Saint-Gobain CHR 2345-2 is a pressure-sensitive tape assembled from a 0.002 in (0.051 mm) polyimide film backing and a 0.0015 in (0.038 mm) silicone adhesive layer, yielding a nominal total thickness of 0.0035 in (0.089 mm). The -2 suffix in the CHR 2345 series identifies the carrier thickness rather than the finished tape thickness. The product is specified for high-temperature masking in powder-coat and e-coat cure ovens, coil and transformer interlayer insulation, splicing of silicone-coated release liners, and temporary surface protection at process temperatures up to 260 °C.

In powder-coat masking, the tape is applied over threads, grounding pads, bearing seats, and flange faces before parts enter forced-air convection cure ovens. Polyester and epoxy powder schedules commonly operate at 190 °C to 210 °C for 10–25 min. Under these conditions, the polyimide carrier displays dimensional stability superior to polyester film tape. Linear dimensional change measured by ASTM D1204 for polyimide film at 260 °C is typically below 0.5%, while polyester backing can shrink or distort above 150 °C. Tape edges remain anchored to degreased machined steel when a roller force of 2–3 kg is applied with a 75 Shore A rubber roller. The bond stabilizes after an ambient dwell of 10–30 min, and the silicone PSA does not require oven cure before service.

Removal after bake is performed at a peel angle of 30° to 60° and a peel speed below 300 mm/min. Faster removal on textured powder-coated surfaces can generate adhesive stringing. Silicone PSA leaves lower carbonaceous residue than acrylic PSA after exposure to 220 °C because the siloxane network degrades predominantly into volatile cyclic species rather than char. A thin siloxane film can nonetheless remain at the interface. If subsequent topcoat adhesion is required, the surface should be cleaned and checked with dyne inks under ASTM D2578. A surface energy of at least 38 mN/m is commonly set as the minimum acceptance value before topcoating or adhesive bonding.

Why the silicone adhesive layer alters removal behavior after powder-coat cure cycles

Silicone PSAs consist of high-molecular-weight siloxane polymers compounded with an organosilicate or MQ resin reinforcing network. The resulting adhesive has a glass-transition temperature below −70 °C, which allows low-temperature peel without brittle failure. Room-temperature peel adhesion to stainless steel under ASTM D3330/D3330M is typically 6.5–7.5 N/25 mm. This value is lower than many acrylic PSA tapes, but the silicone system retains cohesive strength above 150 °C, where acrylic and ester-based adhesives soften, foam, or oxidize. Silicone PSA remains stable through repeated excursions to 260 °C; short-term exposure above that limit may bubble the adhesive and embrittle the polyimide carrier.

Low-molecular-weight siloxane fractions can migrate along a masked interface by 1–5 mm during extended bake cycles. The migration is not always visible but can disrupt subsequent coating adhesion. Masking layouts on critical sealing surfaces therefore require a 3–6 mm setback from the edge of the coated zone. The effect is most pronounced on surfaces with high surface energy, such as freshly machined aluminum or stainless steel, and is reduced by wiping with a volatile low-siloxane solvent before tape application.

Compared with a 1 mil polyimide-silicone construction from the same family, CHR 2345-2 provides greater stiffness and higher dielectric capacity but lower conformability around conductors below 1 mm diameter. For flat bus-bar protection and slot-liner wrapping, the 2 mil carrier reduces pinhole defects and maintains crease resistance during coil insertion. For small wire harness breakouts below 0.5 mm conductor diameter, a thinner backing is usually preferred because the thicker film can spring back and lift after wrapping.

Polyimide backing versus polyester and PTFE carriers in high-temperature masking

Against polyester film tape, the primary difference is thermal dimensional stability. Polyester carriers begin to shrink above 150 °C and can tear during extended cure cycles. Polyimide retains serviceability near 260 °C and provides higher dielectric strength per unit thickness, making it less prone to pinholing when hand-wrapping square or rectangular conductors. Against skived PTFE tape, polyimide is thinner at equivalent dielectric strength and exhibits lower cold flow under clamping pressure. PTFE may be preferred where a low coefficient of friction or resistance to hot strong acids is required. Polyimide is degraded by hot aqueous alkali, including 10% sodium hydroxide above 80 °C, and by prolonged exposure to concentrated amines.

On high-speed slitting lines, the polyimide carrier is relatively hard and causes more blade wear than polyester or PTFE. Slitter blades are typically inspected each shift and replaced when edge radius exceeds 0.0005 in (0.013 mm). Heat generated during rotary shear slitting can soften the silicone PSA and produce lateral squeeze-out at the tape edge. Converters sometimes hold knife anvils at 10–14 °C to control adhesive flow. Rolls are wound at low tension to prevent telescoping and blocking during elevated-temperature storage.

When the tape is used in coil insulation and motor winding processes

When the tape is used in coil insulation and motor winding processes, it is applied either as an interlayer separator or as a final wrap before vacuum-pressure impregnation with epoxy or polyester varnishes. Taping heads running at 200–600 rpm require controlled unwind force. The silicone PSA is compatible with many solventborne varnishes, but edge penetration should be tested for the specific varnish formulation. The polyimide backing withstands dip-varnish bake cycles of 150–180 °C. If the varnish contains aromatic amine curing agents, the hydrolytic stability of the polyimide film at elevated temperature should be confirmed, because amine systems can attack the imide linkage over extended exposure.

Electrical insulation performance is characterized by dielectric breakdown strength under ASTM D149 and by thermal aging performance under ASTM D1000. For a 0.0035 in polyimide-silicone construction, published breakdown values are generally in the range 6.5–7.5 kV. Practical working voltage is reduced by overlap, contamination, and mechanical damage. In hand-wrapped bus-bar joints, a 50% overlap with two layers is commonly used. The assembly is then proof-tested at 1000 V + 2 × rated voltage according to the equipment acceptance standard. Cut edges should be inspected under 10× magnification because slitting burrs can reduce local dielectric strength.

The following matrix summarizes supplier-published physical-property ranges for CHR 2345-2. These values are not lot-release criteria unless confirmed by the certificate of analysis for the specific roll.

Silicone pressure-sensitive tapes are moisture-stable and do not require oven drying before application, unlike some heat-activated adhesive systems. Rolls should be stored in a dry area at 21 °C and 50% RH, suspended or on edge to prevent blocking. A shelf life of 24 months from date of manufacture is commonly assigned for silicone PSAs under these storage conditions. Extended ultraviolet exposure can yellow the polyimide film and embrittle the adhesive; yellowing alone does not necessarily reduce dielectric strength, but UV-generated ozone may harden exposed silicone edges.

For printed-circuit assembly masking during wave solder or reflow, the tape can be applied to edge connectors because the silicone adhesive resists flux splatter and brief contact with molten solder. However, exposure to a solder float at 260–280 °C for more than 10–20 s may sinter the adhesive and embrittle the backing. Peak reflow profiles above 260 °C require process verification with the specific oven profile. Silicone adhesive is not recommended for direct use on surfaces where subsequent soldering, plating, or adhesive bonding must occur, because siloxane contamination can reduce wetting. Plasma cleaning or solvent wiping may be required before final processing.

Published data for continuous outdoor ultraviolet exposure of this specific silicone-adhesive polyimide construction is limited. The product is not normally selected for exterior weathering or for continuous immersion in strong alkaline process baths. If such exposure cannot be avoided, qualification should include ASTM G154 accelerated weathering or the specific chemical immersion protocol. Peel retention should be measured at intervals because silicone adhesives can harden under ozone generated by high-voltage corona discharge, and polyimide film can be degraded by prolonged contact with hot aqueous alkali or concentrated amine solutions.