Slot Liner Abrasion and Layer Insulation in Form-Wound Coils

In form-wound stator and rotor coil production, CHR M705 polyester film/acrylic pressure-sensitive tape is applied as a slot liner supplement and outer wrap at a coil winding station. The taping head is set to a 50% overwrap default because this balance supports edge coverage without creating a build-up that restricts slot closure. Backing caliper is verified by ASTM D3652/D3652M; tensile strength and elongation are verified by ASTM D3759/D3759M; peel adhesion to steel is verified by ASTM D3330/D3330M. The tape must not be substituted for groundwall insulation; it functions as an auxiliary mechanical layer. Dielectric strength is measured in air at 23°C ± 2°C using a guarded disk electrode system per ASTM D149. The material’s electrical insulation classification is evaluated under IEC 60454-3 and, where required by the motor builder, UL 510. During coil insertion into varnished laminations, the polyester backing experiences shear and abrasion at the slot mouth. The film is selected for its tensile modulus and tear resistance, but a crush-cut edge with micro-tears will propagate at insertion. Slit-edge quality is inspected at 20× magnification before the tape enters the automatic taping head. Rolls with visible edge nicks are rejected because these defects become flagging points under thermal cycling.

Before varnish impregnation, wound coils are preheated at 110°C–130°C to remove winding moisture. At 130°C, the acrylic adhesive is close to its practical upper service temperature, and overtensioning can press adhesive into absorbent paper slot liners. The condition is evaluated by a 24 h heat exposure at the measured preheat temperature; after cooling, the wrap is removed and adjacent insulation is inspected for adhesive transfer. If transfer is detected, taping-head tension is reduced in 0.5 N increments until the transfer disappears. Thermosetting impregnating resins generate exotherm during cure. Thermocouples placed in the slot core frequently record 15°C–25°C above oven air temperature. If the slot thermocouple exceeds 130°C, the acrylic layer may soften and migrate. The tape is then considered a process risk for varnish adhesion because acrylic residue becomes a bond-line contaminant. This boundary is re-tested after any change in resin catalyst level, part mass, or oven loading density. The tape contains no silicone, which is required for downstream conformal coating adhesion on many rotating machines.

On zinc-phosphated and alkaline-cleaned rack fixtures, the tape is applied to masked threads, bearing journals, and grounding pads before powder coating. Powder coating lines commonly cure at 177°C–204°C for 10–25 min. The polyester backing is dimensionally stable in that range, but the acrylic adhesive is not a high-temperature silicone and must be treated as a removal-limited material. Rack line speed from 1.2 m/min to 3.5 m/min produces uneven part heat soak. Tape on a thin bracket reaches oven temperature faster than tape on a heavy cast bearing seat. The backing must not cockle. Sharp die-cut corners concentrate stress and lift; corner radii above 3 mm are preferred. Powder collects on exposed adhesive edges. During cure, that powder melts and forms bridging flash over the mask line. After cure, removal above 60°C may cause cohesive failure of the acrylic adhesive. The removal procedure is to cool the part below 50°C and peel the tape back on itself at an included angle of 90°–120°. If the racking line uses chromate conversion coating, initial adhesion is higher than on clean steel because acrylic wetting is affected by the conversion-coating microroughness. Peel adhesion on the actual coated rack surface must be measured per ASTM D3330/D3330M; values obtained on stainless steel are not transferable. Paint adhesion after masking is checked by cross-cut per ISO 2409 or ASTM D3359. Any acrylic residue left on the coated surface is a foreign material layer. The line audit uses a 10× optical comparator to inspect the mask line for adhesive stringers and fiber shedding. For low-cure powder systems, the masking process may be acceptable; for high-temperature powder systems that use 220°C peak metal temperature, a silicone-adhesive tape or alternative masking must be evaluated.

What Limits Acrylic Adhesive Residue Transfer on Flexible Printed Circuit Carrier Prep?

For roll-to-roll flexible printed circuit carrier operations, the residue limit is controlled by the next surface-finish step, because any adhesive transferred to the polyimide coverlay can form a wetting barrier during electroless plating or a contaminant after immersion tin. The tape is applied at 70°C–90°C under 0.2–0.5 MPa nip pressure. The polyester backing gives dimensional stability during indexing, while the acrylic adhesive may creep at the free edge during dwell. If the panel is stored for 8–24 h at relative humidity above 60% RH, surface moisture can collect at the exposed adhesive edge. Pre-drying at 40°C–50°C for 2–4 h in a desiccated cabinet is used to reduce the risk. Automated peel removal runs at 3–8 m/min; higher peel speeds increase cohesive failure and residue transfer. After tape removal, surface insulation resistance is tested per IPC-TM-650 2.6.3.6. Ionic contamination is extracted and measured per IPC-TM-650 2.3.25. The materials and process engineer should verify that no low molecular weight acrylic fraction migrates to the coverlay. Published data for this specific configuration is limited; therefore a three-lot qualification at the actual lamination temperature and dwell time is required. If peel residue is detected, reduction of nip pressure and shorter dwell are more effective than increasing peel speed. Because solder reflow peak temperatures commonly reach 245°C–260°C, this tape is limited to pre-reflow carrier and routing operations, not solder-mask wave masking.

Facilities producing immersion silver or ENIG finishes may apply tighter ionic cleanliness limits than standard ROSE acceptance values. The extraction test is then run on both as-received tape and tape subjected to the maximum carrier dwell. Any measurable increase in extractable ionic species after dwell indicates adhesive-edge moisture uptake or backing additive migration. The carrier process should maintain dry storage at 30%–45% RH for die-cut tape rolls. Rolls that have been exposed outside this range for more than one production shift are preconditioned before lamination.

When Polyester Film Tape Replaces Polyimide in Harness Bundling Under 130°C

When a vehicle program replaces polyimide film tape with polyester film/acrylic PSA tape for harness bundling, the substitution is restricted to body-cavity or cabin branches where the measured tape-seat temperature stays below the acrylic ceiling. Harness taping machines use overlap ratios of 40%–70% and tension between 2 N and 6 N, depending on bundle diameter. The polyester backing resists abrasion and edge nicking during routing through sheet-metal apertures, but under-hood thermal spikes near exhaust heat shields can exceed the service window. The boundary condition is set by embedding thermocouples under the tape on the test vehicle. If the thermocouple records 125°C for more than 30 minutes per maximum drive cycle, the tape is not specified for that branch. Peel adhesion after heat aging is tested per ASTM D3330/D3330M on the actual wire insulations, because polyethylene, cross-linked polyethylene, and PVC jacket surfaces produce different wetting. A 7-day heat-aging exposure at 100°C is used to screen for adhesive drying and backing shrinkage. Flagging resistance is visually assessed after 24 h at 85°C/85% RH. The acrylic adhesive has lower thermal resistance than silicone, but it is silicone-free and therefore preferred for branches that route near connectors where silicone transfer is a known failure mechanism for connector locking lubricants. If the harness process includes a foam-wrapped or shrink-sleeved section, the tape must be tested for compatibility with the sleeve adhesive. Published data for this specific configuration is limited; each harness manufacturer applies its own tape-layering specification. The tape is not used on direct exhaust-adjacent branches where peak temperatures exceed 130°C; polyimide or glass-cloth tapes are used in those locations.

Lithium-ion cell assembly processes adopt polyester film/acrylic PSA tape for insulation wrap and tab masking only after the production electrolyte is tested for solvent absorption. The electrolyte mixture commonly contains ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate. Acrylic pressure-sensitive adhesives can swell in carbonate solvents. The tape is not a hermetic barrier. In prismatic cell assembly, the film may be inserted between the electrode stack and the aluminium housing to prevent side-wall shorting. A hot-pressing step at 80°C–100°C and 0.05–0.2 MPa is applied. Higher localized pressure can extrude the adhesive from the laminate. Qualification includes a 72 h immersion test in production electrolyte at 25°C and 45°C. Dimensional stability is measured per ASTM D1204. Extractable weight must remain below the cell manufacturer’s internal limit. Because dry-air dielectric breakdown per ASTM D149 does not predict behaviour in wet electrolyte, a separate guarded-electrode wet dielectric test is required. If the electrolyte contains high fractions of linear carbonate, the acrylic may swell more than in cyclic carbonate-rich mixtures. The cell maker must verify non-swelling and non-leaching for each electrolyte formulation; published data for this specific configuration is limited.

Varnish Impregnation Masking Without Silicone Transfer Remains Process-Dependent

Transformer and armature manufacturers use polyester film/acrylic PSA tape for temporary masking during varnish dip when the process cannot tolerate a silicone adhesive. Silicone migration from masking tape degrades conformal coating adhesion and creates solderability failures on terminal leads. Acrylic PSA does not contain silicone, but it can leave residue when varnish cure exceeds the adhesive limit. In trickle impregnation lines, the armature is preheated at 100°C–120°C, varnish is applied at 60°C–80°C, and cure is run at 130°C–150°C for 1–2 h. The tape masks commutator risers and OD surfaces. At cure temperatures above 130°C, the acrylic adhesive can flow at the tape edges. After cure, removal can leave an adhesive stringer on the varnish topcoat. The process limit is set by a 10-part confirmation run with thermocouples inserted under the tape on the commutator. If the measured peak under-tape temperature stays below 125°C, release without residue is generally achievable. If it exceeds 135°C, silicone-free release cannot be guaranteed. Masking tape should be removed while the armature is at 50°C–60°C. Pulling at ambient temperature can increase cohesive failure. The polyester backing is not used in oil-filled transformers because hot mineral oil may extract acrylic components. For those applications, a different tape material is specified.

At the end of a film capacitor winding, the tape is applied around the outer wrap to prevent telescoping before thermal treatment. The winder indexes the tape at a set tension; 1.5–3 N is typical for small cylindrical capacitors. The tape is selected for low ionic content and absence of silicone. Acrylic adhesive must not bleed into the capacitor element. Thermal treatment is run at 90°C–110°C; the polyester film has low shrinkage in this range, and dimensional stability is checked per ASTM D1204. If the capacitor receives a short-term aging step at 130°C, the outer wrap remains mechanically in place but the adhesive may soften; this is acceptable only when the wrap is inside a housing or beneath an overwrap. The user validates that no low molecular weight acrylic component transfers to the film stack by performing an extractables test in the production solvent system. Published data for this specific configuration is limited, so each capacitor design and thermal profile is qualified separately.