Emulsão BJ-707F VAE

The emulsion’s molecular weight distribution governs adhesion to low-energy surfaces.

The BJ‑707F VAE Emulsion is a carboxylated vinyl acetate–ethylene copolymer dispersion stabilized with a mixed anionic/nonionic surfactant system. Its distinguishing feature relative to conventional VAE grades is a narrow molecular weight dispersity (Đ = 2.1–2.4, determined by GPC‑MALLS using DMAc/LiCl eluent) coupled with a high ethylene incorporation of 18–20 wt%. This combination depresses the dry‑state glass transition to  −8 °C (DSC midpoint, 10 K/min under nitrogen) while maintaining a minimum film‑forming temperature (MFFT) of 3 °C per ISO 2115, enabling coalescent‑free film formation above that threshold without volatile organic solvents. The elevated ethylene content simultaneously plasticizes the vinyl acetate backbone, eliminating the need for external phthalate or benzoate plasticizers and thereby reducing potential migration in skin‑contact adhesives tested under FDA 21 CFR 175.105 conditions.

In side‑by‑side cross‑linkable wood adhesive formulations, BJ‑707F delivers a wet shear strength value of 5.2 MPa on beech after 4 h cold‑water soak (EN 204 D3) when combined with 3 wt% polymeric MDI, compared with 3.8 MPa for a standard VAE containing 10 % ethylene and an equivalent isocyanate loading. The improvement is attributed to the higher concentration of ethylene sequences, which enhance backbone mobility during isocyanate crosslinking, and to a controlled carboxylic acid content of 0.6–0.8 mmol/g that provides co‑reactive sites for metal‑ion or aziridine post‑cure without destabilizing the dispersion.

Typical physical properties of BJ‑707F as‑supplied

Property	Value	Test method
Solids content	55.0 ± 1.0 %	ISO 3251 (2 h, 105 °C)
Viscosity (Brookfield LV, sp. 3, 12 rpm, 25 °C)	2500–4000 mPa·s	ISO 2555
pH	4.5–5.5	ISO 976
Average particle size	0.45 µm	ISO 22412 (DLS, intensity‑weighted)
Minimum film‑forming temperature	3 °C	ISO 2115
Density at 20 °C	1.07 g/cm³	ISO 2811‑1
Surface tension	36 mN/m	Du Noüy ring, 25 °C
Residual vinyl acetate monomer	< 50 ppm	GC‑FID headspace

In contrast to high‑solids PVAc homopolymers, BJ‑707F does not require external coalescents for ambient‑temperature film formation, yet its shelf life remains 12 months in unopened containers stored between 5 °C and 35 °C. Freeze‑thaw stability is limited: after one cycle of −5 °C for 24 h followed by thawing at 25 °C, the average particle size increases to 1.2 µm and the coagulum content on a 40 µm screen rises to 0.08 %, making winter shipment without heated logistics inadvisable. Where cold‑weather storage is unavoidable, the addition of 2–3 wt% propylene glycol (on wet emulsion) has been shown to suppress freeze‑induced coagulation on pilot‑scale storage trials, though it depresses wet‑end tack development by approximately 15 %.

Why does BJ‑707F outperform standard VAE dispersions in plasticizer‑free pressure‑sensitive adhesives?

The answer lies in the architecture of the polymer‑water interface. BJ‑707F employs a block‑copolymer surfactant envelope comprising ethoxylated nonylphenol‑free alkyl polyglucoside (HLB 13.5) and a sulfosuccinate anionic component. This design produces a low‑foam dispersion that can be processed on a high‑speed reverse‑roll coater at line speeds up to 120 m/min without antifoam additives that often migrate and reduce loop tack. Peel adhesion on untreated polypropylene (ASTM D3330, 180° peel, 20 min dwell) reaches 3.8 N/25 mm for a 25 µm dry film of the neat BJ‑707F film, while an equivalent VAE with 10 % ethylene and a conventional octylphenol ethoxylate surfactant delivers 0.9 N/25 mm under identical conditions. This more than four‑fold increase is attributable to the higher ethylene sequences that increase the van der Waals component of the surface free energy to 28 mJ/m² (calculated from Owens‑Wendt analysis using contact angles of water and diiodomethane), enabling wetting of low‑energy substrates without primer treatment.

Processing on a pilot‑coater equipped with a 40 µm gap and forced‑air drying at 90 °C for 2 min repeatedly yielded a coating weight variation below ±0.5 g/m². When BJ‑707F was compounded with 15 wt% (dry/dry) of a pentaerythritol ester tackifier dispersion (softening point 95 °C), the resulting 180° peel on stainless steel increased to 8.1 N/25 mm with a loop tack of 12.3 N (FINAT FTM 9), placing the performance envelope between permanent and removable filmic labels. In this regime, cohesive failure is the practical limit: the SAFT (shear adhesion failure temperature, 1 kg load, 1 °C/min ramp) was 145 °C, well above the 80–100 °C range typical for highly plasticized PVAc PSAs, again reflecting the internal plasticization of the ethylene segments.

Particle Size and Surfactant Architecture

The 0.45 µm median particle size was selected to balance colloidal shear stability with high‑speed filterability. On a 200‑mesh screen (74 µm), the as‑supplied emulsion passes with less than 50 ppm grit. When subjected to a high‑shear transfer pump (Waukesha Universal PD, 1200 rpm, 30 min recycle), the coagulation fraction remained below 0.02 %. The surfactant architecture also controls viscosity response to pH adjustment: increasing pH to 7.0 with 10 % ammonium hydroxide raises the low‑shear viscosity to 9500 mPa·s, allowing the same base emulsion to be used as a viscosity builder in carpet pre‑coat formulations without additional thickener. Subsequent shear at 100 s⁻¹ (cone‑plate rheometer) reduces the viscosity to 280 mPa·s, demonstrating pronounced pseudoplasticity suitable for roller‑applied adhesives.

BJ‑707F coalesces into films with a water‑vapor transmission rate of 45 g/m²·day at 38 °C, 90 % RH (ASTM E96 desiccant method) for a 100 µm film. This moderate breathability, combined with the absence of coalescing solvent, makes the dispersion a candidate for temporary protective films in the building envelope, where seasonal moisture buffering must not trap liquid water. However, the carboxylic acid functional groups are ion‑sensitive; films immersed in 0.1 M NaOH solution for 24 h exhibit a weight loss of 12 wt% and a tensile strength reduction from 4.1 MPa to 1.2 MPa (ISO 37 type 3 dumbbells). Thus, direct contact with alkaline cementitious surfaces requires a barrier primer or post‑crosslinking with ammonium zirconium carbonate (3 wt% of emulsion solids) that reduces weight loss to 2 wt% under the same alkaline immersion.

When compounding BJ‑707F with polyvinyl alcohol for remoistenable envelopes

The interaction with fully hydrolyzed PVOH (degree of hydrolysis > 98 mol%, 4 wt% solution) is non‑Newtonian and must be managed to avoid macroscopic phase separation. Pilot‑scale trials on a planetary mixer (40 L capacity, blade speed 60 rpm) demonstrated that slow co‑addition of the PVOH solution pre‑neutralized with a volatile base (ammonia, pH adjusted to 6.8) into the emulsion yields a homogeneous adhesive with a remoistening tack time of  < 2 s at 50 % RH. The critical parameter is the ratio of acetate groups to free carboxylic acid: if the PVOH dominates the hydrogen‑bond network prematurely, a skin forms on the static adhesive surface, which raises remoistening time to  > 8 s and makes the product commercially unviable. In contrast to earlier VAE grades that required 0.5–1.0 wt% urea as a humectant to suppress premature skinning, BJ‑707F’s higher ethylene content and the glucoside‑based surfactant reduce film‑surface ordering, so skinning can be controlled by holding the adhesive at  > 55 % RH during packaging. The same formulations meet EN 71‑3 migration limits for antimony, arsenic, barium, and cadmium when used in envelope‑grade adhesives for children’s stationery.

In a production environment, the adhesive is coated onto offset paper (90 g/m²) via a three‑roll engraved applicator. Line speed trials showed that a wet‑film thickness of 35 µm dried in a 4‑zone convection oven with a peak web temperature of 85 °C yields a moisture content of  < 2 % and a dry adhesive weight of 4.5 g/m². The product achieved an average machine‑direction bond strength of 2.8 N/15 mm (TAPPI T 494) without fiber tear on the first pull, fulfilling the requirement for a tacky but non‑blocking seam.

As far as wood‑furniture assembly is concerned, BJ‑707F has been evaluated against a Type‑II interior classification. When compounded with 2 wt% butyl benzyl phthalate and 0.5 wt% glutaraldehyde crosslinker (solids basis), the adhesive spread at 150 g/m² on oak and pressed at 0.7 MPa for 3 h achieved a cold‑set shear strength of 9.6 MPa (EN 205). After the EN 204 D2 water‑resistance cycle (4 days cold water), the average value was 2.1 MPa, exceeding the 2.0 MPa threshold. The use of glutaraldehyde with BJ‑707F requires a pot‑life management strategy because the carboxylic acid groups accelerate the crosslinking reaction at near‑neutral pH. Production workshops report that pot life at 25 °C drops to 45 min after addition, necessitating a two‑component mixing head on the roller coater. An alternative formulation replacing glutaraldehyde with polymeric isocyanate (pMDI, 4 wt% of emulsion solids) extends pot life to 90 min while maintaining D2 shear of 2.4 MPa, albeit at a higher cost.

A second comparative table positions BJ‑707F against two common emulsion types used in woodworking.

Adhesive performance on birch plywood, 150 g/m² spread, 1 MPa clamping, 24 h conditioning at 23 °C, 50 % RH

Adhesive system	Dry shear strength (MPa) EN 205	Wet shear D3 (MPa) EN 204	Water soak delamination (%)	Free formaldehyde (mg/kg)
BJ‑707F + 4 % pMDI	10.2	5.2	2.1	< 5 (EN 717‑1 chamber)
Standard VAE (10 % ethylene) + 4 % pMDI	8.4	3.8	6.8	< 5
PVAc homopolymer + 10 % diisobutyl phthalate	11.5	2.0	12.4	< 5

The practical limit of BJ‑707F in open‑time applications is its humidity sensitivity during film coalescence. A relative humidity below 35 % at 20 °C leads to a skin‑over time of less than 30 s, which prevents adequate penetration into porous wood species. Conversely, at  > 70 % RH, the drying rate becomes insufficient for chair‑clamping schedules and a hot‑air pulsed dryer is recommended to bring the adhesive line temperature to 50 °C within 2 min. Published data for this specific configuration is limited to in‑house field reports from pan‑European window‑frame laminators, where the combination of BJ‑707F, pMDI, and a montmorillonite rheology modifier (0.5 wt%) yielded D4‑passing constructions with zero formaldehyde, outperforming melamine‑fortified UF systems in terms of indoor air quality compliance under AgBB and AFSSET protocols.

When replacing alkylphenol ethoxylate‑stabilized dispersions in nonwoven binder applications

BJ‑707F eliminates alkylphenol ethoxylates (APEOs) from the wet‑end, which is mandatory for OEKO‑TEX Standard 100 product class I certification. The dispersion applied via a foam‑impregnation unit at 8 % solids add‑on to a 40 g/m² carded PET web yields a dry tensile index of 6.3 Nm/g (ISO 9073‑3) in the machine direction after curing at 130 °C for 2 min. A nonylphenol ethoxylate‑stabilized VAE of similar Tg gives 5.1 Nm/g, with the difference attributed to BJ‑707F’s finer particle size leading to more uniform fiber‑junction coverage visible under scanning electron microscopy at 500×. The wet tensile retention after 1 h water immersion (ISO 9073‑3) is 65 %, identical to the APEO‑based control, but the lotion‑wet repellency is higher, making it suitable for household wipes that must retain strength during cleaning tasks. Formulations containing quaternary ammonium antimicrobials must be screened, however, because aqueous solutions of benzalkonium chloride above 0.05 wt% cause macroscopic coagulation of the anionic‑stabilized BJ‑707F within 6 h at 40 °C; compatibility tests conducted according to ASTM D3709 (modified for emulsion‑additive mixtures) demonstrated immediate phase separation at 0.1 % benzalkonium chloride. This represents a hard boundary for hygiene‑product formulators, who may need to switch to a non‑ionically stabilized VAE designed for cationic environments.

Co‑polymerization of ethylene in the BJ‑707F backbone also manifests in superior adhesion to corona‑treated LDPE film. Peel values on 30 µm corona‑treated polyethylene (38 dyn/cm surface energy) reach 2.2 N/15 mm after lamination with a nonwoven scrim, compared to 0.8 N/15 mm for an equivalent all‑acrylate binder. Substrate‑failure analysis indicates that the failure mode remains adhesive in both cases, but the lower glass transition and higher ethylene content of BJ‑707F enable polymer‑chain inter‑diffusion under light pressure (0.2 MPa, 10 s dwell time). The producer’s specification sheets caution, however, that corona treatment must be performed in‑line, because the treated surface energy decays to  < 34 dyn/cm within 48 h under warehouse conditions, and adhesion falls below 1.0 N/15 mm.