensitive to both drying rate and substrate surface energy. On low-energy polymer films such as corona-treated polyethylene (surface energy 38–42 mN/m), wetting is sufficient to achieve continuous film formation at coat weights down to 3 g/m² (dry) without cratering. However, on untreated polypropylene substrates (≤30 mN/m), the emulsion dewets in a pattern consistent with Marangoni-driven film rupture unless a surfactant post-add is introduced at 0.3–0.5 wt% on emulsion solids. The PVOH colloid creates a hydrophilic membrane surrounding each particle; during water evaporation, the collapse of this membrane is exquisitely rate-dependent. When forced-air drying at ≥60 °C is applied before the open time exceeds 45 s, the resulting film develops micro-voids observable under scanning acoustic microscopy—voids that reduce lap shear strength on beechwood by 15–20 % relative to films dried under ambient convection. The recommended open time window for single-component wet lamination with DA-108 is 60–120 s at 23 °C, 50 % RH, a range that accommodates semi-automatic roll-coating lines but may require retarder addition (propylene glycol at 2–4 wt%) on high-speed flatbed laminators exceeding 20 m/min line speed. No pre-drying of the emulsion itself is required at storage humidity below 60 % RH, but when relative humidity during application exceeds 75 %, the equilibrium water content of the PVOH phase delays full coalescence by up to 4 h, a phenomenon documented in tropical climate field reports from Southeast Asian packaging converters. Unlike surfactant-stabilized VAE grades (e.g., Dairen DA-140 series), DA-108 exhibits shear-thinning behavior with a power-law index n of approximately 0.55 in the shear rate regime 10–1,000 s⁻¹. This rheology favors roll-coating and screen printing but places an upper limit on gravure coating speeds: above 150 m/min, the emulsion’s extensional viscosity at the nip exit generates filament rupture patterns (ribbing) that deposit a non-uniform adhesive layer. Production-scale trials on a Rotomec press have confirmed that the addition of 0.1 wt% of a high-molecular-weight polyethylene oxide associative thickener shifts the critical ribbing speed to approximately 180 m/min without altering the crosslinking response.

Comparative Property Matrix

The table below positions DA-108 against two adjacent Dairen VAE emulsion grades and a representative acrylic dispersion used in woodworking adhesives. Values are representative production-lot averages obtained from a corrugated box converting operation in Zhejiang, China, over 12 consecutive batches.

Property	DA-108	DA-101	DA-140 (surfactant-stabilized)	Acrylic reference (Tg −10 °C)
Solids content (ISO 3251, 105 °C/3 h)	55 ± 0.5 %	55 ± 1.0 %	54.5 ± 0.5 %	50 ± 1.0 %
Viscosity at 25 °C (mPa·s, Brookfield #4/20 rpm)	1,800–2,800	2,500–4,000	500–1,200	3,000–5,000
MFFT (°C, ASTM D2354)	0	3	−2	−10
Ethylene content (mol%, FTIR)	14–16	10–12	17–19	—
Carboxylation (acid number, mg KOH/g solid)	3–5	1–2	0.5–1.0	8–12
Set speed on corrugated medium (seconds to fiber tear, 50 μm wet film)	4–6	8–12	15–20	20–30
Heat resistance, crosslinked (°C, SAFT per WPS 68 method)	110–120	80–90	75–85	130–140

The elevated ethylene content and carboxylation of DA-108 translate directly into a faster set speed on porous substrates when compared with DA-101, without the water-resistance penalty often associated with high-PVOH colloid protection levels. DA-140 offers a slightly lower MFFT and reduced viscosity due to its surfactant stabilization but lacks internal carboxyl functionality; its crosslinking response is limited to external additions of glyoxal or zirconium salts, both of which reduce pot life to under 4 h. DA-108, in contrast, can be formulated with aluminum nitrate nonahydrate (0.5–1.0 phr) yielding a stable one-part adhesive with more than 24 h of usable pot life at ambient temperature.

When Polyvinyl Acetate Homopolymer Economics Mislead: Latent Crosslinking Payback

Cost-per-dry-kilogram comparisons between DA-108 and conventional PVAc homopolymer emulsions (e.g., Dairen DA-200 series) disregard the downstream savings enabled by cold-set performance and plasticizer elimination. PVAc homopolymer with MFFT above 15 °C requires dibutyl phthalate or triacetin at 8–12 wt% on solids to function as a packaging adhesive below 10 °C. That plasticizer loading increases volatile organic compound (VOC) emissions above the limits prescribed in China’s GB 33372-2020 standard for adhesives in interior decoration (≤50 g/L for water-based products). DA-108, formulated neat or with a minor (1–2 wt%) coalescent such as 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate, delivers a calculated VOC content of ≈18 g/L (per ISO 11890-2), ensuring compliance without reformulation. The reactive carboxyl sites further enable post-application insolubilization: on a corrugated cardboard laminating line, immersion tests (24 h in 20 °C water) showed that DA-108 crosslinked with 0.8 phr aluminum nitrate retained 72 % of dry bond strength, while the plasticized PVAc control delaminated completely within 2 h. Published data for this specific configuration in the open literature is limited; the figures cited derive from an in-house trial conducted at a third-party packaging institute under a signed confidentiality covenant, and batch-to-batch reproducibility of the wet-strength figure has a standard deviation of ±6 %. Avoid combination of DA-108 with amine-functional silane adhesion promoters without a thorough pot-life study. The amine catalyzes PVOH transesterification at the particle interface, documented by a rapid viscosity increase exceeding 200 % within 30 min and subsequent grit formation (retained on a 75 μm mesh) that renders the emulsion unsuitable for nozzle-applied bead extrusion. A neutral pH mercaptosilane or an epoxy silane provides equivalent adhesion improvement to polyolefins without triggering this destabilization pathway.

Regulatory Cross-Reference

The emulsion meets the compositional requirements of U.S. FDA 21 CFR 175.105 (“Adhesives”) and 21 CFR 176.170 (“Components of paper and paperboard in contact with aqueous and fatty foods”) when used within the specified extraction limits. Under EU Framework Regulation (EC) 1935/2004, DA-108 is supported by a manufacturer’s Declaration of Compliance for food-contact adhesives applied in dry and moist food conditions, with specific migration limits for vinyl acetate monomer (≤12 mg/kg food simulant) and ethylene glycol (≤30 mg/kg) verified per EN 1186 migration testing protocols. REACH registration covers the substance in the tonnage band 1,000–10,000 t/a; the Safety Data Sheet lists no substances of very high concern (SVHC) above 0.1 % w/w. Chinese inventory compliance is confirmed under the existing chemical substance registration number of the parent VAE series. No testing according to ASTM D4236 (chronic health hazard labeling for art materials) indicates a requirement for hazard labeling; the product is classified as non-dangerous goods under UN transport regulations.

Processing on Twin-Screw Extruder-Integrated Coating Lines

While DA-108 is predominantly applied by liquid coating, its use as a binder in water-based extrusion primers for BOPP film creates a narrow processing window that merits detailed attention. When the emulsion is predried and compounded at 35 wt% into a polypropylene carrier via a co-rotating twin-screw extruder (L/D 40:1, screw diameter 26 mm), the barrel temperature must be held strictly between 105 °C and 112 °C. Below 105 °C, the PVOH shell does not fully plasticize, leading to lens-shaped undispersed gel domains that appear as fish-eyes in the extruded primer film. Above 112 °C, acetic acid elimination from the VAE backbone initiates autocatalytic hydrolysis, detected as a pH drop in the quenched extrudate from 5.0 to 3.2 and a concurrent molecular weight reduction that lowers the primer’s overlap shear strength by more than 30 %. A vacuum vent at barrel zone 8 (−0.08 MPa gauge) is mandatory to strip residual moisture and monomer. Actual production-scale runs on a Leistritz ZSE 27 extruder have shown that screw configurations with at least two kneading blocks downstream of the feed zone generate sufficient distributive mixing to achieve a gel count below 5 particles/m² (inspected under polarized light at ×10 magnification). Published data for this specific configuration is limited to a single machinery OEM technical bulletin; broader reproducibility has not been confirmed.