The Saint-Gobain CHR 2975-8R glass-silicone backing silicone adhesive pressure-sensitive tape is a composite pressure-sensitive tape constructed from woven glass cloth, a red silicone rubber impregnation and surface coating, and a silicone pressure-sensitive adhesive. The catalogue number encodes the nominal total thickness and color: the suffix 8 designates a nominal thickness of 0.008 in (0.203 mm), and the suffix R identifies the red-pigmented silicone elastomer system. The tape is supplied in slit roll form and is specified where the backing must remain flexible, electrically insulating, and dimensionally stable after exposure to elevated surface temperatures while the adhesive maintains peel and shear performance after thermal cycling. The product is used in high-temperature masking, thermal spray protection, electrical harness wrapping, release-surface applications, and composite processing controls. The silicone pressure-sensitive adhesive is not a thermoset and does not require heat curing; adhesion develops through dwell time and applied pressure at ambient conditions.

What thermal and mechanical boundaries govern the tape in masking and insulation service?

Continuous-use temperature limits for silicone-coated glass fabric pressure-sensitive tapes are governed by the oxidative stability of the polydimethylsiloxane network and by the glass transition and crystallization behavior of the silicone adhesive. For this product class, the published continuous operating range is typically −73 °C to 260 °C (−100 °F to 500 °F). At temperatures above 260 °C, oxidative degradation of methyl groups in the silicone elastomer becomes measurable, and embrittlement of the backing can occur during prolonged exposure. Published data for this specific catalogue number above 260 °C is limited; qualification testing under the actual process heat flux is required before use. At cryogenic conditions below −73 °C, the silicone adhesive retains some tack, but the glass fabric and elastomer layer increase in modulus and may resist conformability on small radii. Peel adhesion after elevated-temperature dwell should be evaluated according to ASTM D3330/D3330M. The tape is not recommended for continuous immersion in ketone, ester, or aromatic hydrocarbon solvents because the silicone rubber backing can swell and lose dimensional stability.

Construction architecture and lot-dependent dimensional control

The woven glass cloth carrier is impregnated with a silicone saturant to fill interstices and to reduce wicking of the adhesive or process fluids. The red silicone rubber coating is applied over the glass fabric to generate a homogenous, elastomeric surface with controlled release character. The silicone pressure-sensitive adhesive is applied to one face. Lot-to-lot variation in glass weave, coating thickness, and adhesive coat weight can affect tensile strength, elongation, dielectric strength, and adhesion values. Those values are supplied on the manufacturer certificate of analysis and are not always replicated in open literature for this exact catalogue number. Incoming inspection should include thickness measurement under ASTM D1000 and conditioning under ASTM D3330/D3330M at 23 ± 2 °C and 50 ± 5 %RH before converting or application. The table below reports attributes derivable from the product designation and generic construction family.

The silicone adhesive is not a high-tack acrylic system; initial room-temperature peel on low-surface-energy substrates is lower. On stainless steel or aluminum, full peel strength typically requires dwell time and firm lamination pressure. For surfaces with surface free energy below 20 mN/m, such as untreated polyethylene or polytetrafluoroethylene, the silicone PSA may not develop adequate peel without surface treatment. This limitation is inherent to the adhesive chemistry and is independent of the backing construction.

In plasma spray and thermal spray masking operations, the tape is applied over non-coated surfaces such as turbine component bolt holes, cooling channels, and flange faces. The red pigmentation provides visual confirmation of mask placement inside a spray booth. The glass-silicone backing must withstand impingement from ceramic or metallic grit streams without mechanical breakthrough. Edge lifting is the primary production failure mode, and it is influenced by substrate surface preparation, tape tension during application, and the temperature reached at the leading edge of the mask. Surface preparation with 2-propanol or methyl ethyl ketone should be performed before tape application, followed by drying at 23 °C and 50 %RH. Lamination pressure should be uniform across the tape width to reduce air entrapment. The silicone PSA does not require a heat cure, but dwell time at ambient conditions is recommended before exposure to high-velocity particle streams.

When a silicone-glass backing replaces polyimide or PTFE-coated glass in a specification

Relative to polyimide tape, the CHR 2975-8R construction has a substantially thicker elastomeric layer and lower in-plane tensile modulus at the same nominal width. Polyimide tapes are commonly supplied at 0.002 in to 0.003 in thickness, while the CHR 2975-8R nominal total thickness is 0.008 in. This thickness difference generates a larger cross-sectional area for mechanical load distribution and allows the tape to bridge cooling channels and edge breaks more effectively than a thin polyimide film. The tradeoff is greater edge build-up in coating operations and increased stiffness in rolled or folded configurations. Polyimide offers higher tensile strength per unit thickness and better resistance to puncture at low thickness, but it lacks the conformable elastomeric mass required for masking recessed cavities under aggressive blast or spray conditions.

Relative to PTFE-coated glass fabric tape, the silicone rubber surface of CHR 2975-8R has higher surface free energy and a different release character. Polydimethylsiloxane surfaces typically exhibit surface free energy in the range of 22–24 mN/m, whereas PTFE surfaces are generally 18–20 mN/m. This difference affects adhesive wetting and release after thermal exposure. PTFE-coated glass tape provides lower friction and better chemical inertness in acid or halogen environments, but it has lower abrasion resistance under high-pressure mechanical scour. The silicone rubber surface of CHR 2975-8R produces higher friction and more positive grip on metal masks, which can reduce mask shifting during grit blast, but it is more prone to swelling in organic solvent immersion than PTFE-coated glass. When the specification requires sustained chemical exposure to strong acids or halogenated solvents, PTFE-coated glass should be considered. When the specification requires abrasion resistance, visual contrast, and elastomeric bridging under thermal spray conditions, the silicone-glass construction is selected.

Acrylic adhesive glass cloth tapes are limited to approximately 150 °C continuous service and are not recommended for repeated autoclave or thermal spray cycles above 180 °C. Silicone pressure-sensitive adhesive remains functional at 260 °C after sustained exposure because the siloxane backbone has greater oxidative stability than acrylic ester chemistry. The limitation is that silicone PSA can transfer residues to the substrate if shear load is applied at high temperature or if the tape is left in place beyond the intended process window. The residue is typically transparent and can interfere with subsequent painting or adhesive bonding. Paint adhesion after tape removal should be verified under ASTM D3359 if the part is destined for coating or bonding.

Surface preparation, dwell time, and removal-force variables

Surface preparation is critical for reliable performance. The substrate should be cleaned with 2-propanol, methyl ethyl ketone, or another solvent compatible with the substrate and with the silicone PSA. After cleaning, the surface should be dried at 23 ± 2 °C and 50 ± 5 %RH before tape application. Application at temperatures below 18 °C can reduce adhesive wetting and increase the probability of edge lift. The tape should be applied without stretching, because residual tension in the glass fabric can generate peel stress at the leading edge during heating. A dwell time of at least 24 h at 23 °C is commonly used to stabilize peel adhesion before thermal exposure. Removal force must be characterized on the actual production substrate, because silicone PSA transfer increases with dwell time, temperature, and substrate roughness. If the tape is removed cold from a rough metal surface, cohesive splitting of the adhesive may occur. If removal is delayed after high-temperature exposure, the adhesive may soften and leave a thin residue. A solvent wipe with methyl ethyl ketone or a suitable silicone remover may be required for residue-free surface preparation.

Silicone pressure-sensitive adhesive should not be used where silicone migration is prohibited, such as optical bond lines, telecommunication surfaces, or surfaces to be painted without subsequent cleaning verification. Amine-based primers and condensation-cure systems should be avoided in contact with the silicone adhesive because alkaline amine chemistry can accelerate siloxane degradation at elevated temperature. The tape should be stored in a cool, dry environment and kept sealed before use to avoid contamination of the adhesive by airborne dust or plasticizer vapors.

For turbine blade cooling-hole masking after grit blasting, the tape is applied over cleaned nickel alloy surfaces and removed after thermal spray coating. Incoming inspection per ASTM D1000 thickness and per ASTM D3330/D3330M adhesion is required because lot-to-lot glass weave variation can shift edge-lift behavior and removal-force response. Process qualification should replicate the actual thermal spray standoff distance, gun traverse speed, and part temperature. Published data for this specific configuration under production-scale thermal spray conditions is limited, so the final operating window must be established through part-level trials rather than generic tape-class data.