Saint-Gobain CHR M823 Polyester Film Backing Silicone Adhesive Pressure Sensitive Tape is a single-coated pressure-sensitive laminate consisting of biaxially oriented polyethylene terephthalate film and a silicone adhesive mass. The polyester backing is supplied at a nominal thickness of 1.0 mil (0.025 mm), while the total tape caliper is commonly reported between 1.9 mils and 2.1 mils (0.048–0.053 mm). The product is specified for masking, splicing, coil wrapping, and electrical insulation operations in which process temperatures exceed the tolerance of rubber-resin PSA systems but remain within the dimensional stability limits of polyethylene terephthalate. Published adhesion, tensile, and dielectric values are obtained under standardized conditions including ASTM D3330, ASTM D3759, and ASTM D149. The silicone adhesive demonstrates improved wet-out on low-energy surfaces such as silicone-coated release liners, polyethylene, polypropylene, and fluoropolymer films compared with acrylic PSA tapes. However, the silicone chemistry also creates a contamination boundary that must be evaluated before painting, bonding, or silicone-sensitive assembly.

In high-temperature masking, web splicing, and electrical insulation, the selection of M823 depends on the interaction between the adhesive’s thermal stability and the polyester backing’s dimensional stability. The silicone adhesive tolerates short-term exposure at temperatures up to 200°C without abrupt oxidative degradation, but biaxially oriented polyethylene terephthalate begins to shrink measurably above 150°C. The product therefore occupies an intermediate position between general-purpose rubber adhesive tapes and polyimide-backed silicone tapes. It is not intended for continuous use above 180°C, and it is not suitable for processes in which trace silicone transfer is prohibited.

How does silicone adhesive chemistry alter the operating envelope of M823?

Silicone pressure-sensitive adhesives are typically composed of high-molecular-weight polydimethylsiloxane polymers or silicone gum, often condensed with silicate resin to produce a crosslinked network with pressure-sensitive tack. The siloxane backbone has higher thermo-oxidative stability than the ester bonds in acrylic adhesives and the unsaturated sites in natural rubber. As a result, silicone PSA tapes show lower loss of peel strength after exposure to 150°C for 168 h than acrylic PSA tapes of similar adhesive thickness. Peel adhesion of M823 to stainless steel, measured according to ASTM D3330, is commonly reported in the range of 18–25 oz/in (0.20–0.27 N/mm). The lower initial peel compared with some acrylic systems is offset by greater retention after thermal aging and by the ability to wet low-energy surfaces without priming.

Silicone adhesives can release low-molecular-weight siloxane species during heating. These species may condense on adjacent surfaces, reduce wetting tension, and interfere with paint adhesion or adhesive bonding. The surface energy of a contaminated substrate can fall below the wetting threshold for subsequent coatings, which is one of the main reasons the tape is restricted from silicone-sensitive painting lines. For adhesion after mask removal, manufacturers often require crosshatch testing per ASTM D3359 on representative test panels to determine whether silicone transfer compromises the coating system. If surface wetting tension measured by dyne pens drops below the coating supplier’s minimum requirement, solvent cleaning is not always sufficient to restore adhesion.

The backing defines the upper operating temperature. Biaxially oriented polyethylene terephthalate has a glass-transition temperature near 70–80°C, but crystalline orientation provides mechanical strength above the glass transition. Thermal shrinkage measured by ASTM D1204 on standard PET film commonly shows 1–3% after 30 min at 150°C. At 180°C, shrinkage can reach 5%, depending on heat history and film grade. For tape removal after a bake cycle, dimensional movement of the backing can create edge lift, allowing powder or coating material to penetrate under the mask. This is the primary processing conflict: the adhesive survives, but the film can move. Qualification trials should include a thermal profile test at the highest expected oven temperature rather than relying solely on adhesive temperature ratings.

Differences from acrylic, rubber, and polyimide-backed tape systems.

M823 is specified against three alternate tape classes. Acrylic adhesive polyester tapes generally provide higher room-temperature adhesion to polar substrates such as steel and glass, but their peel strength falls faster after thermal aging and they may embrittle or leave residue after powder coating cure cycles. Natural rubber adhesive tapes are unsuitable above 120°C because the elastomer oxidizes and hardens. Polyimide-backed silicone tapes have higher continuous use temperature, often 260°C, but at higher cost and with different mechanical properties. M823 offers an intermediate solution for processes at 130–180°C where silicone release characteristics are beneficial and polyimide is not required. The silicone adhesive also adheres to low-energy substrates such as silicone-coated release papers, polyethylene, and polypropylene, where acrylic adhesives exhibit poor wet-out because of higher surface tension.

The table presents typical industrial values from supplier technical literature and standard test methods. They are not batch-specific guarantees. Acrylic PSA tapes may show higher initial peel on polar surfaces, but the peel after 7 days at 150°C is typically lower than that of silicone PSA. Natural rubber systems are excluded from the table because their oxidative failure modes occur below 120°C. For applications requiring silicone-free surfaces, M823 is generally not recommended because silicone transfer may interfere with subsequent paint adhesion or bonding.

Powder coating masking is one of the principal production uses for M823. Pre-bake ovens typically operate between 120°C and 180°C, within the polyethylene terephthalate backing’s short-exposure range but above the continuous limit of rubber adhesives. The tape is applied to threaded holes, bearing journals, grounding surfaces, and machined surfaces before electrostatic powder is sprayed. Its 1.0 mil polyester backing minimizes the edge step left in the cured coating, and the silicone adhesive conforms to sharp edges without lifting under high-velocity spray air. After cure, removal from a hot part can be performed, but the removed tape and the masked surface must be inspected for adhesive transfer. If residual siloxane remains, cleaning with isopropanol or a solvent compatible with the substrate is required before overpainting, because silicones can reduce surface energy and compromise crosshatch adhesion measured by ASTM D3359.

In vacuum bagging of epoxy or polyester composite laminates, M823 is used for sealing the bag edge, holding thermocouple wires, and temporarily fixing release film during layup. The silicone adhesive remains tacky at low layup temperatures and does not harden under autoclave pressure of 90 psi (0.62 MPa). Silicone transfer from the tape edge onto the prepreg or bond surface can create a contamination boundary. Composite shops using silicone-sensitive bonding primers should either avoid direct contact with the adhesive edge or use a non-silicone flash tape at the bond line. Published data for bond strength reduction in silicone-contaminated composite laminates is specific to the resin system; users should validate by lap shear testing per ASTM D1002 after process simulation.

In splicing operations for silicone-coated release liners, M823 bonds to the silicone surface because the PSA chemistry is compatible with low-energy silicone layers. Acrylic adhesive tapes often peel away from silicone release coatings because they cannot wet the surface sufficiently. The splice is used in label converting, tape manufacture, and paper coating lines where a splice must pass through ovens at temperatures up to 150°C. The splicing tape must be thin enough to avoid caliper interference in nip rolls; the 2.0 mil total thickness of M823 may be acceptable for many web paths but should be validated against roller pressure specifications and web tension settings.

When continuous process temperatures exceed the polyester glass-transition region.

Although the silicone adhesive can withstand short spikes to 260°C, the polyethylene terephthalate backing cannot support continuous use at that temperature. Biaxially oriented PET film undergoes thermal shrinkage, loss of tensile strength, and potential embrittlement as crystallinity increases. In a conveyorized curing oven with long residence times above 170°C, the tape may curl at free edges and disturb the mask line. The onset of measurable shrinkage is dependent on film heat history, but standard PET films show shrinkage values between 1% and 3% after 30 min at 150°C per ASTM D1204. At 180°C, shrinkage can reach 5% or higher. This is the critical process requirement that separates M823 from polyimide-backed silicone tapes. If thermal imaging shows substrate surface temperatures above 180°C, a polyimide-backed product should be specified for the next qualification run.

In hot air impingement ovens, the thin polyester film heats faster than the underlying metal substrate, so the tape can reach a higher temperature than the part itself. This thermal lag effect must be considered when setting oven setpoints. A tape rated for 150°C continuous can experience 170–180°C at the film surface even when the metal part remains below 150°C. The resulting backside adhesive flow or edge lift is a known processing failure in high-velocity powder coat cure lines. Adjusting oven profile or using polyimide tape are the standard corrective actions.

Dielectric failure modes in high-voltage coil wrap and busbar masking.

Polyethylene terephthalate film has dielectric strength commonly reported between 5,000 V/mil and 7,000 V/mil when tested per ASTM D149 short-time methods. M823’s silicone adhesive layer displaces air at the film-substrate interface, which can reduce partial discharge intensity in low-voltage coil insulation. The tape is not a primary insulation system by itself; it is an interlayer or overwrap material in assemblies that meet a specific thermal class under IEC 60085 or UL 1446. Qualification requires thermal aging at the system level, because the interaction between silicone adhesive and magnet wire enamel may affect insulation resistance. Published data for M823 in high-voltage partial discharge environments is limited; manufacturers frequently require a dielectric withstanding voltage test per ASTM D1389 after environmental conditioning.

For oil-filled transformers, silicone adhesive swelling in mineral oil should be evaluated, although silicone PSA typically exhibits resistance to mineral oil. For dry-type assemblies, the tape should not be operated above 150°C continuously or the PET film may shrink and reduce creepage distances. The total tape thickness of approximately 2.0 mils (0.051 mm) yields a thin insulation layer, so layer count must be calculated based on final assembly voltage class and partial discharge acceptance criteria.

Storage is recommended at 21°C and 50% relative humidity in original packaging. The polyethylene terephthalate backing absorbs negligible moisture, but the silicone adhesive surface can be contaminated by fingerprints, oils, and solvent vapors. Roll goods should be rotated to avoid prolonged static pressure that can cause adhesive bleeding at the edge. Before conversion, incoming inspection should include thickness per ASTM D3652, peel adhesion per ASTM D3330, and tensile strength per ASTM D3759. Users should verify current compliance with REACH and RoHS Directive 2011/65/EU against the supplier’s certificate, as material formulations may change without notice.