Saint-Gobain CHR SG25-10(R) is a pressure-sensitive tape built on a primary glass-PTFE backing: a woven glass-fabric carrier coated on one face with polytetrafluoroethylene and on the opposite face with a cured silicone adhesive. The SG prefix in the manufacturer nomenclature identifies the glass-cloth/silicone construction, and the 10 suffix corresponds to the nominal 0.010 in backing thickness. The R designation is part of the order code and should be verified against the manufacturer’s current product coding schedule; it is used for roll-form supply. In this construction the glass fabric provides tensile strength, tear resistance, and dimensional stability under web tension; the PTFE coating supplies a low-surface-energy release face; and the silicone adhesive provides bond retention through repeated elevated-temperature cycles. Manufacturer-published data list nominal total thickness as 0.25 mm and continuous service temperature from -73 °C to 260 °C. Total thickness tolerance is typically ±0.025 mm; the current commercial specification should be obtained from the supplier. The PTFE surface is formed by coating and fusing the fluoropolymer into the glass fabric rather than by laminating a separate film. This mechanical anchorage reduces the risk of backing delamination when the tape is removed from heated tooling. Because the adhesive layer is a small fraction of total gauge, compressibility is lower than that of foam-supported acrylic tapes, and hot-bar jaw gap control remains more stable.

Compared with skived PTFE film tapes, the glass-reinforced backing limits elongation at break to approximately 5 % and increases puncture resistance. Skived PTFE tapes are more conformable around small radii but stretch under tension and lose dimensional registration in automated placement. The glass fabric also permits higher tensile loading at elevated temperature; this is relevant when the tape is used as a release surface on rotating heat-seal wheels or as a dielectric wrapper on motor coils. Because the woven structure is directional, machine-direction and cross-direction tensile strength are not identical. Manufacturer data should be reviewed for warp and fill values when the tape is cut on the bias or formed around a compound curve. The fiberglass reinforcement is abrasive to slitting blades and increases knife-change frequency relative to polyester-film tapes; converters that process SG25-10(R) typically require carbide or ceramic-edged shear slitting systems.

How Should the Silicone-Adhesive PTFE Class Be Evaluated Against Acrylic Alternatives?

Evaluation of the silicone system against acrylic transfer tapes begins with ASTM D3330/D3330M-04 for 180° peel adhesion to stainless steel and ASTM D3652/D3652M-20 for shear holding power at elevated temperature. Acrylic-adhesive PTFE cloth tapes typically exhibit higher room-temperature peel values, often in the range of 40 oz/in to 60 oz/in depending on adhesive thickness and cure. The silicone adhesive used on SG25-10(R) is specified at a nominal peel adhesion of 25 oz/in to stainless steel. This lower initial room-temperature peel is not a processing defect; it results from the lower surface energy and cohesive density of a silicone pressure-sensitive adhesive. The performance difference reverses above 150 °C. Acrylic adhesives begin oxidative decomposition and lose cohesive strength after sustained exposure above 150 °C, whereas the silicone adhesive remains stable through the rated continuous-service limit of 260 °C. In hot-bar sealing, jaw temperatures of 180 °C to 220 °C are common; under these conditions acrylic adhesives fail cohesively after repeated cycles, leaving residue on the stainless-steel jaw face and causing polyethylene film to adhere. Silicone adhesive is also less sensitive to plasticizer migration from polyvinyl chloride and polyethylene films. When plasticizer concentration exceeds 15 parts per hundred resin in flexible PVC, an acrylic adhesive can soften and creep, while a silicone adhesive maintains higher shear holding power. The offset is chemical resistance: silicone adhesives are more readily swollen by ketones, esters, and chlorinated solvents than crosslinked acrylic adhesives. The application environment should therefore be reviewed for solvent exposure before substituting SG25-10(R) for an acrylic tape.

On form-fill-seal packaging lines, the tape is applied to the heated jaw face to prevent molten polyethylene or polypropylene film from fouling the sealing surface. Dwell times are typically 0.5 s to 2.0 s at jaw temperatures of 180 °C to 220 °C, depending on film gauge and seal-bar pressure. The glass fabric backing prevents elongation and deformation under repeated jaw pressure, which is commonly 0.4 MPa to 0.7 MPa at the seal interface. The silicone adhesive absorbs differential thermal expansion between the stainless-steel jaw and the glass-PTFE backing. In continuous rotary band sealers, tape life is influenced more by edge wear and accumulated carbonized product residue than by adhesive debond. Cleaning is performed with isopropanol or aliphatic hydrocarbon solvents; ketone-based cleaning agents, ester-bearing solvents, and chlorinated solvents should be avoided because they swell the silicone adhesive and reduce shear strength. When liner removal is performed on automated placement equipment at speeds above 20 m/min, an ionizing air bar should be positioned after the unwind roll to dissipate static charge generated by the low-conductivity PTFE surface. Static charge on the backing can draw airborne dust to the adhesive and produce inconsistent jaw release. The release liner is removed at an angle greater than 90° on high-speed equipment; lower peel angles can transfer adhesive to the liner or tear the glass fabric at the liner edge.

When the Tape Functions as a Composite Cure Release Surface

In epoxy prepreg layup and autoclave or oven cure, SG25-10(R) is placed on tooling flanges, caul plates, and vacuum-bag seal areas. The PTFE face is the release interface; the glass fabric resists tearing when the tape is stripped after cure. Typical cure cycles for epoxy prepreg are 120 °C to 180 °C for 1 h to 4 h, which falls within the continuous-temperature envelope of the tape. The silicone adhesive is chosen over rubber or acrylic systems because rubber pressure-sensitive adhesives soften below 100 °C and acrylic systems can crosslink, embrittle, and lose peel strength after repeated exposure above 150 °C. Uncured prepreg solvents often include methyl ethyl ketone and toluene; these solvents can migrate through the PTFE coating at the lap edge and reduce adhesive anchorage. Continuous immersion or heavy solvent wiping at the exposed edge should be avoided. Release performance against cured epoxy is not defined by a single ASTM peel test because cured-resin adhesion depends on resin formulation, hardener stoichiometry, cure pressure, and tool surface finish. Tooling trials at maximum cure temperature are required. Published data for this specific configuration is limited; the manufacturer supplies generic fluoropolymer release-surface data, but end-use verification on the actual prepreg system is necessary. When the tape is used as a vacuum-bag sealing surface, the low coefficient of friction of the PTFE face can permit bag movement under differential pressure; mechanical clamps or high-temperature polyimide tape anchors should be used at the bag edge.

Electrical insulation duty uses the glass-PTFE backing for dielectric separation in coil wrapping, slot insulation, and high-temperature wire bundling. Manufacturer literature lists dielectric breakdown at 8,000 V for the nominal 0.25 mm backing when tested in accordance with ASTM D149-20. Because the silicone adhesive surface can attract moisture at elevated relative humidity, insulation resistance should be verified with ASTM D257-14 if the tape is used above 60 % relative humidity. The woven glass carrier has lower dielectric strength than homogeneous PTFE film at the same thickness but offers higher cut-through resistance and mechanical protection. UL 510 recognition applies to the tape as a component; the end-use assembly is subject to the equipment manufacturer’s certification. When the tape is wrapped with a 50 % overlap for motor phase insulation, the overlap doubles the dielectric path but also increases thermal resistance and can reduce heat transfer from the winding.

In thermal spray and plasma spray masking, the tape is applied to adjacent surfaces to prevent coating deposition. The silicone adhesive is selected because acrylic adhesives carbonize and fail after short exposure to hot overspray. The PTFE surface is not wetted by most molten metal droplets; the glass fabric resists tearing when overspray builds up. Masking life depends on standoff distance and spray angle; published data for this specific configuration is limited. The tape is removed before the accumulated coating reaches a thickness that causes thermal conduction into the adhesive. Edge lifting can occur when the spray stream impinges directly on the tape edge; the tape should be applied with the outermost edge outside the direct spray path or protected by a metal shroud. This application remains within the continuous service temperature only when the overspray does not transfer enough heat to raise the adhesive above 260 °C. If the workpiece is preheated above 200 °C, the tape should be applied after preheating to avoid thermal shock and liner contraction.

Chemical and thermal boundaries are set by the PTFE coating and the silicone adhesive. The PTFE surface is inert to most industrial chemicals, but molten alkali metals and elemental fluorine attack fluoropolymers and must not contact the tape. Sodium naphthalene etchants and strong oxidizing acids above 60 °C degrade the fluoropolymer surface and impair release. The silicone adhesive tolerates aliphatic hydrocarbons and low-molecular-weight alcohols, but immersion or repeated wiping with toluene, xylene, methyl ethyl ketone, or ethyl acetate should be avoided because these solvents plasticize the silicone network and reduce peel strength. At temperatures above 260 °C, PTFE decomposition products can include tetrafluoroethylene and hexafluoropropylene; the tape should not be used in open-flame or high-temperature radiant applications without adequate local exhaust ventilation. The maximum continuous operating temperature is limited by the silicone adhesive and not by the PTFE coating, which can withstand higher bulk temperatures. Intermittent exposure above 260 °C may be possible only with reduced service life and should be validated on the specific assembly. For food-contact applications, the PTFE skin may be evaluated under 21 CFR 177.1550, but the complete tape, including the silicone adhesive and release liner, requires end-use verification under the applicable food-contact regulation. The article is commonly supplied with a RoHS Directive 2011/65/EU conformance certificate; EU REACH SVHC status should be confirmed with the supplier for the current manufacturing lot.

Slit-Width Tolerance, Winding Tension, and Edge Quality

Converters and equipment builders should specify edge quality because the glass fabric is abrasive and reduces blade life relative to polyester-film or skived PTFE tapes. Standard roll stock is commonly supplied from 12 mm to 1000 mm width; slit widths below 6 mm are attainable but may require single-knife crush slitting or laser cutting. Carbide or ceramic-edged shear slitting is preferred for long runs. Winding tension for rolls should be kept below 100 N per meter of width to prevent telescoping, because the PTFE surface has a low coefficient of friction and the silicone adhesive is compressible. The release liner is usually a densified kraft or polyester film; liner removal at high speed on automated placement equipment requires a peel angle greater than 90° to avoid tearing the glass-PTFE backing. If the tape is applied to a curved surface with radius less than 5 mm, the glass fabric may wrinkle. In such cases, a skived PTFE film tape with acrylic adhesive is a more conformable alternative but has lower temperature resistance, higher elongation, and lower puncture resistance. The difference is critical in coil winding where a low radius is combined with high thermal load; the glass-reinforced product is specified only when the minimum bend radius is acceptable because wrinkles create air voids that reduce dielectric strength. When a die-cut part is required, the glass fabric causes more punch wear than polymer film; steel-rule dies should be inspected after every 5,000 to 10,000 cycles, and the die-cutting station should be equipped with a solvent-wipe system to remove adhesive transfer from the punch face. These processing details define the operational window for high-volume placement and are observable on production converting lines.