What Separates CW FS-Ⅱ from Standard VAE Dispersions?
CW FS-Ⅱ is a carboxylated vinyl acetate-ethylene copolymer emulsion engineered specifically for adhesion-demanding flexible substrates where conventional VAE grades exhibit bond decay under dynamic flexural loading. The product carries a solids content of
54.5 ± 1.0% with a Brookfield LVF viscosity of
1,200–2,000 mPa·s (spindle 3, 30 rpm,
25°C) and a pH of
4.5–5.5. Its minimum film-forming temperature (MFFT) of
≤0°C eliminates the need for coalescing solvents in many ambient-cure processes, enabling formulation of adhesives and coatings that comply with EU Directive 2004/42/CE Stage II VOC limits without sacrificial plasticizer migration. The emulsifier system is APEO-free, and the product meets the voluntary emission class
EC1 PLUS criteria per GEV testing protocol.
A recurring failure mode in commodity VAE-based laminating adhesives is interfacial delamination after repeated bending or stretch-recovery cycles, particularly on corona-treated polyethylene and biaxially oriented polypropylene. CW FS-Ⅱ mitigates this through a bimodal particle size distribution centered at
380 nm and
1.2 µm, which densifies film coalescence and reduces capillary pathways for moisture ingress. In cycled T-peel testing according to
ASTM D1876 on
30 µm corona-treated LDPE, the emulsion maintains
2.8 N/15mm after
1,000 flex cycles at
23°C and
50% R.H., whereas an unmodified VAE dispersion of equivalent Tg typically drops below
1.0 N/15mm within
400 cycles.
Why Film Formation on Silicone-Coated Release Liners Demands Low Water-Soluble Ion Content
When CW FS-Ⅱ is applied as a repositionable adhesive layer onto silicone-coated PET release liners, ion migration into the silicone interface can raise surface energy beyond
30 mN/m, crippling release performance. The emulsion exhibits a conductometric ash residue of
≤0.15% and an extractable chloride ion concentration below
50 ppm, values that minimize ionic contamination of the release surface. In production trials on a Bachofen & Meier comma coater running
15 m/min line speed with
120°C oven profile, transfer coating of CW FS-Ⅱ onto
36 µm polyester liner resulted in release forces remaining within
2–5 cN/cm after
7 days’ aging at
50°C, as measured per
FTM 3. By comparison, a general-purpose VAE with a surfactant-stabilized system typically sees release force drift upward to
15–20 cN/cm under identical conditions, necessitating liner substrate changes.
The low ion profile also reduces electrochemical corrosion risk when the adhesive is used on metallized films. In aluminum-metallized BOPET (
OD 2.0,
60 ohm/sq), immersion in CW FS-Ⅱ wet laminate for
48 hours at
40°C produced no visible metal loss at the adhesive interface, unlike an anionic surfactant-rich VAE where pitting corrosion became evident within
12 hours. This characteristic is leveraged in flexible printed circuit coverlay attachment and EMI shielding tape constructions where adhesive-metal contact integrity is critical.
Physical and Film Properties of CW FS-Ⅱ
| Property | Specification | Test Method |
|---|
| Solids content | 54.5 ± 1.0% | ISO 3251:2019 |
| Viscosity (Brookfield LVF, sp. 3, 30 rpm, 25°C) | 1,200–2,000 mPa·s | ISO 2555:2018 |
| pH | 4.5–5.5 | ISO 976:2013 |
| MFFT | ≤0°C | ISO 2115:2001 |
| Tg (midpoint, DSC) | −5 ± 2°C | ISO 11357-2:2020 |
| Particle size (D50) | 380 nm /1.2 µm bimodal | ISO 22412:2017 (DLS) |
| Surface tension (Du Noüy ring) | 38–42 mN/m | DIN 53914 |
| Ash content (600°C) | ≤0.15% | ISO 3451-1:2019 |
Without a dedicated header, a critical processing window emerges during high-shear roll application onto extensible nonwoven substrates. When CW FS-Ⅱ is coated onto
25 gsm spunbond polypropylene via 3-roll reverse gravure with
80-line chrome-plated cylinder, the shear rate at the nip exceeds
104 s⁻¹. The emulsion’s pseudoplastic behavior—apparent viscosity drops from
1,500 mPa·s at
1 s⁻¹ to approximately
180 mPa·s at
10,000 s⁻¹, per cone-and-plate rheometry at
23°C—permits clean transfer without misting or web break. If the formulation batch exhibits viscosity above
2,200 mPa·s at low shear, air entrainment in the gravure cells increases, leading to patchy coating. Operators must monitor press-side viscosity daily with a Zahn cup #3; a reading above
28 seconds warrants dilution with deionized water within
2–5% by weight, strictly limited to preserve cohesive strength. Over-dilution beyond
5% causes the MFFT to drift upward by
1–2°C and reduces calender compaction capability in subsequent lamination stages.
Adhesion to Low-Energy Substrates Without Primer or Corona Re-Treatment
Adhesive formulators frequently report that VAE copolymers fail to wet surfaces with free surface energy below
38 mN/m unless priming or inline corona treatment is applied. CW FS-Ⅱ incorporates a controlled level of long-chain branching via a proprietary ethylene sequence redistribution during polymerization, which lowers the dynamic contact angle on untreated PET from
72° (for linear VAE) to
55° as measured by sessile drop at
0.5 seconds wetting time. On flame-treated polypropylene film with surface energy
34 mN/m, a
10 µm dry film of CW FS-Ⅱ achieves
4.2 N/25mm peel strength to paper face stock (
AFERA 5001) without primer. This eliminates a separate primer coating station, reducing process cost and the complexity of monitoring primer batch life.
In flexible packaging laminations, the bond between CW FS-Ⅱ and aluminum foil (
9 µm, matte side) reaches
6.0 N/15mm after
3 days’ cure at
23°C and
50% R.H., according to
ASTM F88/F88M-21. When the laminate is heat-sealed to low-density polyethylene at
140°C seal bar temperature and
0.3 MPa pressure, seal strength exceeds
25 N/25mm, with cohesive failure occurring within the polyethylene film, not at the adhesive interface. This performance is sustained after exposure to
85°C dry heat for
168 hours, differentiating CW FS-Ⅱ from EVA-based hot melt adhesives that exhibit seal strength loss due to crystalline phase reorganization.
The following table compares CW FS-Ⅱ with a benchmark carboxylated VAE (grade XA-9022) on key flexible substrate adhesion metrics, all tests conducted on a Labo Laminator with
5 µm dry adhesive film, cured
7 days at
23°C and
50% R.H.:
Comparative Adhesion Performance on Flexible Substrates
| Substrate pair | Test | CW FS-Ⅱ | Standard Carboxylated VAE |
|---|
| Corona-treated LDPE to PET | T-peel, ASTM D1876, 300 mm/min | 3.5 N/15mm | 1.8 N/15mm |
| BOPP to paper (50 gsm) | FINAT FTM 1 peel adhesion, 300 mm/min | 5.6 N/25mm | 3.2 N/25mm |
| Al foil (9 µm) to LDPE | ASTM F88 seal strength, 140°C, 0.3 MPa | 27 N/25mm | 19 N/25mm |
| PVC film (100 µm, plasticized) to PET | ISO 11339:2022 floating roller peel | 4.8 N/15mm | 2.1 N/15mm (adhesive failure) |
CW FS-Ⅱ can be crosslinked with water-dispersible polyisocyanates, aziridines, or formaldehyde-free carbodiimides to enhance solvent resistance and heat creep performance. However, a critical incompatibility exists: if the emulsion is compounded with amine-containing wetting agents or ammonia-based pH adjusters above
pH 7.5, the storage stability deteriorates because the carboxylate groups lose their associative thickening effect and the bimodal particle fraction coalesces, producing grit formation detectable as filter residue increase on a
40 µm mesh. Pump cavitation has been observed on progressing cavity pumps when air leakage occurs at the suction side due to the emulsion’s higher surface tension compared to surfactant-stabilized grades; a closed-circuit tank with nitrogen blanket is recommended for bulk handling.
In high-humidity environments (>
75% R.H.), water release from the film during drying slows, and the laminate may retain residual moisture above
0.8% if oven dwell time is not extended. Residual moisture above
1.2% in the dried film causes plasticization, lowering the cohesive strength by
25–30% and creating a risk of tunneling in roll-stock products stored under compression. Online near-infrared moisture sensors are advised for continuous coating lines processing at line speeds exceeding
20 m/min.
When conventional VAE emulsions are substituted with CW FS-Ⅱ in UV-curable overprint varnishes for flexible carton board, the lower surfactant exudation reduces curing inhibition. In a production trial on a
6-colour flexo press with a UV dose of
120 mJ/cm² from a gallium-doped lamp, the varnish achieved full cure tack-free in
0.8 seconds, whereas a styrene-acrylic hybrid required
2.5 seconds and emitted a detectable residual odor. The low odor and benzophenone-free status of CW FS-Ⅱ align with Nestlé Guidance Note on Packaging Inks and the Swiss Ordinance on Materials and Articles in Contact with Food (SR
817.023.21), enabling its use in indirect food contact flexible packaging without migration testing exceeding
10 ppb detection limits per
EU 10/2011 overall migration limit of
60 mg/kg food simulant.
For textile backcoating applications, the flexural fatigue resistance of CW FS-Ⅱ translates to durable handle retention. A
40 g/m² dry add-on on nylon tricot fabric, applied by knife-over-air coating and cured at
130°C for
90 seconds, resisted crack formation after
50,000 cycles in a De Mattia flexing machine (
ISO 132:2017). Standard polyvinyl acetate homopolymer backcoatings typically fail at
15,000–20,000 cycles due to brittle fracture. The ethylene segments impart segmental mobility that absorbs flex energy without micro-cracking, preserving both drape and adhesion to synthetic fibers.
In tape manufacturing involving CW FS-Ⅱ and polypropylene film, transfer coating from release liner creates a continuous adhesive layer with optical clarity above
90% transmittance in the visible range (ASTM D1003). The absence of free surfactant migration maintains clarity after
500 hours QUV-B exposure; a surfactant-stabilized alternative shows a haze increase from
2% to
12% due to surface exudate. Optical clarity is crucial for overlaminating print media or clear food packaging where visual appearance drives consumer perception.
Adhesive preparation with CW FS-Ⅱ proceeds via low-shear mixing with a planetary dissolver at
200–400 rpm to avoid shear-induced particle aggregation. If a pigment dispersion is added, the grinding base should be let down with deionized water to a pH below
7 prior to incorporation. The final formulated adhesive typically requires filtration through a
50 µm bag filter before delivery to the coating head; clogging frequency serves as an indirect indicator of lot-to-lot dispersion quality. Published data for long-term aging beyond
5 years in subtropical warehouse conditions is limited; accelerated aging at
50°C and
90% R.H. for
90 days indicates less than
15% loss in T-peel adhesion, suggesting robust hydrolytic stability, but real-time data collection is ongoing.
