PTFE emulsion impregnation is the core process for producing PTFE high-temperature fabric. The base PTFE dispersion alone does not always wet, penetrate, or bond perfectly to fiberglass fabric. To achieve uniform coating, strong adhesion, and defect-free surfaces, manufacturers add a range of functional auxiliaries.
Aokai PTFE has optimized impregnation formulations across many products. This guide explains the eight most common auxiliaries – what they do, how they work, and when to use them.
Wetting and Penetrating Agents – The Core Additive
Raw PTFE emulsion has relatively high surface tension, which leads to poor infiltration into fibers and fabrics. Wetting agents reduce surface tension, allowing the emulsion to spread and penetrate effectively.
Chemours Capstone series (short-chain, PFOS/PFOA-free)
Ultra-low surface tension, excellent penetration into hard-to-wet substrates. Dosage must be strictly controlled to avoid degrading surface performance after sintering.
Key note: Fluorocarbon surfactants are highly effective but require careful dosing. Excess can migrate to the coating surface during sintering and reduce non-stick performance.
Thickeners and Rheology Modifiers – Controlling Coating Pick-Up
Thickeners adjust emulsion viscosity to prevent dripping and precisely regulate coating thickness.
Water-soluble, burn off completely during sintering
Alkali-swellable acrylic thickeners (ASE)
ASE series
High efficiency, adjustable thixotropy (neutralized with ammonia water)
Polyurethane associative thickeners (HEUR)
HEUR types
Excellent leveling, anti-splash
Inorganic thickeners
Fumed silica, bentonite
Enhance thixotropy and heat resistance; may reduce coating clarity
Practical tip: For thin, uniform coatings on tight-weave fabric, use low-viscosity formulations with minimal thickener. For heavy coatings or open-weave fabrics, increase thickener to control penetration depth.
pH Regulators and Emulsion Stabilizers
PTFE emulsions are generally stabilized by anionic surfactants and maintained at pH 9–10 to prevent coagulation.
Ammonia water (28 wt%): The most widely used regulator. It volatilizes completely during drying/sintering, leaving no residues that compromise performance.
Auxiliary stabilizers: Anionic surfactants such as sodium dodecyl sulfate (SDS) and secondary alkyl sulfonate (SAS) improve shear resistance of the emulsion during pumping and agitation.
Adhesion Promoters – Bonding Resins and Coupling Agents
Pure PTFE has extremely weak bonding force with substrates. Adhesion promoters are essential.
1. Silane coupling agents
Examples: Aminosilane (KH-550), epoxy silane.
Mechanism: After hydrolysis, they form chemical bonds with fiberglass – Si-O-Si bonds between silane and glass, and organic functional groups that interact with PTFE or other polymers.
Caution: Must be added carefully to avoid emulsion breaking. Pre-hydrolysis or post-treatment (applying to fabric before impregnation) is recommended.
Application: Core materials for non-stick coatings and common binders for impregnated fiberglass filter media and membrane materials. They improve adhesion and cohesion in the final composite.
Film-Forming Aids – Lowering Sintering Temperature
PTFE has extremely high melt viscosity. Film-forming aids facilitate particle fusion during sintering.
PFA (perfluoroalkoxy resin) – lower melting point than PTFE
FEP (fluorinated ethylene propylene copolymer) – lower melting point than PTFE
These melt-processable fluoropolymers form molten bonding phases between PTFE particles during sintering, boosting coating compactness and interfacial adhesion. They are particularly useful for thick coatings or when lower sintering temperatures are desired.
Functional Fillers – Custom Properties on Demand
Fillers are directly dispersed into the emulsion to impart specific properties.
Important: Fillers require appropriate wetting dispersants (e.g., polycarboxylates) to prevent agglomeration and ensure uniform distribution.
Defoamers – Preventing Pinholes
Severe foaming occurs during impregnation, causing pinhole defects on coatings.
Type
Features
Silicone-free defoamers (preferred)
Polyether-based, mineral oil-based. Eliminates risk of silicone residues interfering with secondary adhesion or surface treatment.
Silicone defoamers
Powerful defoaming capacity, but use is limited to applications where trace silicone residue is acceptable.
Recommendation: For PTFE tapes that will be used in high-performance bonding or coating applications, silicone-free defoamers are strongly preferred.
Film-Forming Humectants – Occasional Use
Trace high-boiling-point solvents or polyols (propylene glycol, ethylene glycol) are occasionally added to slow water evaporation and prevent cracking from rapid drying.
Important: These are rarely used in sintering processes, as all organic components must fully decompose during sintering. Overuse can leave carbon residues.
Summary – Choosing the Right Auxiliary Package
Goal
Recommended Auxiliary
Improve wetting and penetration
Nonionic or fluorocarbon wetting agent
Control coating weight
Thickener (cellulose or HEUR)
Stabilize emulsion, prevent coagulation
pH regulator (ammonia water) + anionic stabilizer
Strengthen PTFE-substrate bond
Silane coupling agent or PAI/PPS resin dispersion
Improve film formation, lower sintering temp
PFA or FEP dispersion
Add wear resistance
Alumina or silicon carbide filler
Add conductivity
Carbon black, graphite, or CNT
Prevent pinholes from foam
Silicone-free defoamer
Slow drying for thick coatings
Humectant (propylene glycol) – use sparingly
Aokai PTFE can formulate custom impregnation blends for specific applications. Contact us with your substrate, coating thickness requirement, and performance targets.
If you wish to learn more about detailed specifications, application scenarios and customized solutions for our full product range, including PTFE high-temperature fabrics, PTFE high-temperature tapes, PTFE mesh belts, seamless bonding machine belts, single-sided PTFE cloth, high-temperature resistant conveyor belts and high-temperature resistant fiberglass fabrics, please contact us:
